GEOLOGIC STUDIES IN ALASKA 

by the U.S. Geological Survey 

during 1987 

U.S. Geological Survey Circular 1016 
Front cover: View northeast to terminus of Hubbard 

Glacier, June 13, 1986. Glacier has advanced to tip of 

Gilbert Point (right center of photograph), blocking 

Russell Fiord. Photograph by L.R. Mayo. 

Back cover: Terminus of Hubbard Glacier from Osier 

Island, january 12, 1986. Photograph by L.R. Mayo. 
Geologic Studies in Alaska 

by the U.S. Geological Survey 

during 1987 

JOHN P. GALLOWAY and THOMAS D. HAMILTON, 

Editors 

U.S. GEOLOGICAL SURVEY CIRCULAR 1016 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade names and trademarks 

in this publication is for descriptive 

purposes only and does not constitute 

endorsement by the U.S. Geological Survey 

Library of Congress Catalog Number 76-608093 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988 

Free on application to the Branch of Distribution 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Publication authorized by the Director, U.S. Geological Survey, March 30, 1988 
CONTENTS 

Introduction 

John P. Ga 11 away and Thomas D. Hamil ton, editors 1 

ARTICLE OF SPECIAL INTEREST 

Advance of Hubbard Glacier and Closure of Russell Fiord, Alaska--Environmental Effects and Hazards in the 

Yakutat Area 

Lawrence R. Mayo 4 

NORTHERN ALASKA 

A Major Unconformity Between Upper Ordovician and Lower Devonian Strata in the Nanook Limestone, Shublik 

Mountains, Northeastern Brooks Range 

Robert B. Blodgett, David M. Rohr, Anita G. Harris, and Rang Jia-yu 18 

Ostracode and Molluscan Assemblages from the Late Neogene Nuwok Member of the Sagavanirktok Formation, 

North Slope 

Elisabeth M. Brouwers and Louie Marincovich, Jr. 24 

Nearshore Marine Environments of the Alaskan Beaufort Sea During Deposition of the Flaxman Member of the 

Gubik Formation 

L. David Carter, Elisabeth M. Brouwers, and Louie Marincovich, Jr. 27 

Stromatolite- and Coated-Grain-Bearing Carbonate Rocks of the Western Brooks Range 

Ju 1 i e A. Dumoulin 31 

Off-Platform Silurian Sequences in the Ambler River Quadrangle 

Julie A. Dumoulin and Anita G. Harris 35 

Late Wisconsin Eolian Activity and Related Alluviation, Central Kobuk River Valley 

Thomas D. Hamilton, John P. Gall away, and Eduard A. Koster 39 

Decollements in the Endicott Mountains Allochthon, North-Central Brooks Range 

J.S. Kelley and Diedra Bohn 44 

A Thermal Cross Section for the Permafrost and Hydrate Stability Zones in the Kuparuk and Prudhoe Bay Oil 

Fields 

Arthur H. Lachenbruch, S. Peter Galanis, Jr., and Thomas H. Moses, Jr. 48 

EAST-CENTRAL ALASKA 

A Late Silurian Age Determination for the Limestone of the Lost Creek Unit, Livengood 

C-4 Quadrangle, East-Central Alaska 

Robert B. Blodgett, Ning Zhang, Allen R. Ormiston, and Florence R. Weber 54 

A Comparative Petrologic Study of Sandstone from the Wilber Creek, Cascaden Ridge, and Wickersham Units in 

the Livengood Quadrangle 

L.D. Gergen, J.E. Decker, and George Plafker 57 

Tertiary Gold-Bearing Gravel at Livengood, Alaska 

Susan M. Karl, Thomas A. Ager, Karl Hanneman, and Steve D. Teller 61 

Reconnaissance Geochemical Investigations of the White Mountains National Recreation Area, East-Central 

Alaska 

Thomas D. Light, Gregory K. Lee, Richard B. Tripp, and Elizabeth A. Bailey 64 

CONTENTS III 
Ultramafic Rocks of the Livengood Terrane 

Robert A. Loney and Glen .R. Himmelberg 68 

Mineral Resource Assessment for Part of the White Mountains National Recreation Area 

Richard B. McCammon, Thomas D. Light, and C. Dean Rinehart 71 

Stratigraphy, Sedimentology, and Structure of the Wickersham Terrane in the Cache Mountain Area, EastCentral Alaska 

Thomas E. Moore and Warren J. Nokl eberg 75 

Gold Mineralization by Metamorphic Fluids in the Chandalar District, Southern Brooks Range--Fluid Inclusion 

and Oxygen-Isotopic Evidence 

Scott C. Rose, William J. Pickthorn, and Richard J. Goldfarb 81 

WEST-CENTRAL ALASKA 

Factor Analysis of the NURE Stream-Sediment and Lake-Sediment Geochemical Data from the Iditarod 

Quadrangle 

John E. Gray, Sarah C. Smith, and Richard J. Goldfarb 86 

Glacial Geologic History of the Salmon Lake Area, Seward Peninsula 

Darrell S. Kaufman, David M. Hopkins, and Parker E. Calkin 91 

Lahar Deposit in the Iditarod Volcanics, Southwestern Iditarod Quadrangle 

Robert G. McGimsey and Marti L. Miller 95 

Right-Lateral Offset Solution for the Iditarod-Nixon Fork Fault, Western Alaska 

Marti L. Miller and Thomas K. Bundtzen 99 

Geologic Setting and Petrography of the Phyllite and Metagraywacke Thrust Panel, North-Central Alaska 

John M. Murphy and W.W. Patton, Jr. 104 

SOUTHERN ALASKA 

Middle Pennsylvanian Plutonic Rocks Along the Southern Margin of the Wrangellia Terrane 

John N. Aleinikoff, George Plafker, and Warren J. Nokleberg 110 

Source of the Sanford Volcanic Debris Flow, South-Central Alaska 

Donald H. Richter, Henry R. Schmoll, and Dana J. Bove 114 

Hydrocarbon Source Potential and Thermal Maturity of the Sanctuary Formation (Middle Miocene), Northern 

Foothills of the Alaska Range 

Richard G. Stanley 117 

Mineralogy and Stage Assignment of Some Tertiary Coal from the Tikishla Park Drill Hole, Anchorage, Alaska 

G.D. Stricker, M.E. Brownfield, L.A. Yehle, and J.A. Wolfe 121 

SOUTHWESTERN ALASKA 

Petrogenesis of the Crooked Mountains Pluton, Bethel Quadrangle: A Preliminary Report 

Thomas P. Frost, James P. Calzia, Ronald W. Kistler, and Davison V. Vivit 126 

Geochemical Anomalies in the Eastern Katmai Region of the Alaska Peninsula 

Richard J. Goldfarb, John E. Gray, and R.B. Tripp 132 

SOUTHEASTERN ALASKA 

Relative Timing of Porphyroblast Growth, Foliation Development, and Ductile Shear in Pelitic Metamorphic 

Rocks from the Juneau Area, Southeastern Alaska 

Robert L. Bauer, Glen R. Himmelberg, David A. Brew, and Arthur B. Ford 138 

CONTENTS IV 
A Reexamination of the Contacts and other Features of the Gravina Belt, Southeastern Alaska 

David A. Brew and Susan M. Karl 143 

Megafossils (Buchia) Indicate Late Jurassic Age for Part of Kelp Bay Group on Baranof Island, Southeastern 

Alaska 

David A. Brew, Susan M. Karl, and John W. Miller 147 

Major-Element Geochemistry of Metabasalts of the Juneau-Haines Region, Southeastern Alaska 

Arthur B. Ford and David A. Brew 150 

Petrography of Sandstones of the Orca Group from the Southern Trans-Alaskan Crustal Transect (TACT) Route 

and Montague Island 

L. D. Gergen and George Pl afker 156 

H2S-Rich Vein-Forming Fluids at the Sumdum Chief Gold Mine, Southeastern Alaska 

Richard J. Goldfarb, Albert H. Hofstra, Gary P. Landis, and David L. Leach 160 

New K-Ar Ages for Plutons on Western Chichagof Island and on Yakobi Island 

Susan M. Karl, Bruce R. Johnson, and Marvin A. Lanphere 164 

Geochemistry and Petrography of Lamprophyre Dike Rocks in the Coast Mountains, Southeastern Alaska 

John S. Lu 11 and George Pl afker 169 

Alteration Zoning and Origin of the Alaska-Juneau Gold Deposit 

Rainer J. Newberry and David A. Brew 17 4 

OFFSHORE 

Construction of an Arctic Barrier Island by Alternating Sea-Ice Pileup and Overwash 

P.W. Barnes and Erk Reimnitz 180 

Sea-Floor Feeding Traces of Gray Whales and Walrus in the Northeast Chukchi Sea 

R. Lawrence Phillips and Mitchell W. Colgan 183 

Late Cretaceous Sediments from the Northeast Chukchi Sea 

R. Lawrence Phillips, LedaBeth G. Pickthorn, and Douglas M. Rearic 187 

Evidence for Sea-Ice Impact on Icy Reef, Beaufort Sea Coast 

Erk Reimnitz and P.W. Barnes 190 

BIBLIOGRAPHIES 

Reports about Alaska in USGS Publications Released in 1987 

compiled by Ell en R. White 194 

Reports about Alaska in Non-USGS Publications Released in 1987 Which Include USGS Authors 

compiled by Ellen R. White 201 

SUBJECT INDEX 208 

AUTHOR INDEX 213 

AUTHORS' ADDRESSES 214 

CONTENTS V 

Geologic Studies in Alaska by the 

U.S. Geological Survey during 1987 

By John P. Galloway and Thomas D. Hamilton, editors 

Introduction 

This volume is a continuation of the annual 

United States Geological Survey (USGS) Circulars 

reporting results of work in progress on earth science 

investigations in Alaska. The series began in 1975 

under the title "The United States Geological Survey in 

Alaska--Accomplishments during 19xx" and has 

continued since 1986 under the present title. The 40 

short papers and the feature article presented here 

report on some of the geologic studies undertaken in 

Alaska during 1987 by the USGS, cooperating agencies, 

and universities. 

The reports presented here begin with an article 

of special interest followed by papers related to the 

five regional subdivisions of Alaska and to areas 

offshore on the Alaska continental shelf (fig. 1). 

Regional papers are presented in sequence from north 

to south. This year, a keynote article of special 

interest is devoted to a topic that was prominent in 

the news during 1987: the advance of Hubbard Glacier 

and its damming of Russell Fiord near the community 

of Yakutat in southern Alaska. This report, which 

deals with a particularly dynamic and hazardous aspect 

of Alaska's environment, is given a greater depth of 

coverage than the other papers in this volume. 

Photographs on the front and back covers illustrate 

some aspects of Hubbard Glacier's activities. 

The 40 other reports in this volume provide a 

representative sample of current USGS research in 

Alaska. The topics range widely from mineral 

resources, including fossil fuels (eight papers), to 

paleontology, petrology of igneous, metamorphic, and 

sedimentary rocks, structural geology, and Quaternary 

geology (four or five reports each). Other papers 

cover coastal hazards, geochronology, and marine 

geology. 

Two bibliographies following the reports of 

investigations cover (1) reports about Alaska in USGS 

publications released in 1987 and (2) reports about 

Alaska by USGS authors in outside publications in 

1987. Author and subject indexes and author addresses 

are appended at the back of the volume. A 

bibliography and index of the short papers in past 

USGS Circulars devoted to Geological Research and 

Accomplishments in Alaska (1975-1986) has recently 

been published as USGS Open-File Report 87-420. 

View southwest across Cold Bay to four of Alaska's many volcanoes (from left to right): Frosty Peak and its northwest slope; smooth, 

snow-covered Roundtop Mountain; "mouse-eared" lsanotski Peaks; and the classic cone of Shishaldin Volcano. 

INTRODUCTION 1 
...., 

Q 

~ 

0 

as. (') 

;a 

c: 

9: 

~ 

s· 

> i 

C" 

'< 

.... 

~ 

c 

tn 

~ g. 

~ rs· 

e. 

' ~ 

ij 

~· 

..-

CQ 

co 

""' 

, 

f2J . . 

~ " 

\ 

~ 

0 

~ 

"/?:--; y 

~ 

s 

, . 11 /,. 1((' 1/1 

~ !( 

0 (' 

