LAUSR

Abstract The palynological analysis of the Eocene–Oligocene succession from the Tattofte section in the western External Rif (northwestern Morocco) reveals the presence of well-preserved and diverse assemblage, rich in dinoflagellate cysts (dinocysts). Qualitative analyses, especially of the dinocysts, differentiate the individual stages of the deposits, while quantitative analyses permit paleoenvironmental and paleoclimatic interpretations. We assign the lower part of the Tattofte section to the Middle Eocene (Lutetian and Bartonian) and its upper part to the Upper Oligocene (Chattian), and define a hiatus spanning the Late Eocene (Priabonian) and Early Oligocene (Rupelian). The dinocyst marker events used for the biostratigraphic interpretations include the first and last occurrences of marker species, such as Batiacasphaera compta , Castellodinium compactum , Cerebrocysta bartonensis , Distatodinium biffii , Distatodinium paradoxum , Distatodinium ellipticum , Enneadocysta arcuata , Homotryblium floripes , Hystrichokolpoma bullatum , Impagidinium velorum , Lentinia serrata , Pentadinium imaginatum , Rhombodinium spinula , Saturnodinium perforatum and Ynezidinium brevisulcatum , as well as the Chiropteridium spp. acmes. And we equate the Chattian with the dinocyst Distatodinium biffii Zone of Brinkhuis et al. (1992). Changes in the relative abundances of selected dinocyst groups, spores and pollen lead to the distinction, from oldest to youngest, of four marine environments: 1) marginal marine to coastal inner neritic under relatively warm-water during the Middle Eocene; 2) outer neritic to oceanic during a transgressive regime in the early Chattian; 3) fluctuating restricted to open marine in the middle Chattian; and 4) shallow coastal to open marine due to sea-level fall at the top of the section in the latest Chattian, suggested by the Chiropteridium spp. acmes. The acmes of selected thermophilic dinocyst taxa, such as Polysphaeridium spp. and Homotryblium spp. suggest warm water marine conditions, which may be related to the Middle Eocene climatic optimum (MECO) and Late Oligocene warming.