BI-1

Chapter BI

BIOSTRATIGRAPHIC FRAMEWORK

by C. Wylie Poag1

in The Oil and Gas Resource Potential of the 1002 Area, Arctic NationalWildlife Refuge, Alaska, by ANWR Assessment Team, U.S. GeologicalSurvey Open File Report 98-34.

1999

1 U.S. Geological Survey, Woods Hole, MA 02543

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorialstandards (or with the North American Stratigraphic Code). Use of trade, product, or firm names is fordescriptive purposes only and does not imply endorsement by the U. S. Geological Survey.

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TABLE OF CONTENTS

BIOSTRATIGRAPHIC INTERPRETATIONSGeneral FrameworkProblems of Interpretion

PALEOENVIRONMENTAL INTERPRETATIONSREFERENCES

PLATESBI1 Biostratigraphy from Micropaleo Consultants and Bujak DaviesBI2 Composite Biostratigraphy

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BIOSTRATIGRAPHIC INTERPRETATIONS

General Framework

The biostratigraphic framework used in this report is derived from publicyavailable reports prepared by two private consultant companies: MicropaleoConsultants, Inc. (formerly known as BioStratigraphics) and the BujakDavies Group. These two competing companies analyzed different groupsof microfossils for their interpretations. Micropaleo Consultants usedbenthic foraminifera and palynomorphs (1983, 1984, 1988, 1989, 1991,1992, 1993a, b, c); Bujak Davies used only palynomorphs (1985; see alsoPaul, 1994) . The companies reached quite divergent interpretations ofseveral wells, including the East Mikkelsen Bay State-1, West Staines -1,Alaska State A-1, and Aurora (Plates BI1, BI2). The differences are mostpronounced in the Aurora well, in which Micropaleo Consultants (1988)recognized 11,260 ft of Eocene or probable Eocene section (Plate BI1-A),whereas the Bujak Davies Group recognized only about a third as muchEocene (4,810 ft; Plate BI1-B). Similar differences can be seen in theinterpretations of Cenozoic strata in the other three wells analyzed by bothgroups. In particular, the Bujak Davies Group defined upper and lowerOligocene sections, whereas Micropaleo Consultants did not clearly separatethe Oligocene from the Miocene. Furthermore, in the East Mikkelsen BayState-1 well, there is a 4,100 ft difference in the placement of theCretaceous-Tertiary contact. Micropaleo Consultants placed it at 12,400(Plate BI1-A); Bujak Davies placed it at 8,300 ft (Plate BI1-B).

For this report, I use a composite biostratigraphy (Plate BI2). I apply theinterpretations of the Bujak Davies Group where available (East MikkelsenBay State-1, West Staines-1, Alaska State A-1, Aurora), in part, becausethey subdivided the Cenozoic section more completely than did MicropaleoConsultants. The other wells are correlated using Micropaleo Consultants’data, but I arbitrarily divided some of their undivided sections intoapproximately equal parts (Plate BI2).

In the Belcher well, Micropaleo Consultants placed the Eocene/Paleoceneboundary somewhere within the interval 7900-10,640 ft. I have furtherconstrained the boundary interval to 7900-8780 ft based on the consistentoccurrences of the pollen taxon Paraalnipollenites confusus below 8780 ft(Norman O. Frederiksen, written comm., 1997).

BI-4

Problems of Interpretion

Drastic divergences in the placement of stratigraphic boundaries, especiallynotable in the Aurora well (Plate BI1), arise from a variety of correlationproblems, due to both natural and drilling-related causes. A primary drilling-related problem is the necessity of using mainly rotary ditch samples. Suchsamples are composites, representing 10-30-ft intervals (or more), and aresubject to extensive contamination from downhole caving. In situ coresamples are sparse and widely spaced in most wells.

