Coral- and oyster-microbialite patch reefs in the aftermath of the Triassic–Jurassic biotic crisis (Sinemurian, Southeast France)

Abstract

The end of the Triassic and the Early Jurassic are intervals characterised by profound biotic and environmental changes, accompanied by dramatic decreases in marine fauna diversity. Corals were strongly affected and assemblages underwent a severe reduction; compared with those of the Upper Triassic, the Early Jurassic is traditionally defined as holding a “reef gap”. A Sinemurian coral-microbialites patch reef, located in southern France in the Hérault department (Le Perthus locality), is here described. This bioconstruction developed in a shallow mixed siliciclastic-carbonate inner ramp setting. The reef volume is composed of up to 70% of an intercoral facies mostly microbialites, with subordinated sediments (approximately 20–30% of the intercoral facies). Therefore, the patch reef can be defined as a coral-microbialite bioconstruction, in which microbialites were the main framebuilders. The coral assemblage has low diversity and is dominated by massive to branching colonies of Chondrocoenia clavellata. This highlights the reef diversity after the T/J boundary crisis. The Le Perthus patch reef could have acted as an edge for the dominant currents and probably induced reductions in hydrodynamic energy and sedimentation on one of its sides. Consequently, it could have triggered the growth of small lateral bioconstructions, composed of oysters and microbialites, uniquely on one of its sides. The evolution of the facies shows that the Le Perthus patch reef grew in a shallowing-upward setting accompanied by an increase in siliciclastic inputs. The rate of bioerosion and the faunal assemblage suggest that the bioconstructions could have been developed in a mesotrophic environment.