Chapter WF

FRAMEWORK GEOLOGY OF FORT UNION COAL IN

THE WILLISTON BASIN

By R.M. Flores,1 C.W. Keighin,1 A.M. Ochs,2 P.D. Warwick,1

L.R. Bader,1 and E.C. Murphy3

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

1

U.S. Geological Survey

2

Consultant, U.S. Geological Survey, Denver, Colorado

3

North Dakota Geological Survey, Bismarck, North Dakota
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Contents

Structural Setting...............................................................................................................WF-1

Stratigraphic Setting.........................................................................................................WF-1

Depositional Setting.........................................................................................................WF-2

Coal Quality.......................................................................................................................WF-3

Stratigraphy and Depositional Environments of Coal Units and

Associated Rocks..............................................................................................................WF-3

Stratigraphy..................................................................................................................WF-3

Depositional Environments......................................................................................WF-4

Bowman-Dickinson Coalfield, Harmon-Hansen coal zone...................................WF-6

Distribution ..................................................................................................................WF-6

Stratigraphic Framework ..........................................................................................WF-7

Harmon and Hansen Coal Zones Interpretive Cross Section A-A’.........WF-8

Harmon and Hansen Coal Zones Interpretive Cross Section B-B’..........WF-9

Harmon and Hansen Coal Zones Interpretive Cross Section C-C’.......WF-10

Harmon and Hansen Coal Zones Interpretive Cross Section D-D’......WF-11

Center-Falkirk Coalfield, Hagel Coal Zone.............................................................WF-13

Distribution ...............................................................................................................WF-13

Stratigraphic Framework .......................................................................................WF-13

Hagel Coal Zone Interpretive Cross Section A-A’....................................WF-14

Hagel Coal Zone Interpretive Cross Section B-B’.....................................WF-15

Hagel Coal Zone Interpretive Cross Section C-C’.....................................WF-16

Hagel Coal Zone Interpretive Cross Section D-D’....................................WF-17
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Contents—Continued

Beulah Coalfield, Beulah-Zap Coal Zone................................................................WF-17

Distribution ...............................................................................................................WF-17

Stratigraphic Framework .......................................................................................WF-18

Beulah-Zap Coal Zone Interpretive Cross Section E-E’..........................WF-19

Beulah-Zap Coal Zone Interpretive Cross Section F-F’ ..........................WF-20

Beulah-Zap Coal Zone Interpretive Cross Section G-G’.........................WF-21

Beulah-Zap Coal Zone Interpretive Cross Section H-H’.........................WF-22

References.......................................................................................................................WF-24

Figures

WF-1. Location map showing the Williston Basin.

WF-2. Composite stratigraphic section for the assessment region showing the

studied coal beds and zones with age relationships based on palynology.

Assessment units in the Williston Basin are highlighted in red.

WF-3. Composite correlation of Paleocene sections based on palynostratigraphy.

WF-4. The Harmon and Hansen coal beds and zones in the lower part of the picture

are exposed along the valley wall of the Little Missouri River. The coal beds

and zones are overlain by fluvial deposits.

WF-5. The Rhame bed in the lower part of the picture is exposed along the valley

wall of the Little Missouri River. This paleosol is overlain by the Harmon

and Hansen coal beds and zones.

WF-6. The Harmon coal zone is overlain by fluvial channel sandstone in the

Gascoyne mine.

WF-7. The Beulah-Zap coal zone in the Freedom mine is overlain by mudstone.
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Figures—Continued

WF-8. The Beulah-Zap coal zone in the Freedom mine is overlain by a thin rider

coal and mudstone.

WF-9. Thin, trough-crossbedded, fluvial channel sandstone overlies the BeulahZap coal zone in the Freedom mine.

WF-10. The fluvial sandstone shows a deep erosional base (see hammer for scale

in the photo).

WF-11. Thick, fluvial channel sandstone overlies the Beulah-Zap coal zone in the

Freedom mine.

WF-12. Bowman-Dickinson coalfield, Williston Basin, North Dakota, and

generalized interpretive cross-section layout.

WF-13. Harmon and Hansen coal zones interpretive cross section A-A’, BowmanDickinson coalfield, Williston Basin, North Dakota.

WF-14. Lower Mississippi River delta plain in Louisiana showing subdeltas and

swamps.

WF-15. Crevasse splay and associated swamps in the lower Mississippi River delta

plain, Louisiana.

WF-16. Peat swamp in the upper Mississippi River delta plain, Louisiana.

WF-17. Abandoned river channel and peat swamp in the Florida Everglades,

Florida.

WF-18. Harmon and Hansen coal zones interpretive cross section B-B’, BowmanDickinson coalfield, Williston Basin, North Dakota.

WF-19. Contemporaneous delta plain swamps and river channel in the lower

Mississippi River delta plain, Louisiana.

WF-20. Harmon and Hansen coal zones interpretive cross section C-C’, BowmanDickinson coalfield, Williston Basin, North Dakota.
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Figures—Continued

WF-21. Lake, floodplain, and swamp environments associated with the Beluga

River in Alaska.

WF-22. Harmon and Hansen coal zones interpretive cross section D-D’, BowmanDickinson coalfield, Williston Basin, North Dakota.

WF-23. Center-Falkirk coalfield, Williston Basin, North Dakota, and generalized

interpretive cross-section layout.

WF-24. Hagel coal zone interpretive cross section A-A’, Center-Falkirk coalfield,

Williston Basin, North Dakota.

WF-25. Interdistributary swamps and floodplains in the upper Mississippi River

delta plain, Louisiana.

WF-26. Hagel coal zone interpretive cross section B-B’, Center-Falkirk coalfield,

Williston Basin, North Dakota.

WF-27. Interdistributary channel in the upper Mississippi River delta plain.

Louisiana.

WF-28. Hagel coal zone interpretive cross section C-C’, Center-Falkirk coalfield,

Williston Basin, North Dakota.

WF-29. Hagel coal zone interpretive cross section D-D’, Center-Falkirk coalfield,

Williston Basin, North Dakota.

WF-30. Beulah coalfield, Williston Basin, North Dakota, and generalized

interpretive cross-section layout.

WF-31. Beulah-Zap coal zone interpretive cross section E-E’, Beulah coalfield,

Williston Basin, North Dakota.

WF-32. Interchannel swamps and floodplains in the South Carolina coastal plain.

WF-33. Crevasse splays and swamps in the lower Mississippi River delta plain,

Louisiana.
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Figures—Continued

WF-34. Beulah-Zap coal zone interpretive cross section F-F’, Beulah coalfield,

Williston Basin, North Dakota.

WF-35. Peat deposit in the Florida Everglades.

WF-36. Beulah-Zap coal zone interpretive cross section G-G’, Beulah coalfield,

Williston Basin, North Dakota.

WF-37. Beulah-Zap coal zone interpretive cross section H-H’, Beulah coalfield,

Williston Basin, North Dakota.
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STRUCTURAL SETTING

• The Williston Basin (fig. WF-1) underlies most of North Dakota, northwestern 

South Dakota, eastern Montana, and southern Saskatchewan, Canada (Whitaker and

others, 1978).

• The Fort Union Formation (Paleocene) and associated beds exist at the surface

and in the subsurface; they dip 1-2 degrees toward the center of the basin in western

North Dakota.

