Karnak Limestone Member

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Lithostratigraphy: Mammoth Cave Limestone Megagroup >>Ste. Genevieve Limestone >>Karnak Limestone Member
Chronostratigraphy: Paleozoic Erathem >>Mississippian Subsystem >>Valmeyeran Series >>Genevievian Stage
Allostratigraphy: Kaskaskia 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)

Elwood Atherton, Charles Collinson, and Jerry A. Lineback


Original description

The Karnak Limestone Member of the Ste. Genevieve Limestone (Swann, 1963, p. 28-29, 71).


Named for Karnak, Pulaski County, about 4 miles southeast of the type section.

Other names


Type section

Type location

The type section of the Karnak Limestone Member is located in Johnson County (SW SW 32, 13S-2E, and NW NW 5, 14S-2E), where the top 16 feet of an estimated 20-25 feet of limestone is exposed in cuts on Illinois Highway 37.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

Extent and thickness

The Karnak is a persistent unit and is generally traceable throughout the area of the Ste. Genevieve (fig. M-22), but in western Washington County it thins and grades laterally into the Aux Vases Sandstone. The Karnak is generally 10-35 feet thick.


The limestone is relatively pure, oolitic, crinoidal, mostly light gray, and cross-bedded.




Well log characteristics


Age and correlation

Environments of deposition

Economic importance

“Ohara” is an informal name applied to producing zones in the Karnak Limestone Member of the Ste. Genevieve Limestone.



SWANN, D. H., 1963, Classification of Genevievian and Chesterian (Late Mississippian) rocks of Illinois: Illinois State Geological Survey Report of Investigations 216, 91 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation