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L'analyse approfondie des associations de Foraminiferes depuis les termes du passage Bedoulien-Gargasien jusqu'au Gargasien moyen a ete realisee dans le secteur de Cassis-La Bedoule (SE France), stratotype historique du Bedoulien (Aptien inferieur), particulierement favorable a ce niveau en raison de la continuite et de la dilatation de la serie ainsi que de la diversification de la microfaune. L'eventail des formes benthiques se revele assez stable mais quelques especes (Praedorothia praeoxycona, Lenticulina cf. nodosa, Astacolus crepidularis, Globorotalites bartensteini) s'eteignent a la fin du Bedoulien et peuvent etre utilisees pour differencier ce sous-etage par rapport au Gargasien. L'aire stratotypique offre aussi la possibilite de suivre pas a pas l'evolution des formes planctoniques a un moment crucial de leur histoire, lorsque les processus de speciation et les liens phylogenetiques s'averent particulierement complexes. La grande variabilite morphologique des formes planctoniques durant l'Aptien ne facilite pas le choix de marqueurs stratigraphiques stables; il est cependant possible de proposer une biozonation comportant cinq zones (a Cabri, Luterbacheri, Ferreolensis, Barri, Algerianus) pour l'intervalle considere, habituellement subdivise en trois zones. L'etude populationnelle, et non pas seulement typologique, des associations nous a enfin permis d'apporter quelques precisions taxinomiques nouvelles, en particulier sur certaines formes planctoniques d'acception controversee ou meme de validite douteuse. ––– The Gargasian (Middle Aptian) strata from Cassis-La Bedoule (Lower Aptian historical stratotype, SE France): planktonic and benthic foraminiferal assemblages and biostratigraphy.- This paper presents a thorough analysis of foraminiferal assemblages ranging in age from the Bedoulian-Gargasian transition to the middle Gargasian in the Cassis-La Bedoule area (SE France), the historical stratotype of the Lower Aptian substage. This region is particularly suitable for detailed studies of Aptian foraminifera owing to rapid and continuous sediment depositional rates and well-diversified microfaunas. The ranges of benthic forms appear to be fairly stable but some species (Praedorothia praeoxycona, Lenticulina cf. nodosa, Astacolus crepidularis, Globorotalites bartensteini) become extinct at the end of the Bedoulian and thus can be used to separate this substage from the Gargasian. The stratotypic area also offers an opportunity to follow the evolution of planktonic forms step by step at a crucial period of their history, when modalities of speciation and phylogenetic relationships appear to be particularly complex. The important morphologic variability of Aptian planktonic foraminifera does not help finding stable stratigraphic markers; nevertheless, we are able to propose a biozonation comprising five zones (Cabri, Luterbacheri, Ferreolensis, Barri, Algerianus) for the interval under consideration, usually subdivided into three zones. Our study of foraminiferal assemblages and species took into account the range of variability among populations and not just the characteristics of a single specimen, such as the holotype. As a result this paper provides new taxonomic precisions on certain planktonic species hitherto controversial or possibly of doubtful validity.

carnets de géologie/carnets de géologie

Le Gargasien (Aptien moyen) de Cassis-La Bédoule (stratotype historique de l'Aptien inférieur, SE France) : associations et biostratigraphie des Foraminifères benthiques et planctoniques