GEOLOGIC STUDIES IN ALASKA 

by the U.S. Geological Survey 

during 1986 

/_, ·. ~~~----------~~~~-----~~ 

U.S. Geological Survey Circular 998 
Photographs on front and back covers are of 1986 eruption of Augustine Volcano. 

See article on p. 4-13. 

Front cover 

Increasingly vigorous vapor plumes and melting of snow cover on volcano's summit were early signs of an 

impending eruption. View from northeast on March 21. 

Back cover 

Top right: Small amounts of ash were emitted along with increased vapor plume during weeks prior to 

eruption. Ash which fell from plume extends from summit toward foreground. View from east on 

February 22. 

Top left: On first day of eruption, hot pyroclastic material falling on upper cone caused mudflows that 

extended down gullies on south and west sides of volcano. An ash-rich eruption column was almost 

continuous during first five days of eruption. View from southwest on March 27. 

Center left: Rainfall accentuated contrast between dry, hot pyroclastic material deposited during March 

eruptive phase (light) and damp, lightly vegetated deposits of previous eruptions (dark). View of north side 

of mountain from east on April 18. 

Center right: Oblique view of dark, blocky lava flow extending northward (toward bottom of picture) from 

summit. Photograph taken April 27. 

Bottom left: Dramatic ash plume over Homer, Alaska, resulted from last large explosion of March 

eruptive phase which occurred at approximately 10:00 A.M. AST, March 31. Use of photograph by 

permission of photographer Chlaus Lotscher is gratefully acknowledged. 

Bottom right: Lobate nose of a pyroclastic flow on upper slope of volcano. Flows such as this moved at 

estimated speeds greater than 35 meters per second (80 mph); temperature of their deposits measured 

several weeks after eruption exceeded 550 °C (120 °F). Photograph taken on north side of cone April 27. 
GEOLOGIC STUDIES IN ALASKA 

by the U.S. Geological Survey 

during 1986 

Thomas D. Hamilton and John P. Galloway 

Editors 

U.S. Geological Survey Circular 998 

Short papers describing results 

of recent geologic investigations 

and lists of published reports 

1987 
Department of the Interior 

DONALD PAUL HODEL, Secretary 

U.S. Geological Survey 

Dallas L. Peck, Director 

Library of Congress Catalog Number 76-608093 

Free on application to the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 
CONTENTS 

INTRODUCTION 

Thomas D. Hamilton and John P. Galloway, editors 1 

ARTICLE OF SPECIAL INTEREST 

The 1986 eruptions of Augustine Volcano, Alaska: hazards and effects 4 

M. Elizabeth Yount, Thomas P. Miller, and Bruce M. Gamble 

STATEWIDE 

Status of Alaska Mineral Resources Data System 15 

Kenneth R. Leonard and Donald F. Huber 

The Aniakchak tephra deposit, a late Holocene marker horizon in western Alaska 19 

James R. Riehle, Charles E. Meyer, Thomas A. Ager, Darrell S. Kaufman, and Robert E. Ackerman 

NORTHERN ALASKA 

Geochemical and geologic controls on the inferred occurrence of natural gas hydrate in the Kuparuk 2D-15 

well, North Slope, Alaska 24 

Timothy S. Collett, Keith A. Kvenvolden, Leslie B. Magoon, and Kenneth J. Bird 

Use of factor analysis in locating base metal mineralization in the Killik River quadrangle, Alaska 27 

Karen A. Duttweiler 

Preliminary evaluation of geochemical anomalies in the Baird Mountains quadrangle, Alaska 31 

Peter F. Folger, Richard J. Goldfarb, and Jeanine M. Schmidt 

Glacial advance of late Wisconsin (Itkillik II) age in the upper Noatak River Valley -- a radiocarbon-dated 

stratigraphic record 35 

Thomas D. Hamilton, George A. Lancaster, and Deborah A. Trimble 

Ordovician and Silurian fossils from the Doonerak anticlinorium, central Brooks Range, Alaska 40 

John E. Repetski, Claire Carter, Anita G. Harris, and J. Thomas Dutro, Jr. 

Organic carbon occurrence and content in carbonate rocks from the Omar Copper Prospect, Baird 

Mountains, Alaska 43 

Jeanine M. Schmidt and Peter F. Folger 

Plant megafossils, vertebrate remains, and paleoclimate of the Kogosukruk Tongue (Late Cretaceous), 

North Slope, Alaska 47 

Robert A. Spicer and Judith Totman Parrish 

Petrography of the Baird Mountains schistose lithologies, northwestern Alaska 49 

Mark R. Zayatz 

iii 
EAST-CENTRAL ALASKA 

A Late Ordovician age reappraisal for the Upper Fossil Creek 

Volcanics, and possible significance for glacio-eustasy 54 

Robert B. Blodgett, Karen L. Wheeler, David M. Rohr, Anita G. Harris, and Florence R. Weber 

Preliminary geology, including the Tintina fault system, of part of the southwestern Charley River 

quadrangle, Alaska 59 

Helen L. Foster and Terry E.C. Keith 

Platinum-group element concentrations in a biotite-rich clinopyroxenite suite, Eagle C-3 quadrangle, 

Alaska 62 

Terry E. C. Keith, Norman J Page, Robert L. Oscarson, and Helen L. Foster 

Sources of placer gold in the southern part of the White Mountains Recreation Area, east-central Alaska 67 

Thomas D. Light, John W. Cady, Florence R. Weber, Richard B. McCammon, and C. Dean Rinehart 

Lithostratigraphy, petrology, and geochemistry of the Ordovician Fossil Creek Volcanics, White Mountains, 

east-central Alaska 70 

Karen L. Wheeler, Robert B. Forbes, Florence R. Weber, and C. Dean Rinehart 

Placer gold related to mafic schist(?) in the Circle District, Alaska 74 

Warren Y eend 

SOUTHWESTERN ALASKA 

Late Mesozoic structural and stratigraphic framework, eastern Bethel quadrangle, southwestern Alaska 78 

Stephen E. Box and John M. Murphy 

Early Cretaceous cessation of terrane accretion, northern Eek Mountains, southwestern Alaska 83 

John M. Murphy 

Petrology and provenance of sandstones of the Naknek Formation, Alaska Peninsula 86 

Michael W. Mullen 

SOUTHERN ALASKA 

Earthquake-caused sedimentary couplets in the Upper Cook Inlet region 92 

Susan Bartsch-Winkler and Henry R. Schmoll 

Late Triassic and Early Cretaceous fossil ages from the McHugh complex, southern Alaska 96 

Steven W. Nelson, Charles D. Blome, and Susan M. Karl 

Effects of weathering on petroleum-source evaluation of coals from the Suntrana Formation near Healy, 

Alaska 99 

Richard G. Stanley 

Thermal maturity and petroleum-source potential of the Cantwell Formation (Paleocene), Alaska Range 104 

Richard G. Stanley 

An application of oblique rotation R-Mode factor analysis in the Mount Hayes quadrangle, Alaska (abstract) 108 

J.D. Hoffman 

iv 
SOUTHEASTERN ALASKA 

Structural fabric analysis of the Perseverance Slate and gold-bearing quartz veins in the south ore body of 

the Alaska-Juneau lode system, southeastern Alaska 110 

Christopher C. Barton and Thomas D. Light 

The Meade Glacier fault-- an important tectonic boundary in the Northern Cordillera, southeastern Alaska 113 

David A. Brew and Arthur B. Ford 

The Wright Glacier volcanic plug and dike swarm, southeastern Alaska 116 

Arthur B. Ford and David A. Brew 

Ultramafic and mafic sills in the vicinity of the Treadwell gold deposits, Douglas Island, southeastern 

Alaska 119 

David A. Brew, Glen R. Himmelberg, Arthur B. Ford, and Robert C. Jachens 

Newly discovered molybdenite occurrence near Boundary Creek, Coast Mountains, southeastern Alaska 124 

Richard D. Koch, David A. Brew, and Arthur B. Ford 

Salt Chuck palladium-bearing ultramafic body, Prince of Wales Island 126 

Robert A. Loney, Glen R. Himmelberg, and Nora Shew 

The Alaska-Juneau gold deposit; remobilized syngenetic versus exotic epigenetic origin 128 

Rainer J. Newberry and David A. Brew 

Paleomagnetic evidence for a latest Pliocene and early Pleistocene age of the upper Yakataga Formation 

on Middleton Island, Alaska 132 

Edward A. Mankinen and George Plafker 

Cenozoic magmatism in southeastern Alaska (abstract) 137 

David A. Brew 

OFFSHORE 

Beaufort Sea coastal currents: a divergence near Barter Island, Alaska? 139 

Peter W. Barnes, Scot Graves, and Erk Reimnitz 

Volcanic-arc dacite and early Miocene basalt dredged from the Shumagin margin, Alaska 143 

Terry R. Bruns, Tracy L. Vallier, Leda Beth Pickthorn, and Roland von Huene 

GLORIA images of Zhemchug Canyon and Bering channel-fan system, Bering Sea 147 

Herman A. Karl, James V. Gardner, and Quentin Huggett 

GLORIA side-scan and geophysical surveys of the central Bering Sea in 1986 152 

Michael S. Marlow, Paul R. Carlson, Shawn V. Dadisman, Douglas M. Rearic, Edward J. Maple, and 

Lindsay M. Parson 

Vibracore stratigraphy of the northeastern Chukchi Sea 157 

R. Lawrence Phillips and Mitchell W. Colgan 

Thirty-four-year shoreface evolution at a rapidly retreating arctic coastal site 161 

Erk Reimnitz and Edward W. Kempema 

v 
Petrology, age, and original tectonic setting of basalt from the St. George Basin COST No. 1 Well, southern 

Bering Sea 165 

Tracy L. Vallier and Bruce M. Herman 

GLORIA images obtained in the TACT corridor of the Aleutian convergent margin, northern Gulf of Alaska 

(abstract) 170 

Terry R. Bruns, Michael A. Fisher, Paul R. Carlson, Douglas M. Rearic, and Lindsay M. Parson 

BffiLIOGRAPIDES 

Reports about Alaska in USGS publications released in 1986 172 

compiled by Ellen R. White 

Reports about Alaska in non-USGS publications released in 1986 which include USGS authors 181 

compiled by Ellen R. White 

SUBJECT INDEX 187 

AUTHOR INDEX 193 

AUTHORS ADDRESSES 194 

vi 
Walrus on Round Island in Bristol Bay. Photo by S.E. Box, 1982. 

GEOLOGIC STUDIES IN ALASKA 

BY THE U.S. GEOLOGICAL SURVEY DURING 1986 

Thomas D. Hamilton and John P. Galloway, Editors 

INTRODUCTION 

This volume is a continuation of the annual 

circulars that formerly were titled "The United 

States Geological Survey in Alaska--

Accomplishments during 19xx." The 39 short 

papers and three abstracts presented here report 

on some of the geologic studies performed in 

Alaska by the U.S. Geological Survey (USGS) and 

cooperating agencies during 1986. The reports are 

presented in their geographic order of occurrence, 

beginning with investigations that are statewide in 

scope and followed by papers related to five 

regional subdivisions of Alaska and to areas 

offshore on the Alaskan continental shelf. The 

regional papers are generally presented in 

sequence from north to south. Author and subject 

indexes and full addresses of all authors are 

appended at the back of the volume. We also 

include two bibliographies that cover (1) reports 

about Alaska in USGS publications released in 1986 

and (2) reports about Alaska by USGS authors in 

other publications in 1986. 

The 42 reports in this volume provide a 

representative sample of current U.S. Geological 

Survey research in Alaska. Sixteen papers are 

devoted to mineral resources--six on precious 

metals, six on other metallic resources, three on 

fossil fuels, and one on statewide inventory 

systems. Basic framework studies comprise an 

additional 16 papers that focus on a wide range of 

1 

topics, including geochronology, structural 

geology, stratigraphy, petrology, and paleoclimatology. Comparable studies carried out 

offshore comprise seven additional papers. 

Geologic hazards in Alaska's dynamic environment 

are discussed in three reports that cover volcanic 

hazards, earthquake recurrence intervals, and 

coastal erosion. 

This year we depart from custom by 

publishing "an article of special interest" devoted 

to a topic that was prominent in the news during 

1986--the eruption of Augustine Volcano and its 

impact on population centers around Cook Inlet. 

That paper, which begins on the following page, is 

longer and more fully illustrated than the other 

papers in this volume, and its illustrations include 

the photographs on the front and back covers. 

The two bibliographies that follow the short 

reports were compiled by Ellen R. White, and the 

mosaic of cover photographs was prepared by M. 

Elizabeth Yount and Robert F. Gilmore. We would 

like to particularly acknowledge the efforts of 

Susan Bartsch-Winkler and Katharine M. Reed, the 

editors of the three preceding (1983-1985) volumes 

in the "Accomplishments" series, who set a high 

standard of dedication and quality that we have 

been hard pressed to maintain. We have borrowed 

liberally from their ideas in preparing the present 

volume. 
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ARTICLE OF SPECIAL INTEREST 

Geologist sampling steep, blocky face of lava flow that was erupted during April 1986 at Augustine 

Volcano. Photo by M.E. Yount, May 6, 1986. 

3 
THE 1986 ERUPTIONS OF 

AUGUSTINE VOLCANO, ALASKA: 

HAZARDS AND EFFECTS 

M. Elizabeth Yount, Thomas P. Miller, 

and Bruce M. Gamble 

Au~ustine Volcano, 1,227 m high, forms a 

8xll km island 280 km southwest of Anchorage 

and is the southernmost of five volcanoes in the 

Cook Inlet region (fig. 1). Since its discovery by 

Captain Cook in 1778, Augustine has had six 

recorded eruptions: 1812, 1883, 1935, 1963-64, 

1976, and 1986 (Kienle and Swanson, 1985). The 

last four eruptions have each involved explosive 

venting of ash, pyroclastic flows and mudflows, 

and, in the later phases, eruption of lava and 

formation of a new dome within the summit 

crater. The most violent historic eruption of 

Augustine Volcano occurred in 1883 when major 

explosive activity triggered a tsunami in lower 

Cook Inlet that caused minor damage to nearby 

coastal communities (Davidson, 1884). The 1986 

eruption consisted of three main episodes on 

March 27-April 2, April 23-28, and August 22-

September 1. 

The following account, intended for 

geologists and non-geologists, briefly summarizes 

the perceived hazards from eruptions of Augustine 

volcano, the 1986 activity and its effects, and the 

distribution and chemistry of airborne ash from 

the 1986 eruption. 

Potential hazards 

Knowledge of Augustine Volcano's eruptive 

history allows inferences about the potential 

hazards of future activity (Kienle and Swanson, 

1983, 1985). The most likely and widespread 

hazard is posed by airborne ash, whose abrasive 

and corrosive properties can cause severe damage 

to exposed mechanical and electronic equipment. 

Major disruption to transportation and 

communication networks can occur in areas of 

heavy ashfall; for example, two Boeing 747 jets 

over Indonesia in 1982 experienced in-flight failure 

of engines due to ingestion of airborne ash (Blong, 

1984). Several air traffic corridors pass within 50 

km of Augustine; at least five aircraft were 

damaged during the 1976 eruption (Kienle and 

Swanson, 1985, p. 31). Although unlikely to be 

erupted in quantities large enough to pose a major 

direct threat to life in lower Cook Inlet 

communities, ash may exacerbate existing health 

problems. 

Eruption-induced tsunamis (sea waves), 

although less commqn, are potentially more 

devastating to nearby coastal communities than 

the ubiquitous ash. A tsunami caused by a large 

avalanche during the 1792 eruption of Unzen 

volcano in Japan resulted in a death toll of at least 

4 

700 (Blong, 1984). The 1883 explosive eruption of 

Augustine Volcano produced a massive avalanche 

into Cook Inlet (Siebert and others, 1986), causing 

a tsunami 7-9 m high at Port Graham, 90 km to 

the east on the southwest Kenai Peninsula. 

Damage at Port Graham was apparently limited to 

boats; "fortunately it was low water, or all of the 

people at the settlement must inevitably have 

been lost" (Davidson, 1884). Mounds and irregular 

ridges on the north shore of Augustine Island are 

deposits of the 1883 avalanche (fig. 2). Similar 

deposits on the west, northeast, and south sides of 

the island record as many as seven prehistoric 

avalanches (Beget, 1986) and emphasize the 

recurrent hazard of avalanche-generated tsunamis 

at Augustine. 

Recent computer simulation of the 1883 

avalanche by Zygmunt Kowalik, University of 

Alaska, has predicted travel times for a 

comparable tsunami (Kienle and others, 1986). 

The calculated travel time to Port Graham is 

approximately 1 hour (fig. 3) as compared to the 

25-min travel time reported for the 1883 tsunami 

(Davidson, 1884). Imprecise timing estimates in 

1883 or scaling problems with the controlling 

62° 

154° 152° 

<(lt>-

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C/) 

q- •H -..J 

q- .s 

~Augustine 

Volcano 

~Gt. 

150° 

.A 

~>(-

~~ 't-.A (<' 

.A ~-1-

~"9 

Figure 1.--Cook Inlet region, showing location of 

Augustine Volcano, Mount Iliamna (I), Redoubt 

Volcano (R), Mount Spurr (S), and Hayes volcano 

(H). Mountain ranges surrounding Cook Inlet 

caused northward-directed ash to stagnate above 

Cook Inlet for first three days of 1986 eruption. 
Figure 2.--Northeast end of Augustine Island on April 18, 1986. In foreground are mounds and irregular 

ridges which resulted from 1883 avalanche. Deposits of March 1986 pyroclastic flows are light-colored 

material extending upslope from shoreline on left (east). Snow level is about 300 m in this picture. 

154° 

parameters for the computer simulation may 

account for the 35-min difference. These travel- 6 o o 

time estimates place severe constraints on 

warning and evacuation time, which would be 

shorter by the time required by observers or 

analysts to determine that a tsunami had likely 

been generated. Effects of a tsunami might be 

mitigated if the tide were relatively low at the 

time of occurrence (as it was in 1883). 

The 1986 Augustine eruptions 

The first of the 1986 eruptions was preceded 

by more than five weeks of generally increasing 

seismic activity and heat flow to the summit 

area. Most of the thousands of seismic events 

detected by the five seismometers on the island 

before and during the eruption were so small as 

not to be detected by a seismometer at Oil Point, 

32 km to the north. 

The eruption began on March 27 and was 

characterized by an almost continuous, ash-rich 

eruption plume that commonly reached elevations 

5 

Figure 3.--Calculated travel time (in minutes) of a 

tsunami resulting from an avalanche of same size 

and location as 1883 avalanche (after Kienle and 

others, 1986). Computer modeling by Zygmunt 

Kowalik, University of Alaska Institute of Marine 

Sciences. 
of 3,000 to 4,600 m and was punctuated by large 

explosions (fig. 4) that generated columns of ash as 

high as 12,200 m. Hundreds of small pyroclastic 

flows moved down the north flank of Augustine 

during the first few days of the eruption (fig. 5; 

Miller and others, 1987), the largest ones reaching 

the north shore, 5 km from the summit vent. 

Pyroclastic flow activity gradually diminished 

after March 31. 

During the April and August episodes, lava 

erupted from the summit vent, fed a short, steep 

lava flow down a north-facing gully, and built a 

new dome (fig. 6; Kienle and others, 1986; Yount 

and Miller, 1987). The eruption column seldom 

exceeded 3, 700 m in height, and the large 

explosive events of the earlier March 27-31 

episode were not observed. Ash erupted in small 

bursts every few minutes, often followed 

immediately by small pyroclastic flows. 

Distribution and chemistry of ash 

from the March 1986 eruption 

The distribution of airborne ash during 

volcanic eruptions is determined chiefly by the 

height of the eruption column, wind direction and 

speed at various altitudes, amount of precipitation 

during the eruption interval, and size and shape of 

particles erupted. Some of these factors changed 

drastically during the March eruptive episode, 

affecting the pattern of ash distribution. Because 

of these changes and because much of the area 

surrounding Augustine Island is either ocean or 

sparsely inhabited, detailed mapping of the ash 

distribution was not possible. 

Data on the timing and height of explosion 

columns and wind directions during the March 

episode do provide a general picture of the ash 

distribution during the explosive, ash-rich initial 

Figure 4.--Explosive burst of ash, March 28, 1986, photographed approximately 30 seconds after first 

appearance. During first five days of March eruption, such explosions propelled ash as high as 12,200 m 

into the atmosphere. 

6 
Figure 5.--Pyroclastic flow racing down north side 

of Augustine Volcano on March 30, 1986. 

Composed of hot, turbulent mixtures of rock 

chunks ranging from house to sand size and rapidly 

expanding volcanic gases, these flows travelled at 

estimated speeds greater than 100 km per hour. 

phase. Explosion plume heights summarized in 

figure 7 are based on pilot reports, USGS 

observation flights, and radar observations from 

King Salmon and Kenai; the times shown on figure 

7 are only approximate. The elapsed time between 

onset of an explosive event and decay of the 

subsequent eruption column varied from one-half 

to more than one hour. The radar station at Kenai 

was shut down for 24 hours March 28-29 due to ash 

fallout, thereby hampering recognition of major 

explosive events. Airborne observers were scarce 

during the first three days of the eruption because 

ash suspended in the atmosphere over Cook Inlet 

made aircraft operations hazardous. For these 

7 

reasons, correlation of the larger seismic events 

with the large explosive ash bursts was limited. 

General wind directions at the 1,470-m 

(4,500-ft) level are shown on figure 8. Winds were 

generally southerly during the first 36 hours of the 

eruption, sending the eruption plume over the 

western edge of the Kenai Peninsula and 

northward between Anchorage and Mount Spurr. 

The plume did not spread appreciably downwind, 

but remained relatively narrow (fig. 9), thereby 

constraining the width of the area affected by ash 

fallout. Airborne ash was detected as far north as 

the Brooks Range on March 28 (Gary Herbert, 

NOAA, oral commun., April 1986). Much ash 

remained in the atmosphere of Cook Inlet basin 

due to confining effects of surrounding mountains 

(shown on fig. 1) and to varying wind directions at 

different altitudes, which caused atmospheric 

mixing of the ash. At mid-day on March 28, winds 

shifted to westerly (fig. 8), sending eruption 

plumes toward Anchor Point and Homer and 

beginning to disperse ash from the upper Cook 

Inlet atmosphere. The final large explosion on 

March 31 caused spectacular ash clouds over 

Anchor Point (fig. 10) and deposited approximately 

2-3 mm of ash on Anchor Point and Homer. 

Ash samples from the 1986 eruption 

collected in Homer consist of 2- to 30-\lm-sized 

fragments of rock, glass shards, and crystals of 

plagioclase and pyroxene; they are finer grained 

than those collected following the 1976 eruption. 

The chemical compositions of 1986 ash samples 

collected in Anchorage, Drift River, Homer, and 

Seward are shown in table 1, together with several 

1976 samples for comparison. All of the 1986 

samples contain greater than 64 percent silica. 

Samples of 1986 ash are higher in silicon dioxide, 

potassium oxide, and phosphorus pentoxide than 

1976 ash samples, and they are lower in aluminum 

oxide, iron oxide, magnesium oxide, and calcium 

oxide. However, all analyses are within ranges 

typical of continental-margin calcalkaline 

volcanoes. 

Gas sampling downwind of a volcano, when 

done on a regular basis, can indicate an impending 

eruption through changes in levels of so2 and C02 (Harris and others, 1981; Casadevall and others, 

1983). Pre-eruption measurements at Augustine 

are not available; but on April 3, Rose and others 

(1987), using a plane equipped with a correlation 

spectrometer (COSPEC) and flying at the margins 

of the plume, measured a sulfur dioxide (S02) 

emission rate of 24,000 tonnes per day (one of tl'ie 

highest rates ever recorded from an erupting 

volcano) and estimated hydrogen chloride (HCl) 

emission at 6,000 t/d. By contrast, at Mount St. 

Helens on May 25, 1980, seven days after the 

catastrophic May 18 eruption, so2 emission rates 

were 2,500 t/d (Casadevall and others, 1981). By 

July 24, so2 emission at Augustine had dropped to 

380 t/d (Symonds and others, 1987). Acidic 

volcanic gases containing chlorine, bromine, 
Figure 6.--View east toward new dome in summit crater, September 9, 1986. Western crater rim is in 

foreground, east shore of island in background. 

15 

40 IlJJ 

lJJ 

u_ 

~ 10 

~ 30 lJJ 

Ien lJJ 

0 ::;; 

z 0 

~ 20 --' 

-

~ 

::::> 5 0 

J: 

I10 

March 27 March 28 March 29 March 30 March 31 

Figure 7.--Height of observed explosive eruption plumes from summit vent (elevation 1,227 m) of 

Augustine Volcano during March 27-31. All times are Alaska Standard Time. Nighttime hours shaded, lack 

of eyewitness observations accounts for apparent lack of explosive eruptive plumes during nights. Large 

explosive bursts of comparable magnitude were not observed during April and August eruptive episodes. 

8 

en 

a: 

lJJ 

IlJJ 

::;; 

0 

--' 

l<: 
Burr Point 

& summi t 

0 100 200 KILOMETERS 

Figure 8.--General direction of winds at 1,470-m (4,500-ft) level during period March 27-31 as estimated 

from National Weather Service charts based on winds-aloft data from Anchorage, King Salmon, Kodiak, 

and McGrath. Explosive eruption plumes of up to 12,200 m were influenced by directions of higher level 

winds. 

9 
Figure 9.--Satellite image of eruption plume taken 5:18 A.M. AST, March 28, showing narrow ash plume 

extending from Augustine across Kenai and Tyonek toward Skwentna. Westward bend in plume resulted in 

less ashfall in Anchorage than would otherwise have occurred. 

fluorine, and sulfur which vented both during and 

following the eruptive episodes were dispersed and 

diluted downwind, posing no significant health 

threat except perhaps on Augustine Island. Heavy 

rainfall during the August episode was probably 

highly acidic in the immediate vicinity of the 

mountain, accounting for the marked destruction 

of brush on the volcano's slopes noted in early 

September. 

Effects of the eruptions on south-central Alaska 

Because Augustine is a remote, uninhabited 

island, effects of its 1986 eruptions on the 

population centers of Cook Inlet are limited to two 

main categories: those resulting from ash and 

those resulting from the threat of a tsunami. 

Airborne ash disrupted air traffic in south-central 

10 

Alaska, especially in the upper Cook Inlet basin 

from March 27 to 30. The Federal Aviation 

Administration issued Notices To Airmen 

(NOT AMS) warning of the hazard and restricting 

flights around the volcano. Most commercial and 

general aviation flights were either canceled or 

diverted to airports away from the affected area 

as ash stagnated in the atmosphere over Cook 

Inlet. On March 28, when Anchorage International 

Airport would ordinarily have handled 300 flights, 

16 flights were served (The Anchorage Times, 

March 29, 1986). Military aircraft stationed at 

Elmendorf Air Force Base were deployed to other 

bases during the period March 27-30. By March 

31, as the atmosphere around Anchorage cleared, 

aircraft schedules were resumed. Despite these 

precautions, slight damage to aircraft was 

reported. For example, on March 29, a DC-1 0 on 
Figure 10.--Ash cloud over Anchor Point on March 

31, 1986. This remarkable ash plume, resulting 

from final large explosive event at 10:00 A.M. 

AST, dropped approximately 2-3 mm of ash on 

Anchor Point and Homer (analyses 5 and 6, table 

1). Similar billowing clouds of ash were seen over 

eastern Washington following 1980 eruption of 

Mount St. Helens (see Findley, 1981). Use of 

photograph by permission of photographer Linda 

Sandlin is gratefully acknowledged. 

descent into Anchorage flew through a cloud of 

disseminated ash, causing minor damage to engine 

parts and light frosting of its windshield. 

During the first few days of eruption, radio 

stations and newspapers advised residents of 

potential ashfall hazards and how to mitigate 

them. Early predictions of significant ashfall in 

Anchorage prompted concern about electrical 

generating capabilities because generator turbines 

11 

sustained minor abrasion and loss of power during 

the 1976 eruption. Chugach Electric Company 

requested the public to curtail unnecessary 

electrical use on March 27 in anticipation of a 

possible shortfall in power supply due to shutdown 

of t he turbines. Employers responded by sending 

workers home early and shutting down computers 

and other machines sensitive to ash abrasion; a 

13 percent drop in electrical consumption resulted 

(The Anchorage Times, March 29, 1986). On 

March 28," Anchorage municipal health officials 

measur ed airborne particulates in concentration~ 

of up to 862 micrograms per cubic meter, 13 llg/m 

short of a health emergency if sustained for 24 

hours (The Anchorage Times, March 29, 1986). 

Because of the potential for a tsunami in 

lower Cook Inlet, State and local emergency 

management personnel reviewed and revised 

Table I.--Chemical composition of airborne ash 

samples from Augustine Volcano, Alaska 

[Analyses do not represent magma chemical 

composition because larger and denser particles 

drop out of an ash cloud first due to eolian sorting 

and ash samples include rock particles from 

previous eruptions from the vent walls. ~ajor 

element analyses by XRF; analysts: Tom Frost, 

Stuart MacPherson, L.F. Espos, B.W. King, Sarah 

Neil, Lois Schlocker; Rb and Sr analyses by Kevex 

XRF, analyst: Bruce Gamble] 

weight percent 

Si 20 65 . 8 66.8 64 . 0 67.9 64.9 64.6 64.3 63 . 6 63 . 1 

Al 2o 3 15 . 5 15.5 16.2 15 . 2 16 . 1 16 . 0 16.2 16 . 4 16.7 

Fe 2o3 2 . 08 1. 74 1.91 1. 75 1.60 1.66 1.50 2 . 31 2.58 

FeO 2 . 09 1.96 2.44 1. 74 2.61 2 . 58 2. 88 2.48 2. 61 

MgO 1.8 1.7 2.3 1. 30 2 . 0 2.1 2.1 2.27 2.65 

CaO 5. 14 4 . 90 5.25 4 . 14 5 . 55 5 . 50 5.60 5 . 84 6 .41 

Na2o 3.9 3 . 6 3.5 3. 8 3.5 3 . 7 3. 6 3.82 3. 5 1 

K20 1.50 1. 50 1. 30 · 1. 62 1. 30 1. 30 1.25 1:23 1. 04 

H20+ . 35 . 24 . 71 .26 . 14 .1 6 . 19 . 18 .16 

H2o- . 06 .08 .05 < .01 . 12 .09 .14 .12 .06 

Ti02 . 53 . so . 56 . 49 .53 .54 . 55 .59 .62 

P2os .20 .20 .25 . 18 . 23 . 23 .23 .15 .1 5 

NnO .09 .09 . 09 .08 .09 .09 . 09 .09 .1 0 

co2 . 70 . 39 1. 79 . 2 1 < . 0 1 < . 01 < .01 .06 . 08 

Cl . 095 .1 5 .091 .16 .12 .1 1 . 10 . 14 . 07 

.02 .02 . 02 .02 .02 . 02 . 02 

Total S .03 .06 . 06 < . 01 . 12 .1 2 .12 .1 6 . 04 

Parts per million 

Rb 31 29 30 33 29 29 28 

Sr 260 257 282 239 296 306 296 

Rb/Sr .11 9 .113 .106 . 138 . 098 . 095 . 094 

No t es : da t e and pl ace collected , collec t or, comments: 

1-- March 28, 1986, Anc horage , John Decker 

2--March 29, 1986 , Drif t River , f rom deck of o il l oading platform 

3-- March 29 , 1986, A. M., Sewa r d , R. Folge r , overnigh t airfall on 

cars 

4 --Ma r ch 31, 1986 , 8 A . M. AST , Anc horage, Br uce Gamb l e 

5--March 3 1, 1986 A.M ., Home r, Joe Ga ll ega r 

6- -Ma rch 31, 1986 , A.M. , Homer , Deena Benson 

7--April 3, 1986, Home r a i r po rt, FAA- FSS pe rsonne l f r om porch 

raili ng 

8--J anuary 25 , 1976 , Anc hora ge , Tom Miller 

9- - 1976 , Knu tson Bay (Iliamna quadrangl e) , Bru c e Reed 
evacuation plans for residents of low-lying areas. 

This was particularly important because the April 

eruptive episode occurred on a weekend during one 

of the lowest spring tides of the year, when 

several thousand people would normally be digging 

clams on the beaches along the eastern side of 

Cook Inlet. Although no attempt was made to 

restrain public access to the beaches, the Alaska 

Division of Emergency Services and the Kenai 

Peninsula Borough Emergency Management Office 

broadcast radio and television warnings advising 

people of the potential hazard. Other effects due 

to the threat of a tsunami included delay of a 

liquid-natural-gas tanker scheduled for loading at 

Kenai until after the eruption was over. 

The April eruptive episode coincided with 

local fishing season in the . shallow waters 

immediately surrounding Augustine Island. Since 

some of the larger pyroclastic flows generated 

during the March eruptive episode reached the 

ocean, mariners were kept advised of the progress 

of the eruption through broadcast messages from 

the U.S. Coast Guard. Alaska Fish and Game 

personnel were prepared to close the fishing 

season should the hazard become high, but this was 

not deemed necessary. 

Conclusion 

The 1986 eruptions of Augustine Volcano 

have tested and strengthened the volcanic eruption 

monitoring and response capabilities of federal and 

State officials in Alaska. Although damage due to 

airborne ash was minimized by its distribution 

pattern and the response of airline and charter 

aircraft operators, effects of future ashfalls may 

be quite different. Based on ash deposits from 

Cook Inlet volcanoes preserved in sediments over 

the last 10,000 years (Riehle, 1985), inhabitants of 

the Cook Inlet region can expect to be confronted 

with a measureable ash eruption on the average of 

every 30 years. Although no tsunami resulted 

from its 1986 eruptions, tsunamis are a major 

potential .hazard during future eruptions of 

Augustine Volcano. 

REFERENCES CITED 

Beget, James, 1986, Prehistoric tephra eruptions, 

debris avalanches, and tsunamis at Mt. St. 

Augustine--The geologic record (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1260. 

Blong, R.J., 1984, Volcanic hazards, a sourcebook 

on the effects of eruptions: Sydney, 

Academic Press, 424 p. 

12 

Casadevall, T.J., Johnston, D.A., Harris, D.M., 

Rose, W.I., Jr., Malinconico, L.L., Stoiber, 

R.E., Bornhorst, T.J., Williams, S.N., 

Woodruff, Laurel, and Thompson, J.M., 1981, 

so2 emission rates at Mount St. Helens from 

March 29 through December, 1980: U.S. 

Geological Survey Professional Paper 1250, 

p. 193-200. 

Casadevall, T.J., Rose, W.I., Jr., Gerlach, T.M., 

Greenland, L.P., Ewart, J., Wunderman, R., 

and Symonds, R.B., 1983, Gas emissions and 

the eruptions of Mount St. Helens through 

1982: Science, v. 221, p. 1383-1385. 

Davidson, George, 1884, Notes on the volcanic 

eruption of Mount St. Augustin, Alaska, Oct. 

6, 1883: Science, v. 3, no. 51, p. 186-189. 

Findley, Rowe, 1981, St. Helens: National 

Geographic, v. 159, no. 1, p. 3-65. 

Harris, D.M., Sato, Motoaki, Casadevall, T.J., 

Rose, W .I., Jr., and Bornhorst, T.J., 1981, 

Emission rates of co2 from plume 

measurements: U.S. Geological Survey 

Professional Paper 1250, p. 201-207. 

Kienle, Juergen, Davies, J.N., Miller, T.P., and 

Yount, M.E., 1986, 1986 eruption of Augustine 

Volcano: Public safety response by Alaskan 

volcanologists: Eos (American Geophysical 

Union Transactions), v. 67, no. 29, p. 580-582. 

Kienle, Juergen, and Swanson, S.E., 1983, The 

hazards of Augustine: The Northern Engineer, 

v. 15, no. 3, p. 10-14 and 30-37. 

----- 1985, Volcanic hazards from future eruptions 

of Augustine Volcano, Alaska: Fairbanks, 

University of Alaska, Geophysical Institute 

Report UAG R-275, 122 p. 

Miller, T.P., Yount, M.E., and Nelson, S.W., 1987, 

Pyroclastic flow characteristics during the 

initial phase of the 1986 eruption of Augustine 

Volcano, Alaska (abs.): Hilo, Hawaii, 

Abstracts of the Hawaiian Volcano 

Observatory Diamond Jubilee, p. 175. 

Riehle, J.R., 1985, A reconnaissance of the major 

Holocene tephra deposits in the upper Cook 

Inlet region, Alaska: Journal of Volcanology 

and Geothermal Research, v. 26, p. 37-74. 

Rose, W .I., Jr., Heiken, G.H., Wohletz, K.H., 

Eppler, D., Barr, S., Miller, T., Chuan, R.L., 

and Symonds, R.B., 1987, Direct rate 

measurements of Mt. St. Augustine eruption 

plumes: A problem of scaling up and 

uncontrolled variables (abs.): Hilo, Hawaii, 

Abstracts of the Hawaiian Volcano 

Observatory Diamond Jubilee, p. 212. 

Siebert, Lee, Glicken, Harry, and Kienle, Juergen, 

1986, Debris avalanches and lateral blast at 

Mount St. Augustine Volcano, Alaska (abs.): 

Eos (American Geophysical Union 

Transactions), v. 67, no. 44, p. 1259. 
Symonds, R.B., Rose, W .I., Jr., Reed, M.H., Briggs, 

Paul, and Gerlach, T.M., 1987, The speciation 

and fluxes of gases from Augustine Volcano, 

Alaska: A system rich in halides and 

transition metals (abs.): Hilo, Hawaii, 

Abstracts of the Hawaiian Volcano 

Observatory Diamond Jubilee, p. 247. 

13 

Yount, M.E., and Miller, T.P., 1987, The April1986 

eruptive phase of Augustine Volcano and 

associated hazards (abs.): Hilo, Hawaii, 

Abstracts of the Hawaiian Volcano 

Observatory Diamond Jubilee, p. 276. 

Reviewers: S. W. Nelson and J.R. Riehle 
STATEWIDE 

Abandoned gold dredge on Harris Creek, Seward Peninsula. 

Photo by Warren Yeend. 

Alaska Gold Company dredge mining gold from a buried beach deposit near Nome. 

Photo by Warren Yeend. 

14 
STATUS OF ALASKA 

MINERAL RESOURCES DATA SYSTEM 

Kenneth R. Leonard and Donald F. Huber 

The Mineral Resources Data System (MRDS) 

is a computerized file of information pertaining to 

metallic- and nonmetallic-mineral deposits and 

occurrences in the United States and worldwide. 

MRDS stores information about the location and 

economic geology of each deposit or occurrence in 

a record consisting of about 140 individual 

parameters. Data may be searched using any 

selected parameter stored in a given record and 

retrieved using interactive access. Highly 

selective searches allow the user to filter out 

unwanted data in order to focus on specific 

information. 

The Alaska portion of MRDS is composed of 

two separate data sets: (1) an older set of more 

than 4,000 records containing limited commodity 

and location information, and (2) a newer set of 

records intended to expand and replace the older 

records. The current phase of Alaska MRDS work 

has generated 2,051 new records covering 40 

1:250,000-scale quadrangles, mainly in southcentral and southeastern Alaska (fig. 1). The 

records contain available data on location, 

commodities, ore minerals, analytical results, 

exploration and development history, deposit type, 

deposit size and description, geology, production, 

reserves, and pertinent literature. Records vary in 

the amount of information they contain, mainly 

due to variations in the availability of data. Much 

more detailed information is generally available 

for a major mine than for a small prospect or 

mineral occurrence. Alaska MRDS records focus 

on metallic-mineral commodities. Nonmetallicmineral commodities, except for asbestos, barite, 

and important radioactive minerals, are generally 

excluded. New additions are made on the basis of 

1:250,000-scale quadrangle areas with the 

objective of expanding the data base to cover the 

entire State by the end of fiscal year 1987. 

Funding for current Alaska MRDS work is provided 

through the Federal Land Information System 

program managed by the National Mapping 

Division of the U.S. Geological Survey. 

To provide a preliminary overview of the 

important mineral deposits of Alaska, a separate 

file containing only those records for major mines 

and prospects was created. There are currently 

111 records distributed in 50 quadrangles in this 

Major Deposit File. 

Data for the Alaska MRDS records have been 

integrated from a variety of sources, including 

published and unpublished geologic literature. 

Most of the data are derived from a series of 

bibliographies compiled by E.H. Cobb and others 

and published as USGS open-file reports (see Cobb, 

1978). Each bibliography contains data summaries 

15 

and lists of references for discrete mineral 

localities within a specific area of Alaska, 

generally a 1:250,000-scale quadrangle or group of 

quadrangles. The compilations primarily cover 

historically important mining districts, with less 

emphasis on recently active prospects, and are 

drawn mainly from publications of the U.S. 

Geological Survey, U.S. Bureau of Mines, and 

Alaska Division of Geological and Geophysical 

Surveys (now called the Alaska Division of Mining 

and Geology). These data have been expanded and 

updated with information from resource 

assessments prepared for the Regional Alaska 

Mineral Resource Assessment Program (RAMRAP) 

and the Alaska Mineral Resource Assessment 

Program (AMRAP). The AMRAP data sets are 

incorporated into MRDS as they become 

available. Other sources for Alaska MRDS include 

1) unpublished information and non-confidential 

private reports residing in USGS files, 2) M.S. and 

Ph.D. theses, 3) news items culled from mining 

industry journals, and 4) personal communications 

with USGS geologists familiar with specific areas 

of Alaska. 

Locations are recorded in latitude and 

longitude and, in some instances, also in township 

and range coordinates. Recorded locations are as 

accurate as possible within the constraints of the 

available information. No records have been made 

for sites that cannot be located to within a 1-mile 

(1.6-km) radius. A location is designated as 

"accurate" if its position is known to within 500 ft 

(150 m). Generally, this requires that the site has 

been plotted on a large-scale topographic map, 

preferably a USGS base map, or that an 

unambiguous location is corroborated by more than 

one reference source. Most locations are recorded 

as "estimated" and a distance of accuracy is 

given. In some cases, site locations may be 

available only on small-scale maps in which the 

symbol used for the site covers a large area. 

These sites are taken as the center of the symbol 

used to represent them and are given large 

distances of accuracy. Placer deposits, which 

often cover a large area or considerable length 

along a stream, are given an "estimated" location 

with coordinates for a reference point reported in 

the record. 

Consistency in quality and detail is one of 

the principal problems found in any data 

compilation. This is attributable to variations in 

the original data, as well as to differences 

between individual contributors. Alaska MRDS 

records have been compiled by a small number of 

reporters compared to data sets for many of the 

other states, and all new entries are consistent 

with the revised format for MRDS as outlined by 

Huber (1981) and Koch (1984). Individual entries 

for the Alaska MRDS are based on compilations of 

information gathered from various sources and 

presented in summary form. MRDS records are 
..... 

0) 

~ "-,_ '-, 

' 

,jl 0 0 "'"'T1SUIIDS 

~ 

• 

~ 

Not 

Shaded 

EXPLANATION 

Revhed an~ updated recorda completed. 

Currently available on MRDS. 

Reviled and updated recorda completed. 

Currently being entered into databaae . 

Priority quadra:a.glu tentatively acheduled 

for tint half of FY 1987 . 

Updated recorda not yet completed. 

Older record• may be available . 

0 100 200 300 

Kilometer& 

Figure 1.--Status of Alaska Mineral Resources Data System by quadrangle as of the end of fiscal year 1986. 

•J 
135"W 

56"N,------------.------------~------~----~~--~~----,-----~~----.-,-----~--~ 

0 () G ~p!?igenia Bay 

30 

Figure 2.--Computer-generated map of Craig, Alaska 1 x 3 degree quadrangle showing MRDS record 

locations. Coastline boundaries are approximate. 

not meant to supplant the geological literature, 

but are primarily a means of storing, manipulating, 

and retrieving site-specific information. 

Researchers interested in more detailed geological 

information are directed to consult the references 

documented in the database. 

MRDS records provide Federal, State, and 

mineral industry geologists with a readily 

accessible reference source of known or 

potentially locatable mineral resources. MRDS 

also serves as a research tool in the development 

of regional mineral resource assessments, gradetonnage and descriptive deposit models, and 

regional metallogenic studies. MRDS data can be 

easily integrated with other digital data using a 

geographic information system to produce map 

plots showing various relationships, such as the 

number of gold deposits associated with a 

particular rock unit within an area of mineral 

potential. The data base is particularly well suited 

to the rapid production of mineral 

deposit/occurrence spot maps for use in 

exploration or as a means of providing researchers 

with background information on known mineral 

deposits within unfamiliar study areas. 

MRDS resides on the USGS Branch of 

Resource Analysis' PRIME minicomputer which 

uses a modern relational database management 

17 

system called INFORMATION. A compatible 

version of MRDS known as MRDS-REV has been 

developed for use on microcomputers using a data 

base management system called REVELATION 

(Schruben, 1985). Retrieval output is available in 

the form of computer text for entire records or 

sections of records, tabulations of data, or map 

plots for selected areas (fig. 2). 

The Alaska MRDS data set is intended to 

complement other computerized resource files 

that contain information on water and geothermal 

resources, organic fuels, industrial minerals, and 

construction materials (Office of the Data 

Administrator, 1983). Information on the 

economic parameters of mineral resource 

production is available in the U.S. Bureau of Mines' 

Mineral Availability System (MAS), which contains 

fairly detailed data on well-known deposits (U.S. 

Bureau of Mines, 1974). The Mineral Industry 

Location System (MILS), a location subsystem of 

MAS, is similar to MRDS in coverage but contains 

limited geologic data (Berg and Carillo, 1980). 

MAS and MILS data on Alaska are available 

through the U.S. Bureau of Mines, Alaska Field 

Operations Center, P.O. Box 550, Juneau, Alaska 

99802. Mining claims information is available in 

the Alaska Division of Geological and Geophysical 

Surveys' KARDEX file, maintained on cards at the 
Division's Fairbanks Office, 794 University 

Avenue, Fairbanks, Alaska 99701. The KARDEX 

file is the basis for the University of Alaska's 

MINFILE, a computer-processable storage and 

retrieval system developed by the Mineral Industry 

Research Laboratory at the University of Alaska, 

Fairbanks (Heiner and Porter, 1972). 

Information regarding public access to MRDS 

files can be obtained by contacting one of the 

following regional MRDS representatives: 

Antoinette A. Medlin 

Eastern Region Representative 

U.S. Geological Survey, MS 920 

12201 Sunrise Valley Drive 

Reston, VA 22092 

703-648-6136 

Donald F. Huber 

Central and Western Region Representative 

U.S. Geological Survey, MS 984 

345 Middlefield Road 

Menlo Park, CA 94025 

415-329-5358 

REFERENCES CITED 

Berg, A.W., and Carillo, F.V., 1980, MILS: The 

mineral industry location system of the 

Federal Bureau of Mines: U.S. Bureau of 

Mines Information Circular 8815, 24 p. 

Cobb, E.H., compiler, 1978, Summary of 

references to mineral occurrences (other than 

fuels and construction minerals) in the Juneau 

quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 78-374, 156 p. 

18 

Heiner, L.E., and Porter, E., 1972, A computer 

processable storage and retrieval program for 

Alaska mineral information: Fairbanks, 

University of Alaska, Mineral Industry 

Research Laboratory Report 24, v. 1, 145 p. 

Huber, D.F., 1981, Mineral data system, 

computerized resources information bank, 

U.S. CRIB-site form, instructions for 

reporters: U.S. Geological Survey unpublished 

instruction manual. 

Koch, R.D., 1984, Guidelines for compilation of 

Alaska mineral deposit data for entry into 

MRDS: U.S. Geological Survey unpublished 

instruction manual. 

Office of the Data Administrator, compiler, 1983, 

Scientific and technical, spatial, and 

bibliographic data bases and systems of the 

U.S. Geological Survey, 1983, including other 

Federal agencies (revised ed.): U.S. 

Geological Survey Circular 817. 

Schruben, P.G., 1985, MRDS-REV, A mineral 

occurrence/deposit data base for 

microcomputer: U.S. Geological Survey OpenFile Report 86-34, 57 p. 

U.S. Bureau of Mines, 1974, The Bureau of Mines 

minerals availability system and resource 

classification manual: U.S. Bureau of Mines 

Information Circular 8654, 199 p. 

Reviewers: D.A. Brew and W .D. Menzie 
THE ANIAKCHAK TEPHRA DEPOSIT, 

A LATE HOLOCENE MARKER HORIZON 

IN WESTERN ALASKA 

James R. Riehle, Charles E. Meyer, 

Thomas A. Ager, Darrell S. Kaufman, 

and Robert E. Ackerman 

We describe here a Holocene tephra 

(volcanic ash) deposit that, because of its 

widespread occurrence, ready identification, and 

approximately known absolute age, should prove to 

be a useful stratigraphic marker throughout 

western Alaska from the Alaska Peninsula north to 

at least the Seward Peninsula. Moreover, the 

deposit is of interest because we have identified 

its source in the caldera-forming eruption of 

Aniakchak Crater, in the Aleutian volcanic arc on 

the Alaska Peninsula (fig. 1). 

Our analyzed tephra samples are from four 

distal sites--three around Norton Sound and one in 

southwestern Alaska --and three proximal sites on 

the Alaska Peninsula near the source at Aniakchak 

Crater (fig. 1). The distal samples are uniformly 

fine-grained and, where not contaminated, consist 

almost entirely of glass (table 1). Megascopically, 

the glass fragments are clear to pale gray to solid 

or streaked brown. Particles composing the distal 

samples have variable shapes that include bubblewall platelets, fibrous pumice, and equant blocks 

(fig. 2). In most tephra deposits, the ratio of glass 

(nonporous density 2.~-2.5 g em -3) to minerals 

(density >2.56 g em- ) normally increases with 

increasing distance of transport, as for example in 

the May 18, 1980 eruption of Mount St. Helens 

(Sarna-Wojcicki and others, 1981). Thus, the ratios 

of glass to the phenocryst phases are not a 

quantitative basis for correlation among samples. 

However, all of our proximal and distal samples 

are remarkably similar to one another, and are 

distinguishable from other tephra samples from 

the Alaska Peninsula (J.R. Riehle, unpub. data) 

except for the rhyolitic ash of the 1912 Katmai 

eruption (Hildreth, 1983), on the basis of their 

large proportion of glass. The mineral content of 

the samples (plagioclase > orthopyroxene > 

clinopyroxene = amphibole > opaques = apatite = 

zircon [?]) is not unique among tephra deposits of 

the Alaska Peninsula. 

Glass separates have been analyzed by 

microprobe for nine major elements (table 2). To 

compare the degree of similarity of different pairs 

of samples we use a similarity coefficient, s.c. 

(Borchardt and others, 1972), which is the 

averaged ratio of all pairs of oxides (normalized to 

100 percent) where the lesser oxide is the 

numerator. Because analytical uncertainty is 

inversely proportional to concentration, we 

exclude from calculation of the s.c. any oxide 

occurring in concentrations less than an arbitrary 

0.40 percent (MnO, occasionally MgO and Ti02). 

A perfect match of 1.00 is not expected even 

19 

where comparing duplicate analyses of the same 

sample because the average standard deviation of 

the oxides is about 5 percent. Riehle (1985) 

concluded that tephra samples from elsewhere in 

the Aleutian arc are provisionally the same 

deposit, that is, the same fall of tephra, if their 

similarity coefficient exceeds 0.95. He 

interpreted an s.c. of 0.94 or 0.95 to indicate that 

sample pairs are either of different falls of 

coincidentally similar tephra, or may be the same 

tephra fall where analysis of one or more oxides 

was less reliable than usual. Similarity 

coefficients less than 0. 94 were interpreted to 

preclude correlation as the same tephra fall. We 

adopt the same interpretations here. 

Samples of the ash-flow tuff produced during 

formation of Aniakchak Crater, and of the 

antecedent proximal airfall deposits (fig. 3), are 

highly similar (each s.c. >0.95) to one another and 

to each of our distal samples except for the 

sample from site 4 (table 3). The lower similarity 

coefficients for sample 4 are mainly due to a 

single oxide, Ti02 (table 2), which is only 

marginally significant due to its low abundance. 

Because the approximate age and petrographic 

character of sample 4 are similar to those of the 

other distal samples, we still consider it a 

160 

66 

64 

Yukon 

62 

delta 

5 X 111-21 cml 

• 

58 

156 152 

EXPLANATION 

+2 S lte of analyzed 

tephra sample 

9X Site of tephra deposit 

not sampled for analysis 

* Anlakchak Crater 

'Approximate eastern 

,' limit of known tephra 

0 Aniakchak ash-flow 

deposit (from Miller 

and Smith. 1977) 

4 + (2-5 cml 

Figure 1.--Sites in western Alaska where late 

Holocene tephra deposit of Aniakchak Crater has 

been sampled. Thickness of deposit is given at 

distal sites in parentheses and is known to include 

some reworked tephra at sites 5 and 6. 
correlative. Of 130 samples of other tephra 

deposits from the Alaska Peninsula (J.R. Riehle 

and C.E. Meyer, unpub. data), none have a 

similarity coefficient that is greater than 0.94 

with any of these distal samples. Because two to 

four tephra deposits (beds) can be recognized at 

the proximal sites (see fig. 3), the distal samples 

may be a composite of the deposits of two or more 

tephra falls. 

Black glass shards handpicked from the 

sample at site 6 for microanalysis have a 

composition similar to lithic clasts of black 

vitrophyre in tephra deposits that immediately 

overlie and underlie Aniakchak deposits at site 1 

(fig. 3; table 3, "vitrophyre"). The vitrophyre may 

be accessory to the Aniakchak eruptions or it may 

be contamination from nearly contemporaneous 

eruptions. Black glass in rare amounts was 

tentatively identified in the other distal samples 

and provides another criterion for recognition. 

20 

Figure 2.--Representative scanning electron 

micrograph of distal tephra samples of Aniakchak 

Crater. A, Blocky equant clast with a few coarse 

vesicles (upper right), curving platelets (lower 

right and upper left), and fibrous pumice (center); 

site 6. B, Bubble-wall junction (center) from 

which curving platelets in all samples are derived; 

site 7. C, Fibrous pumice (top right), equant 

blocks (center), and curving platelets (center of 

left margin); site 4. Occurrence of equant clasts 

with a few coarse vesicles and with adhering 

microparticles may indicate phreatic component 

of eruption (see Heiken and Wohletz, 1985). 

Photographs taken by Effie Shaw. 

Radiocarbon ages indicate that the 

Aniakchak tephra deposit is of late Holocene age. 

The age of the Aniakchak ash-flow deposit that 

overlies the tephra deposits at proximal sites 2 and 

3 (fig. 3) was originally estimated as 3,300-3,700 

yr (Miller and Smith, 1977). Three samples of 

wood contained in the ash-flow deposit now yield a 

Table !.--Petrographic descriptions of proximal 

and distal tephra samples, Aniakchak calderaforming eruption 

Proximal deposits 

IC: white t o tan pumice and scoriaceous dark glass; mineral abundances 

not determined 

11:':: fibrous, clear to ran pumice; trace of brown microvesicular glass and 

dense gray vitrophyre; 96 4 g lass, 24 plagioclase , 2% mafics by weight 

2~1 : like sample IE 

JF: like sample 11::; 97% glass , 1.5% plagioclase, 1.5% mafics by weight 

3G : like sample IE 

31: dominantly white pumice; rare scoriaceous glass and dense bl ack 

vitrophyre; mineral abundances not determined 

Distal deposits 

4: clear to pale gray glass and fibrous white pumice; trace pale g r ey to 

medium brown scoriaceous glass; r a r e fine black fr agments may be black 

glass shards; estimated 98% glass, remainder is plagioclase and 

pyroxene>amp hi bole)opaques•apat i te•z 1 rcon(?) 

6: like sample 4 

8: like sample 4 

7H: dominantly clear to pale gray glass with some brown streaks; clast 

shapes range from fibrous pumice to curving platelets; estimated 99% glass, 

remainder is plagioclase and pyroxene>amphibole>opaque•apatite•zi r con(?) 
weighted mean age of 3,430 yr (T.P. Miller, USGS, 

written commun., 1986). 

A maximum limiting age for our distal 

sample 8 is 4,000 ± 100 yr B.P. (1-13,990); an 

unanalyzed sample from site 9 petrographically 

resembles the other Aniakchak samples and is 

bounded by ages of 2,400 ± 80 yr B.P. (Beta 7760) 

and 3,340 ± 90 yr B.P. (Beta 7761) {Kaufman and 

Hopkins, 1985). Our analyzed sample 6 is from 

lake sediments cored on St. Michael Island; 

lacustrine sediments in the interval from 0 to 11 

em above the tephra deposit yielded a date of 

4,830 ± 80 yr B.P. {W 4929) and the interval from 0 

to 10 em below yielded a date of 6,430 ± 90 yr B.P. 

{W 4625) (Ager, 1983). A similar tephra deposit at 

site 5 (Tungak Lake) has not been chemically 

analyzed but is correlated with the Aniakchak 

deposit on the basis of petrographic similarity; the 

12-cm interval immediately overlying the tephra 

deposit yielded a date of 3,400 ± 750 yr B.P. (W 

3776) and the interval from 13 to 44 em below the 

tephra deposit yielded a date of 5,645 ± 250 yr 

B.P. (W 3934) {Ager, 1982). The sample from site 

4 contains partially to completely charred wood, 

which may have been mixed by cryoturbation from 

an overlying horizon; it yielded a date of 3,684 ± 

98 yr B.P. (WSU 2759). 

If the available radiocarbon data are taken 

at face value, then the distal tephra deposits must 

span 3,000 years. The apparent lack of soils or 

erosional contacts between the proximal airfall 

deposits, however, weighs against such a 

hypothesis (see fig. 3). Moreover, tephra deposited 

on the Seward Peninsula must be a major 

component of the deposits on St. Michael Island 

because these sites are in line with Aniakchak 

Crater; thus, the ages of the Seward Peninsula and 

St. Michael deposits may differ from the age of 

the ash-flow deposit, but they should themselves 

be identical or at least overlap. Clearly the ages 

do not overlap, and consequently we cannot accept 

Table 2.--Composition of glass separates 

[Analyses by electron microprobe; analysts, C.E. 

Meyer and J.R. Riehle. FeO* is total iron 

reported as FeO. One standard deviation as 

percentage of reported abundance is given in 

parentheses. For brevity, compositions of 

proximal samples are not reported here but are 

available from the authors] 

Ox ide 78 

Si 02 69.9 ( 0. 9 69.9 ( 0.9) 

Al ?03 14.92 (3.1 15.03 (3.1) 

Feb* 2.34 (3.5 2.14 ( 3.5) 

t~gO .49 ( 6. 9 .51 (6. 7 I CaO 1.71 (2 .0 l. 7 2 (2 .0) 

Na?O 5.19 ( 3.4 5.13 (3 .4) 

K)l 2. g 1 (1.8 2. 95 ( 1.8) 

TiOo .46 ( 12) .45 (13) 

Mno" .14 (20) .lS ( 19) 

Tota 1 98.1 98.1 

pumice 

70.1 (0 .9) 

14.58 (3.1) 

2.39 (3 .4) 

.50 ( 6. 7) 

1.72 (2 .a I 5.38 ( 1.0 I z.g1 (1.8) 

.46 (13) 

.13 ( 22) 

98.2 

6 

black glass 

57.1 0 .9) 

15.97 3.1) 

7.16 :.4) 

~?. 92 2. 9) 

6.00 l. 3) 

4.49 3.11 

l. 50 2.2) 

1.34 6. 6) 

·"0 16) 

96.7 

69.7 (2 .1 I 14.31 ( 3. 5) 

2.49 (4 .8) 

.47 (5 .0) 

1.69 (6 .4) 

5.04 ( 3.2) 

2. 97 (5 .1) 

.58 ( 10) 

.13 ( 25) 

98.2 

Table 3.--Similarity coefficients among distal and 

proximal samples, Aniakchak tephra deposits 

[-- , no data] 

Proxima 1 samp 1 es 

Distal 

samples lC lE 2M 

7B 0.97 0.97 0.98 

.96 .96 .98 

6. .96 .97 . 97 

pumice 

4 .95 .95 .95 

6. black glass 

I 5 em 

M 

EXPLANATION 

~Tephra deposit lbedl 

3F 3G 

0.96 0.97 

.96 .97 

.96 .97 

.93 .96 

2 

Site number; locations on fig. 1 

(M Aniakchak pyroclastic deposits; 

sampled beds labelled by letters 

e Analyzed sample to which distal 

samples correlate lsee text) 

(vi trophyre) 

3 I lE lJ 

0.98 

.98 

.97 

.95 

0.98 0.96 

3 

Figure 3.--Geologic sections at proximal sites 

where Aniakchak ash-flow deposit and underlying 

tephra deposits have been sampled. Nonpyroclastic deposits are loess or peat. 

21 
the radiocarbon ages from the distal sites at face 

value. One of several possible sources of error is 

that the lacustrine sediments at site 6 contain 

older reworked organic material. If the ages from 

site 6 are deleted, then the remaining ages limit 

the tephra deposit to between 3,400 yr B.P. and 

about 4,000 yr B.P. In conclusion, the lack of 

evidence for any hiatus between the proximal 

airfall deposits suggests that the age range is no 

more than a few hundred years, from about 3,400 

yr to perhaps 4,000 yr. We cannot rule out an age 

range of as much as 3,000 years for these tephra 

deposits, however, and additional dating of 

samples from western Alaska would help to 

confirm this provisional age assignment. 

In summary, the Aniakchak tephra deposit is 

sufficiently thick to be readily identified where 

preserved in late Holocene deposits that extend 

from its source at Aniakchak Crater north to the 

Seward Peninsula. The deposit may be 

recognizable even north of the Seward Peninsula 

by a high ratio of glass to phenocrysts (>98:2) and 

by the presence in rare amounts of (accessory?) 

black glass shards, but beyond the Seward 

Peninsula its fine grain size will probably make 

chemical analysis intractable. North of the Alaska 

Peninsula, the deposit is probably a mixture of the 

compositionally similar deposits of two or more 

tephra falls. The inferred age of the distal 

deposits ranges from a minimum of 3,400 yr, the 

age of the ash-flow deposit, to probably no more 

than 4,000 yr. 

REFERENCES CITED 

Ager, T.A., 1982, Vegetational history of western 

Alaska during the Wisconsin glacial interval 

and the Holocene, in Hopkins, D. M., 

Matthews, J.V. Jr., Schweger, C.E., and 

Young, S.B., eds., Paleoecology of Beringia: 

New York, Academic Press, p. 75-93. 

22 

1983, Holocene vegetational history of Alaska, 

in Wright, H.E. Jr., ed., Late Quaternary 

environments of the United States, v. 2, The 

Holocene: Minneapolis, University of 

Minnesota Press, p. 128-141. 

Borchardt, G.A., Aruscavage, P.J., and Millard, 

H.T., Jr., 1972, Correlation of the Bishop ash, 

a Pleistocene marker bed, using instrumental 

neutron activation analysis: Journal of 

Sedimentary Petrology, v. 42, p. 301-306. 

Heiken, Grant, and Wohletz, Kenneth, 1985, 

Volcanic ash: Berkeley, University of 

California Press, 246 p. 

Hildreth, Wes, 1983, The compositionally zoned 

eruption of 1912 in the Valley of Ten 

Thousand Smokes, Katmai National Park, 

Alaska: Journal of Volcanology and 

Geothermal Research, v. 18, p. 1-56. 

Kaufman, D.S., and Hopkins, D.M., 1985, Late 

Cenozoic radiometric dates, Seward and 

Baldwin Peninsulas, and adjacent continental 

shelf, Alaska: U.S. Geological Survey OpenFile Report 85-374, 27 p. 

Miller, T.P., and Smith, R.L., 1977, Spectacular 

mobility of ash flows around Aniakchak and 

Fisher calderas, Alaska: Geology, v. 5, 

p. 173-176. 

Riehle, J.R., 1985, A reconnaissance of the major 

Holocene tephra deposits in the upper Cook 

Inlet region, Alaska: Journal of Volcanology 

and Geothermal Research, v. 26, p. 37-74. 

Sarna-Wojcicki, A.M., Shipley, Susan, Waitt, R.B., 

Jr., Dzurisin, Daniel, and Wood, S.H., 1981, 

Areal distribution, thickness, mass, volume, 

and grain size of air-fall ash from the six 

major eruptions of 1980, in Lipman, P. W ., and 

Mullineaux, D.R., eds., The 1980 eruptions of 

Mount St. Helens, Washington: U.S. 

Geological Survey Professional Paper 1250, 

p. 577-600. 

Reviewers: J.E. Beget and M.E. Yount 
NORTHERN ALASKA 

Syngenetic ice-wedges, Titaluk River, Arctic Coastal Plain. These long, narrow wedges grew upward 

during aggradation of the silt in which they occur. Photo by L.D. Carter, 1986. 

23 
GEOCHEMICAL AND GEOLOGIC CONTROLS 

ON THE INFERRED OCCURRENCE OF 

NATURAL GAS HYDRATE IN THE 

KUPARUK 2D-15 WELL, 

NORTH SLOPE, ALASKA 

Timothy S. Collett, Keith A. Kvenvolden, 

Leslie B. Magoon, and Kenneth J. Bird 

Gas hydrates are crystalline substances 

composed of water and gas in which the solidwater lattice accommodates the gas molecules in 

a cage-like structure. Significant quantities of 

naturally occurring gas hydrates have been 

detected in many regions of the Arctic, including 

western Siberia, the Mackenzie Delta of Canada, 

and the North Slope of Alaska; they may represent 

an unconventional source of natural gas 

(Kvenvolden and McMenamin, 1980). However, 

little is known about the physical nature of gas 

hydrates. Direct evidence for gas hydrates on the 

North Slope (fig. 1) comes from a core in the 

Northwest Eileen State 2 well. Indirect evidence 

is provided by drilling information and open-hole 

geophysical logs, which suggest the presence of 

numerous gas-hydrate layers in the area of the 

Kuparuk River Oil Field (Collett, 1983). 

Gas hydrates exist under a limited range of 

pressure and temperature conditions with depth, 

known as the gas hydrate stability field (fig. 2). 

The gas hydrate stability diagram in figure 2 has 

been generated from laboratory data and field 

Kuparuk 2D-15A 

approximate area of 

Kuparuk River Field 

evaluations. The intersection of the methane 

hydrate stability curve with the projected 

geothermal gradient denotes the top and base of 

the methane hydrate stability field. In figure 2, 

"HT" is the top of the methane hydrate stability 

field, and "HB" is its base. Five reservoir and fluid 

properties may affect the stability of in-situ gas 

hydrates: geothermal gradient, gas chemistry, 

pore-fluid salinities, pore pressures, and reservoirrock grain size. Subsurface-temperature data on 

the North Slope come from 46 high-resolution, 

equilibratea wellbore surveys (Lachenbruch and 

others, in press) and from estimates based on 

identification of the base of ice-bearing 

permafrost in 98 other wells (Collett and others, in 

press). Gas chemistry data are from analysis of 

mud logs and well cuttings. Subsurface pressure 

and pore-fluid salinity data have been obtained 

from well-log calculations and formation testing. 

Our North Slope studies suggest that the gas 

hydrate stability field is controlled primarily by 

subsurface temperatures and gas chemistry, and 

that other factors, such as pore-fluid salinity, 

pore-pressure variations, and reservoir-rock grain 

size, appear to have little effect. 

In the Kuparuk 2D-15 well, the estimated 

geothermal gradient ranges from 2.14 °C/100 m 

in the ice-bearing permafrost sequence to 

3.42 °C/100 m below the base of ice-bearing 

permafrost. A 30-m-thick interval is inferred to 

contain gas hydrates in the Kuparuk 2D-15 well 

(fig. 3). The occurrence of gas hydrates is 

NW Eileen ST 2 

-

Prudhoe 

Bay 

approximate area of 

Prudhoe Bay Field 

0 

149 

Figure 1.--Location of Kuparuk 2D-15 and Northwest Eileen State 2 wells. 

24 
TEMPERATURE (°C) 

-20 -10 0 10 20 30 0 0 

300 

.... 2000 600 ]: ..... 

:r: :r: 

E-< E-< 1=4 1=4 

r.:l 3000 900 r.:l 

~ ~ 

" .... I 

<>-~" \ 

4000 0~ \ 1200 

5000 1500 

.___ ____ __J._ _______ _____LlSOO 

Figure 2.--Gas hydrate stability diagram for 

Northwest Eileen State 2 well. "HT" is top of 

methane hydrate stability field; "HB" is its base 

(pore2pressure gradient: 9. 795 k Pa/m or [0.433 

lb/in /ft]). 

suggested by the release of unusually large (up to 

750 ppt) amounts of methane as indicated on the 

mud log (fig. 3, column A), and an increase in 

transit-time velocity (fig. 3, column B) and 

electrical resistivity (fig. 3, column C) on the 

open-hole well logs. Canned drill-cutting samples 

from the Kuparuk 2D-15 well have been analyzed 

to determine the origin and composition of the 

gases from this interval. Headspace-gas analysis 

of the cuttings reveal methane to propane-plusethane ratios [C1/(C2+C3)] typical of biogenic gas, 

with values ranging from 3,300 to 14,500. In 

contrast, the isotopic composition of the methane 

inp!cate~ the presence of thermogenic gas, with 

C /C1 isotope values from -49.13 to 

-38.64 o/oo. Vitrinite reflectance measurements 

(0.4 percent Ro) show that the near-surface, 

potentially gas-hydrate-bearing sediment has 

never been subjected to high enough temperatures 

to generate thermogenic methane. Thus, the 

thermogenic gas must have migrated from greater 

depths, and the gas hydrates may contain a 

mixture of biogenic and thermogenic gases. 

Formation-water samples and well-log calculations 

from the 2D-15 well and nearby wells indicate low 

pore-fluid salinities, ranging from 0.5 to 18.1 ppt. 

The maximum recorded salinity would suppress 

methane hydrate stability temperatures by 

approximately 1.0 °C, thus moving the methane 

hydrate stability curve to the left in figure 2. 

25 

A B c 

'Mud-Methane !Transit Time! Resistivity I 0 750 200 75 2 2000 

ppt m· s/ft ohm-m 

350 

1 400 

'!i 

!:>. 

Cll 

~ 

450 

Figure 3.--Well logs from Kuparuk 2D-15 well, 

showing response considered to indicate gas 

hydrate occurrence. 

Pressure data, obtained from drill-stem testing 

and well-log calculations in nearby wells, indicate 

a hydrostatic lore-pressure gradient (9. 795 kPa/m 

or 0.433 lb/in /ft) within the uppermost 2,000 m of 

sediments, which has no abnormal effect on gas 

hydrate stability. The effect of sediment grain 

size on gas hydrate stability is very difficult to 

evaluate in the absence of laboratory studies. 

However, it is believed that coarse-grained 

sediments do not affect gas hydrate stability. 

Therefore, in the near-surface coarse sand and 

gravel sediment in the Kuparuk River area, grain 

size should have little or no effect on gas hydrate 

stability. 

In summary, the evaluation of geochemical 

and geologic data from the Kuparuk 2D-15 and 

nearby wells indicate that gas hydrates occur in 

the Kuparuk River area, and their stability is 

controlled primarily by subsurface temperatures 

and gas chemistry. This work was partially funded 

by the Morgantown Energy Technology Center 

under the U.S. Geological Survey-U.S. Department 

of Energy Agreement No. DE-AI21-83MC20422. 
REFERENCES CITED 

Collett, T.S., 1983, Detection and evaluation of 

natural gas hydrates from well logs, Prudhoe 

Bay, Alaska, in Proceedings of the Fourth 

International Conference on Permafrost, 

Fairbanks, Alaska: Washington, D.C., 

National Academy of Sciences, p. 169-174. 

Collett, T.S., Bird, K.J., Kvenvolden, K.A., and 

Magoon, L.B., in press, Subsurface 

temperatures and geothermal gradients on the 

North Slope of Alaska: U.S. Geological Survey 

Oil and Gas Map. 

26 

Kvenvolden, K.A., and McMenamin, M.A., 1980, 

Hydrates of natural gas: A review of their 

geologic occurrence: U.S. Geological Survey 

Circular 825, 11 p. 

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., in press, Temperature and 

depth of permafrost on the Alaskan Arctic 

Slope, in Gryc, George, ed., National 

Petroleum Reserve in Alaska: U.S. Geological 

Survey Professional Paper 1399, 38 p. 

Reviewers: L.A. Beyer and R.G. Stanley 
USE OF FACTOR ANALYSIS IN 

LOCATING BASE METAL MINERALIZATION 

IN THE KILLIK RIVER QUADRANGLE, ALASKA 

Karen A. Duttweiler 

A reconnaissance geochemical survey of the 

Killik River quadrangle has been under way since 

1981 as part of the Alaska Mineral Resource 

Assessment Program. Analyses of streamsediment and nonmagnetic heavy-mineral 

concentrate samples were published by Barton and 

others (1982) and Sutley and others (1984). My 

subsequent application of factor analysis to the 

log-transformed emission spectrographic data for 

the concentrate samples was highly successful in 

characterizing the dominant geochemical 

associations in the southern part of the quadrangle 

(fig. 1). Major lithologic differences were 

discerned, and previously unrecognized areas 

favorable for hosting base-metal sulfide deposits 

were clearly defined. 

R-mode factor analysis with varimax 

rotation (Koch and Link, 1971) was used to define 

the geochemical associations in the concentrate 

data. This type of factor analysis groups the 

elements that tend to behave similarly into 

multielement associations, or factors, based on 

their mutual linear correlation coefficients. In 

this way, a large number of variables is reduced to 

only a few variables that best characterize the 

original data. The factors produced from R-mode 

factor analysis reflect geological features and 

geochemical processes. 

I selected a five-factor model as the 

geologically most meaningful solution for the 

reconnaissance geochemical data (table 1). These 

five factors explain 73 percent of the variance 

within the original data set. Factor loadings 

represent the contribution of each element onto 

each factor. Factor scores measure the "effect" 

of a factor on each individual sample. 

Factors 1, 2, and 4 (table 1), accounting for 

about 57 percent of the total data variability, 

represent lithogeochemical associations. Elements 

that load heavily onto factor 1 include Ca, Ti, B, 

Cr, La, Ni, Sc, V, Y, and Zr. Most heavy-mineralconcentrate samples with high scores for this 

factor contain various amounts of rutile, zircon, 

apatite, and sphene. These samples are from 

drainages underlain primarily by the Upper 

Devonian and Lower Mississippian(?) Kanayut 

Conglomerate (Nilsen and Moore, 1984), a rock 

unit composed of conglomerat~, sandstone, 

siltstone, and minor shale (Brosge, and others, 

1979). 

Factor 2 (Ca-Ba-Sr) defines concentrates 

containing abundant barite. Samples with high 

scores for factor 2 are spatially related to 

exposures of limestone and dolomite of the 

Mississippian and Pennsylvanian Lisburne Group, 

27 

and shale and siltstone of the Pennsylvanian to 

Lower Triassic Siksikpuk Formation (Mull and 

others, 1982), which locally contain barite nodules. 

Factor 4 is associated mainly with 

concentrates derived from local mafic rocks in the 

vicinity of Kikiktat Mountain. Magnesiochromite, 

a Mg-rich end member of the chromite solidsolution series, was identified in a few 

concentrates northeast of Kikiktat Mountain. The 

strong Mg-Mn-Cr-V-Sc association characterized 

by factor 4 may be a result of magnesiochromite 

in the concentrates. 

Factors 3 and 5 represent mineralization 

suites. The Fe-Co-Cu-Ni-Zn association that 

characterizes factor 5 defines areas with the 

greatest concentration of pyrite (±chalcopyrite) in 

the heavy-mineral concentrates. The Ag-Pb-ZnCu association (factor 3) indicates the presence of 

galena and sphalerite (±chalcopyrite). Distribution 

of scores for these factors provides a means of 

distinguishing between areas hosting pyrite 

mineralization and those hosting pyrite plus basemetal sulfides. Figure 1 shows the distribution of 

scores for factor 3 (base-metal sulfide factor) and 

factor 5 (pyrite factor). The scores were divided 

into three groups on the basis of percentiles; the 

99th, 95th, and 90th percentiles were chosen to 

represent anomalously high scores for each factor. 

Anomalous scores for both the pyrite and 

base-metal sulfide factors are concentrated in two 

distinct areas (fig. 1), both of which are underlain 

by the Devonian Hunt Fork Shale and reljitively 

younger Kanayut Conglomerate (Brosge, and 

others, 1979). The easternmost area is 

characterized by a central zone of samples with 

high scores for the base-metal sulfide factor 

surrounded by zones of high scores for the pyrite 

factor. Concentrates from the central zone 

Table 1.--Factor loadings for the first five factors 

of heavy-mineral-concentrate data 

[Total variance explained by the five factors 

equals 73 percent. For simplification, all loadings 

less than 0.30 have been omitted] 

Factors 

Fe 

Mg 

Ca 0.52 

Ti .88 Mn 

Ag 

B .60 Ba -.33 

Co 

Cr .77 Cu 

La .87 Ni .31 

Pb 

Sc .39 Sr 

v .75 y .86 

Zn 

Zr .85 

Percent 36.0 

of total data variance 

explained by factor 

-0.33 

.61 

-.48 

0.88 -.37 

.67 

.35 

.84 

.78 

.62 

13.9 12.1 

0.82 

.59 

.41 

.58 

.37 

6.5 

0. 76 

. 75 

.73 

.80 

.38 

5.1 
0 5 10 

I I KILOMETERS e 

1 5. 

EXPLANATION 

Factor 3 Factor 5 

D ~ Drainage basins containing samples with high scores 

3 5 Scores greater than the 99th percentile 

3 5 Scores between the 95th and 99th percentile 

3 5 Scores between the 90th and 95th percentile 

• SamplE' locality with scores less than the 90th percentile 

* Mineralized vein locality 

Figure 1.--Southern part of Killik River quadrangle, showing distribution of samples with high scores for 

factor 3 and factor 5. 

contain abundant sphalerite, galena, pyrite, and 

chalcopyrite; a few samples contain traces of 

arsenopyrite, and one sample contains realgar. 

Although an extensive area of possible 

mineralization is delineated by the two factors in 

this area, the only identified source of the sulfides 

was found to be veins hosted by the Hunt Fork 

Shale. The veins, averaging 1-2 em wide, consist 

primarily of quartz with a few scattered 

occurrences of galena, pyrite, and sphalerite. 

Samples with the highest scores for the basemetal sulfide factor (factor 3) occur in the 

western part of the quadrangle, where they occui?zY 

a total drainage basin area of about 80 km . 

Follow-up studies to locate the source of the 

sulfides was conducted on the basis of the 

anomalous scores for factor 3. Highly mineralized 

veins were found in two areas in the western part 

of the quadrangle. The northernmost area, 

informally named the Kady occurrence, is located 

at the headwaters of a tributary of Outwash Creek 

(fig. 1); the other vein system, the Vidlee 

occurrence, is located at the headwaters of 

Itilyiargiok Creek. 

The Kady occurrence is about 2 km north of 

a major east-west-trending thrust fault that 

separates rocks of the Hunt Fork Shale from the 

underlying but relatively younger Kanayut 

28 

Conglomerate (C.G. Mull and others, unpub. 

mapping). The veins, which are exposed on a 

hillside south of a small east-west-trending 

tributary, are hosted by clastic rocks of the 

Kanayut Conglomerate. The veins trend 

approximately N. 35° W. and can be traced along 

strike for at least 300 m. They range in width 

from 2-cm stockwork veinlets to massive veins 3 

m wide. One zone, consisting of rubble of oxidized 

vein material in a small saddle, was estimated to 

be about 10 m wide. Mineralization consists of 

sphalerite, pyrite, chalcopyrite, and galena in 

stockwork quartz veins. The most highly 

mineralized rocks consist of massive sulfidebearing vein-breccias, in which sphalerite and 

pyrite are the most abundant minerals. Much of 

the mineralized vein material has been weathered 

to form boxwork silica textures; locally, oxidation 

of Fe-sulfides to limonite has resulted in extensive 

bright red- to orange-weathering zones. 

Veins at the Vidlee occurrence (fig. 1) are 

exposed at stream level on the north side of a 

first-order tributary of Itilyiargiok Creek near the 

contact between the Hunt Fork Shale and the 

Kanayut Conglomerate. The vein outcrop, which 

cannot be traced either laterally or vertically 

from this single exposure, is about 5 m wide. 

Compared to those at the Kady location, the veins 
Table 2.--Analytical data for mineralized rocks from the Killik River quadrangle 

[All analyses by semi-quantitative emission spectrography and reported in parts per million. N, not 

detected at the lower limit of determination. Note: gold was not detected by emission spectrographic 

methods and gold data from atomic absorption methods are not yet available] 

Sample No. Ph Zn Cd Ag As Sb Co Cu Ni Sn 

KADY OCCURRENCE 

605C 30 )10,000 100 3 N N 50 1,000 20 N 

605D 500 <200 N .7 N N 10 500 15 N 

605E 50 )10,000 )500 5 700 N 200 2,000 150 200 

605F N )10,000 150 2 N N 20 1,000 10 N 

606A 15 10,000 100 1.5 N N 7 70 5 30 

606C 20 )10,000 )500 1.5 N <100 50 1,000 20 20 

606D 50 )10,000 )500 7 N N 70 200 <10 N 

607C 100 (200 N 150 500 N 30 )20,000 100 200 

607D 10 <200 N 10 N N 15 7,000 20 N 

VIDLEE OCCURRENCE 

608 20,000 )10,000 150 20 

609A 150 500 N 7 

609B 70 2,000 (20 2 

609C 2,000 )10,000 )500 20 

609D 1,000 >10,000 )500 50 

610A 2,000 3,000 20 20 

6108 )20,000 )10,000 )500 300 

610C 15,000 )10,000 >500 150 

at this locality are more massive, less brecciated, 

and less oxidized. Three zones, based on dominant 

sulfide mineralogy, are distinguished within the 

vein system: (1) the pyrite zone, which contains 

little or no galena or sphalerite, (2) the sphalerite 

zone, containing minor galena, and (3) the galenadominant zone, which locally contains 

chalcopyrite. All three are typified by bands of 

sulfides in quartz gangue. 

Mineralized rocks from the Kady area 

contain high concentrations of Zn, Cd, and Cu with 

lesser amounts of Pb, Ag, and As (table 2). 

Mineralized rocks from the Vidlee area contain 

high Pb, Ag, Zn, Cd, Cu, As, and Sb 

concentrations. In addition to the anomalous 

concentrations of these elements, a few rocks 

from the Kady and Vidlee areas contain high 

amounts of Co and Ni, which reflects the 

abundance of pyrite in the veins. Also of interest 

is the high tin content of many of the mineralized 

rocks. For example, two samples from each area 

contain Sn concentrations of 100 ppm or more. 

Each sample containing anomalous Sn also contains 

high concentrations of Cu. Based on this Cu-Sn 

)10,000 500 500 1,500 50 100 

29 

200 <100 50 10,000 20 70 

200 N 50 50 10 N 

N (100 50 500 10 30 

N 200 50 500 7 70 

<200 (100 70 1,000 20 20 

200 2,000 70 7,000 20 300 

N 500 50 300 5 70 

association, I suggest that stannite (Cu2FeSnS4) 

may be present as an accessory mineral in addition 

to pyrite, galena, and sphalerite, although detailed 

petrographic work is needed to confirm this 

inference. 

In conclusion, factor analysis applied to the 

concentrate data from the southern part of the 

Killik River quadrangle was highly successful in 

outlining those areas most favorable for hosting 

base-metal sulfide deposits and in locating two 

specific areas of previously unknown 

mineralization. The Pb-Zn-Ag-Cu association 

characteristic of the mineralized areas was well 

represented by the base-metal sulfide factor 

obtained from the factor analysis. 

REFERENCES CITED 

Barton, H.N., Odland, S.K., O'Leary, R.M., and 

Day, G.W., 1982, Geochemical data for the 

Killik River and Chandler Lake quadrangles, 

Alaska: U.S. Geological Survey Open-File 

Report 82-1026, 52 p. 
Brosg~, W.P., Reiser, H.N., Dutro, J.T., Jr., and 

Nilsen, T.H., 1979, Geologic map of Devonian 

rocks in parts of the Chandler Lake and Killik 

River quadrangles, Alaska: U.S. Geological 

Survey Open-File Report 79-1224, 1 sheet, 

scale 1:200,000. 

Koch, G.S., Jr., and Link, R.F., 1971, Statistical 

analysis of geological data: New York, Dover, 

438 p. 

Mull, C.G., Tailleur, I.L., Mayfield, C.F., 

Ellersieck, Inyo, and Curtis, S., 1982, New 

upper Paleozoic and Lower Mesozoic 

stratigraphic units, central and western 

Brooks Range, Alaska: AAPG Bulletin, v. 66, 

no. 3, p. 348. 

30 

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. 

Sutley, S.J., Duttweiler, K.A., and Hopkins, R.T., 

1984, Analytical results and sample locality 

map of stream-sediment and pannedconcentrate samples from the Killik River 

1 x 3° quadrangle, Alaska: U.S. Geological 

Survey Open-File Report 84-406, 18 p. 

Reviewers: P.F. Folger and R.J. Goldfarb 
PRELIMINARY EVALUATION 

OF GEOCHEMICAL ANOMALIES 

IN THE BAIRD MOUNTAINS QUADRANGLE, 

ALASKA 

Peter F. Folger, 

Richard J. Goldfarb, and 

Jeanine M. Schmidt 

The Baird Mountains quadrangle is underlain 

mainly by low-grade metamorphosed Paleozoic 

marine carbonate, pelitic, and clastic rocks with 

minor amounts of terrigenous clastic rocks (Karl 

and others, 1985). Minor mafic volcanic and 

volcaniclastic rocks and rare felsic volcanic rocks 

occur within the Paleozoic sedimentary 

sequences. Mesozoic marine volcanic rocks and 

minor chert crop out in the extreme northwestern 

part of the quadrangle, and Cretaceous and (or) 

Tertiary conglomerates occur in the southeastern 

corner. Amphibolite-grade Precambrian schist and 

minor metaplutonic rocks of intermediate 

composition are structurally juxtaposed with 

greenschist-grade Paleozoic rocks in the 

northeastern corner of the quadrangle (A. B. Till, 

USGS, written commun., 1986). Pelitic schist and 

phyllite of uncertain age occur in the southern and 

eastern parts of the quadrangle. Folding and 

thrust faulting during the Jurassic(?) to 

Cretaceous Brooks Range orogeny have added 

further complexity to regional stratigraphic and 

structural relationships. 

Known mineralization in the Baird Mountains 

quadrangle (fig. 1) includes the carbonate-hosted 

Omar copper prospect (Folger, 1987), the Frost 

barite-lead-zinc occurrence (Degenhart and 

others, 1978), the Powdermilk zinc - lead - silver 

occurrence (Schmidt and Folger, 1986), and the 

Klery Creek and Timber Creek gold placers 

(Degenhart and others, 1978). With the exception 

of the Klery Creek-Timber Creek area, mineral 

resources have not been commercially exploited in 

the Baird Mountains quadrangle. 

In order to identify additional mineralized 

areas in the Baird Mountains quadrangle, we 

conducted a geochemical reconnaissance survey 

between 1983 and 1985 as part of the Alaska 

Mineral Resource Assessment Program (AMRAP). 

Both stream sediments and heavy-mineral 

concentrate samples we~e collected at an average 

density of 1 per 10 km from low-order drainage 

basins. The minus-80-mesh fraction of stream 

sediments and the nonmagnetic heavy-mineral 

concentrate fraction were analyzed by 

semiquantitative emission spectrography for 31 

elements. The resulting geochemical data for 

1,493 stream-sediment samples and 1,185 heavymineral concentrate samples are tabulated in 

Bailey and others (1987). 

Both data sets were first log-transformed, 

and elements for which the majority of values 

31 

were "greater than" or "less than" the detection 

limits (highly censored elements) were removed. 

Then, R-mode factor analysis with varimax 

rotation was used to identify intercorrelated 

variables within each data set. This analysis 

places similarly behaving experimental variables, 

in this case elemental concentrations, into groups 

termed factors. The number of factors chosen 

from each data matrix, and discussed here, were 

based on the breaks in slope for the plots of factor 

number versus total variance. The streamsediment and nonmagnetic heavy-mineral 

concentrate data were interpreted in terms of 

mineral potential by using both plots of factor 

scores (the "effect" of a factor on each sample) 

and plots of individual concentration values for 

highly censored elements. 

Four factors explain 76 percent of the total 

variance in the stream-sediment data (table 1). 

Factors 1, 2, and 4 apparently represent 

lithogeochemical associations within the Baird 

Mountains quadrangle. Samples with the highest 

scores onto factor 1 are mainly from watersheds 

containing mafic rocks. High factor 2 scores 

identify drainages underlain by relatively pure 

carbonate rocks, mainly in the southwestern and 

west-central part of the quadrangle. The highest 

factor 4 scores occur more irregularly within areas 

of pelitic schist, black shale, and mixed carbonate 

and clastic rocks. 

Factor 3, with high lead and copper, is the 

only association within the stream-sediment data 

that clearly identifies areas of mineral potential. 

Five areas of high factor 3 scores occur within the 

quadrangle (fig. 1). 

Table 1.--Factor loadings for 1,493 stream 

sediment samples 

[Loadings depict the influence of each factor on 

each variable and may be interpreted similarly to 

correlation coefficients. Loadings less than 0.3 

have been omitted] 

Element Factor 1 

Fe 0.81 

Mg 

Ca -.32 

Ti .71 Mn .72 

B .67 

Ba .69 

Be .41 Co .79 

Cr .80 

Cu .70 

La 

Ni .78 

Pb 

Sc .73 

Sr 

v .81 y .49 

Zr .62 

Percent tota 1 

variance 38 

Factor 2 

0.52 

.80 

- .3C 

.87 

12 

Factor 3 

0.42 

.88 

Factor 4 

0.37 

-.47 

-.36 

.55 

.38 

.56 

.51 

.66 

.30 

.73 

.31 

.47 

.38 

.65 

.57 

20 
1620 1590 

68°·r-----------------~----------------------------~----------------------------------~ 

0 

~6{Kilyaktalik !{if(:Peaks 

;: :fi[:;~1~;~"~,:c 

10 20 

KILOMETERS 

84 

67°~------------------------------------------~----------~=-------------------------~ 

Figure 1.--Areas containing geochemical anomalies in Baird Mountains quadrangle. Shaded areas indicate 

anomalous stream sediment values; vertical lines indicate anomalous heavy-mineral concentrate values. 

Labels for anomalous areas are discussed in text. Areas of known mineralization shown by asterisks. 

1. Anomalous amounts of lead with local Cu, Ag, 

Ba, Mo, and Zn, occur within the 

Kilyaktalik Peaks area (81 on fig. 1). The 

spatial association of these samples with 

black to dark-gray shale, and the local 

occurrence of disseminated and massive 

pyrite, suggest high favorability for silverrich base-metal mineralization within 

fine-grained sediments. (These and all 

other mineral occurrences mentioned here 

are from unpublished field observations of 

this study.) 

2. A strong copper and lead anomaly, locally with 

anomalous zinc, occurs within the 

Agashashok River drainage (82 on fig. 1). 

This area is geochemically favorable for 

32 

carbonate-hosted Omar- or Frost-type 

mineralization, for pyrite and base-metal 

mineralization in quartz veins, and for 

disseminated-stratabound base metals 

within the mixed carbonate-clastic 

sequences. 

3. The most extensive area with high factor 3 

stream-sediment scores is area 83 in the 

center of the quadrangle (fig. 1). This 

area is better delineated by the 

distribution of anomalously high 

molybdenum, and to a lesser extent by 

high silver, barium, and zinc. The 83 area 

includes the Omar, Frost, and Powdermilk 

mineral occurrences, and the headwaters 

of the Omar River, Tukpahlearik Creek, 
and Anaktok Creek. The S3 region has 

geochemical favorability for base-metal 

mineralization with variable silver and 

barite in carbonate rocks as well as in 

black and mixed pelitic schists. 

4. In the Kallarichuk Hills (S4; fig. 1), samples 

anomalous in Ba, Cu, Mo, and Pb occur 

within drainages underlain by mixed 

schists, and pelitic rocks of phyllitic to 

garnet grade. Because few sulfide 

occurrences have been noted, and because 

corresponding concentrate samples contain 

only minor amounts of sulfide minerals, 

these stream-sediment geochemical 

anomalies probably reflect high 

lithogeochemical background values. 

5. Samples from the headwaters of the Tutuksuk 

River and Naneilik Creek in the northeast 

corner of the quadrangle (area S5) are 

enriched in Ag, Ba, Cu, Mo, Pb, and Zn. 

This area is underlain by a complexly 

faulted mixture of Paleozoic carbonate 

and mafic rocks; black shale, sandstone, 

and conglomerate of unknown Paleozoic 

age; and minor Proterozoic schist of 

amphibolite grade. Scattered minor 

pyrite, Fe-oxides, and Cu-oxides are 

known from this area, and parts of the 

Naneilik creekbed are intensely ironstained, but the types of mineralization 

possible here are unknown and presently 

unconstrained by the geology. 

Six factors explain 70 percent of the total 

variance in the heavy-mineral concentrate data 

(table 2). Factors 1, 5 and 6 are geochemical 

associations which probably reflect lithologic 

variations of heavy minerals such as Fe- and Tioxides and spinels, because they have no obviously 

related sulfide mineral suite. The elements 

occurring in factor 1, however, are those which 

are common in metal-enriched marine black shales 

(Desborough and Poole, 1983), and may still 

indicate nonsulfide resource potential. Some 

samples with high factor 6 scores in the 

Kallarichuk Hills just north of area S4 contain 

visible cassiterite (G. Bennett, USGS, written 

commun., 1986). The source of cassiterite and the 

factor 6 geochemical association is presently 

unknown. 

Factor 3 loadings are highest for barium and 

zinc. Samples with high factor 3 scores are 

scattered throughout the northwest quarter of the 

quadrangle. Most of these samples have low lead 

and silver values, and may indicate disseminated 

sphalerite and barite in shale and sandstone. 

Two factor associations in the concentrate 

data delineate areas of possible mineral 

potential. Factor 2 loadings are strongest for Co, 

Cu, Fe, and Ni, and high scores identify 

concentrate samples containing pyrite and lesser 

amounts of chalcopyrite. Samples with high factor 

33 

4 scores outline areas with high silver, lead and 

zinc; galena and (or) cerussite and sphalerite are 

visible in some of these samples (G. Bennett, 

USGS, written commun., 1986). 

Factor 2 and 4 scores outline four 

geochemically favorable areas not identified by 

anomalous stream-sediment samples: 

1. Samples with anomalous Co, Cu, Fe, and Ni 

(±Mn) cluster in the headwaters of Nakolik 

and Nakolikurok Creeks (areas C1 and C2 on 

fig. 1), and probably reflect disseminated 

pyrite and chalcopyrite mineralization noted 

in some sandstones. 

2. High Ag, Pb, and Zn in samples from area C3 

(overlapping part of S2) may be derived from 

sandstone-hosted, disseminated and vein basemetal mineralization with high silver values. 

3. Samples with anomalous Pb, Zn, and Ag in area 

C4 apparently reflect carbonate-hosted 

mineralization, possibly similar to the 

Powdermilk occurrence. Samples anomalous 

in zinc with lesser lead and silver are 

scattered between area C4 and the southern 

part of area C2, and may reflect the 

lithologic transition from carbonate-hosted to 

sandstone-hosted mineralization. 

An individual element concentration plot for 

tungsten indicates anomalous values across a broad 

area (C5) including the Klery Creek/Timber Creek 

placer gold area. Many of the anomalous samples 

contain visible scheelite (G. Bennett, USGS, 

written commun., 1986). Three concentrate 

samples containing visible gold also have high 

tungsten values, suggesting that area C5 has 

potential for vein-related gold-tungsten 

mineralization. 

Table 2.--Factor loadings for 1,185 heavy-mineral 

concentrate samples 

[Loadings less than 0.3 have been omitted] 

Element Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Factor 6 

Fe .88 

Mg -.88 

Ca -.56 -.33 -.49 

Ti .65 .56 

Mn .41 .33 

Ag .80 

B .72 

Ba .74 

Be .32 .61 

Co .85 

Cr .80 

Cu .83 

La .46 .42 .36 Nb .45 .46 .32 Ni .88 

Pb .81 

Sc .73 Sn .70 

v .81 y .46 .74 

Zn .57 .44 

Zr .37 .36 .65 

Percent of total 

variance 18 17 12 
The reconnaissance data indicate that at 

least 25 percent of the Baird Mountains quadrangle 

is geochemically favorable for the occurrence of 

additional mineral deposits. The most likely 

deposit types are stratabound and stratiform, and 

occur within continental margin sedimentary 

rocks, that are unrelated to igneous activity. 

REFERENCES CITED 

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. 

Degenhart, C.E., Griffis, R.J., McQuat, J.F., and 

Bigelow, C.G., 1978, Mineral studies of 

certain ANCSA 17(d)(2) lands in Alaska, 

performed under contract J0155089: U.S. 

Bureau of Mines Open File Report 103-78, 

p. 250-279. 

Desborough, G.A., and Poole, F.G., 1983, Metal 

concentrations in some marine black shales of 

the United States, in Shanks, W.C., ed., 

Cameron Volume on unconventional mineral 

deposits: New York, Society of Mining 

Engineers, p. 99-110. 

34 

Folger, P.F ., in press, Geology and mineralization 

at the Omar Copper prospect, Baird 

Mountains quadrangle Alaska: U.S. Geological 

Survey Open-File Report, 99 p. 

Karl, S.M., Schmidt, J.M., and Folger, P.F., 1985, 

Selected anomalous rock and sediment 

samples from central and northwestern Baird 

Mountains quadrangle, in Bartsch-Winkler, 

Susan, ed., The Unites-States Geological 

Survey in Alaska--Accomplishments during 

1984: U.S. Geological Survey Circular 967, 

p. 8-13. 

Schmidt, J.M., and Folger, P.F., 1986, Pb-Zn-Ag 

mineralization in Paleozoic dolostones, 

Powdermilk prospect, Baird Mountains B-4 

quadrangle, in Bartsch-Winkler, 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. 19-21. 

Reviewers: K.A. Duttweiler and Harley King 
GLACU~L ADVANCE OF LATE WISCONSIN 

(ITKILL,IK ll) AGE IN THE UPPER NOATAK 

RIVER VALLEY-A RADIOCARBON-DATED 

STRATIGRAPIDC RECORD 

Thoma:1 D. Hamilton, George A. Lancaster, 

and Deborah A. Trimble 

The last major glaciation of the central 

Brooks Range, the Itkillik II advance of Hamilton 

and Porter (1975), has been dated at between 

about 24 and 11.5 ka (thousand years before 

present) based on indirect evidence such as 

periglacial mass wastage, river alluviation, and 

eolian activity (Hamilton, 1982; Ashley and others, 

1984). W•e report here seven new radiocarbon 

dates on three measured stratigraphic sections 

along the Noatak River that provide a direct age 

bracket for the advance and retreat of the glacier 

that filled 'lts upper valley during Itkillik II time. 

Detailed field mapping (Hamilton, 1981, 

1984a, b) shows that late Pleistocene valley 

glaciers flowed north and west from highland 

source areas and extended as far as 140 km down 

the Noatak: valley from its head. Three principal 

advances of probable late Pleistocene age are 

recognized.. These have been assigned to the 

Itkillik glaeiation of Detterman and others (1958) 

and informally designated as phases lA, IB, and II 

(Hamilton and Porter, 1975; Hamilton, 1984a, b, 

1986a, b). Our radiocarbon dates bracket the 

advance of Itkillik II age and provide an age limit 

on the next-older (Itkillik 18) glacial expansion. 

ThreE! prominent river bluffs along the 

Noatak River near Douglas Creek (fig. 1) intersect 

the end-moraine belt of Itkillik II age, the outwash 

apron that formed in front of it, and a lake basin 

that formed as the glacier retreated upvalley. The 

three bluffs, which range in height from 18 to 70 

m, expose diamict, alluvium, outwash, and 

lacustrine sediments, capped by about a meter of 

sod, peat, a.nd frost-churned stony silt. 

Exposure A (fig. 2A), a south-facing, 70-m 

bluff within the end moraine of Itkillik II age, is 

situated 5.S km below Douglas Creek. The bluff 

intersects an irregular surface that contains 

numerous kettles and several river-terrace 

remnants that formed as drainage became 

reestablished during retreat of the glacier from its 

end moraine. The lowest stratigraphic unit (unit 

1), which forms vertical buttresses near the base 

of the section, consists of compact pebble-smallcobble gravel with a silty sand matrix. The upper 

part of the deposit is structureless, but overturned 

folds and one near-vertical, 30-cm bed of 

deformed peaty silt are present at greater depth. 

The peaty silt bed has an apparent radiocarbon age 

of 34,990 ± 230 yr 8.P. 

Overlying alluvium (unit 2) consists of 

packages of parallel-bedded to crossbedded sand, 

pebbly sand, and pebble-small-cobble gravel about 

35 

50 em thick. Beds of oxidized organic silt with in 

situ rootlets 4 m and 2 m below the top of the 

alluvium are dated at 34,840 ± 950 yr 8.P. and 

30,070 ± 470 yr 8.P., respectively. Gravel beds at 

greater depth dip upvalley at angles of 12-34 ° then 

level out and fine laterally to form a paleobasin 

floor composed of muddy sand. This closed 

depression within the gravel may have resulted 

from continued melt of buried glacier ice during 

deposition of unit 2. 

The upper diamict (unit 3) is interpreted as 

massive till in its upper part and redeposited river 

gravel in its lower part. Unsorted, rounded to 

subrounded, striated clasts up to boulder size 

dispersed in a compact, gray, silty matrix grade 

downward at about 3.5 m depth into compact 

rounded pebbles and small cobbles that resemble 

the diamict of unit 1. Like unit 1, this deposit 

exhibits faint, highly deformed size 

stratification. Clasts of peaty silt incorporated in 

the diamict 70 em above its base are dated at 

34,010 ± 350 yr 8.P., and clearly were redeposited 

from unit 2. 

Unit 4 consists of rounded to subrounded 

alluvial pebbles and cobbles in a poorly sorted 

matrix of sand with phyllite chips. The alluvium 

contains several near-horizontal sand beds 10-30 

em thick that are continuous laterally for at least 

20 m. A lag concentration of boulders up to 60 em 

diameter occurs at the base of the alluvium and on 

the upper surface of the underlying diamict. 

Exposure 8 (fig. 28), 13 km downvalley from 

Douglas Creek, intersects an outwash terrace that 

originates at the end moraine of Itkillik II age. 

The terrace surface is planar for about 1 km 

upvalley from the exposure, then it degenerates 

into kame-and-kettle topography that may 

represent the downvalley limit of glacier ice of 

Itkillik II age. Other kettle fields downvalley from 

the exposure (hachured areas on fig. 1) probably 

developed from melting of older glacial ice of 

Itkillik IB age. The outwash at exposure 8 consists 

of alluvium which coarsens progressively upward 

and lacks obvious erosion surfaces or 

unconformities. In the basal part of the exposure, 

beds of medium to coarse sand up to 25 em thick 

alternate with beds of sandy pebble-small-cobble 

gravel about 50 em thick. The central part of the 

section consists of faintly bedded rounded pebbles, 

small cobbles, and sparse medium cobbles with 

some 10-cm interbeds of pebbles, of well-sorted 

coarse sand, or of muddy gravel. Pebbles, small to 

medium cobbles, and sparse larger cobbles in a 

matrix of nonoxidized medium to coarse sand and 

granules predominate in the upper part of the 

deposit. Progressive changes in clast lithology 

show increasing dominance of upvalley sources as 

sediment size increases. Locally derived 

carbonate rocks decrease upward from 30 percent 

of all clasts near the base of the section to about 

10 percent near the top. Granitic rocks from 
0 25 km 

EXPLANATION 

b Alluvium 

D Alluvial fan deposit 

Q Terrace gravel 

fES} Till 

G:EiJ Ice-contact 

[;]Outwash 

Deposits of 

Itkillik n 

age 

~ Drift of Itkillik I age, 

L..:.:_J undifferentiated 

0 Solifluction deposit 

~ Bedrock, undifferentiated 

• Measured section <see fig. 2) 

0 Kettle field 

Figure I.--Geologic map of Douglas Creek area, upper Noatak valley, showing location of measured 

stratigraphic sections. Note that drift of Itkillik I age (unit id1) is locally divisible into older (id1A) and 

younger (id18) components. Geology from Hamilton (1984a). 

36 
m 

80 

60 

40 

20 

0 

m 

30 

20 

10 

0 

5 

4 

3 

2 

0 

2 

0 

A 

34,010 ±350 

Covered 

B 

·o -.,· o·o· 

~ 0""" c.- ."<>~9 ~.,_~·g:o 

~:~c:i;~:\: · o~:~,' c:;-e•~.!' o .;o;, 

K~:fr{(:t: otil D· 0 0 , , o, , •. 

;.~:.:.~o~; ~o C:o.o~~. 

:~?~~·; ~·".:.:_·:·.~~~- OoooOOOO<>o 

Oooo.ooo•o• 

~-~- ;· ;· ·.;_ ~-~: ~- .~--~~~:_ 

34,990 ±230 

(USGS-2454) 

30,160 ±410 

(USGS-1837> 

SECTION A 

THICKNESS 

UNIT (m) 

0.7 

4 22 

3 10.1 

2 18 

10.5 

0 9.7 

SECTION B 

THICKNESS 

UNIT (m) 

1.1 

24.5 

0 6 .o 

DESCRIPTION 

BLUFF CAP. Peat above frost-mixed silty peat that 

grades downward into silty gravel. 

COARSE ALLUVIUM. Pebbles and cobbles in matrix of 

poorly sorted sand with phyllite chips. Contains some 

sand interbeds. 

UPPER DIM1ICT. Clasts up to boulder size dispersed in 

compact gray silt. Grades downward into compact, 

deformed, pebbles and small cobbles in silty matrix. 

FINE ALLUVIUM. Fine to medium sand, pebbly sand, and 

pebble-small-cobble gravel. Contains 20-cm bed of 

oxidized organic silt 4 m below upper contact. 

LOWER DIAMICT. Rounded pebbles and small cobbles in 

matrix of compact silty sand to sandy silt. 

Structureless near top; faintly bedded and deformed 

near base. 

DEBRIS APRON. 

DESCRIPTION 

BLUFF CAP. Sod (0.3 m) above frost-churned stony silt 

(0.8 m). 

OUTWASH AND ALLUVIUM. Heakly stratified pebbles and 

cobbles in matrix of medium to coarse sand and 

granules (upper 8 m of deposit). Grades downward 

into pebble-small-cobble gravel with some sand and 

pebble interbeds (middle 8 m), then into interbedded 

sand and pebble-small-cobble gravel (basal 8 m). 

DEBRIS APRON. 

SECTION C 

w c 

15,030 ±200 

(1-12,514) 

9280 ±150 

(1-13,396) THICKNESS 

E 

3~~~~~~~~~~~~~ UNIT (m) DESCRIPTION 

2 3 

-.- ·-·- -:-:-_·_-_ 

~--------v 20 0 m -------~ 

0.7 

4.8-2.5 

12.0-14.3 

BLUFF CAP. Surface sod above peaty to 

stony silt. 

GRAVEL. Pebbles and small cobbles, with 

some larger cobbles. Sand interbeds 

occur in W part of unit. 

LACUSTRINE BEDS. Steeply dipping deltaic 

sand and fine gravel; grades westward 

(downvalley) into horizontally bedded 

fine sand, silty fine sand, and clayey 

silt. 

Figure 2.--Measured stratigraphic sections with radiocarbon dates, Noatak River near Douglas Creek. 

USGS, U.S. Geological Survey radiocarbon laboratory, Menlo Park, Calif.; I, Teledyne Isotopes, Westwood, 

N.J. Locations on figure 1. 

37 
glacial source areas near the valley head show an 

inverse gradation from less than 1 percent of all 

clasts near the base of the section to about 10 

percent near the top. A bed of dark-gray (5Y 4/1) 

clayey silt and gray (5Y 5/1) silty fine sand 8.5 m 

above river level contains sparse rootlets and 

organic detritus that are dated at 30,160 ± 410 yr 

B.P. 

Exposure C (fig. 2C), on the north side of the 

Noatak River near the mouth of Douglas Creek, 

intersects an 18-m alluvial terrace that is inset 

within the end-moraine belt. Separate sections 

were measured at the eastern and western ends of 

the exposure, and one radiocarbon sample was 

taken from each section. The eastern (upvalley) 

section consists dominantly of deltaic foreset beds 

that dip downvalley at angles as steep as 26°. 

Fine to medium sand, stony sand, and fine gravel 

alternate in beds 10-50 em thick. Near the center 

of the exposure, the deltaic sediments grade 

downward and westward into gray (5Y 5/1), 

horizontally bedded, well sorted fine sand with 

some 20-cm interbeds of clayey silt to silty fine 

sand. Near the west end of the bluff, dark gray 

organic silt grades upward into sandy fine gravel. 

Small wood fragments and rootlets from along 

bedding planes 1.4 m below the base of the gravel 

are dated at 15,030 ± 200 yr B.P. Unit 2 is fluvial 

gravel that consists of pebbles, small cobbles, and 

some larger cobbles in a sparse sandy matrix. The 

gravel thickens downvalley, where an inactive fan 

of Douglas Creek is graded to the gravel terrace. 

A bed of black (5Y 2.5/1) autochthonous peat 2-8 

em thick at the contact between the gravel and 

the underlying deltaic beds is dated at 9,280 ± 150 

yr B.P. The peat extends through the eastern part 

of the bluff, indicating that deltaic sediments 

were exposed subaerially for some time before the 

Noatak River overran the site. 

Radiocarbon dates and stratigraphic 

relations in the Douglas Creek area demonstrate 

that the associated end moraine (id2 on fig. 1) is of 

Itkillik II age as defined by Hamirton and Porter 

(1975) and as dated by Hamilton (1982). 

Deposition of fine alluvium prior to the ice 

advance began some time before 35 ka and 

continued until some time after 30 ka. Subsequent 

expansion of the Itkillik II glacier is recorded by 

coarsening-upward sediments with increasing 

upvalley lithologies at site B and by the upper 

diamict at site A. The glacier initially deformed 

and redeposited preexisting alluvium from the 

valley center, but it later deposited massive, 

bouldery, silt-rich till at the site. A minimum age 

for deglaciation is provided by the date of about 

15 ka on lake sediments that formed as the glacier 

retreated from its end moraine. 

The lower diamict at site A was originally 

interpreted as glacial drift on the basis of (1) its 

generally unsorted character, (2) high degree of 

compaction, and (3) incorporation of overturned 

38 

and evidently ice-thrust sediments near its base. 

However, our radiocarbon date of 34,990 ± 230 yr 

B.P. on this unit suggests the alternative 

possibility that the diamict may have been 

deposited as a component of a rapidly aggrading 

alluvial sequence. If the date is correct, then the 

deformation features in the lower diamict may 

have resulted from melting of underlying stagnant 

glacier ice rather than from later thrusting 

beneath an advancing glacier. We cannot 

ascertain at present whether the radiocarbon date 

or the original field interpretation is correct. 

Regardless of how the lower diamict is 

interpreted, our radiocarbon dates place a 

minimum age limit of about 35 ka on the Itkillik IB 

glacial advance, which formed the prominent 

lateral moraine near the northern valley wall (unit 

idlB on fig. 1). We believe that the Itkillik IB 

event probably is of early Wisconsin age (isotope 

stage 4 of the marine record) because (1) its drift 

is only slightly more subdued and weathered than 

drift of the Itkillik II advance, (2) the alluvium 

that separates the lower and upper diamicts at site 

A lacks identifiable paleosols, weathering 

horizons, or unconformities, and (3) kettle fields 

downvalley from site B (fig. 1) indicate that 

stagnant glacier ice from the older advance still 

was present on the valley floor when the outwash 

train of Itkillik II age was being deposited. 

REFERENCES CITED 

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

1984, Epiguruk bluff--Chronology and regional 

correlations (abs.): Geological Society of 

America Abstracts with Programs, v. 16, 

no. 5, p. 267. 

Detterman, R.L., Bowsher, A.L., and Dutro, J.T., 

Jr., 1958, Glaciation on the Arctic Slope of 

the Brooks Range, northern Alaska: Arctic, 

v. 11, p. 43-61. 

Hamilton, T.D., 1981, Surficial geologic map of 

the Survey Pass quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Field Studies 

Map MF-1320, scale 1:250,000. 

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. 

1984a, Surficial geologic map of the Ambler 

--River quadrangle, Alaska: U.S. Geological 

Survey Miscellaneous Field Studies Map MF1678, scale 1:250,000. 

1984b, Surficial geologic map of the Howard 

--Pass quadrangle, Alaska: U.S. Geological 

Survey Miscellaneous Field Studies Map MF1677, scale 1:250,000. 

1986a, 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. 9-49. 
1986b, Glaciation of the Brooks Range, in 

--Heginbottom, J.A., and Vincent, J.-S., eds~ 

Correlation of Quaternary deposits and events 

around the margin of the Beaufort Sea: 

Geological Survey of Canada Open-File 

Report 1237, p. 27-29. 

39 

Hamilton, T.D., and Porter, S.C., 1975, Itkillik 

glaciation in the Brooks Range, northern 

Alaska: Quaternary Research, v. 5, 

p. 471-497. 

Reviewers: L.D. Carter and J.S. Kelley 
ORDOVICIAN AND SILURIAN FOSSILS 

FROM THE DOONERAK ANTICLINORIUM, 

CENTRAL BROOKS RANGE, ALASKA 

John E. Repetski, Claire Carter, 

Anita G. Harris, and J. Thomas Dutro, Jr. 

The Doonerak anticlinorium, a structural 

high in the central Brooks Range, Alaska, exposes 

lower Paleozoic stratified rocks and mafic 

intrusive rocks that lie unconformably beneath 

Devonian and Carboniferous beds (fig. 1). Until 

recently, no fossils had been found in this 

dominantly argillite and volcaniclastic sequence. 

In 1981, Middle Cambrian trilobites were collected 

from calcareous beds in the dark pelitic sequence 

that stratigraphically underlies a siliceous 

volcaniclastic sequence (Dutro and others, 1984a, 

1984b). 

Conodonts identified as Periodon sp. (fig. 2), 

collected by D.L. Jones from the siliceous 

volcaniclastic rocks (cherts) on the north flank of 

the Doonerak anticlinorium (locality 1 in fig. 1 and 

table 1), indicate an Ordovician age range from 

Arenigian through Caradocian. Current taxonomic 

practice divides the conodont genus Periodon into 

three species. These occur in phylogenetic 

sequence from the late Early through the early 

Late Ordovician. Because the few specimens from 

the Doonerak area are limited to ramiform 

elements, a relatively conservative element in the 

conodont apparatus, assignment to species is not 

currently possible. 

In the past two years, Ordovician conodonts 

have also been identified by A.G. Harris (Dillon 

and others, in press) from rocks near Snowden 

Mountain in the Chandalar quadrangle. These 

collections, from carbonaceous phyllite and 

metacarbonate, occur in the Hammond subterrane 

(of the Arctic Alaska terrane) southeast of the 

Doonerak anticlinorium. Representatives of 

Periodon aculeatus Hadding are the most common 

elements in the collections. This species and other 

more biostratigraphically diagnostic taxa indicate 

an approximate Llandeilan to earliest Caradocian 

(middle Ordovician) age for these rocks. We 

tentatively correlate these two areas and suggest 

that they both represent the same lower Paleozoic 

basement in the south-central Brooks Range. 

In 1983, Michael Churkin, Jr. made two 

collections of graptolites from dark-gray, 

calcareous, chloritic phyllite and argillite just 

west of Fish Creek and north of Kachwona 

Creek. This locality is about 5 km west of the 

Ordovician conodont locality, in rocks overlying 

the Ordovician cherts (loc. 2, fig. 1, and table 1). 

The graptolites include Orthograptus? sp., 

Pristiograptus? sp., Monograptus sp. (with lobed 

thecae), Monograptus? sp., and indeterminate 

biserial forms (perhaps diplograptids). Carter 

suggests that this assemblage is middle to late 

40 

Early Silurian (Llandoverian). In 1984, Dutro 

collected, from the graptolite locality, a sample 

that yielded conodonts. According to Harris, these 

consist chiefly of representatives of Dapsilodus 

and a few digyrate and dolabrate ramiform 

elements of post-Ordovician morphotype. Taken 

together, these conodonts indicate a Silurian age. 

Dikes of two ages (470 and 350 Ma) intrude 

the lower Paleozoic terrane of the anticlinorium 

(Dutro and others, 1976). According to 

radiometric calibrations of the early Paleozoic 

(Harland and others, 1982; Odin, 1982), the older 

of these dike systems approximately corresponds 

either to the Arenigian-Llanvirnian boundary 

(Odin, 1982) or to the upper Llanvirnian (Harland 

and others, 1982). However, Ross and others 

(1982) placed the 470 Ma level in the lower 

Caradocian. In any case, the strata that are 

mapped stratigraphically high in the Doonerak 

structure (Dillon and others, in press) are also 

reasonably interpreted as middle Ordovician in 

age. 

Because the dated intrusive rocks do not 

directly cut the rocks that yielded the Ordovician 

conodonts, but instead intrude the older pelitic 

sequence, it can be argued that these dikes might 

have been feeders for the volcanic activity that is 

recorded in the siliceous volcaniclastic suite. 

Consequently, the 470 Ma radiometric age might 

date the fossiliferous Ordovician beds rather 

closely. The stratigraphic range reported for 

these conodonts spans about the same time 

interval as do the three interpretations of the 

radiometric date described above. 

Table 1.--Fossil localities in Doonerak 

anticlinorium (see fig. 1) 

North of Frigid Crags on the west side of North 

Fork of Koyukuk River, Wiseman 1:250,000 

quadrangle, Alaska. 

1. Ordovician: USGS loc. 9473-CO. Wiseman B-2 

quadrangle; 67°51.5' N., 150°56' W.; 

greenish-gray to red chert (siliceous 

volcaniclastics); approximately 30-mthick cliff. Collector: D.L. Jones, 1982. 

2. Silurian: Field Number 83BR 781MC and 84 

ADu 5 (USGS loc. 11447-SD). Wiseman 

B-3 quadrangle; 67°51.2' N., 151 °03' W.; 

small stream valley north of Kachwona 

Creek and west of Fish Creek; elev. 

approx. 1050 m (3500 ft); black to darkgray, calcareous, chloritic phyllite and 

argillite. Collectors: Michael Churkin, 

Jr., 1983; J.T. Dutro, Jr., 1984. 
152° Mz 

G 

D 

0 

D 

~ 

EXPLANATION 

Cretaceous and Jurassic rocks 

Triassic, Permian and 

Carboniferous rocks 

Upper Devonian Hunt Fork 

Shale , Kanayut Conglomerate 

Devonian rocks older than 

Hunt Fork Shale 

Silurian, Ordovician and 

Cambrian rocks 

Volcan ic rocks of 

Mount Doonerak 

Quartz -mica schist and ca lcareou s schist 

Contact 

_ *- Syncline 

-+- Anticline 

...A.____&_ Thrust fault 

- saw teeth on upper plate 

Figure 1.--Index map and generalized structural map of Doonerak anticlinorium and adjacent areas. 

Circled dot, Cambrian locality; 1, Ordovician locality; 2, Silurian locality; A, Anaktuvuk Pass; DA, axis of 

Doonerak anticlinorium; D, Mount Doonerak; F, Falsoola Mountain; I, Itkillik Lake; NF, North Fork 

Koyukuk River; S, Shainin Lake; SS, Savioyuk synclinorium; W, Wiseman; WL, Wild Lake. Geology modified 

from Dutro and others (1976). 

Consequently, we now know that the layered 

rocks of the Doonerak anticlinorium include 

Middle Cambrian, middle Ordovician, and Lower 

Silurian fossiliferous strata, that they were 

intruded by dikes about 470 Ma and 350 Ma, and 

that they have been folded, cleaved, faulted, and 

subsequently overstepped unconformably by 

shallow-water marine sequences in both late 

Middle Devonian and Early Mississippian times. 

REFERENCES CITED 

Dillon, J.T., Brosg~, 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, 1 sheet, 

scale 1:250,000. 

Dillon, J.T., Harris, A.G., and Dutro, J.T., Jr., in 

press, Preliminary description and correlation 

of lower Paleozoic fossil-bearing strata in the 

Snowden Mountain area of the south-central 

Brooks Range, Alaska, in Tailleur, I. L. and 

41 

1 mm 

Figure 2.--Periodon sp. from Ordovician siliceous 

volcaniclastic rocks, locality 1, north flank of 

Doonerak anticlinorium, USGS loc. 9473-CO; 

ramiform element on bedding surface, 

photographed under glycerine: USNM 414609. 

Specimen reposited in collections of the 

Department of Paleobiology, U.S. National 

Museum of Natural History, Washington, D.C. 
Weimer, Paul, eds.: Alaska North Slope 

geology: Pacific Section Society of Economic 

Paleontologists and Mineralogists and Alaska 

Geological Societ~. 

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. 

Dutro, J.T:, Jr., Palmer, A.R., Repetski, J.E., and 

Brosge, W .P ., 1984a, The Doonerak 

anticlinorium revisited, in Coonrad, W .L and 

Elliott, R.L., eds., The United States 

Geological Survey in Alaska: 

Accomplishments during 1981: U.S. 

Geological Survey Circular 668, p. 17-19. 

42 

___ 1984b, Middle Cambrian fossils from the 

Doonerak anticlinorium, central Brooks 

Range, Alaska: Journal of Paleontology, 

v. 58, no. 6, p. 1364-1371. 

Harland, W.B. and others, 1982, A geologic time 

scale: Cambridge, U.K., Cambridge 

University Press, 131 p. 

Odin, G.S., 1982, The Phanerozoic time scale 

revisited: Episodes, v. 5, no. 3, p. 3-9. 

Ross, R.J., Jr., and others, 1982, The Ordovician 

System in the United States: International 

Union of Geological Sciences Publication 12, 

73 p. 

Reviewers: J.M. Berdan and John Pojeta, Jr. 
ORGANIC CARBON OCCURRENCE AND 

CONTENT IN CARBONATE ROCKS FROM THE 

OMAR COPPER PROSPECT, 

BAIRD MOUNTAINS, ALASKA 

Jeanine M. Schmidt and Peter F. Folger 

Complexly faulted carbonate rocks of 

Ordovician through Devonian age underlie most of 

the Squirrel River basin in the southwestern Baird 

Mountains (Dumoulin and Harris, 1985 and in 

press). The Omar copper pros~ect (fig. 1) covers 

an area of approximately 8 km along a tributary 

of the Omar River, 45 km north of the Squirrel 

River. At the prospect, irregularly distributed 

copper sulfides and tetrahedrite form 

disseminations and occur within vein-breccias that 

crosscut Lower and Middle Devonian dolostones 

(Degenhart and others, 1978; Folger and Schmidt, 

1986). After mineralization, these rocks 

underwent syndeformational greenschist to 

glaucophane-schist facies metamorphism during 

the Jurassic-Cretaceous Brooks Range orogeny 

(Snelson and Tailleur, 1969). 

White to dark-gray dolostone and limestone 

at the prospect contain varying amounts of organic 

matter. Organic material also occurs as discrete 

millmeter- to centimeter-sized blebs and fillings 

within Cu-bearing veins. In order to determine the 

variability, type, and thermal history of organic 

material at Omar, 14 samples were submitted to 

ExLog Laboratories for total organic carbon (TOC) 

analyses and Rock-Eval pyrolysis (Tissot and 

Welte, 1978). Such information from the organic 

material would ideally reflect its source, the 

conditions under which it was deposited with 

sulfide minerals, and the subsequent history of the 

rocks. Twelve rock samples submitted (table 1) 

are representative of all types of carbonate rocks 

exposed in the prospect area: unmineralized 

Ordovician and Devonian (Emsian and Eifelian) 

dolostones, unmineralized Ordovician(?) 

argillaceous limestone, and mineralized Devonian 

dolostone. Two samples of organic blebs from 

within the mineralized breccia were also analyzed. 

All samples were washed, dried, split and 

crushed. For TOC analysis, 1 g of crushed sample 

was used, and carbonate minerals were dissolved 

by heating for 3 hr at 60 °C in 50 mL of 3 M HCl. 

The residue, vacuum filtered onto a glass-fiber 

mat, was washed and then dried at 80 °C for 1 hr 

in preparation for analysis. A Rock-Eval II 

pyrolysis instrument was used, with helium gas and 

a temperature ramp of 25 °C per minute. 

Analyses were calibrated with standards and 

blanks every 10 samples. 

The total organic carbon content of some 

lithologic units within the Omar prospect area is 

distinct. Unmineralized Ordovician dolostone and 

argillaceous limestone contain 0.07-0.15 weigh'tpercent carbon and unmineralized Emsian 

43 

dolostone 0.19-0.22 weight-percent carbon. Three 

other samples of carbonate rocks of probable 

Ordovician age (J.A. Dumoulin, USGS, oral 

commun., 1986), from approximately 8 km 

southeast of Omar, have TOC contents (0.06-0.14 

weight percent) similar to those at Omar. These 

values suggest that the organic content of 

carbonate rock units may be distinctive and 

int~rnally homogeneous over areas as large as 20 

km • Mineralized Devonian dolostones have both 

the lowest and highest (0.05 and 0. 73 weight 

percent) carbon contents. This difference in TOC 

is probably accounted for by the presence of 

organic blebs in some of these samples. 

sl and s2 peak values produced during 

pyrolysis are measures of the hydrocarbon yield of 

a rock. s 1 measures the free hydrocarbons 

distilled at low temperatures (below 300 °C); s 2 measures the additional hydrocarbons produced by 

heating of the remaining kerogen in the rock 

(Bustin and others, 1985). An X-ray diffraction 

peak at 26° 29 indicates that the organic blebs 

have structures that approach crystalline graphite 

(Joel Leventhal, USGS, oral commun., 1986). s 2 peak values were below detection limits for 4 of 5 

Devonian samples, therefore productivity ratios 

(S1/ s 1 +S2

) for these rocks cannot be determined. 

Productivity ratios for the Ordovician rocks are 

relatively high (0.62-0.94, avg. 0.84), indicating 

that all rock types at Omar contain mainly free 

hydrocarbons and have been heated well beyond 

the thermal windows necessary for production of 

oil (100-200 °C) and gas (150-250 °C; Tissot and 

Welte, 1978). 

Table 1.--Total organic carbon contents, conodont 

alteration indices and selected Rock-Eva! pyrolysis 

data from the Omar Cu prospect and nearby 

[na, not applicable; *, values greater than 1,000 

are due to low total organic carbon or presence of 

carbonate in sample. See text for explanation of 

symbols] 

Rock-Eval ~~ro 1 ·ys 1 s Conodonts 

Sample Sample roc s1 s, s 3 S2JTOC s3!TOC CAl Tmin 

type No. (wt pet.) (m9/9i (mg/9) (m9/g) (HI) (OJ) oc 

Omar prospect 

Hydrocarbon !59 A na 0.50 0.60 12.33 

blebs 1598 !.52 .54 10.40 

Mineralized 9 0.05 .19 -- 6.32 ( 12 ,640)* -- (Ems ian) 74A .05 .46 -- 2.49 (4,980)* -- dolostone 74B .69 .56 -- 2.89 419 77 .73 .09 -- .37 51 

Ems ian 55 .22 .49 .05 .17 23 77 5-5.5 300-350 dolostone 83 .19 .02 -- .16 84 5.5 350 

Ordovician(?) 8 .11 .97 .08 . 10 73 91 1 imestone ll .10 .64 .11 .19 110 190 

Ordovician 52 .09 .59 .04 .10 44 Ill dolostone 57 .07 .3] .03 .08 43 114 5.5-6 350-400 

86 .08 .28 .08 .73 100 912 6-7 400-450 112 .15 .24 .15 .34 100 227 5.5 350 

8 km south of Omar 

Ordovician(?) 5JS59A 0.14 0.37 -- 0.19 136 

1 imestone 

Mineralized 5JS39 .06 .08 -- 4.42 17 (7,367)* 

Ordovician(?) 5JS628 .12 1.20 0.27 3.35 225 (2 ,792)* 

dolostone 
161° 30' 

0 

I 20 I 

Figure 1.--Map of Omar copper prospect. Shaded pattern shows areas underlain by Devonian dolostones. 

Cross-hatches indicate areas of sulfide mineralization. Triangles indicate sample locations (table 1). 

All mineralized samples and hydrocarbon blebs are from within largest cross-hatched area. Contour 

intervals in feet. 

The organic clots are paragenetically late in 

the mineralization sequence and fill interstices 

within the dolostone breccia (fig. 2). 

Approximately 20 percent of these blebs are 

spherical, suggesting transport as an immiscible 

phase, probably a hydrocarbon, in an aqueous 

solution. The spheres occur only within 

mineralized rocks at Omar, and are always 

enclosed by vein-filling, hydrothermal dolomite or 

calcite. Similar spherical carbon blebs with 

hydrothermal carbonate occur in mineralized 

breccias and vugs in some unmetamorphosed Pb-Zn 

deposits of the Viburnum trend in southeastern 

Missouri (Marikos, 1984). Hydrothermal fluids 

associated with mineralization transported the 

clots in both the Viburnum trend and Omar, but 

later metamorphism heated the organic material 

44 

at Omar to its present near-graphite 

composition. Lower productivity ratios (0.45 and 

0.74) of the blebs relative to the whole rocks may 

reflect their isolated and homogeneous habit, in 

which they may have been less affected by 

metamorphic heating than disseminated organic 

material in the whole rocks. 

Of the 14 samples, 7 yielded Tmax values 

(334-416 °C) from the 8_2 pyrolysis peak. 

However, Tmax values are difficult to interpret in 

rocks that have been metamorphosed and 

undergone possible surface weathering (Joel 

Leventhal, USGS, oral commun., 1986). These 

pyrolysis-derived Tmax values are compatible with 

low greenschist to glaucophane-schist facies, 

which are the conditions suggested for the Omar 

area by the mineralogy of noncarbonate rocks 
Figure 2.--0rganic, carbon-rich sphere 

thermal dolomite (white) within 

dolostone breccia. Sphere is 5 m m in 

Photograph by Joel Leventhal (USGS). 

in hydroDevonian 

diameter. 

(Armstrong and others, 1986). A tem[Jerature 

range of 300-450 °C is indicated by the color 

alteration indices (CAl's) of conodont microfossils 

from the same sam[Jles (Anita Harris, USGS, 

written commun., 1985, 1986; table 1). These 

tem[Jerature ranges suggest that metamor[Jhic 

heating consistently over[Jrinted any mineralrelated paleothermal anomaly in rocks of the 

Omar area. 

The s3 value is a measure of the [Jyrolysisderived organic oxygen in the rock. Mineralized 

sam[Jles and organic globules at Omar have organic 

C02 values an order of magnitude higher than 

unmineralized sam[Jles (5.80 mg/g versus 0.23 

mg/g average). This suggests that the solutions 

that trans[Jorted and de[Josited sulfide minerals 

with dolomite and hydrocarbons were oxidizing, or 

caused oxidation of organic matter by reaction 

with so4• Alternatively, the mineralized rocks 

may have become more fractured and [Jermeable, 

and localized later oxidizing fluids unrelated to 

the mineralizing event. Variation in organic C02 

content between unmineralized samples is small. 

Plots of oxygen index (OI) versus hydrogen 

index (HI) are used to indicate the type of organic 

material originally present in fresh rock samples 

and the degree of maturation of that material 

(Bustin and others, 1985). HI values of sam[Jles 

from Omar are low (23-110) and indicate that the 

organic matter is highly evolved in terms of its 

hydrogen content relative to carbon. The OI 

values are widely scattered, and some are much 

higher than those characteristic of overmature 

hydrocarbon source rocks (typically <100). The 

anomalously high OI values of these rocks result 

from ex[Josure to oxidizing conditions independent 

of the normal burial-maturation [Jrocess, and 

therefore are not useful for inter[Jreting the ty[Je 

45 

of organic source material or the path of its 

evolution. The source is [)resumed to be marine 

algal matter, since these are [Jlatform carbonate 

rocks. Oxidizing conditions may have occurred 

during mineralization, [Jrimary dolomitization, or 

surface weathering. Anomalously high CAl values 

of 7-8 versus a regional 5-6 average indicate that 

oxidation also occurred during local bleaching of 

dolostone (J.A. Dumoulin, USGS, oral commun., 

1985). 

Com[Jarison of organic material at Omar 

with that from Ruby Creek, a similar CO[J[Jer 

deposit hosted in Devonian carbonate rocks 200 km 

to the east in the Ambler River quadrangle 

(Hitzman, 1983), shows that the TOC contents of 

both host and mineralized rocks at Omar are lower 

than those at Ruby Creek, where both black and 

carbonaceous carbonates occur, and where 

hydrocarbon seams, disseminations, and blebs are 

common. The oxygen content of hydrocarbons in 

mineralized rocks at Ruby Creek is consistently 

low. Their position on a H/C versus 0/C plot 

reflects maturation to a point beyond both the oil 

and gas windows. Temperatures of sulfide 

deposition at Ruby Creek are 120-217 °C (from 

fluid-inclusion studies), much lower than the CAl 

temperatures indicated at Omar. CAl's from 

Silurian and Devonian carbonate rocks in the Ruby 

Creek area are 5-6 (Anita Harris, USGS, written 

commun., 1985, 1986), indicating m1mmum 

temperatures of 300-350 °C, which also represents 

the later metamorphic overprint. 

Unmineralized Ordovician and Devonian 

carbonate rock units have distinct TOC contents 

within a spatially restricted area (8 km 2) around 

the Omar [Jrospect. All rocks in this area have 

been heated well beyond the windows necessary 

for production of oil and gas; all hydrocarbons 

in the rocks are overmature. Oxidizing conditions 

during mineralization, bleaching, dolomitization(?), or surface weathering apparently altered 

the oxygen content of the hydrocarbons. However, 

organic matter in all mineralized rocks contains 

much higher C02 than that in unmineralized 

samples. Temperatures suggested for metamorphism by conodont CAl's are consistent with 

mineral assemblages within the rocks. No 

conclusions can be drawn regarding the type of 

organic material originally present, or its 

maturation path, although a marine algal source is 

most likely for these platform carbonate rocks. 

REFERENCES CITED 

Armstrong, R.L., Harakal, J.E., Forbes, R.B., 

Evans, B.W., and Thurston, S.P., 1986, Rb-Sr 

and K-Ar study of metamorphic rocks of the 

Seward Peninsula and southwestern Brooks 

Range, Alaska: Geological Society of 

America Memoir 164, p. 185-203. 

Bustin, R.M., Barnes, M.A., and Barnes, W.C., 

1985, Diagenesis 10: Quantification and 
modelling of organic diagenesis: Geoscience 

Canada, v. 12, no. 1, p. 1-21. 

Degenhart, C.E., Griffis, R.J., McOuat, J.F. and 

Bigelow, C.G., 1978, Mineral studies of 

certain ANSCA 17(d)(2) lands in Alaska: U.S. 

Bureau of Mines Open File Report 103-78, 

529 p. 

Dumoulin, J.A., and Harris, A.G., 1985, Lower 

Paleozoic carbonate rocks of Baird Mountains 

quadrangle, Alaska (abs.): Tulsa, American 

Association of Petroleum Geologists, Program 

and Abstracts, 60th Annual meeting, Pacific 

section, p. 55. 

Dumoulin, J.A., and Harris, A.G., in press, Lower 

Paleozoic carbonate rocks of the Baird 

Mountains, Western Brooks Range, Alaska, in 

American Association of Petroleum 

Geologists Memoir, Tailleur, Irv and 

Weimer, P., eds. 

Folger, P.F., and Schmidt, J.M., 1986, Geology of 

the carbonate-hosted Omar copper prospect, 

Baird Mountains, Alaska: Economic Geology, 

v. 81, p. 1690-1695. 

46 

Ritzman, M. W ., 1983, Geology of the Cosmos Hills 

and its relationship to the Ruby Creek coppercobalt deposit: Stanford, Calif., Stanford 

University, Ph.D. dissertation, 266 p. 

Marikos, M. A., 1984, Relation of bitumen to ore 

in the Magmont West orebody, southeast 

Missouri: Rolla, Mo., University of Missouri, 

M.S. thesis, 122 p. 

Snelson, S., and Tailleur, I.L., 1969, Large scale 

thrusting and migrating Cretaceous foredeeps 

in the western Brooks Range and adjacent 

regions of northwest Alaska, (abs.): American 

Association of Petroleum Geologists Bulletin, 

v. 523, no. 3, p. 567. 

Tissot, B.P., and Welte, D.H., 1978, Petroleum 

formation and occurrence: Berlin, Springer 

Verlag, 538 p. 

Reviewers: J.A. Dumoulin and J. Leventhal 
PLANT MEGAFOSSILS, VERTEBRATE REMAINS, 

AND PALEOCLIMATE OF THE KOGOSUKRUK 

TONGUE (LATE CRETACEOUS), 

NORTH SLOPE, ALASKA 

Robert A. Spicer and Judith Totman Parrish 

The upper part of the nonmarine Kogosukruk 

Tongue of the Prince Creek Formation is well 

exposed along 80 km of the Colville River between 

Uluksrak Bluff and Ocean Point (fig. 1). In the 

summer of 1986, palynological and megafossil 

collections were made at 48 localities as part of a 

study that has the aim of reconstructing the 

vegetation and, subsequently, the paleoclimate of 

the North Slope during the Late Cretaceous. The 

Kogosukruk Tongue is of particular importance to 

paleoclimatic studies because at the time of 

deposition, northern Alaska was at 80° to 85° N. 

paleolatitude (Smith and others, 1981; Ziegler and 

others, 1983). Paleoclimatic information derived 

from the study of the Kogosukruk Tongue is vital 

to the reconstruction of the global latitudinal 

temperature gradient near the close of the Late 

Cretaceous. 

The Kogosukruk Tongue is Campanian and 

Maestrichtian in age, based on .. marine fossils in 

rocks above and below (Brosge and Whittington, 

1966; Marincovich and others, 1985; McDougall, 

1986) and on pollen (Frederiksen and others, 

1986). A variety of sedimentary facies is present 

within the unit. Fluvial and floodplain deposits, 

especially channel-fill and overbank deposits, 

compose the bulk of the sediments, but lacustrine 

and bog deposits also are represented. Coal beds 

composed of autochthonous or allochthonous 

material occur throughout the Kogosukruk. Those 

near the base of the unit tend to be bituminous, 

rich in resin, and thicker than those near the top, 

which also are of lower rank; the coal beds 

typically are 0.5 m, but rarely more than 1.0 m, 

thick. Paleosols and bentonites occur throughout 

the unit. 

We recovered a maximum of 10 megafossil 

taxa from the Kogosukruk Tongue. These consist 

of two conifer forms, Parata:xodium wigginsii 

Arnold and Lowther and a cupressaceous form; one 

terrestrial angiosperm leaf, Hollickia quercifolia 

(Hollick) Krassilov; one aquatic angiosperm, 

Quereu:xia angulata (Lesquereux) Kryshtofovich 

(also referred to "Trapa"); one angiosperm fruit; 

two ferns; the sphenophyte Equisetites sp.; and 

two types of small, ovoid seeds. The preservation 

of intact deciduous conifer shoots, the lack of 

hydraulic size-sorting, and evidence of minimal 

selective mechanical and biogenic degradation in 

most assemblages all suggest rapid deposition near 

the site of growth. The ubiquitous preservation of 

Equisetites rhizome systems in growth position and 

the three-dimensional preservation of a fern in 

growth position within an ash horizon provide 

important data on early colonizers and- ground 

47 

155° 150° 

OCEAN POINT-

- ULUKSRAK BLUFF 

0 50 KILOMETERS 

Figure 1.--North-central Alaska. The Kogosukruk 

Tongue of the Prince Creek Formation crops out 

along the Colville River between Uluksrak Bluff 

and Ocean Point. 

cover within the floodplain environment. The 

Equisetites rhizome systems penetrate sediments 

below paleosols and autochthonous coal beds, and 

this suggests that the plant was an early colonizer 

of floodplain environments, much as Equisetum is 

today in the Yukon River Valley. Equisetites, 

together with ferns, probably composed the ground 

cover over much of the region. 

The plant megafossils show no evidence of 

major vegetational change throughout the period 

of deposition of the Kogosukruk Tongue. However, 

the later coal beds appear to contain less woody 

material than do the earlier ones, which may 

reflect a diminution of the forest ecosystem 

leading to a more open vegetation. The forest 

community was dominated by the deciduous 

conifer Parata:xodium wigginsii, which, because of 

the close association of the leafy shoots with 

branches and logs, we interpret to have reached 

small-tree stature. Structurally preserved 

(calcified and silicified to minimally altered) 

coniferous logs rarely exceed 20 em in diameter, 

and the maximum diameter observed was 50 em. 

No angiosperm wood has been identified, and it is 

likely that the angiosperms formed only a minor 

understory or lake-margin component. No 

angiosperms were recovered from channel-fill 

sediments, suggesting that the riparian, largeleaved angiosperm communities of the 

Cenomanian {Spicer and Parrish, 1986a) had ceased 

to exist. Angiosperm pollen diversity increased in 

latest Maestrichtian time (T.A. Ager, USGS, 

written commun., 1986), but the absence of 

complementary leaf fossils suggests to us that the 

increase may reflect diversification of herbaceous 

elements. 
In 1985, we made a similar study of the midCretaceous Niakogon Tongue of the Chandler 

Formation along the Colville River (Spicer and 

Parrish, 1986a), and recovered 80 to 90 plant 

megafossil taxa from those units. We estimated 

that the mean annual temperature at that time 

was 10 ± 3 °C, based on leaf-margin analysis of 

the angiosperms (67 forms; Wolfe, 1979). Although 

the Kogosukruk Tongue contains too few 

angiosperm leaf forms to permit similar 

quantitative estimates of mean annual 

temperature, the drop in diversity from the midCretaceous strongly suggests a lower mean annual 

temperature in the Campanian and Maestrichtian 

than earlier. We estimate the mean annual 

temperature in the Campanian and Maestrichtian 

to have been at least 5 °C lower than in the midCretaceous. The marked drop in diversity during 

the Late Cretaceous probably cannot be attributed 

to sampling bias because the same sedimentary 

and diagenetic facies occur throughout. 

Analysis of growth-ring characteristics in 

fossil wood from the Niakogon Tongue {Spicer and 

Parrish, 1986b) led us to conclude that the 

Cretaceous light regime was similar to that at 

high latitudes today. At latitude 80° N., summer 

and winter consist of four months of continuous 

daylight and darkness, respectively, and the 

photoperiod during the short spring and autumn 

changes very rapidly. Field examination of the 

fossil wood from the Kogosukruk Tongue suggests 

a similar light regime for the Campanian and 

Maestrichtian interval. However, rings from wood 

of the Kogosukruk Tongue seem to be narrower 

overall and contain more late wood than those 

from the Niakogon Tongue. Thus, growing 

conditions apparently deteriorated during the Late 

Cretaceous. 

The predominance of fluvial sediments and 

the existence of coal beds in the Kogosukruk 

Tongue are indicative of abundant supply of water 

to the regional environment. However, the 

angiosperm leaf is small compared to the leaves 

from the Chandler Formation, and fossil charcoal 

is much more abundant, whereas it is practically 

unknown in the Chandler Formation. These lines 

of evidence suggest drier conditions, under which 

wildfires became much more common. 

In addition to the plant megafossils, we 

recovered remains of ceratopsian (horned) 

dinosaurs from the Kogosukruk Tongue. These 

were a horn core, an occipital condyle (the part of 

the skull that articulates with the spinal column), 

and the distal part of a femur (thigh bone); the 

horn core is from a group of ceratopsians that 

lived during middle Campanian to early 

Maestrichtian time (J.M. Parrish, Univ. of 

Colorado Museum, written commun., 1986). 

Skeletal remains of hadrosaurian (duck-billed) 

dinosaurs and teeth of carnivorous dinosaurs have 

been reported from near the top of the Kogosukruk 

Tongue near Ocean Point (W .A. Clemens, written 

commun., 1985) and, with the discovery of 

48 

ceratopsians, it would appear that a moderately 

diverse dinosaurian fauna occupied the North Slope 

during the Campanian and Maestrichtian. 

In conclusion, plant megafossil evidence 

from the Kogosukruk Tongue of the Prince Creek 

Formation, particularly in comparison with 

evidence from the Chandler Formation, indicates 

that the climate on the North Slope during 

deposition of the Kogosukruk Tongue was cold 

temperate and at least periodically dry. The 

presence of dinosaurs so close to the Cretaceous 

North Pole has important implications for 

dinosaurian ecology. 

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. 501-638. 

Frederiksen, N.O., Ager, T.A., and Edwards, L., 

1986, Comment and reply on "Early Tertiary 

marine fossils from northern Alaska: 

Implications for Arctic Ocean paleogeography 

and faunal evolution: Geology, v. 14, 

p. 802-803. 

McDougall, Kristin, 1986, Maestrichtian benthic 

foraminifers from Ocean Point, Alaska 

(abs.): Geological Society of America 

Abstracts with Program, v. 18, p. 688. 

Marincovich, Louis, Jr., Brouwers, E.M., and 

Carter, L.D., 1985, Early Tertiary marine 

fossils from northern Alaska: implications for 

Arctic Ocean paleogeography and faunal 

evolution: Geology, v. 13, p. 770-773. 

Smith, A.G., Hurley, A.M., and Briden, J.C., 1981, 

Phanerozoic paleocontinental world maps. 

Cambridge, U.K., Cambridge University 

Press, 10 2 p. 

Spicer, R.A., and Parrish, J.T., 1986a, 

Paleobotanical evidence for cool north polar 

climates in middle Cretaceous (AlbianCenomanian) time: Geology, v. 14, 

p. 703-706. 

1986b, Fossil woods from northern Alaska and 

climate near the middle Cretaceous north 

pole (abs.): Geological Society of America 

99th Annual Meeting and Exposition Abstracts 

with Programs, p. 759. 

Wolfe, J.A., 1979, Temperature parameters of 

humid to mesic forests of eastern Asia and 

relation to forests of other regions of the 

northern hemisphere and Australasia: U.S. 

Geological Survey Professional Paper 1106, 

37 p. 

Ziegler, A.M., Scotese, C.R., and Barrett, S.F., 

1983, Mesozoic and Cenozoic paleogeographic 

maps, in Brosche, P., and Siindermann, J., 

eds., Tidal friction and the earth's rotation II: 

Berlin, Springer-Verlag, p. 240-252. 

Reviewers: J.P.Galloway and C.M. Molenaar 
PETROGRAPHY OF THE BAIRD MOUNTAINS 

SCHISTOSE LITHOLOGIES, 

NORTHWESTERN ALASKA 

Mark R. Zayatz 

Metamorphic rocks from the southeast 

corner of the Baird Mountains 1:250,000 

quadrangle consist of two distinct rock units: a 

homogeneous pelitic schist and a mixed schist 

(fig. 1). Petrographic criteria, from approximately 

600 thin sections of metamorphic rocks, were used 

to determine 13 stable mineral assemblages 

indicating blueschist- and greenschist-facies 

conditions. K-Ar cooling ages of 90-110 m.y. from 

micas within the schistose lithologies indicate that 

regional metamorphism and deformation 

associated with the Brooks Range orogeny came to 

an end within the middle Cretaceous (Wilson and 

Turner, 1975). 

The pelitic schist unit consists of dark-green 

to greenish-gray, well-foliated and lineated, fineto medium-grained, polydeformed schist 

characterized by five stable mineral assemblages 

(listed in order of decreasing mineral abundance): 

(1) quartz-albite-white mica-chlorite 

(2) quartz-albite-white mica 

(3) quartz-albite-chlorite 

(4) quartz-albite-white mica-chlorite-chloritoid 

(5) quartz-albite-white mica-chlorite-garnet 

Rare quartz and albite porphyroblasts 

commonly preserve the s1 foliation. Primary 

chlorite forms hypidioblastic to xenoblastic laths 

and aggregates which define primary (S2) 

foliation. Secondary chlorite occurs as crystal 

clots that replace primary minerals along 

fractures. Chloritoid occurs as pleochroic slateblue to green, idioblastic to hypidioblastic, 

elongate crystals which tend to be retrograded to 

white mica + chlorite (fig. 2A). Chloritoid is 

generally oriented subparallel to the pervasive (S2) 

foliation direction. Garnets, which occur rarely 

and only in assemblage 5, are inclusion-free, 

unaltered, idioblastic to hypidioblastic grains 

partially enveloped by a sheath of primary chlorite 

parallel to s2 foliation. Petrographic evidence of 

zoning within garnets was not noted. 

The mixed schist unit consists of quartzmica schist, black carbonaceous schist, marble, 

calcareous-mica schist, micaceous calc-schist, 

chlorite schist, metabasite, and two blueamphibole-bearing lithologies. The micaceous and 

calcareous rocks are characterized by assemblages 

1-5 and four additional assemblages: 

(6) quartz-albite-graphite-white mica-chlorite 

(7) quartz-albite-carbona te-w hi te mica -chlorite 

(8) quartz-feldspar-white mica-chloritestilpnomelane 

(9) quartz-albite-white mica-chlorite-biotite 

Prograde development of biotite from chlorite 

is common along grain boundaries (fig. 28). 

49 

Petrographic evidence of zoning within garnets is 

rarely noted. Shattered garnet grains are 

commonly altered to chlorite+ quartz+ magnetite 

or white mica +quartz +chlorite (fig. 2C). 

Metabasite within the mixed schist unit is a 

very dark green, massive rock with variable grain 

size and an outcrop extent of less than 2 km. This 

lithology is characterized by two stable low-grade 

metamorphic mineral assemblages: 

(1 O) albite-actinolite-chlorite-epidote 

(11) albite-actinolite-epidote-stilpnomelane 

Two distinct blue-amphibole-bearing 

lithologies, which also occur within the mixed 

schist unit, are a massive, glaucophane-bearing 

metabasite (assemblage 12) and a well-foliated and 

well-lineated glaucophane schist (assemblage 13) 

identical to assemblage 1 except for the 

occurrence of amphibole. 

( 12) albi te-chlori te-epidote-actinoli teglaucophane-garnet 

(13) quartz-albite-white mica-chloriteactinolite-glaucophane 

The occurrence of glaucophane-bearing metabasite 

and schist, observed locally in distinct layers 

throughout the mixed schist unit, is probably 

compositionally controlled. Partial to nearcomplete retrograde replacement of glaucophane 

by chlorite + albite (fig. 2D) and of garnet by 

chlorite is common along grain boundaries, 

fractures, and cleavage planes. 

Microfabrics in the various lithologies of the 

pelitic schist and mixed schist units (with the 

exception of the metabasite, which has a 

"directionless fabric") suggest at least three 

pervasive, ductile deformation events. The 

earliest deformation recognized (F .1) is 

characterized by a poorly preserved schistosity 

162' 159' 

68'r;=============::;-----, 

EXPLANATION 

Pelitic schist unit 

0 25 50 KILOMETERS 

Figure !.--Location of pelitic schist and mixed 

schist units within Baird Mountains 1:250,000 

quadrangle. 
Figure 2.--Photomicrographs of selected samples from schistose lithologies of Baird Mountains quadrangle 

taken in plane-polarized light: ab, albite; bt, biotite; cd, chloritoid; cl, chlorite; gl, glaucophane; 

gt, garnet; qz, quartz; wm, white mica. A, Retrograde alteration of chloritoid to white mica and 

chlorite. B, Prograde development of biotite from chlorite. C, Retrograde alteration of garnet to chlorite 

and white mica. D, Retrograde alteration of glaucophane to chlorite and albite. 

50 
RETROGRADE PROGRADE 

BLUESCHIST EPISODE - GREENSCHIST EPISODE --- GREENSCHIST EPISODE 

CHLORITE ZONE BIOTITE ZONE 

garnet chlorite 

+ white mica 

glaucophane - chlorite + albite 

chloritoid ---- white mica 

+ chlorite 

chlorite - biotite 

Figure 3.--Progression of metamorphic episodes and characteristic mineral reactions preserved within 

Baird Mountains schistose rock units. 

(S1) observed within some large helicitic quartz 

and albite porphyroblasts. F 1 folds appear to have 

been obliterated by the tightly crenulated, 

dominant folds of subsequent folding events. 

The prominent folding event (F 2) is 

characterized by tight asymmetric crenulations 

and a dominant schistosity (S2). F 2 folds are in 

turn refolded into gentler, broader folds (F 3) of 

variable style without significantly altering F 2 morphology. Petrofabric analyses of three 

measurements on each of 100 thin sections shows 

that s2 is cut at an angle of 100° to 120° by the 

axial plane cleavage (S3) created during the F 3 event. A fourth (F 4), more brittle deformation is 

developed locally along the western margin of the 

Kallarichuk Hills. 

Both blueschist-facies and greenschist-facies 

metamorphic assemblages are preserved within the 

study area. Blueschist-facies assemblages are 

characterized by glaucophane-bearing metabasite 

(assemblage 12) and metapelite (assemblage 13). 

Petrographic evidence suggests that the 

blueschist-facies rocks may represent the oldest 

regional metamorphic episode preserved within the 

schistose lithologies studied in the southeast 

corner of the Baird Mountains quadrangle. 

Following blueschist-facies metamorphism, 

these rocks were subjected to a retrogressive 

greenschist-facies metamorphism characterized by 

chlorite-zone mineral assemblages. Greenschistfacies chlorite-zone rocks contain retrograded 

glaucophane, garnet, and chloritoid (fig. 3), 

suggesting a lowering of pressure. The 

51 

mineralogies of equilibrium assemblages (1-8, 10, 

11) are representative of the chlorite zone of the 

greenschist facies. Stilpnomelane (assemblage 8) 

suggests that moderate pressures characterized 

the event (Miyashiro, 1973). Since many of the 

same minerals are stable within both the 

blueschist- and greenschist-facies assemblages, 

these minerals probably formed during the 

blueschist episode and remained stable throughout 

the greenschist episode. 

Prograde development of biotite from 

chlorite, observed within the fabric of some 

metapelites of the mixed schist unit, suggests an 

increase in temperature at some time during the 

greenschist-facies episode. This reaction 

characterizes a change within the greenschist 

facies from the lower temperature chlorite zone 

to the higher temperature biotite zone (fig. 3). 

This reaction may not be found within the pelitic 

schist unit due to unfavorable whole-rock 

chemistry. 

The pelitic schist and mixed schist units 

from the southeast corner of the Baird Mountains 

quadrangle are characterized by both blueschistfacies and greenschist-facies metamorphic 

assemblages. Microfabrics suggest that these 

rocks have been involved in at least three 

deformational events. These preliminary findings 

seem to agree with that observed for similar 

polymetamorphosed and polydeformed 

metasedimentary rocks that trend along strike of 

the south flank of the Brooks Range (Dillon and 

others, 1980; Ritzman, 1982). 
REFERENCES CITED 

Dillon, J.T., Pessel, G.H., Chen, J.H., and Veach, 

N.C., 1980, Middle Paleozoic magmatism and 

orogenesis in the Brooks Range, Alaska: 

Geology, v. 7, p. 338-343. 

Ritzman, M. W., 1982, Metamorphic petrology of 

the Ambler district, southwestern Brooks 

Range, Alaska (abs.): Geological Society of 

America Abstracts with Programs, v. 14, 

p. 173. 

52 

Miyashiro, A., 1973, Metamorphism and 

metamorphic belts: London, George Allen and 

Unwin, 492 p. 

Wilson, F.H., and Turner, D.L., 1975, Radiometric 

age map of Alaska--Northern Alaska: Alaska 

Division of Geological and Geophysical 

Surveys Open-File Report AOF-86, 11 p., 

1 sheet, scale 1:1,000,000. 

Reviewers: Cynthia Dusel-Bacon, S. W. Nelson, 

and J.M. Schmidt 
EAST -CENTRAL ALASKA 

Hydraulic mining for gold on the North Fork of Harrison Creek, Circle Mining Distict. 

Photo by Warren Yeend. 

53 
A LATE ORDOVICIAN AGE REAPPRAISAL 

FOR THE UPPER FOSSIL CREEK VOLCANICS, 

AND POSSillLE SIGNIFICANCE FOR 

GLACIO-EUSTASY 

Robert B. Blodgett, Karen L. Wheeler, 

David M. Rohr, Anita G. Harris, 

and Florence R. Weber 

The Fossil Creek Volcanics of Ordovician age 

is exposed in the White Mountains of east-central 

Alaska. This rock unit, which is used here as 

defined by Mertie (1937), consists of more than 

610 m of basalt, agglomerate, and intrusive and 

sedimentary rocks. The Fossil Creek Volcanics 

was divided into two components by Chapman and 

others (1971). The lower component is primarily 

sedimentary, consisting of slate, chert, limestone, 

and a minor amount of mafic intrusive rocks. This 

component grades laterally and vertically into an 

upper component of basalt, tuff, and agglomerate 

that is generally capped by a thin layer of 

volcanic-rich sediments. The Fossil Creek 

Volcanics unconformably overlies the Wickersham 

grit unit of Proterozoic and Cambrian age (Weber 

and others, 1985) and disconformably underlies the 

Tolovana Limestone, a peloid- and ooid-rich 

platform carbonate succession more than 1,200 m 

thick. The Tolovana is of Silurian age in the White 

Mountains proper, but elsewhere its age ranges 

from Silurian to Middle Devonian. 

Fossil collections by R. W. Stone, L.M. 

