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Schematic map showing locations of the Upper Ordovician sections in the Omulev Mountains, Northeast Russia. 1, Mirny Creek; 2, Ina River; 3, Kharkindzha Mountain; 4, Khekandya River; 5, Yasachnaya River; 6, Lukavy Creek.
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A complete Hirnantian sequence comprising the Normalograptus extraordinarius and N. persculptus biozones is well developed at the Mirny Creek section in the Omulev Mountains. The underlying beds are assigned to the Appendispinograptus supernus Biozone, and in the overlying strata the lower boundary of the Silurian is precisely defined at the base o...
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... A worldwide review shows that within the upper stage of the Upper Ordovician Series only a small number of stratigraphically continuous sections have been documented in South Scotland, China, and Kazakhstan, that have good graptolite and benthic faunal control at both the base and top of the stage. The Omulev Mountains in Northeast Russia ( Fig. 1) are another region with a complete and richly fossiliferous succession of Upper Ordovician shelf deposits, which has been the subject of much study (Oradovskaya & Sobolevskaya 1979;Oradovskaya 1988). The Omulev Mountains are located to the west of the Kolyma River and in the central part of the Chersky Mountain Range (Fig. 1). The ...
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... in Northeast Russia ( Fig. 1) are another region with a complete and richly fossiliferous succession of Upper Ordovician shelf deposits, which has been the subject of much study (Oradovskaya & Sobolevskaya 1979;Oradovskaya 1988). The Omulev Mountains are located to the west of the Kolyma River and in the central part of the Chersky Mountain Range (Fig. 1). The best section in the region for studying the detailed biostratigraphy of the Upper Ordo- vician and Lower Silurian deposits, based on graptolites, brachiopods, and corals, is exposed along Mirny Creek, a tributary of the Ina River. Mirny Creek has a narrow valley and cuts the eastern slope of the Omulev Mountains nearly across the ...
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... corals, and other benthic fauna (member 67, sample 107-1/2 ). This level shows a distinctive regressive episode and one can suggest that it correlates with the base of the Hirnantian in other regions, for example in South Kazakhstan ( Appolonov et al. 1988). As no graptolites were found in limestone beds (as it is shown by mistake in Koren′ 1983, p. 13, fig. 62), the lower boundary of the N. extraordinarius Biozone is defined by the first appearance of the index-species at the base of member 68 (Fig. 2, sample ...
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... with the base of the Hirnantian in other regions, for example in South Kazakhstan ( Appolonov et al. 1988). As no graptolites were found in limestone beds (as it is shown by mistake in Koren′ 1983, p. 13, fig. 62), the lower boundary of the N. extraordinarius Biozone is defined by the first appearance of the index-species at the base of member 68 (Fig. 2, sample ...
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... brachiopod biozones have been established in the Tirekhtyakh Regional Stage: Tcherskidium unicum (units M, upper part, N, O, P), and Eoplectodonta nesnakomkaensis and ?Hirnantia (unit Q; Oradovskaya 1988). In the Mirny Creek section (Fig. 2) Eostropheo- donta hirnantensis lucavica and rare cheirurid trilobites occur in the lower part of unit P (samples 108-1/1, 2). Brachiopods assigned to Thebesia admiranda are found together with N. extraordinarius (sample 107-1/2). ...
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... (Dalman), Girardella aff. bella (Bergström), Bipartites paucirugosus Amsden, Thebesia admiranda (Oradovskaya), Eospirigerina putilla prisca Oradovskaya, E. gaspeensis (Cooper) ( ). Among trilobites, Bumastus commodus Apollonov and some species of the genera Stenoporeia and Dicranogmus occur. Dalmanitina olini Temple appears first in member 71 (Fig. 2, samples 107-5/6, ...
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Profound environmental and biodiversity changes take place in the Ordovician-Silurian boundary interval. The Mirny Creek and Neznakomka River bank sections discussed in this paper expose the upper Katian-lower Rhuddanian part of the boundary beds. The succession consists of carbonate rocks, partly with bioherms, alternating with argillaceous and si...
Citations
... Other studies have argued that the HICE was caused by enhanced burial of organic carbon driven by the expansion of marine anoxia, as supported by redox proxy data for the Hirnantian (Zhang et al., 2009;Shen et al., 2018;Zhang et al., 2022). It should be noted that deep-water environments were persistently anoxic ; (B) δ 13 C carb and δ 13 C org profiles of selected sections from South China this study), Laurentia (Ahm et al., 2017;Kozik et al., 2022); Baltica (Hammarlund et al., 2012;Kozik et al., 2022) and Siberia (Koren' and Sobolevskaya, 2008). Obliquity cycles were modified after Zhong et al. (2019). ...
The Hirnantian Stage of the Late Ordovician coincides with a positive carbon isotope excursion (HICE, ~+6‰), a major glaciation, increased volcanic activity, expanded marine anoxia, and one of the largest mass extinctions of the Phanerozoic. The origin of the HICE is debated, with proposed mechanisms favoring enhanced low-latitude carbonate weathering and/or increased efficiency of organic carbon burial. To test those hypotheses, we assembled new and published δ13Ccarb and δ13Corg data and shale phosphorus and carbonate-associated phosphate concentrations from diverse depositional settings on several continents. We then evaluated these results using an integrated carbon cycle model derived from GEOCARB, and a coupled oceanic carbon and phosphorus cycle model. This approach yielded quantitative tests of the response of the global carbon cycle to changes in volcanic degassing, silicate and carbonate weathering rates, and organic carbon burial, individually and in combination, to determine which forcings yield signals most aligned with observed δ13Ccarb and δ13Corg records. On this basis, the most plausible scenario for the HICE involves a ~50% decrease in weathering of silicates and organic carbon at higher latitudes combined with enhanced carbonate weathering (fwcarb = 88%) at lower latitudes. Synchronous, globally enhanced burial of organic carbon was due to more efficient nutrient cycling caused by stronger thermohaline circulation and increased volcanism that further enriched oceanic dissolved inorganic carbon (DIC) in 13C. The influence of increased input of 13C-depleted carbon from volcanism and metamorphism may have been overwhelmed by these drivers of the positive δ13C shift. The Hirnantian Glaciation was likely initiated by secular enhancement of continental weathering due to the expansion of early plants but was terminated by increased volcanism and decreased CO2 consumption by silicate weathering during the cooling. This scenario is consistent with the timeline of known geological events and offers insights into the mechanisms responsible for the associated biotic crisis. Specifically, the onset of the Hirnantian Glaciation induced lower global temperatures, resulting in sea-level fall and a loss of habitat space, while its termination led to enhanced organic carbon export and deep-water anoxia, all of which likely contributed to the Late Ordovician mass extinction.
... These results raise some questions as where the warm-water biota inhabited during the Hirnantian glaciation and how they share close biotic affinities with the pre-Hirnantian assemblages. Some comparable Hirnantian carbonate deposits are known from Baltica (Perens, 1995;Hints et al., 2000;Kröger et al., 2016), Laurentia (Copper, 2001) and Kolyma (Koren et al., 1983;Koren and Sobolevskaya, 2008), all characterized by abundant warm water biota. In particular, these deposits of Baltica and Laurentia contain stromatoporoid-coral patch reefs (Nestor, 1964(Nestor, , 1999Copper, 2001;Nestor et al., 2010;Kröger et al., 2016), which are lacking in Kolyma (Koren et al., 1983;Koren and Sobolevskaya, 2008) and South China (this study; Wang et al., 2015). ...
... Some comparable Hirnantian carbonate deposits are known from Baltica (Perens, 1995;Hints et al., 2000;Kröger et al., 2016), Laurentia (Copper, 2001) and Kolyma (Koren et al., 1983;Koren and Sobolevskaya, 2008), all characterized by abundant warm water biota. In particular, these deposits of Baltica and Laurentia contain stromatoporoid-coral patch reefs (Nestor, 1964(Nestor, , 1999Copper, 2001;Nestor et al., 2010;Kröger et al., 2016), which are lacking in Kolyma (Koren et al., 1983;Koren and Sobolevskaya, 2008) and South China (this study; Wang et al., 2015). The earlier Hirnantian patch reefs are known from the Tõrevere and Siuge members of the Ä rina Formation (early to middle Hirnantian) in Estonia (Baltica), and are composed of stromatoporoids Clathrodictyon, Ecclimadictyon and Pachystylostroma together with tabulate corals Eocatenipora (=Catenipora) and Paleofavosites (Fig. 15.1) (Nestor, 1964(Nestor, , 1999Klaamann, 1966;Kröger et al., 2016). ...
