Chapter WB

BIOSTRATIGRAPHY, WILLISTON BASIN

By D.J. Nichols

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

Contents

Biostratigraphy...................................................................................................WB-1

References .........................................................................................................WB-3

Figures

WB-1. Biostratigraphic reference sections in the Williston Basin.

WB-2. Occurrences of Momipites and Caryapollenites pollen and the

definition of palynostratigraphic zones P1-P6.

WB-3. Palynostratigraphic zones of the Paleocene in the Williston Basin

composite reference section.

WB-4. Distribution of biostratigraphically significant species in the Ludlow

Member.

WB-5. Biostratigraphically significant species of fossil pollen in the Ludlow

Member.

WB-6. Distribution of biostratigraphically significant species in the Tongue

River Member.

WB-7. Biostratigraphically significant species of fossil pollen in the Tongue

River Member.

WB-8. Distribution of biostratigraphically significant species in the BeulahZap seam and Schoolhouse rider, Sentinel Butte Member.

WB-9. Biostratigraphically significant species of fossil pollen in the Sentinel

Butte Member.
WB-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 Williston Basin.

• Palynostratigraphy in the Williston Basin ties reference sections (fig.

WB-1) in selected outcrops and mines to subsurface data for correlation

of coal-bearing intervals.

• Detailed analyses of occurrences and relative abundances of more than

100 taxa of fossil spores and pollen grains in about 70 samples from the

reference sections were summarized and simplified to produce a practical

palynological zonation.

• The zonation is based on 30 key taxa ranging through 500 m (about 1,650

ft) of composite stratigraphic section. Five of the six known Paleocene

palynostratigraphic zones (fig. WB-2) have been identified in this

interval, which includes the Ludlow, Tongue River, and Sentinel Butte

Members of the Fort Union Formation.

• The principal coal zones (fig. WB-3) in the Williston Basin are the

Hansen, Harmon, Hagel, and Beulah-Zap. These coal zones lie within

palynostratigraphic Zones P3 through P5, in the middle to upper part of

the Paleocene.
WB-2

• Key coal beds in the Ludlow Member (fig. WB-4) in the Williston Basin

have been placed within the palynostratigraphic zonation. The

assemblage of fossil pollen that characterizes the Ludlow (fig. WB-5) is

typical of the lower and middle Paleocene. These data contribute to the

framework for correlation of all coal-bearing rocks in the basin.

• Key coal beds in the Tongue River Member (fig. WB-6) in the Williston

Basin also have been placed within the palynostratigraphic zonation. The

assemblage of fossil pollen that characterizes the Tongue River Member

(fig. WB-7) is typical of the middle and upper Paleocene. These data also

contribute to the framework for correlation of all coal-bearing rocks in

the basin.

• Key coal beds in the Sentinel Butte Member (fig. WB-8) in the Williston

Basin have been placed within the palynostratigraphic zonation. The

assemblage of fossil pollen that characterizes the Sentinel Butte Member

(fig. WB-9) is typical of the upper Paleocene. These data similarly

contribute to the framework for correlation of all coal-bearing rocks in

the basin.
WB-3

REFERENCES

Nichols, D.J., 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.

_____ 1998, Palynostratigraphy of the Fort Union Formation (Paleocene) in

the North Dakota part of the Williston basin and its application to coal

resource assessment [abs.]: Geological Society of America, 1998

Annual Meeting, Abstracts with Programs, v. 30, no. 7, p. 366.

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.

Warwick, P.D., Flores, R.M., Nichols, D.J., Murphy, E.C., and Obradovich,

J.D., 1997, Fort Union chronostratigraphic and depositional

sequences, Williston Basin, North Dakota, South Dakota, and

Montana [abs.]: Geological Society of America, 1997 Annual

Meeting, Abstracts with Programs, v. 29, no. 6, p. 204.
Figure WB-1. Biostratigraphic reference sections in the 

Williston Basin.

Biostratigraphic zonation of the 

Paleocene in the Williston Basin 

is based on palynologic analyses 

of samples from reference sections 

in southwestern North Dakota: 

(1) Pretty Butte, (2) Little Missouri 

River, (3) Rabbit Ears area, and 

(4) Medora West; and from (5) the 

BNI mine near Center and (6) the 

Coteau mine near Beulah, N. D.

NORTH

DAKOTA

MONTANA

1

2

3

4

6

5
Figure WB-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
Ludlow

Mbr

Tongue

River

Mbr

Sentinel

Butte

Mbr

T-Cross

Harmon

Hansen

HT Butte

Beulah-Zap

P1

P2

P3

P4

P5

Fort Union Formation

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

in the Williston Basin composite reference section.

The palynostratigraphic zonation

is based on ranges of 30 species 

of fossil pollen. The composite 

stratigraphic section includes 500 m 

(about 1650 ft) of coal-bearing 

Paleocene rocks in western North 

Dakota (uppermost Paleocene rocks

in Zone P6 were not sampled). 

Positions of key coal beds in the 

composite section are shown.

Hagel

50 m
Figure WB-4. Distribution of biostratigraphically significant species

in the Ludlow Member.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

P1

P2

P3

Blue numbers refer to 

names of species shown 

in the next graphic display.

150 m

100 m

50 m
 1. Kurtzipites trispissatus

 2. Kurtzipites circularis

 3. Momipites inaequalis

 4. Wodehouseia spinata

 5. Aquilapollenites reticulatus

 6. Discoidites parvistriatus

 7. Momipites tenuipolus

 8. Wodehouseia fimbriata

 9. Triatriopollenites granulatus

10. Momipites leffingwellii

11. Momipites triorbicularis

12. Momipites waltmanensis

13. Insulapollenites rugulatus

14. Momipites anellus

15. Momipites ventifluminis

Figure WB-5. Biostratigraphically significant species of fossil pollen 

from the Ludlow Member.

7.

10.

15.

illustrations of 

selected specimens
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

P3

P4

P5

150 m

100 m

50 m

Blue numbers refer to 

names of species shown 

in the next graphic display.

Figure WB-6. Distribution of biostratigraphically significant species

in the Tongue River Member.
 1. Momipites leffingwellii

 2. Momipites triorbicularis

 3. Insulapollenites rugulatus

 4. Momipites anellus

 5. Momipites ventifluminis

 6. Caryapollenites prodromus

 7. Momipites actinus

 8. Momipites leboensis

 9. Momipites wyomingensis

10. Aquilapollenites spinulosus

11. Tilia vescipites

12. Caryapollenites wodehousei

13. Caryapollenites veripites

14. Pistillipollenites mcgregorii

15. Pseudoplicapollis sp.

3.

10.

12.

Figure WB-7. Biostratigraphically significant species of fossil pollen 

from the Tongue River Member.

illustrations of 

selected specimens
Figure WB-8. Distribution of biostratigraphically significant species 

in the Beulah-Zap seam and Schoolhouse rider, Sentinel Butte Member.

Blue numbers refer to names of species shown in the next graphic display, 

where some specimens are illustrated.

Schoolhouse

"interburden"

Beulah-Zap

Beulah-Zap

Beulah-Zap

1 2 3 4 5 6 7 8 9 10

Zone

P5
Figure WB-9. Biostratigraphically significant species of fossil pollen 

from the Sentinel Butte Member.

 1. Insulapollenites rugulatus

 2. Momipites anellus

 3. Momipites ventifluminis

 4. Alnipollenites scoticus

 5. Momipites amplus

 6. Momipites wyomingensis

 7. Momipites rotundus

 8. Caryapopollenites wodehousei

 9. Caryapollenites veripites

10. Pistillipollenites mcgregorii

4.

9.

10.

illustrations of 

selected specimens