REVISITING THE DISTRIBUTION AND GEOMORPHOLOGY OF SAND STRINGERS BEYOND THE ICE MARGIN

In the lower Chippewa River Valley (LCRV), Wisconsin, USA, a variety of sandy aeolian landforms have been broadly interpreted, largely based on relative landscape position, as contemporaneous with or post last glacial maximum (LGM). These landforms provide evidence for a predominately west-northwesterly wind regime differing from those east-northeasterly derived deposits that are immediately proximal to former ice margins in the Great Lakes region. Little remains known about the absolute chronology, paleoenvironmental significance, and genesis of these landforms. With the recent acquisition of LiDAR data, “sand stringers” (Zanner, 1999; Koch, 2004) appear widely distributed beyond the ice margin across southeastern Minnesota and western Wisconsin. We utilize remote data sets (e.g. LiDAR, aerial photographs) and prior morphological descriptions in the literature (<20 km long, 10-100 m wide, <1-5 m high) to identify and map >500, NW-SE oriented, sand stringers beyond the ice margin in SE MN and western WI. Zanner (1999) comprehensively investigated a single sand stringer (i.e. Canfield Creek Stringer) in Mower County, MN, and hypothesized that variations in the internal stratigraphy represent fluctuations in the position of Des Moines Lobe margin, and therefore particle size of aeolian sediment supply. Zanner's five thermoluminesence ages from the Canfield Creek Stringer date between 11-15 ka, broadly fitting this interpretation. To test this paleoenvironmental and geochronological hypothesis of sand stringer deposition across this broad spatial extent, we utilize optically stimulated luminescence (OSL) dating, ground penetrating radar, and sediment coring on two recently identified sand stringers in the LCRV. Additional OSL samples were collected from three other sand stringers within the LCRV. Preliminary OSL dates collected from five sand stringers provide ages ranging between 10-15 ka suggesting a similar period of sand stringer deposition across the region.