Fort Union Formation

The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. In the Powder River Basin, it contains important economic deposits of coal, uranium, and coalbed methane. [ [http://www.searchanddiscovery.net/documents/2005/ashley/index.htm "Wyodak Coal, Tongue River Member of the Fort Union Formation, Powder River Basin, Wyoming: "No-Coal Zones" and Their Effects on Coalbed Methane Production", by Mark Ashley, 2005] ]

The Fort Union is mostly of Paleocene age and represents a time of extensive swamps as well as fluvial and lacustrine conditions. The rocks are more sandy in southwestern Wyoming and more coal-bearing in northeast Wyoming and southeast Montana, reflecting a general change from rivers and lakes in the west to swamps in the east, but all three environments were present at various times in most locations. ["Eocene and Paleocene rocks of the southern and central basins", by Robert E. McDonald, "in" Geologic Atlas of the Rocky Mountain Region, Rocky Mountain Association of Geologists, Denver, CO, 1972: p. 248]

Coal in the Fort Union in the Powder River Basin occurs mainly in the Tongue River Member, where as many as 32 coal seams total more than 300 feet in thickness. [ [http://www.searchanddiscovery.net/documents/2005/ashley/index.htm "Wyodak Coal, Tongue River Member of the Fort Union Formation, Powder River Basin, Wyoming: "No-Coal Zones" and Their Effects on Coalbed Methane Production", by Mark Ashley, 2005] ] One such bed, the Wyodak Coal near Gillette, Wyoming, is as much as 110 feet thick. Most of the coals in the Fort Union Formation are ranked subbituminous. ["Cretaceous and Tertiary coals of the Rocky Mountains and Great Plains regions", by R.M. Flores and T.A. Cross, 1991, "in" Economic Geology, U.S., Geological Society of America, Decade of North American Geology Series, vol. P-2, p. 547-571.]

ee also

Uranium mining in Wyoming

References