Oligocene to Middle Miocene evolution of the central Catalan margin (northwestern Mediterranean)

Abstract

The Catalan margin belongs to the northern sector of the margin that separates 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, stratigraphic sections, seismic profiles and well data) enables the present structure of the central Catalan margin to be identified as a major northwest-directed, thick-skinned thrust sheet compartmentalised in a system of NE–SW oriented horsts and grabens. The geometry and depositional features of the Tertiary successions denote that this structure resulted from two successive evolutionary episodes. The first episode was compressional and gave rise to the emplacement of the Catalan major thrust sheet; the second was extensional, linked to the opening of the Valencia trough. The compressional ( pre-extensional) episode is recorded by Lower to lower Upper Oligocene deposits sedimented in a piggyback basin that developed in the present-day offshore. The pre-rift signature of these sedimentary successions is clear (they show constant thickness, are cut by all the normal faults, etc.) and their facies distribution indicates a mostly southwestward spreading 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 Catalan margin and it is recorded by the uppermost Oligocene–lower Burdigalian (Lower Miocene) sediments restricted to the graben troughs. The post-rift stage started in the late Langhian and has continued until the present. It is characterised by the attenuation of the tectonic activity, the sediment spreading over the horsts (most of them were completely overlapped during this stage) and no sediment thickness changes near the faults. The upper Burdigalian 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 early to middle Oligocene as an extensional basin in the Gulf of Lions and as a contractional piggyback basin in the northeastern Valencia trough; (2) the extension started in the early Oligocene in southern France and migrated progressively southwestward, affecting the northeast Valencia trough during the latest Oligocene–Aquitanian.