New stratigraphic and sedimentological investigations on the Middle Eocene-Early Miocene continental successions in southwestern Sardinia (Italy): Paleogeographic and geodynamic implications

In SW Sardinia, the continental Tertiary successions referred up to now to the Cixerri Fm. (Middle Eocene-Lower Oligocene?) have been investigated. Sedimentological analysis suggests these deposits lied down in fluvial environments and comprised between distal braided streams passing eastward to meandering streams/coastal environments (?) under sub-arid climates. The scrutinization of the Cixerri Fm. westernmost successions allowed one to split locally the upper from the lower part based on sedimentological and mineralogical features and indirect dating. Unfortunately, this separation cannot be set everywhere. The few upper outcrops plainly evidenced and well-constrained have been newly named Flumentepido Fm. and assigned to Late Oligocene-Early Miocene: they figure out alluvial fans and proximal braided rivers. This way, the SW Sardinia Tertiary continental sedimentation extends its persistence, contemporaneously changing its tectostratigraphic meaning: from a molassoid context related to the Pyrenean wedge dismantling (Eocene-Oligocene) to a rift-margin succession connected with the opening of the Algero-Provencal back-arc basin due to the Apennine subduction in Oligocene-Miocene times. (C) 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.