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Geologic Unit: Retort
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  • Usage in publication:
    • Retort phosphatic shale member*
  • Modifications:
    • Named
  • Dominant lithology:
    • Mudstone
    • Phosphorite
  • AAPG geologic province:
    • Montana folded belt
Publication:

McKelvey, V.E., Cheney, T.M., Cressman, E.R., Sheldon, R.P., Swanson, R.W., and Williams, J. Steele, 1959, The Phosphoria, Park City, and Shedhorn formations in the western phosphate field, IN Geology of Permian rocks in the western phosphate field: U.S. Geological Survey Professional Paper, 313-A, p. A1-A47., See also "Summary description of Phosphoria, Park City, and Shedhorn Formations in western phosphate field," AAPG Bull., v. 40, no. 12, p. 2826-2863, 1956 (advance summary)


Summary:

Named (Swanson, p. 29-30) as a member of Permian Phosphoria formation. Type locality designated near head of Small Horn Canyon, northwest of Retort Mountain, Beaverhead Co., MT. Section measured in SW1/4 sec 23, T9S, R9W in Beaverhead Co. in Montana folded belt province. Occurs also in Yellowstone province, WY, Wind River and Bighorn basins, WY, Snake River basin, ID, and Wasatch uplift, UT. Composed of medium-hard, dark brownish-gray mudstone and argillaceous, dark brown to black, thin-bedded phosphorite. Is 59.9 ft thick at measured section where it overlies Franson tongue of Park City formation and underlies Tosi chert member of Phosphoria formation. Ranges from 55 to 80 ft thick. Thins northward to 3 to 5 ft in Garrison region. Contains brachiopods, mollusks, and fish.

Source: GNU records (USGS DDS-6; Denver GNULEX).


For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).

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