• Fort Union rocks in North Dakota exist over 32,000 square mile and can be as

much as 1,868 ft thick (Carlson, 1985). The Fort Union Formation makes up about

13 percent of the total sedimentary rocks in the basin, which are more than 15,000 ft

in thickness (Carlson and Anderson, 1966),

STRATIGRAPHIC SETTING

• The Fort Union Formation is composed, from oldest to youngest, of the Ludlow,

Cannonball, Tongue River, and Sentinel Butte Members. The nomenclature follows

the U.S. Geological Survey stratigraphic classification and not that of the North

Dakota Geological Survey (Jacob, 1973; 1975; 1976). The U.S. Geological Survey

considers the Fort Union a formation; although, the North Dakota Geological

Survey considers it a group and recognizes some different formational units within

it.

• All members are coal-bearing except the marine Cannonball Member.

Westward, the Cannonball Member intertongues with and pinches out into the

Ludlow and Tongue River Members. The brackish-marine tongues of the
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Cannonball Member may be present as far west as southeastern Montana (Warwick

and others, 1998).

• Fort Union coal beds generally thicken toward the upper part of the formation.

Coal beds are as much as 20 ft thick in the Tongue River Member and 26 ft thick in

the Sentinel Butte Member.

• In all, 6,033 proprietary and non-proprietary drill holes were used to investigate 

the Fort Union coal in the Williston Basin. The stratigraphic information from drill

holes was interpreted from geophysical logs (for example, gamma, resistivity, and

density) and lithologic logs by geologists of the North Dakota Geological Survey

and other organizations (Murphy and Goven, 1998).

DEPOSITIONAL SETTING

• Depositional environments of the Fort Union Formation include fluvial, deltaic,

tidal, barrier-shoreface, and marine settings (Jacob, 1973, 1975; Cvancara, 1976;

Warwick 1982; Cherven and Jacob, 1985; Warwick and others, 1996). Tidal

deposits are common in the Ludlow Member, barrier deposits are common in the

Cannonball Member, and fluvial-deltaic deposits are abundant in the Tongue River

and Sentinel Butte Members (Warwick and others, 1996; 1998).

• Coal accumulated in peat mires or swamps in interfluvial, interdeltaic, and

intertidal settings. These mires are low-lying and frequently overlain by fluvial,

deltaic, and crevasse splay deposits (Warwick, 1982; Daly and others, 1985).

• Coal in the Ludlow Member, which is generally thin, occurs landward of a

transgressive cycle or landward-stepping progradational events (Warwick and

others, 1998). Coal in the Tongue River and Sentinel Butte Members occurs

landward of a regressive cycle or seaward-stepping progradational events.

Accumulation of the thin Ludlow coal was coincident to sea-level rise, which was
WF-3

theoretically accompanied by a maximum addition of new accommodation space.

The accumulation of the thick Tongue River and Sentinel Butte coal was coincident

to sea-level fall, which was theoretically accompanied by a minimum addition of

new accommodation space (Flores and Cross, 1991). Tectonic movements in the

basin as suggested by Daly and others (1985) may have controlled the

accommodation space during the accumulation of the Sentinel Butte coal.

COAL QUALITY

• Most of the Fort Union coal in the Williston Basin is lignite in rank (Stricker and

others, 1998). However, six coal samples from our study (see Chapter WQ in this

CD-ROM) indicate that some Fort Union coal in the Williston Basin is

subbituminous C in rank ranging from 8,300 to 8,560 Btu/lb (moist, mineralmatter-free basis).

• Coal quality data indicate low sulfur and ash contents (Soundreal and others,

1968; Swanson and others, 1976; Stricker and others, 1998).

• Selected trace-elements of environmental concern have low concentrations

(Stricker and others, 1998).

STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS

OF COAL UNITS AND ASSOCIATED ROCKS

STRATIGRAPHY

• The Fort Union Formation is composed primarily of sandstone, siltstone, and

mudstone and subordinate carbonaceous shale, coal, and limestone. The sandstone
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and mudstone are common rock types of the formation. The Tongue River and

Sentinel Butte Members contain up to 42 percent sandstone locally distributed

throughout the members (Jacob, 1975; Warwick, 1982; Cherven and Jacob, 1985).

• Minable coal beds and zones include the Harmon, Hansen, Hagel, and BeulahZap (fig. WF-2). Four mines developing these deposits accounted about 3 percent

of the total U.S. coal production in 1997 (Resource Data International, Inc., 1997).

• The Harmon and Hansen coal zones are in the lowermost part of the Tongue

River Member and occur in the southwestern part of the basin. The Harmon coal

was mined in the Gascoyne surface mine, which closed in 1996.

• The Hagel coal zone is in the middle part of the Sentinel Butte Member and

occurs in the east-central part of the basin. Hagel coal is mined in the Center and

Falkirk surface mines.

• The Beulah-Zap coal zone is in the upper part of the Sentinel Butte Member and

exists in the east-central part of the basin. The Beulah-Zap coal is mined in the

Freedom surface mine north of Beulah and in the Knife River surface mine south of

Beulah.

• Coal beds of intervening coal zones such as the Antelope Creek and Kinneman

Creek may be relatively thin or thick and merge with the Hagel and Beulah-Zap coal

zones.

• In the Williston Basin, the biostratigraphic zonation of the Fort Union includes

Zones P1-P6 (fig WF-3). The minable coal beds and zones occur in the upper part

of the Paleocene in Zones P4-P6.

DEPOSITIONAL ENVIRONMENTS

• The coal of the Harmon and Hansen coal zones accumulated in peat mires or

swamps in alluvial plain environments (Warwick, 1982). The Harmon and Hansen
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coal zones are interbedded with floodplain mudstone and siltstone (gray) and

overlain by fluvial channel sandstone and interfluvial silty sandstone, siltstone, and

mudstone (shown in yellow) as shown along the valley wall of the Little Missouri

River (fig. WF-4). These coal zones are underlain by bleached-variegated, silcrete

paleosol of the Rhame bed (fig. WF-5). The Harmon coal, which is overlain by

fluvial channel sandstone, was mined at the abandoned Gascoyne surface mine (fig.

WF-6). The Harmon-Hansen fluvial setting was at the western margin of the coastal

plain that trailed the eastward regression of the Cannonball Sea (Cherven and Jacob,

1985). Eastward-flowing streams drained into the deltas of the coastal plain.

• Several contemporaneous, small and large fluvial channels drained the alluvial

plain (Warwick, 1982). They migrated laterally by process of deposition and erosion

in meander belts that shifted across the alluvial plain.

• Interfluvial peat swamps formed in lacustrine-dominated floodplains above the

drainage level of bounding fluvial channels and associated levees. Swamps

encroached on abandoned alluvial ridges and peat accumulated on raised platforms

that were protected from sediment influx.

• These environmental conditions yielded thick, low ash, and areally elongate coal

deposits formed in topographically elevated peat swamps (Warwick, 1982) and

interfluvial peat swamps (Rehbein, 1977).

