Bottom Conditions Research Articles

Paleoredox conditions of bottom water in the northern Indian Ocean since 39 ka

Ocean circulation has undergone significant changes during the glacial and interglacial periods. The redox condition at the sediment-water interface is mainly regulated by export productivity and ventilation of abyssal water mass. The changes in the redox condition associated with bottom water circulation in the Indian Ocean are still unclear. The present study assessed multi redox proxies (Mn/Ti, Mo/Ti, U/Ti, V/Ti, Ni/Ca, Cu/Ca, MnEF, UEF, and VEF) and Corg in the sediment core collected from the Arabian Sea (NW Indian Ocean) to investigate the past variations in bottom water redox condition. The bottom water in the Arabian Sea is presently bathed with the Lower Circumpolar Deep Water (LCDW), consisting of a fraction of both North Atlantic Deep Water (NADW) and Antarctic Bottom Waters (AABW). Our results show significant changes in oxygenation conditions in response to changes in ocean circulation. The present study revealed that bottom water in the northern Indian Ocean was more oxic during LGM than the deglacial period. We interpret the variability in the contribution of NADW and AABW influenced the redox condition at the study location. Comparing the current study results with previously reported Nd isotopes suggests that the contribution of AABW to the Indian Ocean increased during LGM, resulting in a higher oxic condition in LCDW.

Ryazanian (Berriasian) molluscs and biostratigraphy of the Dutch and Norwegian North Sea area (south of Viking Graben)

AbstractHerein, Ryazanian (Berriasian) macrofossils from three well cores in the Central Graben (wells B18-02, L06-02, The Netherlands) and on the Jæren High (well 7/7-2, Norway) in the southern North Sea region are described. Macrofossils are mainly represented by buchiid bivalves (Buchia volgensis) and ammonites (Surites,LynniaandPraetollia?). The genusLynniais recorded for the first time outside its topotypical area, and its systematic position and stratigraphic ranges are discussed. Additionally, the studied core sections yielded coleoid remains and a single limid bivalve. Based on the stratigraphic ranges of key ammonite genera (Lynnia, SuritesandBojarkia), the zonation of the Ryazanian stage is reconsidered. Uppermost Volgian to Ryazanian ammonite faunas are quite consistent and diverse but showing a higher degree of similarity throughout the Panboreal Superrealm as compared to those from rest of the Upper Volgian and the Middle Volgian.Buchia volgensisis the only species known from the southern North Sea and East Anglia, which is in strong contrast to the high diversity ofBuchiain East Greenland and the remainder of the Boreal Realm. We hypothesise that such differences in the distribution of ammonites and bivalves in general, and the absence of buchiid species other thanBuchia volgensissouth of East Greenland in particular, are the result of anoxic bottom water conditions in the southern Viking Strait. The unusually wide geographic range ofB. volgensis, which is known from such distant areas as Mexico and the Crimea, suggests a potential higher tolerance of this species to adverse conditions.

Effect of high temperature and high pressure on the biodegradability and biotoxicity of typical additives in drilling fluid

Under the high-temperature and high-pressure (HTHP) conditions in the ground, the environmental features of drilling fluid additives may change to some extent. But the relevant information of the influence of HTHP environment on drilling fluid additives is very limited. Four typical additives, namely, sulfonate asphalt (SEB), potassium polyacrylamide (KPAM), potassium humate (KHm) and xanthan gum (XG), were treated for 40 min under two typical bottom hole conditions of 7 MPa, 90 °C and 11 MPa, 120 °C. The biodegradability and biotoxicity of these additives before and after treatments were determined. The structures of the four additives were also analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA) and gas chromatography-mass spectrometry (GC-MS). The results revealed no remarkable difference in biotoxicity and biodegradability of each sample between the two conditions. SEB became nontoxic from microtoxic after being treated with HTHP, with the value of EC50 notably increased from 2463 to 33,398 mg L−1, which might be due to the relative increase of light components observed by GC-MS. Original XG was nontoxic (EC50 = 21,000 mg L−1) and easily biodegraded (BC ratio = 0.469), but HTHP treatments increased the toxicity (EC50 = 5701 mg L−1) and decreased the biodegradability (BC ratio = 0.02), which could be attributed to the reduce of the C–OH/C–O–C bonds observed by FT-IR and XPS spectra. Both KPAM and KHm were midtoxic and had low degradability, and only KPAM became highly toxic (EC50 < 100 mg L−1) after HTHP treatments, which might result from the slight increase in the relative peak area of the amide group. The results could provide preliminary insights into the mechanism of how the HTHP conditions impacted the pollution properties of the additives and pave a new and facile route for the screening of environmentally friendly additives, and consequently mitigate the pollution from the source in the oil and gas exploitation industry.

Organic matter and metal loadings influence the spatial gradient of the benthic bacterial community in a temperate estuary

Omics-based monitoring using bacterial marker genes can provide valuable mechanistic insights into the functioning of ecosystems. Here, we present a 2.5-year dataset with monthly sampling of sediment genomic bacterial DNA (n = 160) in a temperate, urbanised estuary in Tasmania, Australia. Molecular data were collected with physical and biochemical bottom water data, sediment organic matter and metal concentrations. Our study supports evidence that sediment-specific variables (organic matter composition) have a larger influence over the sediment bacterial community than do large-scale environmental conditions (seasonal water changes). The observed spatial and temporal differences are interesting, given the significant seasonal variation in bottom water data (e.g. temperature differences of up to 10°C and 3-fold increases for NOx concentrations in the bottom water between summer and winter months). Whereas bottom water parameters changed seasonally, metal concentrations in the sediments did not show seasonal variations. Metal concentrations explained a larger variance in the bacterial community among sites but not on an estuary-wide scale. The disconnect between environmental bottom water conditions and the sediment bacterial communities has important ramifications, because it indicates that seasonal changes have little effect on the compositional dynamics of sediment microbes and may, therefore, be difficult to trace with marker-gene surveys.

Analysis of Horizontal Dynamic Response of a Single Pile in Layered Foundations Based on the Timoshenko–Pasternak Model

To compensate for the deficiencies of the conventional Euler–Bernoulli beam‐dynamic Winkler foundation model in analyzing the horizontal dynamic response of a single pile, in this paper, the Timoshenko–Pasternak model, which considers both the soil shear effect and pile shear deformation, is established to reveal the pile‐soil dynamic interaction accurately. Based on Timoshenko beam theory and Pasternak foundation theory, the pile horizontal vibration control equation considering pile shear deformation and the soil shear effect is derived based on D’Alembert’s principle. On this basis, the transfer matrix method is applied to consider the layering characteristics of the soil, and the dynamic complex impedance frequency domain analytical solution of the pile top is obtained by using the initial parameter method combined with the pile bottom boundary conditions. A comparison with the existing model solution is carried out to verify the correctness and reasonableness of the model in this paper; finally, the parameters of the pile characteristics and soil properties around the pile are analyzed. The results show that (1) the pile bottom boundary condition and pile length have almost no effect on the pile top impedance after the single pile reaches the critical value of the length‐to‐diameter ratio. (2) The trend of pile top impedance becomes increasingly evident with increasing dimensionless frequency. (3) The pile top impedance increases with the decrease in the pile‐soil elastic modulus ratio, and the changing trend becomes increasingly apparent; meanwhile, the influence of the elastic modulus of the surface soil on the pile top impedance is much more significant than the influence of the underlying soil on it.

Numerical study of nonlinear wave flow past vertically submerged plate over uneven bottom

This present study investigates the horizontal wave force and overturning moment on a submerged vertically thin rectangular plate on a free surface (z = 0 m) over a flat and uneven bottom structure under various wave steepness conditions and relative openings in the numerical wave tank (NWT) modelled using ANSYS Fluent software. The interface of the fluids is tracked using the volume of fluid (VOF) method. At the inlet of the NWT, the inflow velocity method is followed to produce the desired waves and at the end, numerical damping is used to minimize the wave reflection. Further, the effects of wave characteristics, relative openings, and uneven bottom conditions on the horizontal wave force and overturning moment are analyzed in the intermediate water depth. The horizontal wave force (Fx) and overturning moment (My) on the vertical plate are registered higher with case 3 (α4 = 37.5%) for different wave steepness attributed to the higher slope of the bottom structure. The present work also incorporates the development of a plate type wave energy converter (WEC) to harvest renewable wave energy from the ocean.

Applicability of high-order unidirectional internal solitary wave theoretical model

Internal solitary waves exist widely in the oceans, and their generations, propagation evolutions, and dissipations have profound effects on the ocean environment, topography, and marine structures. Typically, two basic theoretical models are now being developed to govern the evolutions of internal solitary waves at the interface of two immiscible inviscid fluids. One is a unidirectional wave propagation model described by the KdV (Korteweg-de Vries) equation, and the other is a bidirectional wave propagation model depicted by the Miyata-Choi-Camassa (MCC) equation. Neither of them, however, can effectively characterize the course of the evolution of large-amplitude internal solitary wave. In this paper, a modified unidirectional internal solitary wave model is established by adjusting the coefficients of the original unidirectional model. The adjusted coefficients are determined through asymptotic analysis by matching with the MCC model. The efficacy of the modified coefficients is investigated by comparing the modified model with the original model. The experiments on the generation of internal solitary waves with varying amplitudes are carried out by comparing the internal solitary wave solution of the modified equation. It is shown that the modified model is suitable for describing the waveform of internal solitary waves with small, medium, and large amplitudes within the limiting amplitude of the MCC model. By quantitatively analyzing the agreement of the effective wavelength, wave speed, and waveform of steady-state internal solitary waves between the unidirectional model and the MCC model, the applicability of the modified model in characterization of the properties of steady-state internal solitary waves is further investigated. In addition, the stability of unidirectional theoretical model is analyzed for simulating the propagation of large-amplitude internal solitary wave under flat bottom condition. It is found that the unidirectional model is suitable for initiating its own internal solitary solution provided that the numerical scheme is stable. It is shown that the modified unidirectional model can be used to characterize large-amplitude internal solitary waves, and is also expected to be applied to the study of marine structure hydrodynamics.

The effect of paleo-environment on hydrocarbon generation potential: Example from Vaca Muerta Formation, Neuquén Basin, Argentina

A 137-m continuous core from the Jurassic-Early Cretaceous marine derived oil shale with the maturity Ro about 0.7 %, representing the oil window in the Vaca Muerta Formation, Neuquén Basin, Argentina, was examined using geological, mineralogical, petrographic, and geochemistry techniques. Three distinct intervals were identified within the core: the upper carbonate-rich section with intense bioturbation, indicating dysoxic to oxic conditions that resulted in poor organic matter preservation; a middle section with decreasing carbonate content, suboxic bottom conditions, and higher organic matter content; and a lower section with higher detrital input and low carbonate content, suboxic to anoxic water conditions, and enhanced preservation of organic matter. Based on the presence of indicator fossils and geochemical parameters, a general trend of increasing organic matter content with lower paleo-oxygen levels was observed. The proportion of solid bitumen within organic matter increases with decreasing oxygen content, suggesting that organic matter deposited in anoxic conditions is more prone to transformation and hydrocarbon generation. There is a negative impact of increasing paleo-oxygen levels on the quantity and quality of organic matter, represented by its potential to generate hydrocarbons.

Assessing controls on organic matter enrichments in hemipelagic marls of the Aptian-Lower Albian Blue Marls of the Vocontian Basin (France): an unexpected variability observed from multiple “organic-rich” levels

