Late Neogene evolution of the Taza-Guercif Basin (Rifian Corridor, Morocco) and implications for the Messinian salinity crisis

Magnetostratigraphic and biostratigraphic results are presented from Neogene deposits in the Taza-Guercif Basin, located at the southern margin of the Riffan Corridor in Morocco. This corridor was the main marine passageway which connected the Mediterranean with the Atlantic during Messinian times. Correlation of the biostratigraphy and polarity sequence of the Taza-Guercif composite section to the astronomical time scale, allows an accurate dating of three subsequent events in the Riffan Corridor. (1) The oldest marine sediments marking the opening of the Riffan Corridor were deposited at 8 Ma. At this age, a deep (600 m) marine basin developed in the Taza-Guercif area, marked by deposition of precession-controlled turbidite-marl cycles. (2) Paleodepth reconstructions indicate that a rapid (5 m/ka) shallowing of the marine corridor took place at the Tortonian/Messinian boundary, at an age of 7.2 Ma. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. (3) The Taza-Guercif Basin was emergent at an age of 6.0 Ma and, subsequently, continental sedimentation continued well into the Early Pliocene. We suggest that shallowing and restricting the marine passageway through the Riffan Corridor actually initiated the Messinian salinity crisis, well before the deposition of the Messinian evaporites in the Mediterranean.