Chapter PF

FRAMEWORK GEOLOGY OF THE FORT UNION COAL IN THE POWDER RIVER BASIN

By R.M. Flores,1 A.M. Ochs,2 L.R. Bader,1 R.C. Johnson, 1 and D. Vogler3

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

1U.S. Geological Survey 2Consultant, U.S. Geological Survey, Denver, Colorado 3West Virginia Geological & Economic Survey, Morgantown, West Virginia Contents

Structural Setting...... PF-1 Stratigraphic Setting...... PF-1 Depositional Setting...... PF-2 Coal Quality...... PF-2 Stratigraphy and Depositional Environments of Assessment Units...... PF-3 Stratigraphy...... PF-3 Depositional Environments...... PF-4 Geology of the Tongue River Member (Fort Union Formation) Coal Beds...... PF-4 Distribution ...... PF-4 Stratigraphic Framework ...... PF-5 Basinwide Wyodak-Anderson Coal Zone Structural Cross Sections Wyodak-Anderson Coal Zone Structural Cross Section A-A’...... PF-6 Wyodak-Anderson Coal Zone Structural Cross Section B-B’...... PF-8 Wyodak-Anderson Coal Zone Structural Cross Section C-C’...... PF-10 Wyodak-Anderson Coal Zone Structural Cross Section D-D’...... PF-12 Wyodak-Anderson Coal Zone Structural Cross Section E-E’...... PF-13 References ...... PF-15

Figures

PF-1. Location map showing the Powder River Basin. PF-2. Depositional models of braided, meandering, and anastomosed streams in the Powder River Basin. PF-3. Modern analog of a fluvial system consisting of braided, meandering, and anastomosed channels of the Susitna River in Alaska.

PF-ii Figures—continued PF-4. Modern analog of a peat-forming, low-lying swamps in the Atchafalaya River Basin in Louisiana. PF-5. Cross section of a domed mire with associated vegetation and peat types. PF-6. Depositional model of the Wyodak-Anderson coal zone and associated sediments in the Decker coalfield, Montana. PF-7. Peat exposed along a drainage ditch cut near the margin of a raised bog in central Kalimantan, Borneo. Photograph by C. Blaine Cecil. PF-8. Composite correlation of Paleocene sections based on palynostratigraphy. PF-9. Composite stratigraphic section for the assessment region showing the studied coal beds and zones with age relationships based on palynology. PF-10. Map showing locations of Wyodak-Anderson coal zone cross sections. PF-11. Wyodak Anderson coal zone structural cross section A-A’. PF-12. Vegetation and logging railroad on top of a raised mire in Central Kalimantan, Borneo, Indonesia. PF-13. Domed mire along a drainage ditch that parallels an oil field road between the Siak and Kampar River/estuaries in Sumatra, Indonesia. PF-14. Meandering and anastomosed channels of the Beluga River in the Upper Cook Inlet, Alaska. PF-15. Fluvial channels, overbank, lakes, floodplains, and low-lying swamps of the Saskatchewan River in the Saskatchewan Province, Canada. PF-16. Abandoned crevasse channels, splays, and low-lying swamps of the Saskatchewan River in the Saskatchewan Province, Canada. PF-17. Wyodak Anderson coal zone structural cross section B-B’. PF-18. Wyodak Anderson coal zone structural cross section C-C’. PF-19. Wyodak Anderson coal zone structural cross section D-D’. PF-20. Wyodak Anderson coal zone structural cross section E-E’.

PF-iii STRUCTURAL SETTING

¥ The Powder River Basin (fig. PF-1) is in northeast Wyoming and southeast Montana. ¥ The Powder River Basin is an asymmetrical structural basin with the axis trending northwest and southeast close to the western margin of the basin, and covers an area of more than 22,000 square-miles. ¥ The beds dip on average 20-25 degrees to the east along the west-central margin of the basin and average 2-5 degrees to the west along the eastern margin. ¥ The Paleocene Fort Union Formation outcrops along the basin margin and is overlain by the Eocene Wasatch Formation in the central part of the basin. The Wasatch Formation contains numerous coal beds as much as 250 ft thick (Mapel, 1959). ¥ The Fort Union Formation is more than 6,000 ft thick in the deepest part of the basin, along the axis (Curry, 1971).

