(Table T1) Manganese concentration in pore waters from ODP Leg 181 sites, southwest Pacific

During Leg 181, seven locations (Sites 1119-1125) were drilled off the eastern coast of New Zealand. Although the sites were primarily targeted to reconstruct the stratigraphy and paleoceanography of the region (Shipboard Scientific Party, 1999, doi:10.2973/odp.proc.ir.181.101.2000), they are particularly interesting from a geochemical perspective because, as clearly evidenced by shipboard pore water and gas analyses, recovered sediment cores span an exceptional range of chemical environments. Pore water alkalinity, NH4+, SO4**2-, and PO4**3- concentrations, as well as headspace CH4 concentrations, indicate significant differences in sediment redox conditions across the region (Shipboard Scientific Party, 1999, doi:10.2973/odp.proc.ir.181.101.2000). The distribution of solid and dissolved manganese plays an important role in geochemical interpretations of such sedimentary environments (e.g., Froelich et al., 1979, doi:10.1016/0016-7037(79)90095-4; Thamdrup and Dalsgaard, 2000, doi:10.1016/S0016-7037(00)00496-8). Dissolved Mn2+ concentrations of pore waters at four sites (1119, 1122, 1123, and 1125) drilled during Leg 181 are presented in this report

Chemical composition of sediment samples from ODP Leg 164 sites, Blake Ridge

Ocean Drilling Program (ODP) Sites 994, 995, and 997 were drilled into a large gas hydrate deposit on the crest of the Blake Ridge (southeast U.S. margin) where upward CH4 fluxes (F_OUT) are related to depths of pore water SO4**2- depletion. High-resolution pore water SO4**2- and sediment Ba profiles have been constructed at these sites to assess present and past F_out. Pore water SO4**2- profiles are linear with zero SO4**2- concentration occurring at 21.4, 21.6, and 22.8 mbsf at Holes 994A, 995A and 997A, respectively. Using steady state solutions to diffusion equations with appropriate parameters, the steep SO4**2- gradients support upward CH4 fluxes between 7.2 and 8.6 mol/m**2/ky at present-day, with the range primarily reflecting different approaches for incorporating porosity (phi). Taking into account the generally decreasing phi with depth and the high clay content of the sediment, the best estimates for F_out are 7.9, 7.6 and 7.2 mol CH4/m**2/ky at Sites 994, 995 and 997, respectively. However, non-steady state solutions to diffusion equations show that the SO4**2- gradients do not imply steady state conditions. Elevated Ba concentrations (530–1410 ppm) exist in sediment between 18.23 and 20.65, between 17.31 and 20.31, between 19.40 and 21.80, and between 19.58 and 21.91 mbsf at Holes 994A, 994C, 995A, and 997A, respectively. These Ba fronts coincide with highs in bulk sediment Ba/Al (to 0.025) and are caused by Ba cycling just above time averaged depths of SO4**2- depletion. Because the Ba fronts lie immediately above the present-day depths of pore water SO4**2- depletion, and because no other Ba fronts are found in the upper 25 m at the three sites, the depth of SO4**2- depletion beneath the seafloor has been nearly constant for considerable time (>18000 years). Thus, CH4 fluxes can be determined through SO4**2- gradients and steady state solutions to diffusion equations. More importantly, F_out through the crest of the Blake Ridge has not varied significantly across major changes in sea level and hydrostatic pressure

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 \times\ 10\sp{18} g of carbon as CH\sb4 could have been released during the LPTM, and that this amount of carbon is adequate to explain the observed $-$2 to -3\perthous excursion in \delta\sp{13}C across the LPTM.Ph.D.Earth SciencesGeochemistryGeologyPaleoecologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129846/2/9635508.pd