Historical:Sinsinawa Member

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Wise Lake Formation >>Sinsinawa Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The Sinsinawa Member of the Wise Lake Formation (Templeton and Willman, 1963, p. 126), the lower member, is named for the Sinsinawa River in Jo Daviess County, along which it is well exposed.

Type Section

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 equivalent to the upper, noncherty part of the Prosser Limestone of Minnesota.

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.


TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation