UNITED STATES DEPARTi4ENT OF THE INTERIOR
GEOLOGICAL SURVEY
Geology and Physiography o f the Continental Margin
North of A l a s k a and Implications for t h e
Origin of t h e Canada Basin
BY
Arthur Grantz and Stephen Eittreim
U.S. Geological Survey, Menlo Park, Cal ifornia 94025
Open-File Report 79-238
1979
T h i s r e p o r t i s preliminary and has not been edited or revi er:ied fc;r co:s Formi ty w i t h Geological Survey stir:cards and nonlencl ature
TABLE OF CONTENTS Page
Abs t rac t ............................................................ 1
Physiography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Sea v a l l e y s and submarine canyons ............................ 6
Cont inen ta l she1 f break and Beaufort Ramp .................... '3
Alaska Cont inen ta l Slope and Northwind Escarpment ------------ 11
Canada Cont inen ta l Rise and Abyssal P l a i n and Alaska
Cont inen ta l R ise ........................................... Regional s t r a t i g r a p h y and t e c t o n i c s e t t i n g ........................
F r a n k l i n i a n sequence and Precambrian rocks ------------------- A r c t i c p l a t f o rm and E l lesmer ian sequence ..................... C o l v i l l e foredeep and Brookian sequence ...................... Hope bas in sequence ..........................................
Geology ........................................................... S t r u c t u r a l prov inces ......................................... Barrow arch ..................................................
A r c t i c p l a t f o r m and C o l v i l l e foredeep ........................ Herald and \ rangel arches .................................... Hera ld and Wrangef f a u l t zones ............................... Chukchi syn tax i s ............................................. Hope bas in ...................................................
Geol ogy -- Continued
North Chukchi bas in ......................................... Western Beaufort Shelf sedimentary pr ism .................... D i a p i r i c f o l d s beneath the con t i nen ta l r i s e ----------------- S o l i d gas hydrate ........................................... Canada Basin ................................................. Segmentation o f the Alaskan con t i nen ta l margin --------------
Summary o f t e c t o n i c i m p l i c a t i o n s and c o n s t r a i n t s ----------------- References c i t e d ................................................. I l l u s t r a t i o n s .................................................... Table of con ten ts ................................................
Page
3 0
3 1
38
3 9
40
42
44
4 8
62
6 5
F igu re 1.
ILLUSTRATIONS
Bathymetry and p lace names i n t h e Beaufor t and Chukchi Seas and
v i c i n i t y and l o c a t i o n of se ismic p r o f i l e s i n F igures 10, 11, 13,
and 17.
Phys iographic fea tu res of t h e Beaufor t and Chukchi Seas. Ex ten t o f
g l a c i a t i o n f rom Alaska G l a c i a l Map Cornmi t t e e (1965), Geolog ica l
Survey of Canada (1968), Nelson and Hopkins (1972), and D. M.
Hopkins ( o r a l communication, 1978).
Pos t -T r i ass i c t e c t o n i c p rov inces and sedimentary pr isms o f t h e
Beaufor t and Chukchi Seas and v i c i n i t y .
Phanerozoic s t r a t i g r a p h y o f t h e western No r th Slope o f Alaska.
Phanerozoic s t r a t i g r a p h y of t he eas te rn Nor th Slope o f Alaska.
Geologic s t r u c t u r e and th ickness of sedimentary rock beneath t h e
Western Beau fo r t She l f and southern Canada Basin. See F i g u r e 6
f o r exp lana t ion .
Exp lana t ion f o r geo log i c s t r u c t u r e maps, F igures 5, 8, and 9.
Seismic r e f l e c t i o n s t r u c t u r e and f r e e - a i r g r a v i t y anomalies near
t h e change i n t r e n d of t h e Barrow a rch a t 720 N. l a t , 1600 W. long.
Geologic s t r u c t u r e and t h i ckness of sedimentary rock beneath t h e
n o r t h e r n Chukchi Sea. See F igu re 6 f o r exp lana t i on .
Geologic s t r u c t u r e and th ickness o f sedimentary r o c k beneath t h e
southern Chukchi Sea. See F igu re 6 f o r exp lana t ion .
iii
Figure 10. Geologic cross section interpreted from seismic ref1 ection data
in the eastern Chukchi Sea from the continental shelf break t o
southern Hope basin. See Figures 1 , 8, and 9 for location.
Sedimentary s t r a t a shown are Ng, Neogene(?) cl a s t i c rocks; Pg , Paleogene(?) c l a s t i c rocks; UK,Upper Cretaceous(?) marine
c l a s t i c rocks; LK,Lower Cretaceous marine and nonmarine c l a s t i c
rocks; J-M,Mi ssissippian t o Jurassic (El 1 esmerian) marine and
nonmarine c l a s t i c and carbonate rocks; E-Fr,Lower Ellesmerian or
Franklinian c l a s t i c rocks; and dK,strongly deformed Cretaceous
c l a s t i c rocks. Undifferentiated rock units are pK,pre-Cretaceous;
pM,pre-Mi ssissi ppian; PpG,Pal eozoic and (o r ) Precambrian. Seismic
CDP interval velocities in km/sec.
1 1 A , B , C Geologic interpretation of seismic sections across the North Chukchi
basin. See Figure 1 for 1 ocation. Inferred cl a s t i c sedimentary
rock units a re Q,Quaternary; Ts,Tertiary; Ng,Neogene; Pg,Paleogene;
Ks,Cretaceous; UKs,Upper Cretaceous; LK-J,Jurassic-Early Cretaceous;
pKs, pre-Cretaceous ( ? ) . Seismic sonobuoy interval velocities (Fig.
13C) in km/sec.
12 . Seismic reflection and refraction profiles across shale(?) diapir a t
730 N. l a t , 1630 W. long, North Chukchi basin.
13A,B,C Geologic interpretation of seismic sections across the Western
Beaufort Shelf (Figs. 13A-C) and a cross section near the Canning
River based on correlated t e s t wells (F ig : 1 3 D ) . See Figure 1
for location. Seismic CDP interval velocities in km/sec.
Figure 13A. Inferred c l a s t i c sedimentary rock units a re Ng,Neogene; Pg,Paleogene;
T-UK,Tertiary and (o r ) Upper Cretaceous; K-J,Cretaceous and
Jurassic , possibly only Lower Cretaceous and Jurassic.
13B. Inferred c l a s t i c sedimentary rock units a re PI-P1,Plio-Pleistocene;
Ng,Neogene; Pg,Paleogene; UKpc,Upper Cretaceous Prince Creek
Formation; UKs, Upper Cretaceous Schrader Bluff Formation: L K ~ S ,
Lower Cretaceous "Pebble Shale"; LKkrs,Lower Cretaceous Kuparuk
River Sandstone; Fr, Frank1 inian sequence.
13C. Inferred c l a s t i c sedimentary rock units a re Ng,Neogene: Pg,Paleogene;
UKs,Upper Cretaceous; LKs,Lower Cretaceous; Fr,Franklinian sequence.
130. Generalized structural cross section from Kemik gas f ie ld t o Flaxrnan
Island. Data interpreted from a compilation of geologic formations
encountered in boreholes between the Canning and Colville Rivers by
Tailleur e t a l . (1978). The control points for the cross section
(boreholes) would not suff ice t o delineate any small-scale geologic
structures that might be present.
14, Block g l ides on the Western Beaufort She1 f ,mapped from high-resol ution
seismic prof i 1 es.
15. Bedding plane s l ides on the Western Beaufort Shelf, mapped from h i g h -
resolution seismic profiles.
16. Depth of inner and outer continental shelf breaks on the Western
Beaufort Shelf.
17. Shallow structure interpreted from seismic profiles across the continental
slope in the Western Beaufort Sea where diapir ic folds are present
(Line 720) and absent (Line 748) .
Geology and Physiography of the Continental Margin
North o f Alaska and Implications for the Origin of the Canada Basin
BY
Arthur Grantz and S~ephen Eittreim
U.S. Geological Survey, Menlo Park, Ca1 ifornia
ABSTRACT
The continental margin norzh of Alaska i s of Atlantic type. I t began to
form probably in, Early Jurassic time b u t possibly in middle Early Cretaceous
time, when the oceanic Canada Basin of the Arctic Ocean i s thought t o have
opened by r i f t ing about a pole of rotation near the Mackenzie Delta. Offsets
o f the r i f t along two fracture zones are thought t o have divided t he Alaskan
margin into three sectors of contrasting structure and stratigraphy. I n the
Barter Island sector on the east and the Chukchi sector on the west the r i f t
was closer t o the present northern Alaska mainland than in the Barrow sector ,
which l i e s between them. In the Barter Island and Chukchi sectors the conti-
nental shelf i s underlain by prisms of c l a s t i c sedimentary rocks that are in-
ferred t o include thick sections of Jurassic and Neocomian (lower Lower Creta-
ceous) s t r a t a of southern provenance. In the intervening Barrow sector the
shelf i s underlain by relat ively thin sections of Jurassic and Neocomian s t r a t a
derived from northern sources that now l i e beneath the outer continental shelf.
The r i f ted continental margin i s overlain by a prograded prism of Albian
(upper Lower Cretaceous) t o Tertiary c las t i c sedimentary rocks that comprises
the continental terrace of the western Beaufort and northern Chukchi Seas. On
the south the prism i s bounded by Barrow arch, which i s a hingeline between the
northward-tilted basement surface beneath the continental shelf of the western
Beaufort Sea and the southward-tilted Arctic Platform o f northern Alaska.
The Arctic platform i s overlain by shelf c l a s t i c and carbonate s t r a t a of
Mississippi an t o Cretaceous age, and by Jurassic and Cretaceous c l a s t i c s t r a t a
of the Colville foredeep. Both the Arctic platform and Colville foredeep
sequences extend from northern Alaska beneath the northern Chukchi Sea. A t
Herald f au l t zone in the central Chukchi Sea they are overthrust by more
strongly deformed Cretaceous t o Paleozoic sedimentary rocks o f Herald arch,
which trends northwest f r o m Cape Lisburne. Hope basin, an extensional intra-
continental sedimentary basin of Tertiary age, underlies the Chukchi Sea south
of Herald arch.
SCOPE A N D ACKNOWLEDGMENTS
This paper presents an overview of the physiography and geology of the
Arctic continental margin of Alaska (Fig. 1 ) and discusses some imp1 ications
of the data for the origin o f this margin and the adjacent Canada Basin o f the
Arctic Ocean. Many of the interpretations presented are preliminary, and the
paper does not attempt a comprehensive analysis o f the features discussed.
Some de ta i l s can be found in Grantz e t a l . (1970a, 1975) and Eittreim e t a l . ( i n
press). Our data are mainly sing1 e-channel seismic reflection and sonobuoy
refraction profiles obtained between 1969 and 1973 from U.S. Coast Guard ice-
breakers and a few of the multichannel COP seismic reflection profiles obtained
from the U.S. Geological Survey R / V -- S.P. - LEE in 1977 (Grantz e t a1 . , 1970b,
1971, 1972a, b, 1974, and 1975).
We are indebted to many U.S. Geological Survey colleagues for helping
obtain the data presented, to the Coast Guard and the Naval Arctic Research
Laboratory, Barrow, Alaska for logis t ic assistance, and to David W . Scholl,
Leslie Magoon, David A . Dinter, and Irvin L. Tail leur for reviewing the manu-
sc r ip t and offering helpful suggestions. Olive T. Whitney prepared several
of the i l lustrat ions. This report has not been reviewed
2
f o r conformance t o s t r a t i g r a p h i c nomenclature used by the U.S. Geological
Survey . PHYSIOGRAPHY
Major Features
The r i m o f the A r c t i c Basin i n the western Beaufor t and Chukchi Seas (see
Fig, 2 ) cons is ts o f the narrow Western Beaufor t She l f , the broad Chukchi She l f ,
and the Chukchi Cont inenta l Borderland. These face the Canada Basin (F ig . 3 ) ,
which i s t h a t p a r t o f the deep A r c t i c Ocean basin t h a t 1 i e s between the Lomonsov
Ridge, eastern S iber ia , and North America. The con t i nen ta l s h e l f i n the western
Beaufor t and nor thern Chukchi Seas i s a subsiding, prograding te r race d issected
by submarine canyons. I n cont ras t , the con t i nen ta l she l f i n the c e n t r a l and
southern Chukchi Sea i s a submerged marine-cut p l a t f o r m eroded i n t o the North
American and Eurasian cont inents. Many o f the geologic formations and s t r u c -
tu res t h a t u n d e r l i e these shelves are coextensive w i t h formations and s t ruc tu res
i n nor thern Alaska. The ba thymet r i ca l l y complex Chukchi Cont inenta l Borderland
(F ig . 2 ) , which juts i n t o the Canada Basin, i s i n f e r r e d t o conta in fragments of
con t i nen ta l c rus t . The southern Canada Basin, which l i e s adjacent t o Alaska,
i s f l o o r e d by an abyssal p l a i n i n the west and a con t i nen ta l r i s e b u i l t ou t
from the Canadian A r c t i c Is lands and Mackenzie River Del ta i n the east .
Western Beaufor t She1 f
The r e l a t i v e l y narrow con t i nen ta l s h e l f o f the western Beaufor t Sea ex-
tends between the Mackenzie and Barrow Sea Va l ley , a d is tance o f about 700 km
(Figs. 1 and 2 ) . The s h e l f i s 70 t o 120 km wide and extends seaward w i t h a
g e n t l e g rad ien t f r om b a r r i e r i s l ands o r low b l u f f s a t the coast t o a complex
ou ter cont inenta l s h e l f break a t depths o f 200 t o 800 rn. East o f 1470 W . long
(F igs. 2 and 15) the s h e l f cons is ts o f an i nne r sec t i on w i t h a g rad ien t o f
about 1 m/km t h a t extends from shore t o a slump-controlled break in slope near
the 60-m isobath, and an outer section with a gradient of about 16 m/km that
extends from the 60-m isobath to the outer shelf break. The steeper outer
section i s here named the Baufor t Ramp.
The inner Beaufort Shelf west of the Colville River i s basically a wave-
c u t surface, a1 though predominantly fine-grained Quaternary c l a s t i c sediments
locally as much as 140 m thick have been deposited upon i t . Rocks as old as
Early Cretaceous are truncated a t the base of the Quaternary cover. East of
the Colvil l e River, transportation and deposition of c l a s t i c sediment has been
the dominant Neogene and Quaternary geologic process. Holocene sediment, dom-
inantly l u t i t e , has f i 1 led 1 ocal depressions and smoothly prograded the con-
tinental shelf seaward. Sand and gravel occur in bars near shore, and scattered
accumulations o f re1 i c t gravel are found across the enti re shelf (Barnes and
Reimnitz, 1974). Rodeick (1974) suggests that most o f the re1 i c t gravel,
which i s most abundant on the outer she l f , was derived from the underlying
Gubi k Formation (Quaternary) by erosion during the Holocene transgression.
However, the gravel must also include dropstones from ice islands (tabular
glacial icebergs from Ellesmere Island) that d r i f t across the shelf .
Local re l ie f on the Beaufort Shelf occurs a t nearshore sand bars and ice
gouges. Pleistocene glaciers (Fig. 2 ) apparently reached the she1 f only east
of Barter Island. The ice gouges are generally parallel to the coast and ex-
tend from nearshore to a t l eas t the 75 rn isobath (Reimnitz and Barnes, 1974).
Those related t o the present stand of sea level are abundant to water depths
of 30 m. The gouges are produced by grounding o f deep-draft sea-ice pressure
ridges and ice islands that are driven westward along the shelf by a wind-
driven clockwise current, the Beaufort (Pacif ic) gyre of the Canada Basin.
The deepest ice gouge measured north of Alaska i s 5.5 m (Reimnitz and Barnes,
1974), b u t most are 1 to 3 m deep.
Chukchi Shel f
The Chukchi Shel f (Fig, 2 ) l i e s between Bering S t r a i t on the south,
Barrow Sea Val ley on the east, and the longitude o f Wrangel Island (1800) on
the west. T h i s broad shelf was eroded fa r into the continent and transects
the principal mountain ranges o f northern Alaska. Its north-south and eas t -
west dimensions are both about 900 km. Although the shelf i s characterized by
low bathymetric gradients, underlying geologic control o f i t s major physio-
graphic features i s evident. Hope Sea Valley-Hera1,d Canyon, the largest sea
valley system on the shelf , overlies Tertiary basins, and Herald and Hanna
, Shoals overlie structural highs that expose Paleozoic and Mesozoic rocks a t
the seabed. The shallow southern Chukchi Sea and Kotzebue Sound owe their
shape and extent to Quaternary marine abrasion in the so f t Tertiary s t r a t a of
Hope basin (Fig. 3 ) .
Bottom sediment i n the Chukchi Sea i s dominantly s i l t and very f ine sand
although sand and gravel occur near shore and on shoals. The sand and gravel
on shoals may be l a g deposits winnowed by ice gouging and currents (Toimil and
Grantz, 1976). Gravel in the northern Chukchi Sea also includes glacial erra-
t i c s dropped f r o m ice islands. T h e Holocene sediment blanket on the Chukchi
Shelf ranges in thickness from 0 to 12 m (Creager and McManus, 1967). On the
southern Chukchi Shelf, much of th is young sediment i s from the Yukon River
swept northward in the Alaskan Coastal Water, which flows north through Bering
S t ra i t (Nelson and Creager, 1977). Other sources are the Noatak and Kobuk
Rivers and the smaller rivers that enter the Chukchi Sea north o f Kotrebue
Sound . Small -scale bathymetric features on the Chukchi Shel f include nearshore
sand bars, ice gouges, and large sediment dunes. Pleistocene glaciers reached
the shelf o n l y near Chukotka and Kotzebue Sound (F igs . 1 and 2 ) . Wel l -def ined
i c e gouges have been found where t h e seabed' i s as deep as 60 rn, b u t they a r e
most abundant i n depths o f 25 t o 40 rn ( T o i m i l , 1978). Most a r e 1 t o 3 rn deep.
The deepest i c e kee ls t h a t have been measured i n t h e westzrn A r c t i c do n o t ex-
tend more than 50 m y and most do n o t extend more than 25 rn below sea l e v e l .
