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The timing of speleogenesis of two of Illinois' longest caves (Fogelpole Cave and Illinois Caverns) located in southwestern Illinois' sinkhole plain was investigated by integrating differential erosion and datable sediment and speleothem deposits within the caves. Five locations in the two caves, and three different methods were used to estimate incision rates and timing of the initiation of the caves. Two of the sites investigated in Fogelpole Cave have second-order channels or passages that are now filled with silty subterranean slackwater sediments deposited during dry periods of the Pleistocene and Holocene Epochs; the passages are now raised above the present cave stream bed by benches that are similar to each other in character and height. The other three sites contained speleothems that recorded the age of early cave levels. Radiocarbon dates of disseminated organic matter in the fine-grained sediments and uranium-series dating of the speleothems yielded approximate ages for the benches within the caves. The heights of the benches and cave passages, and the age of the sediments and speleothems on those benches were used to estimate incision rates and the timing of initiation of the two caves. The various techniques and locations within the two caves yielded rates of incision ranging from 0.031 to 0.050 mm/year averaged over the course of 30,000-125,000 years. Based on the rates of incision and passage dimensions, the age of speleogenesis for Fogelpole Cave, Illinois Caverns was estimated to range from 120,000 and 164,000 calendar years before present. Coeval surficial ice-marginal deposits have been mapped about 5 km south of the caves, suggesting a causal relationship between the chemically aggressive glacial melt waters of the penultimate glaciation in Illinois and the onset of speleogenesis. [ABSTRACT FROM AUTHOR]

Abstract: In unglaciated areas of the Mississippi Valley region, the typical full loess–paleosol succession contains the Modern Soil developed in Peoria Silt, weakly developed Farmdale Geosol developed in Roxana Silt, Sangamon Geosol developed in Loveland Silt, and Yarmouth Geosol developed in Crowley''s Ridge Silt. Although a fifth loess called the Marianna Silt is reported at one area, the paleosol that separates the Crowley Ridge and Marianna Silts is not well defined. Previous thermoluminescence (TL) and optical stimulated luminescence (OSL) age chronology has suggested multiple phases of Sangamon Geosol developed in Loveland Silt, but clear morphological evidence of polygenetic Sangamon Geosol profiles have not been found. Recently, a thick loess–paleosol sequence has been studied in the middle Mississippi Valley in unglaciated southern Illinois, USA. Soil morphology and analytical results revealed five loesses and associated paleosol units. Two Sangamon Bt horizons were found separated by a thick ACtk horizon, interpreted to indicate two phases of Sangamon Geosol development. This well-preserved loess–paleosol succession provides one of the most complete mid–late Quaternary loess records in the middle Mississippi Valley to date, and is important for studying the stratigraphic framework and paleoclimate and environment changes. [Copyright &y& Elsevier]