A new Megaslide in the Bradano Foredeep area (Southern Apennines, Ionian Sea).

Along convergent margins, mass-transport represents an important mechanism for sediment distribution within sedimentary basins and, especially if related to seismic activity, it can generate tsunamis. This is also the case of the Gulf of Taranto where mass movements of different size and age are already known. However, a detailed quantitative analysis of geometry, origin, triggering mechanism and final age of their emplacement has not been fully accomplished. In this study, the submerged portion of the Southern Apennine collisional belt within the Bradano foredeep is investigated. A composite data-set including seismic reflection profiles, exploration wells and seafloor morphology, allowed definition of new large-size Mass Transport Deposit, named the “Bradano Basento Mega Slide” (BBMS) and containing a younger slide mass (BBMS1). The BBMS forms a lens 31 by 19.5 km wide, corresponding to an area of ~396 km2 A rough depth-conversion allow to estimate a maximum thickness of about ~600 m and a volume of ~130 km3. The run-out distance is estimated up to few hundreds of meters. These estimates are conservative, since BBMS and BBMS1 likely have an onshore extension, not imaged by our marine data. This is the largest MTD complex described in the Gulf of Taranto. The BBMS and BBMS1 remobilized toward the SE Middle-Late Pleistocene-Holocene clay/silty-clay deposits. Based on stratigraphic correlations, carried out using well-logs and the ages of correlative deposits onshore, it was emplaced in Late Pleistocene and predated the LGM. Several lines of evidence, including the fact that the BBMS gliding surface appears to have been controlled by main tectonic structures in the area, suggest that the most likely trigger mechanism for the emplacement of the MTDs is seismic shaking. Thus, it is suggested that BBMS and BBMS1 should be considered paleoseismological markers of large magnitude earthquakes in the Bradano Foredeep basin. The discovery of BBMS and BBMS1 might be useful to complete the onshore paleo-seismological record and may contribute to clarify the paleo-seismological behavior of this geologically complex area. The discovery of this new megaslide suggests the need for a re-evaluation of the potential for large earthquakes and tsunamis and in general for a reliable geological hazard assessment along the coast of the Gulf of Taranto, a heavily populated area, site of many industrial infrastructures.