PALEOGEOGRAPHIC AND DIAGENETIC ANALYSIS OF CLAY SEDIMENT SUCCESSIONS OF THE ATLAS GULF IN THE CRETACEOUS (WESTERN HIGH ATLAS, MOROCCO)

Clay mineral assemblages of Cretaceous sediments deposited in the Western High Atlas of Morocco are controlled by the evolution of sedimentary environments through time and by diagenetic processes. Detrital influences on the day mineral successions of Western High Atlas depend mainly on tectonic activity, climate and eustatic fluctuations. Active subsidence of the Atlas Gulf associated with the opening of the Atlantic ocean is responsible for the abundance of illite in Early Cretaceous sediments. By contrast, the smectite-rich day sedimentation occurring during Late Cretaceous results from the stabilization of the Atlas Gulf margins. The smectitic day sedimentation is also enhanced in Cenomanian sediments by a decreasing intensity of erosion during that transgressive period. The scarcity of kaolinite suggests arid climatic conditions particularly around the Jurassic/Cretaceous boundary. Burial diagenesis occurs mainly in the southern flank of the High Atlas. Smectite is progressively replaced with depth, by illite in sediments deposited in an open-marine environment (Agadir area) and by corrensite-like minerals in evaporite sediments (Afensou area). Neoformations of clay minerals (kaolinite) occur in pore spaces of sandstones and dolomitic formations outcropping in the Northern flank of the High Atlas.