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VA L E N T I N E

A N T I C L I N E

GEOLOGIC MAP OF THE LOOKOUT RIDGE QUADRANGLE, ALASKA

By

Charles G. Mull,1 David W. Houseknecht,2 G.H. Pessel,3 and Christopher P. Garrity2

2006

1Alaska Division of Oil and Gas, Anchorage, AK 99501, 2U.S. Geological Survey, Reston, VA 20192, 3Alaska Division of Geological and Geophysical Surveys, Fairbanks, AK 99709

Any use of trade, product, or firm names in this publication is for 

descriptive purposes only and does not imply endorsement by the 

U.S. Geological Survey

For sale by U.S. Geological Survey, Information Services Box 25286, 

Federal Center, Denver, CO 80225

ArcInfo coverages and a PDF for this map are available at 

http://pubs.usgs.gov Printed on recycled paper

U.S DEPARTMENT OF THE INTERIOR SCIENTIFIC INVESTIGATIONS MAP 2817–C

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with

ALASKA DEPARTMENT OF NATURAL RESOURCES,

DIVISION OF OIL AND GAS

Figure 3.—Photograph of sandstone and coal in the Nanushuk Formation at the Lili 

Creek locality (sec. 28, T. 1 S., R. 26 W.). Geologist at center is approximately 6 ft 

tall. The observed composite thickness of the coal seam is approximately 27 ft. 

Petrified trees in growth position occur in the portion of overlying fluvial sandstone 

shown in this view, a large one at the left and a smaller one at right center. 

Photograph by Paul Decker (ConocoPhillips, Inc.).

Figure 2.—Photograph of a petrified tree trunk in the Nanushuk Formation at the Lili 

Creek locality (sec. 28, T. 1 S., R. 26 W.). Photograph by Paul Decker (ConocoPhillips, Inc.).

Figure 1.—Chronostratigraphic column for the Colville basin, northern 

Alaska. Red box shows stratigraphic section in the Lookout Ridge 

quadrangle. Abbreviations or symbols are as follows: <?>, uncertain 

relationship; CS, cobblestone sandstone of Fortress Mountain Formation 

(informal unit of Mull and others, in press); ms, manganiferous shale unit 

(informal term); Kemik, Kemik Sandstone (formation) as revised by 

Molenaar and others (1987); LCU, Lower Cretaceous unconformity. 

Geologic time scale from Gradstein and Ogg (1996).

< ? >

< ? >

< ? >

< ? >

LCU

Schrader Bluff Formation

Sagwon Member

White Hills Member

Franklin Bluffs Member

pebble shale unit

Hue Shale ~~

gamma ray zone

lower

upper

Hue Shale

Seabee Formation

SW

Chandler River area

Proximal

NE

Kavik River area

Distal

Canning Formation

Kingak Shale

Fortress

Mountain

Formation

Okpikruak

Formation

Kongakut

Formation

Kemik

CS

Sagavanirktok Formation

ms

150-200 mi

240-320 km

130

140

120

110

100

90

80

70

60

50

40

30

20

10

0

Hauterivian

Valanginian

Berriasian

Barremian

Aptian

Albian

Cenomanian

Turonian

Coniacian

Santonian

Campanian

Maastrichtian

Paleocene

Eocene

Oligocene

Miocene

Pliocene

Quaternary

TERTIARY UPPER CRETACEOUS LOWER CRETACEOUS

Age

(Ma)

Neocomian

Tuluvak

Formation

Prince Creek Formation

Nanushuk

Formation

undivided

Torok Formation

Torok

Formation

< ? >

Quaternary sediments, undifferentiated

Includes Gubik Formation

Nuwok Member of

Sagavanirktok Formation

? ? ? ? ?

