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The distribution of chitinozoans in the Väo Formation (Lasnamägi and Uhaku regional stages, Darriwilian) of the Uuga Cliff, Pakri Peninsula, NW Estonia, was investigated from 62 samples. Chitinozoans are very common and assemblages are diverse, with a total of 36 species and up to 170 specimens per gram of rock. The assemblage is dominated by Belonechitina, Desmochitina, Cyathochitina, and Euconochitina. The relative and absolute frequency of particular taxa displays regular and possibly cyclic patterns, which are not directly reflected in lithology or geochemistry. Abrupt changes in chitinozoan abundance, coinciding with some of the discontinuity surfaces, suggest the presence of stratigraphical gaps. The diversity of chitinozoans is the highest in the lower part of the Väo Formation (Rebala Member), where up to 20 species were identified in one sample and the standing species diversity exceeded 25. Within the studied interval at least 11 biostratigraphical horizons can be distinguished, including the subzonal boundaries within the Laufeldochitina striata Zone. The disappearance of abundant Belonechitina pellifera can be used for tracing the lower boundary of the Uhaku Stage.

Integrated study of the uppermost Ordovician Porkuni Stage in the Stirnas-18 core, western Latvia, has revealed one of the most complete Hirnantian successions in the eastern Baltic region. The interval is characterized by two shallowing upwards depositional sequences that correspond to the Kuldiga and Saldus formations. The whole-rock carbon stable isotope curve indicates a long rising segment of the Hirnantian carbon isotope excursion, with the highest peak in the upper part of the Kuldiga Formation. The bioclast carbon and oxygen curves fit well with the whole-rock carbon data. Micro- and macrofossil data enabled seven combined associations to be distinguished within the Hirnantian strata. The early Porkuni fauna of the Spinachitina taugourdeaui Biozone, with pre-Hirnantian affinities, is succeeded by an interval with a Hindella–Cliftonia brachiopod association, a specific polychaete fauna, the chitinozoan Conochitina scabra, and the conodont Noixodontus girardeauensis. The middle part of the Kuldiga Formation is characterized by a low-diversity Dalmanella testudinaria brachiopod association, high diversity of scolecodonts, and the occurrence of the chitinozoan Lagenochitina prussica. From the middle part of the Kuldiga Formation the youngest occurrence yet known of the conodont Amorphognathus ordovicicus is reported. Also typical of the Kuldiga Formation is the occurrence of the trilobite Mucronaspis mucronata. The uppermost Hirnantian Saldus Formation contains no shelly fauna, but yields redeposited conodonts and at least partly indigenous chitinozoans and scolecodonts. Palaeontological criteria and stable isotope data enable correlation of the Stirnas section with other Hirnantian successions in the Baltic region and elsewhere.

A new Late Ordovician polychaete genus Kaljoprion, with K. laevaensis gen. et sp. nov. as the type species, is described from the Nabala Regional Stage of the Laeva-18 drill core, central Estonia. The genus has a labidognath-type apparatus with the first and second maxillae equipped with anterior denticles developed into characteristic transversal ridges. Similar dentaries are observed in the jaws of distantly related Rhytiprion, suggesting a common feeding habit of both genera and representing a case of convergent evolution among Palaeozoic polychaetes.

A previously unknown outcrop of the Kinnekulle K-bentonite (metabentonite) is reported from the Põõsaspea cliff, NW Estonia. The bed has a sharp lower and a gradational upper contact and comprises ca 28 cm of clay overlain by ca 10 cm of hard K-feldspar-rich variety. The latter contains a layer of breccia, which indicates early onset of recrystallization and hardening of volcanic material. The discovery shows that the Põõsaspea cliff section is younger than previously thought and includes rocks of both Haljala and Keila stages.

The distribution of five groups of fossils in the upper Llandovery (Telychian) and Wenlock of the Viirelaid core section, Estonia, is presented and discussed in terms of their biozones (conodonts and chitinozoans) and mutual positions (scolecodonts, ostracods, and brachiopods). Graphical correlation of the Viirelaid and Paatsalu sections shows a stronger linear correlation for zonal conodonts than for chitinozoans and scolecodonts. In the given case, this is caused by different nature of zones: chitinozoan zones are based on appearances and/or disappearances of ordinal taxa whereas conodont zonation corresponds, as a rule, to evolutionary succeeding species in the Pterospathodus lineage. At the same time, the positions of chitinozoan zones in the Viirelaid, Ruhnu, Aizpute, and Paatsalu cores are oscillating with respect to conodont zones.