Prindle, B.L. Johnson, and Eliot Blackwelder from 

the uppermost part of the Fossil Creek Volcanics 

were examined by Edwin Kirk and assigned a 

Middle Ordovician (Mohawkian) age (Mertie, 

1937). Kirk originally favored a Late Ordovician 

(Richmondian) age, but changed his mind later. 

W.A. Oliver, Jr., U.S. National Museum (in Oliver 

and others, 1975, p. 24), considered several species 

of tabulate and rugose corals from the uppermost 

limestone of the formation to be of "undoubted 

Late Ordovician age." He, however, called this a 

tuffaceous limestone and excluded it from the 

Fossil Creek. 

We have collected fossil assemblages from 

four localities (fig. 1) in the upper volcanic-rich 

sedimentary part of the Fossil Creek Volcanics and 

the overlying Tolovana Limestone. These faunas 

refine previous age determinations on the two rock 

units and allow us to document the magnitude of 

the unconformitv that separates them. 

Locality A (65°37'16" N., 147°21'11" W.) is 

situated in a saddle on a north-south-trending 

ridge spur 0.5 km east-southeast of VABM 4153 

(fig. 1). The contact between the Fossil Creek 

Volcanics and Tolovana Limestone is well exposed 

at this locality, and lithostratigraphy of the 

uppermost Fossil Creek Volcanics was measured in 

detail (see Wheeler and others, this volume). 

Abundant megafossils occur in the uppermost beds 

54 

of sandy clastic and carbonate rocks of the Fossil 

Creek. Fossils were recovered from three 

intervals (fig. 2). Sample "a" was taken from 4.3 

m of green sandstone and minor pebble 

conglomerate containing an abundant and diverse 

fauna, sample "b" was from a 0. 76-m-thick coral 

biostrome composed chiefly of the tabulate coral 

Chaetetipora that grades laterally into bioclastic 

limestone, and sample "c" was from 1.2 m of 

interbedded sandstone, limestone, and minor 

conglomerate. Finally, at the top of the Fossil 

Creek, above the latter unit, is 0.3 m of ironstained calcareous sandstone, with minor 

limy lenses interpreted as having a paleokarst 

surface. Light-yellow, buff- or ochre-weathering 

argillaceous lime mudstone beds of the Tolovana 

Limestone disconformably overlie the Fossil Creek 

Volcanics in this section. 

Brachiopods (determined by R.B. Blodgett) 

from the uppermost beds of the Fossil Creek 

Volcanics at locality A are represented by at least 

seven species that include both inarticulates 

(lingulids and trimerellids) and articulates (orthids, 

strophomenids, and pentamerids). Generic 

identification of most of the brachiopod fauna is 

precluded by the lack of well-preserved interiors. 

65°45' 

65"30 

D 

D 

D 

Cach':_ Mtn. 

EXPLANATION 

Other rocks and 

surficial deposits 

(Quaternary to Proterozoic) 

Tolovana Limestone 

(Silurian) 

Fossil Creek Volcanics 

(Ordovician) 

AREA OF MAP I 

' . . n .. ·--- ALASKA 

·~ \ 

10 KILOMETERS 

__...r--

x 

~ 

\ 

Anticline 

Syncline 

Thrust fault. 

teeth on upper 

thrust sheet 

Measured 

sections A and. D 

Paleonto\ogical 

sites B and C 

Figure 1.--Geology of the Fossil Creek Volcanics 

and Tolovana Limestone in White Mountains, 

Livengood C-1 and C-2 quadrangles generalized 

from Chapman and others (1971). Map shows 

localities A, B, C, and D. 
Meters Locality A Heters Locality D 

70 

60 

50 

Arg illaceous lime 

mudsLonc; disconformable bas a 1 

cont;:tct. 

64 

60 

50 

t,o 

lO 

20 

10 

0 

'lJ 

c 

0 

w 

z 'f) 

-< 'lJ H E 

"" ..... ::> ...J 

...J 

H 

Cll '" c 

"' > 

0 

. ..; 

0 

'"" 

EXPLANATION 

~ Lime packstone and 

~ grainston e 

~ Lime mudstone and 

argillaceous limestone 

W:·BM:l Sandstone 

Sandstone with minor 

pebble conglomerate 

Basalt f lm; 

Agglomerate and 

conglomerate 

~ p 

c 

c 

~ 

~ 

~ 

Peloid-rich lime pack- and 

grainstone, massively bedded 

Argillaceous limestone, 

buf[ to yellow weat hering , 

medium-bedded . 

Interbedded green a nd 

maroon lime mud s ton e , 

thinly-bedded, phyllitic 

sheen. Disconformable 

basal contact. 

Agglome r ate and 

conglomerate . 

p Pentameroid 

pods 

c Conodonts 

s Streptelasma 

brachiasp. 

Disconformity 

Figure 2.--Measured stratigraphic sections at localities A and D (fig. 1) of uppermost part of the Fossil 

Creek Volcanics and Tolovana Limestone in White Mountains of Livengood C-1 and C-2 quadrangles. See 

W.heeler and others, this volume for detailed lithostratigraphy of Fossil Creek Volcanics at locality A. 

55 
Figure 3.--Significant Ashgillian (Late Ordovician) age fossils from uppermost beds (all from interval 

86A8d60a) of the Fossil Creek Volcanics. A, Holorhynchus n. sp., USNM 414983, latex replica of dorsal 

interior, x3.0. 8, C, Maclurites sp., USNM 414984, 8, side view of specimen before acid etching, xl.O, C, 

latex replica of upper surface of shell (made after acid etching) showing a distinct crestal angulation, 

xl.O. Whorl shape is similar to M. manitobensis but does not display spiral ornamentation of that species. 

D, E, Liospira sp., USNM 414985, latex replica of external mold, D, side view, x2.0. E, apical view x2.0. 

F, Trochonemella sp., USNM 414986, side view of latex replica of external mold, x10.0. 

The pentamerids, however, are represented by 

Holorhynchus n. sp. (fig. 3A). This large, smooth 

pentamerid genus was previously known only from 

Ashgillian (Upper Ordovician) rocks of Eurasia 

(Sapelnikov, 1985). Its presence in the uppermost 

Fossil Creek Volcanics affirms the Late 

Ordovician age suggested by Oliver and others 

(1975), and also extends the geographical range of 

the genus to North America. Gastropods 

(identified by D.M. Rohr) from these beds include 

Maclurites sp. (fig. 38 and 3C), Liospira sp. (fig. 

3D and 3E), and Trochonemella sp. (fig. 3F). 

Maclurites and Liospira are widespread genera in 

the Middle and Upper Ordovician. Trochonemella 

is known from the Middle and Upper Ordovician of 

eastern North America, California, west-central 

Alaska, and Seward Peninsula, Alaska. A 

bioclastic limestone laterally equivalent to the 

Chaetetipora interval (fig. 2) yielded one conodont 

56 

element, Belodina sp. indet., indicating a Middle to 

Late Ordovician age. 

Locality 8 (65°37'23" N., 147°20'40" W.) is a 

poorly exposed outcrop of the uppermost part of 

the Fossil Creek Volcanics 0.5 km east-northeast 

of locality A (fig. 1). No section was measured at 

this locality. The rocks at locality 8 consist of 

pebble to cobble conglomerate with clasts of 

rounded to subangular mafic volcanic rocks, green 

chert, and gritty quartzite (2.5-15.2 em in 

diameter) in a matrix of maroon and green silty to 

limy mudstone. Abundant megafossils were 

recovered from the more lime-rich beds. 

Trilobites (determined by A.R. Ormiston, AMOCO 

Production Co.), the most common faunal element, 

include Anataphrus? sp. and a rare 

pteryogemetopid, Denella n. sp., both genera 

known only from Middle and Upper Ordovician 

rocks. Significantly, the genus Denella Ludvigsen 
and Chatterton, is previously known only from 

western Canada, so our discovery significantly 

extends its known geographic range. The 

brachiopod HolorhynchU3 n. sp. also occurs here 

and indicates an Ashgillian age for this horizon. 

Conodonts from this locality (identified by A.G. 

Harris) include 34 small fragments of Belodina sp. 

indet. of Late Ordovician morphotype; their color 

alteration index (CAl) is 6 to 6t , indicating that 

the host rock reached at least 400 °C. The 

contact with the overlying Tolovana Limestone is 

covered at this locality. However, above the 

uppermost exposure of the Fossil Creek Volcanics 

are rubbly yellow- to ochre-weathering 

argillaceous limestone beds about 30-60 m thick of 

the Tolovana Limestone. The basal beds are 

overlain by the more resistant, light-grayweathering outcrops of the peloid- and ooid-rich 

lime pack~tone and grainstone beds, more typical 

of the upper part of the Tolovana Limestone. 

Locality C (65°36'34" N., 147°19'57" W.), in a 

prominent saddle along a northwest-southeasttrending ridge spur near VABM 4153 (fig. 1), 

exhibits the contact between the Fossil Creek 

Volcanics and overlying Tolovana Limestone. The 

uppermost part of the Fossil Creek Volcanics at 

this locality consists mostly of basalt flows. A 

very thin, dark-gray limestone lens approximately 

1-2 m below the top of the Fossil Creek Volcanics 

yielded conodonts of Middle or Late Ordovician 

age. Conodonts recovered from the basal beds of 

the Tolovana Limestone here indicate a Middle 

Ordovician to Middle Devonian, though probably 

Silurian, age. Their CAl is 5 to 5t, indicating that 

the host rock reached at least 300-350 °C. The 

Silurian age suggested by the conodonts is 

confirmed by the associated megafauna, which 

includes pentamerid brachiopods of Silurian 

aspect. 

At locality D (65°32'06" N., 147°31'52" W.), 

the lower part of the Tolovana Limestone rests 

disconformably upon volcanic and agglomeratic 

rocks of the Fossil Creek Volcanics (fig. 2). The 

lowermost 14.6 m of the Tolovana Limestone is 

made up of thin- to medium-bedded, alternating 

green and maroon lime mudstone with a phyllitic 

sheen. The only megafossils were found 2.3-3.0 m 

above the base of this interval and are 

representatives of Streptelasma sp., a solitary 

rugose coral that indicates a Middle Ordovician to 

Early Silurian age (R.J. Elias, written commun., 

1986). Poorly preserved conodonts from the 

lowermost beds are representatives of longranging genera (Middle Ordovician to Early 

Silurian); however, collections taken at 4.6 m, 6.1 

m, and 10.7 m above the base were more age 

specific (early to middle Llandoverian). Because 

the Fossil Creek Volcanics disconformably underlie 

the Tolovana Limestone and because the lower 

part of the Tolovana is lithologically consistent, 

57 

the lowermost Tolovana Limestone is considered 

early or middle Llandoverian (Early Silurian) in 

age. 

The overlying beds (about 30-45 m thick) 

consist of yellowish-brown-weathering, silty, 

argillaceous lime mudstone and wackestone. 

Conodonts recovered at 25.0 m [(Ozarkodina hassi 

(Pollock, Rexroad, and Nicol)] and at 32.8 m 

[Ozarkodina cf. 0. oldhamensis (Rexroad)] also 

indicate an early or middle Llandoverian age. 

Poorly preserved, partly silicified pentameroid 

brachiopods were recovered at 35.4 m above the 

base. The beds above the argillaceous limestone 

interval are peloid- and ooid-rich lime packstone 

and grainstone typical of the upper Tolovana 

Limestone. 

The disconformity between the uppermost 

Fossil Creek Volcanics (Ashgillian) and the 

overlying basal beds of the Tolovana Limestone 

(early or middle Llandoverian) coincides with the 

widespread hiatus recognized at the OrdovicianSilurian boundary in shallow water settings of 

western and Arctic Canada (Lenz, 1976) and 

elsewhere in the world (Berry and Boucot, 1973; 

Sheehan, 1973). This widely recognized 

stratigraphic gap, usually represented by an 

unconformity separating Upper Ordovician and 

Lower Silurian strata, is thought to have been 

caused by a major sea-level drop accompanying 

the Late Ordovician glaciation in Gondwanaland 

(Beuf and others, 1966; Bennacef and others, 

1971). The stratigraphic hiatus in the White 

Mountains fits this pattern, because the faunas and 

sedimentary features indicate extremely shallow 

water marine conditions on both sides of the 

contact. This is the first time that this globally 

widespread stratigraphic hiatus has been 

recognized in Alaska. 

REFERENCES CITED 

Bennacef, A., Beuf, S., Biju-Duval, B., Decharpal, 

0., Gariel, 0., and Rognon, P., 1971, 

Examples of cratonic sedimentation: Lower 

Paleozoic of Algerian Sahara: American 

Association of Petroleum Geologists Bulletin, 

v. 55, p. 2225-2245. 

Berry, W.B.N., and Boucot, A.J., 1973, Glacioeustatic control of Late Ordovician-Early 

Silurian platform sedimentation and faunal 

changes: Geological Society of America 

Bulletin, v. 84, p. 275-284. 

Beuf, S., Biju-Duval, B., Stevaux, J., and Kulbicki, 

G., 1966, Ampleur des glaciations 

"Siluriennes" au Sahara: Leurs influences et 

leurs consequences sur la sedimentation: 

Institut Francais du Petrole, Revue, v. 21, 

p. 363-381. 

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 pl. 

Lenz, A.C., 1976, Late Ordovician-Early Silurian 

glaciation and the Ordovician-Silurian 

boundary in the northern Canadian 

Cordillera: Geology, v. 4, p. 313-317. 

Mertie, J.B., Jr., 1937, The Yukon-Tanana region, 

Alaska: U.S. Geological Survey Bulletin 872, 

276 p. 

Oliver, W.A., Jr., Merriam, C.W., and Churkin, 

M.C., Jr., 1975, Ordovician, Silurian, and 

Devonian corals of Alaska: U.S. Geological 

Survey Professional Paper 823-B, p. 13-44. 

58 

Sapelnikov, V.P., 1985, Sistema i 

stratigraficheskoe znachenie brakhiopod 

podotryada pentameridin: Moscow, Nauka, 

205 p. 

Sheehan, P.M., 1973, The relation of Late 

Ordovician glaciation to the OrdovicianSilurian changeover in North American 

brachiopod faunas: Lethaia, v. 6, p. 147-154. 

Weber, F.R., Smith, T.E., Hall, M.H., and Forbes, 

R.B., 1985, Geologic guide to the FairbanksLivengood area, east-central Alaska: 

Anchorage, Alaska Geological Society, 44 p. 

Reviewers: R.M. Chapman and J.E. Repetski 
PRELIMINARY GEOLOGY, INCLUDING THE 

TINTINA FAULT SYSTEM, OF PART OF THE 

SOUTHWESTERN CHARLEY RIVER 

QUADRANGLE, ALASKA 

Helen L. Foster and Terry E.C. Keith 

The geology of the southwestern part of the 

Charley River quadrangle is poorly known because 

of the remoteness and generally heavy vegetation 

cover of that area. However, this important area 

includes parts of both the Yukon-Tanana and 

Seventymile terranes (Jones and others, 1984) and 

is bounded by strands of the Tintina fault system. 

In addition, it is cut by a northeast-southwesttrending high-angle fault, and it also exhibits 

evidence for thrust faults. Knowledge of the 

geology of this area is critical for interpretation 

of the geologic structure and history of eastcentral Alaska. 

Brabb and Churkin (1969) mapped the area 

included in this report in reconnaissance in 1962. 

Further reconnaissance work was done primarily in 

the Charley River A -5 and A -6 quadrangles by 

H.L. Foster, F.R. Weber, and others in 1982. Some 

additional geologic information was obtained in 

the summers of 1985 and 1986 by the present 

authors with personnel of the National Park 

Service from boat traverses of the northern part 

of the Charley River, and in 1985 from four days 

of helicopter-supported work. Although geologic 

work is far from complete, we are presenting here 

a preliminary map (fig. 1) to demonstrate the 

complexity and importance of the area as well as 

the need for further studies. 

More than half of the area of this report is 

underlain by the northern Yukon-Tanana terrane, 

which is segmented and bounded on the north by 

strands of the Tintina fault system. A major 

strand of the Tintina fault system, the 

Seventymile fault (Foster, 1976), separates the 

metamorphic rocks of the Yukon-Tanana terrane 

from black argillite of uncertain age and 

affinities. The argillite resembles the Glenn Shale 

(Brabb and Churkin, 1969), but other similar black 

argillites are known in the southwestern part of 

the Charley River quadrangle north of the Tintina 

fault zone. Prior to their displacement along the 

Tintina fault system, the greenschist- to 

amphibolite-facies metamorphic rocks of the 

Yukon-Tanana terrane were overthrust by 

greenstone, gabbro, chert and other sedimentary 

rocks, altered hypabyssal intrusive and volcanic 

rocks, and ultramafic rocks of the Seventymile 

terrane (fig. 1; Foster and others, in press). 

The Yukon-Tanana terrane within the map 

area consists primarily of three units: (1) 

amphibolite-facies gneiss, (2) amphibolite-facies 

schist, and (3) greenschist-facies schist. The 

gneiss unit borders the granitic pluton of Twin 

Mountain on the north and occurs as screens and 

59 

roof pendants within the pluton. The gneiss is 

characteristically composed of quartz + biotite + 

feldspar + white mica + garnet ± sillimanite. 

Zircon and opaque minerals occur as accessory 

minerals, and locally biotite has altered to 

chlorite. In some places the crystals of the gneiss 

are shattered and crushed and some 

recrystallization has followed mylonitization. 

The most extensive unit is a pelitic schist 

with interlayered amphibolite of epidoteamphibolite to amphibolite facies. A common 

mineralogy of the pelitic schist is quartz + biotite 

+ white mica + garnet + staurolite ± feldspar. 

Locally, biotite has gone to chlorite and opaque 

minerals may be present. The contact between 

the pelitic schist unit and the gneiss unit north of 

the Twin Mountain pluton is generally sharp, 

suggesting a fault contact, possibly that of a 

thrust fault. 

The greenschist-facies rocks are mostly 

quartz + chlorite + white mica schists which are 

commonly calcareous. The carbonate occurs as 

thin stringers and lenses or as layers up to a few 

centimeters thick. Large orange-brown crystals of 

biotite commonly lie across the foliation. The 

greenschist-facies rocks are in contact with the 

amphibolite-facies pelitic schist unit. This 

contact is also sharp and is probably a thrust fault. 

The Seventymile terrane includes the Mount 

Sorenson ophiolite (Foster and Keith, 1974; Keith 

and others, 1981), composed largely of 

serpentinized peridotite cut by diabase dikes with 

cumulate gabbro, greenstone amphibolite, and 

plagiogranite. Chert, dolomite, limestone, 

argillite, and graywacke, recrystallized in varying 

degrees, are associated with the mafic rocks. 

These rocks are all believed to have been thrust 

over the Yukon-Tanana terrane prior to intrusion 

of the Early Cretaceous Twin Mountain pluton, in 

early Jurassic(?) time (Cushing and others, 1984; 

Foster and others, 1985). 

Fieldwork and study of aerial photographs 

indicate that the Tintina fault system has many 

splays of several different ages, but none of the 

splays have been observed to cut the Twin 

Mountain pluton. The movement along the splays 

is probably right-lateral, as has been previously 

postulated (Roddick, 1967). Total displacement 

along the splays south of the Seventymile strand in 

the southwestern Charley River quadrangle 

appears to have been about 20 km. Cushing and 

others (1986) postulated that displacement along 

what they interpreted to be the most recently 

active main strand, which lies north of this area, 

was less than 100 km. Although more detailed 

study is needed, total displacement in the Tintina 

fault zone in this area does not appear to have 

been as great as that previously postulated for the 

Tintina fault system in Alaska and Canada. A 

highly altered felsic hypabyssal intrusion (map unit 

fph, fig. 1) has been displaced along several 
Kg 

Twin Mountain 

'0--gn 

1° KILOitfE'tERS 

"'-, ', 

aps 

0 I 

142 30 

EXPLANATION 

OIJ 

J-:~Tkc~1 

Alluvium (Holocene) 

Conglomerate (Tertiary and (or) Cretaceous) 

Mount Sorenson ophiolite (age uncertain} 

Consists of: 

~Ita_:@ Argillite; may be equivalent to Glenn Shale (Mesozoic(?)) Gabbro 

cu 

[_~g] 

~ 

~ 

~I 

Yukon-Tanana terrane 

Granite (Tertiary(?) 

Granite of Twin Mountain (Early Cretaceous) 

Gneiss (age uncertain} 

Amphibolite-facies pelitic schist (age uncertain) 

Greenschist-facies schist (age uncertain) 

Seventymi 1 e terrane 

Greenstone, argillite, and chert 

Ultramafic rocks 

Geology north of the Tintina fault system 

Contact or inferred contact 

Fault, dotted where concealed 

Probable fault 

~ Thrust fault, sawteeth on upper plate 

: fph i 

E:;·g~;;J 

Felsic porphyritic hypabyssal breccia (age uncertain} 

Greenstone, chert, argillite, dolomite, limestone, quartzite, 

and amphibolite (age uncertain} 

Figure I.--Preliminary geologic map of part of southwestern Charley River quadrangle, east-central 

Alaska. 

different strands of the Tintina, but its maximum 

single displacement appears to be about 13 km. 

This distinctive felsic rock is mostly coarsely 

porphyritic with phenocrysts of potassium feldspar 

and embayed quartz as long as 2 em. It displays a 

complex history of brecciation followed by intense 

hydrothermal alteration. Fractures formed after 

hydrothermal alteration were filled by quartz. Its 

displacement along strike-slip faults was still 

later. 

A northeast-southwest-trending high-angle 

fault is postulated to lie approximately along the 

course of the Charley River as the rocks there are 

much fractured, shattered, and locally 

brecciated. Rock units that intersect the inferred 

fault are abruptly terminated and apparently 

displaced. Such a fault (or possibly several en 

echelon faults) would approximately parallel the 

Shaw Creek fault to the west (fig. 1). 

60 

The rocks of the Yukon-Tanana terrane are 

generally considered to be of continental origin. 

Although most of the rocks are of unknown age, 

sparse fossils indicate that some protoliths were 

Paleozoic in age, but other protoliths may have 

been of Proterozoic age or included Proterozoic 

material (Aleinikoff and others, 1986). 

The rocks of the Seventymile terrane are of 

oceanic and mantle origin and range in age from 

middle Paleozoic to Triassic. The Seventymile 

terrane is postulated to have been thrust upon the 

Yukon-Tanana terrane in early Jurassic time with 

the closing of the ocean in which its components 

accumulated (Foster and others, 1985). Some of 

the thrusting of the rocks of the Yukon-Tanana 

terrane in the southwestern Charley River 

quadrangle may have also taken place at this 

time. The Tintina fault system appears to have 

become active some time thereafter, but before 
the intrusion in Early Cretaceous time of the 

granite of Twin Mountain, because early strands of 

the Tintina system that show minor strike-slip 

movement do not appear to cut the granite. In 

response to this tectonism, local conglomerates 

were deposited in several places in the area. 

After granitic intrusion, high-angle faulting along 

northeasterly trends followed. Additional faulting 

in thE~ Tintina system also probably occurred after 

intrusion of the granite, and more conglomerates 

were then deposited. 

REFERENCES CITED 

Aleinikoff, J.N., Dusel-Bacon, Cynthia, and 

Foster, H.L., 1986, Geochronology of augen 

gneiss and related rocks, Yukon-Tanana 

terrane, east-central Alaska: Geological 

Society of America Bulletin, v. 97, p. 626-637. 

Brabb, E.E., and Churkin, Michael, Jr., 1969, 

Geologic map of the Charley River 

quadrangle, east-central Alaska: U.S. 

Geological Survey Miscellaneous Geologic 

Investigations Map I-573, scale 1:250,000. 

Cushing, G. W ., Foster, H.L., Harrison, T .M., and 

Laird, Jo, 1984, Possible Mesozoic accretion 

in the eastern Yukon-Tanana Upland (abs.): 

Geological Society of America Abstracts with 

Programs, v. 16, no. 6, p. 481. 

Cushing, G. W ., Meisling, K.E., Christopher, R.H., 

and Carr, T.R., 1986, The Cretaceous to 

Tertiary evolution of the Tintina fault zone, 

east-central Alaska: Geological Society of 

America Abstracts with Programs, v. 18, 

no. 2, p. 98. 

Foster, H.L., 1976, Geologic map of the Eagle 

61 

quadrangle, Alaska: U.S. Geological Survey 

Miscellaneous Geologic Investigations Series 

Map 1-922, scale 1:250,000. 

Foster, H.L, Cushing, G.W., Keith, T.E.C., and 

Laird, Jo, 1985, Early Mesozoic tectonic 

history of the Boundary area, east-central 

Alaska: Geophysical Research Letters, v. 12, 

no. 9, p. 553-556. 

Foster, H.L., and Keith, T.E.C., 1974, Ultramafic 

rocks of the Eagle quadrangle, east-central 

Alaska: U.S. Geological Survey Journal of 

Research, v. 2, no. 6, p. 657-669. 

Foster, H.L., Keith, T.E.C., and Menzie, W.D., in 

press, Geology of east-central Alaska, in 

Plafker, George, and Jones, D.L., eds., The 

Cordilleran Orogen: Alaska: Geological 

Society of America Decade of North 

American Geology v. G-1. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1984, Lithotectonic terrane 

map of Alaska (west of the 141st meridian), 

Part A, in Silberling, N.J., and Jones, D.L., 

eds., Lithotectonic terrane maps of the North 

American Cordillera: U.S. Geological Survey 

Open-File Report 84-523, p. A1-A12. 

Keith, T.E.C., Foster, H.L., Foster, R.L., Post, 

E.V., and Lehmbeck, W.L., 1981, Geology of 

an alpine-type peridotite in the Mount 

Sorenson area, east-central Alaska, in Shorter 

contributions to general geology: U.S. 

Geological Survey Professional Paper 1170-A, 

p. A1-A9. 

Roddick, J.A., 1967, Tintina Trench: Journal of 

Geology, v. 75, no. 1, p. 23-33. 

Reviewers: B~la Csejtey and W .D. Menzie 
PLATINUM-GROUP ELEMENT 

CONCENTRATIONS IN A 

BIOTITE-RICH CLINOPYROXENITE SUITE, 

EAGLE C-3 QUADRANGLE, ALASKA 

Terry E. C. Keith, Norman J Page, 

Robert L. Oscarson, and Helen L. Foster 

Platinum-group elements (PGE) are not 

common in east-central Alaska (Cobb, 1975). 

Occurrences of PG E consisting of alloyed Pt in 

placer gold nuggets were reported by Mertie (1942) 

from three widely separated localities 

approximately 40 to 100 km north of the Eagle C-3 

quadrangle. Anomalous PGE concentrations later 

were reported by Keith and Foster (1973) and 

Foster (1975) in biotite clinopyroxenite of the 

Eagle C-3 quadrangle (fig. 1). Additional samples 

of the ultramafic and associated rocks were 

collected in the summer of 1975 to study the 

mineralogy of the rocks and the possible origin of 

the PGE concentrations. 

The regional geologic framework of the area 

that includes the PGE anomalies consists of a 

complex metamorphic terrane that was 

extensively intruded by granitic rocks of Mesozoic 

age and is part of the Yukon-Tanana terrane 

(Foster, 1976; Foster and others, in press). The 

major portion of an overthrust sheet of 

dismembered ophiolite, known as the Seventymile 

terrane (Foster and others, in press), is exposed 

approximately 45 km to the northwest of the study 

area along the north-central edge of the Eagle 

quadrangle, and small remnants irregularly crop 

out as klippen throughout the area included in this 

report (Foster and Keith, 1974). 

The anomalous PGE values occur in two 

lenses of coarse-grained biotite clinopyroxenite 

and minor biotitite which appear to be pendants, 

along with biotite schist country rock, on a small 

hornblende granodiorite pluton of probable 

Mesozoic age (Foster, 1976). Both ultra~afic 

lenses cover an area of approximately 0.5 km and 

are of unknown thickness. A third lens of similar 

size crops out 2 km to the west, but rocks from it 

have not been analyzed. Coarse-grained felsic 

dikes of irregular size and shape cut the biotite 

clinopyroxenites, parts of which are brecciated 

and included in the dike rock. Hydrothermal 

alteration accompanied intrusion of felsic dikes 

into fractured parts of the ultramafic rocks. 

Although the ultramafic rocks have some outcrop 

characteristics which are similar to concentric 

zoned intrusions, the outcrops here are too 

discontinuous and the vegetative cover too heavy 

to determine a pattern in the course of 

reconnaissance mapping. 

The biotite clinopyroxenite consists of 

anhedral grains of clinopyroxene ranging in grain 

size from approximately 0.25 to 2 em in diameter, 

and biotite of the same size range which usually 

appears to be codepositional. Locally biotite 

62 

composes as much as 90 percent of the rock and 

poikilitically includes small clinopyroxene grains. 

The ratio of biotite to clinopyroxene throughout 

the outcrops varies irregularly from 10 to 90. 

Large grains of primary green amphibole locally 

make up less than 5 percent of the rock; 

orthopyroxene, olivine, and plagioclase were not 

found. Anhedral magnetite occurs as small 

inclusions in clinopyroxene; chromite does not 

appear to be present. 

Felsic dikes intruded the biotite 

clinopyroxenites and formed actinolite, chlorite, 

scarce muscovite, and scarce pyrite locally by 

reaction. The felsic rock textures show evidence 

of extensive hydrothermal alteration in the form 

of exsolution in the plagioclase and alkali feldspars 

and recrystallization along grain boundaries. The 

felsic dikes may be specifically associated with 

the ultramafic rocks and thus unrelated to the 

underlying pluton; they may be a differentiate at 

the top of the hornblende granodiorite pluton, or 

they may be later felsic dikes which cut the entire 

sequence (field relations were not conclusive). 

142°30' 142000' 

0 5 10 KILOMETERS 

EXPLANATION 

&(<-~ G r a n i t i c r o c k s . u n d i f f e r e n t i a t e d 

D Metamorphic rocks, undifferentiated 

II Biotite clinopyroxenite 

Contact-Approximately located 

Fault 

Rivers and creeks 

Figure I.--Generalized geology of Eagle C-3 

quadrangle (after Foster, 1976) showing location of 

biotite clinopyroxenite and associated rocks. 
Random sampling of rocks for background 

geochemical data was done during the course of 

reconnaissance geologic mapping of the Eagle 

quadrangle, and anomalous PGE were discovered in 

samples of the biotite clinopyroxenite and in felsic 

rocks with biotite clinopyroxenite inclusions or 

contact zones (table 1, samples prefixed 1969 and 

1974). For the present study, 20 samples (table 1, 

prefixed 1975) were collected in sequence across 

the northeastern-most of the 3 ultramafic rock 

lenses for the purpose of determining, if possible, 

where in the rocks the PGE were concentrated. 

The 1969 and 1974 samples were analyzed for PGE 

by the fire-assay emission-spectrographic method 

of Haffty and Riley (1968); the 1975 samples were 

analyzed using fire-assay-atomic absorption (AAS) 

methods (Simon and others, 1978). Associated Au 

(table 1) was determined by AAS fire-assay 

method. 

Table I.--Platinum group element and gold analyses (in parts per million) of rock samples from the Eagle 

C-3 quadrangle 

[Analysts for 1969 and 1974 samples: R.R. Carlson and E.F. Cooley; analysts for 1975 samples: A. Love, C. 

Gent, S.G. Crock. N, not detected; na, not analyzed; *, average of 4 runs] 

Sample No. Rock description Pt Pd Rh Au Pt/Pt+Pd 

(BC =biotite clinopyroxenite) 

1969-748B BC 0.3* 0.2* 0.002* na 0.6 

1974-8A BC N .005 N N 

8A1 BC .007 .003 N N .7 

8B1 Actinolite with fe 1 sic dike N N N N 

8B2 Actinolite with felsic dike .007 .005 N N .6 

8C1 BC .015 .015 N .001 .5 

8C3 BC .100 .150 .020 .005 .7 

8C4 BC with felsic dike .070 .030 .007 .001 .7 

8D1 BC with felsic dike .030 .030 N .003 .5 

8D2 BC with felsic dike 3.0 1.5 .030 .020 .7 

8D3 BC with felsic dike .003 .005 .002 .003 .4 

804 BC with fe 1 sic dike .100 .050 .030 N .7 

8D5 BC with felsic dike .200 .050 .005 .002 .8 

Detection limits < .002 < .001 <.002 <.001 

1975-95-1 BC .048 .014 N N .8 

95-3 Clinopyroxenite .021 .012 N .08 .6 

95-6A Felsic dike N N N N 

95-7 BC .036 .009 N N .8 

95-7A Felsic dike N .002 N N 

95-8 Pyroxene biotitite N .004 N N 

95-10 BC .032 .017 N N .7 

95-11 BC .027 .012 N N .7 

95-12 BC with felsic dikea .850 .210 .036 N .8 

95-12A Felsic dike with 

clinopyroxenite inclusions 1.9 .330 N N .9 

95-13 Biotite gneiss with 

clinopyroxenite .160 .065 N N .7 

95-14 BC .037 .012 N N .8 

95-15 BC with felsic dike .017 .008 N N .7 

95-16 BC with 

felsic dike, sulfide .038 .013 N N .8 

95-18 Biotite gneiss N .002 N N 

95-18A Felsic dike N .007 N N 

95-19 BC with felsic dike .036 .013 N N .7 

95-19A Felsic dike N N N N 

95-6 Biotite gneiss N N N N 

Detection limits < .010 < .001 < .001 < .05 

a Ru = .036 ppm; Ir = 0.038 ppm. 

63 
Figure 2.--Scanning electron micrograph of 

backscattered electrons showing a Pt, As mineral 

(sperrylite?) and a Pd, Sb mineral (stibiopalladinite?) 

at contact between a clinopyroxene (cpx) grain and 

oxidized edge (ox) of pyrite (py) grain. 

PGE enrichment was determined to be 

associated with the rocks of the contact reaction 

zone which included fragments of biotite 

clinopyroxenite within felsic dike rock. Biotite 

clinopyroxenite away from the intrusive rocks 

contains lower, but still anomalous, concentrations 

of PGE; the felsic dikes are essentially barren. Ru 

is as high as 0.036 ppm in the few rocks in which it 

was detected (table 1). The Pt/Pt+Pd average is 

0.7 and 0.8 for the 1969-1974 and 1975 groups of 

samples, respectively (table 1). 

Splits of selected samples with anomalous 

PGE content and with pyrite were analyzed for 44 

minor elements by R. Lerner, U.S. Geological 

Survey, using semiquantitative emissiOn 

spectrographic methods. No anomalous traceelement values were found; Cu varied from 9.4 to 

16 ppm, Ni from 9.5 to 83 ppm, Cr from 70 to 700 

ppm, Co from 9.6 to 54 ppm, and V from 65 to 280 

ppm. The low Cu and Ni contents reflect the 

scarcity of Cu and Ni sulfide minerals, suggesting 

that at least some of the PGE are present as 

alloys. 

PGE-bearing minerals typically are 

extremely small and difficult to find under the 

best of conditions (Page and others, 1972; Gray 

and others, 1986). However, polished sections of 

selected rocks for this study were examined under 

the scanning electron microscope (SEM). Scans at 

high magnification using backscattered electrons 

provided extreme visual contrast of PGE minerals, 

because of their high atomic number, with other 

minerals in the rock (fig. 2). This technique 

64 

resulted in locating scarce tiny (usually less than 4 

JJ m diameter, but as large as 25 JJ m x 1 JJm) grains 

of PGE-bearing minerals along cracks in 

clinopyroxene and associated magnetite grains, 

and at grain contacts of clinopyroxene with 

magnetite or pyrite. The energy dispersive X-ray 

spectrographic capability for chemical analysis 

with the SEM permitted chemical verification of 

the PGE-bearing minerals. Several grains, 

including the largest ones, are composed of Pt and 

As and likely are sperrylite. Several grains of less 

than 3 \J m diameter are composed of Pd and Sb 

(stibiopalladinite?). One grain less than 1 JJm 

across consists of Fe, Pt, As, Rh, Ir, Cu, and S 

indicating a complex PGE-bearing sulfide. In 

addition, scarce 5-20 JJm-diameter grains of pyrite, 

galena, and sphalerite were found in biotite 

clinopyroxenite, and similar-sized grains of barite 

were found in the felsic rock. 

Several interpretations for the origin of the 

biotite clinopyroxenite and concentration of 

associated PGE anomalies must be considered: 

1. The biotite clinopyroxenite may be part of a 

dismembered ophiolite sequence that was 

thrust over metamorphic rocks of the 

Yukon-Tanana terrane (Foster and others, 

in press), and therefore it constitutes a 

thrust remnant of the ophiolite of the 

Seventymile terrane. Because the Pt and 

especially the Pd contents appear to be 

too high for normal ultramafic rocks from 

ophiolites as compared to other types of 

occurrences (Page and others, 1979, 1984, 

1985; Oshin and Crocket, 1982; Carlson 

and others, 1986), we do not consider this 

explanation likely. 

2. Pt, Pd, and Au may have been concentrated by 

hydrothermal reactions associated with 

the hornblende granodiorite pluton or by 

hydrothermal reactions generated by the 

felsic dikes. However, chemical 

characteristics of the rocks of this study 

are different from those of hydrothermal 

Pt-rich deposits, such as the New Rambler 

mine, Wyoming, where Pd is much higher 

than Pt, and other metals, Au, Ag, and Cu, 

make up ore-grade deposits (McCallum and 

others, 1976). 

3. The biotite clinopyroxenite may be a portion of 

a concentrically zoned intrusion of the 

Alaska type. The Pt/Pt+Pd ratios of 0. 7 

and 0.8 are acceptable for this type of 

complex, as indicated by examples from 

southwestern Oregon (Gray and others, 

1986), the Tulameen Complex of British 

Columbia (St. Louis and others, 1986), and 

numerous localities in southeastern Alaska 

(Clark and Greenwood, 1972; Page and 

others, 1977). Associated low Au values 

are also characteristic of this type (St. 

Louis and others, 1986). 
The PG E contents and Pt/Pt+ Pd of the Eagle 

C-3 quadrangle biotite clinopyroxenite and the 

PGE minerals found best fit the Alaska-type zoned 

ultramafic deposits. However, the major biotite 

and trace amphibole mineral composition of these 

clinopyroxenites, as well as the lack of major 

magnetite and chromite, are significant 

differences from other reported POE-bearing 

ultramafic rocks. Except for biotite-bearing 

clinopyroxenites at the Pd-bearing ultramafic body 

near Salt Chuck in southeastern Alaska (see Loney 

and others, this volume), biotite is accessory or 

not present in other reported Alaska-type 

ultramafic rocks. 

Other coarse-grained clinopyroxenites and 

associated rocks of the Yukon-Tanana terrane, and 

especially known outcrops in the Eagle quadrangle 

(Foster and Keith, 1974), should be explored for 

the occurrence of anomalous PGE concentrations. 

REFERENCES CITED 

Carlson, C.A., Page, N.J, and Carlson, R.R., 1986, 

The distribution of the platinum-group 

elements and gold in rocks from the western 

half of the Medford 1 x 2 degree quadrangle 

and adjacent areas, Oregon: U.S. Geological 

Survey Miscellaneous Investigations Map MF1832, scale 1:250,000. 

Clark, A.L., and Greenwood, W.R., 1972, 

Geochemistry and distribution of platinumgroup metals in mafic to ultramafic 

complexes of southern and southeastern 

Alaska: U.S. Geological Survey Professional 

Paper 800-C, p. C157-C160. 

Cobb, E.H., 1975, Occurrences of platinum-group 

metals in Alaska: U.S. Geological Survey 

Mineral Investigations Resources Map MR-64, 

scale 1:2,500,000. 

Foster, H.L., 1975, Significant platinum values 

confirmed in ultramafic rock of the Eagle C-3 

quadrangle, in Yount, M.E., ed., U.S. 

Geological Survey Alaska Program, 1975: 

U.S. Geological Survey Circular 722, p. 42-43. 

__ 1976, Geologic map of the Eagle quadrangle, 

Alaska: U.S. Geological Survey Miscellaneous 

Investigations Map I-922, Scale 1:250,000. 

Foster, H.L., and Keith, T.E.C., 1974, Ultramafic 

rocks of the Eagle quadrangle, east-central 

Alaska: U.S. Geological Survey Journal of 

Research, v. 2, p. 657-669. 

Foster, H.L., Keith, T.E.C., and Menzie, W.D., in 

press, Geology of east-central Alaska, in 

Plafker, George, and Jones, D. L., eds., The 

Cordilleran Orogen: Alaska: Geological 

Society of America Decade of North 

American Geology, v. G-1. 

Gray, Floyd, Page, N.J, Carlson, C.A., Wilson, 

S.A., and Carlson, R.R., 1986, Platinum-group 

element geochemistry of zoned ultramafic 

intrusive suites, Klamath Mountains, 

65 

California and Oregon: Economic Geology, 

v. 81, p. 1252-1260. 

Haffty, Joseph, and Riley, L.B., 1968, 

Determination of palladium, platinum, and 

rhodium in geologic materials by fire-assay 

and emission spectrography: Talanta, v. 15, 

p. 111-117. 

Keith, T.E.C., and Foster, H.L., 1973, Basic data 

on the ultramafic rocks of the Eagle 

quadrangle, east-central Alaska: U.S. 

Geological Survey Open-file Report 73-140, 

4 sheets. 

McCallum, M.E., Loucks, R.R., Carlson, R.R., 

Cooley, E.F., and Doerge, T.A., 1976, 

Platinum metals associated with hydrothermal 

copper ores of the New Rambler mine, 

Medicine Bow Mountains, Wyoming: 

Economic Geology, v. 71, p. 1429-1450. 

Mertie, J.B., 1942, Tertiary deposits of the EagleCircle district, Alaska: U.S. Geological 

Survey Bulletin 917-D, p. 213-264. 

Oshin, I.O., and Crocket, J.H., 1982, Noble metals 

in Thetford Mines ophiolites, Quebec, Canada. 

Part I. Distribution of gold, iridium, platinum 

and palladium in the ultramafic and gabbroic 

rocks: Economic Geology, v. 77, p. 1556-

1570. 

Page, N.J, Berg, H.C., and Haffty, Joseph, 1977, 

Platinum, palladium, and rhodium in volcanic 

and plutonic rocks from the Gravina-Nutzotin 

belt, Alaska: U. S. Geological Survey Journal 

of Research, v. 5, p. 629-636. 

Page, N.J, Carlson, C.A., Gray, Floyd, Carlson, 

R.R., Briggs, P.H., Haffty, Joseph, and 

Cooley, E.F., 1985, Map showing geochemical 

characteristics of the North Fork Smith 

Roadless Areas, Del Norte County, California, 

Curry and Josephine Counties, Oregon: U.S. 

Geological Survey Miscellaneous Field Studies 

Map MF-1423-C, scale 1:62,500. 

Page, N.J, Carlson, R.R., Miller, M.S., Gray, 

Floyd, and Carlson, C.A., 1984, Map showing 

geochemical characteristics of platinum group 

elements and gold in rock samples from the 

Kalmiopsis Wilderness, southwestern Oregon: 

U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1240-F, scale 1:62,000. 

Page, N.J, Haffty, Joseph, and Ahmad, Zaki, 1979, 

Palladium, platinum, and rhodium 

concentrations in mafic and ultramafic rocks 

from the Zhob Valley and Dargai complexes, 

Pakistan: U.S. Geological Survey Professional 

Paper 1124-F, 6 p. 

Page, N.J, Riley, L.B., and Haffty, Joseph, 1972, 

Vertical and lateral variation of platinum, 

palladium, and rhodium in the Stillwater 

Complex, Montana: Economic Geology, v. 67, 

p. 915-924. 

St. Louis, R.M., Nesbitt, B.E., and Morton, R.D., 

1986, Geochemistry of platinum-group 

elements in the Tulameen ultramafic 
complex, southern British Columbia: 

Economic Geology, v. 81, p. 961-973. 

Simon, R.O., Aruscavage, P.J., and Moore, R., 

1978, Determination of platinum, palladium, 

and rhodium in geologic material by fire-assay 

and atomic absorption spectroscopy using 

66 

electrothermal atomization (abs.): American 

Chemical Society National Meeting, 176th, 

Paper 19. 

Reviewers: Floyd Gray, R.A. Loney, 

and W .D. Menzie 
SOURCES OF PLACER GOLD IN 

THE SOUTHERN PART OF THE 

WHITE MOUNTAINS RECREATION AREA, 

EAST-CENTRAL ALASKA 

Thomas D. Light, John W. Cady, 

Florence R. Weber, Richard B. McCammon, 

and C. Dean Rinehart 

The White Mountains National Recreation 

Area (NRA), in the northwestern part of the 

Yukon-Ta~ana Upland, comprises an area of about 

3,100 km in the eastern Livengood and western 

Circle quadrangles. The area is underlain by a 

northeasterly trending sequence of Precambrian, 

Paleozoic, and Mesozoic metasedimentary and 

sedimentary rocks, locally intruded by Cretaceous 

and (or) Tertiary granitic rocks that presently 

form topographic highs. Placer gold has been 

recovered from creeks draining the metamorphic 

rocks in the southern part of the White Mountains 

NRA for many years, and we have observed flakes 

of gold in 34 heavy-mineral-concentrate samples 

from Nome, Trail, Ophir, O'Brien, and Bear Creeks 

(fig. 1) during the U.S. Geological Survey's 

investigations of the resource potential of the 

NRA. 

The metamorphic rocks of the southern part 

of the White Mountains NRA consist of the 

Precambrian Fairbanks schist unit of Robinson and 

others (1982), which grades up into the 

Precambrian and Cambrian Wickersham unit of 

Weber and others (1985). The Fairbanks schist unit 

consists chiefly of quartzite and quartz-mica 

schist, whereas the Wickersham unit consists of 

bimodal quartzite (commonly called "grit"), 

quartzite, phyllite, limestone, and a distinctive 

maroon and green slate or argillite (Chapman and 

others, 1971). Although both units are 

metamorphosed to greenschist facies, the 

Wickersham unit is slightly lower grade than the 

Fairbanks schist unit. Quaternary loess, probably 

a by-product of glaciation in the local mountains, 

buries much of the terrain in the southern third of 

the area, and perennially frozen organic-rich silt 

fills the valleys, so that there are very few 

bedrock exposures south of Nome and Beaver 

Creeks. Two periods of tectonism and associated 

metamorphism produced sub-isoclinal, northeastvergent, northwest-trending folds and a later 

generation of northeast-trending folds and 

northwest-vergent thrust faults that control the 

distribution of rock types that are presently 

exposed. The rocks generally strike northeastsouthwest and dip northwest (Weber and others, 

1985). 

Placer gold was reported in the upper 

tributaries of Beaver Creek (fig. 1) prior to the 

turn of the century; the first substantial gold 

discovery in the area was in 1910 when mineable 

deposits were found on Ophir Creek (Ellsworth and 

67 

Parker, 1911). Subsequently, gold was discovered 

on Nome Creek and Trail Creek. The deposits 

along both Ophir and Trail Creeks proved to be 

limited in extent, and although it is not known how 

much gold was produced, the amount probably was 

small. Dredges were operated on Nome Creek for 

many years, beginning in 1926 (Cobb, 1973), and 

gold was recovered from an 11-km stretch 

upstream from the confluence with Moose Creek. 

The upstream extent of placer mining coincides 

with the maximum extent of Pleistocene glacial 

ice from Mount Prindle (Weber and Hamilton, 

1984) that scoured the creek bed and served to 

concentrate gold below the terminus of the 

glacier. A nominal figure for the cumulative 

production from Nome Creek has been estimated 

at between 10,000 and 20,000 oz (300 and 600 kg) 

of gold (W .D. Menzie, written commun., 1986). 

Dragline operations have continued along Nome 

Creek intermittently to the present time. 

We believe that the source of the gold in 

Nome Creek may be the Cleary sequence, a 

distinctive 120-m-thick section of probable 

volcanogenic beds that occurs in the Fairbanks 

schist unit and consists of "interlensing felsic 

schist, laminated white micaceous quartzite, 

actinolitic greenschist, graphitic schist, 

metabasite, metarhyolite, and calcsilicate beds" 

(Robinson and others, 1982, p. 228). This sequence 

is believed to be the source for most of the gold in 

placer deposits in the Fairbanks Mining District 

(Smith and others, 1981). Similar and possibly 

correlative rocks were recognized near Mount 

Prindle (T.E. Smith, oral commun., 1986). Based 

on the regional northeast-southwest strike, these 

rocks project southwestward roughly parallel to 

Nome Creek. Remobilization of the gold in the 

inferred Cleary sequence at the head of Nome 

Creek as a result of the intrusion of the Mount 

Prindle pluton, followed by fluvial concentration, 

provides a reasonable hypothesis for the origin of 

the Nome Creek placers. The gold in Bear Creek 

(fig. 1), which also heads near Mount Prindle, is 

probably of the same origin. 

Trail Creek, Ophir Creek, and an unnamed 

creek east of Ophir Creek (fig. 1) do not originate 

in the Mount Prindle area, therefore the gold in 

these drainages must be derived from some other 

source. Southeast of the Chatanika River in the 

Circle quadrangle, Cady and Weber (1983) 

determined that linear magnetic highs reflected 

magnetic chloritic schists within the Fairbanks 

schist unit (probably in the Cleary sequence 

itself). These highs were inferred to overlie the 

crests of antiforms that bring magnetic schist 

close to the surface. Such linear magnetic highs, 

labeled H1 and H2 on figure 1, extend 

southwestward from Mount Prindle toward the 

heads of Trail and Ophir Creeks and are coincident 

with a known antiform. It is very likely that the 

Cleary sequence is present in this structure, but is 

not recognized in the meager outcrops. 
a> 

00 

65° 

30 ' 

65° 

15' 

147°30' 147° 146°30' 

Figure I.--Aeromagnetic sketch map of portions of southeast Livengood and southwest Circle quadrangle. 

Solid lines are selected magnetic contours outlining magnetic highs (Hl and H2). Dashed lines outline 

magnetic lows (Ll). Total magnetic field in nanoteslas on arbitrary datum. TKg indicates approximate 

outcrop area of Tertiary-Cretaceous granite. Black dots show heavy-mineral-concentrate samples 

containing visible gold. The sample locality of schist containing randomly oriented biotite is shown by 

"X". The alternating short and long dashed line is the approximate boundary of the White Mountains 

National Recreation Area. 
The Mount Prindle granite is nonmagnetic, as 

are felsic hypabyssal intrusions near Mount Prindle 

in the axis of a magnetic low. A belt of magnetic 

lows extends southwestward from Mount Prindle 

toward a strong low (L1 in fig. 1) that also occurs 

near the headwaters of Ophir and Trail Creeks. 

Cady and Weber (1983) suggested that magnetic 

lows indicate continuity of nonmagnetic plutons at 

depth, therefore it is possible that buried plutons 

are present at the heads of these gold-bearing 

creeks. Further evidence that buried plutonic 

rocks may underlie the Ophir and Trail Creek 

drainages was found in a sample of schist collected 

just south of the head of Trail Creek (fig. 1). The 

schist, normally of greenschist facies, was found 

to contain randomly oriented biotite, indicating 

that the metamorphic grade had been locally 

raised sufficiently to crystallize biotite in random 

orientation similar to the fabric in contactmetamorphosed rocks. 

It seems likely, therefore, that the intrusion 

of Cretaceous and (or) Tertiary pluton(s), inferred 

from the aeromagnetic low (L1 in fig. 1), caused 

hydrothermal remobilization of gold from the 

Cleary sequence buried along the northwestern 

flank of an antiform. Hydrothermal fluids 

migrating through dilatant fractures caused by 

warping associated with the intrusion formed goldbearing veins and stringers. Because of the lesser 

degree of erosion as compared to the head of 

Nome Creek, gold-bearing veins may still be in 

place along the ridge south of Trail and Ophir 

Creeks. 

Finally, visible gold found in samples from 

O'Brien Creek (fig. 4) cannot have been derived 

from the Cleary sequence in the Mount Prindle 

area. Cache Mountain, from which part of O'Brien 

Creek originates, represents the upper part of a 

highly evolved granitic pluton with associated tingreisen mineralization. This pluton is similar in 

age, style, and mineralization to the Rocky 

Mountain (Lime Peak) pluton 30 km to the 

northeast (Menzie and others, 1986). 

Hydrothermal mineralization associated with the 

intrusion of the Cache Mountain pluton is likely to 

be the source of the gold in O'Brien Creek. 

REFERENCES CITED 

Cady, J.W., and Weber, F.R., 1983, Aeromagnetic 

map and interpretation of magnetic and 

69 

gravity data, Circle quadrangle, Alaska: u.s. 

Geological Survey Open-File Report 83-17 0-

C, scale 1:250,000. 

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. 

Cobb, E.H., 1973, Placer deposits of Alaska: U.S. 

Geological Survey Bulletin 1374, 213 p. 

Ellsworth, C.E., and Parker, G.L., 1911, Placer 

mining in the Yukon-Tanana region: U.S. 

Geological Survey Bulletin 480, p. 153-172. 

Menzie, W.D., Reed, B.L., and Keith, T.E.C., 1986, 

Lime Peak--An evolved granite with tinenriched alteration, in Bartsch-Winkler, 

Susan, and Reed, K.M., eds., Geologic studies 

in Alaska by the United States Geological 

Survey during 1985: U.S. Geological Survey 

Circular 978, p. 25-27. 

Robinson, M.S., Smith, T.E., and Bundtzen, T.K., 

1982, Cleary sequence of the Fairbanks 

mining district--Primary stratigraphic control 

of lode gold/antimony mineralization (abs.): 

Geological Society of America Abstracts with 

Programs, v. 14, no. 4, p. 228. 

Smith, T.E., Robinson, M.S., Bundtzen, T.K., and 

Metz, P.A., 1981, Fairbanks mining district in 

1981: New look at an old mineral province: 

The Alaska Miner, The Journal of the Alaska 

Miners Association, v. 9, no. 11, p. 8, 28. 

Weber, F.R., and Hamilton, T.D., 1984, Glacial 

geology of the Mt. Prindle area, YukonTanana Upland, !.!!. Short notes on Alaskan 

geology 1982: Alaska Division of Geological 

and Geophysical Surveys, Professional Report 

86, p. 42-48. 

Weber, F.R., Smith, T.E., Hall, M.H., and Forbes, 

R.B., 1985, Geologic guide to the FairbanksLivengood area, east-central Alaska: 

Anchorage, Alaska Geological Society 

Guidebook, 44 p. 

Reviewers: John Antweiler and E.L. Mosier 
LITHOSTRATIGRAPHY, PETROLOGY, AND 

GEOCHEMISTRY OF THE ORDOVICIAN 

FOSSIL CREEK VOLCANICS, 

WHITE MOUNTAINS, EAST-CENTRAL ALASKA 

Karen L. Wheeler, Robert B. Forbes, 

Florence R. Weber, and C. Dean Rinehart 

The White Mountains and surrounding area 

are composed of Proterozoic to Mesozoic 

sedimentary and volcanic rocks deformed by 

southeast-dipping, northwest-verging folds and 

imbricate thrust faults (fig. 1). The core of the 

White Mountains is composed of the Late 

Proterozoic and Cambrian Wickersham grit unit, 

overlain by the Ordovician Fossil Creek Volcanics 

and by the Silurian Tolovana Limestone. 

The Fossil Creek Volcanics, as defined by 

Mertie (1937), includes more than 610 m of mafic 

volcanic flows and pyroclastic deposits and a few 

small bodies of mafic intrusive rocks, 

agglomerate, conglomerate, and bedded 

sedimentary rocks. Chapman and others (1971) 

divided the Fossil Creek into a lower, 

predominantly sedimentary part that interfingers 

with an upper, predominantly volcanic part. 

Thicknesses vary considerably as the facies change 

from volcanic to sedimentary toward the east. 

The Fossil Creek Volcanics unconformably overlies 

the Wickersham grit unit. Its contact with the 

overlying Tolovana Limestone, which is of Silurian 

age within the White Mountains, is interpreted as 

an erosional disconformity. 

The lower sedimentary part of the Fossil 

Creek Volcanics, approximately half of its 

thickness, is composed of (1) thinly interbedded 

calcareous dark-gray slate to light-gray slaty 

phyllite and black tuffaceous shale, (2) gray to 

black calcareous and siliceous siltstone, (3) 

medium-gray sandy platy limestone, (4) black and 

gray banded silty chert, and (5) minor 

intercalations of basalt flows, pillow lavas, and 

gabbroic sills. Early Ordovician (Arenigian) 

conodonts (J.W. Huddle, USGS, written commun., 

1972), and trilobites (M.E. Taylor, USGS, written 

commun., 1972) occur in medium- to dark-gray 

limestone lenses in the light-gray calcareous 

phyllitic slate interpreted to be near the base of 

this unit on Willow Creek. Conodont-trilobite 

faunas suggest that the earliest Fossil Creek 

sedimentary beds were deposited in relatively 

shallow water; but lithology indicates that the bulk 

of the lower section was probably of deep water 

origin with turbiditic characteristics (R.B. 

Blodgett, Oregon State University, oral commun., 

1986). 

The upper volcanic part of the Fossil Creek 

Volcanics consists of abundant thick flows of 

basalt, olive-green agglomerate, and volcaniclastic 

conglomerate. The basalt described by Church and 

Durfee (1961) contains phenocrysts and 

microphenocrysts of clinopyroxene and plagioclase 

70 

in a groundmass of plagioclase, clinopyroxene, 

opaque minerals, and devitrified glass. Aggregates 

of magnesian chlQrite and (or) iddingsite are 

believed to replace olivine. Plagioclase is 

typically decalcified and partially replaced by 

saussuritic aggregates of epidote, albite, sericite, 

and carbonate. Carbonate commonly fills fissures 

and vesicles, and the groundmass of most of the 

basalt contains variable amounts of secondary 

chlorite, sericite, prehnite, leucoxene, and 

iddingsite. Although clinopyroxene has been 

partially replaced by aggregates of chlorite and 

opaque minerals in some of the basalt, it persists 

as relatively unaltered relict phenocrysts and 

microphenocrysts in other variants. 

Four basalt samples were selected for wholerock chemical analysis following the completion of 

Church and Durfee's work in 1961. Unfortunately, 

the analyses were not completed in time to be 

included in their theses, and, until this report, the 

data have not been published. The rocks analyzed 

were the most representative and least altered of 

the basalt units that were collected during the 

1960 field investigations. The analyses (table 1) 

were made by T. Katsura and H. Haramura under 

the auspices of the U.S.-Japan Cooperative 

147. 30 ' 147" 00' 

AREA OF NAP 

I 

·~ ALASKA '., 

ns· 30 ' I 0 

KILOMETERS 

EXPLANATLON 

D Othe~ :ocks and. A-' An ti c line 

surfiCial depo!;lts ~ Syncline 

(Qu:-cterna r y to ProtL•rozoic) ~ 

• 

~ Thru st faull , o~ova~a Limestone tee th 0 11 upper 

' ' (S dun an) th rust s he•· • 

D Fossil Creek VolcaniC's N!:!asured (Ord ov ician) sec ti on 

Figure 1.--Geology of the Fossil Creek Volcanics 

and Tolovana Limestone in White Mountains, 

Livengood C-1 and C-2 quadrangles, Alaska. 

Generalized from Chapman and others (1971). 
Science Program in 1964. All of the basalt 

samples meet the chemical criteria for alkali 

basalt as established by Chayes (1964)--Ti02 

greater than 1. 75 weight percent, and nepheline in 

the norm. The basalt also qualifies as alkaliolivine basalt as discussed by Macdonald and 

Katsura (1964), with nepheline, olivine, and 

diopside in the norm, and compositions that plot in 

t~e alkaline field of the Na2o + K20 I Si02 diagram. 

Although Ti02 and P2o5 are considered to 

be among the least mobile species (along with Cr, 

Ni, Zr, Nb, and Y) during low-grade metamorphism 

of basaltic rocks, the analyzed P2o5 values are 

anomalously low when compared with the 

coexisting Ti02 concentrations in typical alkali 

basalts. Some P 2o5 may have been lost during 

hydration reactions which occurred at 

temperatures of 300° C or greater. 

Overlying or interlayered with the basalt 

flows are agglomerate beds with fine-grained 

basalt matrices that contain both volcanic and 

sedimentary clasts. Volcaniclastic conglomerates 

have sedimentary or tuffaceous matrices. Locally 

the conglomerate is overlain by olive-green 

conglomeratic sandstone and medium- to finegrained calcareous sandstone containing a few thin 

lenses of coralline limestone. Conodonts from a 

gray limestone lens in the uppermost part of the 

Fossil Creek Volcanics are of Middle to Late 

Ordovician age and of Late Ordovician age (A.G. 

Harris, USGS, written commun., 1986). The color 

alteration index (CAl) of these conodonts is 5 1/2, 

indicating temperatures of 300 to 350° C; these 

temperatures are compatible with the low-grade 

metamorphic mineral assemblages characteristic 

of the basalts. Petrographic descriptions provided 

by Church and Durfee (1961) indicate that the 

basalt has undergone zeolite- to lower greenschistfacies metamorphism. 

The upper part of the Fossil Creek Volcanics 

is lithologically variable due to facies changes and 

subsequent erosion. Section A, 0.5 km eastsoutheast of VABM 4153, includes 108.5 m of 

fining-upward sedimentary rocks that locally 

comprise the upper part of the Fossil Creek 

Volcanics (fig. 2). Unsorted boulder-to-granule 

conglomerate and agglomerate are most abundant 

in the lower 100 m of section A. Bedding in the 

lower 58 m is massive with relic large-scale, 

trough-shaped scours. Sorting increases, grain size 

decreases, and bedding thins upsection. Two 

basalt beds occur 93.5 m and 68.6 m above the 

base of the measured section. The lower basalt is 

1.8 m thick and the upper is 0.6 m thick. The 

upper basalt is overlain by 4.3 m of very thinly 

bedded poorly sorted medium- to fine-grained 

greenish-gray calcareous f eldspa tholi thic 

sandstone with lenses of granule conglomerate and 

coquina. Late Ordovician megafossils are 

abundant in this interval (see Blodgett and others, 

71 

Table 1.--Whole-rock analyses and CIPW norms for 

basaltic rocks from the Ordovician Fossil Creek 

Volcanics, White Mountains, Alaska 

MCD82 MCD56 

Whole-rock analyses 

(weight percent) 

48.84 47.00 

2.13 2.43 

18.18 15.68 

9.11 6.22 

1.63 6.60 

.13 .11 

4.37 5.29 

8.16 6.42 

4.83 3.21 . 75 3.19 

.06 .06 

1.72 3.82 

.17 .23 

MCD59 

46.63 

1.87 

15.42 

9.80 

1.79 

.19 

7.37 

9.54 

2.69 

1.50 

.03 

3.22 

.21 

MCD96 

43.30 

1.87 

14.04 

9.51 

3.34 

.17 

8.96 

11.34 

2.66 

1.58 

.07 

3.45 

.23 

Total 100.08 100.24 100.26 100.45 

Cr .0020 .0049 .014 .015 

Ni .0039 .0055 .0081 .010 

CIPW norms 

Orthoclase 4.43 18.85 8.86 9.34 

Albite 32.35 25.95 19.66 4.97 

Anorthite 25.71 18.96 25.57 21.70 

Nepheline 4.61 .66 1.68 9.50 

Diopside 11.94 9.89 17.67 27.66 

Olivine 12.59 7.58 17.16 15.11 

Magnetite 2.36 9.57 2.60 4.84 

Ilmenite 4.05 4.62 3~55 3.55 

Apatite .14 .14 .07 .16 

Percent An in 

Plagioclase An44 An42 An57 An81 

this volume). Coralline limestone, 0. 76 m thick, 

occurs within the upper 2 m and is overlain by a 

thin zone of highly weathered, iron-stained, 

slightly calcareous, feldspathic sandstone. This 

limestone was originally called a tuffaceous 

limestone and included at the very top of the 

Fossil Creek Volcanics by Mertie (1937). Chapman 

and others (1971) and Churkin (1973) had some 

reservations about its inclusion in the Fossil 

Creek, and Oliver and others (1975, p. 25, fig. 16) 

excluded it from the Fossil Creek. Careful 

sampling shows it to be entirely Ordovician in age 

and part of the Fossil Creek Volcanics (see 

Blodgett and others, this volume). Only the lower 

27 m of the Tolovana Limestone, a light-gray 

sparsely fossiliferous argillaceous lime mudstone, 

was measured at section A. 

The clasts within the upper part of the Fossil 

Creek Volcanics are well-rounded maroon and 

green mafic volcanic rocks, pink granite, bimodal 

quartzite, light-gray limestone, and phyllite. Most 
Heters Section A 

120 

Ar gillaceous lime mudstone; light yellow, buf~ or ochre weathering, light- gray on 

fresh, thinly bedded in lmver 27 m, becomes mor e massive upsection. 

Disconformable basal con t cH't l·•ith Fos.c;il Creek Volcanics. 

100 

Volcaniclastic conglomerate; drab olive- green, cobble-granule sized , very well-rounded clasts. Fines upsection. Thin-medium bedded. 

80 

----Basalt flmv, 1.8 m thick, 68.6 m above base of section . 

,-------------------------------~ 

60 EXPLANATION 

40 

20 

Agglomerate and conglomerate; 

drab olive-green, boulder to 

cobble sized, very well- rounded 

maroon and green basalt, pink 

granite, bimodal quartzite, 

limestone, and phyllite clasts 

in altered volcanic and tuffaceous matrix. Internallymassive, amalgamated , largescale, trough- shaped scours. 

Argillaceous lime mudstone 

Calcareous feldspathic and feldspatho -

lithic sandstone 

Calcareous feldspatholithic 

conglomeratic sand stone 

Basalt flow 

Agglome rat e and conglomerate 

0 

Figure 2.--Measured stratigraphic section A in upper part of the Fossil Creek Volcanics and Tolovana 

Limestone. Located at 65°37'16" N., 147°21'11" W. in Livengood C-1 quadrangle. 

of these clasts display local source affinities. 

However, the pink granite clasts are unlike any 

known pre-Late Ordovician rocks in the YukonTanana Upland. This granite is composed of 

massive, medium-grained chlorite-quartzorthoclase-albite and has xenomorphic- to 

hypautomorphic-granular texture, modified only by 

mild protoclasis. Crude zonal distribution of 

alteration products in the albite crystals indicate 

that the original plagioclase was probably more 

calcic--perhaps oligoclase or andesine. The 

chlorite is partly pseudomorphous after biotite, 

indicating that the original unaltered rock may 

have been a common biotite granite or 

granodiorite that was subsequently metamorphosed 

to greenschist facies. 

Because of its well-defined, alkalic 

composition, the basalt of the Fossil Creek 

Volcanics is unlikely to be island arc, mid-oceanridge, or continental tholeiitic basalt. The 

question, therefore, is whether or not the parental 

basalts erupted in an oceanic or a continental 

setting. A few pillow lavas were found in the 

flows associated with the lower, predominantly 

sedimentary section. The clasts in the 

72 

conglomerate and agglomerate of the upper part 

of the Fossil Creek Volcanics are suggestive of 

lahar and debris-flow deposits near a continental 

source area. The coral biostromes and marine 

fossil hash in the upper part of the Fossil Creek 

Volcanics indicate a warm, shallow-marine 

environment. The fining upward of grain size, and 

increasingly mature sandstone compositions and 

textures in the upper part of the Fossil Creek 

Volcanics, are characteristic of nearshore 

shallowing-upward marine deposits. Based on the 

Ordovician faunal assemblages and depositional 

environments, a strong case can be presented for 

the eruption of the alkali-basalt flows in the 

continental margin and (or) shallow-marine (shelf) 

environment. The Silurian Tolovana limy deposits 

prograded over the erosional surface on the Upper 

Ordovician part of the Fossil Creek Volcanics. 

The Fossil Creek Volcanics and the Tolovana 

Limestone are the major formations constituting 

the White Mountains terrane (Churkin and others, 

1982; Jones and others, 1984). We interpret the 

contact between the White Mountains terrane and 

the Wickersham terrane of Jones and others (1984) 

to be simply an unconformity and not a tectonic 
feature. This unconformity is similar to that 

found between rocks of similar types and ages in 

Yukon Territory, Canada, in which Cambrian 

strata have been removed (Thompson and Roots, 

1982, p. 410). 

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, 

scale 1:250,000, 2 sheets. 

Chayes, F., 1964, A petrographic distinction 

between Cenozoic volcanics in and around the 

open oceans: Journal of Geophysical 

Research, v. 69, p. 1573-1588. 

Church, R.E., and Durfee, M.C., 1961, Geology of 

the Fossil Creek area, White Mountains, 

Alaska: Fairbanks, University of Alaska, M.S. 

thesis, 96 p. 

Churkin, M.C., Jr., 1973, Paleozoic and 

Precambrian rocks of Alaska and their role in 

its structural evolution: U.S. Geological 

Survey Professional Paper 7 40, 64 p. 

Churkin, M.C., Jr., Foster, H.L., Chapman, R.M., 

and Weber, F.R., 1982, Terranes and suture 

73 

zones in east-central Alaska: Journal of 

Geophysical Research, v. 87, no. 85, p. 3718-

3730. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1984, Part A--Lithotectonic 

terrane map of Alaska (west of the 141st 

meridian), in Silberling, N.J., and Jones, D.L., 

eds., Lithotectonic terrane maps of the North 

American Cordillera: U.S. Geological Survey 

Open-File Report 84-523, p. A1-12A. 

Macdonald, G.A., and Katsura, T., 1964, Chemical 

composition of Hawaiian lavas: Journal of 

Petrology, v. 5, no. 1, p. 82-133. 

Mertie, J.B., 1937, The Yukon-Tanana Region, 

Alaska: U.S. Geological Survey Bulletin 872, 

276 p. 

Oliver, W .A., Jr., Merriam, C. W ., and Churkin, 

M.C., Jr., 1975, Ordovician, Silurian, and 

Devonian corals of Alaska: U.S. Geological 

Survey Professional Paper 823-B, p. 13-44. 

Thompson, R.I., and Roots, C.F., 1982, Ogilvie 

Mountains Project, Yukon, Part A: A new 

regional mapping program: Geological Survey 

of Canada, Current Research, Part A, Paper 

82-1A, p. 403-411. 

Reviewers: R.M. Chapman and J.H. Dover 
PLACER GOLD RELATED TO MAFIC SCffiST(?) 

IN THE CIRCLE DISTRICT, ALASKA 

Warren Yeend 

The Circle District is one of the major 

placer gold mining districts within Alaska, with 

estimated total production of 1 million oz (31,000 

kg) (Bundtzen and others, 1984). Placer operations 

continue in many of the same creeks that have 

been mined since the original gold discovery in 

1893. Despite many decades of search by 

prospectors and geologists, a lode source for the 

gold placers has eluded discovery. 

The placers occur in the Yukon-Tanana 

Upland (Wahrhaftig, 1965) south of the Tintina 

fault zone where the rocks are dominated by 

widespread, rarely mineralized quartzites and 

quartzitic and mafic schists (Foster and others, 

1983). Early reports refer to the occurrence of 

placer gold fragments with attached quartz 

(Mertie, 1938), and a gold-rich quartz vein in a 

block of quartz schist was described by Spurr 

(1898). In a more recent work, Menzie and others 

(1983) concluded that the distribution of gold by 

rock type and by its location suggests that gold 

occurs in small fracture zones, in veins and in 

association with felsic dikes that developed and 

were emplaced above the granite in the Circle 

Mining District. Thinly laminated muscovite 

schists with traces of gold and sulfides, inferred to 

be a volcanogenic rock, have also been suggested 

as the source for much of the gold in the placers 

(Mining and Minerals, 1985). 

The accordant summits in the upland areas 

drained by the gold-producing creeks might 

suggest an old erosion surface--the location of, 

perhaps, a fossil placer river system. Although it 

would be possible to reconstruct such a drainage 

that could have provided a gold source for the 

existing creek placers, evidence for the existence 

of such a fossil placer is absent. No remnants of 

high-level gravel are present in the summit areas, 

a highland bedrock source for the fossil placer is 

missing, and surrounding areas lack gold placers 

and lodes through which an old river system would 

have flowed. 

It is reasonable therefore to look for a local 

bedrock gold source. Recent mapping in the 

Circle quadrangle (Foster and others, 1983) 

delineates a mafic schist unit within the 

monotonous quartzitic schists (fig. 1) that should 

be seriously considered as a possible gold source 

or, at least, a control on the source. The mafic 

schist crops out within the Circle quadrangle in 

the headwaters of many of the most productive 

gold placer creeks, implying a possible genetic 

relationship. Furthermore, gold production from 

each creek is correlated with the amount of its 

drainage within the outcrop limits of the mafic 

schist. Mastodon Creek, one of the most 

74 

productive creeks in the district, has at least 75 

percent of its drainage basin within the mafic 

schist (fig. 1). Similarly, the very productive 

North Fork of Harrison Creek has almost 100 

percent of its drainage basin within the mafic 

schist. Other very productive creeks, Deadwood, 

Bottom Dollar, Harrison, and Gold Dust, drain 

substantial areas within the mafic schist. 

Bedrock, Boulder, Butte, Ketchem, and Portage 

Creeks, which drain small areas of the mafic 

schist, have been less important gold producers. 

The granites which crop out in several places 

within the Circle quadrangle do not appear to be 

spatially related to the presence of placer gold. 

The granites of the Circle Mining District, mainly 

present within a portion of the drainages of 

Deadwood, Ketchem, and Portage Creeks, were 

determined to be high in tin, however (Menzie and 

others, 1983). 

As described by Foster and others (1983), the 

mafic schist is a green, chlorite-quartz-carbonate 

schist with abundant plagioclase porphyroblasts. It 

is associated with amphibolitic schist, minor 

marble, quartzite, and pelitic schist. Locally it is 

interlayered in the quartzitic schist unit. The 

surrounding rock types, and those most commonly 

present south of the Tintina fault zone, are gray or 

greenish-gray quartzite and quartzitic schist with 

minor pelitic schist, calcsilicate rock, mafic 

schist, and rare interlayered marble (Foster and 

others, 1983). 

The contact of the mafic schist unit with the 

quartzite and quartzitic schist is generally 

gradational. Thin units of mafic schist too small 

to map at 1:250,000 scale are locally present 

interlayered in the quartzite and quartzitic schist 

unit. Assuming that the mafic schist is, in fact, a 

gold source or host rock for gold, these unmapped 

scattered occurrences could explain the presence 

of minor amounts of gold in some creeks where no 

mafic schist has been mapped. The upper portions 

of Loper and Porcupine Creeks would seem to be 

such an area where there could be some small 

exposures of mafic schist. 

The uppermost parts of some gold-producing 

creeks and those creeks with little or no gold 

production which drain areas of mafic schist 

generally possess such steep gradients that they 

transported gravel but allowed little deposition. 

Although incapable of supporting a large placer 

mining operation, they might contain sufficient 

gold to attract small-scale mining. The southflowing Traverse and Portage Creeks, which empty 

into Birch Creek, and several of the southwardflowing tributaries of Harrison Creek, are 

examples of such creeks. 

The contact relationships of the mafic schist 

unit with surrounding rock units are not 

sufficiently well understood to be able to identify 

their structural setting, thus it is unclear whether 

more or less area of mafic schist was available for 
6 5' 15' 

••••• • f.to..,.. 

• • I ... 

EXPLANATION 

,__ _ _.~fcree'Ks: shaded areas mined for placer gold ..... 

~Granite 

~ Mafic schist 

D Quartzite and quartzitic schists: undifferentiated 

surficial deposits north of Hot Springs Fault 

Figure !.--Simplified geologic map of Circle mining district showing relation of gold placers and mafic 

schist (geology from Foster and others, 1983). 

erosion in earlier geologic time. Likewise, it is 

not known what happens to the mafic schist unit at 

depth. More detailed mapping of these contacts 

might reveal this information and allow a better 

understanding of the magnitude and size of the 

original gold source area. 

Although the Circle District has no reported 

production of lode gold, the adjacent Fairbanks 

mining district has produced 245,000 oz (7 ,600 kg) 

of gold from lode sources. The lode gold, present 

within quartz-sulfide veins with associated leadantimony sulfosalts, is hosted by the Cleary 

sequence, a mafic and felsic schist of probable 

volcanic origin (Mining and Minerals, 1985). The 

very productive placers of the Fairbanks District, 

from which 7,555,000 oz (235,000 kg) of gold has 

been taken since 1902, exist in close spatial 

association with the rocks of the Cleary Sequence 

and most probably were derived from them (Mining 

and Minerals, 1985). Placer gold within the Circle 

quadrangle, when analyzed for trace elements, was 

found to be anomalously high in antimony as 

compared to placer gold from other areas in 

75 

Alaska (Yeend, 1985), and might suggest a lode 

association similar to the Fairbanks Mining 

District. 

If the mafic schist is the primary lode gold 

source in the Circle District, the nature of gold 

occurrence within the schist remains to be 

determined. The fact that only one of 44 rock 

samples collected within the mafic schist unit 

contained detectable gold (Menzie and others, 

1983) implies that the gold, if present in 

significant amounts, is not uniformly distributed 

throughout the schist. 

REFERENCES CITED 

Bundtzen, T.K., Eakins, G.R., Clough, J.G., Lueck, 

L.L., Green, C.B., Robinson, M.S., and 

Coleman, D.A., 1984, Alaska's mineral 

industry 1983: Alaska Division of Geological 

and Geophysical Surveys Special Report 33, 

56 p. 
Foster, H.L., Laird, Jo, Keith, T.E.C., Cushing, G., 

and Menzie, W.D., 1983, Preliminary 

geological map of the Circle quadrangle, 

Alaska: U.S. Geological Survey Open-File 

Report 83-170-A, 30 p. 

Menzie, W .D., Foster, H.L., Tripp, R.B., and 

Yeend, W.E., 1983, Mineral resource 

assessment of the Circle quadrangle, Alaska: 

U.S. Geological Survey Open-File Report 83-

170-B, 57 p. 

Mertie, J.B., Jr., 1938, Gold placers of the 

Fortymile, Eagle, and Circle districts, 

Alaska: U.S. Geological Survey Bulletin 897-

C, p. 133-261. 

Mining and Minerals, 1985, In the golden heart of 

Alaska: Fairbanks, North Star Borough, 80 p. 

76 

Spurr, J.E., 1898, Geology of the Yukon gold 

district, Alaska: U.S. Geological Survey 18th 

Annual Report, pt. 3, p. 87-392. 

Wahrhaftig, Clyde, 1965, Physiographic divisions 

of Alaska: U.S. Geological Survey 

Professional Paper 482, 52 p. 

Yeend, Warren, 1985, Trace elements of placer 

gold, 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. 4-7. 

Reviewers: R. M. Chapman and Helen Foster 
SOUTHWESTERN ALASKA 

Kisaralik Lake, Bethel quadrangle. Photo by S.E. Box, 1986. 

