Geometry and structural evolution of Lorbeus diapir, northwestern Tunisia: polyphase diapirism of the North African inverted passive margin

International audienceDetailed geologic mapping, structural analysis, field cross-sections, new dating based on planktonic foraminifera, in addition to gravity signature of Lorbeus diapir, are used to characterize polyphase salt diapirism. This study highlights the role of inherited faulting, which controls and influences the piercement efficiency and the style and geometry of the diapir; and also the localization of evaporite early ascent displaying diapiric growth during extension. Salt was extruded along the graben axis developed within extensional regional early Cretaceous tectonic associated with the North African passive margin evolution. Geologic data highlight reactive diapirism during Albian time (most extreme extension period) and passive diapirism during the late Cretaceous post-rift stage. Northeastern Maghreb salt province gives evidences that contractional deformations are not associated with significant diapirism. During shortening, the initial major graben deforms as complex anticlines where diapirs are squeezed and pinched from their feeding

South Tethyan passive margin paleoslope orientation inferred from soft-sediment deformation and fault kinematic analysis: a case study from the Cretaceous of Borj Cedria area, Tunisia

International audienceThe Cretaceous outcrops of Borj Cedria-Bou Kournine area belongs to the NE-trending Atlas system of northern Tunisia. This area exposes sub-meridian folds associated with numerous N-to NWtrending major fault systems. This study together with previous surveys reveals that this N-trending folding is believed to be related to the inversion of the Jurassic and Early Cretaceous pre-existing fault zones and generated in response to the late compressive deformations. In addition, the study area provides evidence of soft-sediment deformations by good exposures of Cretaceous-aged slump sheets. Slump folds are usually associated with several meso-scale syn-sedimentary normal faulting together with frequent reworked blocs and occasional conglomeratic horizons. All these features indicate sedimentation on irregular seafloor topography. The aim of the present study is to investigate slump folds by applying techniques to reconstruct the contemporaneous slope gradient which has triggered soft-sediment deformations. Moreover, the brittle deformation is quantified using fault kinematic analysis together with the analysis of lithostratigraphic correlation and synsedimentary structures. Considerable thickness variations of Cretaceous deposits are interpreted as controlled by normal faulting activities. Likewise, fault kinematic analysis typifies a regional pure extension that trends NNW during Barremain, NNE during Albian and probably NW during Cenomanian time. Based on slump folds analysis, the inferred submarine paleoslope is believed to have a northward dipping during Barremian and a NNE-dipping during Albian time. On the light of the over-mentioned interpretations, it is believed that Cretaceous sedimentation of the study area is highly controlled by major syn-depositional normal faults associated with intra basin growth faulting. These fault systems seem to be related to the Southern Tethyan expansion of the rifted continental passive margin

Interconnection salt diapir-allochthonous salt sheet in northern Tunisia: The Lansarine-Baoula case study

International audienceSurface and subsurface data are used to illustrate the halokinetic style, structural evolution and kinematics of the Lansarine–Baouala salt structure in the Alpine domain of Tunisia. It corresponds to a salt structure showing a large salt canopy overhanging buried diapir. The salt structure is located along the main fault systems, inherited from the southern Tethyan passive margin periods. The Northern domain of Tunisia is undergoing diapirism, which has been recognized as active during the Upper Aptian and Lower Albian periods. Above the diapir apex, salt flows outward and spreads by gravity downslope. A minibasin has formed during this period of salt outward evacuation. The minibasin has a thickness practically correlated to the budget of salt evacuation toward the diapiric structure. During Cenozoic times, compressional deformation stages do not reflect active diapirism. The Lansarine–Baouala salt structure, consisting of connected salt sheets, was passively transported on the Southeast-verging major thrusts that are deeply rooted in the salt beneath the Mateur basin. The Northern Atlas of Tunisia reveals, as many others salt provinces, an interconnection of salt diapirs and significant laterally spreading allochthonous salt sheets (canopies?). In this domain, the inherited allochthonous Triassic salt sheets interlayered within recent series and connected to buried diapir have a significant role in the shallow structural complexity observed in the sedimentary cover during the subsequent contractional events

Review of the deformation styles during the Cretaceous Tethyan period: inferred from slumps and fault Kinematics analysis along Northern Tunisia

International audienceIn northern Tunisia, the Cretaceous period is described as a spectacular episode of soft-sediment deformations exposed for several kilometers. These gravity-driven deformations are interpreted to be associated with the Tethyan passive margin rifting. Slump folds and fault kinematics are analyzed in order to characterize the structural style of Northern Tunisia basin' during the Cretaceous Tethyan period. As a result, Early Cretaceous sedimentation reflects a syn-rift stage mainly underlined by major basement faulting systems combined with other intra-basin growth normal faults. These faults are tilted northward creating a paleoslope (estimated here to be ± 3°) associated to abundant soft-sediment deformations. Major faults (probably listric) split the study area into various tectonic blocs. Meanwhile, the post-rift Coniacian-Maastrichtian rich-marly deposits seal all the inherited differentiations and were presumably driven by the isostatic response of various inherited major faults. Based on fault kinematic analysis, compressional events were not observed during the whole Cretaceous and the sedimentation mainly occurred under extensional tectonics during this period. Halokinetic movements and salt rise-up are active on the extensional structures essentially during the Mid-Cretaceous period allowing the creation of abundant large depocenters with numerous soft-sediment deformations. Thus, the Tunisian margin is described as an evaporite floored margin where significant part of the Mesozoic sedimentary cover underwent frequent gliding and spreading above the Triassic evaporite detachment layers, as described in several Atlantic-type passive margins. During the Cenozoic shortening, a fault inversion model is mainly accepted for the development of different thrust systems. Thus, a clear field relationship between various inherited structural entities and the present-day geographical repartition of faults and folds belts involves the role of the tectonic inheritance in style and the evolution of the northern Tunisia belt

