Search Results (30)

At approximately 05:51 on 22 January 2024, a catastrophic red-bed rock avalanche with a volume of 16 × 10⁴ m³ occurred in Zhenxiong County, Yunnan Province, southwestern China (105°00′47″ E, 27°28′54″ N). The detached rock mass buried 18 houses, killed 44 people, and caused economic losses of 145 million CNY (23.1 million USD). Field investigations, unmanned aerial vehicle (UAV) imagery, interferometric synthetic aperture radar (InSAR) analysis, and two-dimensional discrete-element modelling using PFC2D were conducted to examine the deformation characteristics, failure causes, and kinematics of the rock avalanche. The results show that internal factors, including high-relief terrain resulting from tectonic activity, fractured rock masses caused by joint cutting and weathering, and a soft–hard interbedded stratigraphic structure associated with argillaceous interlayers, were primarily responsible for the failure. Frost heaving may have been an important triggering factor for the Liangshuicun rock avalanche. Continued attention should be paid to slopes around the rock-avalanche site because ground deformation is still ongoing and may lead to future catastrophic events. The numerical simulation reveals that the kinematic process of the rock avalanche from initiation to final deposition lasted approximately 30 s. About 20 s after failure, the rock debris reached the village, burying houses and killing residents. The maximum velocity and displacement of the rock debris were 45 m/s and 335 m, respectively. These findings provide insight into the instability mechanisms and risk assessment of red-bed rock avalanches in the study area. Full article

The Sichuan Basin serves as a key arena for ultra-deep natural gas exploration. The Nanhuan System Gucheng Formation, characterized by its ancient geological age and great burial depth, lacks almost any drilling data within the basin interior, and its sedimentary features and natural gas potential remain unstudied. Based on outcrop sections of the Nanhuan Gucheng Formation along the northern margin of the Sichuan Basin, sedimentological and hydrocarbon reservoir characteristics were analyzed. The study reveals: ① The lower Gucheng Formation at the Chenkou Yuyang section comprises three lithofacies: deformed-bedding conglomeratic sandstone, massive-bedded medium sandstone, and dark-gray horizontally-bedded mudstone, interpreted as deposits of turbidity channels, turbidite fan lobes, and deep-water shelf mud, respectively; ② The turbidity channel and fan sandstones exhibit dissolution pores, with porosities ranging from 8% to 12%, representing favorable reservoirs with a cumulative thickness exceeding 40 m. The deep-water shelf mud shows TOC values between 0.8% and 1.5%, serving as favorable source rocks with a cumulative thickness over 30 m. These two units are interbedded, forming an effective source-reservoir assemblage; ③ Based on the west–east outcrop transect (Zhenba Xiaoyangba, Chenkou Yuyang, and Mahuang Gou sections), the thickness of the Gucheng Formation displays a thin–thick–thin variation, interpreted as reflecting a sedimentary transition from shallow-water shelf delta to deep-water shelf/turbidite systems and back to shallow-water shelf deposits. A rift depositional model with a gentle western slope and steep eastern slope is proposed. In deep-water shelf areas, turbidite sandstone reservoirs are vertically interbedded with shelf mudstone source rocks, while in shallow-water shelf areas, deltaic sandstone reservoirs are laterally connected to source rocks. Spatially, this constitutes a hydrocarbon distribution pattern characterized by “vertical stacking and lateral connectivity,” providing valuable insights for ultra-deep natural gas exploration in the Sichuan Basin. Full article

