PRELIMINARY GEOLOGIC, 

PETROLOGIC, AND PALEONTOLOGIC 

RESULTS OF THE STUDY 

OF NANUSHUK GROUP ROCKS, 

NORTH SLOPE, ALASKA 

GEOLOGICAL SURVEY CIRCULAR 794 
Cover: 

Corwin Bluff along the Chukchi Sea. 

Note helicopter for scale. 
PRELIMINARY GEOLOGIC, 

PETROLOGIC, AND PALEONTOLOGIC 

RESULTS OF THE STUDY 

OF NANUSHUK GROUP ROCKS, 

NORTH SlOPE, AlASKA 

BY THOMAS S. AHLBRANDT , EDITOR 

GEOLOGICAL SURVEY CIRCULAR 794 

1979 
United States Department of the Interior 

CECIL D. ANDRUS, Secretary 

Geological Survey 

H. William Menard, Director 

Free on application to Branch of Distribution, U.S. Geological Survey 

1200 South Eads Street, Arlington, Va. 22202 
CONTENTS 

Page 

Introduction to geologic studies of the Nanushuk Group, North Slope, Alaska, 

by T. S. Ahlbrandt----------------------------------------------------------------------- 1 

Nanushuk Group deposition and the Late Mesozoic structural evolution of the central 

and western Brooks Range and Arctic Slope, by C. G. Mull--------------------------------- 5 

Depositional framework and reservoir quality studies of selected Nanushuk Group 

outcrops, North Slope, Alaska, by T. S. Ahlbrandt, A. C. Huffman, J. E. Fox, and 

Ira Pasternack--------------------------------------------------------------------------- 14 

Subsurface studies of the Nanushuk Group, North Slope, Alaska, by K. J. Bird and J. Andrews-- 32 

A summary of reservoir characteristics of the Nanushuk Group, Umiat test well 11, National 

Petroleum Reserve in Alaska, by J. E. Fox------------------------------------------------ 42 

Hydrocarbon source potential of the Nanushuk Group and the Torok Formation, a preliminary 

report, by L. B. Magoon and G. E. Claypool----------------------------------------------- 54 

Textural and mineralogical study of some surface and subsurface sandstones from the 

Nanushuk Group, western North Slope, Alaska, by S. Bartsch-Winkler----------------------- 61 

Stratigraphy and petrography of a measured section on the south limb of Barabara Syncline, 

North Slope, Alaska, by A. C. Huffman---------------------------------------------------- 77 

Some Cretaceous plant megafossils and microfossils from the Nanushuk Group, Northern 

Alaska, a preliminary report, by R. A. Scott and C. J. Smiley---------------------------- 89 

Dinoflagellate and Acritarch assemblages from the Nanushuk Group (Albian-Ceonomanian) and 

the Torok Formation (Albian), Umiat test well 11, National Petroleum Reserve in Alaska, 

northern Alaska, by F. E. May------------------------------------------------------------ 113 

Dinoflagellate and acritarch assemblages from the Grandstand Formation (Middle to Upper 

Albian) of the Nanushuk Group, Simpson Core Test 25, National Petroleum Reserve in Alaska, 

northern Alaska, by F. E. May and J. A. Stein-------------------------------------------- 128 

Cretaceous foraminifers from the North Slope of Alaska, by W. V. Sliter---------------------- 147 

References cited----------------------------------------------------------------------------- 158 

ILLUSTRATIONS 

Page 

Figure 1. General North Slope index map----------------------------------------------------- 2 

2. Generalized nomenclature and stratigraphic relationships of Lower Cretaceous 

sediments, western and central North Slope-----------·-··--------------------------- 5 

3. Index map 9f structures and physiographic subdivisions of the North Slope--------- Q 

4. Schematic thrust sheet sequence along north flank of the Brooks Range------------- 11 

5. Stratigraphic nomenclature of Nanushuk Group-------------------------------------- 14 

6. Schematic cross-section of Nanushuk rocks, western North Slope-------------------- 18 

7. Selected measured sections of Nanushuk rocks-------------------------------------- 19 

8. Sedimentary features of Nanushuk rocks in outcrop--------------------------------- 21 

9. Sandstone percent histograms of selected Nanushuk outcrop sections---------------- 23 

10. Index map of selected Nanushuk Group data----------------------------------------- 33 

11. Seismic section through Drew Point 1 well----------------------------------------- 35 

12. Diagrammatic stratigraphic diagram relating rocks of NPRA and Prudhoe Bay--------- 36 

13. Diagrammatic Cretaceous time-stratigraphic chart for northern NPRA---------------- 36 

14. Cretaceous section in Drew Point 1 well------------------------------------------- 36 

15. Directional (paleotransport) data for sediments of the Torok Formation and 

Nanushuk Group------------------------------------------------------------------- 37 

16. Log response and lithofacies in three NPRA wells---------------------------------- 38 

17. Isopach map including both Torok Formation and Nanushuk Group----~---------------- 39 

III 
ILLUSTRATIONS (continued) 

Page 

18. Nanushuk Group isopach map-------------------------------------------------------- 40 

19. Torok Formation isopach map------------------------------------------------------- 41 

20. Index map of Umiat Anticline region----------------------------------------------- 43 

21. Stratigraphic column of Umiat test well 11---------------------------------------- 44 

22. Deltaic interpretation of Lower Cretaceous rocks in eastern NPRA------------------ 46 

23. Description of core 60, Grandstand Formation, Umiat test well 11------------------ 47 

24. Description of cores 56-58, Grandstand Formation, Umiat test well 11-------------- 48 

25. Description of cores 52-53, Grandstand Formation, Umiat test well 11-------------- 49 

26. Description of core 49, Killik Tongue of Chandler Formation, Umiat test well 11--- 49 

27. Description of cores 35-38, Ninuluk Formation, Umiat test well 11----------------- 51 

28. Porosity and permeability relationships of Cretaceous rocks, Umiat test well 11--- 53 

29. Organic geochemistry data for Nanushuk Group and Torok Formation from the 

Kukpowruk type section and Kaolak No. 1 well------------------------------------- 58 

30. Organic geochemistry data for Cretaceous rock units in Topagoruk No. 1 well and 

Umiat test well 11---------------------------------------------------------------- 59 

31. Index map of outcrop and subsurface petrography samples---------------------------- 62 

32. Textural properties of Nanushuk sandstones as determined petrographically---------- 63 

33. Ternary plots of Nanushuk sandstone petrographic data------------------------------ 64 

34. Photographs of pore-linings in sandstones of the Nanushuk Group-------------------- 68 

35. Scanning electron microscope photographs of pore-linings in sandstones of the 

Nanushuk Group-------------------------------------------------------------------- 69 

36. Index map showing sample locations along the south limb of Barabara Syncline------- 77 

37. Ternary diagrams of petrographic data, Barabara Syncline, using Dickson's (1970) 

methods--------------------------------------------------------------------------- 81 

38. Ternary diagrams of petrographic data, Barabara Syncline, using Folk's (1968) 

methods--------------------------------------------------------------------------- 81 

39. Histograms of reservoir quality parameters, Barabara Syncline---------------------- 85 

40. Graphic presentation of petrographic data, Barabara Syncline----------------------- 86 

41. Stratigraphic sequences of Mississippian to Lower Cretaceous rocks, western 

North Slope----------------------------------------------------------------------- 88 

42. Index map showing plant macrofossil and microfossil localities, Nanushuk Group, 

northern Alaska------------------------------------------------------------------- 89 

43. Stratigraphic ranges of selected plant megafossils, northern Alaska---------------- 92 

44. Stratigraphic occurrence and distribution of Nilssoniopteris palymorpha, northern 

Alaska------------------------------------------------------~--------------------- 93 

45. Index map showing location of Simpson core test 25--------------------------------- 129 

46. Columnar section of Grandstand Formation, Simpson core test 25--------------------- 130 

47. Index map showing sample and well localities studied for foraminiferal assemblages- 148 

48. Distribution of foraminifers in Albian to Cenomanian interval of Umiat test 

Plate 1-7. 

8-12. 

13-17. 

18. 

19. 

Table 1. 

2. 

well 11--------------------------------------------------------------------------- 149 

Selected plant fossils of the Nanushuk Group-------------------------------------- 98-111 

Selected dinoflagellates and acritarchs from Umiat test well 11-------------------118-127 

Selected dinoflagellates and acritarchs from Simpson core test 25-----------------136-145 

Selected foraminifers from Torok Formation and Nanushuk Group of Umiat test 

well 11-------------------------------------------------------------------------- 154 

Selected foraminifers from Torok Formation and Nanushuk Group surface sections---- 156 

TABLES 

Synthesis of resource related data gathered in 1977 outcrop studies----------------

Selected Nanushuk outcrop and subsurface data--------------------------------------

IV 

Page 

16 

34 
TABLES (continued) 

Page 

3. Organic geochemical data from outcrop and core material of Cretaceous rock units, 

North Slope----------------------------------------------------------------------- 56 

4. Clast compositions in Nanushuk Group petrographic samples-------------------------- 66 

5. Composition of samples from south limb of Barabara Syncline------------------------ 80 

6. Textural data of samples from south limb of Barabara Syncline---------------------- 82 

7. Uranium and thorium content of samples from south limb of Barabara Syncline-------- 83 

8. Ranges of dinoflagellates and acritarchs from the Nanushuk Group and Torok 

Formation, Umiat test well 11----------------------------------------------------- 115 

9. Ranges of dinoflagellates and acritarchs from the Grandstand Formation, Simpson 

core test 25---------------------------------------------------------------------- 131 

10. Foraminifer-bearing samples from the Kukpowruk type section------------------------ 151 

11. Foraminifer-bearing samples from the Seabee Formation in the Ninuluk Bluff section- 153 

12. Foraminifer-bearing samples from the Tuktu Bluff section--------------------------- 153 

v 

INTRODUCTION TO GEOLOGIC STUDIES OF THE 

NANUSHUK GROUP, NORTH SLOPE, ALASKA 

By Thomas S. Ahlbrandt 

ABSTRACT 

Sediments of the Nanushuk Group of early 

Albian to Cenomanian age are a major hydrocarbon 

play within the National Petroleum Reserve in 

Alaska. In a series of 12 chapters by 15 

authors, basic geologic, geochemical, petrologic, and paleontologic data are summarized. 

Together, they permit a better evaluation of 

the hydrocarbon potential of the Nanushuk 

Group. 

Lower Cretaceous sedimentation on the 

North Slope reflects the uplift of the Brooks 

Range and attendant deposition in a marine 

basin along the north flank of this range. 

Sediments that fill this marine basin demonstrate a change from deepwater deposits. The 

sediments grade upward into the Torok Formation 

(predominantly shale) that is subjacent to the 

shallow-marine, deltaic, and interdeltaic 

sediments of the Nanushuk Group. The generally 

northeast progradation of Nanushuk sediments 

away from the Brooks Range is indicated by 

paleotransport data from outcrops as well as by 

seismic and dipmeter data in wells on the North 

Slope. At least two river-dominated deltas are 

hypothesized for onshore Nanushuk rocks: a 

western Corwin delta and, in the central North 

Slope, the Umiat delta. The composition of 

Nanushuk sandstones differs in the western and 

central North Slope regions, probably reflecting 

different lithologies exposed during Early 

Cretaceous time in the sediment source terrains 

to the south. Nanushuk sandstones are all 

generally classified petrographically as litharenites, and reservoir-quality problems within 

these sandstones are related chiefly to abundant 

clay matrix, carbonate cement, or ductile 

(labile) grains. Sedimentary rock fragments 

are common in the Nanushuk sandstones in the 

western North Slope, but in the central North 

Slope, Nanushuk sandstones commonly contain 

metamorphic rock fragments and have a higher 

quartz sand content than western sandstones. 

Preliminary data indicate that the composition 

of Nanushuk sandstones, particularly in highenergy environments, is relatively better in 

the central area than in equivalents to the 

west; however, reservoir-quality problems in 

sandstone of both areas are numerous and of 

concern. 

1 

Potential hydrocarbon source beds within 

the Nanushuk in the central North Slope are 

relatively less thermally mature than those in 

the western area, which are relatively more 

mature or "gas prone." The relative immaturity 

of potential Nanushuk source beds in the central 

North Slope means, for example, that the oil 

produced from Nanushuk sandstones in the Umiat 

oil field may have migrated, perhaps along 

faults, from pre-Nanushuk sources. Alternatively, the Umiat oil may also have come from 

shales of the Torok Formation, equivalent in 

age to the Nanushuk, or even from overlying 

shales of the Seabee Formation, both of which 

are more deeply buried northeast of Umiat. 

Correlation of rock units of the Nanushuk 

requires the integration of spore, pollen, and 

plant megafossil zonations in nonmarine intervals and of dinoflagellate, foraminiferal, and 

limited faunal zonations in marine intervals. 

These zonations are now established for several 

reference sections in either the western or 

central North Slope. Each zonation is being 

extended to other locations and is being integrated with other fossil zonations. However, 

the problem of revision of the complex stratigraphic nomenclature of the Nanushuk Group is 

avoided here because, in my opinion, data are 

too preliminary and too widely scattered to 

permit such revision and correlation at this 

time. Thus, the general stratigraphic terms of 

Torok Formation and Nanushuk Group with appropriate modifiers (commonly related to depositional environment) or previously named units 

are used here. 

Chapters of this Circular summarize approximately the first half of the present two-year 

Nanushuk study.. The authors have used all data 

available to them, either previously published 

or newly generated. Although the word "preliminary" is part of the title of this Circular, 

the contributions represent the latest analyses. 

and synthesis of data available, and the preliminary label may be an unjust assessment of some 

of the chapters. 

INTRODUCTION 

Sediments of the Nanushuk Group of Cretaceous age (early Albian to Cenomanian) constitute a major hydrocarbon play within the NPRA 
167~ 166" 164" 163" 161" 

EXPLANATION 

Percent of reading Paleotransport directions determined from plunge along axis of symmetrically filled nonmanne channels of 

30 

~ 

o ~ the Nanushuk Group -- Number of measurements indicated by number 10 parenthesis; arrow indicates net 

transport direction; percent of readings in each segment of rose is to the same scale as shown to the left 

SCALEI:l,OOIJ,OOO 

/ 

+--

~-­

@> 

Line of measured section 

Titaluk 1 Well location and name 

Anticline -- Dashed where approximate 

Syncline -- Dashed where approximate 

Approximate outline of basal portion of Nanushuk Group 

(Kukpowruk and Tuktu Formation) 

0 10 20 30 40 50 KILOMETERS 

I 

I 

I 

I se~ I 

Figure 1.--Index map of sections of Nanushuk Group rocks measured in 1977 

(National Petroleum Reserve in Alaska) (Carter 

and others, 1977). Currently, the most significant known oil field within NPRA is in Nanushuk 

Group rocks at Umiat Anticline in the southeastern part of NPRA (estimated reserves of 122 

million barrels; Espach, 1951). The goal of 

this project is to evaluate the resource (principally hydrocarbon) potential of Nanushuk 

Group rocks. The chapters in this Circular 

summarize recent preliminary results of studies 

designed to provide a geologic framework to 

adequately assess the hydrocarbon potential of 

the Nanushuk Group. 

The Nanushuk Group was studied by a number 

of U.S. Geological Survey personnel coincident 

with exploration of Naval Petroleum Reserve No. 

4 (NPR-4) in the 1940's and 1950's, and many 

basic data were published by these geologists. 

The renewed exploration of NPRA in the mid1970's necessitates an updated geologic study 

of the Nanushuk. New concepts such as the 

reservoir-quality problems associated with 

compositionally complex (quartz-poor) sandstones, new biostratigraphic techniques (zona2 

tion with dinoflagellates), recently completed 

organic geochemical analyses of potential 

source beds, new seismic and well data, as well 

as the use of deltaic sedimentary models, 

complement and improve our understanding of the 

Nanushuk. 

The present study has a short duration (2 

years) and is in cooperation with the current 

NPRA exploration program. This publication 

accommodates the need to disseminate information 

as rapidly as possible to assist exploration 

needs as well as provide basic data for subsequent work. The articles are arranged first 

regionally and then topically. A common denominator for the topical articles is the discussion 

of at least one reference section located 

either in the western North Slope region or in 

the central North Slope region (eastern NPRA). 

The sections in the western region include the 

Kaolak 1 well and outcrop sections along ·the 

Kukpowruk River--the type section of the 

Kukpowruk Formation; the Barabara Syncline 

section; and, for nonmarine fossil zonations, 

the Corwin Bluff section, the type section of 
and of well locations in the western and central North Slope areas of Alaska. 

the Corwin Formation as described by Chapman 

and Sable, 1960 (fig. 1). The reference section 

in the central North Slope region is Umiat test 

well 11. 

Umiat test well 11 is important for many 

reasons: (1) it contains the most continuously 

cored, unfaulted section of subsurface Nanushuk 

Group rocks in the eastern NPRA; (2) it contains 

the type section of the Seabee Formation 

(Colville Group), which overlies the Nanushuk 

Group (Collins, 1958a); (3) it has received the 

most detailed sedimentologic, petrographic, and 

reservoir analysis of any well that penetrates 

the Nanushuk in the NPRA (Fox and others, 

1979); and (4) although it is a dry hole, it is 

on Umiat Anticline, which contains the Umiat 

oil field and provides data that demonstrate 

the parameters affecting reservoir quality of 

Nanushuk sandstones. 

The establishment of reference sections, 

particularly Umiat test well 11, from which 

subsequent extrapolations will be made is the 

focus of several of the chapters. Although 

this report is preliminary, many of the zona3 

tions, petrography, and so forth have been 

applied successfully to other wells or sections. 

This paper summarizes the first year's 

work on the project and includes data gathered 

in the 1977 field season. The locations of the 

measured stratigraphic sections, paleotransport 

data gathered in nonmarine channels of the 

Nanushuk, and the outline of marine intervals 

in outcrops of the Nanushuk are shown in figure 

1. The outcrop and well localities referred to 

in subsequent chapters are shown on this figure 

to avoid repetition in each chapter. 

Briefly, the sequence and significance of 

the contributions are as follows: The first 

chapter, by C. G. Mull, discusses the physiography of the North Slope and the structural 

and stratigraphic framework relevant to the 

Nanushuk; it is fundamental to the understanding 

of subsequent chapters. Mull originally proposed the present study of the Nanushuk and has 

generously assisted all members of this project 

since its inception. 

The following chapter by Ahlbrandt, 

Huffman, Fox, and Pasternack summarizes the 
1977 outcrop studies, most of which were made 

in the western North Slope. They use deltaic 

models to provide a depositional framework 

within which potential Nanushuk reservoirs may 

be evaluated. They suggest that Nanushuk 

sediments, as observed in outcrop, may be 

related to at least two river-dominated deltas: 

the Corwin delta in the western North Slope and 

the Umiat delta in the central North Slope. At 

this point, the reservoir quality of Nanushuk 

sandstones of the Umiat delta seems more favorable than that of Corwin delta sandstones. 

The integration of surface (outcrop) and 

subsurface data is a desired goal of this 

project. All outcrop data collected in 1977, 

some 14,600 m of section, were encoded and 

placed in a computer file at Petroleum Information in Denver, Colo. Computer-drawn displays 

of these measured sections are treated as if 

they are well locations and are comparable with 

the Well History Control System (WHCS) of 

Petroleum Information t~at is being used to 

compile NPRA subsurface data. Direct comparison 

of well logs and measured sections of any 

desired parameter allows integration of surface 

and subsurface data. 

The chapter by Bird and Andrews includes 

new seismic and well data and integrates such 

data with outcrop studies (for example, paleotransport directions, isopach maps) when possible. The northeasterly progradation of 

Nanushuk sediments and their relationship to 

the subjacent Torok Formation sediments are 

easily seen on seismic records and correspond 

to similar observations of these sediments in 

outcrop. 

The chapter by Fox, summarizing the study 

by Fox and others (1979) of Umiat test well 11, 

sets the depositional and petrographic framework 

for subsequent chapters and establishes this 

well as the eastern NPRA subsurface reference 

section for dinoflagellates and foraminifera. 

This section will be used for other kinds of 

comparisons as data become available. 

In Magoon and Claypool's chapter, the 

observation that the oil in the Umiat oil field 

has most probably migrated from "hotter, deeper 

4 

strata" may demonstrate the importance of 

fault-bounded structures such as Umiat Anticline 

in providing both hydrocarbon charge and closure 

to reservoir sandstones of the Nanushuk in the 

central North Slope. Their observation of more 

thermally mature source beds within the Nanushuk 

in the western North Slope relative to the 

central North Slope will certainly be of interest for both oil and gas exploration of the 

Nanushuk. 

Diagenesis of compositionally immature 

sandstones is of serious concern regarding the 

reservoir quality of Nanushuk reservoirs. The 

chapter by Bartsch-Winkler provides a regional 

petrographic evalution of both surface and 

subsurface Nanushuk sandstones. The petrographic differences between Nanushuk sandstones 

in the western and central areas of the North 

Slope may also relate to different source areas 

for the two proposed Nanushuk deltas. The 

following chapter by Huffman discusses the 

petrography of Nanushuk sandstones in a western 

reference section (the Barabara Syncline section) in detail. It can be compared to the 

detailed petrographic discussion of Nanushuk 

sandstones of the eastern NPRA reference section 

(Umiat 11) discussed by Lambert in Fox and 

others (1979). 

Correlation of rock units within the 

Nanushuk across the North Slope is a problem 

due in part to the paucity of macrofaunal and 

planktonic foraminiferal assemblages in the 

Nanushuk. Thus, a threefold biostratigraphic 

approach is used. Zonation by spores, pollen, 

and plant megafossils is applied to nonmarine 

intervals (chapter by Scott and Smiley), whereas 

zonation by dinoflagellates (chapters by May, 

and May and Stein) and (or) foraminifera (chapter by Sliter) becomes more useful in marine 

intervals. Key fossils are documented in 

plates found in each of these three chapters. 

At this preliminary stage, the zonations appear 

to integrate well and provide a means of correlating nonmarine and marine sediments within 

the time-transgressive deltaic and interdeltaic 

deposits of the Nanushuk with prodelta and 

basinal strata of the subjacent Torok Formation. 
NANUSHUK GROUP DEPOSITION AND THE LATE 

MESOZOIC STRUCTURAL EVOLUTION OF THE CENTRAL 

AND WESTERN BROOKS RANGE AND ARCTIC SLOPE 

By C. G. Mull 

INTRODUCTION 

Sediments of the Nanushuk Group of Albian 

to Cenomanian Age are widespread on the Arctic 

Slope of northern Alaska, where they crop out 

extensively in the northern foothills of the 

Brooks Range and extend northward under the 

Arctic Coastal Plain. The sediments consist of 

a molassoid wedge that was shed from the north 

flank of the Brooks Range orogenic belt and 

represent the culmination of a sequence of 

Early Cretaceous tectonic events. These rocks 

are of particular interest as a potential 

hydrocarbon reservoir within the National 

Petroleum Reserve in Alaska (NPRA). The tectonic history and depositional setting in which 

the Nanushuk Group was deposited and deformed 

are briefly described in this chapter of the 

Circular, along with some aspects of the history 

which may influence the hydrocarbon potential 

of the Nanushuk sediments. Greater detail on 

the Nanushuk is presented in other chapters. 

The generalized nomenclature and stratigraphic relationships of the Lower Cretaceous 

and Cenomanian sediments of the western and 

central Arctic Slope, including NPRA, are 

summarized on figure 2. Nanushuk nomenclature 

is outlined by Detterman (1956). Generalized 

geologic maps of the Arctic Slope and Brooks 

Range have been compiled by Lathram (1965), 

Beikman (1976, 1978), and Grybeck and others 

(1977). These maps provide the best published 

overview of the geology of northern Alaska. 

In the area of the western and central 

Arctic Slope and Brooks Range foothills, the 

area of the studies reported in this Circular, 

the Cretaceous sediments in general seem to 

grade from a thick basal flysch sequence upward 

to over 3,000 m consisting dominantly of 

shale, and then into a section of shallow 

marine to deltaic sediments, the Nanushuk Group 

of Albian to Cenomanian Age. The sequence thus 

seems to record the progressive filling of the 

Colville basin, a deep asymmetric foredeep 

noLth of the Brooks Range orogenic belt, and 

may be considered a typical gradational flysch 

to molasse sequence, with the Nanushuk Group 

representing post-orogenic molasse deposits. 

5 

If) 

:J 

0 

UJ 

u 

<t 

f--

UJ 

It: 

u 

CEN 

z 

<t 

iii 

_j 

<t 

s N 

NANUSHUK GROUP 

JURASSIC AND OLDER 

Figure 2.--Diagrammatic Lower and Upper 

Cretaceous stratigraphic relationships 

across the Colville basin, from the Brooks 

Range to the Beaufort Sea. 

PHYSIOGRAPHIC SETTING OF THE 

NANUSHUK OUTCROP BELT 

The Northern Foothills Section of the 

Arctic Foothills Province and the Nanushuk 

outcrop belt extend unbroken from the sea 

cliffs of the Cape Corwin area on the west for 

about 650 km eastward to the Sagavanirktok 

River area of the eastern Arctic Slope (fig. 

3). Across this distance the province is 

characterized by generally east-west-trending 

ridges and rolling upland terrain to an elevation of about 960 m. The ridges and uplands 

are broken by numerous generally northwardflowing streams and rivers, many of which rise 

in the Brooks Range. On the west, four small 

rivers--the Pitmegea, Kukpowruk, Kokolik, and 

Utukok--cross the outcrop belt of the Nanushuk 

Group and flow into the Chukchi Sea. These 

streams are relatively small, but in places 

they and their tributaries are incised over 500 

m into the Nanushuk terrain. As a consequence 

of this incision, the Nanushuk exposures on the 

western Arctic Slope are generally better and 

are found over a wider north-south extent than 
168'" 

1 I C 

' ll c 

Cape Se . ,, 

EXPLANATION PPmgs 

r:::=::J NANUSHUK GP. 

~ OUTCROP BELT 

• 

GRANITE BROOKS RANGE 

ALLOCHTHONS 

~MISHEGUK SEQUENCE 

• NUKA SEQUENCE 

~ IPNAVIK SEQUENCE 

~ KELLY SEQUENCE 

D ENDICOTT SEQUENCE 

I 

164° 

0 c c ~ 

"' 

Figure 3.--Physiographic map showing major provinces and tectonic map showing approximate location 

belt, and major anticlinal axes in Nanushuk surface exposures. 

6 

1 
>Be 156° 154( 

50 0 

50 0 

B E 

50 

50 

152c 150( 148( 

u 0 R 

s E 

100 150 MILES 

100 150 KILOMETERS 

CE~=c~====~====~====3 

of major structural features, approximate distribution of major allochthons, the Nanushuk outcrop 

7 
elsewhere on the Arctic Slope. This western 

area is frequently referred to as the UtukokCorwin area and, because of its better surface 

exposures, was the center of the initial outcrop 

studies in this project. 

To the east of the Utukok-Corwin area, the 

Colville River rises in the foothills of the 

DeLong Mountains and has a generally east and 

northeasterly course for more than 360 km to 

near Umiat, where it turns sharply northward 

and flows toward the Beaufort Sea. For more 

than 160 km, between long 160° W. and 156° W., 

the upper Colville River flows south of the 

Nanushuk Group outcrop belt. As a result, the 

major Colville tributaries, which rise in the 

Brooks Range, do not cross the Nanushuk. From 

near the intersection of the Etivluk River with 

the Colville River and continuing eastward to 

the Umiat area, the Colville crosses the Nanushuk 

belt. The major tributaries to the Colville in 

this area--the Kurupa, Killik, Chandler, and 

Anaktuvuk Rivers--all of which rise in the high 

Endicott Mountains to the south, are incised 

into Nanushuk Group rocks. This area, referred 

to as the Chandler River area, contains fair to 

good exposures along the major streams. 

North of the Colville River, exposures of 

the Nanushuk Group are generally poor. This 

area, which encompasses about one third of the 

Nanushuk outcrop belt, is drained by the Kuk, 

Meade, Topagoruk, Ikpikpuk, and Awuna Rivers 

and their tributaries. These rivers all head 

in a low rolling Nanushuk terrain about 300-500 

m in elevation. The Kuk River trends 

northt..restward into the Chukchi Sea; the Meade, 

Topagoruk, and Ikpikpuk drainages flow northward 

to the Beaufort Sea; and the Awuna flows eastward 

into the Colville River. Discharge on these 

streams is generally low and, as a consequence, 

incision into the Nanushuk terrain is limited 

and outcrops are generally poor and few in 

number. In addition, the detailed studies 

carried out in this project suggest that the 

Kuk-Ikpikpuk area may contain interdeltaic 

Nanushuk sediments (Ahlbrandt and others, this 

volume). The resulting sand-poor nature of the 

sediments may also contribute to the limited 

number of outcrops in this area. As a result 

of the limited outcrops, only limited field 

studies have been carried out in the KukIkpikpuk area of the Nanushuk outcrop belt. 

Most of the knowledge of the Nanushuk north of 

the foothills is derived from subsurface control 

from exploratory wells and from seismic data, 

as discussed in other chapters of this Circular. 

STRUCTURAL EVOLUTION OF THE BROOKS RANGE 

Deposition of the Nanushuk Group of the 

central and western Arctic Slope is closely 

tied to the evolution of the Brooks Range 

orogenic belt during the Cretaceous. An understanding of this orogenic belt aids in understanding the nature of the sediment, its 

depositional environment, and the subsequent 

8 

deformation of the Nanushuk Group. These 

factors strongly influence the potential for 

hydrocarbons in the Nanushuk Group both in NPRA 

and in adjacent areas. Generalizations and 

details of the structural and stratigraphic 

evolution of the area have been presented by 

many workers, including Tailleur, Brosge, and 

Reiser (1967); Brosge and Tailleur (1970, 

1971); Tailleur and Brosge (1970); Tailleur 

(1973); Snelson and Tailleur (1968); Rickwood 

(1970); Martin (1970); Detterman (1973); Mull 

(1977); Mull and Tailleur (1977); Mull and 

others (1976); and Mayfield and others (1978) 

and, in general, will not be repeated here. 

The following summary incorporates data presented by the above authors with unpublished 

observations and interpretations of the writer 

and others; it emphasizes the major tectonic 

events and features that appear to have had an 

influence on Nanushuk deposition. 

Neocomian-Aptian Tectonics 

Regional indications of the beginning of 

the Brooks Range orogeny are recorded in Lower 

Cretaceous sediments exposed within and adjacent 

to the DeLong and Endicott Mountains of the 

western and central Brooks Range. These sediments record the abrupt shift in sediment 

dispersal from a predominant northern source 

that persisted through the late Paleozoic and 

early Mesozoic to a major southern and southwestern source derived from a Cretaceous orogenic belt. 

The orogenic belt exposed in the central 

and western Brooks Range is composed of multiple 

allochthonous sheets of mafic igneous and 

sedimentary rock; these are the rocks from 

which at least part of the sediment in the 

Nanushuk Group was derived (for example, the 

hypothesized "Corwin delta" of Ahlbrandt and 

others, this volume). Several major thrust 

sequences can be traced for over 400 km along 

the front of the mountains. Each sequence is 

composed of a distinctive suite of formations, 

most of which maintain a relatively uniform 

character within the sequence but differ markedly from coeval formations in other thrust 

sequences (fig. 4). The allochthons will be 

described in a section entitled "Brooks Range 

Allochthonous Sequences." 

The Brooks Range allochthons were apparently developed as a result of counterclockwise rotation of a crustal plate (Tailleur 

and Snelson, 1969; Tailleur, 1973; Rickwood, 

1970; Newman and others, 1977). Paleomagnetic 

data and regional reconstructions suggest that 

this plate, the Arctic Alaska plate, moved 

relatively southward and was abducted by 

oceanic crust at a south-dipping subduction 

zone (Mull, 1977, p. B31). This apparent 

relative movement and the relationships of 

continental and oceanic crust suggest that the 

Brooks Range allochthons developed by underthrusting (Tailleur and Snelson, 1969) rather 
than by the more commonly visualized mode of 

overthrusting. Underthrusting involves the 

process by which slices are progressively 

detached from the downgoing slab as it approaches the subduction zone (Seely and others, 

1974). In the Brooks Range allochthons, each 

thrust slice underthrusts rocks that were 

formerly more southerly facies equivalents. 

The resulting stack of allochthonous sheets in 

the Brooks Range thus consists of several 

thousand meters of imbricated sedimentary and 

minor igneous rocks overlain by a sheet of 

oceanic rock which is also imbricated. 

Neocomian-Aptian Sedimentation 

The sediments derived from this Lower 

Cretaceous orogenic belt constitute a thick 

section of rhythmically interbedded sandstoneshale sequences that contain many typical 

turbidite characteristics. In addition, at a 

number of localities, a sedimentary chaos or 

olistostrome is present as a part of or closely 

associated with the turbidite sequence. The 

olistostrome deposits are composed of a heterogeneous assemblage of exotic blocks of mafic 

igneous and sedimentary rocks. Where well 

exposed in the DeLong Mountains, the blocks are 

clearly encased in mudstone, graywacke, and 

associated channel conglomerates at sedimentary, 

not fault, contacts (Mull and others, 1976). 

In some cases the blocks exceed tens of meters 

in maximum dimension. 

The total assemblage of flysch and massive 

olistostrome exceeds a kilometer in thickness 

and is typical of deposits derived from an 

active orogenic belt. Regional stratigraphic 

and structural data show that deposition accompanying the orogenic event was northward into 

the Colville basin, a deep asymmetric basin or 

foredeep. The regional relationships also 

indicate that the orogenic belt and foredeep 

migrated progressively northward (Snelson and 

Tailleur, 1968), so that earlier orogenic 

deposits were themselves subsequently involved 

in the orogeny and, in places, were in turn 

eroded to form later deposits. 

The sedimentary rocks that make up the 

allochthonous sheets of the orogenic belt range 

in age from mid-Paleozoic to Neocomian. Fossils 

contained within the flysch portion of the 

allochthons range in age from Berriasian to 

Valanginian. Although Aptian rocks have long 

been suspected to be present, definite Aptian 

fossils have not been reported from orogenic 

sediments of the Brooks Range thrust belt. 

However, Aptian fossils are reported from 

probable equivalent rocks of the basal Torok 

Formation in wells drilled in the area of the 

northern foothills and coastal plain of NPRA 

(Anderson, Warren, and Associates, written 

commun., 1977-78). In addition, in some places, 

evidence indicates that Neocomian orogenic 

sediments have also been displaced and telescoped by extensive thrust faulting. Thrustfaulted sequences containing rocks as young as 

9 

Neocomian are unconformably overlain at several 

localities (for example, Ekakevik, Fortress, 

and Castle Mountains) by thick lower Albian 

conglomerates of the Fortress Mountain Formation. This relationship, which is best illustrated at Ekakevik Mountain in the southeastern 

part of NPRA (Tailleur and others, 1966; Hunter 

and Fox, 1976), suggests that the major orogenic 

activity which formed the Brooks Range was preAlbian in age, began during Berriasian time, 

and continued into the Aptian. 

Pre-Nanushuk Cretaceous 

Stratigraphic Nomenclature 

Stratigraphic nomenclature within the 

Lower Cretaceous orogenic sediments is very 

generalized and not well established. Names 

and inferred relationships are shown in figure 

2. In the orogenic belt, the name Okpikruak 

Formation has been applied to the thick rhythmic 

flysch of Berriasian Age (Patton and Tailleur, 

1964) that is characteristic of some of the 

thrust sequences. Additional Lower Cretaceous 

facies in other thrust sequences, consisting 

dominantly of graywacke, have not been formally 

named. 

On the shallow northern flank of the 

Colville basin, Neocomian rocks correlative 

with the Okpikruak Formation are informally 

called the "pebble shale" (Alaska Geological 

Society Newsletter, 1978; Bird and Andrews, 

this volume) and consist of black organic shale 

which locally has a thin basal sandstone. 

Where penetrated in wells drilled in the coastal 

plain, the "pebble shale" maintains a relatively 

constant thickness of about 100 m. 

In the subsurface of the coastal plain and 

northern foothills, the "pebble shale" is 

overlain by a thick dominantly shale sequence 

named the Torok Formation (Gryc and others, 

1956). South of the coastal plain, seismic 

data indicate that this interval increases 

greatly in thickness and, where seen in outcrop 

in the southern foothills, commonly consists of 

rhythmically and thinly interbedded sandstone 

and shale that have many turbidite characteristics. Part of this flysch-like section is 

apparently equivalent to the coarse conglomeratic proximal deposits of the Fortress Mountain 

Formation (Patton, 1956). Along the north 

flank of the DeLong Mountains, the lower part 

of the Torok grades downward and perhaps 

southward into a distinctive calcareous flysch 

containing conspicuous amounts of detrital 

muscovite. The upper part of the Torok Formation grades upward into the Nanushuk Group. 

Albian to Late Cretaceous Tectonics 

Regional mapping, combined with stratigraphic and structural studies throughout the 

Brooks Range, indicates that the Early 

Cretaceous stage of intense crustal shortening 

was followed by a stage of broad folding and 

smaller scale faulting that warped and deformed 
the pre-existing thrust sheets. This stage of 

deformation may be related to the intrusion of 

a series of granitic plutons in the Schwatka 

and Baird Mountains of the southern Brooks 

Range. These plutons have Cenomanian to 

Turonian cooling ages, indicated by potassiumargon dating (Fessel and others, 1973; Brosge 

and Reiser, 1971; Turner and others, 1978), 

although lead-alpha dates from granite in the 

Chandalar area and regional structural relationships suggest that an early Paleozoic intrusive 

event also occurred in the area. The potassiumargon dates suggest that the core of the Brooks 

Range was mobilized and subjected to dominantly 

vertical uplift beginning in the Albian, after 

the stage of Neocomian-Aptian crustal shortening 

and thrust tectonics. This event coincides 

with the deposition of the Nanushuk Group. 

The greatest amount of intrusion and 

vertical uplift occurred in the Arrigetch 

Peaks-Mt. Igikpak area of the Schwatka Mountains 

in the south-central portion of the Brooks 

Range. To the west, the surface exposures of 

the granitic intrusions become progressively 

smaller and lower in elevation, and so, regionally, the core of the range is a broad, westplunging anticlinorium that has autochthonous 

or parautochthonous rocks exposed along the 

axis. The sediments and mafic igneous rocks on 

the allochthonous sheets that flank the north 

side of the core of the range also define the 

same regional west-plunging character. As a 

result, progressively higher allochthonous 

sequences are found westward down the plunge of 

the regional anticlinorium into the DeLong and 

Baird Mountains. The presence of numerous 

allochthonous sequences in the western Brooks 

Range and the absence of many of the allochthons 

to the east are probably due not to their 

original distribution, but to the increased 

amount of subsequent vertical uplift and erosion 

to the east. This sequence of events within 

the Brooks Range, which affected the preexisting allochthons, probably played a large 

role in the type of sediment and style of 

deposition in the Nanushuk Group. 

Nanushuk Sediment Provenance 

In order to more fully understand the 

reasons for the character of the Nanushuk 

sediments described in detail in other chapters 

of this Circular, the nature of the source of 

the detritus must be examined. 

Geologists have long recognized that the 

Nanushuk sequence progrades and thins northward 

and eastward over the Arctic Slope (Payne and 

others, 1952; Chapman and Sable, 1960). Along 

the outcrop belt in the foothills of the central 

Brooks Range, the source of the detritus appears 

to be from the south. However, in the western 

DeLong Mountains foothills, pronounced northeastward thinning and progressively finer 

grained sediments in the Nanushuk Group suggest 

a component of source derived from the west. 

10 

Paleotransport interpretations from outcrop 

data gathered during this study support northeasterly progradation in the Utukok-Corwin area 

(Ahlbrandt and others, this volume). In the 

area of the Arctic Coastal Plain, seismic and 

subsurface data show a clearly defined progradation to the northeast and east (Bird and 

Andrews, this volume). In addition, two different sediment source areas are suggested by 

stratigraphic and petrologic studies of Nanushuk 

sediments in the Utukok-Corwin area and Chandler 

River area (Ahlbrandt and others, this volume; 

Huffman, this volume; Bartsch-Winkler, this 

volume). The evidence thus suggests that the 

source of clastic material in the Nanushuk 

Group is from both the Brooks Range to the 

south and the northwest-trending Tigara Uplift 

in the area of Cape Lisburne (Payne, 1955), as 

well as its offshore extension beneath the 

Chukchi Sea, the Herald Arch, which has been 

mapped by Grantz and others (1970, 1976). 

Although the exact character of the rocks 

making up the offshore Herald Arch is unknown, 

good regional data are available for the Tigara 

Uplift and the DeLong and Endicott Mountains of 

the main Brooks Range. In the discussion which 

follows, the allochthonous sheets of the western 

and central Brooks Range are described in 

sequence from the top down, because this is the 

order in which they were eroded and progressively became sources of detritus that was 

deposited as the Nanushuk Group. The vertical 

sequence of the allochthons is illustrated in 

figure 4; their present outcrop distribution is 

shown on figure 3. 

Brooks Range Allochthonous Sequences 

The uppermost of the Brooks Range allochthons, the Misheguk sequence, is an igneous 

complex composed dominantly of altered, finegrained, mafic igneous rocks; coarse-grained 

gabbroic rocks; and lesser amounts of ultramafic 

rocks (Roeder and Mull, 1978; Mayfield and 

others, 1978). These rocks are now present as 

isolated klippen with the tops eroded, but 

several kilometers of rock may have originally 

been present on this sequence. Locally, the 

base of the thrust sequence is marked by isolated slivers of Middle Devonian limestone, but 

these rocks constitute only a minute percentage 

of the entire volume of the thrust complex. 

The allochthon is presently exposed primarily 

in the western Brooks Range. It is probably 

not present in the central Brooks Range, but 

abundant mafic igneous and gabbroic clasts in 

the Fortress Mountain Formation and earlier 

Cretaceous conglomerates suggest that the 

Misheguk allochthon was formerly present in 

this area. 

The Misheguk sequence is structurally 

underlain by the Nuka sequence, a distinctive 

series of Mississippian to Permian arkosic 

limestones, limestones, and sandstones (the 

Nuka Formation) (Tailleur and Sable, 1963; 
MISHEGUK SEQUENCE 

Gabbro 

Ultramafic 

THRUST FAULT 

Basalt 

M. Dev. Is. thin 

THRUST FAULT 

NUKA SEQUENCE 

Mudstone 

Permian-Trias. chert, sh. 

M iss.-Perm. Is. arkose. ss 

THRUST FAULT 

IPNAVIK SEQUENCE 

Cretaceous wacke 

Permian-Trias. chert. sh. 

Miss. cht. sh. Is. diabase s1lls 

M. Dev. Is. thin 

THRUST FAULT 

KELLY SEQUENCE 

ENDICOTT 

SEQUENCE (southern fac1es) J.... (northern fac1es) 

Cret. wacke .::Jv Cret. wacke 

Permian-Trias. chert. sh. q_V Permian-Trias. 

Miss. crinoidal Is. cherty 0J.... chert. sh 

/l...-0 Miss. cr1noidal Is (east) Miss. silty Is '<- J.....:f cherts (west) 

/ U Dev qtz1te cgl 

THRUST FAULT U. Dev. sh. 

other 'sedimentary rocks 

Figure 4.--Diagram showing vertical superposition of Brooks Range allochthonous 

sequences. In general, each sequence, 

when present, occurs in the same structural 

position relative to adjacent sequences. 

Each sequence represents southern facies 

equivalents of the rocks in the immediately 

underlying sequence, and has been telescoped 

relatively northward over the underlying 

sequence. 

Tailleur and others, 1973), overlain by PermianTriassic cherts and siliceous shales, and 

having Mesozoic mudstone at the top. This 

sequence is less than 1 km in thickness and has 

a very limited present distribution in the 

western Brooks Range. Thin slivers of Middle 

Devonian limestones locally mark the base of 

the sequence. 

Underlying the Nuka sequence is the Ipnavik 

sequence, a widespread series of dark Mississippian limestones, cherts, and siliceous shales 

intruded by numerous mafic sills and dikes. 

The Mississippian beds are overlain by PermianTriassic cherts and siliceous shales, and by 

Cretaceous graywackes. Minor Middle Devonian 

limestones locally mark the base of the sequence. The Ipnavik sequence has been extensively telescoped and, in some areas, exceeds 2 

km in thickness. It is present as the major 

allochthon cropping out in the central and 

eastern DeLong Mountains. It is also present 

in the western Endicott Mountain foothills 

(Tailleur and others, 1966); isolated exposures 

as far east as the Anaktuvuk Pass area may also 

represent this sequence. 

In the central and western DeLong 

Mountains, the Ipnavik sequence is underlain by 

the allochthonous Kelly sequence, composed 

dominantly of Mississippian limestones containing numerous black chert nodules, some bedded 

chert, and silty to sandy limestones (the 

Kogruk and Utukok Formations of the Lisburne 

Group). This sequence also has thin PermianTriassic siliceous beds and Cretaceous graywackes at its top. In some places it is more 

than 2 km in thickness. 

To the east, in the Endicott Mountains and 

foothills, the Ipnavik sequence is underlain by 

the Endicott allochthon, which forms the entire 

northern part of the Endicott Mountains. This 

allochthon is composed of a thick section of 

Upper Devonian quartzose sandstones, quartz and 

chert pebble conglomerates, and shales (the 

Kanayut Conglomerate and Hunt Fork Shale) 

overlain by Mississippian cherty limestones of 

the Lisburne Group. Permian-Triassic siliceous 

beds (Siksikpuk and Shublik Formations) and a 

thin, distinctive Lower Cretaceous (Valanginian) 

coquinoid limestone forms the top of the sequence. This allochthon is as much as several 

kilometers in thickness, of which the Upper 

Devonian section makes up at least one third. 

Although the sequence is widespread in the 

Endicott Mountains, it crops out only in local 

fensters through the overlying allochthons in 

the DeLong Mountains (fig. 3). The presence of 

the thick quartz-rich Kanayut sediments in the 

source areas of the central Brooks Range during 

Nanushuk sedimentation may explain the petrographic differences between the western and 

central Nanushuk sequences, which may relate to 

the different deltas described by Ahlbrandt and 

others (this volume) and Bartsch-Winkler (this 

volume). 

In addition to the major allochthons 

discussed above, other thin sequences of limited 

distribution are also present. These allochthons are composed of thin slices of Mississippian rocks overlain by the Siksikpuk and Shublik 

Formations, and by Cretaceous graywackes, 

conglomerates, and shales. With the exception 

of the Cretaceous beds at the top, these 

allochthons are characterized by their predominant siliceous character. 

The composition of the rocks of the Herald 

Arch is unknown, but the Tigara Uplift (Lisburne 

Hills) between Cape Lisburne and Cape Thompson 

provides possible information on the makeup of 

the Herald Arch. The Tigara Uplift consists 

mainly of thick limestones of the Lisburne 

Group, overlain by siliceous shales of the 

Lower Permian Siksikpuk Formation and thin 

shales and limestones of the Middle and Upper 

11 
Triassic Shublik Formation. These rocks are 

overlain by thick Lower Cretaceous flysch 

similar to that of the main Brooks Range. The 

sequence in general is similar to the Kelly 

allochthon of the DeLong Mountains. East of 

the Lisburne Hills, Nanushuk sediments, consisting of shale, sandstone, and some very coarse 

boulder conglomerates, apparently unconformably 

overlie the earlier Cretaceous sediments. 

Northeasterly trending sediment transport 

directions, the very coarse nature of some of 

the conglomerates, and their proximity to the 

Lisburne Hills suggest that the conglomerates 

were derived from a source in the Tigara Uplift 

rather than from the DeLong Mountains. None of 

the higher allochthons of the DeLong and 

Endicott Mountains are present in the Lisburne 

Hills. However, several cobble-to-boulder 

conglomerate beds near Cape Corwin consist 

dominantly of chert clasts with occasional 

clasts of mafic igneous rock, granite, schist, 

Devonian limestone, oil shale, and other lithologies. The presence of these clasts suggests 

that the Tigara Uplift also contained displaced 

allochthonous sheets that have been stripped by 

subsequent erosion. If the Herald Arch is the 

offshore continuation of the Tigara Uplift, as 

the apparent structural trends suggest, multiple 

allochthonous sheets similar to those of the 

DeLong Mountains may have been present as part 

of the Nanushuk provenance in both the Tigara 

Uplift and Herald Arch beneath the Chukchi Sea. 

Summary of Nanushuk Sediment Sources 

Regional mapping suggests that at least 

most of the major allochthonous sequences 

discussed above were originally present as 

widespread sheets throughout the DeLong and 

Endicott Mountains. In areas in which no 

outcrops of some allochthons remain, their 

original presence is strongly suggested by 

conglomerate clasts and olistostrome blocks 

(olistoliths) found in pre-Nanushuk deposits. 

Regionally, mafic to ultramafic igneous rocks 

form the highest allochthon. Rocks containing 

abundant chert and siliceous beds are widespread 

in the intermediate allochthons, and rich 

quartz-bearing rocks are present only in the 

lowest allochthon, which is extensively exposed 

only in the Endicott Mountains in the central 

Brooks Range. Granitic and (or) high-grade 

metamorphic rocks of the Brooks Range core zone 

in the Schwatka Mountains area were apparently 

not exposed as a part of the source terrane for 

Nanushuk sediment. 

Using the present vertical and lateral 

distribution of the various major rock types in 

the allochthons and making an extrapolation 

back in time to the Albian, generalizations 

concerning the sediment that should be expected 

to enter the Nanushuk depositional system can 

be made. Nanushuk sediment should show a 

general change in character as the source 

terrane was eroded and lower thrust sheets of 

differing character were progressively exposed 

12 

to erosion. In the area north of the DeLong 

Mountains, basal Nanushuk sediments should show 

the effect of the abundance of mafic igneous 

detritus derived from the Misheguk and Ipnavik 

thrust sequences. Upwards, the Nanushuk should 

show the effects of a greater abundance of 

chert and other siliceous rocks derived from 

the Ipnavik sequence and from various Lisburne 

and Permian-Triassic rocks. However, even with 

the general abundance of chert in some horizons, 

the source terrane for the western part of the 

Nanushuk was highly deficient in stable detritus, as supported by petrographic studies by 

Huffman (this volume). The resulting sediment 

should be expected to be relatively sand poor, 

with a low sand-shale ratio. To the east, 

north of the Endicott Mountains, generally 

dirty sediment, indicating the influence of 

mafic igneous rocks and a quartz-deficient 

terrane, should be present at the base of the 

Nanushuk. Upwards, an increasing influence of 

the quartz-rich Upper Devonian Kanayut Conglomerate section in the source terrane should be 

seen in the Nanushuk, a concept supported by 

regional petrographic studies of Nanushuk 

sediments by Bartsch-Winkler (this volume). An 

increasing sand-shale ratio and some improvement 

in reservoir character of the sandstones should 

be expected as a consequence of the greater 

influx of quartz into the Nanushuk depositional 

system north of the Endicott Mountains. 

Nanushuk Structural Style and 

Hydrocarbon Exploration 

Regional mapping of the Arctic Slope 

indicates that much of the Cretaceous section 

beneath the southern part of the Arctic Coastal 

Plain and the northern foothills belt has been 

folded into a series of long, roughly eastwest-trending gentle synclines and sharp anticlines (Lathram, 1965; Beikman, 1976). In 

general, fold amplitudes decrease from south to 

north and die out in an area of essentially 

homoclinal dip beneath the Arctic Coastal 

Plain. 

In the southern portion of the outcrop 

belt, most of the anticlines are breached 

through the Nanushuk Group into the underlying 

shale of the Torok Formation; in some places, 

south-dipping high-angle reverse faults or 

thrust faults cut the Nanushuk along the anticlinal axes. Although the underlying incompetent shales of the Torok Formation generally 

form very poor exposures, these shales, wherever 

exposed, are generally highly crumpled and 

contorted, in contrast to the gently dipping 

overlying Nanushuk. As a result of the observed 

contrast in deformation between the Nanushuk 

and the thick underlying Torok, the Nanushuk 

Group has long been interpreted as part of a 

decollement in which the relatively competent 

Nanushuk has been deformed independently from 

the underlying earlier Mesozoic and Paleozoic 

strata (Brosge and Tailleur, 1971, p. 71). The 

zone of deformation or detachment was inferred 
to be the incompetent Torok Formation, and this 

has been confirmed by seismic data from NPRA 

and elsewhere that show relatively uniform 

south dip of Jurassic and older strata beneath 

the anticlines and synclines of the Nanushuk 

foothills belt. 

Folding of the Nanushuk Group was probably 

an indirect result of the later stages of 

uplift and compression in the core of the 

Brooks Range. A possible minor gravitational 

component of movement of the Nanushuk northward 

off the Brooks Range uplift may also have 

contributed to the decollement style. Deformation of the Nanushuk probably began during 

early Tertiary or latest Cretaceous time and 

waned during the Tertiary. No clear evidence 

of deformation contemporaneous with either 

Nanushuk or Late Cretaceous deposition is 

known. 

In the part of the foothills belt, generally north of the latitude of the Colville River 

at Umiat, where fold amplitudes decrease, the 

Nanushuk Group extends unbroken across the 

crests of the anticlines. The eastern portion 

of this belt of structures was the focus of 

much of the 1946-52 exploratory drilling by 

the U.S. Navy in Naval Petroleum Reserve No. 4 

(now NPRA). Most of the exploratory wells at 

this stage of exploration tested closures 

evident in Nanushuk surface outcrops or identified from seismic data. In this area, results 

were generally discouraging, with discovery of 

only minor gas potential and of the relatively 

small Umiat oil field having recoverable reserves estimated at 70 million barrels. Although large structures have been identified, 

a major obstacle to production has been the 

absence of thick reservoir beds. Exploration 

suggests that in the northern portion of the 

Nanushuk belt, in which the anticlines are 

unbreached and unfaulted, the sandstones are 

generally finer grained and tighter than to the 

south. In the southern portion of the belt, 

more proximal to the sediment source, the 

sandstones are coarser grained and are potentially better reservoirs, but are almost invariably breached to the surface. The result of 

these relationships, particularly in the eastern 

Nanushuk delta complex described elsewhere in 

this Circular, is a close race northward between 

improving structural setting and apparently 

decreasing reservoir quality. The major objective of the Nanushuk Group study thus has been 

an effort to identify the types and predict the 

distribution of potentially more favorable 

Nanushuk reservoir facies in the areas of most 

favorable structural setting. The more favorable reservoir facies have probably developed 

13 

as a result of the interaction of sediment 

provenance and depositional environment. 

Late Cretaceous and Tertiary Deposition 

Regional compilations of geologic mapping 

of northern Alaska (Beikrnan, 1976; Lathram, 

1965) and the results of drilling in NPRA show 

that post-Nanushuk deposits in northern Alaska 

are confined to the area of the coastal plain 

and northern foothills of the central and 

eastern Arctic Slope. No Upper Cretaceous or 

Tertiary rocks are known to be present on the 

Arctic Slope west of approximately long 157° W. 

In the Umiat area, Upper Cretaceous deposits 

are relatively thin; but to the east of NPRA, 

in the vicinity of the Sagavanirktok River, the 

Upper Cretaceous section is more than 4 krn in 

thickness. In the onshore areas of the depositional basin, Tertiary rocks are even more 

restricted in distribution than the Upper 

Cretaceous rocks, and outcrops are found still 

farther east and north of the majority of the 

Upper Cretaceous exposures. 

In general, the areal distribution of 

Tertiary and Upper Cretaceous rocks relative to 

the distribution of the Lower Cretaceous rocks 

seems to record a continuation of the eastward 

and northward progradation seen in the Lower 

Cretaceous. Late Tertiary and Holocene erosion 

has resulted in stripping of some of these 

deposits. However, some evidence from the 

distribution of nonmarine facies in both the 

Upper Cretaceous and Tertiary suggests that the 

post-Nanushuk deposits may not have been deposited very far west and south of their present 

outcrop limits. 

