(Table 1) Average composition of smectites of sediment core CRP-3

The aim of this work is to evaluate the origin of smectites in sediments of CRP-3 core (Victoria Land Basin, Antarctica), through TEM observations and microanalyses on smectite microparticles and XRD analyses of clay fractions. Smectites in the lower sedimentary section (between 602.05 and 815.86 mbsf), and in some levels of the central section of the core, are intermediate members of the beidellite-saponite series, with lower K and higher Mg contents in interlayer and higher cristallinity values. The clay fraction largely consists of smectite, that is regarded as authigenic. Smectites in the upper (between 6.60 and 101.69 mbsf) and in some other levels of the central section of the core are Al-Fe beidellites, with higher K and lower Mg contents in interlayer sites and lower values of crystallinity. In the clay fraction illite and chlorite also occur. These characteristics suggest that smectites in these sediments are detrital. Smectites in an igneous body (between 901.20 and 919.06 mbsf) have a homogeneous composition and are Al-rich beidellite-montmorillonites; the clay fraction is mostly composed by kaolinite with mixed-layer smectite-illite or kaolinite-smectite. Authigenic smectites probably formed from the alteration of volcanic material (pyroxenes, glasses) and/or through precipitation from fluids of possible hydrothermal origin.