Abstract

The Middle Jurassic brachiopods from the Vivarais-Cevennes (western margin of the French South-East Basin) have been palaeontologically studied on the basis of carefully levelled material collected in numerous profiles and well situated within the Ammonite zones succession. The vertical distribution of the species has been precised. The deduced biostratigraphy confirms and improves our knowledges about the brachiopod zonation of the French Middle Jurassic. The range of the Middle Bathonian brachiopod zones has been checked and modified in order to take in account the chart newly proposed for the ammonites (including the Bremeri Zone), and of its implications for the regional biostratigraphy. The interval zone, previously correlated only with the Progracilis Zone, must be extended upward into the Subcontractus and Morrisi Zones. The Antiptychina bivallata brachiopod Zone must be correlated with the Bremeri ammonite Zone. At last, the fluctuations of the brachiopod communities are positioned within the geodynamic evolution of the Vivarais-Cevennes margin during an episode of strong tectonic decoupling between subsiding and deepening subbasins (ombilics) and more stable shoals.

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