Geosciences

Leak-off pressure (LOP) is a key parameter to determine the allowable weight of drilling mud in a well and the in situ horizontal stress. The LOP test is run in situ and is frequently used by the petroleum industry. If the well pressure exceeds the LOP, wellbore instability may occur, with hydraulic fracturing and large mud losses in the formation. A reliable prediction of LOP is required to ensure safe and economical drilling operations. The prediction of LOP is challenging because it is affected by the usually complex earlier geological loading history, and the values of LOP and their measurements can vary significantly geospatially. This paper investigates the ability of machine learning algorithms to predict leak-off pressure on the basis of geospatial information of LOP measurements. About 3000 LOP test data were collected from 1800 exploration wells offshore Norway. Three machine learning algorithms (the deep neural network (DNN), random forest (RF), and support vector machine (SVM) algorithms) optimized by three hyperparameter search methods (the grid search, randomized search and Bayesian search) were compared with multivariate regression analysis. The Bayesian search algorithm needed fewer iterations than the grid search algorithms to find an optimal combination of hyperparameters. The three machine learning algorithms showed better performance than the multivariate linear regression when the features of the geospatial inputs were properly scaled. The RF algorithm gave the most promising results regardless of data scaling. If the data were not scaled, the DNN and SVM algorithms, even with optimized parameters, did not provide significantly improved test scores compared to the multivariate regression analysis. The analyses also showed that when the number of data points in a geographical setting is much smaller than that of other geographical areas, the prediction accuracy reduces significantly. Full article

We present a generalized Geertsma solution that can consider any number of finite-thickness layers in the subsurface whose mechanical properties are different from layer to layer. In addition, each layer can be assumed either isotropic or anisotropic. The accuracy of the generalized solution is validated against a numerical reference solution. The generalized Geertsma solution is further extended by a linear superposition framework that enables a response simulation due to an arbitrarily-distributed non-uniform pressure anomaly. The linear superposition approach is tested and validated by solving a realistic synthetic model based on the In Salah CO₂ storage model and compared with a full 3D finite element solution. Finally, by means of a simple inversion exercise (based on the linear superposition approach), we learn that the stiffnesses of cap rock and reservoir are the most influencing parameter on the inversion result for a given layering geometry, suggesting that it is very important to estimate high-confidence mechanical properties of both cap rock and reservoir. Full article

The seabed of the Pontine Archipelago (Tyrrhenian Sea) insular shelf is peculiar as it is characterized by a mixed siliciclastic–carbonate sedimentation. In order to reconstruct the Late Quaternary paleoenvironmental evolution of the Pontine Archipelago, this study investigates the succession of facies recorded by two sediment cores. For this purpose, benthic foraminifera and rhodoliths assemblages were considered. The two cores (post-Last Glacial Maximum in age) were collected at 60 (CS1) and 122 m (Caro1) depth on the insular shelf off Ponza Island. The paleontological data were compared with seismo-stratigraphic and lithological evidence. The cores show a deepening succession, with a transition from a basal rhodolith-rich biodetritic coarse sand to the surface coralline-barren silty sand. This transition is more evident along core Caro1 (from the bottom to the top), collected at a deeper water depth than CS1. In support of this evidence, along Caro1 was recorded a fairly constant increase in the amount of planktonic foraminiferal and a marked change in benthic foraminiferal assemblages (from Asterigerinata mamilla and Lobatula lobatula assemblage to Cassidulina carinata assemblage). Interestingly, the dating of the Caro1 bottom allowed us to extend to more than 13,000 years BP the rhodolith record in the Pontine Archipelago, indicating the possible presence of an active carbonate factory at that time. Full article

This study presents a numerical investigation of the source aspect ratio (AR) influence on tsunami decay characteristics with an emphasis in near and far-field differences for two initial wave shapes Pure Positive Wave and N-wave. It is shown that, when initial total energy for both tsunami types is kept the same, short-rupture tsunami with more concentrated energy are likely to be more destructive in the near-field, whereas long rupture tsunami are more dangerous in the far-field. The more elongated the source is, the stronger the directivity and the slower the amplitude decays in the intermediate- and far-fields. We present evidence of this behavior by comparing amplitude decay rates from idealized sources and showing their correlation with that observed in recent historical events of similar AR. Full article

