The Montagne Noire Frasnian (Upper Devonian) Conodont Succession

Abstract

Abstract The Frasnian conodont sequence developed at twelve sections in the Montagne Noire, southwestern France is divisible into thirteen conventional zones, all characterized by abundant and well preserved elements of the Palmatolepis biofacies. This contrasts with the seven-fold subdivision of the standard zonation of the Frasnian. Bases of zones are defined by species of Palmatolepis (in 8 instances), Ancyrodella (in 3), Ancyrognathus (1), and Ozarkodina (1); the zones are provisionally numbered. Resolution is greater than that of the published standard conodont zonation primarily because the Lower asymmetrica Zone, the basal Frasnian zone, was originally defined in the extremely condensed sequences in the Rhenish Slate Mountains, West Germany. In contrast, strata equivalent to the Lower asymmetrica Zone in the Montagne Noire consist of four zones, all of which have been identified in North America. Greater resolution in the superjacent Montagne Noire Frasnian sequence stems from two factors: 1) substantial revision in the definitions and stratigraphic ranges of species of Palmatolepis, resulting from the application of multi element taxonomy and quantification of the platform element; and 2) use of range information from all species that occur in the Palmatolepis biofacies, not restricting the analysis to species of Palmatolepis. Species of other genera such as Ancyrodella and Ancyrognathus show a remarkably consistent stratigraphic position in relation to the ranges of the Palmatolepis species.