&IG

Professional Paper 1748

U.S. Department of the Interior

U.S. Geological Survey

&IG

Stratigraphy and Facies of Cretaceous Schrader 

Bluff and Prince Creek Formations in Colville 

River Bluffs, North Slope, Alaska
Stratigraphy and Facies of Cretaceous 

Schrader Bluff and Prince Creek 

Formations in Colville River Bluffs, 

North Slope, Alaska

By Romeo M. Flores, Mark D. Myers, David W. Houseknecht, Gary D. Stricker, 

Donald W. Brizzolara, Timothy J. Ryherd, and Kenneth I. Takahashi

Professional Paper 1748

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Flores, R.M., Myers, M.D., Houseknecht, D.W., Stricker, G.D., Brizzolara, D.W., Ryherd, T.J., and Takahashi, K.I., 2007, 

Stratigraphy and facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs, North Slope, 

Alaska: U.S. Geological Survey Professional Paper 1748, 52 p.

Library of Congress Cataloging-in-Publication Data

Stratigraphy and facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs, North Slope, Alaska / by 

Romeo M. Flores ... [et al.].

p. cm. -- (Professional paper ; 1748)

ISBN 978-1-4113-2023-9

1. Geology, Stratigraphic--Cretaceous. 2. Facies (Geology)--Alaska--North Slope Region. 3. Alluvium--Alaska--North Slope Region. 4. 

Sequence stratigraphy. 5. Geology--Alaska--North Slope Region. I. Flores, Romeo M. 

QE688.S938 2007

557.98’7--dc22

 2007046717

ISBN 978-1-4113-2023-9
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Stratigraphic Nomenclature and Methods ...............................................................................................4

General Stratigraphy.....................................................................................................................................8

Schrader Bluff Formation ....................................................................................................................8

Prince Creek Formation ......................................................................................................................8

Palynological Ages and Regional Correlations ............................................................................10

Vertical Stratigraphic Framework and Sedimentologic Variations............................................10

Upper Schrader Bluff Formation .............................................................................................10

Description.........................................................................................................................10

Interpretations ..................................................................................................................27

Prince Creek Formation (Lower Part) ....................................................................................27

Description ........................................................................................................................27

Interpretations ..................................................................................................................27

Prince Creek Formation (Middle and Upper Parts) .............................................................29

Description ........................................................................................................................29

Interpretations ..................................................................................................................32

Stratigraphic Facies Variations Within the Sentinel Hill Core Test 1 Well ................................33

Correlations of the Sentinel Hill Core Test 1 to Colville River Bluffs Exposures .............34

Lateral Stratigraphic Variations ......................................................................................................34

Shivugak to Uluksrak Bluffs ....................................................................................................35

Description ........................................................................................................................35

Interpretations ..................................................................................................................35

Anaktuvuk River to VABM Kavik ............................................................................................35

Description ........................................................................................................................35

Interpretations ..................................................................................................................36

Ocean Point Bluff ......................................................................................................................36

Description ........................................................................................................................36

Interpretations ..................................................................................................................36

Previous Stratigraphic Sections, Correlations, and Interpretations of the Ocean Point 

Area .........................................................................................................................................37

Summary of Fluvial System Deposits Between Shivugak and Ocean Point Bluff ...................38

Applications to Oil and Gas Fields in the Central North Slope ............................................................38

Conclusions ..................................................................................................................................................41

Acknowledgments ......................................................................................................................................41

References Cited .........................................................................................................................................44
iv

Figures

1. Map showing location of study area, the National Petroleum Reserve in Alaska, and 

the Colville River, North Slope of Alaska ..................................................................................2

2. Geologic map of the study area from Umiat to Ocean Point, Alaska, showing place 

names as well as locations of palynological samples, measured sections, and 

stratigraphic cross sections along the Colville River Bluffs..................................................3

3. Generalized stratigraphic columns showing nomenclature of Cretaceous rocks 

by Chapman and others (1964) and as modified by Mull and others (2003)........................4

4. Composite stratigraphic column of the Schrader Bluff and Prince Creek 

Formations based on measured sections by Stefansson and others (1947) and 

Stefansson and Whittington (1946)............................................................................................9

5. Vertical stratigraphic facies variations within measured section of the Schrader 

Bluff and Prince Creek Formations in Shivugak Bluff...........................................................11

6. Vertical stratigraphic facies variations within measured section of the Prince Creek 

Formation in Uluksrak Bluff.......................................................................................................12

7. Vertical stratigraphic facies variations within measured section M1a of the Prince 

Creek Formation in the southernmost part of Kavik Bluff....................................................13

8. Vertical stratigraphic facies variations within measured section M8-1 of the Prince 

Creek Formation in the southern part of Kavik Bluff.............................................................14

9. Vertical stratigraphic facies variations within measured section M8-2 of the Prince 

Creek Formation in the central part of Kavik Bluff................................................................15

10. Vertical stratigraphic facies variations within measured section M8-3 of the Prince 

Creek Formation in the northernmost part of Kavik Bluff .....................................................16

11. Vertical stratigraphic facies variations within measured section P4 of the Prince 

Creek Formation in the southern part of the Ocean Point Bluff...........................................17

12. Vertical stratigraphic facies variations within measured section P5 of the Prince 

Creek Formation in the southern part of the Ocean Point Bluff...........................................18

13. Vertical stratigraphic facies variations within measured section P6 of the Prince 

Creek Formation in the central part of the Ocean Point Bluff..............................................19

14. Vertical stratigraphic facies variations within measured section P7 of the Prince 

Creek Formation in the northern part of the Ocean Point Bluff ...........................................20

15. Cross section of the Schrader Bluff and Prince Creek Formations showing 

stratigraphic and sedimentologic facies variations of outcrops, position of 

measured section, and sequence boundaries along Shivugak Bluff .................................21

16. Cross section of the Schrader Bluff and Prince Creek Formations showing 

stratigraphic and sedimentologic facies variations of outcrops, position of

 measured section, and sequence boundaries along Uluksrak Bluff.................................22

17. Cross section of the Prince Creek Formation showing stratigraphic and 

sedimentologic facies variations of outcrops and position of measured sections 

along the bluff between the mouth of the Anaktuvuk River and the vertical angle 

benchmark (VABM) at Kavik......................................................................................................23

18. Cross section of the Prince Creek Formation showing stratigraphic and 

sedimentologic facies variations of outcrops and position of measured sections 

along the Ocean Point Bluff.......................................................................................................24
v

19. Photograph of lower part of the Schrader Bluff Formation showing platy, tuffaceous 

beds in Shivugak Bluff ................................................................................................................25

20. Photograph showing the shoreface sandstones in upper part of the Schrader Bluff 

Formation and Type 1 sandstone in lowermost part of the Prince Creek Formation along 

Shivugak Bluff ..............................................................................................................................25

21. Photograph of Schrader Bluff shoreface sandstone at Shivugak Bluff. A, tabular 

crossbeds. B, bidirectional crossbed sets.............................................................................26

22. Photograph of pebbly, coarse grained, poorly sorted, and large-scale trough 

crossbedded fluvial channel sandstone (Type 1) of the Prince Creek Formation ............28

23. Type 1 sandstone containing pebbles mainly composed of subrounded black 

chert and volcanic rock fragments in the Prince Creek Formation ....................................28

24. Pebbles and cobbles in Type 1 sandstone are imbricated in framework-supported 

lag conglomerate and also occur as float pebbles in a sandy matrix within 

large-scale trough crossbeds ...................................................................................................28

25. Photograph of interbedded coal, carbonaceous mudstone, siltstone, and tonstein 

(white) beds in the Prince Creek Formation between the mouth of the Anaktuvuk 

River and the vertical angle benchmark (VABM) at Kavik ...................................................29

26A. Photograph of Type 2 erosional-based, fining-upward, multiscoured sandstone in 

the Prince Creek Formation between the mouth of the Anaktuvuk River and the 

vertical angle benchmark (VABM) at Kavik ............................................................................30

26B. Photograph of Type 2 sandstone complex consisting of vertically stacked, laterally 

en echelon, and erosional-based mudstone deposits of the Prince Creek Formation....30

27. Photograph of erosional-based mudstone (abandoned channel plug deposit) of 

Prince Creek Formation between the mouth of the Anaktuvuk River and the vertical 

angle benchmark (VABM) at Kavik...........................................................................................31

28. Photograph of interbedded sandstone, mudstone, and siltstone with minor coal 

and carbonaceous shale beds representing flood plain and coarsening-upward 

crevasse splay (Type 3 sandstones) deposits of the Prince Creek Formation..................31

29. Photograph of fine-grained, ripple laminated (climbing ripples) sandstone interbedded 

with a thin coal and mudstone layer above Type 2 sandstone of the Prince Creek 

Formation ......................................................................................................................................32

30. Photograph of elongate fluvial channel sandstone (Type 2) bounded by interbedded 

silty sandstone, siltstone, mudstone, coal, and carbonaceous mudstone........................33

31. Photograph of fining-upward sandstone (trough crossbedded to rippled upward) 

underlain by interbedded siltstone, mudstone, and coaly carbonaceous mudstone 

of the Prince Creek Formation at Ocean Point Bluff..............................................................37

32. Composite stratigraphic section showing variations in fluvial architecture of the 

Prince Creek Formation overlying coarsening-upward barrier shoreface-delta front 

system of the Schrader Bluff Formation..................................................................................39

33. Map showing location of the stratigraphic cross section of the Brookian sequence 

(A–A’) shown in figure 34............................................................................................................40

34. Stratigraphic cross section of the Brookian sequence from U.S. Navy Umiat 1 well 

to ConocoPhillips Ravik 1 well in the west-central North Slope, Alaska...........................42
vi

Table

1. Palynological ages of samples collected from the Schrader Bluff and Prince Creek 

Formations along the Colville River Bluffs from Umiat to Ocean Point Bluff................. 5–7
By Romeo M. Flores,1

 Mark D. Myers,1 David W. Houseknecht,1 Gary D. Stricker,1 Donald W. Brizzolara,2

Timothy J. Ryherd,2 and Kenneth I. Takahashi1

1

 U.S. Geological Survey.

2

 Alaska Division of Oil and Gas.

Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek 

Formations in Colville River Bluffs, North Slope, Alaska

Abstract

Stratigraphic and sedimentologic studies of facies of the 

Upper Cretaceous rocks along the Colville River Bluffs in the 

west-central North Slope of Alaska identified barrier shoreface 

deposits consisting of vertically stacked, coarsening-upward 

parasequences in the Schrader Bluff Formation. This vertical 

stack of parasequence deposits represents progradational 

sequences that were affected by shoaling and deepening cycles 

caused by fluctuations of sea level. Further, the vertical stack 

may have served to stabilize accumulation of voluminous coal 

deposits in the Prince Creek Formation, which formed braided, 

high-sinuosity meandering, anastomosed, and low-sinuosity 

meandering fluvial channels and related flood plain deposits. 

The erosional contact at the top of the uppermost coarseningupward sequence, however, suggests a significant drop of 

base level (relative sea level) that permitted a semiregional 

subaerial unconformity to develop at the contact between the 

Schrader Bluff and Prince Creek Formations. This drop of 

relative sea level may have been followed by a relative sealevel rise to accommodate coal deposition directly above the 

unconformity. This rise was followed by a second drop of 

relative sea level, with formation of incised valley topography 

as much as 75 ft deep and an equivalent surface of a major 

marine erosion or mass wasting, or both, either of which can 

be traced from the Colville River Bluffs basinward to the 

subsurface in the west-central North Slope. The Prince Creek 

fluvial deposits represent late Campanian to late Maastrichtian 

depositional environments that were affected by these base 

level changes influenced by tectonism, basin subsidence, and 

sea-level fluctuations.

Introduction

The Upper Cretaceous Schrader Bluff and Prince Creek 

Formations are spectacularly exposed in the bluffs along the 

west side of the Colville River between Umiat and Ocean 

Point, Alaska (figs. 1 and 2). Formerly assigned to the 

Colville Group (abandoned by Mull and others, 2003), these 

rock units in earlier investigations were given descriptions that 

consisted of composite-measured sections along the bluffs and 

of limited subsurface core and log data (Robinson and Collins, 

1959; Detterman and others, 1963; Brosgé and Whittington, 

1966). In order to better evaluate the relations of these strata 

to oil and gas reservoirs in nearby areas, however, we must 

supplement the information resulting from these rather widely 

spaced observation points with more closely spaced measured 

sections of the Schrader Bluff and Prince Creek Formations. 

This supplementation would (1) provide greater detail on 

facies relations and distribution; (2) subdivide rock units by 

using palynomorphs and sequence stratigraphic boundaries; 

and (3) correlate outcropping rocks with subsurface oil and 

gas reservoirs, also on the basis of sequence stratigraphy. 

For these purposes, several detailed measured sections were 

obtained during the present study and were combined with an 

examination and interpretation of the cored sequence in the 

Sentinel Hill Core Test 1 well (fig. 2).

This study is most applicable to the ongoing development 

of very large volumes of hydrocarbons in the region, including 

viscous oil from the Upper Cretaceous to Paleocene West 

Sak, Schrader Bluff, Orion, Polaris, and Ugnu fields; light oil 

from the Upper Cretaceous Tabasco field; and the likely future 

development of free gas and gas hydrate occurrences in the 

main producing area of the central North Slope. Reservoir 

rocks are mainly sandstones deposited in deltaic and fluvial 

settings that vary in size, distribution, compartmentalization by 

erosional surfaces, and internal sedimentary structures. These 

characteristics are particularly important because they form 

the basis for volumetric estimates of hydrocarbon reserves 

and for performance modeling that is critical to evaluation of 

economic development of oil and gas fields.
Figure 1. Map showing location of study area, the National Petroleum Reserve in Alaska, and the Colville River, North Slope of Alaska.

2 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Alaska

0 200 400 Miles

0 50 100 Miles

Foothills

Colville River

Province

Kuparuk River

Sagavanirktok River

National Petroleum Reserve in Alaska

(formerly Naval Petroleum 

Reserve No. 4)

Colville

R vi er

Fish Creek

Study area

164°

68°

70°

152°

Beaufort Sea

Fish Creek platform

Chukchi Sea

Umiat-Maybe 

Creek region k
Figure 2. Geologic map of the study area from Umiat to Ocean Point, Alaska, showing place names as well as locations of palynological 

samples, measured sections, and stratigraphic cross sections along the Colville River Bluffs. Modified from Brosgé and Whittington (1966).

