Stratigraphie, nannofossiles calcaires et foraminifères de la coupe du Ruisseau de Lespontes à Saint-Lon-Les-Mines (Eocène moyen et supérieur d'Aquitaine, France)
Detailed analysis of a series of outcrop sections along the Lespontes River and its tributaries at Saint-Lon-Les-Mines has led to the identification of three predominantly marly units within the Middle and Upper Eocene of the Bassecq Syncline. The lowermost unit consists of bathyal marls, attributable to the Miretrain Marl Formation, and is of Late Lutetian - Early Bartonian age (NP 15b, NP 15c, NP 16 and base NP 17 ; EPA 9 to EPA 11 (? EPA12) and middle P 11 to top P 12). It is overlain by circalittoral, glauconitic indurate marls unknown up to now. This marly, intensely fractured unit, called the Bagats Marl Member, is defined to represent a new member within the Cote des Basques Marl Formation. It encompasses the Bartonian/Priabonian boundary sensu Berggren et al., 1995 (top NP 17 and base NP 18 ; EPA 13 and middle P 14). The uppermost unit is made up of fine sandy marls, containing several limestone intercalations towards the top. These Brihande Marls are included in the lower part of the Priabonian (NP 18, prohably up to the top of the section; EPA 13, EPA 14 and part of EPA 15, top P 14 and in part PIS). The succession of the Lespontes River is interpreted in terms of sequence stratigraphy, allowing refining its relationship within the Adour Basin. The integration of the data indicates that in Aquitaine the appearance of Chiasmolithus oamaruensis (base of zone NP 18) is prior to the appearance of Globigerinatheka semiinvoluta (base of zone PIS) and that nannofossil interval NP 19 - NP 20 is very difficult to identify in this area, due to the scarcity of the marker species lsthmolithus recurvus