p A C F I C 

UNITO:DSTA TI:S 

DEPARnCENTOf T HE I"T>:RIOk 

GIX>LO<: I<": ALSU IIVJ:Y 

0 

~~~ 1- .. :.__. --r---.--------r 

Figure 1. Regions of Alaska as used in this circular and outlines of 1 :250,000-sca\e quadrangles. 

- 1". 

ALASKA 

o 100 200 KILOMETERS 
ARTICLE OF SPECIAL INTEREST 

Driftwood log at height of about 15 m in forest of Sitka spruce at south end of Russell Fiord. Log was stranded by 

sudden outburst of Russell Lake, which is described in following article. Photographed June 8, 1987, by L.R. 

Mayo. 
Advance of Hubbard Glacier and 

Closure of Russell Fiord, AlaskaEnvironmental Effects and Hazards in the Yakutat Area 

By Lawrence R. Mayo 

Introduction 

Hubbard Glacier originates in the lcefield 

Ranges of Yukon Territory, Canada, and in the St. 

Elias Mountains of Canada and Alaska. It flows south 

and southeast for about 120 km through the St. Elias 

Mountains into Disenchantment Bay and Russell Fiord 

near Yakutat (fig. 1). Hubbard Glacier is the largest 

North American ice stream that presently calve~ into 

tidewater. It covers an area of about 3,400 km and 

extends to sea level from an altitude of about 5,800 

meters on the flank of Mount Logan, Canada's highest 

peak. 

The terminus of Hubbard Glacier has fluctuated 

through a distance of more than 60 km within the past 

1,000 years (fig. 1). Earlier advances that repeatedly 

dammed and released a very large lake in the Russell 

Fiord basin are recorded by ancient lake sediments 

that span the past 7,000 years (George Plafker, U.S. 

Geological Survey, written commun., 1987). 

In a study of glacier-dammed lakes of Alaska, it 

was predicted that Hubbard Glacier would again block 

Russell Fiord by about 1991 (Post and Mayo, 1971). 

The temperature and salinity of Russell Fiord 

consequently were studied by Reeburgh and others 

(1976} to provide background data in anticipation of a 

future conversion of the fiord into a lake. They 

recognized that such a lake could potentially overflow 

at its south end, causing severe flooding near the town 

of Yakutat (fig. 1). 

Historical records show that Hubbard Glacier 

has advanced 2 to 3 km during the past century {the 

actual distance varies along the terminus). In May 

1986, this progressive advance carried it across the 

entrance of Russell Fiord, where it formed a massive 

ice dam. Rapid rise in the surface level of the newly 

created Russell Lake submerged forests to a height of 

26 m and threatened to overflow into the Situk River, 

a highly productive and economically important salmon 

stream near Yakutat (fig. 1). 

Many glaciers of southern Alaska are subject to 

major advances and retreats. These events have 

impacts on lakes, streams, and coastal morphology; on 

forests and wildlife; and on human ecology. 

Continuing studies of Hubbard Glacier by the U.S. 

Geological Survey and other State and Federal 

agencies are aimed at documenting the mechanism and 

impacts of the recent Hubbard Glacier advance and 

reconstructing the history of the glacier's earlier 

fluctuations. Knowledge obtained from these studies 

can be used to predict future changes and their 

environmental effects for Hubbard Glacier and other 

tidewater glaciers. This paper summarizes the 

geologic history and recent advance of Hubbard 

Glacier, its effects, and the implications for 

assessments of glacier changes throughout southern 

Alaska. 

Glacier history 

Varved lake deposits dating 6,310 ± 110 and 

4,890 ± 100 yr B.P. are interbedded with alluvium and 

glacial till in deltas near the south end of Russell Fiord 

(George Plafker, U.S. Geological Survey, and J.J. 

Clague, Geological Survey of Canada, written 

commun., 1987). These deposits indicate that major 

advances of Hubbard Glacier or possibly of neighboring 

glaciers blocked Russell Fiord during middle 

Holocene time, a period when glaciers throughout the 

world are generally believed to have been less 

extensive than at present. 

Plafker and Miller (1958) have shown that 

Hubbard Glacier advanced to the mouth of Yakutat 

Bay about 1130 A.D. (± 160 years) and deposited the 

moraine upon which the present town of Yakutat is 

situated (fig. 1). A distributary ice stream of 

presumably the same age flowed southeast, filled 

Russell Fiord with ice, and deposited a terminal 

moraine at the south end of the fiord. The glacier 

subsequently retreated to an unknown position, then 

readvanced into the head of Yakutat Bay by about 

1700 A.D. (Plafker and Miller, 1958) (fig. 1). 

Hubbard Glacier retreated again after 1700 

A.D. During that retreat, Alessandro Malaspina, an 

Italian explorer who worked for Spain, entered Yakutat 

Bay in 1791. Malaspina carried a map showing the 

possible western end of the elusive "Northwest 

Passage" at the head of the bay (Tarr and Butler, 

1909). His observations within the bay indicate that 

the glacier had retreated at least 20 km since 1700 

A.D., but beyond that point the bay was blocked by 

"perpetual frost." Malaspina named Disenchantment 

Bay for his frustrated hopes of finding a navigable 

passage. Tarr and Butler (1909) concluded that 

Malaspina's "perpetual frost" was probably only tightly 

packed floating icebergs rather than the terminus of 

Hubbard Glacier because the explorers did not report 

calving from the terminus of the glacier, which would 

have been an unforgettable hazard to their small boat. 

In 1890, I.C. Russell, the first modern scientist 

to examine the Yakutat Bay region and the first 

member of the U.S. Geological Survey to study 

glaciers in Alaska, provided an accurate description of 

4 Geologie Studies in Alaska by the U.S. Geological Survey during 1987 
140° 

60° 30' 

Malaspina 

Glacier 

YAK U TAT 8 A Y 

OE:::::;;:::::;;;:31 0====2:10§;;::::::;::::::;;330 K I L 0 METE RS 

\ 

\ <;--/--

\ I 

~I 

Figure 1. Hubbard Glacier system, showing flow directions (arrows), extent of advances about 1130 A.D. and 1700 

A.D., and flood-hazard zone along Situk River. Dashed lines indicate glacier margins. 

Advance of Hubbard Glacier and Closure of Russell Fiord 5 
the position and features of Hubbard Glacier. His 

small-scale map and drawing of Hubbard Glacier 

(Russell, 1891) shows the glacier's terminus 

approximately 2 km from Osier Island, leaving open 

the mouth of a large fiord to the east. That position 

indicated approximately 28 km of retreat since the 

1700 A.D. advance. Russell probably observed 

Hubbard Glacier near its maxim urn recessional 

position. 

In 1891, Russell (1893) traveled into the fiord 

that later was named after him (Gannett, 1902) and 

recognized from the pioneer vegetation and fresh 

shoreline features along its walls that the fiord had 

been the site of a recent glacier-dammed lake. 

An ethnographic description of this lake was 

given in 1952 to Frederica de Laguna (1972, p. 287) by 

Harry K. Bremner, a Tlingit Indian of Yakutat, whose 

father had witnessed the outburst of the lake as a 

child. Bremner stated: "About the middle of the last 

century .•• people were near the lake picking 

strawberries ••• That was what my father was doing. 

Every time he came back to the boat, he found that 

it was going dry, so he would push it off into deeper 

water before going back for another load. When this 

happened a few times he realized that the water was 

really going down. Everybody ran and got into the 

canoes and started down the stream. Suddenly a big 

mass of salt water rushed downstream. Everybody got 

away safely. There was still enough water in the 

stream for the canoes. But after that, Situk River was 

just a little one." 

Elders in Yakutat believe that this event 

occurred about 1860 (Elaine Abraham, oral commun., 

1986). This is supported by annual rings of a spruce 

tree on the former lake bed, which indicate that the 

tree began growth in 1885. 

During the 96 years since Russell's observations, 

Hubbard Glacier has readvanced about 2 km across the 

fiord entrance at the head of Disenchantment Bay (fig. 

2). 

Dynamics of Hubbard Glacier 

From 1961 to 1986, Hubbard Glacier approached 

Gilbert Point near Osier Island (fig. 2), and the rate of 

glacier advance increased locally as it entered 

progressively shallower water at the entrance to 

Russell Fiord (fig. 3). 

Most glaciers advance and retreat 

synchronously as a result of climatic variations which 

produce changes in the rate of snow accumulation or 

ice melting (Nye, 1960). Tidewater glaciers, however, 

are an exception. Glaciers that terminate in seawater 

can advance asynchronously and over long distances 

due to the forward movement of protective submarine 

terminal moraines (fig. 4A; Post, 1975). These glaciers 

can also retreat rapidly by calving into the ice-scoured 

and -deepened fiords behind the moraines if they 

recede only a short distance from the protective 

moraines against which they formerly were grounded 

(fig. 4B). The asynchronous behavior of tidewater 

glaciers is well illustrated by Columbia Glacier, which 

is now in rapid retreat (Meier and others, 1985) while 

Hubbard Glacier is advancing. Glaciers that end in 

deep lakes, such as Portage Glacier southeast of 

Anchorage, behave in a similar way (Mayo and others, 

1977). 

Hubbard Glacier is in the early phase of a major 

new advance that began about 100 to 150 years ago. 

The glacier has a strong positive ice balance because 

its last recession resulted in the loss by rapid calving 

of most of its ablation zone. At present, 95 percent of 

Hubbard Glacier is above the local snowline or 

equilibrium line altitude (ELA) at 1,000 m altitude (fig. 

4), and therefore is within the accumulation zone. A 

glacier that has fully advanced to an equilibrium 

position typically has about 60 to 70 percent of its 

total area within its accumulation zone (Meier and 

Post, 1962). 

The current advance of Hubbard Glacier is 

controlled by the movement of a submarine moraine at 

the ice terminus, which was discovered by ice radar 

and fathometer surveys (Mayo, 1987). The glacier 

terminus is in shallow water that varies from 0 to 50 m 

deep at the crest of this moraine. The fiord is 205 m 

deep 2 km in front of the moraine crest, and the 

glacier bed is 320 m below sea level 2 km behind the 

moraine crest (fig. 5). The shallow water at the 

moraine limits the rate of ice calving (Brown and 

others, 1982). The process of displacement of the 

moraine into Disenchantment Bay by Hubbard Glacier 

is demonstrated by the fact that the glacier bed is now 

more than 300 m below sea level at the position where 

the glacier terminus had been mapped in 1895 by the 

International Boundary Commission (1952). 

Recent glacier advance and lake formation 

Photographs taken during repeated overflights 

of Hubbard Glacier in April and May 1986 by residents 

of Yakutat show that the glacier was advancing rapidly 

across the entrance of Russell Fiord at a rate of 

approximately 10 m per day and that submarine 

deposits were being raised above sea level by the 

plowing action of the glacier. Closure of the mouth of 

Russell Fiord was completed on May 29, 1986, and the 

newly-formed Russell Lake began filling (fig. 6). 

Although Hubbard Glacier advanced toward the 

terminus of Variegated Glacier to the east, the two 

glaciers remained separated by a stream flowing 

between them. Hubbard Glacier began to overrun 

Osier Island during the remainder of 1986, but stopped 

short of the summit of the island (figs. 2 and 3). 

Scientists of the U.S. Geological Survey, the 

U.S. Forest Service, and the University of Alaska 

initiated research projects during the summer of 1986 

in cooperation with the National Park Service, the 

City of Yakutat, and the National Geographic 

Society. Their studies included determination of the 

causes of Hubbard Glacier's behavior, measurements of 

the rate of filling of Russell Lake, precision remapping 

of the Yakutat Forelands, estimation of the flooding of 

the Situk River should Russell Lake overflow, and 

archeology in areas potentially subject to flooding. 

The rapid ice advance in 1986 was caused by a 

weak and short-duration surge of Valerie Glacier, a 

tributary of Hubbard Glacier (fig. 1). The surge, which 

had a measured flow rate of 36 m/d in June 1986, 

produced unusual crevassing and marginal wrench 

faults in Valerie Glacier. The rapid advance of 

6 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Hubbard Glacier resulted in the plowing of shallow 

marine sediments between the glacier and the shore at 

the entrance to Russell Fiord. These sediments were 

pushed above sea level and calving losses at the 

terminus were eliminated, which then resulted in 

continuing advance. (Mayo, 1987). The surge ended in 

late June 1986, and no further rapid advance of 

Hubbard Glacier took place after that time. 

At the same time that significant advance was 

occurring in shallow water near Gilbert Point (fig. 3), 

advance was negligible at locations along the terminus 

MOaAINE7 

CLOSURE 

DISENCHA NTM EN!/ ·.; IJA y 

of Hubbard Glacier where the water was more than 

200 m deep in front of the moraine. This indicates 

that the rate of advance along the terminus of 

advancing tidewater glaciers is related inversely to the 

amount of subglacial sediment required to fill the fiord 

in front of the moraine. The location of the Hubbard 

Glacier ice dam in 1986 was controlled by the presence 

of shallow unconsolidated deposits on bedrock near the 

glacier terminus; but the timing of the closure in 1986 

was controlled by the weak surge of the Valerie 

tributary of Hubbard Glacier. The bedrock core of 

Figure 2. View east to terminus of Hubbard Glacier june 13, 1986. Glacier position in 1895 from International Boundary Commission 

(1952); position in 1961 from U.S. Geological Survey Mount St. Elias (A-4) and (A-5) 1 :63,360 quadrangle maps. Gilbert Point is in the 

right foreground. 

Advance of Hubbard Glacier and Closure of Russell Fiord 1 
Osier Island served as a buttress against rapid ice flow 

and terminus advance in June 1986 (fig. 2). 

During the summer of 1986, Russ2ll Lake rose 

rapidly (fig. 6), inundating about 33 km of forested 

land adjacent to the blocked fiord. Half of its 

drainage basin is occupied by glaciers, and ice melt 

and rainfall runoff from these glaciers produced about 

80 percent of the runoff f~eding the lake. The lake 

area, beginning at 195 km , was equal to about 10 

percent of the basin area, so the measured lake rise 

during the summer of 1986 of 25.5 m (based on data of 

Seitz and others, 1986} was equivalent to an average 

about 2.5 m liquid runoff from the basin. Very high 

runoff rates, 3.8 m per year at Bering Glacier east of 

Hubbard Glacier, had been calculated from observed 

glacier equilibrium line altitudes (Mayo, 1986), but the 

simple volumetric measurement of runoff into Russell 

Fiord is the first direct data obtained for a large basin 

with glaciers in this part of Alaska. 

As Russell Lake rose in the summer of 1986, 

several consequences were possible: (1) the lake could 

overflow and burst out through the new moraine 

formed from submarine sediments plowed against 

Gilbert Point by Hubbard Glacier at the north end of 

Russell Fiord, (2) the lake could overflow onto the 

Yakutat Foreland at the south end of Russell Fiord, or 

(3) the lake could burst out through the ice dam. 

Hubbard Glacier did not advance fully to the bedrock 

ridge at the entrance to Russell Fiord. The marine 

sediments plowed from the fiord in April and May 1986 

were trapped between the glacier ice and the ridge, 

forming a moraine (fig. 2). As the glacier pushed 

forward, the moraine was squeezed and deformed 

60° ~ "' (J 

~ "' "' "' 'll 

<:) " " 

I 

I 

I 

I 

I 

I 

I I HUBBARD 

I 

............... ...... 

' ' ' '---

GLACIER 

-- ___ ...]_9~

Figure 3. Terminal positions of Hubbard Glacier from 1961 to 

June 1987 at entrance of Russel l Fiord. Glacier position in 1961 

from maps cited in figure 2; position in 1978 from Krimmel and 

Sikonia (1986). Arrow indicates diredion of flow. See figure 1 for 

location. 

upward. The overflow point on the moraine rose at a 

rate that was faster than the filling rate of the lake 

(fig. 7), and overflow therefore did not occur. 

Potential lake overflow sites also exist at the 

south end of Russell Fiord, 50 km beyond the terminus 

of Hubbard Glacier. The lowest site is situated 39 m 

above sea level in a recently reforested channel in the 

moraine at the head of Old Situk Creek (fig. 8). The 

overflow channel contains a lag deposit of boulders 

derived from the moraine, and is undoubtedly the 

channel used over a century ago by the Tlingit Indians 

to gain access by boat into Russell Lake. Remapping 

of the Yakutat Foreland (fig. 8} was undertaken as a 

joint project by the U.S. Forest Service and the U.S. 

Geological Survey in 1986 to obtain precise altitude 

data in areas possibly subject to flooding from the 

potential filling and overflow of Russell Fiord (fig. 1). 

Before overflow could occur across the moraine 

at either end of the lake, the lake burst out through 

the 500-m-wide ice dam, which proved to be too 

narrow to contain Russell Lake. The calving rate from 

the Disenchantment Bay side of the ice dam exceeded 

the lateral deformation rate of the dam, causing it to 

become progressively narrower (eventually only 150 m 

wide; see fig. 9). Small ponds of meltwater trapped in 

crevasses at the edge of the ice dam indicated that 

water pressure in the dam was higher than at Russell 

Lake; this increased the calving rate into 

A ADVANCING PHASE 

Retreated stable 

posit iOn 

Early phase of advance 

due to morai ne shoal Advanced 

stable 

pos1tion 

Advanced 

stable 

Figure 4. Cycle of advance and retreat of a tidewater glacier. ElA 

(equilibrium-line altitude) is position on glacier where annual 

snow accumulation equals annual snow melt. 

8 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Disenchantment Bay, resulting in a deep embayment in 

the ice dam during September and early October. 

During the afternoon of October 7, 1986, lake 

water began flowing through the maze of crevasses in 

the ice dam, carrying with it small fragments of ice. 

In the late evening of the same day between 10:15 and 

10:45 p.m. Standard Alaskan Time, when the lake 

hei3ht peaked at 25.5 m above sea level and with 5.3 

km of water stored, the ice dam failed. Thunderous 

B 

calving every few seconds for several hours during the 

night indicated that failure occurred by progressive 

collapse of massive ice blocks into the outburst 

channel (fig. 10). At the same time, the channel 

widened by erosion of alluvial fan deposits and highly 

jointed bedrock on Gilbert Point. 

Measurements of lake height were obtained 

during the outburst at a site located 8 km from the 

failing ice dam (Seitz and others, 1986). The maximum 

Figure 5. View northeast showing surface and bed of Hubbard Glacier. A, Photograph taken June 1 3, 1 986. Turner Glacier in lower left 

corner; Gilbert Point and Russell Lake near right margin. B, Computer-drawn perspective contour map showing exposed land (shaded), 

glacier limits (dashed lines), bed of Hubbard Glacier (unshaded) and fiord bottom (unshaded). Contour interval 50 m; altitudes above 

and below mean sea level. Note submarine moraine at Hubbard Glacier terminus. 

Advance of Hubbard Glacier and Closure of Russell Fiord 9 
discharge rate took place between 1 and 2 a.m. on 

October 8, when the lake dropped 1.68 m. Assuming 

that the entire lake surface fell equally, the av~rage 

discharge rate during the interval was 104,500 m per 

second, which greatly exceeded the highest measured 

rate of fl?!w of the Yukon River, Alaska's largest river 

(29,000 m /~, Jones, 1983). The lake area at that time 

was 224 km • 

Russell Lake poured into Disenchantment Bay 

(fig. 11) with a velocity measured at 11 m/s at dawn, 

which was about 4 hours after the time of peak 

discharge. The momentum of the outburst flood 

carried the turbulent water 5 to 6 km across 

Disenchantment Bay to the west shore where it washed 

against the terminus of Turner Glacier. 

The peak flow rate of the "Russell River" may 

be the greatest water discharge to occur in North 

America and the largest glacier outburst in the world 

measured during the past few centuries (table 1), but 

was much less t~an the estimated peak discharge of 15 

to 17 million m /s from late Pleistocene Glacial Lake 

Missoula when it burst out into the Columbia River 

between 16,000 and 12,000 years ago (O'Connor and 

Baker, 1987; Baker, 1973), creating the Channeled 

Scablands of eastern Washington. Prior to the 1986 

outburst of Russell Lake, the greatest known historical 

outburst was from the June 5, 1976, f~lure of the 

Teton Dam, Idaho, which was 65,000 m /s (Ray and 

Kjelstrom, 1978, Costa, 1985). The largest known 

historic glacier outbursts in Alaska have been from 

Chakachamna Lake, which is dammed by Barrier 

Glacier at Mount Spurr volcano, and from Berg Lake, 

which is dammed by Bering and Stellar Glaciers. 

Russell Lake had not fully emptied by 9 p.m. on 

October 8 when observations stopped, but was still 2 to 

3 m higher than the water surface in Disenchantment 

Bay. A normal tidal current was observed flowing 

from Russell Fiord on the morning of October 9, 

indicating that the outburst had ceased. The outburst 

of the lake probably had continued until about 3 a.m. 

on October 9, when the projected lake height recession 

was equal to the predicted tide level in 

Disenchantment Bay. The total outburst period 

therefore was approximately 28 to 30 hours. 

Figure 6. View southeast across Russell Lake showing flooded 

forest, August 28, 1 986. Lake height was 20 m above sea level 

at this time. 

The outburst eroded the shore of Russell Fiord 

back by as much as 300 m in the vicinity of the failing 

ice dam. Most of the erosion was from an alluvial fan, 

most of which was swept into Disenchantment Bay, but 

as much as 50 m of the highly jointed bedrock also was 

eroded. Only a small remnant of the terminal moraine 

remained, and individual boulders of marble as large as 

15 m in diameter had been carried away. Before the 

outburst, Osier Island had been mantled with glacial 

till and marine gravel, but these deposits and some 

bedrock were eroded and generally only small alder 

roots remained in bedrock fissures. Shrimp found near 

the top of Osier Island could have been derived only 

from the bed of Russell Fiord, where they were 

probably swept up by water turbulence in the lake 

during its outburst. 

Vegetation that had been inundated by the lake 

was severely damaged. Mud and stones dropped from 

icebergs that had been floating in the lake had 

accumulated in tree branches as a form of "arboreal 

diamicton" (fig. 12), and icebergs that had been 

floating near the shore of Russell Lake remained 

grounded in alder forests well above sea level (fig. 

13). A brown algal slime covered all vegetation to a 

height of about 15 m above sea level at the south end 

of the former lake, and some logs that had been 

floating were caught high in tree limbs (see photo on p. 

3). By October 1987, one year after the lake had 

drained, all alder and devil's club vegetation that had 

been inundated was dead. Other vegetation, including 

spruce, hemlock, willows, and grasses, that had been 

flooded for less than a month had partially recovered, 

but was dead where inundated for longer periods. 

Several species of horsetails (Equisetum) were already 

recolonizing the floor of the dead forest in the sum mer 

of 1987. 

(J) 

a: 

w 

1-

w 

2 

~ 

II 

<.:1 

w 

I 

Overflow po int at south end of Russell Fiord 

----------------------

Outburst -

MAY JUNE 

Figure 7. Height of potential overflow point on Hubbard Glacier 

moraine (measured by aneroid altimeter) and height of Russell 

Lake (data from Seitz and others, 1 986), May to October 1 986. 

10 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Peak discharges of largest known historic glacial lake outbursts 

[Sources: Russell and Berg Lakes, D.C. Trabant, and L.R. Mayo, U.S. Geological Survey, unpub. data; Lake George, U.S. 

Geological Survey, 1964, 1971, and unpub. data; other lakes, j.E. Costa, 1985, and j.E. Beget, 1986] 

Location 

l. Russell Lake, Alaska 

2. Grimsvatn, Iceland 

3. Chong Kumdan, India 

4. Berg Lake, Alaska 

5. Chakachamna Lake, Alaska 

6. Lake George, Alaska 

7. Lake George, Alaska 

8. Lake George, Alaska 

9. Lake George, Alaska 

10. Lake George, Alaska 

ll. Gietro, Switzerland 

12. Lake George, Alaska 

13. Lake George, Alaska 

14. Lake George, Alaska 

15. Lake George, Alaska 

16. Lake George, Alaska 

17. Standline Lake, Alaska 

18. Lake George, Alaska 

EXP L ANAT I ON 

L:.·.·.·.·:.-.-.-.J Ancient Russell Lake 

·· · ····· ···· \. ............ l Abando ned flood channel 

16~'• :-I Kettl e lakes 

--- Outer limit o f end mo raine 

... Direction of flow 

Date 

1986 

1934 

1929 

1983 

1971 

1958 

1961 

1957 

1960 

1949 

1818 

1953 

1954 

1955 

1956 

1965 

1984 

1964 

Peak 

dis~harge 

(m /s) 

104,500 

50,000 

22,650 

17,000 

l3' 300 

10,200 

10,100 

9,430 

9,290 

8,100 

8,000 

7,700 

7,450 

7,300 

7,100 

6,680 

6,100 

6,100 

Reference 

See text 

Thorarinsson, 1957 

Gunn, 1930 

Trabant and Mayo, unpub. 

Lamke, 1972 

USGS, 1964 

USGS, 1971 

USGS, unpub. 

USGS, 1964 

USGS, unpub. 

Haeberli, 1983 

USGS, unpub. 

USGS, unpub. 

USGS, unpub. 

USGS, unpub. 

USGS, 1971 

Sturm and Benson, 1986 

USGS, 1971 

Oc = ====='======::::::i2 K l LOMETERS 

CONTOUR INTERVAL 10 M ET ERS 

Figure 8. Situk River overflow site 22 km east of Yakutat at south end of Russell Fiord. Initial overflow point altitude is 39m above sea 

level. Areas subject to flooding by Russell Lake extend to 45 m elevation. Abandoned flood channel is that of previous overflow of 

Russell Lake prior to about 1860. Abandoned shoreline and flood channel interpreted from map and aerial photographs. 

Advance of Hubbard Glacier and Closure of Russell Fiord 11 
The terminus of Hubbard Glacier readvanced 

during the winter of 1986-1987, overriding most of 

Osier Island during January. However, it retreated 

about the same amount during the following summer. 

At the present time, Hubbard Glacier shows no 

evidence of rapidly reclosi ng Russell Fiord. However, 

the steepened bedrock ridge at Gilbert Point exhibits 

incipient landslide scasps, which suggests that 

approximately 500,000 m of rock could slide into the 

narrow opening into Russell Fiord south of the glacier 

terminus (W.O. Powell, U.S. Forest Service, written 

commun., 1987). Although that amount of rock would 

probably not dam the entrance, it could reduce the 

calving rate of Hubbard Glacier and thereby might 

lead to rapid reclosure by the ice. 

Haenke Glacier, which now enters 

Disenchantment Bay about 1 km from the terminus of 

Hubbard Glacier, surged during 1986-1987: it emerged 

from the mountains in February 1987 and advanced 

into Disenchantment Bay by June. Rock debris carried 

by the Haenke Glacier is entering Disenchantment Bay 

near the calving terminus of Hubbard Glacier. This 

additional sediment will decrease the water depth in 

the bay, which in turn could increase the advance rate 

of part of the terminus of Hubbard Glacier. 

Glacial events and environmental effects: 

1988 and beyond 

Hubbard Glacier has advanced for the past 100 

to 150 years by moving a submarine moraine into 

Disenchantment Bay. The glacier will continue to 

advance, reclosing Russell Fiord in a few years. 

Hubbard Glacier is capable of sustaining this strong 

advance because of its unusually large accumulation 

area compared with its ablation area. In addition, 

landslides from Gilbert Point or debris deposited by 

the surging Haenke Glacier could rapidly decrease 

water depth and calving rate at the terminus of 

Hubbard Glacier, further increasing its rate of 

advance. Velocity of Hubbard Glacier is being 

monitored by satellite telemetry (Trabant, 1986) to 

provide data essential for assessing its future rate of 

advance. 

The exact nature of future events at Hubbard 

Glacier is uncertain, but some elements are 

predictable. When the advancing glacier closes Russell 

Fiord again, the ice dam can be expected to be wider 

than it was in 1986 because the glacier currently is 

advancing along its entire terminus (fig. 3). In 

addition, the overriding of Osier Island in 1987 is 

evidence that the glacier is becoming thicker at that 

location. If the ice dam is wider and higher than it 

was in 1986, it may also be stronger; consequently 

Russell Lake may rise higher than it did in 1986. 

The future Russell Lake could rise to the level 

of the channel at the south end of Russell Fiord and 

overflow through it into the Situk River, or it could 

burst out again by either of two processes. An 

outburst could occur between Osier Island and Gilbert 

Point, as it did in 1986, or it could take place through 

the main mass of Hubbard Glacier north of Osier Island 

if the rising lake floats the ice free from the fiord 

floor. In the latter case, a large amount of ice could 

be carried away by the outburst, leaving a truncated 

glacier terminus in deep water behind the protective 

moraine. The stability of the glacier then would be 

threatened because it could retreat catastrophically by 

rapid calving into deep water. 

If Russell Lake were to overflow into the Situk 

River, which would occur about 12 to 18 months after 

the lake began to fill, the lake's surface would 

continue to rise several meters higher than the initial 

... 'ft"~<;·. 

,_. . - ·- .. ...._-~ -

Figure 9. Hubbard Glacier ice dam on October 7, 1986, 10:47 a.m., about 12 hours before its failure. View looking east. 

12 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
overflow point by an amount equal to the depth of 

water in the overflowing river. The lake basin would 

thus fill to a height of about 45 m above mean sea 

level. The extent of the zone of flooding along the 

river, interpreted from channel scars visible on aerial 

photographs, is shown in figure 8. The limits of the 

flood-hazard zone on the Yakutat Foreland closer to 

the Gulf of Alaska (fig. 1) also is evident on aerial 

photographs, but future flooding may not be restricted 

to the former flood channel. The land surface may 

have been differentially uplifted by tectonic activity, 

most notably the 1899 Yakutat earthquake, (Tarr and 

Martin, 1906), and the basin size and runoff rate may 

not be the same in the future as they were during the 

last overflow into the Situk River. Although the main 

channel extends west along Old Situk Creek, a smaller 

distributary channel extends south at the moraine 

front (fig. 8), and it also could carry water during 

times of high future flow. 

The average discharge of water from the 

Russell Fiord basin can be estimated using a runoff 

model that is based on the observed equilibrium line 

Figure 10. Hubbard Glacier ice dam disintegrating during 

outburst of Russell Lake; October 8, 1986, 1:56 p.m. 

Figure 11. Outburst of Russell Lake and flow of "Russell River" 

into Disenchantment Bay; October 8, 1986, 9:01 a.m. Discharge 

rate at that time was approximately 77,000 m3Js, and water 

speed in outburst channel was measured at 1 0.8 m/s soon after 

photograph was taken. 

altitudes of glaciers (Mayo, 1986). Th3 estimated 

average discharge would be about 220 m Is, and the 

peak flow each year could be about five times greater 

(a normal relationship for rivers in Alaska). Unusual 

flooding events could be even greater. In contrast, the 

flow of the Situk River duri!f a rainy period in 

October 1987 was about 30 m Is, ang the average 

discharge rate may be only 10 to 15 m Is. An orderof-magnitude increase in the flow of the river can be 

expected to destroy the forest in the revegetated 

channels, possibly creating sizable log jams that would 

further intensify the flooding. High flow probably 

would also cause erosion of soils and sediments, 

resulting in additional turbidity of the water. Because 

its basin is dominated by glacier runoff, Russell Lake 

would contain a significant concentration of suspended 

clay-size particles that would pass into the river. 

Changes in both flow and turbidity would affect the 

highly prized fish resources of the Situk River. 

Flooding would eradicate sections of the Alsek Road 

(fig. 8), inundate a small airfield, and affect 

subsistence fish camps, but at the same time would 

Figure 12. Rocks and mud deposited on alders from icebergs 

that had been floating in Russell Lake. Photograph taken 

October 9, 1986. 

Figure 13. Icebergs stranded in mud-covered forest that had 

been flooded by Russell Lake. Photograph taken October 9, 

1986. 

Advance of Hubbard Glacier and Closure of Russell Fiord 13 
create a new route by which both boats and fish could 

enter Russell Lake. During times of combined high 

tide and high river discharge, the Yakutat Airport, the 

primary point of access to the Yakutat area, might be 

subject to minor flooding. 

Russell Fiord remains unfrozen at the present 

time owing to tidal inflow during the winter, but 

Russell Lake would probably develop winter ice with a 

cover of snow. The ice and snow cover would increase 

albedo locally as well as decrease the amount of heat 

provided by that body of water to the air during severe 

winter weather. These factors could cause the 

temperature of air blowing across Russell Fiord to be 

colder than at present during winter and spring. 

After closure of Russell Fiord, tidal flux into 

Yakutat Bay would be reduced by the amount of water 

that presently cycles in and out of Russell Fiord. The 

resulting decrease in tidal currents in Yakutat Bay 

could cause a decrease in the rate of iceberg flushing 

from the bay. Migratory fish, which enter Russell 

Fiord from Yakutat Bay at present, would be blocked 

by Hubbard Glacier. However, a new path into Russell 

basin via the Situk River would become available after 

the lake filled. 

The advance of Hubbard Glacier and creation of 

Russell Lake might also increase water pressure on the 

Fairweather fault (fig. 1), a plate boundary transform 

fault, where the fault crosses the Nunatak Arm of 

Figure 14. Terminus of surging Haenke Glacier: A, February 13, 1987; B, june 19, 1987. Haenke Glacier surged 

over fan-delta and terminus of Turner Glacier to become Alaska's newest tidewater glacier. 

14 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Russell Fiord (John Lahr, U.S. Geological Survey, oral 

commun., 1987). In addition the fiord would be 

converted into a lake with fresh water "floating" on 

residual, probably sulfate-rich and anoxic, seawater 

(Reeburgh and others, 1976). This would produce a 

drastic change in the ecosystem of the fiord. 

Conclusions 

The recent advance of Hubbard Glacier provides 

a large-scale example of the environmental and 

economic problems that can result from dynamic 

glacier fluctuations in Alaska. As glaciers advance 

and retreat, new glacier-dammed lakes can be formed, 

drainage basin boundaries can change substantially, the 

flow regime and quality of rivers can change, and 

fisheries and forests can be impacted. These changes 

can, in turn, alter transportation, economic, and 

recreational activities of people in the regions 

affected. 

Detection of a submerged moraine beneath the 

terminus of the advancing Hubbard Glacier and the 

discovery of at least four major glacier advances and 

recessions during the past 7,000 years strengthens the 

hypothesis of Post (1975) regarding the behavior of 

tidewater glaciers. Ongoing studies at Hubbard 

Glacier suggest that the rate of advance of tidewater 

glaciers is controlled by the rate of sediment transport 

by the glacier to its calving terminus, by submarine 

mass wasting at the moraine front, and by the depth of 

water in front of the submarine moraine. 

Measurement of the rate of rise of Russell Lake in 

1986 confirmed previously estimated very high runoff 

rates for the region that had been based on primarily 

observed equilibrium-line altitudes of glaciers. 

Acknowledgments 

Investigations of the Hubbard Glacier and 

Russell Lake were carried out within the Wrangell-St. 

Elias National Park and Preserve, administered by the 

U.S. Department of Interior's National Park Service, 

and the Tongass National Forest, administered by the 

U.S. Department of Agriculture's Forest Service. The 

full cooperation of both agencies greatly faciliated 

this study. Richard Martin and Clarence Summers of 

the National Park Service provided permits and 

equipment. Michael Barton, Kenneth Roberts, Helen 

Clough, Jere Christner, Bud Tomlinson, David Wood, 

James Wolfe, William Powell, Patrick Thrasher, and 

Clarence Rayson of the U.S. Forest Service provided 

permits, funding, photographs, technical information, 

equipment, and full support in Yakutat for the 

investigation. Rod March, Dennis Trabant, and Paul 

Brooks of the USGS, and Gail Mayo assisted with work 

at Hubbard Glacier; Donald Thomas and Benjamin 

Kirkpatrick, USGS, measured the decline of Russell 

Lake under difficult storm conditions during the night 

of the outburst. Larry and Caroline Powell of Yakutat 

made available their library and photographs of the 

Yakutat area, and discussed extensively with me the 

effects of Hubbard Glacier's advance. Stimulating 

discussions with all of the above individuals and with 

many other residents of Yakutat helped develop a full 

appreciation of the broad environmental implications 

of the advance of Hubbard Glacier. 

Helen Clough, U.S. Forest Service, Frederica de 

Laguna, Bryn Mawr College, Thomas Hamilton, USGS, 

and Gerd Wendler, University of Alaska, provided 

helpful reviews of this paper. Maps and line drawings 

were prepared by Robert Gilmore, USGS. 

REFERENCES CITED 

Baker, V.R., 1973, Paleohydrology and 

sedimentology of Lake Missoula flooding in 

eastern Washington: Geological Society of 

America Special Paper 144, 79 p. 

Beget, J.E., 1986, Comment on "Outburst floods 

from Glacial Lake Missoula" by G.K.C. 

Clarke, W.H. Mathews, and R.T. Pack: 

Quaternary Research, v. 25, p. 136-138. 

Brown, C.S., Meier, M.F., and Post, Austin, 

1982, Calving speed of Alaska tidewater 

glaciers, with application to Columbia 

Glacier, Studies of Columbia Glacier, 

Alaska: U.S. Geological Survey Professional 

Paper 1258-C, 13 p., 6 plates. 

Costa, J. E., 1985, Floods from dam failures: 

U.S. Geological Survey Open-File Report 85-

560, 54 P• 

de Laguna, Frederica, 1972, Under Mount Saint 

Elias: The history and culture of the 

Yakutat Tlingit: Smithsonian Contributions 

to Anthropology, Part 1, v. 7, 547 p. 

Gannett, Henry, 1902, Geology and paleontology, 

in Harriman Alaska Expedition: New York, 

Doubleday, Page, v. 2, p. 260-261. 

Gunn, J.P., 1930, The Shyok flood, 1929: The 

Himalayan Journal, v. 2, p. 35-47. 

Haeberli, Wilfried, 1983, Frequency and 

characteristics of glacier floods in the 

Swiss Alps: Annals of Glaciology, v. 4, p. 

85-90. 

International Boundary Commission, 1952, 

Establishment of the boundary between Canada 

and the United States, Tongass Passage to 

Mount St. Elias: Washington, D.C., U.S. 

Department of State, 365 p. 

Krimmel, R.M., and Sikonia, W.G., 1986, Velocity 

and surface altitude of the lower part of 

Hubbard Glacier, Alaska, August 1987: U.S. 

Geological Survey Open-File Report 86-549, 

13 P• 

Jones, S.L., 1983, Floods from small drainage 

basins in Alaska: U.S. Geological Survey 

Open-File Report 83-285, 60 p. 

Lamke, R.D., 1972, Floods of the summer of 1971 

in south-central Alaska: U.S. Geological 

Survey Open-File Report, 88 p. 

Mayo, L.R., 1986, Annual runoff rate from 

glaciers in Alaska; a model using the 

altitude of glacier mass balance 

equilibrium, in Kane, D.L., Cold Regions 

Hydrology Symposium: American Water 

Resources Association Technical Publication 

Series TPS-86-1, p. 509-517. 

----- 198 7, Cause of the advance of Hubbard 

Glacier, Alaska: American Association 

Advancement of Science, Arctic Science 

Conference, 1987, Proceedings, p. 49. 

Advance of Hubbard Glacier and Closure of Russell Fiord 15 
Mayo, L.R., Zenone, Chester, and Trabant, D.C., 

1977, Reconnaissance hydrology of Portage 

Glacier Basin, Alaska-1972: U.S. Geological 

Survey Hydrological Investigations Atlas HA583, 2 sheets. 

Meier, M.F., and Post, A.S., 1962, Recent 

variations in mass net budgets of glaciers 

in western North America: International 

Association of Hydrological Sciences, no. 

58, p. 63-77. 

Meier, M.F., Rasmussen, L.A., and Miller, D.S., 

1985, Columbia Glacier 1n 1984: 

Disintegration underway: U.S. Geological 

Survey Open-File Report 85-81, 21 p. 

Nye, J.F., 1960, The response of glaciers and 

ice-sheets to seasonal and climatic 

changes: Royal Society, Proceedings, Series 

A, v. 256, no. 1287, p. 559-84. 

O'Connor, J.E., and Baker, V.R., 1987, Peak 

flood discharges from late Pleistocene 

Glacial Lake Missoula [abs.]: Geological 

Society of America Abstracts with Programs, 

v. 19, no. 7, p. 792. 

Plafker, George, and Miller, Don, 1958, Glacial 

features and surficial deposits of the 

Malaspina district, Alaska: U.S. Geological 

Survey Miscellaneous Geological 

Investigations Map I-271., scale 1:125,000. 

Post, Austin, 1975, Preliminary hydrography and 

historic terminal changes of Columbia 

Glacier, Alaska: U.S. Geological Survey 

Hydrologic Investigations Atlas HA-559. 

Post, Austin, and Mayo, L.R., 1971, Glacier 

dammed lakes and outburst floods in 

Alaska: U.S. Geological Survey Hydrological 

Investigations Atlas HA-455, 10 p., 3 

sheets. 

Ray, H.A., and Kjelstrom, L.C., 1978, The flood 

in southeastern Idaho from the Teton Dam 

failure of June 5, 1976: U.S. Geological 

Survey Open-File Report 77-765, 48 p. 

Reeburgh, W.S., Muench, R.D., and Cooney, R.T., 

1976, Oceanographic conditions during 1973 

in Russell Fjord, Alaska: Estuarine and 

Coastal Marine Science, p. 129-145. 

Russell, I.C., 1891, An expedition to Mount St. 

Elias, Alaska: National Geographic 

Magazine, v. 3, p. 53-204. 

Russell, I.e., 1893, Second expedition to Mount 

St. Elias, in Powell, J.W., Thirteenth 

annual report of 

Geological Survey to 

Interior, 1891-'92; 

Washington, D~C., 

Office, p. 7-91. 

the United States 

the Secretary of the 

Part II--Geology: 

Government Printing 

Seitz, H.R., Thomas, D.S., and Tomlinson, Bud, 

1986, The storage and release of water from 

a large glacier-dammed lake: Russell Lake 

near Yakutat, Alaska, 1986: U.S. Geological 

Survey Open-File Report 86-545, 10 p. 

Sturm, Matthew, and Benson, C.S., 1986, A 

history of jokulhlaups from Strandline Lake, 

Alaska, U.S.A.: Journal of Glaciology, v. 

31, no. 109, p. 272-280. 

Tarr, R.S., and Butler, B.S., 1909, The Yakutat 

Bay region, Alaska; Physiography and glacial 

geology: U.S. Geological Survey 

Professional Paper 64, 183 p. 

Tarr, R.S., and Martin, Lawrence, 1906, Recent 

changes of level in the Yakutat Bay region, 

Alaska: Geological Society of America 

Bulletin, v. 17, p. 29-64. 

Thorarinsson, Sigurdur, 1957, The jokulhlaup 

from the Katla area in 1955 compared with 

other jokulhlaups in Iceland: Reykjavik, 

Museum of Natural History Miscellaneous 

Papers, no. 18, p. 21-25. 

Trabant, D.C., 1986, Glacier motion by 

telemetered satellite navigation 

positions: American Association Advancement 

of Science, Arctic Science Conference, 1987, 

Proceedings, p. 51. 

U.S. Geological Survey, 1964, Compilation of 

records of surface waters of Alaska, October 

1950 to September 1960: U.S. Geological 

Survey Water-Supply Paper 1740, 86 p. 

U.S. Geological Survey, 1971, Surface water 

supply of the United States 1961-65; art 15. 

Alaska: U.S. Geological Survey Water-Supply 

Paper 1936, 342 p. 

Reviewers: Helen Clough, T.D. Hamilton, 

Frederica de Laguna,and Gerd Wendler 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

16 Geologie Studies in Alaska by the U.S. Geological Survey during 1987 
NORTHERN ALASKA 

View north across Little Kobuk Sand Dunes to Jade Mountains and other peaks of western Brooks Range. See 

article by Hamilton and others. Photograph by J.P. Galloway. 
A Major Unconformity Between Upper Ordovician and 

Lower Devonian Strata in the Nanook Limestone, 

Shublik Mountains, Northeastern Brooks Range 

By Robert B. Blodgett, David M. Rohr, Anita G. Harris, and Rang Jia-yu 

Field studies during 1987 helped to characterize 

a major unconformity separating Upper Ordovician and 

Lower Devonian strata within the uppermost part of 

the Nanook Limestone in the Mt. Michelson C-3 

quadrangle, northeastern Brooks Range. Two sections 

(fig. 1) that include the unconformity were measured, 

and the unconformity was traced between them. 

Responsibility for the paleontologic results reported 

here is: Blodgett and Rong, brachiopods; Harris, 

conodonts; and Rohr, gastropods. 

The Nanook Limestone was named by Dutro 

(1970), who recognized eight informal members and 

suggested that the entire formation was of Middle 

Devonian age. Because an angular unconformity 

separates the Nanook Limestone from the overlying 

Endicott Group, member 8, the uppermost and thickest 

member of the Nanook Limestone, is variably 

preserved. Dutro (1970) gave the thickness for this 

member as 218 m in its type section, but farther to the 

east it thickens to about 625 m. 

Blodgett and others (1986a, b) recognized the 

presence of Late Cambrian, Early Ordovician, Middle 

and (or) Late Ordovician, and late Early Devonian 

(Emsian) and (or) early Middle Devonian (Eifelian) 

faunas within member 8 of the Nanook Limestone. In 

addition, one locality (in section 87NA-1 of this report) 

was suggested as possibly being of Early Silurian age. 

Additional studies of the faunas from member 8 of the 

Nanook now show that both Middle and Late 

Ordovician faunas are present and that the Devonian 

strata, lying unconformably on Upper Ordovician 

strata, are entirely of late Early Devonian (Emsian) 

age. The suggested Lower Silurian (Llandoverian) 

strata are now known to be of Late Ordovician age. 

Measured section 87NA-1 is 76.2 m thick (fig. 

2). The base of the section is at a vertical fault zone 

at the west end of the traverse. The top of the section 

is at a covered interval separating the highest exposed 

beds of member 8 from the overlying beds of the 

Kayak Shale. An unconformity is present 39.6 m above 

the base of the section. The beds below the 

unconformity are lighter (light brown to medium gray) 

than the overlying dark-brown to dark-gray strata. 

Beds immediately above the surface of the 

unconformity are reddish. Conodonts recovered 

throughout the section have a color alteration index 

(CAl) of 4, indicating that the rocks reached burial 

temperatures of at least 200 °C. 

A conodont sample from 1.6 m above the base 

of the section (USGS colin. 10630-CO, fig. 2) produced 

a monospecific collection of AphelognathU3 aff. A. 

divergens Sweet (figs. 3A-E), indicating a 

Richmondian-Gamachian age and a warm, possibly 

very shallow water depositional environment. 

Collections relatively abundant in representatives of 

AphelognathU3 divergens and A. shatzeri Sweet, to the 

virtual exclusion of other conodonts, are also 

characteristic of an 80-meter, massive, burrowmottled dolostone in the Baird Group of the Hub 

Mountain area, northeast Baird Mountains quadrangle, 

western Brooks Range (Dumoulin and Harris, 1987). A 

single specimen of PhragmodU3 n. sp. of Barnes (1974) 

(fig. 3F), together with specimens of AphelognathU3 sp. 

indet., were recovered from 6.1 m above the base of 

the section (USGS colin. 10631-CO). PhragmodU3 n. 

sp. is known from lower Maysvillian strata in the 

Canadian Arctic Islands and also occurs in strata of 

that age in the central Brooks Range (Chandalar D-6 

quadrangle, USGS collns. 10582-CO and 10583-CO). 

Conodonts in overlying collections (USGS colin. 10632-

CO, in particular) in the Nanook section, however, 

suggest that this interval is of Richmondian age. 

Ostracodes were the only other significant faunal 

element noted this low in the section, and their 

abundance also suggests a slightly restricted 

environment. 

SHUBLIK MOUNTAINS 

14 13 18 17 

I 87NA-2 

KI LOMETE R S 

Figure 1. Location of sections (see fig. 2) measured in upper part 

of member 8 of the Nanook Limestone in Mount Michelson C-3 

quadrangle. Base from U.S. Geological Survey, 1955; elevation 

given in feet. 

18 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
..... ~ (/) z 

w w w ow (:J I- o z (/) II ~ oo >- w I- z N (/) (/) (/) 0 

() 

25 0 

"' "' 

~ 0 

... z Ql 

~ II z "' - w ~ -- - z 

0 ~ -

(/) 

> 0 ~ ? 

w ...J w 0 

? 

-

~ 

z 

~ ~ 

- C'- · 

z ...J ~ 

~ ...J z - (:J - ~ () - - I 0 > (/) z 0 ~ 0 

0 ~ 

~ II II I 0 w () 

0... - 0... II 

::J 

0 

38 0' 

87NA-1 

~ 

COVERED 

I I 

1= 1 

1=1 

f- 11837 -S D 

I I 

I I 1 1836-SD 

I I 1 

87NA-2 

COVERED 

I @ 

r I 

I I 

@ @ 

@ 

@ 

@ 

(o')l 

~ ~ 

@ @ I 

!) I ® 

I I 

® I ® 

~ 

= 

~ 

1184 7-S D 

1184 5-SD 

- 1 1844-S D 

I- 11843 -SD 

1184 2-S D 

11 841-SD 

I-

..... 

z w Ow (:J Oz ~ Co 

Z N I0 (/) 

() 

"' "' 

~ 0 

... 

Ql 

"' 

"' "' "' ... 

Ql 

,. z 

~ .:: -

(/) 

~ 

w 

f-.--

"' 0> "' " ... Ql ·.. 

- .Q 0 

... " Ql 0 ... "' 

0> 

- --

-

~ 

183 5-SD 

D ISCONFORM ITY . .../ ~ I11 840-SD '0, 

11839-Sil Q; 1 1838-SD .o J 

I@ I 

~ ~ 

I~ I 

I I 

I I 

0)1 Gl f- 1 0 632-CO 

1- 1063 1-CO 

1 0 63 0 -CO 

FA ULT 

METERS FEET 

200 

50 

100 

0 0 

0 

8 Gi 

'J/) 

w 

ll> ~ I-

~ 

~ 

T 

I 

1 

~ @\ 

I 

~ 

~ 

I 

10636-CO 

063 5-C O 

10634-CO 

" 0 

0. 

EXPLANATION 

Limestone 

~ Dolostone 

~ 

= Amphipora 

G Brachiopod 

@ Crinoid ossicle 

~ Favositid coral 

G) Gastropod 

(/) ~ 

w w 

I- II (/) 

w >- (/) (/) 

z II ~ 

w -

~ z 

0 0 > ...J w 

0 

~ 

z 

~ 

-

...J z ...J 

- ~ 

(:J () 

I - (/) > ~ 0 ~ 0 

II II 

w 0 0... 

0... 

::J 

Figure 2. Columnar sedions of upper part of member 8 of the Nanook Limestone showing correlation of measured 

sections 87NA-1 and 87NA-2. Location of sections shown on figure 1. Ticks to right of each column indicate 

conodont sample. Tick accompanied by USGS collection number indicates that sample yielded re latively 

biostratigraphically useful conodonts. 

Northern Alaska 19 
An unusually rich brachiopod-molluscan faunal 

assemblage was collected 11.0 to 11.3 m above the 

base of the section. The brachiopods consist almost 

exclusively of abundant, disarticulated valves of the 

pentameracean genus Tscherskidium Nikolaev and 

Sapelnikov, 1969. Sapelnikov (1985) reported this 

Figure 3. Scanning electron micrographs of Late Ordovician (A-F) 

and late Early Devonian (G-K) conodonts from uppermost part of 

the Nanook Limestone, Shublik Mountains, Mount Michelson C-3 

quadrangle. A-E, Aphelognathus aff. A. divergens Sweet, USGS 

colin. 1 0630-CO, section 87NA-1. A, Lateral view of Pb element, 

x50, USNM 423445. B, Posterior view of Sal element, x50, 

USNM 423446. C, Upper view of quadriramate Sa2 element, 

x50, USNM 423447. D, Posterior view of Sb element, x50, 

USNM 423448. E, Inner lateral view of Sc element, x40, USNM 

423449. F, Phragmodus n. sp. of Barnes (1 974, pl. 1, fig. 20), 

lateral view of Sa element, xl 00, USNM 423450; USGS colin. 

10631 -CO, section 87NA-1. G, Pandorinellina expansa Uyeno 

and Mason, lateral view of Pa element, xl 00, USNM 423451; 

USGS colin. 11 837-SD, section 87NA-1. H, Ozarkodina cf. 0 . 

paucidentata Murphy and Matti, lateral view of Pa element, xl 00, 

USNM 423452; USGS colin. 1 1839-SD, section 87NA-2. I, J, 

Polygnathus inversus Klapper and Johnson, upper (x40, USNM 

423453) and lower (x50, USNM 423454) views of Pa elements; I 

from USGS colin. 11 843-SD, section 87NA-2; J from USGS colin. 

1 1 842-SD, section 87NA-2. K, Polygnathus aff. P. perbonus 

(Philip), lower view of Pa element, x50, USNM 423455; USGS 

colin. 11 839-SD, same collection as H. 

genus to be restricted to the Ashgillian of northeastern 

USSR (Kolyma and Chukotka) and, possibly, southern 

Kazakhstan. Recently, the genus was reported by 

Rong and Han (1986) from middle Ashgillian strata of 

Jiangxi Province, east-central China. The new species 

in the Nanook Limestone (figs. 4A-D) is conspecific 

with a form identified as Tscherskidium sp. in Rohr 

and Blodgett (1985, p. 667) from Upper Ordovician 

(Ashgillian) strata in the Lone Mountain area, McGrath 

C-4 quadrangle, west-central Alaska. The numerous 

gastropods at this horizon comprise at least eight 

species that include Siskiyouspira sp. (figs. 41-K), 

Murchisonia? sp. (fig. 4H), Ectomaria cf. E. prisca 

(Billings, 1859) (fig. 4L), and Maclurites cf. M. 

manitobensis (Whiteaves). The distinctive genus 

Siskiyouspira Rohr, 1980 is now known from the Upper 

Ordovician of the northeastern Brooks Range, the Lone 

Mountain area of west-central Alaska, and the 

Klamath Mountains of northern California. S. 

majewskei (Rohr and Blodgett, 1985) from westcentral Alaska is smaller than the Nanook form but, 

although more poorly preserved, has the same general 

shape. 

Other mollusks present at this level include 

abundant bivalves and rare orthocone cephalopods. 

Ostracodes, also abundant in this interval, include the 

leperditiid genus Sibiritia, previously known only from 

rocks of Silurian (Llandoverian-early Wenlockian) age 

(J.M. Berdan, U.S. Geological Survey, oral commun., 

1987). Conodonts from this interval (USGS colin. 

10632-CO) include: Aphelognathu.s sp. indet., 

Pseudobelodina cf. P. adentata Sweet, P. aff. P. 

vulgaris Sweet, Drepanoistodu.s suberectus (Branson 

and Mehl), and Panderodus sp. The age of this 

assemblage is late Edenian -Richmondian, more 

probably Richmondian. 

Conodont collections at 22.9 m, 28.9 m, and 

36.6 m above the base of the section, but still beneath 

the unconformity, yielded only long-ranging 

representatives of Panderodus sp. Favositid corals are 

common to abundant from 22.9 to 36.6 m above the 

base. 

The upper part of section 87NA-1 contains 

numerous lenses rich in Amphipora (a sticklike 

stromatoporoid) which, in the absence of typical openmarine faunal elements, suggests a shallow, somewhat 

restricted, lagoonal environment. Conodonts 

recovered at 42.7 m and 51.8 m above the base of the 

section include only long-ranging forms indicative of a 

Wenlockian-Emsian age range. One collection (USGS 

colin. 11837-SD), taken 60.9 m above the base, yielded 

Figure 4. Late Ordovician brachiopods and gastropods from 

upper part of member 8 of the Nanook Limestone. A-D, 

Tscherskidium n. sp., ventral, posterior, and opposite side views 

of pedicle valve, xl, USNM 417633, USGS colin. 1 0632-CO, 

section 87NA-1 . E-G, Eoconchidium sp., side, ventral and dorsal 

views of pedicle valve, xl .5, USNM 417634, 40.6 m above base 

of section 87NA-2. H, Murchisonia? sp., side view, x3, USNM 

417635, same collection as A-D. 1-K, Siskiyouspira sp., USNM 

417636, same collection as A-D; I, oblique side view, x3.5; ], K, 

apical and basal views, x3. L, Ectomaria cf. E. prisca (Billings, 

1 859), apertural view, x3, USNM 417637, same collection as AD. 

20 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Northern Alaska 21 
only platform elements of Pandorinellina expansa 

Uyeno and Mason (fig. 3G), a tropical, relatively 

cosmopolitan species known to range from the 

serotinus Zone into the costatus costatus Zone (latest 

Emsian-earliest Eifelian age). Based on a comparison 

of thickness between this section and nearby section 

87NA-2, we believe that a latest Emsian age is more 

likely. 

Section 87NA-2, which is 115.8 m thick (fig. 2), 

is along a north-south-trending ridge. The base of the 

section is at the base of a prominent yellow dolomitic 

mudstone bed. Underlying strata were not measured 

due to inaccessibility. The top of the section is at the 

north end of a prominent saddle. An unconformity 

occurs at 44.2 m above the base of the section. As in 

section 87NA-1, beds below the unconformity are 

typically lighter shades of gray or brown, whereas beds 

above it are characteristically dark gray. All 

conodonts from section 87NA-2 have a CAl value of 4, 

identical to that for section 87NA-1. 

Megafossils range from absent to abundant 

below the unconformity. The brachiopod 

Tscherskidium n. sp. is present at 7.6 m and 22.6 m 

above the base of the section. Favositid corals are 

abundant between 23.2 to 36.6 m above the base. This 

interval, and its contained corals, is identical to the 

favositid-rich interval below the unconformity in 

section 87NA-1. A coquina layer of disarticulated 

valves of the pentameracean Eoconchidium sp. (figs. 

4E-G) occurs 39.6 m above the base of the section. 

The genus Eoconchidium Rozman, 1967 was reported 

by Sapelnikov (1985) from Ashgillian strata of 

northeastern USSR and Kazakhstan, and, very 

questionably, from lower Ludlovian strata in 

Kazakhstan. Conodonts from 7.6 m, 15.2 m, and 22.6 

m above the base of the section indicate a Middle to 

Late Ordovician age; those from 30.5 m and 39.6 m 

indicate an even broader range. We place the entire 

measured part of the section below the unconformity 

in the Late Ordovician (Ashgillian) on the basis of the 

presence of the pentameracean genera Tscherskidium 

and Eoconchidium in its lower and upper parts, 

respectively. On the basis of paleontologic correlation 

and lithologic similarities to the Upper Ordovician 

strata of section 87NA-2, all the beds below the 

unconformity in section 87NA-1 are also considered to 

be of Late Ordovician age. In addition, the trilobites 

reported in Blodgett and others (1986a) as possibly 

indicating an Early Silurian (Llandoverian) age that 

were recovered from approximately 22.9 m above the 

base of section 87NA-1 are now considered to be of 

Late Ordovician age. 

The part of the section above the unconformity 

consists of dark-gray lime mudstone and wackestone. 

Poorly preserved megafossils are present sporadically 

throughout the section. Two-holed crinoid ossicles, 

considered an index fossil to Emsian and Eifelian 

strata, are found throughout the section and form a 

0.3-m-thick encrinite bed immediately above the 

unconformity. The common megafossils include 

favositid and thamnoporoid tabulate corals and solitary 

rugose corals. Conodonts recovered from 44.2 m and 

44.5 to 44.8 m above the base of the section include 

Polygnathus aff. P. perbonus (Philip) (fig. 3K), 

suggesting the gronbergi Zone (early Emsian age). 

Four samples taken from 71.6 m (USGS colin. 11842-

SD) to 112.8 m (USGS colin. 11845-SD) above the base 

of the section produced abundant representatives of P. 

inversus Klapper and Johnson, indicating an inversus 

Zone through serotinus Zone age range. The highest 

conodont collection from 115.2 m (USGS colln. 11847-

SD) produced abundant specimens of P. inversus 

together with lesser numbers of Pandorinellina 

steinhomensis miae (Bultynck) and Sannemannia aff. S. 

glenisteri (Klapper) and is also assigned to an inversus 

Zone-serotinus Zone interval (middle to late Emsian 

age). The presence of representatives of 

Pandorinellina expansa at only 21.9 m above the 

unconformity in section 87NA-1, suggests that the 

interval from at least 71.6 m to near the top of 

member 8 at 115.2 m in section 87NA-2 is within the 

serotinus Zone. 

These biostratigraphic results document the 

fact that Lower Devonian strata rest unconformably 

on Upper Ordovician strata in member 8 of the Nanook 

Limestone. The general parallelism of beds on either 

side of this boundary indicates a disconformity and 

suggests that no major tectonic events affected the 

present area of the Shublik Mountains during Late 

Ordovician to Early Devonian time. Another 

significant result is the restriction of the uppermost, 

Devonian, part of the Nanook Limestone to the Emsian 

(upper Lower Devonian). 

REFERENCES CITED 

Barnes, C.R., 1974, Ordovician conodont 

biostratigraphy of the Canadian Arctic, in 

Aitkin, J.D., and Glass, D.J., eds., 

Canadian Arctic geology: Calgary, 

Geological Association of Canada and 

Canadian Society of Petroleum Geologists 

Special Volume, p. 221-240. 

Blodgett, R.B., Clough, J.G., Dutro, J.T., Jr., 

Ormiston, A.R., Palmer, A.R., and Taylor, 

M.E., 1986a, Age revisions for the Nanook 

Limestone and Katakturuk Dolomite, 

northeastern Brooks Range, in BartschWinkler, Susan, and Reed, K.M., eds., 

Geologic studies 1n Alaska by the U.S. 

Geological Survey during 1985: U.S. 

Geological Survey Circular 978, p. 5-10. 

Blodgett, R.B., Clough, J.G., Dutro, J.T., Jr., 

Palmer, A.R., Taylor, M.E., and Ormiston, 

A.R., 1986b, Age revision of the Katakturuk 

Dolomite and Nanook Limestone, northeastern 

Brooks Range, Alaska [abs.]: Geological 

Society of America Abstracts with Programs, 

v. 18, no. 2, p. 87. 

Dumoulin, J .A., and Harris, A. G., 1987, Lower 

Paleozoic carbonate rocks of the Baird 

Mountains quadrangle, western Brooks Range, 

Alaska, in Tailleur, Irv, and Weimer, Paul, 

eds., Alaskan North Slope geology: 

Bakersfield, Calif., and Anchorage, Alaska, 

Pacific Section, Society of Economic 

Paleontologists and Mineralogists and Alaska 

Geological Society, v. 1, p. 311-336. 

Dutro, J. T., Jr., 1970, Pre-Carboniferous 

carbonate rocks, northeastern Alaska, in 

Adkison, W.L., and Brosge, W.M., eds., 

22 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Proceedings of the geological seminar on the 

North Slope of Alaska: Los Angeles, 

American Association of Petroleum 

Geologists, Pacific Section, p. Ml-Ml7. 

Rohr, D.M., and Blodgett, R.B., 1985, Upper 

Ordovician Gastropoda from west-central 

Alaska: Journal of Paleontology, v. 59, p. 

667-673. 

Rang Jia-yu and Han Nai-ren, 1986, Preliminary 

report on Upper Ordovician (Mid-Ashgillian) 

brachiopods, Yushan, northeastern Jiangxi 

(Eastern China), in Racheboeuf, P.R., and 

Emig, C., eds., Les-brachiopodes fossiles et 

actuels: Actes du 1er Congres international 

sur les Brachiopodes, Brest, 

Biostratigraphie du Paleozoique, v. 

485-491. 

1986, 

4, P• 

Sapelnikov, V.P., 1985, Sistema i 

stratigraficheskoe znachenie brakhiopod 

podotryada pentameridin: Moscow, Nauka, 205 

P• 

Reviewers: A.J. Boucot and J.T. Dutro, Jr. 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Northern Alaska 23 
Ostracode and Molluscan Assemblages from the Late Neogene 

Nuwok Member of the Sagavanirktok Formation, North Slope 

By Elisabeth M. Brouwers and Louie Marincovich, Jr. 

Neogene marine ostracodes and mollusks 

previously known only from the type section of the 

Nuwok Member of the Sagavanirktok Formation at 

Carter Creek have been recognized at two additional 

localities on the northeastern Alaskan coastal plain, 

Barter Island and Manning Point (fig. 1). Ostracodes 

occur at both new localities, and mollusks only at 

Manning Point. These fossils provide the first 

paleontologic correlation of Carter Creek Nuwok 

strata with other outcrops in northeastern Alaska, and 

imply that Nuwok strata underlie the coastal plain for 

at least the 45 kilometers that separate Carter Creek 

and Manning Point. Additional analysis of the 

ostracodes and mollusks suggests correlations with 

faunas in the northwestern Atlantic and provides 

insights into the marine climate during Nuwok time. 

The type section of the Nuwok Member consists 

of 81 m of interbedded sandstone and siltstone that is 

exposed in the north limb of the Marsh Creek anticline 

along the lower reaches of Carter Creek (Morris, 1954; 

Detterman and others, 1975) (fig. 2). Ostracodes, 

mollusks and large amounts of wood occur at several 

horizons. The upper part of the Nuwok sequence also 

contains sparse calcareous concretions and abundant 

crystal aggregates of glendonite, an unusual calcite 

pseudomorph associated with glaciomarine muds (Suess 

and others, 1982). Correlation of the Barter Island and 

Manning Point beds with the Nuwok type section at 

Carter Creek is based on (1) stratigraphic ranges of 

ostracode and mollusk taxa, (2) the presence of a well 

cemented, mollusk-rich bed at Manning Point and 

Carter Creek, and (3) the co-occurrence of glendonites 

and calcareous concretions at Carter Creek and 

Manning Point. 

Ostracodes at Carter Creek occur in three 

stratigraphically separate assemblages whose 

boundaries are marked by pronounced faunal and 

lithologic changes (fig. 2). Whether these pronounced 

breaks are local facies changes or unconformities 

representing significant temporal hiatuses is not yet 

known. 

The basal ostracode assemblage occurs in the 

lower 5 m of the Carter Creek section and consists 

exclusively of extinct species. Species-level 

morphologic similarities with U.S. East Coast faunas 

of late Miocene and early Pliocene age imply a 

common ancestry, although there are no species in 

common. Nuwok ostracodes assigned to Muellerina, 

Sarsicytheridea, and Cytheretta are most similar to 

species from the Miocene part of the Chesapeake 

Group and the Pliocene Yorktown Formation of 

Virginia and Maryland. Other species belong to 

endemic arctic genera (Rabilimis, Paracyprideis) or to 

cosmopolitan genera of the temperate realm 

( Cytheropteron). 

Living analogs of basal-assemblage species live 

in environments characterized by uniform temperature 

and salinity, in depths ranging from the deeper inner 

shelf to the middle shelf (about 20-50 m). Modern 

temperature preferences of genera such as Cytheretta 

and Muellerina suggest mild to cold temperate 

conditions, which today occur from Cape Hatteras to 

the Gulf of St. Lawrence in the western Atlantic. 

The middle assemblage comprises most of the 

section at Carter Creek and, like the basal 

assemblage, consists entirely of extinct species. The 

minimum age of this assemblage is 3 Ma, based on (1) 

the youngest known occurrence of Rabilimis 

paramirabilis and Pterygocythereis vannieuwenhuisei 

in the stratigraphically higher Gubik Formation 

(Repenning and Brouwers, 1988) and (2) the absence of 

Pacific ostracodes that migrated north following the 

opening of Bering Strait at about 3 Ma (Gladenkov, 

1981). The maximum age of this assemblage is not 

known. Ostracode faunas from Manning Point and 

Barter Island correlate with the middle ostracode 

assemblage at Carter Creek. 

--..BEAUFORT SEA BARTER MANNING 

BROOKS 

.---~ 

0 10 20 30 MILES 

• Sample Locality 0 10 20 30 40 50 KILOMETERS 

Figure 1. Eastern Arctic Coastal Plain, showing trend of Marsh 

Creek anticline and location of outcrops studied at Carter Creek, 

Manning Point, and Barter Island. 

24 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
The middle assemblage indicates a cold 

temperate marine climate, comparable to that of the 

shallow offshore region of New England and the Gulf 

of St. Lawrence today. Some genera of the middle 

assemblage, such as Aurila, are common in temperate 

waters but do not occur in frigid waters. A shallowing 

trend is shown by middle-shelf taxa in the lower part 

of this assemblage and deeper inner-shelf taxa in its 

upper part. Abundant wood occurs near the top of the 

assemblage, although nonmarine and estuarine 

ostracodes are absent. Glendonites and calcareous 

concretions range through the upper half of the middle 

assemblage. 

The upper assemblage occurs in the basal 10 m 

of an upper sand unit, from 63 to 71 m above the base 

of the section at Carter Creek (fig. 2); the assemblage 

consists of both extant and extinct species. The 

maximum age of the upper assemblage is 2. 7 Ma, based 

on the presence of Rabilimis septentrionalis 

(Repenning and others, 1987). An ancestral species, R. 

paramirabilis, is known to be no younger than 2.8-3.0 

Ma (Colvillian), and the derived species, R. 

septentrional is, is known to be no older than 2. 7 Ma 

(Bigbendian). Extant species of the upper assemblage 

are circumpolar in distribution, occurring in subfrigid 

to frigid waters of the shallow inner shelf. 

Carter Creek mollusks occur as two 

stratigraphically separate assemblages that correspond 

to the lower and middle ostracode assemblages (fig. 

2}. The lower assemblage {the Chlamys nuwokensis 

zone) and the upper assemblage (the Arctica 

carteriana zone) have no species in common, but both 

indicate normal marine salinity, temperate water, and 

deposition on the deeper inner shelf (about 25-50 m). 

Whether the difference in faunal composition reflects 

a hiatus or only two roughly coeval habitats is 

CARTER CREEK 

q,"> 

~ ·~ Stratigraphic Ranges of Molluscan * § ob ~ ~rs Ostracode Species Zones 

meters ~0 ~{/ 

• ~ 

1''11 

70 

• ~ Upper 

Assemblage 

60 • n ---- -

• • ' ! l a: 

w 50 

Ill 

:IE II 

il w "' c: 

:IE • ~ ·~ 40 • I Middle ~ .. ~ I "' c 

0 Assemblage " 0 <t N 

:t ~ ::::> 30 ~ z 

' 

~ 

II 

20 ~ 

• ...-v ~ 10 Basal "' <: Assemblage .. 

"" 0 

...-v II '1: .. 

" c 0 <: 0 ..,N 

E "'

~ ~ .!! 

silt, clayey silt concretions -<:: 

(.) 

[2] sand § . pebbles 

m calcareous 

~ gravel cemented zone 

Figure 2. Stratigraphic section of Nuwok Member at type locality at Carter Creek plotted against 

stratigraphic ranges of ostracode species. Note that the molluscan zones, the Chlamys nuwokensis and 

Arctica carteriana zones, correspond to basal and middle ostracode assemblages, respectively. 

Northern Alaska 25 
unknown. Beds at Manning Point contain mollusks 

referable to the Arctica carteriana zone, the upper 

molluscan assemblage at Carter Creek. 

Similarities of several Nuwok molluscan taxa 

with warm temperate to tropical Neogene faunas of 

the eastern United States suggest that provinciality 

based upon temperature was less developed between 

the northwestern Atlantic and Arctic Oceans during 

the Neogene than at present. The presence of even 

seasonal sea ice during deposition of Nuwok strata is 

unlikely. 

Affinities with Pacific faunas are absent in both 

molluscan faunas, and both have strong genus-level 

ties to North Atlantic late Neogene faunas. The 

Nuwok fauna must predate the first appearance of 

North Pacific mollusks at approximately 3 Ma in 

Iceland (Gladenkov, 1981) and in the uppermost 

member of the Yorktown Formation in Virginia. 

Further study of the ties between the Nuwok 

ostracode and molluscan faunas and late Neogene 

faunas of the U.S. middle Atlantic coastal plain will 

provide the basis for more precise correlation and 

dating of the Nuwok beds. 

REFERENCES CITED 

Detterman, R.L., Reiser, H.N., Brosg~, W.P,, and 

Dutro, J.T., Jr., 1975, Post-Carboniferous 

stratigraphy, northeastern Alaska: U.S. 

Geological Survey Professional Paper 886, 46 

P• 

Gladenkov, Y. B. , 

of Iceland 

correlation: 

18-23. 

1981, Marine Plio-Pleistocene 

and problems of its 

Quaternary Research, v. 15, p. 

Morris, Robert, 1954, Reconnaissance study of 

the Marsh Creek anticline, northern 

Alaska: U.S. Geological Survey Open-file 

Report 54-146, 6 p. 

Repenning, C.A. and Brouwers, E.M., 1988, MidPliocene to Late Pleistocene changes in the 

Arctic Ocean borderland ecosystem, in 

Luchterhand, K. and Leopold, E., eds., Longterm restructuring in late Cenozoic 

terrestrial ecosystems: Evanston, Ill., Wm. 

Caxton Ltd. 

Repenning, C.A., Brouwers, E.M., Carter, L.D., 

Marincovich, Louie, Jr., and Ager, T.A., 

1987, The Beringian ancestry of Phenacomys 

(Rodentia: Cricetidae) and the beginning of 

the modern Arctic Ocean borderland biota: 

U.S. Geological Survey Bulletin 1687, 31 P• 

Suess, E., Balzer, W., Hesse, K.-F., Muller, 

P.J., Ungerer, C.A., and Wefer, G., 1982, 

Calcium carbonate hexahydrate from organicrich sediments of the Antarctic shelf: 

Precursors of glendonites: Science, v. 216, 

P• 1128-1130. 

Reviewers: C.A. Repenning and J.A. Wolfe 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

26 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Nearshore Marine Environments of the 

Alaskan Beaufort Sea During Deposition of the 

Flaxman Member of the Gubik Formation 

By L. David Carter, Elisabeth M. Brouwers, and Louie Marincovich, Jr. 

The Flaxman Member of the Gubik Formation 

(Dinter, 1985) is a glaciomarine mud a few meters 

thick that occurs along the Beaufort Sea coast and 

inland to altitudes of about 7 m (fig. 1). Deposition of 

the Flaxman Member occurred during an early 

Wisconsin sea-level highstand that is informally named 

the Simpsonian transgression (Carter and others, 

1986). The Flaxman Member contains ice-rafted 

erratics of Canadian provenance (Rodeick, 1979), and 

transportation of the erratics to the Beaufort Sea 

coast by icebergs records the disintegration of an ice 

sheet in the Canadian Arctic (Hopkins, 1982). Erratics 

occur to the southern limit of the deposit, and so were 

being supplied at the peak of the transgression 

(Hopkins, 1982). Because the Flaxman Member is a 

glaciomarine deposit, it differs from any modern 

sediment accumulations on the inner shelf of the 

Beaufort Sea; this suggests that some aspects of 

nearshore marine environments, particularly salinity, 

temperature, and turbidity, may have been different 

during the Simpsonian transgression than they are 

today. We present faunal data from the Flaxman 

Member that suggest that, at water depths of 20 m and 

less, seasonal fluctuations of salinity and temperature 

were probably similar to the present regime but that 

water temperatures may have been slightly warmer. 

SEA 

• FLAXMAN MEMBER 

68° 

Figure 1. Map of northern Alaska showing distribution of 

Flaxman Member and locations mentioned in text (CS, Cape 

Simpson; DP, Drew Point; WL, "Whale Lake"; Fl, Flaxman Island; 

CR, Canning River; SC, Simpson Cove; MP, Manning Point; PB, 

Pokok Bay; DB, Demarcation Bay; CB, locality near Canadian 

border). 

Our data also suggest that turbidity was high relative 

to today. At some localities east of Flaxman Island, 

however, salinities were less than modern values for 

comparable environments, and we interpret this as 

indicating a higher influx of fresh water into the 

marine environment by meltwater from abundant 

icebergs and an ablating ice sheet. 

One of the best exposures of the Flaxman 

Member is in a coastal bluff near Cape Simpson (figs. 1 

and 2), where the glaciomarine mud has been uplifted 

and anticlinally deformed, probably as a result of 

pressures generated by the development of nearby oil 

seeps. The Flaxman Member at Cape Simpson is about 

2 m thick; it disconformably overlies marine sand and 

is conformably or paraconformably overlain by similar 

marine sand. A previous account referred to the 

Flaxman microfauna at Cape Simpson as impoverished 

(Hopkins and others, 1981), but this resulted from 

interpreting the upper marine sand as the Flaxman 

Member and the underlying glaciomarine mud as of 

last interglacial (Pelukian) age. Thermoluminescence 

ages for the glaciomarine mud show that it is early 

Wisconsin in age and support our designation of this 

unit as the Flaxman Member (Carter and others, 

1986). The marine sand above the Flaxman Member is 

most likely a regressive facies of the Simpsonian 

Figure 2. Coastal bluff about 4 m high near Cape Simpson. 

Dashed line marks contact between Flaxman Member and 

underlying marine sand. Arrows point to erratic stones in 

Flaxman Member. Marine sand that overlies the Flaxman 

Member is out of view to right. 

Northern Alaska 27 
transgression, but may represent a younger sea-level 

highstand. The Flaxman Member contains a sparse but 

relatively diverse benthic microfauna comprising 15 

taxa of marine ostracodes (table 1) and 16 taxa of 

foraminifers (Hopkins and others, 1981). The 

ostracode fauna is especially instructive; it contains 

taxa that occur across the modern inner shelf, but also 

contains Krithe glacialis and Rabilimis mirabilis, two 

taxa that today are restricted to environments of 

normal marine salinity in which there is little seasonal 

variation in either temperature or salinity (McDougall 

and others, 1986). Rabilim is m irabilis occurs today 

only in water depths greater than 20 m (Brouwers, 

1982; McDougall and others, 1986), which is the upper 

lim it of both the pycnocline and halocline {Sharma, 

1979; Coachma11 and Aagaard, 1974). 

The mollusk fauna from the Flaxman Member at 

Cape Simpson is depauperate, consisting only of the 

bivalves Bathyarca glacialis and Astarte borealis (table 

2). Both occur today in the Beaufort Sea, but B. 

glacialis has been found only in water depths greater 

than 23 m. Thus both the mollusks and ostacodes 

indicate that the glaciomarine mud at Cape Simpson 

was deposited below the tops of the halocline and 

pycnocline, and suggest limited seasonal variability in 

salinity and density. 

In coastal bluffs at Drew Point (fig. 1), Flaxman 

ostracode faunas contain only euryhaline and 

eurythermal marine taxa such as Heterocyprideis 

sorbyana, and Rabilimis septentrionalis, which tolerate 

the seasonal salinity and temperature variations that 

occur in modern nearshore, shallow-water 

environments above the 20-m isobath (McDougall and 

others, 1986). In these water depths, modern summer 

temperatures range from -1.5 to 14 °C, and salinity 

ranges from 0. 7 to 31.6 per mil. Winter temperature is 

generally below 0 °C, ranging from -0.5 to 0.5 °C, and 

salinity is somewhat higher than in summer, with a 

range of 21.8 to 31.0 per mil (Sharma, 1979). 

The present-day 20-m isobath occurs about 25 

km offshore from Cape Simpson, and the distances 

from Cape Simpson and Drew Point inland to the inner 

limit of the Flaxman Member are about 20 km and 10 

km, respectively (Carter, 1983). If we assume that 

bathymetric equilibrium-profiles during deposition of 

the Flaxman Member were similar to modern ones, 

then the glaciomarine mud at Cape Simpson would 

have been deposited in water depths of about 20 m, 

and the tops of the pycnocline and halocline would 

have been at about the same depths as they are 

today. Additionally, the deposits at Cape Simpson and 

Drew Point must have been uplifted about 15 m and 5 

to 10 m, respectively. Deposits at the inner limit of 

the Flaxman Member west of Harrison Bay, however, 

have not been uplifted (Carter and others, 1986). 

Slightly warmer water than at present during 

deposition of the Flaxman Member is suggested by the 

presence of the foraminifer Elphidiella groenlandica 

(Cushman) at Cape Simpson, Drew Point, and 

informally named Whale Lake (Hopkins and others, 

1981; Kristin McDougall, U.S. Geological Survey, 

written commun., 1980; fig. 1). Elphidiella 

groenlandica does not live in the Beaufort Sea today, 

but is common south of Norton Sound (Kristin 

McDougall, U.S. Geological Survey, oral commun., 

1987). Furthermore, the Flaxman marine mammal 

fauna at Whale Lake includes Eschrictius sp. (gray 

whale) and Histriophoca fasciata (Zimmermann) 

(ribbon seal) (Repenning, 1983). Both ribbon seal and 

gray whale are now only occasional visitors to the 

Alaskan Beaufort Sea (Moore and Barrowclough, 1984; 

Rugh and Fraker, 1981), and Repenning (1983) pointed 

out that their presence as fossils suggests the 

possibility of warmer waters than at present. 

East of Harrison Bay, Flaxman ostracode faunas 

generally contain the euryhaline and eurythermal taxa 

characteristic of modern shallow-water faunas (table 

1). The molluscan bivalve Cyrtodaria kurriana, present 

at Demarcation Bay and questionably identified at 

Canning River, is abundant in modern nearshore 

sediments of the Beaufort Sea at water depths 

shallower than 5 m, but has not been found at greater 

depths (Carey and others, 1984). Thus seasonal 

variations in temperature and salinity at these two 

localities during deposition of the Flaxman Member 

were probably similar to modern values for water 

depths up to 5 m. 

Conditions different from any known modern 

marine environment of the Alaskan Beaufort Sea are 

indicated by the presence of the marine ostracode 

species Pteroloxa cumuloidea, which composes 63 

percent of the fauna at Simpson Cove and 29 percent 

of the fauna at Pokok Bay. The only modern 

environment in which P. cumuloidea has been found is 

in the nearly fresh-water distributary channel mouths 

of the Ikpikpuk River delta (E.M. Brouwers and L.D. 

Carter, unpub. data). It does not occur in 

environments with slightly higher salinities, such as off 

the mouths of major rivers and in lagoons and bays 

(Brouwers, 1982). The Flaxman Member is not a 

deltaic facies, and the abundant presence of P. 

cumuloidea at Simpson Cove and Pokok Bay is 

interpreted to mean that there was a greater influx of 

fresh water into the marine environment than is known 

to occur anywhere along the coast today. Although 

Simpson Cove is near the mouth of the Katakturuk 

River, it is unlikely that during deposition of the 

Flaxman Member this minor river would have had a 

discharge larger than the modern major rivers. The 

Pokok Bay locality is distant from any potentially 

large source of fresh water. This suggests that a thin 

surficial layer of nearly fresh water may have been a 

regional feature of the eastern Beaufort Sea, perhaps 

generated by higher regional runoff than today, but 

more probably by meltwater from the icebergs and 

ablating ice sheet that supplied the erratics in the 

Flaxman Member. 

If the major source of fresh water was 

meltwater from glacier ice emanating in Canada, we 

expect that the surface layer of low-salinity water 

would have thickened eastward. This may be indicated 

by Pteroloxa venepuncta, which is the only ostracode 

species identified from the Flaxman Member near the 

Canadian border. Pteroloxa venepuncta is unknown in 

modern environments but is believed to have inhabited 

environments similar to closely related P. cumuloidea. 

Glaciomarine deposition of the erratics and 

fine-grained sediment of the Flaxman Member implies 

higher rates of sedimentation than those of the modern 

inner shelf, where much of the area may be undergoing 

net erosion (Reimnitz and others, 1985). The presence 

of icebergs during deposition of the Flaxman Member 

28 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Ostracodes from the Flaxman Member of the Gubik Formation 

[Number of samples examined in parentheses; #, dominates assemblage] 

Species Locality 

CS DP CR SC MP PB DB CB 

(16) (9) (1) (22) (1) (6) (l) (1) 

Marine ostracodes 

Acanthocythereis dunelmensis (Norman) X 

Bythocythere sp. 

Cytheromorpha macchesneyi (Brady & Crosskey) 

C. sp. A 

X X 

X 

X X 

X 

Cytheropteron arcuatum X 

C. montrosiense Brady, Crosskey, and Robertson X X X X X 

C. pseudomontrosiense X 

C. paralatissimum X 

C. aff. C. pyramidale of Swain X 

c. sedovi Schneider 

c. walli Whatley and Masson 

C. sp. (aff. C. occulatum) 

Cytheretta teshekpukensis Swain 

X 

X 

X 

X 

Eucythere sp. X X 

X 

X 

Finmarchinella (Barentsovia) barentzovoensis 

Heterocyprideis sorbyana (Jones) X X X X 

X 

X X# X 

H. fascis X 

Krithe glacialis Brady, Crosskey & Robertson X 

Normanicythere leioderma (Norman) X 

Paracyprideis pseudopunctillata Swain X X X X 

X# 

X 

Pteroloxa cumuloidea Swain X# 

P. venipuncta X 

Rabilimis mirabilis (Brady) X 

R. septentrionalis (Brady) X X X 

Robertsonites tuberculata X 

Roundstania globulifera (Brady) X 

Sarsicytheridea macrolaminata X 

S. bradii X X X X 

Nonmarine ostracodes 

Candona sp. 

Cyclocypris sp. 

Limnocythere sp. 

suggests higher rates of ice gouging than would be 

produced by sea ice alone, which today annually 

disrupts about 2. 7 percent of the sea floor (Barnes and 

Rearic, 1985). An increase in the rate of 

sedimentation and (or) ice gouging relative to today 

must have generated greater turbidity in the water 

column, and the composition and depauperate nature 

of the mollusk faunas suggest that this was indeed the 

case. Only three species of bivalves have been 

identified from any Flaxman locality (table 2), whereas 

Carey and others (1984) reported an average of 7.6 

species per site at water depths of 5 to 25 m in modern 

Beaufort Sea environments. Moreover, 31 species of 

bivalves have been collected from the modern 

Beaufort Sea at water depths of 25 m and less (Carey 

and others, 1984), whereas the presently known 

Flaxman bivalve fauna consists of only seven taxa. 

Species richness on the inner shelf of the western 

Beaufort Sea is thought to be largely determined by 

bottom turbulence (Carey and others, 1984), and so the 

depauperate Flaxman mollusk faunas suggest greater 

turbidity. Furthermore, all the spe<>ies prest:nt in the 

X X 

X 

X 

shallow-water Flaxman faunas east of Cape Simpson 

are capable of surviving in turbid water. Portlandia 

arctica, for example, has been found living adjacent to 

glacier termini where sedimentation rates arE' 

exceptionally high (Lubinsky, 1980; Ockel mann, 1958). 

In summary, faunal data suggest that during 

deposition of the Flaxman Member of the Gubik 

Formation, seasonal fluctuations in temperature and 

salinity in nearshore marine environments west of 

Harrison Bay were similar to those of the present day, 

but average temperatures may have been slightly 

higher. From Flaxman Island east there may have 

been a surficial, eastward-thickening sheet of nearly 

fresh water across much of the nearshore zone during 

part or all of the open water season. Immediately 

below this low-salinity layer, seasonal variations in 

temperature and salinity were probably similar to 

modern values for water depths less than 5 m. 

Turbidity was greater across the entire inner shelf 

than it is today, probably as a result of the relatively 

higher rates of sedimentation and ice gouging in a 

glaciomarine sedimentation regime. 

Northern Alaska 29 
Table 2. Bivalve mollusks from the Flaxman Member of the 

Gubik Formation 

Species Locality 

CS WL CR SC MP DB 

Astarte borealis X 

(Schumacher) 

A. montagui (Dillwyn) 

Bathyarca glacialis (Gray) X 

Cyrtodaria kurriana Dunker 

Hiatella arctica (Linnaeus) 

Portlandia arctica (Gray) 

Serripes groenlandicus X 

(Bruguiere) 

REFERENCES CITED 

X X 

X 

?X X 

X 

X X 

Barnes, P .W., and Rea ric, D.M., 1985, Rates of 

sediment disruption by sea ice as determined 

from characteristics of dated ice gouges 

created since 1975 on the inner shelf of the 

Beaufort Sea, Alaska: U.S. Geological 

Survey Open-File Report 85-463, 35 p. 

Brouwers, E.M., 1982, Analysis of inner neritic 

ostracode assemblages from the Beaufort Sea, 

northern Alaska: Implications for 

interpreting analogous Quaternary sediments, 

in Smith, P.A., and Hopkins, D.M., Offshore 

permafrost studies and shoreline history as 

an aid to predicting offshore permafrost 

conditions: U.S. National Oceanic and 

Atmospheric Administration, Environmental 

Assessment of the Alaskan Continental Shelf, 

Annual Report, Task D-9, Research Unit 204 

and 273, April 1981 to March 1982 [unpaged]. 

Carey, A.G., Jr., Scott, P.H., and Walters, 

K.R., 1984, Distributional ecology of 

shallow southwestern Beaufort Sea (Arctic 

Ocean) bivalve Mollusca: Marine Ecology 

Progress Series, v. 17, p. 125-134. 

Carter, L.D., 1983, Engineering-geologic maps of 

northern Alaska, Teshekpuk Quadrangle: U.S. 

Geological Survey Open-File Report 83-634, 1 

sheet, scale 1:250,000, includes tabular 

text. 

Carter, L.D., Brigham-Grette, Julie, and 

Hopkins, D.M., 1986, Late Cenozoic marine 

transgressions of the Alaskan Arctic Coastal 

Plain, in Heginbottom, J.A., and Vincent, JS., eds~ Correlation of Quaternary deposits 

and events around the Beaufort Sea: 

Geological Survey of Canada Open File Report 

1237, p. 21-26. 

Coachman, L.K., and Aagaard, Knut, 1974, 

Physical oceanography of arctic and 

subarctic seas, in Herman, Y., ed., Marine 

geology and oceanography of the arctic 

seas: New York, Springer-Verlag, p. 1-72. 

Dinter, D.A., 1985, Quaternary sedimentation on 

the Alaskan Beaufort shelf: Influence of 

regional tectonics, fluctuating sea levels, 

and glacial sediment sources: 

Tectonophysics, v. 114, p. 133-161. 

Hopkins, D.M., 1982, Abortive glaciations at 

high latitudes indicated by glaciomarine 

deposits, Gubik Formation, northern Alaska 

[abs.]: Geological Society of America 

Abstracts with Programs, v. 14, no. 7, p. 

518. 

Hopkins, D.M., McDougall, Kristin, and Brouwers, 

Elisabeth, 1981, Microfossil studies of 

Pelukian and Flaxman deposits, Alaska coast 

of the Beaufort Sea, in Smith, P.A., Hartz, 

R.W., and Hopkins, D.M~ Offshore permafrost 

studies and shore! ine hi story as an aid to 

predicting offshore permafrost conditions: 

U.S. National Oceanic and Atmospheric 

administration, Environmental Assessment of 

the Alaskan Continental Shelf, Annual 

Report, Task D-9, Research Unit 204 and 273, 

April 1979 to March 1980, Appendix G, p. 64-

71. 

Lubinsky, Irene, 1980, Marine bivalve molluscs 

of the Canadian central and eastern 

Arctic: Faunal composition and 

zoogeography: Canadian Bulletin of 

Fisheries and Aquatic Sciences, Bulletin 

207, 111 p. 

McDougall, Kristin, Brouwers, Elisabeth, and 

Smith, Peggy, 1986, Micropaleontology and 

sedimentology of the PB borehole series, 

Prudhoe Bay, Alaska: U.S. Geological Survey 

Bulletin 1598, 62 p. 

Moore, S.E., and Barrowclough, E.I., 1984, 

Incidental sighting of a ribbon seal (Phoca 

fasciata) in the western Beaufort Sea: 

Arctic, v. 37, p. 290. 

Ockelmann, K.W., 1958, marine 

Lamellibranchiata. The zoology of east 

Greenland: Meddelelser om Gr~nland Udgiune 

af Kommissionen for Videnskabelige 

Undersogel ser I Gr~nland, Bd. 122, Nr. 4, 

256 P• 

Reimnitz, Erk, Graves, S.M., and Barnes, P.W., 

1985, Beaufort Sea coastal erosion, 

shoreline evolution, and sediment flux: 

U.S. Geological Survey Open-File Report 85-

380, 66 P• 

Repenning, C.A., 1983, New evidence for the age 

of the Gubik Formation, Alaskan North 

Slope: Quaternary Research, v. 19, p. 356-

372. 

Rodeick, C.A., 1979, The origin, distribution, 

and depositional history of gravel deposits 

on the Beaufort Sea continental shelf, 

Alaska: U.S. Geological Survey Open-File 

Report 79-234, 87 p. 

Rugh, D.J., and Fraker, M.A., 1981, Gray whale 

(Eschrichtius robustus) sightings in eastern 

Beaufort Sea: Arctic, v. 34, p. 186-187. 

Sharma, G. D., 1979, The Alaskan shelf: New 

York, Springer-Verlag, 498 p. 

Reviewers: D.M. Hopkins and Kristin McDougall 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

30 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Stromatolite- and Coated-Grain-Bearing Carbonate Rocks of the 

Western Brooks Range 

By Julie A. Dumoulin 

Carbonate rocks characterized by locally 

abundant stromatolites and coated grains have been 

found at several localities in the Baird Mountains and 

Ambler River quadrangles (fig. 1). These rocks are 

part of a belt of metasedimentary and metaigneous 

rocks that constitutes the southwestern flank of the 

Brooks Range; all are included in the parautochthon 

(Schwatka sequence) of Mayfield and others (1983). 

The rocks have been deformed and metamorphosed to 

blueschist and greenschist facies, but primary textures 

and sedimentary structures are locally well preserved. 

Abundant stromatolites and (or) coated grains 

have been found in carbonate rocks west, south, and 

southeast of Mount Angayukaqsraq in the northeastern 

part of the Baird Mountains quadrangle, west of the 

Akiak Mountains in the western Ambler River 

quadrangle, and east of the Redstone River in the 

central Ambler River quadrangle (fig. 2). These rocks 

are included in the Paleozoic marble and quartzite unit 

of Mayfield and Tailleur (1978), and the Kogoluktuk 

Schist of Ritzman and others (1982). Rocks that may 

be equivalent to the carbonate sequence discussed 

here, but which have not yet been closely studied, crop 

out over a large area that extends east through the 

Survey Pass quadrangle (S. W. Nelson, U.S. Geological 

Survey, oral commun., 1987), and into the Wiseman 

quadrangle (A.G. Harris, U.S. Geological Survey, oral 

commun., 1987). The stromatolites in the central 

Sadlerochit 

0 100 200 

'--'---.J 

KILOMETERS 

Figure 1. Index map of northern Alaska showing localities 

discussed in text. Quadrangle designations: AR, Ambler River; 

BM, Baird Mountains; DP, Demarcation Point; MM, Mount 

Michelson; SP, Survey Pass; T, Teller; W, Wiseman. 

Ambler River quadrangle were first noted by Ritzman 

and others (1982); all other occurrences are here 

reported for the first time. 

Stromatolites are organosedimentary structures 

produced through sediment binding, trapping, and (or) 

precipitation by a microbial community (Krumbein, 

1983). Stromatolite morphologies in western Brooks 

Range rocks range from flat or slightly hummocky 

tabular sheets a few centimeters thick to laterally 

linked columnar or club-shaped bodies up to 15 em high 

(fig. 3). At most localities, stromatolitic rocks are 

intercalated with layers and lenses of dolomitic 

grainstone and packstone that contain abundant and 

various coated grains--both ooids and oncoids, 

according to the usage of Wilson (1975). Ooids are 

spherical particles less than 2 mm in diameter with 

smooth, multiple, concentric laminae assumed to have 

formed through inorganic chemical precipitation in 

warm, wave-agitated, saline or hypersaline waters (fig. 

4A). Oncoids are characterized by more uneven 

laminae thought to have formed through biogenic 

encrustation, typically by algae or cyanobacteria (fig. 

4B). The ooid and oncoid grainstone layers are 

typically crossbedded, but may show parallel 

lamination or grading. Fenestral fabric is locally well 

developed. Associated carbonate lithologies include 

storm-generated flat-pebble conglomerate and 

carbonate mudstone. 

The total thickness of the unit containing the 

stromatolites and coated grains is difficult to estimate 

due to structural complexity of the outcrop areas. 

Maximum thicknesses, on the order of several hundred 

meters, occur south of Mount Angayukaqsraq. 

The assemblage of sedimentary features found 

in these carbonate rocks indicates intertidal to shallow 

subtidal depositional environments (Wilson, 1975). 

Modern ooids form in warm, shallow shelf areas of 

0~0 

1 

KILOMETERS 1 

Figure 2. Known locations of stromatolite- and coated-grainbearing carbonate rocks of Baird Mountains and Ambler River 

quadrangles (solid circles). Extent of lithofacies (stippled pattern) 

generalized from Mayfield and Tailleur (1978). 

Northem Alaska 31 
moderate to high wave and current activity; oolitic 

sands are most abundant in waters less than 10 m, and 

typically less than 2 m deep (Choquette, 1978). The 

Bahama carbonate platform, where tidal channels 

contain living columnar stromatolites growing in a 

high-energy environment dominated by ooid sand (Dill 

and others, 1986), may provide a modern analog for the 

depositional environment of the western Brooks Range 

rocks. 

In all of the western Brooks Range localities, 

carbonate rocks containing stromatolites and coated 

grains are associated with quartzose metasedimentary 

and metavolcanic rocks. Layers of quartzite and 

locally calcareous quartz-white mica schist as much as 

15 m thick are intercalated with the carbonate rocks. 

Quartzose metasedimentary rocks in the central 

Ambler River area include metaconglomerates with 

clasts of quartz and chert up to 2 em in diameter. 

Metavolanic rocks include blue amphibole-bearing 

metabasite that locally preserves pillow breccia and 

agglomeratic primary textures, and chlorite-albite 

schist. Southeast of Mount Angayukaqsraq, layers of 

conglomerate contain mafic clasts in a carbonate 

A 

B 

Figure 3. Columnar stromatolites, Akiak Mountains area, 

western Ambler River quadrangle; lens cap is 5 em in diameter. A, 

Top view. B, Side view. 

matrix; this occurrence suggests that the association 

of carbonate and metavolcanic rocks is a primary one 

and not just a later tectonic feature. 

The tectonic setting for the association of 

shallow-water carbonate rocks and mafic metavolcanic 

rocks may have been a rifted carbonate platform; 

several episodes of Proterozoic(?) and Paleozoic 

rifting have been proposed for northwestern Alaska 

(Schmidt, 1987). The central Ambler River quadrangle 

contains a carbonate sequence that may have been 

deposited in a small rift basin (fig. 2, locality A). 

Stromatolite-bearing, shallow-water carbonate rocks 

occur adjacent to black carbonate rhythmites with 

intrastratal deformation (slump folds?). The 

rhythmites are intercalated with beds of carbonate 

breccia tens of meters thick containing clasts of 

white-weathering, locally stromatolitic dolostone in a 

matrix of black lime mudstone. These rocks are 

interpreted to be debris flows that formed along a 

slope bounding a carbonate platform or shelf; the 

light-colored clasts most likely represent earlycemented shallow-water carbonate lithologies that 

were eroded and transported into the basin. 

B 

Figure 4. Coated grains from southeast of Mount 

Angayukaqsraq. A, Ooid with smooth, even laminae. B, Oncoid 

with irregular laminae and multiple nuclei. 

32 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
The age of the stromatolite- and coated-grainbearing sequence is uncertain. Stromatolites are 

known from rocks of Archean age to the present 

(Krumbein, 1983), and other organic remains (including 

trace fossils) have not yet been found in this 

sequence. Relationships with associated rocks suggest 

that the carbonate rocks with stromatolites and coated 

grains are early Paleozoic or older in age. In the 

northeastern Baird Mountains quadrangle, they form a 

series of thrust sheets imbricated with Proterozoic 

amphibolite-facies rocks and lower Paleozoic 

carbonate rocks (Till and others, 1987). The 

stromatolite- and coated-grain-bearing rocks could 

represent upper Proterozoic or lowest Paleozoic 

"cover" of the older Proterozoic "basement." Further, 

deformed and metamorphosed carbonate rocks of 

middle or late Paleozoic age in this part of Alaska 

almost invariably contain at least some megafossil 

debris (for example, corals and brachiopods). 

However, the absence of organic remains other than 

stromatolites in the stromatolite- and coated-grainbearing rocks could be attributed to the fact that both 

stromatolitic supratidal flats and ooid sand shoals are 

environments inhospitable to most invertebrates. Both 

stromatolites and coated grains are rare or absent in 

carbonate rocks of middle and late Paleozoic age in 

the western Brooks Range. 

Regional correlations of the stromatolite- and 

coated-grain-bearing rocks are hindered by the lack of 

age control, but some lithologic correlations can be 

suggested. The Ordovician argillaceous limestone unit 

of Sainsbury (1969) is a thick (1,500 m) Lower 

Ordovician carbonate sequence that crops out in the 

York Mountains of western Seward Peninsula (fig. 1). 

It contains locally abundant coated grains, a variety of 

stromatolitic morphologies, and some beds rich in 

quartz silt (Vandervoort, 1985); however, it also 

contains locally abundant fossils and other carbonate 

lithologies not seen in the western Brooks Range 

sequence. 

The Katakturuk Dolomite, widely exposed in the 

Shublik and Sadlerochit Mountains in the northeastern 

Brooks Range, is a better lithologic match for the 

western Brooks Range sequence. It is thick (greater 

than 3,000 m) and contains subtidal to intertidal 

stromatolites of diverse morphologies associated with 

crossbedded oolitic grainstone and storm-generated 

intraclastic grainstone (Clough, 1986). The Katakturuk 

is considered to be Proterozoic in age (Blodgett and 

others, 1986). A thick sequence of dolostone directly 

beneath the Katakturuk is associated with basaltic 

volcanic rocks, but quartzose sedimentary rocks 

appear to be rare or absent in most of the Katakturuk 

(K.F. Watts, University of Alaska, written commun., 

1987). 

If the stromatolite- and coated-grain-bearing 

carbonate rocks of the western Brooks Range do 

correlate with the Katakturuk Dolomite, a very 

extensive carbonate platform existed in northern 

Alaska during the Proterozoic. A belt of shallowwater carbonates of this size is not unprecedented--

the modern-day Great Barrier Reef east of Australia is 

twice the length of the Brooks Range. 

REFERENCES CITED 

Blodgett, R.B., Clough, J.G., Dutro, J.T., Jr., 

Ormiston, A.R., Palmer, A.R., and Taylor, 

M.E., 1986, Age revisions for the Nanook 

Limestone and Katakturuk Dolomite, 

northeastern Brooks Range, 1n BartschWinkler, Susan, and Reed, K.M., eds., 

Geologic Studies 1n Alaska by the U.S. 

Geological Survey during 1985, U.S. 

Geological Survey Circular 978, p.S-10. 

Choquette, P.W., 1978, Oolite, in Fairbridge, 

R.W., and Bourgeois, Joann~ eds., The 

Encyclopedia of Sedimentology: Stroudsburg, 

Penn., Dowden, Hutchinson, and Ross, p. 510-

515. 

Clough, J.G., 1986, Peritidal sedimentary facies 

and stromatolites of the Katakturuk Dolomite 

(Proterozoic), northeastern Alaska [abs.]: 

12th International Sedimentological 

Congress, Canberra, Australia, p. 64. 

Dill, R.F., Shinn, E.A., Jones, A.T., Kelly, K., 

and Steinen, R.P., 1986, Giant subtidal 

stromatolites forming in normal salinity 

waters: Nature, v. 324, p. 55-58. 

Hitzman, M.W., Smith, T.E., and Proffett, J.M., 

Jr., 1982, Bedrock geology of the Ambler 

District, southwestern Brooks Range, 

Alaska: Alaska Division of Geological and 

Geophysical Surveys Geologic Report 75, 2 

sheets, scale 1:125,000. 

Krumbein, W.E., 1983, Stromatolites--The 

challenge of a term in space and time: 

Precambrian Research, v. 20, p. 493-531. 

Mayfield, C.F., and Tailleur, I.L., 1978, 

Bedrock geology map of the Ambler River 

quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 78-120A, scale 1:250,000. 

Mayfield, C.F., Tailleur, I.L., and Ellersieck, 

Inyo, 1983, Stratigraphy, structure, and 

palinspastic synthesis of the western Brooks 

Range, northwestern Alaska: U.S. Geological 

Survey Open-File Report 83-779, 53 p. 

Sainsbury, C.L., 1969, Geology and ore deposits 

of the central York Mountains, western 

Seward Peninsula, Alaska: U.S. Geological 

Survey Bulletin 1287, 101 p. 

Schmidt, J.M., 1987, Paleozoic extension of the 

western Brooks Range continental margin--

Evidence from mineral deposits, igneous 

rocks, and sedimentary facies [abs.]: 

Geological Society of America Abstracts with 

Programs, v. 19, no. 6, p. 477. 

Till, A.B., Schmidt, J.M., and Nelson, S.W., 

1987, Thrust-involvement of Proterozoic and 

Mesozoic metamorphic rocks, southwestern 

Brooks Range, Alaska [abs.]: Geological 

Society of America Abstracts with Programs, 

v. 19, no. 6, p. 458. 

Vandervoort, D.J., 1985, Stratigraphy, 

paleoenvironment, and diagenesis of the 

Lower Ordovician York Mountain carbonates, 

Seward Peninsula, Alaska: Baton Rouge, 

Louisiana State University, M.S. Thesis, 141 

P• 

Northern Alaska 33 
Wilson, J.L., 1975, Carbonate facies in geologic 

history: New York, Springer-Verlag, 471 p. 

Reviewers: S.E. Box and Keith F. Watts 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