STRATIGRAPHIC SETTING

¥ The Fort Union Formation is divided into the Tullock Member in the lower part, Lebo Member (Wyoming part) or Lebo Shale Member (Montana part) in the middle part, and Tongue River Member in the upper part. ¥ The Tongue River Member contains the most and thickest coal deposits, and the Lebo or Lebo Shale Member contains the least number and thinnest coal beds. ¥ Coal beds in the Tongue River Member of the Fort Union Formation are more than 200 ft thick. The average coal beds are about 20-30 ft thick and increase in thickness toward the upper part of the member.

PF-1 DEPOSITIONAL SETTING

¥ Depositional environments of the Fort Union Formation include fluvial systems (figs. PF-2 and PF-3) consisting of braided, meandering, and anastomosed streams in the basin center, and alluvial fans at the basin margin (Flores and Ethridge, 1985; Flores, 1986). ¥ Coal-forming peat accumulated in low-lying swamps (fig. PF-4) and raised or domed mires (fig. PF-5), in fluvial floodplains (fig. PF-6), abandoned fluvial channels, and interchannel environments (Flores, 1981; Warwick and Stanton, 1988). ¥ The thickest peat deposits accumulated in raised mires well above drainage level (fig. PF-7) and were sustained by rainfall in a tropical-subtropical climate with a mean annual temperature of 20¡C (68¡F) and a precipitation rate of 90.6 in/yr (>2,300 mm/yr) (Nichols and others, 1989). These coal deposits are pod to lenticular shaped (Warwick and Stanton, 1988).

COAL QUALITY

¥ Coal rank is mostly subbituminous with subordinate lignite (Stricker and others, 1998). ¥ Coal quality reflects low percentages of sulfur and ash. The minable Wyodak- Anderson coal zone contains very low sulfur and ash contents (Ellis and others, 1998) ¥ Concentrations of selected trace elements of environmental concern are low (Stricker and others, 1998).

PF-2 STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF ASSESSMENT UNITS

STRATIGRAPHY

¥ The Fort Union Formation in the Powder River Basin ranges in thickness from 2,300 to 6,000 ft (Curry, 1971). The thickest Fort Union Formation is found in the western part of the basin and the thinnest is in the eastern and southern parts. ¥ Biostratigraphic zonations (fig. PF-8) of the formation include zones P1ÐP6. ¥ The Fort Union Formation is composed primarily of conglomerate, sandstone, siltstone, and mudstone, and subordinately of limestone, carbonaceous shale, and coal (Flores, 1981). The sandstone in the Tullock Member ranges from 21 to 88 percent and averages 53 percent; in the Lebo Member it ranges from 6 to 93 percent and averages 31 percent, and the Tongue River Member ranges from 21 to 91 percent and averages 54 percent (Lewis and Hotchkiss, 1981). ¥ The coal beds and zones that were assessed include the Wyodak-Anderson and the laterally equivalent beds, and the Knobloch and Rosebud coal zones (fig. PF-9). ¥ The Wyodak-Anderson coal zone includes as many as 11 coal beds that are found in the upper part of the Tongue River Member of the Fort Union Formation. ¥ This coal zone contains various coal beds named, from bottom to top, Werner, Canyon, Dietz, Anderson, Lower and upper Wyodak, Wyodak, Big George, Sussex, School, Badger, Swartz, and Smith. ¥ The Knobloch and Rosebud coal zones are found in the lower part of the Tongue River Member of the Fort Union Formation. ¥ For this study of the Fort Union coal, 6,909 proprietary and nonproprietary drill holes were used. The stratigraphic information is interpreted by various sources from geophysical logs of coal, oil, and gas drill holes.

PF-3 DEPOSITIONAL ENVIRONMENTS

¥ Depositional environments of the Fort Union Formation consisted of northeastward-flowing fluvial systems comprised of braided, meandering, and anastomosed streams (Flores and Ethridge, 1985). ¥ These basin-axis, trunk-tributary, fluvial systems were fed by alluvial fans that drained surrounding ancestral uplifts. ¥ Thick, low-ash and low-sulfur coal beds of the Tongue River Member formed in raised swamps that developed in interfluvial environments and on abandoned stream deposits. ¥ Thin, high-ash and high-sulfur coal beds of the Tongue River Member were formed in low-lying swamps in interfluvial environments.

GEOLOGY OF THE TONGUE RIVER MEMBER (FORT UNION FORMATION) COAL BEDS

DISTRIBUTION

¥ The Tongue River Member coal beds are stratigraphically distributed in distinct coal zones. ¥ Regionally, the coal zones merge, split, and pinch-out laterally, forming a shingled or overlapping pattern; locally they display a zigzag pattern. ¥ The coal beds are primarily in the subsurface of Campbell and Converse Counties, Wyoming, and Big Horn and Powder River Counties, Montana. ¥ The coal beds of the Tongue River Member are exposed in outcrops along the margin of the Powder River Basin.