• The coal of the Hagel and Beulah-Zap coal zones formed in peat swamps in

upper delta plain (fluvial dominated) environments. This interpretation is based on

the abundance of mudstone (figs. WF-7 and WF-8) and the presence of common

small and large channel-sandstone beds (figs. WF-9, WF-10, and WF-11)

immediately above the coal zones. However, Daly and others (1985) suggested that

deposition of the coal zones took place in a tectonic-fluvial setting.
WF-6

• Low-lying interdeltaic peat swamps were bounded by large, diverging,

interdistributary fluvial channels and by small crevasse channels and splays. The

swamps accumulated thin and laterally discontinuous peat coal deposits.

• However, abandoned interdeltaic peat swamps resulted in the accumulation of

thick and sheet-like coal deposit. The coal formed on raised swamp platforms that

consisted of fluvial-channel deposits. Splitting of the coal deposits suggests

intermittent flooding of the platforms by sediments.

• A few peat deposits, high in ash content and carbonaceous mud, formed in

intertidal marshes drained by tidal channels and were shielded from the sea by a

barrier-beach setting (Warwick and others, 1996).

BOWMAN-DICKINSON COALFIELD, HARMON AND

HANSEN COAL ZONES

DISTRIBUTION

• The Bowman-Dickinson coalfield boundary approximately follows the areal

extent of the Harmon and Hansen coal zone as defined by Rehbein (1977). It

includes mining areas that produced from these coal zones in Bowman and

Hettinger Counties (LeFever and Murphy, 1983).

• The coalfield is defined by the subsurface extent of the Harmon and Hansen coal

zones, as delineated by drill holes, on the east, north, and south (Rehbein, 1977), and

is defined on the west by the Montana-North Dakota state line. The state line is just

west of the only known Harmon and Hansen coal outcrops along the valley walls of

the Little Missouri River (Warwick, 1982; LeFever and Murphy, 1983).
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• The Harmon and Hansen coal zones are found in the lowermost part of the

Tongue River Member of the Fort Union Formation.

• These coal zones occur mainly in the subsurface of Bowman, Adams, Hettinger,

Slope, Golden Valley, Billings, and Stark Counties in the southwestern Williston

Basin, North Dakota (fig. WF-12).

• The coal zones crop out mainly along the Little Missouri River in western

Billings County.

STRATIGRAPHIC FRAMEWORK

• The coal zones in the Bowman-Dickinson coalfield usually consist of a lower

Hansen coal zone and an upper Harmon coal zone. These coal zones are interbedded

with limestone, mudstone, carbonaceous shale, siltstone, and sandstone. The

sandstone beds, which range in thickness from 8 to 74 ft and display an erosional

base in outcrop, were interpreted by Warwick (1982) as a fluvial channel deposit.

Warwick (1982) indicated that a crevasse splay sandstone averages 3-5 ft thick.

These criteria were used as a guide in the interpretation of depositional environments

of the sandstone in the coal zones and associated rocks in the subsurface.

• The thickness of the coal zones ranges from 4 to 42 ft throughout the study area.

• Laterally, the coal beds merge, split, and pinch out. The coal splits into two or

more beds that gradually thin or pinch out or interfinger with other clastic rocks.

• Coal beds pinch out into wash-out areas consisting of carbonaceous shale,

mudstone, siltstone, and sandstone.

• Vertically, the coal zones include as many as 4 coal beds as a result of splitting of

the Harmon and Hansen coal.

• Coal beds are interbedded mainly with mudstone and carbonaceous shale

partings.
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• Rocks above and below the coal zones consist of mudstone, siltstone, sandstone,

and limestone.

• Rocks of this zone were accumulated in fluvial channels and interfluvial

environments of an alluvial plain.

• The Harmon and Hansen coal beds accumulated in interfluvial peat swamps.

HARMON AND HANSEN COAL ZONES INTERPRETIVE CROSS

SECTION A-A’

• The coal beds and zones are in a 5 to 42 ft thick interval consisting of a lower

Hansen coal bed and zone as much as 5 ft thick and an upper Harmon coal zone as

much as 29 ft thick (fig. WF-13). Datum is the base of the Harmon coal zone. The

cross section was drawn using data from 9 drill holes, which are not labeled on the

cross section.

• The Harmon coal zone varies from 5 to 29 ft thick from southeast to northwest

along the 51 mile extent of cross section A-A’. The coal zone locally splits in the

central part of the cross section.

• The Hansen coal zone is lenticular, varies from 4 to 10.5 miles in length, and

pinches out toward the northwest and southeast.

• Interburden rocks between the zones are dominantly mudstone and siltstone and

subordinately sandstone.

• Sandstone bodies range in thickness from 10 to 60 ft and accumulated in either

single or multiple river channels.

• These river channel deposits range from 6 to 18 mi in lateral extent and represent

accumulation in laterally migrating narrow to wide channels.

• The river channels were a part of a drainage network on a delta plain (fig. WF14), which flowed into the nearby Cannonball Sea.
WF-9

• The mudstone and siltstone were deposited in overbank and floodplain

environments, and the sandstone was deposited in crevasse splays (fig. WF-15) in

flood basins between river channels.

• Low-lying areas between the river channels remained below water level and

supported peat swamps (fig. WF-16) where peat deposits were buried by younger

sediments and eventually transformed into lignite. Coal beds that formed in these

peat swamps are thin and laterally discontinuous.

• Peat deposits also accumulated in swamps once occupied by river channel,

overbank, floodplain, and crevasse splay environments later abandoned by the river

(fig. WF-17). Peat deposited in these environments formed thick and laterally

extensive coal beds exemplified by the Harmon and Hansen coal.

HARMON AND HANSEN COAL ZONES INTERPRETIVE CROSS

SECTION B-B’

• These coal zones occur in an 8 to 25 ft thick interval that includes a lower Hansen

coal bed and zone that is as much as 5 ft thick and an upper Harmon coal zone as

much as 12 ft thick (fig. WF-18). Datum is the base of the Harmon coal zone. The

cross section was drawn using data from 10 drill holes, which are not labeled on the

cross section.

• The Harmon coal zone varies from 3 to 12 ft thick from northwest to southeast

along the 56-mi extent of B-B’. It splits to the southeast, pinches out to the

northwest but is present again at the northwest end of the cross section.

• The Hansen coal zone is as much as 5 ft thick and is lenticular along its extent in

the southeast part of the cross section.

• Interburden rocks between the zones are dominantly mudstone and siltstone and

subordinately sandstone.
WF-10

• Other sandstone bodies shown in the cross section range from 50 to more than

100 ft thick. They were deposited in multiple river channels.

• River channel deposits range from 10 to 20 mi in lateral extent. They represent

accumulation in mainly laterally migrating river channels.

• These river channels are areally contemporaneous on a delta plain (fig. WF-19).

They may have merged and diverged as they drained into the nearby Cannonball

Sea.

• The mudstone and siltstone were deposited in overbank and floodplain

environments and the sandstone was deposited in crevasse splays in flood basins

between river channels.

• These low-lying flood basins remained below water level and supported swamps

that accumulated peat that eventually resulted in thin and laterally discontinuous coal

beds.

• Areas once occupied by river channels and their flood basins but later abandoned

by the river served as swamp platforms where the Harmon and Hansen coal

accumulated as thick and laterally extensive deposits.

• The Harmon and Hansen coal zones pinch out suggesting washouts through the

peat swamps.

