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The diversification of Palaeozoic stromatoporoid sponges was interrupted by the Late Ordovician glaciation, which caused the first of the five major extinctions during the Phanerozoic. Glaciation and the subsequent expansion of anoxia during deglaciation are interpreted to have resulted in a persistent scarcity of stromatoporoids during the Hirnantian. Previously, Hirnantian stromatoporoids were only known from two regions: Estonia in Baltica and Anticosti Island in eastern Laurentia. Here we report stromatoporoids from the upper Hirnantian Shiqian Formation of South China, adding to the rare fossil record of Hirnantian stromatoporoids. Three new stromatoporoid taxa are identified: Ecclimadictyon ancipitum Jeon sp. nov., Camptodictyon contortus Jeon & Kershaw sp. nov., and Cystostroma rallus Jeon sp. nov. The appearance of these stromatoporoids in South China is stratigraphically later than solitary rugose corals, but coincides with tabulate corals in the aftermath of the end-Ordovician mass extinction. Compared to the wider palaeogeographical and environmental distributions of rugose and tabulate corals during the Hirnantian, stromatoporoids presumably had a narrower environmental tolerance. The stromatoporoid assemblage in South China during the Hirnantian is dominated by clathrodictyids, which exhibit similar faunal patterns to those found in Baltica and Laurentia during the same period. The rise of clathrodictyid-dominated assemblages began in the middle to late Katian of the Late Ordovician, particularly in peri-Gondwanan regions, and rapidly expanded worldwide during the subsequent Hirnantian and Silurian onwards. The Late Ordovician glaciation significantly hastened the global Ordovician–Silurian stromatoporoid transition, as evidenced by the disappearance of numerous labechiid-type stromatoporoids and the expansion of clathrodictyid-type stromatoporoids in the Hirnantian and the subsequent Silurian. [ABSTRACT FROM AUTHOR]

A new non-mineralised fauna was recently discovered in the Lower Ordovician Madaoyu Formation near Liexi Township, West Hunan Province, South China. Diverse animals are preserved in a thin layer of siltstone interbedded within the limestone. The most peculiar group among this new Fauna is a large quantity of palaeoscolecidan worms with multiple instars, which are only represented by trunks without any other soft tissues such as the introvert, pharynx, and intestine being preserved. The unique characteristic of these worms are that they have a dorsal-ventral differentiation of plates, which are arranged in longitudinal lines, this suggests that the worms probably were exquisite bottom crawlers. The palaeoscolecidans are uniform in morphology and attributed to a new genus and species, Liexiscolex hunanensis Liu & Huang, gen. et sp. nov. This discovery not only enriches our knowledge of the anatomy and palaeoecology but also helps us understand the evolution of palaeoscolecidan worms. Furthermore, it provides a better comprehension of the Lower Ordovician Liexi fauna in South China. [ABSTRACT FROM AUTHOR]

A study in Simeh-Kuh, northern Iran, focuses on Ordovician strata, documenting acritarchs and chitinozoa, and has helped to understand ancient environments. The aim is chronostratigraphical calibration, using palaeontological data including brachiopods, trilobites, and graptolites. Ninety-three surface samples were collected and analysed, yielding a rich collection of 117 morphotypes, including 59 acritarch species and 58 chitinozoan species. Eight acritarch assemblage biozones (A–H) and 14 chitinozoan biozones (1–14) were established. Biozones A–F indicate Late Cambrian to Middle Ordovician ages in the Lashkarak Formation, while biozones G–H indicate the Late Ordovician in the Ghelli Formation. The Eremochitina brevis-Linochitina pissotensis biozones suggest late Floian to late Darriwilian ages, and the Belonechitina robusta-Armoricochitina nigerica biozones support a Late Ordovician age. These findings place the Alborz Mountains in the North Gondwana Domain during the Ordovician. Palynomorphs with a thermal alteration index of 4.0–4.5 indicate overmature organic matter in Lower Palaeozoic deposits, potentially linked to the Ordovician metamorphic event in the southern Caspian Sea. Additionally, four new species were identified: Cyathochitina sp. A, Tanuchitina hosseini-nezhadi sp. nov., Dactylofusa kazzazii sp. nov., and Inflatarium alborzensis sp. nov. Highlights: A palynological study at Simeh-Kuh in the Alborz Mountains, northern Iran has uncovered a richly preserved assortment of Cambrian–Ordovician acritarchs and chitinozoa. Fifty-eight chitinozoan species, spanning 22 genera, were identified from the Lashkarak and Ghelli formations at Simeh-Kuh. This facilitated the delineation of 14 distinct chitinozoan biozones. Fifty-nine acritarch species across 33 genera were identified from the Late Cambrian to Late Ordovician strata, contributing to recognising eight distinct assemblage biozones. The Lashkarak Formation has yielded four distinctive acritarch genera: Arbusculidium, Coryphidium, Striatotheca, and Arkonia. These genera hold notable significance as they are characteristic elements of the Peri-Gondwanan palaeoprovince. The identification of chitinozoans in the Lashkarak and Ghelli formations has facilitated the establishment of 14 chitinozoan biozones. Notably, these biozones are considered classical elements of the Northern Gondwana Domain/Peri-Gondwana palaeoprovince. The Belonechitina robusta, Tanuchitina fistulosa, Acanthochitina barbata, and Armoricochitina nigerica biozones were recognised in the Ordovician deposits at Simeh-Kuh. This discovery marks the region's first confirmation of Sandbian–Katian strata. A significant hiatus exists between the Ghelli and Geirud formations, spanning the Late Ordovician (latest Katian–Hirnantian), Silurian, and Early–Middle Devonian periods. Four new species have been established: Cyathochitina sp. A, Tanuchitina hosseini-nezhadi sp. nov., Dactylofusa kazzazii sp. nov., and Inflatarium alborzensis sp. nov. [ABSTRACT FROM AUTHOR]

Caryocaridids exhibited a wide geographical distribution and high diversity during the Great Ordovician Biodiversification Event. The global geographical distribution, limited taxonomic examination and lack of insight into preservational conditions have collectively contributed to an inadequate systematic assessment of Ordovician caryocaridids. To address this situation, we re-examined Ordovician caryocaridid specimens from Australia and New Zealand. Considering these findings, we establish Rhinopterocaris fordycei sp. nov. This new species is characterized by the presence of a well-developed anterior carapace horn, a rounded, truncated posteroventral margin, and furcal rami that lack triangular expansion and spines. In doing so, we confirm the validity of Rhinopterocaris. We reclassify specimens of Lingulocaris maccoyi Etheridge, 1892 into Rhinopterocaris maccoyi (Etheridge, 1892) and highlight that specimens previously reported as Rhinopterocaris maccoyi belong in Jellicaris stewarti. A phylogenetic analysis of 44 Paleozoic phyllocarids reveals that Rhinopterocaris is basal within caryocaridids and is a sister group to younger caryocaridids. Finally, we present a hypothetical evolutionary lineage of caryocaridids and explore the evolutionary history of the group. [ABSTRACT FROM AUTHOR]

The West Kunlun Orogenic Belt (WKOB) in the northwestern Tibetan Plateau records key information about the tectonic evolution of the Proto-Tethys Ocean. To further constrain the Early Palaeozoic tectonic evolution of the WKOB, we report petrography, geochronology, whole-rock geochemistry, and Sr-Nd-Hf-O isotope data of the newly identified Ordovician Nanpingxueshan gabbros in the southern WKOB. Laser ablation-inductively coupled plasma-mass spectroscopy (LA-MC-ICP-MS) U-Pb zircon dating reveals that the gabbroic intrusion was emplaced during 476–471 Ma. Geochemically, the gabbroic rocks exhibit a tholeiitic signature and can be subdivided into two groups, i.e. normal arc-like gabbros (AGs) and Nb-enriched gabbros (NEGs). The AGs have TiO2 (1.20–1.64%), P2O5 (0.18–0.25%), and Nb (4.60–7.64 ppm) contents, fractionated REE patterns ((La/Yb)N = 2.64–4.11), and Nb-Ta depletion (Nb/La = 0.37–0.50). Compared with AGs, the NEGs have higher TiO2 (1.74–2.68%), P2O5 (0.34–0.55%), and Nb (10.79–14.08 ppm) contents and Nb/La ratios of 0.45–0.53, which are similar to typical Nb-enriched arc basalts. Isotopically, the AGs have depleted whole-rock εNd(t) values of 3.22 to 4.04 and negative to positive zircon εHf(t) values of −1.8 to 7.8, while the NEGs exhibit slightly lower whole-rock εNd(t) values of 0.69 to 3.18, zircon εHf(t) values of −7.8 to 4.6, and mostly δ18O values greater than those of normal mantle zircon. Integrated analyses reveal that the AGs and NEGs can be attributed to a similar mantle source metasomatized by different proportions of subducted sediment-derived melt during the subduction process. Our new data, combined with the results of previous studies, suggest that the southward subduction of the Proto-Tethys Ocean under the WKOB initiated at ca. 530 Ma. The long-term southward subduction led to the formation of the massive Early Palaeozoic accretionary complex in the South Kunlun Terrane, while trench retreat led to migration of the arc magmatism northward from the Mazar – Tianshuihai Terrane to the South Kunlun Terrane, as well as back-arc extension in the Mazar – Tianshuihai Terrane. [ABSTRACT FROM AUTHOR]

We describe a small collection of Late Ordovician gastropods Holopea? sp. Hormotoma sp. Poleumita? sp. Gyronema rupestre; cephalopod Discoceras sp. unidentified Nautiloids, and rare Tentaculites sp. from the Takche Formation (Ordovician-Silurian) exposed in the Tidong Valley (Kinnaur) of the Tethyan Himalaya. This is the first report of mollusc fossils from the Ordovician-Silurian successions of the Tidong Valley, Kinnaur. The reported Late Ordovician gastropods are also known from Baltica, suggesting a probable oceanic link between these remote regions. Tentaculites from the Takche Formation does not resemble any Baltic or North American tentaculitoids and show greater resemblance to the tentaculitoids from the other Gondwanan regions. [ABSTRACT FROM AUTHOR]

The timing and mechanism of the crustal extension that caused blocks of continental crust to rift and drift northwards from the northern Gondwana margin during the Early Palaeozoic are currently debated. Here, we present new field, geochemical and U-Pb zircon data from peri-Gondwanan Central Sakarya terrane in NW Turkey to shed light on the timing and petrogenesis of extensional magmatism and subsequent passive margin development of the northern Gondwana margin. Our 1/25.000 scale mapping of a selected area (250 km2) has revealed a south-vergent thrust stack comprising three slices. The Middle Slice of the thrust stack consists of a gneiss-amphibolite complex that has a basement-cover type stratigraphy (before regional metamorphism). The basement unit consists of meta-granitoids, intruded by meta-syenite and banded amphibolites, with geochemical characteristics reflecting I&S-type, A-type and within plate alkaline/transitional-type magmatism, respectively. The cover meta-clastic sediments have amphibolite lenses with MORB and back-arc basin-type geochemistry. Meta-granitoid bodies yielded zircon U-Pb ages of 507 ± 16 Ma, 503 ± 12 Ma, and 488 ± 2.6 Ma (Late Cambrian-Early Ordovician), whereas the meta-syenites gave ages of 473.9 ± 5.7 Ma and 471.4 ± 2.5 Ma (late Early Ordovician); also, age of the banded amphibolite was dated as 473.3 ± 4 Ma. The youngest detrital zircon population in the pebbly quartzite sample within cover meta-sediments (458 ± 3 Ma) constrains the maximum depositional age to around early Late Ordovician. The late Early Ordovician bimodal magmatism, a key focus of our study, is interpreted to have formed in response to the Rheic Ocean rifting along the northern margin of Gondwana. The Late Cambrian granitic magmatism, a precursor to bimodal magmatism, can be explained by lithospheric thinning and upwelling of the asthenosphere to form anatectic silicic melts. The unconformity between the basement and cover units may represent the initiation of a new phase of extension at the N Gondwana margin that culminated in the northward drifting of the Central Sakarya and the opening of Palaeotethys, associated with back-arc basic magmatism in Late Ordovician-Silurian. [ABSTRACT FROM AUTHOR]

The encrusted bivalve steinkerns in the Upper Ordovician of Estonia suggest that the rapid sea-floor cementation facilitated the early lithification of the sediment within the bivalve shell and the shell valves, likely aragonitic in composition, were dissolved due to calcite sea conditions similarly to many other regions in the Ordovician. The abandoned bivalve shells contained cryptic invertebrates. The coelobite fauna was dominated by encrusting brachiopods, followed by bryozoans and cornulitids. The bryozoans and cornulitids do not prefer specific regions of the shell interior, indicating that the waters within the shell were sufficiently nutrient-rich throughout. Encrusting brachiopods are always confined to valve margins, suggesting that the waters were nutrient-rich enough for the brachiopods only at the edge of the outer environment. Thus, it is possible that bryozoans and cornulitids were better adapted for a cryptic life than the encrusting brachiopods in the Late Ordovician of Estonia. [ABSTRACT FROM AUTHOR]

The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined in-situ U-Pb, δ18O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8–0.55 Ga and 1.1–0.9 Ga with subordinate peaks at ca. 2.2–1.7 Ga and 2.7–2.5 Ga. The δ18O secular variation mirrors global compilations with Archaean zircon defining a restricted δ18O range of ca. 4.0–8.0 ‰ and younger zircon showing wide variation in δ18O up to ca. 14 ‰. The ca. 0.8–0.55 Ga age peak has the largest variation in εHf(t) with about half of all these Neoproterozoic zircon grains being juvenile (εHf(t) > 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved εHf(t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1–0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1–0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ18O of post–Archaean zircon, together with the evolved εHf(t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental–scale homogenization and dispersion process. [ABSTRACT FROM AUTHOR]

The timing and pattern of biotic recovery after the Late Ordovician Mass Extinction (LOME) are highly controversial. Here, we conducted a systematic investigation on ichnofossils from the lower Silurian succession of the northwestern Hunan province, middle-upper Yangtze Block, South China. Biotic recovery of marine benthic ecosystems after the LOME was analysed and discussed for the first time using multiple ichnofossil proxies. The vertical distribution and evolutional trends of trace fossil assemblages suggest that biotic recovery was significantly delayed by the widespread anoxia during the latest Hirnantian to middle Aeronian. The recovery displays a stepwise pattern and reached a relatively high stage during the late Aeronian, although a full recovery was generally not achieved during this interval as proposed elsewhere before. There is a sharp decrease in all trace fossil proxies across the Aeronian-Telychian boundary, indicating a resetting of biotic recovery back to initial stages, most likely linked to a re-onset of anoxia in shallow marine settings during the late Aeronian Event. Subsequent recovery generally followed the patterns of late Aeronian, but was hampered by a low nutrient supply during early Telychian. By the beginning of middle Telychian, a full recovery was achieved, ca. 8.8 Ma after the second pulse of the LOME. [ABSTRACT FROM AUTHOR]

Mineral deposits are commonly associated with and hosted in volcanic successions. Volcanic facies analysis as applied in mineral exploration is powerful for characterising host stratigraphy to understand volcanological and eruption processes, depositional setting, and tectonic processes before, during and after ore-forming events. However, the specialist experience required in studying ancient, deformed successions impedes the uptake of facies analysis as a routinely applied technique in mineral exploration. This challenge is reflected in the literature with a paucity of examples where 3D models are developed directly from facies analysis and is worth addressing, as stratigraphic approaches are commonly inadequate for understanding and modelling the complexities within ancient volcanic terrains. We address this gap by demonstrating a technique that uses digitised graphic logs to construct correlation charts in a graphics editor to interpret 'restored' volcanic successions within fault blocks. This approach is validated with concurrent cross-sections that depict the structural-stratigraphic framework. The work is iteratively revised until the interpretation is internally consistent across both the correlation chart and the cross-section. This technique is presented within a four-phase workflow that guides the reader from initial scoping, through to graphic logging, interpretation of volcanic successions by locality (or fault block) and finally a synthesis and 3D model. This workflow was developed from our experiences in the buried and deformed Ordovician Cowal Igneous Complex that hosts world-class gold deposits that are currently being mined at E42 (open pit) and GRE46 (underground mine). A case study of the Cowal Igneous Complex is presented to demonstrate the value and real-world application of this workflow. Volcanic facies analysis is a powerful tool for the production of 3D models with application to mining and exploration settings. Graphic logging-based techniques and workflows were developed during 3D reconstructions of ancient and buried volcanic successions in the Cowal Igneous Complex of the Ordovician Macquarie Arc of New South Wales. [ABSTRACT FROM AUTHOR]

Chitinozoan investigations on the late Middle to early Late Ordovician in South China are limited. Documented chitinozoan occurrences are mainly from the Miaopo Formation on the Upper Yangtze Platform. The present study reports new data from the Miaopo Formation at the Zhenjin section in the Yichang area. In total, 13 genera and 33 species are recognised, and three new species are described: Spinachitina? coronifera sp. nov., Lagenochitina yichangella sp. nov. and Pellichitina confragosa sp. nov. The Baltoscandian index species, Laufeldochitina striata, is documented in the lowermost part of the formation. This is the first report of this species in South China. The L. striata Biozone is suggested for the basal part of the formation due to the presence of the eponymous species. The index species of the Laufeldochitina stentor Biozone, the Armoricochitina granulifera and Cyathochitina megacalix subzones adopted in the Jieling section, are also observed in the Zhenjin section. However, according to the new data obtained at Zhenjin, the first appearance datum of C. megacalix and A. granulifera coincides with that of L. striata. Therefore, the C. megacalix Subzone is kept but moved to the L. striata Biozone. Armoricochitina granulifera has stable occurrences in almost the entire Miaopo Formation, corresponding to the Nemagraptus gracilis graptolite biozone. It is slightly older than Baltic records but could be useful for recognising this time interval in South China. [ABSTRACT FROM AUTHOR]

