Aquitaine Basin - Geodynamic Setting

Geodynamic Setting

For a better understanding of the geological successions and structures in the Aquitaine Basin, it is important to consider the greater geodynamic setting. Two geodynamic developments are of primordial importance for the basin:

• The break-up of Pangaea and the opening history of the Northern Atlantic (and hence the Bay of Biscay).
• The movements of the microcontinent Iberia.

In the Upper Triassic (Carnian) about 230 million years ago, the supercontinent Pangaea started slowly to break up. In the Atlantic domain, the disintegration began in the area of the Central Atlantic. Already in the Lower Jurassic, the initial rifting process had given way to the marine drifting stage. In the Toarcian about 180 million years ago, the Central Atlantic was spreading and North America, South America and Africa were separating. By Callovian times, the Central Atlantic was fully marine. Spreading continued and gradually also began to affect the Northern Atlantic domain. During the Tithonian about 150 million years ago, a rift arm infiltrated along today's continental margin of northwestern France. Consequently Iberia, so far being positioned right below the Armorican Massif (Brittany), was wedged southward. This gave the Atlantic the chance to directly reach the Aquitaine Basin for the first time. In the wake of the southward drifting Iberia during the Lower Cretaceous, the Bay of Biscay opened up. The microcontinent Iberia underwent in addition to its southward drifting motion a counterclockwise rotational movement that eventually brought it in close contact with southern France (reflected in first tectonic movements in the Pyrenees during the Albian; also documented by metamorphism in the Pyrenees dated between 108 and 93 million years ago and by the transgression of the Cenomanian sea). The final collision happened during the Eocene/Oligocene uplifting the mountain chain and subjecting it to severe erosion at the same time. The main phase of uplift ended with the close of the Aquitanian, followed mainly by isostatic movements lasting to this day.