New Sources for the Glacigenic Loess of the Midwestern United States

Traditionally, loess has been viewed as originating from deserts or valley train outwash sources. In the glaciated, midwestern US, the latter are particularly common. Rivers such as the Mississippi, Missouri, Wabash, and Illinois all carried copious amounts of glacial meltwater and have thick loess blankets on the uplands to their east and west. However, these sources, large and dependable as they were, do not account for the many other (smaller and thinner) loess deposits that occur in the glaciated, northern Midwest. In this paper, I present data on the distribution of loess in two Midwestern states - Wisconsin and Michigan - and use spatial data on texture and mineralogy from these deposits to delineate their possible sources. I conclude that some of the loess sheets in this region originated from recently abandoned lake plains, outwash snadurs, and/or silt-rich lake end moraines (with abundant ice-walled lake plains within), among others. Finally, I note that loess distribution patterns, coupled with a highly lobate ice margin during Midwestern deglaciation, suggest that much of the eolian silt was not transported solely or eve mainly west-to-east, but that winds were highly directionally variable, and that katabatic winds were a factor in the eolian transport of silt. The utility of this work for soil scientists revolves around the explanation of the spatial distribution of soil parent materials - a post- and full-glacial process that recent research is showing to have been more important than was previously thought.