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Gravity and time domain electromagnetic (TDEM) methods were used in this study to investigate the subsurface hydrogeology of the carbonate-rock aquifer in arid environments (central Tunisia, Western Mediterranean province). The El Houdh basin can be considered an appropriate case for evaluating the vulnerability of groundwater resources under present-day climate change. The identification of structural context and the discontinuities affecting the Eocene or Campanian to Maastrichtian carbonates is an important key to recognize water recharge and discharge pathways and to develop effective and long-term groundwater exploration strategies. First, we have produced an available residual gravity field using a specific Gaussian filter. Then, we generated derivative maps, Euler deconvolution solutions map and a 3D gravity model to delineate different anomalies and to estimate the depth-to-basement parameter and the subsurface density contrasts. Positive and negative anomalies mapping and 3D gravity modelling showed that the El Houdh basin is associated with an asymmetric ‘perched syncline’ with a segmentation into NE–SW sub-basins (local negative residual anomalies) separated by NW–SE lineaments. The TDEM survey was calibrated using boreholes to image the karst saturated and unsaturated zone and to deduce the epikarst and endokarst relationship. Finally, the proposed method provides a fast and valuable approach for better management of hydrogeological exploitation. Thematic collection: This article is part of the Climate change and resilience in Engineering Geology and Hydrogeology collection available at: https://www.lyellcollection.org/cc/climate-change-and-resilience-in-engineering-geology-and-hydrogeology

In Mediterranean semi-arid regions, shallow aquifers are generally over-exploited. However, several deeper groundwater boreholes exhibit serious problems of low hydraulic yield and dry wells. The existence of reliable information about the regional geological structure can enhance the success of deep well programmes. Geophysics has proved very useful as a fast and efficient tool to understand the structuring of deep hydrogeology aquifers. Indeed, the identification and characterization of the deep structures of the Bir Drassen–Sidi Toumi region (Cap-Bon, northeastern Tunisia) contribute to a better quantification of the groundwater potential, allowing more sustainable management. This province can be considered as the SW extension of the NE–SW Jebel Abderrahman Atlasic anticline, one of the most prominent geological structures in northeastern Tunisia. To identify the Miocene and Oligocene reservoirs, a geophysical study was carried out using advanced gravity analysis, supported by boreholes, and seismic and geoelectrical calibration. Different gravity filters were applied to reveal the sub-basin architecture and faulting network in the region. By calculating the maxima of the total horizontal gravity derivative and the distribution solutions for Euler's equations, a set of deep faults of different directions was divulged. Time-domain electromagnetic mapping illustrated the influence of these fault zones on the regional arrangement of sub-basin aquifers and their recharge processes. Finally, a 3D residual gravity inversion was carried out to better image the tectonically controlled depocentres associated with prolific thick fluvial–deltaic reservoirs. These ‘deep aquifer valley’ can be suggested as strategic targets for deep hydrogeological exploration planning.

The Jebel Oust region (north-eastern Tunisia) recorded two levels of marine black shale in the Lower Cretaceous marly series. Geodynamic evolution, biostratigraphic and Rock–Eval analysies allow classifying those black shales as unconventional shale oil resource systems that were deposited during two oceanic anoxic events: the Middel Barremian Event "MBE" and the Early Aptian Event "OAE1a". Paleogeographic evolution highlights two transgressive–regressive cycles: the first one is Valanginian-Early Barremian, and the second is Late Barremian–Early Aptian. Each black shale deposit occurs at the end of the transgression that coincides with the highest sea level. During the Barreman–Aptian interval, sedimentation was controlled by extensional faults in a system of tilted fault blocks which were reactivated several times. Kerogen is of type I, II origin in black shales and of type III origin in marls. Tmax values indicate "oil window" stage. Average transformation ratio is around 67% and 82%, respectively, in the Lower Aptian and Middel Barremian source rock related to the relatively high thermal maturity degree due to the deep burial of the later. Estimated initial hydrocarbon generation potential is moderate to high. Oil saturation index records an "oil crossover" indicating expelled and migrated hydrocarbons from the organic-rich to the organic-poor facies. The petroleum system of the two mature source rocks with a high hydrocarbon generation potential enclose all elements characterizing a "shale oil hybrid system with a combination of juxtaposed organic-rich and organic-lean facies associated with open fractures".

Karst aquifers belong to the fractured aquifer family. The Zaghouan region located in NE of Tunisia (North Africa) is characterized by a high degree of karstification due to the climate impact and the development of fracture network. Survey using electrical resistivity tomography (ERT) is deployed to provide a cost-effective characterization of the subsurface karst environments. A total of three ERT profiles with a length of 300 meters were evaluated in Zaghouan region.The area represents an anticline of Jurassic limestone rocks, which is overlain by a thin clay layer. In this study, an ERT survey was conducted to examine the spatial distribution and shape of underground cavities in the karst area of Jebel Bent Saidan. In this study, geological, hydrogeological and electrical resistivity tomography (ERT) methods were applied to determine the geometry of the karst aquifer in the Zaghouan area (NE Tunisia). The area is characterized by fractured and karstic limestone aquifer of Jurassic. Three resistivity profiles were carried out along the study area (Jebel Bent Saidan). The correct resistivity data was interpreted using ZONDRes 2D software. The results of the interpreted geo-electrical sections showed that the resistivity of the carbonate aquifer ranges from 350 to over 4000 Ωm. The thickness of the aquifer varies between 15 and 30 meters, while its depth from the surface is between 10 and 40 meters. The ERT not only provided accurate near-surface information, but was also very useful in establishing the geometry of the aquifer. It was also very useful in establishing the 3D geometry and position of several potential karst cavities and conduits. The results show the presence of two large isolated cavities at different depths. The low resistivity of karst cavities in the Jurassic carbonate of Jebel Bent Saidane was explained by the saturation of groundwater. The ERT imaging technique using to identify and characterize the discontinuities, faults and water investigation of the fractured and karstified limestone aquifers in the Bent Saidan Mounts. The conducted research demonstrated that the ERT method was an effective tool for imaging the subsurface in the karst terrain.Keywords: Bent Saidan (NE Tunisia), karst aquifers, electrical resistivity tomography (ERT), cavities.

The study area Zaghouan Plain (northeastern Tunisia) is unique for its strategic Quaternary aquifer, which is, in a great proportion, composed of sand lenses that vary in thicknesses and forms. Conducting an integrative approach based on regional mapping and local studies helped provide precise calibration to identify convenient areas for hydrogeological explorations, which are focused on heterogeneous alluvial and fluvio-deltaic aquifers. To enhance the location and the extension of low density related to sand lenses porous aquifers, a regional gravity analysis supported by focused seismic interpretation was performed. Thus, advanced analyses were conducted in the Zaghouan Plain through the implementation of a regional–residual separation, a radially averaged power spectrum and tilt/TDX filter density models. During the process, two major negative gravity anomalies, associated with developed lenses system between Zaghouan Mountain and Henchir Bouslim anticline, were revealed. The anomalies differed in direction from E–W to NW–SE. They also varied widthwise from 1000 to 3000 m and depthwise from 1500 to 2000 m. Hence, with the aim of highlighting the detailed geometry of sand lenses and locating the most interesting zone for future hydrogeological exploration and/or recharge process, 1D time-domain electromagnetic and 2D electrical resistivity tomography studies were conducted and various techniques were applied in a local area situated in the main negative gravity anomaly.

In semiarid regions, dams are useful for surface water storage, sediment sequestration, and aquifer recharge. Built in 1987 on the Cap Bon peninsula (in northeastern Tunisia), the Lebna Dam is considered a good example of a multifunctional reservoir. The dam feeds two important irrigation networks, stores large sediment quantities, and allows a significant recharge flow to the underlying aquifer. This work suggests new leakage flow and dam-aquifer interaction characterizations through the development of an approach that combines a water balance calculation, geological field observations, groundwater monitoring, and geophysical research. The hydrological balance calculation performed over the 27-year monitoring period, from 1990 to 2017, shows that an estimated water volume of 3.7 Mm3y-1 has leaked from the Lebna reservoir to the coastal aquifer. Geological mapping of the Lebna Dam basin in summer 2019 revealed the existence of permeable layers of sands to sandstones exposed along the southern banks of the reservoir and extending to an elevation that included the water level when the dam is full; these rocks outcrop at approximately 16 m.a.s.l. A geophysical survey based on 67 vertical electrical soundings and 8 electrical resistivity tomography profiles in the area downstream of the reservoir was carried out to identify the lateral continuity of the recharge zones. Piezometric campaigns consisting of four field surveys in 2019 and 2020 were conducted in the region downstream of Lebna Dam, consisting of 71 water well samples. An interpretation of these geophysical data coupled with available borehole logging and piezometric measurements was used to define the leakage geometry from the reservoir dam to the coastal aquifer. The collected evidence led to the conclusion that concentrated recharge occurs in the downstream sections, especially on the right bank of the aquifer.

Interpretation of gravity data revealed new information about the detailed structure and hydrogeology of the Moulares basin (Southwestern Tunisia). Geophysical data, 3D gravity modeling, and correlation with downhole hydrogeological observations revealed segmentation of the basin into numerous subbasins separated by NW–SE trending lineaments. This structural control on hydrogeological province is fundamental for constraining modeling (recharge, discharge, and water pathways) and for establishing effective and sustainable groundwater management plans. The gravity method is one example of nonseismic geophysics that can be useful in delineating the areal extent and geometry of hydrogeological systems. Potential hydrogeological areas correspond on filtered gravity maps (Residual, Tilt gravity derivative) to an alignment of negative gravity anomalies. Along the axes of the negative gravity anomalies, we acquired Transient Domain Electromagnetic method soundings (TDEM) to deduce the lateral variations of the different alluvial aquifer systems. The interpretation of the TDEM data, calibrated with the hydrogeological wells, revealed that shallow strata at less than 40 m depth correspond to sediments rich in clays to the east of the basin, and to a Plio-Quaternary aquifer overlying coarse-grained clastic sediments toward the west. It also revealed that the Plio-Quaternary aquifer is variable in thickness along the basin and that the Miocene aquifer is encountered at greater depths to the west of the basin. These results are in perfect agreement with the subbasins/faults architecture revealed by gravity analysis.

The Khalled Plain (Northwestern Tunisia, North Africa) is characterized by the development of the Karst system in the fractured Ypresian’s carbonate rocks. This fact enhances the hydrogeological potential of the Eocene aquifer. A multi-scalar geophysical approach is applied (from regional mapping to detailed study) to identify new favorable areas for potential hydrogeological exploration. Seismic reflection analysis attested the existence of a major NE-SW fault zone, called “Khalled Fault Zone,” part of Teboursouk-El Alia regional accident. This fault zone, along the Khalled River, is composed of emergent and blind low-angle branches ramping in the same direction. The deep underexploited Ypresian aquifer, situated below the fault zone (called Khalled Footwall Zone KFZ), was mapped using detailed gravity data analysis (regional-residual separation, horizontal gravity gradient, and 3D density model). Finally, 1D time domain electromagnetic and 2D electrical resistivity tomography revealed the hydrogeological potential of the Eocene reservoir and the step-by-step infiltration process from recharge to discharge areas of this aquifer.

Electric resistivity sounding and tomography, as well as electromagnetic sounding, are the classical methods frequently used for hydrogeological studies. In this work, we propose the development and implementation of an original integrated approach using the unconventional hydro–geophysical methods of gravity and seismic reflection for the fast, large–scale characterization of hydrogeological potential using the Ain El Beidha plain (central Tunisia) as an analogue. Extending the values of vintage petroleum seismic reflection profiles and gravity data, in conjunction with available geological and hydrogeological information, we performed an advanced analysis to characterize the geometry of deep tertiary (Oligocene and Eocene) aquifers in this arid area. Residual and tilt angle gravity maps revealed that most gravity anomalies have a short wavelength. The study area was mainly composed of three major areas: the Oued Ben Zitoun and Ain El Beidha basins, which are both related to negative gravity trends corresponding to low–density subsiding depocenters. These basins are separated by an important NE–SW trend called “El Gonna–J. El Mguataa–Kroumet Zemla” gravity high. Evaluation of the superposition of detected lineaments and Euler deconvolution solutions’ maps showed several NE–SW and N–S relay system faults. The 3D density inversion model using a lateral and vertical cutting plane suggested the presence of two different tectonic styles (thin VS thick). Results from the gravity analysis were in concordance with the seismic analysis. The deep Oligocene and Eocene seismic horizons were calibrated to the hydraulic wells and surrounding outcrops. Oligocene and Eocene geological reservoirs appear very fractured and compartmented. The faulting network also plays an important role in enhancing groundwater recharge process of the Oligocene and Eocene aquifers. Finally, generated isochron maps provided an excellent opportunity to develop future comprehensive exploration surveys over smaller and more favorable areas’ sub–basins.

The El Hamma-Gabes Region in southeastern Tunisia belongs to the crustal shear zone of the South Atlasic Fault Corridor, which corresponds to the Meso-Cenozoic North African margin. So far, most geological works on this region are on the stratigraphic order. However, there are few tectonic and structural studies carried on the style and mechanism of structural deformation. The present work analyzes the subsurface structure of the El Hamma grabens area based on gravity and seismic data , calibrated by stratigraphic and tectonic elements. The El Hamma-Gabes Zone is characterized by a horst and graben system associated with N130˚-150° trending parallel extensive/transtensive faults. Two main grabens are recognized: the El Hamma graben in the west and the Chenchou graben in the east. They are separated by the Jebel Hallouga horst. These structures relate to two N100˚-120° trending principal shear corridors (PSC) arranged in right echelon, being the Oum Ali-Fejej Shear corridor towards the northwest and the Matmata-Medenine Shear corridor towards the southeast. Stratigraphic and structural data collected from several outcrops were correlated with the tectonic events and paleostress reconstruction. New data shows that the PSCs marked a dextral transtensive kinematic framework during the N80° directed Upper Cretaceous extension. The extensional movements are the N150˚-180° Paleogene extension and associated transpression during the N130° Neogene shortening. The dextral sliding generated and maintained the opening of the El Hamma-Gabes graben system, creating a “pull-apart” basin that opened in an extensive ramp between the two PSCs. The overall extension of this ramp is estimated to 15% of the initial width.

The Dakhla syncline is located in the North-Eastern Tunisia. It is bounded by Abd El Rahmene anticline to the North-West, El Haouaria Graben to the North-East, Grombalia Graben to the South-West and the Mediterranean Sea to the East. The main aquifer reservoirs of Dakhla syncline are constituted by stacks of fluvial to deltaic Neogene sequences and carbonates. The interpretation of eight seismic reflection profiles, calibrated by wire line logging data of three oil wells, hydraulic wells and geologic field sections highlighted the impact of tectonics on the structuring geometry of aquifers and their distribution in elevated structures and subsurface depressions. Lithostratigraphic correlations and seismic profiles analysis through the syncline show that the principal aquifers are thickest within the central and northern part of the study area and thinnest to the southern part of the syncline. Seismic sections shows that the fracture/fault pattern in this syncline is mainly concentrated along corridors with a major direction of NW-SE and secondary directions of N-S, E-W and NE-SW with different release. This is proved by the complexity structure of Eastern Tunisia, resulted from the interaction between the African and Eurasiatic plates. Isochron maps of aquifers systems exhibited the structuring of this syncline in sub-surface characterized by important lateral and vertical geometric and thickness variations. Seismic sections L1, L2, L3, L4, L5 and petroleum wells showed an heterogeneous multilayer aquifers of Miocene formed by the arrangement of ten sandstone bodies, separated by impermeable clay packages. Oligo-Miocene deposits correspond to the most great potential aquifers, with respectively an average transmissivity estimated: Somaa aquifer 6.5 10 −4 m2/s, Sandstone level aquifer 2.6 10−3 m2/s, Beglia aquifer 1.1 10−3 m2/s, Ain Ghrab aquifer 1.3 10−4 m2 /s and Oligocene aquifer 2 10 −3 m2 /s. The interpretation of spatial variations of seismic units and the recognition of tectonic structures and their development may reveal some new insights for hydrogeological aspects.

The following work is an attempt to enhance and optimize the potential exploitation of the Hammam Sayala thermal spring (NW Tunisia). This hot spring is located at 10 km of South-western Beja city, with higher temperature values around 42 °C and a low discharge value of about 1 l s −1 . The geological and structural settings of the study area are complex and associated with faults and Triassic intruded salt and evaporate. An integrated geophysical approach using Electrical Resistivity Tomography (ERT), Induced Polarization (IP) and Vertical Electrical Sounding (VES) techniques can provide a high-resolution subsurface image of the principal geothermal plume and associated pathways. These data were used to determine and understand the mechanisms responsible of the rise of hot water flowing out onto the surface. Our results add new information of the hydrothermal system's context in Hammam Sayala area, which can help to create a therapeutic center opening new perspectives in the Beja region and to encourage regional thermal tourism development.

We present a regional-residual separation procedure for potential field data (gravity or magnetic) based on the integration of least-squares polynomial, power density spectrum and Upward continuation techniques. The proposed procedure is composed by 6 fundamental steps: 1) gridding of the total potential field; 2) least-squares polynomial approximation to calculate polynomial regionals; 3) applying power density spectrum technique to estimate the depth of the deepest source; 4) upward continuation to attenuate the effect of shallower sources; 5) comparing the produced polynomial regional approximations and upward continuation to choose the suitable regional and finally 6) computation of the residual. The proposed procedure was applied to synthetic case and real gravity data from Tunisia.

This work aims to investigate the applicability of electrical resistivity tomography (ERT) as a non-destructive tool of agricultural soil characterization after digestate of fruit and vegetable (DFV) amendment application. DFV was applied at 30 t ha−1 in one application (D1), split into 2 (D2) and 6 applications (D6), and compared with initial state (IS) on field plots of 10 m2. The high-resolution 2D ERT prospecting was performed using a ABEM SAS4000 multi-electrode Lund imaging survey system with a set of 16 electrodes evenly spaced 0.1 m. The resistivity values with ERT profiles using the Wenner array range globally from 0 to 200 Ω m. All treatments proposed decreased soil resistivity to 0–30 cm depth profile. Splitting digestate shows more intensive decreasing resistivity in the top layer and less in the bottom, and moves the iso-resistivity lines lower than 30 Ω m from 7 cm depth to 12, 20, and 30 cm depth, respectively, for D6, D2, and D1. The resistivity folding at 15 to 30 cm depth was 87, 80, and 67% then 58, 42, and 37%, respectively, for D1, D2, and D6. The low resistivity values may be due to soil organic matter flow illustrated. Digestate applied once acted on the soil with heterogeneous way along the profile. Splitting it increases the thickness of foam layer homogeneously. ERT seems a promising technique for the survey of soil organic matter content monitoring, dispersion, and assessment.

International audience; Interpretation of lithostratigraphic, seismic and gravity data from Kalaa Khesba Graben shows (i) lateral and in-depth variation of the lithostratigraphic series, (ii) complex structuring of faulting. Reverse faults affected Paleocene to Quaternary horizons with a duplication of Eocene-Paleocene series occurred at subsurface evidenced within well W6. Isochron, isovelocity and isobath maps, combined with gravity data, show subsurface structures oriented predominantly NW-SE to NS and NE-SW to EW. Faults and horizons on the seismic lines, superimposed to gravity lineaments, reveal negative anomalies occurring at shallow depth. Such features may reflect the existence of low density Neogene-Quaternary series, strike-slips and thrust faults within Kalaa Khesba Graben. Depths deduced from Euler deconvolution solutions vary from 0.5 to 4 km. At subsurface, well log data located in the center of the graben, ensured the presence of Triassic bodies. A model of initiation of Kalaa Khesba Graben through a N160° σ1 transpression is proposed.

There is an evidence that the crustal thickness from the Red Sea coastal plain to the interior of Saudi Arabia increases dramatically from 10 km in the Red Sea to about 42 km. In order to give more insights on crustal configuration of the Arabian plate, we proposed to analyze available gravity and aeromagnetic data. The gravity data was analyzed and interpreted within a profile A-B perpendicular to the Red Sea coast along the western margin of the Shield. The analysis included the construction of Bouguer gravity and residual anomaly maps, regional gravity and magnetic anomaly maps based on wavelength filtering and derivative techniques, and 2.5D gravity models were constructed in an integrated method constrained by surface geology and previous work such as the available seismic refraction and broadband models [Hansen et al. in Earth Planet. Sci. Lett., 2007 1]. Our observations of lithospheric structure showed a relative complexity of the gravity and aeromagnetic anomaly controlled by structural complexity and variable lithology of the transect and support a two-stage rifting history along the Red Sea and suggest that the Moho and LAB topography is the result of extension and erosion caused by asthenosphere flow where the thinnest lithosphere is coincident with the rift axis.

International audience; Central Tunisia is characterized by numerous folded graben systems. In this study, the gravity data were analyzed to reveal the Syn-Graben hidden folded structuring associated with the NW-SE Kalaa Khesba graben (northwestern Tunisia). For the regional-residual separation, we adopted the Gaussian Regional/Residual Filter. This Filter was coupled with the Tilt filter to exhibit shallow sources associated with hidden folded structures toward the Kalaa Khesba graben. This method presents a new spatial filter designed to separate short-wavelength anomalies from long wavelength anomalies. After the detailed mapping of positive and negative gravity anomalies associated with respectively, anticlines and synclines, we have produced the Total Horizontal Gravity Gradient map, the Source Edge Detect (SED) map and Euler solution map to delineated the faulting network. Finally, a structural map of the Kalaa Khesba graben was achieved and compared with seismic lines analysis. In this study case, the gravity data analysis can be considered as a preferred method for structural mapping such as hidden faults and faults. The advanced processing of gravity data produces also a fine image of the subsurface geometry of a graben as well as to enable a better understand the structural complexity and the role of the various tectonic features.

This work presents new results from gravity data analyses and interpretation within the Om Ali-Thelepte (OAT) basin, central Tunisia. It focuses on the hydrogeological implication, using several qualitative and quantitative techniques such as horizontal gradient, upward continuation and Euler deconvolution on boreholes log data, seismic reflection data and electrical conductivity measurements. The structures highlighted using the filtering techniques suggest that the Miocene aquifer of OAT basin is cut by four major fault systems that trend E-W, NE-SW, NW-SE and NNE-SSW. In addition, a NW-SE gravity model established shows the geometry of the Miocene sandstone reservoir and the Upper Cretaceous limestone rocks. Moreover, the superimposition of the electrical conductivity and the structural maps indicates that the low conductivity values of sampled water from boreholes are located around main faults.

A procedure for a dip angle determination of a fault plane from gravity field data is presented to constrain a seismic profile interpretation. This procedure is applied on Mahjouba normal fault at the western border of Kalaa Khesba graben (Central Tunisian Atlas Province, North Africa). Seismic and detailed gravity data, in this region, were analyzed to provide more constraints on the geometry of the fault dip angle. The Mahjouba fault is mapped as three major parallel lineaments extended for 2 km with a NW-SE to N-S trend. The dip of the Mahjouba fault is estimated from the gravity modeling data to be 45°E. This study reveals that integrating gravity and seismic data provides accurate mapping of faults geometry and such result provides useful information and constraints on the exploration of natural resources.

This study has led to the identification of the Upper Cretaceous and Lower Eocene (Abiod, Boudabbous/El Gueria Formations) fractured and karstic aquifers in the Amdoun region (Northwestern Tunisia). Geological information (litho-stratigraphy and fractures network study) and geophysical (gravity, wells analysis, seismic reflection, Electrical Resistivity Tomography (ERT)) investigations performed in the area have highlighted, with some detail, images of structures of carbonate aquifers near anticline flanks and along perched synclines. Some factors such as fracture intensity, karsts evolution and structural position have an important influence on the hydrologic productivity of Abiod and Boudabbous/El Gueria reservoirs. Different methodologies were used to characterize the geological and hydro-geological perched aquifers and produce the 3D geo-electrical model of near surface karstic features and cavities of the carbonate limestone in the Ain Sallem site. This study integrates the geological and geophysical information available and can serve as a representative example in the description of the most important hydraulic reserves in the North-western Tunisia.

Hydrocarbon exploration in the Berkine–Ghadames Basin in southern Tunisia has generally followed global economic trends. In recent years, improvements in seismic data acquisition combined with experience gained in log interpretation in low-resistivity reservoirs have resulted in oil and gas discoveries in the Upper Silurian Acacus Formation, enriching the hydrocarbon potential of the Berkine–Ghadames Basin in southern Tunisia. Presently, the Tunisian daily oil production is approximately 43,000 bbl, about half of which comes from the fields located in southern Tunisia and is produced from the Acacus Formation. The Berkine–Ghadames Basin is an intracratonic basin formed during the Pan-African Orogeny. It covers an area of approximately 350,000 km2 (135,135 mi2) and extends into Algeria, Libya, and Tunisia. The sedimentary section within the basin ranges from Cambrian to present and is approximately 7000 m (23,000 ft) thick in the depocenter. The basin has experienced several tectonic events, which have modified its architecture and affected the petroleum systems and hydrocarbon pathways. In this study, the main elements of the petroleum geology systems are described. With the geochemical modeling results, the petroleum potential, hydrocarbon generation, expulsion time, and quantity of hydrocarbon are assessed. The main petroleum systems are also defined. They are represented by the Silurian Tannezuft hot shale source rock with Ordovician Djeffara and Silurian Acacus reservoirs, by Silurian Tannezuft hot shale with Kirchaou reservoirs, and by the Devonian Aouinette Ouinine Formation Member III source rock with Kirchaou reservoirs. The hydrocarbon traps in the area are mainly structural types. The study describes and emphasizes the hydrocarbon migration pathway mechanism from source rocks to traps. To predict and derisk future drilling locations, fairway maps are generated for the three plays: Ordovician, Silurian, and Triassic. Although the paper focuses on southern Tunisia, an attempt is made to introduce Libyan and Algerian knowledge to evaluate the basin in a regional context.

Groundwater from fractures and karst in limestone rocks is an important source of drinking water in the semi-arid climatic environment of North-Western Tunisia where cool and rainy seasons alternate with hot dry seasons. Due to varying climatic conditions and anthropogenic interventions the fractured limestone aquifer systems (Abiod and Boudabbous/El Gueria Formations) tend to be complex. The lack of data on the fractured and karstified aquifers in Amdoun region (NW Tunisia) to establish the hydrogeological potential between different rock formations of Upper Cretaceous and Lower Eocene has often discouraged researchers from attempting to model such aquifers. On the SE flank of the Jebel Sabbah anticline , Electrical Resistivity Tomography Data were collected along three different lines of 315 m of length each. The expected vertical penetration depth was 60 m. This hydro-geophysical investigation consisting of geological, structural, and geo-morphological studies, has demonstrated that groundwater in the carbonate rocks , in Amdoun area, occur in fracture zones and weathered parts of the rocks in the karst aquifers . The hydrochemical data (major ion geochemistry) indicate that these groundwaters are characterized by the dominance a Ca–Mg–HCO3 water type. Geochemical pattern is mainly controlled by the dissolution of carbonate minerals . Generally, TDS increases from the Amdoun Monts towards the discharge area (53 −1 ). These results are assessed using numerous geophysical data such as ERT imaging and geological knowledge. Finally, we show how these results could be used to improve the management of karst groundwater resources in Amdoun (NW Tunisia) complex terrain.

Geophysical methods provide important help to investigate geothermal reservoirs. They permit to delineate deep and near surface structuring and to appreciate fluid circulation. In this study, we performed an integrated geophysical study using regional seismic reflection profiles and local Electrical Resistivity Tomography (ERT) data analyses to identify the relation between faults and specific geothermal pathways around Hammam Sidi Maamar thermal spring site in Hajeb Layoun area (Central Tunisia). The proposed geological model performed from seismic reflection composite sections reveals the geometry in depth series of the Lower Cretaceous from the recharge zone (Jebel Mrhila mountain) to the emergence area of Hammam Sidi Maamar (Jebel Baten Damous mountain) and traces the path of the thermal water, from its recharge area till surfacing, in order to propose a new suitable intake location with higher flow and temperature. The results of seismic and ERT data analysis confirm that the Hammam Sidi Maamar geothermal site is tectonically related to the junction of the NE-SW Baten Damous fault corridor and the NW-SE to E-W northern fault corridor of Hajeb Layoun graben. The water is charged from Lower Cretaceous (Hauterivian to Aptian) outcrop series in Jebel Mrhila Mountain to the West. It flows into the carbonate reservoir below the Hajeb Layoun-Jelma Plain, where the Lower Cretaceous reservoirs are reaching more than 2500 m deep. The reservoir geologic layers show ascent geometry towards Jebel Zaouia Mountain then they sink into the Hajeb Layoun Graben to the East. The thermal water rises to surface thanks to the deep faults that affect the Lower Cretaceous reservoir and the geologic series above. High resolution Electrical Resistivity Tomography panels, we carried out in Hammam Sidi Maamar geothermal site, allowed to locally identify the faulting architecture which controls the flow of hot water. Firstly, filtering and processing of ERT data were performed. 2D ERT modeling, mapping and 3D ERT view interpretation, were also performed to more understand the local tectonic/geothermal flow setting. Finally, to identify the prominent site for lateral and vertical geothermal flow plumes, we propose to drill 50 m–60 m intake well associated with a tectonic junction of the NE-SW Baten Damous fault corridor and the NW-SE to E-W Hajeb Layoun graben fault.

The Maâmoura aquifer is located on the eastern coast of the Cap Bon peninsula. During recent decades, the agricultural exploitation of water has been strongly reinforced, causing an over-pumping of the groundwater resources accompanied by an intrusion of seawater. The geophysical approach based on electrical resistivity tomography has been adopted to obtain high-resolution electrical sections imaging, which allows delineatation of the areas characterized by a high salinization and reconstructs the geometry of the saline wedge front. In fact, the presence of seawater in the aquifers reduces subsurface resistivity values. In this study, five electrical profiles were performed using the Terrameter SAS4000 Lund Imaging System with an array of 64 electrodes. The Wenner configuration was used with a unit electrodes spacing of 5 m. Finally, we use hydrogeological data, and electrical resistivity tomography data superimposed with the location of wells to provide a conceptual framework for the understanding of the freshwater–saltwater interface in the Maâmoura region.

Gravity method can help locate hidden structural blocks bounded by faults related to the Upper Cretaceous carbonate aquifers of Goubellat region (Northwestern Tunisia). The Quaternary deposits are present over the majority of the Goubellat plain basin and cover the Upper Cretaceous carbonate. The produced residual gravity map supported by vertical and tilt angle derivatives was used to reveal the subsurface structural framework of the study area shaped by uplifted (high gravity anomalies) and downlifted areas (low gravity anomalies). The horizontal gravity gradient and Euler deconvolution maps were elaborated in order to locate major faults. These faults are primordial for the subsurface water recharge pathways. Finally, the presented lineament/structural map is very useful for large-scale structures and lineaments mapping giving the principal keys of the preliminary structural configuration of the Goubellat Upper Cretaceous carbonate aquifers.

This study presents original results regarding the use of aeromagnetic to explore deep subsurface structuring in southern part of Tunisian Sahel petroleum province (Eastern Tunisia, North Africa). Several filters and techniques were applied to the total magnetic intensity (TMI) grid. First, an adequate reduce to the pole (RTP) grid was generated. The RTP map shows 17 positive and negative anomalies associated with short- and long-wavelength amplitude anomalies. Positive anomalies correspond to high magnetic basement structures estimated from seismic lines in the area. Circular anomalies are also distinguished locally and can be explained by Cretaceous magmatic rocks recognized in numerous petroleum wells. Second, specific qualitative and quantitative filters (e.g., residual-regional separation, horizontal tilt angle (TDX), tilt angle (TILT), total horizontal derivative of tilt angle (THDTILT)) were applied to elucidate the form and the extent of buried magnetic anomalies and lineaments. The resulting deep structural map revealed the presence of NW-SE, N-S, and E-W regional magnetic basement structures and lineaments and a regional tectonic node surrounding Henchir Keskes-Agareb-Mahres-Hachichina area. Two magnetic inversion models calculated across the study area highlight west to east crustal thinning trend and permit depth to basement estimation. These results are valuable for future conventional and unconventional petroleum exploration in this underexplored southern part of Sahel plain.

The Amdoun region is characterized by a high degree of karstification due to the climate impact (±1500 mm year−1) and the development of fracture network. Survey using electrical resistivity tomography (ERT) is deployed to provide a cost-effective characterization of the subsurface karst environments. A total of seven ERT profiles with lengths of 315 m were evaluated at the Beja governorate (NW Tunisia). The area represents a small syncline of Boudabbous limestone rocks (Lower Eocene), which is covered by a thin layer of clay. In this study, an ERT survey was conducted to examine the spatial distribution and shape of underground cavities in the karst area in Jebel Sabah anticline and Ain Sallem-Zahret Medien syncline. In this study, geological, hydro-geological and electrical resistivity tomography (ERT) methods were applied to determine the geometry of the perched aquifer in the Amdoun region (NW Tunisia). The area is characterized by fractured and karstic limestone aquifer of Late Cretaceous (Abiod Fm.) and Lower Eocene (Boudabbous Fm.). The aquifers have a karstic functioning and drain aquifers of economical interest, despite some wells exploiting them. Seven resistivity profiles were conducted along the survey area at three sites. The orientation, extension and the degree of inclination of those profiles are shown in the location map. The correct resistivity data were interpreted using Earth Imager 2D software. The results of the interpreted geo-electrical sections showed that the resistivity of the carbonate aquifer varied between 2.5 to over 5794 Ωm. The thickness of the perched aquifer ranged from 15 to 50 m, while its depth from the surface lies between 10 and 60 m. The ERT not only provided precise near surface information, but was also very useful for establishing the 3D geometry and the position of several potential cavities and karts. The results show the presence of small to large isolated cavities at various depths. The low resistivity of cavities in the Boudabbous Formation has been explained by the groundwater saturation. The ERT technique could be effectively used for 3D detection of underground limestone cavities.

There are several techniques that were developed for determining the linear features. Lineament extraction from satellite data has been the most widely used applications in geology. In the present study, lineament has been extracted from the digital satellite scene (Landsat 5, TM data), in the region of Zahret Median situated in the north west of Tunisia. The image was enhanced and used for automatic extraction. Several directions of features were mapped. The directions of major invoices are NE-SW and NW-SE oriented. The validation of the obtained results is carried out by comparison with the results geophysics as well as to the studies previous of mapping developed in the sector of study.

