Chemical Identification of Source Regions in the Operationally-Defined Eolian Dust Component of Central Pacific Sediment

Studying the terrigenous component of marine sediment gathered during ODP Leg 199 (Paleogene Equatorial Transect) will help unravel the paleoceanographic evolution of the central equatorial Pacific Ocean. For example, grain size and mineralogic data from the operationally defined eolian dust (ODED) component of marine sediment in the Pacific have commonly been used to assess changes in wind intensity and continental aridity. Assuming this eolian component is representing the weathering products of the upper continental crust, geochemical studies of Th, Sc, and REE distributions (e.g., Olivarez et al., 1991; Weber et al. 1996) have suggested the presence of two endmember components in ODED: the upper continental crust itself (the eolian-transported weathering products) as well as ocean crust (primarily volcanogenic material). Expanding upon these studies, we are examining the complete geochemical composition (major, trace, and REE concentrations) of the extracted eolian component as well as of bulk sediment from ODP Site 1215 (26N, 147.9W, 5396 m water depth) in the sub-tropical central Pacific. While the bulk sediment composition primarily reflects changes in lithology, the extracted "eolian" component reflects the presence of an Asian loess source as well as an undifferentiated volcanogenic component, consistent with previous North Pacific studies. Further application of additional geochemical discrimination strategies, based on REE, Al, Ti, Nb, and Sc relative abundances, indicate the importance of a number of varying terrigenous sources, such as Asian loess, western Pacific arc material, and potentially South American volcanics. Additionally, the complete chemical characterization of the extracted component allows for the development of criteria by which the efficacy of the extraction procedure may be assessed on a sample-by-sample basis.