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En Tunisie centrale, une tectonique synsédimentaire d'âge Paléocène supérieur à Éocène inférieur a été mise en évidence. Ces manifestations tectoniques contrôlent la répartition des domaines paléogéographiques de cette époque et confirment l'importance de la phase de serrage pyrénéenne sur la bordure de la plaque africaine qui a partagé l'histoire structurale de l'Europe méridionale.

Purpose Ichkeul National Park, NW Tunisia, is a UNESCO Biosphere Reserve. Garaet El Ichkeul Lake is known for its seasonal variability in water level and salinity. In recent decades, the waterbody has been affected by the construction of new hydraulic structures. To reduce the impacts of dams and to maintain the sustainability of the ecosystem, a sluice was built at the outlet of the lake, and it operated for the first time in 1996. This paper describes an investigation of recent sedimentation dynamics in Ichkeul Lake, determined by radiometric dating of sediment cores. Materials and methods A sediment core was collected with a UWITEC gravity corer at the deepest, central part of the lake in August 2009. Specific activities of unsupported lead-210 ( 210 Pb) and caesium-137 ( 137 Cs) were measured in the core, enabling calculation of recent sediment accumulation rates (SAR). Published radiometric data from nearby sediment cores, collected in 1997 and 1982, provide a comparison. Results and discussionThe measured excess 210 Pb inventory was 5300±500 Bq m −2 , leading to an estimation of constant flux of 165±16 Bq m −2 yr −1 , a value higher than the best estimate for local atmospheric fluxes (123 ± 12 Bq m −2 yr −1 ) and the flux estimated from the core collected in 1982 (48 Bq m −2 yr −1 ). The 137 Cs inventory was 3550±120 Bq m −2 , two times higher than the historical 137 Cs atmospheric deposition in the area. The 137 Cs profile displayed a distinct peak, but the 137 Cs depth-distribution did not follow the pattern expected from atmospheric deposition. Application of the constant rate of supply (CRS) model, with the reference point method, produced a chronology and SAR values comparable to those found in previous work. The whole 137 Cs profile was quantitatively reconstructed from the historical records of atmospheric deposition, using the system-time-averaged (STA) model. Conclusions The CRS and STA models provide consistent sediment accumulation results for the whole data set, considering the time resolution of the chronology (~6 years) and analytical uncertainties. Results from cores sampled in 1982 , 1997

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En Tunisie centrale, les bassins mio-plio-quaternaires de Sbiba et de Haffouz sont constitués de dépocentres délimités par des failles de direction proche de E-W, NW-SE, N070 o et N-S. Ces accidents bordiers bien identifiés en sub-surface et dont l'activité a été démontrée aux époques éo-crétacées, ont évolué durant le Néogène et le Quaternaire dans un système de décrochements en relais, alliant des structures compressives (plis N040 o à N080 o E, failles inverses, chevauchements…) et des structures distensives correspondant à des grabens et demi-grabens orientés E-W et N120 o à N150 o E. La région a été affectée du Néogène au Quaternaire inférieur par une succession de régimes tectoniques compressifs (liés aux phases tortonienne et villafranchienne) et extensifs (extension post-tectonique oligo-miocène comme dans l'ensemble du Maghreb, mais aussi existence d'une phase d'extension au Miocène terminal-Pléistocène inférieur synchrone du rifting du Bassin tyrrhénien). Cette alternance compression-extension induit plusieurs inversions de subsidence. L'étude tectonique effectuée aux abords de ces décrochements permet non seulement d'apporter des précisions sur l'évolution spatiale des déformations mais aussi d'établir les relations tectono-sédimentaires caractérisant chaque époque du Mio-Plio-Quatemaire : bassins subsidents sur les décrochements, installation de bassins lacustres sur barrages morphostructuraux, variations d'épaisseur et de faciès liées aux failles synsédimentaires. Significance of the E-W fault system in the geodynamic evolution of the Tunisian Alpine Chain foreland. Example of the Sbiba-Cherichira fault system in Central TunisiaAbstract. -The recent sedimentary basins in Central Tunisia correspond to a set of depocenters with complex geometry which are bounded by E-W, N070 and N-S brittle structures. These bordering faults, active during Eocene and Cretaceous times, have been rejuvenated at the end of the Neogene and during Quaternary in a relay pattern system associated with compressive and extensive deformations according to the alternance of extension and compression phases (Tortonian Atlasic Phase of compression, post tectonic top Miocene-early Pleistocene extension associated to the rifting of the Tyrrhenian Basin, and Pleistocene Phase of compression). These tectonic regime changes involve subsidence inversions. Moreover, the neotectonic study carried out along the strike-slip faults corridories and their associated structures enable us :-to precise the timing of the tectonic deformations ; -to establish tectono-sedimentary relationships of Mio-Plio-Quaternary age.