A multi-parameter 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 formed after the retreat of the Illinoian ice sheet (∼130 ka B.P.), and the sedimentary record includes the last interglacial–glacial cycle. Curie temperature measurements, XRD analyses and thermal demagnetization of a low-temperature Jrs indicate that the magnetic fraction is characterized by oxidized magnetite and magnetic iron sulfides. The grain size of the magnetic fraction was estimated from ARM/Jrs ratios, frequency-dependent susceptibility, and hysteresis parameters. These measurements show that glacial sediments contain coarse-grained, presumably detrital, material while interglacial samples have an additional fine-grained magnetic component, which cannot be explained by a single catchment or climatic process. Early interglacial samples show magnetic properties characteristic of authigenic biogenically produced magnetite, while late interglacial samples are probably influenced by pedogenesis around the basin.