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The location of the investigation area is in Oben Village, Nekamese District, Kupang Regency, East Nusa Tenggara Province with coordinates 123° 40'40” E - 123° 41'20” E and 10° 16'0” S - 10° 16'40” S. The geology of the study area is generally occupied by mixed rocks dominated by a gray clay, blackish brown, reddish brown, with foreign chunks consisting of peridotite, sedimentary rock consisting of brown and reddish reddish limestone, silt, micaceous sandstones, metamorphic rock: chlorite schist, with quartzite veins. Of the five samples analyzed, namely four samples of soil matrix and one sample of Peridotite, the following results were obtained: six rare earth elements were contained in 4 samples of the soil matrix, namely Yttrium (Y): 3.63 – 68.75 ppm, Praseudymium (Pr): 7.38 – 38.38 ppm, Scandium (Sc): 4.83 – 4.93 ppm, Lanthanum (La): 21.48 – 91.03 ppm, Cerium (Ce): 32.48 – 184.85 ppm, and Neodymium (Nd): 9.4 – 57 ppm specifically for sample 1 also contains 3 rare earth elements, namely: Gadolinium (Gd): 3.48 ppm concentration the average is lower than its abundance in nature, Samarium Sm: 13.1 ppm, and Dysprosium: (Dy): 6.88 ppm. For rock samples only contain Praseudymium (Pr): 7.78 ppm and Cerium (Ce): 87.88 ppm. [ABSTRACT FROM AUTHOR]

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The Young's modulus and Poisson's ratio determined for the rocks under uniaxial or triaxial loading conditions represent necessary input parameters for solving many geotechnical tasks. However, these effective stiffness moduli, particularly the Poisson's ratios, measured on different samples sometimes substantially differ, even for visually compact and macroscopically homogeneous rock. This has been observed for Brenna sandstone, especially under conditions of conventional triaxial extensions. The aim of this study was, thus, to reveal differences in rock structure that could cause such behavior. Several complementary methods were used to investigate the structure of this sandstone: X-ray computed tomography (CT), visual analysis using optical scanning and stereo-microscopy, and a new method combining water jet erosion with these visualization techniques. Analyses of this structure revealed mechanically more resistant compact thick and adjacent thin weak layers. In rock samples, these layers have different patterns and orientations. To demonstrate the influence of layer orientation on effective stiffness moduli measured under different loading conditions, FEM calculations were performed for idealized structural models. The outcomes of this numerical analysis are in qualitative agreement with the results of the loading experiments and the layered structure revealed in the samples. The ability of the proposed method using water erosion to analyze the rock structure in detail was verified. The method offers an interesting alternative to standard visual and X-ray CT techniques. The numerical calculations indicate the importance of latent layered defects in sedimentary rocks for fine measurements of stiffness moduli (especially the Poisson's ratios) used as inputs for geotechnical applications. Highlights: Rock structure related to stratification has been analyzed by complementary methods. X-ray computed tomography revealed the irregular layered structure of the sandstone. A new method using water jet erosion of the rock surface confirmed the layers. Higher X-ray absorbance approximately corresponds to a higher mechanical resistance. A numerical model of the layers explains the differences in mechanical parameters. [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]

Heavy‐mineral assemblages of sediments and sedimentary rocks record information regarding provenance, including the source rocks involved, tectonic setting, climatic conditions, and modifications from source to sink. Drawing conclusions on provenance and provenance changes requires robust quantification of individual heavy‐mineral species contents, including error estimates. Nevertheless, it is common practice to count sub‐quantities of grains from aliquots and not considering the bias introduced by (a) counting similar numbers of grains from aliquots containing different total numbers of grains, and (b) using variable counting methods. Consequently, reported heavy‐mineral contents estimated from counting sub‐quantities are affected by errors of unknown extent, making it infeasible to determine whether intra‐ or intersample variations are statistically significant. Based on 65 heavy‐mineral aliquots of variable grain size, mineral species contents, total number of grains, and known composition determined by counting all grains (n = 80,393), here >31 million countings of heavy‐mineral sub‐quantities are simulated using (a) ribbon counting with varying ribbon size, ribbon position, ribbon orientation, total number of counts, and ways of aggregating counts from multiple ribbons, and (b) a newly proposed counting technique called cluster counting. I show that (a) error estimation for a specific aliquot requires a finite population correction; (b) compared to adjacent ribbons, aggregating counts of spatially distant ribbons reduces the error; (c) cluster counting further reduces the error, showing the best fit with theory; and (d) the Wilson score interval enables error calculation as well as the number of grains to be counted to achieve an operator‐specific aim. Plain Language Summary: Rocks exposed to rain, ice, and wind will disintegrate, get transported, and end‐up as sediment or sedimentary rock like sand or sandstone, respectively. Such sediments are mainly composed of light mineral grains including quartz and feldspar, but additionally contain heavy minerals with a density >2.85 g/cm3. While being volumetrically subordinate, the types and proportions of different heavy‐mineral species are particularly diagnostic for the original rocks eroded to form the sediment under investigation. Commonly, heavy minerals are separated by standardized lab routines, and finally a portion of heavy minerals is counted under the microscope to estimate their content in the sediment. Unfortunately, there is no standardized routine of (a) how to count the grains, (b) how many grains to count, and (c) how to estimate the counting error. In this work, I computationally simulated countings and their errors using the most common technique (ribbon counting) with varying parameters as well as a newly proposed technique called cluster counting. I show that cluster counting not only reduces the counting error but also, more importantly, improves the predictability of the counting error. This provides scientists with a new tool to argue whether differences between different samples are statistically significant. Key Points: Counting errors and their variations are related to the capability of the applied counting technique to counteract spatial heterogeneityArea counting is inappropriate to counteract spatial heterogeneity, but spacing out ribbons evenly gives reasonable resultsA newly proposed counting technique (cluster counting) reduces the bias, enabling error calculations and the number of grains to be counted [ABSTRACT FROM AUTHOR]

As the anisotropic behavior of sandstones and limestone along the Khorramabad-Zal expressway has not been studied, this research aims to examine the impact of layer orientation on the strength characteristics and failure patterns of layered sedimentary rocks using the Brazilian test. For this purpose, a total of 8 rock blocks were gathered from Kashkan sandstones and Sarvak limestones in three different locations along the Khorramabad-Zal highway in western Iran. The core specimens were drilled with 54 mm diameter and parallel to the laminations. Overall 150 disc-shaped specimens were subjected to Brazilian tensile strength (BTS) in ten different anisotropy angles, which refers to the angle between the loading direction and the lamination plane. The findings revealed that the highest and lowest BTS values were obtained at β = 70° and 20° for all three types of rock. After analyzing the samples that experienced the Brazilian test and examining their failure patterns, three primary modes of failure were identified: parallel to the lamination (PL), across the lamination (AL), and curved fracture (CF). Furthermore, the transitional angle, which signifies the point at which the dominant pattern of failure shifts from PL to AL or from PL to CF, was also determined. [ABSTRACT FROM AUTHOR]

Both igneous and sedimentary rocks affected by water–rock interaction commonly form rhythmic Fe‐oxide bands that provide information on palaeo‐groundwater. This study investigated the formation of Fe‐oxide banded patterns of concentrically banded concretions from the Jurassic Navajo Sandstone (United States) and banded claystone 'zebra rock' from the Neoproterozoic Johnny Cake Shale Member (Western Australia). Micro‐X‐ray fluorescence imaging of both samples revealed uniformly banded patterns of asymmetrical Fe content peaks. This study proposes that their formations were caused by diffusion, with a pH buffering reaction of Fe2+ and O2 due to dissolution of earlier materials by acidic fluids. Based on the model, it is suggested that the acid fluids for Navajo diffused towards the inner side of the concretion, and that for Kimberley they penetrated oblique or perpendicular to bedding. In addition, the Fe‐oxide precipitation has resulted from pH rises of acidic fluids because of diagenetic alteration of earlier calcite concretion in Navajo and that of earlier pyrite‐bearing claystone in Kimberley. The interpretation for Kimberley is based on the δ34S values (<−20‰) of zebra rock, suggesting that the alunite and Fe‐oxide resulted from the supply of SO42− and Fe2+ produced as a result of pyrite oxidation in earlier rocks. The formation rate of the Fe‐oxide band was estimated from the constant width of the Fe peaks and the expected diffusion coefficient for Fe2+ through the rock matrix, and it was found to be on the order of years for Navajo and on the order of tens of years for Kimberley. [ABSTRACT FROM AUTHOR]

The deformation of rocks well below their ultimate strengths is frequently described through the constant stiffness moduli of the linear elasticity theory. In addition, the isotropic material approximation is usually used as the basic approach. Particularly in sedimentary rocks, local inhomogeneities, anisotropy, and irreversible processes, mainly related to the gradual breakage of grain joints, can affect their deformation behavior from the beginning of the loading. Consequently, the stiffness moduli measured under triaxial conditions are effective parameters, which may depend on the loading path in the stress space. Therefore, a complex experimental study of the deformation response of compact sedimentary rock (Brenna sandstone) along various paths in triaxial stress space was prepared to understand this dependence. In addition, a detailed analysis of the rock composition and structure of this compact sandstone was carried out. This paper presents an initial experimental study that is based on a loading method using alternative stress paths that correspond to different modes of the monotonic increase in differential stress from an initial isotropic compression state. In the experiment, the dependence of stiffness moduli on the loading path was found. Differences in rock deformation for conventional triaxial compression and extension can be attributed to a slight rock anisotropy originating from the stratification. The different behavior of deformation and related stiffness moduli along so-called reduced triaxial paths and conventional paths indicates that irreversible processes must be taken into account. Highlights: The study brings new experimental data on the deformation of compact sedimentary rock in specific triaxial stress conditions. The measured effective stiffness moduli of compact sandstone depends on the loading path in the triaxial stress state. In general, the deformation response of the sandstone is nonlinear from the start of loading. The mechanical properties of the sandstone show anisotropy as a consequence of stratification. In standard triaxial tests, failure criterion combining stress and strain conditions can be used for the investigated sandstone. [ABSTRACT FROM AUTHOR]

Abstract—A number of examples are considered in which modern arkose sands as well as arkose and compositionally similar sandstones (all of the above rocks are sediments of the first sedimentation cycle) of different ages have definite provenances composed of granitoids of different "geodynamic" types. The main goal of the work is to analyze how the geochemical characteristics of granitoids are translated into petrogenic sedimentary rocks. The comparison of 245 analyses of sands and sandstones with ~375 analyses of the inferred prototype sources of clastic material showed that the lithogeochemical characteristics of arkose and subarkose sands and sandstones (mainly the HFS element content and ratio) makes it possible in most cases to confidently judge the "geodynamic nature" of source felsic igneous rocks. [ABSTRACT FROM AUTHOR]

Featured Application: The results obtained during this study may be applied to the development of a technology for intensifying oil inflow to production wells in conditions of paraffin flocculation. This paper presents the results of experimental studies on the filtration of reservoir fluid through the rocks under the influence of nonlinear loads. A laboratory rig is assembled that allows for modeling the flow of fluid from the reservoir into the well during the propagation of elastic waves from the well. It is shown that depending on the permeability of the rock matrix as well as on the concentration of paraffins and asphaltenes in crude oil, the effect of the nonlinear load is different. Three types of sandstone are studied: low, medium, and high permeability. The greatest influence of nonlinear loads is observed in high-permeability sandstone. The effect manifests itself in fully unblocking the pore space from paraffins and asphaltenes accumulated in pore throats and restoring the oil permeability to its original value. In the case of medium-permeability sandstone subjected to nonlinear loads, blocking of the pore space is slow. In the case of low-permeability sandstone, the impact of nonlinear loads does not have a significant effect. When studying water filtration in the presence of residual oil saturation, the effect of nonlinear loads is observed as a mobilization of additional oil not previously involved in the filtration process, which also leads to an increase in the water permeability of the rock. [ABSTRACT FROM AUTHOR]

Khon Kaen Geopark, representing an area of dinosaur fossil diversity, was selected for investigations to reveal the origin and tectonic setting of the Khorat Group. The area occupied by Mesozoic sedimentary rocks of four formal formations of the Khorat Group, namely the Phra Wihan Formation (PWF), Sao Khua Formation (SKF), Phu Phan Formation (PPF), and Khok Kruat Formation (KKF). A field investigation and macroscopic observations suggested that the immature sedimentary rocks of the study area are mainly clast-supported, pebbly sandstone and siltstone with few calcretes. The 50 rock samples that were selected for petrographical and geochemical investigations revealed that the sandstones of the PWF and PPF are quartz arenite and sublitharenite, with some subarkose, whereas those of the SKF are mainly subarkose and sublitharenite. In addition, the KKF dominantly presents sublitharenite with pebbles and calcretes. Mesozoic sandstones contain quartz, feldspars, various types of rock fragments, and accessory minerals (biotite, muscovite, zircon, and tourmaline), with siliceous, ferrous, and calcareous cement. Petrographic (Q–F–L) and geochemical (major and trace element) data suggested that the sources of sediments are mostly quartzose sedimentary rocks and some felsic-intermediate igneous rocks. Chondrite-normalized rare earth element patterns indicated that the origins of the studied sandstones are quartzose sedimentary rocks deposited in a passive continental margin or an upper continental crust. Geochemical traits of the sedimentary successions demonstrated that the provenance of the Khorat Basin prior to reworking by fluvial processes was situated in the passive continental margin or recycled orogen of the paleo-volcanic arc during the Mesozoic period. [ABSTRACT FROM AUTHOR]

In sedimentary basins, the determination of the absolute timing of deposition and diagenetic events is a challenging yet critical parameter necessary in the reconstruction of paleo-fluid evolution and burial histories. Here we demonstrate the practical application of in situ calcite U–Pb geochronology on core samples from the Olympic 1 well in the Canning Basin of Western Australia. Using quantitative mineralogy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analytical techniques, we obtained an authigenic calcite U–Pb age of 469.7 ± 4.3 Ma for limestone in the Samphire Marsh Member of the Lower Ordovician Nambeet Formation. This precise depositional age can be independently verified using zircon thermal ionisation mass spectrometry U–Pb ages of 479.4 to 470.2 Ma determined on adjacent volcanic ash beds. Further geochronology studies on calcite cements from the Lower Ordovician Fly Flat Member sandstone from the Nambeet Formation returned a U–Pb age of 365.3 ± 5.8 Ma. This is the first study to place absolute age constraints on the diagenetic event that occluded the intergranular space in a sandstone reservoir. The calcite cementation age suggests that impairment of reservoir quality in the Fly Flat Member sandstone occurred in the Late Devonian, much earlier than major petroleum charge events in the Canning Basin. The calcite U–Pb geochronometer, when combined with complementary quantitative mineralogical analysis, can build direct temporal constraints on the depositional and diagenetic processes in both carbonate and clastic sedimentary rocks in basins worldwide. The integration of automated scanning electron microscopy/energy-dispersive X‐ray spectrometry quantitative mineralogical analysis with LA-ICP-MS analysis enables more reliable and efficient in situ calcite U–Pb dating. An accurate age of 469.7 ± 4.3 Ma is obtained for carbonate sedimentation in the Samphire Marsh Member of the Lower Ordovician Nambeet Formation in the Canning Basin. The calcite cementation age of 365.3 ± 5.8 Ma provides an absolute time constraint on pore-occluding lithification of the Fly Flat Member sandstone reservoir in the Canning Basin. In situ calcite U–Pb dating can place precise temporal constraints on sediment deposition and paragenetic sequence in sedimentary basins. [ABSTRACT FROM AUTHOR]

The sliding failures commonly occur in interbedded formations along the weakness plane of the bedding plane a sedimentary rock or the joint interface. Therefore, studying the shear strength characteristics at the bedding plane or interface is crucial for evaluating the expected failure plane. In this study, the shear strength characteristics of planar jointed Kenny Hill shale, sandstone, and shale-sandstone specimens were investigated using the direct shear box method. The results reveal that the friction angle values for the planar sandstone, shale-sandstone, and shale are 31.28°, 21.1°, and 19.34°, respectively. These findings, combined with the shear stress-strain behavior, suggest that the interface (shale-sandstone) is primarily influenced by the shale characteristics rather than the sandstone characteristics. Hence, it is important to consider failure along the interface when analyzing critical conditions, particularly in slope failure scenarios. [ABSTRACT FROM AUTHOR]

Pore space characterisation is important in assessing the strength and hydraulic characteristics of rock. This paper proposes a new relationship to estimate the porosity of natural rocks using the data from a scanning electron microscope (SEM) and a pore and crack analysis system (PCAS). The obtained results were compared with the data obtained from a series of conventional mercury intrusion porosimetry (MIP) experiments. Three different rocks, namely siltstone, sandstone, and coal, collected from a depth below 400 m, were investigated in this study. The results indicated that the proposed method of digital analysis could accurately identify the pore size and porosity values, which were in agreement with the experimental data. The relationship between the two-dimensional porosity estimated from the digital analysis and the three-dimensional porosity obtained from laboratory experiments was established. A few limitations on the use of the proposed method have also been identified and discussed. [ABSTRACT FROM AUTHOR]

Detailed petrographic, dense minerals and petrofacies investigations were performed on forty nine medium- to finegrained, well-cemented and moderately to well-sorted sandstone samples from the Joyan Member of the Jaisalmer Formation. The grains are sub-angular to sub-rounded in shape, with some well-rounded quartz grains. The framework composition of sandstone consists mostly of monocrystalline and polycrystalline quartz, low-to high-grade metamorphic and sedimentary rock fragments, as well as subordinate feldspar with low plagioclase to total feldspar ratios and accessory minerals. Petrographic investigations reveal that sandstones from the Joyan Member of the Jaisalmer Formation are sublitharenite to litharenite. The sandstone composition suggests that the detritus are derived from the metamorphic, plutonic-volcanic felsic, and recycled sedimentary rocks. Dense mineral analyses also confirm the possibility of mixed provenance for the Joyan Member Sandstone. The sandstone petrofacies indicates their derivation from cratonic interiors, as well as recycled orogenic and quartzose recycled provenances under humid climatic conditions. The petrographic, sedimentological, and dense mineral analyses in agreement with palaeocurrent data suggest that the Joyan Member Sandstone was primarily derived from Erinpura-Godhra-Mount Abu-Sirohi (Balda) granites and Malani volcanics, with a contribution from Archean Aravalli (Berach) granitoids and Aravalli and Delhi orogens. The shift in sediment supply from Aravalli (Berach) granitoids and Aravalli and Delhi orogens to Erinpura-Godhra-Mount Abu-Sirohi (Balda) granites and Malani volcanics supports sedimentation in a tectonically active basin. [ABSTRACT FROM AUTHOR]

Exploring for hydrocarbons in a pyroclastic-affected reservoir is an important research topic. Previous studies have mainly focused on laminated pyroclastic. A large number of dispersed pyroclastic is present in sedimentary rocks, and dispersed volcanic ash strongly influences the diagenetic evolution of sandstone reservoirs. However, these aspects remain understudied. We studied the mechanism of the diagenetic evolution of the Jurassic tuffaceous sandstone reservoir in Qikou Sag of the Bohai Bay Basin by performing inclusion temperature measurements, rock slice identification, and scanning electron microscopy, and using electron microprobes and microzone isotopes. We determined the mechanism of water-rock interaction. Based on microscopic observations, we determined that the main diagenesis included two-stage dolomite cementation, two-stage calcite cementation, quartz cementation, and transformation and dissolution of clay minerals. The hydrolysis and chemical transformation of pyroclastic during burial not only provided an alkaline environment in the early stage of diagenesis but also supplied ions for the formation of microcrystalline quartz and early dolomite and the transformation of clay minerals. Leaching and denudation generated early dissolution caused by a tectonic uplift. Following the epigenetic stage, microbial activity stimulated the formation of early calcite during the shallow burial stage. When the burial temperature of the stratum was 80 °C, the acidic fluid discharged from the thermal evolution of organic matter was neutralized by the soluble components in the pyroclastic, which prevented the formation of a large-scale acidic environment. When the burial temperature exceeded 100 °C, the acidic fluid generated by thermal catalytic decarboxylation of organic matter formed a large quantity of dissolution. The dissolution of plagioclase promoted the overgrowth of quartz and the growth of kaolinite. [ABSTRACT FROM AUTHOR]

The geomechanical strength of rock masses plays a key role in the planning and design of civil and mining construction projects. The uniaxial compressive strength (UCS) of rocks is a crucial property that is widely used in geotechnical engineering to understand the strength and deformability of rock masses. Determination of geomechanical properties both in the field and in the laboratory is time consuming, tedious, and expensive. However, ultrasonic techniques, such as P-wave propagation velocity (VP) measurement, are a simple, cost-effective, and non-destructive method for evaluating the UCS of rocks. In this study, a review of the state of knowledge of the type of empirical correlations that exist for sandstones to predict the value of UCS from VP is developed. The main objective developed is a meta-study on the relationship between UCS and VP. For this, UCS and VP data for sandstonetype sedimentary rock are compiled from various sources. With the results obtained, empirical formulas are proposed that correlate UCS and VP, which can be used as a geotechnical engineering tool to predict the value of UCS from VP in sandstones. [ABSTRACT FROM AUTHOR]

We propose a novel continuum damage model for describing the propagation of compaction bands formed by grain crushing in porous sedimentary rock using the kernel-based approximation and discretization of the meshfree Lagrangian smoothed particle hydrodynamics (SPH) method. In the model, damage is assumed to be caused by grain crushing, and the effects of plasticity are incorporated through a critical state type model which depends on a degradation function designed to capture the abrupt onset of pore collapse following grain crushing. In doing so, we account for the two main forces understood to drive compaction band formation, brittle failure at the grain scale, and plastic dissipation. Through the smoothing length parameter, the SPH method possesses nonlocal properties intrinsic to the method, allowing for the development of a nonlocal integral form of the equivalent strain variable used to compute the damage in addition to a distinct gradient enhanced approach that when discretized using SPH is endowed with two characteristic length scales. We compare and contrast both formulations, as well as the roles of the different length scales. We evaluate our model by performing numerical experiments on Bentheim and Berea sandstone as well as on Tuffeau de Maastricht, in both notched and unnotched specimens, matching experimentally observed results such as a transition from high-angled bands to horizontal bands with increasing confining pressure, and similar compaction band styles to those visible in the field. We lastly consider the effects of material heterogeneity on samples of Tuffeau de Maastricht noting that our model produces precursory low-magnitude localization events which may develop into persistent compaction bands involving localized grain crushing, which is consistent with our understanding of compaction band formation. [ABSTRACT FROM AUTHOR]

Weak interlayers (WI) are common in sedimentary rock masses in deep coal mines. The qualitative effect of the WI on rockbursts is widely acknowledged; however, its influence mechanism still needs further investigation. In the present study, true triaxial unloading rockburst tests of sandstone with WI and calcite veins (CV) were conducted to explore their influence mechanisms. To explore the impact of WI, the rockburst stress, failure modes, acoustic emission (AE) parameters (energy, entropy, and b-value), and spatial energy characteristics of AE events were analyzed. The influence of the area ratio of WI and their distribution patterns (centralization and dispersion) on rockburst were further investigated. The results indicate that the rockburst stress (peak of maximum principal stress) decreased by 4 % for every 1 % increase in the sandstone's dispersion WI area ratio (1.9%–9.3 %). Namely, rockburst is more likely to occur when there is appropriate WI distributed in the sandstone because WI exacerbates the microcrack activities and energy release. The CV will reduce the weakening effect of WI on rockburst stress and can enhance the rockburst intensity, especially in samples with dispersion WI. Moreover, the more considerable AE energy is released around CV for the sandstone with dispersion WI. The interface between WI and matrix is prone to rockburst for the sandstone with centralized WI because of the concentrated energy release. The results of this paper can provide a reference for the prevention and control of rockbursts in mine sedimentary rocks containing WI and CV. [ABSTRACT FROM AUTHOR]