Thus t h e gauges found a t depths o f 60 m i n the n o r t h - c e n t r a l Chukchi Sea were
p robab ly made p r i o r t o 3,000-4,000 years ago, when sea l e v e l was e u s t a t i c a l l y
lower than a t present . Sand waves w i t h wavelengths as much as 400 m a r e common
bottom fea tu res near Ber ing S t r a i t , and sediment dunes as much as 15 m h i g h and
250 m between c r e s t s occur near Sarrow Sea V a l l e y
Several s h o r t cores and sediment grabs from t h e dunes y i e l d e d o n l y l u t i t e .
Sea Va l leys and Submarine Canyons
Several l a r g e sea v a l l e y s and canyons c u t t h e Chukchi and Beau fo r t Shelves
and slopes. Mackenzie Sea Va l ley , t h e largest, i s t h e major c o n d u i t of d e t r i t u s
t o t h e Canada Basin. I c e lobes and m e l t water o f t he P le i s tocene Lauren t ide
i c e sheets were major f a c t o r s i n c a r v i n g t h i s sea v a l l e y (F ig . 2 ) .
Barrow Sea Val l e y and Barrow Canyon
The a x i s o f Barrow Sea V a l l e y (F ig . 2 ) i s i n c i s e d i n t o t h e no r the rn Chukchi
She1 f about 20 km o f f t h e no r theas t - t r end ing A1 aska Coast n o r t h o f Wainwright.
It i s a broad, f l a t - bo t t omed channel 200 km l o n g and 2 t o 8 km wide w i t h an
o v e r a l l a x i a l g r a d i e n t o f about 1 m/km. The e a s t bank o f t h e v a l l e y i s h i ghe r
than t h e west bank owing t o p r e f e r e n t i a l sed imentat ion on t h a t s i de , b u t t he
g r a d i e n t of t h e west bank i s g e n e r a l l y s teeper . About 20 km south of t h e con-
t i n e n t a l she l f break, t h e sea v a l l e y merges i n t o Barrow Canyon. The canyon
a t t a i n s i t s maximum r e l i e f o f 900 rn where i t crosses t h e p r o j e c t i o n of t h e she l f
break. I t s average a x i a l g r a d i e n t i s 30 m/kn b u t a s teep upper segment s lopes
6
48 mlkm. A second canyon, comparable i n r e l i e f t o Barrow Canyon, 1 i e s 55 km
t o t h e eas t and a t h i r d , much sma l l e r canyon l i e s 110 km t o t h e east . The
second, and p o s s i b l y t h e t h i r d , appear t o be abandoned extens ions o f t h e Barrow
Sea Va l ley . T!,ese canyons may have been beheaded b,y the p resen t Barrow canyon,
which a f f o r d s a more d i r e c t r o u t e f rom Barrow Sea V a l l e y t o t h e abyssal p l a i n .
A1 though i t i s t h e o n l y s i z a b l e sea v a l l e y e n t e r i n g t h e Canada Basin west
o f t he Mackenzie, Barrow Sea V a l l e y has o n l y a modest sedimentary wedge and f a n
complex on t h e c o n t i n e n t a l s l ope and r i s e , The volume o f sediment i n t h e wedge
5 3 and fan i s est imated t o be o f t h e o r d e r of 1o4km3, compared t o r ough l y 3x10 km
f o r t h e Mackenzie Cone, suggest ing t h a t Barrow Sea V a l l e y has n o t been a major
sediment condu i t t o the bas in . A d d i t i o n a l Barrow Sea Va l l ey -de r i ved sediment
u n d e r l i e s t he abyssal p l a i n , and some i s s to red on t he c o n t i n e n t a l s h e l f .
The Barrow Sea V a l l e y heads on t h e no r theas t Chukchi She l f , which rece i ves
sediment o n l y f rom r e l a t i v e l y smal l streams w i t h a t o t a l dra inage a rea o f
2 approx imate ly 35,000 km . The o n l y l a r g e sediment sources i n t h e Chukchi Sea
2 a r e t h e Kobuk and Noatak Rivers , which d r a i n about 100,000 km o f nor thwest
Alaska, and t h e Alaskan Coastal Water, which in t roduces s i l t - l a d e n Yukon R i ve r
water v i a Ber ing S t r a i t . These sources a r e sem i - i so la ted from t h e Barrow Sea
V a l l e y by Hera ld Shoal and i t s ex tens ion t o Cape L isburne. I n con t ras t , t h e
2 Mackenzie Sea V a l l e y rece ives sediment f rom t h e 2,000,000-km Mackenzie R i ve r
drainage.
Barrow Sea V a l l e y i s thought t o have been i n c i s e d i n t o t h e s h e l f and s l ope
by subae r i a l streams d u r i n g P le i s tocene regress ions i n sea l e v e l and by t h e
no r theas t - f l ow ing Alaskan Coastal Water d u r i n g i n t e r g l a c i a l t imes. Barrow
Canyon i s presumed t o have been c u t by t u r b i d i t y cu r ren t s . The p r i n c i p a l i n
f l uence o f the Alaskan Coastal Water may have been as a source o f c l a s t i c sed i -
ment f o r t h e t u r b i d i t y cu r ren t s and f o r t h e submarine f a n complex a t t h e mouth
o f t h e canyon. The Alaskan Coastal Water f l ows no r theas t a long t h e coas t f rom
south o f Cape L isburne t o n o r t h of P o i n t Barrow and i t s a x i s f o l l o w s the Barrow
Sea Va l ley . Presumably t h e c u r r e n t i s h e l d a g a i n s t the coas t b y t h e C o r i o l i s
effect. Gar r i son and Becker (1976) argue, on t h e bas i s o f phys i ca l oceano-
g raph i c data, t h a t t h i s canyon a l s o acts as a c o n d u i t f o r exchange o f wa te r
masses between the Chukchi S h e l f and t h e Canada Basin. They p o s t u l a t e t h a t
c o l d s a l i n e water generated on t h e s h e l f i n w i n t e r d ra i ns n o r t h i n t o t h e deep
bas in , and t h a t under c e r t a i n baromet r i c c o n d i t i o n s deep Canada Basin water
w e l l s up onto t he s h e l f v i a t he sea v a l l e y .
Hope Sea V a l l e y and Hera ld Canyon
The P le is tocene and e a r l y Holocene Noatak and Kobuk R ivers crossed the
Chukchi S h e l f v i a Hope Sea Va l l ey and Herald Canyon (Creager and McManus, 1965).
Accord ing t o these workers, t h i s sea v a l l e y system (F ig . 2 ) c o n s i s t s o f a
s e r i e s o f channels i n t e r r u p t e d by areas of del t a i c deposi t i o n represen t ' ng s t i 11
stands dur ing P le i s tocene sea- leve l f l u c t u a t i o n s . Ber ing S t r a i t Sea V a l l e y
(Hopkins e t a1 ., 1976), which f lows n o r t h through Ber ing S t r a i t , may be a t r i b u -
t a r y o f Hope Sea Va l l ey t h a t was s i m i l a r l y mod i f i ed by d e l t a i c depos i t i on .
Because t he d e l t a i c areas l a c k c l e a r l y de f i ned channels, t he a x i s o f t h e sea
v a l l e y system i s d i f f i c u l t t o map. Hera ld Canyon (Fig. 3 ) apparen t l y en te r s
Canada Basin a t t h e Chukchi Abyssal P l a i n between 1700 and 1800 W . (Beal, 1969).
Th is p l a i n , a perched bas in a t about 2,200 m depth, may have rece i ved much o f
i t s sedimentary f i l l from t h e Noatak and Kobuk R ivers and no r the rn Chukotka
v i a t h e Hope Sea Val ley-Hera ld Canyon d ra inage system d u r i n g P le i s tocene g l a c i a l
maxima.
Hanna Sea Val l e y
Hanna Sea V a l l e y ( ~ i g . 2 ) , a broad, eas t -nor theas t - t rend ing f e a t u r e n o r t h
of Hanna Shoal, may be an abandoned l a t e Pleistocene course o f the Hope-Herald
Sea Val 1 ey system. The Noatak-Kobuk effluent and an ancestral northeast-flow-
ing Alaskan Coastal Water, i f i t existed during the l a t e Pleistocene, must have
flawed west of then-emergent Herald Shoal t o reach the Arctic Basin. The cur-
rent may have been deflected northeast and held against the north side o f
Herald and Hanna Shoals by the Coriolis effect . Hanna Sea Val ley might have
been related to th i s postulated current much as Barrow Sea Valley appears t o
be related to the present northeast-advecting Alaskan Coastal Water.
Chukchi Continental Border1 and
The Chukchi Borderland (Figs. 2 and 3 ) , 400 km wide and 600 km long, ex-
tends northward from the Chukchi Shelf between 1600 and 1700 W. long (Beal ,
1969; Hunkins e t a l . , 1962). The borderland consists of a c luster of shallow,
flat-topped plateaus and ridges with an intervening deep basin, Northwind
Abyssal Plain, and sea valleys. Chukchi Cap (Fig. 3 ) , the largest high-standing
plateau in the borderland, has f l a t shelves a t 270 m and 400 to 500 m below
sea level and rises locally to 246 m below sea level. The east margin of the
borderland is the Northwind Escarpment, a steep continental slope that abuts
the deep Canada Basin a t depths near 3,900 m . Gentler slopes, irregular in
plan, characterize the other margins. Bathymetry and geophysical characteris-
t i c s (Shaver and Hunkins, 1964) suggest that the high-standing parts o f the
borderland consist of continental crust .
Continental Shelf Break and Beaufort Ramp
The shelf break in the Chukchi and western Beaufort Seas (Fig. 2 ) has
large regional variations in character and depth that re f lec t the interplay
between tectonic processes and Quaternary sedimentation and slumping ( F i g . 1 7 ) .
The main (outer) shelf break 1 ies a t headwalls of submarine slumps on the
continental slope. I t s depth i s 200 t o 300 m near 150" W . , 450 m near 160" W.,
and about 800 m a t 1390 W . long.
The Beaufort Ramp, a transit ion zone between the low-gradient inner she1 f
and the continental slope, i s the product o f Neogene (Quaternary?) subsidence
and folding. I t s inner edge, near the 60 m isobath, l i e s a t or seaward of the
crests of broad mid-shelf archer and anticlines expressed in Neogene beds.
The slope of the ramp and the dip of the underlying s t r a t a are generally simi-
l a r , about 0.5 to 1.50, which suggests that the s t ra ta and seabed were t i l t e d
together. The f o l d crests apparently acted as dams behind which shelf sedi-
ments ponded and smoothed the seabed of the inner shelf , b u t sediment a l s o
overtopped the f o l d crests and prograded a Quaternary sedimentary wedge seaward
a t the head of the ramp. Headwalls o f bedding plane s l i d e s developed within
th is wedge determine the specific position of the inner shelf break.
On some of o u r seismic profiles (Fiq. 15) , pre-Quaternary beds beneath
deeper parts of the Beaufort Ramp are truncated a t or near the seabed, even
though parts of the ramp are deeper than 800 m , well below the deepest Pleisto-
cene regression. This truncation of bedding indicates that the ramp was once
above wave base and subsequently subsided and t i l t e d seaward. The outer shelf
break along the Beaufort Ramp increases in depth from 200 t o 300 m near 1500 W.
t o 830 m near 1390 W . long (Fig. 16) , a ra te of about 1 . 2 m/km. Deepening of
the shelf break corresponds closely w i t h the easterly increase in thickness of
the sedimentary prism of the Mackenzie Cone and Canada Continental Rise. East-
ward deepening of the shelf break and northward t i l t i n g of the Beaufort Ramp
may therefore be an i sos ta t ic subsidence due t o crustal loading by sediment on
the cone and r i se . This hypothesis i s supported to some extent by the pocket
of earthquakes reported a t the head of the Mackenzie Cone and Canada R i s e by
Wetmiller and Forsyth (1978). These workers suggest ( p . 15) that the earth-
quakes "are possibly related t o i sos ta t ica l ly uncompensated loads o f recent
10
sediments."
Alaska Continental Slope and Northwind Escarpment
The continental slope north of Alaska follows a gentle arc from the
Mackenzi e Sea Val 1 ey to the Chukchi Borderland (see F ig . 2 ) . I t s junction
with the continental r i s e 1 ies a t depths of 1,100 t o 2,000 m and i t s average
slope ranges from 40 t o 1 2 0 , with local steep pitches of 160. The steep,
nearly l inear slope along the east face of the Chukchi Borderland, the North-
wind Escarpment (Figs. 2 and 3 ) , has slopes as steep as 230 (Fisher e t a1 ., 1958). Numerous slumps, landslides, and incised channels characterize the
Alaska Continental Slope. The largest s l ide masses head a t o r near the shelf
break. Along many crossings the vertical drop a t the headwall o f these s l ides
i s 900 t o 1,200 m, and head-to-toe length o f some large slides exceeds 35 km.
Slumps and irregular prograded sedimentary wedges sinii l a r t o these surf ic i a1
features also occur within the Ter t iary section beneath the cutermost Western
Beaufort Shelf (see Fig. 130, C ) .
Seismic and bathymetric profiles show that many canyons incise the Alaska
Continental Slope. Some appear to be slump scars; others contain bedded sedi-
ments, are bordered by levees, and appear t o be turbidity current channels.
I n these channels the upper surface o f the sedimentary f i 11 i s commonly t i l t e d
u p toward the eastern bank owing to the Coriolis effect on the depositing
current.
Canada Continental Rise and Abyssal Plain
and Alaska Continental Rise
The Canada Abyssal Plain, which under1 i e s the western two f i f t h s o f the
Canada Basin, i s about 3,700 m to more than 4,000 m deep (Fig. 2 ) . Its smooth
floor and sparsity of abyssal h i l l s indicate that i t overlies a thick sedimentary
f i l l . The Canada Continental Rise underlies the eastern three f i f t h s o f the
11
basin. I t i s about 3,700 m deep a t i t s gradational boundary with the abyssal
plain on the west and slopes gently upward toward the Arctic Islands and
Mackenzie Delta, where i t abuts the continental slope between the 1,400- and
1,800-m isobath. I t s morpholtgy indicates that the Canada Rise i s underlain
by a thick sedimentary f i l l derived in large part from the Mackenzie Valley
and Arctic Islands. Because these areas were covered by the Laurentide i c e
sheet, i t i s l ikely that glacial detr i tus consti tutes a major part of the
sedimentary f i l l beneath the Canada Rise. The r i s e i s as much as 500 km wide
from the continental slope to the 3,700-m isobath; the other rises fringing
the Canada Basin, including the Alaska Rise, are much narrower. Sedimentation
on the Canada Rise has thus overwhelmed that on the Alaska Rise, and i t s sedi-
ments a b u t , or lap onto, t h e surface o f the Alaska R i s e ( F i g . 2 ) . As the
Canada Abyssal Plain adjoins the Alaska Rise a t depths as great as 4,000 m ,
and the upper part o f the Canada Rise l aps onto i t a t depths o f 1,400 to 1,800
m, sedimentation on the Canada Rise has reduced the vertical re l ie f of the
eastern part of the Alaska Rise and Slope by more than 2,200 m. Concomitantly,
the w i d t h of the Alaska Rise narrows from about 100 km near 1500 W . long to a
wedge edge near Herschel Island. Westward, the Alaska Continental Rise wedges
o u t again a t the base of the steep Northwind Escarpment, where terrigenous
sedimentation was s l igh t . In places the escarpment appears, on reconnaissance
charts, t o plunge direct ly t o the Canada Abyssal Plain. The disparity in s i z e
between the Canada Rise and the other continental r ises of the Canada Basin
demonstrates that the Arctic Islands and Mackenzie Valley were much more impor-
tant sources of l a t e Cenozoic detr i tus t o the Canada Basin than northern Alaska
and the Chukchi Shelf.
Smooth slopes and gent1 e gradients characterize the Alaska Continental
Rise, Gradients range from 0.90 t o more than 2 . 2 0 . Bedding in the underlying
12
sediment i s gene ra l ly p a r a l l e l t o t h e seabed and presumably c o n s i s t s o f tur-
b i d i t y c u r r e n t and disaggregated s l i d e depos i t s . Channels and levees can be
seen on bathymetric p r o f i l e s and, vaguely, on bathymetric c h a r t s of t h e Alaska
Rise. A few r e f r a c t i o n measurements and es t imates of sediment th ickness beneath
t h e nearby Canada Basin and Western Beaufort Shelf (F ig . 5 ) suggest t h a t s ed i -
ment beneath t h e Alaska Rise may be 4 t o 8 km t h i c k . Because i t borders an
At lan t ic - type margin, t he s t r u c t u r a l s i m p l i c i t y observed i n i t s upper beds i s
i n f e r r ed t o c h a r a c t e r i z e t h e e n t i r e Alaskan Rise sedimentary prism. However,
many l a r g e d i a p i r i c f o l d s deform the Alaska Rise and Slope e a s t of 1460 W . long.
REGIONAL STRATIGRAPHY AND TECTONIC SETTING
The geologic formations of northern Alaska and v i c i n i t y a r e d iv ided con-
venien t ly i n t o four t e c t o n i c - s t r a t i g r a p h i c sequences (Frank1 i n i a n , El lesmer-
i an , Brookian, and Hope bas in ) t h a t c o r r e l a t e well with t h e major geologic
events of the region. The c h a r a c t e r o f t he se sequences i s shown i n Figure 44-B,
and t h e i r d i s t r i b u t i o n in Figures 5 , 6 , 8, and 9. The F rank l in i an , El lesmerian,
and Brookian sequences were def ined by Lerand (1973) from rock sequences in
t h e Arc t i c Archipelago of Canada and t h e Brooks Range of Alaska. The Hope
basin sequence i s def ined here from t h e T e r t i a r y Hope basin o f t h e southern
Chukchi Sea. The onshore s t r a t i g r a p h i c and s t r u c t u r a l da t a presented in t h i s
paper inc lude da t a and concepts from A1 aska Geological Soc ie ty (1971, 1972,
1977); Anonymous (1970); Armstrong and Bird (1976) ; Beikman and Lathram (1976);
Bird (1978); Brosgk and T a i l l e u r (1971 ) ; Campbell (1967) ; Chapman and Sable
(1960); Detterman e t a1 . (1975); Jones and Grantz (1964); Kameneva (1977);
King (1969); Lerand (1973); Martin (1970); Norris ( 1 9 7 7 ) ; T a i l l e u r and Brosgb
(1970); T a i l l e u r e t a1 . (1972); U.S. Geological Survey (1978) ; and Young e t a1 . (1976).
