Sedimentation Rates Research Articles

Long-term carbon sequestration in the Eocene of the Levant Basin through transport of organic carbon from nearshore to deep marine environments

This study addresses a specific component associated with mass transport complexes in marine systems: the role of hyperpycnal flows, dense shelf water cascading, submarine canyons, distributary channels, and other transport mechanisms in transferring organic matter from continental and shallow marine settings into deep-marine environments. We speculate that during the Eocene, allowing for only 0.1‰ of shelf carbon to be preserved through transport mechanisms would account for up to 13.7% of all organic carbon burial. As such, the potential to mobilize through this mechanism large quantities of organic carbon is significant.Our case study focuses on a 150 m Eocene sequence composed of organic-rich chalks interleaved with displaced neritic limestones. TOC values range between 1.5 and 14%, averaging 4.5%. Displaced limestones are composed of a variety of poorly cemented mud- and wackestones, with low-diversity assemblages of large benthic foraminifera associated with planktonic foraminifera, suggesting deposition under low-energy conditions within the oligophotic zone on the outer ramp. Transport overprints include soft-sediment deformation, partially lithified rip-ups, folds, small diapirs, bed-scale imbrication, brecciation and syn-sedimentary shear. These features indicate detachment, movement and emplacement following initial sedimentation, in some cases more than once. Emplacement occurs into a chalk facies that can vary in appearance from darker (higher TOC) and lighter (lower TOC) lithofacies.Combination between the sedimentological, petrophysical, and elemental analyses indicates shifts between autochthonous and allochthonous sedimentation, whereas the organic geochemical analysis reveals a correlation between modes of sedimentation and preservation/composition of organic matter. Organic richness seems to increase within intervals of allochthonous sedimentation, with lower TOC values within intervals of autochthonous sedimentation. Organic matter preservation is enhanced due to poor oxygenation of the sea floor, further depleted by rapid burial beneath mass-transport deposits, increasing sedimentation rates and thus organic matter preservation. Horizons rich in organic matter may be derived from three different sources: organic matter with a fingerprint of terrestrial sources (e.g., enhanced contribution of plant leaf waxes) transported from nearshore environments; an allochthonous marine fingerprint with sulfurized hopanoids, which seem to be reworked from pre-existing Cretaceous organic-rich carbonates entrained within fined-grained micro-turbidites in the para-autochthonous facies; and productivity-derived organic matter deposited on the seafloor of the deep marine environment.This study demonstrates how transport mechanisms allow for the long-term burial of organic carbon in marine systems. When taking into consideration similar processes reported to occur in the world oceans today, it is clear that sediment transport and long-term burial of organic carbon is a fundamental part of the global carbon cycle.

Oysters' Integration on Submerged Breakwaters Offers New Adaptive Shoreline Protection in Low‐Energy Environments in the Face of Sea Level Rise

AbstractSea level rise (SLR) and increasing storm frequency threaten coastal environments. Engineering solutions such as breakwaters will become ineffective for wave attenuation and erosion control due to SLR. As a natural alternative, oysters create three‐dimensional, complex reef structures that attenuate wave energy and increase sedimentation rates. If coupled with breakwaters, oysters may maintain breakwaters' efficiency over time as they are expected to grow with SLR. Here, we measured bathymetric changes over 3 years (via GPS) and wave dampening due to four‐made intertidal breakwaters within a small cove of the Choptank River (MD, USA). Then, we modeled the coupling of such gray structures with oysters through Delft3D‐SWAN to evaluate the performances of such hybrid solutions on coastal protection, under future scenarios of SLR and climate change. Modeling hydrodynamic results showed a gradual reduction in wave attenuation due to SLR. However, when oysters were included in the modeling, wave dampening in 100 years was 75% and 60% greater than gray breakwaters, at high and low tides, respectively. Morphodynamic results showed increasing net export of sediment from the coast due to SLR. Oyster addition also provided shoreline protection and sediment retention in 100 years compared with the use of breakwaters alone, thanks to oysters' capability to grow with SLR. The coupling between oysters and breakwaters may represent a valuable and effective methodology to protect our coast over a changing climate and a rising sea, where optimal conditions for oyster survivability occur and are maintained over time.

