Pierre Shale

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[1] to New Mexico.

Pierre Shale Stratigraphic range: Campanian PreꞒ Ꞓ 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 Formation
Overlies	Niobrara Formation
Lithology
Primary	Shale
Location
Coordinates	44.395°N 100.412°W / 44.395; -100.412
Region	North America
Country	United States,  Canada
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 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.[2]

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.[3] It correlates with the Lea Park Formation in central Alberta.[4] 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.[5]