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Study of the Ordovician sedimentary sequences of Gorny Altai and Salair has revealed lithological and paleontological features correlating with global sedimentary events:(1) The Acerocare Regressive Event (an initial event in the Early Tremadocian);(2) Black Mountain Transgressive Event (Early Tremadocian);(3) Peltocare Regressive Event (Tremadocian);(4) Kelly Creek Regressive Event (Late Tremadocian);(5) Ceratopyge Regressive Event (Late Tremadocian);(6) Billingen Transgressive Event (Early Floian);(7) Stein Lowstand Event (Middle Darriwilian);(8) Vollen Lowstand Event (Sandbian);(9) Arestad Drowning Event (Middle Sandbian);(10) Frognerkilen Lowstand Event (Early Katian);(11) Linearis Drowning Events 1 and 2 (Middle Katian);(12) Terminal Husbergoya Lowstand Event (Hirnantian); and(13) Hirnantian Lowstand Event (HICE) (Late Ordovician).The chronostratigraphic levels with traces of the global sedimentary events in the Uymen-Lebed structural-facies zone (SFZ) (Gorny Altai) differ from those in the Charysh-Inya and Anui-Chuya SFZ (Altai). In the Ordovician, the Altai basin located in the Charysh-Inya and Anui-Chuya SFZ was a marine area separated from both the Uymen-Lebed basin and the coeval Salair basin. The traces of the global sedimentary and/or biotic events in the Altai and Salair sections can be used as a precise basis for direct correlation of the local stratigraphic units with the units of the International Stratigraphic Chart.

The Pin Formation of the northern Indian Himalaya may contain a record of the late Katian (Late Ordovician) warming event (the Boda Event). Palynological samples collected from two members of this ...

Strata of the Solvik Formation in the central Oslo Region (upper Hirnantian through most of Aeronian) are very fossiliferous and provide a good record relating to the survival and recovery faunas after the end-Ordovician mass extinctions. The ribbed atrypide fauna is especially rich with 21 species present. Samples from most of these taxa have been sectioned to reveal internal structures for taxonomic study. Of these, 13 species belong to the family Atrypidae, three of which are described in the present paper;Dihelictera engerensisn. sp.,Gotatrypa vettrensisn. sp., andRhinatrypa henningsmoenin. gen. The family Atrypidae follows a global pattern of recovery with an increase in diversity registered in upper Rhuddanian and further diversification in Aeronian strata. The focus of this paper is the family Atrypinidae, which shows a different pattern. They are common and fairly diverse near the base of the Rhuddanian in deeper waters and rare further up, especially in the Aeronian. One new genus,Bockeliena, and two new species,Plectatrypa rindiandEuroatrypa?sigridiare defined. The relationship between the subfamilies Spirigerininae and Plectatrypinae is clarified through thin sections of material from the Ordovician/Silurian boundary layers. The plectatrypids originated in Baltica through transitional species found in upper Katian to Hirnantian strata leading from the cosmopolitanEospirigerinato thePlectatrypalineage with imbricate ribbing and, separately, toBockelienaand others with lamellose, widely spaced ornamentation. The Oslo Region probably acted as a nexus for survival and spread of brachiopods after the end-Ordovician mass extinction.UUID:http://zoobank.org/95340b41-5537-4192-9338-211a2940bea8.

A previously unreported calymenid trilobite, Gravicalymene bakeri sp. nov., is described herein from Late Ordovician (latest Eastonian, Katian) shales of the Gordon Group, Tasmania. This is the fir...

[Selective chronology of foreland platform and basin development in the Ottawa Embayment, western Quebec Basin and northern Appalachian Basin (New York, Vermont). , Abstract The Middle to Upper Ordovician foreland succession of the Ottawa Embayment in central Canada is divided into nine transgressive‐regressive sequences that defines net deepening of a platform succession over ~15 m.y. from peritidal to outer ramp settings, then a return to peritidal conditions over ~3 m.y. related to basin filling by orogen‐derived siliciclastics. With a backdrop of net eustatic rise through the Middle to Late Ordovician, there are several different expressions of structural influence on sequence development in the embayment. During the Middle Ordovician (Darriwilian), foreland‐basin initiation was marked by regional onlap with abundant synsedimentary deformation across a faulted trailing‐margin platform interior; subsequent craton‐interior uplift resulted in voluminous influx of siliciclastics contemporary with local structurally influenced local channelization; then, a formation of a platform‐interior shale basin defines continued intrabasin tectonism. During the Late Ordovician (Sandbian, early Katian), structural influence was superimposed on sea‐level rise as indicated by renewed local development of a platform‐interior shale basin; differential subsidence and thickness variation of platform carbonate successions; abrupt deepening across shallow‐water shoal facies; and, micrograben development coincident with foreland‐platform drowning. These stratigraphic patterns are far‐field expressions of distal orogen development amplified in the platform interior through basement reactivation along an inherited buried Precambrian fault system. Comparison of Upper Ordovician (Sandbian‐lower Katian) sequence stratigraphy in the Ottawa Embayment with eustatic frameworks defined for the Appalachian Basin reveals greater regional variation associated with Sandbian sequences compared to regional commonality in base level through the early Katian.]

Subject. The Upper Ordovician reef Bol’shaya Kos’yu, located on the western slope of the Northern Urals in the basin of the Ilych River is a unique object among coeval reefs due to the weak dolomitization of rocks and the ability to trace the phases of its development. Materials and methods. The article presents the results of paleontological, paleoecological and microfacial analyses of reef limestones selected by the author from 12 natural outcrops with a total capacity of about 150 m located along both banks of the Bol’shaya Kos’yu River. Results. The structure of the reef, morphology and taxonomic composition of the frame-forming biota were established, and the important role of sphinctozoal sponges was first identified. Among the reef limestones in the main genetic characteristics that reflect specific depositional environments, was identified three types of microfacies. Type 1 – reef microfacies – framestones and buflestones. Type 2 – microfacies of interbiohermic space and inter-carcass cavities exposed to wave and tidal action – bioclastic and peloid pakstones, biolithoclastic grainstones and lithoclastic rudstones. Type 3 – microfacies of the hidden microcosmic cavities, protected from the active wave impact – wackstone. Сonclusion. The composition of the microfacies and frame-forming biota characterize difficult differentiated, both on a section, and structure the reef, which was formed in the conditions of the carbonate platform-shelf margin with active hydrodynamics. Its growth occurred during transgression, which ended by the end of the middle katian a major regression that stopped its development. The revealed paleontological, paleoecological and microfacial data indicate that starting from the middle katian the first identified sphinctozoal sponges could settle in sublittoral environments with active hydrodynamics at depths up to 20 m.

The Ordovician stratigraphy of southern-central Xizang (Tibet) has been revised based on new conodont data recovered from 43 samples in four stratigraphic units and their integration with existing nautiloid and graptolite data. The Histiodella holodentata and Pygodus serra biozones have been identified respectively in the Alai and Jiaqu formations of the Chiatsun Group exposed near Alai village in Nyalam County within the Himalayan terrane, and the Yangtzeplacognathus foliaceus Subbiozone (lower part of the Pygodus serra Biozone) in the Sangqu Formation exposed at the Guyu section within Zayu County in the Lhasa terrane. Recognition of these biozones has increased the precision of correlation of the middle-upper Darriwilian strata in the region. Regional reassessment of the Ordovician stratigraphy permitted by new biostratigraphic data has allowed revised definitions for the Chiatsun and Keerduo groups and the Sangqu and Xainza formations. The Chiatsun Group is defined herein to include three lithologically distinctive formations in descending order, the Jiaqu, the Alai and the Adang formations. The stratigraphic age for the Jiaqu and Alai formations in the type area ranges from the middle Darriwilian (Histiodella holodentata Biozone) to middle Katian (Hamarodus brevirameus Biozone), but the age of the Adang Formation remains less certain.