The Marnes Bleues Formation from the Vocontian Basin (Southeastern France) shows many dark-colored levels, some concomitant to oceanic anoxic events OAE1a (the so-called Goguel Level) and OAE1b (the Jacob, Kilian, and, above all, Paquier levels). These levels are usually referred to as being organic-rich; they are scattered through a thick, rather homogeneous, succession of marls, that is poor in organic matter (OM). Through a multi-parameter approach, the dark levels from the Aptian-Albian were characterized. Our results show that all dark levels are not OM-rich and that the dark levels exhibit variable characteristics, such as OM nature (marine vs. continental), sedimentation and accumulation rates, redox conditions, surface-water productivity and relative sea level, but they all show low to modest enrichments in OM. Furthermore, all the levels share in common the fact that they formed under conditions of normal to low productivity and oxic to suboxic conditions. Thus, our results strongly suggest that, in the absence of high productivity and anoxic bottom conditions, the other factors reputed to favor OM accumulation only led to sporadic and low enrichments in organic contents. It is as if such factors could only enhance OM accumulation but could not induce it alone. What was true for the Vocontian Basin may be extended to other settings, regardless of their time of deposition or location.

Analysis and Optimization of Blasting Practices at the Sangaredi Mine

Generally, the Mos hardness of bauxite is 2.5 to 3.5. According to the specific conditions of the Sangaredi bauxite deposit, that is, the rock hardness coefficient is between 3 and 6, and there is a clayey zone in the bauxite mining area, it is necessary to carry out blasting work before mining. This article mainly analyzes and optimizes the blasting practice of the Sangaredi open pit bauxite mine. The subject was finally extended to the reduction of nuisances due to blasting, that is to say essentially due to vibrations: this presupposed a study around the vibration data available, and the proposal of methods to limit these vibrations. The bottom conditions of the Sangaredi bauxite ore zone are studied. Bauxite reserves are very rich and the market is huge. The analysis of mine blasting practices, mainly the types of explosives, the selection and analysis of explosives and blasting equipment and choosing the mode of longitudinal blasting, the link of the blasting site of the mining area, further study the optimization of mining blasting practice, the choice of drilling and process to determine reasonable blasting parameters, which improving the drilling method. The experimental results show that this optimization scheme improves efficiency blasting of the bauxite mine but also promotes an increase in production.

Uranium-thorium isotope systematics of cold-seep carbonate and their constraints on geological methane leakage activities

Marine methane hydrates are a huge and dynamic carbon reservoir found mainly at the continental margins, and their stability might be affected by climate-associated pressure and temperature changes on the seafloor. Reconstructing the growth history of cold-seep carbonates, which formed during seafloor methane leakage, could help to constrain methane hydrate stability in the geological past. However, U-Th isotope systematics of these complex carbonate cements have not yet been systematically investigated on the micro-scale, leaving uncertainties in the U-series geochronology which is commonly applied to date the seep carbonates. In this study, we have developed multiple in-situ analytical methods, including U-Th isotope analysis by laser ablation MC-ICPMS, elemental concentration mapping by laser ablation ICPMS, as well as organic distribution mapping by Raman Spectroscopy, to provide insights into the U-series geochemistry and geochronology for the different types of cold-seep carbonates. Our result demonstrates that 238U and 232Th of these carbonates are dominantly derived from seawater and detrital particles, respectively. As the [230Th/232Th] (activity ratio) of micro-domains with high [232Th/238U] is negligibly affected by U decay, we have directly determined the initial [230Th/232Th] of the cold-seep carbonates which is 0.7 ± 0.1 (2 SD, n = 12). In general, U-series isotopes show closed-system behavior within our studied analytical precision in the interior of the seep cements, and the initial [230Th/232Th] derived from the isochron approach is consistent with the in-situ direct determination. A notable exception is a calcitic pipe sample with highly enriched U in its rim which has also experienced post-depositional mobilization. Our method is then applied to a large set of seep carbonate samples from the upper continental slope of the northern South China Sea (SCS). The obtained U-series ages provide evidence that cold seep was likely continuously active since at least ∼72 ka in the northern SCS, but the timing and duration of methane leakage vary between different sites within this region. While the upper continental slope methane hydrates are highly susceptible to destabilization under changing bottom water conditions, our extensive dating on seep carbonates from the SCS further indicates that bottom water P-T conditions could exert contrasting impacts on methane hydrate stability at different depths within the same geological setting. Overall, the in-situ U-series geochronological method developed in our study has the potential to date cold-seep carbonates efficiently and reliably, offering new opportunities to probe into the history of methane leakage in the late Quaternary.

