(Table 1) List of studied samples with vestimentiferan tubes

Vestimentiferan tube worms are prominent members of modern methane seep communities and are totally reliant as adults on symbiotic sulphide-oxidizing bacteria for their nutrition. The sulphide is produced in the sediment by a biochemical reaction called the anaerobic oxidation of methane (AOM). A well-studied species from the Gulf of Mexico shows that seep vestimentiferans 'mine' sulphide from the sediment using root-like, thin walled, permeable posterior tube extensions, which can also be used to pump sulphate and possibly hydrogen ions from the soft tissue back into the sediment to increase the local rate of AOM. The 'root-balls' of exhumed seep vestimentiferans are intimately associated with carbonate nodules, which are a result of AOM. We have studied vestimentiferan specimens and associated carbonates from seeps at the Kouilou pockmark field on the Congo deep-sea fan and find that some of the posterior 'root' tubes of living specimens are enclosed with carbonate indurated sediment and other, empty examples are partially or completely replaced by the carbonate mineral aragonite. This replacement occurs from the outside of the tube wall inwards and leaves fine-scale relict textures of the original organic tube wall. The process of mineralization is unknown, but is likely a result of post-mortem microbial decay of the tube wall proteins by microorganisms or the precipitation from locally high flux of AOM derived carbonate ions. The aragonite-replaced tubes from the Kouilou pockmarks show similar features to carbonate tubes in ancient seep deposits and make it more likely that many of these fossil tubes are those of vestimentiferans. These observations have implications for the supposed origination of this group, based on molecular divergence estimates.

(Table T1) Geochemical composition of xenoliths and host rocks from ODP Hole 193-1188A and dredge haul MD-138, PACMANUS field

A number of intensely altered, dark xenoliths with palimpsest quench textures were recorded within altered dacitic host rocks at Site 1189 (Roman Ruins, PACMANUS) during Ocean Drilling Program (ODP) Leg 193. Several of these displayed puzzling marginal fringes, apparently of altered plagioclase with variolitic texture, protruding into adjacent host rocks. Despite their alteration, the xenoliths were interpreted as fragments of rapidly chilled, possibly olivine-bearing basalts incorporated into the dacitic magmas either within the crustal plumbing system or during eruption at the seafloor (figures F15, F16, F17, F42, and F43 in Shipboard Scientific Party, 2002, doi:10.2973/odp.proc.ir.193.104.2002). An additional example of formerly spinifex-textured xenolith, the first from Site 1188 (Snowcap) and the first from the upper cristobalite-bearing zone of alteration, has been revealed by postcruise studies. Furthermore, a pristine sample of the parent lithology has been found within a dredge haul (MD-138, Binatang-2000 Cruise of Franklin; 3°43.60'S, 151°40.35'E, 1688 meters below sea level) from the Satanic Mills hydrothermal field at PACMANUS, near ODP Site 1191. The purpose of this report is to document these discoveries and thereby to confirm and build on shipboard interpretations. To my knowledge, similar xenoliths have never before been found in modern island arc or backarc volcanic sequences. Spinifex textures are most common in Archean komatiites, some of which are bimodally associated with calc-alkaline felsic volcanic rocks.

Chemistry of the massive sulfide deposit at DSDP Hole 63-471

We report here chemical analyses of sulfide and other minerals occurring in the massive sulfide deposit cored at Site 471. Details of the mineralogy and inferred paragenesis of the deposit will be reported elsewhere. The sulfide deposit at Site 471 occurs between overlying pelagic sediment and underlying basalt. The deposit is vertically zoned and consists, from top to bottom, of the following mineral assemblages: (1) pyrite, chalcopyrite, and Zn-sulfide in chert and calcite gangue (about 35 cm thick); (2) a 5-cm-thick metalliferous sediment layer described in detail by Leinen (this volume); and (3) a 4-cm-thick chert layer. The overlying sediment is a calcareous silty claystone that contains middle Miocene coccoliths (Bukry, this volume). The underlying basalt has been extensively chloritized and veined with calcite. In places feldspars are albitized, and calcite occurs as pseudomorphs after olivine. Relict textures suggest that the basalt grades into diabase and gabbro with increasing depth. Neither stock work nor disseminated sulfides was observed in the altered rocks.