The Brechin Lagerstätte of southern Ontario contains an exceptionally diverse and well-preserved Late Ordovician (Katian) crinoid fauna. We describe four genera and eight species of camerate crinoids from the Brechin Lagerstätte, including six new species. Consequently, the total diversity of the fauna now stands at 27 genera and 39 nominal species, thereby making it the most taxonomically diverse Ordovician crinoid fauna known. Taxa described include the diplobathrid Pararchaeocrinus kiddi new species and the monobathrids Glyptocrinus ramulosus Billings, 1856, Periglyptocrinus priscus (Billings, 1857a), Periglyptocrinus astricus new species, Periglyptocrinus kevinbretti new species, Periglyptocrinus mcdonaldi new species, Periglyptocrinus silvosus new species, and Abludoglyptocrinus steinheimerae new species. We summarize the taxonomic composition, diversity, and abundance distribution of all known crinoids from the Brechin Lagerstätte to better characterize the paleoecological structure and complexity of the community. We establish that the fauna is dominated by the subclass Pentacrinoidea, both in terms of abundance and species richness. In addition, we analyze species-level abundance data using Relative Abundance Distribution (RAD) models to evaluate the ecological complexity of the paleocommunity. We found that community structure of the Brechin Lagerstätte is best explained by an ecologically ‘complex’ RAD model, which suggests that species partitioned niches along multiple resource axes and/or the presence of multiple ecological ways of life. These results indicate that the Brechin Lagerstätte is significant not only for being the most taxonomically diverse Katian crinoid assemblage, but also for being an early ecologically complex fauna that developed in the wake of the Great Ordovician Biodiversification Event.UUID: http://zoobank.org/f86582ed-5db6-469E-befe-34b801f9a113

A Late Ordovician brachiopod fauna from the Black River quadrangle (D-1 1:63,360 scale) of east-central Alaska comprises taxa typical of the Late Ordovician brachiopod fauna in the pericratonic epeiric seas of Laurentia, including Hesperorthis pyramidalis (Twenhofel, 1928), Plaesiomys occidentalis (Okulitch, 1943), Eoplectodonta sp., Holtehdalina sp., Leptaena sp., Brevilamnulella minuta n. sp., Tcherskidium tenuicostatum n. sp., Rhynchotrema iowense Wang, 1949, and Whitfieldella sp. The presence of Plaesiomys occidentalis and Tcherskidium tenuicostata n. sp. indicates a latest Katian age by correlation with similar species in the Mackenzie Mountains, southern Manitoba, Anticosti Island, the American midcontinent, Kolyma, and Siberia. Cluster analysis based on 20 well-studied late Katian brachiopod faunas from various regions within Laurentia and elsewhere in other tectonic plates suggests that the small brachiopod faunule from Alaska has the strongest paleobiogeographic affinity with Laurentia, confirming that the Black River quadrangle of Alaska was part of Laurentia during the Late Ordovician.UUID: http://zoobank.org/6b387856-61d5-4685-a592-faf5287c1e0f

Previously undescribed trilobites from the Late Ordovician (latest Eastonian, mid Katian) Gunningbland Formation of central New South Wales include the calymenid Prophalaron jonesi gen. et sp. nov....

The Upper Ordovician Bobcaygeon Formation of southern Ontario is a widespread unit that spans the Sandbian–Katian stage boundary and contains exceptionally preserved invertebrate fossil assemblages, including the famed ‘Kirkfield echinoderm fauna.’ However, the precise correlation of this interval remains poorly understood. This paper presents new data on high-resolution sequence and carbon isotope chemostratigraphy of the Bobcaygeon interval based on new quarry exposures and introduces refined definitions of unit boundaries based on allostratigraphic criteria. Sequence, chemo-, and biostratigraphic evidence indicate that the Bobcaygeon Formation represents a composite unit as it encompasses a major erosional unconformity. The Coboconk and Kirkfield formations, described in the early 20th century, were merged into a single unit, the Bobcaygeon, out of concern that the original lithostratigraphic divisions would be conflated with biostratigraphic zones of the same names. However, these biostratigraphic zones are no longer favoured, and the lower member of the Bobcaygeon is here elevated again to the status of formation (Coboconk Formation) and represents the uppermost portion of the Sandbian M4 sequence. The middle and upper members of the Bobcaygeon, herein reassigned to the Kirkfield Formation, represent the upper Sandbian to lower Katian M5A and M5B sequences recognized widely in the eastern and central United States. The term Bobcaygeon is retained and elevated to the rank of subgroup. The Kirkfield Formation is divided into three members and contacts are refined, placing a 1–2 m transgressive grainstone at the base of each sequence. These units are correlated with equivalent strata of New York and the Cincinnati Arch.

The Wufeng organic-rich shale is widespread in the Upper Yangtze platform, and it is one of the most advantageous shale gas producers in China. Its deposition commenced with the onset of the Boda warming event in the late Katian and terminated at the Hirnantian glacial maximum. The depositional mechanism of the Wufeng Formation was poorly understood owing to its relatively thin thickness, being interpreted as the result of organic matter (OM) accumulation in a shelf setting under anoxic conditions. This study integrated detailed geochemical analyses based on the core samples from three boreholes which are located in the outer-, middle- and inner-shelf of the Upper Yangtze platform, in order to investigate the depositional environments during the deposition of the Wufeng Formation. Geochemical redox proxies (Mo-EF, U-EF, and V/Cr) and productivity proxies (P, Baxs, Sixs) indicate that the deposition of the Wufeng Formation was associated with four intervals (WF1 to WF4), each characterized by its unique geochemical features related to sea-level fluctuations. Black siliceous mudstones deposited during WF1 and WF2 are relatively organic-lean due to low productivity, less favorable preservation conditions, and terrestrial dilution. Whereas black siliceous mudstone deposited during WF3 and WF4 is organic-rich due to high paleoproductivity and conducive preservation conditions. The geochemical proxies (Cd/Mo, Co x Mn) associated with the modern upwelling settings were replicated in the Wufeng Formation, revealing that the outer-shelf of the Upper Yangtze platform was dominated by persistent upwelling. The upwelling-driven primary productivity is considered as the first-order control for the OM enrichment at the outer-shelf of the Upper Yangtze platform. Seasonal upwelling may influence the middle-shelf of the Upper Yangtze Platform, where both primary productivity and preservation played essential roles in the OM accumulation. In contrast, the OM accumulation at the inner-shelf was fundamentally driven by good preservation conditions.

The earliest Petroxestes borings were excavated in large trepostome bryozoans in the Sandbian (earliest Late Ordovician) of Estonia. The Estonian specimens are morphologically similar to the type material from the later Katian of North America. Petroxestes pera is rare in the Sandbian of Estonia and occurs only in biogenic hard substrates. Petroxestes borings occur in muddy environments that were preferred by macroborers in the Hirnantian and early Silurian of North America. It is possible that muddy environments supported higher bioerosion intensities and higher diversity of bioerosional traces in the shallow epicontinental seas of the Late Ordovician. The discovery of Petroxestes in the Sandbian of Estonia supports the idea that there was an earliest Late Ordovician peak in the diversification of borings in Baltica. It is possible that there was a migration of bioerosional trace makers from Baltica to Laurentia in the Late Ordovician.

Upper Ordovician (Katian) to Lower Silurian (Rhuddanian) strata in the Middle–Upper Yangtze Block, South China contain extensive chert beds, although the origin of microcrystalline silica in these cherts is largely unknown. In this study, the mineralogy and structure of chert as well as major, trace, and rare earth elements are used to determine the origin of microcrystalline silica in 29 chert samples from Longmaxi Formation (Rhuddanian) in Baizitian outcrop, west of Kangdian Uplift (KU). Results show that 21 of the 29 chert samples have a biogenic origin, 2 indicate a hydrothermal origin, and 6 show a mixed origin. Cherts from Baizitian outcrop are compared to contemporaneous cherts deposited east of KU. Cherts both east and west of KU are mainly biogenic in origin, which is attributed to high productivity in the paleo-seaway. Hydrothermal microcrystalline silica is relatively uncommon in the Longmaxi Formation across the Middle-Upper Yangtze Block, and only occurs in Baizitian outcrop. Terrigenous influx contributed to chert accumulation both east and west of KU; however, cherts east of KU received much more clastic material than those in Baizitian outcrop. A comparison of chert composition and geochemistry to geological reconstructions of the Middle-Upper Yangtze Block reveal that accumulation of hydrothermal chert is closely linked to tectonic evolution. During the Early Silurian, the Middle-Upper Yangtze Block was in a compressional tectonic regime with limited heat supply, and hence, low hydrothermal circulation; this is manifested in the paucity of hydrothermal microcrystalline silica in cherts east of KU. In contrast, hydrothermal microcrystalline silica in cherts west of KU is interpreted to have formed in an extensional tectonic regime with sufficient heat supply. This research demonstrates that chert source is, in part, tectonic controlled, and chert geochemistry can be used in reconstructing paleoenvironments.

Core samples from the Huaying well, Sichuan Province, have been analyzed for both graptolite biostratigraphy and carbon isotope chemostratigraphy. The result shows a stratigraphic sequence of Lituigraptus convolutus, Stimulograptus sedgwickii and Spirograptus guerichi biozones, and records a strong positive shift of δ13Corg at the base of the Stimulograptus sedgwickii Biozone, which coincides with those from Cornwallis Island (Arctic Canada), Arisaig (Nova Scotia, Canada), and the Barrandian area (Bohemia). Two outcrops were also studied in the Huaying region. The Yanwanggou section shows a continuous, but complicated, stratigraphical sequence, from the upper Katian to the lower–middle Rhuddanian, then a sedimentary hiatus of ∼3.26 Ma, and finally a continuous sequence from the upper Aeronian to the lower Telychian, whereas the Liziya section and the Huaying well exhibit significant hiatus, which lasted from Hirnantian to middle Rhuddanian or early Aeronian times. Therefore, the eastern boundary of the Central Sichuan Oldland during the Ordovician and Silurian transition can be precisely constrained to a narrow area between the Huaying well-Liziya section and the Yanwanggou section, which indicates that the Central Sichuan Oldland was much larger than previously considered. The present data also indicate the existing of a so far unidentified stage of the Kwangsian Orogeny, which resulted in the uplift of some portions of the Yangtze Platform region and the consequent delay of the transgression in those places. The multi-stage hiatus, spanning at least from the upper Katian to middle Aeronian in the study area, resulted from a combined effect of the Hirnantian glacio-eustatic sea-level fall and the regional tectonic activity of the Kwangsian Orogeny.

Hardgrounds from the Upper Ordovician strata of eastern Laurentia exhibit a wide range of morphologies, though the development of their complex surface topographies remains poorly understood. These early lithified seafloors, which can be laterally very extensive, may provide key information about basin dynamics and global ocean fluctuations. Based on spectacular exposures and newly-excavated material, we examined a suite of hardgrounds from the Upper Ordovician (Katian) of southern Ontario and the Cincinnati Arch region and documented the processes of genesis, development, and modification of simple, complex, and block hardgrounds. In this study, we used extensive field work, petrology, and cathodoluminescence to determine the evolution and shaping of hardgrounds as a result of intense submarine erosion and prolonged exposure of these surfaces and reveal a progression from simple to complex hardgrounds and ultimately to isolated cobble- to boulder-sized block hardgrounds. We survey the distribution of hardgrounds in a sequence stratigraphic framework to determine allocyclic controls on hardground development, highlight the important role that mixed siliciclastic-carbonate environments play in promoting the development of heterogeneous hardground topographies, and analyze the effects of high surface reliefs on local depositional and erosional regimes. In addition, we interpret the impact of increasingly abundant complex hardgrounds throughout the Ordovician on hard-substrate community diversification and their contribution to the Great Ordovician Biodiversification Event. We also discuss time-specific aspects of the Late Ordovician that made it a peak interval of hardground proliferation.

Deposition of the organic-rich shales of the Wufeng and lowermost Longmaxi formations (late Katian through Hirnantian) occurred in a relatively stable tectonic setting and commenced at approximately 4.5 Myr prior to the end-Ordovician glacial maximum. These organic-rich shales are important because they provide a continuous sedimentary record of high-frequency eustatic changes associated with ice-sheet expansion and shrinkage. Here, we carried out a high-resolution cyclostratigraphic study of Fe3+ series and associated geochemical analysis of the Wufeng and lowermost Longmaxi shales in order to better understand sea-level cyclicity in the late Katian through Hirnantian ocean. The organic-rich shales deposited during this interval in the EHD1 drill core (Yichang, China) record four major Myr-scale eustatic cycles, which were associated with third-order sea-level fluctuations. Within each of these major cycles, 3–4 minor eustatic cycles corresponding to 405-kyr long eccentricity astronomical cycles were recognized and representing fourth-order eustatic changes. The cyclostratigraphic age of this study is generally in agreement with the radiometric dates in GTS2012, although the duration of the Hirnantian stage is ~0.5 Myr longer than previously thought. This study also infers glacial controls on the depositional environment of the organic-rich shales, as enhanced cooling triggered ice-sheet expansion and concurrent sea-level fall, leading to higher thermohaline circulation intensity and enhanced paleoproductivity through upwelling and terrestrial influx. In contrast, warming intervals led to ice-sheet shrinkage and concurrent deepening characterized by water column stratification and reduced nutrient supply. The results provide evidence in support of continuous continental glaciation in the late Katian through Hirnantian.

A diverse benthic fauna containing exceptionally preserved soft-bodied organisms is described from the new Vaureal Konservat-Lagerstatte from the Upper Ordovician Vaureal Formation (Katian) of Anticosti Island, Canada. These fossils occur as pyritic (or goethitic, if weathered), calcitic aggregates or sediment-filled voids on micritic bedding planes of a marlstone-limestone alternation originated on a shallow tropical carbonate ramp. Many organisms are preserved in association with their traces (e.g. burrows, trails), whose changing shapes indicate increasing cohesiveness of the substrate. Rapid burial (obrution) under dysoxic bottom conditions must have favoured exceptional preservation. Although anatomical details of the organisms are often lacking due to recrystallization, members of different groups of organisms could be interpreted based on their shape and other characteristic features, including those of which represent their oldest fossil record (i.e. Acoelomorpha, Turbellaria, Nemertea, Nematoda), beside Polychaeta, Sipuncula, Ostracoda and other Arthropoda. In parallel with molecular data, which recently have changed the phylogenetic status of some clades, this soft-bodied fauna and their traces not only record their appearance but add to the understanding of their body plan and behaviour. The new Konservat-Lagerstatte provides important information about a diverse benthic community in the Late Ordovician after the Great Ordovician Biodiversification Event (GOBE), and represents a calibration point for comparison across the Late Ordovician mass extinction. Moreover, comparable Fossil-Lagerstatten are probably more common in shallow-marine carbonates than currently known but might have been simply overlooked.

The atrypide brachiopod Schachriomonia is documented here for the first time from the upper Katian Hadabulaktag Formation on the northeastern edge of Tarim Basin in Northwest China. These shells are conspecific with the earlier reported Rhynchotrema pentagonia Fang in Liu and Fang, 1990 from the same region. This species is most similar to Schachriomonia parva Popov et al., 1999 described from the Upper Ordovician of the Chu-Ili and Chingiz terranes and less closely resembles species from North and South China, indicating a close paleogeographic connection between these plates and terranes and Tarim during the Late Ordovician. Its dominance at three horizons in the study area may indicate that this species was an opportunistic colonizer of the seafloor following ecological disruption, or alternatively that the larvae were substrate-selective. Variation in shell shape from a nearly circular shell outline with a dorsal sulcus and ventral fold in the smallest shells to a wider outline with a more reversed dorsal fold and ventral sulcus in the largest is an example of ontogenic development. This may have been an adaptation to accommodate the growing lophophore or development of gonads in the mantle cavity over the life of the brachiopod. A stronger tooth-socket connection in larger shells strengthened the hinge area to better withstand the stresses caused by the mass of a larger shell.

