Geosciences, Volume 12, Issue 6 (June 2022) – 36 articles

We present a data set of calcite twinning strain results (n = 209 samples; 9919 measured calcite twins) from the internal Alpine nappes northwestward across the Alps and Alpine foreland to the older extensional margin along the Atlantic coast in Ireland. Along the coast of Northern Ireland, Cretaceous chalks and Tertiary basalts are cross-cut by calcite veins and offset by calcite-filled normal and strike-slip faults. Both Irish sample suites (n = 16 with four U-Pb vein calcite ages between 70–42 Ma) record a sub-horizontal SW-NE shortening strain with vertical extension and no strain overprint. This sub-horizontal shortening is parallel to the margin of the opening of the Atlantic Ocean (~58 Ma), and this penetrative fabric is only observed ~100 km inboard of the margin to the southeast. The younger, collisional Alpine orogen (~40 Ma) imparted a stress–strain regime dominated by SE-NW sub-horizontal shortening ~1200 km northwest from the Alps preserved in Mesozoic limestones and calcite veins (n = 32) in France, Germany and Britain. This layer-parallel shortening strain (−3.4%, 5% negative expected values) is preserved across the foreland in the plane of Alpine thrust shortening (SE-NW) along with numerous outcrop-scale contractional structures (i.e., folds, thrust faults). Calcite veins were observed in the Alpine foreland in numerous orientations and include both a SE-NW layer-parallel shortening fabric (n = 11) and a sub-vertical NE-SW vein-parallel shortening fabric (n = 4). Alpine foreland strains are compared with twinning strains from the frontal Jura Mountains (n = 9; layer-parallel shortening), the Molasse basin (n = 26; layer-parallel and layer-normal shortening), Pre-Alp nappes (n = 39; layer-parallel and layer-normal shortening), Helvetic and Penninic nappes (Penninic klippe; n = 46; layer-parallel and layer-normal shortening plus four striated U-Pb calcite vein ages ~24 Ma) and calcsilicates from the internal Tauern window (n = 4; layer-normal shortening). We provide a chronology of the stress–strain history of the European plate from 58 Ma through the Alpine orogen. Full article

Climate warming in the Arctic, accompanied by changes in permafrost soil properties (mechanical, thermal, filtration, geophysical), is due to increasing unfrozen pore water content. The liquid component in frozen soils is an issue of key importance for permafrost engineering that has been extensively studied since the beginning of the 20th century. We suggest a synthesis and new classification of various experimental and calculation methods for the determination of unfrozen water content. Special focus is placed on the method of applying measurements to the water potential, which reveals the impact of permafrost warming on unfrozen water content. This method was applied to natural soil samples collected from shallow permafrost from northern West Siberia affected by climate change, and confirms the revealed trends. The obtained results confirm that unfrozen water content is sensitive not only temperature but also particle size distribution, salinity, and the organic matter content of permafrost soils. Full article

Dry-stone retaining walls can be found worldwide and constitute critical assets of the built heritage for many sloped territories, holding cultural and economic value. Their design currently follows empirical rules, though the first steps towards a static safety assessment have recently been proposed in the scientific and engineering literature. However, the seismic design of these structures still lacks research studies. Therefore, this work conducts discrete element simulations to assess their dynamic behaviour. First, the approach is validated through existing scaled-down shaking table experiments, and it is found that the numerical simulations are conservative (i.e., on the safe side). Next, full-scale dry-stone retaining walls are subjected to harmonic excitations as an idealisation of earthquakes. Finally, based on a simplified limit-equilibrium analytical tool, their seismic behaviour factor is estimated for the first time in the literature, which falls within the proposed values of the European standards (Eurocode 8). This will allow engineers to adopt a validated behaviour factor in practice to assess and design dry-stone retaining walls with a pseudo-static approach. Full article

Fieldwork teaching methodology (FTM) and active learning are effective strategies for geoscience education. However, traditional field trips require significant resources, time, physical abilities, and the expertise of teachers. In this study, we provide a supplementary virtual field trip experience by showing how different kinds of geoscience videos can be spatially organized into one digital interactive virtual environment. Here, we present the Google Earth Geoscience Video Library (GEGVL) which uses Google Earth and location-specific videos about Earth events, to create a virtual field-based learning experience. Using Google Earth, GEGVL organizes field-based videos by location and links pertinent non-field-based videos, and allows users to roam the globe in search of geoscientific videos that are pertinent to them or their students. Currently, GEGVL contains 150 videos organized into ten different geoscience disciplines: Plate Tectonics, Minerals, Structural Geology, Metamorphism, Magmatism, Hydrology, Environmental Science, Sedimentology, Paleontology, and Paleomagnetism. Despite stability challenges with Google Earth integration, results of user surveys among lower-division undergraduates show that the design logic of GEGVL is a promising virtual field-based learning organizer for increasing students’ interest in and helping them learn about Earth sciences. Full article

The literature has highlighted the behaviour of several weak rocks and the role of structure in determining them. The need for understanding their behaviour is due to the instabilities or collapse that may involve human settlements built on these materials which are widespread all over the world. In previous studies, the authors highlighted that in Marsala, Sicily, underground calcarenite quarries have been involved in a number of collapses that have seriously damaged numerous overlying buildings. In order to investigate the influence of destructuration on the behaviour of the calcarenite of Marsala, this paper presents a preliminary investigation of the compression behaviour of the intact rock and of the same weak rock in a destructured state. A petrographic and physical characterisation of the material was carried out together with oedometer and isotropic compression tests. The investigation has highlighted behaviour not previously identified for other weak rocks in which the pores seem to play a key role; the destructured material can no longer be considered, as generally assumed for other weak rocks, as a reference. Full article