Four species of Conchicolites and two species of Cornulites occur in the Hirnantian of Estonia. Two new cornulitids Conchicolites corbalengus sp. nov. and Cornulites levigatus sp. nov. have been described from the Siuge Member. This Hirnantian cornulitid tubeworm association is dominated by species of Conchicolites. Most likely, the studied tubeworms represent true dwarf forms among the cornulitids. It is possible that local waters above the organic rich mud on the seafloor were especially rich in nutrients and allowed cornulitid tubeworms to flourish. The Hirnantian fauna of small cornulitids resembles very much that of late Katian of Estonia and shows no decline in the diversity. It appears that the Late Ordovician mass extinction did not immediately affect small cornulitids, if it did at all. [ABSTRACT FROM AUTHOR]

The abundant shells and hardgrounds in the Cincinnatian Group (Upper Ordovician, Katian) of the upper midwestern United States were commonly encrusted and bored by a variety of organisms. Numerous studies of these sclerobiont communities have provided valuable data for models of ecological succession, symbiosis, space and food resource competition, and taphonomy. An underlying assumption of this work is that most of the skeletal encrusters have remained in place, firmly attached to their hard substrates. This is especially the case with the most common encrusters, thick trepostome bryozoan and cystoporate skeletons, on their most common substrates, flat strophomenide brachiopods. We present evidence here, though, that these bryozoans were often dislodged from their brachiopod hosts, leaving no evidence of their attachment other than horizontal borings in semi-relief from organisms that excavated tunnels (Trypanites and Palaeosabella) at the interface of the brachiopod shell and attaching bryozoan. Similar borings are found on the bases of dislodged bryozoans and in bryoimmured mollusc external moulds. These borings along the bryozoan attachment surfaces caution us that there are significant numbers of missing skeletal encrusters on these hard substrates. [ABSTRACT FROM AUTHOR]

North China was a key centre of Middle Ordovician stromatoporoid diversification. However, detailed studies of the subsequent Late Ordovician stromatoporoid development in this terrane are lacking; thus, the spatiotemporal development of North Chinese stromatoporoids is poorly understood. The Beiguoshan Formation (middle Katian age, Late Ordovician) contains the youngest Ordovician stromatoporoids in North China, comprising a unique stromatoporoid fauna, consisting of 12 species across 10 genera and three orders of traditional taxonomic groupings: labechiids Rosenella woyuense Ozaki, 1938, Pseudostylodictyon poshanense Ozaki, 1938, Pseudostylodictyon chunhuaensis (Jiang et al., 2011), Labechia sp., Labechiella gondwanense Jeon in Jeon, Liang, Kershaw, Park, and Zhang, 2022, Labechiella regularis (Yabe & Sugiyama, 1930a); clathrodictyids Clathrodictyon sp. cf. Cl. mammillatum (Schmidt, 1858), Camptodictyon amzassensis (Khalfina, 1960), Ecclimadictyon tiewadianensis (Jiang et al., 2011), Plexodictyon xibeiense Jeon sp. nov., Petriterastroma exililamellatum Jeon and Kershaw gen. et sp. nov.; and the stromatoporellid Simplexodictyon conspicus Jeon and Kershaw sp. nov. This assemblage is distinguished by: (1) succeeding Darriwilian species of North China, (2) few peri-Gondwanan species, and (3) stromatoporoid genera common in Siluro–Devonian assemblages. Plexodictyon and Simplexodictyon species (commonly found in middle Palaeozoic rocks) are here recorded in the Ordovician for the first time. Their stratigraphical occurrence in the middle Katian reveals an interval of absences before their faunal development in the middle Silurian, a stratigraphical gap caused by the Huaiyuan Epeirogeny, which largely shaped and controlled the regional stratigraphy of North China. This unique assemblage of Katian stromatoporoids is not known from other contemporary terranes, supporting the interpretation that North China was separated from the north-eastern peri-Gondwanan regions, thus constituting an independent palaeobiogeographical unit during the Late Ordovician. Early occurrence of these common Siluro–Devonian-type stromatoporoids indicates a prologue of the Ordovician–Silurian stromatoporoid faunal transition in North China, characterized by a decrease in labechiids and rapid diversification of clathrodictyids and related stromatoporoids of typical Silurian types. [ABSTRACT FROM AUTHOR]

The Lashkarak Formation (Lower–Middle Ordovician) in the Gerdkuh locality, 10 km west of Damghan city, northern Iran, has been found to contain acritarchs and chitinozoans. This study aimed to understand these chitinozoan and acritarch successions as well as brachiopods in this part of the Alborz Mountains, in a novel manner. Ninety-seven surface samples from this succession were collected and analysed. Thirty samples yielded well-preserved palynomorph taxa such as acritarchs, chitinozoans, and scolecodonts, as well as graptolite remains. In total, 53 taxa were identified among the acritarchs (38 species belonging to 21 genera) and chitinozoans (15 species belonging to 10 genera). Although scolecodonts and graptolite remains were also observed, they were not studied in detail. The palynological analyses revealed the presence of several diagnostic acritarchs in the Lashkarak Formation, including Vulcanisphaera simplex, Arbusculidium filamentosum, Coryphidium bohemicum, Dactylofusa velifera, Striatotheca mutua, Arkonia virgata, and Orthosphaeridium ternatum. These acritarchs allowed the recognition of five acritarch assemblage zones. Similarly, seven chitinozoan biozones were recognised: Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Cyathochitina protocalix, Cyathochitina calix, Siphonochitina formosa, and Laufeldochitina clavata. These findings confirm the inclusion of the Alborz Mountains in the peri-Gondwana palaeoprovince during the Early–Middle Ordovician. The co-occurrence of the acritarch and chitinozoan taxa with previously identified brachiopods allowed for the establishment of a more detailed Early–Middle Ordovician biozonation, demonstrating their potential usefulness for global chronostratigraphy. Based on palynological and brachiopod assemblages, a shallow marine inner shelf setting is suggested for the Early–Middle Ordovician at the Gerdkuh locality. Moreover, in this study, four new morphotype species were erected, consisting of one new chitinozoan (Cyathochitina gerdkuhensis sp. nov.) and three new acritarchs (Baltisphaeridium razii sp. nov., Navifusa alborzensis sp. nov., and Orthosphaeridium iranense sp. nov.). However, Othosphaeridium cf. ternatum was left in open nomenclature. Palynomorphs from the Lower–Middle Ordovician (Lashkarak Formation) were recorded from the Alborz Mountains. 15 chitinozoan species (10 genera) were recorded from the Lashkarak Formation, S. Caspian Sea. 38 acritarch taxa (21 genera) were identified, indicating the N. Gondwanan Domain. The diagnostic acritarch taxa are Arbusculidium, Coryphidium, Striatotheca, and Arkonia. Chitinozoan biozones are E. brevis, D. ornensis, B. henryi, C. protocalix, C. calix, S. formosa, and L. clavata. Baltisphaeridium razii sp. nov., Navifusa alborzensis sp. nov., Cyathochitina gerdkuhensis sp. nov., and Orthosphaeridium iranense sp. nov. is recorded for the first time. A major hiatus corresponds to the Late Ordovician, Silurian, and Early–Middle Devonian. [ABSTRACT FROM AUTHOR]

The rapid diversification of conodonts during the Ordovician has been extensively studied by several authors, each presenting distinct diversity curves for different paleocontinents. This study analyzes trends in conodont biodiversity in the Precordillera region, spanning from the late Tremadocian to the early Sandbian ages. A conodont dataset, incorporating species previously identified in sections across Central and Eastern Precordillera, is utillized. This contribution presents the conodont diversity curve for the Lower to early Upper Ordovician in the Precordillera for the first time. The resulting conodont biodiversity pattern reveals that the initial peak of diversification occurs during the O. intermedius Zone (middle-late Floian). A sharp decline in biodiversity is observed during the Dapingian. Finally, during the early Darriwilian, there is a rise in the diversification of conodont species, reaching a peak in the L. pseudoplaunus Zone. This pattern is also compared to curves from Baltica, South China, North China, and Tarim, showing similar trends among them. The variation in Lower-Middle Ordovician conodont diversity in the Precordillera may be linked to different pulses or events within the ‘GOBE’ (Great Ordovician Biodiversification Event). [ABSTRACT FROM AUTHOR]

