Uppermost Katian Research Articles

Latest Ordovician jawed polychaetes, chitinozoans and depositional environments of the Levín section, Prague Basin, Czech Republic

Jawed polychaetes evolved and diversified extensively during the Ordovician. However, Ordovician polychaete jaws (scolecodonts) have remained poorly documented for many regions. This applies for the Prague Basin of peri-Gondwana, from where the previous study on Late Ordovician scolecodonts was published more than 70 years ago, with just two species preliminarily identified. The aim of the present paper was to fill this research gap and to study organic-walled microfossils from the boundary interval of the Králův Dvůr and Kosov formations (uppermost Katian and lowermost Hirnantian) at the Levín locality. As a result, a diverse assemblage of scolecodonts and chitinozoans was discovered. Chitinozoans are represented by at least 24 species from 15 genera, i.e., a relatively diverse assemblage whose species composition points toward the Ancyrochitina merga and Tanuchitina elongata biozones. The recovered jawed polychaete fauna contains at least 19 species from 14 genera. Taxa with labidognath and prionognath type maxillary apparatuses predominate in samples, whereas placognath and ctenognath taxa are relatively rare. A similar pattern is typical for the Laurentian samples but contrasts with the Baltic polychaete faunas. Polychaetaspids dominate in the Levín assemblage, followed by other families such as ramphoprionids, paulinitids, and atraktoprionids. The studied interval in the Levín section is represented by a succession of thin-bedded silty shales with diamictite beds, practically devoid of shelly fossils and with a variable degree of bioturbation. The deposits are interpreted as distal turbidites and debrites, reflecting sea-level changes driven by the growth and retreat of glacial ice and possibly also local tectonics. Reduced diversity and abundance of scolecodonts was recorded in the uppermost part of the Králův Dvůr Formation, which correlates with less bioturbation and finer silt fraction. The reported discovery shows wide geographical distribution and diversity of jawed polychaetes before and during the Hirnantian glaciation and mass extinction.

A new discoid heliolitid (Proporidae) from the Upper Ordovician of the Baltic area: Morphology and modalities of increase

A species of Proporidae (Heliolitida) forming very small, discoid coralla, is fully described. It is mainly preserved in natural moulds in the Öjlemyr chert, an erratic silicified limestone found in Eridanos deposits surfacing in the west and north-east of the Dutch Overijssel-province and adjoining German area, generally accepted to be Uppermost Katian. The material is assigned to the rehabilitated Pinacopora Nicholson & Etheridge, 1878, a genus closely allied to Propora Milne-Edwards & Haime, 1849, and a new species, Pinacopora baltica is named. The main feature of this species, besides the characteristics of the genus and the biometric data, is the presence of wide, short, and convex septal ridges bearing scattered septal spines, alternating with narrow interseptal furrows. For the first time in heliolitids a pleurodictyoid pattern of growth is described. Only two species of Pinacopora are recorded: P. baltica n. sp. (Upper Ordovician) and P. grayi Nicholson & Etheridge, 1878 (Lower Silurian), respectively from Baltica and Laurentia.

Uppermost Katian (Ka4, Upper Ordovician) conodonts in South China: Biostratigraphy, biofacies, and paleobiogeography

The conodont fauna from the Daduhe Formation in southwestern Sichuan and northeastern Yunnan, southwestern China, is analyzed and correlated with the uppermost Ordovician Amorphognathus ordovicicus conodont Biozone. This age assignment is further supported by the graptolites from the same sections, indicating a Ka4 Stage Slice, i.e., from the Dicellograptus complexus to Paraorthograptus pacificus graptolite biozones. Two common conodont species of the Upper Ordovician, Hamarodus brevirameus and Scabbardella altipes, are reported for the first time from the upper Katian in South China. The analysis of conodont biofacies indicates that the conodont fauna in the Daduhe Formation belongs to the cool-water Hamarodus brevirameus–Dapsilodus mutatus–Scabbardella altipes Biofacies. This discovery provides additional evidence for the cold tongue model during the Late Ordovician. The distribution of Yaoxianognathus yaoxianensis confirms the close biogeographical ties among South China, North China and Tarim. This distinctive species of eastern Gondwana might have originated in North China and dispersed to Tarim and South China.

Upper Katian (Upper Ordovician) trans‐Atlantic δ13C chemostratigraphy: the geochronological equivalence of the ELKHORN and PAROVEJA excursions and its implications

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.

