Digging deeper: why we need more Proterozoic algal fossils and how to get them.

Known Proterozoic algal fossils raise compelling questions about the origin and diversification of cyanobacteria and eukaryotic algae, and their ecological influence in deep time. This Perspectives article describes particular examples of persistent evolutionary and biogeochemical issues whose resolution would be aided by additional algal fossil evidence from Proterozoic deposits, which have been the subjects of recent intensive study. New Proterozoic geosciences literature relevant to the early diversification of algae is surveyed. Previously underappreciated algal traits that might improve taxonomic attributions of fossil remains are highlighted. Processes that phycologists could use to improve detection of algal fossils are recommended. Potential geological sources of new Proterozoic fossils are suggested.

Microtopography effects on pedogenesis in the mudstone-derived soils of the hilly mountainous regions.

Topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are referred to microtopographies. In hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physicochemical, and geochemical attributes of profiles were analyzed. The results showed that from the summit to the toeslope, soil thickness increased significantly and profile configuration changed from A-C to A-B-C. The total contents of Ca and Na decreased at the summit, backslope, and footslope, while the total contents of Al, Fe and Mg showed an opposite trend. On the summit and shoulder of the hillslope, weathered materials were transported away by gravity and surface erosion, exposing new rocks. As a result, soil development in these areas was relatively weak. In flat areas such as the footslope and toeslope with sufficient water conditions, the addition of weathered components and the prolonged contact between water, soil, and sediment led to further chemical weathering, resulting in highly developed characteristics. Microtopography may influence physicochemical properties, chemical weathering, and redistribution of water and materials, causing variations in pedogenic characteristics at different slope positions.

Long-term performance of the adsorption layer system for the recycling and repurposing of arsenic-bearing mudstone as road embankment.

The adsorption layer system has shown great potential as a cost-effective and practical strategy for the recycling and management of excavated rocks containing potentially toxic elements (PTEs). Although this system has been employed in various civil engineering projects throughout Japan, its long-term performance to immobilize PTEs has rarely been investigated. This study aims to evaluate the effectiveness of the adsorption layer system applied in an actual road embankment approximately 11 years after construction. The embankment system is comprised of a layer of excavated arsenic (As)-bearing mudstone built on top of a bottom adsorption layer mixed with an iron (Fe)-based adsorbent. Collection of undisturbed sample was carried out by implementing borehole drilling surveys on the embankment. Batch leaching experiments using deionized water and hydrochloric acid were conducted to evaluate the water-soluble and acid-leachable concentrations of As, Fe, and other coexisting ions. The leaching of As from the mudstone layer was likely induced by As desorption from Fe-oxides/oxyhydroxides naturally present under alkaline conditions, including the oxidation of framboidal pyrite, which was identified as a potential source of As. This was supported by electron probe microanalyzer (EPMA) observations showing the presence of trace amounts of As in framboidal pyrite crystals. Arsenic leached from the mudstone layer was then immobilized by Fe oxyhydroxides found in the adsorption layer. Based on geochemical modeling and X-ray photoelectron spectroscopy (XPS) results, leached As predominantly existed as the negatively charged HAsO42- oxyanion, which is readily sequestered by Fe oxyhydroxides. Moreover, the effectiveness of the adsorption layer was assessed and its lifetime was estimated, and the results revealed it still possessed enough capacity to adsorb As released from mudstone in the foreseeable future. This prediction utilized the maximum potential amount of As that could leach from the excavated rock layer with time.

Study on Seepage Characteristics of Grouting Slurry for Water-Absorbing Mudstone with Rough Fissure.

