Usage:
Spechts Ferry Shale Member of Decorah Formation of Galena Group (IL*,IA*,MN*,MO*,WI*)
Spechts Ferry Formation of Decorah Group (IL*,MO*-notably in St. Louis region)
Spechts Ferry Member of Decorah Formation of Sinnipee Group (WI)
Subunits:
FORMATION STATUS --all in IL*,MO*: Castlewood Limestone Member, Glencoe Shale Member.
MEMBER STATUS --all in IL*,IA*,MN*,MO*,WI*: Deicke K-bentonite Bed, Millbrig K-bentonite Bed.
Geologic age:
Late Ordovician (Mohawkian)*
Type section, locality, area and/or origin of name:
Type section: along a ravine just southwest of the Chicago, Milwaukee, St. Paul, and Pacific RR station of Spechts Ferry, Dubuque Co., eastern IA (Kay, 1928; Templeton and Willman, 1963).
AAPG geologic province:
Illinois basin*
Iowa shelf*
Ozark uplift*
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 ([ ]).