Introduction 3

PS (DH-028)

PS (M-14+2 CRO221)

Kpk

Kpk

Kpk

Kpk

Kpk

Kpk

Qg

Qg

Qg

Qg

Qg

Qg

Qg

Qg

Qg

Qg

Qg

Kck

Kck

Kg

Kn

Kn

Kn

Kpt

Kpt

Kpt

Ks

Ksb

Ksb

Ksb

Ksb Ksb

Ksb

Ksb

Kse

Kse

Kse

Ksr

Ksr

Ksr

Ksr

Ksr

Ksr

Kss Kss

Kss

Kss

Kss

Kss

Kss

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qal

Qth

Qth

Qth

Qth

Qth

Qtl

Qtl

Qtl

Umiat

Colville

River

Colville

River

Low-level terrace deposits (Qtl)

High-level terrace deposits (Qth)

Gubik Formation (Qg)

Kogosukruk Tongue of Prince Creek Formation and upper part 

of Sentinel Hill Member of Schrader Bluff Formation undifferentiated (Kpk)

Lower part of Sentinel Hill Member and Barrow Trail Member 

of Schrader Bluff Formation undifferentiated (Ks)

Lower part of Sentinel Hill Member of 

Schrader Bluff Formation (Kss)

Barrow Trail Member of Schrader Bluff Formation (Ksb)

Rogers Creek Member of Schrader Bluff Formation (Ksr)

Tuluvak Tongue of Prince Creek Formation (Kpt)

Black shale and bentonite containing limestone concretions; 

Shale Wall and Ayiyak Member not differentiated (Kse)

Ninuluk Formation (marine) and Niakogon Tongue of 

Chandler Formation (nonmarine), undifferentiated (Kn)

Grandstand Formation (predominantly marine) (Kg)

Killik Tongue of Chandler Formation 

(largely nonmarine) (Kck)

Unmapped

0 5 10 MILES

69°30N

70°0’N

153°0’W 152°30’W 152°0’W 151°30W

Alluvium (Qal)

EXPLANATION

PS

ALASKA

Colville

River Area of

map

Line of cross section

Shivugak Bluff cross section

(fig. 15)

Uluksrak Bluff cross section

(fig. 16)

Kavik Bluff cross section

(fig. 17)

Chandler

Measured section P7

PS(P7-1, P7-3)

 (fig. 14)

Measured section P5

(fig. 12)

Measured section P4

(fig. 11)

PS (CR-0220-1)

Measured section P6, PS(P1-P6)

(fig. 13)

Sentinell Hill 

Core Test 1

Measured 

section M1a

(fig. 7)

Measured 

section M8-2

 (fig. 9) 

Measured 

section M8-1

 PS(8A-1, 

M8-1)

(fig. 8) 

Measured 

section Uluksrak

PS (M7-1, M7-2)

(fig. 6)

Measured section

Shivugak

PS(M3 SH1, M3 SH2)

(fig. 5)

Measured section M8-3 (fig. 10)

Umiat anticline

Kogosukruk River

Kikiakrorak River

VABM Kavik

Ocean Point Bluff cross section (fig. 18)

Creek

Anaktuvuk

River

River

Prince

Pollen sample location

PS (M8 CRO2-12)

Ocean Point Bluff

A

A'
4 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Stratigraphic Nomenclature and 

Methods

Outcrops of the Schrader Bluff and Prince Creek 

Formations in the Colville River bluffs area were studied 

by measuring and describing 13 stratigraphic sections along 

the 60-mi distance between Umiat and Ocean Point (fig. 2). 

These units include marine strata that were recognized as 

the Sentinel Hill Member of the Schrader Bluff Formation 

and as the mostly nonmarine 

Kogosukruk Tongue of the Prince 

Creek Formation prior to the major 

stratigraphic nomenclature revisions 

of Mull and others (2003) (fig. 3). 

Among other changes, that revision 

abandons the formal member 

designations within the Schrader 

Bluff Formation, so the lowermost 

units of this study are recognized 

informally as the upper part of the 

Schrader Bluff Formation (fig. 3). 

It should be emphasized, however, 

that this reference is strictly of local 

significance and that this part of the 

Schrader Bluff is probably older 

than much of the formation in the 

subsurface to the east. In addition, 

the Prince Creek Formation is 

now redefined to consist entirely 

of strata formerly assigned to 

the Kogosukruk Tongue of the 

Prince Creek Formation (fig. 3). 

Except for references to previous 

investigations that used the former 

stratigraphic names, this report 

adheres to the revised nomenclature 

of Mull and others (2003).

The 13 measured sections 

include descriptions of the lithology, 

color, grain size, nature of contacts, 

trace and body fossil contents, and 

sedimentary structures. Lateral 

variations within the rock units 

were studied by using photographs 

of outcrops taken during helicopter 

flybys and while rafting the Colville 

River during fieldwork in the 

summer of 2002; photomosaics 

were also taken in earlier years. 

The photographs were then pieced 

together and used to trace the lateral 

continuity of rock units, especially 

sandstone and coal beds. The 

traced units were transferred to clear 

plastic overlays and digitized to 

generate interpretive cross sections. 

Nine of the measured stratigraphic sections were keyed to the 

cross sections to complement detailed lithology and thickness 

data of the rock units and to guide facies interpretations.

Twenty-eight coal and carbonaceous shale samples 

were collected from 12 measured sections of the Prince 

Creek Formation for determining the ages of their contained 

palynomorphs by the U.S. Geological Survey in Denver, 

Colo., and Irf Group, Inc., in Anchorage, Alaska. Nineteen 

samples yielded rich recovery with good preservation of spore 

and pollen that provided ages (table 1).

Figure 3. Generalized stratigraphic columns showing nomenclature of Cretaceous rocks by 

Chapman and others (1964) and as modified by Mull and others (2003). Fm, Formation. 

Chapman and others, 1964

Chandler River region and south Anaktuvuk and

Nanushuk Rivers

Alluvium Quaternary

Hiatus

Colville River Basin,

Northern Alaska

Mull and others, 

2003

Not Present

Sagavanirktok

Formation

Prince

Creek

Formation

Schrader

Bluff

Formation

Tuluvak

Formation

Seabee

Formation

Nanushuk

Formation

Torok

Formation

Tertiary Upper Cretaceous Lower Cretaceous

Lower Cretaceous Upper Cretaceous

Colville Group Nanushuk Group

Schrader

Bluff Fm

Prince 

Creek Fm

Seabee

Fm

Nlnuluk Fm Grandstand Formation Tuktu Formation Fortress Mountain and Torok Fms

Killik Tongue

(nonmarine)

Niakogon Tongue

(nonmarine)

Shale Wall Member

Ayiyak Member

Tuluvak Tongue

(nonmarine)

Barrow Trail

Member

Kogosukruk Tongue

(nonmarine)

Sentinel Hill Member

Rogers Creek

 Member
Stratigraphic Nomenclature and Methods 5

Table 1. Palynological ages of samples collected from the Schrader Bluff and Prince Creek Formations along the Colville River Bluff 

from Umiat to Ocean Point.

[See fig. 2 for locations. Stratigraphic position of samples is shown in figs. 5–14. M/L, middle-late; indet., indeterminate; rew., reworked. A, abundant; C, common; 

N, numerous; R, rare; I, indeterminate] M8 CR02-12 M8 CR013-1 M8 CR013-3 M-14+2 CR0221 CR-0220-1

M7-1

M7-2M8-1

P5-1

M3 SH2

M3 SH1

P7-1 

(Phillips 12)

P7-3

(Colville River)

 02 DH-028

P-1-3

Base P-2

P-3 

Liscomb Bed

8A-1

02 P1-01

lat 69.53495°N.,long 151.48449°W.lat 69.53104°N.,long 151.48146°

W.

lat 69.53495°N.,long 151.48449°W.lat 69.93679°N.,long 151.59789°W.

lat 69.81456°N.,long 151.56445°W.lat 69.49430°N.,long 151.50850°W.lat 69.49430°N.,

long 151.50860°W.

lat 69.52602°N.,long 151.47640°W.

lat 70.08283°N.,long 151.56176°W.

lat 69.42740°N.,long 151.69018°W.

lat 69.42740°N.,long 151.69018°W.

lat 70.08909°N.,long 151.51025°W.

lat 70.08909°N.,long 151.51025°W.lat 70.08410°N.,long 151.55301°W.lat 70.08283°N.,long 151.56176°W.

lat 70.08283°N.,long 151.56176°W.lat 70.08283°N.,long 151.56176°W.lat 70.08283°N.,long 151.56176°W.lat 69.52602°N.,long 151.47640°W.

Indeterminate

M/L Maastrichtian

Maastrichtian

Early MaastrichtianEarly Maastrichtian

Indeterminate

Early MaastrichtianEarly MaastrichtianEarly Maastrichtian

Late Campanian

Maastrichtian

Early MaastrichtianEarly MaastrichtianEarly Maastrichtian

Early Maastrichtian

Early MaastrichtianEarly Maastrichtian

Indeterminate

Early Maastrichtian

Prince Creek

Prince Creek

Prince CreekPrince CreekPrince Creek

Prince CreekPrince Creek

Prince CreekPrince Creek

Prince Creek

Schrader Bluff

Prince CreekPrince CreekPrince CreekPrince Creek

Prince Creek

Prince CreekPrince Creek

Prince Creek

Sample ID Formation Age Location

TAXON 

Aequitriradite sp.

Aequitriradites cf. spinulosus

Alete clavate indet.

Anacololsidites sp.

Anacolosidites sp. 1

Annulispora sp.

Aquilapollenites amygdaloides

Aquilapollenites cf. dentatus

Aquilapollenites sp.

Aquilapollenites spp.

Aquilapollenites trialatus

Azonia cf. cribrata

Balmeisporites sp.

Bisaccate gymnosperm pollen

Botryococcus braunii

Camarozonosporites ambigens

Cibotiumspora sp.

Cicatricosisporites cf. dorogensis

Cicatricosisporites sp. 1

Cicatricosisporites spp.

Cingulizonates bialatus

Cingutriletes cf. congruens

Circulodinium sp.

Clavatisporites sp.

cf. Converrucosisporites sp.

Crassispora? cf. apisulacea

Cycadopites fragilis

Deltoidospora spp.

Dictyophyllidites sp.

Erdtmannipollis procumbentformis

A

N

I,A

I,A

I,C

I,R

I,AI,A

I,C

I,C

I,CI,CI,C

I,C

I,R

I,RI,R

I,A

I,R

I,CI,CI,C

I,CI,CI,C

I,A

I,N

I,C
6 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Table 1. Palynological ages of samples collected from the Schrader Bluff and Prince Creek Formations along the Colville River Bluff 

from Umiat to Ocean Point.—Continued

[See fig. 2 for locations. Stratigraphic position of samples is shown in figs. 5–14. M/L, middle-late; indet., indeterminate; rew., reworked. A, abundant; C, common; 

N, numerous; R, rare; I, indeterminate]

Expressipollis cf. accuratus

Fibulapollis scabratus

Foraminisporis undulosus

Foveosporites sp.

Gleicheniidites senonicus

Hannisporis amplus

Hannisporis scollardensis

Impardecispora marylandensis

Inundatisporis tappaniae

Ischyosporites sp.

Integricorpus sp.

Kurtzipites trispissatus

Laevigatosporites sp.

Laevigatosporites spp.

Laricoidities magnus

Leiosphaeridia "stellata"

Linear septate fungal hypha

Lunatadinium dissolutum

Lycopodiacidites sp.

Mancicorpus pseudosenonicus

Matonisporites sp. indet

Osmundacidites wellmanii

Ovoidites arcticus

Ovoidites parvus

Ovoidites sp.

Ovoidites? sp.

Podocarpidites sp.

cf. Polycingulatisporites reduncus

cf. Proteacidites sp.

Pulcheripollenites krempii

M8 CR02-12M8 CR013-1M8 CR013-3

M-14+2 

CR0221

 CR-0220-1

M7-1

M7-2M8-1

P5-1

M3 SH2

M3 SH1

P7-1 

(Phillips 12)

P7-3

(Colville River)

 02 DH-028

P-1-3

Base P-2

P-3 

Liscomb Bed

8A-1

02 P1-01

lat 69.53495°N.,long 151.48449°W.lat 69.53104°N.,long 151.48146°

W.

lat 69.53495°N.,long 151.48449°W.lat 69.93679°N.,long 151.59789°W.

lat 69.81456°N.,long 151.56445°W.lat 69.49430°N.,long 151.50850°W.lat 69.49430°N.,

long 151.50860°W.

lat 69.52602°N.,long 151.47640°W.

lat 70.08283°N.,long 151.56176°W.

lat 69.42740°N.,long 151.69018°W.

lat 69.42740°N.,long 151.69018°W.

lat 70.08909°N.,long 151.51025°W.

lat 70.08909°N.,long 151.51025°W.lat 70.08410°N.,long 151.55301°W.lat 70.08283°N.,long 151.56176°W.

lat 70.08283°N.,long 151.56176°W.lat 70.08283°N.,long 151.56176°W.lat 70.08283°N.,long 151.56176°W.lat 69.52602°N.,long 151.47640°W.

Indeterminate

M/L Maastrichtian

Maastrichtian

Early MaastrichtianEarly Maastrichtian

Indeterminate

Early MaastrichtianEarly MaastrichtianEarly Maastrichtian

Late Campanian

Maastrichtian

Early MaastrichtianEarly MaastrichtianEarly Maastrichtian

Early Maastrichtian

Early MaastrichtianEarly Maastrichtian

Indeterminate

Early Maastrichtian

Prince Creek

Prince Creek

Prince CreekPrince CreekPrince Creek

Prince CreekPrince Creek

Prince CreekPrince Creek

Prince Creek

Schrader Bluff

Prince CreekPrince CreekPrince CreekPrince Creek

Prince Creek

Prince CreekPrince Creek

Prince Creek

Sample ID Formation Age Location

I,N

I,C

I,A

I,CI,C

I,A

I,AI,C

I,C

C

C

N

CCCCCC

N

TAXON 
Stratigraphic Nomenclature and Methods 7

Table 1. Palynological ages of samples collected from the Schrader Bluff and Prince Creek Formations along the Colville River Bluff 

from Umiat to Ocean Point.—Continued

[See fig. 2 for locations. Stratigraphic position of samples is shown in figs. 5–14. M/L, middle-late; indet., indeterminate; rew., reworked. A, abundant; C, common; 

N, numerous; R, rare; I, indeterminate]

Pulcheripollenites? sp.

reticulate alete ? algal

Reticulatisporites labiatus rew.

Reticuloidosporites sp.

Retispora lepidophyta

Retitriletes sp.

Retitriletes spp.

cf. Santalacites sp.

Scabratricolp(or)ites? sp.

Scabratricolpites sp.

Scabratricolpites sp.

Selagosporis sp. 1

Sigmopollis sp.

Skochorate?

Spelaeotriletes cf. pretiosus

Spelaeotriletes cf. triangulus

Stereigranisporis regius

Stereisporites sp.

Syncolporites sp.

Taxodiaceaepollenites hiatus

Tetracolpites sp.

Triatriate pollen

Tricolpate

Tricolpites sp.

Tricolporopollenites sp.

Trilete zonate

Trilites sp.

Tsugaepollenites sp.

Undulatisporites sp.

cf. Verrucosisporites sp.