Carbon cycle dynamics and ecology revealed by the carbon isotopic composition of single organic microfossils during the Late Devonian Biotic Crisis.

We apply a new approach for the δ13 C analysis of single organic-walled microfossils (OWM) to three sites in the Appalachian Basin of New York (AB) that span the Late Devonian Biotic Crisis (LDBC). Our data provide new insights into the nature of the Frasnian-Famennian carbon cycle in the AB and also provide possible constraints on the paleoecology of enigmatic OWM ubiquitous in Paleozoic shale successions. The carbon isotope compositions of OWM are consistent with normal marine organic matter of autochthonous origins and range from -32 to -17‰, but average -25‰ across all samples and are consistently 13 C-enriched compared to bulk sediments (δ13 Cbulk ) by ~0-10‰. We observe no difference between the δ13 COWM of leiospheres (smooth-walled) and acanthomorphic (spinose) acritarch OWM, indicating that our data are driven by ecological rather than taxonomic signals. We hypothesize that the offset between δ13 COWM and δ13 Cbulk is in part due to a large δ13 C gradient in the AB water column where OWM utilized relatively 13 C-enriched dissolved inorganic carbon near the surface. Thus, the organisms producing the balance of the total organic carbon were assimilating 13 C-depleted C sources, including but not limited to respired organic carbon or byproducts of fermentation. We also observe a systematic decrease in both δ13 COWM and δ13 Cbulk of 3‰ from shoreward to open-ocean facies that may reflect the effect of 13 C-enriched dissolved inorganic carbon (DIC) derived from riverine sources in the relatively enclosed AB. The hypothesized steep carbon isotope gradient in the AB could be due to a strong biological pump; this in turn may have contributed to low oxygen bottom water conditions during the LDBC. This is the first time single-microfossil δ13 Corg analyses of eukaryotes have been directly compared to bulk δ13 Corg in the deep-time fossil record.

Using the acoustic emission method for testing aboveground vertical storage tank bottoms

This paper presents use of the acoustic emission (AE) method for diagnostic testing of aboveground vertical storage tank bottoms. This method allows evaluation and location of active corrosion damage of bottom material and micro-leaks in the tested object. To prepare a tank for AE testing, it is not necessary to drain the storage medium, which provides a high state of security with significant diagnosis and operational cost savings. The methodology and AE test results carried out on three storage tanks of crude oil are presented. Data recorded during the measurements have been analyzed. The conclusions drawn from this analysis give the location of detected AE sources and an evaluation of the integrity of the tank bottoms. Assessment of detected acoustic sources allowed for classification of tank bottom surface conditions and estimation of the recommended operational time until the next required test.

Retention Pool As Alternative For Flood Control Case Study Of Bapertarum Housing, Sumenep Regency

Indonesia is a water country with thousands of rivers and hundreds of deep seas. This causes Indonesia to become a country that is very prone to flooding. But basically, there are several factors that cause this to happen, namely: natural events, drainage damage and environmental degradation caused by human activity itself. Geographically, Bapetarum Housing is an area located in a rainwater catchment area so that it is prone to flood events. High rainfall intensity can cause flood inundation as high as 30 cm. The purpose of this study is to calculate the adequacy of the retention pond to cope with flooding. The procedure for collecting research data begins with analyzing the flood, namely primary and secondary data. Meanwhile, the data analysis techniques used are planning rain analysis, rainfall intensity, flood discharge analysis, retention pond capacity. The retention pond capacity is sufficient because the dimensions of the retention pond are larger than the volume of the retention pond capacity when the flood is 6750m3&gt;6447m3. The retention pond is planned in the downstream area of the residential river with a pool area of 50 x 40 meters and a depth of 4.5 m. The bottom condition of the pond is saturated because it is always inundated with water, the infiltration rate is constant (fc). The constant infiltration for clayey soil type is 0.5 m/day, the infiltration volume rate that occurs at the bottom of the pond is 179 m3/hour, the volume is below the threshold 8283.21 m3, infiltration time is 46 hours.