The Katian (Upper Ordovician) Shiyanhe Formation at the Sigang section, Neixiang area, Henan Province, central China, has been investigated for carbon isotope (δ13Ccarb) chemostratigraphy. The carbon isotopic data document signal between the two major Ordovician positive shifts in δ13C, the early Katian Guttenberg and the Hirnantian excursions. The Kope (Ka1/2), Fairview (Ka2/3), Waynesville (Ka3/4), Whitewater (Ka4) excursions and a doubtful Elkhorn (Ka4) excursion are identified herein. The continuous and well-defined conodont zonal succession of the Sigang section provides a secure biostratigraphic framework for the mid-late Katian carbon isotope chemostratigraphy in China. Correlation between carbon-isotope data curve and the relative sea-level changes shows no clear correspondence, and hence the sea-level change is probably not the main driver of δ13C excursions during the Katian. Intercontinentally, the mid–late Katian carbon isotope excursions, identified mainly in the North American and Baltoscandian successions, are useful for improving long-distance stratigraphic correlations. This further suggests that these excursions represent global perturbations in the carbon cycle.

The end-Ordovician mass extinction (EOME) is widely interpreted as consisting of two pulses associated with the onset and demise of the Gondwana glaciation, respectively, with the second pulse eradicating the distinctive, glacially related Hirnantian benthic biota (HBB). A global review of occurrence data of latest Ordovician benthic marine organisms reveals that virtually all warm-water benthic assemblages previously assigned to the HBB comprise two distinct and clearly postglacial faunas, both younger (middle and late Hirnantian, respectively) than the cool-water Hirnantia fauna (latest Katian to early Hirnantian). The newly recognised three Transitional Benthic Faunas (i.e., TBFs 1–3) can be closely tied to graptolite, conodont, and chitinozoan biozonations, the Hirnantian Isotope Carbon Excursion (HICE), and the glaciation, thereby providing an integrated, much higher-resolution timescale for understanding the tempo and nature of the EOME. At this finer resolution, we postulate a more profound impact of the first pulse of the EOME than hitherto envisaged, as evidenced by opportunistic expansion of the Hirnantia fauna globally and the complete absence of metazoan reefs in its immediate aftermath. We also argue, based on high-quality data from well-documented benthic groups in South China (i.e., brachiopods, tabulate and rugose corals, trilobites, and sponges), that the magnitude of the second pulse of the EOME caused by the deglaciation has been overestimated because the two postglacial faunas (i.e., TBFs 2–3) were part of a subsequent recovery phase of marine ecosystems rather than contributing to biodiversity decline. Thus, it is more plausible to reinterpret the EOME as a single-pulse, rapid event that was followed by a prolonged initial recovery intermittently impeded by climatic shocks through the Hirnantian, prior to the onset of a progressive reestablishment of marine ecosystems during the early Silurian (Rhuddanian and Aeronian) associated with an overall amelioration of climatic conditions.

There is no doubt that organic matter plays an important role in shale gas accumulation and storage. Thus, successful evaluation and production strategies of organic-rich shale deposits require an understanding of the range of factors that contribute to the accumulation and preservation of organic matter in these deposits. This paper reports results of a multi-faceted study of two Ordovician–Silurian transition sections of the Upper Yangtze Platform of South China. Organic and inorganic geochemical data are used to reconstruct paleoenvironmental changes across this critical interval of Earth history and to identify those factors that were most important to organic matter accumulation. Deposition of organic-rich shale of the Katian lower Wufeng Formation was favored by rising sea level and diminished clastic sediment content. Black shale of the upper Wufeng preceded Hirnantian glaciation whereas the overlying lower Longmaxi Formation accumulated in association with a post-glacial rise of sea level as well as the peak of Caledonian tectonism. The carbonaceous deposits appear to reflect the combined effects of elevated primary productivity as suggested by Si/Al and Ti/Al ratios, especially in the upper Wufeng, and consequent depletion of water column oxygen (preservation). Consideration of the relationships of redox-sensitive trace element concentrations and total organic carbon content suggest that bottom water conditions fluctuated between anoxic and euxinic during this period, perhaps related to rapid oscillations of sea level. Moreover, the basin appears to have remained connected with the global ocean in spite of Caledonian uplift of bordering areas. Thus, black shale sedimentation on the Upper Yangtze Platform at the Ordovician-Silurian boundary reflects the interplay of climate change and tectonism and their influences on sea level, clastic sediment content, and paleo-productivity.

This study examines oncoids and their diagenetic structures in the lower Ordovician (Katian Stage) Lianglitage Formation in the Tarim Basin, Northwest China. Oncoid morphologies range from spherical and sub-spherical to irregular. Individual oncoids generally range from 4 to 10 mm in diameter, with an average of 8 mm and a maximum of 18 mm. Microbial fossils, including gastropods, sponges, trilobite skeletons, and bryozoans, are abundant in oncoid nuclei. Densely packed, calcified microbial clumps are also observed in some nuclei. Microbial remnants in oncoid cortices appear mainly as filaments. Alternating light and dark laminae are obvious in the oncoid cortices, and both sets of laminae contain extracellular polymeric substances, nanoparticles, and microcrystalline calcite. This suggests that oncoid formation was the result of interaction between microbial chemical processes and the external environment. Microbes and heterotrophic organisms provide the building material for oncoid nuclei formation, and frequent fluctuations in sea level provide favorable hydrodynamic conditions.

The Ordovician peri-Laurentian Grangegeeth Terrane in eastern Ireland and the adjacent Katian to Wenlock Rathkenny Tract are together a relict of the closing Iapetus Ocean. The Rathkenny Tract succession is part of the Laurentian Southern Uplands–Down–Longford Terrane accretionary prism, but the contact between the Rathkenny and Grangegeeth terranes is cryptic. Two cores of Lower Paleozoic strata along a buried projection of the Rathkenny–Grangegeeth outcrops contain volcaniclastic units within a succession of mudstone and siltstone. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of zircons from volcanogenic horizons yielded a maximum depositional age of c. 450 Ma. Nearly 98% of the zircon ages are 480–445 Ma, indicating a proximal volcanic source. The trace element geochemistry of the Ordovician zircons indicates a host magma sourced from continental crust. A diverse ostracod fauna in the mudstones suggests a Katian age and includes species with Baltic, Laurentian and Avalonian affinities. We propose a paired subduction zone model for the emplacement of the Grangegeeth–Rathkenny succession, with the Rathkenny strata deposited on an oceanic plate between the Laurentian margin accretionary prism and the 480–450 Ma Grangegeeth peri-Laurentian microcontinental arc. Volcaniclastic detritus fed into the Rathkenny basin was then incorporated into the accretionary prism. The mixed fauna indicates that the Iapetus Ocean was narrow by Katian time. Supplementary material: Navan zircon U–Pb geochronology and geochemistry data are available at https://doi.org/10.6084/m9.figshare.c.4358243

A revised conodont biozonal scheme for the Ordovician of South China is presented herein based on extensive studies following the pioneer work by the late Professor An and his co-workers in the 1980s. This new classification of 33 biozones and subbiozones includes the conodont succession of the Yangtze Platform (29 biozones and subbiozones), the Jiangnan Slope (17 biozones), and a unique succession in the Qinling Orogen (four Katian biozones). The proposed biozone scheme provides more accurate correlations of the Ordovician strata in South China. As the best known and most detailed Ordovician conodont biozone succession in eastern Gondwana and peri-Gondwana, it will serve as a standard reference for correlation not only in this region but also for comparisons with the well-established biozone successions in Baltoscandia and North America. Furthermore, this new scheme has the potential to improve the precision in reconstruction of the conodont biofacies architecture in space and time. It will also assist in advancing our understanding of the timing and magnitude of biodiversification, oceanographic, and geological events at both the local and global scale.

