H. B. Willman and T. C. Buschbach
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.
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.
|Stratigraphic Code||Geo Unit Designation|