Chapter BI BIOSTRATIGRAPHIC FRAMEWORK - USGS · BI-1 Chapter BI BIOSTRATIGRAPHIC FRAMEWORK by C....
Transcript of Chapter BI BIOSTRATIGRAPHIC FRAMEWORK - USGS · BI-1 Chapter BI BIOSTRATIGRAPHIC FRAMEWORK by C....
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.
BI-2
TABLE OF CONTENTS
BIOSTRATIGRAPHIC INTERPRETATIONSGeneral FrameworkProblems of Interpretion
PALEOENVIRONMENTAL INTERPRETATIONSREFERENCES
PLATESBI1 Biostratigraphy from Micropaleo Consultants and Bujak DaviesBI2 Composite Biostratigraphy
BI-3
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.
BI-6
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