GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 265-11
Presentation Time: 9:00 AM-6:30 PM


JOHNSTON, John W.1, ARGYILAN, Erin P.2, BAEDKE, Steve J.3, MORRISON, Sean1, LOOPE, Henry M.4, LEPPER, Kenneth5, THOMPSON, Todd A.6 and WILCOX, Douglas A.7, (1)Department of Earth and Environmental Sciences and Water Institute, University of Waterloo, 200 University Ave West, Waterloo, ON N2L3G1, Canada, (2)Dept. of Geosciences, Indiana University Northwest, 3400 W. Broadway, Gary, IN 46408, (3)Dept of Geology and Environmental Science, James Madison University, Harrisonburg, VA 22807, (4)Indiana Geological Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405-2208, (5)Department of Geosciences, North Dakota State University, P.O. Box 6050, Dept. 2745, Fargo, ND 58108-6050, (6)Indiana Geological and Water Survey, Indiana University, 611 North Walnut Grove, Bloomington, IN 47405-2208, (7)Environmental Science and Ecology, SUNY-The College at Brockport, 350 New Campus Drive, Brockport, NY 14420,

The most detailed Laurentian upper Great Lakes paleohydrographs have been reconstructed by studying strandplains of beach ridges or lateral chronosequences of many well-preserved ancient shorelines that have filled embayments just prior to and following the peak Nipissing high water-level stand at 4,500 years ago. Systematic and detailed study of subsurface sedimentary contacts in individual beach ridges yield the most accurate past water-level elevation and optically stimulated luminescence dating of foreshore deposits within beach ridges yield the most accurate age model for the strandplain sequence. Measured elevation and modeled age data are combined to create relative paleohydrographs. They are called “relative” paleohydrographs because they are in reference to a specific strandplain site from which paleohydrographs were reconstructed. Also within these relative paleohydrographs are clues to past lake-level variations due to (1) glacial isostatic adjustment (GIA), observed as long-term trends in strandplain relative paleohydrographs and (2) climate, shown as the short-term oscillations about the long-term trend. An iterative process of adjusting each paleohydrograph to remove GIA helps to find oscillations common to many paleohydrographs and is used to reconstruct outlet paleohydrographs for each lake basin. This research investigates methods to improve age models and estimates of GIA, to substantiate the assignment of climate to relatively short-term oscillations in paleohydrographs, and to isolate the potential for past changes in outlet conveyance (erosion and sedimentation) that would be reflected in all paleohydrographs within common lake basins.