PF-4 ¥ Strippable coal beds are found in the south, east, and northwest flanks of the basin. ¥ Lateral and vertical distributions of the WyodakÐAnderson coal beds and zones are shown in a network of cross sections with cross ties (fig. PF-10). The term “rocks,” which is used on the cross sections, indicates undifferentiated sandstone, siltstone, and mudstone. The cross sections do not necessarily use the same number of drill holes for stratigraphic control.

STRATIGRAPHIC FRAMEWORK

¥ The Tongue River Member coal beds are interbedded with mudstone, limestone, carbonaceous shale, siltstone, sandstone, and conglomerate. ¥ The Wyodak-Anderson coal zone is within an interval as much as 900 ft thick. This coal zone consists of as many as eleven coal beds including the Werner, Swartz, Smith, Sussex, Big George, Canyon or Monarch, Dietz, Anderson, Badger, and School (Wyoming part), which merge into a single bed more than 200 ft thick. ¥ The Knobloch and Rosebud-Robinson coal zones are within a 175-ft-thick interval. These coal zones consist of four beds, the Knobloch, Calvert, Nance, and Flowers-Goodale (Culbertson and Saperstone, 1987). Coal beds equivalent to this coal zone include the Sawyer, Lay Creek, and King according to Sholes and Daniel (1992). The Rosebud coal has been laterally correlated by Sholes and Daniel (1992) to the upper split bed of the Knobloch coal. ¥ Laterally, coal beds of these coal zones 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. ¥ The split coal beds are interbedded with limestone, mudstone, siltstone, and sandstone.

PF-5 ¥ Merged coal beds are interbedded with thin carbonaceous shale partings. ¥ Rocks above and below the Tongue River Member coal beds and zones consist of mudstone, siltstone, and sandstone. In outcrop investigations, sandstone greater than 5 ft thick was interpreted as a crevasse-splay deposit and sandstone greater than 5 ft thick was interpreted as a fluvial channel deposit (Flores, 1981; 1986). These criteria were used as a guide in interpreting genetic rock types in the subsurface. ¥ The sediments that formed these rocks were deposited in channels, overbank floodplains, floodplain lakes, and crevasse channel splays in a fluvial system drained by meandering, anastomosed, and braided streams. ¥ The peat that formed the coal beds was deposited in raised mires and low-lying swamps associated with distal floodplains, at margins of floodplain lakes, and on abandoned fluvial channels and crevasse-splay lacustrine deposits (Flores, 1981, Flores and Ethridge, 1985; Flores and Moore; 1994; Moore, 1994).

BASINWIDE WYODAK-ANDERSON COAL ZONE STRUCTURAL CROSS SECTIONS

WYODAK-ANDERSON COAL ZONE

STRUCTURAL CROSS SECTION A-A’

¥ Structural cross section A-A’ (fig. PF-11) extends about 115 mi along the eastern side of the Powder River Basin; it shows the Wyodak-Anderson coal zone and associated rocks. At the north end of the cross section, the rocks dip to the west-southwest, and at the south end the rocks dip to the west-northwest. The cross section was drawn using data from 126 drill holes, which are not labeled on the cross section.

PF-6 ¥ The Wyodak-Anderson coal zone includes all coal beds from the Werner at the bottom to the Smith at the top in the northern part of the cross section. In the southern part of the cross section the coal zone includes all coal beds from the lower to upper Anderson.

¥ Throughout most of this cross section the Wyodak-Anderson coal zone consists of four merged coal beds that form a 115-ft-thick bed. Laterally this merged coal bed is continuous for 15-40 mi, and it exists as a series of lenticular bodies that accumulated in raised mires (figs. PF-12 and PF-13).

¥ These lenticular coal bodies of the Wyodak-Anderson coal zone are laterally split by, and pinch out into, sandstone (shown in yellow), which was deposited in fluvial channels (fig. PF-14), and mudstone (shown in green), which was deposited in overbank, floodplain, and floodplain-lake environments (fig. PF-15).

¥ The lenticular coal bodies in the northern half of the cross section are laterally discontinuous. They are split and re-split by fluvial deposits, displaying a zigzag pattern on the cross section. They merge to form bodies that vary from 3 to 12 mi in length. Re-splitting of coal bodies may be caused by sediments deposited in crevasse channels and splays.

