(Table 1) Compressional and shear wave velocities and elastic constants of DSDP Hole 83-504B basalts

Compressional and shear wave velocities at confining pressures to 6 kb, densities, and porosities were measured for 32 samples obtained from 836 to 1350 m below seafloor (BSF) in Hole 504B, the section drilled on Leg 83 of the Deep Sea Drilling Project. These data in combination with similar measurements on 28 basalt samples from the section from 274.5 to 836 m, drilled on Legs 69 and 70, provide a comprehensive set of physical property data for over 1000 m of oceanic crust. The velocities, densities, and porosities measured in the laboratory exhibit greater variability in the upper portion of the hole. In general, compressional and shear wave velocities and densities increase with depth, reaching average values at 1 kbar of Vp = 6.45 km/s, Ks = 3.45 km/s and p = 2.94 g/cm3 within the sheeted dike section. Porosities decrease with depth to values generally less than 1% near the bottom of the hole

Geochemistry of bulk sediment from the Cape Basin

A technique for onsite application of X-ray fluorescence (XRF) spectrometry to samples from sediment cores aboard a research vessel was developed and tested. The method is sufficiently simple, precise, and fast to be used routinely for high-resolution analyses of depth profiles as well as surface samples. Analyses were performed with the compact high-performance energy-dispersive polarisation X-ray fluorescence (EDPXRF) analyser Spectro Xepos. Contents of the elements Si, Ti, Al, Fe, Mn, Mg, Ca, K, Sr, Ba, Rb, Cu, Ni, Zn, P, S, Cl and Br were simultaneously determined on 200-225 samples of each core within 24 h of recovery. This study presents a description of the employed shipboard preparation and analysis technique, along with some example data. We show land-based datasets that support our decisions to use powder samples and to reduce the original measuring time for onboard analyses. We demonstrate how well the results from shipboard measurements for the various elements compare with the land-based findings. The onboard geochemical data enabled us to establish an element stratigraphy already during the cruise. Correlation of iron, calcium and silicon enrichment trends with an older reference core provided an age model for the newly retrieved cores. The Spectro Xepos instrument performed without any analytical and technical difficulties which could have been caused by rougher weather conditions or continuous movement and vibration of the research vessel. By now, this XRF technique has been applied during three RV Meteor cruises to approximately 5,000 Late Quaternary sediment samples from altogether 23 gravity cores, 25 multicorer cores and two box cores from the eastern South Atlantic off South Africa/Namibia and the eastern Atlantic off NW Africa.

Osmium isotope composition of leachates and bulk sediment from ODP Holes in the Bengal Fan

Os isotopic compositions and OS and Re concentrations were measured in H2O2-H2SO4 leachates and bulk sediment samples from Holes 717C and 718C of ODP Leg 116 in the Bengal Fan. Os isotopic results indicate that, at the sediment surface, the leachable Os fraction is derived from seawater. In contrast, leachable Os from Ganges River sediments has 187Os/188Os ratios (Pegram et al., 1994, doi:10.1016/0012-821X(94)90172-4) much higher than the marine value. This difference suggests that the leachable radiogenic Os carried by the river sediments is completely released to the oceans prior to sediment deposition in the Fan. A simple calculation, assuming these sediments to be typical of those delivered by the Ganges-Brahmaputra river system, suggests that this process can account for a substantial part of the rise in the seawater Os isotopic ratio observed over the past 16 m.y. Bengal Fan leachate 187Os/188Os ratios increase with increasing depositional age, in contrast to the seawater Os isotopic ratio, which decreases with increasing age. Several lines of evidence suggest that, at the time of sediment burial, the leachate Os compositions most likely reflected the seawater values. Thus, the current divergence is probably the result of post-depositional processes. One such process, in situ radiogenic ingrowth of 187Os, can be excluded because the measured Re concentrations of these sediments are too low. Similarly, since most of the bulk rock Os isotopic ratios were lower than those of the associated leachates, the high leachate 187Os/188Os values cannot be explained by in situ sediment alteration. Instead, it is proposed that the increase with age results from radiogenic OS brought in by thermoconvective circulation from further upslope in the Fan. The ultimate source of this 187Os would then be alteration of radiogenic sediments or post-depositional radioactive decay of Re in sediments rich in organic carbon. Finally, the divergence between the results obtained on Bengal Fan sediments and those obtained in the open ocean (Pegram et al., 1992, doi:10.1016/0012-821X(92)90132-F) by the same leaching technique suggest that Os sediment leachate data must be interpreted with caution.

Grain size distribution, carbon content and wet bulk density of sediment cores in the equatorial Atlantic and the Norwegian Sea

Near-surface sediments from the equatorial east Atlantic and the Norwegian Sea exhibit pronounced shear strength maxima in profiles from the peak Holocene and Pleistocene. These semi-indurated layers start to occur at 8-102 cm below the sediment surface and can be explained neither by the modal composition nor by the effective overburden pressure of the sediments. However, scanning electron microscope and microprobe data exhibit micritic crusts and crystal carpets, which are clearly restricted to (undisturbed) samples from indurated layers and form a manifest explanation for their origin. The minerals precipitated comprise calcite, aragonite, and in samples more proximal to the African continent SiO2 needles, and needles of as yet unidentified K-Mg-Fe-Al silicates, crusts of which dominate the indurated layers in the Norwegian Sea. By their stratigraphic position in deep-sea sediments the carbonate-based shear strength maxima are tentatively ascribed to dissolved adjacent pteropod layers from the early Holocene and hence to short-lived no-analogue events of early diagenesis. Possibly, they have been controlled by a reduced organic carbon flux, leading to increased aragonite preservation in the deep sea.