Search Results (2,684)

In order to master the strength and deformation characteristics, including the macro–micro failure mechanism of soft rock samples with penetrating joints under triaxial loading, a series of numerical triaxial tests have been carried out. The strength and deformation characteristics, failure modes, crack propagation, distribution of force chains, and the influences of joint dip angles and confining pressures have been analyzed and compared with the laboratory test results. The results show that (1) the residual strength ratio of jointed rock samples generally increases first and then decreases with the increase in joint dip angles under the same confining pressure and reaches the maximum value around 23–24°. Poisson’s ratio increases with the increase in the confining pressure or the joint dip angle. The elastic modulus increases with the increase in the confining pressure and decreases with the increase in the joint dip angle. (2) The jointed rock samples with different joint dip angles compact with relatively small volumetric strains and then dilate up to failure with relatively large volume expansions. Lower confining pressure and smaller dip angles will lead to a more pronounced dilation phenomenon and less obvious volume shrinkage rules. (3) The low-angle jointed rock samples all exhibit the X-type shear failure. The jointed rock samples with a joint dip angle of 45° exhibit hybrid failure with both slippage and shearing, which are controlled by both the matrix and the joint. (4) The change in the number of cracks includes three stages: the slow crack initiation stage, rapid growth stage, and crack coalescence stage. The total number of shear or tensile cracks all decrease with an increase in the joint dip angles, with the number of tensile cracks being approximately twice that of shear cracks. The tension cracks are mostly horizontal, and the shear cracks are mostly vertical. (5) The number of force chains shows a decreasing trend after the cracks begin to grow. The jointed rock samples for the intact, 15° and 30° cases all form a main force chain during the failure process, while there is no main force chain for the 45° case. Full article

Quaternary volcanoes from the southeastern Tibetan Plateau occur at the Tengchong volcanic field (TVF). The Daliuchong volcano is the largest volcano in the TVF, which has the most felsic compositions with explosive eruptions. The eruption history and origin of the Daliuchong volcano are a matter of debate. In the present paper, we report the groundmass K-Ar ages, whole-rock Sr-Nd-Pb-Hf isotopes, zircon U-Pb ages, and Hf-O isotopic compositions for the Daliuchong volcano to constrain its eruption history and petrogenesis. The groundmass K-Ar ages and zircon U-Pb ages indicate mid-Pleistocene (0.6 Ma to 0.3 Ma) eruptions. The presence of zircon phenocrysts with enriched mantle-like O-Hf isotopes (δ¹⁸O < 6‰, and ε_Hf about −2) suggests the involvement of mantle-derived basaltic magmas. The whole-rock Pb isotope compositions and Sr-Nd isotope modeling reveal the involvement of magma from the lower crust. The zircon xenocrysts reveal previously unrecognized 20-Ma magmatic activity at the TVF and contamination of late Cretaceous (66–80 Ma) S-type granites during the formation of the Daliuchong dacites. The dacite magma at Daliuchong was formed by mixing of the mantle-derived magma and lower-crust-derived magma and subsequently contaminated by upper crustal materials, including late Cretaceous S-type granitic rocks. Full article

Upper Miocene volcanic and plutonic rocks on Kos island preserve a record of magmatic and tectonic events in the transition zone between the Aegean and Anatolian microplates. Their field setting, syn-intrusion deformation, mineralogy, and geochemistry were investigated. Volcanic rocks, including trachyandesite flows and trachyandesite to rhyolite domes, were extruded on a central E–W horst and directly overlie Alpine basement. Thick successions of trachytic flow tuffs are interbedded with fluvial and lacustrine basinal sediments to the south of this horst. Volcanism was synchronous with the emplacement of the Dikeos monzonite pluton, which is geochemically similar to some lithic clasts in the thick flow tuffs and is cut by mafic dykes including lamprophyres. Two main types of mafic magma were present: a K-rich lamprophyric magma that evolved to trachyandesite and more calc-alkaline magma similar to mafic enclaves in the monzonite. Syn-intrusion structures in the monzonite indicate emplacement during E–W sinistral strike-slip faulting that created local transtensional deformation, providing accommodation for a Dikeos magma reservoir. A change in the style of deformation in the Late Miocene led to NW-striking extension in the footwall, occupied by mafic dykes and mineralized veins, and extensional detachment of the hanging wall, resulting in unroofing of the monzonite. Full article

Tight oil reservoirs are considered important exploration targets in lacustrine basins. High-quality reservoir prediction is difficult as the reservoirs have complex distributions of depositional facies and diagenesis processes. Previous research has found that the diagenesis process of tight oil sandstones varies greatly in different depositional facies. However, diagenesis variation in different depositional facies is still poorly studied, especially in distributary channels of shallow water delta deposits in lacustrine basins. Based on the description of core samples, the observation of rock slices, the interpretation of well logging data, and the analysis of porosity and permeability data, the differences in the lithofacies types, diagenesis processes, and pore structures of different distributary channels have been clarified. Ultimately, a model of diagenesis and reservoir heterogeneity distribution in the shallow-water delta of Chang 8 Member of the Yanchang Formation in the Caijiamiao area of the Ordos Basin has been established. This research indicates that the main distributary channels in the study area are dominated by massive bedding sandstone lithofacies, while the secondary distributary channels are primarily characterized by cross-bedding sandstone lithofacies. There are significant differences in the compaction, dissolution, and cementation of authigenic chlorite and carbonate among different parts of the distributary channels. Plastic mineral components, such as clay and mica, are abundant in sheet sands, and are more influenced by mechanical and chemical compaction. Influenced by the infiltration of meteoric water and hydrocarbon generation, dissolution pores are relatively well-developed in the underwater distributary channel reservoirs. A large amount of carbonate cementation, such as calcite and siderite, is found within the sandstone at the interface between sand and mud. The occurrence of authigenic chlorite exhibits a clear sedimentary microfacies zonation, but there is little difference in the kaolinite and siliceous cementation among different microfacies reservoirs. Finally, a model of diagenetic differences and reservoir quality distribution within dense sand bodies has been established. This model suggests that high-quality reservoirs are primarily developed in the middle of distributary channels, providing a theoretical basis for the further fine exploration and development of oil and gas in the study area. Full article

Traditional seismic wave-based tunnel advanced geological forecasting techniques are primarily designed for drill and blast method construction tunnels. However, given the fast excavation speed and limited prediction space in tunnel boring machine (TBM) construction tunnels, traditional methods have significant technical limitations. This study analyzes the characteristics of different types of TBM construction tunnels and, considering the practical construction conditions, identifies an effective observation system and data acquisition method. To address the challenges in advanced forecasting for TBM construction tunnels, a method of ellipsoid positioning velocity analysis, which takes into account the constraints of three-component data directions, is proposed. Based on the characteristics of the advanced forecasting observation system, this method compares the maximum values on the spatial isochronous ellipsoidal surface to determine the average velocity of the geological layer rays, thereby enabling accurate inversion of the spatial distribution ahead. Utilizing numerical simulation, a model for the advanced detection of typical unfavorable geological formations is established by obtaining the wave field response characteristics of seismic waves in three-dimensional space, and the velocity structure of the model is retrieved through this velocity analysis method. In the engineering example, the fracture property, water content, and weathering degree of the surrounding rock are predicted accurately. Full article

The sustainable development of arid regions is significantly constrained by the availability of water resources, which play a crucial role in this context. It is necessary to deeply investigate and analyze the hydrochemical characteristics and major ion sources. This study, which was based on data from 183 water samples collected from the Jinghe River Basin, provided a comprehensive analysis of the river water hydrochemistry. The results show that the average TDSs (total dissolved solids) was measured at 49.8 mg·L⁻¹. HCO₃⁻ (82.4%) and Ca²⁺ (77.1%) were the ions present in the highest abundances. The river water was classified as the HCO₃⁻-Ca²⁺ hydrochemical type. The Gibbs diagrams indicated that the ion composition was primarily influenced by rock weathering. Additionally, the Na-normalized molar ratio diagrams suggested that the chemical composition was primarily governed by the weathering and dissolution of silicate rocks, while the carbonate rock dissolution played a lesser role. This study demonstrates a critical aspect of water resources quality evaluation, which is of great significance for the sustainable development, utilization and environmental protection of regional water resources. Full article

Different coal failure impact types exhibit different damage statuses and failure modes, resulting in distinct signal characteristics of infrared radiation (IR) and acoustic emission (AE). This paper combines IR and AE monitoring methods to innovatively establish coal damage and failure precursor warning models and obtains the IR and AE precursor characteristics for different coal failure impact types. This research shows that there is a good correspondence between IR and AE timing and spatial distribution of different coal impact types. As the impact tendency increases, the intensity of IR and AE signals increases with coal failure, and the AE positioning points and IR high-temperature areas tend to concentrate. The coal body gradually changes from tensile failure to shear failure. The shear cracks in the failure stage of coal with no, weak, and strong impact are 39.9%, 50.9%, and 53.7%, respectively. The IR and AE instability precursor point of coal with no, weak, and strong impact occurred at 55.2%, 66.3%, and 93.4% of coal failure, respectively. After the IR and AE combined instability precursor point, the dissipated energy and combined damage variable increase rapidly, and the coal body will undergo instability and failure. The research results provide a theoretical basis for comprehensive monitoring of coal body failure and rock burst. Full article

Given the vulnerability of surface water to the direct impacts of climate change, the accurate prediction of groundwater levels has become increasingly important, particularly for dry regions, offering significant resource management benefits. This study presents the first statewide groundwater level anomaly (GWLA) prediction for Arizona across its two distinct aquifer types—unconsolidated sand and gravel aquifers and rock aquifers. Machine learning (ML) models were combined with empirical Bayesian kriging (EBK) geostatistical interpolation models to predict monthly GWLAs between January 2010 and December 2019. Model evaluations were based on the Nash–Sutcliffe efficiency (NSE) and coefficient of determination (R²) metrics. With average NSE/R² values of 0.62/0.63 and 0.72/0.76 during the validation and test phases, respectively, our multi-model approach demonstrated satisfactory performance, and the predictive accuracy was much higher for the unconsolidated sand and gravel aquifers. By employing a remote sensing-based approach, our proposed model design can be replicated for similar climates globally, and hydrologically data-sparse and remote areas of the world are not left out. Full article

Petrographic studies have been carried out on the Early Miocene Darnó Conglomerate Formation, which consists only of debris of ophiolitic mélange and is found today on Darnó Hill in SW Bükk, NE Hungary. The studied sediments are bounded by the Darnó line from Darnó Hill. The aim of this work was to show if it is possible to reconstruct the petrographic composition of the source area only from its debris. The rock types were determined in thin sections using a polarizing microscope, and a quantitative analysis of the different rock types was carried out using the grain counting method, the results of which were interpreted as volume ratios. The main rock types observed in the studied samples (textural varieties of basalt, dolerite/microgabbro, claystone, siltstone, and radiolarite) are similar to the rock types of the mélange assemblage of Darnó Hill. Based on the volume calculations of basaltic detrital grains with different textures characteristic for pillow basalts, it could be established that pillow basalts dominated the igneous rocks in the source area of the Darnó Conglomerate on Darnó Hill already in the Miocene. Thus, this work shows that the lithological composition of a source area can be precisely outlined by a detailed petrographic analysis of the debris eroded from the immediate vicinity. Full article

Carbonate rocks are highly reactive and exhibit higher ratios of chemical weathering compared to most other rock types. A chemo-mechanical mechanism, which is particularly effective in groundwater due to higher ion concentrations, is common in fine-grained carbonates at the nanoscale. As a result, the weathering of carbonate aquifers produces a substantial number of carbonate nanoparticles (CNPs). In this study, we utilized high-resolution transmission electron microscopy (HRTEM) to analyze CNPs formed by water–rock reactions in two types of groundwater from Shandong Province, China. Our findings reveal a significant presence of naturally occurring CNPs in groundwater. The HRTEM results show that CNPs display spherical, cubic, hexagonal, and irregular shapes, with some forming aggregates. Energy-dispersive spectrometry indicates that most nanoparticles contain O, C, Ca, and Fe, with some also containing Si, Mg, S, Sr, and Cl. Selected area electron diffraction (SAED) patterns show that CNPs are mainly amorphous, with some crystalline forms. The diverse shapes and complex compositions of these CNPs suggest that they are not man-made but formed through the weathering of carbonate minerals via chemo-mechanical mechanisms. This discovery provides new insights into carbonate mineral evolution and mineralization during weathering. Given their widespread presence, CNPs in groundwater could represent the transportation of elements in the form of particles. Full article

