A PRELIMINARY STRATIGRAPHIC FRAMEWORK FOR THE SAGINAW LOBE, BARRY AND CALHOUN COUNTIES, MICHIGAN

Since 2006, 12 rotasonic borings have been drilled in Barry and Calhoun Counties, south central Michigan, as part of a Great Lakes Geological Mapping Coalition project. Seven of these borings reached bedrock. Natural gamma ray logs were collected at each location and detailed descriptions and grain size analysis have been completed for five of these cores. All but one of these borings are located north of the Kalamazoo Moraine of the Saginaw Lobe, which was constructed during retreat of the lobe after the LGM. Two of the eleven cores (BA-10-02 and BA-09-02) contain at least 3 or more distinct diamicton units separated by thick lacustrine sequences. The only core located south of the Kalamazoo Moraine contains 4 diamictons, separated by sand and gravel units rather than lacustrine sediment. Preliminary analysis suggests that the drift is entirely Late Wisconsin in age and the objective of the project is to correlate the diamicton units across the lobe. It is currently not known whether these diamictons represent distinct advances of the ice or a fluctuating ice margin.