Species migration events are common features of the fossil record, but the impacts of immigration events vary. In this paper, the pattern and impact of two types of immigration events are compared: ephemeral invasion and biotic immigration events (BIMEs). Specifically, this study focuses on biotic patterns preserved in Edenian, Maysvillian, and Richmondian (Late Ordovician, Katian) age strata in the Cincinnati, USA region. New Edenian occurrences of rhynchonelliformean brachiopod taxa belonging to the classic “Richmondian Fauna” are documented, and the ecological and evolutionary impacts of these short-lived pre-Richmondian invasions and the sustained Richmondian Invasion are compared. The Richmondian Invasion produced substantial ecological changes and evolutionary impacts within the Cincinnatian paleocommunity; however, the ephemeral invasions that occurred in the Kope Formation did not produce a marked or lasting impact on ecological relationships within Cincinnatian paleocommunities. In each instance, an Edenian novel immigration or biotic event was limited in temporal duration and did not exceed the time to deposit a single sedimentary package. Although such ephemeral invasions do not result in community-scale changes, they nevertheless provide important information about basin connectivity, provide insight into abiotic environmental conditions, and can be useful stratigraphic indicators.

A new species of the Paleozoic bryozoan genusPtilotrypaof the order Cryptostomata is described from the lower part of the Yong Limestone Formation, Katian, Upper Ordovician of the Kumaun Tethys Himalaya:Ptilotrypa bajpaiinew species. The presence of the genusPtilotrypain the Tethyan Himalaya suggests paleogeographic connections to the Upper Ordovician of North America and, consequently, Upper Ordovician age for the lower part of the Yong Limestone Formation. This species displays a reticulate colony shape, which suggests an efficient filtering capacity in an environment with a high primary production. Morphological peculiarities and systematic assignment of the genusPtilotrypaare discussed.UUID:http://zoobank.org/898276c8-2924-4da2-ae96-3392cb2ebbc3

Ordovician material from the Platteville Formation (Sandbian) of southern Wisconsin and Big Hill Formation (Katian) of northern Michigan is described that provides novel information about the phylogenetic affinity, taxonomic diversity, and stratigraphic range of the nonbiomineralized taxaButhograptus,Callithamnopsis, andChaetocladus. Two new species ofButhograptus, a previously monotypic genus, are erected on the basis of the Platteville Formation material,Buthograptus gundersonin. sp. andB.meyerin. sp., and new occurrences ofB.laxusare recorded from several localities and two distinct stratigraphic levels within this unit. On the basis of scanning electron microscopic investigation of the material and the fact that each of the threeButhograptusspecies has a close counterpart in the frond morphology of an extant species ofCaulerpa,Buthograptusis interpreted as a member of the green algal order Bryopsidales. New specimens from the Platteville Formation assigned toCallithamnopsisreveal new morphological details for the type species,C.fruticosa(Hall, 1865), aspects of which indicate that the genus belongs to the family Triploporellaceae rather than Seletonellaceae within the green algal order Dasycladales, andChaetocladusmaterial from the Big Hill Formation includes specimens that are formally assigned toChaetocladus dubius(Spencer, 1884), a species of dasycladalean alga known previously only from the mid-Silurian of Ontario.

The Late Ordovician mass extinction (LOME) was a severe biocrisis during the Phanerozoic and in this extinction, trilobites, brachiopods, mollusks, graptolites, conodonts and other types suffered severe mortality, and 85% of marine invertebrate species were eliminated. The potential cause of this mass extinction remains unclear, although glaciation and marine anoxia have received the greatest attention. Herein, we present findings on pyrite morphology, pyritic sulfur isotopic composition and total organic carbon content (TOC) to analyze the evolution of redox conditions across the Ordovician-Silurian boundary in the Yangtze area of South China. Our results show that long-term euxinic conditions interrupted by episodic dysoxic/oxic events occurred from the upper Katian stage to the lower Rhuddanian stage. The two extinction pulses of LOME were coincident with euxinic conditions, suggesting that marine euxinia may have been the main cause of this mass extinction event.

Two new graptolite assemblages are identified from discrete intervals within the Phu Ngu Formation, Na Ri District, Bac Kan Province, north-east Vietnam. The graptolites occur in laminated mud/siltstones thought to be distal turbidite deposits. A low-diversity diplograptid sensu lato assemblage occurs in mud-rich layers that are interlaminated with silty and sandy horizons containing the dendroid graptolite Dictyonema sp. This level also contains orthoconic nautiloids and conulariids. A few metres stratigraphically above, a second more diverse graptolite assemblage comprises a single Dicellograptus, tentatively identified as D. flexuosus, together with Climacograptus dorotheus and Orthograptus truncatus pauperatus in mud and silt laminae that also yield brachiopods, orthoconic nautiloids, conulariids, fragmentary trilobites, and ostracods. The ostracods include the first East Asian occurrence of the typically Baltic genus Kinnekullea, and we describe the new species Kinnekullea gaia. The graptolites suggest a Late Ordovician Katian age, most probably in the Dicranograptus clingani Biozone, this being older than previous biostratigraphical constraints on the Phu Ngu Formation.

The Late Ordovician late Katian was a period of generally warm, transitional greenhouse to icehouse climate with sea-level oscillations dominated by moderate-amplitude eustasy. This study aims to improve the understanding of the climatic and sea-level fluctuations prior to the end-Ordovician glaciation, using a comprehensive core, wireline log, and thin-section dataset spanning the topmost Red River-Stony Mountain Formation within the subsurface of North Dakota, Williston Basin, North America. Eleven facies are identified, interpreted, and grouped into four facies associations, including salina to peritidal evaporative, restricted-marine subtidal, open-marine subtidal, and open-marine deeper water. Stratigraphic trends, basin-wide facies variations, and correlation of individual surfaces for ~380 km across the study area, suggest that the facies were deposited under different climatic and sea-level regimes as part of the long-term Stony Mountain sequence. The sequence (37–52 m) is bounded by anhydrites (basin center) and their correlative thin exposure-related breccias (updip proximal basin), and contains a set of high-frequency sequences (HFS; 2–26 m) that can be traced across the study area. The lowstand systems tract (LST) anhydrites formed in a shallow and well‑oxygenated setting under an arid climate during relatively short periods of the basin restriction. The sea-level rise during the early transgressive system tract (TST) resulted in a higher evapotranspiration rate and an increasingly humid climate that peaked during the late TST with the input of siliciclastics off the Transcontinental Arch. The increased precipitation and runoff resulted in quasiestuarine circulation. Return to semi-arid conditions characterizes the highstand systems tract (HST), with increasingly more restricted, shallow-marine and oxygenated setting with antiestuarine circulation. The work provides insight into the interaction of siliciclastic input, climate, and sea-level changes on depositional dynamics and sequence architecture of a mixed carbonate-siliciclastic-evaporite succession that formed in a tropical epicontinental basin setting prior to the end-Ordovician glaciation.

The evolution of Ordovician cephalopod diversity in the Middle Yangtze region of South China has been analysed. The cephalopods in this region appeared in the earliest Tremadocian, radiated in the Early–Middle Floian and Middle Ordovician, and went through an extinction period during the Late Katian and Hirnantian. The composition of the cephalopod fauna underwent major changes in the Late Floian. Specifically, all the genera occurring in previous time periods disappeared and Tarphyceratida, Actinoceratida, and Orthoceratida appeared and prospered. Differences in the evolution of cephalopod diversity between Middle Yangtze region and other regions were detected, which were caused by differences in the vertical sequence and horizontal combination of controlling factors. Changes in living environments and the distribution of food resources prompted Ordovician cephalopods to evolve adaptations for life in deep-water environments. The low-temperature ocean current near the western coastline of Gondwana created favourable conditions for the Floian peak of cephalopod diversity in South China. The tectonic movements, high rainfall, and relatively closed environment of the Middle Yangtze region led to rapid sea level rise and hindered cephalopod diversification. These processes explain the low cephalopod diversity in the Late Ordovician and the absence of the previously reported Katian radiation peak in this region.

