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Silurian is a period with the shortest duration in Phanerozoic except for the Neogene and Quaternary. It represents an important and unique interval when the biotic diversity recovered quickly after the end-Ordovician mass extinction, different paleoplates or terranes conjoined, big oceans disappeared or narrowed, climate and sea level changed frequently, global biotic provincialism became weaker, some primitive plants started to occupy the land. Silurian is also the first system of which all the chronostratigraphic stratotypes (i.e. the GSSPs) including four series and seven stages were established by the International Subcommission on Silurian Stratigraphy (ISSS). Nonetheless, during the post-GSSP studies conducted by ISSS in the middle 1980s, some Silurian GSSPs were found to have some congenital defects such as no index fossils available that hinder the high resolution subdivision and correlation on a regional or global scale. In this paper, based on the latest development of Silurian study in China, the progress in biostratigraphy, chronostratigraphy, event stratigraphy (such as facies differentiation, heterochrony of black shales, marine red beds, carbonate rocks and reefs), chemostratigraphy, and tectonic stratigraphy (e.g., widespread of the late Silurian rocks in South China and its tectonic implication) are systematically summarized. Some existing problems and the areas to be focused in future work are also discussed. It is suitable for chronostratigraphic study to concentrate not only on the boundary but also doing multidisciplinary analysis on the biotic, chemical, magnetic, environmental, and chronologic aspects, in order to enhance the reliability and the potential for regional and global correlation of a certain GSSP. Some important achievements are expected in these areas in the Silurian study in China: (1) ecostratigraphy and basin analysis of the Llandovery, and the correlation of integrative stratigraphy with a high resolution; (2) establishment of the Wenlock to Pridoli chronostratigraphic framework; (3) the chemo- and magnetic stratigraphy and the age of some key intervals and horizons; (4) further investigation on paleogeography and plate tectonics; and (5) origin and early evolution of the terrestrial ecosystem. Some new breakthroughs might occur in the restudy on some of those problematic GSSPs of some particular series and stages.

Marine red beds (MRBs) occur in many locations in the world during the Telychian Stage but it is unclear how they were related with the highly dynamic Silurian Earth system. To address this question, we conducted a case study involving geochronology, palaeogeographic reconstruction, facies analysis and sea-level history of the middle Telychian MRBs on the western Yangtze Platform of South China. Their distribution pattern indicates that the clastic MRBs owe their origin to the nearby oldlands. Facies analysis indicates that rocks during the study interval generally fall into three depositional belts: shallow subtidal, deep subtidal and shaly basinal belts. A chronostratigraphic framework constrained by both biostratigraphic data and eustatic events shows that, during the early Monoclimacis crenulata interval, olive-gray strata dominated both shallower (shallow and deep subtidal belts) and deeper (shaly basinal belt) settings, while distribution of the MRBs was restricted to deeper waters (shaly basinal belt) on the open-sea side of the platform. This situation changed after the middle M. crenulata interval when the MRB deposition was dominant in both shallower and deeper settings. The diachronous onset pattern of the MRBs coincided with prominent transitions in climatic conditions (from cooler to warmer), eustatic states (from regression to transgression), benthic faunas (decline of normal marine fauna and development of euryhaline assemblages) and reduced primary productivity in the shelf settings, most likely indicative of a change between different oceanic modes. Comparative studies suggest that, the widespread Telychian MRBs in both shallow and deeper water settings owe their origin to a very low organic carbon burial rate, which could be results of higher oxygen content in the ocean water and lower primary productivity.

Network and frequency distribution analyses of global brachiopod occurrences in the earliest Silurian (Rhuddanian–Aeronian) revealed that brachiopod recovery from the end-Ordovician mass extinction during the early–late Rhuddanian was represented mainly by the reestablishment of Late Ordovician cosmopolitan holdover taxa. Brachiopods nearly doubled their generic diversity from Rhuddanian to Aeronian, owing to the radiation of both endemic and cosmopolitan taxa, associated with an overall post-glacial amelioration of global environment and increased habitat heterogeneity as a result of marine transgressions and expansion of epeiric seas. A drastic turnover from the Ordovician-type to Silurian-type brachiopod faunas took place in the Aeronian, several million years after the terminal Ordovician mass extinction. Compared with the orders of orthides and strophomenides that radiated and predominated in the Ordovician, the atrypides and pentamerides displayed pulses of drastic diversification from the Rhuddanian to Aeronian, mainly in tropically located paleoplates, to become the most abundant and diverse brachiopod orders in the Silurian. Atrypides recovered in the early Rhuddanian, whereas diversification of pentamerides was delayed until the Aeronian and becoming widespread in South China, Kazakhstan terranes, Baltica, Avalonia, and Laurentia.

The end Ordovician mass extinction (EOME) was the second most severe biotic crisis in Phanerozoic, and has been widely linked to a major glaciation. However, robust geochronology of this interval is still lacking. Here we present four successive high-precision zircon U–Pb dates by isotope dilution thermal ionization mass spectrometry (ID-TIMS) for biostratigraphically well-constrained K-bentonites of a continuous Ordovician-Silurian boundary section at Wanhe, SW China. They include 444.65 ± 0.22 Ma (middle Dicellograptus complexus Biozone), 444.06 ± 0.20 Ma (lower Paraorthograptus pacificus Biozone), 443.81 ± 0.24 Ma (upper Tangyagraptus typicus Subzone), and 442.99 ± 0.17 Ma (upper Metabolograptus extraordinarius Biozone). Calculations based on sedimentation rates suggest a duration of 0.47 ± 0.34 Ma for the Hirnantian Stage, which is much shorter than previously thought (1.4 ± 2.05 Ma in the International Chronostratigraphic Chart ver. 2019/05). The new data also constrain the Hirnantian glacial maximum to ∼0.2 Ma, supporting that its brevity and intensity probably triggered the EOME. Keywords: ID-TIMS, K-bentonite, End Ordovician mass extinction (EOME), Hirnantian stage

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.

Huang, B., Baarli, B.G., Zhan, R.B. & Rong, J.Y., October 2015. A new early Silurian brachiopod genus, Thulatrypa, from Norway and South China, and its palaeobiogeographical significance. Alcheringa 40, xxx–xxx. ISSN 0311-5518.The smooth atrypoid brachiopod Thulatrypa gen. nov. incorporates two species, a younger (T. gregaria) from Norway, and an older (T. orientalis) from South China, which collectively span the middle Rhuddanian through Aeronian. In Baltica, the genus thrived just below the storm wave base in a tropical BA4 setting extending slightly into BA3 and BA5 respectively, whereas in South China, its representative occurs in a much shallower assemblage (BA2–3). Their palaeobiogeographical implications are carefully investigated. This study supports the arguments that Thulatrypa may have originated in South China in the middle Rhuddanian and extended its range to eastern Baltica in the late Rhuddanian. Larvae may have drifted along a channel from the east to the southwest of Baltica, which suppor...

Classification of extinction events and their severity is generally based on taxonomic counts. The ecological impacts of such events have been categorized and prioritized but rarely tested with empirical data. The ecology of the end Ordovician extinction and subsequent biotic recovery is tracked through abundant and diverse brachiopod faunas in South China. The spatial and temporal ranges of some 6500 identified specimens, from 10 collections derived from six localities were investigated by network and cluster analyses, nonmetric multidimensional scaling and a species abundance model. Depth zonations and structure of brachiopod assemblages along an onshore-offshore gradient in the late Katian were similar to those in the latest Ordovician–earliest Silurian (post–extinction fauna). Within this ecological framework, deeper-water faunas are partly replaced by new taxa; siliciclastic substrates continued to be dominated by the more ‘Ordovician’ orthides and strophomenides, shallow-water carbonate environments hosted atrypides, athyridides and pentamerides, with the more typical Ordovician brachiopod fauna continuing to dominate until the late Rhuddanian. The end Ordovician extinctions tested the resilience of the brachiopod fauna without damage to its overall ecological structure; that commenced later at the end of the Rhuddanian.

The origin and pigmentation of red beds have long been investigated, but mainly on continental settings and carbonate facies (including deep marine red beds). This paper focuses on the shallow marine clastic red beds developed in South China during the Silurian. Based on the sedimentological and geochemical analyses on red layers, green layers and laminae of the Rongxi Formation (Llandovery, Lower Silurian) of Xiushan, southeastern Chongqing, known as the ‘lower red beds’ (LRBs), the following observations are made: (1) the LRBs are primary red beds whereas the green layers are secondary (i.e., formed during early diagenesis); (2) the color differentiation of sediments shows little relevance to the bottom redox potential shift but has a close relationship to grain size and sediment sorting which may be caused by sea level changes and tides. The controlling factors of LRBs pigmentation are significantly different from those of deep marine red beds, and some coeval red beds in North America and Europe. It is noted that, among the shallow marine clastic red beds, the sedimentological and geochemical signatures from the laminae seem to better indicate the environmental conditions than those derived from the layers.

A Foliomena fauna is reported for the first time from the Tarim paleoplate, and stratigraphically from the Yinpingshan Formation (upper Katian, Upper Ordovician) of Querqueke, Kuruktag region, northeastern Tarim, southern Xinjiang, Northwest China. The fauna includes seven species of brachiopods, amongst which three are new and four indeterminate: Anomaloglossa ? sp., Orbiculoidea ? sp., Foliomena xinjiangensis n. sp., Sericoidea minuta n. sp., Kassinella tarimensis n. sp., Rostricellula ? sp., and Anazyga ? sp. These species formed a Sericoidea - Kassinella Association, characterized by very small and well-preserved brachiopods, and well-developed laminations in its hosted mudstone, indicating a deep water environment (corresponding to lower BA5 to BA6). The faunal and sedimentological features suggest its affinity to the typical Foliomena faunal group of deep water origin. Numerical analyses show that the Foliomena fauna in late Katian time differentiated into two major paleogeographically related groups, and the Tarim association has a close faunal affinity to the representatives of this fauna in South China, indicating an active faunal exchange between Tarim and South China before the end-Ordovician mass extinction.

Silurian brachiopods of Middle Llandovery (Aeronian) ages are reviewed, and 215 genera are identified here, compared with 109 in the preceding Early Llandovery (Rhuddanian), indicating a recovery-radiation interval after the end-Ordovician mass extinction. The chief regions in which they are found are the continents of South China, Avalonia-Baltica, Laurentia and Siberia, which were all at tropical latitudes with the exception of Avalonia. In addition, the very large superterrane of Gondwana, although with patchy brachiopod distribution, included temperate faunas, as well as subtropical faunas (in Iran and Afghanistan). Aeronian brachiopods greatly increased in diversity, with dominance of four major groups: orthides and strophomenides (which had flourished previously in the Rhuddanian), pentamerides and atrypides (which became dominant in the Aeronian), and many newly evolved taxa, and occupied deeper water and wider ecological niches (level bottom and reef) than those in the Rhuddanian. Each of the continents has some endemic genera, but there is a greater proportion of them in South China, where some groups (such as the pentamerides and atrypides) are more diverse and others, such as the orthides, are much less common than elsewhere. Affinity indices (AI) show that two megaunits can be recognized: South China and Avalonia-Baltica-Laurentia (ABL); Siberia seems to have been loosely connected with ABL and even more loosely to South China presumably because of its geographical separation in the Northern Hemisphere. The separation of South China from the other megaunits is further supported by cluster analysis.

The brachiopod genus Dicoelosia is generally considered a typical deep-water taxon. New data suggest that some species of the genus may have invaded relatively shallow-water habitats during its geological history. However, there is scant evidence for its invasion of shallow-water environments after the terminal Ordovician mass extinction. Dicoelosia occurs in the shallower-water benthic shelly assemblages of the lower Niuchang Formation (upper Rhuddanian, Llandovery) of Meitan County, northern Guizhou Province, South China. Evidence of a move to shallow water includes its morphology and population structure, regional paleogeography, sedimentology, together with the abundance and diversity of its shallow-water associates. Following the biotic crisis, deep-water environments were barely habitable, and may have driven Dicoelosia into shallower-water niches. The taxon endured the less suitable shallow-water environments until the deep-water benthic zones ameliorated after the recovery, implying a shallow-water refugium existed after the biotic crisis. A new species Dicoelosia cathaysiensis is erected herein. There is only one record of this genus in South China and this unique occurrence may reflect the distinctive paleobiogeography and environments of this region.

The phylogeographical evolution and the consequent changing distribution and diversity of rhynchonelliform brachiopods through the Ordovician are linked to the dynamic palaeogeography of the period. The Early Ordovician (Tremadocian and Floian) is characterized by globally low-diversity faunas with local biodiversity epicentres, notably on the South China Palaeoplate; low-latitude porambonitoid-dominated faunas with early plectambonitoid and clitambonitoid representatives, as well as high-latitude assemblages mostly dominated by orthoids, can be recognized, but many taxa are rooted in Late Cambrian stocks. The Early Ordovician displays a steady increase in rhynchonelliformean biodiversity, which was mostly driven by the increasing success of the Porambonitoidea and Orthoidea, but the billingsellids and early plectambonitoids also contributed to this expansion. During the Early to Mid Ordovician (Dapingian–Darriwilian), marine life experienced an unprecedented hike in diversity at the species, genus and family levels that firmly installed the suspension-feeding benthos as the main component of the Palaeozoic fauna. However, this may have occurred in response to an early Darriwilian annihilation of existing clades, some of which had been most successful during the Early Ordovician. New clades rapidly expanded. The continents were widely dispersed together with a large number of microcontinents and volcanic arcs related to intense magmatic and tectonic activity. Climates were warm and sea-levels were high. Pivotal to the entire diversification is the role of gamma (inter-provincial) diversity and by implication the spread of the continents and frequency of island arcs and microcontinents. The phylogeographical analysis demonstrates that this new palaeogeographical configuration was particularly well explored and utilized by the strophomenides, especially the Plectambonitoidea, which radiated rapidly during this interval. The porambonitoids, on the other hand, were still in recovery following the early Darriwilian extinctions. Orthides remained dominant, particularly at high latitudes. Biodiversity epicentres were located on most of the larger palaeoplates, as well as within the Iapetus Ocean. Provincial patterns were disrupted during the Sandbian and early Katian with the migration of many elements of the benthos into deeper-water regimes, enjoying a more cosmopolitan distribution. Later Katian faunas exhibit a partition between carbonate and clastic environments. During the latest Katian, biogeographical patterns were disrupted by polewards migrations of warm-water taxa in response to the changing climate; possibly as a consequence of low-latitude cradles being developed in, for instance, carbonate reef settings. Many clades were well established with especially the strophomenides beginning to outnumber the previously successful orthides, although this process had already begun, regionally, in the mid to late Darriwilian. At the same time, atrypoid and pentameroid clades also began to radiate in low-latitude faunas, anticipating their dominance in Silurian faunas. The Hirnantian was marked by severe extinctions particularly across orthide-strophomenide clades within the context of few, but well-defined, climatically controlled provincial belts. Supplementary material: The individual localities and a reference list for the data sources are provided at: http://www.geolsoc.org.uk/SUP18667

Extinction events usually disrupt palaeobiogeographical patterns, but there have been few detailed studies of the Early Silurian survival–recovery period after the Late Ordovician mass extinction. This paper summarizes and revises published information on the recovery of Early and Late Rhuddanian brachiopod faunas. The global dataset consists of 137 occurrences, 72 genera, and 13 localities of Early Rhuddanian (survival interval), and 271 occurrences, 91 genera, and 26 localities of the Late Rhuddanian (early recovery interval). The data are analyzed using Cluster Analysis, Nonmetric Multidimensional Scaling, and Minimum Spanning Tree using Yule's Y coefficient and the Raup–Crick coefficient (probabilistic index of similarity). The results display palaeolatitudinal distribution patterns for brachiopods during their survival and recovery. Frequency analysis of the data indicates that cosmopolitan taxa before the mass extinction decreased in their post-extinction distribution. The survivors were mostly confined to one palaeoplate or even one locality in the survival interval, but expanded progressively in the subsequent recovery period.

A diverse brachiopod fauna from a relatively deep water carbonate facies of the Upper Ordovician Beiguoshan Formation (uppermost Caradoc – lower Ashgill, middle Katian) is characterized by small shells and contains the oldest known Dicoelosia and Epitomyonia, two diagnostic taxa of deep water brachiopod palaeocommunities during the Late Ordovician and Silurian. Three new species are recognized: Dicoelosia cordiformis sp. nov., Dicoelosia perbrevis sp. nov. and Epitomyonia fui sp. nov. These pioneer forms of the family Dicoelosiidae show a relatively high degree of morphological plasticity. The shells of Dicoelosia from the Beiguoshan Formation range from the typical slender-lobed form with a concavoconvex profile to the strongly equibiconvex, fat-lobed morphotype that was not known previously until the late Silurian. The Beiguoshan dicoelosiids point to an important attribute of the deep water brachiopods: small generalists with high morphological plasticity, which make them ideal candidates as progenitors for the evolution of shallow water brachiopod faunas in shelf and platform depositional environments.

Located northwest of the Jiangshan-Shaoxing Fault Zone, western and northwestern Zhejiang and northeastern Jiangxi provinces experienced major changes in bio- and litho-facies and paleogeography through the Ordovician-Silurian transition (late Katian, Hirnantian, and early Rhuddanian), as manifested by stratigraphic, paleontologic and synecologic records. Three geographic units under consideration are South, Central, and North areas. The western margin of the South area was occupied by the Huaiyu Mountains, whereas the other two parts were covered by the Zhe-Gan Sea during late Katian (Late Ordovician) time. In the early stage of the Changwu Formation deposition (late Katian), the sea was deepening northeastward, but with shallower conditions in the southwest and deeper conditions in the northeast. During mid to late stages of Changwu Formation deposition (latest Katian), the sea became much shallower and the sea bottom was uplifted substantially, which occurred somewhat prior to the global trend. During the Hirnantian (latest Ordovician) and early Rhuddanian (earliest Silurian), the study region became a shallow bay under expansion of the Cathaysian Oldland. There occurred a major drop of sea level and great changes in benthic biota with the occurrence of many new immigrants through the Ordovician-Silurian transition, which are closely related to a unique regional orogeny. The Yangtze and Cathaysian blocks may have amalgamated within the South China Paleoplate during this interval to cause the continuous uplifting and northwestward expansion of the Cathaysian Oldland.

In the immediate aftermath of global extinctions, organisms were normally much smaller than those prior to these events. This ‘Lilliput Effect’ can be subdivided into two types: 1) a specific type, following the original definition of the effect which targets species-level taxa associated with inhospitable environments, and 2) a more general type, related to the reactions of higher-rank taxa above the species-level. The body sizes of brachiopods from South China through the Ordovician and Silurian transition (Late Katian, Hirnantian, and earliest Rhuddanian) are compared at generic, superfamilial, ordinal, and class levels. The results indicate that the body sizes of the taxa of lower rank (e.g. genus-level) are highly variable within these different intervals. The type of evidence for the Lilliput Effect through the end Ordovician mass extinction is thus quite different from that of the end Permian mass extinction probably reflecting differences in the intensity of these two major bioevents. However, the relationships between the contrasting trends in body-size change of some taxa of higher rank (e.g. at the ordinal-level) and the relative dominance of these taxa in the latest Ordovician and earliest Silurian suggest that the brachiopods of the two major Ordovician groups, the strophomenoids and orthoids, adopted different survival strategies during and immediately after the crisis from those of the pentamerides and rhynchonellides, that were common in Silurian assemblages.

The Global Stratotype Section and Point (GSSP) for the base of the Silurian System was defined in 1985. Since that time, a number of researchers have suggested that this section has serious deficiencies for use as a GSSP. As a result, in 2000, the Subcommission Silurian Stratigraphy (SSS) proposed undertaking a formal restudy of this GSSP, which was subsequently approved by the International Commission of Stratigraphy (ICS). The result of this restudy was the formal proposal that the current GSSP, at 1.6 m above the base of the Birkhill Shale, at Dob's Linn, Scotland, should be maintained as the same locality and stratigraphic level, but the biostratigraphical definition of the boundary should be revised. The previously defined, basal Silurian graptolite zone, the Parakidograptus acuminatus Zone, should be subdivided into lower Akidograptus ascensus Zone and a higher P. acuminatus Zone. The base of the A. ascensus Zone, marked by the first appearance of A. Ascensus, should be regarded as the biostratigraphic mark for the base of the Silurian. The proposal has now been formally approved by the SSS and ICS, and ratified by International Union of Geological Sciences. This is the first GSSP to undergo formal restudy and redefiniton and the proposal also included a recommended procedure for restudy of GSSPs.

A moderately diverse brachiopod and trilobite assemblage, the Leangella–Dalmanitina (Songxites) Assemblage, occurs in the upper Yankou Formation (Hirnantian, probably equivalent to the Normalograptus persculptus Biozone) at Shizi Hill, Yuhang, west of Hangzhou, northern Zhejiang, E China. The brachiopods are rare, characterised by minute, thin shells with very small body cavities, preserved in mudstones as moulds. They may have inhabited quiet, deep-water and dysaerobic slope environments with low levels of nutrients, equivalent to Benthic Assemblage 5. Most genera were adapted for life in deep water and either remained there or alternatively migrated into relatively shallower habitats to evade perturbations during the first phase of the end Ordovician extinctions. The slope environments were recolonised from outer shelf and upper slope communities during the early Hirnantian, but isolated biotas may also have survived in deeper-water habitats by reducing their population size and diversity during the cri...

Late Ordovician strophomenide brachiopods (superfamilies Strophomenoidea and Plectambonitoidea) from the upper Changwu Formation (mid Ashgill, late Katian) of Jianglutang, 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.

Stegerhynchus eoborealis sp. nov. from the Dalmanitina Beds (Hirnantian, uppermost Ordovician), Borenshult, Ostergotland, Sweden, is described in this study as the earliest known species of Stegerhynchus, within the family Rhynchotrematidae. This implies that Stegerhynchus originated during the latest Ordovician mass extinction event, and radiated in the Silurian Period to become one of most common rhynchonellide brachiopod genera in shallow tropical seas. In the early evolutionary stage of the genus, Stegerhynchus eoborealis already exhibited a notable reduction in the size of septalium compared to the closely related genus Rhynchotrema. Compared to its Silurian counterparts (e.g. Stegerhynchus borealis and S. peneborealis), Stegerhynchus eoborealis has some variable characters within single populations, particularly in the number of costae in the sulcus and on the fold, implying a morphological plasticity during the early evolutionary stage of the genus. During the Hirnantian mass extinction events, five rhynchonellide families were represented by small taxonomic groups, but only the Rhynchotrematidae and Trigonirhynchiidae diversified into many highly successful clades of rhynchonellides during the Silurian and Devonian. However, the Ancistrorhynchidae, Orthorhynchulidae, and Sphenotretidae largely disappeared by the end of the Ordovician, with a few species (such as Plectothyrella sp.) surviving into the earliest Silurian but shortly becoming extinct.

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.

Lower to Middle Ordovician transitional strata (Acrograptus filiformis Biozone to Exigraptus clavus Biozone) of the Upper Yangtze Platform contain rich and diverse brachiopods, particularly in the Daguanshan Formation of Sichuan Province, the Meitan Formation of Guizhou Province, and the Yingpan Formation of Houping, Chongqing City. On the basis of multivariate analyses of 207 samples (about 15 000 brachiopod specimens) and 61 species from these strata, 23 brachiopod-dominated communities and associations are delineated through six graptolitic biozones (Acrograptusfiliformis to Exigraptus clavus biozones). The disparity of brachiopod associations or beta-diversity, as measured by the number of contemporaneous associations across variable ecological settings, was low in the A. filiformis Biozone and increased through the overlying graptolitic biozones to reach an acme in the Azygograptus suecisus and Expansograptus hirundo biozones, where as many as nine different brachiopod associations thrived in mid-shelf and also established in inner- and outer-shelf environments. Despite a sharp increase in a-diversity within the Didymograptellus eobifidus Biozone, beta-diversity remained relatively low, with only three distinct brachiopod communities. The diversity of brachiopod associations suffered an abrupt drop in the E. clavus Biozone, as a result of a major faunal turnover event, with only a single Metorthis Community present in an upper mid-shelf setting. Temporally, brachiopod associations appear to be most stable in mid-shelf settings, with the Paralenorthis, Sinorthis, Desmorthis, and Euorthisina communities having a relatively high a-diversity and lasting through two to five graptolitic biozones. In both species composition and temporal duration, the brachiopod associations at the shallow- (BA1 to upper BA2) and deep-shelf (BA4) settings are unstable, characterized by low a-diversity and rapid vertical changes. This study implies that, during the Early and Mid Ordovician, brachiopod communities already attained a high level of organization in mid-shelf settings, but remained poorly established in high-stress environments of very shallow or very deep shelf settings. Copyright (c) 2006 John Wiley & Sons, Ltd.

