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 g raben system is proposed using field observations and the interpretation of onshore and offshore seismic profiles. The major structural events are tie d to the general geodynamic evolution of the Western Central Mediterranean. Thus, the extensional late Oligocene - Aquitanian event is a consequence o f an 'Apenninic' westward subduction process associated with a volcanic arc (29-30 to 15-16 My) which is particularly well exposed in Sardinia. Deposi tion of Sub-aerial clastics, was followed by transgression of the rift depr ession at the beginning of the Aquitanian. Subduction terminated at the ope ning of the oceanic Provencal Basin and the rotation of Sardinia-Corsica du ring Burdigalian time (20-21 to 15-16 My). The Messinian compressional even t (NE-SW oriented), documented from microtectonic data, strongly affected t he Oligo-Miocene basin. The superimposed Plio-Quaternary Campidano Graben, which is probably related to the formation of the Tyrrhenian Basin, contain s more than 600 m of syntectonic deposits. A change in polarity of the mast er faults bounding the Oligo-Miocene rift created a central horst-type twis t zone separating two depocenters in the Oristano and Cagliari regions. Emp lacement of large volcanic bodies and inversion of the basin during the Mes sinian in Cagliari area has reduced the areas with potential for hydrocarbo n exploration. The two remaining prospective zones are the Oristano sub-bas in and the offshore, south of Cagliari where burial of lower Miocene marine organic matter may have been sufficient to generate hydrocarbons. Potentia l reservoirs could be pre-rift Mesozoic or Eocene strata but are mainly exc ellent Miocene sands derived from erosion of the granitic basement in tilte d blocks. (C) 2001 Elsevier Science Ltd. All rights reserved.