Abstract: Possible Rift Control of the Evolution of Thrusting in the Tunisian Atlas

Alastair W. Baird, Chris J. Clayton

The Mejerda zone of the Tunisian Atlas thrust belt traditionally has been described as a "zone of diapirs." More recently the zone has been interpreted as a thrust system in which much of the thrusting has been out-of-sequence. We propose radically different model for the evolution of the zone which integrates its stratigraphical, sedimentological, structural and geophysical evolution and addresses the major problems associated with earlier models.

In this model, the Mejerda zone consists of a series of linked half-grabens of Early Cretaceous to Palaeogene age. The basin-bounding faults generally dip towards the southeast. Uplift and tilting has exposed Triassic rocks in the footwalls to the Northwest of the faults. The tilted fault-block geometries have controlled Sedimentary thicknesses and facies variations throughout their evolution. During the Atlasic orogeny basin inversion occurred when southeast vergent thrusts frequently decapitated the crests of the tilted extensional fault blocks and carried them southeastwards into the adjacent half grabens.

We highlight aspects of the geological and geophysical evolution of the area which are central to this model but which were problematic within previous models. These aspects include; the evolution of topography, uplift and erosion; gravity anomalies; the tectonic processes responsible for unusual stratigraphic juxtapositions; the geometries and petrographic characteristics of Triassic rock masses: and the unusual facies and thickness variations within Cretaceous to Neogene stratigraphic sequences.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France