Earliest Rhuddanian (Silurian) brachiopods are recorded from the basal part of the Lower Llandovery Shiyang and Anji formations in western Zhejiang and northeastern Jiangxi provinces, East China. Associated graptolites including Normalograptus jerini indicate the lowest Rhuddanian Akidograptus ascensus Biozone. The surviving brachiopod fauna includes 19 genera dominated by orthids and strophomenids, whereas pentamerids and atrypids that inhabited mainly warmer water regimes, and were almost absent in the cool/cold Hirnantia Fauna, occur rarely in the studied fauna. Each family is represented by a single genus that seeded their recovery. The predominance of these long-ranging and widely distributed genera is one of major characters of the brachiopod survival in east China. From qualitative and quantitative analysis of faunal composition, diversity and abundance, with evidences from palaeoecology and palaeogeography, the Levenea qianbeiensis Association, Katastrophomena-Leptaena-Levenea Association, and Glyptorthis-Epitomyonia-Levenea Association are recognized and assigned to BA (Benthic Assemblage) 2, BA3, and an ecozone close to the BA3-4 boundary respectively. No Lazarus genera are recorded in this study. Skenidioides and Epitomyonia were chiefly regarded as deeper-water taxa in the Ordovician and Silurian, but are recorded from shallow-water in east China during the early Rhuddanian, indicating an ecologic experiment with these taxa migrating from deep into shallower, better-oxygenated sites at the crisis time and during the subsequent survival interval. This study further demonstrates that the brachiopod faunal turnover after the end-Ordovician extinctions may not have been completed until the late Rhuddanian in South China.

Global analyses of 88 families and 284 genera of brachiopods from middle Ashgill, Late Ordovician, to early–middle Rhuddanian, Early Silurian, indicate that 18.6% and 12.5% of families and 51.0% and 41.3% of genera were eliminated in the first and second phases of the end-Ordovician mass extinction, respectively, with the total loss of 28.4% of families and 69.0% of genera in the crisis. New investigation demonstrates that brachiopods, at both generic and familial levels, suffered greater during the first phase than during the second phase. Four groups (victims, relicts, survivors, and new arrivals) are distinguished by their stratigraphical ranges. Generic survivors, occurring in the Kosov Province during the Hirnantian, can be split into three types with respect to their changing abundance: increasing, declining, and Lazarus taxa. Among the 88 genera that survived, numerous declining genera occurred in the Hirnantian: 16 Lazarus families and 18 Lazarus genera are provisionally known and may be regarded as end members of the declining type. Comparison of the abundance, population size, and distribution patterns of declining and Lazarus taxa shows important similarities between these two types which contribute to a better understanding of the nature of Lazarus taxa. In addition to these biological attributes, taphonomic failure and generally poor preservation, together with collecting bias and inadequate systematic data, are clearly involved. More collections will undoubtedly globally reduce the number of Lazarus taxa. A single, common refugium for end-Ordovician brachiopods probably did not exist; rather, these taxa used paleogeographically scattered locations in a range of environments for survival.

Affected by paleogeographic position, paleoclimatic condition and depositional environments, the increase of the Early-Mid Ordovician brachiopod diversity of South China commenced at the beginning of the Ordovician (early Tremadoc), accelerated from the Tetragraptus approximatus Biozone (base of Arenig), and reached its first acme in the Didymograptus eobifidus Biozone (mid early Arenig) when the number of brachiopod genera was over 7 times as great as that at the start of the Ordovician. This was the first radiation in the history of brachiopod macroevolution in South China, which occurred nearly 5 graptolitic biozones earlier than the global trend of the great Ordovician biodiversification (in the lower part of the Undulograptus austrodentatus Biozone). It is also characterized by (1) the origination or first occurrences of some major groups, such as the punctate dalmanelloids and the pseudopunctate strophomenoids including Plectambonitoidea (cardinal process simple or absent) and Strophomenoidea (cardinal process bilobed) in South China; (2) niche expansion, particularly in the first occupation of deeper water benthic regimes by the Euorthisina-Nocturnellia Association developed at Houping, Chengkou, northern Chongqing; and (3) the differentiation of brachiopod faunas under different environmental conditions. The gradual and increasing separation from Gondwana may have been one of the factors responsible for the radiation in South China.

