Usage:
Mason City Member of Shell Rock Formation of Cedar Valley Group (IA)
Geologic age:
early Late Devonian (Frasnian)
Type section, locality, area and/or origin of name:
Named from exposures at Mason City, Cerro Gordo Co., IA (Norton, 1897).
Type exposure: at Nora Springs, "because the zones there are more distinct and their faunas more readily determined than at Mason City." (Belanski, 1927).
AAPG geologic province:
Iowa shelf
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 ([ ]).