Palaeogeography and clay mineralogy of mid-Cretaceous flysches in the Gibraltar Arc area

Abstract

A combined sedimentological and mineralogical study of several mid-Cretaceous sequences of the western Betic Cordillera and northern Rif has lead to the distinction of three main palaeogeographic areas. The basins of these areas received influxes of terrigenous sediments from different source areas. The southern Iberian margin was fed from the Iberian palaeocontinent and its clay-mineral association is characterized by a high content of well crystallized illite and kaolinite; the distal part of this margin was locally starved of continental sedimentation, but contains a considerable clayey contribution, probably oceanic in origin, made up mainly of smectites, illite and palygorskite. The sediments in the North African margin and the southern part of the North African Flysch Trough came from the African continent, the typical Aptian-Albian clay-mineral association being well crystallized illite, illite-smectite mixed layers, kaolinite, chlorite and lesser quantities of vermiculite. The terrigenous supply to the Mauritanian Realm of the North African Flysch Trough came from the Meso-Mediterranean terrane, and its usual Aptian-Albian clay association is illite, vermiculite, illite-smectite mixed layers and kaolinite. A significant change in the clay mineralogy occurred during the late Albian-early Cenomanian in the two former areas, consisting of a decrease in the detrital supply and a concomitant increase in smectites and palygorskite. The sedimentological and mineralogical evolution of this area was controlled by a combination of tectonic, eustatic and climatic changes in the westernmost Tethys during the mid-Cretaceous.