Photosynthetic Production Determines Bottom Water Oxygen Variations in the Upwelling Coastal South China Sea Over Recent Decades

Dissolved oxygen (DO) in seawater is fundamental to marine ecosystem health. How DO in coastal upwelling areas responds to upwelling intensity under climate change is of particular interest and vital importance, because these productive regions account for a large fraction of global fishery production and marine biodiversity. The Yuedong upwelling (YDU) in the coastal northern South China Sea can be served as a study case to explore long-term responses of DO to upwelling and climate due to minor influence of riverine input. Here, bottom water DO conditions were recovered by sedimentary C28Δ22/Δ5,22 ratios of steroids in three short cores, with lower ratio value indicating higher DO concentration. The ratio records showed oscillations in varying degrees and exhibited no clear trends before ∼1980s, after which, however, there occurred a persistent decreasing trend or basically remained at lower values. Thus, inferred DO variations by the C28Δ22/Δ5,22 ratio records are not compatible with regional YDU-involved physical processes under climate change, such as southwesterly wind-induced onshore advection of reduced-oxygenated source waters from outer shelf and oceanic warming that would rather lead to less oxygenation in bottom waters in recent decades. Intriguingly, the alcohol records of n-C20:1/C28Δ5,22 and br-C15/C28Δ5,22 ratios, indicative of the relative strengths between biogeochemical oxygen consumption (i.e., by zooplankton and microbes) and photosynthetic oxygen production (i.e., by phytoplankton), changed almost in parallel with the C28Δ22/Δ5,22 records in three cores. Accordingly, we propose that net photosynthetic oxygen production outweighs source water– and warming-induced increasing deoxygenation in the study area. This study may suggest an important biogeochemical mechanism in determining bottom water DO dynamics in shallow coastal upwelling regions with minor contribution of riverine input.

High polarization and wake-up free ferroelectric characteristics in ultrathin Hf0.5Zr0.5O2 devices by control of oxygen-deficient layer

The formation of an interfacial layer is believed to affect the ferroelectric properties in HfO2 based ferroelectric devices. The atomic layer deposited devices continue suffering from a poor bottom interfacial condition, since the formation of bottom interface is severely affected by atomic layer deposition and annealing process. Herein, the formation of bottom interfacial layer was controlled through deposition of different bottom electrodes (BE) in device structure W/HZO/BE. The transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy analyses done on devices W/HZO/W and W/HZO/IrO x suggest the strong effect of IrO x in controlling bottom interfacial layer formation while W/HZO/W badly suffers from interfacial layer formation. W/HZO/IrO x devices show high remnant polarization (2P r) ∼ 53 μC cm−2, wake-up free endurance cycling characteristics, low leakage current with demonstration of low annealing temperature requirement as low as 350 °C, valuable for back-end-of-line integration. Further, sub-5 nm HZO thicknesses-based W/HZO/IrO x devices demonstrate high 2P r and wake-up free ferroelectric characteristics, which can be promising for low power and high-density memory applications. 2.2 nm, 3 nm, and 4 nm HZO based W/HZO/IrO x devices show 2P r values 13.54, 22.4, 38.23 μC cm−2 at 4 MV cm−1 and 19.96, 30.17, 48.34 μC cm−2 at 5 MV cm−1, respectively, with demonstration of wake-up free ferroelectric characteristics.

Increasing the Depth of a Land Surface Model. Part I: Impacts on the Subsurface Thermal Regime and Energy Storage