We describe the opening of back-arc basins and the associated formation of accretionary wedges through the application of techniques of deformable plate kinematics. These methods have proven to be suitable to describe complex tectonic processes, such as those that are observed along the Africa–Europe collision belt. In the central Mediterranean area, these processes result from the passive subduction of the lithosphere belonging to the Alpine Tethys and Ionian Ocean. In particular, we focus on the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain. We divide the area of the Apennine Chain and the Tyrrhenian basin into deformable polygons that are identified on the basis of sets of extensional structures that are coherent with unique Euler pole grids. The boundaries between these polygons coincide with large tectonic lineaments that characterize the Tyrrhenian–Apennine area. The tectonic style along these structures reflects the variability of relative velocity vectors between two adjacent blocks. The deformation of tectonic elements is accomplished, allowing different rotation velocities of lines that compose these blocks about the same stable stage poles. The angular velocities of extension are determined on the basis of the stratigraphic records of syn-rift sequences, while the rotation angles are obtained by crustal balancing. Full article

The west Florida shelf (WFS; Gulf of Mexico, USA) is an important area for commercial and recreational fishing, yet much of it remains unmapped and unexplored, hindering effective monitoring of fish stocks. The goals of this study were to map the habitat at an intensively fished area on the WFS known as “The Elbow”, assess the differences in fish communities among different habitat types, and estimate the abundance of each fish taxa within the study area. High-resolution multibeam bathymetric and backscatter data were combined with high-definition (HD) video data collected from a near-bottom towed vehicle to characterize benthic habitat as well as identify and enumerate fishes. Two semi-automated statistical classifiers were implemented for obtaining substrate maps. The supervised classification (random forest) performed significantly better (p = 0.001; α = 0.05) than the unsupervised classification (k-means clustering). Additionally, we found it was important to include predictors at a range of spatial scales. Significant differences were found in the fish community composition among the different habitat types, with both substrate and vertical relief found to be important with rock substrate and higher relief areas generally associated with greater fish density. Our results are consistent with the idea that offshore hard-bottom habitats, particularly those of higher vertical relief, serve as “essential fish habitat”, as these rocky habitats account for just 4% of the study area but 65% of the estimated total fish abundance. However, sand contributes 35% to total fish abundance despite comparably low densities due to its large area, indicating the importance of including these habitats in estimates of abundance as well. This work demonstrates the utility of combining towed underwater video sampling and multibeam echosounder maps for habitat mapping and estimation of fish abundance. Full article

In the frame of a Belgo-Haitian cooperation project (PIC 2012–2016), a study of the local seismic hazard was performed in Fond Parisien, an area located on the foothills of the “Massif de la Selle”, along the easternmost portion of the Enriquillo Plantain Garden Fault (EPGF). The H/V Spectral Ratio (HVSR) technique was applied to study the resonance frequency of the target areas and the azimuth of the wave field. The amplification factors were estimated using Standard Spectral Ratios obtained from earthquakes recorded by a temporary seismic network. Using the Multichannel Analysis of Surface Waves method, the seismic properties of the shallow layers were investigated. Then, the results were compared to local Electrical Resistivity Tomography data. These results highlight, in the central part of Fond Parisien, an E-W zone of low velocities ranging from 200 m/s to 450 m/s and low resistivities between 1 Ωm and 150 Ωm, due both to tectonic folding of the rocks and to the presence of sediment filling in the eastern part. The latter is marked, in most of its sites, by resonances at one or more frequencies ranging from 0.7 Hz to 20 Hz. Infiltration and storage of brackish water in the underground layers also contribute to the low resistivity values. With the noise HVSR data, we also evidenced a significant influence of the EPGF on the main orientation of the seismic wavefield as in the vicinity of this fault, the azimuths are parallel to the orientation of the fault. Overall, the results also show greater potential for site effects in the block formed by the sedimentary basin and strong amplification of the seismic ground motion for the sites bordering the basin to the north and west. We interpret the amplification in the north and south-west as probably originating from topographic irregularities locally coupled with sediment deposits, while in the center of the western part, the site effects could be explained by the presence of folds and related weakened and softened rocks. By the integration of several geophysical methods, we could distinguish areas where it is possible to build more safely. These zones are located in the northern part and encompass Quisqueya Park and neighboring areas as well as the village “La Source” in the southern part. In the rest of Fond Parisien, i.e., in the more central and eastern parts, buildings should be erected with caution, taking into account the nearby presence of the EPGF and the influence of fine sediments on the amplification of the seismic motion. Full article

