Conclusions
The structural and hence sedimentary organisation in the Aquitaine Basin was ultimately influenced by two principal factors:
- By structural inheritance from the Variscan basement.
- By the evolution of the Pyrenean orogen.
The strong northwest-southeast-striking tectono-metamorphic zonation in the basement has profoundly influenced the structural and the sedimentary evolution of the Aquitaine Basin. The same hercynian direction is also followed by the continental edge of northwestern France which formed during the evolution of the Bay of Biscay. The continental edge finds its prolongation in the superdeep Subpyrenean Basin. The system of anticlinal ridges affecting the sedimentary cover is also arranged in this direction. The prominent South Armorican Shear Zone farther north also strikes northwest-southeast, but additionally has a distinct dextral wrenching movement. Like the South Armorican Shear Zone, the anticlinal ridges too are affected by similar shearing movements and are not purely compressional in origin. Even the Parentis Basin is bounded by these transtensional dextral shear zones and can hence be interpreted as an east-west-oriented pull-apart basin. Within the context of the opening of the Bay of Biscay, the Parentis Basin can furthermore be regarded as a failed attempt of the Atlantic to wedge into the continent's interior. The reason for this is the counterclockwise rotational motion of Iberia blocked further rifting.
Since the Cenomanian, the Aquitaine Basin is under the influence of the Pyrenean orogeny with its westnorthwest-eastsoutheast-striking structural grain. The Pyrenean orogen likewise has not merely a compressional origin but also a strong, in this case, sinistral transtensional component. The Pyrenean orogen exerted a very profound influence upon the Aquitaine Basin up to this day, subjecting it not only to more or less north-south-directed compression but also to transtension. The effects were of a penetrative nature — tectonic repercussions of the Pyrenean orogeny can even be seen at the northeastern basin margin in the immediate vicinity of the Massif Central.
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