DEGLACIAL AND POSTGLACIAL LAKE EVOLUTION IN SIMCOE COUNTY, SOUTHERN ONTARIO
Glacial Lake Schomberg formed first, at 300m asl, while meltwater was dammed between the Niagara bedrock escarpment and retreating ice margins to the south, east, and north. Drainage of glacial Lake Schomberg was incremental, ending once ice retreat exposed a connection with water in the Huron basin, forming early Lake Algonquin at 250-270m asl. Early Lake Algonquin was relatively short-lived in the study area and drained catastrophically(?) to form the Kirkfield low phase following exposure of isostatically-depressed outlets at Fenelon Falls around 12.41 – 12.81 14C kyr BP. Subsequent uplift at Fenelon Falls caused a transgression in the southern parts of the basin to form Main Lake Algonquin reaching 220-250m asl. This outlet remained open until differential uplift raised it above the lake’s southern outlet at Port Huron following the Ardtrea phase around 10.2-10.03 14C kyr BP. It remains unclear which outlet(s) received lake drainage during the Upper and Lower Orillia phases. Ice retreat exposed low-level northern outlets creating the sequentially lower shorelines of the Wyebridge through Payette phases of Lake Algonquin. The Stanley low phase is recorded by paleosols and alluvial deposits in Simcoe County. A basin-wide transgression caused by uplift at the North Bay outlet refilled the Huron basin to form the peak Nipissing phase of the Upper Great Lakes at 190-195m asl.