THE UPPER ORDOVICIAN BIOSTRATIGRAPHY OF THE CHUNYA RIVER BASIN (RIGHT TRIBUTARY OF THE PODKAMENNAYA TUNGUSKA RIVER, SIBERIAN PLATFORM)

The article deals with presented results of studying Upper Ordovician sections of the Mangazeya Formation in the Chuya River basin (right tributary of the Podkamennaya Tunguska River) of the Siberian Platform. The given layer by layer section description and new data on leading groups of fauna (ostracods, trilobites, brachiopods, conodonts) allowed for significantly expanding paleontological characteristics of enclosing sediments. The description of the Baksan Horizon deposits is given for the first time, it updates the earlier description of underlying formations in the stratotypic section of the Dolbor Horizon 2 km above the mouth of the Upper Chunku R. (left bank). As a result of biostratigraphic analysis for different groups of fauna, both from published sources and newly obtained data, it has become possible to clarify the stratigraphic position of the section located 0.4 km below the mouth of the Amutkan River. The correlation of studied sections with the Gaindinskaya-3 test well was carried out.