Mohamed Moncef Turki

Tectonic evolution of the northern African margin in Tunisia from paleostress data and sedimentary record

Abstract A reconstruction of the tectonic evolution of the northern African margin in Tunisia since the Late Permian combining paleostress, tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns. The extension lasting from the Late Permian to the Middle Triassic is contemporaneous of the rifting related to the break up of Pangea. During Liassic times, regional extensional tectonics originated the dislocation of the initial continental platform. In northern Tunisia, the evolution of the Liassic NE–SW rifting led during Dogger times to the North African passive continental margin, whereas in southern Tunisia, a N–S extension, associated with E–W trending subsiding basins, lasted from the Jurassic until the Early Cretaceous. After an Upper Aptian–Early Albian transpressional event, NE–SW to ENE–WSW trending extensions prevailed during Late Cretaceous in relationship with the general tectonic evolution of the northeastern African plate. The inversions started in the Late Maastrichtian–Paleocene in northern Tunisia, probably as a consequence of the Africa–Eurasia convergence. Two major NW–SE trending compressions occurred in the Late Eocene and in the Middle–Late Miocene alternating with extensional periods in the Eocene, Oligocene, Early–Middle Miocene and Pliocene. The latter compressional event led to the complete inversion of the basins of the northwestern African plate, originating the Maghrebide chain. Such a study, supported by a high density of paleostress data and including complementary structural and stratigraphic approaches, provides a reliable way of determining the regional tectonic evolution.

Gravity and aeromagnetic constraints on the extent of Cenozoic volcanic rocks within the Nefza–Tabarka region, northwestern Tunisia

Bouguer gravity and aeromagnetic data are analyzed to determine the extent of Miocene magmatism in the Nefza and Tabarka regions of northwestern Tunisia. Construction of magnetic intensity and enhanced analytic signal (EAS) maps indicated the existence of at least two regions containing probable subsurface igneous bodies that correlate to the small scattered igneous outcrops in the Nefza and Tabarka regions. Because of the lack of lateral resolution of the EAS techniques, 3-D magnetic and 2.5-D gravity models were constructed over the anomalies at Nefza and Tabarka. The final models indicate that the maximum depths of the igneous bodies are between 2.5 and 2.7 km with maximum widths between 15 and 22 km. The final models also indicate that the bodies are tabular with a combination of laccolithic and lopolithic shapes and were probably emplaced in the shallow levels of the crust (at least 3 km). These widths greatly expand the region of known Miocene magmatism in northwestern Tunisia. Combined with geochemical and petrological data of the surface volcanic rocks, the gravity and magnetic models imply a wider range of Miocene volcanic activity in northern Tunisia, probably related to a subduction zone.

Geodynamics of the Southern Tethyan Margin in Tunisia and Maghrebian domain: new constraints from integrated geophysical study

The geodynamic evolution of the Southern Tethyan Margin of Tunisia is investigated using geophysical studies. Analysis of gravity and seismic reflection data in the Maghrebian domain and Southern Tunisia reveals the geodynamic role played by the North Saharan Flexure (NSF) in the evolution of the Southern Tethyan Margin. The Saharan Atlas Mountains (Atlasic Basin) and the African Craton (Telemzan High) are separated by the NSF which is a regional-scale feature that may represent a significant basement discontinuity that has controlled the Paleozoic, Mesozoic, and Cenozoic evolution of the Tunisian and Maghrebian Tethyan Basin.

Groundwater resources of a multi-layered aquiferous system in arid area: Data analysis and water budgeting

The Maknassy basin in central Tunisia receives insignificant precipitation (207 mm/y), but the hydrological system retain very small quantities of water due to the steep topography and surface water resource partially mobilised witch is evacuated toward the basin outlet. However, the Maknassy plain support agriculture based on ground water irrigation with increasing water demand last decades. These developments have boosted agricultural productivity in the region. While these problems are mainly due to poor surface water management strategies in the region, the groundwater resources in this basin should be properly assessed and suitable measures taken for uniform surface water mobilization. As a first step in this direction, groundwater resources have been assessed. Regional specific yield (0.017) and groundwater recharge have been estimated on the basis of water table fluctuation method. Groundwater recharge amounting to 61.5 106 m3 in a year takes place in the region through infiltration of rainwater (48.1*106 m3 for phreatic aquifer and 13.4*106 m3 for the deep one), and recharge due to the infiltration in the Leben quady bed (1.57*106 m3). Recharge to deeper aquifers has been estimated at 0.1*106 m3 during dry seasons. Assuming that at least 40 % (102.61*106 m3) of the total precipitation water (256.64*106 m3) makes the runoff water, this important resource can be mobilized in order to increase groundwater recharge. Subject to an arid climate, such region requires an integrated water resource management. It permits to keep aquiferous system equilibrium and participate to the sustainable development which integrates natural resource management.

