Danièle Grosheny

Stratégies adaptatives des foraminifères benthiques et planctoniques à la limite Cénomanien-turonien dans le bassin du sud-est de la France: Essai de compréhension globale

By studying the planktonic foraminifera distribution, at the Cenomanian-Turonian boundary in theVocontian basin, it appears that some periods are r- and others K-dominated in terms of reproductive strategies. During the crisis, globular forms are better represented than keeled morphotypes. This alternation of two types seems to be mainly connected with life cycles that is to say depth of reproduction. At the same time, benthic foraminifera display a drop in diversity and an opportunist strategy. The sequential analysis shows an enhancement of high-frequency sea level oscillations within the great third order Cenomanian-Turonian transgression. To explain such a phenomenon, we express two hypothesis: high-frequency tectonics and glacio-eustasy. By comparing biological and sedimentological data, we evidence that r- and K-strategies are respectively assigned to the rising limb then the falling limb of a third order stratigraphical cycle.

Reconstruction of outer shelf paleoenvironments in the Turonian–Coniacian of Southeast France (micropaleontology – sedimentology:: local and global controlling factors

Abstract Micropaleontological analysis and sedimentological studies were undertaken on the Turonian to the Coniacian strata of the western part of the Vocontian Basin near Nyons, Southeast France, in order to understand the evolution of paleoenvironments. Microfacies examination shows an alternation of two types of deposits: (1) sediments dominated by abundant sponge spicules, echinoderm fragments and quartz packstones–wackestones, suggesting a shallow water environment, and (2) sediments dominated by abundant calcispheres and planktic foraminifera, providing evidence of a deeper water environment. The biostratigraphy is based on a systematic analysis of planktic foraminifera (about 50 taxa). The first appearance of Dicarinella primitiva , associated with Marginotruncana tarfayaensis and Marginotruncana sinuosa , indicates the beginning of the Coniacian. Ostracoda corroborate the Coniacian age given by planktic foraminifera. Amongst the benthic foraminifera, Nodosariidae, Verneuilinidae and Eggerellidae are the most common families represented by the fauna. The qualitative and quantitative changes of benthic and planktic foraminifera population parameters provide precise information about the paleoenvironmental conditions (paleobathymetry, sediment composition, dissolved oxygen). The biological system reflects high-frequency sea level fluctuations. A possible glacially and/or tectonically induced mechanism is discussed in order to explain this kind of variations.