Geomorphometry of a submarine mass-transport complex and relationships with active faults in a rapidly uplifting margin (Gioia Basin, NE Sicily margin)

Along the NE Sicily margin, between Capo Milazzo and Capo Peloro, in the offshore Gioia Basin area facing the Castanea Ridge, a mass-transport complex (MTC) was first imaged by multibeam data acquired by the end of the 1990s. It was interpreted as resulting from the stacking of different mass-transport deposits due to repeated failures of the shelf edge and upper slope area and of the nearby Villafranca slope channel-levee wedge. New high resolution swath bathymetry and seismic data, acquired in 2009–2011, allowed the complete coverage of the headwall area of the 48km3 Villafranca frontally-confined slide, which represents the bulk of the MTC, and that was previously not mapped. Seven smaller individual zones of instability that represent the source areas of distinct mass-transport deposits emplaced in the upper and lower slope, having surface areas between 10km2 and 60km2, were also mapped. The new data show that, although the Villafranca slide and the subsequent more recent failures were not sourced from the same headwall area, they are similarly associated to the activity of the faults that characterize the NE Sicily rapidly uplifting margin. The Villafranca slide has its headwall along a normal fault parallel to the coast, which is visible in the shelf at 80–85m water depth offsetting the seafloor for 30m. The slab slide and the debris flow lobes have their headwalls along a NNE–SSW oriented normal fault, which offsets the seafloor for 30m and is the offshore prolongation of a regional structure on land. The largest debris flow lobe in the area was actually generated through flow transformation mechanisms from an initial slump mass. The main headwall scarps are rectilinear and exploit regional normal faults along which the principal and larger slope failures (slide and slumps) root, possibly during episodes of accelerated uplift, recognized by several authors in the area, both in Late Pleistocene and during the Holocene. Successive morphological modifications and flow transformations, resulting from smaller scale failures (debris flows), generate more complex headwalls. In addition, the MTC is bounded to the NE by a recent reverse fault which prolongs in a structural ridge (Acquarone Ridge) where evidence of seafloor fluid escapes (pockmarks) is present, implying that compressive and transpressive structures can be active in the area and play an underestimated role in the instability of the NE Sicily margin. •A mass-transport complex was investigated i