Illinois was glaciated by the south-central margin of the Laurentide Ice Sheet (LIS) at least four times. New radiocarbon ages, optically stimulated luminescence ages, U-series ages, and amino acid geochronology have fine-tuned parts of the glacial chronology. U series-dated ?13C records from speleothems at Crevice Cave, Missouri, reveal changes in C3/C4 vegetation; the correlation of these records to the physical glacial/interglacial successions continues. Additional investigations include: a) Pre-Illinois episode: Analysis of sediment cores from deep, buried valleys suggests that the pre-Illinois valley-fill of glaciogenic and interglacial deposits spans the Middle to Early Pleistocene; b) Illinois Episode: OSL ages of sand associated with sub-Illinois Episode till are between 135,000 and 150,000 ± 20,000 yr BP, consistent with great continental ice volume during late Marine Isotope Stage 6; c) Sangamon Episode (last interglaciation): Recently determined OSL ages of sand beds in the lacustrine succession at Raymond Basin indicate that warmer-than present conditions suggested by subtropical ostracodes and pollen indicative of southern deciduous forests (e.g., Liquidambar) occurred from about 130,000 to 110,000 ± 15,000 yr BP. These results are in conflict with a wiggle-matching correlation between the well-dated ?13C record from Crevice Cave, Missouri-1, and the pollen record from Raymond Basin-2 that placed the warm-moist conditions from 76 to 71 ka beginning at the onset of Marine Isotope Stage 4-3; d) Wisconsin Episode: refinement of the deglacial chronology (29 to 16 cal ka) is in progress based on the radiocarbon ages of tundra plant fossils entombed in ice-walled lake sediments on a lateral succession of moraines of the Lake Michigan lobe. -1 Dorale et al. 1998. DOI: 10.1126/science.282.5395.1871. -2 Zhu and Baker. 1995. JPL 14: 337-354. -3 Curry, Dorale, and Henson. 2002. GSA Abstr Progr 35: 6:199.
|Original language||English (US)|
|State||Published - 2011|