The study considers the impact of the degree of weathered material constituting the sedimentary rocks on the strength of the Lower Gondwana coal measure rocks. The dependence of the strength of primary rocks on the alteration indices has been previously studied, but it is unknown for secondary/sedimentary rocks. Therefore, in this paper, Lower Gondwana coal measure rocks (sandstone and shale) from the most productive coalfields of India, the Barakar and Raniganj coalfields, have been studied geochemically and geomechanically to find out their correlation. Geochemically, the study revealed that an arid, non-marine, and deltaic depositional environment prevailed during the sedimentation of Barakar and Raniganj Formations. The provenance was deduced to be mafic igneous. It was also deduced that the Lower Gondwana sandstone is clay-rich, and the sandstone samples fall in the shale field in the chemical classification scheme for terrigenous clastic sediments. The weathering indices, along with the uniaxial compressive strength (UCS) of the Barakar and Raniganj Formation coal measure rocks, have been assessed. The dependence of UCS on the weathering indices has been evaluated, and positive relationships were obtained. [ABSTRACT FROM AUTHOR]

Critical processes including seismic faulting, reservoir compartmentalization, and borehole failure involve high‐pressure mechanical behavior and strain localization of sedimentary rocks such as sandstone. Sand is often used as a model material to study the mechanical behavior of poorly lithified sandstone. Recent studies exploring the multi‐scale mechanics of sand have characterized the brittle, low‐pressure regime of behavior; however, limited work has provided insights into the ductile, high‐pressure regime of behavior via in‐situ measurements. Critical features of the ductile regime, including grain breakage, grain micromechanics, and volumetric strain behavior therefore remain under‐explored. Here, we use a new high‐pressure triaxial apparatus with in‐situ x‐ray tomography to provide new insights into deformation banding, grain breakage, and grain micromechanics in Ottawa sand subjected to triaxial compression under confining pressures between 10 and 45 MPa. We observed strain‐hardening at pressures above 15 MPa and strain‐neutral responses at pressures below 15 MPa. Compacting shear bands and grain breakage were observed at all pressures with no significant variation due to grain size, except for minor increases in breakage in less‐rounded sands. Grain breakage emerged at stress levels lower than the assumed yield threshold and more intense breakage was associated with thinner deformation bands. Contact sliding at inter‐grain contacts demonstrated a bifurcation into a bimodal distribution, with intense sliding within deformation bands and reduced but non‐negligible sliding outside of deformation bands, suggesting that off‐band zones remain mechanically active during strain hardening. Plain Language Summary: Sand and sandstone are among the most abundant materials on or near the surface of the Earth. The mechanical behavior of these materials is a critical factor in natural and man‐made processes, including earthquakes, fluid flow in subsurface oil and hydrocarbon reservoirs, and borehole drilling. Until now, the behavior of sand and poorly‐cemented sandstone has rarely been visualized with x‐ray imaging in the laboratory at high confining pressures. Most of the pressures studied with x‐ray visualization in the laboratory are in the so‐called "brittle" regime, in which samples often expand when sheared and do not feature significant grain fracture. In this paper, we have used a new compression device for studying sand samples under significantly higher pressures with x‐ray imaging. Our experiments, in the so‐called "ductile" regime, in which samples compact and fracture significantly when sheared, provide the first direct evidence of deformation localization into bands and the first quantitative analysis of grain size reduction and grain motion. Our results provide valuable data to the community to understand and predict the behavior of soils and sandstones in the Earth's upper crust. Key Points: Sands subjected to pressures in the ductile regime feature strain localizationGrain crushing in the ductile regime begins at small shear strains and stress states classically considered to be elasticMicromechanics analysis reveals sand breakage and rearrangements in shear bands, but non‐dormant grain behavior out of bands [ABSTRACT FROM AUTHOR]

Detrital zircon U–Pb age patterns in sandstones from the Triassic–Cretaceous Clarence-Moreton Basin, eastern New South Wales and Queensland, unexpectedly reveal sediment sources overwhelmingly dominated (>70%) by Precambrian–Cambrian zircons, with virtually no input, as was anticipated, from the nearby Carboniferous, Permian or Triassic magmatic arcs and contemporary accretionary wedge associated with the New England Orogen. Some rare, youngest zircons (<5%) are mostly contemporaneous with the estimated depositional age. The older, reworked zircon populations can only be acquired by postulating either (1) an Australian provenance by long overland sediment pathways from the interior to the west, during one or more transport cycles, perhaps from within the Thomson Orogen, and then bypassing or crossing the New England Orogen without any local contribution from that sector or (2) a North Zealandia provenance with a shorter transport distance from a postulated basement block to the east, within the Northern Lord Howe Rise and Kenn Plateau. This would comprise late Mesoproterozoic (1200–1000 Ma) and late Neoproterozoic–Cambrian (700–500 Ma) igneous and metamorphic complexes, similar to that proposed in South Zealandia. Triassic to Jurassic Clarence-Moreton Basin sedimentary rocks have provenances unlike their hinterland time-correlates in New South Wales and Queensland. The latter better share similarities with those in Murihiku Terrane, North Island, New Zealand. The provenance of Clarence-Moreton sediments is similar to that of time-correlates in New Caledonia, and it is postulated that they share a source region on the northern Lord Howe Rise or Kenn Plateau. [ABSTRACT FROM AUTHOR]

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The tunnels in present-day cities are experiencing varying degrees of loading conditions ranging from static to extreme loading. Therefore, the stability of underground tunnels needs to be analyzed and understood for safer and strengthened design. The present study was conducted to simulate the impact loading conditions due to a missile traveling at a velocity of 5 Mach for different rock tunnels. The nonlinear continuum finite element analysis has been carried out through Abaqus and Explicit. The four different types of sandstones considered in the present study include Kota, Jamrani, Singrauli, and Jhingurda sandstones. An elastoplastic Mohr–Coulomb constitutive material model has been considered to model the behavior of rock surrounding the tunnel opening. The tunnel has an opening of 7 m in diameter (d), and 50 m in height and breadth, with 50 m of longitudinal length. The deformation and stress in the rock and the damage to the concrete lining have been compared in different cases. The Concrete–Damage–Plasticity (CDP) model and the Johnson–Cook model were considered for modelling of the RC lining and steel reinforcement. It was concluded that Jhingurda sandstone has maximum deformations due to impacts caused by missiles. [ABSTRACT FROM AUTHOR]

The current stimulation practice of hydraulic fracturing relies on injection of water-based fluids; however, water can cause significant formation damage, therefore, alternative fracturing methods are an option. The concept of thermal stimulation rests on the idea that a very cold liquid can induce fracture when brought into contact with warmer rock under reservoir conditions. The mechanism for fracture creation consists of a severe thermal shock that imparts to the rock when its volume near the interface rapidly contracts, as the rock loses its heat. In this study, simple laboratory testing was performed to investigate the effectiveness of thermal stresses on the strength of dry and brine saturated rock samples representing two local formations namely Khuff limestone and Biyadh sandstone. Unconfined compressive strength (UCS) of dry rocks were determined and Khuff limestone showed 37% higher UCS value than Biyadh sandstone samples investigated and all appeared to fail along a vertical shear plane with load application. Brine saturated samples of both rock types suffered of water softening effect inducing UCS reduction of 51% and 42.3% for both limestone and sandstone samples, respectively. When dry and brine saturated rock samples of the two types were exposed to thermal stresses induced by exposure to liquid Nitrogen (LN2), both experienced strong thermal gradients reducing rock strength proving the effectiveness of the process. Dry samples experienced axial splitting type fractures upon loading with UCS reduction of 37% and 64% for limestone and sandstone, respectively. Brine saturated samples suffered imminent failure and no loading was needed indicating that strengths of both rocks were completely diminished upon LN2 exposure. Water expansion due to freezing counteracted by the shrinkage of the rock matrix believed to be the reason behind the imminent rock splitting. [ABSTRACT FROM AUTHOR]

