Middle Eocene dinoflagellate cysts from the Tsoul section, eastern External Rif, Morocco: biostratigraphy and paleoenvironmental interpretations

Abstract

This palynological study is carried out on the Eocene sediments in the Tsoul section, which is located in the Taza region, Tsoul Unit, eastern External Rif, northeastern Morocco. It aims their age assessment and paleoenvironmental interpretations, based on palynological data. The palynological content is diverse, well preserved and rich in organic-walled dinoflagellate cysts (dinocysts), whereas spores and pollen are rare. We identified 117 dinocyst species (including some reworked species), among which 6 species and 1 acme are good biostratigraphic markers of the Bartonian (middle Eocene). The main dinocyst bioevents that are used to assign the studied section to the Bartonian include the lowest occurrences (LOs) of Glaphyrocysta semitecta, Impagidinium dispertitum, Lentinia serrata, Membranophoridium aspinatum and Operculodinium divergens, the highest occurrence (HO) of Castellodinium compactum and the acme of Polysphaeridium spp. Regarding the paleoenvironment, the studied section was deposited in a marine environment, characterized by a low productivity inferred from the scarcity of peridinioid cysts and by important environmental changes ranging from restricted inner neritic (lagoon) conditions, inferred from the dominance of Homotryblium and Polysphaeridium, to outer neritic open marine conditions inferred from the dominance of Spiniferites.