Regional Geology of the Tiskilwa Till Member, Wedron Formation, Northeastern Illinois

摘要

The Tiskilwa Till Member, the oldest unit of the Wedron Formation in northern Illinois, was deposited during the early part of the Woodfordian Subage. The wedge-shaped unit is 200 to 300 feet (60 to 90 m) thick in end moraines and 50 to 100 feet (15 to 30 m) in ground moraine areas. Basil till of the Tiskilwa is relatively uniform in composition and texture over a wide area. The sub-Tiskilwa surface has little relief and slopes eastward toward the Lake Michigan Basin. The margin of the Tiskilwa ice sheet was in an enhanced compressive flow regime, and as a result, large amounts of ice and debris were stacked near the ice margin during deposition. Active ice deposition took place over an interval of several thousand years when the southern portion of the Laurentide Ice Sheet was becoming progressively larger.