- Usage in publication:
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- Ahearn member
- Modifications:
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- Original reference
- AAPG geologic province:
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- Williston basin
Summary:
Pg. 197. Ahearn member of Chadron formation. Designated basal member of Chadron formation [White River group not used]. Author previously described unit as "Lower Member" of Chadron (Clark, 1937). Is fossiliferous. Includes red sediments inherited from a lateritic soil on the uplands or from Spearfish and Opeche formations in Black Hills. Underlies Crazy Johnson member (new) of Chadron. Age is Oligocene.
Type locality: at standard section for the Chadron formation in Big Badlands on south fork of Indian Creek, Pennington Co., SD, from sec. 34, T. 3 S., R. 12 E. to sec. 10, T. 4 S., R. 12 E. Named from ranch formerly at mouth of south fork of Indian Creek.
Source: US geologic names lexicon (USGS Bull. 1200, p. 30); supplemental information from 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 ([ ]).