Environmental and Earth Sciences

Abstract: Pisolites are coated carbonate grains whose nucleus–cortex architecture may preserve evidence of changing hydrological conditions, yet their palaeoenvironmental significance remains poorly explored in Pleistocene Mediterranean coastal successions. This study investigates pisolite-bearing horizons from Eivissa (Balearic Islands, western Mediterranean) using field sedimentology, quantitative morphometry, petrography, and X-ray diffraction (XRD). The pisolites occur within fine-grained carbonate-cemented horizons associated with palaeosols and stabilized coastal dune systems, including interdune settings. Morphometric analysis of two closely spaced samples from the same Cala Compte horizon shows significant differences between matrix-associated and isolated fractions in maximum pisolite and nucleus diameters, while cortical thickness differs significantly only in CC2. Petrography reveals successive, locally discontinuous, asymmetric, and variably concentric cortexes, indicating polyphase accretion. XRD shows calcite-dominated pisolites and matrices with subordinate brushite, quartz, and minor unidentified phases. Integrated evidence supports local to near-local formation with limited redistribution under recurrent changes in water availability. The Eivissa pisolites therefore record episodic hydrological variability and polyphase carbonate formation during phases of Pleistocene coastal landscape stabilization.

Abstract: The Curie isothermal surface (CIS) provides important information on crustal magnetic structures and thermal states. Conventional magnetic anomaly spectral methods for CIS inversion commonly rely on manually selected spectral parameters, leading to considerable subjectivity and uncertainty. This study proposes an adaptive CIS inversion method based on multiple geophysical constraints and Bayesian optimization. The method integrates de-fractal spectral analysis with a Tree-structured Parzen Estimator (TPE) to jointly optimize the fractal index, moving-window size, and spectral fitting ranges for estimating the top and centroid depths of the magnetic layer. Multiple constraints, including heat flow, magnetic anomaly characteristics, spatial distribution consistency, inversion uncertainty, and effective data coverage, are incorporated into the objective function. Synthetic experiments show that the proposed method improves inversion accuracy, reducing RMSE and MAE by 25.8% and 28.2%, respectively, compared with the conventional fixed-parameter method. Application to the Ordos Basin and surrounding regions reveals CIS depths of 22–40 km, with deeper values in the basin interior and Yangtze Craton and shallower values in surrounding tectonic zones. The CIS distribution shows consistency with crustal structures, heat flow, and seismicity, providing insights into regional thermal states and tectonic evolution.

Abstract: Antimony (Sb) is a critical raw material whose European supply depends strongly on imports, renewing interest in the metallogenic framework of historical Sb provinces. This review compiles and reassesses 100 Sb deposits and occurrences from Spain and Portugal within a unified geological, structural, and mineralogical framework. Six broad deposit types and twelve mineral associations are recognized, with the Central Iberian Zone containing the largest number and greatest diversity of occurrences. The regional distribution of mineralization indicates a hierarchical control in which long-lived Variscan shear zones and crustal faults organized hydrothermal circulation, whereas second-order fractures, breccias, and favorable lithological or stratigraphic horizons localized ore deposition. Vein-type and stratabound mineralization are therefore interpreted as potentially related expressions of evolving tectono-hydrothermal systems rather than necessarily distinct genetic families. Gold-bearing Sb systems are particularly developed in western Iberia, whereas carbonate-hosted Sb-Hg mineralization characterizes the Cantabrian Zone and Sb-Cu associations are prominent in the South Portuguese Zone. An integrated multistage model is proposed in which heterogeneous pre-ore metal reservoirs, Variscan crustal architecture, late Variscan reactivation, magmatic and thermal activity, and local structural-lithological traps collectively controlled Sb mobilization and deposition. The model emphasizes repeated tectono-hydrothermal reactivation rather than a single universal metal or fluid source.