Geochemistry of DSDP Hole 86-577B samples

THE chemical, mineralogical and isotopic characteristics of deposits at the Cretaceous/Tertiary (K/T) boundary are suggestive of a large impact event, the prime candidate (Sharpton et al., 1992, doi:10.1038/359819a0) being the Chicxulub crater in Yucatan, Mexico. Spinel-bearing spherules, which may be associated with such impacts, have been reported (Smit and Romein, 1985, doi:10.1016/0012-821X(85)90019-6) at several K/T boundary sites worldwide, but their origin is still uncertain. We have examined the spinel-bearing material recovered from K/T boundary deposits at site 577 in the Pacific Ocean (Heath et al., 1985, doi:10.2973/dsdp.proc.86.104.1985) and find two distinct populations of particles: spherules with dendritic spinel textures dispersed throughout the grains and irregularly shaped fragments with spinels essentially confined to the rim. The morphology and composition of the particles are characteristic of melted and partially melted meteoritic ablation debris, but their location is difficult to reconcile with an impact on the Yucatan peninsula, some 10,000 km away. We suggest instead that the spinel-bearing particles at site 577 are derived from the impact of a 2-km asteroid in the Pacific Ocean, and that several accretionary events of this type are required to explain the global distribution of spinel-bearing spherules at the K/T boundary.

Grain shape of sediment from the Weddell Sea

Very fine quartz sand was examined from Paleogene and Neogene sediments of ODP Sites 693, 694, 695, 696, and 697 to determine their grain roundness using Fourier analysis and SEM surface texture characteristics. The objective of this study was to identify grain roundness and surface texture characteristics unique to East (Site 693) and West (Sites 695, 696, and 697) Antarctica and to glacial regimes. Once identified, these distinguishing features could then be used to determine changes in source area and glacial conditions in the central Weddell Sea Basin (Site 694). Three end members of very fine quartz sand are recognized in the Oligocene to Pleistocene sediments of the Weddell Sea: angular, rounded, and intermediate. End member 1 (angular) consists of extremely angular grains with numerous fracture textures. Previous investigations suggested that these sands are derived from crystalline rocks that fractured during formation or deformation and/or were exposed to weathering by ice. In this study, however, the correlation of angularity with ice activity is problematical as the most angular sands were recovered in the lower Oligocene sediments of the South Orkney Microcontinent, a period of temperate climatic conditions. End member 3 (rounded) consists of rounded grains with chemically and mechanically produced surface textures. These sands are presumed to be derived from the Beacon-type rocks in East Antarctica and the sedimentary deposits of the Northern Antarctic Peninsula. End member 2 (intermediate) grains display crystalline nodes and grain embayments. They are thought to be derived from felsic intrusives, East Antarctic quartzites, basement metamorphics of the South Orkney Microcontinent, and/or the Andean intrusive series of West Antarctica. Unfortunately, no features unique to either the East or West Antarctic sediment sources or to glacial conditions could be isolated. Therefore, the objective of determining provenance changes and sediment erosion and transport mechanisms could not be achieved using this approach.

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.

Carbonate aggregate mineralogy and stable isotopes at DSDP Site 87-583

Crystalline aggregates composed of calcium carbonate were recovered in the uppermost 50 m of Nankai Trough sediments during DSDP Leg 87A. These aggregates decomposed with time to masses of sandy calcite as determined by X-ray diffraction analysis. Petrographic and scanning electron microscopy revealed textures suggestive of a precursor phrase prior to calcite, and this precursor has been tentatively identified as the mineral ikaite, CaCO3*6H2O. Stable isotope data suggest a large component of terrigenous organic matter as the carbon source, consistent with the appearance of these aggregates in highly reducing pyritic sediments containing abundant plant remains. We propose that these nodules formed in euxinic basins on the upper part of the Trough slope under normal seafloor conditions of pressure and temperature. Calculated temperatures of formation of this phase are not unusually low. The specimens from Site 583 are the first reported occurrences of ikaite in active margin sediments.

Estimation of cooling of lavas from Serocki volcano

A dynamic crystallization study was undertaken to provide a framework for linking the textural variations observed in the Hole 648B lavas with the size and morphology of cooling units inferred from drilling and submersible observation. The textures produced in cooling rate experiments carried out using a Serocki lava (ALV-1690-20) are comparable to the groundmass textural characteristics of lavas from Serocki volcano. The results of the dynamic crystallization study provide a quantitative link between texture, cooling rate, and eruption temperature. The maximum half-width of cooling units estimated from textural characteristics is on the order of 3 m, a value consistent with constraints from drilling and submersible observation. Textural characteristics indicate that the temperature from which cooling began was slightly above the liquidus. The relation between cooling rate and texture are also tested on a drill core sample of basalt of similar composition from a 9-m-thick flow in DSDP Hole 396B.

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.

