Initiation and evolution of the Valencia Trough (Western Mediterranean) : constraints from deep seismic profiling and subsidence analysis

Abstract

The structure and evolution of the Valencia Trough (western Mediterranean), a Neogene basin bordered in the north by prominent Oligocene-Early Miocene grabens in the Catalan Coastal Ranges and to the south by the Early Miocene thrust sheets of the Betic belt, is investigated through a deep seismic reflection profile shot across the basin. This profile shows that extensional features related to the rifting are concentrated in the Catalan-Valencian domain in the north, whereas in the south, the Betic-Balearic domain shows little extensional structures, and no clear thrusting. The smooth, quite symmetrical, Moho uplift seems to cross-cut strong SE-dipping reflectors which are clearly visible below the Moho in the central basin. Deep seismic data tied on wells and industrial lines are used to establish a regional depth section which is backstripped and along which the history of tectonic subsidence is investigated assuming local isostasy. We find out that observed tectonic subsidence shows a classical exponential decay for the period 0–15.2 Ma, consistently with observed Moho attenuation, even to the south, where a foreland-type mechanism of subsidence is not recognized. Little subsidence is found for the period 25.2–20 Ma. We also indicate that some brittle basement readjustement must have occurred around 15.2 Ma and that the heat flow, although variable, is not inconsistent with theoretical model of uniform lithosphere attenuation. We therefore propose that the development of the Valencia Trough occurred in two rifting stages. The first, the Oligo-Miocene West European rifting event, had minor effects in the deep basin, and affected mostly the Catalan margin. The second, Serravallian in age (15.2–10.2 Ma), is responsible for present-day Moho uplift, and explains the post mid-Miocene basin development. This second rifting is coeval with the opening of the Tyrrhenian Basin. Its significance at the west of the western Mediterranean remains to be investigated.