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A new non-mineralised fauna was recently discovered in the Lower Ordovician Madaoyu Formation near Liexi Township, West Hunan Province, South China. Diverse animals are preserved in a thin layer of siltstone interbedded within the limestone. The most peculiar group among this new Fauna is a large quantity of palaeoscolecidan worms with multiple instars, which are only represented by trunks without any other soft tissues such as the introvert, pharynx, and intestine being preserved. The unique characteristic of these worms are that they have a dorsal-ventral differentiation of plates, which are arranged in longitudinal lines, this suggests that the worms probably were exquisite bottom crawlers. The palaeoscolecidans are uniform in morphology and attributed to a new genus and species, Liexiscolex hunanensis Liu & Huang, gen. et sp. nov. This discovery not only enriches our knowledge of the anatomy and palaeoecology but also helps us understand the evolution of palaeoscolecidan worms. Furthermore, it provides a better comprehension of the Lower Ordovician Liexi fauna in South China. [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. Highlights: Weak siltstones showed evidence of approaching critical states typical of de-structured granular materials when sheared to large deformations after yield. Drained triaxial tests revealed that the stress–strain response and failure mode depend on level of confining pressure and amount of cementation. The artificial siltstone can reproduce the strength, stiffness and mechanical behaviour of weak rock. [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 Highlights: A characteristic stress determination method based on evolution characteristics of multiphase volumetric strain Spoon-shaped evolution characteristics of the cumulative energy dissipation ratio A determination method of plastic energy dissipation and damage energy dissipation Association mechanism between the development of shear and tensile cracks and the evolution of plastic and damage dissipation energy [ABSTRACT FROM AUTHOR]

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 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]

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.

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.

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]

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]

To extract vanadium (V) ions from the ferruginous siltstone at Abu Zeneima in Southwestern Sinai, Egypt, a synthesized chelating N-phenyl acetyl-N-naphthyl hydroxyl amine (PANHA), was used. Complete characterization was carried out successfully to elucidate the structure using several techniques such as FT-IR,1H-NMR, 13C-NMR, GC-MS and TGA analysis performances. Improved experimental measurements, such as pH, shaking time, initial concentration of V(V), PANHA dosage, temp., and stripping agents, have been achieved with the solvent extraction technique. At 25 ℃ and 0.015 mole per liter through 30 minutes, PANHA/CHCl3 has an extreme retention potential of 50 mg per gram at 25 ℃ at pH 1.5 at 1:1 aqueous to organic phase ratio. The linear regression analysis, consisting of a log D track versus pH, shows a straight line with a slope of 0.859, indicates that a mole of H+ was released during the extraction. The stability constant (β), of PANHA-V(V) complex was calculated from the intersection (log β=1.7958), and it was found to equal 63.1. The stoichiometry mechanism among a chelating ligand of PANHA and V(V) indicates a roughly linear correlation with slope of 0.882 which explains that one mole of PANHA chelating ligand can react with one mole of V (V). According to the kinetic and thermodynamic interpretations, the pseudo-second order kinetic model predicted the kinetics of vanadium (V) extraction, the thermodynamic factors ΔS, ΔH, and ΔG were also measured. As the temperature rises, ∆G values rise from -10.45 kJ/mol at 198 K to -2.2 kJ/mol at 353 K. Vanadium may be stripped from the loaded PANHA/CHCl3, by 0.5M NaOH with a 99% efficiency rate. To obtain a vanadium concentrate (NH4VO3, AMV) with a vanadium content of 42.6 percent and pureness of 98 percent, the enhanced variables were finally put to use. [ABSTRACT FROM AUTHOR]

