Slope Mudstones Research Articles

Study on water–rock interaction failure mechanism and constitutive model of mudstone damaged by pre-peak disturbance

The mudstone disturbed by engineering has been damaged to varying degrees before the peak strength, which is often ignored in the existing research. To reveal the failure mechanism and mechanical characteristics of mudstone under the combined action of water and damage. Firstly, this study proposed a pre-peak damage variable (Da) to characterize the degree of damage before peak stress. Then, triaxial tests were conducted to assess the mechanical properties under different Da and the water–rock interaction. The failure mechanisms of mudstone were revealed from both macro and micro perspectives. Finally, a statistical damage constitutive model for mudstone was constructed, and the rationality of the model was verified using experimental results. The results indicate: (1) The reduction of strength parameters caused by engineering disturbance and water rock coupling is the main reason for the instability of mudstone slope after construction. (2) Mudstone strength decreases gradually and then sharply with increasing Da. The Da reduces mudstone strength by 10%-20% on the original conditions. The Da firstly reduces the cohesion, and then the friction angle. (3) The undamaged mudstone mainly exhibits a multiple-failure-plane mode, while damaged mudstone consists of a single-failure-plane mode. The reason is that the damage zone of mudstone is more likely to infiltrate water molecules, leading to lubrication and softening of the mineral particle skeleton, resulting in a single fracture surface failure mode. (4) The constitutive model for mudstone considering the water weakening and Da effectively describes the stress–strain relationship of damaged mudstone under the water–rock interaction. The research provides new insights into the evolution of soft rock damage considering disturbances and water weakening.

Influences of bedding angle and soaking time on the mechanical behaviour of silty mudstone: laboratory testing and theoretical modelling

Silty mudstone is highly susceptible to the influence of hot and humid environments, leading to the deterioration of its mechanical properties presenting a geohazard and even resulting in geological disasters. Accurately characterizing the effects of bedding and water–rock interaction on the mechanical behaviour of silty mudstone is a crucial prerequisite for the protection and reinforcement of silty mudstone slopes. To this end, uniaxial compression tests and Brazilian splitting tests were conducted to examine the mechanical properties of bedded silty mudstone. Based on the test results, the effects of bedding angle and soaking time on mechanical properties such as tensile strength, uniaxial compressive strength and elastic modulus of bedded silty mudstone were revealed. The test results showed that the tensile strength increased exponentially with increasing bedding angle. The observed split failure patterns of bedded silty mudstone encompassed splitting–pulling damage, shear damage and splitting damage. The uniaxial compressive strength of silty mudstone exhibited a U-shaped variation with an increase in bedding angle. The specimen with a bedding angle of 45° had the lowest uniaxial compressive strength at 7.64 MPa. Furthermore, the elastic modulus of silty mudstone was positively correlated with the bedding angle. The failure patterns of bedded silty mudstone under uniaxial compression included splitting-tension damage, shear-slip damage and splitting-shear damage. The saturated tensile strength, uniaxial compressive strength and elastic modulus of bedded silty mudstone exhibited an exponential decrease with increasing soaking time. The test data confirmed the applicability of the Jaeger equation to the uniaxial compressive strength of bedded silty mudstone. Subsequently, a modified Hoek–Brown failure criterion was derived by combining fracture mechanics theory and test results and introducing a softening factor. The parameters A , D and m in the above failure criterion decreased exponentially with increasing soaking time and an empirical Hoek–Brown failure criterion considering the soaking time was established. Compared with previous theoretical models, this model is more adaptable to the actual engineering situation, which results in more accurate calculations.

Influence of Loess–Mudstone Strata Structure on Slope Seismic Stability of Loess Plateau in China

The widely distributed loess–mudstone strata structure in the Loess Plateau of China is one of the fundamental reasons for the susceptibility and group occurrence of seismic landslides in the area. This study took the loess landslides induced by the Haiyuan earthquake as a case study. Through extensive field investigations, the loess cover thickness, mudstone dip angle, slope height, and slope angle were chosen as the influencing factors. Together with mathematical statistics and geotechnical tests, two models, one of a loess–mudstone slope and the other of a pure loess slope, were constructed. Their seismic stabilities under different slope angles and slope heights were compared to analyze the influence of the underlying mudstone strata on the loess slope seismic stability. Meanwhile, a sensitivity analysis of these strata factors affecting the seismic stability of the loess–mudstone slope was carried out based on the orthogonal test. The results showed that ignoring the underlying mudstone strata would lead to smaller calculation results than the actual situation. The sensitivity influence of the factors on the loess–mudstone slope seismic stability comprised the slope angle, loess cover thickness, slope height, and mudstone dip angle from high to low.

Study on the micro mechanism of damage caused by unloading confining pressure of silty mudstone

The excavation and unloading of silty mudstone slopes often precipitate slope instability and collapse. While abundant research addresses the macro deterioration of rock strength, the micro-damage mechanism of silty mudstone remains largely uncharted. To bridge this gap, our study innovatively utilized nano-materials to prepare silt-like mudstone subjected to the triaxial unloading test considering multiple paths. Then we delved into the variation in microstructure using Scanning Electron Microscopy (SEM), binarization, and fractal dimensions. Our findings reveal that: (1) The peak stress, residual stress, and residual strain of silt-like mudstone display a decreasing trend with an increase in initial deviatoric stress while the peak strain initially increases and subsequently decreases; (2) Following unloading, the crack propagation on fracture surface is dictated by both confining pressure and initial deviatoric stress, which profoundly impact porosity, particle fragmentation, and pore expansion; (3) As confining pressure and initial deviatoric stress elevate, the average morphology coefficient rises with a reduction in rate of change. The impact of unloading confining pressure on pore morphology diminishes; (4) The fractal dimension increases with increased confining pressure and initial deviatoric stress, with a transition in the pore surface from smooth to rough.

Stress response characteristics of BFRP anchors on loess mudstone slope under rainfall conditions

Stress response characteristics of BFRP anchors on loess mudstone slope under rainfall conditions

Sedimentologic and stratigraphic criteria to distinguish between basin‐floor and slope mudstones: Implications for the delivery of mud to deep‐water environments

AbstractDeep‐water mudstones overlying basin‐floor and slope sandstone‐prone deposits are often interpreted as hemipelagic drapes deposited during sand starvation periods. However, mud transport and depositional processes, and resulting facies and architecture of mudstones in deep‐water environments, remain poorly understood. This study documents the sedimentology and stratigraphy of basin‐floor and slope mudstones intercalated with sandstone‐prone deposits of the Laingsburg depocentre (Karoo Basin, South Africa). Sedimentologic and stratigraphic criteria are presented here to distinguish between slope and basin‐floor mudstones, which provide a tool to refine palaeogeographical reconstructions of other deep‐water successions. Several mudstone units were mapped at outcrop for 2500 km2 and investigated using macroscopic and microscopic core descriptions from two research boreholes. Basin‐floor mudstones exhibit a repeated and predictable alternation of bedsets dominated by low‐density turbidites, and massive packages dominated by debrites, with evidence of turbulent‐to‐laminar flow transformations. Slope mudstones exhibit a similar facies assemblage, but the proportion of low‐density turbidites is higher, and no repeated or predictable facies organisation is recognised. The well‐ordered and predictable facies organisation of basin‐floor mudstones suggest local point sources from active slope conduits, responsible for deposition of compensationally stacked muddy lobes. The lack of predictable facies organisation in slope mudstones suggests deposition took place in a more variable range of sub‐environments (i.e. ponded accommodation, minor gully/channel‐fills, levees). However, regional mapping of three mudstone units evidence basinward tapering and similar thicknesses across depositional strike. This geometry is consistent with the distal part of basin margin clinothems, and suggests laterally extensive mud delivery across the shelf edge combined with along‐margin transport processes. Therefore, the sedimentology and geometry of mudstones suggests that mud can be delivered to deep‐water dominantly by sediment gravity flows through point source and distributed regionally, during periods of up‐dip sand storage. These findings challenge the common attribution of deep‐water mudstones to periods of basin‐floor sediment starvation.

Root Functional Traits and Water Erosion-Reducing Potential of Two Indigenous C4 Grass Species for Erosion Control of Mudstone Badlands in Taiwan

In southern Taiwan, mudstone badland accounts for over 1000 km2 of the upstream region of watersheds. Rainstorms often induce interrill and surface erosion on the mudstone slopes. Furthermore, the large quantity of soils detached by surface runoff result in severe sedimentation in reservoirs. Thus, soil erosion control of mudstone badlands represents one of the most pressing problems in reservoir watershed management. Cynodon dactylon (L.) Pers. (Bermuda grass) and Eremochloa ophiuroides (Munro) Hack. (Centipedegrass) are two native predominant C4 grass species appearing on mudstone badlands. They play a key role in erosion control and the revegetation of mudstone slopes. Nevertheless, their root functional traits and water erosion-reducing potential have not been investigated. In this study, the root traits were examined. Vertical pullout and tensile tests were conducted to measure root pullout resistance and root tensile strength. Hydraulic flume tests were also performed to evaluate their water erosion-reducing potentials. The results demonstrated that the root systems of C. dactylon and E. ophiuroides grasses all belonged to the fibrous M-type. C. dactylon had remarkably better root traits compared to those of E. ophiuroides. Furthermore, the root tensile resistance of C. dactylon was remarkably higher than that of E. ophiuroides. In addition, hydraulic flume tests showed that C. dactylon has remarkably smaller soil detachment rates than that of E. ophiuroides. Altogether, our data clearly show that C. dactylon has better root traits, root pullout resistance, root tensile resistance and water erosion-reducing potential than E. ophiuroides and is more suitable for erosion control of mudstone badland. Further studies on large-scale implementation techniques of these species for efficient vegetation restoration are needed.

Failure Mechanism of Weak Rock Slopes considering Hydrological Conditions

Landslides frequently occur on cutting slopes with weak rock during the rainy season. An understanding of the failure mechanism is essential for designers to adopt effective measures to mitigate potential impacts caused by landslides. Based on an enormous number of highway slope practices in Guangdong Province, China, this paper presents a whole train of numerical investigations on the hydraulic response and stability of weak rock slopes subject to a subtropical climate where the average annual rainfall is approximately 1,800 – 2,000 mm. This study explored a different failure mechanism of three different types of weak rock slopes in a modeling approach. A physics-based slope model coupled with a hydrological model is used to simulate the factor of safety and porewater pressure development of unsaturated slopes with various rock masses under diverse rainfall scenarios. The input parameters were determined from the rainfall intensity–duration–frequency (IDF) curves of regional hydrological conditions to comprehensively consider the impact of rainfall. The general suction range of rock masses was acquired using three hydraulic characteristic curves associated with sandstone, siltstone, and mudstone. Furthermore, the failure models of weak rock slopes under different rainfall conditions were assessed. Based on the theory of regional hydrology, a unified rainfall and intensity-duration threshold for different weak rock slopes was established. The results indicate that both siltstone and mudstone slopes are more sensitive to long-term rainfall than short-term rainstorms. However, the sandstone slope appears to be unstable under regional rainfall conditions of 40-year return periods. This also proves that the instability mode of the siltstone slope exhibits a retrogressive type in which the sliding surface of the slope increases with an increase in rainfall duration. Translational shallow landslides occurred in the transient saturation zone of the sandstone slope, and the depth of the failure plane was independent of rainfall patterns and duration. This study revealed the instability mechanism and provided a robust early warning measure for weak rock slopes by fusing engineering geology and regional hydraulics, providing insightful information for mitigating potential landslide disasters. The proposed model can also be used to predict the possible infiltration depth of rainfall and the spatial location of the sliding surface, prior to construction to assess whether slope stabilization and reinforcement measures are needed.

Hydrophobic Polymeric Additives toward a Long-Term Robust Carbonaceous Mudstone Slope.

Slopes with carbonaceous mudstone (CM) are widely distributed in the southwest of China and have experienced numerous geological disasters in special climate, especially in rainfall conditions. Therefore, novel materials to stabilize CM slopes have attracted increasing interests. However, developing ultra-stable and cost-effective additives for CM slopes is still a great challenge. Herein, a hydrophobic polymeric material (polyvinylidene fluoride, PVDF) is investigated as an additive to enhance the mechanical strength and long-time stability of CM slopes. The PVDF is uniformly dispersed in CM matrix via interfacial interaction. The contact angle of the PVDF-modified carbonaceous mudstone (PVDF-MCM) can reach as high as 103.95°, indicating an excellent hydrophobicity. The unconfined compressive strength (UCS) and tensile strength (TS) of PVDF-MCM have been intensively enhanced to 4.07 MPa and 1.96 MPa, respectively, compared with ~0 MPa of pristine CM. Moreover, the UCS and TS of PVDF-MCM remain at 3.24 MPa and 1.03 MPa even after curing for 28 days in high humidity conditions. Our findings show that the PVDF can improve the hydrophobicity of CM significantly, which leads to super mechanical stability of PVDF-MCM. The excellent performance makes PVDF a promising additive for the development of ultra-stable, long-lifetime and cost-effective carbonaceous mudstone slopes.

Strontium isotope stratigraphy (SIS) dating of the Bathonian regression in western Tethys (Mallorca island)

The Sr-isotope stratigraphy (SIS) method has been applied to a Middle Jurassic section of Mallorca (Coves d’Arta) to improve its age control. The Middle Jurassic stratigraphy of this section, more than 220 m thick, is unique in the Mallorca island due to the existence of slope mudstones (Sa Talaia mudstones) evolving upward to a shallow oolitic platform (Coves d’Arta limestones). These slope mudstones and oolitic platform prograde over slope deposits of the Cutri Formation, without any evidence of unconformity in between. The age of this distinctive progradation to a shallow oolitic platform in Coves d’Arta is still unresolved due to the scarcity of age diagnostic fossils through the studied succession and the ambiguity of the previous information, despite being crucial information for the paleogeographic reconstructions of the Middle Jurassic of the Balearic Domain and therefore of the Western Tethys. New age estimates using the SIS method throughout the Coves d’Arta succession has allowed to obtain 87Sr/86Sr values ranging from 0.706976 to 0.707082, supporting an age compatible with the Early–Late Bathonian (~ 168.3–166.1 Ma) for the analysed portion of the succession (Upper Member of the Puig d’en Pare Formation to the transition to the Coves d’Arta limestones). This age has important implications for improving the stratigraphic position of other stratigraphic Jurassic units (i.e. Cutri Formation) and for the paleogeographic reconstruction of the Middle Jurassic of Mallorca. In consequence, the toe of slope resedimented oolitic bodies (i.e. Cutri Formation), which deposited in large areas of Mallorca (Serres de Llevant Domain), changed laterally, toward marginal highs, to shallow Bahamian oolitic platforms (Coves d’Arta limestones), which end in a regressive phase of a Middle Jurassic (Bathonian) platform—slope system. This Bathonian regressive sequence is compared with others recognized along Tethyan basin that began at the end of the Bajocian and culminated in the Middle–Late Bathonian.

Biomarker constraints on Mediterranean climate and ecosystem transitions during the Early-Middle Miocene

Paleoenvironmental and paleoclimatic variations experienced by the Mediterranean region during the Miocene Burdigalian-Langhian interval have been investigated through analysis of biomarker signals (n-alkanes and glycerol dialkyl glycerol tetraethers, GDGTs) from slope mudstones of the northern Apennines (Marne di Vicchio Fm). Terrestrial signatures in marine sediments reflected by preserved long-chain n-alkanes with a identifiable odd-over-even carbon number predominance attest to the thermal immaturity of the sedimentary rock. Abundances of n-C27, n-C29 and n-C31 alkanes, coupled with the carbon isotopic signatures of the n-C31 homologue suggest that Mediterranean vegetation crossed a transition phase adapting to arid conditions that may favored a shift from woodland to wooded grassland during the Middle Miocene. This ecosystem evolution could have been favored by the passage from warm humid conditions to a warm drier climate, as indicated by GDGT-based TEX86 and BIT indexes. Strong similarities between these Mediterranean biomarker records and those from the Atlantic (DSDP Sites 94, 516, 608) imply a constant connection of the western Mediterranean to the Atlantic Ocean from ~19 Ma to ~14.5 Ma.

