GEOMORPHIC EVOLUTION OF COASTAL DUNES IN THE NORTHERN PART OF LAKE MICHIGAN: ENVIRONMENTAL CONTROLS, REGIONAL COMPARISONS, AND GEOARCHAEOLOGICAL IMPLICATIONS

Recent research has focused on the formation of coastal dunes along northern Lake Michigan. In contrast to dunes along the southeastern shore, which line the coast for many kilometers, most northern dune fields are associated with embayments. Dunescapes in these environments typically contain several ridges, with the largest (~ 30-m high) usually the most inland. Systematic OSL dating indicates that Nipissing dunes are rare and that the largest ridges formed ~ 3.3 ka. Subsequent pulses of dune formation are distinct and occurred ~ 2.1, 0.9, and from 0.5-0.3 ka. These results may have significant implications regarding eolian sand supply and lake level fluctuations. It appears that eolian sand supply was highest during the post-Nipissing lake regression, suggesting a temporal lag between coastal erosion of sand and its ultimate deposition in dunes. Subsequent periods of eolian sand deposition apparently occurred during periods of high and low lake level, suggesting that the causes of dune growth are complex. A distinct drought at ~ 1 ka may have contributed to a major period of dune activation at that time. Dune ages are time-transgressive, with progressively younger deposits closer to the shore. Thus, isostatic rebound is a key component regarding dune formation in the northern part of the Lake Michigan. When combined with our understanding of dune geomorphology in the southeastern part of the Lake Michigan basin, these data suggest that geoarchaeological relationships in coastal dunes vary in space and time. In general, older sites are more likely to be preserved in the southeastern part of the basin, whereas they are absent northward.