Article: Chitinozoa of the Silurian–Devonian boundary sections in Podolia, Ukraine
Florentin Paris and Yngve Grahn
The Upper Silurian and Lower Devonian beds along the Dnestr River and its tributaries form one of the sections discussed as a possible international Global Stratigraphic Stratotype and Point (GSSP) for the Silurian-Devonian boundary. On the basis of the co-occurrence of a graptolite (Monograptus uniformis angustidens) and a conodont (Icriodus woschmidti) this boundary was drawn at the base of the Tajna Formation. However, chitinozoans from these strata are typical of Pridoli chitinozoan assemblages, and include the index species, Urnochitina urna, and other taxa, e.g. Calpichitina annulata, Linochitina klonkensis, in the lower part of the Tajna Formation. Early Lochkovian chitinozoans, especially the index species Eisenackitina bohemica and associated taxa, e.g. Margachitina catenaria, Pterochitina megavelata, Calpichitina velata, Cingulochitina ervensis, are present in the upper part of the Tajna Formation. The Silurian-Devonian boundary should therefore be drawn in the middle part of the Tajna formation. Neither late Lochkovian nor early Pragian chitinozoan species have been recorded in the investigated material. The differences noted in the respective ranges of the chitinozoan and graptolite index species in Podolia and Bohemia, suggest that the section containing the Stratotype for the base of the Devonian in Bohemia may be less complete than the sequence exposed in Podolia. The Pridoli and Lochkovian chitinozoan assemblages from Podolia show striking similarities to those from south-east Poland, Bohemia and from some northern Gondwana localities. A new species, Angochitina tsegelnjuki sp. nov., is described.