_)., 

Paleozoic and Precambrian Rocks of 

Alaska and Their Role in its 

Structural Evolution 

By MICHAEL CHURKIN, JR. 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 740 

Stratigraphy and correlation of Paleozoic 

and Precambrian rocks of Alaska) tectonic 

framework of sedimentatipn} and their bearing 

on sea-floor spreading and continental drift 

in the Arctic 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1973 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 72-600193 

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 

Price: paper cover-90 cents domestic postpaid, or 65 cents GPO Bookstore Stock Number 2401-00272 
CONTENTS 

Page 

Abstract 1 

Introduction ---------------------------------------- 2 

Interpretation of stratigraphic data-Tectonic frame-

, work of sedimentation-Continued 

Lower Paleozoic rocks-Continued 

Page 

Acknowledgments ----------------------------------- 4 

Yukon ·shelf and Richardson basin ------------ 37 

Ancestral Brooks geosyncline ---------------- 37 

Stratigraphy ---------------------------------------- 4 

Precambrian rocks ------------------------------ 4 

Unmetamorphosed rocks --------------------- 4 

Older schists of uncertain age ----------------, 7 

Upper Paleozoic rocks ------·--------------------- 39 

Cordilleran geosyncline ---------------------- 39 

Yukon shelf -------------------------------- 39 

Brooks basin and related successor basins _____ 39 

Lower Paleozoic cycle· of sedimentation --·--------- 10 

Cambrian rocks ----------------------------- 10 

Ordovician rocks ---------------------------- 10 

Silurian rocks ------------------------------- 14 

Lower and Middle Devonian rocks ------------ 18 

Mesozoic and Cenozoic tectonic events affecting Paleozoic rocks--------------------------------------- 40 

Major structural features of Paleozoic rocks _______ 42 

Upper Paleozoic cycle of sedimentation ----------- 19 

Upper Devonian rocks _______ ------------------_ 19 

Foldbelts of Alaska and their extensions into 

Canada and Siberia ------------------------ 42 

Longitudinal faults and topographic trenches __ 46 

Carboniferous rocks ------------------------- 27 

Permian rocks ---------------------------·--- 31 Correlation of the Paleozoic rocks around the edges of 

Interpretation of stratigraphic data__:_Tectonic framework of sedimentation ----------------------------- 35 

Precambrian rocks ------------------------------ 35 

Lower Paleozoic rocks --------------------------- 36 

Cordilleran geosyncline ---------------------- 36 

the Arctic and northern Pacific Basins and sea-floor 

spreading in the Arctic ---------------------------- 47 

FIGURE 1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

References cited ------------------------------------ 56 

Index ---------------------------------------------- 63 

ILLUSTRATIONS 

Tectonic framework of early Paleozoic (Cambrian to Middle Devonian) 

sedimentation ------------------------------------------------

Precambrian rocks and metamorphic complexes that may include Precambrian strata ---------------------------------------------- Columnar sections of late Precambrian and Cambrian rocks in eastcentral Alaska --------~-------------------------------------­

Map showing Cambrian rocks of Alaska ----------------------------

Map showing Ordovician rocks of Alaska ---------------------------

Correlation chart of Ordovician rocks ------------------------------

Map showing Silurian rocks of Alaska -------------------------------

Correlation chart of Silurian rocks ---------------------------------

Index map of southeastern Alaska ---------------------------------

Correlation chart of major rock types of Paleozoic age in southeastern Alaska showing rapid lateral changes in stratigraphy due 

to facies changes and, in some cases, structural dislocations _____ _ 

Map showing Devonian rocks. Excludes coarse terrigenous rocks of Late 

Devonian and Mississippian age (Nation River, Kanayut, and 

Kekiktuk Formations) _________ .:_ _____________________________ _ 

Correlation chart of Devonian rocks --------------------------------

Map showing Devonian coarse terrigenous rocks. Includes Mississippian 

Kekiktuk Conglomerate ----------~----------------------------

Map showing Carboniferous rocks of Alaska ------------------------

Correlation chart of Carboniferous and Permian rocks ---------------

Page 

3 

5 

8 

11 

12 

13 

15 

16 

18 

20 

22 

24 

26 

28 

30 

III 
IV CONTENTS 

Page 

FIGURE 16. Map showing Permian rocks of Alaska ----------------------------- 32 

17. Tectonic framework of Carboniferous and Permian sedimentation _____ 40 

18. Late Mesozoic and Tertiary tectonic features .-----:..._________________ 42 

19. Major foldbelts around the northern Pacific and the Canada Basin part 

of the Arctic ·Ocean ------------------------------------------ 43 

20. Major structural features of the northern circumpacific and adjacent 

parts of the Arctic ------------------------------------------- 45 

21. Boundaries of the major crustal plates in the Northern Hemisphere __ 48 

22. Correlation diagrams of the Paleozoic and Precambrian stratigraphy 

around the Canada Basin and central parts of Alaska and Northeast lJ.S.S.R. ------------------------------------------------ 49 

23. Geologic map and sections of the eastern part of the Chukotsk 

Peninsula, Northeast lJ .S.S.R. -------------------------------- 51 

24. Major tectonic features of the Arctic ------------------------------ 53 
PALEOZOIC AND PRECAMBRIAN ROCKS OF ALASKA 

AND THEIR ROLE IN ITS STRUCTURAL EVOLUTION 

By MICHAEL CHURKIN, JR. 

ABSTRACT 

Acknowledging that there are large gaps in the knowledge 

of the geology of Alaska, the following threefold subdivision 

of Alaska into Paleozoic tectonic elements is proposed: 

( 1) Southern Alaska-the Alaska Range and farther south 

-is the northern end of the Paleozoic Cordilleran geosyncline that rims the eastern Pacific. (2) Northern Alaskathe no~heastern Brooks Range and . the Arctic Coastal 

Plain-is underlain by a pre-Late Devonian foldbelt that 

may continue around the rim of the Canada Basin into the 

Franklinian geosyncline of the Canadian Arctic Islands on the 

east and extend west along the outer margins of the Chukchi 

and East Siberian Seas. ( 3) East-central Alaska, with a 

thinner, mainly carbonate rock section, seems to be a western 

extension of the Yukon shelf that separates the circumarctic 

geosyn~linal trend from the Cordilleran geosyncline along the 

Pacific margin of southern Alaska. 

In southeastern Alaska, deposition of graywacke, polymictic conglomerate, and argillaceous rocks interbedded with 

pillow basalts, breccias, and tuffs prevailed throughout most 

of the Paleozoic. One exception, a widespread red-bed conglomerate and crossbedded sandstone sequence of Late 

Silurian (?) and Early Devonian age marks a regional break 

in sedimentation. Local thick limestones made up of fragmented fossils indicate reef and shallow-water shell-bank 

development. Very abrupt facies changes reflect rugged bottom relief largely controlled by volcanic activity. The high 

proportion of volcanic rocks and some plutonic intrusions of 

early Paleozoic age that have closely associated thick lenses 

of synorogenic boulder conglomerates imply high tectonic 

mobility. Isolated exposures of similar Paleozoic rocks in the 

Wrangell Mountains, Alaska Range, and the Alaska Peninsula suggest that the coarse detrital-volcanic belt of southeastern Alaska rims the northern Pacific Basin and may continue west along the edge of the Bering Shelf sea into 

the Koryak Upland of Northeast U.S.S.R., where similar 

sequences occ~r. 

In northern Alaska, a deformed belt of pre-Late Devonian 

strata containing interlayered volcanic rocks occurs in the 

northeastern Brooks Range. Farther west, in the Arctic 

Coastal Plain, boreholes have 'penetrated steeply dipping, 

weakly metamorphosed rocks that probably belong to this 

same foldbelt, thereby suggesting that a largely buried and 

partly destroyed geosyncline of pre-Late Devonian age, including rocks of Cambrian and Silurian age, lies along the 

northern edge of Alaska. Thick sections of chert-rich detrital 

rocks of Late Devonian and, farther north, of Mississippian 

age lie unconformably on this ancestral Brooks geosyncline 

and were derived from uplifts within the geosyncline. These 

clastic deposits, at least in part of nonmarine origin, continue 

around the edge of the Canada Basin .from Alaska east to 

Ellesmere Island and west to Wrangell Island. Absolute age 

determinations indicate that the intrusion of granitic rocks 

around the margin of the Canada Basin was probably related 

to the same middle-Paleozoic orogeny that produced the wedge 

of Upper Devonian and Mississippian clastics. After the 

orogeny, marine shale and carbonate rocks were again deposited around the edges of the Canada Basin. In the Brooks 

Range, the base of the Carboniferous section becomes progressively younger northward, and the whole section has 

more terrigenous detritus in northern parts of the range. 

This northward transgression, in addition to the fact that the 

unconformably overlying Permian (in boreholes north of the 

Brooks Range) is a chert-pebble conglomerate, suggests that 

in the late Paleozoic a source area existed in the northern 

Brooks Range and farther north as it had in the Late 

Devonian. · 

In east-central Alaska, Cambrian through Devonian time 

is represented by a thin, but nearly complete, sequence mainly 

of limestone. Along the Yukon River, which is the south edge 

of the Yukon shelf, thin graptolitic shale and chert and, in 

places, Devonian pillow basalt indicate a transitional facies 

into the Cordilleran geosyncline farther south. In the Late 

Devonian, thick nonmarine conglomerate and sandstone were 

apparently derived from uplifts within the nearby Cordilleran 

geosyncline, starting the upper Paleozoic cycle of higher 

tectonic activity in the interior parts of Alaska. Carboniferous rocks in east-central Alaska form a thin sequence 

of interbedded limestone, shale, and chert. Pre-Permian erosion has removed most of the Carboniferous, and the Permian 

is a thin sequence of conglomerate, sandstone, and limestone. 

Non volcanic, nearly pure carbonate sections in the Seward 

Peninsula, in parts of southwestern Alaska and on St. 

Lawrence Island, especially those representing the lower 

Paleozoic, suggest that the carbonate shelf type of sedimentation characteristic of east-central Alaska extended into 

western Alaska. Similar strata on the Chukotsk Peninsula 

indicate that this belt of mainly carbonate rock continues 

west across the Bering Strait, thereby linking the geology 

of Alaska to Asia. 

During the Mesozoic and Cenozoic the broad Paleozoic stratigraphic belts of Alaska were deformed into numerous 

troughs and uplifts. Batholithic intrusions, volcanism, and 

metamorphism, together with penetrative folding and faulting during the multiple episodes of Mesozoic and Cenozoic 

orogeny, have largely obscured the Paleozoic and older 

structures. However, the patterns of basins and uplifts in 

the Mesozoic and, to a lesser degree, in the Tertiary tend to 

follow the trend of the Paleozoic stratigraphic belts that 

form their basement. The Cordilleran foldbelt that had its 

1 
2 PALEOZOIC ,AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

climactic orogeny during the Mesozoic includes most of 

Alaska and correlates with the Chukotka foldbelt in Northeast U.S.S.R. The younger circumpacific foldbelt of Cenozoic 

age produced folds and general uplift in Kamchatka and the 

Koryak Mountains and in the Gulf of Alaska includes a 

thrust belt. Another, though less obvious, foldbelt of middle 

Paleozoic age discontinuously rims the southern margin of 

the Canada Basin. It is deeply eroded and is largely covered 

by flat-lying Mesozoic and Cenozoic deposits that form the 

Arctic Coastal Plain. 

In evaluating continental drift in the Arctic, there is no 

direct evidence for large-scale drift between Alaska and 

Northeast U.S.S.R. Correlations of stratigraphy, paleogeography, structure, igneous activity, metamorphism, ore deposits, and crustal structure between Alaska and easternmost 

U.S.S.R. indicate that these two continental areas have been 

connected since the Paleozoic and probably since the Precambrian, and that no plate boundary passes through the 

Bering Strait. 

Sea-floor spreading that fcrmed the Atlantic Basin seems 

to have extended across the Eurasia Basin part of the 

Arctic. Modern sea-floor-spreading tectonics on the Gakkel 

submarine ridge of the Eurasia Basin continue landward into 

the Yakutia region of Siberia to produce seismic activity, 

faulting, and volcanism. 

Earlier compressional features of Paleozoic and, especially, 

Mesozoic age on trend with the Arctic Ocean opening, contrast strongly with these modern tensional movements. Stratigraphic, structural, and petrological features suggest that a 

fossil plate boundary within Yakutia marks the western 

boundary of the North American plate. This plate boundary 

and bends in various large-scale structures in Alaska and 

Northeast U.S.S.R. may be in part results of compression 

in this narrow continental segment as the leading edges of 

the Eurasian and North American plates collided in Early 

Cretaceous time, perhaps as a consequence of opening of 

the northern Atlantic. 

INTRODUCTION 

Alaska, being a narrow isthmus connecting North 

America to Eurasia, is a key to understanding the 

geologic correlations around the northern Pacific, on 

the one hand, and the geology of the circumarctic 

areas, on the other. Besides serving as a link between 

North America and Eurasia, Alaska is important in 

evaluating the ancient histories of the Arctic and 

northern Pacific Oceans through a study of its continental margins. Finally, Alaska plays a vital role 

in testing theories of continental drift and sea-floor 

spreading in the Arctic. 

Although a number of stratigraphic aDd tectonic 

summaries of Alaska have been made, these have 

focused mainly on Mesozoic and Tertiary rocks (Mertie, 1930b; Smith, 1939; Eardley, 1948; Payne, 1955; 

Gates and Gryc, 1963). Knowledge of Precambrian 

and Paleozoic rocks in Alaska has substantially increased since Schuchert's first maps covering North 

America were published in 1910. To date, however, 

there is no regional synthesis of the Precambrian 

and Paleozoic history of Alaska using the latest data 

to make modern correlation diagrams, lithofacies 

maps, and paleotectonic maps useful in interpreting 

earth history. It is my goal here to summarize the 

present knowledge of the Precambrian and Paleozoic 

rocks of Alaska and to interpret their role in its tectonic and structural development. 

The first part of the paper summarizes the Precambrian and Paleozoic stratigraphy of Alaska. The 

second part is an interpretation of the tectonic and 

structural evolution of Alaska based on the stratigraphic data and on structural and geophysical data. 

Because of the great variation in the level of our 

'knowledge of the different areas of Alaska, and for 

the sake of brevity, only the more thoroughly studied 

stratigraphic successions in each geologic province 

are discussed and illustrated by columnar sections. 

A list of the major literature references is given to 

guide the reader in obtaining details. 

Acknowledging that there are big gaps in the present knowledge of the Paleozoic rocks of Alaska, 

especially in its southwestern and central interior 

parts, the author proposes a threefold tectonic subdivision of Alaska (fig. 1; see also fig. 17). Apparently, during most of Paleozoic time sedimentation 

in Alaska was controlled by the Cordilleran geosyncline in its southern part and by several geosynclinal 

cycles in northern Alaska along the southern edge 

of the Arctic Basin. In the interior of Alaska the 

Paleozoic record is less clear, but at least in eastcentral Alaska a western extension of the Yu~on 

shelf seemed to have separated these two geosynclinal trends. 

Detailed stratigraphic studies have been made in 

some areas in conjunction with reconnaissance geologic mapping. In most places where Paleozoic rocks 

have been mapped, however, their ages and stratigraphic succession are poorly known because of 

structural complexities and incomplete knowledge of 

fossils and other tools for correlation. The stratigraphic sequences of east-central Alaska and southeastern Alaska are emphasized because they are 

among the most thoroughly studied, seem to be the 

most complete, and are the most familiar to me. It 

must be noted that the correlations, and consequently 

the general interpretations offered, are only preliminary. The accelerated program of geological exploration that has started with the discovery of large oil 

reserves along the Arctic coast of Alaska will provide 

much-needed subsurface information that could re-
INTRODUCTION 3 

I 

"' 

\ 

\ 

I 

/ 

I 

/ 

150 

E X PLANATION 

~ Circumpacific geosynclinal belt Carbonate roc k shelf areas Circumarctic geosynclinal belt Precambrian 

-

shield 

FIGURE 1.-Tectonic framework of early Paleozoic (Cambrian to Middle Devonian) sedimentation. 

sult in major changes in even the broadest tectonic 

outline. 

For a summary of the Paleozoic stratigraphy and 

tectonic history of Canada adjacent to Alaska, the 

reader may refer to Gabrielse (1967), Gabrielse and 

Wheeler (1961), and Zeigler (1969). For a regional 

analysis of parts of the Soviet Union adjacent to 

Alaska, the following references are useful: Belyi, 

1964; Bogdanov, 1963, Bogdanov and Tilman, 1964; 

Egiazarov and others, 1965; Egiazarov, 1969; Gni-
4 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

bidenko, 1969; Krasniy, 1966; Tilman, 1962; and 

Yanshin, 1966. 

ACKNO\VLEDGMENTS 

Most of the references to geologic studies that are 

cited herein are publications of the U.S. Geological 

Survey-the organization long responsible for systematically exploring and mapping Alaska. Specific 

recognition is given the following members of the 

U.S. Geological Survey: E. E. Brabb, for valuable 

discussions of the stratigraphy and structure of eastcentral Alaska; D. A. Brew, for familiarizing me 

with the stratigraphy of the Freshwater Bay-Glacier 

Bay areas; W. P. Brosge and H. N. Reiser, for much 

information on the Brooks Range; R. M. Chapman, 

F. R. Weber, and R. L. Foster, for helicopter reconnaissance and much information on the Livengood 

district ; R. L. Detterman and B. L. Reed, for information on the Alaska Peninsula; G. D. Eberlein, for 

much of th~ basic knowledge of the stratigraphy in 

southeastern Alaska; R. B. Forbes for information 

on the Birch Creek Schist; J. M. Hoare and W. H. 

Condon for data concerning southwestern Alaska;· 

E. H. Lathram, for stimulating discussions on the 

tectonics of northern Alaska; E. M. MacKevett and 

J. G. Smith for information on the Wrangell Mountains; L. J. P. Muffler, for a tour of the Kuiu Island 

area; A. T. Ovenshine, for conodont correlations and 

Silurian and Devonian stratigraphy of the Kosciusco 

Island area; W. W. Patton, for data concerning the 

Koyukuk River area and St. Lawrence Island; George 

Plafker, for discussion of how earth movements in 

the Gulf of Alaska associated with the 1964 earthquake-may relate to the tectonic development of 

Alaska; B. L. Reed, for acquainting me with part of 

the Alaskan Range and for structural information in 

the northeastern Brooks Range; D. H. Richter, for 

data on the stratigraphy of the eastern Alaska 

Range; C. L. Sainsbury, for an excursion and much 

structural and stratigraphic information on the 

Seward Peninsula; and to I. L. Tailleur, for informa:-

tion on the structure and stratigraphy of the western Brooks Range. 

Special thanks are given to the many paleontologists of the Geological Survey, without whose interest in Alaskan fossils many of the correlations would 

not have been possible. The "Annotated Bibliography 

of Alaskan Paleozoic Paleontology" (Dutro, 1956) 

conveniently summarizes much of their earlier work. 

More recently, the following paleontologists have 

been especially helpful in identifying Alaskan Paleozoic fossils: A. K. Armstrong, Jean Berdan, Claire 

Carter, Helen Duncan, R. C. Douglass, J. T. Dutro, 

Jr., R. E. Grant, J. W. Huddle, S. H. Mamay, W. A. 

Oliver, Jr., A. R. Palmer, R. J. Ross, Jr., R. A. Scott, 

E. L. Yochelson. 

I am especially grateful to the Canadian geologists, 

J. W. Kerr, J. A. Jeletzky, H. P. Trettin, D. E. Jackson, A. C. Lenz, B. S. Norford, P. A. Ziegler, and E. 

W. Bamber, and to many Soviet geologists including 

N. A. Bogdanov, V. F. Belyi, B. K.h. Egiazarov, G. S. 

Gnibidenko, Yu. A. Kosygin, L. I. Krasniy, Yu. M. 

Puscharovsky, a:nd A. L. Yanshin for discussion and 

much information on the geology of neighboring 

parts of Canada and Siberia. Thanks are due to the 

U.S. and Soviet Academies of Sciences for sponsoring my visits to the U.S.S.R. in 1967 and 1971 and to 

the Geological Survey of Canada for arranging exchange visits of L. H. Green, E. W. Bamber, and 

J. W. Kerr to Alaska. 

STRATIGRAPHY 

PRECAMBRIAN ROCKS 

Until recently, large areas of metamorphic rocks 

in the central and southern parts of Alaska were considered to be Precambrian (Smith, 1939; Dutro and 

Payne, 1957). With the realization that younger formations extend into these areas of high metamorphism, many of these metamorphic complexes are 

now thought to include much younger rocks. For example, radiometric dating has shown that the metamorphism in the Yukon-Tanana Upland, believed to 

be dominantly Precambrian, is in some part Mesozoic (Wasserberg and others, 1963). One difficulty in 

determining that any rocks are Precambrian is the 

lack of fossil control. Only in a small area of east~ 

central Alaska are there rocks that can be definitely 

recognized as Cambrian by their fossil content. These 

are known to overlie stratigraphically still older 

rocks-the Tindir Group. As a result, many of the 

previous Precambrian assignments outside this small 

area, especially of metamorphic rocks, are somewhat 

in doubt (fig. 2). 

UN METAMORPHOSED ROCKS 

The term Tindir Group was first applied to a thick 

sequence of unmetamorphosed sedimentary rocks 

that conformably underlies fossiliferous Middle Cambrian limestone along the Alaska-Yukon Territory 

boundary (Cairnes, 1914). Mertie (1933) studied the 

Tindir in the vicinity of the Yukon River where it is 

best exposed and subdivided it into seven units. 

More recently, part of this area was mapped and 

studied in greater detail (Brabb and Churkin, 1965; 
STRATIGRAPHY 5 

150° 

I F I C ~ c 

0 

100 0 100 200 300 400 MILES 

EXPLANATION 

DEFINITELY PRECAMBRIAN 

1111 

Predominantly dolomite, 

limestone, and shale 

Canadian • shield 

PROBABLY PRECAMBRIAN 

Ill 

Predominantly quartzite 

and dolomite 

METAMORPHIC ROCKS. AGE 

UNCERTAIN BUT MAY INCLUDE PRECAMBRIAN 

STRATA 

~ 

~ 

Predominantly schist; minor 

gneiss and marble 

FIGURE 2.-Precambrian rocks and metamorphic sequences that may include Precambrian strata. Rock dates 

in millions of years (m.y.). 

SOURCES OF DATA 

1. Charley River area: 

Tindir Group ( Mertie, 1933; Brabb and Churkin, 1969). 

2. Porcupine River: 

Tindir(?) Group (Kindle, 1908; Brosge and others, 

1966). 

3. Eastern Brooks Range : 

Neruokpuk Formation (Brosge and others, 1962; 

Reiser, 1970). 

4. Yukon-Tanana Upland: 

Birch Creek Schist (Mertie, 1930a) 

474±35 m.y. K/ A (Forbes and others, 1968). 

5. Seward Peninsula: 

Slates in Ycrk Mountains and Kigluaik Schist (Moffit, 

490-094 0 - 73 - 2 

1913; Sainsbury, 1969a). 750-m.y. Rb/Sr whole-rock 

date on gneiss; 45Q...-m.y. Rb/Sr whole-rock date on 

dike (Sainsbury, written commun., 1970). 

6. Alexander Archipelago: 

Wales Group (Buddington and Chapin, 1929). 

7. Lower Kuskokwim region: 

Gneiss and schist overlain by unmetamorphosed Devonian limestone (Hoare and Coonrad, 1961). 

8. Chukotsk Peninsula: 

Gneiss mantled by schist, 1587-722 m.y. K/A (Gnibidenko, 1969). 

Argillite in bottom of Simpson well, 592±18-m.y. K/ A wholerock date (M. Lanphere, in Brosge and Tailleur, 1970). 
6 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

1969). The following five map units, totaling more 

than 11,000 feet, were then established: 

Lower Cambrian. 

Adams Argillite: Argillite, siltstone, and quartzite; rare 

limestone lenses and greenstone. Contains archaeocyathids, trilobites, worm ( ?) burrows, ~nd Oldhamia. 

300--600 ft thick. 

Funnel Creek Limestone: Massive limestone and dolomite. Nonfossiliferous. 1,000-1,300 ft thick. 

Conformable contact. 

Precambrian. 

Tindir Group: 

Limestone member: Dark-gray; thin-bedded, and 

laminated limestone with slabby and platy partings; interbeds of greenish-gray shale, siltstone, 

and sandstone; minor sandy limestone, laminated 

dolomite, calcareous dolomite and chert-carbonate 

gritstone. 800--1,500 ft thick. 

Dolomitic sandstone and shale member: Light-gray, 

thin- to medium-bedded doloarenite and olive-gray 

shale; minor gritstone and conglomerate. About 

2,500 ft thick. 

Basalt and red-bed member: Dark-greenish-gray 

basalt, commonly amygdaloidal and with pillow 

structure; minor basaltic tuff. Red and grayishred hematite-rich shale and siliceous iron formation; minor greenish-gray shale, jasper, greenstone-dolomite conglomerate, and vitric tuff and 

lava, largely replaced by hematite and carbonate. 

2,500 ft thick. 

Dolomite and shale member: Light- to medium-gray 

laminated dolomite and grayish-black shale; minor 

chert, doloarenite, and dolomite-chert gritstone. 

Has lentil of stromatolite-bearing limestone. Cut 

by diabase dikes. About 3,000 ft thick. 

Shale member: Grayish-black carbonaceous shale; 

minor interbeds of quartzite, limestone, dolomite, 

and dolomite conglomerate (possible tillite). Cut 

by diabase dikes. Base apparently not exposed. A 

few thousand feet thick. 

Diabase dikes, especially abundant in the lower 

parts of the Tindir, are probably related to the emplacement of the stratigraphically higher lavas. 

The rhythmically bedded siliceous iron formation 

that is associated with the conglomerate of mixed 

composition and the mafic volcanic rocks in the Tindir Group is probably correlative with similar ironrich beds of the Rapitan Formation (Gabrielse, 1967) 

in Yukon Territory. 

Cairnes (1914a, p. 185-187; 1914b, p. 56) originally thought that the Tindir Group was either Precambrian or Cambrian. Mertie (1933, p. 392) considered the Tindir as probably entirely Precambrian, 

but the oldest fossils then known above the Tindir 

were Middle Cambrian trilobites. More recent work 

has shown that archaeocyathids of earliest Cambrian age occur 500 feet above the highest unit of 

the Tindir (Brabb, 1967). Furthermore, Early Cambrian trilobites and archaeocyathids occur in the 

Adams Argillite, more than a thousand feet above 

the top of the Tindir Group. However, no definite 

discontinuity has been recognized as separating 

these fossiliferous horizons from the Tindir Group 

(Brabb, 1967; Palmer, 1968). Thus, the top of the 

Tindir Group is considered by Brabb (1967)· to 

mark the top of the Precambrian in east-central 

Alaska. 

The only fossils known from the Tindir are wellpreserved stromatolites (laminated algal structures) 

from lenticular limestone in the dolomite and shale 

unit of the Tindir some 8,000 feet below the Early 

Cambrian fossils (Brabb and Churkin, 1969). A preliminary examination of these stromatolites indicates 

a close similarity to stromatolites in rocks of late 

middle Riphean age from the Aldan Shield of Siberia 

(M. A. Semihatov, written commun., 1968). 

Lithologically, the Tindir resembles the Belt 

Supergroup exposed in more southerly parts of the 

Cordillera. A direct biostratigraphic correlation of 

the Tindir with the Belt, however, has not been possible because the stromatolites in the Belt, unlike 

those in the Tindir, are not the columnar, or coneshaped, types found to be useful for correlation (M.A. 

Semihatov, oral commun., 1969). A comparison of 

radiometric dates from the Belt (Obradovich and 

Peterman,· 1968) with those from the late Precambrian of Siberia suggests indirectly that the upper 

part of the Tindir is late middle Riphean in age, 

950-1,350 ± 50 m.y. (million years) (M.A. Semihatov, oral commun., 1969), and correlates with the 

upper part of the Belt Supergroup. 

The base of the Tindir is not known, but rare 

boulders of granitic rock and gneiss in the upper 

part of the Tindir suggest that an igneous and 

metamorphic rock basement of earlier Precambrian 

age is not far away. Metamorphic rocks in the 

Yukon-Tanana Upland have been postulated as representing this earlier Precambrian (Mertie, 1937b), 

but isotope dating of these rocks has generally not 

verified their postulated Precambrian age. · 

In the western part of the Charley River quadrangle, 50-70 miles west of the Tindir's type area, 

are unmetamorphosed sequences of limestone, argillite, basaltic lava, and distinctively laminated dolomite that resemble the rocks of the Tindir Group 

(Brabb and Churkin, 1965). Stromatolites like those 

in the dolomite and shale member of the Tindir 

(M. A. Semihatov, writfen commun., 1968) also 

occur in these western exposures, indicating a much 

larger distribution of late Precambrian rocks in 

east-central Alaska than form~rly recognized. Simi-
STRATIGRAPHY 7 

larly laminated dolomites, again closely associated 

with basaltic lavas ·but containing nondiagnostic 

stromatolites that may be either Proterozoic or 

Paleozoic (M. A. Semihatov, oral commun., 1969), 

also occur in the Livengood district still farther 

west (Michael Churkin, Jr., unpub. field data). 

Along the Porcupine River, some 150 miles north 

of the Tindir section on the Yukon, is a section, 

mainly of quartzite and dolomite, that has been 

included in the Tindir Group by Cairnes (1914). 

The following is a composite section made from 

exposures within a 5-mile distance upstream and 

downstream from New Rampart House where the 

international border crosses the Porcupine River 

(Brosge and others, 1966): 

Devonian. 

Massive dolomite and limestone. Abundant Amphipora 

and Cladopora. 

Fault zone. 

Precambrian ( ? ) • 

Tindir( ?) Group: 

Argillaceous dolomite member: Thin bedded to 

laminated, platy and slabby. Black chert nodules 

and layers. About 40 ft thick. 

Upper dolomite member: Massive dolomite. About 

400 ft thick. 

Black shale and thin-bedded limestone member. About 

300 ft thick. 

Lower dolomite member: Massive dolomite. About 

200 ft thick. 

Upper quartzite member: Very light gray, fine 

grained, thin bedded, and cross laminated. About 

800 ft thick. 

Sandstone and shale member: Interbedded quartzarenite, shale, and siltstone; weathers grayish red. 

About 250 ft thick. 

Lower quartzite member: White to light greenish 

gray, fine grained, cross laminated. More than 300 

ft thick. 

Total of 2,650 ft of. rock exposed. 

Base of section covered. 

Correlation of this Porcupine River section with 

the Yukon River section of the Tindir is not possible with the data at hand. The Tindir( ?) of the 

Porcupine River has some of the lithologies exposed 

farther south, but it has proportionately more dolomite and quartzite and less shale (fig. 3). A brachiopod and gastropod collection from a quartzite section 

50 miles north of the Porcupine River suggests that 

some of the Tindir-like rocks in that area may be 

Paleozoic (Brosge and Reiser, 1969). 

OLDER SCHISTS OF UNCERTAIN AGE 

The name "Birch Creek Schist" was first applied 

to schists in the Circle, Fairbanks, and Fortymile 

mining districts of the Yukon-Tanana Upland by 

Spurr (1898). Various authors subsequently extended the term to include most of the high-grade 

metamorphic rocks in the interior of Alaska north 

of the Alaska Range. Then followed a period of 

restricting the term to include only rocks thought 

to be Precambrian (Mertie, 1937b). Originally, the 

Birch Creek Schist was assigned to the Precambrian 

on the basis of its apparent structural position below 

Paleozoic rocks and its high metamorphic grade. 

This Precambrian age assignment has continued 

(Mertie, 1937b; Dutro and Payne, 1957), but with- . J 

out conclusive confirmation of its age based on stratigraphic relations, and more recently was revised 

by Pewe and others (1966) and Wahrhaftig (1968) 

to Precambrian or Paleozoic. 

The Birch Creek Schist in its type ~rea near Circle 

consists largely of quartz-mica schist and chlorite 

schist produced apparently by regional metamorphism of mainly sedimentary rocks. Minor amounts. 

of gneiss, marble-, serpentine, and greenstone are 

interlayered with the schist. Well-developed zones 

of contact metamorphism border most of the granitic intrusions in the Birch Creek Schist. Isotopic 

measurements using strontium-rubidium and potassium-argon on micas from the schist and on granites 

intruding it indicate that the Birch Creek has been 

partly recrystallized at about 180 m.y. in conjunction with the granitic intrusions (Wasserburg and 

others, 1963). Besides the usual Mesozoic dates, a 

474±35-m.y. date has been obtained analyzing 

potassium-argon from hornblende in the schist 

(Forbes and others, 1968). According to Forbes, 

this early Paleozoic date on the polymetamorphic 

rocks of the Birch Creek lends support to their 

being derived in part by metamorphism of Precambrian rocks. 