Abstract: Ground magnetic data were used to investigate crustal magnetic structure beneath the Ulaanbaatar region of central Mongolia. Residual total-field anomalies were analyzed using reduction to the pole, magnetic derivatives, spectral source-depth estimation, and three-dimensional susceptibility inversion. The magnetic field is characterized by short-wavelength anomalies in the south and southeast and broader magnetic domains toward the north. Spectral analysis produces characteristic source-top depths of approximately 3–5 km, centroid depths of 7–10 km, and derived basal depths of about 10–15 km; these values are interpreted as statistical source-depth parameters rather than Curie-point depths. The three-dimensional inversion reproduces the observations with an RMS residual of 2.59 nT and resolves numerous localized upper-crustal susceptibility bodies that merge into fewer, broader domains with depth. Several magnetic boundaries extend beyond mapped lithological contacts and coincide spatially with major structures. In particular, the Avdar and Sharkhai faults are preferentially associated with susceptibility gradients and magnetic-domain boundaries, consistent with reactivation of pre-existing crustal heterogeneity. These results define a three-dimensional magnetic framework for the faulted and repeatedly intruded crust beneath Ulaanbaatar.

Abstract: Research on gas hydrate accumulation in the Shenhu Gas Hydrate Formation in the northern part of the South China Sea has been conducted, determining a vertical distribu-tion pattern with gas hydrates at the top and free gas at the bottom, with both coexisting in the middle of the formation. To address the challenge of quantitative evaluation arising from the interaction between coexisting gas hydrates and free gas in the hydrate-bearing zone during well logging, we established an identification method based on the intersec-tion of three porosity logs that can intuitively display the vertical distribution pattern of the hydrate reservoirs. To quantitatively evaluate coexisting gas hydrates and free gas, we first constructed a model for calculating gas saturation based on the resistivity increase rate and gas content through sedimentary core experiments in the target interval. Based on this, we utilized the neutron density normalization difference to calculate the gas satura-tion in the coexisting zone. By determining the relative contents of bound water and free gas, we obtained the hydrate saturation in the coexisting zone. The hydrate saturation ob-tained using the above methods was consistent with the results of the core experiments, indicating the reliability of the method. The research results can determine the hydrate content in the coexistence zone and provide a reliable basis for the accurate assessment of natural gas hydrate resources in the area.

Abstract: Continuous monitoring of permafrost dynamics remains challenging in remote high-mountain environments due to logistical constraints, harsh climatic conditions, and the limited availability of spatially distributed observations. In addition to direct temperature observations in boreholes, Autonomous Electrical Resistivity Tomography (A-ERT) offers significant potential for long-term monitoring by providing high temporal resolution observations of subsurface electrical properties, which is highly sensitive to freeze/thaw processes. This study presents the field validation of a low-power A-ERT system designed for long-term autonomous operation in extreme environments. The system was deployed at a high-altitude permafrost site near the Kumtor gold mine in the Central Tien Shan, Kyrgyzstan, representing the first application of continuous A-ERT monitoring in the Central Asian mountain ranges. The system operated continuously under harsh environmental conditions with air temperatures as low as −30 °C. Data quality remained consistently high throughout the monitoring period, with less than 1% of measurements removed during filtering, and inversion results with root-mean-square errors generally ranging between 3% and 4%. Time-lapse resistivity observations revealed strong seasonal freeze–thaw dynamics within the active layer and continued seasonal resistivity variations within the underlying permafrost despite permanently frozen conditions. Analysis of depth-dependent resistivity–temperature relationships revealed increasingly pronounced hysteresis behavior below the active layer, indicating that subsurface electrical properties were not controlled solely by temperature. This behavior likely reflects variations in unfrozen water content and pore connectivity within the fine-grained permafrost, where liquid water can persist at sub-zero temperatures. The results demonstrate the capability of the A-ERT system for reliable long-term autonomous monitoring in remote permafrost environments and investigation of coupled thermal and hydrological processes in permafrost systems.

