AN OVERVIEW OF LOESS DISTRIBUTION IN WISCONSIN: POSSIBLE SOURCE AREAS AND PALEOENVIRONMENTS

Wisconsin has a wide variety of loess deposits, as well as many areas that lack loess. This paper is a discussion of the various loess deposits in the state, with emphasis on their distribution and possible source areas. Where possible, loess deposit ages and paleoevironmental signatures, based on OSL dating and thinning patterns (which help to discern paleowind direction), are also presented. Although research on the many loess deposits of Wisconsin is still in its infancy, it is indisputable that loess is thickest near the Mississippi River, which had the glacial outwash sediment of the river valley as its source, and thins eastward. In the interior of the state, several discrete loess sheets also exist, separated by areas with very thin (or no) loess. These interior loess deposits are seldom is thicker than 125 cm; in this paper we focus on the Central Wisconsin loess sheet, the Antigo loess sheet, and the NE Wisconsin loess sheet. The interior loesses originated from various sources and have varying textural characteristics; many are quite sandy. Silt and fine sand sources for these interior loess sheets include, among others, degrading permafrost-cored, bedrock hills, thawed/drained ice-walled lake plains in end moraines, sandy outwash plains, and recently abandoned, glacial lake plains. Additionally, many landscapes in the state have very thin (< 25 cm), patchy/discontinuous deposits of loess. These loesses probably have distinctly local sources, reflecting localized eolian redistribution of silts and fine sands in the immediate post-glacial period, as the landscape stabilized and episodically exposed fresh sediment to wind. The geographic and sedimentologic characteristics of the loess sheets in Wisconsin have only been minimally tapped for the paleoenvironmental information that they contain. Further work is sure to shed light on the rapidly changing nature of the immediate post-glacial landscape in the state.