Le Trias comme période salifère

1. In the Earth history not a system probably comprises so many evaporites than Triassic. They are not restricted to such or such protoocean but cover huge epicontinental cratonic plateforms with very finely bedded deposits as well as they fill rifts located in very diversified geodynamic areas. The first condition in order that such deposits can exist is a severe aridity.
2. Triassic corresponds to an extraordinary transgression in the sense of a new onlap of the sedimentary realm, a reconquest of ancient areas by new deposits, however their facies may be. In that general setting evaporites are themselves remarkably transgressive and from two points of view a) they sometimes onlap directly — that is to say without any basal detritic intercalation — different terms of peneplaned basement, b) these evaporites often succeed Permian emersion or continental detritic deposits of lower parts of Triassic. They extract their salts from Ocean. They often underlie pure marine Jurassic facies. For all these reasons evaporites appear as the first emissaries of oceanic realm and so as the first witnesses of a marine transgression.
3. Evaporites occur in Triassic, particularly in the Middle East, North Africa, on the two present margins of North Atlantic, on Western and Northern Europe, etc. The whole constitutes a huge saline ring round the western part of Triassic Tethysian sea. In that area, on the less tectonized plateforms a grandiose facies distribution pattern appears clearly: going farther from open sea in a centrifugal way, there are salts more and more soluble, until detritic deposits from continent. The pellicular sheets of water which covered the large plateforms resulting from late permian peneplanation should be favourable to modification of chemism, very gradual and at last very total, producing a geographical distribution of salt deposits. The most probable mover of these “floods” could be a very likely multiphase rise of eustatic level, the effects of which we cannot imagine because they occured on plateforms unknown in the geography of recent world. Effects of local morphology which induced a pecular distribution of salts can modify the general plateform distribution pattern.