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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]

Linguliformean and craniiformean brachiopods from the Middle and Upper Ordovician of the Brabant Massif (Belgium) are described for the first time and their palaeoecological and palaeobiogeographical implications are discussed. The restricted and generally poorly preserved material was collected from the Abbaye de Villers (Dapingian–Darriwilian) Formation and from the Katian Huet and Fauquez formations. The dark graptolitic mudstones of the latter unit yielded the most diverse assemblage including seven pseudolingulid, obolid, discinid, and craniopsid species while the Abbaye de Villers and Huet formations only yielded one species each. Due to the scarcity of internal morphological details available, comparison of the pseudolingulid and obolid specimens under investigation here was undertaken by running a Principal Component Analysis using a Log-Shape Ratio transformation of linear measurements. The study of valve shape changes at various growth stages helped identify these Belgian specimens at the family and generic levels. Finally, two unusually long (up to 20 mm) shell repair scars are documented in Pseudolingula and reflect predatory attacks at the anterior margin during early growth stages. [ABSTRACT FROM AUTHOR]

In the middle Sandbian and lower Katian (Upper Ordovician) rocks of the Barrandian area, the fossil remains of conulariids are relatively abundant. Their thecae were sometimes used as solid surfaces for the attachment of epizoans, mostly craniid brachiopods of the genus Petrocrania, more rarely also echinoderms Hemicystites and Agelacrinites, and bryozoans Ceramopora and Spatiopora. The orientation of shells of Petrocrania suggests that conulariids (mostly belonging to the genus Archaeconularia) were dead at the time of the brachiopod attachment, their thecae were partly fragmentary and secondarily replaced. A find of Pseudoconularia grandissima attached to the theca of the cystoid Codiacystis is also reported. [ABSTRACT FROM AUTHOR]

As yet undescribed accumulations of shells of orthoconic cephalopods, which are in some aspects comparable to cephalopod limestones known from the Silurian and Lower Devonian of the Barrandian area and other regions of the world, occur in the Letná and Zahořany formations (middle Sandbian and lower Katian stages, Upper Ordovician, central Bohemia). These accumulated shells are often colonized by sessile organisms. Only a small proportion of these organisms could be attached to shells of alive cephalopods; the majority of them used empty shells as solid substrates. The most abundant epizoan is the cystosporate bryozoan of the genus Ceramopora that often overgrows the cephalopod shells extensively. Holdfasts of the genus Sphenothallus and problematic fossils assigned to the genus Conchicolites are common. Rarer epibionts include the bryozoan Spatiopora, the cystoid echinoderm Codiacystis and the brachiopod Ptychopeltis. Varying sizes of bryozoan colonies occurring on the same cephalopod shell point to several recurring attachment events, probably reflecting reproduction cycles. [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]

Heliolitines are a major tabulate coral group, which experienced their early diversification in the Katian (Late Ordovician). Fossils of this group are well represented in the Kuruktag area of northeastern Tarim Basin, Northwest China, but detailed studies of corals from this area are still lacking. Here, we systematically describe early Katian heliolitines of the Tarim Block based on new material from the lower Katian Yuanbaoshan Formation of southern Kuruktag, which include the plasmoporellids Plasmoporella xinjiangensis and Plasmoporella grandis, the sibiriolitids Mongoliolites obliterans and Mongoliolites sp., the protoheliolitid Wormsipora sp., the proporid Acdalopora sokolovi, the pseudoplasmoporid Navoites irregularis, and the heliolitid Apekinella zeravshanica. A faunal comparison indicates that the biogeographic connections of Tarim Block are closest to Chu-Ili and South Tienshan, but relatively weaker with Qilian and North China.

Machaeridians are armoured annelids that were morphologically diverse during the Palaeozoic. The scleritome developed from fleshy protrusions at the base of each parapodium, with alternating segments giving rise to differentiated inner and outer shell plates. The elytra‐like anatomy of the shell‐bearing soft tissues and distinctive jaw apparatus support an affinity of machaeridians with aphroditacean scaleworms. While frequently found as disarticulated remains, whole scleritomes of machaeridians are rare. Only a few species are represented by multiple articulated individuals, rendering many aspects of our knowledge of scleritome construction and growth uncertain. Here we describe a collection of articulated scleritomes of the plumulitid machaeridian Plumulites tafennaensis Chauvel from the Upper Ordovician (Katian) Upper Tiouririne Formation of Morocco that includes individuals representing both adult and juvenile stages. These scleritomes shed light on the morphology of the anterior region in plumulitids and show an increase in the number of shell plates with increasing size, suggesting that unlike some derived lepidocoleids, at least some plumulitids added segments repeatedly during ontogeny. Shell plates with a distinctive umbo have previously been assigned exclusively to the anterior region, but our material shows that they are present along the scleritome, with corresponding sclerites on the opposite side of the skeleton showing normal morphologies. We suggest that these plates are abnormal and best explained as healed injuries, replacing plates that had been previously removed from the body, demonstrating the capacity for machaeridians to regenerate lost body parts, a feature that is widespread in living annelids. [ABSTRACT FROM AUTHOR]