77 
LATE MESOZOIC STRUCTURAL AND 

STRATIGRAPHIC FRAMEWORK, 

EASTERN BETHEL QUADRANGLE, 

SOUTHWESTERN ALASKA 

Stephen E. Box and John M. Murphy 

In July of 1986 we made a boat traverse 

along the Kisaralik River in the eastern Bethel 

quadrangle (fig. 1) in order to study the initiation, 

evolution, and deformation of the depositional 

basin of the Albian to Coniacian (late Early and 

early Late Cretaceous) Kuskokwim Group in the 

context of the tectonic evolution of the region. 

This report presents our initial field results 

augmented by preliminary petrographic study of 

our samples, and includes a geologic map and cross 

section along the Kisaralik River (fig. 1). 

Pre-mid-Cretaceous rocks of the Togiak and 

Goodnews terranes are exposed along the Kisaralik 

River. The Togiak terrane is a Mesozoic andesitic 

volcanic and volcaniclastic terrane with a Late 

Triassic through Early Cretaceous history (Box, 

1985). The eastern third of the Kisaralik River 

traverse exposes a generally west-dipping section 

of the Togiak terrane divisible into three 

unfoliated stratigraphic units (fig. 1). Fossils of 

Valanginian (early Early Cretaceous) age occur 

about 25 km to the southwest along strike in strata 

apparently correlative with the middle or upper 

unit of the Togiak terrane along the Kisaralik 

River (Hoare and Coonrad, 1978). The Goodnews 

terrane is exposed beneath Kuskokwim 

conglomerates in the core of the Kisaralik 

anticline and at Greenstone Ridge. The Goodnews 

terrane in the Kisaralik anticline is similar to the 

lower unit of the Togiak terrane, but differs in 

that it is overprinted by slaty to phyllitic 

cleavage. The Goodnews terrane at Greenstone 

Ridge consists of greenschist-facies metabasite 

with a southeast-dipping foliation and northeasttrending plagioclase lineation. Actinolite 

separated from a Greenstone Ridge metabasite 

sample yielded a K/ Ar age of 146 ± 15 Ma 

(fig. 1). The structural relationship between the 

rocks at Greenstone Ridge and those of the 

Kisaralik anticline is uncertain, but both 

apparently record an earliest Cretaceous lowgrade metamorphic event. 

Two other terranes underlie the region of the 

Kisaralik traverse, but they are not exposed near 

the Kisaralik River. The Kilbuck terrane occurs 

west of the Goodnews terrane in the southern 

Bethel and northern Goodnews quadrangles (fig. 1, 

inset), and consists of regionally metamorphosed 

Precambrian quartzofeldspathic amphibolitefacies schist (Hoare and Coonrad, 1979), which 

underwent a greenschist-facies overprint about 

150-130 Ma (Late Jurassic and Early Cretaceous 

time) (Turner, 1983). The Nyac terrane crops out 

west of the westernmost part of the Kuskokwim 

Group on the Kisaralik River and consists of 

78 

Middle and Upper Jurassic andesitic volcanic and 

volcaniclastic strata intruded by an Early 

Cretaceous granitic pluton (Hoare and Coonrad, 

1959b; Wilson, 1977). It is uncertain whether the 

Nyac terrane is anywhere overlapped by the 

Kuskokwim Group. 

The Kuskokwim Group covers the contact 

between the Goodnews and Togiak terranes. Basal 

conglomerates overlie foliated metamorphic rocks 

of the Goodnews terrane at Greenstone Ridge and 

along the Kisaralik anticline (fig. 2). Both sections 

exhibit a lower conglomeratic section of local 

provenance and near-sea-level depositional 

setting, and an upper conglomeratic section of 

deep-water origin derived from a terrane of 

quartz-mica schist and granite gneiss, presumably 

the Kilbuck terrane. Basal conglomerates are 

absent on the east side of the Kuskokwim 

depositional basin. 

The basal Kuskokwim conglomerates at 

Greenstone Ridge and the Kisaralik anticline are 

overlain by several kilometers of thin-bedded, fine 

sandstone and shale. This shaly facies of the 

Kuskokwim Group conformably overlaps and 

possibly interfingers with volcanogenic strata of 

the Togiak terrane along .the eastside of the basin 

without an intervening basal conglomerate. 

Coarse sandstone beds occur only at Upper Falls, 

where two 30-m-thick turbidite channel-fill 

sequences are separated by 50 m of thin-bedded 

fine sandstone and shale. Flute marks indicate 

northeast-directed flow within these channels. 

Stratigraphically above the basal conglomerate, 

the depositional environment of the Kuskokwim 

Group along the Kisaralik River is interpreted as a 

deepwater basin dominated by channel and 

overbank deposition along northeasterly directed 

submarine channels. 

Fossils recovered from the Kuskokwim Group 

in the vicinity of the Kisaralik River range from 

Albian to Coniacian in age (Hoare and Coonrad, 

1959a). A middle Albian fossil was recovered from 

the fine-grained turbidite strata just above the 

basal conglomerate flanking the Eek Mountains 

anticline about 40 km to the south-southwest along 

strike from the Kisaralik anticline (see Murphy, 

this volume). The depositional onlap of the finegrained facies onto the Togiak terrane just south 

of the Kisaralik River above Upper Falls (fig. 1) is 

Cenomanian(?) in age (D.L. Jones and J. W. Miller, 

written commun. to W.L. Coonrad, USGS, 1979). 

The younger age of its depositional base, its 

predominantly quartzose composition, and its lack 

of a basal conglomerate indicate that the eastern 

flank of the Kuskokwim depositional basin in the 

Bethel quadrangle was passively onlapped by 

turbidite basin-fill derived predominantly from 

highlands along the western basin margin. 

Strata of the Kuskokwim Group west of 

Golden Gate Falls have subtle lithologic and 

compositional differences from the Kuskokwim 

strata exposed east of the falls. The western 
strata display (1) a much greater proportion of 

sandstone in most outcrops, (2) south-directed 

paleocurrents, and (3) argillites which lack a slaty 

cleavage. The sandstones are superficially similar 

in composition to those from the eastern area, 

except for a much higher percentage of chert 

clasts (5 percent versus a trace amount in the 

eastern sandstones). The compositional and 

paleoflow data imply that the western strata were 

not part of the same depositional system as the 

eastern strata. As age relationships are uncertain, 

these western strata either may be of a different 

age than the eastern strata or were deposited in a 

different depositional basin and subsequently 

faulted against the eastern strata. 

The predominant structural fabric of the 

Bethel quadrangle is a result of Late Cretaceous 

deformation. In the northeastern Bethel 

quadrangle, highly deformed Kuskokwim strata as 

young as Coniacian (87 .5-88.5 Ma) are 

unconformably overlain by volcanic rocks (Hoare 

and Coonrad, 1959a) that have yielded a wholerock K-Ar age of 71.4 ± 2.1 Ma (Robinson and 

Decker, 1986). Along the Kisaralik River this Late 

Cretaceous deformation resulted in the 

development of northeast-southwest-trending tight 

folds, often overturned to the northwest. Shaly 

Kuskokwim strata east of Golden Gate Falls 

generally preserve a moderately to steeply 

southeast-dipping axial planar slaty cleavage. 

Preexisting mineral foliation in the older units at 

Greenstone Ridge and the Kisaralik anticline is 

also folded by the northeast-southwest-trending 

folds. The Kuskokwim Group downstream from 

Golden Gate Falls is also deformed into northeastsouthwest-trending folds, often overturned to the 

northwest, but lacks a slaty cleavage. 

The western flank of Greenstone Ridge is 

marked by a southeast-dipping thrust fault that 

places metabasite over undated Kuskokwim strata 

(fig. 1). As the Kisaralik anticline is asymmetric 

with a steeper western limb, it is suspected that 

this feature also overlies a southeast-dipping 

thrust fault at depth. On our cross section the 

Kisaralik anticline, as well as northwest-vergent 

overturned folds within the Kuskokwim Group, are 

interpreted to continue downward into southeastdipping thrust faults. 

The late Mesozoic history of the northern 

Bristol Bay region has been interpreted by Box 

(1985) to record the partial underthrusting of 

continental crust (Kilbuck terrane) beneath the 

accretionary forearc (Goodnews terrane) of an 

active intraoceanic volcanic arc (Togiak terrane) 

in Early Cretaceous time. Early Cretaceous 

metamorphism of the Kilbuck and Goodnews 

terranes along the crustal suture, as well as Early 

Cretaceous explosive andesitic volcanism 

evidenced in the Togiak terrane, are 

manifestations of this collisional event. 

Subsequent uplift of the metamorphosed Kilbuck 

terrane and the western part of the Goodnews 

79 

terrane in late Early and early Late Cretaceous 

time provided detritus for the deep Kuskokwim 

basin between the uplifted collisional suture and 

the quiescent volcanic-arc terrane. Renewed 

compressional deformation in middle Late 

Cretaceous time resulted in shortening of the midCretaceous basinal strata by northwest-vergent 

thrust faults and associated folds, reactivating the 

structural grain inherited from earlier subduction 

and collision episodes (see Murphy, this volume). 

Late Late Cretaceous volcanism records the 

northward underthrusting of Pacific seafloor under 

the newly consolidated continental mass of 

accreted terranes in western Alaska (Wallace and 

Engebretson, 1984; Moll-Stalcup, in press). 

Whether strike-slip faulting played a significant 

role in the late Mesozoic evolution of this area of 

southwestern Alaska is uncertain. 

REFERENCES CITED 

Box, S.E., 1985, Terrane analysis, northern Bristol 

Bay region, southwestern Alaska, in BartschWinkler, Susan, ed., The United States 

Geological Survey in Alaska: 

Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 32-37. 

Hoare, J.M., and Coonrad, W.L., 1959a, Geology of 

the Bethel quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous 

Investigations Map I-285, scale 1:250,000. 

___ 1959b, Geology of the Russian Mission 

quadrangle, Alaska: U.S. Geological Survey 

Miscellaneous Investigations Map 1-292, scale 

1:250,000. 

1978, Geologic map of the Goodnews and 

~agemeister Island quadrangles region: U.S. 

Geological Survey Open-File Report 78-9-B, 

scale 1:250,000. 

1979, The Kanektok metamorphic complex, a 

--rootless belt of Precambrian rocks in 

southwestern 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. 72-7 4. 

Jones, D.L., Silberling, N.J., Coney, P.J., and 

Plafker, George, 1984, Lithotectonic terrane 

map of Alaska, in Silberling, N.J., and Jones, 

D.L., eds., Lithotectonic terrane maps of the 

North American Cordillera: U.S. Geological 

Survey Open-File Report 84-523, p. A1-A12, 

scale 1:2,500,000, 4 sheets. 

Moll-Stalcup, E.J., in press, Latest Cretaceous and 

Cenozoic magnetism in mainland Alaska, in 

Plafker, George, and Jones, D.L., eds., The 

Cordilleran orogen: Decade of North 

American Geology Special Publication, 

Geological Society of America, Boulder, Colo. 

Robinson, M.S., and Decker, John, 1986, 

Preliminary age dates and analytical data for 

selected igneous rocks from the Sleetmute, 
00 

c 

A 

!Qc:S ?>6 

CD 

A 

"IQO ?>o' () o\i 

'\IQO 

Qs 

() \~ IQ\) 

rf ?>o' ,s':l 8 

8 

IQ\f "ro' 

1- NYAC~ KILBUCK GOODNEWS-? .. -?----- TOGIAK 

0 10 

KILOMETERS 

!t-Ar analytical data: (sample I - 60° 20.5' N, I60° I8.8' W) 

Rock type 

(Hap-unit symbol) 

Metabasite (MzPzb) 

Material 

analyzed 

Amphibole 

Constants used in calculation of age: 

K2o pet. 

(wt. pet.) 

0.0679 

40Ar 

(moles/gxlOll) 

I.8I 

40Ar rad 

40Ar total 

O.I69 

");'fl.= 4.96 x wi 06yr.; i'lc= 0.58I ! Io-10/yr.; 

P k4 /It= I.I67 x w- g/g 

Calculated 

age (Ha) 

I46 ± IS 

() 

..l..'V: 

~ 

61° 

0 

~--------~--~~--------~~60 

162° LOCATION MAP 159° 
QO 

1--' 

Qs 

Qb 

Surficial deposits (Quaternary) 

Olivine basalt (Quaternary) 

EXPLANATION 

OVERLAP SEQUENCES 

TKg 

TKv 

Granitic pluton (early Tertiary and Late Cretaceous) 

Volcanic rocks (early Tertiary and Late Cretaceous) 

Kk Kuskokwim Group (late Early Cretaceous and early Late 

Cretaceous) 

PRE-MID-CRETACEOUS TERRANES 

KJs 

KJv 

KJa 

TOGIAK TERRANE 

Volcaniclastic sedimentary rocks 

(Early Cretaceous and (or) Jurassic) 

Andesitic volcanic rocks 

(Early Cretaceous and (or) Jurassic) 

Tuffaceous argillite and chert 

(Early Cretaceous and (or) Jurassic) 

NYAC TERRANE 

Jv Andesitic volcanic rocks (Jurassic) 

~ 

~ 

CD 

• 

MAP 

Contact--Approximately located. Dashed 

when inferred 

Thrust fault--Teeth on upper plate 

Location of K-Ar dated sample 

Location of Cenomanian(?) fossil 

(discussed in text) 

A._ ~8 Location of cross-section 1 ine A-B 

MzPza 

~1z Pzb 

pfg (?) 

SYMBOLS 

GOODNEWS TERRANE 

Tuffaceous argillite and chert (Mesozoic or Paleozoic)--

Slaty to phyllitic cleavage 

Foliated metabasite and minor marble and metachert 

(Mesozoic or Paleozoic) 

KILBUCK(?) TERRANE 

Granitic gneiss and quartz-mica schist 

(Precambrian)--Only in cross section 

CROSS SECTION 

Conglomerate 

Sandstone turbidite 

Argillaceous rocks 

Volcanic rocks 

Schistosity or phyllitic cleavage 

Figure 1.--Geologic map and cross section of part of eastern Bethel quadrangle along Kisaralik River (map 

adapted from Hoare and Coonrad, 1959a). Inset location map shows terranes of Bethel quadrangle (Jones 

and others, 1984). Stratigraphic sections A and B are shown in figure 1. K-Ar analysis by Krueger 

Enterprise Inc. for w. Connelly, AMOCO (written commun., 1978). 
A. North end, Greenstone Ridge 

thickness 

(meters) 

5 

2 

? 

Interbedded coarse-grained sandstone 

and cobbly sandstone composed of quartzmica-schist and metabasite clasts. 

(Subwave-base marine debris flow deposits) 

Tangential cross-bedded, carbonate 

cemented coarse-grained sandstone and 

gravel composed of quartz-mica-schist 

clasts. (Shallow marine deposits) 

Rounded metabasite boulders dispersed 

in matrix of pebbly conglomerate of 

angular quartz-mica-schist clasts. 

(Either nonmarine or marine debris 

flow deposits) 

Clast-supported, rounded, foliatedmetabasite, boulder conglomerate 

with micaceous quartzose sandstone 

matrix. (Nonmarine(?) deposits) 

Foliated metabasite; depositional 

contact parallels foliation. 

B. East flank, Kisaralik Anticline 

......... 

I liDo o 0 o o ........... 

.......... 

thickness 

(meters) 

? 

20 

10 

Thin-bedded, fine-grained, micaceous, 

quartzose sands tone and sha 1 e. 

(Subwave-base marine turbidites) 

Amalgamated clast- and matrixsupported cobble conglomerate with 

rounded clasts of granite gneiss, 

quartz-mica schist, phyllite, argillite 

and metabasite. (Subwave-base marine 

debris flow deposits) 

·.·.·.·::::.~ 

Thin-bedded sandstone and shale with 

schist-clast gravel interbeds and 

flute-casts indicating northeastward 

paleocurrents. (Subwave-base marine 

turbidites) 

•. (J . • 

i' 

o. o I ~ . : 

20 

8 

? 

Matrix-supported pebble to cobble conglomerate with pebbly matrix of 

angular quartz-mica-schist clasts 

and larger rounded cobbles of 

chlorite schist, metabasite and 

metachert. (Subwave-base marine 

debris flow deposits) 

Calcareous, medium- to coarse-grained, 

micaceous, quartzose sands tone with 

lenticles, lags, and channels of tuffaceous-chert-cobble conglomerate. Has 

trough crossbeds, horizontal burrows 

and Inoceramus sp. prisms. (Shallow 

marine deposits) 

Phyllitic, tuffaceous chert; depositic·r.'ll 

contact parallels foli~tion. 

Figure 2.-- Stratigraphic sections of basal part of the Kuskokwin Group along Kisaralik River (located 

in figure 1). 

Russian Mission, Taylor Mountains and Bethel 

quadrangles, southwestern Alaskan: Alaska 

Division of Mining and Geological and 

Geophysical Surveys, Public-Data File 86-99, 

9 p. 

Turner, D.L., 1983, Geochronology of the Kilbuck 

terrane of southwestern Alaska: Geological 

Society of America Abstracts with Programs, 

v. 15, no. 5, p. 407. 

Wallace, W.K., and Engebretson, D.C., 1985, 

82 

Relationships between plate motions and Late 

Cretaceous to Paleocene magmatism in 

southwestern Alaska: Tectonics, v. 3, 

p. 295-315. 

Wilson, F.H., 1977, Some plutonic rocks of 

southwestern Alaska, a data compilation: 

U.S. Geological Survey Open-File Report 77-

501, 7 p. 

Reviewers: W.L. Coonrad and T.E. Moore 
EARLY CRETACEOUS CESSATION OF 

TERRANE ACCRETION, 

NORTHERN EEK MOUNTAINS, 

SOUTHWESTERN ALASKA 

John M. Murphy 

The Eek Mountains form the northwesternmost boundary of the oceanic Goodnews terrane 

and lie adjacent to the eastern margin of 

Precambrian quartzofeldspathic metamorphic 

rocks of the Kilbuck terrane (Jones and Silberling, 

1979) (fig. 1). Hoare and Coonrad (1979) 

considered the informally named Kanektok 

metamorphic complex (Kilbuck terrane) a rootless 

belt of Precambrian rocks. Box (1985) interpreted 

the Goodnews terrane as a composite subduction 

complex whose subterranes record progressive 

addition of two oceanic terranes and a single 

continental (Kilbuck) crustal terrane to the 

northwest side of the Togiak terrane of Jones and 

Silberling (1982) during late Mesozoic time. Both 

the Goodnews and Kilbuck terranes are overlapped 

unconformably by Lower Cretaceous clastic rocks 

of the Kuskokwim Group (Hoare and Coonrad, 

1959). The northern end of the Eek Mountains, 

Bethel A-4 quadrangle, was mapped at 1:40,000 

scale as part of my M.S. thesis research 

undertaken at the University of Alaska, Fairbanks 

(Murphy, in review). This paper summarizes the 

constraints on timing of accretion of the 

Goodnews and Kilbuk terranes using Lower 

Cretaceous sedimentary overlap assemblages 

mapped in the northern Eek Mountains. 

Two Early Cretaceous proximal turbidite 

units, the Eek Mountains belt and Kuskokwim 

Group, occur in the northern Eek Mountains. 

These units have common sediment sources, but 

they are separated by an angular unconformity 

interpreted as a submarine canyon cut-and-fill 

sequence (Murphy and Decker, 1985a, b). The two 

units differ in age and deformation intensity, and 

they serve to bracket cessation of a collision event 

which placed oceanic components of the Goodnews 

terrane against the continental Kilbuck terrane. 

The oldest dated rocks in the Goodnews 

terrane of the northern Eek Mountains consist of 

pillow basalt flows and associated volcanogenic 

sedimentary rocks intercalated with bioclastic 

limestone composed of fragments of the Permian 

surf-zone bivalve Atomodesma sp. (Hoare and 

Coonrad, 1978; Kauffman and Runneger, 1975) 

(table 1, No. 1; unit Pbl, fig. 1.). The basalt and 

limestone association indicates a Permian oceanisland setting (Murphy and Decker, 1985a, b). 

Pumpellyite, quartz, and carbonate fill vesicles 

and fractures in basalt. Plagioclase consists of 

albite or has been replaced by prehnite. 

Structurally overlying the basalt and limestone 

unit are interbedded and interfoliated 

volcanogenic deposits including flows, debris 

flows, turbidites, argillite, and tuff of Late 

83 

Jurassic or Early Cretaceous age (table 1, Nos. 2, 

3; unit KJv, fig. 1) and late Paleozoic and (or) 

early Mesozoic age (unit MzPzu, fig. 1). The 

Upper Jurassic or Lower Cretaceous volcaniclastic 

rocks are interpreted as elements of the Togiak 

terrane which were either tectonically emplaced 

or stratigraphically overlapped onto the Goodnews 

terrane prior to their shared deformation during 

the late Early Cretaceous. They have 

predominantly southeast-dipping bedding and 

foliation and are cut by veins of prehnite and 

pumpellyite. 

The Valanginian (table 1, nos. 4, 5; unit Ke, 

fig. 1) Eek Mountains belt (Hoare and Coonrad, 

1983), here composed of interbedded grain-flow, 

turbidite, and argillite deposits that comprise an 

inner-fan channel and channel-levee complex, 

shares the southeast-dipping bedding and foliation 

orientations with both the Permian and the Upper 

Jurassic or Lower Cretaceous units; however, the 

Eek Mountains belt contains only detrital 

metamorphic minerals. The absence of 

metamorphic mineral foliation in the Eek 

Mountains belt, coupled with sharing of structural 

fabrics with older rocks, suggests that prehnitepumpellyite-facies metamorphism in the northern 

Eek Mountains predates Valanginian time, but that 

reactivation of structural deformation occurred 

during or soon after deposition of the Eek 

Mountains belt. 

Conglomerates of the Eek Mountains belt 

consist of amalgamated, bimodal, matrixsupported, and poorly sorted beds composed of 

subangular to well-rounded clasts floating in fineto medium-pebble or sand-size matrix. Clast 

types, in decreasing abundance, include green and 

gray chert and tuff, massive porphyritic and 

amygdaloidal greenstone, quartzofeldspathic schist 

and gneiss, white quartz, fine-grained sandstone, 

and siltstone. The chert, tuff, and greenstone are 

diagnostic rock types of the Goodnews terrane; 

however, the quartzose schist and gneiss must 

have been derived from the Kilbuck terrane. This 

is the earliest quartzose metamorphic detritus 

known locally and marks the arrival of the Kilbuck 

terrane into sedimentary proximity of the Eek 

Mountains belt and, therefore, the Goodnews 

terrane during Valanginian time. This provenance 

tie also marks the imminent collision of the 

Kilbuck and Goodnews terranes. 

The Kuskokwim Group unconformably 

overlies the structurally dismembered Goodnews 

terrane, including the Eek Mountains belt, with a 

basal submarine conglomerate at least 550 m thick 

(Hoare and Coonrad, 1959). Conformably 

overlying the conglomerate are thin-bedded 

sandstone turbidites and shale that contain a 

middle Albian (late Early Cretaceous) ammonite 

(table 1, No. 6; W.K. Wallace, University of 

Alaska, written commun., 1985). 

Kuskokwim conglomerates consist of 

laterally extensive, amalgamated, matrix-
meters 8 

1500 

1000 

500 

0 

A 

Ke 

NW 0 2 KILOMETERS SE 

EXPLANATION 

Kk Kuskokwim Group (Lower Cretaceous)--Conglomerate; age is 

middle Albian 

Ke Eek Mountains belt (Lower Cretaceous)--Conglomerate, 

sandstone, and shale; age is Valanginian 

KJv Volcanogenic flows, debris flows, and turbidites (Lower 

Cretaceous or Upper Jurassic) 

MzPzu Undivided basalt, chert, and argillite (lower Mesozoic 

and (or) upper Paleozoic) 

Pbl Pillow basalt flows and bioclastic limestone (Permian) 

Figure 1.--Geologic cross section and location map of northern Eek Mountains study area. Terranes of 

Jones and Silberling (1979) outlined on location map. Cross section simplified from Murphy (in review). 

supported, poorly sorted pebble- to cobbleconglomerate beds composed of subangular to 

well-rounded clasts in a matrix of sandstone and 

fine pebbles. Basic clast types include varicolored 

chert and tuff, limy siltstone, argillite, 

quartzofeldspathic schist and gneiss, massive and 

foliated greenstone, white quartz, and sandstone. 

As in the Eek Mountains belt, the chert, tuff, and 

greenstone are derived from the Goodnews 

terrane, while the schist and gneiss are derived 

from the Kilbuck terrane. Some clasts of limy 

siltstone contain fragments of Atomodesma, thus 

providing firm linkage to the Goodnews source 

terrane (table 1, No. 7). Basal Kuskokwim 

conglomerates at Greenstone Ridge and Kisaralik 

anticline may record an unconformable shallow to 

deep-marine transition (Hoare, 1961; see also Box 

and Murphy, this volume); however, the 

Kuskokwim conglomerates of the Eek Mountains 

are interpreted as deep marine deposits, where 

submarine canyon-facies conglomerate laps onto 

foliated rocks of the Goodnews terrane (Murphy 

and Decker, 1985a, b). 

In summary, cessation of Early Cretaceous 

deformation in the northern Eek Mountains is 

interpreted to correspond with final emplacement 

of the Kilbuck terrane and Goodnews terrane. 

Cessation of this deformation event is constrained 

by the basal submarine unconformity beneath 

conglomerate of the Kuskokwim Group (Hoare and 

Coonrad, 1959). The middle Albian ammonite 

84 

from stratigraphically above the basal Kuskokwim 

conglomerate, and the underlying foliated 

Valanginian Eek Mountains belt deposits bracket 

the time when deformation ceased. The 

Kuskokwim Group was itself folded in the Late 

Cretaceous at a time bracketed by deformed 

deposits of Turonian age at Great Ridge (Hoare 

and Coonrad, 1959) and by undeformed 

crosscutting dikes correlated with the 71 Ma (Shew 

and Wilson, 1981) Mount Oratia pluton. 

REFERENCES CITED 

Box, S.E., 1985, Terrane analysis, northern Bristol 

Bay Region, southwestern Alaska, in BartschWinkler, Susan, ed., The United States 

Geological Survey in Alaska: 

Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 32-37. 

Hoare, J.M., 1961, Geology and tectonic setting of 

the lower Kuskokwim-Bristol Bay region, 

Alaska: American Association of Petroleum 

Geologists Bulletin, v. 45, no. 5, p. 594-611. 

Hoare, J.M., and Coonrad, W.L., 1959, Geology of 

the Bethel quadrangle, Alaska: U.S. 

Geological Survey Miscellaneous Geologic 

Investigations Map 1-285, scale 1:250,000. 

1978, Geologic map of the Goodnews and 

----wagemeister Island quadrangles region, 

southwestern Alaska: U.S. Geological Survey 

Open-File Report 78-9-B, scale 1:250,000. 
Table 1.--Age diagnostic fossils from northrn Eek Mountains 

[Ages reported by J. W. Miller, U.S. Geological Survey] 

USGS Stratigraphic 

collection Latitude unit 

No. Longitude Fossils Age (fig. 1) 

1. M7975 60°04.38' N. Pelecypod Permian 

160°26.25' w. A tomodesma sp. Pbl 

clastic limestone 

2. M7970 60°04. 79' N. Pelecypod Late Jurassic or KJv 

160°23.38' w. Buchia sp. Early Cretaceous 

3. M7969 60°04.75' N. Pelecypod Late Jurassic or KJv 

160°23.32' w. Buchia sp. Early Cretaceous 

4. M7972 60°05.82' N. Pelecypod probably probably Valanginian 

160°22.45' w. Buchia sublaevis Ke 

Keyser ling 

5. M7963 60°03.02' N. Pelecypod Buchia probably Valanginian 

160°24.50' w. sp., probably 

B. Keyserlingi Ke 

(Lahusen) or 

B. Sublaevis Keyserling 

6. M7772 60°05.09' N. Cephalopod middle Albian 

160°27.02' w. Paragastroplites Kk 

flexicostasis Imlay 

7. M7973 60°07.52' N. Pelecypod Permian 

160°21.19' w. A tomodesma sp. Kk 

fragments in clast 

__ 1979, The Kanektok metamorphic complex, a 

rootless belt of Precambrian rocks in 

southwestern 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. B72-B74. 

____ 1983, Graywacke of Buchia Ridge and 

correlative Lower Cretaceous rocks in the 

Goodnews Bay and Bethel quadrangles, 

southwestern Alaska: U.S. Geological Survey 

Bulletin 1529-C, 17 p. 

Jones, D.L., and Silberling, N.J., 1979, Mesozoic 

stratigraphy--The key to tectonic analysis of 

southern and central Alaska: U.S. Geological 

Survey Open-File Report 79-1200, 41 p. 

___ 1982, Mesozoic stratigraphy--the key to 

tectonic analysis of southern and central 

Alaska in Leviton, A.E., and others eds., 

Frontiers of geological exploration of western 

North America: Pacific Section, American 

Association for the Advancement of Science, 

p. 139-153. 

Kauffman, E.G., and Runnegar, B., 1975, 

Atomodesma (Bivalvia), and Permian species 

of the United States: Journal of 

85 

Paleontology, v. 49, no. 1, p. 23-41. 

Murphy, J.M., 1987, Geology, sedimentary 

petrology and tectonic synthesis of Early 

Cretaceous submarine fan deposits, northern 

Eek Mountains, southwest Alaska: Fairbanks, 

University of Alaska, M.S. thesis (in review). 

Murphy, J.M., and Decker, John, 1985a, The 

Goodnews terrane and Kuskokwim Group in 

the Eek Mountains, southwest Alaska: Open 

marine to trench-slope transition: American 

Association of Petroleum Geologists Bulletin, 

v. 69, no. 4, p. 672. 

1985b, The Goodnews terrane and Kuskokwim 

--Group in the Eek Mountains, southwest 

Alaska: Deep marine to trench-slope 

transition, in Rosel, J., Remacha, E., and 

Zamorano, M., eds., Abstracts and poster 

abstracts: International Association of 

Sedimentologists, European Regional Meeting, 

6th, p. 622-623. 

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 82-866, 26 p. 

Reviewers: S.E. Box and W.L. Coonrad 
PETROLOGY AND PROVENANCE OF 

SANDSTONES OF THE NAKNEK FORMATION, 

ALASKA PENINSULA 

Michael W. Mullen 

The Upper Jurassic Naknek Formation crops 

out in an extensive belt throughout much of the 

Alaska Peninsula from Kamishak Bay to Black 

Hill. In the study area (fig. 1), it reaches a 

maximum thickness of more than 3,000 m, but its 

thickness averages between 1, 700 and 2,000 m 

(R.L. Detterman, USGS, unpub. data). The 

formation was deposited in a series of arc-trench 

gap basins in depositional environments ranging 

from nonmarine fluvial to outer shelf (Detterman 

and others, 1981a, 1985). During recent 

investigations on the Alaska Peninsula as part of 

the Alaska Mineral Resource Assessment Program, 

R. L. Detterman collected sandstone samples from 

several measured sections. Samples from four 

sections have been analyzed for composition in 

order to determine the source rocks and the 

depositional history of this formation. This 

information in turn will be of value in determining 

regional tectonic uplift and the duration of 

magmatic arc activity. 

Sandstone samples from measured sections 

at Indecision Creek, Wandering Ridge, Northeast 

Creek, and Clark River (fig. 1) were analyzed by 

standard thin-section techniques, scanning 

electron microscope (SEM), and X-ray probe 

microanalyzer. The Indecision Creek and 

Wandering Ridge sections represent the upper 

sandstone member of the Naknek Formation; the 

Northeast Creek and Clark River sections 

represent the Snug Harbor Siltstone Member and 

the lower sandstone member of the Naknek 

Formation (fig. 2). The four sections therefore 

represent almost the entire formation. 

Modal analyses of 40 thin sections indicate 

that samples from Indecision Creek and Wandering 

Ridge (upper sandstone member) are generally 

richer in quartz and lithic fragments than samples 

from Northeast Creek and Clark River (Snug 

Harbor Siltstone Member and lower sandstone 

member), with the exception of one fine grained, 

quartz-rich wacke from the Clark River locality 

(fig. 3). The sandstones from the Indecision Creek 

and Wandering Ridge sections range from finegrained, moderately sorted, subangular lithic 

arkoses and litharenites to very fine grained, very 

poorly sorted, angular feldspathic and lithic 

wackes (sandstone terminology of Dott, 1964, and 

Folk, 1974). The samples from the Northeast 

Creek and Clark River sections, in contrast, are 

medium-grained, well-sorted, subangular to 

subrounded arkoses to very fine grained, poorly 

sorted, angular feldspathic wackes. 

Light-mineral suites in the Naknek 

sandstones (table 1) are mainly monocrystalline, 

slightly undulose quartz, minor polycrystalline 

86 

quartz (ranging from polygonal to straight 

borders), plagioclase (mainly oligoclase, but 

varying in amounts of albite and andesine), minor 

orthoclase, rare microcline and perthite, and very 

rare chalcedony. The major heavy minerals are 

biotite, hornblende, epidote, clinozoisite, 

muscovite, chlorite, and magnetite. These 

components vary in abundance from sample to 

sample, but together they compose from 6 to 20 

percent of the total grains. Minor heavy minerals 

generally compose less than 1 percent individually, 

but up to 1 percent when summed; these are 

zircon, apatite, garnet of almandine-spessartine 

composition (fig. 4), sphene, augite, and rare 

allanite, tremolite, and pumpellyite. 

Lithic fragments within the Naknek 

sandstones are primarily plutonic and metamorphic 

grains, although volcanic fragments also are 

abundant in a few samples from the Clark River 

section (fig. 3). The plutonic rock fragments are 

mainly ··quartz-plagioclase, quartz-plagioclasebiotite, and quartz-hornblende composites, and 

include graphic intergrowths of quartz and 

plagioclase. The metamorphic rock fragments are 

chiefly metaquartzite, micaceous metaquartzite, 

quartz mica schist, mica schist, and rare phyllite, 

metalimestone, and epidote-quartz-hornfels. 

Volcanic rock fragments are present in about 60 

percent of the samples, but are usually very rare 

and of the altered silicified type. They are most 

abundant in two samples from the Northeast Creek 

section near its top and from three samples from 

the Clark River section. The weakly altered 

andesitic to basaltic grains from medium-grained 

arkoses of the Clark River section commonly 

exhibit pilotaxitic structure, and the larger grains 

contain zoned phenocrysts of plagioclase. 

Sedimentary rock fragments are absent or 

uncommon in most samples except for softsediment rip-up clasts, which were excluded from 

the calculations in order not to confuse the 

provenance determinations. The chief 

sedimentary rock fragments are chert, mudstone, 

argillite, and limestone. All framework grains are 

summarized in table 1. 

The components of the sandstones from the 

Naknek Formation indicate a largely magmatic arc 

provenance with associated metamorphosed 

country rock. The granitic rock fragments, 

especially the graphic grains, and monocrystalline 

grains such as microcline and perthite, point to an 

igneous plutonic source. Also, minor heavy 

minerals, namely allanite (determined by X-ray 

microanalysis, fig. 4), occur almost exclusively in 

granitic rocks (Deer, Howie, and Zussman, 1962). 

The volcanic rock components may be associated 

with the plutons or may be part of older country 

rock, since many grains are highly silicified. The 

metamorphic grains, including epidote, 

clinozoisite, garnet, tremolite, and pumpellyite, 

were probably eroded from country rock which the 

plutons intruded, as indica ted by the presence of 
57° 

159° 

BRISTOL BAY 

Chlonlk ~Jn 

Clark River •I 

,Jn 

PACIFIC 

OCEAN 

EXPLANATION 57° 

Naknek Formation (Jurassic) 

Granitic rocks (Jurassic) --

includes older metamorphic 

rocks 

Contact 

- • · • Fault, dotted where concealed 

H Location of measured section 

and sample sites 

50 100 KILOMETERS 

156° 

Figure 1.--lndex map of study area showing distribution of the Naknek Formation, location of measured 

sections, and exposed granitic source rocks. Geology from Detterman and others (1981b, 1985) and 

unpub. data. 

hornfels grains. The sedimentary rock fragments 

may be from several sources. The mudstone and 

argillite probably were derived from the 

underlying Middle Jurassic Shelikof and Kialagvik 

Formations and possibly older rocks; the limestone 

and chert probably originated from the Upper 

Triassic Kamishak Formation. Also, the presence 

in a few samples (mainly the Clark River and 

Northeast Creek sections) of well-rounded, 

nonundulose to slightly undulose, monocrystalline 

quartz grains, some with silica overgrowths, 

indicate reworking from older sandstones. 

The closest outcrops of possible plutonic 

source rocks are located on an island near the 

south shore of Lake Becharof and north along the 

drainage of the King Salmon River (fig. 1). These 

rocks are the southernmost outcrops of the 

Alaska-Aleutian Range batholith. They probably 

underlie much of the study area, as indicated by 

well data from the Gulf Oil Corporation Port 

Heiden well, which bottomed in granite of Jurassic 

age, and by gravity and aeromagnetic anomalies 

(Andreasen and others, 1963, Case and others, 

87 

1981). Metamorphic rocks, including 

metaquartzite, phyllite, schist, and gneiss, occur 

as roof pendants in the plutons and are correlated 

with the Kakhonak Complex of Permian(?) through 

Jurassic age in the Iliamna quadrangle to the north 

(Detterman and Reed, 1980). 

(.) 

Ci5 

(/) 

<( 

cr: 

::J 

...., 

cr: 

w 

a.. 

a.. 

::J 

upper 

sandstone 

~ L----===2~-~~=::i_ __ ----1 u.. 

~ 

w 

z 

~ 

<( 

z 

Snug Harbor Siltstone Mbr. 

lower 

sandstone 

mbr. 

Chisik 

Cgl. Mbr. 

Figure 2.-Schematic diagram showing members of 

the Naknek Formation on Alaska Peninsula (R.L. 

Detterman, written commun., 1986). 
• 

• • 

• 

• 

Quartz 

(Excl. chert and metaquartzite) 

• 

.b.. .. • 

• .. • • 

• .... .. G() 

.. I.J.J 

• 0 .lc .~ () 

"" "" G() ~ I.J.J 

G() () 

0 

.lc ! 

Q: "" "" Q. 

G() 

0 

~ 

.. 

• 

... .... 

• 

.. 

• 

• 

• 

• 

• 

.. 

Sedimentary 

• 

• s 

s :r. 

-; ~ (l ~ z ~ 

1'1' y (j) (l 

"1-

1'1' 

(j) ~ 

• 

• 

• 

• 

.. .. • 

• 

lgneou s L:_ • _ • __,,__ _ __,,__ _ __,,___-"--",__-~ ~~-----<....., _ _ _.._.__,...__,'-e-~~Met a-

(mainly plutonic) TTiorphic 

• Indecision Creek • Wandering Ridge • Northeast Creek • Clark River 

Figure 3.--Triangular Q-F-L and Lithic fragment plots for 40 sandstone thin sections from the Nankek 

Formation. Classification modified from Dott (1964) and Folk (1974). 

The persistence of granitic grains in all the 

members indicates the presence of a plutonic rock 

source throughout the depositional history of the 

Naknek Formation on the Alaska Peninsula. 

Sandstones of the Snug Harbor Siltstone Member 

and lower sandstone member at the Northeast 

Creek and Clark River sections are more arkosic 

(fig. 3), and they may have been proximal to the 

granitic source. In addition, the two conglomerate 

members contain up to 30 percent granitic clasts, 

which may indicate two major regional uplifts 

(Detterman and Reed, 1980). The upper sandstone 

member at the Indecision Creek and Wandering 

Ridge sections contains more lithic fragments, 

mainly metamorphic types, and where volcanic 

rock fragments are present, they are mostly the 

resistant silicified type. This may represent 

reworking of sedimentary rocks and the 

destruction of unstable grains, or increasing 

exposure of a metamorphic rock source. The 

88 

Table 1.--Summary of framework grains from the 

Naknek Formation on the Alaska Peninsula 

Light 

minerals 

Quartz 

Plagioclase 

Orthoclase 

Perthite 

Hicrocl ine 

Chalcedony 

Hajor 

heavy 

minerals 

Biotite 

Hornblende 

Epidote 

Cl inozo isite 

Muscovite 

Chlorite 

Magnetite 

Minor 

heavy 

minerals 

Zircon 

Apatite 

Garnet 

Sphene 

Augite 

Allanite 

Tremolite 

Pumpellyite 

Rock 

fragme n ts 

Metaquartzite 

Mica s.::hist 

Plutonic 

Metavolcanic 

Volcanic 

Epidotequartz 

hornfels 

Mudstone 

Argillite 

Limestone 

Phyllite 

Chert 

Metalimestone 
t 

c GARNET 

D ALLANITE 

Figure 4.--Scanning electron micrographs and X-ray probe analyses of selected heavy minerals from 

sandstones of the Naknek Formation. X-ray probe analyses are semiquantitative and show relative 

amounts of elements present. 

89 
presence of large (2.5 mm), weakly altered 

volcanic fragments in some parts of the Snug 

Harbor Siltstone Member and the lower sandstone 

member at the Clark River section may indicate 

active volcanism near the time of deposition. The 

recording of a widespead catastrophic event 

marked by a volcanic graywacke in the Snug 

Harbor Siltstone Member indicates active 

volcanism during the time of deposition 

(Detterman and Miller, 1986). Also, newly 

examined thin sections from Black Hill, farther 

south in the northern Cold Bay quadrangle, are 

from volcanic arenites, which indicate volcanic 

activity during the deposition of the upper 

sandstone member. 

In summary, compositional analyses of 

sandstone samples of the Naknek Formation from 

measured sections shows a largely granitic and 

subordinate metamorphic source, but volcanic 

detritus dominates in a few samples from the Snug 

Harbor Siltstone and lower sandstone members. 

These compositional data indicate that tectonic 

uplift of the Alaska-Aleutian Range batholith was 

nearly continuous throughout the deposition of the 

Naknek Formation, and that volcanic activity, 

though sporadic, also continued through Naknek 

time. 

REFERENCES CITED 

Andreasen, G.E., Dempsey, W.J., and Vargo, J.L., 

1963, Aeromagnetic map of parts of Ugashik 

and Karluk quadrangles, Alaska: U. S. 

Geological Survey Geophysical Investigations 

Map GP-353, scale 1:250,000. 

Case, J.E., Barnes, D.F., Detterman, R.L., Morin, 

R.L., and Sikora, R.F., 1981, Gravity anomaly 

and interpretation map of the Chignik and 

Sutwik Island quadrangles, Alaska: U.S. 

Geological Survey Miscellaneous Field Studies 

Map MF-1053-J, scale 1:250,000. 

Deer, W.A., Howie, R.A., and Zussman, J., 1962, 

90 

Rock-forming minerals v., 1, ortho- and ringsilicates: London, Longman, 333 p. 

Detterman, R.L., Case, J.E., Cox, D.P., Detra, 

D.E., Miller, T.P., and Wilson, F.H., 1981a, 

The Alaska Mineral Resource Assessment 

Program: Background information to 

accompany folio of geologic and resource 

maps of the Chignik and Sutwik Island 

quadrangles, Alaska: U.S. Geological Survey 

Circular 802, 16 p. 

Detterman R.L., and Miller, J.W., 1986, . A 

widespread catastrophic event in the Naknek 

Formation, Alaska Peninsula, in BartschWinkler, Susan, and Reed, K.M~ eds., The 

United States Geological Survey in Alaska --

Accomplishments during 1985: U.S. 

Geological Survey Circular 978, p. 27-29. 

Detterman, R.L., Miller J.W., and Case, J.E., 

1985, Megafossil locality map checklists, and 

pre-Quaternary stratigraphic sections of 

Ugashik, Bristol Bay, and part of the Karluk 

quadrangles, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1053-A, 

scale 1:250;000. 

Detterman, R.L., Miller, T.P., Yount, M.E., and 

Wilson, F.H., 1981b, Geologic map of the 

Chignik and Sutwik Island quadrangles, 

Alaska: U.S. Geological Survey Miscellaneous 

Investigation Map 1-1229, scale 1:250,000. 

Detterman, R.L., and Reed, B.L., 1980, 

Stratigraphy, structure, and economic geology 

of the Iliamna quadrangle, Alaska: U.S. 

Geological Survey Bulletin 1368-B, p. B1-B86. 

Dott, R.H., 1964, Wacke, graywacke, and matrix--

What approach to immature sandstone 

classification?: Journal of Sedimentary 

Petrology, v. 34, p. 625-632. 

Folk, R.L., 1974, Petrology of sedimentary rocks: 

Austin, Tex., Hemphill, 182 p. 

Reviewers: R.L. Detterman and Inyo Ellersieck 
SOUTHERN ALASKA 

\ 

Alaska Range. 

91 
EARTHQUAKE-CAUSED SEDIMENTARY 

COUPLETS IN THE 

UPPER COOK INLET REGION 

Susan Bartsch-Winkler and Henry R. Schmoll 

The Cook Inlet region experiences frequent 

earthquakes as a result of subduction near the 

Aleutian arc. Earthquakes originate beneath and 

north of Cook Inlet on the steeply dipping WadatiBenioff zone, which marks the descent of the 

Pacific plate into the mantle (Stephens and others, 

1986). Although many earthquakes of generally 

low to moderate magnitude are associated with 

the Wadati-Benioff zone, only the large magnitude 

earthquakes that occur closer to the Aleutian 

trench south and east of Cook Inlet are likely to be 

capable of significantly affecting intertidal 

sedimentation in the region. In particular, during 

the 1964 earthquake (moment magnitude 9.2; 

Kanamori, 1977), two areas of regional uplift and 

subsidence were produced in two nearly parallel 

zones trending southwest-northeast above the 

gently dipping Aleutian megathrust (Plafker, 1969, 

fig. 15, p. I-22). Upper Cook Inlet, and especially 

upper Turnagain Arm, lies within the subsidence 

zone, which is centered over the Kenai-Chugach 

Mountains (Plafker, 1969). 

Regional uplift and regional and localized 

subsidence produced by the 1964 earthquake 

affected intertidal and near-intertidal sediments 

in south-central Alaska (Plafker and Rubin, 1967; 

Plafker, 1969; Ovenshine and others, 1976; 

Bartsch-Winkler and Schmoll, 1984a). Relative 

sea-level changes along the coast are recorded in 

sedimentary sequences at the affected sites (figs. 

1 and 2). Areas of accumulating organic 

sediments, particularly marsh areas that have 

undergone earthquake-induced subsidence and are 

preserved beneath subsequently deposited 

sediments, can be dated by the radiocarbon 

method and the age of the earthquake event thus 

determined (Plafker and Rubin, 1967; Plafker, 

1972; Ovenshine, 1976; Bartsch-Winkler and 

others, 1983; Bartsch-Winkler and Schmoll, 1984b; 

Atwater and Grant, 1986). 

In the Portage area at the head of Turnagain 

Arm (fig. 1), upper intertidal or freshwater 

marshlands subsided into the lower intertidal zone 

and were covered with deeper-water (tidal) 

sediment at the time of the 1964 earthquake 

(Ovenshine and others, 1976). The postearthquake 

intertidal deposit, the Placer River Silt of 

Ovenshine and others (1976), and the underlying 

unnamed 1964 marsh deposit were described. The 

subsidence-induced deposition at Portage, which 

totals as much as 2.5 m in thickness in some 

locations, has been subsequently monitored; the 

sedimentation rate has declined to nearly nil and 

the surrounding area has attained a state of 

equilibrium only 20 years after the earthquake 

92 

(Bartsch-Winkler and Garrow, 1982). That is, a 

new marsh and forest have become established in 

an area where marsh and forest were destroyed by 

subsidence into the intertidal zone at the time of 

the 1964 earthquake. 

Our data from Upper Cook Inlet support the 

suppositions of Plafker (1972) and of Ovenshine 

and others (1976) that older submerged marsh and 

forest layers would be found in intertidal zones of 

regions experiencing earthquakes. Such organic 

horizons beneath intertidal silt form depositional 

packages termed "earthquake couplets" by A. T. 

Ovenshine (U.S.G.S., written commun., 1976). 

When dated by radiocarbon methods, these 

couplets provide information on the late Holocene 

earthquake history of the region surrounding 

Anchorage. 

Seventeen sections have been measured in 

the intertidal zone of the Susitna Lowland, Knik 

Arm, and Turnagain Arm (figs. 1 and 2). Two 

sections in the Placer River Silt at Portage (sees. 

16, 17) have been described previously (Ovenshine 

and others, 1976), as have two sections (sees. 5,6) 

in convoluted and hummocky beds of the lower 

intertidal zone at Anchorage and within Knik Arm 

(Bartsch-Winkler and Schmoll, 1984b). Section 10 

was measured in a drainage channel constructed 

after the earthquake in June 1983, and the 

remaining 13 sections (sees. 1-4, 7-9, and 11-15) 

were measured in July 1986. 

The bases of most of the sections are at the 

lower-low tide level or at river level. Tops of the 

sections vary with the availability of exposure at 

each site, but most are within the upper intertidal 

zone. The elevations of the upper, middle, and 

lower intertidal zones vary throughout Upper Cook 

Inlet region; maximum tide range is about 11.4 m 

(35 ft) at the official tide station at Anchorage. 

Records from the unofficial tide station midway in 

Turnagain Arm near Hope indicate a larger mean 

tide range there than at Anchorage. The tide 

range at the mouth of the Little Susitna River is 

not documented. Because the tide range is large 

in this estuary, an effort was made to observe the 

deposits that had bases at tide level when the tide 

range was the greatest for the month (spring tide) 

and at lower-low tide; this enabled measurement 

during maximum exposure at the base of the 

sections. 

Sections 3 and sections 8-11, located within 

the upper intertidal zone, contain the most 

abundant organic material (fig. 2) because of their 

position near the continuous marsh zone. 

Conversely, sections 4-6, located within the lower 

intertidal zone, contain the largest proportion of 

inorganic silt and sand and are the only sections 

that contain shell debris. Sections 1-2, 7, 12-15, 

and 17 are located in a narrow zone in the middle 

of the intertidal region, here called the middle 

intertidal zone. Section 16 was measured within 

the Twentymile River channel, a major fluvial and 
estuarine channel that drains extensive glacial and 

estuarine areas of the Portage flats. With the 

exception of section 16, which contains a large 

amount of sediment carried by this river, the 

sections measured in the middle intertidal zone 

have the greatest number of distinct organic 

layers separated by intertidal silt deposits. 

The middle intertidal zone is the most useful 

region for locating earthquake-induced 

sedimentary couplets. This zone has numerous 

distinct peat and wood layers intercalated with 

silt, a deposit that results from the burial of marsh 

and forest by intertidal sediment after 

earthquake-induced subsidence (fig. 3). 

Earthquake events can be identified by dating 

radiocarbon samples collected from the top of the 

organic layers and correlating them with other 

such radiocarbon-dated layers in the Upper Cook 

Inlet region (table 1). By dating organic material 

from the base of organic layers and measuring 

their thickness, the rate of accretion of the marsh 

might also be determined. 

Lowland 

Kenai 

Kenai 

Mtns 

Table I.--Radiocarbon dates and laboratory 

numbers of samples collected from Upper Cook 

Inlet as of 1983 

Radiocarbon 

date 

(yr B.P.) 

180 ± 45 

350 ± 80 

635 ± 40 

1,000 ± 70 

1,480 ± 50 

1,595 ± 75 

1,825 ± 45 

1,840 ± 50 

2,350 ± 125 

3,040 ± 50 

3,205 ± 110 

3,270 .:!:. 90 

3,280 .:!:. 90 

Laboratory Section Reference 

No. No. 

USGS-332 17 Ovenshine and others (1976) 

I-12,027 5 Bartsch-Wi nk 1 er 

and Schmoll (1984b) 

USGS-1780 10 This paper 

USGS-1781 10 This paper 

USGS-1782 10 This paper 

I-11,767 5 Bartsch-Winkler 

and Schmoll (1984b) 

USGS-1570 Bartsch-Wi nk 1 er 

and Schmoll (1984b) 

USGS-1117 15 This paper 

I-12 ,008 6 Bartsch-Winkler 

and Schmoll (1984b) 

USGS-1573 Bartsch-Winkler 

and Schmoll (1984b) 

I-11,718 Bartsch-Winkler 

and Schmoll (1984b) 

I-11,717 Bartsch-Winkler 

and Schmoll (1984b) 

I-11,706 Bartsch-Winkler 

and Schmoll (1984b) 

EXPLANATION 

.9 

Measured section 

Glacier 

4 8 MILES I It • I 

S 10 KILOMETERS 

Chugach 

Mtns 

Figure 1.--Upper Cook Inlet showing locations of measured stratigraphic sections in intertidal deposits. 

93 
W COOK INLET- E 

KNIK ARM TURNAGAIN ARM 

M Ft Measured sections 

. • 180±45 

·~. 

6 20 

71' 25 

8 

·1~ 

1 Organic (peat) 

=- Organic-rich silt 

] Peat and wood 

Silt 

Gravel 

~ Log horizon 

~ Shell horizon 

3

•

270 ± .90 * Radiocarbon date 

r

* (yrs BP) 

:::::::::~ :: 1,280 ± 90 1 ,840 ±50, 

= auger sample 

(estimated 

interval 

shown) 

Figure 2.--Stratigraphic sections showing organic 

layers and lithologies, wood and shell horizons, and 

radiocarbon-dated samples at 17 sites in Upper 

Cook Inlet. The tide or stream level is indicated 

by wave symbol. Table 1 lists pertinent 

information on radiocarbon dates. 

Earthquake recurrence is more difficult to 

determine from sediment and organic layers 

deposited above or below the middle intertidal 

zone. In the upper intertidal zone, pre- and postearthquake organic layers commonly are deposited 

directly above each other without intervening 

intertidal silt layers (fig. 3.). Discrete log layers 

enclosed in peat are the most likely indicators of 

an earthquake in this zone, because subsidence of 

the coastal forest immediately following an 

earthquake would result in forest kill by saltwater 

incursion (as occurred in 1964 at Portage). In the 

lower intertidal zone, in contrast, the absence of 

in situ organic-rich layers complicates the 

analysis. In this zone, bedding discontinuities, 

94 

such as planar beds that truncate underlying 

contorted beds, are the best criteria for 

distinguishing earthquakes (Bartsch-Winkler and 

Schmoll, 1984b). Because such discontinuities 

might be caused by sedimentary processes other 

than those induced by earthquakes (see BartschWinkler and Schmoll, 1984b, p. 1246-1248), they 

cannot be used alone to date earthquake events in 

these areas. 

As indicated by the sedimentary sequences 

measured in our 17 sections from the intertidal 

zone of Upper Cook Inlet, the most reliable area 

for obtaining earthquake-caused sedimentary 

couplets from the Upper Cook Inlet intertidal zone 

is the narrow, middle intertidal region. The 11 

radiocarbon dates presently available from 4 of 

our 17 sections (table 1) suggest that earthquakerelated events may have occurred repeatedly 

throughout Cook Inlet during late Holocene time. 

This hypothesis is currently being tested by 

radiocarbon dating that is now in progress on over 

50 additional organic samples that we collected 

from our measured sections in 1986. 

REFERENCES CITED 

Atwater, B.F., and Grant, W.C., 1986, Holocene 

subduction earthquakes in coastal Washington 

(abs.): Eos (Transactions, American 

Geophysical Union), v. 67, no. 44, p. 906. 

Bartsch-Winkler, Susan and Garrow, H.C., 1982, 

Depositional system approaching maturity at 

Portage Flats, in Coonrad, W .L., ed., The 

United States Geological Survey in Alaska--

Accomplishments during 1980: U.S. 

Geological Survey Circular 844, p. 115-117. 

Bartsch-Winkler, Susan, Ovenshine, A.T., and 

Kachadoorian, Reuben, 1983, Holocene history 

of the estuarine area surrounding Portage, 

Alaska, as recorded in a 93-m core: Canadian 

Journal of Earth Science, v. 20, no. 5, 

p. 802-820. 

Bartsch-Winkler, Susan, and Schmoll, H.R., 

1984a, Guide to Late Pleistocene and 

Holocene deposits of Turnagain Arm, Alaska: 

Anchorage, Alaska Geological Society, 70 p., 

2 maps (Fieldtrip guide for the 80th 

Cordilleran Section Meeting, Geological 

Society of America). 

1984b, Bedding types in Holocene tidal channel 

sequences, Knik Arm, Upper Cook Inlet, 

Alaska: Journal of Sedimentary Petrology, 

v. 54, no. 4, p. 1239-1250. 

Kanamori, Hiroo, 1977, The energy release in 

great earthquakes: Journal of Geophysical 

Research, v. 82, p. 2981-2987. 

Ovenshine, A.T., Lawson, D.E., and Bartsch, S.R., 

1976, The Placer River Silt--Intertidal 

sedimentation caused by the Alaska 

earthquake of March 27, 1964: U.S. Geological 

Survey Journal of Research, v. 4, no. 2, MarApr 1976, p. 151-162. 
Lower Intertidal Zone Middle Intertidal Zone Upper Intertidal Zone 

Abundant contorted 

sediment and reworked 

wood and peat. May 

contain in-aitu sheila 

Outer marsh zone: sparse coastal foreat and Continuoua bog and discontinuoua forest 

discontinuous bog. Zone of most reliable record 

of earthquake recurrence in sediment 

I 

forest killed 

I 

I 

ephemeral drainage channel 

by saltwater incursion ........._ 

after most recent earthquake" 

I 

I 

past earthquake 

Figure 3.--Diagrammatic section showing characteristics of upper, middle, and lower intertidal zones and 

sedimentary features indicative of earthquake deformation. Model assumes a constant shoreline position 

not subject to progradation or regression. 

Plafker, George, 1969, Tectonics of the March 27, 

1964 Alaska earthquake, in The Alaska 

Earthquake, March 27, 1964: Regional effects: 

U.S. Geological Survey Professional Paper 

543-1, p. 11-17 4. 

Plafker, George, 1972, Alaskan earthquake of 

1964 and Chilean earthquake of 1960--

lmplications for arc tectonics: Journal of 

Geophysical Research, v. 77, no. 5, 

p. 901-925. 

Plafker, George, and Rubin, Meyer, 1967, Vertical 

tectonic displacements in south-central 

Alaska during and prior to the Great 1964 

95 

Earthquake: Journal of Geosciences, Osaka 

City University, v. 10, p. 53-66. 

Stephens, C.D., Fogleman, K.A., Lahr, J.C., and 

Page, R.A., 1986, Seismicity in southern 

Alaska, October 1984-September 1985; in 

Bartsch-Winkler, 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. 81-85. 

Reviewers: A.F. Espinosa and J.R. Riehle 
LATE TRIASSIC AND EARLY CRETACEOUS 

FOSSIL AGES FROM THE McHUGH COMPLEX, 

SOUTHERN ALASKA 

Steven W. Nelson, Charles D. Blome, 

and Susan M. Karl 

The McHugh Complex of southern Alaska 

was recognized and named by Clark (1972, 1973) 

and was considered to be of Late Jurassic and (or) 

Cretaceous age. Plafker and others (1976) 

included the McHugh Complex in the melange 

facies of the accretionary Chugach terrane. In 

general, the McHugh Complex is considered to be 

a melange of low-grade metamorphosed 

sedimentary and volcanic rocks that includes 

irregular sized blocks and clasts of chert, marble, 

plutonic, volcanic, and ultramafic rocks. Clark 

(1973) recognized two chaotically juxtaposed 

lithologic associations within the type locality --a 

metasedimentary association and a metavolcanic 

association. The metasedimentary association, 

which makes up most of the complex, includes 

weakly metamorphosed siltstone, graywacke, 

arkose, and conglomerate. The metavolcanic 

association includes blocks of mafic greenstone, 

ultramafic rocks, and marble associated with 

lenses and blocks of radiolarian chert in siliceous 

argillite, and argillite. The previously reported 

range of paleontologic ages for the McHugh 

Complex in the Anchorage area, summarized by 

Nelson and others (1986), was Pennsylvanian(?) to 

Early Cretaceous. Nelson and others (1986) 

reported new fossil ages of Late Mississippian 

through Early Pennsylvanian and Early Jurassic 

and suggested possible source terranes for rock 

units found in the melange. This report discusses 

new radiolarian fossil ages (Late Triassic and Early 

Cretaceous) determined by Blome from the type 

locality of the McHugh Complex. The Late 

Triassic radiolarians are the first reported from 

this area. The Early Cretaceous radiolarian faunas 

have a similar age range, but somewhat different 

fauna than that reported by Karl and others (1979). 

Two Early Cretaceous sites are located on 

the north side of the Seward Highway in sec. 15, T. 

11 N., R. 3 W., Anchorage A-8 quadrangle, 3.25 km 

and 3.4 km northwest of VABM Isle (fig. 1). The 

more southerly site (#1 on fig. 1) consists of redweathering ribbon chert in layers averaging 4 em 

in thickness. Radiolarians present include 

Archaeodictyomitra excellens (Tan Sin Hok), 

Miri(U3U3 baileyi Pessagno, Parvicingula citae 

Pessagno, Pseudodictyomitra carpatica (Loznyak), 

Pseudodictyomitra depressa Baumgartner, 

Sethocapsa cetia Foreman, and Thanarla conica 

(Aliev). These fauna are considered to be 

Berriasian to Hauterivian in age. This collection 

was made approximately 4 m south of a chert 

locality containing Early Jurassic radiolarians 

(Nelson and others, 1986). 

96 

The more northerly of the two Cretaceous 

sites (#2 on fig. 1) is along a 150-m-long road cut 

that is predominantly massive greenstone with 

subordinate dark-gray argillite and gray chert. 

Radiolarians present include Archaeodictyomitra 

apiara (Rust), Archaeodictyomitra excellens (Tan 

Sin Hok), Parvicingula citae Pessagno, 

Pseudodictyomitra sp. cf. carpatica (Loznyak), 

Sethocapsa sp., and Ri8tola cretacea 

Baumgartner. The age of the fauna is considered 

to be Berriasian to late Valanginian. 

The Triassic site (#3 on fig. 1) is located in 

sec. 23, T. 11 N., R. 3 W. of the Anchorage A-8 

quadrangle, 2.9 km northwest of VABM Isle. Here, 

gray chert occurs as centimeter-sized lenses or 

boudins in a sheared, black argillaceous matrix. 

Approximately 50 percent of the outcrop area is 

composed of the argillite with approximately 30 

percent gray chert lenses and 20 percent green 

metavolcanic (tuff?) in centimeter-scale layers. 

Radiolarians present include Betraccium(?) sp. cf. 

incohatum Blome, Canoptum sp aff. farawayense 

Blome, Canoptum sp., Pseudostylosphaera sp., and 

Triassocampe sp. The age of this fauna is 

considered to be late Carnian or early Norian. It 

is noteworthy that the Triassic chert occurs as 

thin layers alternating with tuff and argillite, 

whereas the younger cherts commonly occur as 

monolithologic blocks of ribbon chert associated 

with greenstone or as independent blocks in an 

argillite matrix. 

Triassic fossil ages from the McHugh 

Complex have not been reported previously from 

the type locality. Triassic fossil ages have, 

however, been recognized from some correlative 

units elsewhere in Alaska that also contain 

younger fossils (fig. 2). Units stratigraphically 

correlative, at least in part, with the McHugh 

Complex are the Kelp Bay Group in southeastern 

Alaska (Decker, 1980; Johnson and Karl, 1985), the 

61"02'30' 

'~t :chorage 18 km 

Potter 

~~ 

.,>. .,..~ 

~ "" . "'S'Q 

"'9',-: ~ 

1 KILOMETER 

149. 45'00' 

Figure 1.--Locality map for microfossil collections 

from the McHugh Complex. 
en 

::) 

0 

w 

0 

~ w 

a: 

0 

0 

Ci5 

en 

c( 

a: 

::) 

..., 

0 

Ci5 

~ a: 

~ 

z 

c( 

~ a: 

~ 

z 

z 

~ 

3 

i 

w 

... 

<C 

_, 

w 

_, 

Q 

i 

> _, 

a: 

<C 

w 

w 

... 

<C 

_, 

ALBIAN 

OXFORDIAN 

A ALEMAN 

HETTANGIAN 

LADINIAN 

DESMOINESIAN REFERENCES 

1. Thla report 

t---;:---"lluc~iOVw~----~---"l~~~--~ 2. Nelaon and other• (19881 I 3. Clark (1973) 

4. Karl and other• (1979) 

5. Winkler and others (1981) 

8. Connelly (1978) 

7. Johnson and Karl (1985) 

Figure 2.--Age range of fossils from the McHugh Complex and related units. 

97 
Seldovia Bay Complex on the Kenai Peninsula 

(Cowan and Boss, 1978), and the Uyak Complex 

(Connelly, 1978) on Kodiak Island. Winkler and 

others (1981) recognized three "belts" of fossil 

ages within the McHugh Complex in the Valdez 

quadrangle; a northern belt containing Late 

Triassic radiolarians only, a middle belt with 

Jurassic and Cretaceous radiolarians, and a 

southern belt with radiolarians as young as midCretaceous. On Kodiak Island, Connelly (1978) 

reported on a hydrozoan from the Uyak Complex 

that is similar to a Late Triassic (Norian) 

hydrozoan found on the Alaska Peninsula; he also 

reported radiolarian ages ranging from Late 

Jurassic into Early Cretaceous (fig. 2). In the 

Seldovia Bay Complex, as recognized by Cowan 

and Boss (1978), Triassic radiolarians were 

identified from a mappable unit of contorted chert 

and greenstone (G. Plafker, 1976, oral commun., in 

Cowan and Boss, 1978). Kelley (1985) however 

believed that the fault-bounded chert and 

greenstone belongs to the Kache mak terrane of 

Jones and others (1981) and that it is separate 

from the Chugach terrane. Kelley (1985) describes 

the McHugh Complex in this area as largely 

composed of an association of graywacke and 

altered volcaniclastic rocks, chert, and no 

metavolcanic association. 

The presence of Triassic fossils from the 

type locality of the McHugh Complex suggests 

that the protolith ages in the McHugh Complex 

span most of the Mesozoic and may represent 

diverse pelagic and hemipelagic environments, and 

that rock units that are elsewhere recognizable as 

separate map units have been structurally 

incorporated into the McHugh Complex in the type 

locality. 

The Early Cretaceous fauna reported herein 

increases the number of radiolarian species of this 

age identified from the McHugh Complex. MidCretaceous fossils from the Valdez quadrangle 

(Winkler and others, 1981) are the youngest yet 

reported and are probably representative of the 

age of accretion of the McHugh Complex (Plafker 

and others, 1985). Thus an accretionary age rather 

than a protolith age may be the most appropriate 

for the McHugh Complex. 

REFERENCES CITED 

Clark, S.H.B., 1972, Reconnaissance bedrock 

geologic map of the Chugach Mountains near 

Anchorage, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-350, 

1 sheet, scale 1:250,000. 

1973, The McHugh Complex of south-central 

--Alaska: U.S. Geological Survey Bulletin 1372-

D, p. D1-D11. 

Connelly, William, 1978, Uyak Complex, Kodiak 

Islands, Alaska -- A Cretaceous subduction 

complex: Geological Society of America 

Bulletin, v. 89, p. 755-769. 

98 

Cowan, D.S., and Boss, R.F., 1978, Tectonic 

framework of the southwestern Kenai 

Peninsula, Alaska: Geological Society of 

America Bulletin, v. 89, p. 155-158. 

Decker, John, 1980, Geology of a Cretaceous 

subduction complex, western Chichagof 

Island, southeastern Alaska: Stanford, Calif., 

Stanford University, Ph.D. thesis, 135 p. 

Johnson, B.R., and Karl, S.M., 1985, Geologic map 

of western Chichagof and Yakobi Islands, 

southeastern Alaska: U.S. Geological Survey 

Miscellaneous Investigations Series Map 1-

1506, 2 sheets, scale 1:250,000, 15 p. 

Jones, D.L., Silberling, N.J., Berg, H.C., and 

Plafker, George, 1981, Tectonostratigraphic 

terrane map of Alaska: U.S. Geological 

Survey Open-File Report 81-792, 2 sheets. 

Karl, Susan, Decker, John, and Jones, D.L., 1979, 

Early Cretaceous radiolarians from the 

McHugh Complex, south-central 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. B88-B90. 

Kelley, J.S., 1985, Geology of the southwestern tip 

of the Kenai Peninsula, in Sisson, A., ed., 

Guide to the geology of the Kenai Peninsula, 

Alaska: Anchorage, Alaska Geological 

Society Guidebook, p. 50-68. 

Nelson, S. W ., Blome, C.D., Harris, A. G., Reed, 

K.M., and Wilson, F.H., 1986, Late Paleozoic 

and Early Jurassic fossil ages from the 

McHugh Complex, Alaska, in Bartsch-Winkler, 

Susan, and Reed, K.M.,- eds., Geological 

Studies in Alaska by the U.S. Geological 

Survey during 1985: U.S. Geological Survey 

Circular 978, p. 60-63. 

Plafker, George, Jones, D.L., Hudson, Travis, and 

Berg, H.C., 1976, The Border Ranges fault 

system in the Saint Elias Mountains and the 

Alexander Archipelago, in Cobb, E.H., ed., 

The United States Geological Survey in 

Alaska--Accomplishments during 1975: U.S. 

Geological Survey Circular 7 3 3, p. 14-16. 

Plafker, George, Nokleberg, W.J., and Lull, J.S., 

1985, Summary of 1984 TACT geologic studies 

in the northern Chugach Mountains and 

southern Copper River Basin, in BartschWinkler, Susan, ed., The United States 

Geological Survey in Alaska--

Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 76-79. 

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 80-892A, 

2 sheets, scale 1:250,000. 

Reviewers: J.H. Dover and M.L. Miller 
EFFECTS OF WEATHERING ON 

PETROLEUM-SOURCE EVALUATION OF COALS 

FROM THE SUNTRANA FORMATION NEAR 

HEALY, ALASKA 

Richard G. Stanley 

Rock-Eva! pyrolysis is a rapid and effective 

laboratory method of evaluating the quality and 

thermal maturity of prospective petroleum source 

rocks (Peters, 1986). Since its introduction about 

10 years ago, the Rock-Eva! method has been 

widely accepted by petroleum geologists and 

applied to samples from both surface outcrops and 

wells. The procedure m1m1cs the natural 

hydrocarbon-generation processes which occur at 

much slower rates within the earth when 

sediments containing kerogen (organic matter) are 

buried progressively deeper and subjected to 

higher temperatures (Waples, 1985). In Rock-Eva! 

pyrolysis, pulverized samples of rock are gradually 

heated from 300 °C to 550 °C at 25 °C per minute 

in an oxygen-free atmosphere (Peters, 1986). 

Heating causes the release of water, carbon 

dioxide, and two batches of hydrocarbons from the 

rock. The first batch of hydrocarbons is released 

at about 300 °C and consists of volatile organic 

compounds, such as oil and gas, that are already 

present in the rock. A detector on the Rock-Eval 

apparatus measures the quantity of these first 

hydrocarbons (HC), called S1, in milligrams HC per 

gram of rock. As the temperature rises above 

350 °C, a second batch of hydrocarbons called S2 

(also measured in milligrams HC per gram of rock) 

is released. S2 represents the organic compounds 

generated by thermal degradation of the remaining 

kerogen in the rock, and is an important indicator 

of the remaining ability of the rock to generate oil 

and gas. The temperature at which S2 is at a 

maximum--generally about 400 °C to 500 °C--is 

known as Tmax and is an indicator of thermal 

maturity. A third quantity, called S3, is the 

amount of carbon dioxide (in milligrams per gram 

of rock) that is generated during pyrolysis, stored 

in a collector, and measured at the end of the 

procedure. S3 is thought to be related to the 

amount of oxygen in the kerogen. Other important 

Rock-Eval parameters include TOC, the total 

organic carbon in weight percent; HI, the hydrogen 

index, defined as the product of 100 times 

(S2/TOC); and OI, the oxygen index, defined as the 

product of 100 times (S3/TOC). 

As part of a project aimed at assessing the 

petroleum resources of interior Alaska, I am using 

the Rock-Eval technique to evaluate the 

petroleum source potential of Tertiary nonmarine 

coals and mudrocks that crop out in the central 

Alaska Range (fig. 1). These Tertiary nonmarine 

strata are believed to be similar in age and 

lithology to subsurface strata in the middle Tanana 

basin (fig. 1), a prospective petroleum province 

99 

(Miller and others, 1959; Hite and Nakayama, 

1980). Well samples from this frontier area are 

scarce, and identification of potential source rocks 

must therefore be based mainly on outcrop 

samples. In order to properly evaluate such 

surface samples, it is important to understand the 

effects of weathering on organic matter and on 

the results of Rock-Eva! pyrolysis. Published data 

on this subject are sparse, however. Studies by 

Clayton and Swetland (1978) and Leythaeuser 

(1973) used wet-chemical methods (not Rock-Eval 

pyrolysis) to show that surface weathering can 

result in a decrease in the amount of organic 

matter as well as changes in its composition. 

Peters (1986), in an otherwise thorough discussion 

of Rock-Eva! pyrolysis, noted that weathered 

samples commonly show depletion in S1 and S2 as 

well as elevated S3 and Tmax, but provided no 

data to support these conclusions. 

Ten samples of subbituminous coal from 

fresh excavations and weathered outcrops were 

collected from coal beds of the middle Miocene 

Suntrana Formation (Wahrhaftig and others, 1969) 

and studied using Rock-Eval pyrolysis and thermal 

alteration index (TAl). (Thermal alteration index 

is a method of using the color of pollen grains and 

other kerogen, as viewed through a microscope 

using transmitted light, to determine the thermal 

maturity of the rock.) The purposes of this 

investigation were (1) to evaluate the petroleum 

source potential of the coals and (2) to determine 

whether there are any systematic differences in 

Rock-Eva! results between coals collected from 

fresh excavations and stratigraphically equivalent 

coals collected from weathered outcrops. 

Six relatively fresh samples of coal were 

obtained from open-pit excavations in the "Poker 

Flats" area of the Usibelli coal mine near the town 

of Healy, in the Healy (D-4) quadrangle (fig. 1). 

Coal bed number 3 was sampled in an excavation 

about 17 days old, and coal bed number 4 was 

sampled in an excavation less than 24 hours old 

(Wendel Parker, Chief Engineer, Usibelli Coal 

Mine, Inc., oral commun., 1985). Four additional 

samples of coal were obtained from coal beds 3 

and 4 at weathered outcrops along strike and about 

800 m east of the Poker Flats excavations. All of 

the samples were transported from the field to the 

laboratory in sealed plastic bags to prevent 

contamination. Splits of the samples were 

analyzed using Rock-Eva! pyrolysis by T.A. Daws 

(U.S. Geological Survey, Denver, Colo.) and 

thermal alteration index (TAl) by Hideyo Haga 

(Micropaleo Consultants, Inc., San Diego, Calif.). 

The results (tables 1 and 2) allow some preliminary 

conclusions regarding the quantity, type, and 

thermal maturity of organic matter in the sampled 

coals, and also show some systematic differences 

between fresh and weathered samples. 

The quantity of organic matter in the 

samples is indicated by TOC, S1, and S2. The TOC 
Table 1.--Rock-Eval and thermal alteration index (TAl) data for samples of coal from the Suntrana Formation near Healy, Alaska 

[See fig. 1 for location of samples. See text for explanation of symbols in headings] 

Sample 

No. 

Coal 

bed 

No. 

TOG HI 

(wt. pet.) 

Sample 

or weight 

(mg) 

51 

(mg HC/ 

g rock) 

52 

(mg HC/ 

g rock) 

53 

(mg co 2 1 g rock) 51 

S1+S2 52/53 

Tmax 

<•c) TAl Interpretation* 

A. "Poker Flats" pit (fresh excavations), lat 63°54'09"N., long 148°55'54"W.: 

A1 

A2 

A3 

A4 

AS 

A6 

58. 1 2 

54.26 

55.28 

59.54 

62. 19 

62.52 

156 

167 

150 

141 

131 

. 141 

47 10.9 2.66 

48 1 2. 5 4.08 

55 7. 7 2.46 

54 8.9 2.13 

55 11.5 2. 1 7 

55 10.4 l. 92 

91.00 27.88 o. 03 3.26 

90.88 26.24 .04 3.46 

83.11 30.64 .03 2. 7 1 

84.49 32.35 .02 2.61 

82.08 34.78 .03 2.35 

88.46 34.61 .02 2.55 

392 

393 

400 

407 

399 

409 

2.0 

2.0-2.5 

2.0 

2.3? 

2.5-3.5 

2.5-3.5? 

GOP, IM 

GOP, IM 

GP, IM 

GP, IM 

GP, IM 

GP, IM 

B. "Poker Flats" area (weathered roadcut), lat 63° 54 '02"N., long 148°54'50"\ol,: 

B1 

B2 

57.98 

39. 11 

129 56 

185 107 

9.5 3.05 74.94 

10.5 2.85 72.38 

32.84 0.04 2.28 

41.90 .04 l. 7 2 

400 

400 

2.0-2.5 

2.0 

GP, IM 

GOP, IM 

c. "Poker Flats " area (weathered streamcut), lat 63°54'10'"N,, long 148°54'54''W,: 

C1 

C2 

58.48 126 85 8.3 

39.07 155 115 10.6 

2. 16 

l. 32 

74.21 

60.75 

50.12 

45.28 

0.03 1.48 408 2.0-2.3 

.02 1.34 420 2.0-2.3 

GP, IM 

GOP, IM 

*Abbreviations: GP, gas prone; GOP, gas and oil(?) prone; IM, thermally immature with respect to the oilgenerative zone. An interpretation of "GOP'" was assigned to any rock that showed Hl)150 or 52/53)3,0. 

50 100 

I I I 

KILOMETERS 

Figure 1.--Location map. Filled circle at "Poker 

Flats" pit gives general location of sample sites A, 

B, and C (table 1). Vertical ruling denotes 

subsurface "middle Tanana basin" as mapped by 

Miller and others (1959). 

of the sampled coals ranges from 39.07 percent to 

62.52 percent (table 1), indicating that these rocks 

have "very good" generative potential according to 

the classification of Peters (1986). The TOC 

values of samples from fresh excavations are 

generally but not consistently higher than those 

from weathered outcrops (table 2). Both fresh and 

weathered samples exhibit values of S1 greater 

than 1.3 and S2 greater than 60, indicating that all 

of the samples have "good" to "very good" 

generative potential according to the 

classification of Peters (1986). Values of S1 are 

about the same in fresh and weathered samples, 

100 

but S2 is consistently higher in the fresh coals and 

S3 higher in the weathered coals (table 2). 

The type of organic matter in the samples is 

shown on a modified van Krevelen diagram (fig. 2) 

and also is indica ted by the hydrogen index (HI), 

oxygen index (01), and the ratio S2/S3. A modified 

van Krevelen diagram (fig. 2) is a plot of HI 

against 01 that is used to compare sample results 

with four idealized types of kerogen. Type I and 

Type II kerogens are "oil prone", or capable of 

generating oil; Type III kerogens are "gas prone", 

or capable of generating gas but little or no oil; 

and Type IV kerogens are variously regarded as oil 

prone, gas prone, or inert (Smyth, 1983; Tissot and 

Welte, 1984; Peters, 1986). All of the sampled 

coals from the Suntrana Formation--both fresh and 

weathered--plot between kerogen types II and III 

but closer to type III on the van Krevelen diagram 

(fig. 2), suggesting that the coals are capable of 

generating gas and perhaps small amounts of oil. 

In addition, several of the samples exhibit HI 

greater than 150 or S2/S3 ratios greater than 3 

(table 1), also suggesting that these samples have 

gas and oil generative potential, according to the 

classification of Peters (1986). However, this 

interpretation should be viewed with caution 

because the Rock-Eval technique typically 

overestimates the oil generative potential of coals 

due to poorly understood analytical problems 

(Peters, 1986). 

The thermal maturity of organic matter in 

the samples is indicated by the Tmax (in °C) and 

thermal alteration index (TAl). Both fresh and 

weathered samples exhibit Tmax of 420 °C or less 

and TAl generally less than 2.5 (table 1). 

Comparison of these values with the maturation 
...... 

Q 

~ 

Table 2.--Summary and comparison of Rock-Eval and TAl results from fresh and weathered samples of coal 

beds in the Suntrana Formation near Healy, Alaska 

[See table 1 for complete data set] 

roc range 

mean 

HI range 

mean 

OI range 

mean 

S1 range 

mean 

S2 range 

mean 

S3 range 

mean 

S1/ range 

(S1+S2) mean 

S2/S3 range 

mean 

Tmax range 

(oC) mean 

TAl range 

Coal bed No. 3 

Fresh 

excavation 

(3 samples) 

59.54-62.52 

61.42 

131-141 

138 

54-55 

55 

1.92-2.17 

2.07 

82.08-88.46 

85.01 

32.35-34.78 

33.91 

0.02-0.03 

0.02 

2.35-2.61 

2.50 

399-409 

405 

2.3-2.5 

Weathered 

outcrop 

(2 samples) 

39.07-58.48 

48.78 

126-155 

141 

85-115 

100 

1.32-2.16 

1.74 

60.75-74.21 

67.48 

45.28-50.12 

47.70 

0.02-0.03 

0.03 

1.34-1.48 

1.41 

408-420 

414 

2.0-2.3 

Coal bed No. 4 

Fresh 

excavation 

(3 samples) 

54.26-58.12 

55.89 

150-167 

158 

47-55 

so 

2.46-4.08 

3.07 

83.11-91.00 

88.33 

26.24-30.64 

28.25 

0.03-0.04 

0.03 

2.71-3.46 

3.14 

392-400 

395 

2.0-2.5 

Weathered 

outcrop 

(2 samples) 

39.11-57.98 

48.55 

129-185 

157 

56-107 

82 

2.85-3.05 

2.95 

72.38-74.94 

73.66 

32.84-41.90 

37.37 

0.04-0.04 

0.04 

1.72-2.28 

2.00 

400-400 

400 

2.0-2.5 

Differences: 

fresh vs. weathered 

Fresh generally higher 

No consistent difference 

Weathered consistently higher 

No consistent difference 

Fresh consistently higher 

Weathered consistently higher 

No consistent difference 

Fresh consistently higher 

Weathered generally higher 

No consistent difference 
,......., 

I 

"""' 

>< 

Q) 

"'0 

c 

c 

Q) 

0> 

0 

~ 

"'0 

~ 

I 

600 

450 

300 

150 

EXPLANATION 

Suntrana Formation 

0 Coal bed no. 4 (weath.) 

0 Coal bed no. 4 (fresh) 

• Coal bed no. 3 (weath.) 

• Coal bed no. 3 (fresh) 

..,.Type II 

0 

• Type Ill 

r 

0

o 50 100 150 

Oxygen Index (01) 

Figure 2.--Modified van Krevelen diagram (Peters, 

1986) showing idealized kerogen types (solid lines) 

and results from weathered and fresh samples of 

coal from the Suntrana Formation near Healy, 

Alaska. Type I and Type II kerogens are oil prone; 

Type III kerogens are gas prone; Type IV kerogens 

are variously regarded as oil prone, gas prone, or 

inert (Smyth, 1983; Tissot and Welte, 1984; Peters, 

1986). 

range chart (fig. 3) indicates that all of the 

samples are immature to marginally mature with 

respect to the oil-generative zone. The 

anomalously high values of TAl (up to 3.5) in 

samples A5 and A6 (table 1) may be due to 

contaminants or to the presence of oxidized or 

recycled organic material that was incorporated 

into the coals at the time of deposition. Values of 

Tmax are generally but not consistently higher in 

the weathered samples, while values of TAl are 

about the same in both fresh and weathered 

samples. 

In summary, the data presented above 

indicate that coals in the Suntrana Formation near 

Healy are potential sources of gas and perhaps oil, 

but are thermally immature. Similar coals may 

occur in the subsurface in the middle Tanana basin 

(Miller and others, 1959); if so, and if the 

subsurface coals have been buried deeply enough 

to reach an appropriate level of thermal maturity, 

they may have generated commercial quantities of 

gas and oil. Accumulations of gas derived from 

coal are commercially produced in northwestern 

Europe, Russia, Alabama, New Mexico, and 

Colorado (Meissner, 1984; Rightmire, 1984; Tissot 

102 

and Welte, 1984). Crude oils associated with coals 

and perhaps derived from them occur in Germany, 

France, the United Kingdom, Indonesia, Australia, 

and Venezuela (Tissot and Welte, 1984; Waples, 

1985). 

Compared to the fresh samples, weathered 

coals from the Suntrana Formation exhibit lower 

values of TOC, S2, and S2/S3 and higher values of 

01, S3, and Tmax. Apparently, there are no 

systematic differences between fresh and 

weathered coals in HI, S1, and TAl. Taken as a 

whole, the Rock-Eval results indicate gas and oil 

generative potential for both fresh and weathered 

samples, but slightly less favorable oil generative 

potential for the weathered samples. 

The differences in Rock-Eval results 

between fresh and weathered samples most likely 

are due to oxidation of organic matter during 

surface weathering, but this interpretation is 

based on only 10 samples. The lower TOC of the 

weathered samples may reflect lower initial 

amounts of organic matter rather than the results 

of weathering. Another problem is that the 

sample weights (7. 7 to 12.5 mg) are much less than 

the 75 mg minimum recommended by Peters 

(1986). Such low sample weights are required 

because larger amounts of coal would saturate and 

overload the Rock-Eval apparatus. Nevertheless, 

the results of this study suggest that weathering 

can affect the results of Rock-Eval pyrolysis in 

systematic ways that lead to less favorable 

estimates of oil-generative potential. Further 

Coal Rank 

PEAT 

LIGNITE & 

SUB· 

BITUMINOUS 

BITUMINOUS 

Rock-Eval 

Tmax (°C) 

Vitrinite 

Reflectance 

(%Ro) 

Thermal 

Alteration 

Index 

(TAl) 

IMMATURE 

430-445-+- 0.5-0. 7--+--- 2.0-2. 7-

OIL-GENERATIVE ZONE 

(OIL WINDOW) 

-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-

SEMI· 

ANTHRACITE POST-MATURE 

& (DRY-GAS GENERATIVE ZONE) ANTHRACITE 1 1 1-------t------t--1 -4.0 I 4.0-

META· 

ANTHRACITE 

LOW-GRADE METAMORPHIC 

(BARREN) 

I I 

Figure 3.--0rganic geochemical parameters and 

levels of thermal maturation, compiled from Hunt 

(1979), Tissot and Welte {1984), Graham and 

Williams (1985), Waples (1985), Peters (1986), and 

Bayliss and Magoon (1987). 
research is needed to test this hypothesis on other 

rock types, to identify the specific geochemical 

processes involved, and to explain why weathering 

causes changes in some Rock-Eval parameters 

(TOC, 01, S2, S3, Tmax) but not others (HI, S1). 

REFERENCES CITED 

Bayliss, G.S., and Magoon, L.B., in press, Organic 

facies and thermal maturity in the National 

Petroleum Reserve in Alaska: 

Intercalibration of visual kerogen assessment, 

vitrinite reflectance, and c 1-to-C4 hydrocarbons, in Gryc, George, ed., Geology 

of the National Petroleum Reserve in 

Alaska: U.S. Geological Survey Professional 

Paper 1399. 

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. 

Graham, S.A., and Williams, L.A., 1985, Tectonic, 

depositional, and diagenetic history of 

Monterey Formation (Miocene), central San 

Joaquin Valley, California: American 

Association of Petroleum Geologists Bulletin, 

v. 69, no. 3, p. 385-411. 

Hite, D.M., and Nakayama, E.N., 1980, Present 

and potential petroleum basins of Alaska, in 

Landwehr, M.L., ed., Exploration and 

economics of the petroleum industry: New 

ideas, new methods, new developments: 

Dallas, Institute on Petroleum Exploration and 

Economics, p. 511-5 54. 

Hunt, J.M., 1979, Petroleum geochemistry and 

geology: San Francisco, W.H. Freeman, 617 p. 

Leythaeuser, Detlev, 1973, Efects of weathering 

on organic matter in shales: Geochimica et 

Cosmochimica Acta, v. 37, no. 1, p. 113-120. 

103 

Meissner, F.F., 1984, Cretaceous and lower 

Tertiary coals as sources for gas 

accumulations in the Rocky Mountain area, in 

Woodward, Jane, Meissner, F.F., and Clayton, 

J .L., eds., Hydrocarbon source rocks of the 

greater Rocky Mountain region: Denver, 

Rocky Mountain Association of Geologists, 

p. 401-431. 

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. 

Rightmire, C.T., 1984, Coalbed methane resource, 

in Rightmire, C.T., Eddy, G.E., and Kirr, J.N., 

eds., Coalbed methane resources of the 

United States: American Association of 

Petroleum Geologists Studies in Geology 17, 

p. 1-13. 

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. 

Tissot, B.P., and Welte, D.H., 1984, Petroleum 

formation and occurrence (2nd ed.): Berlin, 

Springer-Verlag, 699 p. 

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: L. B. Magoon, K.E. Peters, 

and Clyde Wahrhaftig 
THERMAL MATURITY AND PETROLEUMSOURCE POTENTIAL OF THE 

CANTWELL FORMATION (PALEOCENE), 

ALASKA RANGE 

Richard G. Stanley 

The Paleocene Cantwell Formation is a 

highly deformed sequence of nonmarine 

sedimentary and volcanic rocks that is widely 

distributed in the central Alaska Range and is 

more than 3,000 m thick in places (Wolfe and 

Wahrhaftig, 1970). Mudstone and coal beds in the 

Cantwell Formation were deposited in a variety of 

lacustrine, fluvial overbank, and swamp 

environments and are of interest as potential 

source rocks of petroleum. Thirty-eight samples 

of mudstone and bituminous coal were collected 

from 10 outcrops of the Cantwell Formation and 

analyzed using Rock-Eval pyrolysis (see preceding 

article by Stanley, this volume), vitrinite 

reflectance, and thermal alteration index. The 

results suggest that these rocks are potential 

sources of gas and minor amounts of oil. 

Rock samples were collected from outcrops 

along ridge tops and from cuts along streams, 

highways, and the Alaska Railroad (fig. 1). The 

rock samples were excavated from depths of 10-30 

em below the outcrop surfaces and transported to 

the laboratory in sealed plastic bags. Splits of the 

samples were analyzed using Rock-Eval pyrolysis 

by T.A. Daws (U.S. Geological Survey, Denver, 

Colo.), thermal alteration index by Hideyo Raga 

(Micropaleo Consultants, Inc., San Diego, Calif.), 

and vitrinite reflectance by M.J. Pawlewicz (U.S. 

Geological Survey, Denver, Colo.). The basic 

principles and terminology of Rock-Eval pyrolysis 

and thermal alteration index are briefly discussed 

in the preceding article in this volume. Vitrinite 

reflectance is a method of determining the 

thermal maturity of a rock by measuring the 

ability of vitrinite, a type of kerogen formed from 

terrestrial plant material, to reflect incident light 

(Tissot and Welte, 1984; Waples, 1985). 

The samples were collected from widely 

scattered geographic locations (fig. 1 and table 

1). The relative stratigraphic positions of the 

samples within the Cantwell Formation are 

uncertain. Little is known about the internal 

stratigraphy of the Cantwell except that volcanic 

rocks are more abundant near the top of the 

formation (Wolfe and Wahrhaftig, 1970). 

Stratigraphic correlations within the Cantwell 

Formation are hampered by the lack of 

paleontologic and biostratigraphic control, rapid 

lateral changes in facies and thickness, wide areas 

of cover between outcrops, and complicated 

structure that includes numerous faults, igneous 

intrusions, and tight folds that in places are 

overturned. 

104 

The results of the sample analyses (table 1) 

allow some preliminary conclusions regarding the 

quantity, type, and thermal maturity of organic 

matter in the mudstone and coal beds of the 

Cantwell Formation. 

The quantity of organic matter in the 

samples is indicated by the TOC (total organic 

carbon in weight percent) and the quantities S1 

and S2. All but one of the 38 samples have TOC 

greater than 0.5 percent, which generally is 

regarded as the lower limit for potential source 

rocks of petroleum (Tissot and Welte, 1984). 

Twenty-nine of the samples have TOC greater 

than 1.0 percent, and therefore have good to very 

good generative potential, according to the 

classification of Peters (1986). However, the 

values of S1 and S2 generally are less than 0.5 and 

2.5, respectively, suggesting poor generative 

potential (Peters, 1986). The reasons for this 

depletion in S1 and S2 are unknown, but may be 

related to (1) surface weathering of the sampled 

outcrops and (2) initially poor generative potential 

due to a high proportion of humic (woody) and 

inertinitic (oxidized) kerogens. Many but not all of 

the Cantwell samples contain visible remains of 

terrestrial plants, including woody stems and 

leaves; however, no detailed optical studies of 

kerogen morphology have been done. 

The type of organic matter in the Cantwell 

samples is indicated by the hydrogen index (HI), 

oxygen index (01), and the ratio S2/S3. Most of 

the samples exhibit HI less than 150 and S2/S3 less 

than 3; comparison of these values with table 2 of 

Peters (1986) indicates that most of the Cantwell 

samples are "gas prone", or capable of generating 

gas but little or no oil. A few of the samples, 

including some coals, exhibit HI as great as 169 or 

S2/S3 as great as 18.64 and therefore may be 

capable of generating oil in addition to gas. 

However, this interpretation should be viewed with 

caution because coals may yield spuriously large 

HI and S2/S3 values due to poorly understood 

analytical problems that cause the Rock-Eval 

method to overestimate the liquid hydrocarbon 

potential of coaly rocks (Peters, 1986). 

Plots of HI against OI on a modified van 

Krevelen diagram (fig. 2) indicate that kerogens in 

the Cantwell samples are mainly types III and IV. 

Kerogens of type III are inferred to be gas prone 

(Tissot and Welte, 1984; Peters, 1986), but the 

source potential of type IV kerogens is 

controversial. Smyth (1983) argued that type IV 

kerogens (also known as "inertinites") can be 

sources of both oil and gas, while Peters (1986) 

believed that type IV kerogens have little or no 

source potential. 

The thermal maturity of organic matter in 

the Cantwell samples is indicated by the Tmax of 

Rock-Eval pyrolysis (in °C), vitrinite reflectance 

(percent Ro), and thermal alteration index (TAl). 
Table 1-- Rock-Eval, vitrinite reflectance (Ro), and thermal alteration index (TAl) data from the Cantwell 

Formation 

[Rock-Eval parameters (TOC, HI, 01, etc.) are discussed in the preceding article in this volume. See fig. 1 

for sample locations] 

53 

Sample Rock TOC HI 

Sample 

or weight 

(mg) 

Sl 

(mg HC/ 

g rock) 

52 

(mg HC/ 

g rock) 

(mg co 2 ; • Sl S2/S3 Tmax Median TAl Interpretation* 

No. type (wt. pet) g rock) 51+52 ("C) Ro (%) 

AI 

A2 

A3 

Bl 

B2 

B3 

c I 

C2 

01 

02 

03 

04 

05 

06 

El 

E2 

E3 

E4 

Fl 

F2 

F3 

F4 

F5 

F6 

F7 

Gl 

G2 

G3 

G4 

HI 

J I 

Kl 

K2 

K3 

K4 

K5 

K6 

K7 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

coal 

mdst 

1. 2 6 

2. 3 7 

1. 4 2 

1. 3 2 

1.19 

1. 19 

0.56 

0.46 

3.09 

6.02 

6.05 

9.68 

33.07 

3.62 

coal 26.77 

mdst 1.90 

mdst 14.17 

mdst 2.40 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

3.52 

0.99 

1. 69 

1. 7 4 

3. 7 3 

1. 3 2 

3. 3 7 

mdst 3.76 

mdst 1.28 

coal 50.18 

mdst 1.21 

coal 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

mdst 

5. II 

0. 5 I 

8.65 

0.99 

0.88 

3.86 

0. 77 

0.63 

0.58 

22 

28 

18 

12 

13 

10 

A. Boundary Creek area (ridge top), lat 63"29'29" N., long 150"19'20" W.: 

68 125.0 

22 139.6 

45 120.6 

B. Stony Creek 

44 161.4 

36 136.2 

29 156.2 

0.03 

.OS 

.03 

0.0 

• 0 

. 0 

0.28 

.68 

.26 

0.86 

• 53 

.64 

0. I 0 

.07 

.11 

0.32 

1. 28 

.40 

514 

488 

509 

1.18 

.89 

• 9 8 

Barren 

Barren 

2. 3? 

(ridge top), lat 63"30'20" N., long 150"17'12" W.: 

0. I 7 

• 16 

• I 2 

0.59 

.4 4 

• 3 5 

0.0 

• 0 

.o 

0.28 

.36 

.34 

1.41 2.5-2.8? 

1.20 No data 

1.13 No data 

C. East Fork Toklat River (stream cut), lat 63"35'06" N., long 149"52'12" W.: 

33 175.3 

43 198.8 

0.0 

.o 0.0 

.o 1 

0. 19 

.20 

0.0 

.o 0.0 .OS 

2.89 

Barren 

3.8 

3.8 

0. East Fork Toklat River (stream cut), lat 63"35'06" N., long 149"52'12" W.: 

55 

73 

56 

68 

169 

31 

67 

45 

37 

35 

5 

9 

1 7 

51.4 

41.4 

2 6 .o 17.5 

12.3 

36.9 

0.36 

.43 

• 61 

.80 

2.84 

.10 

1. 7 I 

4.44 

3.42 

6.62 

55.93 

1. 1 3 

0.29 

• 3 6 

.46 

• 57 

3.00 

.62 

0.17 

.09 

.1 5 

.11 

.OS 

.08 

5.89 

12. 3 3 

7.43 

II. 6 I 

18.64 

1. 8 2 

463 

473 

474 

477 

470 

497 

1.00 

.98 

1.13 

1.18 

1. 21 

1.19 

2.5-2.8 

2.5? 

2.5 

2.5 

2.5-3.0 

2.5 

E. Polychrome Pass area (road cuts), lat 63"31'36" N., long 149"54'00" W.: 

28 13.9 

60 242.5 

51 10. 7 

67 77.9 

0. 2 1 

.02 

• 0 

• 0 2 

18. 12 

.86 

5.32 

.84 

7.62 

1.15 

7.28 

1. 61 

0.01 

.02 

.o 

.02 

2.37 

• 7 4 

• 7 3 

.52 

451 

437 

448 

449 

0.71 2.8-3.0? 

• 71 3. 0? 

.74 3.0? 

.69 3.0? 

F. Cathedral Mountain area (stream cut), lat 63"35'02" N., long 149"36'06" W.: 

2 

6 

24 

27 

43 

28 

38 

16 75.7 

19 108.1 

31 104. 5 

43 88.4 

30 94.2 

48 131.0 

23 82.4 

0.01 

.01 

.02 

.02 

.05 

.01 

• 15 

0.09 

.06 

.42 

• 48 

1.61 

.38 

1. 31 

0.58 

• 19 

.54 

.76 

1.14 

.64 

.80 

0.10 

• 1 7 

.05 

.04 

.03 

• 0 3 

.10 

0.15 

.31 

.77 

.63 

1.41 

.59 

1.63 

495 

457 

449 

455 

461 

3.23 

2.0 

1. 34 

I. 14 

1.07 

.84 

1.13 

3. 7 

3.0 

2.5? 

2.5-3.0 

2.5-3.0 

2.5 

3.0? 

G. McKinley Village (railroad cut), lat 63"39'12" N., long 148"50'24" W.: 

77 40 71.7 

55 78 75.4 

80 17 10.0 

3l 129 164.7 

0.06 

• 0 3 

.1 0 

.o 

2.92 

• 7 I 

40.40 

• 3 8 

1. 53 

1. 00 

8.80 

1. 57 

0.02 

.04 

• 0 

.o 

1. 90 

• 7 I 

4.59 

.24 

443 

442 

466 

442 

0.66 2.5-2.8 

.63 2.5-2.8 

.94 2.5-3.0 

.70 2.5-3.0 

H. Yanert coal mine (tailings pile), lat 63"38'40" N., long 148"50'32" W.: 

!!7 II 36.4 0.24 4.45 0.60 0.05 7. 4 1 452 0.93 2.5-3.0 

J. Carlo area (ridge top), lat 63"32'00" N., long 148"45'12" W.: 

0 

0 

0 

0 

0 

41 18 7. 5 o.o 0.01 0. 2 I 0.0 0.04 3. 6 5 

K. Carlo area (ridge top), lat 63"30'27" N., long 148"44'57" W.: 

54 

30 

26 

19 

3 I 

30 

29 

23.6 

75.0 

122.8 

33.6 

7 2. I 

184.4 

154.8 

o.o 

.o 

.o 

• 0 

.o 

• 0 

• 0 

0.04 

.o 

.o 

.o 

.0 

.0 

.o 

4.74 

.30 

• 2 3 

• 77 

.24 

. 19 

.17 

0.0 

• 0 

• 0 

• 0 

.0 

.0 

.o 

0.0 

.o 

.o 

.o 

.o 

• 0 

• 0 

2. 9 3 

2.01 

1. 3 7 

2.74 

1. 48 

4.28 

1. 9 9 

3.5 

3.5 

3.8 

3.5-3.8 

3.5-3.8 

3.5~3.8 

3.8 

3.8 

GP I oz GP, OZ 

GP, OZ 

GP, GZ 

GP, OZ 

GP, OZ 

PM 

PM 

GOP, OZ 

GOP, OZ 

GOP, OZ 

GOP, OZ 

GOP, OZ 

GP, OZ 

GP, OZ 

GP, OZ 

GP, OZ 

GP, OZ 

PM 

PM? 

GP I GZ 

GP, OZ 

GP, OZ 

GP, OZ 

GP I oz 

GP; OZ 

GP, OZ 

GOP, OZ 

GOP, OZ 

GOP I oz 

PH 

PM 

PM 

PM? 

PM 

PM? 

PM? 

PM 

*Abbreviations: GP, gas prone; GOP, gas and oil(?) prone; OZ, oil-generative zone ("oil window"); GZ, wet-gas 

generative zone; PM, post-mature (dry-gas generative zone). An interpretation of "GOP" was assigned to any rock that 

showed HI>l50 or 52/53>3.0. Tmax values for samples with 52(0.2 were rejected because they are probably unreliable 

(Peters, 1986). 

105 
150°00' 

0 5 10 

&Cantwell 

• 

EXPLANATION 

Cantwell Formation (Paleocene) 

Volcanic rocks A• sample locality 

A settlement Sedimentary rocks 

Figure 1.--Sample localities in the Cantwell Formation. Outcrop area generalized from Wolfe and 

Wahrhaftig (1970) and Jones and others (1983). Major rivers (from west to east): TKR, Toklat River; EFTR, 

East Fork Toklat River; TLR, Teklanika River; SCR, Sanctuary River; SVR, Savage River; NR, Nenana 

River. 

Comparison of the Cantwell data (table 1) with the 

maturation range chart (fig. 3) shows that the 

coals are bituminous and that the thermal 

maturity of the mudstones ranges from mature to 

post-mature with respect to the oil and wet-gas 

generative zones. The reasons for this wide range 

in thermal maturity are unclear but may be 

related to variations in burial depth as well as to 

local heating near igneous intrusions and faults. 

Another problem is that several of the samples 

exhibit values of Tmax that are too high compared 

to Ro and TAl values from the same sample, 

possibly as a result of oxidation during outcrop 

weathering (see preceding article by Stanley, this 

volume). However, Peters (1986) noted that 

unusually high Tmax can also reflect the presence 

of highly mature, recycled, or type IV kerogens as 

well as interference from the clay mineral matrix. 

In conclusion, limited data indicate that 

some but not all nonmarine mudstones and coals in 

the Paleocene Cantwell Formation are potential 

106 

sources of gas and minor amounts of oil. These 

results are encouraging, but little can be said 

about the overall petroleum resource potential of 

the Cantwell Formation until more is known about 

potential reservoirs, trapping · conditions, and 

general structure and stratigraphy. Given the 

tight folds, abundant faults, igneous intrusions, and 

rapid lateral facies changes that are evident in 

outcrop, it seems likely that petroleum 

accumulations in the Cantwell Formation--if any 

exist--will be small and difficult to find. 

However, the presence of potential petroleum 

source rocks in the Cantwell suggests that other 

Tertiary nonmarine formations in central Alaska 

also may include potential petroleum sources. 

Speculatively, Tertiary nonmarine source rocks 

similar to those in the Cantwell Formation may 

occur in the subsurface in sedimentary basins such 

as the middle Tanana and Yukon Flats basins 

(shown by Miller and others, 1959) and may have 

generated hydrocarbons in commercial quantities. 
450 EXPLANATION 

" I 

"--' Cantwell 

X Formation 

Q) 300 

"'0 coal 

c • """"Type II 

• mudstone c 

Q) 

0> 150 0 

'-

"'0 

>a 

I 

0 

0 50 100 150 

Oxygen Index (01) 

Figure 2.--Modified van Krevelen diagram (Peters, 

1986) showing idealized kerogen types (solid lines) 

and analytic results from the Cantwell 

Formation. Type I and Type II kerogens are oil 

prone; Type III kerogens are gas prone; Type IV 

kerogens !ire variously regarded as gas prone, oil 

prone, or mert (Smyth, 1983; Peters, 1986). 

REFERENCES CITED 

Bayliss, G.S., and Magoon, L.B., in press, Organic 

facies and thermal maturity in the National 

Petroleum Reserve in Alaska: 

Intercalibration of visual kerogen assessment, 

vitrinite reflectance, and C -to-e 4 hydrocarbons, in Gryc, George, ed., Geology 

of the National Petroleum Reserve in 

Alaska: U.S. Geological Survey Professional 

Paper 1399. 

Graham, S.A., and Williams, L.A., 1985, Tectonic, 

depositional, and diagenetic history of 

Monterey Formation (Miocene), central San 

Joaquin basin, California: American 

Association of Petroleum Geologists Bulletin, 

v. 69, no. 3, p. 385-411. 

Hunt, J.M., 1979, Petroleum geochemistry and 

geology: San Francisco, W. H. Free man, 617 p. 

Jones, D.L., Silberling, N.J., Gilbert, W.G., and 

Coney, P.J., 1983, Interpretive bedrock 

geologic map of the Mt. McKinley region: U.S. 

Geological Survey Open-File Report 83-11, 

2 sheets, scale 1:250,000. 

107 

Vitrinite Thermal 

Rock-Eval Alteration Coal Rank Reflectance Tmax (°C) (%Ro) Index 

(TAl) 

PEAT 

LIGNITE & IMMATURE SUB430-445 + 0.5-0.7 + 2.0-2.7-

BITUMINOUS 

OIL-GENERATIVE ZONE 

(OIL WINDOW) 

BITUMINOUS f.- 465-475 --t- 1.2-1.4 ---t- 2.9-3.5-

WET -GAS GENERATIVE ZONE 

495-500 + 1.9-2.0 + 3.3-3.8-

SEMIANTHRACITE POST-MATURE 

& (DRY-GAS GENERATIVE ZONE) ANTHRACITE I I 1 4.0 1 4.0-

META- LOW-GRADE METAMORPHIC 

ANTHRACITE (BARREN) 

I I 

Figure 3.--0rganic geochemical parameters and 

levels of thermal maturation, compiled from Hunt 

(1979), Tissot and Welte (1984), Graham and 

Williams (1985), Waples (1985), Peters (1986), and 

Bayliss and Magoon (1987). 

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. 

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. 

Tissot, B.P., and Welte, D.H., 1984, Petroleum 

formation and occurrence (2nd ed.): Berlin, 

Springer-Verlag, 699 p. 

Waples, D.W., 1985, Geochemistry in petroleum 

exploration: Boston, International Human 

Resources Development Corporation, 232 p. 

Wolfe, J.A., and Wahrhaftig, Clyde, 1970, The 

Cantwell Formation of the central Alaska 

Range: U.S. Geological Survey Bulletin 1294-

A, p. A41-A46. 

Reviewers: K. J. Bird, L. B. Magoon, 

and K.E. Peters 
AN APPLICATION OF OBLIQUE ROTATION 

R-MODE FACTOR ANALYSIS IN THE 

MOUNT HAYES QUADRANGLE, ALASKA 

(ABSTRACT) 

J.D. Hoffman 

As part of the Alaska Mineral Resource 

Assessment Program (AMRAP), a reconnaissance 

geochemical sampling program was conducted to 

aid in the evaluation of known mineral resources 

and the exploration for potential mineral resources 

in the Mount Hayes quadrangle, eastern Alaska 

Range. An extreme variable, oblique rotation Rmode factor analysis procedure was used to reduce 

the analytical data from the sampling program in 

an attempt to define and locate geochemical 

signatures that may represent mineralization. 

Factor analysis can discern subtle relationships 

among data that may not be readily apparent. As 

exploration geochemical data may be 

intercorrelated, the oblique rotation was used to 

allow for these possible intercorrelations in the 

data. The oblique rotation, as with other 

rotations, also has the advantage of maximizing 

factor loadings. The program used 19 elemental 

analyses of 1,343 rock outcrop samples, provided 

by semiquantitative emission spectrography and 

atomic absorption spectrophotometry. 

The ability of factor analysis to generate 

multielement associations, or factors, that 

distinguish mineralization signatures from 

lithologic signatures depends in part on the ratio 

of regional variance in the data to that of more 

108 

local variance. To push the factor analysis 

procedure toward describing mineralization 

signatures and not simply lithologic signatures, the 

data were grouped into five lithotectonic 

subterranes and terranes; the factor analysis 

procedure was then applied to these separate 

groups. The number of samples in each group was 

at least 105. 

The elemental associations as shown by 

factor loadings can be related to mineralization 

types in the quadrangle; some of the associations 

may be related to previously unreported 

mineralization. Plots of the factor scores agree 

well with the locations of known mineral 

occurrences and deposits. For example, in the 

Maclaren terrane, factor 4 (lead, zinc, and 

manganese) score plots may indicate vein-type· 

base-metal mineralization in the Maclaren 

metamorphic belt. The Maclaren belt rocks 

incorporate schist, amphibolite, argillite, and 

metagraywacke. As another example, in the Slana 

subterrane, factor 1 (chromium, nickel, cobalt, 

magnesium, and iron) score plots probably indicate 

known chromite occurrences in the Mesozoic 

Nikolai Greenstone. Lastly, in the Jarvis terrane, 

a terrane of metamorphosed plutonic and volcanic 

rocks, factor 3 (lead, zinc, and copper) score plots 

are related to known Kuroko-type massive sulfide 

deposits and occurrences. These three examples 

illustrate the capability of factor analysis to 

discern and locate geochemical signatures that 

may indicate mineralization. 

Reviewers: M. Allen and J.B. Cathrall 
SOUTHEASTERN ALASKA 

Fairweather Range, Glacier Bay National Monument. Photo by D.A. Brew. 

109 
STRUCTURAL FABRIC ANALYSIS OF 

THE PERSEVERANCE SLATE 

AND GOLD-BEARING QUARTZ VEINS 

IN THE SOUTH ORE BODY 

OF THE ALASKA-JUNEAU LODE SYSTEM, 

SOUTHEASTERN ALASKA 

Christopher C. Barton and Thomas D. Light 

The Juneau gold belt extends for almost 200 

km along the western flank of the Coast Mountains 

in southeastern Alaska. The Alaska-Juneau lode 

system is located near the center of the gold belt 

in the vicinity of the city of Juneau (fig. 1). The 

deposit has produced 3.5x106 oz (110,000 kg) of 

gold (Berg, 1984), ranking it as the largest lode 

gold deposit in the state. We report here on the 

structural fabric analysis of the host rock and gold 

veins in order to place vein formation into the 

context of the tectonic history. Our work has 

been confined to the southwestern half of the 

open-pit mine in the south ore body of the AlaskaJuneau lode system (fig. 1) in the Silverbow Basin, 

4.5 km east of Juneau. The pit is divided into 

northeastern and southwestern halves by a 

northwest-southeast-striking ridge of unmined 

rock. The southwestern half is ovoid in plan and 

measures 250 m long, 125 m wide, and 125 m deep; 

the long axis strikes N. 60° W. The pit walls are 

subvertical and provide good cross-sectional 

exposures of the host-rock and vein fabrics. The 

bottom of the pit was collapsed by block-cave 

mining from below and is composed of coarse rock 

debris which slopes away from the walls. 

The Perseverance Slate is the host rock for 

the gold-bearing quartz veins. It is a 1.5-km-wide 

belt of carbonaceous and graphitic quartz sericite 

phyllite, schist, and black slate with minor 

carbonaceous limestone and numerous sill-like 

lenses of amphibolite (Brew and Ford, 1984 a, b, 

c). Regionally, the slate strikes N. 50°-70° W., 

parallel to the regional structural trend (Brew and 

Ford, 1985). The protolithic age of the 

Perseverance Slate is now considered as late 

Triassic, based on ammonites and Halobeid 

pelecypods from within the unit; it was 

metamorphosed during latest Cretaceous and early 

Tertiary time (D. A. Brew, USGS, oral commun., 

1986). 

The Alaska-Juneau deposit is cut by the 

Silverbow normal fault, a few tens of meters north 

of the pit. The fault strikes nearly east-west, dips 

75° north, and has oblique normal offset. The 

north (hanging wall) side has moved down about 

550 m and about the same distance to the west 

(Wayland, 1939). 

In the southwestern half of the pit, the 

Perseverance Slate is silver-black carbonaceous 

phyllite. The strike of the compositional layering 

ranges from N. 55° W. to S. 85° E. The dip of 

layering changes smoothly from 80° NE at the 

southwest wall of the pit, flattens, and then over a 

distance of a few meters, bends to 87° SW at the 

wall dividing the pits. The layering describes an 

open asymmetric synform whose axis bears 

S. 81° E. and plunges 36° SE (fig. 2). Two 

penetrative cleavages are well developed 

throughout the Perseverance Slate in the pit. The 

first is parallel to the plane of the quartz veins 

(fig. 3); it dips vertically and strikes from N. 5° W. 

to N. 57° W., averaging N. 45° W. The second 

strikes from N. 46° W. toN. 60° W. and dips 57°-

760 NE. Neither cleavage appears to penetrate 

the gold-quartz veins. Neither cleavage is axial 

planar to or fans about the synclinal fold axis. 

Planar zones of intense shearing are also present. 

They range in width from a few centimeters to as 

much as 5 m. The rock in the zones contains shear 

planes spaced millimeters apart. The zones and 

EXPLANATION 

Rock units 

(After Brew and Ford, 19851 

~ Perseverance Slate 

I TKto I Tonolite sill 

C!R!J Undivided schist 

I KJss I Cretaceous -Jurassic 

turbidites 

Map symbols 

Mines 

1 Ebner 

2 Alaska-Juneau North Pit 

3 Alaska-Juneau South Pit 

4 Persev.-ance 

5 Treadwell 

6 700 Ft 

7 Mexican 

8 Ready Bullion 

Normal fault showing 

direction and amount of dip 

Figure I.--Generalized geologic map showing the 

location of major structural features and mines. 

110 
EXPLANATION 

Foliation (31 polntsl 

j3 -axis 

Figure 2.--Lower-hemisphere equal-area projection of poles to compositional layering. B-axis to 

great circle fit to poles is the bearing and plunge 

of the synform axis. 

the shear planes within them are in the same 

orientation as the second of the two penetrative 

cleavages. The sense of shear is up the dip line of 

the shear planes, as determined by the slickenlines 

and the offset of veins. 

Joints are not pervasive throughout the pit, 

but rather well-defined sets are developed only in 

small areas. Only one set of joints is present in 

each of the areas sampled. The joints are not 

spatially or genetically related to any other 

structural elements. The mean orientation for 

each of the four joint sets sampled are: 

(1) N. 30° E., 90° 

(2) N. 47° E., 82° SE 

(3) N. 25° W., 56° SW 

(4} N. 70° W., 65° NE 

The Perseverance Slate has been penetrated 

by a system of noncontiguous sulfide-bearing veins 

of the Alaska-Juneau system. The veins range in 

width from a few centimeters to as much as 1 m. 

The height-to-width ratios of those in the pit walls 

range from 1:1 to more than 50:1. The spacing 

between veins ranges from a few centimeters to a 

few meters. The veins are about 95 percent 

quartz with subsidiary ankerite, pyrrhotite, galena, 

sphalerite, arsenopyrite, pyrite, and gold 

Figure 3.--Photograph of near-vertical boudinaged 

gold-bearing quartz vein and, plane-parallel to it, 

penetrative cleavage in the pit wall. 

(Twenhofel, 1952). The gold is concentrated with 

sulfide minerals along the edges of some of the 

veins, in fractures in quartz, and in the ankerite 

which normally bounds the edges of the veins and 

separates the quartz from the country rock. 

111 

The strike of the veins in the pit ranges from 

N. 5° W. toN. 57° W. and averages N. 45° W. The 

veins are nearly vertical except within the shear 

zones, where they have been mechanically sheared 

and rotated partly or completely into the plane of 

shearing. We were not able to distinguish 

different generations of vemmg based on 

orientation or crosscutting relations. The veins 

are not spatially related to either the joints or 

compositional layering (fig. 4). The veins pinch 

and swell in both vertical and horizontal sections 

(fig. 3). We interpret this as "chocolate tablet 

structure" (Ramsey and Huber, 1983); a type of 

boudinage where the competent mass is extended 

in all directions, producing a complex of crossing 
s 

EXPLANATION 

Compositional layering (3 points) 

Vein ( 8 points) 

o Joint (4 points) 

Figure 4.--Lower-hemisphere equal-area projection of poles to foliation, veins, and joints at one 

of eight stations along the southeast pit wall. 

boudin necks. We infer at least one phase of 

boudinage development with the least principal 

stress in the plane of the veins. 

Our observations of structural overprinting 

indicate the following stages in the geologic 

history for the south ore body: (1) deposition of 

the protoliths of the Perseverance Slate, (2) 

accretion, metamorphism, and folding of the 

Perseverance, (3) emplacement of quartz veins, (4) 

boudinage of veins and development of cleavage 

parallel to them, (5) development of shear zones 

and a cleavage parallel to the shear zones, and (6) 

unroofing and development of joints and formation 

112 

of the Silverbow fault. Although each stage 

occurred in sequence, events that are grouped 

together did not necessarily occur simultaneously. 

REFERENCES CITED 

Berg, H.C., 1984, Regional geologic summary, 

metallogenesis, and mineral resources of 

southeastern Alaska: U.S. Geological Survey 

Open-File Report 84-572, 299 p. 

Brew, D.A., and Ford, A.B., 1984a, 

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. 

1984b, Timing of metamorphism and 

deformation of the Coast plutonicmetamorphic complex near Juneau, Alaska 

(abs.): Geological Society of America 

Abstracts with Programs, v. 16, no. 5, p. 272. 

1984c, The northern Coast plutonicmetamorphic complex, southeastern Alaska, 

and northwestern British Columbia, in 

Coonrad, W.C., and Elliot, R.L., eds., The 

United States Geological Survey in Alaska: 

Accomplishments during 1981: U.S. Geological 

Survey Circular 868, p. 120-124. 

1985, Preliminary reconnaissance geologic 

--m-ap of the Juneau, Taku River, Atlin, and 

part of the Skagway quadrangles, southeastern 

Alaska: U.S. Geological Survey Open-File 

Report 85-395, scale 1:250,000. 

Ramsey, J.G., and Huber, M.I., 1983, The 

techniques of modern structural geology, 

volume I: Strain analysis: New York, 

Academic Press, 307 p. 

Twenhofel, W.S., 1952, Geology of the AlaskaJuneau lode system, Alaska: U.S. Geological 

Survey Open-File Report 52-160, 180 p. 

Wayland, R.G., 1939, Geology of the Juneau 

region, Alaska, with special reference to the 

Alaska Juneau ore body: Minneapolis, 

University of Minesota, Ph.D. dissertation, 

93 p. 

Reviewers: E.R. Verbeek and R.J. Goldfarb 
THE MEADE GLACIER FAULTAN IMPORTANT TECTONIC BOUNDARY 

IN THE NORTHERN CORDILLERA, 

SOUTHEASTERN ALASKA 

David A. Brew and Arthur B. Ford 

One of the persistent questions about the 

tectonic history of southeastern Alaska concerns 

the existence and the nature of the boundary 

separating composite tectonostratigraphic 

terranes I and II of Monger and others (1982). This 

boundary must lie within the granitic and 

metamorphic rocks of the Coast crystalline belt 

and would separate the Stikine terrane (part of 

terrane I) on the east from the Alexander terrane 

and Gravina overlap assemblage (both part of 

terrane II) on the west (fig. 1). The existence of 

this boundary has been questioned by Brew (1983) 

and Brew and Ford (1983, 1984). 

Recent fieldwork in the Atlin quadrangle 

established the existence of a post-Late Triassic, 

pre-60 Ma north-northwest-trending fault zone 

with apparently significant right-lateral and westside-down separation . that may be the only 

remaining exposure of the terrane boundary (Brew 

and others, 1985; Himmelberg and others, 1985, 

1986; D.A. Brew and A.B. Ford, unpub. data). 

Recognition of this potentially important tectonic 

boundary in the Atlin quadrangle led us to examine 

its possible northern and southern extensions. This 

article reports progress so far in our efforts to 

trace the informally named Meade Glacier fault. 

In its only known exposures (fig. 2), the fault 

lies close to the southwest side of the northwestsoutheast-trending portion of the Meade Glacier 

and separates simply deformed low-metamorphicgrade Middle and Upper(?) Triassic volcanic, 

clastic, carbonate, and volcaniclastic rocks on the 

west from a package of inferred pre-Late Triassic 

multiply deformed medium- to high-metamorphic 

grade quartz-rich gneiss and schist, marble, and 

metavolcanic rocks on the east. The rocks to the 

west are intruded by an ultramafic body of 

uncertain (but post-Triassic, pre-Tertiary) age that 

consists mostly of peridotite (Himmelberg and 

others, 1985). The rocks to the east are intruded 

by a crosscutting hornblende-biotite granodiorite 

pluton whose age is inferred to be 50 Ma on the 

basis of compositional and structural similarities 

to dated plutons both north and south of the Meade 

Glacier area. Rocks in the fault zone include 

highly tectonized quartz-rich schist, augen gneiss 

and marble derived from the package to the east, 

and similarly tectonized peridotite derived from 

the rocks to the west. Minor structures in the 

fault zone indicate that some of the movement 

postdated the major folding of the schist and 

gneiss, but we were unable to get a consistent 

sense of vergence from the younger folds or from 

strain-sense indicators in the augen gneiss. The 

113 

fault is healed to the north and south of Meade 

Glacier by granitic plutons that are about 60 Ma in 

age (G.R. Tilton, University of California at Santa 

Barbara, written commun., 1986). 

0 

(() 

~ 

\.---.. :: 

( 

' ' 

' ' ' ' ' ' ' ' 

. ' 

' 

\ 

\ "' \/ 

) 

I 

( tJ) 

-4 

~ 

-

z 

"" 

0 50 100 150 200 KILOMETERS 

Figure 1.--Map showing boundaries of northern 

Coast crystalline belt (area between long dash 

lines), United States and Canada, and extent of 

Meade Glacier fault (heavy solid line). 
0 5 km E3 E3 E3 

Contour 200 feet in U.S., 50 feet in Canada 

EXPLANATION 

Area underlain by volcanic and 

foss iliferous carbonate rocks, 

turbidites and mudstone 

(Triassic) 

Peridotite (Himmelberg and others, 

1985) (Cretaceous?) 

Tectonized ultramafic rocks and 

some schist (Himmelberg and 

others. 1985) (Cretaceous?) 

Rock types dominant in other areas shown 

by labels 

• Fossiliferous sect ions 

Figure 2.--Map of Meade Glacier area showing 

known extent of Meade Glacier fault, and rocks on 

either side. 

We have not been able to trace the fault 

northward into the Skagway quadrangle because of 

the abundance of younger plutonic rocks and the 

absence of detailed mapping in that area. Further 

north, into British Columbia and Yukon Territory, 

the fault itself is not known to be exposed, but its 

geologic expression is recognized as far as about 

latitude 62° N. This is based on the distribution of 

the Kluane schist and gneiss of probable original 

Late Jurassic and Cretaceous age on the west and 

114 

of the Yukon Group of uncertain (but probably 

early Paleozoic or late Proterozoic) age on the 

east (Gabrielse and others, 1980; J.O. Wheeler, 

Geological Survey of Canada, oral commun., 

1986). The present interpretation (Gabrielse and 

others, 1980) of the mapping of Kindle (1953) 

suggest that near latitude 61° N, Mesozoic age 

granitic rocks separate two contrasting rock 

units. The unit to the west consists of quartzmica schist, quartz-biotite-feldspar gneiss, slate, 

and minor quartz-sericite-andalusite schist, 

hornblende schist, sericite-cordierite schist, and 

garnet-mica schist belonging to the Kluane schist 

and gneiss unit; the unit to the east consists of 

somewhat similar rocks, mainly quartz-mica 

schist, quartz-mica gneiss, quartz-biotite gneiss, 

and garnet-quartz-biotite gneiss, that are 

interlayered with distinctive thick coarse-grained 

white marble and minor limestone and are assigned 

to the Yukon Group. 

To the south, the possible terrane boundary 

passes through the abundant 50 Ma granitic rocks 

of the Juneau Icefield (Brew and Ford, 1985) and 

crosses the Taku Riv~r several kilometers 

downstream from the U.S.-Canada boundary (fig. 

1). At this latitude the pre-granitic rocks west of 

the fault belong to the medium- to high-grade 

metamorphic package of phyllite, schist, and 

gneiss, studied in detail near Juneau (Ford and 

Brew, 1973, 1977; Brew and Ford, 1977; 

Himmelberg and others, 1984a, b), that includes 

rocks with original ages ranging from Permian to 

Cretaceous. The rocks east of the fault are in 

part higher grade metamorphic rocks like those at 

the Meade Glacier and in part low- to mediumgrade semischists and phyllite. They have been 

described by Souther (1971) and Brew and Ford 

(1985). Further south, the boundary passes through 

more granitic rock into the Sumdum (Tracy ArmFords Terror) area described by Brew and Grybeck 

(1984). There only a few small outcrop areas of 

metamorphic rocks immediately adjacent to the 

U.S. - Canada boundary are inferred to belong to 

the quartz-rich schist and gneiss unit east of the 

tectonic boundary (D.A. Brew and A.B. Ford, 

unpub. data). Mapping in the Petersburg area still 

further south (Brew and others, 1984) and our work 

in the areas beyond indicate that the boundary 

probably passes into Canada somewhere in the 

Bradfield Canal quadrangle. In this region, in the 

Canadian portions of the Chutine (Souther, 1958) 

and Bradfield Canal (Geological Survey of Canada, 

1957) map-areas, the oldest rocks to the east of 

the projection of the Meade Glacier fault are 

schist, gneiss, greenstone, limestone, shale, and 

clastic sedimentary rocks of original 

Carboniferous and Permian age. These rocks are 

all interpreted (Souther and others, 1979) to belong 

to the same package as those east of the Meade 

Glacier fault where the fault trace is exposed 

(fig. 2). 
The available evidence is not conclusive as 

to whether the Meade Glacier fault is the 

boundary between composite terranes I (Stikine, 

etc.) and II (Alexander, etc.) of Monger and others 

(1982). It is strongly suggestive that it may be, 

however, and more studies along its possible 

continuations in Canada both north and south of its 

known extent in Alaska would undoubtedly add to 

our understanding of its nature and significance in 

the tectonic development of the northern 

Cordillera. 

REFERENCES CITED 

Brew, D.A., 1983, Evaluation of suspect terranes 

in the Coast plutonic-metamorphic complex, 

southeastern Alaska and part of British 

Columbia (abs.): Geological Society of 

America Abstracts with Programs, v. 15, 

no. 5, p. 324. 

Brew, D.A., and Ford, A.B., 1977, Preliminary 

geologic and metamorphic-isograd map of 

parts of the Juneau A-1 and A-2 quadrangles, 

Alaska: U.S. Geological Survey Map MF-847. 

___ 1983, Comment on Monger, J.W.H., Price, 

R.A., and Tempelman-Kluit, D.J., 1982, 

Tectonic accretion and the origin of the two 

major metamorphic and plutonic welts in the 

Canadian Cordillera: Geology, v. 11, 

p. 427-429. 

__ 1984, Tectonostratigraphic terrane analysis in 

the Coast plutonic-metamorphic complex, 

southeastern Alaska (abs.), in BartschWinkler, Susan, and Reed, K.M~ eds., The 

United States Geological Survey in Alaska: 

Miscellaneous geologic research 1982: U.S. 

Geological Survey Circular 939, p. 90-93. 

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, 23 p., scale 

1:250,000, 2 sheets. 

Brew, D.A., Ford, A.B., and Garwin, S.L., 1985, 

Fossiliferous Middle and(or) Upper Triassic 

rocks within Coast plutonic-metamorphic 

complex southeast of Skagway, Alaska, in 

Bartsch-Winkler, Susan, ed., The United 

States Geological Survey in Alaska: 

Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 86-89. 

Brew, D.A., and Grybeck, Donald, 1984, Geology 

of the Tracy Arm-Fords Terror wilderness 

study area and vicinity, in Mineral resources 

of Tracy Arm-Fords Terror wilderness study 

area and vicinity, Alaska: U.S. Geological 

Survey Bulletin 1525, p. 19-52. 

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. 

115 

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 parts of the Juneau A-1 and A2 quadrangles, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-847, 

scale 1:31,680. 

Gabrielse, H., Tempelman-Kluit, D.J., Blusson, 

S.L., and Campbell, R.B., 1980, MacMillan 

River 1:1,000,000 geological Atlas: 

Geological Survey of Canada Map 1398A. 

Geological Survey of Canada, 1957, Stikine River 

area, British Columbia: Geological Survey of 

Canada Map 9-1957, scale 1:253,440. 

Himmelberg, G.R., Brew, D.A., and Ford, A.B., 

1986, Chemical composition of olivine and 

orthopyroxene in peridotite in the Coast 

plutonic-metamorphic complex near Skagway, 

Alaska, in Bartsch-Winkler, Susan, ed., The 

United States Geological Survey in Alaska: 

Accomplishments during 1985: U.S. 

Geological Survey Circular 978, p. 95-98. 

Himmelberg, G.R., Ford, A.B., and Brew, D.A., 

1984a, Progressive metamorphism of pelitic 

rocks in the Juneau area, southeastern Alaska, 

in Coonrad, W .c., and Elliott, R.L., eds., The 

United States Geological Survey in Alaska: 

Accomplishments during 1981: U.S. 

Geological Survey Circular 868, p. 131-134. 

1984b, Reaction isograds in pelitic rocks of the 

Coast plutonic-metamorphic complex near 

Juneau, Alaska (abs.), 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. 105-108. 

1985, Ultramafic bodies in the Coast plutonicmetamorphic complex near Skagway, Alaska, 

in Bartsch-Winkler, Susan, ed., The United 

States Geological Survey in Alaska: 

Accomplishments during 1984: U.S. 

Geological Survey Circular 967, p. 92-93. 

Kindle, E.D., 1953, Dezadeash map-area, Yukon 

Territory: Geological Survey of Canada 

Memoir 268, 68 p. 

Monger, J. W .H., Price, R.A., and TempelmanKluit, D.J., 1982, Tectonic accretion and the 

origin of the two major metamorphic and 

plutonic welts in the Canadian Cordillera: 

Geology, v. 10, p. 70-75. 

Souther, J.G·., 1958, Chutine, British Columbia, 

map-area: Geological Survey of Canada Map 

7-1959, scale 1:253,440. 

1971, Geology and ore deposits of Tulsequah 

--map area, British Columbia: Geological 

Survey of Canada Memoir 362, 84 p. 

Souther, J.G., Brew, D.A., and Okulitch, A. V., 

1979, Iskut River 1:1,000,000 Geological 

Atlas: Geological Survey of Canada Map 

1418A. 

Reviewers: G.R. Himmelberg and S.M. Karl 
THE WRIGHT GLACIER VOLCANIC PLUG 

AND DIKE SWARM, SOUTHEASTERN ALASKA 

Arthur B. Ford and David A. Brew 

The distribution of early and late Cenozoic 

granitic plutons and of related late Cenozoic dike 

swarms in the Coast crystalline belt of 

southeastern Alaska is known from extensive 

reconnaissance work (Brew and Morrell, 1983; D.A. 

Brew, unpub. data), but no late Cenozoic plutons 

or dike swarms have been reported from this belt 

north of the latitude of Wrangell. These plutons 

and dike swarms are of interest because of their 

association with the large molybdenite deposit at 

Quartz Hill near the southern tip of southeastern 

Alaska (Hudson and others, 1979) and with 

molybdenite occurrences at Burroughs Bay, Cone 

Mountain, and Groundhog Basin near Wrangell 

(Hudson and others, 1979; Grybeck and others, 

1984) (fig. 1). In the vicinity of Juneau, Souther 

(1971) mapped a northeast-southwest-striking 10-

km-wide dike swarm of aplite and felsite on the 

Canadian side of the international boundary mainly 

on the north side of Mount Ogden, not far south of 

the Taku River east of Juneau. Several 

molybdenite occurrences accompany the swarm. 

We recently mapped the extension of that swarm 

into Alaska and found that it consists of rhyolite 

that is apparently associated with a dacite plug 

(fig. 2). This report briefly describes that swarm 

and plug. 

The dike swarm is well exposed on both the 

northeast and southwest sides of the northwestflowing Wright Glacier, about 7 km above the lake 

at the terminus of the glacier (fig. 2). The 

conspicuous, 1- to 5-m-wide, vertically dipping, 

northeast-southwest-striking dikes occur 

sporadically over the 6.5 km width of the swarm. 

Although the dikes are common, there are few 

localities with a concentration of more than two 

or three dikes within 100 m. The dikes cut 

granitic rocks inferred to be about 50 Main age as 

well as the pre-Late Triassic gneiss and schist 

referred to as the Tulsequah sub-belt (Brew and 

Ford, 1985). The dikes are well jointed and locally 

are miarolitic. They weather light yellow and are 

slightly iron-stained in places. Small quartz 

phenocrysts are present in almost all samples. Our 

geochemical sampling to date has not shown any 

pattern of significantly anomalous concentrations 

of molybdenum or other metals. 

The 0.5-by-1.0-km dacite body that we infer 

to be plug-like is at an elevation of about 6,500 

feet (1,980 m) about 6 km south-southeast of 

Wright Glacier lake at the terminus of Wright 

Glacier (fig. 2). It forms the relatively 

inaccessible peak labelled 6,882 feet (2,098 m) and 

intrudes 50 Ma granodiorites; most of the contacts 

with the surrounding rock are concealed by 

glaciers. The rock is well jointed and is medium 

116 

gray in color, weathering grayish brown; it is both 

conspicuously fragmental and consistently 

plagioclase porphyritic in hand specimen. The 

maximum size volcanic fragment observed in 

outcrop was about 15 em. Small quartz 

phenocrysts are present, but are rare. In thin 

section the fragments are seen to be dominantly 

silicic volcanic rock, some of which have been 

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

( 

\ 

I 

( 

\ 

\ 

\ 

\ 

\ 

I 

I 

( 

J 

1\1 

I 

0 50 100 150 200 KILOMETERS 

Figure 1.--Map showing significant molybdenite 

occurrences in Coast crystalline belt (area 

between long dashes), southeastern Alaska, and 

area of figure 2. 
m 

133° 25' 

0 2 3 4 5 KILOMETERS L_ __ _L ____ L_ __ _L ____ L_ __ ~ 

EXPLANATION 

,--;;-(~ Glaciers and permanent 

~ snowfields (Holocene) 

.. 

58°30' 

Figure 2.--Map of Wright Glacier area, Coast crystalline belt, showing location of Wright Glacier rhyolite 

dike swarm and dacite plug. Base map from U.S. Geological Survey Taku River B-5 1:63,360 series 

topographic map. 

subjected to biotitic alteration, but fragments of 

silicic schist like that exposed nearby are also 

present. Some fine-grained disseminated sulfide is 

present. Chemically, the rock has a Si02 content 

of 63.3 percent and is a calcalkalic dacite of 

average K-content in the classification of Irvine 

and Baragar (1971). It is a high-K dacite according 

to Peccarillo and Taylor (1976). Semiquantitative 

spectrographic analysis indicates that the rock 

contains amounts of molybdenum that are 

detectable but less than 5 ppm and contains 10 

ppm arsenic (S.J. Sutley and J.D. Hoffman, USGS, 

written communs., 1986). 

We are uncertain of the exact age of the 

plug and the dikes, but the nature of the lithic 

fragments in the plug, the intrusive relations with 

the 50 Ma granitoids, and time inferred to have 

elapsed between the emplacement of the granite 

and its uplift and subsequent intrusion by the 

dacite, all indicate that the plug and dikes are 

probably appreciably younger than the granitic 

rocks. The relations between the plug and the 

dikes have not been observed, although dikes occur 

117 

in granitic rock close to the plug. We presently 

interpret them to be of the same age and suggest 

that the dikes and the plug, which is located at the 

northwestern end of the dike swarm, came from 

the same concealed source. 

The Wright Glacier dacite plug and rhyolite 

dike swarm are the northernmost expression of 

late Cenozoic magmatism reported to date in 

southeastern Alaska (see also Koch and others, this 

volume). Their presence suggests that the 

northwest to southeast crustal extension that 

localized the somewhat younger dike swarms 

further south in southeastern Alaska and the 

volcanic fields of west-central British Columbia 

was locally active elsewhere in the northern 

Cordillera and that a concentration of late 

Cenozoic activity may have occurred in the Coast 

Mountains east of Juneau. 

REFERENCES CITED 

Brew, D.A., and Ford, A.B., 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, 23 p. 

Brew, D.A., and Morrell, R.P., 1983, Intrusive 

rocks and plutonic belts in southeastern 

Alaska, in Roddick, J.A., ed., Circum-Pacific 

plutonic -terranes: Geological Society of 

America Memoir 159, p. 171-193. 

Grybeck, D.J., Berg, H.C., and Karl, S.M., 1984, 

Map and description of the mineral deposits in 

the Petersburg and eastern Port Alexander 

quadrangles, southeastern Alaska: U.S. 

Geological Survey Open-File Report 84-83 7, 

87 p. 

Hudson, Travis, Smith, J.G., and Elliott, R.L., 

1979, Petrology, composition, and age of 

intrusive rocks associated with the Quartz 

118 

Hill molybdenite deposit, southeastern 

Alaska: Canadian Journal of Earth Sciences, 

v. 16, no. 9, p. 1805-1822. 

Irvine, T.N., and Baragar, W.R., 1971, A guide to 

the chemical classification of the common 

volcanic rocks: Canadian Journal of Earth 

Sciences, v. 8, no. 5, p. 523-548. 

Peccarillo, A., and Taylor, S.R., 1976, 

Geochemistry of Eocene calcalkalic volcanic 

rocks from the Kastamonu area, northern 

Turkey: Contributions to Mineralogy and 

Petrology, v. 58, p. 63-81. 

Souther, J.G., 1971, Geology and ore deposits of 

Tulsequah map area, British Columbia: 

Geological Survey of Canada Memoir 362, 

84 p. 

Reviewers: R.D. Koch and T.G. Theodore 
ULTRAMAFIC AND MAFIC SILLS 

IN THE VICINITY OF 

THE TREADWELL GOLD DEPOSITS, 

DOUGLAS ISLAND, SOUTHEASTERN ALASKA 

David A. Brew, Glen R. Himmelberg, 

Arthur B. Ford, and Robert C. Jachens 

A group of ultramafic and mafic sills occurs 

close to the Treadwell deposits of the Juneau Gold 

Belt (fig. 1). They may have some role in the 

origin and localization of the deposits and are 

described here so that workers concerned with the 

genesis of these important lodes, which produced 

3.2 million ounces (about 100,000 kg) of gold 

between 1881 and 1926 (Wells and others, 1985), 

may evaluate their significance. 

The Treadwell deposits consist of free gold 

and various sulfide minerals in calcite veins and 

disseminated in a highly altered felsic granitic 

rock. Their geology has been described by Becker 

(1898) and Spencer (1904, 1905a, b, 1906) and their 

exploration and production history by Cobb (1972), 

Stone and Stone (1980), Wells and others (1985), 

and Redman and others (1986). The regional 

setting is shown on the maps of Ford and Brew 

(1973) and Brew and Ford (1985). The occurrence 

and possible significance of the sills was called to 

our attention by George A. Moerlein in 1986; 

several of the small areas of mafic rock had been 

mapped in our previous fieldwork (unit "sdb" of 

Ford and Brew, 1973), but the extent of the bodies 

had not been recognized. 

The sills are poorly exposed along Gastineau 

Channel on the northeastern shore of Douglas 

Island starting just south of the former site of the 

Alaska-Mexican shoreline facility and extending to 

the point of land just north of the mouth of Ready 

Bullion Creek (fig. 1). Their sill-like occurrence is 

inferred from the distribution of scattered 

several-meter-wide outcrops of mafic and 

ultramafic rock in relation to intervening outcrops 

tens of meters wide of graywacke semischist, 

slate, and minor greenstone and greenschist that 

are considered to belong to the Seymour Canal 

Formation of the Stephens Passage Group of Late 

Jurassic and Early Cretaceous age (Lathram and 

others, 1965). It is possible that they are not 

continuous sills at all, but instead are a series of 

irregular lumps conformable with the country 

rock. As discussed below, we infer that the 

surface outcrops are connected at depth to a 

major mafic-ultramafic feature. 

Field observations indicate that the hanging 

wall of the northwest-southeast-striking, 

northeast-dipping Treadwell ore-bearing altered 

felsic rock sill must locally be within a few meters 

of the ultramafic sills at the surface, but evidence 

indicates that there is at least some greenstonegreenschist in between everywhere. We do not 

know if the now-inaccessible mine workings cut 

any mafic-ultramafic rock. In addition to the 

119 

shoreline exposures, another ultramafic sill (not 

shown on fig. 2) occurs in the country rocks on the 

footwall side of the Treadwell ore-bearing sill 

(G.A. Moerlein, Houston Oil and Minerals, Co., 

oral commun., 1986). The sills appear to be 

confined to a northwest-southeast-trending zone 

no more than a kilometer wide adjacent to the 

Gastineau Channel fault; none were found along 

the course of Ready Bullion Creek, which affords 

good exposures across the structure of the 

footwall for a few kilometers. 

The southernmost exposures of the sills 

contrast with those farther north. At the point of 

land just north of the mouth of Ready Bullion 

Creek, a body of magnetite-bearing hornblende 

diorite and hornblendite a few tens of meters wide 

has locally well-developed banding and cockscomb 

layering. These rock types are not exposed to the 

north, where the dominant sill rocks are the 

clinopyroxenite described below. Large (to 1 m 

maximum) boulders of orange-weathering 

harzburgite (sample 86DB069B) are found in 

several places on the beach just north of the 

hornblendite and hornblende diorite outcrops. 

Their origin is uncertain; they are not likely to 

belong to the clinopyroxenite-hornblendite-diorite 

suite. Nevertheless, all of the boulder occurrences 

that are known are in this one place. No other 

harzburgite occurrences have been reported from 

Douglas Island or elsewhere in the vicinity of 

Juneau, and the provenance of these probably 

ophiolite-related boulders remains a puzzle. 

The ultramafic rocks samples are 

magnetite-bearing clinopyroxenite, hornblende 

clinopyroxenite, and plagioclase-bearing 

clinopyroxenite (samples 86DB064A, 86DB068A, 

and 86DB069A, respectively on table 1). They are 

brown weathering, hard, dense, and have a coarse 

serrate texture with pyroxene grains up to 1 em 

maximum dimension. From a distance they look 

enough like the augite-bearing greenstones in the 

Douglas Island Volcanics of the Stephens Passage 

Group to have fooled two of us (DAB and ABF) 

repeatedly as we walked this stretch of beach. A 

phenocryst from a sample of those greenstones 

(86DB066A) just south of the mouth of Ready 

Bullion Creek was analyzed for comparative 

purposes. The chemical compositions and 

structural formulas based on microprobe analyses 

of the pyroxenes in clinopyroxenite, harzburgite, 

and greenstone are given in table 1, those of the 

olivine from the harzburgite in table 2, and the 

pyroxene compositions are plotted in figures 2 and 

3. In general the pyroxene values group closely, 

differ appreciably from those from the Blashke 

Islands (Himmelberg and others, 1986), but are 

similar to those reported from Duke Island (Irvine, 

197 4) and other southeastern Alaskan-type 

ultramafic complexes. These diagrams show that 

the Treadwell suite has petrogenetic affinity with 

normal alkalic basaltic rocks. 
GREENSTONE 

AND 

GREENSCHIST ISLAND 

~~'(.. c~ 

GREENSTONE 

AND 

GREENSCHIST 

MIXED 

0 1.0 

Figure !.--Generalized geologic map of Treadwell mine area, Douglas Island, showing sample locations (+) 

and mafic-ultramafic sills. 

Figure 2.--Mg-Fe-Ca triangular diagram show~ng 

compositions of pyroxenes from Treadwell mme 

area ultramafic sills (solid circles), from the 

Douglas Island Volcanics (open circle), from 

harzburgite float (solid square), and fro~ 

peridotite-gabbro suite at Blashke Islands. (s?hd 

triangles, Himmelberg and others, 1986). T1e lines 

connect clinopyroxene and orthopyroxene in the 

same sample. 

120 

The recognition of the mafic-ultramafic sills 

helps explain a hitherto enigmatic prominent 

linear aeromagnetic anomaly close to Gastineau 

Channel (U.S. Geological Survey, 1984). That 

anomaly extends southeastward to include the 

exposed magnetite-bearing mafic-ultramafic rocks 

at the Midway Islands and in Port Snettisham 

(Jachens, 1984; Brew and Grybeck, 1984) and is 

more or less in line with an inferred belt of linear 

magnetic anomalies to the northwest that 

accompanies the mafic and ultramafic rocks 

exposed at Haines and Klukwan (Decker and 

others, 1981). Strong to moderate gravity 

anomalies accompany all the magnetic anomalies 

(D.F. Barnes, oral commun., 1986). Although no 

detailed models have been prepared, preliminary 

studies of the magnetic properties of oriented 

samples from the Douglas Island sills indicate that 

the rocks have susceptibilities that could produce 

the observed anomaly provided that the sills 

reflect a larger body with comparable magnetic 

susceptibility at depth. Preliminary twodimensional models of the magnetic anomaly 

southeast of Douglas Island suggest that the source 

body is about 8 km wide at its top and extends to a 

significant depth. 
(j) 

~ 

z 

w 

(.) 

0:: 

w 

CL. 

~ 

:I: 

(!) 

~ 48 

0.15 

<( 

_J 

:::> 0.10 

~ 

0:: 

0 

LL 

0:: 

w 

CL. 

0.05 

• 

• 

• 

• • • • 

A 

Sub-alkaline 

• 

Normal-alkaline _,.,.A.,._...-"_,. 

.,..,..,.-"' . / 

-"'""Per-alkaline 

2 4 6 8 

WEIGHT PERCENT Al 2 0 3 

Alkaline basalts 

Tholeiitic and 

calc-alkaline basalts 

c 

• 

•• 

0.00~--~--~----~--~~~~ 

0.5 0.6 0.7 0.8 0.9 1.0 

(Co - No) PER FORMULA 

Figure a.--Clinopyroxene discrimination diagrams. 

Solid circles Treadwell mine area ultramafic sills; 

open circle, Douglas Island Volcanics; solid 

triangles, Blashke Island rocks (Himmelberg and 

others, 1986); open triangles, Duke Island rocks 

(Irvine, 197~ A, Sio2 versus Al20 3 (Le Bas, 

1962); B, Al versus Tt02 (Le Bas, 1962); C, Ti 

versus (Ca+Na) (Leterrier and others, 1982). 

121 

<( 

.-JI2 

:::> 

~ 

0:: 

0 

LL 

o::8 

w 

CL. 

;:: 

<( 

4 

Normal-alkaline 

Sub-alkaline 

0~--~--~--~--~---L--~ 

0 I 2 3 

WEIGHT PERCENT Ti 0 2 

Table 1.--Chemical composition (in weight 

percent) and structural formula of pyroxene in 

Douglas Island ultramafic and volcanic samples 

SiD2 TiD 

A1 263 FeD 

MnD 

MgD 

CaD 

Na 2D 

Sum 

Si 

AliV 

Sum T 

AlVI 

Ti 

Fe 

Mn 

Mg 

Ca 

Na· 

Sum 

1DD Mg/ 

Mg+Fe+Mn 

86DB64A 

CPX 

49.DD 

.91 

5.64 

7.61 

.19 

12.6D 

23.7D 

.43 

1DD.D8 

1.816 

.184 

2.DDD 

.D68 

.D25 

.236 

.DD6 

.697 

.942 

.031 

4.DOD 

74.2 

86DB68A 

CPX 

5D.60 

.68 

4.24 

6.62 

.13 

14.00 

23.4D 

.24 

99.91 

1.87D 

.130 

2.00D 

.D55 

.019 

.2D5 

.DD4 

.772 

.928 

.017 

4.DDD 

78.7 

86DB69A 

CPX 

47.50 

.92 

6.14 

7.81 

.21 

12.7D 

23.40 

.36 

99.04 

1.777 

.223 

2.000 

.048 

.D26 

.245 

.007 

.709 

.939 

.026 

4.0DD 

73.8 

86DB69B 

DPX 

55.30 

.OD 

4.D5 

6.D5 

.14 

32.4D 

l.DD 

.00 

98.94 

1.9L9 

.D71 

2.000 

.D96 

.DOD 

.177 

.004 

1.686 

.037 

.DDD 

4.DDO 

9D.3 

86DB66A 

CPX 

52.2D 

.26 

2.66 

5.80 

.17 

16.00 

22.3D 

.24 

99.63 

1.919 

.D81 

2.DOO 

.D35 

.007 

.178 

.005 

.878 

.880 

.D17 

4.000 

82.7 
Table 2.--Chemical composition in weight percent 

and structural formula of olivine in Douglas Island 

harzburgite 

[n.d., not determined] 

86DB69B 

Olivine 

Si02 41.90 

FeO 9.30 

MnO .14 

MgO 48.20 

CaO .00 

NiO n.d. 

Sum 99.54 

Si 1.033 

Fe .192 

Mn .003 

Mg 1. 772 

Ca .000 

Ni . 000 

Sum 3.000 

100 Mg/ 

Mg+Fe+Mn 90.1 

As mentioned earlier, the relations (if any) 

of the ultramafic and mafic sills to the 

mineralization at the Treadwell mines and perhaps 

to the Alaska-Juneau mine on the northeast side of 

Gastineau Channel are not known. The 

northwestern part of the magnetic anomaly clearly 

underlies the Treadwell deposits, and the northern 

edge of the magnetic source beneath almost a top 

the Alaska-Juneau and nearby gold deposits. It is 

intriguing to speculate about the possible linkages, 

however, given the strong similarities among the 

mesothermal gold deposits throughout the northern 

Cordillera (Nesbitt and others, 1986) and the 

spatial association of ultramafic rocks with the 

most important concentrations of lode deposits in 

the Sierran foothills (Bohlke and Kistler, 1986). 

R.P. Ashley (USGS, written commun., 1986) has 

pointed out that although there are strong 

associations of Sierran gold deposits with 

ultramafic rocks on a regional scale and on a local 

scale in some mining districts, it is entirely 

possible that those relationships are fortuitous; the 

low-sulfide gold-quartz vein deposits and the 

ultramafic rocks may both be controlled by the 

same major regional structures, but may not 

necessarily be related to each other. 

122 

REFERENCES CITED 

Becker, G.F., 1898, Reconnaissance of the gold 

fields of southern Alaska, with some notes on 

general geology: U.S. Geological Survey 18th 

Annual Report, pt. 3, p. 1-86. 

Bohlke, J.K., and Kistler, R.W., 1986, Rb-Sr, K-Ar, 

and stable isotope evidence for the ages and 

sources of fluid components of gold-bearing 

quartz veins in the northern Sierra Nevada 

Foothills metamorphic belt, California: 

Economic Geology, v. 81, no. 2, p. 296-322. 

Brew, D.A., and Ford, A.B., 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, 23 p. 

Brew, D.A., and Grybeck, Donald, 1984, Geology 

of the Tracy Arm-Fords Terror wilderness 

study area and vicinity, in Mineral resources 

of Tracy Arm-Fords Terror wilderness study 

area and vicinity, Alaska: U.S. Geological 

Survey Bulletin 1525, p. 19-52 • 

Cobb, E.H., 1972, Metallic mineral resources map 

of the Juneau quadrangle, Alaska: U.S. 

Geological Miscellaneous Field Studies Map 

MF-435, scale 1:250,000. 

Decker, John, Mullen, M.W., and Schwab, C.E., 

1981, Aeromagnetic profile map of 

southeastern Alaska: U.S. Geological Survey 

Open-File Report 82-505, scale 1:1,000,000. 

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. 

Himmelberg, G.R., Loney, R.A., and Craig, J.T., 

1986, Petrogenesis of the ultramafic complex 

at the Blashke Islands, southeastern Alaska: 

U.S. Geological Survey Bulletin 1662, 14 p. 

Irvine, T.N., 1974, Petrology of the Duke Island 

ultramafic complex, southeastern Alaska: 

Geological Society of America Memoir 138, 

240 p. 

Jachens, R.C., 1984, Interpretation of the 

aeromagnetic data, in Mineral resources of 

Tracy Arm-Fords Terror wilderness study area 

and vicinity, Alaska: U.S. Geological Survey 

Bulletin 1525, p. 53-62. 

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, p. Rl-R48. 

LeBas, M.H., 1962, The role of aluminum in 

igneous clinopyroxenes with relation to their 

parentage: American Journal of Science, v. 

260, p. 267-288. 
Leterrier, Jacques, Maury, R.C., Thonon, Pierre, 

Girard, Danielle, and Marchal, Michele, 1982, 

Clinopyroxene composition as a method of 

identification of the magmatic affinities of 

paleovolcanic series: Earth and Planetary 

Science Letters, v. 59, no. 1, p. 139-154. 

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. 

Redman, E., Roberts, W .S., Clough, A., and 

Kurtak, J., 1986, Preliminary mine, prospect, 

and sample location maps and descriptions, 

Juneau Gold Belt area: U.S. Bureau of Mines 

Open-File Report 85-86, 68 p. 

Spencer, A.C., 1904, The Juneau gold belt, 

Alaska: U.S. Geological Survey Bulletin 225, 

p. 28-42. 

1905a, The geology of the Treadwell ore-

--cieposits, Douglas Island, Alaska: Transactions 

American Institute of Mining Engineers, v. 35, 

p. 473-510. 

1905b, The Treadwell ore deposits, Douglas 

--Island: U.S. Geological Survey Bulletin 259, 

p. 69-87. 

1906, The Juneau gold belt, Alaska: U.S. 

--G-eological Survey Bulletin 287, p. 1-137. 

Stone, David, and Stone, Brenda, 1980, Hard rock 

gold, the story of the great mines that were 

the heartbeat of Juneau: Seattle, Wash., 

Vanguard Press, 108 p. Reprinted in 1983. 

123 

U.S. Geological Survey, 1984, Aeromagnetic map 

of the Juneau area, Alaska: U.S. Geological 

Survey Open-File Report 84-296, scale 

1:250,000. 

Wells, D.E., Pittman, T.L., Brew, D.A., and 

Douglass, S.L., 1985, Map and description of 

the mineral deposits in the Juneau, Taku 

River, Atlin, and part of the Skagway 

quadrangles, Alaska: U.S. Geological Survey 

Open-File Report 85-717, 332 p. 

Reviewers: R.P. Ashley and R.A. Loney 
NEWLY DISCOVERED MOLYBDENITE 

OCCURRENCE NEAR 

BOUNDARY CREEK, COAST MOUNTAINS, 

SOUTHEASTERN ALASKA 

Richard D. Koch, David A. Brew, 

and Arthur B. Ford 

A previously unknown molybdenite 

occurrence was discovered during fieldwork in the 

Coast Mountains east of Juneau during 1986. This 

occurrence is close to the "Boundary Creek 

occurrence" discovered and described by Brew and 

Ford (1969) (fig. 1). Based on very limited data, 

the mineralization at this newly discovered 

locality appears to cover a larger area than that at 

the other locality. This article reports what we 

presently know of this new "Boundary Creek 2" 

occurrence. Further surface work is planned to 

define better the extent and grade of the 

mineralized rock. 

The regional geologic setting of the newly 

discovered occurrence is shown on the map of 

Brew and Ford (1985). Compared with "Boundary 

Creek 1," the local setting of "Boundary Creek 2" 

is relatively simple; it occurs well within a large 

mass of granodiorite, granite, and alkali granite 

rather than near the margin (fig. 2). In detail, the 

newly discovered occurrence is at an elevation of 

about 3,800 ft (1,160 rn) in alkali leucocratic 

granite on a broad south-extending shoulder of the 

main ridge that is north and east of Boundary 

Creek. Four grab samples were collected in alkali 

granite near the crest of that shoulder about 1.2 

krn west of lake 2880 (fig. 2). The alkali granite 

also occurs at one locality examined east of the 

occurrence, near lake 2880. 

The rock at the newly discovered 

molybdenite locality is well-jointed, light-grayweathering, fine- to coarse-grained, seriatetextured biotite alkali granite with a color index 

of 1. Some potassium feldspar grains are as large 

as 2 ern. Aplite dikes as wide as 25 em cut the 

main rock. The age of the alkali granite is not 

known, except that it must be no older than the 50 

Ma age of the dominant granodiorite pluton with 

which it is spatially associated (Brew and Ford, 

1985); the alkali granite may be a phase of that 

intrusion or it may be younger. If it is younger and 

intrusive into the granodiorite, then we favor an 

age of about 15-30 Ma for it, based on the general 

compositional analogies with the molybdenitebearing pluton at Quartz Hill, with the host rocks 

for the molybdenite occurrence at Burroughs Bay 

(Hudson and others, 1979), and with molybdenite 

occurrences at Cone Mountain and Groundhog 

Basin (Grybeck and others, 1984) in southern 

southeastern Alaska (fig. 1). 

