Comparative study of the Lower and Mid-Cretaceous sequences on different Maghrebian shelves and basins-their place in the evolution of the North African Atlantic and Neotethysian margins

Abstract

The Lower and Mid-Cretaceous sequences known from Morocco (coastal Essaouira-Agadir-Safi Basin and Eastern Rif Foreland), in Western Algeria (Daǐa Mountains) and finally in Southern Tunisia (Chott Range and Saharian Shelf) are presented from a biostratigraphic and sedimentologic viewpoint. This work shows, for the period considered, common features in the geodynamic evolution of the different regions, such as: 1. - generalization of the carbonate facies in the Early Cretaceous (Berrisian) and at the end of the Mid-Cretaceous (Cenomanian-Turonian) times; 2. - delineation of important discontinuities in the Valanginian and Bedoulian times. This evolution gives evidence of an undeniable influence of eustatism in this Northern part of Africa. Nevertheless, detailed differences allow us to distinguish: 3. - an “Atlantic-type” evolution characterized by discontinuities with gaps (Safi) or sudden variations of thickness (Essaouira-Agadir) at the Berriasian/Valanginian boundary, related to the Neocimmerian rifting and block-faulting phase. Later on, this evolution is underlined by a progressive acceleration of subsidence at the Aptian/Albian boundary, due to the removal of the mid-oceanic doming; 4. - a “Neotethysian-type” evolution (Eastern Rif Foreland, Western Algeria and Southern Tunisia) where local tectonic movements have probably generated the rapid growth of the external marly Bedoulian basins and the spreading of the Wealdian-type (Valanginian to Barremian) and Utrillas (Albian) terrigenous depositional systems. The latest event is linked to the Austrian tectonic phase responsible of variable gaps towards the Aptian to Albian transition.