Usage:
Marcus Formation (IL)
Marcus Member of Hopkinton Formation (IL,IA)
Geologic age:
early Silurian (Llandovery)
Type section, locality, area and/or origin of name:
Type section: Abandoned quarry in southern part of Mississippi Palisades State Park, Carroll Co., northwestern IL. Named from village of Marcus, 6.5 km northwest of type section (Willman, 1973).
AAPG geologic province:
Wisconsin 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 ([ ]).