Franklinian Sequence.and Precambrian Rocks
Basement for standard seismic reflection and sonobuoy refraction surveys
in northern Alaska and i t s continental shelves occurs within the Franklinian
sequence o r , i n places, Precambrian rocks. T h e Precambrian rocks are mainly
s l a t e , phyl l i te , sch is t , gneiss, marble, and metavolcanic rock. The Franklinian
sequence was named for the Franklinian geocyncline of the Arctic Archipelago.
In the archipelago the sequence i s of Middle Cambrian to Devonian age and was
derived mainly from northern sources. I t s southern facies are mainly carbon-
ate . In northern Alaska the Franklinian sequence consists of generally strongly
deformed Cambrian t o Devonian miogeocl inal and eugeocl inal rocks (Fig. 4A -8)
strongly disrupted by thrust fau l t s in the Brooks Range and in the Seward and
Chukotsk Peninsulas. I n places the sequence i s mildly metamorphosed, and
loca1l.y i t i s intruded by plutonic rocks. I t i s thought t o extend seaward t o
the continental slope, and i t may underlie the Chukchi Borderland.
Arctic Platform and El 1 esmerian Sequence
The Franklinian rocks were strongly deformed and truncated by regional
erosion during the Late Devonian-Early Plississippi an E l lesmerian (Ant1 er ) orogeny,
creating a s table shelf , the Arctic platform o f northern Alaska. The
platform maintained a remarkable s t ab i l i t y for 200 mil 1 ion years, from Early
Mississippian to Cretaceous time. During th i s interval a diverse su i t e of
mature marine and nonmarine c l a s t i c and carbonate rocks, the Ellesmerian
sequence, was deposited on the platform. The sequence i s named for the Elles-
merian orogeny. I t is typically exposed in the Sverdrup basin of the Arctic
Archipelago, where i t consists of Mississippian to Jurassic rocks of mainly
easterly and southerly provenance. In northern A1 as ka , however, the El 1 esmerian
sequence, which i s also called t h e Arctic Alaska basin (Tailleur and Brosgf!,
1970), was derived mainly from norther1.y source terranes. I t s constituent rock
14
u n i t s (F ig. 4 ~ - B ) i n general t h i n , coarsen, and l a p toward t h i s source
terrane, which i s c a l l e d Bar rov ia ( T a i l l e u r , 1973). On the Barrow arch Miss is -
s ipp ian t o Jurass ic beds o f t he sequence t h i n t o a wedge edge owing i n p a r t t o
sedimentary thin-iling and i n p a r t t o e ros iona l t runcat ion , and they are over -
stepped by the Neocomian "Pebble Shale, " This shal low-water organic shale i s
the youngest u n i t i n nor thern Alaska w i t h a nor thern source. Outcrops o f
Jurass ic and Neocornian s t r a t a i n nor thern Yukon T e r r i t o r y and on the A r c t i c
Coastal P l a i n of nor theastern Alaska (Young e t a1 . , 1976; and Reiser e t a l . , d ,Lowesf C+etoceoos
1978) and the i n t e r p r e t e d presence o f 1,800 m o f Kingak Shale (Jurassicd be-
neath the Beaufor t She l f n o r t h o f Yukon T e r r i t o r y o orris, 1977) suggest t h a t
the Jurass ic and e a r l i e s t Cretaceous s t r a t a o f these areas become s h a l i e r t o
the no r th and are o f southern provenance. I n nor thern Yukon T e r r i t o r y the
Kingak Shale oversteps M iss i ss ipp ian t o T r i a s s i c beds o f n o r t h e r l y provenance
1 ower i n the E l 1 esmerian sequence.
The boundary between the El lesmer ian and ove r l y i ng Brookian sequence,
according t o Lerand (1973, p. 3 7 3 ) , cou ld be placed e i t h e r a t the o ldes t beds
(Middle Ju rass i c ) t h a t rece ived sediment from southern sources o r a t t he
youngest beds (Neocomi an) t h a t received sediment from nor thern sources. Lerand
a r b i t r a r i l y placed the boundary a t the base o f t he Cretaceous. In t h i s r e p o r t
the boundary i s placed between the "Pebble Shal el'-Kongakut Formation (Neocomian)
o f nor thern provenance and the Torok Fownati on-Nanushuk Group (A1 b i an) o f
southern provenance beneath t h e A r c t i c Coastal P la in , nor thern A r c t i c Foot-
h i 1 l s , and Chukchi and Western Beaufort Shelves o f nor thern Alaska (F igs. 2
and 4A-B) . I n the southern A r c t i c F o o t h i l l s and nor thern Brooks Range the
boundary i s placed between Upper T r i a s s i c beds o f nor thern provenance and
Middle Jurass ic tu f faceous sandstone t o Neocomian (Okpikruak Formation)
t u r b i d i t e o f southern provenance. Since the boundary 1 i e s a t t he t o p of the
"Pebble Shale" over most o f northe,:.n Alaska and i t s continental shelves, the
term Brookian in t h i s report refers to post-Neocomian rocks unless otherwise
specified. The character of the Jurassic and Neocomian beds o f northern prove-
nance suggests tha t the northern source terrane was then senescent.
Colville Foredeep and Brookian Sequence
The long period o f tectonic quiescence recorded by the Ellesmerian sequence
ended during Jurassic and ea r l i e s t Cretaceous time, when deformation began that
created the Brooks Range orogen along the southern part of the Arctic platform.
Paleozoic and Mesozoic rocks were thrust northward onto the southern part of
the platform and created a southward deepening, asymmetric foreland basin, the
Colville foredeep, north of the ancestral Brooks Range. The load of the thrust
sheets and of the Jurassic and Creta:eous sedimentary rocks subsequently deposi-
ted in the foredeep caused i t t o deepen and broaden and t i l t e d the Arctic
p l atfom southward. Concomitantly, southern sources f i r s t supplemented, then
supplanted northern sources o f sedi,nent t o the newly formed basin.
The oldest s t r a t a deposited i n the Colville foredeep were Middle Jurassic
tuffaceous beds and Upper Jurassic t o Neocomian turbidites of southern proven-
ance now exposed in the northern Brooks Range and adjacent footh i l l s . These
a re coeval with condensed shale and coquinoid shale deposited on an intrabasin
high and with euxinic basin and shelf deposits o f northern provenance (Jones
and Grantz, 1964) in the upper part of the Ellesmerian sequence to the north.
Higher beds of the foredeep--namely Albian, Upper Cretaceous, and Tertiary
s t r a t a of the Brookian sequence, a l l of southern provenance--extend from the
Brooks Range across the en t i re Arctic platform to the Western Beaufort Shelf.
The Cretaceous sedimentary rocks of the Colville foredeep exceed 6,000 rn
in thickness on the south, where they consist mainly of turbidites and paralic-
del ta ic wedges. These s t r a t a thin northward to about 500 m to 2,000 m where
they onlap Barrow arch. The Cretaceous beds on the arch, and probably on
the Chukchi Shelf, a re of paralic and ner i t ic to upper bathyal facies. In
northwestern Alaska and on the Chukchi Shelf, they include del ta ic deposits
with thick coal beds. I n the northern Chukchi Sea and the Canning-sagavanirk-
t o k Rivers area, wedges o f northward-thickening Tertiary sedimentary s t r a t a
overl ie the Cretaceous rocks of the northern part of the Colville foredeep
and Barrow arch. Nonmarine facies in the Tertiary and Cretaceous sequences
appear t o give way northward t o marine facies , and, the northward prograded
sedimentary s t r a t a beneath the Western Beaufort S h e l f are probably mainly
marine. However, some nonmarine beds o f both sequences reach the coast and
appear on seismic records t o extend offshore. Seaward, the prograded Srookian-
equivalent beds thicken from about 500 t o 2,000 m on the Barrow arch t c more
than 6,000 m in places on the outer shelf.
Cessation of sedimentation from northern terranes that geographically
occupied the present area of the southern Canada Basin argues for a r i f ted
origin of the Canada Basin. Tailleur (1969, 1973) suggests, i n addition, that
the early phase of the Brooks Range orogeny was produced along the leading edge
of the southward-rotating northern Alaska plate in response to opening of the
Canada Basin. However, Late Jurassic to mid-Cretaceous Brooks Range tectonic
events a re generally similar and synchronous with those i n the Cordillera
south of Alaska. Accordingly, we be1 ieve that the ancestral Brooks Range and
i t s structures are a foreland thrust bel t related t o a broader subduction and
collision zone between crustal plates of the Pacific region and the North Am-
erican plate. Opening o f the Canada Basin possibly increased the ra te o f sub-
duction south of the Brooks Range, b u t any specific effects of th i s increased
ra te in the geologic record have not been documented.
Hope Basin Sequence
The young sedimentary rocks of Hope basin in the southern Chukchi Shelf
have not been dated, and the i r correlation with the bedded rocks of adjacent
land areas i s conjectural. Outcrops of l a t e Neogene marine sedimtary rocks
along the margins o f the basin (Hopkins and MacNeil, 1960; Belevich, 1969)
and scattered outcrops o f Paleogene and Neogene nonmarine sedimentary rocks
on the northern Seward Peninsula and in the Selawi k Lowland (Hudson, 1977;
Patton and Miller, 1968) belong t o formations that probably extend into Hope
basin. Nonmarine rocks o f Late Cretaceous or early Tertiary age on the east-
ern Seward Peninsula (Sainsbury, 1976) possibly also extend into t h e basin.
Hope basin sequence was deposited in local intracontinental basins south of
the Brooks Range, and i s tectonically d i s t inc t from the Brookian sequence of
northern A1 aska.
GEOLOGY
Structural Provinces
The continental shelf and slope of the western Beaufort and northern
Chukchi Seas i s underlain by a thick prism of Cretaceous t o Quaternary, and
locally Jurassic, sedimentary s t r a t a that prograded seaward on a subsiding
shelf. A thick correlative sedimentary sequence a1 so under1 i e s the adjacent
continental r i s e and abyssal plain of the Canada Basin. I n two places the pro-
graded prism widens into sizable sedimentary basins. A southwestward bend of
the Barrow arch in the northern Chukchi Sea creates an embayment wherein l i e s
the North Chukchi basin ( F i g . 3 ) , which is f i l l e d with inferred Cretaceous,
Tertiary, and perhaps older sedimentary rocks; and different ial subsidence
between Harrison Bay and Camden. Bay has produced the Cretaceous and
18
Tertiary Camden basin (Fig. 5). This basin under1 ies both the continental shelf
and a large area of coastal plain near the Colville and Sagavanirktok Rivers.
The central and southern Chukchi Shelf i s dominated s t ructural ly by two
positive (antic1 inorial ) and two negative (synclinorial ) tectonic elements
(Figs. 3 and 8-10). The positive elements, which bring Paleozoic rocks close
t o the surface, are the Barrow and Herald-Wrangel arches. The negative ele-
ments a re the Colville foredeep, which contains thick accumulations of Juras-
s i c , Cretaceous and 1 ocal ly Tertiary sedimentary rocks, and Hope basin, which
i s f i l l e d with Tertiary sedimentary s t r a t a . T h e basement underlying the Col-
v i l l e foredeep i s the Ellesmerian sequence. I n Hope basin basement i s the
Precambrian t o Lower Cretaceous rocks which trend toward i t from the western
Brooks Range and Chukotsk Peninsula.
Barrow Arch
Barrow arch i s the dominating structure of the Western Beaufort and north-
ern Chukchi Shelves. Emerging near the Canning River from beneath a thick Ter-
t i a ry section in the Camden Bay area, i t s c res t ( F i g s . 3, 5 , 7 , 8, 10, and 1 1 C )
follows the coast westward t o Barrow, then cuts seaward to 700 N . , 1600 W. in
the northern Chukchi Sea. From here the arch turns southwest and persis ts as a
more complex, b u t s t i l l broad structure t o i t s termination in the west near' the
crosscutting Herald f au l t zone.
East of 1600 W . long the Barrow arch trends westerly, i s only s l ight ly
asymmetric (steeper flank north), and has low flank dips and generally s imple
structure (Fig. 10) . West of 1600 W . long, the arch trends southwest and the
northwest f l a n k i s considerably steeper than the southeast flank (Fig. 7 ) .
The northwest flank west of 1600 W . long contains large normal fau l t s and i s
parallel t o a strong gravity gradient tha t s t r ikes northeast. Free-air
anomaly values descend from 50 mgal over the arch to 0 t o -10 mgals over the
North Chukchi basin. These features suggest t h a t the northwest flank of the
Barrow arch may have resulted from truncation of the Arctic platform west of
16d0 W. long by a northeast-stri king structure related to formation of the
North Chukchi basin.
The Barrow arch i s the broad structural culmination of the r i f ted and south-
ward-ti 1 ted Arctic platform of northern A1 aska. Crustal heating associated with
the i n i t i a l Jurassic and Early Cretaceous r i f t i n g of the Canada Basin i s thought
to have up1 if ted and t i 1 ted the northern part o f the platform t o the south
along the arch (Rickwood, 1970). The south t i 1 t i s also partly Mississippian
to Jurassic paleoslope and partly t i l t produced by Cretaceous loading o f the
southern part of the Arctic platform by nappes and voluminous de t r i tus from the
nascent Brooks Range. The north flank o f the arch i s the modified r i f t scarp
reduced in re l ie f by down-to-the-north normal faul t ing, Jurassic and Early
Cretaceous erosion, and regional pos t - r i f t subsidence. Such subsidence, com-
monly observed along r i f ted continental margins (see, for example, .Watts and
Ryan, 1976) may be a consequence of pos t - r i f t cooling of the crust beneath the
r i f ted zone and subsequent sedimentary loading on and near the newly created
continental margin. These processes are thought to have shifted the c res t of
the Barrow arch south by 50 t o 100 km to the vicini ty of the present coastl ine
from an original position beneath the continental slope (Fig. 5 ) .
Arctic Platform and Colville Foredeep
Between Cape Lisburne and Barrow, the bedded rocks of northern Alaska
trend northwest beneath the Chukchi Sea. Here the Ellesrnerian and Brookian
rocks a re limited on the southwest by the Herald arch and f au l t zone and thin
northward toward the Barrow arch. O u r seismic data do not show t o wha t extent
Ellesmerian s t r a t a continue across the crestal zone o f the arch to underlie
the North Chukchi basin. Brookian rocks do extend across the Barrow arch and
dominate the sedimentary prisms o f the Western Beaufort Shelf and North Chukchi
basin.
A sedimentary sequence a t l eas t 3 km thick designated "E-Fr" on cross
section Figure 10 has been recognized in the northeastern Chukchi Sea, although
i t s extent has not been determined. The sequence i s interpreted to be overlain
by Albian o r older Early Cretaceous rocks i n the north and by Mississippian beds
low in the Ellesmerian sequence in the south. I t yields seismic interval velo-
c i t i e s (prel iminary) of 5.0 kmlsec or more and res t s on bedded rocks with pre-
1 iminary interval velocities of 6.0 kmlsec or more. The sequence i s tenta-
t ively postulated t o be ei ther a local thickening of Lower t o mid-Mississippian
c l a s t i c sedimentary rocks (Endicott Group) a t the base o f the Ellesmerian
sequence or beds in the upper part o f the Franklinian sequence that a r e
s t ructural ly more orderly than the Ordovician and Silurian a r g i l l i t e and gray-
wacke found in boreholes in northern Alaska (Carter and Laufeld, 1975). The
Endicott Group i s represented in the subsurface o f northern Alaska by more than
550 m of conglomerate and sandstone o f the Itkilyariak Formation, Kekiktuk Con-
glomerate, and Kayak Shale. These beds r e s t with angular unconformity on the
strongly deformed Ordovician and Silurian beds.
In northwestern Alaska, the Ellesmerian sequence thickens from a wedge
edge in the crestal region of the Barrow arch to a t l eas t 4,000 rn, and perhaps
more than 8,000 m , in the southern part of the North Slope and the western
Brooks Range (Fig. 4 A ) . Offshore, s i n g l e-channel seismic ref1 ections and sono-
buoy refractions were received from the Ellesmerian rocks only north o f Icy
Cape (un i t J-M in Fig. 10) . I n t h i s area the i r seismic velocity i s about
3 .7 t o 4.3 krnlsec, and they consist of a gently south-dipping, southward-
thickening packet of strong ref1 ectors. An interpretation of the structure of
these rocks in the eastern Chukchi Sea, which i s speculative south of 70050'
N. l a t , i s presented in Figure 10.
The Brookian sequence of northwest Alaska consists of del ta f ront foreset
beds and shallow marine and paralic topset c l a s t i c beds and coal, a l l of south-
er ly source and l a t e Early Cretaceous (Albian) age. Tertiary beds of the
Brookian sequence overlie the crestal zone of the Barrow arch and the northern
part of the Arctic platform everywhere except in the region between 1530 W. and
1580 W. long ( F i g s . 5 and 8 ) . The Brookian sequence, thinned by erosion, i s
400 to 600 rn thick and of Albian age i n the vicini ty o f South Barrow gas f i e l d ,
on the crest of the Barrow arch. Southward, as noted p rev ious l y , i t thickens
to a t l eas t 6,000 m near the Brooks Range. Northward, beneath t he Western
Beaufort Shelf, the Brookian sequence contains Cretaceous and Tertiary beds and
thickens to a t l ea s t 6,000 rn.
The Cretaceous rocks of the central Chukchi Shelf have stratigraphic fea-
tures, interpreted from seismic reflection profi les , that permit some of them
to be correlated with subsurface s t r a t a of northern Alaska as described, for
example, by Brosgb and Tailleur (1971), and Woolson (1962) . On the Chukchi
Shelf a thick seismic u n i t with irregular weak to moderately strong reflec-
tors and many north or northeasterly dipping clinoform beds i s well developed
north o f the foreland folds of the southern part of the Colville foredeep
(Fig. 8 ) . This unit i s correlated with the Torok Formation of Albian age, a
thick lutaceous unit containing turbidi te beds. An overlying unit typified
by strong parallel ref lectors under1 ies the region of the foreland folds. I t
i s correlated with the para1 i c and del ta ic A1 bian and Cenomanian(?) Nanushuk
Group, which consists of sandstone, l u t i t e , conglomerate, and coal. West of
2 2
the foreland folds l i e s an extensive terrane characterized by weak ref lectors ,
small irregular folds , and poor seismic penetration. This terrane also has a
re lat ively high positive free-air gravity anomaly (see Ruppel and McHendrie,
1976). Taken together, these features suggest tha t the terrane o f weak ref-
lectors i s s t ructural ly elevated l u t i t e low in the Brookian sequence (Torok
Formation) or high in the Ellesmerian sequence ("Pebble Shale" or Kingak
Shale) . Structurally the rocks of the Colville foredeep beneath the eastern Chukchi
Shelf resemble those onshore. North o f Icy Cape they are almost unbroken by
f au l t s or folds and dip gently and uniformly south. S o u t h o f Icy Cape they are
folded into long, east-west-striking ant icl ines and broad, shallow synclines
(Fig. 8 ) . The amp1 itude and tightness of folding increase t o the south, and
the southern folds show thrusting, incipient core diapirism, and northern ver-
gence--features that indicate re la t ive northward movement of the upper beds.
