EUSTATIC TRENDS IN CONODONT DIVERSITY ACROSS THE FRASNIAN-FAMENNIAN BOUNDARY IN THE STRATOTYPE AREA, MONTAGNE NOIRE, SOUTHERN FRANCE

Trends in generic diversity of successive conodont communities are ana lysed in sections of different environmental settings across the Frasn ian-Famennian (F-F) boundary in the stratotype area, Montagne Noire, F rance. The evolution of conodont biofacies and abundances matches the overall pattern already observed in many sections elsewhere in the wor ld and supports the interpretation of an important eustatic sea-level fall during the Upper Kellwasser event. The change from late Frasnian deep-water palmatolepid-polygnathid biofacies to shallower-water polyg nathid-icriodid biofacies during the Upper Kellwasser event occurred i n all sections studied. The shallowing trend culminated at the end of the Kellwasser Event as indicated by the substantial increase of forme rly poorly represented icriodids, whereas palmatolepids concomitantly diminished. This event occurred earlier on oxygenated outer platform s ubmarine rises than in oxygen-depleted depressions. The sudden sea-lev el fall prior to the Frasnian-Famennian boundary was followed, at the beginning of the Famennian, by a deepening trend when palmatolepids do minated again. These changes in conodont generic associations and abun dances occurred rapidly and synchronously. As a result, the stratigrap hic resolution obtained with the evolution of biofacies is higher: it permits not only a more accurate location of the base of the Upper Kel lwasser event in environments where it cannot be distinguished litholo gically, but it also allows the recognition of intrazonal gaps.