The availability of high-quality surface data acquired by recent Mars missions and the development of increasingly accurate methods for analysis have made it possible to identify, describe, and analyze many geological and geomorphological processes previously unknown or unstudied on Mars. Among these, the slow and large-scale slope deformational phenomena, generally known as Deep-Seated Gravitational Slope Deformations (DSGSDs), are of particular interest. Since the early 2000s, several studies were conducted in order to identify and analyze Martian large-scale gravitational processes. Similar to what happens on Earth, these phenomena apparently occur in diverse morpho-structural conditions on Mars. Nevertheless, the difficulty of directly studying geological, structural, and geomorphological characteristics of the planet makes the analysis of these phenomena particularly complex, leaving numerous questions to be answered. This paper reports a synthesis of all the known studies conducted on large-scale deformational processes on Mars to date, in order to provide a complete and exhaustive picture of the phenomena. After the synthesis of the literature studies, the specific characteristics of the phenomena are analyzed, and the remaining main open issued are described. Full article

We aimed to contribute to a shift in higher education teaching and learning methods by considering problem-based learning (PBL) as an approach capable of positively affecting students from a geology and environment (GE) curricular unit. In a convenience sample from a Portuguese public university, two groups of students were defined: (1) an experimental group (n = 16), to which an intervention program (IP) based on PBL was applied, and (2) a comparison group (n = 17), subjected to the traditional teaching approach. For nine weeks, students subject to the IP faced four problem scenarios about different themes. A triangulation of methods was chosen. The study involved two phases: (1) qualitative (sustained on content analysis of driving questions raised by students, registered in a monitoring sheet) and (2) quantitative (quasi-experimental study, based on data from a prior and post-test knowledge assessment). The qualitative results point to the development of more complex cognitive-level questioning skills after increasing familiarity with PBL. The data obtained in the quantitative study, which included both a “within-subjects” and a “between-subjects” design, show higher benefits in the experimental group, documenting gains in terms of scientific knowledge when using the PBL methodology. Full article

Southern Ozark Mississippi Valley-type ores are enriched in radiogenic Pb, with isotopic signatures suggesting that metals were supplied by two end-member components. While the less radiogenic component appears to be derived from various shale and sandstone units, the source of the more radiogenic component has not yet been identified. Analyses of cherts from the Early Ordovician Cotter Dolomite and tripolitic chert from the Early Mississippian Boone Formation contain highly radiogenic Pb, with isotopic ratios comparable to those of ores. However, most samples have lower ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb for a given ²⁰⁶Pb/²⁰⁴Pb compared to ores. These relationships demonstrate that the enriched Pb isotopic values of the ore array cannot be related to the host and regional lithologies sampled, suggesting that the source of high ratios may lay further afield. The slope of the linear trend defined by the Pb isotope ratios of ores corresponds to an age of about 1.19 Ga. Therefore, an alternative for the linear array is the involvement of Precambrian basement in supplying ore Pb. Rare earth element patterns show that diagenetic processes involving the action of groundwater and hydrothermal fluids affected the sampled lithologies to various degrees, with Cotter Dolomite having experienced the highest degree of alteration. Full article