Based on the computed tomography scanning, which abbreviation is CT scanning, and fractal theory, geometric parameters of mudstone fissures are obtained. The physical model of a single fissured channel is obtained in combination with Barton standard curves and 3D printing technology, and similar materials of mudstone are developed based on the water absorption of natural mudstone to prepare single fissured water-absorbing grouting test blocks with different roughness levels for the grouting simulation testing. By analyzing the viscosity change characteristics of grouting slurry before and after grouting, the seepage characteristics of the grouting slurry in the rough fissures of the water-absorbing mudstone are revealed. The results show that when the roughness is small, the grouting slurry will have an obvious water loss effect after passing through mudstone fissures. However, with the flow of the slurry, the water loss effect of the subsequent grouting slurry will be weakened. For fissures with high roughness, the water absorption properties of the rough surfaces and the walls of the mudstone fissures work together, leading to the sedimentation and blockage of the fissure channels, thereby hindering the flow of slurry.

Revisiting Eothyrsites holosquamatus Chapman (Trichiuroidea: Gempylidae), an Eocene gemfish from the Burnside Mudstone, Dunedin, New Zealand.

The remains of a unique fossil bony fish were discovered in late Eocene (39.1-36.7 Ma: NZ Kaiatan stage) mudstone at Burnside near Dunedin, New Zealand in the 1930s and subsequently named and described by Frederick Chapman. He interpreted the type specimen as being a large-scaled relative of the modern Thyrsites of the Gempylidae (Scombroidei: Trichiuroidea), known to be swift, large oceanic predators. However, Chapman is unlikely to have seen all of the fossil, and did not discuss the skull and caudal skeleton. Additional material now allows these to be included in the expanded description herein, including key morphologic features of the fish such as the presence of premaxillary fangs. This study describes the rather complex history of the specimen and re-examines this significant fossil fish in the University of Otago collections, giving a more complete understanding of Eothyrsites morphology, paleoecology and relationships. In summary, we suspect Eothyrsites represents an ancestral form of gempylid, closely related to the gemfish group, an important Southern Hemisphere macrofossil record from the Eocene seas around Zealandia.

Experimental study on the punching failure model of soft red rock subgrade by BPT-BVM methods and it's assessment of the load bearing capacity.

The recommended bearing capacity of medium weathering mudstone foundation is less than the capacity of the rock structure to withstand loads in Southwest China. A comprehensive failure characterization of medium weathering mudstone in Chengdu has been performed including bearing plate test (BPT), binocular vision measurement (BVM) test, uniaxial compressive strength test, trial trench test of shallow rock surface and 3D imaging in this paper. Failure behavior of rock has been modeled with 3D imaging algorithm that utilizes Zhang's calibration method in BVM system combination with trial trench test of shallow rock surface. The bearing capacity of medium weathering mudstone foundation were extracted from uniaxial experiments and BPT-BVM test by fitting relevant material properties to the data. The results revealed that: Bearing capacity of medium weathering mudstone of layered isotropic in Chengdu is undervalued. Specifically, the characteristic load carrying value is in the range 1500-2500 kP, that is 50% higher than in the local standard system. Failure process is different from Hoek-Brown Failure Criterion, presenting a wave peak transfer phenomenon of the increment displacement into the distance. Thus, it can be reduced to that of punching failures for thin bedded structures of Moudstone foundations. Compressive strength of soft rock proves to be main factor limiting the bearing capacity, a clear correlation between the uniaxial compressive strength reduction coefficient and the bearing capacity has been used to establish, leading to the proposal of a load bearing capacity prediction model.

Hydraulic property variations with depth in a loess mudstone landslide.

In areas where loess is distributed, landslides represent a significant geohazard with severe implications. Among these events, loess-mudstone landslides are particularly prevalent, posing substantial risks to the safety and property of local residents, and moisture plays a pivotal role as a key factor in causing these disasters. In this study, the hydraulic properties of the soils along the longitudinal section of an ongoing loess-mudstone landslide are investigated through the variation of soil water characteristic curves, which are subsequently fitted by utilizing van Genuchten model. Moreover, a comprehensive experimental investigation was conducted on the loess, mudstone, and loess-mudstone mixtures to facilitate analysis, including X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) observation, particle size distribution (PSD) analysis, along with fundamental geotechnical tests for parameter determination. It is found that mudstone and loess have distinct SWCC distribution. The SWCC of loess at various depths exhibits a similar distribution pattern due to the occurrence of landslide. The SWCC distribution of loess-mudstone mixture displays a transitional trend between the SWCC of mudstone and that of loess, and the water retention capacity increases as the mudstone content increases. The experimental findings have demonstrated notable agreement between each other and exhibited a satisfactory level of concurrence with the observed phenomena in geological surveys.

