A volcanic stratigraphic marker in the continental shelf offshore the Volturno river (Northern Campania, Southern Italy): inferences from high resolution seismic stratigraphy and tephrostratigraphy

A volcanic stratigraphic marker in the continental shelf offshore the Volturno river, located in the Northern Campania has been recovered and discussed through seismo-stratigraphic and tephrostratigraphic data. The seismo-stratigraphic data include a Subbottom Chirp and Sparker seismic grid collected in the frame of research programmes of marine geological mapping of the continental shelf off Campania Region. Cores have been also collected for a better calibration of seismic profiles. Although several tephrostratigraphic studies have been carried out in Southern Italy, regarding in particular the Somma-Vesuvius and the Ischia and Procida offshore, only few of them have linked the geological aspects on tephrostratigraphy detected through geochemical, sedimentological and SEM analyses with high resolution seismic profiles. In the Ischia stratigraphic succession the oldest tephra layers are distinguished by a well preserved layer, thick about 30 cm, which is correlated with the Phlegrean products of the Campanian Ignimbrite event (39 ky B.P.). The marine counterpart layer is named the C13 tephra layer in the Tyrrhenian sea. The sedimentological and petrophysical analysis of cores has evidenced the occurrence of a volcanic stratigraphic marker, corresponding to a highly continuous and parallel seismic reflector on the seismic sections. Seismo-stratigraphic analysis has evidenced that the volcanic level, interpreted as a tephra deposit is interlayered in transgressive system tracts deposits, pertaining to the Late Quaternary depositional sequence, well detected in the whole Campania Tyrrhenian margin. The volcanic level, mapped on six seismic profiles, is located at different depths, ranging between 70 and 155 m below the sea bottom, interrupting in correspondence to the shelf break. Sedimentological and petrophysical analyses have shown that the tephra layer corresponding to a seismic reflector consist of a thick sandy deposit with pumiceous clasts, whose analysis in terms of tephrostratigraphy is still in progress.