Tertiary and Quaternary calcareous nannoplankton biostratigraphy of ODP Leg 112 holes

Positions of all cores recovered during Ocean Drilling Program (ODP) Leg 112 off Peru are shown in the standard calcareous nannoplankton zonation. Stratigraphic and regional occurrences and preservation of calcareous nannoplankton are discussed for all sites, and fossil lists are presented for selected samples. Late Miocene to Holocene nannoplankton assemblages in the upwelling systems off Peru and scattered blooms, especially of Gephyrocapsa species and Helicosphaera carteri, are described. Scyphosphaera assemblages found in late Miocene Zone NN9 {Discoaster hamatus Zone) at Site 684 are compared with similar assemblages from Gabon on the west coast of Africa. Remarkable subsidence is indicated by early and middle Eocene nearshore and shallow-water nannoplankton assemblages for Sites 682, 683, and 688. Besides several local hiatuses, major regional hiatuses were noted at Site 682 (upper Eocene, uppermost middle Eocene, and part of the lower and middle Oligocene missing), Site 683 (uppermost middle Eocene to lower part of the middle Miocene missing), and Site 688 (part of the middle Eocene, uppermost middle Eocene to upper Oligocene, and parts of the lower and middle Miocene missing).

Consolidation tests of ODP Leg 113 samples

Examination of the geotechnical characteristics of Weddell Sea, Maud Rise, and South Orkney microcontinental margin sediments recovered during ODP Leg 113 reveals that the reduction in porosity (consolidation) of the siliciclastic, calcareous, and diatomaceous sediments is primarily a process governed by vertical stresses created by overburden. The initial porosity of the sediments in these areas is governed by the amount of diatoms present. The more diatoms, the higher the porosity. Surficial diatom-rich sediments are everywhere overconsolidated. This is attributed to the strong microfabric created by the diatoms, calcareous and clay particles. The deeper diatom-free sediments of Maud Rise range from slightly underconsolidated to normally consolidated. The silty clays and clays of the Weddell Sea and South Orkney margin are underconsolidated. The degree of underconsolidation of these sediments is similar to that determined in a number of different locations throughout the world's oceans. The very low permeability of the Weddell Sea and South Orkney margin sediments appears to account for this underconsolidation.

Bromine and iodine concentrations in sediments and pore fluids of ODP Leg 112

At the Peruvian convergent margin, two distinct pore fluid regimes are recognized from differences in their Cl- concentrations. The slope pore fluids are characterized by low Cl- concentrations, but elevated Br- and I- concentrations due to biogenic production. The shelf pore fluids exhibit elevated Cl- and Br- concentrations due to diffusive mixing with an evaporitic brine. In the slope pore fluids, the Br-, I-, and NH4+ concentrations are elevated following bacterial decomposition of organic matter, but the I- concentrations are in excess of those expected based on mass balance calculations using NH4+ and Br- concentrations. The slope sediment organic matter, which is enriched in iodine from oxidationreduction processes at the oxygenated sediment-water interface, is responsible for this enrichment. The increases in dissolved I- and the I- enrichments relative to NH4+ and Br- correlate well with sedimentation rates because of differential trapping following regeneration. The pore-fluid I-/Br- ratios suggest that membrane ion fiitration is not a major cause of the decreases in Cl- concentrations. Other possible sources for low Cl- water, including meteoric water, clathrate dissociation, and/or mineral dehydration reactions, imply that the diluting component of the slope low-Cl- fluids has flowed at least 1 km through the sediment. The low bottom-water oxygenation in the shelf is responsible for the low (if any) enrichment of iodine in the shelf sediments. Fluctuations in bottom-water oxygen concentrations in the past, however, may be responsible for the observed variations in the sediment I/Br ratios. Comparison of Na+/Cl- and Br-/Cl- molar ratios in the pore fluids shows that the shelf high-Cl- fluid formed from mixing with a brine that formed from seawater concentrated by twelve to nineteen times and probably was modified by halite dissolution. This dense brine, located below the sediment sections drilled, appears to have flowed a distance >500 km through the sediment.

Characteristics of ice-rafted pebbles from ODP Leg 178 holes

Pebbles (>10 mm) sampled from three drill sites on the continental rise west of the Antarctic Peninsula during Ocean Drilling Program Leg 178 were classified by shape and roundness. In addition, pebble lithology and surface texture were visually identified. To increase the pebble sample number to 331, three sites that were drilled 94 to 213 km from the continental shelf edge were integrated into the data set using magnetostratigraphy for core correlation. Pebbles were compared in three groups defined by the same stratigraphic intervals at each site: 3.1-2.2 Ma (late Pliocene), 2.2-0.76 Ma (late Pliocene-late Pleistocene), and 0.76 Ma to the Holocene. Pebble lithologies originate from sources on the Antarctic Peninsula margin. Most pebbles are metamorphic and sedimentary pebbles are rare (<6%), whereas mafic volcanic and intrusive igneous lithologies increase in abundance upsection. Pebbles from 3.1 to 0.76 Ma, plotted on sphericity-roundness diagrams, indicate original transport as basal and supraglacial/englacial debris. Pebbles are abundant and of diverse lithology. From 0.76 Ma to the present, the number of pebbles is low and their shape characteristics indicate they originated as basal debris. Observed changes in ice-rafted pebbles can be explained by growth of an ice sheet and inundation of the Antarctic Peninsula topography by ice ~0.76 Ma. Prior to this, outlet and valley glaciers transported debris at high levels within and at the base of the ice. The mass accumulation rate of sand fluctuates and includes rounded quartz grains. Ice-sheet growth may have been accompanied by overall cooling from subpolar to polar glacial regimes, which halted meltwater production and enhanced the growth of ice shelves, which consequently reduced sediment supply to icebergs.

Abundance estimates of diatoms in ODP Leg 207 sediments

Twenty-eight core catcher samples were provided to the author by the shipboard party for evaluation of fossil diatoms. Samples are from Ocean Drilling Program Leg 207 Holes 1257A, 1257B, 1257C, and 1258A. The samples range from 50 to 112 meters below the seafloor (mbsf) at Site 1257 and from ~22 to 60 mbsf at Site 1258. At Site 1257, samples range in age from middle Eocene (foraminifer Zone P14-13) to late Paleocene (mid-foraminifer Zone P4). At Site 1258, the samples range from middle Eocene (foraminifer Zone P11) to early Eocene (foraminifer Zone P5) according to the preliminary biostratigraphic reports (Erbacher, Mosher, Malone, et al., 2004, doi:10.2973/odp.proc.ir.207.2004). All samples were processed at Florida State University Antarctic Research Facility. Treatment included acidization and sieving through stacked 38- and 63-µm sieves. Strew slides were made from each fraction and the catcher pan. A Zeiss Photoscope II microscope was used for examination of the prepared slides. Samples from Holes 1257A, 1257B, and 1257C showed that most of the samples are barren of siliceous microfossils. Only a few radiolarians and fragments of radiolarians were observed.

Mineral composition and experimental results from XRD analyses of sediments from ODP Leg 190 sites

X-ray diffraction analyses of the clay-sized fraction of sediments from the Nankai Trough and Shikoku Basin (Sites 1173, 1174, and 1177 of the Ocean Drilling Program) reveal spatial and temporal trends in clay minerals and diagenesis. More detrital smectite was transported into the Shikoku Basin during the early-middle Miocene than what we observe today, and smectite input decreased progressively through the late Miocene and Pliocene. Volcanic ash has been altered to dioctahedral smectite in the upper Shikoku Basin facies at Site 1173; the ash alteration front shifts upsection to the outer trench-wedge facies at Site 1174. At greater depths (lower Shikoku Basin facies), smectite alters to illite/smectite mixed-layer clay, but reaction progress is incomplete. Using ambient geothermal conditions, a kinetic model overpredicts the amount of illite in illite/smectite clays by 15%-20% at Site 1174. Numerical simulations come closer to observations if the concentration of potassium in pore water is reduced or the time of burial is shortened. Model results match X-ray diffraction results fairly well at Site 1173. The geothermal gradient at Site 1177 is substantially lower than at Sites 1173 and 1174; consequently, volcanic ash alters to smectite in lower Shikoku Basin deposits but smectite-illite diagenesis has not started. The absolute abundance of smectite in mudstones from Site 1177 is sufficient (30-60 wt%) to influence the strata's shear strength and hydrogeology as they subduct along the Ashizuri Transect.

Neogene silicoflaggelates in ODP Leg 104 holes

A quantative study was made of silicoflagellates recovered from Sites 642 (lower Miocene-upper Pliocene), 643 (lower Miocene-upper Miocene), and 644 (upper Pliocene-Quaternary) on the Voring Plateau. Although disconformities are present in these sequences, they represent a much more complete record of the Neogene than was recovered previously in the Norwegian Sea by DSDP Leg 38. Silicoflagellates are rare or absent for glacial sequences younger than 2.65 Ma, and generally sparse and poorly preserved in the lower upper Pliocene and upper Miocene. Lower and middle Miocene assemblages are diverse and generally well preserved. Temporal changes in the silicoflagellate assemblage are indicative of major paleoceanographic changes in the Norwegian Sea. A regional zonation for the Neogene of the Norwegian Sea is proposed, consisting of eleven zones: Naviculopsis lata Zone, N. quadrata Zone (emended), N. ponticula Zone (emended), Distephanus speculum hemisphaericus Zone (new), Caryocha ernestinae Zone (new), Bachmannocena circulus var. apiculata/Caryocha Zone (new), Distephanus crux scutulatus Zone (new), Bachmannocena diodon nodosa Zone (new), Distephanus boliviensis Zone (new), Ds. jimlingii Zone (elevated from subzonal to zonal status) with Subzones a and b (new), and Ds. speculum Zone (new). The ranges and abundances of over 100 species and morphotypes are tabulated.

Organic carbon, freely extractable lipids and ketone recovery of ODP Leg 199 sediments

Six samples from Sites 1219 and 1221 ranging in age from early Eocene to early Oligocene were analyzed for freely extractable lipids to determine whether the low organic carbon (Corg) sediments of the Eocene equatorial Pacific (Corg content typically 0.03%) are appropriate for biomarker studies. Only one sample from the Oligocene equatorial Pacific (Sample 199-1219A-13H-3, 50-54 cm) contained any biomarkers of interest to paleoceanography. The only lipids identified in the remaining samples appear to be contaminants from drilling or subsequent handling. Sample 199-1219A-13H-3, 50-54 cm, contained alkenone biomarkers specific to haptophyte algae that are used for estimating past mean annual sea-surface temperature (maSST). If the Holocene calibration of maSST is appropriate for the Oligocene, the estimated equatorial temperature is >=28.3°C, or at least 3°C warmer than modern equatorial maSST at a similar longitude.

Interstitial-water chemistry of ODP Leg 119 sites

Ocean Drilling Program inorganic geochemistry procedures routinely overlook more than 99% of the sediment column. Present and past biogeochemical reactions alter the sediment record; however, most of these reaction zones are bypassed by the normal methods where samples are collected every 30 m. A new approach to increase resolution was introduced during Leg 119. Ten milliliters of sediment provided interstitial-water samples for ammonia, silica, sulfate, magnesium, and calcium analyses. The new method introduced some systematic differences in concentrations, as well as some decrease in precision. A number of advantages, however, may warrant using the method in some instances. In cases where routine interstitial-water data showed anomalous results, core sections were retrieved from the storage facility and resampled. The new high-resolution procedure was used to provide water samples in cases were water contents were low and routine squeezing could not recover pore water.

Magnetic susceptibility anisotropy in deformed sediments of ODP Leg 110

The anisotropy of magnetic susceptibility documents the generation of tectonically produced fabrics in sediments that macroscopically show no evidence of this disruption. The fabric observed in initial accretion is largely produced by overprinting of the original sedimentary susceptibility anisotropy by an E-W horizontal tectonic shortening and vertical extension. The response of the sediments to stress during initial accretion is variable, particularly near the sediment surface, and appears to reflect the inhomogeneous distribution of strain rate in the overthrust sequence. The susceptibility anisotropy of sediments possessing scaly fabric is consistent with the strong orientation of Phyllosilicates seen in thin section, producing a Kmin normal to the scalyness. The slope sediments deposited on the accreted sequence are also affected by tectonic shortening. The accreted sequences at Sites 673 and 674 show a complex history of fabric modification, with previous tectonic fabrics overprinted by later fabric modifications, pointing to continued tectonic shortening during the accretion process. The form of the susceptibility anisotropy axes at Sites 673 and 674 is consistent with NESW shortening, probably reflected in the NW-SE surface expression of the out-of-sequence thrusts. The susceptibility anisotropy appears to document a downhole change in the trend of shortening from E to W at the surface to more NESW at depth, probably as a result of the obliquely trending basement ridge, the Tiburon Rise.

Distribution of radiolarians from ODP Leg 128 holes

The analysis of radiolarians from Japan Sea subsurface sediments recovered during Leg 128 of the Ocean Drilling Program reveals that a warm-water assemblage similar to that of the North Pacific was replaced by unique post-middle Miocene faunas probably as a result of the restriction of Oceanographic circulation. The modern fauna was gradually established only in the Pleistocene. No attempt was made to establish the radiolarian zonation because of low species diversity and the absence of generally recognized index forms in the North Pacific. In the diagenetically altered quartz section, however, a radiolarian assemblage correlative to the middle Miocene Cyrtocapsella tetrapera Zone of western Honshu was identified from Hole 799B.

Volume of natural gas within gas-hydrate and free-gas occurrences in ODP Leg 164 sites

Leg 164 of the Ocean Drilling Program was designed to investigate the occurrence of gas hydrate in the sedimentary section beneath the Blake Ridge on the southeastern continental margin of North America. Sites 994, 995, and 997 were drilled on the Blake Ridge to refine our understanding of the in situ characteristics of natural gas hydrate. Because gas hydrate is unstable at surface pressure and temperature conditions, a major emphasis was placed on the downhole logging program to determine the in situ physical properties of the gas hydrate-bearing sediments. Downhole logging tool strings deployed on Leg 164 included the Schlumberger quad-combination tool (NGT, LSS/SDT, DIT, CNT-G, HLDT), the Formation MicroScanner (FMS), and the Geochemical Combination Tool (GST). Electrical resistivity (DIT) and acoustic transit-time (LSS/SDT) downhole logs from Sites 994, 995, and 997 indicate the presence of gas hydrate in the depth interval between 185 and 450 mbsf on the Blake Ridge. Electrical resistivity log calculations suggest that the gas hydrate-bearing sedimentary section on the Blake Ridge may contain between 2 and 11 percent bulk volume (vol%) gas hydrate. We have determined that the log-inferred gas hydrates and underlying free-gas accumulations on the Blake Ridge may contain as much as 57 trillion m**3 of gas.

Magnetic stratigraphy of ODP Leg 133 sites

This study is a synthesis of paleomagnetic and mineral magnetic results for Sites 819 through 823 of Ocean Drilling Program (ODP) Leg 133, which lie on a transect from the outer edge of the Great Barrier Reef (GBR) down the continental slope to the bottom of the Queensland Trough. Because of viscous remagnetization and pervasive overprinting, few reversal boundaries can be identified in these extremely high-resolution Quaternary sequences. Some of the magnetic instability, and the differences in the quality of the paleomagnetic signal among sites, can be explained in terms of the dissolution of primary iron oxides in the high near-surface geochemical gradients. Well-defined changes in magnetic properties, notably susceptibility, reflect responses to glacio-eustatic sea-level fluctuations and changes in slope sedimentation processes resulting from formation of the GBR. Susceptibility can be used to correlate between adjacent holes at a given site to an accuracy of about 20 cm. Among-site correlation of susceptibility is also possible for certain parts of the sequences and permits (tentative) extension of the reversal chronology. The reversal boundaries that can be identified are generally compatible with the calcareous nannofossil biostratigraphy and demonstrate a high level of biostratigraphic consistency among sites. A revised chronology based on an optimum match with the susceptibility stratigraphy is presented. Throughout most of the sequences there is a strong inverse correlation both between magnetic susceptibility and calcium carbonate content, and between susceptibility and d18O. In the upper, post-GBR, sections a more complicated type of magnetic response occurs during glacial maxima and subsequent transgressions, resulting in a positive correlation between susceptibility and d18O. Prior to and during formation of the outer-reef barrier, the sediments have relatively uniform magnetic properties showing multidomain behavior and displaying cyclic variations in susceptibility related to sea-level change. The susceptibility oscillations are controlled more by carbonate dilution than by variation in terrigenous influx. Establishment of the outer reef between 1.01 and 0.76 Ma restricted the supply of sediment to the slope, causing a four-fold reduction in sedimentation rates and a transition from prograding to aggrading seismic geometries (see other chapters in this volume). The Brunhes/Matuyama boundary and the end of the transition period mark a change to lower and more subdued susceptibility oscillations with higher carbonate contents. The major change in magnetic properties comes at about 0.4 Ma in the aggrading sequence, which contains prominent sharp susceptibility peaks associated with glacial cycles, with distinctive single-domain magnetite and mixed single-domain/superparamagnetic characteristics. Bacterial magnetite has been found in the sediments, particularly where there are high susceptibility peaks, but its importance has not yet been assessed. A possible explanation for the characteristic pattern of magnetic properties in the post-GBR glacial cycles can be found in terms of fluvio-deltaic processes and inter-reefal lagoonal reservoirs that develop when the shelf becomes exposed at low sea-level.