Seahorne Limestone Member

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Lithostratigraphy: Kewanee Group >>Spoon Formation >>Seahorne 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 Seahorne Limestone Member of the Spoon Formation (Wanless, 1931a, p. 191).


Named for Seahorne Branch in Fulton County.

Other names


Type section

Type location

The type section consists of exposures along the Seahorne Branch stream (S 1/2 SE 5, 3N-3E) (Wanless, 1956, p. 9; 1957, p. 76, 200).

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

Extent and thickness

The Seahorne is best known in western Illinois, where it varies from limestone nodules in claystone to a solid ledge of limestone more than 6 feet thick. The Seahorne is not persistent but occurs at many places in Illinois and adjacent states.


It is usually light gray. In some places it is conglomeratic or brecciated and consists of dark gray fragments that contain abundant brachiopods embedded in a light gray matrix that is dominated by a diverse gastropod fauna. Another fauna, Spirorbis and ostracodes, is found at places and is generally considered nonmarine. It is the caprock of the Tebo coal in Missouri (Wanless, 1957).




Well log characteristics


Age and correlation

Environments of deposition

Economic importance



WANLESS, H. R., 1931a, Pennsylvanian cycles in western Illinois: Illinois State Geological Survey Bulletin 60, p.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.
WANLESS, H. R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey Bulletin 82, 233 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation