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The decimeter-scale 3-D network structure of the Upper Ordovician Pagoda Formation in South China has been an enigmatic sedimentary feature and a case of non-uniformitarian carbonate depositional system, without modern analog. The network bands are developed pervasively throughout the entire Pagoda Formation, superficially resembling desiccation or syneresis cracks, especially in bedding-plane view, with decimeter-scale sub-polygonal to irregularly sinuous patterns. Detailed petrographic analysis, however, shows that the crack-like network bands have the same carbonate matrix, skeletal grains, and overall fabrics as the rock they surround. In this study, we demonstrate that the network structure is not generated by shrinkage cracks but is rather a time-specific lithofacies. It originated from prolonged growth of nodular carbonate, controlled by the convergence of several geological and paleoclimatic factors, including a) a protracted sea-level highstand lasting for about 5 Myr, b) an interval of tectonic quiescence favoring the dominance of carbonate production, with minimal siliciclastic input, and c) location of the South China paleoplate in the hurricane-free paleoequatorial zone devoid of severe storm disturbances between the fairweather and maximum storm wave bases (normally 15–120 m depths), favoring long-term, uninterrupted growth of CaCO 3 meganodules on a mid-shelf substrate. This study corroborates recent paleogeographic reconstructions that position the South China paleoplate on the Equator during the Late Ordovician. [ABSTRACT FROM AUTHOR]

Late Ordovician strophomenide brachiopods (superfamilies Strophomenoidea and Plectambonitoidea) from the upper Changwu Formation (mid Ashgill, late Katian) of Jianglütang, Chun’an County, western Zhejiang Province, consist of ten genera and 12 species. Five new species of three new genera are recognized: Chunanomena triporcata, Chunanomena sembellina, Cheramomena subsolana, Lateriseptomena modesta, and Lateriseptomena rugosa. The strophomenide brachiopods from the upper Katian strata described in this study and those from the border region of Zhejiang and Jiangxi provinces reported in previous work contain 16 strophomenoid and 12 plectambonitoid genera, and most of the strophomenoids are endemic to South China. Numerical analysis of well-documented late Katian strophomenide brachiopod faunas indicates a strong provincialism, characterized by the highly distinct North American province (Laurentia), the South China-Kazakhstan province, and the Avalonia-Baltica province (Wales, Belgium and Sweden). Surprisingly, the Girvan district of Scotland, which was a peri-Laurentian terrane during the Ordovician, contains a late Katian brachiopod fauna that is more closely related to the contemporaneous brachiopods of Avalonia-Baltica than to those of North America. [ABSTRACT FROM AUTHOR]

Brachiopods from the lower Tonggao Formation (Floian, late Early Ordovician) of Sandu, southeastern Guizhou Province, represent a deep-water benthic shelly fauna from the Jiangnan Slope facies of the South China paleoplate. The fauna contains 16 brachiopod taxa, with orthides, lingulates, and pentamerides being the common groups. Concurrent graptolites confine the brachiopod fauna to the Tetragraptus approximatus and the Acrograptus filiformis biozones (early Floian). The first appearance datum (FAD) of several brachiopod genera, such as Paralenorthis, Protoskenidioides, and Nereidella, in the Sandu slope facies is one or two graptolitic biozones lower than their FAD in shallower water facies on the Yangtze Platform. Later in the late Floian, these genera became major components of the Sinorthis fauna that flourished over much of the Yangtze Platform, suggesting a migration of the benthic shelly fauna from slope to platform facies during the Floian radiation in South China. Compared to the platform fauna, the deep-water brachiopod fauna of the Sandu area has a lower level of richness, diversity, and community organization. Three brachiopod associations are recognized: the Paralenorthis–Nereidella, the Palaeoglossa longa, and the Lingulella–Protoskenidioides associations. An upsection decrease in shell size, faunal richness, and species diversity in the Tonggao Formation indicate a deteriorating environment towards hypersalinity in the Sandu area, resulting in the ultimate disappearance of the deep-water brachiopod fauna. [ABSTRACT FROM AUTHOR]

Abstract: The Ordovician radiation is the earliest and most important biodiversification event in the evolution of the Paleozoic Evolutionary Fauna (PEF), when the basic framework of PEF was established. The radiation underwent a gradual, protracted process spanning more than 40 million years and was marked by several diversity maxima of the PEF. Case studies conducted on the Upper Yangtze Platform (South China Palaeoplate) showed that the Ordovician radiation was characterized by drastic increases in α- and β-diversity in various groups of organisms. During the radiation, brachiopods, trilobites, and graptolites of the PEF became more diverse to dominate over the Cambrian Evolutionary Fauna (CEF) in all marine environments. At either global or regional scales, however, the Ordovician radiation was highly heterogeneous in time and space, and the rate and pattern of radiation exhibited by different major fossil groups were also variable. [Copyright &y& Elsevier]

Sixteen species from the Lower Silurian (mostly Aeronian and rarely Telychian) of South China have been assigned previously to the brachiopod family Pentameridae, mainly to the genus Pentamerus. Study of intrapopulation variation suggests that 13 species from the upper Aeronian Lojoping Formation of the Yichang area, western Hubei Province, can be synonymized with Sulcipentamerus dorsoplanus, the most abundant pentamerid species of South China but confined to the Yichang area. The conspicuously high and obtuse ventral umbo, strong ventribiconvexity and a sulcate anterior commissure warrant genus status for Sulcipentamerus, independent of Pentamerus. True Pentamerus is rare in South China, known only from upper Aeronian rocks of Guizhou Province. Multivariate analyses indicate that Aeronian pentameride brachiopods of South China are characterized by a high level of provincialism, distinct from those of Laurentia. Also, the Aeronian pentamerides of South China or Laurentia have a low degree of similarity to those of Baltica, Siberia, Avalonia, Kazakhstan and other palaeotropically located plates or terranes. Besides South China and Laurentia, the pentamerides of other palaeotropical regions constituted a relatively tight cluster. This suggests that the palaeogeographical positions of South China and Laurentia only allowed limited or periodic faunal exchange of these generally large-shelled brachiopods adapted to living in relatively shallow, warm waters. [ABSTRACT FROM AUTHOR]

Systematic and statistical study of brachiopods from the Dawan Formation of the Yichang area, western Hubei Province, central China, indicates that, at generic and specific levels, the α diversity of Early to Mid Ordovician brachiopods in the study area reached the first acme at the beginning of the Corymbograptus deflexus Biozone, marked by the diverse Sinorthis typica Community. This diversity maximum of brachiopods occurred approximately one biozone later than that of the Upper Yangtze Platform. In taxonomic constituents, the main contributors to the diversity maximum were orthoids, which experienced a major increase in the number of genera in the upper Didymograptellus eobifidus Biozone and the lower C. deflexus Biozone. In brachiopod communities or associations, orthoids and pentameroids were the dominant elements. Analyses of Early–Mid Ordovician brachiopods from the Upper Yangtze Platform indicate that a high level of brachiopod community organization, with temporal and spatial stability, was achieved by the Sinorthis Community, which persisted from the D. eobifidus to the Azygograptus suecicus biozones (early Arenig). In the D. eobifidus Biozone, the Sinorthis Community thrived across a wide ecological range (BA3 to upper BA4) in the siliciclastic facies of the central part of the Upper Yangtze Platform and, by the latest D. eobifidus interval, invaded more carbonate-rich substrates in more offshore settings in the northeastern part of the platform (the present Yichang area). [ABSTRACT FROM AUTHOR]

