Landslides occur frequently in the middle reaches of the Nujiang River due to its complex tectonic and geological environment. Landslide susceptibility assessment can effectively identify areas with high landslide susceptibility, thereby significantly improving disaster prevention and mitigation efficiency in this region. Based on historical data, remoting sensing interpretation, and filed investigations, a total of 3358 medium- to large-scale landslides (volume >105 m3) were identified to construct a landslide inventory for the middle reaches of the Nujiang River. Twelve conditioning factors, including topography, basic geology, hydrology, environmental influences, and external triggering factors, were selected using variance inflation factor (VIF) and tolerance analysis. The landslide samples from the southern part of the study area, where landslides are relatively concentrated, were used as the training set, while those from the remaining regions served as the test set, achieving an approximately 1∶1 ratio between training and test sets. This spatial partitioning strategy was employed to evaluate the cross-regional generalization ability of machine learning models. Random Forest (RF), Naive Bayes (NB), and eXtreme Gradient Boosting (XGBoost) models were applied to predict landslide susceptibility across the entire study area. The results indicate that very high and high susceptibility zones are primarily concentrated in the valleys of the Nujiang River and its tributaries, influenced by faults, intense topographic rockmass, and well-developed drainage networks. These patterns are generally consistent with the actual spatial distribution of landslides in the study area. Among the three models, RF model achieved highest precision (AUC = 0.880), followed by NB (AUC = 0.862), and XGBoost (AUC = 0.853). Furthermore, the landslide susceptibility map generated by the RF model demonstrates higher accuracy (86.5%) and reliability (kappa = 0.730). SHAP (SHapley Additive exPlanations) interpretation reveals that elevation is the most important factor influencing landslide susceptibility in all three models (RF, NB, and XGBoost). The results indicates that the RF, NB, and XGBoost models all exhibit strong cross-regional generalization capabilities. However, the RF model achieves the highest AUC value and is therefore more suitable for landslide susceptibility assessment in areas characterized by large elevation gradients and complex geological environments.

The role of biotite alteration in micro-fracturing of sandstone artefacts merit further investigation. The mineralogy, elemental geochemistry, and micro-structural characteristics of sandstones in the Nankan grotto were analysed to explore the weathering-induced fracturing mechanism. The results show that significant leaching of major elements (Ca, Na, K, Al, and Si) occurred as a consequence of calcite and feldspar dissolution. In contrast, Fe and Mg showed a more pronounced depletion, which is primarily linked to biotite alteration. As weathering progressed, the content of clay minerals increased, accompanied by enhanced smectitization of I/S. During biotite weathering, structural Fe(II) is inferred to undergone oxidation to Fe(III) first, forming lenticular-shaped hematite embedded in the cleavage planes of biotite. Three sub-stages of biotite weathering process were clarified: relative fresh biotite, medium weathered biotite, and intense weathered biotite. In the initial stage, the relative fresh biotite, with a lattice spacing of 10.5 & Aring;, exhibited elevated FeO and MgO concentrations. This was attributed to the Fe2+ oxidation within the biotite. Upon reaching the medium weathering stage, approximately 50% of Fe and Mg were leached. In the advanced weathering stage, the intense weathered biotite displayed distorted lattice spacings of 10.5 & Aring;, 12 & Aring; and 20 & Aring;, accompanied by low FeO and negligible MgO level. Molecular dynamics simulations demonstrated that the lattice spacing expanding from 10.5 & Aring; to 12 & Aring; (or 20 & Aring;) was achieved by hydration of biotite. The formation of hematite in pristine biotite and hydration-driven lattice expansion induced considerable volumetric expansion, which in turn promoted the development of microcracks both in the biotite and adjacent quartz. Such weathering-induced fractures create fresh reactive surfaces, thereby accelerating subsequent weathering reactions and promoting the overall deterioration of the sandstone. Overall, our research underscores the critical function of biotite weathering in the fracturing processes of sandstone, offering a more comprehensive understanding of the degradation mechanisms in sandstone grottoes.

