Oligocene to middle miocene evolution of the central Catalan margin (northwestern Mediterranean)

The Catalan margin belongs to the northern sector of the margin that separa tes the extremely thinned continental crust of the Valencia trough from the undeformed or thickened crust of the Iberian microplate. The integration of the available onshore and offshore data (mapping, strati graphic sections? seismic profiles and well data) enables the present struc ture of the central Catalan margin to be identified as a major northwest-di rected, thick-skinned thrust sheet compartmentalised in a system of NE-SW o riented horsts and grabens. The geometry and depositional features of the T ertiary successions denote that this structure resulted from two successive evolutionary episodes. The first episode was compressional and gave rise t o the emplacement of the Catalan major thrust sheet; the second was extensi onal, linked to the opening of the Valencia trough. The compressional (pre-extensional) episode is recorded by Lower to lower U pper Oligocene deposits sedimented in a piggyback basin that developed in t he present-day offshore. The pre-rift signature of these sedimentary succes sions is clear (they show constant thickness, are cut by all the normal fau lts, etc.) and their facies distribution indicates a mostly southwestward s preading of the sediments. The extensional episode includes the syn-rift and post-rift stages. The syn -rift stage resulted in the present horst-and-graben structure of the Catal an margin and it is recorded by the uppermost Oligocene-lower Burdigalian ( Lower Miocene) sediments restricted to the graben troughs. The post-rift st age started in the late Langhian and has continued until the present. It is characterised by the attenuation of the tectonic activity, the sediment sp reading over the horsts (most of them were completely overlapped during thi s stage) and no sediment thickness changes near the faults. The upper Burdi galian and lower Langhian sequences record that the transition between the syn-rift and post-rift stages was not sharp. These units show intermediate features since they concealed some minor faults and overlapped horsts, but were still affected by most of the major normal faults. The onshore and offshore tectono-sedimentary and palaeogeographic evolution show that: (1) the northwestern Mediterranean basin existed during the ear ly to middle Oligocene as an extensional basin in the Gulf of Lions and as a contractional piggyback basin in the northeastern Valencia trough; (2) th e extension started in the early Oligocene in southern France and migrated progressively southwestward, affecting the northeast Valencia trough during the latest Oligocene-Aquitanian. (C) 1999 Elsevier Science B.V. All rights reserved.