A LONG LOESS RECORD IN SOUTHERN ILLINOIS: 5 INTERGLACIAL, 2 PROMINENT INTERSTADIAL PALEOSOLS, AND 5 LOESS UNITS

The Mississippi valley loess record in unglaciated areas contains up to 3 interglacial soils – the Modern Soil, the Sangamon Geosol (Geosol 1), and the Yarmouth Geosol (Geosol 2), and 4 glacial loess units – the Peoria, Roxana, Loveland, and Crowley's Ridge Silts. A fifth loess unit, the Marianna Silt and its equivalent, has been reported in some places, but correlations are difficult at many sites because of lack of the well preserved geosol 3 unit. The TL (thermoluminescence) and OSL (Optical Stimulated Luminescence) age chronology revealed multiple phases of Sangamon Geosol developed in Loveland Silt but clear morphological evidence of polygenetic Sangamon profiles were not found. Recently, a thick loess record has been discovered at a loess bluff in unglaciated southern Illinois. Soil morphology and analytical results revealed Peoria, Roxana, Loveland, Crowley Ridge, and Marianna loesses and Modern Soil, Sangamon Geosol, Yarmouth Geosol, Geosol 3 and Geosol 4, and 2 relatively strong interstadial class soils. In addition, two Sangamon Bt horizons were found separated by a thick caliche bed, implying multiphase development of the Sangamon Geosol. Two relatively strong interstadial geosols containing Bw horizons were found in lower Roxana and lower Crowley's Ridge Silts. The geosol in lower Roxana is known as Chapin Geosol in Illinois and the one in lower Crowley's Ridge is informally named as Prairie Du Rocher geosol. This loess-paleosol succession provides the most complete mid-late Quaternary loess record in the middle Mississippi Valley to date for studying the stratigraphy as well as paleoclimatic and paleoenvironmental changes.