The full extent of the mineralization is not 

known. Granite in an area of about 100 rn by 100 

rn contains a trace to about 2 volume percent 

visible molybdenite, and an intensely iron-stained 

124 

'~----- ... , \ •, 

\ J\1 I 0 I I I ~ 

' \ ~ 

\ \ 

\ 6/o 

Sso I 

I 

{ 

J 

I 

( 0 

~ 

~ 

0 50 100 150 200 KILOMETERS 

Figure !.--Significant molybdenite occurrences in 

Coast crystalline belt, southeastern Alaska. 

zone about 2 x 10 m in area contains up to 5 

percent molybdenite as disseminated small grains 

and as composite flakes as large as 5 mm. Pyrite 

accompanies the molybdenite, and its oxidation is 

the cause of the iron stain. Widely spaced, 

narrow, coarse-grained pyrite-bearing quartz veins 

cut the mineralized rock, but they do not contain 

molybdenite. Semiquantitative spectrographic 

analyses of grab samples show that the large 

expanse of molybdenite-bearing rock contains 
gd 

BOUNDARY 

CREEK 2 • 

OCCURRENCE 

\ 

gd 

0 2 4 KILOMETERS 

EXPLANATION 

r;;n GLACIERS AND PERMANENT SNOWFIELDS 

~ (HOLOCENE) 

~SPHENE-BEARING HORNBLENDE-BIOTITE 

GRANODIORITE, APLITE, ALKALI GRANITE 

(EOCENE) 

~ MIGMATITE/INTRUSION BRECCIA 

~ (EOCENE AND OLDER) 

r::-1 SCHIST AND GNEISS OF TULSEQUAH 

~ SUB-BELT OF BREW AND FORD 

(1985) 

/.·· GEOLOGIC CONTACT, DOTTED WHERE 

CONCEALED 

Figure 2.--Sketch map showing Boundary Creek 

molybdenite occurrences and vicinity. Base from 

U.S. Geological Survey Taku River (C-6) 1:63,360 

series topographic map. 

125 

5 ppm Mo and a trace of Ag; the small exposure of 

higher grade rock contains 1,500 ppm Mo and 1.5 

ppm Ag; and the quartz veins contain 30 ppm Mo, 

10 ppm Bi, 200 ppm Cu, and 2 ppm Ag (E.A. 

Bailey, and 0. Erlich, written commun., 1986). 

The significance of this newly discovered 

locality cannot be evaluated fully with the data at 

hand. Given the proximity to the Boundary Creek 

1 occurrence, to the molybdenite deposits near 

Mount Ogden some 25 km to the southeast 

(Souther, 1971), and to the possible young volcanic 

plug and dike swarm that is near those deposits but 

on the Alaska side of the border (see Ford and 

Brew, this volume), we suggest that an area with 

both significant late Cenozoic intrusive rocks and 

potential for molybdenite resources may exist in 

the Coast Mountains near Juneau. 

REFERENCES CITED 

Brew, D.A., and Ford, A.B., 1969, Boundary Creek 

molybdenum-silver occurrence, southeastern 

Alaska: U.S. Geological Survey Circular 615, 

p. 12-15. 

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, 23 p., scale 

1:250,000, 2 sheets. 

Grybeck, D.G., Berg, H.C., and Karl, S.M., 1984, 

Map and description of the mineral deposits in 

the Petersburg and eastern Port Alexander 

quadrangles, southeastern Alaska: U.S. 

Geological Survey Open-File Report 84-83 7, 

87 p. 

Hudson, Travis, Smith, J.G., and Elliott, R.L., 

1979, Petrology, composition, and age of 

intrusive rocks associated with the Quartz 

Hill molybdenite deposit, southeastern 

Alaska: Canadian Journal of Earth Sciences, 

v. 16, no. 9, p. 1805-1822. 

Souther, J.G., 1971, Geology and ore deposits of 

Tulsequah map area, British Columbia: 

Geological Survey of Canada Memoir 362, 

84 p. 

Reviewers: S.L. Douglass and T.G. Theodore 
SALT CHUCK PALLADIUM-BEARING 

ULTRAMAFIC BODY, 

PRINCE OF WALES ISLAND 

Robert A. Loney, Glen R. Himmelberg, 

and Nora Shew 

The ultramafic intrusive body north of Salt 

Chuck, at the head of Kasaan Bay, southeastern 

Pr-ince of Wales Island, forms a tadpole-shaped 

outcrop that trends west-northwest for a distance 

of 7.3 km; its maximum width is about 1.6 km at 

its western end (fig. 1). The ultramafic body 

intrudes mainly basalt flows and pyroclastic rocks 

of the Descon Formation (Lower Ordovician 

through Lower Silurian) (Eberlein and others, 

1983), in which it has produced a contact aureole 

at least a few meters wide. The Salt Chuck Mine 

located in the middle part of the intrusion, is th~ only mine in the body. It operated intermittently 

from J.905 to 1941 and produced about 300,000 

tons (270,000 t) of milling ore (chiefly bornite in 

clinopyroxenite) estimated to have averaged 0.95 

percent Cu, 0.36 oz (12 ppm) Au, 0.17 oz (5.8 ppm) 

Ag, and 0.63 oz (22 ppm) Pd per ton (Holt and 

others, 1948). 

The intrusive body has been included by 

previous authors in the belt of Cretaceous 

ultramafic bodies that extends from Klukwan to 

Duke Island (Lanphere and Eberlein, 1966; Brew 

and Morrell, 1980; Himmelberg and others, 1986). 

These bodies have been called zoned ultramafic 

complexes of the Ural-Alaskan type (Taylor, 1967) 

and concentric complexes (Jackson and Thayer, 

1972). A recent potassium-argon study on biotite 

c~inopyroxenite from the Salt Chuck body has 

yielded an age of 429 Ma (chloritized biotite). The 

K20 values of the altered biotite are low (table 1), 

thus making the Paleozoic age suspect. However, 

the extreme age difference between the Salt 

Chuck ultramafic body and the others in the 

Klukwan-Duke Island ultramafic belt implies that 

it should be considered separately from them. 

Our field mapping in 1986 showed the Salt 

Chuck intrusive body to consist of clinopyroxenite 

and gabbro that grade irregularly into one another 

with no regular pattern. Most exposures are 

massive and homogeneous, although isomodal 

layers 2 to 8 em thick with mineral ratio contacts 

are locally present in some gabbros. The 

clinopyroxenites are clinopyroxene-magnetite 

cumulates with late (postcumulus) plagioclase and 

biotite. Most gabbros are anhedral granular or 

subhedral granular clinopyroxene-plagioclasemagnetite adcumulates with postcumulus biotite. 

The postcumulus biotite occurs in clinopyroxenite 

commonly in a poikilitic texture in which it forms 

enclosing crystals (oikocrysts) as large as 2 to 3 

em in size. Grain size of all the rocks is generally 

1-2 mm, with the exception of the biotite 

oikocrysts noted above. 

Figure 1.--Location of Salt Chuck ultramafic body. 

126 

Our initial petrographic study indicates that 

although the rocks are extensively altered, a close 

approximation of the original modal amounts of 

primary minerals can be made. These amounts are 

as follows: clinopyroxene, greater than 90 percent 

to 35 percent; plagioclase, less than 1 percent to 

10 percent in clinopyroxenite, 20 to 65 percent in 

gabbro; magnetite, generally 5 to 10 percent in 

clinopyroxenite and gabbro, although some gabbros 

contain as little as 2 percent magnetite; biotite, 1 

to 10 percent in clinopyroxenite and gabbro. 

Trace amounts of hornblende are present in some 

samples of both rock types, apatite is a common 

accessory mineral in both types, and interstitial 

potassium feldspar was noted in one gabbro 

sample. The rocks are extensively altered and 

veined by epidote. Plagioclase in most samples is 

100 percent altered to mixtures of white mica, 

zoisite/clinozoisite, epidote, and in some cases 

minor calcite and prehnite. Unaltered grains of 

biotite are present in some clinopyroxenite, but in 

most grains biotite is altered to chlorite, epidote, 

and prehnite. Clinopyroxenite generally remains 

unaltered, except for minor chloritic alteration 

along fractures and cleavage in some samples. 
Table 1.--Potassiurn-argon analytic~J data, Salt Chuck mine, !\llf:sk_, _

10 _

1 [Constants used: 4 K/K = 1.16 x10 mol/mol; xe: = 0.581x10 yr ; x6 = 4.962x10 yr 1 

Sample Rock Mineral K20 Arrad Arrad Age Lat. 

(x1o- No. Long. type dated (wt pet) 9moles/g) (pet) (Ma) 

84ASh 35c 55°37 1

35 11 N. Clino- Biotite 5.98 4.2436 96.8 429±11 

132°33 117 11 w. pyroxenite (altered) 6.06 4.1527 97.6 

Bornite, the principal ore mineral of the Salt 

Chuck Mine, occurs as interstitial grains in 

clinopyroxenite in amounts up to 15 percent; it 

occurs similarly in gabbro in lesser amounts. 

Significant bornite occurrences are primarily 

restricted to the workings of the mine. 

REFERENCES CITED 

Brew, D.A., and Morrell, R.P., 1980, Intrusive 

rocks and plutonic belts of southeastern 

Alaska, U.S.A.: U.S. Geological Survey OpenFile Report 80-78, 34 p. 

Eberlein, G.D., Churkin, Michael, Jr., Carter, 

Claire, Berg, H.C., and Ovenshine, A.T., 1983, 

Geology of the Craig quadrangle, Alaska: 

U.S. Geological Survey Open-File Report 83-

91, 23 p. 

Himmelberg, G.R., Loney, R.A., and Craig, J.T., 

1986, Petrogenesis of the ultramafic complex 

at the Blashke Islands, southeastern Alaska: 

U.S. Geological Survey Bulletin 1662, 14 p. 

127 

x=6.o2 

Holt, S.P., Shepard, J.P., Thorne, R.L., Tolonen, 

A. W ., and Fosse, E.L., 1948, Investigation of 

the Salt Chuck copper mine, Kasaan 

Peninsula, Prince of Wales Island, 

southeastern Alaska: U.S. Bureau of Mines 

Report of Investigations 4358, 16 p. 

Jackson, E.D., and Thayer, T.P., 1972, Some 

criteria for distinguishing between stratiform, 

concentric, and alpine peridotite-gabbro 

complexes: International Geological 

Congress, 24th, Montreal, Proceedings, 

section 2, p. 289-296. 

Lanphere, M.A., and Eberlein, G.D., 1966, 

Potassium-argon ages of magnetite-bearing 

ultramafic complexes in southeastern 

Alaska: Geological Society of America 

Special Paper 8 7, p. 94. 

Taylor, H.P., Jr., 1967, The zoned ultramafic 

complexes of southeastern Alaska, !.!!. Wyllie, 

P.J., ed., Ultramafic and related rocks: New 

York, John Wiley, p. 96-118. 

Reviewers: T.E.C. Keith and W.H. Nelson 
THE ALASKA-JUNEAU GOLD DEPOSIT; 

REMOBILIZED SYNGENETIC VERSUS 

EXOTIC EPIGENETIC ORIGIN 

Rainer J. Newberry and David A. Brew 

The Alaska-Juneau (AJ) deposit is the largest 

lode producer of gold in Alaska. The AJ deposit is 

located at Juneau, near the northern end of a 10-

km-wide, 150-km-long belt of lode gold deposits 

(the "Juneau gold belt") from which the majority 

of Alaska's lode gold has been produced. The AJ 

deposit is a swarm of sub-parallel quartzankeri te±bioti te-m uscovi te-chlori te-gold-sulfide 

veins of probable mid-Tertiary age. The deposits 

are described by Wernecke (1932), Twenhofel 

(1952), and Wayland (1960). Brew and Ford (1985) 

summarized the regional geology. 

Current and continuing efforts to assess the 

undiscovered gold endowment of the Juneau gold 

belt are tied into genetic models of deposit 

formation. Traditionally, these deposits have been 

viewed as epigenetic veins and vein swarms, with 

an origin ascribed to boiling of circulating late 

metamorphic fluids (Goldfarb and others, 1986). 

Several industry geologists (for example, T.R. 

Turner, Calista Corp., written commun., 1986), 

however, support an origin by remobilization of a 

gold-enriched chemical sediment formed by 

volcanogenic ("exhalative") processes. If the 

epigenetic hypothesis is correct, then localization 

of orebodies depends principally on the presence of 

structural foci, and undiscovered endowment can 

be assessed by consideration of typical deposit 

densities in other structure-related vein districts 

(as in the Mother Lode district of California). If 

the remobilization hypothesis is correct, then 

there is a strong potential for undiscovered 

stratiform gold orebodies in the district, and the 

presence of such stratiform orebodies is a vital 

prerequisite to the formation of vein ores. In this 

article we review the evidence for both views and 

conclude that the deposits are most likely 

epigenetic in origin. 

Several lines of evidence support a 

remobilized syngenetic model for gold 

mineralization in the AJ area. (1) The vein 

swarms are broadly stratabound in the sense that 

they occur in one lithostratigraphic unit, and may 

be in one part of that unit as suggested by 

alignment of the major open-pit orebodies 

(fig. 1). (2) The deposits occur in a black phyllite 

unit with many intercalated mafic and felsic 

rocks, structurally above a thick volcanic unit. (3) 

Extensive, broadly stratiform zones of ankeritebearing rocks (units "ags" and "b" on fig. 1) are 

present in the area, adjacent to both intercalated 

mafic rocks (unit "a") and to the thick volcanic 

unit (unit "gs"). Such rocks are compositionally 

similar to "carbonate exhalites," that is, Fecarbonate-rich rocks which host disseminated gold 

128 

ores, as at the Agnico-Eagle deposit in Quebec 

(Barnett and others, 1982) and the Homestake 

deposit in South Dakota (Slaughter, 1968) 

Four major lines of evidence argue for ~n 

epigenetic and against a remobilized syngenetic 

origin: (1) non-stratabound mineralizat.ion, (~) .the 

minor role of syn-sedimentary volcamc activity, 

(3) evidence for broad-scale post-metam~rphic 

hydrothermal activity, and (4) the lack of evidence 

for stratiform gold enrichment. Although the 

major orebodies of the AJ area are broadly 

stratabound, detailed mapping of the contact 

between the phyllite (unit "p" on fig. 1) and the 

greenstone units ("gs", "ags", and "clgs" on fig. ~) 

shows that the orebodies move away from this 

contact in the progression Perseverance-SouthNorth pits. The Humboldt prospect, the largest 

prospect north of the North. pit, is ~till farther 

upsection from the greenschist-phyllite contact. 

Structural mapping (Ford and Brew, 1973; Brew 

and Ford, 1977) indicated the presence of a major 

overturned antiform in the vicinity of the 

orebodies with the main pits in one limb of the 

fold; if the ore was truly stratabound then goldbearing rocks would be expected to occur on both 

limbs of the fold. Finally, sampling of quartz 

veins in the AJ area (table 1) and locations of 

known prospects and adits (fig. 1) indicate that in 

detail the mineralization is not stratabound, but 

rather occurs over a wide stratigraphic interval 

and in a variety of different rock types. 

Mafic bodies in the phyllite unit have been 

described as either metabasalt (Herreid, 1962) or 

metamorphosed gabbroic-dioritic sills (Wernecke, 

1932). These bodies consist of foliated amphibole 

and plagioclase with access~ry magnetite ~nd 

ilmenite. Contact relations with the surroundmg 

phyllites are obscure and do . not <:o~clusively 

demonstrate intrusive or extrusive ortgms. Our 

mapping, however, indicates (1) that thicker b?dies 

are coarser grained (up to 2 em) whereas thm~er 

bodies are finer grained (2-4 m m) and (2) all bodies 

examined have fine-grained margins and coarsegrained interiors. Thus, they are intrusive and not 

metavolcanic rocks. 

Felsic rocks do not show clastic features; 

locally (fig. 1) they crosscut foliation, indicating 

either an intrusive or alteration origin and not a 

syn-sedimentary volcanic origin. The occurrence 

of graphitic, pyrrhotite-bearing muscovite-9uartz 

schist slightly crosscutting the regional strike .of 

the graphitic phyllite near the Perseverance pits 

(fig. 1) suggests that the pyrrhotite-.b~aring ~chi~t 

originated by alteration of the graphitic phyllite m 

this area. Most of the quartzite and micaceous 

quartzite in the AJ area is probably of 

sedimentary_ origin and is not metamorphosed from 

volcanic rock. 

Although usually well-laminated, ankeritebearing rocks in the AJ area distinctly show 
EXPLANATION 

m Chlorite-altered greenschist 

B Ankerite-altered greenschist 

~ Biotite-ankerite altered amphibolite 

~ Amphibolite Foliation 

~ Biotite-garnet schist 

8 Micaceous quartzite 

0 Graphitic phyllite 

"t. Fold axial plane 

-< Mine adit 

x Prospect 

c ..-.\ H =Humboldt · Open pit mine 

l[ 

Gastineau 

Peak 

y 

~ Greenschist (metabasalt) 

----Fault N:::: North, S = South, 

Contact P =Perseverance 

!KILOMETER 

Figure 1.--Bedrock geologic map of Alaska-Juneau mine area, Juneau quadrangle, Alaska. Modified from 

Wernecke (1932), Twenhofel (1952), Ford and Brew (1973), Brew and Ford (1977), based on mapping 1985-

1986. Topographic base and prospect locations from USGS 1:24,000 Juneau and vicinity map, 1948. 

crosscutting features. We recognize two major 

varieties: ankerite-altered amphibolite and 

ankerite-altered greenschist. Map relations (fig. 

1) indicate that biotite-ankerite rocks surround 

amphibolite (meta-diorite/gabbro) sills in the 

vicinity of orebodies. Detailed mapping indicates 

that contacts between foliated amphibolite and 

laminated biotite-ankerite rock are gradational 

over 1-3 m; these contacts also commonly cut 

across foliation. Quartz veins with biotiteankerite margins are present in amphibolites; 

although the veins distinctly crosscut foliation in 

the amphibolite, the biotite-ankerite margins 

possess the foliation of the rock they replace. 

Similarly, 1- to 5-m blocks of unaltered, ankeritefree greenstone occur within the ankeritechlorite-biotite altered greenschist unit (unit "ags" 

on fig. 1). The presence of unaltered remnant 

blocks with the same foliation attitude indicates 

that the foliation is pseudomorphous after the 

original foliation. Finally, post-metamorphic 

quartz veins are found only within phyllites, 

altered greenschists, and altered amphibolites, 

129 

which implies that the ankerite-biotite alteration 

is related to the post-metamorphic veins and that 

both are products of broad-scale postmetamorphic hydrothermal activity. 

Pyrrhotite-pyrite relations provide further 

evidence of a hydrothermal ortgm for the 

alteration and veins. Petrographic examination of 

the altered rocks from the AJ area indicates a 

consistent alteration assemblage of ankeritepyrrhoti te-ilmeni te±bioti te-chlori te-rn uscovi tetourmaline. Pyrite is rare and only occurs as a 

late phase in quartz veins, whereas pyrrhotite is 

ubiquitous. The assemblage ilmenite-pyrrhotite is 

not reported from metamorphosed volcanogenic 

deposits but is described from mesothermal vein 

deposits (Ramdohr, 1980). Indeed, pyrrhotite is 

not the dominant iron sulfide in any 

unmetamorphosed volcanogenic sulfide deposit, 

and metamorphism to granulite facies is required 

to convert the bulk of pyrite to pyrrhotite in 

volcanogenic sulfide deposits (Rockingham and 

Hutchison, 1980). For example, the Homestake 

deposit, which has been metamorphosed to 
Table 1.--Gold contents of rocks from the Alaska-Juneau mine area, Juneau quadrangle, southeastern Alaska 

[Analyses by atomic absorption; N, not detected at 50 ppb (0.05 ppm) detection limit; L, detected, but below 

50 ppb; abbreviations: qtz, quartz; po, pyrrhotite; bio, biotite; ank, ankerite; gl, galena; chl, chlorite; tour, 

tourmaline; alt'd, altered] 

Sample 

No. 

Au 

(ppm) Rock type and alteration Location 

Black phyllite 

Carbonate rock 

300 m SW of N pit 

N pit 

85Rnl16a 

85Rn124b 

85 Rn124c 

85Rn124d 

85 Rn124e 

85Rn124f 

85Rn130b 

85Rn131a 

85Rn140 

85Rn140c 

85Rn183b 

85Rn184a 

85Rn192a 

85Rn194a 

86Rn24a 

N 

N 

N 

L 

N 

Chert, interlayered with carbonate 

Black phyllite with qtz-po-bio veins 

Alt'd amphibolite 

N pit 

N pit 

N pit 0.1 

N 

Alt'd amphibolite with qtz-ank veins N pit 

70 

N 

N 

N 

N 

N 

N 

Qtz-po (5%)-musc-cal vein in phyllite 

Qtz-po-gl-ank vein in bio-alt'd amphibolite 

Composite of 500 m of chl-alt'd greenschist 

3 m thick felsic vole in greenschists 

Uground, N orebody 

Uground, N orebody 

Gold Ck. at the Horn 

Gold Ck. at the Horn 

Chl alt'd amphibolite Near Mt. Juneau 

Ankeritic schist (alt'd greenschist) 

Chl alt'd amphibolite 

Mt,. Juneau 

Near Sheep Mtn. 

Near Mt. Roberts 

Mt. Juneau 

Marble 

0.1 Qz-ank-tour veins in ank alt'd greenschist 

amphibolite facies, contains subequal pyrite and 

pyrrhotite (Slaughter, 1968). The stratabound 

Morro Velho gold deposit (Brazil), metamorphosed 

to mid greenschist facies, also has high pyrite 

contents (Gair, 1962). Since there is no evidence 

that rocks of the AJ area have been 

metamorphosed higher than amphibolite facies 

(Brew and Ford, 1985), a metamorphic origin for 

the pyrrhotite is unlikely. Tourmaline has been 

noted at approximately 18 localities in the AJ 

area; it occurs exclusively in the altered rocks and 

is in all of the alteration types. Although 

tourmaline occurs with some stratabound gold 

deposits (Slaughter, 1968) and with some 

volcanogenic sulfide deposits (Taylor and Slack, 

1984), it is also very common with mesothermal 

gold vein deposits (Hodgson and MacGeehan, 1982) 

and with geothermal systems (Watanabe, 1967) and 

is thus not a diagnostic feature of either type of 

deposit. In general, the occurrence of a consistent 

opaque-silicate assemblage in all the altered rocks 

of the AJ area points to a single hydrothermal 

system; the fact that much of this alteration is 

demonstrably post-metamorphic suggests that it is 

all post-metamorphic. 

We have evaluated the possibility of 

stratiform gold enrichment by reconnaissance 

sampling of the rocks in the AJ area; the results 

(table 1) indicate that (1) altered rocks with quartz 

veins contain gold values equal or greater than 0.1 

ppm, (2) altered rocks (such as foliated ankeritebearing rocks) which lack quartz veins contain low 

(less than 0.5 ppm) gold values, and that (3) 

unaltered rocks (such as metacherts and marbles) 

130 

also contain low gold values. In contrast, 

stratabound gold deposits commonly contain gold 

concentrations of 10 ppm in non-veined rocks 

(Barnett and others, 1982) and background Au 

values for most rocks are approximately 0.01-

0.005 ppm. Although our conclusions are limited 

by the detection limits of the analytical method 

used, the fact that only quartz-carbonate-veined 

rocks contain significant gold values suggests that 

gold was introduced into the rocks during veining, 

not remobilized from the rocks during veining. 

In summary, the available evidence supports 

an epigenetic origin for the alteration and 

mineralization in the AJ area, and by inference, an 

exotic origin for the gold in the deposit. The map 

data also indicate that several cubic kilometers of 

ankeritic alteration resulted from the large 

hydrothermal system that operated in the AJ mine 

area. Goldfarb and others (1986) presented 

evidence for fluid boiling in the AJ veins and 

for vein formation at greater than 230° C and 

1.5 kilobars. Such boiling results in C02 loss 

and carbonate deposition. We suggest that the 

accompanying loss of H2S during boiling would 

result in Au deposition by decomplexation of 

Au(HS), as the experimental data on gold solubility 

in H2S-bearing fluids (Seward, 1973) indicate 

that Au solubility drops by 2 orders of magnitude 

for every order of magnitude decrease in H2S 

activity. In addition, gold solubility is sufficient1y 

high under the proposed conditions of deposition 

(approximately 1-0.1 ppm; Seward, 1973) for 

circulating fluids to leach gold from any subjacent 

rock types. The establishment of the required 
hydrothermal cell necessitates a major structural 

anomaly, and we suggest therefore that structural 

controls probably represent a dominant influence 

on the development of ores in the area. 

REFERENCES CITED 

Barnett, E.S., Hutchinson, R. W ., Adamcik, Anton, 

and Barnett, R.J., 1982, Geology of the 

Agnico-Eagle gold deposit, Quebec, in 

Hutchinson, R. W ., Spence, C.D., and Franklin, 

J.M., eds., Precambrian sulfide deposits: 

Geological Association of Canada Special 

Paper 25, p. 403-426. 

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. 

___ 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. 

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. 

Gair, J.E., 1962, Geology and ore deposits of the 

Nova Lima and Rio Acima quadrangles, Minas 

Gerais, Brazil: U.S. Geological Survey 

Professional Paper 341-A, p. A1-A65. 

Goldfarb, R.J., Light, T.D., and Leach, D.L., 1986, 

Nature of the ore fluids at the Alaska-Juneau 

gold deposit, in Bartsch-Winkler, 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. 

Herreid, Gordon, 1962, Preliminary report on 

geologic mapping in the Coast Range mineral 

belt: Alaska Division of Mines and Minerals 

Geologic Report 1, 22 p. 

131 

Hodgson, C.J., and MacGeehan, P.J., 1982, A 

review of the geological characteristics of 

"gold-only" deposits in the Superior Province 

of the Canadian shield: Canadian Institute of 

Mining and Metallurgy, Special Vol. 24, 

p. 211-229. 

Ramdohr, Paul, 1980, The ore minerals and their 

intergrowths, 2d edition: Oxford, U.K., 

Pergamon, 1205 p. 

Rockingham, C.J ., and Hutchison, R. W ., 1980, 

Metamorphic textures in Archean copper-zinc 

massive sulfide deposits: Canadian Institute 

of Mining and Metallurgy Bulletin, v. 73, 

p. 104-112. 

Seward, T.M., 1973, Thio complexes of gold and 

the transport of gold in hydrothermal ore 

solutions: Geochemica et Cosmochimica 

Acta, v. 37, p. 379-401. 

Slaughter, A.L., 1968, The Homestake mine, in 

Ridge, J.D., ed., Ore deposits of the United 

States: New York, American Institute of 

Mining Engineers, p. 1436-1459. 

Taylor, B.E., and Slack, J.F., 1984, Tourmalines 

from Appalachian-Caledonian massive sulfide 

deposits: Textural, chemical, and isotopic 

relationships: Economic Geology, v. 79, 

p. 1703-1726. 

Twenhofel, W .S., 1952, Geology of the AlaskaJuneau lode system, Alaska: U.S. Geological 

Survey Open-File Report 52-160, 170 p. 

Watanabe, Takeo, 1967, Geochemical cycle and 

concentration of boron in the earth's crust, in 

Vingradov, A.P., ed., Chemistry of the earth's 

crust, Vol. II: Jerusalem, Israel Program for 

Scientific Translations, p. 167-178. 

Wayland, R.G., 1960, The Alaska Juneau gold ore 

body: Neues Jahrbuch fiir Mineralogie 

Abhandlungen v. 94, p. 267-279. 

Wernecke, Livington, 1932, Geology of the ore 

zones: Engineering and Mining Journal, 

v. 133, p. 494-499. 

Reviewers: R.P. Ashley and W .H. Nelson 

• 
PALEOMAGNETIC EVIDENCE FOR A 

LATEST PLIOCENE AND EARLY PLEISTOCENE 

AGE OF THE UPPER YAKATAGA FORMATION 

ON MIDDLETON ISLAND, ALASKA 

Edward A. Mankinen and George Plafker 

The Yakataga Formation, along the northern 

Gulf of Alaska margin, records late Cenozoic 

glaciation in a sequence with an aggregate outcrop 

thickness of about 5,000 m (Plafker and Addicott, 

1976). The youngest part of the Yakataga 

Formation (1,170 m thick) exposed in outcrop is on 

Middleton Island, located in the Gulf of Alaska 

approximately 130 km southwest of Cordova 

(fig. 1). 

A reconnaissance paleomagnetic sampling of 

the Yakataga Formation on Middleton Island was 

made in 1967 by R.R. Doell and George Plafker. 

Encouraged by preliminary results from that study, 

we revisited the island with Doell in 1970 to try to 

sample a geomagnetic polarity transition in this 

thick and rapidly deposited sequence and to refine 

the age of the sequence. We collected samples for 

paleomagnetic analysis from sections exposed on 

intertidal reefs at the southwest and northeast 

ends of the island that were well exposed as a 

result of tectonic uplift of about 4 m during the 

1964 Alaskan earthquake. At the same time, we 

described the stratigraphy of these sections and 

collected samples for paleontological study. 

Although we were unable to sample across a 

polarity transition in detail, our paleomagnetic 

results provide the best age data presently 

available on the Middleton Island section and 

indicate that it is latest Pliocene and early 

Pleistocene in age. 

The Yakataga Formation at Middleton Island 

is made up mainly of poorly to moderately 

indurated siliciclastic sedimentary rocks of both 

marine and glaciomarine origin (Miller, 1953; 

Plafker and Addicott, 1976; Plafker, 1981; Eyles 

and others, 1985). Measured sections on the 

southwest and northeast ends of the island are 

1,170 m and 585 m thick, respectively (figs. 1 and 

2). The sequence consists primarily of thick, 

massive beds of till-like, mud-matrix diamictite 

(86 percent), subordinate amounts of lenticular, 

channel-fill conglomerate (9 percent) with sand or 

sandy-mud matrix, and minor sandstone, siltstone, 

and mudstone. Scattered boulder- to pebble-size 

clasts, some of which have faceted and striated 

surfaces and are interpreted as dropstones, are 

present in all lithologic types, but especially in the 

diamictite and the laminated siltstone or 

mudstone. Fine-grained sediment that composes 

the diamictite matrix, as well as most of the 

siltstone and mudstone, was primarily derived as 

glacial rock flour from coastal glaciers and 

floating ice. 

The combined paleontologic and 

sedimentologic data suggest a cold, shallow-water, 

132 

inner to middle sublittoral depositional 

environment for the Yakataga Formation at 

Middleton Island. Sediment derived from the 

mainland to the north was deposited in a shallow 

shelf basin that received variable amounts of 

glaciomarine detritus. The occurrence of both a 

massive conglomerate interpreted as a subglacial 

channel fill and striated pavements in the section 

indicate that ice sheets extended across the shelf 

to Middleton Island during deposition of the upper 

part of the section (Plafker and Addicott, 1976, p. 

29-30). Local disconformities in the section are 

marked by thin horizons of well-sorted sandstone 

and conglomerate with abundant mollusks (fig. 2). 

Paleontologic dating of the abundant fauna 

in the formation has been inhibited by a high 

degree of faunal provincialism coupled with the 

tendency for the late Cenozoic cold-water forms 

to be unusually long-ranging in time. The base of 

the formation at Cape Yakataga on the mainland 

has not been dated more closely than early middle 

Miocene to late Miocene (Plafker, 1986). 

Mollusks, foraminifers, siliceous microorganisms, 

and ostracodes from the highest exposed part of 

the formation at Middleton Island are considered 

to be of probable Pleistocene (Miller, 1953; 

Addicott and others, 1978) or Pliocene and 

Pleistocene age (Plafker and Addicott, 1976; Rau 

and others, 1983). A sparse nannofossil fauna, 

including the short-ranging species Gephyrocapsa 

caribbeanica Boudreaux and Hay from near the top 

of the section is of Pleistocene age (David Bukry, 

USGS, written commun., 1972). 

Our detailed magnetostratigraphy on 

Middleton Island was based on one sample per 

horizon in the northeast section and 3 or 4 samples 

per horizon, laterally separated by approximately 

one meter, in the southwest section. A total of 

161 separate horizons were sampled throughout 

the two sections (fig. 2). Paleomagnetic samples 

were obtained with a portable core drill and were 

oriented using a magnetic compass. Remanence 

measurements were made using spinner 

magnetometers, and samples were magnetically 

cleaned in alternating fields using tumbling 

demagnetizers. Only four of the horizons from 

which multiple cores were obtained had mean 

magnetization directions that failed to satisfy the 

Vincenz and Bruckshaw (1960) test for nonrandomness, and these were omitted when 

determining the magnetic stratigraphy. 

Acceptable mean directions were transformed to 

virtual geomagnetic poles (VGP) according to the 

magnetic dipole formula. 

A magnetic polarity was initially assigned to 

each horizon on the basis of its VGP latitude (fig. 

2). However, because of the considerable 

variation in the precision of the magnetic 

directions and the large deviations away from the 

expected local field direction in our data set, an 

erroneous polarity assignment could result if based 

solely on the VGP latitude. For this reason, a 
) ,. r·, 

) 

/ 

APPROXIMATE MEAN MEAN HIGHER HIGH WATER~· / 

LOWER LOW WATER" _.... .· 

)l ..--· 

/·...__;- --· -· ......._ .-·· 

---- -----

" · ........ ___ ·-

0 05 1.0 

KILOMETER 

Figure 1.--Map of Middleton Island showing locations of measured and sampled sections of the upper 

Yakataga Formation (dashed). Numerals indicate thickness in meters and correspond to section thickness 

shown on figure 2. Dotted intervals are zones of normal polarity corresponding to those shown on figure 

2. Long dashed lines indicate strike of resistant beds; heavy black line is a normal fault (D, downthrown; 

U, upthrown). 

reversal of polarity was assumed only if a definite 

switch in both inclination and declination 

accompanied a change of VGP latitude from one 

hemisphere to another. 

A similar pattern of magnetozones in both 

sections (fig. 2) indicates that the normal 

polarities are not the result of a recent, postfolding remagnetization. However, the 

magnetozones in the two sections do not appear to 

match if the bedding trends are extrapolated to 

the southwest end of the island. The mismatch 

could result from offset of the sequence by the 

normal fault at that end of the island (fig. 1) or 

from an unrecognized angular unconformity. A 

short, normal-polarity interval was recorded by 

two horizons with a stratigraphic separation of 

about 5.5 m in the northeast section, but the same 

interval was not sampled in the southwest 

section. The thickness of the reversed 

magnetozone at about 700-800 m in the southwest 

section is not well determined because the coarsegrained diamictite in this part of the section made 

sampling difficult. The sediment character 

suggests to us that this particular magnetozone 

may not represent as much time as might be 

inferred by its apparent thickness. Three short, 

normal-polarity magnetozones are indicated near 

the bottom of the southwest section. Because 

Pliocene and Pleistocene fossils have been found in 

these sections and no major unconformities are 

evident, the predominance of reversed polarities 

throughout the sequence indicates deposition 

during the latter part of the Matuyama ReversedPolarity Chron. The Matuyama is the only 

extended period of reversed polarity during the 

late Pliocene and Pleistocene (Mankinen and 

Dalrymple, 1979). 

The magnetozones determined for the two 

sections are compared to the geomagnetic polarity 

time scale in figure 3. The three short, normalpolarity intervals near the bottom of the 

southwest section can be correlated with the 

Reunion Normal-Polarity Subchron. However, the 

number and durations of the Reunion intervals are 

still uncertain, although available evidence 

indicates that there are probably two and possibly 

three (Mankinen and Dalrymple, 1979). The 

youngest normal-polarity interval in the northeast 

section probably represents the Cobb Mountain 

Subchron, currently the only one identified as 

occurring in this part of the Matuyama. The 

interval is too thin to realistically be considered as 

representing the Jaramillo Normal-Polarity 

Subchron, especially since other normal-polarity 

magnetozones in the section are considerably 

thicker. 

The two larger, normal-polarity intervals in 

both sections can be interpreted in two ways. In 

the first (alternative 1 in fig. 3), the top of the 

longest interval is considered to be the top of the 

Olduvai Normal-Polarity Subchron and the younger 

interval possibly represents an undocumented 

episode at about 1.55 Ma. Evidence for the 

younger episode may have been found in eastcentral Arizona by Castro and others (1983), who 

reported several normal-polarity lava flows 

133 
EXPLANATION 

~ Diamict1te 

~ Mudstone and siltstone 

D Sandstone 

0 Conglomerate 

o Disconform1ty 

Polarity 

E +---NORMAL 

+---REVERSED 

TUDE 

Figure 2.--Generalized stratigraphic sections of the upper Yakataga Formation and corresponding virtual 

geomagnetic pole (VGP) latitude, and interpreted magnetic polarity (POL). Locations shown on figure 1. 

134 
yielding radiometric ages of about 1.5 Ma. 

However, this possible correlation should be 

considered tentative because their full report is 

still unpublished. Additional evidence for a short 

normal-polarity interval following the Olduvai 

Subchron has been found in deep-sea cores 

(Opdyke, 1972; Clement and Kent, 1985) and in an 

onshore sedimentary sequence in Pakistan 

(Burbank and Tahirkheli, 1985). 

The second alternative (fig. 3) considers the 

reversed-polarity interval to be an episode within 

the Olduvai. Some evidence for such an episode 

has been noted in onshore sedimentary sequences 

(Theyer and others, 1985; Seward and others, 1986) 

and appears to be present in some deep-sea cores 

(Glass and others, 1967). Thus, some evidence to 

support both alternatives has been published, but 

none can be considered conclusive. 

Regardless of which alternative best explains 

the two thickest, normal-polarity magnetozones 

(N2 and N3), it is evident that the sequence that 

was sampled paleomagnetically spans a period of 

more than 1 million years from just before the 

oldest Reunion interval (2.14 Ma) to some time 

between the Jaramillo (0.97 Ma) and Cobb 

Mountain (1.10 Ma). This corresponds with the 

latest Pliocene and early part of the Pleistocene 

Epochs (Berggren and others, 1985). 

If our correlations to the polarity time scale 

are correct, rough estimates of sedimentation 

rates for part of the Yakataga Formation on 

Middleton Island can be made. The interval 

between the Cobb Mountain and Olduvai in the 

northeast section must have been deposited at an 

average rate of about 70 cm/ka (1,000 yr) using 

alternative 1 in figure 3, or about 60 cm/ka using 

alternative 2. Only the lower part of the 

southwest section is well constrained (between the 

top of the Olduvai and the bottom of the Reunion), 

and rates of 45 cm/ka or 70 cm/ka can be 

calculated using alternatives 1 and 2, respectively. 

REFERENCES CITED 

Addicott, W.O., Winkler, G.R., and Plafker, 

George, 1978, Preliminary megafossil 

biostratigraphy and correlation of selected 

stratigraphic sections of the Gulf of Alaska 

Tertiary province: U.S. Geological Survey 

Open-File Report 78-491, 2 plates. 

Berggren, W.A., Kent, D.V., Flynn, J.J., and Van 

Couvering, J.A., 1985, Cenozoic 

geochronology: Geological Society of 

America Bulletin, v. 96, p. 1407-1418. 

Burbank, D.W., and Tahirkheli, R.A.K., 1985, The 

magnetostratigraphy, fission-track dating, and 

stratigraphic evolution of the Peshawar 

intermontane basin, northern Pakistan: 

Geological Society of America Bulletin, v. 96, 

p. 539-552. 

135 

Polarity Time-Scale 

BRUNHES 

CD 

~~---""" ... uo Cobb Mtn 

MATUYAMA 

REVERSED 

POLARITY 

CHRON 

Figure 3. --Correlation of magnetozones of 

northeast and southwest sections sampled on 

Middleton Island with portion of geomagnetic 

polarity time scale of Mankinen and Dalrymple 

(1979) modified by addition of the Cobb Mountain 

Normal-Polarity Subchron (Mankinen and others, 

1978; Mankinen and Gromme, 1982). Solid 

intervals correspond to periods of normal 

polarity. 1 and 2 are alternative interpretations of 

magnetozones in lower part of both sections (see 

text). 

Castro, Joyce, Brown, Laurie, and Condit, C.D., 

1983, Paleomagnetic results from the 

Springerville-Show Low volcanic field, eastcentral Arizona: Eos (Transactions American 

Geophysical Union), v-. 64, p. 689. 

Clement, B.M., and Kent, D. V., 1985, Details of 

short geomagnetic polarity chronozones as 

recorded at DSDP site 609: Eos (Transactions 

American Geophysical Union), v. 66, p. 872. 
Eyles, C.H., Eyles, Nicholas, and Miall, A.D., 1985, 

Models of glaciomarine sedimentation and 

their application to the interpretation of 

ancient glacial sequences: Palaeogeography, 

Palaeoclimatology, Palaeoecology, v. 51, 

p. 15-84. 

Glass, B., Ericson, D.B., Heezen, B.C., Opdyke, 

N.D., and Glass, J.A., 1967, Geomagnetic 

reversals and Pleistocene chronology: Nature, 

v. 216, p. 437-442. 

Mankinen, E.A., and Dalrymple, G.B., 1979, 

Revised geomagnetic polarity time scale for 

the interval 0-5 m.y. B.P.: Journal of 

Geophysical Research, v. 84, p. 615-626. 

Mankinen, E.A., Donnelly, J.M., and Gromme, 

C.S., 1978, Geomagnetic polarity event 

recorded at 1.1 m.y. B.P. on Cobb Mountain, 

Clear Lake volcanic field, California: 

Geology, v. 6, p. 653-656. 

Mankinen, E.A., and Gromme, C.S., 1982, 

Paleomagnetic data from the Coso Range, 

California and current status of the Cobb 

Mountain normal geomagnetic polarity 

event: Geophysical Research Letters, v. 9, 

p. 1279-1282. 

Miller, D.J., 1953, Late Cenozoic marine glacial 

sediments and marine terraces of Middleton 

Island, Alaska: Journal of Geology, v. 61, p. 

17-40. 

Opdyke, N.D., 1972, Paleomagnetism of deep-sea 

cores: Reviews of Geophysics and Space 

Physics, v. 10, p. 213-149. 

Plafker, George, 1981, Late Cenozoic 

glaciomarine deposits in the Yakataga 

Formation, Alaska, in Hambrey, M.J., and 

Harland, W.B., eds., Earth's pre-Pleistocene 

glacial record: New York, Cambridge 

University Press, p. 694-699. 

___ in press, 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--Beaufort Sea to Baja California: 

Circum-Pacific Council for Energy and 

Mineral Resources, Earth Science Series NoPlafker, George, and Addicott, W.O., 1976, 

Glaciomarine deposits of Miocene through 

Holocene. age in the Yakataga Formation 

along the Gulf of Alaska margin, in Miller, 

T.P., ed., Recent and ancient sedimentary 

environments in Alaska: Anchorage, Alaska 

Geological Society, p. Q1-Q23. 

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 Oil and Gas 

Investigations Chart OC-120. 

Seward, Diane, Christoffel, D.A., and Lienert, B., 

1986, Magnetic polarity stratigraphy of a 

Plio-Pleistocene marine sequence of North 

Island, New Zealand: Earth and Planetary 

Science Letters, v. 80, p. 353-360. 

Theyer, Fritz, Burbank, Doug, Lund, S.P ., and 

McRaney, John, 1985, High-resolution 

magnetic field transitions and related secular 

variation from Matuyama-aged lake sediments 

in Kashmir, India: Eos (Transactions 

American Geophysical Union), v. 66, p. 872. 

Vincenz, S.A., and Bruckshaw, J. MeG., 1960, Note 

on the probability distribution of a small 

number of vectors: Proceedings Cambridge 

Philosophical Society, v. 56, p. 21-26. 

Reviewers: J. W. Hillhouse and L.N. Marincovich 

136 
CENOZOIC MAGMATISM IN 

SOUTHEASTERN ALASKA 

(ABSTRACT) 

David A. Brew 

A recently completed synthesis indicates 

that late Mesozoic and Cenozoic magmatic belts 

cover most of southeastern Alaska (fig. 1), but 

they are concentrated in the Chugach terrane in 

the western part of the region, in the western part 

of the Alexander terrane mainly adjacent to the 

Chugach terrane, and along the Alexander-Stikine 

terrane boundary in the Coast Mountains. The late 

Mesozoic and Cenozoic magmatic events are part 

of a continuum that began in the Jurassic. 

Early(?) and Middle Jurassic magmatic events 

formed the roots and extrusive products of a 

Jurassic-Cretaceous arc developed on the 

Alexander terrane; these are the 180 Ma to 110 Ma 

granitic events. Their distribution are not shown 

on the map. Linear belts of plutons in the middle 

and Late Cretaceous coincided spatially with the 

Lower and middle Cretaceous flysch- and volcanic 

rock-filled rift between the Alexander and Stikine 

terranes; these are the 110 Ma ultramafic event 

and the 100 Ma and 90 Ma granitic events. Their 

distributions are also not shown on the map. 

Latest Cretaceous and Cenozoic magmatic 

events are indicated by mostly plutonic rocks 

related to the collision of the Chugach terrane 

with the Alexander/Wrangellia terrane; these are 

the 70-55 Ma, 55-45 Ma, and 45-35 Ma granitic 

events (fig. 1). Subsequent volcanic and plutonic 

activity of the 35-5 Ma events was related to the 

transition from collision to regional extension. 

These events were followed by the volcanic and 

plutonic activity of the 5-0 Ma events, which 

accompanied transform movement on Pacific plate 

bounding faults. 

The products of these latest Cretaceous and 

Cenozoic magmatic events form distinct belts that 

cover much of the region. The 70-55 Ma events 

were concentrated in a narrow belt inboard (east) 

of the Alexander terrane and adjacent to (but 

almost entirely west of) the locus of intrusion of 

the 55-45 Ma events. Activity then shifted to the 

Chugach terrane on the outboard (west) side of the 

Alexander terrane for the 45-35 Ma events and 

shifted eastward onto the Alexander terrane 

during the end of that episode. The 35-5 Ma 

volcanic and plutonic events are concentrated in a 

lengthy belt that cuts across the previously 

established regional structures and 

tectonostratigraphic terranes. The youngest 

volcanic events (less than 5 Ma) also may be 

137 

YUKON 

PACIFIC 

OCEAN 

YUKON ------ ----BC--

? __ !~P KILOMETERS 

Figure I.--Cenozoic magmatic belts of southeastern Alaska. 120 km of right-lateral (northsouth) separation on Lynn Canal-Chatham Strait 

fault has been removed. 

interpreted to form a crude discontinuous belt 

across all previous emplaced tectonostratigraphic 

terranes and magmatic belts. 

Rocks of the latest Cretaceous through 

Holocene episodes have a wide variety of chemical 

and modal compositions, but most are calc-alkalic 

except for parts of the 5-35 Ma episode, which are 

alkalic to peralkalic, and the youngest (less than 5 

Ma) episode, which is alkalic. Different segments 

of the linear plutonic belts are dominantly 

metaluminous, mixed metaluminous and 

peraluminous, or peraluminous. These 

compositional contrasts, as well as different 

orientations of some of the belts, may be related 

to thickness and composition of the subducted slab 

and overlying crust. Available rare-earth- and 

trace-element information shows moderately 

fractionated patterns and arc affinities for all but 

the youngest magmatic episode. 

Reviewers: R.D. Koch and J.G. Smith 
OFFSHORE 

Diver resting on wave-agitated slush ice during studies of ice rafting in the Beaufort Sea. 

Photo by P. W. Barnes. 

138 
BEAUFORT SEA COASTAL CURRENTS: 

A DIVERGENCE NEAR BARTER 

ISLAND, ALASKA? 

Peter W. Barnes, Scot Graves, and Erk Reimnitz 

Several lines of evidence suggest that water 

on the Beaufort Sea shelf may flow eastward and 

westward from a divergence located near Barter 

Island (fig. 1). First, ice gouges on the Alaskan 

sector of the shelf are created mostly by ice keels 

plowing east to west, subparallel to the coastline 

(Barnes and others, 1984). In contrast, gouges on 

the Canadian Beaufort shelf are dominantly 

formed by ice plowing from west to east (Harper 

and Penland, 1982). Second, on the Alaskan shelf, 

surface currents are wind-driven and generally 

flow to the west (Aagaard, 1984), whereas off 

northwestern Canada, easterly-flowing currents 

dominate (Harper and Penland, 1982). Third, in 

1972 surface drifters were released on the Alaskan 

shelf between Barter Island and Point Barrow 

(Barnes and Toimil, 1979). Most of the drifters 

traveled westward; however, several drifters 

originating from the easternmost drop-points 

moved eastward into Canada. 

The location and character of the suggested 

divergence has not been documented, although its 

presence would have significant impact on the 

interpretation of westward or eastward pollutant 

pathways on the shelf of the Alaskan and Canadian 

Beaufort Sea (Thomas, 1984). As part of an 

ongoing study of inner shelf circulation patterns, 

sediment transport, and nearshore processes in the 

Alaskan Beaufort Sea, we released 1,000 seasurface and 1,000 seafloor drifters between 

Camden and Demarcation Bays off northern 

Alaska in August 1983 (table 1, fig. 2). The 

drifters were designed to move with the surface 

and bottom currents, with some portion carried 

BEAUFORT SEA 

Figure I.--Location map of study area showing 

dominant directions of ice gouging and prevailing 

shelf currents. 

139 

Table 1.--Summary information on drifter release 

and recovery 

Date 

released 

Released from 

coastal vessel, 

8/7-8/83 

Released from 

low flying aircraft, 

8/18/83 

Total 

Re 1 eased from 

coastal vessel, 

8/7-8/83 

Re 1 eased from 

low flying aircraft, 

8/18/83 

Total 

Number 

released 

400 

600 

1,000 

400 

600 

1,000 

Number Percent 

recovered recovered 

Surface drifters 

24 6.0 

22 3.6 

46 4.6 

Bottom drifters 

33 8.2 

6 1.0 

39 3.9 

ashore where the finder would report the location 

and serial number. Information on shelf current 

speed and direction can be inferred from a 

knowledge of timing and locations of deployment 

and recovery, and of the assumed drifter 

trajectories. A major goal of this drifter release 

was to better define the suggested divergence in 

water motion between the Alaskan and Canadian 

Beaufort Seas. 

Virtually all of the 85 drifters recovered 

through the fall of 1985 from the 1983 release 

traveled east (fig. 2). This is a true representation 

of the drift as one of us (ER) flew along the entire 

coastline in 1984 collecting drifters. Coastal 

travel by the local population (and drifter 

recovery) commonly occurs westward from the 

village at Barter Island. A few of the drifters 

traveled several hundred kilometers to recovery 

sites well east of Herschel Island while others 

traveled the few kilometers to the coast (fig. 2). 

Recoveries indicate the dominance of eastward 

drift in this part of the Beaufort Sea. Drifters 

recovered during 1984 and 1985 may have been 

stranded at their recovery site since 1983. 

Recovery locations logged during the two 

months following drifter release (August and 

September 1983) and prior to winter freeze-up 

provided trajectory endpoints for velocity 

calculations. The data on 15 surface and 9 bottom 

drifters from 12 release points provide minimum 

travel time and travel distance, which was used to 

estimate minimum current velocities during the 

fall of 1983 (table 2). Estimates of current 
.... 

~ 

c 

70° 

145° 

EXPLANATION 

• Drifter release location 

Drifter recoverY location 

...------------ Assumed drifter trajectories 

143° 

BEAUFORT SEA 

141° 

\ 

<·< 

~·o 

r./)\c:( <Z 

_.Jc:( 

139° 

-50-- 50 meter isobath 

0 50 KILOMETERS <:o 

s9" e- · ' ' ~ I 

l.'tgure z.-Reg\onal map of study area locating drifter release stations and idealized trajectories of 

drifters recovered through 1985. 
Table 2.--Drifter speed and displacement 

Surface drifters Bottom drifters 

max. min. avg. max. min. avg. 

Speed (em/ s) 18.2 0.3 6.3 16 .o 0.3 3.7 

Distance ( km) 154 45.8 137 31.8 

velocity generated from these data are mm1mum 

values as the drifters may have been discovered 

some time after the drifter had reached shore. 

Based on drifters recovered prior to the freeze-up 

in the fall of 1983, the minimum eastward 

velocities for surface and near-bottom waters are 

between 0.3 and 18.2 cm/s and averaged about 5 

cm/s over distances up to 154 km. The low 

velocities recorded for most inshore drifters may 

not reflect slow coastal currents, but may reflect 

the sparse human population along the coast in the 

study area. The highest current velocity values 

calculated were those indicated by the recovery of 

drifters released along the two offshore lines. The 

bottom drifters showed no difference in direction 

of travel, although the velocities averaged about 

half the speed of the surface drifters. 

Prevailing winds have a major impact on 

shelf currents and sea level in the Alaskan 

Beaufort Sea, as astronomic tides are only 10-20 

em; strong westerlies raise sea level and easterlies 

lower it (Barnes and Toimil, 1979). Therefore 

currents flow parallel to the coast, driven by the 

winds (Aagaard, 1984). As a result, debris and 

drifters at the shoreline during westerly storms 

will strand higher on the beaches than debris left 

from easterly wind events. Thus, a majority of the 

flotsam, and drifters, found along the Beaufort Sea 

coasts may reflect a preservation biasing of 

eastward transport events from westerly winds. 

Although the western Beaufort Sea off 

Alaska experiences mostly northeasterly winds 

during the summer (Barnes and Toimil, 1979), the 

distribution of summer winds along the eastern 

Beaufort Sea coast indicate winds from both the 

west and east (fig. 3). The westerly winds at 

Barter Island are related to the effect of mountain 

topography (Kozo and Robe, 1986); thus, the 

movement of our drifters to the east does not 

violate the summer wind pattern. The wind data 

(fig. 3), however, also show a significant easterly 

component that is not seen in the movement of 

either our surface or bottom drifters (fig. 2). We 

believe that the the bulk of the recovered drifters 

moved rather swiftly eastward (table 2) and 

stranded during the persistent westerly winds that 

followed their deployment in 1983 (Kozo and Robe, 

1986). The lack of westward drift indicated by 

figure 2 suggests that the drifters stranded during 

the 1983 period of westerly winds and have not 

been available for westward transport since that 

time. 

141 

The ocean becomes ice-covered subsequent 

to freeze-up in October, and surface drifters 

would be arrested until breakup the following 

July. Little is known about currents acting 

beneath the ice canopy on the shelf (Aagaard, 

1984), thus the movement of bottom drifters 

during the period of ice cover is not well 

understood. Because it is quite conceivable that 

many of the drifters, both surface and seafloor 

types, are in corpora ted in the seasonal ice canopy, 

our trajectory data may incorporate the motion of 

ice. In the winter, that portion of the ice cover 

not held fast to the land may move westward with 

the prevailing winds and ice motions (Aagaard, 

1984; Kozo and Robe, 1986). Drifters incorporated 

in the ice may be displaced and re-released far to 

the west or even carried entirely out of the 

Alaskan Beaufort Sea. 

The divergence suggested by the earlier 

drifter studies (Barnes and Toimil, 1979) and by 

the ice gouge orientations remains unconfirmed. 

In the present study the shelf, currents responded 

to forcing from westerly winds. As westerly winds 

are a major component of the wind regime in the 

eastern Beaufort Sea (fig. 3), we predict that 

eastward flowing currents would be a major 

component of the current regime. As the wind and 

current data on the western Beaufort Sea shelf 

2 3 4 5 

Barter Komakuk Shingle Tuktoyaktuk Sachs 

Island Beach Point Harbour 

only) EXPLANATION 

[3] Annual winds 0 Summer winds 

Figure 3.--Beaufort Sea showing annual and 

summer (open water) winds along coast of eastern 

Beaufort Sea. Data from NOAA climatologic 

summaries and Harper and Penland (1982). 
(Barnes and Toimil, 1979) indicate that westward 

currents would dominate, the need for a zone of 

divergence between these two regimes still exists. 

Drifters caught up in the landfast ice, on the 

other hand, may be held in position during the 

winter and re-released in the spring, fairly near 

their position of capture in the autumn. Landfast 

ice is of shallow draft, and thus, after the early 

summer breakup, it responds almost solely to the 

wind effects. 

We conclude that waters on the eastern 

Beaufort Sea shelf moved eastward in the fall of 

1983 at velocities which ranged from less than 1 to 

more than 15 cm/s in response to persistent 

westerly winds. Suspended sediments and (or) 

pollutants entrained in the upper waters can be 

expected to travel at similar speeds, on similar 

trajectories that commonly move from Alaska into 

Canada. 

This study was funded in part by the Minerals 

Management Service through an interagency 

agreement with the National Oceanic and 

Atmospheric Administration, as part of the Outer 

Continental Shelf Environmental Assessment 

Program. 

REFERENCES CITED 

Aagaard, Knut, 1984, The Beaufort Undercurrent, 

in Barnes, P.W., Schell, D.M., and Reimnitz, 

Erk, eds., The Alaskan Beaufort Sea: 

Ecosystems and Environments: Orlando, Fla., 

Academic Press, p. 47-71. 

142 

Barnes, P. W., Rearic, D.M., and Reimnitz, Erk, 

1984, Ice gouging characteristics and 

processes, in Barnes, P.W., Schell, D.M., and 

Reimnitz, Erk eds., The Alaskan Beaufort 

Sea: Ecosystems and Environments, Orlando, 

Fla., Academic Press, p. 185-212. 

Barnes, P.W., and Toimil, L.J., 1979, Inner shelf 

circulation patterns, Beaufort Sea, Alaska: 

U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1125. 

Harper, J.R. and Penlana, Shea, 1982, Beaufort 

Sea sediment dynamics: Geological Survey of 

Canada, Atlantic Geoscience Centre, Open 

File Report, 12 7 p. 

Kozo, T.L., and Robe, R.Q., 1986, Modeling winds 

and open-water bouy drift along the eastern 

Beaufort Sea coast, including effects of the 

Brooks Range: Journal of Geophysical 

Research, v. 91, p. 13011-13032. 

Thomas, D.R., 1984, Interaction of oil and arctic 

sea ice, in Barnes, P. W., Schell, D. W., and 

Reimnitz,-Erk, eds., The Alaskan Beaufort 

Sea: Ecosystems and environment: Orlando, 

Fla., Academic Press, p. 441-460. 

Reviewers: E.W. Kempema and M.A. Noble 
VOLCANIC-ARC DACITE AND 

EARLY MIOCENE BASALT 

DREDGED FROM THE 

SHUMAGIN MARGIN, ALASKA 

Terry R. Bruns, Tracy L. Vallier, 

Leda Beth Pick:thorn, and Roland von Huene 

The Shumagin continental margin lies along 

the Alaska Peninsula between Kodiak Island and 

Unimak Pass. The geology of the shelf islands and 

interpretations of multichannel seismic-reflection 

data indicate that much of the Shumagin shelf is 

underlain by Upper Cretaceous turbidites of the 

Shumagin Formation and by Paleocene 

granodiorite. These rocks are in turn overlain 

above a regional erosional unconformity by 

sedimentary rocks of late Miocene and younger 

age. Early Tertiary rocks like those of the Kodiak 

Island region are not known to crop out on the 

Shumagin shelf islands, but they presumably 

extend on strike southwestward and underlie the 

outer shelf and slope of the Shumagin margin 

(Bruns and others, in press). However, samples 

from three dredge sites are the only available 

evidence with which to characterize the rocks that 

underlie the outer shelf and slope. 

During 1979, sedimentary .and igneous rocks 

were sampled at three dredge sites, numbered 2, 3, 

and 4, on the Shumagin margin (fig. 1). Dredge 

sites 2 and 3 were located on the north and south 

flanks respectively of Unimak Seamount, a 

prominent midslope bathymetric high about 60 km 

south of Sanak Island (fig. 2). Unimak Seamount is, 

in turn, the highest point on Unimak ridge, an 

extensive bathymetric and structural high that 

extends about 100 km southwest of Sanak Island to 

Unimak Pass (Bruns and others, in press; Lewis and 

others, in press). Dredge site 4 was located on the 

west wall of a submarine canyon south of the 

Shumagin Islands. 

Dredge site 2 yielded only sedimentary 

rocks. Dredge sites 3 and 4 yielded basalt and 

dacite respectively. Detailed descriptions of rock 

samples from the dredge hauls are given in Bruns 

and others (1985; in press) and are only 

summarized here. In this paper, we report the 

recently determined volcanic-arc chemistry of the 

igneous rocks and the radiometrically determined 

early Miocene age of one basalt sample from site 

3, and speculate about the implication of finding 

volcanic-arc basalt on Unimak ridge. 

Dredge site 4 yielded undated dacite and 

nodular limestone and calcareous siltstone, dated 

by diatoms as Pliocene and Pleistocene. The 

amount of dacite recovered was too small to 

radiometrically date the rocks. Chemical analyses 

of the dacite samples show that they represent 

three chemically distinct units, possibly individual 

flow units; samples 4-4 and 4-11 are similar, as are 

4-8 and 4-9, and sample 4-12 forms the third 

unit. The chemistry also indicates that the dacite 

samples have calc-alkaline affinities that are 

typical of an island-arc setting (tables 1 and 2, and 

fig. 3). 

Dredge sites 2 and 3 yielded four rock units 

(Bruns and others, 1985; in press): (1) an Eocene 

unit indicated by a single mudstone from site 2, 

163° 162° 161 ° 160° 54°30' ,------;o::::-----------,------ --------,----------------,------, 

~~ EXPLANATION 

D2 

1-----1 Dredge location 

SANAK Y, Bathymetric cont ou rs in meters 

ISL AN D r:, 25 

KILOMETERS 

Figure !.--Locations of dredge hauls from Shumagin margin. Bathymetry south of dashed line from 

Seabeam data of Lewis and others (in press). 

143 
:JJ 

:::J 2 

z 

:) 

:_) 

jJ 

:JJ 

~ 

jJ 

~ 

_J 4 jJ 

> 

<( 

:r: 

>- 5 <( 

5: 

:) 

5: 6 

NW LINE 2 

Figure 2.--Single-channel seismic-reflection line showing location of dredge stations 2 and 3 on Unimak 

Seamount; line location shown in figure 1. Vertical exaggeration about 4:1. 

dated by foraminifers, but considered as suspect 

by Bruns and others (1985; in press) because the 

sample could be an erratic; (2) a lower and middle 

Miocene unit from site 2, represented by a large 

suite of mudstone, siltstone, and sandstone 

samples dated by abundant diatoms; (3) a Pliocene 

and younger unit represented by two mudstone 

cobbles from site 3, also dated by diatoms; and (4) 

the basalt unit from site 3, represented by two 

large (30x30x20 em) angular pieces with freshappearing edges. The Miocene sedimentary rocks 

are apparently locally derived. They contain 

abundant pumice and glass shards, indicating 

proximity to ah active arc during deposition. The 

sandstones also contain abundant plutonic debris 

derived from quartz diorite or granodiorite source 

rocks, probably the Paleocene granitic batholiths 

exposed on the nearby Shumagin and Sanak Islands. 

The basalt samples are moderately altered, 

containing olivine and glass that is partly 

converted to clay minerals. The basalt is probably 

the source rock for a pronounced magnetic 

anomaly coincident with Unimak ridge (Bruns and 

von Huene, 1977). 

Although a volcanic-arc origin for the dacite 

samples at site 4 is clear from the obvious calcalkaline chemistry, the origin of the basalt 

samples from site 3 is less obvious. 

The chemistry of the site 3 basalt samples 

(tables 1 and 2; fig. 3) indicates that they are more 

closely related to volcanic-arc basalts than to 

either mid-ocean ridge basalt (MORB) or ocean 

island (and seamount) basalt (OIB). Sample 3-1 has 

higher Al2o3 and lower Ti02 and light rare-earth 

element (LREE) abundances than OIB, and higher 

Al20 3, K20, and Ba contents, lower CaO and Ti02 

144 

values, and enriched LREE contents compared to 

MORB. Thus, sample 3-1 is unlike both OIB and 

MORB. Sample 3-3 has alkali (K and Na) element 

contents that are too high for MORB. It also has 

higher Al2o3, lower Ti02, and lower contents of 

high-field-strength trace elements (Zr, Y, Nb) than 

OIB, and is thereby more similar to volcanic-arc 

rocks than to OIB. Furthermore, the higher Si02, 

K2o, rare earth elements (REE), Y, Zr, and Hf 

contents in sample 3-3 show that it is more 

50,-,--,--,--,-,--,--,--r-.--.--,--,-,--, 

La Ce 

EXPLANATION 

X 3-3 

0 4-8 

• 4-4 

~ 4-12 

.._ 3- I 

Sm Eu Tb 

RARE-EARTH ELEMENTS 

Yb Lu 

Figure 3.--Plot of rare-earth elements (REE) for 

dredged volcanic rocks normalized to chondrite 

values of Masuda and others {1973). Sample 

numbers in tables 1 and 2. Samples 4-9 and 4-11 

are not plotted because of their close REE 

similarities with samples 4-8 and 4-4 respectively. 

SE 
fractionated than sample 3-1 and might be better 

classified as a basaltic andesite. Thus, the REE 

patterns of both rocks are similar to those from 

arcs; sample 3-3 is definitely calc-alkaline, and 

sample 3-1 is transitional between island-arc 

tholeiite and calc-alkaline basalt. Thus, we believe 

that samples 3-1 and 3-3 both have a volcanic-arc 

origin. 

Attempts were made to date plagioclase 

from samples 3-1 and 3-3 by conventional 

potassium-argon (K-Ar) and by argon 40/39 total 

fusion techniques. However, because of the 

altered nature of the basalt and the low potassium 

content, only sample 3-3 could be dated, and only 

by the argon 40/39 total fusion technique. Two 

separate runs yielded an average date of 19.8 ± 1.0 

m.y. (early Miocene). The plagioclase looks 

somewhat altered in thin sections. Thus, the 

measured date represents a minimum age for the 

basalt because some argon may have been lost due 

to alteration of the plagioclase. The age is, 

however, consistent with that of the associated 

lower and middle Miocene sedimentary rocks. 

If the basalt samples are from bedrock, and 

if the measured age is correct, then the chemical 

and age data have important tectonic implications. 

First, the arc-type chemistry of the dredged basalt 

shows that Unimak ridge, and hence the entire 

continental slope landward of the ridge, is 

underlain by arc-related rocks rather than by 

accreted sedimentary rocks or an accreted oceanic 

seamount complex. Second, the basalts were most 

likely emplaced into the Shumagin margin before 

deposition of the associated sedimentary rocks, 

Table 1.--Trace element concentrations (ppm) in igneous rocks from dredge sites 3 and 4, cruise S7-79-WG 

[Analysts are L.Schwarz (instrumental neutron activation analysis) and R. Johnson (X-ray fluorescence, 

XRF). XRF values are noted by *; uranium value for sample 3-1 was below detection limit] 

Element 3-1 3-3 4-4 4-8 4-9 4-11 4-12 

Rb* 9 10 24 54 51 19 36 

sr* 415 349 358 400 397 354 796 

Ba* 101 234 466 619 621 466 386 

Th .67 2.27 3.0 5.82 5.91 3.14 4.01 

u .68 1.08 2.10 2.10 1.19 1.2 

La 4.8 14.6 12.0 14.6 14.8 11.6 9.3 

Ce 11.7 32.2 23.9 27.6 27.5 23.0 15.3 

Nd 13 23 13 14 16 14 8 

Sm 2.37 5.18 3.24 3.51 3.54 2.99 1.84 

Eu .85 1.59 .99 1.02 1.01 .92 1.04 

Tb .41 .75 .52 .39 .37 .47 .23 

Yb 1.38 2.44 2.14 1. 75 1.47 2.13 1.12 

Lu .206 .342 .366 .241 .259 .315 .180 

y * 16 27 20 17 16 21 11 

zr* 80 138 134 110 ~07 134 150 

Nb* 6 6 6 7 6 7 6 

Hf 1.57 2.97 2.93 2.78 2.85 2.97 3.46 

Ta .27 .29 .35 .22 .27 .36 .31 

Co 43 31 14 21 19 14 14 

Cr 205 97 21 54 51 19 39 

Sc 30 30 15 27 26 14 22 

Zn 76 92 86 56 55 84 55 

145 
Table 2.--Major and minor element oxides (wt pet) 

of igneous rocks from dredge sites 3 and 4, cruise 

S7-79-WG 

[Rock elemental oxides summed to 100 percent 

and H2o+, H2o-, and co2 values included. 

Analyses by X-ray fluorescence and wet chemical 

methods; A. Bartel, D. Kobilis, and J. Pastor 

analysts] 

Oxides 3-1 3-3 4-4 4-8 4-9 4-11 4-12 

Si Oz 48.79 52.12 61.52 60.51 60.76 62.05 60.27 

Ti02 1.05 1.55 . 73 .77 • 76 . 76 .81 

A1 2o3 18.55 18.74 18.75 18.19 13.10 18.62 17.83 

Fe2o3 3.97 5. 75 3.17 3.91 3.98 3.41 3.01 

FeO 4. 73 3. 79 3.16 1.45 1. 35 2.94 2.40 

MnO .15 .18 .12 .05 .05 .11 .08 

MgO 8. 76 5.59 2.91 2.16 2.21 2.78 3.66 

CaO 10.99 7.35 5.01 7.96 7.74 4.65 7.23 

Na 2o 2.51 3.57 3.45 3.11 3.07 3.53 3.27 

K20 .38 1.01 .99 1.84 1.83 .96 1.38 

P2o5 .12 .25 .19 .15 .15 .19 .06 

H2o+ 1.40 2.40 2.20 .87 . 95 2.10 1.10 

H2o- .97 2.90 1.20 1.50 1.20 1.30 1.20 

C02 .02 .02 .02 .02 .02 .02 .02 

FeD* /MgO .95 1.61 2.07 2.25 2.23 2.16 1.40 

because (1) the basalt is at least as old or older 

than the clastics, (2) basalt is not a major 

constituent of the associated sandstones, and (3) 

the sedimentary rocks are thermally immature and 

thus were not affected by an intrusive event 

(Bruns and others, 1985; in press). Third, the 

basalts have no clear relation to the bulk of 

eruptive volcanic rocks along the Aleutian arc, 

whose ages are dominantly Eocene through 

Oligocene, corresponding to the major 

development time of the so-called Meshik arc of 

Wilson (1985), and late Miocene through Holocene, 

corresponding to development of the Aleutian 

Arc. The age of the dredged basalt best 

corresponds to the youngest recorded age of early 

Miocene for Meshik arc volcanic rocks, but could 

also indicate an entirely different and younger 

volcanic event than the Meshik arc events. 

Finally, the dredged volcanic- arc rocks from site 

3 are at present anomalously close to the Aleutian 

trench (about 60 km) compared to normal eruption 

sites of lavas along the Aleutian chain or other 

146 

island-arc volcanic chains. These basalts could 

have been emplaced by forearc volcanism during a 

volcanic episode separate from either the Meshik 

or Aleutian arc events. Another possibility, and 

the one that we prefer, is that the basalts were 

originally emplaced in a normal arc-axis position 

relative to the early Miocene trench and volcanic 

arc, and that the outer part of the margin has been 

subsequently removed by tectonic erosion (Bruns 

and others, in press). 

REFERENCES CITED 

Bruns, T.R., and von Huene, Roland, 1977, 

Sedimentary basins on the Shumagin shelf, 

western Gulf of Alaska: Ninth Annual 

Offshore Technology Conference Proceedings, 

Houston, Tex., v. 1, p. 41-50. 

Bruns, T.R., von Huene, Roland, Culotta, R.C., and 

Lewis, S.D., 1985, Summary geologic report 

for the Shumagin Outer Continental Shelf 

(OCS) planning area, Alaska: U.S. Geological 

Survey Open-File Report 85-32, 58 p. 

Bruns, T.R., von Huene, Roland, Culotta, R.C., 

Lewis, S.D., and Ladd, J. W ., in press, Geology 

and petroleum potential of the Shumagin 

margin, Alaska, 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 -- Beaufort Sea to Baja California: 

Circum-Pacific Council for Energy and 

Mineral Resources Earth Science Series, 84 p. 

Lewis, S.D., Ladd, J. W., Bruns, T.R., and von 

Huene, Roland, in press, Structural 

development of an accretionary prism by 

thrust and strike-slip faulting: Shumagin 

region, Aleutian Trench: Geological Society 

of America, Bulletin. 

Masuda, A., Nakamura, N., and Tanaka, T., 1973, 

Fine structures of mutually normalized rareearly patterns of chondrites: Geochimica et 

Cosmochimica Acta, v. 37, p. 239-248. 

Wilson, F.H., 1985, The Meshik arc -- An Eocene 

to earliest Miocene magmatic arc on the 

Alaska Peninsula: Alaska Division of 

Geological and Geophysical Surveys, 

Professional Report 88, 14 p. 

Reviewers: M.A. Fisher and M.S. Marlow 
GLORIA IMAGES OF ZHEMCHUG CANYON 

AND BERING CHANNEL-FAN SYSTEM, 

BERING SEA 

Herman A. Karl, James V. Gardner, 

and Quentin Huggett 

The deep-sea part of the Exclusive Economic 

Zone (EEZ) of Alaska is being surveyed as a 

continuation of the EEZ- SCAN project of the U.S. 

Geological Survey (Gardner, 1984). The primary 

survey tool is a long-range side-scan sonar, the 

GLORIA III system (Somers and others, 1978; 

Swinbanks, 1986). Two-channel digital seismicreflection profiling, 3.5- and 10-kHz profiling, 

gravity, and magnetics systems provide ancillary 

geophysical data. The first of four planned Alaska 

field seasons began in the summer of 1986 with 

four cruises. One brief cruise surveyed a small 

corridor of about 50,000 km2 in the Gulf of 

Alaska, and three long~r cruises covered 

approximately 700,000 km of the Beringian 

continental slope, the abyssal seafloor of the 

Aleutian Basin, and the north slope of the Aleutian 

Ridge (fig. 1). We report here only the highlights 

of preliminary interpretations of the shipboard 

GLORIA side~scan imagery from cruise F3-86 that 

covered a rectangular area of approximately 

200,000 km2 in the Bering Sea from Zhemchug 

Canyon southeastward along the margin to just 

north of Pribilof Canyon and southwestward across 

the Aleutian Basin to Bowers Ridge. 

Some of the largest submarine canyons in the 

world incise the Beringian continental margin, and 

Zhemchug Canyon is the largest of these canyons. 

Zh)mchug Canyon has a volume of at least 5,800 

km , more than an order of magnitude larger than 

Astoria ~anyon on the Oregon continental margin 

(425 km ) and H~dson Canyon on the New York 

margin (300 km ) (P.R. Carlson, USGS, oral 

commun., 1986). Previous investigators 

recognized evidence of mass transport of sediment 

in the Beringian canyons (Scholl and others, 1970; 

Carlson and Karl, 1984). However, the GLORIA 

images reveal that products of mass transport are 

much more common than previously interpreted 

and that mass-wasting is the dominant erosional 

process on the continental slope (fig. 2). Earlier 

studies of Zhemchug Canyon utilized seismicreflection data and sediment samples as 

interpretive tools. The new perspectives of the 

canyon provided by the GLORIA images enable us 

not only to refine previous descriptions of the 

morphology and evolution of the canyon, but also 

to offer new insight into the origin of the canyon. 

For example, there is a large sediment mass at the 

base of Zhemchug Canyon that is clearly visible on 

the GLORIA mosaic (fig. 2). Although this mass 

had been observed on single- channel seismicreflection records collected on earlier cruises, its 

dimensions were unknown and its relationship to 

147 

the canyon was unclear. Our preliminary data 

suggest that Zhemchug Canyon originated when 

this large block broke away from the margin and 

slid intact onto the abyssal plain. Headward 

erosion by sediment failure progressed 

northeastward until it reached the southernmost of 

two parallel normal faults on the outer shelf. 

These faults were identified on earlier cruises, and 

we agree with previous interpretations (Scholl and 

others, 1970) that at this stage of canyon 

evolution, sediment in the structural basin 

between the faults was preferentially eroded to 

the northeast, northwest, and southeast and 

produced the winged shape of Zhemchug Canyon. 

As masses of sediment became detached from the 

slope, the resulting blocks, slumps, and slides 

clogged major sediment dispersal pathways in the 

growing gorge and formed a labyrinth of 

channels. These products of mass sediment 

transport, in turn, were eroded by numerous 

gullies. The amount of sediment contributed to 

the Aleutian Basin from and via Zhemchug Canyon 

is unknown. However, it appears that the canyon 

is not presently an important source of modern 

sediment because no channels from the canyon 

extend onto the abyssal plain. 

The GLORIA mosaic, however, has enabled 

us to identify the principal routes of sediment 

transport to the basin. We have recognized a 

channel that enters the study area from the east, 

apparently originating from Bering Canyon (fig. 

3). Although a channel at the mouth of Bering 

Canyon had been suggested on bathymetric maps, 

it was not known that it extends onto the abyssal 

plain for more than 500 km. Unlike other known 

deep-sea channels, such as Cascadia channel on 

the abyssal plain off Oregon and Washington, 

Bering channel is not deeply incised but, as seen on 

high- resolution and seismic-reflection profiles, 

rather shallow and broad, being about 10-20 m 

deep and and as wide as 25 km, with a low but 

well-developed levee on the north side. Bering 

channel terminates in a newly discovered deep-sea 

fan, informally called Bering fan, which is being 

constructed in the deepest part of the eastern 

Aleutian Basin. Bering fan is a very low relief 

feature with a complex system of distributaries 

and located in the middle of the abyssal seafloor, 

whereas most submarine fans are large-volume 

high-relief sediment bodies built up at the base of 

the continental slope (Bouma and others, 1985). 

Moreover, Bering fan lacks the distinctive upper, 

middle, and lower fan morphology and channellevee systems that generally are present on other 

fans. Instead, it is a thin veneer of sediment 

disgorged by Bering channel. We surmise that 

most transport and deposition on the fan is by 

sheet- flow rather than channelized flow as in the 

traditional models of fan development (Bouma and 

others, 1985). We cannot yet determine from our 

initial analysis of the data whether Bering fan 
St. MattheW Is. 

BERING SEA SHELF 

<J prlbiiOf Is. 

100 200 300 

KILOMETERS 

180" 176"W 

Figure 1.--Location map showing area of each Bering Sea cruise and major canyons that incise Beringian margin. Bathymetric contours in meters. 

148 
0 50 100 • 

KILOMETERS 

·. 

• ' \ 

' ' ' ' \ 

' \ 

.. 

' \ 

174· w 

I 

' ' •, 

. . 

' ' . . 

. 

N 

Figure 2.--Top, sonographic mosaic of Zhemchug Canyon and adjacent continental slope and abyssal 

seafloor. A, large block at base of Zhemchug mentioned in text. Note numerous gullies and sediment 

masses that evidence mass-wasting. Mosaic constructed onboard ship. Lines signify areas of no data under 

ship's track. Bottom, line drawing of sonograph showing major channels and outlining large block at 

base of canyon. Dots indicate ship's track for orientation with features on sonograph. 