Rhynchostreon oyster assemblages across the Central European region: Three types of environment and an alternative view in the intraspecific variability of Rhynchostreon suborbiculatum (Lamarck, 1801)

The morphological variability in Rhynchostreon suborbiculatum (Lamarck, 1801) is a well-known phenomenon in the Cretaceous palaeobiology. The current study focuses on two morphotypes differentiated by the presence/absence of radial ribs on the apical part of the left valve, while the fusion of palaeoecological and morphological results allows the study of the evolution of R. suborbiculatum under specific environmental conditions. Based on analyses of grain size, concentration of major oxides and oyster taphonomy in five Cenomanian–Turonian oyster-bearing localities, three habitats that differ in substrate, energy level and salinity regime were recognised: the dynamic Cenomanian nearshore environment (environment B), the Turonian hemipelagic environment (environment C) and the Cenomanian–Turonian marginal marine environment influenced by river dynamics (environment A). An analysis of the size distribution and morphotype structures of three palaeopopulations of R. suborbiculatum shows lithofacial dependence in morphotype distribution, indicating substrate granularity and level of environmental energy. The higher prevalence of ribbed morphs in smaller size classes as well as in fine-grained deposits suggests that apical ribbing is an adaptive trait with a stabilising effect, especially during the early growth stages or when colonising low-energy environments with very soft substrates. The distribution of the large size classes, combined with the shell thickness and vaulting, suggest that the compensation provided by the ribs is insufficient in high energy environments, where strong waves, turbulent flow, and higher sedimentation rates are the main selection pressures. Thus, other adaptations, such as body size and massiveness of the shell, become more critical for the survival of individuals.

Fire, volcanism and climate change: the main factors controlling mercury (Hg) accumulation rates in Tropical Lake Lantoa, Sulawesi, Indonesia (∼16,500–540 cal yr BP)

The effects of climate change on long-term mercury (Hg) cycling are still not well understood, as climate changes are usually gradual and can only be assessed using high-resolution archives. Our study site (a small, lowland tectonic lake in Sulawesi, Indonesia) provides a unique opportunity to further understanding of Hg cycling in the Southeast Asian (SEA) tropics during the transition from the Pleistocene to the Holocene, a period of significant climate variability. We present a high-resolution record of Late Glacial and Holocene Hg deposition within the sediments of tropical Lake Lantoa, Sulawesi. Using a multi-proxy framework (including pollen, charcoal, carbon:nitrogen ratio and high-resolution geochemistry records) we investigate the response of Hg accumulation rates (HgAR) in sediments to shifts in climate between ∼16,488 and 538 cal BP. This period encompasses the Bølling-Allerød (BA) warming, Younger Dryas (YD) cooling and Holocene warming events, providing new insights into the effects of global climatic transitions on HgAR in SEA sediments. The Pleistocene Termination had the highest HgAR and substantial variability (µ = 11.32, 5.38–33.91 μg m−2 yr−1), when drier conditions and high charcoal accumulation rates suggest that fire activity was the main source of Hg to the lake. The Holocene Transition was marked by a decrease in HgAR (µ = 8, 3.50–18.84 μg m−2 yr−1) as humid conditions precluded forest burning, followed by high HgAR (µ = 11.35, 3.30–158.32 μg m−2 yr−1) in the Early Holocene. Mercury accumulation rate in the Late Holocene (µ = 3.80, 1,67–43.65 μg m−2 yr−1) was the lowest in the Lake Lantoa record, marked by the lowest fire events and a stable catchment. An increase in carbon:nitrogen ratios during the Late Holocene, coupled with a decrease in HgAR, suggests that the establishment of lowland forest resulted in suppressed Hg erosion/leaching. Our results demonstrate that forest fires, vegetation change and volcanism are important drivers of Hg inputs to Lake Lantoa, a relationship which is strongly mediated by climate and lake-catchment dynamics.

Experimental Study on the Influence of Different Dam Body on the Sediment Interception and Discharge Capacity of the Cascade Permeable Dams

Sediment deposition is an ecological and environmental problem faced by most water bodies. In view of the poor structural stability and unrepeatable use of existing permeable structures, this paper proposes a cascade permeable dam, which consists of four dam bodies. As the composition of the dam material is the key to sediment interception and discharge capacity, this study sets up two groups of dam material particle sizes for experiments. The results show that the sediment interception performance of the cascade permeable dam is good. When the dam material with a small particle size is selected, the percentage of intercepted sediment mass inside the four dam bodies is 75–89%. The interception sediment rate is much greater than that of the dam material with a large particle size, which tends to decline one by one along the flow direction. The discharge capacity of the dam gradually decreases with time, and there is an obvious decrease in the permeability coefficient of 1# dam. The results of this study provide programmatic support for reducing sediment entering shallow lakes and rivers, which can further optimize the structure design of permeable dams.

Elderly-Onset Rheumatoid Arthritis: Characteristics and Treatment Options.