¥ The rocks below the Wyodak-Anderson coal zone consist of a more than 1,000- ft-thick interval of interbedded fluvial channel sandstone and overbank, floodplain, and lacustrine mudstone. Thin to thick, lenticular coal bodies of the interval, as much as 50 ft thick, formed from peat deposited in raised mires and low-lying swamps.

PF-7 ¥ The rocks above the Wyodak-Anderson coal zone consist of an interval more than 800 ft-thick of interbedded fluvial channel sandstone and overbank-floodplain- lacustrine mudstone. The thin lenticular coal bodies in the interval formed from peat deposited in low-lying swamps (fig. PF-16).

¥ The rocks of the Wyodak-Anderson coal zone were deposited in peat swamps and mires drained by meandering, anastomosed, and braided streams (Flores, 1981; 1986).

WYODAK-ANDERSON COAL ZONE

STRUCTURAL CROSS SECTION B-B’

¥ Structural cross section B-B’ (fig. PF-17) extends about 200 mi along the western side of the Powder River Basin; it shows the Wyodak-Anderson coal zone and associated rocks. At the north end of the cross section, the rocks dip to the east- southeast, and at the south the rocks dip east-northeast. The cross section was drawn using data from 91 drill holes, which are not labeled on the cross section.

¥ The Wyodak-Anderson coal zone in the northern part of the cross section includes all coal beds from the Canyon at the bottom to the Anderson at the top. In the southern part of the cross section the coal zone includes all coal beds from the School at the bottom to the Badger at the top. The Wyodak-Anderson coal zone is called the Big George and Sussex coal zones in the central part of the basin (see cross section).

PF-8 ¥ The Wyodak-Anderson coal zone consists of two merged coal beds that form a bed 202 ft thick (see the south-central part of the cross section). This merged coal bed is found as discontinuous, lenticular coal bodies that laterally vary in length from 31 to 40 mi. The coal-forming peat was deposited in raised swamps.

¥ The lenticular Wyodak-Anderson coal bodies are laterally split by, and pinch out into, sandstone (shown in yellow) that was deposited in fluvial channels and mudstone (shown in green) that was deposited in overbank, floodplain, and floodplain-lake environments.

¥ The lenticular coal bodies of the Wyodak-Anderson coal zone are overlapping, laterally offset, and shingled, as best displayed from the central to southern parts of the cross section (see Big George through School-Badger coal zones). This indicates a younger age from the central to the southern part of the coal zone.

¥ The age differentiation of the overlapped coal zones is indicated by pollen and spore biozones that range from P5 in the Big George coal zone to P6 in the School- Badger coal zone.

¥ The rocks below the Wyodak-Anderson coal zone consist of an interval more than 700 ft thick of interbedded fluvial-channel sandstone and overbank-floodplain- lacustrine mudstone. The thin to thick lenticular coal beds in this interval formed from peat deposited in low-lying swamps.

¥ The rocks above the Wyodak-Anderson coal zone consist of an interval more than 1,000 ft thick of interbedded fluvial-channel sandstone, and overbank-

PF-9 floodplain-lacustrine mudstone. The thin lenticular coal beds in this interval formed from peat deposited in low-lying swamps.

¥ The rocks of the Wyodak-Anderson coal zone were deposited in peat swamps and mires drained by meandering, anastomosed, and braided streams.

WYODAK-ANDERSON COAL ZONE

STRUCTURAL CROSS SECTION C-C’

¥ Structural cross section C-C’ (fig. PF-18) extends about 52 mi from west to east through the central part of the Powder River Basin; it shows the Wyodak-Anderson coal zone and associated rocks. At the east end of the cross section, the rocks dip to the west. The cross section was drawn using data from 58 drill holes, which are not labeled on the cross section.

¥ In the eastern part of the cross section, the Wyodak-Anderson coal zone, about 480-ft-thick, includes a merged coal bed more than 160 ft thick. This bed splits toward the west and east along a belt more than 8 mi wide, and pinches out toward the east.

¥ In the western part of the cross section, the Wyodak-Anderson coal zone, about 900 ft thick, includes a merged coal bed that is as much as 200 ft thick. This bed repeatedly splits and merges, forming a zigzag pattern along a belt 35 mi wide.

¥ The coal zone on the west is overlapped by the coal zone on the east, indicating that the latter zone is younger.

PF-10 ¥ The age differentiation of the overlapped coal zones is indicated by pollen and spore biozones that range from P5 on the west to P5-P6 on the east.