A new rare Upper Ordovician mound dwelling palaeoloricate chiton is described as Crassaplax collicola gen. et sp. nov. from three large isolated intermediate valves from the Katian carbonate mud mounds of the Boda Limestone in the Siljan district of central Sweden. Together with the previously known Spicuchelodes? sp., also from the Boda Limestone, these are the only known Late Ordovician mound dwellers so far among the palaeoloricates, adding to Ordovician environments with reported chiton remains. Crassaplax collicola is distinguished from other Ordovician palaeoloricate chitons by their thick and large valves that can be 2 cm in length, and especially the clear differentiation between the lateral and central valve areas.

In situ LA-ICP-MS U–Pb geochronology has been performed on apatite and zircon within thermally recrystallized clast-laden and clast-poor impact melt rocks from the Brent impact structure. A total of 377 laser analyses on 120 impact melt-grown (n = 9) and impact-recrystallized zircon grains (n = 111) were obtained, from which a concordia age of 452.8 ± 2.7 Ma (MSWD 0.57, n = 11), and a weighted average mean 206Pb/238U age of 453.2 ± 2.9 Ma (MSWD 0.60) (n = 11) are calculated. A total of 300 laser analyses from 100 relict apatite grains were obtained, with an unanchored regression through all data yielding a lower intercept age of 453.2 ± 6.0 Ma (MSWD 5.8, n = 300), that overlaps within error of zircon. 207Pb/206Pb ratios obtained from feldspar clasts within clast-laden impact melt retain the same initial Pb composition as the target rocks from which they are derived, while feldspars that crystallized from impact melt have 207Pb/206Pb ratios indicative of isotopic re-equilibration between basement lithologies of two different ages. A similar variability in 207Pb/206Pb is recorded by apatite. This provides evidence for the involvement of Neoproterozoic Lake Nipissing alkaline suite, as well as Mesoproterozoic Grenville gneisses in the production of impact melt at Brent. Recrystallized apatite grains exhibit enrichments in light rare earth elements (LREEs) along neoblast grain boundaries, indicative of trace element substitution and phase precipitation during impact-induced recrystallization. An age of 452.8 ± 2.7 Ma from zircon and 453.2 ± 6.0 Ma from apatite places the impact event in the Late Ordovician, at or near the Sandbian–Katian boundary, confirming Brent’s involvement in the Middle to Late Ordovician crater cluster event—a period of enhanced impactor flux to Earth related to the L-Chondrite parent body disruption.

The paper presents the latest state of knowledge on the vertical and lateral ranges and characteristics of prospective zones (PZ) within the Lower Paleozoic unconventional hydrocarbon systems in the Baltic-Podlasie-Lublin Basin (Poland). The PZ were identified within the prospective formations based on rigorously determined criteria with the application of stratigraphic, sedimentological, mineralogical, petrographic, geochemical, petrophysical, and geomechanical studies, and interpretations of borehole logs. Archival geological data and information acquired from boreholes drilled recently in concession areas have also been applied in the interpretations. Following these criteria, four prospective zones have been distinguished. The deposits encompass partly or almost completely the Piaśnica, Sasino, and Jantar formations and the lower part of the Pelplin Formation. The characteristic feature of the Lower Paleozoic deposits at the East European Craton (EEC) margin in Poland is the diachronous appearance of the Sasino and Jantar black shale formations from west to east. The Baltic area is most prospective for the occurrence of unconventional hydrocarbon reservoirs in shale formations, specifically the Łeba Elevation, where all 4 prospective zones have been distinguished. The occurrence of liquid and gaseous hydrocarbons is expected in all zones. Due to the very high TOC content and geochemical characteristics, the Piaśnica Formation within PZ1 is the main petroleum source rock in the Polish part of the Baltic Basin. PZ2 (partly corresponding to the Sasino Formation) present in a large part of the Baltic Basin, is the next important prospective unit, despite not being uniform. PZ3 within the Jantar Formation was distinguished only on a limited area of the ˜eba Elevation. Due to the low content of organic matter, the Lublin area is characterized by the lowest hydrocarbon potential. However, low values of that parameter are compensated by a greater thickness and lateral range of PZ4, partly corresponding to the Pelplin Formation. Comparison with other areas within the Lower Paleozoic Baltic Basin reveals the occurrence of shale deposits that may constitute a potential source of hydrocarbons, and that demonstrate diachronism. Towards the east and south-east, ever younger deposits possess the potential for hydrocarbon accumulations. In Poland, in the western part of EEC, these are: the Furongian and the Lower Tremadocian Piaśnica Formation, the Sandbian and Katian Sasino Formation and the Lower/Middle Llandovery (Rhuddanian and Aeronian) Jantar Formation. In the central part of the Baltic Basin (Lithuania), these are the Upper Ordovician and Aeronian shale successions. In the southeastern part of the basin (Ukraine), the Ludlow strata are considered to be the most promising in terms of the potential unconventional hydrocarbons accumulations.

Since 2010 when the North American ELKHORN and Baltoscandic PAROVEJA isotope excursions were first described and named, their mutual age relations have remained uncertain, if not controversial. This was at least partly due to the incompleteness of the ELKHORN excursion in its reference section in western Ohio. The unexpected discovery of an apparently complete ELKHORN excursion in a drill core from St Marys in western Ohio has led to the conclusion that in terms of stratigraphical position and δ13C curve correspondence, the ELKHORN and PAROVEJA excursions are so similar that they apparently represent the same isotopic curve perturbation. The ELKHORN/PAROVEJA excursion occurs in the D. pacificus Graptolite Zone and uppermost A. ordovicicus Conodont Zone in the uppermost Katian Stage (Stage Slice Ka4 of Bergstrom et al. Lethaia 42, 97–197, 2009). Because the designation PAROVEJA was published two months before that of ELKHORN, it has priority as excursion designation. This excursion is particularly well represented in the carbonate successions in the Great Basin of western United States. Chemostratigraphy and biostratigraphy in that region show that the Richmondian transgression was contemporaneous with the beginning of the middle Katian WHITEWATER/MOE excursion. The onset of the Richmondian transgression has long been controversial but now available evidence suggests that it is of essentially the same age across large regions of the southern, western and central United States.

The origin of the organic-rich shale in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation is complex and controversial. This paper reports the geochemical data of Wufeng-Longmaxi Formations in the Upper Yangtze region to restore the paleoenvironment and explore the accumulation mechanism of organic matter. The total organic carbon (TOC) content of the Wufeng Formation was relatively high, with an average of 2.86%. The Lower Longmaxi Formation showed the highest TOC content, with an average of 3.99%, and the upper part was a continuously low value with an average of 1.22%. The paleoproductivity proxies (Babio, Cu/Al, Ni/Al, Siexcess) showed that in the Katian and Rhuddanian-Aeronian Stages, the Upper Yangtze Sea had high primary productivity, indicating that organic matter accumulation was more affected by terrigenous influx and redox conditions. Al, Zr, and Zr/Al indicated that terrigenous influx was relatively high in the Kaitian-Hirnantian Stages, it was at a constant low in the Rhuddanian Stage, and increased again in the Aeronian Stage. The correlations between redox-sensitive trace elements (Mo, U, V) and TOC indicate that the organic-rich shale of the Wufeng Formation was deposited in the anoxic&ndash, euxinic environment. In the Longmaxi Formation, organic-rich shales formed in a more hypoxic environment, and overlying organic-lean shales formed in a suboxic environment. Therefore, the anoxic&ndash, euxinic conditions of the Late Ordovician Yangtze Sea were the main reason for the organic matter accumulation, but the high terrigenous influx caused by regression and/or structural controls diluted the organic matter to some extent. For the Early Silurian, a complete transgression&ndash, regression cycle changed terrigenous influx and redox conditions, resulting in significant differences in organic matter accumulation.

