Detailed stratigraphic correlation of the Neogene sedimentary sequences on the Ontong Java Plateau by well logging; ODP Sites 803, 805, 806, 807, and DSDP Site 586

We used well logs, in some cases combined with shipboard physical properties measurements to make more complete profiles and to correlate between sites on the Ontong Java Plateau. By comparing sediment bulk density, velocity, and resistivity logs from adjacent holes at the same site, we showed that even subtle features of the well logs are reproducible and are caused by variations in sedimentation. With only minor amounts of biostratigraphic information, we could readily correlate these sedimentary features across the entire top of the Ontong Java Plateau, demonstrating that for most of the Neogene the top of the plateau is a single sedimentary province. We found it more difficult, but still possible, to correlate in detail sites from the top of the plateau to those drilled on the flanks. The pattern of sedimentation rate variation down the flank of the plateau cannot be interpreted as simply controlled by dissolution. Site 805, in particular, oscillates between accumulating sediment at roughly the same rate as cores on top of the Ontong Java Plateau, and accumulating sediment as slowly as Site 803, 200 m deeper in the water column. These oscillations do not match earlier reconstructions of central Pacific carbonate compensation depth variations

Variations of porosity in calcareous sediments from the Ontong Java Plateau

Based on index properties measurements made on board the JOIDES Resolution, we studied porosity changes with depth in the fairly homogeneous deep-sea calcareous sediments cored during Ocean Drilling Program Leg 130 on the Ontong Java Plateau. Using Leg 130 data, we present evidence that the rate of porosity decrease with burial in calcareous oozes and chalks is related to the depth of deposition and thus probably depends on the conditioning of calcareous sediments by winnowing or dissolution processes during the time of deposition. The ooze-to-chalk transition is not clearly reflected in porosity profiles. In the ooze-chalk sections studied (the upper 600 mbsf), mechanical compaction is most likely the major process controlling the porosity decrease with depth of burial, whereas the chalk-limestone transition (at about 1100 mbsf at Site 807) is characterized by an intense chemical compaction leading to a drastic decrease in porosity values within 100 m. In oozes and chalks, porosity values were corrected to original (uncompacted) values using site-specific empirical regression equations. When plotted vs. age, corrected porosity profiles appear to correlate quite well from site to site in the sediments deposited during the last 15 m.y. This observation has considerable implications for seismic stratigraphy. Our attempt to correlate variations in porosity (or wet-bulk density) profiles with changes in carbonate content remained unsatisfactory. Index properties changes are likely caused by changes in the foraminifer content. If this is the case, we propose that large-scale porosity fluctuations that correlate from site to site are the result of changes in the surface productivity that lead to changes in the foraminifers-to-nannofossils ratio

Seismic modelling and paleoceanography at DSDP Site 574

The analysis of high-resolution watergun seismic profiles collected in support of DSDP Leg 85 drilling reveals sev eral major, regionally traceable reflectors that can be correlated over more than 360,000 km2 in the central equatorial Pacific. Synthetic seismograms generated from shipboard physical property measurements (carefully corrected to in situ values) for DSDP Site 574 show excellent agreement with the field records; the agreement suggests that the traveltime to-depth conversion is accurate and permits the precise (± 5 m) location of reflectors in the cored section. The reflectors can be dated (±0.5 Ma) as follows: Orange, 21.5 to 22.5 Ma; Yellow, 20.5 to 21.5 Ma; Lavender, 16 to 17 Ma; Red, 13.5 to 14.5 Ma; Purple, 11 to 12 Ma; Brown, 7 to 8 Ma; and Green, 3 to 4 Ma. Similar analyses at the other Leg 85 sites result in identical ages. The reflectors are thus time surfaces; this chapter relates them to major paleoceanographic events and changes in the relative sea-level curve. The Orange and Yellow reflectors are associated with a marked increase in δ 1 3C, a major change in planktonic foraminiferal assemblages, the development of the deep Circum-Antarctic Current, and the establishment of steep thermal gradients between tropical and polar regions. This reorganization of the oceanic circulation system was probably a response to the opening of the Drake Passage, and it resulted in changes in the chemistry of tropical Pacific waters that caused the induration (and thus impedance contrasts) associated with these reflectors. The Lavender reflector is associated with a large carbonate minimum, the Chron 16 carbon shift, a widespread hiatus (NH2), major eustatic sea-level fluctuations, and a significant increase in silica deposition in the Pacific. It is not associated with 18O enrichment or climatic cooling. We conclude that this event represents an intensification in Antarc tic Bottom Water (AABW) circulation and the partitioning of silica between the Atlantic and the Pacific, caused by the introduction of North Atlantic Deep Water (NADW) in response to paleobathymetric and tectonic events. The Red re flector is associated with a subdued carbonate minimum, a widespread hiatus (NH3), a sea-level drop, significant changes in microfossil assemblages, and a major increase in δ 1 8 that has been linked with the buildup of Antarctic ice. Detailed isotopic analyses reveal that this isotopic shift occurred within an interval of 30,000 yr. and precisely at the depth of the Red reflector. The Purple reflector is associated with an extremely large carbonate minimum, a change in the style of carbonate deposition in the Pacific, a major lithologic boundary, a widespread hiatus (NH4), an increase in the provincialism be tween low and high latitudes in all planktonic microfossil assemblages, an apparent fall in eustatic sea level, an enrich ment in δ 1 8 , and a major North Atlantic reflector interpreted as representing an intensification of North Atlantic bot tom-water circulation. The Brown reflector is roughly associated with a small carbonate minimum, an enrichment in δ 1 8 , the late Miocene 1 3C depletion, a drop in the relative sea-level curve, and major faunal changes. The Green reflector is associated with a large carbonate minimum, an enrichment in δ 1 8 , a major western North Atlantic erosional event, and a widespread eastern Atlantic seismic reflector. The bulk of evidence supports correlation with the onset of Northern Hemisphere glaciation, but detailed isotopic analyses indicate that this isotopic event may be linked to the establishment of colder bottom waters without major ice-sheet development. Several types of reflectors have been identified. The reflectors in the older section result from diagenetic effects; the regionally correctable reflectors are associated with global events. In the younger (post-18 Ma) section, local reflectors are characterized by velocity contrasts, whereas regional reflectors are associated with density contrasts caused by car bonate minima. Two modes of generation of carbonate minima (and thus of reflectors) spanning the equatorial Pacific are (1) the intensification of AABW without the concurrent intensification of NADW and so without fractionation of silica between the Atlantic and the Pacific; this mode results in the less extreme carbonate minima; and (2) the intensifi cation of AABW in response to the intensification of NADW; this mode results in extreme carbonate minima and a cor relation of equatorial Pacific reflectors with North Atlantic events

Laboratory and Well-Log Velocity and Density Measurements from the Ontong Java Plateau: New in-situ corrections to laboratory data for pelagic carbonates

