EVOLUTION OF ANTICLINES ACCOMMODATING LATERAL PROPAGATION DURING THE QUATERNARY INSIGHT GEOMORPHIC ANALYSIS, A CASE STUDY OF SOUTH RIFIAN RIDGES, NORTHERN MOROCCO

The South Rifian Ridges (SRR) latéral ramps constitute the Northern and Southern boundaries of Volubilis piggy-back basin and are related to propagation folds of the western and eastern arc. It has been allocated to strike-slip reactivation along major basement fault systems under Pliocene stress shortening, wich is still active in response to the Africa-Eurasia convergence. In this context these faults should be actives and propagate laterally leading, with frontal ramps, the Southwestern displacement of SRR.

Little is known about the evolution of lateral propagation of reverse faulting and folding and the ways in wich they accommodate deformation through proximal basin. In order to identify the latéral direction of the Eastern (Jebel Tselfat-Jebel Bou Kenfoud) and the Western anticlines (Jebel Bou Draa-Jebel Outita) we assessed geomorphic criteria and drainage patterns Such as elevation of wind gaps, drainage diversion and stream captures, that result from growing anticlines, decrease in drainage density and degree of dissection and decrease in relief of the topographic profile along the crest. In order to analyse deformation of younger deposits into Volubilis basin, we applied geomorphometric tools such as hypsometry, swath profile analysis as well as different numerical surfaces and slope parameters combined with field observations.

Lateral propagation of anticlinal folds proved an explanation of drainage network evolution which was useful for the interpretation of the Volubilis topography development. Indeed folds growth controlled drainage divesions and captures as well as migrating and tilting of plio-Quaternary deposits. These latters are the remnant of fluvial sediments in the southern part of the basin and form a planation surface like a Cuesta.