¥ The coal beds of the Wyodak-Anderson coal zone formed in raised mires that were laterally split by, and pinch out into, sandstone (shown in yellow) that was deposited in fluvial channels. The mudstone (shown in green) was deposited in overbank, floodplain, and floodplain-lake environments.

¥ The rocks below the Wyodak-Anderson coal zone consist of an interval more than 700 ft thick of interbedded fluvial-channel sandstone, and overbank, floodplain, and lacustrine mudstone. The thin to thick lenticular coal beds formed from peat deposited in low-lying swamps.

¥ The rocks above the Wyodak-Anderson coal zone consist of an interval more than 1,000 ft thick of interbedded fluvial-channel sandstone, and overbank, floodplain, and lacustrine mudstone. The thin lenticular coal beds formed from peat deposited in low-lying swamps.

¥ The rocks of the Wyodak-Anderson coal zone, and rocks above and below the coal zone, were deposited in peat-forming fluvial environments drained by meandering, anastomosed, and braided streams.

PF-11 WYODAK-ANDERSON COAL ZONE

STRUCTURAL CROSS SECTION D-D’

¥ Structural cross section D-D’ (fig. PF-19) extends about 64 miles from west to east through the south-central part of the Powder River Basin; it shows the Wyodak- Anderson coal zone and associated rocks. At the east end of the cross section, the rocks dip to the west. The cross section was drawn using data from 69 drill holes, which are not labeled on the cross section.

¥ In the eastern part of the cross section, the Wyodak-Anderson coal zone consists of a merged coal bed, about 150 ft thick, which splits toward the west and east along a belt 30 mi wide.

¥ In the western part of the cross section, the Wyodak-Anderson coal zone, about 800 ft thick, includes a merged coal bed, as much as 200 ft thick. This bed splits and merges westward and eastward along a belt 40 mi wide, forming a zigzag pattern.

¥ The coal zone on the west is overlapped by the coal zone on the east, exhibiting a shingled pattern and indicating that the latter coal zone is younger.

¥ The age differentiation of the overlapped coal zone is indicated by pollen and spore biozones P5 to the west and P5-P6 to the east.

¥ The coal beds of the Wyodak-Anderson coal zone, which formed in raised mires, are laterally split by, and pinch out into, sandstone (shown in yellow) that

PF-12 was deposited in fluvial channels and mudstone (shown in green) that was deposited in overbank, floodplain, and floodplain-lake environments.

¥ The rocks below the Wyodak-Anderson coal zone consist of an interval 1,500 ft thick of interbedded fluvial-channel sandstone and overbank, floodplain, and lacustrine mudstone. The thin to thick lenticular coal beds formed from peat deposited in low-lying swamps.

¥ The rocks above the Wyodak-Anderson coal zone consist of an interval 1,500 ft thick of interbedded fluvial-channel sandstone, and overbank, floodplain, and lacustrine mudstone. The thin lenticular coal beds formed from peat deposited in low-lying swamps.

¥ The rocks of the Wyodak-Anderson coal zone, and rocks above and below the coal zone, were deposited in peat-forming fluvial environments drained by meandering, anastomosed, and braided streams.

WYODAK-ANDERSON COAL ZONE

STRUCTURAL CROSS SECTION E-E’

¥ Structural cross section E-E’ (fig. PF-20) extends about 59 mi from west to east through the south-central part of the Powder River Basin; it shows the Wyodak- Anderson coal zone and associated rocks. At the east end of the cross section, the rocks dip to the west. The cross section was drawn using data from 32 drill holes, which are not labeled on the cross section.

PF-13 ¥ The Wyodak-Anderson coal zone, about 490 ft thick, includes a merged coal bed more than 100 ft thick that splits toward the west and east.

¥ The coal beds of the Wyodak-Anderson coal zone formed in raised mires; the coal zone is laterally split by, and pinches out into sandstone (shown in yellow) that was deposited in fluvial channels. The mudstone (shown in green) was deposited in overbank, floodplain, and floodplain-lake environments.

¥ The rocks below the Wyodak-Anderson coal zone consist of an interval more than 1,500 ft thick of interbedded fluvial-channel sandstone, and overbank, floodplain, and lacustrine mudstone. The thin to thick lenticular coal beds formed in low-lying swamps.

¥ The rocks above the Wyodak-Anderson coal zone consist of an interval more than 1,000 ft thick of interbedded fluvial-channel sandstone, and overbank, floodplain, and lacustrine mudstone. The thin lenticular coal beds formed in low- lying swamps.

¥ The rocks of the Wyodak-Anderson coal zone, and rocks above and below the coal zone, were deposited in peat-forming fluvial environments drained by meandering, anastomosed, and braided streams.