Detachment in these foreland folds i s inferred t o occur within the early Albian
Torok Shale and the youngest rocks affected are the Nanushuk Group of Late
Albian age (see Woolson, 1962; Chapman and Sable, 1960). Apparently related
structures in the Ogotoruk Creek area, southeast of Point Hope, appear to trend
westward beneath Paleogene(?) s t r a t a in Hope basin. The detachment folds are
therefore inferred t o have formed during Laramide (Late Cretaceous-early Ter-
t i a ry time. Along the Herald arch and f a u l t zone, which bound deposits of the
Colville foredeep on the southwest, the detachment folds a re intersected
ob1 iquely by large thrust-folds (elongate f o l d s with thrust-faul ted cores) of
the Herald f au l t zone ( F i g . 8 ) . These folds and related fau l t s extend far ther
west than the detachment folds and appear to be younger.
Herald and Wrangel Arches
Herald arch, the dominant structural feature of the central Chukchi Sea,
i s a bel t of strongly ref lect ive rock 20 t o 100 km wide that trends N 50° w.
from Cape Lisburne toward Herald Island (Figs. 3 , 8, and 9 ) . Near 700 3C' 14. l of; long
1730 W.,the arch merges with a zone of north-south structures tha t connect i t
with the broad zone of shallow acoustic basement called Wrangel arch (F igs . 3
and 8 ) . Because the Brooks Range and Wrangel Island are underlain by similar
rocks of the Ell esmerian and Frankl inian sequences (Kameneva, 1977), Herald
and Wrangel arches a re thought to form a structural connection between the
two areas. Wrangel arch resembles Barrow arch because i t i s underlain by
simil a r correlatives of the Frankl inian and E l 1 esmerian sequences and bounds
the North Chukchi basin on the south (Figs. 3 and 8 ) . Unlike Barrow arch,
b u t similar t o Herald arch, i t i s bounded on the north by south-dipping re-
verse faul ts .
The strongly ref lect ive rocks in Herald arch are onlapped from the south
by Tertiary rocks in Hope basin. The south-dipping unconformity a t the base
of the Tertiary rocks constitutes the south flank of the arch. The north
flank is formed by the northeast-verging, northwest-striking Herald f a u l t zone,
which brings the strongly ref lect ive rocks of the arch against well-bedded,
less strongly ref lect ive rocks of the Colvil l e foredeep.
The character of "acoustic basement" in Herald and Wrangel arches can be
inferred from outcrops on Lisburne Peninsula and Wrangel Island, a reported
occurrence of Jurassic(?) plutonic rocks on Herald Island (N . A . Bogdanov,
oral communication, 1970), and three dredge hauls taken from the north side
of Herald arch near 700N. l a t , 1680 to 1700 W. long by the University of Wash-
ington (Fig. 8 ) . The dredge samples are predominantly we1 1 -indurated graywacke
sandstone and s i l tstone ( P l a t t , 1975) that most resemble Lower Cretaceous
graywacke and shale in the western Brooks Range and Lisburne Peninsula, b u t a
positive correlation could not be made. On the northeast side of the arch,
"acoustic basement" produces scattered, dismembered patches of steeply dipping
b u t coherent ref lectors suggesting strongly deformed bedded rocks ( dK? on
Figs. 8 , 9 , and 10). T h e strongly deformed beds of Lower Cretaceous graywacke
and shale in the western Brooks Range and Lisburne Peninsula ( dK in Figs. 8
and 9), which str ike northwest from the north s ide of Cape Lisburne into the
area of "dismembered" ref lectors , could produce th i s observed acoustic pattern.
"Acoustic basement" southwest of the be l t of dismembered ref lectors has few
internal ref1 ectors and i s inferred to comprise 1 ower El 1 esmerian c1asti.c and
carbonate rocks and strongly deformed Franklinian c l a s t i c rocks (Iviagik Group
of Martin, 1970) as crop o u t on the Lisburne Peninsula. Limited acoustic data
over the Wrangel arch suggest that a similar boundary may underlie i t s northern
part.
Herald and Wrangel Fault Zones
Herald and Wrangel arches a re bounded on the north by the Herald and
Wrangel f a u l t zones (Figs. 8 and 9 ) . A 1 though both f a u l t zones e x h i b i t reverse
s l i p and border the north sides of similar large belts of acoustic basement,
they appear t o d i f f e r in character and age. Herald f au l t zone consists of
several thrust folds and fau l t s tha t dip southwest a t low angles (about 1 5 0 ? ) .
The thrust folds are best developed a t the southeast end of the f au l t zone
where they involve well-bedded competent rocks interpreted t o represent the
Cretaceous Nanushuk Group. Northwestward the d i p of the fau l t zone becomes
difficui t to map, b u t may be steeper, and the larae thrust folds along the
northeast side o f the fau l t zone diminish in amplitude and apparently lack
thrust-faulted cores. This difference in structural response may correspond
to a change in 1 i tho1 ogy. seismic reflectians suggest tha t northwestward from
Cape L i sburne the rocks of the Colvil l e foredeep probably change from we1 1 - bedded sandstone and l u t i t e of the Nanushuk Group in the region o f the foreland
folds t o harder, poorly bedded rocks belonging to the older Torok or Kingak
Shales far ther west. A1 ternatively, the faul t s ty l e may change from dominantly
easterly directed low-angle reverse s l i p near the Lisburne Peninsula t o moderate
or high-angle reverse s l i p with a large component of s t r i ke-sl ip west of 1690
W. long for reasons not direct ly related to lithology.
Offshore the Heral d f au l t zone separates moderately deformed Cretaceous
sandstone and l u t i t e to the northeast and more stronqly deformed Cretaceous
c l a s t i c rocks to the southwest (Figs. 8 and 9 ) and s t r ikes toward a similar
contact on the north s ide o f the Lisburne Peninsula. A more important break,
however, may l i e t o the southwest, between the area of acoustic basement with
many bedding traces (Cretaceous(?) map unit dK? ) and acoustic basement with
few bedding traces (pre-Cretaceous(?) map unit pK ) . This boundary s t r ikes
toward a southwest dipping thrust-faul t zone on the Lisburne Peninsula between
Ellesmerian carbonates to the west and deformed younger rocks, mainly Cretaceous
shale and graywacke to the east . Herald f a u l t zone i s younger than the Nanushuk
Group s t r a t a (A1 bian), which i t o f fse ts , and older than the Palmgene(?) beds
in Hope basin, which overlie i t. Wrangel f au l t zone, in contrast (Figs. 8, 11A,
B), separates presumed Paleoaene and (o r ) Cretaceous s t r a t a in the North
Chukchi basin from strongly ref lect ive rocks in the Wrangel arch. A younger
Tertiary uni t , perhaps Neogene, overlies the f au l t zone and i s not deformed.
The f au l t zone may therefore be Late Cretaceous o r early Tertiary, b u t def ini t ive
evidence for the age of the limiting rocks i s lackina. A1 though i t was seen on
only a few profiles, the f au l t appears t o be a steep south-dipping reverse fau l t
with a number o f splays on the north side (Figs. 11A , 3 ) . T h e splays bound
2 6
subsidiary upthrown faul t s l ivers t h a t resemble horsts on seismic sections.
Chukchi Syntaxis
The Chukchi syntaxis (Tail leur and Brosgk, 1970) i s the right-angle junc-
tion o f the westerly striking thrust faulted Paleozoic and Triassic terrane of
the Brooks Range with the north and northwest-striking Lisburne Hills and
Herald arch (Fig. 3 ) . Tailleur and Brosgk suqgest that the Lisburne Hills and
Herald arch are a simple extension o f the Brooks Range structural trend that
was rotated into i t s present position, re la t ive to the Brooks Range, by o ro -
clinal bending a t the Chukchi syntaxis. I n th i s model, Herald f a u l t zone i s a
seaward extension o f the frontal thrust fau l t s o f the Brooks Range beyond a
re lat ively minor kink a t the Lisburne Peninsula. Grantz e t a l . (1970a) consider
the Herald arch and fau l t zone t o be the leading edge of an easterly directed,
somewhat younger thrust f au l t system that crosscuts the Brooks Range and i t s
thrusts. I n th i s case, the Chukchi syntax's was created by the superposition
of the Herald fau l t zone across the western Brooks Range and the detachment
folds that l i e in front of i t .
The Herald f au l t zone trends across the detachment folds o f the Colville
foredeep a t an angle of 450, y e t there appears t o be no faulting between the
outer thrust folds of the f au l t zone and the intersected detachment folds (Figs.
8 o r 9, and Grantz e t a1 . , 1970a). These relations are most simply explained
i f the Herald fau l t zone and i t s inferred onshore extension, the thrust fau l t
system that bounds the east side of the Lisburne Hil ls , postdate and are super-
imposed across the detachment folds (see also Chapman and S a b l e , 1960; and
Martin, 1970). The suggested superposition c o u l d have created the Chu kchi syn-
taxis. Additional evidence bearing on the origin of the syntaxis comes from
pal eomagneti c poles in Mississippian (lower Lisburne Group) beds on the Lisburne
Peninsula and in the western Brooks Range (Newman e t a l . , in press). Prelim-
inary data suggest that these poles have a common orientation even though they
occur on both flanks of the syntaxis. This resu l t i s d i f f i c u l t t o reconcile
with t he orocline hypothesis b u t i t i s a t l eas t compatible with the superposi-
tion hypothesis fo r the origin o f the syntaxis. The age of the syntaxis i s
Late Cretaceous o r early Tertiary since Albian s t r a t a are strongly deformed in
i t s core and i t s apex i s blanketed by Paleogene(?) beds in Hope basin.
Hope Basin
Hope basin (Figs. 9 and 10) 1 ies between the presumed Paleozoic rocks of
the Herald arch to the northeast and the Paleozoic and Precambrian rocks of
Seward and Chukotsk Peninsulas to the southwest. I t overlies strongly deformed
Lower Cretaceous (Albian) and older rocks (Campbell, 1967) o f the Brooks Range
orogen. Low seismi c velocities ( V p = 1 . 7 t o 3.3 km/sec) , the age of the under-
lying rocks, and the character and age of nearby onshore sedimentary basins
suggest t h a t Hope basin i s f i l l e d with Tertiary and possibly some Upper Creta-
ceous sediments. A series of basement ridges subdivides the basin into a number
o f east-west troughs in which sediment thicknesses locally exceed 3,000 m. The
largest of the basement ridges i s Kotzebue arch, a structural high that trends
westerly across the southern part of the basin (Fig. 9 ) . This arch, which ap-
pears to have existed since the early Tertiary, is overlain by several hundred
meters of Tertiary sediments. The smaller ridges that 1 i e between the Kotzebue
and Herald arches are more deeply buried. Kotzebue arch i s a1 ined a t Cape
Krusenstern with the east and east-northeast-trending Igichuk Hil ls , which may
be i t s onshore extension, Indeed, an easter ly-s tr i king positive 1 inear gravity
anomaly along the arch (Ostenso, 1968) trends onshore and follows the western
Igichuk and Kiana Hills t o the Kobuk River near Kiana (Barnes, 1976), 150 km
inland.
During Neogene time, a deep, east-west e longate sub-basi n developed i n
eastern c e n t r a l Hope bas in n o r t h o f Kotzebue arch. The a x i s of the sub-basin
i s def ined by a th icken ing o f t he sedimentary sec t i on above a key reg iona l
se ismic r e f l e c t o r which i s be l ieved t o approximate the Neogene/Paleogene boun-
dary. Subsidence of t h e sub-basin was accommodated by numerous a n t i t h e t i c and
normal f a u l t s (F ig . l o ) , and the arch i t s e l f was concur ren t ly u p l i f t e d several
hundred meters. Between Po in t Hope and Cape Krusenstern the Neogene sub-basin
i s bounded by normal f a u l t s p a r a l l e l t o t he coast t h a t a lso form the western
boundary o f the De Lonq Yountains and the western Brooks Range. The nor thern
boundary o f t h e sub-basin i s a ser ies o f monoclines and normal f a u l t s t h a t
b r i n q o lde r rocks t o the sur face i n Herald arch. Westward, the Neoqene sub-
basin qradua l ly diminishes i n depth, and near 1710 W. l onq i t s r i d g e and trough
s t ruc tu res d i e ou t e n t i r e l y .
An episode o f vo lcan ic and t e c t o n i c a c t i v i t y s t ronq ly a f fec ted the Seward
Peninsula and lower Kobuk Va l ley beginning i n l a t e Miocene time. P l i o - P l e i s t o -
cene basa l ts f looded a l a r g e area south o f Kotzebue Sound and t e c t o n i c warping
and f a u l t i n g o f fse t Miocene gravels and Ple is tocene g l a c i a l deposi ts . These
displacements were accompanied by the formation o f s i z a b l e nonmarine sedimentary
basins and by b lock f a u l t i n g i n and adjacent t o the K ig lua i k and Bendeleben
Mountains o f the Seward Peninsula and the Waring Mountains o f the lower Kobuk
Va l ley (Hudson, 1977; Patton, 1973). This tectonism may a l so have been respon-
s i b l e f o r the Neogene subsidence, arching, and f a u l t i n g i n Hope basin.
Hope basin developed i n two steps. A Neogene sub-basin l ess than 100 km
wide resu l ti ng from 1 a t e T e r t i a r y extensional t e c t o n i sm formed w i t h i n a broader
mid-Ter t ia ry o r Paleogene basin more than 200 km wide t h a t was produced by Late
Cretaceous-Early T e r t i a r y subsidence. Regional onshore s t r a t i g r a p h y suggests
t h a t both basins cons i s t a t l e a s t p a r t l y , and perhaps l a r a e l y , of nonmarine
rocks. However, a few marginal outcrops o f Neogene marine s t r a t a and the p e r i -
od i c m ig ra t i on o f Neogene marine faunas across Ber ing S t r a i t (Hopkins, 1967)
i n d i c a t e t h a t some marine beds must occur i n the Neogene sub-basin, which sub-
sided r a p i d l y . I n bo th the o l d e r and yuunger basins marine rocks may rep lace
nonmarine rocks away from shore.
North Chukchi Basin
The North Chukchi basin (Grantz e t a l . , 1975, p. 687-690) under l i es t h e
nor thern Chukchi She l f between the western Barrow and Wrangel arches on the
east and south and the Chukchi Cont inenta l Borderland on the no r th ( F i g . 3 ) .
The wester ly ex ten t o f the basin i s no t known.
The North Chukchi bas in conta ins a t h i c k prograded sequence of Brookian
c l a s t i c sedimentary rock. Our seismic r e f l e c t i o n data and a long r e f r a c t i o n
l i n e by Hunkins (1966) i n d i c a t e t h a t t he t o t a l sec t ion i s more than 6 km t h i c k
(F igs . 8 and 11). Se ismic p r o f i l e s show t h a t some beds i n the bas in onlap the
Barrow arch on the south, b u t we l ack data from t h e i r contac t w i t h the Chukchi
Borderland t o the nor th . Although both nonmarine and marine beds occur i n the
Brookian sequence i n northwest Alaska, the equ iva len t rocks i n the North Chukchi
basin a re probably mainly, and perhaps e n t i r e l y marine. The basin fill can be
d i v ided i n t o two to f o u r s t r a t i g r a p h i c packets on the basis o f unconformit ies
seen on single-channel seismic r e f l e c t i o n p r o f i l e s . Sonobuoy r e f r a c t i o n ve lo -
c i t i e s and c o r r e l a t i o n s w i t h the s t r a t i g r a p h y o f nor thern A1 aska suggest t h a t
these u n i t s are Neogene, Paleogene, Cretaceous and pre-Cretaceous.
S t ra ta i n the southern p a r t of the North Chukchi bas in d i p as much as 150
no r the r l y . Basinward, t o the nor th, d i ps decrease t o between 00 and lo nor th-
e r l y . The absence o f beds w i t h a souther ly d i p component, even on l i n e s near
74' N. l a t w i t h i n 50 km o f the Chukchi Borderland, suggests t h a t the North
Chukchi rocks were deposited on th inned con t i nen ta l o r oceanic c r u s t r a t h e r
30
than in a subsiding intracontinental basin. I f so, these rocks may onlap high-
standing blocks of pre-Cretaceous (Frank1 inian(?) ) rocks in the Chukchi Border-
1 and.
Well-developed diapirs (Figs. 5 and 8 ) pierce Tertiary beds in the North
Chukchi basin t o within a few tens of meters of the seabed (Grantz e t a l . , 1975,
p . 689-693). Low sonobuoy veloci t ies , apparent lack o f strong gravity or mag-
netic anomalies (Fig. 1 2 ) , and regional stratigraphy suggest that the diapirs
are probably shale, rather than s a l t , gypsum, or igneous rocks. Possibly the
diapirs consist of so f t Jurass ic (?) or Lower Cretaceous prodel t a shale, an early
deposit in the basin subsequently deeply buried by rapidly deposited slope,
shale, or del ta ic sediment. Such shale, being weak and of relat ively l ow densi-
ty , might have risen buoyantly toward the seabed under the load of thick over-
lying sediments, piercing and bending the adjacent beds upwards in the process.
Five diapirs (two crossings, three near-misses) have been identified in the
basin to date. The best studied i s about 2 km in diameter and extends t o 3 km
or more beneath the seabed. Judging from the number found and the density of
our 1 ine coverage, something 1 i ke 33 or 40 diapirs may be present.
Western Beaufort Shelf Sedimentary Prism
Sediments
A re lat ively narrow northward-prograded sedimentary pri srn consisting
primarily of Brookian rocks underlies the continental terrace of the western
Beaufort and northeast Chukchi Seas (Fig. 3 ) . Between the North Chukchi basin
and Camden Bay, the prism overlies Franklinian rocks on the north flank of the
Barrow arch, Beneath the southern part of the shelf , the sequence includes
locally thick sections of upper Ellesmerian Jurassic and Neocomian beds of
northern provenance (Fig. 13B) and, in places near shore, the northern wedge
edges of ~re - Ju ras s i c Ellesmerian formations. Between Harrison and Camden Bays
the Tertiary beds of the Brookian sequence thicken and extend more than 100 km
inland t o form the Camden basin.
