Chemical composition of phosphorites and host sediments

Paleotemperature curves were drawn from oxygen-isotope ratios in CaCO3 of planktonic foraminiferal tests and by the micropaleontological method using quantitative relationships of their species. Two series of curves yield similar results. These data confirm that isotope composition of oxygen reflects primarily temperature, and not isotope composition in ocean water. Temperature of the upper layer of ocean water increased from north to south both during the last two glaciations and in the interglacials. All three sediment cores collected from different latitudes show approximately the same amplitudes of fluctuation of mean annual temperature during times of their accumulation, as determined independently by different methods; these amplitudes are estimated as 5-7°C.

Chemical composition of ocean Fe-Mn ores

The monograph includes the study of chemical and mineral compositions of terrestrial and marine manganese ores, methods of their analysis, dependence of manganese crust geochemistry on tectonic position of their formation, problems of manganese genesis and sources of manganese in ocean ores in connection with geohistorical aspects of ocean formation and development. A hypothesis is offered that formation of giant manganese mineral basins on continental margins resulted from a large asteroid fall to the ocean.

Chemical element concentrations and speciations in bottom sediments from the Ob River mouth area

According to data from Cruise 54 of R/V Akademik Mstislav Keldysh (September 2007) results of geochemical studies of redox processes in bottom sediments from the Ob River mouth area as applied to redox indicator elements (such as manganese, iron, and sulfur) are presented. Parameters of bottom sediments and distribution of these elements evidence not only a significant role of mixing processes at an geochemical profile of bottom sediments in the estuary but also a role of postsedimentation (diagenetic) processes.

(Table 1) Redox potential and chemical element contents in CaCO3 and amorphous silica free matter in surface layer bottom sediments of the Pacific Ocean from Hawaiian Islands to Mexico coast

Distribution of Fe, Mn, P, Ti, Cu, Ni, Co, V, Cr, W, Mo, and As in the surface sediment layer on the section from the Hawaiian Islands to the coast of Mexico (Mexico section) is studied. Contents of all studied elements increase from biogenic-terrigenous sediments off the coast of Mexico to pelagic red clays of the Northeast Basin, and more sharply for mobile elements - Mn, Mo, Cu, Ni, Co, and As. In near Hawaii sediments rich in coarsely fragmented volcanic-terrigenous and pyroclastic material of basaltic composition with high contents of Ti, Fe, V, Cr, W, and P, contents of these elements increase sharply, and contents of Mn, Mo, Ni, Co, and Cu for the same reason decrease sharply in comparison with red clay. Abnormally high contents of Mn, Mo, Cu, Ni, Co, and As in the upper layer of hemipelagic and transition sediments of the Mexico section result from diagenetic redistribution and their accumulation on the surface. Processes of diagenetic redistribution in hemipelagic and transition sediment mass of the Mexico section are more rapid than in similar sediments of the Japan section due lower sedimentation rates and higher initial concentrations of Mn. Basic similarity of element distribution regularities in sediments of Japan and Mexico sections is shown.

Chemical and isotopic compositions of authigenic carbonates from bottom sediments of Northwest Pacific marginal seas

The paper presents data on authigenic carbonate distribution in Holocene - Upper Pleistocene deposits of the Okhotsk, Japan, East China, Philippine and South China Seas. Description of carbonate samples, their chemical and isotope compositions are given. Chemical analysis of the samples indicates that almost all authigenic carbonates are composed of calcite or magnesian calcite; and only in one case, of siderite. Oxygen isotopic composition (d18O) ranges from +37.7 to +26.1 per mil (SMOW); it is, probably, connected with different temperatures of carbonate formation. A distinct geographic regularity is traced. Decrease in d18O values is observed from the cold Okhotsk Sea to the warm South China Sea. A very wide range of carbon isotopic composition (d13C from -42 to +3.8 per mil) indicates different sources of carbonic acid required for formation of these carbonates. As a basis for carbon isotopic composition we can distinguish three sources of carbonic acid in the studied sediments: microbiological methane oxidation, organic matter destruction during sediment diagenesis, and dissolved organogenic limestone. Thus, formation of authigenic carbonates in sediments from the marginal seas of the Northwest Pacific results from: 1) sediment diagenesis, 2) methane oxidation in zones of gas anomalies, 3) their precipitation from the supersaturated by carbonates sea shoal waters of tropical sea lagoons.