Integrated palaeontological and sedimentological study of the Upper Ordovician Vormsi Stage in the Lelle drill core section, Central Estonia, revealed an association of shelly fauna containing the endemic saukrodictyid brachiopod Hulterstadia cor (Wiman), which is otherwise known only from erratic boulders close to Hulterstad in the southeastern area of the Island of Öland, Sweden. In the Lelle core this fauna occurs in the uppermost Fungochitina spinifera chitinozoan Biozone of mid-Vormsi age. Cyclic changes in the content of siliciclastic material in the carbonate section, and in the predominance of shallower- and deeper-water scolecodonts in the interval of the distribution range of H. cor, suggest sea-level oscillations during mid-Vormsi time. Upper Vormsi strata, corresponding to the Tanuchitina bergstroemi chitinozoan Biozone, including the Acanthochitina barbata Subzone, are characterized by common occurrence of sponge remains. Lithologies of the uppermost part of the Lelle section indicate sedimentation in channel environments. Taxonomic composition of the macrofauna in the core differs considerably from that of North Estonia, but has some similarity with the deeper-water Ashgill faunas in other regions (e.g. Fosse Formation of Belgium and Portrane Limestone of Ireland). The Estonian specimens of Hulterstadia cor are described.

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

The end of the Ordovician witnessed major perturbations in the ecosystem, seriously affecting global marine biodiversity. Nevertheless, some marine organism groups and their crisis-bound palaeogeographic distribution are still understudied. Among the outliers are eunicid polychaetes, even though they flourished and diversified extensively during the Ordovician. A collection of seven genera of jaw-bearing polychaetes, including the new ramphoprionid genus Spitiprion Tonarová, Suttner, & Hints, with type new species of Spitiprion khannai Tonarová, Suttner, & Hints, is described here from Katian (Upper Ordovician) deposits of Spiti, northern India. The new species is preserved as isolated maxillae and a jaw cluster, and 3D models of the maxillary apparatus are reconstructed based on submicron-CT. Along with the scolecodonts, a low-diversity assemblage of chitinozoans was recovered, comprising five genera. The most common chitinozoan species are Acanthochitina cf. cancellata and Spinachitina suecica. [ABSTRACT FROM AUTHOR]

A restudy of the palynology of the Whirlpool Formation and Power Glen Formation in New York (USA) yielded a diverse fossil assemblage with cryptospores, glomalean fungi, acritarchs, chitinozoans, scolecodonts, and [...]

The present study focuses on determining the position of the lower boundary of the Silurian System in the eastern Baltic region. To achieve this, we conducted a comprehensive analysis of stable isotopic curves, combined with previously published data on the graptolite record. Our isotopic correlations are primarily based on the δ13Corgcurve of the Dob’s Linn section, the GSSP of the Silurian System, and the δ13Ccarb curve of the Monitor Range section in Nevada. Our results provide robust evidence for correlating the basal Varbola Formation, the lower part of the Õhne Formation and the Stačiūnai Formation, and suggest their latest Ordovician age. The integration of stable isotopic data and graptolite records allows for a more accurate characterisation of the Ordovician–Silurian boundary in this region. [ABSTRACT FROM AUTHOR]

We report the discovery of a rich assemblage of latest Katian and Hirnantian scolecodonts (polychaete jaws) from a new Ordovician–Silurian boundary outcrop in the Reinu quarry, northern Estonia. The recovered polychaete fauna contains at least 40 species attributed to 11 families. Many common taxa appear to range from the latest Katian to the Hirnantian and into the Rhuddanian, indicating the resilience of jawed polychaetes to the end-Ordovician mass extinction. The Reinu assemblage is similar to the coeval faunas known from other Baltic sections, as well as from Anticosti Island, Canada, although with some specific features. The study revealed the highest abundance of scolecodonts in the Ordovician of Baltica, with ca 5400 maxillae per kilogram of rock recorded in the Siuge Member of the Ärina Formation, Porkuni Regional Stage, early Hirnantian. [ABSTRACT FROM AUTHOR]