This study presents an integrated approach using organic geochemistry and incident-light organic petrographic microscopy techniques to characterize the kerogen type, hydrocarbon potential, thermal maturity, and effective depositional environment of the Eocene Liushagang Formation intervals in the western Huangtong Sag, eastern Bailian Sag, central Huachang Sub-uplift, and Southern Slope Zone area in the Fushan Depression, Beibuwan Basin. The results show that the hydrocarbon potential of these organic-rich lacustrine shale areas is mainly dependent on the depositional environment and the present-day burial depth of sediments. Oscillations and transitions between (i) rocks with dominant allochthonous organic matter (including primary/reworked vitrinite and inertinite macerals and terrestrial debris particles) representing a large influence of continental sediments (e.g., source supply direction) and (ii) rocks with dominant autochthonous organic matter (e.g., alginite) indicate a distal and stable lacustrine basin depositional environment. The source rock thickness ranges from 40.1 to 387.4 m. The average TOC of the Liushagang Formation in the Fushan Sag is between 0.98% and 2.00%, with the highest organic matter abundance being in the first and second sections of the Liushagang Formation, presenting as high-quality source rocks. The organic matter is predominantly Type II₁ and Type II₂. The highest vitrinite reflectance (1.14%) is in the Huangtong and Bailian Sags. The source rocks of the second section of the Liushagang Formation are primary hydrocarbon generators, contributing 55.11% of the total generation. Hydrocarbon sequestration peaks at %Ro 0.80%, with a maximum efficiency of 97.7%. The cumulative hydrocarbon generation of the Liushagang Formation is 134.10 × 10⁸ tons, with 50.52 × 10⁸ tons having been expelled and 83.58 × 10⁸ tons remaining. E₂L_2X and E₂L_2S have maximum hydrocarbon displacement intensities of 184.22 × 10⁴ t/km² and 45.39 × 10⁴ t/km², respectively, with cumulative displacements of 52.99 × 10⁸ tons and 15.58 × 10⁸ tons. The oil and gas accumulation system is highly prospective, showing significant exploration potential. Full article

Detrital zircons from two samples of metasandstones from the Lykhmanivka Syncline, Middle Dnieper Domain of the Ukrainian Shield (Skelevate Formation of the Kryvyi Rih Group), have been dated by the LA-ICP-MS U-Pb method. Metasandstones from the northern part of the syncline yield zircons belonging to four age groups: 3201 ± 12 Ma, 3089 ± 11 Ma, 2939 ± 8 Ma, and 2059 ± 4 Ma. All three Archean groups originated from similar rock types that crystallized at different times from the same mafic source (lower crust) with a ¹⁷⁶Lu/¹⁷⁷Hf ratio of about 0.020. In contrast, zircon from metasediments from the southern end of the Lykhmanivka Syncline fall within two age groups: 3174 ± 13 Ma, and 2038 ± 9 Ma. In terms of Hf isotope compositions, the detrital zircons from the two oldest age groups in both samples are very similar. The source area was dominated by rocks of the Auly Group (3.27–3.18 Ga) and the Sura Complex (3.17–2.94 Ga). The proportion of zircons dated at 2.07–2.03 Ga, which reflects the timing of metamorphism, is 5%. The metamorphic nature of the Paleoproterozoic zircon allows us to define the maximum depositional age of the metasandstones of the Lykhmanivka Syncline at ca. 2.9 Ga, which is in good agreement with the earlier results from the metaterrigenous rocks of the Kryvyi Rih–Kremenchuk Basin. Our data also indicate the local nature of sedimentation and the absence of significant transport and mixing of detrital material within the basin. Full article