The Ordos Basin hosts significant shale gas resources in China, yet its marine-continental transitional sedimentary setting causes intense reservoir heterogeneity that severely hinders accurate sweet spot identification in the Permian Shanxi Formation. This study aims to reveal the synergistic controls of lithofacies, mineralogy, and organic matter on shale gas sweet spot formation in the southern Yishan Slope of the eastern Ordos Basin. A multi-dimensional characterization approach was adopted, integrating drilling/logging data and systematic core analyses including X-ray diffraction (XRD), organic geochemical testing, porosity/permeability measurement, and on-site gas content desorption, to quantify reservoir heterogeneity across lithofacies, mineralogy, organic geochemistry, and petrophysical properties. The results show that three lithofacies associations are identified in the target interval: mud-wrapped sand, sand-mud interbedding, and sand-wrapped mud, among which sand-mud interbedding and mud-wrapped sand associations exhibit higher total organic carbon (TOC) contents and strong inter/intra-well heterogeneity. The organic matter in the reservoir is dominated by Type III kerogen, with TOC values ranging from 0.04% to 12.15%, and the Shan 2 Member shows significantly higher average TOC (2.55%) than the Shan 1 Member (1.36%). The reservoir is characterized by ultra-low porosity (average of 0.77%) and low permeability (average of 0.26 × 10⁻³ μm²), with mesopores and macropores contributing over 99% of the total pore volume and showing a significant positive correlation with gas content. Quartz (average of 34.86%) and clay minerals present strong vertical heterogeneity, with the Shan 2 Member being more heterogeneous than the Shan 1 Member due to differences in sedimentary environment evolution. A TOC threshold of 1.5% is determined for sweet spot identification in the study area, and shale gas sweet spots are synergistically controlled by high TOC abundance, moderate brittle mineral content, and 0.1–3 m thick sandy interbeds. This study enriches the theoretical understanding of marine-continental transitional shale reservoirs and provides a scientific basis for sweet spot prediction and development optimization in similar heterogeneous shale gas systems worldwide. Full article

To address stability issues induced by dynamic fracture of weak interlayers in sandstone–mudstone interbedded slopes during blasting excavation, this study investigates the Qingnian Hub diversion channel project of the Ping-Lu Canal through an integrated methodology combining field blasting tests, laboratory dynamic rock experiments, and numerical simulation validation. Field monitoring captured slope dynamic responses, while ultrasonic testing and Split Hopkinson Pressure Bar (SHPB) dynamic splitting tests determined rock mass mechanical parameters. A high-fidelity 3D numerical model developed in ANSYS/LS-DYNA was validated against experimental data, demonstrating reliability with relative errors in peak particle velocity (PPV) below 20% at most monitoring points. Results reveal that increasing interlayer dip angle reduces fracture length along the lower interface while causing internal oblique cracks to initially lengthen and then shorten, with optimal oblique crack development observed at 10–15°. Conversely, greater interlayer spacing first decreases and then stabilizes lower-interface fracture length, whereas oblique crack length peaks at 4.8 m for a 4 m spacing. Based on 25 parametric simulations, a safety criterion using crack-initiation vibration velocity was established, yielding a predictive model dependent on dip angle and spacing. The derived criterion defines a critical vibration velocity range of 5.6–10.0 cm/s for the studied slope configurations. Compared to existing empirical guidelines that rely solely on peak particle velocity, the proposed criterion innovatively incorporates the controlling influence of geological stratigraphic geometry. This study provides theoretical and practical guidance for optimizing blasting parameters and ensuring slope stability in similar engineering contexts. Full article