M8 CR02-12M8 CR013-1M8 CR013-3

M-14+2 

CR0221

 CR-0220-1

M7-1

M7-2M8-1

P5-1

M3 SH2

M3 SH1

P7-1 

(Phillips 12)

P7-3

(Colville River)

 02 DH-028

P-1-3

Base P-2

P-3 

Liscomb Bed

8A-1

02 P1-01

lat 69.53495°N.,long 151.48449°W.lat 69.53104°N.,long 151.48146°

W.

lat 69.53495°N.,long 151.48449°W.lat 69.93679°N.,long 151.59789°W.

lat 69.81456°N.,long 151.56445°W.lat 69.49430°N.,long 151.50850°W.lat 69.49430°N.,

long 151.50860°W.

lat 69.52602°N.,long 151.47640°W.

lat 70.08283°N.,long 151.56176°W.

lat 69.42740°N.,long 151.69018°W.

lat 69.42740°N.,long 151.69018°W.

lat 70.08909°N.,long 151.51025°W.

lat 70.08909°N.,long 151.51025°W.lat 70.08410°N.,long 151.55301°W.lat 70.08283°N.,long 151.56176°W.

lat 70.08283°N.,long 151.56176°W.lat 70.08283°N.,long 151.56176°W.lat 70.08283°N.,long 151.56176°W.lat 69.52602°N.,long 151.47640°W.

Indeterminate

M/L Maastrichtian

Maastrichtian

Early MaastrichtianEarly Maastrichtian

Indeterminate

Early MaastrichtianEarly MaastrichtianEarly Maastrichtian

Late Campanian

Maastrichtian

Early MaastrichtianEarly MaastrichtianEarly Maastrichtian

Early Maastrichtian

Early MaastrichtianEarly Maastrichtian

Indeterminate

Early Maastrichtian

Prince Creek

Prince Creek

Prince CreekPrince CreekPrince Creek

Prince CreekPrince Creek

Prince CreekPrince Creek

Prince Creek

Schrader Bluff

Prince CreekPrince CreekPrince CreekPrince Creek

Prince Creek

Prince CreekPrince Creek

Prince Creek

Sample ID Formation Age Location

I,NI,N

C

N

CC

N

I,NI,NI,N

I,N

I,N

TAXON 
8 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

General Stratigraphy

In addition to hosting several large accumulations of 

predominantly heavy oil in the Kuparuk River Unit, Milne 

Point Unit, and Prudhoe Bay Unit areas, sandstones of the 

Schrader Bluff and Prince Creek Formations serve as potential 

shallow gas reservoirs in the National Petroleum Reserve 

in Alaska (NPRA), which is bounded on the east and south 

by the Colville River (fig. 1). Early geologic investigations 

by Brosgé and Whittington (1966) from 1944 to 1953 in the 

Umiat-Maybe Creek region in southeastern NPRA, adjacent 

to the Colville River (fig. 1), reported the presence of gas 

reserves in the lower part of the Colville Group. There, 

the Upper Cretaceous section is more than 5,000 ft thick 

and consists (in ascending order) of the Seabee Formation, 

Tuluvak Tongue of the Prince Creek Formation, Schrader 

Bluff Formation, and Kogosukruk Tongue of the Prince Creek 

Formation (fig. 3). According to Mull and others (2003), 

these formations are generally regressive marine and coastal 

facies broken up by minor retrogradational successions. The 

focuses of this study—the Schrader Bluff and Prince Creek 

Formations—constitute a large-scale prograding complex of 

shallow marine to marginal marine facies and coastal plain 

facies (Mull and others, 2003).

Schrader Bluff Formation

The Schrader Bluff Formation was originally defined 

by Gryc and others (1951) to include all marine rocks of 

the Upper Cretaceous Colville Group. At the type section 

in Schrader Bluff (fig. 2), it was redefined by Whittington 

(1956) to consist of the predominantly marine interval of the 

Colville Group overlying the nonmarine Tuluvak Tongue of 

the Prince Creek Formation (fig. 3), which now constitutes 

the upper portion of the shallow marine to nonmarine Tuluvak 

Formation of Mull and others (2003).

In the study area along the bluffs west of the Colville 

River between Umiat and Ocean Point (figs. 1 and 2), the 

upper part of the Schrader Bluff Formation consists of 

shallow marine sandstones, which are locally incised by 

nonmarine channel deposits overlain by nonmarine sandstone, 

conglomerate, and carbonaceous mudstone and coal beds 

of the Prince Creek Formation (fig. 3). Examination of 

the Sentinel Hill Core Test 1 well (which is located about 

6.5 mi north of the Anaktuvuk River [fig. 2]) by Robinson 

and Collins (1959) combined with measured stratigraphic 

sections along the lower Colville River by Stefansson and 

others (1947), Stefansson and Whittington (1946), and Brosgé 

and Whittington (1966) indicated that the Schrader Bluff 

Formation contains marine fossiliferous fauna (for example, 

Mytilus sp., Tellina sp., Gyrodes sp., Pecten sp., Protocardia

cf., Panope sp., and a variety of foraminifera (fig. 4).

The Schrader Bluff Formation is mainly composed 

of marine bentonitic shale and claystone with interbedded 

bentonite, ash, tuff, sandstone, and siltstone (Brosgé and 

Whittington, 1966). Calcareous and arenaceous foraminifera 

(for example, Eoeponidella strombodes) and pelecypods 

(for example, Protocardia, Tellina, Panope, and Gyrodes) 

are abundant throughout the formation; they are of Late 

Cretaceous age, with the microfossils indicating a more 

specific range in age from post-Turonian to Maastrichtian 

(Brosgé and Whittington, 1966). Coal beds in the upper 

Schrader Bluff Formation (formerly the Sentinel Hill 

Member, fig. 3) at different localities were used by Brosgé 

and Whittington (1966) to document the northward to 

northeastward trend of the shoreline in Campanian and 

Maastrichtian time.

Prince Creek Formation

The Prince Creek Formation was first defined by Gryc 

and others (1951) as being located 9 mi upstream from Umiat 

on Prince Creek, a tributary of the Colville River. They, as 

well as others (including Detterman and others [1963] and 

Brosgé and Whittington [1966]), described the formation as 

containing predominantly nonmarine strata of the Tuluvak 

Tongue in the lower part and of the Kogosukruk Tongue in 

the upper part, separated by marine sandstone and shale of 

the Schrader Bluff Formation (fig. 3). More recently, the 

Tuluvak Tongue was interpreted to be much more closely 

linked genetically to the shallow marine sandstones formerly 

designated as the Ayiyak Member of the Seabee Formation 

than to the Kogosukruk Tongue (fig. 3). Consequently, Mull 

and others (2003) (1) removed the Tuluvak strata from the 

Prince Creek Formation, removed the Ayiyak strata from the 

Seabee Formation, and combined them to form the Tuluvak 

Formation of current usage; and (2) designated strata formerly 

assigned to Kogosukruk Tongue as constituting the entire 

Prince Creek Formation. In our study area north of the Umiat 

anticline, most of the nonmarine rocks exposed in the bluffs 

along the west side of the Colville River from Shivugak Bluff 

to Ocean Point (fig. 2) are now considered to be in the Prince 

Creek Formation. The contact between the Prince Creek 

Formation and the underlying Schrader Bluff Formation is 

exposed in the Shivugak Bluff (fig. 2). The sharp (probably 

erosional) contact between the Prince Creek Formation and 

the overlying Sagavanirktok Formation crops out “only in the 

vicinity of the Sagavanirktok River” (Mull and others, 2003, p. 

17), well to the east of our study area (fig. 1).

Stefansson and others (1947) measured nearly complete 

sections of the stratigraphic sequence formerly assigned to 

the Kogosukruk Tongue (now the Prince Creek Formation) 

exposed along the Kogosukruk and Colville Rivers. Later, 

Brosgé and Whittington (1966) designated exposures in 

the Colville River Bluffs near the mouth of the Anaktuvuk 

River to Ocean Point as the type section of the Kogosukruk 

Tongue because of the continuously well-exposed sequence 

of mudstone, claystone, siltstone, sandstone, conglomerate, 

tuff, bentonite, coal, and carbonaceous shale. The coal and 

carbonaceous shale distinguish these strata (now the Prince 
General Stratigraphy 9

Panope sp.,

Gyrodes sp.,

Gastropods { 

Sentinel Hill Core Test 1

modified from Robinson and

Collins (1959)

Yoldia sp.,

Mytilus cf. M.

subarcuatus,

Mytilus sp.,

Tellina sp.,

Leptosolen sp.,

Panope sp.,

Gyrodes sp.,

Haminea sp.

Pecten sp.,

Pholadomya sp.,

Protocardia cf.

P. borealis,

Tellina

Panope sp.

{ f

f

f

f

f

f

f

f

f

f

f

f

f

f

f

1,180 T. D.

0

695

1,159

1,475

1,811

2,200

0

469

469

371

109

231

840

949

Member or Tongue

Formation

Group

Series

Kogosukruk Tongue

Prince Creek Formation

Group Colville

Sentinel Hill Member

Schrader Bluff Formation

Kogosukruk Tongue

Prince Creek Formation

Sentinel Hill Member

Schrader Bluff Formation

Colville River below Umiat, Alaska,

measured by Stefansson and

others (1947), and Stefansson

and Whittington (1946)

Feet

Feet

EXPLANATION

Conglomeratic sandstone

Conglomerate

Sandstone

Siltstone

Mudstone

Silty shale and 

shaly siltstone

Coal

Tuffaceous

Covered

Bentonite

Ironstone concretions

Fossil

Figure 4. Composite stratigraphic column of the Schrader Bluff and Prince Creek Formations based on measured sections by 

Stefansson and others (1947) and Stefansson and Whittington (1946). This column is correlated to the stratigraphic section penetrated 

in the Sentinel Hill Core Test 1 well as described by Robinson and Collins (1959). 
10 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Creek Formation) from the marine rocks of the underlying 

Schrader Bluff Formation.

Locally, the contact between the Prince Creek and 

Schrader Bluff Formations is characterized by interfingering 

(fig. 3). In the 1,180-ft-thick succession penetrated in the 

Sentinel Hill Core Test 1 (fig. 4), for example, Robinson 

and Collins (1959) recognized a 371-ft-thick predominantly 

marine tongue of upper Schrader Bluff Formation above a 

109-ft-thick basal unit of the predominantly nonmarine Prince 

Creek Formation. These thicknesses are revised by Flores and 

others (2007), following their interpretation of depositional 

environments and formation contacts in the core. Mull and 

others (2003) interpreted the Schrader Bluff and Prince Creek 

Formations as an interfingering sequence of shallow marine 

to marginal marine units and coastal plain units resulting 

from transgressive-regressive cycles within a dominantly 

progradational (regressive) system. The sequence was 

assigned a probable Campanian or younger age by Brosgé and 

Whittington (1966).

Palynological Ages and Regional Correlations 

Palynomorph analysis results of 19 coal, carbonaceous 

mudstone, and shale samples collected from the Prince Creek 

Formation between the mouth of the Chandler River and 

Ocean Point are shown in table 1. Locations of the measured 

sections containing the samples are shown in figure 2, and 

table 1 lists the locations, rock intervals in which the samples 

were collected, microfossil assemblages and ages, and species 

abundances (observation frequency).

The samples contain moderately diverse and wellpreserved, organic-walled palynomorphs. Ages range 

from late Campanian (sample M3 SH2) to middle late 

Maastrichtian (sample M8 CR013-1), with the majority 

being early Maastrichtian (table 1); one sample (8A-1), with 

an indeterminate age, is tentatively assigned a Paleocene 

age. Bisaccate gymnosperm pollen is the most abundant 

microfossil in all samples.

The late Campanian sample (M3 SH2) is from a coal 

bed in the lowermost part of the Prince Creek Formation, 

directly above the contact with the underlying Schrader 

Bluff Formation at Shivugak Bluff (fig. 2). The middlelate Maastrichtian sample (M8 CR013-1) is from a coal and 

carbonaceous shale bed in the upper part of the Prince Creek 

Formation (see table 1). The early Maastrichtian samples 

(M7-2 and M8-1) are mainly from coal, carbonaceous shale, 

and mudstone in the lower units of the Prince Creek. Because 

of the general northward dip of the Prince Creek Formation 

between Umiat and the Sentinel Hill area (Brosgé and 

Whittington, 1966), it was assumed that the Ocean Point beds 

were the youngest in the study area. Despite this assumption, 

samples (P-1-3, P-2, P-3, P5-1, P6-1, P6-3, and 02 P1-01) 

from hadrosaur-bearing coal and carbonaceous mudstone beds 

of the uppermost Prince Creek Formation in the Ocean Point 

area (see line of cross section in fig. 2) are early Maastrichtian, 

age equivalent to the strata exposed in the river bluffs between 

the mouths of the Chandler and Anaktuvuk Rivers. The 

youngest strata in the formation in the study area (sample M8 

CR013-1) are located just below the mouth of the Anaktuvuk 

River (fig. 2).

For the Ocean Point Bluff locality, Phillips (1988, 

1989) described marine fossil-bearing rocks of the (former) 

Kogosukruk Tongue. The early Maastrichtian age of these 

rocks indicates that they are likely equivalent to the (formerly 

recognized) Sentinel Hill Member of the upper part of the 

Schrader Bluff Formation. The observation that the section 

exposed at Ocean Point is older and stratigraphically lower 

than portions of the section to the south near the mouth of 

the Anaktuvuk River indicates that the Ocean Point area is 

structurally elevated. This interpretation is consistent with 

previous subsurface and seismic mapping of Lower and Upper 

Cretaceous horizons in NPRA (Bird, 1988, figs. 16.8 and 

16.9), which reveals a broad, gently east-plunging structural 

nose in the area, possibly related to late reactivation of the 

Fish Creek platform (fig. 1).

Vertical Stratigraphic Framework and 

Sedimentologic Variations

The stratigraphic framework and sedimentologic 

variations within the upper part of the Schrader Bluff 

Formation and within the Prince Creek Formation were 

determined from measured sections (figs. 5–14) and cross 

sections constructed from photomosaics of continuous 

outcrops (figs. 15–18) along the Colville River Bluffs 

(fig. 2). The measured stratigraphic sections were used as 

control points, and the photomosaics were used to extend 

interpretations to beds in between. The following section 

presents descriptive observations, which are followed by 

interpretive discussions.

Upper Schrader Bluff Formation

Description

Figure 5 illustrates a stratigraphic section measured 

at Shivugak Bluff (see fig. 2 for location), which exhibits 

the vertical stratigraphic and sedimentologic variations of 

the upper part of the Schrader Bluff Formation. The upper 

part of that formation and the lower part of the Prince 

Creek Formation are represented in a 480-ft-thick section 

measured at Shivugak Bluff (fig. 5). The strata consist 

of interbedded mudstone, siltstone, tuff, and sandstone 

arranged in coarsening-upward, 50- to 120-ft-thick intervals 

or parasequence sets (figs. 5, 19, and 20). The lower three 

parasequence sets contain sandstones ranging from 5 to 

30 ft thick with gradational bases and sharp tops; they 

are upward-coarsening parasequences consisting of gray 

bentonitic and burrowed mudstone at the base interbedded 
General Stratigraphy 11

Type 1 sandstone

 PS (M3 SH2)

100

Prince Creek Formation Schrader Bluff Formation

0

Carbonaceous mudstone

B

Platy tuffaceous

 PS

(M3 SH1)

B

SHIVUGAK BLUFF

(Prince Creek and Schrader 

Bluff Formations)

200

300

Parasequence

Parasequence

Parasequence

Parasequence

Sequence boundary

(mid-Campanian unconformity)

Sequence boundary

Feet

Sandstone

Mudstone (clay) 

Coal and carbonaceous shale

EXPLANATION

Conglomerate

Tuffaceous

Ripple laminations

Bidirectional crossbeds

Covered

Trough crossbeds

Root marks

B Bentonitic

Palynology sample

(sample no.)