The tectonic setting of the southernmost part of the eastern margin of Laurentia during the Blountian tectophase (~472–452 Ma) of the Ordovician Taconic Orogeny remains unresolved. Tephras produced by explosive volcanism during this early phase of the orogeny are now K-bentonites, and in many locations, they are interbedded with mature to supermature quartz arenites. We conducted U-Pb analyses of detrital zircons from the sandstones, and of zoned magmatic zircons from the K-bentonites, to constrain the tectonostratigraphic setting with more precision. We also used geochemical fingerprinting of apatite phenocrysts to correlate the K-bentonites in these sandstones along the tectonic front, and we then integrated these results with a depositional systems study of the quartz arenites to further constrain and test competing models of the regional tectonomagmatic setting during that time. The general dearth of detrital zircons that have ages contemporaneous with the volcanic activity, coupled with the predominantly Precambrian ages of the zircons in these Lower Paleozoic quartz arenites that otherwise lack volcaniclastic components—such as detrital VRFs or a muddy matrix derived from an eroding volcanic arc—suggests that magmatic zircons from the tephra layers entered the depositional system only occasionally, and that the volcanic centers were separated geographically from where these quartzose sands were being deposited. Our findings support a tectonostratigraphic and tectonomagmatic model analogous to a combination of select modern settings in the western Pacific and Indonesia, specifically (1) New Guinea, where mature quartz arenites occur in the Cenozoic foreland succession, and (2) Sumatra, where the enormous Toba caldera formed in association with subduction beneath the Cretaceous-aged continental crust of Sumatra. [ABSTRACT FROM AUTHOR]

The present work analyses the numerical distribution data of ostracods in the Late Ordovician (Katian) deposits of Estonia for establishing trends in carapace morphology along a facies profile from a shallow shelf to a deep basin. We present a quantitative analysis of facies-related trends in carapace size, shape and ornamental features. In addition, changes in diversity as well as major changes in the taxonomic composition of the assemblages are addressed, based on the number of individuals. The quantitative analysis of ostracod distribution data reveals distinct trends in the offshore direction: carapaces become larger and shorter, the dominance of smooth valves decreases and the share of ornamented valves increases. Tuberculate valves are most common in open-shelf environments. Species diversity decreases in the offshore direction. The taxonomic composition changes from a clear majority of podocopes to an association of podocopes and palaeocopes, and further to a majority of binodicopes. The fact that these patterns are persistent throughout the Late Ordovician (within three chronostratigraphic units) suggests that they represent environmental control. Some of the results are not in full agreement with previous observations.

Highly diverse and well preserved organic-walled phytoplankton were recorded from the Darriwilian–early Katian interval of the Borenshult-1 drillcore. We identified 154 species in 53 genera, and three assemblages were distinguished; Assemblage A of a late Darriwilian age, Assemblage B of a Sandbian age (further subdivided into sub-assemblages B1 and B2), and Assemblage C dated as Katian. Taxa with "Silurian affinities" with previous first appearance datum in the early Silurian, Hirnantian, such as Metaleiofusa and Visbysphaera, are here recorded from the late Darriwilian and Sandbian respectively. These occurrences question the relationship between the appearance of pioneering phytoplankton morphotypes and the Hirnantian glaciation. Other taxa with no pre-Silurian records such as Visbysphaera pirifera subsp. minor, Petaloferidium cazurrum and Dorsennidium cf. D. estrellitae are here present in the Sandbian, where bentonite beds are intercalated. The diversity curve of acritarchs shows similarities with those proposed for the Darriwilian-Katian of Baltica with main differences in the interval with bentonite beds representing an intense volcanic activity. The species Metaleiofusa arcuata Wall is here emended and a new combination is proposed: Petaloferidium cazurrum (Cramer) comb. nov. The genus Fankea is recorded for the first time from Swedish strata, suggesting a dominant high- to middle latitudinal distribution instead of a Perigondwanan distribution. We contend that the location of paleo-southern Sweden contributed to the great diversity seen, since a middle-low latitude provided a suitable habitat with warm, shallow water, rich in nutrients. [ABSTRACT FROM AUTHOR]

Conodonts are an important biostratigraphic tool for many Phanerozoic stages. Along with graptolites, they define all global Ordovician Stage boundaries. Within the Upper Ordovician interval, a known species of Amorphognathus tvaerensis (Bergström) is present in both Sandbian and Katian stratotype sections. Study of changes in the succession of A. tvaerensis revealed that elements in the upper part of its range differ morphologically quite distinctly from those in its lower part. Here, they are described as a new conodont species, A. viirae sp. nov. This new species is recognized in several Estonian and Swedish sections, with apparent occurrence also in Mójcza Quarry, Holy Cross Mountains, Poland and Black Knob Ridge, Oklahoma, USA. Detailed analysis of early Amorphognathus elements from Estonian and Swedish sections revealed the absence of A. inaequalis (Rhodes) in both regions, although a conodont subzone based on this species was identified earlier by some authors. Both the absence of A. inaequalis (Rhodes) and recognition of the new species A. viirae sp. nov. resulted in the revision of the conodont zonation, and a new version of it is proposed for the Sandbian Stage in the Atlantic Realm. The new zonation includes (from below) Pygodus anserinus , Baltoniodus variabilis , A. tvaerensis , B. gerdae , A. viirae and B. alobatus Conodont zones. [ABSTRACT FROM AUTHOR]

The present work analyses the numerical distribution data of ostracods in the Late Ordovician (Katian) deposits of Estonia for establishing trends in carapace morphology along a facies profile from a shallow shelf to a deep basin. We present a quantitative analysis of facies-related trends in carapace size, shape and ornamental features. In addition, changes in diversity as well as major changes in the taxonomic composition of the assemblages are addressed, based on the number of individuals. The quantitative analysis of ostracod distribution data reveals distinct trends in the offshore direction: carapaces become larger and shorter, the dominance of smooth valves decreases and the share of ornamented valves increases. Tuberculate valves are most common in open-shelf environments. Species diversity decreases in the offshore direction. The taxonomic composition changes from a clear majority of podocopes to an association of podocopes and palaeocopes, and further to a majority of binodicopes. The fact that these patterns are persistent throughout the Late Ordovician (within three chronostratigraphic units) suggests that they represent environmental control. Some of the results are not in full agreement with previous observations. [ABSTRACT FROM AUTHOR]