Basement structure of southern Tunisia as determined from the analysis of gravity data: implications for petroleum exploration

Gravity data were analysed in the Ghadames Basin and surrounding regions in southern Tunisia in order to determine the basement structure of the region and its relationship to petroleum exploration in relatively unexplored basins. The analysis included the construction of regional Bouguer gravity anomaly and horizontal gravity gradient maps. These maps indicate that the Ghadames Basin is not a simple sag basin but consists of a series of sub-basins and uplifts. The northern boundary of the basin which we call the Telemzan–Ghadames transition zone is marked by a NE-trending high amplitude gravity gradient anomaly which decreases in amplitude toward the east and breaks into a series of north–south- and east–west-trending anomalies implying a more structurally complex region. When the known petroleum fields are overlain on to the gravity gradient anomaly maps, the fields mostly occur along or next to linear alignments of horizontal gravity gradient maxima. We interpret the correlation of the petroleum fields and horizontal gravity gradient maxima to indicate that the basement was involved in forming the petroleum traps. This study illustrates that a regional gravity analysis can be useful in determining where additional exploration can be applied in relatively unexplored basins.

Preuves de la non-stratification du Trias dans le Turonien de la Koudiat Sidii (Nord-Ouest de la Tunisie)

Abstract The cartographic and biostratigraphic datings carried out at Koudiat Sidii do not confirm the interbedding of the Triassic rocks within the Turonian sediments. Interrelationships between cartographic, drill holes and gravimetric dating show that the Triassic rocks form the core of a large anticline, flanked by Cretaceous and Neogene outcrops. Of this structure, in large parts collapsed and buried under a thick Quaternary deposit, we only see the western flank, formed by dolomitic breccia of Triassic rocks supporting a set that spreads from Upper Cenomanian to Upper Senonian. The occurrence of Triassic debris flow reworked in the Turonian allows us to interpret the Triassic material as a diapiric extrusion, which reached the surface during the Turonian times, in the tectonic corner of ancient faults trending north–south and NE–SW. During the Tertiary tightening phases, oriented NW–SE, the induced folded structures are strongly controlled by these tectonic directions. Particularly, the meridian fold corresponds to the torsion of J. Hout NE–SW fold in the neighbourhood of the north–south palaeofaults.

Blocs basculés au Crétacé inférieur dans la région du Kef (Tunisie nord-occidentale)

Abstract Stratigraphic and tectono-sedimentary analysis of the Lower Cretaceous series in the Le Kef area, north-western Tunisia, provides information on their geodynamic history from the Valanginian to the Albian. Extensional tectonics induced tilted blocks and half-grabens. Two main stages were distinguished: the first pre-Aptian and the second Late Aptian and Albian. These periods could be related to extensional episodes that caused the opening of the central Atlantic and the Ligurian Tethys (Jurassic-Early Cretaceous) and later the Mesogean sea (Late Aptian).

Analysis of Recent Deformation in the Southern Atlas of Tunisia Using Geomorphometry

In this work, we propose to locate, characterize and quantify some topographic deformations linked to the seismotectonic context, and anthropogenic actions in the southern Atlas of Tunisia. The analysis of morphometric parameters (Residual Topography, Hypsometric Integral, Drainage anomalies, Maximum curvatures and Roughness) has revealed that three structures in the study area, J. Ben Younes, J. Bou Ramli and J. El Abiod, are distinguished by a specific morphometric and anomalous response which may reflect an important morphodynamic activity caused principally by the numerous reactivation of the Gafsa fault.

The Sub-thrust And Sub-salt Exploration Potential In Tunisia, New Exploration Challenges

Searching for new challenges and exploration strategies, new-old techniques used abusively in the Gulf of Mexico (sub-thrust and sub-salt exploration) are applied for the first time in Tunisia. Beginning with the Sub-thrust prospectivity: In Central Tunisia North-South Axis (NSA) and Kairouan areas, 2D seismic acquisition shows series of high-angle reverse and thrust faults running through NE-SW trend across the area forms the boundary between the uplifted Atlas Foothill s terrain to the northwest and the low lying Pelagian Basin to the southeast. Alternatively, in Kairouan area (in the sub-surface), four investigated wells show a number of drilled thrusted hanging-wall structures. Basin modeling analysis using Basin Mod 1D; 2D and Basin view as well as seismic interpretation prove the existence of a theoretical potential on the sub-thrust footwall of these faults to the southeast, where they could be sourced directly from the Pelagi an Basin. Seismic lines show Cretaceous and Tertiary sediments dipping away from these faults into the basin. Potential reservoirs are the Ypresian El Garia (nummulitic limestone facies) and the Campanian Abiod formations they could be reservoir targets for this play. However, 2D seismic surveys are very limited and are of poor quality at present, but some initial lead areas have been already defined For the Subsalt prospectivity: targets are very poor understood in the northern African domain (Algeria, Tunisia and Libya). Using basin modeling and seismic data, several salt-canopies like structures have been identified and several leads have been defined notably in the southern Gulf of Gabes and in Gulf of Tunis.