The Oligo-Miocene Graben System of Sardinia (Italy) : a Novel Insight from New Seismic Profiles and Revised Bio-Stratigraphy

Giulio Casula, Antonietta Cherchi, Thomas Chrest, and Lucien Montadert

New seismic profiles acquired by Saras SpA in the Central and Southern part of the Oligo-Miocene Graben System of Sardinia for hydrocarbons Exploration, revised bio-stratigraphy of Oristano 1 and Campidano 1 wells and new calibration of the seismic profiles shed a new light on the geological history of the area in the context of the NW Mediterranean geodynamic evolution.

A major result is the evidence of a very thick (4.5-5.5 km) syn-rift sediments section. The total sediments infilling is at least 6 to 8 km in the Graben System, in agreement with the gravity data. Calibration to the wells shows that the deeper section is pre-Late Chattian-Early Aquitanian in age. Two distinct phases of rifting are well defined: 1- Oligocene, essentially with continental environments. 2- Late Chattian-Early Aquitanian to Base Middle Miocene with marine environments. The transgression is of tectonic origin and the rapid water depths increase is well established by the micro-paleontological data, the deposition of turbidites and the existence of deltaic fans on the flanks of the graben whose geometry implies several hundred metres water depths. These new observations are in good agreement with the present interpretation of similar graben in southern France and in the Gulf of Lion and the geodynamic evolution of the area.

As shown already by field data, a change of tectonic regime occurred in the Late Miocene with a broadly N-S shortening direction. Reactivation of the Oligo-Miocene faults resulted in the formation of elongated pull-apart Plio- Quaternary graben and spectacular inversions of the Oligo-Miocene infilling particularly on the eastern flank of the Campidano Graben.This regime is still active today as shown by folding and faulting of the Quaternary interbedded basalt flows. It shows that the compressive regime in the Corsica-Sardinia Block after its rotation since the Late Miocene, resulted essentially from the convergence between Africa and Eurasia.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013