Retracted: The taphonomy of a trilobite fauna from an uppermost Katian echinoderm Lagerstätte in South West Wales

Summary: The uppermost Katian (Rawtheyan) Slade and Redhill Mudstone Formation, in the Llanddowror area of Carmarthenshire in South West Wales, contains an horizon yielding abundant, articulated crinoids, cystoids, mitrate ‘carpoids’, asteroids and ophiuroids. This echinoderm Lagerstatte also includes a rich trilobite fauna dominated by illaenids and is thus unlike any of the other trilobite faunas in the formation, as is the occurrence of several enrolled or partially enrolled specimens. The trilobites and echinoderms provide the same taphonomic signal – the rapid transport and burial of organisms, leading to their death. Transport occurred within sand‐grade sediment without causing disarticulation of skeletons of the animals that were alive immediately prior to the event.

The highest-latitude Foliomena Fauna (Upper Ordovician, Portugal) and its palaeogeographical and palaeoecological significance

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.

Refining 2 km of Ordovician chronostratigraphy beneath Anticosti Island utilizing integrated chemostratigraphy

New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the chronostratigraphic resolution of the nearly 2 km thick Ordovician section below Anticosti Island. A total of 1414 horizons, spaced at 1.0–1.5 m intervals, were sampled from the New Associated Consolidated Paper (NACP) drill core and analyzed for major and trace elemental composition by portable X-ray fluorescence analyzer (pXRF). Select micrite and calcareous shale powders were then analyzed for δ13Ccarb (number of samples, N = 364) and 87Sr/86Sr (N = 25). Our results indicate a Floian to early Darriwilian (F3–Dw1) age for the Romaine Formation, a middle Darriwilian to Sandbian (Dw2–Sa1) age for the Mingan Formation, a lower to mid-Katian (Ka1–Ka2) age for the Macasty Formation, an upper Katian (Ka3) age for the lower Vauréal Formation, an uppermost Katian (Ka4) age for the upper Vauréal, and a Hirnantian (H1) age for the Ellis Bay Formation. This integrated chemostratigraphic and biostratigraphic synthesis establishes the position of numerous unconformities, the duration of the intervening depositional sequences, and rates of sedimentation.

Mean grain size fluctuations of the siliciclastic component in the Aizpute-41 core: implication for end-Ordovician glaciation; pp. 257–263

The article deals with grain size distribution of the insoluble residue of Upper Ordovician carbonate rocks of the Baltoscandian Basin in the West Latvian Aizpute-41 core. Great fluctuations in mean grain size in the sections of the Pirgu (uppermost Katian) and Porkuni (Hirnantian) stages are considered as indications of eustatic sea level fluctuations, pointing to the glaciation in the Hirnantian and its prelude in Pirgu time. An alternative cause of grain size fluctuations might be the up-and-down tectonic movements. Nevertheless, the synchronicity of cessation of fluctuations with the end of the Hirnantian glaciation supports the glaciation-related reasons.

Hirnantian (latest Ordovician) δ13C chemostratigraphy in southern Sweden and globally: a refined integration with the graptolite and conodont zone successions

The δ13Corg chemostratigraphy of the Hirnantian and lower Rhuddanian in the biostratigraphically well-controlled Röstånga-1 drillcore from west-central Scania is used for an improved integration of the Hirnantian Isotope Carbon Excursion (HICE) with the standard graptolite zonation. In this drillcore succession, the end of the HICE corresponds to the top of the range of Metabolograptus persculptus. Baseline δ13Corg values occur in the uppermost Hirnantian Avitograptus avitus Faunal Interval as well as in the Rhuddanian Akidograptus ascensus Zone, and the isotope curve is also tied to the Swedish uppermost Katian and Hirnantian trilobite zonation. Chemostratigraphic data from sections in Västergötland confirm that the beginning of the HICE is at, or very close to, the base of the Skultorp Member of the Loka Formation. The biostratigraphically less precisely controlled end of the HICE is at least locally in the Upper Member of the same formation. The graptolite biostratigraphy in the Mt. Kinnekulle succession indicates that the lowermost Kallholn Formation, which has long been known as the Leonaspis (formerly Acidaspis) Shale, is of Hirnantian rather than earliest Silurian age which is consistent with the age of the lowermost Kallholn Formation in the Röstånga-1 drillcore. Comparisons with Hirnantian sections in the United Kingdom, North America and China make it possible to improve the calibration of the HICE with conodont and graptolite biostratigraphy and confirm the usefulness of δ13Corg chemostratigraphy for detailed correlations. The upper Katian carbon chemostratigraphy in key sections in North America and eastern Baltoscandia indicates that the Elkhorn and Paroveja excursions are the same. Available data are used for a new Hirnantian eustasy-climate-faunal evolution model.

