H. B. Willman and T. C. Buschbach
The Glenhaven Member of the Guttenberg Formation (Templeton and Willman, 1963, p. 113), the upper member, is named for Glenhaven, Grant County, Wisconsin, 2.5 miles northeast of the type section.
The type section of the Glenhaven Member is located in the same exposure as the type section for the Garnavillo Member (the roadcut of U.S. Highway 52 on the northwest side of Guttenberg (SW SW 5, 92N-2W)), where the Glenhaven is 14.8 feet thick.
Extent and Thickness
The Glenhaven Member thins southward from the type area to 10-12 feet in northwestern Illinois and 7-9 feet in southwestern Illinois.
In northwestern Illinois the Glenhaven is commonly separated from the overlying Dunleith Formation by a transition zone as much as a foot thick. The Glenhaven consists of tan, white-weathering, lithographic to very fine-grained limestone in beds 1-4 inches thick that are separated by layers of dark brown-red shale, generally thin but locally as much as 2 inches thick. The lower part is consistently more shaly, thinner bedded, and has wavier bedding planes than the upper part. The upper is purer and has more fossil debris and calcarenite layers. Lenses of chert are widely present in a single layer 1-2 feet above the base of the upper part and are scattered through the lower foot in the southwestern outcrops. In places in subsurface the entire formation is cherty. A bentonite bed up to 1 inch thick is widely present at the base of the Glenhaven in both northern and southern outcrop areas.
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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