During Ocean Drilling Program Leg 130, sonic velocity and bulk density/porosity well logs were measured in five separate holes drilled through the sequence of pelagic carbonate oozes, chalks, and limestones that comprise the thick, continuous sedimentary cover on the Ontong Java Plateau. An internally consistent and continuous suite of shipboard laboratory velocity and sediment physical properties measurements were made from the top of each hole down through the entire logged interval. Because of the high quality of the data, extensive overlap of 500 m or more between the log and laboratory measurements at each hole, and the homogeneous nature of the sediments, we have been able to compare laboratory and in-situ log measurements in detail and to evaluate factors that alter laboratory data from their in-situ values. For measurements of bulk density and porosity, differences between laboratory and in-situ log measurements are very small and remain constant over the entire range of depths studied. We have applied a simple hydraulic rebound correction to the laboratory data that compensates for pore fluid expansion after removal of a sediment sample from in-situ conditions. The small, correctable differences between the laboratory and log data imply that mechanical rebound is significantly less than previous estimates (maximum near 5%) of rebound in pelagic carbonates. Furthermore, porosity rebound cannot be used to correct laboratory sonic velocity measurements to in-situ values. Such a rebound correction implicitly requires that laboratory and in-situ data must occupy identical fields on velocity-porosity crossplots. This condition is not met for the Ontong Java Plateau results because laboratory and in-situ logging data occupy distinct trends with little overlap between the two types of measurement. Mechanical rebound in pelagic carbonates cannot be used to correct either laboratory porosity or velocity measurements to in-situ values. The complex porosity systematics of these carbonates resulting from varying abundances of hollow foraminifer grains precluded use of an empirical correction derived from the log porosity and velocity data. Laboratory sonic velocity measurements can be corrected to in-situ values at all of the Ontong Java Plateau sites using a depth-based function derived from downhole differences between log and laboratory velocities in Hole 807A. The applicability of the depth correction implies that the effect of overburden pressure reduction on sediment elastic moduli is the most significant factor affecting laboratory velocity measurements. The depth correction to laboratory velocity measurements appears to be generally applicable to pelagic carbonate oozes and chalks of the Ontong Java Plateau, regardless of depositional depth or sediment age

Seismic stratigraphy of the Ontong Java Plateau

The Ontong Java Plateau, a large, deep-water carbonate plateau in the western equatorial Pacific, is an ideal location for studying responses of carbonate sedimentation to the effects of changing paleoceanographic conditions. These carbonate responses are often reflected in the physical properties of the sediment, which in turn control the appearance of seismic reflection profiles. Seismic stratigraphy analyses, correlating eight reflector horizons to each drill site, have been conducted in an attempt to map stratigraphic data. Accurate correlation of seismic stratigraphic data to drilling results requires conversion of traveltime to depth in meters. Synthetic seismogram models, using shipboard physical properties data, have been generated in an attempt to provide this correlation. Physical properties, including laboratory-measured and well-log data, were collected from sites drilled during Deep Sea Drilling Project Legs 30 and 89, and Ocean Drilling Program Leg 130, on the top and flank of the Ontong Java Plateau. Laboratory-measured density is corrected to in-situ conditions by accounting for porosity rebound resulting from removal of the sediment from its overburden. The correction of laboratory-measured compressional velocity to in situ appears to be largely a function of increases in elastic moduli (especially shear rigidity) with depth of burial, more than a function of changes in temperature, pressure, or density (porosity rebound). Well-log velocity and density data for the ooze intervals were found to be greatly affected by drilling disturbance; hence, they were disregarded and replaced by lab data for these intervals. Velocity and density data were used to produce synthetic seismograms. Correlation of seismic reflection data with synthetic data, and hence with depth below seafloor, at each drill site shows that a single velocity-depth function exists for sediments on the top and flank of the Ontong Java Plateau. A polynomial fit of this function provides an equation for domain conversion: Depth (mbsf) = 44.49 + 0.800(traveltime[ms]) + 3.308 × 10 4 (traveltime[ms]2 ) Traveltime (ms) = -35.18 + 1.118(depth[mbsf]) - 1.969 × KT* (depth[mbsf]2 ) Seismic reflection profiles down the flank of the plateau undergo three significant changes: (1) a drastic thinning of the sediment column with depth, (2) changes in the echo-character of the profile (development of seismic facies), and (3) loss of continuous, coherent reflections. Sediments on the plateau top were largely deposited by pelagic processes, with little significant postdepositional or syndepositional modification. Sediments on the flank of the plateau are also pelagic, but they have been modified by faulting, erosion, and mass movement. These processes result in disrupted and incoherent reflectors, development of seismic facies, and redistribution of sediment on the flank of the plateau. Seismic stratigraphic analyses have shown that the sediment section decreases in thickness by as much as 65% between water depths of 2000 m water depth (at the top of the plateau) and 4000 m (near the base of the plateau). Thinning is attributed to increasing carbonate dissolution with depth. If this assumption is correct, then changes in the relative thicknesses of seismostratigraphic units at each drill site are indicative of changes in the position of the lysocline and the dissolution gradient between the lysocline and the carbonate compensation depth. We think that a shallow lysocline in the early Miocene caused sediment thinning. A deepening of the lysocline in the late-early Miocene caused relative thickening at each site. Within the middle Miocene, a sharp rise in lysoclinal depth occurs, concurrent with a steepening of the dissolution gradient. These events result in sediment thinning at all four sites. The thicker sections in the late Miocene likely correspond to a deepening of the lysocline, and a subsequent rise in the lysocline again hinders accumulation of sediment in the very late Miocene and Pliocene

