The Yunkai Massif is one of the Precambrian metamorphic crystalline basements within the South China Block. To better understand the Indosinian deformation characteristics in the Yunkai area, the Shili ductile shear zone at the northwestern margin of the Yunkai Massif was selected for this study.

Through detailed field investigations, finite strain measurements, kinematic vorticity analyses, and ⁴⁰Ar/³⁹Ar geochronology, the structural characteristics and evolutionary process of the shear zone were constrained.

The Shili ductile shear zone generally strikes WNW–ESE with NNE-directed thrusting. It has undergone four phases of deformation. Among which, the D2 to D4 deformations all indicate movement from SSW to NNE. D2 to D4 formed under a unified tectonic stress field, reflecting an evolution from ductile shear through brittle-ductile deformation to folding during the Late Triassic. Mylonites formed synchronously with the ductile shear deformation yield a muscovite ⁴⁰Ar/³⁹Ar plateau age of 232 ± 2.3 Ma (MSWD = 3.65). The Flinn index (K) is 0.06–0.77, the Lode parameter (ν) is 0.13–0.89, the Effective strain (E_s) is 0.41–0.51, and the kinematic vorticity value (W_k) is 0.70–0.78. These parameters indicate a flattening-type strain regime dominated by general shear, with comparable contributions of pure shear and simple shear. The dynamic recrystallization of minerals suggests that the deformation environment reached the upper greenschist facies.

This study indicates that the mylonitization, crenulation cleavage development, and folding within the Shili ductile shear zone were dynamically driven by the propagation of far-field stress resulting from the NE–SW collision between the Indochina and South China blocks during the Indosinian period.

These findings provide critical constraints on the Indosinian tectono-thermal event and its geodynamic framework in South China.

A series of Early Cretaceous sedimentary basins developed in the Hexi Corridor along the northeastern margin of the Tibetan Plateau. These basins preserve critical records of the regional pre-Cenozoic tectonic evolution, forming the basis for understanding the Cenozoic growth mechanism of the Tibetan Plateau. However, the nature of these Early Cretaceous basins remains controversial, impeding a clear understanding of the late Mesozoic tectonics in this critical area.

Focusing on the Minle Basin in the central Hexi Corridor, this study carried out systematic field structural investigations and paleo-stress reconstructions. Through detailed structural analysis, the formation and post-depositional modification processes of the Minle Basin were re-evaluated.

Our investigation reveals that the Lower Cretaceous strata in the Minle Basin are characterized by abundant syn-sedimentary normal faults with initial nearly N-S strikes, indicating that the basin was an extensional fault basin controlled by E-W-directed extension during the Early Cretaceous. Subsequent deformation is represented by two sets of folds with NE-SW and NW-SE axial trends, together with shortening structures in Lower Cretaceous rocks, revealing that the basin underwent bidirectional (NE-SW and NW-SE) horizontal shortening during the Late Cretaceous.

The Early Cretaceous extension in the Minle Basin was consistent with the widespread extensional deformation and extensional stress direction across East Asia during this period, resulting from the slab rollback of the Paleo-Pacific Plate and associated mantle flow. The bidirectional Late Cretaceous shortening resulted from the superimposition of the remote effects of simultaneous compression events in the Tethys and Pacific tectonic domains, respectively, along the southern and eastern margins of the Eurasian Plate. [Significance] The deformation characteristics demonstrate that the influence of the subduction of the Paleo-Pacific Plate extended westward to at least the Hexi Corridor and the northern margin of the Tibetan Plateau.

Large-scale thrust-nappe structures have a significant impact on the regional geological environment and are important factors controlling the development of karst systems. Quantitative analysis of karst geological fractal characteristics in such settings provides essential scientific insights into the nonlinear behavior of complex karst systems.

Focusing on the karst region along the Qingfeng fault zone, the box-counting dimension method of geological fractal theory was used to quantify key geological elements. We evaluated the fractal characteristics across both regional scales and watershed units to determine their fractal dimensions and scaling properties.