Recent mapping in the Yukon-Tanana Upland 

(Brabb and Churkin, 1969; H. L. Foster, 1969), the 

Fairbanks district (Pewe and others, 1966; Forbes 

and others·, 1968), and the northern Alaska Range 

(Wahrhaftig, 1968; J. M. Hoare, unpub. data, 1967) 

indicates that the Birch Creek Schist is composed 

of polymetamorphosed sequences in which the metamorphic grade, as determined by different mineral 

assemblages, changes from place to place. Some of 

these mineralogical . changes, accompanied by 

changes in penetrative structures, are abrupt and, 

according to Forbes and others (1968), can be related to juxtaposition of different metamorphic 

facies by faulting. In the Charley River quadrangle 

southeast of its type area, the biotite- and garnetbearing Birch Creek Schist grades irregularly into, 

or in places is faulted against, lower grade chlorite 
8 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

I 

SYSTEM 

AND STAGE 

SERIES 

z 

<t: 

u .... Arenigian and Q) 

> ~ 

0 0 Tremadocian Cl _J 

a:: 

0 

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

Trempealeauan 

.... 

Q) 

c. 

c. Franconian 

z ::::> 

<t: Dresbach ian 

-

a:: Q) 

~~--,_ 

CD ~ 

::E - <t: 

---- ~ 

.... u Q) 

~ 

0 

_J 

zi 

PORCUPINE RIVER 

Kindle (1908) and Brosge 

and others (1966) 

Q) 

c 

0 

-

en 

Q) 

E 

·-

_J 

Q) 

tlD 

"0 

·- ~- a:: -· 

- - -· "} 

Q) 

c 

0 

-, 

CHARLEY RIVER 

Mertie (1933), Brabb (1967), and 

Brabb and Churkin (1969) 

Jones Ridge 

Area 

Tatonduk 

River Area 

I Road River Formation 

'~ ~ '\ 

\ \. 

~ \ 

\ 

~v 

~ ~ 

Lower member Hillard Limestone, 

3000 ft 100-500 ft 

massive ~ limestone 

and 

dolomite ---. 

0~ 

(!/ Adams Argillite, 

0 ~ 300-600 ft 

Funnel Creek 

0 Limestone, 

50-1300 ft 

.-

. t oevonian d aga,ns .--+--.---L-------------L------------------1 faulte dolomite 

Thin-bedded dark limestone, 500-1500 ft 

NORTHWEST END OF 

YUKON-TANANA UPLAND 

(Mount Schwatka and 

Crazy Mountains) 

Churkin and Brabb (1956b) 

and Michael Churkin, Jr. 

(field observations, 1968) 

I 

Top uncertain; 

probably overlain 

by chert pebble 

conglomerate that 

resembles Nation River 

Formation of Late 

Devonian age 

I 

<?> Oldhamiu.-bearing 

argillite and 

quartzite, minor 

chert structurally complex; 

probably 

thousa.nds of 

feet thick. 

I <t: ~ r~l Argillaceous dolomite, 

~400ft 

Base unknown 

r---------------------------------{-----?-----7----~ 

- Dolomite, ~400ft c. Dolomitic sandstone and shale, 2500 ft maximum 

a:: 

CD Q; 

::E c. 

c. 

::::> <t: 

u 

LLJ 

c. ::J 

::J Shale and limestone, e 

e ~300ft (!} Basalt and red beds, 2500 + ft (!} .... 

:0 ..... Dolomite, ~200 ft c '1::::' i= ISI3 :0 Quartzite, ~sao ft Dolomite and shale, ~3000 ft c 

i= 

Sandstone and shale, ~250ft Shale. Few thousand feet 

a:: 

a.. 

Quartzite, ~300 + ft 

II II II iiti illii!Yttl H n n m 1 r rm1 r rm iiii 1TIIIIiil rm1 r rm1 r r1T 1 *Oldhamia, fan-shaped trace fossil of probable Cambrian age 2 Nondiagnostic of age 3 Baicalia sp., late middle Riphean age (M.A. Semihatov, written 

commun., 1968) (950-1350 m.y.) 

EXPLANATION 

! Graptolites 

~ Trilobites 

0 Archaeocyathids 

v Brachiopods 

lSI Stromatolites 

<?> Oldhamia 

FIGURE 3.-Columnar sections of late Precambrian and Cambrian rocks in east-cenhal Alaska. 

and sericite schists, phyllite, and sheared conglomerate arid chert (Brabb and Churkin, 1969). 

In the lower grade rocks, relicts of original sedimentary layering are readily visible, and in several 

places marble interstratified with schist contains 

crinoid columnals (Mertie, 1930b, p. 44), presumably of Paleozoic, but possibly of younger age. Two 

of these crinoid localities are especially significant 

because they occur along the international boundary 

in rocks that were mapped by Cairnes (1914) as 

part of the Yukon Group that he considered to be 

Precambrian in age and to include the Birch Creek 

Schist. Fossil fungi of probable Paleozoic age (P. 

E. Cloud and G. Lucari, oral commun., 1968) have 

also been identified from within this belt of lower 

grade rocks. 

North and west of its type area, the Birch Creek 

Schist is again rimmed by a belt of lower grade 
STRATIGRAPHY 9 

metamorphic rocks. Remnants of shelly fossils in 

highly deformed and recrystallized limestones in the 

Crazy Mountains and, farther west, in the Livengood 

area indicate that these low-grade metamorphic 

rocks are at least in part Phanerozoic in age (R. 

M. Chapman, F. R. Weber, and Michael Churkin, 

Jr., unpub. field observations). The presence of the 

fan-shaped trace fossil Oldhamia in phyllitic shale 

interbedded with quartzite indicates that part of 

this sequence is probably Cambrian (Churkin and 

Brabb, 1965b). Positive evidence that the Birch 

Creek Schist is derived in part from Precambrian 

strata depends on future isotopic dating of some 

relict minerals that have not been recrystallized 

by the Mesozoic intrusive bodies and later structural events, or on definitely. establishing the stratigraphic position of the schist below an as yet undiscovered fossiliferous section of Cambrian age. 

In the highlands between the Yukon and Kuskokwin Rivers of western Alaska (fig. 2), there are 

extensive areas of metamorphic rock. These schists, 

although sometimes correlated with the Birch Creek 

Schist, are without any positive evidence of their 

age. 

In the Seward Peninsula the oldest rocks, long 

thought to be Precambrian, are slate and sandstone 

at the west tip of the peninsula and schists of the 

Kigluaik and Nome Groups in the vicinity of Nome 

(Moffit, 1913). A limestone of Ordovician age, the 

oldest fossil-bearing rock in the Seward Peninsula, 

was believed to overlie these weakly metamorphose~ 

slates of supposed Precambrian age (Collier, 1902; 

Steidtmann and Cathcart, 1922). Regional mapping 

by Sainsbury (1969a) indicates that the Ordovician limestones, formerly assigned to the nowabandoned Port Clarence Limestone, are not in 

stratigraphic contact with the underlying slate but, 

instead, are thrust over it. According to Sainsbury 

(1969a), the Ordovician limestone is conformably 

underlain by a nonfossiliferous argillaceous and 

dolomitic limestone sequence several thousand feet 

thick that could include rocks of Cambrian or even 

late Precambrian age. The Kigluaik Group exposed 

in the west-central part of the Seward Peninsula 

presents the best evidence that it and other highgrade metamorphic rocks in the area are considerably older than the surrounding lpwer Paleozoic 

limestones and may be Precambrian. The Kigluaik 

Group, consisting mainly of mica schist, is exposed 

in a long west-trending structural arch that exposes 

higher grade gneisses in its core (Collier and others, 

1908; C. L. Sainsbury, oral commun., 1968). The 

schistosity and compositional layering are arched 

along the axis of the structure, and lower grade 

schists interlayered with marble form the structurally higher parts of the sequence (C. L. Sainsbury, oral commun., 1968). Massive limestones rich 

in early Paleozoic fossils flank this arch and are 

virtually unmetamorphosed, thereby suggesting that 

they are considerably younger than the schists. 

Radiometric dating using potassium-argon isotopes 

of metamorphic rocks and associated intrusions in 

the Seward Peninsula generally indicates metamorphic-plutonic events of Mesozoic age (Sainsbury, 

1969a). In exception, Sainsbury (written commun., 

1970) has obtained a 750-m.y. date on gneiss from 

the core of the Kigluaik Mountains using the rubidium-strontium whole-rock method. A dike cutting 

this gneiss, according to Sainsbury, gives a 450-m.y. 

Rb:Sr date. 

Metamorphic rocks with structural and stratigraphic relations similar to those in the Seward Peninsula have been described from Chukotsk Peninsula 

across the narrow Bering Strait (Belyi, 1964; 

Krasniy, 1966, p. 46; Gnibidenko, 1969). ·Based 

largely on their high metamorphic grade, these 

rocks in Chukotka have generally been considered 

Precambrian (Tilman, 1962; Belyi, 1964). Radiometric dating (24 separate analyses) shows that in 

the Chukotsk Peninsula, as in other metamorphic 

terranes around the northwestern Pacific, the age 

of the metamorphism ranges from Paleozoic to 

Mesozoic but is mostly Mesozoic in the interval of 

130-60 m.y. (Gnibidenko, 1969). In eastern Chukotka, numerous older dates, ranging from about 

1,500 to 700 m.y., have been obtained on rocks in 

the same vicinity as those giving the younger dates 

(Gnibidenko, 1969). These dates suggest that some 

Precambrian rock may be involved in the mainly 

Mesozoic metamorphism. It seems reasonable to 

consider these metamorphic rocks as earliest Paleozoic where they grade into fossiliferous Paleozoic 

rocks and as provisionally Precambrian where there 

is a sharp structural break between them and fossiliferous lower Paleozoic rocks. 

In addition to the belt of metamorphic rocks 

across the center of Alaska, there are metamorphic 

rocks in other regions of Alaska that some have 

suspected of being early Paleozoic in age and others 

have suspected of being Precambrian-the Wales 

Group of southeastern Alaska (Buddington and 

Chapin, 1929); a narrow belt of rocks along the 

southern margin of the Brooks Range (Patton, 

1957; Brosge, 1960); and the Neruokpuk Formation of the northeastern Brooks Range (Brosge and 

others, 1962; Reiser, 1970). These rocks, without 
10 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

further work, cannot be accurately dated; but some 

are almost certainly of Paleozoic age. The occurrence of any strata conclusively dated as Precambrian in these metamorphic complexes has not been 

recorded. However, the discovery of Cambrian trilobites (J. T. Dutro, Jr., W. P. Brosge, and H. N. 

Reiser, written commun. and unpub. data, 1971) in 

the Neruokpuk Formation, and the knowledge that 

Silurian graptolites in the Barn Mountains-Yukon 

Territory are closely associated with rocks correlated with the Neruokpuk, indicate that some earliest Paleozoic strata are included in the metamorphic rocks of the northeastern Brooks Range. 

LOWER ;pALEOZOIC CYCLE OF SEDIMENTATION 

The Cambrian through Middle Devonian rocks 

in east-central Alaska seem to be part of a cycle 

of nearly continuous sedimentation. In contrast, 

starting in the Late Devonian, apparently older 

geosynclinal rocks within the Cordilleran and ancestral Brooks geosynclines were uplifted, and wedges 

of coarse siliceous sediments, in part nonmarine, 

were deposited towards the interior of Alaska. 

CAMBRIAN ROCKS 

Cambrian rocks have been found in Alaska only 

in a small area at the west end of the Ogilvie Mountains, where the Yukon River crosses the international boundary (fig. 4) .

1 Fossils of definite Cambrian age were first reported here by Cairnes 

(1914), and the stratigraphic succession has been 

subsequently described by Mertie (1933) and Brabb 

(1967). Kobayashi (1935) and Palmer (1968) have 

described the trilobite and brachiopod faunas. 

The Cambrian in most of this area is represented 

by a limestone and dolomite section that has shale 

and quartzite in its middle part (Charley River area, 

fig. 3). In exception, the Cambrian exposures in the 

northeastern part of the area (Jones Ridge to 

Squaw Mountain) are all limestone and dolomite. 

The contact of the Cambrian with rocks of the Tindir Group is accordant and probably conformable. 

The Hillard Limestone, at the top of the ·cambrian 

section, is overlain by a chert and shale unit (Road 

River Formation), the basal part of which contains a rich late Early Ordovician graptolite fauna 

(Churkin and Brabb, 1965a). The Road River Formation rests unconformably on different beds of the 

Hillard Limestone ranging in age from Early Cambrian to Early Ordovician (Brabb, 1967; fig. 3). 

Abundant specimens of Oldhamia, a fossil of probable Cambrian age found in the Adams Argillite, 

1 Cambrian trilobites more recently have been found in the Neruokpuk 

Formation of the northeastern Brooks Range (J. T. Dutro, Jr .. W. P. Brosge, and H. N. Reiser, written commun. and unpub. data, 1971). 

also occur in similar argillite and quartzite near 

Mount Schwatka in the Crazy Mountains (fig. 4), 

about 180 and 100 miles, respectively, west of the 

Cambrian section along the international boundary. 

Their occurrence suggests that large areas of terrigenous rocks in the central interior of Alaska, 

mapped originally by Mertie (1937b) as "undifferentiated noncalcareous rocks of Devonian age" or as 

"undifferentiated noncalcareous rocks of Mississippian age," include much older rocks of probable 

Cambrian age ( Churkin and Brabb, 1965b). 

Other areas in which Cambrian rocks may eventually be recognized are primarily the areas of Ordovician outcrop shown in figure 5. Especially promising are the well-bedded limestone sequences on the 

Seward Peninsula where, according to Sainsbury 

(1969a), there are thousands of feet of argillaceous 

and dolomitic limestone stratigraphically below massive limestone containing Early Ordovician fossils. 

ORDOVICIAN ROCKS 

Ordovician rocks of different facies have been 

recognized in many widely separated areas of 

Alaska (fig. 5). The stratigraphic succession within 

these areas of Ordovician strata, however, is known 

in any detail only in the Eagle area of east-central 

Alaska (Churkin and Brabb, 1965a), in the Craig 

area of southeastern Alaska (Eberlein and Churkin, 

1970), and in the Seward Peninsula (Sainsbury, 

1969a). The remaining areas of Ordovician rock 

shown in figure 5 either are based on collections of 

Ordovician fossils made during the earliest reconnaissance surveys (locs. 2-4) or are structurally 

complex areas in which the stratigraphic relations 

of the Ordovician rocks to other rocks is unknown 

(locs. 5, 7) . 

Two facies of Ordovician rocks are developed in 

the Charley River area near the international boundary (fig. 6). Along the south edge of the area, 

graptolitic shale and chert (Road River Formation) 

form a belt that extends for 35 miles along the 

Yukon River. Only 7 miles north of exposures of the 

graptolitic shale facies is a contemporaneous pure 

limestone section (Jones Ridge Limestone) that is 

several times as thick as the shale. This abrupt 

change in lithology is believed to reflect a rapid 

facies change and is comparable to similar changes 

of graptolitic shale into carbonate rock farther east 

in Yukon Territory (Churkin and Brabb, 1967). 

The graptolitic shale and chert section, in the 

lower part of the Road River Formation, rests unconformably on the Hillard Limestone. The base of 

this section is marked by a few feet of black bedded 
0 

DEFINITE CAMBRIAN: 

Predominantly • limestone 

and dolomite 

1 Charley River area. 

Lower part of Hillard· Limestone, 

Adams Argillite 

and Funnel Creek 

Limestone; (Brabb, 

1967) 

100 

PROBABLE CAMBRIAN 

BASED ON OLDHAMIA. 

FAN-SHAPED TRACE 

FOSSIL (CHURKIN 

AND BRABB. 1965Bl: 

Ar~llite 

~ and quartzite 

0 Nation River area 

03 Crazy Mountains 

04 Mount Schwatka 

STRATIGRAPHY 

0 

150° 

I f I C 

f\ c 

100 200 300 

EXPLANATION 

0 

400 MILES 

NONFOSSILIFEROUS STRATA OF POSSIBLE 

CAMBRIAN AGE BELOW KNOWN ORDOVICIAN ROCKS: 

~5 

Argillaceous and dolomitic limestone 

below Ordovician 

limestone (Sainsbury, 1ll69a) 

~6 

Argillite and platy 

limestone below 

Lower Ordovician 

graptolitic shale 

(Michael Churkin, 

Jr., B. L. Reed, and 

J. W. Kerr, field 

data 1969) 

FIGURE 4.-Cambrian rocks of Alaska. 

7 Cambrian trilobitebearing limestone, 

volcanic rocks and 

chert within the 

Neruokpuk Formation (J. T. Dutro, 

Jr., W. P. Brosge', 

and H. N. Reiser, 

written commun. 

and.unpubl. data, 

1971) 

11 
12 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

180° 

0 

170° 

IIIII 

Predominantly limestone 

and dolomite 

1. Seward Peninsula: 

100 

150° 

1 f I C 

f\. c 

140° 130° 

0 100 200 300 400 MILES 

EXPLANATION 

~ 

~-- Graptolitic shale 

and chert 

Volcanic-bearing rock, graywacke, 

shale and chert assemblage 

FIGURE 5.-0rdovician rocks of Alaska. 

SOURCES OF DATA 

/ ./ 

Limestone (Steidtmann and Cathcart, 1922; Sainsbury, 

1969a). 

Jones Ridge Limestone ( Churkin and Brabb, 1965a; 

Brabb, 1967). 

7. Livengood area: 2. Upper Kuskokwim River: 

(Eakin, 1918; Brown, 1926). 

3. Alaska Range: 

Tatina Group (Brooks, 1911). 

Terra Cotta Mountain sequence (Michael Churkin, Jr., 

B. L. Reed, and J. W. Kerr, field observations, 1969). 

4. White Mountain area: 

(Sainsbury, 1965) . 

5. Porcupine River: 

(Kindle, 1908; Cairnes, 1914a, b; Brosge and others, 

1966). 

6. Charley River area: 

Lower part of Road River Formation, upper part of 

Fossil Creek Volcanics (Mertie, 1937b); shelly fossils 

reported to be in uppermost Fossil Creek Volcanics 

can be interpreted as coming from basal part of overlying Tolovana Limestone (Michael Churkin, Jr., field 

observations, 1968). 

8. Alexander Archipelago: 

Lower part of Descon Formation (Buddington and 

Chapin, 1929; Brew and others, 1966; Eberlein and 

Churkin, 1970). 

Radiometric date: 

446 ± 22 m.y. Bokan Mountain area, southeastern Alaska 

(Lanphere, MacKevett, and Stern, 1964). 
SYSTEM 

PORCUPINE 

RIVER 

AND EUROPEAN STAGE Kindle ( 1908) and 

SERIES Brosge and others 

(1966) 

z 

.... 

Q) 

0. 

0. 

:::> 

Llan..,doverian 

Ashgillian 

Relation to Silurian 1---'------

dolomite uncertain 

STRATIGRAPHY 

CHARLEY RIVER 

Churkin and Brabb (1965) 

and Brabb (1967) 

JONES RIDGE 

Unnamed chert, 

O shale and 

limestone 

! 

I 

TATONDUK 

RIVER AREA 

c: 

0 

1--- ----- ro ~ t 

Upper member E ~ ~ 

t

? 60 ft bioclas- I 0 .._ ,- ~ 

tic limestone t 0 8 lij V" ro u.. ..... Ql 

0 ~ .... ~~ 

SEWARD 

PENINSULA 

Steidtmann and 

Cathcart ( 1922) 

and Sainsbury 

(1969a) 

Unnamed massive 

0 limestone and 

dolomite -v 

Caradocian ~ ~ Q) 0. (/) O Unnamed w .3 > lij ..g 

v- 0 limestone, c: I ·- :~ '% ""C 

(.) ~ < 100 ft exposed o I a:: -c ro 

: ""C 0~ 

""C 

Base unexpr .J ~ 1--------+.,-.,---I 

Llandeilian 

> ~-+-----------~ E 

~ I 

I 

0 

a:: 

0 

a:: 

0 

0 

....J 

Qj 

0. 

0. 

:::> 

Llanvirnian 

Arenigian 

Tremadocian 

....J 

Ill) 

""C 

a:: 

~ 

~ a:: 

0 

u.. 

z 

0 

(.) 

c: !Blv- 0 

~ -, Lower member, 

~3000 ft 

~massive Bl 

limestone -v 

and dolomite 

Hillard 

Limestone 

Argillaceous and 

dolomitic limestone, 

nonfossiliferous; 

may include 

Cambrian rocks 

EXPLANATION 

0 Corals 

v- Brachiopods 

!Bl" Trilobites 

0 Gastropods and 

Cephalopods 

f Graptolites 

FIGURE 6.-Correlation chart of Ordovician rocks. 

13 

ALASKA SOUTHEASTERN 

RANGE ALASKA, CRAIG 

Brooks (1911) and AREA 

Michael Churkin,Jr., Eberlein and Churkin 

B. L. Reed,and (1970) and Churkin 

J. W. Kerr (field and others (1971) 

observations, 1969) 

I 

I 

I 

I 

I 

I 

Q) 

c: 

B 

(/) 

Q) 

E 

0 

c: .E 

""C 

c: 

ro 

-e 

Q) 

-£~ _o 

QJO c:N 

Btl 

<llO 

-co 

c: ..... ro.-. 

(/) 

ai 

c: 

B 

~ ·u; 

ai 

-ro 

..c: 

(/) 

I Thin-bedded 

limestone 

and silty shale 

1-----?---

I 

I 

I 

lc: 

0 

.,_E 

0 

t'-

~0 

c: 

lo 

a 

I 

""C 

'c: :::ro 

o.Q) 

airo +'..c: 

~ (/) 

Q) u E:;; 

o:..= 

-o !lll..., 

c:o. 

o ro u .... -Ill) 

Q) .... 

c: 0 0 c: 

~-E 

::J ·- E -~ 

ai~ ..:.:.Gl 

u .... ro.O 

~""C 

>-c: 

ro ro 

tio -

~~ // 

+ ~ ') 0.0 .... ( 0 .... ) 

o_ ~~u( o- ~ 

..... ~ 

/ 

/ 

)Part of 

/ Wales 

\...> Group 

'-""") Green 

/ Schist 

Base unexposed 

chert and chert conglomerate containing a coquina 

of phosphatic shells of the pod-shaped crustacean, 

Caryocaris ( Churkin, 1966). A rich sequence of 

graptolite faunas indicates that the Road River includes all the Ordovician except for the earliest 

Ordovician (Tremadocian and lower part of the 

Arenigian). The Road River Formation is discontinuously exposed, but in all the sections that span 

the Ordovician-Silurian boundary there is no evidence of a stratigraphic break coinciding with the 

systemic boundary (Churkin and ~rabb, 1965a). 

In the Jones Ridge area near the Alaska-Yukon 

Territory boundary the Ordovician is represented by 

pure limestone, except for a 60-foot, largely covered, 

interval of chert, shale, and minor limestone that 

may represent a wedge of Road River Formation 

lithology (Brabb, 1967). Farther north, along the 

international boundary, the Ordovician seems to be 

represented by a pure limestone section that continues north as far as the Porcupine River. Along 

the Porcupine River itself, there is very fine grained 

limestone that contains the easily identifiable tabulate coral Tetradium together with other Ordovician 

shelly fossils (Kindle, 1908; Brosge and others, 

1966). 

Outside of east-central Alaska the only other areas 

490-094 0 - 73 - 3 
14 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

with Ordovician rocks that are mainly carbonate lie 

in western Alaska. In the Seward Peninsula, the 

Port Clarence Limestone of former usage and 

numerous mappable subdivisions consist mainly of 

limestone but also have dolomitic and argillaceous 

interbeds. In the central York Mountains these rocks 

aggregate at least 8,000 feet in thickness and include 

Lower, Middle, and Upper Ordovician rocks (Sainsbury, 1969a). 

Farther south in the upper reaches of the Kuskokwim River, northeast of McGrath, Ordovician 

shelly faunas have been reported from a nearly pure 

limestone and dolomite section (Eakin, 1918; Brown, 

1926). The Holitna Group of virtually pure carbo- . 

nate rock farther west in the central Kuskokwim 

area may also include Ordovician rocks because 

Silurian and Devonian faunas were collected from 

its upper horizons (Cady and others, 1955). Farther 

south in the White ·Mountain area, Ordovician fossils 

were found in limestone sections that have many 

interbeds of argillaceous, silty, and sandy rocks 

(Sainsbury, 1965). Very similar Ordovician limestones on Chukotsk Peninsula (Krasniy, 1966, p. 74; 

S. G. Byalobzheskii, oral commun., 1967; Gnibidenko, 1969) suggest this belt. of carbonate rock in 

west-central Alaska continues from the Seward 

Peninsula west beneath the Bering Strait to the 

northeastern tip of the U.S.S.R. 

In the Terra Cotta Mountains of the Alaska 

Range south of Farewell, a thin, though relatively 

complete, section several thousand feet thick of 

graptolitic shale interbedded with limestone and 

sandstone has been established as ranging in age 

from the earliest Ordovician through the Silurian 

(Michael Churkin, Jr., and B. L. Reed, unpub. data). 

These sections in the Alaska Range, like the Road 

River Formation farther east, suggest a transition 

from the carbonate rock facies exposed in isolated 

areas across the center of Alaska to the coarse 

detrital rock sequences of southeastern Alaska. 

In contrast to the predominantly carbonate facies 

of Ordovician rock in the interior and western parts 

of Alaska, a thick sequence of graywacke, argillaceous rock, and conglomerate rich in volcanic 

detritus and interlayered with pillow lavas, tuffs, and 

breccias is exposed in southeastern Alaska (Buddington and Chapin, 1929; Sainsbury, 1961; Eberlein and Churkin, 1970). Limestone is absent in this 

sequence, except for scattered thin lenses of nonfossiliferous dark limestone and for rare cobbles and 

boulders of dense limestone in graywacke conglomerates. Graptolite faunas in this sequence indicate 

that all the major subdivisions of the Ordovician are 

present, except for the lower parts of the Early 

Ordovician (Tremadocian and lower Arenigian) , 

which may be present but may not be exposed because the base of the section is not known. Deposition of the graywacke-volcanic assemblage was continuous through most of the Ordovician and Early 

Silurian (Llandoverian) but changed locally into 

very thick limestone accumulation by Middle Silurian 

(Wenlockian) time (Eberlein and Churkin, 1970). 

The · volcanic rocks that appear sporadically 

throughout the entire Paleozoic section of south:.. 

eastern Alaska are alkali-rich basaltic to andesitic 

pillow lavas, breccias, and tuffs grading in many 

places into conglomerates and sandstones rich in 

volcanic fragments. Graptolites from interbedded 

shales in the lower part of the section date a succession of submarine volcanism from different centers during Early Ordovician through Early Silurian 

time. Local disconformities and thick wedges of 

volcanic-boulder conglomerate indicate repeated uplift that was in part probably related to volcanism. 

A potassium-argon isotope date of 446 ± 22 m.y. on 

a quartz monzonite pluton in Prince of Wales Island 

(Lanphere and others, 1964) further indicates that 

a period of magma generation accompanied the 

orogenic activity. Granitic boulders in the Ordovician conglomerates could have been locally derived 

from intrusions of about this age. 

In contrast to the generally coarsely detrital 

sediments in southeastern Alaska, there is also a 

lithofacies of thinly and rhythmically interbedded 

black chert and siliceous graptolitic shale (member 

of the Descon Formation). These rocks, in their 

lithology and fossils, very closely resemble parts of 

the Road River Formation of east-central Alaska 

and the graptolitic shales in the Terra Cotta Mountains of the Alaska Range. 

SILURIAN ROCKS 

The Silurian rocks closely parallel the pattern of 

sedimentary facies established in Ordovician time. 

Furthermore, there does not seem to be a pronounced 

break in sedimentation across the OrdovicianSilurian boundary anywhere in Alaska ( Churkin, 

1972a). 

The best known Silurian rocks are in the YukonPorcupine Rivers area and in southeastern Alaska 

(figs. 7, 8). Other areas from which Silurian fossils 

have been reported, but where the stratigraphy is 

less well known, are the Livengood-White Mountains area (fig. 7, No. 1), the Nixon Fork area in 

the upper Kuskokwim River drainage (fig. 7, No.4), 

the middle Kuskokwim area (fig. 7, No. 5), and the 
STRATIGRAPHY 15 

v 

~ 

/ / 

(?= I C 

C I f 

f f\ 

0 

100 0 100 200 300 400 MILES 

EXPLANATION 

Mainly dolomite • and limestone Nonvolcanic • shale and chert Volcanic rock, graywacke, conglomerate, shale and chert assemblage; thick limestone occurrences indicated by pattern 

FIGURE 7.-Silurian rocks of Alaska. 

SOURCES OF DATA 

1. Livengood area: 

Lower part of Tolovana Limestone ( Mertie, 1937b; 

Church and Durfee, 1961; Pewe and others, 1966). 

2. Porcupine River: 

(Kindle, 1908; Churkin and Brabb, 1967). 

3. Charley River area: 

Middle part of Road River Formation ( Churkin and 

Brabb, 1965a). 

4. Upper Kuskokwim River: 

(Brown, 1926). 

5. Kuskokwim River: 

Lower part of Holitna Group (Cady and others, 1955). 

6. Alaska Range (Terra Cotta Mountain sequence): 

(Michael Churkin, Jr., B. L. Reed, and J. W. Kerr, 

field data, 1969). 

7. York Mountains: 

(Sainsbury, 1969a). 

7 a. Northeastern Baird Mountains: 

Thrust slice of Skajit(?) Limestone (Tailleur and 

other~ 1967, p. 1352). 

8. Glacier Bay: 

Willoughby Limestone; Tidal Formation; Pyramid 

Peak Limestone; and Rendu Formation (Rossman, 

1963). 

9. Kosciusko Island: 

Bay of Pillars Formation; Kuiu Limestone (Muffler, 

1967). 

10. Prince of Wales Island area: 

Upper part of Descon Formation; Heceta Limestone; 

lower part of Karheen Formation (Buddington and 

Chapin, 1929; Brew and others, 1966; Eberlein and 

Churkin, 1970; Ovenshine and Webster, 1970). 

Radiometric dates: 

431 m.y. Satellitic intrusion to main granite body in 

Romanzof Mountains (Reiser, 1970). 

406 m.y. Tenakee area, Chichagof Island (Lanphere and 

others, 1965). 

416 m.y. Annette Island (Berg, 1970). 
16 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

SYSTEM 

AND 

SERIES 

z 

~ 

z 

0 

> 

UJ 

0 

z 

0::: 

...J 

z 

<X: 

(3 

> 0 

0 

0::: 

0 

.._ 

(I) 

~ 

0 

...J 

.._ 

~ a. 

::::> 

EUROPEAN 

STAGE 

Em sian 

Siegenian and 

Gedinnian 

Ludlovian 

Wenlockian 

Llandoverian 

Ashgillian and 

upper Caradocian 

1 Limestone in lower part of McCann Hill 

Chert-conodonts, ostracodes, tentaculitids, 

brachiopods, pelecypods, corals, fish, 

trilobites, bryozoa. (Churkin and Brabb, 1967) 

PORCUPINE RIVER 

Kindle (1908), Brosge 

and others (1966) 

and Churkin and Brabb 

(1967) 

Salmontrout Limestone, 

600ft 

1------------ I 

I 

I 

Unnamed graptolitic 

shale, 110ft 

,I Fault separates dolomite 

W from shale above llJ ..L..J.U....I..L..J.I....I....I..J....l.LI... 

0 Unnamed dolomite, 

V' ~ 250+ ft 

~ 

fTITT ITITT IT ITT TT rT 

Relation to Ordovician 

limestone uncertai~ 

? 

l 

Unnamed limestone 

I 

I 

I 

I 

I' 

I 

YUKON RIVER 

Churkin and Brabb (1965a) 

Lower part of 

McCann Hill Chert, 1 

200-800 ft 

PRINCE OF WALES 

ISLAND AREA 

SOUTHEASTERN ALASKA 

Eberlein and Churkin ( 1970) 

and Ovenshine ::tnd Webster 

(1970) 

Kahrheen Formation 

~ Red conglomerate, sandstone, 

f and minor platy limestone, 

3000+ ft 

-vo~ 

I 

0-v 

\ 

( 

\ 

( 

~ I 

( 

EXPLANATION 

~ Conodonts (A. T. Ovenshine, ~ Trilobites 

~ Gastropods 

I Graptolites 

oral commun., 1968) 

0 Corals 

-v Brachiopods 

FIGURE B.-Correlation chart of Silurian rocks. 
STRATIGRAPHY 17 

central York Mountains of the Seward Peninsula 

(fig. 7, No.7). 

In the southern Brooks Range, a widely distributed massive limestone, the Skajit Limestone, was 

assigned to the Silurian until Dutro (in Brosge and 

others, 1962) determined that the large brachiopods 

in the Skajit first thought to be Conchidium, a 

Silurian guide fossil, are really Stringocephalu.s, a 

cosmopolitan genus known only from the Devonian. 

More recently, a pentameroid brachiopod of probable Silurian age (Dutro, in Tailleur and others, 

1967) is reported from limestone questionably 

mapped as Skajit in the northeastern part of the 

Baird Mountains of the western Brooks Range. 

Silurian and older rocks may be present in the lowgrade metamorphic belt in the southern Brooks 

Range, within the thick N eruokpuk Formation of 

the northeastern Brooks Range (especially since 

Silurian graptolites have been reported in close 

association with the N eruokpuk Formation in the 

Barn Mountains of northern Yukon Territory) and 

in the Sadlerochit Mountains where a thick sequence of dolomite occurs below limestone of 

Devonian age (Dutro, 1970). A single potassiumargon isotope date of 475 m.y. on hornblende in a 

·mafic volcanic rock from the Doonerak Mountain 

area of the south-central Brooks Range suggests 

that the volcanic rock and associated slate and shale 

there may be Ordovician (Lanphere, 1965), thus 

supporting an early Paleozoic age for some of the 

weakly metamorphosed nonfossiliferous rocks that 

are widely distributed in the Brooks Range. 

