Usage:
Gregory Member of Pierre Shale (NE*,ND*,SD*)
Geologic age:
Late Cretaceous (Campanian)*
Type section, locality, area and/or origin of name:
Named from Gregory County (Searight, 1937).
Type section: along Missouri River in cut bank at south end of Rosebud (Wheeler) Bridge, [in SE/4 sec. 7, T. 96 N., R. 67 W.], eastern Gregory Co., central southern SD, south of Wheeler, which is in Charles Mix Co., central southern SD. [Bridge and town no longer exist; type section now submerged beneath Lake Francis Case.] Also well exposed to east of Missouri River, especially south of U.S. Highway 18 in Charles Mix Co., central SD (Searight, 1937; see also Crandell, 1950, Schultz, 1965).
Principal reference section: near Landing Creek, in NW/4 sec. 25, T. 100 N., R. 72 W., [Dixon 7.5-min quadrangle], Gregory Co., central southern SD (Schultz, 1965, USGS Prof. Paper 392-B).
Reference locality: Chamberlain section, in and above first big roadcut north of U.S. Highway 16 at west end of highway bridge across Missouri River at Chamberlain, in NW/4 NE/4 sec. 17, T. 104 N., R. 71 W., Lyman Co., SD (Schultz, 1965).
Reference sections (for Pierre Shale): (1) near Little Yellowstone Park, about 20 mi south of Valley City, in sec. 31, T. 137 N., R. 57 W., and in secs. 35 and 36, T. 137 N., R. 58 W., Barnes Co., ND; (2) Pembina Mountain section, measured in sec. 24, T. 161 N., R. 57 W., Cavalier Co., ND (Gill and Cobban, 1965).
AAPG geologic province:
Williston basin*
Sioux uplift*
Chadron arch*
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 ([ ]).