EARLY HOLOCENE MOBILIZATION OF EOLIAN SAND IN EASTERN LOWER MICHIGAN

Dune fields are geomorphically sensitive landforms that are excellent indicators of paleoenvironmental change. Most research on North American dune fields has focused on grassland and desert systems where widespread mobilization of eolian sand occurred in the late Holocene. Forested dunes that occur in glaciated regions, in contrast, have generally received less attention. Nevertheless, research indicates that now forested dunes developed because of 1) deflation of unvegetated deglacial/lacustrine surfaces (e.g., Connecticut, Saskatchewan) during the late Wisconsin; 2) fire during cold/dry intervals in the Holocene (e.g., Quebec); and 3) increased mid-Holocene aridity (e.g., Minnesota). A place that contains a number of forested dune fields is the interior of Michigan. One of the largest interior dune fields is the Saginaw dune field, which covers the Saginaw lowland in Michigan's eastern lower peninsula. This dune field contains mostly parabolic and transverse dunes, largely with northwestern (~ 315°) orientations, that mantle the lacustrine surface created by pro-glacial Lake Saginaw ~ 16,000 cal. yrs B.P. In general, these dunes are thought to have formed shortly after subaerial exposure of the lake plain. This hypothesis was recently tested through OSL dating of eolian sand and radiocarbon dating of basal peats. Basal radiocarbon dates (2s) provide maximum-limiting dates ranging between ~ 16,200 and 12,900 cal yrs B.P. OSL dating indicates that widespread mobilization of eolian sand last occurred between ~ 11 and 9 ka. Thus, it appears that the landscape of eastern lower Michigan may have stabilized more slowly following deglaciation than previously thought. A contributing variable may have been the rapid drop in the level of Lake Huron to the Stanley phase in the early Holocene, which may have lowered the regional water table sufficiently to promote mobilization of eolian sand in the interior. Localized reactivation of dunes occurred in the late Holocene, with burial of paleosols occurring at ~ 1,100, 850, 425, and 200 cal yrs. B.P.