ISGS Hosts 54th Friends of the Pleistocene Field Conference

Attendees climb a cliff during one of the stops on the trip.The Illinois State Geological Survey hosted about 115 geologists for the 54th Friends of the Pleistocene Field Conference, The Deglacial History of Northeastern Illinois. The conference was based in DeKalb, Illinois. Led by Brandon Curry, the field trip included stops that featured topics ranging from Paleozoic cave fills containing fossils of the earliest conifers; beds of sand and gravel that were folded and faulted by overriding glacial stresses about 18,000 years ago; and the Aurora mastodons at Phillips Park, including three remarkably well-preserved skulls and toothed jaws that have recently been radiocarbon dated. One specimen is currently the youngest known ancient elephant to have roamed the spruce forests of Illinois about 14,000 years ago. The trip included discussions of multiple deglacial floods that affected the geomorphology and sediments of the Illinois River valley. The group looked at evidence of the oldest known torrent of 19,000 years ago—a large, linear gap across the Marseilles Moraine located between the towns of Oswego and Yorkville. The gap is underlain by 30 feet of lake sediment containing fossils of tundra plants, which provided material for the radiocarbon dating of the event. Also featured was a stop at a DeKalb mound. Thought to be the deposit of an ice-walled lake, this landform and other DeKalb mounds located throughout northeastern Illinois have yielded fossil tundra plants that have been radiocarbon dated. The results are providing new details and new insight into the deglacial history of northeastern Illinois. For example, stable isotopic ratios (18O/16O) indicate that the lakes were filled with water derived from the Gulf of Mexico as opposed to glacial meltwater. Wedron Quarry was also visited to allow field trip participants to examine the type section of the Wedron Group, the unit that comprises glacial tills and related deposits of the last glaciation. Featured at this stop was a discussion of the glacial stresses that resulted in evidence of strain during sedimentation. An introduction to the geology of northeastern Illinois and discussion of the geology of the field trip stops were published as ISGS Open File Series 2008-1.