Physical properties, grain size distribution and clay mineralogy of ODP Leg 117 sites

The fabric of sediments recovered at sites drilled on the Indus Fan, Owen Ridge, and Oman margin during Ocean Drilling Program Leg 117 was examined by scanning electron microscopy to document changes that accompany sediment burial. Two sediment types were studied: (1) biogenic sediments consisting of a variety of marly nannofossil and nannofossil oozes and chalks and (2) terrigenous sediments consisting of fine-grained turbidites deposited in association with the Indus Fan. Biogenic sediments were examined with samples from the seafloor to depths of 306 m below seafloor (mbsf) on the Owen Ridge (Site 722) and 368 mbsf on the Oman margin (Sites 723 and 728). Over these depth ranges the biogenic sediments are characterized by a random arrangement of microfossils and display little chemical diagenetic alteration. The microfossils are dispersed within a fine-grained matrix that is predominantly microcrystalline carbonate particles on the Owen Ridge and clay and organic matter on the Oman margin. Sediments with abundant siliceous microfossils display distinct, open fabrics with high porosity. Porosity reduction resulting from gravitational compaction appears to be the primary process affecting fabric change in the biogenic sediment sections. Fabric of illite-rich clayey silts and silty claystones from the Indus Fan (Site 720) and Owen Ridge (Sites 722 and 731) was examined for a composite section extending from 45 to 985 mbsf. In this section fabric of the fine-grained turbidites changes from one with small flocculated clay domains, random particle arrangement, and high porosity to a fabric with larger domains, strong preferred particle orientation roughly parallel to bedding, and lower porosity. These changes are accomplished by a growth in domain size, primarily through increasing face-to-face contacts, and by particle reorientation which is characterized by a sharp increase in alignment with bedding between 200 and 400 mbsf. Despite extensive particle reorientation, flocculated clay fabric persists in the deepest samples examined, particularly adjacent to silt grains, and the sediments lack fissility. Fabric changes over the 45-985 mbsf interval occur in response to gravitational compaction. Porosity reduction and development of preferred particle orientation in the Indus Fan and Owen Ridge sections occur at greater depths than outlined in previous fabric models for terrigenous sediments as a consequence of a greater abundance of silt and a greater abundance of illite and chlorite clays.

Index properties, consolidation characteristics and sediment rebound of ODP Sites 167-1020 and 167-1021 sediments

Drilling during Leg 167 at the California margin was scheduled to recover continuous sedimentary sections. Multiple advanced piston core (APC) holes drilled at different depth offsets provided core overlap in successive APCs. Correlation of high-resolution laboratory physical properties data from adjacent APC holes was used to compile composite depth sections for each site. The composite depth sections were used to confirm continuous recovery and enable high-resolution sampling. The meters composite depth (mcd) scale differs from the shipboard meters below seafloor (mbsf) scale because of (1) core expansion following recovery (MacKillop et al., 1995, doi:10.2973/odp.proc.sr.138.118.1995), (2) coring gaps, and (3) stretching/compression of sediment during coring (Lyle, Koizumi, Richter, et al., 1997, doi:10.2973/odp.proc.ir.167.1997). Moran (1997, doi:10.2973/odp.proc.sr.154.132.1997) calculated that sediment expansion accounted for 90%-95% of the Leg 154 depth offset between shipboard mbsf and the mcd scales. Terzaghi's one-dimensional theory of consolidation (Terzaghi, 1943) describes the response of sediments to stress loading and release. Mechanical loading in marine environments is provided by the buoyant weight of the overlying sediments. The load increases with depth below seabed, resulting in sediment volume reduction as water is "squeezed" out of the voids in the sediment. Stress release during core recovery results in expansion of the sediment and volume increase as water returns to the sediment. The sediment expansion or rebound defines the elastic properties of the sediment. In this study we examine the elastic deformation properties of sediments recovered from Sites 1020 and 1021. These results are used to (1) correct the laboratory index properties measurements to in situ values and (2) determine the contribution of sediment rebound to the depth offset between the mbsf and mcd scales.