The global Spinachitina fragilis Chitinozoan Biozone has been considered the lowermost Silurian zone in most publications. S. fragilis was first described from the Ohesaare drill core, Estonia, and utilised as a Baltic regional zonal taxon together with Ancyrochitina laevaensis. Despite its wide geographical occurrence, S. fragilishas remained poorly documented in its type region. This has created confusion in taxonomy and distribution of the species. Herein, we have restudied material from the type locality and supplementary sections in the East Baltic region. S. fragilis generally has a very short stratigraphic range, which, according to new data on carbon isotope chemostratigraphy, coincides with the falling limb of the Hirnantian carbon isotope excursion. This suggests the latest Hirnantian rather than the early Rhuddanian age of the Spinachitina fragilis Chitinozoan Biozone in Baltoscandia. Based on this view, we revise the latest Ordovician chitinozoan biozonal scheme for the region. Globally, the S. fragilis Biozone may span across the Ordovician–Silurian boundary. [ABSTRACT FROM AUTHOR]

Micropalaeontological investigations of Upper Ordovician carbonate mud-mounds and enclosing strata of subsurface Gotland, Sweden, demonstrate that jaw-bearing polychaetes formed the most diverse faunal element associated with these build-ups. Although not present within the mound cores (intra-mound facies), scolecodonts, or polychaete jaws, occur abundantly immediately below and particularly above the mounds; the supra-mound facies also has the most diverse fossil assemblages. By contrast to the scolecodont distribution, the most diverse conodont faunas were recorded in the intra-mound facies. This reinforces the fact that scolecodont and conodont abundance and diversity numbers are commonly inverse to one another, suggesting that these metazoans occupied different niches and responded differently to taphonomical processes. The polychaete assemblage has no less than 27 species belonging to 12 genera, of which Oenonites, Mochtyella and Pistoprion are the most abundant. The assemblage has a characteristic Baltic signature and is similar in taxonomic composition to coeval ones from other areas of the Baltoscandian palaeobasin, such as that of present-day Estonia. A principal component analysis clusters the Gotland assemblage most closely to those recorded from shallow to transitional shelf environments of Estonia, indicating that the mud-mounds were formed in such environments. Keywords: benthos, scolecodonts, polychaete jaws, mud-mounds, Upper Ordovician, Gotland, Sweden.

The Ordovician–Silurian (~485–419 Ma) was a time of considerable evolutionary upheaval, encompassing both great evolutionary diversification and one of the first major mass extinctions. The Ordovician diversification coincided with global climatic cooling and paleocontinental collision, the ecological impacts of which were mediated by region-specific processes including substrate changes, biotic invasions, and tectonic movements. From the Sandbian–Katian (~453 Ma) onward, an extensive carbonate shelf developed in the eastern Baltic paleobasin in response to a tectonic shift to tropical latitudes and an increase in the abundance of calcareous macroorganisms. We quantify the contributions of environmental differentiation and temporal turnover to regional diversity through the Ordovician and Silurian, using brachiopod occurrences from the more shallow-water facies belts of the eastern Baltic paleobasin, an epicontinental sea on the Baltica paleocontinent. The results are consistent with carbonate shelf development as a driver of Ordovician regional diversification, both by enhancing broadscale differentiation between shallow- and deep-marine environments and by generating heterogeneous carbonate environments that allowed increasing numbers of brachiopod genera to coexist. However, temporal turnover also contributed significantly to apparent regional diversity, particularly in the Middle–Late Ordovician. [ABSTRACT FROM AUTHOR]

The Baltoscandian lower Palaeozoic succession is well known for the abundance, diversity and excellent preservation of various groups of microfossils, such as acritarchs, chitinozoans, scolecodonts and conodonts. This paper describes a new enigmatic Middle Ordovician organic-walled microfossil Vikisphaera kundana gen. et sp. nov., characterized by a dark brown to black hollow spherical shell, 90-200 µm in diameter, with an equatorial groove and lack of openings. The specimens of Vikisphaera have been collected from several localities across Baltoscandia including Estonia, Sweden, Latvia and northwestern Russia, and their stratigraphic range is restricted to the Kunda Regional Stage, lower Darriwilian. The wide geographical distribution and short temporal range of Vikisphaera imply its biostratigraphic utility. The shape and characteristics of the shell wall of Vikisphaera are different from those of prasinophytes and other organic-walled microfossils common in lower Palaeozoic rocks. The new microfossil resembles egg shells of some invertebrates, such as arthropods, suggesting that it could represent egg capsules of a group of marine metazoans, possibly soft-bodied creatures with low fossilization potential. However, before the metazoan origin of Vikisphaera is confirmed, it can be considered as an acritarch - an organic-walled microfossil of unknown affinity. [ABSTRACT FROM AUTHOR]