Soil erosion in the hilly and gully region of the middle reaches of the Yellow River is severe, threatening regional ecological security and the water–sediment balance of the Yellow River. The area features fragmented topography and significant spatial heterogeneity in soil thickness, forming a unique binary “soil–rock” structural system. The soil in the study area is characterized by silt-based loess, and the underlying bedrock is an interbedded Jurassic-Cretaceous sandstone and sandy shale. It has strong weathering, well-developed fissures, and good permeability, rather than dense impermeable rock layers. However, the spatiotemporal differentiation mechanism of soil moisture in this system remains unclear. This study focuses on the typical hilly and gully region—the Geqiugou watershed. Through field investigations, soil thickness sampling, multi-scale soil moisture monitoring, and analysis of meteorological data, it systematically examines the cascade relationships among microtopography, soil–rock combinations, soil moisture, and meteorological drivers. The results show that: (1) Based on the field survey of 323 sampling points in the study area, it was found that soil samples with a thickness of less than 50 cm accounted for 85%, which constituted the main structure of soil thickness in the region. Macrotopographic units control the spatial differentiation of soil thickness, forming a complete thickness gradient from erosional units (e.g., Gully and Furrow) to depositional units (e.g., Gently sloped terrace). Based on this, five typical soil–rock combination types with soil thicknesses of 10 cm, 30 cm, 50 cm, 70 cm, and 90 cm were identified. (2) Soil–rock combination structures regulate the vertical distribution and seasonal dynamics of soil moisture. In thin-layer combinations, soil moisture is primarily retained within the shallow soil profile with higher dynamics, whereas in thick-layer combinations, under conditions of substantial rainfall, moisture can percolate deeply and become notably stored within the fractured bedrock, sometimes exceeding the moisture content in the overlying soil. (3) The response of soil moisture to precipitation is hierarchical: light rain events only affect the surface layer, whereas heavy rainfall can infiltrate to depths below 70 cm. Under intense rainfall, the soil–rock interface acts as a rapid infiltration pathway. (4) The influence of meteorological drivers on soil moisture exhibits vertical differentiation and is significantly modulated by soil–rock combination types. This study reveals the critical role of microtopography-controlled soil–rock combination structures in the spatiotemporal differentiation of soil moisture, providing a scientific basis for the precise implementation of soil and water conservation measures and ecological restoration in the region. Full article

The primary strata of western Taiwan are Cenozoic sedimentary rocks. Characterized by low cementation and high porosity, these rocks exhibit a pronounced wetting–softening effect. Long-term exposure to warm, humid tropical and subtropical climates significantly degrades their engineering geological properties due to weathering. This study, based on a sandstone-shale interbedded highway slope in central Taiwan that has repeatedly collapsed, investigated the slope’s failure mechanism using remote-sensing image interpretation of previous landslides, surface geological surveys, kinematic analysis, photogrammetric mapping, laboratory artificial weathering experiments, and Distinct Element Method (DEM) simulations. The study revealed that the fundamental cause of collapse on this type of oblique-slope interbedded sandstone-shale is the sliding and toppling of sandstone blocks, driven by weathering and erosion of the shale. Based on artificial weathering experiments, the strength loss rate of the shale in the Kuantaoshan Sandstone Member of the Kueichulin Formation after weathering is 6.6 times that of the sandstone. The estimated collapse area from the two-dimensional Distinct Element Method analysis is consistent with the actual value from the photogrammetric model. This type of landslide caused by rock weathering always forms stepped surface where sandstone overhangs above shale. A shale erosion amount of 0.78–0.91 of the spacing of the joint approximately parallel to the slope surface was found to be the critical erosion before collapse and can serve as the early warning indicator. Full article

Predicting favorable reservoirs controlled by source-to-sink systems in rift basins is a current research focus. Using seismic, core, drilling, logging, and thin-section data, this paper systematically identifies fan types and their reservoir characteristics controlled by two boundary faults in the southern steep-slope zone of Wushi Sag, Beibuwan Basin, South China Sea. The analysis compares differences in (1) source–channel–margin–sink systems and (2) diagenetic facies, dividing the sink area into migratory and progradational fans. Results show that migratory fans are associated with denudation. Sediments migrate through wide, deep “V”-shaped valleys, forming fan deltas that are large in area but short in progradation. Lithology is dominated by fine sandstone with siltstone interbeds, reservoirs’ diagenetic evolution is weak, pores are mainly primary, and Type I–II reservoirs are developed. In contrast, progradational fans reflect weaker source area denudation, with sediments prograding through narrow, shallow “U”-shaped valleys. These form broom-shaped fan deltas that are small in area but long in progradation, with lithology dominated by fine sandstone interbedded with mudstone. Reservoirs show strong diagenetic evolution, well-developed secondary porosity, and Type II–III reservoirs. Reservoir prediction models indicate that high-quality migratory reservoirs are large, with excellent physical properties and oil-bearing capacity, mainly in fan stacking zones. High-quality progradational reservoirs are concentrated in the fan midsections, with strong cementation and secondary porosity. These findings provide a theoretical basis for reservoir prediction and oil and gas exploration in the southern steep-slope zone of Wushi Sag. Full article