Runoff and soil loss from small plots of erosion-prone marl soil inoculated with bacteria and cyanobacteria under real conditions

Land degradation is a major global concern that is exacerbated in the erosion-prone marl and calcium carbonate-rich mudstone slopes. Several studies have therefore focused on finding ways to inhibit soil erosion among which, soil inoculation has been recently introduced as a new technique. However, the success of such treatment has not been adequately taken into account. Following this, in this study, we assessed the hydrological responses of an erosion-prone marl soil due to surface inoculation of bacteria and cyanobacteria. The individual bacteria and cyanobacteria and their combination were inoculated (in three repetitions) on 0.5 m × 0.5 m-sized plots filled by marl soil from the Marzanabad Region in the north of Iran. The entire plots were thoroughly exposed to natural conditions in an open area at the campus of Faculty of Natural Resources of Tarbiat Modares University in Noor, Mazandaran Province, Iran. After 32 days of inoculation, five erosive natural rainfalls occurred on the experimental plots, from 10 to Jan. 29, 2018. The rainfalls on control plot led to a relatively high runoff yield (i.e., 223–2010 ml) and coefficient (i.e., 2.3–7.6%), a considerable soil loss (i.e., 1.32–17.96 g), and sediment concentration (i.e., 2.4–9 g l−1). Whilst, in the inoculated (i.e., bacteria, cyanobacteria, and bacteria + cyanobacteria) plots, the runoff volume, runoff coefficient, soil loss, and sediment concentration varied between 56 and 1116 ml, 2.3–9.4%, 0.16–4.04 g, and 1.01–3.61 g l−1, respectively. It, therefore, verified that the soil inoculation decreased the runoff yield and coefficient (29–77%), soil loss (77–89%), and sediment concentration (60–76%), as compared to the control. On the whole, we found that the soil inoculation technique could be considered as a bio-strategy to conserve/restore marl soil lands, where the viability of conventional methods is low.

River‐dominated and tide‐influenced shelf‐edge delta systems: Coarse‐grained deltas straddling the Early–Middle Jurassic shelf–slope break and transforming downslope, Lajas–Los Molles formations, Neuquén Basin, Argentina

AbstractThe three‐dimensional facies and architecture variability of shelf‐edge deltaic units cropping out at the transition between the Lower–Middle Jurassic Lajas and Los Molles formations of southern Neuquén Basin, Argentina, is presented here, as well as their stratigraphic relationship to uppermost deep‐water slope channel systems. Deep‐water, slope mudstones with thin turbidite beds merge upward with prodelta mudstones and thin sandstones, which are truncated by delta‐front to mouth‐bar sandstones. The latter sandstones are then downcut by large‐scale, trough cross‐stratified coarse‐grained sandstones and conglomerates of distributary channel systems and along‐strike, amalgamated with cross‐bedded sandy units showing evidence of tidal reworking. Proximal–distal facies and architecture variability within a shelf‐edge deltaic succession demonstrates that distributary channel‐complexes become wider and deeper basinward, forming channelized river‐dominated distributary fairways separated by tidally reworked inter‐distributary sand belts at the shelf edge. Evidence from depositional‐dip oriented outcrops shows a lack of collapsed and slumped strata at the shelf edge, and that the coarse shelf‐edge distributary channel fills continue far down the deepwater slope, and conglomerates transform to become high‐density turbidites to mainly thick‐bedded, sand‐matrix‐supported debrites. The interplay between flood tides and river currents is interpreted to have primarily modulated the focusing of river drainages, and consequently coarse‐grained sediment transport, along preferential routes on the outer‐shelf to shelf‐edge and down onto the slope. This contribution documents a unique example of coarse‐grained (mostly conglomeratic) shelf‐edge delta systems, tying bed‐scale facies and architecture data to a seismic‐scale shelf‐margin morphology, thus providing outcrop analogue data for the characterization of shelf‐edge delta systems in the subsurface.

