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