Major-oxides and trace-elements at DSDP Hole 78-543A

Four chemically distinct basalts were cored in 44 m of basement penetration at Deep Sea Drilling Project Site 543, in Upper Cretaceous crust just seaward of the deformation front of the Barbados Ridge and north of the Tiburon Rise. All four types are moderately fractionated abyssal tholeiites. The four types have different magnetic inclinations, all of reversed polarity, suggesting eruption at different times which recorded secular variation of the earth's magnetic field. Extensive replacement of Plagioclase by K-feldspar has occurred at the top of the basalts, giving analyses with K2O contents up to 5 %. The earliest stages of alteration were dominantly oxidative, resulting in fractures lined with celadonite and dioctahedral smectite, and pervasive replacement of olivine and most intersertal glass with iron hydroxides and green clay minerals. Latef, non-oxidative alteration resulted in formation of olive-green clays and pyrite veins in a portion of the rocks. Basalts affected by this alteration actually lost K2O (to abundances lower than in adjacent fresh basalt glasses), and gained MgO (to abundances higher than in the glasses). Finally, fractures and interpillow voids were lined with calcite, sealing in much fresh glass. Oxygen-isotope measurements on the calcite indicate that this occurred at 12 to 25C. Either altering fluids were warm or the basalts had become buried with a considerable thickness of sediments, such that temperatures increased until a conductive thermal gradient was established, when the veining occurred.

Biomass and bioturbation in surface sediments of the Arctic Ocean

Little is known about the benthic communities of the Arctic Ocean's slope and abyssal plains. Here we report on benthic data collected from box cores along a transect from Alaska to the Barents Abyssal Plain during the Arctic Ocean Section of 1994. We determined: (1) density and biomass of the polychaetes, foraminifera and total infauna; (2) concentrations of potential sources of food (pigment concentration and percent organic carbon) in the sediments; (3) surficial particle mixing depths and rates using downcore 210Pb profiles; and (4) surficial porewater irrigation using NaBr as an inert tracer. Metazoan density and biomass vary by almost three orders of magnitude from the shelf to the deep basins (e.g. 47 403 individuals m**-2 on the Chukchi Shelf to 95 individuals m**-2 in the Barents Abyssal Plain). Water depth is the primary determinant of infaunal density, explaining 39% of the total variability. Potential food concentration varies by almost two orders of magnitude during the late summer season (e.g. the phaeopigment concentration integrated to 10 cm varies from 36.16 mg m**-2 on the Chukchi Shelf to 0.94 mg m**-2 in the Siberia Abyssal Plain) but is not significantly correlated with density or biomass of the metazoa. Most stations show evidence of particle mixing, with mixing limited to <=3 cm below the sediment-water interface, and enhanced pore water irrigation occurs at seven of the nine stations examined. Particle mixing depths may be related to metazoan biomass, while enhanced pore water irrigation (beyond what is expected from diffusion alone) appears to be related to total phaeopigment concentration. The data presented here indicate that Arctic benthic ecosystems are quite variable, but all stations sampled contained infauna and most stations had indications of active processing of the sediment by the associated infauna.

Nannofossil bioevents and biozones of ODP Holes 197-1203A and 197-1204A on Detroit Seamount

Calcareous nannofossils were studied in sedimentary successions recovered from two holes on the Detroit Seamount in the northwestern Pacific Ocean. Preservation of calcareous nannoflora assemblages varies from poor to good throughout the sediments recovered from both Holes 1203A and 1204A. Biostratigraphic investigation allowed the identification of 19 nannofossil zones in Hole 1203A and 7 in Hole 1204A. The sedimentary cover in Hole 1203A ranges from lower Eocene (Zone NP12) to upper Miocene (Zone NN9). The sedimentary interval investigated directly overlying the basalt recovered at Hole 1204A is late Campanian in age (Zones CC22-CC23), and the top of the section is middle Eocene (Zone NP15) in age. Major unconformities were observed in Hole 1204A between upper Campanian (Zones CC22-CC23) and lower Thanetian (Zone NP7) sediments and between upper Thanetian (Zone NP8) and upper Ypresian (Zone NP12) sediments.

Stable isotopic ratios, shell lengths and organochlorine compounds in four bivalve species collected in July 2009 around Svalbard

Organochlorine compounds (OC) were determined in Arctic bivalves (Mya truncata, Serripes groenlan-dicus, Hiatella arctica and Chlamys islandica) from Svalbard with regard to differences in geographic location, species and variations related to their size and age. Higher chlorinated polychlorinated biphenyls (PCB 101-PCB 194), chlordanes and alpha-hexachlorocyclohexane (alpha-HCH) were consistently detected in the bivalves and PCBs dominated the OC load in the organisms. OC concentrations were highest in Mya truncata and the lowest in Serripes groenlandicus. Species-specific OC levels were likely related to differences in the species' food source, as indicated by the d13C results, rather than size and age. Higher OC concentrations were observed in bivalves from Kongsfjorden compared to the northern sampling locations Liefdefjorden and Sjuoyane. The spatial differences might be related to different water masses influencing Kongsfjorden (Atlantic) and the northern locations (Arctic), with differing phytoplankton bloom situations.