A few collections from limestones on the Seward 

Peninsula have been reported to contain Silurian 

and Devonian shelly fossils along with the more 

numerous Ordovician faunas (Smith and Eakin, 

1911; Sainsbury, 1969a). Undoubtedly, with further 

work it will be possible to separate units of widely 

varying ages in this area of predominantly carbonate rocks. Work in the Don River area north of 

-Teller has established a richly fossiliferous limestone-dolomite succession that spans the OrdovicianSilurian boundary with no apparent stratigraphic 

break (Sainsbury and others, 1971). The virtually 

pure carbonate rocks in the Kuskokwim region ·suggest that this stratigraphic belt covers much of 

southwestern Alaska before it becomes an argillaceous facies along the southern margin of the Kuskokwim region (Cady and others, 1955). 

Farther south, in the Alaska Range, Silurian rocks 

had not been reported until recently. The Paleozoic 

sequences there are mainly siliceous, detrital, and 

volcanic rocks that appear to be transitional and, in 

some places, similar to the volcanic-rich siliceous 

detrital facies of south Alaska. In 1969 the first 

Silurian fossils were found in this remote area 

(Michael Churkin, Jr., B. L. Reed, and J. W. Kerr, 

unpub. data). They are well-preserved graptolite 

faunas near the top of a rather thin interval of 

rhythmically interbedded shale and siliceous shale. 

Subsequently, Silurian graptolites have been found 

froin a number of horizons in a stratigraphically 

higher platy limestone and sandstone section. 

In the central interior of Alaska and extending 

·across the Porcupine-Yukon triangle is an area of 

discontinuous exposures of carbonate rock of 

Silurian age. In the White Mountains north of Fairbanks, the 2,500-foot-thick Tolovana Limestone rests 

on the Fossil Creek Volcanics, reportedly of Ordovician age (Mertie, 1937b). In detail, the massive 

limestone and dolomite of the Tolovana is directly 

underlain by a poorly exposed section several feet 

thick of tuffaceous carbonate rock containing tabulate corals in growth position (Michael Churkin, Jr., 

R. M. Chapman, and F. R. Weber, field observations, 

1968). The tuff grades downward into a thick ·conglomerate made of volcanic and plutonic rock 

boulders which, in turn, lies on a section, thousands 

of feet thick, of siliceous clastic rocks and pillow 

lavas, the Fossil Creek Volcanics proper. 

Farther east along the Porcupine River, massive 

limestone and dolomite of Silurian age form high 

bluffs in the Lower Ramparts area. A thin (100-ftthick) unit of black shale, best exposed at the mouth 

of the Salmontrout River, has Late Silurian (Ludlovian) graptolites in its lower part and Early 

Devonian graptolites in its url)er part (Churkin and 

Brabb, 1967). Similar shale with the same Late 

Silurian graptolites is exposed downstream in the 

Lower Ramparts where it seems to overlie the 

massive Silurian carbonate rocks. Thus, the Silurian 

succession along the Porcupine River resembles the 

Ordovician facies on the Seward Peninsula, being 

mainly carbonate rock with a thin horizon of graptolitic shale. Apparently, the predominantly carbonate 

facies exposed along the Porcupine River continues 

south into the Charley River quadrangle, where the 

Silurian section rapidly changes from carbonate 

rock at Jones Ridge to the ·pure graptolitic shale and 

bedded chert farther south along the Yukon River. 

The Silurian-Devonian boundary in the Porcupine 

River section, as in the Yukon River section, is not 

marked by a stratigraphic break but lies within a 

graptolitic shale formation. 

From east-central Alaska this thin graptolitic 

shale and chert section continues eastward into 
18 . PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Yukon Territory, where it is interrupted by a thick 

limestone\ buildup in the Illtyd Range, and finally 

grades into a platform section of dolomite mantling 

the Canadian Shield in Northwest Territories (Churkin and Brabb, 1967, fig. 10). Northeastward from 

the Charley River area, the graptolitic shale and 

chert thicken towards the Richardson Mountains, 

the type area of the Road River Formation (Jackson 

and Lenz, 1962). 

Silurian rocks in southeastern Alaska are exposed 

in a series of islands at the continental margin (fig. 

7) . In the Craig area of southeastern Alaska, the sequences, mainly graywacke, shale, and conglomerate, 

characteristically have abundant volcanic detritus 

and are interlayered with submarine volcanic rocks 

(fig. 8). They are accurately dated as Early Silurian 

by graptolites ( Churkin and Carter, 1970; Churkin, 

Carter, and Eberlein, 1971). The Middle and Upper 

Silurian in the same area, in sharp contrast with 

the underlying Lower Silurian and Ordovician, is 

mainly limestone (more than 10,000 ft thick on 

Heceta Island; Eberlein and Churkin, 1970; Ovenshine and Webster, 1970). Silurian limestones also 

occur in Glacier Bay, on Northern Kuiu Island, on 

Heceta-Tuxekan Islands, and on Long Island 

(figs. 9, 10). The limestones vary from light-colored 

massive sublithographic limestone that makes up 

much of Heceta Island (Heceta Limestone) to dark 

thin-bedded argillaceous limestone (Tidal Formation) in Glacier Bay. Locally, thick lenses of polymictic conglomerate rich in volcanic detritus, limestone breccia, sandstone, and argillaceous rocks are 

interbedded with the purer limestone. Most of these 

limestones are rich in corals, stromatoporoids, 

brachiopods, gastropods, pelecypods, bryozoa, and 

calcareous algae. However, calcareous sandstone and 

argillite (Bay of Pillars Formation) that contain 

Late Silurian graptolites show that, in restricted 

areas, limestone deposition did not commence until 

the Late Silurian (Muffler, 1967). 

LOWER AND MIDDLE DEVONIAN ROCKS 

Devonian rocks are widespread in Alaska and 

form a nearly continuous belt in the Brooks Range 

across the northern part of the State (fig. 11). The 

Devonian System in Alaska was summarized for the 

International Symposium of the Devonian System 

held at Calgary ( Gryc and others, 1967; Tailleur 

and others, 1967; Churkin and Brabb, 1967). 

In t4e northern and east-central parts of Alaska, 

the Middle and, more rarely, the Lower Devonian 

sections, mainly limestone and dolomite, are part of a 

lower Paleozoic cycle of nearly continuous sedimen56" 

Prince of Wales 

Island 

50 0' 

FIGURE 9.-Index map of southeastern Alaska. Hatch lines 

and letters indicate location of stratigraphic columns 

shown in figure 10. 

tation that started in the latest Precambrian or 

Cambrian. Other areas where carbonate rocks predominate are in the Seward Peninsula and in the 

Kuskokwim River region (fig. 11) where relatively 

pure carbonate sections are known to contain Ordovician as well as Silurian and Devonian faunas. 

In addition to these areas, more recent studies 

report the following occurrences of Devonian carbonate rocks: a dolomite section on St. Lawrence 

Island that lies below limestone that correlates with 

the Lisburne Group mainly of Carboniferous age 

(Patton and Dutro, 1969)·; coral-rich limestone just 

south of Farewell in the Alaska Range (B. L. Reed, 

oral commun., 1968; Michael Churkin, Jr., unpub. 

field observations, 1969); and limestone and dolomite 

in the Sadlerochit Mountains of northeastern Alaska 

(Dutro, 1970). 

Besides these nearly pure carbonate sections, 

there are widely scattered areas of siliceous detrital 

and volcanic rocks that include subordinate limestones with Devonian fossils (locs. 8-13). These 

rocks probably represent a northern continuation of 

the stratigraphic belt in southeastern Alaska. 
STRATIGRAPHY 19 

The section of thinly and rhythmically interbedded dark shale and chert (McCann Hill Chert 

and the uppermost part of the Road River Formation) in the Eagle area of east-central Alaska seems 

to represent an intermediate facies separating the 

predominantly carbonate rocks found farther north 

from the siliceous detrital and volcanic rocks in 

southeastern Alaska (fig. 12). This relatively thin 

shale and chert section of Early Devonian age 

grades eastward into thicker limestone in the N ahoni Range-Blackstone River area of Yukon Territory (Churkin and Brabb, 1967, fig. 10). The 

Silurian-Devonian boundary in this- graptolitic shale 

sequence is placed above a Monograptus nilssoniLinograptus fauna of Late Silurian age and below 

shale with Monograptus yukonensis, in accordance 

with modern interpretations of this boundary elsewhere. Above the shale with M. yukonensis are thin 

limestone beds with a remarkably varied shelly 

fauna of Early Devonian age (Churkin and Brabb, 

1967). At Jones Ridge, a short distance north of 

the Yukon River, these limestones thicken markedly. 

Mucl~ farther north, the argillites at the bottom 

of a borehole at Point Barrow (Payne and others, 

1951) and the Lower or Middle Devonian plantbearing shale and chert-pebble conglomerate from 

the Topagoruk test well, 50 miles farther south 

(Collins, 1958), seem to indicate a northward change 

of the Brooks Range Devonian carbonate section 

into siliceous terrigenous rocks. In the northeastern 

Brooks Range the largely clastic N eruokpuk Formation may include equivalents to these Devonian 

rocks found in the subsurface. In the Sadlerochit 

Mountains farther north, however, there is a thick 

Devonian carbonate section (Dutro, 1970). The 

Sadlerochit Mountain section is difficult to interpret; it may be an isolated buildup of carbonate 

rock, or it may indicate another major belt of carbonate rocks parallel to that of the central Brooks 

Range (fig. 11). 

The Devonian of southeastern Alaska, like the 

underlying Ordovician and much of the Silurian, is 

mainly a graywacke, shale, and conglomerate sequence interbedded and intertongued with basaltic 

to andesitic pillow lava, breccia, and tuff. These 

submarine lavas and associated sedimentary rocks 

rich in volcanic detritus grade rapidly into thick 

limestones made up largely of fragmented fossils, 

especially in Glacier Bay, Freshwater Bay, and in 

several places along the west coast of Prince of 

Wales Island (fig. 10). 

A good example of rapid facies change is seen 

in the vicinity of Craig where a nearly pure limestone section about 1,000 feet thick (Wadleigh 

Limestone), composed mainly of varying proportions of fragmented corals and stromatoporoids, 

intertongues at a place 4 miles to the south with 

1,500 feet of basaltic tuff, breccia, and pillow lava. 

Several miles still farther south this limestone is 

entirely absent, apparently due to a facies change 

to a thick sequence (Port Refugio Formation) of 

pillow basalt, tuff, and volcanic breccia interbedded 

with graywacke, conglomerate, and shale (Eberlein 

and Churkin, 1970). The only limestone known in 

this sequence is a silty and tuffaceous limestone 

only a few tens of feet thick. 

Over a large area of southeastern Alaska, the 

base of the Devonian is marked by a distinctive) 

unit, predominantly conglomerate, sandstone, and 

shale, the Karheen Formation, that is characterized 

by red beds and festoon crossbedding. In the 

Heceta-Tuxekan Islands area, the Karheen conformably overlies thick limestonei(Heceta\Limestone) of 

Early through Late Silurian age and which, according to Kirk and Amsden (1952), has a Late Silurian 

brachiopod fauna above its base. Conodonts (A. T. 

Ovenshine, written commun., 1969) and a tentaculitid fauna (Claire Carter, written commun., 1969) 

from these beds seem to suggest instead an Early 

Devonian age. Farther south, the Karheen Formation rests unconformably on Ordovician to Lower 

Silurian volcaniclastic rocks and has an unusual assemblage of graptolites, vascular plants, and corals 

. of Early Devonian age (Churkin and others, 1969, 

1970). 

UPPER PALEOZOIC CYCLE OF SEDIMENTATION 

UPPER DEVONIAN ROCKS 

The Upper Devonian Series is dominated by clastic rocks throughout Alaska. Chert-pebble conglomerate, sandstone, and shale (Kanayut and Hunt 

Fork Formations of the Brooks Range and the 

Nation River Formation of east-central Alaska) derived from uplifts within adjacent geosynclinal belts 

start a cycle of thick accumulation of coarse siliceous detrital sediments in interior Alaska (fig. 13). 

In the northeastern Brooks Range, Mississippian 

conglomerate (Reiser, 1970) unconformably overlies 

the Neruokpuk Formation (regionally metamorphosed Devonian or older siliceous sedimentary 

rocks), and as much as 10,000 feet of Neruokpuk 

strata were removed by erosion below the unconformity (Reed, 1968). 
20 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

A B 

GLACIER BAY-CHILKAT NORTHERN CHICHAGOF 

SYSTEM RANGE ISLAND 

Rossman (1963) and Loney, Condon, and Dutro 

( 1963) and Loney and Lathram and others (1959) others,(1963) 

TRIASSIC 

N9t recognized 

Not recognized 

c 

PYBUS-GAMBIER AREA 

ADMIRALTY ISLAND 

Loney (1964) 

D 

KEKU STRAIT AREA 

Muffler (1967) 

E 

HECETA-TUXEKAN ISLANDS 

AREA 

Eberlein and Churkin 

(1970) 

z 

<( 

z 

0 

> 

UJ 

j l l j J 2 50+ ft .. -'--..--....,..; 

c:, 

-,'1-lnieBiackCap 

J ~~ 10 '71 

it~{;; ~_e:.~:~~~~:f:~-~y2 ;-••-••• :-:Hoo~ BaY 

<I~%17Jat ·$!;ormation· . . .·. GaJb,ma~@~w::;:~;~.; . .... ·. . . . .. -, 

0 

z 

<( 

0: 

~ 

-' 

-Pyramid Peak Ls~::~-?09.{ :::·,.··:·.:··.:·:·.: .. :·: .. :: .... :.-.::.·:·>"<·.> .. :;·:-:··.:·.·: ~.~-.~_2500 f.!_,-)_1,....... Heceta Limest~J 

~~ff~~;~ J••••-•••• .. vXS+ift ,i; · --·· ·••Tg;~t~~~~( i~lO;Oj±ft i• X .. (/) 

z 

<( 

(.) 

> 

0 

0 

0: 

0 

Graywacke, mudstone, and conglomerate; minor 

pillow basalt, breccia, and volcaniclastic sedimentary 

rocks 

Conglomerate containing mafic volcanic, sedimentary, 

and plutonic rock 

clasts and red sandstone; festoon 

crossbedded, car-

.bonate cemented; 

minor platy limestone 

EXPLANATION 

PREDOMINANT LITHOLOGY 

§§§ 

Limestone generally 

bioclastic 

D v 

v 

Prominent basaltic 

and andesitic lavas 

including pillow 

basalt, breccia, and 

tuff 

~ 

~ 

Highly calcareous argillaceous and 

sandy rocks 

.··.:··.: , ...... ::;·.:·:.<.:.:::. . _: . . . ': . ·. . . : · ..... ~- .. :. ·. : 

)> 0·;~g~~Q~'o"? 

::.:·/ .. (::'::,-.":.:: .': . .'· ·: ·.·:: :..· ... : ..... . 

Ch)Xii;\·····-·-·-· 

Felsic 

~ 

~ volcanic 

rocks 
F 

CRAIG-KLAWOCK AREA 

Eberlein and. Churkin 

(1970) 

G 

SUEMEZ-SHELIKOF ISLAND 

AREA 

Eberlein and Churkin 

(1970) 

t=fLPeratrovich Formation=rhTPerat~ovi~h F~rm~tion~ 1--r'-----.---.1000± ft _i I I 11000+ ft r-fI 

I I I I I I 

STRATIGRAPHY 

KLAKAS INLh-soUTHERN 

H 

THORNE-KASAAN BAYS 

EASTERN PRINCE OF 

WALES ISLAND 

PRINCE OF WALES ISLAND SYSTEM 

G. D. Eberlein (written com-

, Sainsbury (1961) mun., 1968) and Churkin, Ja~er, and Eberlein(1970' 

·. ·. ·, ·, ·. ·. ·. · .. ·.·.·.·.·. ~-

300+ ft 

!TRIASSIC 

z 

<( 

~-

a:: 

w 

a.. 

z 

<( 

z 

0 

> 

w 

0 

z 

<( 

0:: 

:::::> 

...J 

en 

z 

<( 

u 

> 

0 

0 

0:: 

0 

FIGURE 10.-Correlation chart of major rock types of Paleozoic age in southeastern Alaska showing 

rapid lateral changes in stratigraphy due to facies changes and, in some places, structural 

dislocations. See figure 9 for location of areas. 

490-094 0 - 73 - 4 

21 

. -
22 

a 

PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Mainly limestone and dolomite. 

In Brooks Range upper part 

includes shale and sandstone 

170° 

100 0 

150° 

C 1 f I C 

~ 

100 200 300 

EXPLANATION 

140° 

400 MILES 

Limestone in mainly siliceous detrital-volcanic terranes of uncertain , 

age 

Mainly shale and chert, some 

sandstone 

3 

Sources of data 

130° ,o· 12oo 

Volcanic-rich graywacke, conglomerate, and shale and chert assemblage. Locally includes thick 

limestone 

FIGURE 11.-Devonian rocks. Excludes coarse terrigenous rocks of Late Devonian and Mississippian age (Nation River, 

Kanayut, and Kekiktuk Formations) (cf. Gryc and others, 1967). 
STRATIGRAPHY 23 

SOURCES OF DATA FOR FIGURE 11 

1. Porcupine River: 

Salmontrout Limestone (Churkin and Brabb, 1967; 

Brosge and others, 1966). 

2. Jones Ridge area: 

Thick limestone below McCann Hill Chert ( Churkin 

and Brabb, 1965a). 

3. West and Central Brooks Range: 

Skajit Limestone, unnamed lip1estone and siltstone, 

and Hunt Fork Shale (Brosge and others, 19Q2; 

Sable and Dutro, 1961; Bowsher and Dutro, 1957; 

Tailleur and others, 1967; Chapman and others, 

1964). 

3a. Sadlerochit-Shublik Mountains and vicinity:· 

Nanook Limestone and Katakturuk Dolomite (Dutro, 

1970) .. 

3b. Northeastern Brooks Range: 

Neruokpuk Formation (Devonian(?) and older) 

(Brosge and others, 1962; Sable, 1965; Reed, 1968; 

Reiser, 1970) . 

4. White Mountains: 

(Sainsbury, 1965). 

5. Central Kuskokwim River: 

Upper part of Holitna Group (Cady and others, 1955). 

6. Seward Peninsula: 

(Revised after Smith and Eakin, 1911, and earlier 

workers). 

7. Topagoruk test well: 

500 feet + chert pebble conglomerate and shale (Collins, 1958) . 

7a. Charley River area: 

Upper part of Road River Formation, McCann Hill 

Chert ( Churkin and Brabb, 1965a; 1967). 

8. Livengood area: 

Upper part of Tolovana Limestone (Pewe and others, 

1966; Church and Durfee, 1961). 

9. Yukon River: 

Woodchopper Volcanics ( Mertie, 1930a; Brabb and 

Churkin, 1969). 

10. East Alaska Range: 

(Moffit, 1954). 

11. Central Alaska Range: 

Limestone overlying Tonzona Group (Brooks, 1911). 

Limestone in vicinity of Farewell, Alaska (B. L. 

Reed, oral commun., 1968). 

12. Upper Kuskokwim River: 

(Revised after Smith and Eakin, 1911). 

13. Lower Kuskokwim River: 

(Hoare and Coonrad, 1961; Hoare, 1961). 

14. Glacier Bay: 

Black Cap Limestone (Rossman, 1963). 

15. Chichagof Island: 

Freshwater Bay Formation, Cedar Cove Formation, 

Kennel Creek Limestone (Loney and others, 1963). 

16. Admiralty Island, Keku Strait: 

Hood Bay Formation, Gambier Bay Formation 

(Loney, 1964; Muffler, 1967). 

17. Prince of Wales Island: 

Wadleigh Limestone, Coronados Volcanics, and Port 

Refugio Formation (Eberlein and Churkin, 1970). 

18. Chukotsk Peninsula: 

(Krasniy, 1966; Gnibidenko, 1969). 
24 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

SYSTEM 

AND 

SERIES 

EUROPEAN STAGE 

Famennian 

Frasnian 

z 

<( 

- Givetian 

z Cl> 

=c 

"'0 

0 ~ 

> Eifel ian 

u.J 

0 

Emsian 

~ Siegenian ,...J 

Gedinnian 

Ludlovian 

1 (Brosge and Reiser, 1965) 2 K/ A on hornbtende, (Lanphere,· 1965) 

EASTERN AND CENTRAL BROOKS RANGE 

NORTHERN BELT 

Brosge and others (1962) and 

Gryc and others (1967) 

0 Kayak(?) Shale 

SOUTHERN BELT 

Brosge and others (1962) and 

Gryc and others (1967) 

Kayak Shale 

0 

0-400 ft .. Quartz and chert 

~le 

~ 

conglomerate 

C) Kanayut Conglomerate, 

PORCUPINE RIVER 

Churkin and Brabb (1967) 

Unnamed limestone. 

Thin shale at base 

'V' C) 

Phyllite and chert 

unit, 3000 + ft 

~5000ft 

O Hu_n_t_F_o-rk_S_h_a-le-,-----!l 

c 

0 

·-

-ro 

E ...::- ... Cl> 

0~ 

~ 5 

c 

ro 

·c: ~ ~ 

Limestone unit, 

1000+ ft 

2500-5000 ft 

~ U:::::: _ 0 'V' Ls 1 -

)\ ~ Cgl and phyllite 

I• r Unnamed phyllite, ~ ~ siltstone, 400- l..l LJ . ..P 250ft 

0'V'O 

Skajit Limestone 

(Middle? and 

Upper Devonian), 

500+ ft 

:JO ' 

c.-<1>---------------------

ro ~:::. 

0 

:J. 

z 

Quartzite-schi:!t unit, 

3500-4000 ft (Age 

unknown, base not 

exposed) 

Relations 

uncertain 

f.-------------

Unnamed silty phyllite 

(Ag~ 

EXPLANATION 

c? Dolomite and minor 

limestone, 500ft 

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

0 

~ 

Contact inferred 

Calcareous siltstone 

and shale, 200 ft 

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

6. 

0 

6. 

Salmontrout 

Limestone, 

600ft 

6. 0 

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

I 

I 

Unnamed graptolitic 

shale, 110 ft 

Base not exposed 

C) Pollen and plants 

6. T entaculitids 

~Conodonts 

t? Amphipora (tube-shaped stromatoporoid) 

o Pycinodesma (large, thick shelled clam) 

I Graptolites 

'V' Brachiopods 0 Gastropods 

0 Corals PI Trilobites 
y u K 0 N R I v E R 

EAGLE AREA WOODCHOPPER 

AREA 

Churkin and Brabb (1965a),Churkin 

and Brabb ( 1967), and Brabb and 

Churkin (1969) 

Unnamed siliceous shale 

and chert, 3000 ft 

Unnamed 

argillite 

and chert 

~----------------------~~--- ~ --- ~ 

t: 

Q) 

.s::. 

(.) 

:I: 

c 

c 

l1l 

(.) 

(.) 

~ 

I 

I 

I 

Nation River Formation. Nonmarine sandstone, shale, and 

chert-pebble conglomerate, 

3000 ft 

~ 

0 

Chert and shale 

member 

o· 

00 

I 

0 

0 

N 

Limestone and shale 

member, as much 

as 250ft 

t:. o ~ ""7 a 

Road River Formation 

Graptolitic shale and 

chert 

Devonian part about 

100ft 

Relations 

uncertain 

'E IJ) ~ ·~iddle Dev. ro IJ) Is. 

~~ 

~~ Q)C. 

~~ 

_g6 

.gg 

g .... 3: 

__ Fatill_ __ 

Base not 

exposed 

STRATIGRAPHY 

YUKON 

TANANA 

AREA 

Modified from 

Mertie (1 937b) 

0 

S 0 U T H E A S 

FRESHWATER BAY 

CHICHAGOF ISLAND 

Loney and others (1963) 

lyoukeen Formation 

Limestone and shale, 

3000± ft 

Fr.eshwater Bay Formation 

Greenstone, rhyolite and 

andesite tuff flows and 

T E 

1'-'-''-'--L..L...I..-L..J....J.....L-J....L....L..j .,.. breccia, 51)00 fi · · ~ 

0 Upper part is ill ~ Upper g Middle or Up- . member ~ ~ per Devonian limestone, 8 6 

tuff, and ..... c dolomite ~ .Q 

0 

IJ) 

Q)-Q) 

E~ "C 

·- c l1l 

IJ) 

...J ::l 

0 

£ 

ro"iii Qj 

c [j 

en l1l 

> 

0 

0 

1-

~ Lower member: 

graywacke, argillite, limestone, 

and cgl 

Q)- UE 

0 

u... 

'--------- ---

c? Kennel Creek Limestone, 

2200-5000 ft. Age not 

o conclusively documented. 

Considered Silurian by 

Kirk (1927) 

R N A L A S K A 

PRINCE OF WALES ISLAND 

Eberlein and Churkin ( 1970) 

0 

0""7 

0 

c? 

Peratrovich Formation 

Limestone, bedded 

chert in lower part, 

1000± ft 

Wadleigh Limestone, 1000 +ft. 

Composed largely of fragmented 

fossils 

Karheen Formation 

Reddish conglomerate, 

sandstone, shale, 

and minor limestone, 

5000+ ft 

Lower part is 

O Silurian ~------------../'-__, Heceta Limest~ne ~rgillite, graywacke, . /Massive Limestone, 

1------------1 I and conglomerate, minor conglomerate 

Fossil Creek . 5000+ ft 

Volcanics 

FIGURE 12.-Correlation chart of Devonian rocks. 

SYSTEM 

AND 

SERIES 

Qj 

c. 

c. 

~ 

z 

25 

<( 

~ 

-

z 

0 

> 

LLJ 

Cl 

Q) 

=c 

"C 

~ 

.r----

..... 

Q) 

~ 

0 

...J 

..... 

Q) 

c. 

c. 

~ 
26 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Upper Devonian 

-

and, in 

northeastern Brooks. 

Range, Lower Mississippian 

100 

Lower Devonian. Includes 

some Upper Silurian 

150° 

C 1 f I C 

f [\. 

0 100 200 300 400 MILES 

EXPLANATION 

Major sources '* of coarse 

detritus 

+ 310 m.y. 

Granitic intrusions with 

absolute age in millions 

of years 

+ 405 

310 

Romanzof Mountains, 

Sable (1965) 

+ 355 

Mount Sedgwick, Wanless 

and others (1965) 

+ ~i~' 

Mount Fitton, Wanless and 

others (1965); Baadsgard 

and others (1961) 

* Graywacke, conglomera.te and 

shale (F. R. Webber, oral 

commun., 1968) 

FIGURE 13.-Devonian coarse terrigenous rocks. Includes Mississippian Kekiktuk Conglomerate. 

Much farther south and on the other side of the 

Yukon shelf, similar coarse clastic rocks (Nation 

River Formation) have a gradational contact with 

Devonian siliceous shale and chert below. However, 

clastic rocks similar to the Nation River Formation 

in the Livengood district lie with a marked unconformity on altered mafic volcanic rocks and serpentinites, and the basal conglomerate has fragments 

of these igneous rocks (Foster, 1967; F. R. Weber 

and Michael Churkin, Jr., field observations, 1968). 

These facts suggest that the Devonian clastic rocks 

in the interior of Alaska had sources separate from 

similar clastic rocks in the Brooks Range. 

In southeastern Alaska there is similar evidence 

that plutonic activity and synorogenic uplift affected the Cordilleran geosyncline at various times 

during the Paleozoic (Lanphere and others, 1964; 

Brew and others, 1966; Eberlein and Churkin, 

1968). Branched plant stems and spores are common in many of these clastic sediments and suggest 

a nonmarine or, more probably, a nearshore deltaic 

origin. 
STRATIGRAPHY 27 

Absolute age determinations of granitic intrusion 

in the northeastern Brooks Range and in other 

places around the edge of the Arctic Ocean basin 

indicate that plutonic activity was probably related 

to the same mid-:-Paleozoic uplifts that produced 

the wedge of Upper Devonian clastic sediments 

(Tailleur and others, 1967; Trettin, 1967; Churkin, 

1969). 

CARBONIFEROUS ROCKS 

Fossils of Carboniferous age have been found in 

Alaska in different lithic sequences ranging from 

pure limestone to predominantly volcanic rocks (fig. 

14). Although rocks of Mississippian age are widespread, rocks of Pennsylvanian age have only recently been positively identified, and their known 

distribution is limited. 

The most continuous belt of Mississippian rocks 

in Alaska is along the Brooks Range. The Mississippian is represented there by the Lisburne Group, a 

2,000- to 4,000-foot-thick, mainly carbonate section 

that has variable amounts of nodular chert and 

minor shale (Bowsher and Dutro, 1957; Brosge and 

others, 1962; Armstrong, 1970a) (fig. 15). The Mississippian carbonate rocks are generally separated 

from the Upper Devonian conglomerate and sandstone by a 100- to 1,000-foot-thick unit of shale and 

argillite (Kayak Shale) that has sandstone in its 

lower part and limestone at its top (Tailleur and 

others, 1967; Brosge and Tailleur, 1970). In excep-._ 

tion, in the Sadlerochit Mountains in the northeast 

corner of Alaska, the Kayak Shale is locally absent 

or very thin, and Mississippian carbonate rocks rest 

unconformably on Devonian limestone and dolomite 

and, in places, on clastic rocks of Devonian ( ?) age 

(Reiser, 1970; Armstrong and others, 1970). Progressively younger carbonate rocks of the Lisburne 

overlap one another to the north, so that in the 

central Brooks Range they are Lower and Upper 

Mississippian and farther north, in the northeastern 

Brooks Range, the section ranges from Upper Mississippian at its base through the Middle Pennsylvanian at its top ( cf.· Brosge and others, 1962; 

Armstrong and others, 1970). For the Lisburne 

Peninsula, at the west end of the Brooks Range, 

Campbell (1967, p. 6) also reports that the base of 

the Lisburne may transgress time, becoming progressively younger~Early Mississippian in the 

south to early Late Mississippian in the north. This 

fact suggests a northward migration of a nearby 

west-oriented shoreline through much of Carboniferous time. 

Assuming that a shallow shelf existed north of 

the Brooks Range and that the Lisburne Group 

was deposited during a northward marine transgression onto this shelf, a series of facies maps has 

been drawn for various subdivisions of Carboniferous time by Armstrong and Mamet (1970). They 

also proposed the following depositional model of 

environments from south to north: starved basin 

(lime mud and chert), slope (lime mud), crinoid 

garden (crinoid and bryozoan-rich clean carbonate 

sandstone), oolite bank, back bank (bryozoan-crinoid sandstone with an increase in lime mud landward), and supratidal fla-t (lime mudstone and dolomite). 

South of the Brooks Range, Carboniferous rocks 

are known from many small areas widely separated 

by Mesozoic rock cover or whose lateral connections are obscured by igneous or metamorphic activity. 

In the Porcupine-Yukon Rivers area the Mississippian and probably some part of the Pennsylvanian 

(E. E. Brabb and Michael Churkin, Jr., unpub. data) 

are represented by a section of interbedded limestone and shale that forms the rhythmically banded 

section at Calico Bluff. A thin-bedded chert and 

shale unit of Devonian and Mississippian age (Ford 

Lake Shale) lies below the limestones of the Calico 

Bluff Formation and separates them from the underlying sandstone, conglomerate, and shale (Nation 

River Formation) of Late Devonian age (Brabb, 

1969; Brabb and Churkin, 1969). Pre-Permian erosion in this area has removed much of the Carboniferous section (Churkin and Brabb, 1967, figs. 

9, 10). 

In the northwestern part of the Yukon-Tanana 

region there is a poorly known sequence, mainly of 

noncalcareous sedimentary rocks including banded 

cherts (Livengood Chert), that, on the basis of a few 

fossil collections from rare limestones, had been 

assigned to the Mississippian (Mertie, 1937b). The 

occurrence of Oldhamia from Mertie's belt of "undifferentiated noncalcareous rocks of Mississippian 

age" suggests that at least some of the rocks previously considered Mississippian are probably Cambrian or older ( Churkin and Brabb, 1965b; Michael 

Churkin, Jr., field data, 1968). More work is clearly 

necessary in this structurally complex region to 

determine the distribution and stratigraphy of 

Carboniferous rocks. 

Siliceous detrital rocks and volcanic rocks southwest of the Yukon-Tanana· region in the Kaiyuh 

Hills area and in Kuskokwim drainage (Mertie, 

1937a; Cady and others, 1955) have been questionably 

assigned to the Mississippian on the basis of lithic 
28 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

150° 

/ / 

f 

1 f I C 

. p... c 

100 0 100 200 300 400 MILES 

EXPLANATION ' 

Mainly limestone, minor shale, 

sandstone,and chert 

Limestone, shale, and sandstone Limestone, graywacke, conglomerate, shale, and chert in sequence 

with volcanic rocks 

FIGURE 14.-Carboniferous rocks of Alaska. See opposite page for sources of data. 

similarity and their supposed stratigraphic position 

below fossiliferous Permian rocks. No conclusive 

evidence supporting a Carboniferous age for any 

rocks in this vast region is known to date. 

During the Devonian this same lower YukonKuskokwim area was a southwestern extension of 

the predominantly carbonate sedimentation of eastcentral Alaska .. However, in the Permian and presumably starting with the Carboniferous, southwestern Alaska as far north as Norton Sound was 

an area of siliceous detrital and volcanic rock 

accumulation (Cady and others, 1955, fig. 4). 

