Date of Award
Master of Science
Giddings cores on upland areas indicate the Evansville Quadrangle includes both pre-Illinois and Illinois Episode glacial ice advances. Upland stratigraphy predominantly consists of Wisconsin Episode loess overlying Illinois Episode diamicton overlying bedrock or bedrock residuum. At one site in the northern part of the quadrangle, pre-Illinois diamicton is distinguished from Illinois diamicton by the presence of the Yarmouth Geosol. Pre-Illinois and Illinois Episode glacial boundaries (or diamicton boundaries) exist in the Evansville Quadrangle. The pre-Illinois Episode diamicton boundary includes the northern portion of the quadrangle, whereas the Illinois Episode diamicton boundary exists below 167.6 m (550 feet) on the uplands in the southern part of the quadrangle. However, Illinois Episode ice may have advanced farther south at lower elevations in the Kaskaskia River valley. The Kaskaskia River valley contains a modern floodplain, as well as at least three separate terraces resulting from alternating periods of aggradation and incision in the Kaskaskia Valley. The uppermost terrace is an Illinois Episode terrace occurring from approximately 129.5 - 134.1+ m (425 - 440+ feet), and consists of Peoria Silt overlying Roxana Silt overlying outwash sands of the Pearl Formation. The middle terrace is Wisconsin Episode in age occurring from 121.9 - 129.5 m (400 - 425 feet), and consists of the Peoria Silt overlying the Equality Formation. The Equality Formation was deposited in a slackwater lake that formed as a result of backflooding of the Kaskaskia River during flooding events of the Mississippi River. A low terrace and floodplain are Holocene in age. The Holocene terrace occurs from 117.3 - 121.9 m (385 - 400 feet), and consists of thin Cahokia Formation (clayey facies) overlying the Equality Formation. This terrace represents a back swamp created as slackwater lake levels rose in the Kaskaskia Valley. Finally, a floodplain deposit of the Kaskaskia River occurs at 117.3 m (385 feet) or less. Bedrock exposures are relatively limited but were observed in stream beds, such as Little Nine Mile Creek (a tributary stream of the Kaskaskia River) in the southeastern part of the quadrangle. Exposed bedrock also occurs along the bluffs of the Mississippi River and could occur in sinkholes close to the land surface, although sinkhole geology was not investigated for this study.
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