Coarsening upward

Silty sandstone 

Carbonaceous mudstone

PS

Figure 5. Vertical stratigraphic facies variations within measured section of the Schrader Bluff and Prince Creek Formations in 

Shivugak Bluff. See figure 2 for section location, and compare to outcrop profile in figure 15. Mid-Campanian unconformity adopted 

from Decker (2007). 
12 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Type 1 sandstone

(Sequence boundary

below this rock type)

Type 2 sandstone

Type 2 sandstone

Type 2 sandstone

Type 2 sandstone

Type 3 sandstone

Type 2 sandstone

(bentonitic)

Bentonitic

Bentonitic

Bentonitic

200

100

0

PS 

PS

(M7-1)

PS

(M7-2)

300

400

200

Type 1 sandstone

Tonstein

Feet Feet

Sandstone

Mudstone (clay) 

Coal and carbonaceous shale

Siltstone

EXPLANATION

Conglomerate

Silty sandstone 

Tuffaceous

Ripple laminations

Bidirectional crossbeds

Covered

Trough crossbeds

Root marks

ULUKSRAK BLUFF

(Prince Creek Formation)

Palynology sample

(sample no.)

Figure 6. Vertical stratigraphic facies variations within measured section of the Prince Creek Formation in Uluksrak Bluff. See figure 2 

for section location, and compare to outcrop profile in figure 16. 
General Stratigraphy 13

Sandstone

Mudstone (clay) 

Coal and carbonaceous shale

Siltstone

EXPLANATION

Conglomerate

Ripple laminations

Trough crossbeds

Root marks

Silty sandstone 

Tuffaceous

Type 2 sandstone

Type 3 sandstone

Type 3 sandstone

Type 3 sandstone

Type 3 sandstone

Tuffaceous

200

100

0

v v v v v vvvvvv 

KAVIK BLUFF

Measured section M1a

(Prince Creek Formation)

Feet

Figure 7. Vertical stratigraphic facies variations within measured section M1a of the Prince Creek Formation in the southernmost part 

of Kavik Bluff, between the mouth of the Anaktuvuk River and the vertical angle benchmark (VABM) at Kavik. See figure 2 for section 

location, and compare to outcrop profile in figure 17. 
14 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

40

 PS

(8A-1)

0

Type 3 sandstone

Type 3 sandstone

Type 3 sandstone

20

PS

(M8-1)

PS 

KAVIK BLUFF

Measured section M8-1

(Prince Creek Formation)

Feet

Sandstone

Mudstone (clay) 

Coal and carbonaceous shale

EXPLANATION

Ripple laminations

Root marks

Convolution

Palynology sample

(sample no.)

Silty sandstone 

Siltstone

Figure 8. Vertical stratigraphic facies variations within measured section M8-1 of the Prince Creek Formation in the southern part 

of Kavik Bluff, between the mouth of the Anaktuvuk River and the vertical angle benchmark (VABM) at Kavik. See figure 2 for section 

location, and compare to outcrop profile in figure 17. 
General Stratigraphy 15

100

0

Type 2 sandstone

Type 2 sandstone

Type 2 sandstone

Type 2 sandstone

Type 3 sandstone

Type 3 sandstone

B

B

B

B

B

B

B

B

B

B

B

Petrified

wood

Tonstein

200

300

Feet

Sandstone

Mudstone (clay) 

Coal and carbonaceous shale

EXPLANATION

B

Covered

Trough crossbeds

Root marks

Bentonitic

Tuffaceous

Siltstone

KAVIK BLUFF

Measured section M8-2

(Prince Creek Formation)

Figure 9. Vertical stratigraphic facies variations within measured section M8-2 of the Prince Creek Formation in the central part of 

Kavik Bluff, between the mouth of the Anaktuvuk River and the vertical angle benchmark (VABM) at Kavik. See figure 2 for section 

location, and compare to outcrop profile in figure 17.
16 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Type 2 sandstone

Type 2 sandstone

Type 2 sandstone

Type 2 sandstone

Type 3 sandstone

Type 3 sandstone

Tuffaceous or bentonitic

300

200

100

0

Feet

Sandstone

Mudstone (clay) 

Coal and carbonaceous shale

EXPLANATION

Silty Sandstone 

Tuffaceous

Ripple laminations

Trough crossbeds

Root marks

vvvvvvvvvvvvvvvvvvv 

KAVIK BLUFF

Measured section M8-3

(Prince Creek Formation)

Siltstone

Figure 10. Vertical stratigraphic facies variations within measured section M8-3 of the Prince Creek Formation in the northernmost 

part of Kavik Bluff, between the mouth of the Anaktuvuk River and the vertical angle benchmark (VABM) at Kavik. See figure 2 for 

section location, and compare to outcrop profile in figure 17. 
General Stratigraphy 17

Sandstone

Mudstone (clay) 

Coaly carbonaceous shale

EXPLANATION

Ripple laminations

Root marks

Silty Sandstone 

Dinosaur bones

Mottles

Siltstone

Type 3 sandstone

Type 3 sandstone

Type 3 sandstone

Type 3 sandstone

OCEAN POINT BLUFF

Measured section P4

(Prince Creek Formation)

20

10

0

30

Feet

Figure 11. Vertical stratigraphic facies variations within measured section P4 of the Prince Creek Formation in the southern part of the 

Ocean Point Bluff. See figure 2 for section location, and compare to outcrop profile in figure 18. 
18 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Mudstone (clay) 

Coaly carbonaceous shale

EXPLANATION

Ripple laminations

Root marks

Silty sandstone 

Siltstone

Type 3 sandstone

OCEAN POINT BLUFF

Measured section P5

(Prince Creek Formation)

10

20

0

Type 3 sandstone

Feet

Figure 12. Vertical stratigraphic facies variations within measured section P5 of the Prince Creek Formation in the southern part of the 

Ocean Point Bluff. See figure 2 for section location, and compare to outcrop profile in figure 18. 
General Stratigraphy 19

Sandstone

Mudstone (clay) 

Coaly carbonaceous shale 

EXPLANATION

Ripple laminations

Root marks

Silty sandstone 

Bidirectional crossbeds

Tuffaceous

Siltstone

Type 2 sandstone

Type 3 sandstone

Type 3 sandstone

Type 3 sandstone

Tuffaceous

OCEAN POINT BLUFF

Measured section P6

(Prince Creek Formation)

10

20

0

30

40

Feet

Figure 13. Vertical stratigraphic facies variations within measured section P6 of the Prince Creek Formation in the central part of the 

Ocean Point Bluff. See figure 2 for section location, and compare to outcrop profile in figure 18. 
20 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

10

20

0

40

50

Type 2 sandstone

Type 2 sandstone

Type 2 sandstone

PS (P7-3)

OCEAN POINT BLUFF

Measured section P7

(Prince Creek Formation)

PS (P7-1)

30

Sandstone

Mudstone (clay) 

EXPLANATION

Ripple laminations

Trough crossbeds

Root marks

Silty sandstone 

Siltstone

Mudstone and carbonaceous fragments lag

Planar crossbeds

Mottles

Conglomerate

Palynology sample

(sample no.)

PS 

Feet

Figure 14. Vertical stratigraphic facies variations within measured section P7 of the Prince Creek Formation in the northern part of the 

Ocean Point Bluff. See figure 2 for section location, and compare to outcrop profile in figure 18. 
General Stratigraphy 21

Colville River

Colville River

 Feet

300200100

0.5 Miles 0.25 0

Measured section

Conglomeratic sandstoneSandstoneSiltstoneMudstoneCarbonaceous mudstoneCoal and carbonaceous shale

CoveredBed projectionRiver boundary

EXPLANATION

MCU Mid-Campanian 

unconformity

Shivugak Bluff cross section

W E

? ? 

? ? ? ? ? ? 

? ? 

? ? 

? ? ? ? ? ? 

? ? 

Measured section (fig. 5)

Covered

Covered

Covered

Covered

Prince Creek

Formation

Schrader Bluff

Formation

MCU sequence boundary

Sequence boundary

Figure 15. Cross section of the Schrader Bluff and Prince Creek Formations showing stratigraphic and sedimentologic facies variations of outcrops, position of measured section, and sequence boundaries along Shivugak Bluff. See figure 2 cross section location. Cross section was reconstructed from photomosaics. Mid-Campanian unconformity adopted from Decker (2007).
22 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs 0.2 Miles 0 Feet 400 200 0.1 Uluksrak Bluff cross section Covered Covered Covered Covered Covered Covered Covered

Colville River Colville River

Measured section

Conglomeratic sandstoneSandstoneSiltstoneMudstoneCarbonaceous mudstoneCoal and carbonaceous shale

CoveredBed projectionRiver boundary

EXPLANATION

MCU Mid-Campanian 

unconformity

SW NE Measured section (fig. 6)

MCU sequence

boundary

Prince Creek

Formation

Schrader Bluff

Formation

Sequence boundary

Prince Creek Formation

Schrader Bluff Formation

Figure 16. Cross section of the Schrader Bluff and Prince Creek Formations showing stratigraphic and sedimentologic facies variations of outcrops, position of measured section, and sequence boundaries along Uluksrak Bluff. See figure 2 for cross section location. Cross section was reconstructed from photomosaics. Mid-Campanian unconformity adopted from Decker (2007).
General Stratigraphy 23

Covered Covered Covered

Covered

Covered

Covered

Covered

Covered Covered

SandstoneMudstone and siltstoneCoal CoveredPartially covered Bed projection

300200100

0

0.5 1.0 Miles

Feet

Feathered sandstone(deposited in meandering river)

EXPLANATION

Kavik Bluff cross section

Measured 

section M8-2

(fig. 9)

Measured 

section M8-3

(fig. 10) Measured 

section M1a

(fig. 7)

S N

Measured 

section M8-1

(fig. 8)

Prince Creek

Formation

Measured section

Elongate

sandstones

Lenticular

sandstones

Elongate

sandstones

Lenticular

sandstones

Figure 17. Cross section of the Prince Creek Formation showing stratigraphic and sedimentologic facies variations of outcrops and position of measured sections along the bluff between the mouth of the Anaktuvuk River and the vertical angle benchmark (VABM) at Kavik. See figure 2 for cross section location. Cross section was reconstructed from photomosaics.
24 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs 100 Sandstone Siltstone and mudstone Carbonaceous mudstone

Tuffaceous sandstone lens 0

Dinosaur bonesFaultBed projectionMeasured section

Silty sandstoneGubik FormationCoveredRoots

Ocean Point Bluff cross section

0.5

50

0.25

Measured

section P4

Measured

section P5

(fig. 12)

Measured

section P6

(fig. 13)

Measured

section P7

(fig. 14)

A

(SW)

A' 

(NE)

(fig. 11)

Feet

Mile

EXPLANATION

Figure 18. Cross section of the Prince Creek Formation showing stratigraphic and sedimentologic facies variations of outcrops and position of measured sections along the Ocean Point Bluff. See figure 2 for cross section location. Cross section was reconstructed from photomosaics.
General Stratigraphy 25

Tuaceous beds

with, and grading upward 

into, light gray rippled 

and burrowed siltstone 

and tuff beds that thicken 

upward and grade into 

the sandstone beds. The 

lowermost parasequence 

set contains a succession 

of thin to thick sandstone 

beds capping upwardcoarsening mudstonesiltstone-sandstone 

cycles. The sandstones 

are light gray and fine 

grained, with mudstone 

and siltstone rip-up lags 

and sparse Macaronichnus

burrows (Mull and others, 

2003); they commonly 

exhibit hummocky and 

swaley cross stratification 

(HCS and SCS) sets 

as much as 2.5 ft high. 

The HCS and SCS are 

commonly associated 

with wave, ripple, and 

flat laminations that are 

locally bioturbated. The 

upper two parasequence sets contain tabular and bidirectional 

crossbedded sandstones, each as much as 55 ft thick (figs. 21A

and 21B), that are fine to very fine grained and have finingupward profiles from the underlying fine-grained sediments.

Figure 19. Photograph of lower part of the Schrader 

Bluff Formation showing platy, tuffaceous beds in 

Shivugak Bluff. For scale, the tuffaceous beds are from a 

few inches to 1 ft thick.

Shoreface sandstones (Schrader Bluff Formation)

Type 1 channel sandstone 

(Prince Creek Formation) 

Formation

contact

Figure 20. Photograph showing 

the shoreface sandstones in upper 

part of the Schrader Bluff Formation 

and Type 1 sandstone in lowermost 

part of the Prince Creek Formation 

along Shivugak Bluff. For scale, the 

uppermost shoreface sandstone and 

interbedded mudstone together are 65 

ft thick.
26 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

4ABULARCROSSBEDS

&IG!

Figure 21. Photograph 

of Schrader Bluff 

shoreface sandstone at 

Shivugak Bluff. 

A, tabular crossbeds. 

For scale, man in 

photograph is about 6 

ft tall. B, bidirectional 

crossbed sets (1–2 ft 

thick).

"IDIRECTIONAL

CROSSBEDS

"IDIRECTIONAL

CROSSBEDS

&IG"

A

B
General Stratigraphy 27

Interpretations

The coarsening-upward parasequence sets of mudstone 

grading upward into siltstone, tuff, and sandstone beds are 

interpreted as prograding offshore to delta-front deposits. 

The HCS and SCS; wave, ripple, and flat laminations; and 

Macaronichnus trace fossils indicate deposition in a stormwave-dominated shoreface environment. During storms, 

the shoreface sand is reworked by shallowing, oscillatory 

waves, whereas during fair-weather conditions mud and silt 

settle from suspension offshore, where the sediments are 

bioturbated. The upper beach face and shoreface sandstones 

probably developed on a barred coastline, as indicated by 

the uppermost two sandstones with tabular and bidirectional 

crossbedded sandstones in figures 21A and 21B. That this 

coastline was affected by storm waves is indicated by the HCS 

and SCS.

