GSA Connects 2021 in Portland, Oregon

Paper No. 31-5
Presentation Time: 2:35 PM


GIBBS SCHNUCKER, Sara, Environmental and Conservation Sciences Program/Department of Geosciences, North Dakota State University, P.O. Box 6050 / 2745, Fargo, ND 58108-6050 and LEPPER, Kenneth, Department of Geosciences, North Dakota State University, P.O. Box 6050 / 2745, Fargo, ND 58108-6050

Strandplains, or ridge and swale topography, occur throughout the Great Lakes shoreline system; past research has shown these strandplain sequences can record paleolake-level change over the Holocene. The Stockton Island tombolo, of the Apostle Islands National Lakeshore, holds such a record, however this data is at risk of being erased. This is due to its uncommon position in a region of subsiding glacial isostatic adjustment (negative GIA). In order to help recover this vanishing record the objectives of this study were to provide geologic dates to evaluate the formation of the tombolo and its evolution over time. 16 samples were collected from ridges within a pair of strandplains that form the tombolo, including transects across its eastern and western shorelines. It may be anticipated that tombolo strandplains would form symmetrically, however the Stockton Island tombolo shows what can be interpreted as a truncation of the western set by the eastern with both sets being truncated by modern shoreline erosion. Samples were dated using OSL SAR techniques. The results from the Stockton Island strandplains may be correlated with and compared to other Great Lakes strandplain sequences, as well as existing paleohydrographs. These age results will provide useful geochronological context for future ecological research on the tombolo. The chronology will also benefit archaeological work by providing a constraining age framework for various prehistoric sites of Indigenous activity. Finally, understanding past lake-level variations can be used to enhance public education on water resources and climate change, and the potential impacts of these issues on the Great Lakes environment.