GEOGRAPHY AND PRELIMINARY AGES OF COASTAL SAND DUNES IN THE NORTHERN PART OF LAKE MICHIGAN

Abundant research has been conducted on sand dunes along the eastern coast of Lake Michigan from Indiana Dunes National Lakeshore to Petoskey State Park in the past ~ 30 years. The configuration of dune fields on this coast is largely determined by location relative to the “isostatic hinge line”, which arcs across northern Lower Michigan. Dunes south of this feature are generally transgressive systems on lake terraces or located at the mouth of bays. Those north, in contrast, tend to be perched on high headlands or are found at the head of embayments as progradational sequences. Research collectively demonstrates that dune growth along the shore generally occurred in three phases, including 1) during the Nipissing high stand and subsequent regression, 2) the Algoma high stand and subsequent regression, and 3) after a high lake stage at ~ 1.7 ka. These pulses were likely driven by a combination of factors related to fluctuations in sand supply, storminess, and even relative drought.

Additional dune fields occur in the northern end of the Lake Michigan basin that have been less well studied. The most geographically extensive of these dunes are on the north shore of Lake Michigan where they developed in broad embayments associated with the Nipissing and Algoma transgressions and regressions. Eolian landforms in these isostatically raised areas consist of parabolic dunes, complex dunes, and dune and swale topography. OSL ages of ~ 4.2 and ~ 2.0 ka have been obtained from one of the most inland dune ridges, which contains imbedded parabolic dunes. Complex dunes apparently began forming about 1 ka. Dunes also occur on six of the islands in northern Lake Michigan. Most of these dunes are perched on high bluffs on the western side of the islands, although some smaller dune fields occur on topographically lower surfaces. Little is known about their overall history, but preliminary dating suggests mobilization of eolian sand in the past 1 ka, and especially < 0.5 ka. Well-developed parabolic dunes are common and indicate formation largely by southwesterly winds. Similar dune orientations on the northern shore of Lake Michigan indicate southwesterly winds also mobilized wind-blown sand in this area. More research is necessary in these areas to test chronological relationships with dunes on the lake’s eastern shore.