Effects of remoulding and wetting-drying-freezing-thawing cycles on the pore structures of Yanji mudstones

The pore structure governs the physical and mechanical behaviours of geomaterials, thereby affecting the stability of the infrastructures built on these materials. This study investigated the effects of remoulding and wetting-drying-freezing-thawing (WDFT) cycles on the pore structures of two Yanji mudstones using scanning electronic microscopy (SEM), mercury intrusion porosimetry (MIP) and nitrogen adsorption (NA) techniques. The results show that the pores of both the yellow-brown and magenta mudstones become rounder and more disordered after remoulding. Remoulding leads to an increase in the inter-aggregate pore volume and a decrease in the intra-aggregate pore volume because of the exposure of intra-aggregate pores after crushing and the compaction of aggregates during the compression process. The W-D-F-T cycles make the pores of the remoulded yellow-brown mudstone more disordered and flatter and induce an increase in the inter-aggregate pore volume due to the formation of cracks and large pores. Meanwhile, the intra-aggregate pore volume decreases owing to the contraction of aggregates during the drying process. According to the increased inter-aggregate pore volume and decreased intra-aggregate pore volume, an increase in the hydraulic conductivity and a decrease in the shear strength can be expected after remoulding and W-D-F-T cycles, which decrease the stability of mudstone slopes.

Pore-water chemistry and its influence on rock mechanical properties and hydrogeophysical processes in a mudstone slope in the southwestern Taiwan badlands

Bedrock characteristics and its influence on hydrogeophysical processes in a Plio-Pleistocene mudstone slope were examined in southwestern Taiwan. Previous works carried out in this area indicated seasonal patterns of the bedrock physical properties and deterioration of the mechanical strength during weathering to generate extremely high rates of erosion during heavy rainfall, thereby forming badland topography. This area has a humid subtropical climate that is characterised by distinct dry and rainy seasons. During the rainy season, high rates of erosion of the weathered mudstone occur during rainfall events. To investigate impact of characteristics of bedrock physical properties on hillslope weathering and erosion processes in this area, we analysed the pore-water chemistry, specific surface area, and swelling of the mudstone of the studied slope and performed in situ monitoring of water content and pore-water electrical conductivity at 2.5–40 cm depths near the slope surface. The results indicate that the mudstone contains saline pore water, is categorized as dispersive, and has a dense fabric, thereby favouring the occurrence of rock mechanical breakdown due to chemical osmosis. The influence of rock mechanical properties and bedrock behaviour on the hydrogeophysical processes near the slope surface varies with the season. During the dry season, the water content of the mudstone near the slope surface decreases, causing desiccation cracks to form and concentrating salt on rock surfaces. Water contents at 40 cm depths increased within 1 h after rainfalls during the monitoring intervals of the dry season, suggesting that surface water infiltrates rapidly by gravity into networks of cracks during infrequent rain events. During the following rainy season, intense rainfall events moisten the slope surface layer and increase the volume of the mudstone by swelling caused by chemical osmosis. The swelling is associated with an enlargement of the pore size of the mudstone during the dilution of saline water by fresh rainwater, with the greatest amount of swelling occurring at or near the surface where salt is most concentrated. Water contents at 40 cm depths scarcely responded to rainfalls during the monitoring intervals of the rainy season, suggested that this swelling closes desiccation cracks and prevents surface water from migrating downwards into the slope. The resulting seasonal erosion occurs by slope surface wash caused by intense rain during the late rainy season. The newly exposed mudstone on the slope starts to become desiccated during the subsequent dry season, and a new cycle of weathering commences.

