Tab.1: Representative bulk-rock and trace element chemistry

High-pressure/low-temperature metabasites occupy a definite geological position within the structure of the Polar Urals and have a very important bearing on the understanding of the early history of the Ural Mountains. Recently obtained geological, petrographic, geochemical and isotope data allow some conclusions on this history. The metabasites of the Khord"yus and Dzela complexes contain relics of a Neoproterozoic (578 ±8 Ma) oceanic crust. This crust formed part of the base of the early Paleozoic (500 Ma) ensimatic island arc and experienced Ca-Al-Si±Na metasomatism and, probably, partial melting with the formation of boninite melts. However, so far no boninite volcanics have been found. The metabasites at the base of the island arc took part in the collision and as a consequence experienced glaucophane schist and greenschist facies metamorphism during the collision and obduction over the passive Baltic margin 350 ±11 Ma ago.

Physics, geochemistry and bulk sedimentology on cores from the Peru Basin

Empirical relationships between physical properties determined non-destructively by core logging devices and calibrated by carbonate and opal measurements determined on discrete samples allow extraction of carbonate and opal records from the non-destructive measurements in biogenic settings. Contents of detrital material can be calculated as a residual. For carbonate and opal the correlation coefficients (r) are 0.954 and ?0.916 for sediment density, ?0.816 and 0.845 for compressional-wave velocity, 0.908 and ?0.942 for acoustic impedance, and 0.886 and ?0.865 for sediment color (lightness). Carbonate contents increase in concert with increasing density and acoustic impedance, decreasing velocity and lighter sediment color. The opposite is true for opal. The advantages of deriving the sediment composition quantitatively from core logging are: (i) sampling resolution is increased significantly, (ii) non-destructive data can be gathered rapidly, and (iii) laboratory work on discrete samples can be reduced. Applied to paleoceanographic problems, this method offers the opportunity of precise stratigraphic correlations and of studying processes related to biogenic sedimentation in more detail. Density is most promising because it is most strongly affected by changes in composition.

Stable carbon and oxygen isotope ratios of bulk sediment from the Weddell Sea

Carbon isotope measurements were made on bulk sediments from the well preserved calcareous sequences recovered at ODP Sites 689 and 690 on the Maud Rise, Weddell Sea, Antarctica. The very positive delta13C values that characterize the late Paleocene and the rapid trend toward lighter values in the early Eocene established in other sites are clearly recorded here and may be of value for long-distance stratigraphic correlation. However, values in the late Eocene are significantly more positive than have been reported from other areas. The general pattern of the records from Sites 689 and 690 is sufficiently unlike those previously reported from lower latitudes that we suggest that carbon isotope data should be used only with considerable caution for correlating sequences from such high latitudes with lower latitude records.

Composition and stable isotope record of bulk sediment and belemnite rostra from ODP Hole 122-761C

A sedimentary sequence documenting the early history of the proto-Indian Ocean was drilled at Site 761 on the Wombat Plateau, northwest Australia. Directly above the post-rift unconformity, two lithologic units were recovered which reflect deposition in incipient oceanic environments. The lower unit, composed of sandstone, contains abundant belemnites and a few lenses composed of low-diversity coccolith assemblages. The second unit, composed of chalk, contains abundant calcispheres, thoracospheres, low-diversity coccolith assemblages, and a few radiolarians. Belemnites and organisms that produced calcispheres and thoracospheres are thought to be opportunistic. Their abundance, and the absence of a normal marine fauna and flora, reflects an unstable early ocean environment. Stable oxygen and carbon isotopic data for the two units fall into almost separate fields. Heavy delta18O values for the belemnites indicate that they have not been affected by recrystallization. Instead, these isotopic values are thought to indicate either the deep, cool habitat of the belemnites or strong vital effects. A bulk chalk delta18O value from the belemnite sand is 3 to 4 parts per mil lighter than the belemnite delta18O values, possibly because it is largely composed of coccoliths which inhabited warmer surface waters. Light delta13C values for bulk calcisphere-bearing nannofossil chalk samples are thought to be a direct result of upwelling or of vital effects. Heavy delta18O values for the chalk unit are interpreted as resulting from upwelling of cool waters. Assemblage and isotopic data are consistent with this incipient ocean basin being highly productive, either as a result of upwelling or runoff of nutrient-rich waters from nearby land areas. However, it is not possible to rule out the control of vital effects on the isotopic signature of any of the fossil groups.

Carbon and oxygen stable isotope composition of bulk sediment and abundance of Braarudospahaera in ODP Site 122-762 (Table 1)

Nannofossil assemblages enriched in Braarudosphaera occur in lower Oligocene to lower Miocene sediments at Ocean Drilling Program Sites 762 and 763 on the central Exmouth Plateau. Braarudosphaerids appear here rather abruptly in the lower Oligocene (in Zone NP21). They reach their greatest numbers in the lower Oligocene (in Zones NP22 and NP23), where they comprise up to 10% of some samples. Braarudosphaera bigelowii is the overwhelmingly dominant species, occurring together with rare specimens of B. discula and Micrantholithus pinguis. The holococcoliths Peritrachelina joidesa and Lantemithus minutus are also associated with the Braarudosphaera enrichment. There are two populations of B. bigelowii: one of normal size (10-14 µm) and one of large specimens (20-22 µm). The larger braarudosphaerids are more common than the smaller forms. Braarudosphaera-rich sediments are absent at Wombat Plateau sites during the same time interval. We attribute this to latitudinal control, because the Wombat sites are about 4° north of the central Exmouth Plateau sites. We believe that the occurrence of braarudosphaerids is related to an Oligocene to early Miocene oceanographic event on the Exmouth Plateau. We suspect that mid-ocean up welling of cool, low-salinity, nutrient-rich water along a divergent zone created the Braarudosphaera-nch sediments in the South Atlantic and Indian oceans.