... Stromatoporoids (mostly Ecclimadictyon and minor Clathrodictyon and Labyrinthodictyon) and microbial organisms are less common than the corals (Copper, 2001;Nestor et al., 2010). The earlier late Hirnantian tabulate coral assemblage in Kolyma (the member 70 of unit Q in Koren and Sobolevskaya, 2008) is composed of Proheliolites, Catenipora and Propora (Koren et al., 1983;Koren and Sobolevskaya, 2008), which share similar faunal affinity with those of the Shiqian Formation. Although the ages of these warm-water carbonates vary from the early to late Hirnantian (Koren et al., 1983;Hints et al., 2000;Copper, 2001;Koren and Sobolevskaya, 2008;Kaljo et al., 2012;Copper et al., 2013;Wang et al., 2015Wang et al., , 2019Wang et al., , 2020, they share a common biotic feature with many of the benthic organisms in the pre-Hirnantian at the higher taxonomic level (Harper et al., 2014). ...
The Late Ordovician Mass Extinction (LOME) occurred between two significant biotic diversifications: the Great Ordovician Biodiversification Event and the Silurian–Devonian Nekton Revolution. Upper Hirnantian carbonate deposits therefore are critical archives for understanding warm-water biotas, biodiversity resurgence and trophic chain development in the immediate aftermath of the LOME. In this study, we use microfacies analysis to investigate composition and biodiversity of the upper Hirnantian carbonates developed in northeastern Guizhou Province of China. These carbonates lay along the northern margins of the Dianqiangui landmass and are composed of intraclastic pack- to grainstone, mud- to wackestone, and bioclastic wacke- to packstone. Depositional age of the carbonates is estimated to be late Hirnantian, chiefly indicated by their coincidence with the Hirnantian Carbon Isotope Excursion and the brachiopods Cathaysiorthis and Eospirigerina. The development of carbonates containing diverse warm-water fossils at this transitional time reflects glacio-eustatic changes in the aftermath of the maximum Hirnantian glaciation and LOME, and the consequence of regional Kwangsian Orogeny in South China. Supposed autotrophic organisms in the carbonates are represented by calcimicrobes Allonema and Girvanella, and calcareous algae Amsassia, Dasyporella and Dimorphosiphon. Heterotrophic organisms are also abundant, including bryozoans (Atactoporella, Dekayia, Eridotrypa, Hallopora, Moorephylloporina and Ptilodictya?), trilobites (Dicranopeltis, Eoleonaspis, Mucronaspis (Songxites), Niuchangella and an aulacopleurid-like trilobite), rugose corals (Axiphoria, Eurogrewingkia, Meitanolasma and Grewingkia), tabulate corals (auloporid coral, Catenipora, Halysites, Paleofavosites and Propora), stromatoporoids (Camptodictyon, Ecclimadictyon and Cystostroma), conodonts (Ozarkodina and Walliserodus), benthic graptolites (Desmograptus), gastropods (at least two genera), and ostracods. Such a high biodiversity is evidence of a complex trophic web after the extinction pulses in South China. The biotic development of the warm-water benthic community might have been triggered by short-lived localized favourable environment that facilitated the survival of warm-water biota during the Hirnantian, which is postulated to have pioneered further Silurian reef recovery in South China.
... В ордовике Горного Алтая она выделяется в ранге тейль-зоны вида-индекса, охватывая нижнюю часть подзоны clingani зоны quadrimucronatus [29,86]. В ордовике Северо-Востока России [17] [9,22,71]. ...
... В Китае для этого стратиграфического интервала могут использовать два вида-индекса -extraordinarius / ojsuensis[59, 95]. В России зона extraordinarius выделяется в ордовике Северо-Востока (Колыма)[9, 22,71]. На Таймыре обнаружены слои с Normalograptus extraordinarius (Sobolevskaya) [33]. ...
