Correlation of late Wisconsin glacial phases in the western Great Lakes area

Abstract

Late Wisconsin glacial phases of the Superior Lobe in Wisconsin and adjacent Minnesota are tentatively correlated across northern Wisconsin and adjacent Michigan to phases of the Green Bay and Lake Michigan Lobes. Spanning the period from about 26,000 yr B.P. to about 9500 yr B.P., 7 phases of the late Wisconsin Laurentide Ice Sheet are discussed, but only 2 of these are precisely dated. Ice advanced out of the basins of Lakes Superior and Michigan and stabilized during the St. Croix-Hancock phase, the most extensive late Wisconsin phase in most of the area, between about 18,000 and 15,000 yr ago. Following the St. Croix-Hancock phase, the general wasting of the ice was interrupted by stillstands or readvances of the ice margin during the intermediate and Mountain phases. The ice then wasted into the Superior basin before readvancing, over a landscape containing ice masses from earlier phases, during the Winegar-early Athelstane phase. This phase is believed to have occurred just prior to growth of the Two Creeks Forest in eastern Wisconsin. The ice then wasted back and advanced three more times during the Marenisco-late Athelstane, Porcupine (about 11,000 yr B.P.), and Marquette (about 9900 yr B.P.) phases.