3D seismic interpretation of MTDs in the Adriatic Basin (Italy) and comparison with modern examples

The Plio-Pleistocene sedimentary sequence of the Pescara Basin (Central Adriatic Basin, Italy) has been investigated through the analysis of commercial 3D seismic reflection data. It consists of a complex of progradational and aggradational large scale eastward-dipping clinoforms (200 ms - 500 ms high). Conventional seismic facies interpretation, combined with seismic geomorphology techniques, and rollover trajectories analysis have permitted to recognize two large scale mass-transport deposits (MTDs) of different age, buried within the slope clinoforms succession of the Pescara Basin. The two MTDs (named MTD1 and MTD2) affect the entire clinoform surface, from the shelf-break to the basin floor. The older deposit (MTD1), buried at around 800ms below the present day seafloor, is the largest, with a failed area of around 90 km2, and is associated with a descending rollover point trajectory. The evacuated main headwall of MTD1 is roughly spoon-shaped, and is around 10 km wide and fairly smooth and linear. It also indentents the shelf-break. The basal shear surface of MTD1 has a ridge and through morphology, with small internal headwalls, that could be indicative of a retrogressive mechanism of failure. Steep lateral ramps of the basal shear surface abut against the undeformed slope sediments in strike profiles. In the accumulation area, at the toe of the slope, the slumped material overruns the former seabed. In some portions of the MTD1, frontal ramps connect with the basal shear surface resulting in a partially emergent landslide. The geometry of the landslide can act a lateral seal of unfailed units both along the sidewalls and along the frontal region of the landslide. MTD2 (buried at around 650m), covers an area of around 57 km2, and is associated with a high-angle positive roll over trajectory. The evacuation area is smaller and shallower, with an arcuate headwall scar around 5 km wide, that affects also the continental shelf-break. MTD2 appears characterized by sectors with different internal deformation: a blocky area, that is scattered mainly to the south, and a northern sector, where the seismic facies analysis suggest the presence of completely remoulded deposits likely corresponding with debrites. It has been observed that, especially in the case of MTD1, the topography created by the irregularities of the MTDs form stratigraphic traps through the ponding of sand-prone sediment gravity currents, resulting in discrete packages of possible sand-rich material. In addition, since the headwall scars of both the MTDs indent the shelf-break, it is possible that shelf-margin progradational successions have been mobilized and incorporated in the extensive chaotic bodies, bringing coarse grained material to the base of the slope. A comparison of the two buried MTDs, with modern landslide exposed at the seafloor in the southern Adriatic basin, permits to link the interpretation of seafloor mapping and VHR seismic profiles of modern mass-transport complexes with industry-standard geophysical data.