34 Geologie Studies in Alaska by the U.S. Geological Survey during 1987 
Off-Platform Silurian Sequences 1n the 

Ambler River Quadrangle 

By julie A. Dumoulin and Anita G. Harris 

Lithofacies changes in coeval upper Paleozoic 

rocks have been used to unravel the tectonic history of 

northern Alaska (for example, Mayfield and others, 

1983). Conodont biostratigraphy and detailed 

petrologic studies are now revealing facies differences 

in lower Paleozoic rocks that can also be used to 

constrain their tectono-sedimentary framework 

(Dumoulin and Harris, 1987). A basic element of basin 

analysis is the discrimination of shallow-water shelf 

and platform sequences from deeper water slope and 

basinal deposits. This report documents several new 

localities of deeper water, off-platform Silurian 

deposits in the Ambler River quadrangle and briefly 

outlines some of their paleogeographic implications. 

Mayfield and Tailleur (1978) first described a 

sequence of metasedimentary rocks from two areas in 

the north-central Ambler River quadrangle (fig. 1). 

They recognized "turbidite textures, flute casts, and 

graded beds" in these rocks and assigned them to the 

Devonian siltstone and slate unit (fig. 2, unit 1). This 

unit was considered Devonian in age because it 

contained favositid corals of Silurian or Devonian age 

and lay between Mississippian quartz conglomerate 

(Me) and carbonate rocks of the Silurian and Devonian 

Skajit Limestone (Mayfield and Tailleur, 1978). Our 

recent studies of unit 1 rocks confirm that they are 

turbidites, but indicate that they are, at least in part, 

Silurian in age. 

A measured section 8 km east of Kavachurak 

Creek (fig. 2, locality A) contains more than 25 m of 

metasandstone, phyllite, and metalimestone, and a 

sequence of similar rocks 16 km to the west is at least 

200 m thick (fig. 2, locality 8). The rocks are 

recrystallized and locally folded, but primary 

sedimentary features are generally well preserved. 

Conodonts from these rocks have color alteration 

indices of 5, indicating the host rock reached 

temperatures of at least 300 °C. Siliciclastic 

metasandstone makes up at least 30 percent of unit 1; 

it is primarily medium to coarse grained and slightly 

schistose (fig. 3). Most samples contain 5 to 30 

percent monocrystalline and polycrystalline quartz 

clasts, variable (as much as 30 percent) amounts of 

carbonate detritus, and 5 to 10 percent sedimentary 

lithic grains (mudstone, siltstone, and phyllite). Other 

clast types include feldspar (many of the grains are 

zoned), volcanic lithic grains (most with lathwork 

textures), and chert. Some chert clasts contain 

recrystallized radiolarians. About 50 to 60 percent of 

unit 1 is fine-grained quartzose siltstone and dark-grey 

to black, light-brown-weathering phyllite, with locally 

abundant calcareous concretions as much as 30 em in 

diameter. The siliciclastic rocks have many features 

characteristic of turbidites, including complete to 

partial Bouma sequences, convolute laminae, flame 

structures, and a variety of flute, scour, and prod 

marks. The strata form packages 1 meter to tens of 

meters thick that coarsen and thicken upward. 

Recrystallized, locally dolomitic, limestone 

layers 5 to 80 em thick make up the remaining 10 to 20 

percent of unit 1; they are intercalated with the 

siliciclastic rocks and increase in abundance upward. 

Carbonate rock types include calcirudites containing 

clasts as large as 10 em, calcarenites, and 

calcilutites. The coarser grained layers typically show 

channelized bases, local grading, and parallel and 

convolute laminations; clasts are mostly dolostone and 

limestone, plus a few percent mudstone and quartz. 

~e interpret these rocks as carbonate turbidites and 

debris flows made up of redeposited shallow-water 

detritus. The calcilutites probably represent 

carbonate mud eroded from a slope or pla tform. 

Conodonts recovered from four samples 

distributed through our 25-m measured section at 

Locality A are of Middle to early Late Silurian age 

(~enlockian to Ludlovian) and represent a normalmarine, relatively warm, shallow-water biofacies (figs. 

4A-M). Megafossils recovered from locality A and 8 

include corals, gastropods, bryozoans, brachiopods, 

conularids, and orthocone cephalopods; they indicate a 

Silurian or Devonian age (Mayfield and Tailleur, 1978; 

J. T. Dutro, Jr., U.S. Geological Survey, written 

0 

67 

1 4 1 ° 

(j~Lisburne Pen. 

BM 

2 

Pen. 0100200 

'---4----.J 

KILOMETERS 

Figure 1. Index map of northern Alaska showing localities 

discussed in text and general distribution of Silurian shallowwater (s) and deeper water (d) lithofacies (from Dumoulin and 

Harris, 1987, and unpub. data). Quadrangle designations: AR, 

Ambler River; BM, Baird Mountains; SP, Survey Pass. 

Northern Alaska 35 
EXPLANATION 

Siltstone and slate 

(unit 1) 

Limestone, schist, and 

phyllite (unit 2) 

Phyllite and siliceous 

phyllite (unit 3) 

dlfl~ ~ 

0 5 10 

KILOMETERS ~~ 

Figure 2. Location of Silurian fossil localities and lithologic units of Mayfield and Tail leur (1 978), northern part of 

Ambler River quadrangle; extent of lithologic units generalized from Mayfield and Tail leur (1 978). Letters indicate 

USGS collection localities referred to in text; A, 11 507-SD to 1151 0-SD; B, 11511 -SD; C, 11 769-SD; D, 1151 6-SD. 

See figure 1 for location. 

commun., 1978). Elements of this megafauna as well 

as the conodonts are characteristic of shallow-water 

environments, and probably they were hydraulically 

transported basinward from a platform. We believe 

that the conodonts found in unit 1 indicate the true 

age of the unit, however, and were not derived from 

older rocks because the species association is 

consistent in age and biofacies throughout the 

measured section. 

The intercalation of siliciclastic and carbonate 

layers in these Silurian off-platform deposits could 

reflect sediments derived from two separate source 

areas--one dominantly siliciclastic and the other 

dominantly carbonate. Alternatively, hybrid sequences 

can accumulate in response to sea-level fluctuations 

(Droxler and Schlager, 1985). Siliciclastic basin 

deposits tend to accumulate during relative lowstands, 

when sediment bypasses the platform and shelf and is 

carried basinward; carbonate basin deposits are 

favored during highstands, when carbonate production 

on the platform and shelf is enhanced and terrigenous 

deposits are trapped near shore. 

Rocks lithologically (and perhaps genetically) 

related to unit 1 crop out across the central and 

eastern Ambler River quadrangle and make up the 

Devonian black limestone, calcareous schist, and black 

siliceous phyllite unit of Mayfield and Tailleur (1978) 

(fig. 2, unit 2). Unit 2 phyllites contain probable 

recrystallized radiolarians; rare metasandstones 

consist mostly of quartz, feldspar, and sedimentary 

lithic grains. Unit 2 was considered "stratigraphically 

equivalent" to "less metamorphosed" rocks in the 

Survey Pass quadrangle that contain Middle and Late 

Devonian brachiopods by Mayfield and Tailleur 

(1978). However, several metalimestone layers in unit 

2 (locality C in fig. 2) contain some of the same 

conodonts (Pelekysgnathus n. sp.) that date unit 1 as 

Wenlockian to Ludlovian in age. These conodonts are 

of uniformly small size and were probably winnowed as 

they were transported basinward from a shallower 

water environment. Unit 2 may well include rocks of 

Figure 3. Siliciclastic turbidites at locality B. A, Outcrop view. B, 

Photomicrograph of coarse-grained metasandstone rich in chert 

(C) and sedimentary lithic (5) clasts. 

36 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Figure 4. Scanning electron micrographs of Silurian conodonts 

from off-platform deposits in Ambler River quadrangle. A-1, 

Pelekysgnathus n. sp., x75, from locality A (fig. 2); C from USGS 

colin. 11507-SD (9 m above base of section), all others from 

1151 0-SD (25 m above base of section). Although these 

specimens represent a new species, we believe the composition 

of the apparatus, which includes P elements and two series of M 

and S elements (an alate and a roundiform series) indicates a 

Wenlockian or Ludlovian age. Thus far, alate M and S elements 

have not been reported from the apparatus of Pelekysgnathus, 

but it seems likely that such morphotypes would characterize 

early representatives of the genus. Representatives of 

Ozarkodina excavata (Branson and Mehl) and Panderodus sp., 

long-ranging Middle Silurian to Early Devonian forms, are the 

only other conodonts in the samples which produced 

Pelekysnathus n. sp. A, B, inner and outer lateral views of P 

element, USNM 423456. C, D, Postero-lateral views of 

roundiform M and Sa elements, USNM 423457-423458. E-1, 

Alate M (E), Sa (F, posterior view; G, antero-lateral view), Sb (H), 

and Sc (I) elements, USNM 423459-423463 . J-M, Ozarkodina 

excavata (Branson and Mehl), Pa, M, Sa, and Sc elements, xSO, 

USNM 423464-423467, from USGS colin. 11507-SD (9 m 

above base of section, loc. A, fig. 2). N, Pterospathodus 

pennatus (Walliser), upper view of Pa element, x50, USNM 

423645, from USGS colin. 11516-SD (fig. 2, loc. D). The 

presence of this species indicates a range from the eel/ani Zone 

to the lower part of the amorphognathoides Zone (very latest 

Llandoverian). 

several ages, but at least part of it is of Silurian age 

and correlative with unit 1. 

Off-platform deposits of Silurian age have also 

been found in the western Ambler River quadrangle. 

Middle Silurian (late Wenlockian) graptolites (Claire 

Carter, U.S. Geological Survey, written commun., 

1977) were recovered from the Paleozoic black 

phyllite and siliceous phyllite unit of Mayfield and 

Tailleur (1978) (fig. 2, unit 3) east of Nanielik Creek; a 

possible correlation has been suggested between these 

rocks and parts of unit 2 (Mayfield and Tailleur, 

1978). Black siliceous phyllite in unit 3 (fig. 2, locality 

D) contains recrystallized radiolarians. Thin 

interlayers of black, recrystallized limestone at this 

locality contain conodonts of latest Early Silurian 

(very latest Llandoverian) age (fig. 4N), slightly older 

than those found in units 1 and 2. 

Off-platform deposits of established Silurian 

age are not common in northern Alaska whereas 

shallow-water Silurian deposits are widespread. 

Shallow-water Silurian sequences occur in several 

localities in the eastern Ambler River quadrangle (fig. 

1), and fossiliferous black marble in the southeastern 

part of the quadrangle contains the same new species 

of Pelekysnathu.s (USGS colin. 11381-SD) found in units 

1 and 2. Middle to Upper Silurian dolostones in the 

central and eastern Baird Mountains quadrangle 

contain conodont assemblages and sedimentary 

structures indicative of deposition in a range of 

peritidal environments (Dumoulin and Harris, 1987). 

Fossiliferous marble in the eastern Baird Mountains 

quadrangle contains late Early Silurian (late 

Llandoverian) conodonts (USGS colin. 11768-SD) 

correlative with those found in unit 3. Other shallowwater carbonate rocks of Silurian age are known from 

the central and western Seward Peninsula, and from 

several localities in the central Brooks Range (see 

summary in Dumoulin and Harris, 1987). 

Deep-water deposits of Silurian age in northern 

Alaska are known from the Seward and Lisburne 

Peninsulas (fig. 1). On the central Seward Peninsula, 

the Ordovician to Devonian black metalimestone and 

marble unit of Till and others (1986) contains probable 

peri-platform oozes and carbonate turbidites of Middle 

Silurian age. On the Lisburne Peninsula, strongly 

deformed, locally calcareous slaty turbidites of the 

Iviagik Group of Martin (1970) contain Ordovician and 

late Early Silurian (late Llandoverian) graptolites and 

conodonts (Grantz and others, 1983). The Lisburne 

Peninsula turbidites have been correlated with slaty 

distal turbidites penetrated in wells on the North Slope 

that contain Ordovician and Silurian graptolites and 

chitinozoans (Grantz and others, 1983). 

Both deep- and shallow-water Silurian deposits 

of the western Brooks Range are included in the 

parauthochthon (Schwatka sequence) of Mayfield and 

others (1983). The proximity of coeval, lithologically 

and environmentally distinct Silurian deposits in the 

Baird Mountains-Ambler River area suggests a more 

complex early Paleozoic paleogeography and (or) 

tectonic history than has previously been inferred. 

Northern Alaska 37 
REFERENCES CITED 

Droxler, A. W., and Schlager, W., 1985, Glacial 

versus interglacial sedimentation rates and 

turbidite frequency in the Bahamas: 

Geology, v. 13, p. 799-802. 

Dumoulin, J.A., and Harris, A.G., 1987, Lower 

Paleozoic carbonate rocks of the Baird 

Mountains quadrangle, western Brooks Range, 

Alaska, in Tailleur, I.L., and Weimer, Paul, 

eds., ~laska North Slope Geology: 

Bakersfield, Calif., Pacific Section, 

Society of Economic Paleontologists and 

Mineralogists and Alaska Geological Society, 

v. 1, p. 311-336. 

Grantz, Arthur, Tailleur, I.L., and Carter, 

Claire, 1983, Tectonic significance of 

Silurian and Ordovician graptolites, 

Lisburne Hills, northwest Alaska [abs.]: 

Geological Society of America Abstracts with 

Programs, v. 15, no. 5, p. 274. 

Martin, A.J., 1970, Structure and tectonic 

history of the western Brooks Range, De Long 

Mountains and Lisburne Hills, northern 

Alaska: Geological Society of America 

Bulletin, v. 81, no. 12, p. 3605-3622. 

Mayfield, C.F., and Tailleur, I.L., 1978, 

Bedrock geology map of the Ambler River 

quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 78-120A, scale 1:250,000. 

Mayfield, C.F., Tailleur, I.L., and Ellersieck, 

Inyo, 1983, Stratigraphy, structure, and 

palinspastic synthesis of the western Brooks 

Range, northwestern Alaska: U.S. Geological 

Survey Open-File Report 83-779, 53 pA 

Till, A.B., Dumoulin, J.A., Gamble, B.M., 

Kaufman, D.S., and Carroll, P.I., 1986, 

Preliminary geologic map and fossil data, 

Solomon, Bendele ben, and southern Kotzebue 

quadrangles, Seward Peninsula, Alaska: U.S. 

Geological Survey Open-File Report 86-276. 

Reviewers: J.T. Dutro, Jr., W.W. Patton, Jr. 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

38 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Late Wisconsin Eolian Activity and Related Alluviation, 

Central Kobuk River Valley 

ByThomas D. Hamilton, John P. Galloway, and Eduard A. Koster 

The central Kobuk River valley is located near 

the south margin of the Brooks Range about 200 km 

from the coast (fig. 1). This segment of the valley 

contains thick sand deposits that were derived 

primarily from glacial erosion of quartzose rocks 

within the Brooks Range. Glaciers and meltwater 

streams transported sandy till and outwash to the 

south flank of the range; sand then was winnowed from 

the glacial deposits and redeposited across the Kobuk 

valley floor by glaciolacustrine, alluvial, and eolian 

processes (Hamilton, 1984). 

Presently active dune fields in the central 

Kobuk River ~alley consist of the Great Kobuk Sa~d 

Dunes (62 km ), the Little Kobuk Sand Dunes (8 km ~· 

and the informally named Hunt River dunes (2 km ) 

opposite the mouth of Hunt River (fig. 1). The Great 

and Little Kobuk Sand Dunes were built dominantly by 

southeasterly winter winds, which formed niveo-eolian 

deposits of interstratified sand and snow (Koster and 

Dijkmans, 1988). The dunes near Hunt River were 

built dominantly by northerly winds that funneled 

through the valley of Hunt River from the low pass at 

its head. Granulometry and mineralogy of the eolian 

sands are described by Galloway and Koster (1984) and 

by J. W.A. Dijkmans (University of Utrecht, The 

Netherlands) and J.P. Galloway (unpub. data, 1988). 

Calcretes of the Great Kobuk Sand Dunes have been 

discussed by Cox and Lawrence (1983), Galloway and 

others (1985), and Dijkmans and others (1986). 

Extensive areas of stabilized and tundracovered or forested dunes in the central Kobuk River 

valley have been mapped by Fernald (1964), Hamilton 

67°15' 

Little Kobuk 

Sand Dunes s-~: 

C.--...-~'...'.. 

0 10 20 

159°00' KILOMETERS 158° 00' 

Figure 1. Central Kobuk River valley (CKV), showing location of 

active dune fields. 

(1984), and Kuhry-Helmens and others p985). These 

stabilized features cover about 650 km of the Kobuk 

valley floor (Kuhry-Helmens and others, 1985), forming 

a sand sea (very large dune field) that extends north to 

Epiguruk bluff on the Kobuk River (fig. 2). Eolian 

sand, loess, and alluvium at Epiguruk bluff are exposed 

in an arcuate cutbank about 3 km long (Hamilton and 

others, 1984). 

l:_tp: l Flood plain 

0 Slip-off slope 

EXPLANATION 

~Inactive 

~sand dunes 

~Younger 

~ valleylill 

~ ~ Little Kobuk 1: sa 'fl Older . · · valleyf1ll Sand Dunes (active) 

~'-...... Active 

--..:...... '\ channel 

~Abandoned \ " channel 

A E Epiguruk 

"- bluff 

Figure 2. Surficial geology and geomorphology of area around 

Little Kobuk Sand Dunes and Epiguruk bluff. Meter designations 

along Epiguruk bluff are positions along surveyed base line. 

Solid triangle marks exposure at west end of Little Kobuk Sand 

Dunes. Form lines on dune fields represent transverse, 

parabolic, and hummocky dune types. 

Northern Alaska 39 
In this paper, we present stratigraphic evidence 

and radiocarbon dates which show that (1) a 

widespread episode of dune formation in the central 

Kobuk River valley was associated with alluviation of 

the Kobuk River by 15 m or more at Epiguruk bluff, 

and that (2) dune activity and alluviation were broadly 

synchronous with late Wisconsin (Itkillik II) glaciation 

of the central Brooks Range as dated by Hamilton 

(1982) and Hamilton and others (1987). Although late 

Pleistocene dune-building has been widely reported in 

Alaska (Hopkins, 1982, and references therein; Carter, 

1983), our radiocarbon-dated sections are the first to 

demonstrate that a distinct episode of dune formation 

is assignable to the Itkillik II glacial substage of the 

Brooks Range and to the late Wisconsin glacial episode 

of Alaska. 

At the west end of the Little Kobuk Sand Dunes 

(fig. 2), an incision up to 20 m deep formed by 

headward sapping of a small tributary to Tunutuk 

Creek (fig. 3) exposes a paleosol within cross-bedded 

eolian sand. The paleosol typically consists of an A 

horizon of brownish, organic, structureless very fine 

sand above a B horizon of oxidized sand about 35 em 

thick that contains cryoturbation structures. In one 

place, the buried soil forms horizontally laminated 

deposits of very fine sand and organic-rich silt. The 

paleosol declines in height toward the east end of the 

exposure where it forms the floor of a former channel 

about 3 m deep (fig. 4). Within the channel floor, the 

paleosol consists of a 5-cm layer of bryophytic peat, 

mainly consisting of Scorpidium turgescens, above 

oxidized sand. Radiocarbon ages of 24,560 ± 720 and 

24,930 ± 200 yr B.P. (I-12,206 and GrN-11.111, 

respectively) were obtained from peat on the channel 

floor, and a sample from the organic-rich-silt facies of 

the paleosol has an age of 24,000 ± 550 yr B.P. (GrN11.112). The three radiocarbon ages, which broadly 

overlap at double their counting error (a confidence 

interval of about 95 percent), indicate that the entire 

paleosol complex was buried by renewed deposition of 

eolian sand about 24,000 years ago. 

Radiocarbon ages from Epiguruk bluff show a 

similar history of paleosol formation terminated by 

accumulation of fluvial and eolian sand derived from 

the central Kobuk River valley sand sea (Hamilton and 

others, 1984). Throughout two segments of the bluff 

(300-600 m and 2,200-2,600 m), the prominent paleosol 

illustrated by Hamilton and others (1984, fig. 8) began 

forming about 34-33 ka (thousand yr B.P.) at heights of 

3-5 m above modern river level (table 1-A). The 

paleosol later was buried beneath sandy alluvium about 

24 ka (table 1-B). The paleosol occurs at a higher level 

(about 9-12 m above the river) throughout the segment 

of the bluff between 1,100 and 1,600 m (Hamilton and 

others, 1984, fig. 8). Within this part of the bluff, 

sandy alluvium was deposited at progressively greater 

heights up to more than 15 m above the river between 

about 23 and 18.5 ka (table 1-C). Eolian sand (unit sdi 

in fig. 2) extended across the southern part of the bluff 

area (1,950-2,600 m) sometime after 19 ka; the dunes 

later became stabilized and were incised by the 

abandoned channel shown on figure 2. Wood within the 

channel-filling deposits is dated at about 10.5 ka (table 

1-D). 

Figure 3. Small tributary to Tunutuk Creek near west edge of Little Kobuk Sand Dunes. Arrow indicates 

.site where radiocarbon samples were taken 0-12,206 and GrN 11.111 ). 

40 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
WEST 

m 

20 

10 

0 

EXPLANATION 

u~l Eolian sand 

B Peat 

EAST 

Laminated 

organic silt 

Oxidized 

horizon 

Figure 4. Sketch showing radiocarbon dates and stratigraphic 

relationships exposed at west end of Little Kobuk Sand Dunes. 

The radiocarbon ages from Epiguruk bluff 

support those from the Little Kobuk Sand Dunes in 

showing paleosols forming on stable sand surfaces until 

about 24 ka. This suggests that the paleosol in the 

Little Kobuk Sand Dunes is of regional significance and 

represents stabilization of the entire dune field during 

mid-Wisconsin time. The paleosol at the Little Kobuk 

Sand Dune locality was buried beneath reactivated 

sand dunes, and active dunes must have reached the 

Kobuk River at or above Epiguruk bluff at about the 

same time in order to cause the river to alluviate with 

well-sorted fine to medium sand (Hamilton and others, 

1984). 

The William River, which cuts through the 

Athabascan Sand Dunes of western Canada (Smith and 

Smith, 1984), provides a modern analog for the 

alluviating Kobuk River. The bed load of the William 

River increases forty-fold as it encounters the dune 

field; its channel pattern changes from meandering to 

braided, and channel width increases five-fold (Smith 

and Smith, 1984). In the Kobuk River valley, Kavet 

and Ahnewetut Creeks exhibit similar broadly braided 

channel patterns where they intersect the Great Kobuk 

Sand Dunes. The late Pleistocene Kobuk River 

similarly developed a broad, shallow channel with 

westward-directed paleocurrents that lacks point-bar 

structures and other evidence for meandering flow 

patterns. Downcutting of the Kobuk River at Epiguruk 

bluff probably began after about 18.5 ka, and 

development of a broad slip-off slope (fig. 2) indicates 

that the river had reverted to its meandering channel 

pattern by about 16 ka (T.D. Hamilton, unpub. data). 

Our radiocarbon ages from the Little Kobuk Sand 

Dunes and from Epiguruk bluff show that reactivation 

of the Kobuk sand sea was synchronous with late 

Wisconsin glaciation of the central Brooks Range and 

the north-central Alaska Range (Hamilton, 1982; Ten 

Brink and Waythomas, 1985), but dune activity 

evidently began to wane several thousand years before 

major retreat of glaciers from their end-moraine 

positions about 13-12 ka (Hamilton, 1986). 

A contributing local cause of dune reactivation 

must have been exposure of the broad Bering Platform 

by glacioeustatic lowering of sea level (Hopkins, 1982), 

which would have deprived the central Kobuk River 

valley of a major source of summer precipitation. 

However, an extensive sand sea was also active on the 

Arctic Coastal Plain at this time (Carter, 1981), and 

this extensive dune field and associated sand wedges 

suggest a dry, barren, windswept environment with 

little snow cover in winter (Carter, 1983). The sand 

seas of the central Kobuk River valley and the Arctic 

Coastal Plain, together with numerous late Pleistocene 

dune fields in the Koyukuk River valley (T .D. 

Hamilton, unpub. field mapping), indicate that aridity 

was widespread in northern Alaska during the last 

glaciation and was not localized in regions close to the 

Bering Platform. 

REFERENCES CITED 

Carter, L.D., 1981, A Pleistocene sand sea on 

the Alaskan Arctic Coastal Plain: Science, 

v. 211, p. 381-383. 

1983, Fossil sand wedges on the Alaskan 

Arctic Coastal Plain and their 

paleoenvironmental significance, in 

Permafrost International Conference 

Proceedings, 4th, Fairbanks, Alaska, July 

1983: Washington, D.C., National Academy 

Press, p. 109-114. 

Cox, G.W., and Lawrence, W.T., 1983, Cemented 

horizons in subarctic Alaskan sand dunes: 

American Journal of Science, v. 283, p. 369-

373. 

Dijkmans, J.W.A., Koster, E.A., Galloway, J.P., 

and Mock, W.G., 1986, Characteristics and 

origin of calcretes in a subarctic 

environment, Great Kobuk Sand Dunes, 

northwestern Alaska, U.S.A.: Arctic and 

Alpine Research, v. 18, p. 377-387. 

Fernald, A. T., 1964, Surficial geology of the 

central Kobuk River valley, northwestern 

Alaska: U.S. Geological Survey Bulletin 

1181-K, 31 p. 

Galloway, J.P., and Koster, E.A., 1984, 

Comparison of grain-size statistics from two 

northern Alaska dune fields, in Coonrad, 

W.L., and Elliott, R.L., eds., The U.S. 

Geological Survey in Alaska--Accomplishments 

during 1981: U.S. Geological Survey 

Circular 868, p. 20-21. 

Galloway, J.P., Koster, E.A., a11d Hamilton, 

T.D., 1985, Comments on cemented horizon in 

subarctic Alaskan sand dunes: AmeriLan 

Journal of Science, v. 28), p. 186·190. 

Hamilton, T.D., 1982, A late Pleistocene glacial 

chronology for the southern Brooks Range--

Stratigraphic record and regional 

significance: Geological Society of America 

Bulletin, v. 93, p. 700-716. 

Northem Alaska 41 
Table 1. Selected radiocarbon dates from Epiguruk bluff, central Kobuk River Valley 

Date and 

lab. no. 

Material 

dated 

D. Channel filling at 1,650-1,950 rn 

Stratigraphic position 

Height above 

river (rn) 

10,340 ± 150 Wood and peat 

(I-12,462) 

Near top of channel filling 

(redeposited?) 

9 

10,370 ± 150 Wood (Salix) 

(I-12,438) 

Base of channel filling 5 

C. Fluvial sand above paleosol, 1,100-1,600 rn 

17,370 ± 280 

(I-12,440) 

18,500 ± 320 

(I-13,209) 

19,080 ± 350 

(I-13,218) 

20,290 ± 90 

(USGS-1449) 

21,020 ± 460 

(I-13,208) 

23,560 ± 160 

(USGS-1442) 

Detrital wood 

(Salix) 

Rooted shrubs 

(Salix) 

Detrital wood 

(Salix) 

Rooted shrubs 

(Salix) 

Rooted shrubs 

(Salix) 

In situ roots 

(Salix) 

Base of channel filling 

(downcutting phase?) 

Within alluvium 

Within alluvium. 

sand dune 

Within alluvium 

Within alluvium 

Underlies 

Alluvium-paleosol contact 

15 

14.5 

13 

12 

13 

9 

B. Paleosol at 300-600 rn and 2,200-2,600 rn 

21,450 ± 230 Peat Near base of alluvium 8 

(USGS-1653) 

22,770 ± 100 Peat Paleosol-alluvium contact 6 

(USGS-1445) 

24,050 ± 620 Rooted shrubs Paleosol-alluvium contact 8 

(I-12,471) (Salix) 

24,290 ± 720 Wood fragments Paleosol-alluvium contact 6 

(GX-1446) (From Schweger, 1982) 

A. Alluvium beneath paleosol 

32,830 ± 730 Detrital wood Alluvium at base of paleosol 3 

(USGS-1661) and peat 

33,670 ± 280 Detrital twigs Alluvium interstratified with 5 

(USGS-1443) (Salix) base of paleosol 

1984, Surficial geologic map of the 

Ambler River quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-1678, scale 1:250,000. 

1986, Correlation of Quaternary glacial 

deposits in Alaska, in Richmond, G.M., and 

Fullerton, D.S., - eds., Quaternary 

glaciations in the United States of 

America: Quaternary Science Reviews, v. 5 

(Quaternary Glaciations in the Northern 

Hemisphere), p. 171-180. 

Hamilton, T.D., Ashley, G.M., Reed, K.M., and 

Van Etten, D.P., 1984, Stratigraphy and 

sedimentology of Epiguruk bluff--A 

preliminary account, in Reed, K.M., and 

Bartsch-Winkler, Susan, eds., The United 

States Geological Survey in Alaska--

Accomplishments during 1982: U.S. 

Geological Survey Circular 939, p. 12-15. 

Hamilton, T.D., Lancaster, G.A., and Trimble, 

D.A., 1987, Glacial advance of late 

Wisconsin (Itkillik II) age in the upper 

Noatak River valley--A radiocarbon-dated 

stratigraphic record, in Hamilton, T.D., and 

Galloway, J. P., eds.-;- Geologic studies in 

Alaska by the U.S. Geological Survey during 

1986: U.S. Geological Survey Circular 998, 

p. 35-39. 

Hopkins, D.M., 1982, Aspects of the 

paleogeography of Beringia during the late 

Pleistocene, in Hopkins, D.M., Matthews, 

J.V., Jr., Schweger, C.E., and Young, S.B., 

eds., Paleoecology of Beringia: New York, 

Academic Press, p. 3-28. 

Koster, E.A., and Dijkmans, J.W.A., 1988, Niveoeolian deposits and denivation forms with 

special reference to the Great Kobuk Sand 

Dunes, northwestern Alaska: Earth Surface 

42 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Processes and Landforms [in press]. 

Kuhry-Helmens, K.F., Koster, E.A., and Galloway, 

J.P., 1985, Photo-interpretation map of 

surficial deposits and landforms of the 

Kobuk Sand Dunes and part of the Kobuk 

Lowland, Alaska: U.S. Geological Survey 

Open-File Report 85-242. 

Schweger, C.E., 1982, Late Pleistocene 

vegetation of eastern Beringia--Pollen 

analysis of dated alluvium, in Hopkins, 

D.M., Matthews, J.V., Jr., Schweger, C.E., 

and Young, S.B., eds., Paleoecology of 

Beringia: New York, Academic Press, p. 95-

112. 

Smith, N.D. , 

River--An 

widening 

and Smith, 

outstanding 

and braiding 

D.C., 1984, 

example of 

caused by 

William 

channel 

bed-load 

addition: Geology, v. 12, p. 78-82. 

Ten Brink, N.W., and Waythomas, C.F., 1985, Late 

Wisconsin glacial chronology of the northcentral Alaska Range--A regional synthesis 

and its implications for early human 

settlements, in Powers, W.R., and others, 

North Alaska -Range Early Man Project: 

Washington, D.C., National Geographic 

Society Research Reports, v. 19, p. 15-32. 

Reviewers: L.D. Carter and O.J. Ferrians 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Northern Alaska 43 
Decollements in the Endicott Mountains Allochthon, 

North-Central Brooks Range 

By j.S. Kelley and Diedra Bohn 

Recently compiled mapping and our field 

observations in the Chandler Lake quadrangle (Kelley, 

1988) identify widespread decollements in the Endicott 

Mountains allochthon in the central Brooks Range (fig. 

1). The decollements occur in near-continuously 

exposed Upper Devonian to Lower Cretaceous strata in 

the southern Chandler Lake quadrangle. These 

features are likely sites of extensive and possibly 

large-scale thrust faulting, thus raising the possibility 

that the allochthon includes a structural assemblage of 

strata rather than a simple structural block. 

Strata that comprise the Endicott Mountains 

allochthon were first considered to make up an 

extensive structural block in the western Brooks Range 

(Martin, 1970), and the allochton subsequently was 

traced nearly the breadth of northern Alaska (Mayfield 

and others, 1983). Martin (1970) described Devonian to 

Lower Cretaceous strata in an extensive thrust sheet, 

referred to as the Brooks Range sequence, that 

extends into the central Brooks Range. Mayfield and 

others (1983) refined the stratigraphy of Martin (1970), 

renamed the sequence the Brooks Range allochthon, 

and suggested that the allochthon extends the breadth 

of the Brooks Range. In the central Brooks Range, 

Mull (1979) referred to the Upper Devonian to Lower 

Cretaceous strata as the Endicott Mountains sequence 

and subsequently as the Endicott Mountains allochthon 

(Mull, 1985). 

Previous workers have proposed two models for 

emplacement of the Endicott Mountains allochthon 

relative to penetratively deformed rocks that crop out 

south of the Chandler Lake quadrangle. Dutro and 

others (1976) suggested that the strata of the Endicott 

Mountains allochthon: (1) could originally have lain 

north of the penetratively deformed rocks in the 

Doonerak area or (2) could have been thrust into their 

present position from south of the penetratively 

deformed rocks in the Doonerak area. Subsequent 

workers (Mull, 1982; Mull and others, 1987a; 1987c) 

argued that the Endicott Mountains allochthon 

originated south of the Doonerak area and was thrust 

northward more than 55 km as a coherent block to its 

present position north of the Doonerak area. 

Our work in the Chandler Lake quadrangle 

suggests that six major decollements defining five 

structural blocks occur in the Endicott Mountains 

allochthon (fig. 2). The areal :rxtent of ea~ 

decollement ranges from 2,070 km to 4,660 km • 

Each decollement separates tabular structural blocks 

that show independent styles of deformation and 

appear to have formed through delamination of a 

presumably near-horizontal sedimentary sequence. 

The decollements occur within (1) laterally extensive 

beds possessing low shear strength and (2) lithologic 

transitions, especially those transitions associated with 

contrasting shear strengths. Major decollements occur 

along the base of the Hunt Fork Shale, between the 

undivided Kanayut Conglomerate and Noatak 

Sandstone and the Hunt Fork Shale, in the Kayak 

Shale, and in the Permian and younger strata above the 

Lisburne Group. Less extensive decollements also 

occur along the base of the upper part of the Kanayut 

Conglomerate and between the wacke and shale 

members of the Hunt Fork Shale. 

The basal shale member of the Hunt Fork Shale 

in the eastern part of the Chandler Lake quadrangle 

occurs in imbricate blocks, and faults that underlie the 

blocks sole into a basal thrust that detaches the shale 

member from unknown substrata. Farther to the west, 

imbricate fault blocks involving the shale member are 

not mapped but can be inferred from abrupt thickness 

changes and localized structural complexities. These 

features and relationships reflect the presence of an 

extensive decollement within or along the ba';E' of the 

Hunt Fork Shale. 

Deeply eroded thrust sheets in the southeastern 

part of the Chandler Lake quadrangle expose an 

areally limited detachment between the shale and 

wacke members of the Hunt Fork Shale. Imbricate 

thrust faults produce multiple repetitions of the shale 

member independent of the overlying wacke member 

166° 

70' 

sa· 

66° 

0 

154° 

EXPLANATION 

DISTRIBUTION OF THE ENDICOTT 

MOUNTAINS ALLOCHTHON 

CHANDLER LAKE QUADRANGLE 

I 

I 

\ 

Figure 1. Northern Alaska, showing Chandler Lake quadrangle 

and distribution of Endicott Mountains allochthon. 

44 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
(fig. 3). The d~collement between members of the 

Hunt Fork Shale appears widespread in the southern 

and southwestern parts of the Chandler Lake 

quadrangle but not in exposures of Devonian strata 

farther to the northeast. 

An extensive d~collement between the Hunt 

Fork Shale and overlying Noatak Sandstone and 

Kanayut Conglomerate is exposed in eroded thrust 

sheets in the southeastern part of the Chandler Lake 

quadrangle. Multiple repetitions of the Hunt Fork 

NORTH 

RANGE 

FRONT 

Kl~ 

J"Ro ~- Ps 

Ml 

Dkn 

Dhw 

EXPLANATION 

Kl Coquinoid limestone (Cretaceous) 

J"Ro Otuk Formation (Jurassic and Triassic) 

Ps 

Psi 

Ml 

Mk 

Siksikpuk Formation of Mull and 

others ( 1987a) 

Sadlerochit Group, part <Permian> 

Lisburne Group (Mississippian) 

Kayak Shale (Mississippian) 

Kanayut Congomerate (Lower Mississippian? 

and Upper Devonian) 

MDks Stuver Member (Lower Mississippian? and 

Upper Devonian)--Divided into: 

Dku Upper part (Upper Devonian>--Mapped in 

southernmost part of quadrangle only 

Dks Shainin Lake Member (Upper Devonian) 

Shale occur independently of the overlying Kanayut 

Conglomerate and Noatak Sandstone (fig. 3). The Hunt 

Fork Shale is structurally complex throughout the 

exposure of Devonian strata in the Chandler Lake 

quadrangle, whereas the Kanayut Conglomerate and 

Noatak Sandstone are not. The d~collement produces 

complex relations in the Noatak Sandstone, typically 

separating more massive rocks of this unit from thin 

beds and lenses in gradational contact with the 

underlying Hunt Fork Shale. 

SOUTH 

68°N 

-0 Km 

Psi 

-1 

Mk 

Dku -2 

Dkn 

-3 

Dh 

-4 

Dkn Kanayut Conglomerate and Noatak 

Dh 

Dhw 

Dhs 

Sandstone, undivided (Upper 

Devonian>--As mapped, Kanayut 

Conglomerate consists of the 

Ear Peak Member 

Hunt Fork Shale, undivided (Upper 

Devonian)--Locally divided into: 

Wacke member 

Shale member 

Figure 2. North-south transect across southern Chandler Lake quadrangle, showing distribution of decollements in Endicott Mountains 

allochthon. 

Northern Alaska 45 
B 

Figure 3. Examples of complex imbrication in thrust sheets. A, 

Imbrication involving a single decollement. B, Imbrication and 

development of duplexes involving two decollements. Arrows 

show relative movement. 

Where present, the upper part of the Kanayut 

Conglomerate typically occurs in imbricate fault 

blocks. The faults underlying the imbricate blocks sole 

into a d~collement at the base of the upper part of the 

Kanayut Conglomerate. Where the laterally 

equivalent massive-weathering Shainin Lake and 

Stuver Members of the Kanayut Conglomerate are 

present, extensive detachment in the equivalent 

horizon along the base of the Shainin Lake Member is 

recognized. 

A widespread d~collement in the Kayak Shale is 

indicated by widespread imbricate faulting in the 

overlying Lisburne Group and structural disruption of 

the Kayak Shale. Imbricate thrust faults that repeat 

the Alapah and Wachsmuth Limestones of the Lisburne 

Group sole into the Kayak Shale. The Kayak Shale is 

structurally thickened in some localities, nearly 

removed in others, and elsewhere appears little 

disturbed. 

A d~collement occurs above the Lisburne Group 

over most of the exposure of the Endicott Mountains 

allochthon in the Chandler Lake quadrangle. Imbricate 

thrust faults repeat the Lisburne Group, selvages of 

the Permian Siksikpuk Formation of Mull and others 

(1987b), and locally part of the Sadlerochit Group. The 

d~collement steps up section along the range front--

the Otuk Formation occurs locally along the range 

front whereas the Siksikpuk Formation is the principal 

unit that occurs farther south. In the southwestern 

part of the Chandler Lake quadrangle, where the 

Alapah and Wachsmuth Limestones are radically 

thinner than elsewhere and are silicified, the Lisburne 

Group, Siksikpuk Formation, Otuk Formation, and 

coquinoid limestone are repeated by imbricate thrust 

faults that sole into the Kayak Shale. 

In summary, the Endicott Mountains allochthon 

within the Chandler Lake quadrangle is an assemblage 

of structural blocks separated by extensive 

d~collements. Structural delamination of a probable 

near-horizontal sedimentary sequence has produced 

five structural blocks with undetermined amounts of 

structural transport between blocks. The extensive 

distribution of the d~collements and evidence for 

extensive faulting however, suggest structural 

segmentation and telescoping on a scale not previously 

appreciated in strata assigned to the Endicott 

Mountains allochthon. Analysis of the structural 

integrity of the Endicott Mountains allochthon, 

however, requires construction of retro-deformable 

regional cross sections that incorporate the 

d~collements recognized here. 

REFERENCES CITED 

Dutro, J.T., Jr., Brosge, W.P., Lanphere, M.A., 

and Reiser, H.N., 1976, Geologic 

significance of Doonerak structural high, 

central Brooks Range, Alaska: American 

Association of Petroleum Geologists 

Bulletin, v. 60, no. 6, p. 952-961. 

Kelley, J.S., 1988, Preliminary geologic map of 

the Chandler Lake quadrangle: U.S. 

Geological Survey Open File Report 88-42, 2 

sheets, scale 1:125,000. 

Martin, A.J., 1970, Structure and tectonic 

history of the western Brooks Range, DeLong 

Mountains, and Lisburne Hills, northern 

Alaska: Geological Society of America 

Bulletin, v. 81, no. 12, p 3605-3622. 

Mayfield, C.F., Tailleur, I.L., and Ellersieck, 

Inyo, 1983, Stratigraphy, structure, and 

palinspastic synthesis of the western Brooks 

Range, northwestern Alaska: U.S. Geological 

Survey Open-File Report 83-779, 58 p., 5 pl. 

Mull, C.G., 1979, Nanushuk Group deposition and 

late Mesozoic structural evolution of the 

central and western Brooks Range and Arctic 

Slopes, in Ahlbrandt, T.S., ed., Preliminary 

geologic~ petrologic, and paleontologic 

results of the study of Nanushuk Group 

rocks, North Slope, Alaska: U.S. Geological 

Survey Circular 794, p. 5-13. 

----- 1982, Tectonic evolution and structural 

style of the Brooks Range, Alaska: An 

illustrated summary, in Powers, R.B., ed., 

Geologic studies of the Cordilleran thrust 

belt: Denver, Rocky Mountain Association of 

Geologists, v. 1, p. 1-45. 

----- 1985, Cretaceous tectonics, depositional 

cycles, and the Nanushuk Group, Brooks Range 

and Arctic Slope, Alaska, in Huffman, A.C., 

Jr., ed., Geology of the Nanushuk Group and 

related rocks, North Slope, Alaska: U.S. 

Geological Survey Bulletin 1614, p. 7-36. 

Mull, C.G., Adams, K.E., and Dillon, J.T., 

1987a, Stratigraphy and structure of the 

Doonerak fenster- and Endicott Mountains 

allochthon, central Brooks Range, Alaska, in 

Tailleur, I.L., and Weimer, Paul, eds~ 

Alaskan North Slope geology: Bakersfield, 

Calif., Pacific Section, Society of Economic 

Paleontologists and Mineralogists, and 

Alaska Geological Society, v. 2, p. 663-679. 

46 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Mull, C.G., Crowder, R.K., Adams, K.E., Siok, 

J.P., Bodnar, D.A., Harris, E.E., Alexander, 

R.A., and Solie, D.N., 1987b, Stratigraphy 

and structural setting of the Picnic Creek 

allochthon, Killik River quadrangle, central 

Brooks Range, Alaska: A summary, in 

Tailleur, I.L., and Weimer, Paul, eds., 

Alaskan North Slope geology: Bakersfield, 

Calif., Pacific Section, Society of Economic 

Paleontologists and Mineralogists, and 

Alaska Geological Society, v. 2, p. 649-661. 

Mull, C.G., Roeder, D.H., Tail leur, I .L., 

Fessel, G.H., Grantz, Arthur, and May, S.D., 

1987c, Geologic sections and maps across 

Brooks Range and Arctic Slope to Beaufort 

Sea, Alaska: Geological Society of America, 

Map and Chart Series MCH-28S, scale 

1:250,000. 

Reviewers: J.Y. Bradshaw and S.W. Nelson 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Northem Alaska 4 7 
A Thermal Cross Section for the Permafrost and Hydrate 

Stability Zones in the Kuparuk and Prudhoe Bay Oil Fields 

By Arthur H. Lachenbruch, S. Peter Galanis, Jr., and Thomas H. Moses, Jr. 

The first borehole temperature measurements 

made under the Department of Energy/Department of 

Interior, U.S. Geological Survey, North Slope Gas 

Hydrate Project (DOE Contract No. DE-AI21-

83MC20422) were completed in September 1987. The 

USGS geothermal logging truck, which was transported 

to off-road sites on a Rolligon tractor, was used to log 

ten wells in the Kuparuk, Milne Point, and Prudhoe Bay 

oil fields to depths totaling 9,550 m (31,332 ft). 

Although the data are still being processed, we 

present here preliminary results along with our earlier 

equilibrium temperature measurements at Prudhoe Bay 

(Lachenbruch and others, 1982a). Together these 

temperature measurements provide a cross section 

showing the thermal stability fields for permafrost and 

methane hydrate across the Kuparuk and Prudhoe Bay 

oil fields (figs. 1 and 2). 

Recently logged wells are shown by the solid 

and open circles west of the Kuparuk River in figure 1; 

well symbols east of the Kuparuk River mark the sites 

of our earlier study (Lachenbruch and others, 1982a). 

A 

5 

5 

+ KILOMETERS 

0 5 10 

0 5 

MILES 

-------- Roads 

15 

Thickness of the methane hydrate stability zone (HSZ) 

is based on the assumptions that the material in the 

pores has hydrostatic pressure and zero salinity. The 

depths to the top and bottom of the HSZ were 

determined from the direct temperature 

measurements (corrected for drilling disturbance 

where necessary) and the appropriate methane hydrate 

stability curve (equation 4-4 and table 4-1 of Kuustraa 

and Hammershaimb, 1983). These depths can easily be 

adjusted for other conditions of pressure, salinity, or 

gas composition (see for example Holder and others, 

1987). The solid circles in figure 1 denote sites where 

direct measurements of near-equilibrium temperature 

were obtained to depths at least as great as the 

bottom of the HSZ; their overall uncertainties are only 

a few meters. Where the bottom of the HSZ is 

extrapolated (open circles, fig. 1), values are enclosed 

in parentheses when the estimated uncertainty is± 30-

50 m, and in square brackets when it is± 50-100 m. At 

those well sites with no three-digit number for 

thickness of the HSZ, the measurements were too 

0 

(") 

oco 

...,. 

+ 70°30'' 

PBL 

0 

Figure 1. Arctic coastal plain in vicinity of Prudhoe Bay, Kuparuk, and Milne Point oil fields showing location of 

thermal cross section (figure 2). Numbers near contours and well sites are thickness, in meters, of methane 

hydrate stability zone (see text for additional explanation). 

48 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
ti ; -; "' I -; 

WEST ti ~ ti EAST 

N I 

m co 

A A" u.o (!) 0 mn. m ~ a.e 0. 

0 0 

200 

1000 

400 

~ 

5 

g I 

II 2000 600 fu 

I- 8 CL 

UJ 

0 

800 

3000 

1000 

? 

4000~--~--------------------~--------------------------~~~~----~----------~ 1200 

permafrost 

methane hydrate 

stability zone 

Figure 2. Cross section A-A' (see fig. 1) through Kuparuk and Prudhoe Bay oil fields showing zones of methane hydrate 

stability (HSZ) and permafrost. Operators' designations for holes in parentheses. For further explanation of symbols see text. 

shallow or the drilling disturbance was too large to 

permit a useful estimate; such sites generally provided 

good values for the depth of permafrost and other 

isotherms, however. 

The zones of methane hydrate stability and 

permafrost are shown by contrasting patterns in the 

cross section of figure 2, and the relation of these 

zones to temperature profiles is shown for sites near 

the east and west ends of the section in figure 3. The 

base of permafrost (by definition, Muller, 1947) is the 

0 °C isotherm shown as a solid curve in fi§'ure 2. 

Other selected isotherms (-4 °C, +4 °C, + 12 C) are 

shown by dotted curves. The top of permafrost is 

generally within a meter of the ground surface and 

cannot be shown on this scale. Most of the control 

points for the curves in figure 2 are shown by solid 

circles, which represent reliable direct measurements 

and an overall depth uncertainty of only a few 

meters. Those control points represented by open 

circles involve some extrapolation and are less 

reliable. 

The dashed curve just above the base of 

permafrost denoted "base of ice-rich sediments" (fig. 

2) is the depth of an "elbow" or "gradient break" that 

commonly occurs in thermal profiles in the Prudhoe 

Bay region (Lachenbruch and others, 1982a). It is 

marked by arrows for the wells illustrated in figure 3. 

At this depth, an abrupt downward increase in thermal 

gradient is caused by the thermal conductivity 

contrast between interstitial ice (above the break) and 

interstitial water (below) (Gold and Lachenbruch, 

1973). Hence the temperature at the gradient break 

represents the local freezing-point depression, and as 

such, it contains important information about pore 

pressure, capillarity, and chemistry near the base of 

permafrost. (Other vertical gradient changes, 

unrelated to the permafrost base and freezing-point 

depression (e.g., at 280 m in WK11, fig. 3) will, of 

course, occur at any lithologic boundaries with a 

contrast in the abundance of ice or other conductive 

minerals). As originally pointed out by Stoneley 

(1970), this depth (when it exists) can be detected also 

from routine (nonthermal) well logs, a method that has 

been exploited to map the base of "ice-bonded" or 

"ice-bearing" permafrost where temperature 

measurements are not available (for example, 

Osterkamp and Payne, 1981). An additional step is 

often taken by assuming a value for temperature at 

the base of ice-rich sediments, the depth of which is 

estimated from a nonthermal well log. Further 

assumptions for thermal gradients are then used to 

construct a thermal profile and to estimate the 

configuration of the HSZ (for example, Collett, 1983; 

Holder and others, 1987; Kamath and others, 1987). 

Northern Alaska 49 
The method can be useful in the Prudhoe Bay area 

where there is some temperature control and where 

the meaning of the gradient break is clear because 

coarse-grained, high-porosity sediments extend above 

and below the base of permafrost. Over most of the 

North Slope, however, the hypothetical "base of icerich sediments" is obscure or absent, and these indirect 

methods of determining thermal regime can be 

uncertain or misleading (Osterkamp and Payne, 1H81; 

Lachenbruch and others, 1982a, 1987). There is no 

good substitute for reliable direct temperature 

measurements. 

Even in the restricted area represented by 

figure 1, direct temperature measurements reveal 

systematic changes in the thermal gradients and 

"freezing-point depression," quantities that are 

assumed to be known in the indirect methods. The 

isotherms converge to the west (fig. 2) indicating· an 

increasing thermal gradient both in and below 

permafrost; this results in a westward thinning of both 

permafrost and the HSZ. These effects are illustr~Lted 

in figure 3 where the inset gives a scale of increa:;ing 

thermal gradient (curves a, b, c, and d). From PBM to 

WKll, the average gradient in permafrost increases 

roughly from a to b and in the underlying thawed 

formations from c to d. Thermal conditions at WK11 

in the Kuparuk oil field are intermediate between 

those at Prudhoe Bay 100 km to the east and those at 

Naval Petroleum Reserve Alaska on the coastal plain 

50 to 400 km farther to the west. At WKll, 

permafrost depth is about 480 m compared to more 

than 600 m at Prudhoe Bay and 200 to 400 m in NPRA. 

The effects of geographic variations in 

geothermal gradient can result from corresponding 

variations in thermal conductivity of the formations or 

from variation in the rate of heat flow from the 

earth. The variation in heat flow can, in turn, result 

from regional changes in deep crustal heat flux or 

from patterns of fluid circulation in the sedimentary 

basin (Lachenbruch and others, 1987). There is little 

doubt that the very deep permafrost and anomalously 

low thermal gradient at Prudhoe Bay result primarily 

from the abundance of high-conductivity constituents 

such as quartz and ice in the porous sands and gravels 

there (Lachenbruch and others, 1982a). Higher 

gradients and thinner permafrost in NPRA can be 

explained in part by a correspondingly greater 

proportion of low-conductivity constituents such as 

clay and possibly capillary water in permafrost. 

However, an important role for heat-flow variations on 

the North Slope cannot be ruled out and the cause of 

the trend in figure 2 cannot be established without 

further study of the properties of the sediment there. 

In addition to the gradient trends, the new data show 

that the "bottom of ice-rich sediments" (dashed curve, 

fig. 2, arrows fig. 3) is closer to the bottom of 

permafrost (0 °c curve) in the Kuparuk field than in 

the Prudhoe Bay field indicating that "freezing-point 

depression" is less in the Kuparuk field. Together 

these trends have implications for variations in 

thermal conductivity, heat flow, fluid circulation, pore 

pressure, and fluid chemistry. Their study can lead to 

more confident predictions of the configuration of the 

hydrate stability region and to a better understanding 

of the geothermal setting of the North Slope Basin. 

TEMPERATURE r>c) 

-IS -10 -5.0 0.0 5.0 10.0 15.0 20.0 

see 

-.........=::::~--- - ---- ----r ~oc: ......_ 

·"> 

100e '~1'1 

-,~..,& ~ 

~ 40(1 ] '-' ~ 

1500 ~ I I 1- N 1- c... (/) c... UJ :c ::2: UJ 0 2000 al ":,(!() 0 0.. 

N 

(/) 

:c 25e0 8[1~1 

3ee0 

':CllXI 

3500 

Figure 3. Temperature profiles and their relation to zones of 

methane hydrate stability (HSZ) and permafrost near west 

(WK11) and east (PBM) ends of cross section (figures 1 and 2). 

Base of permafrost is denoted by 11pf. 11 

REFERENCES CITED 

Collett, T.S., 1983, Detection and evaluation of 

natural gas hydrates from well logs, Prudhoe 

Bay, Alaska, in International Conference on 

Permafrost, --4th, Fairbanks, Alaska, 

Proceedings: Washington, D.C., National 

Academy of Sciences, p. 169-174. 

Gold, L.W., and Lachenbruch, A.H., 1973, Thermal 

conditions in permafrost--A review of North 

American literature, 1n Permafrost--North 

American Cont ri but ion, Second International 

Conference, Yakutsk, USSR: Washington, 

D.C., National Academy of Sciences, p. 3-25. 

Holder, G.D., Malone, R.D., and Lawson, W.F., 

1987, Effects of gas composition and 

geothermal properties on the thickness and 

depth of natural-gas-hydrate zones: Journal 

of Petroleum Technology, September, p. 1147-

1152. 

Kamath, V.A., Godbole, S.P., Ostermann, R.D., 

and Collett, T.S., 1987, Evaluation of the 

stability of gas hydrates in northern 

Alaska: Cold Regions Science and 

Technology, v. 4, p. 107-119. 

Kuustraa, V.A., and Hammershaimb, E.C., 1983, 

Handbook of gas hydrate properties and 

occurrence: Office of Scientific and 

Technical Information, U.S. Department of 

Energy, 234 p. 

Lachenbruch, A.H., Sass, J.H., Marshall, B.V., 

and Moses, T.H., Jr., 1982a, Permafrost, 

heat flow, and the geothermal regime at 

Prudhoe Bay, Alaska: Journal of Geophysical 

Research, v. 87, p. 9301-9316. 

50 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Lachenbruch, A.H., Sass, J.H., Lawver, L.A., 

Brewer, M.C., and Moses, T.H., Jr., 1982b, 

Depth and temperature of permafrost on the 

Alaskan Arctic Slope; preliminary results: 

U.S. Geological Survey Open-File Report 82-

1039. [Note: Superseded by next-listed 

reference.] 

Lachenbruch, A.H., Sass, J.H., Lawver, L.A., 

Brewer, M.C., Marshall, B.V., Munroe, R.J., 

Kennelly, J.P., Jr., Galanis, S.P., Jr., and 

Moses, T.H., Jr., 1987, Temperature and 

depth of permafrost on the Alaskan Arctic 

Slope, in Tailleur, I.L., and Weimer, Paul, 

eds., Alaskan North Slope Geology: 

Bakersfield, Calif., Pacific Section, 

Society of Economic Paleontologists and 

Mineralogists, and Alaska Geological 

Society, v. SO, p. 545-558. 

Muller, S.W., 1947, Permafrost, or permanently 

frozen ground, and related engineering 

problems: U.S. Engineers Office, Strategic 

Engineering Study Special Report 62, 136 p. 

Osterkamp, T.E., and Payne, M.W., 1981, 

Estimates of permafrost thickness from well 

logs in northern Alaska: Cold Regions 

Science and Technology, v. 5, p. 13-27. 

Stoneley, Robert, 1970, Discuss ion, in Adkison, 

W.L., and Brosge, M.M., eds., Proceedings of 

the Geological Seminar on the North Slope of 

Alaska: Los Angeles, Pacific Section, 

American Association of Petroleum 

Geologists, p. J2-J4. 

Reviewers: L.S. Magoon and T.S. Collett 

Geologic Studies 1n Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Northern Alaska 51 

EAST-CENTRAL ALASKA 

Pinnacles of Devonian limestone in Mt. Schwatka area, Yukon-Tanana Upland. 

Photograph by F.R. Weber. 
A Late Silurian Age Determination for 

the Limestone of the Lost Creek Unit, 

Livengood C-4 Quadrangle, East-Central Alaska 

By Robert B. Blodgett, Ning Zhang, Allen R. Ormiston, and Florence R. Weber 

The age and stratigraphic relations of a 

limestone found by R.M. Overbeck in 1918 on a 

tributary of Lost Creek 14 km west of Livengood (fig. 

1) have long been a matter of conjecture. Mertie 

(1937, p. 110) placed this locality in the Livengood 

Chert and used the fossils found there (identified by 

G.H. Girty as provisionally Late Mississippian in age) 

to define the age of the formation. New data suggest 

that, instead, the age of this limestone is Late 

Silurian. 

In the course of geologic mapping of the 

Livengood 1:250,000 quadrangle (Chapman and others, 

1971) in the 1960s and 1970s the old and new fossil 

collections were reevaluated (series of written 

commun. from A.G. Epstein, J.T. Dutro, Jr., W.A. 

Oliver, Jr., U.S. Geological Survey) and were thought 

to range in age from Middle Ordovician to Middle 

Devonian, but with Middle Silurian as the best 

possibility. 

Chapman and others (1980) abandoned the 

Livengood Chert and named the rocks that had 

previously been assigned to the lower, predominantly 

chert unit of that formation the "Livengood Dome 

Chert"; they established a Late Ordovician age for this 

new formation based on discovery of graptolites 

(identified by Claire Carter, U.S. Geological Survey, 

1980) in a borrow pit 1.6 km north of the Lost Creek 

fossil locality. At that time, the rocks at the Lost 

Creek locality, because of their differing lithologies, 

were not assigned to the Livengood Dome Chert. 

We carried out new studies of Overbeck's Lost 

Creek locality between 1985 and 1987. Our purpose 

was to identify some of the faunal elements found in 

our newly made collections from the limestone 

exposure and to redefine the stratigraphic relations of 

this exposure. 

The base of the limestone exposure is 30-45 m 

above the bottom of the northwest edge of Hill 1335 

(fig. 2), and is situated in the Livengood C-4 

quadrangle (lat. 65° 30.9' N., long. 148° 51.2' W.). This 

locality consists of a massive limestone 12-15 m thick, 

interbedded with irregularly folded calcareous or silty 

shale, minor chert, and graywacke. Laterally the 

limestone body pinches out. The limestone is 

composed of light-gray lime mudstone and wackestone. Small to medium-sized chert clasts, angular to 

well rounded, are present both at the base and top of 

the exposure, and are also abundant in the lateral 

pinch-out margins. The limestone is interpreted to be 

a carbonate debris flow within a deeper water clastic 

unit. 

South-dipping shale and claystone underlie the 

limestone at the downhill (north) end of the exposure. 

These argillaceous rocks are underlain by tightly 

folded greenish-gray chert, possibly in unconformable 

contact. Shale and graywacke turbidites are present 

uphill from the limestone, but covered intervals make 

structures difficult to interpret. A northward dip of 

85° was measured in the turbidites, and there is a 

suggestion of overturned beds. Farther up the hill at a 

sharp topographic break, chert on the other side of the 

poorly exposed contact shows different structural 

attitudes from the graywacke, suggesting the 

possibility of a fault here between the two 

lithologies. The uppermost part of Hill 1335 is 

composed of the Livengood Dome Chert. 

Megafossils were collected by Blodgett from 

the central part of the main limestone exposure. They 

include, in decreasing order of abundance, brachiopods, 

crinoidal debris (including articulated columnals), 

ostracodes, trilobites, rare solitary rugose corals, and 

possible calcareous algal remains. 

v'" 

Liven good 

0'f. Dome 

)u.1dra ny,Jc 

r.oc·;ll ion 

10 

KILOMETERS 

Figure 1. Generalized location map of fossil site and vicinity. 

54 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
0 2 

KILOMETERS 

Figure 2. Detailed map showing Hill 1335 and 

location (arrow) of Lost Creek fossil locality in 

Livengood C-4 quadrangle. Elevation of hill crest in 

feet; contour interval 1 00 feet. 

Brachiopods (identified by Zhang and Blodgett) 

form the most numerous and diverse taxonomic group 

found at this locality. Taxa present include Lingula 

sp., Leptaena sp., Severella cf. S. magnificaformis 

Sapelnikov, 1963, clorindid, Gypidula sp., n. gen.? 

gypidulinid (aff. Gypidulina), Ancillotoechia cf. A. 

shannonensis (Amsden, 1949), Spirigerina? sp., 

Lissatrypa? sp., Eospinatrypa sp. (finely ribbed), 

Metaplasia cf. M. sp. Lenz, 1970, Janius? sp., and 

Spirinella sp. Severella magnificaformis Sapelnikov, 

1963 is known from the lower Ludlovian of the eastern 

slope of the Urals. Ancillotoechia shannonensis 

(Amsden, 1949) occurs in the Brownsport Formation 

(Ludlovian) of Tennessee. Metaplasia sp. Lenz, 1970 is 

reported from strata of either late Ludlovian or early 

Pridolian age in the Road River Formation of the 

Prongs Creek area, Yukon Territory. The genus Janius 

is known from Wenlockian to Ludlovian, as well as 

younger strata. Its presence is listed equivocally here, 

since it is based on a single deformed fragment. 

Spirinella is commonly reported from Wenlockian to 

Ludlovian strata, though a single occurrence of the 

genus is reported from the Lower Devonian of 

Nevada. The overall aspect of the brachiopod fauna 

indicates a Wenlockian to Ludlovian (early to middle 

Late Silurian) age. 

Trilobites (identified by Ormiston) are an 

uncommon faunal element of this assemblage, and 

belong to a single species, Contracheirurus n. sp. The 

genus Contracheirurus was established by Chatterton 

and Perry (1984) and based upon two species, known 

only from the Mackenzie Mountains, northwestern 

Canada. The type species, C. zuvegesi Chatterton and 

Perry, 1984, occurs in lower Wenlockian strata of the 

Delorme Formation, and the other species, C. n. sp. 

Chatterton and Perry, 1984, is known from upper 

Wenlockian or possibly lower Ludlovian strata of the 

same formation. Although the species from the Lost 

Creek locality is not conspecific with either described 

species, the Wenlockian to Ludlovian stratigraphic 

range of the genus is accordant with ages suggested 

above for the brachiopods in the Lost Creek fauna. 

Several attempts were made to obtain a 

conodont-based age for the limestone exposed at Lost 

Creek, but the results (Wenlockian to early Emsian; 

A.G. Harris, U.S. Geological Survey, written commun., 

1987) were less definitive than that based upon the 

megafauna. 

The overall aspect of the fauna is suggestive of 

a shallow-marine carbonate platform. Because the 

limestone is interpreted to be a lenti('ular dehris-flow 

deposit, it likely was tran:sfJurttd duw1slope and 

deposited in a deeper water envirunmt>• t. 

Although the limestone is age-equivalent to 

part of the Road River Formation in east-central 

Alaska and the Yukon Territory, it is not considered a 

part of the Livengood Dome Chert. The Livengood 

Dome Chert is age-equivalent to a stratigraphically 

lower part of the Road River Formation. Nor is it 

presently considered a part of the "Amy Creek unit," a 

dolomite and black chert unit described by Weber and 

others (1985). The relation of the "Amy Creek unit" to 

both the Livengood Dome Chert and to the Lost Creek 

unit remains undetermined at this time. 

The collective ranges of our fossils indicates a 

Late Silurian age for the limestone at the Lost Creek 

locality. The clastic unit which encloses this limy 

debris flow must be of the same age. This unit, herein 

called the "Lost Creek unit," probably represents a 

hitherto unrecognized but mappable unit present 

stratigraphically between the Upper Ordovician 

Livengood Dome Chert and the Middle Devonian 

Cascaden Ridge unit of Weber and others (1985) and is 

of intermediate age between these two units. A 

similar small limestone body present on Willow Creek 

(north side of Livengood Dome) may also belong in the 

Lost Creek unit, but these limestone debris flows 

probably make up only a minor lithology in the Lost 

Creek clastic rock section. 

REFERENCES CITED 

Amsden, T.W., 1949, Stratigraphy and 

paleontology of the Brownsport (Silurian) of 

western Tennessee: Peabody Museum of 

Natural History, Bulletin S, 138 p. 

Chapman, R.M., Weber, F.R., Churkin, Michael, 

Jr., and Carter, Claire, 1980, The Livengood 

Dome Chert, a new Ordovician formation in 

central Alaska, and its relevance to 

displacement on the Tintina fault: U.S. 

Geological Survey Professional Paper 1126-F, 

13 P• 

Chapman, R.M., Weber, F .R., and Taber, Bond, 

1971, Preliminary geologic map of the 

Livengood quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 71-66, 2 

plates. 

Chatterton, B.D.E., and Perry, D.G., 1984. 

Silurian cheirurid trilobites from the 

Mackenzie Mountains, northwestern Canada: 

Palaeontographica Abt. A, v. 184, p. 1-78. 

East-Central Alaska 55 
Lenz, A. C., 1970, Late Silurian brachiopod~ of 

Prongs Creek, northern Yukon: Journal of 

Paleontology, v. 44, p. 480-500. 

Mertie, J.B., Jr., 1937, The Yukon-Tanana 

region, Alaska: U.S. Geological Survey 

Bulletin 872, 276 p. 

Sapelnikov, V.P., 1963, Novye predstaviteli 

zamkovykh brakhiopod iz siluriiskikh 

otlozhenii urala: Sverdlovsk, Trudy 

Sverdlovskogo Gornogo Instituta im. V.V. 

Vakhrusheva (Vyp. 42, Geologiya i polezno 

iskopaemye urala), p. 15-19. 

Weber, F.R., Smith, T.E., Hall, M.H., and 

Forbes, R.B., 1985, Geologic guide to the 

Fairbanks-Livengood area, east-central 

Alaska: Anchorage, Alaska Geological 

Society, 44 P• 

Reviewers: A.J. Boucot and S.M. Karl 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

56 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
A Comparative Petrologic Study of Sandstone from the 

Wilber Creek, Cascaden Ridge, and Wickersham Units 1n the 

Livengood Quadrangle 

By L.D. Gergen, J.E. Decker, and George Plafker 

The Livengood, Manley, White Mountains, and 

Wickersham tectonostratigraphic terranes of Jones and 

others (1987) occur within the Livengood quadrangle of 

east-central Alaska (fig. 1). Rocks of the Livengood 

terrane include the Livengood Dome Chert 

(Ordovician) and overlying Amy Creek unit (dolomite, 

chert, and volcanic rocks), serpentinite, and Devonian 

Cascaden Ridge unit (fossiliferous shale, sandstone, 

grit, and minor limestone; Jones and others, 1987). 

The Manley terrane consists of complexly deformed 

flyschoid Mesozoic sedimentary rocks assigned to the 

Wilber Creek unit (Jones and others, 1987). The White 

Mountains terrane consists of Ordovician volcanic and 

volcaniclastic rocks and conglomerate of the Fossil 

Creek unit, overlain by Silurian and Devonian 

limestone and dolomite, and undated clastic rocks 

(Jones and others, 1987). The Wickersham terrane 

includes Precambrian and Cambrian quartz-rich 

sandstone and grit, shale, and maroon to green slate of 

the Wickersham unit (Jones and others, 1987). The 

Wilber Creek, Cascaden Ridge, and Wickersham units 

are turbidite sequences. 

This report presents the first published 

quantitative data of sandstone petrology of the Wilber 

Creek, Cascaden Ridge, and Wickersham units. This 

pilot study was undertaken to determine the feasibility 

of distinguishing between these units with sandstone 

petrology and to provide a basis for interpretation of 

sandstone provenance. The petrologic distinction 

between sandstones in these units and a knowledge of 

their source is essential for tectonic and 

paleogeographic reconstructions in this structurally 

complex region. 

Eight samples were collected for sandstone 

petrologic study by one of us (Decker) in 1984. Point 

counts were made on four samples from interbedded 

graywacke and quartzite within the Wilber Creek unit, 

two samples from graywacke of the Cascaden Ridge 

unit, one sample of graywacke from an isolated area 

that is tentatively correlated with the Cascaden Ridge 

unit, and one sample from quartzite of the Wickersham 

unit. The Gazzi-Dickinson point- counting method was 

employed following the general procedures outlined by 

Dickinson (1970) and Ingersoll (1978) and discussed by 

Ingersoll and others (1984). The maximum possible 

grid spacing was chosen that allowed 500 points to be 

counted on each slide. One thin section (sample 5) was 

stained for magnesium (to differentiate dolomite from 

calcite), but none of the other thin sections were 

stained. Point-count data for each sample are 

presented in table 1 and are shown on figure 2. 

Sample 1, from one of the quartzite beds within 

the Wilber Creek unit, consists primarily of 

monocrystalline quartz (Q90F 7L.3); Qp/Q 

(polycrystalline quartz to quartz ratio) 1s 0.02 (table 

1). Lithic clasts, which are uncommon, include impure 

chert, argillite, and shale. Sample 1 contains 

moderately to well sorted, subangular to rounded 

grains, and is predominantly fine sand with some grains 

ranging from silt to medium-sand size. 

Samples 2, 3, and 4 are from the graywacke in 

the Wilber Creek unit. They contain low proportions 

of quartz, moderate proportions of feldspar, and 

moderate to high proportions of lithics (Q9_20F 25_

44 L36_

66). Qp/Q ranges from 0.04 to 0.24. -volcamc 

Figure 1. livengood area showing terrane boundaries 

(Jones and others, 1987}, clastic units of Chapman and 

others (1971} and Weber and others (1987}, and sandstone 

sample sites. Kjwc, Wilber Creek unit (Cretaceous and 

jurassic}; Ocr, Cascaden Ridge unit (Devonian); €p€w, 

Wickersham unit (Cambrian and Precambrian}. Refer to table 

1 for field numbers. 

East-Central Alaska 57 
Table 1. Point-count data for sandstones from the Livengood quadrangle 

[Values rounded to nearest whole number and may not sum to 100. QFl, quartz-feldspar-lithic fragments; lmlvls, metamorphic-volcanic-sedimentary lithic 

fragments; Qplvmlsm,polycrystalline quartz-volcanic + metavolcanic-sedimentary+ metasedimentary lithic grains; QmFlt, monocrystalline quartz-feldspar-l + Qp; 

Qp/Q, polycrystalline quartz to quartz ratio; Fmwk%M, framework percent mica; Fmwk%D, framework percent dense (excluding opaque minerals), Fmwk%0, 

framework percent opaque minerals] 

Sample Field QFL% *lmLvi.s% *QpLvmi.sm% QmFLt% 

Unit Number Number Q-F-L Im-Lv-I.s Qp-Lvm-Ism Qm-F-Lt QpjQ Fmwk%M Fmwk%D Fmwk%0 

Wilber 1 84JD356E 90-07-03 88-07-05 .023 0 0 0 

Creek 2 84JD359B 14-42-44 13-58-29 05-58-37 12-42-46 .170 4.1 4.8 0.6 

3 84JD381A 09-25-66 13-67-19 03-66-31 07-25-68 .242 2.3 1.6 0.6 

4 84JD382A 20-44-36 10-65-25 02-65-33 20-44-36 .036 3.3 2.6 1.4 

cascaden 5 84JD362A 47-21-32 06-05-89 15-04-81 42-21-38 .122 0 0 3.0 

Ridge 6 84JD364D 56-24-20 02-05-93 38-03-59 43-25-32 .220 0.2 0 0.8 

cascaden 7 84JD355D 17- 0-83 01- 0-99 17- 0-83 0-0-100 .985 0 0 5.8 

Ridge(?) 

Wickersham 8 84JD350A 99- 0-01 - - - 99- 0-01 0 0.2 0 0 

*Not calculated for samples with less than 10 percent lithics 

fragments dominate the lithic grains (58 to 67 

percent); sedimentary (19 to 29 percent) and 

metamorphic (10 to 13 percent) grains are subsidiary. 

Most (49 to 60 percent) of the volcanic grains are 

altered sufficiently that the original texture is 

destroyed. However, when grain types can be 

distinguished, lathwork textures are the most common 

type (22 to 35 percent of total volcanic grains). 

Sedimentary lithic fragments consist of impure chert 

(chert containing clay or iron-oxide impurities), 

argillite, shale, and chert-rich argillite. Most of the 

metamorphic grains display tectonite fabrics. Opaque 

minerals compose 0.6 to 1.4 percent of the framework 

grains. Dense minerals are predominantly epidote; 

rare amphibole and pyroxene are found in sample 2. 

Phyllosilicate minerals include chlorite, minor biotite, 

and rare muscovite and stilpnomelane. Grain size and 

sorting vary among the samples. Samples 2 and 3 

contain very poorly sorted grains ranging from silt to 

granule or pebble size, whereas sample 4 contains 

poorly to moderately sorted fine sand, with some 

grains ranging from silt to medium-sand size. Grains 

are very angular to subrounded, and the matrix is 

recrystallized clayey lutum. Samples 2, 3, and 4 are 

similar to each other in composition but differ 

markedly from sample 1. Because of their similarity 

to each other, they may represent the overall 

composition of the graywacke in the Wilber Creek 

unit. 

Two samples from the Cascaden Ridge unit 

(samples 5 and 6) have moderate to high proportions of 

quartz, and low to moderate proportions of feldspar 

and lithics (Q47_56F21_24L20_32; table 1). Twelve to 

22 percent of the quartz is po1ycrystalline (or chert). 

Sedimentary lithic grains predominate, and only minor 

amounts of volcanic and metamorphic rock fragments 

are present (Lm2_

6Lv5Ls89_

93). Impure chert 

composes the highest proportion of the sedimentary 

lithic fragments (70 to 82 percent). Remaining 

sedimentary lithic grains consist of argillite, shale, 

chert-rich argillite, and chert-rich shale. Opaque 

minerals compose 1 to 3 percent of the framework 

grains. The samples are predominantly fine-grained 

sand, but contain some grains ranging from very fine 

to coarse sand size. They are moderately to well 

sorted and have angular to subrounded grains. The 

matrix is recrystallized clayey lutum; sample 5 also 

has both dolomite and calcite cements. 

The remaining sample, tentatively assigned to 

the Cascaden Ridge unit (sample 7), contains abundant 

lithic fragments {Q17F 0L83; table 1). The lithic part 

of this sample is almost entirely sedimentary and 

consists of approximately equal proportions of impure 

chert (51 percent), and argillite, shale, chert-rich 

argillite, and chert-rich shale (49 percent). 

Polycrystalline quartz (chert) makes up 98.5 percent of 

the total quartz. Six percent of the framework grains 

are opaque minerals. The sandstone contains very 

poorly sorted, angular to subrounded grains ranging 

from very fine sand to granules. Matrix (14.4 percent 

of the total rock) consists of iron oxides, oxidized iron 

oxides, and clay. The lithology suggests probable local 

derivation from nearby outcrops of the Livengood 

Dome Chert unit, and may represent a lithic-rich endmember composition of the Cascaden Ridge unit. 

The quartzite sample from the Wickersham unit 

(sample 8} consists almost entirely of monocrystalline 

quartz {Q99F 0_

2L0_8; table 1). Gr~ins are subrounded 

to well rounded, range from very fme sand to granule 

size, and are poorly to moderately sorted. The matrix 

(4.2 percent of total rock) consists of recrystallized 

clayey lutum. 

Recalculated point-count parameters for the 

eight samples are plotted on four triangle diagrams 

(fig. 2). The QFL diagram (fig. 2A) depicts relative 

proportions of quartz {Q), feldspar (F), and lithic 

fragments (L). It shows relatively low Q and high L 

proportions for graywacke of the Wilber Creek unit 

(samples 2, 3, and 4) compared to the quartzite of the 

Wilber Creek unit (sample 1), the Cascaden Ridge unit 

58 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Q 

CRATON e Wilber Creek unit CRATON 

INTERIOR 

• Cascaden Ridge unit 

TRANSITIONAL 

A 

--- ---.4 - / / .2 ,/ 

//.3 

/ / UNDISSECTED ARC 

B 

F L F 

c 

RIFTED 

CONTINENTAL 

D 

ARC OROGEN 

RIFTED CONTINENTAL MARGINS 

Figure 2. Ternary diagrams for Wilber Creek, Cascaden Ridge, 

and Wickersham units of Chapman and others (1 971) and 

Weber and others (1 987). See text for explanation of 

abbreviations. A and B, QFL and QmFLt diagrams modified from 

(samples 5 and 6), and the Wickersham unit (sample 

8). Sample 7, from the Cascaden Ridge(?) unit, 

contains the highest L proportions, and sample 8 

(Wickersham unit) contains the highest Q and lowest L 

proportions of the three units. 

The QmFLt plot (fig. 2B) shows relative 

proportions of monocrystalline quartz (Qm), feldspar 

(F), and lithic fragments plus polycrystalline quartz 

(Lt). It reveals the predominance of Qm in sample 8 of 

the Wickersham unit, and in the quartzite (sample 1) of 

the Wilber Creek unit. Samples of the Cascaden Ridge 

unit (except sample 7) have higher Qm proportions 

than graywacke samples of the Wilber Creek unit, and 

lower Qm proportions than the sample of the 

Wickersham unit. The lithic-rich end-member sample 

that is tentatively assigned to the Cascaden Ridge unit 

(sample 7) is at the Lt apex of the diagram because it 

is composed of a high proportion of polycrystalline 

quartz and sedimentary lithic fragments. 

The LmLvLs diagram (fig. 2C) depicts relative 

proportions of metamorphic (Lm), volcanic (Lv), and 

sedimentary (Ls) lithic fragments. It emphasizes the 

Lvm 

Dickinson and others (1 983). C, Lmlvls diagram modified from 

Ingersoll and Suczek (1 979); D, Qplvmlsm diagram, showing 

dashed-line fields from Dickinson and Suczek (1 979) and solidline fields from Ingersoll and Suczek (1979). 

low proportions of Lm in the graywacke of the Wilber 

Creek unit and in the samples of the Cascaden Ridge 

unit. The greywacke samples of the Wilber Creek unit 

contain distinctly higher Lv and lower Ls proportions 

than the samples of the Cascaden Ridge unit. 

The QpLvmLsm plot (fig. 2D) shows relative 

proportions of polycrystalline quartz (Qp), volcanic 

plus metavolcanic lithic grains (Lvm), and sedimentary 

plus metasedimentary (Lsm) lithic grains. It shows 

that the graywacke of the Wilber Creek unit has 

smaller proportions of Qp and Lsm and larger 

proportions of Lvm than the graywacke of the 

Cascaden Ridge unit. 

The four ternary diagrams indicate a probable 

magmatic-arc provenance for the three graywacke 

samples of the Wilber Creek unit (fig. 2). Units from 

adjacent terranes that could have contributed volcanic 

detritus to the Wilber Creek unit include the Fossil 

Creek Volcanics of the White Mountains terrane and 

the Amy Creek unit (dolomite, chert, and volcanic 

rocks) of the Livengood terrane. Geochemical analysis 

of major elements of basalt of the Fossil Creek 

East-Central Alaska 59 
Volcanics shows that the basalts are alkalic and 

therefore are not likely to be island-arc, mid- ocean 

ridge, or continental tholeiitic basalts (Wheeler and 

others, 1987). (Compositional differences of volcanic 

lithic fragments are not distinguishable on the triangle 

diagrams in figure 2.) However, the lack of carbonate 

lithic fragments, carbonate matrix, or interbedded 

carbonate muds within the Wilber Creek unit suggests 

that the White Mountains terrane is an unlikely 

magmatic-arc source area. Basalt is a minor 

constituent of the Amy Creek unit and therefore the 

Livengood terrane is also considered an unlikely source 

area. Therefore, it is possible that the source area for 

the Wilber Creek unit is no longer adjacent to the 

Manley terrane. Fieldwork during 1987 by the TACT 

project members shows that the quartzites and 

graywackes of the Wilber Creek unit are locally 

interbedded, and therefore that different source areas 

may have existed on opposite sides of the depositional 

basin. 

We draw three preliminary conclusions about 

the provenance of these few samples from the 

Livengood quadrangle. (1) The Wilber Creek unit has 

at least two source areas, one that shed graywacke 

from a possible magmatic-arc source and another that 

shed quartzite from a craton interior source; these two 

source terranes may have been on opposite sides of the 

depositional basin. (2) Two of the sandstones from the 

Cascaden Ridge unit have a high proportion of quartz, 

chert, and sedimentary lithic grains, and may have 

been derived from a collision orogen source. The other 

sample consists almost entirely of silicious lithic 

grains, and may be locally derived from underlying 

chert units. (3) The quartzite sample from the 

Wickersham unit is almost exclusively monocrystalline 

quartz and is compatible with a craton interior 

provenance. 

REFERENCES CITED 

Chapman, R.M., Weber, F .R., and Taber, Bond, 

1971, Preliminary geologic map of the 

Livengood quadrangle, Alaska: U.S. 

Geological Survey Open-File Map [71-483], 2 

sheets, scale 1:250,000. 

Dickinson, W.R., 1970, Interpreting detrital 

modes of graywacke and arkose: Journal of 

Sedimentary Petrology, v. 40, no. 2, p. 695-

707. 

Dickinson, W.R., Beard, L.S., Brakenridge, G.R., 

Erjavec, J.L., Ferguson, R.C., Inman, K.F., 

Knepp, R.A., Lindberg, F.A., and Ryberg, 

P.T., 1983, Provenance of North American 

Phanerozoic sandstones in relation to 

tectonic setting: Geological Society of 

America Bulletin, v. 94, no. 2, p. 222-235. 

Dickinson, W.R., and Suczek, C.A., 1979, Plate 

tectonics and sandstone compositions: 

American Association of Petroleum Geologists 

Bulletin, v. 63, no. 12, p. 2164-2182. 

Ingersoll, R. V., 1978, Petrofacies and 

petrologic evolution of the Late Cretaceous 

fore-arc basin, northern and central 

California: Journal of Geology, v. 86, p. 

335-352. 

Ingersoll, R.V., Bullard, T.F., Ford, R.L., 

Grimm, J.P., Pickle, J.D., and Sares, S.W., 

1984, The effect of grain size on detrital 

modes: A test of the Gazzi-Dickinson pointcounting method: Journal of Sedimentary 

Petrology, v. 54, no. 1, p. 103-116. 

Ingersoll, R. V., and Suczek, C .A., 1979, 

Petrology and provenance of Neogene sand 

from Nicobar and Bengal fans, DSDP Sites 211 

and 218: Journal of Sedimentary Petrology, 

v. 49, no. 4, p. 1217-1228. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1987, Lithotectonic terrane 

map of Alaska (west of the 141st 

meridian): U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1874-A, 

scale 1:2,500,000. 

Weber, F.R., Wheeler, K.L., Dover, J.H., 

Rinehart, C.D., Blodgett, R.B., Cady, J.W., 

Karl, S.M., McCammon, R.B., and Miyaoka, R., 

1987, Geologic framework, in Administrative 

Report on the Mineral Resource Assessment 

for the White Mountains National Recreation 

Area, Alaska: U.S. Geological Survey, 

prepared for the Bureau of Land Management, 

p. 3-59. 

Wheeler, K.L., Forbes, R.B., Weber, F.R., and 

Rinehart, C.D, 1987, Lithostratigraphy, 

petrology, and geochemistry of the 

Ordovician Fossil Creek Volcanics, White 

Mountains, east-central Alaska, in Hamilton, 

T.D., and Galloway, J.P., eds~ Geologic 

Studies in Alaska by the U.S. Geological 

Survey during 1986: U.S. Geological Survey 

Circular 998, p. 70-73. 

Reviewers: T.E. Moore and K.L. Wheeler 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

60 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Tertiary Gold-Bearing Gravel at Livengood, Alaska 

By Susan M. Karl, Thomas A. Ager, Karl Hanneman, and Steve D. Teller 

Pollen analysis of a sample of organic-rich silt 

from gold-bearing gravel at Livengood, east-central 

Alaska, yielded evidence for a late Tertiary 

(Pliocene?) age for the deposit. This is significant 

because these gold-bearing gravels were previously 

thought to be Quaternary in age (Eberlein and Menzie, 

1978). Our new information invites reinterpretation of 

the geomorphic history of the area and of other buried 

placer deposits in this region of Alaska. 

Livengood Creek has historically been the 

largest placer gold producer in the Tolovana mining 

district; production through 1987 exceeded 200,000 

troy oz (6,200 kg) (unpub. State of Alaska Records, 

T.K. Bundtzen, oral commun., January 1988). The 

present Livengood Creek flows on the south side of the 

southwest-trending Livengood drainage basin (fig. 1). 

The original discovery in the district was made in 

Livengood Creek in 1914 (Brooks, 1916). Soon 

afterward, more productive auriferous gravel was 

discovered in deeply buried channels on the north side 

of the Livengood drainage basin. Auriferous gravel in 

these deeply buried channels forms a body 10 km long 

that is separated from the present Livengood Creek by 

a discontinuous bedrock ridge 12 m high. The ancient 

alluvium in the buried channels is as much as 350 m 

wide; it is 3 to 15 m thick and is covered by 15 to 35 m 

of frozen colluvium and silt. Primarily because the 

surface elevation along the axis of the deposit is 15 to 

25 m higher than the present stream, the deposit has 

historically been known as the Livengood bench. The 

base of the ancient gravels, however, is lower than the 

present stream (fig. 2). No economic gold placers 

occur in the tributaries on the north side of the valley; 

however gold has been mined for many years from the 

modern Livengood Creek and tributaries on the south 

side of the valley, as well as from the buried channels 

on the north side. 

Livengood Creek and the South Fork of Hess 

Creek, which is immediately to the northeast, have 

had a long and complicated geomorphic history. One 

or more episodes of stream capture were described by 

Mertie (1917). Local base level has repeatedly shifted 

up and down, with sequences of downcutting, channel 

filling, and channel migration, followed by renewed 

downcutting (Mertie, 1917}. During the final stages of 

valley evolution, a thick section of windblown silt 

(loess) was deposited and reworked by colluvial and 

alluvial action. Subsequently, Livengood Creek 

established a new channel on the south side of the 

valley, cutting through silt and down into bedrock, so 

that it became separated from the buried auriferous 

channels by the bedrock ridge that extends 

discontinuously from the town of Livengood northeast 

to the mouth of Amy Creek (Mertie, 1917) (fig. 1). 

Drilling data that show an abrupt change in depth to 

bedrock near the mouth of Myrtle Creek suggest that 

rejuvenation of Livengood Creek may have been 

influenced by activity on a large north-south-trending 

normal fault that intersects the Livengood valley at 

this locality (fig. 1). 

Bedrock underlying the buried auriferous 

channel gravels is pyritic black chert, black siliceous 

argillite, greenstone, and silicified limestone and 

dolostone of the Amy Creek unit (Weber and others, 

1985). In some places, placer gold has penetrated into 

decomposed bedrock as much as 60 em. The character 

of the gold is quite variable over the length of the 

deposit: it ranges from light yellow to dark and ironstained, fine to coarse, porous to dense, rounded to 

angular, and in some places is of mixed varieties. 

Heavy minerals from pan concentrates include 

magnetite, ilmenite, hematite, chrome spinel, pyrite, 

cinnabar, stibnite, and less abundant barite, scheelite, 

cassiterite, zircon, and uranium-thorium minerals 

(Mertie, 1917; Eberlein and Menzie, 1978). The source 

of the gold is believed to be metalliferous quartzcalcite veins that constitute small lodes associated 

with quartz monzonite dikes of Tertiary(?) age on the 

south side of the valley (Eberlein and Menzie, 1978). 

Cambrian mafic and ultramafic intrusive bodies also 

~ Placer mine operations 

MAP LOCATION 

KILOMETERS 

Figure 1. livengood area, showing faults, drainage features, and 

location of pollen sample. Cross section A-A' shown on figure 2. 

East-Central Alaska 61 
A 

EJ Unconsolidated material 

[] Auriferous gravel 

Silicified 

dolostone, 

chert, argillite, 

greenstone 

Fault 

A' 

Figure 2. Schematic cross section A-A' (see fig. 1) showing 

bedrock ridge that separates auriferous gravels from present-day 

Livengood Creek. Diagram not to scale. 

occur on the south side of the valley (Weber and 

others, 1985), and one platinum nugget was reported by 

Overbeck (1920). Platinum-bearing grains from Amy 

Creek were reported by Cathrall and others (1987). 

We collected a sample for pollen analysis from 

auriferous gravel in that part of the buried channel on 

the Livengood bench north of the town of Livengood 

(figs. 1 and 2) that currently is being mined. The 

sample was collected from a lens 80 em long and 10 

em thick of dark-brown organic-rich silt which 

included pieces of woody material up to 0.5 by 1.0 em 

in size (fig. 3). The lens occurs within moderately 

sorted alluvium of coarse sand to cobble size with 

poorly defined decimeter-scale lenticular beds; it 

probably represents a quiet-water deposit behind a bar 

within a braided channel. The coarse alluvial gravel is 

subrounded and consists of silicified carbonate, chert, 

greenstone, argillite, and intermediate intrusive rock, 

commonly with slightly rusty weathering rinds; clasts 

of intrusive rock are commonly highly decomposed. 

The gravel is overlain by approximately 30 m of frozen 

silt, stony silt, and organic-rich silt (fig. 3). 

The silt sample contained well-preserved pollen 

and abundant fern spores representing a coniferdominated forest with spruce (Picea), pine (Pinus), and 

small amounts of hemlock (Tsuga). The sample also 

contained alder (Alnus), birch (Betula), sedge 

(Cyperaceae), grass (Gramineae), rare grains of Jacob's 

ladder (PoZemonium), sphagnum moss spores, and 

several types of fern spores. All other dated pollen 

and macrofossil assemblages containing pine and 

hemlock in central and northern Alaska are older than 

Pleistocene (D.M. Hopkins, University of AlaskaFairbanks, written commun., 1987). The pollen 

assemblage from Livengood Creek suggests a Pliocene 

age, but a late Miocene age is also possible (T.A. Ager, 

unpub. data). The presence of pine and hemlock in this 

assemblage suggests that the climate at that time was 

somewhat warmer and more moist than today. 

The older, oxidized gravel from which this 

pollen age was obtained may be correlative with the 

Cripple Gravel of P~w~ (1975), which is the deepest 

gravel exposed in placer workings in the Fairbanks 

District. This gravel is found on buried bedrock 

benches; it contains decomposed clasts of intrusive 

igneous rock and iron-oxide-coated clasts and is 

overlain by tan gravel and thick silt deposits. P~w~ 

(1975) inferred the Cripple Gravel to be of late 

Pliocene and (or) early Pleistocene age. 

The Nenana Gravel, found in the Healy area on 

the north flank of the Alaska Range, probably is late 

Miocene to early Pliocene in age on the basis of a 

small megafossil flora (Wolfe and Tanai, 1980). Most 

of the pollen types found in lignitic horizons in the 

Nenana Gravel also occur in the Livengood sample. 

This suggests approximate age equivalency (T.A. Ager, 

unpub. data). Clasts in the Nenana Gravel also have 

oxide coatings and include decomposed coarse-grained 

intrusive rocks. Although possibly time equivalent, the 

Nenana Gravel, the Cripple Gravel, and the Livengood 

gravel unit are widely separated in space. 

The possibility of older buried channels in the 

vicinity of known sources of gold has historically been 

investigated in the Tolovana and other mining districts 

of central Alaska. Other deeply buried channels are 

known near Hess Creek north of Livengood and the 

South Fork of Hess Creek (Brooks, 1916), but these 

have not yielded significant gold. However, to our 

knowledge, this is the first major gold placer in 

interior Alaska that has yielded evidence of a Tertiary 

age. Our data confirm for the first time the formerly 

speculative assumption that many of the interior 

Alaska gold-producing placer deposits may have 

formed during Tertiary time. 

40 

30 

20 

10 

Frozen silt, stoney silt 

and organic-rich silt 

Organic-rich silt sample 

Lenticularly bedded stream gravels 

Greenstone and silicified dolostone 

Figure 3. Generalized stratigraphic section at pollen-sample 

locality on north side of Livengood valley. 

62 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
REFERENCES CITED 

Brooks, A.H., 1916, Preliminary report on the 

Tolovana District: U.S. Geological Survey 

Bulletin 642, p. 201-209. 

Cathrall, J.B., Antwei1ler, J.C., and Mosier, 

E.L., 1987, Occurrence of platinum in gold 

samples from the Tolovana and Rampart mining 

districts, Livengood quadrangle, Alaska: 

U.S. Geological Survey Open-File Report 87-

330, 15 p., 1 sheet, scale 1:250,000. 

Eberlein, G.D., and Menzie, W.D., 1978, Maps and 

tables describing areas of metalliferous 

mineral resource potential of central 

Alaska: U.S. Geological Survey Open-File 

Report 78-1-D, 47 p., 2 sheets, scale 

1:1,000,000. 

Mertie, J.B., Jr., 1917, The gold placers of the 

Tolovana district, Alaska: U.S. Geological 

Survey Bulletin 662D, p. 260-268. 

Overbeck, R.M., 1920, Placer m1n1ng in the 

Tolovana district: U.S. Geological Survey 

Bulletin 712, p. 178-184. 

Pewe, T.L., 1975, Quaternary stratigraphic 

nomenclature in unglaciated central 

Alaska: U.S. Geological Survey Professional 

Paper 862, 32 p. 

Weber, F.R., Smith, T.E., Hall, M.H., and 

Forbes, R. B., 1985, Geologic guide to the 

Fairbanks-Livengood area, east-central 

Alaska: Anchorage, Alaska Geological 

Society field trip guide, 44 p. 

Wolfe, J.A., and Tanai, T., 1980, The Miocene 

Seldovia Point flora from the Kenai Group, 

Alaska: U.S. Geological Survey Professional 

Paper 1105, 52 p. 

Reviewers: D.M. Hopkins and F.R. Weber 

Geologic Studies 1n Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

East-Central Alaska 63 
Reconnaissance Geochemical Investigations of the 

White Mountains National Recreation Area, 

East-Central Alaska 

By Thomas D. Light, Gregory K. Lee, Richard B. Tripp, and Elizabeth A. Bailey 

In 1986 and 1987 we conducted a reconnaissance 

geochemical study of a portion of the White Mountains 

National Recreation Area (NRA) of east-central 

Alaska as part of an assessment of the mineral 

resource potential of that area (fig. 1). The White 

Mountains NRA lies within the Yukon-Tanana Upland 

of east-central Alaska. The geologic setting in the 

vicinity of the White Mountains has been described by 

Weber and others (1985). The predominant lithologies 

in the area are Precambrian to Mesozoic quartzitic, 

pelitic, calcic, and mafic metasedimentary rocks and 

some metamorphosed mafic and felsic igneous rocks. 

These rocks are intruded by Cretaceous and Tertiary 

granitic rocks and minor amounts of intermediate and 

mafic rocks. Large northeast-southwest-trending 

thrust faults and strike-slip splays of the Tintina fault 

zone cross the area (Chapman and others, 1971, F.R. 

Weber, U.S. Geological Survey, written commun.). The 

potential for undiscovered mineral resources in the 

White Mountains NRA is evaluated by McCammon and 

others (this volume). 

During this study, 620 rocks, 461 streamsediment samples, 364 moss-trap-sediment samples, 

and 340 heavy-mineral concentrates were collected 

from the White Mountains NRA. All samples were 

analyzed for 31 elements using a semiquantative, 

direct-current arc emission spectrographic method 

(Grimes and Marranzino, 1968). Stream-sediment and 

moss-trap-sediment samples were also analyzed for 

As, Bi, Cd, Sb, and Zn by atomic absorption 

spectrophotometry using the method of O'Leary and 

Viets (1986). Analytical data are published in Sutley 

and others (1987a, 1987b). The nonmagnetic fractions 

of heavy-mineral concentrates were examined under a 

binocular microscope to determine the presence of 

specific ore-related minerals. Identification of 

unusual or unknown species was confirmed by X-ray 

diffraction. The analytical data were processed using 

the USGS STATPAC computer programs (VanTrump 

and Miesch, 1977) to determine univariate statistics. 

Nineteen target and pathfinder elements (Ag, As, Au, 

B, Ba, Be, Bi, Cd, Cu, Fe, La, Mo, Nb, Pb, Sb, Sn, Th, 

W, and Zn) were selected as potential indicators of 

mineralized areas. The thresholds used to define 

anomalous concentrations of these selected elements 

were subjectively determined by visual inspection of 

histograms and by inflection points in cumulative 

frequency plots. 

The occurrence and distribution of elements and 

minerals in geochemical samples from the White 

Mountains NRA were used to determine the areas of 

anomalous metal concentrations shown in figure 1 and 

listed in table 1. In the following paragraphs we 

discuss these areas in their probable decreasing order 

of importance based on our current level of 

information. 

The Nome Creek area (area 3; fig. 1 and table 

1), which includes Trail and Ophir Creeks, is underlain 

by greenschist-facies metamorphic rocks of the 

Precambrian Fairbanks schist unit. Anomalously high 

concentratons of Ag, As, Au, Be, Cu, Fe, Pb, Sb, Sn, 

and W were observed in samples from this area, and 

heavy-mineral concentrates collected from its eastern 

part contained gold, cassiterite, scheelite, pyrite, and 

arsenopyrite. Approximately 29,000 oz (900 kg) of 

gold was recovered prior to 1948 from placer oprations 

along Nome Creek (U.S. Bureau of Mines file data), 

and during this study visible gold was observed in 

numerous samples from the Nome Creek area. Given 

the abundance of gold observed, we expect that 

additional placer gold and perhaps lode gold will be 

found in the Nome Creek area. 

Cache Mountain (area 1) is a highly evolved 

Tertiary granitic intrusion dated at about 58 Ma 

(Holm, 1975). Fluorite, tourmaline, cassiterite, and 

scheelite, in addition to high concentrations of Ag, B, 

Be, Bi, Cd, Pb, Sb, Sn, and Zn, occur in this area. The 

association of light and transition metals suggests the 

possible presence of Sn-bearing greisen or vein 

mineralization in and around the Cache Mountain 

pluton. 

Scattered localities around the periphery of the 

Victoria Mountain pluton (area 10) contain high values 

of a wide range of base and precious metals. The 

abundance of scheelite and cassiterite in streams 

draining Victoria Mountain suggests the possibility of 

skarn mineralization in dolomitic rocks along the 

borders of the intrusion. The continuation of this 

association of anomalous elements to the north of 

Victoria Creek may represent dispersion of 

hydrothermal fluids outward from the pluton along 

local faults. 

Samples from the Warren Creek-Moose Creek 

area (area 11) contain anomalously high values of Ag, 

As, B, Ba, Bi, Cd, Cu, Fe, La, Mo, Pb, Sb, Th, and Zn, 

along with occurrences of pyrite, barite, and sphalerite 

from Paleozoic to Mesozoic reduced slate, shale, and 

siltstone. This association suggests the possibility of 

sedimentary exhalative and (or) epigenetic base-metal 

sulfide deposits. In addition, high concentrations of 

base metals in areas of Paleozoic clastic sedimentary 

and volcanic rocks suggest the possible presence of 

polymetallic vein deposits peripheral to granitic 

intrusions to the south (outside our study area). 

Anomalous concentrations of As, B, Be, La, Th, 

and Y were observed in samples from the syenite of 

64 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Roy Creek (area 4). A concentrate sample from Roy 

Creek contained thorite, allanite, cassiterite, 

scheelite, and sapphire corundum. One sample from a 

mineralized fracture zone in the syenite contained 

Tg 

Kg 

Ks 

MzPzs 

0 10 

KILOMETERS 

DEFINITION OF MAP UNITS 

Granite (Tertiary) 

Quartz monzonite (Cretaceous) 

Syenite (Cretaceous) 

Quartzite, phyllite, limestone, 

conglomerate, shale, basalt, 

minor gabbro and diorite 

(Paleozoic and Mesozoic) 

20 

greater than 2000 parts per million thorium. 

Additional fractures containing thorium and rare-earth 

elements (REE) possibly occur in the syenite of Roy 

Creek. 

-€p£s 

Area 

not assessed 

by USGS 

Schist, quartzite, phyllite, slate, 

grit, and shale (Precambrian 

and Cambrian) 

EXPLANATION 

~ Thrust fault, barbs on upper plate; 

~ .. · dashed where inferred 

- - - High-angle fault, dashed where inferred 

Figure 1. Geochemically anomalous areas (patterned) in White Mountains National Recreation Area. See table 1 for description 

of numbered areas. VABM, Vertical Angle Bench Mark. 

East-Central Alaska 65 
Table 1. Geochemically anomalous areas in the White Mountains National Recreation Area 

[aln=allanite, ars=arsenopyrite, bar=barite, cas=cassiterite, cin=cinnabar, cpy=chalcopyrite, cyr=cyrtolite, flu=fluorite, gal=galena, mon=monazite, pyr=pyrite, 

tour=tourmaline, saph=sapphire, sch=scheelite, sph=sphalerite, stib=stibnite, uth=uranothorite] 

Area name Bedrock Geochemical anomalies Possible source of anomaly 

Elements 

1. Cache Mountain Granite of Ag, B, Be, Bi, 

Cache Mountain Pb, Sb, Sn, Zn 

2. Lost Horizon Conglomerate, Ag, Ba, Cd, Cu, 

Creek shale, graywacke Pb, Zn 

3. Nome Creek Fairbanks schist Ag, As, Au, Be, 

unit Fe, Pb, Sb, Sn, 

4. Roy Creek Syenite of Roy As, B, Be, La, 

Creek y 

5. Upper Victoria Wickersham unit La, Nb, Pb, W, 

Creek 

6. VABM Duncan Conglomerate, Ag, Cd, Cu, Pb, 

shale, graywacke Zn 

7. VABM Globe Limestone, slate, Ba, Cu, Ho, w quartzite, basalt, 

mafic sills and 

dikes 

8. VABM Victoria Wickersham unit Ag, Ba, Be, Cd, 

Nb, Pb, Zn 

9. Victoria Cr. Dolomite, slate, Ag, As, Ba, Cd, 

Beaver Creek grit, mafic and Zn 

Ridge ultramafic rocks 

10. Victoria Mtn- Quartz monzonite Ag, As, Au, B, 

Glacier Creek of Victoria Mtn., Co, Cu, Fe, La, 

grit, slate, Ni, Pb, Sb, Sn, 

shale, dolomite w, Zn 

11. Warren Creek- Slate, quartzite Ag, As, B, Ba, 

Moose Creek grit Cd, Cu, Fe, La, 

Pb, Sb, Th, Zn 

12. Willow Creek Conglomerate, Ag, As, B, Ba, 

slate, graywacke, Cu, Nb, Pb, Sb, 

shale 

13. Windy Creek Quartzite, slate, Ag, As, Cd, Cu, 

phyllite, shale Mo, Nb, Sb, Pb, 

w, Zn 

Samples from Lost Horizon Creek (area 2) and 

from drainages along the flanks of the ridge between 

Victoria and Beaver Creeks (area 9) contain high 

concentrations of Ag, Ba, Cd, Pb, and Zn. Although 

the source of the metals is not known, the rocks that 

are potential hosts for sedimentary exhalative 

mineralization in the Warren Creek-Moose Creek area 

(area 11) do not occur in these areas. The occurrence 

of cinnabar together with pyrite and barite in heavymineral concentrates from the Lost Horizon Creek and 

the ridge between Victoria and Beaver Creeks suggests 

the presence of epithermal mineralization, possibly in 

polymetallic veins or channeled along low-angle thrust 

faults. 

Minerals 

Cd, bar, cas, flu, pyr, Sn-bearing greisen or 

sch, sph, tourveins 

bar, cin, pyr, sph Polymetallic veins 

Cu, ars, bar, cas, cin, Placer Au, vein Au 

w gold, pyr, sch 

Th, aln, cas, sch, saph, Th- and REE-bearing veins 

uth 

Zn bar, gal, pyr, sch, Shales and mafic rocks 

spblymetallic veins 

Sb, bar, cas, cpy, pyr, Polymetallic veins, 

sph, stib shales 

bar, cas, cin, sch Polymetallic veins(?) 

La bar, gold, pyr, sch, Polymetallic veins(?) 

sph 

Pb, bar, cas, cin, pyr, Polymetallic veins(?) 

sch 

Bi, ars, bar, cas, cpy, Skarn, polymetallic 

Ho, gold, pyr, sch, sph, veins 

Th, uth 

Bi, aln, ars, bar, cyr Sedimentary exhalative, 

Mo, flu, gal, mon, pyr, polymetallic veins 

tour, sch, sph, 

stib, uth 

Cd, bar, cas, cin, pyr, Polymetallic veins 

Zn sph, sch 

Fe, bar, cin, gal, pyr, Polymetallic veins 

Th, sch, sph, stib 

Samples from the Windy Creek area (area 13) 

contain anomalous concentrations of Ag, As, Cd, Cu, 

Fe, Mo, Nb, Sb, Pb, Th, W, and Zn. The source of the 

anomalies is unknown. They could be derived from 

indigenous metals in the underlying JurassicCretaceous flysch or from polymetallic veins formed 

by the migration of hydrothermal fluids along local 

faults. 

Anomalous concentrations of ore-related 

elements also occur near the headwaters of Victoria 

Creek (area 5), near VABM Duncan (area 6), northeast 

of VABM Globe (area 7), south of VABM Victoria (area 

8), and along Willow Creek (area 12). There is no 

known source for these metals, and no evidence of 

66 Geologie Studies in Alaska by the U.S. Geological Survey during 1987 
epithermal mineralization was observed. Given the 

lack of evidence for widespread mineralization, we 

speculate that the metals may be from small fracture 

fillings caused by the migration of weakly mineralized 

hydrothermal fluids channeled along local faults or 

that the metals may occur in polymetallic veins. 

In summary, geochemical anomalies in the 

White Mountains NRA and their geologic associations 

suggest the presence of a wide variety of 

