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National Geologic Map Database

Geologic Unit: Spechts Ferry

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 usage by the U.S. Geological Survey. Other usages by state geological surveys.

"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 does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).