The Beishan orogenic zone is a key area to understand evolution of the Central Asian Orogenic Belt that is an accretionary factory well‐enough preserved in the Paleozoic. In early Paleozoic, the tectonic mélange zone containing the coherent unit and mélange unit is triggered by the complicated accretionary process of the Beishan area. The early Paleozoic tectonic evolution of the Beishan orogenic zone is investigated in this study using sedimentology and stratigraphic correlations of the lowe Paleozoic deposits. From the Cambrian to the middle Ordovician, this region was characterized by geographically extensive, flat‐bedded siliceous mudstone, indicating the existence of a large ocean basin. The oceanic plate entered the convergence phase in terms of the Wilson Circle during the Middle Ordovician, when numerous magmatic arcs formed along two opposite sides of the ocean. The magmatic arcs became the widest during the Silurian, suggesting that the Hongliuhe‐Niujuanzi‐Xichangjing Ocean (HNX; a southern branch of the Paleo Asian Ocean) was reduced to a small residual ocean in the central Beishan region by that time, and probably lasted till the Carboniferous or later by newly published data. [ABSTRACT FROM AUTHOR]

The oldest Foliomena fauna was, until now, known from the middle-upper Miaopo Formation ( Nemagraptus gracilis Biozone, lower Sandbian, basal Upper Ordovician) of South China. In this study, the oldest record of the fauna is set back to the latest Darriwilian (upper Hustedograptus teretiusculus Biozone), represented by Foliomena jielingensis and some typical constituents of the Foliomena fauna from the basal Miaopo Formation at Jieling, northern Yichang, western Hubei Province, central China. The Miaopo Formation is characterized by its organic-rich dark-grey shale facies, unique in its localized distribution on the Yangtze Platform, and distinguished by its rich and diverse benthic and graptolitic faunas. This suggests an origin of the Foliomena fauna in periodically oxygen-starved local depressions on the Yangtze Platform during the Middle-Late Ordovician transition. [ABSTRACT FROM AUTHOR]

