Chemical and mineral compositions of recent and ancient sediments and sedimentary rocks from the Mariana Trench

On the bed and on the ocean slope of the southern latitudinal part of the Mariana Trench ancient sediments, as well as sedimentary and igneous rocks are exposed. In the lower part of the sampled part of the studied section Late Oligocene to Early Miocene chalk-like limestones and marls occur. Upward marly tuffites and tuffs (apparently alternating with carbonate rocks) occur. These rocks are overlain by Early Miocene tuffaceous clays and siliceous-clayey muds. In the upper part of the section there are Pleistocene pelagic clays and ethmodiscus oozes.

Stable carbon and oxygen isotope ratios of carbonates of ODP Site 103-639

A Tithonian sequence of shallow-water limestones, intercalated with siliciclastics and overlain by dolomite, was recovered during drilling at ODP Site 639 on the edge of a tilted fault block. The carbonates were strongly affected by fracturing, dolomitization, dedolomitization, and compaction. The chronology and nature of the fractures, fracture infilling, and diagenesis of the host rock are established and correlated for both the limestone and the dolomite. A first phase of dolomitization affected limestone that was already, at least partially, indurated. In the limestone unit, fractures were filled by calcite and dolomite; most of the dolomite was recrystallized into calcite, except for the upper part. In the dolomitic unit, the first-formed dolomite was progressively recrystallized into saddle dolomite, as fractures were simultaneously activated. The dolomitic textures become less magnesian (the molar ratio mMg/mCa goes from 1.04-0.98 to 0.80), and the d18O (PDB) ranges from -10 per mil to -8 per mil. The varying pores and fissures are either cemented by a calcic saddle dolomite (mMg/mCa ranging from 0.95 to 0.80) or filled with diverse internal sediments of detrital calcic dolomite, consisting of detrital dolomite silt (d18O from -9 per mil to -7 per mil) and laminated yellow filling (with different d18O values that range from -4 per mil to +3 per mil). These internal sediments clearly contain elements of the host rock and fragments of saddle crystals. They are covered by marls with calpionellids of early Valanginian age, which permits dating of most of the diagenetic phases as pre-Valanginian. The dolomitization appears to be related to fracturing resulting from extensional tectonics; it is also partially related to an erosional episode. Two models of dolomitization can be proposed from the petrographic characteristics and isotopic data. Early replacement of aragonite bioclasts by sparite, dissolution linked to dolomitization, and negative d18O values of dolomite suggest a freshwater influence and 'mixing zone' model. On the other hand, the significant presence of saddle dolomite and repeated negative d18O values suggest a temperature effect; because we can dismiss deep burial, hydrothermal formation of dolomite would be the most probable model. For both of these hypotheses, the vadose filling of cavities and fractures by silt suggests emersion, and the different, and even positive, d18O values of the last-formed yellow internal sediment could suggest dolomitization of the top of the sequence under saline to hypersaline conditions. Fracturing resulting in the reopening of porosity and the draining of dolomitizing fluids was linked to extensional tectonics prior to the tilting of the block. These features indicate an earlier beginning to the rifting of the Iberian margin than previously known. Dolomitization, emersion, and erosion correspond to eustatic sea-level lowering at the Berriasian/Valanginian boundary. Diagenesis, rather than sedimentation, seems to mark this global event and to provide a record of the regional tectonic history.

Global Ocean Colour for Carbon Cycle Research (full product set)

