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Evolutionary history of Early Paleozoic pentamerids, which first appeared in the Late Ordovician and existed until the Early Devonian in the Timan-North Ural Basin is closely related to changes in sedimentation conditions, processes of the reef formation, and considerable rearrangements in marine ecosystems. Several parallel pentamerid communities...
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... greenlandensis Armstrong, ozarkodina waugoolaensis Bischoff (Соколова, 2012). Аэронский возраст отложений толщи определяет присутствие в ней остатков брахиопод P. oblongus широкого географического распространения (Безносова, 2008;Beznosova, 2014). Эта толща в разрезе лолашорского горизонта отвечает максимальному повышению относительного уровня моря. ...
... Считается, что эта ассоциация брахиопод занимала пространство на морском дне выше штормовой волновой базы (Johnson, 2006). В западноуральских разрезах распространение этого вида охватывает нижнюю часть лолашорского горизонта (Опорные…, 1987;Безносова, 2008;Beznosova, 2014). Полученные результаты изучения условий седиментации и развития биоты в лландовери позволяют сделать предположение, что формирование рифогенных толщ на Приполярном и Северном Урале, которое сопровождалось крупной перестройкой экосистем, происходило в лолашорское, а не в филиппъельское время, как это принято считать (Опорные…, 1987; Антошкина, 2003; Безносова, 2008). ...
... Постепенное сокращение биоразнообразия, связанное с началом обмеления бассейна в среднелолашорское время, продолжалось в позднелолашорское и в филиппъельское время. Логично предположить, что сообщества рифолюбивых брахиопод harpidium angustum Kirk (Полярный Урал), Pseudoconchidium kozhimicum Nikiforova и Virgianella vaigatshensis Nikiforova (Приполярный и Северный Урал), которые так же, как и сообщество ровного дна Pentamerus oblongus, принадлежат к БК 3 (Boucot, 1975), существовали в одно и то же лолашорское время в североуральском морском бассейне, и отложения, заключающие эти виды, представляют собой синхронные биофации (Безносова, 2008, с. 137, 167;Beznosova, 2014). Важным доказательством возраста толщ, заключающих эти брахиоподы, является установленный факт залегания слоев с V. vaigatschensis непосредственно на сланцах с граптолитами зоны Demirastrites convolutus среднего лландовери в бассейне р. ...
Research subject. The article presents the results of studying traces of the global Late Aeronian biotic and isotopic (δ ¹³ C carb ) events preserved in a new reference section of the Lower Silurian in the Subpolar Urals.
Materials and methods. The samples of sedimentary rocks and microfauna, the results of isotope analysis, as well as the collections with remains of benthic fauna collected by the authors in different years during fieldwork were investigated. The studies were confirmed by sedimentological, biostratigraphic and chemostratigraphic data obtained by the authors.
Results . The The event-stratigraphic interval, established in the upper part of the Lolashor stage (Aeronian) of the Silurian, is characterized by increasing regressive tendencies, decreasing biodiversity, disappearance of Pranognathus tenuis conodonts and brachiopods of the genus Pentamerus, as well as by δ ¹³ C carb anomalies in the upper strata of the Lolashor stage.
Conclusions . The obtained data indicate a eustatic drop in the sea level, a major ecosystem restructuring, and a sedimentation gap at the end of the Lolashor time. The boundary between the Lolashor and Philippel stages (Aeronian and Telychian) records a sharp negative isotopic shift of δ ¹³ C carb , which was first observed in the Lower Silurian section in the European Northeast of Russia.
... More significantly, available data show that Tcherskidium, the largest ribbed shells among late Katian virgianids, occurred exclusively at or just north of the Late Ordovician equator (Fig. 1) when plotted on recent paleogeographic maps (Torsvik and Cocks, 2013;Popov and Cocks, 2017;Cocks and Torsvik, 2021). The other two key taxa of the fauna, Proconchidium and Holorhynchus, have a similar paleogeographic distribution (see Fig. 1) but have also been found in northern Baltica (Timan-northern Ural region, see Beznosova, 2014), southern Norway (St. Joseph, 1938;Cocks, 1982), southern Sweden, Estonia, and Lithuania (for a summary, see Rong et al., 1989). ...
... Upper Katian, southern Norway. The type species was identified also from coeval strata (Archalyk beds), Zeravshan Range, southern Tyan Shan (Sapelnikov, 1985), and northern Urals (Baltica; see Beznosova, 2014). ...