149 
ll _~~ 

Figure 3.--Bering channel and Bering fan. Note complex backscatter pattern that distinguishes fan. Levee 

cannot be distinguished easily on the unprocessed sonograph and its approximate position and trend are 

labeled. 

150 

100 
represents an early developmental stage of a 

normal submarine fan or a new class of deep-sea 

fan. Debris shed from the Aleutian Ridge and 

funneled down its flanking canyons appears to 

accumulate in the immediate vicinity of Bering 

fan as well (A.J. Stevenson, USGS, written 

commun., 1986), thus this area seems to be the 

primary loci of modern deposition in the Bering 

Sea. 

REFERENCES CITED 

Bouma, A.H., Normark, W.R., and Barnes, N.E., 

eds., 1985, Submarine fans and related 

turbidite systems: New York, SpringerVerlag, 351 p. 

Carlson, P.R., and Karl, H.A., 1984, Mass 

movement of fine-grained sediment to the 

deep-basin floor, Bering Sea, Alaska: GeoMarine Letters, v. 4, p. 227-234. 

Gardner, J.V., 1984, Program EEZ-SCAN: A 

reconnaissance view of the western U.S. 

Exclusive Economic Zone, in Clarke, S.H., ed., 

U.S. Geological Survey highlights in marine 

research: U.S. Geological Survey Circular 

938, p. 125-132. 

Scholl, D.W., Buffington, E.C., Hopkins, D.M., and 

Alpha, T.R., 1970, The structure and origin of 

the large submarine canyons of the Bering 

Sea: Marine Geology, v. 8, p. 187-210. 

Somers, M.L., Carson, R.M., Revie, J.A., Edge, 

R.H., Barrow, B.J., and Andrews, A.G., 1978, 

GLORIA n--An improved long range side-scan 

sonar: Oceanology International 78, p. 16-24. 

Swinbanks, D., 1986, New GLORIA in record 

time: Nature, v. 320, p. 568. 

Reviewers: B.D. Edwards and T.L Vallier 

151 
GLORIA SIDE-SCAN AND GEOPHYSICAL 

SURVEYS OF THE CENTRAL BERING SEA 

IN 1986 

MichaelS. Marlow, Paul R. Carlson, 

Shawn V. Dadisman, Douglas M. Rearic, 

Edward J. Maple, and Lindsay M. Parson 

During the summer of 1986, about 225,000 

km 2 of the central Bering Sea continental slope 

and abyssal plain were surveyed with the GLORIA 

side-scan sonar system on the MV Farnella 

(fig. 1). This cruise was part of a cooperative 

program between the U.S. Geological Survey and 

the British Institute of Oceanographic Sciences in 

which the deep-water parts of the Alaskan EEZ 

(Exclusive Economic Zone) are being surveyed 

using the GLORIA system. 

Prominent geomorphic features of the Bering 

Sea were imaged, including Navarinsky, Pervenets, 

and Zhemchug Canyons along the Beringian 

margin, the abyssal floor of the Aleutian Basin, 

and the northern part of Bowers Ridge (Bering Sea 

EEZ Scan 86 Group, 1987). Large slump and slide 

features, some measuring kilometers across, occur 

along the margin, showing that mass movement is 

a major sediment transport mechanism on the 

continental slope. A wide variety of slides and 

flows previously have been identified on the 

Beringian margin from seismic-reflection profiles 

(Carlson and Karl, 1984/85), and mass wasting has 

been inferred to be an important erosional 

process. The extent of mass wasting, however, 

was not recognized until the margin was imaged 

with GLORIA. Evidence of mass transport is 

common not only on the Beringian slope, but also 

along Bowers Ridge. 

Along the Beringian slope and on both sides 

of Bowers Ridge, sediment-flow patterns fan out 

into the basin from the numerous canyons and 

gullies incised in the slopes. Major channels are 

absent across that part of the northern Aleutian 

abyssal plain surveyed by us, suggesting that sheet 

flow is the dominant mode of sediment transport 

in the northern Aleutian Basin (Carlson and others, 

1986). 

Large sand waves, 600 m long and 2-5 m 

high, are visible on the GLORIA images in 

Navarinsky and Pervenets Canyons (fig. 2). These 

sand waves were previously recognized on seismicreflection profiles and interpreted by Karl and 

Carlson (1982) and Karl and others (1986). The 

GLORIA side-scan imagery provides a plan view of 

the sand waves that allows us to determine the 

orientation and continuity of these large-scale 

bedfor~s. The sand waves cover about 1,400 and 

800 km of the heads of Navarinsky and Pervenets 

Canyons, respectively. These sand waves, some of 

which are relict, buried features, reach a 

maximum stratigraphic thickness of 120 m and 

consist of several crossbedded sets (fig. 2). 

152 

Along with the GLORIA survey, we also 

collected two-channel seismic-reflection, gravity, 

gradiometer (magnetic), and bathymetric data. 

The seismic-reflection data show that the western 

Aleutian Basin is underlain by six linear basement 

ridges, 30 to 140 km long, which are buried by an 

average of 1.5 to 2.0 km of sediment (fig. 1 and 

table 1). Two of the ridges, Sounder and Bartlett, 

were discovered by Cooper and others (1976b, 

1979). The other four subsurface ridges, A, B, 

Farnella and Pear, were discovered in 1986 by 

seismic-reflection profiling on the MV Farnella. 

The six ridges occupy an area south of the 

continental margin of eastern Siberia (USSR) 

extending southwest toward the junction of 

Bowers, Shirshov, and the western Aleutian Ridges 

(fig. 1). The ridges are built on oceanic crust of 

presumed Mesozoic age interpreted to be part of 

the Kula plate (Cooper and others, 1976a, b). Two 

of the ridges, Sounder and Bartlett, have 

associated positive and negative magnetic 

anomalies, respectively. Local buried basement 

highs associated with several of the ridges, 

including Farnella ridge, extend to within a few 

hundred meters of the sea floor (fig. 3). Farnella 

ridge shows two such local highs, which are draped 

by differentially compacted sediment over the 

tops of the highs. These local highs are probably 

ancient seamounts rising along the linear basement 

ridges. 

The basement ridges range from being 

oblique to perpendicular to the north-southstriking linear magnetic anomalies of presumed 

Mesozoic origin that were first described by 

Cooper and others (1976b). For instance, the 

spreading anomalies in the Aleutian Basin are 

interrupted or possibly terminated to the 

northwest by Sounder ridge, which may occupy an 

ancient fracture zone now trending nearly eastwest. The basement ridges could be the same age 

or younger than the underlying oceanic crust. 

The north-south-striking linear magnetic 

anomalies fan to the southwest. These spreading 

anomalies, which originate from the oceanic crust 

beneath the Aleutian Basin (Cooper and others, 

1976a, b), may have formed along a propagating 

rift system similar to rift systems suggested for 

the fanning Mesozoic magnetic anomalies in the 

northern central Pacific, which were first noted by 

Larson and others (1972) and discussed by Tamaki 

and others (1979). 

The seismic-reflection data collected in 1986 

also revealed 280 acoustic anomalies in the 

reflection horizons beneath the Aleutian Basin 

(Rearic and others, 1986). Over 88 percent of 

these anomalous reflectors are distinguished as 

VAMPs, the velocity-amplitude anomalies of 

Scholl and Cooper (1978), and exhibit velocity or 

time-based pulldowns such as that shown in 

fig. 4. Maximum amplitude of the pulldowns 

averages 25 ms and can be more than 70 ms. The 
USSR 

0 100 

PERVENETS 

CANYON 

ALEUTIAN 

BASIN 

\

BASEMENT 

RIDGE 

KILOMETERS 

BATHYMETRIC CONTOURS IN METERS 

EXPLANATION 

1 Ridge A 

2 Sounder Ridge 

3 Farnella Ridge 

4 Ridge B 

5 Bartlett Ridge 

6 Pear Ridge 

Figure I.--Ship's tracks for first GLORIA leg in Bering Sea in 1986. Note location of buried basement 

ridges in western Aleutian Basin. Albers equal-area projection. 

153 
0 2 3 

NW KILOMETERS SE 

c;; • -o I c: 

0 

u 

., 0.4 I_ .!!!. 300 ~ 

., ~ E "' i= .... 

0 Q) 

> 0 .5 -o "' 0 - .= ~ 

400 >- 3 0 ~ 3: 0.6 "' I .... 0 e. J: 

1- .: ~~··-

';:.>;·: - :~ ri;;~ -· ;..:7"-~~ I., '~ ·I .. - 500 

N KILOMETERS 

' 0 10 

Figure 2.--Minisparker seismic-reflection profile (top) and unprocessed GLORIA imagery across Navarinsky 

sand-wave field. 

154 
5 

(f) 6 

0 

z 

0 

0 

w 

(f) 

~ 

w 7 ::2 

f= 

_j 

w 

> 

<( 

a: 

I-

>-

<( 8 ~ 

6 

~ 

I9 

Figure 3.--Single-channel seismic-reflection profile across Farnell ridge. Ridge is buried by 450-500 m of 

sediment. Note associated magnetic anomaly across ridge, which trends obliquely to regional magnetic 

anomaly trends. Note the two basement highs. 

5 

CJ) 

0 

z 

0 

0 

6 

w 

CJ) 

z 

uj 

~ 

~ w 

> <( 

7 a: 

I-

>- <( 

3: I 

0 

3: 

I8 

Figure 4.--Seismic-reflection profile from southern Aleutian Basin. VAMP at center exhibits many 

characteristics commonly observed in anomalous reflectors in Aleutian Basin (pull-down, phase inversion, 

arching of overlying reflectors, and diffraction hyperbola with bowtie structure). 

155 
anomalous reflectors range in width from 0.5 km 

to 9 km and average 1.5 km. The anomalies are 

interpreted as indicating gas-charged sediment. 

Table I.--Basement ridges beneath western 

Aleutian Basin 

LENGTH( km) 

Ridge A 

Sounder ridge 

Farnella ridge 

Ridge B 

Pear ridge 

Bartlett ridge 

58.92 N. 179.86 E. 

58.65 N. 179.33 E. 

57.34 N. 177.96 E. 

56.95 N. 177.28 E. 

56.85 N. 175.71 E. 

56.49 N. 174.97 E. 

58.75 N. 179.44 E. 

58.43 N. 178.52 E. 

57.12 N. 177.74 E. 

56.49 N. 176.78 E. 

56.20 N. 175.83 E. 

55.35 N. 173.90 E. 

REFERENCES CITED 

30 

140 

30 

60 

75 

140 

Bering Sea EEZ Scan Group 86, in press, Longrange side-scan sonar and geophysical survey 

of Aleutian Basin: Eos (Transactions 

American Geophysical Union). 

Carlson, P.R., and Karl, H.A., 1984/85, Mass 

movement of fine-grained sediment to the 

basin floor, Bering Sea, Alaska: Geo-Marine 

Letters, v. 4, p. 221-225. 

Carlson, P.R., Marlow, M.S., Rearic, D.M., 

Dadisman, S. V., and Parson, L.M., 1986, 

GLORIA side-scan imagery of central Bering 

Sea EEZ: Eos (Transactions American 

Geophysical Union), v. 67, p. 1228-1229. 

Cooper, A.K., Scholl, D. W., and Marlow, M.S., 

1976a, A plate tectonic model for evolution of 

the eastern Bering Sea Basin: Geological 

Society of America Bulletin, v. 87, p. 1119-

1126. 

1976b, Mesozoic magnetic lineations in the 

--Bering Sea marginal basin: Journal of 

Geophysical Research, v. 81, p. 1916-1934. 

156 

Cooper, A.K., Scholl, D.W., Marlow, M.S., Childs, 

J.R., Redden, G.D., Kvenvolden, K.A., and 

Stevenson, A., 1979, Hydrocarbon potential of 

Aleutian Basin, Bering Sea: American 

Association of Petroleum Geologists Bulletin, 

v. 63, p. 2070-2087. 

Karl, H.A., Cacchione, D.A., and Carlson, P.R., 

1986, Internal-wave currents as a mechanism 

to account for large sand waves in Navarinsky 

Canyon head, Bering Sea: Journal of 

Sedimentary Petrology, v. 56, p. 706-714. 

Karl, H.A. and Carlson, P.R., 1982, Large sand 

waves in Navarinsky Canyon t)ead, Bering 

Sea: Geo-Marine Letters, v. 2, p. 157-162. 

Larson, R.L., Smith, S.M., and Chase, C.G., 1972, 

Magnetic lineations of Early Cretaceous age 

in the Western Equatorial Pacific Ocean: 

Earth and Planetary Science Letters, v. 15, p. 

315-319. 

Rearic, D.M., Williams, S., and Carlson, P.R., 

1986, VAMPs and other acoustic evidence of 

gas-charged sediment in the abyssal Aleutian 

Basin, Bering Sea, Alaska (abs.): Eos 

(Transactions American Geophysical Union), 

v. 67' p. 1211. 

Scholl, D.W., and Cooper, A.K., 1978, VAMPs --

Possible hydrocarbon-bearing structures in 

Bering Sea basin: American Association of 

Petroleum Geologists Bulletin, v. 62, p. 2481-

2488. 

Tamaki, K., Joshima, M., and Larson, R.L., 1979, 

Remanent Early Cretaceous spreading center 

in the Central Pacific Basin: Journal of 

Geophysical Research, v. 84, p. 4501-4510. 

Reviewers: S.L. Eittreim and H.A. Karl 
VIBRACORE STRATIGRAPHY OF THE 

NORTHEASTERN CHUKCID SEA 

R. Lawrence Phillips and Mitchell W. Colgan 

Shallow epicontinental seas, such as the 

Cretaceous intercontinental seaway, are common 

throughout geologic history, but there are few 

modern analogs. The Chukchi Sea is one such 

analog. In this paper we present our preliminary 

findings of the stratigraphy of the northeastern 

part of that water body. 

The Chukchi Sea is a shallow (<60 m deep) 

epicontinental sea that is ice-covered for 9 to 10 

months a year. Sediment input is low because few 

rivers enter the Chukchi Sea, and an extensive 

barrier island system traps much of their sediment 

(Grantz and others, 1982). Consequently, a thin 

sediment cover (generally less than 6 m thick) 

overlies gently to steeply dipping folded and 

faulted bedrock. A northward-flowing shoreparallel current (the Alaska Coastal Current) 

dominates the Chukchi Sea's eastern flank; 

converging currents off Cape Lisburne, Icy Cape, 

and Point Franklin deposit the thickest sediment 

cover in the eastern Chukchi Sea. Storms, ice 

gouging, and local currents rework the shelf 

sediments. 

In September and October 1985, we used the 

NOAA R V Discoverer to conduct geological and 

geophysical surveys of the Chukchi Sea. Our study 

area is bounded by Point Hope to Point Barrow on 

the east, the US-USSR 1867 Convention Line to 

the west, and the shelf break to the north (fig. 1). 

Our data are based on seismic records obtained 

from a high-resolution seismic system and a 3.5-

kHz sub-bottom profiler along 2,600 km of 

trackline and 22 vibracore samples of 9 em 

diameter and up to 6 m long. This report examines 

the shelf stratigraphy from 14 of those cores taken 

at 26-48 rn water depth. We examined core 

subsarnples for texture, mineralogy, and fossils 

(diatoms, sponge spicules, foraminifers, 

ostracodes, mollusks, and insects) to define the 

stratigraphic units. Clay mineralogy was 

determined by X-ray diffraction. 

Our high-resolution seismic records were 

used to define the bedrock surface on which the 

younger sediments were deposited. A series of 

channels of unknown age incise the bedrock 

(fig. 2). The vibracores record a sedimentary 

history of erosion and limited deposition. At least 

five major laterally continuous stratigraphic units 

--volcanic ash, pebbly mud, pebbly to muddy sand, 

iron stained sand, and pebbly muddy sand-- occur 

above bedrock. In addition, two minor units, a 

consolidated silty clay and a laminated sand, are 

recognized. 

The deepest stratigraphic unit is 204 ern of 

consolidated silt and clay, which rests on inclined 

bedrock and coarsens upward (core 53 in fig. 2). 

157 

The silt fraction is composed of glass shards, 

quartz grains, and biotite and is suspended in a 

mixed clay that consists of smectite, illite, and 

chlorite. This unit contains horizontal parallel 

laminations, black organic-rich beds, and large 

burrows. 

Volcanic ash is found at the base of five 

cores over a distance of 160 krn north-south and 97 

krn east-west, and it blankets directly or rests 

within 2 rn of an irregular bedrock surface that 

causes the deposit to thicken or thin above it. The 

thickness of the ash ranges from 152 ern in core 53 

to a possible maximum thickness of 6 rn 

(determined from high-resolution seismic records 

at station 62). Horizontal parallel graded 

laminations of volcanic glass and black organic 

material form the major sedimentary structures. 

The ash, where not altered, consists of greater 

than 95 percent glass shards that range from 425 

J.lm (medium sand) to 4 J.lm (very fine silt) with a 

median size of 62.5-125 J.lffi (fine sand). Mineralogy 

consists of rhyolite vitric ash (Si02 = 76.1 percent) 

and altered tephra (clay). The vitric ash is 

colorless and consists of a mixture of bubble wall 

junction shards, vesicular shards, and bubbles; the 

shards have a refractive index of 1.500 ± 0.002. 

The altered tephra contains a clay mixture of 

smectite-illite, kaolinite, and chlorite with 

zeolites. Marine microfossils of diatoms, sponge 

spicules, and foraminifers are sparsely distributed 

in the ash deposit. The upper 1 rn of the deposit 

contains scattered rounded quartz and chert 

pebbles as well as two pebble beds. 

Overconsolidated cobbly to pebbly sandy 

mud containing gravel clasts (up to 6 em in 

length), ash beds (up to 12 ern thick), and 

bioturbated mud conformably overlies altered 

tephra, and in one case (core 66) may rest directly 

on or near bedrock. The deposit ranges in 

thickness from 30 em to at least 180 em, and 

pinches out to the east (toward shore) and the 

north. Quartz grains, biotite, glass shards, 

diatoms, rare foraminifers, and sponge spicules are 

found in the sand-size fraction. 

The pebbly to muddy sand unit was found 

only in five northwestern cores (51, 54, 56, 57, and 

58). The vibracore did not penetrate below this 

unit at any of those stations, and its lower contact 

therefore could not be determined. The unit 

ranges in thickness from 17 em (core 51) to 220 em 

(core 56). The sand-size fraction is composed of 

quartz grains, abundant muscovite, glass shards, 

sponge spicules, and foraminifers (locally abundant 

Elphidium sp.). Horizontal parallel laminations, 

thin organic-rich beds, scattered pebbles (up to 1 

em diameter), shell beds, and abundant 

bioturbation are common. In the thickest section, 

in core 56, sediment texture coarsens upward. 

The lowermost unit of core 67 is a 155-cmthick sequence of repeated parallel sand laminae 

that rests on or near bedrock. Sand grains consist 
72° 168° 166° 

~'" 

71° " 

164° 

43 

• 

6 

PT. BARROW 

6~'L---~----~~----~------~------._------------~ 

Figure 1.--Vibracore locations in northeastern Chukchi Sea. A-A' and A'-B designate core profiles. 

of white and clear quartz, amphiboles, pyroxenes, 

and books of biotite. Heavy-mineral content 

(specific gravity >2.96) ranges from 13.4 to 15.7 

percent, with heavy minerals concentrated in 

laminae. Neither fossils nor biogenic structures 

are evident. 

Iron-stained, quartz-rich sand to locally 

pebbly sand is found in eight cores (fig. 2). 

Thickness varies from 19 em (core 56) to 245 em 

(core 67), and the unit thins to the west. The ironstained sand rests on an erosional contact above 

either weathered tephra, laminated sand, pebbly 

mud, or pebbly muddy sand (fig. 2). Well-rounded 

quartz sand, brown peat laminae and beds, 

scattered isolated pebbles and pebble lags, and 

thin muddy gravel beds characterize this 

sequence. The organic-rich laminae contain 

abundant insect remains, ostracodes (nonmarine), 

algal filaments, seeds, and wood, but macrofossils 

are absent. 

158 

Silty mud to sandy gravel deposited since the 

last transgression forms the uppermost sequence. 

These sediments range in thickness from 50 to 440 

em and rest on either iron stained sand, pebbly 

mud, or pebbly to muddy sand. The unit consists 

of bioturbated horizontal laminae to intensely 

bioturbated massive sediment with a few scattered 

pebbles. Sediment texture fines westward. All 

cores from 65 westward have a thin surface mud 

layer over sand, but the mud layer is absent to the 

east, where the Alaska Coastal Current erodes the 

sea bed (cores 66 to 68). Quartz grains, glass 

shards, macrofossils (bivalves, gastropods, 

barnacles, and echinoids), and microfossils 

(ostracodes, foraminifers, diatoms, and sponge 

spicules) occur in the sand fraction. A gravel-shell 

lag usually marks the base of this sequence. 

Although direct correlation of our units is 

tentative pending age determination, core 
en 26-

o::: 

w 

tw 30- ~ 

~ 

:i' 

t- 37-

(L. 

w 

0 

0::: 41-

w 

t- 44-

c( 45- 64 

3: 47 -11..-----.--~-r 

en 

0::: 

w 

tw 

~ 

~ 40-

::C 44-

t- 45- fu 46-

047- 58 

0::: 48- .------.------.---.,....-

w 

tc( 

3: 

BASE OF CHANNEL 

IS 32-34. M BELOW 

SEA FLOOR 

-EAST 

63 

HDPEBBLY 

MUDDY SAND 

mTITITIJIRON-ST AI NED 

G llilliillJ SAND 

C VOLCANIC F ~LAMINA TED 

ASH ~SAND 

B ~CONSOLIDATED [ill PEBBLY TO 

~SILT & CLAY E :-:-:- MUDDY SAND 

A ~BEDROCK 0 ~~PEBBLY MUD 

51 

Figure 2.--Vibracore stratigraphy across northeastern Chukchi Sea. See figure 1 for core locations. Depth 

to bedrock surface determined from high-resolution seismic records. Core meter scale is on core 53. 

159 
stratigraphy suggests a consistent regional 

sequence. The origin of the deepest depositional 

unit, unit B in core 53, is uncertain because of its 

limited areal distribution and the lack of fossils. 

However, the presence of abundant glass shards 

and laminated sediment suggest either an altered 

tephra or weathered bedrock with ash 

contamination from the overlying tephra. The 

general absence of sediment between bedrock and 

tephra reveals that erosion was the predominant 

shelf process prior to deposition of the tephra. 

The ash fell into the ocean where currents 

redistributed it, resulting in locally abnormally 

thick deposits (unit C, fig. 2) The presence of 

well-rounded detrital quartz grains and pebbles in 

the uppermost section of the ash signals the 

initiation of ice-rafted sedimentation during the 

later stage of ash deposition. The end of ash 

deposition was followed by marine clastic 

sedimentation with continued ice-rafting of 

pebbles and cobbles (unit D). 

A transgressive-regressive cycle best 

explains the deposition of units overlying the 

tephra and marine pebbly mud. A transgression 

resulted in deposition of marine sediment (unit E) 

and a possibly related beach sand (unit F). Later 

sea-level lowering exposed the shelf, and eolian 

and fluvial sediment were deposited (unit G). The 

last transgression eroded most of the previously 

deposited units and deposited the uppermost 

marine sequence (unit H). Modern shelf processes 

(storms, currents, ice, and bioturbation) then 

reworked these sediments, resulting in areas of 

thin sediment cover (cores 66, 67, and 68) and 

areas of deposition (core 63). 

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, the 

officers, and crew of the RV Discoverer for their 

help. 

REFERENCE CITED 

Grantz, A., Dinter, D.A., Hill, E.R., Hunter, R.E., 

May, S.D. McMullin, R.H., and Phillips, R.L., 

1982, Geologic framework, hydrocarbon 

potential, and environmental conditions for 

exploration and development of proposed oil 

and gas lease sale 85 in the central and 

northern Chukchi Sea: U.S. Geological Survey 

Open-File Report 82-1053, 84 p. 

Reviewers: P.J. Quinterno and Erk Reimnitz 

160 
TIDRTY-FOUR-YEAR SHOREFACE EVOLUTION 

AT A RAPIDLY RETREATING 

ARCTIC COASTAL SITE 

Erk Reimnitz and Edward W. Kempema 

Erosion rates for vast stretches of circumArctic coastlines are among the highest on the 

globe. Long-term erosion rates in arctic USSR 

typically are 5-10 m/yr, commonly 15 m/yr, and in 

places as high as 50 m/yr (Are, 1980; Zenkovich, 

1985). Similarly high average erosion rates occur 

along much of northern Alaska and the Yukon 

Territory in Canada (Reimnitz and others, 1985; 

Forbes and Frobel, 1985). The high coastal retreat 

rates in arctic regions are commonly attributed to 

processes of thermal erosion (Are, 1980; National 

Research Council, Marine Board, 1982), driven by 

the temperature differential between frozen 

sediments of surrounding coastal plains and the 

relatively warm sea. 

Recognizing that the advancing sea 

dramatically slices off the coastal plains above sea 

level around the Arctic Ocean, and that the same 

processes have acted at least since sea level 

approached its present position about 5,000 years 

ago, inevitably leads to considerations of the 

adjoining shelf profile (for example, Harper, 

1978). At the seaward limit of modern erosion, a 

break in slope or ramp should form, and given the 

high rates of coastal retreat, such ramps should be 

wide. Wide, well-developed terraces do not 

surround the Arctic basin at sea level. Therefore, 

submarine processes must be maintaining the 

typically concave-upward continental shelf profile 

in some type of equilibrium. But the precise 

mechanisms of profile maintenance remain 

obscure (Reimnitz and others, 1985). 

Russian scientists believe that thermal 

energy and related processes play the most 

important role in shaping the arctic shelf profile. 

Tomirdiaro (1975) stated "The eastern Arctic seas 

are largely young Holocene bodies of water formed 

by thermo-abrasional processes." Thus the seafloor 

simply settles as ice-rich underlying sediments 

thaw, and therefore little lateral transport of 

clastic detritus is required. In fact, thaw 

settlement of the inner shelf should produce 

depositional basins for concurrent sediment supply 

(Harper, 1978). In contrast, Reimnitz and others 

(1985) argued that mechanical energy is more 

important than thermal energy for the 

maintenance of the dynamic equilibrium profile, 

but they lacked proof in the form of long-term 

comparisons of shoreface profiles. Knowledge of 

how the shoreface responds to extensive shoreline 

displacement is important not only for evaluating 

whether the seafloor provides a sediment sink or 

sediment source, but also for evaluating such 

problems as the fate of inundated archaeological 

sites and the design of oil pipeline crossings of 

161 

arctic coasts. In this report we present the results 

of a shoreface study from a site where the coast 

locally retreated 400 m over a 30-year period 

(fig. 1). 

The earliest bathymetry in the study area 

(fig. 1) stems from Hydrographic Survey 7922, 

done by the U.S. Coast and Geodetic Survey in 

July and August 1951 at a scale of 1:40,000. Most 

of the dense trackline pattern of that survey, 

shown in an inset of figure 1, was controlled by the 

use of Shoran, and the soundings were referenced 

to mean lower low water (MLLW). The original 

reference tidal bench marks still exist about 25 km 

west of the study site. The coastline was 

remapped by the State of Alaska and the National 

Ocean Survey, and again referenced to the same 

bench marks, in 1981. This new coastline is also 

shown on figure 1. The 30-yr average retreat rate 

for a 23-km-long coastal segment centered on 

figure 1 is 7.5 m/yr (Reimnitz and others, 1985). 

In 1985 we used the RV Karluk and a skiff to 

run a hydrographic transect perpendicular to the 

coast and regional isobaths. From the beach to 2-

m depth, the skiff, equipped with an echo sounder 

and an acoustic ranging system, was rowed along a 

range-line, and distances to a transponder moored 

on the crest of a nearshore bar (fig. 2) were 

recorded (distance errors less than 0.5 m). The 

emergent crest of the bar (fig. 3) on either side 

near our transect was surveyed by the State of 

Alaska in 1984 and 1985. Therefore this inner part 

of our depth profile is accurate for the purpose of 

a comparison with the original hydrographic 

survey. Seaward from a depth 1.5 m on that same 

range, partly overlapping the inner profile, the RV 

Karluk was positioned at 2-min intervals by means 

of a range/range navigation system using three 

shore stations. Shore stations A and B (fig.1) are 

survey monuments, positioned according to 

national mapping standards. Trading post Esook is 

located within 3 m of such a monument. Problems 

with the ranging system resulted in poor closures, 

which were satisfactorily resolved by adding 321 m 

to the distances from station B. This resulted in 

an excellent match in water depths in the 

overlapping parts of the two separate surveys. 

Because of navigational uncertainties farther than 

3 km from the coast, that part of our survey will 

not be discussed. 

We adjusted the water depths recorded in our 

surveys with reference to MLLW. The datum was 

carried to the study area from the previously 

mentioned bench marks by use of a skiff in radio 

contact with the RV Karluk, while it continued 

monitoring water level at the bench marks until 

the skiff party had established new ones. The 

possible datum error for our hydrographic survey is 

probably less than 10 em. 

Figure 2 shows the changes that occurred in 

the shoreface profile from the beach 3.2 km 

seaward to the 6-m isobath over the 34-yr 
interval. At the very shoreline is a possible 

uncertainty of 25 m, as the coast continued to 

retreat an unknown amount since mapped in 1981, 

and the acoustic ranging system failed shortly 

before the beach was reached. The comparison 

shows a profile that deepened substantially during 

the time period, and maintenance of a bar system 

that advanced shoreward at a rate comparable to 

that of the coastal retreat. At 6 m depth the two 

profiles merge, but from 2 m seaward, our forcing 

of navigational closure may have displaced the 

recent profile seaward. The deepening indicated 

between 2 and 6 m water depths, therefore, is very 

conservative. 

To calculate that portion of the deepening 

that may have resulted from thaw settlement, we 

EXPLANATION 

&A Shore station 

Bar crests 

~ 1951 

~filRlilMl I 9 8 5 

+ Above mean lower 

low water in I 984 

[::::::::::::::::1 30 year erosion 

lsobaths in meters 

0 2 

used published data from a geologically similar 

part of the coastal plain west of the study area 

(Sellmann and others, 1975) to remove excess ice 

content (interstitial ice exceeding 37.5 percent of 

the frozen sediment volume) from the 1951 

profile. By doing this, we found, that from the 

1951 shoreline to the 1-m water depth (3-4 m 

below the tundra surface), only 14 percent of the 

indicated deepening can be attributed to thaw 

settlement. At more than 1.5 m water depth, none 

of the profile deepening can be due to thaw 

settlement. From the upper 3 m of the section 

eroded since 1951 we subtracted an additional 20 

percent to account for the maximum volume of ice 

that may occur in the form of ice wedges 

(Sellmann and others, 1975). Figure 2 shows that 

12 

3 4 

KILOMETERS 

Figure 1.--Water depths of study area, contoured from Hydrographic Survey number 7991 of 1951, and 

coastlines as mapped in 1951 and 1981. Inset shows typical density of data points defining former bars over 

inner part of our 1985 survey. Bars in 1985 are sketched from our field observations, and from surveys of 

emergent points by State of Alaska in 1984 (N. Johnson, written commun., 1986). 

162 
3 ,..---.---,-,-- Tundra surface---.---..-. 

settlement 

2 

0 

(f) 

a: -1 w 

1-

w -2 

::2! 

-3 

-4 

-5 

-6 

0 1000 2000 3000 

METERS 

Figure 2.--Shoreface evolution from 1951 to 1985 

along transect shown in figure 1. Portion of 

profile change that can be attributed to thaw 

settlement is indicated (blank areas). In 

submerged portion of profile virtually no thaw 

settlement occurs, and most change is due to 

mechanical energy and sediment transport. 

the maximum amount of thaw settlement possible 

according to the wealth of published data can 

account for only a small portion of the section 

that is eroded below sea level. We therefore 

conclude that the shoreface is an important 

sediment source rather than a sediment sink, a 

finding that is supported by shallow seismic 

profiles, borings, mapping of outcrops, and other 

kinds of evidence (Reimnitz and others, 1985). 

During the course of our fieldwork we also 

discovered a series of elongated gravel bars that 

reach sealevel and higher (fig. 3) in numerous 

locations at distances of 250 to 1,000 m from 

coastal bluffs. At four locations (A, B, Esook, and 

the site of the tidal bench marks west of figure 1) 

we managed to cross a bar and find relatively deep 

water in a trough that provides safe anchorage 

protected against storms and ice. The islets along 

the crests, important for defining coastal 

boundaries, were surveyed by the State of Alaska 

in 1984 and 1985, and served as aids to locate the 

bars in figure 2. A study of the 1951 soundings 

reveals the existence of a similar system of 

troughs and bars, locally emergent, at a slight 

angle to the coast. The bars consist of sand and 

gravel, materials absent in local bluffs, and 

probably migrate obliquely shoreward. The islet 

north of A, consisting of "sticky clay, apparently 

163 

bulldozed by pack ice" (N. Johnson, oral commun., 

1986), was very different from the elongated, 

wave-washed gravel bars (fig. 3),. and had 

disappeared by the following year. This 

observation suggests that ice gouging of strata 

exposed on the shoreface, and subsequent 

winnowing by waves and currents, may provide 

coarse material for bar construction where such 

materials are absent in coastal bluffs. In any case, 

such a migrating mini-lagoon system, which here 

spans a distance of at least 40 km of shoreline, has 

not been described previously, and apparently is an 

important component of the shoreface. 

The deepening of the shoreface by over 1 m, 

of which only a small portion can be attributed to 

melting of excess ice, and the migrating bar 

system, demonstrate that mechanical energy is far 

more important than thermal energy for the 

landward shift of the arctic shoreface. The 

deepening extends seaward to at least the 6-m 

isobath. If erosion terminated at the 6-m isobath, 

a bench roughly 10 km wide would have formed 

there during the last 1,000 yr. A study of shelf 

bathymetry nowhere reveals a flat bench which 

can be interpreted as the seaward limit of modern 

erosion, and that question therefore remains 

unanswered. 

FIGURE 3.--View north to 12-m-long gravel islet 

due north of shore station Bin 1985. 

REFERENCES CITED 

Are, F.E., 1980, Thermal abrasion of sea shores (in 

Russian): Moscow, Nauka, 157 p. 

Forbes, D.L., and Frobel, D., 1985, Coastal erosion 

and sedimentation in the Canadian Beaufort 

Sea, in Current Research, Part B: Geological 

Survey of Canada Paper 85-lB, p. 69-80 
Harper, J.R., 1978, The physical processes 

affecting the stability of tundra cliff coasts: 

Baton Rouge, Louisiana State Univesity, Ph.D. 

dissertation, 212 p. 

National Research Council, Marine Board, 1982, 

Understanding the Arctic sea floor for 

engineering purposes: Washington, D.C., 

National Academy Press, Committee on 

Arctic Seafloor Engineering, 141 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, 74 p. 

Sellmann, P.V., Brown, Jerry, Lewellen, R.I., 

McKim, H., and Merry, C., 1975, The 

classification and geomorphic implications of 

thaw lakes on the arctic coastal plain, 

Alaska: Hanover, N.H., U.S. Army Cold 

Region Research and Engineering Laboratory, 

Research Report 344, 21 p. 

164 

Tomirdiaro, S. V., 1975, Thermo abrasion-induced 

shelf formation in the eastern arctic seas of 

the USSR during the Holocene: Earth Science 

Sections, v. 219, no. 1-6, p. 23-26. 

Zenkovich, V.P., 1985, Arctic USSR, in Bird, 

E.C.F. and Schwartz, M.L., eds., The-world's 

coastline: New York, Van Nostrand Reinhold, 

p. 863-871. 

Reviewers: J.R. Dingler and H.A. Karl 
PETROLOGY, AGE, AND ORIGINAL 

TECTONIC SE'ITING OF BASALT FROM THE 

ST. GEORGE BASIN COST NO. 1 WELL, 

SOUTHERN BERING SEA 

Tracy L. Vallier and Bruce M. Herman 

The St. George COST No. 1 well is about 25 

km south of the St. George graben on the outer 

continental shelf of the southern Bering Sea (fig. 

1). St. George graben extends from near the 

Pribilof Islands southeast 300 km towards the 

Alaska Peninsula. Sediment thickness in places 

exceeds 12 km (Comer and others, in press). The 

graben probably opened in response to strike-slip 

motion related to oblique subduction of the Kula 

Plate beneath the Beringian margin in the early 

Tertiary (Marlow and Cooper, 1980). The major 

phase of opening occurred in the early Paleogene 

to late Paleogene (late Oligocene) interval when 

extensive vertical and strike-slip movement 

occurred along a fault that now forms the graben's 

north boundary (Comer and others, in press). 

Subsequent vertical displacement along the fault 

has offset the seafloor. Other young faults within 

the St. George graben also offset the seafloor 

(Gardner and Vallier, 1981). Outside the St. 

George graben, near the COST No. 1 well, faults 

younger than probable middle Eocene are rare 

(Comer and others, in press). 

ST PAUL ISLAND • 

ISLANDS 

STGEORGE ~ 

? ISLAND 

BERING SEA 

The COST No. 1 well penetrated more than 3 

km of Cenozoic sediments and sedimentary rocks 

that unconformably overlie a volcanic rock 

sequence (Turner and others, 1984). The 

sedimentary section ranges in age from middle 

Eocene through Pleistocene (fig. 2) and consists 

mostly of well-stratified sandstone and siltstone 

beds that were deposited in an inner neritic to 

middle bathyal environment (Bolm, 1984a; Larson, 

1984a). A middle Eocene or older basalt and tuff 

sequence was encountered below the unconformity 

at a depth below sea level of 3,164 m (10,380 ft) 

and subsequently was drilled to a total depth of 

4,198 m (13, 771 ft). Regional magnetic studies 

indicate that this igneous sequence is less than 30 

km across (Comer and others, in press). 

Highly vesicular basalt was sampled for 

chemical analyses from depths of 3,326.1 m 

(10,912.5 ft; sample SG-2), 3,327.4 m (10,916.8 ft; 

sample SG-3), 3,328.8 m (10,921.2 ft; sample SG4), and 4,195.3 m (13, 764 ft; sample SG-6). We 

were interested in the petrology, age, and original 

tectonic setting of these rocks, which provide 

clues for interpreting the evolution of the 

Beringian margin. 

The highly vesicular nature of the basalt and 

the large diameter (>1 em) of some vesicles 

suggest that the flows were erupted either 

subaerially or in shallow water. Textures are 

EXPLANATION 

.L..J.FAULT (hachures on down side) 

----- BATHYMETRIC CONTOUR 

COSTNO.l~ 

-<> 

...................... ~68° l66o COST N0.2 

Figure 1.--Index map of St. George Basin area showing locations of major faults, Pribilof Islands, and two 

COST wells. 

165 
porphyritic, hyalopilitic, pilotaxitic, and 

intersertal. All are altered by weathering and 

low-grade metamorphism. Glass m the 

groundmasses has been replaced by chlorite, 

calcite, smectite, and zeolites. Plagioclase 

crystals in some samples are partly replaced by 

zeolites and calcite. Mafic minerals are replaced 

predominantly by chlorite and zeolites. High H20 

and C02 contents (table 1) support the 

petrographic evidence for extreme alteration. The 

alteration probably has affected some of the 

major-element contents, except possibly titanium 

and total iron. Therefore, the major-element data 

alone are not adequate for interpreting either the 

tectonic setting of eruption or the original magma 

-

en 

~ 

l:.tl 

f-.! 

.._ 

~ 

..J 

l:.tl 

> l:.tl 

..J 

< l:.tl 

en 

~ 0 

..J 

l:.tl 

a:l 

:r: 

6: 

l:.tl 

0 

165 

237 

488 

1097 

1637 

2563 

3164 

4198 

TD 

AGE AND LITHOLOGY 

MIDDLE AND LATE PLEISTOCENE (COREHOLE 

PLIOCENE TO PLEISTOCENE 

sandstone, mudstone, and siltstone 

PLIOCENE LATE 

sandstone,siltstone EARLY and mudstone 

MIOCENE LATE 

mudstone,siltstone, ?-

and sandstone EARLY TO 

MIDDLE 

OLIGOCENE LATE 

sandstone,siltstone, 

mudstone and 

conglomerate EARLY 

EOCENE 

siltstone, sandstone, LATE 

mudstone, and 

con_g_lomerate MIDDLE 

MIDDLE EOCENE 

OR OLDER 

BASALTIC BASEMENT 

Figure 2.--Stratigraphic summary of St. George 

COST No. 1 well (modified from Larson, 1984a). 

Middle and late Pleistocene sediments are sand 

and silt. Order of lithology gives relative 

abundance with first lithology dominant. 

166 

characteristics of the rocks. 

The Ti02 contents (table 1), too high for 

volcanic arc basalt (Gill, 1981), are comparable to 

ocean island, continental plateau, and rift 

basalts. Even after considering the possible 

mobility of major elements, the high alkali (Na2o + K 0) content of sample 6 suggests that it is an 

alkalic basalt. The consistently low K2o contents 

in samples 2, 3, and 4 suggest that they are 

tholeiitic. Furthermore, K contents of 19 other 

rocks from the well are low (Bolm, 1984a, tables 2 

and 3; range, 0.027 to 1.5 percent; average, 0.38 

percent), which also suggests that they are 

tholeiitic. 

We can assume that, in addition to Ti, many 

of the trace elements (table 2) were essentially 

immobile during rock alteration, particularly the 

high field strength elements (HFSE) such as Nb, 

Zr, and Ta (Pearce and Cann, 1973); others that 

may have been essentially immobile are the heavy 

rare earth elements (HREE) Lu and Yb, plus the 

elements Y, Th, U, and Hf. The elements Sr, Ba, 

Rb, Cs and some of the light rare earth elements 

(LREE), such as La, Ce, and Nd, may have been 

mobilized by small amounts during alteration. 

Normalized plots of rare earth elements (figure 3) 

show LREE enrichments in all four samples with 

La:tf/YbN ratios of 2.1 to 2.6. Sample 6 is more 

enriched in all rare earth elements than the other 

samples: La is about 60 and Lu about 20 times 

chondrite values. The other samples (2, 3, and 4) 

have similar REE contents and their plots are 

essentially parallel, with La about 30 and Lu about 

Table I.--Major and minor element oxides (wt pet) 

of COST well No. 1 samples, St. George Basin 

region, Bering Sea 

[Analyses by X-ray fluorescence (J. Ardith, J • 

Bartel, J. Stewart, and J. Taggart, USGS, 

analysts). Volatiles and FeO determined by 

gravimetric and wet chemical techniques (S. 

MacPherson, analyst). Major and minor element 

oxides are recalculated to 100 percent after 

subtracting volatiles] 

Oxide SG-2 SG-3 SG-4 SG-6 

Si02 46.04 52.04 45.45 48.25 

Ti02 2.72 2.54 3.11 3.77 

Al203 16.33 16.64 17.08 15.00 

Fe

0

o3 8.64 9.80 6.20 4.81 

Fe 5.84 2.99 7.09 9.56 

MgO 11.62 7.26 9.30 4.16 

MnO .19 .10 .45 .39 

CaO 4.45 4.48 7.81 7.91 

Na20 3.15 3.36 2.71 3.35 

K20 .69 .47 .45 2.00 

P205 .33 .32 .35 .80 

H2o+ 5.12 3.26 3.92 3.02 

H o- 3.39 2.48 2.63 .75 

C02 .26 .23 .18 .92 
100 

80 

60 

40 

30 --6- 20 

:::::::::::::::3-

z10 

6La Sm Eu Tb Yb Lu 

RARE EARTH ELEMENTS 

Figure 3. --Rare earth elements (REE) normalized 

to chondrite values of Masuda and others (1973). 

Sample SG-4 values plot very close to those of 

sample SG-2 and are not shown on the diagram. 

10-12 times chondrite values. Based in part on the 

higher Na2o and K.20 contents and enriched LREE 

patterns, and particularly on the high Y, Zr, Ti, 

Nb, and Hf contents, it is apparent that sample 

SG-6 is alkalic. Trace-element data for the other 

samples indicate that they most likely are 

tholeiitic, but the LREE enrichments suggest that 

they possibly are transitional between tholeiitic 

and alkalic. 

Table 2.--Trace elements (ppm) in basaltic rocks 

from the COST well No. 1, St. George Basin 

region, Bering Sea 

[Methods are X-ray fluorescence (T. Frost, 

analyst) and neutron activation analysis (F. Frey, 

analyst). ---, means not determined] 

Element SG-2 SG-3 SG-4 SG-6 

Rb 4.8 1.7 

Cs 1 0.8 

Sr1 175 275 265 275 

Ba 65 65 60 460 

Sc 35 36 41 36 

Cr 85 82 79 4 

Co 43 46 47 30 

G~ 22 21 

y 29 28 26 58 

zrl 140 160 175 335 

Nh 1 12 12 10 19 

Hf 3.7 3.9 4.3 8.0 

Ta .59 .58 .72 l.l 

Th . 5 .5 .4 1.6 

La 11.5 11.6 10.il 22.5 

Ce 32.2 34.8 29.7 63.6 

Nd 20.0 23.0 19.2 39.3 

Sm S.2 5.'J2 5.27 10.4 

Eu 2.04 2.31 1. 99 3.62 

Tb 1.01 1.03 .99 1.83 

Ho 1., 1.2 1.3 2.2 

Yb 3.17 3.61 3.15 5.81 

Lu .49 . 54 .47 .87 

l X-ray fluorescence techniques 

167 

Fourteen rocks, 12 from the volcanic 

sequence and 2 clasts in the overlying 

conglomerate beds, were radiometrically dated by 

conventional K-Ar methods (table 3). Duplicate 

samples were dated for four of the rocks to 

provide a measure of analytic precision. Ages 

range from about 23 to 136 m.y., but the two 

oldest reported ages are from rocks with very low 

K20 contents, and therefore can be discounted. 

Tfi.e ages of 10 samples cluster between 23 and 38 

m.y. and are thereby younger than the overlying 

sedimentary rocks. Furthermore, two basalt clasts 

from middle Eocene conglomerate beds (the 

uppermost two samples in table 3) show extreme 

variability in ages, and the 27 ± 4 m.y. age is 

definitely too young. Although we did not examine 

thin sections of the samples listed in table 3, we 

believe that most of the K-Ar ages are unreliable 

because of extensive alteration. If all of the 

radiometrically dated basalts are flows (based on 

their highly vesicular character and their 

association with tuffs), then they must be middle 

Eocene or older (older than about 40 million 

years). However, if some of the dated samples are 

sills and are not as altered as the samples we 

examined, then many of the young ages could be 

reliable. This would mean that Oligocene igneous 

intrusive activity took place within the basement 

volcanic sequence. Such a thermal event could 

account for the low-grade metamorphism. 

Unreliable K-Ar ages and an absence of 

fossils in the volcanic rock sequence below the 

regional unconformity make it necessary to 

estimate age by a different technique. Comer and 

others (in press) used seismic-reflection profiles to 

determine interval velocities in acoustically 

stratified rocks beneath the unconformity 10 to 20 

km north of the COST well. Because these rocks 

are from an area beyond the magnetic anomaly 

associated with the volcanics at the well, they are 

believed to be sedimentary. Based on the 

structural and stratigraphic relationships between 

these strata and the volcanic strata at the COST 

No. 1 well, Comer and others (in press) concluded 

that the volcanic rocks are also of Tertiary age. 

Analysis of seismic velocities and magnetic 

field data elsewhere in the region, however, show 

that in many places the rocks beneath the 

unconformity have relatively high interval 

velocities and low magnetic signatures, thereby 

suggesting the presence of upper Mesozoic 

sedimentary rocks (Comer and others, in press). 

At the COST No. 2 well (fig. 1), Oligocene or older 

(possible Eocene) strata unconformably overlie 

Lower Cretaceous and Upper Jurassic sandstone 

and siltstone (Bolm, 1984b; Larson, 1984b). These 

data and the occurrence of Upper Jurassic 

sedimentary rocks dredged from the Pribilof 

Ridge, which are thought to be the volcanic-lithic 

equivalent of the Naknek Formation (Vallier and 

others, 1980; Marlow and Cooper, 1983; Comer and 

others, in press), suggest that rocks beneath the 
regional unconformity probably have different 

ages and are more complex than previously has 

been recognized. 

We used the Ti/100-Yx3-Zr discrimination 

diagram (fig. 4) of Pearce and Cann (1973) to 

interpret the original tectonic setting of the 

basalt. The diagram indicates that the basalts 

were erupted in a within-plate setting (field D on 

fig. 4), but the diagram does not discriminate 

between oceanic island (and seamount) and 

continental plateau or rift basalts. The chemical 

data including HFSE contents and high Ti02 values, plus the plotted points on the Ti/100-Yx3-

Zr diagram (fig. 4), clearly show that the rocks are 

not related to convergent margin (volcanic arc) or 

to mid-ocean ridge volcanism (fields A, B, and 

C). All but sample 6 are overlapped by the 

Pribilof basalt field. 

Basalt sampled at the COST No. 1 well had a 

different magma source than the Pliocene and 

Pleistocene alkalic basalts from the Pribilof 

region, but probably erupted in a similar rift 

setting. Samples 2, 3, and 4 from the COST well 

have lower Sr, Ba, Cr, Th, and light REE, and 

higher Zr, Y, and HREE contents than most of the 

Pribilof samples (Lee-Wong and others, 1979; T.L. 

Vallier, unpub. data). Sample 6, an alkalic basalt, 

has Ti02

, Nb, La, and Th contents comparable to 

Ti/100 

Figure 4.--Ti/100-Yx3-Zr discrimination diagram 

of Pearce and Cann (1973). Fields shown are: B, 

ocean floor basalt; A and B, low-potassium 

tholeiite; C and B, calc-alkalic basalt; and D, 

within-plate basalt. Basalt from mid-ocean ridge 

generally plots within fields A and B. Basalt from 

volcanic arcs plots in fields A, B, or C. Field D 

basalt may have erupted either on oceanic 

seamounts, oceanic islands, or within continental 

framework. Numbered samples are from COST 

No. 1 well. Dashed field is basalt from the 

Pribilof Islands (N=36; Lee-Wong and others, 1979; 

T.L. Vallier, unpub. data). 

168 

the Pribilof basalts, but has high Ba, Y, Zr, and 

HREE concentrations. When plotted on the 

Ti/100-Yx3-Zr discrimination diagram (fig. 4), the 

Pribilof basalt samples generally have higher Ti 

values and thereby plot closer to the Ti apex than 

the COST well samples. 

The COST well basalts most likely are riftrelated and were erupted along the continental 

margin during transtension related to the 

transform or strike-slip tectonic regime that 

occurred in the early Tertiary. In the COST No. 1 

well area, eruption of basalt along the early 

Tertiary rifted Beringian continental margin built 

a large volcanic edifice which was subsequently 

eroded and then was buried by middle Eocene 

sediments as the margin subsided. 

Table 3.--K-Ar radiometric ages of basalt samples 

from St. George Basin COST No. 1 well (Bolm, 

1984a, p. 60) 

[The two shallowest samples are clasts from a 

conglomerate at the base of the sedimentary 

section; all others are from the volcanic 

basement. Analyses by Teledyne Isotopes (T) and 

Mobil Research and Development Corporation 

(M). Duplicate samples indicate precision] 

Depth be low sea iev"l K Age 

m ft (wt pet) (x106 yr) ~bora tory_ 

3149.5 10,333 0.027 120 ± 16 

3162.3 10,375 1.50 27 ± 4 T 

3324.5 10,907.2 .21J7 25.7 ± 1.3 H 

3324.5 10.907.2 .297 22.9 ± 1.2 H 

3330 10,925.3 .410 35.5 ± 1.7 M 

3330 10,925.3 .410 35.1 ± 1.7 M 

3331.5 10,930.2 .386 31.7 ± 1.5 M 

3331.5 10,930.2 • 386 )2.4 ± 1.6 M 

3332.7 10,934 .35 38 ± 6 T 

3335.3 10,942.6 .372 29.2 ± 1.5 M 

3335.3 10,942.6 .372 31.1 ± 1.5 M 

3986.8 13,080 .589 33.7 T 

3991.7 13,096 1.08 28.2 T 

3995.9 13,110 .298 27.3 T 

3999.9 13,123 .086 63.3 

4194.1 13,760 .878 30.2 ± 1.5 T 

4196.5 13,768 .094 136.4 ± 6.9 T 

4196.9 13,769.5 .226 52.2 ± 2.6 T 

REFERENCES CITED 

Bolm, J.G., 1984a, Lithology and well log 

interpretation, in Turner, R.F ., ed., 

Geological and operational summary, St. 

George Basin COST No. 1 well, Bering Sea, 

Alaska: U.S. Minerals Management Service 

OCS Report MMS 84-0016, p. 41-78. 

1984b, Lithology and well log interpretation, 

--in Turner, R.F ., ed., Geological and 

operational summary, St. George Basin COST 

No. 2 well, Bering Sea, Alaska: U.S. Minerals 

Management Service OCS Report MMS 84-

0018, p. 42-72. 

Comer, C.D., Herman, B.M., and Zerwick, S.A., in 

press, Geologic report for the St. George 

Planning Area, Bering Sea, Alaska: U.S. 

Minerals Management Service OCS Report. 
Gardner, J. V., and Vallier, T.L., 1981, Faulting in 

the outer continental shelf of southern Bering 

Sea: American Association of Petroleum 

Geologists Bulletin, v. 65, p. 1568-1573. 

Gill, J.B., 1981, Orogenic andesites and plate 

tectonics: New York, Springer-Verlag, 390 p. 

Larson, J.A., 1984a, Paleontology and 

biostratigraphy, in Turner, R.F., ed., 

Geological and operational summary, St. 

George Basin COST No. 1 well, Bering Sea, 

Alaska: U.S. Minerals Management Service 

OCS Report MMS 84-0016, p. 24-40. 

1984b, Paleontology and biostratigraphy, in 

--Turner, R.F., ed., Geological and operational 

summary, St. George Basin COST No. 2 well, 

Bering Sea, Alaska: U.S. Minerals 

Management Service OCS report MMS 84-

0018, p. 28-37. 

Lee-Wong, F., Vallier, T.L., Hopkins, D.M., and 

Silberman, M.L., 1979, Preliminary report on 

the petrography and geochemistry of basalt 

from the Pribilof Islands and vicinity, 

southern Bering Sea: U.S. Geological Survey 

Open-File Report 79-1556, 51 p. 

Marlow, M.S., and Cooper, A.K., 1980, Mesozoic 

and Cenozoic structural trends under the 

southern Bering Sea shelf: American 

Association of Petroleum Geologists Bulletin, 

v. 64, p. 2139-2155. 

169 

1983, Wandering terranes in southern 

Alaska: The Aleutia microplate and 

implications for the Bering Sea: Journal of 

Geophysical Research, v. 88, p. 3439-3446. 

Masuda, A., Nakamura, N., and Tanaki, T., 1973, 

Fine structures of mutually normalized rareearth patterns of chondrites: Geochimica et 

Cosmochimica Acta, v. 37, p. 239-248. 

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. 

Turner, R.F., McCarthy, C.M., Comer, C.D., 

Larson, J.A., Bolm, J.G., Banet, A.C., and 

Adams, A.J., 1984, Geological and operational 

summary, St. George Basin COST No. 1 well, 

Bering Sea, Alaska: U.S. Minerals 

Management Service OCS Report MMS 84-

0016, 105 p. 

Vallier, T.L., Underwood, M.B., Jones, D.L., and 

Gardner, J. V., 1980, Petrography and geologic 

significance of Upper Jurassic rocks dredged 

near the Pribilof Islands, southern Bering Sea 

continental shelf: American Association of 

Petroleum Geologists Bulletin, v. 64, p. 945-

950. 

Reviewers: A.K. Cooper and M.S. Marlow 
GLORIA IMAGES OBTAINED IN THE 

TACT CORRIDOR OF THE ALEUTIAN 

CONVERGENT MARGIN, 

NORTHERN GULF OF ALASKA 

(ABSTRACT) 

Terry R. Bruns, Michael A. Fisher, 

Paul R. Carlson, Douglas M. Rearic, 

and Lindsay M. Parson 

The Geological Long-Range Inclined Asdic 

(GLORIA) side-scanning sonar system was used 

during June 1986 in the northern Gulf of Alaska to 

acquire images of the seafloor over the 

continental slope and rise in the vicinity of 

Middleton Island, at the southern end of the TransAlaska Crustal Transect (TACT) corridor. The 

GLORIA images provide data on details of 

structural development and continuity, slope 

morphology, and depositional processes along an 

active margin which are not resolvable from 

available coarse bathymetric data or widely 

spaced seismic-reflection data. The tectonic 

setting changes markedly within this region. East 

of Middleton Island, the continental margin 

includes the allochthonous Yakutat terrane which 

is presently colliding with southern Alaska. 

Southwest of Middleton Island, the continental 

margin is part of the Aleutian convergent margin 

and is characterized by compressional deformation 

associated with subduction along the Aleutian 

Trench. The two tectonic regimes have very 

different surface morphologies. 

East of Middleton Island, the continental 

slope is characterized by well-developed dendritic 

drainage patterns that are located between major 

glacially-carved shelf sea valleys, and by large 

sediment masses which have accumulated on the 

170 

upper slope below the sea valleys. These late 

Quaternary(?) sediments bury older dendritic 

drainages. Compressional structures of Pamplona 

Spur, Khitrov Ridge, and associated structures 

caused by the ongoing Yakutat terrane collision 

are clearly visible on the GLORIA images. These 

structures in part form lower-slope barriers to 

downslope sediment transport. 

Southwest of Middleton Island, dendritic 

drainages are absent. The slope is characterized 

by a succession of partly buried, slope-parallel, 

anticlinal ridges with relief of up to 1,000 m. 

These ridges are structurally continuous along the 

100-km-long slope covered by the GLORIA images, 

but are broken into morphologically discontinuous 

segments about 20 to 25 km long. Sediment 

pathways from the shelf break to the Aleutian 

trench are clearly discernible on the slope and pass 

between these ridge segments. The slope sediment 

largely originates at the mouths of the shelf sea 

valleys, and is subsequently either deposited 

around the anticlinal ridges of the slope or 

funneled circuitously downslope between the 

discontinuous ridge segments into the trench. In 

plan view, the initial deformation front at the base 

of the slope is scalloped, a form also evident at 

other convergent margins. Multichannel seismic 

data across the Aleutian convergent margin in this 

region do not resolve whether some of the slope 

structures are compressional anticlines or diapiric 

structures. The extensive continuity of these 

structures expressed on the GLORIA data 

indicates that the structures are most likely 

caused by folding associated with the ongoing 

Pacific plate subduction, rather than by diapirism. 

Reviewers: H.A. Karl and D.S. McCulloch 
BIBLIOGRAPHIES 

Alaska Range 

171 
Reports about Alaska in 

USGS publications released in 1986 

compiled by Ellen R. White 

Some reports dated 1985 did not become available 

until 1986; they are included in this listing 

Affolter, R.H., and Stricker, G.D., 1986, 

Geochemistry of some Tertiary alluvial 

lowland coals from the Capps and Chuitna 

coal fields, Cook Inlet region, Alaska, in 

Garbini, Susan and Schweinfurth, S.P ., eds., 

Symposium proceedings; a national agenda for 

coal-quality research: U.S. Geological Survey 

Circular 979, p. 215. 

Alger, C.S., and Brabb, E.E., 1985, Bibliography of 

United States landslide maps and reports: 

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

585, 119 p. 

Anders, D.E., and Magoon, L.B., 1986, Geochemical 

study of surface oil shows and potential 

source rocks in the Arctic National Wildlife 

Refuge (North Slope Alaska) (abs.), ~ Carter, 

L.M.H., ed., 1986, USGS research on energy 

resources 1986, program and abstracts: U.S. 

Geological Survey Circular 97 4, p. 1-2. 

Angeloni, L.M., Wilson, F.H., and Sutley, Stephen, 

1986, Map and tables showing preliminary rock 

geochemical data, Port Moller, Stepovak Bay, 

and Simeonof Island quadrangles, Alaska: U.S. 

Geological Survey Open-File Report 85-470, 

180 p., scale 1:250,000, 1 sheet. 

Bader, J.W., and Bird, K.J., 1986, Geologic map of 

the Demarcation Point, Mt. Michelson, 

Flaxman Island, and Barter Island quadrangles, 

northeastern Alaska: U.S. Geological Survey 

Miscellaneous Investigations Series Map 

I-1791, scale 1:250,000, 1 sheet. 

Barnes, D.F ., 1986, Gravity data indicate large 

mass and depth of the gabbro body at Haines, 

in Bartsch-Winkler, Susan, and Reed, K.M., 

ed.s., Geologic studies in Alaska by the U.S. 

Geological Survey during 1985: U.S. 

Geological Survey Circular 978, p. 88-92. 

Barnes, P.W., 1986, Sedimentology and stratigraphy 

in the Beaufort Sea, in Miley, J.M., and 

Barnes, P. W ., eds., 1985 field studies, Beaufort 

and Chukchi Seas, conducted from the NOAA 

ship DISCOVERER: U.S. Geological Survey 

Open-File Report 86-202, p. 29-30. 

Barnes, P.W., Miley, J.M., and Phillips, R.L., 1986, 

Introduction, methods, and equipment, in 

Miley, J.M., and Barnes, P. W., eds., 1985 field 

studies, Beaufort and Chukchi Seas, conducted 

from the NOAA ship DISCOVERER: U.S. 

Geological Survey Open-File Report 86-202, 

p. 2-28. 

Bartsch-Winkler, Susan, 1986, Channel migration in 

Turnagain Arm, in Bartsch-Winkler, Susan, 

and Reed, K.M., eds., Geologic studies in 

172 

Alaska by the U.S~ Geological Survey during 

1985: U.S. Geological Survey Circular 978, 

p. 29-33. 

Bartsch-Winkler, Susan and Reed, K.M., eds., 1986, 

Geologic studies in Alaska by the U.S. 

Geological Survey during 1985: U.S. 

Geological Survey Circular 978, 173 p. 

Bartsch-Winkler, Susan, and Reed, K.M., 1986, 

Geologic studies in Alaska by the U.S. 

Geological Survey during 1985; abstract, 

introduction, in Bartsch-Winkler, 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. 1-2. 

Bird, K.J., Magoon, L.B., and Molenaar, C.M., 

1986, Advance in understanding North Slope 

oil and gas accumulations (abs.), in Carter, 

L.M.H., ed., 1986, USGS research on energy 

resources - 1986, program and abstracts: U.S. 

Geological Survey Circular 97 4, p. 6. 

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, 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. 5-10. 

Blome, C.D., and Reed, K.M., 1986, Triassic and 

early Jurassic radiolarian faunas, Brooks 

Range, Alaska: U.S. Geological Survey OpenFile Report 86-120, 27 p. 

Blueford, J.R., 1986, New radiolarian data from 

the Orca Group, Prince William Sound, ~ 

Bartsch-Winkler, 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. 33-34. 

Bolm, J.G., and McCulloh, T.H., 1986, Sandstone 

diagenesis, in Magoon, L.B., ed., Geologic 

studies of the lower Cook Inlet COST No. 1 

well, Alaska Outer Continental Shelf: U.S. 

Geological Survey Bulletin 1596, p. 51-53. 

Bouma, A.H., and Hampton, M.A., 1986, 

Environmental geology, in Magoon, L.B., ed., 

Geologic studies of the lower Cook Inlet 

COST No. 1 well, Alaska Outer Continental 

Shelf: U.S. Geological Survey Bulletin 1596, 

p. 11-15. 

Brown, C.S., Rosenblum, L.A., and Meier, M.F., 

1986, Bed topography inferred from airborne 

radio-echo sounding of Columbia Glacier, 

Alaska: U.S. Geological Survey Professional 

Paper 1258-G, 26 p. 

Brunett, J.O., 1986, Ground-water levels in Alaska, 

water year 1983: U.S. Geological Survey 

Open-File Report 86-56, 225 p. 

Buck, R.A., 1986, Federal response planning in 

Alaska, in Hays, W. W ., and Gori, P .L., eds., 

Proceedings of Conference XXXI, a workshop 
on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 215-219. 

Buck, R.A., 1986, Social effects and disaster 

response, in Hays, W.W., and Gori, P.L., eds., 

Proceedings of Conference XXXI, a workshop 

on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 249-255. 

Cady, J.W., 1986, Geophysics of the YukonKoyukuk province, in Bartsch-Winkler, 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. 21-25. 

Campbell, D.L., and Nokleberg, W.J., 1986, 

Magnetic model of a profile across northern 

Copper River basin, northeastern Gulkana 

quadrangle, in Bartsch-Winkler, 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. 35-38. 

Carte, G. W ., 1986, Improving tsunami preparedness 

in Alaska, in Hays, W.W., and Gori, P.L., eds., 

Proceedings of Conference XXXI, a workshop 

on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 193-199. 

Carter, L.D., and Galloway, J.P., 1986, Engineering 

geologic maps of northern Alaska, Umiat 

quadrangle: U.S. Geological Survey Open-File 

Report 86-335, 17 p., scale 1:250,000, 2 pis. 

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., scale 1:250,000, 2 pis. 

Carter, L.M.H., ed., 1986, USGS research on 

energy resources 1986, program and 

abstracts: U.S. Geological Survey Circular 

974, 84 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. 

Case, J.E., Burns, L.E.,and Winkler, G.R., 1986, 

Maps showing aeromagnetic survey and 

geologic interpretation of the Valdez 

quadrangle, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1714, 

scale 1:250,000, 2 sheets. 

Case, J .E., Fisher, M.A., Moore, G. W ., Moore, 

J.C., and Nelson, S.W., 1986, Preliminary 

geologic interpretation of the aeromagnetic 

map of Afognak and Shuyak Islands, Alaska: 

U.S. Geological Survey Miscellaneous Field 

173 

Studies Map MF-1718, scale 1:250,000, 

1 sheet. 

Childs, J.R., Magistrale, H. W., and Cooper, A.K., 

1985, Free-air gravity anomaly map of the 

Bering Sea: U.S. Geological Survey 

Miscellaneous Field Studies Map MF 1728, 

scale 1:2,500,000, 1 sheet. 

Church, S.E., Gray, J.E., and Delevaux, M.H., 1986, 

Use of Ph-isotopic signatures for geochemical 

exploration in the Healy quadrangle, eastern 

Alaska Range, in Bartsch-Winkler, 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. 38-41. 

Clark, S.D., 1986, Bathymetry in the western 

Beaufort Sea, in Miley, J.M., and Barnes, 

P. W ., eds., 1985 field studies, Beaufort and 

Chukchi Seas, conducted from the NOAA ship 

DISCOVERER: U.S. Geological Survey OpenFile Report 86-202, p. 47-48. 

Claypool, G.E., 1986, Petroleum geochemistry, in 

Magoon, L.B., ed., Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, p. 33-39. 

Collett, T.S., Bird, K.J., Magoon, L.B., 

Kvenvolden, K.A., and Claypool, G.E., 1986, 

Gas hydrates, North Slope of Alaska (abs.), in 

Carter, L.M.H., ed., 1986, USGS research on 

energy resources 1986, program and 

abstracts: U.S. Geological Survey Circular 

974, p. 11-12. 

Combellick, R.A., 1986, Geologic-hazards 

mitigation in Alaska: a review of federal, 

state, and local policies, in Hays, W. W ., and 

Gori, P.L., eds., Proceedings of Conference 

XXXI, a workshop on "evaluation of regional 

and urban earthquake hazards and risk in 

Alaska": U.S. Geological Survey Open-File 

Report 86-79, p. 262-373. 

Cooper, A.K., Marlow, M.S., and Mann, D.M., 1986, 

Multichannel seismic-reflection profiles 

collected in 1977 in the northern Bering Sea: 

U.S. Geological Survey Open-File Report 86-

207, 4 p., scale 1:2,500,000, 1 pl. 

Cooper, A.K., Marlow, M.S., and Scholl, D.W., 

1986, Future hydrocarbon studies in the Bering 

Sea (abs.), in Carter, L.M.H., ed., 1986, USGS 

research on-energy resources - 1986, program 

and abstracts: U.S. Geological Survey 

Circular 974, p. 12. 

Cooper, A.K., 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 1986: U.S. Geological 

Survey ppen-File Report 86-596, 19 p. 

Csejtey, Bela, Jr., Mullen, M.W., Cox, D.P., 

Gilbert, W.G., Yeend, W.E., Smith T.E., 

Wahrhaftig, Clyde, Craddock, Campbell, 

Brewer, W .M., Sherwood, K. W ., Hickman, 
R.G., Stricker, G.D., St.Aubin, D.R., and 

Goerz, D.J ., III, 1986, Geology and 

geochronology of the Healy quadrangle, 

Alaska: U.S. Geological Survey Open-File 

Report 86-396, 96 p., scale 1:250,000, 4 pls. 

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 OpenFile Report 86-589-A, 97 p. 

Davies, J.N., · 1986, Seismicity, seismic gaps and 

earthquake potential in Alaska, in Hays, W. W ., 

and Gori, P .L., eds., Proceedings of 

Conference XXXI, a workshop on "evaluation 

of regional and urban earthquake hazards and 

risk in Alaska": U.S. Geological Survey OpenFile Report 86-79, p. 43-63. 

Detter man, R.L., and Miller, J. W ., 1986, A 

widespread catastrophic event in the Naknek 

Formation, Alaska Peninsula, in BartschWinkler, Susan, and Reed, IEM., eds., 

Geologic studies in Alaska by the U.S. 

Geological Survey during 1985: U.S. 

Geological Survey Circular 978, p. 27-29. 

Detterman, R.L., Miller, J. W., and Case, J.E., 

1986, Megafossil locality map, checklists, and 

pre-Quaternary stratigraphic sections of 

Ugashik, Bristol Bay, and part of Karluk 

quadrangles, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF 1539-B, 

scale 1:250,000. 

Dillon, J.T., Brosge, W.P., Jr., and Dutro, J.T., Jr., 

1986, Generalized geologic map of the 

Wiseman quadrangle, Alaska: U.S. Geological 

Survey Open-File Report 86-219, scale 

1:250,000, 1 sheet. 

Duttweiler, K.A., 1986, Sulfide occurrences in the 

Itkillik River region, southeast Chandler Lake 

quadrangle, Brooks Range, in Bartsch-Winkler, 

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. 10-13. 

Egbert, R.M., 1986, Petrography, provenance, and 

tectonic significance of Middle and Upper 

Jurassic sandstone from Tuxedni Bay, in 

Magoon, L.B., ed., Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, p. 61-63. 

Ehrlich, Edward, 1986, Geology of the calderas of 

Kamchatka and Kurile Islands with 

comparison to calderas of Japan and the 

Aleutians, Alaska: U.S. Geological Survey 

Open-File Report 86-291, 303 p. 

Erickson, B.M., Severson, R.C., and Crock, J.G., 

1986, Analytical results of plant and soil 

samples collected near Flat, Iditarod, and 

Livengood, Alaska, in 1984: U.S. Geological 

Survey Open-File Report 86-473, 24 p. 

Espinosa, A.F., Brockman, S.R., and Michael, J.A., 

1986, Modified Mercally intensity distribution 

for the most significant earthquakes in 

Alaska, 1899-1981: U.S. Geological Survey 

Open-File Report 86-203, 1 sheet. 

Espinosa, A.F., Schmoll, H.R., Brockman, S.R., 

Yehle, L.A., Odum, J.K., Michael, J.A., and 

Rukstales, K.S., 1986, Seismic hazard studies, 

Anchorage, Alaska, in Hays, W. W ., and Gori, 

P.L., eds., Proceedings of Conference XXXI, a 

workshop on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 161-177. 

Fisher, M.A., 1986, Correlation of the COST No. 1 

well data and the marine seismic data, in 

Magoon, L.B., ed., Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, p. 23-27. 

Fisher, M.A., von Huene, Roland, and Hampton, 

M.A., 1986, (release date), Summary geologic 

report for petroleum lease sale #100, Kodiak 

shelf, Alaska: U.S. Geological Survey OpenFile Report 84-24, 51 p., scale 1:500,000, 1 pl. 

Fogleman, K.A., Stephens, C.D., Lahr, J.C., and 

Rogers, J.A.,l986, Catalog of earthquakes in 

southern Alaska for 1984: U.S. Geological 

Survey Open-File Report 86-99, 106 p. 

Fuis, G.S., and Ambos, E.L., 1986, Deep structure 

of the contact fault and Prince William 

terrane - preliminary results of the 1985 

TACT seismic-refraction survey, 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. 41-45. 

Fukuhara, C.R., 1986 (1987), Description 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., 1986, Landslides in Alaska: A 

bibliography of the literature describing 

landslides and other forms of slope 

instability: U.S. Geological Survey Open-File 

Report 86-329, 57 p. 

Glass, R.L., 1986, Hydrologic conditions in Connors 

Bog area, Anchorage, Alaska: U.S. Geological 

Survey Water-Resources Investigations 

86-4044. 

Glass, R.L., 1986, Hydrologic conditions in the 

Klatt Bog area, Anchorage, Alaska: U.S. 

Geological Survey Water-Resources 

Investigations Report WRI 85-4330. 

Goldfarb, R.J., Light, T.D., and Leach, D.L., 1986, 

Nature of the ore fluids at the Alaska-Juneau 

gold deposit, !!! Bartsch-Winkler, 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. 92-95. 

174 
Grantz, Arthur, Mann, D.M., and May, S.D., 1986, 

Multichannel seismic-reflection data 

collected in 1978 in the eastern Chukchi Sea: 

U.S. Geological Survey Open-File Report 86-

206, 4 p., scale 1:1,000,000, 1 pl. 

Grantz, Arthur, Mann, D.M., and May, S.D., 1986, 

Multichannel seismic-reflection data 

collected in 1980 in the eastern Chukchi Sea: 

U.S. Geological Survey Open-File Report 86-

405, 4 p., scale 1:1,000,000, 1 pl. 

Gray, J.E., Church, S.E., and Delevaux, M.H., 1986, 

Lead-isotope results from gold-bearing quartz 

veins from the Valdez and Orca Groups, 

Chugach National Forest, in Bartsch-Winkler, 

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. 45-50. 

Harris, A.G., Tailleur, I.L., and Lane, H.R., 1986, 

Conodont thermal maturation patterns in 

Paleozoic and Triassic rocks, northern Alaska 

- geologic and exploration implications (abs.), 

in Carter, L.M.H., ed., 1986, USGS research on 

energy resources 1986, program and 

abstracts: U.S. Geological Survey Circular 

97 4, p. 21. 

Hays, J.L., 1986, Earthquakes and public policy, !!! 

Hays, W. W ., and Gori, P .L., eds., Proceedings 

of Conference XXXI, a workshop on 

"evaluation of regional and urban earthquake 

hazards and risk in Alaska": U.S. Geological 

Survey Open-File Report 86-79, p. 1-3. 

Hays, W.W., and Gori, P.L., 1986, Background and 

summary of the workshop on "Evaluation of 

regional and urban earthquake hazards and 

risk in Alaska", in Hays, W.W., and Gori, P.L., 

eds., Proceedings of Conference XXXI, a 

workshop on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 4-37. 

Hays, W. W ., and Gori, P .L., eds., 1986, Proceedings 

of Conference XXXI, A workshop on 

"Evaluation of regional and urban earthquake 

hazards and risk in Alaska", September 5-7, 

1985, Anchorage, Alaska: U.S. Geological 

Survey Open-File Report 86-79, 388 p., 

Appendices. 

Hill, P .L., 1986, Bibliographies and location maps 

of aeromagnetic and aeroradiometric 

publications for Alaska and Hawaii: U.S. 

Geological Survey Open-File Report 86-525-E, 

26 p. 

Himmelberg, G.R., Brew, D.A., and Ford, A.B., 

1986, Chemical composition of olivine and 

orthopyroxene in peridotite of the Coast 

plutonic-metamorphic complex near Skagway, 

in Bartsch-Winkler, 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. 95-98. 

175 

Himmelberg, G.R., Ford, A.B., and Brew, D.A., 

1986, The occurrence and chemical 

composition of chloritoid in the metamorphic 

rocks of the Coast plutonic-metamorphic 

complex near Juneau, !!! Bartsch-Winkler, 

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. 99-102. 

Hodel, K.L., 1986, The Sagavanirktok River, North 

Slope Alaska: Characterization of an arctic 

stream:U.S. Geological Survey Open-File 

Report 86-267, 29 p. 

Hudson, Travis, 1986, Plutonism and provenance; 

implications for sandstone compositions, !!! 

Magoon, L.B., ed., Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, p. 55-60. 

Hunt, S.J., 1986, Structural analysis of plutonic and 

metamorphic rocks in an area east of 

Wrangell, Alaska: U.S. Geological Survey 

Open-File Report 86-50, 25 p. 

Hunt, S.J., and Brew, D.A., 1986, Geometric 

structural analysis of part of the western 

Coast plutonic-metamorphic complex east of 

Wrangell, in Bartsch-Winkler, 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. 102-108. 

Jennings, P.C., 1986, Formulating earthquake 

resistant design criteria, in Hays, W. W ., and 

Gori, P.L., eds., Proceedings of Conference 

XXXI, a workshop on "evaluation of regional 

and urban earthquake hazards and risk in 

Alaska": U.S. Geological Survey Open-File 

Report 86-79, p. 148-160. 

Kaufman, D.S., 1986, Surficial geologic map of the 

Solomon, Bendeleben, and southern part of the 

Kotzebue quadrangles, western Alaska: U.S. 

Geological Survey Miscellaneous Field Studies 

Map MF 1838-A, scale 1:250,000, 1 sheet. 

Kayen, R.E., 1986, Geotechnical sampling, in 

Miley, J.M., and Barnes, P. W ., eds., 1985 field 

studies, Beaufort and Chukchi Seas, conducted 

from the NOAA ship DISCOVERER: U.S. 

Geological Survey Open-File Report 86-202, 

p. 49-51. 

Knott, J.M., Lipscomb, S.W., and Lewis, T.W., 

1986, Sediment transport characteristics of 

selected streams in the Susitna River basin, 

Alaska, October 1983 to September 1984: U.S. 

Geological Survey Open-File Report 86-424 W. 

Kockelman, W.J., 1986, Reducing losses from 

earthquakes through personal preparedness, in 

Hays, W. W ., and Gori, P .L., eds., Proceedings 

of Conference XXXI, a workshop on 

"evaluation of regional and urban earthquake 

hazards and risk in Alaska": U.S. Geological 

Survey Open-File Report 86-79, p. 374-388, 

Appendices. 
Lahr, J.C., Stephens, C.D., and Page, R.A., 1986, 

Regional seismic monitoring jn southern 

Alaska: application to earthquake hazards 

assessment, in Hays, W. W ., and Gori, P .L., 

eds., Proceedings of Conference XXXI, a 

workshop on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 64-75. 

