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The Zafra de Záncara anticline (also known as the El Hito anticline), located in the Loranca Cenozoic Basin (part of the Tagus Basin, Central Spain), had been studied by several oil companies during the late 1960s and early 1970s. In 2009, within the 'Plan for selection and characterization of suitable structures of CO2 geological storage', this anticline was selected as a potential CO2 storage site. A preliminary three‐dimensional geological model, based on five geological cross sections that were constrained with the interpretation of the available seismic profiles (that are rather old and do not have very good quality), was created. With the aim of improving the geological knowledge of the Zafra de Záncara anticline and helping to investigate the suitability of a nearby anticline, namely La Rambla, as another structural closure that might make it a possible CO2 storage site, a local gravity survey (1 station every km2) was carried out in the area, seven new geological cross sections, based on these existing seismic profiles and field geology, were build, and a new three‐dimensional geological model that included both anticlines, improved through three‐dimensional stochastic gravity inversion, was constructed. The densities needed for the geological formations of the model come from the analysis of rock samples, logging data from El Hito‐1 drillhole and petrophysical information from Instituto Geológico y Minero de España database. The inversion has improved the knowledge about the geometry of the anticlines' traps and seals as well as the geometry of the basement relief and the structural relationship between basement and cover. [ABSTRACT FROM AUTHOR]

This study highlights three-dimensional variability of stratigraphic geometries in the ramp crest to basin of mixed carbonate–siliciclastic clinoforms in the Permian San Andres Formation. Standard field techniques and mapping using ground-based lidar reveal a high degree of architectural complexity in channellized, scoured and mounded outer ramp stratigraphy. Development of these features was a function of location along the ramp profile and fluctuations in relative sea-level. Deposition of coarse-grained and fine-grained turbidites in the distal outer ramp occurred through dilute and high-density turbidity flows and was the result of highstand carbonate shedding within individual cycles. In this setting, high-frequency cycles of relative sea-level are interpreted on the basis of turbidite frequency, lateral extent and composition. Submarine siliciclastic sediment bypass during lowstand cycles resulted in variable degrees of siliciclastic preservation. Abundant siliciclastic material is preserved in the basin and distal outer ramp as point-sourced lowstand wedges and line-sourced early transgressive blankets. In mounded topography of the outer ramp, siliciclastic preservation is minimal to absent, and rare incised channels offer the best opportunity for recognition of a sequence boundary. Growth of mounded topography in the outer ramp began with scouring, followed by a combination of bioherm construction, fusulinid mound construction and isopachous draping. Intermound areas were then filled with sediment and continued mound growth was prevented by an accommodation limit. Mound growth was independent of high-frequency cycles in relative sea-level but was dependent on available accommodation dictated by low-frequency cyclicity. Low-angle ramp clinoforms with mounded topography in the outer ramp developed during the transgressive part of a composite sequence. Mound growth terminated as the ramp transformed into a shelf with oblique clinoform geometries during the highstand of the composite sequence. This example represents a ramp-to-shelf transition that is the result of forcing by relative sea-level fluctuations rather than ecologic or tectonic controls. [ABSTRACT FROM AUTHOR]

The present study attempts to combine direct current and induced polarization methods for 3D geological modelling and preliminary volume estimation of gold mineralization targets in the Simi locality, Adamawa, Cameroon. To begin, resistivity and chargeability data were collected along seven profiles oriented in N150E using the electrical tomography technique. A geological investigation was also carried out and allowed in addition to the geological formations to highlight the existence of gold mineralization in the study area. The interpretation of the inversion results was done by taking into consideration the geological field data and the existing resistivity charts. The 3D distribution of the interpreted sections allowed us to make a horizontal correlation between the different sections and to elaborate the 3D geological model of the study area by using the deterministic inverse distance method. The estimated model indicates a volume of 621,130.625 m3 of the possible gold complex. The gold complex was then divided into two mineralization domains based on chargeability ranges (mV/V): A first domain is associated with a major mineralization zone (39–60 mV/V) with a volume of 10,842 m3, and a second domain is associated with secondary mineralization zone (18–39 mV/V) with a volume of 610,288 m3. This model allows to compartmentalize the gold complex and can be used as a base model for the gold investigation in the study area. [ABSTRACT FROM AUTHOR]

The propagation of microseismicity in subsurface media is complex. We developed an anisotropic petrophysical model based on an empirical formula, linear slip theory and the bond transform method considering real underground conditions. Using Biot's equations, the seismic response to a general dislocation source in fracture‐induced anisotropic two‐phased media was solved using a staggered grid high‐order finite‐difference algorithm. To understand the relationship between the microseismic wave and fracture parameters, we then designed several different models to calculate the wavefield snapshots and analyse the effect of the fracture volume ratio and orientation. The modelling results indicate that the shear faulting source generates three types of waves in two‐phase media. Fractures can render homogeneous media anisotropic, and anisotropy becomes more noticeable with an increase in the fracture volume ratio. This decreases the velocity of the fast longitudinal and transverse waves in the vertical direction and increases the velocity of the slow longitudinal wave in a certain range. The fracture orientation mainly influences the moment tensor and then affects the wavefronts. These simulations lay the foundation for further studies on microseismic wave propagation in fracture‐induced anisotropic media. [ABSTRACT FROM AUTHOR]

Geo‐hydrological phenomena, including gullies, contribute significantly to soil erosion and land degradation. To address this, proper management of basins and hillslopes should consider the mechanism, timing, and location of gully development and how gullies interact with other hillslope processes. Yet, conventional modelling techniques for such processes are rare, frequently being limited to applications of only single processes and typically requiring high‐resolution input data. Further, existing tools for characterizing basins and hillslopes tend to be based on static descriptions of geo‐environmental conditions, and thus are not effective for modelling changes such as the seasonal triggering conditions of gully phenomena over time. This study proposes a method to integrate open remote sensing data (Sentinel‐2) and an existing modelling tool (LANDPLANER) using simplified input data to better predict and forecast gullies' spatial and temporal occurrence. The study investigates the seasonal conditions responsible for the triggering of gullies at the catchment scale using different erosion modelling schema in the Toscana region of Central Italy. Geomorphological gully inventory data were collected and used as benchmarks to test the proposed approach. The results show that the occurrence of gully erosion in the studied region changes seasonally, and the proposed method was able to effectively discriminate spatial and temporal differences of the gully phenomena. The proposed method can be applied to similar regions worldwide, allowing for the investigation of gully erosion over time, even in places with limited data availability. [ABSTRACT FROM AUTHOR]

The Central‐Eastern Mediterranean region is known to be a complex area due to the interaction of four tectonic plates, namely Arabia, Africa, Anatolia and Eurasia, and by the presence of an ancient oceanic crust in the Herodotus and Ionian Basins. The analysis of the available literature highlights that the distribution of the freely available geophysical data (i.e. seismic, gravity and magnetic observations) is quite disparate. In this framework, high‐resolution global gravity field models, such as XGM2019e, mainly based (offshore) on satellite data, can be profitably used as a uniform dataset to study, in a coherent way, large regions. In the current work, we exploit the XGM2019e model, together with a set of a priori information, derived mainly from geophysical data retrieved from the literature, to study the structure of the crust in the Central‐Eastern Mediterranean area. The study is organized in three different phases: in the first one, we enhanced the map of geological crustal provinces by means of an automatic Bayesian classification algorithm applied to the second radial derivatives of the gravitational potential. In the second phase, using as observation a grid of gravity anomalies, we applied a full three‐dimensional inversion procedure (always based on a Bayesian paradigm) to estimate the mass density variations and the geometries of the main geological units in the whole study area. Finally, in the third phase, we performed a refined three‐dimensional local inversion on the Cyprus area to improve the modelling of the shallowest layers. The main results of this study, carried out in the framework of the European Space Agency GIADA project, are freely available, upon request, at https://www.g‐red.eu/geophysics/. [ABSTRACT FROM AUTHOR]

Direct current electrical resistivity method has experienced significant breakthroughs during the last decades with the development of advanced instrumentation and sophisticated inversion algorithms. These have substantially benefitted the field of archaeological prospection to extract quantitative information for the buried archaeological material in a complete three‐dimensional (3‐D) context. The obvious continuation of past human occupation and associated settlements in the ultra‐shallow part of coastal zones generated the necessity to compile methodologies for mapping submerged cultural assets. This study investigates the efficiency of dynamic floating and submerged 3‐D Electrical Resistivity Tomography (ERT) for mapping archaeological relics buried beneath the sediments in ultra‐shallow marine environments. Extensive testing is performed through numerical simulation and 3‐D inversion of synthetic apparent resistivity tomographic data. The generic resistivity model including a complex resistive structure embedded in a stratified conductive environmental regime simulated typical scenario of an archaeological feature submerged below the sea water layer. Different array configurations including Dipole–Dipole (DD), Gradient (GRD), Reciprocal Wenner (RecWEN) and Wenner‐Schlumberger (WS), which can be appropriately programmed for continuous off‐shore measurements with associated multichannel resistivity instruments, are validated in order to determine the most efficient one for such surveys. Densely spaced multiple parallel two‐dimensional (2‐D) ERT lines along a single direction composed the survey layout to extract the 3‐D apparent resistivity data set for the different electrode arrays using a 3‐D finite element program. The synthetic tomographic data were corrupted with 3% Gaussian noise and inverted with an iterative smoothness constrained inversion algorithm. The comparative results from the various tested arrays manifest the superiority of the DD in reconstructing the optimum resistivity inversion model for both the floating and submerged survey modes. Additional tests were made concerning the resolving capabilities of ERT with variable seawater thickness and target characteristics. Although accurate 'a priori' information regarding the water resistivity and thickness are essential for constraining the 3‐D inversion, erroneous estimation of these parameters can result to misleading results, especially for submerged survey modes. The simulation of floating and submerged 3‐D ERT surveys through synthetic modelling documented the benefits of such approach in reconstructing structured cultural material in shallow off‐shore environments. Finally, the results of a 3‐D dynamic floating ERT survey from a submerged archaeological site in Greece verified the theoretical outcomes, proposing at the same time techniques to overcome problems that can occur due to the unique conditions of the ultra‐shallow marine environment. Overall, this work enhances the conclusion that 3‐D marine ERT is a robust method to reconstruct submerged archaeological structures related to ancient built environment in ultra‐shallow marine regions. [ABSTRACT FROM AUTHOR]

A gravity survey was conducted at a salt mine in Nemocón, Cundinamarca, Colombia, located in the axial part of the Eastern Cordillera of the northern Andes. This part of the Eastern Cordillera is characterized by successions of synclines and anticlines sometimes containing salt bodies at their core, and the mine is located at the top of one of these anticlines called the Nemocón anticline. As is typical for salt and other mines in Colombia, very little data on the internal structure and geology are publicly available. The purpose of our study is to show how gravity data and modelling can be used to infer near‐surface properties above the mine in the absence of other sources of information. Relative gravity measurements were made over an irregular grid of 107 stations and tied to the Instituto Geográfico Augustin Codazi national absolute gravity network. The total and residual Bouguer anomalies as well as the analytic signal were calculated over the area of the salt body. Using grid data, we first determine the main inversion parameters (e.g., depth weighting) and model resolution using a checkerboard model with the addition of random noise. Then, applying 3D inversion modelling to the residual Bouguer anomaly, we find that the positive and negative anomalies correspond to few zones of positive density contrasts and two main zones of negative density contrasts. Some of the positive anomalies are located above the fault trace putting in contact the Arenisca Dura formation with the Conejo formation containing the salt body. The negative anomalies are not well correlated with the underground position of the salt mine, but some influence of the low‐density 'rute' material, consisting of black clays with shaly claystone parts covering the salt body might be important. This study showcases how 3D inverse modelling can provide important information on the near‐surface structure of a salt mine. [ABSTRACT FROM AUTHOR]

ABSTRACT: The sequestration of CO2 in subsurface reservoirs constitutes an immediate counter‐measure to reduce anthropogenic emissions of CO2, now recognized by international scientific panels to be the single most critical factor driving the observed global climatic warming. To ensure and verify the safe geological containment of CO2 underground, monitoring of the CO2 site is critical. In the high Arctic, environmental considerations are paramount and human impact through, for instance, active seismic surveys, has to be minimized. Efficient seismic modelling is a powerful tool to test the detectability and imaging capability prior to acquisition and thus improve the characterization of CO2 storage sites, taking both geological setting and seismic acquisition set‐up into account. The unique method presented here avoids the costly generation of large synthetic data sets by employing point spread functions to directly generate pre‐stack depth‐migrated seismic images. We test both a local‐target approach using an analytical filter assuming an average velocity and a full‐field approach accounting for the spatial variability of point spread functions. We assume a hypothetical CO2 plume emplaced in a sloping aquifer inspired by the conditions found at the University of Svalbard CO2 lab close to Longyearbyen, Svalbard, Norway, constituting an unconventional reservoir–cap rock system. Using the local‐target approach, we find that even the low‐to‐moderate values of porosity (5%–18%) measured in the reservoir should be sufficient to induce significant change in seismic response when CO2 is injected. The sensitivity of the seismic response to changes in CO2 saturation, however, is limited once a relatively low saturation threshold of 5% is exceeded. Depending on the illumination angle provided by the seismic survey, the quality of the images of five hypothetical CO2 plumes of varying volume differs depending on the steepness of their flanks. When comparing the resolution of two orthogonal 2D surveys to a 3D survey, we discover that the images of the 2D surveys contain significant artefacts, the CO2‐brine contact is misplaced and an additional reflector is introduced due to the projection of the point spread function of the unresolvable plane onto the imaging plane. All of these could easily lead to a misinterpretation of the behaviour of the injected CO2. Our workflow allows for testing the influence of geological heterogeneities in the target aquifer (igneous intrusions, faults, pervasive fracture networks) by utilizing increasingly complex and more realistic geological models as input as more information on the subsurface becomes available. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate a novel way to introduce resistivity models deriving from airborne electromagnetic surveys into regional geological modelling. Standard geometrical geological modelling can be strengthened using geophysical data. Here, we propose to extract information contained in a resistivity model in the form of local slopes that constrain the modelling of geological interfaces. The proposed method is illustrated on an airborne electromagnetic survey conducted in the region of Courtenay in France. First, a resistivity contrast corresponding to the clay/chalk interface was interpreted confronting the electromagnetic soundings to boreholes. Slopes were then sampled on this geophysical model and jointly interpolated with the clay/chalk interface documented in boreholes using an implicit 3D potential-field method. In order to evaluate this new joint geophysical-geological model, its accuracy was compared with that of both pure geological and pure geophysical models for various borehole configurations. The proposed joint modelling yields the most accurate clay/chalk interface whatever the number and location of boreholes taken into account for modelling and validation. Compared with standard geological modelling, the approach introduces in between boreholes geometrical information derived from geophysical results. Compared with conventional resistivity interpretation of the geophysical model, it reduces drift effects and honours the boreholes. The method therefore improves what is commonly obtained with geological or geophysical data separately, making it very attractive for robust 3D geological modelling of the subsurface. [ABSTRACT FROM AUTHOR]

It is widely accepted that the fossil record suffers from various sampling biases - diversity signals through time may partly or largely reflect the rock record - and many methods have been devised to deal with this problem. One widely used method, the 'residual diversity' method, uses residuals from a modelled relationship between palaeodiversity and sampling (sampling-driven diversity model) as 'corrected' diversity estimates, but the unorthodox way in which these residuals are generated presents serious statistical problems; the response and predictor variables are decoupled through independent sorting, rendering the new bivariate relationship meaningless., Here, we use simple simulations to demonstrate the detrimental consequences of independent sorting, through assessing error rates and biases in regression model coefficients., Regression models based on independently sorted data result in unacceptably high rates of incorrect and systematically, directionally biased estimates, when the true parameter values are known. The large number of recent papers that used the method are likely to have produced misleading results and their implications should be reassessed., We note that the 'residuals' approach based on the sampling-driven diversity model cannot be used to 'correct' for sampling bias, and instead advocate the use of phylogenetic multiple regression models that can include various confounding factors, including sampling bias, while simultaneously accounting for statistical non-independence owing to shared ancestry. Evolutionary dynamics such as speciation are inherently a phylogenetic process, and only an explicitly phylogenetic approach will correctly model this process. [ABSTRACT FROM AUTHOR]

