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

Abstract

A mud volcano field was recently discovered within the Malta Plateau in the Strait of Sicily (Central Mediterranean Sea). Box-core sediments and associated authigenic carbonates have been collected in water depths of 140–170 m from two distinctive sectors of the area, and analyzed for major, trace and rare earth elements, stable isotopes, and mineralogy. Relative homogeneity in the mineralogy and geochemistry of bulk sediments, and 210Pb activity distributions, argue against an active mud ejection activity. In the Malta Plateau western sector, the sediments show high concentrations of Fe, As, Sb, and Mo, exceeding the background values estimated for the Strait of Sicily. Active fluid seepage in this area is thought to be responsible for these enrichments and for the formation of authigenic carbonate crusts. Evidence of bacterial involvement in carbonate (mainly aragonite) formation is recorded in the authigenic crusts, which contain flat and spiralled filaments resembling Beggiatoa-like sulphide oxidising bacteria and biofilm-like remains which occur inside the interspaces. Carbonate crusts consistently show extremely negative δ13C values (down to −49‰) that suggest contribution of carbon originating from anaerobic methane oxidation. Heavy oxygen isotopic compositions of the authigenic carbonates (2−3‰ higher than those in box-core sediments) are interpreted as due to precipitation from fluids enriched in 18O due to seepage of deep, isotopically-heavy, relict Messinian brines.