In 2005, the International Ocean Colour Coordinating Group (IOCCG) convened a working group to examine the state of the art in ocean colour data merging, which showed that the research techniques had matured sufficiently for creating long multi-sensor datasets (IOCCG, 2007). As a result, ESA initiated and funded the DUE GlobColour project (http://www.globcolour.info/) to develop a satellite based ocean colour data set to support global carbon-cycle research. It aims to satisfy the scientific requirement for a long (10+ year) time-series of consistently calibrated global ocean colour information with the best possible spatial coverage. This has been achieved by merging data from the three most capable sensors: SeaWiFS on GeoEye's Orbview-2 mission, MODIS on NASA's Aqua mission and MERIS on ESA's ENVISAT mission. In setting up the GlobColour project, three user organisations were invited to help. Their roles are to specify the detailed user requirements, act as a channel to the broader end user community and to provide feedback and assessment of the results. The International Ocean Carbon Coordination Project (IOCCP) based at UNESCO in Paris provides direct access to the carbon cycle modelling community's requirements and to the modellers themselves who will use the final products. The UK Met Office's National Centre for Ocean Forecasting (NCOF) in Exeter, UK, provides an understanding of the requirements of oceanography users, and the IOCCG bring their understanding of the global user needs and valuable advice on best practice within the ocean colour science community. The three year project kicked-off in November 2005 under the leadership of ACRI-ST (France). The first year was a feasibility demonstration phase that was successfully concluded at a user consultation workshop organised by the Laboratoire d'Océanographie de Villefranche, France, in December 2006. Error statistics and inter-sensor biases were quantified by comparison with insitu measurements from moored optical buoys and ship based campaigns, and used as an input to the merging. The second year was dedicated to the production of the time series. In total, more than 25 Tb of input (level 2) data have been ingested and 14 Tb of intermediate and output products created, with 4 Tb of data distributed to the user community. Quality control (QC) is provided through the Diagnostic Data Sets (DDS), which are extracted sub-areas covering locations of in-situ data collection or interesting oceanographic phenomena. This Full Product Set (FPS) covers global daily merged ocean colour products in the time period 1997-2006 and is also freely available for use by the worldwide science community at http://www.globcolour.info/data_access_full_prod_set.html. The GlobColour service distributes global daily, 8-day and monthly data sets at 4.6 km resolution for, chlorophyll-a concentration, normalised water-leaving radiances (412, 443, 490, 510, 531, 555 and 620 nm, 670, 681 and 709 nm), diffuse attenuation coefficient, coloured dissolved and detrital organic materials, total suspended matter or particulate backscattering coefficient, turbidity index, cloud fraction and quality indicators. Error statistics from the initial sensor characterisation are used as an input to the merging methods and propagate through the merging process to provide error estimates for the output merged products. These error estimates are a key component of GlobColour as they are invaluable to the users; particularly the modellers who need them in order to assimilate the ocean colour data into ocean simulations. An intensive phase of validation has been undertaken to assess the quality of the data set. In addition, inter-comparisons between the different merged datasets will help in further refining the techniques used. Both the final products and the quality assessment were presented at a second user consultation in Oslo on 20-22 November 2007 organised by the Norwegian Institute for Water Research (NIVA); presentations are available on the GlobColour WWW site. On request of the ESA Technical Officer for the GlobColour project, the FPS data set was mirrored in the PANGAEA data library.

Geochemistry of vein rocks of ODP Hole 118-735B

Rock samples from Hole 735B, Southwest Indian Ridge, were examined to determine the principal vein-related types of alteration that occurred, the nature of fluids that were present, and the temperatures and pressures of these fluids. Samples studied included veined metagabbro, veined mylonitic metagabbro, felsic trondhjemite, and late-stage leucocratic diopside-bearing veins. The methods used were standard petrographic analysis, mineral chemical analysis by electron microprobe, fluid inclusion petrography and analysis by heating/freezing techniques and laser Raman microspectroscopy, and oxygen isotopic analyses of mineral separates. Alteration in lithologic Units I and II (above the level of Core 118-735B-3OR; approximately 140 meters below the seafloor) is dominated by hydration by seawater-derived fluids at high temperature, up to about 700°C, and low water/rock ratio, during and immediately after pervasive ductile deformation. Below Core 118-735B-30R, pervasive deformation is less common, and brittle veining and brecciation are the major alteration styles. Leucocratic centimeter-scale veins, often containing diopside and plagioclase, were produced by interaction of hot (about 500°C) seawater-derived fluid and gabbro. The water/rock ratio was locally high at the veins and breccia zones, but the integrated water/rock ratio for the lower part of the hole is probably low. Accessory hydrous magmatic or deuteric phases formed from magmatic volatiles in some gabbro and in trondhjemite. Most subsequent alteration was affected by fluids that were seawater-derived, based on isotopic and chemical analyses of minerals and analyses of fluid inclusions. Many early-generation fluid inclusions, associated with high-temperature veining, contain appreciable methane as well as saline water. The source of methane is unclear, but it may have formed as seawater was reduced during low water/rock interaction with ultramafic upper mantle or ultramafic and mafic layer 3. Temperatures of alteration were calculated on the basis of coexisting mineral chemistry and isotopic values. Hydrothermal metamorphism commenced at about 720°C and continued to about 550°C. Leucocratic veining took place at about 500°C. Alteration within brecciated horizons was also at about 500° to less than 400°C, and the trondhjemite was altered at about 550° to below 490°C. Pressures calculated from a diopside-bearing vein, based on a combination of fluid inclusion and isotopic analysis, were 90 to 100 MPa. This pressure places the sample, from Core 118-735B-70R in Unit V, at about 2 km below the seafloor.