Long, C.L., and Thompson, Bill, 1986, Audiomagnetotelluric resistivity traverses in the 

Baird ·Mountains quadrangle, 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. 13-16. 

McLean, Hugh, 1986, Sandstone petrography, in 

Magoon, L.B., ed., Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, p. 47-49. 

Magoon, L.B., 1986, Conclusions, in Magoon, L.B., 

ed., Geologic studies of the lower Cook Inlet 

COST No. 1 well, Alaska Outer Continental 

Shelf: U.S. Geological Survey Bulletin 1596, 

p. 91-99. 

Magoon, L.B., ed., 1986, Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, 99 p. 

Magoon, L.B., 1986, Introduction, in Magoon, L.B., 

ed., Geologic studies of the lower Cook Inlet 

COST No. 1 well, Alaska Outer Continental 

Shelf: U.S. Geological Survey Bulletin 1596, 

p. 5-9. 

Magoon, L.B., 1986, Present-day geothermal 

gradient, !.!! Magoon, L.B., ed., Geologic 

studies of the lower Cook Inlet COST No. 1 

well, Alaska Outer Continental Shelf: U.S. 

Geological Survey Bulletin 1596, p. 41-46. 

Magoon, L.B., 1986, Stratigraphic units of the 

COST No. 1 well, in Magoon, L.B., ed., 

Geologic studies of the lower Cook Inlet 

COST No. 1 well, Alaska Outer Continental 

Shelf: U.S. Geological Survey Bulletin 1596, 

p. 17-22. 

Magoon, L.B., and Egbert, R.M., 1986, Framework 

geology and sandstone composition, in 

Magoon, L.B., ed., Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, p. 65-90. 

March, R.S., Mayo, L.R., and Trabant, D.C., 1986, 

Geodetic survey stations near Mount Spurr 

Volcano, Alaska: U.S. Geological Survey 

Open-File Report 86-137, 14 p. 

Marston, S.A., 1986, Evaluation of the workshop on 

"evaluation of regional and urban earthquake 

hazards and risk in Alaska", in Hays, W.W., 

and Gori, P .L., eds., Proceedings of 

Conference XXXI, a workshop on "evaluation 

176 

of regional and urban earthquake hazards and 

risk in Alaska": U.S. Geological Survey OpenFile Report 86-79, p. 38-42. 

May, S.D., and Grantz, Arthur, 1985, Digital 

marine gravity data collected in the Chukchi 

Sea in 1982: U.S. Geological Survey Open-File 

Report 85-7 42, 4 p. 

Mayo, L.R., and Trabant, D.C., 1986, Recent 

growth of Gulkana Glacier, Alaska Range, and 

its relation to glacier-fed river runoff, in 

Subitzky, Seymour, ed., Selected papers in the 

hydrologic sciences 1986; January 1986: U.S. 

Geological Survey Water-Supply Paper 2290, 

p. 91-99. 

McLean, Hugh, 1986, Tectonics and the potential 

for hydrocarbons in offshore basins of western 

North America (abs.), in Carter, L.M.H., ed., 

1986, USGS research on energy resources 1986, 

program and abstracts: U.S. Geological 

Survey Circular 974, p. 39-40. 

Meador, P.J., Ambos, E.L., and Fuis, Gary, 1986, 

Data report for the North and South 

Richardson Highway profiles, TACT, seismicrefraction survey, southern Alaska: U.S. 

Geological Survey Open-File Report 86-274, 

53 p., scale 1:500,000, 1 sheet. 

Menzie, W.D., Reed, B.L., Foster, H.L., Sutley, 

S.J., Cushing, G. W ., and Jones, G.M., 1986, 

Analyses of selected rock samples from the 

Lime Peak area, Circle C-6 quadrangle, 

Alaska: U.S. Geological Survey Open-File 

Report 86-358, 35 p., scale 1:63,360, 1 pl. 

Menzie, W.D., Reed, B.L., and Keith, T.E.C., 1986, 

Lime Peak - an evolved granite with tinenriched alteration, in Bartsch-Winkler, 

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. 25-27. 

Miley, J.M., and Barnes, P.W., eds., 1986, 1985 field 

studies, Beaufort and Chukchi Seas, conducted 

from the NOAA ship DISCOVERER: U.S. 

Geological Survey Open-File Report 86-202, 

57 p., 5 pis. 

Molenaar, C.M., Bird, K.J., and Collett, T.S., 1986, 

Regional correlation sections across the North 

Slope of Alaska (abs.), in Carter, L.M.H., ed., 

1986, USGS research on energy resources -

1986, program and abstracts: U.S. Geological 

Survey Circular 97 4, p. 43. 

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. 

Morgenson, L., Vallier, T., and Lamothe, P., 1985 

(1986), Chemical data from Tertiary igneous 

rocks, Atka and Amlia Islands, central 

Aleutian Island arc, Alaska: U.S. Geological 

Survey Open-File Report 85-741, 28 p. 
Mosier, E.L., and Lewis, J.S., 1986, Analytical 

results, geochemical signatures, and sample 

locality map of lode gold, placer gold, and 

heavy-mienral concentrates from the 

Koyukuk-Chandalar mining district, Alaska: 

U.S. Geological Survey Open-File Report 86-

345, 174 p., scale 1:250,000. 

Mull, C.G., and Nelson, S. W., 1986, Anomalous 

thermal maturity data from the Orca Group 

(Paleocene and Eocene), Katana-Kayak Island 

area, in Bartsch-Winkler, 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. 50-55. 

Mullen, M. W ., and Csejtey, Bela, Jr., 1986, 

Recognition of a Nixon Fork terrane 

equivalent in the Healy quadrangle, in 

Bartsch-Winkler, 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. 55-60. 

Nelson, S. W ., Blome, C.D., Harris, A. G., Reed, 

K.M., and Wilson, F.H., 1986, Late Paleozoic 

and Early Jurassic fossil ages from the 

McHugh Complex, in Bartsch-Winkler, 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. 60-64. 

Nelson, S. W ., Dumoulin, J.A. and Miller, M.L., 

1986, Geologic map of the Chugach National 

Forest, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF 1645-B, 

scale 1:250,000. 

Nishenko, S.P., and Jacob, Klaus, 1986, Hazards 

evaluation for large and great earthquakes 

along the Queen Charlotte-Alaska-Aleutian 

seismic zone: 1985-2005, in Hays, W. W ., and 

Gori, P.L., eds., Proceedings of Conference 

XXXI, a workshop on "evaluation of regional 

and urban earthquake hazards and risk in 

Alaska": U.S. Geological Survey Open-File 

Report 86-79, p. 83-92. 

Nokleberg, W .J., Aleinikoff, J.N., and Lange, I.M., 

1986, Cretaceous deformation and 

metamorphism in the northeastern Mount 

Hayes quadrangle, eastern Alaska Range, in 

Bartsch-Winkler, 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. 64-69. 

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, !.!!_ Bartsch-Winkler, 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. 69-74 

Odum, J.K., 1986, Compilation of .field and 

laboratory geotechnical test data for U.S. 

Geological Survey drill holes 1C-79, 2C-80, 

CW81-2,and CE82-1, Beluga resource area, 

upper Cook Inlet region, Alaska: U.S. 

Geological Survey Open-File Report 86-382, 

10 p., 4 pls. · 

Odum, J.K., Yehle, L.A., Schmoll, H.R., and 

Gilbert, Chuck, 1986, Description and 

interpretation of geologic materials from 

shotholes drilled for the Trans-Alaska Coastal 

Transect Project, Copper River basin, Alaska, 

May 1985: U.S. Geological Survey Open-File 

Report 86-408, 18 p. 

O'Leary, R.M., Hoffman, J.D., Risoli, D.A., and 

Tripp, R.B., 1986, Analytical results and 

sample locality map of stream-sediment and 

heavy-mineral-concentrate samples from the 

Circle quadrangle, Alaska: U.S. Geological 

Survey Open-File Report 86-204, 126 p., scale 

1:250,000, 1 pl. 

Olsen, H. W ., 1986, Sensitive clays in the 

Bootlegger Cove Formation, !.!!_ Hays, W. W ., 

and Gori, P.L., eds., Proceedings of 

Conference XXXI, a workshop on "evaluation 

of regional and urban earthquake hazards and 

risk in Alaska": U.S. Geological Survey OpenFile Report 86-79, p. 119-133. 

Page, R.A., and Basham, P. W ., 1985, Earthquake 

hazards in the offshore environment: U.S. 

Geological Survey Bulletin 1630, 69 p. 

Page, R.A., Campbell, D.L., Plafker, George, Fuis, 

G.S., Nokleberg, W.J., Ambos, E.L., Mooney, 

W .D., and Fisher, M.A., 1986, Accretion, 

subduction, and underplating in southern 

Alaska - Initial results from the Trans-Alaska 

Crustal Transect (abs.), in Carter, L.M.H., 

ed., 1986, USGS research on energy resources 

1986, program and abstracts: U.S. 

Geological Survey Circular 97 4, p. 50. 

Parrish, J.T., 1986, The Shublik Formation - A 

model for deposition in an ancient marine 

upwelling zone (abs.), in Carter, L.M.H., ed., 

1986, USGS research on energy resources 1986, 

program and abstracts: U.S. Geological 

Survey Circular 97 4, p. 54. 

Phillips, R.L., 1986, Sedimentology and 

stratigraphy in the Chukchi Sea, in Miley, 

J.M., and Barnes, P.W., eds., 1985 field 

studies, Beaufort and Chukchi Seas, conducted 

from the NOAA ship DISCOVERER: U.S. 

Geological Survey Open-File Report 86-202, 

p. 52-53. 

Plafker, George, and Jacob, K.H., 1986, Seismic 

sources in Alaska, !.!!_ Hays, W. W ., and Gori, 

P.L., eds., Proceedings of Conference XXXI, a 

workshop on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 76-82. 

177 
Plafker, George, Nokleberg, W .J., Lull, J.S., 

Roeske, S.M., and Winkler, G.R., 1986, Nature 

and timing of deformation along the contact 

fault system in the Cordova, Bering Glacier, 

and Valdez quadrangles, in Bartsch-Winkler, 

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. 74-77. 

Prensky, S.E., 1986, List of released wells and 

availability of digital well-log data for 

Atlantic, Pacific and Alaskan OCS regions 

through December 31, 1985: U.S. Geological 

Survey Open-File Report 86-48, 42 p. 

Preuss, Jane, 1986, Implementation framework to 

reduce potential losses from tsunami hazards 

in Alaska, in Hays, W. W., and Gori, P.L., eds., 

Proceedings of Conference XXXI, a workshop 

on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 93-107. 

Ramirez, P.C., 1986, Pebble lithology in the 

Chukchi Sea, in Miley, J.M., and Barnes, P.W., 

eds., 1985 field studies, Beaufort and Chukchi 

Seas, conducted from the NOAA ship 

DISCOVERER: U.S. Geological Survey OpenFile Report 86-202, p. 54-57. 

Rearic, D.M., 1986, Beaufort Sea ice gouge studies, 

!.!! Miley, J.M., and Barnes, P.W., eds., 1985 

field studies, Beaufort and Chukchi Seas, 

conducted from the NOAA ship 

DISCOVERER: U.S. Geological Survey OpenFile Report 86-202, p. 41-46. 

Reai'ic, D.M., 1986, Temporal and spatial character 

of newly formed ice gouges in eastern 

Harrison Bay, Alaska, 1977-1982: U.S. 

Geological Survey Open-File Report 86-391, 

54 p. 

Reed, K.M., and Blome, C.D., 1986, Use of 

radiolarian biostratigraphy in stratigraphic 

problems in the Otuk Formation, 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. 16-19. 

Reimnitz, Erk, Kempema, E. W ., and Barnes, P. W ., 

1986, Anchor ice and bottom freezing in highlatitude marine sedimentary environments: 

observations from the Alaskan Beaufort Sea: 

U.S. Geological Survey Open-File Report 86-

298, 22 p. 

Robb, James, 1986, Geophysical data from the 

upper continental slope in the Beaufort Sea, in 

Miley, J.M., and Barnes, P.W., eds., 1985 field 

studies, Beaufort and Chukchi Seas, conducted 

from the NOAA ship DISCOVERER: U.S. 

Geological Survey Open-File Report 86-202, 

p. 31-40. 

Rogers, J.A., 1986, Increasing dynamic range in 

analog seismic data systems used in Alaska: 

178 

U.S. Geological Survey Open-File Report 86-

78,17p. . 

Sable, E.G., Stricker, G.D., and Affolter, R.H., 

1986, Nanushuk Group coal investigations -

North Slope of Alaska (abs.), in Carter, 

L.M.H., ed., 1986, USGS research on energy 

resources 1986, program and abstracts: U.S. 

Geological Survey Circular 974, p. 59-60. 

Schmidt, J.M., and Folger, P.F., 1986, Pb-Zn-Ag 

mineralization in Paleozoic dolostones, 

Powdermilk Prospect, Baird Mountains B-4 

quadrangle, in Bartsch-Winkler, 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. 19-21. 

Schmoll, H.R., 1986, USGS engineering geology 

projects in the Anchorage area, Alaska: a 

review, in Hays, W.W., and Gori, P.L., eds., 

Proceedings of Conference XXXI, a workshop 

on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 134-147. 

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. 

Selkregg, L.L., 1986, A planning and administrative 

model for risk and mitigation, in Hays, W.W., 

and Gori, P .L., eds., Proceedings of 

Conference XXXI, a workshop on "evaluation 

of regional and urban earthquake hazards and 

risk in Alaska": U.S. Geological Survey OpenFile Report 86-79, p. 238-248. 

Selkregg, L.L., 1986, Present planning for, and 

management of seismic risk mitigation, in 

Hays, W. W ., and Gori, P .L., eds., Proceedings 

of Conference XXXI, a workshop on 

"evaluation of regional and urban earthquake 

hazards and risk in Alaska": U.S. Geological 

Survey Open-File Report 86-79, p. 229-237. 

Shearer, C.F., 1986, Minutes of the National 

Earthquake Prediction Evaluation Council, 

September 8 and 9, 1985, Anchorage, Alaska: 

U.S. Geological Survey Open-File Report 86-

92, 268 p. 

Sheinberg, B.J., 1986, Recent and anticipated 

changes in utilization of earthquake hazard 

information for siting considerations; 

Anchorage, Alaska, in Hays, W. W ., and Gori, 

P.L., eds., Proceedings of Conference XXXI, a 

workshop on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 190-192. 

Silverstein, B.L., Brady, A.G., and Mork, P.N., 

1986, Processed strong-motion records from 

the southern Alaska earthquake of January 1, 

1975 0355GMT: U.S. Geological Survey OpenFile Report 86-191, 101 p. 
Simpson, S.L., 1986, Selected geological and 

geophysical remotesensing publications by 

U.S. Geological Survey authors, 1961-1984: 

U.S. Geological Survey Open-File Report 86-

41, 60 p. 

Sloan, C.E., Emery, P.A., and Fair, Diana, 1986, 

Effect of glacier ablation on the Snettisham 

hydroelectric project, Long Lake and Crater 

Lake basins, Alaska, with a section on 

Streamflow records, by R.D. Lamke: U.S. 

Geological Survey Water-Resources 

Investigations WRI 85-4315, 22 p., 1 pl. 

Sloan, C.E., Kernodle, D.R., and Huntsinger, 

Ronald, 1986, Hydrologic reconnaissance of 

the Unalakleet River basin, Alaska 1982-83: 

U.S. Geological Survey Water-Resouces 

Investigations Report 86-4089. 

Stanley, W .D., 1986, Magnetotelluric study of a 

compressed flysch system in the Healy and 

adjacent quadrangles, in Bartsch-Winkler, 

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. 78-81. 

Steinbrugge, K. V., 1986, Earthquake damage - 1964 

lessons learned and relearned, in Hays, W. W ., 

and Gori, P .L., eds., Proceedings of 

Conference XXXI, a workshop on "evaluation 

of regional and urban earthquake hazards and 

risk in Alaska": U.S. Geological Survey OpenFile Report 86-79, p. 178-189. 

Stephens, C.D., Fogleman, K.A., Lahr, J.C., and 

Page, R.A., 1986, Seismicity in southern 

Alaska, October 1984 - September 1985, in 

Bartsch-Winkler, 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. 81-85. 

Stone, D.B., Page, R.A., and Davies, J.N., eds., 

1986, Trans-Aalska lithosphere investigation -

Program prospectus: U.S. Geological Survey 

Circular 984, 24 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., 1986, USGS research onenergy resources 

1986, program and abstracts: U.S. 

Geological Survey Circular 974, p. 65-66. 

Sutley, S.J., O'Leary, R.M., and Goldfarb, R.J., 

1986, Analytical results and sample locality 

map of moraine-sediment, stream-sediment, 

and heavy-mineral-concentrate samples from 

the Cordova and Middleton Island 1 by 3 

qudrangles, Alaska: U.S. Geological Survey 

Open-File Report 86-381, 117 p., scale 

1:250,000, 1 pl. 

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

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

Preliminary geologic map and fossil data, 

179 

Solomon, Bendeleben, and southern Kotzebue 

quadrangles, Seward Peninsula, Alaska: U.S. 

Geological Survey Open-File Report 86-276, 

69 p., scale 1:250,000, 3 pls. 

Turner, L.I., and Sey, Jim, 1986, Emergency 

preparedness planning in Alaska, in Hays, 

W.W., and Gori, P.L., eds., Proceedings of 

Conference XXXI, a workshop on "evaluation 

of regional and urban earthquake hazards and 

risk in Alaska": U.S. Geological Survey OpenFile Report 86-79, p. 220-228. 

Turner, R.F., 1986, Paleontology and 

biostratigraphy of the COST No. 1 well, in 

Magoon, L.B., ed., Geologic studies of the 

lower Cook Inlet COST No. 1 well, Alaska 

Outer Continental Shelf: U.S. Geological 

Survey Bulletin 1596, p. 29-31. 

U.S. Geological Survey, 1986, 1986 annual report on 

Alaska's mineral resources: U.S. Geological 

Survey Circular 983, 4 7 p. 

Updike, R.G., 1986, Engineering geologic maps of 

the Government Hill area, Anchorage, 

Alaska: U.S. Geological Survey Miscellaneous 

Investigations Series Map 1-1610, scale 

1:48,000. 

Updike, R.G., 1986, Status of earthquake hazard 

research in the Anchorage area and upper 

Cook Inlet, Alaska, in Hays, W. W ., and Gori, 

P.L., eds., Proceedings of Conference XXXI, a 

workshop on "evaluation of regional and urban 

earthquake hazards and risk in Alaska": U.S. 

Geological Survey Open-File Report 86-79, 

p. 108-118. 

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. 

von Huene, Roland, 1986, Potential gas generation 

in subducted sediments of the eastern 

Aleutian Trench area (abs.), in Carter, 

L.M.H., ed., 1986, USGS research-on energy 

resources 1986, program and abstracts: U.S. 

Geological Survey Circular 974, p. 69. 

Vyas, Y.K., 1986, An assessment of earthquake 

hazards offshor.e southern Alaska, in Hays, 

W. W ., and Gort, P .L., eds., Proceedings of 

Conference XXXI, a workshop on "evaluation 

of regional and urban earthquake hazards and 

risk in Alaska": U.S. Geological Survey OpenFile Report 86-79, p. 200-214. 

Wade, .w_.M., Nokleberg, W.J., Ferrians, O.J., and 

Wtlhams, J.R., 1986, Geologic bibliography of 

the Gulkana quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 86-332, 

17 p. 

White, E.R., Galloway, J.P., and Booth, S.E., 1986, 

Reports about Alaska in non-USGS 

publications released in 1985 that include 

USGS authors, in Bartsch-Winkler, 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. 160-168. 

White, E.R., Galloway, J.P., and Booth, S.E., 1986, 

Reports about Alaska in USGS publications 

released in 1985, in Bartsch-Winkler, 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. 146-159. 

Wiggins, J.H., 1986, Legal liability problems in 

earthquake preparedness, in Hays, W. W ., and 

Gori, P.L., eds., Proceedings of Conference 

XXXI, a workshop on "evaluation of regional 

and urban earthquake hazards and risk in 

Alaska": U.S. Geological Survey Open-File 

Report 86-79, p. 256-261. 

Wiley, T.J., 1986, Sedimentary basins of offshore 

Alaska and adjacent regions: U.S. Geological 

Survey Open-File Report 86-35, 122 p., scale 

1:2,500,000, 1 pl. 

Wiley, T.J., 1986, Tectonics - First-order control 

of sediment distribution and hydrocarbon 

potential: Examples from the western margin 

of North America (abs.), in Carter, L.M.H., 

ed., 1986, USGS research on energy resources 

1986, program and abstracts: U.S. 

Geological Survey Circular 974, p. 74-75. 

Williams, J.R., 1986, New radiocarbon dates from 

the Matanuska Glacier bog section, in 

Bartsch-Winkler, 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. 85-88. 

Williams, J.R., and Galloway, J.P., 1986, Map of 

western Copper River basin, Alaska, showing 

lake sediments and shorelines, glacial 

moraines, and location of stratigraphic 

sections and radiocarbon-dated samples: U.S. 

Geological Survey Open-File Report 86-390, 

33 p., scale 1:250,000, 1 pl. 

Wilson, F .H., Gajewski, S.Z., and Angeloni, L.A., 

1986, Geological literature of the Alaska 

Peninsula to 1985: U.S. Geological Survey 

Open-File Report 86-176, 114 p. 

Wilson, F.H., and O'Leary, R.M., 1986, Maps and 

tables showing data and analyses of 

semiquantitative emission spectrometry and 

atomic absorption spectrophotometry of rock 

samples, Ugashik, Bristol Bay, and part of 

Karluk quadrangles, Alaska: U.S. Geological 

Survey Miscellaneous Field Studies Map MF 

1539-C, scale 1:250,000. 

Winkler, G.R., 1986, Data releases and folio 

reports prepared for the Alaska Mineral 

Resource Assessment Program and the 

Regional Alaska Mineral Resource Assessment 

Program listed alphabetically by quadrangle, 

in Bartsch-Winkler, 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. 110-145. 

Winkler, G.R., and Grybeck, D.J., 1986, The Alaska 

Mineral Resource Assessment Program in 

1985, in Bartsch-Winkler, 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. 3-5. 

Wolf, S.C., Barnes, P. W., Rearic, D.M., and 

Reimnitz, Erk, 1986, Shallow seismic 

stratigraphy between the Canning River and 

Demarcation Bay, Beaufort Sea, Alaska: U.S. 

Geological Survey Open-File Report 86-582, 

37 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, 

12 p., 1 pl. 

180 
Reports about Alaska in non-USGS 

publications released in 1986 which 

include USGS authors, marked by 

an asterisk (*) 

compiled by Ellen R. White 

Some reports dated 1985 did not become available 

until 1986; they are included in this listing 

* Ager, T.A., 1986, Ice-marginal vegetation 

development in southern Alaska during the 

late Pleistocene and early Holocene: Pollen 

evidence from Cook Inlet region (abs.), in 

American Quaternary Association, Biennial 

meeting, 9th, Urbana, University of IllinoisChampaign, 1985, Program and Abstracts, 

p. 11-12. 

*Ager, T.A., and Brubaker, Linda, 1985, 

Quaternary palynology and vegetational 

history of Alaska, in Bryant, V.M., Jr., and 

Holloway, R.G., eds~ Pollen records of LateQuaternary North American sediments: 

American Association of Stratigraphic 

Palynologists Foundation, p. 353-384. 

*Ager, T.A., *Edwards, L.E., and *Oftedahl, 0., 

1985, Eocene palynomorphs from the Franklin 

Bluffs, Arctic Slope, northeast Alaska (abs.), 

in American Association of Stratigraphic 

Palynologists, Inc., Annual Meeting, 18th, El 

Paso, Tex., 1985, Program and Abstracts, 

no. 18, p. 7. 

*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: Micropalentology, 

v. 32, no. 4, p. 303-315, pls. 1-2. 

*Aleinikoff, J.N., *Dusel-Bacon, Cynthia, and 

*Foster, H.L., 1986, Geochronology of augen 

gneiss and related rocks, Yukon-Tanana 

terrane, east-central Alaska: Geological 

Society of America Bulletin, v. 97, no. 5, 

p. 626-637. 

*Arth, J.G~, *Barker, Fred, *Stern, T.W., and 

*Zmuda, Clara, 1986, The Coast batholith 

near Ketchikan, southeast Alaska: 

geochronology and geochemistry (abs.): 

Geological Society of America, Abstracts 

with Programs, v. 18, no. 6, p. 529. 

*Barker, Fred, *Arth, J.G., and *Stern, T.W., 

1986, Evolution of the coast batholith along 

the Skagway Traverse, Alaska and British 

Columbia: American Mineralogist, v. 71, 

no. 3-4, p. 632-643. 

*Barker, Fred, and *Stern, T. W., 1986, An arc-root 

complex of Wrangellia, E. Alaska Range 

(abs.): Geological Society of America, 

Abstracts with Programs, v. 18, no. 6, p. 534. 

*Barnes, D.F., 1986, Gravitational expression of 

terranes crossed by the southern TACT 

181 

profile, Alaska (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 44, p. 1197. 

*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. 

*Bird, K.J., 1985, The framework geology of the 

North Slope of Alaska as related to oil-source 

rock correlations, in *Magoon, L.B., and 

*Claypool, G.E., eds.-;-Alaska North Slope oilrock correlation study; Analysis of North 

Slope crude: Tulsa, Okla., American 

Association of Petroleum Geologists Studies 

in Geology 20, p. 3-29. 

Biswas, N.N., *Lahr, J.C., and *Page, R.A., 1986, 

Some results on the seismicity of Alaska 

(abs.): Eos (American Geophysical Union 

Transactions), v. 67, no. 44, p. 1236. 

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

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

A.R., 1986, 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. 

*Blome, C.D., 1986, Late Triassic radiolarian 

paleogeography for western Cordilleran 

accreted terranes (abs.): Geological Society 

of America, Abstracts with Programs, v. 18, 

no. 2, p. 87. 

*Box, S.E., 1986, Early Cretaceous shoshonites in 

western Alaska: changing mantle sources 

during arc-continent collision (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1278. 

*Brewer, M.C., 1985, Petroleum exploration and 

environmental protection on the Alaskan 

National Petroleum Reserve, in Gerwick, 

B.C., ed., Arctic Ocean engineering for the 

21st century, Spilhaus Symposium, 1st, 

Williamsburg, Va., 1984, Proceedings: Marine 

Technology Society, p. 203-205. 

*Brooks, P .D., and *O'Brien, T .J ., 1986, The 

evolving Alaska mapping program: PE & RS 

(Photogrammetric Engineering, Remote 

Sensing), v. 52, no. 6, p. 769-777. 

*Bruns, T.R., *Fisher, M.A., *Carlson, P.R., and 

Parson, L.M., 1986, The Yakutat terrane and 

Aleutian convergent. margin, northern Gulf of 

Alaska - GLORIA images obtained in the 

TACT corridor (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 44, p. 1197. 

*Bruns, T.R., *von Huene, R., *Culotta, R.D., 

Lewis, S.D., and Ladd, J.W., 1986, Geology and 

petroleum potential of Shumagin continental 

margin, western Gulf of Alaska (abs.): 

American Association of Petroleum 

Geologists Bulletin, v. 70, no. 7, p. 915. 
Bundtzen, T.K., *Miller, M.L., and Kline, J.T., 

1985, Geology of heavy mineral placer 

deposits of the Iditarod and Innoko precincts, 

western Alaska, in Madonna, J.A., ed., 

Alaskan placer mining, Annual conference, 

7th, Fairbanks, 1985, Proceedings: Fairbanks, 

Alaskan Prospectors Publishing, p. 35-41. 

*Campbell, D.L., *Barnes, D.F., and *Jachens, 

R.C., 1986, Models using isostatic gravity 

anomaly of structures near the northeastern 

edge of the subducting Pacific plate, southcentral Alaska (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 44, p. 1195. 

*Carlson, P.R., *Marlow, M.S., *Rearic, D.M., 

*Dadisman, S.V., and Parson, L.M., 1986, 

GLORIA side-scan imagery of central Bering 

Sea EEZ (abs.): Eos (American Geophysical 

Union Transactions), v. 67, no. 44, 

p. 1228-1229. 

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

*Marincovich, Louie, Jr., *Pease, V.L., and 

*Hillhouse, J. W ., 1986, Late Cenozoic Arctic 

Ocean sea ice and terrestrial paleoclimate: 

Geology, v. 14, no. 8, p. 675-678. 

*Cathrall, John, * Antweiler, John, *Mosier, 

Elwin, *Tripp, Richard, and Lueck, Larry, 

1985, Progress report on U.S. Geological 

Survey Alaskan Gold Project, in Madonna, 

J.A., ed., Alaskan placer mining, Annual 

conference, 7th, Fairbanks, 1985, 

Proceedings: Fairbanks, Alaskan Prospectors 

Publishing, p. 42-47. 

*Colburn, R.H., and *Fuis, G.S., 1986, Velocity 

structure across the northern boundary of the 

Peninsular terrane, Copper River basin, 

Alaska (abs.): Eos (American Geophysical 

Union Transactions), v. 67, no. 44, p. 1198. 

*Collett, T.S., *Bird, K.J., *Kvenvolden, K.A., 

and *Magoon, L.B., 1986, The effect of 

freezing-point depression on ice-bearing 

permafrost, North Slope, Alaska (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 949. 

*Cooper, A.K., *Marlow, M.S., and *Scholl, D.W., 

1986, Frontier basins of Bering Sea (abs.): 

American Association of Petroleum 

Geologists Bulletin, v. 7 0, no. 7, p. 917. 

*Davis, A.S., and *Plafker, George, 1986, Eocene 

basalts from the Yakutat terrane: evidence 

for the origin of an accreting terrane in 

southern Alaska (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 44, p. 963-966. 

*Detterman, R.L., 1986, Glaciation of the Alaska 

Peninsula, in *Hamilton, T.D., *Reed, K.M., 

and Thorson, R.M., eds., Glaciation in Alaska, 

the geologic record: Anchorage, Alaska 

Geological Society, p. 151-170. 

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

and Mook, 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, no. 4, p. 377-387. 

*Drake, D.E., and *Cacchione, D.A., 1986, Field 

observations of bed shear stress and sediment 

resuspension on continental shelves, Alaska 

and California: Continental Shelf Research, 

v. 6, no. 3, p. 415-429. 

Eichelberger, J.C., and *Hildreth, Wes, 1986, 

Research drilling at Katmai, Alaska: Eos 

(American Geophysical Union Transactions), 

v. 67, no.41, p. 778-780. 

*Engdahl, E.R., 1986, Aseismic extension of the 

central Aleutian slab (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 16, p. 380. 

*Engdahl, E.R., 1986, Relocation of teleseismically 

recorded earthquakes in the region of the May 

7, 1986, Andreanof Islands earthquake (abs.): 

Eos (American Geophysical Union 

Transactions), v. 67, no. 44, p. 1081. 

*Engdahl, E.R., and Billington, Selena, 1986, Focal 

depth determination of central Aleutian 

earthquakes: Bulletin of the Seismological 

Society of America, v. 76, no. 1, p. 77-93. 

*Espinosa, A.F., and *Rukstales, K.S., 1986, 

Seismological mapping of the Benioff Zone in 

Alaska and the Aleutian Islands and in central 

western South America (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 16, p. 303. 

*Fierstein, Judy, and *Hildreth, Wes, 1986, Ejecta 

dispersal and dynamics of the 1912 eruptions 

of Novarupta, Katmai National Park, Alaska 

(abs.): Eos (American Geophysical Union 

Transactions), v. 67, no. 44, p. 1246. 

*Fisher, M.A., *Brocher, T.M., *Page, R.A, 

*Plafker, George, *Fuis, G.S., *Nokleberg, 

W.J., and *Campbell, D.L., 1986, Seismic 

reflection images of deep-crustal features of 

south-central Alaska: preliminary results of a 

survey for TACT (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 44, p. 1196. 

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. 

*Frederiksen, N.O., *Ager, T.A., and *Edwards, 

L.E., 1986, Comment on "Early Tertiary 

marine fossils from northern Alaska: 

implications for Arctic Ocean paleogeography 

and faunal evolution": Geology, v. 14, no. 9, 

p. 802-803. 

*Frederiksen, N.O., * Ager, T.A., *Oftedahl, O.G., 

and *Edwards, L.E., 1985, Palynological 

samples near the Cretaceous/Tertiary 

boundary, North Slope of Alaska (abs.), in 

182 
SEPM Annual Midyear Meeting, 2nd, Golden, 

Colo., 1985, Abstracts: Tulsa, Okla., Society 

of Economic Paleontologists and 

Mineralogists, p. 31. 

*Fuis, G.S., *Ambos, E.L., *Mooney, W.D., *Page, 

R.A., and *Campbell, D.L., 1985, Crustal 

structure of southern Alaska - Preliminary 

results of the TACT 1984 seismic refraction 

experiment (abs.): Earthquake Notes, v. 55 

(sic), v. 56, no. 1, p. 23. 

*Gardner, J.V., *Karl, H.A., and Huggett, Q., 

1986, Origin and development of Zhemchug 

Canyon (Bering Sea), adjacent continental 

margin, and abyssal plain as revealed by 

GLORIA (long-range side-scan sonar) and 

seismic data (abs.): Eos (American 

Geophysical Union Transactions), v. 67, no. 

44, p. 1229. 

*Godson, R.H., 1985, Preparation of magnetic 

anomaly maps of Alaska and Hawaii, in Hinze, 

W .J., ed., The utility of regional gravity and 

magnetic anomaly maps: Tulsa, Okla., 

Society of Exploration Geophysicists, 

p. 25-32. 

Goodwin, E.B., *Ambos, E.L., *Fuis, G.S., 

*Mooney, W .D., *Page, R.A., and *Campbell, 

D.L., 1986, The crustal structure of 

Wrangellia, southern Alaska, from seismic 

refraction measurements (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1196. 

*Gryc, George, 1985, Arctic minerals, in Gerwick, 

B.C., ed., Arctic Ocean engineering for the 

21st century, Spilhaus Symposium, 1st, 

Williamsburg, Va., 1984, Proceedings: Marine 

Technology Society, p. 87-88. 

*Hamilton, T.D., 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. 9-49. 

*Hamilton, T.D., *Reed, K.M., and Thorson, R.M., 

1986, Glaciation in Alaska - Introduction and 

overview, in *Hamilton, T.D., *Reed, K.M., 

and Thorson, R.M., eds., Glaciation in Alaska, 

the geologic record: Anchorage, Alaska 

Geological Society, p. 1-8. 

*Hamilton, T.D., *Reed, K.M., and Thorson, R.M., 

eds., 1986, Glaciation in Alaska -The geologic 

record: Anchorage, Alaska Geological 

Society, 265 p. 

*Hampton, M.A., (1983) 1986, Geotechnical 

framework study of the Kodiak Shelf, Alaska, 

in Environmental Assessment of the Alaskan 

Continental Shelf Final Reports of Principal 

Investigators: U.S. Department of 

Commerce, NOAA, OCSEAP Final Report v. 

48, U.S. Department of the Interior OCS 

Study, MMS 86-0065, p. 1-94. 

183 

Harbert, William, *Scholl, D. W ., *Vallier, T.L., 

*Stevenson, A.J., and *Mann, D.M., 1986, 

Major evolutionary phases of a forearc basin 

of the Aleutian terrace: relation to North 

Pacific tectonic events and the formation of 

the Aleutian subduction complex: Geology, 

v. 14, no. 9, p. 757-761. 

*Hildreth, Wes, and *Fierstein, Judy, 1986, Nearvent ejecta around Novarupta, eruption of 

1912, Katmai National Park, Alaska (abs.): 

Eos (American Geophysical Union 

Transactions), v. 67, no. 44, p. 1246. 

*Hillhouse, J. W., *Gramme, C.S., and *Csejtey, 

Bela, Jr., 1985, Tectonic implications of 

paleomagnetic poles from Lower Tertiary 

volcanic rocks, south central Alaska: Journal 

of Geophysical Research, v. 90, no. B14, 

p. 12,523-12,535. 

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., *Jones, D.L., and *Schermer, E.R., 

1985, Tectonostratigraphic terranes of the 

Circum-Pacific region, in Howell, D.G., ed., 

Tectonostratigraphic terranes of the CircumPacific region: Houston, Tex., CircumPacific Council for Energy and Mineral 

Resources, p. 3-30. 

*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., 

Collisiontectonics, Special Publication 19 of 

the Geological Society of London: Palo Alto, 

Calif., Blackwell Scientific Publications, 

p. 367-387. 

*Karl, H.A., *Cacchione, D.A., and *Carlson, 

P.R., 1986, Internal-wave currents as a 

mechanism to account for large sand waves in 

Navarinsky Canyon head, Bering Sea: Journal 

of Sedimentary Petrology, v. 56, no. 5, 

p. 706-714. 

*Kaufman, D.S., and Hopkins, D.M., 1986, Glacial 

history of the Seward Peninsula, in 

*Hamilton, T.D., *Reed, K.M., and Thorsorl, 

R.M., eds., Glaciation in Alaska, the geologic 

record: Anchorage, Alaska Geological Society, 

p. 51-77. 

*Keith, T.E.C., 1986, Distribution of hydrothermal 

alteration associated with Novarupta caldera, 

Katmai National Park, Alaska (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1246. 

Kienle, J., Davies, J.N., *Miller, T.P., and *Yount, 

M.E., 1986, 1986 eruption of Augustine 

Volcano: public safety response by Alaskan 

geologists: Eos (American Geophysical Union 

Transactions), v. 67, no. 29, p. 580-582. 
*Kvenvolden, K.A., and *von Huene, Roland, 1985, 

Natural gas generation in sediments of the 

convergent margin of the eastern Aleutian 

trench area, in Howell, D.G., ed., 

Tectonostratigraphic terranes of the CircumPacific region: Houston, Tex., CircumPacific Council for Energy and Mineral 

Resources, p. 31-49. 

*Lachenbruch, A.H., and *Marshall, B. V., 1986, 

Changing climate: geothermal evidence from 

permafrost in the Alaska Arctic: Science, 

v. 234, no. 4777, p. 689-696. 

*Lahr, J.C., *Page, R.A., *Fogleman, K.A., and 

*Miller, T.P., 1985, The 1984 Sutton 

earthquake: New evidence for activity of the 

Castle Mountain fault (abs.): Earthquake 

Notes, v. 55 (sic), v. 56, no. 1, p. 23. 

*Lahr, J.C., *Page, R.A., *Stephens, C.D., and 

*Fogleman, K.A., 1986, Sutton, Alaska, 

earthquake of 1984: Evidence for activity on 

the Talkeetna segment of the Castle Mountain 

fault system: Bulletin of the Seismological 

Society of America, v. 76, no. 4, p. 967-983. 

Lange, I.M., *Nokleberg, W.J., Plahuta, J.T., 

Krouse, H.R., and *Doe, B.R., 1985, Geologic 

setting, petrology, and geochemistry of 

stratiform sphalerite-galena-barite deposits, 

Red Dog Creek and Drenchwater Creek areas, 

northwestern Brooks Range, Alaska: 

Economic Geology, v. 80, no. 7, p. 1896-1926. 

*Lee, H.J. and *Schwab, W .C., 1983 (1986), 

Geotechnical framework, northeast Gulf of 

Alaska, in Environmental Assessment of the 

Alaskan Continental Shelf Final Reports of 

Principal Investigators: U.S. Department of 

Commerce, NOAA, OCSEAP Final Report, 

v.48, U.S. Department of the Interior OCS 

Study, MMS 86-0065, p. 95-547. 

*Lee, H.J., Asce, M., and *Edwards, B.D., 1986, 

Regional method to assess offshore slope 

stability: Journal of Geotechnical 

Engineering, v. 112, no. 5, p. 489-509. 

(Covers Yakutat slump, and Icy Bay -

Malaspina slump.) 

*Leonard, B.F., 1986, Memorial of A.F. 

· Buddington, November 29, 1890 - December 

25, 1980: American Mineralogist, v. 71, 

no. 9-10, p. 1268-1273. 

Lewis, S.D., Ladd, J.W., *Bruns, T.R., and *von 

Huene, Roland, 1986, Structural development 

of the accretionary prism, Shumagin region of 

the Aleutian trench, from SEABEAM and 

seismic reflection curves (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1197. 

*Lisowski, Michael, and *Savage, J.C., 1986, 

Extremely high shear strain rate measured 

across the Fairweather fault near Yakutat, 

Alaska (abs.): Eos (American Geophysical 

Union Transactions), v. 67, no. 44, p. 907. 

Little, T.A., *Blome, C.D., and *Wolfe, J.A., 1986, 

Paleocene - Eocene sedimentation and wrench 

tectonics along the Border Ranges fault 

system, north-central Chugach Mountains, 

Alaska (abs.): Geological Society of America, 

Abstracts with Programs, v. 18, no. 2, p. 127. 

*Magoon, L.B., and *Bird, K.J., 1985, Alaskan 

North Slope petroleum geochemistry for the 

Shublik Formation, Kingak Shale, pebble shale 

unit, and Torok Formation, in *Magoon, L.B., 

and *Claypool, G.Ed., eds., Alaska North 

Slope oil-rock correlation study; Analysis of 

North Slope crude: Tulsa, Okla., American 

Association of Petroleum Geologists Studies 

in Geology 20, p. 31-48. 

*Magoon, L.B., and *Claypool, G.E., eds., 1985, 

Alaska North Slope oil-rock correlation study; 

Analysis of North Slope crude: Tulsa, Okla., 

American Association of Petroleum 

Geologists Studies in Geology 20. 

Marincovich, Louie, Jr., and Kase, Tomoki, 1986, 

An occurrence of Turritella (Hataiella) sagai 

in Alaska: implications for the age of the Bear 

Lake Formation: Tokyo, Japan, Bulletin of 

the National Science Museum, Series C 

(Geology and Paleontology), v. 12, no. 2, 

p. 61-66. 

*Marincovich, Louie, Jr., *Brouwers, E.M., and 

*Carter, L.D., 1986, Reply to comment by 

*Frederiksen, N.O., and others, on "Early 

Tertiary marine fossils from northern Alaska: 

implications for Arctic Ocean paleogeography 

and faunal evolution": Geology, v. 14, no. 9, 

p. 803-804. 

*Markon, Carl, and Strong, Laurence, 1985, 

Development of land cover and terrain data 

bases for the Arctic National Wildlife Refuge, 

Alaska, using Landsat and digital terrain data 

(abs.), in International Symposium on Remote 

Sensing- of Environment, 19th, Ann Arbor, 

Mich., 1985, Proceedings: Ann Arbor, Mich., 

Environmental Research Institute of 

Michigan, v. 1, p. 333-334. 

*Marlow, M.S., Parson, L.M., *Carlson, P.R., and 

*Cooper, A.K., 1986, Buried basement ridges 

and linear magnetic anomalies in the western 

Aleutian basin, Bering Sea (abs.): Eos, 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1227. 

*McDougall, Kristin, 1986, Maestrichtian benthic 

foraminifers from Ocean Point, Alaska 

(abs.): Geological Society of America, 

Abstracts with Programs, v. 18, no. 6, p. 688. 

*Molnia, B.F., 1986, Glacial history of the 

northeastern Gulf of Alaska - A synthesis, in 

*Hamilton, T.D., *Reed, K.M., and Thorsorl;-

R.M., eds., Glaciation in Alaska, the geologic 

record: Anchorage, Alaska Geological Society, 

p. 219-235. 

184 
*Moore, T.E., 1986, Stratigraphic framework and 

tectonic implications of pre-Mississippian 

rocks, northern Alaska (abs.): Geological 

Society of America, Abstracts with Programs, 

v. 18, no. 2, p. 159. 

Morley, J.J., and *Robinson, S. W., 1986, Improved 

method for correlating late 

Pleistocene/Holocene records from the Bering 

Sea: application of a biosiliceous/geochemical 

stratigraphy: Deep-Sea Research, v. 33, 

no. 9, p. 1203-1211. 

Motyka, R.J., Kodosky, L.G., and *Evans, W ., 1986, 

A review of gas sampling at Augustine 

Volcano, Alaska: 1982-1986 (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1260. 

*Nokleberg, W.J., and *Plafker, George, 1986, 

Structural and tectonic analysis of major 

sutures, eastern Chugach Mountains, Alaska 

(abs.): Eos (American Geophysical Union 

Transactions), v. 6 7, no. 44, p. 1195. 

*Nokleberg, W.J., *Plafker, George, and *Roeske, 

S.M., 1986, Structural analysis and 

accretionary tectonics of Cretaceous and 

early Tertiary flysch sequences juxtaposed 

along the Contact fault, eastern Chugach 

Mountains, Alaska (abs.): Geological Society 

of America, Abstracts with Programs, v. 18, 

no. 2, p. 164. 

*Page, R.A., *Fuis, G.S., *Ambos, E.L., and 

*Stephens, C.D., 1986, Relocated earthquakes 

along the TALI corridor in the Chugach 

Mountains, southern Alaska (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1197-1198. 

*Page, R.A., *Plafker, George, *Fuis, G.S., 

*Nokleberg, W.J., *Ambos, E.L., *Mooney, 

W.D., and *Campbell, D.L., 1986, Accretion 

and sub-duction tectonics in the Chugach 

Mountains and Copper River basin, Alaska: 

Initial results of the Trans-Alaska Crustal 

Transect: Geology, v. 14, no. 6, p. 501-505. 

Peteet, D.M., and *Rubin, Meyer, 1986, 

Paleoecology of the Malaspina and Bering 

Glacier districts, Alaska (abs.), in American 

Quaternary Association, Biennial meeting, 

9th, Urbana, University of Illinois-Champaign, 

1985, Program and Abstracts, p. 13. 

*Phillips, R.L., *Barnes, P.W., *Colgan, M.W., and 

*Miley, J.M., 1986, Quaternary stratigraphy of 

northern Chukchi Sea, Alaska (abs.): 

American Association of Petroleum 

Geologists, Annual Convention, Atlanta, Ga., 

1986, Book of Abstracts, p. 632. 

*Phillips, R.L., *Barnes, P.W., *Colgan, M.W., and 

*Miley, J.M., 1986, Quaternary stratigraphy of 

northern Chukchi Sea, Alaska (abs.): 

American Association of Petroleum 

Geologists Bulletin, v. 70, no. 5, p. 632. 

*Plafker, George, *Ambos, E.L., *Fuis, G.S., 

*Mooney, W.D., *Nokleberg, W.J., and *Page, 

R.A., 1986, Late Mesozoic and Early Tertiary 

185 

accretion and subduction along the southern 

Alaska continental margin (abs.): Geological 

Society of America, Abstracts with Programs, 

v. 18, no. 2, p. 171. 

*Plafker, George, and *Nokleberg, W .J., 1986, 

Evolution of the continental margin of 

southern Alaska along the Trans Alaska 

Crustal Transect (TACT) (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1195. 

*Rearic, D.M., Williams, S., and *Carlson, P.R., 

1986, VAMP's and other acoustic evidence for 

gas-charged sediment in the abyssal Aleutian 

basin, Bering Sea, Alaska (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1211. 

*Reynolds, R.L., *Karachewski, J.A., *Fishman, 

N.S., and *Rosenbaum, J.G., 1986, Magnetic 

properties of greigite-bearing Cretaceous 

strata, North Slope, Alaska (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 923. 

*Roeske, S.M., and Mattinson, J.M., 1986, Early 

Jurassic blueschists and island arc volcanism 

in southern Alaska: A paired metamorphic 

belt? (abs.): Geological Society of America, 

Abstracts with Programs, v. 18, no. 2, p. 178. 

*Roeske, S.M., *Nokleberg, W.J., and *Plafker, 

George, 1986, Structural analysis of the Orca 

Group on the east limb of the Alaska orocline, 

Cordova, eastern Prince William Sound 

(abs.): Geological Society of America, 

Abstracts with Programs, v. 18, no. 2, p. 178. 

*Savage, J.C., and *Lisowski, M., 1986, Strain 

accumulation in the Shumagin seismic gap, 

Alaska: Journal of Geophysical Research, 

v. 91, no. B7, p. 7447-7454. 

*Savage, J.C., and *Lisowski, M., 1986, Strain 

accumulation in the Yakataga seismic gap, 

southern Alaska: Journal of Geophysical 

Research, v. 91, no. B9, p. 9495-9506. 

*Savage, J.C., *Lisowski, M., and *Prescott, 

W.H., 1986, Strain accumulation in the 

Shumagin and Yakataga seismic gaps, 

Alaska: Science, 

v. 231, no. 4738, p. 585-587. 

*Schmidt, J.M., 1986, Stratigraphic setting and 

mineralogy of the Arctic volcanogenic 

massive sulfide prospect, Ambler district, 

Alaska: Economic Geology, v. 81, no. 7, 

p. 1619-1643. 

*Schmoll, H.R., and *Yehle, L.A., 1986, 

Pleistocene glaciation of the Upper Cook Inlet 

basin, in *Hamilton, T.D., *Reed, K.M., and 

Thorson, R.M., eds., Glaciation in Alaska, the 

geologic record: Anchorage, Alaska 

Geological Society, p. 193-218. 

*Scholl, D. W ., and *Ryan, H.F ., 1986, Crustal 

structure and evolution of the Aleutian 

forearc in the vicinity of the Andreanof 

earthquake (abs.): Eos (American Geophysical 

Union Transactions), v. 67, no. 44, p. 1081. 
*Scholl, D. W., *Vallier, T.L., and *Stevenson, 

A.J., 1986, Terrane accretion, production, and 

continental growth: A perspective based on 

the origin and tectonic fate of the AleutianBering Sea region: Geology, v. 14, no. 1, 

p. 43-47. 

*Scholl, D.W., *Vallier, T.L., *Stevenson, A.J., 

and *Ryan, H.F., 1986, Contrasting processes 

controlling basin formation in Cenozoic island 

arcs, Tonga and Aleutian ridges (abs.): 

American Association of Petroleum 

Geologists Bulletin, v. 70, no. 5, p. 646. 

*Scholl, D.W., *Vallier, T.L., *Stevenson, A.J., 

and *Ryan, H.F., 1986, Contrasting processes 

controlling basin formation in Cenozoic island 

arcs, Tonga and Aleutian ridges (abs.): 

American Association of Petroleum 

Geologists, Annual Convention, Atlanta, Ga., 

1986, Book of Abstracts, p. 646. 

Shasby, Mark, and *Carneggie, David, 1986, 

Vegetation and terrainmapping in Alaska using 

Landsat MSS and digital terrain data: PE & 

RS (Photogrammetric Engineering, Remote 

Sensing), v. 52, no. 6, p. 779-786. 

*Silberling, N.J., 1985, Biogeographic significance 

of the Upper Triassic bivalve Monotis in 

Circum-Pacific accreted terranes, in Howell, 

D.G., ed., Tectonostratigraphic terranes of 

the Circum-Pacific region: Houston, Tex., 

Circum-Pacific Council for Energy and 

Mineral Resources, p. 63-70 

Sisson, V.B., Hollister, L.S., and *Plafker, George, 

1986, Rapid two-stage metamorphism of the 

eastern Chugach Mountains, southern Alaska 

(abs.): Geological Society of America, 

Abstracts with Programs, v. 18, no. 2, p. 186. 

Spicer, R.A., and *Parrish, J.T., 1986, Fossil woods 

from northern Alaska and climate near the 

middle Cretaceous North Pole (abs.): 

Geological Society of America, Abstracts 

with Programs, v.18, no. 6, p. 759. 

Stephens, G.C., Evenson, E.B., Clinch, J.M., and 

*Detra, D.E., 1985, In Alaska; geochemical 

research program underway: Geotimes, v. 30, 

no. 7, p. 14-17. 

*Stevenson, A.J., and *Vallier, T.L., 1986, 

Evolution, structure, and petroleum potential 

of Aleutian subduction complex (abs.): 

American Association of Petroleum 

Geologists Bulletin, v. 70, no. 7, p. 935. 

Taber, J.J., *Fuis, G.S., *Ambos, E.L., *Mooney, 

W .D., and *Page, R.A., 1986, Seismic velocity 

structure of the Prince William terrane, 

Alaska (abs.): Eos (American Geophysical 

Union Transactions), v. 67, no. 44, p. 1196. 

Taber, J.J., Jacob, K.H., and *Engdahl, E.R., 1986, 

Seismicity of the Aleutian Arc (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1236. 

Thorson, R.M., and *Hamilton, T.D., 1986, Glacial 

geology of the Aleutian Islands. Based on 

contributions of Robert F. Black, in 

186 

*Hamilton, T.D., *Reed, K.M., and Thorson, 

R.M., eds., Glaciation in Alaska, the geologic 

record: Anchorage, Alaska Geological Society, 

p. 171-191. 

Tolbert, G.E., and *Ericksen, George, 1986, 

Memorial to Helmut Wedow, Jr. 1917-1984: 

Geological Society of America Memorials, 

v. 16. 

*Torresan, M.E., *Schwab, W.C., and *Oscarson, 

R.L., 1985, Controls on the formation of 

fabric in marine sediment from the Gulf of 

Alaska (abs.), in SEPM Annual Midyear 

Meeting, 2nd, Golden, Colo., 1985, Abstracts: 

Tulsa, Okla., Society of Economic 

Paleontologists and Mineralogists, p. 89. 

Underwood, M.B., and *Stevenson, A.J., 1986, 

Dispersal of volcanic sediment in central 

Aleutian forearc and trench (abs.): American 

Association of Petroleum Geologists Bulletin, 

v. 70, no. 5, p. 657-658. 

Underwood, M.B., and *Stevenson, A.J., 1986, 

Dispersal of volcanic sediment in central 

Aleutian forearc and trench (abs.): American 

Association of Petroleum Geologists, Annual 

Convention, Atlanta, Ga., 1986, Book of 

Abstracts, p. 657-658. 

*Vallier, T.L., 1986, Tectonic implications of arcaxis (Wallowa terrane) and back-arc 

(Vancouver Island) volcanism in Triassic rocks 

of Wrangellia (abs.): Eos (American 

Geophysical Union Transactions), v. 67, 

no. 44, p. 1233. 

*von Huene, Roland, *Box, Stephen, *Detterman, 

·Bob, *Fisher, Michael, *Moore, Casey, and 

*Pulpan, Hans, 1985, Centennial 

Continent/Ocean Transect #6: A-2 Kodiak to 

Kuskokwim, Alaska: Geological Society of 

America, 14 p. 

*von Huene, Roland, *Keller, G., *Bruns, T.R., 

and *McDougall, K., 1985, Cenozoic migration 

of Alaskan terranes indicated by paleontologic 

study, in Howell, D.G., ed., 

Tectonostratigraphic terranes of the CircumPacific region: Houston, Tex., CircumPacific Council for Energy and Mineral 

Resources, p. 121-136. 

*Weber, F.R., 1986, Glacial geology of the YukonTanana Upland, in *Hamilton, T.D., *Reed, 

K.M., and Thorson, R.M., eds., Glaciation in 

Alaska, the geologic record: Anchorage, 

Alaska Geological Society, p. 79-98. 

Wolf, L.W., Levander, A.R., and *Fuis, G.S., 1986, 

Upper crustal velocity structure of the 

accreted Chugach terrane, Alaska (abs.): Eos 

(American Geophysical Union Transactions), 

v. 67, no. 44, p. 1195. 

*Yeend, Warren, 1985, Experimental abrasion of 

detrital gold, in Madonna, J.A., ed., Alaskan 

placer minini,"" Annual conference, 7th, 

Fairbanks, 1985, Proceedings: Fairbanks, 

Alaskan Prospectors Publishing, p. 1-8. 
SUBJECT INDEX 

COAL GEOLOGY 

Effects of weathering on petroleum-source evaluation of coals from the Suntrana Formation near Healy, 

Alaska 99 

Richard G. Stanley 

ECONOMIC GEOLOGY 

Structural fabric analysis of the Perseverance Slate and gold-bearing quartz veins in the south ore body of 

the Alaska-Juneau lode system, southeastern Alaska 110 

Christopher C. Barton and Thomas D. Light 

Ultramafic and mafic sills in the vicinity of the Treadwell gold deposits, Douglas Island, southeastern 

Alaska 119 

David A. Brew, Glen R. Himmelberg, Arthur B. Ford, and Robert C. Jachens 

Preliminary ·evaluation of geochemical anomalies in the Baird Mountains quadrangle, Alaska 31 

Peter F. Folger, Richard J. Goldfarb, and Jeanine M. Schmidt 

The Wright Glacier Volcanic Plug and dike swarm, southeastern Alaska 116 

Arthur B. Ford and David A. Brew 

Platinum-group element concentrations in a biotite-rich clinopyroxenite suite, Eagle C-3 quadrangle, 

Alaska 62 

Terry E. C. Keith, Norman J Page, Robert L. Oscarson, and Helen L. Foster 

Newly discovered molybdenite occurrence near Boundary Creek, Coast Mountains, southeastern Alaska 124 

Richard D. Koch, David A. Brew, and Arthur B. Ford 

Status of Alaska Mineral Resources Data System 15 

Kenneth R. Leonard and Donald F. Huber 

Sources of placer gold in the southern part of the White Mountains Recreation Area, east-central Alaska 67 

. Thomas D. Light, John W. Cady, Florence R. Weber, Richard B. McCammon, and C. Dean Rinehart 

Salt Chuck palladium-bearing ultramafic body, Prince of Wales Island 126 

Robert A. Loney, Glen R. Himmelberg, and Nora Shew 

The Alaska-Juneau gold deposit; remobilized syngenetic versus exotic epigenetic origin 128 

Rainer J. Newberry and David A. Brew 

Organic carbon occurrence and content in carbonate rocks from the Omar Copper Prospect, Baird 

Mountains, Alaska 43 

Jeanine M. Schmidt and Peter F. Folger 

Placer gold related to mafic schist(?) in the Circle District, Alaska 74 

Warren Y eend 

GENERAL GEOLOGY 

Cenozoic magmatism in southeastern Alaska (abstract) 137 

David A. Brew 

The Meade Glacier fault-- an important tectonic boundary in the Northern Cordillera, southeastern Alaska 113 

David A. Brew and Arthur B. Ford 

187 
Ultramafic and mafic sills in the vicinity of the Treadwell gold deposits, Douglas Island, southeastern 

Alaska 119 

David A. Brew, Glen R. Himmelberg, Arthur B. Ford, and Robert C. Jachens 

The Wright Glacier volcanic plug and dike swarm, southeastern Alaska 116 

Arthur B. Ford and David A. Brew 

Preliminary geology, including the Tintina fault system, of part of the southwestern Charley River 

quadrangle, Alaska 59 

Helen L. Foster and Terry E.C. Keith 

Newly discovered molybdenite occurrence near Boundary Creek, Coast Mountains, southeastern Alaska 124 

Richard D. Koch, David A. Brew, and Arthur B. Ford 

Paleomagnetic evidence for a latest Pliocene and early Pleistocene age of the upper Yakataga Formation 

on Middleton Island, Alaska 132 

Edward A. Mankinen and George Plafker 

The Alaska-Juneau gold deposit; remobilized syngenetic versus exotic epigenetic origin 128 

Rainer J. Newberry and David A. Brew 

GEOCHEMISTRY 

Geochemical and geologic controls on the inferred occurrence of natural gas hydrate in the Kuparuk 2D-15 

well, North Slope, Alaska 24 

Timothy S. Collett, Keith A. Kvenvolden, Leslie B. Magoon, and Kenneth J. Bird 

Use of factor analysis in locating base metal mineralization in the Killik River quadrangle, Alaska 27 

Karen A. Duttweiler 

Preliminary evaluation of geochemical anomalies in the Baird Mountains quadrangle, Alaska 31 

Peter F. Folger, Richard J. Goldfarb, and Jeanine M. Schmidt 

An application of oblique rotation R-Mode factor analysis in the Mount Hayes quadrangle, Alaska (abstract) 108 

J.D. Hoffman 

Lithostratigraphy, petrology, and geochemistry of the Ordovician Fossil Creek Volcanics, White Mountains, 

east-central Alaska 70 

Karen L. Wheeler, Robert B. Forbes, Florence R. Weber, and C. Dean Rinehart 

GEOPHYSICS 

Ultramafic and mafic sills in the vicinity of the Treadwell gold deposits, Douglas Island, southeastern 

Alaska 119 

David A. Brew, Glen R. Himmelberg, Arthur B. Ford, and Robert C. Jachens 

Sources of placer gold in the southern part of the White Mountains Recreation Area, east-central Alaska 67 

Thomas D. Light, John W. Cady, Florence R. Weber, Richard B. McCammon, and C. Dean Rinehart 

Paleomagnetic evidence for a latest Pliocene and early Pleistocene age of the upper Yakataga Formation 

on Middleton Island, Alaska 132 

Edward A. Mankinen and George Plafker 

MARINE GEOLOGY 

Beaufort Sea coastal currents: a divergence near Barter Island, Alaska? 139 

Peter W. Barnes, Scot Graves, and Erk Reimnitz 

188 
GLORIA images obtained in the TACT corridor of the Aleutian convergent margin, northern Gulf of Alaska 

(abstract} 170 

Terry R. Bruns, Michael A. Fisher, Paul R. Carlson, Douglas M. Rearic, and Lindsay M. Parson, 

Volcanic-arc dacite and early Miocene basalt dredged from the Shumagin margin, Alaska 143 

Terry R. Bruns, Tracy L. Vallier, Leda Beth Pickthorn, and Roland von Huene 

GLORIA images of Zhemchug Canyon and Bering channel-fan system, Bering Sea 147 

Herman A. Karl, James V. Gardner, and Quentin Huggett 

GLORIA side-scan and geophysical surveys of the central Bering Sea in 1986 152 

Michael S. Marlow, Paul R. Carlson, Shawn V. Dadisman, Douglas M. Rearic, Edward J. Maple, and 

Lindsay M. Parson 

Vibracore stratigraphy of the northeastern Chukchi Sea 157 

R. Lawrence Phillips and Mitchell W. Colgan 

Thirty-four-year shoreface evolution at a rapidly retreating arctic coastal site 161 

Erk Reimnitz and Edward W. Kempema 

Petrology, age, and original tectonic setting of basalt from the St. George Basin COST No. 1 Well, southern 

Bering Sea 165 

Tracy L. Vallier and Bruce M. Herman 

MINERALOGY 

Use of factor analysis in locating base metal mineralization in the Killik River quadrangle, Alaska 27 

Karen A. Duttweiler 

PALEONTOLOGY/MICROPALEONTOLOGY 

Late Triassic and Early Cretaceous fossil ages from the McHugh complex, southern Alaska 96 

Steven W. Nelson, Charles D. Blome, and Susan M. Karl 

Plant megafossils, vertebrate remains, and paleoclimate of the Kogosukruk Tongue (Late Cretaceous}, 

North Slope, Alaska 47 

Robert A. Spicer and Judith Totman Parrish 

Ordovician and Silurian fossils from the Doonerak anticlinorium, central Brooks Range, Alaska 40 

John E. Repetski, Claire Carter, Anita G. Harris, and J. Thomas Dutro, Jr. 

A Late Ordovician age reappraisal for the Upper Fossil Creek Volcanics, and possible significance 

for glacio-eustasy 54 

Robert B. Blodgett, Karen L. Wheeler, David M. Rohr, Anita G. Harris, and Florence R. Weber 

PETROLEUM GEOLOGY 

Geochemical and geologic controls on the inferred occurrence of natural gas hydrate in the Kuparuk 2D-15 

well, North Slope, Alaska 24 

Timothy S. Collett, Keith A. Kvenvolden, Leslie B. Magoon, and Kenneth J. Bird 

Effects of weathering on petroleum-source evaluation of coals from the Suntrana Formation near Healy, 

Alaska 99 

Richard G. Stanley 

Thermal maturity and petroleum-source potential of the Cantwell Formation (Paleocene}, Alaska Range 104 

Richard G. Stanley 

189 
PETROLOGY - IGNEOUS 

Cenozoic magmatism in southeastern Alaska (abstract) 137 

David A. Brew 

Ultramafic and mafic sills in the vicinity of the Treadwell gold deposits, Douglas Island, southeastern 

Alaska 119 

David A. Brew, Glen R. Himmelberg, Arthur B. Ford, and Robert C. Jachens 

Volcanic-arc dacite and early Miocene basalt dredged from the Shumagin margin, Alaska 143 

Terry R. Bruns, Tracy L. Vallier, Leda Beth Pickthorn, and Roland von Huene 

The Wright Glacier volcanic plug and dike swarm, southeastern Alaska 116 

Arthur B. Ford and David A. Brew 

Platinum-group element concentrations in a biotite-rich clinopyroxenite suite, Eagle C-3 quadrangle, 

Alaska 62 

Terry E. C. Keith, Norman J Page, Robert L. Oscarson, and Helen L. Foster 

Salt Chuck palladium-bearing ultramafic body, Prince of Wales Island 126 

Robert A. Loney, Glen R. Himmelberg, and Nora Shew 

Petrology, age, and original tectonic setting of basalt from the St. George Basin COST No. 1 Well, southern 

Bering Sea 165 

Tracy L. Vallier and Bruce M. Herman 

Lithostratigraphy, petrology, and geochemistry of the Ordovician Fossil Creek Volcanics, White Mountains, 

east-central Alaska 70 

Karen L. Wheeler, Robert B. Forbes, Florence R. Weber, and C. Dean Rinehart 

PETROLOGY - METAMORPIDC 

Petrography of the Baird Mountains schistose lithologies, northwestern Alaska 49 

Mark R. Zayatz 

PETROLOGY- SEDIMENTARY 

Petrology and provenance of sandstones of the Naknek Formation, Alaska Peninsula 86 

Michael W. Mullen 

Lithostratigraphy, pet.rology, and geochemistry of the Ordovician Fossil Creek Volcanics, White Mountains, 

east-central Alaska 70 

Karen L. Wheeler, Robert B. Forbes, Florence R. Weber, and C. Dean Rinehart 

QUATERNARY GEOLOGY 

Earthquake-caused sedimentary couplets in the Upper Cook Inlet region 92 

Susan Bartsch-Winkler and Henry R. Schmoll 

Glacial advance of late Wisconsin (Itkillik II) age in the uppe.r Noatak River Valley -- a radiocarbon-dated 

stratigraphic record 35 

Thomas D. Hamilt'on, George A. Lancaster, and Deborah A. Trimble 

The Aniakchak tephra deposit, a late Holocene marker horizon in western Ala~ka 19 

James R. Riehle, Charles E. Meyer, Thomas A. Ager, Darrell S. Kaufman, and Robert E. Ackerman 

190 
SEDIMENTOLOGY 

Beaufort Sea coastal currents: a divergence near Barter Island, Alaska? 139 

Peter W. Barnes, Scot Graves, and Erk Reimnitz 

Earthquake-caused sedimentary couplets in the Upper Cook Inlet region 92 

Susan Bartsch-Winkler and Henry R. Schmoll 

A Late Ordovician age reappraisal for the Upper Fossil Creek Volcanics, and possible significance 

for glacio-eustasy 54 

Robert B. Blodgett, Karen L. Wheeler, David M. Rohr, Anita G. Harris, and Florence R. Weber, 

Thirty-four-year shoreface evolution at a rapidly retreating arctic coastal site 161 

Erk Reimnitz and Edward W. Kempema 

Lithostratigraphy, petrology, and geochemistry of the Ordovician Fossil Creek Volcanics, White Mountains, 

east-central Alaska 70 

Karen L. Wheeler, Robert B. Forbes, Florence R. Weber, and C. Dean Rinehart 

STRATIGRAPHY 

Lithostratigraphy, petrology, and geochemistry of the Ordovician Fossil Creek Volcanics, White Mountains, 

east-central Alaska 70 

Karen L. Wheeler, Robert B. Forbes, Florence R. Weber, and C. Dean Rinehart 

Late Mesozoic structural and stratigraphic framework, eastern Bethel quadrangle, southwestern Alaska 78 

Stephen E. Box and John M. Murphy 

Glacial advance of late Wisconsin (Itkillik II) age in the upper Noatak River Valley -- a radiocarbon-dated 

stratigraphic record 35 

Thomas D. Hamilton, George A. Lancaster, and Deborah A. Trimble 

Paleomagnetic evidence for a latest Pliocene and early Pleistocene age of the upper Yakataga Formation 

on Middleton Island, Alaska 132 

Edward A. Mankinen and George Plafker 

Petrology and provenance of sandstones of the Naknek Formation, Alaska Peninsula 86 

Michael W. Mullen 

Early Cretaceous cessation of terrane accretion, northern Eek Mountains, southwestern Alaska 83 

John M. Murphy 

Late Triassic and Early Cretaceous fossil ages from the McHugh complex, southern Alaska 96 

Steven W. Nelson, Charles D. Blome, and Susan M. Karl 

Vibracore stratigraphy of the northeastern Chukchi Sea 157 

R. Lawrence Phillips and Mitchell W. Colgan 

Ordovician and Silurian fossils from the Doonerak anticlinorium, central Brooks Range, Alaska 40 

John E. Repetski, Claire Carter, Anita G. Harris, and J. Thomas Dutro, Jr. 

The Aniakchak tephra deposit, a late Holocene marker horizon in western Alaska 19 

James R. Riehle, Charles E. Meyer, Thomas A. Ager, Darrell S. Kaufman, and Robert E. Ackerman, 

Plant megafossils, vertebrate remains, and paleoclimate of the Kogosukruk Tongue (Late Cretaceous), 

North Slope, Alaska 47 

Robert A. Spicer and Judith Totman Parrish 

191 
Effects of weathering on petroleum-source evaluation of coals from the Suntrana Formation near Healy, 

Alaska 99 

Richard G. Stanley 

Thermal maturity and petroleum-source potential of the Cantwell Formation (Paleocene), Alaska Range 104 

Richard G. Stanley 

STRUCTURAL GEOLOGY- TECTONICS 

Structural fabric analysis of the Perseverance Slate and gold-bearing quartz veins in the south ore body of 

the Alaska-Juneau lode system, southeastern Alaska 110 

Christopher C. Barton and Thomas D. Light 

Late Mesozoic structural and stratigraphic framework, eastern Bethel quadrangle, southwestern Alaska 78 

Stephen E. Box and John M. Murphy 

Cenozoic magmatism in southeastern Alaska (abstract) 137 

David A. Brew 

The Meade Glacier fault-- an important tectonic boundary in the Northern Cordillera, southeastern Alaska 113 

David A. Brew and Arthur B. Ford 

GLORIA images obtained in the TACT corridor of the Aleutian convergent margin, northern Gulf of Alaska 

(abstract) 170 

Terry R. Bruns, Michael A. Fisher, Paul R. Carlson, Douglas M. Rearic, and Lindsay M. Parson, 

Volcanic-arc dacite and early Miocene basalt dredged from the Shumagin margin, Alaska 143 

Terry R. Bruns, Tracy L. Vallier, Leda Beth Pickthorn, and Roland von Huene 

Early Cretaceous cessation of terrane accretion, northern Eek Mountains, southwestern Alaska 83 

John M. Murphy 

Petrology, age, and original tectonic setting of basalt from the St. George Basin COST No. 1 Well, southern 

Bering Sea 165 

Tracy L. Vallier and Bruce M. Herman 

VOLCANOLOGY 

The Aniakchak tephra deposit, a late Holocene marker horizon in western Alaska 19 

James R. Riehle, Charles E. Meyer, Thomas A. Ager, Darrell S. Kaufman, and Robert E. Ackerman, 

The 1986 eruptions of Augustine Volcano, Alaska: hazards and effects 4 

M. Elizabeth Yount, Thomas P. Miller, and Bruce M. Gamble 

192 
AUTHOR INDEX 

Page Page 

Ackerman, R.E. 19 Lancaster, G.A. 35 

Ager, T.A. 19 Leonard, K.R. 15 

Light, T.D. 67' 110 

Barnes, P. W. 139 Loney, R.A. 126 

Barton, C.C. 110 

Bartsch-Winkler, Susan 92 Magoon, L.B. 24 

Bird, K.J. 24 Mankinen, E.A. 132 

Blodgett, R.B. 54 Maple, E.J. 152 

Blome, C.D. 96 Marlow, M.S. 152 

Box, S.E. 78 McCammon, R.B. 67 

Brew, D.A. 113, 116, 119, Meyer, C.E. 19 

124, 128, 137 Miller, T.P. 4 

Bruns, T.R. 143, 170 Mullen, M.W. 86 

Murphy, J.M. 78, 83 

Cady, J. W. 67 

Carlson, P.R. 152, 170 Nelson, S. W. 96 

Carter, Claire 40 Newberry, R.J. 128 

Colgan, M. W. 157 

Collett, T.S. 24 Oscarson, R.L. 62 

Dadisman, S. V. 152 Page, N.J 62 

Dutro, J. T., Jr. 40 Parrish, J.T. 47 

Duttweiler, K.A. 27 Parson, L.M. 152, 170 

Phillips, R.L. 157 

Fisher, M.A. 170 Pickthorn, Leda Beth 143 

Folger, P.F. 31, 43 Plafker, George 132 

Forbes, R.B. 70 

Ford, A.B. 113, 116, Rearic, D. M. 152, 170 

119, 124 Reimnitz, Erk 139, 161 

Foster, H.L. 59, 62 Repetski, J.E. 40 

Riehle, J. R. 19 

Galloway, J.P. 1 Rinehart, C.D. 67, 70 

Gamble, B.M. 4 Rohr, D.M. 54 

Gardner, J. V. 147 

Goldfarb, R.J. 31 Schmidt, J.M. 31, 43 

Graves, Scot 139 Schmoll, H.R. 92 

Shew, Nora 126 

Hamilton, T.D. 1, 35 Spicer, R.A. 47 

Harris, A.G. 40, 54 Stanley, R.G. 99, 104 

Herman, B.M. 165 

Himmelberg, G.R. 119, 126 Trimble, D.A. 35 

Hoffman, J.D. 108 

Huber, D.F. 15 Vallier, T.L. 143, 165 

Huggett, Quentin 147 

von Huene, Roland 143 

Jachens, R.C. 119 

Weber, F.R. 54, 67, 70 

Karl, H.A. 147 Wheeler, K. L. 54, 70 

Karl, S.M. 96 

Kaufman, D.S. 19 Yeend, Warren 74 

Keith, T.E.C. 59, 62 Yount, M.E. 4 

Kempema, E.W. 161 

Koch, R.D. 124 Zaya tz, M. R. 49 

Kvenvolden, K.A. 24 

193 
AUTHORS ADDRESSES 

U.S. Geological Survey 

Geologic Division Mail Stop --

345 Middlefield Road 

Menlo Park, CA 94025 

Barnes, P. W. 

Bird, K.J. 

Box, S.E. 

Brew, D.A. 

Bruns, T.R. 

Carlson, P.R. 

Carter, Claire 

Collett, T.S. 

Dadisman, S. V. 

Fisher, M.A. 

Ford, A.B. 

Foster, H.L. 

Galloway, J.P. 

Gardner, J. V. 

Graves, Scot 

Huber, D.F. 

Jachens, R.C. 

Karl, H.A. 

Keith, T.E.C. 

Kempema, E. W. 

Koch, R.D. 

Kvenvolden, K.A. 

Leonard, K.R. 

Loney, R.A. 

Magoon, L.B. 

Mankinen, E.A. 

Maple, E.J. 

Marlow, M.S. 

Meyer, C.E. 

Mullen, M. W. 

Murphy, J.M. 

Oscarson, R.L. 

Page, N. J 

Phillips, R.L. 

Pickthorn, Leda Beth 

Plafker, George 

Rearic, D.M. 

Reimnitz, Erk 

Rinehart, C.D. 

Stanley, R.G. 

Trimble, D.A. 

Vallier, T.L. 

von Huene, Roland 

White, E.R. 

Y eend, Warren 

Mail Stop 

999 

999 

904 

904 

999 

999 

915 

999 

999 

999 

904 

904 

917 

999 

999 

984 

989 

999 

910 

999 

904 

999 

984 

904 

999 

937 

979 

999 

975 

917 

904 

916 

941 

999 

999 

904 

999 

999 

901 

999 

937 

999 

999 

955 

904 

194 

U.S. Geological Survey 

Branch of Alaskan Geology 

4200 University Drive 

Anchorage, AK 99508-4667 

Gamble, B.M. 

Hamilton, T.D. 

Karl, S.M. 

Lancaster, G.A. 

Miller, T.P. 

Nelson, S. W. 

Riehle, J. R. 

Schmidt, J.M. 

Shew, Nora 

Yount, M.E. 

Zayatz, M.R. 

U.S. Geological Survey 

Branch of Alaskan Geology 

PO Box 80586 

Fairbanks, AK 99708 

Weber, F.R. 

Wheeler, K.L. 

U.S. Geological Survey 

Geologic Division Mail Stop--

Box 25046, DFC 

Denver, CO 80225 

Barton, C.C. 

Blome, C.D. 

Cady, J.W. 

Duttweiler, K.A. 

Hoffman, J.D. 

Light, T.D. 

Parrish, J. T. 

Schmoll, H. R. 

U.S. Geological Survey 

5946 Mcintyre Street 

Golden, CO 80403 

Goldfarb, R.J. 

Mail Stop 

913 

919 

964 

973 

955 

955 

971 

972 
U.S. Geological Survey 

Museum Natural History E-503 

Washington, D.C. 20560 

Dutro, J.T., Jr. 

Harris, A.G. 

Repetski, J.E. 

U.S. Geological Survey 

National Center Mail Stop--

12201 Sunrise Valley Drive 

Reston, VA 22092 

Ager, T.A. 

Bartsch-Winkler, Susan 

McCarn mon, R.B. 

Mail Stop 

970 

920 

920 

U.S. Mineral Management Service 

949 E. 36th Avenue Rm 110 

Anchorage, AK 99508-4302 

Herman, B.M. 

Ackerman, R.E. 

Blodgett, R.B. 

Colgan, M. W. 

Washington State 

University 

Department of 

Anthropology 

Pullman, WA 99164 

Oregon State Unviersity 

Department of Geology 

Corvallis, 0 R 

University of Santa Cruz 

Earth Sciences Board, 

Santa Cruz, CA 95064 

Folger, P.F. 

Forbes, R.B. 

Himmelberg, G.R. 

Huggett, Quentin 

Parson, L. M. 

Kaufman, D.S. 

Newberry, R.J. 

Rohr, D.M. 

Spicer, R.A. 

195 

University of Montana 

Department of Geology 

Missoula, MT 59812 

Division of Geological 

and Geophysical Surveys 

400 Willoughby Bldg 

Juneau, AK 99801 

University of Missouri 

Geology Department, 

Columbia, MO 65201 

Institute of 

Oceanographic Sciences 

Wormley, London 

United Kingdom 

University of Washington 

Department of 

Geological Sciences 

Seattle, WA 98195 

University of Alaska 

Department of Geology 

and Geophysics 

Fairbanks, AK 99775-0760 

Sul Ross State University 

Department of Geology 

Alpine, TX 79830 

Goldsmiths' College 

University of London 

London SE8 3BU 

United Kingdom