Holorhynchus giganteus Kiaer, 1902, a common Late Ordovician (mid-Ashgill) pentameride brachiopod in the Baltic region, Kazakhstan, and southern Tien Shan, is documented for the first time from the Badanjilin Formation (mid-Ashgill) of western Inner Mongolia (Alxa block), North China. Serial sections of the Chinese material confirm the presence of a vestigial ventral median septum in the early growth stage of H. giganteus, but the septum becomes embedded in the secondary shell thickening at the adult growth stage. A survey of the type material from Norway and additional material from other regions indicates that the incipient ventral median septum is a much more commonly developed structure than was previously believed. The presence of a well-developed pseudodeltidium in the Tien Shan material of H. giganteus and the absence of such a structure in conspecific material from many other regions require a systematic revision of the generic group. Holorhynchus has rodlike crura (=brachial processes) t...

Here we present Sr, C, and O isotope curves for Ordovician marine calcite based on analyses of 206 calcitic brachiopods from 10 localities worldwide. These are the first Ordovician-wide isotope curves that can be placed within the newly emerging global biostratigraphic framework. A total of 182 brachiopods were selected for C and O isotope analysis, and 122 were selected for Sr isotope analysis. Seawater 87Sr/86Sr decreased from 0.7090 to 0.7078 during the Ordovician, with a major, quite rapid fall around the Middle–Late Ordovician transition, most probably caused by a combination of low continental erosion rates and increased submarine hydrothermal exchange rates. Mean δ18O values increase from −10‰ to −3‰ through the Ordovician with an additional short-lived increase of 2 to 3‰ during the latest Ordovician due to glaciation. Although diagenetic alteration may have lowered δ18O in some samples, particularly those from the Lower Ordovician, maximum δ18O values, which are less likely to be altered, increase by more than 3‰ through the Ordovician in both our data and literature data. We consider that this long-term rise in calcite δ18O records the effect of decreasing tropical seawater temperatures across the Middle–Late Ordovician transition superimposed on seawater δ18O that was steadily increasing from ≤−3‰ standard mean ocean water (SMOW). By contrast, δ13C variation seems to have been relatively modest during most of the Ordovician with the exception of the globally documented, but short-lived, latest Ordovician δ13C excursion up to +7‰. Nevertheless, an underlying trend in mean δ13C can be discerned, changing from moderately negative values in the Early Ordovician to moderately positive values by the latest Ordovician. These new isotopic data confirm a major reorganization of ocean chemistry and the surface environment around 465 to 455 Ma. The juxtaposition of the greatest recorded swings in Phanerozoic seawater 87Sr/86Sr and δ18O at the same time as one of the largest marine transgressions in Phanerozoic Earth history suggests a causal link between tectonic and climatic change, and emphasizes an endogenic control on the O isotope budget during the Early Paleozoic. Better isotopic and biostratigraphic constraints are still required if we are to understand the true significance of these changes. We recommend that future work on Ordovician isotope stratigraphy focus on this outstanding Middle–Late Ordovician event.

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.

The Central Guizhou and Yichang Uplifts are present in central Guizhou to western Hubei. Biostratigraphic evidences from more than 20 sections in 14 counties of this region provide the data about the duration of these uplifts. Although this duration differs from locality to locality, it is mainly from Ashgillian to Rhuddanian. The uplifts result from a horizontally driven movement to the South China Paleoplate from an uncertain block in southeast. Global sea-level drop during the end of the Ordovician made the uplifts obvious, particularly the Central Guizhou Uplift. It might have emerged above sea level in the short interval between the Ordovician and Silurian.

Recent field studies on Upper Silurian stratigraphy and paleontology in the Inner Mongolia Autonomous Region (for short Inner Mongalia) near Bater Obo (=Bateaobao) resulted in the discovery of a small continental island with fossil invertebrates preserved as encrusters (stromatoporoids and corals) attached directly to a rocky shore surface and buried by silty clay mud. The Bater island (oamed herein) is 610 m × 200 m in size and composed of Ordovician igneous rock (diorite). Limestone strata dating from the Ludlow Epoch (about 420 Ma) surround the island and dip away from the igneous core in a radial pattern. The encrusting fossils occur on the sheltered (south and southeast) side of the island, whereas the north side was exposed to stronger wave activity based on a basal conglomerate unit composed of diorite boulders. This is the first record of an ancient island in China and the first report worldwide of stromatoporoids as members of a rocky-shore community. The island clearly shows distinct windward and leeward deposits comparable to geologically younger islands from the Mesozoic and Cenozoic outside China.