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ABSTRACT

This field trip is an excursion to exposures of Pennsylvanian bedrock at Grand Ledge, Michigan, as a backdrop for interdisciplinary examination of the sedimentologic, stratigraphic, and hydrologic research conducted on these important bedrock aquifer units.

The areal extent of Pennsylvanian rocks in the central Lower Peninsula of Michigan is ~28,490 km2. Pleistocene glacial deposits overlie these units throughout the state, but the drift is thin and locally absent along the Grand River Valley, in and around Grand Ledge, Michigan. The geology of the Pennsylvanian deposits is known almost entirely from subsurface research, although sparse outcrops occur near Parma and Jackson in Jackson County and at Grand Ledge in Eaton County. These outcrops, especially the ones at Grand Ledge, constitute the only exposures of coal-bearing strata in Michigan where visitors can see massive sandstone, shale, coal, and associated strata, and fine-grained, chaotic, riverbank-slump facies.

The sections of the field trip will attempt to relate Grand Ledge area deposits to the Pennsylvanian section at the state and regional scale. First, general geologic and stratigraphic relations will be described on the basis of knowledge from the nearby cities of Lansing and Mason, where diamond drill cores and geophysical logs from extensively studied groundwater contamination sites are available. Lithologic and geophysical logs from these sites will be reviewed under the pavilion. Next, lithologic type sections of the Pennsylvanian material in outcrop will be observed and discussed. An example of core from a nearby industrial site will be studied under the pavilion during lunch, and a final trip to outcrop will be made to discuss stratigraphic relationships in an effort to bring into perspective the complexities of Pennsylvanian strata in the Michigan Basin.

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