Data analysis methods have scarcely kept pace with the rapid increase in Earth observations, spurring the development of novel algorithms, storage methods, and computational techniques. For scientists interested in Mars, the problem is always the same: there is simultaneously never enough of the right data and an overwhelming amount of data in total. Finding sufficient data needles in a haystack to test a hypothesis requires hours of manual data screening, and more needles and hay are added constantly. To date, the vast majority of Martian research has been focused on either one-off local/regional studies or on hugely time-consuming manual global studies. Machine learning in its numerous forms can be helpful for future such work. Machine learning has the potential to help map and classify a large variety of both features and properties on the surface of Mars and to aid in the planning and execution of future missions. Here, we outline the current extent of machine learning as applied to Mars, summarize why machine learning should be an important tool for planetary geomorphology in particular, and suggest numerous research avenues and funding priorities for future efforts. We conclude that: (1) moving toward methods that require less human input (i.e., self- or semi-supervised) is an important paradigm shift for Martian applications, (2) new robust methods using generative adversarial networks to generate synthetic high-resolution digital terrain models represent an exciting new avenue for Martian geomorphologists, (3) more effort and money must be directed toward developing standardized datasets and benchmark tests, and (4) the community needs a large-scale, generalized, and programmatically accessible geographic information system (GIS). Full article

The Puquios of the Salar de Llamara in the Atacama Desert, northern Chile, is a system of small lakes that is characterized by evaporitic mineral deposition and that commonly hosts microbial communities. This region is known for its extreme aridity, solar irradiance, and temperature fluctuations. The Puquios are a highly diverse ecosystem with a variety of sedimentary bottom types. Our previous results identified electrical conductivity (EC) as a first-order environmental control on bottom types. In the present paper, we extend our analysis to examine the effects of additional environmental parameters on bottom types and to consider reasons for the importance of EC as a control of sedimentology. Our results identify microbially produced extracellular polymeric substances (EPS) as a major player in the determination of bottom types. The relative amounts and properties of EPS are determined by EC. EPS, in turn, determines the consistency of bottom types, exchange of bottom substrate with the overlying water column, and mineral precipitation within the substrate. Low-EC ponds in the Puquios system have flocculent to semi-cohesive bottom types, with low-viscosity EPS that allows for high-exchange with the surrounding waters and mineral precipitation of granular gypsum, carbonate, and Mg–Si clay in close association with microbes. Ponds with elevated EC have bottom types that are laminated and highly cohesive with high-viscosity EPS that restricts the exchange between sediments and the surrounding waters; mineral precipitation in these high-EC ponds includes granular to laminated gypsum, carbonate and Mg–Si, which also form in close association with microbes. Bottom types in ponds with EC above the threshold for thriving benthic microbial communities have insufficient EPS accumulations to affect mineral precipitation, and the dominant mineral is gypsum (selenite). The variations in EPS production throughout the Puquios, associated with heterogeneity in environmental conditions, make the Puquios region an ideal location for understanding the controls of sedimentary bottom types in evaporative extreme environments that may be similar to those that existed on early Earth and beyond. Full article

Here it is shown that the crystal radii of ions are represented by a simple relation r_cryst = r_B³√(10 m)/N, where m and N are small integer numbers determined by the principal and orbital quantum numbers and valence, and r_B is the Bohr radius. The relation holds to within 5%. This finding elucidates that despite their original definition crystal- and ionic radii are not classical but represent the limiting case of spherically symmetric spatial averages of the valence electron states and, therefore, are able to reflect changes in the valence electron configuration with pressure and temperature. The relation is used to show general pressure-effects on the radii, in particular the increase of bond coordination with pressure and metallization as limiting state. The pressure-effect is exemplified for the elements Mg and Si as major constituent cations in the Earth’s mantle, and for Ba as a large ionic lithophile element. It is found that at least to about 140 GPa the radii depend linearly on pressure. Further, if a generalization is permitted for just three elements, the pressure-dependence is lesser the higher the charge of the ion. The three elements exhibit a much weaker pressure-dependence than previously calculated non-bonding radii. For mantle geochemistry this finding implies that elements incompatible in the upper mantle remain so for the main lower mantle minerals bridgmanite and periclase and are hosted by davemaoite. Full article

The investigation of mass movements is of major interest in mountain regions as these events represent a significant hazard for people and cause severe damage to crucial infrastructure. The torrential rainfall event that mainly occurred on the 14 July 2021 in western Central Europe not only led to severe flooding catastrophes (e.g., Meuse, Ahr and Erft rivers) but also triggered hundreds of mass movements in the low mountain range. Here, we investigate a hillslope debris flow that occurred in Biersdorf in the Eifel area (Rhenish Massif, Rheinland-Pfalz) using a comprehensive geomorphological–geophysical approach in order to better understand the triggering mechanisms and process dynamics. We combined field studies by means of Electrical Resistivity Tomography (ERT), Direct Push Hydraulic Profiling (HPT) and sediment coring with UAV-generated photogrammetry, as well as debris flow runout modelling. Our results show that for the Biersdorf hillslope debris flow, the geomorphological and geotectonic position played a crucial role. The hillslope debris flow was triggered at a normal fault separating well-draining limestones of the Lower Muschelkalk, from dense weathered clay and sandstones of the Upper Buntsandstein. The combination of a large surface runoff and strong interflow at the sliding surface caused a transformation from an initial translational slide into the high-energy and widespread hillslope debris flow. We further created and validated a stand-alone model of the debris flow on a local scale achieving promising results. The model yields a 97% match to the observed runout area as well as to deposition spreads and heights. Thus, our study provides a pathway for analyzing hillslope debris flows triggered by torrential rainfall events in low mountain ranges. General knowledge on hillslope debris flows, risk assessment and hazard prevention were improved, and results can be transferred to other regions to improve risk assessment and hazard prevention. Full article

