Las facies detríticas de la plataforma continental de Cádiz (tramo Chipiona-Trafalgar) en relación con la evolución de la dinámica sedimentaria reciente

Resum

Sediments of the continental shelf of the Gulf of Cadiz, among the estuary of the Guadalquivir river and Cape of Trafalgar, have been studied in order to know the facies distribution, mineralogical associations, source areas, deposit conditions and recent sedimentological evolution. Sediments have siliciclastic character and two sectors can be distinguished: to the S of the parallel of Cadiz prevail bioclastic quartziferous sands, accumulated in relatively energetic areas during low sea level, currently in imbalance with the prevailing oceanographic regime. To the N, in relation with the estuary of the Guadalquivir river, argillaceous muds appear progradating toward the southeast. The observed mineralogical associations are: quartz-calcite in the bulk fraction, illite-kaolinite in the clay fraction and epidote-garnet-rutile in the heavy fraction, similar to those determined in next continental surface outcroppings, being almost constant the detritus from the Upper Pliocene until present time. The source areas are found by the N and NE in Sierra Morena and Betic Cordillera respectively. By the S and SE in the Subbetic Units, Campo de Gibraltar Units and the Neogene materials of the "Depresion del Guadalquivir". Under recent sediments it is observed the existence of a weathering surface and filled fluvial canals excavated during low relative sea level. The high relative sea level is indicated by the existence of prodeltaic muddy formations. It is concluded that the distribution of the detrital facies is conditioned by: a) the fluctuations of sea level during the Holocene; b) the different sedimentation rate among the N and S areas; c) the dominant direction of the coastal and marine currents toward the SE; and d) the orientation of the coast line and continental margin.