Abstract: Between 1922 and 1926, the Geological Mission of Angola, set up by the High Commissioner Norton de Matos and based in the city of Huambo, surveyed over 30,000 km across the former Portuguese colony, while assembling large collections of fossils and rocks. Led by António Sousa Torres, an experienced naturalist at the Mineralogical Museum of the Faculty of Sciences in Lisbon, the expedition was mentored by the Swiss geologist Ernest Fleury, a renowned teacher on the engineering courses in Lisbon. For those purposes he named three of his former students to join the expedition, for each of them destinated to lead a field brigade. The knowledge generated was disseminated through international conferences and scientific publications produced in collaboration with distinguished foreign specialists. Nevertheless, the Mission’s most significant achievement was the Geological Map of Angola (1:2,000,000) published in 1933. This accomplishment not only fulfilled a political objective but also secured Portugal’s full participation in the International Geological Map of Africa, prepared in accordance with the guidelines adopted at the International Geological Congresses in Madrid (1926) and Pretoria (1929). It also established the basis of the modern geological chartography of Angola, followed by an actualised version in 1954.

Abstract: To investigate the difference of shallow water delta front subfacies reservoir, Moxizhuang area, located in the central Junggar Basin, was selected. Four sedimentary microfacies combination styles, including superimposed underwater distributary channel combination, truncated underwater distributary channels combination, superimposed estuarine dam combination and upper channel and lower residual dam combination, were identified, and the typical identification marks were analyzed. The typical characteristics of reservoirs developed by different sedimentary microfacies combination styles were summarized in combination with hydrodynamic index, physical property parameters and thin sections. The results indicate that the shallow water delta front subfacies mainly develop superimposed underwater distributary channel combination, truncated underwater distributary channels combination, while the development of superimposed estuarine dam combination and upper channel and lower residual dam combination is relatively limited. Superimposed underwater distributary channel combination and superimposed estuarine dam combination are mainly formed under relatively weak hydrodynamic conditions, while truncated underwater distributary channels combination and upper channel and lower residual dam combination are mainly formed under strong hydrodynamic conditions. The reservoir developed by superimposed underwater distributary channel combination type is dominated by sandstone deposition with good sorting, developed rigid debris, weak cementation, strong dissolution, high porosity and permeability, and weak reservoir heterogeneity. It is the most favorable reservoir type of shallow water delta front subfacies.

Abstract: Historical underground workings in the Maleia–Livezeni sector of the Petroșani Coal Basin were reconstructed from four archival mining plans and a coordinate-referenced Drawing Exchange Format (DXF) dataset. Twelve extraction-sector polygons, principal galleries, exploitation limits, dated mining stages, and 567 validated mining-elevation annotations associated with Coal Seam No. 3 were integrated in a geographic information system (GIS) using the Romanian Stereo 70 coordinate reference system (EPSG:3844). Net elevation differences between 2007 and 2026 at seventeen surface benchmarks were used as response variables. Nearest-feature relationships and mining-exposure indicators for 50, 100, and 150 m neighbourhoods were evaluated using exploratory Spearman rank correlations. Cumulative gallery length within 50 m showed the strongest association with elevation-loss magnitude (ρ = 0.734, p = 0.0008, q = 0.010), while extraction-sector coverage and gallery length remained positively associated at broader scales. R19 showed the greatest immediate extraction-sector exposure, whereas R14, which recorded the largest elevation loss, was characterised by a broader concentration of surrounding workings. R09 recorded the smallest elevation change and was approximately 470 m from the nearest reconstructed extraction sector. Cumulative mining configuration was more informative than nearest-sector distance alone for interpreting spatially variable post-mining deformation and highlighted the limitations of archival GIS reconstruction.

Abstract: Unmanned aerial vehicles (UAVs) have gradually become an important technical platform for geophysical exploration because of their high mobility, low cost, adaptability to complex environments, and increasing capacity for autonomous operation. Conventional geophysical survey methods often face difficulties in equipment deployment, operational risk, and insufficient spatial resolution in mountain canyons, polar regions, volcanic areas, mining districts, and disaster-affected zones, whereas UAV platforms provide a new technical pathway for efficient, high-resolution, and low-disturbance geophysical observation. This review summarizes recent progress in UAV-based geophysical exploration, focusing on UAV platforms and intelligent control, UAV magnetic surveys, UAV gravimetry, UAV radiometric surveys, UAV electromagnetic surveys, UAV-based ground-penetrating radar, UAV seismic exploration, and UAV remote sensing for geological hazard monitoring. Although UAV geophysical exploration has made substantial progress, it still faces challenges related to payload capacity, sensor miniaturization, high-precision positioning, data quality control in complex environments, and multi-physics data fusion and interpretation.

