STRATIGRAPHIC SEQUENCE, ELEMENTAL CONCENTRATIONS AND HEAVY-METAL POLLUTION IN HOLOCENE SEDIMENTS FROM THE TINTO-ODIEL ESTUARY, SOUTHWESTERNSPAIN

The Holocene filling of the Tinto-Odiel Estuary comprises seven lithof acies over a Mio-Pliocene substrate. The sequence includes three syste m tracts: lowstand system (10000 to 8700 years BP), transgressive syst em (8700 to 7000 years BP), and regressive system (7000 to Recent). Tw enty sediment samples from the 50-m borehole were analyzed for their m ajor components and minor element concentrations. Two multivariate ana lysis methods, principal component analysis and cluster analysis, were performed in the analytical data set to help visualize the sample clu sters and the element associations. Samples corresponding to unpollute d, pre-mining sediments are clearly separated by cluster analysis, mai nly as a result of the low content in sulphide-associated heavy metals such as Cu, Zn, As, Ag, and Pb. So, these sediments may be utilized a s a background for geochemical analysis (bulk sample) in other adjacen t estuaries, both in sandy and silty-clayey sediments. As a consequenc e of large-scale mining and smelting operations occurred since prehist orical times on the river banks, a rapid rise in the metal pollution w as found in the upper 2.5 m of the natural filling, with values exceed ing up to ten times the natural background levels. In addition, since the mid-1960s, large amounts of waste and pollutant effluents have bee n discharged from industries located around the estuary, increasing th e heavy metal content in the last 0.3 m of the natural sedimentation.