Chemical composition of sepiolites and palygorskites from bottom sediments of the Eastern Indian

In fault zones of the East Indian Ridge and adjacent areas of ocean floor almost monomineral sepiolite- and palygorskite clays have been found. They have been studied by a complex of optical and physical methods. Formation of authigenic sepiolites and palygorskite had occurred under influence of Mg- and Si-rich hydrothermal solutions by metasomatic replacement of montmorillonite clays, or by precipitation from saturated solutions in cracks of various rocks.

Chemical and isotopic compositions of samples from the Haakon Mosby mud volcano and nearby

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active methane-bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanotrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH4 oxidation. Isotopically light carbon (aver. d13C = -28.9 per mil) of CO2 produced during CH4 oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (aver. d18O = 5 per mil) in carbonates is inherited from seawater sulfate. Rapid sulfate reduction (up to 12 mg S/dm**3/day) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this carbonates can only be formed in surface sediments near the water-bottom interface. Salinity as well as CO3/Ca and Mg/Ca ratios correspond to the field of non-magnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. Radiocarbon age of carbonates is about 10 Ka.

Chemical composition of ferromanganese concretions and host bottom sediments from the Black Sea

Ferromanganese concretions spread out on the bottom of the shallow northwest part of the Black Sea are mainly represented by Fe and Mn nodules on shells and substituted worm tubes. Element composition of these formations was measured by methods of chemical, atomic absorbtion, neutron activation, and ICP-MS analyses. It was established that Fe and Mn contents and Mn/Fe ratio in the concretions varied considerably and which controlled occurrence of several associated metals and minor elements; some of them have not been studied in Black Sea concretions before.

Chemical composition of basalts from DSDP Hole 46-396B

Samples of crystalline basalt from Site 396 B are all more or less altered, usually in strongly zoned patterns. Evidence has been found for several related or independent alteration stages, including (1) minor localized deuteric (amphibole and mixed clay minerals in miarolitic voids); (2) minor widespread nonoxidizing (pyrite on walls of vugs and cracks); (3) localized diffusion-controlled rug filling ("glauconite" in black halos); (4) pervasive low level oxidizing (transformation of titanomagnetite to cation-deficient titanomaghemite); (5) localized diffusion-controlled strongly oxidizing (breakdown of olivine and titanomaghemite in brown zones). Plagioclase and pyroxene are essentially unaltered. Detailed analyses of gray and brown zones in pillow basalts show that low temperature oxidation has proceeded in a step-wise fashion, with the relative stabilities of the igneous minerals controlling the steps. Secondary minerals that crystallized from pore fluids on to the walls of vugs may or may not be related to local alteration of primary phases. During the most intense stage of alteration, brown oxidation zones grew into basalt fragments behind diffusion controlled fronts. The specific reactions and products of this stage differ among the lithologic units at the site. A model is proposed whereby efficient seawater circulation through the pillow units maintains the pH and the concentrations of Mg2+ and SiO2 dissolved at low levels in pore fluids, so that olivine is replaced by hydrous ferric oxides, and Mg and SiO2 are removed from the system. In the massive basalt unit, circulation is somewhat less effective and Mg and SiO2 are retained in smectites. Deposition of authigenic minerals in the sequence saponite/Fe-Mn oxides/phillipsite/calcite in vugs and cracks may reflect the gradual closing of the systems and probably signals the end of localized oxidation in parts of the core. Mineral compositions indicate that most of these deposits formed from seawater at very low temperature.