SCALE 1:250 000

5 0 5 10 15 20 25 KILOMETERS

5 0 5 10 15 20 MILES

CONTOUR INTERVAL 100 FEET

NATIONAL GEODETIC VERTICAL DATUM OF 1929

ALASKA

QUADRANGLE LOCATION

Base from U.S. Geological Survey, 1956

Universal Transverse Mercator projection

1927 North American Datum

100,000-foot grid ticks based on Alaska coordinate system, zone 4

APPROXIMATE MEAN

DECLINATION, 2005

20°

TRUE NORTH

MAGNETIC NORTH

Geology by G.H. Pessel and C.G. Mull, 1964; aerial photographic 

revisions by C.G. Mull, 2002

Digital cartography and compilation by Christopher P. Garrity

Edited by Elizabeth D. Koozmin

GEOLOGIC MAP OF THE LOOKOUT RIDGE QUADRANGLE

By

Charles G. Mull, David W. Houseknecht, G.H. Pessel, and

Christopher P. Garrity 

INTRODUCTION

The Lookout Ridge quadrangle (1:250,000) is located in the east-central Arctic 

North Slope of Alaska. This geologic map of the quadrangle is a compilation of 

unpublished geologic mapping by Pessel and Mull (1964) for Richfield Oil Corporation 

combined with data on location of structural axes from regional maps by Payne and 

others (1951), Lathram (1965), Mayfield and others (1988) and unpublished mapping 

by Martin and others (1968) for British Petroleum Company. The report incorporates 

recent revisions in stratigraphic nomenclature by Mull and others (2003). Stratigraphic 

and structural interpretations were revised with the aid of modern high-resolution 

color infrared aerial photographs, which were invaluable for the delineation of 

previously unrecognized areas of probable outcrop of the Seabee Formation.

HISTORY OF EXPLORATION

The area of the Lookout Ridge quadrangle is in the most remote part of the 

foothills belt of northern Alaska and has been mapped by most workers only at a 

regional scale in reconnaissance fashion. The Lookout Ridge quadrangle is located in 

the central part of the National Petroleum Reserve in Alaska (NPRA), which was 

established in 1923 as Naval Petroleum Reserve #4 (NPR-4). The first geological 

traverse of the area was in 1924 by a U.S. Geological Survey (USGS) field party 

headed by P.S. Smith. This party crossed the Brooks Range to the headwaters of the 

Killik River in the winter of 1924 and, after the ice breakup in the spring, descended 

the Killik River in canoes to the junction with the Colville River (Smith and others, 

1926; Smith and Mertie, 1930). The canoes then were towed by hand up the Colville 

River to the mouth of the Awuna River. The Awuna River was found to be relatively 

sluggish and was ascended by paddling and poling to a small stream flowing in from 

the north that the field party named Birthday Creek. From there, the boat and supplies 

were portaged northward over a divide to and part of the way down a north-flowing 

drainage that was assumed to flow into the Meade River. Instead, this drainage was 

found to be a tributary of the Kigalik River, which flowed eastward into the Ikpikpuk 

River. In spite of this disappointment, the party traversed a significant part of the 

foothills fold belt and was the first to document the long, linear, west-east-oriented 

anticlines and synclines, which decrease in amplitude toward the north.

A summary report by Smith and others (1926) and a generalized cross section from 

the Brooks Range mountain front to the Ikpikpuk River, east of the Lookout Ridge 

quadrangle, provided the first description and illustration of the belt of regional 

anticlines and synclines of decreasing amplitude to the north that deform the 

Cretaceous rocks of the foothills fold belt. This report also discussed the logistical 

constraints to oil exploration and development, and pointed out that (1) a railroad or 

1,000-mile-long pipeline (with the attendant defense issues), and (2) enormous capital 

expenditures would be needed to develop oil resources on the North Slope. The 

report also recommended further study and the drilling of shallow stratigraphic test 

holes on the North Slope.

 Additional field studies in the region did not occur again until the late 1940s as 

part of an intensive program of exploration in NPR-4 by the U.S. Navy. This time, 

extensive field geological mapping and geophysical surveys were conducted to the east 

of the Ikpikpuk River and Umiat quadrangles following the initial exploration and the 

discovery in 1946 of oil at Umiat and gas at Gubik (see discussion by Mull and others, 

2004). Several exploratory wells were drilled by the Navy in 1951 and 1952 on 

anticlines in the Ikpikpuk River quadrangle, resulting in the discovery of 

subcommercial gas accumulations at Square Lake and Wolf Creek. The results of this 

period of exploration in NPR-4 are summarized by Reed (1958). Subsequently, a 

regional map compilation of the geology of the North Slope and Brooks Range by 

Lathram (1965) incorporated the results of the NPRA exploration and named a 

number of the regional anticlines in the foothills fold belt. 