PF-14 REFERENCES

Culbertson, W.C., and Saperstone, H.I., 1987, Structure, coal thickness, and overburden thickness of the Knobloch coal resource unit, Birney area, Big Horn, Rosebud, and Powder River Counties, Montana: U.S. Geological Survey Coal Investigations Map C-112, scale: 1:100,000. Curry, W.H., 1971, Laramide structural history of the Powder River Basin, Wyoming: Wyoming Geological Association Guidebook, 23rd Annual Field Conference, p. 49-60. Ellis, M.S., Stricker, G.D., Flores, R.M., and Bader, L.R., 1998, Sulfur and ash in Paleocene Wyodak-Anderson coal in the Powder River Basin, Wyoming and Montana: a fuel source beyond 2000: 23rd International Technical Conference on Coal Utilization and Fuel System Proceedings, Clearwater, Florida, p. 849-858. Flores, R.M., l981, Coal deposition in fluvial paleoenvironments of the Paleocene Tongue River Member of the Fort Union Formation, Powder River area, Powder River Basin, Wyoming and Montana, in Ethridge, F.G., and Flores, R.M., eds., Nonmarine Depositional Environments: Models for Exploration: Society of Economic Paleontologists and Mineralogists, Special Publication 3l, p. l69-l90. _____1986, Styles of coal deposition in Tertiary alluvial deposits, Powder River Basin, Montana and Wyoming, in Lyons, P.C., and Rice, C.L., eds., Paleoenvironmental and Tectonic Controls in Coal-forming Basins of the United States: Geological Society of America, Special Paper 210, p. 79-104. Flores, R.M., and Ethridge, F.G., l985, Evolution of intermontane fluvial systems of Tertiary Powder River Basin, Montana and Wyoming, in Flores, R.M.,

PF-15 and Kaplan, S.S., eds., Cenozoic Paleogeography of the West-Central United States: Society of Economic Paleontologists and Mineralogists, Rocky Mountain Section, Symposium 3, p. l07-l26. Flores, R.M., and Moore, T.A., 1994, Mechanisms of splitting of the Anderson- Dietz coal bed in the Decker area, Montana: a synthesis, 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. 153-161. Lewis, B.D., and Hotchkiss, W.R., 1981, Thickness, percent sand, and configuration of shallow hydrologic units in the Powder River Basin, Montana and Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Map I-1317. Mapel, W.J., 1959, Geology and coal resources of the Buffalo-Lake de Smet area, Johnson and Sheridan Counties, Wyoming: U.S. Geological Survey Bulletin 1078, 148 p. Moore, T.A., 1994, Organic compositional clues to a stacked mire sequence in the Anderson-Dietz 1 coal bed (Paleocene), Montana, 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. 163-172. Nichols, D.J., Wolfe, J.A., and Pocknall, D.T., 1989, Latest Cretaceous and early Tertiary history of vegetation in the Powder River Basin, Montana and Wyoming: 28th International Geological Congress, Field Trip Guidebook T132, p. T132:28ÐT132:33. Sholes, M.A., and Daniel, J.A., 1992, The Knobloch coal bed, Powder River and Rosebud Counties, Montana: correlation and petrography, in Sholes, M.A., ed., Coal Geology of Montana: Montana Bureau of Mines and Geology,

PF-16 Special Publication 102, p. 105-135. Stricker, G.D., Ellis, M.S., 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 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, p. 967-976. Warwick, P.D., and Stanton, R.W., 1988, Depositional models for two Tertiary coal-bearing sequences in the Powder River Basin, USA: Journal of the Geological Society of London, v. 145, p. 613-620.

PF-17 108¡ 106¡ 104¡

Custer Treasure Rosebud Fallon Carter North Dakota 46¡ South Dakota Powder River

Big Horn Montana 45¡ Sheridan Wyoming Campbell

Crook

44¡

Weston Johnson Niobrara Natrona

43¡

10 0 10 20 Miles Converse

Figure PF-1. Location map showing the Powder River Basin. CREVASSE SPLAY SYSTEM CREVASSE CHANNEL OF AVULSION

