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Groat sandstone bed of Pierre Formation

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Gray, ferruginous and glauconitic, fine- to coarse-grained sandstone, siltstone, and sandy to silty gray shale. Offshore marine. Pinches out laterally. Thickness as much as 100 m (328 ft).
State Montana
Name Groat sandstone bed of Pierre Formation
Geologic age Cretaceous
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone (Bed, Glauconitic)
Sedimentary > Clastic > Siltstone (Bed)
Minor
Sedimentary > Clastic > Mixed-clastic > Siltstone-mudstone (Bed)silty shale
Sedimentary > Clastic > Mixed-clastic > Sandstone-mudstone (Bed)sandy shale
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