The oil discovery at Umiat and the gas discovery at Gubik served as the impetus for 

active oil industry exploration on the North Slope that began in 1958. Geophysical 

surveys and drilling of several wildcat wells east of NPR-4 led to the 1968 discovery of 

the supergiant Prudhoe Bay oil field (217 miles (mi) northeast of the Lookout Ridge 

quadrangle) by Atlantic Richfield Company and Humble Oil Company (now 

ExxonMobil). Following the success of industry exploration, the U.S. Navy and U.S. 

Department of the Interior carried out renewed exploration of the renamed National 

Petroleum Reserve in Alaska from 1974 to 1982, including additional geophysical 

surveys in the northeastern part of NPRA. The results of this second phase of 

government exploration in NPRA were published in Gryc (1988). A regional map of 

NPRA by Mayfield and others (1988) in Gryc (1988) also included names for some of 

the regional anticlines in the foothills fold belt.

Four Federal lease sales were held in NPRA in the 1980s, but only two exploration 

wells were drilled by industry and neither discovered any oil or gas. Following a 

10-year hiatus in exploration activity, NPRA again became a focus of interest with the 

1996 announcement of the discovery of the Alpine oil field, located northeast of the 

Lookout Ridge quadrangle just outside NPRA. Federal lease sales were held in 1999, 

2002, and 2004 in northern NPRA that included land in the northern part of the 

Lookout Ridge quadrangle. Several exploration wells were drilled by industry during 

subsequent winter drilling seasons, but none of them were located within the Lookout 

Ridge quadrangle; several of those wells were announced as oil and gas discoveries.

REGIONAL SETTING

The geology of the Lookout Ridge 1:250,000 quadrangle spans part of the 

transition from the deformed rocks of the foothills of the northern Brooks Range into 

the undeformed rocks of the Arctic coastal plain. Rocks exposed in the quadrangle 

(fig. 1) are part of the gently south dipping northern flank of the Colville basin, which 

is a deep, asymmetrical foreland basin of Cretaceous and Tertiary age that lies north of 

the Brooks Range orogenic belt. The Colville basin is underlain by a Devonian and 

older, deformed and weakly metamorphosed basement complex (Dumoulin, 2001) 

assigned to the Franklinian sequence (Lerand, 1973; Hubbard and others, 1987a,b; 

Bird and Molenaar, 1992). A relatively thin section of Carboniferous to lowest 

Cretaceous (lower Neocomian) strata representing platform deposits of the Ellesmerian 

and Beaufortian sequences (Bird and Molenaar, 1992) overlies the basement.

The rocks of the Colville basin are assigned to the Brookian sequence, a thick 

section of Lower Cretaceous to Miocene foreland basin deposits (see regional map in 

Mull and others, 1987, or Moore and others, 1994). Brookian sediments were eroded 

and transported northward from orogenic belts in the Brooks Range and eastward 

from the Chukchi platform, an ancestral highland that now lies beneath the Chukchi 

Sea west of northern Alaska (Mull, 1979). The basin fill comprises a thick (more than 

12,000 feet (ft)), eastward-prograding clastic wedge consisting of deep marine basin 

and slope deposits (Torok Formation) and overlying shallow-marine shelf, deltaic, and 

nonmarine deposits (Nanushuk Formation) (Molenaar, 1985). The Nanushuk 

Formation forms most of the surface exposures in the foothills fold belt and underlies 

most of the coastal plain of northern Alaska. Following the eastward progradation of 

the Torok-Nanushuk clastic wedge to an ultimate shelf margin east of the Colville 

River in the eastern Umiat quadrangle, the top of the Nanushuk was flooded by a 

regional marine transgression, which led to deposition of the Upper Cretaceous 

(Cenomanian to Coniacian) Seabee Formation (fig. 1). Renewed progradation of 

clastic depositional systems subsequently resulted in deposition of shallow-marine 

through nonmarine strata of the Upper Cretaceous (Turonian through Maastrichtian) 

Tuluvak, Schrader Bluff and Prince Creek Formations, and the early Tertiary 

Sagavanirktok Formation east of the Lookout Ridge quadrangle. Deposition of these 

shallow-marine to nonmarine sediments to the east completed the filling of the Colville 

basin. Exposures of the Brookian sequence in the Lookout Ridge quadrangle consist 

of (in ascending order) the Torok, Nanushuk, and Seabee Formations. No Brookian 

strata younger than the Seabee Formation are known to be present in the Lookout 

Ridge quadrangle.

The northern part of the Lookout Ridge quadrangle is part of the Arctic coastal 

plain and consists almost entirely of tundra cover, shallow tundra lakes (thaw lakes), 

and a few meandering streams that have no bedrock exposures within. The southern 

half of the quadrangle consists of upland areas that are dominantly underlain by 

relatively resistant rocks of the Nanushuk Formation and locally less resistant rocks 

that are probably part of the lower part of the Seabee Formation, which is probably 

present in the axes of some of the regional synclines. This upland area is partly incised 

by the headwaters of the Awuna, Kigalik, and Titaluk Rivers, Shaningarok Creek, and 

other tributaries of the Meade River. Rubble exposures, which are an expression of 

surface weathering of the Nanushuk Formation, are widespread in parts of this area 

and greatly facilitated the 2002 interpretation of modern color infrared aerial 

photographs that is incorporated in this map. These rubble exposures allow mapping 

of outcrop patterns of the Nanushuk Formation in areas of poor bedrock exposure.

Of particular interest in the Lookout Ridge quadrangle is an area where there are 

several petrified trees, some more than 2 ft in diameter and 14 ft high, preserved in 

growth position in the upper part of the Nanushuk Formation (figs. 2 and 3). This 

locality is near the head of Lili Creek, a tributary of the Meade River at 69°19.310'

N., 158°11.258' W., sec. 28, T. 1 S., R. 26 W. (Decker and others, 1997).

REGIONAL STRUCTURE

The succession of relatively resistant Cretaceous (Albian to Turonian) clastic rocks in 

the Lookout Ridge and adjacent quadrangles is regionally deformed into a series of 

linear, open synclines and generally tighter anticlines that are commonly faulted in the 

southern part of the quadrangle. The fold amplitudes generally decrease to the north 

so that the northernmost structures are markedly more subdued than those to the 

south. These structures developed above a décollement in relatively incompetent 

shales and mudstones of the underlying Torok Formation (probably Aptian to Albian 

in the subsurface across this area) and Kingak Shale (Jurassic to Lower Cretaceous). 

The Torok Formation is exposed in the cores of the anticlines in the southern part of 

the quadrangle, but the Kingak Shale is not exposed in the Lookout Ridge quadrangle. 

The magnitude of shortening within the Nanushuk Formation in the fold belt appears 

to increase toward the Colville River to the east but cannot be quantified.

The anticlinal axes, which are better exposed in the southern part of the 

quadrangle, are characterized by both north- and south-vergent thrust faults that occur 

in the Nanushuk Formation. The Kigalik anticline, which is particularly prominent, 

can be traced westward for nearly 100 mi from the Kigalik River drainage in the 

western part of the adjacent Ikpikpuk River quadrangle to the western part of the 

Lookout Ridge quadrangle. Along its entire length, the crest of this anticline is marked 

by a significant north-vergent thrust fault. This fault is particularly evident along the 

eastern end of the anticline, where the Nanushuk Formation on the south is thrust 

northward over the north-dipping uppermost part of the Nanushuk and probable 

Seabee Formation in the Pahron Creek syncline (new name), a regional syncline in 

the headwater tributaries of the Titaluk River. South of the Kigalik anticline, a regional 

synclinal trend composed of two separate synclines (here named the Discovery Creek 

and Section Creek synclines) can be traced from the Colville River in the adjacent 

Ikpikpuk River quadrangle westward across the entire Lookout Ridge quadrangle. 

In the southeast part of the quadrangle, south of the Discovery Creek and Section 

Creek synclinal trend, the structural style becomes more complex and is marked by 

several shorter, low-amplitude anticlinal and synclinal axes and a regional anticlinal 

trend within the Nanushuk Formation. The crestal part of this anticlinal trend is 

marked by both north- and south-vergent thrust faults. In the western part of the 

quadrangle, the Wix anticline is marked by a north-vergent thrust fault, but in the 

eastern end of the quadrangle, the Birthday Pass anticline (new name) is marked by an 

apparent south-vergent thrust fault that extends eastward into the Ikpikpuk River 

quadrangle (Mull and others, 2005). This south-vergent thrust fault overrides rocks of 

the upper part of the Nanushuk Formation on the flanks of both the Birthday Pass 

syncline (new name) and Awuna anticline, which plunges eastward into the Ikpikpuk 

River quadrangle (Mull and others, 2005). In the southwestern part of the quadrangle 

south of the Awuna syncline, the Carbon Creek anticline and Lookout Ridge syncline 

are relatively simple, long, regional, symmetrical folds that are well expressed in the 

Torok and Nanushuk Formations.