The Zigui Basin, located in the Three Gorges Reservoir Area, has developed numerous landslides due to its interlayering of sandstone and mudstone, geological structure, and reservoir operations. This study identifies a fourth type of landslide failure mode: an oblique-dip slope wedge (OdSW) landslide, based on the Wanshuitian landslide. Following four heavy rainfall events from 3 to 13 July 2024, this landslide exhibited significant deformation on the 17th and was completely destroyed within 40 min. The dimensions of the landslide were 350 m in length, 160 m in width, and 20 m in thickness, with a volume estimated at 8.0 × 10⁵ m³. The characteristics of landslide deformation and the changes in moisture content within the shallow slide body were ascertained using unmanned aerial vehicles, moisture meters, and mobile phone photography. The landslide was identified to have occurred within the weathered residual layer of mudstone, situated between two sandstone layers, with the eastern boundary defined by an inclined rock layer. Upon transitioning into the accelerated deformation stage, the landslide initially exhibited uniform overall sliding deformation, culminating in accelerated deformation destruction. The dip structure created terrain disparities, resulting in a step-like terrain on the left bank and gentler slopes on the right bank, with interbedded soil and rock in a shallow layer, because the interlayered soft and hard geological conditions caused varied weathering and erosion patterns on the riverbank slopes. The interbedded weak–hard stratum layer fostered the development of the oblique-dip slope wedge landslide. Based on the improved Green–Ampt model, we developed a stability prediction methodology for an oblique-dip slope wedge landslide and determined the rainfall infiltration depth threshold of the Wanshuitian landslide (9.8 m). This study aimed not merely to sharpen the evolution mechanism and stability prediction of the Wanshuitian landslide but also to formulate more effective landslide-monitoring strategies and emergency management measures. Full article

Rock slopes exhibiting anti-inclined interbedded strata have widespread distribution and complex deformation mechanisms. In this study, we used a physical model test with basal friction to replicate the evolution process of the slope deformation. Digital Image Correlation (DIC) and Particle Image Velocimetry (PIV) methods were used to capture the variation in slope velocity and displacement fields. The results show that the slope deformation is conducted by bending of soft rock layers and accumulated overturning of hard blocks along numerous cross joints. As the faces of the rock columns come back into contact, the motion of the slope can progressively stabilize. Destruction of the toe blocks triggers the formation of the landslides within the toppling zone. The toppling fracture zones form by tracing tensile fractures within soft rocks and cross joints within hard rocks, ultimately transforming into a failure surface which is located above the hinge surface of the toppling motion. The evolution of the slope deformation mainly undergoes four stages: the initial shearing, the free rotation, the creep, and the progressive failure stages. Full article

The Cretaceous oceanic red beds (CORBs) and their implications for “oceanic oxic events” have been widely studied by geologists globally. In southern Tibet, CORBs are extensively distributed within the Upper Cretaceous strata of the northern Tethyan Himalaya (NTH). A well-exposed, CORB-bearing, mixed carbonate–shale sequence is found in the Zhangguo section of Rilang Township, Gyangze County. The Chuangde Formation in this section is characterized by well-preserved CORBs, which include reddish shale, limestone, marlstone, and interbedded siltstone. These CORBs are stratigraphically overlain by the Jiabula/Gyabula Formation (predominantly shale) and underlain by the Zongzhuo Formation (“mélange”). However, the precise age, depositional environments, and regional/global correlations of these CORBs, as well as their implications for synchronous versus diachronous oceanic oxic events, remain to be fully understood. In this study, a comprehensive analysis of foraminiferal biostratigraphy and microfacies is conducted for the CORB-bearing Chuangde Formation and the upper Jiabula (Gyabula) Formation in the Zhangguo section. Five planktic foraminiferal biozones including Dicarinella asymetrica, Globotruncanita elevata, Contusotruncana plummerae, Radotruncana calcarata, and Globotruncanella havanensis are identified through detailed biostratigraphic analysis, confirming a Campanian age for the Chuangde Formation and its CORBs. These findings are broadly correlated with typical Upper Cretaceous CORBs in pelagic–hemipelagic settings across the NTH in southern Tibet. Nine microfacies and four facies associations are identified within the Upper Cretaceous strata of Gyangze and adjacent areas through field and petrographic analyses. Notably, it is indicated that planktic foraminiferal packstone/grainstone CORBs were deposited in outer shelf to upper slope environments, while radiolarian chert CORBs are inferred to have formed in deep-water, basinal settings below the carbonate compensation depth (CCD). Full article

