ALLUVIAL AND EOLIAN DEPOSITIONAL HISTORY OF THE BARRENS FAN, NORTHWESTERN WISCONSIN

The Barrens fan is a high terrace of the St. Croix River that formed when Superior Lobe meltwater streams flowed into Glacial Lake Anoka during the late Pleistocene. Today, the Barrens Fan has a complex surface consisting of large, stable eolian transverse dunes, and stream scarps that were cut during more recent alluvial activity. To date there has been only relative age control for both the deposition of the sediments that form the Barrens Fan and the movement of the dunes on its surface. This study uses optically stimulated luminescence dating to determine when the alluvial sediments within the Barrens Fan were deposited, and when the dunes were active on its surface. Although previous studies suggested that the dunes may have formed during mid-Holocene droughts, our geomorphic and geochronologic evidence suggests that the dunes formed shortly after the abandonment of the Barrens Fan terrace. Our data does show evidence for minor dune reactivation during the mid-Holocene, however, dune activity was likely limited to individual dunes, rather than a large scale reactivation.