Geology
The Bighorn Basin forms a geologic structural basin filled with more than 20,000 feet (6,100 m) of sedimentary rocks from Cambrian to Miocene in age. Since the early 20th century the basin has been a significant source of petroleum, and has produced more than 1,400,000,000 barrels (220,000,000 m3) of oil. The principal reservoir of oil is the Pennsylvanian Tensleep Formation; Other important petroleum horizons are the Mississippian Madison Limestone, Permian Phosphoria Formation and the Cretaceous Frontier Sandstone.
Some uranium has been mined in the northern part of the basin, along the Bighorn Mountains.
The eastern section of the basin is famously rich in fossils, with formations such as the Cretaceous era Cloverly Formation yielding numerous dinosaur fossils.
The alluvial strata of the Willwood and Fort Union Formations of the Bighorn Basin contain a well-documented record of the Paleocene-Eocene Thermal Maximum (PETM). Analysis of paleosols here shows that the Bighorn Basin became more arid during the PETM, with wet/dry cycles superimposed over this general increase in aridity. These changes in environment are coupled with changes in paleoecology.
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