Abstract The representation of the thermal and hydrological states in land surface models is important for a realistic simulation of land–atmosphere coupling processes. The available evidence indicates that the simulation of subsurface thermodynamics in Earth system models is inaccurate due to a zero-heat-flux bottom boundary condition being imposed too close to the surface. To assess the influence of soil model depth on the simulated terrestrial energy and subsurface thermal state, sensitivity experiments have been carried out in piControl, historical, and RCP scenarios. A deeper bottom boundary condition placement has been introduced into the JSBACH land surface model by enlarging the vertical stratification from 5 to 12 layers, thereby expanding its depth from 9.83 to 1416.84 m. The model takes several hundred years to reach an equilibrium state in stand-alone piControl simulations. A depth of 100 m is necessary, and 300 m recommendable, to handle the warming trends in historical and scenario simulations. Using a deep bottom boundary, warming of the soil column is reduced by 0.5 to 1.5 K in scenario simulations over most land areas, with the largest changes occurring in northern high latitudes, consistent with polar amplification. Energy storage is 3–5 times larger in the deep than in the shallow model and increases progressively with additional soil layers until the model depth reaches about 200 m. While the contents of Part I focus on the sensitivity of subsurface thermodynamics to enlarging the space for energy, Part II addresses the sensitivity to changing the space for water and improving hydrological and phase-change interactions.

First record of the early Toarcian Oceanic Anoxic Event in the Hebrides Basin (UK) and implications for redox and weathering changes

The early Toarcian (~183 Ma) was characterized by a prominent volcanism-induced warming event associated with a massive addition of 12 C-enriched carbon to the ocean-atmosphere system. This warming likely contributed to marked ocean deoxygenation during this time, giving the event its name: the early Toarcian Oceanic Anoxic Event (T-OAE). Although the T-OAE has been recognized globally, clear geographic differences in the character of the event and its environmental effects have been noted. Here we present new carbon isotope, element abundance and organic geochemical data from a lower Toarcian succession on the Isle of Raasay, Scotland (Hebrides Basin, Northwest European Shelf). These data provide the first evidence of the T-OAE in Scotland. The succession is generally enriched in organic matter through the T-OAE interval, though redox-sensitive trace element data indicate that oxic-suboxic bottom water conditions prevailed, potentially interspersed with ephemeral anoxic episodes. Our elemental data contrast with evidence for persistent anoxia/euxinia in nearby basins, and emphasize how deoxygenation was spatially variable and dependent on water depth and basin hydrography. Similarly, the data emphasize how anoxia was not a prerequisite for the deposition of organic-rich lithologies during the T-OAE. Sedimentological evidence, coupled with inorganic geochemical data, indicates increased coarse-grained detrital flux and enhanced chemical weathering during the T-OAE. Our findings support emerging evidence for a marked strengthening of hydrological cycling and increased storminess at tropical and subtropical latitudes globally in response to global warming during the T-OAE. • Toarcian Oceanic Anoxic Event described from Hebrides Basin (sub-Boreal realm) for the first time. • Negative organic carbon isotope excursion (~-2.7‰) during the early Toarcian • Oxic to suboxic conditions through the T-OAE, in contrast to strong anoxia in nearby basins • Significant strengthening of continental weathering through T-OAE at sub-tropical latitudes

Ichnology, sedimentology, and orbital cycles in the hemipelagic Early Jurassic Laurasian Seaway (Pliensbachian, Cardigan Bay Basin, UK)

