A HIGH-LEVEL PROGLACIAL LAKE IN WEXFORD COUNTY, MICHIGAN, AND ITS SIGNIFICANCE FOR THE BOUNDARY OF THE LAKE BORDER MORAINE IN NORTHWEST LOWER MICHIGAN

The Lake Border moraine in northwestern lower Michigan has recently been reexamined in western Wexford County. Leverett and Taylor (1915) mapped the Lake Border moraine (much of which exceeds 400 m altitude in Wexford County) in contact with the Valparaiso/Charlotte interlobate moraine at the latter’s northwest corner near Harrietta. Just south of Wexford County, they mapped a convex to the west trending reentrant (67 km long, 45 km wide) in the Lake Border moraine that bends back to the east in Newaygo County.

Recent mapping of deposits in the Lake Border moraine in Wexford County reveal glaciodeltaic deposits from topset sand and gravel through to bottomset (varves) silt and clay. The ice-margin configuration suggested by Leverett and Taylor (1915) cannot support a proglacial lake at the altitudes indicated by recent mapping and drill holes. At the maximum extent of the Lake Border glacier, a high level (~380 m altitude) proglacial lake must have been bounded by the glacier on the west and southwest, older interlobate deposits to the southeast, and possibly the Saginaw lobe to the east. The reentrant as currently drawn could not have held a proglacial lake at the altitude demonstrated by this project. The drainage divide exposed by the reentrant is 100m below the lake level of the lacustrine sediments in the glaciodeltaic morphosequence.

On the basis of this evidence, the Lake Border moraine is mapped without a reentrant. That is, it remains close to the western edge of the Valparaiso-Charlotte interlobate moraine through to the Lake-Newaygo County line where preliminary mapping indicates that the western edge of the uplands is also composed of similar glaciodeltaic deposits.