THE RECORD OF DUNE GROWTH AND MIGRATION PRESERVED IN SMALL LAKES WITHIN A LAKE MICHIGAN COASTAL DUNE COMPLEX

During periods of sand dune mobility windblown sand may accumulate in lakes within dune complexes. The history of dune growth and migration is derived independently from the study of dune paleosols and OSL analyses, and is tested and refined by examining the record of sedimentation in two small (<0.1 km2) lakes within a Lake Michigan coastal dune complex southwest of Holland, Michigan. Three sediment cores obtained by piston vibracoring were studied from Gilligan Lake and one core from Kelly Lake 2 km to the north. Sporadic thin (0.5 to 2 cm) layers and lenses of medium-grained sand occur in the sapropels and peats in the middle portion of all cores. The 3 Gillligan Lake cores contain 13, 11 and 5 sand lenses respectively and the Kelly Lake Core contains 6. Twenty radiocarbon ages indicate that all but two sand lenses were deposited during the active period of dune growth and migration that began with the Nipissing high water levels in the Lake Michigan basin and continued for nearly 3000 years. The 2 remaining lenses were deposited during the relatively recent remobilization of the dunes. Between these two periods there was a roughly 1,500 year interval of relatively little eolian activity. No sand lenses were found in deposits from this time. Relative sand concentrations in cubic centimeter size samples, each representing approximately 20 years of sedimentation, are being determined in the sediment outside of the lenses by sieving after loss on ignition. Initial results show peaks with sand concentrations of 15% to 30 % (compared to an average background of ~ 5%) in the sediments deposited during both periods of active dune growth. The correspondence in the chronology of growth and migration in the dunes with the chronology of sand deposition within the lake indicates that concentrations of sand in small lakes can act as a proxy for eolian activity in adjacent dunes.