Grain size composition of sediments from the Theresa Clavenes Bay, Laptev Sea

A comparative analysis of grain size composition of shallow water terrigenous sediments from the southeastern Laptev Sea was carried out using methods developed by V.P. Petelin and A. Atterberg. Potential of these methods and possibilities of improvement of domestic techniques for grain size analysis are discussed.

Abundance of benthic Foraminifera in the Kara Sea

Taxonomic composition and structure of assemblages of the present-day benthic Foraminifera in the Kara Sea has been studied on the base of 37 samples of surface sediments. Three assemblages have been distinguished by composition of dominant species. The assemblage Cribrostomoides subglobosus-Tritaxis nana with prevalence of agglutinating forms, typical for abyssal areas of the World Ocean, occurs in brown oozes in the deep western part of the sea at depths 70-375 m under conditions of considerable bottom stratification. The assemblage Elphidium clavatum-Cassidulina reniforme consists predominantly of species with calcareous shells and is characterized by a wide range of species; this assemblage occurs in the eastern part of the sea at depths 30-90 m in a well-aerated area. Species typical for sublittoral areas of polar regions are dominant. The assemblage Elphidium clavatum-Haynesina orbiculare occupies the littoral estuarine part of the sea. This assemblage is poor in species and not abundant, and it occurs under influence of freshened water masses undersaturated with dissolved carbonaceous matter.

Composition of Fe-Mn micronodules, nodules and host bottom sediments from the Northeast Pacific Basin

Authigenic ferromanganese manifestations in bottom sediments from two horizons (0-10 and 240-250 cm) located in the low/high bioproductive transitional zone of the Pacific Ocean were studied. In addition two compositionally different types of micronodules, crusts and ferromanganese nodules were detected in the surface horizon (0-1 cm). Three size fractions (50-100, 100-250, and 250-500 µm) of manganese micronodules were investigated. In terms of surface morphology, color, and shape, the micronodules are divided into dull round (MN1) and angular lustrous (MN2) varieties with different mineral and chemical compositions. MN1 are enriched in Mn and depleted in Fe as compared with MN2. Mn/Fe ratio in MN1 varies from 13 to 14. Asbolane-buserite and birnessite are the major manganese minerals in them. MN2 is mainly composed of vernadite with Mn/Fe ratio from 4.3 to 4.8. Relative to MN1, fraction 50-100 µm of MN2 is enriched in Fe (2.6 times), W (1.8), Mo (3.2), Th (2.3), Ce (5.8), and REE (from 1.2 to 1.8). Relative to counterparts from MN1, separate fractions of MN2 are characterized by greater compositional difference. For example, increase in size of micronodules leads to decrease in contents of Fe (by 10 rel. %), Ce (2 times), W (2.1 times), Mo (2.2 times), and Co (1.5 times). At the same time one can see increase in contents of other elements: Th and Cu (2.1 times), Ni (1.9 times), and REE (from 1.2 to 1.6 times). Differences in chemical and mineral compositions of MN1 and MN2 fractions can be related to alternation of oxidative and suboxidative conditions in the sediments owing to input of labile organic matter, which acts as the major reducer, and allochthonous genesis of MN2.

Contencentrations of reduced inorganic sulfur forms in Mediterranean Sea waters

The first data on content of inorganic reduced sulfur compounds [H2S, S°, S2O3(2-), SO3(2-)] were obtained at two stations in the northeastern Levant Sea (Mediterranean Basin). With lower detection limit for the mentioned sulfur forms of 30 nM, sulfide forms were not found, while thiosulfate concentration varied from 178 to 890 nM (from 24 to 78 % of total reduced S), and S° varied from 156 to 1090 nM. Vertical distribution of these compounds showed irregular character; correlation between total reduced S maxima, fluorescence, and increase of nutrient element content near the lower pycnocline boundary was observed. The maximum total sulfur concentration in the surface layer was likely due an anthropogenic influence. The ''starting'' mechanism that controls appearance and distribution of sulfur compounds in oxygen-containing water is the process of bacterial sulfate reduction in micropatches of fresh organic detritus. Reduced sulfur forms participate further in a series of chemical and biochemical processes. Contribution of hydrolysis of organic sulfur-containing compounds is insignificant for the region in study.

