Tidally influenced deposits in the Río Alías Strait connecting a marginal basin with the Mediterranean Sea (Pliocene, South-East Spain)

The Río Alías Strait developed in the Early Pliocene as a narrow marine corridor at the connection of the microtidal Mediterranean Sea and the north-eastern margin of the Almería-Níjar Basin in the eastern Betic Cordillera (South-East Spain). The orientation and topography of the strait were controlled by the transpressive Carboneras and Polopos/South Cabrera fault systems. Ten sedimentary facies occur in the up to 150 m thick mixed biogenic carbonate-terrigenous succession distinguished on the basis of their lithology, components, grain size, stratal geometries and sedimentary structures, which were observed in seven sections at well-exposed outcrops of four sectors. The sedimentary record of the Río Alías Strait reflects the morphological constraints, which conditioned its sedimentary dynamics and facies distribution. Even in this microtidal setting, tidal current amplification through narrow constrictions produced thick accumulations of large cross-stratified bodies up to 15 m thick formed by the opposite migration of three-dimensional simple and compound dunes. The Río Alías Strait reconstruction shows: (1) a very narrow constriction in the central sector from which “constriction-related deltas” (CRDs) formed in the flood downstream (westward) and ebb (upstream) directions and (2) a relatively deep depression (>65 m water depth) separating the eastern and central-east sectors, where tidal current energy was attenuated and dunes were not generated. The closure of the strait resulted from the tectonic uplift of the antecedent upland of Sierra Cabrera at the northern side, which promoted the southward progradation of deltaic systems over the strait. The Río Alías Strait represents the only clear record of a microtidal strait in the Betic Cordillera since the Miocene. The case study presented here improves existing models on the sedimentary dynamics of ancient tidal-dominated straits by expanding the knowledge on their spatial environment variability.