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Based on comprehensive investigations of Dupouy-Camet and extensive oil geological exploration, including geophysics and deep drilling, by the Société Nationale des Pétroles d’ Aquitaine (SNPA), the author describes the main occurrences of diapiric and semidiapiric structure in the Aquitanian Basin of southern France. Included are remarks on the stratigraphy and geological history of Aquitania and a brief discussion of the structural complexities in the north Pyrenean foothills and the Aquitanian “Basin.”

The stratigraphy is summed up by means of six columnar sections. A structural sketch map of west Aquitania and the northern Pyrenees illustrates the paleogeographic relationship between the Upper Cretaceous miogeosynclinal shelf of the Pyrenean foreland, the adjacent eugeosynclinal trough marked by a mainly Senonian flysch association, and the axial zone of the Pyrenees characterized by Paleozoic formations and igneous rocks. The last is separated from the eugeosynclinal part by an important thrust fault along the north Pyrenean front.

Partly owing to the Pyrenean orogeny, but partly owing to earlier diapiric ascent, the evaporites of the Keuper have developed into numerous diapiric and semidiapiric accidents varying in pattern from sheet diapirism along major fault planes to full-fledged circular salt domes obviously displaying similar genetic conditions as the well-known salt domes of the United States Gulf Coast.

Emphasis is placed on the genetic-interpretational aspect of the Aquitanian diapirism and its close association with the various orogenic phases of the area under review. The fundamental problem is whether we are concerned with a phenomenon of buoyancy or if purely orogenic forces account for the accidents observed. In other words, was buoyancy an active tectonic force, or are the intrusions and effusions of evaporites into anticlinal cores and fault planes a result of structural emplacement?

There is sound evidence that some diapiric accidents occurred as early as Middle Cretaceous, independent from and definitely preceding the earliest orogenic phase of folding. On the other hand, there is little doubt that the evaporites of the Keuper furnished a gliding horizon that greatly facilitated disharmonic folding, thrusting, and detachment from the substratum in the course of the Pyrenean orogeny.

The author concludes that at an early date, buoyancy was an important active force indeed; later the results of orogenic deformation were superimposed onto the early diapiric structure; the combined effect, as presently in evidence, tends to obliterate the early diapirism.

An attempt is made to clarify the role of gravitational, tensional, and synsedimentary tectonics as opposed to orogenic-compressive folding. Such gravitational tectonics probably are particularly active and important in areas of diapirism, but may occur anywhere in the sedimentary, i.e. preorogenic, stage. They have often been mistaken as precursory orogenic phases which they are not, but might subsequently be reactivated by genuine orogenic forces.

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