Shallow Section Research Articles

Geochemical and mineralogical differences between supergene and hypogene gold mineralization and influence on gold recovery: A case study of the Faina gold deposit, Pitangui greenstone belt, Brazil

The Faina gold deposit, located in the Pitangui Greenstone Belt, NW of the Quadrilátero Ferrífero, Brazil, has produced gold from the oxidized portion of the deposit between June 2010 and June 2013. However, the deeper hypogene (sulfide-rich) section of the deposit has shown lower-than-expected recovery rates after direct leaching, leading to the interruption of gold production. This research presents a multi-methodological approach (drill core description, multi-element geochemical analyses and mineral characterization using microscopy and X-ray diffraction) to investigate describe the Faina gold deposit and identify the cause of low recoveries from the hypogene zone. The stratigraphy at Faina consists of a sequence of meta-mafic and meta-sedimentary rocks, with a thick (>40m) saprolite horizon (oxidized portion). Both the meta-mafic rocks and saprolite host gold mineralization, which is identified by distinct geochemical and mineral signatures: 1) Au-As-W in the hypogene zone, with gold associated with sulfides or as disseminations in silicates and 2) Au-As-W in the oxide-rich shallower section with free-milling gold associated with quartz, iron oxide-hydroxides and clay minerals. Geochemical, mineral and textural relationships in the hypogene zone show that submicroscopic gold particles associated with minerals, that consume leaching solution minerals (arsenopyrite, pyrrhotite and berthierite) may cause refractoriness during direct leaching. Separation of gold from these mineral phases, in addition to concentration methods during ore processing may increase gold recovery. The results presented in this research emphasize the importance of a detailed geochemical and mineral characterization to reveal the contrasting mineral and chemical compositions between hypogene and oxidized zone, which may influence gold recovery.

VIV mechanisms of a non-streamlined bridge deck equipped with traffic barriers

Vortex-induced vibration (VIV) has been addressed in the literature mostly for quasi-streamlined and shallow π-deck sections, typical of long-span bridges, since the latter are particularly prone to wind-induced oscillations. In contrast, although full-scale observations demonstrate that even steel-box girder bridges, usually characterized by a shorter span length if compared to suspension and cable-stayed bridges, can experience a violent VIV response, systematic studies for these bluffer cross-section geometries are less frequent. In addition, the aerodynamic optimization of non-structural additions (barriers, screens, fairings) is rarely carried out for this bridge typology. Therefore, a wind tunnel investigation is conducted on a non-streamlined box-girder sectional model (inspired by the Volgograd Bridge, Russia) equipped with two typologies of traffic barriers giving rise to a large ratio of barrier height to deck width. A realistic range of angles of attack (from −3° to 3°) are considered, and static forces, aeroelastic vibrations and wake velocity fluctuations are measured. A large and even unexpected variability in the vibration amplitude and lock-in curve pattern is found, emphasizing the possible existence of competing excitation mechanisms. Indeed, low-porosity barriers can alter the characteristics of vortex shedding, in particular creating a cavity on the upper side of the deck, which is known to foster the impinging-shear-layer instability, as in H-shaped sections. This vortex-shedding mechanism may co-exist with Kármán-vortex shedding and may be responsible for significant anticipation of the VIV onset compared to the predictions based on the Strouhal number measured during static tests. The intensity of a secondary excitation mechanism and its interaction with the dominant mechanism strongly depend on the angle of attack and is largely responsible for profound changes in the VIV bridge response, both in terms of qualitative pattern and peak amplitude. In some cases, the tracks of these competing vortex-shedding mechanisms are even clearly visible in the VIV response curves of the tested bridge model. Finally, the wind tunnel results are also reconsidered based on the quasi-steady theory, highlighting some, even qualitative, discrepancies.

