Reconstruction of the last cretaceous anoxic event in the Tarfaya Laayoune basin (South of Morocco): Biostratigraphy and Paleoenvironment of the Oum Debaa Formation

The Tarfaya-Laayoune coastal basin developed in a stable passive margin, where sedimentation occurred in shallow bays. During the Late Cretaceous, bituminous and phosphatic series were deposited in the shallow depression such as Sebkha Oum Debaa. In this work, the age of these Cretaceous layers are refined using a palynological approach and their paleoenvironments are described using organic geochemistry. Based on quantitative and qualitative palynological analyses, the sediments revealed a rich and diverse dinoflagellate cyst assemblage (65 taxa); among them 9 important biostratigraphic markers: Andalusiella inflata, Andalusiella ivoirensis, Andalusiella mauthei, Cerodinium diebelii, Cerodinium speciosum, Dinogymnium acuminatum, Odontochitina porifera, Trichodinium castanea, and Trithyrodinium evittii. According to the reported stratigraphic dinoflagellate taxa distribution, an age range of late Campanian to early Maastrichtian is herein proposed for the Oum Debaa Formation. This biostratigraphy update has been correlated to the Tethyan and Sub-Boreal domains. On the paleoenvironmental level, geochemical proxies have displayed an anoxic lagoon depositional which is dominated by an intermediate climate between hot / humid and arid with an often low paleoproductivity regime which induces redox conditions.