Evidence against pervasively deformed bed material beneath rapidly moving lobes of the southern Laurentide Ice Sheet

During the Wisconsin Glaciation, the ice lobes of the southern part of the Laurentide Ice Sheet moved rapidly as the result of elevated subglacial water pressure. The rapid movement was probably not accompanied by wide-spread pervasive deformation of unfrozen material under the ice. The till stratigraphy of much of this area is well known, and it is clear that the stratigraphic sequence is generally intact. Therefore, such deformation, if it occurred, would have been restricted to the till sheet that was currently being deposited. However, this seems unlikely as well, because the till of the region commonly contains lenses and clasts of unlithified bedded sand that should have been destroyed by pervasive shearing. If unfrozen deformed-till layers were widely present, they must have been confined to the thin upper parts of till sheets. ?? 1989.