Cobbles and boulders on the seafloor are of high ecological value in their function as habitats for a variety of benthic species, contributing to biodiversity and productivity in marine environments. We investigate the origin, physical shape, and structure of habitat-forming cobbles and boulders and reflect on their dynamics in coastal environments of the southwestern Baltic Sea. Stone habitats are not limited to lag deposits and cannot be sufficiently described as static environments, as different dynamic processes lead to changes within the physical habitat structure and create new habitats in spatially disparate areas. Dynamic processes such as (a) ongoing exposure of cobbles and boulders from glacial till, (b) continuous overturning of cobbles, and (c) the migration of cobbles need to be considered. A distinction between allochthonous and autochthonous habitats is suggested. The genesis of sediment types indicates that stone habitats are restricted to their source (glacial till), but hydrodynamic processes induce a redistribution of individual cobbles, leading to the development of new coastal habitats. Thus, coastal stone habitats need to be regarded as dynamic and are changing on a large bandwidth of timescales. In general, wave-induced processes changing the physical structure of these habitats do not occur separately but rather act simultaneously, leading to a dynamic type of habitat. Full article

At the very end of the year 2020, on 29 December, a hazardous earthquake of M_w = 6.2 hit the area of Petrinja and its surroundings, in the NW of Croatia. The earthquake was felt across the area of 400 km, leaving an inconceivable damage in the vicinity of the epicenter, devastated towns and ruined lives. In order to map the spreading of earthquake waves and to determine the coseismic ground displacement after the mainshock, we have analyzed open satellite radar images of Sentinel-1 and the GNSS data from the nearest CORS station related to the epicenter, along with the seismic faults. In this paper, we addressed and mapped the displacement linear surface ruptures detected by the SAR interferometry. The results show the vertical ground displacement to the extent of −12 cm in the southern area and up to 22 cm in the north-western part of a wide area struck by the earthquake impact, related to the epicenter. Subsidence and uplift in a range of ±5 cm over a wider affected area indicate a spatial extent and hazardous impact made by the earthquake. The ground displacement of 30 cm to the West and 40 cm to the East has been identified considering the intersection of Pokupsko and Petrinja strike-slip fault system in the seismic zone of Pannonian basin. Accordingly, we obtained matching results of 5 cm south-easting shift and −3 cm subsidence on Sisak GNSS CROPOS station, addressing the tectonic blocks movement along the activated complex fault system. The results compared with the geology data confirm the existence of two main faults; the Pokupsko and the Petrinja strike-slip faults and interpret the occurrence of secondary post-seismic events over the observed area. Full article

Since 2016, Stromboli volcano has shown an increase of both frequency and energy of the volcanic activity; two strong paroxysms occurred on 3 July and 28 August 2019. The paroxysms were followed by a series of major explosions, which culminated on January 2021 with magma overflows and lava flows along the Sciara del Fuoco. This activity was monitored by the soil CO₂ flux network of Istituto Nazionale di Geofisica e Vulcanologia (INGV), which highlighted significant changes before the paroxysmal activity. The CO₂ flux started to increase in 2006, following a long-lasting positive trend, interrupted by short-lived high amplitude transients in 2016–2018 and 2018–2019. This increasing trend was recorded both in the summit and peripheral degassing areas of Stromboli, indicating that the magmatic gas release affected the whole volcanic edifice. These results suggest that Stromboli volcano is in a new critical phase, characterized by a great amount of volatiles exsolved by the shallow plumbing system, which could generate other energetic paroxysms in the future. Full article

