Detailed Geological Information Research Articles

Innovative Approaches to Geoscientific Outreach in the Napo Sumaco Aspiring UNESCO Global Geopark, Ecuadorian Amazon Region

The Napo Sumaco Aspiring UNESCO Global Geopark (NSAUGG) in Ecuador represents a genuine variety of geological, cultural, and natural heritage, which aims to promote sustainable development through geotourism. This study describes the significance of NSAUGG, emphasizing its geological diversity which includes a variety of geosites, and focusing on three recently annexed geosites: the Wawa Sumaco Quarry, Puka Urku, and the Pucuno River, where geological analyses, including petrographic and mineralogical assessments, were conducted. To enhance community engagement and educational outreach, a multi-platform mobile application, “SumAppGeo”, was developed using ArcGIS and Flutterflow. This application serves as an interactive tool for visitors and local communities, providing detailed geological information, interactive maps, and educational content. The findings reveal the presence of significant geological features, such as haüyne-bearing alkaline rocks, which indicate specific volcanic activity in this region and are an element of geodiversity, validating the Wawa Sumaco Quarry, Puka Urku, and the Pucuno River as geosites. The implementation of SumAppGeo aims to foster a deeper understanding of the region’s geodiversity while promoting responsible tourism practices. This initiative not only supports the recognition of NSAUGG as part of the UNESCO Global Geoparks Network but also contributes to the socio-economic development of local communities through sustainable tourism practices.

Large-Scale Urban 3D Geological Modeling Based on Multi-Method Coupling Under Multi-Source Heterogeneous Data Conditions

The development and utilization of urban underground space represents a crucial strategy for achieving sustainable urban development. Three-dimensional (3D) geological models provide a data foundation and technical support for research in urban planning and construction, as well as the prevention and control of environmental geological issues. However, current urban 3D geological modeling generally faces the challenge of multi-source heterogeneous modeling data. This often necessitates varying degrees of generalization in data processing, resulting in the majority of current urban 3D geological models being relatively coarse and insufficient to fulfill the demand for detailed geological information in contemporary urban development and management. Therefore, determining how to formulate or optimize the 3D geological modeling schemes to enhance the utilization of multi-source heterogeneous data is a key challenge in current urban 3D geological modeling. This study, taking the 3D geological structure modeling of Wuhan’s metropolitan development area (MDA) as an example, develops an automated scheme for standardizing modeling data based on multi-scale geological chronostratigraphy. By utilizing the standardized stratigraphy as a unified and independent geological framework for layered modeling, a high-precision 3D geological model of Wuhan’s MDA, characterized by large-scale and ultra-complex geological conditions, is constructed through a methodology that integrates the global discrete constrained points modeling approach with the global layered modeling approach, without generalizing the multi-source heterogeneous modeling data. This research not only holds significant practical implications for the prevention and control of comprehensive urban geological issues in Wuhan but also provides novel technical insights into the methodology of 3D urban geological modeling.

SHALLOW SUBSURFACE STRUCTURES AND QUATERNARY DEFORMATIONS ON THE EASTERNMOST MATANO FAULT, INDONESIA, REVEALED BY ELECTRICAL RESISTIVITY TOMOGRAPHY

In active fault studies, electrical resistivity tomography (ERT) with wide electrode spacing (10 m) and fewer than 60 electrodes is typically utilized. However, this configuration limits the ability of ERT to resolve detailed geological information, such as fault geometry and motion, small-scale offset, and thickness of Quaternary layers. High-resolution electrical resistivity tomography (ERT) with narrow electrode spacing (1.5‒5 m) and 112 electrodes offers an opportunity to uncover finer geological information. This study combines ERT measurements with geological data from trenches and field observations to investigate the subsurface structures and Quaternary deformation on the easternmost Matano fault. On ERT sections, the easternmost Matano fault is characterized by deformed resistivity layers and resistivity contrasts. The subsurface fault structures dip steeply and indicate reverse and normal motions for the vertical component, with the displacement related to the Quaternary faulting ranging from 3 to 26 m. Notably, fault structures on ERT sections are not necessarily expressed by geomorphic features, suggesting obscured tectonic features. This study demonstrates the reliability of high-resolution electrical resistivity tomography (ERT) in unveiling geological information, such as fault location and geometry, fault vertical motions, buried fault structures, small-scale vertical offsets, stratigraphy, and Quaternary sediment thickness, which are essential for seismic hazard assessment.

Late Quaternary Deformation of the Ambon fault, Indonesia: Preliminary Results

The Ambon fault in the northern Banda Arc has capability of generating Mw 6.9 earthquake. The Ambon fault poses a significant seismic hazard to Ambon Island because the fault is located near populous areas, the Ambon City. Recent seismicity in Ambon Island and surrounding areas indicates that this region is actively deforming. Ambon Island has experienced many damaging earthquakes since the 17th century. However, the potential seismic hazard on this island remains enigmatic due to the lack of detailed geological information, such as fault traces, slip rate, and paleoseismic history. This study reports the preliminary results of tectonic geomorphic investigations and ground-penetrating radar (GPR) surveys on the Ambon fault. Tectonic geomorphic features, such as fault scarps, warped surfaces, and sag ponds indicate the late Quaternary activity of the Ambon fault. The Ambon fault predominantly shows a normal sense of motion with a dip of ~60-70°. The Ambon fault is related to the extensional tectonics in the Banda Sea.

Towards a conceptualization of the hydrological processes behind changes of young water fraction with elevation: a focus on mountainous alpine catchments

Abstract. The young water fraction (Fyw*), defined as the fraction of catchment outflow with transit times of less than 2–3 months, is increasingly used in hydrological studies that exploit the potential of isotope tracers. The use of this new metric in catchment intercomparison studies is helpful to understand and conceptualize the relevant processes controlling catchment functioning. Previous studies have shown surprising evidence that mountainous catchments worldwide yield low Fyw*. These low values have been partially explained by isolated hydrological processes, including deep vertical infiltration and long groundwater flow paths. However, a thorough framework illustrating the relevant mechanisms leading to a low Fyw* in mountainous catchments is missing. The main aim of this paper is to give an overview of what drives Fyw* variations according to elevation, thus clarifying why it generally decreases at high elevation. For this purpose, we assembled a data set of 27 study catchments, located in both Switzerland and Italy, for which we calculateFyw*. We assume that this decrease can be explained by the groundwater storage potential, quantified by the areal extent of Quaternary deposits over a catchment (Fqd), and the low-flow duration (LFD) throughout the period of isotope sampling (PoS). In snow-dominated systems, LFD is strictly related to the snowpack persistence, quantified through the mean fractional snow cover area (FSCA). The drivers are related to the catchment storage contribution to the stream that we quantify by applying a cutting-edge baseflow separation method to the discharge time series of the study sites and by estimating the mean baseflow fraction (Fbf) over the PoS. Our results suggest that Quaternary deposits could play a role in modulating Fyw* elevation gradients via their capacity to store groundwater, but subsequent confirmation with further, more detailed geological information is necessary. LFD indicates the proportion of PoS in which the stream is sustained and dominated by stored water coming from the catchment storage. Accordingly, our results reveal that the increase of LFD at high elevations, to a large extent driven by the persistence of winter snowpacks and the simultaneous lack of a liquid water input to the catchments, results in lower Fyw*. In our data set, Fbf reveals a strong complementarity with Fyw*, suggesting that the latter could be estimated as Fyw*≃1-Fbf for catchments without stable water isotope measurements. As a conclusion, we develop a perceptual model that integrates all the results of our analysis into a framework for how hydrological processes control Fyw* according to elevation. This lays the foundations for an improvement of the theory-driven models.

A system for inspecting karst voids during construction of cast-in-place pile foundations

Karst voids at pile locations are highly adverse to the bearing capacity and construction safety of cast-in-place pile foundations. This study developed an inspection system prototype of karst voids during cast-in-place pile foundation construction. The system consists of a multifrequency borehole sonic probe, two pile hole sonar probes, an in situ computer, and a corresponding signal analysis method. Borehole and pile hole detection are conducted during the investigation and pile hole drilling to inspect karst voids around the borehole and beneath the bottom of the pile hole. The analysis of the synthetic data verifies the effectiveness of the proposed method. A field inspection of karst voids during cast-in-place pile foundation construction was conducted. Comprehensive geophysical methods, including borehole optical imaging, 3D laser scanning, and borehole logging were deployed for comparison. The results show that the system can provide detailed geological information to the design of piles and ensure the construction safety of foundations.

3-D pre-stack diffraction separation by extending the PWD method with parametrized local slope

SUMMARY Diffractions comprise the seismic response of subsurface geological discontinuities and thus can provide detailed geological information during 3-D seismic exploration. The separation of weak diffractions from specular reflections is challenging, especially when the diffractions and reflections have similar kinematical characteristics in the 3-D pre-stack case. Conventional separation methods often estimate the local slope based on optimization or the Hilbert transform, which directly depends on the distribution behaviour of seismic events and may lead to the aliasing effects of the hyperbolic reflected and diffracted slopes in the shot domain. In this study, a different method is employed: local slopes are parametrized and constrained to the normal moveout velocity and ray parameter, which can distinguish reflections and diffractions in the shot domain and enhance the stability and accuracy of local slopes. Interestingly, when the receiver line and the geological edge are coplanar, the corresponding edge diffractions and reflections exhibit extremely similar behaviour, rendering them indistinguishable. Considering this phenomenon, a 3-D pre-stack diffraction separation strategy is proposed based on the estimation of the local slopes in two orthogonal directions. Thus, the accurate local slope can be used for plane-wave destruction when separating diffractions in the 3-D pre-stack domain. Synthetic and field data applications demonstrate that the proposed separation strategy is effective and can obtain high-quality diffraction wavefields for detecting the subsurface discontinuous structure.

Reexamination of Eruptive Activity of Akanfuji in the Me-Akan Volcano, Eastern Hokkaido, Japan

Eruption history of Akanfuji in the Me-akan volcano, eastern Hokkaido, has been examined by comparing multiple natural outcrops. In a previous study, at least 17 layers of scoria fall deposits were recognized. To obtain more detailed geological information and reexamine the eruptive activity of Akanfuji, we conducted trench surveys. At each survey site, the scoria fall deposits from Akanfuji are layered with a total thickness of several tens of centimeters to 1 m. A light brown volcanic ash layer is deposited just under the lowest layer of Akanfuji, and the fresh glass in the light brown volcanic ash shows the glass composition of the volcanic ash that erupted at Tarumai volcano 2500 BP. In addition, volcanic ash ejected from Ponmachineshiri of the Me-akan volcano is deposited on top of the newest deposits in the Akanfuji series with a thin soil layer in between. The volcanic ash ejected from Ponmachineshiri contains patches of volcanic ash from the Mashu volcano that erupted 1000 years ago. Therefore, Akanfuji was active from about 2500 to 1000 years ago. Akanfuji ejected scoria fall deposits at least 17 times (Akf-1 to Akf-17), and assuming that it erupted an average number of times during the activity period, it would be once every 90 years. The eruption rate was estimated to be 0.12 km3 DRE/ka.

Pleistocene northward thrusting of the Danghe Nanshan: Implications for the growth of the Qilian Shan, northeastern Tibetan Plateau

Understanding the tectonic history of the Qilian Shan provides significant insights into the growth pattern of the northern Tibetan Plateau. Due to the limitation of methodology and lack of detailed geological information over remote mountain ranges, there has been less information on the Pleistocene evolution of the southern Qilian Shan. Existing models for the Qilian Shan growth also fail to specify whether the southern Qilian Shan grew northward or southward during the late Cenozoic. Here we present provenance data on fieldwork paleocurrents, petrography, heavy mineral analysis, and zircon UPb ages from the Danghe valley between Danghe Nanshan and Yema Nanshan, southern Qilian Shan. Results show a ‘seesaw-like’ change of provenance from Yema Nanshan to the north during the early Pleistocene to Danghe Nanshan to the south, which suggests the northward thrusting of Danghe Nanshan. Integrated with previous studies, our inference of a Quaternary rapid exhumation of the southern Qilian Shan reinforces the argument of northward propagation of the southern Qilian Shan during the Pleistocene and suggests a complex growth pattern of the Qilian Shan, northeastern Tibetan Plateau.

Reflection imaging of complex geology in a crystalline environment using virtual-source seismology: case study from the Kylylahti polymetallic mine, Finland

Abstract. For the first time, we apply a full-scale 3D seismic virtual-source survey (VSS) for the purpose of near-mine mineral exploration. The data were acquired directly above the Kylylahti underground mine in Finland. Recorded ambient noise (AN) data are characterized using power spectral density (PSD) and beamforming. Data have the most energy at frequencies 25–90 Hz, and arrivals with velocities higher than 4 km s−1 have a wide range of azimuths. Based on the PSD and beamforming results, we created 10 d subset of AN recordings that were dominated by multi-azimuth high-velocity arrivals. We use an illumination diagnosis technique and location procedure to show that the AN recordings associated with high apparent velocities are related to body-wave events. Next, we produce 994 virtual-source gathers by applying seismic interferometry processing by cross-correlating AN at all receivers, resulting in full 3D VSS. We apply standard 3D time-domain reflection seismic data processing and imaging using both a selectively stacked subset and full passive data, and we validate the results against a pre-existing detailed geological information and 3D active-source survey data processed in the same way as the passive data. The resulting post-stack migrated sections show agreement of reflections between the passive and active data and indicate that VSS provides images where the active-source data are not available due to terrain restrictions. We conclude that while the all-noise approach provides some higher-quality reflections related to the inner geological contacts within the target formation and the general dipping trend of the formation, the selected subset is most efficient in resolving the base of formation.

Results of implementation of mechanical logging for additional investigation of the geological structure of the Olon-Shibirskoe coal deposit

Mining coal requires detailed geological information about the structure of the coal seam and the quality of coal seams that allows to minimize the risks associated with the complicating mining and geological factors and changes in the quality characteristics of coal. The article discusses the experience of applying the mechanical logging method as an express method of operational exploration in the Olon-Shibirsk coal deposit. The mechanical logging data were compared with core sampling data and geophysical well surveys. As a result, criteria for dividing the coalbearing sequence of the deposit into lithotypes were identified. According to these criteria, it is possible to identify a general pattern for the considered coal seam: drilling speed increases with decreasing grain size, drilling speed also increases with increasing the content of organic matter in the rock, the maximum drilling speed is characterized by coal seams. The drilling speed is the determining parameter, while the other drilling parameters complement its readings in case of ambiguity in the interpretation of the graph. For coal seams, the dependence of drilling speed on ash content was determined. At the same time, the dependence is most correct for coal seams with thickness more than one meter. On the basis of operational exploration data using mechanical logging for some areas, the morphology of coal seams, as well as the complexity of their structure and ash content, which allowed to specify the reserves and quality by geological blocks. In the final comparison with the fact was confirmed an increase in the accuracy of calculations using the method of mechanical logging. Practical significance of the results of the study is to improve the quality of operational exploration in the field while reducing costs.

Petrogenesis and tectonic implications of late Permian and Triassic granitoids on Hainan Island, South China

Hainan Island is a key part of the eastern Tethyan region and contains detailed geological information that can enhance our understanding of the tectonic evolution of this region since the late Palaeozoic. In this paper, we report geochronological, geochemical, and Sr–Nd isotopic data for granitoids from Baomei and Chahe in the northern part of Hainan Island. Three new zircon U–Pb ages of 243.3 ± 1.7 Ma, 237.1 ± 5.1 Ma, and 257.0 ± 4.0 Ma were obtained for these granitoids. The late Permian Chahe granite (257 Ma) is weakly peraluminous to peraluminous, and has rare earth element patterns and Ga/Al and FeOT/MgO ratios typical of A‐type granites formed in an extensional tectonic setting. The Middle Triassic Baomei granitoids (243–237 Ma) are weakly peraluminous, and exhibit a negative correlation between P2O5 and SiO2, which is typical of I‐type granites. All the granitoids have EM II‐type‐enriched mantle Sr–Nd isotopic compositions, which indicate that they were derived from a mantle source that had experienced enrichment and metasomatism. Hainan Island was in an extensional tectonic setting from the late Permian to Middle Triassic when widespread A‐ and I‐type granites were generated. We speculate that Hainan Island was mainly affected by the Tethyan tectonic domain during the Permian–Triassic, which involved closure of the Palaeo‐Tethys Ocean, collision of the Indochina and South China blocks, and subsequent post‐collisional extension.

Groundwater exploitation in Awka (Anambra – Nigeria) and environs: Prospects, and challenges while drilling and its mitigation measures

Groundwater exploitation (borehole drilling) was carried out around Awka and environs in Anambra State, Southeastern Nigeria, to understand the underlying rock units encountered while drilling, differentiate boreholes with confined aquifers from those with unconfined aquifers, delineate the probable aquiferous zones from the borehole data, evaluate the challenges encountered while drilling (both geologic and technical), and identify mitigation measures employed to address these challenges. Detailed geologic log information of the boreholes was produced to illustrate the rock units encountered while drilling. Four rock units were identified, namely: shale, sandstone, clay, and gravel. These rock units were exposed within the Imo Formation and the Nanka Formation that underlie the study area. Results from the geologic log information of the boreholes indicate that the water table within the study area ranges from 11.2 m to 56.5 m from the soil surface, and the probable aquiferous zones vary from 6.8 m to 23.3 m in thickness. A detailed look at the lithologic logs of the boreholes show that 50% of the drilled boreholes possess confined aquifers while the remaining 50% have unconfined aquifers. A careful appraisal of the challenges encountered, which are mainly geologic, is strictly attributed to the geologic formation of the study area. Other technical challenges have been derived from mechanical faults developed during drilling.

Mapping of Coastal Zones Using Unmanned Aerial Vehicle (UAV) Video Sequences

Han, D. and Lee, C., 2021. Mapping of coastal zones using Unmanned Aerial Vehicle (UAV) video sequences. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 400–404. Coconut Creek (Florida), ISSN 0749-0208. Collecting accurate and detailed geological and dynamic information on coastal processes is required for coastal erosion and coastal facility monitoring. Over the past decades, video monitoring systems have demonstrated to be a cost-effective method. Nevertheless, extracting information with consistent accuracy of the coast with video processing is difficult due to the limitation of the geometric field of view from the top of the tower. In this work we apply a framework for geographic mapping in coastal videos using Unmanned Aerial Vehicles (UAV). Specifically, we address the coast modeling using video frames. The system is designed to be deployed utilizing inexpensive, off-the-shelf hardware, in such a way that the results can be easily replicated by other applications. Therefore, it was possible to obtain geometrical accuracy similar to using photo to video frames.

Integrating uncertainty into geotechnical design of underground openings in tectonically undisturbed but lithologically varied sedimentary environments

A systematic but straightforward probabilistic approach was adopted for the preliminary design using a tunnel case in Egnatia Odos Highway. This tunnel was excavated in a heterogenous molassic formation in Northern Greece, and more specifically in tectonically undisturbed but lithologically varied sedimentary series. This research aimed to identify sources of uncertainty and evaluate its governance during the selection of the geotechnical design parameters. Rigorous analyses of the critical parameters and factors were undertaken following a standardised method for designing underground structures based on the probability theory. Initially, the statistical analysis of the intact rock strength parameters and project-specific geological and geotechnical factors allowed the development of understanding in determining these sources of uncertainty and assisted in quantifying them. The lithological units encountered in the tunnel alignment were classified into first, Geological Units and, secondly, into Rock Mass Types (Geotechnical Units). Finally, the latter were grouped into anticipated Rock Mass Behaviour Types, which were numerically investigated using RS2 for the Finite Element Method analysis and Unwedge to assess these Rock Mass Types' failure modes. For this purpose, the Point Estimate Method was used in the FEM analysis to evaluate the effect of uncertainty in the strength parameters. Ultimately, the numerical analysis results subsequently led to the preliminary design of the respective support sections. Although this investigation was limited by the geotechnical information provided, it was concluded that the approach followed proved to be adequate in identifying the primary sources of uncertainty and its impact on geotechnical design. It was also noted that with more detailed geological information, this probabilistic approach could be used to produce a robust final support tunnel design.

Quantitative evaluation of hydrothermal fluids and their impact on diagenesis of deep carbonate reservoirs: Insights from geochemical modeling

Hydrothermal dolomitization is an important diagenetic process that affects the quality of carbonate reservoirs. While geochemical modeling is a useful tool to improve our understanding of this process, comparatively little research has been focused on producing reservoir intervals. This study examines deeply buried (over 4500 m deep), Lower Ordovician dolomitized limestones (more than 50 m revealed by the borehole) in an exploration well in the Tazhong Uplift, Tarim Basin. The well penetrated a fault zone that was affected by extensive hydrothermal activity during the Permian. Batch geochemical modeling and reactive transport modeling (RTM) were used to evaluate the potential sources of hydrothermal fluid and the associated mechanisms that resulted in a relatively restricted distribution of dolomitization in the study area. Simulation results show that the RTM, which can include geological heterogeneity, provides more reliable constraints for the volume of hydrothermal fluids required for the observed scale of dolomitization, compared to batch geochemical modeling. According to the simulation results, the interstitial fluids released from underlying Cambrian formations due to high pressure and high temperature are not the only source of hydrothermal dolomitization. Other mechanism like long-lasting recharge of seawater-derived basement brines may be took place. Scenario simulations also indicate that the patterns of hydrothermal dolomitization and porosity distributions are strongly related to permeability heterogeneity in the formation. This study shows the ability and feasibility of geochemical modeling as a tool to quantitatively evaluate and further understand hydrothermal dolomitization processes, which are also helpful for other similar geological process research. However, reliable and detailed geological information, geological constrains, especially geological heterogeneity distributions, are crucial to achieve beneficial conclusions.

Optimization Analysis of Suki Kinari Underground Powerhouse Caverns Based on an Efficient CATIA-Abaqus Model

Underground powerhouse caverns, which are large-scale, complex-type, and intersecting circuits, are considered as a complicated, constrained, and irreversible nonlinear system. They are divided into several layers for excavation. Various stress states occur whenever they are subjected to excavation; therefore, deformation and failure arise because of stress redistribution and concentration. Based on the determinate excavation scheme, the sectional shape of underground powerhouse caverns, especially the aspect ratio of the main powerhouse, is the key factor that affects the stability of the surrounding rock masses. Furthermore, during the excavation process, the integrity and stability of rock pillar, whose thickness is determined by the interval of caverns, are considered as crucial issues, because damage occurs in the thinner rock pillar. Consequently, the interval of caverns is the important parameter that needs to be investigated. In this study, we combine building information modeling with numerical analysis to investigate the effect of the aspect ratio of the main powerhouse and the interval between the main powerhouse and the main transform chamber. For the Suki Kinari (SK) underground powerhouse caverns, the 3D terrain and geological model was created in accordance with the detailed geological information. The parameterized underground powerhouse model and the supporting system were designed by CATIA, and the numerical model that involves the excavation scheme was generated by ABAQUS. The results show the following: (1) As the aspect ratio increases, the deformation of the main powerhouse exhibits various features, indicating that the arch crown settlement reduces while the deformation of the sidewalls increases. (2) As the aspect ratio increases, the overall deformation of the particular parts exhibits the characteristic of rapidly decreasing and then gradually forming a convergent trend. (3) Intense disturbance occurs on the rock pillar because of bidirectional unloading during the excavation process, and the rock pillar weakens rapidly and then gradually stabilizes as the thickness increases, suggesting the property of exponential function of the total deformation. Finally, the conclusions are applied on the SK underground powerhouse caverns to reveal the optimal aspect ratio and interval.

Aquifer characterization using vertical electrical soundings and remote sensing: A case study of the Chott Ech Chergui Basin, Northwest Algeria

The aim of this study is to provide detailed geological and structural information about groundwater aquifers in the Chott Ech Chergui region using geophysical and remote sensing data. The Chott Chergui region is a large endorheic depression situated in the northwestern part of Algeria. It is submerged in water, and for that reason, it is considered to be a humid zone even though the region is considered to be a semiarid area. The largest quantities of water come from the northern mountains of Saïda and Tlemcen. Some water recharge comes from the Ksour and Amour mountains to the south. Large amounts of this water reach the underground aquifers through a dense fracture network. These water resources are stored in a lithological complex that is composed of three closely related aquifer formations, namely, the continental Tertiary aquifer, the Senonian aquifer and the Aaléno-Bathonian aquifer.The Kheiter and Ain Skhouna areas are known for their gushing water springs that exhibit high flow rates (80 l/s for Ain Skhouna). It is for this reason that we focus on these two regions to understand their flow mechanisms and attempt to construct a conceptual model that illustrates the functional mechanism of the Ain Skhouna spring.This work was accomplished employing a combined approach involving Remote Sensing method and electrical resistivity, specifically, the vertical electrical sounding (VES) technique. The VES technique was used to understand the aquifer geometries and their spatial extents, while the remote sensing results were used to detect some structures and lineaments that favor groundwater exploration. The aquifer geometry was analysed by integrating the results obtained from the interpretations of VES with stratigraphic columns of wells and boreholes using a geographic information system. The results of this study show that three geological levels present aquifer potentialities. The geologic zones are the Aaleno-Bathonian aquifer, which is the most important aquifer in the study area with an average thickness of 250 m, the Senonian aquifer and Tertiary aquifer. The aquifers recharge mainly from fractures in the Saïda and Tlemcen Mountains for the Aaleno-Bathonian aquifer, and from direct infiltration from the accumulated surface waters for the Senonian and Tertiary aquifers. Many water sources are sporadically distributed in the Chott Ech Chergui, but the gushing waters seems to be controlled by E-W accidents, especially in Ain Skhouna hot spring. A schematic model of the spring is presented.

