The stratigraphy of the Devonian sediments in the north-eastern part of the Altai

The Devonian section of the north-eastern part of the Altai Mountains is characterized by alternating marine and continental sediments with sea fauna and the remains of plants, which make it possible to safely justify the age of its constituent formations. The majority of the researchers believe that volcanism is most evident in the Emsian. On the basis of the signs of volcanism in the Kondratiev suite, we concede that the first Devonian volcano appeared at the end of the Praghian time. Volcanism was not synchronous in different structures. It stopped in the north-eastern parts of the Altai in the second half of the Givetian time. The Devonian section of the northeastern part of the Altai deposits is represented by the Lochkovian, Praghian, Emsian, Eifelian, Givetian, Frasnian and top Famennian stages. They formed on the continent, or near it, and were the formations of the clastic-carbonate and volcanic shelf. The petrochemical characteristics of volcanic rocks reconstructed collision situations in the Lower Devonian of the western and central Altai, the Lower Devonian back rift in the eastern Altai. The sedimentary clastic-carbonate shelf is characterized by large rhythmic lenticular-striped and periodically observed cross beddings; mainly polymictic, sub-arkosic, arkosic and quartz composition of clastic rocks; alternating marine and continental conditions for the formation of sedimentary and volcanic rocks; conglomerates and grits at the base of major transgressive cycles occasionally observed in the Devonian section. Their formation is associated with the increasing erosion of the Siberian continent with periodical advances of the sea. The Kuyagan-Baragash group of grabens and Sarasinsk graben are characterized by the prevailing sea elements with rich complexes of tabulate and rugose corals, trilobites and brachiopods. The Remnevskaya, Yakushenskaya, Kireevskaya, Kuvashskaya, Mukur-Tcherginskaya, Matveeskaya, Kondratiev, Bolshetikhinskaya, and Medvedevskaya suites allocated in the Devonian sediments of the Kuyagan-Baragash group of grabens should enter the regional stratigraphic diagram of the Gorny Altai as mappable and palaeontologically described stratigraphic units. The partition scheme of the Devonian sediments of the Sarasinsk graben is sufficiently substantiated (upward): the Komarskaya, Basarginskaya, Terentevskaya, Rudnikovskaya suites. These suites should also enter the regional stratigraphic scheme. In the Ongudaysky graben, in the Uymenskiy and Lebedskiy depressions, in the Karakokshinskaya group of grabens continental deposits are dominant. The Emsian tabulate and rugose corals and brachiopods are regular for the Pyzhinoozernaya suite, while the Kuboyskaya suite has the Lower Devonian plants. Karakudyurskaya, Ongudayskaya, Kuratinskaya, Nyrninskaya, Saganskaya and Ulusukskaya suites contain plant remains. A rich set of brachiopods, bryozoans, rugose and tabulate corals of the Upper Givetian time (the Mazalovo-Kitat horizon) is found in the Tayozenskaya suite. The Late Givetian brachiopods of the Mazalovo-Kitat horizon are found in the Tuektinskaya and Bichiktubomskaya suites. The Boguchinskaya suite contains Late Givetian - Lower Frasnian brachiopods. Within the Lebedskiy depression there is a break at the base of the Baygolskaya suite of the Frasnian age. We made a stratigraphic correlation of the Devonian deposits of the Kuyagan-Baragash group of grabens and the Sarasinsk graben with the sections of the Ongudaysky graben, the Uymenskiy and Lebedskiy depressions, and the Karakokshinskaya group of grabens.

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