DEFINITION OF THE FRASNIAN FAMENNIAN STAGE BOUNDARY

The boundary for the Frasnian/Famennian Stage Global Stratotype Sectio n 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 Mon tagne Noire, France. The position of the boundary was selected by the Subcommission on Devonian Stratigraphy in 1991 to coincide with the lo wer boundary of the Lower Palmatolepis triangularis Zone in the conodo nt biostratigraphy. The revised definition of the lower boundary of th e zone, proposed herein, excludes the extremely rare occurrences of Pa lmatolepis triangularis a few centimetres lower, within the uppermost conodont zone. The GSSP also coincides with the boundary between the C rickites holzapfeli Zone and the Phoenixites frechi Zone in the goniat ite scale. The position of the GSSP is immediately above a major horiz on of extinction within the Devonian and is stratigraphically somewhat lower than formerly used boundary levels for the base of the Famennia n.