Geologists Have an Angle on Past Glaciations in Illinois

Drilling in Champaign, Illinois, to study the hydrogeology of the Mahomet aquifer A 245-foot-long borehole was drilled in Champaign, Illinois, by the Illinois State Geological Survey (ISGS) as part of ongoing research to study the geology and hydrogeology of the Mahomet aquifer. Continuous core was collected from the land surface into bedrock, and geophysical tests were performed in the borehole to characterize the subsurface materials.

One objective of this drilling was to test new technologies that incorporate magnetic and gravimetric sensors to measure the orientation (azimuth and dip direction) of boreholes. Sediments record the direction of the Earth's magnetic field as they are deposited. This magnetic memory can be measured in the lab and correlated to the Geomagnetic Polarity Time Scale to obtain a precise, absolute age for the sediments. The ISGS is the first to utilize these technologies to acquire oriented cores from unconsolidated sediment, and this study may provide a blueprint for future researchers aiming to conduct paleomagnetic measurements on sediment that is deeply buried and not exposed at the land surface.

The borehole was drilled at an angle of 10 degrees to utilize these downhole tools, which were developed by Reflex Instruments and supplied by IDS (International Directional Services LLC). Mining companies and geotechnical consultants prefer these tools over other orientation systems because they allow continual in-hole measurements that therefore reduce the drilling cost per foot. These tools allow geologists to carefully reorient samples of the core in the lab, which in turn, will allow geophysicists at the University of Minnesota's Institute for Rock Magnetism to determine the age of the sediments encountered during drilling

Initial results of this drilling program confirm the recent findings of a study of the Mahomet aquifer that was jointly undertaken by the ISGS and Illinois State Water Survey (ISWS), suggesting that certain sand and gravel deposits, important to the carrying capacity of the aquifer, are not present at this site. However, shallower sand and gravel deposits were encountered during drilling that may serve as a water source for the surrounding area. The dual-agency Mahomet aquifer study is funded by the Illinois American Water Company. Additional data obtained from this drilling activity further supports findings from a current study of the Mahomet aquifer that has provided a better understanding of the subsurface geology that could impact the future management of water resources.

Finally, the core was subsampled for additional measurements that will determine the physical, chemical, and biological properties of these subsurface materials. Scientists from the Department of Civil and Environmental Engineering at the University of Illinois will study the microbial communities present in these sediments. It is hoped that the results will provide an improved understanding of the microbial communities present in anaerobic (oxygen-poor) environments that can be applied to the development of bioenergy and the bioremediation of toxic chemicals and radioactive materials.

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