Conant Limestone Member

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Lithostratigraphy: Kewanee Group >>Carbondale Formation >>Conant Limestone Member
Chronostratigraphy: Paleozoic Erathem >>Pennsylvanian Subsystem >>Desmoinesian 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 Conant Limestone Member of the Carbondale Formation (Kosanke et al., 1960, p. 35).


Named for Conant, Perry County.

Other names

It previously was called the Jamestown Limestone (Bell et al., 1931, p. 3).


Type section

Type location

Conant is near the type locality (NW NE 34, 5S-4W) (Wanless, 1939, p. 17, 88; 1956, p. 10).

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

Extent and thickness

The Conant is widespread from St. Clair to Gallatin Counties in southern Illinois (fig. P-3B) but is not recognized a short distance north of that area. It is also present locally in eastern Illinois. For most of its extent the limestone is less than 1 foot thick and lies immediately above the thin Jamestown Coal, but in Perry County it is as much as 4 feet thick in places and is separated from the Jamestown Coal by an equal thickness of dark gray shale. It is overlain by gray silty shale.


The Conant Limestone Member is quite argillaceous and locally resembles the Brereton Limestone.




Well log characteristics


It is characterized by an open-marine fauna dominated by the large productid brachiopod Dictyoclostus.

Age and correlation

Environments of deposition

Economic importance



BELL, A. H., C. G. BALL, and L. C. MCCABE, 1931, Geology of the Pinckneyville and Jamestown areas, Perry County, Illinois: Illinois State Geological Survey Illinois Petroleum 19, 22 p.
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.
WANLESS, H. R., 1939, Pennsylvanian correlations in the Eastern Interior and Appalachian coal fields: Geological Society of America Special Paper 17, 130 p.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation