Stratigraphic significance of Devonian brachiopods of the Urals

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

Geochemical Indicators of the Carbonate Sedimentation Depositional Environments and Geodynamic Conditions in the East of the Middle Urals in the Kizelovian Time

Изучена геохимия известняков кизеловского горизонта Восточно-Уральской зоны (р. Реж, Средний Урал): изотопный состав углерода и кислорода, концентрации малых элементов, значения редокс-индикаторов. Предполагается, что карбонатные отложения формировались в мелководной, богатой кислородом обстановке в условиях высокой биопродуктивности тепловодной экосистемы в пределах изолированной карбонатной платформы при стабильном погружении территории. Ряд признаков свидетельствует о том, что осадконакопление в кизеловское время могло происходить во внутренней лагуне достаточно крупной атолловидной структуры. Современными аналогами Режевской карбонатной платформы могут быть некоторые атоллы Мальдивского архипелага.Geochemical characteristics of the limestones of Kizelovskian substage of the Eastern Urals zone (Rezh River, Middle Urals), such as carbon and oxygen isotopic composition, concentration of minor and trace elements, and redox value indicators, were studied in details. Based on the results of data interpretation and analysis of lithological features, it was assumed that carbonate deposits formed in shallow oxygen-rich environment with high bioproductivity warm water ecosystem, and within the isolated carbonate platform with a steady sinking territory. Some signs indicate that sedimentation during the Kizelovian time occurred in the inner lagoon of a large atoll. The Maldivian archipelago could be a contemporary analogue of the Rezhevskaya carbonate platform

To Comparison of Bulk Chemical Composition of Lower Permian Clay Rocks (Uruzano-Sylvinskaya and Belsk Depression)

В результате анализа литогеохимических особенностей глинистых пород нижней перми Бельской и Юрюзано-Сылвинской впадин Предуральского прогиба установлено отсутствие принципиальных различий между ними, что может свидетельствовать об общем источнике сноса. В целом валовый химический состав глинистых пород нижней перми Предуральского прогиба сопоставим с PAAS по содержаниям SiO2, TiO2, Al2O3, FeOобщ, K2O и P2O5, некоторое отличие наблюдается лишь по MgO, CaO и Na2O. Содержания Cr, Co, Ni и Zn в большинстве образцов аргиллитов Бельской впадины выше, чем Юрюзано-Сылвинской впадины, в то же время для аргиллитов из бассейна р. Уфы характерны несколько более высокие концентрации Sc, Sr, Y, Mo и РЗЭ. Распределение РЗЭ в аргиллитах обеих впадин сопоставимо. Общая обедненность их, относительно PAAS, легкими лантаноидами, а также слабо выраженная положительная Eu аномалия предполагают присутствие в составе пород существенной доли продуктов размыва основных магматических образований.Analysis of the lithogeochemical characteristics of the Lower Permian clay rocks from Belsk and Uruzano-Sylvinskaya depressions of the PreUralian foredeep indicates that there are no principal differences between them, which may indicate the presence of a single source of deposited material. Bulk chemical composition of the Lower Permian clay rocks is comparable to PAAS content of SiO2, TiO2, Al2O3, FeOtot, K2O and P2O5. A difference of composition is observed only in MgO, CaO and Na2O. Content of Cr, Co, Ni, and Zn in most mudstone from Belsk depression is higher than in Uruzano-Sylvinskaya depression. Simultaneously, mudstone from the basin of Ufa River has slightly higher concentrations of Sc, Sr, Y, Mo and REE. Distribution of REE in mudstone of the two basins is comparable. Their general depletion by light lanthanides in comparison with PAAS, and a low positive Eu anomaly suggest the presence a substantial portion of the products of erosion of the basic magmatic complexes in the clay rocks

Devonian palaeogeography of the Southern Urals

Devonian deep-water deposits of the Southern Urals are represented mainly by flysch and cherty units. The main sedimentary basins (marginal sea and back-arc basin) and their origin, evolution and principal depositional environments are characterised. The main sources of clastic material were the Uraltau microcontinent (especially in the Famennian, when a mountain range formed following collision with an island arc) and two island arcs: the Irendyk, at the end of the Early and at the beginning of the Mid Devonian; and the Magnitogorsk, in the Mid to Late Devonian. Comparison with transgressive-regressive cycles established in Devonian epicontinental basins worldwide indicates that these global sea level fluctuations were recorded also in the Southern Urals deep-water settings. This applies primarily to the Eifelian and Frasnian-Famennian transgressive-regressive cycles

Sections in the western slope of the south urals perspective for the choice of the famennian regional boundary stratotype point

The Bol’shaya Barma, Akkyr, Ryauzyak and Kuk-Karauk sections in the western slope of the South Urals are considered to be perspective sections for the identification of Famennian Regional Boundary Stratotype Point (RBSP). In the studied sections the Frasnian-Famennian (F/F) boundary is at the bottom of the Barma Horizon. It is established within a lithologically homogeneous brachiopod coquina by simultaneous emergence of the conodonts Palmatolepis triangularis Sann. and brachiopods Parapugnax markovskii (Yud.). The F/F boundary interval is subdivided into the Upper rhenana, linguiformis, Lower and Middle triangularis zones which are thoroughly characterized by means of conodonts and brachiopods