Accurately predicting the spatial distribution of heavy metals in weathered soils derived from black rock series is essential for ecological development and pollution control in geochemical high-background areas. Due to the complex composition of black rock series parent rocks， traditional interpolation methods often fail to capture spatial heterogeneity effectively， while machine learning （ML） models have demonstrated promising performance in mountainous regions but lack systematic comparison. This study focuses on the spatial prediction of soil chromium （Cr） in the black rock series-dominated high-background region of eastern Chongqing. Twelve environmental variables from six categories-geological， topographic， climatic， soil， anthropogenic， and vegetation-were selected as auxiliary predictors. Four models were constructed and compared： ordinary Kriging （OK）， regularized random forest （RRF）， light gradient boosting machine （LightGBM）， and multilayer perceptron （MLP）. Cross-validation was employed to evaluate model performance and identify the optimal model for predicting the spatial distribution of Cr. The results showed that 25.3% of Cr concentrations exceeded the regional background value， but all remained below the agricultural risk screening and control thresholds， indicating localized Cr enrichment within a manageable range. Among the models， RRF achieved the highest predictive accuracy （R2=0.855， RMSE=4.044）， followed by LightGBM （R2=0.823）， MLP （R2=0.801）， and OK （R2=0.323）， demonstrating the superior performance of RRF. While all models captured similar spatial trends， RRF provided more detailed and accurate identification of high-concentration zones， with LightGBM performing moderately well， MLP showing localized overestimations， and OK exhibiting the weakest fit. Variable importance and SHAP analysis based on the RRF model revealed that Cr distribution was mainly influenced by geological factors （Fe2O3， MgO， and K2O）， soil organic carbon （SOC）， distance to rivers， and annual precipitation. Overall， the RRF-based spatial prediction approach demonstrates significant advantages in geologically complex regions and offers methodological support for heavy metal risk assessment and environmental management in geochemical high-background areas.

Softening of soft red-bed rocks subjected to rainfall-evaporation cycles is commonly characterized by rapid disintegration and is often accompanied by cracking, resulting in degradation of the mechanical properties of the rock, which can lead to slope instability or rockfalls. The microstructural changes in soft red-bed rocks after immersion were imaged, and two-dimensional (2D) images of cracks under water absorption-evaporation conditions were obtained. The dynamics, fractal characteristics, and geometry of the cracks were analyzed using digital image processing and analysis based on morphological algorithms. The results indicate that the face–face particle bonds become point–face bonds with numerous micropores with sizes of 1–5 μm. The evolution of cracks generated after water absorption can be divided into four stages: edge crack initiation, crack propagation, crack coalescence forming the main crack, and subcrack segmentation. The evolution of the dynamic characteristics of cracks during water absorption and drying cycles can be effectively described by the crack intensity factor, crack density, and average width. The fractal dimension increases to a stable value with increasing soaking time, whereas drying increases the crack complexity, resulting in fractal dimensions ranging from 1.106 to 1.126. The geometry results indicate that the crack directions are mainly at angles of 30°–70° after soaking and primarily in the range of 50°–60° after 10 drying cycles. The transition of the crack intersection angle from a bimodal to a unimodal distribution suggests that water absorption and drying processes tend to form Y-shaped and T-shaped cracks, respectively. Finally, the evolution of the water–rock interface induced by particle dissolution, ion exchange, expansion force, and liquid surface tension was used to explain the mechanism of crack evolution related to water entry and evaporation. These results provide a theoretical basis for evaluating the cracking behavior of soft red-bed rocks.

Subgrade long-term uplift of high-speed railway threatens operational safety, which is usually caused by rock swelling in red-bed rock regions. In this study, we present results on red-bed mudstone and siltstone to trace the properties of rock swelling under different heat treatment temperatures and to evaluate the swelling of siltstone after cyclic load simulating train operation. The results show that drying temperature before the swelling experiment affects the initial water content and microfractures of rock samples. Initial water content affects their swelling properties, and the swelling rate is positively correlated with the heat treatment temperature (mudstone, R2 = 0.49; siltstone, R2 = 0.73). In addition, cyclic load alters the microstructure of the rocks, increasing to further release of swelling. Compared to the normal load, the shape of the particles on the failure surface is closer to ellipsoids under cyclic loading. Swelling rates were positively related to critical stress ratios (CSRs) (R2 > 0.89) and negatively related to circumferential pressure (R2 > 0.54); no significant correlation with loading frequency was observed. Based on the above experimental results, the mechanism for the subgrade uplift of the Neijiangbei station is discussed. This study provides not only an experimental basis for the swelling mechanism of red-bed rocks but also insight for the mechanism of subgrade uplift at the red-bed rock regions.

