Cenozoic tectono-sedimentary evolution of the onshore-offshore Tunisian Tell: Implications for oil-gas research

A review of the paleogeographic and tectonic reconstruction of the onshore and offshore Tunisian margin during the Cenozoic is discussed. Five unconformities (A to E) and associated stratigraphic gaps of various vertical extents allow subdivision of the stratigraphic record into depositional units in the following time intervals: (i) Paleocene-Oligocene, (ii) Oligocene-early Aquitanian, (iii) early Aquitanian-Burdigalian, (iv) late Burdigalian- Langhian and (v) Langhian-late Miocene. These intervals can in turn be grouped into four main sedimentary cycles (SC1–SC4) dated to the (1) Paleocene-Oligocene, (2) Oligocene–Burdigalian, (3) Burdigalian-Langhian and (4) Langhian-late Miocene. The oldest depositional unit reflects Eo-Alpine tectonics in the Maghrebian Flysch Basin (MFB); the others are related to the Neo-Alpine syn- and late orogenic tectonic deformation affecting the MFB. The uppermost unit represents post-orogenic deposition. Early Miocene synsedimentary tectonism led to (1) deposition of thick successions owing to a large sediment supply and (2) the occurrence of various tectofacies (unconformities, slumps, mega-turbidites, olistostromes, growth folds, chaotic intervals and heterogenous lithofacies), that all, together with the occurrence of lateral change of facies, clearly indicate non-cyclical sedimentation. During the middle Miocene the Tunisian Tell underwent polyphase thrust tectonism, followed by late Miocene strike-slip deformation with contemporaneous rejuvenation of halokinetics and magmatism (the La Galite Archipelago) that may be traced as far as the Algerian Tell. The margin experienced deep-seated compressional tectonism during the Paleogene, a foreland basin during the early Miocene, and nappe stacking during the middle Miocene, with the occurrence of wedge-top sub-basins. The evolution of the region makes the existence of petroleum resources within either the thrust belt, the foredeep and/or the foreland systems plausible. Oil and/or gas may have been trapped in either i) deep buried allochthonous thrust wedges that are located below the Numidian Nappes, and/or in ii) the imbricate Medjerda Valley domain of the Tell foredeep. The offshore area between northern Tunisia and the La Galite Archipelago may also hold potential for large oil/gas fields, as has been confirmed by exploration of the same overthrust belt in other areas such as in Sicily and the Southern Apennines

Cenozoic tectono-sedimentary evolution of the onshore-offshore Tunisian Tell: Implications for oil-gas research

A review of the paleogeographic and tectonic reconstruction of the onshore and offshore Tunisian margin during the Cenozoic is discussed. Five unconformities (A to E) and associated stratigraphic gaps of various vertical extents allow subdivision of the stratigraphic record into depositional units in the following time intervals: (i) Paleocene-Oligocene, (ii) Oligocene-early Aquitanian, (iii) early Aquitanian-Burdigalian, (iv) late Burdigalian-Langhian and (v) Langhian-late Miocene. These intervals can in turn be grouped into four main sedimentary cycles (SC1–SC4) dated to the (1) Paleocene-Oligocene, (2) Oligocene–Burdigalian, (3) Burdigalian-Langhian and (4) Langhian-late Miocene. The oldest depositional unit reflects Eo-Alpine tectonics in the Maghrebian Flysch Basin (MFB); the others are related to the Neo-Alpine syn- and late orogenic tectonic deformation affecting the MFB. The uppermost unit represents post-orogenic deposition. Early Miocene synsedimentary tectonism led to (1) deposition of thick successions owing to a large sediment supply and (2) the occurrence of various tectofacies (unconformities, slumps, mega-turbidites, olistostromes, growth folds, chaotic intervals and heterogenous lithofacies), that all, together with the occurrence of lateral change of facies, clearly indicate non-cyclical sedimentation. During the middle Miocene the Tunisian Tell underwent polyphase thrust tectonism, followed by late Miocene strike-slip deformation with contemporaneous rejuvenation of halokinetics and magmatism (the La Galite Archipelago) that may be traced as far as the Algerian Tell. The margin experienced deep-seated compressional tectonism during the Paleogene, a foreland basin during the early Miocene, and nappe stacking during the middle Miocene, with the occurrence of wedge-top sub-basins. The evolution of the region makes the existence of petroleum resources within either the thrust belt, the foredeep and/or the foreland systems plausible. Oil and/or gas may have been trapped in either i) deep buried allochthonous thrust wedges that are located below the Numidian Nappes, and/or in ii) the imbricate Medjerda Valley domain of the Tell foredeep. The offshore area between northern Tunisia and the La Galite Archipelago may also hold potential for large oil/gas fields, as has been confirmed by exploration of the same overthrust belt in other areas such as in Sicily and the Southern Apennines.Research supported by Research Project PID2020-114381 GB-I00, Spanish Ministry of Education and Science; Research Groups and Projects from M. Martín-Martín, Alicante University (CTMA-IGA)