Abstract: Acoustic logging while drilling (LWD) provides formation shear-wave velocity in real time during drilling, supporting geosteering and geomechanical evaluation. Shear-wave velocity is currently extracted by slowness–time coherence (STC) processing, which relies on a grid search for the global extremum; its hard decision is prone to dense outlier spikes in multi-event wavefields, and its computational burden is unfavorable for downhole real-time evaluation. We propose a lightweight convolutional neural network (CNN) that regresses the inter-receiver moveout directly from array waveforms; five-fold cross-validation on a synthetic dataset yields a median relative velocity error of 2.51% ± 0.16%. The numeric and image-inversion domains, with either a threshold mask or an Attention U-Net segmentation mask, give consistent velocities, with differences between mask methods of ≤0.6%, and 2.5–4.5 kHz band-pass filtering brings the two domains into convergence. As a control, supervised regression labeled by a measured STC log attains per-gather r = 0.72 over the full well interval under random splitting, but r drops to 0.20 under depth-blocked cross-validation that removes near-neighbor leakage, delimiting the applicability boundary of this proxy route. Inference is a single deterministic forward pass, the model occupies only 266 KB, and it runs approximately 25× faster than vectorized STC, making it suitable for edge deployment.

Abstract: Magnetotelluric (MT) signals are easily contaminated by strong cultural interference and random noise in complex observation environments, leading to distortion of estimated transfer functions. We proposed a joint denoising method integrating Transformer-based noise identification and particle swarm optimization-based variational mode decomposition (PSO-VMD). The Transformer model is first used to identify and locate strong interference noise in the original MT time series, after which abnormal segments are removed and reconstructed to suppress impulsive interference. Meanwhile, VMD is performed on the original signal, with PSO introduced to adaptively optimize the mode number K and penalty factor α, enabling the automatic search for the optimal parameter combination and the acquisition of the best decomposition result. Based on the optimized VMD results, the lower frequency mode components dominated by noise characteristics are removed, and the reconstructed signal from the remaining modes are further filtered to reduce random high-frequency noise. Finally, the filtered PSO-VMD components are superimposed on the Transformer output signal to reconstruct the final denoised MT time series. Both synthetic and observed experimental results show that the proposed method effectively improves the signal-to-noise ratio of MT time series, and further enhances the robustness of transfer functions, providing an effective technical approach for MT data processing in complex noise environments.

Abstract: Global terrestrial water storage change (TWSC) induces hydrological loading, a core driver of nonlinear deformations in GNSS benchmark coordinate time series. High-precision hydrological load models are essential for refining the Terrestrial Reference Frame (TRF) and investigating global climate change mechanisms. To address GRACE's coarse spatiotemporal resolution, discrepancies among reanalysis models, and the common reliance on single-source fusion without uncertainty quantification, we propose an LS-based scale-factor fusion scheme. Integrating GRACE Mascon data with the multi-model ACH-VCE product, we develop GHLW1.0. On a 1°×1° grid, LS determines optimal scale factors between GRACE and ACH-VCE, calibrating GRACE TWSC and fusing with ACH-VCE to produce the GHLW1.0 dataset (2000–2016). Multi-dimensional validation shows GHLW1.0 matches GRACE Mascon in linear trend, RMS of temporal signals, seasonal amplitude, and phase lag. Its phase difference relative to GRACE is ~15 days, substantially better than ACH-VCE's ~30 days, and captures finer spatial details. Applying GHLW1.0-derived vertical displacements to correct 300 GNSS stations, over 90% show correlation >0.7 between modeled and observed. Average correction efficiency is 76%, peaking at 79% (3% above ACH-VCE), with only 5% fluctuation across tests, indicating superior stability. Our LS fusion strategy compensates single-source deficiencies, enhancing TWSC retrieval and GNSS correction, and offers a novel pathway for high-precision stable hydrological load models. Future work will use Singular Spectrum Analysis to decompose homogeneous signals and optimize performance.

