Southern Illinois Paleoclimate Determined From Variations In Iron Oxide Content

Abstract

Diffuse reflectance spectroscopy was used to determine the relative abundance of the iron oxides hematite and goethite in a loess and paleosol sequence from an unglaciated area of southern Illinois. Factor analysis of first derivatives of the spectral data yielded a four factor solution which explained more than 94% of the cumulative variance. Factors 2 and 3, which represent hematite and goethite respectively, were the most useful for interpreting paleoclimatic conditions at the site. Hematite, which is indicative of warmer conditions with periodic seasonal rainfall, shows a strong response not only to climatic variations but also to glacial lobe proximity. Goethite is generally associated with loess where conditions favored a cooler and moister environment and exhibits a strong correlation to glacial intervals with the exception of the Roxana loess, where large amounts of quartz and secondary carbonate interfere with the signal. Together, factor 2 (hematite) and factor 3 (goethite) illustrate a paleoclimatic record of southern Illinois for the last 11 glacial/interglacial episodes.