Birds Member

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Lithostratigraphy: Hunton Limestone Megagroup >>Wilhelmi Formation >>Birds Member
Chronostratigraphy: Paleozoic Erathem >>Silurian System >>Alexandrian Series
Allostratigraphy: Tippecanoe 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)

H. B. Willman and Elwood Atherton


Original description

The Birds Member of the Wilhelmi Formation (Willman, 1973, p. 13).


Named for the railroad siding at Birds, 2 miles northwest of the type section.

Other names


Type section

Type location

The type section of the Birds Member is part of the Wilhelmi Formation type section, located in a railroad cut about 5 miles southwest of Wilhelmi Airport (SE SW SE 35, 35N-9E).

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Birds Member overlies the Schweizer Member of the Wilhelmi Formation.

Extent and thickness


The uppermost part of the member and its contact with the overlying Elwood Formation are exposed in a ravine half a mile northeast (NW NW SE 36, 35N-9E). The Birds Member consists of 10-20 feet of slightly to moderately argillaceous, slightly cherty, thin-bedded, medium-gray dolomite. It is distinguished by several thin beds of relatively pure, finely laminated, fossiliferous dolomite.




Well log characteristics


Age and correlation

Environments of deposition

Economic importance



WILLMAN, H. B., 1973, Rock stratigraphy of the Silurian System in northeastern and northwestern Illinois: Illinois State Geological Survey Circular 479, 55 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation