The late Early to early Middle Ordovician is a key interval for chitinozoan macroevolution, during which chitinozoans diversified significantly, reaching their first enormous radiation later in the Darriwilian. The South China palaeoplate is one of the classical regions for Ordovician palaeontological research; however, published chitinozoan data for this interval remain insufficient. This study presents new data from the Gudongkou section, western Yichang, western Hubei Province, in the central part of the South China palaeoplate. A total of 13 genera and 31 species are recognised, including three new species: Conochitina clavatus sp. nov., Conochitina tenellensis sp. nov., and Lagenochitina yangtzensis sp. nov. Systematical remarks on some taxa are provided, including Conochitina decipiens, C. ordinaria, and the group of Sagenachitina oblonga, S. striata, S. dapingensis, and Cyathochitina? dispar. Network analysis is applied based on the data from the Dawan Formation and its contemporaneous units on the Yangtze Platform to test whether chitinozoan assemblages vary among different lithological units that represent different palaeoenvironments. The result shows that chitinozoan assemblages may have palaeogeographical significance. The chitinozoan assemblage from the Dawan Formation at the Gudongkou section seems to be a more independent community compared with those from the Meitan and Zitai formations. However, shared taxa, including the zonal species Bursachitina maotaiensis and Sagenachitina dapingensis, and some other widely distributed, characteristic taxa, such as C. decipiens and C. poumoti, are well-preserved in almost all sections. The biostratigraphical significance of the Dawan chitinozoans, discussed herein, indicates an age ranging from the latest Floian to the earliest Darriwilian, consistent with prior understanding of this formation.

A diverse shallow-water shelly fauna, dominated by brachiopods, gastropods, corals, and stromatoporoids, was recovered from the carbonate-rich Koumenzi Formation (Katian, Upper Ordovician) in the Qilian Mountains, Northwest China. From this assemblage, 100 bellerophontoid gastropod specimens were systematically identified as four genera (Sinuites?, Qilianodiscus n. gen., Pterotheca, and Cymbularia) and two new species (Qilianodiscus qilianensis n. sp. and Cymbularia sinensis n. sp.). Among these, the new genus Qilianodiscus is established based on its distinctive lenticular, thick-shelled morphology with a nearly closed umbilicus and reflected aperture. The wellpreserved shells, found together with abundant brachiopods and bivalves retaining conjoined valves, indicate in-situ preservation, providing valuable information for paleoecological reconstruction. Functional morphology analysis indicates that features such as aperture thickening and lateral expansion served as adaptations to soft substrates and for maintaining balance in high-energy settings. The diverse filter-feeding community and carbonate microfacies indicate a nutrient-rich, shallow marine environment with abundant green algae. Furthermore, the study establishes a spatial and ecological association between these shell-rich deposits and adjacent reef buildups. These reef structures acted as physical buffers that reduced disturbance on the benthic habitat. (c) 2026 Nanjing Institute of Geology and Palaeontology. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The North Qilian Mountains region is an important component of the Proto-Tethys Archipelagic Palaeocean. The Koumenzi Formation (Katian, Upper Ordovician) in the region yields a significant number of Ordovician fossils, of which cephalopods have rarely been systematically studied and recorded. Herein, a moderately preserved cephalopod collection from the Koumenzi Formation is presented from the North Qilian Mountains, Qilian Orogenic Belt. This fossil assemblage, obtained from the section near the upper reaches of the Tianbao River, Qilian County, Qinghai Province, consists of Anaspyroceras sp., Geisonocerina? sp., Paradnatoceras nyalamense, as well as some unnamed oncoceratoid and orthoceratoid cephalopods. Furthermore, quantitative palaeoecological analyses based on global occurrences, uncover notable provincialism of Katian cephalopods. Two cephalopod provinces related to palaeolatitude are recognised by cluster analysis and weighted network analysis. Global oceanic currents might have been responsible for the pattern of the (c) 2025 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Trabeculate heliolitids characterised by well-developed trabecular coenenchyme are an important component of Late Ordovician ulate corals. To better understand their distribution and faunal composition in North Qilian Mountains, we systematically evaluate previously poorly known records of this heliolitid group from the Koumenzi Formation in Menyuan and Qilian areas, northeastern Qinghai, Northwest China, based on both described and new fossil material. The fauna includes the plasmoporellids Plasmoporella chinghueiensis, P. sp., P.? sp., and Leleshusia spinosa, and the sibiriolitid Mongoliolites contiguus, indicating a middle Katian age the Koumenzi Formation. Faunal comparison reveals its closest biogeographic affinities with Kazakhstan and Australia. (c) 2026 Nanjing Institute of Geology and Palaeontology. Published by Elsevier B.V. All rights are reserved, including those for text and mining, AI training, and similar technologies.

A deformed carbonate succession traditionally designated the "Great Limestone Series" at Cheongpung (Jecheon, central Okcheon Belt, Korea) lies along the western margin of the Taebaeksan Complex, where intense deformation and limited fossils have long hindered reliable stratigraphic correlation and age determination. Here we present integrated conodont and brachiopod evidence from thin micritic limestone beds of the Danri Limestone interval (the Gomyeongri Formation in previous stratigraphic usage). Conodonts include Rossodus tenuis (Miller, 1980) and Teridontus sp., indicating a Tremadocian (Early Ordovician) age for the fossil-bearing horizon. The same beds yield abundant silicified billingsellide brachiopods assigned to Tritoechia cheongpungensis n. sp., which is closely comparable to the Early Ordovician Tritoechia faunas reported from North and South China. This study provides the first reliable age data for the Danri Limestone, enabling improved correlation of the western-margin Joseon Supergroup with well-studied Lower Ordovician successions in Korea and adjacent regions. It further establishes a temporal framework for evaluating Early Palaeozoic carbonate-platform develop (c) 2026 Nanjing Institute of Geology and Palaeontology. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Stromatoporoid faunas in the peri-Gondwanan regions during the Katian of the Late Ordovician exhibit a greater diversity of taxa compared with those from other contemporaneous continents and terranes. Geographical separation due to the numerous microplates comprising peri-Gondwana was a potential driver of this high diversity, but stromatoporoid faunas in many of these microplates have not been studied in detail because of their remote present-day locations. In this study, we report 12 genera and 16 species of stromatoporoids from the Upper Ordovician (Katian) Koumenzi Formation, exposed in the upper reaches of the Tianbao River, Qilian County, Qinghai Province, Northwest China, representing a unique occurrence in the North Qilian Mountains. This fauna includes Cystostroma inconstans Jeon n. sp., Pseudostylodictyon poshanense Ozaki, 1938, Labechia conglomerata Dong and Wang, 1984, Labechia shanhsiensis Yabe and Sugiyama, 1930 (Yabe and Sugiyama, 1930a), Labechia sp., Labechiella gondwanense Jeon in Jeon et al., 2022a, Radiostroma astroqilianus Jeon and Zhan n. sp., Aulacera arbuscula Jeon n. sp., Sinabeatricea crassicentra Jeon n. sp., Lophiostroma leptolamellatum Jeon n. sp., Clathrodictyon idense Webby and Banks, 1976, Clathrodictyon sp. cf. Cl. mammillatum (Schmidt, 1858), Ecclimadictyon tiewadianensis (Jiang et al., 2011), Ecclimadictyon nestori Webby, 1969, Plexodictyon qilianense Jeon n. sp., and Simplexodictyon uniplexum Jeon n. sp. In comparison with other peri-Gondwana regions and other adjacent areas, this fauna consists of a relatively high proportion of endemic taxa and some pandemic taxa, with species-level affinities most closely linking the North Qilian Mountains to North China, and to a lesser extent, South China. The occurrence of genera such as Radiostroma, Plexodictyon, and Simplexodictyon, previously restricted to Baltica and North China extends their known palaeogeographical ranges. The stromatoporoid assemblage of the North Qilian Mountains represents a transitional fauna between the Ordovician and Silurian, characterised by persistent labechiid dominance alongside the appearance of clathrodictyids and stromatoporellids, and the presence of both long-ranging Ordovician taxa and morphologically advanced genera, reflecting diversification trends also seen in the contemporaneous North China assemblage. Relatively high endemism of this stromatoporoid fauna is attributed to the island arc volcanic setting during the Late Ordovician, emphasizing the role of island arc setting in stromatoporoid diversification during the Ordovician. (c) 2025 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

A bivalve association reported herein was recently discovered from the Xiazhen Formation (upper Katian, Upper Ordovician) at Zhuzhai, southern Yushan County, northeastern Jiangxi Province, East China. Nine genera and ten species are systematically documented including four new species: Palaeoneilo rectus sp. nov. (most abundant), Palaeoneilo cf. constricta, Goniophorina volvens, Modiolopsis elegantulus, Cyrtodontula sp., Cuneamya? sp., Trigonoconcha brevis sp. nov., Similodonta minor sp. nov., Concavodonta varius sp. nov., and Paulinea cf. parva. The association is mainly composed of Protobranchia (Nuculiformii and Nuculaniformii) and subordinate Pteriomorphia, suggesting a relatively low palaeolatitudinal setting. The dominance of infaunal protobranch bivalves is notable, and against the trend of rapid diversification of pteriomorphs during the Late Ordovician. This discrepancy is likely attributable to a cold water tongue extending from then South Pole to South China palaeoplate, and the ecological pressure from those much more abundant brachiopods on the substrate surface, both hindering the development of epifaunal pteriomorphs in the region. Significantly, this bivalve association shares several common genera with its coeval bivalve fauna from the Oslo region, Norway.

A new bivalve association is reported from the Koumenzi Formation (middle-upper Katian, Upper Ordovician) of the upper reaches of Tianbao River, Ebao Town, Qilian County, northeastern Qinghai Province, Northwest China. It comprises 11 species of eight genera including one new species and two indeterminate taxa: Fidera flexa n. sp., Trigonoconcha brevis, Praenucula bohemica, P. cf. applanans, Praeleda compar, Palaeoneilo sp., Colpomya cf. hugini, ?Callodonta sp., Modiolopsis cuyana, Pterineidae gen. et sp. indet. 1, and Pterineidae gen. et sp. indet. 2. This assemblage is formally designated as the Fidera flexa association, named after its most abundant taxon. It is mainly composed of protobranch bivalves (Nuculiformii and Nuculaniformii) together with a few pteriomorph bivalves, indicating a low palaeolatitudinal setting. The prevalence of the protobranch bivalves could have been influenced by a cold-water tongue then, which is known to have affected the distribution of other Ordovician organisms, such as trilobites, cephalopods, and brachiopods. The excellent preservation of these body fossils makes them valuable for future studies on shell microstructure and Ordovician bivalve phylogeny. (c) 2026 Nanjing Institute of Geology and Palaeontology. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The recovery of trilobites following the Late Ordovician Mass Extinction (LOME) was previously considered to have commenced in the late Rhuddanian, whereas new evidence indicates an earlier starting point. The spatiotemporal distribution of trilobites after the second episode of LOME during the late Hirnantian–Rhuddanian is reviewed based on a new dataset compiled from 10 paleoplates and terranes. Within a high-resolution biostratigraphic framework, these trilobite faunas are analyzed using numerical methods (including CA, NA, NMDS, and PCoA) to investigate their recovery and biogeographic patterns after the LOME. Two evolutionary trilobite faunas, the Ordovician-type and the Silurian-type, are recognized for two macroevolutionary phases, i.e., the survival phase (Hirnantian) and the recovery phase (late Hirnantian–Rhuddanian) respectively. The former one is represented by the Mucronaspis fauna, while the latter includes the Acernaspis, the Sinoencrinurus/Pepodes, and the Trimerus faunas. Their distribution was primarily influenced by environmental factors, such as water depth, substrate, latitude, and geographic position. Trilobites began to recover immediately following the second episode of the Hirnantian crisis, approximately 1.4 Myr earlier than previously thought. Their recovery showed a heterochronous pattern, characterized by dual centers of origin in shallow-water habitats and subsequent expansion into deeper-water environments. The spread of recovery trilobites was mainly limited by widely anoxic environments. The rapid post-LOME recovery of trilobites resulted from multiple interconnected factors. Vacant niches formed from the extinction, followed by rapid recolonization and differentiation of shallow-water habitats, provided ecospaces for adaptive radiation and reduced interspecific competition. The evolutionary potential of certain trilobites provided the capacity for their rapid recovery, while the geographic isolation accelerated such process. Biogeographically, three trilobite provinces (the Mucronaspis, the Acernaspis, and the Sinoencrinurus/Pepodes provinces) are identified for the interval of late Hirnantian–Rhuddanian, with their differences mainly controlled by macroevolutionary process and geographic isolation.

The Late Ordovician mass extinction (LOME) caused an intense global biotic turnover. In South China, the Edgewood-Cathay (EC) Fauna replaced the cool-water Hirnantia Fauna. An important representative of the EC Fauna was mainly reported from southeastern China. Based on 1224 brachiopod specimens from the Wulipo Bed (upper Hirnantian–lower Rhuddanian) in Meitan County, northern Guizhou, Southwest China, this study documents the first rich EC Fauna from this region of the South China plate. It includes 13 genera, with Eospirigerina, Hindella, and Cathaysiorthis as its dominant constituents, and represents one of the earliest known post-LOME recovery benthic communities developed during the transition from the survival to the early recovery interval. Palaeoecological analysis shows a deepening upward trend from the Eospirigerina–Hindella association (BA2) to the Eospirigerina–Cathaysiorthis association (BA3). This provides ecological evidence for a sea-level rise caused by global warming after the second pulse of the LOME. Comparison shows that the brachiopod fauna in northern Guizhou is very similar to that of eastern China and may represent an earlier recovery stage than the EC Fauna in Xichuan, Henan Province, Central China. This finding extends the known palaeogeographical range of the fauna and provides key information for understanding the earliest recovery and palaeoenvironmental background after the LOME. Additionally, the Shiqian Formation and Weiba Formation are herein synonymized as junior synonyms of the Wulipo Bed.

Twenty-one trilobite species belonging to 16 genera and subgenera, 11 families and seven orders are systematically documented from the uppermost Ordovician and the lowermost Silurian strata (upper Hirnantian-Rhuddanian) at three sections in north-eastern Yunnan and northern Guizhou provinces, south-west China. Together with those trilobites previously reported from the Yanping section of northern Guizhou, these trilobites constitute the earliest known recovery trilobite faunas in South China after the Late Ordovician mass extinction (LOME) and are characterized by the Silurian-type Sinoencrinurus gen. nov. and Ciliscutellum faunas. Two new genera (Sinoencrinurus gen. nov. and Yunnanoproetus gen. nov.) and four new species (Ciliscutellum rhaxerosides sp. nov., Meadowtownella yunnanensis sp. nov., Batocara tuberosus sp. nov. and Yunnanoproetus shanshuensis gen. et sp. nov.) are described. The monophyly of Sinoencrinurus gen. nov. is well supported by the results of phylogenetic analysis, and it may form a sister group to Coronocephalus. Two genera, Meadowtownella and Batocara, have their first records in South China. Supported by evidence from faunal composition, lithology and numerical analyses, six trilobite associations are recognized along environmental gradients from nearshore to inner shelf. These associations had prominent ecological differentiation and strong endemicity to South China. Their ecological differences and distribution were mainly controlled by oxygen levels, depth gradients and substrate conditions. The mode of life and environmental tolerance of different trilobite taxa may also be part of the controlling factors. https://zoobank.org/urn:lsid:zoobank.org:pub:8B5C65ED-9523-4ACD-ABD4-86EE01127975

A centre of radiation for Ordovician bivalves is identified based on an abundant and diverse fauna from the Hsiangyang Formation (Darriwilian, Middle Ordovician) of Dali, western Yunnan, Southwest China. It consists of 22 species of 18 genera including 1) one new genus and four new species: Rhomboconcha tresdentes n. gen. n. sp., Fasciculodonta curvata n. sp., Glyptarca symmetrica n. sp., and Paracyclas initium n. sp.; 2) three taxa known from elsewhere but initially found in Dali: Praeleda sp., Glyptarca sp., and Redonia deshayesi; 3) other taxa previously reported by Fang and Cope (2004). Numerical analysis of the distribution of 11 Middle Ordovician bivalve faunas from different regions shows two distinct faunal groups, the HPL group, representing the bivalves that lived in higher palaeolatitudes, and the LPL group (including Australia and South China) in lower palaeolatitudes. The bivalve fauna from Dali correlates with both groups, indicating that the Indochina Palaeoplate was located between these two groups, and in middle-high palaeolatitudes. Thus, the Indochina Palaeoplate was probably an isolated centre for bivalve radiation during the Middle Ordovician; those genera confined to Dali did not then spread to other palaeoplates. (c) 2024 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

During the Late Ordovician, a series of significant biotic and geological events occurred globally and more specifically in South China. The development of a high-resolution orbital cyclostratigraphic framework and a precise radioisotope dating has greatly enhanced our understanding of the factors controlling these events. In this study, quantitative proxies for palaeo-water depths, derived from sedimentological analyses, serve as indicators for orbital cyclostratigraphic assessment. Relatively shallow-marine carbonates with well-developed shallowing-upward cycles were deposited in the western Yangtze Platform during the Late Ordovician. High-resolution geochronological data were obtained from high-precision isotope dilution thermal ionization mass spectrometry (ID-TIMS) zircon dating of K-bentonite beds at the studied section. This facilitated sedimentary facies and environmental analyses, as well as the recognition of sedimentary cycles. Based on mud content, bioclastic content, and laminations, four sedimentary facies, twelve sedimentary microfacies, and forty-eight shallowing-upward sedimentary cycles were identified in the Daduhe Formation. Through comparative time series analysis of depth rank, lime mudstone-calcareous mudstone binary data, non-carbonate content, and anhysteretic remanent magnetization (ARM), astronomical cycles and trends in sedimentation rates have been identified. This study confirms the reliability of radioisotope dating, establishing a 0.46 Myr duration for the Dicellograptus complexus graptolite biozone and a 0.96 Myr duration for the Paraorthograptus pacificus graptolite biozone, both with an empirical uncertainty of 0.1 Myr. This research proposes a reliable method for identifying astronomical cycles through high-precision sedimentary microfacies and cyclostratigraphy, in comparison with rock magnetic cyclostratigraphy studies. (c) 2024 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The Lhasa terrane, once part of Gondwana until the Permian/Triassic, rifted away and accreted to Eurasia, forming a core part of the Tibetan Plateau. Pinpointing its palaeogeographical position is essential for understanding both the reconstruction of Gondwana and the plateau's evolution. However, considerable controversy persists over its exact position before separation, with geochemical and isotopic data suggesting ties to Australian, Indian or African sections of eastern Gondwana. Here, we use newly acquired, palaeobiogeographically sensitive fossils from the Baingoin area of central Tibet to determine the terrane's affinities. This late Darriwilian-Sandbian (Middle-Late Ordovician, ca. 457-453 Ma) biota lay along a palaeolatitudinally differentiated biotic gradient, indicative of a distinctly closer palaeobiogeographical affinity to northeastern India than to Australia or Africa. This finding, confirmed by a critical review of existing fossil and geochemical data, strongly supports a northeastern Indian origin of the Lhasa terrane.

Cool-water settings characterize Ordovician occurrences of Phanerozoic ooidal ironstones (POIs), contrasting sharply with the warm and humid climate typical of other POIs. This geological puzzle was deciphered in this study based on a complex suite of Middle-Late Ordovician POIs in South China hosted in tropical sediments of a warm-water origin, and coeval ferruginous ooid-bearing sediments and ferruginous microbialites that accumulated in a relatively cool-water setting. Here, we demonstrate that, despite their different depositional settings, all Ordovician ferruginous deposits of South China share similar petrographic ultrastructures and delta 56Fe isotopic signatures. This suggests that the formation of POIs was not likely controlled by water temperature but instead is attributable to a microbial iron factory, associated with active upwelling generated from frequent cool-water incursions from Gondwana. This model also explains the predominant occurrence of Ordovician ferruginous deposits in cool-water realms in peri-Gondwana. The Darriwilian peak of their abundance corresponds to the onset of an icehouse episode and a paleotropical cold-water tongue that created complex depositional environments across the South China plate.

The Late Ordovician mass extinction (LOME) included two phases (I and II) of high species turnover that have been hypothetically linked to the Hirnantian glaciation and subsequent rapid warming, respectively. However, the timing and tempo of the LOME remain uncertain, which hinders our understanding of the feedback between the LOME and paleoclimatic change. Here, we present high-precision radioisotopic dates for the Ordovician-Silurian transition in South China that reveal the LOME began at 442.76 + 0.35/−0.22 million years ago, with the two phases lasting for 0.34 + 0.46/−0.34 and 0.06 + 0.31/−0.06 million years, respectively. The rapid switch from icehouse to greenhouse conditions, along with the higher mean rate of temperature change during LOME II, resulted in a much higher mean extinction rate during LOME II than I (71.6% versus 8.4% species loss per 100 thousand years, respectively), implying that the rate of climate change was a primary control on the tempo of the LOME.

The first set of Silurian marine red beds(FSRB) in South China exhibits distinct identification markers and spatial distribution. The origin of these red beds is intricately linked to the regional and global tectonic, paleo-oceanic, and paleoclimatic evolutionary processes. However, the scarcity of key fossils and the endemic characteristics of discovered taxa have posed challenges to intercontinental correlation and have led to divergent opinions regarding their age assignment, thereby impeding further in-depth research. Drawing upon fossil evidence from graptolites, conodonts, chitinozoans, brachiopods, and trilobites,this study comprehensively analyzes the age of the FSRB formed under varying paleogeographic conditions in South China. The findings reveal that the FSRB generally situated within the middle Aeronian to lower Telychian, Llandovery(ca. 436–439 Ma),corresponding to the graptolite Lituigraptus convolutus Biozone(LM7), the Stimuloraptus sedgwickii Biozone(LM8), the Spirograptus guerichi Biozone(LM9), and the S. turriculatus Biozone(LM10). A notable diachronous pattern is observed for the base of the FSRB, becoming younger from east to west and from south to north. Specifically, the FSRB first emerged along the south margin of the Dabie Oldland during the middle Aeronian. Subsequently, they appeared progressively in the MiddleLower Yangtze/Jiangnan district during late Aeronian and in the Upper Yangtze region near the Aeronian/Telychian boundary.Finally, they occurred around the Chuanzhong Oldland during early Telychian. While the top boundary of the FSRB varies at different localities, it consistently lies below the middle Telychian strata containing the Xiushan Fauna. In the context of global oceanic oxidation in tropic seas, the dynamic spatiotemporal distribution of the FSRB in South China reflects a gradual retreat of anoxic and semi-anoxic waters from shallow seas towards the open ocean, replaced by oxygenated waters over a period of approximately 3 million years across the Aeronian/Telychian boundary. This process is closely associated with the continuous and rapid uplift of the seabed triggered by the northwestward expansion of the Cathaysian Oldland during the Kwangsian Orogeny.

A shallow-water trilobite fauna, with low diversity (seven species of six genera), from the Koumenzi Formation (Katian) in the Qilian area, northeastern Qinghai Province, Northwest China, is recognised as the Pliomerina Association. Of these, Dulanaspis and Amphilichas are reported for the first time in the North Qilian Mountains. The shallow-water Pliomerina and relatively deep-water BirmanitesSinocybele associations were found to occur in the Qilian and Menyuan areas, respectively, during the Katian. They exhibit a distinctive ecological differentiation with water depth from inner shelf to outer shelf environments. The Pliomerina Association of the Qilian area clearly belongs to the Pliomerina and/or Sinocybele Province of the Proto-Tethys Archipelagic Ocean. Faunal evidence indicates that the palaeogeographical position of the North Qilian Mountains area was situated closer to the Kazakh terranes during the Katian, particularly to the Chu-Ili and Chingiz-Tarbagatai terranes. (c) 2025 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.