Gravity data were analyzed to determine the structural development of the northern boundary of the Ghadames Basin in southern Tunisia. The Ghadames Basin which also occurs in eastern Algeria and northwestern Libya is one of the most prolific hydrocarbon producers in North Africa with several of the largest oil fields occurring along its northern boundary. The Ghadames Basin was formed during a series of tectonic events ranging from the Early Paleozoic to the Early Cenozoic. These tectonic events produced a basin in southern Tunisia that has a complex basement configuration which is not completely known. A residual gravity anomaly map constructed using polynomial trend surfaces, and vertical and horizontal gravity derivative maps indicate that the northern boundary contains a series of maxima and minima anomalies that trend in two prominent directions: northeast–southwest and east–west. The horizontal and vertical derivative gravity anomaly maps indicate that the width of the basement structures range between 10 and 20 km in width. Three-dimensional (3D) Euler deconvolution and 3D forward modeling constrained by well data, one seismic reflection profile and remote sensing data confirm the width of the basement structures and indicates that the depth of basin varies between 1.5 and 5 km, with deeper sections in general more numerous in the southern sections of the boundary. The gravity analysis constrained by the seismic reflection profile and well data implies that the basement topography may have been formed during the Pan African and/or late Mesozoic rifting. However, additional seismic reflection and well data are needed to confirm this conclusion. The discovery of the numerous basement structures suggests that there may exist additional hydrocarbon traps within the northern boundary of the Ghadames Basin.

The Gafsa and Chotts intracratonic basins in south-central Tunisia are transitional zones between the Atlasic domain to the north and the Saharan platform to the south. The principal aim of this paper is to unravel the geodynamic evolution of these basins following an integrated approach including seismic, well log and gravity data. These data are used to highlight the tectonic control on the deposition of Jurassic and Lower Cretaceous series and to discuss the role of the main faults that controlled the basin architecture and Cretaceous–Tertiary inversion. The horizontal gravity gradient map of the study area highlights the pattern of discontinuities within the two basins and reveals the presence of deep E–W basement faults. Primary attention is given to the role played by the E–W faults system and that of the NW–SE Gafsa fault which was previously considered active since the Jurassic. Facies and thickness analyses based on new seismic interpretation and well data suggest that the E–W-oriented faults controlled the subsidence distribution especially during the Jurassic. The NW–SE faults seem to be key structures that controlled the basins paleogeography during Late Cretaceous–Cenozoic time. The upper Triassic evaporite bodies, which locally outline the main NW–SE Gafsa fault, are regarded as intrusive salt bodies rather than early diapiric extrusions as previously interpreted since they are rare and occurred only along main strike-slip faults. In addition, seismic lines show that Triassic rocks are deep and do not exhibit true diapiric features.

Tunisia is enriched by many natural resources (natural water and geothermal water) that are located along the South to the North. This paper aims mainly to evaluate the resources water potential. The available remote sensing images for two typical examples (SE Jeffara basin and Utique basin) are analyzed and many seismic profiles are interpreted to delineate the surface and subsurface structures. The 3-D structures of Mio-Plio-Quaternary and Upper Cretaceous aquifers in South-East of Jeffara basin show an important reservoirs of water resources. The Upper Cretaceous aquifer "Complexe Terminal" is one of the most typical examples of exploitation features in hydrogeological research. It is formed by fractured limestones. The 3D-structure of Utique basin shows an important variation of thickness of Mio-Plio-Quaternary and Triassic series. The Mio-Plio-Quaternary series is formed by sand, clays and gypsum. The Triassic series is considered typical example for research the hydrogeological and hydrothermal water in Tunisia, especially in the North. In the subsurface, the triassic aquifer of Utique regions is formed by carbonates series. The hot spring in Utique basin is directly related to the Triassic dolostones which are extensively fractured [1]. A geophysical survey was undertaken for groundwater in Tunisia. The interpretation of seismic reflection sections and petroleum wells allowed to precise the geometry in subsurface structure.

The Exploration complex geological structures like crystalline basement, significant to hydrocarbon exploration, is complicated in seismic interpretation. Gravity data were analyzed at a Guelb Ahmer horst situated to northern border of Ghadames basin (Southern Tunisia). The average radial spectrum from an area of 40x40 km of the gravity data grid reveals the deep and intermediate basement sources depths. 3D Euler deconvolution technique illustrates also the limits of the crystalline basement sources running essentially between 2000 and 3000 meter deep. The geometries of Mesozoic rocks, Paleozoic strata and Precambrian basement rocks are estimated by five 3D gravity models. These models give a significant support for the determination of potential structural traps related to the Guelb Ahmer horst.

ResumeCette etude basee sur l’analyse des donnees gravimetriques a pour but d’ameliorer la connaissance des structures effondrees du Nord-Est de la Tunisie. La carte de l’anomalie residuelle a d’abord ete calculee a partir de la carte de l’anomalie de Bouguer en enlevant un gradient regional. La residuelle calculee fournit des informations sur la variation de la densite dans les bassins sedimentaires de l’Oued Chafrou-Khlidia, de Mornag et de Grombalia. Afin de mettre en evidence les differentes structures geologiques (failles, bassins, etc.) dans le secteur d’etude, differentes techniques (gradient vertical, gradient horizontal, prolongement vers le haut, deconvolution d’Euler) ont ete appliquees a la carte gravimetrique des structures effondrees du Nord-Est de la Tunisie. Les resultats obtenus ont permis de dresser une carte structurale presentant le systeme de failles responsable de la structuration de la zone d’etude. Cette carte constitue un document tres utile pour orienter les recherches hydrogeolo...