HARMON AND HANSEN COAL ZONES INTERPRETIVE CROSS

SECTION C-C’

• These coal zones occur in a 15-ft-thick interval consisting of a lower Hansen coal

zone that is as much as 6 ft thick and an upper Harmon coal zone as much as 10 ft

thick (fig. WF-20). They merge to form a single zone as much as 14 ft thick.

Datum is the base of Harmon coal zone. The cross section was drawn using data

from 7 drill holes, which are not labeled on the cross section.
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• The Harmon coal zone varies from 5.5 to 10 ft thick along parts of the 72.6 mi

extent of cross section C-C’. The coal zone pinches out toward the central part of the

cross section.

• The Hansen coal zone is 0 to 6 ft thick and merges to the east with the Harmon

coal zone (see western part of cross section).

• Interburden rocks are dominated by mudstone and siltstone and secondarily by

sandstone.

• Other sandstone bodies shown in the cross section average 50 ft in thickness and

probably were deposited in a multiple channel complex.

• The sandstone bodies range from 15 to 20 mi in lateral extent and represent

deposition in laterally migrating river channels that drained into the Cannonball Sea.

• The mudstone and siltstone were deposited in lake (fig. WF-21) and floodplain

environments and the sandstone was deposited in crevasse splays in flood basins

between river channels.

• These flood basins remained below water level, supporting small peat swamps,

which later formed thin and laterally discontinuous coal beds.

• The Harmon and Hansen coal zones formed in peat swamps on abandoned river

channel and flood basin deposits. However, the lateral extent of these coal beds was

affected by crevasse washouts in flood basins.

HARMON AND HANSEN COAL ZONES INTERPRETIVE CROSS

SECTION D-D’

• These coal zones are in an interval 2 to 40 ft thick consisting of a lower Hansen

coal bed and zone as much as 10 ft thick and an upper Harmon coal zone as much

as 13 ft thick (fig. WF-22). These coal zones consist of up to four beds. Datum is
WF-12

the base of the Harmon coal zone. The cross section was drawn using data from 10

drill holes, which are not labeled on the cross section.

• The Harmon coal zone varies from 5 to 13 ft in thickness from southwest to

northeast along the 45.2 mi extent of cross section D-D’. The coal zone pinches out

towards the southwest.

• The Hansen coal zone is 0 to 9 ft thick and pinches out towards the southwest.

• Interburden rocks are dominated by mudstone and siltstone and subordinately by

sandstone.

• Other sandstone bodies shown in the cross section range from 20 to 90 ft in

thickness and form single to multiple channel complexes.

• The sandstone is 4.5 to 11 mi in lateral extent. These deposits accumulated in

areally alternating narrow and wide river channels that flowed into the Cannonball

Sea (See Chapter WS).

• The mudstone and siltstone were deposited in overbank and floodplain

environments and the sandstone was deposited in crevasse splays in flood basins

between river channels.

• Drowned flood basins supported numerous small and disconnected peat swamps

that formed thin and laterally discontinuous coal beds.

• The Harmon and Hansen coal zones formed in continuous peat swamps on

abandoned river-channel and flood-basin deposits abandoned by the river.

However, the extent of these coal zones was controlled by washouts in the riverchannel margins and flood basins.

• Flood-basin washouts may be caused by lake and crevasse-splay deposition.
WF-13

CENTER-FALKIRK COALFIELD, HAGEL COAL ZONE

DISTRIBUTION

• The Center-Falkirk coalfield (fig. WF-23) boundary approximately follows the

areal extent of the Hagel coal zone as defined by Groenewald and others (1979). It

includes early and current mining areas that produced from this coal zone in Center

and Falkirk in McLean, Mercer, and Oliver Counties (Leonard, 1908; Groenewold

and others, 1979; Oihus, 1983).

• The coalfield is delineated by the subsurface extent of the Hagel coal zone on the

east, west, north, and south, which were locally removed at the surface by

Quaternary river and glacial processes. Data available for this study also limit the

extent of the coal zone shown.

• The Hagel coal zone is in the lower part of the Sentinel Butte Member of the Fort

Union Formation.

• The coal zone is in the subsurface of McLean, Mercer, and Oliver Counties in the

east-central part of the Williston Basin, North Dakota.

• The coal zone crops out along the valleys of the Missouri River and Knife River

and their tributaries in McLean, Mercer, and Oliver Counties.

STRATIGRAPHIC FRAMEWORK

• The Hagel coal zone is an interval usually consisting of five coal beds. These coal

beds are interbedded with mudstone, carbonaceous shale, siltstone, and sandstone.

The sandstone, which ranges from 16 to 131 ft in thickness and fines upward (based

on subsurface geophysical and lithologic logs interpretation), was interpreted by
WF-14

Daly and others (1985) and Groenewold and others (1979) as a fluvial channel

deposit. Daly and others (1985) indicated that a crevasse-splay sandstone is less

than 16 ft in thickness and coarsens upward. These criteria were used as a guide in

interpretation of the depositional environments of the sandstone in this study.

• The interval ranges in thickness from 50 to 500 ft throughout the study area.

• Laterally, these coal beds merge, split, and pinch out. The coal splits into two or

more beds and gradually interfingers with clastic rocks.

• Coal beds pinch out into washout areas of mudstone, siltstone, and sandstone.

• Coal beds are interbedded with carbonaceous shale and mudstone partings.

• The rocks above and below the coal zone consist of mudstone, siltstone, and

sandstone.

• These rocks accumulated in distributary channels and interdistributary areas of an

upper delta plain.

• The Hagel coal zone accumulated in interdistributary peat swamps.

• The Hagel coal zone and associated rocks were partly to totally eroded and

infilled by glacial till consisting of yellowish-brown silt, clay, sand, and gravel.

HAGEL COAL ZONE INTERPRETIVE CROSS SECTION A-A’

• This west-to-east cross section (fig. WF-24) shows the Hagel coal zone in the

Center mining area. Datum is the base of the lowermost coal bed of the zone. The

cross section was drawn using data from 17 drill holes, which are not labeled on the

cross section.

• The coal zone is a 50-ft-thick interval and consists of four coal beds. The lower

bed is as much as 12 ft thick and the upper bed is as much as 7 ft thick.
WF-15

• These four coal beds merge into two beds toward the western part of the cross

section and split toward the east. Splitting resulted from re-occupation of floodplains

by peat swamps.

• The Hagel coal zone accumulated in interdistributary swamps (fig. WF-25) and

is interbedded with mudstone or other interburden rocks formed in interdistributary

floodplains.

• The overburden dominantly consists of mudstone, and subordinately consists of

siltstone and sandstone. The sandstone was deposited in distributary channels and

the mudstone was deposited in floodplains.

• The Hagel coal zone was deposited on sandstone of abandoned distributary

channels and mudstone of interdistributary floodplains.

• Glacial till infilled local surfaces of erosion on the overburden.

HAGEL COAL ZONE INTERPRETIVE CROSS SECTION B-B’

• This west-to-east cross section (fig. WF-26) shows the Hagel coal zone in the

Falkirk mining area. Datum is the base of the lowermost coal bed of the zone. The

cross section was drawn using data from 18 drill holes, which are not labeled on the

cross section.

