Chapter PB

BIOSTRATIGRAPHY, POWDER RIVER BASIN

By D.J. Nichols

in U.S. Geological Survey Professional Paper 1625-A
PB-ii

Contents

Biostratigraphy....................................................................................................PB-1

References ..........................................................................................................PB-3

Figures

PB-1. Biostratigraphic reference sections in the Powder River Basin.

PB-2. Occurrences of Momipites and Caryapollenites pollen and the definition of

palynostratigraphic zones P1-P6.

PB-3. Coal zones and palynostratigraphy of the Paleocene in the Powder River

Basin.

PB-4. Summary of age data, Wyodak-Anderson coal zone, Powder River Basin.

PB-5. Distribution of biostratigraphically significant species in the upper part of

the Fort Union Formation.

PB-6. Biostratigraphically significant species of fossil pollen in the upper part of

the Fort Union Formation.

PB-7. Relative abundances of major groups of spores and pollen in WyodakAnderson coal.

PB-8. Ratio of relative abundances of selected pollen genera in Wyodak-Anderson

coal.
PB-1

BIOSTRATIGRAPHY

• The most common fossils in coal and coal-bearing rocks are pollen grains

and spores. Thus, biostratigraphy based on pollen and spores

(palynostratigraphy) has been used to determine the age of the coal beds

and coal zones in the Powder River Basin.

• Palynostratigraphy in the Powder River Basin ties reference sections (fig.

PB-1) in selected outcrops and cores to subsurface data. Such data are

used to correlate coal beds and coal zones.

• There are six palynostratigraphic zones (fig. PB-2) within the Paleocene

of the Powder River Basin, designated (from lowest to highest) P1 to P6,

which are defined by occurrences of certain species of fossil pollen.

• The principal coal zone being mined in the Powder River Basin is the

Wyodak-Anderson (fig. PB-3). This coal zone is within

palynostratigraphic Zones P5 and P6, in the upper part of the Paleocene.

• Palynostratigraphy reveals the areal distribution of coal deposits of late

Paleocene age in the Powder River Basin (fig. PB-4). These deposits,

which are all in palynostratigraphic Zones P5 and P6, are in the WyodakAnderson coal zone.
PB-2

• Palynostratigraphy in the Gillette coalfield makes use of core from a

USGS drill hole at the Black Thunder mine. Palynological samples from

this core have been analyzed in detail, and a palynological database has

been constructed from these data. Samples from other mines in the

coalfield supplement this database.

• These data and others from similar studies are the basis of detailed

correlations in the upper part of the Fort Union Formation (fig. PB-5)

within and beyond the Gillette coalfield.

• Samples from the mines in the Decker, Montana, area yield fossil pollen

that are characteristic of uppermost Paleocene Zone P6 (fig. PB-5). They

indicate that the Anderson-Dietz and Dietz coal beds in this area are

correlative with the upper part of the Wyodak-Anderson coal zone in the

Gillette area.

• Fossil pollen and spores (fig. PB-6) also can reveal much about the

composition of plant communities that inhabited ancient coal-forming

mires, and thus can contribute to studies on the origin of coal.

• Detailed analyses of occurrences and relative abundances of fossil spores

and pollen grains (fig. PB-7) in samples from Black Thunder core

BT558 (USGS locality D7141) support studies on the origin and nature

of the Wyodak-Anderson coal. Detailed analyses also help to refine the

palynostratigraphic zonation (fig. PB-8).
PB-3

REFERENCES

Nichols, D.J., 1994, Palynostratigraphic correlation of Paleocene rocks in

the Wind River, Bighorn, and Powder River basins, Wyoming, in

Flores, R.M., Mehring, K.T., Jones, R.W., and Beck, T.L., eds.,

Organics and the Rockies Field Guide: Wyoming State Geological

Survey Public Information Circular No. 33, p. 17-29.

_____ 1995, The role of palynology in paleoecological analyses of Tertiary

coals: International Journal of Coal Geology, v. 28, p. 139-159.

_____ 1996, Palynological zonation of the Paleocene of Rocky Mountain

intermontane basins [abs.]: Geological Society of America, 1996

Annual Meeting, Abstracts with Programs, v. 28, no. 7, p. 372.

Nichols, D.J., and Ott, H.L., 1978, Biostratigraphy and evolution of the

Momipites-Caryapollenites lineage in the early Tertiary in the Wind

River Basin, Wyoming: Palynology, v. 2, p. 93-112.

Pocknall, D.T., 1987, Palynomorph biozones for the Fort Union and

Wasatch Formations (upper Paleocene-lower Eocene), Powder River

Basin, Wyoming and Montana: Palynology, v. 11, p. 23-36.

Pocknall, D.T., and Nichols, D.J., 1996, Palynology of coal zones of the

Tongue River Member (upper Paleocene) of the Fort Union

Formation, Powder River Basin, Montana and Wyoming: American

Association of Stratigraphic Palynologists Contributions Series, No.

32, 58 p., 7 pls.
MONTANA

WYOMING

Figure PB-1. Biostratigraphic reference sections in the 

Powder River Basin.

