Pierre Formation

Dark gray, partly silty shale with abundant bentonite beds and zones of gray, calcareous concretions. Marine. Thickness as much as650 m (2,133 ft). Only upper 50 m (164 ft) exposed.
State Montana
Name Pierre Formation
Geologic age Cretaceous
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale (Bed, Calcareous)
Sedimentary > Clastic > Mudstone > Claystone > Bentonite (Bed)
References

Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana - Compact Disc: Montana Bureau of Mines and Geology: Geologic Map 62-C, 73 p., 2 sheets, scale 1:500,000. This map was digitized in 2012 as a result of a contract between the U.S. Geological Survey and the Montana Bureau of Mines and Geology.

NGMDB product
Counties Carter - Dawson - Fallon - Prairie - Wibaux