The tectonic setting of the southernmost part of the eastern margin of Laurentia during the Blountian tectophase (~472–452 Ma) of the Ordovician Taconic Orogeny remains unresolved. Tephras produced by explosive volcanism during this early phase of the orogeny are now K-bentonites, and in many locations, they are interbedded with mature to supermature quartz arenites. We conducted U-Pb analyses of detrital zircons from the sandstones, and of zoned magmatic zircons from the K-bentonites, to constrain the tectonostratigraphic setting with more precision. We also used geochemical fingerprinting of apatite phenocrysts to correlate the K-bentonites in these sandstones along the tectonic front, and we then integrated these results with a depositional systems study of the quartz arenites to further constrain and test competing models of the regional tectonomagmatic setting during that time. The general dearth of detrital zircons that have ages contemporaneous with the volcanic activity, coupled with the predominantly Precambrian ages of the zircons in these Lower Paleozoic quartz arenites that otherwise lack volcaniclastic components—such as detrital VRFs or a muddy matrix derived from an eroding volcanic arc—suggests that magmatic zircons from the tephra layers entered the depositional system only occasionally, and that the volcanic centers were separated geographically from where these quartzose sands were being deposited. Our findings support a tectonostratigraphic and tectonomagmatic model analogous to a combination of select modern settings in the western Pacific and Indonesia, specifically (1) New Guinea, where mature quartz arenites occur in the Cenozoic foreland succession, and (2) Sumatra, where the enormous Toba caldera formed in association with subduction beneath the Cretaceous-aged continental crust of Sumatra.

The Late Ordovician mass extinction (LOME) has long been known for its association with the Hirnantian glaciations. Two extinction pulses seem to reflect global cooling and warming, respectively. The effects climate change had on Ordovician life are well documented through palaeontological evidence, several geochemical proxies and further simulated in modelling scenarios. Preceding the Hirnantian extinction interval was a phase of prolific faunal migrations in notably the later parts of the Katian. Well-documented evidence shows that low-latitude faunas dispersed to high latitudes, and taxa that had previously been endemic to particularly Baltica and South China, suddenly began to appear in Laurentia. These events, referred to as the Boda warming event and the Richmondian invasion, have been suggested to reflect a biotic response to warmer climate indicating that the onset of the subsequent Hirnantian icehouse marked a considerable environmental shift from the latest Katian warming phase. Whereas a lot of focus has been on untangling the selective effects of the two Hirnantian extinction pulses on different clades, less focus has been on what led to the transition from the Middle Ordovician biodiversity rise to the dispersal phase seen during the Katian. It appears that most clades did not â during any point of time in the Ordovician â surpass the richness levels they had achieved by the earliest Katian. Rather, a plateau was established when all metazoan clades are compiled together. This could suggest that extinction rates began to increase relative to originations. Either a threshold was reached by the early Katian prohibiting ecosystems to expand, or an extinction pulse occurred that decimated overall biodiversity accumulation. Two lines of evidence suggest the latter to be the case. Firstly, several new clades became hugely diverse by the Katian. These include bryozoans, crinoids, rugose and tabulate corals, as well as molluscs such as bivalves and gastropods, and show that obviously increased ecosystem complexity with, for instance, more epifauna and tiering occurred. Secondly, large richness datasets compiled from all metazoan clades differ from biodiversity curves based on individual clades in that they show a drop in richness already by the earliest Katian (as opposed to the classic two-pulsed Hirnantian scenario). This discrepancy has long been an overlooked conundrum that arguably has been ascribed to the larger datasets having been temporally less well-resolved. However, these new multiclade Ordovician biodiversity curves are â in some cases â resolved down to the scale of millennia, and they still depict this large fall in richness levels during the early Katian. As this pattern is observed across vastly dispersed regions, it is arguably a true signal depicting a global extinction pulse that precedes the two classic Hirnantian extinction waves by several million years. If such a three-phased âextended-LOMEâ interval is to be corroborated, it would imply a con­siderably different extinction scenario from the classic Hirnantian one. For instance, most of the Katian would then have to be viewed as being part of a protracted survival phase. In such a scenario, the global dispersal of faunas during the Boda and Richmnondian events could reflect faunas adapting to changing climatic and environmental conditions during not just the classic Hirnantian icehouseâgreenhouse scenario but as part of a prolonged phase culminating with the Hirnantian extinctions. It would further entail a new perspective on the possible mechanisms driving this long extinction phase. Several extinction determinants, both intrinsic and extrinsic may be culprits, but it is hard to overlook the apparent correlation between the start of this âextended-LOMEâ phase and some of the largest volcanic eruptions known in Earthâs history. Future better temporally resolved research into both the interplay between life and the environment during the earlier parts of the Late Ordovician hopefully will shed more light on this fascinating mass extinction event.

