Ordovician marine sediments of Tyva, Altai-Sayan folded area: biostratigraphy, facies, composition and specific features of fauna assemblages and paleogeographic locality
We present new lithological and biostratigraphic data on stratotype and paleontologically representative marine sedimentary sections of the Malinovka Group (Borlug, Tarlyk and Tamzyrin formations) in the Uyuk area of the region, Shemush-Dag Group (Ayangaty and Adyr-Tash formations) and Chergaky Group (Alavelyk Formation) in the Khemchik area of the region, Chergaky Group (Alavelyk Formation) in the Alash area of the region, Kargy Formation in the Kargy area of the region. The materials on the Sistig-Khem Group (Uza, Ust-Khamsary and Kugar formations) in the Sistig-Khem area of Tyva are considered. We specified the chronostratigraphic position of the Tarlag-Aksy Horizon and justified the identification of a new Borlug Horizon. We found out that the Tyva Ordovician marine sediments are currently located in individual tectonically isolated blocks and are not fragments of a single paleobasin. Based on the analysis of the taxonomic composition of fauna assemblages and trace fossils, we suggest that the Alash-Khemchik, Uyuk and Kargy blocks with outcrops of Ordovician marine sediments of Tyva are paleozoogeographically close to the marine paleobasins of the Gondwana group of continents. At the same time, we note a low migration potential of their fauna assemblages relatively to the possibilities of communication with coeval communities of the Altai Basin and of that of the Siberian Platform and Taimyr. The Sistig-Khem block of Tyva, having effusive-sedimentary sequences of marine genesis, was not only significantly distant from the listed Siberian paleobasins, but was also separated from the group of Alash-Khemchik, Uyuk and Kargy blocks with Ordovician marine sediments.