Chemical weathering of lithologies with high geochemical backgrounds such as black shale has been proposed to be a critical source for toxic elements in soil and water systems. However, mechanisms controlling the release, migration and enrichment of toxic elements during black shale weathering are poorly understood. This study utilized a suite of micro analytical techniques such as TESCAN integrated mineral analyzer (TIMA), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and electron micro-probe analysis (EMPA) to elucidate the intimate relationship between mineralogical transformations and elemental behaviors from profile scale to mineral scale. Mineralogical and elemental compositions for a black shale weathering profile (and surface strongly weathered materials) suggest a dominant sequence of mineral reactions as oxidation of sulfides, dissolution of carbonates, alteration of aluminosilicates, and transformation of clay minerals. Most of the toxic elements were largely released from the weathering profile and significantly enriched in the strongly weathered materials. Black shale weathering was initiated by oxidation of pyrite, sphalerite and molybdenite, and these chemical reactions dominated the release of toxic elements (e.g., As, Cd, Mo, Mn, Ni and Zn). During oxidation of pyrite, Fe (hydr)oxides pseudomorphically replaced pyrite grains, along with the release of As and Mn and their subsequent retention in Fe (hydr)oxides. Sulfuric acid generated by oxidation of sulfides firstly dissolved surrounding calcite and dolomite to significantly improve the pore-fracture networks in the weathered shale, allowing more water fluxes and transportation of Fe (hydr)oxides and concomitant migration of associated toxic elements. Then, albite and minor orthoclase were altered to illite that was responsible for the secondary enrichment of Tl throughout the weathering profile. In intense weathering stage, Fe/Mn (hydr)oxides were substantially delivered to re-precipitate in fractures and contributed to considerable enrichment of As, Ni, Co, Zn and Cd. Meanwhile, transformation of illite to kaolinite may also influence the enrichment of toxic elements. This work highlights the importance of understanding the control of mineralogical transformation on release, migration and enrichment of toxic elements during black shale weathering, such that this mineral-dependent mechanism can be implemented to risk prediction and assessment of toxic elements in black shale regions.

Red-bed mudstone is a typical soft rock with significant swelling characteristics, which often leads to expansion deformation when used in (ultra)high-speed railway subgrades. Given the widespread presence of soluble salts in natural environments, it is essential to investigate the influence of external ions on the rock expansion behavior. In this study, a multiscale approach integrating macroscopic expansion tests, microstructural evolution analysis, and molecular dynamics simulations was employed to elucidate the mechanism by which salt solutions inhibit mudstone expansion. The results demonstrate that salt solutions significantly suppress mudstone expansion within low concentration ranges, with a reduced expansion potential correlated to increased concentration or decreased cation valence. The critical concentrations for the equilibrium state of mudstone expansion in NaCl and CaCl2 solutions are 1.20 and 1.00 mol/L, respectively. Positive correlation between the concentration of Na2SO4 solution and the expansion rate can be well predicted using a logistic model. Mudstone expansion induced by Na2SO4 includes three stages: a rapid expansion stage, a slow expansion stage, and an expansion growth stage. Three stages correspond to gypsum expansion, saltpeter expansion, and the crack-penetration crystal-expansion cycle. The ability of monovalent cations to neutralize the negative charge on the surface of clay minerals is weak, and the thicker double layer formed implies a wider diffusion layer and a larger water film thickness, while divalent cations significantly compress the thickness of the double layer. Molecular dynamics simulation reveals the nanoscale mechanisms of influence of monovalent and divalent ions on water-rock reactions, where cations reduce the diffusion rate of water molecules and weaken the interaction energy at the water-rock interface. Diffusion coefficient under the influence of Ca2+ is 0.62 x 10-6 cm2/s and 0.17 x 10-6 cm2/s, lower than that under the influence of Na+, indicating that divalent cations have a more significant inhibitory effect on the diffusion behavior of water molecules than monovalent cations. This multiscale study provides theoretical insights into the deformation mechanisms of red-bed mudstone in salt-rich environments, offering valuable guidance for the design and maintenance of (ultra)high-speed railway subgrades.

This work aimed to explore the influences of different salts and temperatures on the salt weathering of sandstone in the Nankan Grotto. Capillary salt weathering tests were designed under different conditions. The geochemical, physical, and mechanical properties of sandstone were also analysed. After the tests, the electrical conductances (EC), anion concentrations, masses, P-wave velocities, and porosities of specimens increased as the test temperature was changed from 15 degrees C to 35 degrees C within individual experimental settings. Under 6% Na2SO4 + 3% NaNO3 condition, only Na2SO4 exerted crystallization pressure, which exceeded the tensile strength of Nankan sandstone (2.20 MPa). Under 3% Na2SO4 + 6% NaNO3 condition, NaNO3 crystallized at 25 degrees C and 35 degrees C, and Na2SO4 crystallized at 35 degrees C. Their crystallization pressures exceeded the tensile strength of Nankan sandstone. Temperature influences the physical properties of a salt solution, which determines the salt weathering intensity. Our research suggests that salt weathering issues in grottoes should be evaluated in different seasons.

The functional relationship between chemical weathering and topography is central to understanding global sediment flux and elemental cycling. In this study, mineralogy, major and rare earth elements (REEs) of eleven black shale weathering profiles developed in contrasting topographies on the Yangtze Platform were systematically investigated to understand the topographic control on chemical weathering of silicate rocks. Results demonstrated that, in contrast to high-relief terrains, black shale weathering profiles in low-relief terrains were characterized by more loss of plagioclase and illite and by more depletion in major elements (Ca, Na, Si, Fe, Mg, K, Al), while kaolinite and K-feldspar tended to enrich. The weathering intensity quantified by chemical index of alteration (CIA) values decreased with the increase of relief amplitude and slope gradient, which is probably attributed to the reduction of residence time of weatherable materials in high-relief terrains as a result of strong surface erosion. The mass transfer coefficient of plagioclase (tau Pl, Ti) exhibited significant positive correlations with both relief amplitude (r = 0.82) and slope gradient (r = 0.80), indicating the loss of plagioclase was limited by relief enhancement. Illite showed enrichment in the weathering profiles in relatively high-relief terrains while it was depleted in low-relief terrains, which is probably due to the shift from plagioclase weathering to the dominance of illite weathering under the supply limitation scenario of plagioclase. This rate-limitation framework driven by topographic forcing also contributed to REEs mobilization as evidence by the favorable correlation between REEs mass fluxes and tau Ill, Ti values in soil sequences (r = 0.81). Finally, topography also had an important impact on the geochemical fractionation of REEs, which was realized by modulating the weathering intensity. Overall, this study highlights the critical role of topography in regulating weathering intensity, dissolution and formation of minerals and elemental behaviors during black shale weathering, which would provide new insights into better understanding the primary controls on chemical weathering processes with emphasis on topography.

This study focused on the automated extraction of lineaments, geology, and structural geology in the Sarpol Zahab region. Two data processing techniques were utilized. First, the PCI Geomatica program algorithm was used for automatic extraction, with principal component analysis (PCA) applied to the Landsat 8 OLI satellite image, following image enhancement directional filtering in four different directions (N00°, N45°, N90°, and N135°). Second, shading was applied to create a lineament map in four different directions (N00°, N45°, N90°, and N135°), using SRTM (DEM) data to emphasize run linear structures, followed by tracing the detected lineaments. The extracted lineaments resulted in the directions of North–South (N–S), East–West (E–W), Northeast-Southwest (NE–SW), and Northwest-Southeast (NW–SE). A no abundance of lineaments in the NE–SW direction was found to be perpendicular to the major faults, with the predominant direction of the faults and lineaments being NW‒SE. Density maps revealed high concentrations in the northwestern, southeastern, and southern near the seismic zone. These results were validated by comparing them with geological maps and two validation criteria. The lithological component showed that the lineaments are often concentrated on rocks, such as the Southeast NW‒SE trending surface anticlines of limestones and the Oligocene to Miocene sandstones and conglomerates in the West. Another component was the overlay of the lineaments on the slope map, which revealed a concentration of steep slopes, indicating faulting activity. The structural lineament extraction method is considered beneficial for this kind of study, providing an accurate method for selecting striatal lineaments.