West o f Harrison Bay the sedimentary prism consists mostly of Lower Creta-
ceous marine rocks with a Tertiary wedge o f unk~own character beneath the outer
shelf and slope. The thickness o f t h i s sequence i s 1 to 3 km near the coast
and 6 t o 8 km beneath the outer shelf. Between Harrison and Camden Bays, how-
ever, the prism consists mainly of Upper Cretaceous and Tertiary beds, with
the Tertiary becoming dominant near Camden Bay. Here the prism i s 3 to 6 km
thick a t the coast and 6 to 8 krn thick on the outer shelf. Onshore correlatives
of these rocks are b o t h marine and nonmarine. The lower part of the Tertiary
and probably the upper part of the Upper Cretaceous section in the Camden embay-
ment contain coal beds (Alaska Geological Society, 1977). B o t h the Tertiary
and Cretaceous beds are presumed to become more marine and f iner grained sea-
ward.
Eas t from Camden Bay, Jurassic and Neocomian deposits as well as l a t e r
Cretaceous and Tertiary deposits crop o u t on the Arctic Coastal Plain and are
interpreted t o project offshore beneath the Western Beaufort Shelf. Dark-gray
Kingak Shale with Middle Jurassic (Bajocian) marine foss i l s (Reiser e t a l . ,
1978) crops out on the coastal plain 30 km southeast of Barter Island. The o u t -
crops are surrounded by Early Cretaceous (Neocomian) and Late Cretaceous
(Turonian) marine shale. Farther eas t , Norris (1977) interprets about 1,800 m
of Kingak Shale (Jurassic and lowest Cretaceous) to extend northward beneath
the Beaufort Shelf from outcrops near the Yukon coast, where the formation over-
laps pre-Ellesmerian rocks. The outcrops o f Kingak Shale near Barter Island
l i e 30 km north of the easterly projection o f the truncation edge (zero iso-
pach) o f the northward-thinning Kingak Shale. This isopach trends from near
Barrow on the west t o the eastern Sadlerochit Mountains, 50 km south-southwest
of Barter Island. Thus, a thick and extensive section of the Jurassic Kingak
Shale appears to be included a t the base of the Western Beaufort Shelf sedi-
mentary prism beneath the shelf t o the east , b u t not t o the west, of eastern
Camden Bay.
Structure
The Western Beaufort Shelf contains three terranes of contrasting geologic
structure. In the f i r s t structural terrane, which extends from Camden Bay t o
the Alaska-Yukon boundary, the inner half o f the shelf i s underlain by two
large, compound structural arches or antic1 ines and several much small e r ant i -
cl i nes (Figs. 5 and 13A). The 1 argest arch exceeds 200 km in 1 ength and 10 t o
15 km in width; i t s maximum amplitude exceeds 4 km. The arches and anticlines
are subparallel t o the adjacent arcuate coastl ine and t o long, large-amplitude
onshore folds, such as Marsh ant icl ine, that l i e in front of the northward
sa l ien t of the Brooks Range in northeasternmost Alaska and northern Yukon Ter-
r i tory . The folds terminate along the projection of the structural front which
bounds the west face of th i s sa l ien t (Fig. 5 ) . This feature was informally
named the Shaviovi k Front by the l a t e Sankey L . Blanton (oral communication,
1977). The outer half o f the shelf in the f i r s t terrane i s underlain by a mono-
cl ine that dips seaward subparallel t o the seabed out to the main shelf break,
where the beds are dropped by slumping onto the continental slope.
The crests of the large arches are underlain a t depths as shallow as 0 .5 km
by s t r a t a with seismic velocities of 3.5 km/sec or more, which are appropriate
f o r the Cretaceous and Jurassic c l a s t i c sedimentary rocks of the region. Pre-
liminary interpretations o f CDP seismic sections indicate that i n places the
arches also contain south-dipping reverse fau l t s t h a t , on one seismic l ine ,
apparently dip about 150 S (Fig. 13A). The folding i s as young as Neogene, and
locally Quaternary, since beds o f these ages are affected in Marsh ant icl ine,
which underlies the Arctic Coastal Plain near Camden Bay.
The arches and associated folds are somewhat similar in geometry and
tectonic position t o the long, west-trending, dkcollement-related thrust-folds
of the Colville foredeep north of the Brooks Range and west of the Shaviovik
Front, although the folding occurred a t very different times in these two
areas. The eastern folds are thought t o be related to Neogene up1 i f t and nor-
thernward translation of the northeast sa l ien t of the Brooks Range, whereas the
f o l d s of the Colville foredeep are related to Laramide (Cretaceous and early
Tertiary) up l i f t and relat ive northward translation of the Brooks Range west of
the Shaviovik Front. A Laramide age is inferred because the thrust folds deform
Albian and Upper Cretaceous beds north o f the Brooks Range and are in turn
deformed in the Chukchi syntaxis, w h i c h is onlapped by Paleogene(?) beds i n
Hope basin.
The northern, and apparently larger, o f the offshore arches dies o u t near
western Camden Bay, O f f Canning River, 15 km west of our westernmost crossing
o f t h i s structure, only down-to-the-basin normal fau l t s with displacements o f -
100 or 200 m are seen on seismic profiles. Shallow water limited our profiles
here t o the outer two-thirds of the continental shelf , so we have no data a s
t o whether the southerly arch or related structures continue westward on the
inner shelf.
The second structural terrane of the Western Beaufort Shelf , which l i e s
offshore between the Canning River and Cape Halkett, i s characterized by a
monocl ine that dips typically 20 t o 60 m / k m seaward (Fig. 13B). This feature
is broken on the inner and mid-shelf by small down-to-the-basin normal fau l t s
that are more o r less parallel t o the she l f edge. The fau l t s become more numer-
ous toward the she1 f edge, where large down-to-the-basi n gravitational fa i 1 ures
dominate the structure.
The third structural terrane l i e s west of Cape Halkett. Here normal
fau l t s are prominent and a long structural high (Fig. 13C) under1 i e s the outer-
most shel f . The sedimentary section beneath t?e outer shel f contains intrafor-
mational slumps and growth fau l t s a t l eas t as f a r west as 1600 W . long (Figs,
10 and 13C). The outer shelf structural high i s syn- and post-depositional,
and i t therefore did not serve as a dam which trapped the deposits of the West-
ern Beaufort Shelf sedimentary prism. The high i s 20 to 25 km wide and extends
as a continuous or semicontinuous feature from western Harrison Bay t o a t l eas t
1600 W . , a distance of 350 km (Figs. 5 and 7 ) . I t s amplitude i s typically
0.3-0.5 km a t depths o f about 1 km, and in places as much as 1.5 km a t depths
o f 7.5 t o 2 . 0 km. Preliminary interpretation suggests that the feature was
produced by rotation along normal or growth fau l t s ( F i g . 13C) during Late
Cretaceous and Tertiary time, On one COP seismic section the growth fau l t dips
about 500 N. and displacement i s down to the north about 1.5 km. An analogous
b u t smaller and discontinuous feature, locally obscure, extends from Harrison
Bay t o Camden Bay.
Block Glides
The surface o f the outermost continental shelf between 1550 W. long on the
east and beyond 158030' W. long on the west i s broken by mu1 t i p l e open cracks
that deepen seaward toward the shelf break (Figs. 2 and 14). Water depth in
the affected areas i s 70 to a t leas t 350 m. Similar features buried beneath
Holocene sediment and low scarps border the zone on the south. The cracks and
associated features are thought to be the resul t o f Holocene block gliding.
The affected sediments are f l a t lying, as much as 140 m thick, and readily
penetrated by low-energy acoustic signals. They probably consist of poorly
consolidated Quaternary deposits. Reflection character is t ics and the ab i l i t y
to support deep open cracks suggest that the upper part of the section, which
i s well bedded, consists of l u t i t e and f ine sand. The lower part i s more homo-
geneous and probably 1 u t i t e , except for interval s characterized by broken, i r-
regular ref lectors . These intervals a re inferred to be s l i p zones over which
the large blocks bounded by the observed cracks glide toward the shelf break.
The gentle seaward dip of the s l i p zones, about l o , and the inferred parallel-
ism of the s l i p zones and bedding suggest that the slippage occurs within beds
that are weak or susceptible t o liquefaction. The block-glide terrane i s adja-
cent to Barrow Sea Valley and the northeast-flowing Alaskan Coastal Water,
which may be supplying sediment in the s i l t and very f ine sand grades tyoical
of 1 iquefiabl e sediments.
The open cracks are commonly as deep as 8 rn t o 17 m, and one exceptional
crack i s 37 m deep. Downward, they persis t as f i l l ed cracks and closed frac-
tures t o depths of 40 or 50 m, and locally t o 75 m below the seabed, ending a t
the inferred s l i p zones. The cracks are typically a1 ined subparallel to the
shelf break and spaced 100 m to 500 m apart. Their spacing in general de-
creases seaward. The fac t that many o f the cracks are unfilled indicates that
the block gliding i s s t i l l an active, or potentially active, process. Three
lower-level s l i p zones and glide sheets have been recognized in places beneath
the active, or quasi-active surf ic ial glide sheet on hiqh-resolution seismic
records.
Beddi ng P l ane Sl ides
A mosaic of bedding plane s l ides similar in origin and character to the
block glides underlies the upper half o f the Beaufort Ramp between 1480 W . l o n g
and the Mackenrie Sea Valley, a distance of about 300 km (Figs. 2 and 1 5 ) . The
slides are 10 t o 43 km long in the direction o f s l i p and 70 to 230 m thick.
36
The dip of the basal s l i p planes i s typically 0.50 to 1.50. The s l ides occur in
a downsl ope-thinni ng prograded wedge o f quaternary(?) sediment beneath the up-
per Beaufort Ramp seaward from the crestal zones of mid-shelf ant ic l ines . Over
most of the i r length the upper parts of the s l ide masses are slabs of soft.seci5-
ment broken by many extensional fractures. The lower beds appear on seismic
profiles to be churned and dismembered. Variation in thickness of the s l ides
of about 20 to 50 percent, caused by internal flowage in the lower beds, i s
superimposed upon a general downslope thinning o f the wedge of sediment in
which the sl ides developed.
A t the landward margin of the Beaufort Ramp, near the 60-m isobath, the
s l ides are bounded by well-defined slip-plane scarps and pull-apart grabens.
The s l ide toes are usually low bulges that merge with the gently sloping seabed.
Presumably, the s l i p planes diss ipate the i r displacement downsl ope mainly by
internal distortion within the lower part o f the s l ide . The s l i p planes a r e
subparallel t o bedding, a geometry that suggests the shearing occurred in rela-
t ively weak or sensit ive s t ra ta . Estimates of the horizontal s l i p a t the head
of well-developed s l ides range from 0.2 to 2 . 3 km, with a median value of about
1 km.
Near 1450 W . long the lower 15 km o f the s l ide i s only 20 t o 30 m thick
and consists o f surf ic ial sediment with we1 1 -developed bedding that i s para1 le l
t o the seabed and the s l ide plane. This thin part of the s l ide i s character-
ized by numerous extens ion cracks 0.25 to 1.5 km apart , measured down the slope,
and closely resembles the block q l ides west o f 1510 W. long. The thin s l ide
extends t o the shelf edge, where i t slumps down the upper continental slope.
According t o Hopkins (1973), sea level in the Bering Sea dropped to about
130 m be1 ow the present level during the penultimate Pleistocene regression,
approximately 125,000 years ago, and t o 90 t o 100 m below present sea level
dur ing the maximum l a t e . Wisconsin regression, approximately 15,000 t o 20,000
years ago. .The heads of t h e bedding-plane s l i des , now l y i n g a t depths o f 57 t o
70 m (F ig. 15) , were thus emergent du r ing the Ple is tocene regressions i n sea
1 eve1 . Emergence, which increased the g r a v i t a t i o n a l load on the sediment a t
the head of t he ramp by removing the buoyant support o f t he upper p a r t of the
water column, i s thought t o have t r i g g e r e d the bedding-plane s l i d e s . Grabens
and scarps a t t he head of t he s l i d e s and the l a c k of evidence f o r undercu t t ing
a t the toes support t h i s hypothesis. The apparent morphologic youthfu lness
( i .e., roughness) o f the s l i d e s suggests t h a t they moved dur ing o r a f t e r t he
maximum l a t e Wisconsin regression r a t h e r than du r ing the o lde r , penul t imate
regression some 110,000 years e a r l i e r . Superimposed m u l t i p l e s l i p planes ob-
served w i t h i n the s l i d e masses on some o f our h igh - reso lu t i on seismic p r o f i l e s
suggest the p o s s i b i l i t y t h a t the remnants o f o lde r s l i d e s , perhaps r e l a t e d t o
o l d e r regressions, may be present beneath the i n f e r r e d l a t e Wisconsin s l i d e s .
Diapi r i c Folds Beneath the Cont inenta l Rise
D i a p i r i c f o l d s d i s r u p t bedding i n t h e sedimentary rocks of t he lower Alas-
kan Continental Slope and Rise and adjacent p a r t s o f the Canada Rise east of
1460 W. l ong (F igs. 5, 13A and 17) . The f o l d s a re 5 t o 10 km apar t along l i n e s
normal t o t he slope and as much as 0.5 km i n amplitude. Some appear t o be
elongate p a r a l l e l t o the slope, b u t f o r most,our 1 ines are too w ide ly spaced t o
d i s t i n g u i s h between r i d g e o r dome shapes. The geometry and p o s i t i o n of the
d i a p i r i c f o l d s suggest t h a t they rose as a consequence o f the load ing o f l a r g e
s l i d e s and t h i c k c l a s t i c sediment onto the lower con t i nen ta l s lope and r i s e .
Equal ly l a r g e s l i d e s and t h i c k sediment a re found, however, on the slopes west
o f the d i a p i r s . This d i s t r i b u t i o n suggests t h a t an e a s i l y deformed sedimentary
u n i t suscept ib le t o d iap i r i sm under l ies the cont inenta l s h e l f and r i s e east,
bu t no t west, o f 1460 W. long. Seismic i n t e r v a l v e l o c i t i e s i n the d i a p i r i c
m a t e r i a l va ry f rom 2.6 t o 3.0 km/sec, a p p r o p r i a t e t o shale, whereas se ismic
v e l o c i t i e s i n t h e neighborhood o f 4.6 km/sec, a p p r o p r i a t e t o s a l t , were n o t ob-
served. On t h e bas i s o f t h e i r apparent s t r a t i g r a p h i c p o s i t i o n ( F i g . 13A), we
t e n t a t i v e l y suggest they may be lower T e r t i a r y ,
Because t h e d i a p i r i c f o l d s buck le t h e seabed and pond t h e youngest (Holo-
cene) sediments and slumps on t h e c o n t i n e n t a l s l ope and r i s e , i t i s l i k e l y t h a t
d i a p i r i s m i s a c t i v e now, o r a t l e a s t was a c t i v e d u r i n g t h e Holocene. The phys io-
g raph ic d i s t i n c t i o n between c o n t i n e n t a l s lope and r i s e i s obscured 'n t h e area
o f t h e d i a p i r i c f o l d s because the f o l d s have f o c a l l y t ransformed the Alaska
R i s e from a smooth sedimentary apron t o a s e r i e s o f ba thymet r i c steps. I n
places the d i a p i r i c fo lds have so thorouah ly d i s r u ~ t e d t he A laska R i s e sedimen-
t a r y p r i sm t h a t bedding i s obscure. Beneath ad jacen t p a r t s o f t h e Mackenzie
Cone, however, some d i a p i r i c folds u n d e r l i e und is tu rbed beds more t 1 u n 1,500 rn
t h i c k . Low se ismic v e l o c i t i e s and est imated sedimentat ion r a t e s i n l i c a t e t h a t
t h e und is tu rbed beds a re Neogene and P le is tocene. T h u s , some o f t h ? d i a p i r s
appear t o have been i n a c t i v e s i nce t h e Neogene.
S o l i d Gas Hydrate
Much o f the c o n t i n e n t a l s lope and r i s e n o r t h o f Alaska i s u n d e r l a i n by an
unusua l l y s t r ong se ismic r e f l e c t o r (Grantz e t a1 ., 1976) t h a t crosses bedding
planes a t many p laces. The r e f l e c t o r mimics, or s imu la tes , t h e bathymetry o f
t he sea f l o o r , y e t 1 i e s some 200 t o 600 rn beneath i t (F igs . 13A, 13E, and 17) .
Th i s bo t tom-s imu la t ing r e f l e c t o r (BSR) occurs o n l y where the sea i s deeper than
400 t o 600 m and was recognized beneath waters as deep as 3,200 m, The BSR was
i d e n t i f i e d beneath some 60 percen t o f our se ismic l i n e s on t h e Alaska Slope
and Rise where t he water depth exceeded 400 t o 600 m. I t i s most s t r o n g l y
developed beneath ba thymet r i c highs and weakest, and indeed commonly absent,
beneath ba thymet r i c lows. I n a few p laces where i t i s p a r t i c u l a r l y w e l l deve l -
3 9
oped beneath h ighs, the unde r l y i ng r e f 1 ec to r s a r e bowed downward, These gbser-
v a t i o n s suggest t h a t t a e BSR represen ts t h e i n t e r f a c e of a zone o f f r e e gas i n
t h e sediments and an o v e r l y i n g impervious cap. Because t h e BSR l i e s a t t he ap-
prox imate pressure- temperature boundary a t which s o l i d gas hydra tes o f methane
and some mult icomponent n a t u r a l hydrocarbon gases break down t o a gas t water
phase, we p o s t u l a t e t h a t i t i s produced by f r e e gas t rapped beneath an irnper-
meable cap of sediment cemented w i t h gas hydrate.
Canada Basin
Water depths exceeding 3,500 m and d i s p e r s i o n pa t t e rns o f Lg-phase se ismic
waves (01 i v e r e t a1 . , 1955) i n d i c a t e t h a t t h e Canada Basin i s u n d e r l a i n by
oceanic c rus t , and was t h e r e f o r e formed by s e a - f l o o r spreading. Some workers
( e . g . , Vogt and Ostenzr, 1970; H a l l , 1973) have pos tu l a ted t he spreading center
t o be the Alpha-Mende'zev Ridge, which crosses t h e bas in from Greenland t o
eas te rn S ibe r i a . Carey (1 958), T a i l 1 eur (1969 and 1973) , and Rickwood (1970)
suggest t h a t the Canada Basin opened by a r e l a t i v e r o t a t i o n o f n o r t h e r n Alaska
away from the Canadia.~ A r c t i c Is lands about a p o l e near t h e Mackenzie D e l t a o r
i n Alaska. Herron e t a1 . (1 974) p o s t u l a t e t h a t t h e Canada Basin formed by
r i f t i n g o f t h e Kolymski mass i f o f eas te rn S i b e r i a away f rom t h e Canadian A r c t i c
I s l ands a long a n o r t h e r l y t r e n d i n g spreading a x i s , and Yorath and N o r r i s (1975)
propose a n o r t h e r l y t r e n d i n g a x i s of assymetr ic spreading beneath the head o f
t h e c o n t i n e n t a l r i s e i n t he eas te rn Beaufo r t Sea.
The i n f e r r e d th ickness o f sediment i n t h e southern p a r t o f t h e Canada
Basin i s shown by d o t ~ e d isopach fo rml ines i n F igu re 5 . The th icknesses a re
based on t h r e e sonobuoy r e f r a c t i o n p r o f i l e s and t h e assumption t h a t d i f f e r e n c e s
i n depth o f t h e seabed r e f l e c t d i f f e r e n c e s i n t h e th ickness o f sediment t h a t has
accumulated on oceanic c r u s t i n t he bas in . As t h e age o f t h e Canada Basin i s
i n f e r r e d from s t r a t i g r a p h i c r e l a t i o n s t o be Ju rass i c o r Early Cretaceous,
d i f fe rences i n age from the center t o t he sides a r e probably n o t s i g n i f i c a n t
t o th ickness estimates. We the re fo re assumed t h a t a l l p o i n t s i n the bas in a r e
i n i s o s t a t i c e q u i l i b r i u m and generated isopach form1 ines from the bathymetr ic
contours by c o r r e l a t i n t he isobaths w i t h sediment th ickness a t t h ree sonobuoy ( ~ i g - 5y.
r e f r a c t i o n s t a t i o n s i Sediment dens i t y f o r our model was based on the sonobuoy-
der ived v e l o c i t i e s , which suggest t h a t the average dens i ty o f the sedimentary
3 f i l l beneath the Canada Rise i s about 2.2 g/cm . We assumed a mantle dens i ty
3 of 3.4 gm/cm and t h a t the 5.3 krn/sec, 4.9 km/sec, and 4.6 km/sec r e f r a c t o r s
are from the top o f oceanic l a y e r 2 ( b a s a l t ) . On the bas is o f these assump-
tions, about 4 . 5 km o f sediment under l i es the Canada Abyssal P l a i n . Hall (1973),
on the basis o f seismic r e f l e c t i o n data, repo r t s t h a t more than 2 krn o f sed i -
ment under l ies the nor thern p a r t o f t h i s p l a i n .
An est imate o f the age o f the Canada Basin can be made from the thickness
o f sediment t h a t i t conta ins. I f we assume t h a t oceanic c r u s t beneath the
basin was i s o s t a t i c a l l y depressed by the ove r l y i ng sedimentary prism, we can
c a l c u l a t e the depth o f an "unloaded1' c r u s t and compare i t w i t h empir ica l . age-
depth curves f o r the A t l a n t i c and P a c i f i c sea f l o o r . Such curves were compiled
3 most r e c e n t l y by Parsons and Sc la te r (1977). Using mantle dens i t y 3.4 g/cm ,
sediment dens i ty 2.2 g/crn3, and water dens i t y 1.03 g/crn3, our data from the
th ree sonobuoys i n deep water g i v e a "corrected" depth t o basement o f 6 .4 km
for the southern Canada Basin. This depth corresponds t o a c r u s t a l age greater
than 120 m.y.b.p. on the Parsons-Sclater curves. I n t h i s region, however, the
curves have a low slope, and small u n c e r t a i n t i e s i n t he unloaded depth produce
l a r g e unce r ta in t i es i n age o f sea f l o o r . Thus the s ign i f i cance o f t he "unloaded"
depth we obtained (6 .4 km) i s t h a t i t argues f o r a Mesozoic age fo r the c r u s t
of the Canada Basin.
4 1
Segmentation of the Alaskan Continental Margin
The continental margin no r th of Alaska consists of three sectors of con-
t rast ing geology separated by onshore extensions of possible oceanic fracture
zones. The Chukchi sector i s characterized by the North Chukchi basin and the
Chukchi Continental Borderland; the Barrow sector is characterized by the Bar-
row arch, where Cenozoic sedimentary rocks are relat ively thin o r absent and
where Mississippian t o Neocomian sedimentary rocks coarsen, thin, and wedge o u t
to the north; and the Barter Island sector i s characterized by thick Cenozoic
as well as Jurassic and Cretaceous e l a s t i c sedimentary rocks that appear to have
been der ived from the south and t o become thicker and f iner grained t o the
north. Large Neogene folds in Jurassic t o Neogene s t r a t a and the northward
sal ient of the northeastern Brooks Range a l s o characterize th i s sector.
The Chukchi and Barrow sectors are postulated t o be separated by a fracture
zone along the northwest flank of the Barrow arch west of 1600 W . lons. The
Chukchi Borderland may consist of fragments of continent that were transported
relat ively north-northeast, away from the Chukchi Shelf, along the fracture
zone t o create the North Chukchi basin. The Barrow and Barter I s l a n d sectors
may be separated by a fracture zone near eastern Camden Bay, b u t i t s location
and trend have n o t been recognized. The northern coastal plain and shelf east
of the postulated fracture zone i s apparently underlain by a thick section o f
Jurassic sedimentary rocks that i s thin or absent to the west ( F i g . 13A, 130) .
The character and distribution of the Jurassic and Neocomian bedded rocks
are c r i t i ca l fo r understanding the geometry and age of the r i f t ed Alaskan mar-
gin. On the east , in the Barter Island sector, Jurassic and Neocomian sedi-
mentary rocks in northern Yukon Territory (Kingak Shale) appear to have southern
sources and to f ine northward (Young e t a1 . , 1976; Figs. 4 , 5 , and 7 ) . These
rocks are interpreted to be 1,800 m thick under the adjacent Beaufort Shelf
(Norri s , 1977). As noted above, the Kingak Shale and the Neocomi an Kongakut
Formation also crop out on the Arctic Coastal Plain 30 km southeast o f Barter
Island. In the Barrow sector, in contrast , Jurassic and Neocomian s t r a t a have
northern sources and fine southwa~d. I f projected east or east-southeast along
the general trend of the depositional s t r ike and the truncation edge of Jurassic
s t r a t a on the Barrow arch, the source area would s t r ike into the area of thick
Jurassic and Neocomian marine s t ra ta inferred to underlie the coastal plain and
shelf in the Barter Island sector. I f projected west-northwest, the source area
would s t r ike into the deep North Chukchi basin of the Chukchi sector. These
relations, and the fac t that the Upper Triassic rocks of both the Barrow and
Barter Island sectors were derived from northern sources (Tai 11 eur, 1969 and
1973; BrosgP and Tai 11 eur, 1971 ; Detterman e t a1 . , 1975; Norris, 1977) indicate
that r i f t i ng of the Alaskan margin began in Early Jurassic time.
A northern source for the Kingak Sha le and Neocomian s t r a t a of the Barrow
sector i s supported by subsurface stratigraphic data, b u t a southern source for
these beds beneath the coastal plain and shelf in the Barter Island sector i s
less firmly based. As noted here, a southern source i s inferred from a few out-
crops in the Arctic Coastal Plain, preliminary interpretation of seismic records
on the continental shelf, and extrapolation of facies maps o f Jurassic and
Cretaceous sedimentary rocks in the Mackenzie Del t a region. I f t h i s d i s t r i bu-
tion of source terranes i s correct, i t implies that in the Barter Island and
Chukchi sectors Barrovia, the northern source terrane fo r the Ellesmerian se-
quence o f the Arctic platform, was r i f ted away from the platform i n Early Juras-
s i c time. In the Barrow sector , however, the r i f t would have lain far ther north,
within Barrovia, and a large east-west-trending welt or island of the Barrovian
highlands would have remained attached t o the Arctic platform. The south shore
of the island would have faced the epicontinental sea that covered the Arctic
platform in Jurassic and Neocomian time. We propose that the postulated island
was t h e waning no r the rn provenance area f o r t h e J u r a s s i c and Neocomian sed i -
mentary rocks (Kingak Shale, Kuparuk R i v e r Sandstone, and "Pebble ~ h a l el')of
t h e Barrow sec to r of n o r t h e r n Alaska. I f a d d i t i o n a l work shows t h a t t h e Juras-
s i c and Neocomian beds beneath t h e coas ta l p l a i n and s h e l f o f t h e B a r t e r I s l a n d
s e c t o r were der i ved from t h e no r th , r a t h e r than f rom t h e south, then t he age of
r i f t i n g would have been E a r l y Cretaceous. I t would have accompanied o r pos t -
dated d e p o s i t i o n o f t he Neocomian "Pebble Shale" o f t h e Barrow sec to r , when
sedimentat ion f rom no r the rn sources was waning, and predated the a r r i v a l of
south-sourced (Brook ian) c l a s t i c sediments on the Western Beaufort S h e l f i n A l -
b i a n t ime.
SUMMARY OF TECTONIC IMPLICATIONS AND CONSTRAINTS
1. The c o n t i n e n t a l marg in n o r t h o f Alaska i s o f At1 a n t i c t ype and was formed
by r i f t i n g . Our da ta a re compat ib le w i t h t h e proposals o f Carey (1958),
T a i l l e u r (1969 and 1973), Rickwood (1970), and Neman e t a l . ( i n p ress)
t h a t t he Canada Basin was formed by r i f t i n g i n v o l v i n g a r e l a t i v e r o t a t i o n
o f n o r t h e r n Alaska away f rom t h e Canadian A r c t i c I s l ands . The pole of
r o t a t i o n was probably i n the r e g i o n o f t h e Mackenzie De l ta , as suggested by
Rickwood.
2 . Northern sources f o r t h e M i s s i s s i p p i a n t o Lower Cretaceous c l a s t i c sediments
a long t h e Barrow arch o f no r t he rn Alaska d im in ished i n importance i n Juras-
s i c and Neocomian t ime and were removed by t h e c l o s e o f Neocomian t ime.
Removal i s a t t r i b u t e d by T a i l l e u r (1969 and 1973) t o opening o f t h e Canada
Basin by r i f t i n g i n pos t -T r i ass i c , probably E a r l y Ju rass i c t ime. Rickwood
(7970) proposes opening i n t h e La te Ju rass i c and E a r l y Cretaceous. Our
t e n t a t i v e i n t e r p r e t a t i o n o f data on t h e cha rac te r an3 d i s t r i b u t i o n o f Juras-
s i c and Neocomian s t r a t a i n the B a r t e r I s l a n d sec to r i n Young e t a1 , (1976),
N o r r i s (1977); Reiser e t a l . (1978) and t h e present r e p o r t suggests t h a t
r i f t i n g may have begun du r i ng the E a r l y Ju rass i c . A submarine canyon c u t
44
more than 1.4 km into seaward-prograded Albian marine c l a s t i c deposits be-
tween Barrow and Harrison Bay and f i l l e d with Turonian marine sediments
(Collins and Robinson, 1967, p . 183) indicates that the Canada Basin was
open by middle Cretaceous time.
3. Continental extensions of oceanic fracture zones related t o the geometry of
r i f t i ng are postulated t o have divided the northern Alaska continental
margin into three sectors o f contrasting structure and stratigraphy. The
northeasterly trend of the postulated fracture zone between the a n d
ChukchiABarrow sectors i s compatible with proposals that r i f t i ng occurred
about a pole o f rotation near the Mackenzie Delta. Stratigraphic contrasts
in the three sectors suggest that the postulated r i f t lay far ther south in
the Chukchi and Barter Island sectors than in the Barrow sector. These
relations also imply that in early pos t - r i f t (Jurassic and bleocornian) time
Barrovia was reduced to an easterly-trending jsland beneath the present
outer continental she1 f and slope in the Barrow sector. East and west of
the island lay deep marine embayments of the Chukchi and Barter Island
sectors.
4 . The Western Beaufort Shelf i s underlain by a sedimentary prism o f A1 bian
( l a t e Early Cretacecus) t o Quaternary age that was prograded across a
subsiding shelf underlain mainly by bedded rocks of the Franklinian sequence.
5. The great thickness of seaward-prograded sediment in the North Chukchi basin
and i t s position between the Chukchi Borderland and the Barrow and Wrangel
arches suggest that the basin i s floored by oceanic crust or thinned con-
tinental crust.
6 . I f continental out1 iers of the Chukchi Borderland originally occupied what
i s now the North Chukchi basin, i t would remove a major obstacle t o a simple
geometric f i t of opposite margins of the Canada Basin. Such a f i t would
be required i f the basin formed by rotation in the manner proposed by Carey
45
(1958), Tail 1 eur (1969 and 1973) and Rickwood (1 970).
7. The shale(?) d i a p i r s t h a t u n d e r l i e the North Chukchi bas in and the con t i n -
en ta l s lope and r i s e o f f the Bar te r I s l a n d sec tor occur i n the deepest
basins along the present nor thern Alaskan con t i nen ta l margin.
8. Pre-Mi ss i ss ipp ian basement ( t he Frank1 i n i a n sequence) under1 i e s the Barrow
sec tor o f the Western Beaufor t She l f and extends seaward t o the upper con-
t i n e n t a l s lope (Fig. 130). This d i s t r i b u t i o n suggests t h a t t he s lope may
approximate the p o s i t i o n o f the i n i t i a l r i f t t h a t i s pos tu la ted t o have
formed the Canada Basin. A zone o f subsided con t i nen ta l crust seaward of
the boundary i s not precluded.
9. Barrow arch may be thought of as a h inge l i ne created by Jurass ic t o Neo-
comian r i f t i n g o f the A r c t i c p la t fo rm. The no r th f l a n k o f the arch was
created by subsidence, normal f a u l t i n g , and eros ional t r u n c a t i o n near the
r i f t e d margin. The south f l a n k i s a compound o f paleoslope and o f t i l t i n g
o f the southern p a r t o f the A r c t i c p la t fo rm i n response t o sediment loading.
The sediments consis ted o f J u r a s s i c ( ? ) and Ear l y Cretaceous nappes o f the
Brooks Ranqe fo re land t h r u s t b e l t and t h e t h i c k Brookian pr ism of Jurassi 'c,
Cretaceous and T e r t i a r y c l a s t i c sediment deposi t ed i n the Col v i 11 e foredeep
and on the adjacent A r c t i c p la t fo rm.
10. The progressive increase i n depth o f the she1 f break eastward from 1500 W .
long toward the Mackenzie Del ta may be r e l a t e d t o format ion o f the sea-
w a r d - t i l t e d Beaufor t Ramp. These fea tures suggest t h a t t he ou ter p a r t o f
the Western Beaufort She l f east o f 1500 W . long subsided i n response t o
load ing o f the adjacent Canada Basin by sediments o f t he Mackenzie Cone.
11. Thickness o f sediment and depth t o basement imply a Mesozoic o r o l d e r age
f o r the Canada Basin, assuming i t i s under la in by oceanic c r u s t and t h a t
the age versus depth r e l a t i o n s of Parsons and Sc la te r (1977) f o r t he
North Atlantic and P a c i f i c Oceans are applicable.
The broad region of Hope basin, Kotzebue Sound, lower Kobuk Val ley, and
Seward Peninsula appears t o have constituted a Tertiary province of re-
gional north-south crustal extension characterized by basin subsidence and
block faulting . Late cretaceous ( ? ) and Pal eogene (Laramide) extension
created Hope basin athwart the western Brooks Range, a compressional oro-
genic bel t formed principally during Jurassic, Cretaceous, and early
Tert iary(?) time. Probably in part because o f this extension the be1 t o f
Brooks Range rocks i s much wider across Hope basin (400 k m ) than across
the central Brooks Range (200 k m ) . The paleoslope and normal fau l t s that
form the east edge o f Hope basin terminated the physiographic Brooks Range
a t Kotzebue Sound by mid-Tertiary time. Neogene-Quaternary extension
created normal f a u l t s , sub-basins, and ridges within Hope basin, and small
sedimentary basins and block fau l t s elsewhere in the province.
Chukchi syntaxis, the sharp swing in trend o f typical Brooks Range rocks
and structures a t the Lisburne Peninsula, i s thought t o be the resu l t of
the superposition of thrust plates of the Herald f au l t zone across western
Brooks Range structures during Late Cretaceous or early Tertiary time.
REFERENCES CITED
Alaska Geological S o c i e t y , 1971 , West t o east s t r a t i g r a p h i c c o r r e l a t i o n s e c t i o n ,
P o i n t Barrow t o Ignek Val1 ey, Arct4c North S lope , A1 aska , Alaska Geological
S o c i e t y , Anchorage.
Alaska Geological S o c i e t y , 1972, Northwest t o s o u t h e a s t s t r a t i g r a p h i c c o r r e l a -
t i o n s e c t i o n , Prudhoe Ray t o Ignek Val ley , A r c t i c North S lope , Alaska,
Alaska Geological S o c i e t y , Anchorage.
Alaska Geological S o c i e t y , 1977 , North t o sou th s t r a t i g r a p h i c c o r r e l a t i o n sec-
t i o n , Beaufor t Sea-Prudhoe Bay-Nora No. 1, A r c t i c S lope , Alaska, Alaska
Geological S o c i e t y , Anchorage.
Alaska Glac ia l Map Committee, 1965, Map showing e x t e n t o f g l a c i a t i o n s i n Alaska
U.S. Geological Survey Miscel laneous Geologic I n v e s t i g a t i o n s Map 1-41 5 ,
s c a l e 1 :2,500,000.
Anonymous, 1970, I s l a n d s o f e a s t e r n S i b e r i a and t h e Chukchi Sea, in Geologia
SSSR (B. Tkachenko a n d B. k h . Egiazarov, e d s . ) , v . 26 , y p . 377-404.
Armstrong, A . K . , and Bi rd , K. J . , 1976, Fac ies and environments o f d e p o s i t i o n
o f Carboniferous r o c k s , A r c t i c Alaska, Alaska Geological S o c i e t y Symposium
1975, Anchorage, Alaska, pp. A1 -A1 6.
