Piasa Limestone

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Lithostratigraphy: McLeansboro Group >>Modesto Formation >>Piasa Limestone
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 Piasa Limestone Member of the Modesto Formation (Culver, 1925, p. 20).


Named for Piasa Creek in Jersey County.

Other names

The Piasa was formerly called the Cutler Limestone in southern Illinois.


Type section

Type location

The type section consists of exposures along Piasa Creek (E 1/2 25, 8N-10W) (Wanless, 1956, p. 11).

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

In much of southwestern Illinois the Piasa lies only a few feet above the Danville (No. 7) Coal and is separated from it by either variegated claystone, gray shale, or, in places, black fissile shale.

Extent and thickness

The Piasa occurs in southwestern and southern Illinois. It is generally less than 4 feet thick.


The Piasa is commonly light gray, fine-grained, argillaceous limestone, and is commonly associated with red and variegated claystone.




Well log characteristics


The Piasa contains an open-marine fauna dominated by crinoids (mainly in the lower part) and brachiopods. In many places it contains numerous fusulinids, especially at the base.

Age and correlation

Correlations with other units in Illinois are not definite, but the Piasa appears to be equivalent to the lower part of the West Franklin Limestone Member of southeastern Illinois and southwestern Indiana and to the Madisonville Limestone Member of western Kentucky.

Environments of deposition

Economic importance



CULVER, H. E., 1925, Coal resources of District III (western Illinois): Illinois State Geological Survey Mining Investigations Bulletin 29, 128 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