The gorges of Oppedette

Before the Alps, a reef sea in Barrémien

A link in the history of the Alps…. 

In the Lower Cretaceous, the Alpine Ocean continued to expand between Europe in the north and Africa (and its dependencies) in the south.

The south-east of France is still under the sea. Its deepest part, called the Vocontian basin, is bordered to the south and west by shallow platforms. Towards the east, the sea opens onto the ocean basin.

In the Barremian (-125 million years old), the Oppedette site belongs to the southern platform. The tropical sea has encouraged the development of a reef environment, a veritable reservoir of biodiversity.

The thick layer of rock in which the spectacular gorges of Oppedette are cut corresponds to a particular facies called Urgonien, from the name of the town of Orgon in the Vaucluse. It is a so-called "constructed" limestone, it was built by organizations. In the Urgonian, these constructing organisms are bivalve molluscs, rudists. They are not corals like most reefs.

The rudists have a very thick shell, they have two very different valves. One of them, usually the largest, often conical or "tube" shaped, is attached to the bottom. The other, smaller, acts as an operculum. These marine animals, living in colonies, have built enormous limestone buildings.

They totally disappeared at the end of the secondary era, 66 million years ago, due to the same cataclysmic event that saw the end of ammonites and dinosaurs.

… In connection with 22 other geosites

Further east, the rocks of the Lac de Castillon site are contemporary with those of the Oppedette gorges (Barrémien, -125 million years old). However, the latter are very different, much less massive. They show an alternation of fine layers of limestone and marl which have formed in a deeper environment and without harshness. On the other hand, there are ammonites there.

The limestones of the Verdon gorges are also constructed limestones. In the late Jurassic (-145 to -50 million years ago), at the level of the shoals of the platform, the clear and shallow tropical waters favored the development of coral reefs this time.

What we can decipher from the current landscape

The entire landscape of the Luberon and Oppedette is structured by Urgonian limestones forming large massifs typical of karsts. Very dry on the surface, they favor the establishment of xerophilic vegetation adapted to arid environments. On the other hand, they shelter in depth important sources which circulate in the underground networks.

 A little anecdote?

Did you find any rudist fossils on the site? Impossible ! Indeed, their calcite shell has disappeared by dissolution. On the other hand, you can admire it at the Orgon municipal museum.