Performance of SRC unequal-depth beam-column irregular joint in NPP under progressive collapse

The prototype structure of this study is taken from the main shield building of nuclear power plant (NPP) conventional island facilities. Emphasis is on steel reinforced concrete (SRC) unequal-depth beam-column irregular joints, studying their resistance to progressive collapse via analysis of two 1/5 scale irregular joints. Vertical monotonic loading tests were conducted on the joints, followed by numerical simulations to analyze their mechanical properties, failure modes, and progressive collapse resistance. Experimental analyses focused on irregular joint failure modes, central column load changes with displacement, beam deformations, strain variations in critical sections, and resistance mechanism development. Finite element (FE) software modeled these behaviors and was validated against experimental data. Then, according to the various beam section depths of the connected beams, this research applied the validated numerical models to examine the load-bearing capacity of the irregular joints. The results indicate that the damage of the unequal-depth beam-column irregular joint exhibits significant asymmetric characteristics. In terms of load performance, the performance of the irregular joint depends on the component performance of the shallow beam section. Within a certain range, the greater the height difference between the various beams, the greater the joint bearing capacity, but the stability of the bearing performance deteriorates. The fracture yield of H-shaped steel significantly reduces the bearing capacity, and it is recommended to reinforce shallow beams. Providing data reference for the design of the irregular joints has important practical significance.

Do red marine carbonates represent oxic environments? New understanding from the Upper Ordovician marine limestone in Tarim Basin, China

Marine red beds (MRBs), typically colored by Fe- and Mn-rich minerals, are often interpreted as indicators of bottom water oxygenation. However, their continuous formation requires long-term input of aqueous derived Fe-Mn oxides and/or stable sources of Fe2+ and Mn2+ ions, challenging the traditional concept of “red equals oxic environment.” This study investigates two coeval Upper Ordovician Sandbian MRB carbonate intervals in the Tarim Basin. Previous studies attributed the pigment origin to hematite. Th/U values and total rare earth element and yttrium (REY) contents increased in the MRB interval, indicating a terrestrial source of iron. Hematite was observed within the intercrystal pores of calcite precipitating from porewater, consistent with high Nicarb abundance and MREE-enriched bulge pattern in the red intervals. Both sections exhibit high Fecarb and Mncarb, pointing to substantial reductive dissolution of Fe and Mn oxides. Simulation shows that isotopic discrimination (Δ13C) between carbonate and organic carbon could be biased by increasing benthic Fe-Mn flux, leading to decreased Δ13C values in MRB intervals. Ce/Ce∗ values in the high-Mncarb interval reflect the releasing of Ce by reductive dissolution of Mn oxides. The commonly used carbonate-based redox proxy I/(Ca + Mg) ratio is correlated positively with Mncarb in the shallower section and with TOC in the deeper section, while it is negatively correlated with TOC in the shallower horizon, suggesting that iodine behavior may be influenced by adsorption and releasing of Mn hydro-oxides and organic matter besides oxygen contents. This study links MRB coloring to Fe and Mn mineral cycling in pore water through reductive dissolution and oxidative precipitation, and highlights potential biases of carbonate-based redox proxies that might be susceptible to other electron acceptors/donors such as Fe-Mn oxides and organic matter, in addition to free oxygen in seawater.

Use of three-dimensional crossgradient joint inversion of marine controlled-source electromagnetic (CSEM) and seismic refraction data for overburden geohazards mapping.