Abstract: Numerous landslides appeared in the region of Atsuma (Hokkaido, Japan) as a result of the 2018 Hokkaido Eastern Iburi Earthquake. Despite their devastating consequences, the emergence of mass movements may provide a unique opportunity to gain insight into specific chapters of Earth’s history by exposing new natural outcrops and revealing rock strata. In the region, geological formations, including the studied Middle Miocene Kawabata Formation, composed primarily of sedimentary rocks, reflect various deep-sea environments, especially the continental slope and basin plain of a foreland basin. For such a reason, the exposed bedding plane consisting of polygonal features in an outcrop formed at the scarp of a landslide aroused interest. Mud cracks or desiccation marks often form in the tidal zone due to exposure to the subaerial environment, but not in the aforementioned deep-sea facies. An additional series of evidence of wet and dry cycles in a near-shore (coastal) environment was revealed, such as limonite grain coatings and hypocoatings, and biotite exfoliation. Based on that evidence, a new Middle Miocene facies, a newly discovered stratigraphic member, was proposed in the Kawabata Formation, indicating a tidal palaeoenvironment.

Abstract: Oil-based mud filtrate (OBMF) invasion significantly alters the petrophysical response of nuclear magnetic resonance (NMR) logging, severely compromising the accuracy of reservoir fluid identification and petrophysical evaluation. However, the NMR relaxation behavior of OBMF under elevated temperatures (up to 100 °C) and low-frequency (< 2MHz) conditions remains poorly understood. In this study, temperature-dependent NMR experiments were conducted from 30°C to 100°C at a fixed frequency of 21MHz, while frequency-dependent experiments were performed from 1 MHz to 21MHz at 30°C. Using combined analysis of T₂ spectra and T₂-T₁ two-dimensional spectra, the effects of temperature and magnetic field frequency on the relaxation characteristics of OBMF were investigated under the conditions of this study. The results show that increasing temperature shifts the T₂ distribution toward longer relaxation times, increases T₁ values, and decreases the T₁/T₂ ratio. In contrast, decreasing frequency leads to prolonged T₂ relaxation times, shortened T₁ relaxation times, and a decreased T₁/T₂ ratio. Based on these experimental findings, a dual-parameter model incorporating both temperature and frequency was established for OBMF. The proposed model serves as a theoretical reference for the analysis and correction of NMR logging data acquired under oil-based mud invasion conditions.

Abstract: Distributed acoustic sensing (DAS) deployed in submarine telecom cables is bound to revolutionize the earthquake monitoring routine currently performed by seismic network operators, particularly in domains where most of seismic activity is originated offshore. In this work we analyze one year DAS data recorded on a submarine telecommunication cable joining the Islands of Faial and Flores in the Azores, an area where seismic crisis of volcano-tectonic origin are frequent. We explore whether spatially decimated channels can be added to the operation routine without major changes. During the DAS operation the land network recorded 368 local and regional earthquakes. The best of these events were jointly analyzed and earthquake parameters were compared between original locations and adding DAS picks. Despite the larger picking uncertainty on DAS channels, adding P and S or S-wave picks only from DAS data showed a considerable improvement on earthquake parameters, reducing the error ellipse area and the focal depth uncertainty. These results demonstrate that in domains where offshore seismicity is a concern and submarine telecom cables are available, integrating DAS channels into the routine operation of seismic networks considerably improve the accuracy earthquake parameter estimation. A procedure to accomplish these results is presented.