Another drilling-related problem is the occasional use of lignitic drilling mud,which contains palynomorphs abundant enough to mask the in situ flora.Paul (1994) cites this as a problem in the Aurora well. Even sidewall coresare subject to contamination from drilling mud that may contain its ownpalynoflora, or may entrain microfossils from other parts of the well bore(e.g., Micropaleo Consultants, 1988).

A notable natural problem encountered in nearly all the cited wells is thepresence of large numbers of specimens interpreted to be reworked fromolder strata. For example, Mesozoic foraminifera are abundant in theMiocene, Oligocene, and early Paleocene sections of the Aurora well (PlateBI2). In the Wild Weasel and Kuvlum -2 wells, abundant Eocene dynocystsare present in the early Oligocene section. The latter occurrences areparticularly difficult to interpret, because the “reworked” specimens arevery close in age to the section into which they were reworked. Thedilemma in these examples is whether the Eocene taxa have been reworkedinto the Oligocene section, or the Oligocene taxa have fallen down the borehole into the Eocene section. Furthermore, if no cores are available forsuch a section (as is the case in several of the wells studied), it is nearlyimpossible to determine whether any of the microfossils are actually inplace. Paul (1994) and the Bujak Davies Group (1985) discuss theseproblems more thoroughly and cite specific well examples.

Another fundamental natural problem is the difficulty of correlating high-latitude microfossil assemblages with their low-latitude counterparts, whichgenerally are used as standard references. For example, the dominantlyagglutinated benthic foraminiferal assemblages characteristic of so much ofthe Alaskan section, are extremely difficult to correlate with standardbiostratigraphic sections developed in low latitudes using planktoniccalcareous taxa. Marine dinocyst zonations also were originally developed

BI-5

from low-latitude sections, and are difficult to apply in high latitudes.Moreover, because the biogeographic distribution of the parent plants ofspore and pollen taxa are controlled by paleoclimate, the stratigraphic rangesof these taxa also vary between different paleolatitudes.

In short, because of the myriad natural and drilling-related correlationproblems inherent to the wells cited herein, the biostratigraphic frameworkmust be considered tentative; it may be subject to considerable revision asnew data become available.

PALEOENVIRONMENTAL INTERPRETATIONS

Paleoenvironmental interpretations given in this report (Plate BI2) arederived entirely from the reports of Micropaleo Consultants, Inc. Theinterpretations are based principally on the presence (or absence) andrelative abundance of benthic foraminiferal species, and upon the ratio ofmarine microfossils (benthic foraminifera, dinoflagellates, molluskfragments, fish skeletal debris, marine diatoms, marine ostracods, spongespicules) to nonmarine taxa (spores, pollen, nonmarine ostracods). TheBujak Davies Group (1985), which relied entirely on palynology, providedbroad paleoenvironmental interpretations based mainly on the presence-absence of marine taxa and on kerogen type. Their interpretations generallyagree with those of Micropaleo Consultants.

Paleoenvironmental terminology used on Plate BI2 is very broadly definedby Micropaleo Consultants, Inc; the terms are relative, not strictly equatedto specific water depths. Neritic means essentially continental-shelf ordeltaic environments; bathyal means continental-slope, prodelta, or starvedbasin (far from sediment source) environments. In many sections, onlygross approximations of paleodepth are given. A notable example is themiddle to early Miocene section of the Galahad well, in which thepaleodepth estimate is inner neritic to bathyal.

Mesozoic sections accumulated in deeper water than Cenozoic sectionsthroughout the study area, except for the Aurora well. In Cenozoic strata,Paleocene and Eocene sections tend to be deeper-water deposits thanOligocene-Pliocene sections at onshore locations (Canning River and WestStaines wells). At the easternmost offshore locations (Aurora, Belcher),however, Oligocene and Miocene paleodepths equaled or exceeded most ofthe Eocene and Paleocene paleodepths.

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REFERENCES

BioStratigraphics, 1983, Biostratigraphic Analysis, EXXON Canning RiverB-1 Well, North Slope, Alaska: Consultants Report, 20 p.

Bujak Davies Group, 1985, Palynology of Mobil West Staines # 1 andExxon Alaska State A-1, Alaska North Slope: Consultants Report, 52 p.

Micropaleo Consultants, Inc., 1984, Biostratigraphic Analysis, Mobil WestStaines State # 2, North Slope, Alaska: Consultants Report, 18 p.

Micropaleo Consultants, Inc., 1988, Biostratigraphic Analysis, TennecoOCS-Y-0943 # 1 (Aurora) Well, Beaufort Sea, Alaska: ConsultantsReport, 29 p.

Micropaleo Consultants, Inc., 1989, Biostratigraphic Analysis, Amoco OCS-Y-0917 # 1 (Belcher) Tract 724, Beaufort Sea, Alaska: ConsultantsReport, 20 p.

Micropaleo Consultants, Inc., 1991, Biostratigraphic Analysis, OCS-Y-1092# 1 (Galahad) Well, Beaufort Sea, Alaska: Consultants Report, 24p.

Micropaleo Consultants, Inc., 1992, Biostratigraphic Analysis, ARCO OCS-Y-0866 # 1 (Kuvlum) Well, Beaufort Sea, Alaska: Consultants Report,19 p.

Micropaleo Consultants, Inc., 1993, Biostratigraphic Analysis, ARCO OCS-Y-0865 # 1 (Kuvlum # 2) Well, Beaufort Sea, Alaska: ConsultantsReport, 24 p.

Micropaleo Consultants, Inc., 1993, Biostratigraphic Analysis, ARCO OCS-Y-0866 # 2 (Kuvlum # 3) Well, Beaufort Sea, Alaska: ConsultantsReport, 20 p.

Micropaleo Consultants, Inc., 1993, Biostratigraphic Analysis, ARCO OCS-Y-1597 # 1 (Wild Weasel) Well, Beaufort Sea, Alaska: ConsultantsReport, 20 p.

BI-7

Paul, Lawrence E., ed., 1994, Geological, Geochemical, and OperationalSummary, Aurora Well, OCS y-0943-1, Beaufort Sea, Alaska: MineralsManagement Service, OCS Report MMS 94-0001, 71 p.

U.S. Department of the InteriorOpen File Report 98-34U.S. Geological SurveyPlate BI1By C. Wylie Poag

A

B

10000

12000

0

2000

4000

14000

16000

18000

8000

6000

MICROPALEO CONSULTANTS

2,340

13,600

14,93015,480

17,473

18,130

270

Miocene

Oligocene to

Paleocene

PaleoceneEocene -

Lo

we

r C

reta

ceo

us

UpperJurassicE.-M. Jur.?

Ab

un

da

nt

rew

ork

ed

Me

sozo

ic

fora

ms

be

low

th

is le

vel

Aurora E. Mikkelsen Bay St-1

W. Staines - 1

800

3,500

5,750

7,750

12,500

13,000

Canning River-B-1

7,490

1,340

800

6,070

7,7307,8507,9708,370

10,803

ProbableTertiaryUndiff.

?

Paleocene

Maestr.-

Campanian

Sant.-Turon.Cenomanian - Albian

Barr.-HautUndifferentiated

No

Samples

15,205

7,200

5,550

3,750

12,400

Pliocene

and

Miocene

Miocene

and

Oligocene

Eocene

Paleocene

Cretaceous and Older

Kuvlum-2

11,125

1,030

1,590

LateMiocene?

2,460

Middle to Early Miocene

3,540

Early Miocene

5,820

LateOligocene

8,820

EarlyOligocene

Galahad

550460

700

1,690

5,230

9,238

Pleist.-Pliocene LatePliocene

EarlyPliocene

?Late?Miocene

Middle to EarlyMiocene

Wild Weasel

1,020

1,770

2,790

3,930

5,910

8,720

9,314

E. Plio. toL. Mio.

Middle to EarlyMiocene

EarlyMiocene

LateOligocene

EarlyOligocene

?EarlyOligocene?

