Brown, S. R., 2001, Quaternary geology of Door county, Wisconsin, and implications for regional flow patterns of the Green Bay Lobe: Madison, Wisconsin, M.S. Thesis, University of Wisconsin, 144 pp.

Abstract

Door County was covered by the Green Bay lobe of the Laurentide Ice Sheet during late Wisconsin time. Pre-Wisconsin diamicton is lacking in Door County, though a compact silty, gray diamicton identified in several boreholes may correlate to pre-Wisconsin deposits identified by Chapel (2000). The silty, sandy Liberty Grove Member of the Holy Hill Formation was deposited during minor readvances as the lobe retreated from its Late Wisconsin maximum extent between 15,000 and 22,000 radiocarbon years BP (RCYBP).

The reddish-brown, clayey Glenmore Member of the Kewaunee Formation was deposited following the Two Creeks interval (after 11,700 RCYBP). Glenmore diamicton is typically very thin in southern Door County, and almost entirely absent in the north. Thick deposits of Glenmore diamicton are present at the base of the Niagara Escarpment and along the flanks of streamlined promontories in the southern part of the county.

The bedrock topography in northern Door County closely approximates the surface topography. In southern Door County several valleys in the bedrock are present that are partially filled with Quaternary sediment. One wraps around the northern edge of the streamlined promontory south of Brussels, where it meets the Ahnapee valley. A second runs parallel to the Ahnapee valley, about two miles (3.2km) to the east. The trends of all valleys in Door County match well with the dominant joint orientations of the bedrock. Large-scale karst features are not present in Door County, except for the large depression in the middle of Rock Island.

No flow indicators that suggest ice flow from the Lake Michigan basin are present in Door County. Striations, drumlins, moraines, streamlined promontories, and pebble fabrics all show flow from the Green Bay basin, even in the extreme southeastern part of the county. 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 to 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. Rapid retreat of the Lake Michigan lobe due to calving would have left the eastern margin of the Green Bay lobe unconfined, allowing subsequent advances of the Green Bay lobe to cross the peninsula.

Glenmore ice most likely covered the northern part of the Door Peninsula, but deposited very little sediment there. The steepness and height of the escarpment in northern Door County, along with the bedrock ridge in Green Bay north of Chambers Island, may have prevented the deposition of Glenmore diamicton (reworked lake clay) in northern Door County. The presence of the Sturgeon Bay lowland, along with the fact that the escarpment is gentler in the south, may have allowed basal debris to top the escarpment and be deposited across southern Door County.