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Cemented pavement materials (CPMs) are essential components in pavement structures, yet accurately predicting their service life due to fatigue damage remains challenging. Laboratory fatigue test results are commonly employed to predict the service life of CPMs by applying a lab-to-field shift factor (SF). However, traditional approaches rely heavily on experimental data, posing challenges in ensuring the certainty of lab-to-field results. Additionally, inconsistencies in lab-to-field fatigue failure criteria further complicate SF development. To address these challenges, this study proposes a mechanism-based methodology for developing SF. This methodology comprises a rigorous two-scale fatigue model developed by the authors to characterise the fatigue performance of CPMs at the lab scale and predict their performance at the field scale, thereby facilitating the development of SFs. These SFs are established based on a consistent lab-to-field fatigue failure criterion (i.e. the modulus reduction of CPMs). By accounting for strain differences between laboratory and field scales, SFs are derived in the strain-fatigue life space. Application of this approach to typical Australian CPMs, namely siltstone and hornfels, yields mechanism-based SFs of 1.19 and 1.21, respectively. [ABSTRACT FROM AUTHOR]

Cretaceous siltstone, which is widely distributed in the Yichang region, is a type of soft rock characterized by its low strength and its susceptibility to softening and disintegration when exposed to water. To gain a better understanding of the impact of wet–dry cycles on the disintegration characteristics and mechanisms of Cretaceous siltstone, a series of rock disintegration experiments were conducted. These experiments involved microscopic structure analysis and solution ion concentration tests on the specimens. The results of the experiments revealed that with an increase in the number of wet–dry cycles, the Cretaceous siltstone progressively fractured and disintegrated, with larger fragments transitioning into smaller ones. Microscopic structure analysis indicated that continuous wet–dry cycles altered the specimen's microscopic structure, resulting in the formation of new microcracks and pores. The results of solution ion concentration tests showed significant mineral dissolution losses during specimen immersion in the solution. Furthermore, a comparative analysis of various disintegration parameters highlighted that each metric emphasized specific aspects of Cretaceous siltstone disintegration characteristics. Therefore, adopting a multi-metric approach allows a comparison of the validation and assessment of the disintegration features of Cretaceous siltstone from many aspects. Finally, based on the experimental findings, a concise description and summary of the disintegration mechanisms of Cretaceous siltstone under wet–dry cycle conditions are provided; then, combined with its disintegration mechanisms, engineering prevention and control suggestions for timely drainage and a reduction in thermal contact are put forward from the perspectives of waterproofing and heat insulation, which can be used for reference. [ABSTRACT FROM AUTHOR]

The fossil record of the genus Carcharodon (Lamniformes: Lamnidae) dates to the late Oligocene and has a near global distribution. Today the genus is represented by a single species, the white shark Carcharodon carcharias. However, multiple extinct species are recognised in the Cenozoic including Carcharodon hastalis, Carcharodon hubbelli and Carcharodon planus comb. nov. Here we present the first occurrences of Carcharodon hubbelli and Carcharodon planus from New Zealand/Aotearoa, from the South Island/Te Waipounamu. Carcharodon hubbelli is previously reported from late Miocene deposits in the Pacific basin of North and South America, Asia, and Australia. Whereas Carcharodon planus has been reported from the Miocene of North America and Asia. One tooth from Carcharodon hubbelli is reported from the presumed late Miocene of Motunau Beach, North Canterbury, while one upper early Miocene tooth recovered from the Kakahu River, South Canterbury and an earliest Miocene tooth from the Big River mouth, Tasman District are referred to Carcharodon planus. In addition to being the first reported occurrences of these two species in New Zealand, the teeth of Carcharodon planus represent some of the earliest occurrences of the taxon as well as its southernmost occurrence. [ABSTRACT FROM AUTHOR]

In this study, an approach to the phylogeny of Nummulites was made by performing biometric analysis on measurements of Nummulites forms collected from sedimentary environments of Cuisian - early Lutetian (early - middle Eocene) age outcropping in the Fındıcak and Yenisölöz localities (northwestern Anatolia) in northwestern Turkey. The Cuisian (early Eocene) aged Fındıcak Formation, characterized by carbonate-dominated conglomerate, sandstone, siltstone, limestone, and marl sequences, the early Lutetian (middle Eocene) aged Dürdane Formation, and the Priabonian (late Eocene) aged Soğucak Formation were examined for macro- and microspheric forms of Nummulites individuals. The biometric analysis of the macro- and microspheric forms of the collected Nummulites individuals with radial-granular and radial-white spotted characteristics identified the species Nummulites burdigalensis de la Harpe (Cuisian) and Nummulites uranensis de la Harpe (early Lutetian). A table was created containing the breakdown of the data for the two localities based on biometric measurements. As a result of the overlapping distributions of the two species, some clues were obtained about the genus characteristics of Nummulites, their developmental stages starting from the initial locus, and the changes they underwent until becoming adult individuals. Considering these changes, the phylogenetic development of the Nummulites from the study area, represented within the underlined species, was revealed as the lineage Nummulites burdigalensis → uranensis. [ABSTRACT FROM AUTHOR]

Fossil tetrapod burrows from the Cerro Azul Formation (Late Miocene-Early Pliocene) of southwestern Buenos Aires Province, Argentina, are described and interpreted. The local sedimentary sequence is composed of massive siltstone, with two interbedded calcareous palaeosols, that were deposited in a loessic plain under a semiarid climate. The burrow systems are recognised as Maneraichnus pampeanum igen. and isp. nov., an ichnotaxon that is typified by long ramps that lead to a main chamber located at bifurcation, with chambers forming at least one-third of the total tunnel/ramp volume. A rodent producer is indicated by the presence of interconnected burrow systems with a subcircular cross-section (average RDI = 0.98) and by paired, blunt, incisor traces. The large ratio of chamber volume to tunnel/ramp volume (0.45) is indicative of a communal species and a body mass ranging from 0.9 to 4.6 kg is inferred for the producer. Considering the mentioned constrains and the fossorial mammals of the Cerro Azul Formation, it is proposed that the burrow systems belonged to Lagostomus (Late Miocene-Recent). The fossil burrows also match extant L. maximus ('vizcacha') burrow systems in overall architecture, passive fill, and similar size of claw traces. Miocene species of Paedotherium (Notoungulate) is discussed as an alternative potential digger. [ABSTRACT FROM AUTHOR]

This study elucidated cement-grouted rocks' tensile strength and failure characteristics through pull-off testing. By subjecting four distinct rock types (siltstone, sandstone, slate, and granite) to examination, encompassing both natural and artificially induced joint surfaces, we scrutinized the interplay of influential factors such as rock strength and surface roughness on the mechanical behavior of cement-grouted rocks. Our findings revealed a direct correlation between the rocks' unconfined compression strength (UCS) and their tensile strength post-grouting, with specimens boasting higher UCS demonstrating enhanced tensile resilience. The cement-grouted siltstone type I exhibiting rock failure primarily attributable to its diminished UCS. Contrastingly, siltstone type II and slate showcased failure propagation predominantly along the interface between the rock and cement material. Conversely, distinguished by their robust UCS, sandstone and granite displayed a dual failure mode involving both interface and cement degradation. Additionally, the surface roughness of the rocks emerged as a critical determinant in failure behavior. Specimens characterized by pronounced surface roughness demonstrated a more pronounced cement failure propensity, resulting in superior tensile strength compared to counterparts with lower roughness profiles. [ABSTRACT FROM AUTHOR]

