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Geologic Unit: Pedro
Map showing publication footprint
  • Usage in publication:
    • Pedro bentonite bed*
  • Modifications:
    • Named
  • Dominant lithology:
    • Clay
    • Tuff
  • AAPG geologic province:
    • Powder River basin
Publication:

Rubey, W.W., 1931, Lithologic studies of fine-grained Upper Cretaceous sedimentary rocks of the Black Hills region, IN Shorter contributions to general geology, 1930: U.S. Geological Survey Professional Paper, 165-A, p. A1-A54.


Summary:

Named as a bed at base of Gammon ferruginous member (new) of Pierre shale for exposures near Pedro, sec 5, T45N, R63W, Weston Co, WY in Powder River basin. Consists of hard, white, massive clay and tuff. Locally 20 ft thick but not extensive. Type section not designated. Overlies Niobrara formation with possible unconformity. Late Cretaceous in age.

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


Map showing publication footprint
  • Usage in publication:
    • Pedro bentonite zone
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Chadron arch
Publication:

Gries, J.P., 1942, Economic possibilities of the Pierre shale: South Dakota Geological Survey Report of Investigations, no. 43, 79 p.


Summary:

Correlated with a zone of fissile shale and contrasting beds of bentonite in Sharon Springs member of Pierre shale south of Black Hills in Fall River and Custer Co, SD on Chadron arch.

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


Map showing publication footprint
  • Usage in publication:
    • Pedro Bentonite Bed*
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Powder River basin
Publication:

Mapel, W.J., and Pillmore, C.L., 1963, Geology of the Newcastle area, Weston County, Wyoming, IN Contributions to general geology, 1961: U.S. Geological Survey Bulletin, 1141-N, p. N1-N85.


Summary:

Pedro Bentonite Bed is basal bed of Mitten Black Shale Member (rather than Gammon Member) of Pierre Shale. Is thickened equivalent of Ardmore Bentonite Bed.

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


Map showing publication footprint
  • Usage in publication:
    • Pedro Bentonite Bed*
  • Modifications:
    • Revised
Publication:

Love, J.D. (compiler), Christiansen, A.C. (compiler), and McGrew, L.W. (compiler), 1977, Geologic map of the Newcastle 1 degree x 2 degrees quadrangle, northeastern Wyoming and western South Dakota: U.S. Geological Survey Miscellaneous Field Studies Map, MF-883, 1 sheet, scale 1:250,000


Summary:

Term "Black Shale" deleted from formal name Mitten; Mitten Member of Pierre Shale used. [Includes Pedro Bentonite Bed.]

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


Map showing publication footprint
  • Usage in publication:
    • Pedro Bentonite Bed*†
  • Modifications:
    • Abandoned
Publication:

Schultz, L.G., Tourtelot, H.A., Gill, J.R., and Boerngen, J.G., 1980, Composition and properties of the Pierre Shale and equivalent rocks, northern Great Plains region, IN Geochemistry of the Pierre Shale and equivalent rocks of Late Cretaceous age: U.S. Geological Survey Professional Paper, 1064-B, 114 p. [Available online from the USGS PubsWarehouse: http://pubs.er.usgs.gov/pubs/pp/pp1064B]


Summary:

Pedro Bentonite Bed of Mitten Member of Pierre Shale abandoned in favor of Ardmore Bentonite Beds in the Black Hills in SD and WY, Williston and Powder River basins.

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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