The Upper Ordovician (mid-Ashgill) Xiazhen and Changwu formations in the Zhejiang-Jiangxi border region of southeastern China contain an abundant and diverse suite of brachiopods. A cluster analysis of 59 key samples from 180 collections (over 23 000 specimens) allowed delineation of eight distinct brachiopod communities, herein named the Ectenoglossa minor Community, the Eospirifer praecursor Community, the Ovalospira dichotoma Community, the Antizygospira liquanensis – Sowerbyella sinensis Community, the Kassinella shiyangensis Community, the Altaethyrella zhejiangensis Community, the Tcherskidium jiangshanensis Community and the Foliomena folium Community. These communities occur predominantly in limey, clayey, to silty mudstone facies, similar to Ziegler's Early Silurian brachiopod communities in the Welsh Borderland. On the basis of lithological, faunal, and paleogeographical evidence, the eight communities are interpreted to have distributed along an onshore–offshore gradient from BA1 to BA6 settings on the northeastern margin of the Zhe-Gan Platform. In a broad paleo-embayment and mixed carbonate–siliciclastic shelf setting, the distribution of the eight brachiopod communities appears to have been controlled primarily by water depth because a given brachiopod community can be found in different lithofacies. Substrate types, however, must have played an important role, as some of the communities show preferred lithofacies. This study shows that the ecological zonation and community organization of the Late Ordovician pre-extinction brachiopods were similar to those of Early Silurian post-extinction brachiopods, although pronounced brachiopod provincialism during the Ashgill makes it difficult to directly correlate these communities with coeval brachiopod communities reported from other paleo-plates.Les formations de Xiachen et de Changwu de l'Ordovicien tardif (Ashgillien moyen) dans la région de la frontière Zhejiang-Jiangxi du Sud-Est de la Chine contiennent une suite abondante et diversifiée de brachiopodes. Une analyse typologique de 59 échantillons clefs provenant de 180 collections (plus de 23 000 spécimens) a permis de délimiter huit communautés distinctives de brachiopodes nommées ici la communauté Ectenoglossa minor, la communauté Eospirifer praecursor, la communauté Ovalospira dichotoma, la communauté Antizygospira liquanensis–Sowerbyella sinensis, la communauté Kassinella shiyangensis, la communauté Altaethyrella zhejiangensis, la communauté Tcherskidium jiangshanensis et la communauté Foliomena folium. Ces communautés se retrouvent surtout dans des faciès de mudstone à chaux, d'argileux à silteux, semblable aux communautés de brachiopodes de Ziegler du Silurien précoce dans la Bordure Galloise (Angleterre). Selon les évidences lithologiques, fauniques et paléogéographiques, les huit communautés se seraient distribuées le long d'un gradient côtier et extracôtier dans des environnements BA1 à BA6 sur la bordure nord-est de la plate-forme de Zhe-Gan. Dans un environnement de grande paléobaie ouverte et de plate-forme à mélange de carbonates et de siliclastiques, la distribution des huit communautés de brachiopodes semble avoir été contrôlée surtout par la profondeur de l'eau puisqu'une communauté donnée de brachiopodes peut se retrouver dans différents lithofaciès. Les types de substrats ont cependant dû avoir joué un rôle important puisque quelques communautés présentent des lithofaciès préférentiels. La présente étude montre que la zonation écologique et l'organisation des communautés des brachiopodes avant extinction à l'Ordovicien tardif étaient semblables à celles des brachiopodes post-extinction du Silurien précoce, bien que le provincialisme prononcé des brachiopodes au cours de l'Ashgillien rende difficile la corrélation directe entre ces communautés et les communautés contemporaines de brachiopodes provenant d'autres paléoplaques.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The latest Katian (Late Ordovician) is marked by the third biodiversity climax of the Great Ordovician Biodiversification Event (GOBE) prior to the Late Ordovician mass extinction (LOME). In this study, the Chemical Index of Alteration (CIA) is used to determine the paleoenvironmental change recorded in the Arisu Member, the Siltstone Member, and the Sandstone Member of the Terekawat (= Tierekeawati) Formation (upper Katian) in the Tarim Basin, northwestern China. CIA values from these members are plotted in A–CN–K ternary diagrams respectively. Linear regression and 95% confidence interval estimation results indicate that these deposits were derived from the same parent rock, and the corrected CIA (CIA corr.) values reveal significant paleo-climate changes during Late Ordovician. Sea-surface temperatures (SSTs) have been estimated by comparing 31 modern estuary systems. These data show that the CIA corr. values dropped from 77.41 to 64.83, corresponding to an interpreted temperature drop from 20.5 to 10.2 °C in the Dicellograptus complexus graptolite Biozone of the upper Katian (Ka-4). CIA corr. values varied within a range of 67.63–70.16, implying temperature fluctuations between 12.5 and 14.6 °C in the lower to middle Paraorthograptus pacificus Biozone. CIA corr. values rose again from 69.09 to 76.05, corresponding to a temperature rise from 13.7 to 19.4 °C in the upper Paraorthograptus pacificus graptolite Biozone of the latest Katian. This is interpreted to be a cooling and warming cycle, corresponding to the mid-Boda cooling and the late-Boda warming events. This study suggests that the climate change during late Katian was more intense than previous thought, especially in subtropical zones of Paleo-Tethys. This cooling event enhanced the thermohaline ocean circulation and became one of the major factors causing the well-known late Katian faunal dispersal (i.e. the Boda event). Hirnantian glaciation would have further promoted global oceanic cooling, over-stressed the ecosystems, and triggered the LOME. • Chemical Index of Alteration and confidence interval estimation are used to reconstruct climate change. • A temperature drop from 20.5 to 10.2°C and a subsequent rise are estimated in the Tarim Basin during the Late Ordovician. • This cooling event enhanced the thermohaline ocean circulation and contributed to the faunal dispersal (i.e. Boda event). • Hirnantian glaciation event doubled the cooling effect on ecosystem compared with this cycle. [ABSTRACT FROM AUTHOR]

