GIS ANALYSIS OF NORTHERN WISCONSIN GLACIAL TILL UNITS

Grey, silty, calcareous till of the Pierce and Marathon Formations (deposited >400 ka) is present in western and north-central Wisconsin. These calcareous till units are overlain by pre-Late Wisconsinan, reddish-brown, sandy till of the River Falls and Lincoln Formations. Reddish-brown, sandy Copper Falls Formation till (deposited 25 -12 ka) is found at the surface throughout most of northern Wisconsin.

Glacial till samples have been analyzed since 1973 at the UW-Madison Quaternary Geology Lab. These till data (2,300 samples) have been compiled in an Excel spreadsheet and mean till characteristics have been analyzed. A DNR lookup table was used to convert section/township/range location information into Wisconsin Transverse Mercator coordinates. ArcView 8.1 has been used to display till data in visual formats and analyze magnetic susceptibility, grain size, and carbonate content for till lithostratigraphic units in northern Wisconsin.

GIS analyses have revealed several trends. Pierce and Marathon till units have similar matrix textures (40:40:20 sand:silt:clay %) but display calcite to dolomite ratios of 4:1 and 0.4:1, respectively. An increase in magnetic susceptibility values for River Falls till from west to east may reflect ice flow lines that crossed banded iron formation units in northern Wisconsin and the Upper Peninsula of Michigan. Lincoln Formation till samples are sandy (55:31:14), but Lincoln till samples in northern Clark and southern Taylor Counties are less sandy (and more silty) than along the eastern, western, and southern boundaries of the till unit. Silty till of the Marathon Formation underlies the Lincoln Formation in northern Clark and southern Taylor Counties, and glacial erosion of Marathon till may have "contaminated" Lincoln till with silt in those areas. Tills of the Merrill and Bakerville Mbrs. of the Lincoln Fm. and the Copper Falls Fm. display anomalously low magnetic susceptibility values in southern Oneida, eastern Lincoln, and western Langlade Counties.