HR: 0830h
AN: U11B-0007    [PDF]
TI: Downcore Contrasts in the Provenance of Cenozoic Pelagic and Hemipelagic Sediment, Central North Pacific: Deep Ocean vs. Near-Continental Margin Sites
AU: Gleason, J D
EM: jdgleaso@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109
AU: * Rea, D K
EM: davidrea@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109
AU: Hall, C M
EM: cmhall@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109
AU: Moore, T C
EM: tedmoore@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109
AU: Owen, R M
EM: rowen@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109
AU: Blum, J D
EM: jdblum@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109
AU: Hovan, S A
EM: hovan@iup.edu
AF: Indiana University of Pennsylvania, Geoscience Department, Indiana, PA 15705
AB: We are currently investigating the source characteristics and downcore variation of detrital components extracted from pelagic and hemipelagic clays covering a large area of the central Pacific Ocean basin. Eolian dust is the primary component of red clays forming in the Pacific pelagic clay province today. We have begun assembling a database from 14 new piston cores that span some 30 degrees of latitude in the central North Pacific. These cores contain a record of Neogene pelagic sedimentation that will allow us to track changes in the source and flux of eolian dust over time. Stratigraphic ages and continental source areas can be precisely determined for the extracted dust component using radiogenic isotopes. We have developed a reliable method for dating red clay cores by matching the strontium isotopic composition of cleaned fish teeth with the Cenozoic seawater strontium isotope curve. Age-resolution down to the ñ0.5 m.y. level can be obtained this way for intervals younger than 40 Ma. Radiogenic isotopic signatures of the associated eolian dust extract can then be used to identify distinct continental source areas for this component. Nd-Sr-Pb-Ar isotopic analysis the sub 5-micron dust fraction in these cores demonstrates the increasing dominance of Chinese loess as the primary source of Pacific dust deposited north of the Intertropical Convergence Zone (ITCZ) during the Neogene. This Asian component, becoming dominant in the late Pliocene, is characterized by an average 40Ar/39Ar retention age of ~220 Ma. The longest, most continuous record of eolian dust accumulation comes from Giant Piston Core LL44-GPC3, recovered near 30 degrees North in the central Pacific. The 70 m.y. record from LL44-GPC3 reveals systematic downcore changes in the provenance of the dust component which, when corrected for plate motion, are suggestive of significant latitudinal excursions of the paleo ITCZ. Work is proceeding to improve the age-resolution for these apparent excursions, particularly a large shift that occurs at, or near, the Eocene-Oligocene boundary. By contrast, the downcore record from hemipelagic muds near the North and South American continental margins reveals distinctly different continental sources, demonstrating the unique source signature carried by the eolian component in Pacific pelagic clays. These findings will help us to correctly interpret changing source characteristics through time for the recently returned ODP Leg 199 cores. Combined, these data should provide us with the most detailed record yet of climatic transitions recorded in the central Pacific basin since the late Cretaceous.
DE: 4215 Climate and interannual variability (3309)
DE: 4267 Paleoceanography
DE: 4825 Geochemistry
DE: 4835 Inorganic marine chemistry
DE: 4860 Radioactivity and radioisotopes
SC: U
MN: 2003 Fall Meeting