Sedimentology and Stratigraphy of Pre-Wisconsin Drifts, Coteau Des Prairies Eastern South Dakota
1993-11
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Sedimentology and Stratigraphy of Pre-Wisconsin Drifts, Coteau Des Prairies Eastern South Dakota
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1993-11
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The Quaternary sediments and landforms of east-central South Dakota, southwest Minnesota and northwestern Iowa were examined in order to refine the stratigraphy of pre-Late Wisconsin drift units found at the surface and in the subsurface of the central portion of the Coteau des Prairies. Five geomorphic regions are recognized in the study area. The Crooks Drift Plain/Iowan Erosion Surface relates to a pre-Late Wisconsin glacial advance, while the Brookings Till Plain is apparently Early Late Wisconsin in age. The Toronto Till Plain, the next oldest Late Wisconsin geomorphic surface, is typified by a well developed drainage network, few undrained depressions, and broad, flat drainage divides. The Bemis Moraine marks the farthest extent of the Late Wisconsin Des Moines Lobe. It is a fairly continuous ridge on the east side of the Coteau des Prairies. Behind the Bemis Moraine is kame-and-kettle topography typical of that left by stagnant ice. The Dakota Moraine marks the maximum extent of the James Lobe on the western side of the Coteau des Prairies. A total of eight drift units were identified from two hollow stem auger cores, along with four diamictons and one possible supraglacial facies. Four of these units are given names in this study. From oldest to youngest they are: the Renner Till; the Brandon Till; the Big Souix Till; and the Hartford Till. Five of the eight drift units are exposed at the surface, along with one drift unit that did not appear in either core. Eleven of these units are pre-Late Wisconsin in age. Clast lithologies indicate that most of the pre-Late Wisconsin glaciers advanced from the north-northeast. Four units of Late Wisconsin age were recognized in the study area. The Toronto Till is the oldest definite Late Wisconsin till. The Toronto Till as described by Gilbertson (1990) appears to be composed of two tills of very similar composition. The earliest of these was deposited between 30,000 and 20,000 years ago, with the later deposited shortly thereafter. The till of the Bemis Moraine (New Ulm Till) was deposited by the Des Moines Lobe beginning approximately 14,000 yrbp. The till of the Dakota Moraine was deposited by the James Lobe beginning only a few hundred years after the deposition of the Bemis Moraine. Younger tills of both lobes are present outside of the current study area.
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A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Joane Marie Lineburg in partial fulfillment of the requirements for the degree of Master of Science, November 1993.
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