Calibrating the Wisconsin in the eastern Great Lakes of North America using optically stimulated luminescence (OSL) dating of the Quaternary sediments at Sand Hill Park, north shore of Lake Erie, Ontario

The eastern Great Lakes Late Quaternary timescale is based on older thermoluminescence dates and on uncalibrated radiocarbon dates from extensive sections along the north shores of Lakes Erie and Ontario. New optically stimulated luminescence dates from Late Quaternary delta sediments from the north shores of Lake Erie at Sand Hills Park give consistent ages of 23.5 to 20.5 ka. This is 4 to 7 ka older than previously assigned based on lithologic correlation with 16.5 ka calibrated radiocarbon dated sediments 5 km to the west at Vanderven. On the existing eastern Great Lakes stratigraphy, it puts deposition of these Sand Hills Park sediments in the Erie interstadial and not in the fluctuating postglacial glacial retreat of the Mackinaw phase to which the Vanderven sediments belong. The Sand Hills delta and underlying diamicts must have been overridden by the Porty Bruce advance at 18 ka. IntCal20 calibration of existing radiocarbon ages suggests that the physical stratigraphic relations of the various Wisconsin units are accurate and that the existing timescale is simply too young.