DOWNCORE ND-SR-PB-AR ISOTOPIC PROVENANCE OF PACIFIC PELAGIC CLAYS: EXTRACTING THE NORTHERN HEMISPHERE CENOZOIC DUST FLUX RECORD

New techniques are being applied to resolve the downcore provenance of eolian dust in Pacific pelagic clays. The Pacific pelagic clay province represents one of the planet’s main repositories for wind blown dust, yet little is known about changing flux rates and sources through time. A detailed record of Cenozoic paleoclimate and atmospheric circulation can potentially be constructed using this material, provided that the stratigraphic age and continental source can be precisely determined. Many of these ‘red clay’ cores are undatable by conventional methods (biostratigraphy/magnetostratigraphy) due to lack of fossils and extremely low sedimentation rate. We have developed a reliable method for dating red clay cores using the strontium isotopic composition of cleaned fish teeth, matched to the newly refined Cenozoic seawater strontium isotope curve. This provides stratigraphic age resolution down to the ±0.5 m.y. level for core material younger than 40 Ma. The conventional isotopic provenance tracers Nd-Sr-Pb allow the signatures of distinct continental source areas for the eolian dust extract from dated intervals to be determined. 40Ar/39Ar ages for the sub 5-micron dust fraction have also been obtained for several cores, and show remarkable co-variation with Nd-Sr-Pb isotopic compositions. These data demonstrate increasing dominance of Chinese loess as the primary source of Cenozoic Pacific dust deposited north of the Intertropical Convergence Zone (ITCZ). This Asian component, which becomes dominant in the late Pliocene, is characterized by an average Ar-Ar retention age of ~220 Ma. A detailed 70 m.y. Ar-Ar record for the giant piston core LL44-GPC3 (north central Pacific) reveals downcore changes in dust provenance which, corrected for plate motion, are suggestive of significant latitudinal excursions of the paleo ITCZ.