Description, geochemistry and mineral composition of ODP Site 193-1189 jasperoids, PACMANUS field

Bright red "jasperoids" were recovered at three positions during Leg 193 drilling below Roman Ruins (Site 1189) in the PACMANUS hydrothermal field. These do not represent fossil exhalative oxide deposits equivalent to those associated with sulfide chimneys at the Roman Ruins seafloor. Rather, they constitute an integral, relatively early stage involving oxidized fluids in the development of veins and breccias that characterize the mostly sulfidic stockwork zone intersected below Roman Ruins in Hole 1189B. They formed by growth of quartz in open spaces created by hydrofracturing, the characteristic feature being mostly euhedral cores dusted by tiny hematite flakes. In one occurrence there are also frondlike aggregates and possible earlier cavity linings of hematite, overgrown by quartz, that potentially formed by maturation of ferruginous gels first deposited in the openings. The trace element geochemistry of the jasperoids, apart from minor enrichment in uranium, provides no indication that they represent subsurface conduits for fluids that deposit Fe-Mn-Si at the seafloor, though this remains a possibility for some such deposits.

Geochemistry and mineralogy of ODP Leg 107 basalts

During ODP Leg 107, the basement of the Tyrrhenian Sea was drilled at Site 650, located in the Marsili basin, and at Sites 651 and 655, both located in the Vavilov basin. In addition, a lava flow was drilled at Site 654 on the Sardinia rifted margin. Mineral and whole rock major and trace element chemistry, including rare earth element (REE) and Sr and Nd isotopic ratios, were determined in samples of these rocks. Site 654 lava was sampled within uppermost Pliocene postrift sediments. This lava is a basaltic andesite of intraplate affinity, and is analogous to some Plio-Pleistocene tholeiitic lavas from Sardinia. Site 650 basalts, drilled beneath 1.7-1.9-Ma-old basal sediment, are strongly altered and vesicular suggesting a rapid subsidence of the Marsili basin. Based on incompatible trace elements, these basalts show calc-alkaline affinity like some products of the Marsili Seamount and the Eolian arc. The basement of the two sites drilled within Vavilov basin shows contrasting petrologies. Site 655, located along the Gortani ridge in the western part of the basin, drilled a 116-m-thick sequence of basalt flows beneath 3.4-3.6-Ma-old basal sediments. These basalts are chemically relatively homogeneous and show affinity to transitional MORB. Four units consisting of slightly differentiated basaltic lavas, have been identified. Site 655 basalts are geochemically similar to the high Ti lavas from DSDP Leg 42, Site 373 (Vavilov Basin). The basement at Site 651, overlain by 40 m of metalliferous dolostone covered by fossiliferous sediments with an age of 2 Ma, consists of two basalt units separated by a dolerite-albitite intrusive body; serpentinized harzburgites were drilled for 30 m at the base of the hole. The two basalt units of Site 651 are distinct petrochemically, though both show incompatible elements affinity with high-K calc-alkaline/calc-alkaline magmas from Eolian arc. The cpx chemistry and high K/Na ratio of the lower unit lavas suggest a weak alkaline tendency of potassic lineage. Leg 107 basement rock data, together with data from DSDP Site 373 and from dredged samples, indicate that the deepest basins of the central Tyrrhenian Sea are underlain by a complex back-arc basin crust produced by magmas with incompatible element affinities to transitional MORB (Site 655 and DSDP Site 373), and to calc-alkaline and high-K calc-alkaline converging plate margin basalts (Sites 650 and 651). This petrogenetic complexity is in accordance with the back-arc setting of the Vavilov and Marsili basins. Other back-arc basin basalts, particularly those from ensialic basins such as the Bransfield Strait (Antarctica), show a comparable petrogenetic complexity (cf., Sounders and Tarney, 1984).

Chemical composition of bottom sediments from the Deryugin Basin, Sea of Okhotsk

This paper reports data including new analyses of contents of Ni, Co, V, Mo, Fe, Mn, Zn, Ba, Sc, Y, Cd, Rb, Cs, and W in bottom sediments of the Deryugin Basin. Features of chemical element distribution in the bottom area were identified and zones of maximum accumulation of major and trace elements were allocated. A correlation between the elements was shown.

Chemical composition of surficial bottom sediments from the Chukchi Sea and adjacent part of the Arctic Ocean

This paper presents data on chemical composition of bottom sediments from the Chukchi Sea and the adjacent Arctic Ocean. Multivariate statistical techniques were used for analysis of the data set and revealed that grain size fractionation of the original terrigenous component during sedimentation was the major factor of clustering of the samples in study. Secondary factors include accumulation of biogenic siliceous and carbonate material and chemogenic or biochemical accumulation of iron, manganese, and some trace elements. The latter factor was significant in areas of tectonic activity within the graben-rift system of the Chukchi Sea.

Geochemical parameters and element contents in a peat section of the Kyzyltun (Bokarevskii) ryam bog

The paper reports geochemical parameters of units in a peat bed from a raised bog in the southern Tyumen territory. Based on radiocarbon dates and variability of geochemical data the following four evolutionary stages of the bed in Holocene are distinguished: an ancient lake (5600-5750 years B.P.), lowland-bog peat (4550-5600 years B.P.), transitional-type peat (4200-4550 years B.P.), raised-bog peat. The major-component technique was applied to analyze relations between various parameters of the bed and evaluate variations in conditions, under which the bog evolved with time, including climatic conditions (in relative units). An anthropogenic signal of accumulation of certain metals in bog systems is distinguished.

(Table 1) Sulfur isotopes and sulfur content at DSDP Leg 64 Holes

Hydrothermal pyrite samples from Holes 477, 477A, and 478 have sulfur isotope values ranging from about 10 to 11 per mil. Samples with negative sulfur isotope values generally have low sulfide sulfur contents and reflect mixed bacterial and hydrothermal sulfur sources. At higher sulfur contents, the hydrothermal component predominates, producing positive isotope values. Hydrothermal sulfide derives from reduction of seawater sulfate and may contain a significant basaltic component. Hydrothermal anhydrite is restricted to a narrow zone beneath a dolerite sill at Site 477 and, because of partial sulfate reduction in the circulating waters, has isotopic values (23.5-25 per mil), heavier than seawater.