Sull'origine delle terre rosse in Sardegna: gli elementi in traccia nella caratterizzazione di suoli e rocce madri

The trace elements in the characterization or red soils and parent rocks. The genesis of red soils (Terre Rosse) formed on limestone or dolomite rock bed is yet an unsolved question. A theory suggests that these soils are the final step of an intense decarbonation process of the parent rock followed by the change of the materials in the insoluble residue into iron oxides and clay minerals. A number of trace elements, most1y transition metals, was determined in Sardinian Terre Rosse and parent rocks by instrumental neutron activation analysis performing different irradiations in the TRIGA Mark II nuclear reactor of the University of Pavia. Induced radioactivity measurement was carried out by gamma-ray spectrometry using a High Purity germanium detector coupled to an analyzer-computer system. The same elements were also determined in some standard reference rocks, released by United States Geological Survey, in order to evaluate the accuracy of the employed analytical method. Average values of the trace element content in the Terre Rosse and in the parent rocks are presented and discussed, together with the evaluation of precision and accuracy. Trace element profiles at different horizons are reported as well. A comparison of trace element distribution among soils belonging to the same geological era is also presented.