Application for Terrestrial LiDAR on Mudstone Erosion Caused by Typhoons

Storms are important agents for shaping the Earth’s surface and often dominate the landscape evolution of mudstone areas, by rapid erosion and deposition. In our research, we used terrestrial scanning LiDAR (TLS) to detect surface changes in a 30 m in height, 60 m in width mudstone slope. This target slope shows the specific erosion pattern during extreme rainfall events such as typhoons. We investigate two major subjects: (1) how typhoon events impact erosion in the target slope, and (2) how rills develop on the hillslopes during these observation periods. There were three scans obtained in 2011, and converted to two observation periods. The permanent target points (TP) method and DEMs of differences were used to check the accuracy of point cloud. The results showed that the average erosion rate was 5 cm during the dry period in 2011. Following the typhoons, the erosion rate increased 1.4 times to 7 cm and was better correlated with the increase in the rainfall intensity than with general precipitation amounts. The hillslope gradient combined with rainfall intensity played a significant role in the geomorphic process. We found that in areas with over 75° gradients with larger rainfall intensity showed more erosion that at other gradients. The gradient also influenced the rill development, which occurred at middle and low gradients but not at high gradients. The rills also created a transition zone for erosion and deposition at the middle gradient where a minimal change occurred.

Criteria for recognizing shelf‐slope clinoforms in outcrop; Jurassic Lajas and Los Molles formations, S. Neuquén Basin, Argentina

AbstractSeismic‐reflection data show that most deepwater (>200 m water depth) basins are filled by sand and mud dispersed across clinoformal geometries characterized by gently dipping topsets, steeper foresets and gently dipping bottomsets. However, the entire geometry of these ubiquitous clinoforms is not always recognized in outcrops. Sometimes the infill is erroneously interpreted as “layer cake” or “ramp” stratigraphy because the topset‐foreset‐bottomset clinoforms are not well exposed. Regional 2‐D seismic lines show clinoforms in the Lower to Middle Jurassic Challaco, Lajas, and Los Molles formations in S. Neuquén Basin in Argentina. Time equivalent shelf, slope and basin‐floor segments of clinoforms are exposed, and can be walked out in hundreds of metres thick and kilometres‐wide outcrops. The studied margin‐scale clinoforms are not representing a continental‐margin but a deepwater shelf margin that built out in a back‐arc basin. Lajas‐Los Molles clinoforms have been outcrop‐mapped by tracing mudstones interpreted as flooding surfaces on the shelf and abandonment surfaces (low sedimentation rate) in the deepwater basin. The downslope and lateral facies variability in the outcrops is also consistent with a clinoform interpretation. The Lajas topset (shelf) is dominated by fluvial and tidal deposits. The shelf‐edge rollover zone is occasionally occupied by a 40–50‐m‐thick coarse‐grained shelf‐edge delta, sometimes incising into the underlying slope mudstones, producing oblique clinoforms expressing toplap erosion on seismic. A muddy transgressive phase capping the shelf‐edge deltas contains tidal sandbodies. Shelf‐edge deltas transition downslope into turbidite‐ and debris flow‐filled channels that penetrate down the mud‐prone Los Molles slope. At the base‐of‐slope, some 300m below the shelf edge, there are basin‐floor fan deposits (>200 m thick) composed of sandy submarine‐fan lobes separated by muddy abandonment intervals. The large‐scale outcrop correlation between topset–foreset–bottomset allows facies and depositional interpretation and sets outcrop criteria recognition for each clinoform segment.

Failure mechanism of a mudstone slope embedded with steep anti-dip layered sandstones: case of the 2016 Yanchao catastrophic landslide in Taiwan

On September 28, 2016, the torrential rainfall carried by Typhoon Megi induced a catastrophic mudstone landslide in the Yanchao District of Kaohsiung City, Taiwan. The total volume of the sliding mass was approximately 8700 m3, which blocked an industrial road and displaced a duplex house in the downslope, leading to three deaths. Unprecedentedly, the 2016 Yanchao landslide was large and quickly raised public awareness regarding the possibility of large landslides that could occur in the nearby mudstone areas. Based on field surveys, topographic and geological maps, unmanned aerial vehicle (UAV) photography, and remote-sensing imagery, the failure mechanism of the 2016 Yanchao landslide is described in this study. The results revealed that steep anti-dip layered sandstones embedded with the mudstones play a critical role in large, rainfall-induced landslides. In the case of Yanchao landslide, the bedding joint between two formations was associated with the runoff infiltrating the low permeability mudstone. The kinematic process of the landslide consisted of two phases: a circular failure in the lower formation (alternation of mudstone and sandstone) and the subsequent regressive failure in upper formation (thick sandstone interbedded with mudstone). This study discloses the role of steep anti-dip layered sandstone influencing mudstone slope failure behaviors and presents a preliminary guide for assessing large, rainfall-induced landslides in mudstones. The results could also provide useful information for calibrating the numerical modeling of large landslides that may occur in the mudstone area in the future.

