LES EvtNEMENfS BIOSTRATIGRAPHIQUES DE LA ZONE PREPYRENEENNE D'ARAGON (ESPAGNE), DE L'EOCENE MOYEN A L'OLIGOCENE INFERIEUR BIOSTRATIGRAPHIC EVENTS FROM THE MIDDLE EOCENE TO THE LOWER OLIGOCENE IN THE PREPYRENEAN ZONE OF ARAGON (SPAIN)

The micropaleontological study (Planktonic Foraminifera, Larger Foraminifera, Calcareous Nannoplancton, Charophyta) has allowed the setting of a detailled bio and chronostratigraphic frame, since the Middle Eocene to the Lower Oligocene, for an important sector of the Pyrenean chain. A set of events during this interval has been pointed out : - The extinction of the Plankonic Foraminifera: M. senni. G. frontosa. G. possagnoensis. G. inaequispira. and G. higginsi at the top of the M. Lehnen zone (P 12). Those extinctions, which constitute the most important event during the Middle Eocene, lead the authors to propose to displace the Lutetian/Bartonian boundary, generally situated in the upper part of the zone P 12, to its top. - The extinction of the typical Middle Eocene spiny Planktonic Foraminifera at the Bartonian/Priabonian boundary that appears as a further relevant event. - The turn over of several species of Nummulites in the lower part of the N. fabianii zone (Lower Priabonian), that has allowed the proposition of a more suitable zonation for that type of facies located in such a latitude. - The discovery of two assemblages of Charophyta, respectively of Upper Priabonian and Lower Stampian age. The presence of those organisms contributes to precise the moment of the passage from the marine sedimentation to the continental one. Morover, they contribute to identify the Eocene/Oligocene boundary inside the overlying continental sediments. In conclusion, the paleogeographical evolution of the region is redrawn in its chronostratigraphical frame. Mots-cles : Foraminiferes planctoniques - Foraminiferes benthiques - Nannoplancton calcaire - Charophytes - Eocene - Oligocene - Espagne - Paleogeographie - Chronostratigraphie.