mineralization types within the study area. Varieties 

of mineralization include known occurrences of placer 

gold and Th-REE veins, probably occurrences of lode 

gold, and possible occurrences of polymetallic veins, 

sedimentary exhalites, Sn greisen, W skarn, and ThREE veins. 

REFERENCES CITED 

Chapman, R.M., Weber, F.R., and Tabor, Bond, 

1971, Preliminary geologic map of the 

Livengood quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 71-066, 

scale 1:250,000. 

Grimes, D.J., and Marranzino, A.P., 1968, 

Direct-current arc and alternating-current 

spark emission spectrographic field methods 

for the semiquantitative analysis of 

geologic materials: U.S. Geological Survey 

Circular 591, 6 p. 

Holm, Bjarne, 1975, Bedrock geology and 

mineralization of the Mount Prindle area, 

Yukon-Tanana Upland, Alaska: Fairbanks, 

University of Alaska, M.S. thesis, 55 p. 

O'Leary, R.M., and Viets, J.G., 1986, 

Determination of antimony, arsenic, bismuth, 

cadmium, copper, lead, molybdenum, silver, 

and zinc in geologic materials by atomic 

absorption spectrometry using a hydrochloric 

acid-hydrogen peroxide digestion: Atomic 

Spectroscopy, v. 7, no. 1, p. 4-8. 

Sutley, S.J., Ryder, J.T., Light, T.D., and 

Weber, F.R., 1987a, Analytical results and 

sample locality map of rock samples from the 

White Mountains National Recreaton Area, 

Livengood and Circle quadrangles, eastcentral Alaska: U.S. Geological Survey 

Open-File Report 87-284, 61 p. 

Sutley, S.J., O'Leary, R.M., Lee, G.K., and 

Light, T .D., 1987b, Analytical results and 

sample locality map of stream-sediment, 

moss-trap sediment, and heavy-mineralconcentrate samples from the White Mountains 

National Recreation Area, Livengood and 

Circle quadrangles, east-central Alaska: 

U.S. Geological Survey Open-File Report 87-

285, 110 P• 

VanTrump, G., Jr., and Miesch, A.T., 1977, The 

U.S. Geological Survey RASS-STATPAC sys tern 

for management and reduction of geochemical 

data: Computers and Geosciences, v. 3, p. 

475-488. 

Weber, F.R., Smith, T.E., Hall, M.H., and 

Forbes, R.B., 1985, Geologic guide to the 

Fairbanks-Livengood area, east-central 

Alaska: Anchorage, Alaska Geological 

Society Guidebook, 44 p. 

Reviewers: M.S. Allen and M.L. Miller 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

East-Central Alaska 67 
Ultramafic Rocks of the Livengood Terrane 

By Robert A. Loney and Glen R. Himmelberg 

The ultramafic rocks of the Livengood area are 

part of a narrow, discontinuous belt of sheared, highly 

serpentinized ultramafic rocks that extends more than 

190 km from near Manley Hot Springs on the southwest 

through Livengood to the Beaver Creek area on the 

northeast (Chapman and others, 1971; Chapman and 

others, 1982). Foster (1967, 1969} called the belt the 

"Livengood ultramafic trend" and considered it to be a 

fault-bounded, tectonically emplaced, alpine-type 

serpentinite. Reconnaissance fieldwork during 1987 

generally supports Foster's view, with the assumption 

that by "alpine-type" he meant serpentinite derived 

from an ophiolitic harzburgite-dunite complex (Wyllie, 

1967). However, the generally poor exposures make it 

difficult to be certain of many of the details of the 

belt, particularly the contacts and internal 

composition. 

In the Livengood area, the largest mass of 

ultramafic rock occurs in Cascadan Ridge about 10 km 

southeast of Livengood (localities 10 and 11, fig. 1), 

but it is poorly exposed at these localities. It appears 

to be depositionally overlain on the south side of the 

ridge by the Devonian Cascadan Ridge unit of Weber 

and others (1985), and on the north side by the 

Ordovician Livengood Dome Chert. The serpentinite 

on Cascadan Ridge, although predominant, is cut 

through by numerous lenticular bodies of gabbro. In 

the immediate vicinity of Livengood, however, diorite 

and gabbro dominate, and most serpentinite occurs as 

small, scattered masses in and around the dioritegabbro bodies. 

The serpentinite is largely serpentinized 

harzburgite (and minor dunite) that had a primary 

mineralogy consisting of olivine, orthopyroxene (15 to 

20 percent), and accessory chromian spinel. Foster 

(1966) reported minor amounts of clinopyroxene in the 

ultramafic rocks, but we saw none in the samples we 

collected. The primary texture, as interpreted from 

bastite pseudomorphs after orthopyroxene, was 

anhedral granular with an average orthopyroxene grain 

diameter of about 3 to 4 mm. Serpentine minerals 

consist of lizardite and clinochrysotile. The primary 

mineralogy and texture of the serpentinized 

harzburgite are characteristic of mantle peridotite of 

ophiolite complexes. 

Similar serpentinite mineralogy and texture, 

including bastite, was reported by Foster (1969) from 

the Beaver Creek area at the northeast end of the 

Livengood ultramafic trend (locality 9, fig. 1), 

indicating a probable mantle peridotite prototype for 

that area also. The isolated southwest end of the 

trend in the Manley Hot Springs area (Serpentine 

Ridge; locality 12, fig. 1) has been so intensely 

recrystallized to antigorite plus magnetite that we 

could see no relict textures that might further identify 

its protolith. Tectonic inclusions of rodingitized 

hornblende-augite gabbro are common, however, and 

ar-e similar to the disrupted gabbr-o dikes in the 

Livengood area. Ther-e is nothing in this evidence 

against the serpentinite being a continuation of the 

ultramafic rocks of the Livengood area because the 

difference in mineralogy may be only a product of 

r-ecr-ystallization. Antigorite is a higher- temperature 

serpentine mineral than lizardite and chrysotile, which 

dominate in the Livengood area (Evans and others, 

1976; Mellini and other-s, 1987). The heat source 

r-esponsible for this recrystallization is not known. 

Because the serpentinite lies str-uctur-ally above, and 

possibly in fault contact with, a poorly dated clastic 

sedimentar-y unit of Jurassic or Cretaceous age 

(Chapman and others, 1982), it was previously included 

in the Manley terr-ane rather than the Livengood 

terr-ane (Jones and others, 1987). 

Near Livengood the serpentinite is intruded by 

dior-ite composed lar-gely of brownish-green hornblende 

and plagioclase, and 10 to 20 km to the southwest the 

serpentinite commonly contains disrupted hornblendeaugite gabbro dikes. Some of these dikes have finegrained "chilled" margins, indicating intrusion into the 

cooler ultramafic rocks. The diorite and gabbro seem 

petr-ologically similar, and, in view of the similar K-Ar 

isotopic ages of 518-633 Ma for hornblende (Donald L. 

Turner, University of Alaska, written commun., 1987}, 

they probably represent the same intrusive event. 

Sedimentary and volcanic rocks of Middle 

Devonian age (Cascadan Ridge unit} on the south side 

of Cascadan Ridge and the sedimentary rocks of 

Ordovician age (Livengood Dome Chert) on the north 

side of the ridge both appear to unconformably overlie 

the ultramafic rocks. Although ultramafic clasts 

(serpentinite) have been reported from the 

conglomerates near the contact with the serpentinite 

outcr-ops (Foster, 1966; Weber and others, 1985), our 

brief search did not substantiate the occur-rence of 

ultramafic clasts. Clasts that appeared to be 

serpentinite in hand specimen were determined to be 

chlorite upon X-ray and microprobe analysis. 

However-, the presence of chromian spinel clasts in the 

conglomerate is highly suggestive of a harzburgite or 

dunite sedimentary source. 

Accordingly, if the above sedimentary and 

structural relations are valid, the serpentinite would 

be pre-Ordovician in age, which would be compatible 

with it being pre-diorite-gabbro (518-633 Ma). It is 

suggested then that the ultramafic rocks were 

pr-obably emplaced as part of an ophiolite sometime in 

the Late Pr-oter-ozoic (more than 633 Ma), followed by 

diorite-gabbr-o intrusion in the Late Proter-ozoic to 

Cambrian interval; they ultimately were eroded and 

over-lapped by sediments in the Ordovician (Livengood 

68 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Dome Chert) and by sedimentary and volcanic deposits 

in the Middle Devonian (Cascadan Ridge unit). This 

general structural relationship seems to continue to 

the northwest to the Beaver Creek area, where a 

major serpentinite mass is in contact with similar 

sedimentary rocks along its northwestern contact, but 

is in fault contact with the Mesozoic sedimentary 

rocks of the Manley terrane (locality 9, fig. 1). This 

package of rocks has been called the Livengood 

terrane (Jones and others, 1987). 

The Livengood terrane as thus defined is 

composed of, in addition to the Proterozoic(?) 

serpentinized mantle peridotite, Late Proterozoic to 

Cambrian diorite-gabbroic intrusive rocks, and still 

later marine sedimentary and volcanic rocks that are 

170. 

sa· 

unrelated to the partial ophiolite represented by the 

serpentinite. Thus, in contrast to the probable 

Mesozoic Kanuti ophiolite terrane (locality 6, fig. 1; 

Loney and Himmelberg, 1985; Loney and Himmelberg, 

in press), the Livengood terrane seems not to represent 

primary emplacement of ophiolite from the mantle, 

but instead a later, unrelated event. As reflected in 

figure 1, the Kanuti ophiolite terrane (or equivalent 

terranes) occurs in widely scattered outcrops as a 

thrust sheet overlying a lower thrust sheet composed 

mainly of pillow basalt and radiolarian chert 

(Angayucham terrane). Such relationships are not 

present in the ultramafic rocks of the Livengood 

terrane. 

liB 

• 

EXPLANATION 

Manley terrane--Mesozoic flyschoid 

sedimentary rocks; black area is 

Serpentine Ridge Lhrust sheet(?) 

Baldry and similar, adjacent 

terranes--early to middle 

Paleozoic metasedimentary rocks 

Angayucham and equivalent 

terranes--black areas Kanuti 

and equivalent ophiolite 

thrust sheets 

Cenozoic and Cretaceous 

deposits 

Ruby terrane and equivalent 

subtcrranes of Arctic Alaska 

tcrrane-.-on north flank of 

Yukon-Koyukuk basin 

North Slope sublCTTane of 

Arctic Alaska terrane 

Seward terrane--Precambrian and 

Paleozoic metamorphic rocks 

Endicott subterrane of Arctic 

Alaska terrane 

200 KILOMETERS 

Figure 1. Livengood terrane and ultramafic rocks (1 0) relative to other major ophiolites 

and lithotectonic terranes of Alaska (adapted from Patton and others, 1977; and Jones 

and others, 1987). 1, Avan Hills; 2, Asik Mountain; 3, Misheguk; 4, Siniktanneyak; 5, Jade 

Mountains; 6, Kanuti; 7, Yuki River; 8, Mount Hurst; 9. Beaver Creek; 10, Livengood; 11 , 

Cascadan Ridge; 12, Manley Hot Springs. 

East-Central Alaska 69 
REFERENCES CITED 

Chapman, R.M., Weber, F.R., and Taber, Bond, 

1971, Preliminary geologic map of the 

Livengood quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 71-66, 2 

sheets, scale 1:250,000. 

Chapman, R.M., Yeend, W.E., Brosg~, W.P., and 

Reiser, H.N., 1982, Reconnaissance geologic 

map of the Tanana quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 82-734, 

20 p., 1 sheet, scale 1:250,000. 

Evans, B. W., Johannes, W., Oterdoom, H., and 

Trommsdorff, V., 1976, Stability of 

chrysotile and antigorite in the 

serpenttntte multisystem: Schweizerische 

Mineralogische Petrographische Mitteilungen, 

v. SO, p. 481-492. 

Foster, R.L., 1966, The petrology and structure 

of the Amy Dome area, Tolovana mining 

district, east-central Alaska: Columbia, 

Missouri, University of Missouri, 227 p. 

1967, Tectonic inclusions from a 

serpenttntte, east-central Alaska: U.S. 

Geological Survey Professional Paper 575-D, 

p. Dl20-Dl22. 

1969, Nickeliferous serpentinite near 

Beaver Creek, east-central Alaska: u.s. 

Geological Survey Circular 615, p. 2-4. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1987, Lithotectonic terrane 

map of Alaska (west of the 14lst 

meridian): U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1874-A, 

scale 1:2,500,000. 

Loney, R.A., and Himmelberg, G.R., 

Distribution and character of 

1985, 

the 

peridotite-layered gabbro complex of the 

southeastern Yukon-Koyukuk ophiolite belt, 

Alaska, in Bartsch-Winkler, Susan, and Reed, 

K.M., eds., The United States Geological 

Survey in Alaska--Accomplishments during 

1983: U.S. Geological Survey Circular 945, 

P• 46-48. 

The Kanuti ophiolite terrane, Alaska: 

Journal of Geophysical Research, p. 1-60. 

[in press] 

Mellini, M., Trommsdorff, V., and Compagnoni, 

R., 1987, Antigorite polysomatism: Behavior 

during progressive metamorphism: 

Contributions to Mineralogy and Petrology, 

v. 97, P• 147-155. 

Patton, W.W., Jr., Tailleur, I.L., Brosg~, W.P., 

and Lanphere, M.A., 1977, Preliminary report 

on the ophiolites of northern and western 

Alaska, in Coleman, R.G., and Irwin, W.P., 

eds., North American ophiolites: Oregon 

Department of Mineral Industries Bulletin 

95, p. 51-57. 

Weber, F.R., Smith, T.E., Hall, M.H., and 

Forbes, R.B., 1985, Geologic guide to the 

Fairbanks-Livengood area, east-central 

Alaska: Anchorage, Alaska Geological 

Society, p. 1-44. 

Wyllie, P.J., 1967, Alpine type ultramafic 

associations, I. Introduction, in Wyllie, 

P.J., ed., Ultramafic and related rocks: 

New York, John Wiley, p. 135-136. 

Reviewers: Willis Nelson and George Plafker 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

70 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Mineral Resource Assessment for Part of the 

White Mountains National Recreation Area 

By Richard B. McCammon, Thomas D. Light, and C. Dean Rinehart 

In 1986 and 1987 the U.S. Geological Survey 

conducted a mineral resource assessment of most (75 

percent) of the White Mountains National Recreation 

Area (NRA) in east-central Alaska for the Bureau of 

Land Management. Field mapping, geochemical 

sampling of stream sediments and rocks, and 

aeromagnetic, gravity, audiomagnetotelluric, and 

magnetotelluric studies were carried out within this 

study area (fig. 1). Results of these multidisciplinary 

studies were integrated and evaluated to define the 

areas within the NRA that have the best probability 

for containing undiscovered mineral resources. The 

purpose of this report is to present a summary of this 

resource evaluation, and to enumerate the areas within 

the NRA that have the highest favorability for mineral 

endowment. 

The White Mountains NRA is a part of the 

Yukon-Tanana Upland, which is primarily a terrane of 

quartzitic, pelitic, calcareous, and volcaniclastic 

metasedimentary rocks with some metamorphosed 

mafic and felsic igneous rocks that has been intruded 

by Mesozoic and Cenozoic granitic rocks and minor 

amounts of intermediate and mafic rocks {Chapman 

and others, 1971). The major faults in the area are 

thrust faults and strike-slip fault splays of the Tintina 

fault zone (F.R. Weber, US Geological Survey, written 

commun.). Historically, the major mineral resource of 

the area has been placer gold, which has been 

recovered in the southern part of the White Mountains 

NRA since about 1910 {Ellsworth and Parker, 1911). 

For example, approximately 29,000 oz (900 kg) of gold 

was recovered from Nome Creek prior to 1948 (U.S. 

Bureau of Mines, file data), and exploration and mining 

activity have continued sporadically to the present. 

The White Mountains as a whole have been prospected 

over the years for base and precious metals and, most 

recently, for uranium (Burton, 1981). 

Our assessment of the undiscovered mineral 

resources of the White Mountains NRA is based on the 

concept of mineral deposit models, which are defined 

as the set of attributes common to a particular class 

of mineral deposit. The mineral deposit models used 

here (with the exception of high-calcium limestone and 

thorium- and rare-earth element-bearing (REE) veins) 

have been described by Cox and Singer (1986). We 

combined the results of our geological, geochemical, 

and geophysical studies with all information available 

from previous investigations to identify areas within 

the White Mountains NRA that are geologically 

permissive for the occurrence of mineral deposits and 

that possess attributes similar to existing models. 

Both positive and negative evidence (the presence and 

absence of attributes, respectively) were considered in 

postulating the occurrence of undiscovered deposits 

with respect to a particular model. 

We determined that there is significant 

evidence for the occurrence of nine mineral deposit 

types in the portion of the White Mountains NRA that 

we evaluated (fig. 1 and table 1). The areas favorable 

for each of these deposit types were individually 

assessed to determine the undiscovered resources using 

a method of Drew and others (1986) as adapted to a 

computer program known informally as MARK3. This 

program uses Monte Carlo methods to estimate the 

contained metal content in undiscovered deposits 

based on estimates of the number of undiscovered 

deposits for each deposit type. To use MARK3, 

subjective probabilistic estimates were made of the 

number of undiscovered deposits for specific deposit 

types for each of the tracts identified; a separate 

estimate was made for the probability that no 

undiscovered deposits exist (table 1). These estimates 

were then combined with grade-tonnage data (from 

Cox and Singer, 1986) as input to MARK3, which, in 

turn, generated estimates of the contained metal in 

the undiscovered deposits. In those cases where a 

metal occurs in more than one model, the estimate of 

the total contained metal was obtained by convolving 

the probability distributions of the separate contained 

metal distributions. 

We made probabilistic estimates for the 

occurrence of undiscovered metallic resources in eight 

tracts, and for high-calcium limestone in one tract 

(table 1). Our estimates of the undiscovered resources 

include the estimate of the mean endowment as well 

as estimated endowment at the 95th and 5th percentile 

confidence levels. The quantity of undiscovered highcalcium limestone was estimated using a volumetric 

method (Finch and McCammon, 1987). Our analysis 

depends on two critical assumptions. First, in order to 

make use of existing grade-tonnage data, we assume 

that future discovery of the types of mineral deposits 

considered in our assessment will be of similar size and 

grade as those deposits described in the model. 

Second, our estimates are based on present knowledge 

about the deposit types and would be modified by 

improved knowledge of present deposit types and 

future recognition of new deposit types. 

Tracts evaluated as favorable for resource 

occurrence are outlined in figure 1, and geochemically 

anomalous areas in the White Mountains NRA, that 

include these tracts are described by Light and others 

(this volume). Tract 1 encompasses the silica-rich 

leucogranite of Cache Mountain and is permissive for 

East-Central Alaska 71 
the occurrence of tin greisen. The granite contains 

anomalously high tin values, but does not appear to be 

composed of multiple intrusions. We estimate a 10 

percent probability of an undiscovered tin greisen 

deposit (table 1). Small veins or breccia zones bearing 

thorium and rare-earth oxides (REO) are associated 

with syenite in tract 2. We estimate a 10 percent 

probability for undiscovered Th/REE vein deposits in 

this area. Scheelite and base metals in stream 

sediments suggest the possibility of tungsten skarn 

deposits in thin carbonate lenses near the Victoria 

Mountain pluton (tract 3), where we estimate a 5 

0 10 20 

KILOMETERS 

percent probability for the occurrence of undiscovered 

skarn deposits. Based on the presence of sulfides, 

proximity to felsic intrusions, and a geologic setting 

similar to the Keno Hill-Galena Hill area in the Yukon 

Territory, we estimate a 50 percent probability for at 

least one polymetallic vein deposit in tract 5. 

Intrusion of buried Cretaceous or Tertiary 

granitic plutons inferred from aeromagnetic lows 

(Cady and Weber, 1983) may have caused hydrothermal 

remobilization of gold to form gold-bearing veins and 

stringers in tract 6 (Light and others, 1987). We 

estimate a 10 percent probability of one or more lode 

--,--------l 

I 

Area 

not assessed 

Figure 1. White Mountains National Recreation Area showing tracts with potential for undiscovered mineral resources 

(indicated by pattern and heavy-line drainage). Part of NRA indicated as "not assessed by USGS" was assessed by Alaska 

Division of Geological and Geophysical Surveys. Numbers refer to table 1. VABM, Vertical Angle Bench Mark. 

72 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Probabilistic estimates for resource endowment, White Mountains NRA 

[(1 ), probability that one or more deposits exist; (2), given the existence of undiscovered deposits, the number of deposits will equal or exceed the indicated number at the 

0.9, 0.5, or 0.1 probability level] 

Tract 

l 

2 

1 

4 

5 

6 

7 

8 

9 

Deposit model 

Sn greisen 

Th/REE veins 

W skarn 

High-calcium limestone 

Polymetallic vein 

Lode Au 

Placer Au 

Sedimentary exhalative (Zn,Pb) 

Serpentine-hosted asbestos/ 

stratiform mafic-ultramafic 

(Bushveld) Cr 

Probability(l) 

0.1 

.1 

.05 

1.0 

• 5 

.1 

• 5 

.l 

0 

Expected number(2) 

0.9 0.5 0.1 

1 1 1 

1 1 1 

1 1 1 

-Not applicable1 1 2 

1 1 2 

1 2 3 

1 1 1 

-Not applicableTable 2. Estimates of undiscovered mineral resources in the White Mountains NRA 

[Gold and silver in troy ounces, all other values in short tons (1 ton= 909 kg). "Probability," probability of endowment at the given confidence level. Estimate for 

gold at the 95th percentile confidence level based on regression model described by Bliss and others (1987)] 

Commodity Mean undiscovered Probability 

endowment 

Gold 46,000 

Silver 4,200,000 

Zinc 310,000 

Lead 180,000 

Tin 500 

Tungsten 2,100 

Thorium 7,000 

REO 6,000 

High-calcium 

limestone 27 billion 

gold deposits within this area. We estimate a 50 

percent probability that one or two placer gold 

deposits (and a 10 percent probability of three or more 

placer deposits) remain along Nome, Trail, and Ophir 

Creeks (tract 7). Tract 8 contains sulfides in 

tuffaceous rocks, dark argillite, and conglomerate in a 

geologic setting similar to the Selwyn Basin, Yukon 

Territory; we estimate a 10 percent probability for at 

least one sedimentary-exhalative Pb-Zn deposit in this 

tract. Tract 9 encompases a mafic and ultramafic 

complex that is a permissive environment for 

serpentine-hosted asbestos or stratiform chromite 

deposits. However, the complex is relatively thin and 

has been well explored, and we do not consider it to be 

a potential resource for asbestos, chromium, or nickel. 

The largest potential resource within our study 

area is high-calcium limestone, which is generally 

defined as having a minimum of 93 percent Caco3• 

Ten grab samples taken from the Tolovana Limestone, 

which composes the core of the White Mountains (tract 

4), averaged 98.6 percent Caco3. These 10 samples 

contain a higher average percentage of carbonate than 

95 percent 5 percent 

6,500 94,000 

0 14,000,000 

0 1,200,000 

0 520,000 

0 1,100 

0 0 

0 25,000 

0 32,000 

8.4 billion 45 billion 

99 percent of 2,829 high-calcium limestones from 

Alaska, Idaho, Oregon, and Washington that have been 

analyzed by Hill and others (1972). Based on a 

volumetric method of Finch and McCammon {1987), we 

estimate that 27 billion tons may be present within the 

White Mountains NRA, but a comprehensive sampling 

program would need to be undertaken to determine 

more accurately the extent and thickness of the highcalcium layers within the Tolovana Limestone and to 

refine our preliminary estimate. 

With the exception of gold and high-calcium 

limestone, the probability that undiscovered resources 

exist within the White Mountains NRA is considered to 

be low (table 1), and the size of the deposits that 

might exist is considered to be small. Therefore, our 

estimate of commodity endowment at the 95 percent 

confidence level is zero for all commodities except 

gold and high-calcium limestone (table 2). Gold is an 

exception because of its known occurrence within 

placer deposits in the White Mountains NRA and the 

virtual certainty that additional placer resources are 

present. 

East-Central Alaska 73 
REFERENCES CITED 

Bliss, J.D., Orris, G.J., and Menzie, W.D., 

1987, Changes in grade, volume, and 

contained gold during the mining life-cycle 

of gold placer deposits: Canadian Institute 

of Mining, v. 80, no. 903, p. 75-80. 

Burton, P.J., 1981, Radioactive mineral 

occurrences, Mt. Prindle area, Yukon-Tanana 

Uplands, Alaska: Fairbanks, University of 

Alaska, M.S. thesis, 72 p. 

Cady, J.W., and Weber, F.R., 1983, Aeromagnetic 

map and interpretation of magnetic and 

gravity data, Circle quadrangle, Alaska: 

U.S. Geological Survey Open-File Report 83-

170-C, scale 1:250,000. 

Chapman, R.M., Weber, F.R., and Tabor, Bond, 

1971, Preliminary geologic map of the 

Livengood quadrangle: U.S. Geological 

Survey Open-File Report 71-66, scale 

1:250,000. 

Cox, D.P., and Singer, D.A., 1986, Mineral 

deposit models: U.S. Geological Survey 

Bulletin 1693, 379 p. 

Drew, L.J., Bliss, J.D., Bowen, R.W., Bridges, 

N.J, Cox, D.P., DeYoung, J.H., Jr., 

Houghton, J.C., Ludington, S., Menzie, W.D., 

Page, N.J, Root, D.H., and Singer, D. A., 

1986, Quantitative estimation of 

undiscovered mineral resources--A case study 

of U.S. Forest Service Wilderness Tracts in 

the Pacific Mountain System: Economic 

Geology, v. 81, p. 80-88. 

Ellsworth, C.E., and Parker, G.L., 1911, Placer 

m1n1ng in the Yukon-Tanana region: U.S. 

Geological Survey Bulletin 480, p. 153-172. 

Finch, W.I., and McCammon, R.B., 1987, Uranium 

resource assessment by the Geological 

Survey--Methodology and plan to update the 

National Resource Base: U.S. Geological 

Survey Circular 994, 31 p. 

Hill, T.P., and Werner, M.A., 1972, Chemical 

composition of sedimentary rocks in Alaska, 

Idaho, Oregon, and Washington: U.S. 

Geological Survey Professional Paper 771, 

319 P• 

Light, T.D., Cady, J.W., Weber, F.R., McCammon 

R.B., and Rinehart, C.D., 1987, Sources of 

placer gold in the southern part of the 

White Mountains Recreation Area, EastCentral Alaska, in Hamilton, T. D., and 

Galloway, J.P., eds., Geologic studies in 

Alaska by the U.S. Geological Survey during 

1986: U.S. Geological Survey Circular 998, 

p. 67-69. 

Reviewers: J.D. Bliss and W.J. Nokleberg 

Geologic Studies 1n Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

74 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Stratigraphy, Sedimentology, and Structure of the 

Wickersham Terrane in the Cache Mountain Area, 

East-Central Alaska 

By Thomas E. Moore and Warren j. Nokleberg 

The Wickersham terrane is a small terrane of 

continental affinity that lies between the northern 

margin of the metamorphosed Yukon-Tanana terrane 

and the southern limit of the lower grade White 

Mountains, Manley, and Livengood terranes in central 

Alaska (fig. 1). The Wickersham terrane is interpreted 

by Jones and others (1984, 1986, 1987) to have an 

unknown or "suspect" origin because of its position 

outboard, or south of a possible suture bounding the 

Manley terrane and the North American craton. 

However, Wheeler and others (1987) and Pessel and 

others (1987) interpreted the Wickersham terrane as a 

stratigraphic link between the higher grade terranes to 

the south and the less metamorphosed terranes to the 

north in central Alaska. Despite its critical position 

for tectonic reconstructions of central Alaska, little is 

known about the sedimentologic and structural 

character of the Wickersham terrane. During the 1987 

field season of the Trans-Alaska Crustal Transect 

(TACT) geologic studies project, we collected 

sedimentologic and structural data from the Cache 

Mountain area (fig. 2) in order to ascertain the 

stratigraphy and environment of deposition of the 

Wickersham terrane. Our observations suggest that, at 

least locally, the Wickersham terrane is a gently 

southward-dipping homoclinal succession of turbidites 

with a stratigraphic succession opposite from that 

previously described. 

The Wickersham terrane, originally called the 

Beaver terrane by Churkin and others (1982), was 

distinguished by Jones and others (1984} on the basis of 

its quartz-rich composition and sedimentary 

character. Geologic mapping by Chapman and others 

(1971}, Smith and Pessel (1987), and F.R. Weber (U.S. 

Geological Survey, written commum., 1987} shows that 

the terrane consists of two major units in the vicinity 

of Cache Mountain. The structurally lower unit 

consists primarily of gray, maroon, and green slate 

that contains local units of quartzose sandstone and 

granule to pebble conglomerate; thinner and less 

abundant beds of dolomite and dark micritic limestone 

are also present. The upper unit consists primarily of 

thick-bedded quartzose sandstone and granule to 

pebble conglomerate which locally is intercalated with 

sparse, thinner units of gray or green slate. Sandstone 

in both units consists dominantly of monocrystalline 

and polycrystalline quartz with minor feldspar and 

metamorphic rock fragments (Pessel and others, 

1987}. Weber and others (1985} informally called these 

units the "maroon and green slate member" and the 

"basal grit unit," respectively, of the Wickersham unit 

and considered them to be overlain by the "Takoma 

bluff member," which is not exposed in the Cache 

Mountain area. The thickness of the two lower 

members is estimated at about 3,000 m by F.R. Weber 

(written commun., 1987) and more than 7,000 m by 

Pessel and others {1987, fig. 2.8}. The contact 

between the two lower units in the study area was 

shown as conformable, but overturned, by Chapman 

and others (1971} and as a thrust fault by F.R. Weber 

(written commun., 1987) and Smith and Pessel {1987}. 

Although lacking the pervasive metamorphic 

minerals and foliation of the Yukon-Tanana terrane, 

both of the units of the Wickersham terrane display a 

weak to prominent slaty cleavage in fine-grained rocks 

and schistosity in coarser grained rocks. Metamorphic 

minerals are mainly chlorite, white mica, and quartz. 

The metamorphic fabric is weakly developed and dips 

southeastward in the northwestern part of the terrane, 

but appears to generally increase in prominence 

toward the southeast where it changes orientation to a 

gentle northward dip. The increasing strain gradient 

and general similarity of composition led Weber and 

others {1985) and Pessel and others (1987) to conclude 

that the Wickersham terrane is the less deformed and 

metamorphosed sedimentary cover for the YukonTanana terrane which lies to the south. Chapman and 

Figure 1. Map showing terranes of east-central Alaska. 

Abbreviations: RB, Ruby terrane; TZ, Tozitna terrane; BRY, 

Baldry Mountain terrane; MNK, Minook terrane; WS, 

Wickersham terrane; WHM, White Mountains terrane; LG, 

Livengood terrane; MAN, Manley terrane; MN, Minchumina 

terrane; CZ, Crazy Mountains terrane; YT, Yukon-Tanana 

terrane; Cz, Cenozoic successor basin deposits. 

East-Central Alaska 75 
others {1971), however, showed this contact as a northdipping fault which Churkin and others (1982) 

postulated to be a major structural break separating 

the two terranes. Foster and others (1987) also 

interpret this contact as a fault. The northern margin 

1/ 

Ofc 

of the Wickersham terrane is nearly everywhere 

mapped as a high-angle fault by all workers, though it 

was interpreted as a faulted unconformity by Pessel 

and others (1987), Wheeler and others (1987), and F.R. 

Weber (written commun., 1987). 

.;I 

I 

£p£sl 

Oldhamia 

£p£sl :-'34 ./' .· ./65 . . · ...... -/'30 '•/.)7 . ·: .. 

14 7° 3 o' 

v " 115 I ~\ 

";/ 70 °' y 01' 

' /45 \ 

,.,(65 3or- • .. 28 ... ''. 45 ,Y . . 0 .. ' 

. ~ ·"j-o; ~-. .. .. . . ·. ' _ ............ 1' ....... . 

·. : : 2~·_.-·.· _,.-IN~·.· 

~o(JI) • • , • • • 2 5I . · . ~ . . . 

. . '---'<l,"rJ·· :--....... .._,_ Cr . ." '/ .. ·/' ... J t -

~ 

, .,.. r / 

. : £pBg ~~((,· ~e1r ·_ / TKg ./ 

('.· 25-\·-';" \ ' \· . . . . . I / .. 

.. '• 

A. NW SE 

WHITE 

MOUNTAINS 

TERRANE 

v " " v Ofc v v v )

METERS 

WICKERSHAM TERRAN~ . :-'";''; 1500 

. . . 1000 

' . . . 500 

. £p£g· • • • • Sea Level 

EXPLANATION 

6J Granitic rocks (early Tertiary or Late Cretaceous) 

WHITE MOUNT A INS TERRANE 

~ Tolovana Limestone (Silurian) 

~ Fossil Creek Volcanics (Ordovician) 

WICKERSHAM TERRANE 

Grit unit (Early Cambrian and (or) Precambrian) 

Maroon and green slate unit (Early Cambrian 

and (or) Precambrian) 

Figure 2. Geologic map of Wickersham terrane in vicinity of Cache 

Mountain, Livengood C-1 and Circle C-6 quadrangles. Geologic 

mapping modified from F.R. Weber (U.S. Geological Survey, 

written commun., 1987) in Livengood C-1 quadrangle and Smith 

and Pessel (1987) in Circle C-6 quadrangle. Heavy symbols 

show bedding attitudes from this study; lighter symbols show 

bedding attitude data compiled from F.R. Weber (written commun., 

1987) and Smith and Pessel (1987). Contact between units €pCsl 

. . . /'-_.-<38 .' . . 

0 2 4 

KILOMETERS 

B. NW 

C. NW 

6 8 

SE 

~ .__§p£sl SE 

-----.. METERS 

1500 

1000 

500 

Sea Level 

and £pCg is interpreted as conformable although shown as a 

thrust fault by F.R. Weber (written commun., 1987) and Smith and 

Pessel (1987). G.H. Pessel (written commun., 1987) and Michael 

Churkin (unpub. field notes and oral commun., 1988) reported 

overturned bedding not shown in region east of long 147o. 

Cross sections show three differing interpretations along line of 

section shown on map; see text for details. 

76 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Because of the regional south-dipping foliation 

surfaces developed in the northwestern half of the 

terrane, Chapman and others (1971) hypothesized that 

strata of the terrane form a southwest-trending, 

northwesterly vergent, map-scale recumbent fold (fig. 

2, cross section B). This structural interpretation 

suggests that the grit unit, now structurally higher, 

was emplaced northward over the maroon and green 

slate unit. The structural model of Chapman and 

others (1971) concluded that the grit unit is older and 

occurs at a stratigraphically lower position than the 

maroon and green slate unit. 

The age of the strata of the Wickersham 

terrane is based on the occurrence of the Early 

Cambrian or possibly Late Proterozoic trace fossil 

Oldhamia (Hofmann and Cecile, 1981) near the top of 

the maroon and green slate unit at the locality shown 

on figure 2 (Foster and others, 1983). Utilizing the 

structural model and stratigraphic interpretation of 

Chapman and others (1971), most workers (for 

example, Smith and others, 1987) have considered this 

fossil locality to date strata near the top of the 

Wickersham terrane, implying that the grit unit is no 

younger than Early Cambrian and may be Late 

Proterozoic in age. 

In order to better understand the sedimentary 

history and structure of the Wickersham terrane, we 

examined this terrane in short traverses at about 20 

localities in the vicinity of Cache Mountain (fig. 2). In 

general, we found that sandstones of both the 

structurally lower maroon and green slate unit and 

structurally higher grit unit display Bouma sequences 

which we interpret as evidence of deposition by 

turbidity currents. Sedimentary structures observed 

include graded bedding, erosional bases, ripup clasts, 

A. Maroon and green slate unit 

• •• ••• 

. ~~ 

0 

-

+ 

parallel lamination, ripple cross lamination and 

possible sole markings including load casts. In many 

locations, cleavage and schistosity surfaces are 

parallel or acutely oblique to sedimentary bedding and 

tend to obscure sedimentary structures, particularly in 

the finer grained rocks. These features confirm the 

interpretation of Pessel and others (1987) and F.R. 

Weber (written commun., 1987) that the succession 

consists largely of turbidites and allows description of 

the strata by the classification system of Mutti and 

Ricci Lucchi (1978). 

The maroon and green slate unit consists mainly 

of slaty and phyllitic siltstone, shale, and sandstone, 

locally displays distinctive maroon and green 

coloration, but is generally gray. A dark-gray micritic 

limestone, about 3 m thick, and thin diabase dikes 

were observed at two localities. The sandstone-toshale ratio of the unit is low, probably on the order of 

1:100, but this is difficult to estimate because of poor 

outcrop. Locally, however, sandstone-to-shale ratios 

are as high as 2:1. These sandstone-rich intervals are 

as thick as 3 m and contain fine- to coarse-grained 

sandstone in graded beds 5 to 20 em thick. Where 

examined, these sandstone beds display abbreviated 

Bouma sequences that appear to be laterally 

continuous (facies D) although similar, but laterally 

discontinuous beds (facies E) were observed at one 

location. At another location, the sandstone intervals 

appeared to be organized into multiple 3-m-thick 

thinning- and fining-upward sequences. 

The structurally higher grit unit consists largely 

of thick packages (greater than 5 m) of sandstone and 

has an overall sandstone-to-shale ratio greater than 

10. The sandstone intervals generally are medium to 

coarse grained, but commonly include granule to fineB. Grit unit 

• • .~;~0 

·~ 0 • + \) 

• • 

• 0 

• 0 

• THIS STUDY 

0 PREVIOUS WORK 

6_ OVERTURNED BEDDING 

Figure 3. Lower hemisphere stereogram projections showing poles to bedding for rocks of maroon and green slate unit (A) and the grit 

unit (B) of the Wickersham terrane. Data from Smith and Pessel (1987), F.R. Weber (written commun., 1987), and this study. Some of the 

data reported by Smith and Pessel (1987) are now considered to be possibly overturned by G.H. Pessel (oral commun., 1988). 

East-Central Alaska 77 
pebble conglomerate. Some of these units have 

channelized basal contacts, but most do not display 

internal sedimentary structures and instead appear 

massive throughout. In one location, thin 

discontinuous siltstone laminae were observed within a 

thick sandstone package, suggesting that most of the 

sandstone-conglomerate packages consist of 

amalgamated sandstone beds (facies A and B). Finer 

grained intervals, 3 to 25 m thick, separate the 

sandstone-conglomerate packages. The finer grained 

intervals have sandstone-to-shale ratios of 3:1 to 1:1 

and consist of interbedded fine to medium-grained 

sandstone and slaty siltstone and shale. The sandstone 

beds are 10 to 100 m thick and commonly display 

complete to incomplete Bouma sequences and 

erosional bases (facies C and D). Some thin ripple 

cross laminated sandstone beds appear to be laterally 

discontinous, suggesting the presence of facies E 

turbidites within these intervals. 

The contact between the structurally lower 

maroon and green slate unit and the overlying coarser 

grained grit unit is generally easily identified and 

mapped. We examined this contact in several places, 

and found it to be generally conformable and 

gradational. North of Cache Mountain, an interval of 

facies A and B turbidites 10 to 20 m thick occurs 

within maroon and green slate and phyllite about 50 m 

below the mapped contact. This sandstone interval 

appears to thin upward toward the slate below the 

contact. Likewise, east of Willow Creek and near the 

A. METERS 

z 7000 <( 

a: 

::l 

...J 

Cii 

6000 

FOSSIL CREEK VOLCANICS 

z 

~ basalt and basaltic breccia and WHITE conglomerate at top; 

northern margin of the Wickersham terrane, part of 

the grit unit is mapped as outliers in the maroon and 

green slate unit. The sandstone units at this location 

dip moderately to the southeast and compose welldeveloped megasequences 10 m thick that thin and fine 

upward. These sandstone intervals are separated by 

apparently conformable gray, green, and maroon slaty 

intervals of somewhat greater thickness. Where 

examined, the sandstone intervals displayed sharp, 

erosional conglomeratic bases of facies A and B 

turbidites which succeeded upward into facies C, D, 

and E turbidites. Ripple cross lamination at the top of 

the sequence suggests paleotransport generally toward 

the southeast. On the basis of existing mapping and 

our observations, it appears that these sandstone units 

are laterally discontinuous over distances of 1 to 5 km 

and are encased by fine-grained strata of the maroon 

and green slate unit. 

Bedding attitude data at 26 locations where 

sedimentary structures such as graded bedding, 

erosional basal contacts, and ripple cross lamination 

allowed identification of sedimentary facing 

directions, are plotted in figure 3 along with 

comparable data reported by Smith and Pessel (1987) 

and F.R. Weber (written commun., 1987) for the 

Wickersham terrane. These data are internally 

consistent and show that strata from both units of the 

Wickersham terrane have an average strike and dip of 

about N. 55° E. and 30° SE, respectively. A few 

bedding attitudes from the Wickersham grit and 

B. METERS 

1000 

GRIT UNIT 

thick-bedded medium- to 

~ 

> argillite, thin-bedded limestone, MOUNTAINS 

coarse-grained sandstone, 

granule and pebble conglomerate, 

and gray slate and phyllite; 

characterized by facies A and B 

turbidites 0 5000 0 

a: 

0 

4000 

z 

<( 

a: 

CD 

::!; 

<( 3000 

calcschist, black chert, and 

maroon and green slate at base; TERRANE 

basal units are structurally confused 

MAROON AND GREEN 

SLATE UNIT 

inner fan to upper 

mid-fan deposits 

(,) WICKERSHAM 

TERRANE 

MAROON AND GREEN 

SLATE UNIT 

gray, maroon, and green slate 

with thin-bedded sandstone 

and rare micritic limestone 1 

characterized by facies D 2000 turbidites GRIT UNIT 

z 

<( 

a: 

CD terrane boundary --------- lower mid-fan deposits 

::!; 

<( 1000 

(,) 

lJJ 

a: 

ll. 

YUKON-TANANA 

TERRANE quartz-mica schist 

Figure 4. Schematic stratigraphic columns. A, Reconstructed 

stratigraphy for east-central Alaska preferred by Pessel and 

others (1987) and F.R. Weber (written commun., 1987) showing 

stratigraphic relationships between Yukon-Tanana, Wickersham, 

and White Mountains terranes. Diagram also shows possible 

stratigraphic position of terrane boundaries mapped by Jones 

and others (1984); B, Column summarizing our stratigraphic and 

sedimentologic interpretations in Cache Mountain area. Arrows 

pointing up and to left indicate sandstone thinning- and finingupward megasequences commonly considered indicative of midfan turbidite deposition. 

78 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
maroon and green slate units, however, appear to 

cluster about average orientations of N. 35° E. and 25° 

NW and N. 60° E. and 75° NW, respectively, but our 

field observations indicate that most of these data 

represent the short limbs of upright folds. The 

northwestward dips may be variable because of the 

contrast in thickness and competence of the bedding 

involved in the two units. Also, inspection of the maps 

of other workers suggests that some steep 

northwesterly dips are associated with the major fault 

bounding the northern margin of the Wickersham 

terrane, whereas others are located adjacent to the 

Late Cretaceous or early Tertiary granitic plutons that 

intrude the terrane. We found neither overturned 

bedding nor any bedding with dips steeper than 70°, 

although F.R. Weber (written commun., 1987) showed 

one overturned bed with a southeasterly dip of 12° 

northwest of Cache Mountain in the grit unit. In view 

of our data, we believe that the overturned facing 

direction determined in the Cache Mountain area must 

be viewed as local rather than regional in extent. 

Nearly all of the data shown in figure 3 were collected 

along the axis of the large recumbent fold shown in the 

cross section of Chapman and others (1971) (fig. 2, 

cross section B). Because such a fold would require 

steep and overturned bedding, these data appear to 

argue against a recumbent fold structural 

interpretation. 

Taken together, the presence of mostly upright 

facing directions, apparently conformable bedding 

attitudes in both units, and presence of a gradational 

contact between the maroon and green slate unit and 

the grit unit suggest that the Wickersham terrane in 

the Cache Mountain area consists of a southeastdipping homoclinal succession of turbiditic strata (fig. 

2, cross section A). Furthermore, these data indicate 

that the structurally lower maroon and green slate unit 

should be interpreted as lying conformably beneath the 

coarser grained grit unit in this area (fig. 4B). If 

representative of the enire terrane, this stratigraphic 

interpretation would conflict with that reported by 

Chapman and others (1971), Weber and others (1985), 

Smith and Pessel (1987) and Pessel and others (1987). 

Our sedimentologic and stratigraphic data suggest that 

the strata of the Wickersham terrane in the Cache 

Mountain area comprise a quartz-rich, upwardcoarsening submarine-fan complex that prograded into 

a basin on, or adjacent to, a continent during Cambrian 

time (fig. 4B). Pessel and others (1987) concluded 

independently that the Wickersham terrane east of the 

area was deposited in a submarine-fan system. 

Although the contact between the maroon and 

green slate unit and the grit unit is locally tectonized 

or faulted, and dip reversals are locally present along 

the contact, we found no evidence of a regional fault 

contact between the units as mapped by Smith and 

Pessel (1987) and F.R. Weber (written commun., 

1987). However, this contact is commonly concealed, 

and it may be permissable to interpret the contact as a 

bedding-plane thrust fault. If such a fault exists, it 

may have small displacement, assuming the 

stratigraphy proposed above. In contrast, the 

stratigraphic interpretation of Weber and others (1985) 

and Smith and Pessel (1987) would require substantial 

displacement across the hypothetical bedding plane 

fault in the Cache Mountain area. Cross section C 

(fig. 2) shows a structural model interpreting this 

contact as a large-scale duplex that is compatible with 

their stratigraphy and the bedding facing direction 

data repoted here. This model predicts the presence 

of the grit unit at depth beneath the maroon and green 

slate unit and hangingwall and footwall cutoffs and 

other features of fold-thrust belts, none of which have 

been observed by us in the Cache Mountain area. 

Additionally, this model would require a decollement 

at depth, either within the grit unit or perhaps at the 

contact between the Wickersham and Yukon-Tanana 

terranes. Although not shown by Smith and Pessel 

(1987), Michael Churkin (unpub. field notes and 

personal commun., 1988) and G.H. Pessel (written 

commun., 1988) report overturned beds and isoclinal 

folds east of the Cache Mountain area (east of long. 

147° on fig. 2). These features may be evidence for a 

higher degree of strain and a different deformational 

style in the Wickersham terrane east of our study area. 

Alternatively, the grit unit may be viewed as 

one or more depositional wedges of relatively proximal 

coarser grained clastic strata that interfinger with and 

are encased by the finer grained and relatively more 

basinal strata of the maroon and green unit. G.H. 

Pessel (written commun., 1988) reports that the 

sandstone-to-shale ratio in the grit unit east of our 

study area is substantially lower than we have found 

for that unit, suggesting that lateral as well as vertical 

facies changes exist within the terrane. Large-scale 

interfingering of the units is consistent with the 

variable stratigraphic relationships between the two 

mapped units discussed here but may not require faults 

of significant displacement within the study area. Pell 

and Simony (1987) recently described a similar 

stratigraphic interpretation for the grit and finer 

grained units of the Windermere Supergroup in British 

Columbia with which the strata of the Wickersham 

terrane are commonly correlated (for example, 

Tempelman-Kluitt, 1984; Weber and others, 1985). 

REFERENCES CITED 

Chapman, R.M., Weber, F.R., and Tabor, Bond, 

1971, Preliminary geologic map of the 

Livengood quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 483, 2 

sheets, scale 1:250,000. 

Churkin, Michael, Jr., Foster, H.L., Chapman, 

R.M., and Weber, F.R., 1982, Terranes and 

suture zones in east central Alaska: 

Journal of Geophysical Research, v. 87, p. 

3718-3730. 

Foster, H.L., Laird, Jo, Keith, T.E.C., Cushing, 

G.W., and Menzie, W.D., 1983, Preliminary 

geologic map of the Circle quadrangle, 

Alaska: U.S. Geological Survey Open-File 

Report 83-170A, scale 1:250,000. 

Foster, H.L., Keith, T.E.C., and Menzie, W.D., 

1987, Geology of east-central Alaska: U.S. 

Geological Survey Open-File Report 87-188, 

59 P• 

Hofmann, H.J. and Cecile, M.P., 1981, Occurrence 

of Oldhamia and other trace fossils in lower 

Cambrian (?) argillites, Niddery Lake map 

area, Selwyn Mountains, Yukon Territory: 

East-Central Alaska 79 
Geological Survey Canada Paper 81-lA, p. 

281-290. 

Jones, D.L., Silberling, N.J., and Coney, P.J., 

1986, Collision tectonics in the cordillera 

of western North America: Examples from 

Alaska, in Coward, M.P., and Ries, A.C., 

eds., Collision tectonics: Geological 

Society of London, Special Publication 19, 

P• 367-387. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1984, Lithotectonic terrane 

maps of the North American Cordillera, Part 

A--Lithotectonic terrane map of Alaska, 

sheet 1 of 4: U.S. Geological Survey OpenFile Report 84-523, scale 1:2,500,000. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1987, Lithotectonic 

terrance map of Alaska (West of the 41st 

Meridian): U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1874-A, 

scale 1:2,500,000. 

Mutti, Emiliani, and Ricci Lucchi, Franco, 1978, 

Turbidites of the Northern Apennines: 

Introduction to facies analysis: 

International Geology Review, v. 20, p. 125-

166. 

Pell, J., and Simony, P.S., 1987, New 

correlations of Hadrynian strata, southcentral British Columbia: Canadian Journal 

of Earth Sciences, v. 24, p. 302-313. 

Pessel, G.H., Reifenstuhl, R.R., and Albanese, 

M.D., 1987, Regional geology, in Smith, 

T.E., Pessel, G.H., and Wiltse, M:A"., eds., 

Mineral assessment of the Lime Peak-Mt 

Prindle area, Alaska: Fairbanks, Alaska 

Department of Natural Resources, Division of 

Geological and Geophysical Surveys, p. 2-1 

to 2-26. 

Smith, T .E., and Pessel, G.H., 1987, Bedrock 

geologic map of the Lime Peak-Mt. Prindle 

area, east-central Alaska: Alaska Divis ion 

of Geological and Geophysical Surveys, 

Report of Investigations 87-4, plate 2-1A, 

scale 1:63,360. 

Tempelman-Kluitt, Dirk, 1984, Counterparts of 

Alaska's terranes in Yukon, in Symposium of 

Cordilleran geology and mineral exploration; 

Status and future trends: Vancouver, 

Geological Association of Caraca, p. 41-44. 

Weber, F.R., Smith, T.E., Hall, M.H., and 

Forbes, R.B., 1985, Geologic guide to the 

Fairbanks-Livengood area, east-central 

Alaska: Anchorage, Alaska Geological 

Society, 44 p. 

Wheeler, K.L., Forbes, R.B., Weber, F.R., and 

Rinehart, C.D., 1987, Lithostratigraphy, 

petrology, and geochemistry of the 

Ordovician Fossil Creek Volcanics, White 

Mountains, east-central Alaska, in Hamilton, 

T.D., and Galloway, J.P., eds:: Geologic 

studies in Alaska by the U.S. Geological 

Survey during 1986: U.S. Geological Survey 

Circular 998, p. 70-73. 

Reviewers: H.L. Foster and R.M. Chapman 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

80 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Gold Mineralization by Metamorphic Fluids in the 

Chandalar District, Southern Brooks RangeFluid Inclusion and Oxygen-Isotopic Evidence 

By Scott C. Rose, William J. Pickthorn, and Richard j. Goldfarb 

The Chandalar mining district is located 320 km 

north of Fairbanks in the southern Brooks Range (fig. 

1). The four gold-quartz lodes examined in this study 

(Mikado, Summit, Envelope, Little Squaw) have seen 

limited production, but placers in drainages 

surrounding the lode deposits have produced more than 

40,000 oz (1,244 kg) of gold (Heiner and Wolff, 1968). 

Bedrock in the district consists of pelitic schist of 

Devonian age that is locally intruded by Devonian (?) 

dikes and sills of mafic to intermediate composition 

(Chipp, 1970). These rocks were subjected to two 

periods of upper greenschist-facies metamorphism 

during the Cretaceous; northeast-vergent thrust 

faulting accompanied the second metamorphic event 

(Chipp, 1970; Dillon, 1982). 

The gold-quartz lodes are localized in 

subparallel high-angle shear zones that trend N. 60° 

W. These features cut across metamorphic fabric and 

were clearly emplaced within the metasediments after 

peak metamorphism. Veins consist of both high-grade 

ribbon quartz, and low-grade to barren milky quartz. 

Vein mineralogy is consistent within all lodes. Quartz 

is the dominant gangue mineral with minor carbonate; 

the most abundant sulfide minerals are arsenopyrite, 

galena, stibnite, pyrite, pyrrhotite, and sphalerite. 

Gold replaces galena, sphalerite, and arsenopyrite and 

also occurs as isolated grains in quartz. 

We conducted fluid inclusion and oxygen-isotope 

studies to determine the physical and chemical nature 

of the fluids responsible for ore genesis. Fluid 

inclusion data can provide important constraints on the 

pressure, temperature, and composition of ore fluids, 

and oxygen-isotope data can help identify the source 

and exchange history of these ore fluids. 

A previous fluid inclusion study of some of 

these deposits (Ashworth, 1983) identified variable 

gas-to-liquid ratios in fluid inclusions and concluded 

that boiling of ore fluids led to gold deposition. Our 

study has also identified variable gas-to-liquid ratios in 

similar samples. We interpret these as secondary 

inclusions formed by necking down (Roedder, 1984) of 

former primary inclusions. We see no evidence for 

trapping of immiscible fluids or boiling. Ore-stage 

quartz is often a banded, ribbon-type quartz that 

forms by repeated episodes of dilation, quartz 

precipitation, and subsequent shearing. This repeated 

shearing results in numerous zones of necked, 

secondary inclusions. The common spatial association 

between gold grains and ribbons of wallrock suggests 

that chemical reactions between the ore fluids and the 

wallrocks may have played a role in destabilizing goldbisulfide complexes. 

Primary and (or) pseudosecondary fluid 

inclusions found in unstrained quartz from the four 

lode deposits were chosen for microthermometric 

study (fig. 2). They range from less than 5 

micrometers to greater than 70 micrometers in 

maximum dimension. Only one type of primary fluid 

inclusion has been identified in both the high-grade 

ribbon quartz and the low-grade milky quartz. These 

fluid inclusions generally contain three phases at room 

temperature; C02 vapor, C02 liquid, and water. Some 

inclusions have only two phases at room temperature, 

C02 liquid, and water liquid, but generate a C02 vapor 

phase upon cooling a few degrees. The inclusions have 

consistent co2:H2.0 volume ratios of 0.30 to 0.35. 

Similar relationsl:hps were observed in a limited 

number of fluid inclusions in sphalerite from the 

Mikado mine. The small range in clathrate melting 

temperatures and C02 homogenization temperatures 

along with the consistent gas-to-liquid ratios for all 

the lodes indicate trapping of a one-phase fluid under 

similar pressures and temperatures. There is no 

evidence of fluid immiscibility or boiling in these 

samples. 

148 00 

67" 35'.------------,---.,..-----------,--------, 

67" 25' 

Figure 1. Location of the lode-gold mines examined in the Chandalar district. 

East-Central Alaska 81 
Melting of solid C02 ranges from the triple 

point for pure co2 of -56.6 °C to -58.2 °C (fig. 2A). 

Depression of the melting temperature below -56.6 °C 

is evidence of minor amounts of CH4 and (or) N2 in the 

gas phase (Roedder, 1984). Clathrate melting 

temperatures ranged from 8.4 °C to 10.8 °C (fig. 2B) 

for all studied inclusions. The melting temperatures 

above 10.0 °C indicate that a few mole percent CH4 definitely occurs in some inclusions. Depression of the 

temperature below 10.0 °C results from the presence 

of salt and perhaps minor N2 within the fluids. 

HomOJ.enization of C02 occurs between 22.8 °C and 

27.6 C (fig. 2C), cor5esponding to densities between 

0. 79 and 0. 76 g/cm , respectively. Final homogenization occurred at temperatures between 265 °C 

and 300 °C (fig. 2D), representing minimum estimated 

temperatures of mineralization. 

Using relationships from Swanenburg (1980) and 

Burruss {1981), the bulk density and composition of the 

fluid inclusions can be estimated. Inclusions generally 

contain approximately 86 to 88 mole percent H20, 12 

to 14 mole percent C02, 0.6-0. 7 mole percent CH , 

<3-3.5 mole percent N2, and <3.0 equivalent weigfit 

percent NaCl. These compositions were used to select 

>--

u 

z 

w 

::J 

Cl 

w 

IT 

LL 

>-

u 

z 

w 

::J 

Cl 

w 

a: 

LL 

CO? Mt_l T TEMPEFiA T LJRE 

241 

22~ - LITTLE :"QlJAW 

20 ~ SUMMIT 

18 ~'Ll ENVELOE 

16 ~ MIKADO 

14 

12 

10 

B 

6 

4 

2 

0 -L-,-----,-.- -,~'!"L-""'i""--

-59 -58 6 -58.2 -57.8 -57.4 -57 -56.6 -56.2 

A TEMPERATURE (° C) 

C02 HOMOGENIZATION TEMPERATURE 

20 

18 

16 

14 

12 

10 

B 

- LITTLE SGUAW 

~ SUMMIT 

IZ22l ENVELOE 

~ MIKADO 

22 22. B 23. 6 24 . 4 25. 2 26 26. B 27. 6 

c TEMPERATURE (° C) 

an appropriate solvus for the fluids, and to select 

isochores which help constrain the pressuretemperature environment of ore deposition. A 

minimum trapping pressure of 75 MPa (750 bars) is 

defined by the final homogenization temperature and 

the experimentally determined solvus for a 12 to 14 

mole percent C02 fluid (Swanenberg, 1980). Maximum 

trapping pressures and temperatures of 56 GPa (5.6 

kbar) and 470 °C were determined by intersecting the 

fluid inclusion isochores (Brown and Lamb, 1986) with 

the albite + epidote = oligoclase line. This reaction 

boundary defines the upper limit of regional 

metamorphism in the vicinity of the Chandalar district 

(Ashworth, 1983). The true trapping pressure must lie 

on the isochores somewhere between the C02-H20 

solvus and the reaction line. 

Seven samples were analyzed in our preliminary 

oxygen-isotope study (table 1): two high-grade ribbon 

quartz samples and four barren milky quartz samples 

from the lode deposits; and one concordant 

metamorphic segregation quartz sample taken 

approximately 300 m from any discordant gold-bearing 

vein. The o18o values for high-grade and barren 

quartz from the gold lodes are relatively constant, 

>-

u 

z 

w 

::J 

Cl 

w 

a: 

LL 

>-

u 

z 

w 

::J 

Cl 

w 

a: 

LL 

CLATHRATE MELT TEMPERATURE 

28 ,- - -~-

26 - LITTLE SQUAW 

~ SUMMIT 24 

22 

20 ~ ENVELOE 

18 ~ MIKADO 

16 

14 

12 

10 

8 

6 

4 

2 

0 

__ ij ~-

B 8.4 8.8 9.2 9 6 10 10.4 10.8 

B TEMPERATURE (° C) 

FINAL HOMOGENIZATION TEMPERATURE 45 - . - -- . -- --

[

- LITTLE SGUAW 

40 ~ SUMMIT 

35 I22ZI ENVELDE 

J ~ MIKADO 

30 I 

25 

20 

15 

10 

5 

0~-,-~~~~~~~~~~~~~~-,-~~ 

260 268 276 284 292 300 

D TEMPERATURE (° C) 

Figure 2. Histograms of microthermometric data from primary fluid inclusions. 

82 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Oxygen isotope data from quartz veins 

[Fluid values calculated using temperature of 280 °C and quartz-water fractionation equation of Clayton and others (1972)] 

Sample Description 

Little Squaw High-grade ribbon qtz 

Mikado High-grade ribbon qtz 

Mikado Barren milky qtz 

Enveloe Barren milky qtz 

Summit Barren milky qtz 

Little Squaw Barren milky qtz 

Summit Segregation qtz 

ranging from +15.4 per mil to +16.1 per mil. The 

estimated o 180 values of the vein-forming fluids, 

ranging from +7 .2 per mil to +7 .9 per mil, were 

calculated using an average fluid inclusion 

homogenization temperature of 280 °C and the quartzwater fractionation equation of Clayton and others 

(1972). The isotopically heavy values are consistent 

with those for other mesothermal gold deposits within 

the northern North American Cordillera (Gamble and 

others, 1985; Nesbitt and others, 1986; Goldfarb and 

others, 1987) and are significantly heavier than in most 

epithermal gold systems (Ohmoto, 1986). The actual 

source for the fluids is still uncertain. However, if the 

ore-forming fluids were deeply circulating meteoric 

waters with required initial oD values at least as light 

as -150 per mil, they would require an oxygen shift of 

more than 25 per mil. We doubt that such a large shift 

is likely with the relatively high water-to-rock ratio 

required to produce the thick, high-grade veins. Using 

relationships from Field and Fifarek (1985), water-torock ratios of less than 0.1 would be required at 300 

°C if meteoric fluids were invoked for ore genesis at 

the Little Squaw lode prospect. Thus we believe that 

the isotopically heavy ore fluids are more likely 

derived from deep crustal sources. 

The isotope compositions and fluid inclusion 

compositions are similar to C-0-H fluids commonly 

observed in medium-grade metamorphic rocks 

(Crawford and Hollister, 1986). Such fluids are 

inferred to have been released during devolatilization 

reactions, and reflect compositions buffered by the 

surrounding mineral assemblages. Gold is believed to 

have been mobilized from the pelitic metasediments 

by these metamorphic fluids. 

Wood and Walther (1986) documented fluid-torock ratios of 6:1 in greenschist-to amphibolite-grade 

metamorphosed pelitic rocks. In the Chandalar area, 

thrust faults may have channelized large volumes of 

the fluids released during Cretaceous metamorphism, 

resulting in even higher concentrations of fluids. We 

suggest a hydraulic fracturing model similar to the 

model proposed by Ashworth (1983) for the formation 

of the gold lodes of the Chandalar district. Rapid 

uplift due to tectonic unloading results in a decrease in 

lithostatic pressure. When the fluid pressure exceeds 

confining pressure, hydraulic fracturing and the 

release of metamorphic fluids will occur. Decreasing 

pressure-temperature and changing redox conditions, 

o18o quartz olBo fluid 

(permil) (permil) 

15.6 7.4 

15.6 7.4 

15.9 7.7 

16.1 7.9 

16.1 7.9 

15.4 7.2 

18.4 

in part due to wallrock reactions, are the most likely 

parameters controlling deposition of gold by the 

hydrothermal fluids. 

REFERENCES CITED 

Ashworth, K.K., 1983, Genesis of gold deposits 

of the Little Squaw Mines, Chandalar mining 

district, Alaska: Bellingham, Western 

Washington University, M.S. thesis, 98 p. 

Brown, P.E., and Lamb, W.M., 1986, Mixing of 

H2o-co2 in fluid inclusions; Geobarometry 

and Archean gold deposits: Geochimica et 

Cosmochimica Acta, v. 50, p. 847-852. 

Burruss, R.C., 1981, Analysis of phase 

equilibria in C-0-H-S fluid inclusions, in 

Hollister, L.S., and Crawford, M.L., eds~ 

Short Course in fluid inclusions: 

Applications to petrology: Mineralogical 

Association of Canada, Short Course 

Handbook, v. 6, p. 39-74. 

Ch.ipp, E.R., 1970, Geology and geochemistry of 

the Chandalar area, Brooks Range, Alaska: 

Alaska Division of Mines and Geology Report 

42, 39 p. 

Clayton, R.N., O'Neil, J.R., and Mayeda, T.J., 

1972, Oxygen isotope exchange between quartz 

and water: Journal of Geophysical Research, 

v. 77, no. 17, p. 3057-3067. 

Crawford, M.L., and Hollister, L.S., 1986, 

Metamorphic fluids: The evidence from fluid 

inclusions, in Walther, J.V., and Wood, 

B. J., eds., Fluid-rock interact ions during 

metamorphism, advances in physical 

geochemistry, v. 5: New York, SpringerVerlag, p. 1-35. 

Dillon, J.T., 1982, Source of lode and placer 

gold deposits of the Chandalar and Upper 

Koyukuk districts, Alaska: Alaska Divis ion 

of Geological and Geophysical Surveys, 

Alaska Open-file Report 158, 22 p. 

Field, C. W., and Fi rarek, R.M., 1985, Light 

stable-isotope systematics in the epithermal 

environment, in Berger, B. R., and Bethke, 

P.M., eds., Geology and geochemistry of 

epithermal systems: Society of Economic 

Geologists, Reviews in Economic Geology, v. 

2, P• 99-128. 

East-Central Alaska 83 
Gamble, B.M., Ashley, R.P., and Pickthorn, W.J., 

1985, Preliminary study of lode gold 

deposits, Seward Peninsula, in BartshWinkler, Susan, ed., The United States 

Geological Survey 1n Alaska: 

Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 27-29. 

Goldfarb, R.J., Nelson, S.W., Berg, H. C., and 

Light, T.Dq 1987, Distribution of mineral 

deposits in the Pacific Border Ranges and 

Coast Mountains of the Alaskan Cordillera, 

in Elliot, I., and Smee, B.W., eds., 

Geoexpo/87, Exploration in the North 

American Cordillera: Association of 

Exploration Geochemists, p. 19-41. 

Heiner, L.E., and Wolff, E.N., 1968, Mineral 

resources of northern Alaska: Mineral 

Industry Research Laboratory, University of 

Alaska, Report 16, 306 p. 

Nesbitt, B.E., Murowchick, J.B., and 

Muehlenbachs, K., 1986, Dual origins of lode 

gold deposits in the Canadian Cordillera: 

Geology, v. 14, p. 506-509. 

Ohmoto, Hiroshi, 1986, Stable isotope 

geochemistry of ore deposits, in Valley, 

J.W., Taylor, H.P., and O'Neal, ~R., eds., 

Stable isotopes in high temperature 

geological processes: Mineralogical Society 

of America, Reviews in Mineralogy, v. 16, p. 

491-556. 

Roedder, Edwin, 1984, Fluid inclusions, in 

Ribbe, P.H., ed., Mineralogical Society of 

America: Reviews in Mineralogy, v. 12, 644 

P• 

Swanenberg, H.E.C., 1980, Fluid inclusions 1n 

high-grade metamorphic rocks from S. W. 

Norway: Geologica Ultraiectina, University 

of Utrecht, Netherlands, no. 25, 147 p. 

Wood, B.J., and Walther, J.V., 1986, Fluid flow 

during metamorphism and its implications for 

fluid-rock ratios, in Walther, J.V., and 

Wood, B.J., eds., Fluid-rock interactions 

during metamorphism, advances in physical 

geochemistry, v. 5: New York, SpringerVerlag, p. 89-108. 

Reviewers: Albert Hofstra and John Gray 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

84 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
WEST-CENTRAL ALASKA 

Angayucham terrane in Jade Mountains. Mafic-ultramafic thrust panel (high ridge) resting in thrust contact on 

phyllite-metagraywacke thrust panel, low area in foreground and middle distance. See article by Murphy and 

Patton. Photograph by W.W. Patton, Jr. 
Factor Analysis of the NURE Stream-Sediment 

and Lake-Sediment Geochemical Data from 

the lditarod Quadrangle 

By John E. Gray, Sarah C. Smith, and Richard J. Goldfarb 

The U. S. Department of Energy conducted a 

reconnaissance geochemical study of the Iditarod 

quadrangle, that was completed in 1981 and was part 

of the National Uranium Resource Evaluation (NURE) 

program. During the study, 888 stream-sediment and 

505 lake-sediment samples were collected to assess 

the uranium resource potential of the quadrangle. 

Composite stream-sediment samples were collected 

from small first-order streams. These samples were as 

evenly distributed throughout the quadrangle as 

pos~ible, av~raging approximately one sample per 23 

km (9 mi ). However, in swampy areas streamsediment sampling was usually not possible and lakesediment samples were collected instead. All samples 

were analyzed at the Los Alamos National Laboratory 

by various methods including X-ray fluorescence, 

instrumental neutron-activation, arc-source emission 

spectrography, and delayed-neutron counting (NURE, 

1983). The U.S. Geological Survey is currently in the 

process of evaluating the mineral resource potential of 

the Iditarod quadrangle as part of an AMRAP (Alaskan 

Resource Mineral Appraisal Program) study. The 

purpose of this paper is to use the NURE data to 

identify areas of potential mineralization in the this 

quadrangle. 

R-mode factor analysis was used to identify the 

major geochemical associations in the stream and 

lake-sediment data sets. This technique groups 

elements into "factors". Different types of mineral 

deposits and rock lithologies have different 

geochemical signatures that can be identified with this 

method. A six-factor model was selected to account 

for the stream-sediment data (table 1). 

The first three stream-sediment factors are 

related to bedrock geochemistry in the quadrangle. 

Factor 1 contains high loadings for Ce, Eu, Lu, Sm, Th, 

U, Zr, Hf, and Na. Samples with high scores onto this 

factor (fig. 1) correlate with the distribution of 

intermediate to felsic igneous rocks including 

monzonites in the Beaver Mountains (Bundtzen and 

Laird, 1982) and felsic dikes in the Crooked Creek area 

(Miller and Bundtzen, 1987). Factor 2, which contains 

high loadings for Cr, Co, V, Sc, Ni, and Mg, represents 

a mafic rock association. Samples with the highest 

scores for factor 2 are found in the north-central part 

of the quadrangle near resistant ridges that are 

underlain by mafic volcanic rocks (fig. 1). A 

correlation between Pb, Cs, and Cl defines factor 3. 

This association is most likely a reflection of 

partitioning of these elements into feldspars and micas 

(and perhaps also apatite in the case of Cl) in more 

alkalic igneous rocks. Samples with the highest factor 

3 scores cluster in watersheds underlain by quartz 

monzonite and syenite. 

Factor 4 includes high positive loadings for Al, 

Ba, Ca, Dy, K, and Ti. This factor is interpreted to be 

representative of refractory minerals and organic and 

clay-rich sediments retained in marshy lowland areas. 

Such lowands are prevalent in the western part of the 

quadrangle. 

Factor 5 has high positive loadings for Fe, Mn, 

and As. This factor is thought to delineate areas with 

high geochemical favorability for epithermal preciousmetal occurrences. Samples with the highest scores 

for this factor occur near areas of known preciousmetal lode or placer activity (such as the Moore, 

Ganes, and Crooked Creek mining areas). In addition, 

samples with high scores for this factor are also found 

in previously unrecognized locations, as indicated on 

figure 1. In some cases, these samples are spatially 

related to intermediate to felsic igneous rocks, such as 

near monzonites in the Flat area and felsic dikes in the 

Crooked Creek area. Although Sb and W were 

eliminated from the factor analysis because most 

samples were below the detection limit for these 

elements, samples with high factor 5 scores often show 

anomalous concentrations of one or both of these 

elements. This is especially true of Sb in the Crooked 

Creek area and W and Sb in the Flat and Moore Creek 

areas. Only one anomalous silver value is reported in 

the NURE data, and it occurs in a stream sediment 

sample in Ganes Creek in the eastern Beaver 

Mountains. There are no gold values above the 

detection limit in the NURE stream-sediment data 

set. Therefore, although there are numerous areas of 

placer activity in the quadrangle, the association of 

gold with factor 5 is poorly documented. 

High positive loadings for Cu, and to a lesser 

degree Cs and Ni, characterize factor 6. This factor 

association is interpreted to be representative of 

copper-rich base-metal mineralization. Samples with 

the highest scores onto factor 6 often correlate with 

igneous rocks of intermediate to felsic composition, 

especially in the Beaver Mountains. Bundtzen and 

Laird (1982) identified several localities of copper 

mineralization in the Beaver Mountains, most of which 

had associated anomalous Ag, and less commonly 

anomalous Pb, As, Sb, Zn, and Sn. Other areas with 

high scores onto this factor are shown on figure 1. 

The geochemical results from lake sediments 

collected during the NURE project were also examined 

using R-mode factor analysis. A five-factor model 

86 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Factor loadings for the stream sediments 

[Total variance explained by the 6-factor model equals 72 percent. Loadings less than 0.30 have been omitted) 

Element 1 2 

Al 

As 

Ba 

Ca 

Ce 0.82 

Cl 

Co 0.75 

Cr .89 

Cs 

Cu 

Dy .45 

Eu .70 

Fe .33 

Hf .82 

K .30 .32 

La .48 

Lu .67 

Mg .83 

Mn .45 

Na .68 .31 

Ni .78 

Pb 

Sc .50 .62 

Sm .71 

Th .82 

Ti .37 

u .59 .36 

v .44 .62 

Zr .74 

Percent of 

total variance 

explained by 

factor 39 12 

was used for evaluating these data (table 2). However, 

the relatively poor proximity of the lake-sediment 

samples to well-exposed bedrock in the quadrangle 

makes interpretation of these factor analysis results 

difficult. 

Factor 1 is thought to be related to high 

organics and clays in the lake sediments and is 

therefore analogous to factor 4 for the stream 

sediments. Samples with high scores for this factor 

are most prevalent in the western part of the Iditarod 

quadrangle where there are abundant marshy lowlands 

(fig. 2). 

Factor 2 is similar to factor 5 in the stream 

sediments and may be a precious-metal association. 

Only one anomalous gold value occurs in the NURE 

lake-sediment data. This sample is located just west 

of Swinging Dome in the western part of the 

quadrangle (fig 2). The bedrock geology is poorly 

exposed in this area, but appears to be predominantly 

intermediate to felsic volcanic rocks (Miller and 

Bundtzen, 1987). If there is a close association of gold 

Factors 

3 4 5 6 

0.87 

0.30 0.72 

.80 

.60 

.37 

.63 

.38 

.56 .32 0.37 

.82 

.76 

.77 

.69 

.45 

.63 

.44 

.32 

.55 

.44 

.35 

.76 

.32 .43 

7 

.41 

.40 

5 5 4 

mineralization with these volcanic rocks, it is not well 

understood at this time. 

Lake-sediment factor 3 is similar to the 

intermediate to felsic rock factor (factor 1) for the 

stream sediments. It is difficult to obtain any useful 

information from this factor, because most of these 

lakes are spatially removed from bedrock exposures. 

Factor 4 for the lake sediments is a base-metal 

association and is similar to factor 6 for the stream 

sediments. As with the stream sediment factor 6, 

samples with the highest scores for this factor occur in 

lakes in the Beaver Mountains where base metal 

mineralization has been recognized. 

Factor 5 for the lake sediments is analogous to 

the mafic rock association that characterizes factor 2 

in the stream sediments. The distribution for this 

factor is also similar to that of stream sediment factor 

2 in the north-central part of the quadrangle. 

Factor analysis of the geochemical results from 

the NURE project stream and lake sediments does 

appear to be useful for targeting potential areas of 

West-Central Alaska 87 
Factor 5 (precious-metal factor) 

'llflllllllll' Factor 6 (base-metal factor) 0 5 10 15 20 KILOMETERS 

Figure 1. lditarod quadrangle showing distribution of stream-sediment factors (1-6). Stipple and line patterns are for factors 5 and 6 

as indicated. 

mineralization in the Iditarod quadrangle. A basemetal and a precious-metal association have been 

identified in both data sets. Base-metal associations 

are commonly correlative with intrusive rocks of 

intermediate composition and are somewhat analogous 

to porphyry copper systems. The precious-metal 

factors appear to be related to epithermal deposits 

that are, in some cases, proximal to known igneous 

activity. However, rare anomalous gold and other 

pathfinder elements makes interpretations of 

mineralization factors somewhat difficult. The lake 

sediments are not evenly distributed throughout the 

quadrangle and are not as useful as the stream 

sediments for delineating areas of potential 

mineralization. 

REFERENCES CITED 

Bundtzen, T.K., and Laird, G.M., 1982, Geologic 

map of the Iditarod D-2 and eastern D-3 

quadrangles, Alaska: Alaska Division of 

Geological and Geophysical Surveys, Geologic 

Report 72, 1 sheet, scale 1:63,360. 

Miller, M.L., and Bundtzen, T.K., 1987, Geology 

and mineral resources of the Idi tarod 

quadrangle, west-central Alaska, in Sachs, 

J.S., ed., U.S.G.S. research on-mineral 

resources 1987--programs and abstracts: 

U.S. Geological Survey Circular 995, p. 46-

47. 

National Uranium Resource Evaluation Project 

(NURE), 1983, The geochemical atlas of 

Alaska: Los Alamos National Laboratory 

publication GJBX-32 (83). 

Reviewers: D.E. Detra and S.C. Rose 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

88 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
. ·.·.··· Factor 2 {precious- metal factor) 

·illllllllll! Factor 4 {base-metal factor) 0 5 10 15 20 KILOMETERS 

Figure 2. lditarod quadrangle showing distribution of lake-sediment factors (1-5). Stipple and line patterns are for factors 2 and 4 as 

indicated. 

West-Central Alaska 89 
Table 2. Factor loadings for lake sediments 

[Total variance explained by the 5-factor model equals 77 percent. Loadings less than 0.30 have been omitted] 

Factors 

Element 1 2 3 4 5 

Al 0.85 

As 0.87 

Ba .83 0.34 

Ca .74 

Ce .64 0.53 .45 

Cl -.81 

Co .41 .39 .59 

Cr .40 .39 .68 

Cs .40 .30 0.62 

Cu .53 

Dy .88 

Eu .55 .60 

Fe .50 .50 .31 .43 

Hf .54 .64 .36 

K .75 .31 

Lu .31 .74 

Mg .45 .65 

Mn .56 .62 

Na .80 .37 

Ni .37 .66 

Pb .74 

Sc .69 .36 .42 

Srn .75 

Th .58 .55 .44 

Ti .81 .36 

u .69 .34 

v .51 .57 

Zr .73 .34 .35 

Percent of 

total 

variance 

explained 

by factor 56 8 5 4 4 

90 Geologie Studies in Alaska by the U.S. Geologieal Survey during 1987 
Glacial Geologic History of the Salmon Lake Area, 

Seward Peninsula 

By Darrell S. Kaufman, David M. Hopkins, and Parker E. Calkin 

In the Salmon Lake area of southwestern 

Seward Peninsula (fig. 1), glacial deposits formed by 

four ice advances of Pleistocene age are clearly 

exhibited; they lie in close proximity to one another 

and are accessible by unpaved road from Nome. 

Recent refinements in the area's glacial chronology 

(Kaufman and Hopkins, 1986; Calkin and others, 1987) 

are combined in this paper with our detailed field 

mapping during 1983-87, our quantitative relative-age 

data on moraines, and a significant new radiometric 

age. These data provide a new perspective on an area 

that has been described in reconnaissance studies since 

the turn of the century (Brooks, 1901; Hopkins, 1953). 

EXPLANATION 

The Salmon Lake area encompasses the rugged, 

ice-sculptured peaks and valleys of the eastern 

Kigluaik Mountains and extends to the rolling uplands 

beyond. It includes two major valley systems, 

occupied by Grand Central River and Crater Creek, 

that preserve an extensive glacial record. This glacial 

record can be correlated with the youngest four 

Pleistocene events of the regional glacial sequence 

described by Kaufman and Hopkins (1986)--the Nome 

River, Stewart River, Salmon Lake, and Mount Osborn 

glacial advances. During the oldest glacial episodes, 

the most recent of which is the Nome River glaciation, 

ice carved broad U-shaped troughs and advanced south 

[] Alluv1um 0 

§ Dri~ of Stewart River glac1al Interval ~ Lake wave-cut scarp 

~~ Rock-glacier deposits 

~ Till of Mount Osborn glaciation - Show1ng 

,. loop morame of late Mount Osborn age 

[] Dn~ of Salmon Lake glaciation 

MTll Dnft of .Nome .R1ver glac1at1on . 

~ X 1nd1cates Isolated errat1cs ~ Mountain front 

-Outwash ~ Windy Creek rad1ocarbon s1te 

Figure 1. Generalized surficial geologic map of principal study area, Kigluaik Mountains. Center insert map 

shows inferred extent of Nome River age glaciers. 

West-Central Alaska 91 
more than 60 km to points beyond the present-day 

northern coast of the Bering Sea. Subsequent glacier 

advances affected an area nearly an order of 

magnitude less extensive. During the two earliest of 

these advances, the Stewart River and the Salmon 

Lake, glaciers flowed short distances beyond the 

mountain front. The most recent major ice advance, 

the Mount Osborn, was restricted to the highest 

tributary valleys. 

Drift of Nome River age, believed to be more 

than 0.8 m.y. old (Kaufman and Hopkins, 1986), is 

recognized in only a few small tracts in the Salmon 

Lake area. The nearly featureless drift (table 1) is 

mantled by a thick blanket of frozen, wind-blown silt 

that supports a continuous cover of cottongrass 

(Eriophorum vaginatum) tussocks. Erratic boulders 

found scattered on frost-rived bedrock and in the beds 

of river channels record glacial activity considerably 

beyond the drift limit. South of Pilgrim River, 

erratics dating to the Nome River glaciation and 

probably older glacial episodes have been mapped up to 

an altitude of 290 m. 

Kaufman and Hopkins (1986) named the Stewart 

River glacial interval for moraine complexes, thought 

to be older than the last interglacial interval, situated 

5 to 10 km beyond the limits of younger Salmon Lake 

drift deposits on the south side of the Kigluaik 

Mountains. Ice occupying the Grand Central River 

valley flowed beyond the mountain front forming a 

large, tri-lobed piedmont glacier (fig. 1). On the west, 

the glacier topped a low divide at the Nome River 

valley, merged with ice from the Sinuk River valley, 

and flowed south to terminate at David Creek, leaving 

a conspicuous moraine and adjacent outwash plain. A 

second tongue flowed south a short distance into 

Eldorado River valley, depositing a low moraine that 

forms the drainage divide at the head of that valley. 

The east margin of the former ice tongue is marked by 

a sharp-crested lateral moraine at an altitude of 245 m 

in the valley of Jasper Creek. A train of erratic 

boulders can be traced up the western wall of Eldorado 

River valley to a similar altitude. The eastern lobe of 

ice from Grand Central River valley coalesced with 

ice flowing from Crater Creek valley, then moved 

northeastward down the valley of the Pilgrim River to 

form a multiple-crested moraine near the lower course 

of Homestake Creek. Although more complex than 

most, the morphology is typical of moraines of Stewart 

River age as summarized in table 1. The generally 

smooth terrain is punctuated by solitary, gravelly 

ridges and hillocks that commonly are armored by 

pebbly gravel. 

The Salmon Lake glaciation is represented by 

extensive lobate moraines deposited by glaciers that 

advanced to within several kilometers of the former 

Stewart River glacial limit. In several places, glaciers 

failed to top drainage divides traversed by older ice. 

Hopkins' (1953) type locality for drift of Salmon Lake 

age is the morainal complex at the east end of Salmon 

Lake. This moraine delineates the terminus of a broad 

valley glacier that flowed from Grand Central River 

valley but did not merge with ice originating from the 

valley of Crater Creek. 

Textural and morphologic differences 

distinguish the moraines of Salmon Lake age generated 

by the two independent glaciers in the valleys of Grand 

Central River and Crater Creek. The Crater Creek 

moraine is exceptionally bouldery and displays 

abundant primary microrelief. In contrast, the 

moraine east of Salmon Lake is largely composed of 

sandy gravel and is devoid of microrelief features. 

These disparities can partly be attributed to 

differences in transport distance and composition of 

valley-filling sediments. The Crater Creek moraine 

was deposited by a glacier nearly half the length of the 

glacier that occupied Grand Central River valley. 

Furthermore, the walls of the narrow Crater Creek 

valley were probably more severely undercut, thus 

delivering abundant rockfall debris to the glacier. The 

Grand Central glacier, on the other hand, flowed 

through a broad valley underlain by fine-grained 

alluvial and possibly lacustrine sediments, and 

incorporated these into its end moraine. 

During the Salmon Lake glaciation, ice from 

Crater Creek valley advanced to block the Pilgrim 

River valley and impounded a shallow proglacial lake 

Table 1. Select morphologic data derived from topographic profiles of moraines in the Kigluaik Mountains 

[Group mean values ±1 standard deviation are shown; see Kaufman (1987) for a complete discussion of methodology] 

Glacial age 

Morphologic 

parameter 1 Mount Osborn Salmon Lake Stewart River Nome River 

Axial crest mean slope (deg) 6.4 ± 1.7 5.0 ± 1.6 3.2 ± 1.0 0.4 ± 0.0 

Axial crest slope standard 6.4 ± 2.6 5.6 ± 1.3 4.5 ± 1.6 0.5 ± 0.0 

deviation (deg) 

Cross section mean slope (deg) 9.8 ± 1.1 8.6 ± 2.3 4.7 ± 1.2 1.7 ± 0.2 

Crest width (m) 19.5 ± 5.5 25.4 ± 12.4 39.3 ± 12.0 410.0 ± 5.0 

Number of moraines studied 6 10 6 2 

l Mean and standard deviation of slope angles were calculated by slope-frequency analysis. 

92 Geologie Studies in Alaska by the U.S. Geological Survey during 1987 
at an altitude of about 150-m. Poorly defined 

shoreline scarps of this lake extend around the western 

side of the Crater Creek moraine and are notched into 

both sides of the Salmon Lake moraine (fig. 1). A 

delta exposed in the banks of an artificially diverted 

channel of Nugget Creek at the west end of Salmon 

Lake is also graded to the 150-m shoreline. A section 

measured on the south bank of the channel (fig. 2) 

revealed more than 1.5 m of deltaic foreset gravel 

overlain by about 1 m of horizontally bedded gravel 

and a thin (0.3 m) layer of eolian sand from which a set 

of ice-wedge pseudomorphs originates. The eolian 

sand is in turn overlain by about 2 m of cobbly gravel, 

possibly outwash of Mount Osborn age, and about 0.8 m 

of eolian silty sand containing fine-grained tephra 

from the 3,400-4,000 yr B.P. eruption of Aniakchak 

Crater (Riehle and others, 1987). A second set of icewedge pseudomorphs extends downward from the 

capping silty sand. 

The presence up-glacier from the Salmon Lake 

moraine of deltas and shoreline scarps of a preglacial 

lake dammed by the Crater Creek glacier indicate that 

the maximum advances of the Grand Central River and 

Crater Creek glaciers during Salmon Lake time were 

asynchronous. The preglacial lake probably caused an 

early and rapid calving retreat of the Grand Central 

River glacier. Furthermore, because a large portion of 

this glacier spans a narrow altitude range, a small 

change in snowline altitude would have greatly altered 

its accumulation area. As snowline rose following the 

Salmon Lake maximum, a large area that had 

previously lain in the accumulation zone no longer 

nourished the glacier. An equivalent rise of snowline 

in the shorter and steeper Crater Creek valley would 

have had a less significant effect upon that glacier's 

accumulation area. 

Meters UNIT THICKNESS 

The Salmon Lake glaciation is older than 40,000 

yr B.P. and has long been considered of early Wisconsin 

age (Kaufman and Hopkins, 1986). However, our data 

do not exclude the possibility that it predates the last 

major interglaciation. Relative-age data from the 

Salmon Lake area and other places in the Kigluaik 

Mountains provide only a relative chronology for the 

glacial sequence (Kaufman, 1987, Calkin and others, 

1987, tables 1 and 2). The data show that differences 

in postdepositional modification between moraines of 

Salmon Lake and Stewart River age are greater than 

the difference between those of Salmon Lake and 

Mount Osborn age, suggesting that successively older 

advances were separated by intervals of increasing 

duration. 

The Mount Osborn glaciation is represented by 

sharply defined moraines enclosing freshly eroded 

walls of tributary valleys throughout the Kigluaik 

Mountains. Trimlines developed during Mount Osborn 

time are prominent on many valley walls and are 

traceable into terminal moraines that delimit former 

glaciers about 3 km long. All tributary valleys of 

Grand Central River and Crater Creek were occupied 

during Mount Osborn time, but the glaciers failed to 

fill the major trunk valleys that contained ice during 

the preceding Salmon Lake glaciation. 

Based on similarities in weathering 

characteristics, the Mount Osborn glaciation has been 

correlated with the Itkillik II glaciation of the Brooks 

Range (Hamilton and Hopkins, 1982), dated by 

Hamilton (1982, 1986) as occurring between 25,000 and 

11,500 yr B.P. A new radiocarbon age of 11,530 ± 450 

yr B.P. (1-15,041) on peat collected by W.B. Whitford 

(State University of New York, Buffalo, written 

commun., 1987) from a shallow cirque of Windy Creek 

(fig. 1) indicates that this west-facing cirque was iceDESCRIPTION 

0.8 m 

SIL TV SAND AND TEPHRA (EOLIAN). Very fine sand and silt 

with rare pebbles; grayish brown to light olive gray. Thin (1-3cm) 

fine-grained, pale yellowish brown tephra at 70 em depth 

4 

4 1.5-

2.0 m 

3 0.3 m 

2 1.0-

1.5m 

>1.5 m 

COARSE GRAVEL (OUTWASH). Crudely stratified and imbricated pebbles, cobbles, and rare boulders in coarse, moderate 

brown matrix of sand and granules; cut by ice-wedge 

pseudomorphs 

SAND (EOLIAN?). Thin (1-2 em) beds of alternating fine and 

coarse sand 

GRAVEL (ALLUVIAL). Horizontally bedded pebbly sandy gravel; 

contains blocks, 0.5-1.0m, of stratified fine sand and silt; cut by 

ice-wedge pseudomorphs; possible buried soil at top 

GRAVEL (DELTAIC). Steeply dipping (25°-30°), beds 10-15 em 

thick, of clean, cobble-pebble gravel and coarse sand; top of 

unit at approximately 150 m altitude 

Figure 2. Stratigraphic section from Nugget Creek delta; location shown on figure 1. 

West-Central Alaska 93 
Table 2. Select surface-boulder weathering characteristics for deposits ranging in age from Salmon Lake glaciation to 

Holocene, in the Kigluaik Mountains 

[Group mean values ±1 standard deviation are shown; data from B.j. Przybyl, State University of New York, Buffalo, written commun., 1987] 

Surface-boulder 

weathering 

parameter 

Roundness index 1 

Frequency (per 100 m2 ) 

Protrusion (em) 

Number of sites 

Holocene 

l. 78 ± 0.26 

>150 

64.5 ± 18.5 

2 

Moraine 

Mount 

Recessional 

2.27 ± 0.11 

54.4 ± ll. 0 

18.1 ± 4.4 

10 

age 

Osborn 

Terminal Salmon Lake 

2.31 ± 0.08 2.65 ± 0.15 

55.0 ± 15.7 24.6 ± 10.2 

15.3 ± 4.0 10.4 ± 3.2 

12 16 

1calculated as a weighted mean by assigning values to each roundness catagory as follows; 

1, angular; 2, subangular; 3, subrounded; 4, rounded. 

free by 11,500 yr B.P. Because the cirque was last 

occupied by ice during Mount Osborn time, the 

radiocarbon age supports our correlation of the Mount 

Osborn with the Itkillik II glaciation. 

Another set of distinctive moraines is found in 

several north-facing cirques of the study area. The 

moraines are situated well up-valley from Mount 

Osborn terminal moraines, and about 1 km beyond the 

headwalls of cirques that presently lack glacier ice. 

They bear a discontinuous sod cover, a dense growth of 

lichens on boulders, and consist of low, solitary ridges 

that form nearly complete semicircles. Subsurface 

and surface-boulder weathering characteristics of 

these distinctive loop moraines and nearby recessional 

moraines are indistinguishable from the outermost 

moraines of Mount Osborn age (table 2). These 

moraines evidently record a glacial stillstand or 

readvance late during the Mount Osborn glaciation. 

However, they are distinctly older than the pair of 

Holocene moraines flanking the glacier at the head of 

Grand Union Creek (fig. 1 and table 2). 

REFERENCES CITED 

Brooks, A.H., 1901, A reconnaissance of the Cape 

Nome and adjacent gold fields of Seward 

Peninsula, Alaska in 1900, in Brooks, A.H., 

Richardson, G.B., Collie~ A.J., and 

Mendenhall, W.C., Reconnaissance in the Cape 

Nome and Norton Bay regions, Alaska 1n 

1900: U.S. Geological Survey, p. 1-180. 

Calkin, P.E., Przybyl, B.J., and Kaufman, D.S., 

1987, Latest Quaternary glaciation, Kigluaik 

Mountains, northwestern Alaska [abs.]: 

Geological Society of America Abstracts with 

Programs, v. 19, no. 1, p. 8. 

Hamilton, T.D., 1982, A late Pleistocene glacial 

chronology for the southern Brooks Range--

Stratigraphic record and regional 

significance: Geological Society of America 

Bulletin, v. 93, p. 700-716. 

1986, Late Cenozoic glaciation of the 

central Brooks Range, in Hamilton, T.D., 

Reed, K.M., and Thorson, R.M., eds., 

Glaciation in Alaska--The geologic record: 

Anchorage, Alaska Geological Society, p. 9-

50. 

Hamilton, T.D., and Hopkins, D.M., 1982, 

Correlation of northern Alaskan glacial 

deposits--A provisional stratigraphic 

framework, in Coonrad, W.L., ed., The United 

States Geological Survey in Alaska--

Accomplishments during 1980: U.S. 

Geological Survey Circular 844, p. 15-18. 

Hopkins, D.M., 1953, Seward Peninsula, in Pewe, 

T.L., ed., Multiple glaciation in Alaska--A 

progress report: U.S. Geological Survey 

Circular 289, p. 10-11. 

Kaufman, D.S., 1987, Morphometric analysis of 

Pleistocene glacial deposits in the Kigluaik 

Mountains, northwestern Alaska: Seattle, 

University of Washington, M.S. thesis, 50 p. 

Kaufman, D.S., and Hopkins, D.M., 1986, Glacial 

history of the Seward Peninsula, in 

Hamilton, T.D., Reed, K.M., and Thorso~ 

R.M., eds., Glaciation in Alaska--The 

geologic record: Anchorage, Alaska 

Geological Society, p. 51-78. 

Riehle, J.R., Meyer, C.E., Ager, T.A., Kaufman, 

D.S., and Ackerman, R.E., 1987, The 

Aniakchak tephra deposit, a late Holocene 

marker horizon in western Alaska, in 

Hamilton, T.D., and Galloway, J.P., eds., 

Geologic studies in Alaska by the U.S. 

Geological Survey during 1986: U.S. 

Geological Survey Circular 998, p. 19-22. 

Reviewers: J.E. Beget and T.D. Hamilton 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

94 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Lahar Deposit in the lditarod Volcanics, 

Southwestern lditarod Quadrangle 

By Robert G. McGimsey and Marti L. Miller 

A volcanic field, termed the Iditarod Volcanics 

(Miller and Bundtzen, this volume), forms a prominent 

upland southeast of the Iditarod River in the 

southwestern part of the Iditarod quadrangle (fig. 1). 

The Iditarod Volcanics consists of two informal map 

units--lower and upper--which range in overall age 

from Late Cretaceous to early Tertiary. The 

heterogeneous lower unit, which is composed mainly of 

breccias and pyroclastic rocks, underlies mafic and 

intermediate lava flows of the upper unit. The 

volcanic field is bounded to the northwest by the 

Iditarod-Nixon Fork strike-slip fault and by 

unconsolidated Quaternary deposits. Interbedded 

sandstone, siltstone, and shale composing the turbidite 

sequence of the upper Lower and Upper Cretaceous 

Kuskokwim Group (Bundtzen and Laird, 1983; Cady and 

others, 1955) crop out south and east of the volcanic 

belt. Extensive colluvial and vegetative cover in this 

area of low relief conceals the exact nature of the 

contact between the Kuskokwim Group and the 

158° 30' 

62° 15' .-------,--..,--,,.-,--r",----r------, 

v-';1-./ ldltarod \) River ;;; :5</ Y: ,../ / \ ""\ \ \ 

' '1 '- /\., a. v..i'";.~ ( Kk '- -. ., 

1 <,0; . '- "\ \__::_-...TKi 

9~ /.,I \ \ ~ #( I \ ' 

' 0<{ • ·y (, ' 35 1 ~'t-<1:'• / 5 / fl HAYSTACK \ / TKi ./ ...-

$ . /. '\ BUTTE 'I ~] " ...-/ 

·Y TKi , TKi~----1· so v;· '-\ • ' '\ ,- I '\ . . I / . f"'\.. oO . ./ / '-.__ 

V "'· y· '-- ~Lahar / I f . ....__ / . Dopoalt \ ~/ f Kk '\ 

\._\., ( ~ 

\ Kk \ -'~ ·-< -~ . . / . --,-="-'-.-----1 

~ 

N URCY 

U/

,., qt/

·

· 

, 

~-£\ • 

\"'- KILOMETERS i: ·,, i'!J ""' ~ ' ~bc::. .. oo ~ 

~ ) Map Location 

62' oo· _____ ;__I__._ ________ -J 

158° 30' 

Figure 1. Generalized geologic map of lditarod A-5 quadrangle. 

Map-unit symbols are: Qs, surficial deposits (Quaternary); TKi, 

lditarod Volcanics (lower Tertiary and Upper Cretaceous); Kk, 

Kuskokwim Group (Upper and Lower Cretaceous), sedimentary 

rocks. 

Iditarod Volcanics. Both sequences are broadly folded 

with fold axes generally oriented northeast-southwest. 

Isolated exposures of volcaniclastic deposits and 

minor mafic lava flows assigned to the Iditarod 

Volcanics apparently overlie the Kuskokwim Group as 

outlying erosional remnants southeast of the main 

volcanic field (fig. 1). One such deposit occurs about 3 

km east of the main volcanic field where it forms a 

cluster of three steep-sided, hummocky spires that rise 

prominently above the surrounding terrain (fig. 2). The 

most conspicuous of these is Haystack Butte. The 

other two outcrops, located 2 km southwest of 

Haystack Butte, contain ungraded and nonbedded 

matrix-supported clasts of volcanic rock, sandstone, 

and shale randomly distributed in an unsorted clay- to 

sand-sized matrix that appears to be tuffaceous, 

though devitrified. Both outcrops contain a continuum 

of grain sizes from clay to boulders. 

Two distinct types of clasts are present. The 

first type, which occurs primarily in the southernmost 

outcrop, is subrounded to well-rounded elongate clasts 

that range in size from large cobbles to boulders as 

much as 75 em in maximum dimension. These clasts 

consist mainly of fine-grained lithic sandstone and 

minor shale, similar to that of the subjacent 

Kuskokwim Group (fig. 3); their smoothness and degree 

of rounding suggests that they formed in a fluvial 

environment. 

The second type of clast ranges in size from 

small pebbles to small cobbles, are angular to 

subrounded, and consist dominantly of porphyritic 

volcanic rock and subordinate fine-grained lithic 

sandstone. Many of the volcanic rock clasts are from 

mafic and intermediate lava flows, as indicated by 

pilotaxitic textures and the presence of feldspar and 

clinopyroxene phenocrysts; some clasts are 

substantially more altered than others and contain 

abundant iron-oxide minerals. Some of the cobblesized sandstone clasts are angular and display no 

evidence of fluvial rounding but instead resemble 

fragments of talus. The matrix consists mainly of 

poorly sorted lithic clasts in an apparently devitrified 

tuff (fig. 4). Subordinately included are subrounded to 

subangular grains of quartz and feldspar and equant 

clinopyroxene and plagioclase. The fine-grained part 

of the matrix contains microlitic feldspar, and a few 

shard-like structures are still recognizeable despite 

pervasive diagenetic alteration (fig. 4B). Clast and 

grain boundaries are commonly oxidized, and 

interstitial pore spaces are filled by matrix material 

indicating that the deposit was water saturated and 

probably warm. Lack of interstitial secondary 

mineralization suggests that oxidation is a primary 

West-Central Alaska 95 
Figure 2. View north showing outcrops of lahar deposit. Distant knob in upper right is Haystack Butte. 

feature rather than a consequence of diagenesis 

(T.E.C. Keith, U.S. Geological Survey, written 

commun., 1987). 

Haystack Butte consists mainly of poorly 

sorted, matrix-supported, subangular to subrounded 

clasts of intermediate volcanic rock, sandstone, and 

shale. As in the neighboring outcrops, volcanic clasts 

outnumber those of sedimentary origin. Clast size 

ranges from coarse sand to small pebbles; the matrix is 

poorly sorted, altered, devitrified lithic tuff very 

similar to that in the other two outcrops. The deposit 

also lacks any discernible internal structures such as 

grading and bedding. The main difference between the 

Haystack Butte outcrop and those to the southwest is 

that the larger well-rounded clasts of sedimentary 

rocks are not present at Haystack Butte. 

We interpret the outcrops to be remnants of a 

volcanic debris flow rather than fluvial deposits 

because of the lithology and physical characteristics of 

the clasts and matrix, their internal structures, and 

areal distribution of the deposit. Most clasts are of 

volcanic rock, which is typical of lahars (Fisher and 

Schmincke, 1984), and sedimentary rock clasts are 

minor. Many of the sedimentary rock clasts are highly 

angular, and therefore unlikely to have been 

transported by fluvial processess. The finest part of 

the matrix also lacks the granularity typical of fluvial 

sedimentary deposits, and the presence of altered 

microlitic structures and a few shard-like relics 

suggests that it originally was tuffaceous. The deposit 

Figure 3. Well-rounded SO-em-long sandstone clast in poorly 

sorted tuffaceous matrix. From southernmost outcrop of those 

shown in figure 1. 

96 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
A 1 MILLIMETER 

~- --~ 

Figure 4. Photomicrographs of matrix of lahar deposit. A, 

Continuum of grain sizes from clay to sand. B, Finer portion of 

matrix; presence of rei ict feldspar microlites (arrows) suggests 

that matrix may originally have been tuffaceous. 

lacks any discernible bedding or grading, and poorly 

sorted clasts of all sizes are randomly distributed in 

the supporting matrix. Although some lahars have a 

crude vertical grading and tend to become more 

graded and better sorted distally from their source 

(Riehle and others, 1981; Williams and McBirney, 1979, 

p. 177), they are typically distinguished from fluvial 

deposits by their lack of internal stratification. 

Finally, distribution can be an important characteristic 

in determining the origin of lahars (Crandell, 1971). 

The outcrops around Haystack Butte are anomalous in 

that no similar outcrops occur anywhere else in the 

vicinity, and their limited distribution, though not 

conclusive in itself, is consistent with our 

interpretation of the deposit as a lahar. Deposits of 

fluvial origin would typically be more widely 

distributed or might form recognizable channel 

patterns. 

A clue to the origin of the lahar may be the 

presence of the well-rounded large clasts of 

sedimentary rock that occur in the two southern 

exposures. The size and shape of the clasts suggest 

that they were fluvially transported from a source 

area having at least moderate relief. In order to 

account for the relatively local extent of these wellrounded clasts in a debris flow-like deposit composed 

mostly of volcanic material, we envision a channelized 

lahar that engulfed and incorporated preexisting 

stream deposits. The Haystack Butte exposures, which 

contain smaller rounded clasts, might represent a more 

distal facies of the lahar. 

An alternative model is one in which the lahar 

engulfed an unlithified, isolated or remnant fluvial or 

glacial deposit. However, it seems unlikely that such a 

deposit would exist on or near the flanks of an active 

volcano within the path of a nonconstricted debris 

flow. It is also doubtful that a lithified deposit 

containing the clasts could have been eroded by and 

incorporated in the lahar because lahars tend not to 

scour and erode the beds over which they travel 

(Crandell, 1971; Fisher and Schmincke, 1984; Riehle 

and others, 1981). Therefore a model in which a 

channelized lahar incorporates stream deposits from a 

stream bed seems more viable. 

Another interesting aspect of the lahar 

concerns the source of the well-rounded sandstone and 

shale cobbles and boulders. Megascopically and 

microscopically, they are very similar to both the 

sedimentary rocks of the Kuskokwim Group and to 

sedimentary rocks of Early Cretaceous age (preKuskokwim) that occur 65 km north of the volcanic 

field and extend farther to the north and northwest in 

the Yukon-Koyukuk basin (M.L. Miller, unpub. data; 

Patton, 1973). Determining the origin of the clasts 

