Deciphering the 3D structure and development of the Venere mud volcano (southern Italy) using integrated geophysical methods

Mud volcanoes (MVs) have been found in various geological settings on passive and active margins. Here, we present results from Venere MV located at the southern rim of the Crotone forearc basin of the Calabrian Arc, offshore southern Italy at ∼1500 m water depth. The near-circular dimension of Venere MV from its bathymetric expression is ∼4 km in diameter and has two cones. To contribute to the knowledge of the internal structure across Venere MV, we conducted a geophysical study using multichannel and wide-angle seismic data constraining the P-wave velocity variation. The upper 200 m below the seafloor consist of sub-parallel layers, while a prominent reflection at that depth is a regionally occurring unconformity representing the onset of the Calabrian uplift. The seismic data and the P-wave velocity indicate two separate feeder conduits of the cones. Seismic imaging yields subseafloor dimensions of Venere MV that exceed its seafloor dimensions by at least twice. Combining the wide-angle and reflection data allowed a reconstruction of the history of Venere MV's structural change over time. An initial phase of mud volcanism formed a semi-circular mound with rigid rims and an internal mud-pie. After a period of quiescence associated with subsidence, this mud-pie was covered with hemipelagic sediments. A second phase formed the double-cone structure re-mobilizing previously extruded mud and creating a complex pattern of overlapping mud flows. The formation of steep cones instead of a mud-pie indicates a change in viscosity of the extruded mud during the second phase of mud volcanism.