Depositional conditions of Messinian diatomites in carbonate platform setting from diatom assemblages (Djebel Murdjadjo, Algeria)

Diatomitic accumulations occur in the outer part of the Messinian carbonate platform of Oran vicinity. The diatom assemblages reveal the environmental evolution during the platform edification with two different diatomitic ep isodes. The first one contains diatom assemblage of tropical open sea and m arks the distal talus of prograding bioclastic and reefal units. The second diatomitic episode, following the prograding coral reef complex, represent s for numerous authors the equivalent of the base of the so-called salinity crisis. The diatom assemblage reveals a littoral marine environment, with variable salinity, in relatively stagnant warm water. This evolution is con sequent with the hypotesis of a general infilling of accomodation during th e carbonate platform development which lead to a restrictive marine circula tion conditions.