The Late Ordovician (late Katian) Tcherskidium fauna consisted of large-and thick-shelled virgianid pentamerid brachiopods characterized by large and ribbed shells of Tcherskidium and Proconchidium and usually associated with Holorhynchus, Deloprosopus, and Eoconchidium. This unique fauna was widely distributed across several tectonic plates, largely confined to the paleoequatorial and especially the northern paleotropical zones, such as northern Laurentia, accretionary terranes of Alaska, Kolyma, Baltica, Siberia, Kazakh and adjacent terranes, and South China. In Laurentia, the eponymous genus Tcherskidium was predominant in regions north of the paleoequator and, in sharp contrast, was absent south of the paleoequator. In this study, Tcherskidium lonei n. sp. and Proconchidium schleyi n. sp. are described from Alaska and North Greenland, respectively, adding new data on the Tcherskidium fauna of the Late Ordovician Northern Hemisphere. Shell gigantism, together with the sharp paleobiogeographic division, suggests that the Late Ordovician (late Katian) Northern Hemisphere had a prevailing warm-water mass, probably due to the lack of large landmass beyond the northern tropics. This was in sharp contrast to the Southern Hemisphere, which was frequently influenced by cold-water invasions from the ice-bearing Gondwana supercontinent centered on the South Pole. UUID: http://www.zoobank.org/25d9b772-bd7d-4ad6-bfc6-ba02b1567cf3
... During the latest Katian, the catastrophic environmental change severely affected faunas in both shallow water, for example, the early virgianid pentamerides (large shelled, e.g., Holorhynchus: Rong and Harper, 1988;Hints, 1993;Beznosova, 2011Beznosova, , 2014 among others) the rhynchonellides (e.g., Altaethyrella: Zhan and Cocks, 1998;Hiscobeccus: Jin, 2001), and deep water Foliomena Fauna, usually associated with the Cyclopyge trilobite Fauna (Harper, 1981;Cocks and Rong, 1988;Sheehan, 2001;Zhou et al., 2004;Harper et al., 2013;Zhan et al., 2014;Finnegan et al., 2017 and therein). Fig. 21 shows the global occurrences of warm-water biotas in low latitudes, including the large shelled virgianids which were replaced by a small shelled virgianid counterpart, the genus Brevilamnulella . ...
... Fig. 21. Global occurrences of early virgianid brachiopods (chiefly from Rong and Boucot, 1998;Jin and Copper, 2000;Jin et al., 2006Jin et al., , 2007Beznosova, 2014), associated with the Foliomena Fauna (red hexagon) Villas et al., 2002;Zhan and Jin, 2005;Zhan et al., 2014;Colmenar et al., 2018) in middle-late Katian based on the global reconstruction of Torsvik and Cocks (2017). Blue triangle: Brevilamnulella; yellow circle: Holorhynchus; light purple square: Proconchidium, or Tcherskidium, or Deloprosopus. ...
The temporal and spatial distribution of Hirnantian brachiopod faunas are reviewed based on a new, comprehensive dataset from over 20 palaeoplates and terranes, a revised correlation scheme for Hirnantian strata and numerical methods including network analysis. There were two successive evolutionary faunas: 1. the widespread and diachronous Hirnantia Fauna related to the glacial acme in the early−mid Hirnantian, including shallow, deeper and deep-water communities that diversified in much more complicated environmental conditions than hitherto envisaged; and 2. the Edgewood-Cathay Fauna (new term) thrived during post-glacial, warmer, shallow-water regimes with both carbonate and siliciclastic facies from low latitudes in the late Hirnantian−early Rhuddanian. The two survival faunas can occur in the same order in different regions, immediately following the first and second phases of the Hirnantian crisis, respectively. This faunal succession records two climatic perturbations, one with a glaciation, associated with climatic cooling and a global low-stand, during which the Hirnantia Fauna flourished, and a second characterized by melting ice, global warming, and sea-level rise (with global anoxia), aligned to the development of the Edgewood-Cathay Fauna and the repopulation of the seas by many animals adapted to warmer water, e.g., metazoan reefs, massive tabulates, and sponges. Changes in many properties of the Hirnantia Fauna may have resulted from the heterogeneity of global climate change in time and space; contrasts in the Edgewood-Cathay faunas record differences between carbonate and siliciclastic deposition, respectively, at low latitudes. Intense climate changes, sea-level fluctuations, and oceanographic ventilation and anoxia, had important roles in brachiopod evolution through the Hirnantian extinctions as first taxa confined to warm-water and then cool-water conditions were the main victims. During the Hirnantian, higher originations of new taxa may have been a response to crises, which increased the rate of phyletic evolution due to extreme climatic conditions.
The new results of studying of the geological structure of the Upper Silurian deposits on the Western slope of the Subpolar Urals
are presented. Data analyses and synthesis allow us to establish bio- and event-stratigraphical boundary of the Ludlow-Pridoli and
discover disconformity at the terminal Ludlow. These results suggest revision of the correlation of the Ludlow-Pridoli boundary beds
of the Subpolar Urals and Estonia.