Friction properties of rock are closely connected with the anisotropy. The anisotropy of rock friction can provide a valuable assessment for geotechnical and geological engineering. In this study, the rotary friction tests were conducted to analyze the water effect on the friction property and the friction anisotropy of the four types of rock. The drilling response model (DD-model) was employed to characterize the rotary friction behavior of the rocks. The parameters of this model include the three types of friction parameters: 1/ς, μ, and f, where 1/ς and μ are constant, and f is a variable. A quantitative method is proposed for assessing the anisotropy of rock friction. The results of the rotary friction tests indicate that the relation between torque force and thrust force conforms to the DD-model. The changes of two friction constants 1/ς and μ from dry state to water-saturated state suggest that the water effect on the friction strength of the rocks exhibits significant anisotropy. The friction strength determined by the friction variable f increases first, then decreases, and finally stabilizes with the increasing of depth. AIf is an anisotropy index calculated by the proposed method. The percentage difference of the average value of AIf between water-saturated and dry states shows the degree of the water effect on the friction anisotropy of the rocks, mudstone (MU) > granite (GR) > fine sandstone (FS) > argillaceous siltstone (AS). The quantitative model is hopefully constructed for characterizing the relation between the anisotropic friction strength of rock and the moisture state in future. [ABSTRACT FROM AUTHOR]

A series of ordinary concrete is casted in order to examine the influence of the manganiferous siltstone rocks on the physical, mechanical, and gamma-ray shielding properties. Thus, a partial replacement for the coarse aggregates by siltstone rocks was performed during the fabrication of the currently ordinary concrete. The test revealed that raising the siltstone concentration improved the mechanical characteristics and density of the developed concretes. The addition of siltstone rocks at concentrations ranging from 0 to 40 wt% of the coarse aggregate concentration raises the density of the concrete from 2.05 g/cm3 to 2.3 g/cm3. Furthermore, partial substitution of basalt with siltstone rocks improves gamma-ray shielding properties. The experimental results for the linear attenuation coefficient show an increase in its value from 0.146 cm1 to 0.160 cm−1 when the siltstone concentration is increased between 0 and 40 wt% at 0.662 MeV. Furthermore, increasing the concentrations of siltstone affected the half-value thickness, which varied between 4.759 and 4.319 cm at 0.662 MeV. Therefore, the replacement presents a new alternative coarse aggregate that can enhance the mechanical and radiation shielding properties of ordinary concretes.

A section measured from the upper part of the Pimienta Formation and the lowest part of the Tamaulipas Formation located in the central-eastern part of the state of Hidalgo, NE Mexico was studied. The lower part of the succession consists of an argillaceous and laminated dark gray limestone, black shale, black calcareous shale, siltstone and bentonite; the Pimienta–Lower Tamaulipas transition is marked by the sporadic appearance of light-colored limestone in the upper part of the Pimienta and the shift to a succession dominated by thicker beds of yellowish and bioturbated limestone. The microfossil assemblage consists of calpionellids, radiolarians, and planktonic and benthic foraminifers. The biostratigraphic study of the calpionellids enabled three zones to be identifi ed: Calpionella, Calpionellopsis and Calpionellites as well as fi ve subzones, Elliptica, Oblonga, Murgeanui, Darderi and Major, ranging from early late Berriasian to early Valanginian. This allows a chronostratigraphic correlation to be drawn between the Tethys and the Southeastern Pacifi c provinces. In addition, we report the occurrence of abundant radiolarians and planktonic and benthic foraminifers. The paleoenvironmental inferences in the studied section are documented from the predominant wackestone texture and microfossil association, indicating a pelagic basin environment. The abundant occurrence of radiolarians mostly in the Elliptica and Oblonga subzones could suggest an increase in the input of nutrients. [ABSTRACT FROM AUTHOR]

A novel electro-hydraulic servo point load meter has been developed to address the limitations of existing point load meters, which cannot provide continuous and uniform loading. This new meter enables continuous and uniform loading with variable rates, thereby reducing the dispersion of test data and offering a technical solution for revising the current point load strength calculation formula. Experimental investigations were conducted to analyze the influence of loading rates (0.1 kN/s, 0.5 kN/s, 1.0 kN/s) on the existing point load strength correction method. Four types of rock samples, namely, fine-crystalline granite, coarse-crystalline granite, siltstone and marble, were utilized in the study. Each rock sample was tested at four different sizes: 203 mm3, 303 mm3, 403 mm3, 503 mm3. The objective was to examine how the loading rate affects the accuracy and effectiveness of the point load strength correction method. Initially, the correction index "m" from various domestic and foreign regulations was employed to calculate and analyze the test data, determining the appropriate correction index m, loading rate, and range of rock sample sizes. Subsequently, the relationship between the standard point load strength and uniaxial compressive strength was analyzed based on these findings. The research results indicate the following: (1) the larger the strength of the rock sample, the smaller the point load correction index m and all four rock samples demonstrated an increase in standard point load strength when solved using the four correction indices (m1, m2, m3, m4) with increasing loading rate. (2) With increasing sample size, the standard point load strength solved using correction indices m2, m3, m4 still exhibited a significant size effect, while the dimensional effect of the standard point load strength solved using m1 was not evident. (3) The conversion factors obtained through zero-intercept linear regression analysis for fine-crystalline granite, coarse-crystalline granite, siltstone, and marble were 16.45, 15.38, 15.17 and 14.83, respectively. These results indicate that the conversion factors for rocks with lower strength are smaller compared to those with higher strength. Highlights: The impact of four different rock samples with varying sizes on the existing point load strength correction method is analyzed under three loading rates. An investigation is conducted to determine the appropriate point load strength correction index for the four rock samples. The study identifies the optimal loading rate and size range for rock samples based on the modified correction index. The relationship between standard point load strength and uniaxial compressive strength is examined. [ABSTRACT FROM AUTHOR]

The first of two communications is devoted to the study of lithogeochemical features of the pilot collection of Upper Precambrian sandstone and siltstone samples taken from four boreholes: Bogushevskaya 1, Bykhovskaya, Lepel 1, and Kormyanskaya (Belarus). This article analyzes the general features of their bulk chemical composition and shows the possibilities and limitations for further reconstructions. It has been established that Riphean and Vendian rocks included in the pilot collection, visually identified as sandstones, are actually quartz, feldspar–quartz, and arkosic varieties with different cement types. In terms of geochemical characteristics, the Vendian "siltstones" correspond to the coarse- and fine-grained siltstones and, to a greater extent, mudstones with a predominance of illite, as well as various admixtures of berthierine, kaolinite, and smectite. Based on the comparison of enrichment factor (EF) of the trace element, these rocks are marked by several dissimilarities related to both variations in the source rock composition and sedimentary environment. Data points of the samples on the Zr/Sc–Th/Sc diagram indicate that all of the studied Riphean and Vendian rocks are dominated by the first sedimentation cycle material, suggesting that the lithogeochemical characteristics of the pilot collection rocks quite correctly reflect similar features of the source rock complexes. Therefore, they can be used to reconstruct the paleogeodynamic and paleoclimatic factors that controlled the accumulation of Riphean and Vendian sedimentary sequences in Belarus. [ABSTRACT FROM AUTHOR]

Crack stress thresholds in rocks have long been a popular subject in rock mechanics and engineering research. In this study, the applicability of existing methods for determining the crack stress thresholds of granite and weakly cemented porous siltstone is investigated using step loading and unloading tests. In addition, a novel method for decomposing the volumetric strain into solid-phase linear elastic strain, gas-phase nonlinear elastic strain, and plastic volumetric strain is presented. A quantitative calculation method for determining these thresholds is proposed based on the evolution law of the gas-phase volumetric strain and the physical significance of crack stress thresholds. The initiation and termination points of the stationary stage of the gas-phase volumetric strain are determined as σ cc and σ ci ; the point at which the gas-phase strain changes from positive to negative is determined as σ cd . To validate the proposed method, statistical results of the existing methods after screening are compared with the results of the proposed method. The results show that the proposed method provides reasonable crack stress thresholds for siltstone and granite and is applicable to rocks with similar stress–strain behaviors. The proposed method offers the advantages of independence from other methods, suitability across high and low confining pressures, and the capability for the quantitative calculation and processing of numerous samples. [ABSTRACT FROM AUTHOR]

The Gulong shale demonstrates high clay content and pronounced thin laminations, with limited vertical variability in log curves, complicating lithofacies classification. To comprehend the distribution and compositional features of lithofacies in the Gulong shale for optimal sweet spot selection and reservoir stimulation, this study introduced a lithofacies classification scheme and a log-based lithofacies evaluation method. Specifically, the ΔlgR method was utilized for accurately determining the total organic carbon (TOC) content; a multi-mineral model based on element-to-mineral content conversion coefficients was developed to enhance mineral composition prediction accuracy, and the microresistivity curve variations derived from formation micro-image (FMI) log were used to compute lamination density, offering insights into sedimentary structures. Using this method, integrating TOC content, sedimentary structures, and mineral compositions, the Qingshankou Formation is classified into four lithofacies and 12 sublithofacies, displaying 90.6% accuracy compared to core description outcomes. The classification results reveal that the northern portion of the study area exhibits more prevalent fissile felsic shales, siltstone interlayers, shell limestones, and dolomites. Vertically, the upper section primarily exhibits organic-rich felsic shale and siltstone interlayers, the middle part is characterized by moderate organic quartz-feldspathic shale and siltstone/carbonate interlayers, and the lower section predominantly features organic-rich fissile felsic/clayey felsic shales. Analyzing various sublithofacies in relation to seven petrophysical parameters, oil test production, and fracturing operation conditions indicates that the organic-rich felsic shales in the upper section and the organic-rich/clayey felsic shales in the lower section possess superior physical properties and oil content, contributing to smoother fracturing operation and enhanced production, thus emerging as dominant sublithofacies. Conversely, thin interlayers such as siltstones and limestones, while producing oil, demonstrate higher brittleness and pose great fracturing operation challenges. The methodology and insights in this study will provide a valuable guide for sweet spot identification and horizontal well-based exploitation of the Gulong shale. [ABSTRACT FROM AUTHOR]

To study the seepage law and sectional morphological characteristics in splitting sandstones of different grain sizes, three‐dimensional morphological scanning tests and seepage characteristics tests are conducted on the splitting rock samples of siltstone, fine‐, medium‐ and coarse‐grained sandstone, and the differences in morphological characteristics and seepage law in different grain size sandstones are compared and analyzed. The test results show that the sections of siltstone and fine‐grained sandstone have the overall morphological characteristics of "one high and one low" with large undulation, while the sections of medium‐ and coarse‐grained sandstone have a more uniform distribution and less undulation. In the relationship between pressure gradient and flow velocity, siltstone and fine‐grained sandstone are precisely characterized by the Forchheimer formula, and medium‐ and coarse‐grained sandstone are well characterized by the Izbash formula, and the fitting effect is good. The results of the study are of great reference significance for improving the cross‐sectional morphological characteristics and seepage law of the splitting rock samples. [ABSTRACT FROM AUTHOR]

The Middle Benue Trough (MBT) in Northcentral Nigeria is a geologically significant area with vast mineral resource potential. Employing airborne magnetic and radiometric data, this study utilized the Centre for Exploration Targeting on enhanced total magnetic intensity data to reveal geologic structures, lithological units and mineralization zones. Lineaments predominantly trended in NE-SW direction, with noteworthy orientations in NNE-SSW and E-W. Radiometric anomalies correlated with distinct lithological units, pinpointing granitic gneiss, alluvium, shale, siltstone and sandstone. A magnetically concentrated and potassium-rich area indicated potential polymetallic-magnetic mineralization. The 2D model illustrated igneous intrusions influencing prevalent geologic structures, such as sediment baking and doming. Thorough analysis, including source parameter imaging, standard Euler deconvolution and 2D forward modelling, revealed sediment thicknesses below 1500 m. This research enhances understanding of the MBT's geological features, offering valuable insights for mineral exploration and resource assessment in the region. [ABSTRACT FROM AUTHOR]

The purpose of this research is to study the strengthening effect of cyclic load on the weakly cemented rock and reveal its microscopic mechanism. In this study, a series of cyclic‐to‐monotonic loading tests with different cycle numbers were conducted on siltstone. Results show that the strengthening and weakening effects of siltstone under cyclic loading depend on the upper limit of cyclic load. The microfracture mode that was changed by cyclic load is the essential reason for the strengthening effect, according to the study of acoustic emission b‐value, sources, and microscopic fracture morphology. Under the cyclic load test, the skeleton area of siltstone can bear the axial load increased. However, the burst of acoustic emission signals is delayed, and the crack scale is small due to the strengthening effect. The difficulty of geotechnical engineering disaster prediction and prevention has increased significantly, and attention should be paid to similar geotechnical engineering. Highlights: The strengthening and weakening effects under cyclic loading were compared.The strengthening effect on mechanical properties of siltstone was analyzed.The micro fracture mechanism of strengthening effect was revealed. [ABSTRACT FROM AUTHOR]

Uniaxial step cyclic loading and unloading tests on siltstone were conducted to investigate the mechanisms and evolution characteristics of rock deformation, including elastic, viscoelastic, and plastic aspects. This study proposes a method for separating dissipated energy into damage energy, which is used for particle slippage and structural fractures, and plastic energy, which remains in cracks that do not open after unloading. Additionally, elastic energy is divided into particle elastic energy, released by particle rebound, and crack elastic energy, released by the reopening of compacted cracks. The results indicate that as the stress amplitude increases, the damage energy consumption, plastic energy consumption, particle elastic energy, and crack elastic energy increase. At peak stress, significant expansion and penetration of cracks within the rock sample occur, leading to a sharp increase in damage energy consumption and a dramatic decrease in the rock sample's mechanical properties, with the particle elastic energy dropping quickly. Plastic energy dissipation relates solely to cracks that do not reopen during unloading, with minimal change after reaching peak stress. The calculated damage variables, based on damage energy consumption, align with the deformation and energy characteristics of the rock, providing a reasonable description of the damage development process of the rock under cyclic loading and unloading. [ABSTRACT FROM AUTHOR]

To quantitatively represent the deterioration law of the mechanical properties of siltstone after exposure to supercritical CO2(SC-CO2), experiments were conducted to test the mechanical parameters of rocks under the coupling effect of CO2–water–rock interactions. The purpose of this study is to determine the evolution law and damage characteristics of each siltstone mechanical parameter under the action of SC-CO2. In combination with numerical simulation results, this study revealed the damage evolution characteristics of rocks in a CO2 geological storage reservoir. The research findings indicate that SC-CO2 exhibits a certain time effect and causes non-uniform damage to siltstone. Both the deterioration law of the mechanical parameters and soaking time exhibited an exponential relationship. With increasing soaking time, both the uniaxial compressive strength and elastic modulus showed a decreasing tendency, whereas the Poisson's ratio showed a varying degree of increase. The total degree of deterioration gradually increased as the soaking time increased and approached a stable value. After exposure to SC-CO2, the damage deformation and failure mode transitioned from brittle to plastic in the siltstone samples. In addition, there was a shift from a single axial crack failure pattern to a complex failure mode with multiple cracks. This study also derived a uniaxial compressive strength prediction model for siltstone based on soaking time, constructed an elastic modulus damage model, and established a fluid–solid coupling model considering damage in the CO2 geological storage process. The experimental and numerical simulation results revealed that microstructural alterations occurred in the siltstone after exposure to SC-CO2. Furthermore, it was discovered that damage accumulation from the micro- to macroscale ultimately led to a gradual deterioration in mechanical properties. The research results provide a theoretical basis for mechanical stability evaluation in CO2 geological storage.

