Definition of the Frasnian/Famennian Stage boundary

Abstract

The boundary for the Frasnian/Famennian Stage Global Stratotype Section and Point (GSSP) has been ratified by ICS and IUGS and is drawn in a section exposed near the Upper Coumiac Quarry in the southeastern Montagne Noire, France. The position of the boundary was selected by the Subcommission on Devonian Stratigraphy in 1991 to coincide with the lower boundary of the Lower Palmatolepis triangularis Zone in the conodont biostratigraphy. The revised definition of the lower boundary of the zone, proposed herein, excludes the extremely rare occurrences of Palmatolepis triangularis a few centimetres lower, within the uppermost conodont zone. The GSSP also coincides with the boundary between the Crickites holzapfeli Zone and the Phoenixites frechi Zone in the goniatite scale. The position of the GSSP is immediately above a major horizon of extinction within the Devonian and is stratigraphically somewhat lower than formerly used boundary levels for the base of the Famennian.