Compositional and Textural Analyses of Kansan and Tazewell Till in a Portion of Northwest Iowa

11 Compositional and Kansan and Tazewell tills can be distinguished by compositional and textural properties throughout portions of Buena Vista, Cherokee, Clay and O\u27Brien counties in northwest Iowa. Kansan till contains more clay than silt or sand while Tazewell till is composed of nearly equal portions of clay, silt and sand. Coarse sand is more abundant in Tazewell till than Kansan till. Siliceous rounded shale grains are common in Tazewell till but scarce or absent in Kansan till. Igneous and metamorphic rock fragments are more common in the coarse sand of Kansan than Tazewell till. Significantly more carbonate grains occur in the medium sand fraction of Tazewell till than Kansan till. The lithology of Tazewell till suggests ice occupied the Minnesota-Des Moines rivers\u27 lowland by 20,000 radiocarbon years before the present