could prove useful in interpreting the timing of 

Iditarod volcanism relative to deposition of the 

Kuskokwim Group. Samples of the shale clasts from 

the lahar were submitted for palynological and 

foraminiferal analysis in an attempt to obtain age 

data, but they proved to be barren of microfossils. 

The presence of the lahar and the well-rounded 

cobbles and boulders within it implies that the source 

terrane had considerable topographic relief and 

probably consisted of one or more volcanoes that 

adjoined or were built upon an upland composed of 

sedimentary rocks. However, neither vent-facies 

rocks nor associated plutonic rocks occur within or 

near the Iditarod Volcanics, and neither the 

stratigraphy nor the distribution of rocks in this 

volcanic field indicates a local, centralized source. 

The source area must have been eroded away, covered 

by the products of subsequent volcanic activity, or 

structurally displaced. Interestingly, a similar 

volcanic sequence and associated plutonic complex 

occurs in rugged terrain about 90 km to the northeast 

across the Iditarod-Nixon Fork fault, and the lack of a 

source area for the lahar might be explained by rightlateral offset along the fault (Miller and Bundtzen, this 

volume). 

REFERENCES CITED 

Bundtzen, T.K., and Laird, G.M., 1983, Geologic 

map of the Iditarod D- 1 quadrangle, 

Alaska: Alaska Division of Geological and 

Geophysical Surveys Professional Report 78, 

1 sheet, scale 1:63,360. 

West-Central Alaska 97 
Cady, W.M., Wallace, R.E., Hoare, J.M., and 

Webber, E .J., 1955, The central Kuskokwim 

region, Alaska: U.S. Geological Survey 

Professional Paper 268, 132 p. 

Crandell, D.R., 1971, Postglacial lahars from 

Mount Rainier Volcano, Washington: U.S. 

Geological Survey Professional Paper 677, 75 

p. 

Fisher, R.V., and Schmincke, H.-U., 1984, 

Pyroclastic rocks: New York, SpringerVerlag, 472 p. 

Patton, W.W., Jr., 1973, Reconnaissance geology 

of the Northern Yukon-Koyukuk Province, 

Alaska: U.S. Geological Survey Professional 

Paper 774-A, 17 p. 

Riehle, J .R., Kienle, Jurgen, and Emmel, K. S., 

1981, Lahars in Crescent River Valley, Lower 

Cook Inlet, Alaska: Alaska Division of 

Geological and Geophysical Surveys Geologic 

Report 53, 10 p. 

Williams, Howell, and McBirney, A.R., 1979, 

Volcanology: San Francisco, Freeman, Cooper 

and Co., 397 p. 

Reviewers: T.E.C. Keith, E.J. Moll-Stalcup, and 

J.R. Riehle 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

98 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Right-Lateral Offset Solution for the 

lditarod-Nixon Fork Fault, Western Alaska 

By Marti L. Miller and Thomas K. Bundtzen 

The Iditarod-Nixon Fork fault, a major 

northeast-southwest-trending strike-slip fault in 

western Alaska, is marked throughout its 365-km 

length by aligned streams, fault scarps of Holocene 

age, and contrasting regional structural grain (fig. 1). 

Grantz (1966) ascribed probable right-lateral strikeslip (plus possible dip-slip) movement to this vertical 

to steeply dipping fault, but was unable to firmly 

es.tablish the amount of offset. Using the geologic 

mapping of Brown (1926), Grantz (1966) estimated that 

Cretaceous rocks were offset by 110 km in a rightlateral sense; when he used the less detailed mapping 

of Fernald (1960), only 35 km offset was found. In a 

more recent paper on the regional geology of western 

Alaska, Gemuts and others (1983) suggested 

approximately 80 km of offset based on the apparent 

offset of a contact between lower Paleozoic and 

Cretaceous sedimentary rocks. In the lditarod 

quadrangle, which is bisected by the fault on a 

northeast-southwest diagonal (fig. 1), our work has 

revealed a distinct volcanic section that we believe 

firmly documents between 88 and 94 km of rightlateral movement since the Late Cretaceous. The 

offset volcanic rocks are shown in figure 1 as the two 

areas labeled BMVF (for Beaver Mountains volcanic 

field) and the Iditarod Volcanics, defined herein. 

From 1984 to 1986, under a cooperative 

agreement between the U.S. Geological Survey and the 

Alaska Division of Geological and Geophysical Surveys, 

we mapped the Iditarod quadrangle as part of an 

AMRAP (Alaska Mineral Resource Assessment 

Program) study. The study area is largely underlain by 

interbedded sandstone, shale, and conglomerate of the 

upper Lower and Upper Cretaceous Kuskokwim Group 

(fig. 1). Deep-water turbidite-facies rocks dominate, 

but shallow shoreline-facies rocks are also present. 

Late Cretaceous to early Tertiary volcano-plutonic 

complexes locally intrude and overlie the Kuskokwim 

Group. Comagmatic volcanic rocks of these 

complexes either overlie or are in fault contact with 

monzonite plutons; locally, the plutons intrude and 

partially assimilate the volcanic rocks (Miller and 

Bundtzen, 1987). The Kuskokwim Group and overlying 

volcanic rocks have been deformed into broad, open, 

northeast- to east-west-trending synclines and 

anticlines. Numerous high-angle faults, the largest of 

which is the Iditarod-Nixon Fork fault, cut the regional 

structure at a slightly oblique angle. In two areas 

along its length (BMVF and the Iditarod Volcanics, fig. 

1), the Iditarod-Nixon Fork fault juxtaposes volcanic 

rocks against Kuskokwim sedimentary rocks. The 

BMVF north of the fault is the volcanic section of the 

moderately well exposed volcano-plutonic complex of 

the Beaver Mountains (fig. 2). The Iditarod Volcanics, 

south of the fault, consists of a poorly exposed 

volcanic section in the vicinity of Decourcy Mountain 

(fig. 2) that is strikingly similar to the BMVF but that 

lacks exposures of associated plutonic rocks. 

The BMVF was first mapped and described by 

Bundtzen and Laird (1982, 1983) and by Bundtzen and 

others (1987). The dominantly subaerial volcanic 

section is 350 to 500 m thick and overlies sedimentary 

rocks of the Kuskokwim Group. To accommodate the 

1:250,000 scale of our AMRAP studies, we have 

combined the original five map units of Bundtzen and 

others (1987) into two. The basal unit ("tuff" unit t, 

figs. 2 and 3), a heterogeneous unit about 250 m thick, 

is characterized by lithic and crystal tuff, volcanic 

breccia, and light-tan to brick-red altered fine-grained 

andesite to dacite, but it also has minor, apparently 

interlayered, quartzose sublithic sandstone, shale, and 

volcaniclastic sediments. The groundmass of volcanic 

rock samples from this unit is commonly altered to 

silica + carbonate ±chlorite. The basal unit is overlain 

by a unit ("lava-flow" unit mv, figs. 2 and 3) that is 

characterized by lava flows consisting of fine-grained 

to porphyritic olivine-clinopyroxene basalt, basaltic 

andesite, and clinopyroxene-plagioclase andesite; 

volcanic breccia is sometimes present and probably 

interfingers with the flow rocks. Most of the volcanic 

rocks are at least in part altered: olivine phenocrysts 

to serpentinite and (or) iddingsite and groundmass to 

chlorite ± carbonate ± hematite. The lithologic 

similarity of the quartzose sublithic sandstone and 

shale interbedded with the basal tuff unit and the 

lithic to sublithic sandstone and shale of the underlying 

Kuskokwim Group led Bundtzen and others (1987) to 

suggest that the contact was conformable. However, 

no fossils have been found in either unit, and it is 

possible that the sandstones are not the same and that 

a disconformity does exist. 

The volcanic rocks of the Decourcy Mountain 

area, on the southeast side of the Iditarod-Nixon Fork 

fault, were formally designated the Iditarod Basalt by 

Cady and others (1955). We propose to redefine the 

formation as the Iditarod Volcanics because rocks of 

intermediate composition are as common as mafic 

rocks in the unit. Bedrock in this area is poorly 

exposed and outcrops are isolated, thus obscuring 

contact relationships. We estimate the volcanic 

section to be between 500 and 600 m thick, and it 

probably thins outward. We recognize two mappable 

units within the Iditarod Volcanics that are 

lithologically identical to the two units of the BMVF, 

West-Central Alaska 99 
thus we have used the same lithologic-unit symbols 

("mv" and "t") in both areas (figs. 2 and 3). In the 

Iditarod Volcanics, the basal tuff unit is characterized 

by lithic tuff, water-laid tuff, and altered lava flows 

of intermediate composition, but it also includes a 

volcaniclastic deposit interpreted to be a lahar (see 

McGimsey and Miller, this volume). Most rocks of this 

heterogeneous tuff unit are weakly or intensely altered 

to secondary silica, carbonate, ± chlorite. In the 

Iditarod Volcanics, the overlying lava-flow unit is 

primarily composed of fine-grained to porphyritic 

olivine-clinopyroxene basalt and lesser plagioclaseclinopyroxene andesite. Volcanic breccia locally 

interfingers with flow rocks. Alteration of the 

volcanic rocks is extensive--olivine to serpentinite ± 

carbonate or to white mica ± serpentinite; 

~·· 

Location of -<----~ 

RUSSIAN 

MISSION 

Fig. 2 

I 

SLEETMUTE 

0 50 

clinopyroxene to actinolite ± carbonate; and 

groundmass to chlorite ± carbonate. Plagioclase 

phenocrysts are generally little altered. The nature of 

the contact between the Iditarod Volcanics and the 

underlying Kuskokwim sedimentary rocks is 

enigmatic. Cady and others (1955) interpreted the 

contact to be disconformable because they believed 

the base (our tuff unit) was basal breccia. However, in 

the same paper, they acknowledged that further south 

the Iditarod Volcanics possibly intertongues with the 

Kuskokwim Group and might therefore be referred to 

as a formation of that group. The critical exposures in 

our study area are ambiguous, and we cannot say 

whether the contact is conformable or disconformable. 

Limited radiometric age data from both the 

BMVF and the Iditarod Volcanics are summarized in 

64°~~----------------------

100 km 

~Ka 

MCGRATH 

EXPLANATION 

mt~~~ Monzonite (Tertiary and Cretaceous) 

I TKvj Volcanic rocks (Tertiary and Cretaceous) 

I Ks I Sedimentary rocks (Cretaceous) 

I Pl:aj Sedimentary rocks (Paleozoic) 

~ Contact 

...-- Fault 

Points A and B show offset 

of contact between units Ks and Pzs 

Figure 1. Map showing lditarod-Nixon Fork fault, proposed offset volcanic rocks of Beaver Mountains volcanic field (BMVF) and 

lditarod Volcanics, and associated volcanic rocks and monzonite plutons. Geology modified from Chapman and others (1985) for 

Ophir quadrangle, Patton and others (1980) for Medfra quadrangle, and Beikman (1980) for Russian Mission and Sleetmute 

quadrangles. 

100 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
table 1. Samples suitable for age determinations have 

been difficult to obtain due to hydrothermal and 

thermal effects of underlying plutons throughout the 

region. Nevertheless, the five ages indicated on table 

1 are consistent with field interpretations. In the 

Decourcy Mountain area, the lower unit of the Iditarod 

Volcanics yields a 77 Ma age whereas the upper unit 

yields 66 Ma (minimum age) and 63 Ma ages (fig. 3). In 

the Beaver Mountains area, the base of the upper unit 

yields a 76 Ma age whereas its upper part bears a 58 

Ma age. Taking into account the limits of analytical 

error, these ages are in remarkable agreement. 

In summary, the lithology, stratigraphic 

succession, and radiometric ages of the BMVF and the 

Iditarod Volcanics are very similar. Both sections 

overlie sedimentary rocks of the Kuskokwim Group and 

have similar stratigraphic successions. The sequences 

differ somewhat in the reported nature of the contact 

with underlying sedimentary rocks of the Kuskokwim 

Group; however, local unconformities are common in 

volcanic environments where rapid deposition occurs 

EXPLANATION 

~ Surficial deposits (Quaternary) 

l:='·"'*~'i::j Rhyolite (Tertiary and Cretaceous) 

I::TK,;.d Monzonite (Tertiary and Cretaceous) 

Rocks of Beaver Mountains 

volcanic field and lditarod 

Volcanics, undivided 

(Tertiary and Cretaceous)--

Consists of: 

G Mafic to interm. volcanic rocks 

c=!:J Tuff, lava, and volcaniclastic rocks 

~ Sedimentary rocks (Cretaceous)--

Kuskokwim Group 

---- Faults-dashed where 

approximated 

~ Axis of syncline-dashed 

---. where approximated 

Axis of anticline-dashed 

where approximated 

\ 

3 

K-Ar sample (table 1) 

e:fJ oo· 

0 

(Williams and McBirney, 1979). We believe that the 

two sections are the same and that, therefore, they 

document 88 to 94 km of right-lateral offset along the 

Iditarod-Nixon Fork fault. 

Several other lines of evidence support our 

conclusion. First, the Iditarod Volcanics are typical of 

volcanic rocks associated with volcano-plutonic 

complexes in west-central Alaska, yet there are no 

exposed monzonitic plutons spatially associated with 

these rocks. However, when the right-lateral 

movement is restored, the Iditarod Volcanics are 

spatially associated with the monzonites of Camelback 

Mountain (fig. 1). Second, the amount of movement 

that we have proposed approximates the offset of the 

Paleozoic-Cretaceous contact in the Medfra 

quadrangle (points A and B, fig. 1). Third, when the 

right-lateral movement is restored, the volcanoplutonic complex of Chicken Mountain in the Iditarod 

quadrangle and that of the Russian Mountains further 

to the southwest (fig. 1) line up along a north-south 

line. The emplacement of the plutons and volcanic 

10 20 km 

Figure 2. Detailed geologic map of Beaver Mountains volcanic field and lditarod Volcanics of north-central and southwestern lditarod 

quadrangle. 

West-Central Alaska 101 
500 

meters 

mv 

58.1 

m.y. 

Beaver Mountains Volcanic Field 

(BMVFl 

75.71----.....,..J 

Olivine-pyroxene basalt, basaltic 

andesite, pyroxene andesite, and 

volcanic breccia 

m.y. 

62.7 

mv m.y. 

Lithic-crystal tuff, altered andesite 

and dacite, quartzose sandstone, 

chalcedonically altered volcanics 

_ Quartzose sublithic sandstone, 

!Kuskokwim Group) 

Decourcy Mountain Uditarod Volcanics) 

Olivine-pyroxene basalt, 

pyroxene andesite, and interfingering 

66.1 1--------,,.J volcanic breccia 

600 m.y. 

meters Lithic tuff, water laid tuff, altered 

- andesite (?), and lahar deposits; most 

lithologies altered to carbonate and silica 

- Undifferentiated Kuskokwim Group 

Figure 3. Composite sections of Beaver Mountains volcanic field 

(BMVF) and lditarod Volcanics showing stratigraphic 

subdivisions and locations (1-5, table 1, fig. 1) of K-Ar samples 

(ages in Ma). mv, mafic to intermediate volcanic rocks; t, tuff, 

lava, and volcaniclastic rocks. 

rocks appears to be controlled by high-angle faults 

(Miller and Bundtzen, 1987), and we have mapped a 

fault of this type that trends north-south through 

Chicken Mountain. We suggest that the offset 

extension of this fault runs along the eastern edge of 

the Russian Mountains. 

Because the volcanic sections are Late 

Cretaceous to early Tertiary in age, the 88-94 km of 

movement along the Iditarod-Nixon Fork fault has 

taken place since that time. Bundtzen and others 

(1987) reported that a prominent escarpment cuts 

Quaternary fan-terrace deposits in the lditarod C-3 

quadrangle, strongly suggesting that activity has 

continued into the Holocene. 

REFERENCES CITED 

Beikman, H.M., compiler, 1980, Geologic map of 

Alaska: U.S. Geological Survey, 2 sheets, 

scale: 1:2,500,000. 

Brown, J.S., 1926, The Nixon Fork country: U.S. 

Geological Survey Bulletin 783-D, p. 97-150. 

Bundtzen, T.K., and Laird, G.M., 1982, Geologic 

map of the Iditarod D-2 and eastern D-3 

quadrangles, Alaska: Alaska Division of 

Geological and Geophysical Surveys Geologic 

Report 72, scale 1:63,360. 

Table 1. Potassium-argon analytical data for volcanic rocks from the Beaver Mountains volcanic field 

(BMVF) and from the lditarod Volcanics 

[Locality numbers are shown on figure 2. Constants used: 40KIK = 1.167 x 10-4 mol/mol; Ae = 0.581 x 10-1 0yr-1; A.b = 4.962 x 10-10 yr-1] 

Map No. 1 

(Field No.} 

1 

(82BT392} 

2 

(84BT277) 

3 

(85BT106) 

4 

(85AM46A) 

5 

(84BT256) 

Field2 Rock 

(unit) type 

BMVF 

(base of Andesite 

mv} 

BMVF Olivine 

(mv} basalt 

Iditarod Olivine 

(mv} basalt 

Iditarod Olivine 

(mv} basalt 

Iditarod Andesite 

( t} 

Material 

dated 

Plagioclase 

Whole 

rock 

Plagioclase 

Whole 

rock 

Whole 

rock 

1Refers to K-Ar localities on figure 2. 

(wt pet} 

x=0.600 

2.653 

2.760 

x=2.760 

0.582 

0.579 

x=0.579 

2.120 

2.150 

x=l. 308 

l. 303 

l. 313 

x=l.308 

Arrad Arrad 

(pet} 

( xlo-llmoles/g) 

6.68 35.3 

23.02 33.6 

5.32 79.7 

20.70 67.6 

14.76 15.3 

2BMVF = Beaver.Mountains volcanic field; Iditarod Iditarod Volcanics. 

102 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 

Age 

(Ma} 

75.7 ± 2.3 

58.1 ± 1.9 

62.7 ± 1.9 

66.1 ± 2.0 

76.7 ± 2.3 
1983, Preliminary geology of the 

northeastern Iditarod C-3 quadrangle, 

Alaska: Alaska Division of Geological and 

Geophysical Surveys Report of Investigations 

83-13, scale 1:63,360, 6 p. 

Bundtzen, T.K., Laird, G.M., and Lockwood, M.S., 

1987, Geology of the Iditarod C-3 

quadrangle, Alaska: Alaska Division of 

Geological and Geophysical Surveys 

Professional Report 96, scale 1:63,360, 11 

p. 

Cady, W.M., Wallace, R.E., Hoare, J.M., and 

Webber, E.J., 1955, The central Kuskokwim 

region, Alaska: U.S. Geological Survey 

Professional Paper 268, 132 p. 

Chapman, R.M., Patton, W.W., Jr., and Moll, 

E.J., 1985, Reconnaissance geologic map of 

the Ophir quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 85-203, 

scale 1:250,000, 17 p. 

Fernald, A.T., 1960, Geomorphology of the upper 

Kuskokwim region, Alaska: U.S. Geological 

Survey Bulletin 1071-G, p. 191-279. 

Gemuts, I., Puchner, C.C., and Steffel, C.I., 

1983, Regional geology and tectonic history 

of western Alaska, in Symposium on Western 

Alaska Geology and Resource Potential 

Proceedings, February 16 and 17, 1982, 

Anchorage, Alaska: Journal of the Alaska 

Geological Society, p. 67-85. 

Grantz, Arthur, 1966, Strike-slip faults in 

Alaska: U.S. Geological Survey Open-File 

Report 267, 82 p. 

Miller, M.L., and Bundtzen, T.K., 1987, Geology 

and mineral resources of the Idi tarod 

quadrangle, west-central Alaska: U.S. 

Geological Survey Circular 995, p. 46-47. 

Patton, W.W., Jr., Moll, E.J., Dutro, J.T., Jr., 

Silberman, M.L., and Chapman, R.M., 1980, 

Preliminary geologic map of the Medfra 

quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 80-811A, scale 1:250,000. 

Williams, Howell, and McBirney, A.R., 1979, 

Volcanology: San Francisco, Freeman, Cooper 

and Co., 397 p. 

Reviewers: T.E.C. Keith and W.W. Patton, Jr. 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

West-Central Alaska 103 
Geologic Setting and Petrography of the Phyllite and 

Metagraywacke Thrust Panel, North-Central Alaska 

By John M. Mu rphy andW.W. Patton, Jr. 

Exposures of a laterally persistent thrust panel 

composed of pelitic phyllite and quartzose 

metagraywacke border the southern Brooks Range and 

both flanks of the Ruby geanticline in north-central 

Alaska (fig. 1). The phyllite and metagraywacke thrust 

panel is the lowest of three thrust panels composing 

the Angayucham-Tozitna terr ane (Patton and others, 

in press). It is structurally overlain by a laterally 

extensive thrust panel of imbricated basalt and chert 

of Devonian to Early Jurassic age, which in turn is 

D 

L:..::...J 

~ 

,..--, 

~ 

1 oo + -------

Overlap Ass emblages 

Volcan i c rock and unconsolidated deposits 

(Cenozoic) 

Granitic rocks {Cretaceous) 

Terrigenous sedimenta ry rocks {mid- and 

Upper Cretaceous) 

Acc r e t ed Te rranes 

Koyukuk terrane (J urassic and Lower 

Cret ac eous volcanic arc assemblage) 

Angayucham- Tozi tna terrane : 

Phyllite and metagraywack e thrust panel 

(De vonian(? ) quartzos e turbidites) 

Mafic and ultra1nafic thrust panels 

(De voni an to Jurassic oph i ol ite) 

overlain by a thrust panel of gabbro and peridotite 

(Patton and Box, 1985), which are not separated on 

figure 1. Obduction of the three thrust panels onto the 

Precambrian to middle Paleozoic miogeoclinal rocks of 

both the southern Brooks Range and the Ruby 

geanticline is believed to have occurred in latest 

J urassic to Early Cretaceous time due to collision of 

the intraoceanic Koyukuk arc (Patton and Box, 1985}. 

The purpose of this report is to summarize the 

distribution, structural position, emplacement history, 

-- +-- --

r=::::l 

L=...=J 

Conti nenta 1 Borde rl ands 

Souther n Brooks Range (Precambrian and 

lower Paleozoic) 

Ruby Geanticline (P recambrian {?} and 

lo·Ner Paleozoic ) 

~ 

/ - Thrust fault- teeth on 

upper plate 

/- Contact 

Fault - high angle 

Fossil locality (table 1) 

a - Sample lo ca lity {table 2, 

fig . 2) 

Figure 1. Generalized geologic map of north-central Alaska showing distribution of overlap assemblages, accreted terranes and 

continental borderlands. Numbers refer to fossil localities given in table 1. Letters refer to petrographic data given in table 2 and plotted on figure 2. Geology modified from W.W. Patton (unpub. data). 

104 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
age, sedimentology and petrography of the phyllite and 

metagraywacke thrust panel. 

Our mapping shows that the phyllite and 

metagraywacke thrust panel can be correlated for 

more than 500 km along the southern Brooks Range 

and for more than 400 km along both the northeast and 

southwest flanks of the Ruby geanticline. Sparse 

fossils have been recovered from the thrust panel, 

primarily from the southern Brooks Range, but also 

from the east flank of the Ruby geanticline (fig. 1 and 

table 1). The maximum range of ages given by these 

fossils is late Early Devonian to Triassic or Early 

Jurassic. This large and poorly constrained age range 

is compatible with regional geologic relations. For 

example, the youngest possible depositional age of 

rocks in the thrust panel is Early Cretaceous, 

constrained by recycled metagraywacke clasts in 

deposits of Albian age (Dillon and Smiley, 1984), by 

crosscutting mid-Cretaceous granitic plutons in the 

Ruby geanticline (Patton and Box, 1985), and by reset 

K-Ar ages of schistose metamorphic rocks of the 

southern Brooks Range (Turner and others, 1979; 

Turner, 1984). We believe, however, that only the 

Devonian fossils give reliable ages because the cherts 

giving younger ages have been interpreted as faultbounded blocks in the phyllite (table 1, Jones and 

others, in press). If the nonmarine deposits of the 

Upper Devonian to Lower Mississippian(?) Kanayut 

Conglomerate (Nilsen and Moore, 1984) are correlative 

with the deep marine deposits of the phyllite and 

metagraywacke thrust panel, then deposition in the 

thrust panel may have ceased around Mississippian 

time. 

Sedimentary structures within the phyllite and 

metagraywacke panel are exposed in outcrops along 

the southern Brooks Range and in borrow pits near the 

Dalton highway along the Ruby geanticline. These 

features indicate that original sediment deposition 

occurred on shale-dominated submarine turbidite 

systems with abundant fine- to medium-grained 

turbidites and minor debris flows. The average ratio 

of phyllite to graywacke is about 4:1. Exposures near 

the Kobuk, Koyukuk, and Christian Rivers show thinto medium-bedded sandstone beds with erosive bases, 

shale rip-ups, normal grading, and well-developed 

Bouma sequences (W. W. Patton, U.S. Geological Survey 

unpub. field notes, 1970, 1973, 1984; W.P. Brosge, U.S. 

Geological Survey unpub. field notes, 1962, 1963). At 

locality 1 (fig. 1 and table 1), impure limestone 

turbidites and carbonate debris associated with 

vesicular volcanic flow-breccia contain reworked 

fossils derived from middle Paleozoic platformcarbonate deposits, suggesting deposition adjacent to a 

continental margin (Patton and others, in press). The 

petrography of metagraywacke, discussed below, 

supports this interpretation. The presence of 

radiolarian chert interbedded with graywacke 

turbidites suggests that deposits near the Koyukuk 

River may have formed in a deep submarine 

environment (Dillon and others, 1986). For the same 

area, however, Gottschalk (1987) reports oscillatory 

ripples and hummocky cross-stratification, both of 

which indicate deposition above storm-wave base. 

Because the shallow-marine indicators are limited, we 

suggest that deposits composing the phyllite and 

metagraywacke thrust panel are mainly deep-marine 

turbidites. 

Preliminary petrographic studies of 51 thin 

sections of sandstone from the phyllite and 

metagraywacke thrust panel resulted in the selection 

of 13 thin sections from widely separated areas for 

point-counting. Point counts of over 400 detrital 

grains per thin section were performed using the 

traditional method of counting. Criteria for counting 

focused on decreasing the combined effects of 

incipient foliation, matrix recrystallization, pressure 

Table 1. Fossils from the phyllite and metagraywacke thrust panel 

Locality Age 

(fig. 1) 

1 Devonian to Late 

MississippianPennsylvanian(?) 

2 Late-Early 

Devonian 

(Siegian-Emsian) 

3 Mississippian and 

Triassic 

4 Mississippian, 

and TriassicEarly Jurassic 

5 Possible Middle 

or Late Devonian 

5, 6 Probable Devonian 

6 Probable Late 

Devonian 

Fossil and host 

lithology 

Conodonts reworked 

from shallow water in 

limestone turbidites 

Palynomorphs in 

phyllite 

Radiolarians in chert 

interbedded with 

graywacke 

Radiolarians in fault 

slices of chert in 

phyllite 

Palynomorphs in 

shale 

Plant fragments in 

shale and graywacke 

Spiriferid brachiopod 

in impure limestone 

beds in graywacke 

Author 

A.G. Harris, 

USGS 

(1984) 

Gottschalk 

(1987) 

Dillon and others 

(1986) 

Jones and others 

(in press) 

Brosge and Reiser 

(1962) 

Brosge and Reiser 

(1962); Brosge, 

and others (1973) 

Brosge and others 

(1973) 

West-Central Alaska 105 
solution, and sorting on bulk rock composition. All 

sand-size grains (0.0625-0.5 mm) were counted. Grains 

smaller than 0.0625 mm were counted as matrix. 

Sandstones from the phyllite and 

metagraywacke thrust panel are compositionally 

mature, texturally immature, quartzose litharenites. 

They consist predominantly of angular to subangular, 

very fine to medium-grained, moderately sorted grains 

in pelitic, clay-silt matrix. Matrix ranges between 5 

and 25 percent. Framework grains include polygonalpolycrystalline quartz, monocrystalline quartz, 

unfoliated chert, plagioclase, K-feldspar (microcline), 

volcanic lithics, sedimentary lithics, metamorphic 

lithics and plutonic lithics. Volcanic lithics include 

microlitic and lathwork grains, and greenstone with 

unfoliated chlorite matrix. Sedimentary lithics are 

mainly shale and siltstone, with minor recycled quartzchert sandstone. Metamorphic lithics are 

predominantly quartz-mica schist and gneiss with 

polygonal internal crystal margins. Minor pelitic 

phyllite, quartz-tourmaline schist and rare quartzepidote schist also occur. Plutonic lithics are granitic, 

composed of aggregates of quartz, feldspars and 

micas. Because of point-counting conventions and the 

fine grain size of sandstones, amounts of plutonic 

clasts are underestimated. The unfoliated pelitic 

gneiss clasts counted as metamorphic lithics probably 

had plutonic sources. Accessory detrital minerals are 

white mica, biotite, chlorite, undifferentiated opaques, 

zircon, tourmaline, sphene, carbonate, myrmekite, and 

epidote. 

Detrital modes from point counts indicate that 

samples from widely separated areas of the phyllite 

and metagraywacke thrust panel have similar 

compositions (table 2). Quartzose grains (including 

chert) predominate, as single crystals and as plutonic 

and metamorphic rock fragments. On a QFL 

provenance diagram (fig. 2A), all samples plot near the 

Q pole, corresponding to the recycled orogen 

provenance field of Dickinson (1985). On the QmFLt 

diagram (fig. 2B) all but two of the samples shift into 

either the transitional- or lithic recycled-orogen 

provenance fields when chert and polycrystalline 

quartz are moved from the Q pole to the Lt pole. Two 

samples with greater than 10 percent plagioclase 

overlap slightly into the transitional arc provenance 

field. These two samples also contain significant 

lathwork volcanic grains, indicating local volcanic 

sources. 

Although the source areas suggested by 

provenance diagrams are mainly compressional 

regimes, including lithic- and transitional-recycled 

orogens, the unfoliated nature of chert, polycrystalline 

quartz, and metamorphic lithic fragments suggests 

that the source region(s) may have been uplifted in a 

noncompressional (extensional or transform) setting. 

The textural immaturity of sandstones from the 

phyllite and metagraywacke thrust panel indicates 

rapid erosion and redeposition. In contrast, their 

consistent quartzose compositions indicate 

compositional maturity, which argues either for 

intense chemical or physical reworking of a 

heterogeneous source, or for simpler distribution from 

a homogeneous source. At present, we consider the 

source region(s) to have had a limited original 

composition range, that is, one dominated by granitic 

plutonic and unfoliated quartzose metamorphic rocks, 

and by unfossiliferous, unfoliated chert. The source 

must also have produced abundant pelitic shale, which 

during deformation became phyllite. 

In summary, recent regional geologic 

compilations and new petrographic data indicate that a 

laterally persistent thrust panel composed of lowgrade pelitic phyllite and quartzose metagrawacke is 

the lowest of three internally imbricated thrust panels, 

composing the Angayucham-Tozitna terrane, that were 

obducted onto continental platform rocks of both the 

southern Brooks Range and the Ruby geanticline during 

latest Jurassic to Early Cretaceous time. The phyllite 

and metagraywacke thrust panel was deposited as 

Table 2. Point-count data for the phyllite and metagraywacke thrust panel 

[Qm = monocrystalline quartz, Qp = polycrystalline quartz, C =chert, P = plagioclase, K = potassium feldspar, Lv =volcanic lithics, Ls = sedimentary lithics, Lm = metamorphic lithics. Q* = Qm + Qp + C; F = P + K; L- = Lv + Ls + Lm; Lt = L- + Qp +C. See figure 2 for triangular plots of the data. Q*FL-is equivalent to QFL of Dickinson 

(1985). Sample localities are plotted on figure 1.] 

Grain type A G K M 

"lin 72 1:17 94 109 105 70 72 123 167 133 65 38 7 5 

()p 167 2LJO 195 85 90 112 102 154 118 135 165 163 244 

c 57 40 50 103 106 139 85 58 59 95 60 lOS 49 

61:1 J? 19 28 31 26 66 12 16 

3 3 2 

Lv 12 17 23 22 27 17 75 1 13 11 

Ls 12 18 28 21 23 22 18 9 16 15 16 18 

Lm 26 32 26 34 29 33 17 50 46 23 7 3 51 15 

Biotite 4 3 4 8 2 10 15 7 1 

White ~lica 11 2 3 

Chlorite 4 3 2 

Opaque 18 8 10 

Zircon 

Tourmaline 

Sphene 1 

Matrix 38 61 39 59 49 48 32 110 69 135 61 40 28 

Total Points 457 492 459 495 474 486 482 526 503 573 478 458 443 

Total Grains 419 431 420 436 425 431:1 450 416 434 438 417 418 415 

Pet. ~latrix tl 12 8 12 lU 10 6 21 14 24 13 9 6 

()* :F:L- 72: 16: 12 78:6: 16 HZ: 5:13 7 3:7:20 73:8:19 76:6:17 61: 14:25 91:0:9 83:0:17 89:0:11 72:3:25 76:4:20 91:0:9 

Qm: F: Lt 17:16:67 21:6:73 23:5:72 27:7:66 26:8:66 17:6:77 16:14:70 33:0:67 42:0:58 33:0:67 16:3:78 10:4:86 19:0:81 

Skip dist. LJ.4 mm 0.5 mm 0.4 mm 0.5 mm 0.4 mm 0.4 mm 0.5 mm 0.3 mm 0.4 mm 0.4 mm 0.4 mm LJ.5 mm u.3 mm 

106 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
A 

og 

OROGEN 

TRANSITIONAL 

RECYCLED 

RECYCLED 

OROGEN 

Lt 

Figure 2. Triangular diagrams showing compositional modes of metagraywacke from phyllite and metagraywacke thrust panel. Q*FLdiagram is equivalent to QFL of Dickinson (1985). Provenance fields from Dickinson (1985). Letters correspond to sample data given in 

table 2 and sample localities on figure 1. See table 2 for explanation of symbols. __......, 

continent-derived quartzose turbidites mainly during 

Devonian time. Compositions of sandstones indicate 

that sediments were derived from granitic, quartzose 

metamorphic, unfoliated sedimentary, and minor 

volcanic sources. The texturally immature sandstones, 

deposited as turbidites, suggest their rapid transport 

and deposition. The unfoliated nature of most clasts 

suggests that the source region was uplifted by 

extensional processes, perhaps by rifting along a 

passive continental margin. 

REFERENCES CITED 

Brosge, W.P. and Reiser, H.N., 1962, Preliminary 

geologic map of the Christian quadrangle, 

Alaska: U.S. Geological Survey Open-File 

Map 62-229, 2 sheets, scale 1:250,000. 

Brosge, W.P., Reiser, H.N., and Yeend, Warren, 

1973, Reconnaissance geologic map of the 

Beaver quadrangle, Alaska: U.S. Geological 

Survey Miscellaneous Field Studies Map MF525, scale 1:250,000. 

Dickinson, W.R., 1985, Interpreting provenance 

relations from detrital modes of sandstone, 

in Zuffa, G.G., ed., Provenance of arenites, 

Proceedings of NATO Advanced Studies 

Institute on reading provenance fro~ 

arenites: Amsterdam, D. Reidel, p. 333-361. 

Dillon, J.T., Brosge, W.P., and Dutro, J.T., 

Jr., 1986, Generalized geologic map of the 

Wiseman quadrangle, Alaska: U.S. Geological 

Survey Open-File Report 86-219, 2 sheets, 

scale 1:250,000. 

Dillon, J.T., and Smiley, C.J., 1984, Clasts 

from the Early Cretaceous Brooks Range 

orogen in Albian to Cenomanian molasse 

deposits of the northern Koyukuk Basin, 

Alaska [ abs.]: Geological Society of 

America, Abstracts with Programs, v. 16, no. 

5, p. 279. 

Gottschalk, R.R., Jr., 1987, Structural and 

petrologic evolution of the Southern Brooks 

Range near Wiseman, Alaska: Houston, Rice 

University, Ph.D. thesis, 263 p. 

Jones, D.L., Coney, P., Harms, T.A., and Dillon, 

J. T., [in press], Interpretive bedrock 

geologic map and supporting radiolarian data 

from the Angayucham terrane, Coldfoot area, 

southern Brooks Range, Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-. 

Nilsen, T.H., and Moore, T.E., 1984, 

Stratigraphic nomenclature for the Upper 

Devonian and lower Mississippian(?) Kanayut 

Conglomerate, Brooks Range, Alaska: U.S. 

Geological Survey Bulletin 1529-A, 64 p. 

Patton, W.W., Jr. and Box, S.E., 1985, Tectonic 

setting and history of the Yukon-Koyukuk 

bas in, Alaska: Eos [American Geophysical 

Union Transactions], v. 66, no. 46, p. 1101. 

Patton, W.W., Jr., Box, S.E., Moll-Stalcup, 

E.J., and Miller, T.P., 198 , Geology of 

west-central Alaska, in Plafke-r, G., Jones, 

D.L., and Berg, H.C., ed., Geology of 

Alaska: Boulder, Colo., Geological Society 

America, The Geology of North America. 

West-Central Alaska 107 
Turner, D.L. 

widespread 

ages in 

[abs.]: 

Abstracts 

338. 

1984, Tectonic implications of 

Cretaceous overprinting of K-Ar 

Alaskan metamorphic terranes 

Geological Society of America 

with Programs, v. 16, no. 5, p. 

Turner, D.L., Forbes, R.B., and Dillon, J.T., 

1979, K-Ar geochronology of the southwestern 

Brooks Range, Alaska: Canadian Journal of 

Earth Sciences, v. 16, p. 1789-1804. 

Reviewers: S.E. Box and S.M. Karl 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

108 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
SOUTHERN ALASKA 

Head of Nenana Glacier, Alaska Range. Photograph by Be la Csejtey. 
Middle Pennsylvanian Plutonic Rocks Along 

the Southern Margin of the Wrangellia Terrane 

By John N. Aleinikoff, George Plafker, and Warren J. Nokleberg 

We present two new U-Pb ages on zircon and 

sphene from granitoid rocks along the southern margin 

of the Wrangellia terrane (Jones and others, 1984). 

These samples were collected in the northern Chugach 

and western Wrangell Mountains as part of geologic 

field studies of the Trans-Alaskan Crustal Transect 

(TACT} program. Our results document previously 

unrecognized Middle Pennsylvanian plutonism in this 

area that may be representative of widespread 

plutonism of the same general age in adjacent regions 

of the Wrangellia and Alexander terranes. 

In our study area (fig. 1}, the Wrangellia 

terrane, which is part of the allochthonous Wrangellia 

microplate (Jones and others, 1984}, is juxtaposed 

along the Taral-West Fork faults against Early Jurassic 

andesitic arc rocks of the Peninsular terrane to the 

west. Along their southern margins, the Wrangellia 

and Peninsular terranes are relatively underthrust on 

the order of 40 km along the Border Ranges fault by 

accreted oceanic rocks (schists of Liberty Creek and 

Iceberg Lake, McHugh Complex, Valdez Group} that 

make up the Chugach terrane (Nokleberg and others, 

1986; Plafker and others, 1985). 

Within the Wrangellia terrane, notable 

differences exist in stratigraphy, plutonism, and 

metamorphism across the Chitina fault system (fig. 1), 

a plexus of Early Cretaceous southwest-dipping thrust 

faults that separate greenschist- to lower amphibolitefacies rocks to the south from relatively 

unmetamorphosed to lower greenschist-facies rocks to 

the north (MacKevett, 1978; Gardner and others, 

1986). The characteristic Upper Triassic sequences of 

the Wrangellia terrane, the Nikolai Greenstone and 

Chitistone Limestone, occur on both sides of the 

fault. These two parts of the Wrangellia terrane are 

herein informally referred to as the northern and 

southern Wrangellia assemblages. 

The northern Wrangellia assemblage consists of 

andesitic rocks (of the Skolai Group) at least as old as 

Middle Pennsylvanian that are overlain by a Lower 

Permian marine sedimentary sequence and a 

distinctive Mesozoic (pre-Middle Jurassic} sequence 

that includes Triassic tholeiitic basalt, carbonate 

rocks, and argillaceous sedimentary rocks of oceanic 

affinities (MacKevett, 1978; Winkler and others, 

1981). The metamorphic rocks are intruded by massive 

to moderately foliated Middle Pennsylvanian syenite 

and monzonite in the eastern Wrangell Mountains and 

by quartz diorite to granite (dominantly tonalite and 

granodiorite) of probable Late Jurassic age. 

The southern Wrangellia assemblage consists of 

penetratively deformed meta-andesite, metagraywacke, metachert, and abundant linear units of 

marble and schistose marble as described by 

MacKevett {1978} and Winkler and others (1981}. This 

assemblage corresponds with the Strelna Formation of 

Moffit (1938}, which is at least in part of Early 

Pennsylvanian age (Plafker and others, 1985}. The 

metamorphic rocks are intruded by gneissic to 

mylonitic plutonic rocks of Middle Pennsylvanian age 

(including those reported on here}, and abundant 

variably foliated plutonic rocks of the Late Jurassic 

Chitina Valley batholith (MacKevett, 1978; Winkler 

and others, 1981). 

The Middle Pennsylvanian metaplutonic rocks 

dated in this study are from the southern Wrangellia 

assemblage (fig. 1}. In the Dadina River area (locality 

of sample 84ANK 069A--hereafter called sample 069}, 

metamorphic rocks that are locally exposed in a 

narrow belt between the late Cenozoic Wrangell Lavas 

and associated hypabyssal intrusive rocks on the east 

and the Quaternary fill of the Copper River basin on 

the west compose the unnamed metamorphic complex 

of Winkler and others (1981). In the Chugach 

Mountains west of the Copper River (locality of 

sample 84ANK 186A--hereafter called sample 186}, 

the southern assemblage is exposed as a large thrust 

sheet remnant that is part of the Haley Creek terrane 

of Winkler and others (1981}. In both areas, 

metagranodiorite and metagranite compose a 

relatively minor part of the generally more mafic 

metaplutonic suites. However, mapping was not 

sufficiently detailed to determine the areal 

distribution of these plutons or their relationship to 

the country rocks. 

The dated samples are blastomylonitic to 

gneissic metagranodiorite. Sample 069 contains about 

35 percent plagioclase, 33 percent quartz, 17 percent 

potassic feldspar, 12 percent biotite, and 3 percent 

combined epidote, sphene, and iron oxides. Sample 186 

contains about 45 percent plagioclase, 30 percent 

quartz, 15 percent potassic feldspar, and 10 percent 

epidote with < 1 percent hornblende altered to epidote, 

and accessory tourmaline, sphene, and stilpnomelane. 

Geochemically, the two samples are remarkably 

similar; they are calc-alkalic with strong enrichment 

of light relative to heavy rare-earth elements (Plafker 

and others, 1988}. 

Six size fractions of zircon and one fraction of 

sphene were analyzed from each sample. Zircons from 

sample 069 are euhedral, clear to light brown, and 

stubby (length-to-width ratio of 1-3); zircons from 

sample 186 are medium to dark brown, euhedral with 

some rounded tips, and stubby (length-to-width ratio of 

110 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
1-3). The color difference of the two samples is 

probably due to uranium content. The darker zircons 

contain about twice as much uranium as the lighter 

zircons (table 1). 

Isotopic data (fig. 2) from both samples yield 

well-defined linear arrays with concordia intercept 

ages of 310 ± 29 and 91 ± 87 Ma (sample 069) and 309 ± 

11 and 101 ± 70 Ma (sample 186). The coarsest size 

fraction (+ 150 mesh) has been omitted from each 

regression because they plot off the discordias in 

excess of analytical error, suggesting a minor amount 

of inherited radiogenic lead in these large zircons. 

Sphene from sample 069 is concordant at about 150 

Ma; sphene from 186 has an age of about 200-220 Ma. 

Figure 1. Locations of dated Middle Pennsylvanian metaplutonic 

rocks (black squares) relative to terranes, major geologic units, 

and structural features in part of the eastern Wrangell 

Mountains, northern Chugach Mountains, and Copper River 

basin. Map units: 1, southern Wrangellia assemblage; 2, 

The Middle Pennsylvanian metaplutonic rocks 

in the southern Wrangellia assemblage are recognized 

in this study as a discrete plutonic suite that predates 

the dominantly Late Jurassic plutonism in these same 

areas. The influence of the Jurassic reheating is 

evident from the 150-Ma age of sphene in sample 

069. The somewhat older sphene from sample 186 may 

reflect another thermal event. Alternatively, the 

difference in the sphene ages may be due to 

differential uplift, whereby the sample from the 

northern Chugach Mountains passed through the 

closure temcr.erature for the U-Pb system in sphene 

(about 550 C) about 50 m.y. earlier than the sample 

from the Dadina River area. We are unable to 

northern Wrangellia assemblage; 3, Peninsular terrane; 4, 

Chugach terrane; 5, unconsolidated deposits. Geology 

generalized from MacKevett (1978), Winkler and others (1981 ), 

Nokleberg and others (1986), Plafker and others (1985), and 

Plafker (unpub. data). 

Southern Alaska 111 
Table 1. U-Th-Pb concentration and isotopic composition data from zircon and sphene from metaplutonic rocks of southern Wrangellia 

assemblage 

[Leaders(---) mean not determined. Constants: 2351.. = 9.8485 E-10/yr; 23~ 1.55125 E-10/yr; 232~..= 4.9475 E-11/yr; 238ut235u = 137.88 (Steiger and J~ger, 1977)) 

Sample and Weight Concentration Pb composition1 Ages (Ma) fraction (mg) (ppm) 206pb 206Pb 206Pb 206Pb 2o7Pb zo7Pb 20sPb 

u Th Pb 20Ltpb 207Pb 208pb 2380 2350 206pb 232Th 

84ANK 069A 

(+150) 14.90 756.7 31.81 34870 18.930 9.8236 267 271 303 

(-150+200)NMD 14.95 680.0 28.42 11300 18.672 10.318 266 269 297 

(-200+250)NMD 15.70 679.1 27.60 4213 17.972 10.012 257 261 293 

(-250+325)NMD 15. 11 702.9 28.66 53140 19.088 10.592 262 265 290 

(-325)NMD 15.01 817.0 32.38 11450 18. 711 10.278 253 257 293 

(-325)Hag 14.33 752.7 29.44 138700 19.153 10.648 251 25:; 290 

sphene 18.56 353.4 282.1 10.51 510.9 12.899 3.1246 151 151 143 147 

84ANK186A 

(+150)NM 7.21 1475 71.10 2134.6 16.826 5.8123 284 287 310 

(-150+200)NMD2 2.21 1448 71.28 3001.8 17.435 5.9885 293 294 306 

(-150+200)NMA 3.16 1498 77.69 1811.2 16.524 5.299 301 301 304 

(-200+250)NMD 11.39 1634 77.26 1921.3 16.668 5.9794 280 282 302 

(-250+325)NMD 3.46 1619 75.33 2170.5 16.943 6.0799 277 279 297 

(-400)NMD 11.39 1975 91.25 1557.4 16.227 6.1461 273 276 295 

sphene 31.27 256.4 65.49 10.92 196.2 7.9748 3.4899 201 203 221 246 

1 Blank and fractionation corrected. Common lead corrections use values for 310-Ma lead 

2 

from Stacey and Kramers (1975). Chemical extractions methods modified from Krogh (1973). 

Abraded. 

distinguish between these two hypotheses: if the latter 

is true, then the ages of the sphenes are only 

constrained to pre-200 Ma. The lower intercepts of 

the zircon data suggest a poorly constrained 

Cretaceous disturbance to the U-Pb systematics. 

However, because of the large uncertainties, the lower 

intercept ages may be as old as the 150-Ma sphene. 

Thus, the U-Pb isotopic information obtained in this 

study indicates intrusion of a suite of Middle 

Pennsylvanian plutons followed by heating in the Early 

Jurassic(?), Late Jurassic, and Cretaceous(?). 

Middle Pennsylvanian metaplutonic rocks may 

be part of a belt of lithologically variable plutonic 

rocks of the same age that is widely exposed in the 

Wrangellia and adjacent Alexander terranes to the east 

in Alaska and Canada. Possibly correlative suites 

within the southern assemblage are: (1) parts or all of 

the undated gabbro and orthogneiss complex of 

MacKevett (1978) within the McCarthy area and (2) 

undated metaplutonic rocks in the metamorphic 

complex of the Gulkana River along the northern 

margin of the Copper River basin (Nokleberg and 

others, 1986). Possibly correlative suites within the 

northern assemblage are: (1) the monzonitic-granitic 

complex (MacKevett, 1978), dated with U-Pb on zircon 

at 308 ± 8 Ma (Gardner and others, in press), that 

extends from the Wrangellia terrane into the 

Alexander terrane in the eastern Wrangell Mountains 

and adjacent parts of Canada ("Icefield Ranges 

plutonic suite" of Campbell and Dodds, 1985), and (2) a 

diorite-gabbro-tonalite-anorthosite suite in the eastern 

Alaska Range that has yielded four U-Pb ages on 

zircon of 290 to 316 Ma (Barker and Stern, 1986). As 

noted by Barker and Stern (1986), the close association 

:::::J 

CD 

(T) 

(\J 

0.048 

~ 0. 044 

a.. 

CD 

0 

(\J 

0 84ANK 186A 

SPHENE • 200-220 Ma 

0 84ANK 069A 

SPHENE • 150 Ma 

0 0 

• 

INTERCEPTS AT 

309 ± 11 and 101 ± 70 Ma 

CMSWD=3.1) 

310±29 and 91±87 Ma 

CMS!-10=2.5) 

Figure 2. Concordia plot of U-Pb data from zircon from 

metagranodiorite samples 069 and 186. Solid black symbols 

denote values not used in regression calculation. 

in time and space of Middle Pennsylvanian plutonism 

with the lower part of the late Paleozoic andesitic 

rocks of the Skolai Group suggests that at least some 

of these plutonic rocks represent shallow to 

intermediate levels of the Pennsylvanian Skolai 

magmatic arc. Their widespread distribution indicates 

that Middle Pennsylvanian plutonic rocks and the 

metamorphic country rocks that they intrude may 

constitute the basement for much of the Wrangellia 

terrane in Alaska. 

112 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
REFERENCES CITED 

Barker, Fred and Stern, T.W., 1986, An arc-root 

complex of Wrangellia, eastern Alaska Range 

[abs.]: Geological Society of America 

Abstracts with Programs, v. 18, no. 6, p. 

534. 

Campbell, R.B., and Dodds, C.J., 1985, Geology 

of the Mount St. Elias map area (115B and C 

(E1/2)): Canadian Geological Survey Openfile 830, 2 sheets, scale 1:125,000. 

Gardner, M.C., MacKevett, E.M., and McClelland, 

W.D., 1986, The Chitina fault system of 

southern Alaska--An Early Cretaceous 

collisional suture zone [abs.]: Geological 

Society of America Abstracts with Programs, 

v. 18, no. 2, p. 108. 

Gardner, M.C., Bergman, S.C., MacKevett, E.M., 

Jr., Plafker, George, Campbell, R.C., 

Cushing, G.W., Dodds, C.J., McClelland, 

W.D., and Mueller, P.A., 1988, Middle 

Pennsylvanian pluton stitching of Wrangellia 

and the Alexander terrane, Wrangell 

Mountains, Alaska: Geology, [in press]. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1984, Lithotectonic terrane 

map of Alaska (west of the !41st meridian), 

in Silberling, N.J., and Jones, D.L., eds., 

Lithotectonic terrane maps of the North 

American cordillera: U.S. Geological Survey 

Miscellaneous Field Studies Map 1874-A, 

scale 1:2,500,000. 

Krogh, T.E., 1973, A low-contamination method 

for hydrothermal decomposition of zircon and 

extraction of U and Pb for isotopic age 

determinations: Geochimica et Cosmochimica 

Acta, v. 37, p. 485-494. 

MacKevett, E.M., Jr., 1978, Geologic map of the 

McCarthy quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous 

Investigations Series Map I-1032, scale 

1:250,000. 

Moffit, F.H., 1938, Geology of the Chitina 

Valley and adjacent area, Alaska: U.S. 

Geological Survey Bulletin 894, 137 p. 

Nokleberg, W.J., Wade, W.M., Lange, I.M., and 

Plafker, George, 1986, Summary of geology of 

the Peninsular terrane, metamorphic complex 

of Gulkana River, and Wrangellia terrane, 

north-central and northwestern Gulkana 

quadrangle, in Bartsch-Winkler, Susan, and 

Reed, Katherine, eds., Geologic studies in 

Alaska by the U. S. Geological Survey during 

1985: U.S. Geological Survey Circular 978, 

P• 69-74. 

Plafker, George, Nokleberg, W.J., and Lull, 

J. S. , 1985, Summary of the 1984 TACT 

geologic studies in the northern Chugach 

Mountains and southern Copper River bas in, 

in Bartsch-Winkler, Susan, ed., The U.S. 

Geological Survey in Alaska: 

Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 76-79. 

1988, Bedrock geology and tectonic 

evolution of the Wrangellia, Peninsular, and 

Chugach terranes along the Trans-Alaskan 

Crustal Transect in the northern Chugach 

Mountains and southern Copper River basin, 

Alaska: Journal of Geophysical Research, 

[in press]. 

Stacey, J.S. and Kramers, J.D., 1975, 

Approximation of terrestrial lead isotope 

evolution by a two-stage model: Earth and 

Planetary Sciences Letters, v. 26, p. 207-

221. 

Steiger, R.H. and Jager, E., 1977, Subcommission 

on Geochronology: Convention on the use of 

decay constants in geo- and 

cosmochronology: Earth and Planetary 

Sciences Letters, v. 36, p. 359-362. 

Winkler, G.R., Silberman, M.L., Grantz, Arthur, 

Miller, R.J., and MacKevett, E.M., Jr., 

1981, Geologic map and summary geochronology 

of the Valdez quadrangle, southern Alaska: 

U.S. Geological Survey Open-File Report 80-

892-A,, 2 sheets, scale 1:250,000. 

Reviewers: G.R. Winkler and F. Barker 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southern Alaska 113 
Source of the Sanford Volcanic Debris Flow, 

South-Central Alaska 

By Donald H. Richter, Henry R. Schmoll, and Dana J. Bove 

The Sanford volcanic debris flow occurs in a 

thick sequence of Pleistocene glaciolacustrine, glacial, 

and fluvial deposits in the center of the Copper River 

basin along the northwest flank of the Wrangell 

Mountains, which are dominated by Pleistocene 

volcanoes (fig. 1). This extensive volcanic debris flow 

was first described by Ferrians and others (1958), who 

referred to it as the Sanford volcanic mudflow, after 

exposures along the Copper River at the mouth of the 

Sanford River. They suggested that debris flowed 

more than 50 km down the ancestral Sanford and 

Copper River valleys from the large amphitheater on 

the southwest face of Mount Sanford (4,949 m) at the 

head of Sanford Glacier in the Wrangell Mountains. 

Nichols and Yehle (1985) described the debris flow in 

more detail and reiterated that the likely source area 

was the amphitheater on Mount Sanford. They further 

suggested that both the amphitheater and the debris 

flow were the result of a lateral-blast eruption, 

possibly similar to the 1980 eruption of Mount St. 

Helens. 

During the course of geologic investigations in 

the western Wrangell Mountains in the summer of 

1987, we discovered that the source of the Sanford 

volcanic debris flow is probably a collapsed dacite 

dome on the east flank of Mount Drum (3,661 m). This 

note briefly describes the debris flow and its source, 

and speculates on its origin. Although we disagree 

with Nichols and Yehle as to the source of the debris 

flow, we are indebted to them for their detailed 

descriptions of the physical characteristics of the 

flow, and we base the descriptions that follow mainly 

on theirs. We did not observe the debris flow near the 

village of Chistochina (fig. 1), where a questionable 

occurrence was noted by Nichols and Yehle (1985). 

The Sanford volcanic debris flow is exposed 

discontinuously at elevations between 350 and 615 m in 

bluffs along the Copper and lower Sanford Rivers (fig. 

1). Near the confluence of the Sanford and Copper 

Rivers, the debris flow is 1 to 6 m thick and forms a 

conspicuous pink bed about 20 m above river level in 

the 150-m-high bluffs (O.J. Ferrians, Jr., and H.R. 

Schmoll, U.S. Geological Survey, written commun., 

1957). It conformably overlies fluvial gravel and is 

disconformably overlain by similar fluvial gravel. This 

stratigraphic association with fluvial gravel indicates 

that the debris flow was emplaced during a nonglacial 

interval, when glacier ice was confined to the higher 

parts of the Wrangell Mountains as it is today. Two 

sequences of mainly glaciolacustrine deposits that 

overlie the gravel indicate that at least two major 

episodes of glaciation occurred subsequently (Ferrians 

and others, 1983, p. 151). The debris-flow deposit is 

weakly indurated and consists dominantly of angular to 

subrounded volcanic clasts, as large as 3 m in diameter 

but commonly 8 to 15 em, in a matrix of silt and 

sand. No sorting or bedding is evident. Rounded 

cobbles of nonvolcanic rock that were probably 

entrained during flowage are present locally. The 

volcanic clasts in the debris flow are nearly all pink 

and gray porphyritic dacite of similar mineralogy. 

They contain about 10 to 20 percent phenocrysts, 1 to 

3 mm long, consisting chiefly of plagioclase and 

hornblende and minor, but characteristic, green 

pyroxene. The gray-colored varieties generally exhibit 

glassy groundmasses; the darker gray rocks are the 

most glass rich. All clasts are coated by a thin layer 

of fine-grained pink matrix material that imparts an 

overall pinkish cast to the deposit. 

The apparent source of the Sanford volcanic 

debris flow is a collapsed dacite dome at an elevation 

of about 1,900 m on the east flank of Mount Drum (fig. 

1). The dome was probably similar to, and is arcuately 

aligned with, the series of dacite domes associated 

with the second cycle of Mount Drum conebuilding 

about 200,000 to 300,000 years ago (Richter and 

others, 1979). The collapsed dome is now a massive 

pile of dacite rubble, approximately 3.2 km long by 2.4 

km wide and more than 200 m thick, that consists of 

pink and gray, angular to subrounded blocks of dacite 

in a matrix of pink silt to sand. Individual blocks are 

up to tens of meters in diameter, but most probably 

average less than one meter. Lithologically, the 

remnant dome is a coarse-grained replica of the 

debris-flow deposits exposed more than 50 km away. 

The dacite from the dome is megascopically identical 

to the dacites in the debris flow, containing 10 to 30 

percent phenocrysts of plagioclase and hornblende and 

minor green pyroxene. 

Large boulders of pink dacite occur scattered 

over volcanic bedrock in at least two known areas in 

the general vicinity of the dome, a small one 5 km 

north of the dome at an elevation of 1,370 m, and a 

larger one 5 km east of the dome at an elevation of 

1,580 m (fig. 1). The boulders, especially those in the 

eastern occurrence, may represent either shorter 

debris flows or lag deposits remaining after passage of 

the principal debris flow. 

Lack of observable volcanic bombs, pumice 

blocks, or scoria in the debris-flow deposits or at the 

collapsed dome suggests that the dome was mature and 

probably contained very little juvenile magma when it 

was destroyed. Destruction therefore may have been 

the result either of a large phreatic explosion caused 

114 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
by entry of glacial meltwater into a near-surface 

subvolcanic heat reservoir, or possibly of a 

combination of phreatic and renewed magmatic 

activity. In either case, the explosion-eruption could 

have formed a vertical debris column which then 

collapsed to form the rubble dome and the debris 

flow. Mobility of the debris flow may have been 

enhanced by cascading down steep mountain flanks 

into the Sanford valley of which at least the upvalley 

part was glacier-filled. Based on the size and 

geometry of other domes in the Mount Drum ringdome complex, the dome flay have had an original 

volume of 4 to 6 km which upon collapsing 

contributed as much as 2 km3 to the debris flow. 

The dome is located outside of the boundaries 

of well-developed lateral moraines that border and 

extend downvalley from Sanford Glacier and that we 

attribute to at least two major episodes of glaciation. 

No evidence of the Sanford volcanic debris flow is 

found within the boundaries of these moraines, 

suggesting that the debris flow is older. Evidence of 

older glaciations, found elsewhere on the slopes of the 

Wrangell Mountains, is absent in the vicinity of the 

dome, perhaps obliterated by events associated with 

145°00' 

MAP LOCATION 

62°30' 

62°00' '-----~--

dome collapse. These relationships, which suggest that 

the collapse occurred prior to at least two major 

episodes of glaciation and subsequent to earlier, more 

extensive, glaciations, are compatible with the 

stratigraphic position of the Sanford volcanic debris 

flow in exposures along the Copper River. The Sanford 

volcanic debris flow, already useful as a stratigraphic 

marker in the central Copper River basin, thus may 

become a much-needed means of correlating between 

the stratigraphy of the central basin and the moraines 

of the basin margin as well. 

Outcrops within the the amphitheater at the 

head of the Sanford Glacier (fig. 1), the area 

previously considered to be the source of the Sanford 

volcanic debris flow, are nearly inaccessible because 

of the spectacular 2,900-m-high amphitheater wall. A 

helicopter reconnaissance revealed that the wall is 

composed principally of medium to thick lava flows, 

flow breccias, mudflows, and vent(?) breccias, all 

probably of andesitic composition, cut by dark-colored 

dikes and small irregular intrusive masses. Near the 

top of the wall, a laccolith or mushroom-shaped dome 

is separated from the underlying flow sequence by as 

much as 100 m of thin-bedded pyroclastic rocks or lava 

144°00' 

Figure 1. Location of principal exposures of Sanford volcanic debris flow (heavy stipple pattern) and 

collapsed dacite dome (heavy ruled pattern) believed to be its source. light ruled pattern, areas of large 

dacite boulders; light stipple pattern, glaciers and icefields. Contour interval 1,200 m. 

Southem Alaska 115 
flows. Because the amphitheater wall exhibits a 

diverse assemblage of volcanic rocks, it is not a likely 

source of the much more nearly monolithologic 

Sanford volcanic debris flow. 

REFERENCES CITED 

Ferrians, O.J, Jr., Nichols, D.R., and Schmoll, 

H.R., 1958, Pleistocene volcanic mudflow in 

the Copper River basin, Alaska [abs.]: 

Geological Society of America Bulletin, v. 

69, no. 12, pt. 2, p. 1563. 

Ferrians, O.J., Jr., Nichols, D.R., and 

Williams, J.R., 1983, Copper River basin, in 

P~w~, T.L., and Reger, R.D, eds., Guidebook 

to permafrost and Quaternary geology along 

the Richardson and Glenn Highways between 

Fairbanks and Anchorage, Alaska. 

International Conference on Permafrost, 4th, 

1983: Alaska Division of Geological and 

Geophysical Surveys Guidebook 1, p. 137-175. 

Nichols, D.R., and Yehle, L.A., 1985, Volcanic 

debris flows, Copper River basin, Alaska, in 

Committee for International Exchange of 

Landslide Technique, eds., International 

Conference and Field Workshop on Landslides, 

Proceedings, Fourth: Tokyo, The Japan 

Landslide Society, p. 365-372. 

Richter, D.H., Smith, R.L., Yehle, L.A., and 

Miller, T.P., 1979, Geologic map of the 

Gulkana A-2 quadrangle, Alaska: U.S. 

Geological Survey Geologic Quadrangle Map 

GQ-1520, scale 1:63,360. 

Reviewers: J.C. Ratt~ and L.A. Yehle 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

116 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Hydrocarbon Source Potential and Thermal Maturity of the 

Sanctuary Formation (Middle Miocene), Northern Foothills 

of the Alaska Range 

By Richard G. Stanley 

The middle Miocene Sanctuary Formation, part 

of the Usibelli Group (Wahrhaftig, 1987), crops out 

sporadically in the Nenana coal field of the northern 

foothills of the Alaska Range (fig. 1). The Sanctuary 

Formation is locally as much as 100 m thick and 

consists mainly of mudrocks and fine sandstone that 

accumulated in a large shallow lake (Wahrhaftig and 

others, 1969). Worldwide experience indicates that 

lakebed sediments can be prolific petroleum source 

rocks (Fouch and Dean, 1982; Tissot and Welte, 1984). 

With this in mind, 21 samples of mudrocks were 

collected from six outcrops of the Sanctuary 

Formation (fig. 1) and analyzed using Rock-Eval 

pyrolysis, vitrinite reflectance, and thermal alteration 

index. The results, discussed below, suggest that 

Sanctuary mudrocks are potential sources of gas and 

are thermally immature to marginally mature with 

respect to the oil-generative zone. 

Rock samples were collected from exposures in 

road cuts, stream cuts, headwalls of landslides, and 

landslide deposits. The samples were taken about 10 

to 30 em back from the outcrop faces in order to 

obtain the freshest available material. Splits of the 

samples were analyzed using Rock-Eval pyrolysis by 

T.A. Daws (U.S. Geological Survey, Denver, Colo.), 

vitrinite reflectance by M.J. Pawlewicz (U.S. 

Geological Survey, Denver, Colo.), and thermal 

alteration index by Hideyo Haga (Micropaleo 

Consultants, Inc., San Diego, Calif.). 

Rock-Eval pyrolysis is a widely used method of 

rapidly evaluating the quality and thermal maturity of 

prospective petroleum source rocks (see, for example, 

Tissot and Welte, 1984). Pulverized samgles of rock 

are gradually heated from 300 °C to 550 C at 25 °C 

per minute in an oxygen-free atmosphere, causing the 

release of water, carbon dioxide, and hydrocarbons 

from the rock. Several parameters are measured by 

the Rock-Eval apparatus (table 1). The quantity S1 is 

the amount of hydrocarbons (HC), measured in 

milligrams HC per gram of rock, that is released upon 

initial heating to about 300 °C; this quantity includes 

the oil and gas already present in the rock. The 

quantity S2 (also measured in milligrams HC per gram 

of rock) is the amount of hydrocarbons generated by 

pyrolytic degradation of the remaining organic matter 

in the rock, and is an indicator of the potential of the 

rock to generate additional oil and gas. Tmax is the 

temperature--generally about 400 °C to 500 °C--at 

which S2 is at a maximum, and is an indicator of 

thermal maturity. S3 is the amount of carbon dioxide 

(in mg C02 per gram of rock) generated during 

pyrolysis, and is thought to be related to the amount of 

oxygen in the pyrolyzed organic matter. Additional 

Rock-Eval parameters include the total organic carbon 

(TOC) in weight percent; the hydrogen index (HI), 

defined as the product of 100 times (S2/TOC); and the 

oxygen index (01), defined as the product of 100 times 

(S3/TOC). 

Vitrinite reflectance (Ro) and thermal 

alteration index (T AI) are common methods of 

assessing thermal maturity. Vitrinite reflectance is 

determined by measuring the percentage of light 

reflected by vitrinite, a type of kerogen formed from 

terrestrial plant material. Thermal alteration index 

(TAl) is obtained by examining the colors of pollen 

grains and other organic particles in transmitted light 

under the microscope (Tissot and Welte, 1984; Waples, 

1985). 

Analytic results from the Sanctuary Formation 

are shown in table 1. All but 5 of the 21 samples have 

total organic carbon (TOC) greater than 0.5 percent, 

which is generally regarded as the lower limit for 

potential petroleum source rocks (Tissot and Welte, 

1984). Thirteen of the 21 samples have TOC greater 

MIDDLE 

TANANA 

BASIN 

STUDY 

AREA ALASKA RANGE 

c 

EXPLANATION 

e sample locality .& settlement 

Figure 1. Sample localities in the Sanctuary Formation. Inset 

shows outlines of middle Tanana basin (Miller and others, 1959) 

and Nenana coal field (Merritt and Hawley, 1986). A, 

Suntrana area; B, Sanderson Creek area; C, California Creek; D, 

Sanctuary River; E, Teklanika River area; F, Sushana River area. 

Southern Alaska 117 
Table 1. Rock-Eva!, vitrinite reflectance (Ro), and thermal alteration index (TAl) data from the Sanctuary Formation 

[Rock-Eval parameters (TOC, HI, 01, and so forth) are discussed in the text. See figure 1 for sample locations. NA, not available or not applicable. Tmax values for samples 

with 52 less than 0.2 were rejected because they are probably unreliable (Peters, 1986)] 

Sample Sample S1 S2 S3 

No. weight (mg HC/ (mg HC/ (mg co2; S1 S2/S3 TOC HI OI Tmax Median TAl 

(mg) g rock) g rock) g rock) S1+S2 (wt. pet) (oC) Ro (%) 

A. Suntrana area (road cuts), lat 63°51'24"N., long 148°50'24"W. 

A1 106.5 0.0 0.83 2.62 0.0 0.31 2.19 37 119 439 0.32 2.3 

A2 113.7 .o .74 2.25 .o .32 1.62 45 138 433 .33 2.3 

A3 115.1 .o .91 2.64 .o .34 1.84 49 143 433 .30 2.3-2.5 

A4 132.3 .o .47 3.86 .0 .12 1.01 46 382 428 .34 2.3-2.5 

AS 144.8 .o .33 3.97 .o .08 .91 36 436 425 .37 2.3-2.5 

A6 95.8 .02 .83 8.68 .02 .09 1.40 59 620 434 .33 2.0-2.3 

B. Sanderson Creek area (road cut), lat 63°55'00"N, long 148°41 '44"W. 

B1 179.9 0.01 0.18 1.55 0.06 0.11 0.48 37 322 NA 0.27 2.3 

B2 195.1 .o .11 1.53 .o .07 .43 25 355 NA .29 2.3 

B3 174.4 .o .14 2.84 .o .04 .63 22 450 NA .27 2.3 

C. California Creek (stream cut) lat 64°06'06"N., long 148°44'00"W. 

C1 158.0 0.0 0.62 8.30 0.0 0.07 1.47 42 564 412 0.31 2.0-2.3 

C2 132.0 .16 10.42 2.54 .02 4.10 3.59 290 70 416 .32 2.0-2.3 

C3 171.3 .02 3.12 8.03 .01 .38 2.16 144 371 407 .34 2.3-2.5 

C4 244.5 .o .56 38.74 .o .01 .39 143 9933 448 NA 2.3-2.5 

C5 154.2 .07 5.03 4.46 .01 1.12 2.67 188 167 407 .36 2.3-2.5 

D. Sanctuary River (stream cuts), lat 63°47'34"N., long 149°30'24"W. 

D1 184.7 0.0 0.31 3.98 0.0 0.07 1.10 28 361 427 0.28 2.0-2.3 

D2 189.2 .o .32 2.28 .o .14 1.03 31 221 429 .28 2.0-2.3 

D3 138.6 .0 .36 5.07 .o .07 1.01 35 501 423 .30 2.0-2.3 

E. Teklanika River area (headwall scarp of landslide) , lat 63°45'58"N., long 149°36'06"W. 

E1 175.1 0.0 0.06 2.10 0.0 0.02 0.45 13 466 NA NA 2.0-2.3 

E2 159.2 .o .27 3.61 .o .07 1.08 25 334 423 0.31 2.3 

E3 169.3 .0 .12 1.84 .o .06 .62 19 296 NA NA 2.0-2.3 

F. Sushana River area (landslide deposit), lat 63°44'24"N., long 149°42'18"W. 

F1 136.8 0.0 0.0 0.40 0.0 

than 1.0 percent, and therefore show good to very good 

generative potential, according to table 1 of Peters 

(1986). TOC can be significantly reduced by outcrop 

weathering (Leythaeuser, 1973; Clayton and Swetland, 

1978; Stanley, 1987); therefore, the TOC results from 

the Sanctuary outcrops (table 1) should be regarded as 

minimum values. 

The relatively high TOC values of the Sanctuary 

samples contrast with the generally low values of S1 

and S2 (table 1). All of the Sanctuary samples exhibit 

S1 less than 0.5, and all but three samples have S2 less 

than 2.5, suggesting poor generative potential by 

comparison with table 1 of Peters (1986). The reasons 

for the generally low S1 and S2 are unclear but may be 

related to (1) surface weathering of the sampled 

outcrops, (2) initially poor generative potential due to 

a large proportion of woody (humic) and oxidized 

o.o 0.05 0 800 NA NA 2.3-2.5 

(inertinitic) kerogens, and (3) adsorption on clay 

minerals of the hydrocarbons produced during pyrolysis 

(Peters, 1986; Stanley, 1987). 

The Sanctuary samples (table 1 and fig. 2) 

exhibit relatively low hydrogen indices (HI) and 

anomalously high oxygen indices (01). Nineteen of the 

21 samples have HI values less than 150, which 

indicates that these rocks are "gas-prone," or capable 

of generating gas but little or no oil (see table 2 of 

Peters, 1986). Samples C2 and C5 (table 1) have HI 

values of 290 and 188, respectively, and therefore are 

capable of generating oil in addition to gas. The 

generally low values of HI probably reflect the 

predominantly woody (humic) origin of the organic 

matter in the samples; this interpretation is supported 

by the abundant occurrence of terrestrial plant 

fragments in the sampled outcrops. Other possible 

118 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
causes of low HI include (1) oxidation of organic 

matter during sedimentation, diagenesis, and outcrop 

weathering, and (2) adsorption of hydrocarbons onto 

clay minerals during pyrolysis (Peters, 1986). 

Seventeen of the 21 Sanctuary samples have 

oxygen index (OI) values greater than 150 (table 1 and 

fig. 2); such values are unusually high (Katz, 1983). 

Elevated values of OI can be caused by (1) oxidation of 

organic matter in the samples by outcrop weathering 

(Peters, 1986; Stanley, 1987); and (2) generation of 

carbon dioxide during pyrolysis by thermal degradation 

of carbonate minerals such as calcite, dolomite, and 

siderite (Katz, 1983; Peters, 1986). Either or both of 

these problems may have affected the Sanctuary data, 

because the samples were collected from surface 

exposures susceptible to weathering, and because the 

samples were not treated with acid to remove 

carbonate before pyrolysis. 

The Sanctuary samples exhibit relatively low 

vitrinite reflectance (percent Ro range from 0.27 to 

0.37), thermal alteration index (TAl range from 2.0 to 

2.5), and Tmax (range from 407 to 448 °C). These 

results indicate that the Sanctuary rocks are thermally 

immature to marginally mature with respect to the 

oil-generative zone (fig. 3). 

In conclusion, limited data from outcrop 

samples suggest that mudrocks in the Sanctuary 

Formation are gas-prone and thermally immature to 

marginally mature. These preliminary interpretations 

should be tested by further research, including 

elemental analysis and microscopic examination of 

organic matter. Speculatively, lacustrine strata 

similar to the Sanctuary may occur in the subsurface 

in the middle Tanana basin and other Tertiary 

sedimentary basins in central Alaska (Miller and 

others, 1959), and may have generated significant 

amounts of hydrocarbons. 

600 EXPLANATION 

Sanctuary Formation sample localities: 

e Suntrana area 

E 450 0 Sanderson Creek area 

& California Creek X 

(j) 

"'0 

c £:, Sanctuary River 

- 300 c • Teklanika River area 

(j) 

OJ 

0 

u ::t 150 Type Ill'>... • 

~~ype/V£:, • o~--~----~10~0----~~~20~0----L---~----~---~400 

Oxygen Index (OJ) 

Figure 2. Modified van Krevelen diagram (Peters, 1986) 

showing idealized kerogen types (solid lines) and results from 

13 of 21 samples analyzed from the Sanctuary Formation (table 

1 ). In eight additional samples not shown in this diagram, 01 

values exceed 400 and HI values are less than 150. Type I 

and Type II kerogens are oil-prone while Type Ill kerogens are 

gas-prone. Interpretation of Type IV kerogens is controversial; 

they are variously regarded as oil-prone, gas-prone, or inert 

(Smyth, 1983; Peters, 1986). 

Coal Rank 

PEAT 

Rock-Eval 

Tmax (°C) 

Vitrinite 

Reflectance 

(%Ro) 

Thermal 

Alteration 

Index 

(TAl) 

L/Gs"J~~ & ·:·:·:·:·:·:·:·:·:·:·:·:·:·:·.1 ~ .~ ~! .~ .~.E::·:·:·:·:·:·:·:·:·:·:·:·:·:· r---B_IT_U_M_I_N_O_U_s---r:..:....:·:·:·~·~~~·~·~§·:·:·f:·:·:··b·_'~·~6~f··:·:·:1·:·:·:·~·~6·:~·:·i·:::::: 

OIL-GENERATIVE ZONE 

(OIL WINDOW) 

BITUMINOUS -465-475 -t- 1.2-1.4 -t- 2.9-3.5-

WET-GAS GENERATIVE ZONE 

1-------+- 495-500-+- 1.9-2.0-+- 3.3-3.8-

SEMIANTHRACITE POST-MATURE 

& (DRY-GAS GENERATIVE ZONE) 

ANTHRACITE 1\ I 1---------i------+--4.0 4.0-

METAANTHRACITE 

LOW-GRADE METAMORPHIC 

(BARREN) 

I I 

Figure 3. Organic geochemical parameters and levels of 

thermal maturation, compiled from several sources by 

Stanley (1987). Stippled area shows approximate range of 

data from the Sanctuary Formation (table 1 ). 

REFERENCES CITED 

Clayton, J.L., and Swetland, P.J., 1978, 

Subaerial weathering of sedimentary organic 

matter: Geochimica et Cosmochimica Acta, v. 

42, no. 2, p. 305-312. 

Fouch, T.D., and Dean, W.E., 1982, Lacustrine 

and associated clastic depositional 

environments, in Scholle, P.A., and 

Spearing, Darwin, eds., Sandstone 

depositional environments: American 

Association of Petroleum Geologists Memoir 

31, P• 87-114. 

Katz, B.J., 1983, Limitations of "Rock-Eval" 

pyrolysis for typing organic matter: 

Orgapic Geochemistry, v. 4, no. 3/4, p. 195-

199. 

Leythaeuser, Detlev, 1973, Effects of weathering 

on organic matter in shales: Geochimica et 

Cosmochimica Acta, v. 37, no. 1, p. 113-120. 

Merritt, R.D., and Hawley, C.C., 1986, Map of 

Alaska's coal resources: Alaska Division of 

Mining and Geological and Geophysical 

Surveys Special Report 37, scale 

1:2,500,000. 

Miller, D.J., Payne, T.G., and Gryc, George, 

1959, Geology of possible petroleum 

provinces in Alaska: U.S. Geological Survey 

Bulletin 1094, 131 p. 

Peters, K.E., 1986, Guidelines for evaluating 

petroleum source rock using programmed 

pyrolysis: American Association of 

Petroleum Geologists Bulletin, v. 70, no. 3, 

p. 318-329. 

Southern Alaska 119 
Smyth, Michelle, 1983, Nature of source material 

for hydrocarbons in Cooper basin, Australia: 

American Association of Petroleum Geologists 

Bulletin, v. 67, no. 9, p. 1422-1428. 

Stanley, R.G., 1987, Effects of weathering on 

petroleum-source evaluation of coals from 

the Suntrana Formation near Healy, Alaska, 

in Hamilton, T.D., and Galloway, J.P., eds., 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1986: U.S. 

Geological Survey Circular 998, p. 99-103. 

Tissot, B.P., and Welte, D.H., 1984, Petroleum 

formation and occurrence [2nd ed.]: Berlin, 

Springer-Verlag, 699 p. 

Wahrhaftig, Clyde, 1987, The Cenozoic section at 

Suntrana, Alaska, in Hill, M.L., ed., 

Geological Society oT America, Cordilleran 

Section, Centennial Guide, v. 1, p. 445-450. 

Wahrhaftig, Clyde, Wolfe, J.A., Leopold, E.B., 

and Lanphere, M.A., 1969, The coal-bearing 

group in the Nenana coal field, Alaska: 

U.S. Geological Survey Bulletin 1274-D, 30 

P• 

Waples, D.W., 1985, Geochemistry in petroleum 

exploration: Boston, International Human 

Resources Development Corporation, 232 p. 

Reviewers: C.M. Isaacs and T.J. Wiley 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

120 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Mineralogy and Stage Assignment of Some Tertiary Coal 

from the Tikishla Park Drill Hole, Anchorage, Alaska 

By G. D. Stricker, M.E. Brownfield, L.A. Yehle, and J.A. Wolfe 

Anchorage is underlain by a wedge of 

Quaternary deposits (Miller and Dobrovolny, 1959) that 

thins eastward from about 300 m (reinterpreted from 

Church, 1969, 1970) near Cook Inlet and terminates 

against the Chugach Mountains where Mesozoic 

metamorphic rocks crop out (fig. 1). Beneath the 

Quaternary deposits is a wedge of Tertiary rocks that 

also thins eastward (Plafker and others, 1982). These 

rocks are concealed in the Anchorage area, but they 

crop out along Eagle River about 20 km northeast of 

downtown Anchorage (fig. 1) (Wolfe and others, 1966; 

Magoon and others, 1976). We here present new 

mineralogic and paleontologic data from a coal horizon 

within the poorly known Tertiary sedimentary rocks in 

the subsurface beneath Anchorage. 

To inventory and characterize some of the 

lithofacies underlying Anchorage, a hole 232 m deep 

and 150 mm in diameter was drilled in 1984 and 

accompanying geophysical studies were completed in 

1985 (Yehle and others, 1986). The hole (USGS A-84-1) 

is located southeast of downtown Anchorage in 

Tikishla Park (fig. 1), and is steel cased to a depth of 

about 43 m. Drilling penetrated about 155 m of 

Quaternary nonlithified deposits and 76 m of Tertiary 

rocks (fig. 2). Sampling was by coring, by collecting 

cuttings from drilling slurry, and by scraping from the 

bit assembly itself. Best samples of coal and an 

underlying siltstone were from a depth of about 167 m, 

and these were chosen for mineralogic and 

paleontologic study. 

0 5 I I I I I I 

KILOMETERS 

Downtown 

7

Anchorage 

Figure 1. Anchorage area and vicinity, showing Tikishla Park drill 

hole, plant fossil locations, and line of cross section (figure 3). 

Our tests and studies included vitrinite 

reflectance and mineralogy by Stricker and Brownfield 

and palynology by Wolfe. Mineralogical data were 

derived from the coal sample by first reducing it to 

ash by heating to temperatures of 150 °C, following 

procedures of Gluskoter (1965), and then by 

interpretation of X-ray diffractograms of the ash. The 

mean random vitrinite reflectance value of the coal is 

0.41 percent, which relates to a coal rank of 

subbituminous C (Stach and others, 1975). Total ash 

content of the material was 39.5 percent. The mineral 

assemblage of the coal ash was determined to be 

primarily quartz and kaolinite with lesser illite, 

chlorite, and sodic plagioclase, and trace amounts of 

apatite and crandallite-group minerals. Composition 

of the siltstone underlying the coal bed was 

determined to be dominantly quartz and plagioclase, 

with some kaolinite and minor illite, chlorite, apatite, 

and crandallite group minerals. 

We are studying minerals of the crandallite 

group because of their role as indicators of geologic 

terranes that have elevated levels of volcanic activity 

(Stricker and others, 1986; Brownfield and others, 

1987). This mineral group was previously identified in 

Alaska coal samples from drill holes (Chleborad and 

others, 1980; Odum and others, 1983) west of Cook 

Inlet (P.D. Blackmon, U.S. Geological Survey, written 

DEPTH 

(METERS) 

0 

50 

100 

150 

200 

232 T.D. 

~ Sandy gravel, silty sandy gravel, 

~ interbedded diamicton 

~ Siltstone, sandstone, 

~ and minor claystone 

D Fine sandstone 

- c- Thin coal bem 

Sample 

06865-D 

Figure 2. Abbreviated lithologic log of Tikishla Park drill hole, 

Anchorage, Alaska (modified from Yehle and others, 1986). T.D., 

total depth. 

Southern Alaska 121 
commun., June 19, 1981; Stricker and others, 1986; 

Brownfield and others, 1987). From the presence of 

crandallite minerals reported here, and from previous 

work (Stricker and others, 1986; Brownfield and others, 

1987), it is becoming apparent that this mineral 

assemblage has a wider regional and temporal 

distribution within Tertiary coals than earlier thought 

probable. 

The coal and enclosing sedimentary rocks in the 

Tikishla Park drill hole were considered by Yehle and 

others (1986) and Schmoll and Barnwell (1984) to be 

probably part of the Tyonek Formation and of Tertiary 

age. This conclusion was based on comparison with 

outcrops of the nearest similar rocks, those exposed 

along Eagle River, which were assigned by Wolfe and 

others (1966) on the basis of plant fossils to the 

Seldovian Stage (Miocene). Detailed examination of 

pollen and spores from the coal sample at the 167 m 

depth revealed a flora similar to that found in 

Clamgulchian Stage assemblages by Wolfe and others 

(1966) at their type locality. Flora present in our 

sample include: Lycopodium, Osmunda, Taxodiaceaetype, Larix/Pseudotsuga, Picea, Pinus, Tsuga 

heterophylla-type, Alnus, Betula, Myrica, and 

Ericaceae. Because the Sterling Formation 

(Calderwood and Fackler, 1972) contains floral 

assemblages of the Clamgulchian Stage of latest 

Miocene extending into Pliocene (Wolfe, 1981), we 

suggest that the sampled material and probably the 

underlying rocks penetrated by the drill hole should be 

assigned to the Sterling Formation rather than to the 

Tyonek Formation. An earlier interpretation 

suggesting the presence of the Sterling Formation in 

the subsurface in the western part of the Anchorage 

area was published by Church (1969). His geologic 

cross section included the Yukon Services, Inc. 

~ 

-- ~ 

(i) ·c: a3 

CL .c::> Q) 

a. ... ,.... a3 0 Ec: .c .c al·o o C/) 

OCLZ ~ "i: DEPTH i= "0 (METERS) A 

0 

100 Quaternary deposits 

200 

232 T.D. 

300 

400 

..,.? 

500 Tyonek Formation 

(Tertiary) 

1500 f1446 T.D. 

0 5 ! 1 I I I ! 

KILOMETERS 

C/) 

.c c: 

~:§ O')C: 

:::J ::I 

.c 0 

()~ 

A' 

.~ 

.c 

c. 

~ 

0 

E 

a3 

-Q) 

E 

.~ 

0 

N 

0 

C/) 

Q) 

~ 

Figure 3. Generalized geologic cross section connecting Campbell 

Point Unit No. 1 and Tikishla Park drill holes and Chugach 

Mountains. See figure 1 for location. T.D., total depth. 

Campbell Point Unit No. 1 drill hole (fig. 1). The 

information we present affirms his 1969 interpretation 

and extends the distribution of the Sterling Formation 

closer to the Chugach Mountains (fig. 3). A 

lithologically more varied prism of relatively soft 

sedimentary rocks exists beneath Anchorage than 

previously was believed, and we speculate that 

geologic structures also may be more complex than 

inferred by earlier workers. 

REFERENCES CITED 

Brownfield, M.E., Affolter, R.H., and Stricker, 

G.D., 1987, Crandallite group minerals in 

the Capps and Q coal beds, Tyonek Formation, 

Beluga energy resource area, south-central 

Alaska, in Rao, P.D., ed., Focus on Alaska's 

coal '8~ Proceedings of the Conference 

held at Anchorage, Alaska, October 27-30, 

1986: Fairbanks, University of Alaska 

Mineral Industry Research Laboratory, MIRL 

Report Number 72, p. 142-149. 

Calderwood, K.W., and Fackler, W.C., 1972, 

Proposed stratigraphic nomenclature for 

Kenai Group, Cook Inlet basin, Alaska: 

American Association of Petroleum Geologists 

Bulletin, v. 56, no. 4, p. 739-754. 

Chleborad, A.F., Yehle, L.A., Schmoll, H.R., and 

Gardner, C.A., 1980, Preliminary field 

geotechnical and geophysical logs from a 

drill hole in the Capps coal field, Cook 

Inlet region, Alaska: U.S. Geological 

Survey Open-File Report 80-393, 17 p. 

Church, R.E.(chairman), 1969, South to north 

stratigraphic correlation section, Anchor 

Point to Campbell Point, Cook Inlet Basin, 

Alaska [Cook Inlet Basin stratigraphic 

study]: Anchorage, Alaska Geological 

Society, Stratigraphic Committee, Year 1968-

69, 5 pl. 

1970, South to north stratigraphic 

correlation section, Campbell Point to 

Rosetta, and west to east stratigraphic 

correlation section, Buga River to Wasilla, 

Cook Inlet Basin, Alaska [Lower Susitna-Knik 

arm stratigraphic sections]: Anchorage, 

Alaska Geological Society, Stratigraphic 

Committee, Year 1969-70, 2 pl. 

Gluskoter, H.J., 1965, Electric low-temperature 

ashing of bituminous coal: Fuel, v. 44, no. 

4, p. 285-291. 

Magoon, L.B., Adkinson, W.L., and Egbert, R.M., 

1976, Map showing geology, wildcat wells, 

Tertiary plant fossil localities, K-Ar age 

dates, and petroleum operations, Cook Inlet 

area, Alaska: U.S. Geological Survey 

Miscellaneous Geological Investigations Map 

I-1019, scale 1:250,000. 

Miller, R.D., and Dobrovolny, Ernest, 1959, 

Surficial geology of Anchorage and vicinity, 

Alaska: U.S. Geological Survey Bulletin 

1093, 128 p. 

Odum, J.K., Gardner, C.A., Yehle, L.A., Schmoll, 

H.R., and Dearborn, L.L., 1983, Preliminary 

lithologic, geotechnical, and geophysical 

122 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
data from drill hole CW-81-2, Chui tna West 

coal field, Cook Inlet region, Alaska: U.S. 

Geological Survey Open-File Report 83-78, 12 

P• 

Plafker, George, Bruns, T.R., Winkler, G.R., and 

Tysdal, R.G., 1982, Cross section of the 

eastern Aleutian arc, from Mount Spurr to 

the Aleutian trench near Middleton Island, 

Alaska: Geological Society of America, Map 

and Chart Series MCH-28p, scale 1:1,000,000. 

Schmoll, H.R., and Barnwell, W.W., 1984, Eastwest geologic cross section along the DeBarr 

line, Anchorage, Alaska: U.S. Geological 

Survey Open-File Report 84-791, 10 p. 

Stach, E., Taylor, G.H., Mackowsky, M. T., 

Chandra, D., Teichmuller, M., Teichmuller, 

R., Murchison, D.G., and Zierke, F., 1975, 

Textbook of coal petrology: Berlin, 

Gebrllder Borntraeger, 428 p. 

Stricker, G.D., Affolter, R.H., and Brownfield, 

M.E., 1986, Geochemical characterization of 

selected coals from the Beluga Energy 

Resource Area, south-central Alaska: Site 

of a proposed coal mine [ abs.], in Carter, 

L.M.H., ed., USGS research on energy 

resources--1986 program and abstracts: U.S. 

Geological Survey Circular 974, p. 65-66. 

Wolfe, J .A., 1981, A chronologie framework for 

Cenozoic megafoss i 1 floras of northwestern 

North America and its relation to marine 

geochronology, in Armentrout, J.M., ed., 

Pacific Northwest Cenozoic biostratigraphy: 

Geological Society of America, Special Paper 

184, p. 39-47. 

Wolfe, J.A., Hopkins, D.M., and Leopold, E.B., 

1966, Tertiary stratigraphy and paleobotany 

of the Cook Inlet region, Alaska: U.S. 

Geological Survey Professional Paper 398-A, 

29 p. 

Yehle, L.A., Odum, J.K., Schmoll, H.R., and 

Dearborn, L.L., 1986, Overview of the 

geology and geophysics of the Tikishla Park 

drill hole, USGS A-84-1, Anchorage, 

Alaska: U.S. Geological Survey Open-File 

Report 86-293, 10 p. 

Reviewers: S.B. Roberts and H.R. Schmoll 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southem Alaska 123 

SOUTHWESTERN ALASKA 

A gold dredge at Nyac (about 95 km east-northeast of Bethel) disgorges gravel from its tail boom. Photograph by 

E. Yount. 
Petrogenesis of the Crooked Mountains Pluton, 

Bethel Quadrangle: A Preliminary Report 

By Thomas P. Frost, James P. Calzia, Ronald W. Kistler, and Davison V. Vivit 

During the summer of 1987 we began a 

systematic study of the granitoids between lat. 60 and 

61° N. in the eastern part of the Bethel quadrangle 

(figs. 1 and 2), as part of the Alaska Mineral Resource 

Assessment Program. This report presents our initial 

field results and preliminary petrographic data, along 

with compositional and isotopic data on samples from 

a traverse through the Crooked Mountains pluton (fig. 

2), that pertain to the origin and evolution of 

southwestern Alaskan granitoids. Field studies were 

carried out by the first two authors (Frost and Calzia), 

isotopic analyses were done under the direction of 

Kistler, and X-ray fluorescence analyses were done by 

Vivit. 

Plutons of the Bethel quadrangle appear to be 

part of a broad belt of plutonic and volcanic rocks (fig. 

1) of Late Cretaceous to early Tertiary age which 

extend beneath the Bering Sea to the southwest and 

appear to terminate near the Kaltag fault to the 

northeast (Wilson, 1977; Shew and Wilson, 1981; Moll 

and Patton, 1982; Wallace and Engebretson, 1984; 

Robinson and Decker, 1986; Bergman and Doherty, 

1986; Bergman and others, 1987). Plutons emplaced 

between 63 Ma and 80 Ma are dominantly calc-alkalic 

and have increasing K20 content (at 57.5 percent 

Si02) with increasing distance from the Gulf of 

Alaska; plutons emplaced between 45 and 63 Ma do not 

vary significantly in K20 content (at 57.5 percent 

Si02) throughout the region (Bergman and others, 

1987). 

Plutons in the Bethel quadrangle cut the 

accreted Nyac, Goodnews, and Togiak terranes as well 

as the Albian to Coniacian turbidites of the 

Kuskokwim Group (fig. 2), but none are known to 

intrude the Tikchik terrane in the Bethel quadrangle 

(Hoare and Coonrad, 1959a; Box and Murphy, 1987). 

Only a few plutons in the quadrangle have been dated 

radiometrically (table 1); the ages determined range 

between 66 and 120 Ma (Wilson, 1977; Robinson and 

Decker, 1986; Bergman and Doherty, 1986). 

Intermediate to rhyolitic flows and domes(?) of Late 

Cretaceous to early Tertiary age (Hoare and Coonrad, 

1959a; Wilson, 1977; Robinson and Decker, 1986), as 

well as abundant mafic to rhyolitic dikes, cut all other 

rock types. 

Granitoid plutons in the region are typically 

elliptical in plan and are as large as 8 by 40 km (fig. 2), 

although elliptical bodies as small as a few hundred 

square meters with plutonic textures are scattered 

throughout the quadrangle. Most plutons are in sharp, 

discordant contact with their wallrocks and have welldeveloped thermal aureoles as wide as 2 km. The 

thermally metamorphosed sedimentary and 

volcaniclastic wallrocks are commonly resistant to 

erosion and form prominent ridges encircling many of 

the plutons. 

Quartz-rich hornblende-biotite granodiorite, 

quartz monzodiorite, and granite are the most common 

plutonic rock types in the Bethel quadrangle, although 

tonalite, hornblende diorite, and anorthositic 

hornblende gabbro are also present (Wilson, 1977; 

Robinson and others, 1986). Most plutons are slightly 

zoned to unzoned, medium grained, and equigranul·ar, 

although porphyritic facies are common locally. Finegrained ellipsoidal mafic enclaves, composed of 

abundant hornblende, biotite, and plagioclase and 

lesser quartz, potassium feldspar, and sphene, are 

present in most of the quartz-bearing plutons. 

Enclaves are typically less than 20 em in maximum 

dimension; most are subequant, although near pluton 

margins many are strongly flattened. At the 

164° 160° 

Sew ar d 

62° 

8 A Y 

156° 

EXP LA NATIO N 

1 Pl u t o n 

J Contact 

/ F aul t 

0 50 tOO 150 

KILOME TERS 

Figure 1. Southwestern Alaska showing distribution of plutonic 

rocks of Late Cretaceous to early Tertiary age of Kuskokwim 

Mountains belt. Plutons in Alaska Range and on Seward 

Peninsula are not shown. Small box in area of figure 2 shows 

outline of Bethel quadrangle. Adapted from Beikman (1 980) and 

Wallace and Engebretson (1 984). 

126 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
northwestern margin of the Cripple Mountains pluton 

(fig. 2), enclaves are most abundant within 50 m of 

contact, where they compose about 5 percent of the 

outcrop. 

The Crooked Mountains pluton intrudes 

Mesozoic intermediate volcanic and volcaniclastic 

rocks of the Togiak terrane (Box and Murphy, 1987). 

The rock is predominantly equigranular hornblendebiotite granodiorite and quartz monzodiorite, although 

0 

C\1 

~ 

~/ Co11tact, dashed 1vhere apptoxirnately 

_,---..... Fa.ult, dashed v1here approxirna.te 

dotted where inferred 

...........,... Thrust f.'\ult, teeth on upper ;Jlate 

61° 

Qs 

OVERLAP SEQUENCES 

Qs Surficial deposits (Quaternary) 

TKv Volcanic rocks (early Tertiary and 

Late Cretaceous) Basalt to rhyolite 

flows and domes, includes some 

hypa byssa 1 rocks 

Kk Kuskokwim Group (Late and Early 

Cretaceous) 

GRANITOID PLUTONS 

(early Tertiary to Late Cretaceous) 

Identified by number, corresponding to numbers 

in table 1. 

it is slightly porphyritic near the pluton margin. The 

pluton is rimmed on its western side by a 

homogeneous, medium-grained, equigranular border 

phase of clinopyroxene quartz diorite which contains 

prominent, dark-colored, euhedral plagioclase. The 

border phase is sharply cut by dikes of the main felsic 

phase of the pluton. Enclaves are present throughout 

the pluton, although their abundance is typically less 

than 1 percent of outcrop. 

Qs 

PRE-MID-CRETACEOUS TERRANES 

Togiak terrane (Early Cretaceous and (or) Late Jurassic) 

KJt Andesitic volcanic rocks, volcaniclastic 

sedimentary rocks, and tuffaceous 

argillite 

Nyac terrance (Jurassic) 

Jn Andesitic volcanic rocks 

Goodnews terrane (Mesozoic or Pa 1 eozoi c) 

MzPzga Tuffaceous argi 11 i te and chert, 

some basalt 

MzPzgb Foliated metabasite, metachert, 

and marble 

Tikchik terrane (Mesozoic and Paleozoic) 

MzPzt Metavolcanic rocks, metachert, graywacke, 

and 1 i mes tone 

K i l buck terrane (Precambrian) 

p£k Amphibolite facies orthogneiss and 

quartz-mica schist 

Figure 2. Regional geology of Bethel quadrangle and parts of Russian Mission and Goodnews quadrangles 

(adapted from Hoare and Coonrad, 1959a,b, 1978; Wilson, 1977; Box and Murphy, 1987; Bergman and 

Doherty, 1 986; Bergman and others, 1987; Robinson and Decker, 1986). 

Southwestem Alaska 127 
Table 1. Summary of plutonic rocks, Bethel quadrangle region, southwestern Alaska 

[Numbers key each pluton to figure 1. Hbl, hornblende; bio, biotite] 

Pluton name 

1. Nyac 

2. Spruce Creek and 

Bonanza Creek 

3. Sawpit Creek 

Predominant compositions 

hbl-bio granodiorite and 

(porphyritic) biotite 

granodiorite and granite 

fine grained biotie granite 

and granodiorite 

granodiorite (?) 

Age, Ma (K-Ar) 

101.1 ± 3.0 (hbl) 

108.5 ± 3.3 (bio) 

120 ± 3.6 (bio) 

References 

1,2,4,5, 

6,R 

2,5 

2 

4. Fox Creek biotite granodiorite, associated ~~.6 ± 2.0 (bio) 2,6 

with gabbro (?) and diabase 

5. Mt. Plummer and 

Marvel Dome 

hbl-bio granodiorite to Quartz 

monzodiorite 

1,8 

6. Powerplant concentrically (?) zoned hbl 

diorite to bio-hbl granodiorite 

1,8 

7. Fisher Dome porphyritic bio granite, cut by 

stibnite-ouartz veins 

1,8 

8. Cripple Mountains bio-hbl granodiorite to granite 1,8 

<}. Gemuk Mountain anorthositic hbl gabbro and 1 ,4 

anorthosite (labradorite) 

10. North Fork hbl-bio granodiorite 

11. Crooked Mountains hbl-bio granodiorite, granite, 

and ouartz monzodiorite 

71.7 ± 2.7 (bio) 

73.0 ± 3.7 (hbl) 

1,8 

1,7,8 

12. Canyon Creek bio-hbl (cpx) Quartz diorite 

to granodiorite 

1,8 

13. Mt. Oratio 

14. Eek River 

15. Kwethluk River 

16. Columbia Creek 

bio-hbl Quartz monzodiorite 

tonalite and cpx diorite 

(porphyritic) two-px diorite 

hbl-bio granodiorite and granite 

71.1 ± 2.1 (bio) 3,4 

1,4 ,8 

1,4,8 

1,8 

References: 1, Hoare and Coonrad (1959a); 2, Hoare and Coonrad (1959b); 

3, Hoare and Coonrad (1978); 4, Wilson (1977); 5, Decker and others (1984); 

6, Robinson and Decker (1986); 7, Bergman and Doherty (1986); 8, this report 

The compositional variation in the Crooked 

Mountains pluton indicates that it is of calc-alkalic 

affinity. The main phase of the pluton is restricted in 

its compositional range to 69 to 72 percent Si02 (data 

normalized anhydrous) and has 4.5 to 5 percent K 0; 

trace-element contents exhibit little variation (tatle 

2, fig. 3). The border phase on the western margin is 

also homogeneous in all elemental concentrations and 

has 63.2 to 63.8 percent Si02 (table 2 and T.P. Frost, 

unpub. data). All rock types plot in the volcanic arc 

granites field on Rb versus Y+Nb and Nb versus Y 

diagrams (Pearce and others, 1984). 

The ellipsoidal mafic enclaves are the most 

variable and erratic in composition of all rock types of 

the Crooked Mountains pluton (table 2, fig. 3). Silica 

content is 57.7 to 64.1 percent, Na2o content is 5.5 to 

5.8 percent, and K20 content is 2.2 to 3.8 percent. 

Rubidium is between 60 and 82 ppm; Sr content is 

widely variable (fig. 3). The compositional variation in 

the enclaves suggests that they do not represent early 

mafic cumulates or early differentiates of either the 

border phase or the main-phase granodiorite (for 

example, Walawender and Gross, 1986), nor could they 

all represent a single mafic magma which quenched as 

enclaves in the magma of the main phase (for example, 

Vernon, 1983; Reid and others, 1983; Frost and 

Mahood, 1987), or residual unmelted material from the 

source regions of the main phase granodiorite (for 

example, White and Chappell, 1977). Other origins 

which have been proposed for similar enclaves in other 

plutons include liquid immiscibility (for example, 

Bender and others, 1982), and reequilibrated wallrock 

inclusions, although these are usually recognizable in 

the field (for example, Didier, 1973). 

Despite the wide variation in major- and traceelement abundances, and the lack of an apparent 

coherent fractionation trend between enclaves, border 

phase, and main phase (fig. 3), wdf.le-ggck samples of 

all rock types yield an apparent Sr/ S~1socgson of 

66.6 ± 7.9 Ma, with an apparent initial Sr/ Sr of 

0. 7036 ± 0.0002 (fig. 4). If the apparent isochron is 

assumed to represent the true age for all rocks 

analyzed, then the isotopic data suggest that either 

the enclaves have reequilibrated isotopically with the 

host magma, or their initial isotopic composition was 

coincidentally very close to that of the host magma. 

Barbarin and Bateman (1986) also observed apparent Sr 

isotopic equilibration between mafic enclaves and host 

granitoids in the Sierra Nevada batholith of 

California. Compositional data suggest that the 

128 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 2. Representative analyses, Crooked Mountains pluton, Bethel quadrangle, Alaska 

[Most X-ray fluorescene (XRF) determinations (except Rb and Sr) by D.V. Vivit, USGS. Rb and Sr (by XRF) and isotopic 

analyses by A.C. Robinson, USGS, Menlo Park, Calif.] 

Rock type Border Enclaves 

Sample1 046 050 049-I 043A 

Si02 62.6 56.2 63.2 63.3 

TiO .92 l. 22 .78 .78 

Al2632 15.3 17.2 16.0 16.5 

Fe

6

o 3 5.38 7.12 4.94 4. 77 

Mn .09 .11 .08 .09 

MgO 2.90 2.80 1.90 1.10 cao 4.24 5.60 3.86 2.82 

Na

6

o 3.90 5.60 5.70 5.40 

K2 3.10 2.22 2.44 3.64 

P603 .20 .28 .22 .26 

L I .50 .37 .13 . 75 

Total 99.1 99.0 99.3 99.4 

Trace elements, in ppm4 

Cr [ 20 l 78 22 

Ni [20] 22 

Cu [20] 175 

Zn 64 88 70 80 

Rb 75 60 65 95 

Sr 308 449 146 177 y 28 32 56 38 

Zr 280 235 265 265 

Nb 12 12 16 14 

Ba 870 700 300 620 

La [ 30 l 38 32 

Ce 60 54 96 86 

Isotope data 

H9/Sr 0.244 0.134 0.445 0.538 

Rb/86sr .706 .389 1. 288 1. 558 87 s5;86 sr .7043 .7041 .7048 .7050 

Sri .7036 .7037 .7035 .7035 

~All sample numbers prefixed by 87ATf. 

3Total ir~n :e~orted as Fe 2o 3 . 

Main Ehase 

0438 051 052 039 049-H 041 

67.6 68.0 68.1 68.1 68.7 71.0 

.52 .52 .52 .48 .52 .36 

15.1 15.1 15.0 15.1 15.0 14.1 

3.26 3.14 3.14 2.95 3.04 2.38 

.06 .05 .05 .05 .05 .04 

.65 .70 .65 .60 .65 .40 

2.02 l. 92 1.90 l. 88 1. 88 l. 40 

4.10 4.30 4.40 4.20 4.30 3.90 

4.62 4.62 4.58 4.66 4.56 4. 72 

.12 .12 .12 .10 .12 .08 

1.87 .50 .63 .88 .37 .38 

99.9 99.0 99.1 99.0 99.2 98.8 

46 52 50 48 54 50 

119 117 123 134 116 148 

156 180 166 162 176 142 

40 38 36 38 34 44 

350 345 355 370 365 280 

14 14 14 14 12 14 

1100 1100 1050 1100 1100 770 

36 36 30 40 40 46 

68 78 66 84 64 82 

0.763 0.650 0.741 0.827 0.659 l. 042 

2.207 1. 881 2.144 2.393 1. 907 3.015 

.7057 .7056 .7055 .7059 .7054 .7066 

.7035 .7037 .7033 .7035 .7034 .7035 

Los~ on ~gn~t~on at 920 °c. 

Ind~cated is [detection limit]. Non reported abundances are less than 

5detectioo limit. 

Initial 87sr;86sr calculated at 72 Ma. 

enclaves and border phase are not differentiation 

products of a single magma, and that the enclaves and 

the main phase are also not differentiation products of 

a single magma. 

Although the Sr isotopic data define an 

apparent isochron for the Crooked Mountains pluton, 

an age is not assigned to the pluton in this report due 

to the present uncertainty in the relationship between 

the origin of the enclaves, their host, and the border 

phase. The apparent isochron determined for all 

samples in this study is compatible, within the 

analytical uncertainty limits, with the K-Ar mineral 

ages of 71.7 to 73.0 Ma determined by Bergman and 

Doherty (1986). An apparent isochron calculated using 

only the enclave data is 56.7 ± 8.6 Ma; an apparent 

isochron calculated using only the main phase data is 

69.1 ± 34.9 Ma. 

Initial strontium isotopic ratios for the samples 

from the Crooked Mountains pluton, recalculated using 

Bergman and Doherty's (1986) K-Ar ages, range from 

0. 7033 to 0. 7037 (table 2), but do not show a 

systematic difference between enclaves, border phase, 

and main phase. The low initial Sr isotopic ratio for 

the Crooked Mountains pluton suggests that little or no 

old radiogenic crustal component was involved in its 

genesis and that Precambrian basement (Hoare and 

Coonrad, 1959a, 1978; Turner and others, 1983) 

exposed 40 km to the west in the Kilbuck terrane (fig. 

2) does not extend east beneath the Crooked 

Mountains. The magma may have had its source in the 

mantle and (or) in nonradiogenic mafic and 

intermediate Mesozoic supercrustal rocks. 

The chemistry determined for the Crooked 

Mountains pluton of the Kuskokwim Mountains indicate 

a subduction-related origin, although the distance to 

the subduction zone during its emplacement is 

uncertain. Wallace and Engebretson (1984) and 

Bergman and Doherty (1986) suggested that Late 

Cretaceous to early Tertiary magmatism in the 

Kuskokwim Mountains was part of a very broad 

magmatic belt from the Alaska Range to the Kaltag 

fault which developed in response to gently-dipping, 

rapid subduction of the Kula plate. Bergman and 

others (1987) have further delineated southwestern 

Alaska magmatism into a Late Cretaceous (89-66 Ma) 

calc-alkaline group which formed in response to rapid 

subduction of the Kula plate, and an early Tertiary 

(66-45 Ma) group that may not be subduction related, 

but formed instead by post-subduction lithospheric 

(including crust) melting. Compositional and isotopic 

data presented here for the Crooked Mountains pluton 

are compatible with Bergman and others (1987) 

conclusions regarding the older magmatic group. 

Southwestern Alaska 129 
2 0 

FeO 

0 • 

• 8 GEl 

6 

4 ~ 0 

0 0 .. MgO 

0 0 

0 0 

~~ 0 'to) 

0 Na20 

50 

• ~ 0 4l l •• 0 ~ 58 60 b2 64 b6 68 70 12 

Si02 

u 14 o 0 MAIN PHASE 

e BORD~R PHASE I?J> 

0 0 ENCLAVES 

'~ 12 

10 0 Q 

J Rb - 8( 

_6:i 0 

IS! 60 

400 Sr 

300 • 20 0 

.R\ 

0 

~ 

~0 

&0 360 

0 

• r9 30( J 

• 0 

GEl 

Zr 240 <SJ 

58 60 62 64 66 68 70 72 

Si02 

Figure 3. Variation with silica content for seleded elements, 

Crooked Mountains pluton. Major elements in weight percent, 

trace elements are in parts per million. Total iron reported as FeO. 

All data recalculated anhydrous. Data from table 2 and D.V. 

Vivit, written communication. See text for discussion. 

0.7070.-----.-----~----~-----~~----~----~,--~ 

CROOKED MOUNTAINS PLUTON (;;;Y/ 

T = 66.6 ± ?.9 Ma ///. 0.7062t- / 

c Sci 0. ?0363 ± 0. 000~-~·/' 

en o. 7054 t- Q /~ w /0 

6;0.7046-

~ / /~~ 

/ 

0.7038// 

~/-~/ 0 MAIN PHASE 

• BORDER PHASE 

® ENCLAVES 

-

-

-

-

0.70300~----L-----~~~----~----~~~----L---~~~--~ 

B7Rb/B6sr 

Figure 4. Rb/Sr evolution diagram, Crooked Mountains pluton. 

Ellipse size indicates error in determinations. See text for 

discussion. 

REFERENCES CITED 

Barbarin, Bernard, and Bateman, P.C., 1986, 

Origin and evolution of mafic magmatic 

enclaves and mafic rocks associated with 

some granitoids of the central Sierra Nevada 

[abs.]: International Mineralogical 

Association Abstracts with Programs, v. 14, 

P• SO. 

Beikman, H.E., 1980, Geologic map of Alaska: 

U.S. Geological Survey Special Map, 2 

sheets, scale 1:2,500,000. 

Bender, J.F., Hanson, G.N., and Bence, A.E., 

1982, The Cortlandt complex: evidence for 

large-scale liquid immiscibility involving 

granodiorite and diorite magmas: Earth and 

Planetary Science Letters, v. 58, p. 330-

344. 

Bergman, S.C., and Doherty, D.J., 1986 Nature 

and origin of 50-75 Ma volcanism and 

plutonism in W. and S. Alaska [abs.]: 

Geological Society of America Abstracts with 

Programs, v. 18, p. 539. 

Bergman, S.C., Hudson, T.L., and Doherty, D.J., 

1987, Magmatic rock evidence for a Paleocene 

change in the tectonic setting of Alaska 

