Examination of a section which cuts into the Dreuilhe anticline in the southern Aquitaine basin (Plantaurel) reveals a similarity between the deposits there and those in the northern part of the basin. In the core of the anticline the Maestrichtian lower red marls contain clays and red sandstone with montmorillonite and kaolinite, suggesting deposition in a vast depression lacking sufficient drainage, and in a medium rich in Ca (super ++) and Mg (super ++) . The upper red marls in the hard band of Montian lacustrine limestone with Microcodium have an analogous composition and correspond to calm tectonic and climatic conditions. Lacustrine marls with attapulgite directly underlie the transgressive Thanetian marine deposits. The passage from the Thanetian to the Sparnacian is marked by lacustrine facies, predominantly montmorillonite, and an increasing abundance of illites. The dominance of montmorillonite in a tectonically unstable area suggests that the adjacent continental mass was of low relief and was characterized by a tropical climate with alternating dry and humid seasons. The increase in kaolinite accompanying the arrival of the coarse detritus of the Ypresian is interpreted as the result of rhexistasy. The Lutetian is characterized by sandstones and limestones with associated montmorillonite, illite, and kaolinite. This phase represents the return of the sea, and the detrital nature of the deposits is a result of the uplift of the Pyrenean massifs. These phenomena are analogous to those that have been reported previously from the Paleocene series of Bordelais (northern part of the basin) suggesting a similar paleogeographic evolution for the two areas.

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