Coggan Member

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Lithostratigraphy: Hunton Limestone Megagroup >>Wapsipinicon Limestone >>Coggan Member
Chronostratigraphy: Paleozoic Erathem >>Devonian System >>Middle Devonian Series
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)

Charles Collinson and Elwood Atherton


Original description

The Coggan Member of the Wapsipinicon Limestone (Norton, 1894, p. 23-24).


Named for Coggan, Linn County, Iowa.

Other names


Type section

Type location

The type section of the Coggan Member is at the Illinois Central Railroad crossing of the Buffalo River near Coggan, Linn County, Iowa.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Coggan Member is at the base of the Wapsipinicon Limestone in Illinois.

Extent and thickness

The Coggan Member is not exposed in Illinois, but it occurs locally in subsurface and is as much as 20 feet thick in the area between Galesburg, Knox County, and Muscatine, Iowa.


The Coggan Member consists of massive, buff, cherty dolomite. It also contains a thin bentonite that has been correlated with the Tioga Bentonite Bed, which occurs near the top of the Grand Tower Formation southeast of the Sangamon Arch.




Well log characteristics


Age and correlation

Environments of deposition

Economic importance



NORTON, W. H., 1894, Notes on the lower strata of the Devonian Series in eastern Iowa: Iowa Academy of Science Proceedings 1, part 4, p. 22-24.

ISGS Codes

Stratigraphic Code Geo Unit Designation