Bighorn through Park Formation: Bighorn, Red Lion, Pilgrim, and Park Formations

Bighorn Formation (Ob): Yellowish gray to very pale orange crystalline dolomite with local basal sandstone. Marine shelf. Thickness as much as 120 m (394 ft). Red Lion Formation: Gray limestone with siliceous lamina and black calcareous shale interbedded with thin limestone. Shallow marine. Thickness as much as 115 m (377 ft). Pilgrim Formation: Gray, commonly mottled limestone that may contain intraformational limestone conglomerate. Shallow marine. Thickness as much as 180 m (590 ft). Park City Formation: Gray limestone, tan dolomite, and interbedded sandstone, phosphatic shale, and cherty carbonate. Marine shelf. Thickness as much as 115 m (377 ft).
State Montana
Name Bighorn through Park Formation: Bighorn, Red Lion, Pilgrim, and Park Formations
Geologic age Ordovician and Cambrian
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Carbonate > Dolostone (Bed)
Minor
Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed, Calcareous)
Sedimentary > Clastic > Conglomerate (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Incidental
Sedimentary > Clastic > Mudstone > Shale > Phosphatic-shale (Bed)
Sedimentary > Chemical > Chert (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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Counties Madison