Vegetation climate and marine environmental reconstruction in the western Mediterranean (southern Rifian corridor, Morocco) over the Tortonian-Messinian transition

The Southern Rifian Corridor was a gateway connecting the Mediterranean Sea to the Atlantic Ocean in the Late Miocene. Its rapid narrowing at the Tortonian - Messinian transition around 7.2 Ma, resulting from very intense tectonic activity, has triggered an ecological crisis well before the deposition of the Messinian Salinity crisis evaporites. The sedimentary successions deposited in the Saïs Basin have recorded different events regarding biostratigraphic, environmental, tectonic, and eustatic that characterized the area during the late Miocene. In order to get information on the marine and continental environment during the Tortonian-Messinian Transition (TMT), a palynological and biostratigraphic study was carried out on two boreholes in the Saïs Basin. The biostratigraphic analyses based on the planktonic foraminifera of the boreholes studied reveals the succession of several biostratigraphic events, allowing us to attribute these sedimentary deposits to the late Tortonian - early Messinian time interval including the recognition of the T/M boundary. The abundance of continental inputs (pollen, spores, BOM, WOM, and COM in the palynofacies) and the low D/S ratio values indicated that the Saïs basin was a neritic epicontinental environment suffering a significant influence of terrigenous inputs. The temperature index shows that the thermal conditions of the surface water were warm. In the late Tortonian, faunal and floristic assemblages indicate an open, relatively deep, outer platform type marine environment with a slight tendency towards an inner platform context. At the Tortonian-Messinian boundary, there is an increase in land inputs and relative reduction in the diversity of both microfauna and microflora. The presence of cold-water taxa probably indicates moderate cooling. In Lower Messinian the marine environment, was external platform with tendencies towards an internal area. The cover is opened and dominated by herbaceous plants that colonize the low altitudes, while trees colonized the middle altitudes. The climate was hot and humid in the mid-altitude and dry in the lowlands.