The stratigraphic boundaries at both regional and watershed scales exhibit pronounced fractal characteristics. Karstification significantly enhances boundary complexity, leading to higher fractal dimensions in areas with more advanced karst development. Furthermore, thrust-nappe structures and tectonic movements strongly influence drainage network fractals, modifying the conventional spatial mapping between surface and groundwater systems. The fractal dimensions of surface drainage systems show a positive correlation with those of subsurface karst drainage systems. Peak landforms in the study area exhibit youth-stage peak-cluster characteristics, indicating an early stage in the regional karst geomorphic cycle.

Karst in the region exhibits fractal characteristics, and the peak evolution follows the three-stage patterns common in karst areas. Surface and groundwater systems have positively correlated fractal patterns, and stratigraphic boundary dimensions serve as a robust indicator of karst development intensity.

Clarifying the self-similarity of karst in thrust-nappe tectonic zones provides a quantitative reference and theoretical basis for assessing the relationships between faulting, karst distribution, and evolutionary dynamics, offering a valuable methodological approach for addressing similar karst geological issues.

The Wushi region in Xinjiang is located at the intersection of multiple tectonic units, characterized by frequent tectonic activity, making it a critical region for stress concentration and release. On January 23, 2024, an M 7.1 earthquake struck Wushi (epicenter: 41.26°N, 78.63°E; depth: 22 km), representing the largest event in this area over the past decade. To better understand the regional seismogenic environment and assess future seismic hazards, this study utilizes comprehensive focal mechanism data to investigate the regional tectonic stress field and quantitatively evaluate the impact of the M 7.1 Wushi earthquake on the stress regime.

Based on 148 focal mechanism solutions (January 1976 to March 2025) compiled from multiple domestic and international institutions, we applied the damped stress tensor inversion method to determine the stress field characteristics across subregions and systematically evaluate changes in the stress field before and after the earthquake.

Stress tensor inversion reveals that the Wushi region is dominated by a compressional stress regime under N–S compression. Except for the area near the Jiashi earthquake cluster where R > 0.5, the azimuth of the maximum principal compressive stress (σ₁) gradually rotates from NNW in the south to approximately N–S in the north (azimuth range: 168.75°–183.45°; plunge range: 6.85°–19.58°). The Jiashi seismic cluster exhibits a strike-slip stress regime characterized by NNE–SSW compression and NWW–SEE extension, with thrust faulting dominating to its north and strike-slip faulting to its south. Comparative analysis shows that the optimal σ₁ direction adjusted from an azimuth/plunge of 178.91°/6.24° before the earthquake to 167.61°/7.98° after the earthquake, corresponding to an azimuth deviation of 12.53° and a total spatial rotation of 15.06°. This indicates that the mainshock exerted a relatively minor impact on the regional stress field, which remains under the dominant compressional regime.

The tectonic stress field in the Wushi region is driven by the northward collision of the Indian plate against Eurasia, which transmits near-N–S horizontal compression northeastward into the Tianshan orogenic belt, causing crustal shortening and thrusting between the Tarim Basin and the Tianshan Mountains. The M 7.1 earthquake caused only localized adjustments, leaving the overall regional stress regime controlled by deep-seated tectonic processes. Furthermore, the northern Jiashi earthquake cluster, located at the boundary between the northern Tarim plate and the Tianshan Mountains, exhibits a strike-slip stress mechanism, marking a major tectonic transition zone between the Tarim Basin and the Tianshan orogenic belt.

This study provides a refined characterization of the tectonic stress field in the Wushi region and clarifies the limited impact of the M 7.1 mainshock on regional stress states. These findings deepen our understanding of the tectonic interactions between the Tianshan orogenic belt and the Tarim Basin, providing critical scientific constraints for regional tectonic segmentation and seismic hazard assessment.

Unconventional oil and gas development is frequently hindered by complex reservoir structures and unquantified rock mechanical properties. To optimize horizontal well trajectories and hydraulic fracturing designs—thereby expanding the stimulated reservoir volume, mitigating casing deformation risks, and ensuring efficient production—high-resolution rock mechanical models are essential. This study proposes an integrated workflow combining statistical regression and 3D prestack seismic inversion to accurately characterize the vertical and lateral variations of rock mechanical parameters in target zones.

