| Glaciotectonic deformation has been observed and analyzed across parts of the Valparaiso, Kendall, and Inner Kalamazoo Moraines in southwest Michigan, USA. Deformation structures such as folds and faults have been analyzed using techniques typically used by structural geologist along with the fabric of elongated clasts in the surficial diamicton. The structures are consistent with simple shear, horizontal compressional stresses, and pure shear. A series of drumlin fields exist along the western boundary of the study area. Direct investigation of the deformed sediments was conducted at a gravel pit in one of these drumlins. Lacustrine derived sediments interbedded with coarse sand and gravel dominate the stratigraphy of the study area. The rheology of the sediments is responsible for the deformation observed as the Lake Michigan Lobe (LML) readvanced across the area to the Kalamazoo Moraine. The LML readvanced into a proglacial lake system impounded between the ice margin and the Kalamazoo Moraine. The lacustrine sediments, restricting the flow of subglacial water, increases the pore water pressure, which in turn decreased the shear strength of the sediments promoting the deformation of these sediments. Advancing ice deformed sediments in two stages, proglacially along a decollement at the margin, then subglacially as ice overrode the sediments. |
