OSL DATING OF BEACH RIDGES IN THE NEGWEGON EMBAYMENT OF LAKE HURON - FROM THE MODERN SHORE UP AND OVER THE NIPISSING RISE

The hydrologic and glacioisostatic history of large glacial lakes can be recorded by the progressive development of shoreline features such as beach ridges and beach dunes. On the shores of the upper Great Lakes beach ridge and swale sequences are particularly well expressed landward of coastal embayments. A detailed chronology of the formation of these ridge sequences would refine our understanding of the history of lake level during the Holocene and could be used to help predict the impacts of future climate-driven lake-level changes on near-shore ecosystems. Past work on ridge and swale sequences on the shores of Lakes Michigan and Superior foreshadowed the potential of optically stimulated luminescence (OSL) dating to be used independently of other dating methods to develop reliable strandplain chronologies for reconstruction of lake-level histories.

A sequence of over 100 ridges preserved south of Alpena, Michigan in the Negwegon embayment of Lake Huron records lake-level since the Nipissing high-water phase approximately 4,500 years ago. In this study sediment samples were collected for OSL dating from excavated soil profiles in basal dune and upper foreshore deposits of 25 of these ridges at a frequency of approximately every fourth ridge. Clean quartz sand, generally in the grain-size range of 150-250 microns, was isolated and dated using single aliquot regenerative dose (SAR) data collection procedures. Data was collected from 92 to 102 aliquots from each field sample. Samples in this study yielded normally distributed data sets such that the mean and standard error were used as the basis for the OSL age calculations. The OSL results produce a highly self-consistent chronology that correlates with the accepted view of late Holocene lake-level changes. The quality of the OSL geochronology provides the resolution to show time gaps in the embayment's progradational history and permit modeling of lake level change through time that is more sophisticated than a simple linear relationship.