Channel, dune and sand sheet architectures of strait-adjacent deltas, Rifian Corridor, Morocco

Sea straits are elongate basin geometries that are common in the sedimentary record and play a key role in oceanography and climate. Due to the intricate confluence of marine processes and the typically complex structural settings of sea straits, many sedimentary and stratigraphic characteristics of these depositional systems are not fully understood. To better resolve these, we study excellent exposures of marginal sea strait deposits, which crop out in the Fez-Meknes region of northern Morocco. These mixed carbonatesiliciclastic deposits represent the sedimentary fill of the Rifian Corridor, which was an ancient sea strait that existed throughout most of the Miocene, until its tectonically-driven disappearance at roughly 6 ma. This event played a crucial role in the isolation and desiccation of the Mediterranean Sea during the Messinian salinity crisis. The multi-km, seismic-scale exposures at the Ben Allou locality (sometimes called Sidi Chahed), contain two >30 m thick sandstone layers that represent strait-adjacent, tide-dominated deltas. Paleotidal ranges for these deltas are inferred to be macrotidal, and experienced significant amplification from the sea strait paleogeographic setting. This setting also caused winds to be restricted and the rivers that fed these deltas likely had small hinterland drainages. These deltas thus formed under a process regime that was uniquely dominated by tides, with very little wave and fluvial influence. This unique setting led to a gradual development from proximal to distal, tidal dune and channel bearing delta architectures. In the deeper, seaward parts of the deltas, stacks of mud-free, 2 to 4 m thick tidal dunes and large >100 m wide channels dominate. Dune thicknesses and heights gradually decrease toward the shallower, landward part of the delta, where thin dunes are replaced by laterally extensive sand sheets and mud drapes.