Conodonts and ostracodes from the givetian-frasnian shallow-water deposits of the Southern Timan

Conodont and ostracode distribution in the Timan (Middle - Upper Devonian, Upper Givetian - Lower Frasnian), Ust’-Yarega (Upper Devonian, Lower Frasnian) and Yba (Middle? - Upper Devonian, Upper Givetian? - Lower Frasnian) formations of Southern Timan was analyzed. The regional and interregional correlation of the established associations was conducted. The significant changes in conodont and ostracode associations are observed almost at the base of the Ust’-Yarega Formation, and they are associated with a gradual increase in the depth of the paleobasin. The conodonts of Ancyrodella rugosa and Mesotaxis asymmetricus appearing at this level characterize the Ancyrodella rugosa conodont Zone. The ostracodes of the Ust’-Yarega Formation are represented by the assemblage of the Cavellina chvorostanensis - Entomozoe (R.) scabrosa Zone. The significant changes in the conodont associations of the Yba Formation reflect an important sequence of appearance of the index-species: Mesotaxis falsiovalis , Ancyrodella rotundiloba soluta , Ancyrodella rotundiloba rotundiloba . The Ancyrodella soluta conodont Zone provide a reliable correlation of the sections of the Timan-North Urals Region and are essential for resolving the issue of the lower boundary of the Frasnian stage of the Upper Devonian in the East European Platform.