Geochemistry of DSDP Hole 91-596

Geochemical analyses of sediments from the top 24.5 m of Deep Sea Drilling Project hole 596 (23°51.20'S, 169°39.27'W) show great variability in the composition of pelagic clays accumulated in the South Pacific since the late Cretaceous. Elemental associations indicate that most of this variability can be attributed to variations in abundances of six sediment end-member components: detrital (eolian), andesitic (volcanic), hydrothermal, hydrogenous, phosphate (fish debris), and biogenic silica. We develop a sedimentation model which is used to infer processes that might have influenced the accumulation rates of these components over the last 85 million years. The accumulation of eolian detritus in the South Pacific shows some similarities to that observed in the North Pacific and has been largely controlled by global climate trends in the Cenozoic. Much of the variation in the accumulation of other sediment components likely reflects the paleoceanographic evolution of the South Pacific. The most notable change in the sedimentary environment occurred at about the Paleogene/Neogene boundary. At that time, significant changes in the color, mineralogy, and chemistry of the sediment probably reflect major shifts in climate mode as well as oceanic circulation in the central South Pacific region.