Recently, a new strain rate map of Italy and the surrounding areas has been obtained by processing data acquired by the persistent scatterers (PS) of the synthetic aperture radar interferometry (InSAR) satellites—ERS and ENVISAT—between 1990 and 2012. This map clearly shows that there is a link between the strain rate and all the shallow earthquakes (less than 15 km deep) that occurred from 1990 to today, with their epicenters being placed only in high strain rate areas (e.g., Emilia plain, NW Tuscany, Central Apennines). However, the map also presents various regions with high strain rates but in which no damaging earthquakes have occurred since 1990. One of these regions is the Apennine sector, formed by Sannio and Irpinia. This area represents one of the most important seismic districts with a well-known and recorded seismicity from Roman times up to the present day. In our study, we merged historical records with new satellite techniques that allow for the precise determination of ground movements, and then derived physical dimensions, such as strain rate. In this way, we verified that in Irpinia, the occurrence of new strong shocks—forty years after one of the strongest known seismic events in the district that occurred on the 23 November 1980, measuring Mw 6.8—is still a realistic possibility. The reason for this is that, from 1990, only areas characterized by high strain rates have hosted significant earthquakes. This picture has been also confirmed by analyzing the historical catalog of events with seismic completeness for magnitude M ≥ 6 over the last four centuries. It is easy to see that strong seismic events with magnitude M ≥ 6 generally occurred at a relatively short time distance between one another, with a period of 200 years without strong earthquakes between the years 1732 and 1930. This aspect must be considered as very important from various points of view, particularly for civil protection plans, as well as civil engineering and urban planning development. Full article

The abandoned mining district of Linares (South Spain) is marked with waste from the mining and the processing of metal ores that pose an environmental hazard to watercourses. A combined analysis of waste, sediments and water was carried out to analyse the impact of a smelter on Baños Creek. The composition of the facility waste was determined using X-ray diffractometry and scanning electron microscopy. The total contents of the metal(loid)s in the waters and sediments of the watercourse were analysed, and sequential metal(loid) extraction of solid samples was carried out. The facility wastes consisted mainly of secondary minerals, such as natropharmacosiderite and spertiniite, as well as rare metal salts, such as mopungite and NaPb₂(CO₃)₂(OH). The leachates generated by these wastes were highly alkaline, with a pH of 10 and a total dissolved solids concentration of approximately 9 g L⁻¹. This Na-bicarbonate-type water had an As concentration above 200 mg L⁻¹ and elevated levels of Pb, Sb and Zn (5029 µg L⁻¹, 841 µg L⁻¹ and 525 µg L⁻¹, respectively). This highly contaminated lixiviate had a significant effect on the chemical quality of the waters and the bioavailability of metal(loid)s in the creek sediments, especially in the headwaters. In this zone, the As, Pb, Sb and Zn concentrations in the most mobile fraction of the sediments reached 1035 mg kg⁻¹, 261 mg kg⁻¹, 45 mg kg⁻¹ and 30 mg kg⁻¹, respectively. By comparison, smelter slag and mining waste have a much lower impact on the waters and the mobile fraction of the sediments, while significantly increasing the total concentration of these potentially toxic elements in creek sediments. Full article

The Late Holocene was characterized by several centennial-scale climate oscillations including the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period and the Little Ice Age. The detection and investigation of such climate anomalies requires paleoclimate archives with an accurate chronology as well as a high temporal resolution. Here, we present ²³⁰Th/U-dated high-resolution multi-proxy records (δ¹³C, δ¹⁸O and trace elements) for the last 2500 years of four speleothems from Bunker Cave and the Herbstlabyrinth cave system in Germany. The multi-proxy data of all four speleothems show evidence of two warm and two cold phases during the last 2500 years, which coincide with the Roman Warm Period and the Medieval Warm Period, as well as the Dark Ages Cold Period and the Little Ice Age, respectively. During these four cold and warm periods, the δ¹⁸O and δ¹³C records of all four speleothems and the Mg concentration of the speleothems Bu4 (Bunker Cave) and TV1 (Herbstlabyrinth cave system) show common features and are thus interpreted to be related to past climate variability. Comparison with other paleoclimate records suggests a strong influence of the North Atlantic Oscillation at the two caves sites, which is reflected by warm and humid conditions during the Roman Warm Period and the Medieval Warm Period, and cold and dry climate during the Dark Ages Cold period and the Little Ice Age. The Mg records of speleothems Bu1 (Bunker Cave) and NG01 (Herbstlabyrinth) as well as the inconsistent patterns of Sr, Ba and P suggests that the processes controlling the abundance of these trace elements are dominated by site-specific effects rather than being related to supra-regional climate variability. Full article