Regional structural and stratigraphic analysis and apatite fission-track data suggest 

that the deformation of the western and central parts of the Brooks Range foothills 

fold belt probably occurred during early Tertiary time in response to a late stage of 

uplift of the Brooks Range orogenic belt to the south (Mull and others, 1997; 

O’Sullivan and others, 1997).

ACKNOWLEDGMENTS

Many of the authors whose work is cited in this report freely shared their data and 

insights with us. Over the years, field observations and discussions with a large 

number of colleagues have contributed immensely to our knowledge and 

understanding of the geology of the Alaskan Arctic Slope and northern Brooks 

Range. Special thanks go to field companions H.S. Sonneman, D.H. Roeder, and 

G.W. Newman of Exxon Company, USA; M.D. Mangus of Atlantic Richfield 

Company; J.E. Decker, J.T. Dillon, R.R. Reifenstuhl, E.E. Harris, and D.L. LePain of

GEOLOGIC MAPS OF NORTHERN ALASKA

Edited by

David W. Houseknecht

Arctic Alaska hosts a spectrum of geology and a wealth of natural resources 

matched by few areas on Earth. Prior to the 1940s, geologic investigations in the 

region mostly were limited to coastal surveys and inland reconnaissance studies. 

Nevertheless, the potential for petroleum accumulations beneath Alaska’s North 

Slope and for mineral deposits in the Brooks Range was recognized through the 

observations of the early expeditions. World War II demonstrated an urgent need for 

domestic energy and mineral resources and stimulated the initial systematic geologic 

mapping in northern Alaska as a basis for energy and mineral exploration. The 

geologic maps generated by those initial efforts also served as the foundation for 

additional petroleum exploration in the wake of the oil embargo of the 1970s. A few 

years into the 21st century, the natural resources of northern Alaska again are a 

focus of national attention. The need for detailed geologic maps is greater than ever, 

not only as a basis for petroleum and mineral exploration, but also for land-use 

planning and mitigating the environmental impacts of developing those resources.

The U.S. Geological Survey (USGS) performed the initial systematic mapping 

of the geology of Alaska’s North Slope, including the northern front and foothills 

of the Brooks Range, between 1944 and 1953. Maps resulting from that work 

were published between 1960 and 1966 as USGS Professional Paper 303. Since 

that time, numerous geologic maps of individual quadrangles, or parts of 

quadrangles, have been published by the USGS and by the Alaska Division of 

Geological and Geophysical Surveys (ADGGS). Until now, no attempt was made 

to produce an integrated set of geologic maps using a uniform scale and 

cartographic standards, and consistently applied stratigraphic nomenclature. 

SIM–2817 is a set of digital geologic maps comprising individual 1:250,000 

quadrangles, each assigned a unique letter (for example, this map of the Lookout 

Ridge quadrangle is SIM–2817–C). The objective of these reports is to provide a 

new unified set of geologic maps of the northern flank and foothills of the Brooks 

Range using a uniform scale and cartographic style, as well as consistent 

stratigraphic nomenclature.

Although this collection of geologic maps incorporates significant contributions by 

many geologists who have mapped in northern Alaska during the past six decades, it 

would not be possible except for one geologist. This compilation is a testament to 

the career contributions of Charles G. (Gil) Mull, who has spent nearly forty years 

mapping the geology of the region for the petroleum industry, the USGS, the 

ADGGS, and the Alaska Division of Oil and Gas.

the Alaska Division of Geological and Geophysical Surveys. M.D. Myers of the Alaska 

Division of Oil and Gas, and I.L. Tailleur, J.T. Dutro, Jr., W.W. Patton, Jr., H.N. 

Reiser, C.M. Molenaar, I. Ellersicck, C.F. Mayfield, T.E. Moore, C.J. Schenk, and C.J. 

