MAGNETIC SUSCEPTIBILITY AND ITS CAUSES IN THE PALOUSE LOESS, EASTERN WASHINGTON

Loess deposits can archive Quaternary paleoclimate data. Loess sequences have been used successfully for paleoclimate reconstruction on the Chinese loess plateau, in Europe, Argentina, the Lower Mississippi Valley in the United States, and other regions. The Palouse region of southeastern Washington, northeastern Oregon, and western Idaho contains extensive loess deposits overlying Miocene Columbia River basalts. Earlier work on the magnetostratigraphy of the Palouse loess demonstrates that loess has been accumulating for as much as 2 Myr, making it a potentially extraordinary record of terrestrial paleoclimate for the Quaternary. Numerous (15+) paleosols are preserved in the loess, representing periods of increased stability where pedogenesis outpaced deposition. For this study, we collected a sequence of loess samples along depth profiles at the well-studied CLY-2 site in southeastern Washington State, representing deposits that accumulated throughout the past ca. 50 ka. We measured magnetic susceptibility and other magnetic properties including isothermal remanent magnetism and magnetic hysteresis. We also measured other properties including iron content, grain size, and carbonate concentrations to see what factors drive differences in magnetic susceptibility in the Palouse. Magnetite and/or maghemite are likely responsible for nearly all of the susceptibility signal. We did not find magnetic susceptibility to be a reliable proxy for chemical weathering in the weakly-developed paleosols of the Palouse, but it does provide stratigraphically consistent data at the outcrop scale that can be useful for correlating outcrops.