Historical:Garnavillo Member
Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Decorah Subgroup >>Guttenberg Formation >>Garnavillo Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence
Authors
H. B. Willman and T. C. Buschbach
Name Origin
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.
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.
Description
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.
References
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
ISGS Codes
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