The North Pyrenean (Aquitaine Basin) post-retro-foreland evolution from Bartonian times – implications for the sediment routing system..
Résumé
The North Pyrenean retro-foreland basin is connected westward to a passive margin –the Landais Plateau – that passed to the abyssal plain of the Biscaye Bay, end of the sediments routing system. The objective of this work is (1) to establish the timing of the retro-foreland basin and its post-foreland evolution, (2) the timing of the Pyrenees growth view from the basin (volumes and types of sediment) and (3) the consequences on the sedimentary systems and their architectures. This study is based on a sequence stratigraphic and structural analysis of seismic lines both onshore and offshore calibrated in age, lithology and facies on industrial wells. The end of the Bartonian is characterized by a important change of the subsidence localisation in the flexural basin. It evolved to a piggy-back basin characterized by northward propagation of thrusts coeval with salt diapirs growths that controlled the main depocenters that are not any more located in front of the North Pyrenean thrust. This differential subsidence (l=x10 km) is active up to end-Chattian times, transition to a typical passive margin with a low subsidence flexural (l=x100 km) regime over the former piggy-back area. Two main unconformities at Aquitaine Basin scale recorded deformation during this passive margin period, end Chattian (the base unconformity) and base Tortonian times. They both record uplifts of the Western Pyrenees. The modern relief of the western part of the Pyrenees is inherited from base Upper Miocene. These unconformities recorded changes of sediment routing systems. From Bartonian to end-Chattian times, the sediments are stored both onshore and offshore in the troughs between the thrust-controlled salt ridges. From end-Chattian to base Tortonian, sediments are mainly preserved offshore, with large low subsiding palustrine to lacustrine domains onshore. Since Late Miocene the onshore is a large by-pass domain with upstream river incisions along the Lannemezan and Ger Plateaus, feeding large progradational wedges reworked by deep-sea currents. This work is funded and carried out in the framework of the BRGM-TOTAL project Source-to- Sink.