Experimental Study on Mechanical Properties and Permeability Characteristics of Calcareous Mudstone under Different Confining Pressures.

Calcareous mudstone, a type of red-bed soft rock, is prevalent in the surrounding rock of the Central Yunnan Water Diversion Project (CYWDP) in Yunnan Province, China, significantly impacting both construction and operation. The mechanical properties of calcareous mudstone vary with depth. This study investigates its mechanical properties, permeability characteristics, energy evolution, and macro- and micro-failure characteristics during deformation using triaxial compression tests under different confining pressures. Results reveal distinct stage characteristics in the stress-strain behavior, permeability, and energy evolution of calcareous mudstone. Crack propagation, permeability evolution, and energy dissipation are closely linked, elucidating the deformation and failure process, with fluid pressure playing a crucial role. The confining pressure σ3 increased from 2 MPa to 4 MPa and 6 MPa, while the peak stress σc (Pw = 1 MPa) of the calcareous mudstone increased by 84.49% and 24.89%, respectively. Conversely, the permeability at σc decreased from 11.25 × 10-17 m2 to 8.99 × 10-17 m2 and 5.72 × 10-17 m2, while the dissipative energy at σc increased from 12.39 kJ/m3 to 21.14 kJ/m3 and 42.51 kJ/m3. In comparison to those without fluid pressure (Pw = 0), the value of σc at Pw = 1 MPa was reduced by 36.61%, 23.23%, and 20.67% when σ3 was 2, 4, and 6 MPa, respectively. Increasing confining pressure augments characteristic stresses, deformation and failure energy, and ductility, while reducing permeability, crack propagation, and width. These findings enhance our understanding of calcareous mudstone properties at varying depths in tunnel construction scenarios.

Experimental study on the mechanical characteristics of weakly cemented mudstone under different loading rates.

With the gradual shift of coal mining to the western coal mining region of China, floor heave in weakly cemented mudstone roadways has become an issue affecting the safety and efficiency of coal mine production. Additionally, different mining rates can lead to fluctuating support stresses on the roof and floor of weakly cemented mudstone roadways. Therefore, obtaining a comprehensive understanding of the mechanical properties of weakly cemented mudstone at different loading rates is conducive to improving the issue of floor heave in such roadways and provides a theoretical basis for further study. In this context, a series of uniaxial mechanical tests with concurrent acoustic emission monitoring were conducted on specimens of weakly cemented mudstone under various loading rates (0.005, 0.01, 0.05, and 0.1 mm/s). The stress‒strain and acoustic emission response curves were obtained to effectively characterize the strength, deformation, damage, macroscale instability, and crack propagation characteristics of the mudstone under the influence of loading rate effects. The research results support the following findings: (1) With increasing loading rate, the peak strength and elastic modulus of weakly cemented mudstone significantly increase, while the peak axial strain and peak radial deformation significantly decrease. (2) With increasing loading rate, the stress required to trigger the expansion of weakly cemented mudstone gradually increases, and a significant power-law relationship arises between the strain of the mudstone at the start of expansion and the loading rate. (3) With increasing loading rate, the acoustic emission ringing count of weakly cemented mudstone increases: The failure of weakly cemented mudstone changes from small-range progressive failure to sudden failure, and the failure mode transitions from shear failure to tensile‒shear composite failure. (4) The studied mudstone damage variables increase with increasing loading rate, following an approximate exponential function. The conclusions obtained in this work can provide a theoretical basis for the evolution mechanism and control of floor heave in deep roadway mining.

Influence of mudstone on coal spontaneous combustion characteristics and oxidation kinetics analysis.