Chemical composition of DSDP and ODP cherts

Rare earth element (REE), major, and trace element abundances and relative fractionations in forty nodular cherts sampled by the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) indicate that the REE composition of chert records the interplay between terrigenous sources and scavenging from the local seawater. Major and (non-REE) trace element ratios indicate that the aluminosilicate fraction within the chert is similar to NASC (North American Shale Composite), with average Pacific chert including ~7% NASC-like particles, Indian chert ~11% NASC, Atlantic chert ~17% NASC, and southern high latitude (SHL) chert 53% NASC. Using La as a proxy for sum REE, approximations of excessive La (the amount of La in excess of that supplied by the detrital aluminosilicate fraction) indicate that Pacific chert contains the greatest excessive La (85% of total La) and SHL chert the least (38% of total La). As shown by interelement associations, this excessive La is most likely an adsorbed component onto aluminosilicate and phosphatic phases. Accordingly, chert from the large Pacific Ocean, where deposition occurs relatively removed from significant terrigenous input, records a depositional REE signal dominated by adsorption of dissolved REEs from seawater. Pacific chert Ce/Ce* <<1 and normative La/Yb ~ 0.8-1, resulting from adsorption of local Ce-depleted seawater and preferential adsorption of LREEs from seawater (e.g., normative La/Yb ~0.4), which increases the normative La/Yb ratio recorded in chert. Chert from the Atlantic basin, a moderately sized ocean basin lined by passive margins and with more terrigenous input than the Pacific, records a mix of adsorptive and terrigenous REE signals, with moderately negative Ce anomalies and normative La/Yb ratios intermediate to those of the Pacific and those of terrigenous input. Chert from the SHL region is dominated by the large terrigenous input on the Antarctic passive margin, with inherited Ce/Ce* ~1 and inherited normative La/Yb values of ~1.2-1.4. Ce/Ce* does not vary with age, either throughout the entire data base or within a particular basin. Overall, Ce/Ce* does not correlate with P2O5 concentrations, even though phosphatic phases may be an important REE carrier.

Geochemistry and K-Ar dates of the Mazagan granodiorite at V30-225, VA79-96KD and DSDP Hole 79-544A, off Moroccan coast

Gneissic granodiorite was recovered by drilling at the base of the Mazagan escarpment, 100 km west of the Casablanca, Morocco, at 4000 m water depth. Coarse, predeformative muscovite yielded dates of -515 Ma, fine-grained muscovite of -455 Ma, biotite -360 and 335 Ma, and feldspar -315 Ma. These dates are tentatively correlated with the microscopic results. We assume a minimum age of middle Cambrian for the granodiorite, an Ordovician deformation and mylonitization, and a Late Carboniferous overprint under upper greenschist facies conditions.

