Albian extrusion evidences of the Triassic salt and clues of the beginning of the Eocene atlasic phase from the example of the Chitana-Ed Djebs structure (N.Tunisia): Implication in the North African Tethyan margin recorded events, comparisons

In the northern part of Tunisia, close to Testour/Slouguia, new observations and updated biostratigraphy make it possible to highlight the relation between the Triassic saliferous mass and the surrounding Mesozoic beds (T. M.). Near the (T. M.) boundary, the formations observed consist dominantly of Triassic evaporites reworked in the Early and Late Albian deep-water sedimentary deposits. Throughout the studied area, Jurassic rocks are absent. We propose to interpret the Chitana-Ed Djebs structure originally emplaced as gravitational stretch masses in a passive margin in the same way as the salt bodies of widespread salt province in the Gulf of Mexico. A reconstructed schematic position of the Chitana-Ed Djebs salt body displays a scenario of setting of the salt mass on a submarine palaeo-slope. Moreover, the starting clues of the paroxysmal event of the Late Mesozoic tectonic inversion clearly fossilized through the discordance of the Middle Eocene–Early Lutetian limestone on the Albian series.     

Atlantic-Type Passive Margin Structural Style of the Cretaceous Basin in Northern Tunisia: Paleoslope Reconstruction and Regional Tectonics

Geotectonics - The purpose of this paper is to characterize the configuration of northern Tunisia’s basin during the Cretaceous on the basis of abundant slump folds and frequent...     

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

Detailed 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.     

Temporal and spatial changes of the submarine Cretaceous paleoslope in Northern Tunisia,inferred from slump folds analysis

This paper presents the first comprehensive, non-exhaustive, study of the genetic relationship between slump folds and the synsedimentary paleoslope during Cretaceous time in northern Tunisia. Slump folds occur mainly in the Cretaceous marl-dominated lithofacies, which exposes numerous slump folds structures. In addition, fault kinematic analysis is conducted to define the paleostress fields and the stress states characterizing the Cretaceous extension that triggers soft-sediment deformation and slumping. The MAM and the APM methods are used to deduce the paleoslope in several localities. The calculated values of paleoslope trend derived from MAM and APM methods precise the variation of the paleoslope trend during Cretaceous times in northern Tunisia. This paleoslope is ～NW-dipping during Berriasian, ～SSW-dipping during Valanginian, ～NW-dipping during the Barremian and ～N- to ～NNE or ～S- to ～SSW-dipping during Aptian–Albian period. The results of the back-tilted fault diagram show a ～North to ～Northeast-trending tectonics extension. The back-tilting of Cenomanian slump axis and poles of axial planes (MAM and APM methods) give close results with ～Southward or ～Northward-dipping paleoslope. The restored fault diagrams show ～North to ～Northeast-trending extension during Cenomanian times. Coniacian-Santonian marls deposits seal all the gravity-driven deformation structures. North Tunisian area exposes evidences for abundant soft-sediment deformation and slumping atop a northward facing submarine slope, which was probably dominant from the Early Cretaceous to Santonian with ～North-South tectonic extension related to the Southern Tethyan rifted continental margin evolution.     

Cretaceous paleomargin tilted blocks geometry in northern Tunisia: stratigraphic consideration and fault kinematic analysis

New stratigraphic data, lithostratigraphic correlations, and fault kinematic analysis are used to discuss the basin geometry and sedimentation patterns of the northeastern Tunisia during Cretaceous times. Significant facies and thickness variations are deduced along the northeastern Atlas of Tunisia. The NW-SE 80-km-long regional correlation suggests a high sedimentation rate associated with irregular sea floor. The fault kinematic analysis highlights N-S to NE-SW tectonic extension during Early Cretaceous. During Aptian–Albian times, an extensional regime is recognized with NE-SW tectonic extension. The Cenomanian–Turonian fault populations highlight a WNW-ESE to NW-SE extension, and Campanian–Maastrichtian faults illustrate an NW-SE extension. The normal faulting is associated to repetitive local depocenters with a high rate of sedimentation as well as abundant syntectonic conglomeratic horizons, slump folds, and halokinetic structures. The sequence correlation shows repetitive local depocenters characterizing the basin during Early Cretaceous times. All the above arguments are in favor of basin configuration with tilted blocks geometry. This geometry is shaped by major synsedimentary intra-basin listric normal faults, themselves related to the extensional setting of the southern Tethyan paleomargin, which persisted into the Campanian–Maastrichtian times. The results support a predominant relationship between tilted blocks geometry and sedimentation rather than E-W “Tunisian trough” as it was previously accepted.