Spring Geological Science Field Trips Popular with Participants
Approximately 100 people attended the Illinois State Geological Survey spring Geological Science Field Trips on April 25, and May 31, 2008. The field trips highlighted the geology and natural resources of the Horseshoe Lake State Conservation Area and surrounding areas and included six stops within Alexander County.
The first field trip stop was south of Miller City at the base of the Santa Fe Levee. There participants viewed the landscape changes that occurred following the levee breach during the Great Flood of 1993. The second stop was to an Eocene age sand and gravel deposit within Black Powder Hollow, south of Thebes, where a large number of participants collected a variety of agates. The third stop was Rock Springs Hollow, where the Ordovician age Girardeau Limestone is bounded by a number of faults and related fractures that have created a series of small waterfalls. Following lunch at Horseshoe Lake, the participants learned that this oxbow lake formed approximately 6,000 years ago when the Mississippi River changed course, cutting off a large meander. The fourth stop, to the Olive Branch-Sandy Ridge Novaculite Quarry, provided an excellent view of the ancient Ohio River valley and an opportunity to discuss the geological history of the Ohio River, its abandonment of its former course through what is now the Cache Valley during the last glaciation, and its present course. The participants were able to view a large fault within the quarry and collect a number of loess kindchen(unusually shaped calcareous concretions) that form in the overlying windblown loess deposits. The fifth stop was Birk-McCrite tripoli quarry, operated by Unimin Speciality Minerals Inc. The participants learned about the quarry operation and the uses of tripoli, a microcrystalline silica. Some of the more common uses of tripoli include buffing and polishing compounds and use as a filler and extender in plastics, paints, and rubber. The participants collected Devonian age fossils and a variety of mineral specimens at this quarry. The final stop on the trip was to the Tatumville Novaculite Quarry, where participants examined a rare exposure of a graben (a downthrown block of bedrock bounded by two faults) within the quarry highwall and collected samples of novaculite, a microcrystalline chert. Novaculite is typically used as a base for road construction and also as a fine sharpening stone. As the day came to an end, ISGS geologists spent time answering a number of questions from individual participants. A question on a number of minds, given the number of faults seen on the field trip, concerned the recent 5.2 earthquake in southern Illinois and its relationship to the New Madrid Seismic Zone.