“TWO-STORIED SOILS” AND THEIR RELEVANCE TO HOLOCENE LANDSCAPE HISTORY IN EASTERN UPPER MICHIGAN

The availability of detailed Holocene hydrographs of the upper Great Lakes has stimulated research of coastal landforms as well as questions of how lake-level change on the Great Lakes might have influenced inland and upland sites. “Two-storied soils”, soils whose profiles clearly suggest drastic changes in their genetic history, are common within the Tahquamenon River watershed that drains to Lake Superior in eastern Upper Michigan. Well-developed spodic horizons overlain by a varying thickness of peat or muck characterize about 20% of the basin. These soils apparently reflect several thousand years of development under pineland vegetation followed by landscape drowning by a rising water table. It has been suggested that just such a widespread rise in the upland water table would have accompanied a rising regional base level during the Nipissing transgression of the upper Great Lakes. Another possibility is that coastal dune building stemming from lake high stands led to channel aggradation which diminished upstream gradients, impounded shallow reservoirs and initiated wetland growth. To gain insight as to whether either of these scenarios is likely, we examined modern soils data for Luce and Chippewa County, MI, noting the relative watershed position of soil series with “two-storied” profiles. In addition, we vibracored wetlands within the Tahquamenon River watershed where “two storied” soils are mapped. We split and described the cores using standard soil stratigraphic methods and submitted organic material from key horizons for 14C dating. Our results should shed light on the history of wetland initiation and growth relative to Great Lakes hydrographs.