Middle Eocene dinoflagellate cyst biostratigraphy from the southwestern Tethyan margin: Revised age assessments of sediments near Larache Province, northwestern Morocco

Abstract

Palynological analyses are performed on the imprecisely dated ‘Upper Cretaceous–lower Eocene’ marly and marly limestones succession from the Thare section at Arbaa Ayacha, western External Rif (northwestern Morocco) to reassess the previous calcareous microplankton-based age determination of the sediments. The succession yields well to moderately preserved palynological associations that are mainly composed of organic-walled dinoflagellate cysts, suitable for biostratigraphic analysis. The sediments are here reassessed as being of middle Bartonian age using the recently well-calibrated distribution patterns of several index taxa like Glaphyrocysta semitecta, and Rhombodinium perforatum. These, taken together with the composition of the background assemblages allow quite precise designation of the section to the interval corresponding to magnetochrons C18n.1r to C18n.1n following correlation to the Bartonian/Priabonian Global Stratotype Section and Point (GSSP) section at Alano di Piave, NE Italy. Our results further underline the potential of marine palynological analysis emphasizing organic-walled dinoflagellate cysts in biostratigraphic and paleoenvironmental analyses of the Mediterranean Paleogene.