The Late Ordovician Tafilalt Biota of the Moroccan Anti-Atlas includes a diverse range of soft-bodied organisms, including palaeoscolecids, paropsonemid eldonioids, graptolites and cheloniellid arthropods, as well as a rich assemblage of mineralised taxa, among them conulariids, trilobites and echinoderms, often found as articulated skeletons. The new fossil locality, not far from the original Bou Nemrou site, has produced two new palaeoscolecid taxa, the new genus and species Anguiscolex africanus and the new species Wronascolex superstes. They are preserved as compression fossils in fine-grained mudstones, where the original phosphatic sclerites have been diagenetically substituted by pyrite and later weathered to iron oxides, giving them a characteristic rusty colour. This area of Gondwana was located adjacent to the Late Ordovician South Pole and both Anguiscolex africanus gen. et sp. nov. and Wronascolex superstes sp. nov. present a degree of polar gigantism, which has been suggested for other taxa in such high palaeolatitudes such as bryozoans, conulariids, trilobites and radiodonts. Lastly, the occurrence of Wronascolex extends the distribution of this typically Cambrian taxon into the Late Ordovician, indicating a total range for the genus exceeding 60 million years, more than any other palaeoscolecid genus described to date. [ABSTRACT FROM AUTHOR]

The Bohemian Massif of Central Europe is a Variscan collage of lithospheric fragments that formed at the northern margin of Gondwana during the late Neoproterozoic. A key geodynamic process that shaped this margin before it became involved in the Variscan orogen was the Cambro–Ordovician rifting that opened the Rheic Ocean. This rifting event has been studied extensively, yet a number of issues remain unresolved, among which are its geodynamic causes. New U–Pb zircon ages of orthogneisses from the mid-crustal Moldanubian unit, in combination with available information on magmatism and basin subsidence in the upper-crustal Teplá–Barrandian unit of the Bohemian Massif, are here used to reconstruct in detail the mechanism of the Cambro–Ordovician rifting. We argue that extension occurred in three phases defined by (1) protracted ~524–480 Ma intermediate to felsic plutonism (including the dated ~490–480 Ma orthogneisses), (2) basaltic submarine volcanism at ca. 470 Ma, and (3) rapid subsidence at ca. 458–452 Ma. This relative timing is interpreted to reflect stretching of the lower lithosphere before upper lithospheric rifting. In a broader context, these inferences are compatible with contrasting, rheologically controlled modes of northern Gondwana break-up during the early Ordovician, in which the westerly Avalonian-type terranes were rifted away from Gondwana, whereas the easterly Cadomian-type terranes formed a hyperextended Gondwanan shelf. [ABSTRACT FROM AUTHOR]

The Cincinnati Museum Center has opened a new permanent exhibit called "Ancient Worlds Hiding in Plain Sight," which showcases the geologic riches of the Cincinnati region. The exhibit spans the majority of the Paleozoic Era, from the Ordovician Period to the Carboniferous Period, and features over 400 specimens, including fossils of trilobites, brachiopods, and corals. The gallery aims to connect the study of deep time with current issues such as climate change and evolution. The exhibit also includes interactive elements, such as hands-on displays and a life-sized image of an Ordovician hardground. The gallery is a collaboration between the Cincinnati Museum Center and local amateur collectors, and it aims to educate visitors, inspire future scientists, and foster a connection to the natural world. [Extracted from the article]

The ultra-deep oil and gas are a promising exploration direction in petroleum industry recently. The geochemical feature of natural gas in four various fault zones were analyzed, and found that the natural gas is oil associated gas in the North Shuntuoguole area (Shunbei area), Tarim Basin. K1 and K2 values are used to judge the source of oil and gas. They are only associated with the parent material type of oil and gas, but not to the maturity. The changing trends of the K1 and K2 values are basically the same, indicating that the natural gas in the Shunbei comes from the same oil and gas system. Through the analysis of drilling data, showing that different fault zones have different hydrocarbon enrichment laws, and the same fault zone has different hydrocarbon enrichment laws at different locations. It provides a new insight for future exploration in study area and has reference significance for ultra-deep oil and gas exploration at home and abroad. [ABSTRACT FROM AUTHOR]

The evolution and closure timing of the Paleo-Asian Ocean are controversial in the Eastern Tianshan orogen, southern Altaids. The Dananhu arc of the Eastern Tianshan was involved in the long-lived evolution and terminal tectonic events during the formation of the Altaids, and its magmatic rocks are the faithful recorder. To constrain the subduction history of the Paleo-Asian Ocean, we review the tectonic of the Dananhu arc, by summarizing the geochemical and geochronological data of granites and volcanic rocks and mineral deposits, which will shed light on the accretionary history, closure of the Paleo-Asian Ocean, and the continental growth in Altaids. Zircon U-Pb ages of the granitic rocks across the middle of the Dannanhu arc range from 453 Ma to 227 Ma and demonstrate overall southward younging through four main areas: the Kalatage belt (ca. 453–299 Ma), the Keizer belt (ca. 401–268 Ma), the Tuwu belt (360–302 Ma), and the Kanguer subduction complex (ca. 288–227 Ma). These granitic rocks are calc-alkaline arc-related and adakitic granites that are enriched in Si and K. They increase in Th/Yb and decrease in Cr and Ce/Pb southwards over time. The consistent geochemical variations indicate progressive maturity of the arc crust. Their whole-rock εNd(t) and zircon εHf(t) values coordinated with the progressive change in the crustal thickness estimated by the granites indicate a multi-phase switching of subduction. The Ordovician to Permian granitic rocks in the arc have stable high whole-rock εNd(t) values (ca. +5 – +10), and zircon εHf(t) values (ca. +7-+16), which significantly shifted to +2 – +4 and +4 – +12 during ca. 243–227 Ma. These changing relations accompanied a sudden crustal thickening, suggesting that continental crustal material was involved in the petrogenesis of these rocks during the convergence among the Dananhu arc, the Harlik and the Yamansu-central Tianshan continental arc. [ABSTRACT FROM AUTHOR]

The depression of the ancient Lumparn meteorite impact structure is partly infilled by Cambrian and Ordovician sediments, lying nowadays below the seawater. The Ordovician carbonate succession at this site, recognised through erratic boulders and by the drilling project in the late 1950s, is of particular interest due to its isolated and distant location from other areas with Ordovician sediments in the Baltoscandian Palaeobasin. In this study, we present new data on ostracod biostratigraphy and stable carbon isotope chemostratigraphy obtained from three old drillcores. Comparison of ostracod distribution with sections in Estonia generally supports the previous interpretations of a Darriwilian and Sandbian age for the lowermost Tranvik Limestone (which we propose renaming the "orthoceratite limestone" in the Åland Islands area). The uppermost Östersjö Limestone spans almost the entire Katian age. We also observe the global MDICE and GICE carbon isotopic excursions, as well as Katian Rakvere and Saunja excursions, within the Lumparn succession. The Ordovician succession in Lumparn Bay is facially resembling the Estonian Shelf facies of the Baltoscandian Palaeobasin. [ABSTRACT FROM AUTHOR]

A unique internal mould of the patelliform mollusc Eesticonus aariensis n. gen. n. sp. is described from the Middle Ordovician (Darriwilian Series, Kunda Stage) of northern Estonia. Well-preserved muscle attachment scars are compared to those of Floripatella from strata of Middle Ordovician (Dapingian Series) age in Utah, originally considered to be the oldest known patelloidean gastropod but possibly an untorted mollusc. Comparison with the muscle scar pattern in Archinacellina from the Ordovician of Bohemia suggests that Eesticonus is an archinacelloidean gastropod, but not a patellogastropod. [ABSTRACT FROM AUTHOR]

New detrital zircon ages from biostratigraphically well-controlled Ordovician sandstones in southeast Australia are compared with published counterparts in southern Zealandia. During Rodinia supercontinent assembly (RA), Australia and Zealandia age patterns are similar, everywhere with ubiquitous late Mesoproterozoic magmatic zircon sources. However, during earliest Gondwana supercontinent assembly (GA), the age patterns have different sediment sources: (1) those of late Neoproterozoic age are more strongly represented in Zealandia but of uncertain location, but (2) those of late Cambrian-Ordovician age are more prominent in eastern Australia, having probable origins in the Ross-Delamerian Orogen. In particular, a distinctive zircon component, ca. 600–650 Ma, is ubiquitous in Zealandia but rare in Australia. Early Paleoproterozoic and Archean (Nuna, NU) zircon sources (2000–3200 Ma) become important (and locally up to 25% total) in Zealandia but not in Australia. It is difficult to reconcile all these sediment source requirements within disparate and distant Australian-Antarctic Precambrian complexes. Instead, it is proposed that, through the early Palaeozoic, Zealandia had only local sediment sources in a discrete Rodinia basement continental block outcropping in South Zealandia that was formerly adjacent to South China. [ABSTRACT FROM AUTHOR]