To explore the spontaneous combustion characteristics and hazards of the low-temperature oxidation (LTO) stage in the process of spontaneous combustion of coal and mudstone, the pore structure, spontaneous combustion characteristic parameters, and exothermic characteristics of coal and mudstone were tested and studied, and the oxidation kinetic parameters were calculated. The results show that mudstone has a larger specific surface area and pore volume than coal. From the fractal characteristics, the pore structure of mudstone is more complex than that of coal. According to the comparison of theoretical and actual gas generation and oxygen consumption rate curves, it is found that there is an interaction between coal and mudstone in the LTO process. With the increase of mudstone mass ratio, gas production, and its oxygen consumption rate increase. Among them, CM-4 (Coal:Mudstone = 1:1) has the highest exothermic intensity and the exothermic factor (A) and fire coefficient (K) increase with the increase of mudstone content. The apparent activation energy of the mudstone sample is lower than that of the raw coal, indicating that the sample after adding mudstone is more likely to have spontaneous combustion in the LTO stage.

Review of methods for alumina recovery from mudstone and coal fly ash.

Developing recovery methods from coal mine waste like mudstone and coal fly ash (CFA) is crucial to expanding the alumina supply beyond bauxite. This review explores various approaches for alumina recovery from mudstone and CFA. Six main leaching techniques are discussed-caustic soda, nitric acid, Sulphuric acid, hydrochloric acid, and leaching roasted coal mine wastes. Due to high silica content, these techniques differ from those for bauxite minerals. Alkaline solutions, like sodium and calcium hydroxide, show promise but are cost-intensive. Sulphuric acid, combined with calcium hydroxide or sodium carbonate before roasting, yields efficient results, surpassing 90 % recovery. Microbial extraction also shows promise, but commercialisation faces equipment accessibility challenges. Heat treatment and optimal calcination temperatures are crucial, especially with acid reagents like Sulphuric and hydrochloric acids, preferred for insolubility in silica and better recovery. Sustainable alumina recovery requires further research into economically viable and ecologically friendly technology. This review underscores the need for feasible, high-purity alumina recovery techniques from mudstone and CFA for industrialisation.

Mapping the composite nature of clay matrix in mudstones: integrated micromechanics profiling by high-throughput nanoindentation and data analysis.

Mudstones and shales serve as natural barrier rocks in various geoenergy applications. Although many studies have investigated their mechanical properties, characterizing these parameters at the microscale remains challenging due to their fine-grained nature and susceptibility to microstructural damage introduced during sample preparation. This study aims to investigate the micromechanical properties of clay matrix composite in mudstones by combining high-speed nanoindentation mapping and machine learning data analysis. The nanoindentation approach effectively captured the heterogeneity in high-resolution mechanical property maps. Utilizing machine learning-based k-means clustering, the mechanical characteristics of matrix clay, brittle minerals, as well as measurements on grain boundaries and structural discontinuities (e.g., cracks) were successfully distinguished. The classification results were validated through correlation with broad ion beam-scanning electron microscopy images. The resulting average reduced elastic modulus (E r ) and hardness (H) values for the clay matrix were determined to be 16.2 ± 6.2 and 0.5 ± 0.5 GPa, respectively, showing consistency across different test settings and indenter tips. Furthermore, the sensitivity of indentation measurements to various factors was investigated, revealing limited sensitivity to indentation depth and tip geometry (when comparing Cube corner and Berkovich tip in a small range of indentation depth variations), but decreased stability at lower loading rates. Box counting and bootstrapping methods were applied to assess the representativeness of parameters determined for the clay matrix. A relatively small dataset (indentation number = 60) is needed to achieve representativeness, while the main challenges is to cover a representative mapping area for clay matrix characterization. Overall, this study demonstrates the feasibility of high-speed nanoindentation mapping combined with data analysis for micromechanical characterization of the clay matrix in mudstones, paving the way for efficient analysis of similar fine-grained sedimentary rocks. Supplementary Information: The online version contains supplementary material available at 10.1007/s40948-024-00864-9.

