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 Neogen e deposits in the Taza-Guercif Basin, located at the southern margin of the Rifian Corridor in Morocco. This corridor was the main marine passageway w hich connected the Mediterranean with the Atlantic during Messinian times. Correlation of the biostratigraphy and polarity sequence of the Taza-Guerci f composite section to the astronomical time scale, allows an accurate dati ng of three subsequent events in the Rifian Corridor (I) The oldest marine sediments marking the opening of the Rifian Corridor were deposited at 8 Ma . At this age, a deep (600 m) marine basin developed in the Taza-Guercif ar ea, marked by deposition of precession-controlled turbidite-marl cycles. (2 ) Paleodepth reconstructions indicate that a rapid (5 m/ka) shallowing of t he marine corridor took place at the Tortonian/Messinian boundary, at an ag e 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 c ontinental sedimentation continued well into the Early Pliocene. We suggest that shallowing and restricting the marine passageway through the Rifian C orridor actually initiated the Messinian salinity crisis, well before the d eposition of the Messinian evaporites in the Mediterranean. (C) 1999 Elsevi er Science B.V. All rights reserved.