This study documents Middle to Late Ordovician conodont faunas primarily from the Billabong Creek Formation exposed in the Gunningbland area located west of Parkes and northwest of Forbes in central New South Wales. Forty-four identifiable conodont species recovered from 105 limestone samples in this area form the basis of the most complete biostratigraphic succession in shallow-water facies known through this interval from Australia. Four conodont biozones are recognised, extending from the middle Darriwilian Histiodella holodentata–Eoplacognathus pseudoplanus and Eoplacognathus suecicus biozones, through the upper Darriwilian Pygodus serra Biozone, to the Pygodus anserinus Biozone spanning the uppermost Darriwilian to basal Sandbian interval. A lower to middle Sandbian carbonate gap coincides with an unzoned interval, followed by the successively younger Belodina compressa, Phragmodus undatus and Taoqupognathus blandus conodont biozones in the upper Sandbian to lower Katian. The T. blandus Biozone directly correlates with the detailed conodont biozonation established in Katian limestones of the Molong Volcanic Belt further east. These age determinations provide much improved precision for correlation within Phases 2 and 3 in the mineral-rich Macquarie Volcanic Province. Analysis of conodont biofacies data supports an enhanced understanding of the geological evolution of the Macquarie Volcanic Province by interpreting the interplay between volcanic activity and carbonate deposition. Conodont studies in the Billabong Creek Formation of the Gunningbland area reveal the only known biostratigraphic succession in Australia that extends continuously from the middle Darriwilian to basal Sandbian. Three Late Ordovician (late Sandbian to early Katian) conodont biozones in the upper Billabong Creek Formation correlate precisely with carbonates of the Molong Volcanic Belt to the east. Revised stratigraphic definitions of the Billabong Creek and Gunningbland formations are provided. [ABSTRACT FROM AUTHOR]

Ziyang Fauna is a significant early Ordovician Floian fossil Lagerstätte, recovered from blackish-grey mud limestone and calcareous mudstone of possible slope facies in the Yangtze platform in Ziyang County, Shaanxi Province, China, distinguished by predominate trilobites, accompanied with graptolites, brachiopods, arthropods and some trace fossils. It is marked by high abundance of exceptionally preserved Seleneceme (Trilobita). Two trilobite species named Caputrotundum bashanense and C. ziyangensis, are reassigned here to Seleneceme based on a detailed study of more than one hundred well-preserved specimens. The taxonomic generic and ontogeny characters of Seleneceme are as follows: cephalon semicircular in outline, with axial spine and genal spines; without eye lobes; glabella subcircular in outline, with deep longitudinal glabellar furrows; thorax and pygidium with much parallel segments. The morphological variation during ontogeny of Seleneceme is characterised by the gradual increase of the length/width ratio (L/W) of the body, but with a constant width/length ratio (W/L) of the cephalon, and also a faster growth rate in the pygidium than in the thorax. [ABSTRACT FROM AUTHOR]

Based on a new deep drilling on southern Gotland (Sweden), this study is the first to document the carbon isotope chemostratigraphy of the Upper Ordovician through lowermost Silurian sedimentary record from the central parts of the Baltic Sea subsurface. The lithological record of the Stora Sutarve core has similarities with adjacent successions in both the Viki core in the East Baltic area and the Borenshult core in the Swedish mainland. The core includes the Kahula (including 13 bentonites in the "Kinnekulle K-bentonite complex"), Hirmuse(?), Rägavere, Paekna, Jonstorp, Loka, Motala and Kallholn formations. Several of the internationally recognized upper Ordovician δ13C excursions have been identified in the core, including the Guttenberg Isotope Carbon Excursion (GICE), Moe excursion, Hirnantian Isotope Carbon Excursion (HICE), and an undefined early Silurian carbon isotope excursion, presumably the Early Aeronian Carbon Isotope Excursion (EACIE). We particularly address the microstratigraphy of the Hirnantian Stage and the finer details of the HICE, which is not fully complete and entirely confined to the 2.09-m-thick Loka Formation. This formation yields abundant, but low-richness brachiopod faunas characteristic of the Hirnantian Stage and is, based on erosional-depositional surfaces and facies, interpreted as reflecting interglacial warming and eustatic transgression related to ice-sheet contraction in Gondwana. Based on very dense carbon isotope sampling we identify four clusters of δ13C values that aid to define significant changes in the preserved record of the HICE and which may facilitate global correlation of the succession and the herein interpreted sea-level record. [ABSTRACT FROM AUTHOR]

The new hexactinellid stiodermatid Turgidaspongia porosa gen. et sp. nov. is described from the Ordovician-Silurian boundary sequence in Beigong of Jingxian County, south Anhui Province, China. The spherical, thin-walled species possessed unique features including unusually large parietal gaps on the body wall, swollen hexactines as hypodermalia, and two different sizes of stauractines as dermalia and parenchymalia respectively. Based on the new material, the family Stiodermatidae is revised here, including five genera after reassessment, i.e., Rigbyella, Thoracospongia, Stioderma, Uralonema, and Turgidaspongia porosa gen. et sp. nov. The new species is well preserved with typical enlarged hypodermal hexactines with swollen rays and large, subcircular parietal gaps, giving an illuminating insight into the affinity between the new species and other taxa in Stiodermatidae. It also provides a link between the Cambrian stiodermatid lineage and late Palaeozoic stiodermatid lineage. The uneven distribution of the swollen dermalia in the new species may relate to the sloughing of the dermal spicules causing by the nutrient deficiency. The unique rigid skeleton structure and unusually large parietal gaps probably represent new attempts on the skeletal evolution of hexactinellids in the Palaeozoic. [ABSTRACT FROM AUTHOR]

Most major crinoid clades first appear in the fossil record during the Ordovician, but the evolutionary origins of many higher taxa remain unresolved. Here, the first camerate crinoids from the Katian (Upper Ordovician) of Estonia with complete calyces are described. Phylogenetic analyses are conducted to determine the affinities of two new genera and to assess the evolutionary origins of the families Opsiocrinidae (Diplobathrida) and Glyptocrinidae (Monobathrida). Sakucrinus krossi gen. et sp. nov. is identified as the earliest known member of Opsiocrinidae and demonstrates that: (1) the family originated much earlier than was previously assumed; (2) features previously considered plesiomorphic for the family are instead derived; and (3) the family is likely closely related to the Dimerocrinitidae. Family Pachycephalocrinidae fam. nov. is established to accept the monocyclic glyptocrinid Pachycephalocrinus jaanussoni gen. et sp. nov. Pachycephalocrinus jaanussoni displays morphological features that are unique among monobathrid crinoids, including a large periproct in the calyx side. Inclusion of Pachycephalocrinus in the first phylogenetic analysis focusing on Ordovician monobathrid crinoids elucidates evolutionary relationships among Ordovician monobathrids and calls into question the validity of superorder Compsocrinina. The new genera described here provide important insight into the timing of origination and morphological diversity of higher taxa during the early evolutionary history of camerate crinoids. [ABSTRACT FROM AUTHOR]

An Early Ordovician fauna of linguliform brachiopods and euconodonts is described from the Alum Shale Formation in northernmost Västerbotten County, northern Sweden. The fauna was recovered from a single carbonate concretion collected at an exposure near the northern shore of Lake Storvindeln. Despite of the fragmentary and tectonized preservation of the obtained fossils, at least eight different taxa of linguliform brachiopods and four species of euconodonts could be identified. Among the brachiopods, the ephippelasmatid Pomeraniotreta biernatae Bednarczyk, 1986 is most common; it is associated among others with the acrotretids Eurytreta cf. sabrinae (Callaway, 1877) and Ottenbyella sp., and a spinose specimen potentially representing the zhanatellid Thysanotos. Two of the brachiopod taxa appear to present new species, Pomeraniotreta n. sp. and Mytoella? n. sp., but additional material would be needed for a formal description. Euconodont specimens are rare and comprise coniform elements of Drepanodus arcuatus Pander, 1856, Drepanoistodus aff. amoenus (Lindström, 1955) sensu Löfgren (1994), Paroistodus numarcuatus (Lindström, 1955) and Rossodus aff. manitouensis Repetski & Ethington, 1983. Evaluation of the stratigraphic distribution of the different taxa of brachiopods and euconodonts under consideration of the local geology, suggests that the investigated sample represents a level in the upper part of the Tremadocian (Tr2) part of the Alum Shale Formation. The fauna represents the northernmost occurrence of age diagnostic Early Ordovician (Tremadocian) fossils in Sweden. [ABSTRACT FROM AUTHOR]

We present new zircon U-Pb and Hf isotopic as well as whole-rock geochemical data for volcanic rocks from the eastern margin of the Xing’an Massif, Northeast China, in order to further our understanding of the suture location between the Xing’an and Songnen-Zhangguangcai Range massifs. Zircon secondary ion mass spectrometry U-Pb dating indicates that the volcanic rocks formed during the Early-Middle Ordovician (473-463 Ma). Compared with the coeval Moguqi basalts (rare earth element [REE] = 171-183 ppm; εHf(t) = +0.3 to +2.7; TDM1 = 1074-977 Ma), the Duobaoshan andesites exhibit lower overall REE abundances (109-131 ppm) with relatively high heavy REE contents, stronger high-field-strength element depletion, higher εHf(t) values (+13.0 to +14.8), and much younger TDM1 ages (559-484 Ma). This suggests that the primary magma for the andesites was generated by the partial melting of a relatively depleted mantle wedge that was metasomatized by subduction-related fluids. The primary magma for the basalts in the Moguqi area was probably derived from the partial melting of a relatively enriched lithospheric mantle that was also modified by fluids sourced from a subducted slab. These interpretations suggest that the andesites in Duobaoshan formed in a newly accreted island arc setting, whereas the coeval basalts in Moguqi formed along an active continental margin. We therefore attribute the Early-Middle Ordovician volcanism along the eastern margin of the Xing’an Massif to the northwestward subduction of the Nenjiang-Heihe oceanic plate beneath the Xing’an Massif. Furthermore, considering coeval igneous activity in the southern parts of the Xing’an Massif, we suggest that a magmatic arc existed along the margin of the Xing’an Massif in the early Palaeozoic (490-420 Ma). We conclude that the location of the suture between the Xing’an and Songnen-Zhangguangcai Range massifs runs from Airgin Sum, via south of Xilinhot, to Ulanhot, Moguqi, Nenjiang, and finally Heihe. [ABSTRACT FROM AUTHOR]

Globally significant geoheritage features of the Cliefden Caves area, in the Belubula River Valley between Orange and Cowra in central western New South Wales, comprise a richly fossiliferous shallow-water limestone succession of Late Ordovician age (the Cliefden Caves Limestone Subgroup) overlain by deep-water laminites and allochthonous limestones of the Upper Ordovician Malongulli Formation. Key features of the Ordovician geology of the Cliefden Caves area that have been identified using the Geoheritage Toolkit as being of international significance are the abundance of unique and exceptionally diverse fossils in the Fossil Hill Limestone (forming the lower part of the Cliefden Caves Limestone Subgroup), which supplement detailed interpretation of carbonate-dominated deposition within an Ordovician volcanic island setting. The fossiliferous limestones preserve biostromes and local small bioherms of stromatoporoids and corals, and recurrent in situ and disarticulated/imbricated Eodinobolus shell beds formed in shallow, quiet-water, dominantly muddy carbonate sediments that passed up-sequence to clay-free carbonate environments. These mud-dominated carbonate sediments are interspersed with higher-energy conditions, represented by skeletal, lithoclastic and calcrete-ooid grainstones overlying disconformities, leading to the identification of subaerial disconformities and associated diagenesis in the Fossil Hill Limestone. The Fossil Hill Limestone is succeeded by massive limestones in the middle part of the Cliefden Caves Limestone Subgroup and then, in turn by the Vandon Limestone and the deeper-water graptolitic laminites of the Malongulli Formation—this completes a succession that is rarely preserved in the geological record, further enhancing the geoheritage significance of the Cliefden Caves area. [ABSTRACT FROM AUTHOR]

The Ordovician plutons in the Erguna Block, NE China, can be classified into two groups: Early Ordovician diorites with zircon U-Pb ages ranging from 486 to 485 Ma and Middle Ordovician gabbros and granites with zircon U-Pb ages ranging from 466 to 463 Ma. The diorites are calc-alkaline in nature and are characterized by weak to moderate enrichments of large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE) and heavy rare earth elements (HREE). The gabbros and granites have high total alkali contents, and all samples are enriched in LREE and LILE and depleted in HFSE such as Nb, Ta, and Ti. Isotopically, Early Ordovician diorites display values that are less radiogenic [εHf(t) = + 9.9-+16.8] compared to those of Middle Ordovician gabbros [εHf(t) = − 3.0-+5.0]. Middle Ordovician granites have positive εHf(t) values of +1.4 to +4.3 and two-stage Hf model ages (TDM2) of 1167 to 1356 Ma. These data indicate that the diorites may have been generated by the partial melting of a recently metasomatized mantle source, whereas the gabbros and granites may have been formed by the partial melting of enriched lithospheric mantle and Mesoproterozoic crust, respectively. Our results, combined with other regional results, suggest that Early Ordovician magmatism was likely associated with the northward subduction of the Heihe-Xilinhot oceanic plate beneath the Erguna-Xing'an Block, whereas the Middle Ordovician gabbros and granites were most likely formed in an extensional setting controlled by the rollback of this subducted oceanic plate. [ABSTRACT FROM AUTHOR]

A siliciclastic succession is exposed at the Faraghan mountain, northern Persian Gulf, southeastern Iran. A detailed, high-resolution palynological analysis was performed on the Zardkuh, Seyahou, Dargaz, and Sarchahan formations to verify the exact age and palaeogeographic position of the High Zagros Mountains. Two hundred surface samples from this succession were collected and analysed. Most samples yielded abundant and well-preserved chitinozoans, acritarchs, scolecodonts, and cryptospores. Fifty-three chitinozoan species (21 genera) were identified that permitted to establish the Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Siphonochitina formosa, Belonechitina robusta, Tanuchitina fistulosa, Acanthochitina barbata, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, Spinachitina oulebsiri, and Spinachitina fragilis biozones in ascending stratigraphic order as was previously established for the North Gondwana Domain. These results indicate that the Zagros Mountain Belt of Iran was part of the North Gondwana palaeo-province during the Ordovician-Silurian. On the other hand, these chitinozoan biozones and other associated fauna (e.g. graptolites, trilobites, brachiopods, and conodonts) suggest a late Early Ordovician (Floian) to Early Silurian (Rhuddanian) age range, with unconformities, for this succession. Based on chitinozoan biozones, a distinctive hiatus is present between the Zardkuh and Seyahou formations at Faraghan mountain, which corresponds to the absence of jenkinsi-tanvillensis chitinozoan biozones, encompassing the latest Middle Ordovician (latest Darriwilian: stage slice Dw3) and the early Late Ordovician (Sandbian: the stage slices Sa1 to Sa2 and time slices 5a to 5b). Two chitinozoan species were erected: Belonechitina bifurcaspina sp. nov., Angochitina persianense sp. nov., and Eremochitina cf. brevis was left in open nomenclature. Siliciclastic deposits of the Faraghan mountain yielded rich chitinozoan assemblages. Fifty-three identified chitinozoan species resulted in 12 chitinozoan biozones. Kerogenous black shales contain both the S. oulebsiri and N. persculptus biozones. A hiatus was identified, corresponding to the Dw3 and Sa1–Sa2 stage slices. Two new taxa: B. bifurcaspina and A. persianense, are proposed. [ABSTRACT FROM AUTHOR]

Suecipora ebbestadi gen. n. sp. n. (Bryozoa) is described from the Upper Ordovician of Siljan District, Dalarna, central Sweden. This taxon is characterized by long peristome-like tubes with keel-shaped projections, as well as apparent angular kenozooecia. These morphologies are regarded being homologous to the post-Palaeozoic cyclostomes. Colonies of Suecipora are mainly multilayered developed by budding of new sheets from peristome-like tubes. The morphology of Suecipora suggests its adaptation to an environment with soft substrate and strong sediment influx. It is supposed that the colonies of this bryozoan were partially elutriated and experienced fresh water diagenesis. [ABSTRACT FROM AUTHOR]

The structure of the shell wall in the Ordovician Orthoceras differs from that in the extant Nautilus. It consists of two equal thick layers: an outer probably nacreous layer and an inner prismatic layer. The two layers are separated from each other by a thin intermediate sub-layer that is rich in organic substance and has indistinct boundaries. The intermediate sub-layer and the inner prismatic layer contain a hitherto undetected pore-canal network that consists of vertical and horizontal canals. Horizontal canals are arranged in a single layer in the outermost part of the intermediate sub-layer. The vertical canals are arranged in parallel rows, and the canals in each row open into one of the horizontal canals. The canals have thin walls of calcified organic fibres. The walls are preserved in the intermediate sub-layer, whereas in the inner prismatic layer, they are partially dissolved. The canal network is absent in the shell wall of the extant Nautilus, but the horizontal canals occur in the shell wall of the Carboniferous orthocerid-like coleoid Mitorthoceras and the bactritid-like coleoid Shimanskya. Thus, the pore-canal network had an important, still unknown, function for the animal, and it existed, without changes, at least 150 ma. [ABSTRACT FROM AUTHOR]

