Contrasting styles of the Holocene highstand sedimentation and sediment dispersal systems in the northern shelf of the Gulf of Cadiz

Abstract

An approach to the interpretation of the Holocene highstand depositional systems and the influence of shelf circulation patterns on sediment dispersal in the northern Gulf of Cadiz shelf (SW Iberian Peninsula) is reported. The study area comprises the transition from the southern Portuguese shelf, lacking major fluvial input, to the Guadiana and Guadalquivir shelves, receiving sediments from fluvial sources. An integrated study using high-resolution seismic profiles and meteorological and physical oceanography data was undertaken to reach the proposed goals. A lateral transition of shelf environments is evidenced during the most recent sea-level highstand period. The Portuguese shelf can be considered as a moderate to high-energy environment, where the dominance of storm events led to the construction of a significant infralittoral prograding wedge, as a consequence of normal incidence of storm waves and steep shelf profile. The Guadiana shelf shows a distinct partition of depositional systems, as a result of a moderate fluvial supply and significant reworking wave and current activity over morpho-structural highs. Proximal facies are attributed to poorly developed prodeltas, whereas distal facies are interpreted as muddy belts. The Guadalquivir shelf is a fluvially dominated environment, as the most prominent feature is a thick, widespread prodelta whose formation has been controlled by significant fluvial supply, moderate hydrodynamic regime and smooth shelf topography. The comparison between sediment transport patterns evidenced in geophysical records and shelf circulation patterns enables us to propose a model for the sediment dispersal during the Holocene highstand period. Sediment dispersal is controlled by an intermittent counter current system, which seems to be intimately linked with the wind regime. Eastward dispersal on the middle to outer shelf is led by the general anticyclonic circulation, dominant under the influence of westerly winds. Westward dispersal occurs in the inshore zones, mainly led by the entrance of warm water tongues on the shelf under the action of easterly winds. These two opposing patterns of sediment dispersal are bounded by zones of current shear (Huelva Front and Strafford Shear).