DEGLACIAL AND POSTGLACIAL LAKE EVOLUTION IN SIMCOE COUNTY, SOUTHERN ONTARIO

Simcoe County, Ontario hosts an abundance of shoreline features recording the existence of a series of glacial lakes during deglaciation. Recent surficial mapping investigations in the region have led to the identification of numerous new shoreline features and high resolution imagery and digital elevation models have facilitated analysis and correlation of these data. Shore bluff and beach features are used in conjunction with deltas and fluvial terraces, as well as sedimentological studies and new radiocarbon dates, to create new detailed paleogeographic maps that show water body evolution in central Ontario from the earliest phases of deglaciation (approximately 13 ¹⁴C kyr BP) to present. Analysis of the shoreline indicators supports and augments previous work completed in the region, helps to better constrain glacial isostatic adjustment, and permits interpretation of prevailing winds in the midcontinent during deglaciation.

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.