Using core test results and well log data, quantitative empirical relationships were established between elastic attributes and rock mechanical properties. A 3D prestack seismic inversion was subsequently performed using integrated drilling and seismic datasets to extract precise elastic parameters, including compressive wave velocity, bulk density, Poisson's ratio, and Young's modulus.

The workflow was applied to tight glutenite reservoirs in the Bonan Sag, yielding three key findings: (1) Young's modulus demonstrated a strong correlation (e.g., R² > 0.75) with Uniaxial Compressive Strength (UCS) . In these low-porosity glutenites, rock mechanics are primarily governed by lithology and gravel content rather than burial depth, justifying a unified prediction model. (2) By integrating well logging and a time-depth velocity field, a depth-domain structural framework was established. Attribute extraction and property modeling generated a continuous 3D volume of rock mechanical parameters, bridging the spatial gaps inherent in discrete log and core measurements. (3) The resulting 3D mechanical volume provides critical input for hydraulic fracturing optimization. It enables precise profiling along horizontal wellbores, rational stage and cluster spacing, pumping parameter optimization, and improved fracture conductivity, thereby maximizing single-well productivity.

Integrating prestack seismic inversion with statistical regression offers a robust approach for 3D geomechanical characterization in heterogeneous tight glutenites. This methodology successfully bridges the gap between petrophysics and seismic geophysics, resolving key uncertainties in complex unconventional plays.

This study provides a practical and scalable framework for predicting 3D rock mechanical properties. The findings offer a reliable data foundation for defining mechanical boundaries and optimizing stimulation treatments in heterogeneous unconventional reservoirs.

The Chang 7 and Chang 6 Members of the Yanchang Formation in the Jingbian area of the Ordos Basin are important source rock intervals. However, systematic studies on their hydrocarbon generation potential and contributions to hydrocarbon accumulation remain limited, which has hindered further exploration efforts in this region. Therefore, this study applies geochemical analytical methods to systematically characterize the distribution and the geochemical properties of the Chang 7 and Chang 6 source rocks in the Jingbian area. In addition, the geochemical signatures of the crude oils from the Yan 9 and Chang 2 reservoirs in the Jingbian Oilfield were investigated.

By comparing the geochemical parameters of the Chang 7 and Chang 6 source rocks in the study area with those of the Zhangjiatan Shale in the basin center, the potential sources of the Yan 9 and Chang 2 reservoir oils were identified through oil–source correlation.

The Chang 7 source rocks are moderate to excellent-quality source rocks, characterized by wide distribution, large thickness, Type Ⅰ–Ⅱ₂ kerogen, and a mature thermal evolution stage. Biomarker characteristics indicate mixed organic matter inputs and deposition under reducing conditions with relatively low salinity. Low Pr/Ph ratios and high C₂₇/C₂₉ regular sterane ratios suggest that the organic matter was predominantly derived from aquatic algae and other lower organisms and accumulated in a reducing freshwater to brackish-water depositional environment. In contrast, the Chang 6 source rocks are moderate to good-quality source rocks, dominated by Type Ⅱ₂–Ⅲ kerogen, and generally at the low-maturity to mature stage. Moderate Pr/Ph ratios and relatively low C₂₇/C₂₉ regular sterane ratios indicate a predomint innput of terrigenous higher plantsand deposition under weakly reducing conditions. Oil-source correlation results reveals that the Yan 9 and Chang 2 crude oils have the same originand were primarily sourced from the Chang 7 source rocks, with a minor contribution from the Chang 6 source rocks. The distinct geochemical characteristics of the Zhangjiatan Shale compared with the Yan 9 and Chang 2 crude oils further suggest that the Zhangjiatan Shale was not the major hydrocarbon source for these oils.

(1) The Chang 7 Member is the primary and high-quality source rock in the Jingbian area, exhibiting advantages over the Chang 6 Member in terms of thickness, lateral distribution, organic matter abundance, and hydrocarbon generation potential. (2) Distinct biomarker signatures differentiate the Chang 7 (aquatic/algal-derived organic matter under reducing conditions), Chang 6 (terrigenous organic matter under weakly reducing conditions), and Zhangjiatan Shale (highly aquatic organic matter under strongly reducing conditions) source rocks. (3) The Yan 9 and Chang 2 crude oils share a common origin and were primarily sourced from local Chang 7 source rocks, with possible minor contributions from the Chang 6 source rocks. These oils show no direct genetic relationship with the Zhangjiatan Shale in the basin center, supporting a predominantly local hydrocarbon charging model in the Jingbian area. [Significance] This study provides critical geochemical evidence for understanding the local hydrocarbon system, resolving uncertainties regarding oil sources, and evaluating exploration potential in the Jingbian area of the Ordos Basin.