• The coal zone is as much as 48 ft thick and consists of four coal beds. The lower

bed is as much as 6 ft thick and the upper bed is as much as 13 ft thick.

• These four coal beds merge and split repeatedly along a 24.8-mi extent of the

cross section. Splitting resulted from re-occupation of floodplains by peat swamps.

• The Hagel coal beds, which accumulated in interdistributary swamps, are

interbedded with mudstone or interburden rocks deposited in interdistributary

floodplains.
WF-16

• The Hagel coal zone was deposited on sandstone of abandoned distributary

channels and mudstone of interdistributary floodplains.

• The overburden contains abundant mudstone, and subordinate siltstone and

sandstone. The sandstone was deposited in distributary channels (fig. WF-27) and

the mudstone formed in floodplains.

• Glacial till infilled local surfaces of erosion on the overburden.

HAGEL COAL ZONE INTERPRETIVE CROSS SECTION C-C’

• This south-to-north cross section (fig. WF-28) shows the Hagel coal zone in the

Center mining area. Datum is the base of the lowermost coal bed of the zone. The

cross section was drawn using data from 20 drill holes, which are not labeled on the

cross section.

• The coal zone is a 90-ft-thick interval and consists of five coal beds. The lower

bed is as much as 10 ft thick and the upper bed is as much as 6 ft thick.

• These five coal beds merge into two beds and split repeatedly laterally along a

20.5-mi extent of the cross section. Splitting resulted from re-occupation of

floodplains by peat swamps and shifting of distributary channels.

• The Hagel coal beds, which accumulated in interdistributary swamps, are

interbedded with mudstone deposited in interdistributary floodplains and with

sandstone deposited in distributary channels.

• The overburden includes dominantly mudstone, and subordinately sandstone.

The sandstone was deposited in distributary channels and the mudstone formed in

floodplains.

• The Hagel coal zone was deposited on sandstone of abandoned distributary

channels and mudstone of interdistributary floodplains.

• Glacial till infilled local surfaces of erosion on the overburden.
WF-17

HAGEL COAL ZONE INTERPRETIVE CROSS SECTION D-D’

• This north-to-south cross section (fig. WF-29) shows the Hagel coal zone in the

Falkirk mining area. Datum is the base of the lowermost coal bed of the zone. The

cross section was drawn using data from 19 drill holes, which are not labeled on the

cross section.

• The coal zone (75-ft-thick interval) consists of six coal beds. The lower bed is as

much as 6 ft thick and the upper bed is as much as 3 ft thick.

• These six coal beds merge and split repeatedly along a 16.75-mi extent of the

cross section. Splitting resulted from re-occupation of ancestral floodplains by peat

swamps due to shifts in environments.

• The Hagel coal beds, which accumulated in interdistributary swamps, are

interbedded with mudstone deposited in interdistributary floodplains.

• The overburden dominantly consists of mudstone, and very minor sandstone.

The sandstone was probably deposited in crevasse-splay channels and the mudstone

in floodplains.

• Sandstone and mudstone below the Hagel coal zone formed in distributary

channels and interdistributary floodplains, respectively. Minor swamps developed in

distal floodplains as shown by thin, lenticular coal beds.

• Glacial till infilled local surfaces of erosion on the overburden.

BEULAH COALFIELD, BEULAH-ZAP COAL ZONE

DISTRIBUTION

• The Beulah coalfield (fig. WF-30) boundary approximately follows the areal

extent of the Beulah-Zap coal zone as defined by Groenewold and others (1979). It
WF-18

includes early and current mining areas that produced from this coal zone in the

vicinity of Beulah and Zap in Mercer and Oliver counties (Leonard, 1908;

Groenewold and others, 1979; Oihus, 1983).

• The coalfield is delineated by the subsurface extent of the Beulah coal zone on the

east, west, and south, which were locally removed by Quaternary fluvial and glacial

processes. On the north, it is delineated by the Fort Berthold Indian Reservation.

Data available for this study also limit the extent of the coal zone shown.

• The Beulah-Zap coal zone is found in the middle part of the Sentinel Butte

Member of the Fort Union Formation.

• The coal zone exists in the subsurface of McLean, Mercer, and Oliver Counties

in east-central part of the Williston Basin, North Dakota.

• Surface occurrence of the coal zone is in the valley walls of the Knife River and

its tributaries in Mercer and Oliver Counties.

STRATIGRAPHIC FRAMEWORK

• The Beulah-Zap coal zone is an interval usually consisting of five coal beds.

These coal beds are interbedded with mudstone, carbonaceous shale, siltstone, and

sandstone. The sandstone bodies, which range in thickness from 16 to 131 ft and

fine upward (based on subsurface geophysical and lithologic logs interpretation),

were interpreted by Groenewold and others (1979), and Daly and others (1985) as

fluvial channel deposits. Daly and others (1985) indicated that crevasse-splay

sandstone is less than 16 ft in thickness and coarsens upward. These criteria were

used as a guide in interpreting the depositional environments of the sandstone in this

study.

• The interval ranges in thickness from 3.5 to 50 ft throughout the study area.

• Laterally, these coal beds merge, split, and pinch out.
WF-19

• The coal beds pinch out into washout areas of mudstone, siltstone, and

sandstone.

• Coal beds are interbedded with carbonaceous shale and mudstone partings.

• The rocks above and below the coal zone consist of mudstone, siltstone, and

sandstone.

• These rocks were accumulated in distributary channels and interdistributary areas

of a upper delta plain.

• The Beulah-Zap coal beds accumulated in interdistributary and abandoned delta

peat swamps.

• The Beulah-Zap coal zone and associated rocks were partly to totally eroded and

infilled by glacial till consisting of yellowish-brown silt, clay, sand, and gravel.

• The Beulah-Zap coal zone is underlain by the Antelope Creek and Kinneman

Creek coal zones, together consisting of as many as eight coal beds, which are each

as much as 8 ft thick.

BEULAH-ZAP COAL ZONE INTERPRETIVE CROSS SECTION E-E’

• This southwest-to-northeast cross section (fig. WF-31) shows the Beulah-Zap

coal zone through the Knife River and Freedom mining areas. Datum is the base of

the lowermost coal bed of the zone. The cross section was drawn using data from

50 drill holes, which are not labeled on the cross section.

• The coal zone is an interval more than 30-ft-thick and consists of five coal beds.

The lower bed is as much as 9 ft thick and the upper bed is as much as 18 ft thick.

• These five coal beds merge into one bed, as much as 20 ft thick, that splits

repeatedly along the 73.9-mi extent of the cross section. Splitting resulted from reoccupation of floodplains by peat swamps due to shifts in environments.
WF-20

• The Beulah-Zap coal, which accumulated in interdistributary swamps (fig. WF32), is interbedded with mudstone that was deposited in interdistributary

floodplains.

• The overburden includes abundant mudstone and sandstone. The sandstone was

deposited in river channels and crevasse splays (fig. WF-33) and the mudstone was

formed in floodplains.

• Sandstone and mudstone below the Beulah-Zap coal zone formed in abandoned

distributary channels and interdistributary floodplains, respectively. Well-developed

swamps accumulated the Antelope Creek and Kinneman Creek coal zones.