Meandering stream

Aggrading crevasse splay systems

ANASTOMOSING STREAMS

Raised swamp Anastomosed fluvial deposits

Abandoned meander belt deposits Figure PF-2. Depositional models of braided, meandering, and anastomosed streams in the Powder River Basin, adapted from Flores (1986). Figure PF-3. Modern analog of a fluvial system consisting of braided, meandering, and anastomosed channels of the Susitna River in Alaska. Photograph by J.H. McGowen. Figure PF-4. Modern analog of a peat-forming, low-lying swamps in the Atchafalaya River Basin in Louisiana. Photograph by R.M. Flores. CONIFEROUS, SHRUBBY AND HERBACEOUS CONIFEROUS, BROAD-LEAVED, PLANTS, FERNS, ALGAE, BROAD-LEAVED, AND RIPARIAN PLANTS AND SPHAGNUM AND RIPARIAN PLANTS

WOOD PEAT FIBROUS PEAT CLASTIC SEDIMENT (HUMINITE-RICH COAL) (DENSINITE-RICH COAL) PARTING

Figure PF-5. Cross section of a domed mire with associated vegetation and peat types, adapted from Warwick and Stanton (1988). el nn a h Raised Mire C

Point Bar Lake

Cr eva sse Sp l lay ne an h Peat C

Floodplain

Figure PF-6. Depositional model of the Wyodak-Anderson coal zone and associated sediments in the Decker coalfield, Montana. Adapted from Moore (1986) and Flores and others (1989). Figure PS-7. Peat exposed along a drainage ditch cut near the margin of a raised bog in central Kalimantan, Borneo. Photograph by C. Blaine Cecil. Hanna and Carbon Basins Powder River Greater Basin Green River Williston Basin Basin

P1 P2 P3 Zones: 500 Meters P4 P5 P6

Figure PF-8. Composite correlation of Paleocene sections based on palynostratigraphy. units inthePowderRiverBasinare highlightedinred. studied coalbedsandzoneswithage relationshipsbasedonpalynology.Assessment Figure PF-9.Compositestratigraphic sectionfortheassessmentregionshowing Paleocene middle (Zones (Zones (Zones P1-P2) P3-P4) P5-P6) early late Knobloch Johnson-107 Hagel Hanna Nos.77-79,81 Beulah-Zap Wyodak-Anderson 25, 31,50,&65 Ferris Nos.23, Deadman Seams1-5 Hansen Harmon Rosebud ...... } ...... } ...... } ...... Greater GreenRiverBasin Powder RiverBasin Powder RiverBasin Williston Basin Williston Basin Williston Basin Carbon Basin Hanna Basin Hanna Basin 108¡ 106¡ 104¡

Custer Treasure

Fallon

North Dakota 46¡ South Dakota

Powder River Powder River Basin B Rosebud

Carter Montana 45¡ Big Horn A Sheridan Crook Wyoming

C'

D' Weston C E' 44¡ D

E Washakie Johnson Campbell Converse Niobrara Natrona A'

43¡ B'

10 0 10 20 Miles

Figure PF-10. Map showing locations of Cross section with nonproprietary A A' Wyodak-Anderson coal zone cross sections. drill holes North South 114.78 Miles

37.6 Miles 12.61 Miles 8.40 Miles 8.55 Miles 16.08 Miles 21.29 Miles 10.25 Miles A A' Elevation Elevation (feet) (feet) 5100 WYODAK-ANDERSON 5100 5100 WYODAK-ANDERSON 5100 WYODAK-ANDERSON 5100 WYODAK-ANDERSON COAL ZONE COAL ZONE

COAL ZONE D-D' 4900 COAL ZONE 4900 4900 4900 4900 E-E' E-E' E-E' E-E' 4700 4700 4700 4700 C-C' C-C' C-C' C-C' C-C'

4500 C-C' 4500 4500 C-C' C-C'

4300 4300

4100 4100

3900 3900

3700 3700

3500 3500 3500

3300 3300 3300

Coal 3100 Sandstone 3100 3100 3100 Mudstone "Rock" Datum = Sea Level Datum = Sea Level 2900 No record 2900 2900 2900 2900

The term "rock" indicates undifferentiated sandstone, siltstone, mudstone, and limestone. Figure PF-11. Wyodak-Anderson coal zone structural cross section A-A'. Figure PF-12.V e getation and logging railroad on top of a raised mire in Central Kalimantan, Borneo. Photograph by C. Blaine Cecil. Figure PF-13. Domed mire along a drainage ditch that parallels an oil field road between the Siak and Kampar River/estuaries in Sumatra, Indonesia. Photograph by C. Blaine Cecil. Figure PF-14. Meandering and anastomosed channels of the Beluga River in the Upper Cook Inlet, Alaska. Photograph by R.M. Flores. Figure PF-15. Fluvial channels, overbank, lakes, floodplains, and low-lying swamps of the Saskatchewan River in the Saskatchewan Province, Canada. Photograph by N.D. Smith. Figure PF-16. Abandoned crevasse channels, splays, and low-lying swamps of the Saskatchewan River in the Saskatchewan Province, Canada. Photograph by N.D. Smith. North South 199.5 Miles

