ILLINOIS STATE GEOLOGICAL SURVEY (2005)
BibTeX
@MISC{Stumpf05illinoisstate,
author = {Andrew J. Stumpf and Michael L. Barnhardt and William W. Shilts},
title = {ILLINOIS STATE GEOLOGICAL SURVEY},
year = {2005}
}
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Abstract
The surficial geology of the Antioch Quadrangle is primarily the result of glacial activity of the last (Wisconsin Episode) glaciation occurring between about 25,000 and 14,000 radiocarbon years ago. During this period, diamicton (a mixture of clay, silt, sand, and rocks) was deposited under, on top of, and adjacent to the ice sheet. Meltwater generated from the glaciers was drained through subglacial channels or in rivers flowing away from the ice. Where glaciers or sediment blocked drainage (marginal to and on top of the ice), lakes were formed. Since about 14,000 years ago (Hudson Episode), the ice melted and the materials have been reworked by modern water and slope processes. The surface diamicton unit in the map area, the Wadsworth Formation, forms a hummocky morainal upland comprising segments of the Valparaiso Morainic System and Tinley Moraine west of Lake Michigan (fig. 1). The Wadsworth diamicton is a till that was deposited beneath the glacier. The diamicton is fairly uniform, however, it can also be comprised of interbeds of sorted material (glacial, river, and lake sediments), suggesting that materials deposited by debris-rich ice were significantly reworked at the margin and under the ice sheet. Although predominantly fine-grained, the upper part of the diamicton may have a sandier texture, especially at the base of slopes or in depressions on the 2uplands, where it has been modified by slope processes or water.
Keyphrases
illinois state geological survey ice sheet slope process wadsworth diamicton valparaiso morainic system map area surficial geology tinley moraine west hummocky morainal upland subglacial channel modern water radiocarbon year antioch quadrangle hudson episode wadsworth formation glacial activity debris-rich ice wisconsin episode lake michigan upper part surface diamicton unit
