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Abstract

The present thesis documents and revises the systematics and biostratigraphy of the Perisphinctoidea (Ammonoidea) faunas across the Tithonian/Berriasian boundary from three basinal sections (i.e. Charens, Le Chouet and Les Combes) of eastern Drôme (South East France). Emphasis is laid on the specific diagnosis, ontogeny and dimorphism of new and little-studied Himalayitidae Micracanthoceras, Protacanthodiscus, Boughdiriella, Pratumidiscus, Ardesciella, Chapericeras and Praedalmasiceras, Neocomitidae Pseudargentiniceras, Busnardoiceras, Berriasella, Elenaella, Delphinella, Pseudoneocomites and Strambergella as well as the Olcostephanidae Proniceras. New data is provided on the systematic and age of the Neocomitidae Pseudosubplanites, Hegaratella and Retowskiceras. The distribution of these key biochronological genera is plotted next to accurate litho-logs and compared to the calpionellid zonation documented in the three sections. This provides the sound basis for a refined zonal scheme. The base of the upper Tithonian is fixed at the First Appearance Datum (FAD) of M. microcanthum that falls within the upper part of the tintinnid Chitinoidella Zone. The revision of the “Mediterranean Durangites” supports the rejection of a Durangites spp. Zone as part of the standard zonation for the upper Tithonian, and its replacement by the P. andreaei Zone. The lower boundary of the zone is fixed at the FAD of Protacanthodiscus andreaei that falls within the lower part of the calpionellid C. intermedia Subzone of the Crassicollaria Zone. Both zones are workable at the scale of the Mediterran-Caucasian Subrealm. The Elenaella cularense biohorizon that typifies the base of the Berriasella jacobi Zone auctorum is documented for the first time in South East France and occurs in the uppermost part of the calpionellid C. intermedia Subzone of the Crassicollaria Zone. This occurrence confirms the diachronism between the base of the B. jacobi Zone auctorum and those of the Calpionella Zone previously documented in southern Spain. This diachronism strongly alters the current definition of the Tithonian/Berriasian boundary. Re-examination of the type specimens of Berriasella jacobi supplemented by newly collected material show that this taxon should be transferred to the genus Strambergella. Preliminary integrated data on the stratigraphic distribution of Strambergella jacobi questions its value as an index species for the base of the Berriasian. No major faunal turnover is documented across the Tithonian/Berriasian boundary and the provincialism of Mediterran-Caucasian Perisphinctoidea is much higher than it was previously assumed in the literature. As a result, no ammonite species can be considered as consistent candidate for a primary boundary marker for the base of the Berriasian.