Minerals, geochemistry and x-ray power characteristics at DSDP Sites 54-424, 60-458 and 60-459

Secondary minerals filling veins and vesicles in volcanic basement at Deep Sea Drilling Project Sites 458 and 459 indicate that there were two stages of alteration at each site: an early oxidative, probably hydrothermal, stage and a later, low-temperature, less oxidative stage, probably contemporaneous with faulting in the tectonically active Mariana forearc region. The initial stage is most evident in Hole 459B, where low-Al, high Fe smectites and iron hydroxides formed in vesicles in pillow basalts and low-Al palygorskite formed in fractures. Iron hydroxides and celadonite formed in massive basalts next to quartz-oligoclase micrographic intergrowths. Palygorskite was found in only one sample near the top of basement in Hole 458, but it too is associated with iron hydroxides. Palygorskite has previously been reported only in marine sediments in DSDP and other occurrences. It evidently formed here as a precipitate from fluids in which Si, Mg, Fe, and even some Al were concentrated. Experimental data suggest that the solutions probably had high pH and somewhat elevated temperatures. The compositions of associated smectites resemble those in hydrothermal sediments and in basalts at the Galapagos mounds geothermal field. The second stage of alteration was large-scale replacement of basalt by dioctahedral, trioctahedral, or mixed-layer clays and phillipsite along zones of intense fracturing, especially near the bottom of Holes 458 and 459B. The basalts are commonly slickensided, and there are recemented microfault offsets in overlying sediments. Native copper occurs in one core of Hole 458, but associated smectites are dominantly dioctahedral, unlike Hole 459B, where they are mainly trioctahedral, indicating nonoxidative alteration. The alteration in both holes is more intense than at most DSDP ocean crust sites and may have been augmented by water derived from subducting ocean crust beneath the fore-arc region.

Late Cretaceous planktonic foraminiferal assemblages from the Exmouth Plateau, ODP Sites 122-762 and 122-763, eastern Indian Ocean

The evolution of planktonic foraminifera during the Late Cretaceous is marked in the Santonian by the disappearance of complex morphotypes (the marginotruncanids), and the contemporary increasing importance and diversification of another group of complex taxa, the globotruncanids. Upper Turonian to lower Campanian planktonic foraminiferal assemblages from Holes 762C and 763B (Ocean Drilling Program, Leg 122, Exmouth Plateau, 47°S palaeolatitude) were studied in detail to evaluate the compositional variations at the genus and species level based on the assumption that, in the Cretaceous oceans as in the modern, any faunal change was associated with changes in the characteristics and the degree of stability of the oceanic surface waters. Three major groups were recognised based on gross morphology, and following the assumption that Cretaceous planktonic foraminifera, although extinct, had life-history strategies comparable to those of modern planktonics: 1 - r-selected opportunists; 2 - k-selected specialists; 3 - r/k intermediate morphotypes which include all genera that display a range of trophic strategies in-between opportunist and specialist taxa. Although planktonic foraminiferal assemblages are characterised by a progressive appearance of complex taxa, this trend is discontinuous. Variation in number of species and specimens within genera has allowed recognition of five discrete intervals each of them reflecting different oceanic conditions based on fluctuations in diversity and abundance of the major morphotypes. Planktonic forms show cyclical fluctuations in diversity and abundance of cold (r-strategists) and warm taxa (k-strategists), perhaps representing alternating phases of unstable conditions (suggesting a weakly stratified upper water column in a mesotrophic environment), and well-stratified surface and near-surface waters (indicating a more oligotrophic environment). Interval 1, middle Turonian to early Coniacian in age, is dominated by the r/k intermediate morphotypes which alternate with r-strategists. These cyclical alternations are used to identify three additional subintervals. Interval 2, aged middle to late Coniacian, is characterised by the increasing number of species and relative abundance of k-strategists. After this maximum diversification the k-strategists show a progressive decrease reaching a minimum value in Interval 3 (early to late Santonian), which corresponds to the extinction of the genus Marginotruncana. In the Interval 4, latest Santonian in age, the k-strategists, represented mainly by the genera Globotruncana, increase again in diversity and abundance. The last Interval 5 (early Campanian) is dominated by juvenile globotruncanids and r-strategists which fluctuate in opposite phase. The positive peak (Interval 2) related to the maximum diversification of warm taxa (k-strategists) in the Coniacian seems to correspond to a warmer episode. It is followed by a marked decrease in the relative abundance of warm taxa (k-strategists crisis) with a minimum in the late Santonian (Interval 3), reflecting a decrease in temperature. Detailed analysis of faunal variations allows the Santonian faunal turnover to be ascribed to a cooling event strong enough to cause the extinction of the marginotruncanids.

Barium in sediments and pore waters of several ODP Leg 170 and Leg 205 sites

Barium concentrations were measured on 17 pore fluid and 13 sediment samples from Sites 1253 and 1254 drilled offshore Costa Rica during Ocean Drilling Program (ODP) Leg 205. An additional 83 pore fluid and 29 sediment samples were analyzed for Ba concentrations from Sites 1039 and 1040 drilled during ODP Leg 170 offshore Costa Rica. Sites 1039/1253 and 1040/1254 are part of a transect across the Middle America Trench offshore Nicoya Peninsula. The entire incoming sediment section is being underthrust beneath the margin, providing an ideal setting to examine Ba cycling in the shallow levels of the subduction zone. Results from these analyses indicate that a significant amount of Ba is liberated from the mineral barite (BaSO4) in the uppermost hemipelagic sediments arcward of the trench. The shallow distillation of Ba may impact the amount of sedimentary Ba reaching the deeper subduction zone.

Sulphate and d34S in pore waters and d13C, d18O and mineral composition of carbonate nodules from ODP Leg 188 sites

Carbon and oxygen isotopic compositions of authigenic carbonate nodules or layers reflect the diagenetic conditions at the time of nodule growth. The shallowest samples of carbonate nodules and dissolved inorganic carbon of pore water samples beneath the sulfate reduction zone (0-160 meters below seafloor [mbsf]) at Site 1165 have extremely negative d13C values (-50 per mil and -62 per mil, respectively). These negative d13C values indicate nodule formation in association with anaerobic methane oxidation coupled with sulfate reduction. The 34S of residual sulfate at Site 1165 shows only minor 34S enrichment (+6 per mil), even with complete sulfate reduction. This small degree of apparent 34S enrichment is due to extreme "open-system" sulfate reduction, with sulfate abundantly resupplied by diffusion from overlying seawater. Ten calcite nodules from Site 1165 contain minor quartz and feldspar and have d13C values ranging from -49.7 per mil to -8.2 per mil. The nodules with the most negative d13C values currently are at depths of 273 to 350 mbsf and must have precipitated from carbonate largely derived from subsurface anaerobic methane oxidation. The processes of sulfate reduction coupled with methane oxidation in sediments of Hole 1165B are indicated by characteristic concentration and isotopic (d34S and d13C) profiles of dissolved sulfate and bicarbonate. Three siderite nodules from Site 1166 contain feldspar and mica and one has significant carbonate-apatite. The siderite has d13C values ranging from -15.3 per mil to -7.6 per mil. These siderite nodules probably represent early diagenetic carbonate precipitation during microbial methanogenesis.

Radiometric age determinations for basements of ODP Sites 123-765 and 123-766

The results of experiments in 40Ar/39Ar age dating using fresh basement material from Sites 765 and 766 of Leg 123 of the Ocean Drilling Program are inconsistent and cannot be used to constrain the basement age of the Argo Abyssal Plain in the Indian Ocean. However, a celadonite sample, which was precipitated during a low-temperature alteration event that affected the basement at Site 765, yielded a K-Ar age of 155.3 ±3.4 Ma. Celadonites, which have been dated using Rb-Sr methods for basement in the Atlantic Ocean (Staudigel et al., 1981, doi:10.1016/0012-821X(81)90186-2) and by K-Ar methods for the Troodos Ophiolite (Staudigel et al., 1986, doi:10.1130/0091-7613(1986)14<72:AASAOC>2.0.CO;2), and for sediments from the Pacific Ocean (Peterson et al., 1986, doi:10.2973/dsdp.proc.92.132.1986) yield ages that are up to 15 Ma younger than the age for the formation of basement. Thus, the celadonite age is retained as a reliable minimum age for basement at Site 765. This radiometric age is inconsistent with biostratigraphic ages, which indicate a maximum of late Berriasian (approximately 140 Ma) for Site 765, but is consistent with geophysical interpretations of marine magnetic anomalies and with the early north-south seafloor spreading history of the Argo Abyssal Plain region of the Indian Ocean.