In order to study the stress–strain–permeability coefficient relationship of overlying strata in a fractured zone after coal mining, taking the Changcun coal mine in the Changzhi basin as an example, the permeability evolution law of coarse sandstone, fine sandstone, siltstone and mudstone during a stress–strain process was analyzed through a triaxial compression permeability test. The generalized model of the rock mass permeability evolution process under mining stress was summarized, and then a coupling model of the stress–water pressure–permeability coefficient of fractured rock was established based on the continuum model of rock mass. The results showed that the maximum permeability coefficient of different coal overburden types was quite different, and the peak strength of the rock mass preceded the maximum permeability coefficient during the rock mass failure process; the permeability coefficient first decreased and then increased, reaching its maximum value after the peak stress, which occurred during the strain-softening stage; the generalized model of rock mass permeability included the compaction stage, elasticity stage, stable fracture stage, unstable fracture stage, macroscopic failure stage and residual strength stage. [ABSTRACT FROM AUTHOR]

Extralow-permeability reservoirs have emerged as a significant area of focus for CO2 geological sequestration due to their stable subterranean structure and expansive storage capacity, offering substantial potential in addressing global climate change. However, the full extent of CO2 geological sequestration potential within these extralow-permeability reservoirs remains largely unexplored. To address this gap, this paper utilizes the Shahejie Formation (Es1 member) of the Shuang 229 block in the Liaohe oilfield, Bohai Bay Basin, as a case study. This section is characterized by its abundant oil-gas reserves and serves as an exemplar for conducting experimental research on CO2 storage within extralow-permeability reservoirs. The results demonstrate that the reservoir lithology of the Es1 member is fine sandstone and siltstone, with high compositional and structural maturity. Moreover, the average porosity is 14.8%, the average permeability is 1.48 mD, and the coefficient of variation of the reservoir is approximately 0.5, which indicates a low- to extralow-permeability homogeneous reservoir. In addition, the overburden pressure is >2.0 MPa, the fault can withstand a maximum gas column height of >200 m, and the reservoir exhibits favorable overburden and fault sealing characteristics. Notably, stepwise increasing gas injection in the Shuang 229-36-62 well reveals that the injected liquid CO2 near the wellhead exhibits a relatively high density, close to 1.0 g/cm3, which gradually decreases to approximately 0.78 g/cm3 near a depth of 2000 m underground. The injected fluid changes into a supercritical state upon entering the formation, and the CO2 injection speed is optimal, at 0.08 HCPV/a. According to these findings, it is predicted that the highest burial CO2 volume via the injection of 1.5 HCPVs in the Wa 128 block area is 1.11 × 105 t/year, and the cumulative burial volume reaches approximately 2.16 × 106 t. This shows that the CO2 sequestration potential of extralow-permeability reservoirs is considerable, providing confidence for similar instances worldwide. [ABSTRACT FROM AUTHOR]

To extract V5+ ions from the ferruginous siltstone in the Abu Zeneima region of Southwestern Sinai, Egypt, a chelating polyimine ligand (PVAm-Ben) was synthesized via a condensation reaction involving polyvinyl amine and a-hydroxy ketone (Benzoin). The structure of PVAm-Ben underwent comprehensive characterization employing various techniques, namely; FT-IR, 1HNMR, 13C-NMR, and GC/MS analyses. Experimental factors controlling such as pH, time, initial concentration, dosage, temperature, and stripping, were systematically optimized to enhance measurement accuracy. Under conditions of 25°C, 0.015 mol/L, and 30 minutes, PVAm-Ben/C2H4Cl2 exhibited remarkable retention capacity at pH 3. Linear regression analysis results suggested the release of a mole of H+ during the extraction process. The stability constant (log ß = 2.1882) of the PVAm-Ben/V5+ complex was determined, yielding a value of 154.24. The stoichiometry mechanism between PVAm-Ben and V5+ ions displayed a linear correlation (slope: 0.9922), signifying 1 mole of PVAm-Ben reacting with 1 mole of vanadium. The pseudosecond-order kinetic model indicated an exothermic, spontaneous, and advantageous extraction process at low temperatures. Efficient stripping of PVAm-Ben/C2H4Cl2 loaded with vanadium was achieved using 0.05 M NaOH with a 99% efficiency rate. Ultimately, enhanced variables were employed to yield a V2O5 concentrate with a vanadium content of 55% and a purity level of 98.21%. [ABSTRACT FROM AUTHOR]

The remarkable effect of a double primary support has been proven in squeezing soft rock tunnels, but the research on the excavation and support time is still insufficient. In this study, the causes and failure mechanism of the large deformation in the Dongmachang I tunnel were investigated from the geostress field and the surrounding rock conditions. The supporting mechanism of the single and double primary supports in a tunnel and the deformation laws of different bench excavation lengths and support times were analyzed. Based on the Burgers model, creep materials similar to the argillaceous siltstone and materials similar to the concrete and steel arch of the double primary support were designed. The effects of the different bench lengths and the second primary support time on tunnel stability were evaluated by model tests. It was shown that increasing the bench length and delaying the second primary support time makes the second primary support safer, but if the bench length was too long or the second primary support time was too late, then the tunnel supporting structure failed. In the model test of this study, a middle bench length of 20.4 m and a second primary support time of 28 days were more satisfactory. [ABSTRACT FROM AUTHOR]

The accurate reconstruction of the early Cambrian paleoclimate and paleoceanographic conditions on the Yangtze Plate is crucial for understanding the ancient environment during the Cambrian Explosion. It is also a key factor in understanding the ecological habits of organisms during the Cambrian Explosion. The study utilized field outcrops, thin section analysis, and major and trace elements to investigate the sedimentary environment, provenance, paleoweathering, and paleoclimate of the Lower Cambrian Hongjingshao (HJS) Formation (Cambrian Stage 3, ~515 Ma) in the Yangtze Basin, eastern Yunnan, SW China. The HJS sandstones are composed of 10 lithofacies, including massive and weakly bedded gravel supported by coarse sandstone (Gm), trough cross-bedded sandstone (St), planar cross-bedded sandstone (Sp), ripple cross-laminated sandstone (Sr), horizontal bedded sandstone (Sh), scour-fill sandstone (Se), massive sandstone (Sm), fine to medium sandstone with thin bed muddy siltstone (Fl), muddy siltstone (Fsc), and mudstone (Fm). On the basis of these lithofacies, channel fill and over-bank deposits in delta and shallow shelf depositional environments are suggested for HJS Formation. The major elements-based provenance discriminant function and mineral composition indicate that felsic rocks from the recycled orogen and continental block are the main sediment source terrane for the HJS sandstones of the study area. CIA, PIA, and CIW values range from 71.29 to 93.72, indicating an intermediate to intense chemical weathering and semiarid to humid climate conditions in Cambrian Stage 3. The research findings have clarified the paleoclimate and paleoceanographic environment of the Early Cambrian in the Yangtze region, which is of significant importance for understanding the early biological and ecological marine environment in the study area. [ABSTRACT FROM AUTHOR]

During underground engineering projects, siltstone—a porous, weakly cemented rock—commonly undergoes cyclical states of creep and fatigue, raising questions about its mechanical stability under such conditions. To investigate, this study employed laboratory experiments, featuring a creep-fatigue alternation action test and uniaxial reloading test, with the absolute expansion stress serving as the upper load limit. Results reveal a counterintuitive synergy between creep and fatigue actions. Fatigue processes reduced the viscoplastic deformation capacity of siltstone, prolonging its creep rupture life. Besides, creep actions amplified the fatigue life of siltstone by over 168%, attributable to the filling and embedding of rock debris particles in the rock matrix. Additionally, siltstone’s elastic modulus and Poisson’s ratio displayed a periodic “rise-drop” oscillatory pattern under the creep-fatigue regime. Plastic strain values emerged as a robust metric for quantifying damage. Intriguingly, creep-fatigue alternation increased the absolute expansion stress by 11.7%, bolstering the rock’s damage resistance. However, this cyclical regime exacerbated the postpeak fracture behavior of siltstone, underscoring the complexity of its mechanical response. [ABSTRACT FROM AUTHOR]

