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

Sea straits are elongate zones where geographic constriction can amplify marine currents. Sediment deposits that formed in sea straits are relatively well studied in the rock record and more recently, models of tidal strait depositional systems have been developed. However, models and descriptions of strait-adjacent systems remain uncommon and are thus poorly understood. In this study, we present detailed outcrop descriptions of Miocene deposits that formed in the Rifian Corridor, which was an ancient sea Northern Morocco. The km-scale outcrops at the Ben Allou locality (30 km north of Fez, Morocco) contain a succession of claystones, siltstones and sandstones which have sedimentary architectures that have been affected by sea strait-adjacent process regimes, like marine current constriction, tidal amplification, and reduced wave activity. Detailed descriptions of the sandstone architectures reflect a development from mud drape bearing sand sheets in the proximal regions of the system, to stacked cross strata and finally thick stacked cross strata containing channel forms. In the deeper, more distal reaches of this system, sediment grainsizes are much finer (silt and clay) and are sparsely interbedded with turbidites. These results confirm existing models which show that strait-adjacent systems tend to be tide-dominated, and wave and fluvial influence can be overprinted by tidal processes. Some insights into the formation of tidal dunes are discussed. For example, it is shown that compound tidal dunes may not be preserved differently than simple tidal dunes in this area, which is relevant for predicting sedimentary architectures and fluid flow properties of ancient tidal successions.