Geogenic inputs have become a vital source for rare earth elements (REE) in the surrounding environments with black shale outcrops. However, the geochemical fractionation and differential accumulation of REE in the rock-soil system of black shale regions still remain unclear. Therefore, this study performed a typical sampling of paired bedrocks and soils in contrasting topographies in a black shale catchment in southwestern China to characterize the geochemical enrichment and fractionation of REE during black shale weathering and soil formation and evolution. The results indicate that black shale bedrocks have elevated total concentrations of REE compared to the North American Shale Composite and the Upper Continental Crust; while surface soils have total REE concentrations higher than the Chinese soil background value. The contrary REE distribution patterns for upland soils (concave-up) and lowland soils (convex-up), together with a higher (La/Sm)N value (1.11 ± 0.18) and a lower (Gd/Yb)N value (1.13 ± 0.11) in the upland soils and a lower (La/Sm)N value (0.95 ± 0.11) and a higher (Gd/Yb)N value (1.32 ± 0.31) in the lowland soils, indicate the obvious fractionation of REE between the two soil types and the preferential enrichment of MREE (and HREE) in the lowland soils, which was attributed to the release of MREE (and HREE) from the weathering of upland black shale bedrocks and their downward translocation by water fluxes and subsequent precipitation in lowlands. In addition, the lowland soils are more enriched in LREE than the upland soils, which should be associated with the downward transportation of LREE-rich mineral particles caused by soil erosion on the hillslope. Overall, this study points out that MREE enrichment in the lowland soils of black shale regions and its associated health risks should be noticed.

This study aimed to compare the prediction performance of single and ensemble machine learning (ML) models in terms of landslide susceptibility mapping in areas affected by the 2017 Jiuzhaigou earthquake. The single ML models selected were the logistic regression (LR) and naïve Bayes (NB) algorithms, and the selected ensemble ML models were the C4.5 decision tree (C4.5 DT), random forest (RF), light gradient boosting machine (LightGBM), extreme gradient boosting (XGBoost), RF coupled with information value (RF‒IV), and XGBoost‒IV. In total, 2482 landslides were identified and used to create training (75

To address the limitations of traditional groundwater quality assessment and prediction methods, this study integrates game theory and machine learning to investigate the drinking quality of groundwater in the southwestern Qinghai–Tibet Plateau. The results showed that the groundwater in the study area is generally weakly alkaline (mean pH: 8.08) and dominated by freshwater (mean TDS: 302.58 mg/L), with hardness levels mostly ranging from soft to medium. Major cations follow the concentration order: Ca2+ > Na+ > Mg2+ > K+; anions are in the sequence of HCO3− > SO42− > Cl−. The hydrochemical type is mainly Ca-HCO3. A few samples exceed the limit values specified in the Groundwater Quality Standard. Through multivariate statistical analysis, ion ratio analysis, and saturation index calculations, water-rock interaction is identified as the primary factor influencing groundwater chemistry. It consists of carbonate dissolution and silicate weathering, accompanied by cation exchange. The water quality index improved based on game theory, integrated subjective weights (from analytic hierarchy process) and objective weights (from entropy-weighted method), shows that the overall groundwater quality in the study area is good: 95.97% of the samples are high-quality water (WQI ≤ 50), more than 99% of the samples have a WQI < 150, which is suitable as drinking water sources; only 0.81% of the samples are of extremely poor quality, presumably related to local pollution. Linear regression achieved the best performance (R2 = 0.99, RMSE≈0.00) with strong stability, followed by support vector machines (test R2 = 0.98), while the extreme gradient boosting model showed overfitting. This study provides a scientific basis for groundwater management in river basins.

Mudstone swelling capacity is an important factor that determines the quality of engineering constructions, in particular, roads, tunnels, dams, etc. The most important parameter is the content of water that determines the stability/behavior of mudstone under different conditions, e.g., under variable temperature and humidity. Laboratory thermal treatment is a widely used method to measure the content of water in mudstone, which controls its swelling capacity. Exploring the swelling properties of samples treated at different temperatures will help to further understand the impact of water content on swelling properties. In this paper, we present new results on the heat treatment of red-bed mudstones of the Shaximiao Formation exposed in the eastern Sichuan Province of SW China in order to trace variations of mass, pore content, microstructural patterns and swelling characteristics. The swelling was traced by scanning electron microscopy and pore tester. The heat treatment changes the microstructure and pore characteristics of the mudstone and its swelling properties. The mudstones yielded three types of water loss patterns caused by the presence of free, absorbed and constitutional waters. The swelling properties appeared to depend on the pattern of the loss of three water types at different temperatures. The increasing temperature resulted in faster dehydration of clay minerals, stronger damage of original textures and microstructures (pore pattern) and stronger swelling. Our results provide a new guideline for selecting a temperature of heat treatment and controlling the content of water during red-bed swelling experiments.