Although the magnitude, extent, and effect 

of late Tertiary and Holocene uplift and erosion 

are unknown, the evidence suggests that the 

Nanushuk deposits of the western Arctic Slope 

may have had a rather shallow and short burial 

history, in contrast to the much greater burial 

history of correlative beds in the eastern 

Arctic Slope. However, data from the Kugrua 

No. 1 and South Meade No. 1 wells drilled in 

1978 in central and western NPRA on the western 

Arctic Slope indicate that the level of organic 

maturity is reached at a shallower depth than 

in wells to the east (Magoon and Claypool, this 

volume). The combination of indications of 

short burial history and shallow level of 

organic maturity suggests a higher thermal 

gradient, which may have implications concerning 

the hydrocarbon source potential and reservoir 

potential of at least the upper portion of the 

Nanushnk Group and perhaps deeper portions of 

the stratigraphic section on the western Arctic 

Slope. 
DEPOSITIONAL FRAMEWORK AND RESERVOIR-QUALITY 

STUDIES OF SELECTED NANUSHUK GROUP OUTCROPS, 

NORTH SLOPE, ALASKA 

By Thomas S. Ahlbrandt, A.Curtis Huffman, Jr., 

James E. Fox, and Ira Pasternack 

INTRODUCTION 

The Nanushuk Group can be traced as a 

gross lithologic unit from outcrops at Corwin 

Bluff along the Chukchi Sea eastward for 

approximately 650 km to the Sagavanirktok River 

southeast of Umiat (fig. 1). Exposures are 

largely confined to the Foothills north of the 

Brooks Range. Possible Nanushuk Group rocks 

have been reported east of the Sadlerochit 

Mountains in the Sabbath Creek area (Detterman 

and others, 1975). In the western North Slope 

area (west of long 158°), rocks of the Nanushuk 

Group are more continuously exposed than in the 

central or eastern regions, facilitating the 

interpretation of depositional environments 

there. Of the 22 sections measured during the 

1977 field season, 19 were in the western area 

and 3 in the central. 

The Nanushuk Group has previously been 

described in four separate areas: (1) in 

outcrop studies of the western area of the 

North Slope (Chapman and Sable, 1960; Smiley, 

1966, 1969b); (2) in outcrop studies of the 

central part of the North Slope (Gryc and 

others, 1956; Detterman and others, 1963; 

Chapman and others, 1964; Brosge and 

Whittington, 1966; Smiley, 1969a); (3) in 

outcrop studies of the eastern part of the 

North Slope (Detterman and others, 1975); and 

(4) in subsurface studies of wells in the NPRA 

(National Petroleum Reserve in Alaska) (U.S. 

Geological Survey Professional Paper 305-A to 

305-L by Collins and Robinson, 1956-61). These 

studies of the Nanushuk have resulted in the 

development of different stratigraphic terminology for each of the areas (fig. 5). Integration 

of these studies is difficult, however, because 

of the absence of known fossil or lithologic 

datum horizons. 

The Nanushuk Group, where examined in 

outcrop, is a regressive depositional sequence 

as much as 2,750 m thick that includes marine, 

transitional, and nonmarine intervals (table 

1). Age determinations of the Nanushuk Group 

sediments, based on faunal and floral megafossil, pollen, dinoflagellate, and foraminiferal zonations, demonstrate a range from 

early Albian to Cenomanian (Imlay, 1961; Smiley, 

14 

1966, 1967, 1969a, b; Scott and Smiley, this 

volume; May, this volume; Tappan, 1962; 

Bergquist, 1966; Sliter, this volume), The 

facies of the Nanushuk Group are time transgressive, becoming younger to the north and northeast away from the Brooks Range (Chapman and 

Sable, 1960; Detterman and others, 1963; Brosge 

Cll 

:::l 

0 

w 

() 

<1: 

1-

w 

a: 

() 

OUTCROP 

WEST CENTRAL 

Prince Schrader 

Bluff 

Prince Creek (?) Creek Formation 

Formation Formation 

Seabee Formation 

~~~------------~--------J 

.3 

SUBSURFACE 

a. Prince Creek ~ 

w Formation ....J 

....J (Tuluvak Tongue) > ....J 

0 

() Seabee Formation 

::.:: Chandler Formation 

~ (Killik Tongue) 

Cll 

~ Grandstand Formation <1: 

z 

Topagoruk Formation 

Oumalik Formation 

Figure 5.--Stratigraphic nomenclature for the 

Nanushuk Group and adjacent rock units 

from the North Slope of Alaska, as used in 

outcrop studies (Chapman and Sable, 1960, 

p. 70) and subsurface studies (Collins, 

1958a, p. 74). Time and stratigraphic 

correlation of units should not be inferred 

from this chart. Generalized stratigraphic 

relations for the western area of the 

North Slope are shown in figure 6. 

and Whittington, 1966; Smiley, 1969a, b; May, 

this volume). Generally, the Nanushuk conformably overlies the black and greenish-black 

shales of the Torok Formation of Albian Age 

(Imlay, 1961; May, this volume) and is unconformably(?) overlain by light-gray bentonitic 

units of the Colville Group of Cenomanian to 

Maestrichtian(?) age (Gryc and others, 1956, 

Bergquist, 1966; Smiley, 1969a). 

Smiley (1966, 1967, 1969a, b) used plant 

megafossils to establish a floral zonation of 

the Nanushuk Group rocks. It is difficult, 

however, to use plant megafossils as zonal 
indicators in marine intervals or in subsurface 

intervals where cores are not available. 

Therefore, zonation of the Nanushuk Group using 

microfossils including spores and pollen (Scott 

and Smiley, this volume), dinoflagellates (May, 

and May and Stein, this volume), and foraminifera (Sliter, this volume) is underway to 

establish new reference sections or to complement existing ones. 

Faunal megafossils are generally sparse 

and poorly preserved (generally only as molds 

or casts) and are, with very few exceptions, 

restricted to marine or brackish-water sandstones (D. L. Jones, oral commun., 1978). 

Megafauna! assemblages in the Nanushuk Group 

are identified in selected measured sections in 

this chapter. For a more complete megafauna! 

listing, see Chapman and Sable (1960) and 

Detterman and others (1963). Trace fossils, 

with the exception of borings of wood fragments 

and a few tracks, are also associated with 

marine or brackish-water deposits and were 

found extremely useful as aids in the interpretation of depositional environments. 

The stratigraphic nomenclature used here 

includes the Nanushuk Group, with appropriate 

modifiers such as marine, transitional, or 

nonmarine, and the Torok Formation. The Torok 

Formation includes marine shales of Albian age 

over which the deltaic and interdeltaic sediments of the Nanushuk prograded. The subsurface 

terms Oumalik and Topagoruk Formations (for 

example, Collins, 1958a) are dropped in favor 

of the more widely accepted Torok Formation. 

Where previously defined stratigraphic names 

are used, the author who named or has most 

recently defined the unit will be cited. 

The goal of this project is to determine 

the depositional framework and petroleum reservoir quality of the Cretaceous Nanushuk Group 

in northern Alaska. Statements in this chapter 

should be viewed as preliminary and of a reconnaissance nature owing to the short (2-year) 

duration of this project and the enormous 

region on the North Slope where rocks of the 

Nanushuk Group occur. 

PROCEDURE 

During the 1977 field season, 22 stratigraphic sections totaling 14,600 m were measured 

and described in detail (figs. 6, 7, table 1). 

Data recorded at the outcrop included color; 

sedimentary structures; bedding thickness; 

lamination types and style; biologic constituents including trace fossils; transport directions; scintillometer readings; and estimates 

of grain size, sorting, roundness, percent 

framework, interstitial cement, and porosity. 

Grain-size and rounding determinations were 

made in the field, using an American Stratigraphic Company visual grain-size comparison 

chart. 

Data from the measured sections were 

recorded using a standardized format at a scale 

15 

of 1.8 em= 1m (1 in. =10ft). The data were 

subsequently encoded for computer display as 

shown for the Killik Bend section (appendix 1). 

Data from the remaining measured sections have 

been encoded in the same computer-drawn format. 

Subsurface core descriptions will be recorded 

using the same format as for the measured 

sections in order to facilitate subsurface and 

surface data synthesis. The computer-drawn 

displays show visual-porosity estimates of the 

sandstones that increase to the left from the 

lithology column to simulate a spontaneous 

potential curve (appendix 1, fig. 7). The 

grain-size column increases to the right from 

the lithology column to simulate a resistivity 

curve. 

Laboratory analyses are currently being 

conducted on a total of 1,472 samples collected 

from the outcrops. These include 426 samples 

for petrographic, porosity and permeability, 

and delayed-neutron studies; 295 for organicgeochemistry analyses; 418 for dinoflagellate 

and pollen and spore content; and 285 for 

foraminifera content; 48 samples contain macrofossils and trace fossils. Data from these 

various efforts will be stored in a computer 

file at Petroleum Information Corp. in Denver, 

Colo., as they become available. 

Data considered applicable to this chapter 

are summarized in table 1. Stratigraphic 

relations are based primarily on those sections 

that have excellent exposures (table 1); more 

poorly exposed sections are useful mainly to 

demonstrate gross lateral changes. Sandstone 

and coal thicknesses probably represent minimum 

values for the poorly exposed sections. The 

locations of sections measured by the authors 

are shown on figure 1 and table 1. Isopach 

maps of the Nanushuk Group incorporating both 

outcrop and subsurface data are presented by 

Bird and Andrews (this volume). Pelecypod 

identifications shown on figure 7 were made by 

D. L. Jones and J. W. Miller of the U.S. Geological Survey. 

Sandstone samples were collected for 

reservoir-quality analysis on the basis of 

several criteria: (1) representative of the 

interval being sampled, (2) relatively free of 

weathering in order to minimize surface diagenetic effects, (3) without obvious fractures 

which could adversely affect permeability 

measurements, and (4) with a minimum sample 

dimension of 2.5 em. Although attempts were 

made to collect representative samples, the 

sampling was biased toward thicker and coarser 

grained units, considered to be potential 

reservoir intervals. Samples were oriented 

with respect to bedding by marking them with an 

"up" arrow for proper alinement of permeability 

tests either parallel or normal to bedding. 

Attempts to collect sandstone samples 

using a portable coring device proved largely 

unsuccessful. The coring rate was very slow 

and the plugs obtained were of a poor quality, 

having very irregular walls. The advantage of 

obtaining plug samples from depth behind the 
Table !.--Synthesis of resource-related data from 1977 

[M, marine; T, transitional; NM, nonmarine; thick., thickness; m, meters; ss, sandstone; %, percent; no., number; ave., 

on 

Measured section 

Corwin Bluffs _______________ _ 

Type Kukpowruk---------------

Barabara Syncline------------

Ninuluk Bluff----------------

Tuktu Bluff------------------

Killik Bend------------------

Carbon Creek Anticline-------

Tupikchak Mountain-----------

Tupikchak Syncline-----------

Kokolik Warp Syncline--------

Lookout Ridge Syncline-------

Folsom Point Syncline--------

Pitmegea Syncline------------

Coke Basin-------------------

Meat Mountain----------------

Archimedes Anticline---------

Igloo Mountain---------------

East Archimedes Ridge--------

Dugout Syncline--------------

South Limb Snowbank Anticline 

Kukpowruk Syncline-----------

Seaview Syncline-------------

Interval 

M(?),T,NM 

M(?),T,NM 

M,T 

T,NM 

T 

M 

T 

M,T,NM 

M,T,NM 

M,T,NM 

M,T,NM 

M,T 

M,T,NM 

M,T,NM 

M,T,NM 

M,T 

M,T,NM 

M,T 

M,T 

M 

T,NM 

M 

M 

Outcrop 

quality1 

E 

E 

E 

E 

E 

E 

E 

G 

G 

F-P 

F 

F 

F 

F-P 

F-P 

G-F 

G-F 

F 

G-F 

E 

E-G 

E 

E 

Base of section 

Lat N. Long W. 

68°53'20" 

68°53'20" 

69°15'06" 

69°24'46" 

69°07'45" 

68°43'30" 

68°58'55" 

69°17'50" 

68°50'50" 

69°01'27" 

69°10'07" 

69°08'40" 

69°10'43" 

68°45'23" 

68°46'53" 

68°58'55" 

69°14'58" 

68°46'53" 

69°10'23" 

68°48'28" 

69°23'28" 

69°06'13" 

68°50'56" 

164°55'20" 

164°55'20" 

162°42'31" 

162°40'58" 

153°16'55" 

152°15'50" 

153°57'57" 

159°30'40" 

162°00'40" 

162°55'00" 

161°35 1 07" 

159°41'30" 

160°38'28" 

163°54'38" 

163°06'25" 

160°51'25" 

162°41'28" 

162°57'20" 

161°53'06" 

163°57'41" 

162°38'54" 

162°46'12" 

163°51'40" 

Top of section 

Lat N. Long W. 

68°51'34" 

68°51'34" 

69°15'55" 

69°25'17" 

69°07'15" 

68°45'51" 

68°58'30" 

69°14'50" 

68°52'55" 

68°57'45" 

69°06'13" 

69°07'30" 

69°08'07" 

68°44'22" 

68°53'11" 

68°55'38" 

69°14'23" 

68°47'15" 

69°08'25" 

68°48'58" 

69°23'44" 

69°06'26" 

68°51'49" 

165°19'41" 

165°19'41" 

162°47'25" 

162°41'46" 

153°17'30" 

152°08'20" 

153°57'40" 

159°29'50" 

161°52'00" 

162°50'43" 

161°25'11" 

159°36'30" 

160°32'42" 

163°52'56" 

163°07'40" 

160°47'30" 

162°39'58" 

162°56'06" 

161°53'03" 

163°55'44" 

162°39'32" 

162°46'12" 

163°51'40" 

Total 

thick., 

(m) 

4,722.6 

3,444.2 

666.6 

1,423.7 

314.3 

437.7 

157.9 

786.4 

1,256.4 

1,786.2 

2,090.9 

554.7 

810.8 

785.2 

274.3 

442.0 

1,048.5 

309.7 

524.3 

409.7 

200.0 

73.2 

57.3 

Total ss. 

thick., 

(m) 

901.0 

688.2 

99.4 

228.0 

78.9 

168.6 

70.7 

51.5 

157.6 

119.8 

118.9 

36.6 

69.5 

38.1 

41.5 

38.1 

34.4 

32.6 

38.7 

38.1 

23.8 

10.1 

23.5 

1E, excellent--completely exposed; G, good--mostly exposed, covered intervals minimal; F, fair--some covered, some 

well exposed; P, poor--mostly covered, resistant ledges exposed. 2 4.3-m coal bed and 30.5-m fluviatile sandstone channel occur in river cut above top of measured section. 

3Numbers in parentheses reflect number of samples measured. 

4samples having less than 8.0 percent porosity were not measured for permeability. 

5Thickness of this section reflects Chapman and Sable's (1960) original measured section and Smiley's (1969a) revised 

measured section, respectively. 6Slight crack in sample. 

outcrop surface was concluded to be negligible. 

The samples were prepared for porosity and 

permeability determinations in accordance with 

the procedures outlined in American Petroleum 

Institute Recommended Practices 40 (1960) and 

C. H. Wu (written commun., 1977). When possible, a 2.5-cm plug was.cut parallel to bedding. For cases in which the dimension of the 

sample parallel to bedding was less than 2.5 

em, the plugs were cut normal to bedding. The 

plugs were trimmed to a maximum length of 3.2 

em and were not extracted to remove residual 

hydrocarbons. This extraction step was omitted 

to expedite processing and because residual 

hydrocarbons were not observed during hand-lens 

or thin-section study of samples. 

Porosity values were determined by measuring grain and bulk volumes. Grain volumes were 

measured using a Core Laboratories, Inc., 

Helium Gas Expansion Boyle's Law Porosimeter. 

A Ruska Instrument Corp. Universal Porometer 

was used to measure the bulk volumes. Porosities measurable using this equipment range from 

approximately 2 percent to 35 percent, with a 

repeatability of less than ±0.5 percent variation in porosity for regularly shaped, 3.2-cmlong plugs. Irregularly shaped or short plugs 

16 

had a significantly hi'gher variation, probably 

due to errors in bulk-volume measurements. The 

porosity values obtained for the latter type of 

plugs must therefore be considered only as 

approximations, and such data are not utilized 

in this paper. 

Permeabilities were obtained for all plugs 

that had greater than 8 percent porosity. A 

Core Laboratories, Inc., Permeameter employing 

nitrogen gas as the testing fluid was used to 

determine the permeabilities. The minimum 

permeability measurable by the permeameter is 

approximately 0.01 md with an accuracy of ±5 

percent. A Klinkenberg Correction Factor was 

applied to all these measurements to obtain a 

more representative value of liquid permeability. 

The testing methods outlined above are not 

strictly comparable to the methods reported in 

previous papers on the reservoir characteristics 

of sandstone samples from cores obtained as 

part of the National Petroleum Reserve No. 4 

drilling program. The porosity values of the 

previous reports were determined by the Barnes 

vacuum method, which is considered not as 

accurate as the Boyle's Law expansion method. 
measured sections of Nanushuk Group rocks, North Slope, Alaska 

average; max., maximum; leaders (---) indicate not observed; n.d., not determined. Locations of measured sections are shown 

figure 1] 

Ss. % No. Ave. thick. Max. ss. Sandstone reservoir rarameters 3 Coal No. Ave. thick. 

Permeabilitl': 11 ss. beds ss. bed thick. Porosit~ (%) 

(m) (m) Range Ave. 

19.1 278 3.2 24.4 NM 1. 0-10.3 4.98 (20) 

19.8 220 3.1 24.4 NM 1. 0-10.3 4. 98 (20) 

14.8 29 3.4 24.4 NM 2.1-14.9 7.05 (31) 

16.0 154 1.5 25.0 NM .7-15.6 8.28 (40) 

25.1 33 2.4 13.1 T 5.2-11.2 8.11 :16) 

38.5 28 6.0 25.9 M 3.8-16.4 7.43 (17) 

44.8 24 3.0 14.6 T 2.6- 9.0 5.58 (12) 

6.6 29 1.8 10.7 M 2.4-14.8 8.31 (16) 

12.5 39 4.0 17.7 NM .5- 8.6 5.99 (26) 

6.7 42 2.9 19.8 NM 1. 9- 8. 6 5.24 (16) 

5.7 65 1.8 6. 7 NM 2.7-13.4 7.47 (18) 

6.6 13 2.8 8.8 M .9-15.4 6.56 (12) 

8.6 22 3.2 18.0 T 1.1-12.8 7.32 (16) 

4.9 20 1.9 6. 7 M 5.2- 9.8 7.00 (8) 

15.1 23 1.8 6. 7 r.JM2 .4-11.3 4.93 (12) 

8.6 14 2.7 6.4 M 2.7-13.5 8.43 (18) 

3.3 18 1.9 7.0 T 2.1- 3.6 3.0 (4) 

10.5 12 2.7 6.4 M 1. 9- 9. 6 5.33 (10) 

7.4 13 3.0 15.5 M 2.2-13.6 8.47 (11) 

9.3 19 2.0 7.6 M 1. 9-10.9 6.19 (20) 

11.9 6 4.0 10.1 NM 1.4-14.5 6.76 (8) 

13.8 8 1.3 1.8M 2.1- 3.6 3.0 (4) 

41.0 4 5.9 9.5 M 2.3- 8.6 5.74 (10) 

DELTAIC SEDIMENTATION 

Weimer (1970) listed eight criteria by 

which deltas may be recognized in the rock 

record, any two of which are sufficient to 

establish the former existence of a delta. 

These criteria include (1) complex intertonguing 

of marine (foreset and bottomset) and nonmarine 

(topset) strata; (2) rapidly changing shoreline 

sandstone trends from one time-stratigraphic 

interval to another; (3) arcuate lithofacies 

pattern of nonmarine strata protruding into the 

marine basin; (4) thickest deposits in the 

general shoreline area (topset and foreset) for 

a given time-stratigraphic unit; (5) greater 

abundance of stream deposits than of deposits 

of other environments of coastal plain; (6) 

lithologic criteria including repetitive sedimentary sequences combined with unusual concentrations of detrital carbonaceous material; (7) 

biological criteria in marine strata, notably 

the dominance of benthonic, arenaceous foraminifera rather than pelagic calcareous foraminifera; and (8) persistence of the above criteria 

in a vertical sequence, indicating that a 

semipermanent drainage produced the deposit. 

Because the Nanushuk Group meets most if not 

all of these criteria, we interpret it as being 

a deltaic and interdeltaic deposit with a 

generally southerly and southwesterly source. 

Two major depositional centers have been identified: a western one, here called the "Corwin 

delta," and an eastern one, the "Umiat delta." 

17 

(md) thick. coal beds coal beds 

Range Ave. (m) (m) 

0.22- 2.90 0.99 (5) 68.34 M 146 0.47 

0.22- 2.90 0.99 {5) 52.12 128 .41 

.09- 2.26 .63 (13) 

.12- 28.01 1.84 (26) 1g.so 20 .98 

.12- 2.60 1.14 (9) ·'+. 27 11 .39 

.1 -232.0 58.18 (4) 

.89- 20.11 10.50 (2) 4.88 12 .41 

.11- 7.95 2.13 (8) 

.10- .80 .45 (2) 

.22- .39 .31 (2) 

.07- 22.8 3.42 (7) 13.10 33 .40 

.20-199.04 66.80 (3) 

.08- 1.0 .41 (8) .31 .31 

.06- .22 .14 (2) 

.42 .42 (1) 3.052 .44 

.05- .42 .16 (12) 

n.d. 4 n.d. 

14.8 (1)6 

.17- 26.58 5.65 {5) 

.10- 1.16 .so (6) 

.19- .84 .56 (3) 3.35 11 .31 

n.d. 4 n.d. 

.04- .24 .14 (2) 

Deltas are commonly divided into three 

categories, reflecting the dominant depositional 

process: river-dominated or high constructional, tide-dominated, and wave-dominated or 

high destructional. The "Umiat delta" has been 

called a river-dominated delta by Fisher and 

others (1969). The authors concluded that the 

Corwin delta also best fits the river-dominated 

delta category, based on the criteria summarized 

in Fisher and others (1969) and more recently 

in Miall (1976). Terminology used in this 

paper follows Fisher and others (1969) and 

Campbell (1971). 

CORWIN DELTA 

If we assume that the Nanushuk Group is 

delta-related, the most pervasive question 

deals with the location of the major loci of 

deposition. For the western region, we propose 

that a major depocenter was in the vicinity of 

Corwin Bluff. Rocks of the Nanushuk Group 

exposed at Corwin Bluff are the oldest, are the 

thickest, contain the coarsest material, and 

have the most nonmarine fossil assemblage of 

any rocks studied in the entire western region 

of the North Slope. Smiley (1969b), on the 

basis of plant megafossils, noted that the 

Nanushuk at Corwin Bluff ranges in age from 

early Albian to late Albian and becomes younger 

away from Corwin Bluff. For example, Smiley 

(1969b) indicated that Nanushuk is of middle 

Albian to Cenomanian(?) age along the Kukpowruk 
..._-----Toward sediment supply Toward basin along direction of progradation-------+ 

sw 

GRAIN SIZE 

+--

NONMARINE 

Sec. 1, 

fig. 3 

NE 

CORWIN FM 

TRANSITIONAL 

KUKPOWRUK FM 

KUKPOWRUK FM 

TOROK FM 

Locally stacked nearshore 

sandstone where major 

distributary channels extend 

bas inward. 

units 

Sandstone . 

Siltstone 

EXPLANATION 

Coal 

~·Ripples 

Burrows 

~ Fossilized tree I Conglomerate 

Claystone or shale ~~~ 

-// .h/ A'-.\._'-.._~ Cross-bedding ~Lenticular sandstone 

~ Contorted bedding ~ Channel sandstone 

Figure 6.--Generalized sedimentologic sequence of Cretaceous Nanushuk Group rocks, western North 

Slope, Alaska. This sequence is applicable for all sections in the western area, with the 

exception of Corwin Bluff, where marine deposits are not well exposed. 

Figure 7.--Measured stratigraphic sections in lower (sections 1, 2), middle (sections 3A, 3B, 4) C> 

and upper (sections 5, 6) parts of the Nanushuk Group. Sections 1, 3A, 3B, and 5 are from 

the western area of the North Slope, and sections 2, 4, and 6 are from the central area. 

The ages of the sections are as follows: (1) Carbon Creek Anticline--Albian (undifferentiated) (Chapman and Sable, 1960), (2) Tuktu Bluff--middle and late Albian (Detterman and 

others, 1963; Smiley, 1969a; Sliter, this volume), (3) Type Kukpowruk--middle Albian and 

late Albian (Smiley, 1969b; Sliter, this volume), (4) Killik Bend--late Albian to Cenomanian? 

(Smiley, 1969a; Sliter, this volume), (5) Barabara Syncline--middle and late Albian (Smiley, 

1969b), and (6) Ninuluk Bluff--Cenomanian (Detterman and others, 1963; Smiley, 1969a; 

Sliter, this volume). 

River sections northeast of Corwin Bluff (vicinity of type Kukpowruk and Barabara Syncline 

sections, fig. 1). 

The Corwin Bluff section was the thickest 

Nanushuk section of any of those measured. 

Originally, Chapman and Sable (1960) measured 

4,723 m of section at Corwin Bluff and designated it the type section of the Corwin Formation. 

Smiley (1969b) recognized only 3,444 m as 

Corwin Formation at Corwin Bluff by interpreting 

repetition of section by faulting in the upper 

part of the sequence. We observed several 

other faults in the basal thousand meters of 

the Nanushuk Group in this section; however, 

2,743 m of undisturbed section was measured. 

Compared to other Nanushuk sections, the 

194-m-thick conglomerate member of the Corwin 

18 

Formation (Chapman and Sable, 1960) exposed at 

Corwin Bluff is anomalous in the abundance and 

thickness of conglomerate-filled channels (as 

much as 38m), large size of clasts (as much as 

30 em) within the conglomerates, and internal 

bedding character of the conglomerate channels. 

Fluvial channels in measured sections other 

than at Corwin Bluff show evidence of meandering 

(that is, lateral and vertical transition from 

trough crossbedding to overbank deposits) and 

contain much less conglomerate than at Corwin 

Bluff (less than several meters). Chapman and 

Sable (1960) used aerial photographs to trace 

a conglomerate bed 25 km inland, where it was 

truncated by a fault. We traced a conglomerate 

bed from Corwin Bluff 10 km east to Thetis 

Creek; in this distance the bed thinned from 15 

m to approximately 1 m. 
16.4°o 232MD 

(33 5 m above sect1on) 

11 _oo, o 53 MDI I 

1 Floating chert pebbles I 

· Vertical 

I 

5.5~o -. \ t• 

t-' 

a· 6.9%1 ff:) Low to mod. trough x-beds 

5 3o,t ~~· >-

': 1 ~RH OOd "rtio"l, 

2 

~%~ 1 

:- w- 83Yo O::I 

~ ~ 6.1%_ lMod.troughx-beds 01MD .' ~~ u /"·Vertical 

1 2cm(w)x20cm( L) . V, 

POROSITY GRAIN SIZE ESTI~ I 

Floating chert pebbles 10.5% __ · -1l:' 

• 0.97MD -. 

7.8%1_-

7.2% 

8.1% 0.1MD 

4.0% 

457.2m 

' FAULT~ 

8.7% 0.13MD y~ 

84% 0.17MO I " 

2. TUKTU BLUFF 

38.5% ss. 

201.2m 

109.7m 

61.0m 

232.3m 

~ 69.2m 

1. CARBON CREEK 

ANTICLINE 

6.6% ss. 

EXPLANATION 

~Shale 

BSiltstone 

D Sandstone 

•coal 

r Plant rootlets 

P Plant debris 

c Fossil iOgs (TB, 

Ioredo borings) 

). Fossil tree in oriQinal position 

"" Bivalve 

1!l Cephalopod 

-.;"' Bone 

V =Normal to bedding 

II= Parallel to bedding 

Sole markings 

-- Symmetric ripples 

Asymmetric ripples 

Climbina ripples (asymmetric) 

-. Scour and fill 

= Tabular planar crossbeds 

Trough crossbeds 

Burrows 

Ar = Arenicolites 

AS= Asterosoma 

SF= Astericiates (starfish) 

Dl = Diplocraterion 

RH = Rhizocorallium 

100!30 80 

60 20 

40 10 

20 

0 0 8.3% Porosity of rock-plug sample OP = Ophiomorpha 

in percent RO = Rosselia FEET METERS 

5.09MD Permeabiltiy of rock-plug SK = Skolithos 

sample in millidarcies /l. Deformed structure 

19 

~~~Large ball & pillow 

9 _3 % 1 _6 4MD ~~~ •.Arcti ca? sp. 

(sl.crk.ll bed.) l~ 

I 

~r ~ I' 

I 

(· 

E, 

u. : 

I 

i:~noceramus sp. i.._ 

1 ;:; Inoceramus sp. f Inoceramus? sp. 

.. Inoceramus sp. ;;;_;cSK, Dl 

Con cr. 

~DI 

~DI 

5. BARABARA 6. NINULUK BLUFF 

SYNCLINE 25.1% ss. 16.0%ss. 

(for entire 

1424m section) 
The clast composition of the Corwin Bluff 

conglomerates (described by Chapman and Sable, 

1960) remains unchanged inland and is notable 

for the relatively low percentage of white 

quartz pebbles, the presence of fossiliferous 

carbonate clasts (limestone of Lisburne Group?), 

and greenish-colored argillites. Maximum clast 

size decreases from about 30 em at Corwin Bluff 

to less than 10 em for the dark chert and 

fossiliferous carbonate clasts (limestone of 

Lisburne Group?) found elsewhere in the western 

area. 

The Corwin delta apparently prograded 

northeasterly across the western North Slope 

and across areas now under the Chukchi Sea, as 

evidenced by paleotransport directions of 

Nanushuk channels (fig. 1). Such data agree 

with paleogeographic determinations of Payne 

and others (1952) and of Chapman and Sable 

(1960), and with the regional framework described by Grantz and Kirschner (1976) and Mull 

(this volume). 

The western DeLong Mountains, Lisburne 

Hills, and their offshore extension, the Herald 

Arch (Grantz and Kirschner, 1976; Grantz and 

others, 1976; Mull, this volume), are the most 

probable source terrains for the Corwin delta 

(see "Reservoir Quality" section; Huffman, this 

volume; Bartsch-Winkler, this volume). Although 

this chapter does not address the offshore 

Nanushuk rocks, the deposition and structural 

style of the Corwin delta are comparable for 

the western onshore area and the immediately 

offshore area in the Chukchi Sea (Mull, this 

volume). The depositional framework discussed 

in this chapter and the palynological zonation 

established by Scott and Smiley (this volume) 

at Corwin Bluff should be most useful for 

offshore Nanushuk studies. 

Rocks of the Nanushuk Group, as observed 

in measured sections shown in figure 7, are 

typified by a sequence of marine (100-300 m), 

transitional (100-300 m), and nonmarine (1,000-

2,700 m) deposits schematically shown in figure 

6. A series of sections measured in 1977 (fig. 

7) illustrate the lower (marine), transitional 

(both marine and nonmarine), and upper (nonmarine) Nanushuk rocks in the Corwin delta 

(fig. 7, sees. 1, 3A, 3B, and 5, respectively). 

The basal contact of the Nanushuk Group with 

the underlying Torok Formation is picked at the 

lowest sandstone bed that is part of or grades 

upward into nearshore-marine sandstones. This 

placement is arbitrary owing to the intertonguing nature of the deltaic sediments. Siltstones 

and very fine grained sandstones occur at 

widely separated intervals within the Torok 

Formation (fig. 7, sec. 1). 

In general, the basal sandstones (Kukpowruk 

Formation; Chapman and Sable, 1960) of the 

Nanushuk are wave-dominated. The sandstones 

grade upward into a transitional interval that 

represents lagoonal and (or) interdistributary 

trough fill (the transitional Kukpowruk of 

Chapman and Sable, 1960). These deposits in 

20 

turn grade upward into nonmarine, delta-plain 

sediments (the Corwin Formation; Chapman and 

Sable, 1960) that are the dominant constituent 

of the Nanushuk in the Corwin delta. 

Depositional environments of sandstones in 

the western area are differentiated primarily 

on the basis of sedimentary structures, lateral 

and vertical facies relations, textural variations, and trace fossil assemblages. The 

nearshore-marine sandstones include foreshore, 

shoreface, offshore-bar, and barrier-island 

deposits and generally increase in grain size 

from the base to the top of the deposit (fig. 

7, sees. 1, 3A). Shoreface sandstone beds are 

thin (<3 m) and commonly have contorted bases 

grading upward into low-angle crossbeds that 

have symmetrically rippled and bioturbated 

upper surfaces (fig. 8A, B). Common trace 

fossils include Gyrochorte (snail trails), 

Helicodromites (spiral burrows), Arthrophycus, 

occasionally Asterosoma, and unnamed large 

pelecypod(?) burrows (5-10 em in diameter). 

The shoreface sandstones gradually become 

thicker upsection and are replaced by prominent 

foreshore sandstones (5-10 m thick) which are 

horizontally bedded to low-angle crossbedded 

and contain relatively few trace fossils, 

commonly Diplocraterion or Skolithos (fig. 8C, 

D). 

Foreshore sandstones are generally imbricated (separated by siltstones or shales), 

perhaps indicating rapid delta progradation, 

and grade laterally into isolated sandstone 

lenses that decrease in size basinward. The 

lenses, interpreted as being offshore bars, are 

commonly <10 m thick and 60 m wide and have 

flat, gradational bases (fig. 6). Locally, 

foreshore sandstones are stacked where major 

distributary channels extended basinward, as 

exemplified by the Tupikchak Mountain section 

(fig. 1, 6). 

The imbrication and direction of thinning 

of the basal Nanushuk marine sandstones were 

the subject of a detailed photogeologic study 

in the western region of the North Slope by 

Chapman and Sable (1960). They concluded that 

the basal, marine Nanushuk interval thins at a 

rate of 20.9 m/km along a northeasterly vector 

(N. 32° E.), the resultant of rates of thinning 

observed in 19 east-west and 16 north-south 

traverse studies. They further concluded that 

depositional strike (shoreline orientation) of 

Nanushuk marine sandstones was about N. 60° W., 

which our paleotransport data support (fig. 1). 

Thus, in the Corwin delta the foreshore sandstones, offshore bars, and barrier islands are 

expected generally to have a northwestsoutheast orientation, and channels to have the 

preferred southwest-northeast elongation. 

Deposits interpreted to be of eolian 

origin were observed in outcrops of the Meat 

Mountain and Folsom Point Syncline measured 

sections (fig. 1). In both locations, the 

deposits are oxidized (reddish-brown), moderate 

to high-angle, crossbedded, well-sorted, nonbur-
Figure 8.--Features observed in western Nanushuk Group exposures along the Kukpowruk River: A, 

basal exposures of Nanushuk at the type Kukpowruk Formation measured section; thin shoreface 

sandstones give way upsection to the thicker foreshore sandstone; man is 1.8 m tall; B, 

burrows (Helicodromites) crossing symmetrically rippled upper surface of one of the shoreface 

sandstones shown in A; C, foreshore sandstone shown in A with horizontal or low-angle 

crossbeds, 10-cm scale; D, vertical burrows (Diplocraterian) in foreshore sandstone at 

level of scale in C; E, contorted beds in transitional interval (lagoonal) above sequence 

shown in A; and F, three-toed tracks in uppermost Nanushuk sediments, north limb of Barabara 

Syncline, lower Kukpowruk River. 

21 
rowed, and fine-grained sandstone lenses. Such 

lenses overlie horizontally bedded foreshore 

sandstone beds and are overlain by mudstones. 

This sequence is interpreted as representing a 

barrier-island deposit. 

Although most of the sandstones of the 

basal Nanushuk are wave-dominated, tidal channels were recognized at several localities. 

The channels observed in the Archimedes Anticline section (fig. 1) occur on the same horizon 

as a foreshore sandstone and contain low- to 

moderate-angle bimodally crossbedded sets. The 

channels, when traced laterally, grade to sandy 

siltstones that contain plant rootlets. At the 

axis of Lookout Ridge Syncline (fig. 1) pelecypods were recovered from basal lag deposits 

within fine-grained conglomerate tidal channels. 

The pelecypods had original shell material, and 

delicate features of the beak and shell ornamentation were preserved, indicating little transport. 

Overlying the foreshore sandstones are 

transitional intervals that generally represent 

infill of interdistributary troughs (bays). 

Near the base of the transitional intervals, 

isolated, thin (<5 m) sandstones that contain 

marine trace fossils or megafossils are common, 

but they are found interspersed with nonfossiliferous~ nonbioturbated channel sandstones that 

become more common upsection. Many of these 

marine (and probably brackish-water) sandstones 

are contorted and have ball-and-pillow structures (fig. 7, sec. 3B; and fig. BE), are 

symmetrically rippled, and contain a variety of 

trace fossils including Arenicolites, Rosselia, 

Rhizocorallium, Diplocraterion, Asteriacites 

(starfish traces), plural tubes, and megafossils 

(fig. 7, sec. 3B). 

Nonmarine sandstones occur as isolated 

channels, crevasse splays, and thin sheet sands 

of possible lacustrine origin. The major 

distributary channels are 10-30 m thick and 

commonly contain thin conglomerate beds or 

pebble lags with clasts of chert, carbonate 

clasts, and quartzite (fig. 7, sec. 3B). 

Fossil tree stumps in original growth position 

occur near the base of some channels. Most 

channel sandstones are 5-10 m thick, are less 

than 200 m wide, and consist of trough crossbed 

sets, in which grain size decreases upward and 

which laterally or vertically grade into asymmetric climbing ripple structures (fig. 7, 

sees. 3B, 5). Penecontemporaneous deformation 

is rare, except for minor channel-margin 

slumps; and trace fossils are limited to root 

traces, borings in fossilized logs, and very 

rare small three-toed dinosaur or bird(?) 

footprints (fig. 8F). 

The upper part of the nonmarine section is 

interpreted as being deposited on a delta 

plain. Coals, as much as 4.3 m thick, are most 

common in this part of the section. Those 

measured sections that generally contain more 

coal and have much less sandstone and conglomerate are interpreted as being interdistributary 

22 

basirt (marsh) deposits (fig. 9, table 1). 

Those sections having greater amounts of coarser 

clastics are interpreted as having been along 

sediment supply routes. For example, the 

Tupikchak Mountain section is probably in a 

distributary lobe, whereas adjacent sections 

such as the Kokolik Warp section to the north 

or Tupikchak Syncline to the west are most 

probably interdistributary sequences and contain 

more coal and less sandstone and conglomerate 

(figs. 1 and 9, table 1). 

The youngest beds of the Nanushuk Group at 

Corwin Bluff and on the north limb of Barabara 

Syncline are bentonitic. Smiley (1969b) redefined the type Corwin Formation at Corwin 

Bluff, indicating that the bentonitic clay 

member of the Corwin Formation as defined by 

Chapman and Sable (1960) was the youngest 

Nanushuk unit exposed there. 

Very friable sandstones were observed on 

the north limb of Barabara Syncline along the 

lower Kukpowruk River (lat 162°46'15" N., long 

69°30'57" W.). The light-gray color, poor 

induration, and abundance of bentonite in the 

outcrops suggested to us that the unit was part 

of the Prince Creek Formation. Chapman and 

Sable (1960) described similar outcrops along 

the lower Utukok and Kokolik Rivers, which they 

called Prince Creek Formation (Upper Cretaceous). However, pollen and megaspore analyses 

show the friable Kukpowruk River samples to be 

of Albian age (see Scott and Smiley, this 

volume), and thus part of the Nanushuk Group. 

Petrographic, X-ray diffraction, and 

scanning-electron-microscopy studies all show 

montmorillonite to be rare in the Nanushuk 

samples except in the very uppermost Nanushuk 

samples (Bartsch-Winkler, this volume). The 

uppermost part of the Nanushuk in the Corwin 

delta is thus characterized by a sharp increase 

in montmorillonite--a feature also observed in 

the subsurface and Nanushuk sequences in the 

central North Slope area. 

UMIAT DELTA 

Rocks of the Nanushuk Group in the central 

North Slope area have previously received more 

extensive study than those in the west because 

of the greater availability of subsurface 

information from wells in the eastern part of 

NPRA, especially around the Umiat oil field. 

Reservoir problems in the Nanushuk at Umiat 

prompted early petrographic work on Umiat test 

wells 1 (Krynine, 1947, 1948) and 9 (Krynine 

and Ferm, 1952). A study by Fox and others 

(1979) discusses the Umiat 11 well in detail 

from the standpoints of depositional environment, petrography, and reservoir quality and is 

summarized by Fox in this volume. Additionally, 

biostratigraphic zonation of the Umiat 11 well 

by Sliter (this volume) and May (this volume) 

and organic geochemical data for this well by 
240 

Corwin Bluff (CB) cij 4723-m section rJJ 

LU -l901 m of sandstone 

z 

!<: 180 180 ~ 

I 

f- rJJ 

LU CC z LU 

0 tu 120 120 

li;:::!; 

~ ~ <( 

rJJ 

~ 60 1 60 

<( 

f0 

f6 9 12 15>15 

Type Kukpowruk (TK) 

667-m section 

71 m of sandstone 

180 

120 

60 

6 9 12 15>15 

Barabara Syncline (BS) 

1424 · m section 

228 m of sandstone 

6 9 12 15>15 

180 

120 

60 

Tupikchak Mountain (TM) 

1256-m section 

158 m sandstone 

6 9 12 15>15 Meters 

INDIVIDUAL-SANDSTONE-BED THICKNESS IN 1.5-M (5-FT) CLASSES 

cij 

rJJ 

w 

~ 180 (.) 

J: 

f- rJJ 

cc LU LU 

z f0 LU 120 f- :::!; rJJ 

0 z z-

<( 

rJJ 

~ 

<( 

f0 

f60 

Kokolik Warp Syncline (KW) 

2091- m section 

119 m of sandstone 

3 6 9 12 15>15 

120 

60 

Tuktu Bluff (TB) 

438-m section 

169 m of sandstone 

3 6 9 12 15>15 

120 

60 

Killik Bend (KB) 

158-m section 

71 m of sandstone 

6 9 12 15>15 

180 

120 

60 

Ninuluk Bluff (NB) 

314-m section 

79 m of sandstone 

6 9 12 15>15 Meters 

INDIVIDUAL-SANDSTONE-BED THICKNESS IN 1.5-M (5-FTl CLASSES 

z 

0 

i= 

(.) 

LU 

rJJ 

~ 

LU 

z 30 0 

frJJ 

0 

z 20 <( 

rJJ 

fz 

LU 10 (.) 

cc 

LU 

n. 

0 

0 

+KB 

+NB 

•BS 

·KW 

•CB 

•TK 

• TM 

+rB 

3 4 6 

AVERAGE BED THICKNESS, IN METER~ 

Figure 9.--A comparison of the thickness and percent of sandstones in five Corwin delta sections 

(CB, TK, BS, TM, KW) with those of three Umiat delta sections (KB, TB, NB). Sandstone is 

more common near major distributary channels (for example, CB) or in distributary lobes 

(for example, TM) compared to interdistributary sections (for example, KW). The Umiat 

delta sections have relatively higher percentages of sandstone than do the Corwin delta 

sections. 

Magoon and Claypool (this volume) will make the 

Umiat 11 well a reference section for the 

east~rn part of NPRA. 

The three sections measured by us in the 

eastern area (Tuktu Bluff, Killik Bend, and 

Ninuluk Bluff; fig. 7, sees. 2, 4, 6) permit a 

limited comparison between the Corwin and Umiat 

deltas (fig. 7, sees. 1, 3A, 3B, 5). The basal 

Nanushuk contact with the Torok Formation in 

23 

the Umiat delta is sharp in contrast to the 

gradational contact at the base of the Corwin 

~delta (fig. 7, compare sees. 1 and 2). In the 

Tuktu Bluff section, prodelta deposits abruptly 

change upward into thick delta-front deposits. 

The delta-front deposits coarsen upward· from 

siltstone to fine-grained sandstone at the top 

of the Tuktu Formation (as defined by Detterman 

and others, 1963; see fig. 7, sec. 2). 
The middle part of Nanushuk strata in both 

deltas probably represents infilling of interdistributary troughs (bays) (fig. 7, sees. 3A, 

4). This stratigraphic sequence is represented 

in the Umiat delta by the Killik Bend section, 

which describes the lower part of the Killik 

Tongue of the Chandler Formation (as defined by 

Detterman and others, 1963). An important 

difference between the two deltas is that coals 

rest directly on marine (or brackish-water) 

sandstones in the Umiat delta, but coals only 

occur in the nonmarine (delta-plain) interval 

of the Corwin delta. The absence of coals in 

marine-transitional intervals of the Corwin 

delta may be explained by rapid progradation or 

lateral migration of streams of this delta, 

such that interdistributary troughs (bays) did 

not completely fill before being breached by 

distributary channels. Interdistributary 

troughs in the Umiat delta may have filled more 

completely, resulting in coals directly overlying the marine sandstones that developed 

around the margins of the bay. 

The composition of conglomerate clasts in 

the Umiat delta is markedly different from that 

in the Corwin delta complex. At the type 

section of the upper part of the Killik Tongue 

of the Chandler Formation, north of Tuktu Bluff 

on the Chandler River, conglomerate units as 

much as 14 m thick are composed of 40 percent 

white, well-rounded quartz pebbles and cobbles 

(Detterman and others, 1963). The striking 

color and compositional contrasts between 

conglomerates in the Corwin delta and those in 

the Umiat delta suggest a different provenance. 

Petrography of sandstones of the Nanushuk from 

both subsurface and outcrop samples demonstrate 

the relative absence of metamorphic rock fragments and a lower quartz content in the Corwin 

delta sandstones relative to the Umiat delta 

sandstones (Huffman, this volume; BartschWinkler, this volume). Such petrographic data 

suggest different source terrains, but paleotransport data are too limited to infer the 

direction of the Umiat delta progradation with 

absolute certainty. However, facies interpretations by Brosge and Whittington (1966) suggest 

northeasterly progradation of the Umiat delta. 

The intertonguing Ninuluk Formation and 

Niakogon Tongue of the Chandler Formation 

(Detterman and others, 1963) represent the 

uppermost part of the Nanushuk in the eastern 

area. At the type locality of the Ninuluk 

Formation, Ninuluk Bluff, the undifferentiated 

Ninuluk/Niakogon rocks are interpreted as 

representing a relative rise of sea level. The 

marine pelecypods and trace fossils in the 

Ninuluk contrast sharply with the delta-plain 

sediments of the uppermost part of the Nanushuk 

in the west (fig. 7, compare sees. 5, 6); no 

similar age relation is inferred, however. The 

Ninuluk/Niakogon unit resembles the transitional 

intervals of either delta (fig. 7, compare 

sees. 3B, 4, 6). The Ninuluk is bentonitic, 

particularly high in the section, and the 

24 

unconformably(?) overlying Seabee Formation is 

very bentonitic (Detterman and others, 1963) 

both in outcrop and in the Umiat 11 well 

(Collins, 1958a). 

RESERVOIR QUALITY 

Assessments of reservoir quality of sandstone units of the Nanushuk in outcrop are 

based on quantitative porosity and permeability 

determinations from 345 sandstone samples in 

measured sections, as summarized in table 1; on 

petrographic studies (Huffman, this volume; 

Bartsch-Winkler, this volume), and on field 

studies of sandstone geometry. 

Sandstones of the Nanushuk Group, where 

studied on the North Slope, are litharenites 

that produce carbonate cement and matrix detrimental to reservoir quality when subjected to 

compaction and diagenesis. Abundant clay 

matrix is a problem common to all of these 

sandstones. The virtual absence of swelling 

clay (montmorillonite) in all but the uppermost 

Nanushuk intervals in both outcrop and subsurface is important to reservoir-quality assessment (Bartsch-Winkler, this volume; Fox, this 

volume). This means, for example, that the 

freshwater muds used in some of the wells in 

the National Petroleum Reserve 4 (NPR-4) 

program did not adversely affect reservoir 

characteristics of most sandstones. 

Sandstones of the Nanushuk Group in the 

western area, in general, are thin, discontinuous, and beset with diagenetic problems related 

to abundant unstable sedimentary rock fragments. 

Carbonate cement and argillaceous matrix greatly 

reduce permeability in these sandstones 

(Huffman, this volume). Three hundred samples 

from the 19 measured sections in the western 

area have porosity values ranging from 0.4 to 

15.6 percent. Most samples are in the 5-8 

percent porosity range, but 105 samples exceeded 

8 percent porosity and were analyzed for permeability. Of these, 6 samples had permeability 

values greater than 5 millidarcies, 2 of these 

6 samples have small fractures, and only 1 

sample has greater than 30 millidarcies permeability (Lookout Ridge section). Reservoir data 

for an additional 72 miscellaneous outcrop 

samples fall within the porosity and permeability ranges noted above, with the exception of a 

channel sandstone in the uppermost part of the 

Nanushuk (maximum dimensions of 6 m thick and 

50 m wide) that had excellent porosity and 

permeability values (Huffman, this volume). 

Subsurface Nanushuk samples from Kaolak 1, 

the only well that penetrates the Corwin delta 

complex, have porosity and permeability values 

comparable to those of the outcrop samples. 

Collins (1958a) reported porosity values for 14 

samples from the Nanushuk interval of the 

Kaolak well (34.5-1,246.6 m depth interval in 

the well) ranging from 8.3 to 14.4 percent, and 

all samples are impermeable. Petrographic 

study of sandstones of the Nanushuk from both 
the Kaolak cores and western outcrop samples 

demonstrate similar rock composition and diagenetic alteration (Bartsch-Winkler, this volume). 

Overall, the Corwin delta has a low sandstone content and thin, laterally discontinuous 

sandstone beds (fig. 9, table 1). The single 

most important depositional unit from a reservoir standpoint is the foreshore sandstone(s) 

within the basal part of the Nanushuk Group. 

These sandstones are easily recognized by their 

prominent, original, nearly horizontal bedding 

and distinctive vertical burrows. Their predictable occurrences in the Nanushuk indicate 

the passage of the paleoshoreline. These highenergy environments have the best reservoir 

potential in the Corwin delta complex because 

they have (1) the best visible porosity in 

outcrop and best measured porosity and permeability (fig. 7, sec. 3A); (2) greatest maximum 

thickness (<25m, commonly 5-10 m); (3) a 

possible adjacent hydrocarbon source (marine 

shale); (4) lateral continuity along the 

paleoshoreline; and (5) a relatively more 

stable composition due to removal of diagenetically unstable grains under relatively higher 

energy conditions (Fox, this volume; Huffman, 

this volume; Bartsch-Winkler, this volume). 

The foreshore, offshore-bar, and barrier-island 

sandstones should have a preferred northwestsoutheast orientation in the western area, 

which is useful for exploration. The Tupikchak 

Mountain section is the only area studied in 

which foreshore sandstones rest directly over 

one another, resulting in an 18-m-thick bed; 

however, porosity values are less than 9 

percent and permeability values less than 1 md 

there. 

Thus, considering the reservoir quality of 

the sandstones in the western area, prospects 

of major oil accumulations in the Corwin delta 

complex seem to be poor; porosity values are 

low to moderate. Thermal-maturation data in 

both western outcrop and subsurface samples 

(Magoon and Claypool, this volume) suggest that 

the Nanushuk is more prone to gas accumulations. 

However, low permeability and discontinuity of 

sandstones in the western area may even be a 

limitation on the size of reservoirs and rate 

of flow of potential gas production. 

25 

Limited data suggest that the reservoir 

quality of sandstone units of the Nanushuk in 

the central North Slope area is better than to 

the west. Porosity values for 45 samples in 

three central sections range from 2.6 to 16.4 

percent, and permeability values are as much as 

232 md. Sandstones in the eastern area are 

thicker, constitute a greater percentage of the 

total sediments (fig. 9), and have a more 

favorable composition (more quartz sand, fewer 

sedimentary.rock fragments) than Nanushuk 

samples in the west (Fox, this volume; Huffman, 

this volume; Bartsch-Winkler, this volume). 

Investigations in the coming year will focus on 

outcrops in the central and eastern areas of 

the North Slope. 
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Appendix 1.--Example of a computer-drawn display of the Killik Bend measured section of the Nanushuk Group. (See fig. 1.) The 

measured section is treated as a well location, such that numbers on the left margin of the plot refer to depth below the 

top of the section. 
~----.. l,. llFf. FS. sl r-_-.=.::-~-~ I rr-L 

~LT f--~- ~ ~~ 

Sc.T ~- -1 Sh/ 

J c:;:-~~ 5ft: 

'" _j =cc-c,,.:":. ··J,.~ !~ ' ' I"''' 1- 1;, : ;; Tr< JP 

t'I-T 

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300 J l I I 1 ~- - - J GEI1tl I I I I I I I E 

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0£ J • 01 

320 ~ t=-~ -:-:--::..'1 

to~oFs I ~rl-F MoE_ rr<t. a~~ 1\) i ~ 811 Tf'fl 

Q) r - ---- Tr< R~ G 

1

cARS EIUAII 1 

1

.. ~ •o 

I m.Fs.e I ~------1 I e-oe 

3~0 -i I I I I t E 1 I I ; I I I I I I I Tr; G ROOT ROS~ ASTR 

Tr< ASTR 

VERT 

CA~ 

WOOO ~·ocH 11114 SA 75 .01 

360 J 110 1L r· . .:.:.:~· .. :: ........... : ..... : ...... :-.-: ... : .. _.:-:·.-_.:: .... _.~·-t 5'16/ 1 J 11000 PLf'fT PURL 

· · · • · • • • • • • • · • • • · · · • Tr< 86r< PLNT "10RU 111.1 Sl'l 80 

P"' G wooo EIURW 

M.XL 

l ~~ .... . ·v··r Tr< ow"' CARS 1 1111.1 s,. •o 8FS.B MOST ~~ J 

~~~~ L 

11 B ~AD Wt HOR'l VERT I IN Sfl u Tr< o BURl-1 

3&o _J .rl. r .. ~ ...... I .... ·I MLI!rl,.'-:-:1. • . . Tr<-A'v b uooo Ro~'z llffitE ~~~R 

SI.TL~- b !1 0111'< G I10R'l -::~ 110 4 N G 110R'l 

u ---- tZO ~~~ H G CARS HOR'l VERT 

~ SLT ; ; ; ; : ... : ... : : : ; :: : : ROOT ... ' ' ..•.......... ' MINS I CHAN NU I 

~ 0 0 _J 7P l SH :':': ::: ': ·_. ': ': ·_. ·_. ·_. ':': ': ':':'.': ·_. A'v ~1.11'< J SCURS 11 Sl'l 80 

AV E CH,.N 
58 f IJ ))))))))))))] 59 /~ 1 1 1\ 1 1 

• Ot 

ROOT LOS PLNT 

1420 _J I~~(~ I I ~j000 

All t ~1811 .I lO 

01:. 

13Qp(M) r IJ/J/1 //////7/l ) E WOOD ... ~~ '0 

All E 

OE 

~P<L> 

~·~~::::~ II TN v Rw 30 v 

L BW G CARB DIPL S~L L SA 85 

IillO _J ( 9P VTN w SA 85 

3P G DII'L NOR! 

FORE CARB LA91'1 S'l't/1 'I TN BURW lr1W SA 80 All t NtOW 16E W A 30 

Tl'l DE 

BURI-I 

~GO -f- 1~0 I I 1\ I ~tf~S'I'~/,\ 111111 

tP N 

VTI'I 

VTI'I 

~GYate 

r 

VT~ CG OIPL BURI-I 

50'1'3/e C6 OIPL BURI-I 

ll80 I ..... ~.\ I. ~ 

ss . ~ E BLSS 

150 1\) 

500 I . "-~ co 

r lwooo H SI'>OL DIPL IISTR I I 80 I f~N OE Ell~ Wl 85 

11' I N B 1- I I, • 0~ 

VTN 

PLNT SA as 

I I~"- I 520 

Appendix 1.--Example of a computer-drawn display of the Killik Bend measured section of the Nanushuk Group. (See fig. 1.) The 

measured section is treated as a well location, such that numbers on the left margin of the plot refer to depth below the 

top of the section.--Continued 
EXPLANATION OF SYMBOLS AND ABBREVIATIONS USED IN APPENDIX 1 

[Abbrev., abbreviation. All abbreviations are found in a dictionary of terms used for these computer displays, which is available from Petroleum 

Information Corp., Denver, Colo.] 

~ 

~ 

[:'::.::::::::::..-::::1 

~ 

~ 

~~ 

~ 

~ 

~---~ 

~~~;:~ 

~ 

1-----1 

1~1 

Lithology 

Conglomerate. 

Sandstone. 

