A mass transport complex controlled by margin topography (South-Western Adriatic Margin, Mediterranean Sea)

Along the South-Western Adriatic Margin (SWAM), a series of large scale submarine failures were initially, partially imaged by multibeam and seismic data in 2003. In particular, the Gondola Slide was originally interpreted as part of a single collapse event that affected the SWAM during the LGM. New high-resolution swath-bathymetry and seismic data were successively acquired to refine and complete the coverage of the Gondola Slide. The new data are used here to detail the architecture of the Gondola Slide, a failed mass involving 40km³ of sediments and affecting an area of 1050km². They permit the subdivision of the Gondola Slide into three elementary mass transport deposits (G1-, G2-, and G3-MTD), linked to distinct failure episodes, and thus to consider the Gondola Slide as a mass-transport complex (GS-MTC). The G1-MTD, which represents 90% of the entire sediment volume involved in the GS-MTC, is the product of a large failure whose source is in the mid-slope area, which propagated toward the upper-slope in a retrogressive style. The shape and the areal extent of the G1-MTD reflect the topographic confinement on the sliding mass by the pre-existing seafloor morphology of the SWAM. A significant part of the material involved in the G1 failure experienced in-situ remolding and deformation, undergoing only short-distance transport. Cross-cutting relationships of geomorphic elements show that the smaller scale G2- and G3-MTDs were emplaced following the main G1 event, likely as a consequence of late readjustment processes at the edges of the main body of the failed material. The re-examination of previously published and new sediment cores coupled with absolute dating control of tephra layers, means that we can infer the G1-MTD emplacement between 62 and 56kyrBP during the Late MIS 4/Early MIS 3. It also constrains the age of G2-MTD between 21 and 34kyrBP. The new age data predate previous estimates, which constrained the age of the entire GS-MTC during the MIS 2-glacial interval. We suggest that earthquakes are the more likely causes for the repeated failure events that struck the SWAM since, at least, the Late Pleistocene.