Mineralogical and geochemical characterization of marine sediments from the mud diapir province of the Paola Basin (Southern Tyrrenian Sea)

The Pola Ridge is a NNW-SSE 60 Km long anticline that confines with the Pola Basin westward (NW Calabrian margin) and is located in the SE portion of the Tyrrhenian Sea. The Paola Ridge had recently been re-interpreted as due a mobile mud belt (including three diapirs:D1,D2 and D3 and two mud volcanoes: MMV and RMV), connected with a set of extensional NW-SE to NNW-SSE trending faults. The MVP11 and MarBeep oceanographic cruises were carried in 2011 and 2014 on board the E/V CNR Urania. During these cruises, other than multi-beam, bathymetric data and CHIRP profiles, gravity coring and box coring samples wre acquired to define the sedimentological , petrographical, mineralogical and geochemical features of the marine sediments. The studied samples were obtained from cores and box cores, collected along the selected structures of the Paola Ridge and were classified, as follows: limestone crusts, carbonates of tubular form, iron oxy-hydroxide crusts, pyrite and sulfur crusts and cohesive mud. Each samples was analyzed by means of optical petrography, XRD, SEM-EDS, XRF, ICP-AES, and ICP-MS. Selected samples were chosen for carbon, oxygen and sulfur isotopic analyses. The petrographical , mineralogical, chemical and isotopic data, presented in this work, allowed to define the depths of the biogeochemical zones and thegeochemical processes affecting the depositional environment into which the marine sediments were deposited. Authigenic calcite and aragonite, associated with chemosymbiotic bivalve assemblages, were discovered on pockmarks along faults cutting the nud diapirs. Stable isotopes (C and O) on these carbonates resulted to be depleted in delta13 C and slightly enriched in delta18 O, suggesting that authigenic carbonates were likely deriving from bacterial oxidation of methane. Several sites were sampled from inside the mud volcanoes,. Iron oxy-hydroxides crusts, mainly consisting of goethite, were found on the seafloor. Pyrite and sulfur crusts showed a mineralogical composition consisting of pyrite and/or sphalerite, quartz and few feldspars. Tubular authigenic carbonates contained siderite, quartz and few phyllosilicates. Stable isotopes (C and O) of siderite showed enrichment in both carbon and oxygen. Cohesive mud samples were dominate by quartz, halite, feldspars, muscovite, and clay minerals (illite, vermiculite, chlorite, kaolinite) while in some samples the presence of calcite or dolomite, siderite, hematite and pyrite was recognized.