Offshore energy-transition activities typically require the construction of new subsurface facilities where overburden heterogeneity and deformation pattern may not be fully understood. Anisotropic marine controlled-source electromagnetic (CSEM) and seismic refraction imaging can be adapted to geohazards assessment of the overburden to mitigate safety and costs risks in such areas. This is investigated using an area in deepwater NW Borneo as the type-example. For this proof-of-concept study, a well-established Multiphysics joint inversion code was extended to handle marine seismic refraction data from conventional towed streamers. Realistic field-scale synthetic models with anomalous resistivities and velocities in the shallow section (∼50-200 m below mudline) were built and their CSEM and seismic refraction responses were first inverted separately and then jointly in 3D using the crossgradient method. The joint inversion recovered the anomalous bodies better than the separate inversions. The velocity model from the joint inversion showed improvement from the separate inversion but required a good starting model. As a further test of the methodology, first-break travel times were picked from legacy 3D seismic data and inverted with the available sparse CSEM data. For model verification, resistivity and velocity profiles from separate and joint inversion models were extracted at a well location in the survey area and compared with actual well logs. The joint inversion models matched the well logs better than the separate inversion models. Moreover, known geohazards (complex fault-sets and lateral-inflows) from independent geomatic study were imaged in the joint inversion models. Also, the resistivity anisotropy ratio tracked anomalous zones that correspond to zones of recent complex faulting and potential lateral inflows in the overburden mass transport systems. Thus, joint inversion of CSEM and seismic refraction data has potential to improve the mapping of overburden hazards offshore, with the associated resistivity anisotropy serving as a proxy for active ground deformation.

Characterization and Quantification of Dam Seepage Based on Resistivity and Geological Information

Dam seepage significantly poses a serious threat to both the reservoir safety and the ecological health of the surrounding area. Characterizing and quantifying seepage zones is essential for effective risk mitigation and reinforcement measures. In this study, Electrical Resistivity Tomography (ERT) was applied to detect seepage on a reservoir dam. The ERT survey included three survey lines along the dam. The results indicated low resistivity in seepage zones, showing a distribution extending to the deep section in the middle of the dam and shallow section on both sides of the dam. The reservoir water came out to the ground surface in the downstream from seepage zones. Five seepage models were constructed to quantify seepage based on geological information. The models were further modeled based on the ERT results. Simulated results revealed the annual seepage of the reservoir is 78,880.16 m3. However, 75.5% of the total seepage is contributed by a region representing 50% of the dam. This concentrated seepage should draw the attention of future safety monitoring and reinforcement efforts. This study combines geophysics, geological, and numerical simulation to quantify dam seepage. This allows for the development of more scientifically sound solutions for preventing seepage and improving drainage ability in reservoir dams.

Vp/Vs structure and Pn anisotropy across the Louisville Ridge, seaward of the Tonga-Kermadec Trench

The Pacific Plate within the collision zone between the Louisville Ridge and the Tonga-Kermadec Trench was formed at the Osbourn Trough, a paleo spreading center that became inactive during the Cretaceous. In this region, the trench shallows from a depth of 8–11 km to ∼6 km below sea surface, while the outer rise topography is obscured by Louisville seamounts that rise 4–5 km above the adjacent seafloor. We derive 2-D P-wave (Vp) and S-wave (Vs) velocity-depth models along a wide-angle seismic profile oriented sub-parallel to the trench axis, intersecting the 27.6°S seamount. The seismic profile is located in the down-going Pacific Plate eastwards from the trench axis (∼100 km distant at the south end and ∼ 150 km at the north end), where bending-related faulting is limited or absent. Using the derived P- and S-wave velocity-depth models we calculate the corresponding Vp/Vs ratio model which shows values of 1.7–1.85 throughout the oceanic crust either side of the Louisville Ridge where it is unaffected by magmatism associated with its formation. This range of observations lies within those documented by laboratory measurements on basalt, diabase, and gabbro. Conversely, in the vicinity of the summit of 27.6°S seamount, the relatively elevated Vp/Vs (∼1.9) ratio observed can be attributed to water-saturated cracks within the shallow sub-seabed section of the intrusive core. Beneath the seamount the uppermost mantle has a Vp ranging from 8.0 to 8.9 km/s. Comparing our P-wave model with a pre-existing model running sub-perpendicularly along the Louisville Ridge axis, we observe an anisotropy of up to ∼6% at a depth of 3–4 km below the Moho. The predominant orientation of the faster axis follows the direction of paleo spreading flow when the plate was formed at the Osbourn Trough.

