Paper No. 6
Presentation Time: 9:00 AM-6:30 PM


WALTERS, Kent A., Department of Geology, The University of Cincinnati, 500 Geology Physics Building, Cincinnati, OH 45221, LOWELL, Thomas V., Department of Geology, University of Cincinnati, 500 Geology/Physics Building, Cincinnati, OH 45221 and PUTNAM, Aaron E., Lamont-Doherty Earth Observatory, Columbia University, 217 Comer, 61 Route 9W - PO Box 1000, Palisades, NY 10964,

The Greenland ice cores record an event which imply a return to near-full-glacial conditions called the Younger Dryas (11.0-10.0 14C or 12.8-11.5 Cal 14C years). Yet, its effect on glaciers is not as well understood. This is especially true for large ice sheets like the Laurentide Ice Sheet (LIS). Here we report the geomorphic sequence generated by the LIS in the Upper Peninsula of Michigan during Younger Dryas (YD) time. In northern Wisconsin the Two Creeks forest bed (11.8 14C or 13.7 Cal 14C years) and the Lake Gribben forest bed (10.0 14C or 11.5 Cal 14C years) in the upper peninsula of Michigan indicate the ice sheet covered this region during YD time.

Surficial mapping with a 10 m digital elevation data set, combined with field investigations, show that ice margin features along the right lateral portion of the Green Bay Lobe are spatially compressed with the Two Creeks and Marquette intervals separated by only 35 km. Between these two limits, mapping revealed a series of four ice contact slopes, each at an interlobate position. This sequence indicates a series of temporary ice contact slope positions during LIS retreat.

Prior work suggests that the Younger Dryas caused the LIS to readvance a substantial distance. This would agree with Greenland ice core data which indicates near-full-glacial conditions. However, multiple ice margins between the YD limits allows for alternative possibilities, one of which is that the LIS retreated in steps during the YD. If so, this implies warmer summers during the Younger Dryas, as has been reported in Greenland and Scandinavia.