Potter of the U.S. Geological Survey participated in some of our field studies and 

broadened our knowledge of the area based on their individual specialties. University 

of Alaska Department of Geology and Geophysics students D.A. Bodnar, J.P. Siok, 

K.E. Adams, R.A. Alexander, R.K. Glenn, A.V. Anderson, W.R. Camber, N.T. Harun, 

T.A. Imm, M.K. Wartes, and faculty members K.F. Watts, R.K. Crowder, and W.W. 

Wallace also made major contributions to some of our studies. Office discussions and 

reviews by K.J. Bird, C.M. Molenaar, J.A. Dumoulin, S.M. Karl, K.D. Kelley, J.H. 

Dover, and A.G. Harris of the USGS added additional valuable data and 

understanding. In addition, we acknowledge the paleontological contributions of M.B. 

Mickey and Hideyo Haga of Micropaleo Consultants, and of W.P. Elder and R.B. 

Blodgett, consultants. W.G. Dow and J.T. Allen of Baseline DGSI, Inc., provided 

valuable organic geochemical analyses. P.B. O'Sullivan and J.M. Murphy contributed 

their knowledge of fission-track dating.

Most of our field observations would not have been possible without helicopter 

pilots such as Joe Nightingale, G.L. Wunsch, Mose Car, and Ken Butters, all of whom 

spent many hours flying us to remote locations under frequently difficult conditions. 

Fixed-wing aircraft pilots Irv Kurtz, Frank Whaley, Jr., Buck Maxson, and Stan 

Parkerson ferried personnel and supplies to our remote field camps on wheels, skis, or 

floats, and also shared our remote camps.

We also are indebted to the management personnel of Richfield Oil Corporation, 

Atlantic Richfield Company, Exxon Company USA, the U.S. Geological Survey, 

Alaska Division of Geological and Geophysical Surveys, and Alaska Division of Oil 

and Gas who provided both the encouragement and financial support to carry out 

the research projects, even though the tangible benefits initially may have seemed 

obscure. Finally, we appreciate the efforts of digital cartographers P.A. Freeman, O. 

Rivero, J.A. East, J.K. Tully, L.C. Bryant, R.D. Crangle, Jr., and M.W. Borella. 

Detailed reviews by K.J. Bird and D.W. Brizzolara contributed significantly to the 

map and text.

REFERENCES CITED

Bird, K.J., and Molenaar, C.M., 1992, The North Slope foreland basin, Alaska, in

Macqueen, R.W., and Leckie, D.A., eds., Foreland basins and fold belts: American 

Association of Petroleum Geologists Memoir 55, p. 363–393.

Black, R.F., 1964, Gubik Formation of Quaternary age in northern Alaska: U.S. 

Geological Survey Professional Paper 302–C, p. 59–91.

Brosgé, W.P., and Whittington, C.L., 1966, Geology of the Umiat-Maybe Creek 

region, Alaska: U.S. Geological Survey Professional Paper 303–H, p. 501–638.

Decker, P.L., Wilson, G.C., Watts, A.B., and Work, D., 1997, Growth-position 

petrified trees overlying thick Nanushuk Group coal, Lili Creek, Lookout Ridge 

quadrangle, North Slope, Alaska, in Clough, J.G., and Larson, Frank, eds., Short 

notes on Alaska geology 1997: Alaska Division of Geological and Geophysical 

Surveys Professional Report 118, p. 63–70.

Detterman, R.L., 1956, New and redefined nomenclature of Nanushuk Group, 

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40

EXPLANATION OF MAP SYMBOLS

Contact—Approximately located

Faults—Dashed where approximately located; dotted where concealed; 

queried where uncertain

Normal fault—U, upthrown side; D, downthrown side

Thrust fault—Teeth on upper plate

Wrench fault—Arrows indicate relative movement

Folds—Approximately located; dotted where concealed; queried where 

uncertain

Anticline—Showing direction of plunge

Syncline—Showing direction of plunge

Traceable beds

Strike and dip of beds

U

D

DESCRIPTION OF MAP UNITS

Surficial deposits, undifferentiated (Holocene and Pleistocene)—

Tundra-covered, fine-grained, organic-rich silt, loess, and local colluvium 

and fine-grained alluvial sand and silt in areas adjacent to upland slopes. 

