Limitations on the application of the Devonian standard conodont zonation

The most commonly used Lower and Middle Devonian conodont zonations that some times have been presented as standard zonations are evaluated. The author questions whether the Frasnian standard conodont zonation based on a phylogenetic succession of species belonging to the pelagicgenera Mesotaxis, Palmatolepis and Siphonodella can be used for world wide correlation. He fa vours the idea of an in ter national cono dont ref er ence scale based on a syn the sis of well established and documented conodont successions (with figured specimens of first and last occurrences of index-species) from key areas representing a variety of facies. Graphic correlation is likely to be the most objective and precise method to provide such a synthesis represented by the composite standard. Such standards have been allready elaborated for the Frasnian and the Middle Devonian. This point of view does not imply that classical biozonations should be abandoned