[abs.]: Geological Society of America 

Abstracts with Programs, v. 19, p. 586-587 • 

Box, S.E., and Murphy, J.M.,.1987, Late Mesozoic 

structural and stratigraphic framework, 

eastern Bethel quadrangle, southwestern 

Alaska, in Hamilton, T.D., and Galloway, 

J.P., eds., Geologic studies in Alaska by 

the U.S. Geological Survey during 1986: 

U.S. Geological Survey Circular 998, p. 78-

82. 

Decker, John, Reifenstuhl, R.R., and Coonrad, 

W.L., 1984, Compilation of geologic data 

from the Russian Mission A-3 quadrangle, 

southwestern Alaska: Alaska Division of 

Geological and Geophysical Surveys, Report 

of Investigations 84-19, scale 1:63,360. 

Didier, J., 1973, Granites and their enclaves: 

New York, Elsevier, 393 p. 

Frost, T.P., and Mahood, G.A., 1987, Field, 

chemical, and rheologic constraints on 

mafic-felsic magma interaction in the 

Lamarck Granodiorite, Sierra Nevada, 

California: Geological Society of America 

Bulletin, v. 99, p. 272-291. 

Hoare, J.M., and Coonrad, W.L., 1959a, Geology 

of the Bethel quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous 

Investigations Series Map I-285, scale 

1:250,000. 

1959b, Geology of the Russian Mission 

quadrangle, Alaska: U.S. Geological Survey 

Miscellaneous Investigations Series Map I292, scale 1:250,000. 

1978, Geologic map of the Goodnews and 

Hagemeister Island quadrangles region, 

southwestern Alaska: U.S. Geological Survey 

Open-File Report 78-9-B, 2 sheets, scale 

1:250,000. 

Moll, E.J., and Patton, W.W., Jr., 1982, 

Preliminary report on the Late Cretaceous 

and early Tertiary volcanic and related 

plutonic rocks in western Alaska, in 

Coonrad, W.L., ed., The United States 

Geological Survey in Alaska: Accomplishments 

during 1980: U.S. Geological Survey 

Circular 844, p. 73-75. 

Pearce, J.A., Harris, N.B.W., and Tindle, A.G., 

1984, Trace element discrimination diagrams 

for the tectonic interpretation of granitic 

130 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
rocks: Journal of Petrology, v. 25, p. 956-

983. 

Reid, J.B., Jr., Evans, O.C., and Fates, D.G., 

1983, Magma mixing in granitic rocks of the 

central Sierra Nevada, California: Earth 

and Planetary Sciences Letters, v. 66, p. 

243-261. 

Robinson, M.S., and Decker, John, 1986, 

Preliminary age data and analytical data for 

selected igneous rocks from the Sleetmute, 

Russian Missian, Taylor Mountains, and 

Bethel quadrangles, southwestern Alaska: 

Alaska Division of Mining and Geological and 

Geophysical Surveys, Public-Data File 86-99, 

8 P• 

Robinson, M.S., Nye, Chris, and Decker, John, 

1986, Preliminary whole rock major oxide and 

trace element geochemistry of selected 

igneous rocks from the Sleetmute, Russian 

Mission, and Taylor Mountains quadrangles, 

southwestern Alaska: Alaska Division of 

Mining and Geological and Geophysical 

Surveys, Public-Data File 86-98, 9 p. 

Shew, Nora, and Wilson, F.H., 1981, Map and 

table showing radiometric ages of rocks in 

southwestern Alaska: U.S. Geological Survey 

Open-File Report 81-866, 26 p. 

Turner, D.L., Forbes, R.B., Aleinikoff, J.N., 

Hedge, C.E., and McDougall, Ian, 1983, 

Geochronology of the Kilbuck terrane of 

southwestern Alaska [abs.]: Geological 

Society of America Abstracts with Programs, 

v. 15, p. 407. 

Vernon, R.H., 1983, Restite, xenoliths, and 

microgranitoid enclaves in granites: 

Journal and Proceedings of the Royal Society 

of New South Wales, v. 116, p. 77-103. 

Walawender, M.J., and Gross, W.W., 1986, 

Geochemistry and origin of mafic inclusions 

~n the granitic rocks of the Peninsular 

Ranges batholith, southern California 

[abs.]: Geological Society of America 

Abstracts with Programs, v. 18, p. 194. 

Wallace, W.K., and Engebretson, D.C., 1984, 

Relationships between plate motions and Late 

Cretaceous to Paleogene magmatism ~n 

southwestern Alaska: Tectonics, v. 3, p. 

295-315. 

White, A.J.R., and Chappell, B.W., 1977, 

Ultrametamorphism and granitoid genesis: 

Tectonophysics, v. 43, p. 7-22. 

Wilson, F.H., 1977, Some plutonic rocks of 

southwestern Alaska, a data compilation: 

U.S. Geological Survey Open-File Report 77-

501, 9 p. 

Reviewers: S.E. Box and E.J. Moll-Stalcup 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southwestern Alaska 131 
Geochemical Anomalies 1n the Eastern Katmai Region of the 

Alaska Peninsula 

By Richard j. Goldfarb, john E. Gray, and R.B. Tripp 

During the 1983-1985 field seasons, the U.S. 

Geological Survey conducted a reconnaissance stream 

sediment geochemical survey of the Alaska Peninsula 

between lat 58° and 59° N. (fig. 1). Stream-sediment 

samples were collected from areas of active 

alluvium. Heavy-mineral concentrates were also 

collected with a standard gold pan at most sediment 

sites, and any magnetic material within these samples 

was removed in the laboratory using a magnetic 

separator. All sediment and nonmagnetic concentrate 

samples were analyzed for 31 elements using a 

semiquantitative emission spectrographic method. The 

methods of collection, processing, localities, and 

chemical results from these samples were described in 

detail by Bailey and others (1986). Mineralogical 

results obtained from the nonmagnetic fraction of the 

EXPLANATION 

AREA ANOMALY 

1a - Au 

1b - Ag, As 

2a- 2d - Fe, Co, Cu, N1 

3 - Hg 

48, 4b - Ag, Cu, Mo, Pb, Zn 

SITES CONTAINING 

Cinnabar - * 

GolO - t 

Mt Katolinat " 

Ht 

concentrates panned from stream sediments were 

given by Bennett and Church (1987). 

Geologic mapping during the course of the 

project (J.R. Riehle, U.S. Geological Survey, written 

commun., 1986) has refined the earlier reconnaissance 

mapping by Keller and Reiser (1959). The eastern part 

of the Katmai region is underlain dominantly by 

Mesozoic siltstone and sandstone of the Naknek and 

Kaguyak Formations, which, in turn, are overlain by 

coal-bearing, continental, Tertiary sedimentary beds 

along much of the eastern edge of the study area. 

Late Tertiary andesitic and dacitic volcanic rocks of 

the Aleutian arc crop out over most of the area 

between Rallo Glacier and Katmai River. 

Intermediate hypabyssal sills, dikes, and plugs intrude 

this stratigraphic interval. The western border of the 

0 5 10 15 20 KflOMETERS 

Cape 

Douglas 

Figure 1. Eastern drainages of Katmai region on Alaska Peninsula, showing distribution of geochemical anomalies. 

132 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
study area for this report is the crest of the Aleutian 

Range. Most of the high peaks are composed largely 

of Quaternary andesite and dacite that make up the 

active volcanoes along the continental portion of the 

Aleutian volcanic arc. 

Univariate and multivariate statistical 

techniques were used to identify anomalous samples 

collected during the geochemical survey. The basic 

statistics for the analytical data from the 347 minusSO-mesh stream sediments and from the 337 

nonmagnetic heavy-mineral concentrates are given in 

tables 1 and 2. Detection ratios, the number of 

determinant (noncensored) values divided by the total 

number of samples analyzed for a given element, 

describe the degree to which the data are censored. 

Minimum, median, and maximum values are tabulated 

to present the range in the geochemical data. The 

90th, 95th, and 98th percentiles are also listed to 

enable the reader to select geochemical thresholds. 

The geometric mean, geometric deviation, and 

expected range are computed for those elements with 

de~ection ratios greater than 0.15. According to 

Miesch (1976), 95 percent of all values for a lognormal 

distribution fall within an expec~ed range from 

Geometric Mean/(Geomftric Dev.) to Geometric 

Mean x (Geometric Dev .) . 

Many elements commonly considered to be 

important pathfinders for mineral occurrences are 

highly censored within the sediment data. 

Additionally, visual inspection of histograms of the 

sediment data showed a relative narrow concentration 

range for most of the remaining elements. Statistical 

interpretation of the sediment data provided very 

limited information that could be used to identify 

geochemically favorable areas for mineral 

occurrences. The wider concentration ranges and 

higher detection ratios for many ore-related elements 

within the data set from the heavy-mineral 

concentrates (table 2) provided greater anomaly 

enhancement. We have therefore relied heavily on this 

data set for our interpretation. 

R-mode factor analysis with Varimax rotation 

was used to identify the dominant geochemical 

associations within the log-transformed concentrate 

data. Before analysis, the more highly censored 

elements were removed from the data matrix. For 

each remaining element, values qualified with N were 

replaced with 0.5 times the lower determination limit, 

those with L were replaced with 0. 7 times the lower 

determination limit, and those with G were replaced 

with 1.3 times the upper determination limit. A fivefactor model that explains 70 percent of the total 

variance was selected as most appropriate for reducing 

the concentrate data, and the resulting factor loadings 

are given in table 3. Factors 1, 3, and 5 are 

interpreted to reflect chemical associations within the 

dominant bedrock lithologies whereas the associations 

within the other two factors appear to be 

representative of accumulations of sulfide minerals. 

Samples with highest factor 1 scores, and thus 

enriched in Ca, Ti, B, La, V, Y, and (or) Zr, were 

collected from streams within Mesozoic sedimentary 

rocks to the west of the Katmai River and within the 

upper Big River watershed northwest of Kaguyak 

Crater. The relative abundance of resistate minerals, 

such as apatite, epidote, rutile, sphene, and zircon, 

within samples from watersheds underlain by the 

Mesozoic sedimentary rocks results in the element 

association characterizing factor 1. Higher 

background concentrations of Cr and Sn within some of 

these common sedimentary rock-forming minerals 

distinguishes the region to the west of the Katmai 

Table 1. Univariate statistical estimates for elements in 347 sediment samples 

[Values for Fe, Mg, Ca, and Ti in percent, all other values in parts per million. Detection ratio, number of samples having determinant concentrations divided by total 

number of samples analyzed for a given element. N, number of samples in which concentrations could not be detected at lower determination limit. L, number of samples in 

which concentrations were detectable but below lower determination limit. G, number of samples in which concentrations were greater than the upper detection limit. 

Expected range is distribution of 95 percent of all data expected for log-normal data) 

Element Detection N L G Minimum Median 90th 95th 98th Maximum Geometric Geometric Expected 

Ratio percentile percentile percentile mean deviation range 

Fe 1.00 0 0 0 1.0 7 10 15 15 20 6.0 1. 8 1.9-19 

Mg 1.00 0 0 0 .7 1.5 2 2 3 3 1.5 1.4 0.8-2.9 

Ca 1.00 0 0 0 .2 1 1.5 2 3 1.0 1. 5 0.4-2.3 

Ti .95 0 0 17 .1 • 7 1 1G 1G .6 1.7 0.2-1.7 

Mn .99 0 0 1 300 1,000 1,500 1,500 2,000 S,OOOG 931 1.5 414-2,095 

Ag .03 319 19 0 .5N .SN .SN .5L .5 2 

As .01 341 5 0 200N 200N 200N 200N 200N 200 

B .76 4 79 0 10N 10 so 150 300 1,500 16 2.6 2.4-108 

Ba 1.00 0 0 0 50 300 500 700 1,000 1,000 262 1. 9 73-946 

Be .03 238 99 0 1N 1N 1L 11 1 1 

Co 1.00 u 0 0 10 30 70 100 100 100 32 2.0 8.0-128 

Cr .99 0 1 0 101 70 150 200 200 300 79 1.7 27-228 

Cu 1. 00 0 0 0 7 20 50 50 70 500 25 1.7 8.7-72 

La .04 333 0 0 20N 20N 20N 20N so 100 

Mo .07 292 29 0 5N 5N 51 5 10 30 

Ni .99 1 0 0 5N 20 30 30 50 70 19 1. 5 8.4-43 

Pb .60 34 104 0 10N 10 20 20 30 200 9.9 1.6 3.9-25 

Sc 1.00 0 0 0 10 20 50 50 so 70 26 1.6 10-67 

Sr .99 2 3 0 lOON 200 300 300 sou 500 203 1.5 'J0-457 

v 1.00 0 0 0 70 200 700 1,000 1,000 1,500 273 2.1 62-1 ,204 

y 1.00 0 0 0 15 30 30 50 50 50 27 1. 3 16-46 

Zn .22 204 66 0 200N 200N 200 300 300 500 129 1.5 57-290 

Zr 1.00 0 0 0 30 100 150 200 300 1,000 92 1.6 36-236 

Southwestern Alaska 133 
River from the Big River headwaters. Samples with 

highest scores onto factor 5 are widely distributed 

over the former area whereas those with anomalously 

low scores are found in the latter. The Cr-Mg-Mn-Sc-

(-Ba) factor 3 association is characteristic of the 

Tertiary volcanic units, and samples with high scores 

onto this factor span across the entire region from 

Hallo Glacier to the Katmai River. 

High factor 2 loadings were calculated for Co, 

Cu, Fe, and Ni, a geochemical relationship indicative 

of abundant pyrite within the collected concentrates. 

Samples with high scores onto this factor generally 

contain 20 to 90 percent pyrite and cluster within 

three areas: (1) the southwest side of Fourpeaked 

Mountain (shown as area 2a on fig. 1), (2) the entire 

Katmai Canyon north of the Barrier Range (2b, fig. 1), 

and (3) the higher elevations of the Kejulik Mountains 

between Martin Creek and the Kejulik River (2c, fig. 

1). In the Fourpeaked Mountain area, both hypabyssal 

bodies and sandstone within the sampled watersheds 

are strongly silicified and contained abundant 

disseminated pyrite. Tertiary intermediate volcanic 

rocks within Katmai Canyon commonly are strongly 

silicified, iron-stained, and contain abundant pyrite. 

Silicified, volcanic breccia float taken near the toe of 

the glacier at the head of the canyon contained up to 2 

ppm Ag, 300 ppm As, 100 ppm Mo, and 6 ppm Sb. The 

source for most of the pyrite in the Kejulik Mountains 

is uncertain. However, volcanic rocks within the 

headwaters of the west branch of Martin Creek are 

extremely silicified and bleached, and consistently 

carry 0.3 to 0.5 ppm Hg and up to 2900 ppm F. 

In addition to the three broader areas described 

above, a few concentrate samples with anomalous 

factor 2 scores and microscopically visible 

arsenopyrite were collected from the Hagelbargers 

Pass area (fig. 1, area 2d). Pyrite-bearing quartz 

breccia within intermediate volcanic rocks was 

sampled at two localities southeast of the pass. One 

sample contained 0. 7 ppm Ag and 0.8 ppm Au, and a 

second contained 0.25 ppm Au and 6 ppm Sb. 

Samples with highest factor 4 scores contain 

anomalous amounts of Ag, Cu, Mo, Pb, and (or) Zn. 

One large cluster of samples includes those from most 

drainages underlain by sedimentary rocks to the south 

of Fourpeaked Mountain (fig. 1, area 4a). These 

samples cover a much more extensive area than the 

pyrite-rich concentrates described above as spatially 

associated with hypabyssal rocks on the southwest side 

of Fourpeaked Mountain. Bennett and Church (1987) 

listed 10 to 40 percent pyrite, arsenopyrite, 

chalcopypyrite, sphalerite, galena, wulfenite, and (or) 

scheelite as occurring within the anomalous samples. 

A single sample contained visible gold. A second 

occurrence of widespread concentrates with high 

factor 4 scores is located to the northwest of Kukak 

Bay (fig. 1, area 4b), an area underlain by both 

intermediate volcanic and hypabyssal rocks. 

Wulfenite, galena, chalcopyrite, and abundant pyrite 

were identified in many of these samples. Intrusive 

and volcanic rocks throughout this area show strong 

sericitic alteration, potassic alteration, and 

silicification, and they contain abundant disseminated 

pyrite with lesser arsenopyrite. 

Wilson and Cox (1983) described porphyryrelated sulfide mineralization irregularly distributed 

over the entire Alaska Peninsula. Geochemical 

signatures within concentrate samples collected across 

Table 2. Univariate statistical estimates for elements in 337 nonmagnetic heavy-mineral concentrate samples 

[Values for Fe, Mg, Ca, and Ti in percent; all other values in parts per million. Column headings same as for table 1 I 

Element Detection N L G Ninimum Ned ian 90th 95th 98th Maximum Geometric Geometric Expected 

Ratio percentile percentile percentile mean deviation range 

Fe 0.99 u u u.s 20 30 30 soc 3.8 2.8 0.5-30 

:lg 1.UU 0 0 0 .s . 7 3 5 7 .6 3.5 0.05-7.4 

Ca 1.1)1) u u () .1 2 5 7 10 2.0 2.0 0.5-8.0 Ti p 0 u 95 .I 2G 2G 2G 2G l.l 2.3 0.2-5.8 

,'In 1.01) u u u su 1 ,ouu 2,0UU 2,000 2,UOO 3,000 738 2.2 lS2-3,572 

Ag .20 247 22 1 IN IN 2 5 20 I,OOOG .8 3.0 0.09-7.2 As • 12 284 13 () SOUN SOON 500 1,000 3,000 10,000 

Au .02 327 1 3 20N 20N 20N 20N 20 I ,OOOG B .713 58 l3 20N su 2,000 5,000 S,OOOG S,OOUG 93 6.1 2.5-3,46I 

Ba 8') 0 3U 29 SOL 1,000 10,000 lO,OOOG 10,000G lO,OOOG 737 6.0 20-26,530 

Be .01 247 88 u 2N 2N 2L 2L 2L 5 

Bi .OS 316 3 u 20N 20N 20N 20 so 1,000 

Cd .04 309 13 () SON SON SON SOL 100 500 

Co .137 8 36 lJ ION 3U 100 150 500 1,000 32 2.8 4.1-251 

Cr .82 2 59 u 20N 50 200 200 300 1,000 51 2.6 7.5-345 

Cu ,91 0 30 u 10L 50 300 500 500 2,000 47 3.7 3.4-643 

La .45 177 7 u SUN SUN 200 300 500 1,000 54 2.5 8.6-338 

rio .20 247 22 ll 10N ION 20 50 200 I,OOO 7.3 2.4 1.3-42 

Nb .OS 254 67 u SON SON SUL SOL so 100 

Ni .70 87 13 (I ION 20 100 200 200 500 21 3.3 1.9-229 

Pb . 6I 64 69 0 20N 20 200 500 1,500 5,000 40 3.9 2.6-608 

Sb .I) l 336 0 0 200N 200N 200N 200N 200N 500 

Sc .89 25 I2 u ION 50 IOO 100 100 200 37 2.5 5.9-231 Sn .20 240 30 0 20N 20N 30 50 70 200 13 1.7 4.5-38 

Sr .59 78 bO 200N 200 700 I,OOO 2,000 lO,OOOG 245 2.4 43-1,411 

v .99 0 l (I 206 150 200 300 300 1,000 126 1.9 35-455 

w .01 330 3 0 IliON lOON lOON lOON IOOL 1,500 

.99 I) u 20L 150 1,500 1,500 1,500 2,000 193 3.3 18-2,102 

Zn .lS 267 2I 0 SOON SOON 500 2,000 5,000 20,000 

Zr .34 u (I 223 20 2,000G 2,000G 2,000G 2,000G 2,000G 1,699 2.5 272-10,620 Th .ou 334 3 0 200N 200N 200N 200N 200N 200L 

134 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 3. Fador loadings for the first five fadors after varimax rotation of the log 

transformed concentrate data 

[Total variance explained by five factors equals 70 percent. Leaders(--), loading less than 10.301 that 

have been omitted] 

Element 2 

Fe 0.89 

Mg -0.43 

Ca .61 

Ti .89 

Mn 

Ag 

B .66 

Ba 

Co .83 

Cr 

Cu .67 

La .79 

Mo 

Ni .88 

Pb .35 

Sc .33 

Sn 

v .69 y .91 

Zn 

Zr .64 

Percent of 

total 

variance 21 15 

many of these systems consist of a widespread Ag-AsAu-Cu-Pb-Zn association surrounding a Cu-Mo-W suite 

closer to the center of the mineralized systems. Areas 

delineated in our study by samples with high factor 2 

or factor 4 scores (fig. 1) represent localities with 

highest geochemical favorability for porphyry and 

epithermal base-metal vein occurrences. 

Gold was only detected within nine of the 

concentrate samples collected within the studied area 

(fig. 1). This may in part reflect the loss of fine gold 

during panning or the loss of iron-oxide coated gold 

grains into the unanalyzed magnetic concentrate 

fraction. Atomic absorption analysis of samples from 

22 of the sites within strongly altered watersheds 

showed three cases where minor amounts of gold were 

detected in magnetic concentrate fractions but not in 

the nonmagnetic fractions or corresponding 

sediments. Similarly, in two cases, gold was only 

detected in the sediments and not within either 

concentrate fraction (R.J. Goldfarb, unpub. data). 

Three of the nine gold-bearing nonmagnetic 

concentrates were collected in drainages underlain by 

Naknek sedimentary rocks between the Swikshak and 

Big Rivers (fig. 1, area 1a). These samples, which also 

have anomalous Ag, As, Bi, Co, Cu, Mo, Pb, W, and Zn 

concentrations, identify an area favorable for 

epithermal gold vein systems. A second target area 

for epithermal vein systems lies within the Ninigak 

River watershed (fig. 1, area 1b), where drainages 

underlain by both sedimentary and volcanic rocks 

yielded concentrates consistently enriched in Ag and 

As and occasionally anomalous in Zn. Five 

concentrates with microscopically visible cinnabar 

were collected along the southern edge of the study 

area, within the sedimentary and volcanic rocks 

between Amalik Bay and the mouth of the Katmai 

River (fig. 1, area 3). This area and the Martin Creek 

region described earlier (within area 2c) represent two 

localities with geochemical favorability for shallowlevel Hg-Au hydrothermal systems. 

Factors 

4 5 

0.74 

-0.34 

.84 

0.76 

-.62 .31 

.55 .64 

.46 

.77 

.76 

.74 . 75 

.38 .34 

-.38 .53 

-.30 

14 11 8 

REFERENCES CITED 

Bailey, E.A., Sutley, S.J., Arbogast, B.F., 

Wilson, W.R., and Church, S.E., 1986, 

Analytical results and sample locality map 

of stream-sediment and heavy-mineralconcentrate samples from the Mount Katmai 

quadrangle, and portions of the Naknek, 

Afognak, and Illiamna quadrangles, Alaska: 

U.S. Geological Survey Open-File Report 86-

586, 126 p., scale 1:250,000. 

Bennett, G.J. and Church, S.E., 1987, Mineralogy 

and sample locality map of the nonmagnetic 

heavy-mineral concentrate samples from the 

Mount Katmai quadrangle and portions of the 

Naknek, Afognak, and Illiamna quadrangles, 

Alaska: U.S. Geological Survey Open-File 

Report 87-615, 39 p., scale 1:250,000. 

Keller, A.S., and Reiser, H.N., 1959, Geology of 

the Mount Katmai area, Alaska: U.S. 

Geological Survey Bullet in 1058-G, p. 261-

298. 

Miesch, A. T., 1976, Geochemical survey of 

Missouri--Methods of sampling, laboratory 

analysis, and statistical reduction of 

data: U.S. Geological Survey Professional 

Paper 954-A, 39 p. 

Wilson, F.H. and Cox, D.P., 1983, Geochronology, 

geochemistry, and tectonic environment of 

porphyry mineralization in the central 

Alaska Peninsula: U.S. Geological Survey 

Open-File Report 83-783, 24 p. 

Reviewers: S.E. Church and J.E. Kilburn 

Geologic Studies 1n Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southwestern Alaska 13 5 

SOUTHEASTERN ALASKA 

U.S.-Canada boundary peak, Devils Paw (right), highest peak of the juneau lcefield region (elevation 8,584 

feet). Michaels Sword on left. Composed dominantly of Permian(?) and Mesozoic(?) hornfels, showing 

contact near base with Tertiary (50 Ma) granodiorite. Photograph by A.B. Ford. 
Relative Timing of Porphyroblast Growth, Foliation 

Development, and Ductile Shear in Pelitic Metamorphic Rocks 

from the Juneau Area, Southeastern Alaska 

By Robert L. Bauer, Glen R. Himmelberg, David A. Brew, and Arthur B. Ford 

A regional metamorphic belt containing mineral 

assemblages that range from the prehnite-pumpellyite 

metagraywacke facies to the upper amphibolite facies 

is exposed along the western margin of the Coast 

plutonic-metamorphic complex in southeastern 

Alaska. Index mineral isograds in the pelitic rocks 

were first documented by Forbes (1959) and have been 

mapped over an extensive area by Ford and Brew 

(1973, 1977) and Brew and Ford (1977). More recently, 

the index mineral isograds on Heintzleman and 

Blackerby Ridges near Juneau (fig. 1) were shown to 

mark particular model reactions and are thus reaction 

isograds (Himmelberg and others, 1984a). 

Metamorphic textures in the pelitic rocks on 

Heintzleman and Blackerby Ridges were described by 

Himmelberg and others (1984b), who noted that an 

older internal foliation (Si) is commonly preserved in 

porphyroblasts of biotite and garnet. si is locally 

curved and at a high angle to the later-formed 

external schistosity (Se>· Recent work on 

porphyroblast growth in deforming metamorphic rocks 

has shown that deformation partitioning between 

porphyroblasts and matrix (Bell, 1981, 1986) and 

porphyroblast growth during the development of 

crenulation foliation (for example, Bell and Rubenach, 

1980, 1983; Bell and others, 1986) can produce curved 

inclusion trails in porphyroblasts that do not require 

porphyroblast rotation for their formation (Spry, 1969). 

In this report we describe metamorphic textures 

and microfabrics that bear on the relationship between 

porphyroblast growth and the deformation history of 

the schists in the Juneau area and are consistent with 

the observations of Bell and coworkers. Our 

observations indicate that porphyroblasts of garnet, 

biotite, kyanite and staurolite grew over and included 

an early foliation (referred to here as s 1) that was 

folded and overprinted by a younger crenulation 

foliation (referred to here as s 2). Inclusion trails in 

the garnet and biotite porphyrotilasts record stages in 

the development of the s 2 crenulation foliation (fig. 

2), and, in cases where s 1 has been completely 

overprinted in the rock matrix, these porphyroblasts 

preserve the only evidence of early S; foliation. 

Local late-stage shearing--evident from biotite 

fish (see fig. 3E for illustration) (Eisbacher, 1970; 

Lister and Snoke, 1984) and shear bands--has 

obliterated evidence for S in the matrix of some of 

the rocks. In these rocks the porphyroblasts preserve 

the only evidence for both S and s 2. The samples 

described here were not orienfed in the field, thus the 

relative sense of shear is uncertain. However, our 

petrographic observations, described below, indicate 

that this is a post-s2 fabric which will require further 

field study in order to establish its distribution and 

relationship to previously identified regional 

deformation features. 

This investigation is part of a larger study of 

the metamorphism and deformation of the rocks near 

Juneau; as recently summarized by Brew and others (in 

press), this metamorphic belt evolved in several stages 

between about 120 Ma and 50 Ma. The textures 

described here are interpreted to have formed during 

two major tectonothermal events, the first sometime 

between 120 and 90 Ma and the second sometime 

between 90 and 70 Ma. 

Poikiloblastic garnet and biotite from the 

Juneau area contain quartz and(or) graphite inclusion 

trails that display a range of forms and relationships to 

matrix foliations (table 1). These relationships allow 

interpretation of the generation of foliations in both 

the porphyroblasts and in the rna trix, and of the 

relative timing of biotite and garnet porphyroblast 

growth. The six observed relationships and their 

interpretations are summarized in table 1. 

The first two relationships are relatively 

uncommon in the Juneau rocks. The type 1 

relationship, with straight porphyroblast inclusions 

continuous into a straight matrix foliation, indicates 

an s 1 foliation with no evidence for younger or older 

foliations. Both biotite and garnet show this 

relationship in outcrops that are relatively unaffected 

by the second deformation. The type 2 relationship, 

with straight porphyroblast inclusion trails in a matrix 

with a crenulation foliation (fig. 3A), was observed in 

some small subhedral garnet porphyroblasts that grew 

early and surrounded inclusions parallel to s 1, but 

stopped growing before the generation of the s 2 crenulation foliation in the matrix. Biotite 

porphyroblasts in the same samples, however, locally 

include curved inclusion trails, indicating that the 

biotite grew during the early (stage 2) development of 

the S crenulation foliation in the matrix. This 

charac1erizes type 3 relationships, and indicates in this 

case that the biotite is younger than the coexisting 

garnet. This relative timing is also indicated by the 

inclusion of garnet in the biotite (fig. 3A). 

The type 3 relationship is much more common 

in the Juneau area rocks than either the type 1 or type 

2 relationships. Curved to distinctly folded inclusion 

trails, representing various stages in the development 

of the matrix crenulation foliation, occur in both 

biotite and garnet. In some cases the inclusion trails 

138 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Index mop of southeastern Alaska, 

showing location of figure I. 

Figure 1. Sketch map of the juneau area, showing regional distribution of metamorphic facies and relation to 

plutonic units of the Coast plutonic-metamorphic complex near juneau . Dashed-line pattern shows 

approximate foliation trends in orthogneiss plutons. Crosses denote little-fol iated post-tectonic granitic pluton. 

Inset topographic map (500 -ft contours) shows first occurrences in northeastward transects on Heintzleman 

and Bl ackerby Ridges of biotite (B), garnet (G), staurolite (ST), kyanite (K), and sillimanite (51), and occurrences 

of chloritoid (C). After Hi mmel berg and others (1984b). 

----- ~ II • '~I W''l''' '8~') 11 111 11 =- -=--- ~1~ 

~~ ~ 1','1 Ill) '' II ,:,~ I, 'l~ \// t: Wi%' Ill II ~~~ I I~ 1

1

.' I '11 1111

1

11[11111' ,r11 ,,, 

~-=--= ..=-.:: II litli,,Jil//11 

2 3 4 5 6 

Figure 2. Six stages in development of new (52) crenu lation foliation, oriented N-S in stages 4, 5 and 

6, from older (51) foliation, oriented E-W in stage 1 (from Bell and Rubenach, 1983). 

Southeastern Alaska 139 
c 

Figure 3. Photomicrographs of Juneau area schists, showing 51-

52 relationships. A, Garnet and biotite porphyroblasts 

containing straight inclusion trails parallel to 51 that are at high 

angle to 52 crenulation foliation in matrix (type 2 relationship). 

Biotite in other parts of sample show curved inclusion trails 

indicating that it grew after garnet in this sample (type 3 

relationship) (sample 81 SK011 A). B, Biotite porphyroblasts 

containing folded inclusion trails of quartz and graphite parallel 

to 51 (type 3 relationship). 52 crenulation foliation in matrix 

continued to develop after biotite growth resulting in offset of 

biotite porphyroblasts (sample 83GH020A). C, Biotite 

porphyroblast containing folded graphite inclusion trails . 

Inclusion trails are the only remnants of 51 and are sharply 

truncated by stage 6 52 foliation in matrix (type 4 relationship) 

(sample 81 DB020A). D, Garnet porphyroblast containing 

crenulated (stage 4) trails that display both 51 and 52 orientations. 

Inclusion trails are sharply truncated by shear-induced foliation 

in matrix that, in this case, is parallel to 52 preserved in garnet but 

overprints 52 in matrix (sample 79GH022A). E, Biotite fish 

porphyroblasts, containing quartz inclusion trails parallel to 51, 

deformed by left-lateral shear. Undeformed retrograde ch lorite 

(c) grows across sheared boundaries of biotite (sample 

79GH022B). F, Garnet porphyroblast consists of outer zone 

containing curved inclusion trails of quartz that has overgrown 

euhedral garnet with straight inclusion trails (sample 

81 GH006C1 ). 

140 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Summary of relationships observed between porphyroblast inclusion trails and matrix foliation in pelitic schists from the 

Juneau area 

[See figure 2 for explanation of foliation stages, which are after Bell and Rubenach (1983)) 

Porphyroblast inclusion fabric Matrix fabric 

Relationship Inclusion Foliation Deformation Foliation Foliation Deformation 

type no. trail forms stage{s) features form stage(s) features 

1 Straight 1 sl 

2 Straight 1 sl 

3 curved 2 or 3 sl & 

4 Curved 2 or 3 sl & 

5 Curved & 4 sl & 

straight 

6 Curved & 4 sl & 

straight 

are continuous into the adjacent crenulation foliation 

in the matrix, but in many cases the inclusion trails 

are truncated by the matrix foliation that continued to 

develop after porphyroblast growth had ceased {fig. 

38). 

When the crenulation foliation continues to 

develop to stages 5 or 6, mica grains that parallel s1 and define the crenulations in the matrix become 

completely aligned parallel to s2• The crenulation 

foliation then becomes a spaced or continuous s2 foliation with no matrix evidence for s1• This results 

in the type 4 relationship {fig. 3C). In this case the 

only evidence for s1 is preserved in the curved 

inclusion trails in the porphyroblasts that are 

truncated by the matrix foliation. This relationship 

occurs in both biotite and garnet porphyroblasts in the 

Juneau rocks. 

In many of the rocks from the Juneau area, 

garnet has overgrown the s2 crenulation foliation after 

new micas were concentrated in zones aligned parallel 

to s2 and separating microlithons containing 

asymmetric crenulation of s1 {stage 4). 

Porphyroblasts of this type (fig. 3D) contain curved s1 inclusion trails tangential to straight zones parallel to 

s2 that are relatively inclusion free as a result of 

overgrowing the mica-rich concentrations that define 

s2 in the matrix. Such inclusion trails occur in both 

the type 5 and type 6 porphyroblast-matrix 

relationships. In the type 5 case, the crenulation 

foliation in the matrix shows the same stage of 

crenulation foliation development as that preserved in 

the porphyroblasts--with both s1 and s2 preserved. In 

the type 6 relationship, the foliation in the matrix has 

progressed to stage 5 or 6 (fig. 2), and the only 

evidence for s1 is in the porphyroblast inclusion trails. 

Biotite porphyroblasts were not observed in 

either type 5 or type 6 porphyroblast-matrix 

relationships, and, with the exception of the coexisting 

type 2 garnet and type 3 biotite porphyroblast 

relationships described above, biotite growth in any 

given sample always began and ended at an earlier 

F2 

F2 

s2 

s2 

Straight 1 sl 

Crenulation 4 sl & s2 

Crenulation 4 sl & s2 

Straight 5 or 6 52 

Crenulation 4 sl & s2 

Straight 5 or 6 s2 

crenulation foliation stage than the garnet 

porphyroblasts. 

Late-stage shearing, younger than the s

2 foliation, is evident locally from biotite fish (fig. 3E), 

typical of the type II 8-C mylonites described by Lister 

and Snoke (1984), and from shear bands that transect 

small-scale F 2 folds. In some samples the plane of the 

shear {C-plane) in the matrix is parallel to s2 as 

defined by inclusion trails in garnet porphyrobfasts 

(fig. 3D). In such cases the shearing could be 

interpreted to be either (1) a result of continued 

displacement associated with formation of the 

crenulation foliation, or (2) a younger shearing event. 

In other samples, however, the matrix shear sense is 

opposite that suggested by the asymmetry of the stage 

4 crenulation inclusion trails in garnet porphyroblasts, 

indicating that the shearing is not directly related to 

the deformation that produced the s2 crenulation 

foliation. Samples displaying these shear fabrics can 

be classified as type II S-C mylonites, as defined by 

Lister and Snoke (1984), but our petrographic 

observations indicate that earlier S-foliations are not 

genetically related to the shearing event. 

Some of the sheared samples contain elongate 

garnet porphyroblasts that have rotated and (or) 

broken up during the shearing. This indicates that 

shear strains were not completely partitioned around 

the porphyroblasts (Bell, 1986; and Prior, 1987). Many 

of the broken porphyroblasts contain subhedral 

overgrowths of garnet around their broken margins, 

indicating that garnet continued to grow after the 

shearing. Undeformed grains of retrograde chlorite 

grow across the shear foliation in some of the samples 

(fig. 3E). 

In summary, textural interpretations of the 

relative timing of porphyroblast growth suggest that 

euhedral to subhedral garnet porphyroblasts grew in 

some of the schists of the Juneau area at an early 

stage before or during the very early stages of s2 formation. This was followed by biotite growth during 

the crenulation stages (stages 2 and 3) of s2 

Southeastern Alaska 141 
formation. Later stage garnet growth occurred in 

many of the rocks during the later (stages 3 and 4) 

development of 82 and was invariably younger than 

biotite growth in a given sample. In rare samples this 

later stage of garnet growth has occurred epitaxially 

over the early euhedral to subhedral garnets (fig. 3F). 

The petrographic observations described in this 

report indicate that amphibolite facies porphyroblasts, 

generated during the major metamorphic event 

between 90 and 70 Ma of Brew and others (in press), 

grew during the progressive development of a 

crenulation foliation and continued to grow during 

late-stage shearing under probable waning 

metamorphic conditions. The 8 and 82 foliations 

described here are interpreted to ~ave formed during 

both the deformational event between 120 and 90 Ma 

and that between 90 and 70 Ma of Brew and others (in 

press). The nature and extent of the observed latestage shearing is unclear, but it may be related to the 

mylonite zone that commonly forms the southwestern 

contact of the great tonalite sill described by Brew 

and others (in press). 

REFERENCES CITED 

Bell, T.H., 1981, Foliation 

contribution, geometry and 

progressive, bulk, 

development--The 

significance of 

inhomogeneous 

shortening: Tectonophysics, v. 75, p. 272-

296. 

1986, Foliation development and refraction 

--i-n metamorphic rocks: Reactivation of 

earlier foliations and decrenulation due to 

shifting patterns of deformation 

partitioning: Journal of Metamorphic 

Geology, v. 4, p. 421-444. 

Bell, T.H., and Rubenach, M.J., 1980, 

Crenulation cleavage development--Evidence 

for progressive bulk inhomogeneous 

shortening from "millipede" microstructures 

in the Robertson River metamorphics: 

Tectonophysics, v. 68, p. T9-Tl5. 

1983, Sequential porphyroblast growth and 

~enulation cleavage development during 

progressive deformation: Tectonophysics, v. 

92, p. 171-194. 

Bell, T.H., Rubenach, M.J., and Fleming, P.D., 

1986, Porphyroblast nucleation, growth and 

dissolution in regional metamorphic rocks as 

function of deformation partitioning during 

foliation development: Journal of 

Metamorphic Geology, v. 4, p. 37-67. 

Brew, D.A., and Ford, A.B., 1977, Preliminary 

geologic and metamorphic-isograd map of the 

Juneau B-1 quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-846, scale 1:31,680. 

Brew, D.A., Ford, A.B., and Himmelberg, G.R., 

1988, Evolution of the western part of the 

Coast plutonic-metamorphic complex, 

southeastern Alaska, U.S.A., in Daly, S.R., 

ed., Evolution of metamorphic belts: 

Geological Society of London Special Paper 

32 [in press]. 

Eisbacher, G.H., 1970, Deformation mechanics of 

mylonitic rocks and fractured granites in 

Cobequid Mountains, Nova Scotia, Canada: 

Geological Society of America Bulletin, v. 

81, p. 2009-2020. 

Forbes, R.B., 1959, The bedrock geology and 

petrology of the Juneau Ice Field area, 

southeastern Alaska: Seattle, University of 

Washington, Ph.D. Dissertation, 260 p. 

Ford, A.B., and Brew, D.A., 1973, Preliminary 

geologic and metamorphic-isograd map of the 

Juneau B-2 quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-527, scale 1:31,680. 

1977, Preliminary geologic and metamorphic-

---isograd map of the northern parts of the 

Juneau A-1 and A-2 quadrangles, Alaska: 

U.S. Geological Survey Miscellaneous Field 

Studies Map MF-847, scale 1:31,680. 

Himmelberg, G.R., Ford, A.B., and Brew, D.A., 

1984a, Reaction isograds in pelitic rocks of 

the Coast plutonic-metamorphic complex near 

Juneau, in Reed, K.M., and Bartsch-Winkler, 

Susan, eds., The United States Geological 

Survey in Alaska: Accomplishments during 

1982: U.S. Geological Survey Circular 939, 

P• 105-108. 

1984b, Progressive metamorphism of pelitic 

rocks in the Juneau area, southeastern 

Alaska, in Coonrad, W.L., and Elliott, R.L., 

eds., The-united States Geological Survey in 

Alaska: Accomplishments during 1981: U.S. 

Geological Survey Circular 868, p. 131-134. 

Lister, G.S., and Snoke, A.W., 1984, S-C 

mylonites: Journal of Structural Geology, 

v. 6, p. 617-638. 

Prior, D., 1987, Syntectonic porphyroblast 

growth in phyllites: textures and 

processes: Journal of Metamorphic Geology, 

v. 5, p. 27-39. 

Spry, A., 1969, Metamorphic textures: Oxford, 

Pergamon Press, 350 p. 

Reviewers: S.L. Douglass and M.M. Donato 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

142 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
A Reexamination of the Contacts and Other Features of the 

Gravina Belt, Southeastern Alaska 

By David A. Brew and Susan M. Karl 

The Gravina belt rocks are part of the GravinaNutzotin belt as defined by Berg and others (1972). 

This report concerns only the part of the belt that is in 

southeastern Alaska, and we therefore refer to the 

rocks as the Gravina belt. As defined by Berg and 

others (1972), the belt consists of flysch, min or 

nonmarine strata, and interbedded andesitic volcanic 

rocks; fossil data cited by them indicate a late Middle 

and Late Jurassic to late Early Cretaceous (Albian) 

age. On the west side of the belt, the rocks are 

inferred to depositionally overlie lower Paleozoic and 

Triassic rocks of the Alexander terrane; at most places 

on the east side of the belt, they are interpreted to be 

overthrust by older and more metamorphosed rocks. 

The relations of the Gravina belt rocks to 

adjacent rocks are important both because they are 

the basis for the argument that the Gravina belt rocks 

actually overlapped the older rocks on the western 

(and perhaps the eastern) margins of the Gravina basin 

and because they constrain post-Gravina fault 

movements. In this paper we (1) examine the features 

that led Berg and others (1972, 1978) to postulate an 

overlap relationship; (2) reinterpret the relations of 

units present in the vicinity of Gravina Island; and (3) 

interpret the Gravina belt rocks as a lithostratigraphic 

unit. 

For this study, we examined (1) almost all of 

the localities where Gravina belt rocks have been 

reported to be in nonfaulted contact with older strata 

of the Alexander-Wrangellia superterrane or with 

highly metamorphosed rocks of the western 

metamorphic belt of the Coast plutonic-metamorphic 

complex; (2) several localities where fault contacts 

have been reported by others and we wished to verify 

the relations; and (3) all nonfaulted and a few faulted 

contacts where we have unpublished information from 

our own mapping. 

The Gravina belt contacts we examined fall into 

four main categories: (1) apparent stratigraphic 

superposition of Gravina belt rocks on older rocks of 

the Alexander-Wrangellia superterrane; (2) apparent 

fault contact between the two; (3) apparent gradation 

from unmetamorphosed (or only somewhat 

metamorphosed) rocks into metamorphic rocks of the 

western metamorphic zone (or belt) of the Coast 

plutonic-metamorphic complex (Brew and Ford, 1984) 

whose protoliths cannot be identified with certainty; 

and (4) apparent fault contact between the Gravina 

belt rocks and metamorphic rocks of the Coast 

plutonic-metamorphic complex. These categories are 

used in table 1, listing the five localities most 

pertinent to this study (and also in a supplemental 

table of 33 localities that is available from the senior 

author) to classify the contact localities we have 

visited (fig. 1). 

Our studies reveal no localities where Gravina 

belt rocks stratigraphically overlie subjacent strata, 

although at five places we believe that an 

unconformable relation may exist. Of these, locality 2 

(fig. 1) (Redman, 1984) is the most certain, with 

granitic clasts forming a basal conglomerate that is 

reported (R.A. Leveille, University of Alaska, oral 

commun., 1987) to locally fill channels cut in the 

granitic rock. 

Near four of these five localities (2, 5a, 6, 7 on 

table 1) conglomeratic rocks mapped as part of the 

Gravina belt contain clasts that are locally derived 

from nearby rocks of the Alexander-Wrangellia 

superterrane. (The same relation exists at 13 other 

localities that are listed in the supplemental table.) 

This does not necessarily demonstrate overlap of the 

Gravina belt rocks on the older rocks, but it does 

demonstrate close proximity of the provenance terrane 

to the margin of the Gravina belt basin and supports 

the overlap interpretation. One of the best examples 

of this is near localities 6 and 7 (fig. 1), where 

limestone clasts containing Permian fossils like those 

in place to the west of the contact occur in a large 

conglomerate unit several kilometers east of the 

contact. 

Although the evidence for unconformable 

contacts and overlap is not conclusive, we interpret 

the above local relations together with the regional 

variation in the inferred substrates to the Gravina belt 

rocks to indicate that no large lateral movements have 

occurred along the margins of the Gravina belt rocks 

during or after their deposition. 

In the vicinity of Gravina and Annette Islands, 

the available evidence (Berg, 1972, 1973; Berg and 

others, 1972; D.A. Brew and S.M. Karl, unpub. data) 

indicates that some of the Gravina belt rocks are older 

and of different affinity than those elsewhere in the 

belt. All fossils reported from Gravina Island are from 

the western part of the island and are late Middle or 

Late Jurassic in age (Berg and others, 1972, p. D3, D5; 

Berg, 1973); those from Annette Island are of the same 

age (Berg, 1972). In contrast, from Etolin Island north 

to the vicinity of Haines, fossils from the belt are 

dominantly Early Cretaceous in age, although Late 

Jurassic fossils are present in the Screen Islands (Brew 

and others, 1984; Berg and others, 1972) and on 

southeastern Admiralty Island (Loney, 1964). No 

Middle Jurassic fossils have been reported north of 

Gravina Island. It is possible that nonfossiliferous 

rocks equivalent in age to those to the north are 

present on the eastern part of Gravina Island, on the 

Southeastern Alaska 143 
Cleveland Peninsula, and on Revillagigedo Island (D.A. 

Brew and S.M. Karl, unpub. data; C.M. Rubin, 

California Institute of Technology, oral commun., 

1987; Rubin and Saleeby, 1987). Furthermore, the 

volcanic rocks in the vicinity of Gravina Island appear 

to be chemically distinct from the volcanic rocks 

elsewhere in the belt (compare Berg and others, 1972, 

with Ford and Brew, this volume; also A.B. Ford, D.A. 

Brew and J.G. Crock, unpub. data). 

These fossil and chemical contrasts indicate 

that the southern part of the Gravina belt includes an 

older unit that is apparently not present elsewhere in 

southeastern Alaska. The major implication is that the 

unusual Middle and Upper Jurassic section on Gravina 

138° 

0 

I 

0 

50 MILES I 

50 KILOMETERS 

Screen 

Islands 

I 

and Annette Islands may be overlapped by the 

dominantly Lower Cretaceous part of the Gravina 

belt. As mapped (Berg, 1972, 1973), this contact is a 

high-angle fault on Gravina Island and a depositional 

contact on Annette Island. We have examined the 

latter locality (table 1, no. 20) and found the contact 

to be covered; both we and C.M. Rubin (oral commun., 

1987) interpret it most likely to be a fault. 

We emphasize here that the Gravina belt rocks, 

as informally defined by Berg and others (1972), would 

constitute a lithostratigraphic supergroup if formally 

defined. No previous effort, including the original 

definition, establishes this point, but it is clear from 

our own and previous studies that two separate 

PACIFIC 

0 C E AN Gravma 

Island 

Figure 1. Distribution of Gravina belt rocks in southeastern Alaska (within heavy outline) showing 

numbered localities referred to in table 1 and the supplemental table. 

144 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Compilation of studied localities in southeastern Alaska where Gravina belt rocks are interpreted as likely to be in stratigraphic 

contact with older rocks of the Alexander-Wrangellia superterrane 

Are field relations compatible 

with fault (F) or stratigraphic 

relations with AlexanderWrangellia superterrane ( S); 

Detailed Is gradational into metamorphic 

If fault, what type: 

vertical (V), highangle reverse (R), 

thrust (T), highangle normal (N), 

AlexanderWrangelliaderived 

clasts nearby 

in Gravina 

belt rocks 

Map Year(s) examina- contact rocks (G), and( or) fault or low-angle Source of visited data tion? exposed? contact with same (D)? normal (L) Remarks 

1a 1969,1985 Yes No F ,S 

1983 No Yes? 

Sa 1982 Yes No F ,S 

1982 No Not known F, S 

1982 No Yes? F ,S 

lithostratigraphic groups are represented in the belt. 

The Stephens Passage Group of central southeastern 

Alaska (Lathram and others, 1965) extends both to the 

south (Brew and others, 1984) and to the north (Brew 

and Ford, 1986), and the named and unnamed units in 

the vicinity of Gravina Island (Berg, 1973; Rubin and 

Saleeby, 1987) comprise a second and informal group. 

Thus, the Gravina belt rocks are a lithostratigraphic 

supergroup. Although informal use of the term 

supergroup is not proposed here, thinking of the 

Gravina belt rocks in this sense both provides more 

specific information than does the widely used, but 

very nonspecific term "belt" and avoids the implication 

that the belt rocks are a tectonostratigraphic terrane. 

In contrast to the original definition of Berg and 

others (1972), we would characterize the rocks of the 

Gravina belt as (1) a sequence of dominantly mudstone 

and sandstone turbidite deposits interbedded and 

interfingered with lesser amounts of basaltic and 

hawaiitic flows and breccias, and locally interbedded 

with significant but minor amounts of both graniticclast-bearing conglomerate and tuffaceous mudstone; 

and (2) as the metamorphic equivalents of these rocks 

where gradational relations are present. This 

conclusion is based on the significant volumes of 

granitic-clast-bearing conglomerate that are present 

(Loney, 1964; Lathram and others, 1965; Redman, 

1984; and Rubin and Saleeby, 1987), on the findings 

(Ford and Brew, this volume) that the dominant 

volcanic rocks are basalts and hawaiites, not andesites, 

and on the large volumes of slightly metamorphosed 

fine-grained mixed volcanic and nonvolcanic mudstone 

locally present as a separate facies within the belt 

(Brew and others, 1984). 

Although this article has focused on the Gravina 

belt rocks in southeastern Alaska, it is worth noting 

that possible outliers of the belt have recently been 

reported in British Columbia to the south (Hill, 1984; 

Douglas, 1986; Crawford and others, 1987). In 

V,R,N Not known Plafker and Fossil locality 7 8APr 136 

Yes 

others ,1979, (see ref.) is Cretaceous, 

this volume not Triassic as originally reported. Locality 

is 1.6 km N. of N. end 

Dalasuga Is. , Skagway 

A-1 quad. 

Redman, 1984 Redman reports stratigraphic contact with clasts 

of Jualin quartz diorite 

in overlapping sediments; 

we did not see the actual 

contact. 

V,R,N Yes Barker, 1957; Locality is 1.6 km W. of 

T,R? 

T,R? 

Yes 

Yes 

Lath ram and Symonds Point, Juneau 

others, 1965 B-3 quad. 

Lathram and Contact crosses creek at 

others, 1965 Accessible Point. 

Lathram and Contact is at base of steep 

others, 1965 cliff formed by Triassic 

volcanic rocks. 

addition, current Canadian stratigraphic 

interpretations now link the Jurassic and Cretaceous 

Bowser Basin of central British Columbia with rocks on 

the western side of the Coast plutonic-metamorphic 

complex; those latter rocks are inferred to be on strike 

with the aforementioned outliers of the Gravina belt 

(Wheeler and McFeely, 1987; J.O. Wheeler, Geological 

Survey of Canada, oral commun., 1987). Such a 

connection was first suggested by Brew and others 

(1966). 

From our systematic field study of mapped 

contacts between the rocks of the Gravina belt and 

older strata, we conclude that (1) none of the contacts 

visited to date are exposed; (2) most contacts may be 

interpreted as faults; (3) the best argument for the 

overlap of the Gravina belt rocks on older strata of the 

Alexander-Wrangellia superterrane (Berg and others, 

1972; 1978) is the incorporation of clasts from the 

superterrane in nearby sediments of the Gravina belt; 

and (4) no evidence exists to suggest that the Gravina 

belt rocks have been moved laterally large distances. 

In addition, age and other relations in the vicinity of 

Gravina Island suggest that some of the Gravina belt 

rocks there are atypical of the belt as a whole; they 

may be part of either the Gravina belt or the 

Alexander terrane, or they may comprise a 

tectonostratigraphic block or miniterrane that is not 

exposed elsewhere in southeastern Alaska. 

Stratigraphically, the Gravina belt rocks are an 

informal supergroup and should be recognized as such. 

REFERENCES CITED 

Barker, Fred, 1957, Geology of the Juneau (B-3) 

quadrangle, Alaska: U.S. Geological Survey 

Geologic Quadrangle Map GQ-100, scale 

1:63,360. 

Southeastern Alaska 145 
Berg, H.C., 1972, Geologic map of Annette 

Island, Alaska: U.S. Geological Survey 

Miscellaneous Geologic Investigations Map I684, scale 1:63,360. 

----- 1973, Geology of Gravina Island, Alaska: 

U.S. Geological Survey Bulletin 1373, 41 p. 

Berg, H.C., Jones, D.L., and Coney, P.J., 1978, 

Map showing pre-Cenozoic 

tectonostratigraphic terranes of 

southeastern Alaska and adjacent areas: 

U.S. Geological Survey Open-File Report 78-

1085, scale 1:1,000,000. 

Berg, H.C., Jones, D.L., and Richter, D.H., 

1972, Gravina-Nutzotin belt--tectonic 

significance of an Upper Mesozoic 

sedimentary and volcanic sequence in 

southern and southeastern Alaska, in 

Geological Survey Research 1972: U.S. 

Geological Survey Professional Paper 800-D, 

p. Dl-D24. 

Brew, D.A., and Ford, A.B., 1984, 

Tectonostratigraphic terranes in the Coast 

plutonic-metamorphic complex, southeastern 

Alaska, in Bartsch-Winkler, Susan, and Reed. 

K.M., eds., The United States Geological 

Survey in Alaska: Accomplishments during 

1982: U.S. Geological Survey Circular 939, 

p. 90-93. 

----- 1986, Preliminary reconnaissance geologic 

map of the Juneau, Taku River, At 1 in and 

part of the Skagway 1:250,000 quadrangles, 

southeastern Alaska: U.S. Geological Survey 

Open-File Report 85-395, 23 p. 

Brew, D.A., Loney, R.A., and Muffler, L.J.P., 

1966, Tectonic history of southeastern 

Alaska: Canadian Institute of Mining and 

Metallurgy Special Volume no. 8, p. 149-170. 

Brew, D.A., Ovenshine, A.T., Karl, S.M., and 

Hunt, S.J., 1984, Preliminary reconnaissance 

geologic map of the Petersburg and parts of 

the Port Alexander and Sumdum 1:250,000 

quadrangles, southeastern Alaska: U.S. 

Geological Survey Open-File Report 84-405, 2 

sheets, 43 p. pamphlet. 

Crawford, M.L., Hollister, L.S., and Woodsworth, 

G.J., 1987, Crustal deformation and regional 

metamorphism across a terrane boundary, 

Coast plutonic complexs British Columbia: 

Tectonics, v. 6, p. 343-361. 

Douglas, B.J., 1986, Deformational history of an 

outlier of metasedimentary rocks, Coast 

plutonic complex, British Columbia, 

Canada: Canadian Journal of Earth Sciences, 

v. 23, p. 813-826. 

Hill, M.L., 1984, Geology of the Redcap Mountain 

area, Coast plutonic complex, British 

Columbia: Princeton, N.J., Princeton 

University, Ph.D. thesis, 216 p. 

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and 

Loney, R.A., 1965, Reconnaissance geology of 

Admiralty Island, Alaska: U.S. Geological 

Survey Bulletin 1181-R, 48 p., 2 pls., scale 

1:250,000. 

Loney, R.A., 1964, Stratigraphy and petrography 

of the Pybus-Gambier area, Admiralty Island, 

Alaska: U.S. Geological Survey Bulletin 

1178, 103 p. 

Plafker, George, Hudson, T.L., and Silberling, 

N.J., 1979, Late Triassic fossils from a 

sequence of volcanic and sedimentary rocks 

on the Chi lkat Peninsula, southeastern 

Alaska, 1n Johnson, K.M., and Williams, 

J.R., eds., The United States Geological 

Survey 1n Alaska--Accomplishments during 

1987: U.S. Geological Survey Circular 804-

B, p. Bl07-Bl10. 

Redman, Earl, 1984, An unconformity with 

associated conglomeratic sediments in the 

Berners Bay area of southeastern Alaska: 

Alaska Division of Geological and 

Geophysical Surveys Professional Report 86, 

P• 1-4. 

Rubin, C.M., 

boundary 

southern 

Peninsula 

[abs.]: 

Abstracts 

826. 

and Saleeby, J.B., 1987, The inner 

of the Alexander terrane in 

SE Alaska, Part 1: Cleveland 

to southern Revi llagigedo Is land 

Geological Society of America, 

with Programs, v. 19, no. 7, p. 

Wheeler, J.O., and McFeely, P., 1987, Tectonic 

assemblage map of the Canadian Cordillera 

and adjacent parts of the United States of 

America: Geological Survey of Canada OpenFile Report 1565. 

Reviewers: Bela Csejtey, Jr. and W.J. Nokleberg 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

146 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Megafossils (Buchia) Indicate Late Jurassic Age for Part of 

Kelp Bay Group on Baranof Island, Southeastern Alaska 

By David A. Brew, Susan M. Karl, and John W. Miller 

Megafossils collected recently on Baranof Island 

from melange of the Khaz Formation (Kelp Bay Group) 

are interpreted to indicate that at least part of the 

unit is Late Jurassic (Tithonian) in age. This collection 

is important for three reasons: (1) it is the first 

megafossil collection of any kind reported from 

Baranof Island, (2) it supplements previous collections 

from Chichagof Island about 30 km to the north that 

indicate a Late Jurassic age for individual displaced 

blocks in the Khaz Formation, and (3) both the matrix 

and the enclosed blocks on Baranof Island contain the 

fossils of Tithonian age, thus implying a Late Jurassic 

age for the deposition of at least this part of the 

melange. These main points, together with 

information on the fossils and on the age of the 

adjacent Sitka Graywacke, are discussed below. 

0 2 3 

Saint John Baptist Bay is a 7-km-long, eastsoutheast-trending indentation on the northwest side 

of Baranof Island (fig. 1). As shown on the 

reconnaissance map of Loney and others (1975) and on 

the generalized maps of Plafker and others (1976, 

1977), the bay cuts across the regional structural grain 

and provides good shoreline exposures of the rocks of 

the Kelp Bay Group. The bay is aligned with an 

inferred fault that has truncated and (or) offset 

contacts within the melange (fig. 1). 

The Kelp Bay Group is the melange facies of 

the Chugach terrane in southeastern Alaska (Plafker 

and others, 1977). East of the head of the bay is the 

Border Ranges fault (fig. 1), which Plafker and others 

(1976) showed as separating the Chugach terrane from 

what we now refer to as the Alexander-Wrangellia 

EXPLANATION 

K haz Formation (late Jurassic 

Jt and Cretaceous) 

Jkku-Undivided 

JKkgm-Massive greenstone and 

pillow basalt 

JKkgg- Gray and green argillite matri 

greenstone, graywacke, and 

chert blocks 

<7-?0'0 JKka-gray argillite matrix,graywacke 

~e~ and argillite blocks . s! • 1/Jfe ' .9..>6 Jl\kge-gray and green argillite 

''ed t ') matrix, greenstone blocks 

JKku 

4 5 

au11 JKkgl- gray and green argillite matrix, 

greenstone and wackestone 

blocks 

Jt- Tonalite 

Thrust fault 

A....AA. barbs on upper 

plate 

KILOMETERS 

Fault dotted where 

concealed 

Figure 1. Geologic sketch map of Saint John Baptist Bay, Baranof Island, southeastern Alaska, showing distribution of informal 

units in the Khaz Formation and location (solid circle) of Buchia fischeriana collection. Geology from Loney and others (1975), 

modified by D.A. Brew and S.M. Karl (unpub. data). 

Southeastern Alaska 14 7 
superterrane. About 3 km west of the mouth of the 

bay (Loney and others, 1975) is the contact of the Kelp 

Bay Group rocks with the Sitka Graywacke, which is 

the flysch facies of the Chugach terrane in 

southeastern Alaska (Plafker and others, 1977). 

Recent detailed mapping of the shoreline of 

Saint John Baptist Bay (D.A. Brew and S.M. Karl, 

unpub. data) indicates that the Khaz Formation of the 

Kelp Bay Group (as defined by Karl and others, 1982, 

and by Johnson and Karl, 1985) is exposed around the 

entire bay. Generalized informal map units are shown 

on the sides of the bay in figure 1; their extent to the 

south and north is not known. On the south side of the 

bay the Khaz Formation is entirely melange, with 

blocks of massive dark-gray graywacke, dark-gray 

argillite, greenish-gray greenstone, and minor 

limestone enclosed in a deformed matrix of dark-gray 

argillite. Also present as matrix are units of thinly 

laminated millimeter- to centimeter-thick layered, 

light-green and dark-gray argillite that are interpreted 

to have been interbedded mudstone and tuff. The 

deformation in the matrix of the melange is shown by 

conspicuously folded and pulled-apart, thin, 

discontinuous, 0.5- to 2.0-cm-thick layers of light-gray 

limestone and calcareous argillite and by disrupted 

layers of the mixed light-green and dark-gray argillite. 

The megafossils were found on the south side of 

the bay about 1.1 km east-southeast of Zeal Point (fig. 

1). They occur in the melange, both in blocks of darkgray argillite a few meters in maximum dimension and 

also in the enveloping argillite matrix. Their 

occurrence in the blocks is clear-cut, as they are 

consistently closely crowded in argillite blocks that do 

not show the folding and pulling-apart that is common 

in the matrix. Scattered individuals occur in adjacent 

argillite that we interpret to be matrix close to the 

blocks. 

Abundant individuals were collected from the 

blocks and a few individuals from the matrix. The 

fossils are Buchia fischeriana (d'Orbigny) of Late 

Jurassic (late Tithonian) age. The same species occurs 

in large blocks in Khaz Formation melange on 

Chichagof Island (Decker, 1980b). Unspecified Buchia 

fossils of Tithonian(?) age were identified and reported 

by W. Connelly (in Decker, 1980b, p. 58) as being in 

turbidites that may be the matrix of part of the Khaz 

Formation at an unspecified locality in Slocum Arm on 

Chichagof Island; this locality was not recovered by 

other workers in the area, and neither Decker 

(1980a,b) nor Johnson and Karl (1985) proposed a Late 

Jurassic age for the matrix of the Khaz Formation. 

Other than the Connelly reference, no fossils have 

been reported from the melange matrix on Chichagof 

Island (Johnson and Karl, 1985, p. 5). 

Both Decker (1980a,b) and Johnson and Karl 

(1982, 1985) assigned a Cretaceous age to the Khaz 

Formation on Chichagof Island; we interpret this new 

locality on Baranof Island to indicate that the unit is 

at least in part Late Jurassic in age. 

This new megafossil collection should be 

considered in relation to the previously available 

megafossil and microfossil data from the Khaz 

Formation on Chichagof and Baranof Islands (table 1). 

Loney and others (1975, p. 20, 25) summarized their 

own and earlier megafossil collections from the 

Chichagof and Baranof Islands area; at that time the 

Buchia collections of Late Jurassic and Early 

Cretaceous age from Chichagof Island were 

interpreted to be from the Sitka Graywacke. Since 

that time re-study of the Chichagof area has resulted 

in both those and new localities being assigned to the 

Khaz Formation (Decker, 1980a,b; Johnson and Karl, 

1985). As noted above, no megafossils have been 

reported previously from Baranof Island. 

Radiolarians have been recovered from chert in 

the Khaz Formation at several localities. Plafker and 

others (1976) reported the occurrence of Valanginian 

to Hauterivian radiolarians on northern Baranof; that 

locality (which was reported by D.L. Jones, U.S. 

Geological Survey, written commun., 1975; and E. 

Pessagno, University of Texas, written commun., 1977) 

consists of stream boulders at Old Sitka, north of Sitka 

(George Plafker, U.S. Geological Survey, oral 

commun., 1976). One of us (Karl) has identified 

radiolarians in in situ cherts on northeastern Baranof 

Island and also at Katlian Bay, which is between the 

Saint John Baptist Bay and the Old Sitka localities, but 

poor preservation precluded determination of their 

age. Radiolarians collected by George Plafker from in 

situ chert at Katlian Bay in 1975 are also poorly 

preserved but were dated as possible Late Tithonian to 

Berriasian by Emile Pessagno (George Plafker, oral 

commun., 1987). This locality was recollected by 

Plafker in 1977 and found to contain a Tithonian 

radiolarian assemblage (George Plafker, oral commun., 

1987). Plafker's Katlian Bay chert locality is in what 

we have mapped as melange consisting of greenstone 

blocks in a matrix of gray and green argillite. 

Our documentation of the age of the blocks and 

matrix of the melange facies of the Chugach terrane 

on Baranof Island indicates that the melange there 

includes blocks of Late Jurassic age in a matrix of the 

same age. We hypothesize that the Chugach terrane 

and the Alexander-Wrangellia superterrane were 

adjacent during the time of melange formation. The 

volcanic arc we infer to have existed on the 

Alexander-Wrangellia superterrane in Middle and Late 

Jurassic time is therefore the likely source for the 

abundant greenstone and tuffaceous argillite and 

phyllite in the melange. That arc, which probably was 

one result of the accretion of the Chugach terrane, 

persisted into Early Cretaceous time. 

Our new information still leaves unanswered the 

question of the age of the Sitka Graywacke, the flysch 

facies of the Chugach terrane in southeastern Alaska. 

It is possible that the Sitka is the same age as the Kelp 

Bay Group or younger (Decker, 1980b). As noted by 

Johnson and Karl (1985), there are no fossil localities 

in the Sitka as it is now mapped. The closest fossil 

localities in rocks that are lithologically somewhat 

similar to the Sitka are the Early Cretaceous 

Inoceramus locality on nearby Emmons Island (Loney 

and others, 1975; Plafker and others, 1976; Johnson 

and Karl, 1985), a poorly documented locality with 

fossils reported to be Early Cretaceous in age in the 

St. Elias Mountains about 300 km to the northwest 

(Sharp and Rigsby, 1956), and Late Cretaceous 

megafossil and microfossil localities in the Yakutat 

Group some 200 km to the northwest (Plafker and 

others, 1976; George Plafker, written commun., 1987; 

Rau and others, 1983). The terrane affinity of the 

first two localities mentioned is uncertain, but that of 

148 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Fossil localities in the Khaz Formation, Kelp Bay Group, Chichagof and Baranof Islands, southeastern Alaska 

["Matrix," we interpret fossils to be in matrix of melange; "Blocks" indicates we interpret fossils to be in blocks in melange] 

Baranof Island Chichagof Island 

Katlian Bay Old Sitka St. John Baptist Slocum Arm 

Bay 

Age G.Plafker, Plafker and This paper Connelly, Decker, Loney and 

written, others, 1976 in Decker 1980b others, 

cornrnun., 1987 1980a 1975 

Cretaceous 

Hauterivian Blocks 

Valanginian Blocks 

Berriasian Blocks Blocks 

Jurassic 

Tithonian Blocks Matrix and Blocks Blocks Blocks 

Tithonian? 

Jurassic or Triassic 

the Yakutat Group localities is not. The affinity of 

the Yakutat Group localities is clearly with the 

Yakutat terrane, a small tectonostratigraphic terrane 

with an early history like that of the Chugach terrane 

and inferred to have been derived from part of the 

Chugach terrane (Plafker, 1987). 

REFERENCES CITED 

Decker, J .E., 1980a, Geologic map of western 

Chichagof Island, southeastern Alaska: U.S. 

Geological Survey Open-File Report 80-150, 2 

sheets, scale 1:63,360. 

----- 1980b, Geology of a Cretaceous subduction 

complex, western Chichagof Island, 

southeastern Alaska: Stanford, Calif., 

Stanford University, Ph.D. thesis, 134 p. 

Johnson, B.R., and Karl, S.M., 1982, 

Reconnaissance geologic map of the western 

Chichagof and Yakobi Islands Wilderness 

Study Area, southeastern Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-1476-A. 

----- 1985, Geologic map of western Chichagof 

and Yakobi Islands, southeastern Alaska: 

U.S. Geological Survey Miscellaneous 

Geologic Investigations Map I-1506, scale 

1:125,000, 15 p. pamphlet. 

Karl, S.M., Decker, J.E., and Johnson, B.R., 

1982, Discrimination of Wrangellia and the 

Chugach terrane in the Kelp Bay Group on 

Chichagof and Baranof Islands, southeastern 

Alaska, in Coonrad, W.L., ed., The United 

States Geological Survey in Alaska: 

Accomplishments during 1980: U.S. 

Geological Survey Circular 844, p. 124-128. 

Loney, R.A., Brew, D.A., Muffler, L.J.P., and 

Pomeroy, J.S., 1975, Reconnaissance geology 

of Chichagof, Baranof, and Kruzof Islands, 

southeastern Alaska: U.S. Geological Survey 

Professional Paper 792, 105 p. 

Uncertain 

Blocks 

Plafker, George, 1987, Regional geology and 

petroleum potential of the northern Gulf of 

Alaska continental margin, in Scholl, D.W., 

Grantz, Arthur, and Vedde~ J.G., eds., 

Geology and resource potential of the 

continental margin of western North America 

and adjacent ocean basins (Circum-Pacific 

Council for Energy and Mineral Resources 

Earth Science Series, v. 6): Houston, 

Circum-Pacific Council for Energy and 

Mineral Resources, p. 11/1-11/38. 

P1afker, George, Jones, D.L., Hudson, Travis, 

and Berg, H.C. 1976, The Border Ranges fault 

system in the Saint Elias Mountains and 

Alexander Archipelago, in Cobb, E.H., ed., 

The United States Geological Survey in 

Alaska: Accomplishments during 1975: U.S. 

Geological Survey Circular 733, p. 14-16. 

Plafker, George, Jones, D.L., and Pessagno, 

E.A., Jr., 1977, A Cretaceous accretionary 

flysch and melange terrane along the Gulf of 

Alaska margin, in Blean, K.M., ed., The 

United States Geological Survey in Alaska: 

Accomplishments during 1976: U.S. 

Geological Survey Circular 751-B, p. B41-

B43. 

Rau, W.W., Plafker, George, and Winkler, G.R., 

1983, Foraminiferal biostratigraphy and 

correlations in the Gulf of Alaska Tertiary 

province: U.S. Geological Survey Oi 1 and 

Gas Investigations Chart OC-120. 

Sharp, R.P., and Rigsby, G.P., 1956, Some rocks 

of the central St. Elias Mountains, Yukon 

Territory, Canada: American Journal of 

Science, v. 254, p. 110-122. 

Reviewers: R.A. Loney and George Plafker 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southeastern Alaska 149 
Major-Element Geochemistry of Metabasalts of the 

Juneau-Haines Region, Southeastern Alaska 

By Arthur B. Ford and David A. Brew 

Variably metamorphosed mafic volcanic rocks 

of greenschist or lower facies are widely distributed in 

areas of northern southeastern Alaska between Juneau 

and Haines (fig. 1). Fossils in associated rocks indicate 

that major basaltic volcanism occurred in three time 

spans: (1) Silurian and (or) Devonian; (2) Permian(?) 

and Triassic; and (3) Late Jurassic and Early 

Cretaceous (Brew and Ford, 1985). Some local units 

are of unknown age. During regional geological 

mapping of this area (Brew and Ford, 1985 and unpub. 

data), we have been systematically sampling the 

metavolcanic units for geochemical characterization 

and comparisons. Our studies are in progress, and we 

here report average major-element compositions of 

units based on presently available data. 

Table 1 shows the compositions of units in 

different geographic areas west of the Coast Range 

megalineament (Brew and Ford, 1978) near Juneau (fig. 

1). The rocks are strongly recrystallized metabasalts 

that range from foliated greenstone to greenschist 

with typical greenschist-facies mineral assemblages of 

chlorite-epidote-albite-actinolite. Relic phenocrystic 

augite is common and plagioclase rare. 

Metabasalts from the Douglas Island area 

consist of Upper Jurassic and Lower Cretaceous 

Douglas Island Volcanics (unit KJsd of Brew and Ford, 

1985) and volcanic members of the Seymour Canal 

Formation that occur on Douglas Island and extend 

northward to Berners Bay (Brew and Ford, 1985). The 

Douglas Island Volcanics and Seymour Canal Formation 

intertongue and thus are approximately coeval; they 

are at least about 3,000 m thick. The Seymour Canal 

Formation is a largely volcanic-derived turbiditic 

graywacke and slate unit with numerous fossil 

localities that estabish a Late Jurassic and Early 

Cretaceous age (Loney, 1964; Brew and Ford, 1985). A 

previous average major- element composition based on 

28 samples was reported by Ford and Brew (1977). 

Samples from Glass Peninsula are of the 

Douglas Island Volcanics on northeastern Admiralty 

Island (Lathram and others, 1965). 

Metabasaltic rocks from Bridget Cove (10 km 

south of Berners Bay) correlate with the Douglas Island 

Volcanics (Irvine, 1973). They are much less deformed 

and recrystallized than the rocks on Douglas Island to 

the south. 

Samples from Barlow Cove are of greenschist 

. (Brew and Ford, 1985) with a protolith age considered 

by Lathram and others (1965) to be Permian and 

Triassic(?). The rocks were mapped by Barker {1957) 

as the Barlow Cove Formation of Jurassic(?) to Early 

Cretaceous(?) age and correlated with the Douglas 

Island Volcanics. No fossils have been found in this 

area. 

Table 2 shows average major-element 

compositions of the metavolcanic units of northern 

Lynn Canal areas and of areas east of the Coast Range 

megalineament near Juneau. The rocks are generally 

well-recrystallized greenstone and greenschist with 

typical greenschist-facies mineral assemblages of 

chlori te-epidote-albi te-actinoli te, and with 

metamorphic biotite only in areas east of the 

megalineament near Juneau (Ford and Brew, 1973). 

Rocks of the Chilkat Peninsula are less altered than 

those elsewhere. 

Samples from the Gastineau Peak area are from 

a 5-km-wide, northwest-southeast-trending belt 

adjoining the Coast Range megalineament on the east 

from Taku Inlet to about 10 km northwest of Gastineau 

Peak (Brew and Ford, 1985). The sampling includes the 

Gastineau volcanic group (of H.M. Eakin and A.C. 

0 KILOMETERS 

Figure 1. Index map of Juneau-Haines area, southeastern 

Alaska. 

150 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Average major-element content (in weight percent) of Mesozoic metabasalt units of 

the Juneau area west of the Coast Range mega lineament 

[Analyses by X-ray fluorescence except by gravimetric and wet chemical methods for FeO and volatiles and by rapid 

rock methods for 28 samples of the Douglas Island unit. Bridget Cove data from Irvine (1973). Mg value calculated 

by method of Hughes and Hussey (1976) correcting Fe20 3/Fe0=0.2] 

Douglas Glass Bridget Barlow 

Island Peninsula Cove Cove 

Figure symbol (DI) (GLS) (BGT) (BLW) 

Number of 

samples 63 5 7 2 

Si02 46.9 48.3 48.2 45.8 

Al 2o3 13.3 14.1 13.1 16.5 

Fe2o3 3.6 3.1 3.34 4.6 

FeO 7.1 7.4 7.39 6.4 

MgO 8.7 7.2 9.0 8.8 

CaO 10.8 ll. 3 10.1 10.0 

Na 2 2.2 2.9 2.6 1.9 

K20 l. 64 l. 37 2.4 .20 

H20+ 2.87 2.66 2. 7l 4.25 

H20- .24 .09 .03 

Ti02 .74 • 77 .7 l. 44 

P205 .32 .32 .41 .11 

MnO .17 .15 .20 .16 

co2 .64 .31 .33 .28 

TOTAL 99.2 100.0 100.5 100.5 

Mg value 65 61 65 65 

Table 2. Average major-element content (in weight percent) of Mesozoic and older metabasalt 

units of the Juneau area east of the Coast Range megalineament and of the northern Lynn Canal 

area 

[Analyses by X-ray fluorescence except by gravimetric and wet chemical methods for FeO and volatiles. 

table 1. Chilkat Peninsula data from Davis and Plafker (1985)] 

Mg value, see 

Gastineau Lions Head Chilkat Chilkat 

Peak Mountain Range Peninsula 

Figure symbol (GST) (LHM) (CHR) (CHP) (CHL) 

Number of 

samples 23 10 l3 7 

Si02 46.1 46.8 46.6 48.9 49.7 

A1 2o3 15.6 l3. 2 14.4 14.4 13.9 

Fe 2o3 2.8 4.8 4.0 4.5 3.9 

FeO 8.7 9.7 8.1 8.2 8.8 

MgO 6.9 7.2 7.4 6.8 6.5 

CaO 10.6 8.6 9.2 10.1 10.7 

Na 2o 2.5 3. 2 2.3 2.5 2.2 

K20 .52 .27 .60 .48 .59 

H20+ 2.56 3.01 3.45 2.11 2.13 

H20- .06 .11 .12 .10 

Ti02 l. 74 2.82 l. 54 l. 43 2.10 

P205 . 39 .22 .20 .17 .20 

MnO .18 .23 .21 .21 .19 

C0 2 .68 .43 1.12 .09 .07 

TOTAL 99.3 100.6 99.2 100.0 101.0 

Mg value 57 53 58 55 53 

Southeastern Alaska 151 
Spencer, quoted by Martin, 1926). The Gastineau 

contains Late Triassic fossils (Martin, 1926), and other 

fossils suggest a protolith age range of Early Permian 

to Late Triassic. Lithologic associations and age 

constraints are described by Brew and Ford (1985). 

The metabasalts from Lions Head Mountain are 

from a widespread but little-mapped northwestsoutheast-trending greenstone unit between Berners 

Bay and Lynn Canal. Age information is unavailable, 

but lithologic comparisons suggest correlation with 

Upper Triassic metabasalt (Plafker and others, 1979) 

of the Chilkat Peninsula on approximate strike to the 

northwest. 

Chilkat Range samples are from a little-mapped 

area of the central Chilkat Range west of Sullivan 

Island (Brew and Ford, 1985). The unit probably 

correlates with greenstone and greenschist to south of 

Silurian and (or) Devonian age. 

Samples from the Chilkat Peninsula extend 

northwestward to near Haines and the upper Chilkat 

Inlet Davis and Plafker's (1985) sampling of Upper 

Triassic metabasalt of a 3,000-m-thick sequence at the 

southern end of the peninsula. Table 2 shows the 

average of Davis and Plafker's (1985) analyses for 

comparison. 

The original composition of the metavolcanic 

rocks is uncertain owing to possible major-element 

mobility in altered volcanic rocks (for example, 

Rollinson and Roberts, 1986). In this preliminary study 

we have not attempted a rigorous discrimination of 

samples that may show chemical migration. However, 

all samples were plotted on Mullen's (1983) 

"spilitization" diagram (fig. 2), and any showing 

unusual sodium enrichment were excluded from the 

averages of tables 1 and 2. (A small percentage from 

most units were thereby excluded.) The average 

compositions of all units lie in the fields of basalt or 

hawaiite (fig. 3) in the lUGS classification of Zanettin 

(1984), and range from high-K basalt and absarokite to 

low-K calc-alkaline basalt and tholeiite according to 

Ewart's (1982) classification (fig. 4). 

..... 10 EXPLANATION 

z 0 Jurassic and Cretaceous rocks / w / 0 8 • Triassic and older rocks 

a: / 

w + Age not known / Q. 

6 / ..... / ~ / BG~ lCHP 

z 4 SPILITE / LHM \ GLS / + 0 0 

0 2 / CHPel, •o--GST 

~ CH._/ T- Dl ~ BLW z NONSPILITE 

0 I 

0 2 4 6 8 10 12 14 

CaO IN WT. PERCENT 

Figure 2. Average composition of metavolcanic units plotted on 

diagram of Mullen (1983). Normalized volatile free. See tables 1 

and 2 for sample-unit symbols. 

The average major-element compositions of the 

metavolcanic rocks of Jurassic to Cretaceous age 

(Douglas Island Volcanics and equivalents) and those of 

Triassic and older age differ greatly. The Jurassic to 

Cretaceous rocks are more magnesian as shown by 

distinctly higher Mg values than the older rocks (Mg 

values 61-65, table 1 versus 53-58, table 2). Although 

Na~O contents of the two age groups of rocks are 

similar (fig. 2), K2o content of the Jurassic to 

Cretaceous rocks 1s much higher (fig. 4), which 

accounts for their higher total alkalis in figure 3. One 

of the most distinctive differences is the much lower 

Ti02 content of the Jurassic to Cretaceous rocks (fig. 

5), as shown in ratios with other oxides in figures 6 and 

7. Additionally, in Irvine and Baragar's (1971) 

classification, the Jurassic to Cretaceous rocks have 

compositions near or across the tholeiite field 

boundary and distinctly apart from the tholeiitic 

compositions of the older rocks (fig. 8). 

..... 

z 

w 

0 

a: 

w 

Q. 

...: 

~ 

~ 

~~ z 

+ 0 

0~ 40 

~ 

GLSo 

LHM 0DI 

GSTtee-CHP 

\e-!CHL t- CHR 

BLW BAS. 

ANDESITE 

48 56 

ANDESITE 

Si02 IN WT. PERCENT 

64 

Figure 3. Average composition of metavolcanic units in JUGS 

classification of Zanettin (1984). Normalized volatile free. 

Symbols of units as in figure 2. 

..... 

z 

w 

0 

a: 

w 

Q. 

...: 

3: 

z 

0 

~ 

~ 

4 

3 

2 

ABSAROKITE SHOSHONITE 

LOW-K ANDESITE 

54 56 58 60 62 

Si02 IN WT. PERCENT 

Figure 4. Plot of average K20 against Si02 (normalized volatile 

free) of metavolcanic units showing rock-type boundaries of 

Ewart (1982). Symbols of units as in figure 2. TH, low-K tholeiite 

field and CLKB, calc-alkali basalt field of Ewart (1982). 

152 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
The greenstones and greenschists of various 

ages are generally difficult if not impossible to 

distinguish on lithological and mineralogical 

characteristics alone, except that coarse, commonly 

euhedral, relic pyroxene, where present, and lack of 

visible plagioclase have been found useful for 

identifying the Douglas Island Volcanics in our 

mapping. Correlations of the greenschists of Barlow 

Cove, the greenstones of Lions Head Mountain, and 

some greenstone and greenschist of Douglas Island and 

tz 

w 

0 2 

a: 

w 

0.. 

~ 

3: 

z 

I oc:.J 

t0 

Mid-ocean ridge and 

back-arc basalt 

2 3 4 

FeO"/MgO 

5 

Figure 5. Plot of average Ti02 against FeO*/MgO (normalized 

volatile free) of metavolcanic units showing basalt-type fields of 

Hawkins and others (1985). FeO* equals total iron expressed 

as FeO. Symbols of units as in figure 2. 

Ti02 

't'~OCEANIC 

+BLW € : eGST 

CHR 

50 

NONOCEANIC 

50 

Figure 6. Average composition of metavolcanic units in Pearce 

and others' (1975) Ti02-K20-P20s discrimination diagram for 

oceanic and nonoceanic basalt. Symbols of units as in figure 2. 

vicinity are particularly uncertain in the absence of 

paleontological ages. Using geochemical 

discriminators shown in figures 3-8 (as well as some 

minor elements), we infer that all greenstone and 

greenschist of Douglas Island and west of the 

megalineament between Douglas Island and Berners 

Bay are part of the Jurassic to Cretaceous sequence of 

metavolcanic and metasedimentary rocks; and that the 

greenschist of Barlow Cove and greenstone of Lions 

Head Mountain are geochemically much more like the 

Mn0x10 

IAT 

I 

I 

MOR~ LH~ / 

\ BLW---:+ • ......-CHL/ 

\ '\ ' \// 

\ CHP••c~GST 

'---------

50 

DI~GLS 

BGT 

50 

Figure 7. Average composition of metavolcanic units in Mullen's 

(1983) MnO-Ti02-P20s discrimination diagram for oceanic 

basalt types. MORB, midocean ridge and marginal basin basalt; 

IAT, island-arc tholeiite; CAB, calc-alkaline basalt. Symbols of 

units as in figure 2. 

CHL 

I LHM4::..CHP 40 

PCHR 

GLS ~BLW 50 

0~~ "-~ GST 

BGT \ '\ 

Dl 

60 

Figure 8. Average composition of metavolcanic units in Irvine 

and Baragar's (1971) AFM diagram showing tholeiitic and calcalkaline boundary. Note that Bridget Cove rocks (BGT) have 

alkaline composition (figures 3 and 4). 

Southeastern Alaska 153 
metavolcanic rocks of Triassic and older age. The 

geochemical data are in agreement with Lathram and 

others' (1960, 1965) age reassignment for the 

greenschist of the Barlow Cove area to Permian and 

Triassic(?), from Barker's (1957) original correlation 

with the Douglas Island Volcanics. 

The tectonic setting of the basaltic magmatism 

events in the Juneau-Haines area is difficult to 

evaluate in terms of major-element chemistry alone. 

The metavolcanic rocks lie in two markedly distinct 

groups in Pearce and others' (1975) Ti02-K20-P_205 diagram: the Jurassic to Cretaceous rocks in the field 

of nonoceanic basalt and the others in or near the field 

of oceanic basalt (fig. 6). Davis and Plafker (1985) 

suggested an intraplate or a back-arc or fore-arc 

extensional setting for the Triassic metabasalt of the 

southern Chilkat Peninsula. Our data are compatible 

with that origin and suggest further that, according to 

the discrimination diagrams of figures 5 and 7, all the 

Triassic and older metavolcanic rocks have a similar 

tectonic setting except possibly the rocks of Gastineau 

Peak. The many geochemical differences between the 

Triassic and older rocks on the one hand and the 

Jurassic to Cretaceous rocks on the other suggest 

differences in setting or sources of magma. Berg and 

others {1972) and Panuska and others (1984) included 

the latter in their "Gravina-Nutzotin belt," a 

magmatic arc of Jurassic to Cretaceous andesite and 

flysch in southeastern Alaska. In our study area, 

however, the rocks of this belt have only basaltic, 

including alkalic basaltic, composition rather than the 

andesitic compositions indicated by Berg and others 

(1972) and Panuska and others (1984). Compositions 

reported here are those of nonoceanic basalt (fig. 6), 

as would be expected in a continental-margin 

magmatic arc, but the rocks are considerably more 

alkalic (fig. 4) than the calc-alkaline volcanic rocks 

found in such an orogenic setting (Ewart, 1982), and an 

origin related to rifting is more likely (Ford and Brew, 

1977), perhaps by movements along an ancestral fault 

of the Coast Range megalineament. 

REFERENCES CITED 

Barker, Fred, 1957, Geology of the Juneau (B-3) 

quadrangle: U.S. Geological Survey Geologic 

Quadrangle Map GQ-100, scale 1:63,360. 

Berg, H.C., Jones, D.L., and Richter, D.H., 

1972, Gravina-Nutzotin belt--Tectonic 

significance of an upper Mesozoic 

sedimentary and volcanic sequence in 

southern and southeastern Alaska, in 

Geological Survey research 1972: U.S. 

Geological Survey Professional Paper 800-D, 

p. Dl-D24. 

Brew, D.A., and Ford, A.B., 1978, Megalineament 

in southeastern Alaska marks southwest edge 

of Coast Range batholithic complex: 

Canadian Journal of Earth Sciences, v. 15, 

p. 1763-1772. 

1985, Preliminary reconnaissance geologic 

----map of the Juneau, Taku River, Atlin, and 

part of the Skagway 1:250,000 quadrangles, 

southeastern Alaska: U.S. Geological Survey 

Open-File Report 85-395. 

Davis, Alice, and Plafker, George, 1985, 

Comparative geochemistry and petrology of 

Triassic basaltic rocks from the Taku 

terrane on the Chilkat Peninsula and 

Wrangellia: Canadian Journal of Earth 

Sciences, v. 22, p. 183-194. 

Ewart, A., 1982, The mineralogy and petrology of 

Tertiary-Recent orogenic volcanic rocks: 

with special reference to the andesiticbasaltic compositional range, in Thorpe, 

R.S., ed., Andesites: New York,John Wiley 

and Sons, 724 p. 

Ford, A.B., and Brew, D.A., 1973, Preliminary 

geologic and metamorphic-isograd map of the 

Juneau B-2 quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-527, scale 1:31,680. 

_________ 1977, Chemical nature of Cretaceous 

greenstone near Juneau, Alaska, in Blean, 

K.M., ed., The United States Geological 

Survey in Alaska: Accomplishments during 

1976: U.S. Geological Survey Circular 751-

B, p. B88-B90. 

Hawkins, J.W., Moore, G.F., Villamor, R., Evans, 

C., and Wright, E., 1985, Geology of the 

composite terranes of east and central 

Mindanao, in Howell, D.G., ed., 

Tectonostratigraphic terranes of the CircumPacific region: Houston, Circum-Pacific 

Council for Energy and Mineral Resources, 

Earth Science Series, v. 1, p. 437-462. 

Hughes, C.J., and Hussey, E.M., 1976, M and Mg 

values in igneous rocks: Proposed usage and 

a comment on currently employed Fe2o3 

corrections: Geochemica et Cosmochim1ca 

Acta, v. 40, p. 485-486. 

Irvine, T.N., 1973, Bridget Cove volcanics, 

Juneau area, Alaska: Possible parental 

magma of Alaskan-type ultramafic 

complexes: Carnegie Institution of 

Washington Yearbook 72, p. 478-491. 

Irvine, T.N., and Baragar, W.R.A., 1971, A guide 

to the chemical classification of the common 

volcanic rocks: Canadian Journal of Earth 

Sciences, v. 8, p. 523-548. 

Lathram, E.H., Loney, R.A, Berg, H.C., and 

Pomeroy, J.S., 1960, Progress map of the 

geology of the Juneau quadrangle, Alaska: 

U.S. Geological Survey Miscellaneous 

Geological Investigations Map I-276, scale 

1:250,000. 

Lathram, E.H., Pomeroy, J.S., Berg, H.C., and 

Loney, R.A., 1965, Reconnaissance geology of 

Admiralty Island, Alaska: U.S. Geological 

Survey Bulletin 1181-R, 48 p. 

Loney, R.A., 1964, Stratigraphy and petrography 

of the Pybus-Gambier area, Admiralty Island, 

Alaska: U.S. Geological Survey Bulletin 

1178, 103 P• 

Martin, G.C., 1926, The Mesozoic stratigraphy of 

Alaska: U.S. Geological Survey Bulletin, 

493 P• 

Mullen, E.D., 1983, MnO/Ti02/P2o5 : A minor 

element discriminant for basaltic rocks of 

oceanic environments 

for petrogenesis: 

and its implications 

Earth and Planetary 

154 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Science Letters, v. 62, p. 53-62. 

Panuska, B.C., Decker, J.E., and Berg, H.C., 

1984, A preliminary paleomagnetic study of 

the Gravina-Nutzotin belt, southern and 

southeastern Alaska, in Coonrad, W. C., and 

Elliot, R.L., eds.,-The United States 

Geological Survey 1n Alaska: 

Accomplishments during 1981: U.S. 

Geological Survey Circular 868, p. 117-120. 

Pearce, T.H., Gorman, B.E., and Birkett, T.C., 

1975, The Tio2-K2o-P2o5 diagram: A method 

of d i scr iminat ing between oceanic and nonoceanic basalts: Earth and Planetary 

Science Letters, v. 24, p. 419-426. 

Plafker, George, Hudson, Travis, and Silberling, 

N.J., 1979, Late Triassic fossils from a 

sequence of volcanic and sedimentary rocks 

on the Chilkat Peninsula, southeastern 

Alaska, in Johnson, K.M., and Williams, 

J.R., eds., The United States Geological 

Survey in Alaska: Accomplishments during 

1978: U.S. Geological Survey Circular 804-

B, p. Bl07-Bll0. 

Rollinson, H.R., and Roberts, C.R., 

correlations and major element 

altered basalts and 

1986, Ratio 

mobi 1 i ty in 

komatiites: 

Contributions to Mineralogy 

v. 93, P• 89-97. 

and Petrology, 

Zanettin, B., 1984, Proposed new 

classification of volcanic rocks: 

v. 7, p. 19-20. 

Reviewers: S.E. Box and George Plafker 

chemical 

Episodes, 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southeastern Alaska 155 
Petrography of Sandstones of the Orca Group from the 

Southern Trans-Alaskan Crustal Transect (TACT) Route and 

Montague Island 

By L.D. Gergen and George Plafker 

The Orca Group is a widespread, thick, strongly 

deformed and weakly metamorphosed (laumontite and 

prehnite-pumpellyite facies) flysch and tholeiitic 

basalt sequence that composes most of the Prince 

William terrane (Winkler, 1976; Winkler and Plafker, 

1981). It is late Paleocene through early middle 

Eocene in age, based on sparse fossils and the K-Ar 

ages of plutons that intrude the sequence (Plafker and 

others, 1985). The Prince William terrane is bounded 

by the Contact fault to the north and west, and by the 

Chugach-Saint Elias and Ragged Mountain faults to the 

east (fig. 1). To the south, it extends beneath the 

continental shelf and possibly beyond (Plafker, 1987}. 

Five hundred grains on each of 25 thin sections 

of selected sandstones of the Orca Group were 

identified using the Gazzi-Dickinson point-counting 

method (Dickinson, 1970) to place constraints on their 

provenance. The samples were collected from the 

area between Prince William Sound and the Copper 

River for the Trans-Alaska Crustal Transect (TACT) 

project during 1985 (fig. 1). 

Point-count data for sandstones from the Orca 

Group are presented in table 1 and summarized on 

figure 2. The sandstones are poorly to moderately 

sorted, with angular to rounded grains. Medium sand 

grains predominate, with some grains ranging from silt 

to pebble size. Average QFL (quartz-feldspar- lithic 

fragments) percentages are 30-41-29. Quartz is 

dominantly monocrystalline; polycrystalline quartz is 

no more than 11 percent of total quartz, averaging 2 

percent. Feldspar is mainly plagioclase, which 

averages 89.4 percent of total feldspar. Rare grains of 

oligoclase and andesine are present, but most of the 

plagioclase is altered, and much appears to be 

albitized. For this reason, original compositions of 

plagioclase minerals cannot be determined. Average 

LmLvLs (metamorphic-volcanic-sedimentary lithic 

fragments) percentages are 20-41-29. The 

metamorphic lithic clasts are of predominantly 

tectonite fabrics, with lesser amounts of 

crystalloblastic textures, and rare schistose grains. 

Some of the fragments are metavolcanic. Volcanic 

lithic fragments exhibit lathwork, microlitic, felsitic, 

hypabyssal, and vitric textures, in decreasing order of 

abundance. The sedimentary lithic grains consist of 

argillite, shale, and impure chert. Limestone clasts 

constituting 2 to 17 percent of total lithic fragments 

are found in three samples from Montague Island 

(samples 21, 23, and 25). Dense minerals compose 5 

percent or less of total framework grains and include 

epidote, sphene, garnet, pyroxene, amphibole, and 

spinel. Phyllosilicate minerals are 0 to 4.8 percent of 

framework grains and consist of biotite, chlorite, 

minor muscovite, and rare prehnite. Some of the 

biotite may be of metamorphic origin. 

The QFL diagram (fig. 2A) shows the wide range 

of feldspar and lithic proportions found in the 

sandstones of the Orca Group. All of the samples have 

less than 50 percent quartz. Lithic constituents form 

two clusters on the LmLvLs diagram (fig. 2B) based on 

relative percentages of sedimentary and volcanic 

grains, with metamorphic lithic grains evenly 

distributed among the two clusters. The sedimentary 

cluster is composed of samples that have more than 50 

percent sedimentary and less than 32 percent volcanic 

lithic fragments. The sedimentary grains, largely 

argillite and shale, are probably derived from erosion 

of flysch sequences. The volcanic cluster consists of 

samples having more than 34 percent volcanic grains 

(inferred to be derived mainly from an active arc 

source) and less than 31 percent sedimentary grains. 

Note that the more lithic-rich samples on the QFL 

diagram (samples 4, 11, 14, 20, 21, 23, and 25) are part 

of the group of samples that make up the sedimentary 

cluster on the LmLvLs diagram. The QmPK 

(monocrystalline quartz- plagioclase- potassium 

feldspar) diagram (fig. 2C) emphasizes the high 

proportion of monocrystalline quartz and plagioclase 

and the low proportion of potassium feldspar. Average 

QmPK percentages are 42-52-7 (table 1). 

Because the samples were not collected from 

measured sections and because of the complex regional 

structure, no vertical or horizontal trends within the 

sequence could be established from the point-count 

data. Sample data were plotted on triangular diagrams 

grouped by turbidite facies (Walker and Mutti, 1973), 

but no apparent trends emerged from the data. 

Samples were also plotted in four groups (table 1) that 

represent fault-bounded tectonic blocks: Group A, 

samples north of the Rude River fault (RRF on fig. 1); 

Group B, samples from a belt with abundant tholeiitic 

basalt and breccia south of RRF and north of the 

Cordova (CF) and Etches (EF) faults; Group C, samples 

south of CF and EF; and Group D, samples south of the 

Patton Bay fault (PBF) on Montague Island. Group D 

samples tend to have higher lithic proportions, and 

Group A and Group D samples tend to have higher 

sedimentary lithic proportions than the other groups. 

156 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
~ r:: 

..... 

::r 

~ ..... 

~ 

i 

,_. 

~ 

-'I 

c." ~"~~' CHUGACH TERRANE ·~ >' 

..;' 

(.>~ .... /6 """~' ,,., 

\ ,I'J( ) > ' 

~ 1'- .)-\>\(., \J_ •• ,, ~i~ ~ .t:, 

~ 

·~~ f!i 

-· 

61 ° 

148° 

.. /1:~ ?.>· 

To 

To e&>" 

~ 

~A:~ 

Tov 

::. -

WILLIAM 

147° 

0 

L 

KILOMETERS 

50 

I 

f \. -rl ) \\;. f I; •II, r 

<: ·' ·~ ' . ' ,ll· 

I 

146° 145° 

... 

~ ~~~ ... , 

r I 

< ' 

'J.~ 'I" J 

~~' ~~ 

.I 

·/, 

YAKUTAT 

TERRANE 

Tov..__}/ ~ : um 1 

. ,.-I 

144° 

Figure 1. Location map of Prince William Sound region showing distribution of Quaternary alluvial deposits (Qall, the Tertiary Orca Group (To, 

undifferentiated siliciclastic and volcanic rocks; Tov, volcanic units) and Tertiary intrusive granitic rocks (Tg), faults mentioned in text, and numbered 

sample localities (refer to table 1 for field numbers). CF, Cordova fault; CHF, Chugach fault; EF, Etches fault; PBF, Patton Bay fault; RMF, Ragged Mountain 

fault; and RRF, Rude River fault. Faults dotted where concealed. 

60° 
Table 1. Point-count data for sandstones of the Orca Group 

[QFL, quartz, feldspar, and lithic fragments; lmlvls, metamorphic,volcanic, and sedimentary lithic fragments; QmPK, 

monocrystalline quartz, plagioclase, K-feldspar; P/F, plagioclase to feldspar ratio; Qp/Q, polycrystalline quartz to quartz 

ratio; Fmwk%M, framework percent mica; Fmwk%0, framework percent dense minerals) 

Sample Field QFL% LmLvLs%1 QmPK% 

Number Number Q-F-L Lm-Lv-Ls Qm-P-K P/F Qp/Q Fmwk%M Fmwk%D 

Group A 

1 85APr78A 37-50-14 24-21-55 42-49-09 0.853 0 2.7 0.7 

2 85ANK90A 30-57-13 15-69-16 34-52-14 0.791 0.016 1.5 5.0 

3 85AWK17 35-54-11 18-24-58 40-52-09 0.855 0 1.6 0.9 

4 85ALu59 31-22-46 11-31-58 55-45-0 1.000 0.109 2.0 0.4 

5 85APrl63A 41-32-28 17-16-68 56-43-01 0.987 0.010 1.8 0 

Group B 

6 85APr73A 49-44-07 52-44-04 0.926 0.011 2.8 1.8 

7 85ALu4C 29-56-15 22-52-26 34-65-01 0.984 0 3.0 0.2 

8 85ASR40A 31-62-07 33-54-13 0. 800 0.015 1.3 2.9 

9 85ALu69A 44-30-26 31-56-13 59-41-0 1.000 0.033 0.8 0.6 

10 85ALu24 41-43-17 18-82-0 49-52-0 1.000 0.017 1.1 1.1 

11 85ALullC 22-26-51 15-25-60 46-49-05 0.904 0.009 0.4 0.4 

Group C 

12 85ALu37A 22-50-29 03-83-14 29-64-07 0.903 0.061 1.7 2.9 

13 85ALul6 37-44-19 43-35-23 45-53-02 0.969 0.013 1.1 2.4 

14 85ALu31A 22-25-52 06-11-83 46-44-10 0.811 0.028 0.2 1.4 

15 85ALul5 28-56-16 28-71-01 33-57-10 0.849 0.008 2.5 3.9 

16 85ALu20 26-57-17 26-61-13 31-58-10 0.848 0.008 2.7 2.3 

17 85APr66A 35-51-13 40-42-19 40-56-04 0.936 0.021 3.9 4.4 

18 85APr62A 40-31-29 10-24-66 55-44-01 0.986 0.034 2.8 0.2 

19 85APr59A 36-50-15 11-62-28 42-54-05 0.921 0 4.8 2.5 

Group D 

20 85ALu53A 19-34-46 29-19-52 36-52-12 0.814 0 0.9 0.4 

21 85ALu52C 08-19-74 28-05-67 30-58-12 0.824 0 0 0 

22 85ALu44A 24-45-31 20-70-10 35-60-05 0.923 0 1.8 1.2 

23 85ALu46C 21-22-57 12-17-71 48-42-09 0.819 0.054 0.2 0 

24 85ALu48B 18-56-26 19-51-30 24-68-08 0.897 0 1.9 1.9 

25 85ALu50B 16-19-65 05-24-72 45-42-13 0.760 0.016 1.3 0.3 

mean 30-41-29 20-41-39 42-52-07 0.894 0.019 1.8 1.5 

standard deviation 10-14-19 10- 2!~- 26 10-08-05 0.076 0.025 1.2 1.4 

1 Not calculated for samples with less than 10 percent lithics 

Otherwise, the sample groups broadly overlap each 

other when plotted on QFL, LmLvLs, and QmPK 

diagrams. 

Other petrographic studies on sandstones of the 

Orca Group include those by Winkler (1976), Nelson 

and others (1985), and Dumoulin (1984). Winkler (1976) 

examined 59 samples, mainly from Hinchinbrook and 

Hawkins Islands, that yielded average QFL percentages 

of 43-46-11, LmLvLs percentages of 7-53-40, Qp/Q of 

0.12, P/F of 0.92, and framework percent mica of 1.6 

percent. He concluded that a composite sedimentary 

and volcanic terrane such as the Valdez terrane in the 

Chugach Mountains is a possible source for the detritus 

in the Orca Group. Nelson and others (1985) analyzed 

20 medium-grained sandstones mainly from western 

Prince William Sound and reported average QFL 

percentages of 31-41-28. They inferred a magmaticarc provenance for the sandstones in the Orca Group 

with continued dissection of the magmatic arc 

exposing the plutonic roots. Dumoulin (1984) showed 

no major compositional differences between the 

detritus in the Orca Group and Valdez Group. She 

found that average QFL percentages for the eastern 

part of the Orca Group are 29-51-20, with volcanics 

dominating the lithic clasts. Detritus of Knight and 

adjacent islands in Prince William Sound have average 

QFL percentages of 52-32-16. Dumoulin (1984) 

concluded that a magmatic-arc provenance was likely 

and that an important subduction-complex component 

is suggested by QpLvLs plots for Knight Island area 

samples. Our study in the vicinity of the TACT route 

generally confirms previous workers' findings regarding 

a combined volcanic and sedimentary source for 

sandstone of the Orca Group. 

The two data clusters shown on our LmLvLs 

diagram (fig. 2B) indicate mixed sources for the 

sandstones of the Orca Group. The volcanic lithic 

fragments and unpublished geochemical data indicate 

first-cycle(?) magmatic-arc derivation. The 

sedimentary lithic fragments could have been derived 

from erosion of the Late Cretaceous Valdez Group and 

correlative units that compose most of the Chugach 

terrane, and (or) recycling of older Orca Group 

deposits due to uplift and erosion along the northern 

margin of the Prince William terrane. 

REFERENCES CITED 

Dickinson, W.R., 1970, Interpreting detrital 

modes of graywacke and arkose: Journal of 

Sedimentary Petrology, v. 40, no. 2, p. 695-

707. 

Dickinson, W.R., Beard, L.S., Brakenridge, G.R., 

Erjavec, J.L., Ferguson, R.C., Inman, K.F., 

Knepp, R.A., Lindberg, F.A., and Ryberg, 

158 Geologic Studies in Alaska by the U.S. Geological Sur"Vey during 1987 
Q 

CRATON /. 

INTERIOR~.·/ 

, I 

TRANSITIONAL . f CONTINENTAL~ /. 

/ RECYCLED 

/ OROGENIC 

'"'-1-- s.l ~~---~~ 9 

.· " I ~ s•~ - -

A 

1... a• ;+-15 ARC ____ .------~ ---

'j~~ .13 ~18 ~-----~ ----~ .§2 1719 DIS.SECTED_..-><_ 

~ ;e ..,-· 14 .> ... 5(j L7 ~--· 22 11. 23 ·~ --~ 12 20• • 5(j / •24 _ _..2-s ~ TRANSITIONAL ARC · ~ 1 / .21 

,__ /~'UNQ!_8_§.ECTED ARC~ 

F 

MIXED MAGMATIC 

ARCS AND 

SUBDUCTION 

COMPLEXES 

B 

Lm 

'\ 

RIFTED 

L 

Increasing Maturity or 

c 

p 

• 

~ 

• • • •••• 

. • . • 

I Stability from 

/~Continental Block · Provenances 

. . ·-/~ ~, .. • 

• 

Increasing Ratio of 

Plutonic/Volcanic Components 

in Magmatic Arc Provenances 

K 

Figure 2. Ternary diagrams for sandstone of the Orca Group. A, 

QFL (quartz-feldspar-1 ithic fragments) diagram modified from 

Dickinson and others (1983). B, Lmlvls (metamorphicvolcanic-sedimentary lithic fragments) diagram modified from 

Ingersoll and Suczek (1979). Dashed lines delineate dominantly 11Sedimentary11 and 11 volcanic11 clusters. Samples with less than 

10 percent lithic grains (6 and 8) were not plotted. C, QmPK 

(monocrystalline quartz-plagioclase-potassium feldspar) diagram 

modified from Dickinson and Suczek (1979). 

P.T., 1983, Provenance of North American 

Phanerozoic sandstones in relation to 

tectonic setting: Geological Society of 

America Bulletin, v. 94, no. 2, p. 222-235. 

Dickinson, W.R., and Suczek, C.A., 1979, Plate 

tectonics and sandstone compositions: 

American Association of Petroleum Geologists 

Bulletin, v. 63, no. 12, p. 2164-2182. 

Dumoulin, J.A., 1984, Composition and provenance 

of sandstone of the Orca and Valdez Groups, 

Prince William Sound, Alaska [abs.]: 

Geological Society of America, Abstracts 

with Programs, v. 16, no. 5, p. 280. 

Ingersoll, R.V., and Suczek, C.A., 1979, 

Petrology and provenance of Ne~gene sand 

from Nicobar and Bengal fans, DSDP Sites 211 

and 218: Journal of Sedimentary Petrology, 

v. 49, no. 4, p. 1217-1228. 

Nelson, S.W., Dumoulin, J.A., and Miller, M.L., 

1985, Geologic map of the Chugach National 

Forest, Alaska: U.S. Geological Survey 

Miscellaneous Field Map MF-1645B, scale 

1:250,000, p. 5-6. 

Plafker, George, 1987, Regional geology and 

petroleum potential of the northern Gulf of 

Alaska continental margin, in Scholl, D.W., 

Grantz, Arthur, and Vedder, J.G., eds., 

Geology and resource potential of the 

continental margin of western North America 

and adjacent ocean basins (Circum-Pacific 

Council for Energy and Mineral Resources 

Earth Science Series, v. 6): Houston, 

Circum-Pacific Council for Energy and 

Mineral Resources, p. 11/1-11/38. 

Plafker, George, Keller, Gerta, Barron, J .A., 

Blueford, J.R., Nelson, S.W., Dumoulin, 

J.A., and Miller, M.L., 1985, Paleontologic 

data on the age of the Orca Group, Alaska: 

U.S. Geological Survey Open-File Report 85-

429, 22 p. 

Walker, R.G., and Mutti, Emiliano, 1973, 

Turbidite facies and facies associations, in 

Turbidites and deep-water sedimentation: 

Anaheim, California, Society of Economic 

Paleontologists and Mineralogists, Pacific 

Section, Short Course Lecture notes, p. 119-

157. 

Winkler, G.R., 1976, Deep-sea fan deposition of 

the Lower Tertiary Orca Group, Eastern 

Prince William Sound, Alaska, in Miller, 

T. P., ed., Recent and ancient sedimentary 

environments in Alaska: Anchorage, Alaska 

