Литосфера (Aug 2017)
Stratigraphic significance of Devonian brachiopods of the Urals
Abstract
The article considers the history of the formation of the regional stratigraphic scale of the Devonian system of the Urals, historically developed on the basis of the study of benthic fauna (mainly brachiopods). Currently, it is represented by the following Regiostages and horizons of stratotypic areas (bottom-up): Mansian (Sarainaya and Sauma Horizons), Vitimian (Vizhai and Toshemka Horizons), Yurtishchian (Karpinsk and Tal'tiya Horizons), Loz'vian (Langur and Vysotinka Horizons), Ryauzyakian (Pashiya, Kyn, Sargaevo, Domanik, Mendym and Askyn Horizons), Zilimian (Makarovo, Murzakaevo, Kushelga and Lytva Horizons). Stratotypes of the four lower superhorizons are located on the eastern slope of the Urals, and two upper ones on its western slope. Regiostages are common to both subregions. The comparison focuses on the regional scale of the Urals with the International stratigraphic scale shows that the borders Pragian/Emsian, Emsian/Eifelian, Givetian/Frasnian, Frasnian/Famennian not coincide with the boundaries of the Ural regional horizons. The lower boundaries of the Devonian stages in the Urals are carried out according to the GSSP at the base of the conodont zones Icriodus woschmidti postwoschmidti (Lochkovian Stage), Eognathodus sulcatus sulcatus (Pragian Stage), Polygnathus dehiscens (Emsian Stage), Polygnathus costatus partitus (Eifelian Stage), Polygnathus hemiansatus (Givetian Stage), inside the lower subzone conodont zone Mesotaxis falsiovalis, higher extinction of Skeletognathus norrisi and coincides with the appearance Ancyrodella rotundiloba (Fransnian Stage), the base conodont zone Palmatolepis triangularis (Famennian Stage). The article deals with the stratigraphic distribution of the key genera and species of the Devonian brachiopods by series, stages and horizons. The regional and interregional correlation possibilities of the studying the brachiopod fauna in the Urals are shown. The tables show the stratigraphic distribution of the key genera of brachiopods in the Devonian sediments of the western and eastern slopes of the Urals according to the authors' data with the use of data of I.A. Breivel`, M.G. Breivel`, V.P. Sapel`nikov, A.P. Tyazheva and A.N. Khodalevich monographs. It is concluded that the brachiopods, due to its multiplicity, diversity, relatively rapid evolution in time and widespread in offshore sediments are widely used in the construction of regional stratigraphic scales. The results of the study of the Devonian brachiopods of the Urals, taking into account the distribution of this group of fauna in other regions, make it possible to reliably correlate the sediments at the regional and interregional levels. Some lag in the rate of evolutionary development from conodonts does not reduce the stratigraphic significance of the Devonian brachiopods, allowing detailed subdivision and the global correlation of Devonian deposits.
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