Résumé
Data on conodont biodiversity are obtained from detailed sampling across the D/C boundary beds in the pelagic limestone sequence at Puech de la Suque and are compared with those available from equivalent sections elsewhere. Five succeeding biofacies can be recognized: bispathodid, bispathodid-palmatolepid, polygnathid-protognathodid, polygnathid-siphonodellid and siphonodellid. The world-wide change from deep-water to shallow-water biofacies, related to the Hangenberg Event, is most spectacular in this section. The timing and dynamics of this Event are recognized by comparison with the D/C stratotype section at La Serre. The deposition of the Hangenberg black shale is considered to coincide with the culmination of the fore-going rise in sea-level which can be demonstrated by the increase of Palmatolepis just before the shale level. The succeeding drop of the sea-level starts well before the Late praesulcata Zone. The Early Tournaisian deepening trend commences within the Upper praesulcata Zone and culminates as early as the top of the Late duplicata Zone where a nearly pure siphonodellid biofacies is developed.