In this chapter, starting with a brief review of the research history and current status in the studies of the Ordovician chronostratigraphy in China, the subdivision of the Ordovician System, definition and recognition of its series and stage boundaries, and possible stratigraphic gaps are discussed in details in order to establish a multidisciplinary stratigraphic correlation through an integrated approach including lithostratigraphy, biostratigraphy, radiometric dating, chemostratigraphy and magnetostratigraphy. Being internationally accepted, the Ordovician System is now subdivided into three series and seven stages, in ascending order, Lower (Tremadocian, Floian), Middle (Dapingian, Darriwilian) and Upper series (Sandbian, Katian, Hirnantian). Three of the seven “Golden Spikes” defining the bases of the Ordovician stages, which were established in 1997–2007, are located in China. As a regionally applied chronostratigraphy, the Ordovician System was subdivided in China into Lower (Xinchangian, Yiyangian), Middle (Dapingian, Darriwilian) and Upper series (Neichiashanian, Chientangkiangian, Hirnantian). This scheme agrees largely with the standard international classification, which can actually be directly applied to China, except for some special circumstances where the Neichiashanian and Chientangkiangian stages of the Upper Ordovician are used. Based on the new studies in recent years and distinctions and differences recognized in the development of the Ordovician System in the constituent terranes of China, a new framework for correlation among the major Chinese palaeoplates or terranes, e.g. South China, North China (including Tarim and Qaidam) and Xizang (Tibet)-western Yunnan, has been established. However, it has been recognized herein that uncertainties still remain on defining the base of the Tremadocian, Dapingian and Katian, and on the correlation between different mega-facies. More specifically, for the Tremadocian, the precise correlation of its base will depend on the better-defined conodont taxonomy, while for the Dapingian and Katian, on the correlation between different mega-facies. It is worthwhile to note that the chemostratigraphic studies of the Ordovician System in China produced the carbonate δ 13C curves for the Darriwilian (Middle Ordovician) and Katian (Upper Ordovician), which show significant differences from the composite global curve. Record of the Ordovician isotopic dating is relatively rare in China, with only three reliable ages from zircons that are all from the upper Katian to Hirnantian of the Upper Ordovician. Abundant bentonite beds in the Upper Ordovician of South China will also provide unique opportunities to advance the isotopic dating and related researches. Studies on the Ordovician magnetostratigraphy need to be significantly enhanced in China, as currently all the available results are restricted to the Lower Ordovician of North China, although they can be correlated with those known from other parts of the world. The analysis of the durational unevenness of the seven stages in the Ordovician supports the possibility to further subdivide the long-durational Tremadocian, Darriwilian and Katian stages, each into two substages.

Thick marine shales occur in the Wufeng Formation and Longmaxi Formation of Sanquan Town of the Nanchuan District, Chongqing Municipality, which is located on the southeast margin of the Sichuan Basin. However, few details of the characteristics of the Wufeng–Longmaxi shales in this area have been reported. In this study, a well approximately 100 m (∼328 ft) deep was drilled. A high-quality shale (total organic carbon [TOC] >2.0 wt. %, clay

A large sample of postembryonic specimens ofDalmanitina proaeva elfridaandD. socialisfrom the Upper Ordovician (Sandbian to Katian) Prague Basin allows for the first reasonably complete ontogenetic sequence of Dalmanitoidea (Phacopina). The material provides an abundance of morphological information, including well-preserved marginal spines in protaspides and meraspides, and hypostome external surfaces throughout. The development ofD. proaeva elfridais unusual due to variability in timing of the first trunk articulation. This broadens our developmental understanding of Phacopina, a diverse group of phacopid trilobites, and also allows us to study the evolution of their specializations in exoskeletal molting behavior. Adult phacopines, unlike most other trilobites, had fused facial sutures. This means that rather than molting through the sutural gape mode, characterized by opening of the facial sutures and separation of the librigenae, they disarticulated the entire cephalon in Salter’s mode of molting. For other phacopine clades (Phacopoidea) the transition to Salter’s mode occurs during the meraspid period or at the onset of holaspis, and its developmental timing is intraspecifically fixed. However, owing to the large sample size, we can see that facial suture fusion likely occurred later inDalmanitina, usually during the holaspid period, and was intraspecifically variable with holaspides of varying sizes showing unfused sutures. Further,D. proaeva elfridaspecimens showed an initial librigenal–rostral plate fusion event, where the librigenae began as separate entities but appear fused with the rostral plate as one structure (the “lower cephalic unit”) from M1, and are discarded as such during molting. Dalmanitoidea is considered to represent the first phacopine divergence, occurring earliest in the fossil record. This material therefore provides insight into how linked morphologies and behaviors evolved, potentially suggesting the timing of facial suture fusion in Phacopina moved earlier during development and became more intraspecifically fixed over geological time.

Storm-dominated siliciclastic shelf deposits in the upper half of the Upper Tiouririne Formation (Upper Ordovician, upper Berounian– c. Katian 1–2) of southern Morocco contain large specimens of at least two species of Archaeoconularia ( A . aff. consobrina and A . cf. imperialis ). Pseudoconularia cf. grandissima occurs in basal beds of the formation, but is far less abundant than Archaeoconularia . The large size of the Archaeoconularia (>500 mm long in some cases) suggests gigantism induced by cold, nutrient-rich waters. Specimens preserving the apical end terminate in a schott, indicating that the conulariids were severed near the apex prior to final burial. Many of the Archaeoconularia occur in monospecific aggregations in which the component specimens exhibit preferential alignment, probably owing to entrainment and burial by storm currents or flows. Some Archaeoconularia are encrusted by edrioasteroids and/or craniid brachiopods, which in certain cases are so closely spaced as to interfere with growth. The edrioasteroids and brachiopods were probably epibionts attached to living, erect or semi-erect conulariids that were partially infaunal. More generally, Late Ordovician conulariid assemblages of South Polar Gondwana and adjacent terranes exhibit low generic diversity relative to those of low- to mid-latitude terranes (Baltica and Laurentia), and are dominated numerically by Archaeoconularia .

The bryozoan fauna from the Xiazhen Formation (Katian, Upper Ordovician) of northeast Jiangxi Province, southeast China is reported here. Seventeen species of bryozoans belonging to fifteen genera and four orders are identified: Homotrypa yushanensis, Homotrypa sp., Prasopora yushanensis, Trematopora sp., Monotrypella sp., Rhombotrypa sp., Orbignyella sp., Constellaria jiangxiensis, Constellaria sp., Stictopora nicholsoni, Trigonodictya parvula, Ptilodictya ensiformis, Stictoporella sp., Pseudopachydictya sp., Nematopora sp., Arthrostylidae sp. indet., and Chasmatoporidae sp. indet. Four of these genera have been reported previously but nine genera (Trematopora, Monotrypella, Rhombotrypa, Orbignyella, Trigonodictya, Ptilodictya, Stictoporella, Pseudopachydictya, and Nematopora), one rhabdomesine and one fenestrate are found for the first time in the Late Ordovician strata of South China. Our palaeogeographical analysis suggests that the bryozoan association is typical for the Katian, which is mostly widespread in Laurentia, Siberia, Baltica and Mediterranean, and displays palaeobiogeographical relationships to the Laurentia–Siberia Province.

