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The Wasatch Formation (Tw)[1] is an extensive highly fossiliferous geologic formation stretching across several basins in Idaho, Montana, Wyoming, Utah and western Colorado.[2] It preserves fossils dating back to the Early Eocene period. The formation defines the Wasatchian or Lostcabinian (55.8 to 50.3 Ma), a period of time used within the NALMA classification, but the formation ranges in age from the Clarkforkian (56.8 to 55.8 Ma) to Bridgerian (50.3 to 46.2 Ma).
Wasatch fauna consists of many groups of mammals, including numerous genera of primates, artiodactyls, perissodactyls, rodents, carnivora, insectivora, hyaenodonta and others. A number of birds, several reptiles and fish and invertebrates complete the diverse faunal assemblages. Fossil flora and ichnofossils also have been recovered from the formation.
The formation, first named as Wasatch Group in 1873 by Ferdinand Vandeveer Hayden, was deposited in alluvial, fluvial and lacustrine environments and comprises sandstones, siltstones, mudstones and shales with coal or lignite beds representing wet floodplain settings.
The Wasatch Formation is an unconventional tight gas reservoir formation in the Uinta and Piceance Basins of Utah and the coal seams of the formation are mined in Wyoming. At the Fossil Butte National Monument, the formation crops out underlying the Green River Formation. In the Silt Quadrangle of Garfield County, Colorado, the formation overlies the Williams Fork Formation.[3]
- ^ Shroba & Scott, 2001, p.3
- ^ Wasatch Formation at Fossilworks.org
- ^ Shroba & Scott, 2001, p.18