6

2

3

5

Biostratigraphic age determination 

of the Wyodak-Anderson coal zone 

is based on palynologic analyses of 

samples from seven reference sections: 

 (1) two mines near Decker, Montana

 (2) cores and outcrop sections in the

 Powder River area 

 (3) outcrop sections in the TA Hills 

 area, south of Buffalo, Wyoming

 (4) core from the Big George coal bed

 (5) outcrops near Linch, Wyoming

 (6) core from the Black Thunder mine

 (7) the Dave Johnston mine near 

 Glenrock, Wyoming

1

4

7
Figure PB-2. Occurrences of Momipites and Caryapollenites 

pollen and the definition of palynostratigraphic zones P1-P6. 

L, M, and U designate lower, middle, and upper Paleocene.

P1

P2

P3

P4

P5

P6

U

M

L

M. inaequalis

M. leffingwellii

M. waltmanensis

M. wyomingensis

M. actinus

M. anellus

M. triorbicularis

M. ventifluminis

C. wodehousei

C. veripites
Tullock

Mbr

Lebo

Mbr

Tongue

River

Mbr

P1

P2

P3

P4

P5

Fort Union Formation

Figure PB-3. Coal zones and palynostratigraphy of the Paleocene 

in the Powder River Basin.

The palynostratigraphic zonation 

for the Powder River Basin is based 

on ranges of fossil pollen and spores 

composited from reference sections. 

These sections include outcrops and 

cores. The economically important 

deposits of the Wyodak-Anderson 

coal zone (uppermost three black 

lines in diagram) are in the upper 

Paleocene palynostratigraphic 

Zones P5 and P6. Other coal beds in

the Tongue River Member are in 

Zones P4 or P5.

P6

150

Meters
MONTANA

WYOMING

Figure PB-4. Summary of age data, Wyodak-Anderson coal zone,

Powder River Basin. 

P5-P6

P5-P6

P5-P6

P5-P6

Age determinations of the Wyodak-Anderson 

coal zone are based on palynologic analyses of 

samples from seven reference sections: 

 (A) two mines near Decker, Montana

 (B) cores and outcrop sections in the 

 Powder River area, Montana and Wyoming

 (C) outcrop sections in the TA Hills area

 (D) core from the Big George coal bed

 (E) outcrop sections near Linch, Wyoming

 (F) core from the Black Thunder mine

 (G) Dave Johnston mine near Glenrock, 

 Wyoming

P6

P5

A

B

C D

E F

G P6

Zones P5 and P6 are late Paleocene in age.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Figure PB-5. Distribution of biostratigraphically significant species 

in the upper part of the Fort Union Formation.

300

100

400

200

D6762, D6763

D6764, D6765

D6766-A, D6767

D6711-A, D6768, D6711-B

D6711-C, -D

D6709-A, -B, -C, -D, D6710-A

D6709-E, -F, -G

D6709-H, -I, -J, -K

D6708-A, -B

D6707-A, -E, -I, D6708-D

D6707-K, -M, -N

D6707-O, -Q, -T

D6707-U, -Z

D6711-E, -F

Smith

Anderson

Canyon

Wall

Pawnee

O'Dell

Local 2

Macklin...

Sawyer

P4

P5

P6

Blue numbers refer to 

names of species shown 

in the next graphic display.

Scale

(Meters)
Figure PB-6. Biostratigraphically significant species of fossil pollen 

in the upper part of the Fort Union Formation.

 1. Momipites ventifluminis

1. 

8. 

10. 

14. 

 2. Momipites wyomingensis

 3. Caryapollenites wodehousei

 4. Triatriopollenites granulatus

 5. Aquilapollenites spinulosus

 6. Polyatriopollenites vermontensis

 7. Caryapollenites inelegans

 8. Caryapollenites veripites

 9. Tilia vescipites

10. Insulapollenites rugulatus

11. Talisiipites pulvifluminus

12. Alnipollenites scoticus

13. Periporopollenites sp.

14. Pistillipollenites mcgregorii

15. Paraalnipollenites sp. cf. P. confusus

illustrations of 

selected specimens
0 20 40 60 80 100%

Sample numbers in Core BT558 (D7141)

Figure PB-7. Relative abundances of major groups of spores 

and pollen in Wyodak-Anderson coal.

Fern spores

Conifer pollen

Angiosperm pollen

As indicated by the abundance 

of pollen, conifers (trees of the 

family Taxodiaceae) were the 

most common kind of plant that 

contributed to development of 

this coal bed, which is 70 ft thick

in USGS core BT558.

1

2

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35
Sample numbers in Core BT558 (D7141)

Figure PB-8. Ratio of relative abundances of selected pollen genera 

in Wyodak-Anderson coal.

Detailed palynostratigraphic 

zonation of the interval is 

possible on the basis of the 

ratio between kinds of fossil 

pollen present in the coal. 

The ratio of the total number 

of specimens of all species 

of the genus Momipites to that 

of specimens of all species of 

the genus Caryapollenites is 

consistently less than 1.0 in 

uppermost Paleocene Zone P6.

These data can be used to place 

the Zone P5-P6 boundary.

0 0.5 1.0 1.5 2.0 2.5 3.0

P6

P5

1

2

9

10

11

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

Ratio of Momipites to Caryapollenites