Genesis and geomorphology of superimposed landforms on Ice-Walled-Lake Plains in Northern Illinois.

摘要

Ice-Walled-Lake Plains (IWLPs) with superimposed landforms have been noted, but never extensively researched, in the DeKalb region of Northern Illinois. This study aims to describe the superimposed landforms (SILs) and propose a theory of their genesis. These SILs appear as circular ramparts with interior depressions. Seventy two total landforms were identified using black and white aerial photography. Two hypotheses were tested; that the SILs were glacial and formed concurrently to the IWLPs, or that the SILs were periglacial and formed after the IWLPs, and after the retreat of the last glacier. Data that was gathered on these superimposed landforms was compared to relict IWLPs in the Midwest, and modern periglacial landforms in the Arctic. After analyzing morphometrics and sedimentology, it was determined that the superimposed landforms are likely relict periglacial frost mounds (pingos). This proves the existence of past permafrost in the Northern Illinois area, and can be used to aid in paleo-climatic reconstructions.