THE EXTENT AND FLOW DIRECTION OF THE GREEN BAY LOBE ON THE DOOR PENINSULA, WISCONSIN

The Door Peninsula of Wisconsin separates Green Bay from Lake Michigan, and was also assumed by many to have been the boundary between the Green Bay and Lake Michigan Lobes of the Laurentide Ice Sheet. However, ice flow indicators in Door County show virtually no evidence of ice movement from the Lake Michigan side of the peninsula. Striations are most commonly oriented due south to south-southeast, with a few striae oriented south-southwest (parallel to the axis of the peninsula). Streamlined bedrock hills and drumlins, both subaerial and submerged, indicate ice flow from the north and northwest, out of the Green Bay basin. Pebble fabrics from two different till units also indicate ice flow from the northwest, even in exposures on the Lake Michigan side of the peninsula. These features suggest that ice flow out of the Green Bay basin dominated the glacial landscape rather than flow from the Lake Michigan Lobe, at least during late Wisconsin time and possibly during earlier ice advances as well. Thus Schneider's frequent assertions during the past 20 years that the northern part of the Door Peninsula was glaciated by the Green Bay Lobe and that ice of the Lake Michigan Lobe did not cover the area are hereby confirmed. Rapid retreat of the Lake Michigan Lobe, due to calving, would allow the Lake Michigan basin to be ice free while a substantial ice mass remained over the western part of the Upper Peninsula of Michigan, allowing ice of subsequent advances to flow across the Door Peninsula toward the Lake Michigan basin.