The Devonian/Carboniferous boundary stratotype section (La Serre, France) revisited

Based on new conodont data, the Devonian/Carboniferous boundary GSSP at La Serre requires re-positioning. The La Serre E section (Montagne Noire, France) has been selected as global D/C boundary stratotype, because it was assumed to be the only section that shows the evolutionary lineage from Siphonodella praesulcata to S. sulcata. However, this section cannot be regarded as an ideal stratotype, because the boundary was fixed within an oolitic sequence, and conodonts and other fossils are reworked. New data show that the first occurrence of the index fossil S. sulcata is much earlier than previously reported, which indicates that the base of the Carboniferous has to be fixed at an older stratigraphical level. Also, the co-occurrence of S. praesulcata and S. sulcata above a facies break shows that the evolutionary lineage from S. praesulcata to S. sulcata, which was previously claimed for the definition of the D/C boundary, is obviously absent at La Serre. Consequently, the GSSP position either needs to be re-located at La Serre, or a new stratotype section must be designated.