Biostratigraphie des kystes de dinoflagellés et paléoenvironnements dans l’Eocène de la coupe d’Ibn Batouta, région de Tanger, Rif Externe occidental, Maroc

Abstract

Palynological investigations of Eocene sediments from the Ibn Batouta section, located in the external Tangier Unit (western External Rif, northwestern Morocco), revealed the presence of well-preserved figured organic matter, rich in dinoflagellate cysts. Qualitative and quantitative analysis of palynological content, mainly dinoflagellate cysts, allowed a biostratigraphic subdivision and a paleoenvironmental reconstruction of these deposits. The dinoflagellate cyst events used for the characterization of the Middle Eocene (Lutetian and Bartonian) in the lower part of the Ibn Batouta section are: the first and last appearances of Castellodinium compactum, Distatodinium craterum, Distatodinium ellipticum, Distatodinium pilosum, Hystrichokolpoma salacia, Phthanoperidinium geminatum, Polysphaeridium biformum, Rhombodinium spinula, Ynezidinium brevisulcatum, the first appearance of Homotryblium floripes and the last appearance of Hystrichokolpoma bullatum. The disappearance of most of these species and the last appearance of Deflandrea phosphoritica are used for deduction of an Upper Eocene–Lower Oligocene age for the upper part of the section. Relative abundance changes of selected dinoflagellate cyst groups and continental palynomorphs (spores and pollen) allowed to highlight, in ascending order, five different marine environments: (1) neritic coastal with important nutrient availability at the base of the section; (2) outer neritic at the beginning of a transgressive phase in the Lutetian; (3) deeper outer neritic to oceanic in full transgressive phase in the Bartonian; (4) probably shallower outer neritic at the beginning of a regressive phase in the upper Bartonian; (5) coastal, probably estuarine in full regressive phase in the Upper Eocene–Lower Oligocene interval. These paleoenvironmental changes coincide with the global climate changes of the Middle Eocene Climatic Optimum (MECO).