Four groups (1 × 10–5/s, 1 × 10–4/s, 1 × 10–3/s and 1 × 10–2/s) of triaxial compression tests at a confining pressure of 30 MPa are carried out to clarify the strain rate effect and damage evolution of siltstone. The elastic modulus, peak stress, strain energy evolution and failure modes of siltstone at different strain rates are analyzed, followed by an interpretation based on statistical damage theory. In the range of the quasi-static strain rate, as the strain rate increases, the elastic modulus, peak stress, total strain energy density and elastic strain energy density at the peak stress of siltstone increase, and the failure mode of the siltstone gradually change from single-plane shear failure to extensile failure. The plastic shear strain is adopted as the random variable of the Weibull distribution to formulate a new statistical damage model, which can better reproduce the post-peak characteristics of the stress–strain curve and interpret the damage evolution process of siltstone; this also reveals that the nonlinear evolution of random variables with axial strain should be considered to capture the post-peak stress–strain curve. The damage variable evolution curves are similar to the dissipated strain energy density curves, which are 'L-shaped'. Finally, a simplified method for determining the influence of strain rate on damage at peak stress Dcr is proposed and discussed. Highlights: In the range of the quasi-static strain rate, four groups of triaxial compression tests are carried out to reveal the strain rate effect of siltstone. Incorporating the plastic shear strain, a statistical damage model is proposed to better interpret the mechanical behaviour of siltstone. Based on the damage theory, a simplified method for determining the influence of strain rate on damage at peak stress Dcr is proposed. [ABSTRACT FROM AUTHOR]

To study the vertical compressive bearing characteristics of large-diameter rock-socketed cast-in-place piles, eight manually-excavated rock-socketed cast-in-place piles were subjected to vertical compressive on-site load and pile stress tests. The test results showed that the load–displacement (Q-s) curves of the eight test piles were all slow-varying, and the settlement of the piles was less than 11 mm, which met the minimum engineering requirements. The unloading rebound rate was between 55 and 75%, and the elastic working properties of the piles were apparent. The pile axial force gradually decreased with depth, and the slope of the axial force distribution curve reached a minimum in the moderately weathered muddy siltstone layer while the pile side friction resistance reached its maximum value. Pile end friction increases with the increase of load. But the pile end resistance was inversely proportional to the single pile length-to-diameter (L/D) ratio and the depth of rock embedment for the pile. The percentage of pile side friction resistance under maximum load was 86%, indicating that these were characteristic friction piles. Based on the test results and the current Chinese code, the friction coefficient of the pile side soil layer η and the total resistance coefficient of the rock-socketed section ζ were introduced. A revision to the calculation equation for the vertical bearing capacity of the rock-socketed cast-in-place pile in the code was proposed, together with an optimization design method for large-diameter rock-socketed cast-in-place piles. [ABSTRACT FROM AUTHOR]

The Santanghu Basin is a typical low-rank coal-bearing basin in northwest China, with abundant coalbed methane (CBM) resources. However, the understanding of the main controlling factors and reservoir formation models of CBM in low-rank coal is still insufficient, which has restricted the exploration and development of CBM in this region. In this paper, the CBM enrichment controlling factors and enrichment models are analyzed based on the aspects of sedimentary environment, reservoir characteristics, sealing conditions, and hydrogeological conditions after systematically analyzing the geological characteristics of coal measures. The research results indicate that the coal seams of the Xishanyao Formation in the Santanghu Basin are stably developed, with the main macerals being vitrinite and a lower degree of coalification belonging to low-rank coal; the highest content of CBM can reach 7.17 m3/t, and the methane is mainly composed of biogenic gas supplemented by thermogenic gas; the roof lithology of the coal seam is mainly mudstone and siltstone, with good sealing conditions. Finally, two enrichment modes of coalbed methane in slope zones are proposed, namely, the CBM enrichment in the slope zone and the CBM enrichment by fault-hydraulic plugging. The results of this study can serve as a guide for the exploration and development of the deep-buried coalbed methane in the low-rank coal areas. [ABSTRACT FROM AUTHOR]

