Abstract

Differential postglacial uplifting in the Huron basin has long been recognized from the observed deformation of raised shorelines, particularly those associated with the Algonquin series of glacial lakes (12 000–10 500 years B.P.) and the postglacial Nipissing Great Lakes. From Nipissing time, about 5500 years B.P., to the present, lake levels apparently fell in the northern Huron – Georgian Bay region as the basin upwarped and the outlet was downcut.Recent emergence of Manitoulin Island in northern Lake Huron was inferred, independently of raised shoreline data, from sediment sequences in a series of 3 beach sites and 8 small lake basins at various altitudes up to 20 m above Lake Huron. Organic sediment (gyttja) in each lake overlies clastic inorganic sand or silt, with the contact horizon demarcating the isolation of each basin as its threshold emerged from the high-energy littoral environment of Lake Huron. Radiocarbon dates and elevations of the basal gyttja sediments and organic beach sediments suggest uplift at a constant rate of 2.2 mm/year over the past 5000 years. This rate refers to Little Current, Ontario, and is for movement relative to the outlet area of Huron basin at Sarnia, Ontario. The value agrees with basin tilting inferred from lake level gauge observations made during the last 100 years.

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