MILLER, Jonson W., Dept. of Geology and Geophysics, Univ. of Wisconsin, 1215 W. Dayton St., Madison WI 53706, jonson@geology.wisc.edu

Sediments from at least three glaciations: the Wisconsin, the Illinoian, and a pre-Illinoian glaciation, are preserved in southern Wisconsin. The limit of the Wisconsin glaciation is represented by the Johnstown, Marengo, and Darien Moraines. Illinoian till is sparsely distributed to the south and west of these moraines. The pre-Illinoian Winslow Till Member of the Glasford Formation is found interbedded with the Silveria Silt-Clay, a lacustrine deposit, along the eastern flanks of the Pecatonica River Valley in southeasternmost Green County, but is found beneath an Illinoian diamicton to the east.

An interglacial soil is developed in the Winslow Till Member directly below Illinoian till in one exposure, demonstrating a pre-Illinoian age for the Winslow Till Member and, consequently, the Silveria Silt-Clay. Measurements of the remnant magnetism of the Winslow Till Member and the Silveria Silt-Clay show a complex magnetic history in which the sediments were

deposited during a reversed chron, indicating that these sediments are, probably, more than 780 ka, the age of the Brunhes-Matuyama reversal. Subsequently, the Silveria Silt-Clay obtained a strong chemical remnant magnetism with highly variable declinations. These results explain and are supported by results from Whittecar (1979) that were, previously, interpreted as ambiguous. The paleosol and the magnetic evidence distinguish the Winslow Till Member from the other members of the Glasford Formation.