Sandstone, trough crossbedding. 

Sandstone, tabular planar crossbedding. 

Siltstone. 

Carbonaceous siltstone. 

Mudstone. 

Claystone (or shale). 

Carbonaceous shale. 

Coal. 

Symmetric ripples. 

Asymmetric ripples. 

Climbing ripples. 

Nondescript ripples. 

Abbrev. 

vtk 

tk 

av 

tn 

vtn 

1 

tnl 

h 

Code 

1 

0 

-1 

-2 

-3 

-4 

-5 

-6 

-8 

Thickness of Bedding 

Thickness and splitting 

description 

Scale 

in. 

Very thickly bedded; massive-----

Thickly bedded; blocky-----------

Average bedded· slab by-----------

Thinly bedd~d; 'flaggy------------

100 

30 -100 

10 - 30 

3 - 10 

40 

12 -40 

4 -12 

1. 2 - 4 

Very thinly bedded---------------

Laminated; platy, shaly----------

Thinly laminated; papery, fissile 

Homogeneous; massive-------------

1 - .4 - 1.2 

.12- .4 

.12 

.3- 1 

.3 

Wentworth Scale for Grain Size of Detrital Rocks 

Grain Size 

Clay---------------------

Silt---------------------

Very fine sand-----------

Fine sand----------------

Medium sand--------------

Coarse sand--------------

Very coarse sand---------

Granule gravel-----------

Fine pebble gravel-------

Medium pebble gravel-----

Coarse pebble gravel-----

Very coarse pebble gravel 

Cobble gravel------------

Boulder gravel-----------

1/256 

1/256-1/16 

1/16-1/8 

1/8-1/4 

1/4-1/2 

1/2-

1-

2-

4- 8 

8- 16 

16- 32 

32- 64 

64-256 

256 

Scale 

in. 

o. 00015 

0. 00015- • 002 

.002 - .005 

.005 - • 01 

.01 - • 02 

.02 - .04 

.04 - .08 

.08 - .15 

.15 - .3 

.3 - .6 

.6 - 1.2 

1.2 - 2.5 

2.5 -10 

10 

Abbreviations for Other Terms Used in Appendb: 1 

Abbrev. Name Abbrev. Name Abbrev. Name 

Facies (informal) Degree of calcareousness Intraclasts 

FLCH Fluvial channel system. SLY Slightly. CLAY Clay clasts. 

CHAN Channel. CAL Calcareous. CLRU Clay rip-up clasts. 

SHFC Shoreface {general). VRY Very. CHRT Chert clasts. 

LSHF Lower shoreface. HLY Highly. COAL Coal clasts. 

USHF Upper shoreface. COQU Coquina! lag clasts. 

FORE Foreshore (general). Sublithology FEST Ironstone clasts. 

LFOR Lower foreshore. LS Limestone clasts. 

UFOR Upper foreshore. CVRD Covered interval. MDRU Mud rip-up clasts. 

BRIS Barrier island. ss Sandstone. MDST Mudstone pebble clasts. 

ESTR Estuarine. LS Limestone. MUD Mud (nondescript) clasts. 

SWMP Swamp. SH Shale. QTZT Quartzite clasts. 

TDFL Tidal flat. SLT Siltstone. QTZ Quartz clasts. 

MRNE Marine (nondescript). MDST Mudstone. RIPU Rip-up (nondescript) clasts. 

TDCH Tidal channel. CSH Carbonaceous shale. OTHR Other (nondescript) clasts. 

WLGN Washover lagoon. CSLT Carbonaceous siltstone. CLCN Clay concretions. 

LAGN Lagoon. COAL Coal. CYCN Cycadophyte concretions. 

OVBK Overbank. CNGL Conglomerate. FECN Iron concretions. 

BKBH Backbeach. 

DLFT Delta front. {grains) LTCN Limonite concretions. ·Degree of sorting CONC Nondescript concretions. 

PDLT Prodelta. BLAC Armored clay balls. 

DLPL Delta plain. vw Very well. BLSS Sandstone balls. 

DMBR Distributary (stream) mouth bar. w Well. NODU Nondescript nodules. 

OFBR Offshore bar. MW Moderately well. 

PTBR Point bar. M Moderate. 

SPLY Splay. MP Moderately poor. 

FLDP Flood plain. p Poor. 

VP Very poor. 

30 
Abbreviations for Other Terms Used in Appendix 1--Continued 

Abbrev. Name Abbrev. Name Abbrev. Name 

Types of laminations Bedding features Bedding plane markings 

MXL Microcross-lamination. A Fault (normal or nondescript). SOLE Sole. 

E Even parallel. A-T Thrust fault. SOLEC Sole casts. 

w Wavy parallel. A-RX Reverse fault (X=displacement SCOUR Scour and fill. 

DE Discontinuous even parallel. in feet). SCURB Scoured base. 

DW Discontinuous wavy parallel. B Fractured. 

c Curved parallel. c Slickensides. Biological constituents DC Discontinuous curved parallel. D Slumping. 

EN Even nonparallel. E Load cast. CARB Carbonaceous material. 

DEN Discontinuous even nonparallel. F Flute cast. COCL Coccoliths. 

WN Wavy nonparallel. G Bioturbated. CORL Coral. 

DWN Discontinuous wavy nonparallel. I Dish. CRiN Crinoid. 

CONV Convolute. J Contorted. ECHI st·arfish (asteroid). 

COL Coaly. K Ball and pillow. 

DCOL Discontinuous coaly. EQUM Equisetum. 

p Boudinage. GAST Gastropod. 

Trace fossils Q Cone-in-cone. ORGN Nondescript organic material. 

u Calcite veining. PLNT Nondescript plant fragments or 

v Clay parting. material. 

BURW Nondescript burrow. w Flame structure. 

USHP u-shaped burrow. X Recumbent fold. STEM Stem (nondescript). 

BILO Bilobate burrow. LEAF Leaf (nondescript). 

OBLQ Oblique burrow. Roundness BRAN Branch (nondescript). 

HORZ Horizontal burrow. LOG Log (nondescript). 

VERT Vertical burrow. ROOT Roots and (or) rootlets. 

SA Subangular. 

TRCK Tracks, type unspecified. A Angular. CYCD Cycadophyte. 

TRAL Trails, type unspecified. SR Subrounded. CYDL Cycadophyte leaf. 

ZIPR Zipper trails. R Rounded. GINK Gingko. 

PURL Pleural tubes. FERN Fern. 

WORM Worm tube, calcareous. Angle of cross beds WOOD Wood and (or) wood impression,s. 

DIPL Diplocraterion. SCAP Scaphopod. 

RZCO Rhizocorallium. H High: greater than zo•. TRTX Tritaxia m. (foraminifera). 

AREN Arenicolites. M Moderate: ll ·-zo•. TREE Tree, growth position. 

ROSL Rosselia. L Low: 10° or less. TRNK Trunk (tree, nondescript). 

!NCR Inoceramus. LOGC Log, conifer. 

ASTR Asterosoma. CEPH Cephalopod. 

31 
SUBSURFACE STUDIES OF THE NANUSHUK GROUP, 

NORTH SLOPE, ALASKA 

By K. J. Bird and Jack Andrews 1 

INTRODUCTION 

The objectives of this part of the Nanushuk 

study are to identify and map the more favorable 

reservoir trends in the subsurface Nanushuk 

Group. To achieve these objectives, we plan to 

relate the more porous intervals in the wells 

to environments of deposition as determined by 

the study of cores and logs, to tie these 

results to similar studies from outcrop, and 

eventually to relate this information to the 

seismic data. Additional porosity measurements 

are being made, and detailed sedimentologic 

studies of the cores are underway. These 

studies are being conducted by Ira Pasternak 

and K. J. Bird. 

The information presented here is based on 

a study of new seismic data and a network of 

correlated well logs. The seismic data, which 

have been obtained since 1974, consist of more 

than 10,000 line-kilometers of coverage on a 

grid approximately 10 x 20 km. Subsurface 

Nanushuk data points consist of 33 wells drilled 

during the U.S. Navy Pet-4 program (1945-53), 

about 14 wells drilled by private industry 

adjacent to the reserve, and 13 wells drilled 

within the reserve between 1974 and 1978. (See 

fig. 1 for locations.) Although all Nanushuk 

data points have been reviewed, only the most 

complete outcrop sections and well penetrations, 

providing the widest geographic coverage, have 

been selected for inclusion in figure 10 and 

table 2. 

STRATIGRAPHY 

From the Nanushuk Series, the Nanushuk 

Group was redefined by Gryc, Patton, and Payne 

(1951, p. 162) as a section of rock composed of 

sandstone, shale, conglomerate, and coal exposed 

along the Nanushuk River south of Umiat (fig. 

10). These rocks have been studied in the 

western and central North Slope in outcrop by 

Chapman and Sable (1960), Detterman, Bickel, 

and Gryc (1963), Chapman, Detterman, and Mangus 

(1964), Patton and Tailleur (1964), and Brosge 

1Tetra Tech, Inc., Houston, Tex. 

32 

and Whittington (1966) and in the subsurface by 

Collins and Robinson (1967). The complex 

stratigraphic nomenclature that resulted from 

these numerous studies and some of the uncertainties in correlating these units are summarized in figure 5. Pending further study and 

better correlation of these rocks, we have used 

the general stratigraphic terminology of 

Colville Group, Nanushuk Group, and Torok 

Formation (instead of the Topagoruk and Oumalik 

Formations). 

An additional rock unit not shown in 

figure 5, but of great importance as a key 

correlation horizon in the subsurface, is the 

Lower Cretaceous (Neocomian) "pebble shale" 

unit (Alaska Geological Society Newsletter, 

1978). This informal rock unit, which overlies 

a regional unconformity and forms the surface 

over which the Torok Formation prograded, 

derives its name from well-rounded quartz sand 

grains and occasional chert granules scattered 

through a dark-gray clay-shale matrix. It is a 

distinct stratigraphic unit generally 100-200 

m thick that is easily correlated over long 

distances by means of lithology, well logs, and 

seismic records. 

Earlier studies clearly demonstrated that 

the Nanushuk Group forms a northward-prograding 

clastic wedge of Early and Late Cretaceous age 

that is overlain and underlain by marine shale 

(Gryc and others, 1951; Payne and others, 

1952). Seismic data showed north to northeast 

dips in the Cretaceous rocks, which are overlain 

and underlain by essentially flat-lying beds. 

Core data from wells confirmed the seismic dips 

and indicated that the dips are in the, finegrained marine sediments (Torok Formation) 

below the Nanushuk. The Torok Formation and 

the Nanushuk Group were considered to be distinct and separate rock units representing 

"orogenic" and "post-orogenic" deposition, 

respectively (Payne and others, 1952). 

New seismic and closely associated well 

data (fig. 11) reveal important stratigraphic 

relationships apparently not clearly shown in 

the earlier data. The most important feature 

of these new seismic data is the continuity of 

some reflectors from topset to foreset to 

bottomset positions, or from undaform to clino-
80 

Kilometers 

o well penetration 

+ outcrop section 

x oil seep 

gas seep 

• good oil show 

* good gas show +2 

I 

I 

I 

I +3 

-t4 

Admiralty seep 

Skull Cliff seep....._ 

*Meade T.W -I 

t Pohron seep 

OCEAN 

~--

-~--· 

Aupuk seeps 7+·, 

Umiat oil field and Um1ot seep 

/ ••• ···· • .• • ·· .--~~ Colville • •...... ··•··· ····· 5+. "t. 

~"'lf>r • ····i· + 6 . +a ·······=.:·9· 

+10 

Nanushuk i ········-~-~~~-~·· .......... ····~-~-~~~ "L···· limit of 

. --.r---· ..,...__,. ~ ~ 

."'-._ 

····:f"ll 

...... ····· Southern 

"-- I 

BROOKS '--·'-.... . I RANGE ~-..._j 

Figure 10.--Index map of a part of the North Slope of Alaska showing selected Nanushuk Group data 

points, hydrocarbon locations, and the major facies boundary. Numbered points refer to 

outcrop localities shown in table 2. Erosional remnants of the Colville Group (not shown on 

map) may be present locally in western NPRA, as reported by Chapman and Sable (1960) and 

Smiley (1966, 1969b). 

form to fondoform in the terminology of Rich 

(1951). On seismic sections longer than that 

shown in figure 11, an individual reflection 

within the Nanushuk can be traced basinward and 

observed to lie progressively lower in the 

group (because of loss of section from the base 

by progradation) until it passes from Nanushuk 

into topset, foreset, and bottomset Torok. 

Each continuous reflector is regarded as a time 

line following paleotopography at some instant 

in geologic time. These new data indicate that 

the Nanushuk Group and Torok Formation are 

lateral equivalents representing a single 

depositional system. The topset seismic reflectors include alluvial-deltaic and shelf deposits 

of the Nanushuk Group and upper part of the 

Torok Formation; foreset reflectors consist of 

slope deposits of the middle part of the Torok 

Formation; and the bottomset reflectors consist 

of basin-floor deposits of the lower part of 

the Torok Formation. The distinction between 

"orogenic" and "post-orogenic," therefore, does 

not apply to this situation. 

Some foreset reflections in figure 11 show 

truncation by topset reflections, demonstrating 

33 

a "toplap" relationship (Mitchum, 1977) that 

probably represents a temporary hiatus resulting 

from bypassing of sediment. It was probably a 

toplap relationship that Collins and Robinson 

(1967, p. 50) regarded as an angular unconformity marking the contact between the Oumalik and 

Topagoruk Formations (fig. 5). 

In contrast to other areas of deltaic 

sedimentation such as the MacKenzie delta or 

the Mississippi delta, no growth faults or 

diapirs have been observed on the seismic 

records. Irregular, discontinuous, and sometimes truncated reflections in the foreset 

interval do suggest considerable sediment 

instability and mass movement. 

The new data also elucidate important 

regional stratigraphic relationships of the 

Cretaceous rocks. Seismic sections near the 

eastern edge of NPRA (National Petroleum Reserve 

in Alaska) show a much reduced thickness of 

Nanushuk Group and the beginning of lowamplitude foreset structures in the overlying 

Colville Group. These data appear to show the 

termination of Nanushuk progradation by a 

relative rise in sea level, westward transgres-
Table 2.--Selected Nanushuk Group data 

Well penetrations 

Well name 

Kaolak T. W.-1 

Kugrua...;l 

Meade T. W.-1 

So. Meade-1 

Skull Cliff C. T.-1 

So. Barrow T. W.-1 

Simpson T. W.-1 

So Simpson-1 

Drew Point-1 

W. T. Foran-1 

Cape Halkett-1 

E. Teshekpuk-1 

Atigaru Point-1 

S. Harrison Bay-1 

Fish Creek T. W.-1 

W. Fish Creek T. W.-1 

Topagoruk T. W.-1 

E. Topagoruk T. W.-1 

Oumalik T. W.-1 

E. Oumalik T. W.-1 

Titaluk T. W.-1 

Wolf Creek T. W.-3 

Square Lake T. W.-1 

Little Twist-1 

Umiat T. W. -1 

Umiat T. W.-11 

Gubik T. W.-1 

Location 

Sec. T. R. 

25 7 N. 34 w. 

8 14 N. 26 w. 

19 8 N. 22 w. 

31 15 N. 19 w. 

23 18 N. 22 w. 

28 23 N. 18 w. 

32 19 N. 13 w. 

22 17 N. 12 w. 

26 18 N. 8 w. 

13 17 N. 2 w. 

1 16 N. 2 w. 

16 14 N. 4 w. 

19 14 N. 2 E. 

6 12 N. 2 E. 

15 11 N. 1 E. 

11 11 N. 1 w. 

25 15 N. 16 w. 

12 14 N. 14 w. 

20 6 N. 16 w. 

13 5 N. 15 w. 

23 1 N. 11 w. 

2 1 s. 7 w. 

2 2 N. 6 w. 

34 3 s. 4 w. 

34 1 N. 2 w. 

27 1 N. 1 w. 

20 1 N. 3 E. 

Outcrop sections 

Location Outcrop name Location 

No. T. R. 

1 Corwin Bluff 6-7 s. 53-56 w. 

2 Barabara Syncline 1 N.-2 s. 44-45 w. 

3 Kokolik Warp Syncline 3-4 s. 40-41 w. 

4 Elusive Syncline 1-3 N. 33 w. 

5 Colville River 5 s. 15-17 w. 

6 Kurupa River 6 s. 12-14 w. 

7 Knifeblade Ridge 3-4 s. 12 w. 

8 Killik River 5-6 s. 6- 7 w. 

9 Mammoth Creek and 7 s. 3 w·. 

Chandler River } 8 s. 2 w. 

10 Big Bend 4 s. 1 E. 

11 Nanushuk River 9 s. 6 E. 

l"+" indicates incomplete Nanushuk section. 

2Alternate placement of Nanushuk-Torok contact. 

3Fault repetition of 229 m has been removed. 

34 

Top 

34+ 

0 

12 

0 

3 

21 

6 

155 

375 

1,061 

950 

491 

1,058 

982 

890 

770 

7 

12 

6 

9 

12 

5 

495 

0 

277 

622 

954 

Nanushuk 

thickness 

(in meters) 1 

4,723+ 

3,444+ 

3,110+ 

2,091+ 

1,977 

1,911+ 

1,728+ 

1,452+ 

1,356+ 

1,490+ 

594+ 

1,097+ 

Nanushuk 

Base 

1,247 

710 

1,050 

616 

137 

212 

302 

713 

901 

1,335 

1,291 

953 

1,295 

1,285 

1,131 

1,091 

648 

693 

843 

834 

1,058 

1,087 

1,192 

937 

863 

937 

1,210 

Source 

Thickness 

(in meters) 1 

1,213 + 

2 (1,554)+ 

710 + 

1,038 + 

2 (1,280)+ 

616 + 

134 + 

191 + 

296 + 

558 + 

526 

274 

341 

462 

237 

303 

241 

321 

641 + 

681 + 

837 + 

835 + 

1,046 + 

1,083 + 

696 

937 + 

3357 + 

315 

256 

Chapman and Sable, 1960. 

Smiley, 1969. 

Chapman and Sable, 1960. 

Ahlbrandt and others, this 

volume. 

Chapman and Sable, 1960. 

Chapman and others, 1964. 

Do. 

Brosge and Whittington, 

1966. 

Detterman and others, 1963. 

:Oo. 

Do. 

Do. 
DREW POINT NO.I 

T.D. 2422m (7,946 It) 0 0 .5mi 

1----+----.' 

0 0 .8 km 

(WEST) LINE 2-74- G- 195 (EAST) 

-0.5 

<I) 

0 

z 

0 

u -1. 0 "' <I) 

z 

"' ::f 

f- -1.5 

>-

... 

~ 

0 

3: -2.0 f-

-2.5 

Figure 11.--Seismic section passing through the Drew Point-1 well location. (See fig. 10 for 

location.) Stratigraphy has been keyed to the seismic section using a synthetic seismogram 

from the well. Note the characteristic topset (undaform), foreset (clinoform), and bottomset (fondoform) reflections and their relationship to the stratigraphy. See figure 14 for 

details of stratigraphy and log response. 

sian of the shoreline in earliest Colville 

time, and subsequent eastward progradation by 

the Colville Group in a style similar to that 

of the Nanushuk Group. When these relationships 

are extended eastward beyond the area of seismic 

coverage by correlated well logs, the Nanushuk 

Group and Torok Formation are not found in the 

Prudhoe Bay area; their absence may be explained 

by pinch-out to very thin "distal" bottomset 

beds (fig. 12). This explanation eliminates 

the need for postulating an unconformity cutout 

of the Nanushuk Group and most of the Torok 

Formation in the Prudhoe Bay area (North Slope 

Stratigraphic Commission, 1971). By incorporating available paleontologic information, these 

data have been converted to a simplified timestratigraphic chart (fig. 13). Note that in 

this interpretation, the Aptian Stage, long 

considered missing and a period of erosion in 

almost all of Alaska, is represented by relatively deep marine shale. A deep marine environment, possibly bela~ the calcite compensation 

depth and possibly low in oxygen, may help to 

explain the near absence of diagnostic Aptian 

fossils. 

35 

Optimum use of the seismic data requires 

accurate matching of the stratigraphy to the 

seismic records. In the newer wells, the 

seismic data can be more accurately related to 

the stratigraphy using synthetic seismograms 

and velocity surveys. Details of the stratigraphy, log response, and structural attitudes 

are shown in relation to the seismic features 

for the Drew Point well in figure 14. Note the 

correspondence of the core dips and dipmeter 

data to the seismic features. The foreset 

interval, characterized by a monotonous log 

response, consists predominantly of shale with 

rare sandstone and siltstone. In contrast the 

bottomset interval, having slightly more log 

character, consists of more siltstone and 

sandstone than the foreset interval. It is 

noteworthy that the bottomset beds lie in the 

same stratigraphic position as the Fortress 

Mountain Formation relative to the Torok Formation in outcrop (fig. 5), suggesting that some 

of the Fortress Mountain Formation may represent bottomset deposition. 

By recognizing the significance of the 

foreset structures, the directions of prograda-

<I) 

a: 

"' f-

"' :IE 

.._ 

0 

<I) 

0 

z 

... 

<I) 

~ 

0 

l:: 

f-

~ 

<I) 

l:: 

fa. 

"' 0 

... 

"' <I) 

I 

ID 

~ 

(/) 
SW-------------------- I~Okm---------------------NE 

Colville Prudhoe 

NPRA R~ver Bay 

--seismic and well do to ---------well data onlyFigure 12.--Diagrarnrnatic section based on seismic and correlated well data showing 

Cretaceous stratigraphic relations between 

the rocks of NPRA and Prudhoe Bay. Termination of the Nanushuk-Torok wedge was 

caused by the Colville Group transgression, 

which was followed by renewed progradation 

in a style similar to that in the underlying rocks. 

sw 

c 

0 

e 

~ z 

NE 

"pebble shale" unit 

Jurassic and older rocks 

Figure 13.--Diagrammatic Cretaceous timestratigraphic chart for northern NPRA 

based on available paleontologic data and 

the relationships shown in figure 12. 

Note that the entire Cretaceous section 

can be explained in terms of continuous 

sedimentation from "pebble shale" unit 

through Colville Group without regional 

erosional hiatus. Diagram does not apply 

to foothills outcrop belt. 

tion, shoreline trends, and basin filling may 

be estimated. Andrews measured apparent foreset 

dip at seismic-line intersections and calculated 

resultant true-dip vectors. These vectors are 

shown in figure 15 along with dipmeter data 

from Nanushuk Group sandstones, direction of 

36 

maximum shale-out of Nanushuk Group sandstones 

from outcrop (Chapman and Sable, 1960, p. 95), 

and Nanushuk paleotransport data collected by 

Ahlbrandt and others. Note the apparent shift 

in directional indicators from northeast to 

east in the southwest to the northeast parts of 

the reserve. The sparsity of foreset dip 

vectors in the southwest half of the reserve is 

partly a reflection of fewer seismic data and 

fewer identifiable foreset structures. The 

remarkable consistency of these data suggest 

that the basin filled initially in a northeast 

direction and later in a more easterly direction. Shoreline trends are assumed to have 

been approximately perpendicular to the direction of progradation. 

NANUSHUK LOG CHARACTERISTICS 

The electric log character of the Nanushuk 

Group shows a systematic change from west to 

east. Three widely spaced wells have been 

selected to illustrate this change (fig. 16). 

DREW POINT -I 

26-IBN-SW 

K 8. 11m 

T. O. 2422m 

COLVILLE 

GROUP 

NANUSHUK 

GROUP 

TOROK 

FORMATION 

S.P 

"pebble shole"unit 

Pre- Cretaceous 

rocks 

1,000 

2.,000 

DIPMETER 

DATA (dip and direction) 

z•-zo• (ave . e•-IQ•J 

to NNE 

z•-3o• tovt s•J 

to E 

ltn than z• 

varioblt direction 

SEISMIC 

FEATURES 

TOPSET 

(undoforml 

FORE SET 

(cllnoforml 

BOTTOMSET 

( fondoform) 

Figure 14.--Cretaceous section in the Drew 

Point-1 well showing the relationship of 

stratigraphy to log response, structural 

attitudes, and seismic data. 
o well penetration 

+outcrop section 

80 

K1lometers 

Percent of ~ 

I 

I 

I 

-

OCEAN 

-

+. . + 

··· ... i + '-.... +··. . ····· .. f · ... ··· 

reodmg Number of (10) measurements I 

Na""'h:.. 1 .. ·--~;:·;~·- · ...... · 2 . :_tN .. u •. mber of 

Average progradation Direction of true d1p 

Poleotransport directions determined 

from nonmarine channels of the 

Nanushuk Group 

direction of Nanushuk foreset reflectors 4 8 readings 

(Chapman and Soble, 1960) Torok Formation Diomefer data from 

Nanushuk Sandstones 

Figure 15.--Plot of directional data from seismic foreset dips in Torok Formation, dipmeter data 

from Nanushuk Group sandstones, direction of Nanushuk progradation from outcrop (Chapman and 

Sable, 1960), and direction of plunge of symmetrically filled no~marine channels of the 

Nanushuk Group as measured by Ahlbrandt and others (this volume). 

The westernmost well (Kaolak T. W.-1) is 

characterized by relatively thin sandstones 

scattered through a predominantly coaly shale 

section. There is no distinct Nanushuk-Torok 

contact in this well; it is placed arbitrarily 

at the base of the lowest significant sandstone 

bed. To the east (Titaluk T. W.-1), the lower 

part of the Nanushuk consists of numerous thick 

sandstone beds separated by shale and siltstone 

beds of approximately equal thickness, and the 

upper part of the Nanushuk consists of thinbedded sandstones in a predominantly coaly 

shale section similar to the section in Kaolak. 

The Nanushuk in the easternmost well (Fish 

Creek T. W.-1) consists of sandstone and shale 

of roughly equal proportion; it is similar to 

the lower part of the Titaluk well, although 

the section is very thin owing to a position 

near the pinch-out of the Nanushuk wedge. 

The coaly shale interval is herein designated facies A and the section having more 

abundant sandstone, facies B. Although future 

core study is expected to provide a more detailed environmental interpretation, gross 

lithologic character and stratigraphic position 

suggest that facies A corresponds to the non37 

marine and transitional environment and that 

facies B corresponds to the marine environment 

of Ahlbrandt and others (fig. 6). 

Recognition of these two facies is thought 

to be important to hydrocarbon exploration, 

because the sandstone beds of facies B grade 

laterally and pinch out into facies A, forming 

potential stratigraphic traps. The easternmost 

extent of facies A is shown in figure 10. 

Stratigraphic traps of this type are expected 

only to the west of this line. It is interesting to note that Umiat oil field lies along 

this boundary. Perhaps the Umiat oil was first 

stratigraphically trapped and later focused by 

the development of Umiat Anticline. 

HYDROCARBON OCCURRENCES 

Hydrocarbon occurrences in the Nanushuk 

Group (fig. 10) consist of the Umiat oil field 

and the Gubik gas field. Significant but 

subcommercial discoveries of gas have been made 

in East Umiat-1, Meade T. W.-1, and Wolf Creek 

T. w.-3 and of oil, in the Simpson T. W.-1 and 

Fish Creek T. W.-1. Lesser oil and gas shows 

are common throughout the Torok Formation and 
"¢- --- 230km ---\>- --- 145km ---\>-

Kaolak T.W.-1 

?-

I 

Titaluk T.W.-1 

Colville 

Fl1h Creek T.W.-1 

N • Nanu1huk Group 

T • Torok Formation 

N 

T 

FACIES A - 1hale predominant, coal common, 

1and1tone thin bedded and dl1continuou1 

FACIES B - 1andllone a1 common a1 1hale, coal 

rare, 1and1tone more thickly bedded 

than in faciu A. 

r

Omotoro 

100 

200 

vtrtlcal ICOII 

Figure 16.--Log response and gross lithofacies 

subdivision in three wells spanning NPRA. 

Nanushuk Group. Surface seeps of oil and gas 

are fairly numerous and are located in figure 

10. 

ISOPACH MAPS 

In recognition of the close genetic relationship of the Nanushuk Group and Torok Formation, isopach maps have been constructed showing 

their combined thicknesses (fig. 17) and the 

thickness of each unit individually (figs. 18 

~pd 19). All three maps show a similar pattern 

Rf northward thinning. The isopachs trend west tR northwest in the southwest portion of the 

r~serve, whereas in the northeast part of the 

r~serve th~y ~:>how a marked deflection to the 

north. Comparison of isopach trends with 

paleotransport directions (fig. 15) shows that 

these two trends are generally perpendicular, 

except in the area about Point Barrow which has 

undergone significant erosion. The effect of 

post-Nanushuk erosion on isopach trends would 

be a shifting of them to the south as at Point 

Barrow. However, in areas far to the south of 

Point Barrow, the similarity of isopach trends 

(fig. 18) in areas that have no Nanushuk erosion 

(between Umiat and the edge of the Colville 

Group) and in areas where Nanushuk has been 

eroded (west of the edge of the Colville Group) 

suggests that the amount of erosion.may be 

relatively insignificant. 

The trend of isopachs on all three maps is 

oblique to that of the present-day Brooks 

Range. Perhaps the isopachs reflect the trend 

of the Nanushuk source terrane. The source 

terrane may have paralleled the Herald Arch, 

the extension of the Brooks Range orogen northwesterly from Cape Lisburne (Grantz and others, 

1976, fig. 3), but it may diverge from the 

Brooks Range trend east of Cape Lisburne. The 

maximum thickness of the Nanushuk Group and the 

Torok Formation in the Cape Lisburne region 

suggests a combination of greater uplift in the 

source area and subsidence of the basin. 

Northeastward progradation is envisioned to 

have continued until the basin was prograded to 

about the position of the 900-m Nanushuk isopach 

(fig. 18). At this time the shift in direction 

of progradation from northeast to more nearly 

due east may have been accomplished by gentle 

eastward tilting of the basin. Slight uplift 

in the west and depression in the east may have 

produced a north-trending shoreline over the 

slightly submerged Barrow Arch, whereas to the 

south, where water depths were probably greater, 

tilting of the basin would not have immediately 

affected the direction of progradation. 

SUMMARY 

New seismic and well data in NPRA reveal 

that the Torok Formation and Nanushuk Group 

constitute a single prograding depositional 

system consisting of topset, foreset, and 

bottomset beds. The direction of progradation 

as indicated by seismic, dipmeter, and outcrop 

data was initially to the northeast and later 

nearly due east. 

Review of the subsurface data suggests 

several hydrocarbon plays in the Torok Formation 

and Nanushuk Group. These include (1) anticlinal traps in the fold belt, (2) structuralstratigraphic traps formed by updip shaling-out 

of basal sandstones of the Nanushuk on the 

south flanks of anticlines, (3) structuralstratigraphic traps formed by shaling-out of 

marine sandstones of the Nanushuk updip into 

transitional and nonmarine shales of the 

Nanushuk, and (4) stratigraphic traps in the 

Torok Formation formed by sandstones on the 

depositional slope being sealed by surrounding 

shales. 

38 
o well penetration 

+ outcrop section 

80 

Kilometers 

contours in meters 

+ 

BROOKS 

OCEAN 

Group 

RANGE 

+ 

"pebble shale" 

unit 

'•=t:' ·._ .. 

................ ·· .... ····+ .......... ·· rocks 

Figure 17.--Isopach map showing the combined thicknesses of the Torok Formation and the Nanushuk 

Group utilizing the structure contour map on the basal Cretaceous horizon (J. Harris and C. 

C. Miller, unpub. mapping, 1977). Structural complexity associated with Brooks Range front 

prevents extension of the contours farther south. 

39 
o well pe~etrotion 

+ outcrop section 

8() 

'-----'-----' K1lometers 

contours in meters 

BROOKS 

I 

"-- I '-·'-- . 

~._J 

OCeAN 

Group 

RANGE 

rocks 

"pebble shale" 

unit 

Figure 18.--Nanushuk Group isopach map based on selected well and outcrop sections. Numbers refer 

to outcrop localities shown in table 2. Note the general northwesterly isopach trend for 

much of the area and the pronounced shift in the trend in the northeastern corner of the 

reserve. 

40 
o well penetration 

+ outcrop section 

80 

Kilometers 

contours in meters 

+ 

BROOKS 

OCEAN 

+. 

·· .. i + 

Nanushuk ~··· .•.....• 

Group 

'--- I '\.... . .......___ ' 

~._J RANGE 

156° 

Isopach 

interval 

+ 

········.+····· 

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

rocks 

COLVILLE GP 

TOROK 

FM 

"pebble shale" 

unit 

. ... ··+ 

Figure 19.--Torok Formation isopach map, which was constructed by plotting the difference between 

contour values shown on figures 17 and 18. Note the similarity in trends to those of the 

previous maps. 

41 
A SUMMARY OF RESERVOIR CHARACTERISTICS 

OF THE NANUSHUK GROUP, UMIAT TEST WELL 11, 

NATIONAL PETROLEUM RESERVE IN ALASKA 

By James E. Fox 

INTRODUCTION 

Umiat Anticline has the largest discovered 

hydrocarbon reserves in Cretaceous rocks of 

NPRA (National Petroleum Reserve in Alaska). 

The anticline is an east-west-trending structure 

located near the southeastern edge of NPRA, 

just north of the Colville River (fig. 20), and 

the primary production is from the Grandstand 

Formation of the Nanushuk Group. From 1945 

through 1952, the U.S. Navy drilled and tested 

11 wells on this anticline. The results of 

this work are discussed by Collins (1958a). 

Fox and others (1979) analyzed logs and 

studied the sedimentology, petrography, and 

paleontology of selected Lower and Upper Cretaceous sandstone units cored in Umiat test well 

11. Test well 11 was selected because cores 

from it had the most complete unfaulted sequence 

of any of the Umiat wells (fig. 20). The 

purpose of the study was to identify the influence on porosity and permeability of sedimentologic factors such as character of sediment 

source rocks and depositional processes, as 

well as burial and diagenesis. Study of these 

factors has led to a better understanding of 

the potential of these units as hydrocarbon 

reservoirs. A summary of the part of the study 

dealing with Lower Cretaceous strata is presented here for comparison of these rocks in 

the central North Slope basin (eastern NPRA) 

with contemporary rocks in the western NPRA 

region, as presented in reports in this Circular. This summary will specifically discuss 

the Grandstand Formation, Killik Tongue of the 

Chandler Formation, and Ninuluk Formation, all 

of the Nanushuk Group. The cored intervals 

summarized in this chapter include the following 

(fig. 21): 

Core 60 (911-916 m), Grandstand Formation; 

Cores 56-58 (865-869 m), Grandstand Formation; 

Cores 52-53 (745-750 m), Grandstand Formation; 

Core 49 (724-729 m), Killik Tongue of 

Chandler Formation; and 

Cores 35-38 (624-639 m), Ninuluk Formation. 

The stratigraphic terminology of Lower 

42 

Cretaceous rocks in the central North Slope 

basin (eastern NPRA) is shown, and it can be 

compared to that used for the western NPRA 

(Ahlbrandt and others, this volume, fig. 5). 

PROCEDURES 

Sedimentology and Depositional Environments 

A detailed sedimentologic study was made 

of the aforementioned cores (Fox and others, 

1979) using a thin slice (1.25 em thick) cut 

from each of these cores. Sandstone beds make 

up a relatively small proportion of the overall 

lithotype of the total cored interval. Interbedded with the thin sandstone units are claystone, siltstone, and coal beds that were not 

studied for this report. The following aspects 

were studied in the core analysis: visualporosity estimate, lithology, color, grain 

size, bedding type, sedimentary structures, 

biologic constitutents, sorting, roundness, oil 

shows, and inferred environment of deposition. 

Data were gathered from the core specimens 

using a hand lens, binocular microscope, and 

black-light (fluorescence) apparatus. Interpretation of depositional environments was primarily dependent upon the identification of sedimentary structures. Because of the finegrained, homogeneous nature of most of the 

sediments and the abundance of interstitial 

clay, the sedimentary structures were difficult 

to see clearly. For this reason, each of the 

thin slices of core was photographed using an 

X-radiography apparatus, and an X-radiograph 

photograph was printed to assist in interpretation. These prints revealed structures not 

otherwise clearly distinguishable. 

Interpretations of depositional environments for each cored interval (fig. 21) were 

incorporated into the regional paleogeographic 

synthesis of Brosge and Whittington (1966). 

Microfossils were especially useful in interpreting the environments. Dinoflagellates and 

foraminifera were identified by F. E. May and 

W. V. Sliter, respectively. Their results, 

which are discussed separately in this Circular, 

were used not only to aid in the paleoenvironmental interpretation, but also to date the 
~ 

(.,) 

25' A 25' 

22'30"1 "k "<;: =:...... ------ =::.........'"" =:........... ---= ::.......... .:=t-----

EXPLANATION 

-- Structure contours on top 

of Grandstand Fm. 

--- Thrust Faults 

-¢- Dry Hole 

+ Shut in oil well 

c:J Colville Group LS.J Nanushuk Group 

0 1 2 Miles 

0 1 2 Kilometers 

--1 ·-

152"30' 257 20' 15 

~ 

~ ~ 

~ 

~ ~ 

SEAl 

2000 

4ooo (1219) 

10' 

(1829) 

8000 (2438) 

A 5' 152°00' 

INDEX MAP 

200MILES 

~0 100 150 200 KILOMETERS 

Figure 20.--Index map showing location of study area, structure contour map of Umiat Anticline, and cross section of 

Umiat Anticline. Modified from Brosge and Whittington (1966). 

151°55' 
en 

g 

-1 

a.. 

>- 1-

::i 

ffi 

< w 

Cii ~ 

a: a: 

w w 

a.. 

z 

0 

~ i= w en w a.. < 1- w C) :::l ~ en a: < 0 a: >- w 1- a: 0 en en en C) u.. 

1-

w 

~ 

J: w 1-

a.. a: w 0 

c (.) 

>- C) >- 1- 0 

-1 Ci5 

0 0 

J: a: 1- 0 ::i a.. 

X: 

z :J 

_J ~ a: <( :J II.. w z z a.. <( z a.. f--

:::::> @' 

a:: :J 

ILl (.!) 

.J z 

625 35-38* 

39 

650 40 

41 

42-44 675 45 

46 

0 0 z 1- 700 47 <( X: I :J u _J 

g 

48 

725 49* 

50 

51 f------ DITCH 

750 52-53* 

a. 

::::> 

0 

a: 775 54 

C) z :::.::: 0 

::::> ~ en I <( 

::::> en ::E 

0 a: ::::> a: 

w w z z 0 u 3: <( <( LL 

<( 0 iD z c 1-

w ...J ...J z 

a: <( <( 

u 1-

en 

c 

z 

<( 

a: 

C) 

~ II.. 

X: 

0 

a:: 

0 

1-

Q) 

u.. u 

c: 0 

z "' '0 1-

z 0 c: 

:::l w i= ~ 

~ Ci5 z 0 "' C) 

0 a.. c: 

a: w ·u; 

> c 

z "' ~ 

w u 

Q) 

w '0 

en ~ 0 ~ Q) a.. c: 0 ·~ ~ ~ (i) 

J: Q) ~ "E en c: E >- ·~ c: 8 :5 0 

-1 0 §. 5 ~ z a: (.) 

• l DELTA Phyllarenite Illite, Kaolinite, 

FRONT Metarenite Chlorite 

• FORESHORE Phyll arenite 

(DEtTA 

Metarenite 

PLAIN 

FLUVIAL 

Phyllarenite 

Chert arenite 

• 

• ~DELTA FRONT Kaolinite, Illite, 

FORESHORE Chlorite 

) DELTA Illite, Chlorite, 

FRONT Kaolinite 

FORESHORE 

• 

DELTA 

FRONT Phyllarenite • FORESHORE Chert arenite Illite, Kaolinite, 

I UP~ER Chlorite 

SHOREFACE 

Phyllarenite 

DELTA 

FRONT 

FORESHORE 

I UP:ER 

SHOREFACE 

I *Cores studied by Fox and others (1979) 

>- 1-

Ci5 

01-

a:z Ow 

a..o 

wa: >W i=a.. 

oz 

wu.. 

u.. 

w 

r 

1'-

~ 

: 

I\. 

' ' ' ' 

L--

\ 

ir' 

D 

\ 

\ 

: 

I 

I 

( ' 

' I 

I 

I 

I 

~ 1-

/ 

I 

I 

I 

I 

I 

\ 

I 

I 

I 

I 

>-~ ~--­ -0 ::!a: al< 

<c 

~3 

~~ ~ 

1\ \ 

\ 

[...--f--G. \ 

\ 

\ 

.) 

~ \ 

\ 

~ 

I 

I 

I 

I 

I 

I 

I 

I> 

I 

I 

I 

I 

I 

I 

l 

let_ / 

1,/ 

Figure 21.--Stratigraphic column of Umiat test well 11 showing cored intervals, shows of oil, 

environments of deposition, rock type, clay type, effective porosity, and permeability. 

rocks and to set up a framework for biostratigraphic correlation. 

Petrography 

Detrital grains and clay minerals were 

studied in order to determine their effects on 

44 

reservoir quality (Fox and others, 1979). P. 

W. Lambert documented the influence of texture, 

fabric, mineralogy, and diagenesis on reservoir 

quality in the study by Fox and others (1979). 

Thirty-one core samples ("perm plugs") from the 

Nanushuk Group, previously used for porosity 

and permeability studies (Collins, 1958a), were 
used in the analyses. These studies were 

supplemented by X-ray diffraction analyses by 

J. K. Pitman of clay and of major mineral 

constituents of 21 samples (taken as close as 

possible to perm-plug locations) from the 

Nanushuk Group (fig. 21). Of special interest 

was the identification of the kinds of interstitial clay in the various sandstone units. 

RESULTS 

Sedimentology and Depositional Environments 

Strata of the Lower Cretaceous Nanushuk 

Group in the Umiat area consist of detrital 

clastic sediments, derived from the Brooks 

Range to the south. These sediments were 

deposited in continental (delta plain, Killik 

Tongue of the Chandler Formation), nearshoremarine (delta front, Grandstand Formation), and 

offshore-marine (prodelta, Torok Formation) 

environments (fig. 22) (Fisher and others, 

1969). These environments prograded from 

southwest to northeast as the Cretaceous sea 

retreated from the area. However, minor transgressions and regressions resulted in complex 

interbedding of nearshore-marine and continental 

facies throughout the area. The Ninuluk Formation represents a transgression of tne sea over 

the delta-plain facies of the Killik Tongue. 

The interpretations of Fox and others 

(1979) generally agree with those of Fisher and 

others (1969). Evidence for the interpretations 

of Fox and others includes outcrop studies by 

Brosge and Whittington (1966), plus paleontologic, sedimentologic, and petrographic interpretations. 

The delta was prograding to the northeast, 

as indicated by thickness relationships shown 

on figure 22 (Fisher and others, 1969). The 

delta-plain facies of the Killik Tongue and the 

delta-front facies of the Grandstand Formation 

thin to the northeast of Umiat Anticline. At 

Wolf Creek Anticline, approximately 32 km west 

of Umiat, the Grandstand is about 378 m thick. 

At Umiat the Grandstand is about 195 m thick, 

thinning about 183 m in 32 km; the Grandstand 

is absent in the Fish Creek well, about 113 km 

north of Umiat. 

Grandstand Formation 

Three lines of compositional and textural 

evidence are used to infer the depositional 

setting of the Grandstand Formation. First, in 

the Knifeblade and Titaluk wells, 80-95 km west 

of Umiat (fig. 22), thin coal beds are common 

throughout the Grandstand. However, at Umiat, 

coal streaks and partings in the Grandstand are 

rare, suggesting more typical marine conditions. 

Second, according to Brosge and Whittington 

(1966), sandstone beds of the Grandstand at 

Umiat Anticline are cleaner (less interstitial 

clay and mica) than those to the west at Wolf 

Creek and Square Lake wells, possibly due to 

winnowing in the foreshore zone. Third, the 

grain size of sandstone of the Grandstand 

Formation decreases to the east, ranging from 

very fine to coarse at Knifeblade, very fine to 

medium at Titaluk, and very fine to fine at 

Wolf Creek and Square Lake (Brosge and 

Whittington, 1966). These regional compositional, textural, and thickness relationships 

suggest that the depocenter for Grandstand 

sandstones lay to the west-southwest of the 

Umiat area. This delta is referred to as the 

Umiat delta by Ahlbrandt and others (this 

volume). The aforementioned interpretation of 

depositional patterns in the Grandstand is 

further supported by the general coarseningupward gradation from shale to siltstone to 

sandstone at Umiat, indicating a progradational 

sequence. 

Faunal evidence suggests a shallow-water 

nearshore-marine environment for deposition of 

the Grandstand sediments at Umiat (fig. 21). 

Nearly all of the shale beds and some of the 

sandstone beds contain abundant benthonic 

arenaceous microfossils of the Verneulinoides 

borealis assemblage (Bergquist, in Collins, 

1958a). Arenaceous forams are commonly present 

in shallow nearshore-marine environments. A 

moderately rich assemblage of dinoflagellates, 

spores, and pollen also occurs throughout the 

Grandstand (May, this volume; E. I. Robbins, 

oral commun., 1976), as would be expected in 

sediments deposited in a nearshore-marine 

environment. The dinoflagellate assemblage is 

of middle to late Albian age (May, this volume). 

Marine invertebrate megafossils (primarily 

mollusks) occur throughout the Grandstand 

sequence (Brosge and Whittington, 1966). 

The following section presents a discussion 

of the compositional and textural aspects and 

the inferred environments of deposition of 

selected cores of the Nanushuk Group, Umiat 

test well 11. 

Cored interval 60 (911-916 m) (fig. 23) is 

near the base of the Grandstand Formation and 

the contact with marine siltstone and shale of 

the underlying Torok Formation. The very fine 

grained to fine-grained, well-sorted, subangular 

to angular nature of the sandstone and the 

predominance of thin, low-angle, parallel 

laminations that are interbedded with some 

homogeneous bioturbated beds indicate deltafront sands deposited in an upper-shoreface 

(bioturbated) and foreshore-marine (low-angle, 

parallel, thin laminations) environment. 

Cored intervals 56-58 (856-869 m) (fig. 

24) are near the top of the basal sandstone 

unit of the Grandstand. The fine-grained, 

well-sorted nature of the sandstone; the presence of a thin (0.6 m), homogeneous, bioturbated 

sandstone interval near the base, which is 

overlain by a thicker interbedded interval (4.5 

m) containing low-angle, parallel laminae; and 

small-scale lenticular crossbed sets support 

deposition as delta-front sands in a dominantly 

foreshore zone. This sequence grades upward 

into another bioturbated homogeneous sandstone 

45 
~ 

0') 

u g: I (l I ....___,_ i~ I A - 8 

0 

~1: ~ 

,:; 

r= 

~ L~ 111 3:: -i 

111 r= ::u 111 

C/1 C/1 

--1 

q 

8 

Lower Cretaceous Upper Cre 

taceous SERIES 

Chandler Formation 

~~;~ka I Nanushuk Group I I tion Grandstand l I -·· Format1on 

GROUP 

FORMATION 

Killik Tongue 

(:::::::::::::::::::::::::::::::::::::::::::::::::1 ~I: I: I: rl ~en~:e~l;1e2A 01 o, 

0!. Knife blade 

Q test well 1 

0 

3 (I) 

c: ;::;: Q.l» 

(/l "'0 

I» iii" ~ :;· 

0 (/l ., 

I» 10 ::l I» Q. ::l (/l ;:;· 

'!' 

MEMBER 

l> 

Composite of 

stratigraphic sections 'K:".-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.--~.,-,.,.,.,.,.,.,.,.,.,., ,., ,., ,., ,., ,., ,-, ,.,.,.,.,.,.,.,.,.,.,.).' Knifeblade wells 

" " - 1 to 4 

~ 

m 

-1 

1\l m 

~ 0~ .- "'T1 ...... 01 om o o m 

0 0 -1 0 

c.> 

-..j 

a> 

q 

-1 

0 

1l 

0 

Q. 

(I) 

;: 

3 

c: 

of Titaluk 

Square 

1 :1>:. 

~ L--...-----, 8 Q. 

(/l 

8 

01_ 

-1 

0 

Torok Formation 

_."11 

011» 

01~ ,,, ... ~ 

~ 01 

c..l"'TI w c..ll» ~ IOc: ~ Q;::;: 

0 ' 

Grandstand 

Formation 

Nanushuk Group 

Lower Cretaceous ·-->Upper Cretaceous 

of Umiat 

MEMBER 

FORMATION 

GF<OUP 

SERIES 
<J 

~ D.. 

w 

0 

z 

0 0 i= Ill 

~ l ~ 0 

LL 

Meters Feet 

911.35 - 2990 

-

912.88 - 2995 

-

914.40 - 3000 

-

915.92 - 3005 

> 0:: 

< 

1-

z 

w 

:1 

i5 

w 

Ill 

w 

0:: 

:::> 

1-

u 

:::> 

0:: 

II/) 

TOP OF CORE #60 

C!) 

~ 

~ 0 

Ill 

WELL 

Ill 

lf1 

z 

0 

z 

:::> 

0 

0:: 

SBAN6-

AN6 

0 

w 

0:: 

~ 

w 

LL 

~ 

1- z ~ 0 :1 i= 

Z LL ~ 

~ 0 0 

> fli z 0 w 

DELTA FRONT 

(FORESHORE) 

I 

(UPPER 

SHOREFACE) 

(FORESHORE) 

(UPPER 

SHOREFACE) 

(FORESHORE) 

(UPPER 

SHOREFACE) 

(FORESHORE) 

(UPPER 

SHOREFACE) 

~ 

EXPLANATION 

SYMBOLS: 

L/{:/:/J Sandstone 

~ Tabular crossbedding 

~ Parallel laminations 

1::~01 ~ _ _ Wavy parallel laminations 

1-zor"""" I Bioturbation 

ABBREVIATIONS: 

VFn Sd - very fine grained sand 

Fn Sd - fine-grained sand 

Med Sd - medium-grained sand 

Cse Sd - coarse-grained sand 

Pbl -pebble 

Ang - angular grains 

Sbang - subangular grains 

Well - well-sorted grains 

Figure 23.--Lithology, sedimentary structures, texture, and inferred environment of deposition, 

core 60, Grandstand Formation, Umiat test well 11. 

Figure 22.--Deltaic interpretation of Lower Cretaceous rocks of eastern NPRA. 

others (1969). Location of test well sites shown by A-A'. 

From Fisher and 

unit, reflecting a slight marine incursion and 

deposition of delta-front sands in a shoreface 

zone. A thin shale bed (0.3 m) separates the 

aforementioned 4.5-m-thick sandstone interval 

from the overlying sequence of sandstone, which 

is of approximately the same thickness. This 

upper sandstone unit differs from the lower by 

having more carbonaceous laminae, more abundant 

rippled laminae (asymmetric), and near absence 

of bioturbation. Occasional flooding during 

deposition of this upper sandstone unit may 

have been responsible for the abundant carbonaceous detritus being carried so far offshore 

and for the formation of the higher energy 

asymmetric ripples. These thin carbonaceous 

laminae may be time-equivalent to thicker coal 

stringers to the west. 

The sequence of predominantly nearshoremarine sandstone is overlain by a marine shale 

sequence (55 m), reflecting continued transgression of the sea. Abundant arenaceous and 

calcareous benthonic foraminifera, abundant 

dinoflagellates, and some spores and pollen 

exist in the shale. This combination of fossils 

is commonly found in modern nearshore-marine 

environments. This shale sequence may have 

been deposited as prodelta muds. 

Cores 52 and 53 (745-750 m) (fig. 25) are 

from about 3 m below the top of the Grandstand 

Formation. This sandstone interval is similar 

to the lower (4.5-m) interval just described 

from cores 56-58 and is also interpreted as a 

delta-front sand deposited in a foreshore 

environment. However, correlation with coal 

stringers to the west-southwest of Umiat is not 

obvious. The only evidence is black carbon 

grains evenly disseminated throughout the 

sandstone and concentrated in thin laminations 

on bedding surfaces. As was the case with the 

foreshore sandstone of interval 60, the sandstone of this interval is also overlain by a 

transgressive shale. In this interval the 

shale is only 10 m thick and contains a rich 

fauna of arenaceous forams (Bergquist, in 

Collins, 1958a). 

Chandler Formation (Killik Tongue) 

The Chandler Formation is predominantly 

nonmarine at its type locality where it consists 

of two major tongues, the Killik Tongue and the 

Niakogon Tongue (Detterman, 1956). The Niakogon 

Tongue is not differentiated from the Ninuluk 

Formation in the Umiat area (Brosge and 

Whittington, 1966). 

Brosge and Whittington (1966) interpreted 

the sandstone, siltstone, shale, and coal of 

the Killik Tongue in the area to the southwest 

of Umiat as having been deposited in fluvial 

and related environments. Between this area 

and Umiat, a facies change occurs, from the 

well-developed delta-plain facies just described 

to a dominantly nearshore-marine facies at 

Umiat. Moreover, at Umiat, coal in the Killik 

Tongue is restricted to just a few thin stringers (10 em) near its top. Furthermore, the 

Killik Tongue progressively thins in a northeasterly direction, from about 1,036 mat 

47 
I: 

..... c lh z c <( 

Meters 

-

858-01 -

-

z 

0 

j: (/) 

<( n. ::!: 0 0:: ..... 

0 

IL 

Feet 

2815 

8 59.53 - 2820 

-

-

862.58 -

-

864.10 - 2835 

-

865.63 - 2840 

-

w 

n. 

> 

..... 

~ 

(.) 

0 

0:: 

> 

0:: 

<( 

..... 

z 

w 

::!: 

0 

w 

(/) 

w 

0:: 

:J 

..... 

(.) 

:J 

0:: 

In 

TOP_OF CORE 

:·,:.):\ :.'·:·:::'.'.'· '::;:;. ~ 

- :::',:< 0::=~: ··:·:: ::: ,_:::. 

-i:?.'/2\/\:': ·::/:-:: ~ ~ 

(.';}\.'!D\h}//>=~ ~ - MA; ~ - ~-~-.· .-:.·: ' ....... ,........ "- ,..,_ 

:.:::,;:-::: /\.:·?' ...,_ ~"'- ~ 

;:: 

~ z <( < z 0:: 

~ (!) 

0 

c 

.... 

-

w 

N 

iii 

t--t--t--

t--t--t--

t--t--t--

f--r--r--

(!) 

z 

j: 

0:: 

0 

(/) 

(/) 

(/) 

w 

z 

c 

z 

:J 

0 

0:: 

WELL ANG-

) SBANG 

WELL SBANG 

I f WELL ANGI 

( 

ANGSBANG 

J 

c. 

w 

0:: 

0:: 

w 

IL 

~ 

..... 

z 

w 

::!: 

z 

0 

0:: 

> z 

w 

IL 

0 

z 

0 

E 

(/) 

0 

lh 

c 

DELTA FRONT 

(FORESHORE) 

(UPPER 

SHOREFACE) 

(FORESHORE) 

EXPLANATION 

SYMBOLS: 

~ 

~ 

~ 

~ 

~ 

§ 

§ 

[?2?J 

Q 

1~-w-1 

Sandstone 

Mudstone 

Tabular crossbedding 

Trough crossbedding 

Parallel laminations 

Wavy parallel laminations 

Discontinuous wavy 

nonparallel laminations 

Curved parallel laminations 

Ripple lamination 

Bioturbation 

ABBREVIATIONS: 

VFn Sd - very fine grained sand 

Fn Sd - fine-grained sand 

Med Sd - medium-grained sand 

Cse Sd - coarse-grained sand 

Pbl -pebble 

- ~r+~f--+--+---+--+---4---------------

t:::t::::t:::: 

Ang - angular grains 

Sbang - subangular grains 

Well - well-sorted grains 

t-r--r--

1-f--f-- I 867.15 - 2845 t-r--r-- WELL SBANG 

-

868.68 - 2850 I 

t-t--r--

t-r--r--

t-r--r--

(UPPER 

SHOREFACE) 

Figure 24.--Lithology, sedimentary structures, texture, and inferred environment of deposition, 

cores 56-58, Grandstand Formation, Umiat test well 11. 

Knifeblade Anticline (fig. 22) to about 90 m at 

Umiat. This thinning is depositional, reflecting increased distance from the source area. 