Sandstone and siltstone beds overlying conglomerate at DSDP Hole 59-439

Massive sandstone and siltstone beds with many shallow-water megafossils overlie acidic volcanic conglomerates at DSDP Site 439. Smear-slides, thin sections from coarse fractions, and heavy minerals of the sandstone and siltstone beds were analyzed. The sandstones and siltstones are very rich in lithic fragments and are classified as lithic arenite and (or) lithic wacke. Hornblende and clinopyroxene are abundant, and zircon is present in most of the examined samples. The proportions of sandstone, chert, and volcanic rock in the coarse fraction are variable, but fragments of clastic rocks and cherts are predominant. Plagioclase crystals of volcanic-rock origin, such as highly zoned plagioclase and very fine, euhedral, lath-shaped plagioclase, are frequently observed. Metamorphic-rock fragments and metamorphic minerals are also observed. Thus, the provenance of the sandstone and siltstone beds appears to have been a slightly mature island arc, the Oyashio ancient landmass, consisting of clastic sediments and metamorphic and volcanic rocks.

Petrology of ODP Leg 210 and Leg 173, and DSDP Leg 47 sites

Sand detrital modes of Albian-Eocene clastic gravity-flow deposits cored and recovered at Ocean Drilling Program Site 1276 reflect the postrift geologic evolution of the Newfoundland passive continental margin. Cretaceous sandstone compositions (average: Q57F23L20; Ls%Lsc = 35; total%bioclasts = 3) are consistent with a source on Grand Banks such as Avalon Uplift. Their relatively low potassium feldspar (Qm71K8P21) contents distinguish them from Iberian sandstones and appear to preclude an easterly source during the early history of the ocean basin. Isolated volcaniclastic input near the Paleocene/Eocene boundary (~60 Ma) at Site 1276 is also present in Iberian samples of this age, suggesting that magmatism was widespread across the North Atlantic during this time frame; the source(s) of this volcanic debris remains equivocal. In the Eocene, the development of carbonate bank facies on the shelf marks a profound compositional change to calcareous grainstones (average: Q27F11L62; Ls%Lsc = 82; total%bioclasts = 55) in basinal gravity-flow deposits at Site 1276. This calcareous petrofacies is present on the Iberian margin and in the Pyrenees, suggesting that it was a regional event. The production and downslope redistribution of carbonate debris, including bioclastic and lithic fragments, was likely eustatically controlled. The Newfoundland (Site 1276 and Jeanne d'Arc Basin) sandstones are mainly quartzolithic. Their composition and the contrast in composition between them and more quartzofeldspathic sandstones from the Iberian margin are likely a product of rifting along a Paleozoic suture zone separating distinct basement terranes. This prerift geologic setting contrasts with that of rifts developed within other cratonic settings with variable amounts of synrift volcanism. When synthesized, the spectrum of synrift and postrift sand compositions produces a general model of passive margin (rift-to-drift) sandstone provenance.

Paleomagnetic and rock magnetic data from IODP Site U1308

Integrated Ocean Drilling Program (IODP) Site U1308 (central North Atlantic) records paleomagnetic directional and relative paleointensity (RPI) variations for the last 1.5 Myr, in 110 m of the sediment sequence at a mean sedimentation rate of 7.3 cm/kyr. A detailed benthic oxygen isotope record was combined with RPI to produce an integrated, high-resolution magneto-isotopic stratigraphy for Site U1308. Apart from the well-known polarity reversals in this interval, the Punaruu excursion is recorded at 1092 ka and the Cobb Mountain Subchron in the 1182-1208 ka interval. The paleointensity proxies are determined as slopes of NRM versus ARM and NRM versus ARMAQ (ARM acquisition) with linear correlation coefficients to monitor the quality of the linear fit. The RPI record for Site U1308 is compared with the three other paleointensity records (one from the Western Equatorial Pacific and two from the North Atlantic) that cover the same time interval and have accompanying oxygen isotope records. The Match protocol of Lisiecki and Lisiecki (2002) is used to optimize the correlation of paleointensity records. Beginning with the original (published) age models for each record, the Match routine is used to optimize the RPI correlations to Site U1308, with checks to ensure compatibility with oxygen isotope records. Squared wavelet coherence (WTC) indicates significant improvement in RPI (and oxygen isotope) correlations after matching each RPI record to Site U1308, particularly for periods > 10 kyr. The level of coherence for the Atlantic RPI records and the lower resolution Pacific record implies synchronous global variability (at scales > 10 kyr) that can be attributed to the axial dipole geomagnetic field.