Ancient karst at the eastern slope of the Middle Urals and the Early-Middle Carboniferous boundary

The paleokarst occurrences associated with Lower Carboniferous limestones in the east of the Middle Urals are considered. We analyse the nature of the Early-Middle Carboniferous boundary. We argue the absence of a long break at the end of the Early Carboniferous in the Middle Urals. Uplifts were in blocks and quickly destroyed. It's most likely that karst is Meso?oic in age. Probably, two types of its manifest related to different mobility of underground waters that filled karst caverns after their formation

Detrital zircons from Lower Triassic sandstones, Belsky depression, Pre-Uralian foredeep: LA-ICP-MS U-Pb isotopic ages and distribution of rare and trace elements

Lower Triassic sandstones in the southern part of Belsky depression (Pre-Uralian foredeep) contain detrital zircons with concordant U-Pb isotopic ages ranging from Neoarchean to the boundary of the Carboniferous and Permian. The distribution of rare and trace elements in zircons suggests that the majority of them fall into the Triassic sandstones due to erosion of basic rocks (or, taking into account the possibility of multiple recycling, most of them are crystallized in the rocks of basic composition). These data indicate a much wider age range of rocks in provenances in the Early Triassic, than it follows from petrographic observations. The micropetrografic data testify that the magmatic complexes which are distributed at present in Sakmara area were the sources of zircons with the Early and Middle Paleozoic datings. Detrital zircons with the Proterozoic and Neoarchean ages are likely redeposited from Riphean-Vendian Ural-Tau zone, where they were brought due to erosion of East European platform base. A small proportion of crystals with Late Paleozoic ages taking into account the geochemical and petrographic data, permits suggest that granite massifs of the Main Granitic axis of the Urals, during the formation of Pre-Uralian molasses has not been involved into erosion. Perhaps they have not yet been withdrawn to the surface, or were placed to the East line of the watershed. At the same time, a significant number of zircons with Precambrian age indicates that the Ural-Tau metamorphic formations were in the erosion zone. Consequently, the orogen watershed at that time was to the east of the zone. This is also evidenced by the presence in the Lower Triassic sandstones few crystals of zircon with Carboniferous age, the source of which could be to the west of modern Magnitogorsk megazone. On the basis of these data we suggest that the forming of coarse clastic formations of the final stage of orogeny in the southern Urals occurred mainly due to erosion of sedimentary, igneous and metamorphic complexes from modern western slope of the axial zone of the Urals

Specific features of carbon and oxygen stable isotopes (δ13C and δ18O) geochemistry in the isolated carbonate platform section on the east of the Urals (the Famennian and Tournaisian Stages)

New data about the stable carbon and oxygen isotopic composition for the Frasnian/Famennian and Devonian/Carboniferous boundary intervals, as well as for middle and upper parts of the Tournasian Stage (the Lower Carboniferous), are represented in this article. Isotopic composition, specific features and depositional conditions which were revealed in the isolated carbonate platform basin are considered

On the finding of brachiopod in metamorphic garnet-bearing rocks on the Middle Urals

The authors provide paleontological and mineralogical description of the finding of the brachiopod of Atrypinae gen. et sp. indet. of the Silurian (Llandovery) – Late Devonian (Frasnian) age in a well-formed garnet-almandine crystal. Field geologist D. L. Suslov was the one who found the brachiopod in high-aluminous gneisses in Verkholovsky garnet mine, which is a part of the Evgenie-Maximilianovsky (Palkinsky) mineral mines located in the southeastern part of the Verkhisetsky granite batholite, on the territory of the historical-landscape park "Istoki Iseti". The Verkholovsky garnet mine is located on the southern slope of Pup Mountain, about 6 km west of Ekaterinburg city, on the eastern slope of the Middle Urals. The stock of the Ural Geological Museum stores the sample containing the brachiopod imprint, its measures are 3 × 2.2 × 1.6 cm and it looks like a parallel aggregate of several garnet-almandine crystals. Main habitus forms of the garnet individuals are rhombododecahedron d{110} and tetragontrioctahedron n{211}, the latter forming thin facets of the rhombododecahedron edges. The shell imprint is not in the garnet crystals, but in the base of the sample, among the fine-grained light-brown mass, whose thickness is not more than 2–3 mm. The fine-grained mass previously probably was a carbonate matrix of the brachiopod, and during the growth of the garnet at the border of two heterogeneous media (carbonate and silicate), a local metasomatic process of substituting the garnet aggregate for the primary (carbonate) substance manifested. The article also contains a brief geological sketch of the place of the finding and an overview of information about other similar findings. Chemical U-Th-Pb-dating allowed to determine the age of monazite inclusions in garnet (344 million years)