At Umiat, the Killik Tongue contains a 

nearshore-marine dinoflagellate and acritarch 

assemblage of low to moderate diversity. This 

assemblage is used to establish an age of 

middle Albian to early Cenomanian(?) (May, this 

volume). 

Core 49 (724-729 m) (fig. 26) is from the 

Killik Tongue. The sandstone of this core is 

fine to very fine grained, well sorted, and 

subangular; it consists of small-scale, lenticular, crossbed sets of thin laminae interbedded 

with small-scale, low-angle, parallel sets of 

thin laminae. 

Although the sedimentologic data are not 

definitive, the flora and fauna, textural 

attributes, and thickness trends suggest deposition near the marine shoreline; the welldeveloped delta-plain facies lies to the west. 

Ninuluk Formation 

In the Umiat area the Ninuluk Formation 

overlies the Killik Tongue of the Chandler 

Formation and is the ~oungest dominantly marine 

formation of the Nanushuk Group. The Ninuluk 

·thins from about 280m near Weasel Creek 

Anticline (fig. 20) to about 29 m at Umiat, a 

distance of about 48 km to the northeast (Brosge 

and Whittington, 1966). This trend to the 

48 
I 

t 

w 

0 

0 

z 

<( 

Meters 

745.43-

-

746.95-

-

748.48-

-

750.00-

z 

0 

i= 

<( 

::E 

11:: 

0 

IL 

(/) 

0.. 

0 

1-

Feet 

= 

II: 

u 

0 

0:: 

w 

0.. 

> 1-

> 

11:: 

<( 

1-

z 

w 

::E 

0 

w 

(/) 

w 

11:: 

:J 

1-

u 

:J 

11:: 

1-

(/) >. 

., 

u 

1-

z 

<( z w z :;{ N 

~ 11:: Ui l!) 0 

0 , , (/) 

, (/) , (/) , c (/) , .., ~ IL c .., ::E iii > IL ::E u "'

• 

(/) 1- z l!) (/) 0 z 0 z w w w z i= 11:: ::E i= 0 11:: z IL Ui 11:: z w 0 0 0 0 :J IL 11:: 0.. (/) 0 ~ > w 11:: 0 jj z 0.. w 

DELTA FRONT WELL ~~~~G- (FORESHORE) { 

I If 

YlfELL SBANGEXPLANATION 

SYMBOLS: 

~ Sandstone 

~ Tabular crossbedding 

~ Trough crossbedding 

~ Parallel laminations 

a Discontinuous wavy ~ nonparallel laminations 

ABBREVIATIONS: 

VFn Sd - very fine grained sand 

Fn Sd - fine-grained sand 

Med Sd - medium-grained sand 

Cse Sd - coarse-grained sand 

Pbl - pebble 

Ang - angular grains 

Sbang - subangular grains 

Well - well-sorted grains 

Mod - moderately sorted grains 

Figure 25.--Lithology, sedimentary structures, textures, and inferred environment of deposition, 

cores 52 and 53, Grandstand Formation, Umiat test well 11. 

1-

> w z w z 11:: 0:: <( 

0.. <( :J z :;{ > 1- 1- ~ 0:: 1- z u l!) 

II: w :J 0 

u ::E 0:: 0 

0 i5 1- , 0:: w (/) 1/) 

~ , c (/) ~ IL u ::E ii) > 

z I 0 0 i= 1/) 

~ z <( 0.. 

w <( ::E 0 

0 0:: 1-

0 

IL 

!Meters Feet 

- TOP OF CORE 

723.90 -

-

-- 725.42 -

-

726.94 -

-

728.47 -

-

-

-

w 

N l!) 

iii ~ 0:: , , 0 , (/) (/) (/) 

(/) , .., c .., Ill jj 

IL ::E u 0.. 

WELL 

I 

\ 

(/) 

(/) 

w 

z 

0 

z 

:J 

0 

0:: 

iS BANGlANG 

I 

DELTA FRONT 

(FORESHORE) 

EXPLANATION 

SYMBOLS: 

W/.)\f(j Sandstone 

~ Tabular crossbedding 

~ Trough crossbedding 

~ Parallel laminations 

~ ~~ Wavy parallel laminations 

~J Curved parallel laminations 

ABBREVIATIONS: 

VFnSd - very fine grained sand 

Fn Sd - fine-grained sand 

Med Sd - medium-grained sand 

Cse Sd - coarse-grained sand 

Pbl - pebble 

Ang - angular grains 

Sbang - subangular grains 

Well - well-sorted grains 

Figure 26.--Lithology, sedimentary structures, texture, and inferred environment of deposition, 

core 49, Killik Tongue of the Chandler Formation, Umiat test well 11. 

northeast in direction of thinning is similar 

to that previously described in underlying 

rocks of the Nanushuk Group. In contrast, the 

overlying marine sequence of the Upper Cretaceous Seabee Formation thickens to the northeast. 

49 

In the Maybe Creek area, approximately 64 

km west of Umiat, the Ninuluk consists of 

complexly interbedded sediments containing 

nonmarine fossils and coal interbedded with 

beds containing shallow-marine fossils (Brosge 

and Whittington, 1966). 
Cores 35-38 (624-639 m) (fig. 27) are from 

the Ninuluk Formation. These rocks are predominantly very fine grained to fine-grained, 

moderately well sorted to well-sorted, angular 

to subangular sandstone. A thin unit (1.2 m) 

near the base is moderately well to poorly 

sorted, is angular to rounded, and contains 

coaly laminae. In this basal unit are thin 

beds of poorly sorted clay pebble conglomerate 

(clay clasts as large as 2.5 em in diameter) in 

a clay matrix, which are interbedded with 

moderately well sorted, thin, very fine grained 

to fine-grained beds. Immediately above this 

basal 1.2-m unit, small-scale, curved-parallel 

and discontinuous, wavy, nonparallel coaly 

laminations are present. The lower part of 

this interval contains a moderately abundant 

assemblage of dinoflagellate (F. E. May, oral 

commun., 1978). These were not datable, but 

they are similar to those of the underlying 

Killik Tongue (middle Albian to early Cenomanian) (May, this volume). In turn, above 

that interval are small-scale, low-angle, 

parallel laminae of sandstone interbedded with 

homogeneous unstructured sandstone overlain by 

a few thin sandstone beds (15 em) having lenticular crossbeds. The upper part of the cored 

interval was barren. 

On the basis of sedimentary structures, 

fossils, and thickness trends, the Ninuluk in 

the Umiat area was deposited, in large part, as 

delta-front sands in a shallow-marine foreshore 

environment, seaward from the typical deltaplain facies of the Ninuluk at the Maybe Creek 

area to the west (fig. 22). The basal 1.2-mthick unit may be a fluvial deposit of a 

delta-plain environment or an intertidal mud 

flat. 

Petrography 

Grandstand Formation and Killik Tongue of 

Chandler Formation 

Detrital clasts.--The following petrographic summary is from Lambert (in Fox and 

others, 1979). Rock samples that were analyzed 

from the Grandstand Formation and Killik Tongue 

of the Chandler Formation are petrographically 

similar. They are primarily composed of wellsorted, very fine to fine, angular to subangular 

detrital grains. These sandstones, although 

texturally mature, are compositionally immature, 

consisting of little quartz, much chert and 

metamorphic rock fragments, and minor feldspar. 

Mineralogically they are classified as chert 

arenites and phyllarenites (fig. 21), relatively 

poor in quartz and rich in lithic fragments. 

Quartz grains are generally strained. Most 

plagioclase grains exhibit albite twinning and 

are generally unzoned and unaltered; grains of 

alkalic feldspar are also mostly unaltered. 

Detrital chert is mostly microcrystalline. 

Chert clasts contain inclusions of clay, 

euhedral crystals of pyrite and dolomite, and 

50 

patches of length-slow and length-fast chalcedonic chert. 

Metamorphic rock fragments include phyllite 

and metaquartzite. Phyllite fragments are 

composed of sericite, chlorite, and anhedral 

crystals of quartz and are squeezed between and 

around other harder detrital grains forming 

pseudomatrix. Metaquartzite fragments are 

identical to phyllite fragments, but contain 

more than 50 percent quartz. This quartz 

content is highly variable. Deformation of 

metaquartzite fragments depends on the abundance 

of sericite; the greater the sericite content, 

the greater the deformation. 

Another assemblage of rock fragments 

exists in trace amounts in several samples. It 

consists of plagioclase microlites oriented in 

a random or subparallel arrangement in a chloritic groundmass. In some samples groundmass 

is more abundant than plagioclase; in others it 

is less abundant. 

Biotite is a minor accessory mineral, 

which is sometimes partially altered to chlorite. Organic matter exists as highly deformed 

masses and stringers as long as 4 mm; it lacks 

cellular form. Other detrital components occur 

in small amounts and will not be discussed. 

(Refer to Fox and others (1979) for further 

information.) 

Matrix material.--The amount of matrix 

(smaller than 30 ~m) is highly variable, and 

matrix is of both detrital and authigenic 

or1g1n. The matrix consists of sericite and 

chlorite flakes and quartz grains, most of 

which are detrital and have resulted from 

disintegration during weathering and erosion of 

parent rock (phyllite and metaquartzite) and 

abrasion during transportation. Illite, chlorite, and kaolinite have been detected by J. K. 

Pitman (written commun., 1978) in the <2~m 

fraction via X-ray diffraction analysis. The 

presence of a sharp, well-ordered 10-A peak for 

clay material identified as illite may indicate 

that it is detrital sericite rather than authigenic illite. Chlorite peaks are also sharp 

and well ordered; the chlorite may be, in part, 

detrital metamorphic rather than authigenic. 

Smectite was not detected. However, many of 

the larger detrital grains are etched and 

slightly embayed by matrix material, indicating 

an authigenic origin of at least some of the 

matrix phyllosilicates. Also, coatings of what 

is very likely authigenic(?) sericite, chlorite, 

and possibly illite exist locally along some of 

the larger detrital grain contacts. 

Quartz overgrowths commonly exist on 

detrital quartz grains, projecting into, but 

rarely completely filling, intergranular pores. 

Other authigenic minerals include intergrown 

masses of vermicular crystals of kaolinite that 

completely fill some pores. Chert, pyrite, 

small flakes of chlorite, and several kinds of 

carbonate minerals also are present. These 

carbonate minerals include dolomite rhombs, 
I Meters 

0 

z 

<( 

-

624.84-

-

626.36 -

-

627.88 -

-

629.41 -

-

630.93 -

-

632.46 -

-

633.98 -

-

635.50 -

-

637.03 -

-

z 

0 

i= II) 

<( D.. 

::E 0 It: 1-

0 

IL 

Feet 

-

-

-

- TOP OF CORE 

- vt\;:::·:=:.=::: ·:: • .::-·.~ - :..... ~-

2050 : r:\:/;".?·}i;.:_::; ':.'.' 

- 2055 

!z 

<( 

z 

~ 

0 

0 

WELL 

WELL 

( 

II 

I 

I 

II) 

II) 

ILl 

z 

0 

z 

::'l 

0 

It: 

ANGRND 

0 

~ It: 

ILl 

IL 

~ 

1-

z 

ILl 

::E 

Z 1L 

0 0 !!;; 

> 

~ 

z 

0 

i= 

(j) 

0 

D.. 

ILl 

0 

DELTA FRONT 

(FORESHORE) 

DELTA PLAIN 

(FLUVIAL?) 

EXPLANA TlON 

SYMBOLS: 

~ Conglomerate 

['i((.};~~;J Sandstone 

~Claystone 

~Coal 

~ Tabular crossbedding 

Trough crossbedding 

Parallel laminations 

Wavy parallel laminations 

Discontinuous wavy 

nonparallel laminations 

Curved parallel laminations 

Microcross- laminations 

ABBREVIATIONS: 

VFn Sd - very fine grained sand 

Fn Sd - fine-grained sand 

Med Sd - medium-grained sand 

Cse Sd - coarse-grained sand 

Pbl - pebble 

Ang - angular grains 

Sbang - subangular grains 

Rnd - round grains 

Well - well sorted grains 

Mod - moderately sorted grains 

Poor - poorly-sorted grains 

Figure 27.--Lithology, sedimentary structures, texture, and inferred environment of deposition, 

cores 35-38, Ninuluk Formation, Umiat test well 11. 

which often replace adjacent detrital silicate 

and siderite grains. These rhombs are single 

crystals of subhedral to euhedral form, which 

are distributed evenly through the rock or 

which occur as equidimensional clusters as much 

as 250 ~m across. Calcite is commonly present 

in small amounts, as sparry anhedral to rhombshaped individuals, each composed of one crystal, or as many small anhedral crystals that 

51 

may represent recrystallized, originally detrital carbonate grains. Many of the grains have 

twin lamellae that are unbent, suggesting 

further that recrystallization occurred after 

compaction. Less commonly, calcite occurs as 

large, optically continuous (poikilotopic) 

crystals as much as 800 ~m across that slightly 

replace detrital silicates. 
Porosity.--Porosity and permeability are 

high for the Grandstand and Killik samples 

studied (fig. 21). Most porosity is primary 

and intergranular; secondary porosity due to 

leaching of feldspar grains is minor. Visible 

pores (visible at magnifications up to about 

800x) have an average size of about 50 vm. 

They are generally triangular, equant, or 

crescent-shaped spaces between noncompressible 

grains such as quartz, feldspar, and chert. 

Many of the pore walls are formed of straightedged quartz overgrowths, and these are free of 

phyllosilicate coatings. 

Ninuluk Formation 

Detrital clasts.--The sandstone samples 

studied from the Ninuluk Formation are very 

fine to fine grained. They are relatively poor 

in quartz and rich in chert and metamorphic 

rock fragments, characteristics similar to 

those of the previously discussed Grandstand 

Formation and Killik Tongue (fig. 21). However, 

other petrographic features of the Ninuluk 

contrast sharply with those of the underlying 

units. First, Ninuluk rocks are more poorly 

sorted, often with a bimodal distribution. 

Second, metamorphic rock fragments are more 

abundant than chert fragments, which is not the 

case for the Grandstand and Killik. Metaquartzite fragments are very common and constitute a 

greater portion of rock fragments in the Ninuluk 

than does phyllite in the underlying units, 

where phyllite is the most abundant. Ninuluk 

samples also contain less detrital quartz than 

do those of the Grandstand and Killik. The 

Ninuluk contains a considerable amount of 

carbonate in its upper part. 

Some phyllite fragments contain relatively 

large flakes of sericite (as large as 100 vm in 

diameter), some contain biotite, and others 

contain clinozoisite(?). The phyllite grains 

are wedged between noncompressible detrital 

grains and, when present, form abundant pseudomatrix that significantly reduces both porosity 

and permeability. 

Matrix material.--Matrix material in the 

Ninuluk, as determined by X-ray diffraction 

analysis, consists of illite, chlorite, and 

kaolinite; smectite is absent (fig. 21). In 

thin section the matrix material is the same as 

that in the Grandstand and Killik, previously 

discussed. 

Authigenic cement in sandstones studied 

consists of calcite, quartz, siderite, and 

chlorite. Calcite in the Ninuluk exists mainly 

as anhedral to euhedral crystals that may be 

recrystallized detrital carbonate grains. Many 

of the grains exhibit twinning, a condition 

similar to that in the Grandstand and Killik. 

Much calcite, though, is definitely authigenic 

and replaces detrital silicate and detrital 

calcite grains along grain boundaries. Quartz 

overgrowths are less abundant in the Ninuluk 

52 

Formation than in the Grandstand Formation and 

Killik Tongue. Siderite crystals occur in 

great numbers along boundaries of detrital 

silicate grains. Siderite grains preferentially 

replace phyllite fragments and locally replace 

calcite. They occur along the contact between 

detrital quartz and quartz overgrowths, but not 

on free surfaces of quartz overgrowths. 

Sparse, green, finely crystalline aggregates of 

chlorite may be authigenic. 

The abundance of metamorphic rock fragments, chert, and detrital carbonate grains, 

and the low content of quartz suggest that the 

source rocks for these sandstones were dominantly limestone and low-grade metamorphic rocks, 

most probably from pre-Cretaceous rocks that 

are present in the Brooks Range to the south 

(Brosge and Tailleur, 1971; Grybeck and others, 

1977; Bartsch-Winkler, this volume). 

Porosity.--Porosity is mostly intergranular. Visible pores average about 35 vm in size 

and are triangular, equant, or elongate. They 

are not filled with matrix, deformed phyllite 

grains, or authigenic carbonate. 

RESERVOIR QUALITY 

The following conclusions regarding factors 

having an effect on porosity and permeability 

of the Grandstand Formation, Killik Tongue of 

the Chandler Formation, and Ninuluk Formation 

are based on a comprehensive petrographic study 

by Lambert and log study by Wu (in Fox and 

others, 1979). On the basis of petrography, 

Lambert made the following conclusions regarding 

reservoir quality: 

1. No relationship exists between compaction (influenced by depth of burial) and porosity and permeability; deeper samples in Umiat 

test well 11 are just as porous and more permeable than shallow samples. This is due to 

abundant intergranular porosity in deeper 

samples and abundant matrix in shallower samples. 

2. Modal grain size is a minor factor 

affecting porosity and permeability. Porosity 

and permeability in all samples increase with 

increasing grain size; a minimum grain size of 

about 175 vm is necessary for good permeability 

(>50 md). 

3. Rocks with the best porosity and 

permeability have very low amounts of compressible grains, matrix, and authigenic carbonate. 

Rocks with the best permeability are chert 

arenites, and those with the poorest permeability are phyllarenites. 

4. Factors controlling phyllite and 

matrix abundance may be related to environment 

of deposition. In high-energy environments, 

phyllite fragments may be disintegrated and 

winnowed away, leaving a more porous and permeable sandstone. The best reservoirs can be 

expected in those parts of the basin where 
high-energy conditions (beaches) existed and 

(or) where only sparse amounts of metamorphic 

rock debris were being deposited. 

5. Petrographically identical phyllite 

fragments occur in both high- and low-phyllite 

sandstones. But, on the other hand, changes in 

phyllite content occur through small vertical 

distances (2-3m). Because of these characteristics, change in provenance does not seem to 

be a factor controlling phyllite abundance in 

Nanushuk rocks of Umiat well 11. 

6. As modal size of visible pores decreases, so does permeability. 

7. As percent of pore wall coated by 

phyllosilicate increases, permeability decreases. 

Porosity values were calculated for each 

of the formations by Wu (in Fox and others, 

1979) using cores and well logs. Weighted 

average porosity values are as follows: 

Lower part of the Grandstand Formation--15.1 

percent; 

Upper part of the Grandstand Formation--15.6 

percent; 

Killik Tongue, Chandler Formation--16.4 

percent; 

Ninuluk Formation--12.6 percent. 

Wu (in Fox and others, 1979) studied relationships between porosity and permeability and 

found that a linear relationship may exist 

between porosity and permeability for rocks at 

depths less than 400 m and for rocks at depths 

greater than 640 m (fig. 28). Permafrost may 

affect the porosity and permeability at depths 

of 400 m or less. Wu predicted that the permeability of rocks at depths greater than 640 m 

will be less than 1 md if porosity is less than 

9 percent. 

Weighted average permeability values are 

as follows: 

53 

Lower part of the Grandstand Formation--58.6 

md; 

Upper part of the Grandstand Formation--

167.0 md; 

Killik Tongue, Chandler Formation--96.2 md; 

Ninuluk Formation--10.7 md. 

-

Q 100 

::E 

-

~ 

~ 

• I I· 

I 

{. 

' i 

I . 1 --

I• 

r 

I 

I 

I 

I 

I 

I 

I 

I 

0 

PERMAFROST 

ZONE(?) 

~DEPTH LESS THAN 400M 

-4-DEPTH GREATER THAN 

640M 

POROSITY (OJo) 

Figure 28.--Porosity and permeability relationships of Cretaceous rocks, Umiat test well 

11. 
HYDROCARBON SOURCE POTENTIAL OF THE 

NANUSHUK GROUP AND THE TOROK FORMATION, 

A PRELIMINARY REPORT 

By Leslie B. Magoon and George E. Claypool 

INTRODUCTION 

Preliminary results are presented here for 

the hydrocarbon source potential of three wells 

and one outcrop section of the Nanushuk Group 

(Lower and Upper Cretaceous) and part of the 

underlying Torok Formation (Lower Cretaceous). 

Additional data on these rocks have yet to be 

acquired, which could modify some of these 

observations. 

The data presented here are part of a 

larger oil and gas source-rock study that has 

two objectives: (1) to help locate and evaluate 

the wells being drilled in NPRA (National 

Petroleum Reserve in Alaska), and (2) to provide 

a data base for a more objective oil and gas 

resource appraisal of NPRA. Geochem Research, 

Inc., under the direction of Stephen J. Martin, 

is primary contractor for the basic analytical 

work. Global Geochemistry, secondary contractor, is doing some of the more specialized 

analytical work. Petroleum Information Corp. 

is building the geochemical data file and 

providing most of the graphical displays. We 

are responsible for the overall management, 

design, and interpretive results of the NPRA 

source-rock program, which includes monitoring 

of quality control and initial interpretation 

of the data. The outcrop samples analyzed for 

this paper were provided by Thomas S. Ahlbrandt. 

The core material from the wells came from the 

U.S. Geological Survey sample library in 

Anchorage, Alaska. 

The location of the four sections of the 

Nanushuk Group included in this report are 

shown in figure 10 (Bird and Andrews, this 

volume) and, from west to east, are as follows: 

(1) type section of Kukpowruk Formation (sec. 

22, T. 2 S., R. 45 W.); (2) Kaolak No. 1 well 

(sec. 25, T. 7 N., R. 34 W.); (3) Topagoruk No. 

1 well (sec. 25, T. 15 N., R. 16 W.), and (4) 

Umiat test well 11 (sec. 27, T. 1 N., R. 1 W.). 

Rather than discuss the amount and type of 

organic material and thermal history of each 

outcrop or well individually, comments will be 

made about each analytical parameter for all 

the sections, with a summary at the end. 

54 

AMOUNT AND TYPE OF ORGANIC MATERIAL 

Organic Carbon Content 

Total organic carbon content is measured 

by the combustion method; it includes both 

"live" carbon--that which can be converted to 

organic compounds--and "dead" carbon. The 

observed organic carbon content, in.weight 

percent, ranges from a low of 0.19 to a high of 

69.79 and is generally greater than 1 (table 

3). Many of the high values are attributed to 

coal. Values for the Kukpowruk type section, 

in which very little coal occurs, range from 1 

to 2 weight percent, whereas in the Kaolak No. 

1 well, the Nanushuk Group includes coaly beds 

that contain more than 5 weight percent organic 

carbon (fig. 29). The Nanushuk Group in the 

Topagoruk No. 1 well and Umiat test well 11 has 

organic carbon values of less than 5 and little 

or no coal is logged (fig. 30). 

A commonly accepted lower limit of organic 

carbon for a hydrocarbon source rock is 0.4 

(Dow, 1977a, p. D2). On the basis of this 

criterion, much of the Nanushuk Group and Torok 

Formation are potential hydrocarbon source 

rocks; and, indeed, oil shows were encountered 

while drilling Kaolak No. 1 well, Topagoruk No. 

1 well, and Umiat test well 11 (Collins, 1958a, 

b, c; figs. 29 and 30). 

TEA-FID 

Thermal-evolution analysis employing a 

flame ionization detector (TEA-FID) was used to 

evaluate the richness, type, and thermal maturity of organic matter in sedimentary rocks of 

the Nanushuk Group. In this analysis, a small 

sample of rock is heated under controlled 

conditions and hydrocarbons are measured as 

they are thermally evolved from the rock. 

Response of the detector is calibrated by 

analysis of known amounts of synthetic standard 

(4.24 percent n-CzoH42 on Alz03). Separately 

measured are (l) hydrocarbons present in the 

rock (peak I), and (2) the absolute temperature 

required to cause a maximum in pyrolysis prod-
ucts of the organic matter in the rock (T peak 

II°C). General interpretation of the results 

of this type of analysis is summarized by 

Barker (1974a, b), Claypool and Reed (1976), 

and Espitalie and others (1977). 

Analyses of rock samples by TEA-FID are 

listed in table 3. Total pyrolytic hydrocarbon 

yield (PHC) is the sum of peak I and peak II, 

reported in weight percent relative to the dry 

weight of the rock. Volatile hydrocarbon 

content (VHC) is the area of peak I only; it is 

reported in weight parts per million because 

this measurement is roughly equivalent to the 

amount of extractable hydrocarbons, which 

conventionally are expressed in parts per 

million. Also listed in table 3 is the ratio 

of pyrolytic hydrocarbon yield to organic 

carbon (PHC/OC). This ratio is analogous to 

the "hydrogen index" of Espitalie and others 

(1977), except that the numerator of our ratio 

is both peak I and peak II, whereas Espitalie 

and others (1977) used the ratio of peak II to 

organic carbon. 

PHC/OC, expressed as percent, is sensitive 

to both types of organic matter and thermal 

maturity. That is, PHC/OC can be low because 

(1) the type of organic matter originally is 

hydrogen-deficient and does not yield hydrocarbons upon pyrolysis, or (2) the organic 

matter is hydrogen-deficient because it is 

thermally post-mature or "overcooked" and has 

previously yielded hydrocarbons. Because none 

of these analyzed rocks are post-mature, the 

results can be interpreted in terms of type of 

organic matter, or the proportion of the total 

organic matter that is "live" and can be converted to hydrocarbons. In this sequence, 

coals and organic matter believed to be more 

"gas-prone" have PHC/OC values of 10-20 percent. 

Potential oil source rocks should have PHC/OC 

values of 30-60 percent, indicating hydrogenrich organic matter (Espitalie and others, 

1977). In terms of this measurement, the 

Nanushuk Group and the Torok Formation are 

"gas-prone," as almost all values are less than 

26 percent (table 3). 

Elemental Analysis 

Elemental analysis of kerogen includes 

values for carbon (C), hydrogen (H), nitrogen 

(N), and ash (table 3). Elemental analysis is 

also a useful indicator of "oil-prone" vs "gasprone" source rocks when values of H and C are 

used to derive the atomic H/C ratio. This 

ratio is determined by dividing the percentage 

of each element in the kerogen by its atomic 

number (H=l.008 and C=l2.01), and then reducing 

the fraction to its decimal equivalent. If the 

kerogen is thermally immature and the values 

are greater than 1.0, then the source rock is 

"oil-prone"; if the ratio is less than one, the 

source rock is "gas-prone" (Harwood, 1977). As 

"oil-prone" kerogen undergoes increased thermal 

alteration, the ratio decreases ~o a value less 

55 

than 1.0, because more hydrogen than carbon is 

lost with the generated and expelled hydrocarbons. 

The data obtained for the Nanushuk Group 

and Torok Formation show ratios of less than 

1.0, or "gas-prone" source rocks. The Kukpowruk 

type section and Kaolak No. 1 well display a 

decrease in the atomic H/C ratio with increasing 

depth; both start at 0.8 and decrease to about 

0.6-0.7. Umiat test well 11 remains at about 

0.7. An exception to this pattern is the 

Topagoruk No. 1 well, in which the atomic H/C 

ratio increases toward the bottom of the hole 

from 0.6 in the Nanushuk Group to 0.8 in the 

pebble shale unit, even though the vitrinite 

reflectance values increase substantially with 

depth. The increase in the atomic H/C ratio 

suggests that the lower interval of the Torok 

Formation and the underlying pebble shale unit 

are richer in hydrogen, even though that part 

of the section is more mature. 

Visual Kerogen 

Rocks rich in organic matter are treated 

with hydrochloric and hydrofluoric acids to 

remove carbonate and siliceous material. The 

kerogen is placed on a glass slide and examined 

by microscope using transmitted light •. Four 

kerogen constituents can be identified: (1) 

amorphous, (2) herbaceous, (3) humic, and (4) 

inert. Amorphous material is algal material or 

sapropel of marine or lacustrine derivation and 

is "oil-prone." Herbaceous material includes 

pollen, spore and plant cuticle, or waxy material; it is generally considered "oil-prone" but 

may also contribute methane gas. Humic material 

constitutes the structural material of land 

plants and makes up a large percentage of humic 

coal. This constituent is "gas-prone." Inert 

is solid black "dead" carbon, which contributes 

neither oil nor gas to the hydrocarbon system. 

The abundance of these four constituents is 

visually estimated and expressed as percentages 

that add up to 100 percent of the material on 

the slide. 

The visual kerogen estimates of the 

Nanushuk Group indicate that at least 50 percent 

of the constituents are herbaceous and amorphous 

material, or "oil-prone" source rocks (table 3, 

figs. 29 and 30). The woody constituent represents less than 25 percent of the total. These 

data appear to contradict the PHC/OC and H/C 

ratios, which suggest that these rocks are 

"gas-prone." If the herbaceous material is 

considered "gas-prone," then the three parameters agree. This apparent discrepancy warrants 

further investigation. 

INDICATORS OF THERMAL HISTORY 

TAI 

As the constituents of visual kerogen are 

being determined, the thermal alteration index 

(TAI), a color variation, is observed and 
Table 3.--0rganic geochemical data for the Nanushuk Group, Torok Formation, and pebble shale unit, 

North Slope, Alaska 

[Data based on material from two outcrops and core from three wells; Sh, shale; Ss, sandstone; Co, coal; Lith, lithology; TAI, thermal alteration index; 

Mn Ro, minimum reflectance; Av Ro, average reflectance; Mx Ro, maximum reflectance; TEA-FID, thermal-evolution analysis employing a flame ionization 

detector; Tpll°C, absolute temperature at which a maximum occurs in the pyrolytic products of organic matter in the rock; PHC, total pyrolytic hydrocarbon yield; VHC, volatile hydrocarbon content; OC, organic carbon; Am, amorphous; Hr, herbaceous; Hu, humic; In, inert. Leaders (---) indicate that 

the me.:1surement was not made] 

Sample No. 

Rock Unit or depth (m) 

Nanushuk 

Group 

Nanushuk 

Group 

Nanushuk 

Group 

Tr_•rO}' 

.C'ol'mation 

77AAH146 

77AAH148 

77AAH150 

77AAH152 

77AAH154 

77AAH155 

77AAH156B 

77AAH159 

77AAH159A 

77AAH160 

77AAH162 

77AAH169 

77AAH172 

77AAH173 

77AAH175 

77AAH176 

77AAH178 

77AAH183 

77AAH186 

67 

174 

235 

285 

302 

305 

366 

427 

465 

468 

506 

512 

556 

619 

677 

678 

735 

750 

751 

796 

852 

899 

963 

969 

994 

1,059 

1,119 

1' 183 

l' 219 

1,2~5 

1,245 

l' 248 

1,273 

l, 274 

1, 353 

1,411 

l ,469 

l' 475 

l' 481 

1, 548 

l, 554 

1, Gl.2 

1,673 

1, 7?2 

l' 754 

1,807 

l ,868 

1,942 

1' 947 

l '957 

2, 010 

~ 1057 

:' 059 

Lith 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Ss 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Ss 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Co 

Sh 

Sh 

Sh 

Ss 

Ss 

Ss 

Sh 

Sh 

Sh 

Sh 

Sh 

Ss 

Sh 

Sh 

Co 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Ss 

Ss 

Sh 

Sh 

Ss 

Sh 

TAI 

2.2 

2.2 

2.1 

2.2 

2.2 

2.1 

2.2 

2.2 

2.1 

2.1 

2.1 

1.8 

1.8 

2.0 

2.0 

2. 0 

2.0 

2. 0 

2.0 

2.0 

2. 0 

2 .l 

2.1 

2.1 

2.2 

2. 2 

Vitrinite reflectance 

Mn Ro Av Ro Mx Ro 

0.45 0.68 0.87 

. 55 .68 . 82 

.42 

.64 

. 73 

.49 

.61 

.46 

. 72 

. 76 

.82 

.67 

. 75 

. 75 

.86 

.93 

.95 

.81 

.91 

.81 

0.43 0.52 0.66 

.42 .51 .69 

0.50 0.58 0.66 

. 46 .60 . 76 

. 50 

. 52 

. 39 

. 50 

. 51 

. 53 

.51 

. 51 

.42 

.65 

.67 

. 58 

. 51 

.63 

.61 

.64 

.65 

.65 

.71 

. 74 

.84 

. 72 

.68 

. 73 

. 73 

. 71 

. 75 

.87 

.93 

.82 

. 71 . 86 l. 01 

. 74 .86 .98 

. 71 .86 1.08 

. 79 l. 08 l. 3 3 

. 95 1.15 l. 29 

TEA-FID 

Tpii°C PHC VHC 

KUKPOWRUK TYPE SECTION 

462 

468 

462 

473 

456 

466 

480 

464 

0.11 

.12 

.11 

.19 

. 34 

.50 

298 

268 

387 

618 

631 

591 

. 33 455 

3.28 2,551 

BARJ'.BARA SYNCLINE 

453 

458 

449 

453 

454 

451 

452 

454 

450 

0.19 

.13 

238 

213 

KAOLAK NO. 1 WELL 

1.80 

.25 

782 

291 

.16 407 

4.78 1,308 

.12 307 

l. 76 684 

1.82 873 

456 . 22 459 

450 17.90 12 '557 

452 .17 308 

454 

457 

464 

468 

475 

464 

482 

.12 270 

1.16 829 

.88 1,157 

4.16 4,912 

.57 1,075 

.1'5 456 

.11 344 

56 

oc 

1.36 

1.10 

1.56 

l. 38 

1.21 

1.61 

l. 76 

• 73 

1.07 

1. 82 

.93 

2. 73 

3.85 

3.28 

1.64 

3.02 

28.18 

l. 95 

1.49 

17.88 

1.81 

3.99 

.62 

.88 

35.88 

61'.62 

2.81 

. 52 

11.03 

. 34 

3.62 

1.09 

7. 97 

1.37 

12.37 

2.17 

3. 24 

69.79 

l. 32 

1.26 

1.08 

.93 

.40 

1.03 

.60 

1.41 

l. 74 

38.82 

6.52 

.25 

1.02 

.65 

65.18 

1.11 

1.55 

4.40 

18.15 

1.25 

1.41 

1.12 

1.21 

2.95 

1.53 

1.28 

2. 78 

1.27 

.19 

1.15 

l. 35 

1.68 

• 31 

1.06 

PHC/OC 

8.09 

7.69 

8.03 

10.05 

12.45 

12.99 

10.93 

11.64 

9. 74 

8. 72 

10.07 

13.81 

18.18 

13.27 

23.08 

15.96 

22.84 

6. 79 

25.65 

15.74 

20.00 

17.79 

20.00 

22.92 

19.32 

11.81 

10.38 

Elemental analysis-kerogen 

N Ash 

H 

c 

Visual kerogen 

Am Hr Hu In 

72.73 3.88 1.39 10.30 0.64 29 29 21 21 

78.07 4.75 1.67 6.15 .73 29 29 21 21 

64.36 3.92 4.88 23.54 • 73 8 33 25 33 

67.23 4.11 1.84 20.88 . 73 31 31 15 23 

72.58 4.62 2.31 13.89 .76 25 33 17 25 

27.89 5.25 1.65 6.16 .81 22 56 11 11 

76.83 4. 73 2.63 7.47 • 74 

68.50 4.66 2.23 10.15 .82 

71.74 4.83 2.13 1.94 0.81 

71.22 4.70 1.74 3.61 .79 

67.51 4.61 1.82 0.48 0.82 

65.48 4.36 1.89 13.20 .80 

25 42 17 l7 

22 56 11 11 

0 42 33 25 

9 36 27 27 

15 38 23 23 

29 36 21 14 

4 7. 61 2. 58 . 70 38.78 • 65 31 31 23 15 

69.46 4.88 1.46 3.04 .84 11 44 22 22 

64.91 4.05 3.66 12.89 • 75 0 55 22 22 

6 7. 42 4. 59 2. 81 l. 37 . 82 10 50 20 20 

68.85 5.10 l. 79 3.88 .89 23 38 15 23 

75.55 4.84 2.28 3.37 .77 23 31 31 15 

75.81 5.44 2.47 . 74 .86 0 22 33 44 

74.60 4.82 2.47 6.13 .78 36 36 18 

72.01 4.07 1.15 9.57 .68 0 36 27 36 

71.45 4.57 2.60 10.21 .77 17 42 25 17 

77.29 4.83 2.13 5;96 • 75 11 56 22 11 

71.36 4. 78 2.29 8.13 .80 10 40 30 20 

81.86 5.13 2.53 2. 7l . 75 11 56 22 11 

70.68 3.93 2.10 15.98 .67 0 45 27 27 

70.59 3.95 2.62 19.43 .67 0 45 27 27 
Table 3.--0rganic geochemical data for the Nanushuk Group, Torok Formation, and pebble shale unit, 

North Slope, Alaska--Continued 

Vitrinite reflectance TEA-FID 

Sample No. 

Rock unit or depth (m) Lith TAI Mn Ro Av Ro Mx Ro Tpii°C PHC VHC oc PHC/OC 

Elemental analysis-kerogen 

H 

Ash c 

Visual kerogen 

Am Hr Hu In 

TOPAGORUK NO. 1 WELL 

Nanushuk 

Group 

Torok 

Formation 

Pebble 

shale unit 

278 

366 

457 

547 

637 

728 

805 

896 

988 

1,085 

1, 250 

1,493 

1, 526 

1, 553 

1, 580 

1,634 

1,670 

1,69C! 

1' 733 

1, 768 

1, 788 

1,814 

1,820 

1,830 

1,836 

1,875 

1,981 

2,057 

2,088 

2,146 

2' 379 

2, 390 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Ss 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

2.0 

1.8 

1.8 

1.3 

1.8 

2.1 

1.9 

1.9 

2.1 

2.0 

2.1 

2 .l 

2. 0 

2.0 

2.0 

2.1 

2.1 

2.1 

2.1 

2. 2 

2. 2 

2. 2 

2.2 

:2.2 

2. 2 

2. 2 

2. 2 

2.2 

2. 2 

~ .4 

2.4 

0.33 0.41 0.56 

.39 .49 .59 

.35 .47 .59 

. 35 

. 34 

.38 

.39 

. 32 

. 38 

.54 

.59 

.45 

.58 

.54 

. 53 

.50 

.49 

.57 

. 56 

.52 

.69 

. 75 

. 77 

. 75 

. 79 

.68 

. 59 

. 79 

.63 

.65 

.85 

.87 

.88 

.96 

.94 

• 79 1. 07 

• 73 .97 

473 

468 

468 

459 

458 

472 

467 

476 

470 

465 

477 

479 

477 

466 

470 

478 

478 

475 

475 

480 

484 

481 

483 

490 

488 

484 

478 

484 

483 

471 

471 

0.23 

.11 

.18 

.08 

.12 

.10 

.15 

.17 

.10 

.19 

.15 

.17 

. 09 

.14 

.17 

.15 

.14 

.14 

.19 

.15 

.16 

.15 

.13 

.14 

.15 

.14 

.17 

.40 

.19 

.06 

.03 

114 

216 

299 

304 

322 

109 

402 

347 

96 

442 

270 

228 

214 

364 

327 

298 

352 

345 

449 

303 

374 

426 

247 

267 

380 

406 

579 

502 

396 

243 

152 

2. 01 

.85 

1.27 

.80 

1.08 

1.14 

1.13 

2. 44 

1.10 

. 38 

1.25 

1.27 

1.08 

1.10 

1.13 

1.29 

1.03 

1.11 

1.15 

1.23 

1. 58 

.93 

1.13 

1.23 

1.10 

1. 31 

1.12 

1.92 

2.98 

1. 70 

.87 

.20 

11.44 

12.94 

14.17 

10.00 

11.11 

8. 77 

13.27 

6. 97 

9.09 

50.00 

12.00 

13.39 

8. 33 

12.73 

15.04 

11.63 

13.59 

12.61 

16.52 

12.20 

10.13 

16.13 

10.57 

12.73 

11.45 

12.50 

8.85 

13.42 

11.18 

6.90 

15.00 

69.47 3.63 2.91 7.63 0.63 

56.30 3.08 1.15 25.39 .66 

66.54 2.83 1.24 15.76 .51 

63.30 3.27 1.24 18.26 .62 

50.91 3.03 3.97 34.48 .71 

70.49 3. 74 1.49 9.17 .64 

71.57 4.01 1.50 7.99 .67 

10.83 1.17 3.28 74.42 1.30 

73.63 4.29 1.75 8.33 .70 

69.25 4.49 2.10 7.84 .78 

52.00 3.67 3.34 23.54 .85 

60.34 3.25 1.03 23.92 .65 

60.23 3.33 8. 71 26.00 .66 

80.25 5.16 2.96 3.66 .77 

76.75 3.89 1.04 7.43 .61 

76.10 4.60 2. 76 8.37 • 73 

74.08 3.92 1.24 11.00 .63 

73.00 4.40 .04 12.63 • 72 

70.67 4.00 2.49 17.12 .68 

80.54 4.63 1.50 4.97 .69 

68. 11 4. 44 7. 68 17. 36 • 78 

0 50 13 37 

0 63 25 13 

0 63 13 25 

0 56 11 33 

33 42 17 

0 44 11 45 

17 42 25 17 

0 63 25 13 

44 33 0 23 

30 50 10 10 

44 11 45 

50 12 38 

0 63 13 25 

63 13 25 

71 14 14 

50 30 20 

50 20 30 

0 56 11 33 

50 20 30 

45 27 27 

31 38 15 15 

0 45 18 36 

0 45 27 27 

0 44 22 34 

70.34 4.27 1.22 12.26 . 73 40 40 10 10 

80.48 4.58 1.40 4.21 .68 0 27 36 36 

66.53 3.66 6.18 19.83 .66 

75.01 4.86 2.53 10.96 • 78 

56.21 3.56 11.59 28.06 • 76 

0 40 20 40 

44 44 11 0 

.0 57 0 43 

44 22 11 22 

40 20 10 30 

UMIAT 1'EST WELL 11 

Colville 

Group 

Nanushuk 

Group 

Torok 

Formation 

76 

85 

105 

106 

120 

143 

144 

149 

155 

164 

165 

171 

219 

238 

247 

309 

315 

375 

511 

597 

634 

646 

658 

664 

671 

677 

684 

701 

707 

732 

823 

829 

895 

1,015 

Sh 

Sh 

Sh 

Co 

Co 

Sh 

Co 

Sh 

Sh 

Ss 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

Ss 

Sh 

Sh 

Sh 

Sh 

Sh 

Ss 

Sh 

Sh 

Sh 

Sh 

Sh 

Sh 

1.9 

1.9 

2. 0 

2.0 

2.0 

2.1 

2.1 

2.1 

2.1 

2. 2 

. 32 

. 38 

. 38 

. 30 

.37 

. 32 

. 31 

.40 

.40 

. 37 

.40 

.42 

. 47 

.42 

.48 

.46 

.42 

.49 

.54 

. 53 

.54 

.53 

• 53 

.55 

.56 

.57 

.59 

.57 

.61 

.66 

444 

444 

441 

447 

450 

447 

450 

452 

452 

452 

.14 

.09 

.06 

.10 

.06 

.13 

.19 

.15 

.17 

.22 

subjectively measured against a standard on a 

scale from 1 to 5 (table 3). Kerogen coloration 

ranges from a pale yellow (1) to black (5), 

with 2 to 4 being the mid-range. 

The TAl for the four sections varies 

57 

532 

438 

284 

311 

130 

265 

428 

403 

474 

434 

o. 33 

1.18 

1.14 

48.98 

17.89 

.93 

41.60 

.28 

.3r; 

.22 

• 74 

.98 

l. 31 

.82 

.60 

• 79 

.99 

.69 

.87 

.59 

.96 

.32 

2.18 

.97 

3.46 

1.27 

1.80 

.43 

.84 

1.41 

.91 

1.11 

4.06 

1.66 

14.29 

15.00 

8. 70 

11.49 

10.17 

10.24 

16.67 

16.48 

15.32 

13.25 

61.71 3.56 1.31 12.39 .69 15 38 23 23 

64.46 3. 48 1. 96 12.00 .65 8 25 33 33 

63.72 3.28 2.88 14.69 .62 0 27 36 36 

67.27 4.21 2.23 9.38 .75 25 33 25 17 

44.07 2.76 1.03 38.57 .75 0 36 27 36 

69.55 4.36 1.34 9.81 . 75 25 42 17 17 

70.95 4.20 2.11 7.17 • 71 0 40 20 40 

0 40 20 40 

0 36 36 27 

74.41 4.26 2.01 4.94 .69 8 42 25 25 

between 1.8 and 2.4, a rather small range when 

compared to the vitrinite reflectance values. 

There is, however, a slight increase in TAl 

down section, as would be expected with increasing temperature or depth of burial. 
TEA-FID 

To C PEAK TI 

VITRINITE REFLECTANCE 

AV RoKUKPOWRUK 

TYPE SECTION 

SEC. 22, T. 2 S., R. 45 W. 

MEASURED SECTION 

ORGANIC CARBON 

wt% 

ATOMIC 

Htc RATIO 

VISUAL KEROGEN 

% 

M 425 450 475 500 04 05 06 07 08 09 0 4 0 0.5 0 25 50 75 100 o-rr 

500-

J 

TEA-FID 

T o C PEAK TI 

M 425 450 475 500 

I 

• I 

• 

• • 

-

1- F? 

NANUSHUK .... 

GROUP 

•••• F 

F= FAULT 

KAOLAK NO. 1 WELL 

SEC. 25, T. 7 N., R. 34 W. 

VITRINITE REFLECTANCE 

AV Ro~ 

05 0 6 0 7 0.8 0.9 I 0 1.25 

r-r-

• 

•\ . • • 

I •\ 

I 

' \ 

• \ 

• 

~ \ 

\ 

' '\ 

•\ 

• 

\ 

• \ 

B Cool 

[§Sandstone 

TOROK 

FM. 

ELEV. 54m K.B. 

• 

• • TO. 2119m 

ORGANIC CARBON 

wt% 

~~------3588 

1--------6162 

-----1103 

4 40 

1815 

~ depth well r" COSing 

ATOMIC 

Htc RATIO 

0 0.5 

X X 

xx 

·I 

I 

X 

J I 

I 

VISUAL KEROGEN 

% 

0 25 50 75 100 

Q Amorphous 

C2J Herbaceous 

CJ Humic 

[_1 

_ _j Shale L:...:.....:J ~ Inertinite 

Figure 29.--0rganic geochemical data for the Nanushuk Group and Torok Formation from the Kukpowruk 

type section and Kaolak No. 1 well. 

58 
TEA-FID 

To C PEAK ll 

TOPAGORUK N0.1 WELL 

VITRINITE REFLECTANCE 

AV Ro--. 

SEC. 25 , T. 15 N., R.16 W. 

ELEV. 13m K.B. 

ORGA~IC CARBON 

wt% 

ATOMIC 

HJc RATIO 

VISUAL KEROGEN 

% 

M 425 450 475 500 0.4 0.5 0.6 0.7 QS 0.9 0 0.5 0 25 50 75 100 

0 

\ . 500-

1000-

1500- X 

X 

X X 

2000-

X 

X 

TEA-FID 

To C PEAK li 

M 425 450 475 500 

0 

500-

1000-

• 

• 

• 

\ 

.\ 

GROUP 

TOROK 

FM . 

.... • 

• 

• 

"PEBBLE 

SHALE 

UNIT" 

T.D. 3201 m 

UMIAT TEST WELL 11 

SEC. 27, TIN., R.l W. 

ELEV. 147m K.B 

VITRINITE REFLECTANCE ORGANIC CARBON 

AV Ro- R R wt % 

0.4 0.5 0.6 

• • 

• COLVILLE .... 

\ . GROUP 

\ 

• \ 

\. 

• 

• \ : •• 

\ 

• 

ATOMIC VISUAL KEROGEN 

H/c RATIO % 

4 0 0.5 0 25 50 75 

XI 

X 

lx 

c 

xJ 

Figure 30.--0rganic geochemical data for the Colville and Nanushuk Groups, Torok Formation, and 

pebble shale unit from the Topagoruk No. 1 well and Umiat test well 11. 

59 

100 
TEA-FID 

The second peak from the thermal analysis 

can be used empirically as an indicator of 

thermal history (table 3, figs. 29 and 30). 

Theoretically, the maximum temperature in 

degrees Centigrade of the second peak increases 

in proportion to the degree of burial heating 

experienced by the organic matter in the subsurface. Interpretation of maturity based on the 

temperature of maximum pyrolysis yield is not 

well established. In general, temperatures 

(Tpll°C) below 460°C suggest thermal immaturity 

and above 480°C suggest maturity (Claypool and 

others, 1977). 

With the exception of the Kukpowruk type 

section, which shows a slight lowering of 

temperature with depth, the temperature of 

maximum pyrolysis yield, or peak II, increases 

with depth and approaches 475°C in all wells. 

Umiat test well 11 approaches 450°C at total 

depth and represents the coolest temperature 

history of the four sections studied. Kaolak 

No. 1 well also records a low temperature history, 

while the Topagoruk No. 1 well and Kukpowruk 

type section record a higher temperature history. Using the criterion of 480°C for maturity, 

these rocks approach but do not reach maturity. 

Vitrinite Reflectance 

Rocks containing organic matter are treated 

with acids to remove non-organic material, 

washed, molded into a cylinder, and mounted in 

a plastic plug for polishing. The polished 

surface is observed by microscope under reflected light. Vitrinite, a type of coaly particle, 

is identified and the percentage of reflected 

light measured. As many as 50 reflectance 

readings for each sample are acquired. Minimum, 

average, and maximum reflectance values are 

reported (table 3). The average values are 

plotted and a straight line is visually fitted 

to them (figs. 29 and 30). 

With the exception of the Kukpowruk type 

section, the average reflectance values increase 

with depth. The reflectance values are greater 

in the west than in the central North Slope or 

eastern part of NPRA, suggesting more uplift on 

60 

the west. The gradients of the reflectance 

values are similar for the Topagoruk No. 1 well 

and Umiat test well 11, but not for the Kaolak 

No. 1 well. This well has a "dog leg" at 1,000 

m for both the reflectance and TEA-FID data, 

suggesting a decrease in the geothermal gradient 

in the west during the time of deposition of 

the middle part of the Nanushuk Group. None of 

the other wells or outcrop, however, expresses 

this change in geothermal gradient. 

General criteria for the threshold of 

maturity for vitrinite reflectance varies with 

authors (Dow, 1977b; Hood and others, 1975), 

but ranges from 0.5 to 0.65. With the exception 

of Umiat test well 11, all wells and the outcrop 

within the Nanushuk Group meet this criterion 

for thermal maturity. In Umiat test well 11, 

the 0.5 value lies just beneath the Nanushuk in 

the uppermost Torok Formation. Caution must be 

exercised in using this and other parameters of 

maturity discussed here (TAl, TEA-FID) as none 

have been calibrated for this basin by comparison with the hydrocarbons extracted from the 

rocks. Until this calibration is completed, 

these indices of maturity are empirical. In 

conclusion, on the basis of empirical use of 

vitrinite-reflectance data, the Nanushuk Group 

is mature in the western and immature in the 

central part of the North Slope. 

CONCLUSIONS 

Preliminary analytical work completed for 

the Kukpowruk outcrop section and Kaolak No. 1 

well, Topagoruk No. 1 well, and Umiat test well 

11 in the Nanushuk Group and Torok Formation 

suggests that the rocks rich in organic matter 

are hydrocarbon source rocks and are more 

likely to generate methane gas than oil. The 

thermal history of the Nanushuk Group in the 

western North Slope may have been hotter than 

in the central North Slope as the rocks have 

higher reflectance and TAl values. The Nanushuk 

Group in the west is mature, whereas the rocks 

in the Topagoruk No. 1 well and Umiat test well 

11 are immature. Oil in sandstones of the 

Nanushuk Group in Umiat oil field migrated from 

hotter, deeper strata, as the shales encasing 

the sandstone are immature. 
TEXTURAL AND MINERALOGICAL STUDY OF 

SOME SURFACE AND SUBSURFACE SANDSTONES FROM 

THE NANUSHUK GROUP, WESTERN NORTH SLOPE, ALASKA 

By Susan Bartsch-Winkler 

INTRODUCTION 

Twenty-one surface and forty-five subsurface samples of sandstone from the Lower and 

Upper Cretaceous Nanushuk Group were examined 

in thin section in order to determine the 

textural and mineralogical factors that might 

affect reservoir characteristics. The surface 

samples were collected by James Fox in July 

1975 from scattered outcrops of the Nanushuk 

Group (fig. 31); their relative stratigraphic 

positions are uncertain. The subsurface samples 

were obtained from cores stored at the U.S. 

Geological Survey warehouse in Fairbanks and 

from "perm plugs" used to determine porosity 

and permeability; their relative stratigraphic 

positions are well known (Robinson, 1956, 1958, 

1959a, b, c, 1964; Collins, 1958b, c, 1959). 

No previous petrographic study has been 

conducted on the surface and subsurface samples 

reported herein, but Krynine (1947, 1948), 

Krynine and Ferm (1952), and Fox and others 

(1979) studied rocks from the Umiat test wells. 

Their descriptions and analyses served as 

excellent and invaluable introductions to the 

complexities and nuances of the Nanushuk 

Group. 

The use of the cathodoluminiscope and the 

able assistance of Eve S. Sprunt, Stanford 

University, are gratefully acknowledged. 

METHODS 

The thin sections were stained with sodium 

cobaltinitrite to aid in identifying potassium 

feldspar and injected with blue plastic to 

enhance the pores; 300 grains were counted per 

section. Whole rock X-ray studies were conducted by Paul D. Blackmon and Harry C. Starkey, 

U.S. Geological Survey, Denver, to identify 

clay types and major mineral constituents. 

Polished thin sections of selected samples were 

examined under cathodoluminescent light in 

order to determine cement relationships and 

possible grain overgrowths. Rock chips from 

the surface samples were coated with goldpalladium and were examined using a Cambridge 

180 scanning electron microscope with an 

attached electron-dispersive X-ray-analyzer to 

further study the relationships between grains, 

pores, and cements. Using the petrographic 

microscope, textural parameters were determined 

by estimation and measurement of sorting, 

packing density, and percent matrix. 

TEXTURE 

The surface samples, and presumably the 

subsurface samples, were collected from a wide 

variety of depositional environments, including 

fluvial-point-bar and channel, prodelta, deltafront, shallow-marine, and marine sandstones; 

and thus various stages and types of weathering, 

cementation, alteration, sorting, and bed types 

are represented in these samples. The samples 

have been grouped into surface and subsurface 

samples, and further grouped according to map 

location to help distinguish compositional 

differences in the rocks. Surface samples east 

of long 156° W. are numbered from 1075 to 30J5; 

those west, from 3275 to 5475. Subsurface 

samples in the eastern suite (east of long 155° 

W.) include samples from Square Lake, Titaluk, 

Knifeblade, Wolf Creek, Gubik, and Grandstand 

test wells; subsurface samples in the western 

suite are from Simpson, Topagoruk, Meade, 

Oumalik, and Kaolak test wells. 

Textural properties of the surface and 

subsurface sandstones are shown in figure 32 

(Winkler and others, 1976, p. 8-12). Generally, 

the most favorable reservoir characteristics 

for each textural category are shown toward the 

right side of the abscissa; the least favorable 

are shown toward the left side. The ordinate 

is the percent of total samples exhibiting the 

particular property indicated. Sorting was 

estimated by referring to sorting images 

illustrated by Pettijohn, Potter, and Siever 

(1972, p. 585). Estimated packing density was 

determined visually using these criteria: 

"high"--framework grains tightly packed with 

abundant penetration involving squeezing of 

relatively soft lithic fragments between and 

around more resistant grains such as quartz and 

feldspar; "moderate"--closely packed framework 

with minor grain interpenetration and little or 

no deformation of lithic fragments; and "low"--

framework separated by or floating in matrix or 

61 
71° 166° 

-<?-Test well 

o Surface sample 

70° ~~~ oL 

'\\L ~L r-; 

69° 

162° 

4375 

4275~4575 

-<{-KAOLAK 

154° 

-<>-MEADE 

AOUMALIK 

150° 

-y -<1QUARE ~ AKE 

WOLF CREEK, UMIAT AGUBIK 

TIT A LU~ '-¢- "' y 

KNIFEBLADE 1875 °

2175 

48750 

03375 

0

3275 

@3675 

3875 

7 ~ \U-;A. 690 

15~~"2~75 2075-¢;; CvLVJL~ @

3075 GRANDSTAND 

158° 

Rlv 1475 

1175~1275 1075 

68° 

150° 

Figure 31.--Index map showing location of test wells and surface-sample localities. Twenty-one 

surface samples and forty-five subsurface samples of sandstones of the Lower and Upper 

Cretaceous Nanushuk Group were studied. 

authigenic cement with no observable grain 

interpenetration. Type of grain contacts 

(Taylor, 1950) include (1) sutured grains, 

mutual stylolitic interpenetration of two or 

more grains (which must be carefully distinguished from grains of polycrystalline quartz), 

usually attributed to much pressure solution; 

(2) concave-convex grain contacts, attributed 

to moderate pressure solution; (3) long or 

straight contacts, indicative of only minor 

compaction and pressure solution; (4) point or 

tangential contacts, having minor or no pressure 

solution; and (5) floating grains, which are 

not in contact with other framework constituents. Most samples exhibit more than one type 

of common grain contact. Textural components 

and cement + matrix were determined from the 

modal analysis of each thin section. Matrix 

(as discussed by Dickinson, 1970) may be high 

in samples having significant amounts of phyllosilicate coatings and (or) "squeezed" or "compacted" lithic fragments. Data from which 

figure 32 was derived are shown in appendix 1. 