Effect of Nitrogen on Microbial Communities of Purple Mudstone Weathering Products in Southwest China: A Column Experiment.

Nitrogen application significantly affects microorganisms in agricultural ecosystems. However, it is still unclear how nitrogen application affects soil chemical properties and microbial communities in purple mudstone weathering products. In this study, a field soil column experiment was conducted in a typical purple soil area with four nitrogen fertilizer application gradients of 0 [CK], 280 [N1], 560 [N2], and 840 [N3] N kg ha-1. Nitrogen addition decreased the bacterial chao1 value and increased the bacterial evenness index. For both α- and ß-diversity, the effect of nitrogen addition on bacteria was much greater than that on fungi. Nitrogen addition significantly increased the relative abundance of Proteobacteria, Gemmatimonadetes, Bacteroidetes, and Ascomycota and decreased the relative abundance of Actinobacteria, Cyanobacteria, and Basidiomycota. Both pH and TC are the most important soil chemical properties influencing the bacterial and fungal communities. With the increases in the nitrogen application rate, the co-occurrence network complexity increased and then decreased. In summary, nitrogen fertilizer application could significantly change the soil chemical properties, microbial community diversity, composition, and co-occurrence network of purple mudstone weathering products. Among them, the N2 treatment (560 N kg∙ha-1) can more effectively stimulate the soil nutrients, enhance microbial network complexity, and promote further weathering of purple mudstone.

Investigation of the pore structure characteristics and fluid components of Quaternary mudstone biogas reservoirs: a case study of the Qaidam Basin in China.

Quaternary mudstone biogas reservoirs in the Qaidam Basin have shown great potential. However, complex pore structures with high clay contents and high heterogeneity limit the understanding of the storage and migration principles of these reservoirs. In this paper, HPMI and nitrogen adsorption experiments, in combination with NMR experiments under water saturation, centrifugation, various drying temperatures and other conditions, were adopted to determine the pore structure characteristics. Specifically, the reservoir space types and pore radius distribution characteristics were clarified. The cutoff values for different types of pores were identified based on the water-saturated mudstone NMR T2 spectra for full aperture distribution scales jointly characterized by mercury injection and nitrogen adsorption experiments. Furthermore, the three pore components and the saturation of different fluids were obtained. The research results indicate that the mudstone biogas reservoir has developed various reservoir spaces, and the pore size is primarily in the micronanometer range. The average total porosity reaches 27.28%, but the proportion of movable water pores is only 9.23% with poor fluid mobility, and the fluids in the pores are mostly capillary-bound water and clay-bound water. Among the different lithologies, argillaceous sand is more likely to become a good production layer.

A quantitative approach for sealing capacity evaluation of caprock in candidate of aquifer gas storage.

The gas sealing capacity of caprock (SCC) is one of the key factors that determine whether aquifer trap can be constructed into underground gas storage (UGS). However, no standard protocol for evaluating SCC of candidate aquifers has been proposed. Based on the core observation, laboratory experiment, and well logging data, the sealing capacity of the target aquifer caprock of Permian mudstone in D5 block of Litan sag, China, is quantitatively evaluated. The important parameters of mineral brittleness, permeability, breakthrough pressure (BP), mechanical brittleness, thickness, and areal extent that affect the SCC are determined. The results of specific tests and data statistics show that the caprock of D5 block is a low permeability rock with a permeability of 10-4 mD, and the BP of undisturbed rock is greater than 38 MPa. Although the brittle mineral quartz is abundant with an average of 38.38%, the mechanical brittleness is not strong under formation conditions. The direct caprock has a thickness of greater than 50 m, and on the top of it is a high-quality indirect caprock that complements the physical closure. The results of a mathematical evaluation model show that except for the sealing index of sample 2, all the other samples have optimal sealing capacity. The field interference test shows that the optimal sealing capacity of the caprock meets the requirements of the construction of underground gas storage (UGS). The rationality of the comprehensive evaluation model can provide a reference for similar evaluation projects in the future.