Understanding ancient climate changes is hampered by the inability to disentangle trends in continental ice volume from records of relative sea-level change. As a unique coastal deposit in tropical and subtropical regions, beachrock has been proved to be reliable for constraining the glacial meltwater signal and thus the total volume of land-based ice in Quaternary. However, beachrock is rarely recognized in the fossil record due to (a) the two-dimensional distribution of beach deposits, as opposed, for example, to extended platform sediments, and (b) the fact that specific environmental conditions are required in order to lithify sediments directly on the beach. By combining the stratigraphic architecture with petrography of characteristic carbonate cements, we demonstrate the first known occurrence of Ordovician beachrock in the Tarim Block, northwestern China. According to biostratigraphic data, a middle Katian (Upper Ordovician) palaeokarst surface is capped by carbonate conglomerate beachrock and this is suggesting a significant relative sea-level rise in late Katian. The beachrock can be correlated with widespread subaerial exposure surfaces and a pronounced stratigraphic gap within the Katian in northwestern Tarim. We suggest that the beachrock âfingerprintedâ a strong melt-water pulse in high latitudes after a short-lived Katian glaciation, which has not received much attention in scientific papers so far.

Study of a subsurface core (named F688) from northern Indiana provides integrated data sets linking Katian chronostratigraphic records of the Appalachian and Midcontinent basins. The F688 core shows a variety of shallow- and deep-water facies containing numerous, well-preserved and zonally significant fossil species and diagnostic chemostratigraphic patterns. The succession belonging to the Cincinnatian Regional Stage in the F688 core is 210 m thick. Detailed benchtop examination of the succession revealed several phosphatic intervals, rich brachiopod faunas, multiple graptolitic horizons, and at least two tephras. Elemental analysis was conducted at 60 cm spacing quantifying lithofacies composition. Based on these results, the succession was assigned to six previously defined lithostratigraphic units (Kope, Waynesville, Liberty, Whitewater, Elkhorn, and Fort Atkinson formations). This lithostratigraphic succession shares components with both the Appalachian and Midcontinent basins, suggesting deposition near their shared margin. Twenty samples yielded abundant, well-preserved, low-diversity conodont assemblages with long-ranging taxa that clearly demarcate the position of the OrdovicianâSilurian boundary at the top of the succession in the core. More than fifty palynologic samples, targeting graptolite-bearing intervals, were processed for chitinozoans and produced important new insights. The Kope Formation contains the chitinozoan species Belonechitina kjellstromi, Hercochitina downiei, and Clathrochitina sp. nov., co-occurring with a graptolite assemblage suggestive of the Geniculograptus pygmaeus Zone. Samples from the overlying Waynesville Formation produced graptolites indicative of the upper G. pygmaeus to Paraorthograptus manitoulinensis zones co-occurring with the long-ranging chitinozoan species Belonechitina micracantha and Plectochitina spongiosa as well as several new species of the genera Tanuchitina and Hercochitina. Higher in the core, the Liberty, Whitewater, Elkhorn, and Fort Atkinson formations yielded chitinozoan species characteristic of the upper Katian biozones of Anticosti Island and Nevada, such as Tanuchitina anticostiensis, Hercochitina longi, and Eisenackitina ripae. Results of δ13Ccarb analysis reveal partial preservation of the Kope, Waynesville, and Elkhorn excursions. A tephra in the rising limb of the Waynesville Excursion yielded needle-shaped clear zircons that will provide a high-precision U-Pb age. The Fort Atkinson Formation is overlain by the Brassfield Formation containing Silurian conodonts and δ13Ccarb values suggesting an Aeronian age. Chronostratigraphic data from our study of the F688 core resolves longstanding uncertainty about correlations between strata of Katian Age in the Appalachian and Midcontinent basins. Integration of core F688 with our other regional chronostratigraphic data in the Midcontinent Basin demonstrates that the Fort Atkinson Formation of the Indiana and Illinois subsurface is age equivalent to the Fernvale Formation of Tennessee, Arkansas, and Oklahoma. Across this area, the Fernvale is overlain by graptolitic shales of the uppermost P. manitoulinensis to basal Dicellograptus complanatus graptolite zones. By contrast, the type Fort Atkinson Formation of Iowa is interpreted to occur completely within the younger D. complanatus Zone. These regional correlations taken as a whole suggest that the uppermost Katian (all of Ka4) and all but the uppermost Hirnantian are missing throughout much of the Appalachian Basin. By contrast, the Midcontinent Basin contains a much more complete upper Katian and Hirnantian succession. Our comprehensive approach is correcting temporal miscorrelation and providing robust chronostratigraphic context for study of biogeochemical events, which will further enable us to disentangle proxy data and identify the processes that drove the Katian diversity peak and culminated in the Late Ordovician mass extinction.

Ordovician marine sedimentary sequences occur in several widely separated structural blocks in Iran, along the northern margin of Gondwana. In northern Kerman Province, the Ordovician sedimentary interval is known as the Katkoyeh Formation, which encompasses ~ 70-300 m of siliciclastic rocks with scarce carbonate and thick pyroclastic beds in its upper part. Previous studies provided several ages for the Katkoyeh Formation, puzzled by the limited number of palaeontological studies, mostly based on spot samples, the presence of regional important stratigraphic gaps, and the inherent structural complexity of the area. In order to adjust the depositional time of the Katkoyeh Formation, a systematic sampling for microfossils was conducted in the Banestan Section, located about 12 km northwest of the city of Zarand, in the vicinity of the Banestan village. Based on the occurrence of important biostratigraphic species, we recorded three conodont intervals in ascending order in the Katkoyeh Formation, namely the Rossodus manitouensis/Paltodus deltifer Concurrent Range Zone (Tremadocian, Lower Ordovician), the Juanognathus variabilis Range Zone (Floian, Lower Ordovician), and the Icriodella superba Range Zone (Katian-Hirnantian, Upper Ordovician). The conodont biostratigraphy is discussed and analysed, improving the Ordovician intrabasinal correlation of Iran as well as correlation with distant palaeobiogeographic domains. The Upper Ordovician conodont assemblage is accompanied by two new species of ostracods: Satiellina zarandensis sp. nov. and Ceratopsis persicus sp. nov., both suggesting palaeobiogeographical affinities mainly with Gondwana and peri-Gondwanan regions. [ABSTRACT FROM AUTHOR]

