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National Geologic Map Database

Geologic Unit: Grand Detour

Usage:

Grand Detour Formation of Platteville Group (IL)


Subunits:

(alphabetical) --all in IL: Clement Member, Cowen Member, Dement Member, Forreston Member, Hely Member, Stillman Member, Victory Member, Walgreen Member.


Geologic age:

Late Ordovician (Mohawkian; Turinian)


Type section, locality, area and/or origin of name:

Type section (=Grand Detour type section): quarry in west bluff of Rock River, on Walgreen estate, in NE/4 sec. 20, T. 22 N., R. 9 E., [approx. Lat. 41 deg. 53 min. 08 sec. N., Long. 89 deg. 28 min. 50 sec. W., Grand Detour 7.5-min quadrangle], Lee Co., northwestern IL (Templeton and Willman, 1963, Illinois Geol. Survey Bull., no. 89, p. 83; Willman and Buschbach, 1975, Illinois Geol. Survey Bull., no. 95, p. 47-87).
Named from Grand Detour, along Rock River, [Grand Detour 7.5-min quadrangle], Ogle Co., northern IL (Templeton and Willman, 1963, p. 83; Willman and Buschbach, 1975).
Notable exposures in Dixon-Oregon area, northern IL (Templeton and Willman, 1952).


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