Iron‐rich nodules occur on the Yangtze Platform, South China, especially along the marginal area, during the late Middle and early Late Ordovician (Darriwilian–Sandbian). Based on the study of samples from the Daling section, Anhui Province, these nodules include: (1) oncoids; (2) coated bioclasts; and (3) coated micritic intraclasts, all of which potentially have a similar biological origin. The nodule‐bearing strata were deposited in a midouter ramp setting, indicating sediment starvation and open marine conditions, possibly combined with anoxia in deeper basinal areas and cool water upwelling during the formation of the nodules, rather than terrestrial input or local tectonic movement. The widespread distribution of iron‐rich nodules at this time was probably favoured by high sea level and cooling climate, conditions that simultaneously favoured the evolutionary radiations of the GOBE in South China. Thus, these nodules form a time‐specific signature of a critical time in the evolution of the marine ecosystem in the context of local environmental background along the marginal Yangtze Platform. [ABSTRACT FROM AUTHOR]

The Kuanyinchiao Formation (Hirnantian, Upper Ordovician), yielding the typical Hirnantia fauna, has commonly been accepted as representing cool-water sediments deposited during the glacial interval in the Hirnantian Global Boundary Stratotype Section and Point (GSSP) region of South China. Recent investigation reveals that the uppermost carbonate-dominated part of this formation yields a warm-water rugose coral fauna with Silurian affinities at many localities of northern Guizhou Province, which substantially differs from the underlying cool-water fauna. This suggests that these carbonates were probably postglacial warm-water sediments, rather than having formed during the Hirnantian glacial interval as previously thought. Such a conclusion is consistent with the evidence from the associated brachiopod fauna, i.e., the Dalmanella testudinaria - Dorytreta longicrura community, which is similarly distinct from the underlying typical Hirnantia fauna. The sedimentological data show warm-water features at the same level (e.g., the presence of oolitic grains), also supporting this new interpretation. [ABSTRACT FROM AUTHOR]

The distribution pattern of early Telychian ( turriculatus-crispus graptolite biozone) red beds in the Eastern Yangtze Platform of South China is reconstructed based on regional geologic data. The red beds are developed in three areas, which are separated by regions without red deposition. The distribution pattern indicates that the Cathaysian Oldland was the provenance of sediment rich in ferric oxides, which are essential for the formation of red beds. Silurian marine siliciclastic red beds, both in China and worldwide, tended to develop during times of relatively low sea level. Coeval hematitic oolites that formed far from the coast may record a change from reducing to oxidizing conditions in the ocean. Furthermore, it is likely that a fall in global sea level, a transition from reducing to oxidizing conditions in the ocean, and a cooling climate, all of which were closely related to the early Telychian Valgu Event, promoted the global development of marine red beds during this period. [ABSTRACT FROM AUTHOR]

Enigmatic millimetre-scale micro-concretions with pseudocrystal faces and dominated by green clay minerals occur in unfossiliferous siliciclastic mudstone of the Lower Ordovician (479.0-466.0 Ma) Tonggao Formation, South China. The fossil-free mudstone unit is associated with local biodiversity decline. The mineralogy and mineral chemistry of these concretions were unknown previously, and this study comprises a preliminary investigation. The concretions are dominated by Fe-rich phyllosilicate minerals including glauconite and clinochlore, with minor quartz and traces of magnetite. The textural relations between the micro-concretions and the surrounding matrix, and the preservation of original mudstone laminations within the concretions, point to an origin during early diagenesis. The mineralogy and chemistry of these concretions are consistent with an origin in a restricted, hypersaline, relatively deep-water environment, in accordance with stratigraphical and paleonotological data. These micro-concretions provide clues for a stressed environment with poor water circulation and anomalies of salinity and oxygen. [ABSTRACT FROM AUTHOR]