Age datums, and abundance of Discoaster brouweri and Coccolithus pelagicus in ODP Site 180-1115 sediments

The relative abundance of warm-water Discoaster brouweri vs. cool-water Coccolithus pelagicus provides a useful proxy for interpreting Pliocene surface water temperature trends at Ocean Drilling Program Site 1115 (Solomon Sea). Surface waters were mostly warm during the early Pliocene with a slightly cooler interval centered on 4.5 Ma. A more pronounced cool interval occurred at ~3.2 Ma. The early and mid-Pliocene cool periods may reflect Antarctic glacial growth. A mid-Pliocene warm interval occurred from ~3.1 to 2.8 Ma. Temperature began to decline beginning ~2.7 Ma, marking the onset of Northern Hemisphere glaciation. This long-term decline in surface water temperature is interrupted by a brief warming event at ~2.3 Ma.

Spherules and basement analyses from DSDP Hole 5-32

Lower Miocene basaltic glass spherules from DSDP Site 32 pelagic sediments in the eastern Pacific are compositionally diverse, and new analyses and interpretations have been added to those of earlier workers. The spherules are of titanian ferrobasalt which is compositionally similar to highly evolved abyssal basalts and to some oceanic island eruptives, and they were most likely shaped during intense lava fountaining during a number of separate eruptions. These eruptions tapped distinct but related magma batches in terms, for example, of distinctively high TiO2 and FeO* contents. Their age overlaps that of some of the eruptions of the Columbia River Plateau Basalts, but they are compositionally distinct from most of the latter basalts. Although about 15 m.y. old, they show little alteration. The low chlorine and sulfur contents compared to those of abyssal ferrobasalts are consistent with degassing prior to quenching during subaerial eruptions, and rule out production of the spherules by submarine fountaining. Lava fountaining alone is insufficient to account for the distance of about 100 km from even the closest possible seamount source. Instead, large phreatomagmatic eruption columns reaching at least 15 km and including lava fountaining immediately after the initial explosion are required. Alternatively, and deemed less likely, is their deposition by turbidites derived from Pioneer Seamount.

(Table 2) Geochemistry of glasses at DSDP Leg 54 Holes

The compositions of 45 natural basalt glasses from nine dredge stations and six Deep Sea Drilling Project Leg 54 sites near 9°N on the East Pacific Rise have been determined by electron microprobe. These comprise 19 distinct chemical groups. Seventeen of these fall in the range of the eastern Pacific tholeiite suite, which is characterized by marked enrichment in FeO*, TiO2, K2O, and P2O5 as CaO, MgO, and Al2O3 all decrease. Based on trace elements, an estimated 50-75 per cent fractionation of plagioclase, clinopyroxene, and olivine is required to produce ferrobasalts from parental olivine tholeiites. Additional chemical variations occur which require source heterogeneities, differences in the degree of melting, different courses of shallow fractionation, or magma mixing to explain. Glass compositions from within the Siqueiros fracture zone are mostly less fractionated than those from the flanks of the Rise, and show chemical differences which require variations in the depth of melting or highpressure fractionation to explain. Some of them could not be parental to East Pacific Rise flank ferrobasalts. Two remaining glass groups, from dredge hauls atop a ridge and a seamount, respectively, have distinctly higher K2O, P2O5, and TiO2 as well as lower CaO/Al2O3 and SiO2 at corresponding values of MgO than the tholeiite suite. These abundances, and whole-rock Y/Zr, Ce/Y, Nb/Zr, and isotopic abundances indicate that these basalts had a deeper, less depleted mantle source than the Rise tholeiite suite. Trace element abundances preclude the "ridge" basalt type from being a hybrid between the "seamount" basalt type and any East Pacific Rise tholeiite so far analyzed. The East Pacific Rise glasses from 9°N compare very closely to glasses dredged and drilled elsewhere on the East Pacific Rise. However, glass compositions from Site 424 on the Galapagos Rift drilled during Leg 54, as well as glasses and basalts dredged from the Galapagos and Costa Rica rifts, indicate that a greater degree of melting prevailed along much of the Galapagos Spreading Center than anywhere along the East Pacific Rise.