Farther west on St. Lawrence Island, there is a section at least 1,000 feet thick of limestone and cherty 

limestone that closely resembles, both lithically and 

faunally, the Mississippian of the Brooks Range 

(Patton and Dutro, 1969). Furthermore, the presence on St. Lawrence Island of Devonian dolomite 

below the Mississippian limestone and a section of 

Triassic and possibly Permian siltstone, shale, and 

chert above it further indicate a close correlation of 

this section with those in the Brooks Range. Coralbearing limestone of probable Mississippian age has 

been reported from the vicinity of Cape Prince of 

Wales at the east tip of the Seward Peninsula 

(Steidtmann and Cathcart, 1922) ~ Sainsbury (oral 

commun., 1970) verified the presence of probable 

Lisburne limestone there, but, according to him, the 
STRATIGRAPHY 29 

SOURCES OF DATA FOR FIGURE 14 

1. Lake Peters : 

Kayak Shale, Lisburne Group (Brosge and others, 

1962). 

2. Shainin Lake: 

Kayak Shale, Lisburne Group (Bowsher and Dutro, 

1957; Patton and Tailleur, 1964). 

3. DeLong Mountains: 

Lisburne Group (Sable and Dutro, 1961). 

4. Lisburne Peninsula: 

Lisburne Group (Campbell, 1967). 

5. Topagoruk test well: 

Red beds of uncertain age (Collins, 1958). 

5a. Prudhoe Bay oil field: 

Kayak Formation and Lisburne Group (Rickwood, 

1970) 0 

6. Cape Mountain: 

( Steidmann and Cathcart, 1922; Sainsbury, oral 

commun., 1969). 

7. St. Lawrence Island: 

Lisburne (?) limestone underlain by Devonian dolomite (Patton and Dutro, 1969). 

8. Kaiyuh Hills: 

Nonfossiliferous volcanic rock (Mertie, 1937a). 

9. Livengood-Yukon River area: 

Livengood Chert ( Mertie, 1937b). 

10. Porcupine River: 

(Brosge and others, 1966). 

11. Eagle area: 

Calico Bluff Formation, upper part of Ford Lake 

Shale (Brabb and Churkin, 1967). 

12. Central Alaska Range: 

Totatlanika Schist (Pewe and others, 1966). 

13. Eastern Alaska Range: 

Rainbow Mountain sequence (Rowett, 1969). 

Chisna Formation (Moffit, 1954). 

14. Chitina Valley: 

Strelna Formation and Klutina Group (Moffit, 1~38). 

15. Kuskokwim River: 

Lower nonfossiliferous part of Gemuk Group (Cady 

and others, 1955). 

16. Nushagak District: 

N onfossiliferous siliceous rocks below Permian limestone (Mertie, 1938). 

17. Chichagof Island: 

Iyoukeen Formation (Loney and others, 1963). 

18. Kuiu Strait area: 

Saginaw Bay Formation (Muffler, 1967). 

~ 19. Craig area: 

Peratrovich ·Formation, Klawak Formation, Ladrones 

Limestone (Eberlein and Churkin, 1970). 

20. Northeast U.S.S.R.: 

(Krasniy, 1966). 

limestone is a ·structurally ·isolated and largely recrystallized mass difficult to correlate. Thus, in 

widely separated areas along the far western edge 

of Alaska ·north of Norton Sound; one finds. a predominantly limestone facies that rims the volcanicrich siliceous detrital · facies of the lower YukonKuskokwim region. 

490-094 0 - 73 - 5 

In the eastern Alaska Range a variety of rocks 

have been questionably assigned to the Mississippian 

because they seem to be structurally below fossili .. 

ferous Permian rocks and lithically resemble rocks 

(Strelna Formation) that contain Mississippian 

fossils in a parallel belt nearly 100 miles farther 

south. These sequences of questionable Mississippian 

age consist of sandstone, argillaceous rock, and conglomerate that are interlayered with prominent 

volcaniclastic rocks and mafic lava flows (Moffit, 

1954). Limestone is relatively rare in the section, 

and all rocks have been altered to various degrees 

by low-grade regional metamorphism. Southwest of 

Fairbanks ori the north side of the Alaska Range, 

the tabulate coral Syringopora, found in the Totatlanika Schist, suggests a post-Ordovician, possibly 

Mississippian, age (Wahrhaftig, 1968). According 

to Wahrhaftig, the schist is derived mainly from 

volcanic rocks. Minor interbedded fossiliferous limestone lenses indicate a marine environment. 

South of the Alaska Range, the Strelna Formation, originally dated as Mississippian by corals and 

brachiopods, is exposed along the Chitina Valley 

which separates the Wrangell Mountains from· the 

C:tJ.ugach Mountains farther south (Moffit, 1938). 

The Strelna Formation is a complex of greenstone 

(bedded basaltic lavas and tuffs) interstratified with 

argillite, greenschist, chert, and minor fossiliferous 

marble that is estimated to be in excess of 6,500 feet 

thick; neither its top nor base is known. Work in 

progress by E. M. MacKevett, Jr., suggests that the 

formation has Permian brachiopods in its type section. Furthermore, the general stratigraphy of the 

Strelna, although it is more metamorphosed, resembles parts of the Permian section nearby (E. M. 

MacKevett, Jr., oral commun., 1969). Somewhat 

higher grade quartz-mica schists and amphibolite 

schists (the Klutina Group and the Dadina Schist), 

west and north ( ?) of the Chitina Valley, are correlated with the Strelna Formation (Moffit, 1938). 

In several parts of the Alexander Archipelago 

of southeastern Alaska there are volcanic-rich se-

. quences similar to those in the Chitina Valley. These 

sequences are the most southerly exposures of Carboniferous rocks in Alaska and are especially important in that the rocks are ·generally ·not altered 

and contain very abundant shelly fossils that permit 

detailed correlations in an area of rapid facies 

changes. Within southeastern Alaska· the northern 

exposures of Mississippian strata on Chichagof Island are predominantly limestone (fig. 10). Farther 

south, in the Keku Strait area, the Mississippian and 

Pen·nsylvanian·section is limestone with volcanic and 
30 

SYSTEM 

POST-TRIASSIC 

TRIASSIC 

PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

ARCTIC COASTAL PLAIN 

TOPAGORUK TEST WELL 

0 

Collins (1958) 

Middle Jurassic 

shale and siltstone 

PRUDHOE BAY OIL 

FIELD 

Rickwood (1970) 

Jurassic shales 

LAKE PETERS, 

NORTHEASTERN 

BROOKS RANGE 

Brosge and others(1962), 

Armstrong and others(1970) 

Detterman (1970), and 

Reiser (1970) 

Jurassic shale, siltstone, 

and sandstone 

LISBURNE PENINSULA 

Campbell (1967) 

Ogotoruk Formation 

Mudstone and sandstone 

DELONG MOUNTAINS, 

WESTERN BROOKS 

RANGE 

Sable and Dutro (1961) 

Tailleur and others (1966) 

Jurassic 

chert and shale 

SHANIN LAKE, 

CENTRAL BROOKS 

RANGE 

Bowsher and Dutro (1957) 

Patton and Tailleur (1964) 

Cretaceous and 

Jurassic shale 

and graywacke 

Sag River Formation f-----------1-------------- ------------ c~- ------- 6) Shublik Formation 

Shale, siltstone, 

sandstone, g. 

f--siS~aiiindilisiitoFcnmenJatOTcift;;:;-h,~~....-rSnh,.,.ub-.-lnik,.,.F-.-ornmn-a-.-tinon,.,.-,-..,-.1 o Shublik Formation o Shublik Formation oc:> Shublik Formation 

740ft e 

t-------l['illliiTlTillill][[ i 

_g 

I ~~~~1~~o:~i~ii:e- mnmm~ 1111111111 ~i:e:~~r::.· ;~gl~, .Li~~~~~~Os-~~ ~nd Li;~~~hneert,s~~~;: 

Sadlerochit 

Formation 

Sandstone, ~~~~~m]l..J.Il.LI..LJ.W..U...I..LJi.J.LUllUJ.l-j.lllli~..LJ.U.I~..LJ.U.I~..L...I.j PERMIAN 

PENNSYLVANIAN 

en 

::J 

0 

0:: 

~ 

z 

0 

al 

0:: 

<( 

(.) 

MISSISSIPPIAN 

DEVONIAN 

Sandstone, siltstone, 

shale, and chert 

pebble conglomerate, 

390ft 

~~~~m]~ 

Red beds (age uncertain) 

Claystone, siltstone, 

and sandstone; minor 

conglomerate, 270 ft 

]~l~[]~ ~r TI'i9n0or~tl>! 

0 Chert pebble 

conglomerate 

and shale, 

500ft 

"'0 

:;, 

ct conglomerate, 

and shale, 900 ft 

Sadlerochit Formation 

Sandstone and shale, 

V' -!300ft 

Siksikpuk Formation 

·Argillite, chert and 

v- shale, 400± ft 

Siksikpuk Formation 

Argillite and chert, 

200-400ft 

Siksikpuk Formation 

Shale and siltstone, 

250-350 ft 

0 

V' 

~I..J.~~~~~~mmrur ~~ g. Wahoo Limestone, 150ft of Tupik 111111 

j : __ :_·_ _ _ f~fujlf~lli ll . ..J..t-L.U~:!-'-'-'--LLLL.LI...l..LI.LI...l I...L.l..'f'--Lf-W..l...L..L.l..l-LJ..JLLL.LI...l...L.l..L...I...J.-j 

Lisburne Group 

Limestone and dolomite 

with chert nodules, 

sandy at base, 2000 ft 

Kayak Formation 

Shale and minor 

sandstone, 600 ft 

J.J: u II IIi 111111 iillJ 

Pre-Upper Devonian 

argillite, graywacke 

:.::; 0 V' V' v-O 

Alapah Limestone Tupik Fo~ation Tupik Formation 

Limestone, dolomite,~ Chert and limestone, Limestone and chert, g ~~=~ ~~~!~~~ minor shale, 5 300 ft a. 135- 700 ft. S shale and chert, 

';;:-- 1300 ft (; Kogruk(?l tormation e 11 k 1000 ft 5 ~ ~ Lim~stone and dolomite, (!) Kogruk m"~d- ~ (; ~ v- .\J. 3000 ft ~ 0 Formation, stone ~ f-_______ _ 

::: Kayak(?) Shale ~ . ~ v- 500- ch~rt ~ Wachsmuth Limestone 

8 Sandstone in lower :.::; 0 N~sorak Formation ~ 1500 ft facii_!S ~ Limestone and dolomite 

:0 part limestone in Limestone and shale, :.::; Utukok Fm~~u~~. 1200 ft ' 

.!5 up~r part, 100- _ -; 2200 ft v-Sandy lime- 000 ft .. 

1000 ekiktuk 0 stone, sandstone, ~~k Shale. Shale, arg1lhte, 

•

Conglomeraw· V' 0 ------ and shale, 2500 ft rrttT m<!ITandstone. 1000 ft 

Mudstone, sandstone, v- 0 Kanayut Conglomerate limestone, and minor 0 Kugururok Formation Nonmarine chert 

conglomerate, 2000 ft. Dolomite, limestone, pebble conglomerate, 

Base not exposed =~~~~; =~~le, sandstone and 

Neruokpuk Formation 

0 Pollen and (or) plants 

oc:> Fish material 

o Pelecypods 

6) Foraminifera 

(b Cephalopods 

conglomerate. 2000 ft shale, 3300± ft 

EXPLANATION 0 F~sulines 

0 Coral 

V' Brachiopods 

0 Gastropods 

FIGURE 15.-Correlation chart of Carboniferous and Permian rocks. 

chert members in its lower part (Muffler, 1967). 

Still farther south, in the Craig-Klawak and 

Suemez-Shelikof Island areas, the Mississippian and 

Pennsylvanian are represented by a section of impure limestone that has chert in its lower part 

(Eberlein and Churkin, 1970; Armstrong, 1970b). 

nian faunas have been recognized only from the 

upper parts of the· Lisburne Group (Brosge and 

others, 1962; Armstrong and Mamet, 1970). Recent 

mapping in the Yukon River area, combined with 

preliminary paleontologic studies of fossils from the 

upper Calico Bluff Formation, suggest that there are 

a few places in east-central Alaska where Pennsylvanian rocks occur. However, most of the PennsylPennsylvanian rocks have not been widely recognized in Alaska. In the Brooks Range, Pennsylva-
YUKON RIVER 

Brabb and Churkin (1969) 

Brabb and Grant (1971), 

and Mamet and Skipp 

(in press) 

~7 Kandik Group 

~ 

~ 

Sandstone and 

C7 Glenn Shale, 

~ oil shale in 

lower part 

PORCUPINE RIVER 

Brosge and others (1966) 

STRATIGRAPHY 

EASTERN ALASKA RANGE EAST WRANGELL 

Moffit (1954), D. H. Richter MOUNTAINS (written commun., 1968), Rowett (1969),and Petocz Moffit (1938),and Smith 

( 1970) and Mackevett ( 1970) 

Jurassic or 

Cretaceous 

argillite 

Post-Triassic 

Upper Triassic 

limestone and 

shale 

KEKU STRAIT, 

SOUTHEASTERN ALASKA 

Muffler (1967) 

Jurassic and Cretaceous 

graywacke, argillite 

and conglomerate 

1111 J IUIIJlllllJlU). Thin-bedded C?~Chitisto~&ai~estone ~pper Triassic volcanics 

limestone c

7 Nikolai Greenstone limestone and 

Top unknown 5000 ft conglomerate, 3000 ft 

-~~~:~~;--- illU Iilli WI WI WI U ill UIJJJlilljlll~ lU lllJlUla Siltstone Wit~ Mankomen Formation Hasen Creek Formation . calcar~us s1lt- (McCallum Creek 0 Chert, shale, sand- Py~us Format1on . 

~~~~~ ~~~~~~~ules sequence) ~ ~~~r:· ~na~ii~~g~~m- v- ~~~~t~~=rt d~~~e, 350 ft ' Sandstone, shale, near top, 900 ft • 

layered with mafic e Fm 0 Halleck Fm '4' 

tuffs and lavas, l' Station Creek Tuffa- Calc. silt- 0 

PRINCE OF WALES 

ISLAND, SOUTHEASTERN ALASKA 

Eberlein and Churkin 

(1970) 

Ste'b (Jahkandit Limestone Limestone, sandy 6000-10,000 ft ~ Formation ceous stone, ss and 

Cgl y Chert pebble con- v- minor shaly inter- ~ Submarine basaltic ~~~illit!cke Is, locally 

___ ±._______ limestone, inter- a. Cann'-ery_,....l....,__

1 

___ tt.-1 

2000ft glomerate at base, beds and chert. flows and volcan- ~e'f't pillow lava. 

,....-1 350 ft Several hundred feet 0 iclastic rocks, pillow and volcam-

? cn-,.n,,.,,..,rr;-rr;-rrrrl v- 6000 ft lava, clastic rocks, 

minor Is, 700 ft 

i-------- -t=2:.=.000=,..:ft..:.:.._:::...... ___ -t Top eroded 

0 ~ 

08> 

v- Calico 

Black shale, limestone 

and chert, minor calcareous sandstone. 

Several hundred feet 

thick 

Rainbow Mountain 

sequence (probably 

correlates with 

0 Tetelna and Chisna 

v- Formations). 

~ Silty limestone Klawak 

v- member Formation 

f---=--:---..,----!Calcareous 

c ~~~~t~~~ ~ siltstone 

,g member, V'~i~~:is 

Ladrones 

Limestone 

Massive 

pure 

limestone, 

1000+ ft 

SYSTEM 

POST-TRIASSIC 

TRIASSIC 

PERMIAN 

PENNSYLVANIAN 

Bluff 

Formation 

Limestone 

and shale, 

!500ft 

Andesitic flows, 

volcaniclastic rocks 

and minor silty 

limestone, > 5000 ft 0---------

~ i-_..iO.Q.+_ft ___ Oand cgl, 

~ ~5~00~-1~000~~----{-----~ 

a; Black chert 

~ e, ~ 

: _____ _j 

V' 

~ 

Ford Lake Shale 

Siliceous shale and 

chert, 1000 ft 

Siltstone and shale. 200 ft i-----------

0 Salmontrout 

Limestone, 

600ft 

1 Strelna Formation may be a more highly metamorphosed 

equivalent of Permian(?) and Permian Skolai Group 

(E. M. MacKevett, oral commun., 1970) 

V'Strelna Formation 1 

and Klutina Group 

Greenschist. argillite, 

metavolcanic rocks 

and minor marble, 

6500 ft 

? 

~ member 

·&, r-------- 0 &'> • • 

Jl Volcanic member Peratrov1ch Format1on 

0 

V' 

0 

V' 

Tuff breccia Limestone and 

pillo:.V lava a~d d~lomite with 

limestone .m.nor chert, IOOO±ft 

Fault 

Crinoidallimestone e, 

unit, 200+ ft OvUpper Devonian 0 W•dl~rt~f"- Lime ?Formlimestone, 50+ ft V' 1000 IOn. Several 

ousand 

eet 

FIGURE 15.-Correlation chart of Carboniferous and Permian rocks-Continued. 

MISSISSIPPIAN 

DEVONIAN 

31 

vanian and a large part· of the Mississippian in eastcentral Alaska have been removed by erosion, and 

Permian strata in many places rest unconformably on 

rocks of Devonian age (Brabb and Churkin, 1967). 

and Churkin, 1970). They are predominantly limestone with varying amounts of nodular chert and 

contain some chert and quartz detritus. 

Farther south, in the Rainbow Mountain area of 

the Alaska Range, a thick succession (about 7,000 ft 

thick) of volcanic graywacke, tuff, siltstone, and 

limestone of Pennsylvania age has been recently 

recognized (Rowett, 1969). 

In contrast to most of Alaska where Pennsylvanian fossils are difficult to identify or are missing, 

Pennsylvanian rocks in southeastern Alaska are 

recognized by rich shelly faunas including an abundance of fusulinids (Dutro and Douglass, 1961; R. C. 

Douglass, written commun., 1968). The Pennsylvanian rocks in southeastern Alaska occur on Kuiu 

Island (Dutro and Douglass, 1961) and in two areas 

on the west side of Prince of Wales Island (Eberlein 

PERMIAN ROCKS 

Permian rocks are known from virtually all the 

ar~as in Alaska that contain older Paleozoic rocks 

(fig. 16). The Seward Peninsula, where Permian 

rocks have not been reported to date, is a noteworthy 

exception. In general, Permian sedimentation 

throughout southeastern Alaska (Muffler, 1967; 

Brew, 1968), the Wrangell Mountains (Smith and 

MacKevett, 1970), and the eastern Alaska Range 

(D. H. Richter, written commun., 1968; Rowett, 

1969; Petocz, 1970) closely paralleled the pattern 

that developed in the Carboniferous, deposition of 

sequences rich in volcaniclastic and volcanic rocks. 

In addition, good Permian faunas are known from 
32 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

150° 140° 130° 

/ / 

f 

I f I C ~ c 

0 

100 0 100 200 300 400 MILES 

EXPLANATION 

1111 

Mainly Limestone Sandstone, • siltstone, shale, Basaltic lavas, volcaniclastic rocks, 

graywacke, conglomerate, shale,· 

chert, and minor limestone 

chert, and, in places, chert 

pebble conglomerate 

FIGURE 16.-Permian rocks of Alaska. See opposite page for sources of data. 

the lower Yukon-Kuskokwim area of southwestern 

Alaska where fossiliferous limestone ·500-1,000 feet 

thick grades stratigraphically upward into mafic 

lavas and tuffs over 4,500 feet thick (Mertie, 1938; 

Smith, 1939, p. 33). In t~e Goo(lnews Bay district, 

on the coast of the Bering. Sea, Permian br~chiopods were first reported (Smith, 1939, p .. 33 ). from 

limestone associated with red and black slates. Subsequent mapping there indicates that the Permian 

limestone grades lat~rally into greenstone (Hoare 

and .Coonrad, 1961). 

Permian limestone in close proximity to basaltic 

breccias, agglomerates, and flows is known from a 

tiny islet off Cape Kekurnoi on the southeast side 

of the Alaska Peninsula oppo.site Kodiak Island 

(Hanson, 1957). This isolated exposure of Permian 

rock is separated from the nearest Paleozoic rocks 

(in the Kuskokwim area) by more.than two hundred 

miles of Mesozoic and Quaternary· cover. 

Even more isolated than the Permian Limestone 

at Cape Kekurnoi is the report of Pennsylvanian or 

Permjan plants from. Adak Island in the middle of 

the Aleutia:n :Island arc (Coats, 1956). The plant 

material consists of about a dozen well-preserved 

leaf impressions in a fine-grained volcanic sandstone. Coats considered the sandstone .as part of a 

predominantly basaltic unit that is similar in appearance to the Tertiary and Quaternary volcanic 
~ 

.. ,.. 

•· 

STRATIGRAPHY 33 

SOURCES OF DATA FOR FIGURE 16 

1. Topagoruk test well: 

Includes some chert pebble conglomerate (Collins, 

1958). 

1a. Prudhoe Bay oil field: 

Lower part of Sadlerochit Formation (Rickwood, 

1970). 

2. Lake Peters: 

Sadlerochit Formation ( Brosge an~ others, 1962; 

Detterman, 1970). 

3. Shainin Lake: 

Siksikpuk Formation (Bowsher and Dutro, 1957; Patton and TaiUeur, 1964). 

3a. Nuka Ridge: 

Upper part of Nuka Fonnation, arkosic sandstone and 

limestone ( Tailleur and Sable, 1963) . 

4. Lisburne Peninsula: 

Siksikpuk Formation (Campbell, l967). 

5. Porcupine River: 

(Brosge and others, 1966). 

6. Eagle area: 

Tahka,ndit Limestone (Brabb and Churkin, 1969). 

7. Yukon River: 

Step Conglomerate (Brabb and Churkin, 1969). 

7a. West edge of Yukon Flats: 

8. 

9. 

. 10. 

11. 

12. 

13. 

Rampart Group of questionable Permian age (Brosge 

and others, 1969). 

Susitna River area: 

(Ross, 1933). 

Eastern Alaska Range: 

Mankomen Formation (Moffit, 1954; D. H. Richter, 

written commun., 1968; Rowett, 1969). 

East Wrangell Mountains: 

Skolai Group of questionable Permian and Permian 

age (Moffit, 1938; Smith and MacKevett~ 1970). 

Lower Yukon River: 

Permian fossil-bearing limestone (500-1,000 ft) overlain conformably by 4,500 feet of greenstone (Smith, 

1939). 

Nushagak area: 

Permian limestone overlain conformably by tuff 

(Mertie, 1938). 

Goodnews Bay district: 

Permian limestone interlayered and grades into finegrained silic~ous sedimentary rocks and volcanic 

rocks (Smith, 1939; Hoare, 1961). 

14. Cape Kekurnoi area: 

Permian limestone associated with volcanic rocks 

(Hanson, 1957). 

15. Chilkat Range: 

Limestone and graywacke (Lathram and others, 

1959). 

16. Chichagof Island: Goon Dip Greenston£ of Permian ( ?) 

and Triassic (?) age (Loney and others, 1963). 

17. Admiralty Island : 

Cannery Formation and Pybus Formation (Loney, 

1964; Muffler, 1967. 

18. Keku Strait area: 

Cannery, Halleck, and Pybus Formations (Muffler, 

1967). 

19. Chukotka, Northeast U.S.S.R.: 

(Krasniy, 1966). 

rocks that form most of the Aleutian Islands. In an 

attempt to explain this unique occurrence of 

Paleozoic rock in the Aleutians, the plant locality on 

Adak Island was studied, and the sandstone matrix 

surrounding the plants was found to contain abundant pollen and some pelecypods that are diagnostic 

of Tertiary age (Scholl and others, 1970). It is 

concluded that these plants, although remarkably 

similary to Paleozoic species, are Tertiary. 

In the Iliamna Lake-Kamishak Bay area of the 

upper Alaska Peninsula, on the Kenai Peninsula, and 

on Kodiak Island, fossiliferous Upper Triassic limestone conformably overlies mafic volcanic flows, 

breccias, and tuffs that have been questionably 

assigned by various authors to the Permian and 

Triassic (Burk, 1965). In these areas, sequences 

of slate, graywacke, chert, and volcanic rock of unknown age seem to be older than the predominantly 

volcanic sequences underneath the Triassic limestone. Considered still older, probably Paleozoic or 

Precambrian, is a metamorphic complex of marble, 

schist, gneiss, and quartzite. Large granitic batholiths that have reconstituted much of the rock in the 

area are known to be Jurassic, and some are as 

young as Late Cretaceous (Reed and Lanphere, 

1969). Thus, some of the more metamorphosed 

rocks, presumed to be the oldest, could be as young 

as early Mesozoic. The single exposure of fossiliferous Permian rocks at Cape Kekurnoi suggests 

that detrital-volcanic rock facies of southeastern 

Alaska extended during the late Paleozoic into what 

is now part of the Alaska Peninsula. 

Permian rocks are widely .. distributed in the 

Wrangell Mountains and adjacent parts of Canada 

(Moffit, 1938; Smith and MacKevett, 1970). The 

Permian in this area consists of a slightly metamorphosed sequence (Skolai Group) more than 8,000 

feet thick of submarine basaltic flows, breccias, and 

tuffs that are interbedded with volcaniclastic sediments, shale, and chert (Smith and MacKevett, 

1970). Cliff-forming massive limestone near the top 

of the sequence consists mainly of fragmented shelly 

fossils that indicate an Early Permian age. Age data 

are lacking on the underlying volcanic flows and 

volcaniclastic rocks. The base of the sequence has 

not yet been recognized, and the more highly metamorphosed and deformed rocks (Strelna Formation) 

in the area that originally were thought to be Mississippian in age are now believed to be more highly 

metamorphosed equivalents of the Skolai Group (E. 

M. MacKevett, Jr., written commun., 1970). Locally, 

the Skolai Group is overlain disconformably by 

Middle Triassic strata and, more extensively, by the 
34 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Nikolai Greenstone of late Middle and (or) early 

Late Triassic age (Smith and MacKevett, 1970). 

Farther north, in the upper Copper River valley 

and eastern Alaska Range, there is a Permian section characterized by an abundance of volcanic rocks 

interbedded with calcareous sediments (Mendenhall, 

1905; Moffit, 1954). In the vicinity of Mankomen 

Lake (type locality of the Mankomen Formation), 

the stratigraphic section, mainly argillaceous and 

sandy sediments about 5,000 feet thick, includes a series of massive limestone lenses as much as 500 feet 

thick (D. H. Richter, written commun., 1969). According to Richter, these rocks are conformably 

underlain by 200-1,700 feet of fine- to coarsegrained volcaniclastic rocks that contain Permian 

corals and fusulinids, and these rocks, in turn, are 

underlain by andesitic lavas of Pennsylvanian ( ?) 

age. Overlying the Mankomen Formation is a section, about 5,000 feet thick, of amygdaloidal basalt 

that has Permian brachiopods in massive reeflike 

limestones. Stratigraphically higher are Triassic and 

Jurassic or Cretaceous strata that rest on the Permian lavas with angular unconformity. 

Farther west, in the Rainbow Mountain-Delta 

River area of the Alaska Range, the Permian section is characterized by volcanic and marine sedimentary strata rich in volcaniclastic detritus (Rowett, 1969; Petocz, 1970). As in the Permian sections near Mankomen Lake farther east, richly fossiliferous limestones occur in the upper part of the 

section, and the lower part is mainly volcaniclastic 

rock interlayered with argillaceous and graywacke 

sediments. Detailed stratigraphic studies in this 

part of the Alaska Range, coupled with studies of 

coral faunas (Rowett, 1969) and of fusulinid faunas 

(Petocz, 1970), make this section an important 

reference point for Permian correlations not only 

in Alaska but with sections that have similar boreal 

faunas in the U.S.S.R., Canada, Greenland, and 

Spitsbergen. 

In the Nation River area north of the Alaska 

Range, the Permian is represented by relatively 

pure, massive limestone-the Tahkandit Limestone. 

The Tahkandit is only about 350 feet thick and has 

glauconitic sandstone and chert-pebble conglomerate 

at its base where it unconformably overlies the 

Nation River Formation of Late Devonian age 

(Brabb and Churkin, 1967; Brabb and Grant, 1971). 

East, west, and north of its type area near the 

mouth of Nation River, the Tahkandit brachiopod 

fauna is found in limy interbeds that are part of 

a predominantly detrital facies of chert-pebble conglomerate, sandstone, and siltstone-the Step Conglomerate (Brabb and Churkin, 1969). Permian 

brachiopods are also known from limestone beds 

in predominantly argillite sections ex:.:>osed in the 

upper Black River, some 50 miles north of the type 

Tahkandit (E. E. Brabb, oral commun., 1968). 

Still farther north, on the Porcupine River, several hundred feet of sandy productoid brachiopodrich limestone and minor shale and chert interbeds 

of Carboniferous age is overlain by medium-darkgray siltstone containing rare corals, branchiopods, 

and cephalopods of Permian age (Brosge and others, 

1966). 

At the west edge of the Yukon Flats, an assemblage of basaltic flows, tuffs, and breccias including 

smaller amounts of interbedded chert, shale, and 

sandstone-the Rampart Group-had been assigned 

to the Mississippian on the basis of a few bryozoa 

from a lens of limestone questionably within the 

volcanic sequence or possibly from a somewhat older 

horizon (Mertie, 1937b, p. 126-127). Examination 

of new collections, as well as the old collections, 

shows that this limestone bed is within the volcanic 

sequence and is more likely to be Permian than 

Mississippian (Brosge and others, 1969). The limestone itself is composed largely of pelecypod prisms 

like those of Inoceramus and, in this respect, resembles similar prisms in Permian limestone beds 

in east-central Alaska (Tahkandit Limestone) and 

in southwestern Alaska (Gemuk Group). Hornblende 

from gabbro that seems to intrude the Rampart 

volcanic rocks has an age of 205 ± 6 m.y. (Triassic) 

based on potassium-argon isotope dating (Lanphere, 

in Brosge and others, 1969). 

Igneous rocks similar to those of the Rampart 

Group but with a smaller proportion of associated 

sedimentary rocks are found farther east in the 

Crazy Mountains and in the vicinity of Circle along 

the south edge of the Yukon Flats. These mainly 

fine-grained igneous rocks of basaltic composition 

were named by Mertie (1930) as the Circle Volcanics and correlated on the basis of lithic similarity with the Rampart Group about 175 miles 

farther west (Mertie, 1937, p. 127-128). A potassium-argon isotope date on hornblende from an 

intrusive(?) rock within the Circle Volcanics is 220 

m.y. (M. A. Lanphere, written commun., 1968). This 

is a Triassic date that closely corresponds to the 

205-m.y. age of gabbro·that seems to intrude Rampart volvanic rocks (Brosge and others, 1969). Aeromagnetic surveys indicate that igneous rocks underlie much of the Yukon Flats and suggest that the 

Circle Volcanics continues west with little interruption and possibly connects up with similar rocks 

-· 

~-
• 

) 

•· 

STRATIGRAPHY 35 

of the Rampart Group (Brosge and others, 1970). 

More recent work in this area indicates that the 

Circle Volcanics in its type area along the Yukon 

River and farther west in the Crazy Mountains does 

not have textural or structural characteristics that 

are exclusively volcanic (Michael Churkin, Jr., 

unpub. field data, 1968) .. The Circle Volcanics,. like 

the volcanics of the Rampart Group, is reported to 

have many siliceous sedimentary rocks interlayered 

with it (Mertie, 1937b). However, an examination 

of the best exposures of Circle Volcanics in contact 

with sedimentary rocks indicates that the so-called 

volcanic rocks have very fine grained chilled margins and that the sedimentary rocks, mainly argillites and quartzitic sandstones, next to them are 

·recrystalized so that argillaceous sedimentary rocks 

are spotted slates (Michael Churkin, Jr., unpub. 

field data, 1968). Furthermore, the Circle Volcanics 

in detail has crosscutting relations with the sedimentary rocks, and fragments of the sedimentary 

rocks have been incorporated into the intrusive 

rocks, in places making up large selvages. A way 

from these contacts, the Circle Volcanics consists of 

diabases or coarse-grained gabbros that are generally porphyritic and, in places, have ;mineralogic 

layering. Taking all these features into acount, I 

believe that the Circle Volcanics is mainly not lava 

flows but intrusive rocks of probable Triassic age. 

Whatever the age of the Circle Volcanics, late Paleozoic or Triassic, its intrusive origin explains the 

absence of volcani~ detritus in the surrounding 

sedimentary rocks of this span of geologic time. 

Permian rocks are widely distributed along the 

Brooks Range (figs. 15, 16) and are generally 

represented by only a few hundred feet of argillaceous rocks, chert, sandstone, and conglomerate of 

the Siksikpuk and the lower part of the Sadlerochit 

Formations (Brosge and others, 1962; Bowsher and 

Dutro, 1957; Patton and Tailleur, 1964; Campbell, 

1967; Detterman, 1970). The Sadlerochit Formation 

is the main reservoir rock in the Prudhoe Bay oil 

fi~ld (Rickwood, 1970; fig. 15). An erosional hiatus representing much of Pennsylvanian time separates these Permian clastic rocks from the Lisburne 

carbonate rocks, but the time gap is younger and 

may decrease towards the front of the northeastern 

Brooks Range where the Lisburne ranges upward 

into the Middle Pennsylvanian (Armstrong and 

others, 1970). All these Permian clastic deposits, in 

turn, are overlain disconformably by the thin sequence of oil shale, limestone, and sandstone of the 

Shublik Formation of Triassic age (Brosge and 

others, 1962; Detterman, 1970). _ 

A notable exception to this general stratigraphic 

sequence of upper Paleozoic rocks is the enigmatic 

section of Mississippian and Permian arkosic sand,.. 

stone and limestone of the N uka Ridge area on the 

north slope of the DeLong Mountains (Tailleur and 

Sable, 1963; Tailleur and Brosge, 1970). 

