A MULTIPARAMETER ROCK MAGNETIC RECORD OF THE LAST GLACIAL-INTERGLACIAL PALEOCLIMATE FROM SOUTH-CENTRAL ILLINOIS, USA

Pittsburg Basin, a small kettle lake in south-central Illinois, was fo rmed after the retreat of the Illinoian ice sheet (similar to 130 ka B .P.), and the sedimentary record includes the last interglacial-glacia l cycle. Curie temperature measurements, XRD analyses and thermal dema gnetization of a low-temperature J(rs) indicate that the magnetic frac tion is characterized by oxidized magnetite and magnetic iron sulfides . The grain size of the magnetic fraction was estimated from ARM/J(rs) ratios, frequency-dependent susceptibility, and hysteresis parameters . These measurements show that glacial sediments contain coarse-graine d, presumably detrital, material while interglacial samples have an ad ditional fine-grained magnetic component, which cannot be explained by a single catchment or climatic process. Early interglacial samples sh ow magnetic properties characteristic of authigenic biogenically produ ced magnetite, while late interglacial samples are probably influenced by pedogenesis around the basin. (C) 1997 Elsevier Science B.V.