North-Central Section - 47th Annual Meeting (2-3 May 2013)

Paper No. 7
Presentation Time: 10:20 AM


JOHNSTON, John W., Department of Physical and Chemical Sciences, University of Toronto Mississauga, 3359 Mississauga Road N, Mississauga, ON L5L 1C6, Canada, ARGYILAN, Erin P., Dept. of Geosciences, Indiana University Northwest, 3400 W. Broadway, Gary, IN 46408, THOMPSON, Todd A., Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405-2208, BAEDKE, Steve J., Department of Geology and Environmental Science, James Madison University, MSC 6903, Harrisonburg, VA 22807, LEPPER, Kenneth, Department of Geosciences, North Dakota State University, P.O. Box 6050, Dept. 2745, Fargo, ND 58108-6050, WILCOX, Douglas A., Dept. of Env. Science and Biology, The College at Brockport, State University of New York, 350 New Campus Drive, Brockport, NY 14420 and FORMAN, Steven L., Earth and Environmental Sciences, University of Illinois at Chicago, 845 W. Taylor Street, Chicago, IL 60607,

The most detailed Lake Superior paleohydrograph relative to the current outlet near Sault Ste. Marie, Ontario/Michigan, was constructed from four strandplains of beach ridges. This provides a history of water-level, glacial isostatic adjustment (GIA), and the active outlet prior to monitoring and regulation. Four relative paleohydrographs that are offset and subparallel owing to differences in GIA were produced from 321 basal foreshore elevations and 56 optically stimulated luminescence ages. Subtracting modeled elevations in defined millennial lake phases between relative paleohydrographs and similarity between an inferred Sault Ste. Marie (hereafter, Sault) paleohydrograph and data near the zero isobase corroborates rates of GIA derived from water-level gauges. A change in trend in the Sault paleohydrograph is related to the final separation of Lake Superior from Lake Michigan/Huron and is the youngest age reported at 1,060 +/- 100 years. A near-horizontal trend in the Sault paleohydrograph for the past millennium has an intercept that is close to the historical average for Lake Superior. A consistently linear trend from about 2 to 1 ka suggests a relatively stable outlet similar to the past millennium, but a decreasing trend from 3 to 1 ka suggests an outlet other than the Sault. Although intercept data beyond the last millennium are similar in elevation to the reported bedrock sill near Chicago (Hansel et al. 1985), we argue that the Port/Huron outlet was the active outlet during this time and the inferred paleohydrograph of Baedke and Thompson (2000) requires reevaluation.