12,910

W. Staines - 2

12,990

12,760

11,985

7,790

5,850

3,420

2,120

811

Tertiary Undiff.

E. Plio. toM. Mio.

Miocene to ProbableOligocene

Eocene

Paleocene

Maast.-Campan.

Sant.-Cenom.Haut.-Barrem.

Alb.

Alaska St-A-1

12,964

11,000

7,000

4,750

Pliocene andMiocene

Miocene and

Eocene

?Paleocene ?

Pre- Miss.

13,500

?

18,325

Eo

ce

ne

din

ocysts

? EarlyOligocene ?

Cha

nnel

d

epos

its? G

rowt

h-fa

ult

d

epos

its?

PALEOCENE

Eo

ce

ne

din

ocysts

7,100

7,700

10,400

LateEocene

EarlyEocene

12,085

Prob. EarlyEocene

10,580

4,642

Rewo

rked M

esoz

oic fo

rms

13,32913,171

14,206

Pre-Miss.

MiddleEocene

JURASSIC

EOCENE

MIOCENE

CRETACEOUS

OLIGOCENE

Dril

l

D

epth

in

F

eet

13,150

Miocene

Late andMiddleEocene

EarlyEocene

Paleocene

1150

1630

2050

4690

7900

10640?

Paleocene

Early Eocene to Late

Belcher

E. Mikkelsen Bay St-1

10000

12000

0

2000

4000

14000

16000

18000

8000

6000

Dril

l

Dep

th

in

Fee

t

BUJAK DAVIES 15,480

17,473

18,130

300

Lo

we

r C

reta

ceo

us

UpperJurassicE.-M. Jur.?

Abundant re

work

ed M

eso

zoic

fora

ms

belo

w this

leve

l

Aurora W. Staines - 1

13,329

900

4,980

7,860

12,450

13,126

15,205

7,200

5,420

3,750

12,400

Miocene

L. to E.Oligocene

MiddleEocene

Carbonif.

Alaska St-A-1

14,206

12,946

10,600

5,260

Miocene

Late to EarlyOligocene

LateEocene

LatePaleocene Pre-Miss.

Pre- Miss.

13,500

?

18,325

2,550

1,180

Pleistocene

to

Pliocene

2,620

EarlyOligocene

6,340

8,000

MiddleEocene

12,300

Pleistocene

to

Pliocene

1,860Miocene

4,260 EarlyOligocene

6,420

LateEocene

Middle to Early Eocene

10,620

Late Paleocene

Early Paleocene

E. Camp.-

Barremian

750880Pliocene

4,460

EarlyOligocene

Late

Eocene

EarlyEocene

6,600

Paleocene

8,3008,600E. Maast.

8,900E. Camp.

9,600

11,400

?

Possible LateSantonian

11,900 Late Santonian

12,100Con.-Tur.L. Aptian

1,650

4,680

5,850

7,360

L. Eo. &

Olig. C

avings

10,720

LateEocene

MiddleEocene

EarlyEocene

LatePaleocene

EarlyPaleocene

LateOligocene

Miocene

EarlyOligocene

MIOCENE

OLIGOCENE

EOCENE

PALEOCENE

CRETACEOUSJURASSIC

Late to EarlyOligocene

EarlyEocene

Belcher

Aurora

Galahad

Wild Weasel

Kuvlum 1, 3

Alaska St-A-1

W. Staines 1

W Staines 2

Canning R. B-1

E. Mikkelsen Bay St-1

Kuvlum 2

ANWR

0 30

miles

1002

U.S. Department of the InteriorOpen File Report 98-34U.S. Geological SurveyPlate BI2By C. Wylie Poag

10000

12000

0

2000

4000

14000

16000

18000

8000

6000

2,550

15,480

17,473

18,130

270

Miocene

Oligocene

Early

Paleocene

LatePaleocene

Low

er

Cre

tace

ous

UpperJurassicE.-M. Jur.?