Anisotropic sedimentary rocks are common around the world. Several factors, such as presence of primary and tectonic structures, type of weathering and rate of cohesion loss due to strength degradation, have significant effect on stability of slopes. In the present research, Geological strength index (GSI) has been used for quantitative comparison of rock mass quality and to investigate the rock mass damage. Other indicators of rock mass strength degradation, such as slake durability index tests, weathering index, were studied to understand the loss of strength with time leading to progressive failure in slopes. The failure pattern in bedded sandstones is controlled by bedding inclination, primary structures, vertical fractures. Folding affects bedding plane inclination and modify the failure mode along cut slopes. The cross-stratification significantly reduces rock quality and creates overhangs. The shape and size of overhangs are controlled by the presence of vertical cracks in addition to the type and scale of cross-stratification and failure generally occurs by block fall rather than block slide. The peculiar steeply plunging wedges associated with vertical fractures are very common in sub-horizontal bedded sandstone. Failure usually occurs by wedge fall rather than slide. Differential weathering affects the pinching strata against the massive beds and the characteristic wedges are common occurrence above this considerably fractured zone. Tectonic structures such as folds modify the style of failure in rock slopes as seen from kinematic analysis. The overall trend of lineaments is parallel to the strike of bedding plane (roughly E-–W) and the lineaments may be associated with reactivation of the major fault passing through the area. This study illustrates that the impact of tectonic damage further enhances the strength degradation caused by weathering, and climatic slaking. Overall rock mass quality lies in good to fair category, but preliminary stability analysis depicts slope in partially stable to unstable condition along SH-5; however, rock mass quality and cut slopes are relatively stable along SH-5A. [ABSTRACT FROM AUTHOR]

The results of studying the material composition of sandy rocks in Cretaceous deposits of the West Sakhalin Terrane are considered. Studies were carried out to reconstruct the paleogeodynamic environment of rock deposition in the terrane, as well as to determine the tectonic type and rock composition in the feeding sources (hereafter, provenances). Based on the mineral-geochemical parameters, sandstones in the terrane correspond to graywackes representing deposits of the petrogenic or first redeposition cycle ("first cycle"). Their detrital part includes products of the destruction of both basic–ultrabasic volcanic rocks and granite-metamorphic rocks. The deposits are characterized by a low degree of maturity of the clastic material formed mainly due to the mechanical destruction of rocks in provenances, weak lithodynamic processing of the material, and high rate of its burial. Paleogeodynamic interpretation of the obtained data was based on their comparison with the composition of ancient rocks and modern sediments accumulated in known geodynamic situations. The results obtained indicate that sediments were accumulated in the Cretaceous along the continent–ocean boundary in a basin associated with large-scale left-sided transform slips of the Izanagi Plate relative to the Eurasian continent. The provenance, which supplied the clastic material to this basin, combined the sialic land (granite-metamorphic and sedimentary rocks), a mature deeply dissected ensialic island arc, as well as fragments of the Sikhote-Alin accretion prisms formed with the participation of ophiolites. [ABSTRACT FROM AUTHOR]

Rock characterization of tropical Kenny Hill weathered sandstone have been an effort to be explored by using non-disruptive testing of pundit and resistivity testing to undertake sustainability issues and providing technical approach in exploration of weak rock materials solving. The purpose of this research is to determine the relationship between resistivity and uniaxial compressive strength of the most problematic rock type in Malaysia, namely Kenny Hill weathered sedimentary rocks, more usually referred to as sandstone. According to earlier study, sandstone has degraded in quality and has a tendency to disintegrate due to the tropical climate. Sandstone has a higher strength feature as compared to shale from Bandar Nusa Rhu, Shah Alam. Series of uniaxial compression were carried out to obtain the strength for rock samples. The strength properties of weathered sandstone are studied to quantify the weathering impact to these materials. Resistivity test and Pundit test were laboratory method conducted on the rock samples for verification of the correlation between resistivity and uniaxial compression. Results from the test were analyzed and their relationship with weathering grade was established. It signifies that sandstone strength increasing with the weathering grade. [ABSTRACT FROM AUTHOR]

This paper presents the results of geochemical studies of sandstones of the Aga–Borshchovochnyi complex in the Onon fragment of the Aga Terrane (Tutkhaltui Valley) within the Mongol–Okhotsk Fold Belt, as well as the results of U–Th–Pb (LA-ICP-MS) geochronological and Lu–Hf isotope geochemical studies of detrital zircons from these rocks. It was established that the youngest population of detrital zircons in the studied sandstones has an age of 196 ± 8 Ma. This indicates the Early Jurassic age of the sediments that were previously dated as Middle Paleozoic. The geochemical features of sandstones suggest that they were deposited in the active continental margin or island arc setting at the final stage of the closure of the Mongol–Okhotsk Paleocean. [ABSTRACT FROM AUTHOR]

Weathering problems of weak sedimentary rocks, especially when subjected to water immersion, are considered one of the serious geotechnical engineering issues. Examples of rock water submersion include foundations subject to seepage, regular irrigation, residence daily activities, service water, frequent plant watering, an increase in groundwater level and heavy rain, in addition to numerous urban and rural water use consequences; hence, it is necessary to quantify the effect of water on the physical and mechanical characteristics of sedimentary rocks. The objective of this study is to assess, evaluate and estimate the strength and stiffness of deterioration of sedimentary rocks in Egypt subject to freshwater soaking in three states (natural/presoaking state, after 48 h and after 30 days of soaking). An extensive laboratory testing program including slake durability, uniaxial compression and point load tests was conducted in the three states on sandstone and limestone specimens collected from Galala, Attaka-Suez Governorate, Egypt. The influence of water immersion on the physical and mechanical characteristics such as rounding, stress–strain envelope, strength and stiffness was studied. The results showed a reduction of up to 87% and 93% in the uniaxial compressive strength and elastic modulus, respectively, post 30 days of freshwater soaking. The limestone showed more resistance to deterioration compared to the sandstone. The stiffness and strength of sedimentary rocks decrease with long contact with water. This paper results provide guidance when assessing, planning and preliminarily evaluating similar rock formation/s considered as a candidate for engineering projects. [ABSTRACT FROM AUTHOR]

Among sites of geomorphological interest in the tableland of the Stołowe Mountains, consisting of clastic sedimentary rocks of Late Cretaceous age, are enigmatic occurrences and clusters of sandstone boulders within plateau levels that are underlain by mudstones and marls. These boulders are allochthonous, having been derived from the quartz sandstone beds that support the upper plateau level and stratigraphically are in excess of 50 m above the altitudinal position of the boulders. Topographic conditions preclude long-distance transport from the escarpment slopes; boulders are hypothesised to be the last remnants of completely degraded outliers (mesas) of the upper plateau. Their present-day altitudinal position is explained by passive 'settling' following disintegration of caprock and denudation of the underlying weaker rocks. Two localities are here presented in detail, Łężyckie Skałki and Pustelnik, along with adjacent boulder trains in the valleys incised into the plateau. It is argued that both localities have considerable geoheritage value and both play the role of geosites, although on-site facilities are so far limited. However, the complex history of boulders sets a series of challenges for successful geo-interpretation. [ABSTRACT FROM AUTHOR]

