Aquitaine Basin
The Aquitaine Basin is, after the Paris Basin, the second largest Mesozoic and Cenozoic sedimentary basin in France, occupying a large part of the country's southwestern quadrant. Its surface area covers 66,000 km2 onshore. It formed on Variscan basement which was peneplained during the Permian and then started subsiding in the early Triassic. The basement is covered in the Parentis Basin and in the Subpyrenean Basin — both sub-basins of the main Aquitaine Basin — by 11,000 m of sediment.
The Aquitaine Basin, named after the French region Aquitaine, is roughly funnel-shaped with its opening pointing towards the Atlantic Ocean. Here it meets for 330 km the straight, more or less north-south trending Atlantic coastline but continues offshore to the continental slope. To the south, it is delimitated for 350 km by the westnorthwest–eastsoutheast trending Pyrenees. In the southeast, the basin reaches the Seuil de Naurouze (also called Seuil du Lauragais) between the Montagne Noire on its northern side and the Mouthoumet range in the south. Just west of Narbonne, the basin is overridden by Pyrenean thrusts. The northeastern boundary of the basin is formed by the arcuate basement outcrops of the Massif Central. Via the 100 km wide Seuil du Poitou in the northeast, the basin is connected to the Paris Basin. In the far north, the basin abuts the east-west oriented Variscan basement of the Vendée, the southernmost part of the Armorican Massif.
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