Geochemistry and mineralogy of sediments and authigenic carbonates from the Malta Plateau, Strait of Sicily (Central Mediterranean): Relationships with mud/fluid release from a mud volcano system

A mud volcano field was recently discovered within the Malta Plateau in the Strait of Sicily (CentralMediterranean Sea). Box-core sediments and associated authigenic carbonates have been collected in waterdepths of 140–170 m from two distinctive sectors of the area, and analyzed for major, trace and rare earthelements, stable isotopes, and mineralogy. Relative homogeneity in the mineralogy and geochemistry of bulksediments, and 210Pb activity distributions, argue against an active mud ejection activity. In the Malta Plateauwestern sector, the sediments show high concentrations of Fe, As, Sb, and Mo, exceeding the backgroundvalues estimated for the Strait of Sicily. Active fluid seepage in this area is thought to be responsible for theseenrichments and for the formation of authigenic carbonate crusts. Evidence of bacterial involvement incarbonate (mainly aragonite) formation is recorded in the authigenic crusts, which contain flat and spiralledfilaments resembling Beggiatoa-like sulphide oxidising bacteria and biofilm-like remains which occur insidethe interspaces. Carbonate crusts consistently show extremely negative δ13C values (down to −49‰) thatsuggest contribution of carbon originating from anaerobic methane oxidation. Heavy oxygen isotopiccompositions of the authigenic carbonates (2−3‰ higher than those in box-core sediments) are interpretedas due to precipitation from fluids enriched in 18O due to seepage of deep, isotopically-heavy, relictMessinian brines.