Kystes de dinoflagellés et palynofaciès: indicateurs des variations bathymétriques dans le bassin de Guercif (Maroc) au Jurassique (bathonien terminal—Oxfordien basal)

Abstract

The basin of Guercif (northeast Morocco) is a large depression at the African margin of the Tethys, filled with Jurassic sediments and discordant Tertiary sediments. The boring MSD1 carried out on in the western subsident part of the basin, has reached the Upper Bajocian at 3600 m. Cores from between 2850 and 1650 m have been studied. The sediments, composed of alternating silty clays, sometimes calcareous, and fine sandstones, are dated at Upper Bathonian ( Ctenidodinium sellwoodii-Ctenidodinium combazii assemblage) to Lower Oxfordian ( Wanaea thysanota-Systematophora areolata assemblage). Lithofacies and palynofacies indicate sedimentation-types ranging from coastal to inner neritic shallow shelf. The continental influx has always been important. The maximum transgression is suggested by the abundance of disaccate pollen, chitinous foraminifers, dinoflagellate cysts with a wide specific diversity, and by low percentages of vascular tissues. Non-marine phases are characterized by the abundance of land-plant tissues, spores of pteridophytes, Classopollis pollen and the absence of dinoflagellate cysts and foraminifers. Three transgressive phases took place in the basin of Guercif from the Upper Bathonian to the Lower Oxfordian. The major marine transgression occurred during the end of the Upper Callovian as suggested by indications of aridity.