Abundant re

work

ed M

eso

zoic

fora

ms

Aurora Belcher W. Staines

1

13,329

900

4,260

6,420

7,860

12,450

13,126

Canning River

B-1

7,490

1,340

800

6,070

7,7307,8507,970

8,370

10,803

ProbableTertiaryUndiff.

?

Paleocene

Maestr.-

Campanian

Sant.-Turon.Cenomanian - Albian

Barr.-HautUndifferentiated

Interval

not

Examined

15,205

7,200

5,420

3,750

12,400

Miocene

L. to E.

Oligocene

MiddleEocene

Paleocene

Carbonif.

Kuvlum 2

11,125

1,030

1,590

LateMiocene?

2,460

Middle to Early Miocene

3,540

Early Miocene

5,820

LateOligocene

8,820

EarlyOligocene

Galahad

550460

700

1,690

5,230

9,238

Pleist.-Pliocene LatePliocene

EarlyPliocene

?Late?Miocene

Middle to EarlyMiocene

Wild Weasel

1,020

1,770

2,790

3,930

5,910

8,720

9,314

E. Plio. toL. Mio. Middle to EarlyMiocene

EarlyMiocene

LateOligocene

EarlyOligocene

?EarlyOligocene?

12,910

W. Staines 2

13,17112,990

12,760

11,985

7,790

5,850

3,420

2,120

811

Tertiary Undiff.

E. Plio. toM. Mio.

Miocene to ProbableOligocene

Eocene

Paleocene

Maast.-Campan.Sant.-Cenom.Haut.-Barrem.

Alb.

Alaska St. A-1

14,206

12,964

6,340

Pliocene

Miocene

LateEocene

LatePaleocene Pre-Miss.

Pre- Miss.

13,500

18,325

Eocene d

inocysts

? EarlyOligocene ?

Eocene d

inocysts

7,100

7,700

10,400

LateEocene

EarlyEocene

10,720

4,680

Rew

ork

ed M

eso

zoic

taxa

MiddleEocene

Dril

l

D

epth

in

F

eet

Nonmarine

Marginal marine

Inner neritic

Middle neritic

Outer neritic

Bathyal

CRETACEOUS

PALEOCENE

EOCENE

OLIGOCENE

MIOCENE

7,360

5,850

OligoceneEarly

Late

Pleistoceneto

1,180

2,620

5,260

Late to EarlyOligocene

EarlyOligocene

8,000

10,600

MiddleEocene

12,300

EarlyEocene

Pleistocene toPliocene

1,860

Miocene

4,980

Late to EarlyOligocene

EarlyOligocene

LateEocene

Middle to EarlyEocene

10,620

LatePaleocene

EarlyPaleocene

750880Pliocene

Early Oligocene

6,600 EarlyEocene

8,3008,6008,900

9,600

11,400

11,90012,100

E. Maast.E. Camp.

?

Possible LateSantonian

Late SantonianCon.-Turon.Late Apt.

LateEocene

Jurassic

COMPOSITE BIOSTRATIGRAPHY

E. Mikkelsen

Bay

St.-1

1,650

Aurora

Galahad

Wild Weasel

Kuvlum 1, 3

Alaska St-A-1

W. Staines 1

W Staines 2

Canning R. B-1

E. Mikkelsen Bay St-1

Kuvlum 2

ANWR

0 30

miles

1002

Belcher

1150

13,150

2050

4690

7900

8780

Boundary interval by Frederiksen 1997

Star indicates biostratigraphy derived from Bujak Davies Group. All other biostratigraphy from Micropaleo� Consultants, Inc.�Paleoenvironments are generalized estimates derived from Micropaleo Consultants, Inc., based on analysis of � benthic formainifera, dinoflagellates, and spores/pollen.

Late andMiddleEocene

EarlyEocene

Paleocene

1630Miocene

10640?

?Paleoenvironments

Exte

nsiv

e r

ew

ork

ing a

nd c

avin

g

Rew

orke

d M

esoz

oic

fora

ms