Headland-associated banner banks generated during the last deglaciation near the Strait of Gibraltar (Gulf of Cadiz, SW Spain)

Abstract

The inception and evolution of large-scale bedforms on the Barbate Platform (Gulf of Cadiz, SW Iberian Peninsula) are investigated based on a detailed study of multibeam bathymetric data, high-resolution seismic profiles and tidal current simulations. Elongated rocky outcrops and several large-scale bedforms classified as sand banks were identified on the platform: Barbate, Zahara, El Palmar, El Varadero and Caños de Meca banks. The Barbate and Zahara banks exhibit the most complex internal stratigraphic architecture, which comprises five seismic units. The basal unit (U1) is interpreted as incised valley infill and is overlain by nearshore bars (U2). Two high-energy growth phases (U3 and U4) that combine progradation and accretion form the present-day external bank shape. Superimposed bedforms covered these banks under the modern hydrodynamic regime (U5). The multiphase accretion and progradation of U3 and U4 in the Zahara and Barbate banks were closely linked to the presence of a palaeo-headland — termed here as palaeo-Cape Trafalgar — and strong tidal current eddies that resulted from the progressive flooding of the Barbate Platform during the last deglaciation. This configuration was relatively stable while the rocky outcrops were exposed to sub-aerial conditions, forming a palaeo-coast with coastal bluffs. We suggest that during this period of coastal stabilization, U3 and U4 grew as banner banks on either side of the palaeo-Cape Trafalgar. The present study proposes that the configuration of palaeo-headland associated with palaeo-banner banks (Zahara and Barbate banks) along each side of the palaeo-Cape Trafalgar represents a transgressive analogue model of headland-associated tidal bank systems developed in funnel-shaped coastal systems terminating in narrow straits.