• Glacial till infilled local surfaces of erosion on the overburden. Locally, erosion

has completely cut out the Beulah-Zap, Antelope Creek, and Kinneman Creek coal

zones.

BEULAH-ZAP COAL ZONE INTERPRETIVE CROSS SECTION F-F’

• This west-to-east cross section (fig. WF-34) shows the Beulah-Zap coal zone

through the Freedom mining area. Datum is at the base of the lowermost coal bed of

the zone. The cross section was drawn using data from 19 drill holes, which are not

labeled on the cross section.

• The coal zone is an interval more than 25 ft thick and consists of three coal beds.

The lower bed is as much as 8 ft thick and the upper bed is as much as 12 ft thick.

• These three coal beds merge into mostly one bed as much as 22 ft thick. This

bed splits laterally on the western and eastern parts of the 16.1 mile cross section.

Splitting resulted from inundation of the ancestral peat swamps by floodplain

sediments.

• The Beulah-Zap coal, which accumulated in interdistributary swamps, is

interbedded with mudstone deposited in interdistributary floodplains.
WF-21

• The overburden consists of mudstone and sandstone. The sandstone was

deposited in river channels and the mudstone in floodplains. Minor swamps formed

in distal floodplains, which accumulated peat deposits (fig. WF-35) resulting in thin,

lenticular coal beds.

• Sandstone and mudstone below the Beulah-Zap coal zone formed in abandoned

distributary channels and interdistributary floodplains and related swamps. Welldeveloped swamps formed the Antelope Creek and Kinneman Creek coal zones

(consisting of eight coal beds) shown in the lower part of the cross section.

• Glacial till infilled local surfaces of erosion on the overburden. Erosion has partly

to completely locally cut out the Beulah-Zap coal zone.

BEULAH-ZAP COAL ZONE INTERPRETIVE CROSS SECTION G-G’

• This west-to-east cross section (fig. WF-36) shows the Beulah-Zap coal zone

north of the Freedom mining area. Datum is the base of the lowermost coal bed of

the zone. The cross section was drawn using data from 16 drill holes, which are not

labeled on the cross section.

• The coal zone, which is as much as 35 ft thick, consists of three coal beds. The

lower bed is as much as 7 ft thick and the upper bed is as much as 11 ft thick.

• These three coal beds merge into one bed as much as 20 ft thick that splits

laterally along the 12.4-mi long cross section. Splitting resulted from inundation of

the ancestral peat swamps by floodplain sediments.

• The Beulah-Zap coal, which accumulated in interdistributary swamps, is

interbedded with mudstone deposited in interdistributary floodplains and sandstone

deposited in a crevasse splay.
WF-22

• The overburden contains abundant mudstone and sandstone. The sandstone was

deposited in river channels and the mudstone in floodplains. Minor swamps formed

in distal floodplains, which formed thin, lenticular peat deposits.

• Sandstone and mudstone below the Beulah-Zap coal zone formed in abandoned

distributary channels and interdistributary floodplains and related swamps. Welldeveloped peat swamps formed the Antelope Creek and Kinneman Creek coal

zones.

• Glacial till infilled local surfaces of erosion on the overburden. Erosion has partly

to completely cut out the Beulah-Zap coal zone locally.

BEULAH-ZAP COAL INTERPRETIVE CROSS SECTION H-H’

• This west-to-east cross section (fig. WF-37)shows the Beulah-Zap coal zone

northeast of Lake Sakakawea. Datum is the base of the lowermost coal bed of the

zone. The cross section was drawn using data from 14 drill holes, which are not

labeled on the cross section.

• The coal zone is as much as 40 ft thick and consists of four coal beds. The lower

bed is as much as 7 ft thick and the upper bed is as much as 5 ft thick.

• These four coal beds are merged and split locally along the 12.4-mi lateral extent

of the cross section. Splitting resulted from inundation of ancestral peat swamps by

floodplain sediments.

• The Beulah-Zap coal accumulated in interdistributary swamps and is interbedded

with mudstone deposited in interdistributary floodplains.

• The overburden is dominantly mudstone and subordinately sandstone. The

sandstone was deposited in river channels and the mudstone in floodplains. A

swamp formed on the distal floodplain that formed thin, lenticular peat beds.
WF-23

• Sandstone and mudstone below the Beulah-Zap coal zone formed in abandoned

distributary channels and interdistributary floodplains.

• Glacial till infilled local surfaces of erosion on the overburden. Erosion has

partly to completely cut out the Beulah-Zap coal zone locally.
WF-24

REFERENCES

Carlson, C.G., 1985, Geology of McKenzie County, North Dakota: North Dakota

Geological Survey Bulletin 80, Part 1, 54 p.

Carlson, C.G., and Anderson, S.B., 1966, Sedimentary and tectonic history of the

North Dakota part of the Williston Basin: American Association of

Petroleum Geologists Bulletin, v. 49, p. 1833-1846.

Cherven, V.B., and Jacob, A.F., 1985, Evolution of Paleogene depositional

systems, Williston Basin, in response to global sea level changes, in Flores,

R., and Kaplan S.S., eds., Cenozoic Paleogeography of the West-Central

United States: The Rocky Mountain Section, Society of Economic

Paleontologists and Mineralogists, p. 127-170.

Cvancara, A.M., 1976, Geology of the Cannonball Formation (Paleocene) in the

Williston Basin, with reference to uranium potential: North Dakota

Geological Survey Report of Investigation 57, 22 p.

Daly, D.J., Groenewold, G.H., and Schmit, C.P., 1985, Paleoenvironments of the

Paleocene Sentinel Butte Formation, Knife River area, west-central North

Dakota, in Flores, R., and Kaplan, S.S., eds., Cenozoic Paleogeography of the

West-Central United States: The Rocky Mountain Section, Society of

Economic Paleontologists and Mineralogists, p. 171-185.

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., The Geology of North

America: The Geological Society of America, v. P-2, p. 547-571.

Groenewold, G.H., Hemish, L.A., Cherry, J.A., Rehm, B.W., Meyer, G.N., and

Winczewski, L.M., 1979, Geology and geohydrology of the Knife River
WF-25

Basin and adjacent areas of west-central North Dakota: North Dakota

Geological Survey, Report of Investigation Number 64, 402 p.

Jacob, A.F., 1973, Depositional environments of part of the Tongue River

Formation, western North Dakota: American Association of Petroleum

Geologists Bulletin, v. 57, p. 1038-1052.

_____1975, Criteria of differentiating the Tongue River and Sentinel Butte

Formations (Paleocene), North Dakota: North Dakota Geological Survey

Report of Investigation 53, 55 p.

_____1976, Geology of the upper part of the Fort Union Group (Paleocene),

Williston Basin, with reference to uranium: North Dakota Geological Survey

Report of Investigation 58, 49 p.

LeFever, R.D., and Murphy, E.C., 1983, Mining resources and potential problems

associated with mining of Cenozoic rocks of the Williston and Powder River

Basins, northern Great Plains: U.S. Department of Interior, Office of Surface

Mining, Division of Technical Services and Research Bulletin No. 83-09-

MMRRI-01, 174 p.

Leonard, A.G., 1908, Lignite deposits of North Dakota: North Dakota Geological

Survey Biannual Report No. 5, 278 p.

