Geomorphic History of Low Perched, Transgressive Dune Complexes along the Southeastern Shore of Lake Michigan
Edward C. Hansen, Timothy G. Fisher, Alan F. Arbogast, and M. Bateman
The majority of the coastal dunes along the southeastern shore of Lake Michigan are perched on topographically low lake plains or barrier bars that are only a few meters above modern lake level. A general geomorphic history of the low perched dunes has been developed by combining new chronological data (radiocarbon ages from dune paleosols and OSL ages from dune sand) from Hoffmaster and Warren Dunes state parks with already published data from Van Buren State Park, Silver Lake State Park and the dunes near Holland Michigan. Fragmentary evidence exists of dune complexes older than 6 ka, but these have been almost obliterated by active dune growth and migration since the Nipissing transgression. The record of aeolian activity begins during the Nipissing transgression and continues with episodic activity during the drop from peak water levels ~ 5000 cal. yrs B.P. In the lake plain complexes this activity resulted in the formation of a broad field of low coastal dunes. In the barrier bar complex at Silver Lake it may have been associated with the westward expansion of a pre-Nipissing barrier bar. A hiatus in dune building activity occurred during the low lake levels that followed the drop from the Nipissing highs. A renewal of aeolian activity was approximately synchronous with the Algoma high-water phase ~ 3200 cal. yrs B.P. In the lake-plain complexes this activity was concentrated on the lakeward edge of the dune complexes leading to the development of large parabolic dunes. In the Silver Lake barrier bar complex this activity is associated with a reactivation of the eastern edge of the dune field leading to the eventual development of a large sand sheet with transverse dunes. The development of large parabolic dunes in lake plain complexes was followed by a period of extensive stability in which dune growth and migration slowed considerably or stopped entirely. The renewal of extensive dune mobility, which continues today, appears to predate the arrival of European settlers. The geometry of the dune complexes appears to largely reflect the local sediment budget. Simple lake plain complexes form in areas of net negative sediment budgets with receding shorelines. Erosion at the lakeward edge of these complexes has prevented the formation of coastal dune ridges and exposes sediment in older dunes to further aeolian transport leading to the preservation of a single set of large parabolic dunes that migrate eastward with the shoreline. Compound lake plain complexes, in contrast, have formed in areas of net positive sediment budget and prograding lake shores. Dune ridges form in these systems through the growth of progressively younger foredune ridges westward as the lakeshore progrades. Blowouts in these ridges subsequently migrate inland forming overlapping and nested parabolic dunes. Barrier bar complexes occur in areas in which a positive sediment budget has led to the formation or expansion of bars since the Nipissing transgression. Narrower bars are dominated by parabolic dunes while wider bars can also include sand sheets and transverse dunes. High lake levels and land use practices contribute to dune mobility but cannot completely account for the pattern of coastal aeolian activity in the last 5000 years.