New data are given on zonal graptolite units in the structure of the new Ordovician stage standard within the framework of the International Stratigraphic Chart. Ordovician zonal graptolite successions in the largest regions of Russia have been analyzed and correlated. Научные дискуссии о независимом параллельном или взаимодополняющем (взаимозаменяющем) использовании двух категорий хроностратиграфических шкал продолжаются уже более 50 лет. К первой категории относится Международная («глобальная» или «планетарная») шкала с ярусными подразделениями и ее российский эквивалент-Общая стратиграфическая шкала, а ко второй-реги-ональные шкалы с подразделениями, именуемыми горизонтами [44]. Инициаторами постановки этого вопроса у нас в стране и последующего его широкого обсуждения были сибирские стратиграфы, воз-главляемые тогда в ведущем отраслевом институте СНИИГГиМС Л. Л. Халфиным [3, 45-47], а в акаде-мическом Институте геологии и геофизики-Б. С. Соколовым [40-43]. Л. Л. Халфин кратко охарактеризо-вал эту проблему следующим образом: «Международная шкала-это счисление времени, хронология, а региональные схемы-это сама история, события которой датируются посредством хронологии» [45, с. 390]. Б. С. Соколов отмечал следующее: «…общая (международная) стратиграфическая шкала по сути своей может быть только синтетической (составной)… независимой от системы реальных геологи-ческих стратонов» и «региональные стратиграфические подразделения и их сопокупность в регионе-это исходная реальность…» [42]. История становления идей автономности и дополнительности стра-тиграфических шкал была недавно подробно рассмотрена А. В. Каныгиным [6]. Не вдаваясь в детали вопроса из-за ограничения объема рамками статьи, следует отметить, что методические приемы корре-ляции и их прикладное применение при сопоставлениях двух параллельных хроно стратиграфических шкал были и остаются в числе наиболее дискуссионных вопросов при пространственно-временных ре-конструкциях и обобщениях. Инстументом такой достоверной корреляции с дробностью необходимого уровня для ордовика и силура служат зональные шкалы по граптолитам и конодонтам. РЕГИОНАЛЬНЫЕ СТРАТИГРАФИЧЕСКИЕ ПОДРАЗДЕЛЕНИЯ ОРДОВИКА И ИХ КОРРЕЛЯЦИЯ С ЯРУСНЫМИ ПОДРАЗДЕЛЕНИЯМИ МЕЖДУНАРОДНОЙ СТРАТИГРАФИЧЕСКОЙ ШКАЛЫ В региональных стратиграфических схемах первый раздел состоит из подразделений соответству-ющей системы Общей стратиграфической шкалы, а второй представляет собой последовательность региональных стратиграфических подразделений с основной таксономической единицей-горизонтом [44]. Горизонты («региоярусы») в ордовике различных регионов России выделялись по комплексам бентосных групп организмов, установленных в опорных разрезах какого-либо геологического регио-на, главным образом трилобитов и брахиопод, вместе с табулятами, ругозами, остракодами и др. Это обеспечивало «внутрирегиональную коррелятивную функцию горизонта»-сопоставление разрезов по комплексам групп организмов, наиболее распространенных в регионе (палеобассейне) по латерали и встречающихся в максимальном спектре фациальных обстановок. Пелагические сообщества (грапто-литы, конодонты, хитинозои, радиолярии) вследствие неравномерной их встречаемости (как по площа-ди, так и в стратиграфическом разрезе) и немногочисленности в большинстве регионов не включались в ранг основных параметров при выделении горизонтов и рассматривались как вспомогательные для межрегиональных корреляций. Этим в какой-то мере принижалась хронометрическая функция гори-зонта-осуществление «прямых» (по одноименным зональным подразделениям) сопоставлений серий разрезов отдельного геологического региона по комплексам пелагических групп организмов с ярусными подразделениями Общей (или Международной) стратиграфической шкалы. ИННГ СО РАН (Новосибирск)
... Eospirigerina gaspéensis is a cosmopolitan species, occurring from the base of Hirnantian throughout Rhuddanian. It was originally described from Quebec, Canada (Schuchert and Cooper, 1930), but may occur in Canada, Britain, Belgium, Sweden, Kazakstan, Omulev Mountains, Tuva, southern Siberia, and Venezuela (Koren and Sobolevskaya, 2008;Nikitina et al., 2015;Sennikov et al., 2015). Description.-Small, ...
