LATE PLEISTOCENE DUNE ACTIVITY IN THE GLACIAL LAKE WISCONSIN BASIN

The basin of Glacial Lake Wisconsin, east of the Wisconsin River, includes eolian sands forming high relief dunes surrounded by a sand sheet with scattered low relief dunes. This paper presents 24 optical luminescence ages and soil data from 11 sites in upland dunes and underlying sediments. Samples for optical dating were collected near the surface (n = 7) and within or near the base of dunes (n = 14) to determine periods of eolian activity. Three samples taken from silt-rich Glacial Lake Wisconsin lacustrine sediments that underlie eolian sands have age estimates ranging from 19.3-13.6 ka. Age estimates taken from within or at the base of the dunes range from 15.8-10.6 ka. Near surface samples were slightly younger, indicating dunes were stabilized around 11.8-5.5 ka. The bulk of the optical age estimates from dunes (18 of 21) indicated that most of the dunes were active between 14-10 ka. The younger ages near the surface of some dunes likely result from either pedoturbation or localized dune crest activation. We favor the first hypothesis because eolian bedding is destroyed to a depth of ~1m where it is exposed. Overall, these ages suggest that significant dune activity in the Glacial Lake Wisconsin basin was over by 10 ka, and that localized activity on dune crests may have occurred later in the Holocene. Soils on the dunes have A horizons with 10-15% more silt (10-12 microns) than the underyling eolian sands and weakly developed Bw horizons. We interpret the increase in fines to result from dust additions after dune stabilization. Continued work will determine if the region's sheet sands and low relief dunes had similar activation and pedogenic histories.