Geological Society, Symposium Proceedings, 

p. R1-R20. 

Winkler, G. R., and Plafker, George, 1981, 

Preliminary geologic map of the Cordova and 

Middleton Island quadrangles, Alaska: U.S. 

Geological Survey Open-File Report 81-1164, 

scale 1:250,000. 

Reviewers: J.E. Case and R.L. Detterman 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southeastern Alaska 159 
H2S-Rich Vein-Forming Fluids at the 

Sumdum Chief Gold Mine, Southeastern Alaska 

By Richard J. Goldfarb, Albert H. Hofstra, Gary P. Landis, and David L. Leach 

The Sumdum Chief mine was the largest gold 

producer within the southern part of the Juneau gold 

belt (fig. 1), yielding 24,000 troy oz (746,000 g) of gold 

and 24,000 troy oz (746,000 g) of silver between 1890 

and 1903 from a mesothermal vein system (Redman 

and others, 1986). This vein system has an unusual 

fluid composition that is exceptionally enriched in 

hydrogen sulfide. The main gold-bearing quartz vein is 

as much as 1 m wide and is largely within a fissile 

graphitic limestone unit of a belt of phyllite and slate 

(Kimball and others, 1984). A sulfidized felsic dike 

also hosts some of the quartz veins approximately 150 

m below the main mine workings. Due to the 

precarious location of these workings, we were only 

able to sample quartz-vein material cropping out along 

the lower valley walls and mineralized float 

undoubtedly fallen from the main workings at higher 

elevations. 

Temperatures of phase changes in fluid 

inclusions in quartz and sphalerite were determined 

using a U.S. Geological Survey gas flow microscope 

stage. All microthermometric measurements were 

made on fluid inclusions appearing as water-dominant, 

two-phase systems at room temperature. Some 

widespread small, dark inclusions and clear, probably 

empty, one-phase inclusions also were present but 

were not examined in this study. Most of the fluid 

inclusions that we studied were pseudosecondary or 

secondary in origin, trapped along fractures that 

subsequently healed. Whenever possible, we restricted 

our microthermometric measurements to inclusions 

that did not occur along recognizable planes. The 

more isolated inclusions most likely contain the older 

fluids, and they were found to contain more dissolved 

gases than inclusions in secondary planes. 

Melting temperatures of ice in the inclusions in 

both sphalerite and quartz ranged from -2 °C to -6 °C, 

corresponding to 4 to 9 equivalent weight percent 

NaCl. These salinities are maximum values because 

the formation of observed gas clathrates removed 

water from the residual fluids and lowered the 

measured melting temperatures. Gas-rich inclusions in 

sphalerite have clathrate melting temperatures 

between 10.3 °C and 11.4 °C, and show melting of 

solid C02 at temperatures as low as -62.5 °C. Both 

the depression of the C02 triple point to temperatures 

below -56.6 °C and the presence of clathrate meltings 

above 10 °C indicate the presence of other volatiles in 

the inclusions in addition to H20 and co2• The 

majority of the measured homogenization 

temperatures for fluid inclusions in sphalerite ranged 

from 215 °C to 290 °C. 

Melting of solid C02 in quartz has not yet been 

observed, although clathrate melting temperatures 

ranged from 10.7 °C to 27.5 °C. Values at the high 

end of this range are among the highest recorded for 

any known gold-bearing vein system and indicate an 

exceptionally anomalous ore fluid composition for 

some of the vein material at the Sumdum Chief mine. 

Proximity of these higher values to the 29.5 °C 

quadruple point for the H20-H2S system (Touray and 

Guilhammou, 1984) suggests substantial H2S in the 

inclusions. Laser Raman microprobe spectroscopy 

(Wopenka and Pasteris, 1986) confirmed the presence 

of H2S in these inclusions, as well as C02, N 2, and 

CH4• Relatively isolated, more regularly soaped 

inclusions in quartz samples yielded homogenization 

temperatures between 240 °C and 320 °C. Just prior 

to homogenization, one 13-micrometer-diameter 

inclusion decrepitated at 330 °C and one 18-

micrometer inclusion decrepitated at 255 °C. 

Experimental decrepitation data for quartz from Leroy 

(1979) and Swanenberg (1980) suggests minimum 

trapping pressures of at least 100 MPa (1 kbar). 

Fluid inclusion gas analyses obtained using a 

quadrupole mass spectrometer (Landis and others, 

1987) quantitatively characterize this H2S-rich gold 

system. This technique allows the identification of gas 

species released from individual fluid inclusions by 

thermal decrepitation in a dynamically pumped 

0 

~ 

50 100 150 

KILOMETERS 

Figure 1. Location of Sumdum Chief gold deposit, southeastern 

Alaska. Shaded area shows extent of Juneau gold belt. 

160 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
vacuum inlet system. Quantitative analyses of 

individual inclusions from quartz and sphalerite are 

listed in tables 1 and 2, which also include bulk 

analyses of gas released from many inclusions 

decrepitated within a given temperature range. 

Bulk extraction data for quartz are fairly 

consistent over the entire temperature range. Ranges 

of volatiles, expressed in mole percent, are 64 to 74 

percent for H20, 8 to 17 percent C02, 5 to 7 percent 

N2, 1 to 3 percent CH4, generally 5 to 6 percent shortcnain hydrocarbons (ethane and propane), <2 percent 

H2, 2 to 4 percent H2s, and <1 percent HCl and Ar. 

Anomalous amounts of short-chain hydrocarbons 

released between 310 °C and 340 °C are also present 

in analyses of individual inclusions that decrepitated in 

this temperature range, (such as the burst at 336 °C) 

(table 1). Individual inclusion bursts for the quartz 

show much wider compositional ranges for H20, C02, 

N2, and H2S, with as much as 40 percent C02, Z5 

percent N2' or 30 percent H2S, than do bulk 

extractions for the same species. Most likely this is 

due to necking of many of the inclusions. Additionally, 

individual bursts generally contain lower 

concentrations of H20 and hydrocarbons than observed 

for the bulk extractions. We suspect many of the 

smaller inclusions that are only measured through the 

bulk extractions are relatively enriched in these 

volatile species. Whether this is indicative of two or 

more ore-related fluids of varying composition is 

uncertain. Higher concentrations of H20 and 

hyrocarbons in the bulk analyses also could reflect 

gradual desorption of these species from vacuum inlet 

surfaces during heating; high background values are 

subtracted from individual burst values. 

Sphalerite contained fewer fluid inclusions than 

quartz, probably reflecting differences in the fracture 

properties of the two minerals. Bulk data are very 

similar to those for quartz, with slightly less H20, 

slightly more N2 and hydrocarbons, and small amounts 

of so2 at about the 1 mole percent level. Similar to 

quartz, bursts from individual inclusions within 

sphalerite show increases in C02 and N2, and 

decreases in H20 and hydrocarbons relative to bulk 

measurements. The one major difference between the 

fluids from the quartz and sphalerite is the 

consistently much lower amount of H2S within 

inclusions from sphalerite (table 2). Almost all of the 

individual inclusions contained less than 1 mole 

percent H2S. Much of the sulfur originally within the 

fluids most likely reacted with Zn to form the 

sphalerite. 

The presence of significant amounts of H2S in 

fluid inclusions from minerals in ore deposits is quite 

rare; the few published accounts of substantial H2S are 

for deposits formed within diagenetic environments 

(Touray and Guilhaumou, 1984). Norman and Sawkins 

(1987), using bulk fluid inclusion data obtained by mass 

spectrometry, found H2S contents of between 0.01 and 

0.0001 mole percent for most ore deposits. 

Thermodynamic models for gold-rich hydrothermal 

systems usually indicate_ H2S a_~d (or) HSconcentrations between 10 2 and 10 molal, even 

where hydrosulfide ligands are believed to form the 

dominant gold complexes. 

Only a handful of studies document H2S 

concentrations in epigenetic occurrences at the 

percent level. Norman and Sawkins (1987) discovered 

0.9 mole percent H2S in quartz from the Creede, 

Table 1. Quantitative analyses (in mole percent) of bulk fluid inclusion gases for ranges of 

decrepitation temperatures (To) and of individual fluid inclusion bursts at specific temperatures 

for quartz from the Sumdum Chief gold deposit 

170-200 

215-245 

260-290 

310-340 

355-385 

400-430 

179 

185 

193 

220 

230 

238 

243 

270 

273 

286 

320 

336 

363 

382 

409 

424 

H20 

72.6 

68.2 

65.2 

63.6 

73.8 

66.9 

61.9 

61.5 

40.6 

73.1 

62.9 

44.5 

45.0 

42.6 

34.6 

19.9 

83.4 

42.7 

55.8 

80.3 

58.9 

14.8 

C02 N2 

11.3 5.7 

14.9 5.4 

14.2 7.3 

7.7 5.0 

9.0 5.5 

16.9 7.3 

13.4 8.4 

11.5 3.1 

27.3 10.8 

8.6 1.5 

19.5 7.3 

11.8 25.3 

29.0 13.4 

24.2 12.9 

34.7 10.0 

41.1 19.1 

8.5 3.6 

13.3 15.4 

16.2 7.1 

9.7 3.0 

27.5 10.1 

34.2 17.1 

CH 4 CnHm 

Bulk 

1.2 6.3 

. 9 5.1 

1.3 6.4 

21.3 

1.4 5.8 

2.8 

Individual 

0.4 

. 5 1.8 

. 5 . 5 

.1 1.3 

. 4 1.1 

. 4 .4 

1.0 1.4 

• 5 .9 

• 9 1.3 

1.5 3.7 

• 5 1.0 

• 5 10.9 

. 3 1.6 

. 6 

.7 

. 8 

HCl Ar H2S so2 H2 

Analyses 

0.2 0.3 1.9 0.6 

. 2 . 3 3.8 0.3 . 4 

.4 . 5 3.5 • 9 

. 3 . 4 1.8 

• 5 .6 2.5 . 9 

.9 1.0 1.8 2.3 

Burst Analyses 

0.4 1.5 13.9 

• 3 .4 19.5 1.4 

.1 .1 20.1 .1 

.1 .1 15.3 

.1 .1 8.7 

.1 17.9 

.1 .1 9.9 

. 3 .1 18.5 

. 2 .1 17.9 . 4 

.1 . 2 12.7 1.3 

.1 2.9 

.1 .7 15.0 1.5 

.1 18.9 

• 2 .3 5.3 . 5 

• 3 .1 1.9 . 5 

• 4 31.0 0.5 1.1 

Southeastern Alaska 161 
Table 2. Quantitative analyses (in mole percent) of bulk fluid inclusion gases for ranges of 

decrepitation temperatures (T 0 ) and of individual fluid inclusion bursts at specific temperatures 

for sphalerite from the Sumdum Chief gold deposit 

To (OC) H20 C0 2 N2 CH 4 CnHm HCl Ar H2S so2 H2 

Bulk Analyses 

190-215 58.3 16.0 9.5 2.1 9.1 0.6 0.5 0.52 1.3 2.2 

230-260 55.8 13.0 8.6 4.9 12.0 .9 .8 .81 1.1 2.1 

Individual Burst Analyses 

191 49.0 25.5 18.1 l.l 

195 34.3 41.8 22.2 . 9 

196 49.1 22.4 21.0 1.2 

198 68.3 20.6 8.0 . 3 

202 25.9 37.5 28.5 . 9 

214 61.9 23.7 12.3 . 8 

244 37.3 34.6 15.6 1.8 

277 48.2 24.5 21.9 1.2 

415 30.9 40.5 16.9 2.4 

Colorado, epithermal Ag system and 3.5 mole percent 

H4s in quartz from the Cochiti, New Mexico, 

epithermal Au system. Hofstra and others (1987) 

described up to 1 mole percent H2S within fluid 

inclusions at the Jerritt Canyon, Nevada, disseminated 

gold deposit. Akhmanova and others (1985), using 

Raman spectroscopy, identified up to 20 mole percent 

H2s in inclusions from quartz veins cutting 

metamorphic rocks in the U.S.S.R. Our H2S 

concentrations within quartz-hosted fluid inclusions 

are by far the highest yet reported for any of the 

mesothermal gold vein systems within the accreted 

terranes of western North America. 

Although a few recent measurements on 

apparently unnecked and unleaked inclusions record 

relatively high homogenization temperatures (>300 

°C), the data (excluding the anomalous H2S) from the 

Sumdum Chief fluid inclusions are generalfy consistent 

with those for other mesothermal gold-bearing quartz 

veins in southern Alaska (Goldfarb and others, in 

press). Fluid-inclusion and stable-isotope data for 

these systems are most compatible with a model in 

which deep-seated fluids are released during 

devolatilization of subducted crustal material, leach 

gold from surrounding rocks, and are channelized 

upward to favorable sites for vein formation. The 

most likely source for the anomalous H2S is 

remobilization of sulfur into the metamorphic fluid 

phase from disseminated sulfides and(or) massive 

sulfide pods deeper in the sedimentary section. One 

such sulfide occurrence is exposed at Point Astley, 

approximately 10 km northwest of Sumdum Chief, and 

consists of massive pyrrhotite and sphalerite with 

abundant porphyroblasts of pyrite (Stowell, 1986). 

Ferry (1981) pointed out that conversion of 

disseminated pyrite to pyrrhotite by desulfidization 

during prograde metamorphism of pelitic schist occurs 

at all metamorphic grades. If this desulfidization is 

indeed significant in the vicinity of the Sumdum Chief 

deposit, then the resulting relatively locally derived 

H2S-rich fluid is believed to have mixed with the more 

regionally derived H2o-co2-N2-CnHm ore-forming 

metamorphic fluids sometime during fluid 

channelization. 

3.3 0.6 0.2 0.03 l.O l.O 

0.4 .l .09 .2 

. 9 .1 .56 .2 4.5 

1.6 . 2 .1 .27 • 6 

2.1 .9 . 3 .34 . 5 3.1 

. 8 . 2 .1 .15 .1 

6.3 .3 . 6 .30 . 8 2.3 

3.5 .1 .29 . 3 

4.0 1.1 .6 l. 32 . 6 1.6 

REFERENCES CITED 

Akhmanova, M.V., Naumov, V.B., and Sobolev, 

A. V., 1985, Use of laser Raman microprobe 

for studies of inclusions in minerals 

[abs.]: Fluid Inclusion Research, v. 18, p. 

3-4. 

Ferry, J.M., 1981, Petrology of graphitic 

sulfide-rich schists from south-central 

Maine: An example of desulfidization during 

prograde regional metamorphism: American 

Mineralogist, v. 66, p. 908-930. 

Goldfarb, R.J., Leach, D.L., and Pickthorn, 

W.J., 1988, Accretionary tectonics, fluid 

migration, and gold genesis in the Pacific 

Border Ranges and Coast Mountains, southern 

Alaska, in Kisvarsanyi, G., and Grant, S.K., 

eds., North American conference on tectonic 

control of ore deposits and the vertical and 

horizontal extent of ore systems: Special 

Publication of the University of Missouri--

Rolla, [in press]. 

Hofstra, A.H., Landis, G.P., and Rowe, W.A., 

1987, Sediment-hosted disseminated gold 

mineralization at Jerritt Canyon Nevada. 

IV--Fluid Geochemistry [abs.]: Geological 

Society of America Abstracts with Programs, 

v. 19, no. 7, p. 704. 

Kimball, A.L., Still, J .C., and Rataj, J .L., 

1984, Mineral deposits and occurrences in 

the Tracy Arm-Fords Terror wilderness study 

area and v1c1n1ty, Alaska, in U.S. 

Geological Survey and U.S. Bureau of Mines, 

eds., Mineral Resources of the Tracy ArmFords Terror Wilderness Study Area and 

Vicinity, Alaska: U.S. Geological Survey 

BulletiP 15?5, p. 105-210. 

Landis, G.P., Hofstra, A.H., Leach, D.L., and 

Rye, R.O., 1987, Quantitative analysis of 

fluid inclusion gases--Application to 

studies of ore deposits [abs.], in Sachs, 

J. S., ed., United States Geological Survey 

Research on Mineral Resources--1987 Program 

and Abstracts: U.S. Geological Survey 

162 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Circular 995, p. 38-39. 

Leroy, Jacques, 1979, Contribution a 

l'~tallonaje de la pression interne des 

inclusions fluides lors de leur 

d~cr~pitation: Bulletin de Min~ralogie, 

v. 102, p. 584-593. 

Norman, D.I., and Sawkins, F.J., 1987, Analysis 

of volatiles in fluid inclusions by mass 

spectrometry: Chemical Geology, v. 61, p. 

1-10. 

Redman, E., Roberts, W.S., Clough, A., and 

Kurtak, J., 1986, Juneau gold belt area--

Preliminary mine, prospect, sample location 

maps and descriptions: U.S. Bureau of Mines 

Open-File Report 85-86, 68 p. 

Stowell, H.H., 1986, Sphalerite geobarometry in 

metamorphic rocks and the tectonic history 

of the Coast Ranges near Holkham Bay, 

southeastern Alaska: Princeton, N.J., 

Princeton University, Ph.D. thesis, 263 p. 

Swanenberg, H.E.C., 1980, Fluid inclusions in 

high-grade metamorphic rocks from southwest 

Norway: Geologica Ultraiectina, University 

of Utrecht, Netherlands, no. 25, 147 p. 

Touray, J.C., and Guilhaumou, Nicole, 1984, 

Characterization of H2s bearing fluid 

inclusions: Bulletin de Min~ralogie, v. 

107, p. 181-188. 

Wopenka, Brigitte, and Pasteris, 

Limitations to quantitative 

fluid inclusions in geologic 

J.D., 1986, 

analysis of 

samples by 

laser Raman microprobe spectroscopy: 

Applied Spectroscopy, v. 40, p. 144-151. 

Reviewers: J.G. Viets and J.B. McHugh 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southeastern Alaska 163 
New K-Ar Ages for Plutons on Western Chichagof Island 

and on Yakobi Island 

By Susan M. Karl, Bruce R. johnson, and Marvin A. Lanphere 

Twelve new K-Ar ages for plutons occurring on 

western Chichagof Island and on Yakobi Island in 

southeastern Alaska (figs. 1, 2, and 3) confirm or 

revise ages for some plutons (Johnson and Karl, 1985) 

and help constrain timing and equivocal field 

relationships for emplacement of these plutons with 

respect to each other and to their country rocks. 

These new ages range from Jurassic to Tertiary (table 

1) and show a general younging from east to west 

(Johnson and Karl, 1985). All of the plutons in the 

study area are intermediate and calc-alkaline in 

composition (table 2, figs. 4 and 5), and the Mesozoic 

plutons are inferred to represent the roots of an arc 

that developed during the progressive accretion of the 

Chugach terrane to the Alexander-Wrangellia 

superterrane (Hudson, 1979; 1983; Brew and Morrell, 

1983; Johnson and Karl, 1985). 

Most of the plutons on Chichagof Island west of 

the Peril Strait fault (fig. 1) were considered 

Cretaceous in age by Loney and others (1975) on the 

basis of lithologic similarity with dated plutons east of 

Peril Strait. Some plutons were inferred to be 

Tertiary in age because they intruded rocks of 

Cretaceous age. Radiometric ages were reported for 

two Jurassic plutons by Loney and others (1967, 

1975). Because of the difficulty in distinguishing the 

Jurassic and Cretaceous bodies in the field, Johnson 

and Karl (1985) extended the age range of the undated 

plutons to the Jurassic. The ages reported here 

provide age control for some of the plutons. Samples 1 

through 10 are from western Chichagof Island (fig. 1); 

samples 11 and 12 are from Yakobi Island (fig. 2). 

Major element chemical data for representative 

samples from six different plutons (table 2) show a 

calc-alkaline trend (fig. 4) consistent with the calcalkaline composition of many other plutons occurring 

within the Mesozoic and Cenozoic plutonic belts of 

southern Alaska (Hudson, 1979, 1983). The Tertiary 

tonalites on Yakobi Island (fig. 2) occur within the 

Fairweather-Baranof belt of Brew and Morrell (1983) 

and the Sanak-Baranof belt of Hudson (1983) (fig. 3). 

The Jurassic and Cretaceous plutons fall within the 

Muir-Chichagof belt of Brew and Morrell (1983) and 

the Tonsina-Chichagof belt of Hudson (1983) (fig. 3). 

Samples 1 and 2 were collected from the 

northernmost of three tonalite plutons on western 

Chichagof Island (fig. 1). This pluton is a locally 

sheared, fault-bounded intrusive body lying in the Peril 

Strait fault zone. It was originally considered to be a 

Tertiary trondjhemite by Loney and others (1975), but 

samples collected away from the main fault zone plot 

mostly as tonalites (Johnson and Karl, unpubl. data). 

5 KILOMETERS 

l__L.__J,_-L-.L-..JI 

CHICHAGOF ISLAND 

Kk 

EXPLANATION 

Granodiorite (Tertiary) 

Diorite (Cretaceous?) 

Granodiorite (Cretaceous)--Equivalent to unit Kt of Loney and others 

(1975), and to unit KJgd of Johnson and Karl (1985) 

Kelp Bay Group (Cretaceous and Cretaceous?)--Sediment~ry and volcanic 

rocks 

Quartz diorite and tonalite (Cretaceous?)--Equivalent to unit Kgd of 

Loney and others (1975) and to unit KJqt of Johnson and Karl (1985) 

Quartz gabbro and gabbro (Cretaceous or Jurassic) 

i3iotite diorite (Cretaceous or Jurassic) 

Tonalite (Jurassic)--Equivalent to unit Tt of Loney and others (1975) 

ancl to unit KJt of Johnson and Karl (1985) 

Quartz diorite (Jurassic)--Equivalent to unit Kt of Loney and others 

(1975) an.j to unit KJq of Johnson and Karl (1985) 

Quartz diorite (Jurass1c) 

White Stripe l~arble and Goon Dip Greenstone, undivided (Triassic?) 

Metasedimentary and metaigneous rocks, undivided (Mesozoic and 

Paleozoic) 

~ Hornfel sed metasedimentary rocks (Paleozoic) 

Figure 1. Part of southwestern Chichagof Island, showing 

geology modified from Johnson and Karl (1985) and locations of 

dated samples (numbers 1 through 1 0). 

164 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Color indices of the three plutons range from 2 to 35. 

Anhedral green poikilitic hornblende generally, but not 

always, exceeds partly altered subhedral light- to 

dark- brown biotite. Accessory minerals include 

epidote, magnetite, garnet, muscovite, apatite, and 

sphene. The pluton is equigranular and weakly foliated 

away from the fault zones. Hornblende from samples 

1 and 2, yielded ages of 155 ± 4.6 Ma and 143 ± 4.3 Ma 

respectively; biotite from sample 1 yielded an age of 

143 ± 5. 7 Ma (table 1). Based on the hornblende ages 

we assign a Jurassic age to this pluton (time scale of 

Palmer, 1983). Because the pluton is entirely fault 

bounded, we do not know its relationship to adjacent 

rocks. 

Samples 3, 4, 5, and 6 are from a quartz diorite 

pluton that crops out on either side of the Jurassic 

tonalite in the vicinity of Hoonah Sound (fig. 1}. This 

pluton was considered to be of Cretaceous age by 

Loney and others (1975). The quartz diorite is medium 

to dark grayish green and contains more hornblende 

than biotite with a color index ranging from 25 to 50; 

it contains as much as 5 percent accessory magnetite 

in places, as well as traces of apatite, epidote, and 

sphene. Angular to rounded fine-grained mafic 

inclusions are common, nebulitic to banded gneiss 

zones occur locally, and the predominant texture is 

hypidiomorphic equigranular. Pyroxene-cored 

hornblende crystals are common locally (Johnson and 

Karl, 1985}. The hornblende in the dated samples is 

anhedral, green, and poikilitic. The biotite is anhedral, 

light to dark brown, and altered to chlorite, epidote, 

sericite and sphene. Hornblende ages of our four 

samples range from 143 ± 7.8 to 182 ± 7.8 Ma, and 

biotite ages range from 148 ± 4.4 to 164 ± 4.9 Ma 

(table 1}. These ages indicate that the pluton was 

emplaced during Jurassic rather than during 

Cretaceous time. 

Samples 7 and 8 yielding ages of 170 ± 5.1 Ma 

and 164 ± 4.9 Ma, respectively (table 1), were 

collected from a quartz diorite pluton (unit Jqd) which 

crops out west of Peril Strait (fig. 1). These ages 

confirm the Jurassic ages reported by Loney and 

others (1967, 1975) for this pluton. The quartz diorite 

contains hornblende, biotite, and accessory minerals 

including magnetite, apatite, epidote, sphene, and 

zircon, with a color index of 30 to 35. The hornblende 

is anhedral, green, and poikilitic in places; it also is 

altered to biotite in places. The pluton is 

hypidiomorphic, equigranular to seriate, and weakly 

foliated. 

Sample 9 is from quartz diorite and tonalite 

body on the north side of Patterson Bay (fig. 1) that 

was thought to be Cretaceous by Loney and others 

(1975). This pluton is variable in composition, with 

hornblende greater than biotite in quartz-diorite 

phases, biotite exceeding hornblende in the tonalites, 

and a color index ranging from 20 to 55. The 

hornblende is subhedral, and pleochroic green and 

brown. Magnetite, epidote, sphene, chlorite, apatite, 

zircon and sericite are accessory minerals. Sample 9 

yielded an age of 139 ± 4.2 Ma based on hornblende 

only. Because the 139-Ma age of this pluton is so close 

to the Jurassic-Cretaceous boundary, we assign a K(?) 

age to this body and recommend further sampling. 

Sample 10, from a granodiorite body (fig. 1), 

was tonalite, with hornblende slightly greater than 

biotite, but the pluton is mostly medium-gray 

granodiorite with approximately equal hornblende and 

biotite. The hornblende that we dated was euhedral, 

twinned, pale brown to green pleochroic, and contained 

inclusions of zircon. The biotite from that sample is 

anhedral, interstitial, and altered to chlorite and 

sphene. Accessory minerals include magnetite, 

sphene, epidote, apatite, sericite and zircon. Sample 

10 yielded a hornblende-only age of 128 ± 3.8 Ma. This 

age refines the Cretaceous(?) age assignment of Loney 

and others (1975) for this pluton to Cretaceous. 

~ 

~ 

~ 

~ 

~ 

~ 

~ 

0 

I I I I I 

KILOMETERS 

Pacific Ocean 

EXPLANATION 

Tonalite (Tertiary) 

Gabbronorite (Tertiary) 

Granodiorite (Tertiary) 

Sitka Graywacke (Cretaceous) 

Diorite (Cretac~ous) 

Kelp Bay Group (Cretaceous and Cretaceous?) 

Quartz diorite and tonalite (Cretaceous?)--Equinlent tu unit Kgd of 

Loney and others (1975) and to u~it V.Jqt of Johnson and Karl (1985) 

Diorite (Cretaceous or Jurassic) 

Tonalite (Jurassic)--Equivalent to unit Tt of Loney and others (1975), 

mapped along Peril Strait fault, and to u~it KJt of Johnson and Karl 

( 1985) 

Quartz diorite (Jurassic)--Equivalent to u~it Kt of Loney and others (1975) and to unit KJq of Johnson and Karl (1935) 

White Stripe Marble and Goon Dip Greenstone, undiv1ded (Tnassic?) 

MetasedimentarY a~d metavolcanic rocks, undivided (Mesozoic and 

Paleozoic) " 

Figure 2. Northwestern Chichagof Island and Yakobi Island, 

showing geology modified from Johnson and Karl (1985) and 

locations of dated samples (numbers 11 and 12). 

Southeastern Alaska 165 
160° 150° 140° 60°~~--~----------~~--------------~--------------~--------------~ 

ALASKA 

0 300 

~-..1.-..............J' 

KILOMETERS 

Gulf of Alaska 

area of figure 2 

area of figure 1 

Baranof Island 

k<::J Sanak -Baran of plutonic belt of Hudson, 1983 

ITIIIID Fairweather-Baranof plutonic belt of Brew and Morrell, 1983 

E__:---_J Tonsina-Chichagof plutonic belt of Hudson, 1983 

~ Muir-Chichagof plutonic belt of Brew and Morrell, 1983 

Figure 3. Plutonic belts of Hudson (1983) and Brew and Morrell (1983) in relation to study area (figs. 1 and 2). 

The Tertiary ages for samples 11 and 12 from 

tonalite on Yakobi Island (fig. 2) were reported in 

Himmelberg and others (1987), but the complete 

analytical data are reported here for the first time 

(table 1). The tonalite, which intrudes Cretaceous 

Sitka Graywacke, has a color index ranging from 5 to 

40, is equigranular to seriate hypidiomorphic, is not 

foliated but locally has cataclastic textures, and is 

associated with small gabbronorite bodies (Johnson and 

Karl, 1985; Himmelberg and others, 1987). Sample 11 

contained subhedral, unaltered biotite and traces of 

subhedral fractured garnet, apatite, muscovite 

(possibly secondary), magnetite, and zircon. Sample 12 

contained anhedral green poikilitic hornblende, 

subhedral light- to medium-brown biotite, and traces 

of magnetite, epidote, apatite, and sphene. Ages of 

39.6 ± 1.2 Ma (hornblende) and 41.7 ± 1.3 Ma (biotite) 

were obtained on sample 12, and a biotite age of 34.1 ± 

1 Ma was measured on sample 11. 

In summary, new radiometric ages (table 1) for 

12 granitic rocks confirm some previous age 

assignments and refine or alter others (see 

explanations for figs. 1 and 2). These limited data 

suggest that the oldest Jurassic plutons west of the 

Peril Strait fault on Chichagof Island are adjacent to 

the Peril Strait fault. All of the Jurassic and 

Cretaceous plutons occur in the belt between the Peril 

Strait fault and the Border Ranges fault (figs 1 and 2) 

which corresponds to Tonsina-Chichagof belt of 

Hudson (1983) and the Muir-Chichagof belt of Brew 

and Morrell (1983). A Cretaceous(?) diorite (Loney and 

others, 1975; Johnson and Karl, 1985) marks the 

eastern wall of the Border Ranges fault (fig. 1), and is 

the farthest west of the Mesozoic plutons. The 

relationships between these Mesozoic plutons are 

unclear due to poor exposure and pervasive faulting, 

but they are all close in space, time, modal 

composition, and chemistry, suggesting that they are 

probably related to one another as the roots of a 

Mesozoic volcanic arc. A Tertiary granodiorite 

intrudes this Mesozoic belt of plutons (fig. 1) and other 

Tertiary plutons intrude Cretaceous rocks west of the 

Border Ranges fault (fig. 2). A wide time gap 

separates the Mesozoic and Cenozoic plutons, and the 

Cenozoic plutons are probably not the roots of a 

volcanic arc. However, the similar calc-alkaline 

composition of the Mesozoic and Cenozoic plutons, and 

high silica and alumina content suggesting 

incorporation of pelitic material, support the 

interpretation that the Tertiary plutons are related to 

tectonic accretion (Hudson, 1979; 1983; Brew and 

Morrell, 1983; Johnson and Karl, 1985). 

REFERENCES CITED 

Brew, D.A., and Morrell, R.P., 1983, Intrusive 

rocks and plutonic belts of southeastern 

Alaska, U.S.A.: Geological Society of 

America Memoir 159, p. 171-193. 

166 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Potassium-argon ages and analytical data for plutonic rocks from western Chichagof and Yakobi Islands, Alaska 

[ lambda E = 0.581 x 1 o-1 Oyr-1, lambda B = 4.692 x 1 o-1 Oyr-1, 401</K = 1.167 x 1 o-4 mol/mol. Errors are estimates of the standard deviation of analytical precision) 

Sample Field No. Mineral K20 40~r 40Ar Calculated 

rag No. (wt pet) (10- mb~?g} (percen } (Ma} 

1 79BJ057A Biotite 7.90 ± 0.113 1.697 79.9 143 + 4. 3 

Hornblende 1. 060 ± 0.005 .2472 83.8 155 + 4.6 

2 79VY259A Hornblende .960 ± 0.002 .2063 62.6 143 + 4.3 

3 78RS053A Biotite 5.445 ± 0.064 1. 282 79.0 157 + 4.7 

Hornblende .909 ± 0.010 .2427 84.7 177 + 7.1 

4 79RB017A Biotite 6.70 ± 0.028 1. 484 90.2 148 + 4.4 

Hornblende 1. 057 ± 0.004 .2704 82.2 169 + 5.1 

5 79VY255A Biotite 5.84 ± 0.001 1. 307 81.8 149 + 4.5 

Hornblende .480 ± 0.004 .1029 72.8 143 + 4.3 

6 79BJ105A Biotite 7.505 ± 0.007 1. 855 87.5 164 + 4.9 

Hornblende .738 ± 0.013 .2030 44.3 182 + 7.8 

7 79RB023A Hornblende .402 ± 0.004 .1032 63.1 170 + 5.7 

8 79VY294A Hornblende .972 ± 0.004 .2406 84.2 164 + 4.9 

9 78BJ027A Hornblende .526 ± 0.002 .1094 78.7 139 + 4.2 

10 78BJ037A Hornblende .993 ± 0.001 .1896 82.0 128 + 3.8 

11 79BJ108A Biotite 9.18 ± 0.001 .5579 45.6 41.7 + 1.3 

12 79BJ119A Biotite 8.86 ± 0.014 .4384 67.0 34.0 + 1.0 

Hornblende .784 ± 0.004 .04518 54.9 39.6 + 1.2 

Table 2. Major element chemistry (in percent oxide) for representative samples from several plutons on Chichagof and 

Yakobi Islands 

[T, recalculated to total iron) 

Field no. 78RS053A 79BJ105A 79VY294A 78BJ027A 78BJ037A 79VY294A 

sample no. 3 6 8 9 10 12 

Si02 57.940 58.187 60.378 58.651 65.237 62.970 

Al 2o3 19.381 18.620 18.398 22.310 17.093 15.442 

Fe 20 3 (T) 6.616 6.993 6.150 3.866 4.511 7.300 

MgO 3.267 3.390 2.805 1.635 2.175 2.286 

CaO 6.717 7.235 6.739 8.036 5.037 5.645 

Na 2o 3.491 3.360 3.161 4.189 3.611 4.091 

K20 1.674 1.326 1.657 .727 1.699 .963 

Ti02 .670 .638 .508 .404 .465 1.073 

P205 .132 .111 .091 .131 .091 .110 

MnO .112 .142 .112 .050 .081 .130 

Total 98.550 98.820 98.380 99.060 98.870 99.730 

FeO 5.954 6.293 5.535 3.480 4.060 6.570 

age 

Himmelberg, G.R., Loney, R.A., and Nabelek, 

P.I., 1987, Petrogenesis of gabbronorite at 

Yakobi and northwest Chichagof Islands, 

Alaska: Geological Society of America 

Bulletin, v. 98, p. 265-270. 

Society of America Memoir 159, p. 159-169. 

Hudson, Travis, 1979, Mesozoic plutonic belts of 

southern Alaska: Geology, v. 7, p. 230-234. 

----- 1983, Calc-alkaline plutonism along the 

Pacific rim of southern Alaska: Geological 

lUGS Subcommission on the Systematics of Igneous 

Rocks, 1973, Classification and nomenclature 

of plutonic rocks, recommendations! Neues 

Jahrbuch fur Mineralog1e Monatshefte, v. 4, 

p. 149-164. 

Johnson, B.R., and Karl, S.M., 1985, Geologic 

map of western Chichagof and Yakobi Islands, 

southeastern Alaska: U.S. Geological Survey 

Southeastern Alaska 167 
3 

1012 

9 6 

8 

10 3 8 

6 

9 

12 

MgO 

CaO 

Figure 4. Alkali-iron-magnesium (AFM) and sodium-potassiumcalcium (AKC) diagrams for representative samples from plutons 

on Chichagof and Yakobi Islands. Sample numbers identified on 

tables 1 and 2. 

Potassium 

Feldspar 

Quartz 

Plagioclase 

Figure 5. Summary of compositional modes for all samples from 

plutons on western Chichagof and Yakobi Islands collected 

during 1978-1980; diagram from lUGS (1973). 

Miscellaneous Geologic Investigations Map I1506, 15 p., scale 1:125,000. 

Loney, R.A., Brew, D.A., and Lanphere, M.A., 

1967, Post-Paleozoic radiometric ages and 

their relevance to fault movements, northern 

southeastern Alaska: Geological Society of 

America Bulletin, v. 78, p. 511-526. 

Loney, R.A., Brew, D.A., Muffler, L.J.P., and 

Pomeroy, J.S., 1975, Reconnaissance geology 

of Chichagof, Baranof and Kruzof Islands, 

southeastern Alaska: U.S. Geological Survey 

Professional Paper 792, 105 p., 4 pl., scale 

1:250,000. 

Palmer, A.R., 1983, The Decade of North American 

Geology 1983 Geologic Time scale: Geology, 

v. 11, p. 503-504. 

Reviewers: D.A. Brew and R.A. Loney 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

168 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Geochemistry and Petrography of Lamprophyre Dike Rocks 

in the Coast Mountains, Southeastern Alaska 

By JohnS. Lull and George Plafker 

A major lamprophyre dike swarm intrudes early 

Tertiary and older rocks of the Coast Range batholith 

and surrounding metamorphic rocks in southeastern 

Alaska. The dikes strike northeast-southwest, are 

steeply dipping to vertical, and occur throughout the 

Coast Mountains of southeastern Alaska and British 

Columbia (Smith, 1973, D.A. Brew, U.S. Geological 

Survey, oral commun., 1987). In some areas the dikes 

comprise as much as 20 percent of the total outcrop, 

indicating substantial northwest-southeast extension 

during emplacement. Smith (1973) mapped and 

described the structure, petrography, and majorelement chemistry of lamprophyre dikes in the Prince 

Rupert-Ketchikan area. This report presents new 

isotopic, petrographic, and geochemical data for five 

lamprophyre samples collected along Tracy and 

Endicott Arms, Behm Canal, and Boca De Quadra in 

the Ketchikan area of southeastern Alaska (fig. 1). 

PACIFIC 

OCEAN 

ALASKA 

0 50 

KILOMETERS ... , 

·'-..... 

·.__··· 

\ 

Figure 1. Ketchikan area, southeastern Alaska, showing 

lamprophyre sample localities. Locality numbers on map 

correspond to field sample numbers as follows: 1, 82APr11; 2, 

82APr13; 3, 82APr7; 4, 82APr5; 5, 82APr12. 

Petrographic data for the lamprophyre dike 

rocks are summarized in table 1. The rocks are 

composed essentially of altered plagioclase, brown 

amphibole (usually in two generations), less abundant 

clinopyroxene, and rare altered olivine. Secondary 

hydrous minerals are common. Although the dike 

rocks are mineralogically and texturally variable, they 

are very similar chemically. Therefore, the 

mineralogic and textural variability is ascribed mainly 

to secondary (deuteric?) processes and differential 

cooling rates. 

Major-oxide and minor-element analyses of five 

lamprophyre samples are given in table 2. Si02 

averages 50 percent and ranges from 45 to 53 percent 

(all figures are given in volatile-free weight percent), 

K20 from 0.8 to 2.4 percent, Na2o from 2.6 to 4. 7 

percent, and Ti02 from 1.5 to 1.g- percent. None of 

the samples are quartz normative; all are olivine 

normative, and two of the five samples are nepheline 

normative. The lamprophyres show no iron enrichment 

on an AFM diagram (fig. 2). Based on normative color 

Table 1. Petrographic data for southeast Alaska lamprophyres 

Samp 1 e Textu•·e Mineralogy (minerals 1 is ted in order 

;lo. of abundance) 

Pan1d1omorphic to 

1 ntergranul ar; 

fi ne-gra 1 ned; 

equi granular·. 

Porphyritic ( phenocrysts 3-5% vol.), 

fine-grained 1 ntergranul ar gt·oundStrongly porphyrit1c; 

Plagioclase, brown amphibole, cl1nopyroxene, 

magnetite, sencite (after plag1oclase), 

carbonate, chlonte, apatite. 

Phenocrysts: Brown amph1bole, clinopy•·oxene. 

§_r'__(l_l!ndmass: Plagioclase (altered), brown 

amphibole, cl1nopyroxene, chlorite 

magnetite, quartz (<1%), apatite. 

Phen_<JS!)'Sts: l11nopyroxene, oliv1ne (•·eplaced 

vet·y fine gt·ained by sericite, chlorite, talc, 

gt·oundmass. carbonate), pi agi ocl nse (altered). 

I nter·gtanul ar ( (J% 

amphibole microphenocrysts); 

fine- gra j ned. 

Porphyn tic; f1 neGroundmass: Plagioclase, cl inopyr·ox.ene, 

magnet1te, pyrite. 

Plagioclase (alte•·ed), brown amphibole, magnet1te, 

chlorite~ apatite, quartz (<1%). 

l'henocrysts: Brown amphibole, maf1c (pyr·oxene?) 

grained groundmass. pseudomorphs composed of chlorite, 

epidote, amph1bole. 

Groundmass: Plagioclase (altered), brown amph1bole, 

epidote, chlonte, magnetite, pynte, 

apatite. 

Southeastern Alaska 169 
Table 2. Major-oxide (normalized 100 percent volatile-free) and minor-element 

composition of lamprophyre dike rocks from southeastern Alaska 

[See figure 1 for field sample numbers. Major elements analyzed by XRF; Lakewood, Colo.; analysts A.j. Bartel, K. 

Stewart, and j. Taggart. H2o+, H2o·, C02, by rock analysis; Menlo Park, Calif.; analyst: L. Espos. Co, Cr, Cu, 

Ni, Sc by optical spectroscopy; Lakewood, Colo.; analyst: M. Malcolm. Ba, Nb, Sr, Zr, Y by XRF; Reston, Va.; 

analysts: j, Leister, G. Wandless, and R. johnson] 

Sample No. Average Smith (1973) 

average 

Major-oxide composition (weight percent) 

SiOz 45.21 49.32 50. 31 52.74 

Al 2o3 15.07 15.40 15.86 15.59 

Fe 2o3 6.26 3. 51 5.03 3.20 

FeD 5. 54 5.29 5.59 5.09 

11g0 10.08 8.89 6. 94 5.64 

CaO 12.21 9. 32 7.70 7.43 

Na 2o 2.64 3. 57 3. 89 4. 73 

KzO .78 2.03 2.06 2.39 

Ti0 2 1. 58 1. 57 1. 70 1. 89 

Pz05 .45 .96 .73 1.19 

t~nO .18 .15 .20 .12 

H2

o+ 2.48 2.10 2.21 1. 62 

HzO- .76 . 21 .85 .06 

COz 2.55 . 21 .75 .81 

Minor-element composition (ppm) 

Sc 31 20 24 16 

Cr 427 356 218 163 

Co 67 46 43 34 

Ni 182 155 75 46 

Cu 7l 42 40 14 

Zn 91 86.8 120 168 

Rb 12 35.4 53.8 45.7 

Sr 1080 1630 621 963 

23 15 30 21 

Zr 194 143 186 316 

i~b 21 20 23 15 

Sb .16 .042 .119 .168 

Cs . 254 . 961 .20 

Ba 1390 1510 1030 922 

La 23. 1 50.8 35. 3 46.0 

Ce 41.2 87.4 68.6 96.5 

Nd 21.4 38.9 35.5 48.8 

Sm 4.23 6.57 6.69 8. 37 

Eu 1. 53 2. 05 2.21 2.51 

Gd 4.00 5. 12 5. 95 6.86 

Tb .620 .674 . 960 . 976 

Tm . 315 .265 .490 .285 

Yb 1. 84 1. 60 2.79 1. 66 

Lu .283 .227 .403 .230 

Ta .740 1. 13 1. 04 . 902 

Th 2.59 3. 76 2.30 7.75 

Hf 2. 46 3. 04 3.58 7.09 

.593 1. 11 .77 1. 48 

index and normative plagioclase composition (Irvine 

and Baragar, 1971), three of the five samples classify 

as alkali basalt, one as trachybasalt, and one as 

picrite-basalt. Major-element abundances reported by 

Smith (1973) for lamprophyres in the Prince Rupert53. 13 50.14 50.71 

16.78 15.74 16.13 

3. 01 4.20 3.31 

5.45 5.39 6.39 

5.82 7.47 7.19 

7.43 8.82 8.32 

3.88 3. 74 3. 89 

2.28 1. 91 1. 67 

1. 37 1. 62 1. 43 

.72 .81 .78 

.15 .16 .17 

1. 93 2. 07 2.20 (Total 

.08 . 39 HzO) 

.49 . 96 .78 

18 

177 

33 

51 

36 

110 

47.8 

7 3?.. 

19 

111 

.122 

. 338 

589 

45.0 

82.0 

31. 0 

6.18 

1. 85 

4.86 

.771 

. 345 

2.15 

. 308 

.895 

4.08 

4. 00 

1.10 

Ketchikan area are nearly identical to those of the 

dike rocks of this study (table 2). 

Minor-element data for the lamprophyres are 

very similar to those of continental flood basalt and 

contrast strongly with those of mid-ocean ridge basalt 

170 Geologie Studies in Alaska by the U.S. Geological Survey during 1987 
(MORB). Plots of rare-earth elements (REE), 

normalized to REE abundances in chondrites, of five 

lamprophyre samples are shown in figure 3A. The 

curves are relatively smooth, and light rare-earth 

elements (LREE) are strongly enriched relative to 

heavy rare earth elements (HREE). La ranges from 75 

to 165 times chondrite and Lu ranges from 7 to 12 

times chondrite. Sample number 1 shows a slight 

positive Eu anomaly, indicating plagioclase 

accumulation. The spidergram plot (fig. 3B) of 

incompatible minor elements shows a moderately steep 

curve (elevated to the left) with Ba at 85 to 220 times 

chondrites and Yb at 7 to 12 times chondrites, a welldefined trough at Nb-Ta (except for sample 1), positive 

peaks at La, Sr, and P, and a negative peak at Th. On 

the Ti-Zr-Y discrimination diagram (Pearce and Cann, 

1973), four of the samples plot in the continental 

basalt field and one Zr-enriched sample plots just 

outside this field (fig. 4A). On a Hf-Th-Ta diagram 

(Wood, 1980), the lamprophyre samples are not 

restricted to one field. Two samples plot as calcalkalic arc-rocks, one as "enriched" MORB, and two 

plot outside all fields (fig. 4B). In contrast to these 

data, MORB is characterized by flat to LREE-depleted 

REE trends, lower Zr/Y (reflected in the Ti-Zr-Y 

diagram), and a spidergram with relatively smooth, 

flat curves and no Nb-Ta trough. 

Based on the chemical data, the lamprophyres 

can be broadly classified as alkali basalts. However, 

Hf, Ta, Nb, and Ti02 abundances are low for alkali 

basalt. Lack of iron enrichment and the Th-Hf-Ta 

ratios (fig. 4B) suggest some calc-alkalic character. 

These rocks therefore appear to be transitional from 

calc-alkalic basalt to alkali basalt. The Th-Hf-Ta 

discrimination diagram (fig. 4B) also suggests this 

possibility. 

The youngest rocks intruded by the lamprophyre 

dikes are plutons of the Quartz Hill-Portland Peninsula 

area that are radiometrically dated at 19-32 Ma (Arth 

and others, in press). The dikes are cut by feeders of 

Pleistocene volcanic rocks (Smith, 1973). Potassiumargon dates on amphibole from four of the samples 

F 

AL-----------------------------------~M 

Figure 2. AFM plot for lamprophyres from southeastern 

Alaska (see figure 1 for field sample numbers). F, FeO*; A, 

Na20+K20; M, MgO. 

described in this report range from 29 to 47 Ma (table 

3). The wide spread in age is probably due to extensive 

alteration and excess argon, resulting in age 

determinations older than the actual age. Based on 

chemical similarity, Smith (1973) suggested that the 

lamprophyres may correlate with Miocene flood 

basalts of British Columbia. 

Smith (1973) made a valid argument for a 

mantle source for the lamprophyres, and the data in 

this paper support his conclusion. The lamprophyres 

clearly could not have been derived from continental 

crust in southeastern Alaska, and their compositional 

similarity over a large area suggests derivation from 

the mantle. The dike rocks are chemically 

indistinguishable from continental flood basalt, and 

may well have fed flood basalts which have since been 

eroded away in southeastern Alaska. 

Although the evidence is inconclusive, the 

possibility of crustal contamination of the 

lamprophyres is suggested by their mildly alkalic 

character, the presence of hydrous minerals and 

altered primary minerals (volatiles may have been 

derived through heating of crustal rocks), scatter on 

the Hf-Th-Ta diagram (Wood and others, 1979), and 

presence of the Nb-Ta trough on the spidergram 

(/) 

-~ 

~ _g 

() 

w 

w 

a: 

.:t: 

u 

0 

a: 

w 

w 

a: 

.,;_ 

.ci 

a: 

200 

10 

a. 200 

Q) 

~ 

~ 

(/) 100 

~ 

~ _g 

() 

c 

Q) 

E 

~ 

w 

.:t: 

u 

0 

a: 

c 

Q) 

E 

Q) 

w 

A 

...... .._.._ 

,- ..... _ 

l:-:,..""-

La Ce Nd Sm Eu Gd Tb Tm Yb Lu 

Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf T1 Tb Y Tm Yb 

Figure 3. Element abundance diagrams for lamprophyres from 

southeastern Alaska (see figure 1 for field sample numbers). A, 

Chondrite-normalized REE plot (chondrite values X 1.31, based 

on Anders and Ebihara, 1982). B, Spidergram plot (Thompson 

and others, 1983; chondrite normalized following Sun, 1980). 

Southeastern Alaska 171 
Ti/100 

A 

ZrL-------------------------------------~Y-3 

8 

.4 ·~~-1 // .2 //" 

Hf/3 

')"""0"' // \\. / )1,\ • " E-TYPE MOAB 

3// 

. . . )~'""" // DESTRUCTIVE PLATE MARGINS 

Th~~----------------------------------~Ta 

Figure 4. Discrimination diagrams for lamprophyre samples 

from southeastern Alaska (see figure 1 for field sample 

numbers). A, Ti-Zr-Y discrimination diagram (Pearce and 

Cann, 1973). Fields: A, (B), low-K tholeiites; B, ocean-floor 

basalts; C, (B), calc-alkalic basalts; D, ocean island or 

continental flood basalts. B, Th-Hf-Ta discrimination 

diagram (Wood, 1980). 

(Thompson and others, 1983). The Nb-Ta trough is also 

characteristic of subduction-related magmas, but the 

dikes were not emplaced during subduction. Sample 1 

has the most mafic composition and does not exhibit a 

well-defined Nb-Ta trough. If crustal contamination 

did take place, this sample may represent a relatively 

uncontaminated member of the lamprophyre suite. 

A model proposed by Thompson and others 

(1983) to explain the chemical characteristics and 

crustal contamination of continental flood basalt may 

be applicable to the southeastern Alaska lamprophyres. 

This model is based on studies of the rise of mafic 

magmas into rigid crust (Weertman, 1971), heat 

released by crystallizing dikes (Patchett, 1980, and 

Turcotte, 1981), and on evidence for an extensive silllike body at about 20 km depth beneath the Rio Grande 

Rift (Rinehart and others, 1979). The model calls for 

the formation of sill complexes of regional extent by 

ponding of upwelling mafic magma along density 

discontinuities (such as the base of the crust). The sill 

complexes feed dike swarms which are eventually 

vented to the surface. Crystallization and cooling of 

the sills and dikes release enough heat to locally fuse 

crustal rocks, allowing contamination of subsequent 

dikes. The regional extent, composition, and 

geochemical homogeneity of the lamprophyre dikes in 

the Coast Mountains of southeastern Alaska and 

British Columbia appear to be compatible with the 

proposed model. 

REFERENCES CITED 

Anders, Edward, and Ebihara, Mitsuru, 1982, 

Solar-system abundances of the elements: 

Geochimica et Cosmochimica Acta, v. 46, p. 

2363-2380. 

Arth, J.G., Barker, Fred, and Stern, T.W., 1988, 

Coast Batholith and Taku Plutons near 

Ketchikan, Alaska; petrography, 

geochemistry, and isotopic character: 

American Journal of Science, Wanes volume. 

[in press] 

Irvine, T.N., and Baragar, W.R.A., 1971, A guide 

to the chemical classification of the common 

volcanic rocks: Canadian Journal of Earth 

Sciences, v. 8, p. 523-548. 

Table 3. Potassium-argon isotopic data on amphiboles from lamprophyre dike rocks of southeastern 

Alaska 

[Analyst: Krueger Enterprises, Inc., Geochron Laboratories Division, Cambridge, Mass .. See figure 1 for field sample numbers] 

Sample 

1 

2 

4 

5 

Percent K 

0.540 

.730 

.582 

.612 

40K(ppm) 

0.658 

.891 

.710 

.747 

40Ar*(ppm) 

0.001140 

.001575 

.001996 

.001569 

172 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 

0.264 

.393 

.382 

.199 

Apparent 

age (Ma) 

29.4 :t 1.9 

30.0 ± 1. 7 

47.4 ± 2.6 

35.6 ± 2.1 
Patchett, P.J., 1980, Thermal effects of basalt 

on continental crust and crustal 

contamination of magmas: Nature, v. 283, p. 

559-561. 

Pearce, J.A., and Cann, J.R., 1973, Tectonic 

setting of basic volcanic rocks determined 

using trace element analyses: Earth and 

Planetary Science Letters, v. 19, p. 290-

300. 

Rinehart, E.J., Sanford, A.R., and Ward, R.M., 

1979, Geographic extent and shape of an 

extensive magma body at midcrustal depths in 

the Rio Grande Rift near Socorro, New 

Mexico, in Riecker, R.E., ed., Rio Grande 

Rift: Tectonics and Magmatism: Washington, 

American Geophysical Union, p. 237-251. 

Smith, J.G., 1973, A Tertiary lamprophyre dike 

province in southeastern Alaska: Canadian 

Journal of Earth Science, v. 10, p. 408-420. 

Sun, S.S., 1980, Lead isotopic study of young 

volcanic rocks from mid-ocean ridges, ocean 

islands and island arcs: Philosophical 

Transactions Royal Society of London, v. 

A297, p. 409-445. 

Thompson, R.N., Morrison, M.A., Dickin, A.P., 

and Hendry, G.L., 1983, Continental Flood 

basalts ••• Arachnids rule OK?, in 

Hawkesworth, C.J. and Norry, M.J., eds., 

Continental basalts and mantle xenoliths, 

Cheshire, U.K., Shiva, p. 159-185. 

Turcotte, D.L., 1981, Some thermal problems 

associated with magma migration: Journal of 

Volcanology and Geothermal Research, v. 10, 

P• 267-278. 

Weertman, J., 1971, Theory of water-filled 

crevasses in glaciers applied to vertical 

magma transport beneath oceanic ridges: 

Journal of Geophysical Research, v. 76, p. 

1171-1183. 

Wood, D.A., 1980, The application of a Th-Hf-Ta 

diagram to problems of tectonomagmatic 

classification and to establishing the 

nature of crustal contamination of basaltic 

lavas of the British Tertiary Volcanic 

Province: Earth and Planetary Science 

Letters, v. SO, p. 11-30. 

Wood, D.A., Juron, J.L., and Trenil, Michel, 

1979, A re-appraisal of the use of trace 

elements to classify and discriminate 

between magma series erupted in different 

tectonic settings: Earth and Planetary 

Science Letters, v. 45, p. 326-336. 

Reviewers: Fred Barker and Betsy Moll-Stalcup 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Southeastern Alaska 173 
Alteration Zoning and Origin of the Alaska-Juneau Go.ld Deposit 

By Rainer J. Newberry and David A. Brew 

The Alaska-Juneau (AJ) deposit, located 4 km 

east of Juneau (fig. 1), is the largest lode producer of 

gold in Alaska. This deposit is part of the 150-km-long 

"Juneau gold belt" of southeastern Alaska, which is 

responsible for the majority of Alaska's lode gold 

production. The AJ deposit was described by 

Wernecke (1932), Twenhofel (1952), and Wayland 

(1960). Ongoing USGS studies of this deposit (Goldfarb 

and others, 1986; Newberry and Brew, 1987) have 

shown it to be an epigenetic deposit and indicate that 

boiling of co2-rich fluids probably was an important 

mechanism of sulfide and gold deposition. Our current 

studies are focused on understanding the timing and 

conditions of formation of the deposit as a prerequisite 

to making a realistic assessment of the undiscovered 

mineral resources of the area. 

Previous interpretations of the source of the AJ 

deposit ore fluid have included (1) magmatic fluids 

A-J DEPOSIT AREA 

Schematic cross section 

A' 

0 

1.5 

4.5 

from the nearby "Coast Range batholith" (Twenhofel, 

1952), (2) deeply circulating meteoric waters 

associated with uplift of the Coast Mountains (Nesbitt 

and others, 1986), and (3) metamorphic fluids from 

deeper levels (Goldfarb and others, 1986). After 

preliminary field mapping (Newberry and Brew, 1987), 

we undertook petrographic studies, microprobe 

analysis of selected minerals, and limited age dating to 

test the various genetic models. 

The AJ deposit consists of several quartzankerite-sulfide sheeted vein swarms, each swarm 50-

300 m wide and up to 1 km long, which occur along a 

northwest-southeast-trending linear band subparallel 

to regional structures. These vein swarms together 

make up the "main ore zone" (figs. 1, 2), which is 

approximately 4 km long. The individual veins, the 

swarms, and the "main ore zone" all cut across the 

regional foliation and map-unit contacts at a low 

Figure 1. Generalized metamorphic facies map and cross section of Juneau area, showing location of AJ main ore zone (black); modified from Himmelberg and others (1984). Dashed line pattern identifies orthogneiss plutons with dashed 

lines approximately parallel to foliation. Crosses denote little-foliated post-tectonic granitic pluton. Location of Coast 

Range Megalineament (CRMU from Brew and Ford (1978). lsograd dips shown on cross section are schematic, taken 

from topography-isograd relationships shown on Ford and Brew (1977) and Brew and Ford (1977). 

174 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
angle, and their emplacement is interpreted to 

postdate the peak of deformation and metamorphism 

(Newberry and Brew, 1987). 

Field mapping and petrographic studies show 

that several types of alteration are present in a broad 

zone that extends up to 1 km away from the main ore 

zone. Wallrock opaque minerals define a series of 

concentric zones surrounding the ore zone (fig. 2), as 

shown by the relative abundance of (primarymetamorphic?) ilmenite relative to secondary 

(hydrothermal) pyrrhotite-pyrite. Sulfides are 

essentially absent in rocks far from the ore zone and 

increase in abundance as ore veins are approached. 

Pseudomorphic textures indicate that sulfide minerals 

replaced ilmenite; released Ti is present as secondary 

sphene (far from the ore zone) or rutile (closer to the 

ore zone). Secondary carbonates show a similar 

zoning, with calcite the characteristic carbonate 

mineral far from the ore zone and ferroan dolomite 

and ferroan magnesite characteristically present in 

wallrocks of the ore zones. Other zonation includes (1) 

the presence of arsenopyrite and tourmaline in 

wallrock in a 100-m zone surrounding the main ore 

zone, (2) an approximately coincident 10-30 ppb gold 

halo, and (3) secondary (post-metamorphic) biotite and 

chlorite in the same zone. The mineralogical changes 

seen in wallrocks indicate that the hydrothermal fluids 

added silica, sulfur, carbon dioxide, boron, arsenic, 

gold, and other elements to rocks surrounding the ore 

zone. 

These secondary minerals in the wallrock of the 

AJ deposit also show distinct zoning in major-element 

compositions. Secondary biotite (fig. 2B), chlorite, and 

tourmaline show decreasing Fe/Fe+Mg as the center of 

the vein swarms is approached, and ferroan dolomites 

show progressive decrease in Fe/Mn ratios. These 

changes are probably caused by progressive increases 

in aqueous sulfur activity toward the center of 

hydrothermal fluid flux, hence progressive loss of 

silicate iron at the expense of sulfide iron toward the 

center of the ore zone. These progressive mineral 

compositional changes also indicate that major 

hydrothermal circulation took place in the AJ area. 

The fact that mineral zoning at AJ cuts across 

lithologic boundaries and metamorphic foliation (fig. 

2A) indicates that it is a secondary effect that 

postdates major metamorphism. The large size of the 

metasomatic aureole also indicates that metasomatic 

fluid flow was not restricted to the quartz-carbonate 

veins, and that a large quantity of water passed 

through the volume of rock enclosing the veins. 

The conditions of ore deposition are indicated 

by compositions of specific sulfide assemblages as 

shown by microprobe analysis. Pressures estimated 

from the iron content in inclusion-free sphalerite 

(Scott, 1973) from sphalerite-pyrite-pyrrhotite 

assemblages indicate a fluid pressure in the range of 

300 to 400 MPa (3-4 kbar) (fig. 3B), slightly below 

estimated peak metamorphic pressure at the deposit of 

about 400 to 500 MPa (4-5 kbar) inferred from 

aluminosilicate geobarometry (G.R. Himmelberg, U.S. 

Geological Survey, oral commun., 1987; Brew and 

others, 1987, in press). Of the samples analyzed, 

higher-iron (low-pressure) sphalerites contain abundant 

pyrite and pyrrhotite inclusions and lower-iron (highpressure) sphalerites do not contain sulfide inclusions. 

Because the high-iron sphalerite samples could have 

picked up iron from the abundant iron sulfides during 

cooling (under low-pressure conditions), these samples 

are probably not indicative of pressure during deposit 

formation. The inclusion-free samples yield pressures 

slightly lower than the peak metamorphic pressure; 

this is compatible with vein formation associated with 

the metamorphic event, as the vein-forming fluids 

experienced a pressure intermediate between 

lithostatic and hydrostatic {approximately 1/3 

lithostatic pressure). As discussed below, however, we 

consider it more likely that these pressure values 

indicate that vein formation took place after the 

beginning of postmetamorphic uplift. 

Temperatures estimated for the AJ samples 

from arsenopyrite compositions in arsenopyrite-pyritepyrrhotite assemblages using the method of 

Kretschmar and Scott (1976) are lower (300 °C to 380 

°C) for the veins than for the surrounding wallrocks 

(380 °C to 470 °C) (fig. 3A). The temperature of the 

deposit estimated by garnet-biotite geothermometry 

for the wallrocks is 420 °C. The temperature data 

indicate that little cooling of the wallrocks took place 

between the peak of metamorphism at the deposit and 

formation of the mineralized veins, and the lower 

temperatures of the veins suggest that the fluids were 

cooler than the surrounding wallrocks. This difference 

in temperature may indicate that the AJ hydrothermal 

fluids were derived from rocks experiencing lower 

temperatures than the metamorphic rocks enclosing 

the AJ; it may also indicate cooling of ore fluids 

caused by enthalpy loss accompanying boiling. 

The timing of vein formation relative to peak 

metamorphism is provisionally estimated by comparing 

age dates for the two events, keeping in mind that 

different minerals possess intrinsically different age 

retention temperatures and that the possible resetting 

of metamorphic wallrock K-Ar ages by the later 50-Ma 

major intrusive event (Brew and Ford, 1986) has not 

been fully evaluated (fig. 4). Considering the 

uncertainties for the various published age estimates 

and the different age retention temperatures (Lund 

and others, 1986), it appears that the AJ veins formed 

within a few million years of the peak metamorphic 

event, as recorded by the published K-Ar ages for 

metamorphic wallrocks (Forbes and Engels, 1970). 

Brew and others (1987, in press), however, argue that 

peak metamorphic conditions were obtained before the 

emplacement of the 10-km-distant 67-Ma syntectonic 

pluton (fig. 4) dated by Gehrels and others (1984), and 

therefore the younger K-Ar ages reported by Forbes 

and Engels (1970) for the metamorphic rocks have been 

reset by younger thermal events. Brew and others (in 

press) interpret the age of metamorphism to be 

somewhere between 90 and 70 Ma, but close to 70 

Ma. Thus approximately 15 m.y. may have elapsed 

between the peak of metamorphism of the deposit and 

the emplacement of the veins. This interval provides 

time for several kilometers of uplift and possibly 

meteoric water incursion. During the 70 to 50 Ma 

interval, the region underwent rapid uplift (Brew and 

others, in press). Although no immediately local 

igneous suite of age similar to the AJ deposit is known, 

published age determinations (Gehrels and others, 

1984) establish that rocks about 18 km to the northnortheast of the deposit were intruded at 60 Ma and 50 

Southeastern Alaska 17 5 
A 

gs 

Silver Bow fault 

I agsl Altered greenschist 

~Greenschist 

~Phyllite and amphibolite 

lbgshi Biotite-garnet schist 

--Fault 

-- Contact 

- Mineral zone boundary 

B 

Sample location 

--A- Fold axial plane 

gs 

Silver Bow fault 

jags I Altered greenschist 

~Greenschist 

~Phyllite and amphibolite 

~Biotite- garnet schist 

--Fault 

Contact 

- Mineral zone boundary 

Sample location 

·--ft- Fold axial plane 

WALLROCK OPAQUES 

•po-py only +po-py > ilm 

•po-py-ilm +ilm >po-py 

• ilm only 

Gastineau 

Peak >Ifill 

I KILOMETER 1 

bgsh 

SECONDARY BIOTITES 

• < .35 +.35-.4 

A .4- .45 • .45-.5 

• >.5 

bgsh 

Gastineau 

Peak • • w 

Mt. 

L I KILOMETER! 

Figure 2. Generalized bedrock geologic map of AJ deposit area (modified from Newberry and Brew, 1987). A, 

Distribution of relative ilmenite (ilm) and pyrite (py)-pyrrhotite (po) abundances in representative polished thin 

sections of vein wallrocks. Zone of highest sulfide abundance in wallrocks is approximately coincident with main AJ 

ore zone (dashed lines). B, Distribution of atomic Fe/Fe+Mg ratios in representative secondary biotites of vein 

wallrocks (based on microprobe analyses performed at Washington State University). Zone of low-iron secondary1 

biotites approximately corresponds to main AJ ore zone. Arrows on faults show relative horizontal movement;' 

relative vertical movement shown by U (up) and D (down). 

176 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Ma, and they may extend closer to the deposit in the 

subsurface. 

Based on extensive regional mapping, Ford and 

Brew {1973, 1977) and Brew and Ford (1977) have 

established the existence of regional northwestsoutheast-trending, steeply east-dipping "inverted" 

metamorphic isograds in the vicinity of the Juneau 

gold belt (fig. 1): rocks formed at lower temperature 

and pressure lie structurally below rocks formed at 

higher temperature and pressure, and both pressure 

and temperature increase toward the structurally 

overlying syntectonic great tonalite sill (Brew and 

others, in press). The rocks that record this 

metamorphism in the AJ area include several 

kilometers thickness of calcite-bearing metavolcanic 

rocks and calcareous phyllite, the carbonate of which 

presumably was formed by to hydrothermal seawater 

alteration of the volcanic rocks. 

Our preferred scenario for AJ deposit 

formation, utilizing both regional geologic data and 

our analytical data, involves upward movement of 

waters released from the underlying rocks during 

prograde metamorphism, with the heat source being 

the structurally overlying syntectonic sill. Dewatering 

of the low-grade metamorphic rocks could have 

produced metamorphic waters with high C02 and 

moderate NaCl contents. As the fluids rose, the 

confining pressure dropped, allowing for C02 exsolution ("boiling") (Bowers and Helgeson, 1983}. 

The boiling event, indicated by fluid-inclusion 

investigations (Goldfarb and others, 1986), caused gold 

deposition through loss of H2S into the vapor phase and 

consequent destruction of gold bisulfide complexes. 

In summary, we suggest that the formation of 

the AJ deposit is intimately tied to the metamorphic 

history of the surrounding rocks. The similarity in 

pressure-temperature conditions of formation, and the 

~ c: 

Q) 

E 

~ ~ 

VI 

c 

Q) 

E 

8 

0 

z 19 

I 

150 

4 Samples 

18 

I 

17 

I 

250 300 

16 15 °/oFe 

I 

350 400 450 Pressure-MPa 

Figure 3. Histograms showing estimated temperatures (A) and 

pressures (B) of ore deposition in AJ deposit, based on sulfide 

mineral analyses. Prograde metamorphism biotite-garnet 

temperature of approximately 420 °C based on compositions of 

coexisting garnet and metamorphic biotite in two samples from 

AJ mine. Microprobe analyses performed at Washington State 

University. 

short interval between peak metamorphism at the 

deposit and vein emplacement indicate a close 

relation. Both meteoric and plutonic fluid sources are 

considered unlikely, although given the high co2 flux 

associated with mineralization, neither can be 

excluded. The deposit probably was formed from an 

enormous flux of metamorphically derived 

hydrothermal fluids, which resulted in the formation of 

the mineralogical aureole around the deposit. The 

focusing of water into a relatively small volume 

probably required some major regional structural 

focus--such as the Coast Range Megalineament (Brew 

and Ford, 1978)--as well as a local structural focus. 

The implication for mineral resource appraisal 

in the Juneau area is that only certain rare 

combinations of metamorphic and structural conditions 

could have resulted in forming major ore deposits. The 

need for both a water source (dewatering of rocks at 

lower metamorphic grade) and a major structural focus 

implies that the gold belt deposits should be restricted 

to areas where the Coast Range Megalineament 

(CRML) intersects the lower greenschist-facies portion 

of the inverted metamorphic isograd belt. This 

conclusion is supported by the fact that the gold belt 

ends some 115 km to the south, where the CRML cuts 

into kyanite-grade metamorphic rocks (Brew and 

others, 1984; Douglass and Brew, 1985). 

Zonation around the AJ "main ore body" 

suggests that it may serve as a guide to ore elsewhere 

in the Juneau gold belt: arsenopyrite and tourmaline 

are rare and fine-grained, but ankeritic carbonate and 

disseminated pyrite-pyrrhotite are common and easily 

identified. 

u 

~ 

Q) 

1-

~ 

-0 

1-

Q) 

Q. 

E 

~ c 

.Q 

-c 

Q) 

-

Q) 

a:: 

Q) 

0' 

<( 

400 

300 

syntectonic 

pluton 

main 

metamorphic 

pluton 

late-metamorphic envelope 

55 60 65 

Age (Ma) 

Figure 4. Relative ages of metamorphism (thinner lines) and ore 

deposition (thicker lines) for rocks of AJ area, plotted as a 

function of age retention temperature, after Lund and others 

(1986). Syntectonic Carlson Creek pluton (14 km east-southeast 

of deposit) and late-tectonic Flat Point pluton (15 km eastnortheast of deposit) Pb/U ages (U) from Gehrels and others 

(1984). Metamorphic hornblende (H) and biotite (B) K-Ar ages 

are from Blackerby Ridge 7 km north of deposit from Forbes and 

Engels (1970). Mineralization ages are from vein minerals (Rb/Sr 

isochron) (R.W. Kistler, U.S. Geological Survey, written 

commun., 1987) and muscovite K-Ar (M) (D.L. Leach, U.S. 

Geological Survey, written commun., 1987). 

Southeastern Alaska 177 
REFERENCES CITED 

Bowers, T.S., and Helgeson, H.C., 1983, 

Calculation of the thermodynamic and 

geochemical consequences of nonideal mixing 

in the system H2o-co2-NaCl on phase 

relations in geologic systems: Equation of 

state for H2o-co2-NaCl fluids at high 

pressures and temperatures: Geochimica et 

Cosmochimica Acta, v. 47, p. 1247-1276. 

Brew, D.A., and Ford, A.B., 1977, Preliminary 

geologic and metamorphic-isograd map of the 

Juneau B-1 quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-846, 1 sheet, scale 1:31,680. 

----- 1978, Megalineament in southeastern Alaska 

marks southwest edge of Coast Range 

batholithic complex: Canadian Journal of 

Earth Science, v. 15, p. 1763-1772. 

----- 1986, Preliminary reconnaissance geologic 

map of the Juneau, Taku River, Atlin and 

part of the Skagway 1:250,000 quadrangles, 

southeastern Alaska: U.S. Geological Survey 

Open-File Report 85-395, 23 p., 2 sheets, 

scale 1:250,000. 

Brew, D.A., Ford, A.B., and Himmel berg, G.R., 

1987, Late Cretaceous sedimentation, 

volcanism, plutonism, metamorphism and 

deformation 1n the northern Cordillera, 

southeastern Alaska [ abs.]: Geological 

Society of America Abstracts with Programs, 

v. 19, no. 7, p. 600. 

----- 1988, Evolution of the western part of the 

Coast plutonic-metamorphic complex, 

southeastern Alaska, U.S.A.--A synopsis, in 

Daly, S.R., ed., Evolution of metamorphic 

belts: Geological Society of London Special 

Paper 32 [in press]. 

Brew, D.A., Ovenshine, A.T., Karl, S.M., and 

Hunt, S.J., 1984, Preliminary reconnaissance 

geologic map of the Petersburg and parts of 

the Port Alexander and Sumdum 1:250,000 

quadrangles, southeastern Alaska: U.S. 

Geological Survey Open-File Report 84-405, 2 

sheets, 43 p. pamphlet. 

Douglass, S.L., and Brew, D.A., 1985, 

Polymetamorphism in the eastern Petersburg 

quadrangle, in Bartsch-Winkler, Susan, ed., 

The United -states Geological Survey in 

Alaska: Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 89-92. 

40; 40 Forbes, R.B., and Engels, J.C., 1970, K Ar 

age relations of the Coast Range batholith 

and related rocks of the Juneau Icefield 

area, Alaska: Geological Society of America 

Bulletin, v. 81, p. 579-584. 

Ford, A.B., and Brew, D.A., 1973, Preliminary 

geologic and metamorphic-isograd map of the 

Juneau B-2 quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field 

Studies Map MF-527. 

1977, Preliminary geologic and 

metamorphic-isograd map of parts of the 

Juneau A-1 and A-2 quadrangles, Alaska: 

U.S. Geological Survey Miscellaneous Field 

Studies Map MF-847. 

Gehrels, G.E., Brew, D.A., and Saleeby, J .B., 

1984, Progress report on U/Pb (zircon) 

geochronologic studies in the Coast 

plutonic-metamorphic complex east of Juneau, 

southeastern Alaska, in Reed, K.M., and 

Bartsch-Winkler, Susan, eds., The United 

States Geological Survey in Alaska: 

Accomplishments during 1982: U.S. 

Geological Survey Circular 939, p. 100-102. 

Goldfarb, R.J., Light, T.D., and Leach, D.L., 

1986, Nature of the ore fluids at the 

Alaska-Juneau gold deposit, in BartschWinkler, Susan, and Reed. K.M., eds., 

Geologic studies in Alaska by the U.S. 

Geological Survey during 1985: U.S. 

Geological Survey Circular 978, p. 92-94. 

Himmelberg, G.R., Ford, A.B., and Brew, D.A., 

1984, Progressive metamorphism of pelitic 

rocks in the Juneau area, southeastern 

Alaska, in Coonrad, W.L., and Elliott, R.L., 

eds., The-united States Geological Survey in 

Alaska: Accomplishments during 1981: U.S. 

Geological Survey Circular 868, p. 131-134. 

Kretschmar, U., and Scott, S.D., 1976, Phase 

relations involving arsenopyrite in the 

system Fe-As-S and their application: 

Canadian Mineralogist, v. 14, p. 364-386. 

Lund, Karen, Snee, L.W., and Evans, K.V., 1986, 

Age and genesis of precious metal deposits, 

Buffalo Hump district, central Idaho: 

Implications for depth of emplacement of 

quartz veins: Economic Geology, v. 81, p. 

990-996. 

Nesbitt, B.E., Murowchick, J.B., and 

Muehlenbachs, K., 1986, Dual origins of lode 

gold deposits in the Canadian Cordillera: 

Geology, v. 14, p. 506-509. 

Newberry, R.J., and Brew, D.A., 1987, The 

Alaska-Juneau gold deposits: Remobilized 

syngenetic versus exotic epigenetic origin, 

in H~milton, T.D., and Galloway, J.P., eds., 

Geologic studies in Alaska by the U.S. 

Geological Survey during 1986: U.S. 

Geological Survey Circular 998, p. 128-132. 

Scott, S.D., 1973, Experimental calibration of 

the sphalerite geobarometer: Economic 

Geology, v. 68, p. 466-474. 

Twenhofel, W. S., 1952, Geology of the AlaskaJuneau lode system, Alaska: U.S. Geological 

Survey Open-File Report 52-160, 170 p. 

Wayland, R.G., 1960, The Alaska Juneau gold ore 

body: Neues Jahrbuch fur Mineralogie 

Abhandlungen, v. 94, p. 267-279. 

Wernecke, Livingston, 1932, Geology of the ore 

zones: Engineering and Mining Journal, v. 

133, P• 494-499. 

Reviewers: Roger Ashley and Raul Madrid 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

178 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
OFFSHORE 

Ice pileup draped with sandy gravel derived from the shoreface along margin of Beaufort Sea. These deposits 

commonly are a major component of arctic barrier islands. See articles by Barnes and Reimnitz and Reimnitz 

and Barnes. · Photograph by Erk Reimnitz. 
Construction of an Arctic Barrier Island by Alternating Sea-Ice 

Pileup and Overwash 

By P.W. Barnes and Erk Reimnitz 

Knowledge of northern Alaska's coastal zone--

its character, history, and processes--is needed for 

determinations of State and Federal lands and for the 

design of coastal structures and pipeline crossings. 

Such knowledge will also serve in reconstructing 

ancient high-latitude environments from the geologic 

record. In this report and its companion (Reimnitz and 

Barnes, this volume), we discuss the stability, 

morphology, probable construction mechanism and 

internal makeup of a unique, sea-ice dominated arctic 

barrier island from a poorly known stretch of the 

Alaskan arctic coast. Our evidence implicates sea ice 

as the sediment-supply agent for the island, and an 

interaction of alternating ice pileups and overwash as 

the geologic processes giving the island its unique 

shape. 

Barrier islands form an almost continuous chain 

fronting the eastern 100 km of Alaska's low arctic 

coastal plain. Coalescing alluvial fans form this part 

of the coastal plain and its extension seaward 

underneath the continental shelf (Carter and others, 

1986; Wolf and others, 1987). A 26-km-long, arcuate 

barrier island named Icy Reef by John Franklin in 1826 

(because of severe coastal ice conditions encountered 

by his party in mid-summer) is one member of the 

island chain (fig. 1). Icy Reef blocks the outflow of 

the Kongakut River from direct access to the sea. 

Between the river delta and Icy Reef is a shallow 

lagoon averaging about 500 m in width and less than 1 

m deep (fig. 1 in Reimnitz and Barnes, this volume). 

144. 

BAATER BEAUFORT SEA ISLMD :::----___.~ 

-~ 

X ALASKA 

1 KONGN<LJT RIVER 

0 KILOMETERS !'il 

Study~ 

\ 

Figure 1. Sketch map of coast and barrier islands in 

northeastern Alaska showing location of Icy Reef (see Reimnitz 

and Barnes, this volume, figure 1, for additional deta ill. 

The Kongakut delta is composed of sandy mud whereas 

the barrier island is constructed of sandy gravel, and 

therefore, the Kongakut River presently is not 

considered a major sediment source for Icy Reef. A 

comparison of the Icy Reef coastline, mapped 30 years 

apart (about 1950 to about 1980), shows a remarkable 

stability in the central third of its length, coinciding 

with an area containing a high hummocky crest that is 

the focus of this paper. 

The low-lying (about 1 m elevation) eastern and 

western extremities of Icy Reef are splayed to widths 

of a few hundred meters and are migrating onshore at 

rates of 1 m per year or more, typical of many barrier 

islands along the arctic coast further to the west 

(Short and others, 1974; Reimnitz and others, 1988). 

The stable central third of the island, where widths of 

75 to 100 m prevail, is characterized by a continuous 

hummocky ridge, up to 4 m high. We visited this part 

of the island briefly in 1981 and again in 1987. Piles of 

sandy gravel 5 to 10 m in length were found to form 

hummocky features with crests 1 to 2 m above the 

surrounding island (fig. 2). In 1987 the seaward face of 

the sediment ridge consisted of erosional scarps that 

exposed three or more horizontal beds of sand and 

gravel about 25 em thick (fig. 3). Laterally these beds 

vary in thickness and may pinch out. Between the 

scarps and the sea was a gently sloping 15-m-wide sand 

and gravel beach similar to beaches elsewhere in the 

Arctic (figs. 2, 3, and 4). The lagoonward slope, which 

gradually dropped to sea level over distances in excess 

of 50 m, had formed from a series of overwash fans 

which originated at saddles along the line of hummocks 

(fig. 2). Kettle-like depressions (Greene, 1970) up to 3 

m in diameter and 75 em deep dotted the lagoonward 

Figure 2. Hummocky crest of Icy Reef in 1981, looking east. 

Note ice-pushed mounds of sandy grave l and overwash 

channels in saddles between mounds. 

180 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
slope of the island; they commonly contained finegrained sediment and new vegetation. Along the 

lagoon shore were patches of fine grained, vegetated 

sediments that contrasted with the sand and gravel 

seaward on the barrier island. Eolian features were 

absent on the barrier island. Offshore surficial 

sediments in water depths to 10 m, which consist of 

sand and pebbly sand, make up a potential sediment 

source for the barrier island and hum mocks. 

The height and irregular profile of the crest of 

Icy Reef are unusual for arctic barrier islands (figs. 2 

and 4) and suggest a unique explanation. The 30-yr 

stability of the shoreline along the high-crested 

central one-third of the island may be a part of the 

explanation, but in itself is not the complete answer. 

Sea ice must be considered, as it can transport 

sediment to elevations not normally reached by waves 

Figure 3. Erosional scarp and hummocky crest of Icy Reef in 

August 1987, showing several horizontal layers of overwash 

deposits. Beach deposits reworked by waves and currents in 

foreground. Offshore is to left; pole is 2.4 m in length. 

A. / 

/ 

B. 

Wave dominated barrier island 

Perched sediments 

from ice pileup 

0 10 20 

METERS 

-----

Ice dominated 

Wave dominated 

barrier island 

Overwash 

deposits 

Figure 4. Conceptual cross sections of (A) wave-dominated 

arctic barrier island (Reindeer Island), "typical" of Beaufort Sea 

barrier islands; and (B) ice-dominated barrier island (Icy Reef) 

superimposed on wave-dominated cross section (stippled 

pattern). Overwash deposits dominate cross sections, but we 

suggest that ice pileups are responsible for providing material to 

the islands as demonstrated at Icy Reef. 

(Kovacs and Sodhi, 1980). Bulldozing of shoreface 

material onto arctic beaches by ice has been noted in 

many instances, and the sediment volumes so 

contributed in some years may be considerable (Barnes 

and others, 1982; McLaren, 1982). Harper and others 

(1985) speculated that onshore transport of sediment 

by ice is the primary sediment supply for the long, 

linear, and stable barrier islands of the western Yukon 

coast, 20 km east of Icy Reef. Reimnitz and Barnes 

(this volume) have summarized the evidence for sea 

ice impacting Icy Reef, and reasoned that ice pileup is 

a more likely mechanism than ice rideup. 

During most pileups, sheets of sea ice break 

near the ice-flotation line on the shore face in water 

depths of 1 to 2 m. Continued onshore pushing and 

piling of ice causes a portion of the broken ice to 

scoop sand and gravel from the shoreface, resulting in 

a rubble-pile mixture of sediment and ice. These 

pileups generally occur within 15 m of the water's edge 

and may be up to 10 m high (Kovacs and Sodhi, 1980). 

Melting of the ice in these piles releases the 

incorporated sediment which settles to the underlying 

surface, forming internally structureless mounds. An 

abundant supply of coarse material on the shoreface is 

another requirement for vertical accretion through 

pileup. Subsequent storms, waves and currents tend to 

smooth out the hummocky relief and irregularities of 

ice pileup. Large waves associated with storm surges 

locally overtop the hummocky ridge, eroding saddles 

and depositing coalescing fans of overwash sediment. 

The regionally smooth backslope of Icy Reef has been 

shaped by such overwash (figs. 2 and 4). Kettles form 

when overwash carries brash ice, which then litters the 

backslope during fan accretion. 

Seaward-facing beaches elsewhere along the 

Beaufort Sea coast generally retreat between 1 to 10 

m/yr, and therefore the sediment accumulations from 

intermittent sea-ice pileups are not preserved. The 

stable part of Icy Reef, where the stratigraphy of the 

erosional scarp records at least three sedimentation 

events that could represent alternating ice pileups and 

smoothing by wave overwash (fig. 3), is an exception. 

These events have resulted in barrier islands 2 to 3 

times as high as islands elsewhere along the Arctic 

coast (fig. 4). 

Rex (1964) and others have noted the virtual 

absence of ice-disturbance structures in arctic 

beaches. Those observations were made on normal 

beach deposits, as in the foreground of figure 3. 

Except for the sea-ice kettles on the overwash fans, 

we too expect that the barrier island at Icy Reef is 

dominated by hydraulic structures (figs. 3 and 4) 

except at their highest points. If preserved in the 

geologic record, steeply dipping, laterally 

discontinuous overwash fans with pit structures should 

reflect stable barrier islands in an ice-stressed 

setting. Such islands, in which the sediment budget is 

dominated by onshore sediment movement through ice 

rather than longshore transport, should contain mainly 

lithologies and clast sizes characteristic of the local 

offshore, rather than those derived from updrift 

sediment sources. The dominance of onshore transport 

from local rather than longshore sediment sources has 

been suggested by studies of pebble lithologies and 

sizes in other barrier islands of the Beaufort Sea 

(Hopkins and Hartz, 1978). 

Offshore 181 
REFERENCES CITED 

Barnes, P. W., 1982, Marine ice-pushed boulder 

ridge, Beaufort Sea, Alaska: Arctic, v. 35, 

P• 312-316. 

Barnes, P.W., Reimnitz, Erk, and Fox, D., 1982, 

Ice rafting of fine-grained sediment, a 

sorting and transport mechanism, Beaufort 

Sea, Alaska: Journal of Sedimentary 

Petrology, v. 52, p. 493-502. 

Carter, L.D., Ferrians, O.J., Jr., and Galloway, 

J.P., 1986, Engineering-geologic maps of 

northern Alaska coastal plain and foothills 

of the Arctic National Wildlife Refuge: 

U.S. Geological Survey Open-File Report 86-

334, 10 p., 2 sheets, scale 1:250,000, 

Greene, H.G., 1970, Microrelief of an arctic 

beach: Journal of Sedimentary Petrology, v. 

40, p. 419-427. 

Harper, J.R., Collins, Arlene, and Reimer, P.D., 

1985, Morphology and processes of the 

Canadian Beaufort Sea coast [abs.], in 

Arctic Workshop, Land-Sea Interactions, 

14th, Dartmouth, Nova Scotia, p. 110-111. 

Hopkins, D.M., and Hartz, R.W., 1978, Coastal 

morphology, coastal erosion and barrier 

islands of the Beaufort Sea, Alaska: U.S. 

Geological Survey Open-File Report 78-1063, 

54 p. 

Kovacs, Austin, and Sodhi, D.S., 1980, Shore ice 

pile-up: Field observations, models, 

theoretical analyses: Cold Regions Science 

and Technology, v. 2, p. 209-288. 

McLaren, Patrick, 1982, The coastal 

geomorphology, sedimentology and processes 

of eastern Melville and western Byam Martin 

Islands, Canadian Arctic Archipelago: 

Geological Survey of Canada Bulletin 333, 39 

P• 

Reimni tz, Erk, Graves, S.M., and Barnes, P. W., 

1988, Beaufort Sea coastal erosion, sediment 

flux, shoreline evolution and the erosional 

shelf profile: U.S. Geological Survey 

Miscellaneous Investigations Map I-1182-G, 

scale 1:82,000, with text, 22 p. 

Rex, R.W., 1964, Arctic beaches, Barrow, Alaska, 

in Miller, R.L., ed. Papers in Marine 

Geology, New York, Macmillan, p. 384-400. 

Short, A.D., Coleman, J.M., and Wright, L.D., 

1974, Beach dynamics and nearshore 

morphology of the Beaufort Sea Coast, 

Alaska, in Reed, J. and Sater, J., eds. The 

coast and shelf of the Beaufort Sea: 

Arlington, Va., Arctic Institute of North 

America, p. 477-488. 

Wolf, S.C., Barnes, P.W., Rearic, D.M, and 

Reimnitz, Erk, 1987, Quaternary seismic 

stratigraphy of the inner continental shelf 

north of ANWR, in, Bird K.J. and Magoon, 

L. B. eds, U. S. Geological Survey Bulletin 

1778, p. 61- 78. 

Reviewers: R.L. Phillips and D.M. Rearic 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

182 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Sea-Floor Feeding Traces of Gray Whales and Walrus 

in the Northeast Chukchi Sea 

By R. Lawrence Phillips and Mitchell W. Colgan 

Sediments in the northeast Chukchi Sea contain 

dense to scattered benthic feeding traces of gray 

whales (Eschrichtius robustus) and walrus (Odobenus 

rosmarus divergens). This study identifies some of the 

northernmost feeding grounds of these mammals and 

sumarizes surface sediment textures, observed feeding 

traces, and fauna living in or near the feeding areas. 

Ice covers the shallow Chukchi Sea for 9 to 10 

months a year. As the ice recedes northward in 

summer, gray whales and walrus move north to feed 

either adjacent to the ice edge (walrus) or in open 

water east of the pack ice (gray whales and walrus) 

where the Alaska Coastal Current is concentrated. 

Within this region the sea floor exhibits variable relief, 

deepening northeastward into the Barrow Sea Valley 

(fig. 1). Along the eastern edge of the Chukchi Sea the 

northward-flowing Alaska Coastal Current affects the 

sea floor, producing active sand wave fields, sand 

ribbons, and extensive gravel lag deposits. All these 

substrates contain rich faunal communities. The area 

west of the influence of the coastal current contains 

sediment varying from muddy fine sand to gravelly 

sand and muddy gravel; these substrates have less 

diversified fauna (fig. 2). 

Reconnassance geological and geophysical 

surveys were conducted using the NOAA RV Surveyor 

Figure 1. Northeast Chukchi Sea, showing bathymetry in meters 

(modified from Hill and others, 1984). 

in 1984 and RV Discoverer in 1985. From sonographs 

collected during these surveys we identified scattered 

to dense benthic feeding traces on the sea floor (fig. 

2). Television and bottom photographs showed the seafloor surface features in greater detail. Box cores 

162° 

sea 

~Mudd y sand 

Large-scale bedform s and 

miora ti on direction KILmiETERS 

160° 158° 

11 cl\i Pack oce edge 

cl\0" .:. . . - oo•"Q>• ( 

/ :::,; · ... Pt. Barrow 

71 ~ 

·< :- e~d ing areas 

~ Gray whales 

EZ23 Walrus 

Figure 2. Northeast Chukchi Sea. A, Surface sediment textures. 

Alaska Coastal Current produces extensive gravel lag deposits 

within head of Barrow Sea Va lley. Sea floor changes to 

bioturbated sand or muddy sand to west. B, Areas containing 

benthic feeding traces of gray whales and walrus. Letters 

indicate locations of sonographs or bottom photographs (see 

figures 3 to 5). 

Offshore 183 
(four cores per site) and dredges in the gravel-rich 

areas were taken to sample the sediment and the 

benthic communities. 

Gray whales move north to feed along an openwater corridor between the pack ice and the coast; 

they reach the vicinity of Barrow and sometimes move 

into the Beaufort Sea (Maher, 1960). The highest 

density of gray whales observed in the Chukchi Sea is 

in the coastal region between Point Hope and Barrow 

(Ljungblad, 1987). We have observed numerous gray 

whales concentrated along the eastern side of the 

Chukchi Sea, especially in the shallow nearshore 

waters from Icy Cape north to Point Franklin where 

the Alaska Coastal Current is actively transporting 

sediment and nutrients. 

Gray whales are benthic feeders that produce 

solitary to multiple sea- floor excavations. They 

ingest sediment and infaunal invertebrates and filter 

the sediment through their baleen (Nerini and others, 

1980; Nerini 1984; Oliver and Kvitek, 1984; Nelson and 

others, 1987; Nelson and Johnson, 1984, 1987). Their 

main food in much of their northern range and 

especially in the northern Bering Sea is infaunal tubedwelling Ampelisca amphipods (Nerini, 1984, Nelson 

and others, 1987). However, in the Chukchi Sea their 

food supply may differ because of opportunistic 

feeding on both epifaunal and infaunal communities 

(Ljungblad, 1987). Ljungblad (1987) reported that gray 

whales apparently were feeding on swarms of 

epibenthic crustaceans (mysids, amphipods, and 

shrimp) over a gravel sea floor near Point Hope; on 

epibenthic isopods north of Cape Lisburne; and on 

infaunal amphipods southwest of Wainwright. 

Gray-whale feeding traces were identified from 

south of Icy Cape to north of Point Franklin (fig. 2). 

Observations of sediment plumes surrounding surfacing 

whales in this region confirm benthic feeding. Serial 

box cores taken where the whales were feeding show 

the sediment texture (gravelly sand) and benthic 

organisms (infaunal tube-dwelling amphipods and two 

other species of amphipods), and sonographs show 

dense sea-floor feeding traces (fig. 3). The feeding 

traces are similar to those initially reported in the 

Bering Sea by Nerini and others (1980) and Nelson and 

Johnson (1984). The highest concentration of feeding 

traces are found at depths of 23 to 34 m on the inner 

shelf between Wainwright and Point Franklin. 

However, a different feeding mode may occur in 

deeper water where an extensive surficial gravel field 

exists. Here, the whales may feed on swarming shrimp 

and amphipods, as suggested by Ljungblad (1987) for 

the gravel areas near Point Hope, and may not 

excavate feeding traces. 

The benthic feeding traces in sand consist of 

multiple elliptical pits to solitary elliptical pits 1.0 to 

3.8 m long and 1.0 to 2.5 m wide (Type I and Type II 

feeding pits of Nelson and Johnson, 1984, 1987). Most 

appear to be enlarged and modified by currents. 

Southwest of Icy Cape, within a region containing 

small-scale bedforms less than 3 em high, solitary and 

scattered feeding pits are common. Here, the extent 

of the gray whale feeding is uncertain because the 

scattered pits may represent "test" feeding areas, or 

active currents may have filled in most of the feeding 

traces, or dense carpets of sand dollars 

(Echinarachnius parma) may restrict whale feeding. 

An abundant food supply exists for whales 

within the coastal region and especially in the shallow 

regions reworked by active coastal currents. Infaunal 

and epifaunal organisms observed in sandy substrates 

on which the whales may be feeding include tubedwelling Ampelisca amphipods, mysids, polychaete 

worms, isopods, and shrimp. Tube-dwelling amphipods 

and mysids were abundant in box cores taken in active 

bedform fields off Point Franklin whereas off Icy Cape 

epifaunal isopods were very abundant on core surfaces 

and infaunal amphipods and polychaetes were common. 

In the gravel-rich areas the whales can feed on shrimp, 

isopods, mysids, and both epifaunal and infaunal 

amphipods. Besides benthic feeding the whales may 

skim the gravel surfaces ingesting swimming prey. 

Like the gray whales, walrus during sum mer 

tend to concentrate near the Alaskan and the Siberian 

coasts rather than in the central part of the Chukchi 

Sea. Most of the walrus that have been observed in 

the eastern Chukchi Sea were less than 20 km from the 

southern pack ice edge with their highest 

concentrations located offshore between Wainwright 

A 

B 

Figure 3. Gray-whale feeding pits from a 500-kHz sonograph 

and associated bedforms. A, Current-modified multiple wha le 

feeding pits in sand at 24 m depth, locality A. B, Smal l-sca le 

ripples in coastal current sand at 31 m depth where whales were 

observed feeding, locality B. Ripples and inclined stalked 

bryozoans indicate currents moving from left to right. Stripes on 

bar scale are 5 em wide. 

184 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
and Point Barrow (Fay and others, 1984). Studies of 

benthic feeding traces of walrus show that they 

excavate an irregular to linear furrow in the sea bed 

while searching for prey and that the furrows may also 

contain deeper scattered hydraulic jetted pits (Oliver 

and others, 1983). Furrow dimensions in shallow water 

in the northern Bering Sea vary with reported 

maximum lengths of 64 m (Oliver and others, 1983) to 

200 m (Nelson and others, 1987). The average furrow 

widths are 45 em, and their depths are 10 to 17 em. 

Walrus are opportunistic feeders that consume 

mainly infaunal prey (primarily pelecypods) but also a 

variety of epifaunal organisms such as gastropods, sea 

cucumbers, soft corals, octopus, polychaetes, fish, 

shrimp, sea pens, amphipods, tunicates, sponges, and 

crabs (Fay and others, 1984; Fukuyama and Oliver, 

1985; Johnson, 1986; and Nelson and others, 1987). 

In the eastern Chukchi Sea, where the walrus 

concentrate in summer, the food supply varies from 

high diversity and high density in the gravel-rich 

regions to low diversity and moderate to low density in 

the sandy regions (fig. 4). The organisms identified in 

the gravel-rich regions on which walrus may feed 

include epibenthic sea cucumbers, sea pens, soft 

corals, sponges, tunicates, isopods, myscids, 

amphipods, pectens (Chlamys), crabs, gastropods 

(Neptunia, Boreotrophon, and Buccinum) and 

brachiopods, whereas the infaunal communities 

identified consist of polychaetes, amphipods, and a 

variety of pelecypods (Nucula, Macoma, Mya, Serripes, 

Astarte, Yoldia, Hiatella, Cyclocardia, and Natica). 

Macoma and Nucula are the most common living 

infaunal prey in the gravel-rich regions. The sandy 

substrate west of the gravel fields contains mainly 

infaunal organisms including polychaetes, amphipods, 

Macoma, Yoldia , and Astarte, with Macoma the most 

abundant prey. 

Walrus feeding traces are found to depths of at 

least 53 m in the northeast Chukchi Sea. The 

excavated traces consist of long, narrow, linear 

Figure 4. Bottom photograph of typical epifaunal communities 

on gravel lag at 47 m depth in Barrow Sea Valley, locality E. 

Sponges, soft corals, tunicates, crab, brachiopod, anemones, 

sea urchins, gastropods, bryozoans and barnacles are visible 

on the gravel surface. 

furrows; gently curved furrows; irregular furrows in 

gravel; and multiple overlapping irregular to linear 

furrows and solitary pits in offshore sand (fig. 5). The 

sea-floor furrows are less than 50 em wide and 2 to 52 

m long. These features can be solitary or may occur, 

especially within the Barrow Sea valley, as linear, 

parallel multiple traces. They can also appear as 

dense, overlapping traces with random orientations 

completely disrupting the sea bed, as for example on 

the south flank of Hanna Shoal adjacent to the pack 

ice edge (fig. 5A). Repeated movement of the pack 

ice harboring abundant numbers of walrus would tend 

to concentrate feeding within a band to the south of 

the ice. This appears to be confirmed by the dense 

feeding pattern observed south of the summer-ice edge 

position. 

In summary, gray whales feed exclusively on 

infaunal amphipods in the northern Bering Sea but 

apparently feed on a variety of epifaunal and infaunal 

prey further to the north. The highest concentration 

of gray whale benthic feeding traces and food supply 

underlies the Alaska Coastal Current Water, where the 

substrate consists of gravel and sand. Walrus feeding 

traces are found in the same areas as whale feeding 

traces, but the highest concentrations of walrus 

feeding traces are identified farther west on the south 

A 

Figure 5. Walrus furrows shown on 500-kHz sonographs. A, 

Dense, multiple walrus furrows in muddy sand at 41 m depth 

south of Hanna Shoal, locality C. B, Irregular walrus furrows in 

gravel at 42 m depth in Barrow Sea Valley, locality D. 

Offshore 185 
flank of Hanna Shoal near the pack ice boundary. Both 

walrus and gray whale feeding traces are readily 

modified by shelf and storm currents, so the record of 

benthic feeding identified in the Chukchi Sea probably 

reflects the minimum area of feeding in this region. 

This study was funded in part by the Minerals 

Management Service through interagency agreement 

with the National Oceanic and Atmospheric 

Administration as part of the Outer Continental Shelf 

Environmental Assessment Program. We thank 

Captain Peterson and Captain Bradly, the officers, and 

crew of the R V Discoverer and RV Surveyor for their 

help. 

REFERENCES CITED 

Fay, F .H., Kelly, B.P., Gehnrich, P.H., Sease, 

J.L., and Hoover, A.A., 1984, Modern 

populations, migrations demography, 

trophies, and historical status of the 

Pacific walrus: U.S. Department of 

Commerce, Final report, Outer Continental 

Shelf Environmental Assessment Program, p. 

231-375. 

Fukuyama, A.K., and Oliver, J.S., 1985, Sea star 

and walrus predation on bivalves in Norton 

Sound, Bering Sea, Alaska: Ophelia, v. 24, 

P• 17-36. 

Hill, E.R., Grantz, Arthur, May, S.D., and 

Smith, M., 1984, Marine geology atlas 

Chukchi Sea: U.S. Geological Survey 

Miscellaneous Investigation Series Map I1182-D. 

Johnson, Kirk, 1986, The bizarre diet of 

walrus: Discovery, v. 19, p. 3-7. 

Ljungb1ad, D.K., 1987, Gray whale distribution 

in the Chukchi and Bering Seas, in Hale, 

D.A., ed., Chukchi Sea information--update: 

U.S. Department of Commerce, Outer 

Continental Shelf Environmental Assessment 

Program, p. 101-106. 

Maher, W.J., 1960, Recent records of the 

California gray whale (Eschrichtius glaucus) 

along the north coast of Alaska: Arctic, v. 

13, P• 257-265. 

Nelson, C.H., and Johnson, K.R., 1984, Gray 

whales, tillers of the sea floor, in Clarke, 

S.H., ed., Highlights in marine geology: 

U.S. Geological Survey Circular 938, p. 99-

107. 

----- 1987, Whales and walrus as tillers of the 

sea floor: Scientific American, v. 255, p. 

501-512. 

Nelson, C.H., and Johnson, K.R., and Barber, 

J.H., Jr., 1987, Gray whale and walrus 

feeding excavation on the Bering shelf, 

Alaska: Journal of Sedimentary Petrology, 

v. 57, p. 419-430. 

Nerini, M., 1984, A review of 

ecology, in Jones, M.L., 

Leatherwood, S., eds., 

Eschrichtius robustus: 

gray whale feeding 

Swartz, S.L., and 

The gray whale 

San Francisco, 

Academic Press, p. 423-450. 

Nerini, M.K., Jones, L., and Braham, H.W., 1980, 

Gray whale feeding ecology, first year final 

report, March-December, 1980: National 

Oceanographic and Atmospheric 

Administration, Outer Continental Shelf 

Environmental Assessment Program, RU 593, 

[contract number R7120828]. 

Oliver, J.S., and Kvitek, R.G., 1984, Side-scan 

sonar records and diver observations of the 

Gray whale (Eschrichtius robustus) feeding 

grounds: Biology Bulletin, v. 197, p. 264-

269. 

Oliver, J.S., Slattery, P.N., O'Connor, E.F., 

and Lowry, L.F., 1983, Walrus, Odobenus 

rosmarus, feeding in the Bering Sea: a 

benthic perspective: Fishery Bulletin, v. 

81, p. 501-512. 

Reviewers: J. H. Barber and R. E. Hunter 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

186 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Late Cretaceous Sediments from the Northeast Chukchi Sea 

By R. Lawrence Phillips, LedaBeth G. Pickthorn, and Douglas M. Rearic 

The shallow epicontinental Chukchi Sea is 

floored by a thin blanket of sediment, mostly 1 to 2 m 

thick but ranging up to 12 m, that overlies folded and 

faulted bedrock. Only in the northwest part of the 

study area (fig. 1) does the sediment cover thicken to 

as much as 64 m in a series of filled fluvial channels. 

The thin sediment cover of the Chukchi Sea is the 

product of ice gouging, storms, shelf currents, and 

repeated transgressions. 

In 1985 we obtained 22 vibracores to a 

maximum length of 6 m in the Chukchi Sea using the 

NOAA RV Discoverer. High-resolution seismic 

profiles were used to identify sediment thickness and 

specific core sites which contained thick strata (up to 

5 m sediment) overlying folded bedrock. Stratigraphic 

investigations identified fresh and altered vitric tephra 

in 5 cores (Phillips and Colgan, 1987) and a crystal 

vitric tephra in one additional core (core 67, fig. 2). 

Core 67 is unique in that a reworked crystal vitric 

tephra deposited in a shallow marine or beach 

environment occurs throughout the laminated sand 

that composes its lowest stratigraphic unit. This paper 

presents the initial results of potassium-argon dating 

of biotite from the crystal vitric tephra. We also 

discuss the deposit's origin and implications of the 

radiometric age data. 

Figure 1. Northeast Chukchi Sea, showing thickness (m) of 

undeformed sediment overlying folded bedrock. Sediment 

cover is mainly Quaternary age, but may include flat-lying older 

strata in some areas. Contours dashed where inferred. 

Core site 67 underlies the strong northwardflowing Alaska Coastal Current at 41 m depth. Three 

stratigraphic units of unconsolidated sediment are 

identified in the core (fig. 3). A thin Holocene 

transgressive sand, 58 em thick, forms the uppermost 

sequence. Underlying the transgressive sand is a 256-

cm-thick unit of iron-stained quartz sand, pebbly mud, 

and brown to black peat containing nonmarine 

ostracodes of probable Pleistocene age. Well-rounded 

quartz sand containing granules overlies the basal 

stratigraphic unit along a sharp irregular contact. 

The basal sequence consists of 152 em of 

biotite-rich horizontally laminated sand containing 

multiple laminae of opaque heavy minerals. Narrow 

burrows, some filled with heavy minerals, are 

scattered in the upper 60 em of the laminated sand, 

but this stratigraphic unit contains no fossils. The 

laminated sand ranges in size from very fine to 

medium size and exhibits a polymodal size distribution 

which reflects varying energy conditions and selective 

grain transport during laminae deposition (fig. 3). The 

sand contains white and clear quartz, zoned 

plagioclase, altered glassy rock fragments, large brown 

biotite in books and thin flakes, green hornblende, 

quartz with biotite, opaque heavy minerals, and clay 

minerals; its heavy mineral content is 13.4 to 15.7 

70° 

69° Vibracore locations 

0 50 100 KLOMETERS 

Figure 2. Location of vibracores in northeast Chukchi Sea 

containing vitric tephra (53, 65), altered tephra (43, 62, 64), and 

crystal vitric tephra (67). Bathymetric contours in meters. 

Offshore 187 
percent, the highest values identified in the Chukchi 

Sea. Clay minerals, which form less than 2 percent of 

the core, are mainly smectite-illite {89 percent) with 

minor amounts of kaolinite and chlorite (11 percent). 

Potassium-argon dating of biotite in two 

samples from the top 30 em and the bottom 30 em of 

the laminated sand yields ages of 92.1 ± 1.2 and 95.2 ± 

1.2 Ma, respectively (table 1). The younger date could 

possibly reflect some alteration of the biotite rather 

than a younger age. These dates place the biotite-rich 

sediments in the Cenomanian stage of the Late 

Cretaceous (using stage boundaries of Kent and 

Gradstein, 1985). 

The high heavy-mineral content of the sand 

indicates a high-energy depositional environment in 

which currents actively concentated both biotite and 

opaque heavy minerals. Three environments which 

may produce such laminae are beach, storms, or shelf 

currents. The specific environment is uncertain, but a 

beach environment is suggested by the stratigraphic 

position of this deposit. The occurrence of nonmarine 

(eolian to fluvial) sediments above the laminated sand 

suggests an overall regressive sequence. Evidence for 

storms or shelf currents exists in the present-day 

regime, and much of the history of the Chukchi Sea 

apparently is erosional. Either storm or shelf currents, 

such as the present Alaska Coastal Current which 

overlies the core site, could produce similar laminae. 

Depth 

(em) Sea floor 

0 " ) 

I\(~\ 

) ) ) \ 

58 ~ ;:..~ ) 

% 

QUATERNARY 

Holocene transg ressive sand, 

shells, to rams, ostracodes, and 

dia toms 

QUATERN ARY (? ) 

Iron-stained sand, gravel, and peat 

beds with nonmarine ostracodes. 

Probable Pleistocene 

Heavy 

-to=---=--= mineral 1 K-Ar date 

F==J- 13.4 r92.1t1.2Ma 

>==::::::J- 14.3 LATE CRETA CEOUS 

Lam ina ted sa nd, biotite- rich 

vitric teohra w ith heavy mineral 

laminations 

K-Ar date r 95.2t1.2Ma 

Figure 3. Stratigraphy of core 67 showing three depositional 

units separated by erosional contacts. Grain-size distribution is 

of sand fraction. 

Any of the three environments--beach, storm, 

or currents--may have produced the laminated deposit 

during either the Quaternary or Cretaceous. However, 

the biotite, which occurs as individual crystals (books), 

as slightly rounded flakes, and in quartz suggests 

limited weathering and transport after deposition of 

the tephra. The relatively unaltered state of the 

plagioclase and hornblende also support this 

interpretation. Therefore, the biotite may represent 

material eroded from a nearby source with limited 

transport or the deposit may in fact be a primary unit 

of Cretaceous age. 

Biotite in the present Chukchi Sea sediments 

and in the other vibracore stratigraphic samples is 

exceedingly limited, and is found only as rare grains in 

the basal stratigraphic units of two cores containing 

vitric tephra (cores 53 and 65). Muscovite, however, is 

common to abundant in all other marine stratigraphic 

units cored in the Chukchi Sea. If biotite were 

reworked by Quaternary transgressions one would 

expect it to be found in more than a single 

stratigraphic sequence. However, biotite is only 

abundant in core 67, thereby suggesting that it is in a 

primary deposit and that the potassium-argon dates 

provide a valid Late Cretaceous age for the basal 

strata at this site. 

At the site of core 67, high-resolution seismic 

profiles show a thin (3 to 4 m) horizontal sediment 

cover that overlies gently westward-dipping strata. 

Although variations in sediment thickness, 

irregularities in the bedrock surface, and ship 

movements during anchoring preparatory to coring did 

not allow exact identification of the sediment 

thickness at the core site, our studies of the core 

suggest that Quaternary sediment cover about 3 m 

thick overlies about 1.5 m of bedrock. 