Abstract The Ordovician (Hirnantian; 445 Ma) hosts the second most severe mass extinction in Earth history, coinciding with Gondwanan glaciation and increased geochemical evidence for marine anoxia. It remains unclear whether cooling, expanded oxygen deficiency, or a combination drove the Late Ordovician Mass Extinction (LOME). Here, we present combined iodine and sulfur isotope geochemical data from three globally distributed carbonate successions to constrain changes in local and global marine redox conditions. Iodine records suggest locally anoxic conditions were potentially pervasive on shallow carbonate shelves, while sulfur isotopes suggest a reduction in global euxinic (anoxic and sulfidic) conditions. Late Katian sulfate‐sulfur isotope data show a large negative excursion that initiated during elevated sea level and continued through peak Hirnantian glaciation. Geochemical box modeling suggests a combination of decreasing pyrite burial and increasing weathering are required to drive the observed negative excursion suggesting a ∼3% decrease of global seafloor euxinia during the Late Ordovician. The sulfur datasets provide further evidence that this trend was followed by increases in euxinia which coincided with eustatic sea‐level rise during subsequent deglaciation in the late Hirnantian. A persistence of shelf anoxia against a backdrop of waning then waxing global euxinia was linked to the two LOME pulses. These results place important constraints on local and global marine redox conditions throughout the Late Ordovician and suggest that non‐sulfidic shelfal anoxia—along with glacioeustatic sea level and climatic cooling—were important environmental stressors that worsened conditions for marine fauna, resulting in the second‐largest mass extinction in Earth history and the only example during an icehouse climate.

Linguliform brachiopods are a minor but distinctive component of the Palaeozoic Evolutionary Fauna. However, there is no formal research on Katian (Late Ordovician) linguliform microbrachiopods in South China. Fossils from the 'Pagoda', 'Linhsiang' and Daduhe formations, Wanhe section of Yunnan Province, South China, provide a unique opportunity to bridge the gap. Here, we report and systematically describe, for the first time, a deep‐water Katian linguliform microbrachiopod association, including 13 species assigned to nine genera, namely Paterula cf. numerosa Popov, Hisingerella tenuis Holmer, Scaphelasma sp., Torynelasma? sp., Biernatia holmi Holmer, ?Biernatia maruiaensis Percival et al., Biernatia pseudoplana Percival et al., Biernatia wrighti Percival et al., Opsiconidion praecursor Popov et al., Opsiconidion sp., Eoconulus puteus Percival et al., Acanthambonia sp. and Nushbiella lillianae Holmer. To explore the composition and distribution model of global deep‐water micromorphic linguliforms in the Katian, a dataset of occurrence of 40 genera from five superfamilies and 10 localities in Baltica, Avalonia, Australian Gondwana, Boshchekul Island Arc and South China is established. Compared with those of other localities, the Chinese association is dominated by Acrotretoidea with no taxon of Discinoidea or Paterinoidea. The global dataset is analysed using non‐metric multidimensional scaling. The results indicate an endemic biogeographical pattern for the Katian linguliform microbrachiopods, which can be explained by oceanic circulation or environmental differences. [ABSTRACT FROM AUTHOR]

Accumulations of cephalopods in the Late Ordovician (Katian [Ka4]) Troutbeck Siltstone Member of the Ash Gill Mudstone Formation at Skelghyll Beck in the Lake District and in the Keisley Limestone Formation of the Cross Fell Inlier contribute toward an understanding of their respective depositional environments as well as the palaeogeography of the southeastern margins of the Lakesman Terrane. The accumulation present in the Troutbeck Siltstone Member is interpreted as having been deposited in a shallow, near-shore lagoon that supported stromatolite growth. The shore lay to the north of this site. Geopetals infilling cephalopods forming concentrations in the Keisley Limestone Formation indicate that the conchs came to rest on angles of 30–40° to horizontal. The lithologies of the matrix suggest that they were deposited in cavities or fissures from which fine-grained carbonate was either excluded or winnowed away. Both observations accord with hypotheses that the Keisley Limestone Formation represents the remnants of a carbonate mud mound, and facilitate comparison with the contemporaneous Boda mounds of Siljan, Sweden. Comparison with local late Katian – Hirnantian successions indicate that the Keisley mound would have formed a prominent feature on the sea floor, becoming largely buried by argillaceous sediments during the Hirnantian. [ABSTRACT FROM AUTHOR]

Three‐dimensionally preserved pyritic internal moulds of the Late Ordovician graptolites Appendispinograptus leptothecalis and Styracograptus chiai from the Upper Ordovician Wufeng Formation of the Daheba section, Hunan Province, South China, were imaged by micro‐CT. The distinctive pea‐shaped pits/dimples aligned in a zigzag line arising from the second/third thecal pair on the tubarium in these species are interpreted as the surface expression of the junction between the lateral thecal walls and the thickened internal cross‐bars that support the nema. The relations between different internal structures such as the nema, median septum, aboral lists, interthecal septa and cross‐bars are summarized, and examples of these supporting systems in different taxa are illustrated. The presence of isolated cross‐bars in different diplograptid tubarium may suggest that they have evolved as a result of constructional restrictions. [ABSTRACT FROM AUTHOR]