36.04 Miles 42.87 Miles 29.45 Miles 18.01 Miles 26.72 Miles 10.69 Miles 21.04 Miles 14.68 Miles B B'

Elevation WYODAK-ANDERSON COAL ZONE (feet) ("BIG GEORGE" COAL ZONE) 5600 5600 WYODAK-ANDERSON COAL ZONE 5400 5400 ("ANDERSON-CANYON" COAL ZONE) 5200 5200 5000 Elevation 4800 (feet) 4600 4600 4600 4600 4600 C-C' 4400 4400 4400 4400 4400

4200 4200 4200 4200 4200 4200

4000 4000 4000 4000 4000 4000

3800 3800 3800 3800

3600 3600 E-E' 3600 3600

3400 3400 3400 3400 D-D'

3200 3200 3200

3000 3000 Datum = Sea Level 3000 2800 2800 WYODAK-ANDERSON COAL ZONE 2600 2600 2600

2400 2400 ("SCHOOL-BADGER" COAL ZONE)

2200 2200 2000 2000 Coal 1800 1800 1800 Sandstone WYODAK-ANDERSON COAL ZONE 1600 1600 1600 Mudstone 1400 1400 1400 "Rock" ("SUSSEX" COAL ZONE) 1200 1200 1200 No record 1000 Datum = Sea Level 1000 1000 The term "rock" indicates undifferentiated sandstone, siltstone, mudstone, and limestone. Figure PF-17. Wyodak-Anderson coal zone structural cross section B-B'. West East 52.60 Miles 25.19 Miles 18.77 Miles 8.67 Miles C C' Elevation Elevation (feet) (feet) 4900 4900 4900

4700 B-B' 4700 A-A' A-A' A-A' A-A' A-A' A-A' A-A' A-A' 4500 4500

4300 4300

4100 4100

3900 3900

3700 3700 WYODAK-ANDERSON 3500 COAL ZONE 3500

3300 3300

3100 3100

2900 2900

2700 2700 Coal 2500 Sandstone 2500

2300 Mudstone 2300 "Rock" 2100 2100 No record 2100

1900 1900 The term "rock" indicates undifferentiated 1900 sandstone, siltstone, mudstone, and limestone. 1700 1700 1700

1500 1500 1500

1300 1300 Datum = Sea Level 1300 Datum = Sea Level Wyodak-Anderson coal zone Figure PF-18. Wyodak-Anderson coal zone structural cross section C-C'. West East 63.92 Miles

25.33 Miles 15.68 Miles 12.21 Miles 10.70 Miles D D' Elevation Elevation (feet) (feet)

5000 5000 5000 5000 A-A' 5000

4800 4800 4800

4600 4600

4400 4400

4200 4200

4000 4000 3800 Wyodak-Anderson 3800 3600 3600 B-B' 3400 Coal Zone 3400 3200 3200

3000 Wyodak-Anderson 3000 coal zone 2800 { 2800 2800 2600 2600 Coal 2600 Sandstone 2400 2400 2400 Mudstone 2400

2200 2200 2200 "Rock" 2200

2000 2000 2000 The term "rock" indicates undifferentiated 2000 sandstone, siltstone, mudstone, and limestone. 1800 1800 Wyodak-Anderson 1800 1800 1600 1600 1600 1600 1400 Datum = Sea Level 1400 Coal Zone 1400 Datum = Sea Level 1400

Figure PF-19. Wyodak-Anderson coal zone structural cross section D-D'. West East 59.45 Miles E E'

Elevation Elevation (feet) (feet) 5000 5000 5000 A-A' A-A' A-A'

4800 4800 A-A' 4800

4600 4600

4400 4400

4200 Wyodak-Anderson coal zone 4200

4000 4000

3800 3800 B-B'

3600 Quaternary Rocks 3600 Coal 3400 3400 Sandstone Mudstone 3200 3200 "Rock" 3000 3000 No record 3000

The term "rock" indicates undifferentiated 2800 2800 2800 sandstone, siltstone, mudstone, and limestone.

2600 2600 2600

2400 2400 Datum = Sea Level 2400 Datum = Sea Level Wyodak-Anderson coal zone Figure PF-20. Wyodak-Anderson coal zone structural cross section E-E'.