Thin, pedoturbated, and locally sourced loess in the western Upper Peninsula of Michigan

Luehmann, M.D., R.J. Schaetzl, B.A. Miller, and M.E. Bigsby. 2012. Thin, pedoturbated, and locally sourced loess in the western Upper Peninsula of Michigan. Aeolian Research 8:85-100. doi:10.1016/j.aeolia.2012.11.003.

Abstract

County soil surveys document thin loess deposits across large tracts of Michigan’s western Upper Peninsula (UP), which we informally call the Peshekee loess. Our study is the first to examine the distribution, thickness and textural characteristics of these loess deposits, and speculate as to their origins. Within this region, loess is typically 20-70 cm thick and commonly underlain by sandy glacial deposits. At most sites, pedoturbation has mixed some of the lower materials into the loess, resulting in a particle size mode within the 25-75 µm fraction (from the loess), but also in a secondary mode in the 250-500 µm fraction (from the pedoturbated sand). We introduce and describe a method by which the mixed sand data are removed, or “filtered out,” of the original particle size data, to better reflect the original textural characteristics of the loess. Our data – from 237 upland sites – suggest that the Peshekee loess deposits were locally sourced from ground moraines, outwash plains, and the floodplains of small meltwater streams – interspersed within the region and at its periphery. Loess textural and thickness attributes change markedly across the region, pointing to the influence of many local sources and suggesting that the loess was transported mainly over short distances. Because of the spatial variability of this loess, we identify four main loess “core” regions, within the study area, each of which has distinct characteristics that set it apart, and describe each of these as a unique “type” of loess with one or more local source areas.

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