Environmental Change as Seen in Lake Sediments From South Central Illinois

C E Geiss, S K Banerjee (Institute for Rock Magnetism, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455; tel. 612 624 1323; e mail: geis0037@gold.tc.umn.edu)
R Teed (Limnological Research Center, Department of Geology and Geophysics, 310 Pillsbury Drive, University of Minnesota, Minneapolis, MN 55455)

Rock magnetic measurements from a 9 m core, taken from the center of Pittsburg Basin (South Central Illinois), a now drained kettle lake show a magnetic signal that correlates well with pollen data from the same site. Pittsburg Basin is situated about 60 km south of the maximum extent of the Wisconsinian ice margin and its sedimentary record is believed to span the period since the last interglacial.
For marine oxygen stage 5 the pollen record shows a period of warmer climatic conditions that were bisected by a prairie advance that indicates dryer, but not necessarily cooler conditions. The rock magnetic signal for this period, however, shows three peaks in the ARM/SIRM curve which might correlate with stages 5a, c, e of the marine oxygen isotope record. Preliminary magnetic measurements suggest that we may be further able to distinguish between warm/wet and warm/dry periods.

EOS supplement, V. 76, p.S100, 1995