Premise of research. Stigmaria ficoides is the main form species of rooting organ for late Paleozoic arborescent lycopsids in the families Diaphorodendraceae and Lepidodendraceae. This organ consisted of four primary axes, each of which divided dichotomously, forming a rooting system complete with a dense network of rootlets. Until now, these dichotomies have mainly been known to be isotomous, unlike the architecture of some sigillarian Stigmaria / Stigmariopsis forms, which bore minor geotropic axes on the underside of the stigmarian arms. Methodology. Two S. ficoides siltstone cast specimens were analyzed with light macrophotography and white-light surface scanning. Fossils were compared to other Stigmaria taxa. Pivotal results. Here, we report two S. ficoides specimens based on the presence of the diagnostic rootlet scar pattern. The two specimens document pronounced anisotomous (i.e., unequal) dichotomous branching. The first specimen is a small cast of the distal portion of the stigmarian rooting system, in which an anisotomous dichotomy occurs amid several isotomous dichotomies. The second specimen is a larger cast of a more proximal portion of the rhizomorph, in which the main broad axis bears two slender secondary axes. Conclusions. This finding adds new context to our understanding of the developmental plasticity of S. ficoides. [ABSTRACT FROM AUTHOR]

A stepped cyclic loading test was designed to investigate the stress memory and acoustic emission characteristics of siltstone under different previous stress levels. This study aims to improve the applicability of the acoustic emission in situ stress measurement method in porous weak cementation strata. The stress memory failure range for siltstone and the memory stress correction formula were determined based on characteristic stress value. The analysis of acoustic emission characteristics revealed the failure mechanism of the Kaiser effect of siltstone, and the following conclusions were obtained. Crack initiation stress can serve as the failure criterion for the stress memory effect in siltstone. Therefore, the failure range for the stress memory effect in siltstone can be defined as a previous stress of less than 15.3 MPa and a memory stress of less than 13.7 MPa. The pore compaction process in siltstone and the friction-generated acoustic emission signal during this process negatively affect stress memory. The primary cause of the stress memory effect in rocks is the irreversible development of new internal cracks. The compression rebound effect of primary soft pores in siltstone mainly causes the Kaiser effect to fail. The compression rebound effect of primary soft pores in siltstone is the main reason for the failure of the Kaiser effect. [ABSTRACT FROM AUTHOR]

The factors that influence dissipated energy and pore pressure generation patterns with respect to the cycle ratio and dissipated energy ratio were analyzed using the results of cyclic triaxial and cyclic direct simple shear tests. These analyses revealed several interesting differences in pore pressure generation patterns when related to cycle ratio than to dissipated energy ratio. Soils with different pore pressure generation patterns when plotted against the cycle ratio were found to have nearly identical pore pressure generation patterns when plotted against the dissipated energy ratio. The differences exist as the result of the fundamental differences between cycle ratio and dissipated energy ratio. The fundamental difference is that pore pressure generation is directly linked to the process of energy dissipation; it is not inherently linked to cycles of loading. Therefore, to achieve an understanding of the pore pressure response of a soil that is independent of the specifics of the applied loading, one needs to evaluate it in terms of energy dissipation, not in terms of cycles of loading, especially irregular loadings. [ABSTRACT FROM AUTHOR]

Driven piles are considered to be an excellent deep foundation design choice due to the economic benefits and availability. However, there is a knowledge gap in assessing pile driving and predicting pile resistance in rock-based intermediate geomaterials (R-IGMs). A better prediction of pile resistances, anticipated refusal depth and pile design methods are essential to alleviate current challenges with piles driven in R-IGMs. This paper presents recommendations for piles driven in weak rocks or R-IGMs based on 39 test piles from 28 bridge projects completed in three US states. Static analysis (SA) methods for predicting unit shaft resistance (qs) are developed based on in situ SPT N-value and unconfined compressive strength (qu) for five different weak rocks: siltstone, claystone, sandstone, mudstone and granite. SA methods for predicting unit end bearing (qb) are developed for siltstone and claystone. The proposed SA methods are compared against existing SA methods and validated using 19 independents test pile data. The proposed SA methods provide more accurate and consistent prediction of qs and qb, resulting in higher LRFD resistance and efficiency factors. The qs increases from 9.7 to 400% in siltstone and 5.9 to 87% in claystone at one day after the end of driving. However, pile relaxation is observed on qb of piles driven into siltstone, claystone and sandstone. [ABSTRACT FROM AUTHOR]

Field data from recent geological mapping over a major part of the north-central Scandinavian Caledonides combined with published information give a detailed view of early Cambrian basin successions, comprising the Gärdsjön formation (Gf; Jämtland supergroup) in the Lower Allochthon and autochthonous equivalents (Dividal Group). The Gf comprises ten units of sandstone and siltstone or mudstone (Gf I—X, > 300 m thick). Green siltstones with red layers (Gf VI, c. 521 to 519 Ma) and green–grey siltstones at the top (Gf X, c. 516.5 to 513.5 Ma) are regional key horizons. Gf V, VI, VII, IX, and X deposition may be related to eustatic events. Restoration of Caledonian shortening reveals a major "Hornavan-Vattudal basin" (HVB; > 330 km NW–SE, > 400 km NE-SW) between the Grong–Olden culmination in the S and the Akkajaure–Tysfjord culmination in the N. Published zircon ages imply the latter separated the HVB from those shed from the Timan orogen in the N. The eastern basin margin straddles the present Caledonian erosional margin. Basement highs identified here within the Nasafjället, Bångonåive, and Børgefjellet "basement" windows define the western margin. They separate the HVB from the outer shelf towards the Iapetus Ocean in the W. The onset of sedimentation is time-related with E–W extension at c. 544–534 Ma. NNE–SSW-directed extension occurs after c. 518 Ma, perhaps related with Timan late-orogenic extension. The HVB is distinctly younger (c. 535–513.5 Ma) than Rodinia break-up and Iapetus ocean formation (> 550 Ma), comparable with post-rift basins in inner parts of modern passive margins. [ABSTRACT FROM AUTHOR]

Thin section and argon-ion polishing scanning electron microscope observations were used to analyze the sedimentary and diagenetic environments and main diagenesis of the Permian Fengcheng Formation shales in different depositional zones of Mahu Sag in the Junggar Basin, and to reconstruct their differential diagenetic evolutional processes. The diagenetic environment of shales in the lake-central zone kept alkaline, which mainly underwent the early stage (Ro<0.5%) dominated by the authigenesis of Na-carbonates and K-feldspar and the late stage (Ro>0.5%) dominated by the replacement of Na-carbonates by reedmergnerite. The shales from the marginal zone underwent a transition from weak alkaline to acidic diagenetic environments, with the early stage dominated by the authigenesis of Mg-bearing clay and silica and the late stage dominated by the dissolution of feldspar and carbonate minerals. The shales from the transitional zone also underwent a transition from an early alkaline diagenetic environment, evidenced by the formation of dolomite and zeolite, to a late acidic diagenetic environment, represented by the reedmergnerite replacement and silicification of feldspar and carbonate minerals. The differences in formation of authigenic minerals during early diagenetic stage determine the fracability of shales. The differences in dissolution of minerals during late diagenetic stage control the content of free shale oil. Dolomitic shale in the transitional zone and siltstone in the marginal zone have relatively high content of free shale oil and strong fracability, and are favorable "sweet spots" for shale oil exploitation and development. [ABSTRACT FROM AUTHOR]