The influence of catchment attributes has been examined to find out whether variations in water quality indicators [electrical conductivity (EC), pH, turbidity, dissolved oxygen (DO), total dissolved solid (TDS), total nitrogen (TN), dissolved organic nitrogen (DON), dissolved inorganic nitrogen (DIN), temperature and nitrogen] could be explained by them for 24 wetlands in west Japan. Urban areas (%) were positively ( P ≤ 0.05) correlated with EC ( r = 0.67), TDS ( r = 0.69), TN ( r = 0.92), DON ( r = 0.60), [NH4+] ( r = 0.47) and with [NO2−] ( r = 0.50). Forest areas (%) were inversely ( P ≤ 0.05) correlated with EC ( r = −0.62), TDS ( r = −0.68), TN ( r = −0.68) and [NH4+] ( r = −0.55) and with DON ( r = −0.43). Agricultural area (%) was positively ( P ≤ 0.05) correlated with EC ( r = 0.40), TDS ( r = 0.45), TN ( r = 0.44) and [NH4+] ( r = 0.56) and with both areas (%) of grey lowland soil ( r = 0.60) and diluvial sand ( r = 0.58). Area (%) of regosol was positively correlated with DO (r = 0.42) but inversely with DON ( r = −0.44, P ≤ 0.05). Rhyolite was positively ( P ≤ 0.05) correlated with the TN ( r = 0.46) but inversely with DON ( r = −0.49) and [NH4+] ( r = −0.47). Regression models were developed for the water quality indicators including EC ( r2 = 0. 62) [ABSTRACT FROM AUTHOR]

ABSTRACT Common shot ray tracing and finite difference seismic modelling experiments were undertaken to evaluate variations in the seismic response of the Devonian Redwater reef in the Alberta Basin, Canada after replacement of native pore waters in the upper rim of the reef with CO2. This part of the reef is being evaluated for a CO2 storage project. The input geological model was based on well data and the interpretation of depth-converted, reprocessed 2D seismic data in the area. Pre-stack depth migration of the ray traced and finite difference synthetic data demonstrate similar seismic attributes for the Mannville, Nisku, Ireton, Cooking Lake, and Beaverhill Lake formations and clear terminations of the Upper Leduc and Middle Leduc events at the reef margin. Higher amplitudes at the base of Upper-Leduc member are evident near the reef margin due to the higher porosity of the foreslope facies in the reef rim compared to the tidal flat lagoonal facies within the central region of the reef. Time-lapse seismic analysis exhibits an amplitude difference of about 14% for Leduc reflections before and after CO2 saturation and a travel-time delay through the reservoir of 1.6 ms. Both the ray tracing and finite difference approaches yielded similar results but, for this particular model, the latter provided more precise imaging of the reef margin. From the numerical study we conclude that time-lapse surface seismic surveys should be effective in monitoring the location of the CO2 plume in the Upper Leduc Formation of the Redwater reef, although the differences in the results between the two modelling approaches are of similar order to the effects of the CO2 fluid replacement itself. [ABSTRACT FROM AUTHOR]

The article presents groundwater flow modelling of the Kwa Ibo River watershed in the Abia State of Nigeria to assess the degree of interaction between the river and the groundwater regime of the thick sandy aquifer. The watershed was modelled with a grid of 65 rows and 43 columns and with two layers, Lateral inflow from the north was simulated with constant heads. the river transverses the middle of the watershed. Results from the modelling show that abstraction is much less than groundwater recharge.