Effects of nitrogen fertilizers on the bacterial community diversity and the weathering of purple mudstone in Southwest China.

Introduction: Rock weathering is crucial in the development of soil. Yet the role of bacteria in the fine particle-forming process of purple mudstone is not fully understood, especially under nitrogen fertilization. Methods: In this study, the particles (0.25 mm to 1 mm) of purple mudstone from Penglai Group (J3p) were selected as the test material. Two nitrogen fertilizers, i.e., urea (U) and ammonium bicarbonate (AB), and four application levels (0, 280, 560, and 840 N kg∙ha-1) with 18 replications were designed in an incubation experiment. The weathering indices and bacterial community structure of the purple mudstone particles were investigated after 120 days of incubation. Results: The results showed that the weathering indices of purple mudstone particles in the AB treatment were higher than that in the U treatment at the same fertilization levels and a reducing trend was observed with increasing nitrogen fertilizer levels under the same nitrogen fertilizer application types. The diversities of the bacterial community were extremely significantly altered by nitrogen fertilizer application (p < 0.01). The effect of the nitrogen fertilizer application level on the beta diversity of the bacterial community (R2 = 0.34) was greater than that of the nitrogen fertilizer application type (R2 = 0.20). Through stepwise regression analysis, the positive effects of nitrification of Nitrobacter (Nitrolancea) (R2 = 0.36), the Phosphorous-dissolving bacteria (Massilia) (R2 = 0.12), and N-NO3- (R2 = 0.35) on the weathering indices of J3p purple mudstone particles could be observed. Structural equation modelling indicated that nitrogen fertilizer application level affects the abundance of the dominant species at the genus level (Nitrolancea and Massilia), and key environmental factor (N-NO3-), which in turn accelerated the weathering indices (59%). Discussion and Conclusion: Our findings imply that the enhancements of nitrification of Nitrobacter (Nitrolancea) and of phosphorus solubilization of Phosphorous-dissolving bacteria (Massilia) by nitrogen fertilization are the key factors affecting the weathering indices of J3p purple mudstone particles.

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths.

To investigate the strength and failure characteristics of silty mudstone using different stress paths, silt-like mudstone specimens were subjected to triaxial unloading tests. The results indicate the following. (1) When subjected to equivalent initial deviator stress levels and differing confining pressures, the peak stress, residual stress, and elastic modulus, exhibited during unloading, increased concordantly with greater initial confining pressure. Both the peak strain and residual strain increased with rising initial confining pressure. The increase in peak strain and residual strain initially decelerated, then noticeably increased, before ultimately decreasing again. Additionally, the unloading failure time and strain rate demonstrated a negative correlation as the confining pressure increased. (2) Under different initial deviatoric stress conditions, the peak stress, residual stress, and residual strain, under unloading confining pressure conditions, decreased as the initial deviatoric stress levels elevated. Conversely, the peak strain and elastic modulus initially increased, then decreased under increasing initial deviatoric stress conditions. The unloading failure time and strain rate were both observed to decrease as the initial deviatoric stress levels increased. (3) Utilizing the Mohr stress circle enabled the characterization of the shear strength variation in the specimens during the unloading process. The cohesion and internal friction angle remained relatively consistent across the different unloading stress paths appraised, with cohesion being greater in path I versus path II, whereas the internal friction angle exhibited an inverse relationship. (4) The specimen failed during unloading due to lateral expansion caused by unloading confining pressure and collapse failure. The failure fracture surfaces predominantly manifested shear failure morphologies.

Degradation of Typical Reverse Sand-Mudstone Interbedded Bank Slope Based on Multi-Source Field Experiments.

