Paleoecology of Pleistocene Gastropods in Glacial Lake Deposits in Southern Illinois/Missouri

E. C. Geiger¹, S. E. Ishman¹, and D. A. Grimley^2
1Southern Illinois University Carbondale
²State Geological Survey

During the Pleistocene Epoch in the central Midwest United States multiple glaciations and interglaciations occurred during the middle to late Quaternary. This study focused on fossiliferous lake deposits from the Illinoian and Wisconsinan glaciations. The advance of glaciers during these glacial stages caused major rivers and their tributaries to aggrade creating slackwater lakes in many tributary valleys to the Mississippi River. Gastropod assemblages, found in such glacial lake deposits, were used to interpret paleoecology during the major glaciations. Gastropods were collected from four sites in southern Illinois and Missouri to compare the Illinoian and Wisconsinan glacial lake deposits to one another. This study identified forty-eight gastropod species which were analyzed using statistical procedures. Hierarchical cluster analyses resulted in the identification of gastropod assemblages that were interpreted using habitat classifications.

The results indicate specific similarities and differences between the Illinoian and Wisconsinan sites regarding environmental and climatic conditions. All four sites indicate slackwater lake deposits that formed in tributaries of the Mississippi River. The fossils at the Illinoian sites, Ogles Creek and Prairie du Pont, indicate coniferous forests located on an upland surface and slackwater lakes that rested at the base. Wisconsinan sites, Highbanks Road and Coldwater Creek, indicate rather large slackwater lakes surrounded by marshes.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas