The Pierre Shale (pronounced /peer shāl/) is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from Pembina Valley in Canada to New Mexico.
The Pierre Shale was described by Meek and Hayden in 1862 in the Proceedings of the Academy of Sciences (Philadelphia). They described it as a dark-gray shale, fossiliferous, with veins and seams of gypsum, and concretions of iron oxide. The Pierre Shale is about 700 feet (210m) thick at the type locality. It overlies the Niobrara division and underlies the Fox Hills beds. It was named for an occurrence near Fort Pierre on the Missouri River in South Dakota.
The Pierre Shale is of marine origin and was deposited in the Western Interior Seaway. It is correlative with other marine shales that occur farther west, such as the Bearpaw Shale, Mancos Shale and the Lewis Shale. It correlates with the Lea Park Formation in central Alberta. The Pierre is overlain by marginal marine deposits of the Fox Hills Formation.
The Pierre Shale is the host formation for commercial oil deposits in the Florence and Canon City fields in Fremont County, Colorado, and the Boulder oil field in Boulder County, Colorado. More recently, natural gas has been extracted in the Raton Basin in southern Colorado. The shale formation is usually too impermeable for hydrocarbon extraction, but produces in areas where it is naturally fractured or fractured by artificial means.
- Claosaurus affinis (hadrosaurid indet) "Pedal phalanx (lost)."
- Several species of Ammonite
- Several species of Baculites
- Canadian Fossil Discovery Centre. "All About Bruce".
- M.E. Maclachlan, New Mexico Geological Society Guidebook, 27th Field Conference, Vermejo Park, 1976
- G.A. Izett and others, The Pierre Shale near Kremmling, Colorado, and its correlation to the east and the west, US Geological Survey, Professional Paper 684-A.
- Lexicon of Canadian Geologic Units. "Lea Park Formation". Retrieved 2009-03-23.
- "Table 20.1," in Weishampel, et al. (2004). Page 442.
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