H. B. Willman and T. C. Buschbach
The Garnavillo Member of the Guttenberg Formation (Templeton and Willman, 1963, p. 113), the lower member, is named for Garnavillo, Clayton County, Iowa, 7.5 miles northwest of the type section.
The type section of the Garnavillo Member is located in the roadcut of U.S. Highway 52 on the northwest side of Guttenberg (SW SW 5, 92N-2W), where the member is 1.7 feet thick.
Extent and Thickness
The Garnavillo is present throughout most of the area where Guttenberg strata occur, but it does not extend as far east as the overlying Glenhaven Member. It is 2-3 feet thick in southwestern Illinois.
The Garnavillo Member consists of gray to gray-tan, white-weathering, argillaceous limestone in medium beds with thin gray-brown shale partings. Phosphatic nodules are widely present in the lower foot in the northwestern outcrop area, where the Kings Lake Formation is missing.
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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