Abstract: Olivine, as (Mg, Fe)2SiO4 solid solution, governs the plastic flow of the Earth's upper mantle. While extensive studies exist on natural olivine-rich rocks, the rheology of its Mg-end member, forsterite (Fo), remains less constrained, particularly for diffusion creep. Here we synthesize high-purity (≥98 vol.%), iron-free forsterite aggregates via pressureless sintering and perform axial compression experiments in a high-stress-precision Paterson gas-medium apparatus at 300 MPa, temperatures of 1423–1523 K, and differential stresses of 50–380 MPa. Our results reveal a stress exponent n = 1.0 ± 0.08, an activation energy Q = 365 ± 22.7 kJ/mol, and a grain size exponent p = 2.9 ± 0.23, demonstrating that forsterite deforms by diffusion creep under these conditions. The grain size exponent, close to the theoretical value of 3 for Coble creep, indicates that grain boundary diffusion is the rate-controlling mechanism. Compared to previous studies on forsterite and natural olivine, our flow law shows good agreement with the activation energy for olivine diffusion creep but provides a significantly better-constrained grain size exponent. Critically, because our samples are chemically synthesized and iron-free, and lack the trace impurities that facilitate defect generation in natural olivine, they exhibit higher strength than natural Fe-bearing olivine. Our flow law therefore defines the Mg-end member for the olivine solid solution system and represents the viscosity upper bound for olivine-dominated mantle rocks deformed dominantly by diffusion creep. These findings not only fill a critical gap in the rheological data for the olivine solid solution end-members but also provide a robust basis for modeling viscosity variations in the upper mantle as functions of grain size, temperature, and iron content.

Abstract: Two breakwaters were constructed between 1959 and 1961 by the U.S. Army Corps of Engineers to form a harbor within Half Moon Bay on the central California coast. Prior to construction, the bay had a smooth hook-shaped or spiral form with a shoreline in equilibrium with waves refracted around a resistant point. Following breakwater completion, wave energy that had previously been dissipated along the equilibrium shoreline of the bay was concentrated at the downcoast end of the breakwater against the low weak bluffs. The original very low (~8 cm/year) bluff recession rates increased rapidly to as much as 2 m/year which led to the destruction of a county road and wastewater transmission line and began to threaten a state highway and a group of homes. Bluff erosion has progressed as far as 1.4 km downcoast which has led to rock revetment placement to protect the highway and homes. Breakwater planning also underestimated the potential for waves to enter the gap between the two breakwaters, so a dogleg extension had to be constructed. This also failed to reduce wave action, which led to construction of an additional set of breakwaters within the harbor to protect moored boats.

Abstract: The identification and delineation of subsurface resistive anomalies beneath sedimentary cover remain challenging for the magnetotelluric (MT) method. In this study, we compared the attenuation behavior of electromagnetic (EM) fields and their response characteristics under surface and/or subsurface observation configurations using both synthetic and field data. The synthetic results show that the conductive cover layer substantially suppresses the EM responses of the subsurface high resistivity body, producing only weak response perturbations at surface stations. In contrast, the response amplitudes recorded at underground stations are enhanced, indicating that underground EM observations provide advantages in resolving subsurface resistive anomalies and constraining their geometric boundaries. The results further reveal distinct attenuation behaviors of the electric and magnetic fields, with the electric field being more sensitive to variations in the bulk conductivity of the sedimentary layer. Furthermore, one-dimensional Bayesian probabilistic inversions of both synthetic and field datasets indicate that underground observations provide more robust and reliable estimates of the resistivity structure. These findings suggest that further exploration of deep underground observations and the deployment of high sensitivity quantum EM sensors have considerable potential for detecting and characterizing weak EM responses from resistive targets in sedimentary environments, while also improving the reliability of inversion results and reducing their uncertainty.

Abstract: To characterise the fracture network geometry of a fluid reservoir, fundamental parameters are used in a DFN simulation algorithm. However, evaluating the hydrodynamic behaviour of such rock bodies also requires apertures of individual fractures. Aperture is usually not treated as an independent variable; rather, it is derived from length. A common approach is a linear relationship, a = A*L, where A is the aperture coefficient. The fracture’s free volume varies with the aperture coefficient, which influences the modelled fractured porosity and permeability. Since post-tectonic fluid-rock interactions can considerably alter the original apertures, the relationship between fracture length and aperture may vary across a reservoir, complicating hydrodynamic modelling. Therefore, from a hydrodynamic perspective, the hydraulic aperture should be used instead of the physical aperture. In this paper, transmissivity data and DFN models are analysed simultaneously to estimate reliable aperture coefficients. The method is demonstrated using the fractured Mórágy Granite body in SW Hungary. In the context of the radioactive waste depository project, numerous wells penetrated the fractured granite. Transmissivity data and DFN models from 238 intervals are used to calibrate aperture coefficient values. The associated porosity data are employed to construct a porosity log for each well, and analyse poro-perm diagrams.