Rock slopes containing weak interlayers are highly prone to instability under the disturbance of blasting vibrations due to the influence of structural planes. To address the limitations of traditional models in predicting vibration attenuation for such slopes, this study conducted in situ blasting tests on sand–mudstone interbedded slopes from the Pinglu Canal project. Based on dimensional analysis, the Sadowsky formula was modified to incorporate both elevation difference (H/R) and soft interlayer dip angle (θ), resulting in an enhanced predictive model. Field data revealed that the proposed model significantly improved prediction accuracy, with determination coefficients (r²) increasing from 0.847 to 0.9946 in the vertical (Z) direction. Compared to traditional models, the root mean square error (RMSE) decreased by 96%, demonstrating superior capability in capturing vibration attenuation influenced by geological heterogeneity. Key findings reveal that steeper interlayer dip angles significantly accelerate PPV attenuation, particularly in the X direction. These findings provide a critical tool for optimizing blasting parameters in layered rock slopes, effectively mitigating collapse risks and enhancing construction safety. The model’s practicality was validated through its application in the Pinglu Canal project, offering a paradigm for similar engineering challenges in complex geological settings. Full article

Bedding rock landslides, characterized by their distinct geological structure, are widely distributed and highly susceptible to sliding under external disturbances, resulting in catastrophic events. This study aims to unravel the geomechanical mechanisms governing rainfall-induced instability through an integrated investigation of a representative landslide in Xing’an Village, Chongqing. Employing multidisciplinary approaches, including field monitoring, geotechnical testing, and dynamic numerical modeling, we systematically revealed two critical failure zones: a front failure zone and a rear potential instability zone. Under rainstorm conditions, the safety factor for both zones was 1.02, indicating a marginally unstable state. The DAN-W simulations indicate that the potential instability zone at the rear of the landslide experienced complete failure within 12 s under heavy rainfall, with a maximum run-out distance of 20 m, a maximum velocity of 4.32 m/s, and a maximum deposition thickness of 8.3 m, which could potentially bury the buildings at the toe of the landslide. The low strength and permeability of the mudstone-dominated Badong Formation, characterized by interbedded mudstone, siltstone, and sandstone within the Middle Triassic geological system, provides a fundamental prerequisite for the landslide. Rainwater infiltration into the mudstone layers degraded its mechanical properties, and excavation at the slope base ultimately triggered the landslide initiation. These findings can provide theoretical support for preventing and managing similar bedding rock landslides with similar geological backgrounds. Full article