Tin Bider is a 6‐km‐diameter complex impact structure, the largest one recognized in Algeria. The crater was excavated in Cretaceous sedimentary rocks composed of, from the base to the top, Albian sandstones, Cenomanian clays, Cenomanian‐Turonian limestones, undifferentiated Coniacian to Maastrichtian clays and limestones. The age of the impact event is poorly constrained to <66 Ma by stratigraphy, the youngest geological unit affected by the event being the ~66 Myr old Maastrichtian limestones. Albian sandstones outcrop in the central sector of the structure and represent the only occurrence at outcrop of this geological unit in the structure. Here we report on a detailed petrographic analysis of eight Albian sandstone samples that were searched for shock‐metamorphic features. We confirm the presence of rare shocked quartz grains with planar deformation features (PDFs) and report on their crystallographic orientations as determined using the universal stage microscope. PDFs oriented parallel to the π{101¯2} and ω{101¯3} orientations are the most abundant ones. For the first time in impactites from Tin Bider, PDFs with basal (0001) orientation, corresponding to amorphized mechanical Brazil twins, are reported. Our results indicate that locally the peak shock pressure was of at least 20 GPa, but much lower in average for the investigated samples. [ABSTRACT FROM AUTHOR]

Groundwater pumped from the terrigenous Middle Devonian (D2) aquifer system is naturally rich in iron (Fe), making it a challenge to fulfil the requirements for drinking water quality. The total iron (Fetot) concentrations are above the limit value set for drinking water (0.2 mg/L) in 81% of the analysed water samples. The highest Fetot values reach up to 26 mg/L in some locations of southern Estonia. Due to the reducing conditions in the aquifer system, most of the Fetotconcentrations are caused by a high Fe2+ content. Infiltrated aerobic water becomes anaerobic and Fe3+ reducing along a deep flow path, leading to the downgradient increase in dissolved Fe concentrations. In order to study the natural sources of Fe in the Middle Devonian aquifer system, rock samples from the Narva, Aruküla, Burtnieki and Gauja stages were used for chemical analyses and leaching experiments. The whole-rock chemical analyses showed large variation in the Fe2O3 content (1.20â9.91%), whereas the values were higher in aquifer-forming siltstones than in sandstones. The amount of the leached Fe in groundwater is partly controlled by the granulometric composition of terrigenous rocks. The highest leached Fetot (up to 1.7 mg/L) concentrations were detected in the rocks where the share of the sand fraction is over 70%. As a rule, water is abstracted from sandstones having large pores and good groundwater yield, therefore water quality problems could only be solved by installing Fe removal facilities in southern Estonia.

This study investigates the depositional setting of the Oligocene sedimentary rocks of the southern Indus Basin according to grain size analysis of sandstones. Twelve sandstone samples were collected and studied from the Oligocene Nari Formation that distributes along the N‐S‐trending Laki Range in the Kirthar Province of Pakistan. The analysis results specify very fine to fine‐grained sediments and unimodal nature of grain size distribution. The sorting values of the studied sandstones vary from 0.66φ to 0.90φ, which indicates that the sediments are moderately to moderately well‐sorted. The skewness values of investigated samples vary from −0.04φ to 0.25φ, which indicate nearly symmetrical to fine‐skewed nature. The kurtosis of the studied samples varies between 0.73φ and 1.44φ which shows platykurtic, mesokurtic, and leptokurtic nature. Linear discriminant function and interpretation diagrams of sediments demonstrate that the Oligocene Nari Formation sediments from Lal Bagh section were being transported as bedload and suspended load with a bimodal to unimodal depositional mode that were deposited in a fluvial to shallow marine deltaic environment of a passive margin. [ABSTRACT FROM AUTHOR]

The hydromechanical properties of single self-propping fractures under stress are of fundamental interest for fractured-rock hydrology and a large number of geotechnical applications. This experimental study investigates fracture closure and hydraulic aperture changes of displaced tensile fractures, aligned tensile fractures, and saw-cut fractures for two types of sandstone (i.e., Flechtinger and Fontainebleau) with contrasting mechanical properties, cycling confining pressure between 5 and 30 MPa. Emphasis is placed on how surface roughness, fracture wall offset, and the mechanical properties of the contact asperities affect the self-propping potential of these fractures under normal stress. A relative fracture wall displacement can significantly increase fracture aperture and hydraulic conductivity, but the degree of increase strongly depends on the fracture surface roughness. For smooth fractures, surface roughness remains scale-independent as long as the fracture area is larger than a roll-off wavelength and thus any further displacement does not affect fracture aperture. For rough tensile fractures, these are self-affine over a larger scale so that an incremental fracture wall offset likely leads to an increase in fracture aperture. X-ray microtomography of the fractures indicates that the contact area ratio of the tensile fractures after the confining pressure cycle inversely correlates with the fracture wall offset yielding values in the range of about 3–25%, depending, first, on the respective surface roughness and, second, on the strength of the asperities in contact. Moreover, the contact asperities mainly occur isolated and tend to be preferentially oriented in the direction perpendicular to the fracture wall displacement which, in turn, may induce flow anisotropy. This, overall, implies that relatively harder sedimentary rocks have a higher self-propping potential for sustainable fluid flow through fractures in comparison to relatively soft rocks when specific conditions regarding surface roughness and fracture wall offset are met. [ABSTRACT FROM AUTHOR]

Thermal conductivity is an important physical parameter of rock, which requires indirect estimates. The existing rock thermal conductivity prediction model established from the perspective of particles has certain limitations, and the thermal conductivity calculation of sedimentary rock is not paid enough attention. In this paper, the thermal conductivity of 36 sedimentary samples is tested by the optical scanning method at a temperature of 300 K, and the calculated values from eight commonly used thermal conductivity prediction models with values obtained from laboratory tests are compared. A new mathematical model called the thermal conductivity entropy model (TCEM) is proposed to calculate the thermal conductivity of the rock from its mineral composition. The models for sandstone and mudstone by using thermal conductivity of the individual minerals are optimized, and the deviations between the measured and calculated values are compared. The results show that the values calculated by the eight models are all smaller than the test values, while the relative deviation of sandstone and mudstone are about 10% and 15%, respectively. TCEM provides a good coupling relationship (R2 = 0.54) for low-porosity sandstone. Due to the metamorphism of internal minerals, the thermal conductivity entropy is not linearly related to thermal conductivity. Therefore, the thermal conductivity entropy of minerals is used to predict the thermal conductivity of mudstone by multiple linear fitting (R2 = 0.62). TCEM eliminates the deviation caused by the spatial distribution of mineral particles in the rock in the traditional model. [ABSTRACT FROM AUTHOR]

Upper Cretaceous sedimentary rocks are widely exposed around Trabzon, Giresun and Gümüşhane in the eastern Pontides. The sedimentary rocks are mainly composed of sandstones and marls, and the thicknesses of these rocks range from 170 to 400 m. This paper focused on Late Cretaceous sandstones of Trabzon, Giresun and Gümüşhane regions to identify the concentrations, sources, deposition environment and conditions of certain heavy metal(loid)s (Zn, Pb, Cu, Ni, As, Co, Mo and V). Enrichment factor (EF), geo-accumulation index (Igeo), Pollution index (Pi), Pollution load index (Pln), Pb isotope and multivariate statistical analysis were performed to elucidate the pollution levels and sources. In general, the evaluation indices exhibited that the sandstones were moderately polluted by As in the Trabzon area, and strongly polluted by Ni and As, moderately polluted by Co and V in the Giresun and Gümüşhane areas. The results of multivariate statistical analyses indicated that As and partly Pb might be originated from anthropogenic sources, whereas other metals were derived from geogenic origin. Lead isotopic analysis demonstrated two characterized signatures of the pollution sources in the sandstones, one related to geogenic origin and the other to coal, gasoline and pesticides. The sandstones were deposited in transition—marine environment under oxic—weak oxic conditions and paleoclimatic conditions ranged from arid to moist during Late Cretaceous period. [ABSTRACT FROM AUTHOR]

Foreland basins have been extensively explored for hydrocarbon resources, geothermal, and gas storage applications, and multidisciplinarily studied to reconstruct orogenic processes. In fact, in the case of the Late Carboniferous Central European Variscan foreland basin, numerous drill cores have been recovered by the hard coal industry and comprehensive geological data sets have been made available by research. These cores and data sets provide a continuous record of the tectono-sedimentary and reservoir evolution over time. For this purpose, we have compiled petrophysical and petrographic literature data of >450 mostly tight (porosity <10%, permeability <1 mD) siliciclastic rock samples from Variscan foreland (Ruhr and Lower Saxony basin, NW Germany) and intramontane basins (Saar-Nahe basin, SW Germany) covering the complete Late Carboniferous stratigraphy. As a result, increases in mean grain size, sorting, detrital quartz, and proportion of metamorphic to sedimentary rock fragment contents, and decreases in detrital feldspar contents along the Westphalian B–C boundary are interpreted as a response to sedimentary recycling and unroofing of the Variscan hinterland due to tectonic uplift in the course of the northwestward propagating Variscan front. Thus, tectonics have a greater influence on sandstone petrography and porosity than the depositional environment. Porosity is mainly controlled by grain size and dissolution porosity. Basin-specific paleogeothermal gradients affect authigenic quartz (up to 25.0%) and chlorite (up to 7.7%) formation. Moreover, quartz cement contents <5% may stabilize the granular framework against mechanical compaction preserving porosity. With increasing quartz cement contents >5%, however, pore space is progressively clogged and the porosity preserving effect diminishes. [Display omitted] • Sandstone petrography unveils Variscan tectono-sedimentary foreland evolution. • Trends in sandstone petrography over time reveal unroofing and sedimentary recycling. • Tectonics exert a greater control on sandstone petrography than depositional facies. • Quartz cement contents <5% enhance porosity, contents >5% deteriorate porosity. • Mean grain size and surface exposure (porosity increase in 5–10% pt) control porosity. [ABSTRACT FROM AUTHOR]

The failure and instability of sedimentary rocks are related to internal weak surface and potential damage. To explore the influence of layer structure on the crack expansion law and deformation characteristics of sandstone, this study investigated the effect of layer structure on apparent crack degree, microscopic damage law, acoustic emission and deformation field under uniaxial compression. The fracture modes include tensile fracture Ⅰ, tensile fracture Ⅱ, shear fracture and composite fracture with an anisotropic characteristics. The apparent crack degree and stress show a simultaneous evolution feature and the sandstone with significant layer deterioration effect have greater damage degree. The peak stress and elastic modulus have nonlinear exponential relation with layer angles. The acoustic emission (AE) behavior has a phased response to the aging fracture, and AE energy warning points and AE b-value dropping abruptly generally occur near the continuous stress drops or peak stress. The deformation field reveals the principal strain and resultant displacement has a spatiotemporal response characteristic and there is a typical damage competition relationship in the deformation concentration area. The fracturing effect intensifies the dissimilation behavior of deformation field, formation of strain concentration zone and banded dissimilation zones indicate the cracks penetration. The displacement field at the fracture tip shows a significant suddenness and strain concentration region is often pregnant with high-level displacement. These findings on the dynamic fracture mechanism are helpful in the deterioration characteristics of sedimentary rock in underground space engineering. • The apparent cracks degree and stress show a simultaneous evolution feature. • The AE b-value dropping abruptly generally occur near the stress drop or peak stress. • There is a typical damage competition relationship in deformation concentration area. • The fracturing effect intensifies the dissimilation behavior of deformation field. [ABSTRACT FROM AUTHOR]

Understanding eodiagenesis is essential to decoding the diagenetic pathways of tight sandstones that act as excellent unconventional oil & gas reservoirs. Great paleoclimate change is capable of influencing eodiagenetic processes of tight sandstones through variations of sedimentary environment. However, it is less noted how climate gradients between the greenhouse and the hothouse conditions impact the eodiagenesis of tight sandstones. We examined eodiagenetic processes that has been operated in the Shaximiao Formation sandstones using petrographic observation, scanning electron microscopy, geochemistry, and XRD analysis to reveal impacts of the transitional climate changes on the differential eodiagenesis and implications for the diagenesis-porosity evolution. Based on sequence stratigraphy, the Shaximiao Formation is divided into four sub-members SXM1, SXM2, SXM3, and SXM4, respectively. Dark sandstones and mudstones mainly occurred in the SXM1 and the SXM2. Grey-green clastic rocks are dominant in the SXM3, whereas red mudstones frequently appear in the SXM4. Paleoclimate indices denote that a cyclical aridification from the warm-humid to hot-semiarid conditions took place from the SXM1 to the SXM4. It could have been caused by the megamonsoon effect and the paleogeographic shift along with the breakup of the Pangaea supercontinent. Combined with the migration of depocenters, the paleoclimate change resulted in transformation of sediment provenances from mafic igneous rocks to quartzose sedimentary rock along with the decreasing textural maturity. Therefore, sedimentary environments varied from the high-saline to low-saline and from low-oxygen to high-oxygen conditions respectively, which had a crucial impact on eodiagenetic cements which were formed in the Shaximiao Formation. Chlorite and laumontite cement precipitation was promoted by high-saline alkaline fluids. Chlorite proportions show an arched trend from the SXM1 to the SXM4, compatible with those of primary and secondary porosities. In contrast, laumontite proportions exhibit a decreasing variation from the SXM1 to the SXM4. High percentages of early cements are favorable to improving resistance to the compaction and preservation of primary pores. However, high chlorite (>5%) and laumontite (>10%) proportions are destructive for the reservoir quality. Large quantities of laumontite cements occupy primary pores and impede diagenetic fluids flowing and are not favorable to the dissolution. By contrast, an excess of chlorite cements can be dissolved to produce secondary pores during the organic acid release. Thus, the SXM2 is potential as a reservoir for oil & gas. Therefore, those eodiagenetic cements can control the late diagenetic evolution and the reservoir quality. Observations made here have implications for understanding tight sandstone reservoirs elsewhere in the world. • A late Middle Jurassic cyclical aridification occurred in the Central Sichuan Basin. • Sources of the Shaximiao Formation transformed from mafic to quartzose detrita. • Sedimentary environments varied with salinity decreasing and oxidation strengthening. • Types and intensity of eodiagenesis control late diagenesis and reservoir quality. [ABSTRACT FROM AUTHOR]

The paper presents the first findings of paleomagnetic studies on Middle Jurassic sedimentary rocks of the Elgon Formation of the Ulban Terrane from the coastal outcrops along the Ulban Bay (53.5° N, 137.7° E). Demagnetization yielded a ChRM component of the pre-folding age. No inclination shallowing effect for the ChRM vector was revealed in sandstone specimens of the Elgon Formation. The paleomagnetic pole coordinates and the paleolatitude at which the studied rocks deposited were calculated: Plat = –34.3 (34.3)°; Plong = 161.2 (341.2)°; dm = 2.7, dp = 5.3, paleolatitude = 0.1° (+2.7°/–2.6°) S. The acquired paleomagnetic data are evidence of the deposition of the rocks of the Ulban Terrane in the Middle Jurassic at the boundary between the Asian paleocontinent and the Paleo-Pacific, which later formed part of the Sikhote Alin Orogenic Belt. [ABSTRACT FROM AUTHOR]

Twenty-one sandstone samples belonging to the intermediate part of Gorgoglione Flysch (GF) dated Middle-Miocene, cropping out in the Southern Apennines (Italy), have been studied to highlight the detritus provenance. Petrographic and chemical composition indicates that the successions consist of feldspatho-quartzose and litho-feldspatho-quartzose arenites interbedded with pelitic and calciclastic layers and reveals a provenance from a basement formed by low- to medium-grade metamorphic rocks with abundant granitoids covered by sedimentary rocks in which a volcanic component was also present. In the Mediterranean area, basements with these characteristics are widespread both in western and southwestern domains. The supply provenance of Gorgoglione Flysch has been better detailed utilizing U–Pb detrital zircon ages recording the geological history of the source rocks. Fifty-eight crystals from six samples of coarse- and fine-grained sandstones have been analysed using the U–Pb isotopic systematic (LA-ICP-MS). They produce 70 concordant zircon ages forming three defined clusters at 672 ± 28 Ma, 458 ± 9 Ma and 297 ± 8 Ma, and four zircon ages corresponding to 24 ± 1 Ma. An evaluation of the entire collected data suggests that the provenance area is better identified in northwestern sectors of the Mediterranean area in which the Sardinia–Corsica (pro-part) block plays a fundamental role. [ABSTRACT FROM AUTHOR]

Several greywacke sandstones considered as Paleozoic rocks are found in three different formations, i.e. the Dohol, Linggiu, and Tanjung Leman Formations within the Palaeozoic East Johor Basin. The compositions of twenty-nine sandstone samples were identified using petrographical and geochemical methods to determine the provenance of sandstones as well as the tectonic setting of pre-and syn-sedimentation. Seven samples of them were examined using point counting method to obtain the mineralogical compositions. This petrographical point counting was done by plotting composition percentages to QFL and QmFLt triangular diagrams, The results showed a magmatic arc for Dohol Formation, a change from a magmatic to a recycled orogen for Linggiu Formation, and a recycled orogen for Tanjung Leman Formation. The recycled orogen tectonic setting of Linggiu and Tanjung Leman may have come from the underlying metamorphic and sedimentary rocks of Mersing and Murau Formations. Meanwhile, twenty-two samples were examined using a geochemical method by utilizing the ratio of K2O/Na2O and SiO2. The samples suggest a tectonic setting from both passive continental margin (PM) and active continental margin (ACM). Based on these findings, it is interpreted that the sedimentary rocks in East Johor were deposited in a subduction-related basin, such as fore-arc, magmatic arc, and back-arc. [ABSTRACT FROM AUTHOR]

Mechanically strong sandstones consider as a potential construction material which can withstand modest load and not associated with any geologic fractures. This work is about understanding the macro-mechanical properties of sandstones by studying several petrographic parameters, which could provide evidence of their influence on mechanical strength. Here the authors were considered the Bhuban sandstones of western Indo-Burmese Ranges (IBR) of north-eastern India to investigate the above criteria. The result shows that sandstones have a mean grain size between 108 to 208 µm. Moderate to poorly sorted (phi scale ranges 0.56-1.5) grains show greater content of rounded constituents (43-68 %) with sphericity between 0.65-0.85; along with moderate packing properties (packing density 54-77 %; packing proximity 32-70 %). The grains join by mostly straight (20-54 %) and concavo-convex (13-45 %) contacts; with lesser point (5-13 %) and sutured contacts (8-44 %). Schmidt Hammer rebound values (R-values) were used to calculate and analyse the uniaxial confined stress (UCS); which again validated with UCS testing of core samples. The comparison between macro-mechanical parameters and the UCS shows interrelationship among rock constituents which hold the key to the mechanical strength of the rock. The presence of angular grains and semi-angular spherical grains diminish the macromechanical strength to some extent. Moreover, FETEM-EDX analysis confirms the microweathering of the angular grains, which have a deformed lattice setting. These findings show that macro-mechanical and micro-nano scale properties of sandstones influence the rock strength. [ABSTRACT FROM AUTHOR]

Through many field geology observations, the authors find that sandstone and carbonate rocks, which were originally thought to be sedimentary, have magmatic characteristics and should classified as magmatic rather than sedimentary rocks. Combining this information with the principles of Bowen's reaction series, the authors infer that the Earth has evolved gradually from high temperature to low temperature and, through crystallization differentiation, has experienced the following stages: high melting point metal to ultramafic rock to mafic rock to neutral rock to acidic rock to sandstone to carbonate rock to mudstone to ice. Since fossils that preserve the remains of creatures, such as fossil fish, occur in magmatic rocks rather than sedimentary rocks, the organisms were not aquatic but lived in high-temperature fluids with magmatic characteristics. Therefore, the authors conclude that during the evolution of rocks from high temperature to low temperature, biological evolution from high temperature to low temperature also occurred on the Earth and that carbon-based life did not originate in the ocean but in high-temperature carbon-containing fluids; this is a subversive statement. This understanding contradicts the original interpretation, that is, that fossils formed under normal temperature and pressure conditions. This point explains the Cambrian explosion and later mass extinctions. [ABSTRACT FROM AUTHOR]

Iron oxide concretions are found in sedimentary rocks on both Earth and Mars. On Earth, concretions are common in eolian formations, such as the Jurassic Navajo Sandstone in Utah, USA and those found in the Cretaceous Djadokhta Formation, Gobi Desert, Mongolia. Although it is known that the formation conditions of the iron oxide concretions were affected by the paleoclimate of these regions, quantitative modeling of such formations still requires development, especially concerning initial and diagenetic conditions. A 1-D diffusion–reaction simulation was conducted by assuming that a calcite concretion was initially located in a homogeneous layer of sandgrains. Favorable conditions for the formation of iron oxide concretions have been found to be 4.5 ⩽ pH ⩽ 6 , and 10 - 7 ⩽ [ Fe 2 + ] f O 2 ⩽ 10 - 5 , where [ Fe 2 + ] and f O 2 are the concentration of ferrous Fe 2 + ions and dissolved oxygen relative to the atmospheric value, respectively. An iron-rinded concretion from ferric Fe 3 + ions is not possible. For the case of Fe 2 + ions, the flow speed of the groundwater should be faster than 2 × 10 - 5 mm s - 1 . The formation timescale is determined by the diffusion flux of the hydrogen ion, and varies between 2.7 × 10 2 and 1.5 × 10 4 years for a calcite concretion with an initial radius of 15 mm. Formation conditions of iron-rinded concretions on Earth and Mars are discussed. [ABSTRACT FROM AUTHOR]

Quartz‐rich sandstones can be produced through multiple sedimentary processes, potentially acting in combination, such as extensive sedimentary recycling or intense chemical weathering. Determining the provenance of such sedimentary rocks can be challenging due to low amounts of accessory minerals, the fact that the primary mineralogy may have been altered during transport, storage or burial and difficulties in the recognition of polycyclic components. This study uses zircon and apatite U‐Pb geochronology, apatite trace elements, zircon‐tourmaline‐rutile indices and petrographic observations to investigate the sedimentary history of mineralogically mature mid‐Carboniferous sandstones of the Tullig Cyclothem, Clare Basin, western Ireland. The provenance data show that the sandstones have been dominantly and ultimately sourced from three basement terranes: older Laurentian‐ associated rocks (ca. 900–2500 Ma) which lay to the north of the basin, peri‐Gondwanan terranes (ca. 500–700 Ma) to the south and igneous intrusive rocks associated with the Caledonian Orogenic Cycle (ca. 380–500 Ma). However, the multi‐proxy approach also helps constrain the sedimentary history and suggests that not all grain populations were derived directly from their original source. Grains with a Laurentian or a Caledonian affinity have likely been recycled through Devonian basins to the south. Grains with a peri‐Gondwanan affinity appear to be first cycle and are potentially derived from south/southwest of the basin. Taken as a whole, these data are consistent with input into the basin from the south and southwest, with the reworking of older sedimentary rocks, rather than intensive first‐cycle chemical weathering, likely explaining the compositional maturity of the sandstones. This study highlights the need for a multi‐proxy provenance approach to constrain sedimentary recycling, particularly in compositionally mature sandstones, as the use of zircon geochronology alone would have led to erroneous provenance interpretations. Zircon, together with U‐Pb geochronology from more labile phases such as apatite, can help distinguish first‐cycle versus polycyclic detritus. [ABSTRACT FROM AUTHOR]