Astronomical calibration of the Ypresian timescale: implications for seafloor spreading rates and the chaotic behavior of the solar system?

Abstract. To fully understand the global climate dynamics of the warm early Eocene with its reoccurring hyperthermal events, an accurate high-fidelity age model is required. The Ypresian stage (56–47.8 Ma) covers a key interval within the Eocene as it ranges from the warmest marine temperatures in the early Eocene to the long-term cooling trends in the middle Eocene. Despite the recent development of detailed marine isotope records spanning portions of the Ypresian stage, key records to establish a complete astronomically calibrated age model for the Ypresian are still missing. Here we present new high-resolution X-ray fluorescence (XRF) core scanning iron intensity, bulk stable isotope, calcareous nannofossil, and magnetostratigraphic data generated on core material from ODP Sites 1258 (Leg 207, Demerara Rise), 1262, 1263, 1265, and 1267 (Leg 208, Walvis Ridge) recovered in the equatorial and South Atlantic Ocean. By combining new data with published records, a 405 kyr eccentricity cyclostratigraphic framework was established, revealing a 300–400 kyr long condensed interval for magnetochron C22n in the Leg 208 succession. Because the amplitudes are dominated by eccentricity, the XRF data help to identify the most suitable orbital solution for astronomical tuning of the Ypresian. Our new records fit best with the La2010b numerical solution for eccentricity, which was used as a target curve for compiling the Ypresian astronomical timescale (YATS). The consistent positions of the very long eccentricity minima in the geological data and the La2010b solution suggest that the macroscopic feature displaying the chaotic diffusion of the planetary orbits, the transition from libration to circulation in the combination of angles in the precession motion of the orbits of Earth and Mars, occurred  ∼  52 Ma. This adds to the geological evidence for the chaotic behavior of the solar system. Additionally, the new astrochronology and revised magnetostratigraphy provide robust ages and durations for Chrons C21n to C24n (47–54 Ma), revealing a major change in spreading rates in the interval from 51.0 to 52.5 Ma. This major change in spreading rates is synchronous with a global reorganization of the plate–mantle system and the chaotic diffusion of the planetary orbits. The newly provided YATS also includes new absolute ages for biostratigraphic events, magnetic polarity reversals, and early Eocene hyperthermal events. Our new bio- and magnetostratigraphically calibrated stable isotope compilation may act as a reference for further paleoclimate studies of the Ypresian, which is of special interest because of the outgoing warming and increasingly cooling phase. Finally, our approach of integrating the complex comprehensive data sets unearths some challenges and uncertainties but also validates the high potential of chemostratigraphy, magnetostratigraphy, and biostratigraphy in unprecedented detail being most significant for an accurate chronostratigraphy

Initial Reports of the Deep Sea Drilling Project, vol. 85

Covering Leg 85 of the cruises of the Drilling Vessel Glomar Challenger Los Angeles, California, to Honolulu, Hawaii March-April 1982. Includes six chapters: 1. INTRODUCTION: BACKGROUND AND EXPLANATORY NOTES, DEEP SEA DRILLING PROJECT LEG 85, CENTRAL EQUATORIAL PACIFIC 2. SITE 571 3. SITE 572 4. SITE 573 5. SITE 574 6. SITE 57

An astronomically dated record of Earth's climate and its predictability over the last 66 million years.

Much of our understanding of Earth's past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states-Hothouse, Warmhouse, Coolhouse, Icehouse-are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics

Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector

The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13