Study on Field Test of Deformation and Stability Control Technology for Shallow Unsymmetrical Loading Section of Super-Large-Span Tunnel Portal

This study focuses on monitoring the deformation of the shallow unsymmetrical section of a super-large-span tunnel portal relying on the newly built Shimentangshan Tunnel, and through numerical simulations, the construction sequence and drift ratios were optimized to address challenges related to the stability of surrounding rock and structure. The findings indicate that employing the double-side drift method results in a maximum settlement value of 107.0 mm and a maximum convergence value of 108.8 mm, leading to larger deformations. Excavating the shallow buried side first followed by the deep buried side proves beneficial for deformation control of the support structure and effectively limits damage to the surrounding rock. A drift ratio of 0.3 ensures optimal support structure security and stability. Considering both structural deformation and surrounding rock damage, a ratio between 0.25 and 0.35 for the drifts is recommended. Taking into account construction efficiency and economic benefits, a construction plan for the shallow buried unsymmetrical section at the portal of super-large-span tunnels is proposed.

Support mechanical response analysis and surrounding rock pressure calculation method for a shallow buried super large section tunnel in weak surrounding rock

At present, China's demand for high-speed railway construction is constantly increasing, and the construction of Multi line high-speed railway tunnels has been put on the agenda. The design and construction issues of super-large-sections tunnels urgently need to be addressed. The Xiabei mountain No. 1 and No. 2 tunnels in the Hangzhou-Taizhou Railway are typical shallow-buried super-large-section-tunnels in weak surrounding rock, and their design and construction issues are representative. Eleven monitoring sections were set up in the tunnel, including tunnel deformation, surrounding rock, shotcrete, steel frames, bolts and temporary support mechanical responses. Taking the monitoring data of the most typical cross-section as an example, the mechanical response of the support structure of a shallow-buried super-large-section tunnel was analyzed in detail. Based on previous research results, this paper discusses and summarizes the common construction problems of this type of tunnel, and puts forward corresponding suggestions. The existing formula for calculating surrounding rock pressure has poor applicability to super-large-section tunnels constructed by step excavation, resulting in conservative support parameters. Therefore, based on the monitoring values of surrounding rock pressure at 10 monitoring sections in Xiabei mountain No. 1 and No. 2 tunnels, empirical parameters reflecting the impact of step excavation were summarized. Based on the Wang formula and combined with the step excavation empirical parameters, an empirical formula for the surrounding rock pressure of shallow-buried super-large-section tunnels considering step excavation was constructed. The calculated results are in good agreement with the on-site monitoring data. This study can provide a good reference for similar projects.

Accretion of the Lower Oceanic Crust at Fast-Spreading Ridges: Insights from Hess Deep (East Pacific Rise, IODP Expedition 345)

Abstract At mid-ocean ridges, melts that formed during adiabatic melting of a heterogeneous mantle migrate upwards and ultimately crystallize the oceanic crust. The lower crustal gabbros represent the first crystallization products of these melts and the processes involved in the accretion of the lowermost crust drive the chemical evolution of the magmas forming two thirds of Earth’s surface. At fast-spreading ridges, elevated melt supply leads to the formation of a ⁓6-km-thick layered oceanic crust. Here, we provide a detailed petrochemical characterization of the lower portion of the fast-spread oceanic crust drilled during IODP Expedition 345 at the East Pacific Rise (IODP Holes U1415), together with the processes involved in crustal accretion. The recovered gabbroic rocks are primitive in composition and range from troctolites to olivine gabbros, olivine gabbronorites and gabbros. Although textural evidence of dissolution-precipitation processes is widespread within this gabbroic section, only the most interstitial phases record chemical compositions driven by melt-mush interaction processes during closure of the magmatic system. Comparing mineral compositions from this lower crustal section with its slow-spreading counterparts, we propose that the impact of reactive processes on the chemical evolution of the parental melts is dampened in the lower gabbros from magmatically productive spreading centres. Oceanic accretion thereby seems driven by fractional crystallization in the lower gabbroic layers, followed by upward reactive percolation of melts towards shallower sections. Using the composition of clinopyroxene from these primitive, nearly unmodified gabbros, we estimate the parental melt trace element compositions of Hess Deep, showing that the primary melts of the East Pacific Rise are more depleted in incompatible trace elements compared to those formed at slower spreading rates, as a result of higher melting degrees of the underlying mantle.

Hyporheic exchange flows in a mountainous river catchment identified by distributed temperature sensing

AbstractElevated stream temperatures under low‐flows, exacerbated by global warming, are a stressor that affects aquatic species directly or in combination with other stressors. Stream temperatures are influenced by energy fluxes across the air–water interface as well as by hydrological exchange processes occurring at the water–riverbed interface. Small‐scale stream temperature dynamics influenced by exchange flows are still underrepresented in stream temperature research. To investigate high‐resolution temperature dynamics and hydrological exchange processes at the sediment–water interface we applied fiber‐optic distributed temperature sensing (FO‐DTS) at two sites in the mountainous Kinzig catchment combined with mapping and measurement of additional environmental conditions. Two types of temperature anomalies could be observed at one site under conditions of low flow and high air temperature. Dampening effects coincided with riverine features such as pools, vegetation roots, fine sediment, and signs of streambank seepage which indicated hyporheic exchange flows. Increased heating of the substrate during the day was identified in shallow sections where sediment was exposed to the air and shading from riparian vegetation was patchy. At another site, at which the cable could not be buried because of the sediment composition, temperature anomalies in the overlying water indicated diffuse groundwater exfiltration. The results show that small‐scale processes in the hyporheic zone, low water tables, and riparian shading influence stream temperature in mountainous streams and can be identified with FO‐DTS under suitable conditions. The results improve our understanding of stream temperatures (in the hyporheic zone) and provide important information on how to improve hydrological modeling.

Paleoenvironment reconstruction of the eastern Tethys during the pre-onset excursion preceding the PETM

A rapid warming event known as the pre-onset excursion (POE) occurred prior to the Paleocene-Eocene Thermal Maximum (PETM). It is less well studied compared to the PETM due to the limited number of well-resolved records globally despite its importance in shaping the subsequent PETM. Shallow marine environments, particularly in low latitudes, are insufficiently documented despite their significant influence on heat and moisture distribution. Here we report high temporal resolution geochemical and magnetic susceptibility records from a well-preserved shallow marine Kuzigongsu section in the Tarim Basin in China to reconstruct the paleoenvironment of the eastern Tethys during the POE. Changes in chemical weathering proxies (e.g., chemical index of alteration [CIA] and Rb/Sr) suggest chemical weathering intensification occurred after the POE. Higher enrichment factors of P, Ba, Ni, and Cu support increased primary productivity due to enhanced river runoff and nutrient input, which aligns with the observed rise in magnetic susceptibility. Concurrently, the eastern Tethys experienced bottom water deoxygenation, which is supported by redox-sensitive proxies (e.g., elevated enrichment factors of U and V, and low Mn* values). Increased δ15Norg values provide additional evidence of enhanced reduction processes due to increased productivity, attributed to enhanced denitrification and 15N enrichment in seawater's NO3− reservoir. The carbon isotope excursion during the POE recovers significantly faster than that during the PETM yet coincides with lingering environmental impacts that are also globally reported for the PETM. These paleoenvironmental proxies reflect notable changes in chemical weathering, ocean productivity, and redox conditions of the eastern Tethys region, potentially setting the stage for the anomalously impactful PETM.

Carbon-Sulfur isotope and major and trace element variations across the Permian–Triassic boundary on a shallow platform setting (Xiejiacao, South China)

We examined microbialites deposited near the Permian–Triassic boundary (PTB) at the Xiejiacao section of South China, including the size and morphology of pyrite framboids, carbonate carbon isotopes (δ13Ccarb), carbonate associated sulfur isotope (δ34SCAS), major and trace elements, and total organic carbon (TOC) concentrations. The microbialite unit is much thicker than the PTB beds in deeper water sections, providing more detailed geochemical records from that time. A prominent negative δ13Ccarb excursion was recognized in association with the second phase of the Permian–Triassic mass extinction (PTME), comparable with that of several other shallow platform facies sections worldwide. δ34SCAS stratigraphic profiles also show a negative excursion, with minimum values occurring slightly later than those of δ13Ccarb. The minimum peak can be calibrated to the middle part of the conodont Isarcicella staeschei Zone, corresponding to the second phase of PTME. Over all, the carbon and sulfur isotopes demonstrate a coupled long-term relationship with large negative excursions during the Permian–Triassic transition followed by gradual recovery in the lowest Triassic, represented an extremely low concentration of sulfate in the ocean during this period. In contrast, the CS isotopes are strongly decoupled within the microbialite unit, which could be linked with the oxygen-poor conditions and microbial sulfate reduction (MSR: Sulfate reducing microorganisms facilitated the precipitation of sulfide and carbonate, such as SO42− + 2CH2O → H2S + 2HCO3−). The second phase of PTME was calibrated to the top of the microbialite unit, which was marked by the second δ13Ccarb-δ34SCAS negative excursions. The distinct marine oxygen deficiency was indicated by the small pyrite framboids, relatively high values of UEF (>1) and Ce/Ce* (>0.8). Combined with the previous biostratigraphic work, we propose that continuous volcanic activity induced intensified marine anoxia, leading to biotic mortality in the second phase of the PTME. Overall, our isotopic and geochemical data, integrated with results of previous studies, provided a new explanation for the carbon and sulfur isotope variations and additional evidences into the concurrent environmental changes during the Permian–Triassic transition.

The Spatial Coupling of Fluid Pathways with Gas Hydrates and Shallow Gas Reservoirs: A Case Study in the Qiongdongnan Basin, South China Sea

Shallow gas reservoirs play a crucial role in the gas hydrate system. However, the factors influencing their distribution and their relationship with the gas hydrate system remain poorly understood. In this study, we utilize three-dimensional seismic data to show the fluid pathways and shallow gas reservoirs within the gas hydrate system in the Qiongdongnan Basin. From the deep to the shallow sections, four types of fluid pathways, including tectonic faults, polygonal faults, gas chimneys, and gas conduits, are accurately identified, indicating the strong spatial interconnection among them. The gas pipes are consistently found above the gas chimneys, which act as concentrated pathways for thermogenic gases from the deep sections to the shallow sections. Importantly, the distribution of the gas chimneys closely corresponds to the distribution of the Bottom Simulating Reflector (BSR) in the gas hydrate system. The distribution of the shallow gas reservoirs is significantly influenced by these fluid pathways, with four reservoirs located above tectonic faults and polygonal faults, while one reservoir is situated above a gas chimney. Furthermore, all four shallow gas reservoirs are situated below the BSR, and their distribution range exhibits minimal to no overlap with the distribution of the BSR. Our findings contribute to a better understanding of shallow gas reservoirs and the gas hydrate system, providing valuable insights for their future commercial development.

Impact of dam construction on sediment transport capacity: A case study of the Three Gorges Reservoir

AbstractReservoir sedimentation affects lifespan, hydropower generation, water resource use, and ecosystem sustainability. In this study, using measured data from the world‐renowned Three Gorges Reservoir (TGR), sediment transport capacity was analysed from 2002 to 2020 at four TGR gauging stations (Cuntan, Qingxichang, Wanxian, and Miaohe). The result indicated that: (1) a significant decrease in sediment transport capacity occurred in the TGR before and after dam construction, with an overall reduction of 82% in the perennial backwater zone. Notably, Qingxichang, Wanxian, and Miaohe experienced reductions of 40%, 91%, and 59%, respectively. Since the initial operation phase, their maximum monthly sediment transport capacity has consistently occurred in July. (2) Changes in the water level in front of the dam, the incoming flow, and sediment influxes were the primary factors driving the annual variations in sediment transport capacity. Among the factors affecting the variation of sediment transport capacity along the TGR, the influence of the cross‐sectional morphology was more pronounced than that of the distance from the dam. Sediment transport capacities in the wide and shallow sections were considerably lower than those in the narrow and deep sections. (3) A sediment transport amplitude index () was proposed to assess the sediment dynamics within the TGR, which effectively characterized the sedimentation conditions based on the relative importance of these influencing factors. These findings provide a theoretical basis for operational strategies in the TGR and offer insights into the patterns of sediment transport capacity changes in reservoir areas before and after dam construction in other river‐type reservoirs.

Excavation method optimization and mechanical responses investigating of a shallow buried super large section tunnels: a case study in Zhejiang

The construction of super large section (SLS) shallow buried tunnels involves challenges related to their large span, high flat rate, and complex construction process. Selecting an appropriate excavation method is crucial for ensuring stability, controlling costs, and managing the construction timeline. This study focuses on the selection of excavation methods and the mechanical responses of SLS tunnels in different types of surrounding rock. The research is based on the Yangjiashan tunnel project in Zhejiang Province, China, which is a four-line highway tunnel with a span of 21.3 m. Three sequential excavation methods were proposed and simulated using the three-dimensional finite difference method: the “upper first and lower later” side drift (SD) method, the central diaphragm method, and the top heading and bench (HB) method. The mechanical response characteristics of tunnel construction under these methods were investigated, including rock deformation, rock pressure, and the internal forces acting on the primary support. By comparing the performance of the three construction methods in rock masses of Grades III to V, the study aimed to determine the optimal construction method for SLS tunnels considering factors such as safety, cost, and schedule. Field tests were conducted to evaluate the effectiveness of the optimized construction scheme. The results of the field monitoring indicated that the “upper first and lower later” SD method in Grade V rock mass and the HB method in Grade III to IV rock mass are feasible and cost-effective under certain conditions. The research findings provide valuable insights for the design and construction of SLS tunnels in complex conditions, serving as a reference for engineers and project managers.

Seismic isolation technology of shallow buried large section utility tunnel with soft soils in seismically vulnerable area

Shallow utility tunnels with exceptionally large cross-sections in weak soil can face significantly more severe seismic risks compared to conventional deep tunnels in seismic hazard areas. This study investigates the seismic response and isolation technologies applied to a large section utility tunnel with 4 compartments in one layer, employing seismic simulations. The engineering context, dynamic motions, and measuring points of the numerical simulation were introduced. Subsequently, the finite element method was employed to explore the seismic behaviors of the large section utility tunnel when subjected to strong earthquake excitations under four conditions. The study explored and comparatively evaluated the seismic isolation effectiveness of three proposed schemes: the grouting scheme, the buffer layer, and the assembly of three-quarters buffer layer, cushion and grouting. The analysis included various indexes such as the deformation, the principal and shear stress, and the safety factor. The finding reveals that the assembly seismic scheme exhibits the most significant seismic effect (95.39%), followed by the buffer layer (38.82%), and the grouting scheme (25.66%). The assembly seismic scheme is recommended for the seismic design in the current large-section utility tunnels. These conclusions provide valuable scientific guidance for the seismic design of large-section utility tunnels, aiding in enhancing earthquake resilience.

Length-Weight-Age Relationship of Schizothorax eurystomus Kessler, 1872 and Comparison to Other Snow Trout Species in Central Asia

This study presents a comprehensive analysis of the length-weight relationship, condition factors, and age of Schizothorax eurystomus in the Shakhimardan River basin in Central Asia, along with a comparative perspective to other Schizothorax species in the region. The study found that S. eurystomus exhibits positive allometric growth, which is consistent with similar patterns observed in this species from the Syr Darya River basin. The two analyzed condition factors showed mean values within the normal range, indicating good feeding and environmental conditions. However, significant disparities between minimum and maximum values of these factors indicated varied growth conditions which may be influenced by anthropogenic factors. Age estimation using opercular bones showed variations in the total length among fish of the same age, and a clear age distribution pattern across different sites. Younger fish predominantly inhabited the shallower, warmer, and lower sections of the river, which is impacted by agricultural water diversion, while older specimens were found in areas with higher discharge and deeper pools. Overall, this research provides valuable insights into the life history traits of S. eurystomus, underlining the need for sustainable fishery management and conservation strategies in the Shakhimardan River basin. The findings also emphasize the importance of considering habitat quality and anthropogenic pressures regarding understanding both fish population dynamics and growth patterns.

Constraining reducing conditions in the Prague Basin during the late Silurian Lau/Kozlowskii extinction event

The Silurian was marked by repeated extinctions, carbon cycle volatility and significant intervals of climatic change. The most notable of these events were the Ludfordian Lau/Kozlowskii extinction and the associated Mid-Ludfordian Lau C isotope excursion, both of which have been linked to a period of global cooling and expanded reducing conditions in the global ocean. We present new data that characterize the marine palaeoredox conditions of the Prague Basin, a peri-Gondwanan terrane. We use I/Ca ratios to assess the local redox conditions in a shallow water carbonate succession and Fe speciation and redox-sensitive trace element concentrations to assess the local redox conditions of a deeper water sequence. Consistently low I/Ca values in the shallow water section suggest either persistent local low-oxygen conditions or possibly diagenetic overprinting. Fe speciation data suggest that the bottom water redox conditions in the deeper shelf setting were consistently anoxic with possible intermittent euxinia. Concentrations of redox-sensitive trace elements consistently higher than upper continental crust values also indicate persistent reducing conditions in the deeper part of the basin. These local redox proxy data from the Prague Basin, including trends in new pyrite S isotope ( δ 34 S pyr ) data, are consistent with previous findings of the expansion of anoxic and/or euxinic oceanic conditions. These data, derived from a mid-palaeolatitude marine setting, fill an important gap in our current global dataset for this interval of the late Silurian. Supplementary material: All the geochemical data reported and discussed herein are available in the Supplemental Data Tables at https://doi.org/10.6084/m9.figshare.c.7008107 Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system

The vertical distribution of fish on two offshore oil platforms

Knowledge of platform ecology is necessary to best inform decommissioning practice. Remotely operated vehicle (ROV) video is often collected during standard industry operations and may provide insight into the marine life associating with offshore platforms, however, the utility of this video for ecological assessments remains unclear. Archival ROV video surveys at the Wandoo oil platforms on Australia’s North West Shelf was evaluated for its utility, with only 4.9% of imagery usable for standardised ecological studies. Based on the subset of usable ROV video, the influence of depth and structural complexity on attributes of the fish assemblage on the Wandoo oil platforms was examined. Vertical ROV transects on three vertical shafts on the Wandoo platforms were stratified into 10 m depth strata from 0 to 50 m, with 111 fish taxa from 25 families identified and counted across all depth strata. At both platforms, taxonomic richness and abundance was significantly highest in shallow regions and declined with depth. Small reef fish were predominantly associated with structurally complex habitat in shallow regions (<22 m), whilst large demersal species dominated below 32 m. Future decommissioning policy in Australia should consider the vertical fish distributions and the importance of shallow sections of platforms. Finally, the dearth of usable video was due to the haphazard method of collection and it is recommended that future surveys should be conducted according to scientific standards to ensure greater utility of the video for both industry use and scientific research.