CONCURRENT STABILIZATION OF SOME INTERIOR DUNE FIELDS IN MICHIGAN

Inland dunes occur over a large part of east-central lower Michigan, w here they mantle glaciolacustrine and outwash surfaces that were expos ed around 12,000 yrs. B.P. The dunes are parabolic, with northwest-ori ented limbs, and occur in swampy landscapes, suggesting that paleoclim atic conditions at the time of their formation were much drier and pos sibly windier. In order to determine whether the dunes stabilized conc urrently or randomly in time and space, surface soils were studied on 30 dunes in the area and quantitatively analyzed for relative differen ces. Soils data from the dunes indicate concurrent stabilization, foll owing a period of regional mobilization of aeolian sand. Surface soils have formed by podzolization, in uniform parent materials, and are mo rphologically similar throughout the area. All the soils are weakly de veloped, with subtle variations on a A-E-Bs-BC-C horizonation sequence . Munsell colors of Bs horizons are remarkably uniform, with 27 of 30 sites exhibiting values of 4 and chromas of 6. Chemical data suggest t hat Fe and Al translocation has been uniform throughout the region. Wh en compared with sails of known age in northwest lower Michigan, the d ata indicate that dunes in the region had stabilized at least by 4000 yrs. B.P., leaving an approximately 8000-yr. interval in which they co uld have formed. In contrast to the prevailing southwesterly winds of today, dune-forming winds were dominantly from the northwest.