The Numidian formation and its Lateral Successions (Central-Western Mediterranean): a review

The widely debated late Oligocene-middle Miocene Numidian Fm (NF) consists of supermature quartzose sediments deposited in the Maghrebian Flysch Basin (MFB) outcropping from the Betic Cordillera to the Southern Apennine passing by the Maghrebian Chain. The NF is commonly composed of three lithostratigraphic members and is characterized by two vertical successions (Type A and Type B) corresponding to different sedimentation areas in the MFB. It is noteworthy the occurrence of widespread lateral successions of the NF (Types C, D and E) indicating in some cases an interference of the Numidian sedimentation with other different depositional systems and supplies. The Type C ‘Mixed Successions’, deposited in depocentre areas, are composed of supermature Numidian supply interfingering with immature siliciclastic materials, coming from the internal portion of the MFB. The Type D consists of supermature Numidian materials supplied from the Africa Margin (external sub-domains) deposited in sub-basins on the Africa-Adria margins, outside the typical Numidian depositional area. The Type E, which stratigraphically overlies both the South Iberian Margin (SIM) and the Mesomediterranean Microplate (MM), represents the migration of the Numidian depositional system to reach the opposite margins of the MFB. The occurrence at a regional scale of all the above-mentioned lateral successions reveals a great evolutionary complexity resulting also from further constraints, which must be considered for palaeogeographic and palaeotectonic reconstructions. Another important point deals with the diachronism of the top of the NF, observed eastward from the Betic-Rifian Arc and the Algerian-Tunisian Tell (Burdigalian p.p.) to Sicily (Langhian p.p.) and up to the Southern Apennine (at least Langhian/Serravallian boundary) which can be related with eastwards delay in the MFB closure. The palaeogeographic reconstruction of the Numidian depositional area presented in this paper, which is also included into a global kinematic model, represents a first attempt to use the software GPlates for this subject

Valorisation du phosphogypse de Tunisie en vue de son utilisation comme substituant au gypse naturel dans la fabrication du ciment

International audienceThe substitution of natural gypsum by raw phosphogypsum residue in the preparation of industrial cement, causes a considerable delay in the cement hardening. The aim of this work is to identify, among the mineral and/or the organic compounds present in the phosphogypsum residue, those which cause such a delay and then to perform tests in order to remove or to decrease such impurities. Several tests have been carried out on the industrial cement by adding several mineral and organic compounds to the cement components, demonstrated that Phosphorus, Organic Matter and Fluorine, are the main and exclusive elements which causes a delay in the cement hardening. When they are present in significant amounts, those elements react with the cement particles, thus inhibiting their hydration, and causing by the same time a considerable delay in the cement hardening. Such result means, that in order to use successfully the phosphogypsum instead of natural gypsum in the preparation of industrial cement, the only need is to find out a method that would be able to remove (or decrease the amounts of) these elements from the phosphogypsum residue. Several tests have been carried out in order to remove (or decrease the amounts of) Phosphorus, Organic and Fluorine compounds, which were previously identified as compounds causing a considerable delay in the setting time of the cement. Treatments such as floatation, calcination, washing with sulfuric acid solution (up to 50% H2SO4) produce a good quality phosphogypsum, which may substitutes to natural gypsum in the cement preparation. The setting times of the cements prepared using treated phosphogypsum were indeed, much more lesser than those obtained with non-treated phosphogypsum. The most acceptable setting times of the cement were obtained when the treatment process decreases the amounts of Phosphorus, Organic matter and Fluorine in the phosphogypsum, respectively to 0,2%, 0,05% and 0,05% or less. Treatments by washing the phosphogypsum with a sulfuric concentrated solution, equal or higher than 40% H2SO4, were found to be the most efficient.L’utilisation du phosphogypse brut en tant que substituant du gypse naturel dans la fabrication du ciment entraine un retard considérable de la prise du ciment. Dans ce travail nous avons cherché à identifier, parmi les impuretés minérales et organiques dans le phosphogypse brut, les éléments qui, par leur présence, occasionnent les retards de prise. Les essais que nous avons menés ont permis de démontrer que, parmi toutes les impuretés présentes dans le phosphogypse brut, la matière organique, le fluor et surtout le phosphore, sont les principaux éléments dont la présence en quantités significatives occasionne des retards de prise du ciment. Ces éléments, en s’adsorbant sur les particules de ciment, empêchent en effet leur hydratation et induisent donc des retards de prise considérables. Ce résultat signifie qu’il suffit de mettre au point un procédé de traitement qui éliminerait ces trois éléments à partir du phosphogypse brut pour que celui-ci puisse être utilise avec succès comme adjuvant au clinker. Les différents traitements réalisés en vue d'éliminer ces éléments pénalisants a partir du phosphogypse montrent que la flottation, la calcination et le lavage avec une solution d’acide sulfurique, sont des traitements qui améliorent sensiblement la qualité du phosphogypse, par rapport au phosphogypse brut. Dans tous les cas, nous avons obtenu des temps de début et de fin de prise de la pâte de ciment inferieurs a ceux obtenus avec le phosphogypse brut. Les temps juges les plus acceptables sont ceux obtenus avec les phosphogypses ou le traitement a pu abaisser les teneurs des impuretés a des valeurs inferieures a 0,2 % pour le phosphore, inferieures a 0,05 % pour le fluor et inferieures a 0,05 % pour la matière organique. De ce point de vue, le mode de traitement le plus efficace est le lavage par des solutions concentrées (≥ 40 %) en acide sulfurique

