Stable isotope composition of pore waters from ODP Site 195-1200 serpentinite mud, South Chamorrow Seamount

The South Chamorro Seamount is a serpentinite mud volcano near the southern end of the Mariana forearc. The mud volcano was sampled by drilling during Ocean Drilling Program Leg 195. Samples of pore water squeezed from serpentinite mud were analyzed for stable isotope compositions of carbon in dissolved inorganic carbon and methane, sulfur in sulfate and sulfide, and oxygen in sulfate.

Mineralogy and stable isotopic composition of carbonates and sulfide minerals from ODP Leg 164 sites

During Ocean Drilling Program Leg 164, gas hydrates were recovered in the Blake Ridge where the top of the gas hydrate zone lies at about 200 meters below seafloor (mbsf) and the bottom-simulating reflector (BSR) is located at about 450 mbsf. There is no sedimentological discontinuity crossing the BSR. The BSR is disrupted by the salt piercement of the Cape Fear Diapir. The authigenic carbonates (dolomite and siderite) are always present in small amounts (a few weight percent) in the sediments; they are also concentrated in millimeter- to centimeter-sized nodules and layers composed of dolomite above the top of the gas hydrate reservoir, and of siderite below the BSR. In the Blake Ridge, the dolomite/siderite boundary is located near 140 mbsf. The distribution with depth of the d18O values of dolomite and siderite shows a sharp decrease from high values (maximum 7.5 per mil) in the topmost 50 m, to very low values (minimum -2.7 per mil) at 140 mbsf, and at greater depth increase to positive values within the range of 1.8 per mil to 5.0 per mil. The d13C distribution is marked by the rapid increase with greater depth from low values (-31.3 per mil to -11.4 per mil) near 50 mbsf to positive values at 110 mbsf, which remain in the range of 1.7 to 5.4 down to 700 mbsf. Diagenetic carbonates were precipitated in pore waters in which d18O and d13C values were highly modified by strong fractionation effects, both in the water and in the CO2-CH4 systems associated with the formation and dissociation of gas hydrates.

Carbonate fraction, magnesium and strontium concentration, oxygen and carbon isotopes at DSDP Hole 92-600C

Strontium, magnesium, oxygen, and carbon isotope profiles of the carbonate fraction of Hole 600C sediments support the lithologic and petrographic observations of extensive CaCO3 dissolution and recrystallization in the Pliocene basal section. Convective fluid flow through the sediments during the first 1 to 1.5 m.y. of the sedimentary history of these sediments may explain these observations.