Ordovician-Silurian boundary graptolites of the Southern Alps, Austria

Seven species of graptoloid graptolites are described from Hirnantian and lower Rhuddanian formations of the Austrian part of the Carnic and western Karavanke Alps. The Plöcken Formation, of latest Ordovician (Hirnantian) age, yields the biozonal index graptolite Metabolograptus persculptus in the Cellon Reference Section and, tentatively, the Feistritzgraben Section. A distinctive graptolite assemblage indicating an earliest Silurian (early Rhuddanian) age comes from the Waterfall Section near Zollnersee Hütte. Along with the presence of the biozonal index Parakidograptus acuminatus and accompanying taxa, common Rickardsograptus? bifurcus (Ye) has been recorded – for the first time outside China. The absence of Neodiplograptus lanceolatus Štorch & Serpagli, Normalograptus trifilis (Manck) and other easily recognizable lowermost Rhuddanian species which are dominant in this level throughout peri-Gondwanan Europe indicates the peculiar character of the acuminatus Biozone assemblage encountered in the Carnic Alps. •