Crinoids are a common and well-studied faunal component of the Upper Ordovician (Katian; Edenian) Kope Formation in the greater Cincinnati Arch region, USA. However, a relatively fresh outcrop exposing the Southgate and McMicken members of the Kope Formation at Cleves, Hamilton County, southwestern Ohio, has yielded a crinoid specimen worthy of description and comment. The specimen is a “logjam” of numerous articulated columns of Iocrinus subcrassus displaying parallel alignment, reflecting the influence of storm-generated currents. Iocrinus is not typically found in such a state; the genera Ectenocrinus and Cincinnaticrinus are generally associated with “logjams” in the type Cincinnatian, making this an unusual occurrence. At least one of the columns has the coiled dististele of another, smaller I. subcrassus tightly wrapped around it. Although I. subcrassus is known to employ a coiled dististele as an attachment strategy, ramose bryozoans are generally utilised as substrates and tight coiling around larger I. subcrassus columns has not previously been reported. Preservation of coiled dististeles, in general, is a feature not previously documented in Cincinnatian crinoid “logjams.” This specimen illustrates that unusual, noteworthy and/or rare material representing relatively common organisms continue to be discovered even within extensively studied units in the type Cincinnatian.

Graptolites recovered from the organic-rich intervals, previously named the Boas River Formation in the Upper Ordovician succession on Southampton, Akpatok, and southern Baffin islands provide a reliable age assessment for the Upper Ordovician petroleum source rocks in the northern Hudson Bay, Hudson Strait, and Foxe basins. They are characterised by Anticostia lata and Anticostia hudsoni in the lower Red Head Rapids Formation on Southampton Island; Anticostia decipiens and Rectograptus socialis in the lower Foster Bay Formation on Akpatok Island; and Diplacanthograptus spiniferus and Amplexograptus praetypicalis in the lower Amadjuak Formation on southern Baffin Island. These data suggest that the organic-rich intervals in the northern Hudson Bay and Hudson Strait basins can be correlated to the Dicellograptus anceps and Paraorthograptus pacificus zones of the upper Katian, and the horizon in the Foxe Basin to the Diplacanthograptus spiniferus Zone of the lower Katian. The Boas River Formation is not deemed appropriate to use as it occurs as an organic-rich interbed in different stratigraphic units in different basins; therefore, it is suggested to abandon it as a stratigraphic term.

The Pagoda Formation is a lithologically and biologically distinctive unit among the Upper Ordovician. The strata are characterized by a nodular limestone, which yields fossil assemblages of high diversity. Conodonts of 14 genera 20 species (6 undetermined species) and ostracods of 14 genera 26 species (16 undetermined species) are identified. In addition, spherical radiolarians and minute-walled foraminifers were first reported from this formation in South China. The conodont assemblage is attributed to the Hamarous europaeus Zone, which indicates the Early Katian Age. The conodont HDS biofacies, along with thin-shelled ostracods, spherical radiolarians and foraminifers, suggest relatively deep and quiet water depositional environment. Accordingly, these fossil materials not only enrich the diversity of the Pagoda biota, but also provide evidence for discussions of depositional environments and stratigraphic correlations for the Pagoda Formation.

Altaethyrella tarimensis, a new species of rhynchonellide brachiopod, is described from the late Katian (Late Ordovician) Hadabulaktag Formation in the Kuruktag region of Xinjiang, Northwest China on the northeastern edge of the Tarim Basin. Serial sections of the shell clearly show no dorsal median septum or septalium in the dorsal valve, and no spiralia or atrypide-style crura. Like other species of the genus, A. tarimensis n. sp. exhibits a high degree of intraspecific variation, including variations in shell shape and size, number of ribs in the sulcus at the anterior, and degree of asymmetry. The discovery of Altaethyrella in Tarim has important paleogeographic implications, indicating a close relationship between the Late Ordovician brachiopod faunas of Tarim and those of the Kazakh terranes and North and South China paleoplates, supporting a recently published paleogeographic projection that places Tarim near the Chu-Ili terrane during the Late Ordovician. The abundant large biconvex shells of A. tarimensis n. sp. would have provided a firm substrate for encrusting filter feeders like bryozoans to establish on the Kuruktag Platform.UUID: http://zoobank.org/df8843cd-4db0-48e7-ba03-bf0ce81c4f01

The 87Sr/86Sr ratio in gypsum and limestones of the Ordovician section of the Moyero River decreases from the bottom upward from 0.7091‒0.7095 in the Irbukli Formation (Nyaian Regional Stage, ~Lower Ordovician Tremadocian Stage) to 0.7080 in the upper part of the Dzherom Formation (Dolborian Regional Stage, ~Upper Ordovician Katian Stage), which is well consistent with biostratigraphic subdivision of the section and existing concept concerning the strontium isotope evolution of the World Ocean. The most characteristic feature of the carbon isotope curve is decrease of δ13С values in carbonates from weakly positive values (0.5…1.1‰) in the Irbukli Formation (Nyaian Regional Stage) to sharply negative values (–5.4...–5.8‰) in the middle part of the Kochakan Formation (top of the Kimaian Regional Stage, ~end of the Dapingian–base of the Darriwilian Stage). Increase of δ18О from 20‒22‰ to 26‒28‰, the negative correlation of δ13С and δ18О, and decrease of δ34S in gypsum from 30‒32‰ to 22‒24‰ in this interval indicate that the 13С depletion of carbonates was not related to the sulfate reduction and oxidation of organic matter during diagenesis and that the negative δ13С excursion was of primary nature. The presence of negative δ13С anomalies at this stratigraphic level in Ordovician sections of the South and North America (Buggish et al., 2003; Edwards and Saltzman, 2014; McLaughlin et al., 2016) indicates the global or subglobal distribution of this event, which was possibly related to the emergence of the oldest ground vegetation. Against the general decrease of δ13С, the lower part of the section reveals three low-amplitude (1‒2‰) positive excursions, the position of which in general confirms the existing correlation scheme of the Moyero River section with the international scale. The upper part of the section is characterized by the alternation of low-δ13С intervals (from–2 to–3‰) and brief positive excursions with amplitude of 0.5‒1.3‰. The positive δ13С excursion terminating the Ordovician section of the Moyero River correlates with the δ13С excursion in the middle Katian Stage, while the δ13С excursion in the lower part of the Baksian Regional Stage correlates with the excursion marking the Katian–Sandbian boundary.

The Brechin Lagerstätte (Katian, Ordovician) from the Lake Simcoe region of Ontario, Canada contains a diverse array of echinoderms. Here, we describe seven disparid and two hybocrinid crinoids (subclass Pentacrinoidea, infraclass Inadunata), including a new disparid species belonging to the Anomalocrinidae (order Homocrinida). In total, the disparids include Anomalocrinus astrictus n. sp.; Cremacrinus guttenbergensis Kolata, 1975; C. inaequalis Billings, 1859; Daedalocrinus bellevillensis Billings, 1883; Eustenocrinus springeri Ulrich, 1925; Iocrinus trentonensis Walcott, 1883; and Isotomocrinus tenuis Billings, 1857b. The hybocrinids include Hybocrinus tumidus Billings, 1857a and Hybocystites problematicus Wetherby, 1880. Previously known from only the holotype, three additional specimens of E. springeri expand our understanding of this unusual crinoid. Nomenclatural acts include: (1) the recommended designation of D. kirki Ulrich, 1925 as a junior synonym of D. bellevillensis is followed; (2) Hybocrinus pristinus Billings, 1858 is designated as a junior synonym of H. tumidus, and previous decisions are followed to retain Hybocystites eldonensis (Parks, 1908) as a junior synonym of H. problematicus; (3) although probably assignable to Anomalocrinus Meek and Worthen, 1865, the aberrant crinoid Glaucocrinus falconeri Parks and Alcock, 1912, and its genus Glaucocrinus Parks and Alcock, 1912, are designated as nomena dubia; (4) Iocrinus similis (Billings, 1857) is also designated as a nomen dubium; and (5) Iocrinus subcrassus torontoensis Fritz, 1925 is designated a junior synonym of I. subcrassus Meek and Worthen, 1865.UUID: http://zoobank.org/90f8580b-ed7e-4405-97b2-73c9069de7f5