Although Katian conodont faunas from high-latitude Gondwanan to peri-Gondwanan regions are widely referred to in the literature, their taxonomy is not yet stabilised, which is critical to biostratigraphically constrain the climate and tectonic events preceding the Hirnantian mass-extinction. In the present contribution, 595 conodont elements and abundant fragmentary conodont material recovered from meta-limestones of the Casaio Formation, northern Central Iberian Zone, is taxonomically and biostratigraphically analysed. The conodont assemblage is characterised by the genera Amorphognathus, Baltoniodus, Drepanoistodus, "Drepanodus", Eocarniodus, Hamarodus, Icriodella, Istorinus, Panderodus, Sagittodontina, Scabbardella, and Walliserodus, and documents the lower Amorphognathus ordovicicus Zone (Ka3) in Northwest Spain. After the taxonomic analysis, Icriodella iberiensis sp. nov. is proposed, and the complexity of the balognathid genera Sagittodontina and Amorphognathus is further discussed. Based on the composition of the major components, a new Icriodella-Sagittodontina-Amorphognathus Biofacies is introduced. Conodont based correlations and cluster analysis verify the strong similarity of the conodont assemblage of the Casaio Formation with the Thuringian conodont faunas from the Upper Ordovician Mediterranean Province. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Conodonts from the type region of the Oandu Regional Stage (Katian, Upper Ordovician) in NE Estonia were studied. Here, the lower boundary of the stage corresponds to a discontinuity surface at the base of the Hirmuse Formation and, in conodont succession, is marked by the disappearance of Semiacontiodus sp. and Besselodus? sp. The most characteristic taxa of the Oandu Stage are Phragmodus undatus, Icriodella cf. superba and Plectodina sp., which are rare or missing below and above this stratigraphic interval in Estonia. The comparison of conodont faunas from North and South Estonia suggests that the strata in North Estonia correspond to the upper part of the Oandu Stage only as identified in sections in South Estonia. However, the position of the lower boundary of the stage in South Estonia is highly problematic. The boundary between the Amorphognathus tvaerensis and A. superbus conodont zones in Estonia lies within the (upper) Oandu Stage.

The Upper Ordovician sediments of the Bohdalec (Katian) and lower layers of the Králův Dvůr (Katian) formations were exposed at Dolní Počernice, a suburb in the eastern part of Prague, during driving of an underground conduit along the Nad Rybníkem Street at the turn of 2017 to 2018. The full sequence of sediments was not accessible and the investigation was restricted to the material deposited on a nearby dump where it was concentrated mainly on the dark grey siltstone and shale of the Bohdalec Formation, which allowed detailed study of this formation exposed only at a few lasting outcrops. Large amount of these rocks (about 3.000 kg) were transported to the storage place of National Museum at Horní Počernice during several months, and subsequently studied in detail. These occasional outcrops provided a poorly diversified assemblage of invertebrates, characterized by dominance of graptolites and trilobites. This paper focuses on the most common trilobite species Onnia superba (Bancroft, 1929). The studied taxon occurred here mainly as meraspid shields, both cephalic and pygidial or as completely preserved (mostly juvenile) specimens. Several hundreds of collected trilobites and their accumulations document almost a complete ontogenetic development from the degree M1 up to the late holaspid specimens (no protaspid specimens were found). Some meraspid trilobites show marks of disarticulation or typical exuviation patterns, and they can be considered as disintegrated exuviae. On the other hand, outstretched or enrolled complete meraspid specimens or their accumulations (regarded as carcasses) were preserved with articulated free cheeks including long genal spines. These specimens and accumulations provide valuable taphonomical and paleoecological information, whose additional interpretations (together with the study of Onnia superba ontogeny) will be a subject of next investigation. [ABSTRACT FROM AUTHOR]

Binocalix dichotomus gen. et sp. nov. is the first British Ordovician aristocystitid diploporite to be named. It is known from a single holotype that is partly disarticulated and incomplete. Nevertheless, it differs from all previously described aristocystitids in having a pair of relatively large ambulacral facets developed above a smooth ambulacral platform and on a single circum‐oral plate. When densely developed, the diplopores become polygonal and have a central tubercle. They closely resemble those of the sphaeronitid subgenus Sphaeronites (Peritaphros), but all species of Sphaeronites s.l. have narrow ambulacral grooves ending in small facets. The similarities in the diplopores are thought to be convergent. Among aristocystitids, only "Calix" inornatus and Triamara are known to have paired ambulacral facets developed on single circum‐oral plates. The former differs from Binocalix in having a smooth thecal surface and flush ambulacral facets. Triamara has raised ambulacral facets but lacks the distinctive ambulacral platforms found in Binocalix. Its diplopores always lack central tubercles, and currently it is only known from the Silurian. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Latest Sandbian to early Katian sequences across Laurentia's epicontinental sea exhibit a transition from lithologies characterized as 'warm-water' carbonates to those characterized as 'cool-water'carbonates. This shift occurs across the regionally recognized M4/M5 sequence stratigraphic boundary and has been attributed to climatic cooling and glaciation, basin reorganization and upwelling of open ocean water, and/or increased water turbidity and terrigenous input associated with the Taconic tectophase. Documentation of oxygen isotopic trends across the M4/M5 and through bracketing strata provides a potential means of distinguishing among these alternative scenarios; however, oxygen isotopic records generated to date have failed to settle the debate. This lack of resolution is because δ18O records are open to multiple interpretations and potentially confounding factors related to local environmental conditions have not been tested by examining the critical interval in multiple areas and different depositional settings. To begin to address this shortcoming, we present new species-specific and mixed assemblage conodont δ18O values in samples spanning the M4/M5 boundary from the Upper Mississippi Valley, Alabama, and Virginia. The new results are combined with previous studies, providing a record of δ18O variability across SE Laurentia. The combined dataset allows us to test for regional trends at a resolution not previously available. Our results document a ~1.5‰ decrease in values across Laurentia instead of increasing δ18O values across the M4/M5 as predicted in various 'cool-water' scenarios. In short, these results do not support a shift to 'cool-water' conditions as an explanation for changes in early Katian carbonates across the M4/M5. [ABSTRACT FROM AUTHOR]