Strata of the Solvik Formation in the central Oslo Region (upper Hirnantian through most of Aeronian) are very fossiliferous and provide a good record relating to the survival and recovery faunas after the end-Ordovician mass extinctions. The ribbed atrypide fauna is especially rich with 21 species present. Samples from most of these taxa have been sectioned to reveal internal structures for taxonomic study. Of these, 13 species belong to the family Atrypidae, three of which are described in the present paper; Dihelictera engerensis n. sp., Gotatrypa vettrensis n. sp., and Rhinatrypa henningsmoeni n. gen. The family Atrypidae follows a global pattern of recovery with an increase in diversity registered in upper Rhuddanian and further diversification in Aeronian strata. The focus of this paper is the family Atrypinidae, which shows a different pattern. They are common and fairly diverse near the base of the Rhuddanian in deeper waters and rare further up, especially in the Aeronian. One new genus, Bockeliena , and two new species, Plectatrypa rindi and Euroatrypa ? sigridi are defined. The relationship between the subfamilies Spirigerininae and Plectatrypinae is clarified through thin sections of material from the Ordovician/Silurian boundary layers. The plectatrypids originated in Baltica through transitional species found in upper Katian to Hirnantian strata leading from the cosmopolitan Eospirigerina to the Plectatrypa lineage with imbricate ribbing and, separately, to Bockeliena and others with lamellose, widely spaced ornamentation. The Oslo Region probably acted as a nexus for survival and spread of brachiopods after the end-Ordovician mass extinction.
UUID: http://zoobank.org/95340b41-5537-4192-9338-211a2940bea8 .
... Marginal Laurentia: Girvan, Scotland (Harper, 1981(Harper, , 2006. Kolyma: Mirny Creek (Apollonov et al., 1980;Kaljo et al., 2012;Koren and Sobolevskaya, 2008). Baltica: Jämtland (Dahlqvist et al., 2010), Scania (Koren et al., 2003), Siljan (Suzuki et al., 2009;Ebbestad et al., 2015;Kröger et al., 2015), and Västergötland (Bergström, 1968;Bergström and Bergström, 1996), Sweden; Oslo-Asker Region, Norway Brenchley and Cocks, 1982;Bockelie et al., 2017); Estonia-Latvia (Harper and Hints, 2016;Hints and Harper, 2015); Holy Cross Mountains, Poland (Masiak et al., 2003). ...
... The corresponding rocks are developed in East Baltica, but the brachiopods are not well known (Harper and Hints, 2016). This fauna was also recorded from the Omulev Mountains, Kolyma with Biparetis, Thebesia, and Eospirigerina (Koren et al., 1983;Koren and Sobolevskaya, 2008); in Gornyi Altai with Thebesia, Brevilamnulella, Eospirigerina and others (Kulkov and Severgina, 1987); and in Zeravshano-Gissar Mountains, Central Asia, with Brevilamnulella, Thebesia, Eospirigerina, Whitfieldella and others (Menakova, 1991) ...
... The Edgewood Fauna in the upper Hirnantian rocks in Sweden, Norway, Estonia, Kolyma, Canada and USA is associated with graptolites and conodonts (Ozarkdina hassi) indicative of (probably the upper part) the M. persculptus Biozone Loydell et al., 2002;Stott and Jin, 2007;Koren and Sobolevskaya, 2008;Bergström et al., 2012aBergström et al., , 2012bBergström et al., , 2014Demski et al., 2015). The presence of Metabolograptus parvulus in the Wilhelmi Formation of Illinois and the Mosalem Formation of Iowa raises the possibility that the lowermost parts of the two formations are of late Ordovician age rather than of early Silurian age as previously thought (Loydell et al., 2002). ...
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.
... В ордовике Горного Алтая она выделяется в ранге тейль-зоны вида-индекса, охватывая нижнюю часть подзоны clingani зоны quadrimucronatus [29,86]. В ордовике Северо-Востока России [17] [9,22,71]. ...
... Hirnantian shelly fossils, including brachiopods and corals that are part of the Edgewood fauna of Laurentia, are best known at Mirny Creek section, in the Omulev Mountains of Northeast Russia (Rong and Harper, 1988;Koren and Sobolevskaya, 2008;Wang et al., 2017). Cooccurring graptolites are indicative of the M. persculptus Biozone (Koren and Sobolevskaya, 2008). ...
... Hirnantian shelly fossils, including brachiopods and corals that are part of the Edgewood fauna of Laurentia, are best known at Mirny Creek section, in the Omulev Mountains of Northeast Russia (Rong and Harper, 1988;Koren and Sobolevskaya, 2008;Wang et al., 2017). Cooccurring graptolites are indicative of the M. persculptus Biozone (Koren and Sobolevskaya, 2008). ...