The planktonic foraminiferal species Globorotalia truncatulinoides is widely used as a biostratigraphic proxy for the Quaternary in the Mediterranean region. High-resolution quantitative studies performed on sediment cores collected in the central and western Mediterranean Sea evidence a significant abundance of G. truncatulinoides during the Middle Holocene. The robust chronological frame allows us to date this bio-event to 4.8–4.4 ka Before Present (BP), very close to the base of the Meghalayan stage (4.2 ka BP). As a consequence, we propose that G. truncatulinoides can be considered a potential marker for the Middle–Late Holocene chronological subdivision. G. truncatulinoides is a deep-dwelling planktonic foraminifer and their distributional pattern in the central and western Mediterranean Sea provides a tool to monitor the onset of the regional deep vertical mixing of the water column. During the Holocene, the significant increase in the abundance of this species is in phase with the end of African Humid Period, which marks the transition from a more humid climate to the present-day semi-arid climate. Full article

Subsurface formations with low compaction, often, due to the presence of underlying cavities, are potential sources of hazards. Thus, understanding the occurrence, properties, and extension of these weak zones poses a major concern in engineering geophysics. In this study, we examine the ability of geophysical methods to map weak areas over carbonates in Northern Oman. The weak zones are known to cause surface depression in many areas. The geophysical methods examined involve Ground-Penetrating Radar (GPR), Seismic Refraction Tomography (SRT), and Electrical Resistivity Tomography (ERT). This integrated geophysical survey was conducted near the Bimmah sinkhole, in the Quriya area, Northern Oman. The survey covers both an area with ground truth (low compaction sediments overlaying a cave) and a part with unknown subsurface properties. GPR velocity analysis using selected diffraction’s fitting helped to identify high-velocity anomalies that were attributed to the cavity. The GPR interpretation was calibrated with SRT and ERT. The former showed a clear drop in P-wave velocity and low ray coverage at the cavity zone, while the latter demonstrated high resistivity anomalies caused by the air filling the cavity. The scope was to examine the geophysical methods response, especially the GPR, and utilize the results of this preliminary approach for a wider exploration investigation in the area. The results from the study indicated that the GPR is capable to serve as a pioneer method in detecting the cavities. Hence, the GPR will cover large area in the site and the other two methods will be used as complementary for the final subsurface conditions’ evaluation. Full article

Located in northern Peru, at the lowest segment of the Central Andes, the Bagua Basin contains a Campanian to Pleistocene sedimentary record that archives the local paleoenvironmental and tectonic history. We present new δ¹⁸O and δ¹³C signatures of pedogenic carbonate nodules from paleosols in the Campanian–Maastrichtian Fundo El Triunfo Formation and in the upper Eocene–middle Miocene Sambimera Formation to reconstruct the isotopic composition of paleo-meteoric water and the floristic biome. We compare these results to modern isotopic values from a newly obtained modern water transect to interpret the environmental evolution of this area and its relationship with the neighboring Eastern Cordillera. A ~2‰ δ¹⁸O depletion between the latest Cretaceous and the latest Eocene reflects a shift from a coastal to inland environment. A negative δ¹⁸O shift of ~3‰ from the middle Miocene to the present day reveals the establishment of the Eastern Cordillera as an orographic barrier for the moisture traveling westward, sometime after deposition of the top of the Sambimera Formation at ~13 Ma. A shift in the δ¹³C signature from ~−25‰ in the Campanian–Miocene deposits to ~−23‰ in modern–Holocene times suggests a change in biome from dominant C3 plants to a mixture of C3 and C4 plants. This environmental shift reflects both the late Miocene global C4 expansion and the transition to more arid conditions in the basin. The Campanian–middle Miocene environmental reconstruction of the Bagua Basin indicates a steady paleoelevation setting in the northernmost Central Andes during most of the Cenozoic and constrains the uplift of the Eastern Cordillera to the late Miocene–Pleistocene. This paleoelevation history contrasts with that of the Central Andean Plateau, which is characterized by two major episodes of surface uplift: early–middle Miocene and late Miocene–Pliocene. The contrasting modern topographic configuration of the Central Andean Plateau and the northernmost Central Andes gives rise to the question of what factors created such a dramatic difference in topographic evolution of the two regions that shared an overall common tectonic history. We discuss the possible factors responsible for this contrasting topographic configuration and suggest that the diachronous flat slab episodes are likely a major factor, resulting in greater shortening and crustal thickness and, ultimately, in earlier surface uplift episodes occurring in the Central Andean Plateau. Full article

We report the occurrence of several sand liquefaction structures, such as sand dikes, in the stratigraphic record of the Campi Flegrei volcano, located both inside and outside the caldera. Five sites were analyzed within the caldera and two outside. The grain size analysis of the sand fillings indicates that these deposits are very fine-to-coarse sands generally poorly sorted. All of the granulometry curves fall within the field of the liquefiable, loose sediments. Frequently, dikes are characterized by two fillings: a rim showing poorly sorted finer sands and a core with extremely poorly sorted coarser sediments. We suggest that seismic-related liquefaction processes triggered the injection of these sand dikes during unrest episodes in the last 15 kyr. In particular, the sand dikes located outside the caldera, characterized by larger thicknesses and lengths, mark an important extensional episode, probably associated with the caldera formation during the Neapolitan Yellow Tuff eruption at 15 ka. Furthermore, liquefaction structures within the caldera are related to the seismic activity, probably occurring during the Agnano–Monte Spina caldera formation and the volcano-tectonic ground deformation, predating Epoch 3b (4.3 ka) and the Monte Nuovo (1538 CE) eruptions. This study highlights that these seismic-related liquefaction structures are common within the volcanic record of the Campi Flegrei, suggesting that the sand source can be both the widespread marine succession underlying the Epoch 3 deposits in the caldera central sector and the primary ash layers extensively present in the volcanic record. Full article

In this work we establish reliable correlations between density and magnetic susceptibility in three paramagnetic granites from the Pyrenees. In total, 128 sites (310 density measurements and >2600 susceptibility ones) were studied in the Mont Louis-Andorra, Maladeta and Marimanha granitic plutons covering the main range of variability of magnetic susceptibility. Regressions were calculated for every granitic body and an integrated linear function was obtained for the entire dataset: ρ (kg/m³) = 2566 (kg/m³) + 0.541κ (10⁻⁶ S.I.) (R:0.97). This relationship is only valid in the paramagnetic domain, where iron is mostly fractioned in iron-bearing phyllosilicates and the occurrence of magnetite is negligible (or at least its contribution to the bulk susceptibility). This relationship, likely different in other bodies, allows for transforming magnetic susceptibility data into density data, helping to constrain gravity modelling when density data from rock samples are scarce. Given the large amount of AMS studies worldwide, together with the quickness and cost-effectiveness of susceptibility measurements with portable devices, this methodology allows for densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signals. Full article

Extended shallow carbonate platform, pelagic, and drift deposits were drilled during International Ocean Discovery Program (IODP) Expedition 359 in the Inner Sea of the Maldives. These sediments yield rich and well-diversified benthic, planktonic foraminiferal and nannofossil assemblages spanning from the early Oligocene to the Recent. We present here the shore-based revised integrated biostratigraphy of these microfossil groups at IODP Hole 359-U1468A together with the paleobathymetric reconstruction. Our data suggests the presence of a late Oligocene carbonate platform, marked by the shallowest water depths of the entire sequence of around 80 m. This carbonate platform sequence occurred from around 29 Ma, the extrapolated minimum age estimate, at least up to 27.5 Ma and possibly up to 25.4 Ma. Up the sequence, similar carbonate production conditions occurred until 22.5 Ma across the Oligocene–Miocene transition, equated at 23.04 Ma, with increased water depths >120 m. Notably, in the time interval approximately from 24 to 21.5 Ma, orbitally induced sapropel layers indicate a change of open to restricted circulation. However, at around 22.5 Ma, pelagic deposition at a distal slope occurred with sedimentation rates of 3 cm/years. This initially occurred in water depths of >350 m but gradually reached deposition in water depths of >500 m, which persisted from 21.12 Ma until approximately the extrapolated age of 12.8 Ma. Sedimentation rates gradually increased to 10.5 cm/1000 years at around 450 m below sea floor, marking the initiation of the drift sequence as identified in seismic lines with an age estimate of 12.8 Ma. The initiation of the drift sequence is also marked by a drastic decrease in the preservation of benthic and planktonic foraminifera from good to very poor at around 12.8 Ma. The drift sequence essentially continued to the present day but was interrupted by two events: the deposition of distinct shallow water benthic shoals and a large hiatus. From 12.8 Ma, a shallowing upward bathymetry is suggested by the occurrence of shallow benthic foraminiferal assemblages that close to around 11.93 Ma reached a maximum water depth of 80 m. This shoal then prograded into the basin and persisted at least until 9.89 Ma. Basin conditions with water depths exceeding 500 m were re-established in the upper part of the sedimentary succession after a hiatus spanning approximately from 9.83 Ma to 2.39 Ma, implying that renewed open ocean conditions occurred in the Pliocene–Pleistocene part of the sedimentary record. Full article

The Lambayeque Valley on the north coast of Peru offers a cautionary case study on the relation between climatic and cultural change. Three archaeological site complexes dating from late in the first millennium AD to the middle of the second millennium AD rose and were abandoned in sequence. Each abandonment was associated with a conflagration on the main pyramidal mound(s). In this region, El Niño is the most significant climatic disruption now and for millennia past. By tracking proxy records for El Niño intensity, we found that only the first episode of abandonment and burning was associated with a strong peak in El Niño intensity, while the final episode was the outcome of the Spanish Conquest of the Andes, a distinctly non-climatic driver. These records suggest that equifinality is operative and urge caution in over-interpreting climate as culture-changing catastrophe. Full article

Known as the “lung of the planet”, the Amazon rainforest produces more than 20% of the Earth’s oxygen. Once a carbon pool for mitigating climate change, the Brazilian Amazônia Biome recently has become a significant carbon emitter due to increasingly frequent wildfires. Therefore, it is of crucial importance for authorities to understand wildfire dynamics to manage them safely and effectively. This study incorporated remote sensing and spatial statistics to study both the spatial distribution of wildfires during 2019 and their relationships to 15 environmental and anthropogenic factors. First, broad-scale spatial patterns of wildfire occurrence were explored using kernel density estimation, Moran’s I, Getis-Ord Gi*, and optimized hot spot analysis (OHSA). Second, the relationships between wildfire occurrence and the environmental and anthropogenic factors were explored using several regression models, including Ordinary Least Squares (OLS), global (quasi) Poisson, Geographically-weighted Gaussian Regression (GWGR), and Geographically-weighted Poisson Regression (GWPR). The spatial analysis results indicate that wildfires exhibited pronounced regional differences in spatial patterns in the vast and heterogeneous territory of the Amazônia Biome. The GWPR model outperformed the other regression models and explained the distribution and frequency of wildfires in the Amazônia Biome as a function of topographic, meteorologic, and environmental variables. Environmental factors like elevation, slope, relative humidity, and temperature were significant factors in explaining fire frequency in localized hotspots, while factors related to deforestation (forest loss, forest fragmentation measures, agriculture) explained wildfire activity over much of the region. Therefore, this study could improve a comprehensive study on, and understanding of, wildfire patterns and spatial variation in the target areas to support agencies as they prepare and plan for wildfire and land management activities in the Amazônia Biome. Full article

Magmatic-hydrothermal systems, especially those causing the formation of tungsten deposits, may be enriched in boron, as is suggested by the presence of hydrothermal tourmaline. This study examines the boron and metal (including tungsten) concentrations of quartz-hosted fluid inclusions in the Lened W-(Be) deposit of the Canadian Cordillera and resolves (i) the analytical challenges involved during fluid salinity calculations of B-rich fluids and (ii) the relationship between fluid chemical composition and ore-forming processes involved at Lened. The aqueous fluid inclusions from this study have high CO₂ and boron contents, indicated by the presence of a carbonic phase and sassolite crystals (H₃BO₃) in fluid inclusions. The boron content of the aqueous liquid phase (0.5 wt. %) was determined using microthermometric and Raman spectroscopic analyses. Boron was judged the most appropriate internal standard for quantifying the LA-ICP-MS data from these inclusions after calculation of salinity in the H₂O-NaCl-H₃BO₃ system (3.5 to 5 wt. % NaCl_eq). Trace element data of the fluids show relatively high concentrations of Li (40 to 474 ppm), Al (56 to 1003 ppm), As (36 to 490 ppm) and Cs (68 to 296 ppm); and lower concentrations of Rb (3.6 to 77 ppm), Sr (0.4 to 23 ppm), Sb (1 to 32 ppm), Ba (0.6 to 163 ppm), Mg (6.9 to 7.6 ppm) and other metals, such as Be (2.4 to 10.2 ppm), W (2.4 to 27 ppm) and Cu (5.1 to 73 ppm). The high Cs and Li concentrations suggest a magmatic origin of the metals, while the moderate concentrations in Sr and Ba are indicative of fluid–rock interaction with the surrounding limestone. The presence of sassolite suggests that these fluids were highly acidic. The neutralization of this fluid through interaction with the surrounding limestone is the most probable trigger for scheelite precipitation. The presence of such high boron content in the magmatic fluid at Lened indicates the potential role in the enrichment of the source melt before fluid exsolution. Full article

In Brazil, the development of gullies constitutes widespread land degradation, especially in the state of South Mato Grosso, where fighting against this degradation has become a priority for policy makers. However, the environmental and anthropogenic factors that promote gully development are multiple, interact, and present a complexity that can vary by locality, making their prediction difficult. In this framework, a database was constructed for the Rio Ivinhema basin in the southern part of the state, including 400 georeferenced gullies and 13 geo-environmental descriptors. Multivariate statistical analysis was performed using principal component analysis (PCA) to identify the processes controlling the variability in gully development. Susceptibility maps were created through four machine learning models: multivariate discriminant analysis (MDA), logistic regression (LR), classification and regression tree (CART), and random forest (RF). The predictive performance of the models was analyzed by five evaluation indices: accuracy (ACC), sensitivity (SST), specificity (SPF), precision (PRC), and Receiver Operating Characteristic curve (ROC curve). The results show the existence of two major processes controlling gully erosion. The first is the surface runoff process, which is related to conditions of slightly higher relief and higher rainfall. The second also reflects high surface runoff conditions, but rather related to high drainage density and downslope, close to the river network. Human activity represented by peri-urban areas, construction of small earthen dams, and extensive rotational farming contribute significantly to gully formation. The four machine learning models yielded fairly similar results and validated susceptibility maps (ROC curve > 0.8). However, we noted a better performance of the random forest (RF) model (86% and 89.8% for training and test, respectively, with an ROC curve value of 0.931). The evaluation of the contribution of the parameters shows that susceptibility to gully erosion is not governed primarily by a single factor, but rather by the interconnection between different factors, mainly elevation, geology, precipitation, and land use. Full article