The Pen-1 West Sag is an important area for future hydrocarbon exploration in the hinterland of the Junggar Basin. However, systematic studies on the characteristics and development mechanisms of its deep to ultra-deep Permian–Triassic reservoirs remain limited.

Core, well-log, analytical, and seismic data were integrated to systematically investigate the petrological characteristics, reservoir properties, pore structures, and diagenetic evolution of the Permian–Triassic reservoirs in the Pen-1 West Sag and to identify the main factors controlling differences in reservoir quality.

The reservoirs are predominantly lithic sandstones, with volcanic lithic fragments accounting for more than 80% on average; intermediate to mafic volcanic rock fragments dominate. Reservoir properties show significant vertical variations. The Karamay and Baikouquan Formations exhibit the best reservoir properties, with porosities mainly ranging from 5% to 13% and permeabilities mostly in the range of 0.1×10⁻³–10.0×10⁻³ mD, indicating relatively high-quality reservoirs. In contrast, the Upper and Lower Urho Formations have poorer reservoir properties. Secondary pores dominate the reservoir pore system, with dissolution pores within zeolite cements and intragranular dissolution pores within volcanic lithic fragments being the most abundant secondary pore types. Secondary pores account for more than 70% of the total pore space in the Baikouquan and Upper Urho Formations, whereas they account for 40%–60% in the Karamay Formation, where residual primary intergranular pores remain important.

Reservoir property differences are jointly controlled by multiple factors, including provenance characteristics, lithology and grain size, diagenetic alteration (grain-coating development, zeolite cementation and dissolution, and clay-mineral filling), the composition of volcanic lithic fragments, and temperature and pressure conditions. Based on the diagenetic evolution sequence and variations in the proportions of pore types, two reservoir property evolution models are proposed: a primary-pore-preservation type, represented by the Karamay Formation, and a secondary-pore-dominated type, represented by the Baikouquan and Upper Urho Formations.

These findings provide an important basis for predicting and evaluating deep clastic reservoirs in the Pen-1 West Sag and in other areas with similar geological conditions.

To elucidate the diffusion mechanisms of shale oil and gas in nano- to microscale pore-fracture systems and overcome the limitations of conventional models in cross-scale prediction, this study investigates the diffusion characteristics and controlling factors of shale fluids across multiscale porous media.

High-temperature and high-pressure diffusion experiments were conducted on matrix and bedding-fractured core samples with varying petrophysical properties. A multiscale diffusion model was developed by coupling fractal theory, a tortuous capillary-bundle representation, and a confinement-corrected Peng–Robinson equation of state to account for pore-size distribution, tortuosity, phase saturation, and nanoscale fluid–wall interactions.

Nanoscale confinement leads to phase-diagram contraction and a leftward shift of the critical point, substantially weakening diffusion capacity in confined spaces. Porosity and permeability are the primary structural controls: when porosity increases from 5.68% to 10.53%, gas and liquid diffusion coefficients increase by approximately one order of magnitude; when bedding-fracture permeability increases from 1.69 ×10⁻¹⁵ m² to 404.88 ×10⁻¹⁵ m², diffusion coefficients rise by about three to four times. Increasing pressure (10~36 MPa) suppresses gas-phase diffusion but enhances liquid-phase diffusion, whereas higher temperatures (80~115 °C) promote diffusion overall.

The proposed fractal–confinement diffusion model accurately matches the experimental results and reveals key nanoscale mechanisms, including a ~10⁻⁵ reduction in effective diffusivity relative to bulk fluids and diffusion capacities in fractures that exceed those of the matrix by one to two orders of magnitude.

This model enables structural-sensitivity analysis and cross-scale prediction of diffusion processes, providing theoretical support for the quantitative characterization of shale-fluid migration and the optimization of reservoir development.

