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

Abstract

Abstract Soil surveys document thin but discontinuous 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. Peshekee loess is typically 20–70 cm thick and 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 a secondary mode in the 250–500 μm fraction (from the pedoturbated sand). We introduce 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 – show that the textural and thickness attributes of the loess change markedly across the region, pointing to the influence of many localized loess sources, and suggesting that this loess was transported mainly over short distances. The Peshekee loess deposits were mainly derived locally from moraines, outwash plains, and floodplains of small meltwater streams – interspersed within the region and at its periphery. We identify and name four main loess “core” regions, 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. Loess from each core area overlaps with neighboring loess deposits.