GEOCHEMICAL FEATURES OF MIOCENIC SANDSTONES (SOUTHERN APENNINES, ITALY)

Ten samples of siliciclastic sandstones belonging to the Serra Palazzo Formation (SPF) (Southern Apennines, Italy) have been studied for their petrographic and geochemical characteristics with the aim to compare their compositions with that of sandstones belonging to the Gorgoglione Flysch Formation (GFF) deposed in the same basin. SPF and GFF outcrop in Southern Apennines (Italy) and are interpreted as turbiditic successions of the foredeep and wedge-top depozones in growing Foreland Basin System (Critelli et al., 2017). SPF consists mainly of a foredeep turbidite succession consisting of siliciclastic and calciclastic arenites having late Burdigalian-Serravallian sedimentation age (Gallicchio & Maiorano, 1999). GFF represents a siliciclastic succession having ≈1500 m thickness consisting of coarse-medium grained turbidites with mudstone layers. The deposition age of detritus was Langhian-Serravallian in a wedge-top basin (Lentini et al., 2002). Sampling was performed near Forenza Village (Potenza) along two different stratigraphic logs having each a thickness of ≈10m: Log 1 (5 samples) consists of an alternation of arenaceous-pelitic layers (thickness up to 80 cm), whereas Log 2 (n=5) consists of prevalent arenite layers (thickness up to 90 cm). According to Herron classification (1988), the sandstones from Log 1 fall over wacke and arkose fields, whereas Log 2 are arkoses, except for one sample falling in wacke field. Log 1 sandstones show a minor SiO2 content (49 wt%) with respect to those of Log 2 (SiO2=57% in average) and higher CaO (19% against 14%), MgO (1.5% against 1.3%) and Fe2O3 (2.4% against 2%) contents. The abundances of TiO2 (≈0.31%), Al2O3 (≈10%), Rb (≈98 ppm), Sr (≈210 ppm), Y (≈16 ppm), Zr (≈140 ppm) and Nb (≈7 ppm) are similar. Overall the Serra Palazzo sandstones show a hybrid character having silicic and calcitic detritic components. The GFF sandstones show a major silicic component as evidenced by major SiO2 content (64%wt) and a minor calcitic abundance (CaO=7,2%wt). From the comparison between SPF and GFF sandstones emerges that SPF arenites show in Herron’s diagram, composition similar to that of Gorgoglione sandstones. This feature is due to similar silicic detrital component whereas the main difference regarding the calcitic portion seem linked to its different origin: the GFF sandstones are decidedly poorer in CaO having only carbonatic cement without calcitic clastic detritus; the SPF sandstones show a higher CaO content for the presence of detrital calcitic component in addition to carbonatic cement. The similarity of SiO2/Al2O3 and Fe2O3/K2O ratios between the two sandstone types has been interpreted as an evidence of common origin of siliciclastic detritus. U-Pb spot dating of detrital zircons, in progress on sandstones of SPF and GFF, could be useful to better constrain the relationships between two turbiditic successions suggesting the potential source-areas of the siliciclastic supply