The Geometry and Evolution of the Tunisian Atlas Thrust and Foreland Basin System: Theoretical Modeling vs. Inheritance of Structure

BAIRD, ALASTAIR W., Kingston Polytechnic, Kingston-Upon-Thames, Surrey, United Kingdom

In a recent re-evaluation of the Atlas Mountains of north and central Tunisia, it has been noted that the Tunisian Atlas thrust system extends up to 200 km further southeastward than previously recognized, and the structures of the "north-south axis" define the mountain-front. The development of the system spanned a significantly longer period than previouely proposed. Deformation began before the Oligocene and propagated southeastward towards the foreland to form the north-south axis mountain front in the middle Miocene. Subsequently, out-of-sequence-thrusts formed farther northwestward along the northeast-southwest-trending Mejerda zone, which was previously and mistakenly recognized as the Atlas mountain front.

The geometry of the thrust-foreland basin system, oblique trend of the mountain front in relation to southeast thrust transport and origin of major lateral structures are considered in terms of lithospheric rheology, flexural loading, and thrust propagation through a discordant older Tethyan passive margin. Theoretical considerations are contrasted with the inherited structural trends, including those related to Palaeozoic basement; Triassic facies control, Jurassic Tethyan margin faults, middle Cretaceous strike-slip systems, and Paleogene basin margins. These trends also control the siting of post-Atlasic grabens.

Such a structural reevaluation necessitates a revision of potential hydrocarbon plays. Areas previously thought to be reactivated foreland are shown to be allochthonous, with thrust-generated antiformal structures. Structural reactivation has also controlled sedimentation and facies distribution throughout much of the Mesozoic and Tertiary.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)