In anisotropic materials such as minerals and rocks, the AC magnetic susceptibility is also anisotropic, and consists of two components, one in-phase with the applied field (ipMS) and the other out-of-phase (opMS). Correspondingly, anisotropies of these components, in-phase magnetic anisotropy (ipAMS) and out-of-phase anisotropy (opAMS), can be defined. In non-conductive dia- and paramagnetic materials, and in pure multi-domain magnetite, the opMS is effectively zero and only ipAMS can be measured. In some ferromagnetic minerals, such as pyrrhotite, hematite, titanomagnetite, or small magnetically viscous grains of magnetite, the opMS is clearly non-zero, and not only ipAMS but also opAMS can be determined. The opAMS can then be used as a tool for the direct determination of the magnetic sub-fabrics of the minerals with non-zero opMS. The precision in measurement of opMS decreases non-linearly with decreasing opMS/ipMS ratio, which may result in imprecise determination of the opAMS if the ratio is very low. It is highly recommended to inspect the results of the statistical tests of each specimen and to exclude the specimens with statistically insignificant opAMS from further processing. In rocks with a mono-mineral magnetic fraction represented by the mineral with non-zero opMS, the principal directions of the opAMS and ipAMS are virtually coaxial, while the degree of opAMS is higher than that of ipAMS. In some cases, the opAMS provides similar results to those provided by anisotropies of low-field-dependent susceptibility and frequency-dependent susceptibility. The advantage of the opAMS is in its simultaneous measurement with the ipAMS during one measuring process, whereas the other two methods require measurement in several fields or operating frequencies. Full article

Calcite twinning is a dominant deformation mechanism at low temperatures. It is often used to reconstruct paleostresses: orientations of the principal stress axes, stress ratios and differential stress. Despite numerous studies, on single crystals and aggregates, questions remain about the initiation and evolution of the twinning. In particular, the existence of a critical value for the activation of twin planes is debated. In this study, Carrara marble samples were uniaxially deformed at low temperature. The experiments were monitored in situ in an SEM (Scanning Electron Microscope) and a deformation analysis was performed at regular intervals using image correlation. Image correlation analysis shows the link between the overconcentration of strains and the appearance of the first twinned planes. This is followed by a densification and a gradual thickening of the twin lamellae. Fracturing only appears in a third stage as a precursor to the collapse of the sample. The inversion, using the CSIT-2 technique, showed that the twinned planes are globally related to the applied macroscopic stress. The inversion allows one to retrieve the macroscopic stress tensor. Schmid factors were extracted from this analysis and correlated to the loading curves. For crystals of about 200 µm diameter, the threshold value is in between 6.75 and 8.25 MPa. Full article

Numerical simulations were generated using a nonlinear shallow-water model of velocity potential to study the fundamental processes of tsunami generation and amplification by atmospheric pressure waves. When an atmospheric pressure wave catches up with an existing tsunami that is propagating as a free wave over an abrupt change in water depth, the amplified tsunami propagates in the shallower water. An existing tsunami propagating as a free wave over a sloping seabed is also amplified by being passed by atmospheric pressure waves. When atmospheric pressure waves travel over an abrupt change in water depth, the water surface profile of tsunamis in the shallower water depends on both the interval of the atmospheric pressure waves and the phase of the tsunami-generation process over the change in water depth. Moreover, when atmospheric pressure waves travel over an abrupt change in water depth, the tsunami amplitude in the shallower water increases, as the water depth of the shallower area is decreased and the Proudman resonance is further reduced. When an atmospheric pressure wave train with positive pressure travels over a sloping seabed, the amplification of tsunami crests propagating as free waves is controlled by leaving the forced water waves following the atmospheric pressure waves. Conversely, the amplitudes of tsunami troughs propagating as free waves increase. Full article

In recent decades, constraining the timing of shear activity has been one of the main topics of research about the tectono-metamorphic evolution of orogenic belts. We present a review of a combined structural and geochronological approach to two major ductile regional shear zones, in two collisional orogens: the first one affecting the Variscan basement in northern Sardinia (Italy) and the External Crystalline Massifs of the Alps (East Variscan Shear Zone; EVSZ), and the second one deforming the medium- to high-grade rocks of the metamorphic core of the Himalaya (High Himalayan Discontinuity). High-resolution, texturally and chemically controlled monazite geochronology applied in separated shear zones of the Variscan belt allowed recognizing a similar timing of activity ranging between c. 340–330 and 300 Ma. This approach led to a better understanding of the evolution of the EVSZ, supporting a model where several branches were active according to a growth by linkage model. Following a similar approach, in situ U-Th-Pb analysis of monazite constrained the timing of top-to-the-S/SW shearing of a regional-scale High Himalayan Discontinuity in the Himalayan belt to between c. 28 Ma and 17 Ma. Earlier exhumation of the hanging wall was triggered by shear zone activity, whereas at the same time, the footwall was still experiencing burial with increasing P-T conditions. The timing of shearing of this shear zone fits with an in-sequence shearing tectonic model for the exhumation of the Himalayan mid-crust. Full article

