Bulk chemical analysis of sediments ODP Hole 110-671B and 110-672A

Chemical analyses for calcium carbonate, organic carbon, and major constituents (Al, Ti, Ca, Mg, K, Fe) of bulk sediments collected in Hole 671B have been carried out. Organic carbon contents in Pleistocene through middle Miocene sediments above the zone of decollement are very low (<0.1%); below the decollement considerably higher concentrations of organic carbon occur (up to 1 %). Changes in Ti/Al and Fe/Al ratios are minor, but K/Al and Mg/Al ratios show clear trends with the age of the sediments. Preliminary comparisons of these ratios with mineralogic information on clays indicate good correspondence with clay abundances. Calculations of the mass flux of magnesium from the overlying ocean into the pore fluids suggest that addition of magnesium to the sediments is difficult to detect, especially in the absence of a background reference concentration.

Inorganic geochemical record of ODP Holes 117-722B and 117-724C

High-resolution sampling from late Pleistocene (last 400 k.y.) sediments of Site 722 (upper 16 m) and Site 724 (upper 70 m), and subsequent inorganic geochemical analysis, has defined the history of productivity in the northwest Arabian Sea. Eolian dust input from the Arabian Peninsula and Somalia is characterized by the record of Ti/Al and Cr/Al. This dust record displays strong precessional periodicity (cycles at 25 k.y.) suggesting the Southwest Monsoon and associated winds play a key role in transporting terrigenous material from the land. High biological productivity results in the accumulation of biogenic CaCO3 and opal in the sediments, the latter having an unexpectedly minor contribution to the total mass flux. Due to dilution of the CaCO3 record by the terrigenous component, the record of biological productivity is best exemplified by Ba. Its record, together with that of other metals recording biological association and redox variability (Cu, Ni, Zn, V, U) clearly identifies the interglacial episodes as being more biologically productive. The striking agreement between Ba and the d18O record in planktonic foraminifers suggests that the supply of nutrients during these periods of high productivity is linked to ocean-wide changes in ocean fertility, and not just local upwelling conditions. High levels of phosphate accumulation in interglacial sediments is attributed to both diagenetic phosphorite formation and biogenic skeletal debris. This study provides a detailed record of productivity variation in the northwest Arabian Sea during the late Pleistocene.

Petrology and geochemistry of altered ocenaic crust of ODP Hole 140-504B

Altered basalt dikes from Hole 504B were partially melted at 1150°C and 1180°C to determine the composition of the first melts as oceanic Layer 2C is assimilated by a magma chamber. The partial melts are chemically similar to actinolite, the most abundant secondary mineral, but the melts are not simply melted actinolite. High TiO2, P2O5, and K2O abundances of the melts indicate that minor secondary minerals that are enriched in these elements also contribute to the melt. The incorporation of partial melts into a ridge-crest magma chamber may explain the local variability that is sometimes found in ocean ridge basalts that are not readily explained fractional crystallization or partial melting.