TRACE-ELEMENTS DISTRIBUTION AND MINERALOGICAL COMPOSITION IN THE LESS-THAN-2-MU-M SIZE FRACTION OF SHALES FROM THE SOUTHERN APENNINES, ITALY

Mineralogical composition and trace elements distribution in the < 2-m u m size fraction of Late Cretaceous-Oligocene shales from the souther n Apennines (Italy) are presented. The clay mineral assemblage consist s of illite, smectite, kaolinite and minor chlorite. Analytical eviden ce points to a detrital micaceous precursor for illite and smectite. A ccessory phases were also found. Chemical data, normalized with respec t to the Post-Archean Australian Shales (PAAS), indicate depletion of Ba, Rb, Y, Zr and enrichment of Nb. PAAS-normalized REE-patterns exhib it a positive Eu anomaly and HREE depletion. A kaolinite-rich sample h as high Sigma REE contents in contrast to smectite-rich fractions. A R EE-pattern without appreciable Eu anomaly is displayed by the illite-r ich sample. Statistical data processing indicates a link between Ti, P , Y, Zr, Nb and Yb, suggesting that accessory phases may play a role i n controlling HREE and that the observed LREE/HREE fractionation may a lso be due to hydraulic sorting of these phases. An important La-kaoli nite relationship accounts for the capability of this phase to host LR EE. Smectite and, thus, adsorption mechanisms, appear to exert a limit ed role in distributing REE. The Eu anomaly is a source inherited feat ure, probably not determined solely by clay minerals.