A continuous record of abundant microspherules, pyrite framboids, and bacterial fossils is obtained from the Upper Ordovician in the Dawangou section of northern Tarim Basin, Northwest China. Chemical and physical characteristics of these microspherules were determined using a scanning electron microscope and an energy dispersive spectrometer. Microspherules were formed as a single spherule, spherule aggregates, and drop‐like particles. Physical morphology of the spherules has no relation to its formational process. Energy dispersive spectrometry results indicate that microspherules are mainly composed of Ca, C, O, Si, Al, S, Fe, and Ti. Thus, these microspherules are further categorized into 5 major types: iron, titaniferous‐iron, siliceous, calcareous, and organic microspherules. The first 3 types of microspherules are likely of volcanic origin rather than extraterrestrial origins (i.e., impact event or cosmic dusts) or modern industrial pollutions due to their morphologies and chemical compositions. Both calcimicrospherules and organic microspherules are biogenic, and they are distributed in the lower part of the studied section (Beds 4–6), in which cephalopods, brachiopods, and bacterial fossils are also commonly present and pyrite framboids are absent. These features generally point to an oxic condition. In contrast, other microspherules are abundant in the upper part of the section (Beds 9–13), in which tiny pyrite framboids (mean diameters 4.6–7.3 μm) are rather abundant and typical of euxinic to dysoxic conditions. Both microspherule and pyrite framboid evidences indicate that the northern Tarim region became oxygen‐poor conditions, which were coupled with intensive volcanic eruptions during the Late Ordovician. [ABSTRACT FROM AUTHOR]

The study of the strophomenide brachiopods of the subfamily Rafinesquininae present in the main Upper Ordovician sections, representing the Mediterranean margin of Gondwana, has revealed an increase in diversity of the group at the region during that time. The studied collections are from the Moroccan Anti-Atlas, the Iberian and the Armorican massifs, the Iberian Chains, Pyrenees, Montagne Noire, Sardinia, and Bohemia. Two genera of the subfamily Rafinesquininae have been recorded. Of them, the cosmopolitan Rafinesquina is the only one previously reported from the region and Kjaerina is found for the first time outside Avalonia, Baltica, and Laurentia. Additionally, two new subgenera have been described, Kjaerina (Villasina) and Rafinesquina (Mesogeina). Furthermore, the new species Rafinesquina (Mesogeina) gabianensis, Rafinesquina (Mesogeina) loredensis, Kjaerina (Kjaerina) gondwanensis, Kjaerina (Villasina) pedronaensis, Kjaerina (Villasina) pyrenaica, and Kjaerina (Villasina) meloui have been described. In addition, other species of these genera previously known from isolated localities in the region, such as Rafinesquina pseudoloricata, Rafinesquina pomoides, and Hedstroemina almadenensis are revised and their geographic range expanded. The adaptive radiation experienced by the rafinesquinines at the Mediterranean region during middle to late Katian, was probably related to changes in the regime of sedimentation and water temperature caused by the global warming Boda event.

A new leptestiid brachiopod species of the genus Sampo and a hesperorthid species of the genus Dolerorthis are described from the Early Katian Oandu Stage of southern Lithuania. The new species Sampo suduvensis and Dolerorthis nadruvensis are common brachiopods for the Howellites wesenbergensis–Hedstroemina subaequiclina–Reushella magna community of the Lithuanian shelf. In the East Baltic the brachiopods of the genus Sampo appear first in the deeper part of the Lithuanian shelf in siliciclastic lithologies. The genus Dolerorthis is identified for the first time in the East Baltic. The new species Dolerorthis nadruvensis differs from other related Hesperorthidae brachiopods in the region. An exception is the Late Katian species Boreadorthis recula from Estonia, which shows similarity with D. nadruvensis in shell size and ornamentation. Still, the generic relationship of these species requires further studies. The new species of brachiopods are a supplement to the brachiopod fauna of southern Lithuania.

Sphenothallus is a problematic fossil with possible cnidarian affinities. Two species of Sphenothallus, S. aff. longissimus and S. kukersianus, occur in the normal marine sediments of the Late Ordovician of Estonia. S. longissimus is more common than S. kukersianus and has a range from early Sandbian to middle Katian. Sphenothallus had a wide paleo-biogeographic distribution in the Late Ordovician. The tubes of Sphenothallus are composed of lamellae with a homo-geneous microstructure. The homogeneous microstructure could represent a diagenetic fabric, based on the similarity to diagenetic structures in Torellella (Cnidaria?, Hyolithelminthes). Tubes of Sphenothallus have an apatitic composition, but one tube contains lamellae of diagenetic calcite within the apatitic structure. Sphenothallus presumably had origi-nally biomineralized apatitic tubes. Different lattice parameters of the apatite indicate that biomineralization systems of phosphatic cnidarians Sphenothallus and Conularia sp. may have been different.

