LATEST PLEISTOCENE AND HOLOCENE DUNE BUILDING IN EASTERN UPPER MICHIGAN

In the 1930s, Stannard Bergquist suggested that the history of interior dunes in eastern Upper Michigan involved the rapid draining of glacial Lake Algonquin ~13,500 cal BP, deflation of its dry sandy lakebed, and subsequent rapid stabilization of resultant dunes by vegetation. This long-standing hypothesis was tested and rejected in 2002 through optically stimulated luminescence dating (OSL) of six scattered sets of interior dunes in eastern Upper Michigan. Investigators concluded that interior dunes developed concurrent with Altithermal drying, ~6,000-6,600 cal BP, and were stabilized during more mesic climates after ~5,000 cal BP. We used OSL to age deposition of seven dune fields within areas adjacent to/covered by Marquette ice ~ 12,000 cal BP, north of the 2002 study sites. Our results lend some support to Bergquist’s lake bed deflation concepts, albeit adjacent to the Minong (and not Algonquin) lake plain. Preliminary optical ages of our samples suggest three episodes of dune activity: ~12,000, ~ 9,000 and ~ 6,000 cal BP. Dunes generated at ~12,000 cal BP may have been driven by adiabatic winds off the retreating Marquette ice sheet. Clustering of optical ages ~9000 cal BP along the eastern edge of the study area suggest that these dunes were the result of deflation of littoral sediments of glacial Lake Minong after the demise of the lake ~9,500 cal. BP. Dune building ~6,000 cal BP is consistent with results of the 2002 study and may represent an Altithermal signal associated with deflation of sand flats exposed after dune-impounded lakes shrank during dryer climates. Recent soil mapping by USDA-Natural Resources Conservation Service on the three sets of dunes identified here supports the hypothesis that they represent distinct age groupings.