Prince Creek Formation (Lower Part)

Description

The Schrader Bluff Formation is in sharp contact with 

the overlying Prince Creek Formation, the base of which is 

marked by a 3-ft-thick bed of coal and carbonaceous shale 

(fig. 5). The lower part of the Prince Creek Formation was 

measured at Uluksrak Bluff (see location in fig. 2). As shown 

in figure 6, the 415-ft-thick section contains three types of 

sandstones. The lower part, more than 200 ft thick, contains 

Type 1 conglomeratic sandstones that are more than 70 ft thick 

and that contain vertically stacked beds with erosional bases 

(multiscours) that grade upward from pebble- and cobblebearing beds to medium-grained, light gray, and poorly sorted 

beds (figs. 6, 16, and 22). The pebbles and cobbles consist 

mainly of black chert, are concentrated along erosional bases 

or trough-crossbed bases (fig. 23), and occur throughout the 

Type 1 sandstones as 2- to 5-in-thick imbricated framework 

lag conglomerate or as float pebbles supported in a sandy 

matrix in beds ranging from 1 to 5 ft thick (figs. 22 and 

24). The lag conglomerates form lensoid units, with the 

float pebbles lying along low-angle cross laminations. The 

conglomeratic Type 1 sandstone is the most common type of 

sandstone in the lowermost 250–350 ft of the Prince Creek 

Formation. In that part of the formation there are only thin (a 

few inches to 1.5 ft thick) coal beds interbedded with rooted 

carbonaceous mudstone and siltstone.

Higher beds in the lower part of the Prince Creek 

Formation are both Type 2 and Type 3 sandstones (fig. 6). 

Type 2 sandstones are erosional based, fine upward from 

medium to fine grained, are light gray to white and bentonitic, 

and contain quartz and black chert pebble conglomerate. 

The sandstones are scour based, range from 5 to 30 ft thick, 

and form either single or multistacked bodies. They contain 

trough crossbeds ranging from a few inches to 2 ft high in the 

lower part and commonly exhibit climbing ripple laminated 

units from a few inches to 5 ft thick in the uppermost part of 

the units. Type 3 sandstones coarsen upward and are sharp 

based, light gray, rooted, and mainly very fine grained and 

rippled (fig. 7). This sandstone type is as much as 2 ft thick 

and occurs as single sand bodies commonly interbedded with 

mudstone, siltstone, and thin-bedded coal and carbonaceous 

mudstone.

Interpretations

Types 1 and 2 sandstones are characterized by erosional 

bases and mainly represent fluvial channel deposits. Type 1 

conglomeratic sandstones, further distinguished by common 

framework- and matrix-supported pebble conglomerates, 

probably represent braided river deposits. The abundant 

coarse grain size (medium-grained to pebbles and cobbles) 

of this sandstone type indicates that it originated as bedload 

deposits typical of braided streams. The framework-supported 

conglomerate consisting of cobbles and pebbles indicates 

bedload deposition as channel lag gravels. Clast imbrication 

reflects deposition on a flat top of a longitudinal bar or on a 

channel floor (Steel and Thompson, 1983). The sand-matrixsupported pebbles, which overlie the lag gravels and are along 

foresets of crossbeds, were deposited on slip or dip slopes of 

sand bars probably during sheet flooding (Reading, 1978). 

These bars commonly split stream flow, creating subchannels 

that give rise to a braided pattern that is most apparent during 

low flow stage. During low flow, sands are deposited on lag 

gravels, and during subsequent high flow the pebbles in lag 

gravels are reworked and deposited along fronts of sand bars 

ranging from 1 to 5 ft high.

Type 2 sandstones, characterized by erosional bases 

overlain by single body or multiscoured bodies, probably 

mainly represent low-sinuousity river deposits. The singlebody sandstone probably represents a single, stable, cutand-fill fluvial channel. The multiscoured sandstone bodies 

represent deposits of a fixed, vertically aggrading fluvial 

channel. These fluvial channels reflect laterally stable 

channels between episodes of abrupt switching (Friend, 1983) 

and resemble those of anastomosed rivers incised in thick, 

fine-grained, overbank-flood plain sediments (Smith, 1983).

Type 3 sandstones—characterized by either sharp 

or gradational bases, coarsening-upward profiles, ripple 

laminations, and root marks—represent crevasse splay 

deposits. These sandstones result from deposition by 

floodwaters breaching the levee crest and spilling into 

flood plains and mires. Incursions of these sediment-laden 

floodwaters resulted in deposition of sheet-like sediments 

by numerous small, anastomosed channels (Smith, 1983). 

Crevasse splay sandstones are commonly interbedded with 

flood plain mudstones and siltstones. These fine-grained 

sediments reflect deposition of suspended sediments 

transported by either crevasse splays or overbank floodwaters, 

or both.
28 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Figure 23. Type 1 sandstone containing 

pebbles mainly composed of subrounded 

black chert and volcanic rock fragments in 

the Prince Creek Formation. Knife is 6 in long 

(for scale). 

&IG

Figure 22. Photograph 

of pebbly, coarse grained, 

poorly sorted, and largescale trough crossbedded 

fluvial channel sandstone 

(Type 1) of the Prince Creek 

Formation. Jacob staff is 3 ft 

long (for scale). 

Figure 24. Pebbles and cobbles in 

Type 1 sandstone are imbricated in 

framework-supported lag conglomerate 

and also occur as float pebbles in a 

sandy matrix within large-scale trough 

crossbeds. Ruler is 1 ft long (for scale). 

&IG
General Stratigraphy 29

Figure 25. Photograph of interbedded coal, carbonaceous mudstone, siltstone, and tonstein (white) 

beds in the Prince Creek Formation between the mouth of the Anaktuvuk River and the vertical angle 

benchmark (VABM) at Kavik. For scale, man in photograph is about 6 ft tall. &IG

Prince Creek Formation (Middle and Upper 

Parts)

Description

The vertical stratigraphic and sedimentologic variations 

of the middle and upper parts of the Prince Creek Formation 

are exhibited in figures 7 through 14 for the Kavik Bluff 

(see fig. 2 for location below the vertical angle benchmark 

[VABM] at Kavik) and Ocean Point Bluff. In general, the 

middle and upper parts of the formation in these areas are 

composed of interbedded coal, carbonaceous shale, mudstone, 

siltstone, tuff, sandstone, and conglomeratic sandstone beds.

Prince Creek coal beds range from a few inches to 11.5 

ft thick and are interbedded with white tonstein, greenish 

bentonitic claystone, and carbonaceous shale and mudstone 

partings that contain root marks and abundant carbonized 

plant leaves and stems (fig. 25). The tonstein partings, as 

much as 6 in thick, are laterally extensive and make good 

marker units. The coal beds, which contain bright and 

dull vitrain bands that are a few inches thick, range in rank 

from lignite to subbituminous (Sable and Stricker, 1987; 

Wahrhaftig and others, 1994). The mudstone is gray to light 

Creek Formation contain mainly Types 2 and 3 sandstones. 

Type 2 sandstones are erosional based, fining upward, fine 

grained, light gray to white, and bentonitic and contain quartz 

and black chert pebble conglomerate. These sandstones 

range from 10 to 60 ft thick; occur as either single body or 

multiscoured, stacked bodies; and are separated by mudstone 

drapes that are as much as a few inches thick (figs. 26A and 

26B). Type 2 sandstones contain trough crossbeds ranging a 

few inches to 6 ft high and climbing ripple laminations from 

a few inches to 10 ft thick; the latter are common in the upper 

part of the sandstone beds. This sandstone type is common 

in the upper part of the Prince Creek Formation, where its 

architecture is laced with erosional-based mudstones (fig. 27). 

Figure 26B exhibits (1) the vertically stacked and laterally 

en echelon architecture of these erosional-based sandstonemudstones and associated dipping (10E–15E) mud-draped 

sandstone-siltstone couplets, (2) the opposing dip of the 

accretionary bedding in vertically adjacent sandstone-siltstone 

couplets that grade into thick-bedded sandstones (see bottom 

of fig. 26A and left of fig. 26B), and (3) the general upward 

fining and widening of the sandstone bodies in the lower part 

and narrowing in the upper part.

gray, is bentonitic, 

and contains reddish 

ferruginous layers and 

nodules equivalent to 

the variegated layers in 

the Sentinel Hill Core 

Test 1 well (Flores 

and others, 2007) 

and macerated plant 

fragments. It is rooted, 

carbonaceous, and dark 

gray and occurs below 

the coal beds and as 

partings. The thickness 

of the mudstone 

beds ranges from a 

few inches to about 

30–35 ft; the thickest 

mudstone units exhibit 

erosional bases. The 

siltstone is gray, rippled, 

ferruginous, and rooted 

and contains abundant 

plant fragments. 

Siltstone occurs either 

as beds a few inches to 

10 ft thick or as lenses 

in the mudstone (a few 

inches thick and a few 

feet long).

The middle and 

upper parts of the Prince 
30 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

4YPECHANNELSANDSTONE

&IG!

%ROSIONAL

CONTACT

Figure 26A. Photograph 

of Type 2 erosionalbased, fining-upward, 

multiscoured sandstone in 

the Prince Creek Formation 

between the mouth of the 

Anaktuvuk River and the 

vertical angle benchmark 

(VABM) at Kavik. Inclined 

sandstone and siltstone 

beds in the lower Type 

2 sandstone are lateral 

accretion deposits. Type 

2 channel sandstone is 50 

ft thick.

Figure 26B. Photograph of Type 2 sandstone complex consisting of 

vertically stacked, laterally en echelon sandstone overlain by erosionalbased mudstone of the Prince Creek Formation. The coal bed below the 

sandstone is split by a Type 3 coarsening-upward splay deposit (see arrow); 

the coal bed merges as the splay deposit thins to the right. For scale, coal 

bed is 5 ft thick.

4YPECREVASSESPLAY

4YPECHANNELSANDSTONE

&IG"

3PLIT
General Stratigraphy 31

4YPECREVASSESPLAYDEPOSITS

&IG

&LOODPLAINANDMIREDEPOSITS

Figure 28. Photograph 

of interbedded sandstone, 

mudstone, and siltstone 

with minor coal and 

carbonaceous shale beds 

representing flood plain 

and coarsening-upward 

crevasse splay (Type 3 

sandstones) deposits of the 

Prince Creek Formation. 

For scale, the crevasse 

splay deposits are 7 ft thick.

4YPECHANNELSANDSTONE

&IG

%ROSIONAL
BASEDMUDSTONE

%ROSIONALCONTACT

Figure 27. Photograph 

of erosional-based 

mudstone (abandoned 

channel plug deposit) of 

Prince Creek Formation 

between the mouth of the 

Anaktuvuk River and the 

vertical angle benchmark 

(VABM) at Kavik. For 

scale, the erosionalbased mudstone is 15 ft 

thick.
32 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Type 3 Prince Creek sandstones are light gray, rooted, 

and sharp to gradational based; they coarsen upward from 

mudstone and siltstone to mainly very fine grained and 

rippled, mainly by climbing ripple laminations (figs. 28 

and 29). These sandstone beds are as much as 10 ft thick 

and occur either as a single body or as paired sand bodies 

commonly interbedded with mudstone, siltstone, and thinbedded coal and carbonaceous mudstone (fig. 28). The coal 

beds are commonly split by these coarsening upward Type 3 

sandstones, as shown in figure 26B.

draped sandstone-siltstone couplets, probably mainly represent 

meandering river deposits (fig. 26B). Each multiscoured 

sandstone body is dominated by trough crossbeds and exhibits 

a fining-upward profile, and the dipping mudstone-draped 

sandstone-siltstone couplets are dominated by root marks and 

ripple laminations. The sandstone bodies represent mixed 

bedload and suspended load deposition of randomly shifting 

and migrating high-sinuosity channels, as in meandering river 

systems. Switching of the fluvial channel within the meander 

belt is indicated by the opposed dip (epsilon crossbeds) of 

the mudstone-draped 

sandstone-siltstone 

couplets and associated 

erosional-based 

mudstones (clay-rich 

deposits; fig. 26B); 

the latter indicates 

abandonment of the 

fluvial channel by 

avulsion or neck cutoff 

and the eventual filling of 

the fluvial channel with 

suspended sediments. 

The mudstone-draped, 

rippled sandstonesiltstone couplets and 

associated thick-bedded, 

crossbedded sandstones 

mainly represent a 

lateral accretion by a 

point bar on an inclined 

surface. The thick, 

crossbedded sandstones 

were deposited in 

the deeper parts of 

the channel that were 

subjected to vigorous 

currents, whereas the 

up-dip, mudstone-draped, 

sandstone-siltstone 

couplets were deposited 

in the shallow part of the 

channel that was mainly affected by water-level fluctuations 

and slack-water conditions. In the shallow part of the channel, 

small chute channels or bars, infilled by sand and mud, may 

have formed during flood and waning stages. In contrast, 

Type 2 sandstones that are single body with just an erosional 

base represent cut-and-fill, low-sinuosity, anastomosed 

fluvial channels, which were stabilized by thick, fine-grained 

overbank and flood plain sediments (fig. 30). Sedimentation 

of anastomosed fluvial channels occurs by vertical accretion of 

both the channel floor and overbank or flood plain sediments.

Type 3 sandstones—characterized by either sharp- or 

gradational-base, coarsening-upward profiles with underlying 

mudstones and siltstones, ripple laminations, and root marks—

represent crevasse splay deposits. These strata resulted from 

&IG

Figure 29. Photograph of fine-grained, ripple laminated (climbing ripples) sandstone interbedded with 

a thin coal and mudstone layer above Type 2 sandstone of the Prince Creek Formation. Some rootlets 

indicated by ferruginous marks are in the sandstone. Hammer is 1 ft long (for scale).

On the basis of the volume of coarse- and fine-grained 

strata as well as of coal beds, the middle and upper parts of the 

Prince Creek Formation may be divided into two major facies 

assemblages, one dominated by Types 2 and 3 sandstones and 

the other dominated by a mudstone-siltstone, coal-rich facies 

(fig. 17). Volumetrically, sandstones constitute approximately 

60 percent, and mudstone, siltstone, and coal beds constitute 

the remainder (fig. 17). The alternating sandstone-dominated 

and mudstone-siltstone-dominated, coal-rich facies are well 

displayed in figures 5–18.

Interpretations

Type 2 sandstones, characterized by erosional bases 

overlain by multiscoured bodies and grading into mudstone-
Figure 30. Photograph of elongate fluvial channel sandstone (Type 2) bounded by interbedded silty sandstone, siltstone, 

mudstone, coal, and carbonaceous mudstone. The fluvial channel sandstone feathers or dovetails with thick coal and 

carbonaceous mudstone beds and with finer grained rocks toward the right (northward) of the photograph. Colville River is in 

the foreground. For scale, the Type 2 channel sandstone is 25 ft thick.

deposition by floodwaters that breached the levee crest and 

spilled into flood plains. Further incursions of these sedimentladen floodwaters from fluvial channels to the peat-forming 

mires deposited sheet-like and lobe-shaped deposits, as 

indicated in figure 26B.

Crevasse splay sandstones commonly overlie and are 

interbedded with flood plain mudstones and siltstones. These 

fine-grained strata contain variegated paleosols in the Sentinel 

Hill Core Test 1 well (Flores and others, 2007) and reflect 

deposition of suspended sediments transported by crevasse 

splays or overbank floodwaters into the flood plain. The 

coarser grained beds (sandstones) represent deposition of 

bedload sediments via crevasse channels during floods, which 

prograded into the flood plain with suspended sediments. 