Geochemistry of Neogene-Quaternary sediments in ODP Site 105-645

Subcontinuously cored early(?)-middle Miocene to recently deposited sediments from ODP Site 645 were studied texturally, mineralogically, and geochemically. The entire sequence contains minerals and associated chemical elements that are chiefly of detrital origin. In particular, the clay minerals, which include smectite, kaolinite, chlorite, and illite, are detrital. No obvious evidence of diagenesis with depth, of burial, of volcanism, or of hydrothermal alteration was observed. The sedimentary textures, clay mineralogy, and <2-µm fraction geochemistry of the early middle Miocene sediments (630 to 1147 mbsf) suggest the pronounced but variable influence of a southward bottom current. Two clay facies are defined. The lower one, Cj (780 to 1147 mbsf), is characterized by the great abundance of discrete smectite (with less than 15% illite interlayers), probably detrital in origin, and reworked older, discrete, smectite-rich sediments. The upper clay facies, C2 (630 to 780 mbsf), shows a net decrease of the fully expandable clay abundances, with a great abundance of mixed-layer, illite-smectite clays (60 to 80% of illite interlayers). Such clay assemblages can be inherited from paleosoils or older sedimentary rocks. An important change occurs at 630 mbsf (clay fraction) or 600 mbsf (sedimentary texture), which may be explained by the beginning of continental glaciation (630 mbsf, ~9 Ma) and the onset of ice rafting in Baffin Bay (600 mbsf, ~8 Ma). Above this level, the characteristics and modifications of the clay assemblages are controlled climatically and can be explained by the fluctuations of (1) ice-rafting, (2) speed of weak bottom currents, and (3) some supply by mud turbiditic currents. Three clay facies (C3, C4, and C5) can be defined by the abrupt increases of the inherited chlorite and illite clays.

Conglomerate and sandstone petrography at DSDP Hole 58-445

Conglomerates and sandstones in lithologic unit V at DSDP Site 445 comprise lithic clasts, detrital minerals, bioclasts, and authigenic minerals. The lithic clasts are dominantly plagioclase-phyric basalt and microdolerite, followed by plagioclase-clinopyroxene-phyric basalt, aphyric basalt, chert, and limestone. A small amount of hornblende schist occurs. Detrital minerals are dominantly plagioclase, augite, titaniferous augite, olivine, green to pale-brown hornblende, and dark-brown hornblende, with subordinate chromian spinel, epidote, ilmenite, and magnetite, and minor amounts of diopside, enstatite, actinolite, and aegirine-augite. Bioclasts are Nummulites boninensis, Asterocyclina sp. cf. A. penuria, and some other larger foraminifers. Correlation of cored and dredged samples indicates that the Daito Ridge is mainly composed of igneous, metamorphic, ultramafic, and sedimentary rocks. The igneous rocks are mafic (probably tholeiitic) and alkalic. The metamorphic rocks are hornblende schist, tremolite schist, and diopside-chlorite schist. The ultramafic rocks are alpinetype peridotites. Mineralogical data suggest that there were two metamorphic events in the Daito Ridge. The older one was intermediate- to high-pressure metamorphism. The younger one was contact metamorphism caused by a Paleocene volcanic event, possibly related to the beginning of spreading of the west Philippine Basin. The ultramafic rocks suffered from the same contact metamorphism. During the Eocene, exposed volcanic and metamorphic rocks on the uplifted Daito Ridge may have supplied pebble clasts to the surrounding coast and shallow sea bottom. The steep slope offshore may have caused frequent slumping and transportation of the pebble clasts and shallow-water benthic organisms into deeper water, forming the conglomerates and sandstones treated here.

Composition and age of bottom sediments from the Southern Ocean

Geomorphology, geology, stratigraphy, lithology and geochemistry of bottom sediments in the South Ocean are under consideration. Regularities of distribution of iron-manganese nodules, features of occurrence of ore components in the nodules, nodule abundance in bottom sediments have been studied.