The approximately 2 km thick fluvio-lacustrine deposits of Pranhita-Godavari Gondwana syn-rift basin, ranging in age from 235 to 196 Ma, track the compositional changes from the Middle Triassic to Early Jurassic. Mineralogical and geochemical investigations, as well as paleocurrent data of the siliciclastic deposits of the four conformable formations—Yerrapalli, Bhimaram, Maleri and Dharmaram—trace the source of sediments to the south and southwest of the Gondwana basin. The dominance of arkosic to sub-arkosic sandstones in all the formations suggests mostly felsic sources. The high value of Zr/Sc, as well a high content of Hf, reflects the addition of zircon by sediment recycling. The index of compositional variability (ICV) and chemical index of alteration (CIA) values of these Gondwana samples suggest intermediate weathering of Proterozoic shales, granites and gneisses. The concentration of Cr and Ni, ratios of Eu/Eu* and (Gd_N/Yb_N) suggest a dominant post-Archean source. The insignificant variation in ICV and CIA values across the studied Mesozoic formations corroborates the continuation of syn-rift tectonics of the Pranhita-Godavari Gondwana basin since the Late Paleozoic. Sandstone samples show a gradual shift from arkose to subarkose in Yerrapalli, Barakar and Maleri formations, and to sublithic arenite sandstones in the younger Dharmaram formation, indicating recycling. However, the insignificant variation of feldspar and/or quartz content throughout these Mesozoic formations suggests lesser tectonic activity. The paleocurrent direction, shifting from NNW to NE direction, suggests a change in basin tectonism and/or sediment supply, which is corroborated by mineralogical and geochemical data. Full article

Titanite is an important mineral in petrochronology studies. Understanding chemical signatures of titanite from different environments can provide significant data in unraveling the complex histories recorded in their textures and compositions. Using a database of over 8500 titanite analyses from both the literature (3829) and our own data (4900), we found that the ratio of Fe/Al is useful for separating igneous titanite (Fe/Al is typically close to 1:1 and almost always > 1:2) from metamorphic titanite (Fe/Al ratio is < 1:2) with few exceptions. Volcanic titanite grains can also be separated from plutonic titanite grains due to their shorter crystallization histories with compositions clustered more tightly in terms of Fe, Al, and F. Compositions of titanite from plutonic rocks often have later metamorphic or hydrothermal overgrowths that are not found on volcanic titanite. Fe/Al ratios in titanite from silica-undersaturated volcanic and plutonic rocks are typically > 1:2 and include titanite with the highest Fe/Al ratios. Although they overlap the field for normal igneous titanite, other elements (particularly high levels of Nb and low levels of Y) allow them to be separated. In most metamorphic rocks, the Fe/Al ratio is < 1:2 except for a few metamorphic titanite grains that formed in mafic rocks. Titanite from ultrahigh pressure metamorphic rocks (eclogite facies) tend to have the lowest Fe/Al ratios, typically < 1:8. Titanite from hydrothermal and pegmatitic environments scatter widely in terms of Fe/Al even within single grains due to crystallization from fluids with highly variable compositions. Charge balancing in metamorphic, hydrothermal, and pegmatitic titanite due to Fe⁺³ and Al⁺³ substitution into the Ti⁺⁴ site is largely accomplished by the coupled substitution of F⁻ for O⁻². However, in volcanic and plutonic titanite, the charge imbalance due to Fe⁺³ and Al⁺³ substitution appears to be mainly coupled with REE⁺³ or Y⁺³ substitution into the Ca⁺² site with a lesser contribution from F⁻. Full article

Electrostatic space accelerometers are high-precision instruments used in gravity and magnetic fields and in fundamental physics missions. From their first use in space, these instruments show disturbances around the read-out frequency. In recent missions like Swarm and GRACE-FO, these instruments are seriously compromised. Their capability cannot be fully exploited or, in the worst case, not used for science data processing at all. We currently neither understand the mechanism nor the cause of the disturbance. For that reason, every correlation, direct or indirect, between signatures in the accelerometer data and other phenomena in the satellite environment is very important to study. In the GRACE mission, some of the disturbances relate to onboard current switching processes, such as switching of heater and torquer currents. In this paper, we examine the phenomena called twangs. The shape of these disturbances is responsible for their name, because they look like a decaying tone. Some of these twangs seem to relate to changing currents, too. They occur when sunlight hits surfaces of the satellite. This can cause the discharging of satellite parts. Here, we focus on special twangs, which we call cloud-related twangs, as recent investigations related them to cloud coverage. How can clouds in the troposphere influence a satellite, orbiting in the ionosphere? We investigated the troposphere–ionosphere coupling and found that the only coupling which can be responsible for disturbances on satellites and which may affect the accelerometers, are electromagnetic waves traveling in the so-called whistler mode at frequencies in the very-low-frequency (VLF) domain. This special propagation mode is a coupled electromagnetic and electrostatic mode. There, the electric field vector has a component in the direction of propagation due to the interaction with ions and the magnetic field in the ionosphere and magnetosphere. This led us to investigate the similarities between whistlers and twangs. The hypothesis that they are related is very important in our further understanding of disturbances on satellite instruments sensible to electromagnetic pulses in the range of very low frequencies and below. Full article

