Geochemical links between paleoceanography and marine sediment-hosted ore deposits

Geochemical concepts relevant to understanding three types of marine sediment-hosted ore deposits are applied to constrain certain paleoceanographic scenarios.; The general depositional model for stratiform manganese ores is tested by examining concentrations of Mn and rare earth elements (REEs) in sediment deposited during the Cenomanian-Turonian Boundary (CTB). Sediment deposited at the CTB is deficient in Mn and REEs relative to pre- and post-boundary sediment, and has a bulk REE pattern similar to that of shale. These observations are consistent with proposed depositional models for stratiform manganese ores.; The above model is used to test a hypothesized latest Miocene-Early Pliocene expansion of the Indian Ocean oxygen minimum zone (OMZ). Concentrations of Mn and Sc are determined for Neogene sediment from locations in the central Indian Ocean that are presently outside of the oxygen minimum zone (OMZ). Sediment at each location displays significant depletions in the flux of Mn and the Mn/Sc ratio during the latest Miocene-early Pliocene. These observations are consistent with the expanded OMZ scenario.; The chemistry and mineralogy of a deep sea umber deposit are examined to test models concerning the origin of the Chinook Trough in the North Pacific. The chemistry and mineralogy of the Late Cretaceous umber deposit is similar to that of Recent hydrothermal sediment on the flanks of the East Pacific Rise, and the accumulation of hydrothermal material in the deposit decreases in an exponential pattern with time and depth upcore. These observations are consistent with an interpretation that the Chinook Trough is a lithospheric scar that marks initiation of Kula-Pacific rifting.; A mechanism involving dissociation of gas hydrate deposits is explored as an explanation for the carbon isotope excursion that occurs during the Latest Paleocene Thermal Maximum (LPTM). It is shown that the inferred ocean temperature increase at the LPTM is sufficient to change sediment geotherms such that 1.1 to 2.1 {dollar}times 10sp{lcub}18{rcub}{dollar} g of carbon as CH{dollar}sb4{dollar} could have been released during the LPTM, and that this amount of carbon is adequate to explain the observed {dollar}-{dollar}2 to {dollar}-3perthous{dollar} excursion in {dollar}deltasp{lcub}13{rcub}{dollar}C across the LPTM.