The tributary valley systems of the Almeria Canyon (Alboran Sea, SW Mediterranean): Sedimentary architecture

摘要

Three tributary valley systems of the Almeria Canyon (Dalias, Andarax and Gata) located on the Almeria Margin (Alboran Sea, SW Mediterranean) were studied using high-resolution techniques including swath bathymetry and TOPAS seismic reflection profiles. A detailed morphological and seismic stratigraphy study shows that the tributary valley systems (TVS) are formed by two types of valleys: gullies and leveed channels. Dalias TVS is the best developed system, covering an area of more than 300 km~2 from the shelf-edge off Cabo de Dalias to the Almeria Canyon (100-1500 m depth). Andarax TVS covers about 65 km2, from the shelf off the Andarax River mouth to the westernmost branch of the Almeria Canyon (40-300 m depth). Gata TVS covers more than 100 km~2 from the shelf-edge off Cabo de Gata to the Almeria Canyon (200-650 m depth). Tributary valley systems can be divided into two models based on the detailed morpho-seismic study: the sea level-controlled model and the sediment supply-controlled model. The sea level-controlled model includes the Dalias and Gata TVS. This model is mainly governed by sea level fluctuations, and the valleys grow as a result of the activity of turbidity currents and hemipelagic sedimentation, displaying a retrogressive upslope pattern. The valleys' development would have been favoured by glacio-eustatic oscillations during the Late Quaternary. A tentative chronostratigraphic correlation has been made, relating the evolution of Dalias and Gata TVS with the Marine Isotopic Stages and sea level curves. Tectonics and margin physiography play a secondary role in the development of this type of valley. The sediment supply-controlled model is applicable to the Andarax TVS. The growth of the valleys is controlled by the ephemeral sediment discharges from the Andarax River. The valleys are small-scale gullies located on the shelf and slope, which would grow as a result of the turbidity currents which channel the fluvial sediment supplied in form of hyperpycnal currents. This model would have been developed during the last highstand of sea level, once the coast-line reached its present situation.