The Zonguldak coal basin is the area with the most important hard coal reserves in Turkey. This study focuses on coal samples extracted from three seams of the Kozlu Formation, specifically from the Kozlu underground mine, to assess the coals’ organic geochemical and petrographic properties. Analytical methods, including TOC-pyrolysis, biomarker analysis, and maceral distribution studies, were employed. Based on these analyses, the paleoenvironmental conditions and hydrocarbon generation potential of the coals were evaluated. The results reveal that the coals, characterized by high TOC, high HI, and low OI, contain type II–III kerogen. These findings, coupled with the high QI and low BI values, suggest the presence of oil–gas prone source rocks. Elevated Tmax (457–466 °C) and Rr (0.89%–1.17%) values indicate a maturity level ranging from mature to overmature stages. High GI and GWI values suggest a significant degree of gelification and wet conditions during formation. The high Pr/Ph (1–6.58), C₃₁R/C₃₀ hopane (<0.25), and low DBT/P (0.27–0.50) ratios show that the Acılık seam was formed in a lacustrine environment under anoxic–suboxic conditions, whereas the Büyük and Domuzcu seams were formed in a fluvial/deltaic environment under oxic conditions. The findings of this study suggest that the paleovegetation in coal-forming environments consisted of aquatic and herbaceous plants. Full article

Land degradation and the effects of climate change are increasing arid lands, accelerating desertification, and leading to the loss of ecosystem services worldwide. This research focused on evaluating how human impact and environmental factors affect the development of Solanum peruvianum in its natural habitat of coastal lomas. The study was carried out in the coastal lomas of Mangomarca-Peru, where phenotypic and ecological data on the plants were collected. Information was also gathered on human impacts on the nutritional characteristics of the soils. Then, five types of organic amendments were used to improve the physical and chemical characteristics of the degraded soil, and the development and photosynthetic activity of S. peruvianum were evaluated. As a result, under the study conditions, it was found that S. peruvianum was established approximately 33.74 cm from the rocks, in a range of 300 to 650 m asl. The maximum height of the plants was 90 cm, with a stem diameter at ground level of 2 cm. S. peruvianum produced fruits between January and July, with a seed germination rate of 36% in 25 days. On the other hand, the anthropogenic impact on the soil reduced 58% of organic material (OM), 71% of nitrogen, 40% of P₂O₅, and 13% of K₂O and increased the concentration of magnesium oxide, calcium oxide, pH, and electric conductivity (EC). The organic amendments bokashi, compost, and biochar, when mixed with the degraded soil, increased the pH, OM, N, P, and EC; however, the plants died after 25 days. On the other hand, the application of the Premix5 substrate for 100 days favored the growth of 52.84 cm and 38.29 cm in the preserved soil and 23.21 cm in the black soil mixed with blond peat, and it should be noted that the substrates presented an acid pH and EC > 0.1. Regarding photosynthetic phenotyping, S. peruvianum plants grown in their natural habitat and in Premix5 showed a higher proton flux (vH+), linear electron flow (LEF), and maximum quantum yield (Fv’/Fm’). On the contrary, they showed a lower NPQt value than plants grown in preserved and black soil mixed with blond peat. Full article

The Permian Qipan Formation (P_1-2q) is the aim horizon for hydrocarbon source rocks in the piedmont area of southwestern Tarim Basin. In the present study, the depositional environment and geochemical characteristics of muddy hydrocarbon source rocks of P_1-2q were systematically evaluated using total organic carbon (TOC), Rock-Eval pyrolysis, vitrinite reflectance (Ro), reflected light microscopy, main and trace element, and biomarker parameters of 167 outcrop samples and 176 core samples. The TOC of P_1-2q is primarily concentrated within the range of 0.36% to 2.77%, with an average of 1.58%. This suggests that the overall evaluation of the hydrocarbon source rock is fair to good. The source rocks of P_1-2q predominately contain Type III and Type II₂ kerogen. The overall Tmax values of P_1-2q hydrocarbon source rocks are notably elevated, with the majority exceeding 490 °C or falling between 455 °C and 490 °C. The Ro value is between 0.90% and 2.00%, indicating that the maturity has reached a high, over-mature evolutionary stage. The trace element and biomarker parameters indicate that hydrocarbon source rocks of P_1-2q are predominantly slightly oxygen-rich, with a minor anoxic component. The asymmetric ‘V’ arrangement of the C₂₇-C₂₉ regular steranes indicates that the hydrocarbon parent material is predominantly derived from algae or aquatic organisms, with varying degrees of mixing with organic matter of terrestrial origin. The study of source rock geochemistry of the P_1-2q makes the exploration target of the southwest depression of the Tarim Basin more accurate in the complex tectonic geological environment. Full article