PARTICLE SIZE DISTRIBUTION ACROSS THE CENTRAL SAND PLAIN OF WISCONSIN

The Central Sand Plain (CSP) of Wisconsin is a relatively flat area covering ~9000 sq km. The CSP includes the basin of glacial Lake Wisconsin, which merges eastward with sandy outwash. Much of the surface was modified by wind into dunes prior to landscape stabilization; however, dune thickness varies throughout the CSP. Large dunes, up to 15m high, are limited to a small area (~150 sq km) in the west central portion of the CSP. Proposed reasons for the distribution of thick eolian sand include melting of permafrost, elevation of the basin in relation to ground water, sediment inputs from the Wisconsin River, and sediment particle-size. Particle-size analysis of the large dunes shows that the median grain-size is between 200-300 microns. Therefore, if the distribution of thick eolian sand is controlled by particle-size, areas without dunes should be deficient in those grains. This project tests this hypothesis by analyzing ~100 samples across the CSP for particle size distribution. Based on this analysis, the northern portions of the CSP are to coarse for eolian transportation. However, the southern portion of the CSP has 300 micron grains but dunes are absent or small.