Field Trips Examine Glacial Features and Major Aggregate Sources

Generalized cross section of the Middle Illinois River valley showing principal lithostratigraphic units at the approximate latitude of Henry, in Marshall County, IllinoisIllinois State Geological Survey scientists conducted several field trips for geological professionals in association with the 48th Annual Meeting of the American Institute of Professional Geologists, which was being held in Bloomingdale, Illinois, September 10-14, 2011.

On Saturday, September 10, Donald McKay and Richard Berg led a field trip attended by 10 participants. They visited three sites along the middle Illinois River valley that best explained the history of the Ancient Mississippi River (which occupied the middle Illinois River valley prior to about 24,000 years ago). Sites included the 105-foot Clear Creek Section, which features a succession of tills and sands and gravels from the last glaciation (24,000 to 12,000 years B.P.); the Sisters Section, which contains perhaps the best preserved Sangamon interglacial soil in the region (130,000 to 75,000 years B.P.); and the Sandy Creek Section, composed of 130 feet of Illinois Episode sands and gravels (180,000 to 130,000 years B.P.).

On Sunday, September 11, Pius Weibel led a field trip on the geology of the St. Peter Sandstone and the Ottawa-LaSalle area. Stops included a large quarry where the sandstone is mined, as well as natural sandstone exposures at Matthiessen and Starved Rock State Parks. Also discussed were the LaSalle Anticline and the origin of the unique landscape in this part of Illinois.

On Wednesday, September 14, Don Mikulic led a field trip on the Silurian geology of the Chicago area and its contribution to the infrastructure of the Chicago region. The trip featured a stop at the Thornton Quarry where participants examined Silurian rocks and collected fossils. Emphasized on the trip was the fact that Silurian dolomites have played a critical role in the region as a major source of aggregate for very large transportation and municipal engineering projects.