Surface sediment samples from several fore-arc basins west and southwest of the Indonesian Archipelago, analyzed by planktonic foraminifera, stable oxygen and carbon isotopic signals and opal and CaCO3 contents in bulk sediment

A total of 69 surface sediment samples from several fore-arc basins located west and southwest of the Indonesian Archipelago was analyzed with respect to the faunal composition of planktonic foraminifera, the stable oxygen and carbon isotopic signal of a surface-dwelling (Globigerinoides ruber) and a thermocline-dwelling (Neogloboquadrina dutertrei) species, and the opal and CaCO3 contents in bulk sediment. Our results show that the distribution pattern of opal in surface sediments corresponds well to the upwelling-induced chlorophyll concentration in the upper water column and thus, represents a reliable proxy for marine productivity in the coastal upwelling area off S and SW Indonesia. Present-day oceanography and marine productivity are also reflected in the tropical to subtropical and upwelling assemblages of planktonic foraminifera in the surface sediments, which in part differ from previous studies in this region probably due to different coring methods and dissolution effects. The average stable oxygen isotopic values (d18O) of G. ruber in surface sediments vary between 2.9 per mill and 3.2 per mill from basin to basin and correspond to the oceanographic settings during the SE monsoon (July-October) off west Sumatra, whereas off southern Indonesia, they reflect the NW monsoon (December-March) or annual average conditions. The d18O values of N. dutertrei show a stronger interbasinal variation between 1.6 per mill and 2.2 per mill and correspond to the upper thermocline hydrology in July-October. In addition, the difference between the shell carbon isotopic values (d13C) of G. ruber and N. dutertrei (Delta d13C) appears to be an appropriate productivity recorder only in the non-upwelling areas off west Sumatra. Consequently, joint interpretation of the isotopic values of these species is distinctive for different fore-arc basins W and SW of Indonesia and should be considered in paleoceanographic studies.

Corg, CaCO3, bulk densities, accumulation rates and ages of ODP Leg 167 sites and three piston cores, California margin

Sediments from five Leg 167 drill sites and three piston cores were analyzed for Corg and CaCO3. Oxygen isotope stratigraphy on benthic foraminifers was used to assign age models to these sedimentary records. We find that the northern and central California margin is characterized by k.y.-scale events that can be found in both the CaCO3 and Corg time series. We show that the CaCO3 events are caused by changes in CaCO3 production by plankton, not by dissolution. We also show that these CaCO3 events occur in marine isotope Stages (MIS) 2, 3, and 4 during Dansgaard/Oeschger interstadials. They occur most strongly, however, on the MIS 5/4 glaciation and MIS 2/1 deglaciation. We believe that the link between the northeastern Pacific Ocean and North Atlantic is primarily transmitted by the atmosphere, not the ocean. Highest CaCO3 production and burial occurs when the surface ocean is somewhat cooler than the modern ocean, and the surface mixed layer is somewhat more stable.

Bulk components and planktonic foraminifera of the Chilean continental margin

A multiparameter investigation including organic carbon, carbonate, opal, and planktic foraminifera was carried out on five sediment cores from the coastal upwelling area between 24°S and 33°S along the Peru-Chile Current to reconstruct the history of the paleoproductivity and its driving mechanisms during the last 40,000 years. Inferred from our data, we conclude that the Antarctic Circumpolar Current as the main nutrient source in this region mainly drives the productivity by its latitudinal shifts associated with climate change. Simplified, its northerly position during the last glacial led to enhanced productivities, and its southerly position during the Holocene caused lower productivities. At 33°S the paleoproductivity was additionally affected by the southern westerlies and records highest levels during the Last Glacial Maximum (LGM). North of 33°S, several factors (e.g., position and strength of the South Pacific anticyclone, wind stress, continental runoff, and El Niño Southern Oscillation events) supplementary influenced upwelling and paleoproductivity, where maximum values occurred prior to the LGM and during the deglaciation.

Chemical composition of bulk sediments from ODP Hole 199-1215A

Elemental concentrations were determined on 21 samples from Hole 1215A to evaluate the influence of hydrothermal sources on bulk sediment composition. Rare earth element (REE) concentrations were also determined on 10 of these samples. Concentration profiles and REE patterns are consistent with a strong hydrothermal influence on sediment composition at the base of Hole 1215A.

Biogenic opal content in bulk sediments of ODP Leg 181 sites, southwest Pacific

Biogenic opal concentrations were measured on bulk sediments recovered at Ocean Drilling Program Sites 1123, 1124, and 1125 off North Island of New Zealand in the southwest Pacific. Site 1124 showed opal contents ranging from approximately 2 to 8 wt%, which is relatively high compared to other sites. The subbottom maximum in biogenic opal content located between 1.0 and 1.5 m composite depth can be recognized at each site. Patterns of biogenic opal content in the uppermost parts of the cores appear to reflect the surface ocean settings relating to the migration of the Subtropical Convergence Zone.