GEOMORPHIC EVOLUTION OF THE COASTAL DUNE LANDSCAPE ALONG THE SOUTHEASTERN SHORE OF LAKE MICHIGAN

A semi-continuous body of large (> 30-m high) dunes exists along the southeastern shore of Lake Michigan. Although the dunes are heavily utilized and managed, there evolution is historically linked to a pair of assumptions: 1) they largely formed during the Nipissing high stand (~ 6000-4000 yrs B.P.); and 2) they grow during relatively low lake stages. Recent research has tested these hypotheses with detailed chronostratigraphic investigations at 9 sites between Manistee, MI and northern Indiana. A total of 40 paleosol radiocarbon dates were correlated with Thompson and Baedke’s (1999) lake level curve.

Data indicate that dunes first formed during the Nipissing stage (~ 5700-5400 cal. yrs BP) at many sites, but ~2900 cal. yrs BP at others. The dunes grew most between ~ 4000-2500 cal. yrs BP, reaching a height of ~ 30 m. The early part of this phase correlates best with receding water levels and a transfer of littoral sediments eroded during the Nipissing period. Accumulation of eolian sand was continuous near Muskegon, MI during this interval but was punctuated by periods of stability south of Holland, MI. These stable periods were < ~ 200 cal. yrs B.P. long, as indicated by Entisols (A/C horizonation). As the dunes grew larger, increased sand supply correlates best with rising lake levels. Following this rapid period of dune growth, most dunes stablized for ~ 2000 yrs, as indicated by the proposed Lake Michigan Paleosol (LMP), an Inceptisol with A/E/Bs/C horizonation. The reason for this extended hiatus is unclear, but may relate to beach progradation and dune protection from basal wave erosion. Near Muskegon, and in backdunes, the LMP is the surface soil, but south of Holland it was buried between ~ 1000-500 cal. yrs BP by an additional ~ 10 m of sand that accumulated episodically. These investigations indicate that previous models regarding coastal dune evolution along Lake Michigan are much too simplistic.