Relationship between tectonic structures and hydrogeochemical compartmentalization in aquifers: Example of the “Jeffara de Medenine” system, south–east Tunisia

Study region: “Jeffara de Medenine” aquifer system in south-eastern Tunisia. Study focus: This study investigates the role of fault structures in the distribution of hydrogeochemical facies and groundwater compartmentalization for the aquifer system. New hydrological insights for the region: The proposed methodology, including seismic structural study, hierarchical cluster analysis and geostatistical methods, allowed an efficient multi-element characterization of the spatial patterns of the structural elements in the aquifers and of the hydrogeological parameters used in a spatial cross-correlation to explore the dependence of the geochemical properties in each “geochemical population” on the hosting structural compartment to delineate the different geochemical compartments. The tectonic studies showed that the lateral extent of the aquifers is controlled by normal faults. The multivariate statistical analysis revealed a strong spatial coherence between hydrogeochemical facies clustering and the reservoir compartments at both large and small scales. The kriged maps of major-ion concentrations and of total dissolved solids in the aquifers were then analyzed and compared with the reservoir facies distribution for each compartment, the geometric characteristics of the aquifer, and the piezometric level trends. This allowed to characterize the hydraulic behavior of the Medenine fault and to understand the underlying physical and chemical processes having led to the spatial distribution of the geochemical properties, and thus, the hydrogeochemical functioning of the aquifers

Stratigraphic update of the Cenozoic Sub-Numidian formations of the Tunisian Tell (North Africa): Tectonic/sedimentary evolution and correlations along the Maghrebian Chain

The Sub-Numidian Tertiary stratigraphic record of the Tunisian Tell has been updated by means of 11 stratigraphic successions belonging to the Maghrebian Flysch Basin (N-African Margin) reconstructed in the Tunisian Numidian Zone and the Triassic Dome Zone. The Sub-Numidian successions studied range from the Paleocene to the Priabonian, representing a major change in the sedimentation from the latest Cretaceous onwards. The Sub-Numidian succession and the Numidian Formation are separated by an Intermediate interval located between two erosive surfaces (local paraconformities). The stratigraphic analysis has revealed diachronous contacts between distal slope to basinal sedimentary formation, allowing the identification of an Early Eocene Chouabine marker bed. The integrated biostratigraphic analysis made by means of planktonic foraminifera and calcareous nannoplankton updates the ages of the formations studied, proving younger than previously thought. The new definition of the Sub-Numidian stratigraphy enables a better correlation with equivalent successions widely outcropping along the Maghrebian, Betic, and southern Apennine Chains. The study proposes a new evolutionary tectonic/sedimentary model for this Tunisian sector of the Maghrebian Chain during the Paleogene after the Triassic–Cretaceous extensional regime. This paleogeographic reorganization is considered a consequence of the beginning of the tectonic inversion (from extensional to compressional), leading to the end of the preorogenic sedimentation. Our results suggest a non-tabular stratigraphy (marked by lateral changes of lithofacies, variable thicknesses, and the presence of diachronous boundaries) providing significant elements for a re-evaluation of active petroleum systems on the quality, volume, distribution, timing of oil generation, and on the migration and accumulation of the oil.Research supported by Urbino University found (responsible F. Guerrera); by CGL2009-09249 and CGL2011-30153-CO2-02 research project (Spanish Ministry of Education and Science) and by Research Groups and projects of the Generalitat Valenciana from Alicante University (CTMA-IGA)