The Duchesne River Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

in the

Uinta Basin The Uinta Basin (also known as the Uintah Basin) is a physiographic section of the larger Colorado Plateaus province, which in turn is part of the larger Intermontane Plateaus physiographic division. It is also a geologic structural basin in ...

of northeastern

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

. It was originally named the Duchesne Formation by Carnegie Museum paleontologist OA Peterson, and modified to the Duchesne River Formation by Carnegie Museum paleontologist JL Kay because Duschesne Formation was previously used for a Jurassic limestone. In naming the formation, no type section was given, only that it is named for the Duchesne River, which flows roughly southeast and east to join the Green River. The formation consists of over 3000 feet (915 m) of fluvial conglomerate, sandstone and fine-grained sedimentary rocks. It is subdivided into four members (below), whose sediments are thought to have eroded from the rising

Uinta Mountains The Uinta Mountains ( ) are an east-west trending mountain range in northeastern Utah extending a short distance into northwest Colorado and slightly into southwestern Wyoming in the United States. As a subrange of the Rocky Mountains, they are u ...

to the north and deposited in river, floodplains and small lakes. Volcanic ash in the formation, derived from volcanoes in the Wasatch Range, East Tintic, and Oquirrh Mountains to west, have provided radiometric dates. These dates range from 38.2 +/-1.8 Ma for the Brennan Basin Member to 28.7 +/-2.0 Ma for the Lapoint Member. Members and their Vertebrate FossilsAndersen, D.W., and Picard, M.D., 1972, Stratigraphy of the Duchesne River Formation (Eocene-Oligocene?), northern Uinta basin, northeastern Utah: Utah Geological and Mineral Survey Bulletin, no. 97, 29 p. Brennan Basin Member: Named for Brennan Basin, Uintah County. Predominately sandstone that varies from yellow-gray to red brown, very fine, fine, medium, to coarse grained, thin to thick to very thick bedded, generally poorly sorted, and may be nodular, silty, pebbly, and cross stratified. Minor beds of green-gray to red brown, silty to sandy, thin to very thin bedded, poorly sorted claystone, red brown, thin-bedded, nodular, poorly sorted

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

, yellow brown, very thin bedded, nodular, poorly sorted, horizontally stratified

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

, and red-purple, sandy, clayey, thin-bedded, medium to coarse crystalline limestone. Contains a diverse late Eocene vertebrate fauna. Reptilia Chelonia

C''ymatholcus longus'' Clark

Crocodilia

''Crocodilus''? ''acer'' Cope

Mammalia Lagomorpha

''Mytonolagus petersoni'' Burke

Rodentia

''Leptotomus kayi'' Burke ?Sciuravid or Myomorph sp. ''Pareumys'' sp. ''Protadjidaumo typus'' Burke ''Mytonomys robustus'' (Peterson) Wood

Carnivora

Pleurocyon? or Uintacyon? sp.

Perissodactyla

''Protitanotherium'' sp. ''Dilophodon leotanus'' (Peterson) Hough ''Epitriplopus medius'' Peterson ''Mesamynodon medius'' Peterson ''Megalamynodon regalis'' Wood

Artiodactyla

''Pentacemylus progressus'' Peterson ''Diplobunops crassus'' Scott ''Protoreodon pumilus annectens'' (Marsh) Gazin ''Protoreodon primus'' (Peterson) Gazin ?Hypertragulid sp.

Dry Gulch Creek Member: Named for Dry CGulch Creek, Uintah County. Consists of pale red, olive gray to yellow brown, coarse, medium, fine to very fine grained, thin-, thick to very thick bedded, massive, moderately to poorly sorted sandstone that may be horizontally or cross stratified and red, gray to brown, very thin, thin- to thick-bedded, moderately to poorly sorted claystone that may be nodular, micaceous, or laminated. Contains plant remains and a sparse vertebrate fauna. Mammalia Carnivora

''Eosictis avinoffi'' Scott

Perissodactyla

''Epihippus'' (''Duchesnehippus'') ''intermedius'' Peterson

Lapoint Member: Named for the town of Lapoint, Uintah County. Composed of olive, green-gray, dark gray, very thin to thin bedded, nodular, poorly sorted, horizontally stratified, laminated claystone; light gray, light brown, gray orange to red brown, thin-bedded, slabby, horizontally stratified, poorly sorted, medium-grained, to thick-bedded, blocky, poorly sorted, coarse-grained sandstone; gray-red to red-brown, thin-bedded, nodular, horizontally stratified, poorly sorted siltstone; and gray-orange, very thick bedded, massive, poorly sorted pebble conglomerate. Abundant late Eocene vertebrates. Reptilia Crocodilia

''Crocodilus''? ''acer'' Cope

Mammalia Insectivora

Protictops alticuspidens Peterson

Rodentia

''Leptotomus kayi'' Burke ''Pareumys guensburgi'' Black ''Protadjidaumo typus'' Burke

Creodonta

''Hyaenodon'' sp.

Mesonychia

''Hessolestes ultimus'' Peterson

Perissodactyla

''Teleodus uintensis'' Peterson ''Epitriplopus medius'' Peterson ''Hyracodon primus'' Peterson ''Mesamynodon medius'' Peterson

Artiodactyla

''Pentacemylus progressus'' Peterson ''Helohyus''(?) sp. ''Poabromylus kayi'' Peterson ''Simimeryx minutus'' (Peterson) Gazin

Starr Flat: Named for John Starr Flat, Duchesne County. Consists of: 1) red- to yellow-brown, light gray, gray- to yellow-orange, pale red to gray red sandstone that ranges from coarse, medium, fine to very fine grained, thin, thick to very thick bedded, sandy, silty, to clayey, cross-stratified to horizontally stratified, flaggy, blocky, massive, brown-gray, gray-red to olive, sandy to silty; 2) very thin bedded, poorly sorted, platy, laminated, nodular to massive claystone; and 3) gray red, sandy, poorly sorted, thin-bedded, nodular, massive siltstone. Sandstone may also be poorly sorted, pebbly, nodular and massive. No fossils found.

References

{{reflist Paleogene geology of Utah Conglomerate formations of the United States Sandstone formations of the United States

See also

References