An uncommonly continuous Lower Jurassic (uppermost Sinemurian and Pliensbachian) section (Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, UK) comprises hemipelagic calcareous mudstone, wackestone/siltstone and subordinate packstone/sandstone. Some beds show bigradational grading, and their sedimentary structures are typical of contourite drift facies. On the basis of the long-term persistence and stability of the currents that formed these deposits, sedimentation was likely controlled by thermohaline-driven geostrophic contour currents circulating between the Boreal ocean and Peri-Tethys through the narrow and relatively deep Cardigan Bay Basin (Cardigan Bay Strait). Trace fossils are strongly dominated by Phycosiphon incertum , which was produced by opportunistic colonizers. Thalassinoides , Schaubcylindrichnus and Teichichnus are common, accompanied by less common Zoophycos , Planolites , Palaeophycus , Trichichnus and dwelling structures such as cf. Polykladichnus , Siphonichnus and Skolithos . The ichnofabrics are usually simple, which results from generally high rates of deposition, unstable, water-saturated soft-ground substrate, and the domination of well-adapted Phycosiphon, but there are also cyclic appearances of more complex ichnofabrics with dwelling structures, reflecting more stable bottom conditions. A new detailed analysis of the core has allowed cycles to be distinguished based on combination of ichnological and sedimentological features, pointing to distinct cyclicity of oceanographic mechanisms influenced by orbital forcing and driving the inferred fluctuations in benthic life conditions, controlled mainly by variation in contour current intensity and oxygenation of bottom water reflected by trace fossils. The ichnological cycles show four-order hierarchy, which can be attributed to the orbital cycles: precession and obliquity (4th order), short eccentricity (3rd order), and long eccentricity (2nd order). The longest (~ 2.5 Myr) 1st order cyclicity is attributable to the longer ‟grand orbital cycles” (period related to the Earth–Mars secular resonance), with long-term impacts on palaeoclimatic and oceanic circulation dynamics, and is recorded in large-scale changes in ichnodiversity, correlating with long-term changes of clay minerals and carbonate content. Possibly, there is also ~ 9 Myr cyclicity, expressed in observed modulation of frequency of precession cycles by eccentricity. Harmonic analysis of the cyclicity gives high confidence of orbital signals and allows refined estimation of duration of the Pliensbachian (~8.4 Myr) and the jamesoni ( ~ 2.8 Myr), ibex (~ 2.0 Myr), davoe i (~ 0.47 Myr), margaritatus (~ 2.33 Myr) and spinatum zones (~ 0.8 Myr) with an overall stable sedimentation rate of 4.5–5.1 cm/kyr. Obtained durations show improved fit between 2nd–4th and 1st order cycle and removes the problem of an anomalously long duration and resulting much lower sedimentation rate for the spinatum Zone, previously obtained by other methods. A higher diversity of trace fossils is noticed in intervals enriched in smectite; most likely, this clay mineral occluded pore spaces and limited the competition from the opportunist Phycosiphon makers, allowing development of other, more specialized forms. The continuous, expanded ichnological record of deep-water hemipelagic/contour drift sediments is sensitive to climatic and oceanographic changes controlled by orbital cycles. The Cardigan Bay Strait played an important role in the Early Jurassic (at least Pliensbachian) oceanic circulation, providing a major link between the northern and southern part of the Laurasian Seaway (and in general between the Boreal and Peri-Tethys domains), funneling currents flowing from the north to the south. • Contourite depositional system in the Laurasian Seaway/Cardigan Bay Basin • Orbital forcing expressed in deep sea sedimentary and ichnological cycles. • Corrected duration of Pliensbachian ammonite zones • Long-term ~2.5 My cycles driven by major oceanographic/climate changes.

Evaluation of deep-water environmental conditions during the latest Maastrichtian-early Danian: Insights from the western south atlantic ocean

The Cretaceous-Paleogene (K-Pg) boundary extinction event affected planktic foraminiferal assemblages worldwide in a dramatic way, but deep sea benthic foraminiferal assemblages were not significantly impacted. However, possible impacts of massive early Danian volcanic eruptions, such as those related to the Deccan Traps, on benthic foraminiferal assemblages are not yet explored. Here we present geochemical and benthic foraminiferal data across the K-Pg boundary and within the earliest Danian interval at Deep Sea Drilling Project (DSDP) Site 356, located on the São Paulo Plateau, western South Atlantic Ocean. Maastrichtian to Danian benthic foraminiferal assemblages are well-preserved and suggest deposition at middle to lower bathyal paleodepths, under an oligotrophic regime with well-oxygenated bottom water conditions. As expected, the K-Pg boundary event did not significantly affect benthic foraminiferal assemblages at Site 356. However, during the early Danian, benthic foraminiferal species richness, heterogeneity, diversity and equitability presented overall opposite trends in relation to the Hg/TOC and Hg/CaCO3 ratios, as well as Hg concentrations, which we consider proxies for intensity of volcanic activity. Our results suggest a possible response of Danian middle to lower bathyal benthic foraminiferal assemblages at Site 356 to changes in bottom water condition possibly associated with massive volcanism eruptions.