Pore-water chemistry of ODP sites 111-677 and 111-678

Sites 677 and 678 were drilled on ODP Leg 111 to test hypotheses about the nature and pattern of hydrothermal circulation on a mid-ocean ridge flank. Together with earlier results from DSDP Site 501/504 and several heatflow and piston coring surveys covering a 100-km**2 area surrounding the three drill sites, they confirm that hydrothermal circulation persists in this 5.9-m.y.-old crust, both in basement and through the overlying sediments (Langseth et al., 1988, doi:10.2973/odp.proc.ir.111.102.1988). Profiles of sediment pore-water composition with depth at the three drill sites show both vertical and horizontal gradients. The shapes of the profiles and their variation from one site to another result from a combination of vertical and horizontal diffusion, convection, and reaction in the sediments and basement. Chemical species that are highly reactive in the siliceous-calcareous biogenic sediments include bicarbonate (alkalinity), ammonium, sulfate, manganese, calcium, strontium, lithium, silica, and possibly potassium. Reactions include bacterial sulfate reduction, mobilization of Mn2+, precipitation of CaCO3, and recrystallization of calcareous and siliceous oozes to chalk, limestone, and chert. Species with profiles more affected by reaction in basaltic basement than in the sediments include Mg, Ca, Na, K, and oxygen isotopes. Reaction in basement at 60?C and at higher temperatures has produced a highly altered basement formation water that is uniform in composition over distances of several kilometers. As inferred from the composition of the basal sediment pore water at the three sites, this uniformity extends from up flow zone to downflow zone in basement and the sediments. It exists in spite of large variations in heat flow and depth to basement, apparently as a result of homogenization by hydrothermal circulation in basement. Profiles for chlorinity, Na, Mg, and other species in the sediment pore waters confirm that Site 678, drilled on a localized heatflow high identified by Langseth et al. (1988), is a site of long-lived upwelling of warm water from basement through the sediments at velocities of 1 to 2 mm/yr. The upflow through the anomalously thin sediments is apparently localized above an uplifted fault block in basement. This site and other similar sites in the survey area give rise to lateral diffusion and possibly flow through the sediments, which produces lateral gradients in sediment pore-water composition at sites such as 501/504. The complementary pore-water profiles at the low-heatflow Site 677 2 km to the south indicate that downflow is occurring through the sediments there, at comparable rates of 1 to 2 mm/yr.

Porosity, gas permeability and grain density of ODP Leg 194 sites

We report analyses of porosity and permeability of core samples from Site 1193 in the Northern Marion Platform, Sites 1196 and 1199 in the Southern Marion Platform, and Sites 1194, 1195, 1197, and 1198 from the slopes of these platforms. The samples include 415 horizontal 1-in plugs, 290 vertical 1-in plugs, and 23 whole-core pieces. Porosity and permeability analyses were possible for most, but not all, samples. Grain density measurements were also obtained for the horizontal plugs. Representative photomicrographs are provided of thin sections from 139 of the horizontal plugs and the 23 whole-core pieces.

Upper Cretaceous-Paleogene stratigraphy of ODP Sites 113-689 and 113-690

This contribution summarizes the biostratigraphy of planktonic foraminifers, calcareous nannofossils, and benthic foraminifers, in combination with the magnetostratigraphy, carbon and oxygen isotope stratigraphy of benthic foraminifers, and CaCO3 stratigraphy for the Maestrichtian through Paleogene calcareous sequences recovered at Sites 689 and 690 on Maud Rise (at about 65°S, eastern Weddell Sea, Antarctica). These data represent the southernmost calciumcarbonate record available for that interval, and thus extend the biostratigraphic and isotopic database to higher latitudes. Sites 689 and 690 form the southernmost anchor of a north-south transect through the Atlantic Ocean for Paleogene biostratigraphy and chemostratigraphy.

Oxygen isotopes and hydrocarbon composition of gas hydrate and hydrate water from ODP Leg 165 sites

Ocean Drilling Program (ODP) Leg 164 recovered a number of large solid gas hydrate from Sites 994, 996, and 997 on the Blake Ridge. Sites 994 and 997 samples, either nodular or thick massive pieces, were subjected to laboratory analysis and measurements to determine the structure, molecular and isotopic composition, thermal conductivity, and equilibrium dissociation conditions. X-ray computed tomography (CT) imagery, X-ray diffraction, nuclear magnetic resonance (NMR), and Raman spectroscopy have revealed that the gas hydrates recovered from the Blake Ridge are nearly 100% methane gas hydrate of Structure I, cubic with a lattice constant of a = 11.95 ± 0.05 angström, and a molar ratio of water to gas (hydration number) of 6.2. The d18O of water is 2.67 per mil to 3.51 per mil SMOW, which is 3.5-4.0 heavier than the ambient interstitial waters. The d13C and dD of methane are -66 per mil to -70 per mil and -201 per mil to -206 per mil, respectively, suggesting that the methane was generated through bacterial CO2 reduction. Thermal conductivity values of the Blake Ridge hydrates range from 0.3 to 0.5 W/(m K). Equilibrium dissociation experiments indicate that the three-phase equilibrium for the specimen is 3.27 MPa at 274.7 K. This is almost identical to that of synthetic pure methane hydrate in freshwater.

