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|Title:||Late Pleistocene lithofacies, paleolimnology and ostracode fauna of kettles on the Illinoian till plain, Illinois, U.S.A|
|Author(s):||Curry, B. Brandon|
|Doctoral Committee Chair(s):||Johnson, W. Hilton|
|Department / Program:||Geology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The response of sediment, vegetation and aquatic environments to climate change during the last glacial--interglacial--glacial intervals were investigated from fossiliferous successions in four breached kettle basins in south-central Illinois. The thickest measured successions of lacustrine/paludal sediment per basin include 16.4 m (Raymond Basin), 9.0 m (Bald Knob Basin), 7.0 m (Pittsburg Basin) and 4.3 m (Hopwood Farm). The age of calcareous, fossiliferous sediment is beyond the limits of the radiocarbon method, but leached, organic-rich sediments at Pittsburg Basin and Bald Knob Basin yielded ages that span from about 45 ka to 21 ka yr B.P. Electron spin resonance analyses on Sangmonian tooth enamel from Hopwood Farm indicate an age between 73 to 137 ka.
Climate change was evaluated by interpreting successions of fossil ostracodes. Modern environments were investigated to determine critical physiochemical parameters that control the distribution of these aquatic microcrustaceans. Two environmental indices, the eurytopicity index (EI) and lotic index (LI), measure the tolerance of ostracodes to physiochemical and current variability. When applied to the abundance profiles of fossil ostracodes from the breached kettle basins, changes in EI and LI values in the stratigraphic record imply changes in water residence time, water depth or shore proximity, environmental parameters that are indirectly linked to moisture balance and climate.
Climatic interpretations are based on implied environmental gradients that affected the results of principal components analyses of ostracode and pollen abundance data, and the autecology, modern analog analyses and environmental indices of ostracodes. Open hydrologic conditions are implied by the overflow channels and by the generally low and invariant TDS values of $<$500 mg/l suggested by Jaccard similarity coefficients. Low TDS is also implied at Raymond Basin by the results of closed-system models that account for the variable and high stable isotope values (C,O) of ostracodal calcite.
Two periods during the Sangamon interglacial had winters warmer than present in Illinois as indicated by the occurrence in the fossil ostracode successions of subtropical Heterocypris punctata. This species lives today adjacent to the Gulf of Mexico, and implies that atmospheric circulation patterns at times were much different during the last interglacial interval than today.
|Rights Information:||Copyright 1995 Curry, Ben Brandon|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9522099|
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