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 T. C. Buschbach
The Sinsinawa Member of the Wise Lake Formation (Templeton and Willman, 1963, p. 126).
Named for the Sinsinawa River in Jo Daviess County, along which it is well exposed.
The type section of the Sinsinawa Member is a roadcut along U.S. Highway 20 on the east side of the Galena River at Galena (SW SE NE 20, 28N-1E), where the member is 33 feet thick, although a few feet at the top (exposed in the Wise Lake type section) is missing.
The Sinsinawa Member is the lower member of the Wise Lake Formation.
Extent and thickness
The Sinsinawa Member is 35-40 feet thick.
Where exposed in the northern outcrop area (fig. O-2B), most of the Sinsinawa Member is medium- to thick-bedded, pure, vuggy dolomite, but it contains a few dense, slightly argillaceous beds. A 1-2 inch bed of bentonite is widely present about 17 feet above the base, and a thin bentonite occurs locally about 7 feet higher.
Well log characteristics
Age and correlation
The Sinsinawa Member is equivalent to the upper, noncherty part of the Prosser Limestone of Minnesota.
Environments of deposition
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
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