Historical:Wise Lake Formation
H. B. Willman and T. C. Buschbach
The Wise Lake Formation is named for Wise Lake, a lake on the Mississippi River floodplain near the type section.
The type section of the Wise Lake Formation is at the north end of a prominent bluff, 6 miles south of Galena, Jo Daviess County (cen. NE 21, 27N-1E), where the formation is 70.9 feet thick.
The Wise Lake Formation consists of strata formerly included in the Stewartville Formation and in the upper part of the Prosser Formation in the Upper Mississippi Valley. It is equivalent to the Steuben Member of the Cobourg Limestone in New York and Ontario, the upper part of the Lexington Limestone in Kentucky, and the upper part of the Bigby-Cannon Formation in Tennessee.
Extent and Thickness
The Wise Lake Formation, persistently 67-75 feet thick, occurs throughout the northern outcrop area (fig. O-2B, C) and southward in subsurface to the central part of the state, where it is sharply truncated by Cincinnatian strata.
The Wise Lake Formation (Templeton and Willman, 1963, p. 125) consists of relatively pure dolomite and limestone overlying the cherty Dunleith Formation and underlying the shaly Dubuque Formation. The Wise Lake consists of noncherty, medium- to thick-bedded, vuggy, pure dolomite in the northern outcrop area. The southern limestone facies is not exposed in Illinois, but in outcrops near New London, in Ralls County, Missouri, it is thick-bedded, fine-grained, to lithographic, pure limestone. The Wise Lake is subdivided into two members; the basal Sinsinawa Member is thinner bedded and slightly less pure than the Stewartville above it. The Wise Lake Formation is the purest of the carbonate formations in the Galena Group and is equivalent and lithologically similar to relatively pure formations throughout much of the continent.
Receptaculites oweni (fig. O-5) is abundant and persistently present in the lower 10-15 feet of the Stewartville Member of the Wise Lake Formation, called the Upper Receptaculites Zone, and is associated with a gastropod-cephalopod fauna. Maclurites cuneata and Hormatoma major (fig. O-5) are common in some localities. The Sinsinawa Member of the Wise Lake Formation is less fossiliferous but contains gastropods and, in places, a few Receptaculites.
The Wise Lake is thought to represent the greatest submergence of the continent during Paleozoic time.
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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