T. C. Buschbach
The Galesville Sandstone (Trowbridge and Atwater, 1934, p. 43), a clean, unfossiliferous sandstone, is named for Galesville, Trempealeau County, Wisconsin.
The type section of the Galesville Sandstone is in an exposure on Beaver Creek near Galesville, Trempealeau County, Wisconsin. The section exposes poorly sorted, fossiliferous sandstone of the Ironton Formation overlying 88 feet of the Galesville Sandstone, which in turn lies on fossiliferous sandstoneand shale of the Eau Claire Formation.
The Galesville Sandstone is also recognized in Iowa, Minnesota, Michigan, and Indiana. It is not traced directly to the Missouri outcrop region, but it probably is equivalent to the upper carbonate beds of the Bonneterre Formation.
Extent and Thickness
The Galesville occurs throughout the northern half of Illinois but is not exposed. It is commonly 40-100 feet thick. At its southern margin, the Galesville grades laterally through a zone of dolomitic sandstone about 50 miles wide to nonsandy dolomite of the Knox Megagroup.
In earlier reports Galesville and Ironton Sandstones were called the Dresbach Sandstone. In many borings in Illinois the Galesville is not easily distinguished from the overlying Ironton Sandstone, and their combined thickness is shown in figure Є-10. The name "Galesville" is applied as far south as the sandy zone can be identified, at which place the formation is terminated by vertical cut-off. The Galesville Sandstone consists of white to light buff, clean to locally silty, fine-grained, moderately well sorted, friable, and generally nondolomitic sandstone (Buschbach, 1964). Locally, light buff to pink dolomite is a cementing material. From a petrographic study and analysis of sedimentary structures, Emrich (1966) concluded that the Galesville and Ironton Sandstones were derived from pre-existing sedimentary rocks north of Illinois and were deposited on a broad, shallow shelf. The Galesville appears to be conformable with both the overlying and underlying formations. The Galesville and the overlying Ironton Sandstone form an important aquifer in northern Illinois.
BUSCHBACH, T. C., 1964, Cambrian and Ordovician strata of northeastern Illinois: Illinois State Geological Survey Report of Investigations 218, 90 p.
EMRICH, G. H., 1966, Ironton and Galesville (Cambrian) Sandstones in Illinois and adjacent areas: Illinois State Geological Survey Circular 403, 55 p.
TROWBRIDGE, A. C., and G. I. ATWATER, 1934, Stratigraphic problems in the upper Mississippi Valley: Geological Society of America Bulletin, v. 45, p. 21-80.
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