Omega Limestone Member

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

Primary source

Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.

Contributing author(s)

M. E. Hopkins and J. A. Simon


Original description

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


Named for Omega, Marion County.

Other names


Type section

Type location

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).

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

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.





Well log characteristics


Age and correlation

It is correlated with the Bonpas Limestone in eastern Illinois.

Environments of deposition

Economic importance



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