In northern part of quadrangle, includes unstratified marine sand, silt, 

and local gravel of Gubik Formation (Black, 1964), which coincides with 

area of abundant shallow lakes in Arctic coastal plain (Brosgé and 

Whittington, 1966) and the topographically lower reaches of stream 

valleys in the northern part of the foothills fold belt

Alluvial deposits, undivided (Holocene and Pleistocene)—Alluvial sand, 

gravel, and silt in active braided and meandering stream flood plains, and 

in adjacent low, lightly vegetated abandoned flood plains and low terraces 

Terrace gravels (Holocene and Pleistocene)—Gravel and sandy gravel, 

forms locally conspicuous terraces adjacent to Colville River in southwest part of quadrangle

Seabee Formation (Gryc and others, 1956; Whittington, 1956; revised 

by Mull and others, 2003) and Nanushuk Formation, undivided 

(Upper Cretaceous, Turonian, to Lower Cretaceous, Albian)— 

Mapped in axes of Pahron, Section Creek, and Discovery Creek synclines 

that flank Kigalik anticline, where presence of scattered areas of whiteweathering frost boils and scattered resistant bedrock traces visible on 

aerial photographs suggests that Seabee Formation probably locally 

overlies Nanushuk Formation. Where better exposed in adjacent Ikpikpuk 

River quadrangle, Seabee Formation is mostly deeply weathered bentonitic mudstone; silty mudstone; and some medium- to dark-gray to black, 

fissile, organic-rich shale with interbedded bentonite and some thin, 

silicified tuff beds. Sandstone in lower part of unit is mostly tundra-covered, 

but is probably dominantly fine- to medium-grained. Contact of map unit 

with underlying Nanushuk Formation poorly constrained

Nanushuk Formation, undivided (Gryc and others, 1951; Detterman, 

1956; revised by Mull and others, 2003) (Upper Cretaceous, 

Cenomanian, to Lower Cretaceous, Albian)

Upper part (Upper Cretaceous, Cenomanian, to Lower Cretaceous, 

Albian)—Dominantly nonmarine to marginal-marine, gray to light-gray 

sandstone, and quartz- and chert-pebble conglomerate interbedded with 

poorly exposed siltstone; dark-gray, silty, carbonaceous shale; and coal; 

interbedded with marine rocks in upper and lower part of unit. Includes 

rocks formerly mapped regionally as Ninuluk, Niakogon, Chandler, and 

Grandstand Formations by Detterman (1956) and Detterman and others 

(1963). In upland areas, forms rolling tundra-covered hills with occasional 

resistant sandstone or conglomerate ledges with scattered rubble traces. 

Contact with overlying Seabee Formation is not exposed and is poorly 

constrained on aerial photographs; in southern part of quadrangle, top of 

unit mapped may contain beds of Seabee Formation. Contact with lower 

part of Nanushuk is approximate, and was determined using aerial 

photography; traces of resistant sandstone beds with less lateral continuity 

are assigned to the upper part of the Nanushuk; resistant beds with 

greater lateral continuity are assigned to the lower part of the Nanushuk. 

Sandstone beds are generally tight with relatively low porosity and permeability, but regionally transgressive, quartz-rich, marine sandstones in 

upper part of this unit have better porosity and permeability

Lower part (Lower Cretaceous, Albian)—Dominantly gray to greenishgray, very fine to fine-grained marine sandstone and minor conglomerate. Contains resistant beds that form rubble traces which display long, 

lateral continuity on aerial photographs. In southern part of quadrangle, 

basal part of unit intertongues conspicuously with upper part of underlying Torok Formation where some resistant horizons prograde eastward 

into nonresistant horizons. Includes rocks formerly named Tuktu Formation by Detterman (1956) and Detterman and others (1963)

Torok Formation (Gryc and others, 1951; Patton, 1956) (Lower 

Cretaceous, Albian to Aptian)—Dark-gray mudstone and silty 

mudstone with lesser amounts of greenish-gray, thin-bedded siltstone. 

Generally poorly exposed, present only in axes of Carbon Creek and 

Awuna anticlines in southern part of quadrangle

Qu

Qal

Knl

Kto

Qtg

Knu

Ksn

UNCONSOLIDATED DEPOSITS

BEDROCK

Qu Qal Qtg QUATERNARY

CRETACEOUS

Upper Cretaceous

Lower Cretaceous

Holocene

Pleistocene

CORRELATION OF MAP UNITS

Albian

Cenomanian

Turonian

Kto

Ksn Knu

Knl

Aptian