Poorly Drained Soils and Geomorphology of Glacial Lake Douglas in Illinois

Abstract

Soil characteristics and geomorphology were investigated in an area designated Glacial Lake Douglas, in Douglas County in east-central Illinois. The study area was once covered by a glacial lake, with a surface elevation of approximately 650 feet, which occupied a broad, shallow depression in the Wisconsinan till plain. Beneath the solum there were clayey, silty, and sandy sediments which had been deposited in a lacustrine environment, and glacial till. X-ray analyses indicated that the solum was mainly of loessial origin, while the lacustrine sediments were outwash materials from the glaciers which deposited the nearby Wisconsinan till. The lakebed sediments were thickest southwest of the Embarras River and became thinner northeast toward Newman. Laminated, clayey sediment was absent in a wide area west-southwest of Camargo, probably because this was a delta when glacial meltwaters filled the lake. Elevation of the top of the clayey sediment was lowest close to the main drainage outlet, and it became higher in an outward-radiating pattern until it reached an average maximum elevation of feet at its outer margin. Total drift thickness over bedrock ranged from approximately 15 to 20 feet over some bedrock uplands near Newman to about 200 feet over parts of the Pesotum bedrock valley. Drainage of Glacial Lake Douglas marked the first time that Embarras River extended this far north. There is a close relationship between the occurrence of the clayey, lacustrine sediment and the principal, poorly drained, dark soil in Glacial Lake Douglas. This lakebed soil has higher clay and sand content, lower silt content, higher bulk density, lower organic carbon levels, and lighter colored Ap and horizons than Drummer silty clay loam, a poorly drained, dark soil that occurs extensively in areas around Glacial Lake Douglas.