CLAY-MINERALS IN RECENT SEDIMENTS OF THE CONTINENTAL-SHELF AND THE BAY OF CADIZ (SW SPAIN)

The distribution of clay minerals in recent sediments on the continent al shelf and in the Bay of Cadiz has been analysed as part of a wider study of sedimentary exchange between the continent and the continenta l margin. The clay minerals included in the muddy sediments consist ma inly of illite, kaolinite, smectite, randomly mixed-layered illite-sme ctite, chlorite, vermiculite and randomly mixed-layered illite-chlorit e. Distribution of the minerals indicates that inheritance from the ad jacent continental areas is the most important process involved. The r elations between the clay minerals were established by Q-mode and R-mo de factor analysis. The main clay mineral associations are: (1) illite -kaolinite, (2) smectite-random mixed-layered illite-smectite, and (3) kaolinite-random mixed-layered illite-smectite-vermiculite. The main sources of sediment supply to the continental shelf are the Guadalquiv ir and Guadiana rivers. Sediment from these rivers and from the rivers flowing into the Bay of Cadiz (mainly the Guadalete) is transported t o the part of the shelf outside the bay by ebb-tide currents. The path of this outflow to the continental shelf, where the sediment is parti ally deposited, is influenced by the morphology of the coast and by hy drodynamic processes.