Sequence stratigraphic analyses of the interaction between tectonically driven sedimentation and sediment transporting bottom currents in the foreland basin of the Rifian Corridor - Case study from the Gharb and Saïss basins, northern Morocco

Abstract

Abstract The Rifian Corridor was one of the main marine connections between the Atlantic and the Mediterranean before the Messinian Salinity Crisis (5.97 – 5.33). Previous studies indicated that the Mediterranean became partially isolated from the Atlantic already at 6.64 – 6.44 Ma because of the restriction of this marine connection. The gradual closure of the Rifian Corridor however has been hardly captured stratigraphically since the latest marine deposits are often eroded. In order to specify the processes leading to the closure of the Rifian Corridor a field study was conducted in the Saïss Basin and in the western end of the Gharb basin, located in the mid-western part of the Rifian Corridor. Magnetostratigraphic, biostratigraphic and grain-size results are presented in combination with a sedimentary log of the Neogene deposits at two study-locations near Meknes. Grain-size results are used to correlate and interpret both study-locations. Correlation of the biostratigraphy and polarity sequence of the marl intervals allows an accurate dating of the composite section. The composite section shows an increase in depth related to basin subsidence and is dated at 6.37 – 6.29 Ma. The turbiditic dominated successions show periodic variances in tectonic activity of the source area while subsidence further affected the type of active sedimentary processes. This study furthermore shows increasing influences of bottom current controlled deposits higher up the stratigraphy, indicating changes in the exchange of Atlantic-Mediterranean bottom sea-water. Both sections show different bottom current regimes, the northern section indicates bi-directional flow (E–W & W-E) whereas the southern section indicates dominantly Mediterranean inflow (W–E). The differences in flow regime observed, can be explained by the effect of Coriolis force acting on the water masses in the Rifian Corridor. This theory however enables two scenarios contrasting to present assumptions: 1) another corridor was open and the corridor comprising the study areas was the shallower of the two connections or 2) at the time of deposition, the Rifian Corridor was wider than the assumed width.