Usage:
Orchard Creek Shale (IL*,MO*)
Orchard Creek Shale of Maquoketa Group (IL*,MO*)
Orchard Creek Formation (MO)
Orchard Creek Shale Member of Scales Formation (IL)
Geologic age:
Ordovician, Late*
Cincinnatian*
Type section, locality, area and/or origin of name:
Type section: along Orchard Creek (now covered), 2 mi south of Thebes, in sec. 21, T. 15 S., R. 3 W., Alexander Co., southern IL (Thompson, 1991).
Reference section: across Mississippi River from southern Cape Girardeau Co., on east bank of Mississippi River 1 mi north of Thebes, in SE/4 SE/4 sec. 5, T. 15 S., R. 3 W., Thebes 7.5-min quadrangle, Alexander Co., southern IL (Thompson, 1991).
AAPG geologic province:
Illinois basin*
Ozark uplift
Upper Mississippi embayment*
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 ([ ]).