A Cretaceous to Eocene transform fault zone between the Adria and Apulia plates

The onshore and offshore geology of Puglia between the Gargano promontory and the town of Brindisi reveals the presence of a boundary between the Mesozoic Apulian platform and the Mesozoic basinal successions. The Mesozoic Apulian platform outcrops in the Puglia region and partly extend into the offshore of the South Adriatic Sea. The existence of a Mesozoic margin was interpreted by Martinis and Pavan (1967) by means of the facies distribution on land in the Gargano promontory and was inferred from seismic and well data at sea (De Dominicis and Mazzoldi, 1987). In particular, De Alteris and Aiello (1993) point out the existence of an eroded carbonate platform escarpment that separate the Mesozoic shallow water facies of the Apulia platform from the pelagic facies relative to the South Adriatic Basin. The structural and stratigraphic interpretation of this area was carried out using multichannel seismic data collected from the Gargano promontory to the town of Brindisi and provided by the Italian Ministry of Industry, together with the stratigraphic analysis of the deep wells collected onshore and offshore. A first analysis of the data reveals: a) A stratigraphic succession characterized by a great variability in thickness of the Mesozoic succession, as well as some important unconformities that mark the drowning and the emersion of different parts of the platform during the Late Cretaceous; b) A complex fault and fold pattern localized along the boundary between the areas of platform and basinal succession. The stratigraphic succession from well data indicate that during the Lower Cretaceous the Platform facies extended in a E-W direction with an almost constant thickness. Toward NW the facies change from platform to basinal and their thickness gradually increase towards the NNW. During the Upper Cretaceous a great variability in the thickness of the carbonatic successions occurs. In the Monopoli area a very thick carbonatic succession was deposited in facies of platform that passes abruptly to very thin carbonatic succession deposited in a basin environment. The thickness of the basinal succession increases toward NW. The abruptly lateral increase of the thickness of the Lower Cretaceous platform; the presence of important erosional unconformities; the thick succession of breccias interlayered between the succession and finally the large scale structure recognized offshore from seismic reflection profiles permitted to infer the existence of an East-West shear zone that was active during the Upper Cretaceous. We argue that the Apulia-Adria shear zone corresponds to a transform fault zone plate boundary.