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National Geologic Map Database

Geologic Unit: Millbrig

Usage:

Millbrig K-bentonite Bed of Spechts Ferry Shale Member of Decorah Formation of Galena Group (IL*,IA*,MN*,MO*,WI*)
Millbrig K-bentonite Bed of Spechts Ferry Shale Member of Decorah Formation of Sinnipee Group (WI)
Millbrig K-bentonite Bed of Glencoe Shale Member of Spechts Ferry Formation of Decorah Group (IL*,MO*-notably in St. Louis region)
Millbrig K-bentonite Bed of Decorah Shale of Galena Group (IA*,MN*)

Millbrig K-bentonite Bed of Eggleston Formation (TN*,VA*,WV*)
Millbrig K-bentonite Bed of Moccasin Formation (TN*,VA*,WV*)
Millbrig K-bentonite Bed of Bays Formation of Chickamauga Group (TN)
Millbrig K-bentonite Bed of Bays Formation (VA)
Millbrig K-bentonite Bed of Tyrone Limestone of High Bridge Group (KY*)
Millbrig K-bentonite Bed of Carters Limestone of Stones River Group (AL*,GA*,TN*)
Millbrig K-bentonite Bed of Stones River Formation (northern AL*)
Millbrig K-bentonite Bed of Colvin Mountain Sandstone (northeastern AL)
Millbrig K-bentonite Bed of Colvin Mountain Sandstone of Chickamauga Group (northeastern AL*)
Millbrig K-bentonite Bed of Chickamauga Limestone (western facies, central AL*)

Also called Millbrig Bentonite Bed*, informal Mud Cave bentonite bed*, informal T-4 bentonite bed*.


Geologic age:

Late Ordovician (Mohawkian; earliest Chatfieldian)*


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

Type section: Millbrig Southeast section, along east bank of Galena River, 1.6 km southeast of Millbrig, in center sec. 34, T. 29 N., R. 1 E., Jo Daviess Co., IL. Named from Millbrig (Willman and Kolata, 1978).


AAPG geologic province:

Appalachian basin
Cincinnati arch
Illinois basin
Iowa shelf
Sioux 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 ([ ]).