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Glaciotectonic deformation along the Valparaiso Upland in southwest Michigan

Brian C. Bird
Brian C. Bird
Research & Collections Division, New York State Museum, Albany, New York 12230, USA
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Alan E. Kehew
Alan E. Kehew
Department of Geosciences, Western Michigan University, Kalamazoo, Michigan 49008, USA
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Andrew L. Kozlowski
Andrew L. Kozlowski
Research & Collections Division, New York State Museum, Albany, New York 12230, USA
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January 30, 2018
01 September 2017


Glaciotectonic deformation of glacigenic deposits in southwestern Michigan is described and analyzed to determine the source of stress of these strained sediments, which manifests as overturned folds and other deformation similar to shallow crustal décollements. The succession is exposed in 11 aggregate mining operations along the Valparaiso Upland, in portions of Berrien, Van Buren, and Allegan Counties in southwest Michigan. Observed deformation includes a complex array of folds, faults, and thrust features as much as 5 m below the surface exposure of the pit face, consistent with horizontal compressional stresses that were generally aligned with ice flow. Fabric measurement of elongated clasts in the surficial till indicates ice flow from northwest to southeast across the area and parallel to drumlins in the area. Stratigraphically, the area is dominated by fine, lacustrine deposits with coarse sand and gravel capped by the Saugatuck Till during the last glaciation. Sediment grain size, pore-water pressure fluctuations, and topographic relief are interpreted to be responsible for the deformation observed as the Lake Michigan Lobe overrode a proglacial lake basin, including fans and deltas, as it advanced eastward to the Kalamazoo moraine. The fine texture and fabric of the lacustrine sediment package restricted the flow of subglacial water and caused abrupt local increases of pore-water pressure and concomitant coupling and decoupling of the bed-substrate interface. Advancing ice deformed sediments in two stages: (1) proglacially along a décollement at the ice margin, and then (2) subglacially as ice overrode the sediments.

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Figures & Tables


GSA Special Papers

Quaternary Glaciation of the Great Lakes Region: Process, Landforms, Sediments, and Chronology

Geological Society of America
ISBN electronic:
Publication date:
January 30, 2018




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