Venting and seepage in the Paola Basin (SE Tyrrhenian Sea) investigated

Cold seeps were first identified between 700 and 900 m water depth along the Paola Ridge (NW Calabrian margin, southeastern Tyrrhenian Sea), with the aid of full-ocean depth multibeam and backscatter data acquired in the ‘90s. Here cold seeps are represented by 2 mud volcanoes (RMV and R1MV) and 3 mud diapirs (D1, D2, D3) characterized by the presence of pockmarks on top of them. Higher resolution acquisition of bathymetry, seafloor backscatter and seismic data plus seafloor sampling were carried out in 2011. The data lead to the discovery of active gas venting at the seafloor and precipitation of oxy-hydroxides, sulfides and siderites, these latter characterized by heavy oxygen and carbon isotopic composition, in the sub-seafloor of the mud volcanoes. Stable isotopes (C, O, S) and REE composition, together with pore water content and XRF core-scanning data are under investigation for tracing fluid migration and early diagenesis of sea bottom sediment. Authigenic calcite and aragonite, associated with dead chemosymbiontic shelly macrofauna, were discovered near the seabed on the pockmarks-punctuated mud diapirs. The carbonates retrieved from the diapirs’ sub-seafloor showed an isotopic signature compatible with formation during sulfate-dependent microbially-mediated anaerobic oxidation of methane. The down-core trend of abundance, radiocarbon dating and isotopic characteristics of both chemosymbiontic clam beds (Lucinoma borealis and Acharax sp.), benthic and planktonic foraminifera (Uvigerina peregrina and Globigerina bulloides), authigenic aragonites and the magnetic susceptibility showed that the diapirs have remained geochemically optimal habitats over a period of more than 40,000 years BP. Episodes of enhanced methane flux have been identified and happened near globally recognized abrupt climate oscillations: the beginning of the Dansgaard/Oeschger cycle 10 (at 41 ka) and during the early part of cycle 8 (at 37.5 ka), the beginning of the Bølling interstadial (at 13.5 ka) of the Bølling-Ållerød cycle (14.6-12.9 ka), at the Younger Dryas-Preboreal transition (~11.6 ka). The youngest radiocarbon dated bivalves have lived just before the Little Ice Age (cal AD ~ 1400). New acquisitions carried out in the summer of 2014 during the MarBeep campaign within the frame of the Ritmare project, lead to gas sampling at the mud volcanoes and measurement of its prevalent CO2 composition. Furthermore, a multichannel seismic survey was undertaken in order to fully image the faults that confine and control the cold seep structures and that play a role in the seepage of fluids. The seismic data disclosed that the mud diapirs lie directly on top of convex bending of the Messinian reflector (M) and develop along deep-rooted normal faults that impinge on the sedimentary sequence below the M reflector. Finally, the authigenic mineralizations, especially oxy-hydroxides, have been analysed for their Critical Raw Materials (as defined by the EU) content and showed a significant enrichment in REE.