Pierre Formation

Pierre Shale Stratigraphic range: Campanian PreЄ Є O S D C P T J K Pg N
A broken concretion with fossils inside; Late Cretaceous Pierre Shale near Ekalaka, Montana.
Type	Geological formation
Underlies	Fox Hills beds
Overlies	Niobrara Formation
Lithology
Primary	Shale
Location
Region	North America
Country	USA,  Canada
Type section
Named for	Fort Pierre
Named by	Meek & Hayden, 1862

The Pierre Shale /pɪər ʃeɪl/ 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.