The capillary water absorption issues of the sandstone have significantly influenced their salt weathering conditions. This work aimed to explore the influences of different salt types and concentrations for the capillary water absorption of sandstone in Nankan Grotto. Three sets of capillary water absorption tests were designed. In addition, the mineralogical, major element, micro-structure, and physical properties of sandstone were also analysed. It is found that the mineralogical compositions of the sandstone were quartz, feldspar, illite-smectite mixed layer, illite, and chlorite. The water absorption weight curves showed three stages: rapid water absorption stage (0–4 h), slow water absorption stage (4–36 h), and inactive water absorption stage (after 36 h). The capillary rise height curves showed two stages: sharp increase in 0–20 min and very slow increase after 20 min. The capillary water absorption coefficient (Acap) results revealed that all of the salt solutions (Na2SO4, NaNO3, and Na2SO4 + NaNO3) promoted the capillary water absorption in sandstone. The promoting effect of Na2SO4 solution was the most remarkable, followed by Na2SO4 + NaNO3 solution. The promoting effect of NaNO3 solution was insignificant. The maximum water absorption velocities under the NaNO3 solution conditions were always greater than those under the Na2SO4 solution conditions, and smaller than that under deionized water. This was due to the highest viscosity of Na2SO4 solution. The Hall model fitted the capillary water absorption curves better than Feng and Janssen model. In addition, the modified model for capillary rise height prediction demonstrated good agreements with those obtained from experiments.

The frequent occurrence of snowdrift hazards in the Tianshan region of China often poses a serious threat to transportation corridors, such as roads and railways. Revealing and understanding the characteristics of snow distribution and using a mixed model to assess the susceptibility to snowdrifts can effectively and quickly evaluate the regional risk of the snowdrift. In this study, the key factors affecting the formation of a snowdrift in the study area, such as snow, are analyzed by utilizing remote sensing interpretation, meteorological monitoring, and field investigation along the Xinyuan-Kutaikelike railway section of Yining to Aksu Railway in China as the study area object. Based on the multi-source data, ten snowdrift susceptibility evaluation factors were extracted with the help of GIS. On this basis, three susceptibility models were used to evaluate the snowdrift susceptibility, namely the subjective evaluation method – Analytic Network Process (ANP) method, the objective evaluation method - CRITIC weighting method, and the combination of subjective and objective Game theory combination method. The evaluation showed that the susceptibility indices obtained by the ANP, CRITIC, and Game theory combination were in the ranges of [0.243, 0.746], [0.202, 0.751], and [0.249, 0.735] respectively, with the percentages of the area of medium susceptibility and above being 67.3%, 67.2%, and 67.5%. All three models exhibited suitable robustness. The predicted results of the three models were verified by the field survey, and it was found that the results of the Game theory combined model were in good agreement with the field survey, which allows it to be suitable for the study of snowdrift susceptibility zoning in the study area. The results revealed that the medium-high susceptibility areas of a snowdrift were mainly in the grassland area of the Small Yultuz Basin and the A'erxian-Bayinguoleng area. The high susceptibility zones were predominately located in the Nalati Ridge, the northern ridge of the Koktag Mountains, the northern ridge of the Huola Mountains, and the pre-mountain alluvial and floodplain areas of these mountain systems. This study provides a scientific basis and methodology for preventing and mitigating snowdrift disasters in cold regions, specifically for major engineering constructions such as transportation corridors.

