EXAMINING CONCEPTS RELATED TO PARABOLIC DUNE DEVELOPMENT IN STABILIZED DUNES ALONG THE SOUTHERN COAST OF LAKE MICHIGAN USING GEOMORPHOLOGY, OPTICAL STIMULATED LUMINESCENCE (OSL) AND PARTICLE SIZE ANALYSIS (PSA)

Two stabilized simple parabolic dunes preserved within the Tolleston Beach along southern Lake Michigan are used to examine concepts related to stages of parabolic dune development. Ten OSL samples were collected from soil pits along the stoss slope, crest, lee slope, and limbs of each dune to provide insight into decadal-scale dune dynamics. Collectively, the optical ages indicate that the inland dunes, that record a west to northwest predominant wind direction, were built from the increased sand supply associated with the lake-level fall from the high waters of the Nipissing Phase and stabilized ~3500 years ago. The model of Fraser and others (1998) for sand transport associated with helical flow patterns within a blowout and Anderson’s (1988) theory of grain fall deposition along the lee slope are tested with optical ages, evaluation of the geomorphology of the stabilized dunes, and particle size analysis (PSA) of the C-horizon. The dune geomorphology suggests that the southern arm of each dune was affected by helical flow patterns within the dunes interior, encouraging the lateral extension of the opposing arm indicative of onshore wind flow. Anderson’s theory of a head scarp recession of the leeward side was not supported by the PSA data. Instead, alternating episodes of the fining and coarsening of material were observed at the base of the leeward slope. Though these dunes overlap in age and are within 10 km of one another, PSA did detect differences in grain-size distributions that are related to dune formation and migration relative to the paleo shoreline. Coarse-sands present in Inland Marsh dunes suggest supply from underlying foreshore deposits, whereas the medium and fine size fractions within the Dune Acres dune suggests a period of additional dune migration. Ultimately the individual optical ages overlap at the 2 standard error level, even so they provide strong evidence that through careful field techniques, OSL yields both precise and accurate ages on dune development and previous studies on coastal dune chronology may underestimate the efficacy of the method.