OSL EVALUATION OF DUNE-SOURCED SAND LENSES FROM GILLIGAN LAKE, MICHIGAN, USA

The Lake Michigan shore hosts the world’s largest freshwater coastal dune system. The dunes record a history of the dynamic interactions among coastal geologic processes and climatic drivers; however, this record can be difficult to decipher due to its complexity. Although there are known triggers for sand dune activation, such as reduced vegetation or increased sand supply, it is not certain as to what specifically has caused the migration of dunes in the Lake Michigan coastal system. Past work has shown that small lakes located downwind from the dunes may contain eolian sand and, therefore, provide another archive of dune activity. Gilligan Lake, south of Holland, Michigan, is situated on the lee side of Green Mountain Dune. Previous lake cores have shown eolian sand laminae and lenses in the deposits of this lake. The objectives of this project are to determine if sufficient quartz sand can be extracted from eolian horizons within a core for dating and to make preliminary OSL age evaluations for the samples. Five sand horizons were identified within the core and OSL samples were collected from three horizons. The thinnest of the sampled horizons was 1 to 1.5 mm thick. The sand is well sorted in the 150-250 micron range and is primarily quartz. The preliminary OSL results in this presentation could be compared with and/or incorporated into a radiocarbon age model for activation of the upwind Green Mountain Dune. However, radiocarbon age models within coastal dune systems can be difficult to assemble at crucial sites and complicated to correlate from site to site. Ultimately, evaluating the record of eolian activity archived in small coastal lakes, such as Gilligan Lake, may allow for better resolution of the triggers for dune activation in the Lake Michigan coastal dune system. OSL dating will be a key aspect of assembling a meaningful and broadly correlatable chronology for future studies.