Bearpaw Formation

Dark gray shale with several zones of calcareous concretions, a basal zone of ferruginous concretions, and numerous thin bentonite beds. Marine. Thickness as much as 300 m (984 ft).
State Montana
Name Bearpaw Formation
Geologic age Cretaceous
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale (Bed, Calcareous)
Minor
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.

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