Jesus, C.C., Miranda, P., Rocha, F. and Oliveira, A., 2007. Fine-fraction mineralogy and geochemistry of beach sediments of SW Portugal as markers of sedimentary dynamics. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 990 – 994. Gold Coast, Australia, ISSN 0749.0208

Mineralogy and geochemistry of fine-grained sediment fractions have been used since the 1960-ies to identify sediment source. Along the Tróia-Sines littoral-arc (SW Portugal) 126 beach-dune profiles have been sampled as well as sea-cliffs and watercourses located close to the study area. Mineralogical analysis of the fine sediment fraction was carried out by XRD, and multi-elemental analysis by ICP-MS was used to determine total Fe, Al, Mg, Ca, K, Sr and Mn. For all fine-fractions only eight different minerals were identified. Their percentages vary significantly: quartz (8-85%), phyllosilicates (1-68%), K-feldspars (2-32%), plagioclases (0-21%), magnesium enriched calcite (0-28%), calcite (0-46%), aragonite (0-32%) and goethite (0-18%). On the basis of mineralogy and geochemistry the studied area can be subdivided into three sectors: 1) northern sector between Tróia and the Carvalhal beach where the Sado estuary, benthic macrofauna communities and the littoral drift constitute the main sediment sources; 2) central sector between Carvalhal and the Melides beach where sea-cliffs are the only identified sediment source; 3) southern sector from Melides to Cape Sines where the volcanic massif and the sea-cliffs were identified as the main sediment sources to the beach system. We conclude that the mineralogical and geochemical composition of the fine sediment fraction provides provenance information for beach and dune sediments, complementing traditional provenance studies with coarser fractions.