Maximum grain size is as much as 1.28 mm 

in one sample from the Square Lake test well 

(appendix 1). The maximum grain size of most 

samples is 0.20 to 0.40 mm, or upper fine to 

medium sand (Folk, 1968), but maximum grain 

sizes are slightly coarser in the eastern 

samples in both the surface and subsurface, 

approaching 0.40 to 0.65 mm (upper medium to 

lower coarse sand). Modal grain sizes are 0.25 

mm or less in most outcrop and subsurface 

62 

samples; most samples are fine-grained to very 

fine grained sandstone and siltstone, although 

some are medium- and coarse-grained sandstone. 

Moderate sorting characterizes the samples, but 

samples in the east are slightly better sorted. 

The majority of grains making up the sandstones 

have long contacts; and a significant number 

have concave-convex contacts, indicating that 

some presolution, formation of quartz overgrowths, or siliceous cementation has taken 

place. Visible porosity is characteristically 

low in the sandstones examined, although 

isolated samples have as much as 18.8 percent 

visible porosity. Estimates of packing densities of the samples are commonly high, but 

surface samples in the eastern suite have 

nearly equal percentages of samples with low 

packing densities. Percentages of matrix and 

cement are greatest in the western surface 

samples (all are greater than 20 percent), and 

significant amounts are present in many of the 

rest of the samples. 

Ternary diagrams (fig. 33) of surface and 

subsurface samples with framework-matrix-cement 

end-members indicate that the sandstones have 

moderate to poor reservoir qualities. Recalculated percentages of matrix range from 3.6 to 

37.0 (mean, 14.6 percent) in the surface samples 

and from 3.6 to 42.0 (mean, 18.3 percent) in 

the subsurface samples (appendix 2). Percentages of cement in the surface samples range 

from 0.9 to 57.4 (mean, 16.1 percent); in the 

subsurface, percentages of cement range from 
WEST of 

long. 156° W. 

n ~ 11 

EAST of 

long. 156° W. 

n K 10 

WEST of 

long. 155° W. 

n. 17 

EAST of 

long. 155° W. 

n. 2a 

MAX 

GRAIN 

SIZE 

{Mm) 

MODAL 

GRAIN 

SIZE 

{Mm) 

SORTING GRAIN TEXTURAL 

CONTACTS COMPONENTS 

MATRIX + CEMENT 

{percent) 

PACKING 

DENSITY 

Figure 32.--Textural properties of the surface and subsurface sandstones from the Nanushuk Group. 

The most favorable reservoir characteristics for each textural category appear toward the 

right of each parameter shown. n, number of samples. 

0.6 to 21.2 (mean, 7.2 percent). The percentage 

of matrix in surface and subsurface rocks is 

nearly the same; however, the amount of calcite 

cement present in surface samples in the west 

is greater than that in any of the rest of the 

samples. Perhaps weathering of calcite grains 

plays a role in the formation of the calcite 

cement in the western suite. In the subsurface, 

it is possible that only the Kaolak test well 

penetrated the western province of the Nanushuk 

Group; in this well, calcareous cement was only 

as high as 5.7 percent, with pseudomatrix, 

constituting as much as 22.3 percent, being the 

dominant intergranular constituent. In the 

subsurface, comparisons of samples from western 

and eastern provinces show more subtle differences than comparisons of surface samples from 

the two provinces. The eastern rocks in the 

subsurface apparently contain slightly more 

matrix material than is present in the surface 

rocks. 

MINERALOGY 

Sandstones of the Nanushuk Group typically 

contain about 50 percent quartzose grains, and 

they are compositionally litharenites (Folk, 

63 

1968). In determining grain compositions, the 

conventions described by Dickinson (1970) were 

followed, except that the polycrystalline 

quartz category includes all polycrystalline 

quartz grains, even though individual crystallite dimensions may have been less than 0.03 

mm. Chert grains include only fibrous or 

chalcedonic varieties. Data from the modal 

analyses are presented in appendix 2. 

Surface and subsurface rocks have similar 

plots on the Q-F-L triangle, but the subsurface 

rocks apparently contain slightly more quartz 

and feldspar. An average surface sample 

contains 50.5 percent monocrystalline and 

polycrystalline quartz, quartzite, and chert 

grains (Q), 4.6 percent feldspar grains (F), 

and 44.9 percent lithic grains (L). In the 

subsurface, an average sample contains 52.6 

percent Q, 5.8 percent F, and 41.7 percent L. 

According to Folk (1968), these rocks are 

litharenites, and their compositions agree with 

those of Nanushuk samples from Umiat test well 

11 studied by Fox and others (1979). A ternary 

plot of monocrystalline quartz (Qm); feldspar 

(F); and total lithic fragments, polycrystalline 

quartz, and chert (Lt) shows patterns similar 

to those of the Q-F-L plots just described. On 
SURFACE 

\~ : \ 

\ 

\ 

. \ •, \ 

\ 

...... \ ............ ___ _.. 

Mat IX Cern nt 

a 

Fg L._ ___________________ _____. L 

Om 

F L----------------------------"Lt 

SUBSURFACE 

Mat ll< Cern nt 

~£_ _______________________________ ______. L 

Om 

F L._ ____________________ _____.lt 

Figure 33.--Ternary plots of surface and subsurface sandstones, Lower and Upper Cretaceous Nanushuk 

Group, Alaska. Squares, with fields enclosed by solid lines, indicate samples from the 

eastern portion of the area (east of long 156° W. in the surface samples and long 155° W. in 

the subsurface samples); circles, with fields enclosed by dashed lines, indicate samples from 

the western part of the area. For convenience, the dotted line on the surface diagrams 

enclose the field of the subsurface plots, which are shown in detail on the right-hand 

64 
SURFACE 

V/LL_ __________________________________________ -JC/0 

Lm 

Chert & Polycrystalline 

Quartz Clasts 

Argilla eous & 

Carb aceous Clasts 

Cal ite 

Cl sts 

SUBSURFACE 

Chert 

diagrams. Q, monocrystalline and polycrystalline quartz, quartzite, and chert; F, feldspar; 

L, lithic grains; Qm, monocrystalline quartz; Lt, total lithic fragments, polycrystalline 

quartz, and chert; P/F, ratio of plagioclase to total feldspars; V/L, ratio of volcanic 

lithic grains to total lithic grains; C/Q, ratio of polycrystalline quartz and quartzose 

grains to total quartzose grains; Lm, metamorphic lithic grains, Lv, volcanic lithic grains; 

and Ls, sedimentary lithic grains. "k" indicates samples from the westernmost well, the 

Kaolak test well. 

65 
the surface, an average sample contains 24.6 

percent Qm, 7.1 percent F, and 68.3 percent Lt. 

In the subsurface, an average sample is composed 

of 39.2 percent Qm, 7.4 percent F, and 53.4 

percent Lt. The subsurface samples are composed 

of about 15 percent more monocrystalline quartz 

than the surface samples. Ternary plots of the 

ratios of plagioclase to total feldspars (P /F), 

of polycrystalline quartz and quartzite grains 

to total quartzose grains (C/Q), and of volcanic 

lithic grains to. total lithic grains (V/L) are 

nearly identical in the surface and subsurface, 

plotting near the midpoint between the C/Q and 

P/F poles. 

A ternary plot of lithic grain types with 

volcanic-sedimentary-metamorphic end-members 

and one of sedimentary lithic clast types with 

total chert and polycrystalline quartz clastscalcite clasts-argillaceous and carbonaceous 

clasts as end-members reveal striking differences in lithic grain compositions between the 

eastern and western suites of rocks, which show 

up particularly well in the surface samples. 

The subsurface samples do not plot as distinctively as the surface samples, though the 

average compositions have subtle variations 

corresponding to those of the surface samples. 

It is noteworthy that samples from the Kaolak 

test well fall within boundaries of the western 

suite on the surface plots. It is also of 

interest that the subsurface plots seem to fall 

between the two provinces of surface samples, 

as though indicating a gradational transition 

or interfingering of lithic types. Average 

lithic and sedimentary clast compositions of 

surface and subsurface samples are shown in 

table 4. These figures show that, in the 

surface and the subsurface, (1) a higher percentage of sedimentary lithic clasts is found 

in the western samples and a higher percentage 

Table 4.--Average compositions of lithic clast and sedimentary lithic 

clast in samples from the Nanushuk Group, western North Slope, 

Alaska 

[Lv, volcanic lithic grains; Ls, sedimentary lithic grains; Lm, 

metamorphic lithic grains; Q, monocrystalline and polycrystalline 

quartz, quartzite, and chert] 

Lithic-clast compositions 

(in percent) 

Surface 

Overall: Lv=l5.1 

Ls=65.4 

Lm=l9.5 

Eastern province: 

Lv=l5.7 

Ls=54.0 

Lm=30.2 

Western province: 

Lv=l4.3 

Ls=76.7 

Lm= 9.0 

Subsurface 

Overall: Lv=lO.l 

Ls=71.6 

Lm=l8.3 

Eastern province: 

Lv= 8.5 

Ls=71.5 

Lm=20.0 

Western province: 

Lv=l2.1 

Ls=72.3 

Lm=l5.6 

Sedimentary lithic-clast compositions 

(in percent) 

samples 

Chert and polycrystalline Q=73.1 

Calcite clasts=l8.4 

Argillaceous-carbonaceous clasts=8.5 

Chert and polycrystalline Q=73.1 

Calcite clasts=l8.4 

Argillaceous-carbonaceous clasts=8.5 

Chert and polycrystalline Q=61.3 

Calcite clasts=31.1 

Argillaceous-carbonaceous clasts=7.6 

samples 

Chert and polycrystalline Q=67.7 

Calcite clasts=l3.6 

Argillaceous-carbonaceous clasts=78.7 

Chert and polycrystalline Q=87.3 

Calcite clasts=2.7 

Argillaceous-carbonaceous clasts=lO.O 

Chert and polycrystalline Q=61.3 

Calcite clasts=31.1 

Argillaceous-carbonaceous clasts=7.6 

66 
of metamorphic lithic clasts is found in the 

eastern samples, (2) a nearly uniform percentage 

of volcanic rock fragments is found throughout 

the area, (3) a higher percentage of quartzose 

grains is found in the eastern samples, and (4) 

a striking increase in percentage of calcite 

clasts is found in the western suite. The 

calcite clasts are recognized by being rounded 

and by their coating of lutum, or reddish-brown 

(hematite?) stain. The grains are characteristically recrystallized and show no internal 

depositional structures or textures. When 

observed under cathodoluminescent light, 

however, the grains luminesce red and orange, 

while the surrounding calcite cement luminesces 

bright yellow, indicating two separate origins 

for the calcite in the grains and in the cement 

(E. S. Sprunt, oral commun., 1978). 

ALTERATION OF THE SANDSTONES 

Nearly all of the sandstones contain at 

least small amounts of pseudomatrix (alteration 

of softer lithic grains by squeezing). Quartz 

grains are commonly strained and cracked, and 

many feldspar twins are offset or bent. The 

sandstones often have a screen of chlorite and 

sericite that alters the framework grains, 

particularly the feldspars, micas, and lithic 

grains. Most micas show the effects of compaction and squeezing, and many have been altered 

to chlorite or "exploded" by calcite or silica 

cement. 

Interstitial secondary cements are typically present. Abundant, though scattered, 

occurrences of siliceous overgrowths and minor 

occurrences of feldspar overgrowths are also 

found. No zeolite cement was observed. The 

amount of siliceous overgrowth, presolution, 

and cementation that has taken place is unknown 

and may not be determined readily. When examined under cathodoluminescent light, most 

quartz grains in the Nanushuk samples luminesce 

dull red, while a small number of grains luminesce blue. Therefore, siliceous overgrowths 

on grains in the Nanushuk rocks have been 

recognized under the microscope as interpenetration of grains or mosaic patches or, where 

present, by a readily visible clay rim around 

the original grain. Silica cement has been 

observed as pore filling as well. In Sample 

No. 3375, two possible stages of silica cementation can be recognized (fig. 34A). In places, 

calcite cement can be seen developing on the 

silica cement. Kaolinite commonly fills pores 

and was probably deposited after a primary, 

iron-rich(?) clay pore-lining stage (fig. 35A). 

An example from the Kaolak test well (937-ft or 

286-m depth) shows a moderate amount of clay 

pore-lining (fig. 35B). Sample No. 2075 shows 

evidence of another sequence of events. 

Leached potassium feldspars, which create a 

secondary porosity (fig. 34B), are then filled 

with kaolinite (fig. 34c). The kaolinite is 

then replaced in some areas by calcite cement. 

67 

The most abundant clay minerals, as determined by X-ray analyses, ·are illite-mica, 

chlorite, and kaolinite (appendix 3). X-ray 

analyses of all samples from the Nanushuk Group 

show that montmorillonite was found in only 

trace amounts. 

POROSITY 

Most pores are lined with a reddish-brown, 

probably iron-rich, coating. All gradations of 

the lining are present, from no pore lining to 

complete closing of the pores. Figure 35C 

shows pore size being decreased by development 

of siliceous grain overgrowth. In the eastern 

province, there are examples of secondary 

porosity being developed by leaching of feldspars. Some of the pores have been successively 

filled by kaolinite; others are left vacant. 

Localized occurrences of secondary porosity, 

which developed as a result of cracking of 

quartzose grains, were also observed. These 

two factors may increase porosity in localized 

areas. 

Appendix 4 lists the porosity and permeability data of the subsurface samples examined 

for this study. The data were summarized from 

Robinson (1956, 1958, 1959a, b, c, 1964) and 

Collins (1958b, c, 1959). Porosity and permeability tests were not conducted on the surface 

samples. 

PROVENANCE 

Monocrystalline and polycrystalline quartz, 

quartzite, and chert grains (Q) typically make 

up about 50 percent of the sandstones from the 

Nanushuk Group, with the feldspar (F) averaging 

about 5 percent and the lithic grains (L) 

averaging 45 percent. These percentages, the 

abundance of detrital carbonate rock in the 

west, and the abundance of finely polycrystalline quartz grains are characteristic of a 

"tectonic" provenance (Dickinson, 1970). Minor 

input from volcanic or plutonic terranes of 

intermediate composition is suggested by the 

high P/F ratios, the low to moderate V/L ratios, 

and the paucity of potassium· feldspar grains in 

most samples. Because many of the quartz 

grains have overgrowths, some of the detritus 

may be recycled. 

Beginning in Jurassic time, uplift and 

northward-directed thrust faulting occurred in 

the Brooks Range and in the Herald Arch (Grantz 

and others, 1976; Grantz and Kirschner, 1976), 

forming a structural high composed, in part, of 

Silurian to Triassic clastic, carbonate, and 

chert sequences. The rising thrust belt shed 

debris into the Colville geosyncline, which 

formed on its north side (Grantz and Kirschner, 

1976). The most likely sources for the Nanushuk 

rocks deposited into the Colville geosyncline 

are the clastic sediments that are found in the 

present-day nappe sequences of the Brooks Range 

(Grybeck and others, 1977). The mineralogical 

characteristics and the general distribution of 
Figure 34.--Photomicrographs of pore-linings in sandstones of the Nanushuk Group. A, Two possible 

stages of silica cementation can be seen in this sample from the western province (Sample No. 

3375, approx. 65X, plain light). B, Same, polarized light. c, Potassium feldspar is often 

leached, creating secondary porosity in some rocks (Sample No. 2075, approx. 65X, plain 

light). D, The pores then sometimes become sites for accumulation of kaolinite clay (same as 

C, polarized light). E, In some samples, cracked grains create secondary porosity (Sample 

No. 2275, approx. 65X, plain light). 

carbonate clasts in the west and quartzose and 

metamorphic clasts in the east suggest two 

different dominant source terranes for the 

sandstones. Extensive carbonate outcrops of 

Mississippian to Pennsylvanian and locally 

Permian Lisburne Group, along with the SilurianDevonian and possibly Ordovician limestones 

making up the Baird Group rocks (Brosge and 

Tailleur, 1971), may be primary sources for the 

calcareous clasts of the western province of 

sandstones of the Nanushuk Group. The Herald 

Arch, in part, may be the structural high from 

which much of the detritus from the western 

province was shed (Grantz and others, 1976). 

The Endicott Group consists of the Upper 

Devonian Hunt Fork Shale and Kanayut Conglomerate and of the Lower Mississippian Kayak Shale 

68 

(Brosge and Tailleur, 1971) in the Endicott 

Mountains and has extensive outcrops in the 

central and eastern Brooks Range. This group, 

as well as the metamorphosed rocks farther to 

the south in the Brooks Range (Grybeck and 

others, 1977), may be the source of the metamorphic lithic and quartzose grains which 

predominate in the eastern province of the 

sandstones of the Nanushuk Group. 

PETROLEUM POSSIBILITIES 

A scattering of subsurface and surface 

samples was studied; a preliminary prognosis is 

that the sandstones have generally marginal 

reservoir characteristics. The amount of 

matrix averages about 18 percent, and all 
samples show evidence of compaction or squeezing 

which has created considerable pseudomatrix. 

Many samples apparently contain quartz grains 

with overgrowths. Cements include primary 

iron-rich(?) clay and secondary illite, kaolinite, calcite, silica, and minor chlorite . 

These diagenetic features all adversely affect 

porosity and permeability of the Nanushuk 

69 

Figure 35.--Scanning electron microscope photographs of pore-linings in sandstones of 

the Nanushuk Group. A, Kaolinite is a 

common, if unwelcome, pore-filling cement 

and was probably deposited after a primary, 

iron-rich(?) pore-lining stage. This 

sample is from the 937-ft or 286-m depth, 

Kaolak test well. B, Often, only moderate 

amounts of clay line the pores (Kaolak 

test well, 937-ft or 286-m depth). c, 

Pores may be considerably narrowed by 

development of siliceous grain overgrowths 

or by presolution of tightly packed grains 

(Sample No. 1475). 

rocks. On the other hand, in one surface 

sample, the visible porosity is 18.8 percent, 

and in the subsurface, average visible porosity 

is slightly improved over that of surface 

samples. This improvement in porosity may be 

related, in part, to leaching of feldspar 

grains and to the cracking of quartz grains 

observed in a few samples. 
""-.1 

0 

Appendix 1.--Textural data from 21 surface and 45 subsurface samples of sandstone from the Lower and Upper Cretaceous 

Nanushuk Group, western North Slope, Alaska 

Sample 

No. 

1075--------------

1175--------------

1275--------------

1475--------------

1575--------------

1875--------------

2075--------------

2175--------------

2675--------------

3075--------------

3275--------------

3375--------------

3675--------------

3875--------------

4275--------------

4375--------------

4575--------------

4875--------------

5175--------------

5375--------------

5475--------------

Meade 2953--------

Meade 4133--------

Wolf Creek 1-867--

Wolf Creek 3-1553-

Wolf Creek 3-2050-

Wolf Creek 3-2532-

Wolf Creek 3-3109-

Wolf Creek 3-3509-

Maximum 

grain size 

0.15 

.45 

.45 

.70 

• 70 

.17 

.77 

.56 

.45 

.18 

.35 

.76 

.36 

.38 

.39 

.92 

.18 

.46 

.45 

.38 

.90 

0.38 

.45 

.58 

.58 

.45 

.46 

.12 

.23 

Modal 

grain size 

0.07 

.20 

.20 

.30 

.40 

.11 

.38 

.18 

.12 

.12 

.18 

.46 

.18 

.18 

.23 

.38 

.15 

.24 

.30 

.16 

.58 

0.23 

.23 

.30 

.30 

.17 

.20 

.09 

.13 

Sorting 

Surface 

Very poor 

Very poor 

Poor-----

ModeratePoor-----

Well-----

ModerateWell-----

Poor-----

Very poor 

Poor-----

ModeratePoor-----

Poor-----

ModeratePoor-----

Poor-----

ModerateWell-----

Very poor 

ModerateSubsurface 

Well-----

Poor-----

Very poor 

Well-----

Poor-----

Poor-----

Poor-----

Poor-----

Type of grain 

contacts 1 

L,P,F 

L,P,F 

C,L 

L,P 

L,P 

C,L 

S,C,L 

C,L 

C,L,P,F 

F 

S,C,L 

S,C,L 

C,L 

S,C,L 

P,F 

C,L 

F 

C, L 

F 

C,L,F 

C,L,P 

C,L 

S,C,L 

S,C,F 

C,L 

S,C,F 

S,C,F 

F 

F 

Cements2 

A 

A 

A 

B 

A,B 

A 

A 

A 

A,B 

B 

A,B 

A 

A,B 

A,B 

B 

A 

B 

A 

B 

B 

A 

A 

A 

B 

A 

A,B 

A,B 

B 

B 

Percent 

matrix 

38.7 

32.6 

28.2 

4.6 

24.6 

19.8 

19.2 

11.7 

29.1 

40.3 

30.3 

29.1 

31.8 

29.6 

51.7 

25.3 

61.0 

28.0 

46.0 

42.4 

20.5 

15.6 

27.2 

24.4 

7.4 

27.1 

25.6 

52.2 

58.4 

Packing 

density 

Low. 

High. 

High. 

Moderate. 

High. 

High. 

High. 

High. 

High. 

Low. 

High. 

High. 

Moderate. 

High. 

Low. 

High. 

Low. 

Moderate. 

Low. 

Low. 

Moderate. 

High. 

High. 

Low. 

Moderate. 

High. 

High. 

Low. 

Low. 
Oumalik 979-84---- .30 .23 Poor----- C,F A,B 24.2 High. 

Oumalik 1606------ .43 .26 Poor----- C,L A,B 26.3 High. 

Oumalik 3260------ .45 .18 Poor----- C,L,P,F A,B 28.3 High. 

Oumalik 3752.5---- .30 .09 Poor----- C,L,F A,B 25.1 High • 

Knifeblade 2A-172- • 45 .30 Moderate- C,L A 19.7 Moderate. 

Knifeblade 2A-792- .77 .40 Poor----- P,F A,B 28.2 Low. 

Knifeblade 2A-1557 .38 .15 Well----- C,L A 22.3 Moderate. 

Kaolak 937-------- .58 .23 Moderate- C,L,F A 24.8 High. 

Kaolak 2453------- .60 .23 Moderate- C,L,F A,B 32.0 High. 

Kaolak 3187------- .30 .18 Poor----- C,L,F A,B 28.9 High. 

Kaolak 4078------- .30 .15 Poor----- S,C,L,F A 28.4 High. 

Simpson 454------- .18 .15 Poor----- C,L,P,F A,B 20.2 High. 

Simpson 829------- .23 .13 Poor----- C,L,P,F A,B 18.1 High • Simpson 979------- • 17 .07 Poor----- L,P,F A,B 17.6 Moderate. 

Grandstand 364-69- .90 .46 Well----- S,C,L A,B 11.0 High. 

Grandstand 862-82- .38 .17 Very poor S,C,L A 16.0 High. 

Grandstand 2484--- .23 .08 Very poor L,P,F B 35.0 Low . 

Topagoruk 304----- • 38 .11 Poor----- L,P,F B 34.8 Low • 

Topagoruk 603----- • 38 .15 Moderate- L,P A 18.9 High • 

....... Topagoruk 1204---- .77 • 23 Moderate- L,P A 18.7 High • 

- Topagoruk 1790---- .23 .10 Moderate- C,L,P,F A,B 28.7 High • 

Titaluk 539------- • 23 .15 Moderate- C,L,P A 23.0 Moderate. 

Titaluk 2675------ .30 .15 Moderate- S,C,L A 17.6 High. 

Titaluk 3004------ .34 .27 Poor----- L,P A 26.3 High. 

Titaluk 3306------ .36 .23 Poor----- C,L,F A,B 20.0 High. 

Titaluk 3431------ .23 .17 Moderate- P,F A,B 25.0 Moderate. 

Gubik 3112-------- .12 .06 Moderate- L,P,F A,B 41.0 Moderate. 

Gubik 3529-------- .45 .17 Poor----- L,P,F A,B 29.3 High. 

Gubik 3645--~----- .77 .23 Poor----- P,F B 36.6 Low. 

Gubik 3822-------- .38 .18 Well----- S,C,L A 12.3 High. 

Gubik 4243-------- .23 .18 Poor----- L,P,F B 31.9 Low. 

Square Lake 1685-- 1.28 .17 Poor----- L,P,F A,B 28.7 Moderate. 

Square Lake 1854-- .23 .13 Moderate- L,P,F A,B 29.3 Moderate. 

Square Lake 1916-- .48 .17 Poor----- L,P,F A,B 19.0 Moderate. 

Square Lake 3036-- .45 .23 Moderate- S,C,L,P A 13.6 Moderate~ 

Square Lake 3480-- .18 .14 Poor----- L,P,F A,B 22.7 Moderate. 

Square Lake 3856-- .34 .11 Poor----- F B 36.0 Low. 

--1s, sutured; C,concavo-convex; L, long, straight; P, point, tangent; F, floating. 2A, grain contacts; B, authigenic cement. 
Appendix 2.--Modal analyses of 21 surface and 45 subsurface samples of sandstone from the Lower and Upper Cretaceous 

Nanushuk Group, western North Slope, Alaska 

[Q, monocrystalline and polycrystalline quartz, quartzite, and chert; Qm, monocrystalline quartz; P, plagioclase; K, potassium 

feldspar; Lv, volcanic lithic grains; Lm, metamorphic lithic grains; Ls, sedimentary lithic grains; Cc, calcite clasts; 

Cq, chert and polycrystalline quartz; Ac, argillaceous and carbonaceous. All values are in percent; and percentages of 

pores, matrix, cement, and framework grains have been recalculated to total 100 percent] 

Sample Q Qm p K Lv Lm Ls Cc Cq Ac Pores Matrix Cement Framework 

No. grains 

Surface 

1075-------------- 32.3 19.7 2.7 o.o 4.4 16.4 19.0 0.1 12.6 6.3 o.o 37.0 1.7 61.3 

1175-------------- 29.7 12.3 2.0 o.o 8.0 21.8 18.8 0.0 17.1 1.7 0.0 25.9 6.7 67.4 

1275-------------- 38.1 11.0 2.7 0.0 7.6 17.6 28.3 0.0 26.3 2.0 2.0 21.6 6.6 69.8 

1475-------------- 52.7 24.8 2.0 0.0 9.9 9.8 29.5 0.0 26.7 2.8 18.8 3.7 .9 76.6 

1575-------------- 42.0 16.7 3.7 0.0 3.1 24.7 25.6 .3 24.5 .8 0.0 10.8 13.8 75.4 

1875-------------- 57.2 34.3 2.3 .3 5.5 8.5 26.8 0.0 22.9 3.9 1.0 18.1 1.7 79.2 

2075-------------- 56.5 15.7 2.0 .7 9.7 9.0 41.6 0.0 38.3 3.3 1.0 13.3 5.9 79.8 

2175-------------- 42.8 21.3 2.0 0.0 12.2 13.9 23.4 .3 20.6 2.5 13.0 9.1 2.6 75.3 

2675-------------- 47.6 29.3 8.3 1.3 4.0 5.6 19.1 o.o 18.0 1.1 1.7 13.8 15.3 69.2 

~ 3075-------------- 31.7 12.3 2.0 0.0 9.9 14.4 20.7 0.0 19.4 1.3 0.0 23.7 16.6 59.7 

3275-------------- 37.5 21.0 7.7 .3 6.5 2.7 28.2 10.0 16.0 2.2 1.7 15.0 15.3 68.0 

3375-------------- 40.2 8.3 2.3 o.o 8.4 2.1 47.7 7.7 31.9 8.1 .3 8.3 20.8 70.6 

3675-------------- 36.9 23.6 6.0 .3 4.7 2.4 30.6 17.3 12.4 .9 0.0 15.3 16.5 68.2 

3875-------------- 40.9 11.3 2.7 0.0 9.7 3.3 43.0 9.7 29.3 4.0 0.0 6.4 23.2 70.4 

4275-------------- 15.2 11.3 .7 .3 1.0 .3 34.3 30.0 3.6 .7 .3 26.0 25.7 48.0 

4375-------------- 49.6 22.3 6.0 0.0 6.3 8.0 31.3 1.7 27.3 2.3 .7 13.0 12.3 74.0 

4575-------------- 25.8 11.4 3.3 0.0 1.0 7.0 15.7 .3 14.4 1.0 0.0 3.6 57.4 39.0 

4875-------------- 36.0 13.3 2.3 0.0 3.6 4.6 47.0 26.0 20.7 .3 o.o 13.6 14.4 72.0 

5175-------------- 30.4 12.7 5.7 .3 3.9 6.9 24.0 2.3 17.7 4.0 0.0 5.3 40.7 54.0 

5375-------------- 32.3 17.7 5.3 3.3 5.0 1.4 24.0 8.7 14.6 .7 o.o 10.4 32.0 57.6 

5475-------------- 43.9 8.0 1.7 0.0 18.5 4.6 39.0 o.o 35.6 3.4 5.4 11.7 8.8 74.1 

Subsurface 

Meade 2953-------- 54.7 36.0 7.7 0.0 5.4 4.3 24.0 0.3 18.7 5.0 6.7 6.0 9.6 77.7 

Meade 4133-------- 35.9 22.3 7.0 0.0 5.4 6.3 27.6 4.0 13.3 10.3 2.7 20.4 6.8 70.1 

Wolf Creek 1-867-- 43.8 20.1 .7 o.o 2.0 21.4 27.4 0.0 23.4 4.0 0.0 11.4 13.0 75.6 

Wolf Creek 3-1553- 69.1 48.2 .3 .3 3.3 4.3 20.6 0.0 20.6 0.0 14.6 3.7 3.7 78.0 

Wolf Creek 3-2050- 47.9 27.1 5.7 .3 7.4 5.0 23.8 1.0 19.8 3.0 2.0 24.4 2.7 70.9 

Wolf Creek 3-2532- 45.0 22.0 3.3 0.0 1.3 12.0 26.0 1.0 22.0 3.0 0.0 22.9 2.7 74.4 

Wolf Creek 3-3109- 39.2 24.9 2.7 .3 .3 .7 15.3 .7 14.3 .3 0.0 35.9 16.3 47.8 

Wolf Creek 3-3509- 28.7 20.0 3.7 .3 1.0 1.0 13.0 3.0 8.7 1.3 0.0 42.0 16.4 41.6 
Ouma1ik 979-84---- 36.7 19.7 5.3 2.0 3.3 1.7 37.7 13.0 17.0 1.7 4.7 17.3 6.9 71.1 

Ouma1ik 1606------ 36.9 21.3 9.3 2.3 6.6 3.9 28.0 4.0 15.3 8.7 1.7 15.3 11.0 72.0 

Ouma1ik 3260------ 40.0 22.0 7.3 0.0 6.0 4.6 27.0 2.0 18.0 7.0 2.3 14.3 14.0 69.4 

Ouma1ik 3752.5---- 46.1 27.7 4.3 0.0 2.4 3.7 26.4 3.7 18.4 4.3 1.7 17.7 7.4 73.2 

Knifeb1ade 2A-172- 50.7 23.7 2.0 0.0 5.0 6.3 31.3 0.0 25.0 6.3 9.7 9.7 10.0 80.6 

Knifeb1ade 2A-792- 43.4 26.3 1.7 0.0 5.3 12.1 20.4 0.0 16.4 4.0 2.3 13.6 14.6 69.5 

Knifeb1ade 2A-1557 40.3 28.3 7.0 1.7 2.4 3.9 27.7 12.3 11.7 3.7 3.7 14.3 8.0 74.0 

Kao1ak 937-------- 46.4 21.7 3.0 0.0 4.7 9.0 31.0 2.3 24.7 4.0 5.3 20.4 4.4 69.9 

Kao1ak 2453------- 38.7 14.7 2.3 0.0 2.7 6.3 32.0 6.0 23.0 3.0 1.0 25.0 7.0 67.0 

Kao1ak 3187------- 39.6 20.3 5.3 1.7 3.3 4.7 29.7 8.7 19.3 1.7 2.3 20.0 8.9 68.8 

Kao1ak 4078------- 42.0 29.3 9.7 0.0 5.0 5.0 17.7 2.3 12.7 2.7 5.0 18.0 10.4 66.6 

Simpson 454------- 43.6 31.4 4.0 1.3 3.3 5.0 33.4 6.3 11.9 15.2 10.6 18.9 1.3 69.2 

Simpson 829------- 31.4 19.7 4.7 1.7 3.6 8.7 27.1 5.4 11.7 10.0 14.4 14.1 4.0 67.5 

Simpson 979------- 38.6 17.3 4.3 .7 3.0 7.0 39.6 9.3 21.3 9.0 9.7 15.6 2.0 72.7 

Grandstand 364-69- 57.6 33.6 0.0 0.0 5.6 9.0 29.0 .7 22.3 6.0 11.6 9.0 2.0 77.4 

Grandstand 862-82- 55.6 38.3 1.0 0.0 1.0 10.3 23.7 0.0 17.0 6.7 8.0 15.0 1.0 76.0 

Grandstand 2484--- 40.3 28.0 1.0 0.0 1.3 4.3 21.6 3.0 12.3 6.3 0.0 29.7 5.3 65.0 

Topagoruk 304----- 36.5 25.6 4.3 1.0 7.7 9.6 16.6 1.0 10.6 5.0 .7 3.6 21.2 64.5 

~ Topagoruk 603----- 36.7 21.7 4.7 1.7 4.0 9.3 23.7 5.3 14.7 3.7 13.7 15.3 3.6 67.4 

Topagoruk 1204---- 40.2 16.1 4.7 2.7 5.0 5.3 33.8 5.7 24.1 4.0 12.4 15.0 4.0 68.6 

Topagoruk 1790---- 35.7 20.0 4.3 2.3 9.7 10.0 25.4 6.7 15.7 3.0 3.0 24.0 4.7 68.3 

Tita1uk 539------- 51.0 32.7 2.0 0.0 3.6 8.7 21.6 .3 17.3 4.0 4.7 20.3 2.7 72.3 

Tita1uk 2675------ 54.7 29.7 3.3 2.7 5.7 5.4 29.3 1.0 24.0 4.3 5.7 9.6 8.0 76.7 

Tita1uk 3004------ 50.2 24.3 3.3 .3 2.6 6.6 30.9 1.3 24.6 5.0 3.0 15.0 11.3 70.7 

Tita1uk 3306------ 49.6 25.0 5.3 2.3 5.3 5.0 34.3 4.0 24.6 5.7 3.3 10.7 9.3 76.7 

Tita1uk 3431------ 35.7 20.3 7.0 0.0 4.3 8.4 30.4 9.7 15.4 5.3 3.3 18.0 7.0 71.7 

Gubik 3112-------- 42.3 30.0 2.7 4.0 .3 1.6 15.3 0.0 12.0 3.3 o.o 36.7 4.3 59.0 

Gubik 3529-------- 28.6 15.0 5.7 2.0 3.3 8.0 29.9 7.3 13.3 9.3 3.3 24.6 4.7 67.4 

Gubik 3645-------- 45.4 31.0 5.7 0.0 .6 3.4 17.4 1.0 13.7 2.7 o.o 33.6 3.0 63.4 

Gubik 3822-------- 64.0 40.0 1.0 .3 .3 10.0 25.3 0.0 24.0 1.3 9.7 11.7 .6 78.0 

Gubik 4243-------- 40.2 21.6 3.3 o.o 1.0 4.7 32.6 10.3 18.6 3.7 1.0 23.6 8.3 67.1 

Square Lake 1685-- 33.8 15.7 2.0 .3 5.6 10.3 27.0 2.3 17.4 7.3 8.0 16.7 12.0 63.3 

Square Lake 1854-- 43.0 32.0 6.0 .7 2.0 5.0 14.0 .7 11.0 2.3 7.0 26.3 3.0 63.7 

Square Lake 1916-- 45.9 23.0 2.0 .7 3.1 6.0 30.9 4.0 21.6 5.3 10.0 12.3 6.7 71.0 

Square Lake 3036-- 63.1 45.7 1.7 1.7 4.0 6.3 18.4 0.0 15.7 2.7 8.7 6.6 7.0 77.7 

Square Lake 3480-- 49.7 36.0 8.0 0.0 1.0 2.7 16.0 0.0 13.7 2.3 10.7 21.0 1.7 66.6 

Square Lake 3856-- 33.8 18.7 3.3 1.0 2.6 6.7 27.7 6.3 14.4 7.0 .7 25.0 11.0 63.3 
~ 

Appendix 3.--Clay-mineral analyses by X-ray diffraction of the clay-fraction separates from each surface sample 

[Oriented mounts were made to aid in identification of the clay minerals; glycolation, potassium-acetate intersalation, and various heating 

techniques were incorporated (amounts estimated in parts per ten); Paul D. Blackmon and Harry C. Starkey, analysts. Leaders (---) indicate 

none present] 

Sample 

No. 

1075----------------

1175----------------

1275----------------

1475----------------

1575----------------

1875----------------

2075----------------

2175----------------

2675----------------

3075----------------

3275----------------

3375----------------

3675----------------

3875----------------

4275----------------

4375----------------

4575----------------

4875----------------

5175----------------

5375----------------

5475----------------

Kaolak 1-937--------

Kaolak 1-2453-------

Kaolak 1-3187-------

Kaolak 1-4078-------

Kaolak 1-6739-------

Illite 

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

-1 

1+ 

1 

-1 

-1 

Illite-mica 

or mica 

4 

4+ 

3+ 

5 

5 

3+ 

2+ 

3+ 

1+ 

3+ 

2 

1+ 

1+ 

1+ 

1+ 

2 

2+ 

1 

1+ 

1+ 

1-

---

---

---

---

---

Illitemontmorillonite, 

mixed 

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

1 

---

1-

Trace 

1+ 

1-

---

---

Trace 

Trace 

Trace 

Montmorillonite 

Surface 

---

---

---

---

---

Trace 

1 

1-

---

---

---

Trace 

1-

Trace 

---

---

---

---

---

---

---

Subsurface 

Trace 

---

---

---

---

Clay types 

Chloritemontmorillonite, 

mixed 

---

---

---

---

---

---

---

---

---

2 

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

Chlorite 

5 

4+ 

2+ 

1 

2 

2+ 

2+ 

2+ 

1+ 

2+ 

2 

1+ 

1-

1 

1-

Trace 

1-

Trace 

Trace 

Trace 

Trace 

Trace 

Trace 

Trace 

Trace 

Trace 

Micachlorite, 

mixed 

---

---

---

---

---

---

---

---

1 

---

---

---

---

---

---

---

---

---

---

---

---

---

---

Kaolinite Serpentine 

2+ 

1 

1+ 

2+ 

2+ 

1+ 

--- 4+ 

--- 3+ 

1-

1+ 

--- 3+ 

5 

4+ 

3+ 

5+ 

4 

3+ 

5+ 

Trace 

-1 

-1 

1 

Trace 
Topagoruk l-304p---- -1 --- Trace --- --- Trace --- Trace 

Topagoruk l-603p---- -1 --- Trace --- --- Trace --- Trace 

Topagoruk l-1204p--- 1 --- --- --- --- Trace --- Trace 

Topagoruk l-1790p--- --- -1 Trace --- --- Trace --- Trace 

Topagoruk 1-5972---- --- -1 --- --- --- Trace --- Trace 

Topagoruk 1-6498---- 1+ --- Trace --- --- Trace 

Simpson 454--------- --- 1 Trace --- --- -1 --- Trace 

Simpson 829--------- --- 1 Trace --- --- -1 --- Trace 

Simpson 979--------- --- 1 --- --- --- -1 --- Trace 

Meade 1-2953-------- -1 --- Trace --- --- Trace --- Trace 

Meade 1-4133-------- -1 --- Trace --- --- Trace --- -1 

Oumalik l-979p------ -1 --- --- --- --- Trace --- Trace 

Oumalik l-1606p----- -1 --- --- --- --- Trace --- -1 

Oumalik l-3260p----- -1 --- Trace --- --- Trace --- Trace 

Oumalik l-3752p----- 1 --- --- Trace --- Trace --- Trace 

Titaluk l-539p------ --- 1+ --- --- --- -1 --- -1 

Titaluk l-2675p----- Trace --- --- --- --- Trace --- Trace 

Titaluk l-3004p----- -1 --- --- --- --- Trace --- -1 

Tita1uk 1-3306------ -1 --- --- --- --- Trace --- Trace 

Titaluk l-343lp----- Trace --- --- --- --- -1 

Wolf Creek 1-867---- --- 1 --- --- --- Trace --- -1 

Wolf Creek 3-1553--- Trace --- --- --- --- Trace --- Trace 

Wolf Creek 3-2050--- -1 --- --- --- --- Trace --- Trace "'-1 

01 Wolf Creek 3-2532--- --- 1+ --- --- --- 1 

Wolf Creek 3-3109--- 1 --- Trace --- --- -1 --- Trace 

Wolf Creek 3-3509--- 1 --- --- --- --- -1 

Grandstand 364-69--- --- -1 --- --- --- Trace --- Trace 

Grandstand 862-82--- --- -1 --- --- --- Trace --- Trace 

Grandstand 2484----- --- 1 --- --- --- Trace 

Knifeblade 2A-172p-- Trace --- --- --- --- Trace --- -1 

Knifeblade 2A-792p-- -1 --- --- --- 1 -1 

Knifeblade 2A-1557n- -1 --- --- --- --- -1 

Square Lake 1685---- 1+ --- --- Trace --- Trace --- Trace 

Square Lake 1854---- 1 --- Trace --- --- Trace --- Trace 

Square Lake 1916---- 1 --- --- --- --- Trace --- Trace 

Square Lake 3036---- -1 --- --- --- --- Trace --- Trace 

Square Lake 3480---- -1 --- --- --- --- Trace --- Trace 

Square Lake 3856---- -1 --- --- --- --- Trace --- Trace 

Gubik 2-3112-------- --- 1+ Trace --- --- -1 

Gubik 2-3529-------- 1+ --- Trace --- --- -1 

Gubik 2-3645-------- 1 --- Trace --- --- Trace --- Trace 

Gubik 2-3822-------- -1 --- --- --- --- Trace --- Trace 

Gubik 2-4243-------~ 1+ --- --- --- --- Trace --- Trace 
Appendix 4.--List of porosity and permeability data from the subsurface samples studied (Robinson, 1956, 195Ba, b, c, 1964; 

Collins, 195Bb, c, 1959) 

Test Depth Effect'ive Air Presence Test Depth Effective Air Presence 

well (ft) 1 porosity permeability2 of coal 3 well (ft) 1 porosity permeability2 of coal 3 

Meade-------- 2,953(p) 19.2 13.48 --- Titaluk------ 539(p) 12.0 Imp. 

Meade-------- 2,953(n) 13.7 9.54 --- Titaluk------ 539(n) 11.7 n.a. 

Meade-------- 4,133 9.35 Imp. --- Titaluk------ 2,675(p) 12.45 17.0 

Titaluk------ 2,675(n) 11.3 8.0 

Wolf Creek 1- 867 5.31 Imp. --- Titaluk------ 3,004(p) 8.25 Imp. 

Wolf Creek 3- 1,553 18.88 305.00 --- Titaluk------ 3,004(n) 9.96 n.a. 

Wolf Creek 3- 2,050 10.6 <1 --- Titaluk------ 3,306(p) 8.98 Imp. 

Wolf Creek 3- 2,532 4.73 Imp. --- Titaluk------ 3,306(n) 8.83 n.a. 

Wolf Creek 3- 3,109 2.4 Imp. --- Titaluk------ 3,43l(p) 10.5 Imp. 

Wolf Creek 3- 3,509 5.5 Imp. --- Titaluk------ 3,43l(n) 12.0 n.a. 

Oumalik------ 979-984 15.2 34.0 --- Gubik-------- 3,112 10.6 Imp. 

Oumalik------ 1,606(p) 10.9 8.8 --- Gubik-------- 3,529 13.46 2.3 

Oumalik------ 3,260 9.2 <4 --- Gubik-------- 3,645 10.36 Imp. 

Oumalik------ 3,752.5 12.0 <1 --- Gubik-------- 3,822 14.07 22.0 

Gubik-------- 4,243 10.35 Imp. 

""-~ Knifeblade 2A 172 41.0 n.a. X 0) . 

Knifeblade 792 14.2 1.3 Square Lake-- 1,685 18.3 28.0 2A X 

Knifeblade 2A 1,557 11.56 <1 X Square Lake-- 1,854 13.5 <1 

Square Lake-- 1, 916 17.5 n.a. 

Kaolak------- 937 11.55 Imp. --- Square Lake-- 3,036 13.3 17.6 

Kaolak------- 2,453 11.90 Imp. X Square Lake-- 3,480 12.7 Imp. 

Kaolak------- 3,187 10.04 Imp. --- Square Lake-- 3,856 8.9 Imp. 

Kaolak------- 4, 078 11.28 Imp. 

Simpson------ 454 31.4 n.a. --- l(p), test plug made to determine permeability parallel to bedSimpson------ 829 28.8 n.a. --- ding; (n), test plug made to determine permeability perpendicular 

Simpson------ 979 30.3 n.a. --- to bedding. 

2Imp., impermeable; n.a., not analyzed. 

Grandstand--- 364-369 10.6 n.a. --- 3 ___ , none present; x, present. 

Grandstand--- 862-882 11.15 <1 

Grandstand--- 2,484 5.02 Imp. 

Topagoruk---- 304(p) 11.0 5.17 

Topagoruk---- 304(n) 11.1 Imp. 

Topagoruk---- 603(p) 27.2 316.2 

Topagoruk---- 603(n) 26.2 219.8 

Topagoruk---- 1, 204 (p) 26.0 200.4 

Topagoruk---- 1,204(n) 23.1 128.9 

Topagoruk---- 1,790 18.1 11.8 
STRATIGRAPHY AND PETROGRAPHY OF A 

MEASURED SECTION ON THE SOUTH LIMB OF 

BARABARA SYNCLINE, NORTH SLOPE, ALASKA 

By A. Curtis Huffman, Jr. 

INTRODUCTION 

This paper discusses the stratigraphy and 

petrography of the middle portion of the Lower 

and Upper(?) Cretaceous Nanushuk Group, with 

emphasis on those properties affecting oil and 

gas reservoir potential as well as uranium 

host-rock potential. The longest and best 

exposed outcrop of this part of the Nanushuk 

Group measured during the 1977 field season was 

on the south limb of Barabara Syncline. The 

section was measured along the Kukpowruk River 

from 69°24'46" N. and 162°40'58" W. to 69°25'17" 

N. and 162°41'46" W. (fig. 36), a distance of 

3.25 km and a stratigraphic thickness of 1,424 

m. Exposure in this interval was nearly 100 

percent; Chapman and Sable (1960, pl. 11), 

166° 162° 

7oo 

however, measured an additional 1,000 m of very 

poorly exposed nonmarine sediments downstream 

from this section. 

This section was selected for detailed 

petrographic and stratigraphic study for the 

following reasons: (1) the outcrop is long and 

very well exposed; (2) it was the northernmost 

section measured; (3) it lies along the general 

sediment-transport direction (Ahlbrandt and 

others, this volume), approximately halfway 

between the Corwin Bluff section to the southwest and the Kaolak test well to the northeast 

(the closest subsurface information on the 

Corwin delta); and (4) it includes a thick 

transitional zone between marine and nonmarine 

sedimentary sequences which is characteristic 

of the Corwin delta. 

158° 154° 150° 

-¢-Kaolak I 

BARABARA SYNCLINE 

SNOWBANK ANTICLINE 

6go • 

·-

I 

Mts 

BROOKS RANGE 0 

I 

0 

I 

50 

50 

I 

I 

100 

I 

I 

II 

100 MILES 

I 

1 50 KILOMETERS 

Figure 36.--Index map showing locations of the south limb of Barabara Syncline (x), the test wells 

(crossed open circle), and surface samples (solid dot) discussed by Bartsch-Winkler (this 

volume). 

77 
By selecting this section for study in 

detail, a preliminary comparison can be made 

between the Corwin delta and the Umiat delta, 

which was studied in comparable detail in Umiat 

test well 11 (Fox and others, 1979; Fox, this 

volume). The section described includes the 

Kukpowruk and Corwin Formations and corresponds 

approximately to the Grandstand Formation and 

lower part of the Killik Tongue of the Chandler 

Formation of the Umiat 11 well. 

STRATIGRAPHY 

The sequence of Lower Cretaceous rocks 

exposed on the south limb of Barabara Syncline 

is very similar to that measured throughout the 

western portion of the North Slope. This 

sequence has been interpreted by Ahlbrandt and 

others (this volume) t"o have been deposited in 

a deltaic environment. Such an interpretation 

is consistent with the results of this detailed 

study; however, the specific type of delta is 

somewhat questionable, as discussed in Ahlbrandt 

and others (this volume). The lower marine 

portion of the Nanushuk Group was not measured 

in this section, but the thick transitional and 

nonmarine portions seem to have been deposited 

in a river-dominated delta system. 

The measured section originated 410 m 

downstream (north) from the approximate axis of 

Snowbank Anticline along the Kukpowruk River. 

At the base of the section, the bedding strikes 

N. 80° E. and dips 56° northwest along the 

western bank of the river; it appears to have a 

much shallower dip along the eastern bank, 

indicating the presence of minor structures. 

Exposures between the base of the section and 

the core of the anticline are very poor and 

nearly flat-lying; however, they appear to be 

composed entirely of marine sandstones and 

shales. From the base of the section northward, 

structural complexity is minimal and dips 

decrease regularly away from the anticline. 

The stratigraphic section on the south 

limb of Barabara Syncline was measured using a 

combination of tape and jacob-staff methods. 

The sandstone intervals were described on a 

meter by meter basis, whereas the shale intervals, although measured by the same methods, 

were described in much less detail. Sampling 

for porosity and permeability determinations 

and for petrographic study was not systematic; 

rather, it concentrated on the coarser grained, 

thicker sandstones, which are of greater interest from a petroleum reservoir standpoint. 

Thirty-four samples were taken from a total of 

154 sandstone beds. The thicker beds were 

frequently sampled at several horizons. 

The basal 90 m of the section is composed 

entirely of marine sandstone, shale, and several 

thin siltstone intervals. The shale is dark 

greenish gray to black and is virtually identical to the marine shale of the Torok Formation 

of Early Cretaceous age, which underlies the 

Nanushuk Group. Fossils recovered from the 

78 

shale include both marine pelecypods and abundant burrows parallel to bedding. Sandstones 

compose 14 percent of the section and are 

generally thin (less than 2m), with the thickest being 6 m. They are light olive gray to 

pale yellowish brown, very fine to fine grained, 

and moderately well to well sorted; they have 

very sparse burrowing and commonly contain 

plant debris and carbonaceous material on the 

bedding planes. Most of these sandstones are 

both symmetrically and asymmetrically rippled; 

the thickest bed also contains low- to moderateangle planar crossbedded sets as thick as 15 

em. 

Above the basal marine section is a 480-mthick sequence of alternating nearshore-marine 

and nonmarine sandstones and shales. This 

thick transitional zone is characteristic of 

the Corwin delta and contains not only the 

highest percentage of sandstone (26 percent) 

but also over 50 percent of the total sandstone 

in this section. The sandstone beds are generally thicker in this interval than in the 

remainder of the section. They average almost 

3 m, and some beds are as much as 14 m. 

Several distinctive environments are 

represented in the transitional zone. They 

include (1) marine (foreshore, shoreface, and 

prodelta); (2) estuarine or lagoonal; and (3) 

nonmarine (channel, overbank, and lacustrine). 

Various combinations of these environments 

alternate in 40- to 80-m-thick, coarseningupward cycles that generally begin with black 

marine shales at the base and progress upward 

into thin siltstone beds, shoreface sands, and 

foreshore sands, which may or may not be capped 

by nonmarine deposits. The marine sediments 

dominate the· lower transition zone, with the 

nonmarine becoming increasingly abundant upward. 

The marine sandstones in the transitional 

zone are generally light brownish gray to pale 

yellowish brown, very fine to fine grained, 

thin to very thin bedded, and moderately well 

to well sorted. They are calcareous and contain 

plant debris and carbonaceous material on 

bedding planes. Sedimentary structures are 

variable, depending on the environment of 

deposition, as are the fossil and trace-fossil 

content. The shoreface sandstones are characterized by contorted bedding, trough and lowto moderate-angle planar crossbedding, ripples, 

and a variety of trace fossils. Foreshore 

sandstones are flat bedded to low angle planar 

crossbedded and contain sparse trace fossils, 

most commonly Skolithos and Diplocraterion, and 

abundant root tubes. The dark-greenish-gray to 

black marine shales are commonly rippled and 

have abundant trace fossils on the bedding 

planes. Marine pelecypods, though not common, 

are more plentiful in the shales than in the 

sandstones. 

Nonmarine deposits in the transitional 

zone vary from thin (less than 1 m) carbonaceous 

shale beds in a predominantly marine sequence 

to 55-m-thick sequences of carbonaceous shale, 
fluvial-channel sandstones, and lacustrine 

shale and siltstone deposits. The carbonaceous 

shale is medium gray to dark greenish gray and 

silty; it often contains leaf and stem imprints 

as well as abundant plant debris. The fluvial 

sandstones are predominantly of braided-channel 

and probable crevasse-splay origin; they are 

light gray to light olive gray, fine to medium 

grained, moderately well to well sorted, very 

thin to medium bedded, and trough crossbedded 

and rippled. Carbonaceous material and plant 

fragments are abundant in the sandstones, and 

well-preserved leaf and stem imprints are 

common in the finer grained beds within the 

transitional zone. 

The nonmarine portion of the section at 

this locality exceeds 860 m in thickness and 

consists of predominantly carbonaceous shale 

and thin sandstone beds. Chapman and Sable 

(1960, pl. 11) reported a total nonmarine 

section of over 2,276 m, but much of this was 

covered. The total amount of sandstone in the 

measured 860 m is very small (less than 12 

percent) and the individual sandstone beds are 

generally very thin, averaging less than 1.5 m; 

however, the thickest single sandstone body in 

the entire section occurs in the nonmarine 

section 58 m above the base. This 25-m-thick 

unit is predominantly pale-yellowish-brown, 

medium- to fine-grained, moderately well sorted, 

medium-bedded to very thin bedded, troughcrossbedded, calcareous sandstone. Also included are flat-bedded, asymmetrically rippled 

sequences and a number of channel lag deposits 

that are predominantly clay rip-up fragments 

and carbonaceous material. The unit is composed 

of several fining-upward sequences beginning 

with coarse-grained lag deposits and ending 

with clay drapes. This thick unit was most 

likely deposited by a meandering stream, interpreted as being the major distributary in this 

portion of the delta primarily because of the 

thickness and large amount of coarse-grained 

material. 

Twenty-four coal beds were measured that 

have a total thickness of 21 m or 2.4 percent 

of the nonmarine portion of the section. The 

thickest bed was 3 m and several were between 1 

and 2 m thick. The coal, although not yet 

analyzed, is of generally low rank and is 

commonly interbedded with carbonaceous shale 

and siltstone. The marshes and swamps on the 

delta plain were evidently of fairly short 

duration and somewhat limited extent. 

PETROGRAPHY 

Methods 

Standard thin sections were cut from each 

sample,- with one half of each section being 

stained with Alizarin Red S to detect calcite 

and the other, with sodium cobaltinitrite to 

detect potassium feldspars. Each sample was 

also injected with blue plastic to enhance the 

pores. 