The physical properties of the rock units associated with the Rio Bonito Formation are presented in this study with the focus on modelling reservoir quality based on petrophysics-derived parameters to evaluate CO2 storage potentials. It involves the modelling of the reservoir depths, thicknesses, flow zone indicators (FZI), and effective permeability (Keff) and presenting the CO2 storage efficiency factors peculiar to the rock units of the study location. Research results presented by this study for the stated objectives are not quite common in the region. Keff values range from 200 mD to higher than 2000 mD, and FZI values are generally above 1.0 mm and up to 13.0 mm within the portions covered by the drilled wells. The sandstone units recorded are up to 20 m thick in some cases. The Keff and FZI models indicate the sandstone reservoirs as permeable units to support the injection and circulation of CO2 within the potential reservoir units of the Rio Bonio Formation across São Paulo State. Apart from some points in the southeastern part of the study location, where the Rio Bonito are delineated at depths less than 800 m (minimum CO2 storage depth based on best practices), other portions are deeper, ranging from 950 m to 3500 m. Thin-bedded layers will affect the integrity of the rocks as CO2 storage tanks or reservoir seals/traps/overburden within the region. Sandstone bed thicknesses are up to 20 m in some cases. However, hybrid CO2 reservoir units are feasible, especially in portions where thin siltstone layers are sandwiched between sandstone units to provide considerable thicknesses based on CO2 storage standards. The current study shows that useable areas considering reservoir thickness, depth, and other physical qualities will significantly control the CO2 storage efficiency of the study location. Further studies featuring a detailed geophysical exploration of the site to confirm the availability and saturations of preexisting fluid (hydrocarbon and water) are encouraged to boost CO2 storage in the region. The related research-based results, as mentioned above, may be combined with the results of this research to determine the area's potentials for CO2 storage or hydrocarbon production with CO2 storage options. [ABSTRACT FROM AUTHOR]

The paper presents new finds of fossil fauna and flora at the rediscovered locality Krsmol "Deep gorge" ("Hluboká rokle") of the Ploužnice Horizon (Semily Formation, Krkonoše Piedmont Basin). Several metres thick reddish to grey tuffaceous siltstones of this lacustrine horizon contain 10 centimetres thick layer of grey, hard, siltstones with good fissility, containing one to two thin layers enriched in isolated osteological fragments of vertebrates at the base. Scales and teeth of actinopterygians, scales and fragments of the pectoral girdle of acanthodians are common, and teeth of chondrichthyans can be occasionally found. Rare scales of actinopterygians, isolated insect wings and sporadic plant remains are also present in the overlying reddish-purple siltstone. The newly found fauna in Krsmol extends the existing knowledge based on the old collections and coincides in species with the findings at other sites of the Ploužnice Horizon. From the biostratigraphic point of view, the findings of scales of actinopterygian fish Sphaerolepis kounoviensis, which is an important representative of the biozone corresponding to the uppermost Carboniferous shark teeth and especially the wings of the insect Sysciophlebia rubida of the family Spiloblattinidae are significant, on the basis of which the strata can be classified as Stefan B/C (Kasimovian/Gzhelian) similarly to the strata at other sites of the Ploužnice Horizon. [ABSTRACT FROM AUTHOR]

• Pressurized sealed shales were used to reveal in-situ oiliness and mobility. • TOC exhibits the opposite effects on the oiliness and mobility of shale oil. • The mobility of free oil is affected by adsorbed oil content and microcracks. • The movable threshold of free oil or OSI increases with increasing adsorbed oil content. Oiliness and mobility are key indicators to evaluate the sweet spots of shale oil. Due to the complex oil occurrence states and the lack of in-situ oiliness related experimental methods, the relationship between oiliness and mobility of shale oil is still unclear, which affects the evaluation of movable oil and the optimization of sweet spots. In this paper, the Upper Cretaceous Qingshankou Formation of lacustrine shale in the Changling Sag, the southern Songliao Basin is taken as the research object. Two-dimensional nuclear magnetic resonance (2D-NMR) experiments were performed on pressurized sealed cores before and after centrifugation to accurately characterize the effective porosity, oiliness, and oil mobility of shale reservoirs, these properties' international relationships and controlling factors were discussed, and then a suitable model for evaluating the movable oil was proposed. Based on 2D-NMR and pressurized sealed samples, shale in-situ oiliness can be accurately revealed, with a free oil content 2.48 times that of pyrolysis free hydrocarbons (S 1), which makes the previously used OSI (S 1 /TOC) calculated by pyrolysis S 1 unable to assess shale oil mobility. The correlation between effective porosity, oiliness, and oil mobility was better in siltstone and limestone interlayers and worse in shale reservoirs. Microcracks can significantly promote the mobility of shale oil, while adsorbed oil has the binding effect on the move of free oil, resulting in that shale oil can move until free oil or OSI reaches a certain threshold. The movable thresholds were redefined through the relationship between movable oil and free oil content, we found that as TOC or the adsorbed oil content increases, the movable thresholds for free oil and OSI also gradually increase, shale oils within different lithologies correspond to different movable thresholds, and using a fixed movable threshold for mobility discrimination will misjudge the sweet spots of shale oil interval. Based on the movable threshold of free oil, a model related to the maximum mobility of shale oil has been developed in this study, which has better applicability and is more accurate than the existing OSI method. The results of the present study are very important for deepening the understanding of the mobile mechanism and guiding the selection of sweet spots for shale oil. [ABSTRACT FROM AUTHOR]

• The strength effects under various cyclic loads were divided into low-stress weakening, low-cycle weakening, strengthening, and fatigue effects. • The correlation between the axial and circumferential ultimate strain, peak strength, and upper limit stress of cyclic load was established. • The mechanisms of rock strengthening and fatigue effects were revealed by AE energy and sources analysis. The purpose of this paper is to reveal the influence mechanism of various cyclic loads on siltstone strength, by conducting a series of coupled cyclic-monotonic loading tests. Firstly, it was found that the peak strength of rock depends on the upper limit and cycle number of cyclic load. The peak strength of siltstone shows low-stress weakening effect, low-cycle weakening effect, strengthening effect, chaotic effect, and fatigue effect. Secondly, the ultimate strain of siltstone under cyclic load is controlled by the peak strain of uniaxial compression test. The peak strength is linearly with the peak strain, and the peak strain under uniaxial compression can be regarded as the critical threshold for fatigue failure. Then, the decrease of AE b value reflects the aggregation of micro cracks, which can predict the damage and failure of siltstone earlier than the burst of AE signals. The propagation paths of cracks under these strength effects show significant differences, by comparing the evolution of three-dimensional AE sources with different energy levels. Finally, the fracture mechanism of the strengthening and weakening effects was discussed through electron microscopy scanning. The results indicate that the micro structures are adjusted by cyclic loadings, its fracture and energy release mode was changed, resulting in the increase of peak strength. [ABSTRACT FROM AUTHOR]

To quantitatively represent the deterioration law of the mechanical properties of siltstone after exposure to supercritical CO 2 (SC-CO 2), experiments were conducted to test the mechanical parameters of rocks under the coupling effect of CO 2 –water–rock interactions. The purpose of this study is to determine the evolution law and damage characteristics of each siltstone mechanical parameter under the action of SC-CO 2. In combination with numerical simulation results, this study revealed the damage evolution characteristics of rocks in a CO 2 geological storage reservoir. The research findings indicate that SC-CO 2 exhibits a certain time effect and causes non-uniform damage to siltstone. Both the deterioration law of the mechanical parameters and soaking time exhibited an exponential relationship. With increasing soaking time, both the uniaxial compressive strength and elastic modulus showed a decreasing tendency, whereas the Poisson's ratio showed a varying degree of increase. The total degree of deterioration gradually increased as the soaking time increased and approached a stable value. After exposure to SC-CO 2 , the damage deformation and failure mode transitioned from brittle to plastic in the siltstone samples. In addition, there was a shift from a single axial crack failure pattern to a complex failure mode with multiple cracks. This study also derived a uniaxial compressive strength prediction model for siltstone based on soaking time, constructed an elastic modulus damage model, and established a fluid–solid coupling model considering damage in the CO 2 geological storage process. The experimental and numerical simulation results revealed that microstructural alterations occurred in the siltstone after exposure to SC-CO 2. Furthermore, it was discovered that damage accumulation from the micro- to macroscale ultimately led to a gradual deterioration in mechanical properties. The research results provide a theoretical basis for mechanical stability evaluation in CO 2 geological storage. • By analyzing the peak stress evolution law of uniaxial loading failure of sandstone samples soaked in supercritical CO 2 , combined with the characterization results of sample failure modes, the uniaxial loading failure mechanism of sandstone considering the effect of soaking time was revealed. • Based on the degradation law of mechanical properties of sandstone after supercritical CO 2 immersion, a prediction model for uniaxial compressive strength and elastic modulus damage of sandstone based on immersion time were established. • A stress seepage damage coupling model for supercritical CO 2 geological storage was established, and the coupling relationship between reservoir stress and damage variables was analyzed, revealing the evolution characteristics of CO 2 geological storage reservoir damage. [ABSTRACT FROM AUTHOR]

