Abstract

Data on ice flow direction compiled from the literature reveal two glacial flow directions in northwestern Lake Huron. Superior ice flowed southeast across the Michigan upper peninsula and northeastern lower Michigan, and Algoma ice flowed southwest across the Ontario mainland and the Sugar–St. Joseph–Drummond–Manitoulin Island group. Sandy calcareous till covers most of the area, and it is commonly drumlinized. Grain size, carbonate content, and heavy mineral assemblages provide no distinction between Superior and Algoma tills.

A succession of glacial and postglacial lake levels affected the area. Plane table profiles show that on St. Joseph Island, most of the Algonquin succession can be identified by correlation with published data from Sault Ste. Marie and Manitoulin Island. These shorelines slope up to the north at 1 m/km and are truncated by Nipissing and Algoma strandlines.

Deglaciation of the region occurred between the Onaway Advance (11,800 yr B.P.) and the Marquette Advance (10,000 yr B.P.). Ice retreat took place as Lake Algonquin spread northward, leaving a series of shorelines during isostatic uplift and opening of the sequence of outlets near North Bay, Ontario. The Nipissing transgression is marked by buried wood and peat 7,300 to 5,900 yr old and by the development of a prominent shoreline above the present lake level.

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