Oligo-Miocene rift of Sardinia and the early history of the Western Mediterranean Basin

Abstract

The geodynamic evolution of the Western Mediterranean Basin, in spite of many studies, is still uncertain. There is some consensus for interpreting this basin as a kind of small oceanic marginal basin. Its opening has generally been related to a subduction process which was active during the Oligocene–Miocene somewhere east of Sardinia–Corsica1–7. As the margins of the basin are deeply buried below Miocene-to-present sediments, direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8–10 or missing altogether. To obtain such data, detailed field studies have been undertaken in Sardinia (Fig. 1), and the first results are presented here. This approach is justified by the fact that in that island, Oligocene and Miocene sediments were deposited in a rift (fossa tettonica sarda of Verdabasso11), which is the easternmost arm of the complex rift system that affected the European plate during Oligocene and Miocene times. One of these arms evolved towards a small oceanic basin—the Western Mediterranean or Algero–Provencal Basin—while others such as the Gulf of Valencia and the Sardinia rift aborted and remained at the rift stage. Its exceptional exposures make it possible to examine the Sardinia rift to clarify the sequence of events which created it, and to establish a sedimentological model which we believe is directly applicable to the Western Mediterranean Basin.