THE EMERGING RECORD OF COASTAL DUNE EVOLUTION ALONG THE SOUTHEASTERN SHORE OF LAKE MICHIGAN

Massive (> 30 m high) coastal dunes occur along the southeastern shore of Lake Michigan. Although the dunes have a long (> 100 yrs) history of qualitative description, very little detailed (chronostratigraphic) data exists. Nonetheless, two broad assumptions exist regarding their evolution: 1) they largely formed during the Nipissing high stand (~ 6000-4000 yrs B.P.); and 2) they enlarge during relatively low lake stages. The hypotheses regarding the evolution of coastal dunes are currently being rigorously tested. This research has focused on exposures near Holland and Van Buren State Park where good chronostratigraphy exists. These dunes contain numerous buried soils, most of which are Entisols (A/C horizonation) that represent brief (< ~ 200 yrs) periods of landscape stability. Radiocarbon data indicate that the dunes began to form during the Nipissing stage (~ 5700 - 5400 cal. yrs B.P.) and then enlarged rapidly and episodically, with burial of Entisols occurring at Holland and Van Buren both concurrently (e.g., ~ 4200, 3200 cal yr. B.P.) and independently (e.g., 2000 cal. yr. B.P.). All of the dunes stabilized ~ 2500 cal. yr B.P. and remained so for about 1500 yrs, resulting in the development of Spodosols (A/E/Bs/C horizonation). The reason for this extended hiatus is unclear. Spodosol burial occurred at ~1000 and 300 cal. yr B.P. at Holland and Van Buren, respectively. Additional growth occurred at both sites at ~ 200 cal. yrs B.P. Although dune formation began during the Nipissing interval, these results indicate subsequent development well after this high lake stage. In addition, it appears that dunes to have enlarged both during high and low lake stands.