Barnes, D. F., 1976, Bouguer gravity map o f A l a s k a , U.S. Geological Survey Geo-
physical Investigations Map GP-913, scal e 1 :2,500,000.
Barnes, P. W., and Reimnitz, E . , 1974, Sedimentary processes on arctic shelves
of the northern coast o f Alaska, - in The coast and shelf of the Beaufort
Sea ( J . C. Reed and J. E. Sater, e d s . ) , Arctic Institute of North America,
Arlington, Virginia, ~ p . 439-476.
Beal, M. A , , 1969, Bathynetry and structure o f the Arctic Ocean, Oregon State
University, Corvall is, doctoral thesis, 204 p.
Beikman, H. M., and Lathram, E. H.. 1976, Prel iminary geologic map o f northern
Alaska, U.S. Geological Surver Miscellaneous Field Studies Map MF-789, 2
sheets, scale 1 :I ,000,000,
Belevich, A . M., 1969, Marine Neogene diatoms at Cape Enrnakai, the north coast
o f the Chukchi Sea, Nauch-Issled. Inst. Geol. Arktiki, Uch. Zap.,
Paleontol . B iostratigr., v. 28, pp. 74-75.
Bird, K. J., 1978, New information on Lisburne Group (Carboniferous and Permian)
in Naval Petroleum Reserve, A1 a s k a , Am. Assoc. Pet. Geol . Bull . 62 :880.
I
BrosgC, W. P,, and Tailleur, I, L,, 1971, Nor thern A laska pet ro leum prov ince ,
i n Future pet ro leum prov inces of t h e Un i t ed S ta tes - -The i r geology and -
p o t e n t i a l (I. H. Cram, e d . ) , American Assoc ia t i on o f Petroleum t i eo l og i s t s
Memoir 15, pp. 68-99.
Campbell, R. H., 1967, Area l geo logy i n t h e v i c i n i t y o f t h e C h a r i o t s i t e , L i s -
burne Peninsula, no r thwes te rn Alaska , U.S. Geolog ica l Survey P ro fess i ona l
Paper 395, 71 p .
Carey, S . H . , 1958, A t e c t o n i c approach t o c o n t i n e n t a l d r i f t , - i n Con t i nen ta l
d r i f t , a symposium ( S . W . Carey, e d . ) , Hobart , Tasmania U n i v e r s i t y , pp.
7 77 -355 .
Car te r , C l a i r e , and Lau fe ld , Sven, 1975, Ordov ic ian and S i l u r i a n f o s s i l s i n
w e l l co res f rom Nor th Slope o f Alaska, Am. Assoc. Pet. Geol . B u l l .
59 :457-464.
Chapman, R. M., and Sable, E. G., 1960, Geology o f t h e Utukok-Corwin reg ion ,
nor thwes te rn Alaska, U.S. Geolog ica l Survey P ro fess i ona l Paper 3 0 3 4 , 164 p.
C o l l i n s , F. R., and Robinson, F. M,, 1967, Subsurface s t r a t i g r a p h i c , s t r u c t u r a l
and economic geology, no r t he rn Alaska, U.S. Geolog ica l Survey Open-Fil e
Report, 250 p.
Creager , J , S . , and McManus, D. A . , 1965, P l e i s t o c e n e d r a i n a g e p a t t e r n s on the
f l o o r o f the Chukchi Sea, Mar. Geol . 3:279-290.
Creager , J . S . , and McMano5, D. A . , 1967, Geol ogy o f t h e f l o o r o f Bering and
Chukchi Seas--American s t u d i e s , - i n The Bering Sea l a n d b r i d g e (D . M .
Hopkins, ed. ) , S t a n f o r d U n i v e r s i t y Press, S t a n f o r d , Cal i f o r n i a , p p , 7-31.
Detterman, R . L., Reiser, H. N . , Brosgh, W . P . , and Dutro, J . T . , J r . , 1975,
Post -Carboniferous s t r a t i g r a p h y , n o r t h e a s t e r n Alaska, U.S . Geological S u r -
vey P r o f e s s i o n a l Paper 886, 46 p .
E i t t r e i m , Stephen, Grantz , A r t h u r , and Whitney, 0. T., in press, Cenozoic s e d i -
mentat ion and t e c t o n i c s o f the Hope b a s i n , sou thern Chukchi Sea , - in Rela-
t i o n s h i p o f p l a t e t e c t o n i c s t o Alaskan geology and r e s o u r c e s ( A . S i s s o n ,
ed . ) , Proceedings o f t h e Alaska Geological S o c i e t y symposium, Anchorage,
Alaska, April 1977.
F i s h e r , R . L., Carso la , A. J . , and Shumway, G . , 1958, Deep-sea bathymetry n o r t h
o f Po in t Barrow, Deep-sea Res. 5 : l - 6 .
Gar r i son , G. R . , and Becker, P . , 1976, The Barrow Canyon; a d r a i n f o r t h e Chukchi
Sea, J . Geophys. Res. 81 :4445-4453.
Geological Survey of Canada, 1968, Glacial map of Canada, Geological Survey o f
Canada Map 1253A, s c a l e 1 :5,000,000.
Grantz, Arthur, Boucher, Gary, and Whitney, 0. T . , 1976, Possible sol I d gas hy-
dra te and natural gas depos i t s beneath the continental s lope o f the Beaufort
Sea, in The United S t a t e s Geological Survey i n Alaska: Accomplishments dur-
ing 1975 ( E . H . Cobb, e d . ) , U.S. Geological Survey Circular 733, p . 17.
Grantz, Arthur, Hanna, M . F . , and Wallace, S . L., 1971 , C h u k c h i Sea seismic re-
f l e c t i o n p r o f i l e s and magnetic d a t a , 1970, between northern Alaska and Herald
Is land, U.S. Geological Survey Open-File Report 71-125, 32 sheets seismic
p r o f i l e s , 2 sheets magnetic d a t a , 1 loca t ion map.
Grantz, Arthur, Hanna, W . F . , and Wallace, S . L . , 1972a, Chukchi Sea seismic re-
f l e c t i o n and magnetic p r o f i l e s , 1971, between northern A l a s k a and Herald
Is land, U . S . Geological Survey Open-Fil e Report 72-1 37, 38 sheets seismic
p r o f i l e s , 2 sheets magnetic p r o f i l e s , 2 loca t ion maps.
Grantz, Arthur, Hanna, W . F. , and Wolf, S . C . , 1970b, Chukchi Sea seismic re-
f l e c t i o n and magnetic p r o f i l e s , 1969, between northern Alaska and Interna-
t i ona l date l ine , U . S . Geological Survey Open-Fi1 e Report 70-1 39, 1 sheet
magnetic p r o f i l e s , 25 sheets seismic p r o f i l e s .
Grantz, A r t hu r , Holmes, M. L., and Kososki, B. A . , 1975, Geologic framework of
t h e Alaskan c o n t i n e n t a l t e r r a c e i n t h e Chukchi and Beau fo r t Seas, Canadian
S o c i e t y o f Petroleum Geologists Memoir 4, pp, 669-700.
Grantz, A r t hu r , Holmes, M. L., R i l e y , 0, C., and Wallace, S. L., 7972b, Seismic
r e f l e c t i o n p r o f i l e s , Pa r t 1 - o f Seismic, magnet ic and g r a v i t y p r o f i l e s - -
Chukchi Sea and ad jacen t A r c t i c Ocean, 1972, U.S. Geolog ica l Survey Open-
F i l e Report 72-138, 19 sheets se ismic r e f l e c t i o n p r o f i l e s , 2 maps.
Grantz, A r t hu r , McHendrie, A. G., N i l sen , T, H., and Yorath, C. J., 1974, Seismic
r e f l e c t i o n p r o f i l e s , 1973, on t he c o n t i n e n t a l she l f and s lope between B e r -
i n g S t r a i t and Barrow, A laska , and t4ackenzie Bay, Canada, U.S. Geolog ica l
Survey Open-File Report 74-42, 49 sheets se ismic r e f l e c t i o n p r o f i l e s , 2
index maps.
Grantz, A r t hu r , Wol f , S. C., Bres lau, Lloyd, Johnson, T. C. , and Hanna, W. F.,
1970a, Reconnaissance geology o f t h e Chukchi Sea as determined by acous t i c
and magnet ic p r o f i l e s , - i n Proceedings of t h e geo log i ca l seminar on t h e
Nor th Slope of Alaska (w. L. Adkison and M. M. Brosgk, e d s . ) , American As-
s o c i a t i o n o f Petroleum Geo log is ts , P a c i f i c Sec t ion , Los Angeles, pp. Fl-F28.
5 3
Hal 1 , J. K . , 1973, Geophysical evidence f o r ancient sea- f loor spreading from
A1 pha Cordil l era and Mendel eyev Ridge, American Association of Petrol eum
Seoiogis ts Memoir 19, pp. 542-561.
Herron, E . M . , Dewey, J. F. , and Pitman, W . C . , 1974, P la t e t ec ton ics model f o r
the evolution of the Arct ic , Geology 2:377-380.
Hopkins, D. M . , 1967, A Cenozoic h i s to ry of Beringia--a syn thes i s , - in The Bering
Land Bridge ( D . M . Hopkins, e d . ) , Stanford University Press, S tanford ,
Cal i fo rn ia , pp. 451 -484.
Hopkins, D. M . , 1973, Sea l e v e l history in Beringia d u r i n g the pas t 250,000
yea r s , Quat . Res. 3:520-540.
Hopkins, D. M., and MacNeil, F. S . , 1960, A marine fauna probably of Late Pl io-
cene age near Kivalina, Alaska, - in Geological Survey Research 1960, U.S.
Geological Survey Professional Paper 400-8, pp. 8339-B342.
Hopkins, D. M . , Nelson, C. H., Perry, R . B., and A1 pha, T. R . , 1976, Physio-
graphic subdivisions of the Chirikov Basin, northern Bering Sea, U.S.
Geological Survey Professional Paper 759-8.
Hudson, Travis , 1977, Prel iminary geologic map of Seward Peninsula, A1 aska,
U.S. Geological Survey Open-Fil e Map 77-1 67A.
Hunkins, Kenneth, 1966, The A r c t i c c o n t i n e n t a l s h e l f n o r t h of Alaska, Geolo-
g i c a l Survey o f Canada Paper 66-1 5, pp. 197-205.
Hunkins, Kenneth, Herron, Thomas, Kutschale , Henry, and P e t e r , George, 1962.
Geophysical s t u d i e s of t h e Chukchi cap, A r c t i c Ocean, J. Geophys, Res.
67 :235-247.
Jones, 0. L., and Grantz, A r t hu r , 1964, S t r a t i g r a p h i c and s t r u c t u r a l s i g n i f i -
cance o f Cretaceous f o s s i l s f rom T ig lukpuk Format ion, no r t he rn Alaska,
An. Assoc. Pet . Geol. B u l l . 48:1462-1474.
Kameneva, G. I . , 1977, The t e c t o n i c s e t t i n g o f Wrangel I s l a n d and i t s Paleozoic
s t r u c t u r a l bonds w i t h Alaska (Yu. E. P o g r e b i t s k i i and M , K. Kos'ko, eds. ),
Tekton ika A r c t i k i s k a d c h a t i i fundament she1 ' f o v i k h sed imenta ts ionn ikh
basseinov, NI IGA, Leningrad, pp. 122-129.
King, P. B., 1969, The t e c t o n i c s o f Vor th America--A d i scuss ion t o accompany
t h e t e c t o n i c map o f Nor th America, s ca le 1 :5,000,000, U.S. Geolog ica l
Survey P ro fess i ona l Paper 628, 94 p .
Lerand, Mont i , 1973, Beau fo r t Sea, - i n The f u t u r e pet ro leum prov inces of Canada--
t h e i r geology and p o t e n t i a l ( R . G. McCrossan, ed. ) , Canadian Soc ie t y o f
Petroleum Geo log is ts Memoir 1 , pp. 31 5-386.
5 5
Mar t i n , A. J., 1970, S t r u c t u r e and t e c t o n i c h i s t o r y o f t h e western Brooks Range,
De Long Mountains and L isburne H i l l s , n o r t h e r n Alaska, Geol . Soc. Am. B u l l .
81 : 360503622.
Musgrave, A , W . , and Hicks, W. G., 1968, O u t l i n i n g sha le masses of geophys ica l
methods, American Assoc ia t i on o f P e t r o l eum Geo log is ts Memoir 8, pp. 122-1 36.
Nelson, H. C., and Creager, J. S. , 1977, Displacement of Yukon-derived sediment
f r o m Ber ing Sea t o Chukchi Sea d u r i n g 9olocene t i m e , Geology 5:141-146.
Nelson, H. C. , and Hopkins, D. M., 1972, Sedimentary processes and d i s t r i b u t i o n
o f p a r t i c u l a t e g o l d i n t h e no r t he rn 3 e r i n g Sea, U.S. Geolog ica l Survey
Pro fess iona l Paper 689.
FJeman, G. W . , M u l l , C. G., and Watkins, N. D., i n press, Nor thern Alaska paleo-
magnetism, p l a t e r o t a t i o n , and t e c t o n i c s , in R e l a t i o n s h i p o f p l a t e t e c t o n i c s
t o Alaskan geology and resources ( A . Sisson, ed. ) , Proceedings o f t h e Alaska
Geolog ica l S o c i e t y symposium, Anchorage, Alaska, A p r i l 7 977.
No r r i s , D. K., 1977, Geolog ica l map o f p a r t s o f Yukon T e r r i t o r y , D i s t r i c t o f
Mackenzie and D i s t r i c t o f Frank1 i n , Geolog ica l Survey o f Canada Open-Fil e
Report 399, 4 p., map and c ross sec t ions , s c a l e 1 :1 ,000,000.
Oliver, J . , Ewing, M . , and Press, F. , 1955, Crus ta l s t r u c t u r e o f t h e Arctic
r e g i o n s from t h e Lg phase , Geol . Soc. Am. B u l l . 66:1063-1074.
Ostenso, N. A . , 1968, A g r a v i t y su rvey o f t h e Chukchi Sea r e g i o n , and i t s bear -
on westward e x t e n s i o n of s t r u c t u r e in n o r t h e r n Alaska, Geol. Soc. Am. B u l l .
79 :241-254.
Parsons , Barry , and S c l a t e r , J . G . , 1977, An a n a l y s i s o f t h e v a r i a t i o n o f ocean
f l o o r bathymetry and h e a t f low with a g e , J . Geophys. Res. 82:803-827.
P a t t o n , W. W . , J r . , 1973, Reconnaissance geology of the nor the rn Yukon-Koyukuk
prov ince , Alaska, U.S. Geological Survey P r o f e s s i o n a l Paper 774-A, pp.
A1 -A1 7 .
P a t t o n , W . W . , J r . , and M i l l e r , T. P., 1968, Regional geo log ic map of the Selawik
and s o u t h e a s t e r n Baird Mountains quadrang les , A1 a s k a , U . S. Geological Survey
Miscel laneous Geologic I n v e s t i g a t i o n s Map 1-530, s c a l e 1 :250,000.
P l a t t , J . B., 1975, Petrography o f U n i v e r s i t y o f Washington d redge samples from
the c e n t r a l Chukchi Sea, U.S. Geological Survey Open-Fil e Report .
Reimni tz , E r k , and Barnes, P. H., 1974, Sea i c e a s a g e o l o g i c a g e n t on the Beau-
f o r t Sea s h e l f o f Alaska, - i n The coast and s h e l f o f t h e Beaufor t Sea ( J . C .
Reed and J . E. S a t e r , e d s , ) , Arctic I n s t i t u t e of North America, A r l i n g t o n ,
V i r g i n i a , pp . 301 -354.
5 7
Reiser , H. N., BrosgC, W. P., Detterman, R. L., and Dutro, J. T. , J r . , 1978,
Geologic map o f t h e Demarcation P o i n t quadrangle, Alaska, U.S. Geolog ica l
Survey Open-Fil e Report 78-526; 1 p l . , scal e 1 :200,000.
Rickwood, F. K., 1970, The Prudhoe Bay f i e l d , - i n Proceedings of t he geo log i ca l
seminar on t h e Nor th Slope o f Alaska ( w . 1. Adkison and M. M. Brosgb, eds.) ,
P a c i f i c Sect ion, American Assoc ia t i on o f Petroleum Geolog is ts , Los Angel es,
p. L1-L11.
Rodeick, C. A., 1974, Marine g rave l depos i ts o f t h e Beaufor t Sea s h e l f ( a b s t r a c t ) ,
i n The c o a s t and s h e l f o f t h e Beaufo r t Sea (J. C . Reed and J . E. Sater , -
eds. ) , A r c t i c I n s t i t u t e o f Nor th America, A r l i ng ton , V i r g i n i a , pp. 301 -354.
Ruppel, 0 . D., and McHendrie, A. G., 1976, F ree-a i r g r a v i t y anomaly map o f t he
eas te rn Chukchi and southern Beaufo r t Seas, U.S. Geolog ica l Survey M isce l -
laneous F i e l d S tud ies Map MF-785.
Sainsbury, C. L., 1976, Geology, ore depos i t s and minera l p o t e n t i a l o f t h e Seward
Peninsula, Alaska, U , S . Bureau o f Mines Open-File Report, 108 p., 3 f i g s .
Shaver, Ralph, and Hunkins, Kenneth, 1964, A r c t i c Ocean geophysical s t ud ies ;
Chukchi cap and Chukchi abyssa l p l a i n , Deep-Sea Res. 11 :905-916.
5 8
I
Tailleur, I. L., 1-969, Rifting speculation on the geology o f Alaska's North
Slope, Oil and Gas Jour. 67:128-130.
Tailleur, I . L., 1973, Probable rift origin o f Canada basin, American Associa-
tion of Petroleum Geologists Memoir 19, pp. 526-535,
Tailleur, I. L., and Brosgh, W. P., 1970, Tectonic history o f northern Alaska,
in Proceedings of the geological seminar on the North Slope o f Alaska -
(W. L. Adkison and M. M. Brosgk, eds.), Pacific Section, American Associa-
tion of Petroleum Geologists, Los Angeles, pp. El-E19.
Tailleur, I. L., Mamet, B. L., and Dutro, J. T., Jr., 1972, Revised age and
structural interpretations of thc Nuka Formation at Nuka Ridge , northwestern
Alaska, U . S . Geological Survey Open-File Report 72-547, 10 p.
