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The Rifian Corridor was one of the Mediterranean–Atlantic seaways that progressively restricted and caused the Messinian Salinity Crisis (MSC). Many key questions concerning the controls on the onset, progression and termination of the MSC remain unanswered mainly because the evolution of these seaways is poorly constrained. Uncertainties about the age of restriction and closure of the Rifian Corridor hamper full understanding of the hydrological exchange through the MSC gateways: required connections to sustain transport of salt into the Mediterranean for the primary-lower gypsum and halite stages. Here we present integrated surface-subsurface palaeogeographic reconstructions of the Rifian Corridor with improved age-control. Information about age and timing of the closure have been derived from high-resolution biostratigraphy, palaeoenvironmental indicators, sediment transport directions, and the analysis of published onshore subsurface (core and seismic) datasets. We applied modern taxonomic concepts to revise the biostratigraphy of the Rifian Corridor and propose astronomically-tuned, minimum-maximum ages for its successions. Finally, we summarise the palaeogeographic evolution in four time slices corresponding to the middle Tortonian (10.57–8.37), late Tortonian (8.37–7.25 Ma), early Messinian (7.25–6.35 Ma), and late Messinian (6.35–5.33 Ma). Several successions record the closure of the corridor via a continuous marine to continental-lacustrine transition. The youngest dated marine sediments represent a good approximation of the age of seaway closure. The closure of the South Rifian Corridor is constrained to 7.1–6.9 Ma; that of the North Rifian Corridor is more uncertain and ranges from 7.35 to ca. 7 Ma. We conclude that the Rifian Corridor was already closed in the early Messinian and did not contribute to the restriction events that resulted in the MSC. Because the Betic Corridor is also closed by the early Messinian, the modern Gibraltar Straits remain the sole option in the Western Mediterranean as last Messinian seaway that was open during the MSC. Our results imply that the Gibraltar Straits could have been established as the exclusive Mediterranean-Atlantic portal already in the late Miocene, and therefore we suggest that future field and drilling campaigns should target the Alboran Sea and the Gibraltar region to investigate water exchange before and during the Messinian Salinity Crisis and its impact on Atlantic circulation and global climate. [ABSTRACT FROM AUTHOR]

The connection between the Mediterranean and the open ocean during the Messinian and the Messinian salinity crisis (MSC) remains largely unsolved; however, such a connection is required to supply the salts required for the formation of the thick evaporite successions deposited during the MSC. A potential candidate for a Mediterranean-Atlantic connection is the northern branch of the Rifian Corridor through Morocco, but existing biostratigraphic constraints of unspecified late Tortonian – Messinian age are insufficient to test the hypothesis. We present new calcareous plankton biostratigraphic data, using among others an improved planktonic foraminiferal zonal scheme that is based on an assemblage- rather than on a typology-based taxonomic concept. The results of this study invariably reveal a late Tortonian age for the youngest open marine sediments in the individual Intramontane Basins in the central part of the North Rifian Corridor (NRC) and no marine sediments of Messinian age have been found. The high sedimentation rates and the observed shallowing in the top part of several NRC successions suggest that, although the marine connection through the NRC may have continued in the earliest Messinian, it was likely closed before ~ 7.0–7.2 Ma, i.e. well before the onset of the MSC. This closure is likely related to a phase of enhanced and localised uplift in the Rif foreland and excludes the North Rifian Corridor as the long-lasting marine connection between the Mediterranean and open ocean during most of the MSC. [ABSTRACT FROM AUTHOR]

Abstract: The Melilla Basin (NE Morocco) formed the easternmost part of the Rifian Corridor, which was an important Mediterranean–Atlantic gateway during the Late Miocene. The sedimentary infill of the basin consists of a shallow marine, precession-related cyclic marl–diatomite succession, laterally grading into a marginal carbonate complex. Three bio-sedimentary events have been recorded within the marl succession: 1) onset of diatomite deposition, 2) major change in foraminiferal assemblages, and 3) transition to Halimeda-rich carbonates and Porites coral reef build-ups. Recent 40Ar/39Ar dating has provided a good age control for the Melilla carbonate sequences, but a high-resolution astronomical time frame is necessary to solve the climatic signature of the basin sediments. This study focuses on the shallow marine marl succession of the Melilla Basin. Integrated magneto-, cyclo- and biostratigraphy allowed a detailed correlation to the astronomical target curve, resulting in a high-resolution time frame for the Late Miocene evolution of the basin. Comparison of the Melilla data with previous results from other Moroccan and Mediterranean basins indicates that the input of Atlantic waters through the Rifian Corridor became restricted after 6.84 Ma, and was minimized by 6.58 Ma. In the final period (6.58–5.96 Ma) towards the Messinian Salinity Crisis, the Melilla Basin can be considered as a marginal basin of the Mediterranean. The astronomical time frame for the marl sequences of the Melilla Basin moreover enables a direct comparison between the independent isotopic and astrochronological dating techniques, as astronomical ages have also been assigned to intercalated volcanic tuffs for which 40Ar/39Ar ages were previously determined. We conclude that the isotopic ages are systematically younger than their astronomical equivalents. [Copyright &y& Elsevier]