As human engineering activities expanded into the Tibetan Plateau and its surrounding areas, slope instabilities—particularly large-scale landslides—in deeply incised valleys have occurred with increasing frequency, posing severe threats to major infrastructure projects and public safety. This study evaluates how regional tectonic activity controls slope stability and outlines key challenges, insights, and strategic recommendations for slope engineering planning and construction in these deeply incised valleys.

Based on an overview of the tectonic activity characteristics across the Tibetan Plateau, the controlling influence of tectonic activity on slope stability was systematically analyzed. Problems encountered in slope engineering planning were identified, leading to practical engineering recommendations and strategic directions for future research.

Tectonic activity exhibits strong spatial consistency and temporal synchronicity with slope instability across the plateau. Tectonic processes provide the essential structural and geomorphic boundaries, material sources, dynamic conditions, and triggering factors for slope failures. Key challenges include the dominant control of regional tectonic stress on valley slope stability, the need to re-evaluate reverse slope stability in deeply incised valleys, and the required paradigm shift regarding the horizontal cover depth for mountain-adjacent underground works. Analysis suggests that slope engineering should prioritize south-, west-, and southwest-facing slopes while avoiding north-, northeast-, and east-facing slopes. Furthermore, the deep-seated stability of consequent slopes is superior to that of reverse slopes, and underground structures along mountain slopes should be situated within the unperturbed in-situ stress zone.

Future research must focus on quantitative investigations into: (1) the morphological characteristics and failure mechanisms of deeply incised valleys; (2) the evolution of in-situ stress fields under rapid tectonic uplift; and (3) the spatial distribution of in-situ stress fields across the plateau.

The findings provide critical theoretical guidelines and engineering references for slope design, infrastructure planning, and geohazard mitigation on the Tibetan Plateau.

To investigate the disaster-causing mechanisms, dynamic evolution, and post-disaster stability trends associated with the reactivation of the Huangci No. 2 landslide in Heifangtai, Gansu Province, on December 10, 2025, field geological investigations and the transient electromagnetic (TEM) surveys were conducted to characterize the deep structure of the landslide.

The entire three-dimensional dynamic sliding process was back-analyzed using the Massflow numerical model, and the three-dimensional limit equilibrium method was employed to quantitatively evaluate the post-event deposit and the stability of the high and steep rear slope and to predict their potential kinematic responses.

(1) The reactivation of the landslide resulted from the coupled effects of slope-toe excavation, long-term irrigation, and winter freezing conditions. The freezing-induced water-retention and pore-pressure buildup effect acted as the direct trigger: surface freezing blocked seepage pathways, causing pore-water pressure to accumulate at depth and triggering a bedding-parallel slide along the loess–mudstone contact. (2) The entire sliding process lasted 22 h 10 min, with a cumulative displacement of 310 m. The Massflow simulation reproduced four stages of the dynamic evolution: creep, accelerated sliding, deceleration and deposition, and stagnation and compaction. The intersection over union (IoU) of the simulated and observed deposition morphologies reached 85.85%. (3) Quantitative calculations indicate that the current deposit has a factor of safety greater than 1.15, suggesting a relatively stable state characterized by settlement and consolidation. However, under extreme saturation conditions, the potential failure volume of the high and steep rear slope could reach 40.9×10⁴ m³, with a maximum sliding distance of approximately 640 m.

The reactivation of the landslide was controlled by freezing-induced water retention and pore-water pressure buildup, together with multiple external disturbances. Although the main landslide body has generally stabilized, the high and steep rear slope remains highly susceptible to secondary failure. A long-term dynamic monitoring system should therefore be established to mitigate the risk of high-elevation secondary hazards.

This study quantitatively demonstrates freezing-induced water retention and pore-water pressure buildup as a distinctive triggering mechanism for winter loess landslides, extending the conventional understanding of loess landslide initiation beyond single hydrodynamic factors such as rainfall and irrigation. The findings provide direct technical references and theoretical support for winter landslide prevention and mitigation, emergency monitoring deployment, and early identification of geological hazards in Heifangtai and other irrigated loess tablelands, thereby contributing to the protection of local communities and their property.