Up to this point,· the paper has summarized the 

stratigraphic data available on Prec~mbrian and 

Paleozoic rocks in Alaska. The rest of the paper attempts to interpret their tectonic significance and 

their role in the structural evolution of Alaska. 

INTERPRETATION OF STRATIGRAPHIC 

DATA-TECTONIC FRAMEWORK OF 

SEDIMENTATION 

PRECAMBRIAN ROCKS 

The Tindir Group of east-central Alaska, the only 

. definite Precambrian rocks known in Alaska, is at 

the northwest end of a long belt of late Precambrian strata that runs south across Yukon Territory and British Columbia into the northern Rocky 

Mountains of Alberta, Washington, and Idaho. The 

better exposed sections of these rocks measure tens 

of thousands of feet. The great thickness of sedimentary rocks (including minor basaltic lavas) distributed in this long belt indicates a major cycle 

of sedimentation of geosynclinal proportions. 

No regional unconformities have thus far been 

found within the Tindir Group, and it seems to be 

accordantly overlain by fossiliferous Cambrian rocks. 

Farther to the southeast, the top of the late Precambrian WinderJllere Series, the Rapitan Group, 

and the Belt Supergroup are all marked by unconformities. Over large areas these unconformities are 

ill defined, but their existence has been proved by 

regional mapping (Yates and others, 1966). In parts 

of southern Yukon Territory, a major unconformity 

within the Proterozoic also separates the Belt Supergroup from the overlying Windermere Series (Gabrielse, 1967), and the Windermere, in turn, is progressively removed by erosion below the Cambrian. 

Paleontologic studies of stromatolites from the 

Tindir may further define the age of the Tindir and 

permit closer correlation with the Belt Supergroup 

farther south on the one hand and, on the other, 

with the stromatolite-rich upper Precambrian rocks 

of the Siberian Platform farther west. 

The base of the Tindir is not known, but rare 

boulders of granitic rock and gneiss in the Tindir 

suggest that an earlier Precambrian igneous and 

metamorphic basement is not distant. Uplifts of 

metamorphosed rock in the central interior of 

Alaska, particularly the Birch Creek Schist, have 
36 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

been postulated as representing the earlier Precambrian. Potassium-argon isotope dating, however, 

has generally not verified their Precambrian age. 

Preliminary rubidium-strontium isotope dating of 

schists in the same area and in the Seward Peninsula 

has also produced a number of Paleozoic and Precambrian dates, and there now seems to be more 

hope of unraveling the metamorphic history of 

Alaska. 

LOWER PALEOZOIC ROCKS 

Cambrian through Middle Devonian rocks in eastcentral Alaska are part of a cycle of nearly continuous sedimentation (Churkin and Brabb, 1967; fig. I). 

Elsewhere in the interior and northern parts of 

Alaska, Devonian and, in places, Ordovician and 

Silurian rocks have been reported from a number of 

widely separated areas. Unfortunately, most of these 

stratigraphic successions are structurally complex 

and incomplete. Cambrian rocks, although known 

with certainty only from east-central and northeastern Alaska, probably occur in the Alaska Range 

(Michael Churkin, Jr., and B. L. Reed, field data, 

1969) and in the Seward Peninsula (Sainsbury, 

1969a). Coarse clastic deposits of Late Devonian age 

in east-central Alaska and of Late Devonian and 

Mississippian age in the Brooks Range indicate indirectly sources of argillite and chert of probable 

early Paleozoic age within the Cordilleran geosyncline to the south and in the ancestral Brooks geosyncline to the north, respectively (fig. 12). Isotope 

age determinations of granitic rocks around the 

margin of the Canada Basin (fig. 13) indicate a 

period of intrusion that is probably related to the 

same middle Paleozoic orogeny that produced. these 

Late Devonian clastic wedge deposits and that 

marks the end of the early Paleozoic sedimentation 

cycle. 

CORDILLERAN GEOSYNCLINE 

In southeastern Alaska where lower Paleozoic 

rocks are exposed along the present continental margin, sedimentation was nearly continuous from the 

Lower Ordovician, the oldest rocks in the area, into 

the Upper Silurian (fig. 10). The high proportion of 

volcanic and volcaniclastic rocks together with conglomerates of mixed composition, rapid facies 

changes, and local disconformities in this section 

imply rapid sedimentation in a tectonically active 

area. In the Early Devonian a widespread sequence 

of terrigenous clastic rocks including red beds 

(upper part of Karheen Formation of Eberlein and 

Churkin, 1970) marks a significant break in sedimentation within the southeastern Alaska part of 

the Cordilleran geosyncline ( Ovenshine and others, 

1969; fig. 13). This same conglomerate has been 

assumed to be a tillite and has been cited as evidence 

of Paleozoic glaciation (Kirk, 1918). The latest 

work, however, does not support a glacial origin. 

Thin to very thick lenticular biogenic limestones 

of Silurian and Devonian age occur in the section of 

the Cordilleran geosyncline exposed in southeastern 

Alaska (fig. 10). The high proportion of reef-building coral and stromatoporoid fragments in these 

biogenic limestones suggests that nearby reefs were 

periodically fragmented to provide the enormous 

volume of fossil material in the limestones. I have 

seen, in the Willoughby Limestone of Silurian age in 

Glacier Bay and in Devonian limestone at several 

places on the west coast of Prince of Wales Island, 

small patch reefs with coral and stromatoporoid 

skeletons preserved encrusting each other in growth 

position. In most of these limestones a nearshore 

shallow-water environment of deposition is indicated 

not only by the shelly fauna but also by stromatolitic algae, intraformational breccias, and oolitic 

limestone. In some of the limestone, thick lenses of 

breccia and conglomerate rich in volcanic fragments 

suggest development of the limestone around volcanic centers and other prominences on the sea floor. 

Lower Paleozoic rocks· of the coarse detrital, 

volcanic-rich facies of southeastern Alaska are 

known farther south in the San Juan Islands and in 

the northern Cascade Mountains of Washington 

(Danner, 1966) and in the Klamath Mountains of 

northern California (Irwin, 1966; Churkin and 

Langenheim, 1960) . From southeastern Alaska this 

part of the Cordilleran geosyncline, rich in volcanic 

rocks, probably continued westward and may have 

connected with similar rocks of the Paleozoic geosyncline in the Koryak Mountains of Northeast 

U.S.S.R. (Bogdanov and Tilman, 1964; Belyi, 1964; 

Egiazarov and others, 1965). In south-central and 

southwestern Alaska, poorly known and structurally 

complex terranes of detrital sedimentary and volcanic rocks that contain some fossiliferous limestones are part of this Cordilleran geosynclinal belt. 

These widely separated sequences probably belong 

to a stratigraphic belt that more or less rimmed the 

northern Pacific Basin and that now is largely 

buried by younger rocks or obscured by regional 

metamorphism and plutonic activity mainly of 

Mesozoic age (fig. 1 ; Churkin, 1969). 

A thick carbonate-quartzite sequence (the Millard 

miogeosynclinal belt of Kay, 1947) should theoretically lie north of the volcanic-rich eugeosynclinal 
.... 

INTERPRETATION OF STRATIGRAPHIC DATA-TECTONIC FRAMEWORK OF SEDIMENTATION 37 

belt of southeastern Alaska. Except for the thick 

carbonate rocks in the Kuskokwim River region of 

southwestern Alaska (Cady and others, 1955; Sainsbury, 1965) and possibly in the Seward Peninsula 

(Sainsbury, 1969a), thick sequences of pure carbonate rock are virtually unknown in central Alaska 

(fig. 1). In parts of the Alaska Range, however, 

limestone sections, especially those of Devonian age, 

· have been reported (Moffit, 1938; Brooks, 1911; B. L. 

Reed, oral commun., 1968). These isolated limestone 

masses seem to be surrounded by predominantly 

terrigenous rocks and may represent biogenic limestone b~ildups in a predominantly clastic section as 

do the similar limestones in southeastern Alaska. 

In the Eagle area of east-ceritral Alaska, on the 

northern edge of the Cordilleran geosyncline Paleozoic sedimentation started with the deposition of 

thin Cambrian limestone conformable on upper 

Precambrian strata. Rapid changes in lithofacies, 

the presence of oolitic intraformational boulder and 

edgewise conglomerate, and rich tribolite, brachiopod, and archeocyathid faunas suggest a shallowwater turbulent marine environment for this area 

during most of the Cambrian (Brabb, 1967). 

In contrast to the generally coarsely detrital rocks 

in southeastern Alaska, near Eagle there is a thinly 

and rhythmically interbedded black chert and siliceous shale lithofacies that has thin interbeds and 

partings of graptolitic shale ( Churkin and Brabb, 

1965a). The Early Ordovician through Early 

Devonian, a span of about 100 million years, seems 

to be represented here by only 900 feet of section 

without any sign of a significant stratigraphic break. 

This unusually thin stratigraphic section probably 

represents a long period of slow, deepwater sedimentation. These siliceous rocks continue east into northern Yukon Territory where they thicken in the 

Richardson basin (Jackson and Lenz, 1962). A 

similar graptolitic shale section that again spans 

most of the Ordovician and the Lower Silurian in 

less than a 1,000 feet of section has recently been 

found in the Alaska Range southeast of Farewell 

(Michael Churkin, Jr., B. L. Reed, and J. W. Kerr, 

field data, 1969 and 1970). Similar, but in places 

reportedly much thicker, sequences of chert and 

graptolitic shale, which in addition contain quartzite 

and minor amounts of pillow basalt, characterize the 

Frazer eugeosynclinal belt of the central Great Basin 

that lies between the volcanic-rich coarsely detrital 

rocks in the Klamath Mountains and the predominantly carbonate-quartzite rocks of the miogeosyncline in the eastern Great Basin (Roberts and others, 

1958; Churkin and Kay, 1967). 

YUKON SHELF AND RICHARDSON BASIN 

The predominantly limestone and dolomite facies 

of the Silurian and the Devonian cover large areas 

across the central part of Alaska (east-central 

Alaska, part of southwestern Alaska and the Seward 

Peninsula) , and extend north into parts of the 

Brooks Range. These rocks, especially in east-central 

Alaska where they have been most thoroughly 

studied, seem to be thin shelf carbonate deposits that 

lie north of the predominantly coarse detrital and 

volcanic rocks of the Cordilleran geosyncline in 

southern Alaska. Siliceous shale sequences along the 

Upper Yukon River and in the Alaska Range seem 

to represent a considerably thinner, but nearly complete, stratigraphic transition from the shelf carbonates on the north to the coarse detrital rocks with 

abundant interlayered volcanic rocks in the south. 

In the early Paleozoic, and especially during the 

deposition of the Road River Formation (Lower 

Ordovician to Lower Devonian), the site of the 

Richardson Mountains in northern Yukon Territory 

was an area of accumulation of ·thick 2'raptolitic 

shale, bedded chert, and argillaceous limestone 

(Jackson and Lenz, 1962). The area of Road River 

sedimentation apparently progressively spread from 

the Richardson Mountains in Early Ordovician time 

to include most of Yukon Territory by the end of the 

Silurian (Norford, 1964). At the same time, however, thin shelf limestones interfingering with thin 

sequences of graptolitic shale were forming laterally over the rest of northern Yukon Territory and 

eastern Alaska (Churkin and Brabb, 1967). Thus, 

the Richardson Mountains basin during the Paleozoic was not, as Jeletzky ( 1962) has already shown, 

a northern extension of the Cordilleran geosyncline 

(Martin, 1961), b_ut was a narrow basin that developed within the Yukon shelf ( Churkin and Brabb, 

1967). 

In conclusion, during the early Paleozoic, the 

Yukon shelf in east-central Alaska, and possibly extending farther west across the center of Alaska, 

seems to have separated two distinct geosynclinal 

belts, the Cordilleran geosyncline in the south from 

the ancestral Brooks geosyncline on the north 

(fig. 1). 

ANCESTRAL BROOKS GEOSYNCLINE 

In the Brooks Range and on the North Slope, few 

rocks have been firmly dated as pre-Middle Devonian 

(pre-Skajit Limestone). However, in the southern 

Brooks Range and, more certainly, in the northeastern Brooks Range, there are thick sequences of 

weakly metamorphosed, predominantly siliceous 
38 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

rocks of pre-Late Devonian age (Brosge, 1960; 

Brosge and Tailleur, 1970). These rocks include the 

Neruopuk Formation in the northeastern Brooks 

Range, a thick sequence mainly of detrital sedimentary rocks (Reed, 1968) but including mafic lavas, 

intrusive rocks, and volcaniclastic sedimentary 

rocks (Reiser, 1970). Similar rocks with rare 

Devonian fossils and including mafic dikes of Paleozoic age form a narrow belt along the axis of the 

Brooks Range (Brosge and Reiser, 1964; 1965). 

Argillites beneath Triassic rocks at the bottom of a 

borehole at Point Barrow (Payne and others, 1951) 

may belong to the belt of weakly metamorphosed 

siliceous rocks exposed in the northeastern Brooks 

Range. High magnetic anomalies along the Arctic 

Slope of Alaska suggest that igneous rock masses 

· like those in the northeastern Brooks Range form a 

large part of the basement below the Mesozoic cover 

farther west (Payne. and others, 1951). In general, 

these rocks in the Brooks Range and farther north 

appear to be thicker and are more detrital than the 

predominantly carbonate rocks of early Paleozoic 

age in east-central Alaska. This fact suggests a 

northward transition from a central Alaskan carbonate shelf into a now birgely buried and partially 

destroyed circum-Canada Basin geosyncline ( Churkin, 1969). More recently, the discovery of Cambrian 

trilobites (J. T. Dutro, Jr., W. P. Brosge, and H. N. 

Reiser, written commun. and unpub. data, 1971), 

recognition of substantial amounts of mafic volcanic 

rocks, and dating of Silurian granitic rocks support 

the idea that a lower Paleozoic geosyncline deformed 

in the middle Paleozoic forms much of the basement 

of the Brooks Range. 

In contrast, in the Shublik and Sadlerochit Mountains adjacent to the Arctic Coastal Plain, there is 

6,500 feet of limestone and dolomite below limestone 

of Carboniferous age (Dutro, 1970). Devonian 

fossils occur in the upper 200 feet of this sequence, 

but its lower part may represent much of the earlier 

Paleozoic as well. The lateral extent of ·these carbonates is unknown, and thus their regional significance is unclear. The carbonate rocks may represent 

a major facies change as the Arctic coast is approached or a localized area of carbonate in a predominantly terrigenous section. 

If parts of the Neruopuk Formation in the northern part of the Brooks Range and in the British 

Mountains of northern Yukon Territory are 

equivalent to rocks of the northern ( eugeosynclinal) 

part of the Franklinian geosyncline of the Canadian 

Arctic Islands much farther east, then the Skajit 

Limestone and perhaps the Hunt Fork Shale (both 

of Devonian age and exposed in a belt south of the 

Neruopuk) could be considered as western equivalents of the carbonate and shale belt (miogeosyncline) of the southern part of the Franklinian 

geosyncline. 

The thick chert-rich detrital rocks of Late Devonian and in part Early Mississippian age in the 

Brooks Range are thought to have been derived 

from a northern source (Brosge and others, 1962). 

Farther east, in northern Yukon and Northwest 

Territories, nonmarine sandstone and shale (Imperial Formation) pass southeastward into marine 

equivalents (Douglas and others, 1963). A similar 

belt of Upper Devonian detrital rocks, apparently 

derived from the northern part of the Franklinian 

geosyncline, occurs in the Canadian Arctic Archipelago as far east as Ellesmere Island (Thorsteinsson 

and Tozer, 1960; Trettin, 1967). In Chukotka and 

Wrangell Island, on the opposite side of Alaska, 

there are similar Upper Devonian ( ?) conglomerates· 

(Bogdanov and Tilman, 1964; Tilman, 1964). Some 

geologists (Shatsky, 1935; Eardley, 1948; Payne and 

others, 1951) have thought that in Late Devonian 

time widespread uplift in what is now the Arctic 

Ocean exposed a Precambrian shield which provided 

coarse sediment to nearby parts of Canada, Alaska, 

and Siberia. However, a shield source seems unlikely because of the mainly chert, quartz, and argillite detritus, coarse grain size, and wedgelike shape 

of the sedimentary body and its apparently nonmarine character. Instead, the highly deformed 

siliceous rocks of the Neruokpuk Formation and 

similar rocks of pre-Late Devonian age in other parts 

of the Brooks Range and in boreholes along the 

Arctic coast more likely were the sources of the 

detritus (Churkin, 1969). Absolute age determinations of granitic rocks around the margin of the 

Canada Basin part of the Arctic Ocean indicate that 

the intrusion of these rocks probably was related 

to the same middle Paleozoic period of deformation and uplift that produced the wedge of Upper 

Devonian clastic deposits (Tailleur and others, 1967; 

Trettin, 1967; Churkin, 1969). Elsewhere in North 

America, at about the same time, clastic wedges 
,, 

INTERPRETATION OF STRATIGRAPHIC DATA-TECTONIC FRAMEWORK OF SEDIMENTATION 39 

were derived from uplifts in the Cordilleran 

(Roberts and others, 1958; Gabrielse and Wheeler, 

1961) and Appalachian (Kay, 1947) geosynclines. 

Late Devonian time was thus one of widespread 

orogeny that marks major breaks in the early 

Paleozoic geosynclinal cycles. 

Permian is represented by a noncalcareous sedimentary sequence mainly of fine-grained detrital 

rocks with abundant chert. Thus, these upper Paleozoic rocks like nearby lower Paleozoic rocks, represent a ·facies transitional into the purer carbonate 

rock sections farther east and north. 

UPPER PALEOZOIC ROCKS YUKON SHELF 

Northeast of the Yukon-Tanana area and across CORDILLERAN GEOSYNCLINE the Tintina trench, Carboniferous and Permian· nonThe Carboniferous and Permian rocks of south- volcanic rocks are known to underlie a large part 

eastern Alaska closely parallel the earlier Paleozoic of the Yukon-Porcupine Rivers area. The Carbonisequences mainly of detrital rocks interlayered with ferous section here consists of thinly interbedded 

submarine lavas. Fortunately, subordinate amounts limestone, shale, and chert. Deep erosion below the 

of highly fossiliferous limestone are generally pres- base of the overlying Permian strata has, however, 

ent and provide a means of correlation. In contrast removed all but a small area of Carboniferous rocks 

to the earlier Paleozoic pattern, good Carboniferous in the vicinity of Calico Bluff. The Permian is a 

and Permian sections similar to those in southeastern Alaska are also known in the Wrangell predominantly detrital facies of chert-pebble conglomerate, sandstone, siltstone, and argillaceous rocks. 

Mountains and the eastern Alaska Range. Further- Locally, limy interbeds occur and these limestones 

more, detrital and volcanic rock sequences of late may reach thicknesses of several hundred feet 

Paleozoic age cover a large area of southwestern (Tahkandit Limestone). Alaska that in the earlier Paleozoic received only The conglomerate and sandstone of Permian age 

carbonate rock (Cady and others, 1955> · along the Yukon River, like the clastic rocks of Late 

The isolated exposure of upper Paleozoic rocks Devonian age, are made up mostly of chert and 

at Cape Kekurnoi suggests that the detrital volcanic argillaceous rock fragments. Part of the detritus 

belt along the Pacific margin in southeastern Alaska in the basal conglomerate of the Permian, where it 

continues west. These upper Paleozoic rocks, asso- unconformably lies on rocks of Late Devonian age, 

ciated with metamorphic rock complexes that may is derived from reworking the older conglomerate, 

represent still older Paleozoic rocks, form the base- sandstone, and argillite (Brabb and Churkin, 1967). 

ment for the thick Mesozoic and, in places, Cenozoic Similar chert-pebble conglomerate of questionable 

sedimentary deposits of the Alaska Peninsula -Permian age occurs farther north on Dave Lord 

(Burk, 1965). The Devonian and Mississippian pure Ridge just . south of where the Porcupine River 

dolomite-limestone section on St. Lawrence Island crosses the international boundary. As is true of the 

provides a northern limit to any extension of this clastic rocks of Late Devonian age, the Permian 

belt across the Bering Shelf (fig. 17) · detrital sediments in the interior of Alaska came 

The northern boundary of the detrital-volcanic from uplifts of siliceous sequences that bordered the 

rock facies that is here for the most part equated 

with the northern limit of the Cordilleran geosyncline is located on the Alaska mainland somewhere 

between the Seward Peninsula and the lower reaches 

of the Yukon. Farther east this boundary, although 

probably complicated by major faults, approximately 

follows the Yukon River (fig. 17). Along the northwest edge of the Yukon-Tanana Upland, in the 

center of Alaska, are the northernmost rocks of 

the upper Paleozoic detrital-volcanic rock facies. Because of complex structure and scarcity of diagnostic · 

fossils, the stratigraphy here is poorly known. It 

seems that the Carboniferous and perhaps the 

area. 

BROOKS BASIN AND RELATED BASINS 

In the Brooks Range the Carboniferous sections 

are mainly limestone and dolomite with variable 

amounts of interbedded shale and chert (Brosge 

and others, 1962). The considerably thinner Permian rocks are predominantly fine-grained detrital 

rocks and chert. The base of the Lisburne Group 

becomes progressively younger and more detrital 

into the northern parts of the Brooks Range. This 

northward transgression, plus the fact that the 

unconformably overlying Permian sandstones and 
40 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

I 

~ 

150° 

EXPLANATION 

Circumpacific geosynclinal belt Circumarctic successor basins 

FIGURE 17.- Tectonic framework of Carboniferous and Permian sedimentation. 

conglomerates are also rich in chert detritus, suggest that in the late Paleozoic a source area existed 

north of the Brooks Range (Brosge and others, 

1962; Detterman, 1970). This source area may reflect renewed uplift of the ancestral Brooks geosynclinal belt that was providing sediment during the 

Late Devonian and Mississippian (Churkin, 1969). 

MESOZOIC AND CENOZOIC TECTONIC EVENTS 

AFFECTING PALEOZOIC ROCKS 

The geologic conditions that prevailed throughout 

Paleozoic time in the southern half of Alaska seem 

to have continued on into early Mesozoic time. 

Triassic rocks in southeastern and southern Alaska, 

although separated in places from Paleozoic rocks 

by an unconformity, are characterized by basaltic 

submarine lavas and associated volcaniclastic rocks 

in a mainly detrital sedimentary sequence that continued the geosynclinal pattern established in the 

Paleozoic (Brew and others, 1966). Thin argillaceous 

limestones occur locally, but massive purer limestone and dolomite sequences like those in the 

Paleozoic are very rare. The only good example of 

·a close parallel to the earlier Paleozoic carbonate 

• 
.... 

.... 

.... 

MESOZOIC AND CENOZOIC. TECTONIC EVENTS AFFECTING PALEOZOIC ROCKS 41 

development in southern and southeastern Alaska 

is the 2,000-foot-thick section of nearly pure limestone and dolomite ( Chitistone and Nizina Limestones) in the Wrangell Mountains (Moffit, 1938; 

Armstrong and others, 1969). In the Kuskokwim 

region, the Gemuk Group, ranging in age from 

Carboniferous to Early Cretaceous (Hoare and 

Coonrad, 1961), is composed of siltstone, chert, 

mafic volcanic rocks, thin limestone, and graywacke 

that seem to be a westward continuation of the 

stratigraphy in southeastern Alaska. 

In the interior and northern parts of Alaska 

where Triassic rocks are known, they generally rest 

on Permian rocks with approximate structural conformity (Lathram, 1965; Detterman, 1970; Brabb 

and Churkin, 1969). The Triassic rocks of northern 

Alaska, composed of thin ·sequences of argillaceous 

sediments interbedded with minor limestone and 

chert, parallel closely the Permian sedimentation 

pattern in the same area (Detterman, 1970). 

In the Jurassic, and in places starting in the 

Cretaceous, began the development of a new pattern of high tectonic activity that lasted throughout most of the Mesozoic and locally continued 

through the Cenozoic. Where once the broad stratigraphic belts of the Paleozoic geosynclines and shelf 

existed, the rocks were now deformed into a series 

of troughs and basins that were separated by uplifts (Payne, 1955); Gates and Gryc, 1963). The 

sediments that filled the depressions were dominantly detrital and were largely derived from nearby 

highlands composed of Paleozoic and Precambrian 

rocks (fig. 18). It was during these episodes of 

orogeny that vast tracts of Precambrian and Paleozoic rocks in the interior of Alaska and farther 

south in the Alaska and Coast Ranges were severely 

deformed, altered by metamorphism, and in places 

ultimately granitized. The general pattern of basins 

and uplifts in the Mesozoic, and to a lesser degree 

in the Tertiary, tends to be arcuate and follows the 

trend of the Paleozoic stratigraphic belts (Payne, 

1955). This parallelism shows the strong influence 

of the Precambrian and Paleozoic basement in con- · 

trolling the tectonic features developed in the Mesozoic and Cenozoic. 

Most of the post-Paleozoic sedimentary rocks of 

Alaska are largely impure sandstones of the graywacke type interbedded with dark argillaceous rocks 

and conglomerate. Furtherm·ore, many of the postPaleozoic sediments contain far more detrital feldspar than the rocks on which they lie. Notable examples are the Cretaceous strata of east-central 

Alaska where the amount of potassium feldspar 

detritus increases markedly in rocks of post-middle 

Early Cretaceous age· (Brabb, 1969); this fact suggests that the earlier Mesozoic intrusive rocks in the 

nearby Yukon-Tanana Upland (Wasserburg and 

others, 1963) were unroofed by late Mesozoic time. 

Another example is along the northern border of 

Matanuska basin· where granitic intrusive rocks cut 

Lower Jurassic strata and furnished debris to form 

Upper Jurassic conglomerates (Gates and Gryc, 

1963, p. 273). Thus, the batholithic intrusions and 

their subsequent uplift, like the differentiation of 

Alaska into positive and negative areas, began in 

the Jurassic and continued intermittently through 

the late Mesozoic and into the Tertiary ( cf. Reed and 

Lanphere, 1969). 

At the end of the Cretaceous and the beginning of 

the Tertiary, widespread orogenic movements affected large areas of Alaska. It was during this time 

that the thick late Mesozoic sequences of the Colville 

basin were intensely folded and thrust faulted northward (Gates and Gryc, 1963). 

Alaska was virtually emergent by the end of the 

Cretaceous and has remained so up to the present. 

In exception, Tertiary basins of marine deposition 

developed along the southern and northern borders 

bf Alaska (fig. 18). The most significant of these . 

was along the Gulf of Alaska where Eocene through 

Pliocene, mostly marine strata total at least ·25,000 

feet in thickness (Stoneley, 1967). In the interior 

of Alaska at various times during the Tertiary, local 

deformation formed small basins that were quickly 

filled by nonmarine coal-bearing sequences of claystone, sandstone, and conglomerate. Several of these 

continental deposits developed in narrow trenches 

along major transcurrent fault zones-the Tintina 

(Brabb and Churkin, 1969) and the Kaltag fault 

zones (Patton and Hoare, 1968). 

Deformation that produced uplift and erosion 

over much of Alaska during the Tertiary apparently 

intensified at the close of the Tertiary and continued 

·into the Quaternary. This orogenic activity has resulted in the strong uplift that produced the present 

mountain ranges . 

Along with the deformation, the Cenozoic orogenic 

events produced widely scattered terrestrial volcanic 

rocks and granitic intrusives. Tertiary granites, although not so extensive as those of the Mesozoic, are 

known from most of the geologic provinces of 

Alaska, but they are rare or absent in east-central 

Alaska, the Brooks Range, and the Arctic Coastal 

Plain. The Aleutian volcanic arc and the associated 

oceanic trench are prominent features of this high 

tectonic activity that started in the Cenozoic and 
42 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

100 0 100 200 300 400 MILES 

EXPLANATION 

D 

Tertiary basins and troug hs of 

detrital sedimentation. Mostly 

nonmarine . M, Marine 

Terrestrial volcanic rocks Late Mesozoic, ma • inly Cret aceous basins and troughs of thi ck detrital sedimentation 

Areas of Mesozoic and in part Tertiary uplift and erosion. Arrows 

indicate direction of sediment 

transport~ 

FIGURE 18.-Late Mesozoic and Tertiary tectonic features. 

continues ii).to the present (Coats, 1956; Burk, 

1965)-

MAJOR STRUCTURAL FEATURES OF PALEOZOIC ROCKS 

Alaska experienced such extensive penetrative 

folding, faulting, metamorphism, and intrusion during multiple episodes of Mesozoic and Cenozoic 

deformation that, as in other far more intensely 

studied parts of the North American Cordillera, any 

Paleozoic or older structures are generally very 

difficult to recognize. The structures that will receive 

attention here are first of all the major foldbelts that 

indirectly reflect the trends and configurations of the 

older tectonic elements, such as basins, troughs, and 

stable areas that controlled the Paleozoic sedimentation patterns. Secondly, some of the large-scale 

faults that may have displaced the Paleozoic stratigraphic belts and juxtaposed different rock types 

will be discussed. 

FOLDBELTS OF ALASKA AND THEIR EXTENSIONS INTO 

CA NADA AND SIBERIA 

Figure 19 shows the distribution of foldbelts in 

Alaska and neighboring parts of Canada and Siberia. Foldbelts on this map are differentiated by gross 

ages of regional deformation, metamorphism, and 

intrusion. Using these criteria to delineate foldbelts, 

most of Alaska's structures were created during the 
.. 

MESOZOIC AND CENOZOIC TECTONIC EVENTS AFFECTING PALEOZOIC ROCKS 

EXPLANATION 

FOLDBELTS 

I++++ +I 

Circumpacific belt 

Mainly of Cenozoic age 

F CA 3 ~I 

Chukotka, Cordilleran, Sverdrup, 

and Verkhoyansk belts· 

Mainly of Mesozoic age 

1:\·:·::;:.:-.:1 

Canada Basin and Cherskiy 

Circumartic belts 

Mainly of Paleozoic age 

PLATFORMS 

I 

Paleozoic and younger deposits and 

within continental interior including Precambrian basement 

CD . Location of columnar sections shown 

in figure 22 

FIGURE 19.-Major foldbelts around the northern Pacific and the Canada Basin part of the Arctic Ocean. 

43 
. 44 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Mesozoic as . parts of the Cordilleran foldbelt that 

lies along the western continental margin of North 

America (King, 1969). 

The earliest deformational features within the 

Cordilleran foldbelt are the high-grade schist and 

gneiss terranes across the center of Alaska that 

form the basement rock of the Seward Peninsula 

and the Yukon-Tanana Upland. Historically, these 

terranes have been considered to be of Precambrian 

age. Numerous Mesozoic ages obtained by isotope 

dating of these schists and associated plutonic rocks, 

especially the ·Birch Creek Schist of east-central 

Alaska (W asserburg and others, 1963) , cast doubt 

on the Precambrian age of these structures. On the 

other hand, new isotopic dates on the metamorphic 

complexes in the Seward Peninsula (C. L. Sainsbury, oral commun., 1970) and the F'airbanks area 

(Forbes and others, -1968) indicate Precambrian, or 

at least earliest Paleozoic, ages of deformation. 

Along the Pacific and the Arctic Ocean margins of 

the Cordilleran foldbelt, there are, in a number of 

places, thick wedges of coarse clastic rocks associated with plutonic activity, ind~cating orogenies 

within the Paleozoic geosynclines (fig. 13). The climactic orogenies of the Cordilleran foldbelt, however, took place during the Mesozoic, and in many 

places, Cenozoic deformation continued and is responsible for much of the present mountainous 

topography within the original foldbelts. High-grade 

metamorphism in southeastern Alaska involving 

lower Paleozoic rocks (Brew and others, 1966) and 

lower grade metamorphism of pre-Upper Devonian 

rocks in the northern Brooks Range (Reed, 1968) 

are other examples of these forerunners of the main 

Cordilleran orogeny. Thus, the Cordilleran foldbelt 

arose from. deformation and in part from metamorphism and plutonism of several geosynclines, 

some of which took form in late Precambrian and 

early Paleozoic time, and others, as late as Mesozoic 

time (King, 1969). 

The Cordilleran foldbelt north of the 49th parallel 

has a nearly constant width until it widens inland to 

form the Mackenzie Mountains in Northwest Territories. There, it is sharply confined along its northeast margin, trends north along the Richardson 

Mountains of Yukon Territory, and turns westward 

across Alaska, widening out to the Bering and 

Chukchi Seas (fig. 19). Easternmost Siberia, 

separated from Alaska by these broad continental 

shelves, is part of the Chukotka foldbelt of Mesozoic 

age (Yanshin, 1966). South of the Chukotka foldbelt is the circumpacific foldbelt, mainly of Cenozoic 

age. It includes the islands surrounding the Sea of 

Okhotsk, Kamchatka, Koryak Mountains, and the 

Gulf of Alaska. 

