SOILS AND GEOMORPHIC EVIDENCE FOR A HIGH LAKE STAND IN A MICHIGAN DRUMLIN FIELD

The objectives of this study were to determine (1) if and where lithologic discontinuities are present in the late Pleistocene Northport drumlins of NW lower Michigan, and (2) the sedimentary processes responsible for the discontinuities. Determining the presence of lithologic discontinuities was achieved through field observations and laboratory analysis. Lithologic discontinuities with varying strengths of expression were found in all upland soils. Upland soils typically have a sedimentologic “cap” dominated by fine sands at the surface with dense, more gravelly till beneath. The occurrence of this cap on upland sites, as well as overlying laminated silts and clays in some inter-drumlin areas, suggests that upland soils in the Northport drumlin field formed from subaqueously reworked glacial till. To accomplish this, the Northport drumlin field must have been inundated by a previously unidentified proglacial lake, after recession of the ice margin during the terminal Pleistocene. The lake may have formed as ice blocks lay in the deep basins to either side of the drumlin field and high morainic uplands spanned the southern edge of the field, which at that time would have been severely isostatically depressed. Key words: deglaciation, proglacial lakes, paleoenvironmental reconstruction, till, soils, flooding, Great Lakes region.]