Historical:Establishment Member

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
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Lithostratigraphy: Ottawa Limestone Megagroup >>Platteville Group >>Plattin Subgroup >>Mifflin Formation >>Establishment Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Blackriveran Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The Establishment Member of the Mifflin Formation (Templeton and Willman, 1963, p. 82) is named for Establishment Creek in Ste. Genevieve County, Missouri.

Type Section

The type section of the Establishment Member is an exposure in a tributary ravine just north of the village of Zell (W1/4 34, 38N-8E), where the member is 5.5 feet thick.

Extent and Thickness

The Establishment Member is 2-8 feet thick in southern Illinois. In northern Illinois it is commonly about 5 feet thick.


The Establishment Member in southern Illinois is a green shale with thin interbeds of argillaceous, chalky limestone. The shale facies appears to be limited to a region bordering the Ozarks and is a persistent marker bed; elsewhere the member is thin-bedded, shaly, brown lithographic limestone. In the northern area, it is limestone, and is gray, dolomite mottled, argillaceous, thin bedded, and shaly. It contains a few thin beds of calcarenite.


TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation