02394nas a2200145 4500008004100000022001800041245008100059210006900140260005300209520179500262100001302057700001802070700002202088856013802110 2018 eng d a978081379530000aGlaciotectonic deformation along the Valparaiso Upland in southwest Michigan0 aGlaciotectonic deformation along the Valparaiso Upland in southw aBoulder, ColoradobGeological Society of America3 a

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.

1 aBird, B.1 aKehew, A., E.1 aKozlowski, A., L. uhttps://pubs.geoscienceworld.org/books/book/2055/chapter/113619031/glaciotectonic-deformation-along-the-valparaiso?redirectedFrom=PDF