Collaborative Research: Theoretical and Paleoenvironmental Implications of Dating and Characterizing Loess Deposits in the Upper Midwest

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Absolute dates and ages for key geomorphic events in the Midwest U.S. are sorely lacking, mainly because of the paucity of wood in glacial deposits for radiocarbon dating. This collaborative research project will address the paucity of geochronologic information that exists for Midwestern glacial and postglacial environments by enriching and making more precise the post-glacial chronology, thereby facilitating a better understanding of the timing of Late Pleistocene landscape evolution for the upper Midwest so important for paleoenvironmental models. To help accomplish this goal the investigators will date loess (wind-deposited silt) deposits with optically stimulated luminescence (OSL) techniques. Doing so will establish the age of the geomorphic/glacial event that sourced the loess, such the draining of a glacial lake or a glacial readvance. In addition to adding critical information regarding the dates of loess deposits, the project will enable the investigators to evaluate the extent to which thin loess deposits can be dated with OSL and the limits to this technique. Because most loess deposits in the Midwest are thinner than two meters in depth, they had been deemed undateable because of surface contamination and mixing processes. The investigators will determine the minimum thickness of loess that allows for accurate OSL dating and provide empirical guidelines for other researchers who wish to sample such deposits. Their goal is to open up a new suite of Quaternary deposits for dating with established protocols and caveats. The project will be centered at several research sites in small to medium-sized loess sheets in Wisconsin and Michigan. At each of these sites the investigators expect that the mean OSL age of several OSL samples in loess will establish the most likely age of a geomorphic event. OSL dating of loess may be the only way that the dates of these geomorphic events can be determined. Because this research will be performed in a highly geographic manner; loess will be sampled systematically, with a keen eye on the spatial spread of the samples. In this way, the spatial character of the loess deposits can be determined and loess sources more clearly elucidated.The project will provide valuable information and insights for the Midwestern glacial literature, and it will yield methodological contributions. The project will enrich the chronologic framework used by geographers, ecologists, paleoenvironmentalists, and geoscientists. It will provide important characterization and spatial data on the thin loess and cover sand deposits that long have puzzled and confounded soil scientists and geologic mappers. Developing a clearer and more accurate understanding of the deglacial chronology for the upper Midwest is essential for continued advances in paleoenvironmental modeling and land use. The project also will provide excellent education and training opportunities for graduate and undergraduate students.