Misconceivement About the Formation of True DeKalb Mounds in DeKalb County, Illinois

摘要

A study is presented here in order to enhance knowledge about an earlier preliminary study of true DeKalb mounds. The DeKalb mounds of DeKalb County, IL are lowland, gigantic, oriented, low-relief, relict hillocks that are unquestionably a product of late Wisconsinan glacial deposition. However, a new controversy weighs them as being either a dead-ice moraine or ice-walled lake plains. The overall debate is based on the following generalities: aspects of the subglacial and supraglacial system; the relative physical geographic setting; sedimentology; paleontology; and isotope data. Specific, relevant issues include: the type of ice cover that existed over the mounds while being influenced by groundwater during their evolution; mound orientation being similar to the orientation of nearby, elevated moraines; superimposed mounds never appearing upon authentic ice walled lake plains; and the mound’s highly dissimilar relief and shape to that of authentic ice-walled lake plains. Besides this study being a reproval concerning the identification of the lowland, gigantic, orientated DeKalb mounds as a dead-ice moraine, it also dismisses a counter-hypothesis of a glacial ice-walled lake origin for them.