Phylogenetic biogeographic analysis of four brachiopod genera was used to uncover large-scale geologic drivers of Late Ordovician biogeographic differentiation in Laurentia. Previously generated phylogenetic hypotheses were converted into area cladograms, ancestral geographic ranges were optimized and speciation events characterized as via dispersal or vicariance, when possible. Area relationships were reconstructed using Lieberman-modified Brooks Parsimony Analysis. The resulting area cladograms indicate tectonic and oceanographic changes were the primary geologic drivers of biogeographic patterns within the focal taxa. The Taconic tectophase contributed to the separation of the Appalachian and Central basins as well as the two midcontinent basins, whereas sea level rise following the Boda Event promoted interbasinal dispersal. Three migration pathways into the Cincinnati Basin were recognized, which supports the multiple pathway hypothesis for the Richmondian Invasion.

A new online resource, “The Digital Atlas of Ordovician Life: Exploring the Fauna of the Cincinnati Region” (www.OrdovicianAtlas.org), provides a tool for exploring the diversity, systematics, biogeography and stratigraphy of Late Ordovician fossils of the Cincinnati, Ohio region. This atlas has been developed using georeferenced specimen-based data that have been newly digitized as part of a collaborative project to mobilize species occurrence data for public use. The goals of this project are to digitize specimens of Late Ordovician (Katian) fossils from the type Cincinnatian Series that crop out in the Cincinnati, Ohio, USA region, develop a comprehensive online atlas of the fossils and develop outreach materials for K-16 (grade school through college) education and avocational paleontologists.

Ostracods are an abundant but long undervalued component of the fossil associations occurring in the Králův Dvůr Formation (Prague Basin; Czech Republic) of the mid Katian to the earliest Hirnantian (Late Ordovician) age. It has been known that they are abundant but it is first evincibly shown that they were also extraordinary diversified. Twenty-eight (plus two dubious) species are described, with only seven (plus the two dubious) having been recorded in the formation before. Ten species are newly established, one established in another area, and ten are kept in open nomenclature. The stratigraphic distribution of the taxa throughout the formation was observed below, inside and above the Perník Bed, the layer of the carbonaceous mudstone interpreted as a response to climatic changes. The taxa from the Perník Bed are described for the first time and those from the interval above this unit have not been studied in detail yet. The pattern of stratigraphic ranges of the species in the Králův Dvůr Formation shows a decreasing diversity toward the top, and a strong but temporary influence by the taxa which appeared in the Prague Basin during the sedimentation of the Perník Bed in the upper part of the formation. It is significant that only several taxa ranging throughout the formation survived above the Perník Bed. They are interpreted as opportunistic, based on such a distribution pattern. All taxa first appeared in the Perník Bed interval (supposed immigrants), and a part of the basin dwellers prior to the sedimentation of the Perník Bed sedimentation disappeared. Such a distribution pattern is interpreted by cooling accompanied by fluctuations in the latest Katian, which is in agreement with the generally accepted model of strong climatic changes in this stratigraphic interval. Analysis of the genera distribution clearly demonstrates the very close relationship of ostracod associations recorded in the Králův Dvůr Formation to Baltica and noticeably weaker migration among the Prague Basin, Avalonia and Laurentia. [ABSTRACT FROM AUTHOR]

Here we report and describe for the first time the Foliomena Fauna fossil record from Portugal (Kralodvorian, upper Katian). This deep-water brachiopod association originates from the uppermost beds of the Porto de Santa Anna Formation (uppermost Katian), cropping out in several localities of the Portuguese Buçaco-Penacova region (Central Iberian Zone). The three studied localities have yielded different associations, composed of 15 species of brachiopods and two trilobites, including both key elements of the deep water Foliomena Fauna and taxa typically from shallower benthic biotas, e.g. the Nicolella Fauna. The mixed character of the associations indicates that they are probably representatives of the atypical Foliomena Fauna, characteristic of relatively shallow benthic assemblages. The Portuguese associations represent the highest-latitude occurrences of the Foliomena Fauna so far and one of the youngest. In the analyses carried out, the two Portuguese associations are grouped together with the other peri-Gondwanan associations (Sardinia and Carnic Alps) and are included within a major grouping including associations previously interpreted as inhabiting deep-water environments and also predominantly late Katian in age. According to these results, the association of Locality 2 may have inhabited a slightly deeper environment than the one present in Locality 3. This agrees with the presence in the former of a greater number of deep-water genera. Despite of the occurrence of a great number of deep-water taxa in the association of Locality 2, the co-occurrence of several elements related to the shallower water Nicolella Fauna, probably transported offshore as a result of the slope of the inclined shelf, suggest that this association probably inhabited slightly shallower environments than those expected for a typical Foliomena Fauna (BA5-6) with no shallow-water elements represented. This inference is also supported by the absence from the association of cyclopygid trilobites. [ABSTRACT FROM AUTHOR]

A trilobite faunule from the Lower Ktaoua Formation at Jbel Tijarfaouine in the eastern part of the Anti-Atlas, Morocco, includes well-preserved articulated specimens of the trinucleid Declivolithus titan sp. nov., the cyclopygids Cyclopyge sibilla Šnajdr, 1982, and Heterocyclopyge sp., and the dalmanitid Eudolatites cf. E. galafrea Šnajdr, 1987. All species are either most closely related to or are conspecific with taxa from the middle Katian Bohdalec Formation in the Prague Basin, consistent with a supposed Katian age for the middle part of the Lower Ktaoua Formation and amplifying the close palaeogeographic affinities of Perunica and west Gondwana in the Late Ordovician. However, the Cyclopyge species is much more widespread, consistent with its supposed pelagic life habit, being found as far eastwards as Xinjiang Province, China. [ABSTRACT FROM AUTHOR]