Determining the transmission rate of radon gas in overburden strata is crucial for conducting a comprehensive study of radon gas's longitudinal and long-distance migration mechanisms. This study investigates the mineral components of rocks in the underground strata of the mining area using the X-ray diffraction method. Additionally, it examines the pore structure parameters of the rocks at different depths using the low-temperature nitrogen adsorption method. This research introduces an approach to inversion calculate the radon gas transmission rate through the activity ratio of radon's characteristic daughters based on the decay law and activity balance of 210Po and 210Pb daughters. In addition, it determines the transmission rates of radon gas in overlying strata at various depths through this method. The relationship between the rock's mineral composition and pore structure is investigated, and the effects of pore structure and mineral composition on the radon gas transmission rate are analyzed. The findings indicated that the pore structure exerts a dual impact on radon gas transport: macropores serve as channels for upward radon gas transport, while micropores offer most of the adsorption area. In contrast, the radon gas transmission rate is indirectly influenced by the mineral composition content associated with the medium's adsorption capacity and pore structure. In the studied lithologies, an increase in quartz content promotes radon gas transmission, while an increase in clay mineral content impedes it. Finally, the mechanisms of radon gas transport, daughter adsorption, and the impacts of rock pore structure and mineral composition on the radon transmission rate are discussed. [Display omitted] • The radon daughter measurement method that can effectively estimates the radon gas transmission rate was proposed. • How the pore structure and mineral components of rock in the underground strata affect radon gas transport rates. • The average radon gas transmission rate across different lithologies is siltite > shale > mudstone > sandstone > limestone. • An increase in quartz content promotes radon transport, while an increase in clay mineral content inhibits it. [ABSTRACT FROM AUTHOR]

Sedimentary rock deposits such as siltstone have been attracting interest due to their potential to store and control the movement of sequestered CO2. An understanding of weak caprocks is required to guarantee the safety of CO2 geo-sequestration projects where weak rocks are encountered. The cost and challenge of obtaining intact samples of weak caprocks from depths relevant to potential geo-sequestration targets has resulted in relatively little data on their mechanical behaviour being available. This paper describes the manufacture and characterisation of artificial siltstones, with properties typical of weak rocks, at stress levels relevant to geo-sequestration. It is shown that the artificial siltstones with properties typical of weak rocks can be simply produced from mixtures of sand, feldspar fines, plaster and water. [ABSTRACT FROM AUTHOR]

The separation and investigation of plastic dissipation energy and damage dissipation energy, and the exploration of the association between energy dissipation and crack development, contribute to revealing the essence of rock failure. In this study, triaxial cyclic loading and unloading tests were performed on porous siltstone widely distributed in mining areas in western China. According to the characteristic stresses and energy evolution characteristics, the failure process of siltstone was divided into five stages. The cumulative energy dissipation ratio shows a spoon-shaped evolution characterized by a significant decline, slight decline, slow increase, significant increase, and stable trend. Importantly, a method for separating plastic dissipation energy and damage dissipation energy was proposed and applied to investigate the evolution characteristics of plastic dissipation energy and damage dissipation energy. Corresponding to the energy characteristics, the acoustic emission activity exhibits significant phased characteristics in five stages. Furthermore, the analysis of crack evolution based on acoustic emission parameters reveals that the proportion of tensile cracks increased significantly near peak failure, and the development of tensile cracks substantially contributed to the damage of load-bearing structures. In particular, the evolution of shear cracks exhibited a strong correlation with the cumulative plastic dissipation energy, while the evolution of tensile cracks showed a strong correlation with the cumulative damage dissipation energy. Finally, the energy dissipation mechanisms of tensile cracks and shear cracks were revealed.Highlight [ABSTRACT FROM AUTHOR]

Oil migration in shale formations across multiple scales from nanometers to meters, a topic without receiving sufficient attention, is of great significance to the accumulation and production of shale oil. Compared with oil migration in conventional reservoirs usually with a long distance, shale oil migration is much shorter, which challenges the applicability of conventional characterization methods for shale formations. In addition, shale oil migration in different types of shale formations occurs at different scales, and their source-reservoir configuration, accumulation mechanism, and exploration plans are also different, greatly complicating a cost-effective and sustainable exploitation of shale oil resources. Accordingly, this review summarizes the experimental methods for characterizing the shale oil migration across multiple scales, and reveals the migration characteristics in three different types of shale oil formations of typical basins in China and USA. The shale oil migration distance in "pure shale-type" formation is the shortest and mainly in nanometer-microns scale. The migration characteristics of "pure shale-type" shale oil are difficult to reveal directly due to its ultra-short migration distance, which may be indicated by the microscale compositional changes at the surface of minerals being interacted with organic fluids and requires additional innovations on the shale oil migration characterization methods with a high accuracy. The shale oil migration distance in laminated-type shale oil formation is at the lamina (micron-millimeter) scale and the shale oil migrates from the organic matter-rich to -lean laminae. The lamina type (felsic, carbonate, or clayey) significantly affects the migration and enrichment of shale oil by providing different types of pore spaces and migration pathways. The shale oil "composition change" method effectively indicates the migration characteristics of shale oil among different laminae, while the "hydrocarbon expulsion efficiency" method is not accurate for the laminated-type shale oil. The migration distance of sandwich-type shale oil is at the millimeter-meter scale, which is the largest among three types of shale oil formations. The reservoir space is mainly intergranular pores and the shale oil migrates from the overlying or underlying organic matter-rich shale to the siltstone interlayer. Both "hydrocarbon expulsion efficiency" and "composition change" methods can be used to clarify the migration characteristics of sandwich-type shale oil. This review overall has a great significance for deeply understanding the characterization methods and migration characteristics of different types of shale oil formations at multiple scales. [ABSTRACT FROM AUTHOR]

• An FDEM coupled model is first used to study the failure mechanism of underground caverns in Longyou Grottoes induced by humidity change. • The input parameters in FDEM are calibrated by uniaxial compression tests on dry and saturated siltstone samples. • Crack patterns of a disk specimen during drying and wetting are simulated to validate the coupled model and calibrated parameters. • Tensile failure is dominant in the surrounding rock under evaporation condition, while shear failure occurs during moisture absorption. • The extent of humidity damage zone (HDZ) of the caverns is greatly reduced by applying a waterproof layer. The stability of underground caverns in Longyou Grottoes is greatly influenced by humidity change since they are mainly composed of argillaceous siltstone, which is highly sensitive to moisture. In this work, a coupled humidity diffusion-fracture model based on the finite-discrete element method (FDEM) is employed to study the fracture characteristics and failure mechanism of underground caverns No.4 and 5 in Longyou Grottoes caused by humidity change. Firstly, the input parameters are calibrated with uniaxial compression tests on dry and saturated siltstone samples. Then, the crack patterns of a disk rock specimen under drying and wetting conditions are captured, which are compared with experimental results to validate the coupled model and calibrated parameters. Subsequently, numerical models of caverns No.4 and 5 in the Longyou Grottoes are established based on the actual geological conditions. The failure processes of the surrounding rock under moisture evaporation and absorption are simulated, and the stress evolution caused by humidity change is analyzed. Results indicate that the caverns primarily experience tensile failure under the evaporation condition with a distribution of tensile cracks perpendicular to the cavern boundary. However, shear failure occurs in the surrounding rock during moisture absorption, and the cracks gradually propagate into the deep rock with humidity diffusion. Additionally, several factors influencing cavern failure are discussed, and the number of cracks is quantified. Finally, it is found that the HDZ of the caverns is significantly reduced by applying a waterproof layer. The findings in this study have practical significance for predicting and improving the long-term stability of underground caverns in Longyou Grottoes under complex climatic conditions. [ABSTRACT FROM AUTHOR]

