The Quaternary geology of the Ames 7.5 minute quadrangle, Monroe and Randolph counties, Illinois

Wisconsin Episode loess overlying Illinois Episode diamicton overlying bedrock is the characteristic sediment package. Silty alluvial deposits are thickest in the lower reaches of Horse Creek where they overlie clay-rich lacustrine deposits. Bedrock is commonly exposed in the channels of the smaller tributary streams. Glacial outwash deposits are locally present below and above diamicton. Pre-Illinois Episode deposits are rare. Unweathered diamicton in the study area contains between 58 and 70% illite, and contains 14 to 26% clay, 53 to 64% silt, and 20 to 32% sand. These properties are consistent with Illinois Episode Glasford Formation diamicton reported in locations north of the study area. The bulk of the diamicton in the study area is interpreted as till. Because all diamicton in the Ames Quadrangle was deposited during the Illinois Episode, the pre-Illinoian glacial boundary, as delineated by the extent of Pre-Illinois Episode diamicton, is located east of the Ames Quadrangle.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat.