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The roof of coal seams are mostly soft rock with weak cementation. To further study the mechanical characteristics and deformation control scheme of the roadway with weakly cemented siltstone as roof, this paper took Linchang coal mine as the research background and adopted field investigation methods, laboratory experiments, and theoretical analysis. Using a scanning electron microscope, it is found that the weakly cemented siltstone is composed of coarse-grained minerals with a high degree of pore development. According to the analysis, the instability factors of weakly cemented siltstone roadway include the late diagenetic age of rock, the low mechanical strength of rock, and the change of surrounding rock properties by pouring water. The selection of grouting reinforcement materials was studied in detail. The test results show that cement-bonded specimens’ strength is lower than that of Marithan polyurethane cement specimens in general. The combined support scheme based on grouting reinforcement is put forward. Field monitoring data show that the designed support scheme can effectively control the surrounding rock deformation of weakly cemented siltstone roadway.

The end-Permian mass extinction represents the most severe biotic crisis for the last 540 million years, and the marine ecosystem recovery from this extinction was protracted, spanning the entirety of the Early Triassic and possibly longer. Numerous studies from the low-latitude Paleotethys and high-latitude Boreal oceans have examined the possible link between ocean chemistry changes and the end-Permian mass extinction. However, redox chemistry changes in the Panthalassic Ocean, comprising ∼85–90% of the global ocean area, remain under debate. Here, we report multiple S-isotopic data of pyrite from Upper Permian–Lower Triassic deep-sea sediments of the Panthalassic Ocean, nowpresent in outcrops of western Canada and Japan. We find a sulfur isotope signal of negative Δ33S with either positive δ34S or negative δ34S that implies mixing of sulfide sulfur with different δ34S before, during, and after the end-Permian mass extinction. The precise coincidence of the negative Δ33S anomaly with the extinction horizon in western Canada suggests that shoaling of H₂S-rich waters may have driven the end-Permian mass extinction. Our data also imply episodic euxinia and oscillations between sulfidic and oxic conditions during the earliest Triassic, providing evidence of a causal link between incursion of sulfidic waters and the delayed recovery of the marine ecosystem.

The deformation in sedimentary rock induced by train loads has potential threat to the safe operation of tunnels. This study investigated the influence of stratification structure on the infrared radiation and temporal damage mechanism of hard siltstone. The uniaxial compression tests, coupled with acoustic emission (AE) and infrared radiation temperature (IRT) were conducted on siltstones with different stratification effects. The results revealed that the stratigraphic structure significantly affects the stress-strain response and strength degradation characteristics. The mechanical parameters exhibit anisotropy characteristics, and the stratification effect exhibits a negative correlation with the cracking stress and peak stress. The failure modes caused by the stratification effect show remarkable anisotropic features, including splitting failure (I: 0°–22.50°, II: 90°), composite failure (45°), and shearing failure (67.50°). The AE temporal sequences demonstrate a stepwise response characteristic to the loading stress level. The AE intensity indicates that the stress sensitivity of shearing failure and composite failure is generally greater than that of splitting failure. The IRT field has spatiotemporal migration and progressive dissimilation with stress loading and its dissimilation degree increases under higher stress levels. The stronger the stratification effect, the greater the dissimilation degree of the IRT field. The abnormal characteristic points of average infrared radiation temperature (AIRT) variance at local stress drop and peak stress can be used as early and late precursors to identify fracture instability. Theoretical analysis shows that the competitive relationship between compaction strengthening and fracturing damage intensifies the dissimilation of the infrared thermal field for an increasing stress level. The present study provides a theoretical reference for disaster warnings in hard sedimentary rock mass.

Weak rock slope instabilities are a common engineering problem during highway construction in South China. This study focused on a siltstone slope instability, which was induced during the construction of an expressway in Guangdong Province of China. Field monitoring and numerical simulation analyses were performed to examine the failure mechanism and formation processes of this landslide which is associated with construction activities and a period of prolonged rainfall. According to the characteristics of the slope deformation and the monitoring data, the slope deformation can be divided into two stages: a period of slow creep caused by excavation and an accelerated sliding period triggered by rainfall. Numerical simulation results show that during the excavation process, large horizontal displacement occurs at the front edge of the slope, and the initial plastic zone develops, resulting in a shallow landslide. During 20 days of continuous rainfall, the water content in the shallow layer of the slope increases continuously, and a transient saturated area forms at the surface of the slope. Within 7 days after the rain stops, the zero pore pressure surface of the slope gradually moves towards the interior of the slope, and the plastic zone begins to extend to the top of the slope. In addition, rainwater seeps down along the cracks to form a penetrating zone, thus accelerating the process of rock and soil mass softening, which further reduces the factor of safety of the slope. The combined effects of the excavation and rainfall ultimately lead to the failure of the siltstone slope; however, continuous rainfall is the key factor triggering deep sliding. The deformation and failure of the slope mainly undergo four stages: local collapse of the slope surface, formation of the plastic zone at the foot of the slope, bulging at the toe, and formation of tension cracks in the crown of the landslide. The failure mode of the siltstone slope belongs to be a retrogressive-type of the front edge bulging and trailing edge tension cracking. Based on the deformation characteristics and the failure mechanism of the landslide, comprehensive control measures including interim emergency mitigation measures and long-term mitigation measures are proposed.

Research on Menanga Formation in Lampung and surrounding areas is still limited, especially research on paleontology. The purpose of this study was to identify the presence of radiolarian fossils in the Menanga Formation. Field observations were carried out at two site in Way Sabu, Pesawaran and Gunungkasih, Tanggamus, Lampung. Twelve samples were extracted from interbedded siltstone and claystone for radiolaria fossils. There were four samples that had radiolarian fossils. Radiolaria from genus Tetraditryma sp., Paronaella sp., Pantanellium sp., Holocryptocanium sp., Archaeocenosphaera sp., Napora sp., Sethocapsa sp., and Orbiculiforma sp. were found in the Menanga Formation indicate Jurassic to Cretaceous age. Based on radiolaria assemblage, Menanga Formation was probably positioned within a warm water current system in the low latitude Mesotethys. The exposed Menanga Formation caused by a collision between Woyla terrane and West Sumatra terrane that occurred in the Late Cretaceous.

Based on drilling core descriptions and micro sedimentary features, combined with regional paleogeographic features, imaging logging and 3D seismic attribute analysis, the sedimentary characteristics and representative identification mark of sand debris flow sandstone in Meishan formation of northern Lingshui Sag, Qiongdongnan basin are discussed in detail, and the sand debris flow sedimentary pattern in the study area is established. Meishan formation sandy debris flow sandstone in the study area is mainly consist of 2 lithological associations, thick massive siltstone to very fine sandstone without sedimentary structure on the upper part and silty mudstone, mudstone and siltstone interbeds with abundant contemporaneous deformation structure on the lower part, and the \"mud-encased sand\" structure in massive sandstone can be used as an important symbolic evidence to identify the sand debris flow deposits. The distribution of sandy debris flow sandstone is controlled by shelf slope break, and the area with relatively gentle, constructive slope, where the slope break line is characterized by \"bulge\" form to the sea, is the most favorable area for the development of sandy debris flow sandstone reservoirs.

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.HighlightsWeak 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.

The rise of atmospheric oxygen fundamentally changed the chemistry of surficial environments and the nature of Earth’s habitability 1 . Early atmospheric oxygenation occurred over a protracted period of extreme climatic instability marked by multiple global glaciations 2 , 3 , with the initial rise of oxygen concentration to above 10 −5 of the present atmospheric level constrained to about 2.43 billion years ago 4 , 5 . Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago 4 , which represents the estimated timing of irreversible oxygenation of the atmosphere 6 , 7 . Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron–sulfur–carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10 −5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated. Sulfur isotope and iron–sulfur–carbon systematics on marine sediments indicate that permanent atmospheric oxygenation occurred around 2.22 billion years ago, about 100 million years later than currently estimated.

Red-bed argillaceous siltstone is a common soft rock in the drawdown area of water diversion project extending from the Yangtze to Huaihe Rivers, with the characteristics of water softening and disintegration, which directly threatens the stability and safety of the diversion project. To better understand the effect of cyclic drying–wetting on the disintegration characteristics and mechanism, disintegration experiments were conducted on the red-bed argillaceous siltstone from the Tongcheng area of the water diversion project extending from the Yangtze to Huaihe Rivers. Experimental results indicated that, with an increasing number of drying–wetting cycles, the red-bed argillaceous siltstone was gradually crushed, large particles gradually transformed into small particles. A microstructural analysis showed that a continuous drying–wetting process resulted in the sample surface becoming disordered and complicated, and new micro-fractures and pores were generated. Notable changes in the concentrations of ions in the soaking solutions indicated continuous dissolution of the minerals, and a large amount of mineral loss under the action of cyclic drying–wetting. Furthermore, the evolution of disintegration parameter further indicated that the disintegration of red-bed argillaceous siltstone was gradually intensified by the increasing number of drying–wetting cycles. The fractal dimension D and the incremental surface energy gradually increased with an increase in the number of drying–wetting cycles. Thus, the proposed energy dissipation model effectively describes the disintegration characteristics of red-bed argillaceous siltstone under the cyclic drying–wetting, and thus, it can be used to guide engineering practices.