Sedimentation and Reservoir Distribution Related to a Tilted Block System in the Sardinia Oligocene-Miocene Rift (Italy)

P. Tremolieres, A. Cherchi, R. Eschard, C. De Graciansky, L. Montadert

In the western Mediterranean basin lies a rift system about 250 km long and 50 km wide and its infilling outcrop (central Sardinia). Seismic reflection surveys show its offshore extension. Block tilting started during the late Oligocene and lasted during Aquitanian-early Burdigalian time.

Two main fault trends, with synthetic and antithetic throws, define the more-or-less collapsed blocks. This morphology guided the transit and trapping of sediments. The sedimentation started in a continental environment then, since the Chattian, in marine conditions. In the central part, the series can reach a thickness of 2,000 m.

The basement composition and the volcanics products related to the main fault motion controlled the nature of the synrift deposits. According to their location in the rift context, the tilted blocks trap either continental deposits or marine siliciclastic or carbonate deposits. In the deeper part of the graben, sands were redeposited by gravity flows into the basinal marls.

The younger prerift deposits are from Eocene to early Oligocene age and locally comprise thick coal layers. Postrift deposits, mainly marls, sealed the blocks and synrift sedimentary bodies.

In middle and late Miocene time some faults were reactivated during compressional events. Then, a Quaternary extensional phase created the Campidano graben, filled with about 1,000 m of sediments superimposed on the Oligocene-Miocene rift.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.