In mires normally beyond the influence of this floodwater 

sedimentation, plant matter accumulated as peat, but the 

presence of mudstone and sandstone partings in coal beds 

suggests intermittent detrital incursions during flood events 

into the peat-forming mires, as shown in figures 25 and 26B, 

indicating that the peat mires probably were mainly low lying 

or flat topogeneous mires prone to floods. The tonstein and 

bentonitic partings indicate deposition of volcanic ash into 

the mires. Thick mudstones characterized by erosional bases 

represent abandoned channel deposits that were infilled by 

suspended mud during floods. These abandoned channels 

(oxbows) are associated with meandering rivers, where 

meander loops are abandoned and rapidly plugged at both 

ends, as well as with abandoned chute channels on point bar 

surfaces.

Stratigraphic Facies Variations Within the 

Sentinel Hill Core Test 1 Well

The Sentinel Hill Core Test 1 well, as described and 

interpreted by Robinson and Collins (1959), provides an 

additional one-dimensional view of the vertical stratigraphic 

variations of the Prince Creek Formation and of the upper 

part of the Schrader Bluff Formation. This well—which was 

cored continuously with good recovery in the depth interval 

of 100–1,180 ft—was redescribed by Flores and others (2007) 

to establish sedimentological facies and to interpret the 

depositional environments.

The Prince Creek Formation as distinguished by 

Robinson and Collins (1959) is predominantly nonmarine, 

and the Schrader Bluff Formation is predominantly marine. 

They subdivided the sequence as follows (in ascending order): 

Sentinel Hill Member of the Schrader Bluff Formation, 231 

ft; Kogosukruk Tongue of the Prince Creek Formation, 109 ft; 

Sentinel Hill Member of the Schrader Bluff Formation, 371 

ft; and Kogosukruk Tongue of the Prince Creek Formation, 

469 ft (fig. 4). These stratigraphic subdivisions were based on 

the presence of coal and plant fossils in the nonmarine units 

of the Prince Creek Formation and of marine macrofossils 

and microfossils (for example, Mytilus sp. and Eoeponidella 

%LONGATE4YPECHANNELSANDSTONE

&IG

General Stratigraphy 33
34 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

strombodes) in the marine strata of the Schrader Bluff 

Formation.

The lithologic observations by Robinson and Collins 

(1959) from the Sentinel Core Test 1 well are compared and 

correlated to those of the measured stratigraphic sections 

and stratigraphic cross sections in the Kavik, Uluksrak, and 

Shivugak Bluffs, which are located about 4, 10, and 13 mi, 

respectively, from the well site (fig. 2). 

Correlations of the Sentinel Hill Core Test 1 to 

Colville River Bluffs Exposures

The Prince Creek and Schrader Bluff Formations in 

the upper part (469 ft and 371 ft thick, respectively) of the 

Sentinel Hill Core Test 1 are probably equivalent in part to the 

Prince Creek Formation at Kavik Bluff and to the Prince Creek 

and Schrader Bluff Formations at the Uluksrak and Shivugak 

Bluffs. Flores and others (2007) redefined the contacts of 

the Prince Creek and Schrader Bluff Formations in the test 

well (on the bases of facies, depositional environments, and 

sequence stratigraphic surfaces) as follows (the first-named 

depth is from Robinson and Collins [1959], and the second 

is that of Flores and others [2007]): (1) in the upper part, 

the contact was moved from the 469-ft depth within a coalbearing interval to the 690-ft depth at the erosional base of 

a conglomeratic channel-sandstone complex interpreted as 

a sequence boundary; (2) in the middle part, the contact was 

moved from the 840-ft depth within a coal-bearing interval 

to the 746-ft depth at the erosional base of a conglomerate 

interpreted as a ravinement lag and sequence boundary; and 

(3) in the lower part, the contact remained about the same 

(949 ft), which is below the lowermost coal beds and above a 

shoreface sandstone.

In the Shivugak and Uluksrak Bluffs (figs. 15 and 16), the 

Prince Creek Formation, which contains mainly Types 2 and 3 

sandstones, is equivalent to the upper Prince Creek Formation 

in the Sentinel Hill Core Test 1. Flores and others (2007) 

described similar sandstone types in the well cores; these 

sandstone types were interpreted as fluvial channel and flood 

plain crevasse splay sandstones. Similarly, these sandstone 

types are interbedded with finer grained flood plain deposits 

(silty sandstone, siltstone, and mudstone) and with coal 

interbedded with carbonaceous deposits (shale and mudstone) 

that formed in freshwater bogs and tonsteins (volcanic ash or 

tuffaceous layers) as airfall deposits.

The lowermost Prince Creek Formation in the Uluksrak 

and Shivugak Bluffs (figs. 15 and 16)—which is dominated 

by Type 1 sandstone with minor coal, carbonaceous shale, 

mudstone, and siltstone—is probably equivalent to the 

lowermost interval of the upper part of the Prince Creek 

Formation in the Sentinel Hill Core Test 1. This interval in 

the core test contains, from bottom to top, (1) multiscoured 

conglomeratic, fine- to coarse-grained sandstones (Type 1) 

overlain by (2) thin coal beds, which in turn grade upward into 

(3) interbedded silty to fine-grained sandstones, siltstones, 

and mudstones. The lower Type 1 sandstone of this 180-ftthick interval is interpreted by Flores and others (2007) as 

a paleovalley deposit that was incised into the marine lower 

shoreface deposits of the upper Schrader Bluff Formation; 

the erosional base of the paleovalley represents a sequence 

boundary. The overlying interval of interbedded Type 3 

sandstone, coal, mudstone, and siltstone beds represents 

coastal bay-estuarine environments. At Uluksrak and 

Shivugak Bluffs (figs. 15 and 16), braided stream deposits 

also overlie the erosion surface that was incised into the 

marine upper shoreface deposits of the Schrader Bluff 

Formation, but in these areas the braided stream deposits are 

overlain by thicker coal beds, indicating more freshwater bog 

settings. The Schrader Bluff Formation in the Uluksrak and 

Shivugak Bluffs, which is more than 400 ft thick (figs. 15 

and 16), is probably laterally equivalent to the thicker lower 

tongue of the Schrader Bluff Formation in the Sentinel Hill 

Core Test 1; the upper tongue of the Schrader Bluff Formation 

in the core test is probably missing farther updip at Shivugak 

Bluff because of erosion during sea-level drop (paleovalley 

incisement).

The lower coal-bearing part of the Prince Creek 

Formation in the Sentinel Hill Core Test 1 may be correlated 

below the lowermost conglomeratic channel sandstone, which 

is shown in figure 5. The conglomerate sandstone in the 

Sentinel Hill Core Test 1 is interpreted as Type 1 sandstone 

deposited above an erosion surface incised into underlying 

thin coal and carbonaceous shale beds. The erosional base of 

the Type 1 sandstone is interpreted as a sequence boundary, 

which in turn is underlain by a marine shoreface sandstone. 

The thinned nonmarine Prince Creek Formation is overlain 

by a thin conglomerate interpreted as a ravinement lag, which 

may be laterally equivalent to the ravinement lag at the 746-ft 

depth in the Sentinel Hill Core Test 1 (see Flores and others, 

2007). These ravinement lags were formed from reworked 

older sediments during marine transgression or sea-level 

rise. The ravinement lag is overlain by interbedded marine 

shoreface sandstone and mudstone beds, which were partly 

eroded during sea-level drop in the Sentinel Hill Core Test 1 

area.

Lateral Stratigraphic Variations

The cross sections in figures 15–18 were constructed 

from photomosaics to display the lateral stratigraphic and 

sedimentologic variations within the upper part of the Schrader 

Bluff Formation and within the Prince Creek Formation in the 

Colville River Bluffs. Figures 15 and 16 exhibit the lateral 

variations in the upper part of the Schrader Bluff Formation 

and the lowermost part of the Prince Creek Formation at 

Shivugak and Uluksrak Bluffs. Figures 7 and 18 exhibit the 

lateral variations in the middle and upper parts of the Prince 

Creek Formation between the mouth of the Anaktuvuk River 

and Ocean Point. These locations and place names are shown 

in figure 2.
General Stratigraphy 35

Shivugak to Uluksrak Bluffs

Description

The stratigraphic cross sections along Shivugak and 

Uluksrak Bluffs show laterally extensive, tabular (more 

than 0.5–1 mi long and as much as 55 ft thick), marine 

sandstone beds in the uppermost part of the Schrader Bluff 

Formation (figs. 15 and 16). These tabular sandstone beds 

cap coarsening-upward parasequence sets that extend laterally 

from the Shivugak to Uluksrak Bluffs for a distance of more 

than 6 mi. These sandstone beds overlie discontinuous, thin to 

thick, coarsening-upward tuffaceous sandstones interbedded 

with siltstone and mudstone. The top of the Schrader Bluff 

Formation is a rooted erosional surface capping the uppermost 

tabular, coarsening-upward sandstone bed, which is overlain 

by a coal bed as much as 2 ft thick.

This basal coal of the Prince Creek Formation is overlain 

by a few interbedded coal and mudstone-siltstone beds. 

These strata are overlain by a fining-upward, erosional-based, 

chert-pebble conglomeratic, multiscoured sandstone unit 

(figs. 15 and 16) that is locally incised as deeply as 75 ft into 

the underlying Prince Creek Formation coals and mudstones 

and into the uppermost coarsening-upward sandstone of 

the Schrader Bluff Formation (fig. 15). The conglomeratic 

sandstones form a laterally extensive blanket-like unit 

from Shivugak to Uluksrak Bluffs; the erosional base was 

informally recognized as mid-Campanian unconformity 

(MCU) by Decker (2007). Coal beds interbedded with the 

conglomeratic sandstones are as much as 5 ft thick and are 

laterally continuous from Shivugak to Uluksrak Bluffs.

Two conglomeratic sandstone beds as much as 55 ft thick 

were observed in Uluksrak Bluff (fig. 16), whereas only one 

conglomeratic sandstone bed was observed in Shivugak Bluff, 

where the upper bed is either obscured or has coalesced with 

the lower bed. In Uluksrak Bluff, the uppermost lenticular 

conglomeratic sandstone bed is overlain by interbedded 

numerous coal beds and lenticular sandstone beds. The 

lenticular sandstone beds are en echelon relative to coal beds 

that are in part laterally equivalent to the sandstone beds.

Overlying the tabular sandstone beds at the top of the 

Schrader Bluff Formation are thin- to thick-bedded coals of 

the Prince Creek Formation that extend laterally for more than 

1 mi (figs. 16, 17, and upper part of measured section in fig. 

6). The coal beds are interbedded with thin-bedded, blanketlike sandstones. The coal interval is sparsely interbedded 

with thick, laterally extensive sandstone beds (fig. 16). Thus, 

the cross sections in figures 16 and 17 depict an alternating 

succession of the sandstone-dominated, coal-poor facies and 

the mudstone-siltstone-dominated, coal-rich facies.

Interpretations

The tabular, bidirectional crossbedded sandstone beds of 

the upper Schrader Bluff Formation shown in figures 15 and 

16 represent barrier-shoreface facies. These beds—which 

are vertically stacked, coarsening-upward sequences—were 

deposited on a prograding paleoshoreline. The presence 

of HCS and SCS, wave, ripple, and flat lamination-bearing 

sandstone reflects in part reworking of the sands by stormgenerated currents (Reading, 1978). The contact between 

the uppermost tabular sandstone bed of the Schrader Bluff 

Formation and the lowermost coal bed of the overlying Prince 

Creek Formation represents a surface of regional erosion into 

the shoreface resulting from lowering of relative sea level; the 

contact is considered a forced regressive surface or sequence 

boundary as recognized by Mull and others (2003).

The erosional surface at the base of the blanket-like 

conglomeratic sandstone beds (Type 1) in the lowermost part 

of the Prince Creek Formation appears to be the result of a 

later, though possibly genetically related, fall in base level 

that took place following the deposition of at least 75 ft of 

basal Prince Creek Formation coals and mudstones. This 

surface presumably developed through headward incision of a 

broad paleovalley whose infilling by braided stream bedload 

conglomerates and sands reflects high sediment supply, 

which is suggestive of tectonic activity in the source terrane. 

Later, a subsequent change to higher accommodation, lower 

depositional gradient conditions, controlled either by basin 

subsidence or eustatic sea-level rise, caused a change in fluvial 

depositional architecture. The deposition of the en echelon, 

lenticular sandstones, which range from 0.1 to 0.5 mi wide 

and are as much as 20 ft thick, reflects fluvial channels infilled 

by sands and subsequently abandoned. These narrow, small 

streams periodically were diverted (avulsed) into topographic 

lows in the flood plains. The flat-lying or topogeneous mires 

in open wet flood plains accumulated thin peat deposits and 

eventually encroached over stable, abandoned, alluvial-belt 

platforms, thereby forming thin to thick, laterally extensive 

“dirty” coal beds.

Anaktuvuk River to VABM Kavik

Description

The stratigraphic cross section from the bluffs between 

the mouth of the Anaktuvuk River and the vertical angle 

benchmark (VABM) at Kavik (fig. 2) represents an interval 

in the Prince Creek Formation above the section described 

in Uluksrak Bluff (fig. 17). The cross section shows both 

fining-upward lenticular and elongate sandstone beds (based 

on length to thickness ratios) interbedded with coal, mudstone, 

siltstone, and silty sandstone beds. The lenticular sandstone 

beds are erosional based, are as much as 80 ft thick, and 

have lateral extents of more than 2.5 mi. The erosional base 

is commonly overlain by pebble conglomerates as much as 

5 ft thick that contain abundant quartzite and metavolcanic 

fragments. These sandstone beds contain “feathered” tops 

marked by clay-draped lateral accretion surfaces. The 

elongate sandstone beds are erosional based, are as much as 

40 ft thick, and have lateral extents from less than 0.1 to 1 
36 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

mi. These beds are associated with tabular, 5- to 10-ft-thick, 

rippled silty sandstone beds underlain by coarsening-upward 

mudstone and siltstone beds. The coal beds, as much as 6 ft 

thick and with lateral extents more than 3.5 mi, split, merge, 

pinch out, and are cut out by the erosional-based sandstones. 

The architecture of these fluvial deposits is shown in figure 

30; note that at the right and left sides of the photograph 

the elongate sandstone can be observed feathering into 

thick, interbedded sandstone, siltstone, mudstone, coal, and 

carbonaceous mudstone.

The stratigraphic cross section for these exposures (fig. 

17) may be divided into a lower part dominated by elongate 

sandstone beds and an upper part dominated by lenticular 

sandstone beds. The elongate sandstone beds are physically 

separate but coeval units along the north-south direction (or 

from right to left in the cross section), whereas the lenticular 

sandstone beds show an en echelon stacking pattern. The en 

echelon pattern of the lenticular sandstone beds is particularly 

apparent where the thickest portions of successive sandstone 

bodies do not directly overlie one another but are slightly en 

echelon, with the thickest portion overlying the fine-grained, 

coal-bearing intervals. In addition, the sandstone beds wedge 

out by interfingering laterally with various fine-grained strata 

and coal. A few of the lenticular sandstone beds are broader at 

their tops than at their bases.

