Chemical and mineral compositions of sediments from ODP Site 127-797

In order to reconstruct past variations in the aeolian dust (Kosa) contribution to the Japan Sea, and to establish a direct link between terrestrial and marine climatic records, we have applied statistical procedures to distinguish and quantify detrital subcomponents within the detrital fraction of the late Quaternary hemipelagic sediments in the Japan Sea. Q-mode factor analysis with varimax and oblique rotation of the factors followed by multiple-regression analysis between mineral composition and factor loadings was conducted using six ''detrital'' elements. Four detrital subcomponents were defined, which are attributed to Kosa derived from ''typical'' loess, Kosa from ''weathered'' loess, and fine and coarse arc-derived detritus, respectively, based on comparisons with the chemical and mineral compositions of probable source materials. Using these detrital subcomponents, the variation in Kosa fraction was reconstructed for the last 200 ky. The results reveal millennial-scale as well as glacial-interglacial scale variations in Kosa contribution. Especially, millennial-scale variability of Kosa contribution suggests the presence of high frequency variation in summer monsoon precipitation in the central to east Asia during the last 200 ky.

Chemical compositions of monomineral fractions from Fe-Mn crusts and of their host rocks, seamounts of the Sea of Japan

It has been established (with use of analytical electron microscopy) that Fe-Mn crusts from two seamounts of the Sea of Japan consist predominantly of an association of birnessite minerals including Ca-birnessite and clinobirnessite. The latter is represented by twins, which form regular integrowths with 14 Å Ca-birnessite. Ore material from the third seamount (Tarasov submarine volcano) consists only of fibrous todorokite, which forms spherulitic nodules, blocks, and laminar formations. Its chemical composition is close to that of todorokite from the Galapagos rift zone.

Mineralogical compositions of sediment samples from the San Francisco Bay coastal system

The mineralogical compositions of 119 samples collected from throughout the San Francisco Bay coastal system, including bayfloor and seafloor, area beaches, cliff outcrops, and major drainages, were determined using X-ray diffraction (XRD). Comparison of the mineral concentrations and application of statistical cluster analysis of XRD spectra allowed for the determination of provenances and transport pathways. The use of XRD mineral identifications provides semi-quantitative compositions needed for comparisons of beach and offshore sands with potential cliff and river sources, but the innovative cluster analysis of XRD diffraction spectra provides a unique visualization of how groups of samples within the San Francisco Bay coastal system are related so that sand-sized sediment transport pathways can be inferred. The main vector for sediment transport as defined by the XRD analysis is from San Francisco Bay to the outer coast, where the sand then accumulates on the ebb tidal delta and also moves alongshore. This mineralogical link defines a critical pathway because large volumes of sediment have been removed from the Bay over the last century via channel dredging, aggregate mining, and borrow pit mining, with comparable volumes of erosion from the ebb tidal delta over the same period, in addition to high rates of shoreline retreat along the adjacent, open-coast beaches. Therefore, while previously only a temporal relationship was established, the transport pathway defined by mineralogical and geochemical tracers support the link between anthropogenic activities in the Bay and widespread erosion outside the Bay. The XRD results also establish the regional and local importance of sediment derived from cliff erosion, as well as both proximal and distal fluvial sources. This research is an important contribution to a broader provenance study aimed at identifying the driving forces for widespread geomorphic change in a heavily urbanized coastal-estuarine system.

Isotope compositions and mineralogy of carbonates and barites from sediments of the Deryugin Basin (Sea of Okhotsk)

Results of studies of mineralogy, geochemistry, and isotope parameters (d13C, d34S, d180, and 87Sr/86Sr) of carbonates and barites from sediments of the Deryugin Basin in the Sea of Okhotsk are presented. Diagenetic nature of carbonates and barites formed due to prolonged activity of cold seeps acting along a fracture zone and supplying methane- and barium saturated fluids is determined. Any signs for hydrothermal activity were not observed.

Calcium carbonate contents and oxygen and carbon isotopic compositions of planktic and benthic foraminifera in sediments at DSDP Site 85-575

Data on the composition of benthic foraminiferal faunas at Deep Sea Drilling Project Site 575 in the eastern equatorial Pacific Ocean were combined with benthic and planktonic carbon- and oxygen-isotope records and CaCO3 data. Changes in the composition of the benthic foraminiferal faunas at Site 575 predated the middle Miocene period of growth of the Antarctic ice cap and cooling of the deep ocean waters by about 2 m.y., and thus were not caused by this cooling (as has been proposed). The benthic faunal changes may have been caused by increased variability in corrosivity of the bottom waters, possibly resulting from enhanced productivity in the surface waters.

Chemical and isotope compositions of rocks from altered ocean crust at DSDP/ODP Sites 417/418

Large-scale compositional domains at DSDP/ODP drill sites 417A, 417D and 418A were analyzed for O, Sr and Nd isotope ratios, and REE, U, K, Rb and Sr abundances, to constrain the bulk chemical composition of the oceanic crust that is recycled at subduction zones. The combination of the three sites gives the composition of the upper oceanic crust in this region over a distance of about 8 km. The d18O(SMOW) and 87Sr/86Sr(meas) of compositional domains 10-100 m in size correlate well, with a range of 7.7-19.2 and 0.70364-0.70744, and mean of 9.96 and 0.70475, respectively. The Rb inventory of the upper crust increases by about an order of magnitude, while Sr contents remain constant. U abundances increase moderately under oxidizing alteration conditions and nearly triple in the commonly reducing alteration environments of the upper oceanic crust. REEs are influenced by alteration only to a small extent, and recycled oceanic crust is similar to MORB with respect to 143Nd/144Nd. Even though the average composition of the upper oceanic crust is well defined, the large scale composition varies widely. Highly altered compositional domains may not have a large impact on the average composition of the oceanic crust, but they may preferentially contribute to fluids or partial melts derived from the crust by prograde metamorphic reactions.