Postglacial Landscape Evolution of Northeastern Lower Michigan, Interpreted from Soils and Sediments

Abstract

In this study, we used spatial data on soils, near-surface stratigraphy, and paleotopography to reinterpret part of the Late Pleistocene history of northeastern (NE) lower Michigan. We determined the relationships between various soil series and their likely sedimentary environments. Maps of these soil series for two counties in NE lower Michigan were then prepared within a geographic information system (GIS) to interpret the spatial patterns of the sedimentary environments on the paleolandscape which had been ‘downwarped’ within a GIS to account for isostatic rebound. Our primary finding centers on the origin and distribution of clayey, lacustrine sediments in the region. These clays are found in swales between drumlins and on ground moraines. They occur, however, at elevations up to 60 m above any previously known paleolake. Although it is widely known that low-lying, clay-dominated areas near the Lake Huron and Lake Michigan basins were inundated by paleolakes in the Late Pleistocene, thick deposits of lacustrine sediments between drumlins in the high interior of this region suggest that it, too, was periodically submerged between 11,200 and 13,000 yrs B.P. Additionally, the crests of these drumlins are covered with 50 — 100 cm of sediment that appears to have been water-worked at some time in the past, overlying a denser, less altered till. We argue that a previously unknown lake, or series of interconnected lakes, existed across the uplands of this landscape. Stratified silts and clays were deposited beneath this water body, which was ponded between the Port Huron moraine to the south and an advancing, stagnant, or retreating ice margin to the north and east, and may have discharged to the south across a low section of the moraine. Our findings underscore the complex interactions among ice sheets, meltwater, and preexisting landscapes during final deglaciation, and should assist those who seek to understand and explain modern soil and biotic patterns on those landscapes. We hope that our preliminary findings facilitate further hypothesis generation and testing regarding this lake(s), this landscape, and their coevolution.