79 

The petrographic analysis was conducted 

according to the methods discussed by Dickinson 

(1970). Three hundred points per thin section 

were counted. The percentages of 27 compositional variables were determined and combined 

into the 12 categories presented in table 5. 

By variously combining these parameters, the 

data can be represented in either the Dickinson 

(1970) (fig. 37) or Folk (1968) (fig. 38) 

classification systems. 

Textural observations made during the 

petrographic study included maximum and modal 

grain size, sorting, roundness, and types of 

grain contacts. Grain size was determined by 

measuring the long axis of individual clasts, 

and sorting was calculated on the basis of 

these measurements. Roundness was estimated by 

comparison with the Krumbein (1941) visual 

estimator. Porosity and permeability measurements were conducted on each sample and are 

reported with the textural data in table 6. 

The uranium and thorium content of each 

sample was determined by the delayed-neutron 

method and is reported in table 7. Field 

measurements of radioactivity were made with a 

ratemeter for most of the thicker sandstone 

beds, as well as for some of the coal seams and 

a few shale intervals. 

Results 

Thirty-four samples from the measured 

section and two from the trough of Barabara 

Syncline -were studied. The results of these 

analyses are presented in tables 5 and 6. The 

following description is presented in such a 

manner as to facilitate comparison with the 

description of Umiat test well 11 (Fox and 

others, 1979), which is summarized by Fox (this 

volume). The measured section described here 

roughly corresponds to the Lower Cretaceous 

Grandstand Formation and lower part of the 

Killik Tongue of the Chandler Formation in the 

report by Fox and others (1979). (See, for 

example, Chapman and Sable, 1960, fig. 12, for 

an approximate correlation.) 

The samples from the south limb of Barabara 

Syncline show little lithologic variation. 

They are light-gray to pale-yellowish-brown, 

well-sorted to moderately well sorted, very 

fine grained to medium-grained chert and 

shale-arenites and calc-lithites. Lithic 

fragments contain chert and polycrystalline 

quartz, argillaceous and carbonaceous fragments, 

and recrystallized calcite. They constitute an 

average of 38 percent of each sample, and the 

percentage of cement, primarily calcite, varies 

from 4 to 50. The detrital grains are subrounded to-subangular, and grain contacts vary 

from smooth and concave-convex to those with 

some suturing and evidence of presolution. The 

softer argillaceous-carbonaceous clasts are 

commonly deformed and squeezed between the 

framework grains, thus filling the pore spaces 

and greatly reducing the porosity and permeability. 
Table 5.--Composition of samples from the south limb of Barbara Syncline 

[Modal percentages based on 300 points per thin section; L, M, or U following sample numbers indicates lower, middle, or upper sampl~ 

from one sandstone unit; Qm, monocrystalline quartz; Pq, polycrystalline quartz (less quartzite); Lv, volcanic lithic fragments; 

Lm, metamorphic lithic fragments; Ls, sedimentary lithic fragments; Ac, Argillaceous and carbonaceous; leaders (---) indicate none 

observed) 

Sample Total Qm Pq Feldspar Lv Lm 

No. quartz 

77AAH: 

184 63.3 22.3 39.7 2.6 2. 7 1.6 

183 49.0 37.3 11.4 7.6 4. 7 1.3 

77ACH: 

129 28.6 21.6 6. 7 5.3 1.0 1.3 

127 38.0 13.7 24.3 5.0 3.3 2.4 

126 34.0 23.6 9.4 6.0 3. 7 1.6 

123 47.3 32.3 14.7 8.6 3.6 . 6 

120U 25.0 13.0 11.7 3.3 1.6 2.0 

120L 34.6 20.0 13.6 3.3 .3 1.0 

116 50.3 22.6 26.3 4.3 .3 1.3 

113 25.3 22.3 3.0 3.3 

110 24.6 11.3 13.3 3.0 3.3 

108U 40.6 26.6 14.0 6.6 1.3 

108M 40.6 25.3 15.3 7.3 .3 

108L 38.6 27.3 11.3 7.6 .6 

104U 56.6 39.3 17.3 12.0 1.0 

104L 50.0 42.0 8.0 10.3 2.0 

lOlU 42.6 31.6 11.0 7. 6 1.6 

101M 42.3 37.3 5.0 5.6 2.3 

lOlL 45.0 36.3 8. 7 7.3 1.3 

100 42.6 30.3 12.3 10.6 2.0 

98U 34.6 21.3 13.3 5.6 1.3 

98L 34.0 22.0 12.0 7. 3 3.0 

97 48.0 29.0 19.0 12.0 2.0 

93U 58.3 26.7 31.6 8.6 3.0 

93M 53.6 29.0 24.6 9.3 5.3 

93L 43.0 20.7 22.3 8.6 3.0 

92 51.0 26.3 24.4 12.6 4.0 .3 

90U 52.6 32.3 20.0 10.0 3.3 .3 

90L 55.7 31.0 24.7 10.6 5.0 .3 

89U 52.0 28.0 23.3 7. 6 s.o 

89L 49.0 28.3 20.7 9. 3 8.0 

87U 44.6 25.3 19.3 12.6 6.6 

87L 54.7 28.0 26.7 7.6 6.6 

85 63.3 34.3 29.0 12.0 3.0 

83 48.6 30.6 18.0 13.3 4.0 

82 51.3 26.0 25.0 17.0 4.0 .3 

Average 44.1 27 .o 17 .o 7.8 2.8 .4 

Quartz includes monocrystalline quartz and 

polycrystalline quartz, chert, and quartzite. 

The monocrystalline grains are commonly 

strained, exhibiting various degrees of undulose 

extinction and, rarely, boehm lamellae. According to Dickinson (1970), the distinction between 

polycrystalline quartz and chert is arbitrarily 

made on the basis of size of the crystallites, 

with chert being less than 0.03 mm, the thickness of a thin section. Every gradation in 

size between the two size categories can be 

seen in the thin sections studied. Also included in the chert designation by Dickinson (1970) 

is the chalcedonic variety, which is very rare 

in these samples. Although an attempt was made 

to separate these various forms of chert during 

the point count, all forms were later combined 

under the polycrystalline-quartz category. 

Polycrystalline quartz, as used here, therefore 

includes chert grains, recrystallized chert, 

and possibly some metamorphic quartzite, although 

this was included in the metamorphic-lithics 

category when recognized. 

Ls Ac Calcite Matrix Cement Mica Other heavy 

clast minerals 

49.3 9.6 1.6 4.4 0.6 

21.0 7. 3 2.3 10.3 12.7 .3 .6 

18.3 7. 3 4.3 .3 so. 7 .6 .6 

39.9 12.6 3.0 4.0 30.3 .3 .6 

20.0 8.3 2.3 1.0 43.3 • 6 

33.0 15.3 3.0 9.0 11.0 1.0 

39.0 3.3 24.0 9.3 30.3 1.0 

58.6 13.0 32.0 3.0 14.6 .6 

41.3 14.0 1.0 9.3 17.3 3. 3 

42.0 9.0 30.0 8.3 22.3 1.6 

42.6 17.0 12.3 s. 3 32.7 .6 1.0 

31.7 13.6 4.1 8.9 21.7 1.6 

31.6 13.0 3.3 5.3 27.3 .3 2.3 

32.0 17.3 3.4 8.0 21.6 2.6 

27.6 8.6 1.7 2.0 13.3 3.3 

21.0 11.7 1.3 8.0 14.6 .6 

31.4 17.7 2. 7 s.o 21.3 1.3 

26.0 19.0 2.0 7. 3 19.0 1.0 

30.0 17.3 4.0 6.3 14.3 1.0 2.0 

33.6 10.0 11.3 5,0 16.0 2. 3 

38.3 13.7 11.3 5. 7 22.6 .6 4.3 

34.0 16.3 s. 7 8.0 20.0 .3 2.0 

35.0 12.3 3. 7 4.6 16.0 1.3 

41.9 9. 7 .6 6.3 11.3 .6 1.3 

36.9 10.7 1.6 6.0 11.6 .3 • 6 

43.3 18.0 3.0 10.0 13.0 1.3 

34.4 10.0 7 .o 11.6 .3 .3 

35.7 15.7 6. 6 10.0 .3 .6 

37 .o 12.3 6.6 6.0 2.0 

37.3 14.0 7.0 10.0 1.3 

34.7 11.0 3.0 8. 7 10.3 .6 

36.3 15.7 1.3 9. 7 7.5 . 6 

42.3 15.6 8.6 5.0 1.0 

36.3 6. 7 .6 4.6 9.0 

27.3 7.0 2.3 9.3 8.9 1.0 

29.7 4.0 • 7 11.4 8.9 .6 

34.3 12.2 5.4 6.5 17.9 .2 1.3 

Feldspar (2.6-27.0 percent) occurs primarily in the form of blocky, partially to totally 

altered grains. Plagioclase (1.3-11.3 percent), 

An 25-35 on albite twinning, is unzoned, normally albite twinned, and commonly altered to some 

extent by sericitization or kaolinization. 

Albite (less than 2 percent) is untwinned and 

fairly fresh, as is much of the potassium 

feldspar (1.0-6.7 percent). Grid twinning is 

exhibited by about 10 percent of the potassium 

feldspar, and grains of perthite and myrmekite 

are rare but found throughout. 

Sedimentary lithic fragments compose a 

large percentage of each sample (18.3-58.6 

percent) and include polycrystalline quartz 

(3.0-39.7 percent), calcite clasts (0-30 percent), and argillaceous-carbonaceous fragments 

(3.3-19 percent). The argillaceous and carbonaceous fragments are here treated together 

because of their close association in many 

grains and the difficulty of differentiation. 

Often, though, the argillaceous fragments are 

finely layered and may contain silt-size or 

80 
Quartz 

Feldspar A Lithic grains 

Framework 

Matrix B Cement 

Figure 37.--Ternary diagrams of the data in 

table 5 showing (a) quartz (monocrystalline 

and polycrystalline quartz, quartzite, and 

chert), feldspar, and lithic grains; and (b) 

framework, matrix, and cement. 0 , marine; 

& , nonmarine; @ , samples not in measured 

section (77AAH183 and 77AAH184) but included 

in the petrographic study. Modified from 

Dickinson (1970). 

---- lowest segment from figure 41; 

middle segment from figure 41; 

------ uppermost segment from figure 41. 

Figure 38.--Ternary diagrams using Folk's (1968)~ divisions and end points, showing (a) 

quartz (monocrystalline quartz and quartzite), feldspar, and lithic fragments 

(including chert and polycrystalline 

quartz); (b) lithics; and (c) sedimentary 

lithics. 0 , marine; & , nonmarine; @ , 

samples not in measured section (77AAH183 

81 

Feldspar 

Volcanic lithic grains 

Calcareous 

Monocrystalline Quartz 

Quartzarenite 

A 

Sedimentary I ithic grains 

I 

A 

;· .. 

Sedimentary-litharenite 

Volcanic-litharenite Phyllarenite 

B 

Argillaceous/Carbonaceous 

c 

Metamorphic lithic grains 

Chert I Polycrystallin e 

and 77AAH184) but included in the petrographic study. 

---- lowest segment from figure 41; 

middle segment from figure 41; 

------ uppermost segment from figure 41. 
Table 6.--Textural data on samples from the south limb of Barabara Syncline 

[Leaders (---) indicate not determined; mD, millidarcy; L, M, or U following sample numbers indicates 

lower, middle, or upper sample from one sandstone unit; V., very; M., moderately; Mod., moderate; Sbrd, 

subround; Shang, subangular; Ang, angular] 

Sample 

No. 

77AAH: 

184 

183 

77ACH: 

129 

127 

126 

123 

120U 

120L 

116 

ll3 

110 

108U 

108M 

108L 

104U 

104L 

101U 

101M 

lOlL 

100 

98U 

98L 

97 

93U 

93M 

93L 

92 

90U 

90L 

89U 

89L 

87U 

87L 

85 

83 

82 

Average 

Maximum 

grain size 

(mm) 1 

0.40 

.20 

.20 

.50 

.50 

.40 

.30 

.40 

.70 

.20 

.60 

.40 

.so 

.40 

.30 

.30 

.60 

.50 

.30 

.30 

.15 

.30 

.25 

.30 

.35 

.25 

.40 

.40 

.40 

.50 

.35 

.25 

.40 

.30 

.25 

.40 

.38 

Modal 

grain size 

{mm) 1 

0.25 

.10 

.10 

.30 

.20 

.15 

.15 

.225 

.30 

.10 

.30 

.20 

.30 

.20 

.175 

.175 

.25 

.25 

.20 

.125 

.10 

.10 

.20 

.15 

.20 

.15 

.25 

.25 

.25 

.30 

.25 

.15 

.25 

.20 

.10 

.25 

.20 

Sorting2 

V. well 

Well---

Well---

Well---

M. well 

Mod.---

Well---

V. well 

M. well 

Well---

M. well 

Well---

Mod.---

Well---

V. well 

V. well 

Well---

M. well 

V. well 

M. well 

V. well 

M. well 

Well---

Well---

Well---

Well---

Well---

V. well 

V. well 

Well---

V. well 

V. well 

Well---

Well---

M. well 

Well---

Well---

Roundness 3 

Sbrd------

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbrd------

Sbang-sbrd 

Sbang-sbrd 

Sbang-----

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-rndSbrd------

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbrd------

Sbang-sbrd 

Sbrd------

Sbrd------

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Sbang-sbrd 

Ang-sbrd--

Ang-sbrd--

Ang-sbrd--

Sbang-sbrd 

Visual 

porosity 

14.6 

4.0 

.6 

.6 

1.0 

1.3 

1.3 

1.3 

2.0 

.3 

.6 

2.3 

.6 

1.3 

.3 

1.0 

.6 

.6 

.6 

2.0 

1.8 

Porosity4 

29.5 

13.5 

0.7 

3.8 

1.3 

9.6 

7.1 

12.8 

8.2 

2.8 

2.3 

i2.0 

8.1 

8.9 

13.6 

14.6 

6.4 

10.4 

12.0 

7.0 

4.7 

8.2 

8.7 

10.5 

10.7 

10.3 

11.3 

11.7 

11.2 

9.5 

7.2 

11.0 

11.4 

11.7 

9.2 

12.6 

9.61 

Permeability 

(mD)l+ 

1,278.8 

.974 

.664 

.673 

.ll7 

.243 

1.223 

1.986 

.710 

.775 

.163 

.189 

.306 

.454 

1.024 

.863 

.860 

1.030 

.401 

.173 

.908 

1.157 

.141 

1.010 

1Measured with petrographic microscope. 2Computed based on measured grain sizes. 

3Estimated by comparison with Krumbein (1941) visual estimator. 

4Measured by I. Pasternack. 

smaller quartz grains, whereas the carbonaceous 

fragments and organic debris are massive and 

nearly opaque or deep orange along a very thin 

edge. Many of the sedimentary lithic fragments 

contain calcareous material, which may vary 

from very finely crystalline to blocky sparry 

calcite. A few of the samples show all stages 

of calcite recrystallization. Although some of 

this alteration may have taken place during 

82 

diagenesis of rocks of the Nanushuk Group, much 

of it probably occurred in ,the source terrain. 

The resultant rounded clasts of recrystallized 

calcite surrounded by blebs or coatings of 

dark-brown to reddish-brown lutum are characteristic of the western area (Bartsch-Winkler, 

this volume). Commonly these sedimentary 

lithic types are found associated with each 

other in various combinations in a single grain. 
Table 7.--Uranium and thorium of samples 

from the south limb of Barbara Syncline 

[Values are in parts per million, as determined by delayed-neutroncounting technique. Values less than 3 ppm Th were not reported 

indicated by leaders (---). Analysts: H. T. Millard, Jr.; c. M: 

Ellis; and C. McFee. 1, M, or U following sample numbers indicates 

lower, middle, or upper sample from one sandstone unit; n.d. not determined] ' 

Sample Th u Sample Th u No. (ppm) (ppm) No. (ppm) (ppm) 

77AM!: 77ACH: 184 n.d. n.d. lOlL 6.32 1.94 183 n.d. n.d. 100 9. 79 2.22 77ACH: 98U 16.14 3.17 129 4.66 1. 31 981 15.33 2.91 

127 n.d. n.d. 97 6.68 1.59 126 8.15 .97 93U 11.65 1.50 123 7. 99 1. 92 93M 6.31 1.34 120U 5.15 1.29 931 8.80 2.11 1201 4.21 .92 92 5.16 • 74 

116 8.43 2.80 90U 7.21 1.03 113 1.88 901 9.12 1.29 110 7.01 1. 91 89U 7.30 • 76 108U 8.62 1.59 891 9.43 .49 108M 6.16 1.45 87U 5.96 1.05 

1081 5.45 2.08 871 7.68 .94 104U 6.29 1. 73 85 4.20 • 74 1041 5.32 2.06 83 6.12 1.22 lOlU 5.71 2.17 82 3.41 1.13 101M 3.98 1.92 Average 7.30 1.58 

Volcanic lithic fragments (0-8 percent) 

are predominantly felsite (0-3.7 percent) but 

also include grains containing subhedral feldspar prisms and pyroxene crystals in a trachytic 

groundmass (0-2 percent). Hypidiomorphicgranular rock fragments are included in this 

category as well and, although not common, were 

present in many sections and constitute as much 

as 4 percent in one section. 

Metamorphic lithic fragments (0-2.4 percent) are rare or absent in most of the samples 

and are almost exclusively quartzite grains in 

the lower portion of the measured section. 

These are strongly undulose, obviously stretched 

quartz grains containing several elongate 

domains that have serrated boundaries and 

occasionally containing muscovite or sericite 

flakes oriented with the elongation of the 

domains. In the upper portion of the section, 

quartzite increases in abundance and grains of 

foliated tectonites (0-0.7 percent) (phyllite 

and schist) and quartz-mica microgranulars (0-

1.7 percent) (probably gneisses and granitic 

gneisses) also increase in abundance. 

Most samples contain minor amounts of 

detrital muscovite, and a few contain small 

amounts of pleochroic straw-yellow to darkbrown biotite in flakes 0.1 to 0.3 mm long and 

nearly a~ways bent or broken by compaction. 

Several flakes of what appeared to be detrital 

chlorite were also noted. Other heavy minerals 

present, in decreasing order of abundance, 

include hematite, magnetite, pyrite, zircon, 

apatite, and sphene. · 

The material classified as matrix in this 

study has been placed in the following two 

categories: (1) pseudomatrix (Dickinson, 

1970), which includes material presumably 

derived from deformed clastic grains that have 

been squeezed into the intergranular spaces; 

and (2) other interstitial material, commonly 

composed of either fine detritus deposited in 

pore spaces or inhomogeneous materials grown 

during diagenesis but lacking the homogeneity 

or clear textural character necessary to be 

called cement. Pseudomatrix predominates in 

most of the samples studied, whereas the amount 

of other matrix material remains fairly constant 

at 1 to 2 percent and only very rarely exceeds 

3 percent. Large intergranular spaces are 

commonly filled with unsorted and randomly 

oriented silt and clay particles composed of 

quartz, chlorite, sericite, and much unidentifiable material. It was suggested by Lambert 

(in Fox and others, 1979) that this type of 

material is detrital and probably represents 

"hash" resulting from the abrasion and disintegration of clastic grains. Many of the framework grains are surrounded by thin layers of 

dark-brown to reddish-brown material composed 

of subparallel flakes of chlorite and sericite 

as well as minute grains of unidentified clay. 

Authigenic material including new growths, 

alteration products, and pore-filling cements 

are included as cement by Dickinson (1970). 

The most common and volumetrically most abundant 

cementing materials in the samples studied are 

calcite, silica, sericite, and kaolinite. Also 

present, but in much smaller amounts, are 

chlorite and small amounts of zeolites. By far 

the most abundant cement is calcite, which 

constitutes as much as 45 percent in one sample 

(77ACH129) and averages almost 8 percent in 

83 

thin sections studied throughout the section. 

In general it varies with the calcite-clast 

content and commonly can be seen growing out of 

these clasts. In the most extreme cases, the 

sparry calcite completely replaces all other 

constituents except for the quartz grains and 

deeply embays many of these. In such samples, 

ghosts of clastic grains can often be detected 

by relict outline of clay material. Also 

present in many samples are small rhombs of 

colorless carbonate which remain unaffected by 

the dye. These are thought to be composed of 

dolomite. 

Silica cement is ubiquitous throughout the 

section. It occurs as overgrowths on quartz 

grains and as pore-filling material. Often the 

contact between the detrital grain and the new 

growth is marked by opaque inclusions. Sericite 

and kaolinite are present mainly as alteration 

of feldspars but also as pore-filling masses of 

intergrown crystals. No consistent sequence of 

diagenetic products was discernible in these 

samples although, in general, silica appears to 

have been formed earlier than calcite. 

DISCUSSION 

Comparison of the petrographic results 

with the stratigraphy yields somewhat ambiguous 

results. In general, the marine sandstones are 

finer grained and slightly better sorted than 
the nonmarine (figs. 39 and 40). The only 

generalities that are immediately obvious are 

that, in the upper part of the section, the 

cement content increases while the feldspar and 

volcanic rock fragments decrease (fig. 41). No 

consistent correlation between depositional 

environment, grain size, or composition is 

discernible. 

Using the patterns that are recognizable 

in the plots of the composition data (fig. 40), 

certain tentative statements can be made concerning the provenance of the sediments in this 

portion of the Nanushuk Group. A pattern 

recognition study of the curves in figure 40 

has resulted in the division of the section 

into three segments: from the base through 

Sample No. 77ACH97, from 77ACH98L through 

77ACH108U, and from 77ACH110 to the top. Each 

of these segments can be characterized using 

the data in table 5. The bottom segment is 

high in chert and polycrystalline quartz, 

feldspar, and volcanic rock fragments and low 

in metamorphic rock fragments, calcite clasts, 

and cement. The middle segment is high in 

argillaceous-carbonaceous rock fragments and 

low in chert and polycrystalline quartz, volcanic rock fragments, and metamorphic rock 

fragments. The uppermost segment is high in 

calcite clasts, calcite cement, and metamorphic 

rock fragments and low in monocrystalline 

quartz and feldspar. These groupings have been 

outlined on figures 37, 38, and 40. Although 

there is much overlap of the groups, reflecting 

similarities of source terrain and mixing 

during transport and deposition, there are also 

significant differences and an obvious transition through time. 

Primarily on the basis of the relative 

percentages of quartz, chert, polycrystalline 

quartz, feldspar, and the various lithic fragments, both Dickinson (1970) and Folk (1968) 

would classify the source of these sediments as 

a tectonically active sedimentary rock terrain. 

Folk (1968, p. 121) would further characterize 

the type of tectonism as horizontal deformation. 

The relative abundance of rounded feldspar and 

altered volcanic rock fragments low in the 

section indicates the presence of volcanic 

material in the source terrain. By far the 

most prominent characteristic of this part of 

the section is the abundance of chert and 

polycrystalline quartz. Higher in the section, 

the dominant lithology is shale mixed with 

chert and monocrystalline quartz. The upper 

portion of the section is dominated by carbonates with significant amounts of chert and 

polycrystalline quartz. The increase in content 

of metamorphic rock fragments indicates a 

contribution from a metamorphic terrain late in 

the deposition of these sediments. 

This sequence of sediments strongly suggests that the primary sources of the Nanushuk 

Group in the middle and upper portions of the 

Corwin delta were the Shublik Formation of 

Middle and Late Triassic age, the Siksikpuk 

Formation of Early(?) Permian age, and the 

84 

Lisburne Group of Mississippian age. Figure 41 

shows composite stratigraphic sequences from 

the DeLong Mountains and Lisburne Hills, as 

compiled by Martin (1970). 

The overlapping of the groups outlined in 

figures 37, 38, and 40 may reflect the tectonic 

style in the source area as well as subsequent 

mixing of sediments during transport and deposition. Structure in the Brooks Range and 

Lisburne Hills is characterized by thrust 

faulting, which juxtaposed rocks of many different lithologies (Tailleur and Brosge, 1970; 

Grantz and others, 1976). Exposure of a fault 

sliver of the Nuka Formation somewhere in the 

source area may help to explain the large 

feldspar and monocrystalline quartz content in 

the lower portions of the section. This formation was described by Tailleur and Sable (1963, 

p. 632) as a "succession of fine clastic, 

feldspathic coarse clastic, and cherty strata" 

and was tentatively correlated with the 

Siksikpuk Formation and the uppermost part of 

the Lisburne Group. 

The major period of deformation in the 

western Brooks Range (DeLong Mountains) and 

Lisburne Hills took place in latest Jurassic 

and earliest Cretaceous time (Tailleur and 

Brosge, 1970; Grantz and others, 1976; Grantz 

and Kirschner, 1976) and continued into Late 

Cretaceous and perhaps Tertiary time (Grantz 

and others, 1976). The stratigraphic and 

petrographic results of this study of the Lower 

Cretaceous (Albian) part of the Nanushuk Group 

strongly support such an interpretation. 

RESERVOIR POTENTIAL 

Data available at this time do not support 

strong conclusions concerning the potential of 

the Nanushuk Group of the western North Slope 

for containing either hydrocarbon or uranium 

and thorium reservoirs, but the results of this 

particular study are not encouraging for either. 

The low porosity and permeabilities (table 6); 

high matrix and cement content (table 5); 

general lack of continuous, stacked sand bodies; 

and overall paucity of sand in the whole western 

system are negative factors for both hydrocarbon 

and uranium potential. It should be noted, 

however, that Sample No. 77AAH184, collected 

from the trough of Barabara Syncline and thus 

the stratigraphically highest sample studied, 

had excellent porosity and permeability, and 

extremely low matrix and cement content. Even 

though this is only a 6-m-thick channel deposit 

that is about 50 m wide, it would make an 

excellent reservoir. Because it is the northernmost exposure of the Nanushuk Group, perhaps 

the subsurface extension to the north would be 

of interest for hydrocarbon potential. 

The Nanushuk Group in the western North 

Slope contains a large volume of plant debris 

and carbonaceous material; was deposited in 

nearshore-marine, estuarine, and nonmarine 

environments; and does not appear to have been 

swept by strongly oxidizing fluids. Bentonitic 
MARINE (12) NONMARINE (24) TOTAL (36) 

100 

ui 

N 

U5 

zl- _z <{W 

0:() 

<!)0: 

w 50 

~a.. 

=>z 

~-

x <{ 

~ 

04 2 0 4 3 2 0 4 

cp cp ¢ 

100 

ui 

N 

WI-z zw 

-o <{a: 50 a:w 

CJa._ 

....lz <{_ 

0 

0 

~ 

3 0 4 3 2 0 4 3 

¢ ¢ ¢ 100 

Iz 

w 

() 

a: 

w 

a.. 

~ 50 

cj 

z 

i= 

a: 

0 

(/) 

0 Poor Moderate Well Very well Poor Moderate Well Very well Poor Moderate Well Very well 

CJ) 100 

Iz 

w 

zl- Oz 

a..w 

~() Oa: 

ow a.. ...J <{Z 

a:-

::::> 

IX 

w 

I- Matrix Frame- Visible Cement Matrix Frame- Visible 

work porosity work porosity work porostiy 

~ 

x 

CI:~ 1--w <{() 

~a: 

+w 

1--0.. 

z 

w 

~ 

w 

() 

0 35 30 25 20 15 10 0 35 30 25 20 15 10 5 0 35 30 25 20 15 10 5 0 

PERCENT PERCENT PERCENT 

Figure 39.--Histograms of some parameters bearing on reservoir quality. Data from tables 5 and 6. 

85 
0 

z 

Q) 

a. 

E 

Cll 

(j) 

0.1 

184 

183 

129 

127u 

126 

123 

120u 

1201 

116 

113 

110 

108u 

104u 

1041 

101u 

1011 

100 

98u 

981 

97 

93u 

93m 

931 

92 

90u 

901 

89u 

891 

87u 

871 

85 

83 

82 

Maximum grain size 

(mm) 

Modal grain size 

(mm) 

0.4 0.8 0.1 

Sorting 

Q) Qj a; 3: a; 

"'0 >- Qj 0 a; ~ 3: > 

Porosity Permeability Monocrystalline Polycrystalline 

(%) (mD) quartz (%) quartz 

(-quartzite) 

(%) 

10 20 30 40 2 10 20 30 40 50 10 20 30 40 

Figure 40.--Graphic representation of data from tables 5, 6, and 7. Segments shown on 

clays occur high in the Nanushuk Group (Chapman 

and Sable, 1960), and the presence of as much 

as 21 percent combined feldspar and volcanic 

rock fragment content indicates volcanism or 

reworking of volcanic detritus in the source 

area. The same negative factors cited above, 

however, are also applicable to uranium potential. During the course of the field investigation, no evidence of possible uranium enrichment 

was seen. Delayed-neutron counts that were run 

on the samples from the Barabara Syncline 

86 

measured section (table 7) yielded two samples, 

77ACH98L and 77ACH98U, anomalous in both uranium 

and thorium. These low-level anomalies correspond to the highest concentration and greatest 

diversity of heavy minerals seen in the entire 

section and occur in an upper shoreface sandstone. Identified heavy minerals include 

muscovite, biotite, hematite, pyrite, apatite, 

sphene, and zircon. This concentration of 

heavy minerals could easily account for these 

very low level anomalies. 
Feldspar Volcanic 

(%) Lithic 

fragments 

(%) 

10 20 5 10 

\ 

Sedimentary 

Lithic fragments 

(%) 

20 30 40 50 60 

Calcite 

clasts 

(%) 

10 20 30 

Matrix 

(%) 

5 10 

Cement 

(%) 

10 20 30 40 50 

Heavy 

Minerals 

(%) 

2 3 4 

Thorium 

(ppm) 

5 10 15 

• 

figures 37 and 38 separated by dashed lines and shown by symbols along far right margin. 

87 

Uranium 

(ppm) 

1 2 3 

• 
E 

LL 

E 

LL 

c. 

(!) 

(I) 

c: 

'-

::::1 

..c 

en 

~ 

r---.. /',. /' 

......... 

~~ 

~ 4 

-=-· ...___. 

~. ~ : .. 4 4 4 

.... 

;,.. .... 

4 4 4 

lA A A 

4 4 ... 

II• 1•1 

4 4 • 

... • ·~ 

-. .,. 

... ... 

I& I 

I.a. I 14 

114 4 I 

U . ..a.l I 

ry V'fj'il 

Lisburne Hills 

Shales 

Cherts and thin shales 

Shales with chert stringers 

Limestones with chert bands 

and nodules 

Limestones 

..::t:. 

::0 E 

::ILL 

.c. 

(f) 

E 

LL 

(I) 

E 

::I 

..c 

en 

~ 

4 ... 4 

.. . ... 

~~ 

~ ...... 

.. .. . 

4 4 4 

... ... ... 

.. 4 4 

-... -..;;:I 

......... 

-, f/ 

~f7 

16 l ~ I£ 

r 7 7 

.. 7 I 

I 

II 

I ... T.i: 7 

I 

I ~ 

rT.-1 I 

/ 

II 

I 

II /T 4 T 

... .. ·'\Jw r~ 

Delong Mts. 

Conglomerates with interbedded 

graywackes and silty mudstones 

Cherts with some interbedded 

pyritic shale 

Limestones and siliceous 

shales and cherts 

Limestones, locally dolomitic 

METERS 

300 

200 

100 

FEET 

1000 

500 

Figure 41.--Stratigraphic sequences of the Mississippian to lowermost Cretaceous section of the 

Lisburne Hills and DeLong Mountains; adapted from Martin (1970, fig. 2). 

88 
SOME CRETACEOUS PLANT MEGAFOSSILS AND 

MICROFOSSILS FROM THE NANUSHUK GROUP, 

NORTHERN ALASKA: A PRELIMINARY REPORT 

Richard A. Scott and Charles J. Smileyl 

INTRODUCTION 

Cretaceous sedimentary rocks crop out 

extensively in the Northern Foothills Belt of 

the Brooks Range, Alaska. Plant megafossils 

are common in many of the nonmarine and 

marginal-marine facies of these deposits 

(Smiley, 1966, 1969a, b, 1972a, b). In the 

western region of the North Slope, the Nanushuk 

Group includes the predominantly marine 

Kukpowruk Formation and the essentially nonmarine Corwin Formation. Both formations 

attain their maximum thicknesses to the west, 

where their type sections were described by 

Chapman and Sable (1960) from exposures along 

the Kukpowruk River and at Corwin Bluff, east 

of Cape Lisburne. Locations and lithologies of 

these and other exposures of the Nanushuk Group 

are given by Ahlbrandt and others (this volume). 

Collecting of the plant megafossils, 

sponsored by the Arctic Institute of North 

America and the U.S. Office of Naval Research, 

was conducted by Smiley during five field 

seasons in seven study areas across the region 

(fig. 42). The collection area extended from 

the Chandler River on the east to Corwin Bluff 

on the west, about 560 km, and from the Northern 

Foothills Belt of the Brooks Range northward to 

the Arctic Ocean. About 10,000 identifiable 

specimens were collected from 250 plant-bearing 

beds, and at least 420 plant megafossil species 

are recognized at present. 

Most of the rock units in northern Alaska 

had been described by geologists of the U.S. 

Geological Survey (Chapman and Sable, 1960; 

Detterman and others, 1963) before the plant 

megafossils were collected. On the basis of 

published descriptions of local sections, where 

available, Smiley was able to determine the 

precise stratigraphic level of plant-bearing 

beds at the time of collection. Fossiliferous 

marine rocks are interbedded in the areas of 

the Chandler, Colville, and Kukpowruk Rivers, 

permitting direct correlations between Smiley's 

floral zonations in nonmarine rocks and established faunal zonations in marine deposits 

(Smiley, 1972a). 

luniversity of Idaho, Moscow, Idaho. 

Pomt Barrow 

0 100 

kilometers 

Figure 42.--Index map of northern Alaska study 

areas. 1, Chandler River; 2, Colville 

River; 3, Kuk River; 4, Kukpowruk River; 

5, Punak Creek; 6, Pitmegea River; and 7, 

Corwin Bluff. 

On the basis of these plant collections, a 

stratigraphic sequence of eight major floral 

zones was established through the Cretaceous 

rocks that are exposed across northern Alaska. 

Furthermore, 21 floral subzones were distinguished on the bases of stratigraphically 

restricted species and overlapping species 

ranges (Smiley, 1972a, b). Each floral zone 

can be recognized from a relatively small 

collection of plant megafossils, and many 

species appear to be good indexes of subzones. 

Forms may be distinguished by characters observable from small fragments (for example, fern 

fronds, conifer shoots). These megafossils 

often can be identified from drill-core samples 

as well as from larger specimens from the 

outcrop. 

Palynological samples have been obtained 

from matrix material of the megafossil collections for most of Smiley's localities. Palynological samples were also made available thrnugh 

the courtesy of J. S. Lowther and the late c~ 

A. Arnold from the megafossil collections of 

Lowther (1957), along the Meade, Kuk, Avalik, 

Kaolak, and Colville Rivers. Additionally, 

89 
some 400 palynological samples were obtained in 

the summer of 1977 as a part of the project 

that is the subject of this publication. Only 

a small proportion of these samples has as yet 

been processed; initial efforts were directed 

toward type and other exposures from the western 

edge of the North Slope. 

The study by Smiley of the fossil leaves 

is well advanced, whereas palynological work, 

other than that done privately by commercial 

companies, is in its beginning stages. Nevertheless, good reasons exist for considering the 

plant megafossils and microfossils jointly. 

Leaves, spores, and pollen are not separate 

organisms; but they are separate parts of 

single organisms--plants--for which a detailed 

and workable biostratigraphic succession already 

is known for the Cretaceous of the North Slope. 

Also, in some areas of northern Alaska, recovery 

of palynomorphs is not adequate to establish an 

independent zonation. 

Although the broad outlines of this megafossil-based biostratigraphy are available 

(Smiley, 1972a), taxonomic descriptions, illustrations, and ranges of individual taxa have 

not yet been published, limiting recognition of 

their usefulness in the field. It is the 

intent of this joint investigation to make 

these data available for individual taxa, to 

apply them to the correlation of beds of the 

Nanushuk Group and other Cretaceous deposits on 

the North Slope, and to utilize the pattern of 

floral succession shown by the megafossils as 

a framework for palynological information from 

both surface and underground rocks. As work 

progresses, data from plants will be integrated 

with those from dinoflagellates and other 

organisms in an effort to tie together events 

in the marine and nonmarine environments of 

deposition. 

FLORAL ZONES BASED ON MEGAFOSSILS 

The five floral zones of the Nanushuk 

Group (Zones IA, IB, II, III, and IV) range 

upward through an essentially continuous 

sequence of occasionally coal-bearing sedimentary rocks that totals a maximum thickness of 

about 5,500 m; the sequence ranges in age from 

possible late Aptian into the Cenomanian. 

Fossil plants were collected from 192 localities 

in this portion of the Cretaceous section. 

In the western region of the Alaskan North 

Slope, plant megafossils from the type section 

of the Corwin Formation represent Zones IA, IB, 

and II. The Corwin Formation elsewhere includes 

younger beds than are present at the type 

locality; such younger beds, containing plants 

from Zone III, crop out along the Kukpowruk 

River near the axis of Barabara Syncline at 

162°43'39" W., 69°29'55" N. Plants from the 

Kukpowruk Formation, including its type locality 

along the Kukpowruk River (Chapman and Sable, 

1960), are assignable to Zones IA and IB. Zone 

90 

IV is not present in the Kukpowruk-Corwin 

region but is found eastward in beds of the 

upper part of the Nanushuk Group. The three 

major floral zones of the overlying Colville 

Group to the east span the time from Turonian 

(Zone V) through Santonian-Campanian (Zone VI) 

to early Maestrichtian (Zone VII). Stratigraphic relationships are discussed by Ahlbrandt 

and others (this volume). 

The plant megafossil zones of the Nanushuk 

Group are distinguishable across the region and 

upward through local sedimentary sections. A 

selection of 30 megafossil species that are 

common, are readily identifiable, and represent 

the five major plant groups of the later Mesozoic (ferns, ginkgophytes, cycadophytes, conifers, and dicots) is included in this report. 

It should be emphasized that this is but a 

sampling of the many taxa that could serve 

equally well for regional correlations of 

nonmarine deposits. The list of plants and 

references to figured specimens on accompanying 

plates are as follows: 

Ferns: 

Arctopteris kolymensis Samylina (pl. 1, fig. 

2) 

A. rarinervis Samylina (pl. 1, fig. 1) 

Coniopteris inenarabilis (Hollick) (pl. 2, 

fig. 1) 

c. onychioides Vass. and Kara-Mur. (pl. 2, 

fig. 2) 

Ginkgophytes: 

Ginkgo paradiantoides Samylina (pl. 3, fig. 

1) 

Ginkgo n. sp. (pl. 3, fig. 3) 

?Ginkgoites (?Baiera) n. sp. (pl. 3, fig. 5) 

Phoenicopsis var 1 (pl. 3, fig. 4) 

Phoenicopsis var 2 (pl. 3, fig. 2) 

Phoenicopsis var 3 (pl. 3, fig. 7) 

Sphenobaiera pulchella (Heer) Florin (pl. 3, 

fig. 6) 

Cycadophytes: 

Nilssonia alaskana Hollick (pl. 4, fig. 2) 

Nilssonia cf. N. orientalis Heer (vars) (pl. 

4, fig. 1) 

Nilssonia cf. N. serotina Heer var 2 (pl. 4, 

fig. 5) 

Nilssoniopteris polymorpha Sveshn. & Bud. 

(pl. 4, fig. 4) 

?Zamites sp. (pl. 4, fig. 3) 

Coniferophytes: 

?Abieitites sp. (pl. 5, fig. 5) 

Elatocladus n. sp. (pl. 5, fig. 4) 

Juniperites n. sp. (pl. 5, fig. 2) 

Pityophyllum var 1 (pl. 5, fig. 3) 

Pityophyllum var 2 (pl. 5, fig. 1) 

Podozamites var 2 (pl. 6, fig. 1) 

Podozamites var 7 (pl. 6, figs. 3, 4) 

Podozamites var 9 (pl. 6, fig. 5) 

Podozamites var 15 (pl. 6, fig. 2) 
Dicotyledons: 

cf. Ampelopsis multesima Hollick (pl. 7, 

fig. 1) 

Cissites comparabilis Hollick (pl. 7, fig. 

2) 

?Cissites sp. (pl. 7, fig. 5) 

cf. Platanus latiloba Seward (pl. 7, fig. 4) 

Pseudoprotyphyllum cf. P. dentatum Hollick 

(pl. 7, fig. 3) 

Of this selected list of plant megafossil 

species, the following occur in the floral 

zones indicated below (*=confined to, or most 

characteristic of, the particular zone): 

Floral Zone IA: 

*Arctopteris kolymensis (entire zone, 

except top) 

Arctopteris rarinervis (top of zone) 

Coniopteris onychioides (entire zone) 

Ginkgo paradiantoides (entire zone) 

Gingko n. sp. (top of zone) 

*Nilssonia cf. N. serotina var 2 (base to 

middle of zone) 

*Phoenicopsis var 1 (base of zone) 

*Phoenicopsis var 2 (middle of zone) 

Phoenicopsis var 3 (top of zone) 

Pityophyllum var 1 (rare in zone) 

*Podozamites var 2 (top half of zone) 

Floral Zone IB: 

Arctopteris rarinervis (entire zone) 

Coniopteris onychioides (entire zone) 

Ginkgo paradiantoides (entire zone) 

Ginkgo n. sp. (entire zone) 

Phoenicopsis var 3 (entire zone) 

*Pityophyllum var 1 (entire zone) 

Podozamites var 2 (rare in lower half of 

zone) 

Podozamites var 7 (rare in zone) 

Podozamites var 9 (rare in zone) 

Sphenobaiera cf. s. pulchella (entire zone) 

*?Zamites sp. (entire zone) 

Floral Zone II: 

*?Abieitites sp. (entire zone) 

Ginkgo paradiantoides (base of zone) 

Ginkgo n. sp. (base of zone) 

Nilssonia alaskana (entire zone) 

Nilssonia cf. N. orientalis vars. (middle 

to top of zone) 

*Nilssoniopteris polymorpha (entire zone) 

Phoenicopsis var 3 (base of zone) 

Pityophyllum var 2 (entire zone) 

*Podozamites var 7 (entire zone) 

Podozamites var 9 (entire zone) 

*Podozamites var 15 (entire zone) 

Floral Zone III: 

?Abieitites sp. (base of zone) 

*cf. Ampelopsis multesima (entire zone) 

91 

*Ciccites comparabilis (base of zone) 

*Coniopteris inenarabilis (entire zone) 

Elatocladus n. sp. (rare in zone) 

*?Ginkgoites {?Baiera) n. sp. (base of zone) 

*Juniperites n. sp. (entire zone) 

Nilssonia alaskana (base of zone) 

*Nilssonia cf. N. orientalis vars (entire 

zone) 

Pityophyllum var 2 (base to middle of zone) 

*cf. Platanus latiloba (base of zone) 

Podozamites var 7 (base of zone) 

Podozamites var 9 (entire zone) 

Podozamites var 15 (rare, base of zone) 

Floral Zone IV: 

cf. Ampelopsis multesima (rare in zone) 

*?Cissites sp. (entire zone) 

*Elatocladus n. sp. (entire zone) 

Podozamites var 9 (base of zone) 

*Pseudoprotophyllum cf. P. dentatum (base of 

zone) 

Figure 43, showing the stratigraphic 

ranges of the selected species from northern 

Alaska, is an example of the tabulation that 

has been done for all plant megafossil species 

collected. Figure 44 shows the stratigraphic 

occurrence and regional distribution of one 

entity, Nilssoniopteris polymorpha, illustrating 

the type of taxonomic-stratigraphic data that 

has been recorded for all Cretaceous plant 

taxa. 

Many of the megafossil forms that seemed 

at first to be long-ranging species, such as 

Coniopteris onychioides (=?Cladophlebis alata 

Fontaine, in Ward, 1905; Knowlton, 1914), were 

found upon more detailed comparisons to represent a complex of several related species 

occurring in stratigraphic sequence. Whereas 

c. onychioides is represented by sterile and 

fertile fronds in Zones IA and IB, a closely 

similar fern that was referred originally to 

this species is now known to be morphologically 

distinct and to be confined to the overlying 

Zone II. These and other morphologicstratigraphic distinctions within apparently 

long-ranging forms currently are being clarified. (For example, four sequential species of 

the fern Arctopteris Samylina have been distinguished; Knowlton (1914) had referred them to a 

single species, Cladophlebis huttoni (Dunker) 

Fontaine.) 

The material at hand shows that plant 

megafossils, when collected on a detailed 

stratigraphic basis, can serve as a valid and 

reliable means for correlations across a paleogeographic province such as the Cretaceous 

coastal plain of northern Alaska. When the 

total plant megafossil record from this region 

is analyzed, the major plant biostratigraphic 

zones of Smiley can be subdivided further into 

subzones for more precise correlations. 
(./') 

w PODOAGES z FERNS GINKGOIDS 'CYCADS' CONIFERS ZAMITES DICOTS 2 (Vars.) 

(U 

~ ci 

Early ~ ..1: ..... C\1 II) 

Q. ~ ...: II) 

".0 ci .... (U c: ...: 

~ Ol IV 0 c: -~ (U (U Ceno- ~ II) E <U ::.. ::.. 0 (I) ...: (U c: ::..,-le ci. .e. (U 

c: - II) t :0 c:: II) ::.. I man ci. ian (I) 0 (U c: 

I .!:: ~ o.- <: 0 ::::. II) (U II) """) 

- (j (I) II) 

~ u 

-~ 

I 

II) ·;: (U ci E (/) II) I (I) "(ij ~ (I) ·- II) a.: II) 

= (I) (I) 1:1 IXl - c: c: 1:1 ~ (I) Q. 0 (I) 

! c:: (U ·;;; 

·~ I ~ ..1: 0 II) 

~ Ill ·- II) .0 II) 

c: ~ -~ (!) u c: - 0 c: ..1: :; 0 ·- c: <:( ::::. ....... (I) (.) u I (U ('.. II) <: ('.. 1:1 ...: 1:1 ::... "-t; I Q. 

iii 

t 

I 

~ ...: (U I I Late c: (U 

~ u ::.. ::.. 0 E ~ 

- -~ (U E 2 

I 

~ .2 Albian -~ ::.. Q. .! (U (U 

.... .... ci (U C\1 .2 ~ E .0 :0 -;, (I) -~ (I) 0 II) C') .0 ...: -;. UJ ·;;; ~ ~ ..1: 

II Q. II) c: Ol 0 (U ..1: Q. 

c: -lC c: ....: c: ::.. ~ (U 2 0 .... .!:: Q. (I) 

~ (U (I) 0 :; ~ Q. 

c: E (!) C!i ::.. ..1: (U 

0 ~ E ~ ::... cL Q. c: a: E II) 0 Q. (.) <:{_ (/) 

0 0 ::::. u 0 

-lC I I Q) I C\1 -~ c: 1:1 

II) ~ II) ::::. 

Middle II) .,._ II) ...: Q. (U 

(I) (I) 

(U 0 II) 

IB .... ...: t ::.. ~ li: II) ct. ~ (U 

Albian ::.. 

I 

Q. -~ Q. C\1 -~ E ...: (.) 0 -~ u ....: c: <:( 

~ II) (U 0 Q. ::.. II) 

<:( 0 ~ 

Early I -~ 

c: a.: ~ (I) I I Albian lA 0 

..1: 

ct. 

? - -~r .Aptian. I 

Figure 43.--Stratigraphic ranges of selected species of plant megafossils from northern Alaska. 

AGE DETERMINATIONS 

FOR THE NANUSHUK GROUP 

The ages ascribed to the floral zones are 

based primarily on ammonite genera, species of 

Inoceramus, and foraminiferal assemblages from 

marine units that are interbedded with plantbearing deposits in some of the study areas 

(Jones and Gryc, 1960; Tappan, 1960, 1962; 

Imlay, 1961; Bergquist, 1966; Sliter, this 

volume). Marine faunal ages are reported to 

range from early Albian to early Cenomanian for 

the Nanushuk Group, and from Turonian to 

Santonian-Campanian for the overlying Colville 

Group. Sedimentary processes seem to have been 

interrupted during the late Cenomanian and 

Coniacian, and the floral and faunal records 

indicate breaks at these times. 

Some of the plant species in the lower 

part of the Corwin Bluff section (fig. 42, 

study area 7) are typical of pre-Albian floras 

in the Siberian region to the west (Samylina, 

1963, 1964). Other species with which they are 

associated are more characteristic of Albian 

floras in Siberia and northern Alaska. Such a 

coincidence of typically older and younger 

species in the same rock unit in northern 

Alaska suggests the possibility that plantbearing rocks of Aptian Age may be represented 

in the lowermost deposits in the western part 

of the Alaskan North Slope. Megaspores in the 

beds at Corwin Bluff indicate a probable Albian 

92 

Age, although pre-Albian strata in the lowest 

part of the Corwin Formation are not precluded. 

(See plant microfossil discussion.) 

The entire Albian Stage seems to be 

represented in the sequence of floras and 

faunas of northern Alaska. These units have 

been correlated by floral and (in part) faunal 

zonations from the Chandler River area on the 

east to the Corwin Bluff area on the west 

(Smiley, 1969b, p. 2086-2088; 1972a, fig. 4). 

A probable early Cenomanian age for the upper 

part of the Nanushuk Group is indicated by the 

rich Inoceramus dunveganensis McLearn fauna 

(Imlay, 1961) in marine sands that are interbedded with plant-bearing deposits near the top 

of Floral Zone III and in Floral Zone IV. An 

episode of folding and truncation, apparently 

representing late Cenomanian time, took place 

prior to deposition of the Turonian Seabee 

Formation (Colville Group). The Seabee Formation is predominantly marine in the ChandlerColville region (one plant-bearing interbed 

occurs in the middle.of the formation) and has 

plant-bearing nonmarine equivalents in the Kuk 

River area to the northwest (Smiley, 1966). 

CORRELATIONS OUTSIDE NORTHERN ALASKA 

Intercontinental high-latitude correlations 

of plant-bearing nonmarine rocks between eastern 

Siberia and northern Alaska were made recently 

by Samylina (1976). She found a close correla-
lA 

.II 

~ 1-

-

•• 

: 

~ 

-lA 

c 

. 

. 

I 

: 

r-rIll 

II 

-

Ill 

3 

II /~-" 

' 

0 

AGES 

Cenomanian 

Late 

Albian 

Middle 

Albian 

Early 

Albian 

?-?-? 

?Aptian? 

Nilssoniopteris polymorpha 

Figure 44.--Stratigraphic occurrence and regional distribution of Nilssoniopteris polymorpha in 

northern Alaska. Numbers 1-7 refer to the seven study areas shown in figure 42. 

tion between the sequence of floras in the 

Kolyma River area of northeastern Siberia and 

that in northern Alaska. Whereas the Siberian 

plant-bearing section of Aptian to Cenomanian 

Age rests on fossiliferous marine units, no 

marine interbeds are known to exist in the 

plant-bearing section itself. Samylina's 

comparison with the Alaskan record thus serves 

to correlate the Kolyma River floral records 

with a similar sequence in a contiguous region 

of the same floral province; in northern Alaska, 

interbedded, fossiliferous, marine units provide 

data for relating the various floral zones to 

the European scale for Cretaceous time. 

Comparisons with Hollick's (1930) Yukon 

River floras south of the Brooks Range orogenic 

belt show that most Yukon River species of 

ferns and gymnosperms occur also in deposits on 

the North Slope, where they are confined to 

units below those containing Floral Zone III. 

Most of the Yukon River dicot species similarly 

are represented in northern Alaskan floras, but 

they are not found in units below Zone III. 

Because dicots are known to have progressed 

from lower to higher latitudes in middle 

Cretaceous time (Smiley, 1967), they probably 

first invaded the Yukon River region south of 

the Brooks Range highlands, becoming mixed with 

fern and gymnosperm species of Zone II age, 

before crossing the Brooks Range uplift and 

becoming established as dominant plants during 

the time of the Zone III floral change. The 

Yukon River species thus correlate with plants 

in Zones II and III of northern Alaska, and 

most likely are temporal equivalents of Floral 

Zone II (late Albian). 

Plant megafossil correlations of nonmarine 

Cretaceous rocks west of the lower Mackenzie 

River were made by Smiley for the Canadian 

Geological Survey (in Young, 1975). Small 

collections of middle and later Cretaceous 

plant megafossils contain species that are 

stratigraphically restricted in the northern 

Alaskan sequence. The correlations made using 

these species conformed well with Young's 

conclusions based on other lines of evidence. 

93 
PLANT MICROFOSSILS 

Little work has been published on pollen 

and spore assemblages from the Alaskan North 

Slope. Spores and pollen from strata along the 

Kuk and Kaolak Rivers were discussed by 

Langenheim, Smiley, and Gray (1960). Material 

from near Umiat representing the Tuluvak Tongue 

of the Prince Creek Formation (Colville Group), 

along with samples from the Corwin Formation at 

Kuk Inlet and Meade River, was studied by 

Stanley (1967). B. D. Tschudy (1969) reported 

on two genera of dicotyledonous pollen from 

Upper Cretaceous rocks along the Colville 

River. A sample from an unspecified locality 

in the Corwin Formation at Kuk Inlet was examined by Brenner (1976). Much more is known 

about the palynology of Cretaceous deposits in 

Canada; this work has been summarized for 

Arctic Canada by Brideaux and Mcintyre (1975), 

and for the western Canadian Interior by Jarzen 

and Norris (1975) and Singh (1975). 

Field collection of palynological samples 

for this study was begun in the western region 

of the North Slope. Initial sample preparation 

concentrated on the type sections of the Corwin 

and Kukpowruk Formations, on which these comments principally are based. It should be 

emphasized that this discussion is both general 

and preliminary owing to incomplete processing 

of samples and poor recovery, both in quantity 

and quality, of palynomorphs. 

Plant microfossils observed in the type 

section of the Corwin Formation include such 

genera as Gleicheniidites, Cyathidites, Osmundacidites, Distyophyllidites, Sphagnum, Lycopodiumsporites, Verrucosisporites, Foveotriletes, 

Cicatricosisporites, and Cycadopites. A 

variety of bisaccate grains are also present, 

among them Vitreisporites, Pristinuspollenites, 

Alisporites, Pteruchipollenites, Piceaepollenites, Abietineaepollenites, Podocarpidites, and 

others in a complex of difficult-to-distinguish 

coniferous pollen. 

The total assemblage represents a ferncycadophyte-conifer complex as demonstrated by 

the plant megafossils, except that the ginkgophyte component represented by leaves is not 

easily detected by pollen. In the section at 

Corwin Bluff, about 50 megafossils species of 

the oldest floral zone, IA, are predominantly 

foliage of ferns, cycadophytes, and ginkgophytes, and some generic change. Zone II 

contains about double the number of species, 

with a marked increase in the number and variety 

of conifers. The highest beds at Corwin Bluff 

are in Zone II; however, both Zones II and III 

are represented in the outcrops of the Corwin 

Formation along the Kukpowruk River. Zone III 

records the first occurrence of dicotyledonous 

plants, along with a sharp increase in number 

of species in all taxa. 

Preliminary indications are that these 

plant zones can be distinguished palynologically 

in the Corwin Formation, although certain 

94 

compositional differences are apparent for the 

plant microfossils. The most striking of these 

is the presence of abundant coniferous pollenfrom Zones IA and IB, where megafossils of 

conifers are sparse. The limited variety of 

other palynological forms in Zone IA consists 

chiefly of fern spores, many of them gleicheniaceous. In Zone,IB, coniferous pollen is accompanied by an increased variety of other forms, 

including occasional examples of Klukisporites, 

Cicatricosisporites, Foveotriletes, Eucommiidites, and Camarozonosporites. The increased 

number of megafossil species in Zone II is 

reflected by increased variety of palynomorphs, among them Rogalskaisporites, cf. 

Distaltriangulisporites, and Reticulisporites. 

Reworked Permian-Triassic pollen was observed 

in this zone, and probable Devonian spores were 

also seen in the Corwin Bluff section. 

Spores and pollen from Zone III were 

recovered from beds at locality 77AAH186 

(162°43'39" N., 69°29'55" W.), about 0.5 m 

south of the axis of Barabara Syncline along 

the Kukpowruk River. This is near Smiley's 

locality 59 (1969b, fig. 2D), where dicotyledonous leaves were found. This palynomorph 

assemblage contains at least three types of 

simple, tricolpate, dicotyledonous pollen. 

