Radiocarbon ages, d13C values and rare earth element content of sediment cores BP00-23/07 and BP00-07/06

Two bottom sediment cores (BP00-23/7 and BP00-7/6) recovered from the Yenisei transect in the southern Kara Sea are described. Data on their grain size composition, clay and heavy mineral assemblages, and distribution of a large group of chemical elements are presented. Radiocarbon dates based on AMS C-14 method suggest the Holocene age of sediments in the cores. Literature data on physical properties and foraminifers have also been analyzed. The facies affiliation of the lithostratigraphic subdivisions has been unraveled. History of the Yenisei River runoff in the Holocene has been reconstructed on the basis of different indicators.

Geochemistry, trace elements and minerals at DSDP Holes 80-550B and 80-551

The Leg 80 basalts drilled on the Porcupine Abyssal Plain 10 km southwest of Goban Spur (Hole 550B) and on the western edge of Goban Spur (Hole 551), respectively, are typical light-rare-earth-element- (LREE-) depleted oceanic tholeiites. The basalts from the two holes are almost identical; most of their primary geochemical and mineralogical characteristics have been preserved, but they have undergone some low-temperature alteration by seawater, such as enrichment in K, Rb, and Cs and development of secondary potassic minerals of the "brownstone facies." K/Ar dating fail to give realistic emplacement ages; the apparent ages obtained become younger with alteration (causing an increase in K2O). Hole 551 basalts are clearly different from the continental tholeiites emplaced on the margins of oceanizing domains during the prerift and synrift stages.

(Table 1) Major and trace elements of basalts at DSDP Hole 72-516F

The geochemistry of basalts recovered during Leg 72 is described with emphasis on trace elements. Only Hole 516F penetrated basement; the basalts recovered are plagioclase-phyric and olivine-phyric and pervasively altered. Chemically, the basalts from Hole 516F are rather uniform in composition. However, four distinct geochemical units can be recognized, although the chemistry of two of the units appears to be controlled by chemical mobility associated with alteration. The two less-altered units cannot be related by fractional crystallization processes. Hole 516F basalts have a trace element chemistry characteristic of T-type mid-ocean ridge basalt; rare-earth element patterns (as indicated by Ce/Y ratios) are mildly fractionated flight rare-earth element enriched), and a number of incompatible element ratios are close to chondritic.

Porosity, permeability, trace elements, and carbon-oxygen isotopes at DSDP Hole 77-536

Talus deposits recovered from Site 536 show evidence of aragonite dissolution, secondary porosity development, and calcite cementation. Although freshwater diagenesis could account for the petrographic features of the altered talus deposits, it does not uniquely account for isotopic or trace-element characteristics. Also, the hydrologic setting required for freshwater alteration is not easily demonstrated for the Campeche Bank. A mixing-zone model does not account for the available trace-element data, but does require somewhat less drastic assumptions about the size of the freshwater lens. Although a seawater (bottom-water) alteration model requires no hydrologic difficulties, unusual circumstances are required to account for the geochemical characteristics of the talus deposits using this model.

(Table 3) Compositions of minerals of native elements from bottom sediments of the Markov Deep, Mid-Atlantic Ridge

An additional ore field in the central part of the MARhas been discovered. Together with previously discovered Logachev (14°45'N) and Ashadze (12°58'N) ore fields, the new ore field constitutes a cluster with preliminarily estimated total ore reserve of >10 Mt, which is comparable with large continental massive sulfide deposits.