We reconstructed the seismotectonic setting of the area comprising the northeastern Friuli Plain and the Julian pre-Alpine border (NE Italy) by integrating geological and seismological data. The study area represents the junction between the SSE-verging polyphase thrust-front of the south-Alpine Chain and the NW–SE-trending strike-slip faults of the eastern Friuli–western Slovenia domain. Following a multidisciplinary approach, the 3D geometry of the Susans–Tricesimo thrust system was reconstructed through the elaboration of four geological cross sections derived from the interpretation of ENI industrial seismic lines. In a second step, the seismogenic volume of the central-eastern Friuli area was investigated through hypocentral distribution analysis: the seismic events of the latest 50 years (1976–1977 and 1978–2019 time intervals) were plotted on four NE-SW-oriented seriated sections together with the fault plane’s geometry. Through this procedure, we were able to investigate the relationship between the NW-SE-striking high-angle faults, which characterize the northern Julian pre-Alps, and the WSW-verging medium-angle reverse fronts located at the piedmont of the Friuli plain, which experienced NW-SE- to NNW-SSE-oriented compression starting at least from the Pliocene. In detail, we examined the involvement of these structures during the seismic sequences of May and September 1976, in terms of activation and/or interaction. The resulting seismotectonic model highlights the interplay between transpressive/strike-slip and reverse planes. In particular, this study suggests that Predjama and Maniaglia transpressive faults strongly control the stress release and likely played a fundamental role both during the 6 May (Mw 6.5) and 15 September (Mw 6.0) Friuli earthquakes. Full article

The stratigraphic development of foreland basins has mainly been related to surface loading in the adjacent orogens, whereas the control of slab loads on these basins has received much less attention. This has also been the case for interpreting the relationships between the Oligocene to Micoene evolution of the European Alps and the North Alpine foreland basin or Molasse basin. In this trough, periods of rapid subsidence have generally been considered as a response to the growth of the Alpine topography, and thus to the construction of larger surface loads. However, such views conflict with observations where the surface growth in the Alps has been partly decoupled from the subsidence history in the basin. In addition, surface loads alone are not capable of explaining the contrasts in the stratigraphic development particularly between its central and eastern portions. Here, we present an alternative view on the evolution of the Molasse basin. We focus on the time interval between c. 30 and 15 Ma and relate the basin-scale development of this trough to the subduction processes, and thus to the development of slab loads beneath the European Alps. At 30 Ma, the western and central portions of this basin experienced a change from deep marine underfilled (Flysch stage) to overfilled terrestrial conditions (Molasse stage). During this time, however, a deep marine Flysch-type environment prevailed in the eastern part of the basin. This was also the final sedimentary sink as sediment was routed along the topographic axis from the western/central to the eastern part of this trough. We interpret the change from basin underfill to overfill in the western and central basin as a response to oceanic lithosphere slab-breakoff beneath the Central and Western Alps. This is considered to have resulted in a growth of the Alpine topography in these portions of the Alps, an increase in surface erosion and an augmentation in sediment supply to the basin, and thus in the observed change from basin underfill to overfill. In the eastern part of the basin, however, underfilled Flysch-type conditions prevailed until 20 Ma, and subsidence rates were higher than in the western and central parts. We interpret that high subsidence rates in the eastern Molasse occurred in response to slab loads beneath the Eastern Alps, where the subducted oceanic slab remained attached to the European plate and downwarped the plate in the East. Accordingly, in the central and western parts, the growth of the Alpine topography, the increase in sediment flux and the change from basin underfill to overfill most likely reflect the response to slab delamination beneath the Central Alps. In contrast, in the eastern part, the possibly subdued topography in the Eastern Alps, the low sediment flux and the maintenance of a deep marine Flysch-type basin records a situation where the oceanic slab was still attached to the European plate. The situation changed at 20 Ma, when the eastern part of the basin chronicled a change from deep marine (underfilled) to shallow marine and then terrestrial (overfilled conditions). During the same time, subsidence rates in the eastern basin decreased, deformation at the Alpine front came to a halt and sediment supply to the basin increased possibly in response to a growth of the topography in the Eastern Alps. This was also the time when the sediment routing in the basin axis changed from an east-directed sediment dispersal prior to 20 Ma, to a west-oriented sediment transport thereafter and thus to the opposite direction. We relate these changes to the occurrence of oceanic slab breakoff beneath the Eastern Alps, which most likely resulted in a rebound of the plate, a growth of the topography in the Eastern Alps and a larger sediment flux to the eastern portion of the basin. Beneath the Central and Western Alps, however, the continental lithosphere slab remained attached to the European plate, thereby resulting in a continued downwarping of the plate in its central and western portions. This plate downwarping beneath the central and western Molasse together with the rebound of the foreland plate in the East possibly explains the inversion of the drainage direction. We thus propose that slab loads beneath the Alps were presumably the most important drivers for the development of the Molasse basin at the basin scale. Full article

A lot of work in geosciences has been completed during the last decade on the analysis in the new concept of time, termed natural time, introduced in 2001. The main advances are presented, including, among others, the following: First, the direct experimental verification of the interconnection between a Seismic Electric Signals (SES) activity and seismicity, i.e., the order parameter fluctuations of seismicity exhibit a clearly detectable minimum when an SES activity starts. These two phenomena are also linked closely in space. Second, the identification of the epicentral area and the occurrence time of an impending major earthquake (EQ) by means of the order parameter of seismicity and the entropy change of seismicity under time reversal as well as the extrema of their fluctuations. An indicative example is the M9 Tohoku EQ in Japan on 11 March 2011. Third, to answer the crucial question—when a magnitude 7 class EQ occurs—whether it is a foreshock or a mainshock. This can be answered by means of the key quantities already mentioned, i.e., the order parameter of seismicity and the entropy change of seismicity under time reversal along with their fluctuations. The explanation of the experimental findings identified before major EQs is given in a unified way on the basis of a physical model already proposed in the 1980s. Full article