The different salt weathering issues of the sandstone in the Nankan Grotto have significantly influenced their preservation conditions. This work aimed to evaluate the petrography and environment constraints for salt weathering of three typical sandstones: yellow sandstone, cyan sandstone, and gray sandstone in the Nankan Grotto. Salt resistance test and acid leaching test were conducted on these three sandstones. In addition, the mineralogy, geochemical mass balance, micro-structure, and water transport properties of these sandstones were also analyzed. It is found that yellow sandstone had high quartz concentration, porosity, and water transport ability. Cyan sandstone had low calcite concentration, high porosity and medium water transport ability. Gray sandstone had high calcite concentration, low porosity and water transport ability. The decay of sandstones in the salt resistance test at 20 °C was faster than those at 5 °C and 35 °C. In addition, yellow sandstone was the most resistant to the salt resistance test, followed by cyan sandstone, and gray sandstone was the most vulnerable to the salt resistance test. In the H2SO4 acid leaching test, efflorescence pattern was the most likely type of decay in yellow and cyan sandstones. Thenardite was the exclusive salt in the yellow sandstone, while gypsum was the mainly salt in the cyan sandstone. Gypsum crust and subflorescence were the most common types of decay for gray sandstone. In the HNO3 acid leaching test, yellow and cyan sandstones did not show obvious variations. For gray sandstone, the secondary minerals were gypsum and dolomite, and crust pattern was observed. In general, the salt weathering of gray sandstone was more severe than yellow and cyan sandstones. The differences in petrography (mainly calcite concentration) and micro-structure of sandstone and the external environment leaded to the differences in the types, amounts, and locations of the salt crystallization in the acid leaching tests. These contributed to the different development of efflorescence, subflorescence, and crust patterns. Our research reveals the petrographic, micro-structural, and environmental constraints for different salt weathering processes of sandstones in the Nankan Grotto.

Red-bed soft rock is a common type of bedrock with the characteristics of water softening and disintegration into particles. Micro mechanical properties and macro engineering behavior of softrock have been proven to be influenced by particle shape. Disintegration durability tests were conducted to study the durability of red-bed soft rocks, and two-dimensional images of disintegration particles with varied particle sizes under different dry-wet cycling states were obtained through optical imaging. Shape parameters of particles were established, and the sensitivity of shape parameters to rock durability were analyzed. The evolution behavior and durability differences of rock disintegration was better measured using the disintegration ratio instead of the traditional slake durability index. Results indicate that the aspect ratio and angularity of particles show a decreasing trend with an increasing number of dry-wet cycles, but roundness displays an increasing trend. The roughness decreases with increasing dry-wet cycles, but increases with decreasing particle size. Correlation between surface roughness and rock durability suggests that a higher roughness will enhance the disintegration of soft rock. And sensitivity analysis revealed that surface roughness with the highest grey relational grade of 0.705 is the optimal shape evaluation parameter for rock durability. Microscopic mechanism of surface roughness influencing rock durability was discussed, and the increase in surface area and stress concentration at contour turning points were considered two main factors that roughness affects the rock durability. Finally, the disintegration probability prediction based on renormalization group theory indicates that disintegration probabilities of the red-bed soft rock micro-unit models with triangular and square structures at critical states are 0.5 and 0.16, respectively. The significance of this study is to further investigate the relationship between the micro particle shape and macroscopic mechanical behavior of granular materials.

Foreland basin tectonics along the eastern Palaeo-Tethys Ocean produced a complex and dynamic pattern of sediment delivery to adjacent basins. Environmental processes at the local scale significantly disrupt regional ones, making the analysis of sedimentary evolution difficult. This study investigated the Lower Permian Liangshan Formation black shale formed in such geological setting, rich in cherts with exceptionally high silica and fluctuating major and trace element concentrations, detected using XRD, XRF, and ICP-MS techniques. Different types of silica, including detrital quartz, recrystallised radiolaria, microcrystalline quartz, and quartz veins, were identified using SEM and SEM-CL imaging. Geochemical characterisation and enrichment pattern analyses indicated that the structural setting was characterised by proximity to the oceanic island arc, continental island arc, and passive margin, and the major zone of sediment accumulation was a semi-restricted back-arc basin under the subduction zone. The processes controlling sediment accumulation included hydrothermal activity, upwelling, biogenic silica, and terrestrial inputs. Although upwelling interfered with the mobility and migration of hydrothermal elements, it introduced abundant nutrients, and together with hydrothermal fluids, it contributed to the subsequent boom in siliceous organisms. Terrigenous inputs induced by land uplift significantly diluted the components from other sources. This multi-source proxies approach not only enables researchers to disentangle local from regional processes but also sheds light on how these diverse environmental forces interact within intricate earth systems, which enhance our comprehension of geologic history and inform ongoing studies focused on climate change mitigation strategies.