167 Preliminary Report


Leg 167 drilled 13 sites along the climatically sensitive California Margin: Sites 1010-1022. These sites are arrayed in a series of depth and latitudinal transects to reconstruct the Neogene history of deep, intermediate, and surface ocean circulation, and to understand the paleoclimatic and geochemical history of this region. Leg 167 sites provide an opportunity to address paleoceanographic questions about the evolution of the California Current and the links between high and low latitudes from millennial and orbital to tectonic time scales. Shipboard results document the suitability of these sediments for addressing these questions. Sites have continuous records of sedimentation at high sedimentation rates, with calcium carbonate present throughout the records, and foraminifers for oxygen- and carbon-isotopic studies are generally abundant. Pioneering biostratigraphy will refine the chronostratigraphic control for this otherwise poorly constrained oceanic regime. Magnetostratigraphy constrains the age models at many sites, and advances in understanding magnetic reversals and the effects of sediment diagenesis on magnetic signals will be possible from these sediments. Significant variations occur in sediment properties on all time scales, as seen in high-resolution nondestructive shipboard measurements (e.g., bulk density, magnetic susceptibility, natural gamma-ray activity, all from the multisensor track, and color reflectance and color video imaging), high- to intermediate-resolution downhole log measurements (e.g., bulk density, resistivity, and magnetic susceptibility), and lower-resolution discrete shipboard measurements (e.g., physical properties and carbon geochemistry). Key topics for investigation include variations in productivity, upwelling, sea-surface temperature, hydrography, sedimentation fluxes, and carbon and nutrient budgets.

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