GLACIAL LAKE MESICK: A PREVIOUSLY UNRECOGNIZED PROGLACIAL LAKE ASSOCIATED WITH THE PORT HURON STADIAL

Field work in western Wexford and eastern Manistee Counties, Michigan, has revealed the presence of a large delta in the Manistee River valley originating on the inner (west) flank of the Lake Border moraine near the confluence of the Lake Michigan lobe and the Traverse Bay sublobe of the Laurentide ice sheet. A significant source of foundry-quality sand, the Slagle delta is the largest in a series of at least four deltas that coalesce at their lateral margins and exhibit deltaic deposits from 300-315 meters altitude. Existing surficial geologic maps have described the area of these deltas as an outwash plain.

Glacial Lake Chicago, Glenwood II phase existed around 13,000 14C years B.P. during the Port Huron stadial with a northern shoreline controlled by the position of the Port Huron moraine. Distal deposits from Slagle delta are found onlapping the eastern (outer) margin of the Port Huron moraine, implying a time correlation. However, the observed surface altitude of the lake in which Slagle delta was deposited is much higher than the closest mapped shoreline of Glenwood II (201 meters in the vicinity of Pentwater, Michigan, 75 km to the southwest), too high to be accounted for by isostatic rebound. This lake, here named Glacial Lake Mesick occupied over 500 km2 and had at least three different levels that overflowed southward through successively lower outlets to the Pere Marquette River and thence to the Glenwood II level. Drainage into Glacial Lake Mesick originated from a glacial lake on the east side of the Lake Border moraine in the Lake Cadillac basin and probably also received drainage from the upper Manistee River.