Geochemistry at DSDP Leg 55 Holes

The tops of the Emperor chain guyots, which were drilled during Leg 55, lie above the carbonate compensation depth (CCD), as well as above the foraminiferal dissolution level, i.e., lysocline. They are therefore the sites of accumulation of pelagic foraminiferal nannofossil ooze, such accumulation having taken place here since the moment of the seamounts' subsidence and the termination of shallow-water carbonate accumulation which was formerly developed on their tops. But the existence of strong bottom currents over the tops and slope scarps limits, and at some places reduces to zero, sedimentation of any pelagic particles. At such areas there are formed thick iron-manganese crusts. The seamounts drilled on Leg 55 are within the northern (Boreal) belt of biogenic silica accumulation, which existed in the northern Pacific throughout the Neogene. This circumstance presupposes a possible enrichment of the relatively fine-grained sediments with biogenic silica - diatoms and radiolarians.

(Table 2) Layer-by-layer chemical composition of barite crusts from the Atlantis II Deep of the Red Sea rift zone

Results of studies of hydrothermal sulfide-sulfate rocks occurring in the Atlantis II Deep of the Red Sea are reported in the paper.

Mineral and chemical compositions of sedimentary and volcano-sedimentary rocks drilled in DSDP Legs 43 and 44

Sedimentary cover on the bottom of the Northwest Atlantic Ocean is underlain by Late Jurassic - Cretaceous tholeiite-basalt formation. It consists of come sedimentary formations with different lithologic features and age. Their composition, stratigraphic position and, distribution are described on materials of deep-sea drilling. Mineralogical and geochemical studies of DSDP Leg 43 and Leg 44 holes lead to new ideas about composition and genesis of some sediment types of and their associations. High metal contents in the chalk formation of black clays on the Bermuda Rise probably result from exhalations. Connection of red-colored and speckled deposits with hiatuses in sedimentation is shown. Main stages of geological history of the North American Basin are reflected in accumulation of the followed formations: ancient carbonate formation (Late Jurassic - Early Cretaceous), formation of black clays rich in organic matter (Cretaceous), formation of speckled clays (Late Cretaceous), siliceous-clayey turbidite formation (Eocene), hemipelagic and pelagic clayey formation (Neogene), and terrigenous turbidite formation (Pleistocene).

Composition of Fe-Mn minerals from island arcs of the West Pacific

This paper presents materials on the chemical and mineralogical composition of Fe-Mn mineralization in island arcs (Kuril, Nampo, Mariana, New Britain, New Hebrides, and Kermadec) in the western part of the Pacific Ocean. The mineralization was proved to be of hydrothermal and/or hydrogenic genesis. The former is produced by hydrothermal Fe and Mn oxi-hydroxides that cement volcanic-terrigenous material in sediments. Some Fe oxyhydroxides can be derived via the halmyrolysis of volcaniclastic material. Crusts of this stage are characterized by fairly low concentrations of trace and rare elements, and their REE composition is inherited from the volcanic-terrigenous material. The minerals of the Mn oxyhydroxides are todorokite and "Ca-birnessite". The Mn/Fe ratio increases away from the discharge sites of the hydrothermal solutions. The hydrogenic Fe-Mn crusts are characterized by high concentrations of trace and minor elements of both the Mn group (Co, Ni, Tl, and Mo) and the Fe group (REE, Y, and Th). The hydrogenic crusts consist of Fe-vernadite and Mn-feroxyhyte. Some of the hydrothermal crusts originally had a hydrothermal genesis. The first data were obtained on crust B30-72-10 from the Macauley Seamount in the Kermadec island arc, which contained anomalously high concentrations of Co (2587 ppm) and other Mn-related trace elements in the absence of hydrogeneous Fe oxyhydroxides.