Landslide from Ben Bulben

In the days leading up to the Republic of Ireland's 2018 abortion referendum, activists from an organization called Sligo for Life erected a 100-metre-tall 'NO' sign made of plastic sheeting high on Ben Bulben in the Dartry Mountains. Over a 24-hour period, reactions played out in the temporary performance space of social media as a spontaneous, improvised performance of satirical images and comments, circulated predominantly on Twitter and Instagram. In this ecofeminist scramble through the limestone and mudstone slopes of Ben Bulben, I propose that at a crucial moment during high-stakes campaigning the performativity of the protest and its aftermath came to stand in for a material and metaphorical peak in what was subsequently widely pronounced as a 'landslide' victory for the 'yes' campaign when the referendum outcome was announced on 26 May. The initial performance on the mountain and its mediatized extension signalled an affective juncture in campaigning that belonged on but also went far beyond Ben Bulben's actual summit, contesting the gendered mountain space in the process. By reasserting Ben Bulben's apparently immovable historical, cultural and ecological significance, the responding community ultimately temporarily communicated the mountainside as an unstable and precipitous -- if not entirely feminist - space.

Facies-dependent δ13C variation and diagenetic overprinting at the onset of the Sturtian glaciation in North-East Greenland

Time-significant surfaces are used to construct a stratigraphic test of the intrabasinal reproducibility of a 16‰ Neoproterozoic carbon-isotope (δ13C) anomaly in the NE Greenland Caledonides. The δ13C excursion from +6‰ to −10‰ occurs in the carbonate-dominated Andrée Land Group and lies below glacial diamictites of the Tillite Group commonly correlated as Sturtian in age (∼720 Ma) and has been widely interpreted to record a global isotopic event reflecting a perturbation in the carbon cycle preceding the initiation of the snowball ice age. δ13C stratigraphic patterns were determined in two strike sections with relatively shallow platform deposits at Kap Weber and slope deposits on Ella Ø preserved directly below the first evidence for glaciation. The top and bottom of the δ13C profile was bounded by contiguous chronostratigraphic surfaces including an unconformity (sequence boundary) at the base recognisable in both sections and a subaerial exposure surface with a basinal correlative conformity at the top. The δ13C profile at Kap Weber shows δ13C values of +6‰ that drop to −8‰ in fine-grained slope deposits before returning to +6‰ in platform carbonates at the base of the glacial diamictite. The slope section on Ella Ø shows similar values for platformal carbonates of +6‰ with a similar drop to ∼−10‰ in slope deposits, but this section lacks the return to platform deposits evident at Kap Weber beneath the diamictite as well as a return to positive δ13C values. The absence of the platformal sediments and positive δ13C values on Ella Ø cannot be attributed to erosional truncation because the contact in this section shows a conformable, interbedded transition into the glacial deposits indicating that a continuous record is preserved. This disparity in δ13C values below the base of the Tillite Group suggests that the most negative δ13C values recorded in slope mudstone facies (−10‰) occur near synchronously with values of +6‰ on the platform. Elemental mapping of the mudstone facies indicates that carbonate is largely pore-filling and authigenic, representing a secondary phase that is unlikely to record a seawater value. Elevated δ13C values in shallow inner-ramp carbonate intervals may record locally modified seawater enriched in 13C by photosynthesis and evaporation. The excursion in δ13C values in the upper Andrée Land Group is therefore interpreted to result from a shift in facies from platform carbonates to carbonate cemented and diagenetically overprinted mudstone and does not record the secular change in seawater δ13C used for correlation or interpretation of biogeochemical events preceding the snowball ice age.