Developing a conceptual model and power capacity estimates for a low-temperature geothermal prospect with two chemically and thermally distinct reservoir compartments, Hawthorne, Nevada, USA

The Hawthorne area in the Basin and Range province in Nevada in the western USA has been the focus of geothermal investigations for over 40 years, with initial discovery of blind resources via anomalously-warm water wells. Subsequent studies and drilling of temperature gradient holes and geothermal wells identified three separate blind geothermal prospects in the Hawthorne part of the Walker Lake basin. In this study, we conducted a detailed review of all existing geoscience data acquired at the site to date to develop a quantitative estimate of geothermal resource potential for one of the Hawthorne geothermal prospects (prospect A — along the southwest side of the basin). This included review of substantial well data from water wells and geothermal exploration wells (downhole temperature logs, lithology, water chemistry, borehole televiewer, and alteration mineralogy), detailed geological and structural mapping information, geophysical data (gravity, magnetic, and seismic reflection), 2-meter temperature data, and an existing 3D geological model of the basin. We find that the thermal anomalies associated with prospect A reflect the influence of two geothermal fluids in close proximity that are chemically-distinct, with different temperatures and spatial extent (lateral and vertical). One fluid represents a deeper resource, hosted in altered, fractured Mesozoic granitic basement along a segment of the Wassuk Range-front fault system, and characterized by equilibrated, alkali-chloride fluids, with ∼4000 ppm total dissolved solids (TDS) and a maximum measured temperature of ∼115 °C at ∼1500 m depth. A second fluid is hosted in Neogene basinal sediments at <400 m depth, with maximum measured temperatures of ∼100 °C, TDS of ∼1000 ppm, and a sodium-sulfate fluid chemistry. The outflow of this shallow resource can be tracked down gradient into the basin using well temperature data, which map a vertically-constrained plume that cools with distance from the inferred upflow location. The data suggest that the deeper resource is conductively transferring heat to the shallow resource, and structural and/or stratigraphic compartmentalization is preventing direct interaction and fluid mixing. Through our development of a new conceptual model of prospect A (with P10, P50, and P90 scenarios), and application of the power density method, we estimate the deep and shallow systems may have resource potential of 7 MWe (P50) and 1.6 MWe (P50) respectively.

A framework for the predictive mapping of forest soil properties in mountain areas

The modelling of forest ecosystems is a broad scientific field, encompassing species distribution, dynamic forest succession, growth and disturbance, and biogeochemical cycles. Soil information is frequently required for a holistic and spatially explicit modelling approach. Information on soil properties at sufficient resolution to be incorporated in spatially distributed models is rare however, in particular for mountain forest areas that are poorly accessible and where the required sampling effort is high. In order to bridge this gap, we aim to develop a concept for predicting spatially continuous forest soil properties in mountain areas and substantiate it by comparing different statistical approaches to digital soil mapping, namely Random Forests and Generalized Additive Models. Therefore, we used field descriptions of 1653 legacy soil profiles from a forest area of 5130 km2 in Tyrol and modelled a variety of soil properties that are essential for the characterisation of forest sites with respect to tree growth. A set of 23 spatially explicit predictor variables, grouped according to geological substrate information, topography, climate, biotic variables, and time–space, were included in the concept and tested. There was a special focus on the predictive relevance of the newly developed geological substrate information, which includes lithogenetic units, lithological composition, and the multilayering of sediments. As a physical soil property, it was possible to predict the plant-available water storage capacity with a significant degree of accuracy, with r2 = 0.49–0.56, while for the biologically driven state variable organic humus layer thickness, r2 = 0.22–0.27 was achieved. For describing soil reaction, Ellenberg’s indicator value of vegetation turned out to be a suitable proxy for soil pH value, and was modelled with a high degree of predictive power with r2 = 0.75–0.77. All model results were verified by different evaluation methods, ranging from cross-validation to comparison with independent datasets, tests for spatial autocorrelation, and considering ecological soundness in variable selection. We were able to show that in addition to variables derived from Digital Terrain Models and climate information, the new type of detailed geological substrate information is the most relevant predictor and is promising for digital soil mapping in mountain areas. This finding was independent of the applied statistical approaches and both Generalized Additive Models and Random Forests showed comparable accuracy and proved to be appropriate for these tasks. In addition, we were able to support the modelling results by interpreting the predictors’ mode of action with regard to the underlying processes controlling soil properties.