The study of sedimentary microfacies of horizontal wells is important for improving oil recovery using horizontal well technology. Vertical well data alone do not provide accurate enough information to determine the sedimentary microfacies of horizontal wells. Therefore, a comprehensive method combining the data of both horizontal and vertical wells was established to identify sedimentary microfacies of horizontal wells and applied to a single horizontal well in the Daqing oilfield in China's Songliao Basin. The results identified the study area as a delta sedimentary environment, mainly subdivided into four microfacies types: a distributary channel, the main overbank sand, the overbank sand, and an interdistributary bay. The criteria for identifying each sedimentary microfacies were established. Among them, the criteria for identifying distributary channels include a natural gamma value continuously less than 90 API; a resistivity value continuously greater than 11 Ω·m; a logging curve, which is typically bell-shaped or box-shaped with very high amplitude and amplitude difference; a mainly siltstone lithology; and a total hydrocarbon content (Tg) continuously greater than 3%. The variations in the two types of channel boundaries (narrowing of the channel boundary and reverse extension of the bifurcated channel boundary) were corrected. The research results can provide guidance for the efficient development of favorable reservoirs in oilfields using horizontal well technology. [ABSTRACT FROM AUTHOR]

In order to reveal the deformation behavior similarity between creep and fatigue, a series of creep and cyclic load tests were performed on siltstone under various load levels. First, the mechanical characteristics of creep and fatigue were compared, by analyzing the strength, ultimate strain, and steady deformation rate of siltstone. Then, a modified fatigue damage creep model was established by connecting a viscoplastic damage element in series with Burgers mode. Finally, the applicability of the model was verified, and the model parameters were analyzed. The results show that the fatigue failure of siltstone is controlled by fatigue strength and limit strain. The modified fatigue damage creep model can accurately describe the whole deformation process of siltstone under cyclic load test. Compared with creep test, the cyclic load hardly affects the elastic modulus of this model. However, the viscosity coefficient of this model is greatly weakened by the cyclic load. Highlights: The deformation behavior between creep and fatigue of siltstone was compared.The modified fatigue damage creep model of siltstone was established.The effect of cyclic load on the creep model parameters of siltstone was analyzed. [ABSTRACT FROM AUTHOR]

This paper presents a case study of the clogging of a slurry-shield tunnel-boring machine (TBM) experienced during tunnel operations in clay-rich argillaceous siltstones under the Ganjiang River, China. The clogging experienced during tunneling was due to special geological conditions, which had a considerably negative impact on the slurry-shield TBM tunneling performance. In this case study, the effect of clogging on the slurry-shield TBM tunneling performance (e.g., advance speed, thrust, torque, and penetration per revolution) was fully investigated. The potential for clogging during tunnel operations in argillaceous siltstone was estimated using an existing empirical classification chart. Many improvement measures have been proposed to mitigate the clogging potential of two slurry-shield TBMs during tunneling, such as the use of an optimum cutting wheel, a replacement cutting tool, improvements to the circulation flushing system and slurry properties, mixed support integrating slurry, and compressed air to support the excavation face. The mechanisms and potential causes of clogging are explained in detail, and the contributions of these mitigation measures to tunneling performance are discussed. By investigating the actual operational parameters of the slurry-shield TBMs, these mitigation measures were proven to be effective in mitigating the clogging potential of slurry-shield TBMs. This case study provides valuable information for slurry-shield TBMs involving tunneling in clay-rich sedimentary rocks. [ABSTRACT FROM AUTHOR]

When the Linear Parallel Bond Model (PBM) in Particle Flow Code is used to simulate intact rocks, a basic problem is how to determine the microscopic parameters that control the macroscopic properties of the modeled rocks. After simplifying the microscopic parameters of the PBM model, this study proposes a new method of inverse performance of the regression equations of the macroscopic parameters by the gray absolute correlation combined with regression analysis, which solves the drawbacks of the current manual trial parameter calibration method to a certain extent. When this method is applied to the calibration of the microscopic parameters of the siltstone, the numerical simulation results produce good agreement between the results derived from the finite element software (ABAQUS) both in terms of macroscopic parameters and damage forms. [ABSTRACT FROM AUTHOR]