Numerous other forms are present, including 

occasional grains of Vitreisporites and Ephedra. 

Some palynomorph genera that are common in 

Lower Cretaceous deposits at lower latitudes, 

for example, in the Potomac Group of Maryland 

(Brenner, 1963), are rare or lacking in the 

type Corwin section. These genera include 

Trilobosporites, Concavissimisporites, Appendicisporites, and Classopollis. Cicatricosisporites, virtually absent in the lower half of 

the Corwin Bluff section, increases slightly in 

its upper half; it is more common, though not 

abundant, in younger, Zone-III beds of the 

Corwin Formation at Barabara Syncline along the 

Kukpowruk River (locality 77AAH186). 

Many genera of s~ores and pollen present 

at the type section of the Corwin Formation are 

typical of cosmopolitan forms widespread in 

Albian time in the Northern Hemisphere. Including the younger Corwin beds exposed in the 

Snowbank Anticline-B~rabara Syncline sequence 

along the Kukpowruk River, the Corwin palynomorph assemblage appears most like that found 

in the Canadian Christopher and overlying 

Hassel Formations, from above 75° N. latitude in 

the Canadian Arctic Archipelago (Hopkins, 1974; 

Hopkins and Balkwill, 1973). The Christopher 

Formation, although marine, contains moderately 

abundant spores and pollen; tricolpate angiospermous pollen is present in the uppermost 

beds of the formation. The Christopher Formation is considered to be mid- to late Albian in 

age, with Albian ammonites present near the top 

of the formation (Hopkins, 1974). Tricolpate 

pollen grains are present throughout the overlying Hassel Formation, thought to be of latest 

Albian or early Cenomanian age (Hopkins and 

Balkwill, 1973). 
Palynologically, strata at the type section 

of the Corwin Formation appear to be in part 

equivalent in age to the Christopher Formation, 

and the younger Zone-III Corwin beds along the 

Kukpowruk River may correspond in age to the 

Hassel Formation. This tentative correlation 

is based principally upon the level of occurrence of tricolpate pollen in these formations; 

some discrepancies of undetermined significance 

exist in the patterns of occurrence of such 

spore genera as Trilobosporites, Pilosisporites, 

Concavissimisporites, Cicatricosisporites, and 

Appendicisporites. 

The Christopher and Hassel Formations 

serve at least to illustrate the difficulties 

of palynological zonation in the Early Cretaceous of the Arctic. Hopkins (1974) detected 

virtually no floral alteration throughout the 

Christopher beds; in the Hassel Formation the 

same palynomorphs were present throughout, with 

only minor differences in relative abundances 

(Hopkins and Balkwill, 1973). 

Megaspores are present in the Corwin 

Formation both at Corwin Bluff and along the 

Kukpowruk River. These have been identified by 

R. H. Tschudy (written commun., 1978). Samples 

at Corwin Bluff from the oldest zone, IA, 

contained Arcellites reticulatus (Cookson and 

Dettmann) Potter, Minerisporites macroreticulatus Singh, and Minerisporites cf. M. marginatus (Kijkstra) Pot. Zone IB at Corwin Bluff 

includes Arcellites reticulatus, Minerisporites 

macroreticulatus, and Paxillitriletes cf. P. 

fairlightensis Batten. Megaspores also were 

obtained from a series of samples at irregular 

intervals, extending upsection from the top of 

the type section of the marine Kukpowruk Formation (Chapman and Sable, 1960) downstream to 

the north through the marine-nonmarine transitional beds into the nonmarine Corwin Formation. 

These localities are: 77AAH160 (162°45 1 23" W., 

69°15 I 12" N.)' 77 AAH165 (162 °45 I 40" w.' 

69°l5 1 2l"N.), 77AAH172 (162°46 1 24" W., 69°15 1 24" 

N.), 77AAH176 (162°47 1 01" W., 69°15 1 40" N.), 

77AAH178 (162°47 115" W., 69°15 1 46" N.), 77ACH74 

(162°39 1 19'' W., 69°23 1 34" N.), and 77ACH79 

(162°39 1 28" W., 69°23 1 38" N.). These localities, not necessarily in stratigraphic sequence 

because of folding, are included in Zones IB 

and II. They contain, in aggregate, these 

megaspores: Arcellites reticulatus, Erlansonisporites reticulatus, Minerisporites macroreticulatus, M. cf. M. Borealis (Miner) Pot., 

M. cf. M. marginatus, M. sp., Paxitriletes cf. 

P. fairlightensis, and Triletes sp. 

The two northernmost localities in this 

series, representing Zone III, are 77AAH183 

(162°46 1 15" W., 69°20 1 57" N.) and 77AAH185 

(162°45 1 52" W., 69°30 1 57" N.), on the north 

limb of Barabara Syncline and apparently at or 

near the stratigraphic level of the dicot leafbearing locality 77AAH186 (162°43 1 39" W., 

69°29 1 55" N.) on the south limb of Barabara 

Syncline. Localities 77AAH183 and 77AAH185 

yielded these megaspores: Arcellites reticulatus, Paxillitriletes cf. P. dakotaensis 

95 

(Hall) Hall and Nicolson, Erlansonisporites 

reticulatus, Minerisporites cf. M. marginatus, 

Triletes sp., and an undescribed new genus. 

R. H. Tschudy comments as follows: 

"All of the above taxa have been reported 

from the Albian of western North America, and 

most of them appear to be limited to the AlbianAptian. However, very few pre-Aptian rocks 

have been examined for palynomorphs in this 

area, and even fewer have been searched for 

megaspores. Consequently, comparatively little 

is known of Neocomian megaspores. 

"Perhaps the most diagnostic taxon is 

Arcellites reticulatus (Cookson and Dettmann) 

Potter. This fossil is known only from the 

Albian of Canada and Australia. A different 

species Arcellites disciformis (Miner) Ellis 

and Tschudy has a range extending from upper 

Barremian to Cenomanian. I re-examined all 

basal Cenomanian megaspore slides available in 

the Denver laboratory to attempt to find out if 

the range Arcellites reticulatus extended into 

the basal Cenomanian (Dakota) of Colorado, 

Utah, and New Mexico. Arcellites disciformis 

was the only species of Arcellites found. 

"The two stratigraphically highest samples, 

77AAH183 and 77AAH185, differed somewhat from 

the other samples in their greater diversity of 

megaspores. Both samples, however, yielded 

specimens of Arcellites reticulatus. It is my 

opinion that all the samples examined pertain 

to the Albian. Because of the incompletely 

known ranges of many of these megaspores, 

future work may extend the ranges of some into 

the Cenomanian. However, in light of present 

knowledge none of the samples can possibly be 

younger than earliest Cenomanian." 

In addition to material from the Corwin 

Formation, palynological preparations have been 

made from the type Kukpowruk Formation, and 

from sections at Coke Basin, Dugout Syncline, 

Seaview Syncline, and Archimedes Anticline. 

Although palynomorphs are present in many of 

these samples, the quality of preservation 

generally is not good. One of the perplexing 

aspects of attempting to utilize palynology 

with Cretaceous rocks of the western North 

Slope is the poor recovery and poor preservation 

of palynomorphs from even such apparently favorable lithologic sequences as the type exposure 

of the Corwin Formation. Here, in some 3,000 m 

of nonmarine beds, sandstones and siltstones 

alternate with organic shales and coals, lithologies that elsewhere commonly contain many 

palynomorphs. In this Corwin section, they 

typically are sparse or lacking in pollen and 

spore content. Many relatively fine grained, 

Cretaceous leaf-bearing beds elsewhere typically 

contain spores and pollen in the matrix material; in the Corwin Formation the siltstones in 

which most leaves are found typically are 

barren, or nearly so, of palynomorphs. 

Several factors are possibly responsible 

for the poor representation of palynomorphs in 
the type Corwin Formation and elsewhere on the 

western North Slope. The lack of pollen and 

spores in the leaf-bearing siltstones probably 

is related to the higher energy levels in this 

depositional environment. Recent studies by 

Retallack (1977) and by Hickey and Doyle (1977) 

have begun to relate the affinities and nature 

of plant remains to their locale of growth and 

preservation in the sedimentary environment. 

By the conclusion of this study, we anticipate 

that it will be possible to adduce such relationships to some degree in connection with the 

work by Ahlbrandt and others (this volume) on 

depositional environments represented by rocks 

of the Nanushuk Group. But lack of suitable 

depositional environments does not appear to be 

a primary cause for the scarcity of palynomorphs. In many cases, biological or chemical 

degradation of the sporopollenin in the palynomorph wall is evident; further study of deterioration in the Nanushuk palynomorphs is planned. 

Many samples unavoidably were taken from oxidized zones near the surface, which may account 

for poor recovery. The degree of maturation of 

the organic material in these rocks is higher 

than was anticipated (Magoon and Claypool, this 

volume) and probably is in part responsible for 

the poor preservation seen in many samples. 

One possible key to an original lack of 

palynomorphs may be furnished by the record of 

the plant megafossils. The oldest floral zone, 

IA, contains about 50 species, mostly ferns, 

ginkgophytes, and cycadophytes. Zone IB includes about 55 species from the same taxonomic 

groups, plus some conifers. Diversity increases in Zone II, with some 102 species, including 

the first rare dicotyledonous leaves. Zone 

III, with 176 species, is characterized by a 

striking increase in the number of species in 

most higher taxa; dicots are first significant 

in this zone (Smiley, 1972b). The beds at the 

Corwin type section are included in Zones IA, 

IB, and II, with floral diversity ranging from 

50 to about 100 species in aggregate. 

It is significant that these species 

counts reflect the total flora of the zones. A 

plant megafossil collection from any given 

level in the rocks typically contains only 

about five or six commonly occurring species. 

These forms are the ones apparently indigenous 

to and best able to reestablish themselves in 

the constantly altering environments of rapid 

deposition reflected in many of the thick 

Corwin beds. Changes in these small associations through time provide the basis for the 

zonation shown in figure 43. The presence of 

megaspores, not usually amenable to longdistance transport, documents the record of 

local vegetation in the Corwin sediments. 

Although some spores and coniferous pollen were 

certainly carried in, the limited variety and 

numbers of palynomorphs reflect in part the 

output of small, local plant associations 

diluted by rapid rates of sedimentation during 

early Corwin time. Interestingly, the oldest 

96 

sample yet found that yielded well-preserved 

palynomorphs in quantity was from Zone-III beds 

of the Corwin Formation on the Kukpowruk River 

(locality 77AAH1862, 162°43'29" W., 79°29'55" 

N.). Megafossil collections document that 

increase in numbers of species had taken place 

in Zone III, increasing the supply of palynomorphs to the sediments. 

The apparent low number of plant species 

at the type section of the Corwin could be 

related to the location of such floras at high 

latitude (Smiley, 1967; Brenner, 1976; Hickey 

and Doyle, 1977). However, the Christopher 

flora, located at even higher latitude, is as 

rich in numbers of species as many Early Cretaceous assemblages from far to the south 

(Hopkins, 1974); and the total number of species 

for Zone I in the Corwin Formation is comparable. On the Alaskan North Slope, the increase 

in numbers of species upward through Smiley's 

zones suggests that palynological efforts will 

become more rewarding as work on the Nanushuk 

Group progresses eastward into younger rocks on 

the North Slope. 

The potentially best palynological datum 

that exists within the ~anushuk Group is the 

first appearance of tricolpate angiospermous 

pollen. In low latitudes, this morphological 

pollen type enters the geological record in the 

Aptian (Hickey and Doyle, 1977); in western 

Canada, tricolpate pollen is first found in 

sediments of middle or late Albian age (Singh, 

1975; Jarzen and Norris, 1975). Brenner (1976) 

reported that, in the the Canadian Arctic and 

northern Alaska, tricolpate pollen does not 

appear until the Cenomanian. Tricolpate pollen 

grains are present in uppermost beds of the 

Christopher Formation, of latest Albian age 

(Hopkins, 1974), and tricolpate grains in the 

Corwin are probably latest Albian or early 

Cenomanian. This apparent poleward progression 

in time is thought to mark the migration of 

early angiosperms from low latitudes. On the 

North Slope, the presence of pollen of the 

first angiospermous plants apparently serves to 

mark the approximate position of the AlbianCenomanian boundary. 

Once present, the angiosperms diversified 

rapidly, evolving a series of pollen types 

with increasingly complex morphology. This 

sequence is significant stratigraphically; it 

has been worked out for Cretaceous deposits in 

western Canada (Jarzen and Norris, 1975; Norris 

and others, 1975; Singh, 1975). A variety of 

dicotyledonous pollen is known to occur in 

post-Albian rocks on the North Slope and should 

be useful in their zonation. 

PALEOECOLOGY 

Uniformity of floral changes across the 

North Slope, shown by plant megafossils from 

the Nanushuk Group, are consistent with regional 

climatic changes (Smiley, 1972b). Some climatic 

inferences have been derived from changes in 
the proportionate representation of major plant 

groups. In Zones IA, IB, and II, such indicators of warm climatic conditions as the cycadophytes were relatively abundant; in Zone III 

they declined to extinction. Conversely, 

conifers, generally indicators of cooler conditions, are poorly represented in Zone IA, 

increase gradually upward, and become codominants in Zone III. Both changes are consistent with a warm period followed by cooling. 

Morphological characteristics of ginkgophyte 

(size attributes) and angiospermous leaves 

(margin features) are also consistent with a 

warm, frost-free environment in the Albian, 

followed by cooler, warm-temperate conditions 

from latest Albian to Turonian time. 

Contrary to their megafossil record, 

conifers are well represented by pollen at the 

Corwin type section. It may be inferred that 

coniferous forests existed on the adjacent 

highlands, from which the Corwin sediments were 

carried to the shoreline environments of deposition. R. H. Tschudy (written commun., 1978) 

has pointed out that the plants which produced 

the megaspore Arcellites, present in the Corwin 

Formation, were undoubtedly water ferns growing 

in freshwater lakes or ponds. Furthermore, 

because of their comparatively large size, 

megaspores generally are not deposited at great 

distances from their points of origin. 

SUMMARY 

Plant megafossil records and biostratigraphic zones based upon them have been shown 

to be useful in correlating nonmarine rocks of 

Cretaceous age across northern Alaska. Such 

97 

correlations also have been demonstrated between 

northern Alaska and adjacent regions to the 

east (northwestern Canada), to the south (central Alaska), and to the west (northeastern 

Eurasia). A unified floral province during 

Cretaceous time seems to have extended at" least 

from the Mackenzie River area on the east to 

west of the Lena River on the west (Vasilevskaya 

and Pavlov, 1963). The province extended from 

the Arctic Ocean to probably the Pacific Ocean 

in Alaska, and from the Arctic Ocean to south 

of the Okhotsk Sea in northeastern Eurasia 

(Lebedev, 1974). Most of the plant megafossil 

species that compose the Cretaceous floras 

within this floral province appear to be restricted to this part of the world, at least 

during middle Cretaceous time. Plant megafossil 

correlations of nonmarine rocks within this 

province are practical and reliable. Correlations with other floral provinces, or with 

floras of significantly different latitudes, 

appear not to be applicable at the species 

level (Smiley, 1967), but the floras may be 

correlative at the generic level. 

Despite problems with inadequate recovery 

of palynomorphs from Lower Cretaceous beds in 

the western region of the Alaskan North Slope, 

preliminary information has been obtained. The 

major floral zones of Smiley appear to be 

recognizable from spores and pollen. Megaspores 

from the type section of the Corwin Formation 

corroborate its Albian Age. The recovery of 

simple, tricolpate, dicotyledonous pollen near 

or somewhat above the Albian-Cenomanian boundary 

in the Corwin Formation establishes a palynological datum that should be recognizable 

eastward along the North Slope. 
PLATES 1-7. All illustrations are about 90 percent of natural size. 

Figure 1. 

2. 

PLATE 1 

Arctopteris rarinervis Samylina. 

A. kolymensis Samylina. 

98 
99 
Figure 1. 

2. 

PLATE 2 

Coniopteris inenarabilis (Hollick). 

c. onychioides Vass. and Kara-Mur. 

100 
101 
Figure 1. 

2. 

3. 

4. 

5. 

6. 

7. 

PLATE 3 

Ginkgo paradiantoides Samylina. 

Phoenicopsis var 2. 

Ginkgo n. sp. 

Phoenicopsis var 1. 

?Ginkgoites (?Baiera) n. sp. 

Sphenobaiera pulchella (Heer) Florin. 

Phoenicopsis var 3. 

102 
103 
Figure 1. 

2. 

3. 

4. 

5. 

PLATE 4 

Nilssonia cf. N. orientalis Heer. 

N. Alaskana Hollick. 

?Zamites sp. 

Nilssoniopteris polymorpha Sveshn. & Bud. 

Nilssonia cf. N. serotina Heer var 2. 

104 
105 
Figure 1. 

2. 

3. 

4. 

5. 

PLATE 5 

Pityophyllum var 2. 

Juniperites n. sp. 

Pityophyllum var 1 and Podozamites sp. 

Elatocladus n. sp. 

?Albieitites sp. 

106 
107 
PLATE 6 

Figure 1. Podozamites var 2. 

2. Podozamites var 15. 

3,4. Podozamites var 7. 

5. Podozamites var 9. 

108 
109 
Figure 1. 

2. 

3. 

4. 

5. 

PLATE 7 

cf. Ampelopsis multesima Hollick. 

Cissites comparabilis Hollick. 

Pseudoprotophyllum cf. P. dentatum Hollick. 

cf. Platanus latiloba Seward. 

?Cissites sp. 

110 
111 

DINOFLAGELLATE AND ACRITARCH ASSEMBLAGES 

FROM THE NANUSHUK GROUP 

(ALBIAN-CENOMANIAN) AND THE TOROK 

FORMATION (ALBIAN), UMIAT TEST WELL 11, 

NATIONAL PETROLEUM RESERVE IN ALASKA, 

NORTHERN ALASKA 

By Fred E. May 

ABSTRACT 

About 50 species of dinoflagellates and 

acritarchs are reported from the Nanushuk Group 

(Albian-Cenomanian) and the Torok Formation 

(Albian) of Umiat test well 11, National 

Petroleum Reserve in Alaska, northern Alaska. 

Twenty-four samples were examined: four from 

the Ninuluk Formation (three were barren); 

twelve from the Killik Tongue of the Chandler 

Formation (three yielded sufficient species to 

report); six from the Grandstand Formation (four 

yielded sufficient species to report); and two 

from the upper part of the Torok Formation (both 

yielded sufficient species to report). 

Although many of the taxa observed appea= 

new, several are useful in making age determinations and for correlations with formations in 

the Canadian districts of Mackenzie and Alberta. 

The presence of dinoflagellates and 

acritarchs indicates that the Nanushuk Group 

units studied (Killik Tongue of the Chandler 

Formation and the Grandstand Formation) and the 

upper part of the Torok Formation are predominantly marine. 

The Nanushuk Group is considered to be of 

middle to late Albian age on the basis of 

dinoflagellates and acritarchs, although a 

Cenomanian Age cannot be ruled out for the 

Killik Tongue and the Ninuluk Formation. 

INTRODUCTION 

Between 1944 and 1953 the U.S. Navy 

conducted a program of petroleum exploration in 

NPR-4 (Naval Petroleum Reserve No. 4) (now 

called NPRA, the National Petroleum Reserve in 

Alaska), northern Alaska. A main part of this 

program was the drilling of numerous test wells 

and core tests, including Umiat test well 11 

(Collins, 1958a). This paper on the Nanushuk 

Group (Albian-Cenomanian) and Torok Formation 

(Albian) in Umiat test well 11 is the first 

published report on dinoflagellate and acritarch 

assemblages from any of these wells. 

113 

To date, very little literature exists for 

North Slope dinoflagellate and acritarch assemblages. Virgil D. Wiggins (1973, 1975) of 

Standard Oil Co. of California has published 

some new genera and species from Jurassic and 

Lower Cretaceous sediments of the North Slope of 

Alaska. In adjacent Arctic and Subarctic 

Canada, several biostratigraphically helpful 

studies have been published (Brideaux, 1971; 

Singh, 1971; Brideaux and Mcintyre, 1975; and 

Brideaux and Fisher, 1976). In this report this 

attempted correlation and age determination of 

the Nanushuk Group are based primarily on 

comparison with Canadian assemblages. Oral 

communications with Wiggins (1977) have also 

been helpful in determining ages and in 

understanding some of the complexities inherent 

in the assemblages. 

This preliminary report is the first in a 

series to be published on dinoflagellate and 

acritarch assemblages from some of the NPR-4 

test wells, especially from Albian-Cenomanian 

Age units. Assemblages are presently being 

studied from Fish Creek test well 1, Simpson 

core test 25, and Grandstand test well 1. 

METHODS 

Standard palynological maceration procedures were employed in processing the core 

samples. HCl was used to digest carbonates, HF 

was used to digest silicates, and Schulze's 

solution was used to break down unwanted 

organics. Nitex monofilament sieve cloth was 

used to concentrate the dinoflagellates and 

acritarchs. Fossil residues were mounted in 

glycerin jelly on microscope slides. 

SLIDE STORAGE 

Microscope slides of Umiat test well 11 

are stored in the palynological laboratories of 

the U.S. Geological Survey, Denver, Colo., and 

are assigned Denver Paleobotany Locality Number 

D4060. 
STUDY LOCALITY 

Umiat test well 11, near Umiat on the 

North Slope of Alaska, was drilled at lat 

69°24'29" N., long 152°05'58" W. to test the 

petroleum production possibilities of the 

sandstone beds of the Grandstand Formation on 

the northern, downthrown side of a fault that 

parallels the axis of an anticline and to 

determine whether oil could be produced from 

any younger sandstone units (Collins, 1958a). 

The well penetrated the Upper Cretaceous 

Tuluvak Tongue of the Prince Creek Formation 

(about 158m thick), the Seabee Formation 

(about 427 m thick), the Ninuluk Formation 

(about 37m thick), the Lower Cretaceous Killik 

Tongue of the Chandler Formation (about 76 m 

thick), the Grandstand Formation (about 228 m 

thick), and the upper 61 m of the Torok Formation 

(the Topagoruk Formation of Collins, 1958a). 

This study reports on the dinoflagellate and 

acritarch assemblages recovered from cores 

taken in the Ninuluk Formation, the Killik 

Tongue of the Chandler Formation, the Grandstand 

Formation, and the upper part of the Torok 

Formation; this is an interval from 622 to 

1,006 m. These formations, except for the 

Torok, compose the Nanushuk Group in this area. 

DISCUSSION OF LITHOLOGIES 

In general, dinoflagellate and acritarch 

recovery is best in marine shales and silty 

sandstones. Several intervals of these lithologies were sampled in Umiat test well 11. 

Recovery was sporadic, but often good. 

The Ninuluk Formation (622-658 m) is 

mainly sandstone; however, a shale interval 

occurs from 638 to 641 m. The top of the shale 

interval was cored, and sparse dinoflagellate 

and acritarch assemblages were recovered from 

one sample (sample 38 at 639 m). 

The Killik Tongue of the Chandler Formation 

(658-737 m) is about half sandstone and half 

shale. Several shale intervals were cored, and 

often diverse assemblages were recovered from 

samples at 658, 676, and 689 m (samples 4la, 

46, and 50, respectively). Other samples were 

either barren or contained very sparse dinoflagellates and acritarchs. 

CHARACTERIZATION OF DINOFLAGELLATE AND 

ACRITARCH ASSEMBLAGES BY SAMPLE 

The ranges of characteristic dinoflagellates and acritarchs from Umiat test well 11 are 

shown by sample on table 8. The taxa listed on 

table 8 and in the text are illustrated in 

plates 8-12. 

Sample 4la (658 m), top of Killik Tongue of 

Chandler Formation.--About 25 species of 

dinoflagellates and acritarchs were recovered. 

Age diagnostic forms are: 

Cleistosphaeridium multispinosum (Singh) 

Brideaux, 1971, middle Albian to early 

Cenomanian; 

Oligosphaeridium irregulare (Pocock) Davey 

and Williams, 1969, early to middle 

Albian of subarctic Canada; range 

extended elsewhere. 

Age: possibly middle Albian. The extended 

range of o. irregulare (BarremianMaestrichtian) elsewhere suggests that the 

age of the sample could extend into the 

Cenomanian. 

Environment of deposition: marine. 

Sample 46 (685 m), upper half of Killik 

Tongue of the Chandler Formation.--About 22 

species of dinoflagellates and acritarchs were 

recovered. Many of these appear to be new 

species and are presently not age-diagnostic. 

Age: not determined. 

Environment of deposition: marine. 

Sample 50 (731 m), near base of Killik 

Tongue of Chandler Formation.--About 10 species 

of dinoflagellates and acritarchs were recovered. 

One of these species, Cleistosphaeridium multispinosum, suggests an age of middle Albian to 

early Cenomanian. 

Age: middle Albian to early Cenomanian. 

Environment of deposition: marine. 

Sample 55 (762 m), upper part of Grandstand 

Formation.--About 11 species of dinoflagellates 

and acritarchs were recovered. Forms that 

suggest an age for the sample are: 

New Genus A. Albian, based on oral communications with Virgil D. Wiggins, 

Standard Oil Co. of California (1977), 

and Hideyo Raga of Anderson, Warren 

and Associates (1977); 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Luxadinium propatulum Brideaux and Mcintyre, 

1975, middle Albian. 

The Grandstand Formation (737-937 m) is 

also about half sandstone and half shale. 

Several shale intervals were cored. Diverse 

assemblages were recovered from 823, 862, and 

893 m (samples 55, 56, and 59, respectively). 

Samples near 774 and 865 m (samples 54a and 58) 

yielded very sparse assemblages. Age: middle Albian. 

The upper part of the Torok Formation 

(originally called Topagoruk Formation) was also 

cored from 1,002 to 1,006 m. This interval is 

entirely shale. A core taken near 1,006 m 

(sample 61) yielded diverse and well-preserved 

dinoflagellates and acritarchs. 

114 

Environment of deposition: marine. 

Sample 56 (860 m), lower half of Grandstand 

Formation.--About 13 species of dinoflagellates 

and acritarchs were recovered. Forms that 

suggest an age for this sample are: 
<.0 

...... 

.t:> 

0'> 

...... 

. I 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

Table 8.--Ranges of characteristic dinoflagellates and acritarchs from the Nanushuk Group 

and Torok Formation of Umiat test well 11, North Slope, Alaska 

[Brid. indicates Brideaux; Mcint. indicates Mcintyre] 

TOROK GRANGSTAND CHAf'WLER 

(Killik Tongue) 

OJ OJOJ OJ ....... ....... 0'> 0'> <.0 0'>0'> N ....... ~ OJ (Jl 

w 0'>0 w w (Jl OJ 

(Jl (Jl(Jl (Jl (Jl (Jl .,. <.0 OJO'> (Jl .,. 0 0'> e PJ "' I 

X X X 

X X X 

x--x .x--x X X X 

x---x--x 

x--x X 

X 

X 

X 

X 

X 

X x---x 

x---x 

x---x X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

x--x X 

X X X 

x--x 

X X 

X X 

X 

X 

X 

x--x X 

X 

X 

X 

X 

X 

X 

X 

D 

s 

c 

·o 

L 

c 

M 

D 

c 

D 

D 

f) 

p 

0 

T 

p 

M 

D 

G 

G 

G 

D 

D 

D 

D 

G 

c 

T 

M 

p 

E 

L 

N 

c 

? 

0 

c 

0 

c 

M 

s 

B 

s 

p 

0 

0 

c 

? 

0 

c 

G 

E 

c 

EPTH (meters) 

AMPLE 

1eistosphaeridium multispinosum 

1igosphaeridium irregulare 

uxadinium sp. A 

1eistosphaeridium sp. A 

uderongia sp. A 

ef 1 andrea sp. 0 

leistosphaeridium sp. C 

eflandrea sp. B 

ef 1 andrea sp. G 

eflandrea sp. H 

olysphaeridium sp. A 

dontochitina costata enua verrucosa alaeostomacystis fragi1is 

uderongia sp. B 

ef 1 andrea sp. A 

onyaulacysta sp. B 

onyau1acysta cf. G. tenuiceras 

onyaulacysta sp. A 

eflandrea sp. C 

eflandrea sp. E 

eflandrea sp. F 

eflandrea sp. J 

ardodinium eisenacki 

leistosphaeridium sp. B enua sp. A 

uderongia sp. A of Brid. & Mclnt. 1975 

a1aeoperidinium cretaceum 

xochosphaeridium sp. A 

uxadinium propatu1um ew Genus A 

yc1onephelium sp. A 

Hystrichokolpoma sp. A 

eflandrea cf. D. minor 

yclonephe1ium sp. A of Brid. 1971 

eflandrea sp. 2 of Mclnt. 1975 

anningia sp. A 

uderongia sp C 

pinidinium vestitum 

atioladinium jaegeri 

ystematophora sp. A 

seudoceratium expo1itum 

phiobolus cf. 0. lapid~ris 

ligosphaeridium sp. B of Brid. 1971 

ribroperidinium intricatum 

Pterodinium verrucosum dontochitina operculata 

yclonephelium compactum 

onyaulacysta edwardsi 

ndoscrinium campanu1um 

anningia colliveri 

0 ligosphaeridium asterigerum 

G onyau1acysta sp. B of Singh 1971 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Muderongia sp. A. of Brideaux and Mcintyre 

(1975), Aptian to early Albian. 

species was observed that suggests an age: 

Cyclonephelium sp A of Brideaux (1971) from the 

early-late Albian. 

Age: early to middle Albian. 

Environment of deposition: marine. 

Age: possibly early-late Albian. 

Environment of deposition: marine. 

Sample 58 (865 m), lower half of Grandstand 

Formation.--About four species of dinoflagellates and acritarchs were recovered. Only one 

Sample 59 (893 m), lower part of Grandstand 

Formation.--About 19 species of dinoflagellates 

and acritarchs were recovered. Forms that 

suggest an age for this sample are: 

115 
Spinidinium vestitum Brideaux, 1971, late 

Albian to early Cenomanian; 

Luxadinium propatulum, middle Albian; 

New Genus A. Albian; 

Pseudoceratium expolitum Brideaux, 1971, 

middle to late Albian; 

Batioladinium jaegeri (Alberti) Brideaux, 

1975, early Valanginian to late 

Albian. 

Age: middle Albian. 

Environment of deposition: marine. 

Sample 61 (1,005 m), uppermost Torok 

Formation.--About 30 species of dinoflagellates 

and acritarchs were recovered. Forms that 

suggest an age for this sample are: 

Oligosphaeridium sp. B of Brideaux (1971), 

late Albian; 

Spinidinium vestitum, late Albian to early 

Cenomanian; 

Luxadinium propatulum, middle Albian; 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Batioladinium jaegeri, early Valanginian 

to late Albian; 

Cribroperidinium intricatum Davey, 1969, 

Albian; 

Cyclonephelium compactum Deflandre and 

Cookson, 1955, Albian to Santonian. 

Age: probably late-middle Albian. 

Environment of deposition: marine. 

AN ASSEMBLAGE FROM THE NINULUK FORMATION 

Sample 38 (640 m), from the middle part of 

the Ninuluk Formation, yielded an assemblage 

much like the ones seen in the Killik Tongue of 

the Chandler Formation (samples 4la, 46, and 

50). This sample is being considered as part 

of a separate problem and will not be discussed 

in detail here. The present assumptions, based 

on this Ninuluk assemblage, are that (1) 

probably no disconformity exists between the 

Ninuluk and Chandler Formations here, and (2) 

the environments of deposition of the parts of 

both units yielding the assemblages are similar, 

the Ninuluk probably being somewhat closer to 

shore. The age of the Ninuluk Formation cannot 

presently be determined from the dinoflagellates 

present; many of the forms appear to be undescribed. 

POSITION OF THE ALBIAN-CENOMANIAN BOUNDARY 

Although the presence of Cenomanian sediments cannot now be determined from the dinoflagellate and acritarch assemblages observed, 

still, the presence of Cleistosphaeridium 

multispinosum (Singh) Brideaux, 1971 in samples 

4la and 50 of the Killik Tongue of the Chandler 

Formation suggests that those samples could be 

as young as early Cenomanian. Considering the 

similarity between the Killik and Ninuluk 

dinoflagellates, it seems unlikely that a 

disconformity exists between these two units. 

116 

A marked difference exists between the assemblages of the Grandstand and the Killik, however. Although this may only reflect change in 

paleoenvironment, it may reflect a disconformity, 

and the poorly known Killik-Ninuluk assemblages 

may in fact be of younger Cenomanian Age. 

Foraminiferal assemblages (Sliter, this 

volume) indicate Albian Ages for samples to the 

top of the Grandstand Formation. Poor recovery 

precludes age dating through the Killik; however, Cenomanian foraminifera are reported from 

the Ninuluk. 

Thus, on the basis of dinoflagellates and 

foraminifera, it can be inferred that the 

Albian-Cenomanian boundary lies between the 

Grandstand and the Killik. At this depth (736 

m) a thin limestone layer exists that may 

represent the boundary; it is the only limestone 

layer on the entire log. 

CORRELATION WITH FORMATIONS 

IN THE CANADIAN ARCTIC 

Comparison with the work of Brideaux and 

Mcintyre (1975) makes possible a general correlation of Nanushuk Group units of Umiat test 

well 11 with the upper part of the Langton Bay 

Formation (Aptian-lower Albian) and the Horton 

River Formation (middle Albian) from the 

District of Mackenzie, western Arctic Canada. 

Six dinoflagellate taxa are common to both 

areas: 

1. Cleistosphaeridium multispinosum 

(Singh) Brideaux, 1971; 

2. Palaeoperidinium cretaceum Pocock, 

1962, ex Davey, 1970; 

3. Batioladinium jaegeri (Alberti) 

Brideaux, 1975; 

4. Muderongia sp. A of Brideaux and 

Mcintyre (1975); 

5. Cyclonephelium compactum Deflandre and 

Cookson, 1955; and 

6. Oligosphaeridium irregulare (Pocock) 

Davey and Williams, 1969. 

Although a detailed correlation is not 

possible at present, the concurrent ranges of 

these taxa in Brideaux and Mcintyre (1975) 

would tend to suggest that the Nanushuk Group 

in Umiat test well 11 is not older than early 

Albian and that it may be no older than middle 

Albian. 

CORRELATION WITH FORMATIONS 

iN CENTRAL ALBERTA, CANADA 

Comparison with the work of Brideaux 

(1971) makes possible a general correlation of 

the Nanushuk Group of Umiat test well 11 with 

the Peace River and Lower Shaftsbury Formations 

of west-central Alberta, and with the Joli Fou 

Formation, Viking Pelikan Formation, and Upper 

Shale of south-central Alberta. Eleven Nanushuk 

dinoflagellate taxa also occur in the central 

Alberta formations: 
1. Palaeoperidinium cretaceum.Pocock, 

1962, ex Davey, 1970; 

2. Oligosphaeridium irregulare (Pocock) 

Davey and Williams, 1969; 

3. Odontochitina operculata (0. Wetzel) 

Deflandre and Cookson, 1955; 

4. Canningia colliveri Cookson and 

Eisenack, 1960; 

5. Cleistosphaeridium multispinosum 

Brideaux, 1971; 

6. Oligosphaeridium anthophorum (Cookson 

and Eisenack) Davey, 1969; 

7. Pseudoceratium expolitum Brideaux, 

1971; 

8. Palaeostomacystis fragilis Cookson and 

Eisenack, 1962; 

9. Cribroperidinium intricatum Davey, 

1969; 

10. Batioladinium jaegeri (Alberti) 

Brideaux, 1975; and 

11. Spinidinium vestitum Brideaux,l971. 

The concurrent ranges for these taxa, 

reported in Brideaux (1971), suggest that the 

age of the Nanushuk Group is late-middle to 

late Albian. 

CONCLUSIONS 

Diverse dinoflagellate and acritarch 

assemblages are present in the upper part of 

the Torok Formation, the Grandstand Formation, 

the Killik Tongue of the Chandler Formation, 

and in at least one interval of the Ninuluk 

Formation. 

The upper part of the Torok and the Grandstand appear to be of middle to late Albian 

age, whereas the Killik Tongue of the Chandler 

may be as young as early Cenomanian. Assemblages of the Ninuluk did not yield agedistinctive forms, although the one assemblage 

reported is very similar to those seen in the 

Killik Tongue of the Chandler, suggesting a 

similar age and paleoenvironment. 

The Albian-Cenomanian boundary is inferred 

to lie between the Grandstand and Killik. This 

inference is based mainly on foraminiferal 

assemblages (Sliter, this volume) and on differences in dinoflagellate assemblages between the 

Grandstand and Killik. 

On the basis of the occurrence of dinoflagellates and acritarchs, parts of the Ninuluk, 

Killik, and Grandstand and the upper part of 

the Torok are interpreted as marine. The 

greatest species diversity is in the upper part 

of the Torok, suggesting deposition farthest 

from shore. The lower species diversities 

found in the units above the Torok suggest that 

they were deposited closer to shore than the 

Torok, but the relative proximities cannot 

presently be determined from dinoflagellates of 

these units. 

117 
Figures 1- 2. 

3. 

4. 

5- 8. 

9-10. 

11. 

12. 

13. 

14-15. 

16-17. 

18-19. 

20. 

PLATE 8 

Canningia sp. A., length 56 ~m. 

Tenua sp. A., length 76 ~m. 

Cleistosphaeridium sp. A., length 34 ~m. 

Cyclonephelium sp A of Brideaux 1971, length range 52-84 ~m. 

Cyclonephelium compactum Deflandre and Cookson 1955. 

Canningia colliveri Cookson and Eisenack 1960 of Singh 1971, length 70 ~m. 

Systematophora sp., length 40 ~m. 

Tenua verrucosa Sarjeant 1968, length 34 ~m. 

New Genus A., length 104 ~m. 

Gonyaulacysta sp. A of Singh 1971, length 100 ~m. 

Gonyaulacysta sp. A., length 64 ~m. 

Gonyaulacysta edwardsi (Cookson and Eisenack) Clarke and Verdier 1967 of Singh 1971, 

length 140 ~m. 

118 
. , 

. 8 

12 

119 
PLATE 9 

Figure 1. Cribroperidinium intricatum Davey 1969, length 102 ~m. 

2. Gonyaulacysta edwardsi (Cookson and Eisenack) Clarke and Verdier 1967 of Singh 1971, 

length 140 ~m. 

3. 

4- 5. 

6. 

7, 11-12. 

8. 

9-10, 13. 

14-15. 

16. 

Gonyaulacysta sp. B., length 84 ~m. 

Gonyaulacysta cf. G. tenuiceras (Eisenack) Sarjeant 1969 of Davey and Verdier 1971, 

length 74 ~m. 

Endoscrinium campanulum (Gocht) Vozzhennikova 1967, length 110 ~m. 

Muderongia sp. A., length range 60-80 ~m. 

Odontochitina operculata (0. Wetzel) Deflandre and Cookson 1955, length 142 ~m. 

Muderongia sp. B., length 70-78 ~m. 

Muderongia sp. A. of Brideaux and Mcintyre (1975), length 80 ~m. 

Muderongia sp. C., width of lateral horn 14 ~m. 

120 
2 

121 
Figures 1- 2. 

3- 4. 

5- 6. 

7. 

8. 

9-10. 

11. 

12-13. 

14-15. 

PLATE 10 

Muderongia sp. C., length 138 ~m. 

Pseudoceratium expolitum Brideaux 1971, length range 84-108 ~m. 

Cleistosphaeridium sp. A., length range 28-32 ~m. 

Cleistosphaeridium sp. B., length of main body 30 ~m. 

Cleistosphaeridium sp. C., length of main body 42 ~m. 

Oligosphaeridium irregulare (Pocock) Davey and Williams 1969, length of main body 36 

~m. 

Polysphaeridium sp. A., length of main body 60 ~m. 

Cleistosphaeridium multispinosum (Singh) Brideaux 1971. 

Oligosphaeridium anthophorum (Cookson and Eisenack) Davey 1969, length of main body 

60 ~m. 

122 
123 
Figure 1. 

2. 

3. 

4,14. 

5- 7. 

8. 

9. 

10. 

11. 

12. 

13,20. 

15. 

16. 

17-18. 

19. 

PLATE 11 

Oligosphaeridium asterigerum (Gocht) Davey and Williams 1969, length of upper 

process 30 ~m. 

Exochosphaeridium sp. A., length of main body 76 ~m. 

Aptea polymorpha Eisenack 1958, length 76 ~m. 

Deflandrea sp. A., length range 60-72 ~m. 

Spinidinium vestitum Brideaux 1971, length range 64-70 ~m. 

Deflandrea sp. 2 of Mcintyre (1973), length 62 ~m. 

Deflandrea cf. D. minor Cookson and Eisenack 1960, length 50 ~m. 

Deflandrea sp. B., length 50 ~m. 

Deflandrea sp. C., length 70 ~m. 

Deflandrea sp. D., length 66 ~m. 

Luxadinium sp. A., length range 60-74 ~m. 

Deflandrea sp. E., length 64 ~m. 

Deflandrea sp. F., length 68 ~m. 

Deflandrea sp. G., length of both specimens 76 ~m. 

Deflandrea sp. H., length 60 ~m. 

124 
125 
Figures 1- 3. 

4. 

5. 

6. 

7- 8. 

9-10. 

11. 

12. 

PLATE 12 

Luxadinium sp. A., length range 70-80 ~m. 

Deflandrea sp. I., length 80 ~m. 

Deflandrea sp. J., length 120 ~m. 

Palaeoperidinium cretaceum Pocock, ex Davey 1970, length 90 ~m. 

Batioladinium jaegeri(Alberti) Brideaux 1975, length range 142-160 ~m. 

Luxadinium propatulum Brideaux and Mcintyre 1975, length 85 ~m. 

Ophiobolus cf. o. lapidaris 0. Wetzel 1933, length of main body 58 ~m. 

Palaeostomacystis fragilis Cookson and Eisenack 1962, length 90 ~m. 

126 
127 
DINOFLAGELLATE AND ACRITARCH ASSEMBLAGES FROM 

THE GRANDSTAND FORMATION (MIDDLE TO UPPER 

ALBIAN) OF THE NANUSHUK GROUP, SIMPSON CORE 

TEST 25, NATIONAL PETROLEUM RESERVE IN 

ALASKA, NORTHERN ALASKA 

By Fred E. May and Jeffrey A. Stein 1 

ABSTRACT 

Sixty-one species of dinoflagellates and 

acritarchs are reported from the Grandstand 

Formation (middle to upper Albian) of Simpson 

core test 25, National Petroleum Reserve in 

Alaska, northern Alaska. Nineteen samples were 

examined from the 203-m interval considered to 

be Grandstand Formation. 

Although many of the observed taxa appear 

to be new, several are useful in making age 

determinations. The Grandstand Formation at 

this locality is considered to be of middle to 

late Albian age. The presence of dinoflagellates and acritarchs indicates that the Grandstand Formation is predominantly marine. 

INTRODUCTION 

During the exploration of NPR-4 (Naval 

Petroleum Reserve No. 4) (now called NPRA, the 

National Petroleum Reserve in Alaska) between 

1944 and 1953, the U.S. Navy and its contractors 

drilled 33 shallow holes on the Simpson Peninsula. This locality was of particular interest 

because of oil seeps that existed in an approximately 52-km2 area some 80 km southeast of Point 

Barrow near Cape Simpson. Simpson core test 25 

was one of 21 shallow wells drilled on the east 

side of the peninsula near Cape Simpson to 

determine the origin of the oil seeps. The 

drilling of core test 25 began in July 1949. It 

was located near seep 3, the southernmost seep. 

Although this was a dry hole, the next well, 

Simpson core test 26, was the discovery well of 

the Simpson oil field (Robinson, 1964). This 

paper on Simpson core test 25 is part of the 

first series of publications on the 

dinoflagellate and acritarch assemblages from 

wells drilled in NPRA. 

Because very little literature exists on 

North Slope dinoflagellate and acritarch assemblages, most palynological comparisons have to 

be made with published assemblages from the 

lstanford University, Department of 

Geology, Stanford, Calif. 

Arctic and subarctic of adjacent Canada 

(Brideaux, 1971; Singh, 1971, Brideaux and 

Mcintyre, 1975; Brideaux and Fisher, 1976; and 

Brideaux, 1977). 

METHODS 

Standard palynological-maceration procedures were employed in processing core samples. 

HCl was used to digest carbonates, HF was used 

to digest silicates, and Schulze's solution was 

used to break down unwanted organics. Nitex 

monofilament sieve cloth (20 ~m) was used to 

concentrate the dinoflagellates and acritarchs. 

Fossil residues were mounted in glycerin jelly 

on microscope slides. 

SLIDE STORAGE 

Microscope slides of Simpson core test 25 

are stored in the palynological laboratories of 

the U.S. Geological Survey, Denver, Colo., and 

are assigned Denver Paleobotany Locality Number 

D4044. 

STUDY LOCALITY 

Simpson core test 25, near oil seep 3 on 

the Simpson Peninsula, was drilled approximately 

93 km southeast of Point Barrow at lat 70°56'10" 

N. and long 154°42'12" W. (fig. 45) to locate 

the source of oil seeping in the vicinity. The 

well penetrated 33 m of Gubik Formation 

(Quaternary), 219m of Seabee Formation 

(Turonian), and 203m of Grandstand Formation 

(Albian) (Robinson, 1964). This paper reports 

on the dinoflagellate and acritarch assemblages 

recovered from the continuous core taken in the 

Grandstand interval. The Grandstand Formation 

constitutes the lower part of the Nanushuk Group 

of Albian to Cenomanian Age. 

DISCUSSION OF LITHOLOGIES 

In general, dinoflagellate and acritarch 

recovery is best in marine claystones, shales, 

siltstones, and silty sandstones. Several 

128 
168° 164° 

7oo 

0 

160° 

50 

I 

100 

I 

156° 152° 148° 

I 

0 I 

50 I 

100 I 150 

I 

200 

150 

I I 

250 

I 

200 MILES 

I 

300 KILOMETERS 

Figure 45.--General map of North Slope, Alaska, showing location of Simpson core test 25 within the 

National Petroleum Reserve in Alaska (modified from Robinson, 1964). 

intervals of these lithologies were sampled in 

Simpson core test 25. 

More than half of the Grandstand in the 

well is claystone, clayey shale, or shale (fig. 

46). Most samples from these lithologies yielded 

dinoflagellates and acritarchs. Recovery was 

fair to good in most samples, with at least 

adequate recovery occurring at the following 

depths: 254, 257, 260, 263, 266, 270, 273, 276, 

301, 309, 312, 318, 334, 351, 376, 412, 431, 

447, and 457 m. Samples at a few other depths 

were either barren or yielded too few specimens 

and taxa to be meaningful and were not reported. 

In general, the lithologies and lack of metamorphism have maintained good preservation in the 

assemblages. 

CHARACTERIZATION OF THE DINOFLAGELLATE AND 

ACRITARCH ASSEMBLAGES BY SAMPLE 

The ranges of characteristic dinoflagellates 

and acritarchs from Simpson core test 25 are 

shown by sample on table 9. The taxa listed on 

table 9 and in the text are illustrated in 

plates 13-17. All samples reported on here are 

considered marine. Species diversities are only 

approximate, based on the microscope slide 

examined. 

Sample 34 (254m), top of Grandstand Formation.--Seven species of dinoflagellates were 

recovered. Age diagnostic forms are: 

129 

Cleistosphaeridium multispinosum (Singh) 

Brideaux, 1971, middle Albian to early 

Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian (because of 

taxonomic complexity in th4s genus, 

the reported range for these forms is 

somewhat in question); 

Batioladinium jaegeri (Alberti) Brideaux 

1975, early Valanginian to late Albian; 

Genus A, Albian (Virgil D. Wiggins, Standard 

Oil Co. of California, oral commun., 

1978). 

Age: probably late Albian. 

Sample 35 (257 m).--Seven species of dinoflagellates were recovered. Age diagnostic 

forms are: 

Pseudoceratium expolitum Brideaux, 1971, 

middle to late Albian; 

Gardodinium eisenacki Alberti, 1961, 

Hauterivian to late Albian. 

Age: probably late Albian. 

Sample 36 (260 m).--Thirty-six species of 

dinoflagellates and acritarchs were recovered. 

Age diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 
C/) 

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SELECTED LITHOLOGIC DESCRIPTION 

Breccia. angular fragments as much as 5 em in diameter 

of Medium-light-gray, medium-gray, and medium-darkgray clay shale, bluish-gray clay shale, brownishyellow clay ironstone, small coal chips,_ and exceedingly rare small, rounded black chert pebbles in a 

matrix of medium-soft, friable, argillaceous sand. A 

fault plane dipping 70°, with breccia on one side and 

clay shale on the other at 24R m; also slickensides. 

Limestone, medium-light to medium-dark-gray, hard, 

dense, argillaceous; grades into medium-light-olivegray, nearly unconsolidated sandstone; 90 percent 

white and clear quartz grains; some coal particles, suba ngul a r. 

Clay shale, medium-gray, hackly-fracture; thin coaly 

streaks; and light-olive-gray, soft and friable siltstone; consists almost entirely of quartz grains and 

numerous ironstone concretions; Ditrupa sp. pelecypods 

and gastropod fragments. 

Claystone, medium-gray to medium-dark-gray, silty, micaceous, carbonaceous, medium-hard; plant impressions 

very rare; streaks of coal, dull black, blocky fracture; numerous sandy streaks. 

Claystone and clay shale, medium-light- to medium-gray, 

moderately hard, silty; pyritized and carbonized plant 

remains. Twenty-five an of coal at 342 m; shiny 

black, blocky fracture. Siltstone, light-gray to 

medium-light-gray, very soft, very slightly sandy; a few laminae of clay. 

Sandstone, medium-light-gray, very soft to practically 

unconsolidated; 75 percent white and clear quartz, 

also orangi sh-ye 11 ow quartz(?), mica, and dark minerals; grains subangular to subrounded. 

Clay shale, medium-light-gray, medium-soft, fair cleavage parallel to the bedding; scattered silty laminae. 

Ditrupa Sp. 

Sandstone, medium-light-gray, nearly unconsolidated, 75 

percent white and clear quartz; remainder of grains 

are dark gray, b 1 ack, opaque white, and ye 11 owi sh 

brown; very small amount of mica, bedding indistinct, 

appears very porous with drop test. 

Siltstone, sandstone, and claystone, 45° fractures, hard 

and "tight." 

Claystone, medium-light-gray; grades into siltstone in 

spots, bedding indistinct, c.oncentration of carbonaceous particles in steeply dipping "swirly" streaks at 

4?7 m, hard, some brown and black fragments. 

Limestone, light-bluish-gray, medium hard, but crumbles 

into chips; cut by veins of white, prismatic aragonite. 

Sandstone, medium-light-gray, very soft, grains subangular, rarely subrounded; 7'5 percent is white and 

clear quartz; coaly micaceous partings. 

r:lay shale, mPdium-gray, medium-soft, fair clPava<JP, 

numerous near-vertical fractures. 

Figure 46.--Columnar section of Grandstand Formation in Simpson core test 25 showing lithologic 

descriptions for core and approximate sample depths; sample depths are within 3 m of where 

samples were taken, indicating tops of sampling intervals (modified from Robinson, 1964). 

130 
Table 9.--Ranges of characteristic dinoflagellates and acritarchs from the Grandstand Formation of 

Simpson core test 25, North Slope, Alaska 

[X indicates specimens present; R indicates specimens probably reworked; Brid. indicates Brideaux; 

Mcint. indicates Mcintyre; C.&E. indicates Cookson and Eisenack] 

G R A N D s T A N D F 0 R M A T I 0 N 

'"' '"' '"' "' w w w ww w fVt.Jf-.Jt.JfVf-..J t..)t.J 

V' '"' ~ >--" " ll' >--" >--"0 0 -.J-.J-.JQ'\0'- 0'> lllV1 

" " N V' ,..... '"' 00 '""' 0\WOO'-WO -......1,::::.... DEPTH (meter !i) 

"' "' "' (X) " "' "' 0 ll' ~ _c....~wwwww 00 V' 0 .1:-- w ll' ;I> ll' ~~ ;I> J--'0\.0CO-......J0"\1../l..P.. SAMPLE 

x-x---x--x X X--X--X-XX X X X~ X X X Oligosphaeridium complex 

Cleistosphaeridium multispinosum 

Cyclonephelium sp. A of Brid. 1971 

Gardodinium eisenackii 

Odontochitina operculata 

Batioladinium jaegeri 

X-X 

X 

x-x 

x-x 

X 

X 

X 

-X 

X 

X 

X 

X X X--X-XX xxxxxx-x x--x X X--X---X-XX-X----X'X XXX X-X 

X X--X X xxx-xxxx )(: X XX-X----XX XXX-X 

X X 

X X--X X-X 

X X X 

X X---X XX -X 

X 

X XX 

X X 

X x--x XX-X 

X 

X x--x x-x X X X 

X X X 

X 

x--x X X X 

x-x-x xxxx-x-x X X X X 

XX X X X 

XXX X X 

X-XX 

;:o-;:o 

XXX X 

xx-x 

XX X 

XXX 

xxxx x-xxxx XXX X 

X-'1. 

X 

x-x 

xx-x 

Genus A 

Pseudoceratium expolitum 

Spiniferites ramosus ramosus luxadinium propatulum 

Exochosphaeridium bifidum 

Muderon9ia tetracantha 

Palaeoperidinium cretaceum 

?Achomosphaera sp. 

Chlamydophorella nyei 

Spinidinium vestitum 

x--x-xx--x---x-xxx 

?Spongodinium extremum 

Gonyaulacysta edwardsi 

Cyclonephelium eisenackii 

Odontochitina cf. 0. operculata 

Tanyosphaeridium sp. A of Brid. 1971 

Oligosphaeridium irregulare 

Hystrichosphaeridium arundum 

Apteodinium granulatum 

Callaiosphaeridium asymmetricum 

Carpodinium granulatum 

Oligosphaeridium anthophorum 

Pterodinium cornutum 

X X 

X 

X 

X X--X 

x--x 

x--x X 

X 

X 

X 

X 

X 

X 

Gardodinium eisenacki, Hauterivian to late 

Albian; 

X 

X 

X-X 

X-X 

X 

X 

xx-x 

Batioladinium jaegeri, early Valanginian to 

late Albian; 

Genus A, Albian; 

Pseudoceratium expolitum, middle to late 

Albian; 

131 

X-X 

X-X 

XX-X 

x-x--.x 

X--X 

XX-X 

XXX 

XX X 

XXX 

x-x X 

;:o 

X 

X 

X X X-X 

X 

X 

;:o 

X 

X 

XXX 

x-x 

XX 

X 

Spiniferites scabrosus 

lithodinia stoveri 

Spiniferites cingulatus 

Genus 8 

Hystrichosphaeridium stellatum 

Kalyptea sp. A of Brid. 1971 

Tenua sp. A 

Tubotuberella rhombiformis 

Cleistosphaeridium sp. 

Cleistosphaeridium polypes 

Polygonomorphid acritarchs 

Kalyptea monoceras 

Hystrlchokolpoma ferox of C.&E. 1974 

Nelchinopsis kostromiensis 

Oligosphaeridium sp. A 

Spiniferites ramosus reticulatus 

Cannllngia colliveri 

Cleistosphaeridium huguonioti 

8 a 1 cat t i a ci r r i fer a 

Herkomorphid acritarchs 

Deflandrea sp. 2 of Mclnt. 1974 

Cyclonephelium compactum 

Muderongia sp. A 

luxadinium primulum 

Scriniodinium sp. 

Palaeostomacystis fragilis 

Genus C 

Deflandrea sp. A 

Pediastrum sp. 