The bank slopes in the Three Gorges Reservoir area (TGRA) have experienced obvious deterioration under the action of the periodic fluctuations in the reservoir water level. Generally, laboratory tests have been used to reveal the evolution trend of the slope banks. However, this method has a certain degree of cross-scale problem, especially for the mechanical state in a complex environment. Therefore, in this study, we took the Yangjiaping bank slope in the TGRA as an example and proposed a comprehensive on-site detection method to further reveal the rock mass degradation phenomenon of this typical reverse sand-mudstone interbedded bank slope. Specifically, multi-scale laser scanning, cross-hole acoustic wave detection, and inclination measurements were performed to analyze the fractures, quality, and deformation of rocky banks. The results showed that the deterioration of the bank slope manifested as the expansion, deepening, and widening of the cracks, as well as the peeling off and loosening of rocky banks. Large-scale laser scanning revealed that the deterioration zone was deformed along large fracture zones and layers. Unlike limestone slopes, the intact sandstone underground might be degraded by changes in water. There are few inclinometers and no deformation or weak deformation, which requires long-term monitoring. The relevant research methods provide an important reference for determining the instability and failure trend of the reservoir bank slopes.

Regional mudstone compaction trends in the Vienna Basin: top seal assessment and implications for uplift history.

Seal quality assessment is not only essential in petroleum systems studies but also in the context of other geo energy applications such as underground hydrogen storage. Capillary breakthrough pressure controls top seal capacity in the absence of faults or other discontinuities. In basins that lack measured capillary pressure data (e.g., from drill cores), regional compaction-porosity trends can be used as a first prediction tool to estimate the capillary properties of mudstones. Mathematical compaction models exist but need to be calibrated for each basin. This study aims to establish a compaction trend based on theoretical models, then compare it with theoretical maximum hydrocarbon column heights inferred from true measured capillary pressure curves. Middle to upper Miocene mudstone core samples from the Vienna Basin, covering a broad depth interval from 700 to 3400 m, were investigated by X-ray diffractometry, with an Eltra C/S analyzer, and by Rock-Eval pyrolysis for bulk mineralogy, total organic carbon, and free hydrocarbon contents. Broad ion beam-scanning electron microscopy, mercury intrusion capillary porosimetry, and helium pycnometry were applied to obtain pore structural properties to compare the mathematical compaction models with actual porosity data from the Vienna Basin. Clear decreasing porosity depth trends imply that mechanical compaction was rather uniform in the central Vienna Basin. Comparing the Vienna Basin trend to global mudstone compaction trends, regional uplift causing erosion of up to ~ 500 m upper Miocene strata is inferred. A trend of increasing Rock-Eval parameters S1 and production index [PI = S1/(S1 + S2)] with decreasing capillary sealing capacity of the investigated mudstones possibly indicates vertical hydrocarbon migration through the low-permeable mudstone horizons. This observation must be considered in future top-seal studies for secondary storage applications in the Vienna Basin. Supplementary Information: The online version contains supplementary material available at 10.1007/s00531-023-02331-4.

Numerical Analysis Method That Considers Weathering and Water-Softening Effects for the Slope Stability of Carbonaceous Mudstone.

The mechanical behavior of carbonaceous mudstone deteriorates greatly when exposed to wet environments, and the precise evaluation of its slope stability has been a difficulty. This study aims to establish a numerical analysis method for the instability problems of its slopes; this method considers the effects of weathering and water-softening by establishing their mathematical expressions. The weathering and water-softening effects are reflected by variations in the mechanical properties (e.g., elastic modulus, angle of internal friction, and cohesion) of carbonaceous mudstone, with the depth following a logistic function and the shear strength parameters varying with wetting duration and degree of saturation. Their weathering and water-softening effects are reproduced with the use of the ABAQUS finite-element software and MATLAB programming. The proposed numerical method is applied to analyze the seepage field and stability of a highway cut slope with and without protection structures; the application results show that the proposed numerical method is reliable in analyzing the slope's instability problem. The use of the herringbone skeleton structures can reduce the water-softening effects and thus increase the safety factor of the slope. The findings of this study could provide guidance to the design and construction of highway cut slopes in mountain areas that are rich in carbonaceous mudstone.