Mud diapirs, mud volcanoes and fluid flow in the rear of the Calabrian Arc Orogenic Wedge (southeastern Tyrrhenian sea)

In the northern Calabrian margin offshore, the Paola Ridge, seaward from the 700 m deep Paola intraslope basin, tops at a depth of around 600 m. Multibeam bathymetry, seafloor reflectivity and seismic data are available. The Paola Ridge consists of circular or elongated ridges cored by a transparent seismic facies that are interpreted as mud diapirs. The diapirs have radius in the order of 5 km and elevate on average 200 m from the adjacent seafloor. The elongated shape of the diapirs is an evidence of a tectonic influence on the pathways exploited by the rising structures. The most recent seismic unit drapes the topographic relief associated with the diapirs showing that diapir rise is at present mainly quiescent. Pockmarks fields and evidence of gas charged sediments are due to degassing from the inactive diapirs. Two mud volcanoes, shown by high backscatter mud flows fed from circular high backscatter areas centred by a collapse feature, are also present on top of one of the dormant diapirs. The only diapir that is actively rising and deforming the seafloor is not associated with pockmarks. Thus, a relationship between fluid expulsion from the diapiric mass and the arrest of the diapir rise is apparent. The increased seafloor steepness due to diapir rise and the presence of gas within the sedimentary succession promotes sediment instability as shown by a thick slump deposit and numerous mass-wasting scars. Sometimes, the diapirs rise in coincidence with extensional faults that offset the Messinian evaporites. The mud remobilization structures are located along a NW-SE trending belt characterized by active extensional faulting. Hence, genetic processes similar to many of the mud diapir and volcano provinces of the Mediterranean, consisting of pre-Messinian source rocks mobilized along discrete belts of active tectonic deformation, is advanced as controlling the setting of the study area.