A HIGH-RESOLUTION LATE HOLOCENE LAKE-LEVEL CHRONOLOGY FOR LAKE HURON GENERATED FROM OPTICAL DATING OF COASTAL STRANDPLAINS

The generation of a late Holocene hydrograph for Lake Huron provides an opportunity to better evaluate the timing of both major lake-phases and multi-decadal scale oscillations in the larger Lake Michigan-Huron basin. This study applies a high-frequency sampling approach to provide optical ages for individual beach ridges at four coastal strandplains adjacent to Lake Huron including sites at Negwegon, Alpena, Oak Point, and St. Vitals Bay. Beach ridges provide the most direct sedimentologic indicator of lake-level, preserving in their internal structure both the waterlain nearshore and eolian sediments that are deposited during processes related to changing rates of sediment supply and water-level change associated with a cycle of a relative rise and subsequent fall in lake-level. The field, laboratory, and analytical approach developed for dating coastal strandplains contains built in quality-control generated from the integration of sedimentologic, geomorphic and chronologic data. The optical ages generated through the single-aliquot regeneration method represent the largest and most internally consistent set of ages for coastal strandplains published for the Great Lakes, which allows for the generation of age models within individual sites to more accurately assess the history of coastal development through time. The comparison of calculated age uncertainties and modeled age errors presented helps to better understand the genuine scale of error associated with optically-based chronologies, especially for the critical time period of the past 2000 years during which Lake Superior separated from Lake Michigan-Huron through glacio-isostatic adjustment. Further, the high-frequency sampling allows for detection of changes in ridge-preservation rate that could not be resolved in earlier studies. The refined approach to constructing hydrographs from coastal beach ridge sequences will allow for increased confidence and a better understanding of the relation between climate, water level, coastal sedimentary processes, and dune activity along the Great Lakes during the late Holocene.