Charred materials (anthracomass) stored within a soil constitute a major part of its pyrogenic archive and could provide evidence of past fire events, both natural and anthropogenic. However, the dynamics of man-made contributions to the total anthracomass of soil at different time scales are insufficiently understood. In this study, we determined the anthracomass concentrations, stocks, and particle-size distribution in anthropogenically transformed soils of different genesis and ages. Materials were collected from the following archaeological sites within Central Russia—3 Upper Paleolithic sites (Avdeevo, Khotylevo-2 and Yudinovo-1), 2 Early Iron Age settlements (Khotylevo-2 and Yaroslavl), and 1 Medieval site (Yaroslavl). Samples from different cultural layers (CLs), plough layers, and native soils (control) were studied. We identified anthracomass accumulation over a wide chronological scale starting from the Upper Paleolithic Period. The high degree of preservation of anthracomass in ancient anthropogenically transformed soils was explained by the presence of large fragments of charred bones, which are more durable in comparison to wood charcoal. The anthracomass concentrations and stocks in the Early Iron Age plough layer were lower than those in the Medieval plough layer. CLs were generally more enriched in the anthracomass than plough layers, due to their sedimentational genesis, which is more favorable for anthracomass preservation than the turbational genesis of plough layers. However, the differences between charred particle sizes in synlithogenic CLs and turbational plough layers were less clear than expected, due to the specific conditions of formation of each particular layer, e.g., burial rate, duration of ploughing, and type of agricultural land use. Full article

This work addresses the contamination of the sediments of an alluvial plain and riverbed of a tributary of the San Francisco River, in the Brazilian state of Minas Gerais, by potentially toxic elements from an industrial unit of metallic alloys production. This area was subdivided into four areas (A1, A2, A3, and A0 (background area)) where sediment samples have been collected followed by geochemical characterization and spatial distribution of the contaminants. This characterization was based on the (1) analysis of dissolved elements in the interstitial waters, (2) identification of exchangeable and carbonates bounded fractions, and (3) leaching tests using deionized water adjusted to the local pH. This analysis revealed high levels mainly in Cd, Pb, and Zn, in the interstitial waters and in the more soluble phases of sediments. The comparison between the levels of these elements in the leached extracts and the more soluble fractions corroborates the high capacity of these elements to be leached from the alluvium following precipitation episodes. The geochemical characterization and spatial distribution of the contaminants will allow, in the near future, a choice of the most appropriate environmental remediation technique(s) for the environmental requalification of this area. Full article

The existence of iron carbide in the upper mantle allows an assumption to be made about its possible involvement in the abyssal abiogenic synthesis of hydrocarbons as a carbon donor. Interacting with hydrogen donors of the mantle, iron carbide can form hydrocarbon fluid. In order to investigate the role of iron carbide in the abiogenic synthesis of hydrocarbons, the chemical reaction between cementite Fe₃C and water was modeled under thermobaric conditions, corresponding to the upper mantle. A series of experiments were conducted using a high-pressure high-temperature Toroid-type large reactive volume unit with further analysis by means of gas chromatography. The results demonstrated the formation of hydrocarbon fluid in a wide range of thermobaric conditions (873–1223 K, 2.5–6.0 GPa) corresponding to the upper mantle. A strong correlation between the composition of the fluid and the pT conditions of the synthesis was illustrated in the investigation. The higher temperature of the synthesis resulted in the formation of a “poor” hydrocarbon mixture, primarily comprising methane, while a higher pressure yielded the opposite effect, converting iron carbide into a complex hydrocarbon system, containing normal and iso-alkanes up to C₇ and benzene. This correlation explains the diversity of hydrocarbon systems produced experimentally, thus expanding the thermobaric range of the possible existence of complex hydrocarbon systems in the upper mantle. The results support the suggestion that the carbide—water reaction can be a source of both the carbon and hydrogen required for the abyssal abiogenic synthesis of hydrocarbons. Full article