A Pridoli (late Silurian) Standard Conodont Zonation

In the last few years the Přídolí, the fourth series of the Silurian System, have been largely investigated by researchers, and a refined conodont zonation is necessary for a detailed correlation worldwide and is critical for a possible subdivision of the Series. However, due to provincialism and limited occurrence of some species in a few areas, we make zonation at “two levels”. One scheme is made by zones based on taxa with a global distribution, integrated in selected intervals by more subdivisions. The base of the Přídolí is defined by the FAD of the graptolite Skalograptus parultimus. Among conodonts, for long lime this level was considered to be linked to the top of the Jeppsonia crispa Zone (= LAD J. crispa), until it was demonstrated that the species is present above the entry of Sk. parultimus. The conodont taxon whose entries best approximate the base of the Přídolí is Zieglerodina zellmeri, which FAD occurs in the uppermost part of the J. crispa Zone. As the latter species is a perfect index taxon and the crispa Zone was inserted in all Silurian conodont zonations as a taxon range Zone, we maintain it in the same definition. The extinction of J. crispa marks the base of the next Zone, which is presently named “Oz.” eosteinhornensis s.l. interval Zone. In the upper part of this zone an interval characterized by the entry of Z. ivochlupachi can be discriminated in some regions. The next global marker is the FAD of Oulodus elegans detortus, that also approximate the FAD of the graptolite Wolynograptus bouceki, the candidate marker for the formal subdivision of the Přídolí series into two stages. The eponymous Oulodus elegans detortus Zone of present schemes can be further subdivided. Within the zone the well-known “Oz.” eosteinhornensis s.s. horizon occurs: at this level Z. planilingua has its FAD. This species is widely documented worldwide, even if not everywhere, but the level of its entry can be approximated by the presence of “Oz.” eosteinhornensis s.s. The Z. planilingua zone ranges up to the Silurian/Devonian boundary, but at places, further subdivisions may be applied by the entries of Z. klonkensis (Prague Synform and other Perigondwana areas), or Belodella coarctata (North America).