CREATING A REGIONAL 3-D MODEL OF QUATERNARY DEPOSITS FOR MAPPING PROJECTS IN NORTHEASTERN ILLINOIS

A regional three-dimensional model of the Quaternary geology in a rapidly urbanizing area of northeastern Illinois (Lake and McHenry Counties) is being developed in conjunction with the Central Great Lakes Geologic Mapping Coalition, STATEMAP, and EDMAP projects. The area, which covers six 7.5 minute quads, includes upland outwash plain, collapsed kamic moraine, kettle-lake lowland, hummocky moraine, and ridge-like end moraine. Drift thickness in the area ranges from about 150 to 350 feet thick; it thins eastward toward the Lake Michigan basin and thickens where moraines overlie bedrock valleys. Data from exposures, borings, sample sets and logs from well drillers, borehole geophysics, and seismic reflection surveys have been used to create the model, which will be refined as detailed 7.5 minute quadrangle mapping proceeds and more data become available. The Quaternary deposits of this region predominantly represent three major events of the last (Wisconsin Episode) glaciation during which the Tiskilwa, Haeger, and Wadsworth tills and associated proglacial sediments were deposited between about 25,000 and 14,000 radiocarbon years B.P. Locally, older drift is present in some bedrock valleys. Two major drift aquifers have been identified, one of which is connected with a bedrock aquifer. Multiple models for deposition of the proglacial and glacial sediments are being investigated with regard to the glacial events of two sublobes in the area.