Another, though less obvious, foldbelt discontinuously rims the southern margin of the 

Canada Basin part of the Arctic Ocean (fig. 19). 

This is the much older circumarctic foldbelt of middle 

Paleozoic age that is known in the Canadian Arctic 

Islands (Thorsteinsson and Tozer, 1960), in the 

British Mountains of northern Yukon Territory, 

and in the northeastern Brooks Range ( Churkin, 

1969, 1970). Farther west, this foldbelt is covered by 

the coastal plain deposits of northern Alaska. Boreholes along the Arctic coast of Alaska, in places at 

rather shallow depths, have penetrated steeply dipping slate, argillite, and graywacke of pre-Late 

Devonian age th~t probably belong to this same foldbelt. These rocks form the basement in the Prudhoe 

Bay oil field (Rickwood, 1970) and the basement of 

the Barrow arch, a broad structure of Mesozoic age 

that parallels the Arctic coast of Alaska (Payne and 

others, 1951). 

One of the most prominent structural features 

within the Cordilleran foldbelt is the belt of folding 

and thrusting that starts along the east side of the 

Canadian Rocky Mountains and continues north into 

Yukon Territory where it turns west to make the 

Brooks Range in northern Alaska (fig. 20) . Most of 

the rocks within this broad belt are Paleozoic carbonate rocks and shales, but rocks as old as late Precambrian or as young as Tertiary are also involved. 

This remarkably continuous belt has several arcuate 

bends (Gabrielse, 1967; King, 1969). At the north 

end of the Rocky Mountains the relatively narrow 

(less than 100 miles wide) and fairly straight foldbelt gives way to the Mackenzie Mountains (fig. 20), 

a broad series of arcuate ranges offset eastward into 

the Yukon shelf. From the Mackenzie Mountains, the 

foldbelt turns gently west into the W ernecke-Ogilvie 

Mountains. At the west end of the Ogilvie Mountains 

near the Alaska-Yukon Territory boundary, the 

foldbelt makes a sharp right-angle bend to form the 

north-south-trending Nahoni Mountains. Farther 

north the N ahoni Mountains give way to the northeast-trending -I' Dave Lord Ridge fold structures. 

North of the Porcupine River the foldbelt turns 

northwestward across the British Mountains in the 

northwest corner of Yukon Territory and crosses 

into Alaska to form the Brooks Range. The trend of 

the Brooks Range segment of the foldbelt is westerly 

for nearly 600 miles, and in the Baird Mountains at 

the west end of the Brooks Range, it bends south 

towards the Seward Peninsula, its northern margin 

making a sharp bend at Cape Lisburne where the 

·• 
. ._. 

MESOZOIC AND CENOZOIC TECTONIC EVENTS AFFECTING PALEOZOIC ROCKS 45 

' 

0 

........ --

'" ' \ 

~ ? \ 

' \ 

A 6 

...... ---- Generalized trend of folds Transcurrent fault. Arrows show 

inferred movement 

Thrust fault. Barbs on 

upthrown side 

Arcuate trends in continental 

margins 

FIGURE 20.-Major structural features of the northern circum pacific an~ adjacent parts of the Arctic (after King, 1969; 

Yanshin, 1966). See list o{]'eatures below. 

STRUCTURAL FEATURES 

1. Denali-Farewell-Holitna fault system. 

2. Chatham Strait fault. 

3. Tintina trench. 

4. Rocky Mountain trench. 

5. Chugach-St. Elias-Fairweather fault system. 

6. Kaltag fault. 

7. Brooks Range, British Mountains thrust and foldbelt. 

8. Richardson Mountains foldbelt. 

9. N ahoni-Ogilvie-Wernecke Mountains foldbelt. 

9a. Dave Lord Ridge. 

10. Mackenzie Mountains thrust and foldbelt. 

11. Koryak thrust and foldbelt. 

12. Verhoyansk foldbelt. 

13. Cherskiy Mountain system thrust and foldbelt. 

folds and faults trend northward under the Chukchi 

Sea (cf. Tailleur and Brosge, 1970). 

The deep recess in the foldbelt in northwestern 

Yukon Territory, where the structures from the 

Mackenzie Mountains· and from the Brooks Range 

curve inward to form a sharp right angle, may be 

related to the structures of the Richardson Mountains located within the recess. The Richardson 

Mountains themselves are apparently a blocklike 

uplift of thick e~ .. ly Paleozoic and Mesozoic basinal 

deposits surrounded by the much thinner rocks of 

the Paleozoic Yukon shelf (Jeletzky, 1962). At the 

time of major folding in the region, the thick body 

of Paleozoic and Mesozoic sedimentary rocks in the 

:Richardson basin possibly acted as a buffer that 

diverted the fold and fault trends in the thinner 

sections of the Yukon shelf around its western and 

southern edge. Large-scale right-lateral movement 

along the Porcupine lineament (Tailleur and Brosge, 

1970), a probable fault zone (Brosge and Reiser, 

1969) that may be an extension of the· Kaltag fault 

(Patton and Hoare, 1968), may also be responsible 

for the right-angle bend in the foldbelt near the 

Alaska-Yukon Territory boundary. 

South of the Brooks Range, folds and thrust 

faults generally do not have the consistency of 

trend that they have in the Brooks Range and along 

the North Slope. The difficulty in distinguishing 

structural trends in southern Alaska is not that the 
46 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

rocks have escaped deformation but that multiple 

periods of deformation have created complex trends. 

The scarcity of good marker horizons in the thick 

eugeosynclinal sequences and multiple batholithic 

intrusions further complicate structural analyses. 

Thrust faults involving Precambrian and Lower 

Paleozoic rocks have been recognized over a large 

part of the Seward Peninsula (Sainsbury, 1969b). 

In the western Seward Peninsula, unmetamorphosed 

carbonate rocks of Ordovician and Silurian age are 

imbricately thrust faulted and are in thrust-fault 

contact with slates and slightly metamorphosed carbonate rocks of probable pre-Ordovician age (Sainsbury, 1969a, 1969b). Farther west, across the Bering 

Strait from the Seward Peninsula, exposures along 

the sea cliffs of Chukotsk Peninsula reveal complicated imbrication of Ordovician and Silurian limestone with Devonian shales and other argillaceous, 

weakly metamorphosed rocks (S. G. Byalobzhevski, 

oral commun., 1967; Gnibidenko, 1969). The proximity of these similar stratigraphic and structural 

features suggests their. correlation across the Bering 

Strait. 

As the stratigraphy of other structurally complicated areas of Paleozoic rock in Alaska is studied, 

more examples of important thrust faulting will 

become known. Preliminary results of regional mapping in the Terra Cotta Mountains area of the 

Alaska Range (B. L. Reed, oral commun., 1969) and 

in the Annette Island area of southeastern Alaska 

(Berg, 1970) indicate that thrust faults involving 

Paleozoic rocks are important in these areas. 

A record of structural juxtaposition of widely 

different rock types has been reported from the 

White Mountains at the west end of the YukonTanana Upland (Church and Durfee, 1961). Here, 

the Tolovana Limestone, consisting of a long and 

narrow outcrop belt of pure limestone and dolomite 

of Silurian and Devonian age, is in contact with 

the Fossil Creek Volcanics of Ordovician age, a unit 

characterized by siliceous sedimentary rocks and 

pillow basalt. According to Church and Durfee 

(1961), the limestone is everywhere thrust faulted 

over the volcanic rocks, however, the massive limestone was found by myself, in company with R. 

Chapman and F. Weber in 1968, to be accordant 

and, where best exposed, gradational over an interval of several feet into calcareous tuff. This interpretation of a stratigraphic contact agrees with the 

original interpretation of Mertie (1937b). This belt 

in the central part of Alaska, where carbonate rock 

sections are in close proximity and are partly interlayered with volcanic rocks and with fine-grained 

siliceous rock facies, marks a zone transitional in 

facies with mainly limestones to the north and volcanic-siliceous sequences to the south. The structure 

within this belt and its relation to the carbonate 

facies on the one hand and metamorphic rocks on 

the other is, however, very complex, and large-scale 

faulting may be partly responsible. for some of the 

abrupt changes in rock types. 

The amount of lateral displacement on the various 

thrust faults in Alaska is poorly known and, except 

for the instances discussed below, is not recognized 

as displacing major stratigraphic belts. 

Several periods of south-to-north overthrusting 

during the Cretaceous and Tertiary affected the area 

that is now the Brooks Range (Lathram, 1965; 

Porter, 1966; Tailleur and others, 1967). Because of 

this multiple thrusting of unknown displacement, 

it is difficult to reconstruct the original facies within 

the Paleozoic rocks of northern Alaska. In the 

western Brooks Range large-scale overthrusts are 

thought to have a cumulative northward displacement probably in excess of 150 miles (Tailleur and 

Snelson, 1968). Thus far, it has not been possible 

to measure accurately amounts of total displacement 

because of the imbricate nature of the faulting. On 

a single fault in the Chandalar area of the central 

Brooks Range, 5 miles of horizontal displacement 

has been measured (W. P. Brosge, oral commun., 

1968). Because scores of subparallel faults have 

been mapped here, their aggregate displacement 

may be very substantial. Preliminary estimates of 

Paleozoic stratigraphic relations south to ·north 

across various parts of the Brooks Range have 

been made using palinspastic reconstruction across 

the multiple thrust sheets (Lathram, 1965; Tailleur . 

and others, 1967). 

LONGITUDINAL FAULTS AND TOPOGRAPHIC TRENCHES 

In Alaska, as in more southern parts of the Cordilleran belt, there are many long fault zones that 

are frequently expressed topographically as trenches 

or valleys (fig. 20). Some of the more conspicuous 

faults and the way in which they affect Paleozoic 

rocks are discussed below. 

The Tintina fault zone in east-central Alaska is 

marked by a narrow valley that parallels the Yukon 

River on its south side (Brabb and Churkin, 1965, 

1970) and extends from Alaska southeastward 

across Yukon Territory to the Liard plain which 

separates the Tintina fault zone from the Rocky 

Mountain Trench. (Roddick, 1967). The Tintina 

fault zone effectively separates the unmetamorphosed Precambrian-through-Mesozoic stratigraphic 
... 

.. 

.. 

• 

MESOZOIC AND CENOZOIC TECTONIC EVENTS AFFECTING PALEOZOIC ROCKS 47 

succession on its north side from the Birch Creek 

Schist-strongly metamorphosed, mainly siliceous 

sedimentary rocks and volcanics of probable Paleozoic and possible Precambrian age--on its south 

side. Granitic and ultramafic intrusions of Mesozoic 

age (except for the so-called Circle Volcanics) cut 

the metamorphic rocks south of the fault but do not 

extend north of the Tintina fault, thus further contrasting the widely different geologic terranes on 

both sides of the fault. Thick sections of nonmarine, 

poorly consolidated sandstone, mudstone, conglome-· 

rate, and minor coal of Late Cretaceous and Tertiary 

age are developed along the fault zone. Steep dips 

and faults cutting even the youngest Tertiary sedimentary rocks along the trenchlike valley indicate 

latest Tertiary and (or) Quaternary deformation. 

Large-scale lateral dislocation has been postulated 

along the fault. By matching an upper Precambrian 

quartzite-shale ("grit") unit north of the fault in 

Yukon Territory with a similar belt in the YukonTanana Upland of east-central Alaska, a rightlateral offset of about 260 miles has been suggested 

(Roddick, 1967). 

The trace of the Tintina fault in the vicinity of 

Circle, Alaska, is not defined. It may continue 

straight into the Yukon Flats northwest of Circle 

or bend sharply westward parallel to the trend 

of the White and Crazy Mountains and possibly 

connect with the Kaltag fault that continues 

southwestward into Norton Sound (Patton and 

Hoare, 1968). Still another possible northern termination of the Tintina may be along a set of sub-

. parallel splays in the Livengood area where anumber of throughgoing faults (F. R. Weber, oral 

commun., 1969) may reflect the taking-up of the 

substantial displacement postulated for the fault 

farther to the southeast. 

The Kaltag fault controls the course of a long 

reach of the Yukon River and, like the Tintina, in 

places is marked by rift valleys and fault scarps that 

cut Tertiary and Quaternary deposits developed 

along it (Patton and Hoare, 1969). Seismic reflection profiles on the shallow Bering Shelf reveal a 

sediment-filled trough that is interpreted to be the 

seaward continuation of the Kaltag fault (Scholl 

and others, 1970). The major geologic trends in the 

area-the Yukon-Koyukuk basin of Cretaceous age 

and a belt of metamorphic rocks of Paleozoic and 

early Mesozoic age--have been displaced between 

40-80 miles right laterally across the fault, and 

modern stream courses are offset as much as 1.5 

miles (Patton and Hoare, 1968). If the Kaltag and 

Titina faults are differently trending segments of 

the same fault system, they have an arcuate tr~nd 

nearly parallel to the Denali fault system farther 

south. 

The Denali fault of southern Alaska is the longest 

throughgoing fault system in southern Alaska (St. 

Amand, 1957). The Denali fault is made up of 

several fairly straight segments that apparently interconnect at slight angles to give it an arcuate trend 

(Grantz, 1966). There are many subsidiary faults 

and strands, especially in its central part in the 

Alaska Range. According to St. Amand (1957), the 

Denali fault system may have had 150 miles of rightlateral strike-slip displacement since the start of the 

Pliocene. Because numerous geologic and topographic anomalies would result from this amount of 

displacement, Grantz (1966) suggested somewhat 

smaller and mainly older, Mesozoic, movement with 

the amount of displacement across the fault varying 

from segment to segment. The Chatham Strait fault 

-a possible continuation of the Denali into southeastern Alaska-separates regions of strongly contrasting geology (Twenhofel and Sainsbury, 1958; 

Lathram, 1964). About 120 miles of right-lateral 

separation is suggested by displacement of Paleozoic 

and Tertiary rocks on either side of the fault (Lathram, 1964). In addition to this lateral displacement, 

several kilometers of vertical movement is assigned 

to the same fault (Loney and others, 1967). 

South of the Denali fault is another group of 

transcurrent faults that are more widely separated 

and seem to have different directions of displacement (fig. 20). In the future, more detailed correlations of Paleozoic stratigraphy will increasingly 

depend on the recognition of _displacements on these, 

and other, major faults. 

CORRELATION OF THE P;\LEOZOIC ROCKS 

AROUND THE EDGES OF THE ARCTIC AND 

NORTHERN PACIFIC BASINS AND SEA· 

FLOOR SPREADING IN THE ARCTIC 

The old idea of continental drift of North America 

from Eurasia has b~en revived by new oceanographic data and incorporated into the theory of seafloor spreading and plate tectonics. In the attempts 

to reconstruct how the drift has occurred, North 

America is considered as a block separate from the 

Eurasian block, and differential movement has been 

postulated between the two blocks (Blackett and 

others, 1965). The mid-Atlantic Ridge and its northern extension across the Arctic Ocean are considered 

by many as the eastern boundary of North America 

(fig. 21). In the Pacific realm, the position of the 

boundary separating North America from Eurasia 
48 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

FIGURE 21.-Boundaries of the major crustal plates in the Northern Hemisphere. 

is less certain, but it has been drawn between 

Chukotka and Alaska (Le Pichon, 1968). If drift 

has occurred in the northern Pacific, there should 

be some geologic evidence of movement between 

these two continent blocks in the Bering Sea region. 

The Cenozoic geology of the Bering Sea area, 

recently summarized by Hopkins (1967), indicates 

that there is a complex record of sea-level changes 

and intermittent land connections across the Bering 

Straits and .that the North American and Eurasian 

continents appear to have been connected at least 

since the early Tertiary. 

No significant breaks in the Mesozoic and Cenozoic 

geologic trends have been reported to substantiate 

continental drift between North America and 

Eurasia where they come together in the northern 

Pacific. If drift occurred, however, it is the preMesozoic rocks and structures that should show the 

greatest displacement. A direct comparison of the 

pre-Mesozoic geology of Alaska with that of Northeast U.S.S.R. will now be made in search of evidence 

of differential movement between the two continents. 

Wrangell Island, connected by a bathymetric 

(Creager and McManus, 1965) and a gravity 

anomaly trend (Ostenso, 1968b) across the Chukchi 

Sea to Lisburne Peninsula, seems to represent a 

westward extension of the pre-Cretaceous rocks of 

the Brooks Range (Holmes and others, 1968; Grantz 

and others, 1970). The oldest fossiliferous rocks, of 

Mississippian age, occur in the central part of 

Wrangell Island as part of a thick sequence of 

marine sedimentary rocks (fig. 22). Nonmarine beds 

of chert-quartz conglomerate form the lower part of 

the sequence. The presence in the western Brooks 

Range of similar conglomerates of Late Devonian 

age in a stratigraphic section comparable to that in 

Wrangell Island has been noted (Bogdanov and Tilman, 1964). These conglomerates are part of a 

series of clastic wedge deposits that continued 

around the edge of the Canada Basin from the 

Soviet Arctic (Chukotka and Wrangell Island), 

across northern Alaska ( Churkin, 1969), and then 

across the Canadian Arctic Islands at least as far as 

Ellesmere Island (Trettin, 1967). 

Intrusive rocks on Wrangell Island include dikes 

and small plutonic bodies, mainly of granitic com-

• 

• 
... 

,.,. 

CORRELATION OF ROCKS AND SEA-FLOOR SPREADING 

WRANGELL ISLAND 

USSR 

212 m.y. x 

300 m.y. 

K/A 

7 

ELLESMERE ISLAND 

CANADA 

Pre-Silurian 

IIOOOm ..,3 000 ft 

8 9 

KOLYMSKICHUKOTSK PENINSULA 

MASSIF USSR 

USSR 

·~:·~-·:-. Gneiss 

x70 m.y.-1500 m.y. KIA 

Skajit 

Limestone 

Pre-Devon ian 

11 

SEWARD 

PENINSULA 

LITHOLOGIC 

EXPLANATION STRATIGRAPHIC 

Limestone 

~ 

1:-: .. :.:':1 

Sands tone 

~-E 

Shale 

Conglomerate 

~ 

~ 

[32] Volcanic rocks 

Strongly deformed and 

low grade metamorphic rocks 

PERIODS 

p£, Precambrian 

£, Cambrian 

0, Ordovician 

S, Silurian 

D, Devonian 

C, Carboniferous 

P, Permian 

li, Triassic 

Subscripts: 

I= Lower 

2=Middle 

3 = Upper 

12 

CHARLEY RIVER 

EAST CENTRAL 

ALASKA Oil shale 

--lip Tahkandit Limestone 

c Calico Bluff Formation 

I I 000m:3000ft 

Fossils= 

ID Bra chi a pods 

.f Plants 

~ Pelecypods 

@J Shelly material 

1-See fig.l9 for loca,~ion 

FIGURE 22.-Correlation diagrams of the Paleozoic and Precambria:J! stratigraphy around the Canada Basin and 

central parts of Alaska and Northeast U.S.S.R. 

49 
50 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

position. They cut the Paleozoic section, but nowhere 

are they reported to affect the Triassic strata. The 

age of these rocks, supported by potassium-argon 

isotope dating, is thought to be late Paleozoic (fig. 

22). Absolute age determinations of granitic rocks 

farther east around the margin of the Canada Basin 

indicate that similar intrusions were probably related to a widespread middle Paleozoic orogeny that 

produced wedges of Upper Devonian conglomerate 

and sandstone (Tailleur and others, 1967; Trettin, 

1967; Churkin, 1969). 

On Wrangell Island the Mississippian rocks, like 

the underlying Upper Devoni~n rocks, are very 

similar to, but thicker than, those in the Brooks 

Range. Permian and Triassic rocks, mainly clastics, 

unconformably overlie the Mississippian, and again 

there is a similarity to the stratigraphy of the 

Brooks Range (fig. 22) . In the Canadian Arctic 

Islands, an even thicker sequence of Carboniferous 

and younger rocks lies unconformably on the older 

Paleozoic rocks of the Franklinian geosyncline and 

forms the Sverdrup Basin (Thorsteinsson and Tozer, 

1960). 

The rocks at the western tip of the Seward Peninsula and at the eastern tip of Chukotsk Peninsula 

where the two continental landmasses come closest 

together should show most clearly evidence of differential movement between the continents. For 

comparison, the basic elements of the geology of 

the Cape Dezhneva area, the easternmost tip of 

Chukotsk Peninsula and the land point nearest to 

the Seward Peninsula, are shown in figure 23. 

In the Cape Dezhneva area, there is a gneiss and 

amphibolite central dome that is surrounded progressively outward by marble and schist that is, in turn, 

interlayered with partially recrystallized limestones. 

Shelly fossils in these limestones are of Ordovician, 

Silurian, Devonian, and Carboniferous age ( Gnibidenko, 1969, p. 11-13). Granite and a syenite intrusion coupled with imbricate thrust faulting (S. G. 

Byalobzhevski, oral commun., 1967) complicate the 

structure. About 15,000 feet of schist and gneiss 

is reported by Gnibidenko to underlie conformably 

the limestone with Late Ordovician fossils. Directly 

across the narrow Bering Strait in the Seward 

Peninsula, the west-trending Kigluaik Mountains expose, in their core, gneiss and biotite schists that 

have a well-defined domal structure (Collier and 

others, 1908, p. 67) (fig. 22). Overlying these highgrade metamorphic rocks are lower grade schists 

characterized by chlorite and muscovite. Marble is 

interlayered with the schist, especially in its upper 

part. Thin-bedded argillaceous limestone seems to 

overlie the schist and, in turn, is overlain to the 

north by a complexly thrust faulted sequence of 

massive limestone containing Ordovician and Silurian fossils (Sainsbury, 1969a). · 

C. L. Sainsbury (written commun., 1970) has 

obtained a 750-m.y. date on gneiss in the Kigluaik 

Mountains using the rubidium-strontium whole-rock 

method. According to Sainsbury, a dike cutting this 

same gneiss gives a 450-m.y. date. On the other 

hand, dating of other metamorphic rocks and a.ssociated intrusives in the general area using the 

potassium-argon method indicates a Cretaceous 

metamorppic-plutonic event (Sainsbury, 1969a). In 

the nearby Chukotsk Peninsula most of the dates 

on intrusive and metamorphic rocks are again Mesozoic, but a number of much older dates, ranging 

from 1,500 to 700 m.y., have been obtained on 

rocks in the same vicinity as those giving Mesozoic 

dates (Gnibidenko, 1969). Thus, there is a close correlation of stratigraphy and metamorphism in the 

oldest rocks across the Bering Strait (Churkin, 

1970). The occurrence of comparable tin deposits 

in both the Seward and Chukotsk Peninsulas (Sainsbury, 1969a) and the occurrence of rare alkali-rich 

plutonic rocks in both regions (Miller, 1972) provide other examples of the close similarity in the 

geology across the Strait. 

A comparison of upper Paleozoic and lower Mesozoic stratigraphy between eastern Chukotka and the 

Seward Peninsula is not possible because only isolated fragments of these rocks are available for 

comparison in Seward Peninsula. On St. Lawrence 

Island, however, in the middle of the Bering Shelf, 

a rather complete Devonian-through-Triassic section 

has been reported by Patton and Dutro (1969). The 

section here closely resembles that of the western 

Brooks Range on the east and the Chukotsk Peninsula on the west (fig. 22). 

On both sides of the Bering Straits, at about the 

same latitude but much farther inland, are rather 

similar and much more complete sequences ranging 

in age from Precambrian to Triassic (fig. 22). In 

Alaska, this is the section exposed in the YukonPorcupine Rivers area (Churkin and Brabb, 1967) ; 

in Siberia, it is the section in the Kolymski massif 

(Bogdanov, 1963). These two relatively stable areas 

are characterized mostly by carbonate rock sections 

nearly surrounded by thicker, more terrigenous deposits. ' 

In Northeast U.S.S.R., as in Alaska, the depth to 

the Mohorovicic discontinuity, except for some deep 

roots below high mountains, generally rises closer 

to the surface as the Arctic and Pacific Ocean basins 

•. 

... 
• 

• 

... 

CORRELATION OF ROCKS AND SEA-FLOOR SPREADING 51 

N 

I 

~Limestone 

• 

~ 

Chlorite- sericite schist 

Biotite schist 

Marble 

W!!!!!J!J Gneiss and amphibolite 

~ Granitic intrusive rocks 

0 50 MILES 

N 

I 

A ==-~~~' m;;~~\~ :~¥<~s~~~ ;,m~~~i%~~~~~, =--1 

N 

I 

BERING 

SEA 

A 

8 

B' 

FIGURE 23.-Geologic map of the t:ape Dezhneva area, easternmost tip of Chukotsk Peninsula, U.S.S.R., 

showing fossil localities and structure sections. 

are approached (Nikolaevskiy, 1964; Woollard and 

others, 1960). The preliminary inference that a 

trend of high crustal thickness across the center 

of Alaska connects with a comparable trend_ across 

the center of Chukotka suggests another correlation of the geology across the Bering Straits. 

One of the most compelling lines of evidence 

against a major discontinuity in the geology of the 

Bering Sea region is a correlation of Paleozoic sections (Churkin, 1970) that leads to the paleotectonic reconstruction shown in figure 1. A Paleozoic 

geosyncline rims the northern Pacific, and another 

geosyncline rims the southern margin of the Arctic 

Basin. Separating the two geosynclines is a narrow 

stable area that received mainly carbonate sediments extending perhaps discontinuously from the 

North American craton to the Kolymski massif of 

Siberia. 

These different lines of evidence considered together indicate a close similarity between the geologic histories of the opposing edges of the Bering 

and Chukchi Seas and a continuity of geologic features between Alaska and eastern Siberia that imply 

these landmasses have been connected since the 
52 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Paleozoic and probably since the Precambrian 

(Churkin, 1970). 

Alternate locations of the western boundary of 

the North American plate have been suggested 

within the Asian continent. In order to evaluate 

these possible boundaries, it is necessary to first 

consider some of the characteristics of the midAtlantic Ridge and the transarctic spreading center 

that apparently runs into the continental margin 

of Asia. 

The seismically and volcanically active mid-Atlantic ridge extends north from Iceland between Greenland and Spitsbergen (Vogt and others, 1970) and 

with apparent decreased seismicity (Sykes, 1965) 

continues across the Eurasia Basin as the Gakkel 

Ridge (Nansen Cordillera) that lies midway between the Lomonosov Ridge and the continental 

margin of Eurasia (Heezen and Tharp, 1965; Demenitskaya and Karasik, 1969) (fig. 2). Magnetic 

profiles associated with the Gakkel Ridge show axial 

symmetry and correlate with profiles in the North 

Atlantic and in the Norwegian Sea (Vogt and 

others, 1970; Wold and Ostenso, 1971). A quantitative attempt to verify these correlations implies that 

the Gakkel Ridge spreading history started about 

40 m.y. B.P. (before present) (Wold and Ostenso, 

1972), but spreading rates of about 1 cm/yr (Vogt 

and others, 1970) calculated for the ridge are admittedly speculative. Estimates. of the rate of seafloor spreading in the North Atlantic are also 

thought to have been about 1 cm/yr (Vine, 1966; 

Vogt and others, 1970), and considerably slower 

than in the central and southern Atlantic. Reconstructions of the history of the Atlantic opening 

(Dietz and Holden, 1970) suggest that its opening 

proceeded northward and reached the Grand Banks 

in about Triassic time. Further extension of the 

Atlantic rift had started to block out the eastern 

margin of Greenland by Cretaceous time, and in the 

Cenozoic the rift extended into the Arctic (Johnson 

and Heezen, 1968; Vogt and others, 1970). 

These data are consistent with the idea that the 

Eurasia Basin (with the Lomonosov Ridge as one 

margin) is a wedge-shaped depression having its 

apex in the Sea of Laptev and its widest part near 

the Atlantic (Wilson, 1963; Churkin, 1970). The . 

pole of rotation or pivot of North America with 

respect to Eurasia to produce the opening of the 

northern Atlantic and Eurasia Basins has been determined to be 78° N., 102° E. The point was determined by using azimuths of fracture zones across 

the northern part of the mid-Atlantic ridge (Morgan, 1968; Le Pichon, 1968). This pole lies in the 

vicinity of the Taimyr Peninsula near the apex of 

the Eurasia Basin. Another estimate of the pole 

of rotation, using the best fit of Greenland to Europe, averages out any changes in direction of spreading and gives a position 73° N., 96.5° E. (Bullard 

and others, 1965). It appears significant that the 

two poles of rotation calculated independently are 

reasonably near the apex of the Eurasia Basin 

opening. 

An analysis of geophysical data suggests that 

the tensional tectonic conditions of the Gakkel 

spreading center do not stop at the head of the 

Eurasia Basin but continue into the continental 

framework of eastern Siberia (Demenitskaya and 

Karasik, 1969). The Sadko trough, an unusually 

large submarine canyon at the head of the Eurasia 

Basin, is alined with the Gakkel Ridge, is the locus 

of earthquakes, and is reported to be a rift feature 

(Demenitskaya and Karasik, 1969) (fig. 24). The 

shallow Laptev Sea, at the head of the Eurasia 

Basin, contains a thick blanket of sediments de·-

posited by the Lena and other major rivers. These 

sediments have obscured the landward extension 

of the Sadko trough or any other structures alined 

with the Gakkel Ridge. The line of earthquake 

epicenters along the Gakkel Ridge and Sadko trough, 

however, continues across the Sea of Laptev where 

it splits into a southerly trend that follows the 

Verkhoyansk Mountains and a more southeasterly 

trend that follows the Cherskiy system of mountain 

ranges and depressions (Rezanov, 1964). According 

to Rezanov, very active Quaternary tectonic movements in the Cherskiy Mountain system have produced large uplifts and depressions in this, the 

most active earthquake belt in Northeast U.S.S.R. 

Faulting and volcanism here has been recognized as 

a landward extension of the sea-floor-spreading tectonics of the Gakkel submarine ridge (Demenitskaya 

and Karasik, 1969). The available data from the 

Laptev Sea area, in my opinion, suggest that the 

tectonic conditions here may be similar to those 

in the Gulf of California where faulting extends 

inland from the East Pacific Rise (Larson and 

others, 1968). 

The western boundary of the North American 

pia te has been assumed to lie in the Verkhoyansk 

Mountains of Yakutia (Wilson, 1963; fig. 24). According to Wilson, the Verkhoyansk Mountains, 

south and on trend with the apex of the Eurasia 

Basin of the Arctic Ocean, were deformed in Late 

Jurassic to early Tertiary and Pliocene to Holocene, 

the major periods of spreading in the Atlantic and 

Arctic. Based on earthquake epicenters that cross 
.. 

, ... 

.. 

.. 

CORRELATION OF ROCKS AND SEA-FLOOR SPREADING 

PLATFORMS 

Ei 

Cenowic and Mesozoic rocks 

Paleozoic roc

~ ks and Precambrian shield 

FO LD BELTS 

~ Cenozoic 

Mesozoic 

EX PLANATION 

D 

Late Paleozoic 

D . 

Middle Paleozoic 

D 

Early Paleozoic 

D 

Ocean Deep 

FIGURE 24.-Major tectonic features of the Arctic. 

• • • 

Major thrust belt 

~, 

Structural trends 

Active spreading center 

- -rFossil spreading center 

Seismic w ne 

53 
54 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Siberia on trend with the Gakkel spreading center 

(Sykes., 1965), a plate boundary separating America 

from Eurasia was also drawn along the Verhoyansk 

Mountains (Heezen and Tharp, 1965; Morgan, 1968). 

These data were summarized (Churkin, 1970) and 

interpreted to suggest a hinge zone in the Laptev 

Sea (as proposed earlier by Wilson) with tension 

north of the zone and compression south of the 

zone. 

Compared to the tectonic activity in the Cherskiy 

system of mountain ranges and depressions, there 

is little evidence for an active plate boundary within 

the Verkhoyansk foldbelt. Except for some seismic 

activity and broad uplifts, the area lacks the 

throughgoing faults and igneous activity that mark 

major plate boundaries (Churkin, 1972b). Evidence 

for a fossil plate boundary within the Verkhoyansk 

foldbelt proper is also· lacking. The rocks of the 

Verkhoyansk foldbelt are deformed into broad open 

folds and, in many places, are flat lying. Largescale displacements of geologic trends, overturned 

folds, thrust faults, melanges, great transcurrent 

faults, and associated high-pressure metamorphism 

and igneous activity that are recorded along plate 

boundaries elsewhere are not reported here (Yanshin, 1966). If there is a major break in the geology 

of the region, it would have to lie below the upper 

Paleozoic and Mesozoic rocks of the Verkhoyansk 

geosynclinal complex. 

Numerous stratigraphic, structural, and petrological features in the Cherskiy Mountain system suggest that this mountain system, where it comes in 

contact with the Verkhoyansk foldbelt, marks a fossil 

plate boundary along which the Eurasian and North 

. American continental plates were sutured. The compressional features of late Paleozoic and especially 

Mesozoic age along this boundary contrast strongly 

with the more recent, mainly tensional movements 

along the east side of this region that have been 

related to sea-floor spreading on the Gakkel Ridge 

and to modern plate motions in the Eurasia Basin 

part of the Arctic. 

Major faults in the Cherskiy Mountain system 

separate three fundamentally different stratigraphic 

sequences of Cambrian through early Carboniferous 

age (Bogdanov, 1963). To the east, the Kolymski 

massif exposes a sequence 1,500-3,000 m (meters) 

thick of carbonate strata interlayered with sandstone and shale of latest Precambrian (Riphean) 

and Cambrian through Devonian age. This sequence 

rests unconformably on complexly deformed Proterozoic basement (fig. 22). West of this platform 

section, in the eastern ranges of the Cherskiy Mountain system, is a tightly folded, mainly carbonate 

rock section of Ordovician through early Carboniferous _age that is much thicker, as much as 13,000 

m. Farther west, along the western edge of the 

Cherskiy Mountains, a largely clastic section of 

Ordovician-through-Carboniferous strata that includes mafic volcanic rocks, is more than 8,000 m 

thick. Th.ese rocks are isoclinally folded and are 

cut by large thrust faults dipping east. The western 

edge of this major fault zone marks the boundary 

of the Paleozoic geosyncline in the Cherskiy Mountains with the early Mesozoic rocks, mainly Triassic 

and Jurassic, of the Verkhoyansk geosynclinal complex (Bogdanov, 1963). In places, Paleozoic rocks 

of the Cherskiy foldbelt are thrust west over the 

Mesozoic rocks of the Verkhoyansk foldbelt. This 

can be explained either as a product of westward 

overthrusting of the Paleozoic rocks or by eastward 

underthrusting of the Mesozoic rocks. High pressure minerals are developed along these faults in 

wide zones of breccia and mylonite (Dobretzov and 

others, 1966). Along this zone of regional faults 

is developed another large-scale feature-a belt 

1,1000 km (kilometers) long of granitic batholiths 

mainly of Early Cretaceous age but including some 

of Late ·Jurassic age. 

In general, the Cherskiy foldbelt that developed 

along the western margin of the Kolymski massif 

represents a long period of geosynclinal sedimentation that lasted through the early and middle Paleozoic, followed by thrust faulting and plutonic 

activity that closely parallels the history of the 

development of the major foldbelts rimming the 

North America craton (King, 1969). In fact, the 

stratigraphy of the Cherskiy foldbelt resembles in 

considerable detail that of the Cordilleran foldbelt 

( cf. fig. 22, cols. 8 and 12). The major distinction 

between the Cherskiy foldbelt and those of North 

America is that the Cherskiy foldbelt, like the Ural 

foldbelt, lies wholely within a continental landmass 

and separates the Siberian platform or craton on 

the west from the Kolymski massif on the east 

(fig. 24). 

The eastern Verkhoyansk-western Cherskiy -region marks the site of a major seaway that separated the Siberian platform from the Kolymski 

massif during the early Paleozoic ( Churkin, 1972b). 

There is some evidence that points to a closing of 

this seaway in the middle Paleozoic. C:oarse clastic 

sediments in the upper parts of the Devonian and 

in the lower Carboniferous sections of the Cherskiy 

foldbelt had western sources from a location now 

occupied by the Verkhoyansk foldbelt (Bogdanov, 

.... 
• 

• 

.. 

--·. 

CORRELATION OF ROCKS AND SEA-FLOOR SPREADING 55 

1963, p. 155, 162). The presence of granitic detritus 

in these conglomerates, together with radiometric 

age dating of small granitic plutons in the western 

part of the area, has been related to a major period 

of uplift and folding during the Carboniferous that 

affected the Cherskiy geosyncline. 

In the Permian, another cycle of sedimentation 

s~arted which resulted in thick Triassic and Early 

Jurassic deposits laid down in the Verkhoyansk 

area. In the Late Jurassic and Early Cretaceous, 

this last period of geosynclinal sedimentation closed 

with a climactic orogeny that deformed the geosynclines into foldbelts and resulted in metamorphism 

and batholithic intrusion. Within Yakutia there is 

ample evidence of compression that requires considerable crustal shortening. The big question, it 

seems to me, is how much lateral transport has 

occurred in closing the Paleozoic and Mesozoic seaways that successively separated the ·siberian platform and the Kolymski massif? Estimates of seafloor spreading in the northern Atlantic indicate a 

rate of spreading (about 1 cm/yr, Vine, 1966) and 

different amounts of Atlantic opening since the 

Triassic (Dietz and Holden, 1970). These estimates 

and reconstructions indicate that more than 1,000 

km of total separation had already occurred on the 

Atlantic side of North America before the Early 

Cretaceous, the time of climactic orogeny in 

Yakutia. If this amount of separation had occurred 

on the Atlantic side of North America, there should 

be some dramatic expression of this drift bringing 

the Pacific sides of North America and Eurasia 

closer together, assuming they were once separated 

(Churkin, 1969, 1970). If global movements of this 

magnitude took place, then the closure of a major 

seaway in the Yakutia region between the leading 

edges of the approaching Eurasian and North 

American continental plates could have culminated 

with continental collision by Early Cretaceous time. 

Sharp bends in the structures of southern Alaska 

and Chukotka have al.so been interpreted as products 

of drift of North America relatively toward Eurasia 

(Grantz, 1968). These curved structures include the 

long faults in southern Alaska (fig. 20) and those 

in the Koryak Mountains of Chukotka. Mesozoic 

and older tectonic elements (figs. 1, 17, 18) that are 

subparallel to these faults also reflect a bend in the 

stratigraphic belts of Alaska. Moreover, the curved 

continental margin of the Bering Sea, Gulf of 

Alaska, and possibly the northward prolongation of 

the Chukchi shelf margin around the Chukchi Cap 

could ·also be products of this movement (fig. 20). 

A complication of this simplified analysis of compressional bending in the Alaska-Chukotka region 

as a· consequence of tensional opening of the Atlantic is that the strongly curved southern continental 

margins of Alaska and Chukotka and some of the 

subparallel trends in the stratigraphic and struc~ 

tural belts farther inland may be the result of 

thrusting of the Pacific floor against the continental 

margins of Alaska and Ch ukotka-a hypothesis 

supported by studies of magnetic anomalies in the 

Gulf of Alaska (Pitman and Hayes, 1968), faults 

and folds along the Gulf of Alaska (Stoneley, 1967) 

and in the Koryak Mountains of Chukotka (Bogdanov in Peive, 1969), and land movements associated with the Alaska earthquake of 1964 (Plafker, 

1969). 

Finally, the geologic history around the margin 

of the Canada Basin, together with geophysical 

data from the basin itself, provides ways of answering questions concerning the age and origin of this 

part of the Arctic Ocean. basin (Churkin, 1969, 

1972b). From the stratigraphic data presented 

earlier, there is evidence that an early Paleozoic 

geosyncline rimmed the Canada Basin. Starting in 

the Late Devonian, uplifts in this geosyncline, accompanied by granitic intrusion, produced wedges of 

coarse clastic sediments that spread southward 

onto adjoining areas of Alaska, Canada, and Siberia. 

On the basis of the early development of geosynclines along the margins of the modern Canada 

Basin, followed by deformation, metamorphism, 

granite intrusion, and major uplift and clastic wedge 

sedimentation, a proto-Canada Basin with continental margin tectonics existed at least from Cambrian 

through Middle Devonian time. In the Late Devonian and Early Mississippian there was a closing of 

the proto-Canada Basin with deformation, metamorphism, plutonic activity, and major uplift that culminated in the accretion of the ancestral Brooks 

and Franklinian geosynclines to the Arctic margin 

of North America. During the Mississippian through 

the Triassic, successor basins with restricted marine 

sedimentation developed on the roots of the earlier 

geosynclines. 

The modern Canada Basin seems to have opened 

in the Late Jurassic or Early Cretaceous when 

coarse clastic sediments were first shed from bordering parts of North America toward the basin. By 

Late Cretaceous time the Canada Basin had 

deepened sufficiently to accommodate the turbidites, 

submarine canyon and delta deposits that lead into 

the basin . 
56 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

REFERENCES CITED 

Annstrong, A. K., 1970a, Mississippian dolomites from Lisburne Group, Killik River, Mount Bupto region, Brooks 

Range, Alaska: Am. Assoc. Petroleum Geologists Bull., 

v. 54, p. 251-264. 

--- 1970b, Mississippian rugose corals, Peratrovich Formation, West Coast, Prince of Wales Island, southeastern Alaska: U.S. Geol. Survey Prof. Paper 534, 44 p. 

Armstrong, A. K., MacKevett, E. M., Jr., and Silberling, 

N. J., 1969, The Chitistone and Nizina Limestones of 

part of the southern Wrangell Mountains, Alaska-A 

preliminary report stressing carbonate petrography and 

depositional environments, in Geological Survey research, 

1969: U.S. Geol. Survey Prof. Paper 650-D, p. D49-D62. 

Armstrong, A. K., and Mamet, B. L., 1970, Biostratigraphy 

and dolomite porosity trends of the Lisburne Group, in 

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

the geological seminar on the North Slope of Alaska: 

Los Angeles, Pacific Sec., Am. Assoc. Petroleum Geologists, p. N1-N15. 

Armstrong, A. K., Mamet, B. L., and Dutro, J, T., Jr., 1970, 

Foraminiferal zonation and carbonate facies of Carboniferous (Mississippian and Pennsylvanian) Lisburne 

Group, central and eastern Brooks Range, Arctic Alaska: 

Am. Assoc. Petro~eum Geologists Bull., v. 54, p. 687-698. 

Baadsgaard, Halfdan, Folinsbee, R. E., and Lipson, J. I., 

1961, Caledonian or Acadian granites of the northern 

Yukon Territory, in Raasch, G. 0., ed., Geology of the 

Arctic, V. 1: Toronto, Ontario, Univ. Toronto Press, 

p. 458-465. 

Belyi, V. F., 1964, K voprosu o zhestkoi strukture vostochnoi 

Chukotki i Alyaske: Materyaly po geologii i poleznym 

iskopaemym Severo-Vostoka SSSR, Magadan, no. 17, 

p. 40--48. 

Berg, H. C., 1970, Paleozoic plutonism and contrasting 

metamorphic terranes, Annette Island, Alaska: Geol. 

Soc. America Abstracts with Programs, v. 2, p. 70. 

Blackett, P. M. S., Bullard, Edward, and Runcorn, S. K. 

(organizers), 1965, A symposium on continental drift: 

Royal Soc. [London] Philos. Trans., Ser. A, v. 258, no. 

1088, 323 p. 

Bogdanov, N. A., 1963 Tektonicheskoe razvitie v Paleozoe 

Kolymskogo Massiva i vostochnoi Arktiki [Tectonic development of the Kolyma Massif and eastern Arctic in 

the Paleozoic]: AkaC:. Nauk SSSR, Geol. Inst., Trudy, 

v. 99, 239 p. 

Bogdanov, N. A., and Tilman, S. M., 1964, Obshchie cherty 

razvitiya Paleozoiskikh struktur ostrova Vrangelya i 

zapadnoi chasti Khrebta Bruksa (Alyaska) [Similarities 

in the development of the Paleozoic structures of Wrangell Island and the western part of .the Brooks Range 

(Alaska), in Soveshchanie po Problem Tektoniki, Moscow, 1963, Skladchatye oblasti Evrazii, Materialy] : 

Moskva, Nauka, p. 219-230. 

Bond, G. C., 1971, Early Permian sedimentation and paleogeography in east-central Alaska Range, and regional 

implications [abs.]: Internat. Symposium Arctic Geology, 

2d, Pacific Sec., Am. Assoc. Petrol. Geologists, p. 8. 

Bowsher, A. L., and Dutro, J. T., Jr., 1957, The Paleozoic 

section in the Shainin Lake area, central Brooks Range, 

Alaska: U.S. Geol. Survey Prof. Paper 303-A, 39 p. 

Brabb, E. E., 1967, Stratigraphy of the Cambrian and 

Ordovician rocks of east-central Alaska: U.S. Geol. 

Survey Prof. Paper 559-A, p. A1-A30. 

Brabb, E. E., 1969, Six new Paleozoic and Mesozoic formations in east-central Alaska: U.S. Geol. Survey Bull. 

1274-I, p. Il-I26. 

Brabb, E. E., and Churkin, Michael, Jr., 1965, Preliminary 

geologic map of the Eagle D-1 quadrangle, east-central 

Alaska: U.S. Geol. Survey open-file map, scale 1:63,360. 

--- 1967, Stratigraphic evidence for the Late Devonian 

age of the Nation River Fonnation, east-central Alaska, 

in Geological Survey research, 1967: U.S. Geol. Survey 

Prof. Paper 575-D, p. D4-D15. 

--- 1969, Geologic map of the Charley River quadrangle, 

east-central Alaska: U.S. Geol. Survey Misc. Geol. Inv. 

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

Brabb, E. E., and Grant, R. E., 1971, Stratigraphy and 

paleontology of a revised type section for the Tahkandit 

Limestone (Permian) in east-central Alaska: U.S. Geol. 

Survey Prof. Paper 703, 26 p. 

Brew, D. A., 1968, The role of volcanism in post-Carboniferous tectonics of southeastern Alaska and nearby regions, North America: Internat. Geol. Cong., 23d, Prague 

1968, v. 2, p. 107-121. 

Brew, D. A., Loney, R. A., and Muffler, L. J. P., 1966, 

Tectonic history of southeastern Alaska, in A symposium 

on tectonic history and mineral deposits of the western 

Cordillera in British Columbia and neighboring parts of 

the United States: Canadian Inst. Mining, spec. v. no. 8, 

p. 149-170. 

Brooks, A. H.; 1911, The Mount McKinley region, Alaska, 

with descriptions of the igneous rocks and of the Bonnifield and Kantishna districts, by L. M. Prindle: U.S. 

Geol. Survey Prof. Paper 70, 234 p. 

Brosge, W. P., 1960, Metasedimentary rocks in the southcentral Brooks Range, Alaska, in Geological Survey research 1960: U.S. Geol. Survey Prof. Paper 400-B, 

p. B351-B352. 

Brosge, W. P., Brabb, E. E., and King, E. R., 1970, Geological interpretation of reconnaissance aeromagnetic survey 

of northeastern Alaska: U.S. Geol. Survey Bull. 1271-F, 

p. F1-F14. 

Brosge, W. P., Dutro, J. T., Jr., Mangus, M. D., and Reiser, 

H. N., 1962, Paleozoic sequence in eastern Brooks 

Range, Alaska: Am. Assoc. Petroleum Geologists Bull., 

v. 46, no. 12, p. 2174-2198. 

Brosge, W. P., Lanphere, M.A., Reiser, H. N., and Chapman, 

R. M., 1969, Probable Permian age of the Rampart 

Group, central Alaska: U.S. Geol. Survey Bull. 1294-B, 

p. B1-B18. 

Brosge, W. P., and Reiser, H. N., 1964, Geologic map and 

section of the Chandalar quadrangle, Alaska: U.S. Geol. 

Survey Misc. Geol. Inv. Map I-375, scale 1: 250,000. 

---. 1965, Preliminary geologic map of the Arctic quadrangle, Alaska: U.S. Geol. Survey open-file report, scale 

1:250,000. 

... 
.. 

· .. 

.... 

.. 

REFERENCES CITED 57 

--- 1969, Preliminary geologic map of the Coleen quadrangle, Alaska: U.S. Geol. Survey open-file report, scale 

1:250,000. 

Brosge, W. P., Reiser, H. N., Dutro, J. T., Jr., and Churkin, 

Michael, Jr., 1966, Geologic map and stratigraphic sections, Porcupine River Canyon, Alaska: U.S. Geol. 

Survey open-file report, scale 1: 63,360. 

Brosge, W. P., and Tailleur, I. L., 1970, Depositional history 

of northern Alaska, in Adkinson, W. L., and Brosge, 

M. M., eds., Proceedings of the Geological Seminar on the 

North Slope of Alaska: Los Angeles, Pacific Sec., Am. 

Assoc. Petroleum Geologists, p. Dl-Dl7. 

Brown, J. S., 1926, The Nixon Fork country, and silver-lead 

prospects near Ruby [Alaska]: U.S. Geol. Survey Bull. 

783-D, p. 97-150. 

Buddington, A. F., and Chapin, Theodore, 1929, Geology and 

mineral deposits of southeastern Alaska: U.S. Geol. 

Survey Bull. 800, 398 p. 

Bullard, Edward, Everett, J. E., and Smith, A. G., 1965, 

The fit of the continents around the Atlantic, in· A 

symposium on continental drift: Royal Soc. [London] 

Philos. Trans., Ser. A, v. 258, no. 1088, p. 41-51. 

Burk, C. A., 1965, Geology of the Alaska Peninsula-Island 

arc and continental margin: Geol. Soc. America Mem. 99, 

250 p. 

Cady, W. M., Wallace, R. E., Hoare, J. M., and Webber, E. J., 

1955, The central Kuskokwim reg:ion, Alaska: U.S. Geol. 

Survey Prof. Paper 268, 132 p. 

Cairnes, D. C., 1914a, Geological section along the YukonAlaska boundary line between Yukon and Porcupine 

Rivers: Geol. Soc. America Bull., v. 25, p. 179-204. 

--- 1914b, The Yukon-Alaska international boundary, between Porcupine and Yukon Rivers: Canada Geol. Survey Mem. 67, 161 p. 

Campbell, R. H., 1967, Areal geology in the vicinity of the 

Chariot site, Lisburne Peninsula, northwestern Alaska: 

U.S. Geol. Survey Prof. Paper 395, 71 p. 

Carey, S. W., 1955, The orocline concept in geotectonics, 

pt. I: Royal Soc. Tasmania Papers and Proc., v. 89, 

p. 255-288. 

Chapman, R. M., Detterman, R. L., and Mangus, M. D., 1964, 

Geology of the Killik-Etivluk River region, Alaska: 

U.S. Geol. Su.rvey Prof. Paper 303-F, p. 325-407. 

Church, R. E., and Durfee, M. C., 1961, Geology of the Fossil 

Creek area, White Mountains, Alaska: Alaska Univ., 

College, M.S. thesis, 96 p. 

Churkin, Michael, Jr., 1966, Morphology and stratigraphic 

range of the phyllocarid crustacean Caryocaris from 

Alaska and the Great Basin: Palaeontology, v. 9, pt. 3, 

p. 371-380. 

--- 1969, Paleozoic tectonic history of the Arctic Basin 

north of Alaska: Science, v. 165, p. 549-555. 

--- 1970, Fold belts of Alaska and Siberia and drift between North America and Asia, in Adkison, W. L., and 

Brosge, M. M., eds., Proceedings of the Geological 

Seminar on the North Slope of Alaska: Los Angeles, 

Pacific Sec., Am. Assoc. Petroleum Geologists, p. Gl-G14. 

--- 1972a, Silurian and Devonian stratigraphy of Alaska 

and the Silurian-Devonian boundary: Internat. Symposium on the Silurian-Devonian boundary and the 

stratigraphy of the Lower and Middle Devonian, 3d, 

Leningrad, U.S.S.R., 1968 (in press). 

--- 1972b, Western boundary of the North American 

continental plate in Asia: Geol. Soc. America Bull., v. 83, 

p. 1027-1036 . 

Churkin, Michael, Jr., and Brabb, E. E., 1965a, Ordovician, 

Silurian, and Devonian biostratigraphy of east-central 

Alaska: Am. Assoc. Petroleum Geologists Bull., v. 49, 

no. 2, p. 172-185. 

--- 1965b, Occurrence and stratigraphic significance of 

Oldhamia, a Cambrian trace fossil in east-central Alaska, 

in Geological Survey research, 1965: U.S. Geol. Survey 

Prof. Paper 525-D, p. D120-D124. 

--- 1967, Devonian rocks of the Yukon-Porcupine Rivers 

area and their tectonic relation to other Devonian sequences in Alaska, in Oswald, D. H., ed., International 

symposium on the Devonian system, Calgary, 1967, V. 2: 

Calgary, Alberta Soc. Petroleum Geologists, p. 227-258. 

Churkin, Michael, Jr., and Carter, Claire, 1970, Earliest 

Silurian graptolites of Alaska and Nevada: U.S. Geol. 

Survey Prof. Paper 653, 51 p. 

Churkin, Michael, Jr., Carter, Claire, and Eberlein, G. D., 

1971, Graptolite succession across the Ordovician-Silurian 

boundary in southeastern Alaska: Geol. Soc. London 

Quart. Jour., v. 126, p. 319-330. 

Churkin, Michael, Jr., Eberlein, G. D., Hueber, F. M., and 

Mamay, S. H., 1969, Lower Devonian land plants from 

graptolitic shale in southeastern Alaska: Palaeontology, 

v. 12, p. 559-573. 

Churkin, Michael, Jr., Jaeger, Hermann, and Eberlein, G. D., 

1970, Lower Devonian graptolites from southeastern 

Alaska: Lethaia, v. 3, p. 183-202. 

Churkin, Michael, Jr., and Kay, Marshall, 1967, Graptolitebearing Ordovician siliceous and volcanic rocks, northern 

Independence Range, Nevada: Geol. Soc. America Bull., 

v. 78, no. 5, p. 651-668. 

Churkin, Michael, Jr., and Langenheim, R. L., Jr., 1960, 

Silurian strata of the Klamath Mountains, California: 

Am. Jour. Sci., v. 258, no. 4, p. 258-273. 

Coats, R. R., 1956, Geology of northern Adak Island, Alaska: 

U.S. Geol. Survey Bull. 1028-C, p. 45-67. 

Collier, A. J., 1902, A reconnaissance of the northwestern 

portion of Seward Peninsula, Alaska: U.S. Geol. Survey 

Prof. Paper 2, 70 p. 

Collier, A. J., Hess, F. L., Smith, P. S., and Brooks, A. H., 

1908, The gold placers of parts of Seward. Peninsula, 

Alaska, including the Nome, Council, Kougarok, Port 

Clarence, and Goodhope precincts: U.S. Geol. Survey 

Bull. 328, 343 p. 

Collins, F. R., 1958, Test wells, Topagoruk area, Alaska: 

U.S. Geol. Survey Prof. Paper 305-D, p. 265-316. 

Creager, J. S., and McManus, D. A., 1965, Pleistocene drainage patterns on the floor of the Chukchi Sea: Marine 

Geology, v. 3, no. 4, p. 279-290. 

Danner, W. R., 1966, Limestone resources of western Washington: Washington Div. Mines and Geology Bull. 52, 

474 p. 

Demenitskaya, R. M., and Karasik, A. M., 1969, The active 

rift system of the Arctic Ocean: Tectonophysics, v. 8, 

p. 345-351. 
58 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Detterman, R. L., 1970, Sedimentary history of the Sadlerochit and Shublik Formations in northeastern Alaska, in 

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

the Geological Seminar on the North Slope of Alaska : 

Los Angeles, Pacific Sec., Am. Assoc. Petroleum Geologists, p. 01-013. 

Dietz, R. S., and Holden, J. C., 1970, Reconstruction of Pangaea; Breakup and dispersion of continents, Permian to 

present: Jour. Geophys. Research, v. 75, p. 4939-4956. 

Dobretsov, N. L., Reverdatto, V. V., Sobolev, V. S., Sobolev, 

N. V., Ushakova, E. N., and Khlestov, V. V., 1966, Karta 

metamorficheskikh Fatziy SSSR [Metamorphic facies 

map of the USSR]: Ministerstvo geologii_ SSSR, scale 

1:7,500,000. 

Douglas, R. J. W., Norris, D. K., Thorsteinsson, Raymond, 

and Tozer, E. T., 1963, Geology and petroleum potentialities of northern Canada: Canada Geol. Survey Paper 

63-31, 28 p. 

Dutro, J. T., Jr., 1956, Annotated bibliography of Alaskan 

Paleozoic paleontology: U.S. Geol. Survey Bull. 1021-H, 

p. 253-287. 

--- 1970, Pre-Carboniferous carbonate rocks, northeastern 

Alaska, in Adkinson, W. L., and Brosge, M. M., eds., 

Proceedings of the Geological Seminar on the North 

Slope of Alaska: Los Angeles, Pacific Sec., Am. Assoc. 

Petroleum Geologists, p. M1-M7. 

Dutro, J. T., Jr., and Douglass, R. C., 1961, Pennylvanian 

rocks in southeastern Alaska, in Short papers in the 

geologic and hydrologic sciences: U.S. Geol. Survey Prof. 

Paper 424-B, p. B239-B241. 

Dutro, J. T., Jr., and Payne, T. G., 1957, Geologic map of 

Alaska: U.S. Geol. Survey, scale 1:2,500,000. 

Eakin, H. M., 1918, The Cosna-Nowitna region, Alaska: U.S. 

Geol. Survey Bull. 667, 54 p. 

Eardley, A. J., 1961, History of geologic thought on the 

origin of the Arctic Basin, V. 1: Toronto, Ontario, 

Univ. Toronto Press, p. 607-621. 

Eberlein, G. D., and Churkin, Michael, Jr., 1970, Paleozoic 

stratigraphy in the northwest coastal area of Prince of 

Wales Island, southeastern Alaska: U.S. Geol. Survey 

Bull. 1284, 67 p. 

Egiazarov, B. Kh., and others, 1965, Geologiya i poleznye 

is~opaemye Koryakskogo nagor'ya [Geology and mineral 

resources of the Koryak Upland]: Trudy Nauchno-Issled. 

Inst. Geol. Arktiki, Leningrad, v. 148, 342 p. 

Forbes, R. B., Pilkington, H. D., and Hawkins, D. B., 1968, 

Gold gradients and anomalies in the Pedro Dome-Cleary 

Summit area, Fairbanks district, Alaska: U.S. Geol. Survey open-file report, 43 p. 

Foster, H. L., 1969, Reconnaissance geology of the Eagle A-1 

and A-2 quadrangles, Alaska: U.S. Geol. Survey Bull. 

1271-G, p. G1-G30. 

Foster, R. L., 1967, Tectonic inclusions from a serpentinite, 

east-central Alaska, in Geological Survey research 1967: 

U.S. Geol. Survey Prof. Paper 575-D, p. D120-D122. 

Friend, P. F., 1967, The growth of the north Atlantic Ocean 

by the spreading of its floor: Polar Rec., v. 13, p. 579-

588. 

Gabrielse, Hubert, 1967, Tectonic evolution of the northern 

Canadian Cordillera: Canadian Jour. Earth Sci., v. 4, 

no. 2, p. 271-298. 

Gabrielse, Hubert, and Wheeler, J. 0., 1961, Tectonic framework of southern Yukon and northwestern British Columbia: Canada Geol. Survey Paper 60-24, 37 p. 

Gates, G. 0., and Gryc, George, 1963, Structure and tectonic 

history of Alaska, in Childs, 0. E., and Beebe, B. W., 

eds., The backbone of the Americas-tectonic history 

from pole to pole, a symposium: Am. Assoc. Petroleum 

Geologists Mem. 2, p. 264-277. 

Gnibidenko, G. S., 1969, Metamor:fi.cheskie kompleksy v 

stryktyrakh severozapadnogo sektora tikhookeanskogo 

poyasa [Metamorphic complexes in the structures of the 

northwestern sector of the circumpacific belt]: Akad. 

Nauk, SSSR Sibersk. Otdeleniye, Nauka, Moscow, 134 p. 

Grantz, Arthur, 1966, Strike-slip faults in Alaska: U.S. Geol. 

Survey open-file report, 82 p. 

--- 1968, Strike-slip faults in Alaska [abs.]: Geol. Soc. 

America and Assoc. Soc. Ann. Mtg., Mexico City 1968, 

Program, p. 117. 

Grantz, Arthur, Wolf, S. C., Breslau, Lloyd, Johnson, T. C., 

and Hanna, W. F., 1970, Geology of the Chukchi Sea as 

determined by acoustic and magnetic profiling, in Adkison, W. L., and Brosge, M. M., eds., Proceedings of the 

Geological Seminar on the North Slope of Alaska: Los 

Angeles, Pacific Sec., Am. Assoc. Petroleum Geologists, 

p. F1-F28. 

Gryc, George, Dutro, J. T., Jr., Brosge, W. P., Tailleur, I. L., 

and Churkin, Michael, Jr., 1967, Devonian of Alaska, in 

Oswald, D. H., ed., International symposium on the 

Devonian system, Calgary, 1967, V. 1: Calgary, Alberta 

Soc. Petroleum Geologists, p. 703-716. 

Hanson, B. M., 1957, Middle Permian limestone on Pacific 

side of Alaska Peninsula: Am. Assoc. Petroleum Geologists Bull., v. 41, no. 10, p. 2376-2378. 

Harland, W. B., 1965, Discussion on the tectonic evolution 

of the Arctic-North Atlantic region, in A symposium on 

continental drift: Royal Soc. [London] Philos. Trans., 

Ser. A, v. 258, no. 1088, p. 59-75. 

Heezen, B. C., and Tharp, Marie, 1965, Tectonic fabric of the 

Atlantic and Indian Oceans and continental drift: Royal 

Soc. [London] Philos. Trans., Ser. A, v. 258, no. 1988, 

p. 90;_106. 

Hoare, J. M., 1961, Geology and tectonic setting of lower 

Kuskokwim-Bristol Bay region, Alaska: Am. Assoc. 

Petroleum Geologists Bull., v. 45, no. 5, p. 594-611. 

Hoare, J. M., and Coonrad, W. L., 1961, Geologic map of 

Goodnews quadrangle, Alaska: U.S. Geol. Survey Misc. 

Geol. Inv. Map I-339, scale 1:250,000. 

Holmes, M. L., Creager, J. S., and McManus, D. A., 1968, 

Structure and history of the Chukchi basin [abs.]: Geol. 

Soc. America and Assoc. Socs. Ann. Mtg., Mexico City 

1968, p. 141. 

Hopkins, D. M., ed., 1967, Bering land bridge: Stanford, 

Calif., Stanford Univ. Press, 495 p. 

Hunkins, Kenneth, Herron, Thomas, Kutschale, Henry, and 

Peter, George, 1962, Geophysical studies of the Chukchi 

cap, Arctic Ocean: Jour. Geophys. Research, v. 67, no. 1, 

p. 235-247. 

Irwin, W. P., 1966, Geology of the Klamath Mountains 

province, in Bailey, E. H., ed., Geology of northern California: California Div. Mines and Geology Bull. 190, 

p. 19-38. 

-< 
• 

• 

.. 

REFERENCES CITED 59 

Jackson, D. E., and Lenz, A. C., 1962, Zonation of Ordovician 

and Silurian graptolites of northern Yukon, Canada: 

Am. Assoc. Petroleum Geologists Bull., v. 46, no. 1, 

p. 30-45. 

Jeletzky, J. A., 1962, Pre-Cretaceous Richardson Mountains 

trough-its place in the tectonic framework of Arctic 

Canada and its bearing on some geosynclinal concepts: 

Royal Soc. Canada Trans., 3d ser., v. 56, sec. 3, pt. 1, 

p. 55-84. 

Johnson, G. L., and Heezen, B. C., 1967, Morphology and 

evolution of the Norwegian-Greenland Sea: Deep-Sea 

Research, v. 14, p. 755-771. 

Kay, Marshall, 1947, North American geosynclines: Geol. 

Soc. America Mem. 48, 143 p. 

Kindle, E. M., 1908, Geologic reconnaissance of the Porcupine 

Valley, Alaska: Geol. Soc. America Bull., v. 19, p. 315-

338. 

King, P. B., compiler, 1969, Tectonic map of North America: 

U.S. Geol. Survey, scale 1:5,000,000. 

Kirk, Edwin, 1918, Paleozoic glaciation in southeastern 

Alaska: Am. Jour. Sci., 4th Sec., v. 46, p. 511-515. 

--- 1927, Pycnodesma, a new molluscan genus from the 

Silurian of Alaska: U.S. Natl. Mus. Proc., v. 71, art. 20, 

9 p. 

Kirk, Edwin, and Amsden, T. W., 1952, Upper Silurian 

brachiopods from southeastern Alaska: U.S. Geol. Survey Prof. Paper 233-C, p. 53-66. 

Kobayashi, Teiichi, 1935, The Briscoia fauna, of the late 

Upper Cambrian in Alaska, with descriptions of a few 

Upper Cambrian trilobites from Montana and Nevada: 

Japanese Jour. Geology and Geography, v. 12, nos. 3-4, 

p. 39-57. 

Krasniy, L. I., ed., 1966, Geologicheskoe stroenie Severozapadnoi chasti tikhookeanskogo podvizhnogo poyasa 

[Geological structure of the northwestern part of the 

Pacific mobile belt]: Ministerstvo geologii SSSR, Vses. 

N auchino-issled. Geol. Inst., Nedra, Moscow, 516 p. 

Lanphere, M. A., 1965, Age of Ordovician and Devonian 

mafic rocks in northern Alaska, in Geological Survey 

research 1965: U.S. Geol. Survey Prof. Paper 525-A, 

p. A101-A102. 

Lanphere, M. A., Loney, R. A., and Brew, D. A., 1965, 

Potassium-argon ages of some plutonic rocks, Tenakee 

area, Chichagof Island, southeastern Alaska, in Geological Survey research 1965: U.S. Geol. Survey Prof. 

Paper 525-B, p. Bl08-Blll. 

Lanphere, M. A., MacKevett, E. M., Jr., and Stern, T. W., 

~ 1964, Potassium-argon and lead-alpha ages of plutonic 

rocks, Bokan Mountain area, Alaska: Science, v. 145, 

no. 3633, p. 705-707. 

Larson, R., Menard, H. W., and Smith, S., 1968, Gulf of 

California: a result of ocean floor spreading and transform faulting: Science, v. 161, p. 781-784 . 

Lathram, E. H., 1964, Apparent right-lateral separation on 

Chatham Strait fault, southeastern Alaska: Geol. Soc. 

America Bull., v. 75, no. 3, p. 249-251. 