Recent spatial and temporal changes in the stress regime along the southern Tunisian Atlas front and the Gulf of Gabes: New insights from fault kinematics analysis and seismic profiles

International audienceTectonic deformations in the southern Atlassic front of Tunisia (SAFT) and the Gulf of Gabes result from the Nubia-Eurasia convergence. This study, based on the inversion of geologically determined fault slip vectors, presents evidences for spatial and temporal changes in the stress state. Fault kinematics analyses reveal a temporal change in states of stress during the Late Cenozoic. A paleostress (Miocene–Pliocene) state is characterized by a regional compressional tectonic regime with a mean N134 ± 09°E trending horizontal maximum stress axis (σ1). A modern (Quaternary to present-day) state of stress also corresponds to compressional tectonic regime with a regionally mean N05 ± 10°E trending horizontal σ1. The SAFT corresponds to two distinct domains: a far-foreland Atlassic front related to contractional deformation associated with southward propagate thrusting, and eastward, the Gulf of Gabes characterized by normal component NW to WNW trending faults at the crustal margin scale probably related with a transtensional tectonic regime. We propose that the spatial and temporal changes in the stress during the Miocene–Pliocene and Quaternary may result from the geodynamic evolution of the Tunisian Atlas in relation to the rotation of Corsica–Sardinia blocks and the separation of the Sicilian continental lithosphere from the Ionian oceanic lithosphere. These temporal and spatial stress changes along the SAFT and the Gulf of Gabes are probably the engine behind the moderate seismicity, leading at the same time to a reactivation of the inherited major structures created during the evolution of the southern Tethyan margin

South Tethyan passive margin paleoslope orientation inferred from soft-sediment deformation and fault kinematic analysis: a case study from the Cretaceous of Borj Cedria area, Tunisia

International audienceThe Cretaceous outcrops of Borj Cedria-Bou Kournine area belongs to the NE-trending Atlas system of northern Tunisia. This area exposes sub-meridian folds associated with numerous N-to NWtrending major fault systems. This study together with previous surveys reveals that this N-trending folding is believed to be related to the inversion of the Jurassic and Early Cretaceous pre-existing fault zones and generated in response to the late compressive deformations. In addition, the study area provides evidence of soft-sediment deformations by good exposures of Cretaceous-aged slump sheets. Slump folds are usually associated with several meso-scale syn-sedimentary normal faulting together with frequent reworked blocs and occasional conglomeratic horizons. All these features indicate sedimentation on irregular seafloor topography. The aim of the present study is to investigate slump folds by applying techniques to reconstruct the contemporaneous slope gradient which has triggered soft-sediment deformations. Moreover, the brittle deformation is quantified using fault kinematic analysis together with the analysis of lithostratigraphic correlation and synsedimentary structures. Considerable thickness variations of Cretaceous deposits are interpreted as controlled by normal faulting activities. Likewise, fault kinematic analysis typifies a regional pure extension that trends NNW during Barremain, NNE during Albian and probably NW during Cenomanian time. Based on slump folds analysis, the inferred submarine paleoslope is believed to have a northward dipping during Barremian and a NNE-dipping during Albian time. On the light of the over-mentioned interpretations, it is believed that Cretaceous sedimentation of the study area is highly controlled by major syn-depositional normal faults associated with intra basin growth faulting. These fault systems seem to be related to the Southern Tethyan expansion of the rifted continental passive margin

South Tethyan passive margin paleoslope orientation inferred from soft-sediment deformation and fault kinematic analysis: a case study from the Cretaceous of Borj Cedria area, Tunisia

International audienceThe Cretaceous outcrops of Borj Cedria-Bou Kournine area belongs to the NE-trending Atlas system of northern Tunisia. This area exposes sub-meridian folds associated with numerous N-to NWtrending major fault systems. This study together with previous surveys reveals that this N-trending folding is believed to be related to the inversion of the Jurassic and Early Cretaceous pre-existing fault zones and generated in response to the late compressive deformations. In addition, the study area provides evidence of soft-sediment deformations by good exposures of Cretaceous-aged slump sheets. Slump folds are usually associated with several meso-scale syn-sedimentary normal faulting together with frequent reworked blocs and occasional conglomeratic horizons. All these features indicate sedimentation on irregular seafloor topography. The aim of the present study is to investigate slump folds by applying techniques to reconstruct the contemporaneous slope gradient which has triggered soft-sediment deformations. Moreover, the brittle deformation is quantified using fault kinematic analysis together with the analysis of lithostratigraphic correlation and synsedimentary structures. Considerable thickness variations of Cretaceous deposits are interpreted as controlled by normal faulting activities. Likewise, fault kinematic analysis typifies a regional pure extension that trends NNW during Barremain, NNE during Albian and probably NW during Cenomanian time. Based on slump folds analysis, the inferred submarine paleoslope is believed to have a northward dipping during Barremian and a NNE-dipping during Albian time. On the light of the over-mentioned interpretations, it is believed that Cretaceous sedimentation of the study area is highly controlled by major syn-depositional normal faults associated with intra basin growth faulting. These fault systems seem to be related to the Southern Tethyan expansion of the rifted continental passive margin