Tailleur, I. L., Pessel , G. H., Levorsen, J. A., and Engwicht, S. E., 1978, Maps
showing land status and well locations and tables of well d a t a , eastern
North Slope petroleum province, Alaska, U.S. Geological Survey Miscell aneous
Field Studies Map MF-928A, 5 sheets.
Toimil , L. J., 1978, Ice-gouged morphology on the floor of the eastern Chukchi
Sea, Alaska: A reconnaissance survey, U.S. Geological Survey Open-File
Report 78-693, 11 3 p.
I
T o i m i l , L. J . , and Grantz, A r t hu r , 1976, O r i g i n o f a b e r g f i e l d i n t h e n o r t h -
eas te rn Chukchi Sea and i t s i n f l u e n c e on t h e sedimentary environment, &
A r c t i c I c e Dynamics J o i n t Experiment (AIOJEX) B u l l e t i n No. 34 (Alma Jonnson,
ed. ), D i v i s i o n o f Marine Resources, U n i v e r s i t y o f Washington, S e a t t l e ,
Washington, 42 p .
U.S. Geolog ica l Survey, 1978, Fol i o , eas te rn Nor th Slope p e t r o l eum prov ince ,
Alaska, U.S. Geolog ica l Survey Minera l I n v e s t i g a t i o n s F i e l d S tud ies Maps
Vogt, P. R., and Ostenso, PI. A . , 1970, t lagnet ic and g r a v i t y p r o f i l e s across t h e
Alpha C o r d i l l e r a and t h e i r r e l a t i o n t o s e a - f l o o r spreading, 3 . Geophys. Res.
75 :4925-4937.
Watts, A . B., and Ryan, W. 0. F., 1976, F lexure o f t h e l i t h o s p h e r e and con t inen-
t a l margin bas ins, Tectonophysics 36 :25-44.
We tm i l l e r , R. J., and Forsyth , 0. A , , 1978, S e i s m i c i t y of t he A r c t i c , 1908-1975,
i n A r c t i c geophys ica l r ev i ew ( 3 . F. Sweeney, ed.) , P u b l i c a t i o n s o f the -
Earth Phys ics Branch, Canadian Department o f Energy, Mines and Resources,
v . 45, no. 4, pp. 15-24.
Woolson, J. R., 1962, Seismic and g r a v i t y surveys o f Naval Petroleum Reserve
No. 4 and a d j o i n i n g areas, Alaska, U.S. Geolog ica l Survey P ro fess i ona l
Pa per 304-A.
Yorath, C. J., and N o r r i s , D. K, , 1975, The t e c t o n i c development o f t h e southern
Beau fo r t Sea and i t s r e l a t i o n s h i p t o t h e o r i g i n o f t h e A r c t i c Ocean:
Canadian Society o f Petroleum GeologSsts Memoir 4, pp. 589-611 .
Young, F. G . , Myhr, D. W . , and Y o r a t h , C . J . , 1976, Geology of the Beaufort-
Yackenz ie basin, Geolog ica l Survey o f Canada Paper 76-11, 65 p .
Figure 2. Phys iographic f ea tu res o f t h e Beau fo r t and Chukchi Seas. Extent :f
g l a c i a t i o n f rom Alaska G l a c i a l Map Comrni t t e e , 1965; Geolog ica l
Survey o f Canada, 1968; Nelson and Hopkins, 1972; and D. M.
Hopkins, personal communication, 1978.
Thrust fault complex 2 - - Str ike slip fau l t * A R C H
SEDIMENTARY PRISMS :$@'z?) #4j:iOceanic bas in , broad r ise .....:..*.. , . . . . . . . ..: . . . .. .. ' .:.::..:..:!: Cont inenta l slope, narrow r ise
!.I.!!. Prograded continental shelf . . . . . , . . . . . , Fofedeep Ypp,~,: Inter ior basin
I I N F E R R E D A G E J u r a s s i c C r e t a c e o u s ' T e r t i a r y u a t e r n a r y
L - P
- - F igure 3 . Post-Triassic t e c t o n i c provinces and sedimentary pri sms o f the
Beau f o r t and -Chukchi Seas and v i c i n i ty .
GENE W W U 4-
ln 3 0 UPPER W u .
U
- LOWER W
a 0 U
N
0 J U I I A S S I C
111
W /
2
T R l A S S l C
, 1 V A N I AN I
- - - - - - - - - - - -. - - - -- w E 9 T L _ R F1 -- P R O V I N C I A L ,- N O R T H S L O P E
S E ~ ~ E ~ C E S S T A A T I G A A P n I C u N I T S L I T H O L o G Y T ~ ~ ~ K H E S S
( w o r ~ h I I U E T E R S l F O m 1 0 M llrx sand. gravel. s i l t , clay. .1m-
d
- G E 0 LOG L C
A G E
M I S S I S S - W
I PPI AN
U - o N
0 -
north - Marine shale with r p l a u c ~ t t i c ndrtone f a c i e ~ .
south - Ilrrlnc shal t , c h a t , 011 $ A l e .
- o X F t h s s h T e ; 7 G e s t o n e , and 9 rucon t c I, 1 tstone and s~txlstone.(lnci udes :a f t i J.1 S5.i 0-225 a To south - shale. chert. o i l r h l e . 9 t r r t o n e .
-
~UATE~HPI I~
To north - Sandstone, conglomtrrte, shrle.and udSt0ne. To south - A r g l l l i t e . chert,rnd shale. O---MH)
P a 6
;
Limestone, dolomi te,and chert w i t h mlnor I 0-so00 randstone and sha le .
WEOOEIIE
PALEO-
I -. - 3dnbsione. n u l J s f o n < a d d ~ t h interbeds o f Itmestone. conglmerate.and coal. O->lOoO
- - -- 1 - - -- p- -.
A r g i l l ~ t e and grdywacke. r n w r a d s of meters.
Figure 4A. Phanerozoic s t r a t i g r a p h y o f t h e wes te rn No r t h Slope o f Alaska .
-- - -- - - - - - - - - - - - --
G E O L O G I C PROVlNClAL E A S T E R N N p R 1 - L S L O P E A G E SEQUENCES o r L I T H O L O G Y (METERS)
T H I C U H E S S
- -~ar;ne sand, s i l t , q-nd c lay 10-200 T W R Y -
0 - NEOGENE
O : Poor ly consol idated normarlne and shal low marine shale. sandstone,and c o n g l a c r a t e 0-2500
N - wl t h sane carbonaceous shale. 1 l gn t to , O I- PAl lO- Z * a F O R M A T I O N and bentoni te
w G E N E U + - _ _ _ _ _ - _ - - - -
UI x Upper beds - Marine dndnormarlne iandstone, s i l tstone. shale.
C O L V L C L E G R O U P conglomerate, c o d l , a d t u f f . 900-3600
UPPER * Lower beds - Marine sandstone, s l l t s t o n e , organic shale.and tuff. 0
W - - -- -
0 a -raywacke, 51 l ts tone, shale(0athtub Grrwacke. Tuktu F m . ) . ~200-1200 m ---
a k- ~ 4 t h rounded u LOWER 40-700 - a U
0
N K I N G A K S H A L E
( I n c t u b n Kuporuh Rawor Marine shale, si l tstone.and organic prpr shale. 0-1200
o J U R I S S J C Sondrlona ot top l 0 ~ 0 l l y )
In / _ - W .
0-140 I T R I A S S I C z
Q Upper b d s - Marine and n o m u r i n r w a r t 2 a d cher t - - S A D L E R O C H I T r i c h sandstone, c o n g l a e r a t e , ludstmt ,and shale. 0-,700
LL lower beds - Marine sandstone and s l l t s t o n e w i t h
PERM IA H w Interbeds o f shale, l oca l c o n g l ~ w r a t t and cher t
U
0 L I S B U R N E G R O U P and s l l t s t ~ . - Marine and normar~ne sandstone, shale, 0-* 1 MI0
I P P I AN - --- -_-___A- _
( P R E -
- ... -
M I S S I S S l P I h H R O C K S ) Arq, l l i t e , qraywacke, I lmestone, dolomite, cher t , Thousands o f meters. quartrose sandstone, and shale and their metamorphic equivalents
- - A
Figure 4 R . Phanerozoic s t r a t i g r a p h y of the eastern Nor th Slope o f A1 as k a .
Figure 5. Geologic s t ructure and thickness of sedimentary rock beneath the
Western Beaufort Shelf,and southern Canada Basin. See Figure 6
fo r e x ~ l anation.
EXPLANATION FOR FIGURES 5, 8, AND 9 .... *; ;r. .: -.,**..: :..: :. :..-
t+: .......v... '..: QUAERNARY A m fERT l ARY ~ L A S T i c $ED IHENTARY ROCKS, M R I NE AND p:z: ...... .,.?:?. . ,;;:::?.*;-:"!.>,:.: NO W A R I H E
QUATERNARY AMD TERTIARY V O L C ~ N I C ROCKS
................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CRETACEOUS C L A S T ~ C SEDIMENTARY ROCKS, MAR 1 NE AND NONMARINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . , , , . . . . . . . . . . . . . . . . . . . . . . . . . d K - WHERE STRONGLY DEFORMED
C K T A EOUS VOLCAN t R C K S ANDESITIC IN ALASKA, ACIDIC IN E H u K o r K A , I J , ~ . S . ~ .
J ' b JURASSIC TO M l S S l S S l P P I A N SHELF CARBONATE AND CLAST I C
SEDIMENTARY ROCKS (ELLESMER IAN SEQUENCE) J - Kingak Shale outcrop southeast o f b r t e r Island
\' PRE-MI SS ISS I PPIAN SEDIMENTARY AND VOLCANl C ROCKS, GENERALLY w\\\ STRONGLY DEFORMED OR HEIuIORPHOSED
:-,w;:;;<;; .;-LO < y::-.- . ,-,,,,. :*.5:- - " .,.,-;,.,:l.i.;7.--: CRETACEOUS TO UPPER PALEOZOIC PLUTON I c R o t KS . - . #7c T-;>:,>*:;%,:
# JURASSIC TO PERMI AN OPH IQLI T E S AND ULTRAMAF l CS
ACOUSTI c BASEMENT. STRONGLY DEFORMED OR METAMORPHOSED CRETACEOUS TO PRECAMBRIAN ROCKS
d K 7 - STRONGLY DEFORMED CRETACEOUS(?) BEDDED ROCKS
- 2 - . . 0-- 2- .. x * STRUCTURE CONTOUR, STRUCTURE FORMLINE ANTICLINE SYNCLI NE ARCH
N FRANKLINIAFI SEQUENCE NORTH OF ERAUI ARCH, ON ACOUSTlC BASEMENT
SOUTH OF HERAU) ARCH # 4 THRUST FAULT, NORMAL FAULT,
- . - 4 A. . / SAWTEETH I N HACHURES ON DOWN- UPPER P L A T E THROWN S I D E ISOPACH FORMLINE, M ~ N I M U M THICK E S S
or SEDIMENT IN CANADA BASIN, & k-@- &
-200- SO BATH, METERS
SWOBUOY STAT I O N SHOWING M l N I M U M T H I C K N E S S OF SEDIMENT, Kn
NORTH L I M I T OF T H L I M I T , 4ERT I ARY
ELLESMER1 AN SEDIMENTARY ROCKS ROCKS. PRE-
0 UNIVERSITY OF WASHINGTON
DREDGE SAMPLES
Figure 6. Explanat ion f o r geo log ic structure maps, Figures 5, 8, and 9.
b v t h Itmn of Tcrlcan( rtralo > Normal foull, boll on downthrown stdc
Figure 7. Seismic re f l ec t ion s t ruc tu re and f r e e a i r gravity anomalies near
the change in trend o f t he Barrow Arch a t 72' N, 160" W .
-> .
Figure 8. Geologic s t ructure and thickness o f sedimentary rock beneath t h e
northern Chukchi Sea. See F igure 6 f o r explanat ion.
Figure 9. Geologic s t r u c t u r e and thickness o f sedimentary rock beneath t h e
southern Chukchi Sea. See Figure 6 f o r explanat ion.
H O P E B A S I N
l l l l l l l l l l l k m -- - -- _ -
V . . l , t O l a . 0 q q e ' 0 l , o " C O L V I L L E - 20 1 F O R E D E E P
, - - - I . - .
Figure 10. Geologic cross section interpreted from seismic reflection data in the
eastern Chukchi Sea between the continental shelf break and southern Hope Basin. I
See Figure 1, 8, and 9 for location. Sedimentary strata shown are "~g"-~eogene(?)
elastics, "Pgl'-Paleogene(?) clastics, "UKW-Upper Cretaceous(?) marine clastics,
"LK"-Lower Cretaceous marine and nonmarine clastics, "J-M"-Mississippian to Juras-
ic (Ellesmerian) marine and nonmarine clastics and carbonates, "E-Fr"-Lower
Ellesmerian or Franklinian clastics, and "dK"-strongly deformed Cretaceous clastics.
Undifferentiated rock units are pK-pre-Cretaceous, pM-pre-Mississippian., PpC-~aleozoic
and(or) Precambrian. Seismic CDP interval velocities in krn/sec. f
HOURS DISTANCE - KM 4
2 1 0.5 0 10 8 I-, 1 I I
6 +-~----T-I
KM 8 6 4 2 I
F igu re 12. Seismic r e f l e c t i o n and r e f r a c t i o n p r o f i l e s across s h a l e ( ? ) d i a p i r
a t 73" N, 163" W, Nor th Chukchi Basin.
F igure 13A,B,C Geolog ic i n t e r p r e t a t i o n s o f se ismic sec t i ons across t h e Western
Beaufort She1 f ( F i g s . 1 3 A - C ) and a c ross s e c t i o n near t h e 'can-
n i n g R i v e r based on c o r r e l a t e d t e s t w e l l s ( F i g . 13D). See
F igu re 1 f o r l o c a t i o n . Seismic CDP i n t e r v a l v e l o c i t i e s (F igs .
13A,B, and C ) i n km/sec.
S O U T H
- -
Figure 13A. Inferred c l a s t i c sedimentary rock units are "Ngtl-Neogene, "Pgl'-
Pal eogene, "T-UK1'-Tertiary and(or) Upper Cretaceous, "K-J"-
Cretaceous and Jurass ic(?) , possibly only Lower Cretaceous and
Jurassic(?).
Figure 138. Inferred c l a s t i c sedimentary rock units are "PI - P I " Pl io-Pleistocene,
"Ngy-Neogene, "Pgl'-Paleogene, "UKpcl'-Upper Cretaceous, Prince
Creek Fowation, "UKsl'-Upper Cretaceous, Schrader Bluff Formation,
"LKpsl'-Lower Cretaceous "Pebble Shal el1, LKkrsl'-Lower Cretaceous, \ .
Kuparu k diver Sandstone, "Fr'l-Frank1 i ni an sequence.
SOUTH NORTH 00- -
1 0 - -
2 0 -
- = 10- W
- I - 4 0 - - L ; so- u
(Nmar I5.l.W Long.) C.lM**. b... .I ...* .a,. I. ..".
Figure 13C. Inferred cl a s t i c sedimentary rock .units are "NgU-Neogene, "Pg"-
Pal eogene, "UKs "-Upper Cretaceous, "LKs "-Lower Cretaceous, "Fr"-
Frank1 i ni an sequence. . - .
:I VCIY*I I..II...,*I . 0 1 6 1
I l n
-9 BRXIKIAN SEW€UC€ KL LFSYERI IN SEWCUFF 7 -7mkrr l S a # m r l r * f e R F a . l l m I LK- m r c-m l k r d h r b n - . ~ a*.) UK- U I P r Cr.t=lml I CAdll. Gnup ) J- J u I e U k IKJwpb W1.1
P( Y -Tno..Ie 10 ~ I u * . ~ m r n (shmik h m t i w . Karin trek Smd*on.. hal.rocnll B-up, L 1 . h h p . Endl~ot l
F/GURE /30 P ~ - P I * - Y ~ * * ~ S I V P I . ~ h p ) rorli*(br.m.nt rocm 101 polrc4eum~
Figure 130. Generalized s tructural cross section from Kerni k gas f i e l d to Flaxman
Island. Data interpreted from a compilation of geologic formations
- encountered i n boreholes between the Canning and Colville Rivers by
Tailleur e t a l . (1978). The control points f o r the cross section
(boreholes) would not s u f f i c e t o delineate any small-scale geologic
s t ructures tha t might be present.
Figure 1 4 . Block g l i d e terrane on the outer Beaufort S h e l f east o f Barrow Sea
Val l ey , mapped from 3 . 5 KHz seismic profiles.
Figure 5. Bedding plane s l i d e s on t he Western Beaufort Shelf east o f 147' W
long., mapped from 3 . 5 KHz s e i s m i c prof i l e s .
Figure 16.
X . ' l . ...
o Innor r h l t braoh - 3.5 KHz high rmaolut~on profilar data Outrr #half brbak - 3.5 KHz high raro lu t~on protilor data
1 Outrr mhrlf brbak - Latimotad from low froquamy, long of f ra t mporhbr protllar data
Depth of inner and outer cont inenta l she l f breaks on the Western
Beaufort S h e l f between 139" W and 160" W long.
N O R T H - I C O N T , N E N 7 A . SLOPE * '3 C ~ A P I R I < FOLDS 1 c A N A P A
..-a , ssti 8 Lll.8
I - LINE 721
144.W LONG - I
1 ' 2
,"l.rr,o be.* .,I 00, *yerat . ,on.
3 -,
I D r D m n # r , c !el04
4 - 1
S L C
Figure 17. Shal l ow structure interpreted from sei smic profi 1 es across the con-
t i n e n t a l s lope in the Western Beaufort Sea where d i a p i r i c f o l ds
are present (L ine 720) and absent (L ine 749).
![Strata Schemes Management Regulation 2016€¦ · Strata Schemes Management Regulation 2016 [NSW] Part 2 Owners corporations and strata committees Part 2 Owners corporations and strata](https://static.documents.pub/doc/80x56/5ea65b07c6140324195ce6bc/strata-schemes-management-regulation-2016-strata-schemes-management-regulation-2016.jpg)
![BC Strata Property Act - bazingahelp.zendesk.com · STRATA PROPERTY ACT [SBC 1998] ... 78 Acquisition of land by strata corporation ... Part 15 — Strata Plan Amendment and Amalgamation](https://static.documents.pub/doc/80x56/5b1695857f8b9a596d8cce51/bc-strata-property-act-strata-property-act-sbc-1998-78-acquisition-of.jpg)
