HEAVY MINERALS IN MODERN SEDIMENTS OF THE BAY OF CADIZ AND THE ADJACENT CONTINENTAL SHELF (SOUTHWESTERN SPAIN): NATURE AND ORIGIN

The content of heavy minerals in modern sediments of the Bay of Cadiz and the adjacent continental shelf were analysed. Their nature and distribution were found to be related to the petrographic nature of the source areas and to the hydrodynamic behaviour of the mineral grains. The relationship between ultrastable and metastable minerals indicates the predominance of the first in sandy and muddy sand deposits. The distribution of this ratio permitted to distinguish both in the Bay of Cadiz and in the adjacent shelf sedimentary environments of variable degree of reworking and maturity. The factorial analysis has allowed the establishment of two mineralogical association (zircon>hornblende> andalusite and garnet> topaz> tourmaline> rutile) that are similar to those defined in different geological units close to the study area. The possible sources of heavy minerals to the study area are related with the Aljibe Sandstone and the calcarenites present in the Guadalete River basin, as well as to the igneous and metamorphic formations (Iberian Massif) of Guadalquivir river basin. The main transport agents are the Guadalquivir and the Guadalete s. Other possible source of supplies is related to the material eroded from exposed coastal cliffs and beaches.