A COMPARISON OF 14 C- AND OSL-BASED LAKE-LEVEL RECONSTRUCTIONS FOR THE PAST ~1200 YEARS DERIVED FROM BEACH RIDGES AT BAILEY'S HARBOR, WISCONSIN, LAKE MICHIGAN
Recent work has shown that optically stimulated luminescence (OSL) dating of quartz separates collected directly from the foreshore facies of individual ridges can improve the accuracy of strandplain chronologies. Questions remain as to whether OSL can provide the accuracy and precision necessary to generate a decadal-scale record of beach-ridge formation necessary for the past ~2000 years. This contribution compares strandplain chronologies, resultant age models, and lake-level reconstructions for the Bailey's Harbor strandplain, Lake Michigan, generated from OSL and existing 14C data used by Thompson and Baedke (1997). Bailey's Harbor preserves ~30 individual beach ridges formed during the past ~1200 years, as determined through previous 14C studies. Five discrete OSL ages provide decadal-scale resolution for the ~30 ridges preserved at Bailey's Harbor. In contrast, 14C ages for ten swales exhibit multiple age ranges, decadal-scale variability, and age reversals, highlighting issues of provenance and variability in the atmospheric production of 14C versus the decay rate of this radioisotope during the past ~1000 years. The results indicate that OSL provides the necessary resolution to reconstruct water-level change during the past ~2000 years, though there is still a need to evaluate differences in local rates of GIA that are produced by geologic, GPS, and tide-gauge approaches of measurement.