Interpretations

The architecture of the sandstone beds and associated 

fine-grained, coal-bearing sediments in the Prince Creek 

Formation indicates fluvial deposition of meandering and 

anastomosed channel systems. The en echelon arrangement 

of the lenticular sandstone beds in the upper part of the 

interval probably resulted from abrupt channel switching in 

response to favorable flood plain gradients. Where a meander 

has been largely infilled by lateral accretion of the point bar 

toward a relatively stationary cut bank, a flooding stream 

tends to be diverted just upstream, cutting off the meander by 

developing a chute channel across the adjacent flood plain. 

The abandoned meander channel bars stood as high and welldrained ridges before subsiding and being covered by mire 

deposits that encroached from adjoining flood plain wetlands.

That the meandering fluvial channels evolved from 

anastomosed channels is indicated by the coeval elongate 

sandstone beds, which dominated the lower part of the 

interval. These narrow fluvial channels may have evolved 

from crevasse splay channels, as they are associated with 

coarsening-upward mudstone, siltstone, and silty sandstone. 

The crevasse splays resulted from the breaching of levees 

during floods that spilled over into the flood plains. As flood 

sediments prograded into the flood plain, crevasse channels 

transformed into well-developed, contemporaneous, narrow, 

deep, anastomosed fluvial channels (fig. 30; Flores, 2003). 

After partial infilling, this system of crevasse splay-fluvial 

channels evolved into wetland mires that accumulated peat. 

Eventually this system transformed into an alluvial plain 

drained by meandering fluvial channels that evolved from the 

anastomosed fluvial channels (Flores, 2003). The progression 

from anastomosed to meandering streams may reflect a change 

from high to low alluvial-plain gradient as influenced by an 

increase of accommodation space through basin subsidence or 

eustatic sea-level rise.

Ocean Point Bluff

Description

The stratigraphic cross section of the Prince Creek 

Formation in the Ocean Point Bluff (fig. 18) appears to 

represent an older interval than that exposed in bluffs from the 

mouth of the Anaktuvuk River to VABM Kavik Bluff. The 

cross section shows lenticular sandstone beds interbedded with 

carbonaceous mudstone, siltstone, and silty sandstone beds. 

The lenticular, fining-upward sandstone beds are erosional 

based, are as much as 50 ft thick, and have lateral extents of 

less than 1 mi. The sandstone beds exhibit multiple erosional 

surfaces marked by rip-up mudstone lag deposits. The 

sandstone beds are interbedded with, and grade laterally into, 

rooted carbonaceous mudstone, siltstone, and silty sandstone. 

In the southern part of the cross section, the carbonaceous 

mudstone is overlain by fossil hadrosaur bones. These 

dinosaur bones are common throughout the interval.

The erosional-based lenticular sandstone beds are 

laterally en echelon, with the thickest part of the beds 

overlying the fine-grained, carbonaceous-mudstone-bearing 

interval. In addition, the sandstone beds wedge out and 

interfinger laterally with the rooted fine-grained rocks and 

carbonaceous mudstone; the latter are interbedded with 

tabular, rooted, and rippled silty sandstone beds. Both 

sandstone beds commonly contain tuffaceous lenses.

Interpretations

The Prince Creek Formation at Ocean Point (fig. 18) 

mainly represents an alluvial belt consisting of extensive 

deposits of slightly meandering fluvial channels partly 

underlain and flanked to the south (top left in fig. 18) by 

overbank-flood plain finer grained deposits and coaly 

carbonaceous mudstone (fig. 31). Lenticular sandstone 

beds exhibiting multiple scours and broad, lateral extents 

indicate deposition in the shifting, migrating subchannels of a 

moderately wandering, low-sinuosity fluvial channel system. 

The en echelon arrangement of the lenticular sandstone beds 

indicates abrupt abandonment of these fluvial channels after 

infilling.

The presence of coaly carbonaceous mudstones 

interbedded with rooted, fine-grained strata indicates active 

inundation of the flood plain by flood sediments, which 

promotes mixing of mud with peat mires. The common 

occurrence of the tabular, rooted, and rippled silty sandstones 

reflects crevasse splay deposition on the flood plains. The 

hadrosaur bones probably represent either in situ accumulation 
of remains of the animals drowned on the flood-ravaged, 

sediment-laden flood plains or represent carcasses transported 

onto or redistributed on the flood plains during floods.

Previous Stratigraphic Sections, Correlations, 

and Interpretations of the Ocean Point Area

Phillips (1988, 1989) measured and described 25 

stratigraphic sections of the Prince Creek and Schrader 

Bluff Formations along the bend of the Colville River near 

Ocean Point. Our study area and the stratigraphic interval 

of the Prince Creek Formation corresponded to those of 

Phillips (1988, 1989; his measured sections 7 through 14) 

(fig. 18). In the eastern part of the study area, Phillips (1989) 

described overbank flood plain deposits of interbedded 

rooted, coarsening-upward mudstone, siltstone, and crevasse 

splay sandstone similar to those we describe in our measured 

sections and interpret as flood plain-crevasse splay deposits. 

In addition, Phillips described organic-rich siltstone 

interbedded with tephra; these overbank flood plain deposits 

are similar to the carbonaceous mudstone and tuffaceous 

siltstone we describe in our measured sections.

In the western part of the study area, Phillips (1989, p. 

102) described “sand-filled channels,” which he interpreted 

as major fluvial distributaries that meandered across a coastal 

plain. He described the sandstones as being fine to medium 

grained, containing large- to small-scale trough and tabular 

crossbeds, and having erosional bases marked by mud rip-up 

clasts, carbonized woody fragments, plant debris, and rare 

dinosaur bone fragments. These sandstones are similar to 

what we described as lenticular fluvial sandstones deposited in 

a low-sinuosity channel system.

Two bone beds containing hadrosaurian remains 

(Clemens and Allison, 1985; Brouwers and others, 1987; 

Davies, 1987; Nelms, 1989) associated with organic-rich 

siltstone beds were described by Phillips (1988, 1989; 

his measured sections 6, 7, and 9—a lower bone bed in 

sections 6 and 7 and an upper bone bed in section 9). 

These disarticulated and vertically size-graded bones were 

interpreted by Phillips (1989) as having accumulated in 

the flood plain and later being reworked and redeposited 

by overbank flooding. Hadrosaurian bones in the fluvial 

distributary sandstones were interpreted as basal lag deposits 

of the distributary fluvial channels (Phillips, 1989).

Figure 31. Photograph of fining-upward sandstone (trough crossbedded to rippled upward) underlain by 

interbedded siltstone, mudstone, and coaly carbonaceous mudstone of the Prince Creek Formation at Ocean 

Point Bluff. For scale, the sandstone is 40 ft thick. &IG

General Stratigraphy 37
38 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Summary of Fluvial System Deposits Between 

Shivugak and Ocean Point Bluff

The continuous exposures between Shivugak and Ocean 

Point Bluff along the Colville River exhibit, in ascending 

order, (1) deposits of barrier shoreface-delta front system in 

the Schrader Bluff Formation and (2) braided, high-sinuosity 

meandering, anastomosed, and low-sinuosity meandering 

fluvial systems in the Prince Creek Formation (fig. 32). These 

sequences represent late Campanian to late Maastrichtian 

depositional systems that were affected by base level changes 

as influenced by tectonism, basin subsidence, and sea-level 

fluctuations.

The barrier shoreface-delta front deposits—consisting 

of vertically stacked coarsening-upward parasequences of 

the Schrader Bluff Formation in the Shivugak and Uluksrak 

Bluffs—represent progradational sequences that were 

affected by shoaling and deepening cycles caused by minor 

fluctuations of sea level (fig. 32). The erosional contact at the 

top of the uppermost coarsening-upward sequence, however, 

suggests a major drop of base level (relative sea level) that 

permitted a semiregional, subaerial unconformity to develop 

at the contact between the Schrader Bluff and Prince Creek 

Formations. This drop of relative sea level may have been 

followed by a relative sea-level rise that accommodated coal 

deposition directly on top of the unconformity above the 

coarsening-upward barrier shoreface sequence of the Schrader 

Bluff.

Accommodation space created by the sea-level rise 

was maintained with additional accumulation of some coal 

beds in the lowermost Prince Creek Formation at Shivugak 

and Uluksrak Bluffs (fig. 32). Ensuing deposition of 

conglomeratic sandstones across the deeply incised surface 

(MCU of Decker [2007]) that overlies these coal beds reflects 

infilling of incised paleovalleys by braided streams. The 

erosion probably resulted from base level change caused by a 

second fall of relative sea level. Sediment infilling by braided 

streams (high-gradient sheet flow) may indicate combined 

tectonic uplift (high sediment supply) and sea-level rise 

(accommodation).

Fluvial deposits in the lower to upper parts of Prince 

Creek Formation exposed between Uluksrak Bluff, the mouth 

of Anaktuvuk River, and VABM Kavik exhibit a change in 

architecture from deposition in braided streams to deposition 

in anastomosed or meandering streams, reflecting a change 

from moderate- to low-gradient drainages (from fixed to 

mobile channel belts) (fig. 32). Both the moderate-gradient 

anastomosing and low-gradient meandering stream systems 

may have developed in a subsiding upper to lower coastal 

plain. Anastomosed streams representing vertical aggradation 

developed on the coastal plain during an episode of high 

accommodation (rapid subsidence or eustatic highstand). The 

meandering streams that represent mainly lateral aggradation 

formed during an episode with less accommodation, which 

was possibly due to slowed subsidence of the coastal plain. 

The meandering pattern of the fluvial channels associated with 

interdistributary deposits (Phillips, 1989) near Ocean Point 

reflects a laterally aggrading fluvial system in a lower coastal 

plain environment during early Maastrichtian time. Continued 

aggradation and northeastward progradation may have 

brought more proximal fluvial facies (for example, middle or 

upper coastal plain) to the Ocean Point area as Prince Creek 

Formation deposition extended into later Maastrichtian time, 

but palynomorph data indicate that strata of that age are not 

preserved there.

Numerous occurrences and widespread distribution of 

thin to thick coal beds in the Prince Creek Formation coincide 

with the fluvial deposits formed by the anastomosed and 

meandering streams formed in a subsiding basin (fig. 32). 

In similar situations in Upper Cretaceous coal-bearing units 

in the Western Interior of the United States, occurrence of 

thick coal beds is attributed largely to the increased amount 

and rate of regional subsidence of Rocky Mountain foreland 

basins (Flores and Cross, 1991). Ultimately, the key factor for 

the accumulation and preservation of thick, widespread coal 

deposits is surplus accommodation space (Flores and Cross, 

1991), whether it is due to basin subsidence or sea-level rise. 

Studies have shown that almost all coals formed at the top of, 

and landward of, shoreface facies within progradational events 

that constitute the transgressive-regressive sequences (Sears 

and others, 1941; Weimer, 1960; Beaumont and others, 1971; 

Fassett and Hinds, 1971; Ryer, 1984, Flores and Cross, 1991); 

however, the thickest, most extensive, and greatest volume of 

coals are in locations where the shoreface facies of successive 

progradational events are vertically stacked (Ryer, 1984; 

Flores and Cross, 1991).

Thus, the Schrader Bluff and Prince Creek Formations, 

interpreted by Mull and others (2003) as a large-scale 

prograding couplet of shallow marine to marginal marine 

and coastal plain facies, probably contain significant internal 

depositional cycles that reflect minor fluctuations of relative 

sea level and tectonically varying sediment supply during 

deposition of these rocks between Shivugak Bluff and Ocean 

Point. These geologic controls on the base level of the coastal 

plain impacted the architecture of fluvial channel deposits, 

coal beds, and associated nonmarine facies of the Prince Creek 

Formation.

Applications to Oil and Gas Fields in 

the Central North Slope

The outcrops along the Colville River Bluffs were 

correlated to hydrocarbon reservoirs in the Prudhoe Bay area 

northeast of the National Petroleum Reserve in Alaska (fig. 

33). Decker (2007) presents a stratigraphic cross section of 

a Brookian sequence and relates Brookian horizons between 

the Umiat and Milne Point fields. This cross section (see 

figs. 33 and 34) utilized our descriptions of the Shivugak 

Bluff outcrops and cores from the Sentinel Hill Core Test 1 
Applications to Oil and Gas Fields in the Central North Slope 39

MCU

Meandering (high- to lowsinousity) and anastomosing 

fluvial systems (Kavik Bluff)

Anastomosing fluvial 

systems (Uluksrak and 

Kavik Bluffs)

Paleovalley 

deposit

Braided 

fluvial 

system

(Shivugak and

Uluksrak Bluffs)

MCU

Barrier shoreface-delta front system

 (Shivugak and Uluksrak Bluffs)

0

200

400

600

800

1,000

Feet 

EXPLANATION

Conglomerate

Sandstone

Siltstone

Mudstone

Coal and 

carbonaceous shale

Lateral accretion 

deposits

Abandoned channel 

deposit

Schrader Bluff 

Formation Prince Creek Formation

Mid-Campanian

unconformity

Figure 32. Composite stratigraphic section showing variations in fluvial architecture of the Prince Creek Formation overlying 

coarsening-upward barrier shoreface-delta front system of the Schrader Bluff Formation. Mid-Campanian unconformity adopted from 

Decker (2007).
40 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

0 25 Miles

'

 Gas accumulation

Oil accumulation

Alaska seaward boundary

Well

EXPLANATION

Arctic

National

Wildlife

Refuge

r 

Colville River

Unit

Kuparuk River Unit

Oooguruk Unit

Tuvaaq Unit

Rock

Flour

Unit

Nikaitchuq Unit

Northstar

Unit

Prudhoe Bay Unit

Duck Island

Unit

Liberty Unit

Badami

Unit

Point Thomson Unit

Dalton Highway

Trans-Alaska Pipeline

Study area

(this paper)

Milne

Point

Unit

Cirque 3 Ravik 1

Wolfbutton 

32-7-8

Ekvik 1

Shivugak Bluff

Umiat Test 1 

Beaufort Sea

National

Petroleum

Reserve

in Alaska

A

A' 

Tulaga 1

Sentinel Hill 

Core Test 1 

Figure 33. Map showing location of the stratigraphic cross section of the Brookian sequence (A–A’) shown in figure 34. Modified from a map drawn by Decker (2007) for the area between Umiat field and oil and gas accumulations in the central North Slope. Location of our study area along the Colville River Bluffs is also shown.
Acknowledgments 41

well, as well as the results of palynological studies by Flores 

and others (2007). The palynological ages range from early 

Campanian through early Maastrichtian, but they are mostly 

late Campanian.