Membranilarnacia leptoderma 

Micrhystridium cf. M. piliferum 

Tenua sp. 8 

Muderongia asymmetrica 

Luxadinium propatulum Brideaux and Mcintyre, 

1975, middle Albian to early 

Cenomanian; 

Spinidinium vestitum Brideaux, 1971, middle 

Albian to early Cenomanian; 

?Spongodinium extremum (Cookson and 

Eisenack) Lentin and Williams, 1976, 
Albian to Cenomanian; 

Cyclonephelium eisenackii Davey, 1969, 

Albian; 

Oligosphaeridium irregulare (Pocock) Davey 

and Williams, 1969, early to middle 

Albian of Alberta, Canada; range 

extended elsewhere; 

Hystrichosphaeridium arundum Eisenack and 

Cookson, 1969, Aptian possibly into 

Cenomanian; 

Apteodinium granulatum Eisenack, 1958, late 

Valanginian to Albian; 

Carpodinium granulatum Cookson and Eisenack, 

1962, emend. Leffingwell and Morgan, 

1977, early Aptian to late Albian; 

Pterodinium cornutum Cookson and Eisenack, 

1962, early Berriasian to Albian; 

Lithodinia stoveri (Millioud) Duxbury, 

1977, Hauterivian to Albian; 

Kalyptea sp. A of Brideaux (1971), Aptian 

to Albian. 

Age: middle to late Albian. 

Sample 37 (263 m).--Twenty-three species of 

dinoflagellates and acritarchs were recovered. 

Age diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to late 

Albian; 

Pseudoceratium expolitum, middle to late 

Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Spinidinium vestitum, middle Albian to 

early Cenomanian; 

?Spongodinium extremum, Albian to 

Cenomanian; 

Cyclonephelium eisenackii, Albian; 

Apteodinium granulatum, late Valanginian to 

Albian; 

Cleistosphaeridium polypes Davey, 1969, 

Barremian to late Cenomanian; 

Hystrichokolpoma ferox of Cookson and 

Eisenack (1974), Albian to Cenomanian. 

Age: middle to late Albian. 

Sample 38 (266 m).--Twenty-nine species of 

dinoflagellates were recovered. Age diagnostic 

forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Batioladinium jaegeri, early Valanginian to 

late Albian; 

Genus A, Albian; 

Pseudoceratium expolitum, middle to late 

Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Spinidinium vestitum, middle Albian to 

early Cenomanian; 

132 

?Spongodinium extremum, Albian to 

Cenomanian; 

Cyclonephelium eisenackii, Albian; 

Oligosphaeridium irregulare, early to 

middle Albian of Alberta, Canada; 

range extended elsewhere; 

Hystrichosphaeridium arundum, Aptian, 

possibly into Cenomanian; 

Apteodinium granulatum, late Valanginian to 

Albian; 

Carpodinium granulatum, early Aptian to 

late Albian; 

Lithodinia stoveri, Hauterivian to Albian; 

Kalyptea sp. A of Brideaux (1971), late 

Albian. 

Age: late Albian. 

Sample 39 (270 m).--Twenty-one species of 

dinoflagellates and acritarchs were recovered. 

Age diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971); 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to late 

Albian; 

Genus A, Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

?Spongodinium extremum, Albian to 

Cenomanian; 

Cyclonephelium eisenackii, Albian; 

Hystrichosphaeridium arundum, Aptian, 

possibly into Cenomanian; 

Pterodinium cornutum, early Berriasian to 

Albian; 

Lithodinia stoveri, Hauterivian to Albian. 

Age: middle to late Albian. 

Sample 40 (273 m).--Eleven species of 

dinoflagellates and acritarchs were recovered. 

Age diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to late 

Albian; 

Genus A, Albian; 

Balcattia cirrifera Cookson and Eisenack, 

1974, Albian to Cenomanian. 

Age: middle to late Albian. 

Sample 41 (273 m).--Thirteen species of 

dinoflagellates and acritarchs were recovered. 

Age diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to late 

Albian; 

Genus A, Albian; 

Apteodinium granulatum, late Valanginian to 

Albian; 
Pterodinium cornutum, early B~rriasian to 

Albian; 

Balcattia cirrifera, Albian to Cenomanian. 

Age: middle to late Albian. 

Sample 49A (301 m).--Ten species of dinoflagellates were recovered. Age diagnostic 

forms are: 

Age: 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Pseudoceratium 

Albian; 

expolitum, middle to late 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Spinidinium vestitum, middle Albian to 

early Cenomanian; 

Apteodinium granulatum, late Valanginian to 

Albian; 

Cleistosphaeridium polypes, Barremian to 

late Cenomanian. 

middle to late Albian. 

Sample 52 (309 m).--Twenty-three species 

of dinoflagellates were recovered. Age diagnostic forms are: 

Age: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Batioladinium jaegeri, early Valanginian 

to late Albian; 

Pseudoceratium expolitum, middle to late 

Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Spinidinium vestitum, middle Albian to 

early Cenomanian; 

Cyclonephelium eisenackii, Albian; 

Oligosphaeridium irregulare, early to 

middle Albian of Alberta, Canada; 

range extended elsewhere; 

Hystrichosphaeridium arundum, Aptian, 

possibly into Cenomanian; 

Apteodinium granulatum, late Valanginian 

to Albian; 

Carpodinium granulatum, early Aptian to 

late Albian; 

Cleistosphaeridium polypes, Barremian to 

late Cenomanian. 

middle to late Albian. 

Sample 53 (312 m).--Ten species of dinoflagellates were recovered. Age diagnostic forms 

are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to 

late Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Apteodinium granulatum, late Valanginian 

to Albian. 

Age: middle to late Albian. 

Sample 55 (318 m).--Four species of 

dinoflagellates were recovered. Age diagnostic 

forms are: 

Age: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Apteodinium granulatum, late Valanginian to 

Albian. 

middle to late Albian. 

Sample 60A (334 m).--Nineteen species of 

dinoflagellates and acritarchs were recovered. 

Age diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to late 

Albian; 

Pseudoceratium expolitum, middle to late 

Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Luxadinium primulum Brideaux and Mcintyre, 

1975, middle Albian; 

Spinidinium vestitum, middle Albian to 

early Cenomanian; 

Cyclonephelium eisenackii, Albian; 

Oligosphaeridium irregulare, early to 

middle Albian of Alberta, Canada; 

range extended elsewhere. 

Hystrichosphaeridium arundum, Aptian 

possibly into Cenomanian; 

Apteodinium granulatum, late Valanginian to 

Albian; 

Cyclonephelium compactum Deflandre and 

Cookson, 1955, Albian to Santonian. 

Age: middle to late Albian. 

Sample 65 (351 m).--Sixteen species of 

dinoflagellates were recovered. Age diagnostic 

forms are: 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to late 

Albian; 

Pseudoceratium expolitum, middle to late 

Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Luxadinium primulum, middle Albian; 

Spinidinium vestitum, middle Albian to 

early Cenomanian; 

Oligosphaeridium irregulare, early to 

middle Albian of Alberta, Canada; 

range extended elsewhere. 

Cleistosphaeridium polypes, Barremian to 

late Cenomanian; 

Cyclonephelium compactum, Albian to 

Spinidinium vestitum, middle Albian Santonian. to 

early Cenomanian; Age: middle to late Albian. 

133 
Sample 73 (376 m).--Sixteen species of 

dinoflagellates and one species of colonial 

Chlorophyta, Pediastrum Meyen, 1829, were 

recovered. Pediastrum, if it is not a contaminant, would suggest the proximity of lacustrine 

environments. Age diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Batioladinium jaegeri, early Valanginian 

to late Albian; 

Luxadinium propatulum, middle Albian to 

early Cenomanian; 

Spinidinium vestitum, middle Albian to 

early Cenomanian; 

?Spongodinium extremum, Albian to 

Cenomanian; 

Cyclonephelium eisenackii, Albian; 

Cleistosphaeridium polypes, Barremian to 

late Albian. 

Age: middle to late Albian. 

Sample 84 (412 m).--Nine species of dinoflagellates and acritarchs were recovered. Age 

diagnostic forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to 

late Albian; 

Cyclonephelium compactum, Albian to 

Santonian. 

Age: probably middle to late Albian. 

Sample 90 (431 m).--Four species of dinoflagellates and acritarchs were recovered. Age 

diagnostic forms are: 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Pseudoceratium expolitum, middle to late 

Albian; 

Micrhystridium cf. M. piliferum Deflandre, 

1937. Specimens called Micrhystridium 

cf. M. piliferum by Brideaux (1971) 

are restricted to the upper Albian of 

central Alberta, Canada. Brideaux's 

specimens are very similar to Simpson 

core test 25 specimens. Thus, a late 

Albian age is being applied here for 

these specimens. 

Age: late Albian. 

Sample 95 (447 m).--Eight species of 

dinoflagellates were recovered. Age diagnostic 

forms are: 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Gardodinium eisenackii, Hauterivian to late 

Albian. 

Age: probably middle to late Albian. 

Sample 98 (457 m).--Nine species of 

dinoflagellates were recovered. Age diagnostic 

forms are: 

134 

Cleistosphaeridium multispinosum, middle 

Albian to early Cenomanian; 

Cyclonephelium sp. A of Brideaux (1971), 

middle to late Albian; 

Gardodinium eisenackii, Hauterivian to late 

Albian; 

Cleistosphaeridium polypes, Barremian to 

late Albian; 

Muderongia asymmetrica Brideaux, 1977, 

Aptian to early Albian. 

Age: possibly early to middle Albian. The 

reported upper range of M. asymmetrica 

(Brideaux and Mcintyre, 1975; Brideaux, 

1977) suggests that this sample could be as 

old as early Albian. 

COMPARISON WITH FORMATIONS 

IN THE CANADIAN ARCTIC 

The taxa present in Simpson core test 25 

generally tend to suggest an age for the 

Grandstand Formation there as middle to late 

Albian. Based on comparison of dinoflagellate 

assemblages reported here and in Brideaux and 

Mcintyre (1975), the Grandstand Formation in 

Simpson core test 25 may correlate, in part, 

with the Horton River Formation in the District 

of Mackenzie, Canada. Species held in common 

are: 

1. Cleistosphaeridium multispinosum 

(Singh) Brideaux, 1971; 

2. Palaeoperidinium cretaceum Pocock, 

1962, ex Davey, 1970; 

3. Batioladinium jaegeri (Alberti) 

Brideaux, 1975; 

4. Cyclonephelium compactum Deflandre and 

Cookson, 1955; 

5. Oligosphaeridium irregulare (Pocock) 

Davey and Williams, 1969; 

6. Gardodinium eisenackii Alberti, 1961; 

7. Kalyptea sp. A of Brideaux (1971); 

8. Luxadinium primulum Brideaux and 

Mcintyre, 1975. 

COMPARISON WITH FORMATIONS 

IN CENTRAL ALBERTA, CANADA 

Comparison with the work of Brideaux 

(1971) makes possible a general correlation of 

the Grandstand Formation of Simpson core test 25 

with the Peace River and Lower Shaftsbury 

Formations of west-central Alberta, and with the 

Joli Fou, Viking, and Pelikan Formations, and 

"Upper Shale Unit" of south-central Alberta. 

Species held in common are: 

1. Palaeoperidinium cretaceum Pocock, 

1962, ex Davey, 1970; 

2. Oligosphaeridium irregulare (Pocock) 

Davey and Williams, 1969; 

3. Odontochitina operculata (0. Wetzel) 

Deflandre and Cookson, 1955; 

4. Canningia colliveri Cookson and 

Eisenack, 1960; 

5. Cleistosphaeridium multispinosum 

Brideaux, 1971; 
6. Oligosphaeridium anthopho~um (Cookson 

and Eisenack) Davey, 1969; 

7. Pseudoceratium expolitum Brideaux, 

1971; 

8. Palaeostomocystis fragilis Cookson and 

Eisenack, 1962; 

9. Batioladinium jaegeri (Alberti) 

Brideaux, 1975; 

10. Spinidinium vestitum Brideaux, 1971; 

11. Oligosphaeridium complex (White) Davey 

and Williams, 1966; 

12. Spiniferites ramosus subsp. ramosus 

(Ehrenberg) Loeblich and Loeblich, 

1966; 

13. Cyclonephelium eisenackii Davey, 1969; 

14. Chlamydophorella nyei Cookson and 

Eisenack, 1958; 

15. Kalyptea sp. A of Brideaux, 1971; 

16. Micrhystridium cf. M. piliferum 

Deflandre, 1937 of Brideaux (1971); 

17. Luxadinium propatulum Brideaux and 

Mcintyre, 1975; 

18. Cyclonephelium sp. A of Brideaux, 

1971. 

The concurrent ranges of these taxa in both 

areas would tend to support the correlation of 

the Grandstand Formation in Simpso_n core test 25 

with the above-mentioned formations in central 

Alberta, and would suggest a middle or late 

Albian age for the Grandstand Formation. Many 

of these same taxa are also found in assemblages 

from the Loon River, Peace River, and Shaftsbury 

Formations of the Peace River area, northern 

Alberta (Singh, 1971), suggesting a middle to 

late Albian age for the Grandstand Formation of 

Simpson core test 25. 

COMPARISON WITH AUSTRALIAN TAXA 

The Perth Basin, western Australia, dinoflagellate assemblages collected from the 

Albian interval of the Moora bore (26-52 m) and 

the Osborne Formation of Albian to Cenomanian 

Age of the Balcatta No. 1 and No. 2 bores 

(Cookson and Eisenack, 1974) show some similarities to the Grandstand assemblages reported 

here. Balcattia cirrifera Cookson and Eisenack, 

1974, from the Osborne Formation of the Balcatta 

No. 1 bore has been rarely reported elsewhere, 

but it occurs in two of the Grandstand Formation 

samples (samples 40 and 41). ?Spongodinium 

extremum (Cookson and Eisenack) Lentin and 

Williams, 1977, also from the Osborne Formation 

of the Balcatta No. 1 bore, occurs in five of 

the Grandstand Formation samples (samples 36, 

37, 38, 39, and 73). Cyclonephelium eisenackii 

135 

Davey, 1969, identified by Cookson and Eisenack 

(1974) as Aptea polymorpha Eisenack, 1958, is 

reported by them only from the Albian interval 

of the Moora bore. c. eisenackii occurs in 

samples 36, 37, 38, 39, 52, 60A, and 73 from the 

Grandstand. A form identified by Cookson and 

Eisenack (1974) as Hystrichokolpoma ferox 

Deflandre, 1937, from the Albian of the Moora 

bore occurs in sample 37 from the Grandstand. 

These similarities in occurrences support the 

Albian Age determined for the Grandstand and 

suggest possible correlations with stratigraphic 

strata as distant as Australia. 

SUMMARY AND CONCLUSIONS 

Diverse dinoflagellate and acritarch 

assemblages are present in the Grandstand 

Formation of Simpson core test 25, North Slope, 

Alaska. Fifty-nine taxa of dinoflagellates, the 

stratigraphic ranges for these taxa, and two 

general acritarch groupings have been identified 

and illustrated. Preservation of the specimens 

is good. 

A middle or late Albian age is suggested 

for the Grandstand Formation samples reported, 

based primarily on comparison with similar 

published Canadian assemblages; supporting 

evidence exists from Australian assemblages. 

Comparison with Canadian assemblages suggests 

that the Grandstand Formation in Simpson core 

test 25 correlates with at least parts of the 

Peace River and Lower Shaftsbury Formations of 

west-central Alberta; the Joli Fou, Viking, and 

Pelican Formations, and "Upper Shale Unit" of 

south-central Alberta; and the Loon River, Peace 

River, and Shaftsbury Formations of the Peace 

River area, northern Alberta. 

Moderate species diversities (between 20 

and 40 species) suggest normal marine conditions 

for some of the samples studied (samples 36, 

37, 38, 39, and 52). Such diversity is not 

nearly as high as in samples observed by the 

authors from normal marine Upper Cretaceous 

Atlantic and Gulf Coast samples (40 to 60 

species); and, therefore, it is suggested that 

these assemblages represent very nearshore 

conditions. Some samples reported here having 

less than 10 or 15 species would seem to represent abnormal marine conditions, possibly 

estuarine or lagoonal (samples 34, 35, 40, 41, 

49A, 53, 55, 84, 90, 95, and 98). This is in 

keeping with the general interpretations of the 

kinds of depositional environments that existed 

for the Grandstand Formation (Thomas S. 

Ahlbrandt, oral cornmun., 1978). 
Figure 1. 

2,6. 

3. 

4,8. 

5. 

7. 

9,10. 

11,14,15. 

13. 

12,16. 

PLATE 13 

Cyclonephelium eisenackii Davey 1969, l~ngth 86 ~m. 

Cyclonephelium sp. A of Brideaux (1971), width range 64-80 ~m. 

Canningia colliveri Cookson and Eisenack, 1960, length 68 ~m. 

Cyclonephelium compactum Deflandre and Cookson, 1955. 

4. Operculum, length 6 ~m. 

8. Specimen lacking operculum, length 102 ~m. 

Tenua sp. A, length 68 ~m. 

Tenua sp. B., length 36 ~m. 

Genus B, width range 84-94 ~m. 

Gonyaulacysta edwardsi Cookson and Eisenack, 1958. 

11. Operculum, length 58 ~m. 

14. Lateral view, length 134 ~m. 

15. Dorsal view, width 122 ~m. 

Apteodinium granulatum Eisenack,l958, dorsal view, 68 ~m. 

?Spongodinium extremum (Cookson and Eisenack) Lentin and Williams, 1976. 

12. Operculum, length 32 ~m. 

16. Ventral view, length 92 ~m. 

136 
"""13 15 16 

137 
Figures 1,2. 

3,4. 

5. 

6,7. 

8,9,13. 

10,14. 

11,12. 

15. 

16,17. 

PLATE 14 

Genus A. 

1. Ventral view, length 120 ~m. 

2. Fragment showing cingulum, width 74 ~m. 

Carpodinium granulatum Cookson and Eisenack, 1962, length range 72-74 ~m. 

Tubotuberella rhombiformis Vozzhennikova, 1967, length 124 ~m. 

Lithodinia stoveri (Millioud) Duxbury, 1977, length range 52-54 ~m. 

Spiniferites cingulatus (0. Wetzel) Serjeant, 1970, length range of main body 40-50 

~m. 

Pterodinium cornutum Cookson and Eisenack, 1962, length range of main body 60-62 ~m. 

Achomosphaera sp., width range of main body 62-70 ~m. 

Spiniferites ramosus subsp. ramosus (Ehrenberg) Loeblich and Loeblich, 1966, length 

of main body 44 ~m. 

Spiniferites scabrosus (Clarke and Verdier) Lentin and Williams, 1975, width range 

of main body 42-54 ~m. 

138 
10 

139 
PLATE 15 

Figure 1. Spiniferites ramosus subsp. reticulatus (Davey and Williams) Lentin and Williams, 

1973, length 46 ~m. 

2,3,4. Pseudoceratium expolitum Brideaux, 1971. 

2,4. Length range without operculum 62-88 ~m. 

3. Length 100 ~m. 

5,9. Odontochitina operculata (0. Wetzel) Deflandre and Cookson, 1955. 

5. Length of operculum 176 ~m. 

9. Length of specimen without operculum 146 ~m. 

6. Muderongia asymmetrica Brideaux, 1977, length 66 ~m. 

7. Muderongia tetracantha (Gocht) Alberti, 1961, length 98 ~m. 

8. Muderongia sp. A, length 144 ~m. 

10. Odontochitina cf. 0. operculata (0. Wetzel) Deflandre and Cookson, 1955, length 148 

~m. 

11,15,16. Balcattia cirrifera Cookson and Eisenack, 1974. 

11. Length of main body 76 ~m. 

15,16. Width of operculum main body 70 ~m. 

12. Genus C, length 116 ~m. 

13,14. Callaiosphaeridium asymmetricum (Deflandre and Courteville) Davey and Williams, 

1966. 

13. Width of main body 60 ~m. 

14. Width of main body 50 ~m. 

140 
• 6 7 8 

11 

141 
PLATE 16 

Figure 1. Exochosphaeridium bifidum (Clarke and Verdier) Clarke and others, 1968, length of 

main body 64 vm. 

2. Hystrichokolpoma ferox of Cookson and Eisenack (1974), length of main body 44 vm. 

3. Membranilarnacia leptoderma (Cookson and Eisenack) Eisenack, 1963, overall width 37 

vm. 

4. Oligosphaeridium sp. A, length of main body 34 vm. 

5. Hystrichosphaeridium stellatum Maier, 1959, length of main body 40 vm. 

6,7. Oligosphaeridium anthophorum (Cookson and Eisenack) Davey, 1969. 

6. Length of main body 54 vm. 

7. Width of operculum 34 vm. 

8. Hystrichosphaeridium arundum Eisenack and Cookson, 1960, length of main body 56 vm. 

9. Tanyosphaeridium sp. A, length 40 vm. 

10. Oligosphaeridium irregulare (Pocock) Davey and Williams, 1969, length of main body 40 vm

11,12. Oligosphaeridium complex (White) Davey and Williams, 1966. 

11. Length of main body 42 vm. 

12. Length of main body 72 vm. 

13. Cleistosphaeridium multispinosum (Singh) Brideaux, 1971, length of main body 46 vm. 

14. Cleistosphaeridium polypes (Cookson and Eisenack) Davey, 1969, length of main body 

44 vm. 

15. Cleistosphaeridium huguonioti (Valensi) Davey, 1969, length of main body 36 vm. 

16,17,18. Chlamydophorella nyei Cookson and Eisenack, 1958. 

16. Length 46 vm. 

17. Length 56 vm. 

18. Length 52 vm. 

19. Cleistosphaeridium sp., length of main body 52 vm. 

20,21. Gardodinium eisenackii (Alberti) Lentin and Williams, 1977. 

20. Length 66 vm. 

21. Length 78 vm. 

142 
• 

143 
Figures 1,2. 

3,4. 

5. 

6,7. 

8. 

9,10. 

11. 

12,13. 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22,23. 

24. 

PLATE 17 

Batioladinium jaegeri Brideaux, 1975. 

1. Length 148 ~m. 

2. Length 116 ~m. 

Kalyptea monoceras Cookson and Eisenack, 1960. 

3. Length 60 ~m. 

4. Length 94 ~m. 

Kalyptea sp. A of Brideaux (1971), length of main body 50 ~m. 

Deflandrea sp. 2 of Mcintyre (1974). 

6. Length 54 ~m. 

7. Length 50 ~m. 

Deflandrea sp. A, length 58 ~m. 

Luxadinium propatulum Brideaux and Mcintyre, 1975. 

9. Width of operculum 56 ~m. 

10. Length 80 ~m. 

Palaeoperidinium cretaceum Pocock ex Davey, 1970, length 88 ~m. 

Spinidinium vestitum Brideaux, 1971. 

12. Length 68 ~m. 

13. Length 64 ~m. 

Luxadinium primulum Brideaux and Mcintyre, 1975; length 58 ~m. 

Nelchinopsis kostromiensis (Vozzhennikova) Wiggins, 1972, length 60 ~m. 

Pediastrum sp., diameter 48 ~m. 

Veryhachium europaeum of Brideaux (1971), a polygonomorphid acritarch, diagonal 

length 54 ~m. 

Veryhachium sp. 2, maximum diameter 20 ~m. 

Palaeostomacystis fragilis Cookson and Eisenack, 1962, width 66 ~m. 

Scriniodinium sp., length 50 ~m. 

Micrhystridium cf. M. piliferum of Brideaux (1971), diameter main body 32 ~m. 

Veryhachium reductum Deunff emend. De Jekhowsky, 1961. 

22. Length of side of main body 20 ~m. 

23. Length of side of main body 80 ~m. 

?Cymatiosphaera sp., a herkomorphid acritarch, diameter 33 ~m. 

144 
5 

1 

17 18 

145 

CRETACEOUS FORAMINIFERS FROM THE 

NORTH SLOPE OF ALASKA 

By William V. Sliter 

The data reported here represent a reexamination of foraminiferal assemblages recovered 

from the Albian to Cenomanian interval of Umiat 

test well 11 and new occurrences from surface 

sections collected during the 1977 summer field 

season (fig. 47; see Ahlbrandt and others, this 

volume). This study is part of a continuing 

project designed to better correlate 

foraminiferal and palynological data and to 

improve environmental interpretations. 

UMIAT 

Foraminifers from Umiat test well 11 

previously were described by Bergquist (1966). 

Reexamination of selected slides from both cores 

and ditch samples confirms the original taxonomic 

interpretations. Foraminiferal occurrence in 

cores from the upper part of the Torok Formation 

and the Nanushuk Group are shown in figure 48. 

The fauna consists of 21 species of which 8 are 

calcareous. Characteristic foraminiferal species 

are shown in plate 18. In general, occurrences 

are sporadic, diversity is low, and preservation 

is poor to moderate. Despite these deficiencies, 

the species distributions are adequate for age 

determinations and correlations. Taxonomic 

identifications used herein follow those of 

Tappan (1962). 

The Ninuluk Formation is assigned to a 36-

m interval of massive, argillaceous sandstone 

with dark-gray siltstone and claystone at the 

base. Foraminifers are restricted to the lower 

siltstone and argillaceous sandstone in cores 40 

and 41 and consist of Trachammina rutherfardi 

Stelck and Wall and Saccammina lathrami Tappan. 

The abundance and taxonomic characteristics of 

T. rutherfardi indicate a Cenomanian Age for 

this interval. Cores 35 to 39 from the massive 

sandstone are barren of foraminifers. Megafossils recovered from the Ninuluk Formation 

are Cenomanian in age (Detterman, 1956; Jones 

and Gryc, 1960; Imlay, 1961). On the basis of 

these occurrences, the Ninuluk Formation is 

correlated with the Belle Fourche Shale of the 

Western Interior of the United States and the 

Dunvegan Formation of British Columbia, both 

considered to be Cenomanian in age. Depositiona! environments represent marginal-marine 

facies at the base of the formation that grade 

upward into brackish-water or nonmarine facies 

at the top. 

The Killik Tongue of the Chandler Formation 

is represented by about 79 m of interbedded 

argillaceous sandstone, siltstone, and claystone 

that has local carbonaceous streaks and coaly 

material. Fish debris is found rarely in the 

sequence, and foraminifers are limited to the 

long-ranging Saccammina lathrami Tappan in core 

48. The remaining cores from this unit, cores 

42 to 47, 49, and 50, are barren of foraminifers. 

Although no foraminifers were recovered from 

samples at the type area of the Killik Tongue 

along the Killik River, exposures of the Killik 

to the north near Umiat contain late Albian 

species such as Verneuilinaides borealis 

Tappan, Haplaphragmoides tapagarukensis Tappan, 

Psamminapelta bowsheri Tappan, and Gaudryina 

canadensis Cushman (Detterman, 1956; Bergquist, 

1966). These occurrences probably represent 

marine interfingers of the adjacent Grandstand 

Formation. Consequently, the regional age 

relationships of the Killik Tongue, especially 

those at the upper boundary with the Ninuluk 

Formation, remain undecided. It is entirely 

possible that the Albian-Cenomanian boundary 

lies within the Killik Tongue and that Cenomanian 

strata extend into the overlying Ninuluk 

Formation. The Killik Tongue is typified by 

delta-platform deposits containing rare 

occurrences of brackish-water and freshwater 

pelecypods and occasional interbeds of marginalmarine deposits that contain fish debris and 

foraminifers. 

A section of·nearly 200m of sandstone, 

claystone, and shale is placed within the 

Grandstand Formation. Moderately diverse and 

continuously occurring foraminifers of Albian 

Age were recovered throughout the section 

beginning with a ditch sample at 740 to 742 m 

in dark-gray siltstone, some 2 m below the 

contact with the overlying Killik Tongue. This 

uppermost assemblage includes Verneuilinaides 

borealis Tappan, Miliammina awunensis Tappan, 

Gaudryina canadensis Cushman, Psamminapelta 

subcircularis Tappan, and HaplaphragmOides 

147 
0 25 50 MILES 

I I I 

0 

A- STARVE SECTION (SEAVIEW SYNCLINE) 

B- TUPIKCHAK MOUNTAIN 

C I - KUKPOWRUK RIVER SECTION 

C2- ARCHIMEDES ANTICLINE 

D - IGLOO MOUNTAIN 

E- KOKOLIK WARP SYNCLINE 

c £ 

F- FOLSOM POINT SYNCLINE 

G - MEAT MOUNTAIN 

H - LOOKOUT RIDGE SYNCLINE 

I - NINULUK BLUFF 

J - TUKTU BLUFF 

N 

• MEASURED SECTION 

• WELL 

Figure 47.--Index map of northern Alaska showing location of 1977 NPRA (National ?etroleum Reserve 

in Alaska) field collections and Umiat test well 11. 

topagorukensis Tappan. Older assemblages 

within the Grandstand Formation from cores 55, 

56, and 59 include species such as Gavelinella 

stictata (Tappan), Ammobaculites wenonahae 

Tappan, Globorotalites alaskensis Tappan, and 

Miliammina manitobensis Wickenden. Cores 52, 

53, 57, 58, and 60 are barren of foraminifers. 

The occurrence of the ammonite Cleoniceras in 

basal beds of the Grandstand Formation suggests 

a middle Albian age (Imlay, 1961, p. 12), whereas 

the upper beds are inferred by stratigraphic 

relationships to be late Albian in age. 

Depositional environments within the Grandstand 

Formation range from neritic to bathyalprodelta to delta-front deposits, with evidence 

of shoaling near the upper boundary. 

148 

Albian foraminifers continue downward 

the Torok Formation represented by some 70 

shale, siltstone, and dark-gray claystone. 

highest-diversity assemblage was recovered 

core 61 at the base of the test well. In 

addition to the Grandstand assemblages, the 

into 

m of 

The 

from 

fauna includes Conorboides umiatensis (Tappan), 

Globulina canadensis Mellon and Wall, and 

Saracenaria projectura Stelck and Wall among 

others. Megafossils in the upper third of the 

Torok Formation, such as the ammonites Gastroplites, 

Paragastroplites, and Cleoniceras, indicate a 

middle Albian age (Imlay, 1961). Outer neritic 

to bathyal-prodelta environments are indicated 

by the foraminiferal assemblage. 

Foraminifers from the upper part of the 
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SERIES 

STAGE 

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DEPTH (METERS) 

CORE 

LITHOLOGY 

Trochammina rutherfordi STELCK AND WALL 

Saccammina lathrami TAPPAN 

Haplaphragmoides topagorukensis TAPPAN 

Verneuilinoides borealis TAPPAN 

Gaudryina canadensis CUSHMAN 

Miliammina awunensis TAPPAN 

Psamminopelta subcircularis TAPPAN 

Gavelinella stictata (TAPPAN) 

Quadrimorphina ruckerae 

Lenticulina macrodisca 

(TAPPAN) 

(REUSS) 

Ammobaculites wenonahae TAPPAN 

Praebulimina nannina (TAPPAN) 

Gaudryinella irregularis TAPPAN 

Bathysiphon vitta NAUSS 

Globorotalites alaskensis TAPPAN 

Miliammina manitobensis WICKENDEN 

Bathysiphon brosgei TAPPAN 

Conorboides umiatensis (TAPPAN) 

Globulina canadensis MELLON and WALL 

Marginulina planiuscula (REUSS) 

Saracenaria projectura STELCK and WALL 
Torok Formation and Nanushuk Group of Umiat 

test well 11 provide correlation with other 

reference sections in the North American Arctic 

area. Most notable are the Arctic Red Formation 

of the northern Yukon and the Christopher 

Formation of the Sverdrup Basin. The Arctic 

Red Formation is dated as early to late Albian 

by Mountjoy and Chamney (1969). Foraminifers 

include Verneuilinoides borealis Tappan, Pseudobolivina rayi (Tappan), Gavelinella stictata 

(Tappan), Ammobaculites fragmentarius Cushman, 

and Globulina canadensis Mellon and Wall among 

others, which provide good correlation with the 

Umiat 11 section. In the Sverdrup Basin, 

foraminifers from the upper unit of the 

Christopher Formation on Ammund and Ellef 

Ringnes Islands correlate closely with those of 

the upper part of the Torok and Grandstand 

Formations of Umiat test well 11 (Sliter, in 

press). These Canadian assemblages include 

foraminifers such as Verneuilinoides borealis 

Tappan, Trochammina rainwateri Cushman and 

Applin, Psamminopelta bowsheri Tappan, Miliammina 

ischnia Tappan, Ammobaculites fragmentarius 

Cushman, and Pseudobolivina rayi (Tappan). 

Megafossils collected along with the foraminiferal assemblages about 30 m above the base of 

the upper unit of the Christopher Formation 

provide an early middle Albian age (J. Jeletzky, 

oral commun., 1974; Geological Survey of Canada 

lac. C-26600). The marine shales of the 

Christopher Formation grade upward into marginalmarine and delta-platform deposits of the 

overlying Hassel Formation. These deposits 

consist of glauconitic sandstone with low-angle 

cross-strata, coarse-grained sandstone with 

high-angle cross-strata, and fine-grained 

sandstone and siltstone with thin coal beds. 

The age of the Hassel Formation, based on 

microflora, is latest Albian and early Cenomanian 

(Hopkins and Balkwill, 1973). The Hassel 

Formation thus corresponds closely in both 

lithology and age to the Killik Tongue of the 

Chandler Formation in Umiat test well 11. 

SURFACE SECTIONS 

Foraminifers collected during the 1977 

summer field season from surface sections along 

the North Slope of Alaska are included as they 

provide new age and environmental data. Of the 

11 sections shown in figure 47, 9 are located in 

the western region of northern Alaska and 2 are 

adjacent to Umiat test well 11 in the eastern 

region. Proceeding from west to east, the 

faunas are briefly described and correlated with 

known sections. Characteristic foraminiferal 

species are shown in plate 19. 

Starve section; Seaview Syncline.--DeLong 

Mountains D-4 quadrangle, measured along the 

south face of Seaview Syncline beginning at 

lat 68°50'56" N., long 163°51'40" W. 

The section consists of 57.6 m of massive 

gray sandstone and black shale of the Torok and 

150 

Kukpowruk Formations. Sample No. 77AAH72, 47.9 

m above the base of the section in black shale 

of the Kukpowruk Formation, contains a poorly 

preserved Albian to possibly Cenomanian assemblage with Verneuilinoides borealis Tappan, 

Hippocrepina barksdalei (Tappan), Bathysiphon 

brosgei Tappan, and Haplaphragmoides topagorukensis Tappan. Foreshore environments are 

indicated by the biotic association. 

Tupikchak Mountain section.--DeLong 

Mountains and Misheguk Mountains quadrangles, 

1,250.6 m of Torok and Kukpowruk Formations 

measured along the Kokolik River. The section 

starts at lat 68°50'50" N., long 162°00'40" W. 

on the northwest side of the river and traverses 

up Tupikchak Mountain. 

The section consists predominantly of silty 

shale and some massive or bioturbated sandstone 

in the lower half and increases in sandstone 

having high-angle cross-stratification, graded 

bedding, and root casts typical of channel 

deposits in the upper half. Sample No. 77AJF21 

from black shale of the Torok Formation at the 

base of the section contains an abundant and 

moderately diverse Albian fauna. Characteristic 

species include Verneuilinoides borealis Tappan, 

Ammobaculites wenonahae Tappan, Quadrimorphina 

ruckerae (Tappan), Pseudobolivina rayi (Tappan), 

and Uvigerinammina manitobensis (Wickenden). 

Middle to outer neritic water depths are· implied 

by this association. A much-reduced fauna was 

recovered from Sample No. 77AJF22 in black 

shales of the Torok Formation 1.5 m above the 

base of the section. The only species present 

are Haplaphragmoides cf. H. topagorukensis 

Tappan and Nodosaria cf. N. doliiformis Eichenberg. 

Albian offshore environments are indicated by 

this meager assemblage. Sample Nos. 77AJF28 and 

77AJF32 from calcareous sandstones that are 

270.4 and 416.2 m, respectively, above the base 

of the Kukpowruk Formation contain rare, poorly 

preserved specimens of Haplaphragmoides. 

Little information can be deduced from these 

occurrences other than the suggestion of marginal marine environmental conditions. Sample No. 

77AJF33, from black shale 457.8 m above the base 

of the Kukpowruk Formation, records a return to 

more marine environments within the Albian 

section. Species include Haplaphragmoides 

topagorukensis, Ammobaculites wenonahae, and 

Uvigerinammina manitobensis. 

Kukpowruk type section (includes the type 

Kukpowruk Formation).--Point Lay B-2, B-3 

quadrangles. Measured on north limb of 

Archimedes Anticline beginning at lat 69°15'06" 

N., long 164°42'31" W. 

The measured section consists of 666.8 m of 

black shale and siltstone with bioturbated, 

cross-laminated sandstone, carbonaceous partings, and root casts becoming abundant in the 

upper half. Samples that contain foraminifers 

and their lithologies are shown in table 10. 
Table 10.--Foraminifer-bearing samples from 

the Kukpowruk type section 

Formation Sample No. Meters Lithology 

77AAH above base 

Kukpowruk and Corwin Formations, 157 448.8 Shale. 

undifferentiated. 156B 439.9 Black shale. 

155 404.0 Black shale. 

Kukpowruk Formation------------- 154A 317.7 Black shale. 

154 194.8 Black shale. 

152 130.2 Black shale. 

150 104.6 Black shale. 

Torok Formation----------------- 146 0 Black shale. 

Sample Nos. 77AAH146 to 77AAH154A within the 

Kukpowruk Formation contain a late Albian 

assemblage with Ammobaculites fragmentarius 

Cushman, A. obliquus Loeblich and Tappan, 

Gaudryina canadensis Cushman, Psamminopelta 

bowsheri Tappan, and Trochammina mcmurrayensis 

Mellon and Wall among others. Foreshore depositional environments are indicated by the biotic 

association; evidence of shoaling upward is 

expressed by species composition of the 

foraminiferal fauna, the reduction of specimen 

size and grain size in the agglutinated species, 

and the increase in carbonaceous material. 

Sample Nos. 77AAH155 to 77AAH157 from the 

undifferentiated Kukpowruk and Corwin Formations 

contain a late Albian fauna with Gaudryina 

canadensis Cushman, Trochammina mcmurrayensis, 

Haplaphragmoides cf. H. hendersonense Stelck and 

Wall, Ammobaculites obliquus, Uvigerinammina 

manitobensis (Wickenden), and Psamminopelta 

bowsheri. This assemblage is indicative of a 

marginal-marine environment. The Kukpowruk 

River section thus correlates with the upper 

portion of the Grandstand Formation and the 

Killik Tongue in Umiat test well 11. The 

transgressive environmental sequence and foraminiferal fauna of the Kukpowruk type section 

are similar to those of the early to middle 

McMurray Formation of the lower Athabasca River 

area of northeastern Alberta (Mellon and Wall, 

1956); however, the Kukpowruk type section 

appears to be younger in age. 

Archimedes Anticline section.--Point Lay 

A-2 quadrangle. Measured along south limb of 

anticline on the east side of the Kukpowruk 

River beginning at lat 69°14'58" N., long 

162°41'28" w. 

The section, which lies stratigraphically 

below the Kukpowruk type section, is represented 

by 948.2 m of mostly black shale with some 

~nterbeds of bioturbated sandstone that contain 

ripple laminations and low-angle crosslaminations. Sample No. 77AJF2, from 18.6 m 

above the base in black shale of the Torok 

Formation, contains a meager fauna of 

Haplaphragmoides topagorukensis Tappan, 

Uvigerinammina manitobensis (Wickenden), and 

Ammobaculites fragmentarius Cushman. Late 

Albian offshore environmental conditions &re 

suggested by this assemblage. Sample No. 

77AJF3, from black shales 83.2 m above the base 

of the Kukpowruk Formation, contains 

Verneuilinoides borealis Tappan, Pseudobolivina 

rayi (Tappan), Ammobaculites wenonahae Tappan, 

and Trochammina rainwateri Cushman and Applin 

among others. This middle and late Albian 

assemblage indicates a continuation of offshoremarine environmental conditions. A much reduced 

fauna of specimens attributed to 

Haplaphragmoides cf. H. hendersonense Stelck 

and Wall was recovered from Sample Nos. 77AJF6 

and 77AJF9 from black shales 324.6 and 565.3 m 

above the base of the Kukpowruk Formation, 

respectively. Sample No. 77AJF11 from silty 

shale just beneath a massive sandstone bed 

631.1 m above the base in the Kukpowruk 

Formation includes Gaudryina canadensis 

Cushman, Miliammina manitobensis Wickenden, 

Psamminopelta bowsheri Tappan, and Hippocrepina 

barksdalei (Tappan). This assemblage implies a 

shoaling of the environment to foreshore conditions in a trend that may have started earlier 

in the section near Sample No. 77AJF6. A middle 

and late Albian age is indicated for Sample No. 

77AJF11, thus correlating the Archimedes section 

with the Torok and Grandstand Formations of 

Umiat test well 11. 

Igloo Mountain section.--DeLong Mountains 

D-2 quadrangle. The section was measured on the 

northwest side of Igloo Mountain in a dry 

canyon beginning at lat 68°46'53" N., long 

162°57'20" w. 

The section is represented by 317 m of 

black shale and bioturbated sandstone interbeds 

that exhibit low-angle cross-laminations, 

scour-and~fill structures, and bivalve shells. 

Sample No. 77AAH189 from black shale of the 

Torok Formation at 1.2 m above the base contains 

Verneuilinoides borealis Tappan, Ammobaculites 

wenonahae Tappan, Pseudobolivina rayi (Tappan), 

Miliammina manitobensis Wickenden, and 

Saracenaria grandstandensis Tappan among others. 

Middle and late Albian offshore depositional 

environments are indicated. Sample No. 77AAH191, 

from black shale 17.4 m above the base in the 

Kukpowruk Formation, yielded two specimens of 

Haplaphragmoides cf. H. hendersonense Stelck and 

Wall, perhaps signifying a shoaling to foreshore 

condition. 

Kokolik Warp Syncline section.--Utukok 

River A-5 quadrangle. The section is located on 

the north flank of Kokolik Warp Syncline along 

the west side of a dry stream beginning at 

lat 69°10'07" N., long 161°35'07" W. A 4.8-km 

east-lateral offset was then made, and sampling 

continued to the axis of the syncline. 

A 2,119-m succession of black shale with 

occasional sandstone interbeds in the lower half 

and an increase in sandstone beds having low- to 

moderate-angle cross-stratification, ripple 

laminations, coal beds and petrified wood, and 

channel fill in the upper half was measured at 

this section. Sample No. 77ACH140 from black 

shale within and 1.5 m above the base of the 

Torok Formation is represented by Verneuilinoides 

151 
borealis Tappan, Ammobaculites wenonahae Tappan, 

Uvigerinammina manitobensis (Wickenden), and 

Haplaphragmoides topagorukensis Tappan. This 

assemblage represents a middle and late Albian 

offshore environment. Sample No. 77ACH141 in 

bioturbated black shale 154.0 m above the base 

but still within the Torok Formation contains a 

much reduced fauna consisting of H. 

topagorukensis and V. borealis of similar age. 

The poor faunal recovery continues into Sample 

Nos. 77ACH142 and 77ACH145 from shale 259.2 and 

370.3 m above the base of the section in the 

Kukpowruk Formation. Species are limited to 

Haplaphragmoides topagorukensis, H. cf. H. 

hendersonense Stelck and Wall, and Uvigerinammina 

manitobensis; and the biotic association is 

suggestive of foreshore environments. Sample 

No. 77ACH148, from a sequence of black shale 

containing coaly material 611.3 m above the base 

of the section in the undifferentiated Kukpowruk 

and Corwin Formations, contains Trochammina 

rainwateri Cushman and Applin, Verneuilinoides 

borealis, Psamminopelta bowsheri Tappan, and 

Eurycheilostoma grandstandensis Tappan of middle 

and late Albian age. The assemblage implies 

increased marine conditions within a sequence of 

foreshore deposits. The Kokolik Warp Syncline 

section correlates with the Torok and Grandstand 

Formations of Umiat test well 11. 

Folsom Point Syncline section.--Utukok 

River A-3 quadrangle. The section was measured 

along the west side of the Utukok River on the 

north limb of the Folsom Point Syncline beginning at lat 69°10'43" N., long 162°38'28" W. 

The section consists of 818.6 m of black 

shale and bioturbated sandstone interbeds with 

scour-fill structures, clay rip-ups, crosslaminations, carbonaceous material, and channels. Sample No. 77AAH6AR from black shale 

161.9 m above the base of the section in the 

Kukpowruk Formation contains Verneuilinoides 

borealis Tappan, Ammobaculites wenonahae Tappan, 

A. fragmentarius Cushman, Quadrimorphina ruckerae 

(Tappan), and Uvigerinammina manitobensis 

(Wickenden) among others. Middle and late 

Albian nearshore environments are indicated by 

this association. Sample Nos. 77AAH7AR and 

77AAH8AR from shale and siltstone 257.3 and 

279.6 m above the base, respectively, and still 

within the Kukpowruk Formation yielded only rare 

specimens of Haplaphragmoides. Again the 

implication of shoaling to foreshore conditions 

is suggested by this meager fauna. 

Meat Mountain section.--Mishiguk Mountains 

quadrangle. The section extends up the northwest spur of Meat Mountain, beginning at 

lat 68°58'55" N., long 160°51'25" W. 

The 446.0-m section contains poorly exposed 

shale sequences with interbeds of sandstone that 

contain ripple laminations, bioturbation and 

trails, low- to high-angle cross-stratification, 

raindrop imprints, and scour-and-fill structures. 

Rare, poorly preserved foraminifers consisting 

152 

of Haplaphragmoides cf. H. topagorukensis Tappan, 

H. cf. H. hendersonense Stelck and Wall, 

Verneuilinoides borealis Tappan, and Dentalina 

cf. D. praecommunis Tappan were recovered from 

shales in Sample Nos. 77AAH6MM, 77AAH7MM, and 

77AAH8MM from 91.8, 103.7, and 115.9 m above the 

base, respectively, in the Kukpowruk Formation. 

Foreshore to shoreface Albian depositional 

environments are implied by this fauna. 

Lookout Ridge Syncline section.--Utukok 

River quadrangle. The section is located on a 

ridge east of an unnamed stream on the northwest 

flank of Lookout Ridge Syncline beginning at 

lat 69°08'40" N., long 159°41'30" W. 

A poorly exposed 518.9-m-thick shale 

sequence with interbeds of bioturbated sandstone 

showing ripple laminations, low-angle crossstratification, carbonaceous material, and 

scour-and-fill structures characterizes this 

section. Four samples from shale intervals 

within the Kukpowruk Formation contain a poorly 

preserved fauna of Albian Age. Sample No. 

77AAH4LO, 7.3 m above the base, contains 

Haplaphragmoides topagorukensis Tappan and 

Dentalina cf. D. basiplanata Cushman. Sample 

No. 77AAH6LO, from 23.8 m above the base, 

includes Trochammina rainwateri Cushman and 

Applin, Miliammina ischnia Tappan, Ammobaculites 

fragmentarius Cushman, and Spiroplectammina cf. 

s. ammovitrea Tappan. Sample No. 77AAH7LO, from 

90.2 m above the base, is represented by 

Haplaphragmoides topagorukensis Tappan, H. cf. 

H. hendersonense Stelck and Wall, Uvigerinammina 

cf. U. manitobensis (Wickenden), and .Gavelinella 

cf. G. awunensis Tappan. And, finally, Sample 

No. 77AAH9LO, from 198.5 m above the base, 

contains Verneuilinoides borealis Tappan, 

Valvulineria loetterli Tappan, and Trochammina 

cf. T. rainwateri Cushman and Applin. Foreshore 

environmental conditions are indicated by this 

biotic association. 

Ninuluk Bluff section.--Ikpikpuk River 

quadrangle. Measured up the Ninuluk Bluff 

cutbank on the southeast side of Colville River 

at lat 69°07'45" N., long 153°16'55" W. 

A section 315.2 m thick is represented by 

bioturbated sandstone with low-angle crossstratification, carbonaceous material, root 

casts, bivalve shells, and ripple laminations 

interbedded with siltstone and shale sequences 

that decrease upwards in both abundance and 

thickness. The eight samples taken from shale 

and siltstone of the Seabee Formation (table 11) 

in the upper portion of the section contain the 

same fauna consisting of Trochammina whittingtoni Tappan and Verneuilinoides fischeri Tappan. 

A Turonian or Senonian Age is implied for this 

limited fauna, representative of offshore to 

foreshore depositional environments. 

Tuktu Bluff section.--Chandler Lake quadrangle. Measured section at Tuktu Bluff, a 

cutbank of the Chandler River at lat 68°43'30" 

N., long 152°15'30" W. 
Table 11.--Foraminifer-bearing samples from the 

Seabee Formation in the Ninuluk Bluff section 

Sample No. Meters Lithology Sample No. Meters LithLllugy 

77 ACH above base 77 ACH above base 

296 311.7 Laminated silt- 292 301.5 Black shale. 

stone-muds tone . 291 299.7 Siltstone. 

295 307.6 Black shale. 289 283.9 Black shale. 

294 304.3 Black shale. 288 272.0 Black shale. 

293 302.8 Black shale. 

Black shale of the Torok Formation is 

overlain by siltstone, shale, and sandstone 

interbeds of the Tuktu Formation in the 439.0 m 

of measured section. The sandstone beds are 

bioturbated and contain ripple marks, moderateangle cross-stratification, carbonaceous debris, 

and flaser bedding. Samples with foraminifers 

are shown in table 12. All samples contain 

Verneuilinoides borealis Tappan, which is 

characteristic of the middle and late Albian. 

Table 12.--Foraminifer-bearing samples from the 

Tuktu Bluff section 

Formation Sample No. Meters Lithology 

77AAH above base 

Tuktu Formation 26TB 268.1 Siltstone. 

Torok Formation 9TB 24.6 Black shale. 

8TB 22.9 Black shale. 

7TB 19.8 Black shale. 

6TB 16.8 Black shale. 

STB 13.7 Black shale. 

4TB 10.7 Black shale. 

3TB 7.6 Black shale. 

2TB 4.6 Black shale. 

lTB 1.5 Black shale. 

Sample No. 77AAH1TB contains the most diverse 

fauna with Ammobaculites fragmentarius Cushman, 

Eurycheilostoma grandstandensis Tappan, Pseudonodosaria kirschneri (Tappan), Lenticulina 

erecta (Perner), and Valvulineria loetterli 

(Tappan) among others. In addition, the assemblage includes rare ostracodes, echinoid debris, 

153 

and radiolarians that are indicative of 

offshore-neritic to bathyal conditions. Sample 

No. 77AAH2TB is similar in composition, but also 

contains Dentalina dettermani Tappan, Ammodiscus 

rotalarius Loeblich and Tappan, and Ammobaculites 

cf. A. wenonahae Tappan. This fauna continues 

through Sample No. 77AAH3TB but is much reduced 

in Sample Nos. 77AAH4TB and 77AAH5TB. In Sample 

No. 77AAH6TB the diversity increases, with 

Haplaphragmoides topagorukensis Tappan, 

Verneuilinoides borealis, and species of 

Ammobaculites continuing throughout the remaining 

samples. Additional species include rare 

occurrences of Psamminopelta bowsheri Tappan in 

Sample No. 77AAH6TB, Pseudonodosaria kirschneri 

in Sample No. 77AAH7TB, and Gavelinella cf. G. 

intermedia (Berthelin) in Sample No. 77AAH26TB. 

The middle and late Albian foraminiferal faunas 

and offshore depositional environments of the 

Tuktu Bluff samples correlate with those of the 

upper part of the Torok and Grandstand Formations 

of Umiat test well 11. 

In summary, surface sections from the 

western region (A to H in fig. 47) are represented by a less diverse, more poorly preserved 

foraminiferal fauna when compared to coeval 

assemblages in Umiat test well 11 and the Tuktu 

Bluff section in the eastern region. Faunas 

from the Torok Formation are most similar in 

both faunal content and depositional environment. 

This is especially true of the basal samples 

from the Torok Formation at Tupikchak Mountain. 

Nevertheless, the species represented, their 

preservation, and the lithology and associated 

biogenic debris suggest shallower water depths 

for the western region. Assemblages from the 

Kukpowruk Formation of the western region, 

however, are noticeably different from faunas in 

the Grandstand Formation of Umiat test well 11. 

Depositional environments are represented by 

foreshore and nearshore marine associations 

compared to correlative offshore assemblages 

that are typical of the Grandstand Formation in 

the eastern region. 
PLATE 18 

Characteristic species from upper part of Torok Formation and Nanushuk Group of Umiat test 

well 11. 

Figure 1. 

2. 

3- 4. 

5. 

6. 

7. 

8- 9. 

10. 

11. 

12-13. 

14. 

15-16. 

17-18. 

Miliammina awunensis Tappan, core 59, 890-893 m, scale 60 ~m. 

Miliammina manitobensis Wickenden, core 61, 1,003-1,007 m, scale 100 ~m. 

Haplaphragmoides topagorukensis Tappan, ditch sample, 972-975 m, scale 100 ~m. 

Ammobaculites wenonahae Tappan, core 55, 823-826 m, scale 100 ~m. 

Haplaphragmoides rota Nauss, ditch sample, 192-195 m, scale 100 ~m. 

Trochammina umiatensis Tappan, ditch sample, 844-847 m, scale 100 ~m. 

Trochammina rutherfordi Stelck and Wall, core 41, 656-659 m, scale 50 ~m. 

8. Spiral view. 

9. Peripheral view. 

Gaudryina canadensis Cushman, core 56, 859.5-862.5 m, scale 50 ~m. 

Verneuilinoides borealis Tappan, core 55, 823-826 m, scale 50 ~m. 

Marginulina gatesi Tappan, ditch sample, 972-975 m, scale 100 ~m. 

12. Side view. 

13. Face view. 

Praebulimina nannina (Tappan), ditch sample, 972-975 m, scale 30 ~m. 

Globorotalites alaskensis Tappan, core 61, 1,003-1,007 m, scale 30 ~m. 

15. Umbilical view. 

16. Peripheral view. 

Gavelinella stictata (Tappan), core 55, 823-826 m, scale 30 ~m. 

17. Umbilical view. 

18. Peripheral view. 

154 
- -

'-----=-

155 
PLATE 19 

Characteristic species from surface sections. 

Figure 1. Ammodiscus rotalarius Loeblich and Tappan, Tuktu Bluff, Torok Formation, Sample No. 

77AAH2TB, scale 50 ~m. 

2. Psamminopelta bowsheri Tappan, Kukpowruk type section, Torok Formation, Sample No. 

77AAH146, scale 100 ~m. 

3. Haplaphragmoides topagorukensis Tappan, Tuktu Bluff, Torok Formation, Sample No. 

77AAH1TB, scale 100 ~m. 

4- 5. Ammobaculites fragmentarius Cushman, scale 100 ~m. 

4. Tuktu Bluff, Torok Formation, Sample No. 77AAH1TB. 

5. Tuktu Bluff, Torok Formation, Sample No. 77AAH2TB. 

6- 7. Trochammina mcmurrayensis Mellon and Wall, Kukpowruk type section, Kukpowruk and 

Corwin Formations, undifferentiated, Sample No. 77AAH155, scale 100 ~m. 

8. Pseudobolivina rayi (Tappan), Archimedes Anticline, Kukpowruk Formation, Sample No. 

77AJF3, scale 50 ~m. 

9-10. Ammobaculites obliquus Loeblich and Tappan, Kukpowruk type section, scale 100 ~m. 

9. Kukpowruk and Corwin Formations, undifferentiated, Sample No. 77AAH155. 

10. Torok Formation, Sample No. 77AAH146. 

11-13. Trochammina whittingtoni Tappan, Ninuluk Bluff, Seabee Formation, Sample No. 

77ACH288. 

11. Spiral view, scale 150 ~m. 

12. Peripheral view, scale 100 ~m. 

13. Spiral view, scale 100 ~m. 

14. Verneuilinoides borealis Tappan, Archimedes Anticline, Kukpowruk Formation, Sample No. 

77AJF3, scale 50 ~m. 

15. Ammobaculites wenonahae Tappan, Tupikchak Mountain, Torok Formation, Sample No. 

77AJF21, scale 150 ~m. 

16. Gaudryina canadensis Cushman, Kukpowruk type section, Kukpowruk Formation, Sample No. 

77AAH154, scale 100 ~m. 

17. Pseudonodosaria kirschneri Tappan, Tuktu Bluff, Torok Formation, Sample No. 

77AAH1TB, scale 100 ~m. 

18. Eurycheilostoma grandstandensis Tappan, Tuktu Bluff, Torok Formation, Sample No. 

77AAH1TB, scale 30 ~m. 

19-20. Valvulineria loetterli (Tappan), Tuktu Bluff, Torok Formation, Sample No. 77AAH1TB. 

19. Umbilical view, scale 60 ~m. 

20. Peripheral view, scale 50 ~m. 

156 
-

- 157 
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