Murphy, E.C., and Goven, G.E., 1998, Thick coals in Dunn and southern

McKenzie Counties, North Dakota: North Dakota Geological Survey, OpenFile Report No. 98-3, 31 p.

Oihus, C.A., 1983, A history of coal mining in North Dakota: North Dakota

Geological Survey Educational Series 15, 100 p.

Rehbein, E.A., 1977, Preliminary report on the stratigraphy and depositional

environments of the lignites in the Fort Union Formation, west-central North

Dakota: U.S. Geological Survey Open-File Report 77-69, 23 p.
WF-26

Resource Data International, Inc., 1997, COALdat-Coal database, 1320 Pearl St.,

Suite 300, Boulder, Colorado 80302.

Soundreal. E.A., Kube, W.R., and Elder, J.L., 1968, Analysis of the northern Great

Plains province lignites and their ash: a study in variability: U.S. Bureau of

Mines Report of Investigations 7158, 94 p.

Stricker, G.D., Ellis, M.E., Flores, R.M., and Bader, L.R., 1998, Elements of

environmental concern in the 1990 Clean Air Act Amendments: A

prospective of Fort Union coals in the northern Rocky Mountains and Great

Plains region, in Sakkestad, B.A., ed., The Proceedings of the 23rd

International Technical Conference on Coal Utilization and Fuel Systems,

Coal & Slurry Technology Association, p. 967-976.

Swanson, V.E., Medlin, J.H., Hatch, J.R., Coleman, S.L., Wood, G.H., Jr.,

Woodruff, S.D., and Hildebrand, R.T., 1976, Collection, chemical analysis,

and evaluation of coal samples in 1975: U.S. Geological Survey Open-File

Report 76-468, 503 p.

Warwick, P.D., 1982, The geology of some lignite-bearing fluvial deposits

(Paleocene), southwestern North Dakota: M.S. thesis, North Carolina State

University, Raleigh, 158 p.

Warwick, P.D., Flores, R.M., Nichols, D.J., and Murphy, E.C., 1996, Depositional

sequences and correlations within the Fort Union Formation, Williston Basin,

North Dakota and Montana: American Association of Petroleum Geologists,

Abstracts with Programs, San Diego, California, p. A147.

Warwick, P.D., Flores, R.M., Nichols, D.J., Murphy, E.C., and Ochs, A.M., 1998,

Lower Fort Union chronostratigraphic depositional sequences, Williston

Basin, North Dakota, South Dakota, and Montana: Geological Society of

America, Abstracts with Programs, Toronto, Canada, BTH 2.
WF-27

Whitaker, S.H., Irvine, J.A., and Broughton, P.L., 1978, Coal resources of southern

Saskatchewan: a model for evaluation methodology: Geological Survey of

Canada, Economic Geology Report 30, 151 p.
46°

48°

0 10 20 Miles

N

Montana

North Dakota

South Dakota

South Williston Basin

Dakota

North

Dakota

ntana

oming

Valley Daniels Sheridan

Roosevelt

Divide

Williams

Burke

Mountrail

McCone Dawson

Prairie

Richland

Wibaux

McKenzie

Billings Golden

Valley

Mercer

Ward

Dunn

Stark

Hettinger

Bowman Adams

Morton

Grant

Slope

McLean

Oliver

Center 

Mine

Falkirk

Mine

Knife

River

Mines

Freedom

Mines

Gascoyne Mine

Little Missouri Rive r
Paleocene

late

(Zones

P5-P6)

middle

(Zones

P3-P4)

early

(Zones

P1-P2)

Wyodak-Anderson

Beulah-Zap 

Hagel 

Harmon

Hansen

Knobloch

Rosebud

Deadman Seams 1-5

}

}

..................Powder River Basin

................................Williston Basin

..........................................Williston Basin

...............................Powder River Basin

...................................Williston Basin

....Greater Green River Basin

Hanna Nos. 77-79, 81

Ferris Nos. 23, 

25, 31, 50, & 65 } ................................Hanna Basin

..........................Hanna Basin

Johnson-107 .......................................Carbon Basin

Figure WF-2. Composite stratigraphic section for the assessment region showing the

studied coal beds and zones with age relationships based on palynology. Assessment

units in the Williston Basin are highlighted in red.

Rhame bed
500 Meters

Greater

Green River

Basin

Hanna and

Carbon Basins Powder River

Basin

Williston

Basin

Zones: P1 P2 P3

P4 P5 P6

Figure WF-3. Composite correlation of Paleocene sections based on palynostratigraphy.
Figure WF-4. The Harmon and Hansen coal beds and zones in the lower part of the picture are exposed along the 

valley wall of the Little Missouri River. The coal beds and zones are overlain by fluvial deposits. Photograph by 

R.M. Flores.
Figure WF-5. The Rhame bed in the lower part of the picture is exposed along the valley wall of the Little 

Missouri River. This paleosol is overlain by the Harmon and Hansen coal beds and zones. 

Photograph by R.M. Flores.
Figure WF-6. The Harmon coal zone is overlain by fluvial channel sandstone in the Gascoyne mine. 

Photograph by R.M. Flores.
Figure WF-7. The Beulah-Zap coal zone in the Freedom mine is overlain 

by mudstone. Photograph by R.M. Flores.
Figure WF-8. The Beulah-Zap coal zone in the Freedom mine is overlain by a thin rider coal and mudstone. 

Photograph by R.M. Flores.
Figure WF-9. Thin, trough-crossbedded, fluvial channel sandstone overlies the Beulah-Zap coal zone in the 

Freedom mine. Photograph by P.D. Warwick. 
Figure WF-10. The fluvial sandstone shows a deep erosional base (see hammer for scale in the photo). 

Photograph by P.D. Warwick. 
Figure WF-11. Thick, fluvial channel sandstone overlies the Beulah-Zap coal zone in the Freedom mine. 

Photograph by P.D. Warwick.
Bowman-Dickinson

Coalfield (HarmonHansen Coal Zone)

WF-12. Bowman-Dickinson coalfield, Williston

North Dakota, and generalized interpretive cross

ayout.

Williston Basin

Cross Section with

nonproprietary drill holes

Bowman-Dickinson coalfield

SLOPE

COUNTY

GOLDEN

VALLEY

COUNTY

BILLINGS

COUNTY

GASCOYNE

MEDORA

STARK

COUNTY

Gascoyne

Mine ADAMS

COUNTY

HETTINGER

COUNTY

BOWMAN

COUNTY 46°

47°

A

A'

B'

D'

C'

C

D

B

A A'

North

Dakota 

South

Dakota 

Montana 

0 20 40 60 Miles
Figure WF-13. Harmon and Hansen coal zones interpretive cross section A-A',

Bowman-Dickinson coalfield, Williston Basin, North Dakota.

No Record

No Record

A A'

0

100 ft

Datum = Base of Harmon

 coal zone

HN HN

HR HR

HR

HN

HN

Harmon coal zone

Hansen coal zone

51.0 Miles

Sandstone

Mudstone

Coal

Siltstone

NW SEB-B'
Figure WF-14. Lower Mississippi River delta plain in Louisiana showing subdeltas and swamps. 

