The Cenozoic graben system of Sardinia (Italy): geodynamic evolution from new seismic and field data

A tectono-sedimentary scenario for the Southern Sardinia (Italy) Cenozoic graben system is proposed using field observations and the interpretation of onshore and offshore seismic profiles. The major structural events are tied to the general geodynamic evolution of the Western Central Mediterranean. Thus, the extensional late Oligocene–Aquitanian event is a consequence of an ‘Apenninic’ westward subduction process associated with a volcanic arc (29–30 to 15–16 My) which is particularly well exposed in Sardinia. Deposition of Sub-aerial clastics, was followed by transgression of the rift depression at the beginning of the Aquitanian. Subduction terminated at the opening of the oceanic Provençal Basin and the rotation of Sardinia–Corsica during Burdigalian time (20–21 to 15–16 My). The Messinian compressional event (NE–SW oriented), documented from microtectonic data, strongly affected the Oligo-Miocene basin. The superimposed Plio-Quaternary Campidano Graben, which is probably related to the formation of the Tyrrhenian Basin, contains more than 600 m of syntectonic deposits. A change in polarity of the master faults bounding the Oligo-Miocene rift created a central horst-type twist zone separating two depocenters in the Oristano and Cagliari regions. Emplacement of large volcanic bodies and inversion of the basin during the Messinian in Cagliari area has reduced the areas with potential for hydrocarbon exploration. The two remaining prospective zones are the Oristano sub-basin and the offshore, south of Cagliari where burial of lower Miocene marine organic matter may have been sufficient to generate hydrocarbons. Potential reservoirs could be pre-rift Mesozoic or Eocene strata but are mainly excellent Miocene sands derived from erosion of the granitic basement in tilted blocks.