Brachiopods belonging to order Atrypida originated in the Middle Ordovician and went extinct in the Late Devonian. Few cladistic studies have been undertaken for this group. Here we investigate their early evolution through Silurian time. We present a parsimony-based phylogenetic analysis of 41 characters and 70 genera representing all the early taxonomic groups within the order. The stratigraphical record of the fossil genera analysed strongly aligns with the phylogeny recovered from our parsimony analysis. Most currently recognized subfamilies and families may be identified within clades, except for the Atrypinae, Idiospirinae, and the Septatrypidae. This warrants subdivision of the former and redefinition of the latter two. The subfamily Atrypinae is redefined, and a new subfamily of the Atrypidae, the Protatrypinae, is split off. Tracing character evolution across the tree indicates that the calcified spiralia and a jugum or jugal processes characterize all members of the Atrypida, except the most basal clade, the Cyclospiridae, which lacks a calcified jugum. Ribs are a homoplasious character, occurring in numerous clades throughout the tree. Darriwillian through Sandbian ages represent times with rapid evolution when most new autapomorphies seen in the atrypides evolved. This interval is the first major part of the Great Ordovician Biodiversification Event (GOBE). Solid teeth, dorsal direction of spiralia, elaborate ornamentation, and frills evolved in the latest Katian into early Silurian time. Solid teeth seen in distantly related clades from latest Katian onwards may be an analogous feature. The Late Ordovician Mass Extinction (LOME) is indicated in the stratigraphical tree together with a possible event at the end of the Aeronian. The tree supports the long-held assumptions that the Plectatrypinae evolved from the Spirigerininae. It further suggests that the genus Tuvaella may be included with the Davidsonioidea. Likewise, the redefined Atrypinae is a sister group of the Lissatrypidae and a derived group in the phylogenetic tree. [ABSTRACT FROM AUTHOR]

The graptolites of the Tøyen Shale Formation of Kinnekulle in Västergötland, south-central Sweden, are described for the first time and their biostratigraphic distribution is documented from drill core and outcrop material. The faunas indicate an age of mid to late Floian (Billingenian), thus showing a reduced biostratigraphic range of the Tøyen Shale as compared to other areas where this rock unit occurs. A considerable stratigraphic gap is apparent at its base, from the late Tremadocian to mid-Floian, as the limestones of the Ceratopyge acicularis trilobite Zone (late Tremadocian Bjørkåsholmen Formation) are followed by shales with a fauna of the Baltograptus jacksoni graptolite Biozone. Unverified records suggest that mid–late Ottenbyan (Hunnebergian) strata (Megistaspis planilimbata trilobite Zone s.l.) locally may be present in the uppermost Bjørkåsholmen Formation as identified herein. There is no indication that the Tøyen Shale reaches into the Dapingian, as Dapingian graptolites have not been recognized. The overlying limestones of the "Lanna Limestone" belong to the Megistaspis polyphemus trilobite Zone and the Baltoniodus triangularis conodont Zone, suggesting a gradual contact of the lithological units. [ABSTRACT FROM AUTHOR]

Conodont speciesIapetognathus fluctivagusandIapetonudus ibexensisare documented for the first time from Australia. The former is the primary marker internationally defining the base of the Ordovician, and the latter is also a distinctive species previously recorded only from the base of the Ordovician in North America. Both species were recovered from a single sample in the Kandie Tank Limestone of the Kayrunnera Group, located about 50 km west of White Cliffs in far western New South Wales. Other species recovered from this sample includeProoneotodusspp.,Cordylodus lindstromi,Cordylodus proavus,Hirsutodontus simplex,Teridontus nakamuraiandVariabiloconussp. Recognition of theIapetognathus fluctivagusBiozone in the Kandie Tank Limestone supports its correlation with the Green Point section (Global Stratigraphic Section and Point for the base of the Ordovician) in western Newfoundland and the Lawson Cove section of Utah (Auxiliary Stratigraphic Section and Point), as well as sections in Asia and South America. Review of other sections in Australia and elsewhere spanning the Cambrian–Ordovician boundary confirms that, in the absence ofI. fluctivagus, the presence ofC. lindstromiis a good proxy for this level. [ABSTRACT FROM AUTHOR]

Ordovician rocks of the Lachlan Orogen consist of two major associations, mafic to intermediate volcanic and volcaniclastic rocks (Macquarie Arc), which aerially comprise several north-south-trending belts, and the quartz-rich turbidite succession. Relationships between these associations are integral to resolving their tectonic settings and opinions range between contacts being major thrusts, combinations of various types of faults, and stratigraphic contacts with structural complications. Stratigraphic contacts between these associations are found with volcaniclastic-dominant units overlying quartz-turbidite units along the eastern boundary of the eastern volcanic belt and along the southern boundary of the central volcanic belt. Mixing between these major associations is limited and reflects waning quartzose turbidite deposition along a gently sloping sea floor not penetrating steeper volcaniclastic aprons that were developing around the growing volcanic centres formed during late Middle Ordovician to early Silurian Macquarie Arc igneous activity. An island arc setting has been most widely supported for the Macquarie Arc, but the identification and polarity of the associated subduction zone remain a contentious issue particularly for the Early Ordovician phase of igneous activity. The Macquarie Arc initiated within a Cambrian backarc formed by sea-floor spreading behind a boninitic island arc and presumably reflects a renewed response to regional convergence as subduction ceased along the Ross-Delamerian convergent boundary at the East Gondwana continental margin. An extensional episode accompanied initiation of the late Middle Ordovician expansion in island arc development. A SSE-dipping subduction zone is considered to have formed the Macquarie Arc and underwent anticlockwise rotation about an Euler pole at the western termination of the island arc. This resulted in widespread deformation west of the Macquarie Arc in the Benambran Orogeny and development of subduction along the eastern margin of the orogenic belt. [ABSTRACT FROM AUTHOR]

This article reports our new interpretations of the depositional environment and provenance of the Dawashan Formation in the Longmuco–Shuanghu–Lancangjiang suture zone (LSLSZ), in the Southern Qiangtang terrane of northern Tibet, in order to gain a better understanding of the Ordovician tectonic evolution of the northern margin of Gondwana. The Dawashan Formation is dominated by greywacke and shale, with interlayered bimodal volcanic rocks that were deposited in a bathyal to abyssal marine basin. The detrital zircons in the greywacke of the Dawashan Formation have peak ages of 550, 988, 1640, and 2500 Ma, indicating a northern Gondwana margin provenance. The bimodal metavolcanic rocks from the Dawashan Formation are dominated by metarhyolite with subordinate metabasalt. The results of zircon LA-ICP-MS U–Pb dating indicate that the metarhyolite formed between 470 and 455 Ma. The metavolcanic samples are bimodal (SiO2 = 45.27–55.05 and 66.09–74.59 wt.%). In comparison, the metabasalt has a wide range of MgO concentrations and Mg#values, contains variable Cr and low Ni concentrations, is depleted in Rb, Ba, and Sr, and is enriched in TiO2, Th, U, Nb, and Ta. Geochemical diagrams show that the metabasalt erupted in an intra-plate environment. The metarhyolites have high SiO2, Th, and U concentrations, low concentrations of MgO, P2O5, Nb, Sr, and Ti, and negative Eu anomalies. The metarhyolites yield negative zirconεHf(t) values (–2.08 to – 4.50) and TCDMmodel ages of 1436–1567 Ma. The metarhyolites formed from magma derived from the partial melting of old continental crust. These data indicate that the Dawashan Formation records Middle–Upper Ordovician bathyal to abyssal turbidite deposition in a deep-water rift basin at the northern margin of Gondwana. [ABSTRACT FROM AUTHOR]

The Lower Paleozoic sediments of Eastern Europe extend from Poland to the Black Sea Coasts. The Lower Ordovician Bakacak Formation and Middle Ordovician–Silurian Karadere, Ketencikdere, and Fındıklı formations of the Western Black Sea Basin contain mudstones and black shales with sandstone and limestone intervals. The mudstones of the Lower Ordovician do not display any potential. But some intervals of the Middle Ordovician–Silurian black shales have potential for unconventional exploration because total organic carbon (TOC) of organic matter contents ranges from 0.11% to 1.94%. Hydrogen index (HI) values of the Karadere, Ketencikdere, and Fındıklı formations are ranging 0–139 mg oil/g TOC. Vitrinite reflection equivalent (Roe) estimation from HI shows that the shales locate within the oil, wet gas-condensate, and dry gas zone. In-situ oil and condensate volumes of the black shales have been calculated between 0 and 2812 mg HC/g TOC. These volumes indicate presence of potentially producible hydrocarbon in the some intervals of the Middle Ordovician–Silurian shales. Mineralogical properties of the Karadere, Ketencikdere, and Fındıklı formations are suitable for hydraulic fracturing because the shales are dominated by quartz/carbonate. Quartz ratio ranges from 12% to 91% with an average 53%. Total calcite/dolomite content is an average of 13/0.5%. Total clay mineral chance between 0% and 39% with an average of 21%. [ABSTRACT FROM PUBLISHER]

By compiling data from literature and unpublished reports a more detailed description is presented on the geographical and stratigraphic distribution of the Alum Shale Formation (ASF) and correlateable units on the East European Platform. In the northern part of Gotland, downfaulted patchy beds of the ASF indicate a former wider extension of the formation. Lower Ordovician (Tremadocian) examples of downfaulted patchy beds are the contemporaneous Sepopol and Nivenskaya formations in northeastern Poland and the Kaliningrad area, as well as the Salantai Formation in the east Baltic area. It is indicated that Furongian-Tremadocian beds, contemporaneous with the Kallavere, Türisalu, Tosna and Koporye formations, in the area of northern Estonia and the northwestern part of the Moscow Basin, extended to the Gotland and the South Bothnian Basin areas. South of Gotland, in the Swedish sector of the Baltic Basin, drill cores show evidence of tectonic movements through the presence of erosional surfaces indicating occasional subaerial exposure. In this region, variations in the areal extent and thickness of the ASF and coeval formations are suggested to be the result of epeirogenic and tectonic block movements. Tremadocian ASF is also indicated to be present south of Gotland. On Gotland, at least 5 m of the ASF is presumed to have been eroded. The Moscow Basin contains 19 m of dark shales (Koporye Formation) which is significantly thicker than in surrounding areas. [ABSTRACT FROM AUTHOR]

Seventeen trilobite species belonging to 16 genera and 13 families are systematically documented from the Houping Formation (upper Dapingian-lower Darriwilian, Middle Ordovician) at the Datangkou and Dacao sections, Chengkou, northern Chongqing. Of these, a new species, Mioptychopyge chengkouensis sp. nov., is established and described. New morphological information is provided for previously known species on the basis of new specimens. Two trilobite associations based on faunal composition and dominant forms are distinguished from the Houping Formation, in ascending order, the Agerina Association (from the lower and middle members) and the Nileus-Illaenus Association (from the upper member). The Agerina Association lived in an inner shelf margin environment with carbonate substrate above storm wave base (<70 m deep), whereas the Nileus-Illaenus Association developed in a shallow outer shelf environment below storm wave base (>70 m deep), indicating a rise of relative sea level corresponding to the early Darriwilian transgression. The cluster and nonmetric multidimensional scaling analyses of the trilobites in the formation show that the fauna had a strong endemicity to South China and a close biogeographic connection with east Peri-Gondwana, especially Tarim, Annamia and central Iran. [ABSTRACT FROM AUTHOR]

Tentaculitoid tubeworms, an extinct invertebrate group, is being reported from the Ordovician strata of Spiti, Tethyan Himalaya, India. External and internal moulds of tentaculitoids are preserved in the lower unit of the Takche Formation which is considered early Late Ordovician in age. The assemblage includes Cornulites cf. sterlingensis, Cornulites zatoni, Cornulites sp., and Tentaculites spp. Cornulites cf. sterlingensis, Cornulites sp., and Cornulites zatoni are recorded and described for the first time from the Ordovician strata of India. Though, the occurrence of genus Tentaculites is previously mentioned from the Early Palaeozoic sequence of Spiti, the detailed documentation is provided herein for the first time from the Ordovician sequence of Spiti, India. The occurrence of solitary-free forms of tentaculitoids from shallow marine settings of Spiti, Tethyan Himalaya, India indicates that unattached free forms might have been more competent in the siliciclastic environment of relatively low palaeolatitude than carbonate platforms of lower palaeolatitudes and siliciclastic environments of the highest palaeolatitudes. [ABSTRACT FROM AUTHOR]

Ordovician trilobites from the important sequences of the Taimyr Peninsula, Arctic Russia have been poorly studied since the work by Balashova (1959, 1960). Newly collected and well-preserved specimens from Late Ordovician sections, along with the original collections of Balashova, form the basis of a reappraisal of 56 Upper Ordovician (Sandbian–Katian) trilobites. New species include Bronteopsis tenuirhachis, Dionide trigintasegmentata, Failleana superba, Pararemopleurides ornatissimus, Raymondella plastron, Robergia subtilis and R. nikolaiseni. Probable new species include: Stenopareia sp. aff. S. glaber, and Stygina sp. aff. S. latifrons. A new subgenus Bilobaspis of the monorakine genus Evenkaspis, and a new species, Evenkaspis (Bilobaspis) mirabilis, are proposed. Thoracic segments and pygidium are correctly associated for the first time with cephala of the hitherto poorly understood Taimyraspis. The genera Effnaspis and Yumenaspis are likely junior synonyms of Taimyraspis. A placement within the Ityophoridae is suggested for Taimyraspis, together with the closely related genera Ityophorus and Frognaspis. Comparison of Goldillaenoides taimyricus with Failleana suggests that these are also closely related. A provisional placement of the former in the Styginidae is adopted. Bronteopsis nannus Balashova could be a juvenile B. tenuirhachis, and is regarded as a nomen dubium. The genus Ceratevenkaspis dominates among the monorakines on Taimyr, while Monorakos itself has not been collected. Robergia nikolaiseni has a narrow cranidial border, which is also present in the type species of Robergia. Two biofacies are identified in the current collections. The first, the raphiophorid association, is widespread around low latitude Ordovician palaeocontinents, identifying marginal shelf sites; the association is not critical in defining palaeocontinents themselves. Inner shelf faunas of the monorakine-cheirurid-illaenid association have taxa that comprise a distinctive group with a strong link between Taimyr and the Ordovician Siberian craton. The trilobites described herein support reconstructions showing Taimyr peripheral to the Siberian craton during the Ordovician. [ABSTRACT FROM AUTHOR]

The assessment of shale gas potential for the Ordovician Pingliang Formation and Carboniferous–Permian Taiyuan and Shanxi formations in the northwest margin of Ordos Basin, China provides insight into how fluctuation in depositional environments has a significant role on lithofacies and shale gas potential. To investigate the shale gas potential, a series of measurements (i.e. Rock-Eval pyrolysis, maceral composition analyses and X-ray powder diffraction, etc.) on representative outcrop samples were conducted to characterise shale properties. The organic matter from marine Pingliang shale is predominantly type I with a strong predominance of sapropelinite, whereas the transitional Taiyuan-Shanxi shales are dominated by types II to III kerogen. Furthermore, the Pingliang shale is characterised as a 'poor' source rock mainly owing to the lower total organic carbon (TOC) content (average 0.79 wt%) and higher maturity [average 1.78% in vitrinite reflectance (Ro)], while the transitional Taiyuan-Shanxi shales are mostly characterised as 'fair' source rocks, and some samples with high TOC content (more than 2.0 wt%) present good source rocks. It is also found that the sedimentary environment, as a key factor determining the organic matter and TOC content, inevitably influences the type and content of minerals in shale, and controls the shale gas potential. For example, the transitional argillaceous Taiyuan-Shanxi shales are significantly different from the siliceous Pingliang shales, specifically, total clay content for the former is more than 50 wt%, while the latter is rich in quartz content (more than 70 wt%). Additionally, the quartz and clay contents of the Taiyuan shale range widely, especially the smectite content of I–S ML. The barrier coastal facies in the Taiyuan Formation are more conducive to the enrichment and preservation of organic matter because the Shanxi shale was deposited in shallow delta facies with a greater terrestrial influence. Conclusively, the Taiyuan and Shanxi formations have relatively good exploitation potential for shale gas, especially the relatively high TOC content (average 2.45 wt%) and moderate Ro value (average 1.25%). For future exploration, selecting areas with relatively large shale thickness, high brittle mineral content, stable tectonics and better preservation conditions are key to optimising favourable exploration areas for shale gas. The shale gas potentials of the argillaceous Taiyuan-Shanxi shales and siliceous Pingliang shale are compared. The influence of sedimentary facies on reservoir parameters of marine and transitional shales is established. This is a first detailed comparison of the marine and transitional shale gas potential in the northwest margin of Ordos Basin, China. [ABSTRACT FROM AUTHOR]

A new brachiopod species, Westonia mardini, from the Furongian of Turkey and a new occurrence of Westonia urbiona from the Cambrian Series 3 of Iberian Peninsula are reported. These new finds of ‘westoniids’ collected in Gondwana allow the discussion of the functional morphology of their terrace ridges. This structure enabled an effective and rapid reburrowing and allowed the occupation of the shallow marine unstable sands and silts in the shoreface environments. This burrowing mechanism, with their pedicle directed downwards, was unknown before the Cambrian Series 2 and was abandoned chiefly in the Early Ordovician. Here we also review the distribution of ‘westoniids’ in space and time to analyse the diversification, decline and replacement of this important group of brachiopods. They became a significant part of the semi-infaunal marine associations beginning with the Cambrian Series 2 and proliferated in shallow arenaceous shelves during the Cambrian Series 3 and during the Furongian in most palaeocontinents. The acme of ‘Westoniid’ obolids associations was in the Furongian, but locally relict associations were present in high-latitude Gondwana until the Tremadocian. Decline of westoniid associations began during the Tremadocian, being replaced by very diverse smooth-shelled obolid associations with a novel burrowing mechanism and deeper lifestyle. http://zoobank.org/urn:lsid:zoobank.org:act:4D74A740-34FD-4E3A-89BA-F80128800C0E [ABSTRACT FROM AUTHOR]