Photograph by R.M. Flores.
Figure WF-15. Crevasse splay and associated swamps in the lower Mississippi River delta plain, Louisiana. 

Photograph by R.M. Flores.
Figure WF-16. Peat swamp in the upper Mississippi River delta plain, Louisiana. Photograph by R.M. Flores.
Figure WF-17. Abandoned river channel and peat swamp in the Florida Everglades, Florida. 

Photograph by R.M. Flores.
D-D'

C-C'

56.0 Miles

B B'

NW SE

0

100 ft HR

Datum = Base of Harmon

 coal bed

? ? No Record

No Record No Record

?

Sandstone

Mudstone

Coal

Siltstone

HN

HR, Harmon coal bed

HN, Hansen coal bed

Figure WF-18. Harmon and Hansen coal zones interpretive cross section B-B',

Bowman-Dickinson coalfield, Williston Basin, North Dakota.
Figure WF-19. Contemponeous delta plain swamps and river channel in the lower Mississippi River delta plain, 

Louisiana. Photograph by R.M. Flores.
B-B'

72.6 Miles

C C'

West East

0

100 ft

HR HR

HN

?

Datum = Base of Harmon

 coal bed

Sandstone

Mudstone

Coal

Siltstone

HR, Harmon coal bed

HN, Hansen coal bed No Record

Figure WF-20. Harmon and Hansen coal zones interpretive cross section C-C',

Bowman-Dickinson coalfield, Williston Basin, North Dakota.
Figure WF-21. Lake, floodplain, and swamp environments associated with the Beluga River in Alaska. 

Photograph by R.M. Flores.
NE

HR HR

HN

D D'

45.2 Miles

0

100 ft

Datum = Base of Harmon coal bed

Sandstone

Mudstone

Coal

Limestone

Siltstone

HN, Hansen coal bed

HR, Harmon coal bed

SW

B-B'

Figure WF-22. Harmon and Hansen coal zones interpretive cross section D-D',

Bowman-Dickinson coalfield, Williston Basin, North Dakota.
 Indian Reservation

North Dakota

South Dakota Montana

MAP

AREA

A'

A

B

B'

C

C' 

D

D'

°30' 102° 101°30' 101° 100°30'

47°

47°30'

McLean

County

Oliver

County

Mercer

County

Williston Basin

Cross section with

nonproprietary drill holes

Lake Sakakawea

County

N

Center-Falkirk coalfield

(Hagel Coal Zone)

-23. Center-Falkirk coalfield, Williston Basin,

ota, and generalized interpretive cross section

A A'

Mines

Li ttl e

Mis

s

o uri

R.

Center

Mine

Falkirk

Mine

0 20 Miles
? 0

50 ft

Glacial till

Sandstone

Siltstone

Mudstone

Clinker

Coal Datum = Base of Hagel coal zone

Hagel {coal zone

A A'

12.4 Miles

West East

Figure WF-24. Hagel coal zone interpretive cross section A-A', Center-Falkirk

coalfield, Williston Basin, North Dakota.

C-C'
Figure WF-25. Interdistributary swamps and floodplains in the upper Mississippi River delta plain, Louisiana. 

Photograph by R.M. Flores.
?

?

?

?

?

? ?

Mudstone

Coal

Glacial till

Sandstone

Siltstone

0

50 ft

Datum = Base of Hagel coal zone

Hagel

coal zone }

24.8 Miles

B B'

West East East C-C'

Figure WF-26. Hagel coal zone interpretive cross section B-B', Center-Falkirk

coalfield, Williston Basin, North Dakota.
Figure WF-27. Interdistributary channel in the upper Mississippi River delta plain, Louisiana. 

Photograph by R.M. Flores.
0

50 ft

Glacial till

Sandstone

Siltstone

Mudstone

Coal

20.5 Miles

C C'

? ? ?

Datum = Base of Hagel coal zone

Hagel

coal zone }

South North A-A' B-B'

Figure WF-28. Hagel coal zone interpretive cross section C-C',

Center-Falkirk coalfield, Williston Basin, North Dakota.
?

?

0

50 ft

Glacial till

Sandstone

Siltstone

Mudstone

Coal

Datum = Base of

Hagel coal zone

16.75 Miles

D D'

Hagel

coal zone }

NW SE

Figure WF-29. Hagel coal zone interpretive cross section D-D',

Center-Falkirk coalfield, Williston Basin, North Dakota.
Fort Berthold

 Indian Reservation

L ittle Miss

o uri R.

F'

G'

E'

H

H'

E

F

G

Beulah Coalfield

Mines

(Beulah-Zap coal zone)

Figure WF-30. Beulah coalfield, Williston Basin, North

Dakota, and generalized interpretive cross section layout.

102°30' 102° 101°30' 101° 100°30'

47°

47°30'

48°

McLean

County

Oliver

County

Mercer

County

Williston Basin

Cross section with

nonproprietary drill holes

Lake Sakakawea

McHenry 

County Ward

County

A A'

N

North Dakota

South Dakota Montana

MAP

AREA

Knife River

Mines

Freedom

Mines

0 20 Miles
?

?

?

?

?

?

? ?

Mudstone

Coal

Glacial till

Sandstone

Siltstone

0

50 ft

Datum = Base of Beulah-Zap coal zone

21.7 Miles 14.9 Miles 37.3 Miles

US46

? ?

? ?

Antelope Creek and

{Kinneman Creek coal zones

Beulah-Zap

coal zone {

SW

E E'

NE

H-H'

F-F'

G-G'

Lake Sakakawea

Figure WF-31. Beulah-Zap coal zone interpretive cross section E-E',

Beulah coalfield, Williston Basin, North Dakota.
Figure WF-32. Interchannel swamps and floodplains in the South Carolina coastal plain. 

Photograph by C. Connor. 
Figure WF-33. Crevasse splays and swamps in the lower Mississippi River delta plain, Louisiana. 

Photograph by R.M. Flores.
Mudstone

Coal

Glacial till

Sandstone

Siltstone

0

50 ft

16.1 Miles

West

F F'

East

Beulah-Zap

coal zone {

Datum = Base of Beulah-Zap coal zone

Antelope Creek and

Kinneman Creek coal zones{ ?

?

?

? ?

West East E-E'

Figure WF-34. Beulah-Zap coal zone interpretive cross section F-F',

Beulah coalfield, Williston Basin, North Dakota.
Figure WF-35. Peat deposits in the Florida Everglades. Photograph by R.M. Flores.
? ?

? ?

0

50 ft

Mudstone

Coal

Glacial till

Sandstone

Siltstone

Beulah-Zap {coal zone

Antelope Creek and {Kinneman Creek coal zones

Datum = Base of Beulah-Zap coal zone

12.4 Miles

West

G

East

G'

West East E-E'

Figure WF-36. Beulah-Zap coal zone interpretive cross section G-G',

Beulah coalfield, Williston Basin, North Dakota.
0

50 ft

Mudstone

Coal

Glacial till

Sandstone

Siltstone

Datum = Base of Beulah-Zap coal zone

Beulah-Zap

coal zone {

9.3 Miles

West

H

East

H'

?

West East E-E'

Figure WF-37. Beulah-Zap coal zone interpretive cross section H-H',

Beulah coalfield, Williston Basin, North Dakota.