The stratigraphic relationship of the reworked 

tephra grains in core 67 to the other tephras we 

recovered is uncertain. Both cores 53 and 65 contain 

identical tephra as indicated by the refractive index of 

the glass {1.500 ± 0.002, Phillips and Colgan, 1987). 

The glass shards in core 67 are altered, therefore the 

refractive index cannot be compared with core 53 and 

65. Either the tephra in core 53 and 65 form a blanket 

deposit over older folded bedrock, or the same bedrock 

tephra was cored as that at site 67. The crystal tephra 

could represent a different phase of the same eruption 

episode that produced the tephra in cores 53 and 65, 

but a resolution of this problem must wait for dating 

of the other tephra deposits. If the crystal tephra in 

core 67 were related to the vitric tephra in core 53 

and 65, then it would define the stratigraphic age of 

the upper bedrock surface and will be a very important 

stratigraphic horizon in the northeast Chukchi Sea. 

Late Cretaceous age (Cenomanian) means that 

the basal strata in core 67 will correlate with the 

uppermost part of the Nanushuk Group (Niakogon 

Tongue of the Chandler Formation) and lowermost part 

of the Colville Group (Seabee Formation) of northern 

Alaska. Both the Niakogon Tongue of the Chandler 

Formation and the Seabee Formation contain tephras. 

The nonmarine Niakogon Tongue of the Chandler 

Formation contains tephra beds up to 3 m thick 

(Brosg~ and Whittington, 1966). The Seabee Formation 

consists of fossiliferous marine shale containing 

numerous bentonite beds up to 1.5 m thick that yield 

188 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Table 1. Argon analyses and age calculation of biotite from crystal tephra recovered in 

[Potassium analyses by l.l. flame photometer using lithium internal standard. Argon analyses by standard techniques 

of isotope dilution. Ages were calculated using the following constants: K40 decay constants: A.e + A.e' = 0.581 x 10-l 0 

year_,; Ab = 4.963 X 1 o-1 ° year-1; abundance ratio: K40;K = 1.167 X 1 o-4 atom percent] 

Ar40 Ar40 

Percent rad rad Apparent age 

Field no. Mineral K20 (mol/g) (Ma) 

(see Ar40 

figure 3) total 

T30 Biotite 8.60 1.167xlo-9 0.908 92.1 ± 1.2 

8.55 

B30 Biotite 8.65 l.217xlo-9 0.955 95.2 ± 1.2 

8.65 

potassium-argon ages on biotite of 91.5 ± 0.9 to 93.6 ± 

1.2 Ma (Lanphere and Tailleur, 1983). The similarities 

in ages (Late Cretaceous), composition (biotite-rich 

tephra), and environment (marine) suggest a 

correlation between the Seabee Formation and the 

basal sediment in core 67. It may correlate with part 

of the Niakogon Tongue of the Chandler Formation as 

well, but there are no radiometric dates for the 

tephras. 

In summary, six vibracores in the northeast 

Chukchi Sea penetrated tephra, and one of these cores 

contain a crystal tephra that was reworked in a beach 

or high-energy shallow marine environment from a 

nearby source. Based on potassium-argon dating, the 

deposit is Late Cretaceous. Although the evidence 

does not allow a definite assessment of whether the 

tephras are (1) folded Cretaceous bedrock, (2) a 

blanket deposit of post-deformation age, or (3) a 

reworked Quaternary deposit, most of our evidence 

appears to favor a primary deposit of Cretaceous age. 

This study was funded in part by the Minerals 

Management Service through interagency agreement 

with the National Oceanic and Atmospheric 

Administration as part of the Outer Continental Shelf 

Assessment Program. We thank Captain Peterson, the 

officers, and crew of the RV Discoverer for their 

help. We also thank L.F. Espos (USGS) for the 

potassium analyses and T.L. Vallier (USGS) for 

petrologic analyses. 

REFERENCES CITED 

Brosg~, W.P., and Whittington, C.L., 1966, 

Geology of the Umiat-Maybe Creek region 

Alaska: U.S. Geological Survey Professional 

Paper 303-H, p. 501-601. 

Kent, D.V., and Gradstein, F.M., 1985, A 

Cretaceous and Jurassic geochronology: 

Geological Society of America Bulletin, v. 

96, P• 1419-1427. 

Lanphere, M.A., and Tailleur, I.L., 1983, K-Ar 

ages of bentonites in the Seabee Formation, 

northern Alaska: A Late Cretaceous 

(Turonian) time-scale point: Cretaceous 

Research, v. 4, p. 361-370. 

Phillips, R.L., and Colgan, M.W., 1987, 

Vibracore stratigraphy of the northeastern 

Chukchi Sea, in Hamilton, T.D., and 

Galloway, J.P., eds., Geologic studies in 

Alaska by the U.S. Geological Survey during 

1986: U.S. Geological Survey Circular 998, 

p 157-160. 

Reviewers: K. J. Bird and T. L. Vallier 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

Offshore 189 
Evidence for Sea-Ice Impact on Icy Reef, Beaufort Sea Coast 

By Erk Reimnitz and P.W. Barnes 

In recent investigations of ice impact along the 

Alaskan coast (Kovacs, 1983, 1984) and global synopses 

of the phenomenon (Kovacs and Sodhi, 1980; Sodhi and 

Kovacs, 1984), the distinction is made between (1) 

rideup, where a sheet of ice may smoothly slide 

landward across beaches and beyond for distances as 

much as 185 m, thereby generally conforming to the 

surface of the land, and (2) pileup, where the icesheet buckles and crumbles at the seaward edge of 

bottom-fast ice. This ice failure then results in piles 

of broken ice up to 20 m high and 10 to 20 m wide, 

much of which comes to rest on the beach. Either iceimpact phenomenon is most likely to occur in fall or 

spring, is over within 15 to 30 minutes at most, and 

commonly leaves a scar of one form or another, which 

along stable coastlines may be preserved for decades. 

Although ice movement onto shore is frequent on a 

regional scale, it is unpredictable for any particular 

site and may be likened to a 50-year flood (Sodhi and 

Kovacs, 1984). Ice rideup is a surficial scraping 

process mostly over frozen ground; it is unlikely to be 

arrested at the same place repeatedly, commonly does 

not result in a mound or ridge of sediment at the 

terminus, can produce such features no higher and 

wider than the ice sheet thickness (generally much less 

than 1 m), and therefore is unlikely to raise the 

elevation of a barrier island. If rideup produces a 

ridge or mound, this consists of materials scraped 

largely from the beach surface and tundra, and 

therefore may include driftwood, soil, and vegetative 

mat. Ice pileups, on the other hand, recur in a narrow 

zone; they commonly contain large amounts of sand 

and gravel from the shoreface dispersed throughout 

the pile, and each event, therefore, can result in a 

broad sediment mound 1 to 2 m high (see Barnes and 

Reimnitz, this volume). In either case, the natural 

scars are not easily datable, and no attempts have 

been made previously to learn about the frequency and 

severity of ice-encroachment from the fate of 

manmade objects along the coast. The present study is 

an attempt to gain such knowledge from objects placed 

on Icy Reef, a poorly known part of the Beaufort Sea 

coast. The knowledge will become useful for any 

future development of the area. 

Icy Reef is an arcuate gravel barrier island, 80 

to 100 m wide, that extends for 26 km along the shores 

of the Arctic National Wildlife Range, at the south 

margin of the Beaufort Sea (fig. 1). The island is 

separated from the Kongakut River delta by a lagoon 

several hundred meters wide that is generally 

shallower than 1 m. The Icy Reef setting is unusual 

for several reasons: (1) The central part of the lagoon 

is seasonally occupied by a large naled (river icing) 

(Harden and others, 1977), which never melts 

entirely. (2) With an unbroken length of 26 km, and a 

crestal elevation of up to 4 m, Icy Reef is the longest 

and highest barrier island in the Beaufort Sea. Other 

more typical barrier islands are only 1 to 2 m high 

(Barnes and Reimnitz, this volume). (3) The gravelly 

crest is hummocky, with over 1 m of relief, as opposed 

to the smooth, overwash-shaped nature of barriers. (4) 

The central, 17-km-long stretch of Icy Reef has 

remained essentially unchanged in outline from 1951 to 

1981 (fig. 1), while other Arctic coastal features have 

undergone remarkable changes (Reimnitz and others, 

1988). Because of its unique character and setting, we 

believe that much of the knowledge gained from 

previous studies of lagoons and barrier islands in the 

Prudhoe Bay area cannot be applied to Icy Reef. 

Thirteen towers were erected along Icy Reef 

for navigational control of hydrographic surveys by the 

U.S. Coast and Geodetic Survey (C&GS) in 1952 (fig. 

1). Most but not all of these towers were positioned on 

triangulation stations, and were generally placed on 

the highest elevation of barrier islands, or several 

meters to landward. The 1968 edition of C&GS chart 

9478 shows eight of the survey targets as having been 

destroyed either by 1955 or 1956. No systematic count 

has been conducted since, but we believe that none of 

the survey towers remain standing at this time. 

In August 1987, we visited triangulation station 

EASY, which was established in 1952 (fig. 1). The 

monument is described as a standard disk on top of an 

iron pipe projecting 12 em above the ground. The 

reference marks RM1 and RM2 on iron pipes were 

located within about 15 m east and south of EASY, 

with a wooden 4-by-4 inch "witness post" near RM1 

(U.S. Department of Commerce, 1977). Remains of 

the tower were reported near the site in 1972 (U.S. 

Department of Commerce, 1977), but neither EASY 

nor its reference marks could be found at that time. 

During our visit, we found EASY, RM1, and remains of 

the witness post (fig. 2). They were located at the toe 

of a subdued erosional scarp 1 to 1.5 m high, seaward 

of the hummocky crest of the island. The base of bent 

RM1 and the stump of the witness post were vertical 

and obviously in place. The sharp bend in the pipe at 

the same level as the break of the sound wooden post 

indicate that both resisted landward shear forces by 

being held in a surface of frozen sediment rather than 

in the loose gravel that exists there during summer. 

The shear plane was slightly above the present beach 

surface, but more than a meter below the present 

crest of the island. RM1 was bent toward the base of 

the 8-m-tall wooden tower 45 m distant, and the 

toppled tower was pointing in the same direction as 

RM1, suggesting to us that both were destroyed by the 

same type of event. 

190 Geologic Studies in Alaska by the U.S. Geological SW'Vey during 1987 
(j) -

loa:. 

0 

u. 

':) 

<( 

w 

en 

i.iJ 

Q) L{) co s: Ol Ol 

(/) 

ro 

0 

0 

(/) 

~ 

Q) 

:;: 

0 

u 

Q) 

>-

0 

~ <0 

(/) L{) 

Q) '-

u~ 

~ Ol Q) 

(f) 

a: 

w 

1--

w 

2 

0 

_j 

~ 

:;: >- 0 0 .0 

Ic: 

Most survey towers placed on beaches and 

barrier islands of the Beaufort Sea around 1950 were 

destroyed before the hundred-year storm surge of 1970 

(Reimnitz and Maurer, 1979), whereas the same kinds 

of towers remain standing on high bluffs between 

Barrow and Peard Bay along the Chukchi Sea coast. 

This fact suggests that the destruction was neither 

from strong winds nor combined icings and winds. 

Storm waves carrying logs are not believed responsible 

for destruction of the site for two reasons: (1) the 

tower lies close to its original location, and (2) the 

ground was frozen, indicating destruction after 

freezeup and cessation of wave action. Thus, sea ice 

most likely damaged the tower and the triangulation 

station EASY within 3 to 4 years after its 

construction. We suspect that most of the other 

towers destroyed on Icy Reef so shortly after 

construction met a similar fate. 

The inability to recover the markers around 

EASY in 1972 and their rediscovery in 1987 about 1 m 

below the present crest of Icy Reef suggest that the 

station had been buried sometime before 1972 and was 

exhumed by the eroding sea since then. The 

hummocky crest of Icy Reef and the buildup of gravel 

to 4 m, as opposed to the 1- to 2-m level of modern 

beaches, suggest that sea-ice encroachment added the 

gravel to the island. The stratigraphy of the gravel 

deposits exposed in the scarp at EASY suggests 

repeated deposition and reworking (Barnes and 

Reimnitz, this volume). Because ice rideup is a 

subaerial scraping process, unlikely to be arrested at 

the same place repeatedly, it cannot raise the general 

elevation of a barrier island. Ice pileups, on the other 

hand, commonly contain shoreface-derived sand and 

gravel, which after melting remains as a broad gravel 

mound. Our evidence thus indicates that much of the 

old and stable central part of this unusual barrier 

island has been repeatedly impacted and elevated by 

ice pileups during the last 35 years. 

Figure 2. Photograph of triangulation station EASY, bent iron 

pipe (RM1 ), and broken witness post on seaward face of Icy 

Reef in August 1987. Placed in 1952 along the highest part of the 

island, these markers were first damaged by ice, then buried by 

gravel from ice pileups, and finally again exhumed by the sea. Ice 

pileups apparently deposited at least 1 m of gravel on top of the 

barrier island since 1952. Note 13-m-long RN KARLUK for 

scale. 

Offshore 191 
Our most intriguing and significant finding is 

that ice pile-up is an important sediment supply 

mechanism for Arctic beaches and barrier islands, and 

can result in net accretion where the coast is stable. 

Ride-up, on the other hand, is geologically less 

important because it contributes little to no sediment. 

This investigation also shows that a comprehensive 

study of datable artifacts along poorly known stretches 

of the Arctic coast can provide much insight on its ice 

hazards and coastal processes. 

REFERENCES CITED 

Harden, Deborah, Barnes, P.W., and Reimnitz, 

Erk, 1977, Distribution and character of 

naleds in northeastern Alaska: Arctic, v. 

30, no. 1, p. 28-40. 

Kovacs, Austin, 1983, Shore ice ride-up and 

pile-up features, Part 1: Alaska's Beaufort 

Sea coast: Hanover, N.H., U.S. Army Cold 

Regions Research and Engineering Laboratory, 

CRREL Report 83-9, 51 p. 

1984, Shore ice ride-up and pile-up 

features, Part 2: Alaska's Beaufort Sea 

coast - 1983 and 1984: Hanover, N.H., U.S. 

Army Cold Regions Research and Engineering 

Laboratory, CRREL Report 84-26, 29 p. 

Kovacs, Austin, and Sodhi, D.S., 1980, Shore ice 

pile-up: Field observations, models, 

theoretical analyses: Cold Regions Science 

and Technology, v. 2, p. 209-288. 

Reimnitz, Erk, and Maurer, D.K., 1979, Effects 

of storm surges on the Beaufort Sea coast, 

northern Alaska: Arctic, v. 32, no. 4, p. 

329-344. 

Reimnitz, Erk, Graves, S.M., and Barnes, P.W., 

1988, Beaufort Sea coastal erosion, sediment 

flux, shoreline evolution and the erosional 

shelf profile: U.S. Geological Survey 

Miscellaneous Investigations Map I-1182-G, 

22 p. 

Sodhi, D.S., and Kovacs, Austin, 1984, Forces 

associated with ice pile-up and ride-up, in 

Proceedings, International Association for 

Hydraulic Research, International Symposium 

on Ice, 7th, Hamburg, v. IV, p. 239-262. 

U.S. Department of Commerce, 1977, Horizontal 

Control Data: QUAD 691414, Station 1004, 

National Ocean Survey. 

Reviewers: P.R. Carlson and R.L. Phillips 

Geologic Studies in Alaska by the U.S. 

Geological Survey during 1987: John P. Galloway 

and Thomas D. Hamilton, editors, U.S. Geological 

Survey Circular 1016. 

192 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
BIBLIOGRAPHIES 

Pingo in channel of Middle Fork Chandalar River, south-central Brooks Range. Stream channel has been forced 

to bifurcate around the actively growing ice-cored mound. Photograph by T.D. Hamilton. 
Reports about Alaska 1n USGS Publications Released 1n 1987 

Compiled by Ellen R. White 

[Some reports dated 1986 did not become available until 1987; they are included in this listing.] 

[Abbreviations used: 

"B 1778" for: Bird, K.J., and Magoon, L.B. eds., Petroleum geology of the northern part of the Arctic National 

Wildlife Refuge, northeastern Alaska: U.S. Geological Survey Bulletin 1778. 

"C 995" for: Sachs, J.S., ed., USGS Research on Mineral Resources - 1987, program and abstracts, third annual 

V.E. McKelvey Forum on Mineral and Energy Resources: U.S. Geological Survey Circular 995. 

ellen page 

"C 998" for: Hamilton, T.D., and Galloway, J.P., eds., Geologic studies in Alaska by the U.S. Geological Survey 

during 1986: U.S. Geological Survey Circular 998. (Short papers describing results of recent geologic 

investigations and lists of published reports.] 

Anders, D.E., Magoon, L.B., and Lubeck, S.C., 1987, 

Geochemistry of surface oil shows and potential 

source rocks: B 1778, p. 181-198. 

Arbogast, B.F., Bailey, E.A., and Frisken, J.G., 1987, 

Analytical results and sample locality maps of 

stream -sediment, heavy-m ineral-concen tra te, 

and rock samples from the Port Moller, Stepovak 

Bay, and Simeonof Island quadrangles, Alaska: 

U.S. Geological Survey Open-File Report 87-502, 

122 p., scale 1:250,000, 2 pls. 

Arbogast, B.F., Madden, Dawn, Hoffman, J.D., and 

O'Leary, R.M., 1987, Analytical results and 

sample locality map of stream-sediment, 

moraine-sediment, and heavy-mineralconcentrate samples from the Anchorage 

quadrangle, south-central Alaska: U.S. 

Geological Survey Open-File Report 87-151, 175 

p., scale 1:250,000, 1 pl. 

Bailey, E.A., Folger, P.F., Thompson, W.B., Sutley, 

S.J., Schmidt, J.M., and Karl, S.M., 1987, 

Analytical results and sample locality map of 

stream-sediment and heavy-mineral-concentrate 

samples from the Baird Mountains quadrangle, 

Alaska: U.S. Geological Survey Open-File Report 

87-65, 155 p., scale 1:250,000, 1 pl. 

Bailey, E.A., Lee, G.K., and Light, T.D., 1987, 

Semiquantitative emtsston spectrographic 

analyses of stream-sediment samples collected in 

the Livengood and western one-third of the 

Circle 1° x 3° quadrangles, Alaska: U.S. 

Geological Survey Open-File Report 87-264, 74 

p., scale 1:250,000, 1 pl. 

Bailey, E.A., Sutley, S.J., Arbogast, B.F., Willson, 

W.R., and Church, S.E., 1987, Analytical results 

and sample locality map of stream-sediment and 

heavy-mineral-concentrate samples from the 

Mount Katmai quadrangle, and portions of the 

Naknek, Afognak, and Iliamna quadrangles, 

Alaska: U.S. Geological Survey Open-File Report 

86-586, 126 p., scale 1:250,000, 1 pl. 

Barnes, P. W ., Graves, Scot, and Reimnitz, Erk, 1987, 

Beaufort Sea coastal currents: A divergence 

near Barter Island, Alaska?: C 998, p. 139-142. 

Barton, C. C., and Light, T.D., 1987, Structural fabric 

analysis of the Perseverance Slate and goldbearing quartz veins in the south ore body of the 

Alaska-Juneau lode system, southeastern 

Alaska: C 998, p. 110-112. 

Barton, H.N., 1987, Sample locality map and results of 

carrier distillation emiSSion spectrographic 

analysis of stream-sediment samples from the 

Chandler Lake quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 87-21, 7 p., 

scale 1:250,000, 1 pl. 

Bartsch-Winkler, Susan and Schmoll, H.R., 1987, 

Earthquake-caused sedimentary couplets in the 

Upper Cook Inlet region: C 998, p. 92-95. 

Beavan, John, 1987, Crustal deformation 

measurements in the Shumagin seismic gap, in 

National Earthquake Hazards Reduction 

Program; summaries of technical reports v. 24: 

U.S. Geological Survey Open-File Report 87-374, 

p. 207-214. 

Billington, Selena, and Kisslinger, Carl, 1987, Central 

Aleutian Islands seismic network, in National 

Earthquake Hazards Reduction - Program; 

sum maries of technical reports v. 24: U.S. 

Geological Survey Open-File Report 87-374, p. 

13-15. 

Bird, K.J., and Bader, J.W., 1987, Regional geologic 

setting and history of petroleum exploration: B 

1778, p. 17-25. 

Bird, K.J., and Magoon, L.B., eds., 1987, Petroleum 

geology of the northern part of the Arctic 

National Wildlife Refuge, northeastern Alaska: 

U.S. Geological Survey Bulletin 1778, 329 p., 5 

pls. 

Bird, K.J., and Molenaar, C.M., 1987, Stratigraphy: B 

1778, p. 37-59. 

Bird, K.J., Griscom, S.B., Bartsch-Winkler, Susan, and 

194 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Giovanetti, D.M., 1987, Petroleum reservoir 

rocks: B 1778, p. 79-99. 

Blodgett, R.B., Wheeler, K.L., Rohr, D.M., Harris, 

A.G., and Weber, F.R., 1987, A Late Ordovician 

age reappraisal for the upper fossil Creek 

Volcanics, and possible significance for glacioeustasy: C 998, p. 54-58. 

Box, S.E., and Murphy, J.M., 1987, Late Mesozoic 

structural and stratigraphic framework, eastern 

Bethel quadrangle, southwestern Alaska: C 998, 

p. 78-82. 

Brabets, T.P., 1987, Quantity and quality of urban 

runoff from the Chester Creek Basin, Anchorage, 

Alaska: U.S. Geological Survey Water-Resources 

Investigations Report WRI 86-4312, 58 p. 

Brew, D.A., 1987, Cenozoic magmatism in 

southeastern Alaska: C 998, p. 137. 

Brew, D.A., and Ford, A.B., 1987, The Meade Glacier 

fault--An important tectonic boundary in the 

northern Cordillera, southeastern Alaska: C 998, 

p. 113-115. 

Brew, D.A., Grybeck, D.J., Cathrall, J.B., Karl, S.M., 

Koch, R.D., Barnes, D.F., Griscom, A., and Berg, 

H. C., 1987, Mineral-resource assessment process 

and results, Petersburg project area, 

southeastern Alaska [abs.]: C 995, p. 8-9. 

Brew, D.A., Himmelberg, G.R., Ford, A.B., and 

Jachens, R.C., 1987, Ultramafic and mafic sills 

in the vicinity of the Treadwell gold deposits, 

Douglas Island, southeastern Alaska: C 998, p. 

119-123. 

Brewer, M.C., 1987, Surficial geology, permafrost, and 

physical processes: B 1778, p. 27-36. 

Brockman, S.R., Espinosa, A.F ., and Michael, J.A., 

1987, Digital intensity catalog of earthquakes 

felt in Alaska and Aleutian Islands, 1786-1981: 

U.S. Geological Survey Open-File Report 87-68, 

12 p. 

Brown, C.S., Rasmussen, L.A., and Meier, M.F., 1986, 

Bed topography inferred from airborne radioecho sounding of Columbia Glacier, Alaska: U.S. 

Geological Survey Professional Paper 1258-G, 26 

p. 

Bruns, T.R., Fisher, M.A., Carlson, P.R., Rearic, D.M., 

and Parson, L.M., 1987, GLORIA images obtained 

in the TACT corridor of the Aleutian convergent 

margin, northern Gulf of Alaska [abs.]: C 998, p. 

170. 

Bruns, T.R., Fisher, M.A., Leinbach, W.J., Jr., and 

Miller, J.J., 1987, Regional structure of rocks 

beneath the coastal plain: B 1778, p. 249-254. 

Bruns, T.R., Mann, D.M., and Sliter, R.W., 1987, 

Multichannel seismic-reflection profiles 

collected in 1978 in the eastern Gulf of Alaska: 

U.S. Geological Survey Open-File Report 8 7-148, 

5 p. 

Bruns, T.R., Vallier, T.L., Pickthorn, L.B., and von 

Huene, Roland, 1987, Volcanic-arc dacite and 

early Miocene basalt dredged from the Shumagin 

margin, Alaska: C 998, p. 143-146. 

Callahan, J.E., Brougham, G. W ., and Bascle, R.J., 

1987, Economically recoverable oil resources: B 

1778, p. 299-307. 

Campbell, D.L., 1987, Profiles showing models of 

magnetic structures in accreted terranes of 

south-central Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1912, scale 

1:500,000, 2 sheets. 

Carlson, P.R., Marlow, M.S., Parson, L.M., and Somers, 

M.L., 1987, GLORIA investigation of the 

Exclusive Economic Zone in the deep Bering 

Sea: U.S. Geological Survey Open-File Report 

87-72, 16 p. 

Case, J.E., and Nelson, W.H., 1986, Maps showing 

aeromagnetic survey and geologic interpretation 

of the Lake Clark quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field Studies 

Map MF-1114-E, 2 sheets. 

Cathrall, J.B., Antweiler, J.C., and Mosier, E.L., 1987, 

Occurrence of platinum in gold samples from the 

Tolovana and Rampart mining districts, 

Livengood quadrangle, Alaska: U.S. Geological 

Survey Open-File Report 87-330, 10 p., 1 pl. 

Cathrall, J.B., Brosg~, W.P., and Dillon, J.T., 1987, 

Stream-sediment geochemical anomalies in the 

Doonerak area, Wiseman quadrangle, Brooks 

Range, Alaska: U.S. Geological Survey Open-File 

Report 87-139, 6 p. 

Cathrall, J.B., Dillon, J.T., Hoffman, J.D., Brosg~, 

W.P., and Bliss, J.D., 1987, Geochemical maps 

and evaluation of stream-sediment geochemical 

data of the Wiseman 1° x 3° quadrangle, Brooks 

Range, Alaska: U.S. Geological Survey Open-File 

Report 87-12, 67 p., scale 1:250,000, 2 pls. 

Cathrall, J.B., McDanal, Steve, and Miesch, A.T., 

1987, Selected geochemical data and 

geochemical plots from U.S. Department of 

Energy - National Uranium Resources Evaluation 

on sediment samples from the Table Mountain 1° 

x 3° quadrangle, Brooks Range, Alaska: U.S. 

Geological Survey Open-File Report 87-424, 55 p. 

Church, S.E., 1987, Studies of lead isotopes in sulfide 

deposits from accreted terranes in the North 

American Cordillera [abs.]: C 995, p. 12-13. 

Church, S.E., Delevaux, M.H., and Gray, J.E., 1987, 

Pb-isotope data base for sulfides from Alaska, 

March 1987: U.S. Geological Survey Open-File 

Report 87-259, 44 p. 

Collett, T.S., and Kvenvolden, K.A., 1987, Evidence of 

naturally occurring gas hydrates on the North 

Slope of Alaska: U.S. Geological Survey OpenFile Report 87-255, 8 p. 

Collett, T.S., Kvenvolden, K.A., Magoon, L.B., and 

Bird, K.J., 1987, Geochemical and geologic 

controls of the inferred occurrence of natural gas 

hydrate in the Kuparuk 2D-15 well, North Slope, 

Alaska: C 998, p. 24-26. 

Cooper, Alan, Hunter, Ralph, Huggett, Quentin, and 

Harris, Malcolm, 1987, GLORIA study of the 

Exclusive Economic Zone off Alaska - southern 

Bering Sea (Bowers basin) initial report for cruise 

F1-87-BS, 28 June to 27 July 1987: U.S. 

Geological Survey Open-File Report 87-579, 19 p. 

Cooper, Alan, Stevenson, Andrew, Kenyon, Neil, and 

Bishop, Derek, 1986, GLORIA study of the 

Exclusive Economic Zone off Alaska - southern 

Bering Sea: initial report for cruise F4-86-BS, 3 

September to 30 September 1986: U.S. 

Geological Survey Open-File Report 86-596, 19 p. 

Cramer, C.H., May, S.D., Hanna, W.F., Grantz, Arthur, 

and Holmes, M.L., 1986, Reconnaissance 

magnetic anomaly map of the Chukchi Sea and 

Bibliographies 195 
adjacent northwest Alaska: U.S. Geological 

Survey Miscellaneous Investigations Series, 

Marine Geology Atlas, Chukchi Sea, I-1182-F, 

scale 1:1,000,000, 1 sheet. 

Cunningham, K.I., Roberts, A.A., and Donovan, T.J., 

1987, Horizontal-gradient magnetic and helium 

surveys: B 1778, p. 209-218. 

Czamanske, G.K., Bennett, P.C., Zientek, M.L., and 

others, 1986, Comprehensive bibliographies on 

mineralized and unmineralized layered mafic 

intrusions in the United States: U.S. Geological 

Survey Open-File Report 86-589-A, 97 p. 

[References for Alaska are intermingled with 

those for other states.] 

Davis, A.S., Wong, F .L., Pickthorn, L.-B.G., and 

Marlow, M.S., 1987, Petrology, geochemistry and 

age of basanitoids dredged from the Bering Sea 

continental margin west of Navarin Basin: U.S. 

Geological Survey Open-File Report 87-407. 

Detterman, R.L., Case, J.E., Wilson, F.H., and Yount, 

M.E., 1987, Geologic map of the Ugashik, Bristol 

Bay, and western part of Karluk quadrangles, 

Alaska: U.s. Geological Survey Miscellaneous 

Investigations Series Map I-1685, scale 1:250,000, 

1 sheet. 

Detterman, R.L., Wilson, F.H., Yount, M.E., and 

Miller, T.P., 1987, Quaternary geologic map of 

the Ugashik, Bristol Bay, and western part of 

Karluk quadrangles, Alaska: U.S. Geological 

Survey Miscellaneous Investigations Series Map I1801, scale 1:250,000, 1 sheet. 

Dolton, G.L., Bird, K.J., and Crovelli, R.A., 1987, 

Assessment of in-place oil and gas resources: B 

1778, p. 277-298. 

Dubois, G.D., Wilson, F.H., and Shew, Nora, 1986, Map 

and tables showing potassium-argon age 

determinations and selected major-element 

chemical analyses from the Circle quadrangle, 

Alaska: U.S. Geological Survey Open-File Report 

86-392, scale 1:250,000, 1 sheet. 

----- 1987, Potassium-argon age determinations from 

the Port Moller and Stepovak Bay quadrangles, 

Alaska Peninsula: U.S. Geological Survey OpenFile Report 87-191, scale 1:250,000, 1 sheet. 

Duttweiler, K.A., 1987, Use of factor analysis in 

locating base metal mineralization in the Killik 

River quadrangle, Alaska: C 998, p. 27-30. 

Espinosa, A.F ., 1987, Seismic hazard studies, 

Anchorage, Alaska, in National Earthquake 

Hazards Reduction Program; summaries of 

technical reports v. 24: U.S. Geological Survey 

Open-File Report 87-374, p. 547-548. 

Fischbein, S.A., 1987, Analysis and interpretation of 

ice-d~formed sediments from Harrison Bay, 

Alaska: U.S. Geological Survey Open-File Report 

87-262, 73 p. 

Fisher, M.A., and Bruns, T.R., 1987, Structure of PreMississippian rocks beneath the coastal plain: B 

1778, p. 245-248. 

Fogleman, K.A., Page, R.A., Lahr, J.C., and Stephens, 

C. D., 1987, Earthquake activity around Valdez, 

Alaska for 1983-1984: U.S. Geological Survey 

Open-File Report 87-58, 44 p. 

Foland, R.L., and Lalla, D.J., 1987, Seismic-reflection 

data acquisition, processing, and interpretation: 

B 1778, p. 235-243. 

Foley, R.C., 1987, Field surveying and topographic 

mapping in Alaska: 1947-83: U.S. Geological 

Survey Circular 991, 98 p., 1 pl. ["A 

chronological review of surveying activities in 

Alaska from 194 7 to 1983 including a brief 

description of camp life and some of the 

hardships and unusual experiences encountered."] 

Folger, P.F., Goldfarb, R.J., and Schmidt, J.M., 1987, 

Preliminary evaluation of geochemical anomalies 

in the Baird Mountains quadrangle, Alaska: C 

998, p. 31-34. 

Ford, A.B., and Brew, D.A., 1987, The Wright Glacier 

volcanic plug and dike swarm, southeastern 

Alaska: C 998, p. 116-118. 

Foster, H.L., and Keith, T.E.C., 1987, Preliminary 

geology, including the Tintina fault system, of 

part of the southwestern Charley River 

quadrangle, Alaska: C 998, p. 59-61. 

Foster, H.L., Keith, T.E.C., and Menzie, W.D., 1987, 

Geology of east-central Alaska: U.S. Geological 

Survey Open-File Report 87-188, 59 p. [Maps are 

page-size.] 

Foster, H.L., Menzie, W .D., Cady, J. W ., Simpson, S.L., 

Aleinikoff, J.N., Wilson, F.H., and Tripp, R.B., 

1987, The Alaska Mineral Resource Assessment 

Program: Background information to accompany 

folio of geologic and mineral resource maps of 

the Circle quadrangle, Alaska: U.S. Geological 

Survey Circular 986, 22 p. 

Friesen, W.B., and Howell, D.G., 1987, A mineralogical 

look at the purple and green phyllitic sheared 

breccia from the Hammond terrane, Chandalar 

D-6, Brooks Range, Alaska: U.S. Geological 

Survey Open-File Report 87-156, 5 p. 

Fukuhara, C.R., 1986, Descriptions of plutons in the 

western part of the Juneau and parts of the 

adjacent Skagway 1:250,000 quadrangles, 

southeastern Alaska: U.S. Geological Survey 

Open-File Report 86-393, 58 p., scale 1:250,000, 1 

pl. 

Galloway, J.P., 1987, A list and index of published 

radiocarbon dates for Alaska with a 

bibliography: U.S. Geological Survey Open-File 

Report 87-517-A, 117 p. 

Galloway, J.P., 1987, Radiocarbon date list for Alaska 

to accompany USGS Open-File Report 87-517-

A: U.S. Geological Survey Open-File Report 87-

517-B. [5 1/4" diskette formatted for IBM-PCs 

using DOS 2.0 in a standard ASCII format.] 

Gamble, B.M., 1987, Gold veins of the Seward 

Peninsula [abs.]: C 995, p. 23. 

Gardner, J. V., Karl, H.A., Huggett, Quentin, and 

Harris, M., 1986, Cruise report for EEZ-SCAN 86 

Cruise F3-86, Zhemchug Canyon and central 

Aleutian Basin, Bering Sea, August 6, through 

September 1, 1986: U.S. Geological Survey OpenFile Report 86-597, 12 p. 

Gautier, D.L., 1987, Petrology of Cretaceous and 

Tertiary reservoir sandstones in the Point 

Thomson area: B 1778, p. 117-122. 

Gautier, D.L., Bird, K.J., and Colten-Bradley, V.A., 

1987, Relationship of clay mineralogy, thermal 

maturity, and geopressure in wells of the Point 

Thomson area: B 1778, p. 199-207. 

Gedney, Larry, 1987, Alaska earthquakes, 1983, !!! 

Stover, C. W., ed., United States earthquakes, 

196 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
1983: U.S. Geological Survey Bulletin 1698, p. 

125. 

Gehrels, G.E., and Saleeby, J.B., 1986, Geologic map of 

southern Prince of Wales Island, southeastern 

Alaska: U.S. Geological Survey Open-File Report 

86-275, 33 p., scale 1:63,360, 1 pl. 

Glass, R.L., 1987, Groundwater levels in Anchorage, 

Alaska, 1985: U.S. Geological Survey Open-File 

Report 87-543, 15 p., 1 pl. 

----- 1987, Water resources near Dillingham in the 

Bristol Bay area, Alaska: U.S. Geological Survey 

Water-Resources Investigations Report WRI 87-

4141, 27 p. 

Goldfarb, R.J., and Smith, S.C., 1987, Geochemical 

map showing distribution of anomalous element 

suites in nonmagnetic heavy-mineral 

concentrates from the Chugach National Forest, 

Alaska: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-1645-G, 18 p., scale 

1:250,000, 1 pl. 

Grantz, Arthur, Dinter, D.A., and Culotta, R.C., 1987, 

Structure of the continental shelf north of the 

Arctic National Wildlife Refuge: B 1778, p. 271-

276. 

Hamilton, T.D., and Galloway, J.P., 1987, Geologic 

studies in Alaska by the U.S. Geological Survey 

during 1986; introduction: C 998, p. 1. 

Hamilton, T.D., and Galloway, J.P., eds., 1987, 

Geological studies in Alaska by the U.S. 

Geological Survey during 1986: U.S. Geological 

Survey Circular 998, 195 p. 

Hamilton, T.D., Lancaster, G.A., and Trimble, D.A., 

1987, Glacial advance of late Wisconsin (Itkillik 

II) age in the upper Noatak River Valley--A 

radiocarbon-dated stratigraphic record: C 998, 

p. 35-39. 

Himmelberg, G.R., Loney, R.A., and Nabelek, P.I., 

1987, Petrogenesis of gabbronorite at Yakobi and 

northwest Chichagof Islands, Alaska [abs.]: C 

995, p. 30-31. 

Hoffman, J.D., 1987, An application of oblique 

rotation R-mode factor analysis in the Mount 

Hayes quadrangle, Alaska: C 998, p. 108. 

Jones, D.L., Silberling, N.J., Coney, P.J., and Plafker, 

George, 1987, Lithotectonic terrane map of 

Alaska (west of the 141st meridian): U.S. 

Geological Survey Miscellaneous Field Studies 

Map MF-1874-A, scale 1:2,500,000, 1 sheet. 

Kanamori, Hiroo, 1987, State of stress near seismic 

gaps, in National Earthquake Hazards Reduction 

Program; summaries of technical reports v. 24: 

U.S. Geological Survey Open-File Report 87-374, 

p. 258-259. [Includes 1986 Andreanof Islands 

earthquake.] 

Karl, H.A., Carlson, P.R., Johnson, K.H., and Rearic, 

D.M., 1987, Grain-size parameters and 

constituent grain composition of surface 

sediment in Navarin basin province, Bering Sea: 

U.S. Geological Survey Open-File Report 87-64, 

32 p. 

Karl, H.A., Gardner, J.V., and Huggett, Quentin, 1987, 

GLORIA images of Zhemchug Canyon and Bering 

channel-fan system, Bering Sea: C 998, p. 147-

151. 

Karl, S.M., Schmidt, J.M., Folger, Peter, Thompson, 

Bill, Long, Carl, Goldfarb, Richard, and 

Ellersieck, Inyo, 1987, Mineral-resource 

assessment of the Baird Mountains quadrangle, 

western Brooks Range, Alaska [abs.]: C 995, p. 

33-34. 

Keith, T.E.C., Page, N.J, Oscarson, R.L., and Foster, 

H.L., 1987, Platinum-group element 

concentrations in a biotite-rich clinopyroxenite 

suite, Eagle C-3 quadrangle, Alaska: C 998, p. 

62-66. 

Kelley, J.S., and Foland, R.L., 1987, Structural style 

and framework geology of the coastal plain and 

adjacent Brooks Range: B 1778, p. 255-270. 

Kisslinger, Carl, 1987, Seismicity patterns and the 

stress state in subduction-type seismogenic 

zones, in National Earthquake Hazards Reduction 

Program; summaries of technical reports v. 24: 

U.S. Geological Survey Open-File Report 87-374, 

p. 78-83. ["Aftershocks of the May 7, 1986 

earthquake and other Aleutian Islands events," 

"Coda Q in the Adak region before and after the 

1986 Andreanof earthquake"] 

Knott, J.M., Lipscomb, S. W ., and Lewis, T. W ., 1987, 

Sediment transport characteristics of selected 

streams in the Susitna River basin, Alaska: data 

for water year 1985 and trends in bedload 

discharge: U.S. Geological Survey Open-File 

Report 87-229, 51 p. 

Koch, R.D., Brew, D.A., and Ford, A.B., 1987, Newly 

discovered molybdenite occurrence near 

Boundary Creek, Coast Mountains, southeastern 

Alaska: C 998, p. 124-125. 

Krimmel, R.M., 1987, Columbia Glacier, Alaska: 

Photogrammetry data set 1981-82 and 1984-85: 

U.S. Geological Survey Open-File Report 87-219, 

104 p. 

----- 1987, Columbia Glacier in 1986: 800 meter 

retreat: U.S. Geological Survey Open-File 

Report 87-207, 7 p. 

Krimmel, R.M., and Sikonia, W.G., 1986, Velocity and 

surface altitude of the lower part of Hubbard 

Glacier, Alaska, August 1978: U.S. Geological 

Survey Open-File Report 86-549, 13 p. 

Lahr, J.C., Stephens, C.D., Page, R.A., and Fogleman, 

K.A., 1987, Alaska seismic studies, in National 

Earthquake Hazards Reduction -program; 

summaries of technical reports v. 24: U.S. 

Geological Survey Open-File Report 87-374, p. 

20-26. 

Lamke, R.D., and Bigelow, B.B., 1987, Floods of 

October 1986 in southcentral Alaska: U.S. 

Geological Survey Open-File Report 87-391, 31 p. 

Lange, I.M., Nokleberg, W.J., Aleinikoff, J.N., and 

Church, S.E., 1987, Genesis and tectonic setting 

of volcanogenic massive sulfide deposits, eastern 

Alaska Range, Alaska [abs.]: C 995, p. 39-40. 

Leinbach, W.J., Jr., Miller, J.J., and Lee, M.W., 1987, 

Seismic-reflection data processing: B 1778, p. 

225-233. 

Leonard, K.R., and Huber, D.F., 1987, Status of Alaska 

mineral resources data system: C 998, p. 15-18. 

Light, T.D., Cady, J. W ., Weber, F.R., McCammon, 

R.B., and Rinehart, C.D., 1987, Sources of placer 

gold in the southern part of the White Mountains 

Recreation Area, east-central Alaska: C 998, p. 

67-69. 

Lipscomb, S. W ., 1987, Sediment-discharge data for the 

Bibliographies 197 
lower reach of Campbell Creek, Anchorage, 

Alaska: May to October 1986: U.S. Geological 

Survey Open-File Report 87-101, 8 p. 

Loney, R.A., and Brew, D.A., 1987, Regional thermal 

metamorphism and deformation of the Sitka 

Graywacke, southern Baranof Island, 

southeastern Alaska: U.S. Geological Survey 

Bulletin 1779, 17 p. 

Loney, R.A., Himmelberg, G.R., and Shew, Nora, 1987, 

Salt Chuck palladium-bearing ultramafic body, 

Prince of Wales Island: C 998, p. 126-127. 

Luedke, R.G., and Smith, R.L., 1986, Map showing 

distribution, composition, and age of Late 

Cenozoic volcanic centers in Alaska: U.S. 

Geological Survey Miscellaneous Investigations 

Series Map 1-1091-F, scale 1:1,000,000, 3 sheets. 

Luepke, Gretchen, Molnia, B.F., and Hein, J.R., 1987, 

Comparison of multiple-year analyses of clay 

mineralogy of the Copper River System and the 

Gulf of Alaska: U.S. Geological Survey OpenFile Report 87-153, 1 sheet. 

Madden, D.J., and Tripp, R.B., 1987, Geochemical 

signatures of mineral deposits and rock types as 

shown in stream sediments from the Chugach and 

Prince William terranes, Anchorage quadrangle, 

southern Alaska: U.S. Geological Survey OpenFile Report 87-131, 8 p. 

----- 1987, Geochemical signatures of mineral deposits 

and rock types as shown in stream sediments 

from the Peninsular terrane, Anchorage 

quadrangle, southern Alaska: U.S. Geological 

Survey Open-File Report 87-129, 8 p. 

Madden, D.J., Silberman, M.L., and Moore-Nall, Anita, 

1987, Ages and geologic relationships in the 

Willow Creek gold mining district, southwestern 

Talkeetna Mountains, southern Alaska: U.S. 

Geological Survey Open-File Report 87-143, 12 p. 

Magoon, L.B., Woodward, P.V., Banet, A.C., Jr., 

Griscom, S.B., and Daws, T.A., 1987, Thermal 

maturity, richness, and type of organic matter of 

source-rock units: B 1778, p. 127-179. 

Mankinen, E.A., and Plafker, George, 1987, 

Paleomagnetic evidence for a latest Pliocene and 

early Pleistocene age of the upper Yakataga 

Formation on Middleton Island, Alaska: C 998, p. 

132-136. 

Marinai, R.K., 1987, Petrography and diagenesis of the 

Ledge Sandstone Member of the Triassic Ivishak 

Formation: B 1778, p. 101-115. 

Marlow, M.S., Carlson, P.R., Dadisman, S.V., Rearic, 

D.M., Maple, E.J., and Parson, L.M., 1987, 

GLORIA side-scan and geophysical surveys of the 

central Bering Sea in 1986: C 998, p. 152-156. 

Mayfield, C.F ., Ellersieck, Inyo, and Tailleur, I.L., 

1987, Reconnaissance geologic map of the 

Noatak C5, D5, D6, and D7 quadrangles, Alaska: 

U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-1814, scale 1:63,360, 

1 pl. 

McLean, Hugh, 1987, Petrology and reservoir potential 

of the Jago River Formation: B 1778, p. 123-126. 

Menzie, W.D., Hua, Renmin, and Foster, H.L., 1987, 

Newly located occurrences of lode gold near 

Table Mountain, Circle quadrangle, Alaska: U.S. 

Geological Survey Bulletin 1682, 13 p. 

Miller, M.L., and Bundtzen, T.K., 1987, Geology and 

mineral resources of the Iditarod quadrangle, 

west-central Alaska [abs.]: C 995, p. 46-4 7. 

Molenaar, C.M., 1987, Introduction: B 1778, p. 3-6. 

1987, Principles of petroleum geology and 

exploration methods: B 1778, p. 7-15. 

Molenaar, C.M., Bird, K.J., and Collett, T.S., 1986, 

Regional correlation sections across the North 

Slope of Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1907, 1 

sheet. 

Monger, J.W.H., and Berg, H.C., 1987, Lithotectonic 

terrane map of western Canada and southeastern 

Alaska: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-187 4-B, 12 p., scale 

1:2,500,000, 1 sheet. 

Moore, E.J., and Addicott, W .0., 1987, The Miocene 

Pillarian and Newportian (molluscan) stages of 

Washington and Oregon and their usefulness in 

correlations from Alaska to California, in 

Yochelson, E.L., ed., Shorter contributions to 

paleontology and stratigraphy: U.S. Geological 

Survey Bulletin 1664, p. A1-A13, 4 pls. 

Moriwaki, Yoshiharu, and Idriss, I.M., 1987, Evaluation 

of ground failure susceptibility, opportunity and 

potential in Anchorage, Alaskan urban area, !!! 

National Earthquake Hazards Reduction 

Program; summaries of technical reports v. 24: 

U.S. Geological Survey Open-File Report 87-374, 

p. 611-615. 

Morrissey, S.-T., 1987, Tiltmeter and earthquake 

prediction program in S. California and at Adak, 

AK, in National Earthquake Hazards Reduction 

Program; summaries of technical reports v. 24: 

U.S. Geological Survey Open-File Report 87-374, 

p. 416-421. 

Mosier, E.L., Cathrall, J.B., Antweiler, J.C., and 

Tripp, R.B., 1987, Some features of the 

composition and distribution of geochemical 

types of placer gold in the Koyukuk-Chandalar 

mining district, Alaska [abs.]: C 995, p. 50-51. 

Mullen, M.W., 1987, Petrology and provenance of 

sandstones of the Naknek Formation, Alaska 

Peninsula: C 998, p. 86-90. 

Murphy, J.M., 1987, Early Cretaceous cessation of 

terrane accretion, northern Eek Mountains, 

southwestern Alaska: C 998, p. 83-85. 

Nelson, S.W., Blome, C.D., and Karl, S.M., 1987, Late 

Triassic and Early Cretaceous fossil ages from 

the McHugh Complex, southern Alaska: C 998, p. 

96-98. 

Newberry, R.J., and Brew, D.A., 1987, The AlaskaJuneau gold deposit; remobilized syngenetic 

versus exotic epigenetic origin: C 998, p. 128-

131. 

Phillips, R.L., and Colgan, M. W ., 1987, Vibracore 

stratigraphy of the northeastern Chukchi Sea: C 

998, p.157-160. 

Pickthorn, W .J., Goldfarb, R.J., and Leach, D.L., 1987, 

"Mesothermal" gold--A metamorphic connection? 

[abs.]: C 995, p. 57. 

Reed, K.M., and Marks, J.K., 1987, Bibliography and 

index of articles in the series of U.S. Geological 

Survey Circulars devoted to geologic research 

and accomplishments in Alaska 1975-1986: U.S. 

Geological Survey Open-File Report 87-420, 110 

p. 

198 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Reeder, J. W ., and Lahr, J.C., 1987, Seismological 

aspects of the 1976 eruptions of Augustine 

Volcano, Alaska: U.S. Geological Survey 

Professional Paper 1768, 32 p. 

Reimnitz, Erk, and Kempema, E. W., 1987, Thirty-fouryear shoreface evolution at a rapidly retreating 

arctic coastal site: C 998, p. 161-164. 

Repenning, C.A., Brouwers, E.M., Carter, L.D., 

Marincovich, Louie, Jr., and Ager, T.A., 1987, 

The Beringian ancestry of Phenacomys (Rodentia: 

Cricetidae) and the beginning of the modern 

Arctic Ocean borderland biota: U.S. Geological 

Suyrvey Bulletin 1687, 31 p., 1 pl. 

Repetski, J.E., Carter, Claire, Harris, A.G., and Dutro, 

J.T., Jr., 1987, Ordovician and Silurian fossils 

from the Doonerak anticlinorium, central Brooks 

Range, Alaska: C 998, p. 40-42. 

Riehle, J.R., Detterman, R.L., Yount, M.E., and 

Miller, J.W., 1987, Preliminary geologic map of 

the Mount Katmai quadrangle and portions of the 

Afognak and Naknek quadrangles, Alaska: U.S. 

Geological Survey Open-File Report 87-593, 

scale 1:250,000, 1 sheet. 

Riehle, J.R., Meyer, C.E., Ager, T.A., Kaufman, D.S., 

and Ackerman, R.E., 1987, The Aniakchak tephra 

deposit, a late Holocene marker horizon in 

western Alaska: C 998, p. 19-22. 

Riehle, J.R., Yount, M.E., and Miller, T.P., 1987, 

Petrography, chemistry, and geologic history of 

Yantarni Volcano, Aleutian Volcanic Arc, 

Alaska: U.S. Geological Survey Professional 

Paper 1761, 27 p., scale 1:63,360, 1 pl. 

Robbins, S.L., 1987, Gravity interpretation of the 

coastal plain: B 1778, p. 219-224. 

Rosenblum, Sam, Carlson, R.R., Nishi, J.M., and 

Overstreet, W.C., 1987, Platinum-group elements 

in magnetic concentrate from the Goodnews Bay 

district, Alaska: U.S. Geological Survey Bulletin 

1660. 

Sachs, J.S., ed., 1987, USGS Research on Mineral 

Resources - 1987, program and abstracts, third 

annual V.E. McKelvey Forum on Mineral and 

Energy Resources: U.S. Geological Survey 

Circular 995, 82 p. 

Schmidt, J.M., and Folger, P.F., 1987, Organic carbon 

occurrence and content in carbonate rocks from 

the Omar copper prospect, Baird Mountains, 

Alaska: C 998, p. 43-46. 

Schmoll, H.R., and Yehle, L.A., 1987, Surficial 

geologic map of the northwestern quarter of the 

Tyonek A-4 quadrangle, south-central Alaska: 

U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1934, scale 1:31,680, 1 sheet. 

Seitz, H.R., Thomas, D.S., and Tomlinson, Bud, 1986, 

The storage and release of water from a large 

glacier-dammed lake: Russell Lake near Yakutat, 

Alaska, 1986: U.S. Geological Survey Open-File 

Report 86-545, 10 p. 

Snyder, E.F., compiler, 1987, Activities of the Alaska 

District Water Resources Division, U.S. 

Geological Survey, 1987: U.S. Geological Survey 

Open-File Report 87-38, 24 p. 

Sohn, I.G., 1987, Middle and Upper Triassic marine 

ostracoda from the Shublik Formation, 

northeastern Alaska, in Yochelson, E.L., ed., 

Shorter contributions to paleontology and 

stratigraphy: U.S. Geological Survey Bulletin 

1664, p. C1-C24, 11 pls. 

Spicer, R.A., and Parrish, J.T., 1987, Plant 

megafossils, vertebrate remains, and 

paleoclimate of the Kogosukruk Tongue (late 

Cretaceous), North Slope, Alaska: C 998, p. 47-

48. 

Stanley, R.G., 1987, Effects of weathering on 

petroleum-source evaluation of coals from the 

Suntrana Formation near Healy, Alaska: C 998, 

p. 99-103. 

----- 1987, Thermal maturity and petroleum-source 

potential of the Cantwell Formation (Paleocene), 

Alaska Range: C 998, p. 104-107. 

Stephens, C.D., Page, R.A., Fogleman, K.A., and Lahr, 

J.C., 1987, Southern Alaska seismicity, 1983, in 

Stover, C. W ., ed., United States earthquakes, 

1983: U.S. Geological Survey Bulletin 1698, p. 

127-130. 

Still, P.J., and Brunett, J.O., 1987, Ground-water 

levels in Alaska, water year 1984: U.S. 

Geological Survey Open-File Report 87-230, 308 

p. 

Sutley, S.J., O'Leary, R.M., Lee, G.K., and Light, T.D., 

1987, Analytical results and sample locality map 

of stream-sediment, moss-trap-sediment, and 

heavy-mineral-concentrate samples from the 

White Mountains Recreation Area, Livengood and 

Circle quadrangles, east-central Alaska: U.S. 

Geological Survey Open-File Report 87-285, 110 

p., scale 1:63,360, 2 pls. 

Sutley, S.J., Ryder, J.T., Light, T.D., and Weber, F.R., 

1987, Analytical results and sample locality map 

of rock samples from the White Mountains 

Recreation Area, Livengood and Circle 

quadrangles, east-central Alaska: U.S. 

Geological Survey Open-File Report 87-284, 61 

p., scale 1:63,360, 2 pls. 

Taber, John, 1987, Seismic monitoring of Shumagin 

seismic gap, Alaska, in National Earthquake 

Hazards Reduction Program; summaries of 

technical reports v. 24: U.S. Geological Survey 

Open-File Report 87-374, p. 40-41. 

Taber, John, and Jacob, K.H., 1987, Analysis of 

seismic data from the Shumagin seismic gap, 

Alaska, in National Earthquake Hazards 

Reduction Program; summaries of technical 

reports v. 24: U.S. Geological Survey Open-File 

Report 87-374, p. 300-302. 

Taber, John, Luchman, M.A., and Rosen, S., 1987, 

Earthquake monitoring in the Shumagin seismic 

gap and eastern Aleutians, Alaska, 1983, in 

Stover, C. W ., ed., United States earthquakes, 

1983: U.S. Geological Survey Bulletin 1698, p. 

125-127. 

Tolson, R.B., Grantz, Arthur, and Mann, D.M., 1987, 

Multichannel seismic-reflection data from the 

southern Chukchi Sea: U.S. Geological Survey 

Open-File Report 87-19, 7 p., scale 1:500,000, 1 

pl. 

Townshend, J.B., and others, 1987, Preliminary 

geomagnetic data, College Observatory, 

Fairbanks, Alaska: U.S. Geological Survey OpenFile Report 87-300 A-1. [Each monthly report 

has its own letter designation; authorship and 

page length vary.] 

Bibliographies 199 
Tripp, R.B., Crim, W .D., Hoffman, J.D., O'Leary, 

R.M., and Risoli, D.A., 1986, Mineralogical and 

geochemical maps showing the distribution of 

selected minerals and elements found in the 

minus-80-mesh stream-sediment and related 

minus-30-mesh heavy-mineral-concentrate 

samples from the Circle quadrangle, Alaska: 

U.S. Geological Survey Open-File Report 83-170 

F, G, H, 7 p., scale 1:250,000, 6 pls. 

U.S. Geological Survey, 1987, Arctic Alaska vegetation 

and land cover, 1981: U.S. Geological Survey 

Land Use and Land Cover Map L-0207, scale 

1:250,000. [Lat. 68° to 69°, long. 144° to 147°.] 

----- 1987, Beechey Point, Alaska, vegetation and land 

cover: U.S. Geological Survey Land Use and 

Land Cover Map L-0211, scale 1:250,000. [Lat. 

70° to 71°, long. 147° to 150°.] 

----- 1987, Pumpage data from public-supply wells at 

Anchorage, Alaska, 1957-1985: U.S. Geological 

Survey Open-File Report 86-542, 48 p., 1 pl. 

----- 1987, Valdez, Alaska, vegetation and land cover: 

U.S. Geological Survey Land Use and Land Cover 

Map L-0209, scale 1:250,000. [Lat. 61° to 62°, 

long., 144° to 147°.] 

----- 1987, Vegetation and land cover, Tetlin National 

Wildlife Refuge, Alaska: U.S. Geological Survey 

Miscellaneous Investigation Series Map I-1813, 

scale 1:250,000, 1 sheet [color]. 

Updike, R.G., 1987, Geologic mapping along the Border 

Ranges fault zone, Anchorage, Alaska, in 

National Earthquake Hazards Reduction 

Program; summaries of technical reports v. 24: 

U.S. Geological Survey Open-File Report 87-374, 

p. 588-589. 

Updike, R.G., and Carpenter, B.A., 1986, Engineering 

geology of the Government Hill area, Anchorage, 

Alaska: U.S. Geological Survey Bulletin 1588, 32 

p. 

Updike, R.G., and Oscarson, R.L., 1987, An atlas of 

microfabrics of the Bootlegger Cove Formation, 

using the scanning electron microscope, rev. Nov. 

1986: U.S. Geological Survey Open-File Report 

87-60, 19 p., 48 pls. 

Vallier, T.L., and Herman, B.M., 1987, Petrology, age, 

and original tectonic setting of basalt from the 

St. George basin Cost No. 1 Well, southern Bering 

Sea: C 998, p. 165-169. 

Walker, K.-M., York, James, Murphy, Dennis, and 

Sloan, C.E., 1986, Digital data base of lakes on 

the North Slope, Alaska: U.S. Geological Survey 

Water-Resources Investigations Report WRI 86-

4143, 13 p. 

Wheeler, K.L., Forbes, R.B., Weber, F.R., and 

Rinehart, C.D., 1987, Lithostratigraphy, 

petrology, and geochemistry of the Ordovician 

Fossil Creek Volcanics, White Mountains, eastcentral Alaska: C 998, p. 70-73. 

White, E.R., compiler, 1987, Reports about Alaska in 

non-USGS publications released in 1986 which 

include USGS authors, marked by an asterisk (*): 

c 998, p. 181-186. 

White, E.R., compiler, 1987, Reports about Alaska in 

USGS publications released in 1986: C 998, p. 

172-180. 

Wilson, F.H., and O'Leary, R.M., 1987, Tables showing 

analyses of semiquantitative spectrometry of 

rock samples collected in the Ugashik, Bristol 

Bay, and western part of the Karluk quadrangles, 

Alaska: U.S. Geological Survey Open-File Report 

87-419, 34 p. 

Wolfe, S.C., Barnes, P. W., Rearic, D.M., and Reimnitz, 

Erk, 1987, Quaternary seismic stratigraphy of the 

inner continental shelf north of the Arctic 

National Wildlife Refuge: B 1778, p. 61-78. 

Yeend, Warren, 1987, Placer gold related to mafic 

schist (?) in the Circle district, Alaska: C 998, p. 

74-76. 

Yehle, L.A., and Schmoll, H.R., 1987, Surficial 

geologic map of the Anchorage B-7NE 

quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 87-416, 20 p., scale 1:25,000, 2 

pis. 

----- 1987, Surficial geologic map of the Anchorage B7 NW quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 87-168, 11 p., scale 1:25,000, 2 

pls. 

Yount, M.E., Miller, T.P., and Gamble, B.M., 1987, The 

1986 eruptions of Augustine Volcano, Alaska: 

Hazards and effects: C 998, p. 4-13. 

Zayatz, M.R., 1987, Petrography of the Baird 

Mountains schistose lithologies, northwestern 

Alaska: C 998, p. 49-52. 

200 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Reports about Alaska in Non-USGS Publications Released 

in 1987 Which Include USGS Authors 

Compiled by Ellen R. White 

[Some reports dated 1986 did not become available until 1987; they are included in this listing. 

USGS authors are marked by asterisks(*).] 

Abbreviations used: 

"North Slope geology" for: Tailleur, Irv, and Weimer, Paul, eds., Alaskan North Slope geology: 

Bakersfield, Calif., Society of Economic Paleontologists and Mineralogists, Pacific Section 

"Eos" for: Eos [American Geophysical Union Transactions] 

"GSA" for: Geological Society of America, Abstracts with Programs 

*Affolter, R.H., and *Stricker, G.D., 1987, 

Geochemistry of coal from the Cretaceous 

Corwin and Chandler Formations, National 

Petroleum Reserve in Alaska (NPRA): North 

Slope geology: v. 1, p. 217-224. 

*Albert, N.R., Evitt, W.R., and Stein, J.A., 1986, 

Lacrymodinium, n. gen., a gonyaulacoid 

dinoflagellate with intercalary archeopyle from 

the Jurassic and Early Cretaceous of California 

and Alaska: Micropaleontology, v. 32, no. 4, p. 

303-315, pls. 1-2. 

* Aleinikoff, J.N., *Dusel-Bacon, Cynthia, *Foster, 

H.L., and *Nokleberg, W .J., 1987, Lead isotope 

fingerprinting of tectono-stratigraphic terranes, 

east-central Alaska: Canadian Journal of Earth 

Sciences, v. 24, no. 10, p. 2089-2098. 

* Arth, J.G., 1987, Regional isotopic variations in the 

Cretaceous plutons of northern Alaska [abs.]: 

GSA, v. 19, no. 6, p. 355. 

Ave Lallemant, H.G., *Kelley, J.S., and Phelps, J.C., 

198 7, Kine rna tic analysis of range-front thrust 

faulting near Anaktuvuk Pass, north-central 

Brooks Range, Alaska: North Slope geology, v. 2, 

p. 639-645. 

*Barker, Fred, 1987, Cretaceous Chisana Island arc of 

Wrangellia, eastern Alaska [abs.]: GSA, v. 19, no. 

7, p. ~80. 

*Barker, Fred, and * Arth, J.G., 1987, Coast batholith, 

southeastern Alaska [abs.]: GSA, v. 19, no. 6, p. 

356. 

*Barnes, D.F., 1987, Gravity anomaly at a Pleistocene 

lake bed in NW Alaska interpreted by analogy 

with Greenland's Lake Taserssauq and its floating 

ice tongue: Journal of Geophysical Research, v. 

92, no. 9B, p. 8976-8984. 

*Barnes, P.W., *Asbury, J.L., *Rearic, D.M., and 

*Ross, C.R., 1987, Ice erosion of a sea-floor 

knickpoint at the inner edge of the stamukhi 

zone, Beaufort Sea, Alaska: Marine Geology, v. 

76, no. 3-4, p. 207-222. 

Beard, J.S., and *Barker, Fred, 1987, Gabbro and 

anorthosite cumulates in the Wrangellia arc-back 

arc substructure, southern Alaska [abs.]: GSA, v. 

19, no. 7, p. 583. 

*Berge, P., *Mooney, W.D., and *Murphy, J.M., 1987, 

Highly-reflective crust identified in a 240-

channel intermediate-offset seismic reflection 

experiment in central interior Alaska [abs.]: Eos, 

v. 68, no. 44, p. 1457. 

*Bernstein, L.R., and *Cox, D.P., 1986, Geology and 

sulfide mineralogy of the Number One orebody, 

Ruby Creek copper deposit, Alaska: Economic 

Geology, v. 81, no. 7, p. 1675-1689. 

*Bernstein, L.R., and *Cox, D.P., 1987, Geology and 

sulfide mineralogy of the Number One orebody, 

Ruby Creek copper deposit, Alaska [abs.]: North 

Slope geology, v. 1, p. 285. [Reprinted from: 

Economic Geology, v. 81, p. 1675, 1986.] 

*Bird, K.J., 1987, The framework geology of the North 

Slope of Alaska as related to oil-source rock 

correlation: North Slope geology, v. 1, p. 121-

143. [Reprinted from: Magoon, L.B., and 

Claypool, G.E., eds., 1985, Alaska North Slope 

oil/rock correlation study: American Association 

of Petroleum Geologists, Studies in Geology no. 

20, p. 3-29.] 

*Bird, K.J., 1987, North Slope oil and gas: the Barrow 

Arch paradox [abs.]: North Slope geology, v. 1, p. 

41. 

*Blome, C.D., 1987, Paleogeographic significance of 

lower Mesozoic radiolarians from the Brooks 

Range, Alaska: North Slope geology, v. 1, p. 371-

380. 

Boak, J.M., Turner, D.L., Henry, D.J., *Moore, T.E., 

and Wallace, W.K., 1987, Petrology and K-Ar 

ages of the Misheguk igneous sequence--an 

allochthonous mafic and ultramafic complex--and 

its metamorphic aureole, western Brooks Range, 

Alaska: North Slope geology, v. 2, p. 737-745. 

*Bohannon, R.G., Dobson, M.R., *Edwards, B.D., and 

Bibliographies 201 
Jacobs, C.L., 1987, Tectonics of north Pacific 

Ocean basin: western Aleutian Island region 

[abs.]: Eos, v. 68, no. 44, p. 1486. 

*Box, S.E., 1987, Late Cretaceous or younger SWdirected extensional faulting: Cosmos Hills, 

Brooks Range, Alaska [abs.]: GSA, v. 19, no. 6, p. 

361. 

*Box, S.E., and *Patton, W.W., Jr., 1987, Early 

Cretaceous evolution of the Yukon-Koyukuk 

basin and its bearing on the development of the 

Brookian orogenic belt, Alaska [abs.]: North 

Slope geology, v. 2, p. 833. 

*Brew, D.A., 1987, Late Mesozoic and Cenozoic 

magmatism in the northern Cordillera: 

southeastern Alaska [abs.]: GSA, v. 19, no. 6, p. 

361. 

*Brew, D.A., *Ford, A.B., and Himmelberg, G.R., 

1987, Late Cretaceous sedimentation, volcanism, 

plutonism, metamorphism and deformation in the 

northern Cordillera, southeastern Alaska [abs.]: 

GSA, v. 19, no. 7, p. 600. 

*Brouwers, E.M., Clemens, W .A., Spicer, R.A., * Ager, 

T.A., *Carter, L.D., and *Sliter, W.V., 1987, 

Dinosaurs on the North Slope, Alaska: High 

latitude, latest Cretaceous environments: 

Science, v. 238, no. 4822, p. 1608-1610. 

*Cady, J. W "b 1987, AeromaBnetic map of Alaska, lat. 

65°-68 N., long. 141 -162° W. [abs.]: GSA, v. 

19, no. 6, p. 364. 

1987, Preliminary geophysical interpretation of 

the oceanic terranes of interior and western 

Alaska: Evidence for thick crust of intermediate 

density, in Leitch, E.C., and Scheibner, Erwin, 

eds., Terrane accretion and orogenic belts: 

Washington, D.C., American Geophysical Union, 

Geodynamics Series v. 19, p. 301-305. 

*Carlson, P.R., *Cooper, A.K., *Gardner, J.V., *Karl, 

H.A., *Marlow, M.S., *Stevenson, A.J., Huggett, 

Q., Kenyon, N., and Parson, L., 1987, GLORIA 

side-scan imagery of Aleutian basin Bering Sea 

slope, and abyssal plain [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 

71, no. 5, p. 536. 

----- 1987, Long-range sidescan sonar and geophysical 

survey of the Aleutian Basin: Eos, v. 68, no. 9, p. 

122-123. 

*Carlson, P.R., *Marlow, M.S., *Rearic, D.R., and 

Parson, L.M.,1987, The GLORIA view of seafloor 

processes in Navarinsky and Pervenets Canyons, 

Bering Sea, Alaska [abs.]: Eos, v. 68, no. 44, p. 

1316. 

*Carter, L.D., 1987, Late Pleistocene marine 

transgressions of the Alaskan arctic coastal plain 

[abs.]: North Slope geology, v. 1, p. 541. 

*Carter, L.D., Heginbottom, J.A., and Woo, Ming-ko, 

1987, Arctic lowlands, in Graf, W.L., ed., 

Geomorphic systems of North America: 

Geological Society of America, Decade of North 

American Geology, Centennial Special Volume 2, 

p. 583-628. 

*Cochrane, G.R., *Cooper, A.K., *Hunter, R., 

*Huggett, Q., and Harris, M., 1987, GLORIA 

side-scan survey of the southwestern Bering Sea 

basin, Alaska [abs.]: Eos, v. 68, no. 44, p. 1498. 

*Collett, T.S., 1987, Physical parameters controlling 

gas hydrate stability and distribution on the 

North Slope, Alaska [abs.]: American Association 

of Petroleum Geologists Bulletin, v. 71, no. 5, p. 

541. 

*Collett, T.S., *Bird, K.J., and *Molenaar, C.M., 1987, 

Cretaceous and Tertiary (Brookian) depositional 

style of the Barrow Arch, North Slope, Alaska 

[abs.]: North Slope geology, v. 1, p. 478. 

*Cook, H.E., *Magoon, L.B., *Stanley, R.G., and 

*Casas, Arturo, 1987, Carbonate submarine fans 

and aprons in frontier petroleum region--

Carboniferous Calico Bluff Formation, eastcentral Alaska [abs.]: American Association of 

Petroleum Geologists Bulletin, v. 71, no. 5, p. 

542. 

*Davis, A.S., *Pickthorn, L.G., *Vallier, T.L., and 

*Marlow, M.S., 1987, Eocene arc volcanism along 

the Beringian margin: Implications for relocation 

of the plate boundary to the Aleutian arc [abs.]: 

Eos, v. 68, no. 44, p. 1516. 

Davis, D.M., and *von Huene, Roland, 1987, Inferences 

on sediment strength and fault friction from 

structures at the Aleutian trench: Geology, v. 

15, no. 6, p. 517-522. 

*Dickinson, K.A., 1987, Profunda! sideritic mudstone 

from an Eocene lake in Alaska [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 

71, no. 8, p. 1003. [Death Valley area, Seward 

Peninsula] 

*Dickinson, K.A., Cunningham, K.D., and *Ager, T.A., 

1987, Geology and origin of the Death Valley 

uranium deposit, Seward Peninsula, Alaska: 

Economic Geology, v. 82, no. 6, p. 1558-1574. 

Dillon, J.T., *Harris, A.G., and *Dutro, J.T., Jr., 1987, 

Preliminary description and correlation of lower 

Paleozoic fossil-bearing strata in the Snowden 

Mountain area of the south-central Brooks 

Range, Alaska: North Slope geology, v. 1, p. 337-

345. 

*Dinter, David, 1987, Late Quaternary depositional 

history of the Alaskan Beaufort shelf [abs.]: 

North Slope geology, v. 1, p. 541. 

*Dumoulin, J.A., and *Harris, A.G., 1987, Cambrian 

through Devonian carbonate rocks of the Baird 

Mountains, western Brooks Range, Alaska [abs.]: 

GSA, v. 19, no. 6, p. 373-374. 

------ 1987, Lower Paleozoic carbonate rocks of the 

Baird Mountains quadrangle, western Brooks 

Range, Alaska: North Slope geology, v. 1, p. 311-

336. 

*Dusel-Bacon, Cynthia, 1987, Metamorphism in Alaska 

as a key to its tectonic evolution [abs.]: GSA, v. 

19, no. 7, p. 649. 

*Dutro, J.T., Jr., 1985, The G. William Holmes 

Research Station, Lake Peters, northeastern 

Alaska, and its impact on northern research, in 

Geological Society of America, Centennial 

Special Volume 1, p. 301-311. 

----- 1987, A brief history of eighty years of geological 

exploration in the central Brooks Range, northern 

Alaska: North Slope geology, v. 1, p. 7-11. 

1987, Revised megafossil biostratigraphic 

zonation for the Carboniferous of northern 

Alaska: North Slope geology, v. 1, p. 359-364. 

*Dutro, J.T., Jr., and *Harris, A.G., 1987, Some 

stratigraphic and paleontologic constraints on 

tectonic modelling of the Brooks Range, Alaska 

202 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
[abs.]: GSA, v. 19, no. 6, p. 374. 

Ehm, Arlen, and *Tailleur, I.L., 1987, Refined names 

for Brookian age elements in northern Alaska 

[abs.]: North Slope geology, v. 1, p. 432. 

Ekstrom, G., and *Engdahl, E.R., 1987, Earthquake 

source parameters and stress distribution in the 

Adak Island region of the central Aleutian Islands 

[abs.]: Eos, v. 68, no. 44, p. 1352. 

*Ellersieck, Inyo, 1987, A structural model of the 

Brooks Range from the stratigraphic viewpoint 

[abs.]: GSA, v. 19, no. 6, p. 375. 

*Ellersieck, Inyo, and *Mayfield, C.F., 1987, The 

western Brooks Range, Alaska: Too much crust 

[abs.]: North Slope geology, v. 2, p. 736. 

[Reprinted from: GSA, v. 16, no. 5, p. 281, 1984.] 

*Emery, P.A., and *Seitz, H.R., 1987, Hubbard Glacier 

is still on the move: Geotimes, v. 32, no. 5, p. 8-

9. 

Farmer, G., *Barker, Fred, and *Plafker, George, 

1987, A Nd and Sr isotopic study of Mesozoic and 

early Tertiary granitic rocks in south-central 

Alaska [abs.]: GSA, v. 19, no. 6, p. 376. 

*Fisher, M.A., *Brocher, T.M., *Plafker, George, and 

*Nokleberg, W.J., 1987, Midcrustal duplexes 

below the accreted Chugach terrane of southern 

Alaska, as revealed by seismic reflection data 

collected for TACT [abs.]: Eos, v. 68, no. 44, p. 

1457. 

*Fisher, M.A., *von Huene, Roland, and Smith, G.L., 

1987, Reflections from midcrustal rocks within 

the Mesozoic subduction complex near the 

eastern Aleutian trench: Journal of Geophysical 

Research, v. 92, no. 88, p. 7907-7915. 

Folger, P.F., and *Schmidt, J.M., 1986, Geology of the 

carbonate-hosted Omar copper prospect, Baird 

Mountains, Alaska: Economic Geology, v. 81, no. 

7, p. 1690-1695. 

----- 1987, Geology of the carbonate-hosted Omar 

Copper prospect, Baird Mountains, Alaska 

[abs.]: North Slope geology, v. 1, p. 286. 

[Reprinted from: Economic Geology, v. 81, p. 

1690, 1986.] 

*Frederiksen, N.O., and *Schindler, K.S., 1987, 

Campanian to Maastrichtian pollen 

biostratigraphy and floral turnover rates, Colville 

River region, North Slope of Alaska [abs.]: 

American Association of Petroleum Geologists 

Bulletin, v. 71, no. 5, p. 558. 

*Fuis, G.S., *Ambos, E.L., *Mooney, W.D., *Page, 

R.A., *Fisher, M.A., *Brocher, T.M., and Taber, 

J.J., 1987, Crustal structure beneath exposed 

accreted terranes of southern Alaska: 

Geophysical Journal of the Royal Astronomical 

Society, v. 89, no. 1, p. 73-78. 

*Fuis, G.S., Beaudoin, B., and *Luetgert, J.H., 1987, 

Seismic refraction/wide angle reflection data 

from central Alaska: results of the TACT 1987 

field season [abs.]: Eos, v. 68, no. 44, p. 145 7-

1458. 

*Goldfarb, R.J., *Leach, D.L., *Light, T.D., Paterson, 

C.J., *Pickthorn, L.B., and *Pickthorn, W.J., 

1987, The Juneau gold belt: A mother lode-type 

system in southeastern Alaska [abs.]: GSA, v. 19, 

no. 6, p. 382. 

*Goldfarb, R.J., *Leach, D.L., *Miller, M.L., and 

*Pickthorn, W.J., 1986, Geology, metamorphic 

setting, and genetic constraints of epigenetic 

lode-gold mineralization within the Cretaceous 

Valdez Group, south-central Alaska, !.!! Keppie, 

J.D., Boyle, R. W., and Haynes, S.J., eds., 

Turbidite-hosted gold deposits: Geological 

Association of Canada, Special Paper 32, p. 87-

105. 

*Grantz, Arthur, and *Moore, T.E., 1987, Crustal 

structure of northern Alaska along geodynamics 

continent/ocean transect (A-3) [abs.]: GSA, v. 

19, no. 6, p. 383. 

*Grantz, Arthur, *Dinter, D.A., and *Culotta, R.C., 

1987, Geology of the continental shelf north of 

the Arctic National Wildlife Refuge, 

northeastern Alaska: North Slope geology, v. 2, 

p. 759-763. 

*Gross, W.K., *Savage, J.C., and *Lisowski, M., 1987, 

Absence of significant deformation in the 

Shumagin seismic gap, southwest Alaska, 1980-

1987 [abs.]: Eos, v. 68, no. 44, p. 1351. 

*Hamilton, T.D., 1986, Correlation of Quaternary 

glacial deposits in Alaska, in Sibrava, V., Bowen, 

D.Q., and Richmond, G.M., eds., Quaternary 

glaciations in the northern hemisphere: New 

York, Pergamon, p. 171-180. [In Quaternary 

Science Reviews, v. 5, no. 1-4.] -

*Hampton, M.A., 1986, Geotechnical framework study 

of the Kodiak Shelf, Alaska, in U.S. Department 

of Commerce, NOAA, OCSEAP, Final reports of 

principal investigators v. 48: Minerals 

Management Service OCS Study, MMS 86-0065, 

p. 1-94. 

*Hampton, M.A., and *Winters, W.J., 1986, 

Geotechnical framework study of the northern 

Bering Sea, Alaska, in U.S. Department of 

Commerce, NOAA, OCSEAP, Final reports of 

principal investigators v. 50: Minerals 

Management Service OCS Study, MMS 86-0112, 

p. 1-386. 

*Hampton, M.A., *Carlson, P.R., *Lee, H.J., and 

Feely, R.A., 1987, Geomorphology, sediment, and 

sedimentary processes, in Hood, D. W ., and 

Zimmerman, S.T., eds., The Gulf of Alaska, 

physical environment and biological resources: 

U.S. Minerals Management Service, OCS Study 

MMS 86-0095, p. 93-143. 

*Harris, A. G., and *Repetski, J.E., 1987, Ordovician 

conodonts from northern Alaska [abs.]: GSA, v. 

19, no. 3, p. 169. 

*Harris, A.G., Lane, H.R., *Tailleur, I.L., and 

*Ellersieck, Inyo, 1987, Conodont thermal 

maturation patterns in Paleozoic and Triassic 

rocks, northern Alaska--Geologic and exploration 

implications: North Slope geology, v. 1, p. 181-

191. 

*Hildreth, Wes, 1987, New perspectives on the 

eruption of 1912 in the Valley of Ten Thousand 

Smokes, Katmai National Park, Alaska: Bulletin 

of Volcanology, v. 49, no. 5, p. 680-693. 

*Hildreth, Wes, and *Fierstein, Judy, 1987, Valley of 

Ten Thousand Smokes, Katmai National Park, 

Alaska, in Hill, M.L., ed., Centennial Field Guide, 

v. 1, Cordilleran Section of the Geological 

Society of America: Geological Society of 

America, Decade of North American Geology 

(DNAG), p. 425-432. 

Bibliographies 203 
*Hillhouse, J.W., 1987, Accretion of southern Alaska: 

Tectonophysics, v. 139, no. 1-2, p. 107-122. 

*Himmelberg, G.R., *Loney, R.A., and Nabelek, P.I., 

1987, Petrogenesis of gabbronorite at Yakobi and 

northwest Chichagof Islands, Alaska: Geological 

Society of America Bulletin, v. 98, no. 3, p. 265-

279. 

Ritzman, M. W ., Proffett, J.M., Jr., *Schmidt, J.M., 

and Smith, T.E., 1986, Geology and mineralization 

of the Ambler district, northwestern Alaska: 

Economic Geology, v. 81, no. 7, p. 1592-1618. 

*Howell, D.G., and *Wiley, T.J., 1987, Crustal 

evolution of northern Alaska inferred from 

sedimentology and structural relations of the 

Kandik area: Tectonics, v. 6, no. 5, p. 619-631. 

*Howell, D.G. *Murray, R.W., *Wiley, T.J., *BoundySanders, Susan, *Kauffman-Linam, Linden, and 

Jones, D.L., 1987, Sedimentology and tectonics 

of Devonian Nation River Formation, Alaska, 

part of yet another allochthonous terrane [abs.]: 

American Association of Petroleum Geologists 

Bulletin, v. 71, no. 5, p. 569. 

*Huggett, Q.J., Somers, M.L., and Stubbs, A.R., 1987, 

Interference fringes on GLORIA side-scan sonar 

images from the Bering Sea and their 

implications (abs.]: Eos, v. 68, no. 44, p. 1375. 

Jones, D.L., *Boundy-Sanders, Susan, *Murray, R. W., 

*Howell, D.G., and *Wiley, T.J., 1987, Tectonic 

contacts of miogeoclinal strata in east-central 

Alaska [abs.]: America Association of Petroleum 

Geolgists Bulletin, v. 71, no. 5, p. 573. 

Kamath, A., Godbole, S.P., Ostermann, R.D., and 

*Collett, T.S., 1987, Evaluation of the stability 

of gas hydrates in northern Alaska: Cold Regions 

Science and Technology, v. 14, no. 2, p. 107-119. 

*Karl, H.A., and *Carlson, P.R., 1986, Seafloor 

hazards and related surficial geology, Navarin 

Basin province, northern Bering Sea, in U.S. 

Department of Commerce, NOAA, OCSEAP, 

Final reports of principal investigators v. 50: 

Minerals Management Service OCS Study 86-

0112, p. 387-636. 

*Karl, H.A., *Vallier, T.L., Masson, D., and 

Underwood, M.B., 1987, Long-range side-scan 

sonar mosaic of the western Aleutian arc and 

trench and the adjacent North Pacific seafloor 

[abs.]: Eos, v. 68, no. 44, p. 1485-1486. 

*Karl, S.M., and *Long, C.L., 1987, Evidence for 

tectonic truncation of regional east-west 

trending structures in the central Baird 

Mountains quadrangle, western Brooks Range, 

Alaska [abs.]: GSA, v. 19, no. 6, p. 392. 

*Kayen, R.E., and *Lee, H.J., 1987, Arctic Ocean 

landslides and gas-hydrate decomposition [abs.]: 

Eos, v. 68, no. 44, p. 1285. 

*Kelley, J.S., and *Molenaar, C.M., 1987, Detachment 

tectonics in the Sadlerochit and Shublik 

Mountains and applications for exploration 

beneath the coastal plain, Arctic National 

Wildlife Refuge, Alaska [abs.]: North Slope 

geology, v. 2, p. 757. 

*Kelley, J.S., *Brosge, W.P., and *Reynolds, M.W., 

1987, Fold-nappes and polyphase thrusting in the 

north-central Brooks Range, Alaska [abs.]: North 

Slope geology, v. 2, p. 647. 

Kennedy, G.L., Hopkins, D.M., and *Pickthorn, W .J., 

1987, Ikaite, the glendonite precursor, in 

estuarine sediments at Barrow, arctic Alaska 

[abs.]: GSA, v. 19, no. 7, p. 725. 

*Krimmel, R.M., and *Vaughn, B.H., 1987, Columbia 

Glacier, Alaska: Changes in velocity 1977-

1986: Journal of Geophysical Research, v. 92, 

no. 9B, p. 8961-8968. 

*Lachenbruch, A.H., *Sass, J.H., Lawver, L.A., 

*Brewer, M.C., *Marshall, B. V., *Munroe, R.J., 

*Kennelly, J.P., Jr., *Galanis, S.P., Jr., and 

*Moses, T.H., Jr., 1987, Temperature and depth 

of permafrost on the Alaskan arctic slope: North 

Slope geology, v. 2, p. 545-558. 

*Lahr, J.C., and *Stephens, C.D., 1986, Earthquake 

activity and ground shaking in anq along the 

eastern Gulf of Alaska, in U.S. Department of 

Commerce, NOAA, OCSEAP, Final reports of 

principal investigators v. 49: Minerals 

Management Service, OCS Study MMS 86-0111, 

p. 29-83. 

Lange, I.M., and *Nokleberg, W.J., 1987, Geologic 

setting, petrology, and geochemistry of 

stratiform sphalerite-galena-barite deposits, Red 

Dog Creek and Drenchwater Creek areas, 

northwestern Brooks Range, Alaska--A reply: 

Economic Geology, v. 82, no. 4, p. 1079-1081. 

[See also: Young, L.E., and Moore, D.W., 1987, 

"***--A discussion": Economic Geology, v. 82, 

no. 4, p. 1077-1079.] 

*Leach, D.L., *Goldfarb, R.J., and *Hofstra, A.H., 

1987, Fluid inclusion characteristics of the 

Juneau gold belt, southeastern Alaska [abs.]: 

GSA, v. 19, no. 6, p. 398. 

*Lee, H.J., and *Schwab, W.C., 1986, Geotechnical 

framework, northeast Gulf of Alaska, in U.S. 

Department of Commerce, NOAA, OCSEAP, 

Final reports of principal investigators v. 48: 

Minerals Management Service OCS Study, MMS 

86-0065, p. 95-547. 

*Lisowski, M., *Savage, J.C., and *Burford, R.O., 

1987, Strain accumulation across the Fairweather 

and Totschunda faults, Alaska: Journal of 

Geophysical Research, v. 92, no. B11, p. 11,552-

11,560. 

Little, T.A., and *Naeser, C.W., 1987, Implications of 

apatite and zircon fission track ages for the 

thermal history of Paleogene rocks along the 

Border Ranges fault system, southern Alaska 

[abs.]: GSA, v. 19, no. 7, p. 748. 

*McDougall, Kristin, 1987, Maestrichtian benthic 

foraminifers from Ocean Point, North Slope, 

Alaska: Journal of Foraminiferal Research, v. 

17, no. 4, p. 344-366. 

*Magoon, L.B., and *Anders, D.E., 1987, Petroleum 

geochemistry of oils and rocks in Arctic National 

Wildlife Refuge, Alaska [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 

71, no. 5, p. 587. 

*Magoon, L.B., *Bird, K.J., 1987, Alaskan North Slope 

petroleum geochemistry for the Shublik 

Formation, Kingak Shale, Pebble Shale Unit, and 

Torok Formation: North Slope geology, v. 1, p. 

145-160. [Reprinted from: Magoon, L.B., and 

Claypool, G.E., eds., 1985, Alaska North Slope 

oil/rock correlation study: American Association 

of Petroleum Geologists, Studies in Geology no. 

204 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
20, p. 31-48.] 

*Mayfield, C.F., *Tailleur, I.L., and *Ellersieck, Inyo, 

1987, Stratigraphy, structure, and palinspastic 

synthesis of the western Brooks Range, 

northwestern Alaska [abs.]: North Slope geology, 

v. 2, p. 735. [Reprinted from: USGS Open-File 

Report 83-779, p.1, 1983.] 

Meehan, G.A., and *Fuis, G.S., 1987, Ray equation 

migration of wide-angle reflections from 

southern Alaska: Journal of Geophysical 

Research, v. 92, no. B1, p. 407-420. 

Meier, M.F., and *Post, Austin, 1987, Fast tidewater 

glaciers: Journal of Geophysical Research, v. 92, 

no. 9B, p. 9051-9058. [Columbia Glacier] 

*Miller, T.P., and *Smith, R.L., 1987, Late Quaternary 

caldera-forming eruptions in the eastern Aleutian 

arc, Alaska: Geology, v. 15, no. 5, p. 434-438. 

*Molenaar, C.M., *Bird, K.J., and Kirk, A.R., 1987, 

Cretaceous and Tertiary stratigraphy of 

northeastern Alaska: North Slope geology, v. 1, 

p. 513-528. 

*Molenaar, C.M., Mull, C. G., and Swauger, D.A., 1987, 

Geologic features of Ignek Valley and adjacent 

mountains, northeastern Alaska, in Hill, M.L., 

ed., Centennial Field Guide, v. 1," Cordilleran 

Section of the Geological Society of America: 

Geological Society of America, Decade of North 

American Geology (DNAG), p. 473-478. 

*Molnia, B.F ., *Luepke, Gretchen, and *He in, J.R., 

1987, Synoptic clay mineralogy of the Copper 

River drainage system, Alaska [abs.]: GSA, v. 19, 

no. 7, p. 775-776. 

*Moore, T.E., 1987, Geochemical and tectonic affinity 

of basalts from the Copter Peak and Ipnavik 

River allochthons, Brooks Range, Alaska [abs.]: 

GSA, v. 19, no. 6, p. 434. 

----- 1987, Geochemistry and tectonic setting of some 

volcanic rocks of the Franklinian assemblage, 

central and eastern Brooks Range, Alaska: North 

Slope geology, v. 2, p. 691-710. 

Moore, T.E., *Brosg~, W.P., Churkin, Michael, Jr., and 

Wallace, W.K., 1987, Pre-Mississippian accreted 

terranes of northeastern Brooks Range, Alaska 

[abs.]: North Slope geology, v. 2, p. 711. 

*Moore, T.E. Roeske, S.M., and *Grantz, Arthur, 1987, 

Crustal structure of central Alaska along 

geodynamics continent/ocean transect (A-3) 

[abs.]: GSA, v. 19, no. 6, p. 434. 

Mull, C.G., Roeder, D.H., *Tailleur, I.L., Pessel, G.H., 

*Grantz, Arthur, and *May, S.D., 1987, Geologic 

sections and maps across Brooks Range and 

Arctic Slope to Beaufort Sea, Alaska: Geological 

Society of America Map and Chart Series MCH28S, 1 sheet. 

*Nelson, C.H., and *Johnson, K.R., 1987, Whales and 

walruses as tillers of the sea floor: Scientific 

American, v. 2 56, no. 2, p. 112-117. [Study area 

is NE Bering Sea] 

*Nelson, C.H., *Johnson, K.R., and *Barber, J.H., Jr., 

1987, Gray whale and walrus feeding excavation 

on the Bering shelf, Alaska: Journal of 

Sedimentary Petrology, v. 57, no. 3, p. 419-430. 

Nelson, R.E., and *Carter, L.D., 1987, 

Paleoenvironmental analysis of insects and 

extralimital Populus from an early Holocene site 

on the Arctic Slope of Alaska, U.S.A.: Arctic 

and Alpine Research, v. 19, no. 3, p. 230-241. 

*Nelson, S.W., and *Koski, R.A., 1987, The Midas 

Mine--A stratiform Fe-Cu-Zn-Pb sulfide deposit 

in Late Cretaceous turbidite near Valdez, Alaska 

[abs.]: GSA, v. 19, no. 6, p. 436. 

*Nelson, S. W ., *Miller, M.L., and *Dumoulin, J.A., 

1987, Resurrection Peninsula and Knight Island 

ophiolites and recent faulting on Montague 

Island, southern Alaska, in Hill, M.L., ed., 

Centennial Field Guide, v. 1-;-Cordilleran Section 

of the Geological Society of America: 

Geological Society of America, Decade of North 

American Geology (DNAG), p. 433-438. 

*Newberry, J.T., Laclair, D.L., and Fujita, Kazuya, 

1986, Seismicity and tectonics of the far western 

Aleutian Islands: Journal of Geodynamics, v. 6, 

no. 1-4, p. 13-32. 

Nilsen, T.H., and *Moore, T.E., 1987, Tectonic 

significance of the Kanayut Conglomerate and 

related middle Paleozoic deposits, Brooks Range, 

Alaska [abs.]: North Slope geology, v. 2, p. 711. 

*Nokleberg, W.J., and *Plafker, George, 1987, 

Structure and tectonics of southern Alaska along 

the Trans-Alaska Crustal Transect (TACT) 

[abs.]: Eos, v. 68, no. 44, p. 1456. 

*Orth, D.J., 1987, North Slope geographic-name 

sources for geologic nomenclature: North Slope 

geology, v. 2, Appendix 3, p. 847-854. [Reprinted 

from: Adkison, W.L., and Brosg~, M.M., eds., 

1970, Proceedings of the Seminar on the North 

Slope of Alaska: Los Angeles, Calif., American 

Association of Petroleum Geologists, Pacific 

Section, p. R1-R10.] 

*Page, R.A., *Stephens, C.D., *Lahr, J.C., and 

*Fogleman, K.A., 1987, The transition between 

the Aleutian and Wrangell Wadati-Benioff zones, 

southern Alaska [abs.]: Eos, v. 68, no. 44, p. 

1456-1457. 

*Parrish, J.T., 1987, Lithology, geochemistry, and 

depositional environment of the Triassic Shublik 

Formation, northern Alaska: North Slope 

geology, v. 1, p. 391-396. 

*Patton, W.W., Jr., *Stern, T.W., *Arth, J.G., and 

Carlson, Christine, 1987, New U/Pb ages from 

granite and granite gneiss in the Ruby geanticline 

and southern Brooks Range, Alaska: Journal of 

Geology, v. 95, no. 1, p. 118-126. 

Petersen, J.K., Kawasaki, Koji, Osterkamp, T.E., and 

*Scott, J.H., 1987, Nuclear well-logging in 

permafrost [abs.]: North Slope geology, v. 2, p. 

570. 

*Phillips, Larry, *Barnes, Peter, *Reimnitz, Erk, and 

*Hunter, Ralph, 1986, Geologic processes and 

hazards of the Beaufort and Chukchi Sea shelf 

and coastal regions, in U.S. Department of 

Commerce, NOAA, OCSEAP, Final reports of 

principal investigators v. 52: Minerals 

Management Service OCS Study, MMS 86-0114, 

p. 343-820. 

*Phillips, R.L., 1986, Current-dominated 

sedimentation in the northeastern Chukchi Sea, 

Alaska [abs.], in Knight, R.J., and McLean, J.R., 

eds., Shelf sands and sandstones: Calgary, 

Alberta, Canadian Society of Petroleum 

Geologists, p. 336-337. 

*Phillips, R.L., 1987, Late Cretaceous to early 

Bibliographies 205 
Tertiary deltaic to marine sedimentation, North 

Slope, Alaska [abs.]: American Association of 

Petroleum Geologists Bulletin, v. 71, no. 5, p. 

601. 

*Pickthorn, W .J., 1987, Stable isotope characteristics 

of the Juneau gold belt, Alaska [abs.]: GSA, v. 

19, no. 6, p. 440. 

Plumley, P.W., and *Tailleur, I.L., 1987, 

Paleomagnetic results from the Sadlerochit and 

Shublik Mountains, eastern North Slope, Alaska 

[abs.]: North Slope geology, v. 2, p. 580. 

Roeske, S.M., *Moore, T.E., and *Grantz, Arthur, 

1987, Crustal structure of southern Alaska along 

geodynamics continent/ocean transect (A-3) 

[abs.]: GSA, v. 19, no. 6, p. 444. 

*Ryan, H.F., and *Scholl, D.W., 1987, Deformational 

effects and the lateral transport of arc basement 

rocks along the central Aleutian oblique 

convergence zone [abs.]: Eos, v. 68, no. 44, p. 

1486. 

*Sable, E.G., and *Stricker, G.D., 1987, Coal in the 

National Petroleum Reserve in Alaska (NPRA): 

framework geology and resources: North Slope 

geology, v. 1, p. 195-215. 

*Schmidt, J.M., 1986, Stratigraphic setting and 

mineralogy of the Arctic volcanogenic massive 

sulfide propsect, Ambler district, Alaska: 

Economic Geology, v. 81, no. 7, p. 1619-1643. 

1987, The Ambler sequence at Arctic Ridge, 

Ambler district, Alaska, in Hill, M.L., ed., 

Centennial Field Guide, v. 1-; Cordilleran Section 

of the Geological Society of America: 

Geological Society of America, Decade of North 

American Geology (DNAG), p. 463-468. 

*Scholl, D. W., and *Stevenson, Andrew, 1987, Ocean 

margin tectonics and North Pacific 

paleoceanography--wonderments about the 

effects of the Pacific-Bering Sea connection 

[abs.]: International Conference on Pacific 

Neogene Stratigraphy, 4th, Berkeley, Calif., 

1987, Abstract Volume, p. 95-97. 

*Sloan, C. E., 1987, Water resources of the North 

Slope, Alaska: North Slope geology, v. 1, p. 233-

252. 

Spicer, R.A., *Wolfe, J.A., and *Nichols, D.J., 1987, 

Alaskan Cretaceous-Tertiary floras and arctic 

origins: Paleobiology, v. 13, no. 1, p. 73-83. 

*Stanley, R.G., 1987, Petroleum resource potential 

and thermal maturity of Cantwell Formation 

(Paleocene), central Alaska Range: A 

reconnaissance study [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 

71, no. 5, p. 617-618. 

*Tailleur, I.L., 1987, Arguments for Cretaceous 

instead of Devonian plutonism in the Brooks 

Range, northern Alaska [abs.]: North Slope 

geology, v. 2, p. 724. [Reprinted from: GSA 

Abstracts with Programs, v. 16, p. 336, 1984.] 

*----- 1987, One presumptive paleogeography for the 

Phanerozoic of what is now the North American 

Arctic [abs.]: North Slope geology, v. 2, p. 831. 

[Reprinted from: GSA, v. 16, p. 336.] 

*----- 1987, A rationalization of the Koyukuk 

"crunch," northern and central Alaska [abs.]: 

North Slope geology, v. 2, p. 832. [Reprinted 

from: American Association of Petroleum 

Geologists Bulletin, v. 64, p. 792, 1980.] 

----- 1987, What Brooks Range collision, continental 

margins? [abs.]: GSA, v. 19, no. 6, p. 456. 

*Tailleur, Irv, and Weimer, Paul, eds., 1987, Alaskan 

North Slope geology: Bakersfield, Calif., Society 

of Economic Paleontologists and Mineralogists, 

Pacific Section, 2 v., 3 pls. 

*Till, A.B., *Schmidt, J.M., and *Nelson, S.W., 1987, 

Thrust-involvement of Proterozoic and Mesozoic 

metamorphic rocks, southwestern Brooks Range, 

Alaska [abs.]: GSA, v. 19, no. 6, p. 458. 

*Torresan, M.E., and *Schwab, W.C., 1987, Fabric and 

its relation to sedimentologic and physical 

properties of near-surface sediment, Shelikof 

Strait and Alsek prodelta, Alaska: Journal of 

Sedimentary Petrology, v. 57, no. 3, p. 408-418. 

Underwood, M.B., *Karl, H.A., *Vallier, T.L., and 

Masson, D., 1987, Sedimentation within the 

Amchitka-Attu corridor of the Aleutian trench 

[abs.]: Eos, v. 68, no. 44, p.1486. 

*Vallier, T.L., *Karl, H.A., and Underwood, M.B., 

1987, Geologic framework of the western 

Aleutian arc and adjacent North Pacific seafloor 

[abs.]: Eos, v. 68, no. 44, p. 1486. 

*Wahrhaftig, Clyde, 1987, The Cenozoic section at 

Suntrana, Alaska, in Hill, M.L., ed., Centennial 

Field Guide, v. 1; Cordilleran Section of the 

Geological Society of America: Geological 

Society of America, Decade of North American 

Geology (DNAG), p. 445-450. 

Walker, K.-M., York, James, and *Murphy, Dennis, 

1987, Identifying water sources on the North 

Slope, Alaska for geologic exploration [abs.]: 

North Slope geology, v. 1, p. 253. 

*Walters, R.A., and Dunlap, W.W., 1987, Analysis of 

time series of glacier speed; Columbia Glacier, 

Alaska: Journal of Geophysical Research, v. 92, 

no. 9B, p. 8969-8975. 

*Wiley, T.J., and *Howell, D.G., 1987, Three 

formations interpreted as westerly scoured 

submarine fans, Kandik area, east-central Alaska 

[abs.]: Eos, v. 68, no. 44, p.1457. 

*Wiley, T.J., *Howell, D.G., *Kauffman-Linam, 

Linden, *Boundy-Sanders, Susan, *Murray, R. W ., 

and Jones, D.L., 1987, Kandik basin stratigraphy, 

sedimentology, and structure [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 

71, no. 5, p. 627. 

*Wilson, F.H., and *Shew, Nora, 1987, K-Ar age 

discordancy in Qua ternary volcanic rocks [abs.]: 

Eos, v. 68, no. 44, p. 1287. 

*Wolfe, J.A., and Tanai, Toshimasa, 1987, 

Systematics, phylogeny, and distribution of Acer 

(maples) in the Cenozoic of western North 

America: Journal of the Faculty of Science, 

Hokkaido University, Japan, Series IV Geology 

and Mineralogy, v. 22, no. 1, 246 p. [Includes 

sections on Alaska.] 

*Wolfe, J.A., and Upchurch, G.R., Jr., 1987, North 

American nonmarine climates and vegetation 

during the Late Cretaceous: Palaeogeography, 

Palaeoclimatology, Palaeoecology, v. 61, no. 1-2, 

p. 33-77. [Includes section on Alaska.] 

*Woodward, P.V., 1987, Regional evaluation of 

formation fluid s~linity by SP log, Ivishak 

Sandstone, North Slope, Alaska [abs.]: American 

206 Geologic Studies in Alaska by the U.S. Geological Survey during 1987 
Association of Petroleum Geologists Bulletin, v. 

71, no. 5, p. 629. 

*Zen, E-an, 1986, Magmatic-epidote-bearing tonalitic 

plutons in the western Cordillera and their 

tectonic significance [abs.], in International 

Mineralogical Association, General Meeting, 

14th, Stanford University, Stanford, Calif., 1986, 

Abstracts with Programs, p. 279. 

*Zierenberg, R.A., and *Schmidt, J.M., 1987, 

Subsurface mineralization and sulfur isotope 

systematics at the Red Dog Zn-Pb-Ag deposit, 

Noatak district, Alaska [abs.]: GSA, v. 19, no. 7, 

p. 905. 

Bibliographies 207 
Subject Index 

COAL 

Mineralogy and Stage Assignment of Some Tertiary Coal from the Tikishla Park Drill Hole, Anchorage, Alaska 

G.D. Stricker, M.E. Brownfield, L.A. Yehle, and J.A. Wolfe 121 

ECONOMIC 

H2S-Rich Vein-Forming Fluids at the Sumdum Chief Gold Mine, Southeastern Alaska 

Richard J. Goldfarb, Albert H. Hofstra, Gary P. Landis, and David L. Leach 160 

Reconnaissance Geochemical Investigations of the White Mountains National Recreation Area, East-Central 

Alaska 

Thomas D. Light, Gregory K. Lee, Richard B. Tripp, and Elizabeth A. Bailey 64 

Mineral Resource Assessment for Part of the White Mountains National Recreation Area 

Richard B. McCammon, Thomas D. Light, and C. Dean Rinehart 71 

Alteration Zoning and Origin of the Alaska-Juneau Gold Deposit 

Rainer J. Newberry and David A. Brew 174 

Gold Mineralization by Metamorphic Fluids in the Chandalar District, Southern Brooks Range--Fluid Inclusion 

and Oxygen-Isotopic Evidence 

Scott C. Rose, William J. Pickthorn, and Richard J. Goldfarb 81 

GEOCHEMISTRY 

Geochemical Anomalies in the Eastern Katmai Region of the Alaska Peninsula 

Richard J. Goldfarb, John E. Gray, and R.B. Tripp 132 

Factor Analysis of the NURE Stream-Sediment and Lake-Sediment Geochemical Data from the Iditarod 

Quadrangle 

John E. Gray, Sarah C. Smith, and Richard J. Goldfarb 86 

Tertiary Gold-Bearing Gravel at Livengood, Alaska 

Susan M. Karl, Thomas A. Ager, Karl Hanneman, and Steve D. Teller 61 

Reconnaissance Geochemical Investigations of the White Mountains National Recreation Area, East-Central 

Alaska 

Thomas D. Light, Gregory K. Lee, Richard B. Tripp, and Elizabeth A. Bailey 64 

GEOCHRONOLOGY 

Petrogenesis of the Crooked Mountains Pluton, Bethel Quadrangle: A Preliminary Report 

Thomas P. Frost, James P. Calzia, Ronald W. Kistler, and Davison V. Vivit 126 

New K-Ar Ages for Plutons on Western Chichagof Island and on Yakobi Island 

Susan M. Karl, Bruce R. Johnson, and Marvin A. Lanphere 164 

GEOPHYSICS 

A Thermal Cross Section for the Permafrost and Hydrate Stability Zones in the Kuparuk and Prudhoe Bay Oil 

Fields 

Arthur H. Lachenbruch, S. Peter Ga 1 ani s, Jr., and Thomas H. Moses, Jr. 48 

208 Subject Index 
MARINE 

Construction of an Arctic Barrier Island by Alternating Sea-Ice Pileup and Overwash 

P. W. Barnes and Erk Re imni tz 180 

Nearshore Marine Environments of the Alaskan Beaufort Sea During Deposition of the Flaxman Member of the 

Gubik Formation 

L. David Carter, Elisabeth M. Brouwers, and Louie Marincovich, Jr. 27 

Sea-Floor Feeding Traces of Gray Whales and Walrus in the Northeast Chukchi Sea 

R. Lawrence Phillips and Mitchell W. Colgan 183 

Late Cretaceous Sediments from the Northeast Chukchi Sea 

R. Lawrence Phillips, LedaBeth G. Pickthorn, and Douglas M. Rearic 187 

Evidence for Sea-Ice Impact on Icy Reef, Beaufort Sea Coast 

Erk Reimnitz and P.W. Barnes 190 

PALEONTOLOGY/MICROPALEONTOLOGY 

A Major Unconformity Between Upper Ordovician and Lower Devonian Strata in the Nanook Limestone, Shublik 

Mountains, Northeastern Brooks Range 

Robert B. Blodgett, David M. Rohr, Anita G. Harris, and Rong Jia-yu 18 

A Late Silurian Age Determination for the Limestone of the Lost Creek Unit, Livengood 

C-4 Quadrangle, East-Central Alaska 

Robert B. Blodgett, Ning Zhang, Allen R. Ormiston, and Florence R. Weber 54 

Megafossils (Buchia) Indicate Late Jurassic Age for Part of Kelp Bay Group on Baranof Island, Southeastern 

Alaska 

David A. Brew, Susan M. Karl, and John W. Mi 11 er 147 

Ostracode and Molluscan Assemblages from the Late Neogene Nuwok Member of the Sagavanirktok Formation, 

North Slope 

Elisabeth M. Brouwers and Louie Marincovich, Jr. 24 

Nearshore Marine Environments of the Alaskan Beaufort Sea During Deposition of the Flaxman Member of the 

Gubik Formation 

L. David Carter, Elisabeth M. Brouwers, and Louie Marincovich, Jr. 27 

Off-Platform Silurian Sequences in the Ambler River Quadrangle 

Julie A. DumoulinandAnitaG. Harris 35 

PETROLEUM GEOLOGY 

A Thermal Cross Section for the Permafrost and Hydrate Stability Zones in the Kuparuk and Prudhoe Bay Oil 

Fields 

Arthur H. Lachenbruch, S. Peter Ga 1 ani s, Jr., and Thomas H. Moses, Jr. 48 

Hydrocarbon Source Potential and Thermal Maturity of the Sanctuary Formation (Middle Miocene), Northern 

Foothills of the Alaska Range 

Richard G. Stanley 117 

PETROLOGY - IGNEOUS 

Middle Pennsylvanian Plutonic Rocks Along the Southern Margin of the Wrangellia Terrane 

John N. Aleinikoff, George Plafker, and Warren J. Nokleberg 110 

Major-Element Geochemistry of Metabasalts of the Juneau-Haines Region, Southeastern Alaska 

Arthur B. Ford and David A. Brew 150 

Petrogenesis of the Crooked Mountains Pluton, Bethel Quadrangle: A Preliminary Report 

Thomas P. Frost, James P. Calzia, Ronald W. Kistler, and Davison V. Vivit 126 

Subject Index 209 
New K-Ar Ages for Plutons on Western Chichagof Island and on Yakobi Island 

Susan M. Karl, Bruce R. Johnson, and Marvin A. Lanphere 164 

Ultramafic Rocks of the Livengood Terrane 

Robert A. Loney and Glen R. Himmel berg 68 

Geochemistry and Petrography of Lamprophyre Dike Rocks in the Coast Mountains, Southeastern Alaska 

John S. Lu 11 and George Pl afker 169 

PETROLOGY - METAMORPHIC 

Relative Timing of Porphyroblast Growth, Foliation Development, and Ductile Shear in Pelitic Metamorphic 

Rocks from the Juneau Area, Southeastern Alaska 138 

Robert L. Bauer, Glen R. Himmelberg, David A. Brew, and Arthur B. Ford 

Geologic Setting and Petrography of the Phyllite and Metagraywacke Thrust Panel, North-Central Alaska 

John M. Murphy and W.W. Patton, Jr. 104 

PETROLOGY - SEDIMENTARY 

A Comparative Petrologic Study of Sandstone from the Wilber Creek, Cascaden Ridge, and Wickersham Units in 

the Livengood Quadrangle 

L.D. Gergen, J.E. Decker, and George Plafker 57 

Petrography of Sandstones of the Orca Group from the Southern Trans-Alaskan Crustal Transect (TACT) Route 

and Montague Island 

L.D. Gergen and George Plafker 156 

QUATERNARY GEOLOGY 

Nearshore Marine Environments of the Alaskan Beaufort Sea During Deposition of the Flaxman Member of the 

Gubik Formation 

L. David Carter, Elisabeth M. Brouwers, and Louie Marincovich, Jr. 27 

Late Wisconsin Eolian Activity and Related Alluviation, Central Kobuk River Valley 

Thomas D. Hamilton, John P. Galloway, and Eduard A. Koster 39 

Glacial Geologic History of the Salmon Lake Area, Seward Peninsula 

Darrell S. Kaufman, David M. Hopkins, and Parker E. Calkin 91 

Advance of Hubbard Glacier and Closure of Russell Fiord, Alaska--Environmental Effects and Hazards in the 

Yakutat Area 

Lawrence R. Mayo 4 

Source of the Sanford Volcanic Debris Flow, South-Central Alaska 

Donald H. Richter, Henry R. Schmoll, and Dana J. Bove 114 

SEDIMENTOLOGY 

Construction of an Arctic Barrier Island by Alternating Sea-Ice Pileup and Overwash 

P.W. Barnes and Erk Reimnitz 180 

A Major Unconformity Between Upper Ordovician and Lower Devonian Strata in the Nanook Limestone, Shublik 

Mountains, Northeastern Brooks Range 

Robert B. Blodgett, David M. Rohr:, Anita G. Harris, and Rang Jia-yu 18 

A Late Silurian Age Determination for the Limestone of the Lost Creek Unit, Livengood 

C-4 Quadrangle, East-Central Alaska 

Robert B. Blodgett, Ning Zhang, Allen R. Ormiston, and Florence R. Weber 54 

Stromatolite- and Coated-Grain-Bearing Carbonate Rocks of the Western Brooks Range 

Julie A. Dumoulin 31 

Off-Platform Silurian Sequences in the Ambler River Quadrangle 

Julie A. DumoulinandAnitaG. Harris 35 

210 Subject Index 
Stratigraphy, Sedimentology, and Structure of the Wickersham Terrane in the Cache Mountain Area, EastCentral Alaska 

Thomas E. Moore and Warren J. Nok l eberg 75 

STRATIGRAPHY 

A Major Unconformity Between Upper Ordovician and Lower Devonian Strata in the Nanook Limestone, Shublik 

Mountains, Northeastern Brooks Range 

Robert B. Blodgett, David M. Rohr, Anita G. Harris, and Rang Jia-yu 181 

A Late Silurian Age Determination for the Limestone of the Lost Creek Unit, Livengood 

C-4 Quadrangle, East-Central Alaska 

Robert B. Blodgett, Ning Zhang, Allen R. Ormiston, and Florence R. Weber 54 

A Reexamination of the Contacts and other Features of the Gravina Belt, Southeastern Alaska 

David A. Brew and Susan M. Karl 143 

Stromatolite- and Coated-Grain-Bearing Carbonate Rocks of the Western Brooks Range 

Julie A. Dumoulin 31 

Off-Platform Silurian Sequences in the Ambler River Quadrangle 

Julie A. Dumoulin and Anita G. Harris 35 

Tertiary Gold-Bearing Gravel at Livengood, Alaska 

Susan M. Karl, Thomas A. Ager, Karl Hanneman, and Steve D. Teller 61 

Right-Lateral Offset Solution for the Iditarod-Nixon Fork Fault, Western Alaska 

Marti L. Miller and Thomas K. Bundtzen 99 

Stratigraphy, Sedimentology, and Structure of the Wickersham Terrane in the Cache Mountain Area, EastCentral Alaska 

Thomas E. Moore and Warren J. Nokl eberg 75 

Geologic Setting and Petrography of the Phyllite and Metagraywacke Thrust Panel, North-Central Alaska 

John M. Murphy and W.W. Patton, Jr. 104 

Hydrocarbon Source Potential and Thermal Maturity of the Sanctuary Formation (Middle Miocene), Northern 

Foothills of the Alaska Range 

Richard G. Stanley 117 

STRUCTURAL/TECTONICS 

Relative Timing of Porphyroblast Growth, Foliation Development, and Ductile Shear in Pelitic Metamorphic 

Rocks from the Juneau Area, Southeastern Alaska 

Robert L. Bauer, Glen R. Himmelberg, David A. Brew, and Arthur B. Ford 138 

A Reexamination of the Contacts and other Features of the Gravina Belt, Southeastern Alaska 

David A. Brew and Susan M. Karl 143 

Megafossils (Buchia) Indicate Late Jurassic Age for Part of Kelp Bay Group on Baranof Island, Southeastern 

Alaska 

David A. Brew, Susan M. Karl, and John W. Mi 11 er 147 

Decollements in the Endicott Mountains Allochthon, North-Central Brooks Range 

J.S. Kelley and Diedra Bohn 44 

Right-Lateral Offset Solution for the Iditarod-Nixon Fork Fault, Western Alaska 

Marti L. Miller and Thomas K. Bundtzen 99 

Stratigraphy, Sedimentology, and Structure of the Wickersham Terrane in the Cache Mountain Area, EastCentral Alaska 

Thomas E. Moore and Warren J. Nokleberg 75 

Subject Index 211 
VOLCANOLOGY 

Lahar Deposit in the Iditarod Volcanics, Southwestern Iditarod Quadrangle 

Robert G. McGimsey and Marti L. Miller 95 

Source of the Sanford Volcanic Debris Flow, South-Central Alaska 

Donald H. Richter, Henry R. Schmoll, and Dana J. Bove 114 

212 Subject Index 
Author Index 

Page Page 

Ager, Thomas A. 61 Marincovich, Louie, Jr. 24 27 

Aleinikoff, John N. 110 Mayo, Lawrence R. 4 

McCammon, Richard B. 71 

Bailey, Elizabeth A. 64 McGimsey, Robert G. 95 

Barnes, P. W. 180 190 Miller, John W. 147 

Bauer, Robert L. 138 Miller, Marti L. 95 99 

Blodgett, Robert B. 18 54 Moore, Thomas E. 75 

Bohn, Diedra 44 Moses, Thomas H., Jr. 48 

Bove, Dana J. 114 Murphy, John M. 104 

Brew, David A. 138 143 147 150 174 

Brouwers, Elisabeth M. 24 27 Newberry, Rainer J. 174 

Brownfield, M.E. 121 Nokleberg, Warren J. 75 110 

Bundtzen, Thomas K. 99 

Ormiston, Allen R. 54 

Calkin, Parker E. 91 

Calzia, James P. 126 Patton, W.W., Jr. 104 

Carter, L. David, 27 Phillips, R. Lawrence 183 187 

Colgan, Mitchell W. 183 Pickthorn, LedaBeth G. 187 

Pickthorn, William J. 81 

Decker, J.E. 57 Plafker, George 57 110 156 169 

Dumoulin, Julie A. 31 35 

Rearic, Douglas M. 187 

Ford, Arthur B. 138 150 Reimnitz, Erk 180 190 

Frost, Thomas P. 126 Richter, Donald H. 114 

Rinehart, C. Dean 71 

Galanis, S. Peter, Jr. 48 Rohr, David M. 18 

Galloway, John P. 1 39 Rong Jia-yu 18 

Gergen, L.D. 57 156 Rose, Scott C. 81 

Goldfarb, Richard J. 81 86 132 160 

Gray, John E. 86 132 Schmoll, Henry R. 114 

Smith, Sarah C. 86 

Hamilton, Thomas D. 1 39 Stanley, Richard G. 117 

Hanneman, Karl 61 Stricker, G.D. 121 

Harris, Anita G. 18 35 

Himmelberg, Glen R. 68 138 Teller, Steve D. 61 

Hofstra, Albert H. 160 Tripp, Richard B. 64 132 

Hopkins, David M. 91 

Vivit, Davison V. 126 

Johnson, Bruce R. 164 

Weber, Florence R. 54 

Karl, Susan M. 61 143 147 164 White, Ellen R. 194 201 

Kaufman, Darrell S. 91 Wolfe, J.A. 121 

Kelley, J.S. 44 

Kistler, Ronald W. 126 Yehle, L.A. 121 

Koster, Eduard A. 39 

Zhang, Ning 54 

Lachenbruch, Arthur H. 48 

Landis, Gary P. 160 

Lanphere, Marvin A. 164 

Leach, David L. 160 

Lee, Gregory K. 64 

Light, Thomas D. 64 71 

Loney, Robert A. 68 

Lull, John S. 169 

Au thor Index 213 
Authors' Addresses 

U.S. Geological Survey 

Geologic Division, Mail Stop --

345 Middlefield Road 

Menlo Park, CA 94025 

Barnes, P.W. 

Brew, David A. 

Calzia, James P. 

Ford, Arthur B. 

Frost, Thomas P. 

Galanis, S. Peter, Jr. 

Galloway, John P. 

Gergen, L.D. 

Kistler, Ronald W. 

Lachenbruch, Arthur H. 

Lanphere, Marvin A. 

Loney, Robert A. 

Lull, John S. 

Marincovich, Louie, Jr. 

Miller, John W. 

Moore, Thomas E. 

Moses, Thomas H., Jr. 

Murphy, John M. 

Nokleberg, Warren J. 

Patton, W.W., Jr. 

Phillips, R. Lawrence 

Pickthorn, LedaBeth G. 

Pickthorn, William J. 

Plafker, George 

Rearic, Douglas M. 

Reimnitz, Erk 

Rinehart, C. Dean 

Stanley, Richard G. 

Vivit, Davison V. 

White, Ellen R. 

U.S. Geological Survey 

Branch of Alaskan Geology 

4200 University Drive 

Anchorage, AK 99508-4667 

Bailey, Elizabeth A. 

Bohn, Diedra 

Carter, L. David 

Dumoulin, Julie A. 

Hamilton, Thomas D. 

Kelley, J.S. 

Light, Thomas D. 

McGimsey, Robert G. 

Miller, Marti L. 

214 Authors' Addresses 

Mail 

Stop 

999 

904 

941 

904 

938 

923 

917 

904 

937 

923 

937 

904 

904 

915 

915 

904 

923 

904 

904 

904 

999 

999 

941 

904 

999 

999 

901 

999 

938 

955 

U.S. Geological Survey 

Branch of Alaskan Geology 

PO Box 80586 

Fairbanks, AK 99708 

Karl, Susan M. 

Weber, Florence R. 

U.S. Geological Survey 

Geologic Division, Mail Stop --

Box 25046, DFC 

Denver, CO 80225 

Aleinikoff, John N. 

Bove, Dana J. 

Brouwers, Elisabeth M. 

Brownfield, M.E. 

Goldfarb, Richard J. 

Gray, John E. 

Hofstra, Albert H. 

Johnson, Bruce R. 

Landis, Gary P. 

Leach, David L. 

Lee, Gregory K. 

Rose, Scott C. 

Schmoll, Henry R. 

Smith, Sarah C. 

Stricker, G.D. 

Tripp, Richard B. 

Wolfe, J.A. 

Yehle, L.A. 

U.S. Geological Survey 

National Center, Mail Stop--

12201 Sunrise Valley Drive 

Reston, VA 22092 

Ager, Thomas A. 

McCammon, Richard B. 

U.S. Geological Survey 

Museum Natural History E-503 

Washington, D.C. 20560 

Harris, Anita G. 

Mail 

Stop 

963 

905 

919 

972 

973 

973 

973 

972 

905 

973 

973 

973 

972 

973 

972 

973 

972 

919 

Mail 

Stop 

970 

920 
U.S. Geological Survey 

Water Resources Divison 

Cold Regions Hydrology Project Office 

800 Yukon Drive 

Fairbanks, AK 99775-5150 

Mayo, Lawrence R. 

U.S. Geological Survey 

Box 79 

Winston, NM 87943 

Richter, Donald H. 

Alaska Division of Geological and Geophysical Surveys 

794 University Avenue 

Fairbanks, AK 99709 

Bundtzen, Thomas K. 

Decker, J.E. 

Alaska Placer Development Inc. 

Fairbanks, AK 99708 

Hanneman, Karl 

Amoco Production Company 

Research Center 

4502 E. 41st Street 

P.O. Box 3385 

Tulsa, OK 74102 

Ormiston, Allen R. 

Geographical Institute 

University of Utrecht 

Heidelberglaan 2 

3584 CS Utrecht 

The Netherlands 

Koster, Eduard A. 

Nanjing Institute of Geology and Paleontology 

Academia Sinica 

Chi-Ming-Ssu 

Nanjing, People's Republic of China 

Rong Jia-yu 

Oregon State University 

Department of Geology 

Corvallis, OR 97331 

Blodgett, Robert B. 

Zhang, Ning 

State University of New York at Buffalo 

Department of Geology 

4240 Ridge Lea Road 

Buffalo, NY 14226 

Calkin, Parker E. 

Sui Ross State University 

Department of Gelogy 

Alpine, TX 79832 

Rohr, David M. 

University of Alaska 

Department of Geology and Geophysics 

Fairbanks, AK 88775-0760 

Hopkins, David M. 

Newberry, Rainer J. 

Teller, Steve D. 

University of Colorado 

Institute of Arctic and Alpine Research 

Campus Box 450 

Boulder, CO 80309 

Kaufman, Darrell S. 

University of Missouri 

Department of Geology 

Columbia, MO 65211 

Bauer, Robert L. 

Himmelberg, Glen R. 

University of Santa Cruz 

Earth Sciences Board 

Santa Cruz, CA 95064 

Colgan, Mitchell W. 

Authors' Addresses 215 
GPO 585-045/78050