TIMING AND IMPLICATIONS FOR SAND DUNE DEVELOPMENT IN THE GREEN RIVER LOWLAND OF ILLINOIS, UPPER MIDWESTERN UNITED STATES

We report ages and suggest a potential sediment source for sand dunes in the Green River Lowland, Illinois, which will provide a better understanding of the dynamic interactions among eolian, glacial, lacustrine and fluvial processes that shaped the landscapes of the upper Midwest. Seven coherent optically stimulated luminescence (OSL) ages obtained from four sites suggest that major dune construction in the Green River Lowland occurred around 17,500 ± 570 yrs ago. Although severe aridity cannot be ruled out as cause for this time period regionally, we suggest sediment supply has played a greater role in the construction of these dunes. Contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the Lake Michigan Lobe retreated from the area, we propose that dunes were formed as a result of formation and drain of two glacial lakes in Wisconsin: Glacial Lake Scuppernong and Oshkosh, from the Green Bay Lobe through the Rock River.

OSL and radiocarbon ages also indicate that dunes were reactivated during the early, middle and late Holocene. Some eolian activation occurred within well-defined dry intervals in the upper Midwest but many ages do not correspond to drier periods. In contrast to the relative coherency of the Pleistocene OSL ages, the Holocene OSL ages do not overlap from one site to another, suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation. Therefore, we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the Holocene. The multiple periods of eolian activity during the Holocene suggest a high potential for future sand activation in the region, and these results are informative for environmental prediction and potential future mitigation.