A new concept of the formation of glauconite from the Paleocene deposits of the sedimentary cover of the southwestern part of the Near-Volga monocline is presented. It was formed as a result of halmyrolysis of ash material in lake conditions. Glauconitization is confined to the Paleogene thermal maximum and the periphery of active volcanism along the entire mobile belt. In this connection, it is widely distributed in the Paleogene deposits. Structural and crystal-chemical features of glauconite, stages of crystallization of its aggregates, paragenetic associations with smectite, kaolinite, and zeolite, as well as the presence of ore minerals indicate its authigenic origin. The authigenic origin is confined to the formations of temporary, episodically submerging shallow marine basins. An applied scheme of discrimination of glauconites by their crystallochemical features has been developed. The discrimination diagram can be used to determine the specific conditions of the sedimentation basin, which are expressed in the progradation cycles of glauconite accumulation. The cycles were controlled by induced depressions within the Russian plate. [ABSTRACT FROM AUTHOR]

The MSL Curiosity rover investigated dark, Mn-P-enriched nodules in shallow lacustrine/fluvial sediments at the Groken site in Glen Torridon, Gale Crater, Mars. Applying all relevant information from the rover, the nodules are interpreted as pseudomorphs after original crystals of vivianite, (Fe2+,Mn2+)3(PO4)2·8H2O, that cemented the sediment soon after deposition. The nodules appear to have flat faces and linear boundaries and stand above the surrounding siltstone. ChemCam LIBS (laser-induced breakdown spectrometry) shows that the nodules have MnO abundances approximately twenty times those of the surrounding siltstone matrix, contain little CaO, and have SiO2 and Al2O3 abundances similar to those of the siltstone. A deconvolution of APXS analyses of nodule-bearing targets, interpreted here as representing the nodules' non-silicate components, shows high concentrations of MnO, P2O5, and FeO and a molar ratio P/Mn = 2. Visible to near-infrared reflectance of the nodules (by ChemCam passive and Mastcam multispectral) is dark and relatively flat, consistent with a mixture of host siltstone, hematite, and a dark spectrally bland material (like pyrolusite, MnO2). A drill sample at the site is shown to contain minimal nodule material, implying that analyses by the CheMin and SAM instruments do not constrain the nodules' mineralogy or composition. The fact that the nodules contain P and Mn in a small molar integer ratio, P/Mn = 2, suggests that the nodules contained a stoichiometric Mn-phosphate mineral, in which Fe did (i.e., could) not substitute for Mn. The most likely such minerals are laueite and strunzite, Mn2+Fe3+2(PO4)2(OH)2·8H2O and –6H2O, respectively, which occur on Earth as alteration products of other Mn-bearing phosphates including vivianite. Vivianite is a common primary and diagenetic precipitate from low-oxygen, P-enriched waters. Calculated phase equilibria show Mn-bearing vivianite could be replaced by laueite or strunzite and then by hematite plus pyrolusite as the system became more oxidizing and acidic. These data suggest that the nodules originated as vivianite, forming as euhedral crystals in the sediment, enclosing sediment grains as they grew. After formation, the nodules were oxidized—first to laueite/strunzite yielding the diagnostic P/Mn ratio, and then to hematite plus an undefined Mn oxy-hydroxide (like pyrolusite). The limited occurrence of these Mn-Fe-P nodules, both in space and time (i.e., stratigraphic position), suggests a local control on their origin. By terrestrial analogies, it is possible that the nodules precipitated near a spring or seep of Mn-rich water, generated during alteration of olivine in the underlying sediments. [ABSTRACT FROM AUTHOR]

The strata in coal mines are often distributed in layers with coexisting lithologies. The precursory indicators obtained from the study of the rock instability of a single lithology can often be challenging to apply in practical engineering. Therefore, it is important to explore the relationship between the fracture process of different lithologic rocks in a coal mine and acoustic emission（AE）parameters and establish various lithologic rock stability evaluation mechanisms based on AE parameters. In view of this, an acoustic emission monitoring system was used to measure three sequential types of lithology rocks（fine sandstone, sandy mudstone and siltstone）taken from coal seams. Through examining the correlation of AE parameters, five AE parameters with low correlation, such as energy, b-value, dominant frequency, apparent stress and apparent volume, are selected as the precursor indexes of the rock failure, and a stability evaluation system suitable for these three lithology rocks is established. The research results provide a basis for coal mine disaster early warning and prediction based on microseismic monitoring in practical engineering. [ABSTRACT FROM AUTHOR]