Grain sizes and mineral composition of the basement of ODP Site 206-1256

Hole 1256C was cored 88.5 m into basement, and Hole 1256D, the deep reentry hole, was cored 502 m into basement during Ocean Drilling Program Leg 206. Hole 1256D is located ~30 m south of Hole 1256C (Wilson, Teagle, Acton, et al., 2003, doi:10.2973/odp.proc.ir.206.2003). A thick massive flow drilled in both holes, Units 1256C-18 and 1256D-1, consists of a single cooling unit of cryptocrystalline to fine-grained basalt, interpreted as a ponded lava, 32 m and at least 74.2 m thick, respectively. This ponded flow gives us a unique opportunity to examine textural variations from the glassy, folded crust of the lava pond recovered from the top of Unit 1256C-18 through the coarse-grained, thick massive lava body to the unusually recrystallized and deformed base cored in Unit 1256C-18. Some detailed descriptions of the textures and grain size variations through the lava pond (Units 1256C-18 and 1256D-1), with special reference to the recrystallization of the base of Unit 1256C-18, are presented here.

Composition and structural formulas of ODP Site 200-1224 Eocene ferrobasalt minerals

The ~46-m.y.-old igneous basement cored during Leg 200 in the North Pacific represents one of the few cross sections of Pacific oceanic crust with a total penetration into basalt of >100 m. The rocks, emplaced during the Eocene at a fast-spreading rate (~14 cm/yr; full rate) are strongly differentiated tholeiitic basalts (ferrobasalts) with 7-4.5 wt% MgO, relatively high TiO2 (2-3.5 wt%), and total iron as Fe2O3 (9.1-16.8 wt%). The differentiated character of these lavas is related to unusually large amounts of crystallization differentiation of plagioclase, clinopyroxene, and olivine. The lithostratigraphy of the basement (cored to ~170 meters below seafloor) is divided into three units. The deepest unit (lithologic Unit 3), is a succession of lava flows of no more that a few meters thickness each. The intermediate unit (lithologic Unit 2) is represented by intermixed thin flows and pillows, whereas the shallowest unit (lithologic Unit 1), comprises two massive flows. The rocks range from aphyric to sparsely clinopyroxene-plagioclase-phyric (phenocryst content = <3 vol%) and from holocrystalline to hypohyaline. Chilled margins of pillow fragments show holohyaline to sparsely vitrophyric textures. Site 1224 oxide minerals present a type of alteration not previously seen, where titanomagnetite is only partially destroyed and the pure magnetite component is partially removed from the mineral, leaving, in the most extreme case, a nearly pure ulvöspinel residuum. As a result of this dissolution, iron, mainly in the oxidized state, is added to the circulating solvent fluids. This means that a considerable metal source can result from low-temperature reactions throughout the upper ocean crust. The coarsest-grained lithologic Unit 1 rocks have interstitial myrmekitic intergrowths of quartz and sodic plagioclase (~An12), roughly similar in mineralogy and bulk composition to tonalite/trondhjemite veinlets in abyssal gabbros from the southwest Indian Ocean and Hess Deep, eastern equatorial Pacific. Based on idiomorphic relationships and projections into the simplified Q-Ab-Or-H2O granite ternary system, the myrmekitic intergrowths formed at the same time as, or just after, the oxide minerals coprecipitated and at low water vapor pressure (~0.5 kbar). Their compositions correspond to SiO2-oligoclase intergrowths that are considerably less potassic than dacitic glasses that erupt, although rarely, along the East Pacific Rise or that have been produced experimentally by partial melting of gabbro. Based on the crystallization history and comparison to experimental data, the original interstitial siliceous liquids resulted from late-stage immiscible separation of siliceous and iron-rich liquids. The rare andesitic lavas found along the East Pacific Rise may be hybrid rocks formed by mixing of these immiscible siliceous melts with basaltic magma.

Records of past mid-depth ventilation: Cretaceous ocean anoxic event 2 vs. recent oxygen minimum zones

Present day oceans are well ventilated, with the exception of mid-depth oxygen minimum zones (OMZs) under high surface water productivity, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or anoxic. The Cretaceous ocean anoxic events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossils preserved in the sedimentary record. Yet assessments of the intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life have been studied thoroughly. Their implications for constraining past bottom-water oxygenation are addressed in this review. We compared OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the north-west African shelf. Holocene laminated sediments are encountered at bottom-water oxygen levels of < 7 µmol/kg under the Peruvian upwelling and < 5 µmol/kg in California Borderland basins and the Pakistan Margin. Seasonal to decadal changes of sediment input are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 µmol/kg. Chondrites has not been reported in Peruvian sediments but centimetre-sized crab burrows appeared around 10 µmol/kg, which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C /cm2 /kyr in laminated OAE 2 sections in Tarfaya Basin, Morocco, matching late Holocene accumulation rates of laminated Peruvian sediments under Recent oxygen levels below 5 µmol/kg. Sediments deposited at > 10 µmol/kg showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In the absence of seasonal laminations and under conditions of low burial diagenesis, this relationship may facilitate quantitative estimates of palaeo-oxygenation. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.