Elderly-onset rheumatoid arthritis (EORA) is a distinct clinical entity defined as the onset of rheumatoid arthritis (RA) in individuals aged over 60 years. EORA presents unique clinical features, including a more equitable distribution of sexes, a potential predilection for male involvement, a higher incidence of acute onset characterized by constitutional symptoms, a propensity for systemic manifestations, elevated sedimentation rates at disease onset, a reduced occurrence of rheumatoid factor positivity, increased titers of anti-citrullinated protein antibodies, a preference for involvement of large joints, elevated disease activity, the presence of bone erosions, and heightened patient disability. RA is recognized to consist of three partially overlapping subsets. One subset mirrors the classical RA clinical presentation, while the remaining subsets exhibit either a polymyalgia rheumatica-like phenotype or present with remitting seronegative symmetrical synovitis accompanied by pitting edema syndrome. In the initial stages of EORA management, non-steroidal anti-inflammatory drugs (NSAIDs) are not typically the first-line treatment choice, because seniors are much more prone to develop side effects due to NSAIDs, and the use of NSAIDs is in reality contraindicated to the majority of seniors due to comorbidities. Disease-modifying antirheumatic drugs (DMARDs), frequently methotrexate, are introduced immediately after the diagnosis is made. In cases where elderly patients demonstrate resistance to conventional DMARD therapy, the introduction of biological or targeted synthetic DMARDs becomes a viable treatment option. EORA presents a unique clinical profile, necessitating tailored treatment strategies. Our study emphasizes the challenges of NSAID use in seniors, highlighting the imperative shift toward DMARDs such as methotrexate. Future research should explore personalized DMARD approaches based on disease activity, comorbidities, and safety considerations, aiming to optimize treatment outcomes and minimize glucocorticoid reliance, thereby enhancing the quality of care for EORA patients.

Large contributions of petrogenic and aged soil-derived organic carbon to Arctic fjord sediments in Svalbard

Svalbard fjords are recognized as hotspots for organic carbon (OC) burial and storage due to their high sedimentation rates, which effectively trap terrestrial sediments and inhibit extensive OC remineralization. In this study, we investigated surface sediments (n = 48) from eight Svalbard fjords, along with bedrock (n = 17), soil (n = 28), and plant (n = 12) samples, to identify the sources of sedimentary OC in these fjords using geochemical parameters. All examined surface sediments from the fjords showed a depletion in 14Corg (− 666.9 ± 240.3‰), indicating that recently fixed terrestrial and marine biomass alone cannot account for the entire sedimentary OC pool. Conventional bulk indicators such as Norg/TOC ratio and δ13Corg were insufficient for fully determining the sources of sedimentary OC. Therefore, we employed a four-end-member approach, using Δ14Corg, δ13Corg, and lignin phenols to assess the relative contributions of petrogenic, soil-derived, plant-derived, and marine OC to the sedimentary OC pool. The analyzed fjord sediments consisted, on average, of 59.0 ± 28.1% petrogenic OC, 16.8 ± 12.1% soil-derived OC, 2.5 ± 2.2% plant-derived OC, and 21.8 ± 18.5% marine OC. This approach highlights the substantial contributions of petrogenic and aged soil-derived OC to present-day sedimentary OC in Svalbard fjords. Considering predicted global warming, accelerated inputs of petrogenic and soil-derived OC into fjords due to rapid glacier retreat may significantly impact the active carbon cycle and potentially contribute to CO2 emissions to the atmosphere, depending on burial efficiency.

210Pb-based dating of recent sediments with χ-mapping versions of the CFCS, CIC, CF and TERESA models

The 210Pb-based method allows for absolute age determination in recent sediments on the centennial scale. The most common sedimentary scenarios involve ideal deposition without any further redistribution. The conventional models apply to such conditions by adding specific assumptions that allow analytical formulations: constant flux (CF), constant initial concentration (CIC), and constant flux with constant sedimentation (CFCS). The χ-mapping models are presented as a novel methodological approach. They generate a large number (105 to 106) of potential solvers, consisting of sets of n (the number of slices in the core) values of initial activity concentrations, A0, and sedimentation rates, w. Empirical data serve to attract the solver that minimizes a χ function after encountering the best sorting along the core of the A0 and w values. The specific assumptions of the above models are reformulated in terms of the statistical distributions of A0 and w. The performance of the χ-mapping versions is demonstrated with a set of cores from the literature with independent chronologies. The main advantages compared to known analytical formulations are: i) χ-mapping provides a more robust fitting method. ii) It overcomes the problem of age reversals often found in the CIC model. iii) The CF model successfully applies to cores with unsteady and/or incomplete inventories. iv) The TERESA model (time estimates from random entries of sediments and activities), without analytical counterpart, is the only model that can manage continuous trends of change in the fluxes of unsupported 210Pb. The work discusses the conditions for compensating model errors in the chronologies, and the use of the palaeorecords of fluxes, A0 and w. The methodology can be extended to other assumptions (models) and provides novel and insightful views on the 210Pb-based dating of recent sediments.

Paleoecological reconstruction during the Holocene in the Middle Branch of Bue Marino Cave (Sardinia, Italy)

This study was conducted in the Middle Branch of Bue Marino Cave (Sardinia, Italy) to reconstruct paleoecological conditions during the Holocene through microfaunal proxies in seven surface sediment samples and a short sediment core (BMD-2018, 18 cm), all collected in 2018 and another core sampled in 2021 (BMD-2021, 28 cm). The first attempt at dating cave sediment through luminescence was conducted on BMD-2021; the derived age was 6.04 ± 0.47 ka at 18 cm depth. Although continuous sedimentation and constant rates are not probable in the cave, this indicates that the sedimentary record dates to the early times after the Holocene flooding of the cave by the sea. Benthic foraminifera and grain size were analyzed in all surface samples and core BMD-2018, while only benthic foraminifera were studied in BMD-2021. The recent foraminiferal assemblages, studied from an ecological point of view, were applied as modern analog to reconstruct the paleoecological conditions in sediment cores. Significant changes in the sedimentary environment were excluded; the two cores showed a similar foraminiferal turnover at a similar depth, from an older assemblage with prevailing indifferent Ammonia inflata to a younger one with prevailing opportunist Eggerelloides advena. This turnover was attributed to changes in the amount and/or quality of available nutrients. Based on these results, this event is likely related to possibly attributable to the effects of climate changes that occurred in the Holocene. However, more extensive studies are necessary to better understand the effects of the climatic/environmental events in the Late-Holocene in the caves. Although it represents a first attempt at paleoenvironmental reconstruction based on sediments from a Mediterranean marine cave, this study demonstrated that benthic foraminifera are refined paleoenvironmental proxies and that the integrated approach with the luminescence dating produces reliable results for studying the effects of global changes in these environments.

The Great Boundary Fault in the Indo-Gangetic foreland basin: A geomorphological perspective

Identifying active faults in alluvial plains with varying sedimentation rates, erosion, and extensive anthropogenic modifications is challenging. In tectonically active foreland basins, tectonics outweighs other controlling factors and produces a set of key fluvial geomorphic markers that are critical for precisely locating active faults. This study employs several key tectonic fluvial morphometric parameters, seismically induced soft-sediment deformation structures (SSDS) as seismites, and the displaced rocks of the Siwalik mountains to mark the surface positions of a buried basement fault system, namely the Great Boundary Fault (GBF) beneath the alluvial cover of the Indo-Gangetic foreland basin.The Great Boundary Fault (GBF) is a NE-SW trending, oblique-slip, branching reverse basement fault running from peninsular India to the Sub-Himalayas. About 400 km length of its NE segment is buried under thick sediments of the Indo-Gangetic foreland basin. This fault's surfaceward propagation deforms the overlying sediments via a network of subsidiary faults, resulting in 20 km wide broad fault zones. The extreme flatness of the Ganga plain conceals the primary faulting evidence but tectonic fluvial geomorphic signatures, the SSDS, and the laterally displaced Siwalik rocks, including south-verging thrusts at the frontal Himalayas, provide collective evidence of neotectonic activity along both fault branches. The primary objectives of this study are to characterise the GBF's buried segment in the Ganga plain through the geomorphic signatures and SSDS, to elucidate its extension up to the Main Boundary Thrust (MBT), and to understand the surfaceward propagation mechanism of its reverse faults through the alluvial-fills.Tectonic geomorphic parameters such as sinuosity spectra and knickpoints were analysed using ArcGIS and Matlab. Meander scar mapping was carried out using Google Earth Pro and Landsat imagery within ArcGIS to characterise the pattern of avulsions and adjustments of the floodplain linked to the tilting directions of the fault blocks.Fourteen prominent knickpoints of 4 to ≥6 m height were derived from the river profiles across the fault zone. Rivers on the up-thrown block possessed low sinuosity (as low as 1.1), whilst those on the down-thrown block had higher sinuosities (up to 3.1), indicating active uplift and rapid subsidence. The deflection of multiple river courses (Ganga, Ramganga, Burhiganga, Sot, Pangaili, and Deoha) and the presence of asymmetrical meander-belts demonstrate an eastward tilting of the tectonic block. The occurrence of liquefaction-induced SSDS close to the GBF corroborates its recent seismogenic nature. Field observation suggests these SSDS are likely related to the Usawan paleo-earthquake (estimated magnitude of 6.5–7.2), epicentered near the GBF. Based on the geometry and the venting characteristics, a new type of SSDS has been recognized, and the term “liquefaction vents” has been proposed for it. Their association with the other types of SSDS that are characteristically formed by >6.5 magnitude earthquakes suggests it is the minimum magnitude of earthquake required for the formation of liquefaction vents. The regional seismic record suggests a significant number of both large and moderate earthquakes around this fault.Finally, we synthesise the results to propose a growth model for the propagation of reverse faulting from the underlying basement bedrock through to the alluvial sediments and the surface of the Ganga plain.

Bayesian age models and stacks: combining age inferences from radiocarbon and benthic δ18O stratigraphic alignment

Abstract. Previously developed software packages that generate probabilistic age models for ocean sediment cores are designed to either interpolate between different age proxies at discrete depths (e.g., radiocarbon, tephra layers, or tie points) or perform a probabilistic stratigraphic alignment to a dated target (e.g., of benthic δ18O) and cannot combine age inferences from both techniques. Furthermore, many radiocarbon dating packages are not specifically designed for marine sediment cores, and the default settings may not accurately reflect the probability of sedimentation rate variability in the deep ocean, thus requiring subjective tuning of the parameter settings. Here we present a new technique for generating Bayesian age models and stacks using ocean sediment core radiocarbon and probabilistic alignment of benthic δ18O data, implemented in a software package named BIGMACS (Bayesian Inference Gaussian Process regression and Multiproxy Alignment of Continuous Signals). BIGMACS constructs multiproxy age models by combining age inferences from both radiocarbon ages and probabilistic benthic δ18O stratigraphic alignment and constrains sedimentation rates using an empirically derived prior model based on 37 14C-dated ocean sediment cores (Lin et al., 2014). BIGMACS also constructs continuous benthic δ18O stacks via a Gaussian process regression, which requires a smaller number of cores than previous stacking methods. This feature allows users to construct stacks for a region that shares a homogeneous deep-water δ18O signal, while leveraging radiocarbon dates across multiple cores. Thus, BIGMACS efficiently generates local or regional stacks with smaller uncertainties in both age and δ18O than previously available techniques. We present two example regional benthic δ18O stacks and demonstrate that the multiproxy age models produced by BIGMACS are more precise than their single-proxy counterparts.

Anabolic and Catabolic Microbial Activity in Hydrocarbon-rich Sediments of Guaymas Basin

Guaymas Basin, located in the Gulf of California, Mexico, is a young marginal ocean basin with high sedimentation rates of >1 mm/year, active seafloor spreading, and steep geothermal gradients in its sediment. It hosts a unique microbial subseafloor biosphere as these conditions lead to thermal cracking of sedimentary organic matter and the production of bioavailable organic carbon compounds and hydrocarbons already at shallow depths. The abundance and diversity of potential microbial substrates raise the question of which substrates are being used for catabolic and anabolic microbial metabolism. We thus analyzed the microbial uptake of hydrocarbons and inorganic nitrogen using nanoscale secondary ion mass spectrometry (NanoSIMS) analysis after incubation with stable-isotope labeled substrates. Incubations were carried out with samples from two International Ocean Discovery Program (IODP) Exp. 385 drill sites. Site U1545 is characterized by undisturbed sedimentary strata and a temperature gradient of 225°C/km, whereas Site U1546 has experienced a sill intrusion at greater depth, below the cored interval. The intrusion led to temporary heating of the sediment, but a temperature gradient of 221°C/km indicates thermal equilibration with the surrounding sediment since sill emplacement. Incubations were carried out with 13C-benzene + 2H-hexadecane + 15NH4Cl or 13C-methane + 15NH4Cl at in-situ temperature (4-62°C) and pressure (25 MPa) for 42 days. Additionally, sulfate reduction rates (SRR) were measured by incubating the samples with four aliphatic hydrocarbons + four aromatic hydrocarbons or methane and radioisotope-labeled 35SO42- for 10 days, also at in-situ temperature and pressure. The NanoSIMS analyses reveal that a few samples showed detectable microbial assimilation of hydrocarbons. Nitrogen was significantly assimilated in some samples incubated with methane. The assimilation mostly occurred in samples from near the seafloor (2 and 44 meter below seafloor (mbsf)). Our results indicate that anaerobic microorganisms in Guaymas Basin take up measurable amounts of hydrocarbons and inorganic nitrogen even in the relatively short incubation time of 42 days. The results of the SRR measurements indicate that a mixture of hydrocarbons and methane increases the SRR in samples from near the seafloor (2 mbsf) and around the sulfate-methane transition zone (44 and 55 mbsf) but not in samples from greater depths. Our results show that anaerobic microorganisms in Guaymas Basin can use hydrocarbons for anabolic and catabolic metabolism in this extreme environment. Given the high abundance of various carbon compounds, nitrogen appears to be a limiting factor for cellular growth.

Regulation of potential denitrification rates in sediments by microbial-driven elemental coupled metabolisms

Microbial driven coupled processes between denitrification and methane/sulfur metabolism play a very substantial role in accelerating nitrogen removal in river sediments. Until now, little is known about how element coupling processes alter nitrogen metabolism by the microbial functional communities. The primary objective of this research was to clarify the contributory role of microbial-mediated coupled processes in controlling denitrification. Specifically, the study sought to identify the key bioindicators (or metabolic pathway) for preferably regulating and predicting potential denitrification rate (PDR). Here, a total of 40 sediment samples were collected from the inflow rivers of Chaohu Lake under nitrogen stress. The results revealed the ecological importance of methanogens and sulfate reducing bacteria in the microbial interaction network. Correlations between quantitative or predicted genes showed that the methanogenic gene (mcrA) was synergistic with denitrifying genes, further unraveling that the key role of methanogenesis in denitrification process for facilitating nitrogen removal. The PDR of sediments ranged from 0.03 to 133.21 μg N·g−1·h−1. The study uncovered specific environmental factors (NH4+ and OM) and microbial indicators (nosZ, mcrA, Paracoccus, Thauera, Methanobrevibacter and Desulfomicrobium) as potential contributors to the variations in PDR. Structural Equation Model (SEM) analysis revealed a significant direct effect of NH4+ on PDR, evidenced by a standardized coefficient (λ) of 0.77 (P < 0.001). Additionally, the findings also emphasized the salient role of methanogens (Methanobrevibacter) and methanogenic gene (mcrA) in indicating PDR. The research's aforementioned findings shed light on the substantial consequences of methanogenesis on nitrogen metabolism in coupled processes, enabling improved control of nitrogen pollution in river sediments. This study provided fresh perspectives on the effects of multiple functional taxa on denitrification, and reinforces the significance of coupling processes for nitrogen removal.

Low temperature and high pressure dramatically thicken the gas hydrate stability zone in rapidly formed sedimentary basins

Rapid sedimentation reduces the temperature and raises the pore pressure in sedimentary basins. During rapid sedimentation (>0.5 mm yr−1), cold sediment is buried fast and there is insufficient heat flow to keep the sediment at its steady state conductive equilibrium temperature. In addition, rapid deposition of low permeability mud results in overpressure due to the inability of the pore fluid to drain. It dramatically expands the thickness of the zone where hydrates are stable (the gas hydrate stability zone or GHSZ). We explore this effect with one-dimensional models. We then simulate the two-dimensional evolution of temperature and pressure of the Terrebonne Basin in the Gulf of Mexico. We use seismic, well data, and salt restoration to provide the initial and boundary conditions. We show that rapid burial reduces the geothermal gradient from ∼30 °C/km, which would be expected under equilibrium pressure and temperature, to as low as ∼10 °C/km; we also show that 25 MPa of overpressure is developed. This deepens the thickness of the GHSZ from ∼600 mbsf (its equilibrium depth) at the basin margin, to as much as 2000 mbsf basin-ward, in response to the increasing sedimentation rates. The model successfully simulates the deepening of the base of GHSZ that is interpreted from a bottom simulating reflection in the seismic data. The model and the observations suggest that the thickness of the GHSZ may be much thicker than commonly presumed and as a result the volume of carbon stored may be underestimated. Furthermore, the thickness of the hydrate stability will change significantly with time as sedimentation rate waxes and wanes implying that the hydrate stability zone is a dynamic component of the carbon cycle.

Holocene Evolution of the Pearl River Delta: Mapping Integral Isobaths and Delta Progradation

The Pearl River Delta (PRD, China) has undergone complex geological development within a multi-island faulted basin, shaped by the interplay of regional tectonic movements, Quaternary sea-level fluctuations, and fluvial-marine interactions. Despite a great number of studies on the Holocene sedimentary sequences and spatial differences of lithofacies and environments, scant attention has been paid to the overarching human influence on deltaic evolution and coastline modifications since the Neolithic epoch. To further elucidate the spatial variation in Holocene sedimentation and its underlying basement topography shaped during the Last Glacial Maximum (LGM), we compiled a comprehensive dataset incorporating borehole data from over 2800 cores (the maximum depth can reach 92.5 m) within the PRD. Subsequently, high-resolution isobath maps of Quaternary deltaic deposits were generated, offering unprecedented insights into sediment distribution. This dataset facilitated a nuanced reconstruction of pre-Holocene topography, revealing a zone characterized by elongated, deep-incised valleys governed by NW-SE fault orientations. Further, we delineated coastline shifts since the period of maximum Holocene transgression (~7000 years BP), contributing to an enhanced understanding of the formation and evolutionary patterns of the delta and river network oscillations. Our findings illuminate an increasing anthropogenic impact on the rate of fluvial sedimentation and land growth, particularly accentuated over the last two millennia, favoring deltaic accretion.

The Pauzhetka tephra (South Kamchatka): A key middle Pleistocene isochron for the Northwest Pacific and Okhotsk Sea sediments

The distal Pauzhetka tephra, formed by a large caldera-forming volcanic eruption in South Kamchatka, has been identified in eleven recently recovered marine sediment cores based on major and trace element compositions of tephra glass. Ten SO264 cores form a transect along the Emperor Seamount Chain (ESC) in the Northwest (NW) Pacific between ∼50.3° and ∼45°N, 800–1200 km southeast of the Pauzhetka caldera. One additional core LV28-41-4 was retrieved in the Okhotsk Sea, ∼600 km west of the caldera. The Pauzhetka tephra glass shards have a characteristic medium-K rhyolite composition and trace element content compatible with the rear-arc position of the source volcano that ensures their identification. In the NW Pacific SO264 cores, the tephra is preserved as layers in cores 33, 47, 49, 53, 55, 56 and 62, as a lens in core 45, and as cryptotephra in cores 57 and 66. It forms a cryptotephra in the Okhotsk Sea core LV28-41-4. Distinctively high XRF-retrieved K/Ti and K/Fe ratios compared to those for the host sediments help identify the Pauzhetka tephra. According to our refined stable oxygen isotope (δ18O)- and magneto-stratigraphy of two studied and two reference cores, the Pauzhetka tephra occurs within a local δ18O maximum during a transition from marine isotope stage 12 to 11c (Termination V) and below a paleointensity minimum referred to as the Bermuda excursion, at ca. 418 ka. Using the tephra age as an isochron, we show that average linear sedimentation rates decrease southward along a transect of the SO264 cores, except in core 55. It partially reflects an intensification of mid-depth currents causing winnowing, erosion or non-deposition along the ESC over the past 418 kyr. An increased linear sedimentation rate in core 55, recovered from the southern leeward side of the Minnetonka Seamount, appears to record the pelagic accumulation protected from the mid-depth current influence. Our findings expand the former ash dispersal area farther southeast in the NW Pacific and southwest in the Okhotsk Sea. The new data on the tephra thickness supports the axis direction of the fallout zone southeast of the Pauzhetka caldera. Our results suggest the Pauzhetka tephra as a key middle Pleistocene isochron for the stratigraphy and correlation of the NW Pacific and Okhotsk Sea sediments.

U–Pb age constraints on the Carboniferous–Permian transition in continental basins of eastern equatorial Pangaea (France): implications for the depositional history and correlations across the late Variscan Belt

Intramontane late Carboniferous–Permian basins of western Europe developed during the latest orogenic stages of the Variscan Mountain Belt in eastern Pangaea, at equatorial palaeolatitudes. Their stratigraphic framework is mainly based on continental subdivisions (e.g. Stephanian and Autunian continental stages), which can be contentious owing to biostratigraphic biases, resulting in long-distance diachronous subdivisions. To provide precise inter-basinal and global correlations to the internationally recognized chronostratigraphic marine stages, this study reports new U–Pb geochronology from the Aumance and Decize–La Machine basins, located in the northern French Massif Central. Zircon grains extracted from three volcanic ash-fall layers give weighted mean 206 Pb/ 238 U ages of 299.11 ± 0.35, 298.73 ± 0.36 and 298.59 ± 0.35 Ma (2 σ total propagated uncertainty) by the chemical abrasion isotope dilution thermal ionization mass spectrometry method, coinciding with the Carboniferous–Permian transition (Gzhelian and Asselian stages). These ages imply that the northern Massif Central basins developed synchronously in relatively short periods of time (&lt;10 myr), reflecting substantial sedimentation rates. Finally, the new chronology of infilling of these basins confirms that they were connected during the late Carboniferous and early Permian periods, improving the knowledge on the late orogenic Variscan geodynamic setting in this area. Supplementary material: Operating conditions and complete analytical results are available at https://doi.org/10.6084/m9.figshare.c.6805228

A multi-proxy reconstruction of the late Holocene vegetation dynamics in Krabi mangroves, Thailand Andaman Sea

Pollen, charcoal, loss on ignition, geochemistry, and geophysical analyses were used to reveal the palaeoenvironment, vegetation, and sedimentary dynamics of the Krabi mangroves and the Andaman coast during the late Holocene. Two sediment cores, radiocarbon dated to ∼4400 cal BP, were collected from the Nai Nang mangroves in Krabi Province, the Thailand Andaman coast. This analysis documented how the area evolved from a tidal channel to a tidal area dominated by mangrove ecosystems. During the tidal channel phase (∼4400–2700 cal yr BP), the study site was characterized by a high-energy depositional environment, where sediment accumulated along tidal channels. Mangrove development began around 4400 cal yr BP and was influenced by varying contributions from tidal and freshwater inputs. Sea level during this period showed a slight rise until ∼4200 cal yr BP, followed by a subsequent fall. From ∼2700 to 1050 cal yr BP, the tidal channel was filled with finer sediments, forming intertidal flats that supported mangroves, back mangroves, and freshwater forest taxa, indicating a transition to mixed coastal vegetation. Sea levels remained relatively low during this period. From around 1050 cal yr BP to the present, mangroves replaced the previous mixed coastal vegetation, most likely driven by rising sea levels, particularly during the last 200 years. The observed sedimentation rates indicate that mangroves in Krabi will need to undergo continued future landward migration to adapt to changing coastal conditions, given the current and projected global sea-level rise.

Determination of hydrocyclone parameters for oil emulsion treatment with forced flow rotation, taking into account changes in rheological properties

The object of research is the process of dewatering oil emulsions by using a hydrocyclone with forced flow rotation taking into account rheological properties.&#x0D; The problem solved in the work is related to production, primary preparation and transportation of oils. The process of oil extraction is accompanied by saturation of the product with water, salts, mechanical particles and light fractions, which requires primary preparation of oil through multi-stage, sometimes long-term, low-productivity processing in order to separate the above-mentioned components. The water content of some deposits, especially marine deposits, is 80%, which makes the process of oil dehydration particularly important for preparing oil for transportation. Among the known methods of dewatering oil emulsions, such as settling, heat treatment, chemical treatment, electrodehydration and centrifugation, the last one allows to significantly influence the separation processes. The essence of the centrifugation process, consists in increasing the rotational speed of the particles of the dispersed phase by replacing the natural force of gravity with a more powerful centrifugal force. The density of water and mechanical impurities is higher than the density of oil, and particles under the action of centrifugal force are pressed against the wall and, coagulating, are removed through the flow separator.&#x0D; In the course of the work, the main regularities of the process were determinedcentrifugation, namely the rate of sedimentation of the water fraction from the rheological parameters of the emulsion and the kinematic characteristics of the hydrocyclone with forced rotation of the flow. It was established that the dependence of the volume of the water fraction of the oil emulsion is a power function of the second order, and the rate is linear. The settling of a water particle has a linear dependence on the size of the particle. Speed The set speed of settling of water particles of an oil emulsion allows you to calculate the length of the turbine depending on the required performance, speed of rotation and rheological properties.&#x0D; The developed theoretical provisions of the process of dewatering oil emulsions by using a hydrocyclone with forced rotation of the flow, taking into account the rheological properties, allow designing machines of this type for various conditions of oil production.

Magnetostratigraphy of the Pliocene Masol Formation, Siwalik Frontal Range, India: Implications for the age of intentional cut-marked fossil bones

The sedimentary Masol Formation, at least 165 m thick, is located in the Indian Siwalik Frontal Range and outcrops in the Chandigarh Anticline. It includes a fossiliferous zone called the Quranwala Zone (QZ) in its lower part. These fossils are characteristic of the Late Pliocene (Tatrot). Previous magnetostratigraphy showed that the QZ was deposited during the Gauss chron, with a short magnetic excursion at the base of the QZ, but the Gauss-Matuyama reversal was imprecisely identified in the stratigraphy of the Masol Formation. Following cut marks on fossil bones discovered in the QZ, we conducted a new magnetostratigraphy study to clarify their age. Our results indicate that detrital hematite is the main magnetic carrier and confirm that the entire Masol Formation was deposited during the Gauss Chron, whereas the Gauss-Matuyama reversal is outside the study area. Comparison between the magnetic excursion previously found at the base of the QZ and others identified elsewhere in a different sedimentary context and dated between 2.62 and 2.95 Ma, gave a range of sedimentation rates between 0.41 and 3.75 m.kyr-1 for the minimum thickness of the Gauss chron recorded in the Masol Formation. However, only rates less than 1 m.kyr-1 are consistent with the Late Pliocene deposits observed in the Siwalik. Magnetostratigraphy and obtained sedimentation rates conclude that the cut and percussion marks on the fossil bones have a minimum age of 2.68 Ma and a maximum age of 2.95 Ma. This evidence of intentional hominin activity is thus the oldest known in Asia.