The end-Ordovician mass extinction (EOME) is widely interpreted as consisting of two pulses associated with the onset and demise of the Gondwana glaciation, respectively, with the second pulse eradicating the distinctive, glacially related Hirnantian benthic biota (HBB). A global review of occurrence data of latest Ordovician benthic marine organisms reveals that virtually all warm-water benthic assemblages previously assigned to the HBB comprise two distinct and clearly postglacial faunas, both younger (middle and late Hirnantian, respectively) than the cool-water Hirnantia fauna (latest Katian to early Hirnantian). The newly recognised three Transitional Benthic Faunas (i.e., TBFs 1–3) can be closely tied to graptolite, conodont, and chitinozoan biozonations, the Hirnantian Isotope Carbon Excursion (HICE), and the glaciation, thereby providing an integrated, much higher-resolution timescale for understanding the tempo and nature of the EOME. At this finer resolution, we postulate a more profound impact of the first pulse of the EOME than hitherto envisaged, as evidenced by opportunistic expansion of the Hirnantia fauna globally and the complete absence of metazoan reefs in its immediate aftermath. We also argue, based on high-quality data from well-documented benthic groups in South China (i.e., brachiopods, tabulate and rugose corals, trilobites, and sponges), that the magnitude of the second pulse of the EOME caused by the deglaciation has been overestimated because the two postglacial faunas (i.e., TBFs 2–3) were part of a subsequent recovery phase of marine ecosystems rather than contributing to biodiversity decline. Thus, it is more plausible to reinterpret the EOME as a single-pulse, rapid event that was followed by a prolonged initial recovery intermittently impeded by climatic shocks through the Hirnantian, prior to the onset of a progressive reestablishment of marine ecosystems during the early Silurian (Rhuddanian and Aeronian) associated with an overall amelioration of climatic conditions.
... Соболевской [Состояние..., 2008]. По их же данным [Кoren', Sobolevskaya, 2008], мелко- водная граптолитовая фауна из разрезов Омулев- ских гор Сибири сопоставляется с аналогичной из разрезов провинции Ванживан в Китае и с глубоко- водными аналогами в разрезах Добс Линн (Dob's Linn) в Шотландии и Винини (Vinini) в централь- ной Неваде США. ...
The results of lithological and geochemical study of the Hirnantian deposits on the western slope of the Subpolar (Ko-BKB and Ko-108/01 sections) and Northern (BK-2 section) Urals are presented. At the beginning of the Hirnantian the regression in the Timan-northern Ural region on the outer zone of the carbonate platform margin (eastern sections of Ko-BKB - the Bad’yashor Fm in the Kozhym River, Subpolar Urals and BK-2 - pack 1 of the Verkh Ruchej Fm in the Ilych River basin, Northern Urals) was manifested in the formation of breccias, erosion surfaces with pockets, carbon and oxygen isotope excursions. In the inner zone of the platform margin (western section Ko-108/01 - pack 1 of the Yunkoshor Fm) was formed bioclastic sands, erosion processes have been significantly weaker. In the late Hirnantian existed shoals with crinoidal-sand facies (sections Ko-BKB - the Kamennaya Baba Fm and BK-2 - pack 2 of the Verkh Ruchej Fm) and more quiet water conditions of lower intertidal zone (section Ko-108/01 - pack 2 of the Yunkoshor Fm). The difference in the sedimentation was due to the existence of paleouplifts and paleodepressions (raised and lowered blocks of composite basement) on the carbonate platform. The similar environments in the sedimentary basin are revealed in the mid-Hirnantian by the negative excursion of carbon and oxide isotope curves clearly expressed in all sections. This shift reaching in the δ18О to 4.7‰ fixed in the section Ko-BKB. Such expressive isotope excursion can apply as the regional geochemical marker of the mid-Hirnantian deposits. This time interval characterizes an abrupt shallowing, intense continental runoff, and influence of fresh-water due to short-term extensive regional regression in the Timan-northern Ural marine basin. For the Hirnantian Stage in stratigraphic scheme of the Western Urals on the basis of sections completeness it is necessary to allocate the “Kozhym” Regional Stage with the stratotype sections in the Kozhym River on the Subpolar Urals, which must be located above the Kyr’ya Regional Stage corresponding to the upper Katian.
... At the time that the GSSP for the base of the Hirnantian was chosen, only one candidate section was formally considered, Wangjiawan North (Chen et al. 2006), where the GSSP was chosen at the level marked by the FAD of Metabolograptus extraordinarius. For the purposes of our study, it can be compared with two other sections that are widely used as graptolitic reference sections for the base of the Hirnantian: Vinini Creek (LaPorte et al. 2009;Storch et al. 2011) (note that the graptolite range data in these more recent papers differ substantially from those in Finney et al. 1999) and Mirny Creek (Koren & Sobolevskaya 2008;Kaljo et al. 2012). We have compared the levels of first occurrence of Fig. 7. Levels of occurrence of Akidograptus ascensus at all sections in which it occurs in our study. ...
