SAND IN SEDIMENT CORES FROM SMALL LAKES IN LAKE MICHIGAN COASTAL DUNE COMPLEXES: A PROXY FOR DUNE GROWTH AND MIGRATION?

Sand laminae and peaks in sand concentrations in sediment cores from small lakes and bogs in the Lake Michigan coastal zone have been used to construct chronologies of dune growth and migration. These chronologies have proven to be consistent with chronologies of dune activity based on dune paleosols and OSL analyses of dune sand, but have the potential to be more complete and to offer higher resolution. Empirical observations show that sand can be transported by aeolian processes to lakes in the lee of large dunes. But other transport mechanisms also need to be considered. Observations include sand suspended in turbulent eddies on the lee slope of large dunes lifted into higher velocity airstreams and blown farther inland. Aeolian sand on and within snow and lake ice also directly records niveo-aeolian transport. Dilution or contamination of aeolian sand in these lakes by riverine input, runoff along the shore, or mass wasting processes can be assessed by detailed sedimentological analysis of cores in transects across the lake including sites adjacent to the river mouth. Sampling sites away from stream inlets in lakes or bogs with a dense growth of emergent vascular plants in the littoral zone acting as a sediment trap can minimize non-aeolian input of sand. Whenever possible aeolian chronologies based on sediment cores should be cross-checked against the upwind dune paleosol and OSL chronologies. In cases where the chronologies agree, the sediment cores can add a greater level of chronological detail. As sediment cores can contain proxies for both climate and local environmental conditions, aeolian chronologies based on lake cores can be placed in the context of other environmental changes.