LOESS AND EOLIAN SEDIMENTS OF NE WISCONSIN

Although it has long been known that several dm of loess caps the uplands of NE Wisconsin and Iron County, Michigan, these deposits have not previously been directly studied. In this research, I provide data, maps and interpretations for this loess and its related, eolian sediments, based on over 60 samples from undisturbed, upland sites.

This area, which was deglaciated roughly 13 cal ka, is characterized by rolling, drumlinized uplands with narrow outwash flats between. Large, outwash heads and plains lie to the west and east of this area. The loess, which is up to a meter thick in some areas, is not represented by a continuous sheet, but rather, is present mainly on discontinuous uplands and typically absent in lowlands, where meltwater likely removed it during dustfall. The loess is typically thickest and siltiest, i.e., of the highest “quality,” along a N-S line through the study area, from about Crystal Falls, MI through Laona and Wabeno, Wisconsin. To the east, the loess thins quickly and gets slightly sandier, as it approaches N-S trending glacial margins in this area, eastward of which the loess is absent. To the west, the loess also gets sandier and thinner, as it approaches its presumed source area - the outwash plains of Vilas and Oneida Counties, Wisconsin. Near these sandy outwash plains, the loess is thin and coarse-textured, while on broad, unkettled uplands within the outwash areas, a thin cap of very fine sand and silt can be observed. I interpret this trend as indicating that the outwash plains were sources of eolian sediment in the time period immediately following deglaciation, and that as distance from this source increased, sorting and sediment coarseness also decreased. Loess thickness appears to be more a function of the amount of time that a given upland was stable, than it is location, elevation or sedimentological composition.