Sedimentary Dynamics of the Aveiro Shelf (Portugal)

Abstract

Clay mineralogy of 95 surface sediments samples of Aveiro shelf (covering the continental shelf and upper slope from Espinho to Aveiro) have been analysed in order to determine sediment provenance, dispersion and deposition of fine-grained sediments. A semi-quantitative X-ray diffraction study of the clay fraction (<2 µm) has been carried out, using peak areas. Illite (average 59%), kaolinite (average 30%), chlorite (average 5%) and smectites (average 5%) are the major clay mineral groups identified. A terrigenous origin of these clay minerals can be supported by their presence in the bottom and suspended sediments of Douro river and Ria de Aveiro lagoon and in the adjacent continental masses. However, the smectites minerals found near Aveiro Canyon may be of an authigenic origin. The main source of fine sediments to the studied area is Douro River discharge through along-shore currents. Other supply processes are coastal erosion and Ria de Aveiro lagoon discharge. The occurrence of kaolinite in coarse-grained deposits is probably related with relict supply processes. The patterns of mineral distribution in the studied clay fraction suggest preferential offshore transport and deposition in lower energy environment of outer shelf and upper slope.