Horizon annealing (HA) provides a method to order all horizons in a chronostratigraphic data set, including marker beds and isotopic excursions, as well as horizons that lack exact local markers (such as taxon first appearances) and are, thus, constrained only by local stratigraphical order. Global stratotype section and point (GSSP) levels placed within an HA composite succession can be precisely correlated with levels in all other sections in the composite that span the same interval. We present two approaches to the quantitative assessment of the uncertainty or error in the placement of horizons within the composite section: a permutation method (jackknife analysis) and a sensitivity analysis (the relaxed fit curve). From jackknife analysis, we calculate a standard deviation (σ) of the variation in horizon placements and estimate the 95% confidence interval of the variation in horizon placement within the composite. We also directly assess the relative stability of event positions using the results of the jackknife. These approaches provide an objective method for assessing the relative strengths of GSSP candidates, in which we prefer those sections and horizons that are the most precisely controlled in the HA composite. Integration of biostratigraphical, chemostratigraphical and lithostratigraphical marker horizons into the HA process markedly improves levels of constraint within the composite compared to biostratigraphical data alone. In a temporally scaled composite, the 95% confidence intervals on horizon placements could be used to estimate temporal resolution. In our study, we estimate that the average temporal resolution is approximately 319 kyr, which approaches the range of that needed to test hypotheses of orbitally driven cyclicity.
... Significantly, they found that the Lower Edgewood fauna did not contain true Hirnantia, but nevertheless retained a probable latest Ordovician (Hirnantian) age for these Laurentian assemblages. Most recently, Harper et al. (2013) defined a widely distributed Edgewood Province of Hirnantian age for rhynchonelliformean brachiopods, extending over much of Laurentia (including the Williston Basin of Manitoba, Canada), to Kolyma of Russia (Koren & Sobolevskaya, 2008), Siberia, Tarim (Chen et al. 2000;Wang & Aldridge, 2010;. Brachiopod succession is based on Rong & Li (1999) and Rong et al. (2013), with the asterisk indicating the horizon of the Dalmanella testudinaria-Dorytreta longicrura brachiopod community. ...
... (3) Recent chemostratigraphic data show that the horizons containing the Edgewood fauna correspond to the decreasing limb of the Hirnantian Isotope Carbon Excursion (HICE) (Bergström, Saltzman & Schmitz, 2006;Koren & Sobolevskaya, 2008;Bergström, Kleffner & Schmitz, 2012;Demski et al. 2015). Age control of these strata is provided by the cooccurrence of the O. hassi conodont Biozone and the M. persculptus graptolite Biozone (Bergström et al. 2014). ...
A complete coral succession through the Ordovician–Silurian transition in South China reveals an adaptive phase during the Hirnantian glaciation, followed by an early survival phase and finally a late survival phase that persisted into the early Silurian. We demonstrate that a coral assemblage of latest Hirnantian to earliest Silurian age, remarkably similar to those from the Edgewood fauna known from Laurentia, occurs stratigraphically above the typical Hirnantian fauna. This, in combination with other evidence (e.g. brachiopods, lithology and chemostratigraphy), suggests the Edgewood fauna probably post-dated the early–middle Hirnantian glaciation, rather than being coeval with the older glacial-related
Hirnantia
fauna. Evidence from South China shows that the Edgewood fauna appeared in the very latest Hirnantian and extended into the middle Rhuddanian, considerably younger than previously believed. Such a new correlation necessitates a reassessment of the influence of the end-Ordovician glaciation on biotas. We argue that this major glaciation probably would have substantially affected the ecosystem even in tropical regions, as shown by the development there of the
Hirnantia
fauna or, alternatively, the presence of a conspicuous stratigraphic hiatus. This suggests a surprisingly rapid biotic recovery during the subsequent postglacial transgression, represented by the flourishing of comparatively diverse shelly faunas (e.g. the Edgewood fauna and the
Cathaysiorthis
brachiopod fauna) in nearshore shallow water environments from Laurentia to eastern peri-Gondwana terranes or blocks (e.g. South China).