Calcareous nannofossil stratigraphy, mass accumulation rates and bulk density of sediments from ODP Leg 173 sites

Drilling on the Iberia Abyssal Plain during Ocean Drilling Program Leg 173 allowed us to recover Upper Cretaceous through Paleocene sediments at Sites 1068 and 1069 and only upper Paleocene sediments at Site 1067, which expands considerably the Upper Cretaceous to Paleocene record for this region. Of these three sites, Site 1068 recovered uppermost Cretaceous sediments as well as the most complete Paleocene record, whereas Site 1067 yielded only uppermost Paleocene sediments (Zone CP8). Site 1069 provided a rather complete upper Campanian through Maastrichtian section but a discontinuous Paleocene record. After a detailed calcareous nannofossil biostratigraphy was documented in distribution charts, we calculated mass accumulation rates for Holes 1068A and 1069A. Sediments in Hole 1068A apparently record the final stages of burial of a high basement block by turbidity flows. Accumulation rates through the Upper Cretaceous indicate relatively high rates, 0.95 g/cm**2/k.y., but may be unreliable because of the lack of datum points and/or possible hiatuses. Accumulation rates in the Paleocene section of Hole 1068A fluctuated every few million years from lower (~0.35 g/cm**2/k.y.) to higher rates (~0.85 g/cm**2/k.y.) until the latest Paleocene, when rates increased to an average of ~2.0 g/cm**2/k.y. Mass accumulation rates for the Upper Cretaceous in Hole 1069A indicate a steady rate of ~0.60 g/cm**2/k.y. from 75 to 72 Ma. There may have been one or more hiatuses between 72 and 68 Ma (combined Zone CC24 through Subzone CC25b), as indicated by the very low accumulation rate of 0.15 g/cm**2/k.y. The Paleocene section of Hole 1069A does not show the same continuous record, which may result from fluctuations in the carbonate compensation depth and poor recovery (average = 40%). Zones CP4 and CP5 are missing within a barren interval; this and numerous other barren intervals affect the precision of the nannofossil zonation and calculation of mass accumulation rates. However, in spite of these missing zones, mass accumulation rates do not seem to indicate the presence of hiatuses as the rates for this barren interval average ~1.0 g/cm**2/k.y. This study set out to test the hypothesis that a reliable biostratigraphic record could be constructed from sediments derived from turbidity flows deposited below the carbonate compensation depth. As illustrated here, not only could a reliable biostratigraphic record be determined from these sediments, but sedimentation and mass accumulation rates could also be determined, allowing inferences to be drawn concerning the sedimentary history of this passive margin. The reliability of this record is confirmed by independent verification by the establishment of a magnetostratigraphy for the same cores.

Bulk and clay mineral composition of ODP Leg 189 sites

Bulk and clay mineral investigations were conducted on ~750 samples from four sites drilled during Ocean Drilling Program Leg 189 on the western Tasmanian margin (Site 1168), the South Tasman Rise (Sites 1170 and 1171), and the East Tasman Plateau (Site 1172). The mineralogy of the bulk sediment is very similar at all sites, and major changes coincide with the boundaries of the three main lithologic units described in the Leg 189 Initial Reports volume. The clay mineral assemblages show significant regional differences, but their major variations coincide at all sites and with major changes in regional tectonics and climate.

Distribution, depositional form and geochemical composition of tephra horizons in ODP Sites 186-1150 and 186-1151

Major element geochemical composition was established for 59 tephra horizons from Ocean Drilling Program Sites 1150 and 1151, located in the Japan forearc. These data, encompassing typically between 15 and 30 individual shard analyses per tephra horizon, were used to investigate the degree to which sediment reworking, postdepositional geochemical alteration, and geochemical uniqueness of individual eruptives facilitate or impede the potential for establishing a tephrostratigraphical framework for the Japan Trench, as well as usage of the tephra record to document arc evolution. Evidence was found that hydration (termed phase 1 alteration) of glass shards increases with age in the Pliocene-Pleistocene, but there is no indication that element leaching (phase 2 alteration) has occurred. Post- or syn-depositional differences in preservational style are shown to have no significant bearing on tephrogeochemical homogeneity and suitability for tephrostratigraphical analysis. Overall, therefore, the volcaniclastic record is suitable for investigating medium- to long-term changes in arc geochemistry and, provided consideration is given to the potential for nonunique geochemical signatures, is suitable for erecting tephrochronological frameworks. A limited number of Pleistocene tephra correlations are suggested in furtherance of this framework goal.

Quaternary benthic foraminifers from DSDP Sites 95-612 and 95-613

The Quaternary benthic foraminifers from Leg 95 Sites 612 and 613 were examined with respect to paleoceanographic trends. Data from the two sites indicate the presence of markedly different bottom-water masses, during both glacial and interglacial periods. The dominant interglacial species at Site 612 is Uvigerinct peregrina, which is barely present in corresponding intervals at Site 613. Dominant glacial species are Elphidium excavatum and Cassidulina reniforme at Site 612 and Epistominella takayanagii at Site 613.