The shelf-edge trajectory is comprehensively controlled by tectonics, sediment supply, sea level, and climate fluctuations; its migration and evolution have a strong influence on what happens in the deep-water depositional system during the Quaternary. The shelf-edge trajectory pattern, sediment-budget partitioning into deep-water areas, and reservoir evaluations are focused topics in international geosciences. In this paper, the Qiongdongnan Basin (QDNB) in the northern South China Sea is taken as an example to study how shelf-edge trajectory migration patterns can influence the types of deep-water gravity flow which are triggered there. Through quantitatively delineating the Quaternary shelf-edge trajectory in the QDNB, four types of shelf-edge trajectory are identified, including low angle slow rising type, medium angle rising type, high angle sharp rising type, and retrogradation-slump type. A new sequence stratigraphic framework based on the migration pattern of shelf-edge trajectory is established. There are four (third-order) sequences in the Quaternary, and several systems tracts named lowstand systems tract (LST), transgressive systems tract (TST), and highstand system tract (HST) are identified. This study indicates that the type of deep-water gravity flow can be dominated by the shelf-edge trajectory migration patterns. When the shelf-edge trajectory angle (α) ranged between 0° and 4°, the continental canyons were mostly small-scaled and shallowly incised, with multiple large-scale sandy submarine fan deposits with few MTDs found in the deep-water area. When the angle (α) ranged from 4° < α < 35°, the size and incision depth of the continental slope canyons increased, relating to frequently interbedded sandy submarine fan deposits and MTDs. When angle (α) ranged from 35° < α < 90°, only a few deeply-incised canyons were present in the continental slope; in this condition, large-scaled and long-distance MTDs frequently developed, with fewer submarine fans deposits. When angle (α) ranged from 90° < α < 150°, the valley in the slope area was virtually undeveloped, sediments in the deep-sea plain area consisted mainly of large mass transport deposits, and submarine fan development was minimal. Since the Quaternary, the temperature has been decreasing, the sea level has shown a downward trend, and the East Asian winter monsoon has significantly enhanced, resulting in an overall increase in sediment supply in the study area. However, due to the numerous rivers and rich provenance systems in the west of Hainan Island, a growing continental shelf-edge slope has developed. In the eastern part of Hainan Island, due to fewer rivers, weak provenance sources, strong tectonic activity, and the subsidence center, a type of destructive shelf-edge slope has developed. The above results have certain theoretical significance for the study of shelf-edge systems and the prediction of deep-water gravity flow deposition type. Full article

This study presents the geological and geomorphological characterization of the Pie de la Cuesta landslide, a large (>60 ha) slow-moving (up 4.5 m/month) landslide in Southern Peru. The landslide has been active since 1975 and underwent a significant re-activation in 2016; the mass movement has caused the loss of property and agricultural land and it is currently moving, causing further damage to property and land. We use a combination of historical aerial photographs, satellite images and field work to characterize the landslide’s geology and geomorphology. The landslide is affecting the slope of the Vitor Valley, constituted by a coarsening upward sedimentary sequence transitioning from layers of mudstone and gypsum at the base, to sandstone and conglomerate at the top with a significant ignimbrite layer interbedded within conglomerates near the top of the sequence. The landslide is triggered by an irrigation system that provides up to 10 L/s of water infiltrating the landslide mass. This water forms two groundwater levels at lithological transitions between conglomerates and mudstones, defining the main failure planes. The landslide is characterized by three main structural domains defined by extension, translation and compression deformation regimes. The extensional zone, near the top of the slope, is defined by a main horst–graben structure that transitions into the translation zone defined by toppling and disaggregating blocks that eventually become earth flows that characterize the compressional zone at the front of the landslides, defined by thrusting structures covering the agricultural land at the valley floor. The deformation rates range from 8 cm/month at the top of the slope to 4.5 m/month within the earth flows. As of May 2023, 22.7 ha of potential agricultural land has been buried. Full article

Greece is expanding its energy grid system with submarine power and fiber optic cables between the mainland and the Aegean Sea islands. Additionally, pipelines have been installed to support natural gas facilities, and sites are being demarcated for the development of offshore wind parks. The above developments have necessitated extensive geotechnical surveying of the seabed; however, the survey data cannot be accessed for academic inspection or for desktop studies of future developments. This is further hindered by the limited geotechnical information in the Aegean and Ionian Seas. This review examines the existing information concerning the geotechnical behavior of the surficial sedimentary layers, including certain challenges associated with geotechnical sampling and CPTu interpretation. Certain prospects are discussed regarding marine geotechnical research in Greece, with examples from other European countries. The marine geotechnical data in Greece include geotechnical analyses of sediments cores and slope stability estimations, which are commonly associated with the seismic profiling of unstable slope areas. Underlying mechanisms of slope failure have mainly been attributed to the interbedded presence of weak layers (e.g., sapropels, tephra and underconsolidated sediments), the presence of gas and the cyclic loading from earthquake activity. Due to the limited geotechnical information, geological studies have contributed considerably to describing the distributions of gravity-induced events and lithostratigraphy. Within this context, a geological/geotechnical database is suggested where data can be collated and utilized for future studies. Full article