• Strength and fatigue properties of argillaceous siltstone under different upper limit loads investigated. • Weakening and strengthening mechanism of argillaceous siltstone under different upper limit loads was revealed. • Increased uniformity of crack size and increased effective bearing surface contribute to rock strengthening. • Crack development tends to become localized and an increase in fracture scale leads to rock weakening. To examine the strength and fatigue characteristics of argillaceous siltstone under varying upper limit loads, cyclic-to-monotonic loads and fatigue failure tests were carried out with the upper limit load in different characteristic stress ranges. At upper limit loads between crack initiation stress and damage stress, the anti-deformation capacity and peak strength of argillaceous siltstone improved considerably after cyclic loading. Rock fatigue failure occurred when cyclic loads surpassed the stress causing damage, and the strain at the control point on the uniaxial compression (UC) curve served as a benchmark for identifying rock fatigue failure. The fatigue strength of the argillaceous siltstone was around 80–89% of the UC strength. The logarithm of fatigue life showed a negative linear correlation with upper limit load. In addition, deformation characteristics and modulus of elasticity also confirmed the weakening and strengthening phenomenon of argillaceous siltstone at various upper limit loads. On the basis of the macroscopic mechanical behaviour and microscopic fracture features of argillaceous quartz sandstone, the weakening and strengthening mechanism of argillaceous siltstone at a range of upper limit loads was revealed. The results indicate that increased uniformity of crack size, reduced degree of fragmentation and increased effective bearing surface contribute to rock strengthening, while crack development tends to become localized and an increase in fracture scale leads to rock weakening. [ABSTRACT FROM AUTHOR]

To understand and quantify fatigue in siltstone, uniaxial cyclic loading was applied on siltstone specimens along with acoustic emission (AE) monitoring. The specimens were pre-treated with cyclic temperatures up to 200 °C, 400 °C, and 600 °C, respectively. The upper limit of cyclic stress was 40% and 60% of the average uniaxial compressive strength of the specimens. The results show that the fatigue behaviour of siltstone can be classified into stiffened and damaged categories. An increase in the cyclic temperature leads to a decrease in the fatigue threshold. The AE cumulative ringing count was recorded during the experiment. A unified model was derived with high accuracy to describe both the stiffened and damaged behaviour of siltstone under post-thermal cyclic loading. • Post-thermal cyclic loading incurred stiffened and damaged behaviour in siltstone. • Elastic modulus (E) was more sensitive to cyclic loading in the damaged specimens. • The first three cycles accounted for up to 81.41% of the variation in E. • An increase in the temperature decreased the fatigue threshold of the siltstone. • A quantitative acoustic emission model unified stiffened and damaged fatigue. [ABSTRACT FROM AUTHOR]

Changes in the mesoscopic fracture characteristics and critical signs of fatigue failure of siltstone due to macroscopic deformation under different limit loads during cyclic loading have been investigated. The fatigue strength of the siltstone is approximately 80%–85 % of the uniaxial compressive strength. The fatigue strength can be identified as the point of changes in the deformation and AE parameters of the siltstone. When the upper limit load is less than the fatigue strength, deformation is predominantly axial compression with minor damages to the siltstone. The residual strain, AE count, AE energy and AE peak frequency undergo two-stages of change. When the upper limit load is higher than the fatigue strength, the specimen undergoes fatigue failure. The upper limit load follows a logarithmic relationship with the fatigue life. The rock deformation is governed by lateral expansion, and a network of cracks on the damaged specimen formed are predominantly penetrating "X-shaped" shear cracks and supplemented by secondary shear cracks. The residual strain, AE count and AE energy show a three-stage process. The peak frequency tends towards the dominant frequency band (low- and mid-frequencies), and the peak frequency of the dominant frequency band increases and then decreases. The strain at the control point of the uniaxial compression curve can be used as a reference value for predicting the fatigue failure of the siltstone. The continuous decrease of AE b -value and the sudden increase of AE RA/AF can be regarded as critical signs of fatigue failure of the siltstone. In addition, when siltstone changes from the damaged fracture phase to the fatigue failure phase, there will be a noticeable critical slowing down phenomenon. Therefore, the sudden increase in the variance and autocorrelation coefficient of AE characteristic parameters (AE count, AE energy and RA/AF) can be considered as a precursor of rock fatigue failure. [ABSTRACT FROM AUTHOR]

As deep learning (DL) gains popularity for its ability to make accurate predictions in various fields, its applications in geosciences are also on the rise. Many studies focus on achieving high accuracy in DL models by selecting models, developing more complex architectures, and tuning hyperparameters. However, the interpretability of these models, or the ability to understand how they make their predictions, is less frequently discussed. To address the challenge of high accuracy but low interpretability of DL models in geosciences, we study rock classification from thin-section photomicrographs of six types of sedimentary rocks, including quartz arenite, feldspathic arenite, lithic arenite, siltstone, oolitic packstone, and dolomite. These rocks' characteristic framework grains and grain textures are their distinguishing features, such as the rounded or oval ooids in oolitic packstone. We first train regular DL models, such as ResNet-50, on these photomicrographs and achieve an accuracy of over 0.94. However, these models make classifications based on features like cracks, cements, and scale bars, which are irrelevant for distinguishing sedimentary rocks in real-world applications. We then propose an attention-based dual network incorporating both global (overall photomicrograph) and local (distinguishing framework grains) features to address this issue. Our proposed model achieves not only high accuracy (0.99) but also provides interpretable feature extractions. Our study highlights the need to consider interpretability and geological knowledge in developing DL models, in addition to aiming for high accuracy. [Display omitted] • Proposed dual network achieves high accuracy (0.99) and interpretable feature extractions for sedimentary rock classification. • Regular DL models achieved high accuracy (>0.94), but relied on irrelevant features for classification. • This study emphasizes importance of interpretability and geological knowledge in developing DL models for geosciences. [ABSTRACT FROM AUTHOR]

We report several raninoid specimens collected from the lower Maastrichtian Lower Siltstone Member of the Potrerillos Formation (Difunta Group), NE Mexico. These specimens were collected from fine-grained sandstones that crop out at the NE edge of the Parras Basin, Coahuila. This outcrop is very close to a structural feature that has been active since Late Jurassic times (San Marcos Fault) and has affected depositional lithostratigraphic units from the Upper Jurassic to Upper Cretaceous. The studied specimens are assigned to Bournelyreidus paredonensis n. sp. (Lyreididae Guinot, 1993) and Coahuilanina difuntaensis n. gen., n. sp. (Raninidae de haan, 1839). A new subfamily, Coahuilanininae is described to accommodate the new genus and species, Coahuilanina difuntaensis. The new frog crabs represent the first formally described raninoids from the lower Maastrichtian portion of Difunta Group, adding to an already diverse assemblage of raninoids from Mexico. • New taxa of crabs. • Upper Cretaceous. • NE Mexico. • Possible chemosynthetic communities. [ABSTRACT FROM AUTHOR]