Geochemical Characteristics of Inorganic Silicate Fractions, Eolian Dust, from the Eocene-Oligocene Transition of the U1334 site in the East Equatorial Pacific

Abstract

Eolian dust, inorganic silicate fraction, extracted from the Eocene-Oligocene transition of U1334 site (IODP Exp. #320) were analyzed for mineral, elemental, and radiogenic isotope (87Sr/86Sr and εNd) compositions to understand changes in zonal wind pattern associated with Oi-1 glaciation that initiated the development of permanent ice sheets in the Antarctic. The inorganic silicate fraction is characterized by smectite-rich mineral composition and elevated Fe/Al, Eu anomaly, and Ba concentrations, indicating considerable contribution of Ba-rich mineral phase and Fe-rich authigenic smectite. A flat shale-normalized REE pattern with strong Eu anomalies and a contemporary seawater 87Sr/86Sr signature of Ba-rich end-member indicate the involvement of hydrothermal/hydrogenous processes that altered the source signals of eolian dust. Thus, mineral composition, elemental chemistry, and 87Sr/86Sr of the inorganic silicate fractions have a limited use for a dust source indicator. In contrast, Nd does not show any meaningful correlations with Fe/Al, Eu anomaly, and Ba concentrations. In addition, Nd concentrations decrease gradually with increasing Fe/Al ratios, thus with increasing amount of Fe-rich smectite, suggesting that detrital Nd signal is preserved in the inorganic silicate fractions through the preferential exclusion of Nd in the authigenic mineral phases. These re