DYNAMICS OF GLACIAL AND POST-GLACIAL LAKES MAY EXPLAIN TWO-STORIED SOILS OF EASTERN UPPER MICHIGAN

Several stages of Glacial Lake Algonquin covered much of eastern Upper Michigan while ice blocked its outlet at North Bay, Ontario. Algonquin drained ~14 -13,000 cal BP as ice retreated from North Bay but Lake Minong was retained in the Superior Basin even as levels of lakes in the Huron and Michigan Basins fell significantly. Minong was subsequently breached starting ~10,600 cal BP as a series of easterly outbursts from Glacial Lake Agassiz coursed through the Superior Basin. The utility of modern soil survey in the generation and testing of hypotheses relating to this complex late Quaternary history is demonstrated in newly-released surveys of Chippewa, Luce, and Mackinac Cos. The three-county area includes many two-storied soils wherein one developmental sequence of horizons is stacked atop another contrasting sequence. This distinctive property requires at least one episode of soil burial. While soil burials in the High Plains have been linked with deterioration of windward vegetation during deep drought, a more likely mechanism for profile burial in more humid Upper Michigan is deflation and deposition of littoral sediments that become mobile when exposed by rapid changes in lake level. To frame possible connections between lake level history and patterns of two-storied soils we: 1) modeled the rebounded shores of three phases of Lake Algonquin and of the shore of Lake Minong onto a DEM of eastern Upper Michigan; 2) stratified digitally mapped polygons of two-storied soil series according to the dominant texture of the upper member of the profile couplet, and 3) displayed results using a GIS. Patterns of two-storied soils appear closely associated with shorelines of ancient lakes. Two-storied soils with fine-textured upper members occur primarily along and slightly inland of the southern shore of ancient Lake Minong and on leeward high topography. Two-storied soils with coarser upper members occur adjacent to the highest topography in Upper Michigan which stood above the highest levels of Lake Algonquin. In both cases, spatial patterns of two-storied soils are consistent with the hypothesis that profile burial stemmed from deflation from sandy littoral flats that were exposed during sudden falls in lake level.