Abstract
The Tunisian Dorsal backland is the Eastern Atlas side of maghrebides. Field data of Fahs area allowed us to develop new interpretations and to characterize the main structural features of the studied devices (Jebel Rouas and Ruissate). Heritage of Zaghouan accident, Triassic salt movements and strike-direction of major synsedimentary faults are the principal causes and results of the skinned and superimposed geometric architecture, generated by the reversed extensional (Jurassic-Cretaceous) tectonics. The actual geometry of Jebel Rouas and Ruissate represents a fault propagation fold, affecting Jurassic and Cretaceous sets. The backland of this thrust fault defines an imbrications structures of Barremian series. Tectonic records activities show the existence of angular unconformities (Oligocene and Eocene series on the Cretaceous sets considered as bedrock), slumps, tectonic breccias and synsedimentary faults are all of them controlled by a deep major accident; N-S to NE-SW and NW-SE. Features of the study area are probably related first; to the blockage of Zaghouan thrust oriented NE-SW in the foreland; then, to the intense halokinetic activity, which facilitates the layers displacement acting as decollment level. The detailed structural and stratigraphic study of Fahs area and its neighbors shows the presence of an intense tangential tectonic during upper Miocene, affecting Meso-Cenozoic sets, because all the structures involved are sealed by Oligocene and Miocene thinned series. This is accentuated by the existence of different sets of decollment at different depths, which are represented by a displacement to the SE through the backland of the Tunisian Dorsal. We define these features as an imbrication and thrusting Out of sequence system.
Highlights
Northern Tunisia corresponds to the most eastern side of Maghrebides
Fahs area is one of the most geodynamic evolution witnesses. Those series retain polyphase tectonic activities and are the seat of several reverse events. It records a structural evolution from the Jurassic to the Quaternary affirming the extensional tectonic of Mesozoic and the compressive events during the Cenozoic
The geometry study of Jebel Rouas structure proves the existence of fault propagation fold (Photo 1(b)) proposed by [6] [23] [26] [27] [31]-[35] and reflects a kinematic evolution of displacement, described by a decollment level generally included in a ductile series
Summary
Northern Tunisia corresponds to the most eastern side of Maghrebides. Its orogeny is the result of a succession of compressive events (Alpine, Atlasic, and Villafranchian). The Jurassic massive of Jebel Rouas is affected in the eastern part by a large thrust fault oriented N-S to NE-SW (Figure 2) facilitated by the salt Triassic decollement level [13]. It is a major accident in the cover structure which is probably rooted in the basement. This extensional heritage is expressed by raised and collapsed blocks grafted to synsedimentary faults oriented NE-SW with NNW dip, which affects Cretaceous series. This half-graben with collapsed blocks is responsible for the structuring and the controlling of depositional process of sedimentary series in study area (Figure 4)
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