The palynology data from the Sentinel Core Test 1 well, 

combined with the mudlog data, indicate that the shallow 

or upper part of the section in the ARCO Tulaga 1 well 

immediately north of the Sentinel Hill Core Test 1 is mostly 

nonmarine Prince Creek Formation (fig. 34). Applying the 

new stratigraphic nomenclature of Mull and others (2003), 

the age ranges given in this paper, and data from Flores 

and others (2007), Decker (2007) (1) correlates some strata 

formerly identified as Sagavanirktok Formation (including the 

informally named “Ugnu sandstones”; see northernmost part 

of fig. 34) as the youngest part of the Prince Creek Formation 

and (2) suggests that the contact of the Prince Creek and 

Sagavanirktok Formations as redefined in outcrops by Mull 

and others (2003) cannot be placed with confidence in the 

subsurface of the cross section shown in figure 34.

The palynostratigraphy and correlations of the Shivugak 

Bluff outcrops and Sentinel Hill Core Test 1 significantly 

impact the Cretaceous stratigraphic sequence correlations 

shown in figure 34. The palynostratigraphy of the Prince 

Creek and Schrader Bluff Formations in the Shivugak Bluff 

outcrops and Sentinel Hill Core Test 1 indicates that these 

rock units are probably older than any of the producing 

Schrader and Ugnu intervals in the West Sak, Milne Point, 

Ugnu, and Orion-Polaris fields (Decker, 2007). Decker (2007; 

oral commun., 2006) ascribes the younger of the sequence 

boundaries at the Shivugak Bluff as correlative with the 

mid-Campanian unconformity (MCU) surface interpreted 

in seismic sections and wells as representing a submarine 

erosion and mass-wasting surface that extends deep into the 

depositional basin in the west-central North Slope. The same 

erosional surface is evident in seismic data in the vicinity of 

the Chevron Malguk 1 well (Houseknecht, 2003; Houseknecht 

and Schenk, 2005).

The informally recognized MCU extends from Shivugak 

Bluff at the base of the Prince Creek Formation through 

the Sentinel Hill Core Test 1 at the base of the upper Prince 

Creek Formation (Flores and others, 2007) and in the ARCO 

Tulaga 1 well (fig. 34). Further basinward, the MCU is at 

the base of the middle Schrader Bluff Formation from the BP 

Kuparuk Uplands Ekvik 1 well to the ConocoPhillips Alaska 

Ravik State 1. The MCU is interpreted to have removed outer 

shelf and deepwater strata of the lower Schrader Bluff and 

Seabee Formations. Correlations by Decker (2007) based on 

the MCU and younger flooding surfaces (fig. 34) indicate a 

strong probability that the Prince Creek and Schrader Bluff 

interval exposed along the Colville River Bluffs is largely time 

equivalent to the middle part of the Schrader Bluff Formation, 

which contains the Tabasco reservoir, and thus is older 

than the major viscous oil reservoir sandstones of the upper 

Schrader Bluff Formation.

Conclusions

Stratigraphic and sedimentologic studies of the Upper 

Cretaceous rocks along the Colville River Bluffs show 

a transition in depositional environments from a barrier 

shoreface system in the Schrader Bluff Formation to braided, 

high-sinuosity meandering, anastomosed, and low-sinuosity 

meandering fluvial systems in the Prince Creek Formation. 

The Prince Creek fluvial deposits, which are late Campanian 

to late Maastrichtian in age, were affected by base level 

changes that were influenced by tectonism, basin subsidence, 

and sea-level fluctuations.

The barrier shoreface deposits consisting of vertically 

stacked, coarsening-upward parasequences of the Schrader 

Bluff Formation in the Shivugak and Uluksrak Bluffs and 

in the west-central North Slope represent progradational 

sequences that were affected by shoaling and deepening cycles 

caused by fluctuations of sea level. This vertical stack of 

parasequence deposits may have served to stabilize accumulation of voluminous coal deposits in the Prince Creek Formation that is exposed in the Colville River Bluffs. The erosional contact at the top of the uppermost coarsening-upward 

sequence, however, indicates a significant drop of base level 

(relative sea level) that permitted a semiregional, subaerial 

unconformity to develop at the contact between the Schrader 

Bluff and Prince Creek Formations. This drop of relative sea 

level may have been followed by a relative sea-level rise to 

accommodate coal deposition directly on top of the unconformity above the Schrader Bluff coarsening-upward, barrier 

shoreface-delta front sequence. This rise was followed by a 

second drop of relative sea level, with formation of incised 

valley topography and an equivalent surface of a major 

marine erosion or mass wasting, which can be traced from the 

Colville River Bluffs basinward to the subsurface in the westcentral North Slope.

Acknowledgments

Financial support for this study was from the Alaska 

Division of Oil and Gas. The paper was reviewed by Ronald 

C. Johnson, Paul L. Decker, William R. Keefer, and Douglas J. 

Nichols.
42 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

Mid-Campanian unconformity

Sequence boundary/erosional surface

Transgressive flooding/ravinement surface

Condensed or bentonitic shale

Shelf to slope mudstone & siltstone

Toe-of-slope turbidites (sand-prone)

Distal shelf sandstone & siltstone

Shallow marine to proximal shelf sandstone

Nonmarine, undifferentiated

sb

fs

Se

Nanush

Fm

Prince

Creek

Fm

500

-500

-1,000

-1,500

0

-2,000

-2,500

-3,000

-3,500

-4,000

-4,500

-5,000

-5,500

-6,000

-6,500

-7,000

-7,500

A 

Feet 

2007) 

Figure 34. Stratigraphic cross section of the Brookian sequence from U.S. Navy Umiat 1 well to ConocoPhillips Ravik 1 well in the west-central 

North Slope, Alaska. See figure 32 for line of section. Modified from Decker (2007). Fm, Formation; LCU, Lower Cretaceous unconformity; MCU, 

mid-Campanian unconformity; HRZ, highly radioactive zone.
Acknowledgments 43

Seabee Fm Nanushuk Fm

ince 

reek Fm

500

-500

-1,000

-1,5000

-2,000

-2,500

-3,000

-3,500

-4,000

-4,500

-5,000

-5,500

-6,000

-6,500

-7,000

-7,500

A‘ 

Feet 
44 Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations in Colville River Bluffs

References Cited

Beaumont, E.A., Shoemaker, J.W., and Kottlowski, F.E., 

1971, Stratidynamics of coal deposition in southern Rocky 

Mountain region, U.S.A.: New Mexico Bureau of Mines 

and Mineral Resources Memoir 25, p. 175–185.

Bird, K.J., 1988, Structure contour and isopach maps of the 

National Petroleum Reserve in Alaska, in Gryc, George, ed., 

Geology of the National Petroleum Reserve in Alaska, 1974 

to 1982: U.S. Geological Survey Professional Paper 1399, 

p. 355–377.

Brosgé, W.P., and Whittington, C.L., 1966, Geology of the 

Umiat-Maybe Creek region, Alaska: U.S. Geological 

Survey Professional Paper 303-H, p. 501–638.

Brouwers, E.M., Clemens, W.A., Spicer, R.A., Ager, T.A., 

Carter, L.D., and Sliter, W.V., 1987, Dinosaurs on the 

North Slope, Alaska; high latitude, latest Cretaceous 

environments: Science, v. 237, p. 1608–1610.

Chapman, R.M., Detterman, R.L., and Mangus, M.D., 1964, 

Geology of the Killik-Etivluk Rivers Region, Alaska: U.S. 

Geological Survey Professional Paper 303-F, p. 325–407.

Clemens, W.A., and Allison, C.W., 1985, Late Cretaceous 

terrestrial vertebrate fauna, North Slope, Alaska: Geological 

Society of America, Abstracts with Programs, v. 17, p. 548.

Davies, K.L., 1987, Duck-billed dinosaurs (Hadrosauridae; 

Ornithischia) from the North Slope of Alaska: Journal of 

Paleontology, v. 61, p. 198–200.

Decker, P.L., 2007, Brookian stratigraphic correlations, Umiat 

field to Milne Point field, west-central North Slope, Alaska: 

State of Alaska Department of Natural Resources, Division 

of Geological and Geophysical Surveys Preliminary 

Interpretive Report 2007-2, 19 p., 1 sheet.

Detterman, R.L., Bickel, R.S., and Gryc, George, 1963, 

Geology of the Chandler River region, Alaska: U.S. 

Geological Survey Professional Paper 303-E, p. 223–324.

Fassett, J.E., and Hinds, J.S., 1971, Geology and fuel 

resources of the Fruitland Formation and Kirkland Shale 

of the San Juan Basin, New Mexico and Colorado: U.S. 

Geological Survey Professional Paper 676, 76 p.

Flores, R.M., 2003, Paleocene paleogeographic, paleotectonic, 

and paleoclimatic patterns of the northern Rocky Mountains 

and Great Plains region, in Reynolds, R.G., and Flores, 

R.M., eds., Cenozoic systems of the Rocky Mountain 

region: The Rocky Mountain Section SEPM (Society for 

Sedimentary Geology), p. 63–106.

Flores, R.M., and Cross, T.A., 1991, Cretaceous and Tertiary 

coals of the Rocky Mountains and Great Plains regions, 

in Gluskoter, H.J., Rice, D.D., and Taylor, R.B., eds., 

Economic geology, U.S.: Boulder, Colo., Geological 

Society of America, The Geology of North America, v. P-2, 

p. 547–571.

Flores, R.M., Stricker, G.D., Decker, P.L., and Myers, M.D., 

2007, Sentinel Hill core test 1—facies descriptions and 

stratigraphic reinterpretations of the Prince Creek and 

Schrader Bluff Formations, North Slope, Alaska: U.S. 

Geological Survey Professional Paper 1747, 34 p.

Friend, P.F., 1983, Towards the field classification of alluvial 

architecture or sequence, in Collinson, J.D., and Lewin, 

J., eds., Modern and ancient fluvial systems: International 

Association of Sedimentologists, Blackwell Scientific 

Publications, Special Publication No. 6, p. 345–354.

Gryc, George, Patton, W.W., Jr., and Payne, T.G., 1951, 

Present Cretaceous stratigraphic nomenclature of northern 

Alaska: Washington Academy of Science Journal, v. 41, no. 

5, p. 159–167.

Houseknecht, D.W., 2003, Brookian stratigraphic plays in 

the National Petroleum Reserve, Alaska (NPRA): U.S. 

Geological Survey Open-File Report 03-039, 36 p., 20 

tables, 14 figs.

Houseknecht, D.W., and Schenk, C.J., 2005, Sedimentology 

and sequence stratigraphy of the Cretaceous Nanushuk, 

Seabee, and Tuluvak Formations exposed on Umiat 

Mountain, north-central Alaska, in Haeussler, P.J., and 

Galloway, J.P., eds., Studies by the U.S. Geological Survey 

in Alaska, 2004: U.S. Geological Survey Professional Paper 

1709-B, 18 p.

Mull, G.G., Houseknecht, D.W., and Bird, K.J., 2003, Revised 

Cretaceous and Tertiary stratigraphic nomenclature in the 

Colville Basin, northern Alaska: U.S. Geological Survey 

Professional Paper 1673, 36 p.

Nelms, L.G., 1989, Late Cretaceous dinosaurs from the North 

Slope of Alaska: Journal of Vertebrate Paleontology, v. 9, p. 

34A.

Phillips, R.L., 1988, Measured sections, paleoenvironments, 

and sample locations in the Prince Creek Formation near 

Ocean Point, Alaska: U.S. Geological Survey Open-File 

Report 88–40.

Phillips, R.L., 1989, Summary of Late Cretaceous 

environments near Ocean Point, North Slope, Alaska, in

Dover, J.H., and Galloway, J.P., eds., Geologic studies 

in Alaska by the U.S. Geological Survey, 1989: U.S. 

Geological Survey Bulletin 1946, p. 101–106.
Reading, H.G., 1978, Sedimentary environments and facies 

(2d ed.): London, Blackwell Scientific Publications, 615 p. 

Robinson, F.M., and Collins, F.R., 1959, Core test, Sentinel 

Hill area, and test well, Fish Creek area, Alaska: U.S. 

Geological Survey Professional Paper 305-I, p. 485–521.

Ryer, T.A., 1984, Transgressive-regressive cycles and the 

occurrence of coal in some Cretaceous strata of Utah, in

Rahmani, R.A., and Flores, R.M., eds., Sedimentology of 

coal and coal-bearing sequences: International Association 

of Sedimentologists Special Publication 7, p. 217–227.

Sable, E.G., and Stricker, G.D., 1987, Coal in the National 

Petroleum Reserve in Alaska (NPRA); Framework 

geology and resources, in Tailleur, I.L., and Weimer, R., 

eds., Alaskan North Slope geology: Society of Economic 

Paleontologists and Mineralogists and Alaska Geological 

Society, book 50, p. 195–216.

Sears, J.D., Hunt, C.B., and Hendricks, T.A., 1941, 

Transgressive and regressive Cretaceous deposits in 

southern San Juan Basin, New Mexico: U.S. Geological 

Survey Professional Paper 193-F, p. 110–121.

Smith, D.G., 1983, Anastomosed fluvial deposits—modern 

examples from Western Canada, in Collinson, J.D., and 

Lewin, J., eds., Modern and ancient fluvial systems: 

International Association of Sedimentologists, Blackwell 

Scientific Publications, Special Publication No. 6, p. 

155–168.

Steel, R.J., and Thompson, D.B., 1983, Structures and 

textures in Triassic braided stream conglomerates (‘Buntyer 

Pebble Beds’) in the Sherwood Sandstone Group, North 

Staffordshire, England: Sedimentology, v. 30, p. 341–367.

Stefansson, Karl, Thurrell, R.F., Jr., and Zumberge, J.H., 1947, 

Preliminary report on the stratigraphy and structure of the 

area of the Colville River north of Umiat, Naval Petroleum 

Reserve No. 4, Alaska: U.S. Geological Survey, NPR4 

Preliminary Report 13, 17 p., 2 sheets, scales 1:24,000 and 

1:95,400.

Stefansson, Karl, and Whittington, C.L., 1946, Preliminary 

report on stratigraphy and structure of the Umiat Anticline, 

Naval Petroleum Reserve No. 4, Alaska: U.S. Geological 

Survey, NPR4 Preliminary Report 6, 5 p., 3 sheets, scales 

1:2,400 and 1:24,000.

Wahrhaftig, Clyde, Bartsch-Winkler, Susan, and Stricker, 

G.D., 1994, Coal in Alaska, in Plafker, G., and Berg, H.C., 

eds., The geology of Alaska: Boulder, Colo., Geological 

Society of America, The Geology of North America, v. G-1, 

p. 937–978.

Weimer, R.J., 1960, Upper Cretaceous stratigraphy, Rocky 

Mountain area: American Association of Petroleum 

Geologists Bulletin, v. 44, p. 1–20.

Whittington, C.L., 1956, Revised stratigraphic nomenclature 

of Colville Group, in Gryc, George, and others, Mesozoic 

sequence in Colville River region, northern Alaska: 

American Association of Petroleum Geologists Bulletin, v. 

40, p. 244–253.

References Cited 45
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Romeo M. Flores and others—Stratigraphy and Facies of Cretaceous Schrader Bluff and Prince Creek Formations—Professional Paper 1748