From foredeep to wedge-top in the Plio-Pleistocene Bradano basin: the Apulia plate as the external front of the Southern Apennines and the Calabrian Arc. Implications for seismic hazard in the Gulf of Taranto

Multi-scale, high-resolution seismic reflection profiles combined with exploration wells and seafloor bathymetry were used to describe the structural and morphostructural setting of the Gulf of Taranto, in the northern Ionian Sea, in order to unravel its tectono-sedimentary evolution during the Pliocene-Pleistocene. Being located between the Ionian Calabrian Margin, to the West, and the Apulian Margin, to the East, the Gulf of Taranto is the site of pervasive tectonic deformation as part of a complex orogenic system that includes five main domains: the Calabrian Arc, the Calabrian Accretionary Wedge, the Southern Apennines and the subducting Apulian Foreland Ramp. Across-strike transcurrent fault zones segment all the above-listed domains. The external fronts of the Calabrian Accretionary Wedge and Southern Apennines progressively migrated toward the ESE overriding and colliding with the subducting Apulia and Ionian lithospheres during the Neogene and Quaternary (Rossi et al., 1983). The collisional setting has been responsible for the formation of the Bradano Foredeep Basin, whose offshore portion is located in the Gulf of Taranto. Various studies revealed that the Apulian Foreland Ramp was uplifted, down-flexed toward west and associated to contraction and transcurrent deformations along E-W trending faults active since the Miocene until recent times (Pieri et al., 1997). In this integrated study, it is shown that thrusts and thrust-related anticlines affected the whole Apulian Foreland Ramp, even underneath the Southern Apennines. Thrust-related folds strike NW-SE and N-S, likely following inherited Mesozoic-Pliocene(?) extensional faults, which might be responsible also for the gentle folding of the Pliocene-Recent deposits. These deep thrusts form very open anticlines, suggesting collision and shortening across the lower Apulian plate, which, in such case, should be considered part of the Apenninic orogenic wedge. The results of the study suggest that during the Pleistocene 1) the Bradano basin ended to be a foredeep basin and it became a wedge-top basin; 2) the Apulia foreland ramp contained the outermost fronts of the Southern Apennines and Calabrian Arc orogenic wedges. The occurrence of basement-involving and positively-inverted extensional faults affecting the Apulian plate allow to reconsider the assessment of the seismic hazards of this highly populated area along the coast around the Gulf of Taranto. Pieri, P., Vitale, G., Beneduce, P., Doglioni, C., Gallicchio, S., Giano, S.I., Loizzo, R., Moretti, M., Prosser, G., Sabato, L., Schiattarella, M., Tramutoli, M. & Tropeano, M. (1997): Quaternary tectonics in the Bradanic-lonian area. Alp. Mediterr. Quat., 10, 535-541. Rossi, S., Auroux, C.C. & Mascle, J. (1983): The Gulf of Taranto (Southern Italy): Seismic stratigraphy and shallow structure. Mar. Geol., 51, 327-346.