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Pierre Shale
Stratigraphic range: Campanian
A broken concretion with fossils inside; Late Cretaceous Pierre Shale near Ekalaka, Montana
Type Geological formation
Underlies Fox Hills Formation
Overlies Niobrara Formation
Primary Shale
Coordinates 44°23′42″N 100°24′43″W / 44.395°N 100.412°W / 44.395; -100.412
Region North America
Country  United States,
Type section
Named for Fort Pierre
Named by Meek & Hayden, 1862
Baculites from the Pierre Shale showing sutures and remnant aragonite; western South Dakota, Late Cretaceous.

The Pierre Shale 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.

Most of the formation was deposited in the Campanian Age of the late Cretaceous. However, the discovery of fossils of Baculites baculus Meek and Hayden in the uppermost beds of the Pierre Shale in the Raton, New Mexico area show that deposition continued here into the early Maastrichtian.

Mineral resources

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.



Hesperornithiformes reported from the Pierre Shale Formation
Genus Species Location Stratigraphic position


B. varneri

South Dakota

Sharon Springs member.

B. sp.


Pembina member.


H. bairdi

South Dakota

Sharon Springs member.

H. chowi

Manitoba & South Dakota

Pembina, Millwood, & Sharon Springs members.

H. lumgairi


Pembina member.

H. macdonaldi

Manitoba & South Dakota.

Gammon, Pembina, Millwood(?), & Sharon Springs members.

H. mengeli

Manitoba & South Dakota.

Pembina & Sharon Springs members.

H. regalis

Manitoba, South Dakota, & Kansas

Gammon, Pembina, & Sharon Springs members.


  • Claosaurus affinis (hadrosaurid indet) "Pedal phalanx (lost)."

Marine vertebrates


  • Inoceramus
  • Several species of ammonites
  • Several species of Baculites
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