Fort Union Formation
Encyclopedia
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
.
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.
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. 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.
A partial ornithurine coracoid bone found in this formation is identical to others found in the older Hell Creek Formation
. At present, this unnamed species is the only known individual bird
species that have survived the K-Pg extinction event.
Geologic unit
A geological unit is a volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features that characterize it....
containing sandstones, shales, and coal beds in Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, and parts of adjacent states. In the Powder River Basin
Powder River Basin
The Powder River Basin is a geologic region in southeast Montana and northeast Wyoming, about east to west and north to south, known for its coal deposits. The region supplies about 40 percent of coal in the United States. It is both a topographic drainage and geologic structural basin...
, it contains important economic deposits of coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
, uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, and coalbed methane
Coalbed methane
Coalbed methane or Coal Bed Methane, coalbed gas or coal mine methane is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, and other countries...
.
The Fort Union is mostly of Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
age and represents a time of extensive swamps as well as fluvial and lacustrine
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
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.
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. One such bed, the Wyodak Coal near Gillette, Wyoming
Gillette, Wyoming
Gillette is a city in and the county seat of Campbell County, Wyoming, United States. The population was 29,087 in 2010. Gillette is a city centrally located in an area involved with the development of vast quantities of American coal, oil, and coal bed methane gas...
, is as much as 110 feet thick. Most of the coals in the Fort Union Formation are ranked subbituminous.
A partial ornithurine coracoid bone found in this formation is identical to others found in the older Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
. At present, this unnamed species is the only known individual bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
species that have survived the K-Pg extinction event.