--- 1965, Preliminary geologic map of northern Alaska: 

U.S. Geol. Survey open-file map, scale 1:1,000,000. 

Lathram, E. H., Loney, R. A., Condon, W. H., and Berg, 

H. C., 1959, Progress map of the geology of the Juneau 

quadrangle, Alaska: U.S. Geol. Survey Misc. Geol. Irtv. 

Map 1-303, scale 1:250,000. 

Lazareva, A. P.,. and Misharina, L. A., 1965, Stresses in 

earthquake. foci in the Arctic seismic belt: Akad. Nauk 

SSSR Isv., Physics of the Solid Earth (in translation) 

1965, no. 2, p. 84-87. 

Le Pichon, Xavier, 1968, Sea-floor spreading and continental 

drift: Jour. Geophys. Research, v. 73, no. 12, p. 3661-

3697. 

Loney, R. A., 1964, Stratigraphy and petrography of the 

Pybus-Gambier area, Admiralty Island, Alaska: U.S. 

Geol. Survey Bull. 1178, 103 p. 

Loney, R. A., Berg, H. C., Pomeroy, J. S., and Brew, D. A., 

1963, Reconnaisance geologic map of Chichagof Island 

and northwestern Baranof Island, Alaska: U.S. Geol. 

Survey Misc. Geol. Inv. Map 1-388, with text, scale 

1:250,000. 

Loney, R. A., Brew, D. A., and Lanphere, M. A., 1967, PostPaleozoic radiometric ages and their relevance to fault 

movements, northern southeastern Alaska: Geol. Soc. 

America Bull., v. 78, p. 511-526. 

Loney, R. A., Condon, W. H., and Dutro, J. T., Jr., 1963, 

Geology of the Freshwater Bay area, Chichagof Island, 

Alaska: U.S. Geol. Survey Bull. 1108-C, p. C1-C54. 

Mamet, B. L., and Skipp, Betty, 1972, Preliminary correlations of Lower Carboniferous strata in North American 

Cordillera: Cong. Carboniferous Stratigraphy and Geology, 6th, Sheffield, England 1967, Proc. (in press). 

Martin, L. J., 1961, Tectonic framework of northern Canada, 

in Raasch, G. 0., ed., Geology of the Arctic, V. 1: 

Toronto, Ontario, Univ. Toronto Press, p. 442-457. 

Mendenhall, W. C., 1905, Geology of the central Copper 

River region, Alaska: U.S. Geol. Survey Prof. Paper 41, 

133 p. 

Mertie, J. B., Jr., 1930a, Geology of the Eagle-Circle district, 

Alaska: U.S. Geol. Survey Bull. 816, 168 p. 

--- 1930b, Mountain building in Alaska: Am. Jour. Sci., 

5th ser., v. 20, p. 101-124. 

--- 1933, The Tatonduk-Nation district: U.S. Geol. Survey Bull. 836-E, p. 347-443. 

--- 1937a, The Kaiyuh Hills: U.S. Geol. Survey Bull. 

868-D, p. 145-178: 

---1937b, The Yukon-Tanana region, Alaska: U.S. Geol. 

Survey Bull. 872, 276 p. 

--- 1938, The Nushagak district, Alaska: U.S. Geol. 

Bull. 903, 96 p. 

Miller, T. P.; 1972, Potassium-rich alkaline intrusive rocks of 

western Alaska: Geol. Soc. America Bull., v. 83, p. 

2111-2128. 

Moffit, F. H., 1913, Geology of the Nome and Grand Central 

quadrangles, Alaska: U.S. Geol. Survey Bull. 533, 140 p. 

--- 1938, Geology of the Chitina Valley and adjacent 

area, Alaska: U.S. Geol. Survey Bull. 894, 137 p. 

--- 1954, Geology of the eastern part of the Alaska Range 

and adjacent area: U.S. Geol. Survey Bull. 989-D, p. 

63-218. 

Morgan, W. J., 1968, Rises, trenches, great faults and crustal 

blocks: Jour. Geophys. Research, v. 73, no. 6, 1959-1982. 
60 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Muffler, L. J. P., 1967, Stratigraphy of the Keku Islets and 

neighboring parts of Kuiu and Kupreanof Islands, 

southeastern Alaska: U.S. Geol. Survey Bull. 1241-C, 

p. C1-C52. 

Nikolaevskiy, A. A., 1964, Sovremyenyi relef poverkhonsti 

mohorovichicha po geofisicheskim dannym [Present-day 

relief along the Mohorovicic discontinuity based on geophysical data], in Tektonika i glubinnoe stroenie severovostoka SSSR: Akad. Nauk SSSR Sibirsk. Otdeleniye 

Severo-Vostoch. Kompleks. N auchno-Issled. Inst. Trudy, 

no. 11, p. 131-149. 

N orford, B. S., 1964, Reconnaissance of the Ordovician and 

Silurian rocks of northern Yukon Territory: Canada 

Geol. Survey Paper 63-39, 139 p. 

Obradovich, J. D., and Peterman, Z. E., 1968, Geochronology 

of the Belt Series, Montana: Canadian Jour. Earth Sci., 

v. 5, p. 737-747. 

Oliver, J. E., Ewing, W. M., and Press, Frank, 1955, Crustal 

structure of the Arctic regions from the Ig phase : Geol. 

Soc. America Bull., v. 66, no. 9, p. 1063-1074. 

Ostenso, N. A., 1968a, Geophysical studies in the Greenland 

Sea: Geol. Soc. America Bull., v. 79, no. 1, p. 107-132. 

---1968b, A gravity survey of the Chukchi Sea region, 

and its bearing on westward extension of structures in 

northern Alaska: Geol. Soc. America Bull., v. 79, p. 

241-254. 

Ovenshine, A. T., Eberlein, G. D., and Churkin, Michael, Jr., 

1969, Paleotectonic significance of Silurian-Devonian 

clastic wedge, southeastern Alaska [abs.]: Geol. Soc. 

America, Cordilleran Sec., Program, p. 50. 

Ovenshine, A. T., and Webster, G. D., 1970, Age and stratigraphy of the Heceta Limestone in northern Sea Otter 

Sound, southeastern Alaska, in Geological Survey research 1970: U.S. Geol. Survey Prof. Paper 700-C, p. 

C170-C174. 

Palmer, A. R., 1968, Cambrian trilobites of east-central 

Alaska: U.S. Geol. Survey Prof. Paper 559-B, p. B1-

B115. 

Patton, W. W., Jr., 1957, A new upper Paleozoic formation, 

central Brooks Range, Alaska: U.S. Geol. Survey Prof. 

Paper 303-B, p. 41-45. 

Patton, W. W., Jr., and Dutro, J. T., Jr., 1969, Preliminary 

report on the Paleozoic and Mesozoic sedimentary sequence on St. Lawrence Island, Alaska: U.S. Geol. Survey Prof. Paper 650-D, p. D138-D143. 

Patton, W. W., Jr., and Hoare, J. M., 1968, The Kaltag fault, 

west-central Alaska, in Geological Survey research 1968: 

U.S. Geol. Survey Prof. Paper 600-D, p. D147-D153. 

Patton, W. W., Jr., and Tailleur, I. L., 1964, Geology of the 

Killik-Itkillik region, Alaska: U.S. Geol. Survey Prof. 

Paper 303-G, p. 409-500. 

Payne, T. G., 1955, compiler, Mesozoic and Cenozoic tectonic 

elements of Alaska: U.S. Geol. Survey Misc. Geol. Inv. 

Map I-84, scale 1:5,000,000. 

Payne, T. G., and others, 1951, Geology of the Arctic slope of 

Alaska: U.S. Geol. Survey Oil and Gas Inv. Map OM126, scale 1:1,000,000 [1952]. 

Peive, A. V., 1969, Okeanicheskaya kora geologicheskogo proshologo [Oceanic crust in the geologic past] : Geotektonika, no. 4, p. 5-23. 

Petocz, R. G., 1970, Biostratigraphy and Lower Permian 

fusulinidae of . the upper Delta River area, east-central 

Alaska Range: Geol. Soc. America Spec. Paper 130, 94 p. 

Pewe, T. L., Wahrhaftig, Clyde, and Weber, F. R., 1966, 

Geologic map of the Fairbanks quadrangle, Alaska: U.S. 

Geol. Survey Misc. Geol. Inv. Map I-455, scale 1:250,000. 

Pitman, W. C., III, and Hayes, D. E., 1968, Sea-floor spreading in the Gulf of Alaska: Jour. Geophys. Research, v. 

73,no. 20,p. 6571-6580. 

Plafker, George, 1969, Tectonics of the March 27, 1964, 

Alaska earthquake: U.S. Geol. Survey Prof. Paper 543-I, 

74 p. 

Porter, S. C., 1966, Stratigraphy and deformation of Paleozoic section at Anaktuvuk Pass, central Brooks Range, 

Alaska: Am. Assoc. Petroleum Geologists Bull., v. 50, p. 

952-980. 

Reed, B. L., 1968, Geology of the Lake Peters area, northeastern Brooks Range, Alaska: U.S. Geol. Survey Bull. 

1236, 132 p. 

Reed, B. L., and Lanphere, M. A., 1969, Age and chemistry 

of Mesozoic and Tertiary plutonic rocks in south-central 

Alaska: Geol. Soc. America Bull., v. 80, p. 23-44. 

Reiser, H. N., 1970, Northeastern Brooks Range-a surface 

expression of the Prudhoe Bay section, in Adkison, W. L., 

and Brosg.e, M. M., eds., Proceedings of the Geological 

Seminar on the North Slope of Alaska: Los Angeles, 

Pacific Sec., Am. Assoc. Petroleum Geologists, p. K1-

K10. 

Rezanov, I. A., 1964, Voprosy noveishei tektoniki SeveroVostoka SSSR [Questions of the modern tectonics of 

North-East U.S.S.R.]: Akad. Nauk, SSSR, Moscow, 148 p. 

Rickwood, F. K., 1970, The Prudhoe Bay field, in Adkison, 

W. L., and Brosge, M. M., eds., Proceedings of the Geological Seminar on the North Slope of Alaska: Los 

Angeles, Pacific Sec., Am. Assoc. Petroleum Geologists, 

p. L1-L11. 

Roberts, R. J., Hotz, P. E., Gilluly, James, and Ferguson, 

H. G., 1958, Paleozoic rocks of north-central Nevada: 

Am. Assoc. Petroleum Geologists Bull., v. 42, no. 12, p. 

2813-2857. 

Roddick, J. A., 1967, Tintina Trench: Jour. Geology, v. 75, 

no. 1, p. 23-32. 

Ross, C. P., 1933, Mineral deposits near the West Fork of 

the Chulitna River, Alaska: U.S. Geol. Survey Bull. 

849-E, p. 289-333. 

Rossman, D. L., 1963, Geology of the eastern part of the 

Mount Fairweather quadrangle, Glacier Bay, Alaska: 

U.S. Geol. Survey Bull. 1121-K, p. Kl-K57. 

Rowett, C. L., 1969, Upper Paleozoic stratigraphy and corals 

from east-central Alaska Range, Alaska: Arctic Inst. 

North America Tech. Paper no. 23, 120 p. 

Sable, E. G., 1965, Geology of the Romanzof Mountains, 

Brooks Range, northeastern Alaska: U.S. Geol. Survey 

open-file report, 218 p. 

Sable, E. G., and Dutro, J. T., Jr., 1961, New Devonian and 

Mississippian formations in De Long Mountains, northern Alaska: Am. Assoc. Petroleum Geologists Bull., v. 

45, no. 5, p. 585-593. 

Sainsbury, C. L., 1961, Geology of part of the Craig C-2 

quadrangle and adjoining areas, Prince of Wales Island, 

~· 

_,-
REFERENCES CITED 61 

southeastern Alaska: U.S. Geol. Survey Bull. 1058-H, 

p. 299-362. 

---1965, Previously undescribed Middle ( ?) Ordovician, 

Devonian ( ?) , and Cretaceous ( ?) rocks, White Mountain 

area, near McGrath, Alaska, in Geological Survey research 1965: U.S. Geol. Survey Prof. Paper 525-C, p. 

C91-C95. 

---1969a, Geology and ore deposits of the central York 

Mountains, western Seward Peninsula, Alaska: U.S. 

Geol. Survey Bull. 1287, 101 p. 

---1969b, The A. J. Collier thrust belt of the Seward 

Peninsula, Alaska: Geol. Soc. America Bull., v. 80, p. 

2595-2596. 

Sainsbury, C. L., Dutro, J. T., Jr., and Churkin, Michael, Jr., 

1971, The Ordovician-Silurian boundary in 'the York 

Mountains, western Seward Peninsula, Alaska, in U.S. 

Geological Survey research 1971: U.S. Geol. Survey 

Prof. Paper 750-C, p. C52-C57. 

St. Amand, Pierre, 1957, Geological and geophysical synthesis 

of the tectonics of portions of British Columbia, the 

Yukon Territory, and Alaska: Geol. Soc. America Bull., 

v. 68,no. 10,p. 1343-1370. 

Scheidegger, A. E., 1966, Tectonics of the Arctic seismic belt 

in the light of fault-plane solutions of earthquakes: 

Seismol. Soc. America Bull., v. 56, p. 241-245. 

Scholl, D. W., Buffington, E. C., and Hopkins, D. M., 1966, 

Exposure of basement rock on the continental slope of 

the Bering Sea: Science, v. 153, p. 992-994. 

Scholl, D. W., Greene, H. G., Marlow, M. S., 1970, Eocene 

age of the Adak "Paleozoic ( ?) " rocks, Aleutian Islands, 

Alaska: Geol. Soc. America Bull., v. 81, p. 3583-3592. 

Scholl, D. W., Marlow, M. S., Creager, J. S., Holmes, M. L., 

Wolf, S. C., and Cooper, A. K., 1970, A search for the 

seaward extension of the Kaltag fault beneath the Bering 

Sea: Geol. Soc. America, Abstracts with Programs, v. 2, 

p. 141-142. 

Schuchert, Charles, 1910, Paleogeography of North America: 

Geol. Soc. America Bull., v. 20, p. 427-606. 

Shatskfy, N. S., 1935, 0 tektonike Arktiki [On the tectonics 

of the Arctic], in U.S.S.R. Glavnoe upravlenie Severnogo 

morskogo puti, Geologo-Razvedochnaia Konferentisiia, 

1st, Moskva, 1935: Geologiia i poleznye iskopaemye 

Sovera SSSR Trudy, v. 1, Geologiia, p. 149-168. 

Smith, J. G., and MacKevett, E. M., Jr., 1970, Skolai Group 

in the McCarthy B-4, C-4, and C-5 quadrangles, Wrangell Mountains, Alaska: U.S. Geol. Survey Bull. 1274-Q, 

26 p. 

Smith, P. S., 1939, Areal geology of Alaska: U.S. Geol. Survey Prof. Paper 192, 100 p. 

Smith, P. S., and Eakin, H. M., 1911, A geologic reconnaissance in southeastern Seward Peninsula and the Norton' 

Bay-Nulato region, Alaska: U.S. Geol. Survey Bull. 449, 

146 p. 

Spurr, J. E., 1898, Geology of the Yukon gold district, 

Alaska: U.S. Geol. Survey 18th Ann. Rept., pt. 3, p. 

87-392. 

Steidtmann, Edward, and Cathcart, S. H., 1922, Geology of 

the York tin deposits, Alaska: U.S. Geol. Survey Bull. 

733, 130 p. 

Stoneley, Robert, 1967, The structural development of the 

Gulf of Alaska sedimentary province in southern Alaska: 

Geol. Soc. London Quart. Jour., v. 123, no. 489, pt. 1, p. 

25-57. 

Sykes, L. R., 1965, The seismicity of the Arctic: Seismol. Soc. 

America Bull., v. 55, no. 2, p. 501-518. 

Tailleur, I. L., 1969, Speculations on North Slope geology: 

Oil and Gas Jour., v. 67, no. 38, p. 215-226. 

Tailleur, I. L., and Brosge, W. P., 1970, Tectonic history of 

northern Alaska, in Adkison, W. L., and Brosge, M. M., 

Proceedings of the Geological Seminar on the North 

Slope of Alaska: Los Angeles, Pacific Sec., Am. Assoc. 

Petroleum Geologists, p. E1-E19. 

Tailleur, I. L., Brosge, W. P., and R~iser, H. N., 1967, Palinspastic analysis of Devonian rocks in northwestern 

Alaska, in Oswald, D. H., ed., International symposium 

on the Devonian system, Calgary, 1967, V. 2: Calgary, 

Alberta Soc. Petroleum Geologists, p. 1345-1361. 

Tailleur, I. L., Kent, B. H., Jr., and Reiser, H. N., 1966, 

Outcrop/geologic maps of the Nuka-Etivluk region, 

northern Alaska: U.S. Geol. Survey open-file maps, scale 

1:63,360. 

Tailleur, I. L., and Sable, E. G., 1963, Nuka Formation of 

late Mississippian to late Permian age, new formation 

in northern Alaska: Am. Assoc. Petroleum Geologists 

Bull., v. 47, no. 4, p. 632-642. 

Tailleur, I. L., and Snelson, Sigmund, 1968, Large-scale 

thrusting in northwestern Alaska possibly related to rifting of the Arctic Ocean [abs.]: Geol. Soc. America and 

Assoc. Socs. Ann. Mtg., Tucson, Ariz., 1968, Program, 

p. 120. 

Thorsteinsson, Raymond, and Tozer, E. T., 1960, Summary 

account of structural history of the Canadian Arctic 

Archipelago since Precambrian time: Canada Geol. Survey Paper 60-7, 25 p. 

Tilman, S. M., 1962, Tektonika i istoriya razvitiya severovostochnogo Prikolym'ya [Tectonics and the history of 

the development of the region northeast of Kolyma]: 

Trudy SVKNII (Sev. Vost. Komplek. Nauchno-Issled. 

Inst.), Magadan, No. 1, 190 p. 

Trettin, H. P., 1967, Devonian of the Franklinian eugeosyncline, in Oswald, D. H., ed., International symposium on 

the Devonian system, Calgary, 1967, V. 1: Calgary, Alberta Soc. Petroleum Geologists, p. 693-701. 

---1969, A Paleozoic-Tertiary fold belt in northernmost 

Ellesmere Island aligned with the Lomonosov Ridge: 

Geol. Soc. America Bull., v. 80, p. 143-148. 

Twenhofel, W. S., and Sainsbury, C. L., 1958, Fault patterns 

in southeastern Alaska: Geol. Soc. America Bull., v. 69, 

no. 11, p. 1431-1442. 

Vine, F. J., 1966, Spreading of the ocean floor-new evidence: 

Science, v. 154, p. 1405-1415. 

Vogt, P. R., and Ostenso, N. A., 1970, Magnetic and gravity 

·.profiles across the Alpha cordillera and their relation to 

arctic sea-floor spreading: Jour. Geophys. Research, v. 

75,no. 26,p. 4925-4937. 

Vogt, P. R., Ostenso, N. A., and Johnson, G. L., 1970, Magnetic and bathymetric data bearing on sea-floor spreading north of Iceland: Jour. Geophys. Research, v. 75, p. 

903-920. 

Wahrhaftig, Clyde, 1968, Schists of the central Alaska 

Range: U.S. Geol. Survey Bull. 1254-E, p. E1-E22. 
62 PALEOZOIC AND PRECAMBRIAN ROCKS AND ALASKA'S STRUCTURAL EVOLUTION 

Wanless, R. D., Stevens, R. D., Lachance, G. R., and Rimsaite, R. Y. H., 1965, Age determinations and geologic 

studies, Part 1, Isotopic ages, Report 5: Canada Geol. 

Survey Paper 64-17, 126 p. 

Wasserburg, G. J., Eberlein, G. D., and Lanphere, M. A., 

1963, Age of the Birch Creek Schist and some batholithic 

intrusions in Alaska [abs.]: Geol. Soc. America Spec. 

Paper 73, p. 258-259. 

Wilson, J. T., 1963, Hypothesis of earth's behavior: Nature, 

v. 198, p. 925-929. 

Wold, R. J., and Ostenso, N. A., 1972, Aeromagnetic evidence 

for origin of Arctic Ocean basin: Internat. Symposium 

Arctic Geology, 2d, Pacific Sec., Am. Assoc. Petroleum 

Geologists (in press) . 

Wollard, G. P., Ostenso, N. A., Thiel, E., and Bonini, W. E., 

1960, Gravity anomalies, crustal structure, and geology 

in Alaska: Jour. Geophys. Research, v. 65, no. 3, p. 1021-

1037. 

Yanshin, A. L., ed., 1966, Tectonic map of Eurasia: Acad. 

Sci. USSR, Geol. lnst., scale 1:5,000,000. 

Yates, R. G., Becraft, G. E., Campbell, A. B., and Pearson, 

R. C., 1966, Tectonic framework of northeastern Washington, northern Idaho, and northwestern Montana, in 

A symposium on the tectonic history and mineral deposits of the western Cordillera, Vancouver, B. C., 1964: 

Canadian Inst. Mining and Metallurgy, Spec. V. 8, p. 

47-59. 

Ziegler, P. A., 1969, The development of sedimentary basins 

in western and Arctic Canada: Alberta, Canada, Alberta 

Soc. Petroleum Geologists, 89 p. 

-. 
• 

Page 

A 

Acknowledgements ----------------- 4 

Adak Island ----------------------- 32 

Adams Argillite ------------------- 10 

Alaska Range, Cambrian rocks ------ 36 

Devonian limestone ------------- 37 

Mississippian rocks ------------- 29 

Paleozoic sedimentation --------- 37 

Pennsylvanian rocks ------------ 31 

Permian reference fossils -------- 34 

Permian rocks ----------------- 32, 34 

Aldan Shield, Siberia --------------- 6 

Aleutian volcanic arc, relati<in to 

orogeny ---------------- Alexander Archipelago --------------

Appalachian geosyncline ------------

Arctic Ocean, sea-floor spreading ----

Atlantic Ocean, sea-floor spreading ---

B 

41 

29 

39 

47 

47 

Barrow arch ---------------------- 44 

Bay of Pillars Formation ----------- 18 

Belt Supergroup ------------------ 6, 35 

Bering Shelf ---------------------- 39 

Bering Straits, sea-level changes ----- 48 

Bibliography ---------------------- 55 

Birch Creek Schist ------------ 7, 35, 44,47 

British Mountains ------------------ 38, 44 

Brooks geosyncline ----------------- 91, 55 

Brooks Range, circumarctic foldbelt -- 44 

Devonian and Mississippian rocks -- 36 

Mississippian rocks -------------

Pennsylvanian fossils -----------

Permian rocks 

tectonic events 

c 

27 

30 

35 

46 

Calico Bluff Formation ------------- 27,30 

Cambrian rocks ------------------- 10 

Canada, extension of foldbelts ------- .u 

Canada Basin ------------------ 38, 44, 55 

Canadian Arctic Islands ------------ 38 

Cape Dezhneva area, comparison 

to Seward Peninsula ----- 50 

Cape Kekurnoi area, Permian 

rocks --------------- 32, 33, 39 

Cape Prince of Wales -------------- 28 

Carboniferous rocks --------------- 21, 99 

Caryocaris ------------------------ 13 

Cascade Mountains ----------------- 36 

Cenozoic tectonic events ------------ 40 

Chatham Strait fault --------------- 47 

Cherskiy geosyncline --------------- ,.55 

Cherskiy Mountain system, U.S.S.R. ___ 52, 54 

Chichagof Island ------------------ 29 

Chitina Valley -------------------- 29 

Chugach Mountains ---------------- 29 

Chukchi Cap ---------------------- 55 

Chukotka ------------------------ 38,55 

Chukotka foldbelt, Siberia ----------- 44 

INDEX 

[Italic page numbers indicate major references) 

Page 

Chukotsk Peninsula, rocks similar to 

Seward Peninsula rocks_ 9, U, 50 

Circle ---------------------------- 34 

Circle mining district -------------- 7 

Circle Volcanics ------------------- 34, 47 

Circumarctic foldbelt -------------- 44 

Circum-Canada Basin geosyncline ----- 38 

Circumpacific foldbelt -------------- 44 

Colville basin --------------------- 41 

Conchidium ----------------------- 17 

Continental drift ------------------- 47 

Copper River valley ---------------- 34 

Cordilleran foldbelt ----------------- 44 

Cordilleran geosyncline ------------- 96, 99 

Correlation, Alaska, Canada, and 

Siberia ---------------- 47 

Craig-Klawak area ----------------- 30 

Crazy Mountains 34 

D 

Dadina Schist --------------------- 29 

Dating, isotope ----- 7, 9, U, 17, 34, 36, 44, 50 

Dave Lord Ridge ------------------ 39 

DeLong Mountains ----------------- 35 

Delta River area ------------------ 34 

Dena~i fault system --------------- 47 

Descon Formation ----------------- U 

Devonian rocks, stratigraphy -------- 18, 19 

tectonics ---------------------- 96 

E 

Eagle area, Paleozoic sedimentation 

Ellesmere Island -------------------

Eurasia Basin 

Eurasian plate 

F 

Fairbanks mmmg district -----------

Faults ----------------~---------- Foldbelts -------------------------

Ford Lake Shale ------------------

Fortymile mining district -----------

Fossil Creek Volcanics --------------

Fossils, Adak Island ---------------

Adams Argillite ----------------

Birch Creek Schist -------------

Carboniferous rocks -------------

Goodnews Bay district ----------

Jones Ridge area --------------

Karheen Formation -------------

Nahoni Range--Blackstone 

River area -------------

Neruokpuk Formation ----------

Permian reference, Alaska Range __ 

Permian rocks -----------------

Rampart Group ----------------

Road River Formation ----------

Skajit Limestone ---------------

Tindir Group ------------------

Totalanika Schist ---------------

37 

38 

52 

47 

46 

42 

27 

7 

17,46 

32 

10 

8 

29 

32 

17 

19 

19 

10 

34 

31 

34 

10 

17 

6, 7 

29 

Page 

Franklinian geosyncline ---------- 38, 50, 55 

Frazer eugeosynclinal belt ----------- 37 

G 

Gakkel Ridge 52 

Gemuk Group --------------------- 34, 41 

Geologic conditions, Mesozoic -------- 40 

Glaciation ------------------------ 36 

Glacier Bay ----------------------- 36 

Goodnews Bay district -------------- 32 

Great Basin 

H 

Heceta Limestone ------------------

Hillard Limestone -----------------

Holitna Group --------------------

Hunt Fork Sh~e ------------------

37 

18, 19 

10 

u 19,38 

Iliamna Lake-Kamishak Bay area ---- 33 

Inoceramus ----------------------- 34 

Introduction ----------------------- 2 

Isotope dating _____ 7, 9, U, 17, 34, 36, 44, 50 

J 

Jones Ridge Limestone ------------- 10 

K 

Kaltag fault ------------------- 41, 45,47 

Kamchatka ----------------------- 44 

Kanayut Formation ---------------- 19 

Karheen Formation ---------------- 19, 36 

Kayat Shale ---------------------- 27 

Keku Strait area ------------------ 29 

Kenai Peninsula ------------------- 33 

Kigluaik Group -------------------- 9 

Kigluaik Mountains ---------------- 50 

Klamath Mountains ---------------- 36, 37 

Klutina Group -------------------- 29 

Kodiak Island --------------------- 33 

Kolymski massif, Siberia --------- 50, 51, 54 

Koryak Mountains, Northeast 

U.S.S.R. ------------ 36, 44, 55 

Kuiu Island ----------------------- 31 

Kuskokwim River region ----------- 37,41 

L 

Laptev Sea 52 

Linograptus ----------------------- 19 

Lisburne Group ----------- 18, 27, 28, 30, 35 

Lithology, Tindir Group ------------ 6, 7 

Livengood Chert ------------------- 27 

Lomonosov Ridge ------------------

Lower Paleozoic rocks, sedimentation __ _ 

tectonics 

63 

52 

10 

96 
64 

Page 

M 

McCann Hill Chert 19 

Mackenzie Mountains --------------- 44 

Mankomen Formation -------------- 34 

Mankomen Lake ------------------ 34 

Marine depos1tion, Tertiary --------- 41 

Matanuska basin ------------------ 41 

Mesozoic tectonic events ------------- 40 

Metamorphism, Paleozoic rocks ------ 41 

Mid-Atlantic ridge ----------------- 47,52 

Mohorovicic discontinuity ----------- 50 

Monograptus nilssoni --------------- 19 

yukonensis -------------------- 19 

Nahoni Mountains 

Nansen Cordillera 

N 

44 

52 

Nation River area ----------------- 34 

Nation River Formation ------ 19, 26, 27, 34 

Neuokpuk Formation ------------- 9, 1~, 38 

Nikolai Greenstone ----------------- 34 

North American plate -------------- 47,52 

Northeast U.S.S.R., correlation of 

Paleozoic rocks --------- 50 

Norton Sound --------------------- 28, 29 

Nuka Ridge area ------------------ 35 

0 

Ogilvie Mountains ----------------- 10, 44 

Oldhamia ----------------------- 9, 10, 27 

Ordovician rocks ------------------ 10 

Orogeny, Canada Basin ------------- 56 

Mesozoic ---------------------- 41 

Siberia ----------------------- 52, 56 

p 

Pacific Basin 

Paleozoic glaciation . ----------------

Paleozoic rocks, correlation, edges of 

Arctic and Pacific Basins -

Lower, sedimentation, tectonic 

framework -------------

stratigraphy ---------------

structural features --------------

Upper, sedimentation, tectonic 

framework -------------

stratigraphy ---------------

Permian reference fossils -----------

Permian rocks --------------------

Plate tectonics --------------------

36 

36 

47 

96 

10 

4B 

99. 

19 

34 

91 

47 

INDEX 

Porcupine lineament ---------------

Porcupine River section, Tindir Group __ 

Porcupine-Yukon Rivers area, 

Page 

45 

Mississippian rocks ------ 27 

Port Clarence Limestone ------------ 14 

Port Refugio Formation ------------ 19 

Precambrian rocks, stratigraphy ----- 4 

tectonic framework ------------- 95 

Prince of Wales Island ------------- 31, 36 

Prudhoe Bay oil field --------------- 35, 44 

R 

Rainbow Mountain area ------------ 31 

Rainbow Mountain-Delta River area__ 34 

Rampart Group ------------------- 34 

Rapitan Formation ---------------- 6 

Rapitan Group -------------------- 36 

Richardson basin ------------------- 97 

Richardson Mountains ----------- 37, 44, 45 

Road River Formation ----------- 10, 18, 37 

Rocky Mountain Trench ------------ 46 

Rotation, North American plate ------ 52 

s 

Sadko trough 52 

Sadlerochit Formation -------------- 35 

Sadlerochit Mountains -------------- 38 

St. Lawrence Island ------------- 28, 39, 50 

San Juan Island, Wash ------------ 36 

Sea-fioor spreading ----------------- 47, 55 

Section, Tindir Group -------------- 6, 7 

Sedimentation, Lower Paleozoic ------ 10, 96 

Precambrian ------------------- 95 

Upper Paleozoic --------------- 19, 99 

Seward Peninsula, basement rocks ___ 44 

Cambrian rocks ---------------- 36 

carbonate rocks ----------------

comparison to Cape Dezhneva area 

oldest rocks -------------------

Permian rocks 

tectonic events 

Shublik Formation 

Shublik Mountains 

37 

50 

9 

31 

46 

35 

38 

Siberian platform ------------------ 54 

. Siksikpuk Formation --------------- 35 

Silurian rocks --------------------- 14 

Skajit Limestone ------------------ 17, 37 

Skolai Group --------------------- 33 

Step Conglomerate ----------------- 34 

Stratigraphic belts ----------------- 41 

Stratigraphy ---------------------- 4, 95 

Strelna Formation ----------------- 29, 33 

Stringocephalus --------------------

Structural features -----------------

Suemez-Shelikof Island area ---------

Sverdrup Basin -------------------

Syringopora 

T 

Tahkandit Limestone 

Page 

17 

42 

30 

50 

29 

34 

Taimyr Peninsula ------------------ 52 

Tectonics ---------------------- 95, 40, 47 

Tetradium ------------------------ 13 

Tidal Formation ------------------ 18 

Tindir Group, correlation with other 

rocks ------------------ 35 

Porcupine River section --------- 7 

stratigraphy ------------------- 4 

Yukon River section ------------ 6 

Tintina fault zone ----------------- 41, 46 

To!ovana Limestone ---------------- 17,46 

Topagorup test well --------------- 19 

Totatlanika Schist ----------------- 29 

Trenches 

u 

Upper Paleozoic rocks, sedimentation __ 

tectonics 

v 

46 

19 

99 

Verkhoyansk Mountains --------- 52, 54, 55 

w 

Wadleigh Limestone 

Wales Group ----------------------

Wernecke Mountains ---------------

White Mountains ------------------

Willoughby Limestone --------------

19 

9 

44 

46 

36 

Windermere Series ----------------- 35 

Wrangell Island ---------------- 38, 48, 50 

Wrangell Mountains 29, 31, 33, 39, 41 

y 

Yakutia -------------------------- 52,55 

Yukon Flats ---------------------- 34 

Yukon-Kuskokwim area ---------- 28, 29, 32 

Yukon-Porcupine Rivers area ------- 39, 50 

Yukon River area ----------------- 30 

Yukon sh~f ---------------------- 9~45 Yukon-Tanana Upland -------- 27, 39, 41,44 

U. S. GOVERNMENT PIHNTING OFFICE : 1973 0 - 490-094.