Historical:Omega Limestone 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: McLeansboro Group >>Mattoon Formation >>Omega Limestone Member
Chronostratigraphy: Paleozoic Erathem >>Pennsylvanian Subsystem >>Missourian Series
Allostratigraphy: Absaroka Sequence


M. E. Hopkins and J. A. Simon

Name Origin

The Omega Limestone Member of the Mattoon Formation (Weller and Wanless, in Lamar et al., 1934, p. 128) is named for Omega, Marion County.

Type Section

The type locality consists of exposures in an abandoned limestone quarry (NW NW NE 30, 3N-4W (Weller and Bell, 1936, p. 29-32; Wanless, 1956, p. 12; Kosanke et al., 1960, p. 81, 82).


It is correlated with the Bonpas Limestone in eastern Illinois.

Extent and Thickness

The Omega is almost 11 feet thick in the type locality and reaches 15 feet in Effingham and Shelby Counties. In Shelby County it varies in thickness and character and is very argillaceous and sandy in areas where it is thick. Although sporadic in occurrence, it appears in a wide area.


KOSANKE, R. M., J. A. SIMON, H. R. WANLESS, and H. B. WILLMAN, 1960, Classification of the Pennsylvanian strata of Illinois: Illinois State Geological Survey Report of Investigations 214, 84 p.
LAMAR, J. E., H. B. WILLMAN, C. F. FRYLING, and W. H. VOSKUIL, 1934, Rock wool from Illinois mineral resources: Illinois State Geological Survey Bulletin 61, 262 p.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.
WELLER, J. M., and A. H. BELL, 1936, Geology and oil and gas possibilities of parts of Marion and Clay Counties, with a discussion of the central portion of the Illinois Basin: Illinois State Geological Survey Report of Investigations 40, 54 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation