Marine Settings Research Articles

Paleomagnetic inclinations and relative paleointensity variations during the upper Aptian to middle Albian in Sergipe-Alagoas Basin, South Atlantic Ocean (NE Brazil)

Summary During the Jurassic and Early Cretaceous, Earth's magnetic field experienced a high frequency of polarity reversals. This hyperactivity period is followed by a ∼38 Myr prolonged period of stable normal polarity from the Aptian until the Santonian, known as the Cretaceous Normal Superchron (CNS; chron C34n, from 121.4 to 83.65 Ma). However, the CNS might have been characterized by more variability than previously thought, but the current databaseis uneven in its spatial and temporal distribution. In this study, we integrate paleomagnetic and biostratigraphic data from the SER-03 sedimentary core, drilled onshore in the Sergipe-Alagoas Basin, NE Brazilian margin, South Atlantic Ocean. The 183-meter cored interval spans 5.2 Myr (114.7–109.5 Ma), including the Aptian–Albian transition. It records the evolution from restricted marine settings to the complete opening of the South Atlantic Ocean. Magnetic remanence and rock magnetic parameters, such as magnetic susceptibility, anhysteretic remanent magnetization, and isothermal remanent magnetization, were measured. Rock magnetic analyses indicated that primary magnetizations were preserved throughout the interval, with detrital magnetite identified as the primary magnetic carrier, predominantly in the pseudo-single domain and low-coercivity states. Normalizations by χ, ARM15mT, and IRM15mT were used to determine relative paleointensity curves and were compared to the curve resulting from the pseudo-Thellier method. The SER-03 relative paleointensity record shows marked changes in both intensity and inclination. Inclination instability results are comparable with those found in volcanic rocks from surrounding the region. The high-resolution SER-03 magnetic record revealed that the field variability was higher than expected during the CNS, but remaining substantially lower than during other periods, such as thelate Jurassic. The new SER-03can serve as a dating and correlation tool for coeval records.

Three-Dimensional Model of Ionic Species Concentration and Flux During Localised Corrosion of Steel in Marine Environment

Localized corrosion, exemplified by pitting and crevice corrosion, presents a significant challenge in industrial and marine settings due to the presence of chloride ions in seawater, brines and industrial fluids. It initiates and spreads at specific points on metal surfaces and its hidden rapid metal degradation beneath intact surface layers complicates detection and monitoring, increasing the risk of unforeseen structural failures and jeopardizing critical infrastructure integrity. Factors influencing its severity include chloride concentration, pH levels, temperature variations and aggressive ion presence, which degrade protective oxide layers and expose metal to accelerated corrosion. This study aims to enhance predictive capabilities to effectively manage corrosion in chloride-rich environments. Using COMSOL Multiphysics software, this study models a microscale geometry representing a micropit and simulates chloride-induced localized corrosion in steel, by integrating Nernst-Planck equations to incorporate electrochemical reactions, ion transport dynamics and three-dimensional geometrical features. Key parameters such as chloride concentration, pH and material properties are crucial in the modelling approach to simulate the formation and growth of corrosion sites. For 0 to 800 seconds simulation, the model displays the flux of ionic species into and out of the pit. At 800 second, the results demonstrate a peak of Fe2+ concentration of approximately 2.53×103 mol/m3 at the deepest section, the Cl- of 7×103 mol/m3 and an increase in H+ inside the pit, reducing the pH from 8 to about 4.9. These concentration changes indicate substantial metal dissolution is actively occurring inside the pit, making COMSOL Multiphysics software a versatile platform for coupling multiphysical phenomena, enabling comprehensive analysis and 3D visualization of corrosion processes.

Low-velocity impact behaviors of TFMLs in hydrothermal and thermal-cycling environments

Thermoplastic fiber metal laminates (TFMLs) have garnered significant attention due to their excellent impact resistance. However, the influence of practical environmental factors on the impact resistance of TFMLs remains inadequately explored. This study endeavor to investigate the impact behaviors and damage tolerance of TFMLs, employing a novel thermoplastic resin, Elium®188, under two simulated marine environments: a thermal-cycling condition (involving 90 days of exposure to 70℃ for 6 h followed by 18 h at room temperature daily) and a hydrothermal environment (consisting of 90 days of immersion in distilled water at 70℃). The impact response and damage characteristics were analyzed through low-velocity impact (LVI) and compression-after-impact (CAI) tests. The findings indicated that under thermal-cycling, the LVI resistance decreased as a result of resin aging, but the resin hardened during aging led to a 48 % increase in CAI strength over the 90-day period. In the hydrothermal environment, the absorbed energy decreased by 5.6 % and CAI strength decreased by 13.7 % after 90 days, primarily due to resin hydrolysis and erosion of the TFMLs’ internal structure by water molecules. This research offers valuable insights into the impact resistance and damage tolerance of TFMLs, serving as a vital reference for practical applications in marine settings.

Depositional and diagenetic evolution of the lower Eocene homoclinic-ramp carbonates (a paradigm from the Salt Range, Pakistan): Sequence stratigraphic, petrographical, diagenetic, and geochemical attributes

Despite the economic significance of the lower Eocene carbonate of the Nammal Formation as a hydrocarbon resource, the influence of depositional facies and diagenetic sequences on the Nammal reservoir quality remains limited. A study on the sedimentological, sequence stratigraphic, diagenetic, and geochemical attributes of the Nammal carbonates has been carried out in three surface sections: Nammal Section (NS), Sethi Section (SS), and Mustafabad Section (MS). To achieve the study target, various petrographic analyses of samples, geochemical analyses (X-ray diffraction (XRD) and X-ray fluorescence (XRF)), and petrophysical measurements (i.e., porosity and permeability) have been done in this study. Our analysis unveils that the Nammal Formation contains mainly alternating marl, shale, and limestone beds. The facies distribution in the middle and upper parts of the Nammal Formation predominantly comprises larger benthic foraminifera, for instance, nummulitids (Nummulites and Assilina), discocyclinids, and rare alveolinids, which demarcate a deepening upward sequence or fining-upward depositional trend. The distribution of these facies is extended from the west to the central parts of the Salt Range, and it is marked as a condensed section in the middle parts of the formation overlain by shallower strata. The upper part of the formation is characterized by a shallowing-up sequence, as there are assemblages of nummulitids, alveolinids, and shallower fauna that extends towards the eastern parts of the Salt Range. The sedimentological analysis of the Nammal Formation depicts the identification of nine microfacies of four recognizable facies associations, revealing the deposition of the Nammal Formation in variable low- to high-energy carbonate ramp sub-environments, including carbonate lagoons, barrier/ shoals, open marine, and deep open marine settings. The Nammal Formation represents the transgressive system tracts (TST) of the Early Eocene carbonate sequence, reflecting carbonate deposition during the rise in sea level in the form of a retrogradational depositional trend of the shallowing upward facies. The Nammal Formation underwent a complex multi-stage diagenetic history taking place over a range of diagenetic settings, including shallow burial, early Eocene uplift and erosion, and subsequent deep burial. Among the recorded diagenetic changes and processes (e.g., dissolution and fracturing) that improved the reservoir properties, others (e.g., cementation, micritization, mechanical and chemical compaction, and pyritization) reduced them by plugging the pore spaces and voids. The Nammal Formation is suggested to be a relatively tight reservoir based on the porosity and permeability values and the nature of compact carbonates. The studied Eocene carbonate deposits preserve carbonate analogues liable for allostratigraphic correlation, identical lithostratigraphic analogues, age constraints, and basin-wide geometrical resemblances. Comparisons of the examined sequence boundaries along the southern Tethys from India to Egypt and in global charts suggest that eustatic and geological effects were relatively simultaneous.

Preparation and Experimental Study of Corrosion-induced Shape-memory Fibers for Crack Repair

Repairing concrete cracks is crucial for enhancing the safety and durability of concrete structures. However, current repair technologies face limitations in corrosive environments such as marine settings. This study presents a novel corrosion-induced shape-memory fiber (CSF) based on the concept of corrosion-induced intelligent fiber (CIF). The CSF1 was made by coating elongated spandex-covered yarn with polyvinyl alcohol, and the CSF2 was prepared by winding stretched nylon fiber with iron wire. Experimental results demonstrate that CSF1 specimens can rapidly heal a 10mm wide crack within two seconds when exposed to water, while CSF2 specimens exhibit obvious shape recovery when exposed to seawater. Moreover, under midspan loads, pre-cracked CSF2-acrylic plate specimens achieve effective crack closure in seawater. These findings confirm the successful transfer of prestress from CSFs to the matrix, thereby validating the feasibility of CIF-based crack repair theory. This research provides experimental evidence for designing and optimizing self-repairing composite materials tailored for various corrosive environments and engineering applications.

The Impact of Perfluorooctanoic Acid (PFOA) on the Mussel Mytilus galloprovincialis: A Multi-Biomarker Evaluation

Perfluorooctanoic acid (PFOA) has been widely studied due to its environmental persistence and bioaccumulation potential, raising concerns about its effects on aquatic life. This research evaluates the impact of PFOA on the antioxidant defenses and stress response systems of the mussel Mytilus galloprovincialis. Mussels were exposed to three concentrations of PFOA (1, 10, and 100 µg·L−1) over 28 days. Several biomarkers, including glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), lipid peroxidation (LPO), total antioxidant capacity (TAC), vitellogenin (VTG), ubiquitin (UBI), and caspase-3 (CASP) were analyzed. The results suggest stress responses, particularly in animals exposed to higher concentrations, as shown by GST and SOD activities which increased according to PFOA concentrations. Additionally, oxidative stress markers such as MDA and CAT showed variable responses depending on the exposure concentration tested. This study underscores the need for further investigation into the effects of PFOA on mollusks but also the need to unveil gender-specific responses in aquatic organisms exposed to this contaminant. The concentrations of PFOA used in our research are lower than those examined in previous studies, providing crucial insights into the impacts of even minimal exposure levels. It highlights the potential of M. galloprovincialis as a bioindicator in environmental monitoring programs, providing crucial insights for environmental management and policymaking regarding regulating and monitoring PFOA in marine settings. Consequently, in a country where seafood consumption is the second largest in Europe, implementing environmental policies and regulatory measures to manage and monitor PFOA levels in marine environments is crucial.

Contrasting responses of commercially important Northwest Atlantic bivalve species to ocean acidification and temperature conditions

Modern calcifying marine organisms face numerous environmental stressors, including overfishing, deoxygenation, increasing ocean temperatures, and ocean acidification (OA). Coastal marine settings are predicted to become warmer and more acidic in coming decades, heightening the risks of extreme events such as marine heat waves. Given these threats, it is important to understand the vulnerabilities of marine organisms that construct their shells from calcium carbonate, which are particularly susceptible to warming and decreasing pH levels. To investigate the response of four commercially relevant bivalve species to OA and differing temperatures, juvenile Mercenaria mercenaria (hard shell clams), juvenile Mya arenaria (soft shell clams), adult and juvenile Arctica islandica (ocean quahog), and juvenile Placopecten magellanicus (Atlantic sea scallops) were grown in varying pH and temperature conditions. Species were exposed to four controlled pH conditions (7.4, 7.6, 7.8, and ambient/8.0) and three controlled temperature conditions (6, 9, and 12°C) for 20.5 weeks and then shell growth and coloration were analyzed. This research marks the first direct comparison of these species’ biological responses to both temperature and OA conditions within the same experiment. The four species exhibited varying responses to temperature and OA conditions. Mortality rates were not significantly associated with pH or temperature conditions for any of the species studied. Growth (measured as change in maximum shell height) was observed to be higher in warmer tanks for all species and was not significantly impacted by pH. Two groups (juvenile M. arenaria and juvenile M. mercenaria) exhibited lightening in the color of their shells at lower pH levels at all temperatures, attributed to a loss of shell periostracum. The variable responses of the studied bivalve species, despite belonging to the same phylogenetic class and geographic region, highlights the need for further study into implications for health and management of bivalves in the face of variable stressors.

Stable and radiogenic strontium isotopes trace the composition and diagenetic alteration of remnant glacial seawater

A remnant of glacial seawater preserved in the pore fluids of sediment cores from the Maldives Inner Sea provided an opportunity to investigate the stable strontium isotopic composition (δ88/86Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of δ88/86Sr as a tracer of early marine diagenesis. We used paired measurements of δ88/86Sr and radiogenic Sr isotope ratios (87Sr/86Sr) in pore fluids and surrounding carbonate sediments to constrain the diagenetic history of the preserved glacial water mass at IODP Sites U1466 and U1468. These pore fluid profiles document variability in δ88/86Sr in a shallow marine setting, revealing distinct diagenetic processes dominating within different depth intervals. We find evidence for isotope fractionation during secondary calcite precipitation at intermediate depths and observe that in aragonite-dominated settings, fractionation during recrystallization may be obscured by the dissolution of aragonite in the uppermost sediments. Correcting for the effect of carbonate recrystallization on pore fluid Sr concentration ([Sr]) and isotopic composition, we estimate that glacial seawater [Sr] was higher (∼98μM) and δ88/86Sr lower (∼0.32‰) compared to the modern ocean, consistent with hypotheses attributing the present-day disequilibrium of the ocean Sr budget to glacial/interglacial changes in shelf carbonate weathering and burial. Our results provide evidence that the ocean [Sr] and δ88/86Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (∼2 Myr) and demonstrate that pore fluid δ88/86Sr measurements are a useful addition to multi-tracer studies of diagenesis in complex marine systems.

Facies Analysis and Depositional Environment of the Euphrates Formation in Selected Sections, Southwestern Iraq

The current study aims to investigate the microfacies, diagenetic processes, and depositional environments of the twenty-three rock samples from the Lower Miocene Euphrates Formation of two outcrops collected at Bahar-Najaf in Najaf governorate and Al-Shinafiya in Diwaniyah governorate, southern Iraq. Thin sections of these samples were prepared; hence, the nature of microfacies and related depositional environments was established. The formation contains abundant benthonic foraminifers and other fossils like miliolids, echinoderm, coral, gastropods, and pelecypods. Seven distinct microfacies were identified: lime mudstone, miliolid packstone, Pelletal Grainstone, Lime Wackestone, Peloidal Grainstone, Oolitic grainstone Microfacies, and fossiliferous packstone packed with bioclasts. Diagenetic processes evidenced in this study are dissolution, neomorphism, cementation, micritization, and dolomitization. The Euphrates Formation was deposited in a shallow marine setting with fluctuating energy levels, ranging from low-energy lagoons to moderate and high-energy shoals and fore-reef environments. Various microfacies indicate a complex depositional environment on a carbonate platform influenced by biota and sedimentary processes. These observations support the inference that the Euphrates Formation accumulated in shallow open marine, inner barrier, and shoal settings, providing a detailed interpretation of its para-depositional and diagenetic development.

Pre‐Vegetation Mixed (Wave‐Tide) Energy Trangressive Nearshore Sedimentation: Evidence From the Proterozoic Passive Margin Sequence of NW Himalaya, India

ABSTRACTThe coupled evolution of the Earth's atmosphere–biosphere system through time has caused irreversible changes in the geodynamics as well as surface processes and sedimentation patterns. One such significant change took place in sedimentation in the Palaeozoic (i.e., Silurian) by the appearance of vascular vegetation. While the impact of evolving vegetation on the terrestrial fluvial environment has been relatively well documented, vegetation‐induced effects down the system in marginal or nearshore marine settings have undergone little study. The Meso‐ to Neoproterozoic Rautgara Formation exposed in the Himalayan Orogenic Belt of NW India, offers a chance to study a well‐preserved fluvial–marine transition to nearshore sedimentation before the appearance of vascular vegetation. A detailed sedimentological analysis identifies six genetically linked facies associations (FA) probably deposited in barrier, back‐barrier, and subtidal deltaic environments. Contrary to the other transgressive barrier models (where beach‐barrier overlie the back barrier environments), in the present case, wave‐dominated barrier deposits mostly occupy the basal part of the stratigraphy. In the middle stratigraphic level, back‐barrier deposits lack thick mud flats and show a dominance of sandstone over mudstone. Stacked subtidal sand bar facies association represents the top part of the sequence. Two sequence stratigraphic surfaces, that is, subaerial unconformity and maximum flooding surface, have been identified and the whole succession is interpreted in terms of HST and TST. Barrier and back‐barrier sediments are deposited during HST and TST, respectively. Subtidal deltaic system developed in late TST. The lack of frequent interbedding between the barrier and back‐barrier facies indicates negligible landward migration of the barrier and demonstrates system stability. The barrier system might have resulted from vertical aggradations akin to modern vegetated systems. The study portrays that sandy barrier systems are common in the Proterozoic. Vegetation and thick mud flats are not always essential for the stability of a barrier‐beach system.

Timing and origin of the Lomagundi-Jatuli Event: Insights from U[sbnd]Pb geochronology, C-O-Fe isotopes and REE compositions from the Jingshan Group, North China Craton

The Lomagundi-Jatuli Event (LJE) represents perhaps the largest and longest positive carbon isotope excursion of Earth history. However, the synchroneity, scale, and linkage of the LJE to Earth's early history of atmospheric oxygenation remain controversial. Strata of the Paleoproterozoic Jingshan Group of the North China Craton that preserve the isotopic record of the LJE excursion in marble layers and abundant graphite deposits provide an opportunity to elucidate the significance of the LJE. Carbon isotopic values (δ13CV-PDB) of the LJE based on analysis of 20 samples of the Lugezhuang Formation, lower Jingshan Group, range from −0.8 to +9.6 ‰ and display positive co-variance with stable oxygen isotope values (δ18OV-PDB). The positive carbon isotope excursion is constrained to 2140.6 ± 8.5 Ma (MSWD = 0.82, n = 25) based on magmatic zircon UPb geochronology of biotite granulite. Variation of facies-dependent carbon isotope values, the presence of graphite deposits of the Douya Formation, upper Jingshan Group, and the absence of a Ce anomaly in PAAS normalized REE patterns of marble samples suggest that the positive carbon isotope excursion is not linked to a marked increase of organic carbon burial and associated significant atmosphere oxygenation. Elevated concentrations of iron and PAAS-normalized middle REE enrichment of analyzed Jingshan Group marble samples point to anoxic and ferruginous oceanic conditions during accumulation of Jingshan Group carbonate. A positive Eu anomaly (average = 1.58), low La (average = 0.23), (Nd/Yb)N (average = 1.27), and Y/Ho (average = 36.6) anomalies, and negative iron isotope values (average δ56Fe = −0.12 ‰) are consistent with accumulation of Paleoproterozoic Jingshan Group carbonate in a restricted marine setting that was affected by high temperature hydrothermal fluids. Enrichment of the studied samples in heavy carbon isotope suggests elevated bio-productivity in the restricted, redox stratified marine setting in which Jingshan Group carbonate accumulated. Thus, it is likely that the positive stable carbon isotope excursion associated with Jingshan Group strata as well as other contemporaneous isotope excursions are local signals that are linked to a global perturbation of the carbon cycle.

A multi-proxy approach to explore paleoenvironmental oscillations and chronostratigraphy of Thanetian carbonates in Eastern Tethys, Pakistan

This study is the first to incorporate geochemical analyses alongside traditional micropaleontological and sedimentological methods to redefine the chronostratigraphy, paleoenvironmental history and regional correlation of the Late Paleocene Lockhart Limestone from four distinct sections covering the entire Upper Indus Basin. Based on the age diagnostic foraminiferal species, we report SBZ3 to SBZ4 (Thanetian age) for the Lockhart Limestone in contrast to previous studies restricting it to SBZ3. The interpretation of eight distinct microfacies reveals a progressively shallowing upward sequence, indicating a dynamic depositional environment with varying energy levels and water depths ranging from inner, middle, to outer ramp settings. Mineralogically, the formation is predominantly composed of calcite, with quartz being the next significant component. Geochemical analyses, specifically the major oxide results, highlight that CaO is the primary constituent, while notable amounts of SiO2, Fe2O3, Al2O3, and MgO are present. The low proportions of SiO2 and Al2O3, combined with their negative correlation with CaO, and high Mg/Ca ratio suggest limited siliciclastic input during the precipitation of limestone that supports the shallow marine depositional environment inferred from the facies analysis. Trace elemental ratios, indicating predominantly oxic conditions, also align with the well-oxygenated waters of a shallow marine setting. Paleosalinity and paleotemperature indicators suggest normal marine and moderate paleotemperature conditions for limestone facies, with lagoonal conditions for shale facies, which is consistent with the interpreted shallow marine environment. The low Total Organic Carbon (TOC) content indicates the presence of type-III and IV organic matter, derived from recycling or continental sources, suggesting limited organic matter preservation in the depositional setting. The clay mineralogy suggests mainly humid conditions with occasional warm climates and alternating humid and arid periods. The deposition of the marine facies of Lockhart Limestone marks the transgression of the Eastern Tethys following a regressive episode that deposited the continental facies of the Hangu Formation, influenced by evolving paleoclimate and geomorphology under Paleo-Tethys tectonism.

Pleistocene to early Holocene paleoenvironmental evolution of the Abrolhos depression (Brazil) based on benthic foraminifera.

The paleoenvironmental evolution of the Abrolhos Depression (AD) on the southern Abrolhos Shelf during the global post-Last Glacial Maximum (LGM) transgression is investigated through benthic foraminifera analysis. Downcore sediment samples (core DA03A-5B) collected at a depth of 63m provide insights into the formation and paleoenvironmental variations of AD over the past 18 kyr BP. The core is divided into four biofacies based on foraminifera assemblages. At the base, the presence of carbonate concretions indicates a karstic surface, marking the initiation of the paleolagoon formation at approximately 13 kyr BP with low density of foraminifera, where species such as Elphidium sp. and Hanzawaia boueana (EH Biofacies) were more abundant. During the Younger Dryas (YD) (12.8-12.5 kyr BP), the AD exhibits two distinct phases: an initially confined lagoon environment with reduced circulation characterized by the dominance of the species Ammonia tepida (At Biofacies), followed by increased circulation characterized by higher density, richness, and diversity of benthic foraminifera. The end of the YD is identified by a significant biofacies change, indicative of a shallow marine environment, where the dominant species were A. tepida and Elphidium excavatum (AE Biofacies), supported by sedimentological and geochemical proxies. This paleoenvironmental shift is associated with Meltwater Pulse (MWP) -1B, suggesting a connection to a shallow marine environment. As sea levels continue to rise, the AD transitions into an open marine setting. However, around 8 kyr BP, a change occurs with the absence of A. tepida and the occurrence of planktonic and other benthic foraminifera typical of the outer shelf, indicating depths greater than 50m (HQ Biofacies). The findings highlight the complex interplay between climate fluctuations, sea-level changes, and the formation of coastal environments during the LGM transgression. This study contributes to our understanding of paleoenvironmental dynamics, adding valuable insights to the evolutionary history of AD. The results emphasize the importance of integrating benthic foraminifera analysis, radiocarbon dating, and geochemical proxies to reconstruct paleoenvironments accurately. Overall, this research enhances our knowledge of global continental shelf evolution during the post-LGM transgression and provides valuable information for future paleoenvironmental studies.

Development and distribution of submarine channels associated with sediment gravity flows in the modern Huanghe (Yellow River) subaqueous delta

BackgroundGravity-driven depositional processes play a pivotal role in shaping the geomorphology of subaqueous deltas worldwide, particularly by eroding the seafloor, leading to the formation of rugged submarine channels (SCs) and triggering various subaqueous geohazards. A comprehensive understanding of SCs is crucial for elucidating these depositional mechanisms and mitigating the risks associated with submarine geohazards. Although SCs in the Huanghe delta front have been previously identified, often described as seafloor gullies or subsurface “disturbed strata,” most studies have primarily concentrated on their engineering geological properties. However, there has been limited research on the scale, morphology, and development of these SCs, especially those that are buried within the stratigraphy.MethodsThis study integrates high-resolution sub-bottom data, sediment core analyses, and historical bathymetric data to investigate the morphology, distribution, and formation mechanisms of SCs in the Huanghe subaqueous delta.ResultsThe SCs, both buried and exposed, are widespread along the middle and upper delta front, predominantly located at or near the landward flank of sediment gravity flow (SGF) -related accumulations. The buried SCs are characterized by cut-and-fill structures with transparent to semi-transparent fills, indicating rapid infilling processes as SGF energy dissipates. These buried channels were preserved within different sets of delta front deposits formed during 1855–1964 CE, 1964–1976 CE, and 1976–2007 CE, with the latter two periods separated by a significant lobe-switching event in 1976 CE. This event, combined with prevailing southeastward sediment transport and erosional regimes, appears to have controlled the preservation of SCs along the delta front: SCs in the Diaokou Lobe's delta front (pre-1976) suffered significant erosion, leaving only one set of channel (erosional remnants) preserved, while the SCs in the Qingshuigou Lobe's delta front (post-1976) are characterized by well-preserved, multi-phase channels at different horizons. The cross-section morphology of the SCs reveal three primary types: symmetrical, asymmetrical, and composite, corresponding respectively to (1) idealized SGF incision, (2) uneven incision intensity on either side of the SCs, and (3) the merging of two or more symmetrical/asymmetrical SCs.ConclusionsWe describe in detail the morphology, distribution and development of SCs in the modern Huanghe subaqueous delta. These findings provide insights into the formation and distribution of SCs in other shallow marine settings, particularly in delta front areas, and potentially offer information for disaster prevention and engineering development in such regions.

Simulating Compaction and Cementation of Clay Grain Coated Sands in a Modern Marginal Marine Sedimentary System

Reservoir quality prediction in deeply buried reservoirs represents a complex challenge to geoscientists. In sandstones, reservoir quality is determined by the extent of compaction and cementation during burial. During compaction, porosity is lost through the rearrangement and fracture of rigid grains and the deformation of ductile grains. During cementation, porosity is predominantly lost through the growth of quartz cement, although carbonate and clay mineral growth can be locally important. The degree of quartz cementation is influenced by the surface area of quartz available for overgrowth nucleation and thermal history. Clay grain coats can significantly reduce the surface area of quartz available for overgrowth nucleation, preventing extensive cementation. Using a coupled-effect compaction and cementation model, we have forward-modelled porosity evolution of surface sediments from the modern Ravenglass Estuary under different maximum burial conditions, between 2000 and 5000 m depth, to aid the understanding of reservoir quality distribution in a marginal marine setting. Seven sand-dominated sub-depositional environments were subject to five burial models to assess porosity-preservation in sedimentary facies. Under relatively shallow burial conditions (<3000 m), modelled porosity is highest (34 to 36%) in medium to coarse-grained outer-estuary sediments due to moderate sorting and minimal fine-grained matrix material. Fine-grained tidal flat sediments (mixed flats) experience a higher degree of porosity loss due to elevated matrix volumes (20 to 31%). Sediments subjected to deep burial (>4000 m) experience a significant reduction in porosity due to extensive quartz cementation. Porosity is reduced to 1% in outer estuary sediments that lack grain-coating clays. However, in tidal flat sediments with continuous clay grain coats, porosity values of up to 30% are maintained due to quartz cement inhibition. The modelling approach powerfully emphasises the value of collecting quantitative data from modern analogue sedimentary environments to reveal how optimum reservoir quality is not always in the coarsest or cleanest clastic sediments.

Gravity wave interaction with compressive VLFS in the presence of thick porous bed

The present study deals with the problem of oblique wave scattering by a finite floating elastic plate over a thick porous bed. A potential flow-coupled thin-elastic plate model has been developed, and the wave flow model resembling the physical scenario is framed into a boundary value problem (BVP). A semi-analytical method has been employed to obtain the hydrodynamic coefficients following the numerical and physical illustrations by varying different geometrical parameters. Prior to wave interaction, dispersive roots are thoroughly analyzed, and a critical frequency is observed above which the group velocity is negative. Within this range, minimum reflection and maximum transmission occur due to the high porosity of the seabed. A discontinuous pattern in the reflection coefficient is observed within the blocking range, which mainly exists for high compression. The findings of this work may be highly valuable for Very Large Floating Structures in marine settings, particularly in situations where interactions are primarily influenced by the thick porous beds.

Quantifying paleoecological impact of the OAE1a on shallow marine ecosystems from southeastern France

Climate and environmental instability during the early Aptian culminated with the unfolding of the Oceanic Anoxic Event (OAE) 1a, which resulted in the deposition of black shales in deep marine settings and a typical negative spike followed by a positive excursion in δ13C values. In Vercors (southern France) the Urgonian platform developed prior to and coeval to the OAE1a, but the impact of this paleoenvironmental crisis on the ecology of benthic ecosystems is yet to be quantified. We gathered field and petrographic data to identify sequence boundaries and maximum flooding surfaces that are biostratigraphically dated and correlated between four localities within the study area. A composite δ13C curve is built where the C3 to C7 isotope segments from the literature are identified, pinpointing the onset of the OAE1a above the last episode of deposition of Urgonian facies rich in rudist bivalves. Furthermore, thin section point counting data are used to quantify the proportion of allochems in samples and to trace changes in the ecology of ecosystems. The principal component analysis of point counting data helps define ecological tiers: a diversified, photozoan association with rudists, green algae, and benthic foraminifera dominated ecosystems before the OAE1a and up to the C7 segment, while a less diversified heterozoan association with bryozoans and crinoids developed after the OAE1a. To explore the triggers for this change, the principal component analysis of elemental geochemical data highlights an increased nutrient and detrital input as major triggering mechanisms for ecological adjustments and changes in the biodiversity of ecosystems. In particular after the OAE1a, an increase in detrital and nutrient input leads to the replacement of photozoan by heterozoan assemblages more adapted to these stressful conditions. This research directly links paleoenvironmental deterioration to paleoecological changes and quantifies the amount of adaptation of ecosystems.

Ocean oxygenation and ecological restructuring caused by the late Paleozoic evolution of land plants

The dramatic increase in ocean-atmosphere oxygen levels during the Devonian and Mississippian is increasingly linked to the diversification of land plants, yet the timing and extent of this event remain uncertain. This study uses the redox-sensitive rare earth element cerium (cerium anomaly—Ce/Ce*) to investigate ocean redox conditions during the deposition of globally distributed Paleozoic carbonate strata. Our Paleozoic Ce/Ce* record suggests that Cambrian, Ordovician, and Silurian oceans had relatively low O2 levels (mean Ce/Ce* = 0.86 ± 0.10, 0.91 ± 0.14, and 0.91 ± 0.10 [±1σ], respectively). In contrast, short-lived ocean oxygenation events, possibly related to the diversification of small land plants, likely occurred throughout the Early and Middle Devonian (mean Ce/Ce* = 0.80 ± 0.07 and 0.58 ± 0.14, respectively). “Modern” Ce/Ce* values (<0.36) first occurred during the Late Devonian, suggesting that the main phase of Devonian and Mississippian oceanic oxygenation was related to the evolution of large vascular plants and the first forests. Despite this, the significant variability of Ce/Ce* values during this time suggests that shallow marine settings were susceptible to redox instability, possibly caused by upwelling of anoxic deep waters. This redox instability potentially provides evidence of a mechanism for contemporaneous mass extinction and metazoan reef collapse events. Development of strongly oxic conditions during the Late Devonian may have resulted in the demise of many Paleozoic-type organisms, facilitated the radiation of the modern evolutionary fauna, and established the modern oxygenated ocean-atmosphere system.

Surface engineering of Q235 carbon steel through a superamphiphobic composite coating enabling robust corrosion resistance and antifouling

Developing an efficient strategy to ensure the resistance of corrosion on Q235 carbon steel from liquid-based contaminants is a challenging work. Although superhydrophobic and superamphiphobic coatings have been fabricated, their susceptibility to oily liquids and poor mechanical robustness still limits their ability to tackle corrosion. Herein, the synthesis and fabrication of a new robust superamphiphobic nanocomposite was presented by combining the reinforcement properties of silicon oxide and the mechanical and thermal stability of zinc oxide into a polytetrafluoroethylene polymer matrix via a colloidal homogenization route. The newly developed composite exhibits a hierarchical bumpy structure, leading to excellent water and oil repellent properties. Importantly, the composite possesses a robust mechanical stability to sandpaper abrasion over a distance of 2000 cm under a 100 g load and a stronger adhesion to substrate. As a result, Q235 coated with this composite exhibits an excellent corrosion resistance in saline water for up to 120 days, and a good self-cleaning and antifouling abilities in most corrosive media. This finding reveals a new pathway for resisting the corrosion attacks on Q235 carbon steel and thereby rendering this strategy with practical application in industrial and marine settings.

Exploring the Potential of High Entropy Alloys: A Comprehensive Review on Microstructure, Properties and Applications: Part I

Over the past few years, there has been a notable surge in research interest surrounding high entropy alloys (HEAs) owing to their exceptional properties. Unlike conventional alloys, HEAs consist of five or more principal elements, which offer endless possibilities for developing new alloy systems. HEAs exhibit a high concentration of mixing elements, resulting in high disorderliness of the atomic structure within the material, known as high entropy. This unique nature provides HEAs with desirable properties, including excellent mechanical and physical properties at elevated temperatures, making them ideal for high-temperature applications like cryogenic engines and gas turbines. Moreover, HEAs have shown remarkable corrosion resistance, positioning them as viable options for applications in demanding environments such as marine settings, oil and gas pipelines and chemical processing plants. This comprehensive review paper analyses recent studies on various HEAs. Part I introduces HEAs and describes their synthesis, microstructure, hardness and strength properties.