Growth characteristics ofProtoheliolites norvegicus(Tabulata; Upper Ordovician; Estonia)

Protoheliolites is an early heliolitine coral characterized by closely spaced corallites separated in places by sparse coenenchyme. Growth characteristics in the type species, P. norvegicus, are revealed by detailed analysis based on serial peels and thin sections of coralla from the uppermost Katian of north-western Estonia. Colonies of this species had a strong ability to recover from damage and partial mortality, resulting in various forms of rejuvenation, regeneration, fusion and reorganization of corallites; in some cases, this involved relatively large areas of undifferentiated soft parts. The shells of commensal cornulitids became enclosed in host coralla during colony growth. Coralla of P. norvegicus exhibit distinctive growth cycles due to responses to seasonal changes. The production of new corallites by coenenchymal increase usually occurred in low-density bands, in which corallites generally display round to subrounded transverse outlines. In high-density bands, the corallites became crenulated, their wall thickness increased, septal development was more pronounced, and the amount of coenenchyme increased. In addition to these cyclomorphic changes, there were significant astogenetic changes during growth. Compared with the early stage of colony development, distinctive characteristics in the late astogenetic stage include a decrease in the growth rate of the colony, better coordination among corallites, maximum development of corallite crenulations and septa in high-density bands, more numerous coenenchymal tubules and a greater proportion of corallum area occupied by coenenchyme. In general, the role of polyps in determining morphological characteristics of individual corallites, such as tabularium area, corallite crenulations and wall thickness, was subordinate to the astogeny of the colony. Growth characteristics including colony-wide coordination of polyp behaviour and subjugation of individuals to restore the colony following damage suggest a strong astogenetic control and high level of colony integration. Protoheliolites probably arose from a heliolitine genus rather than from a nonheliolitine group as some authors have proposed.

Late Ordovician brachiopods from eastern North Greenland: equatorial offshore migration of the Red River fauna

Abstract: Late Ordovician rhynchonelliformean brachiopods, typical of the North American Red River fauna, are found sporadically in the Børglum River Formation of the Centrum Sø area, Kronprins Christian Land, eastern North Greenland. The geographical distribution of this characteristic brachiopod fauna is thus extended to the easternmost extremity of the Laurentian craton. The assemblage compares specifically with the Hiscobeccus brachiopod fauna, based on key taxa such as notably Hiscobeccus gigas (Wang, 1949), and indicates a late Katian age for this part of the succession. For the first time, this typically inland, shallow‐water fauna is found associated with genera like Bimuria, suggesting a transitional marginal facies with outer shelf benthos. The current study describes a Hiscobeccus fauna that lived at the seaward edge of its preferred habitat. Furthermore, an unpublished Hiscobeccus fauna, from the Børglum River Formation of Peary Land, central North Greenland, as well as several occurrences from the Kap Jackson and Cape Calhoun formations in various parts of Washington Land, western North Greenland, are described here. These show a distinct shift from older strata containing H. capax (Conrad, 1842) to younger strata exclusively yielding specimens of H. gigas. As H. gigas occurs in the upper part of the Cape Calhoun Formation in Washington Land, it indicates that the upper boundary of the Cape Calhoun Formation is considerably younger than previous estimates, reaching into the uppermost Katian (middle Cautleyan–Rawtheyan). The Cape Calhoun Formation correlates with the upper member of the Børglum River Formation and further demonstrates that the Hiscobeccus fauna was widespread in Laurentian marginal settings of North Greenland. Even though the Hiscobeccus fauna was pan‐continental during the late Katian (Richmondian), it possesses a strong provincial signal during the later Ordovician. The new occurrences indicate that this fauna extended to the north‐eastern margin of the Laurentian Craton. It lived in close association with cosmopolitan faunal elements that may have been the earliest sign of the succeeding invasion of migrants from Baltica that arrived later during the Hirnantian. The offshore migration of this atypical Hiscobeccus fauna likely demonstrates the path of warm‐water currents as the Centrum Sø locality was located at the equator during the Late Ordovician.

Acritarchs from the Ordovician–Silurian boundary beds of the Valga-10 drill core, southern Estonia (Baltica) and their stratigraphical and palaeobiogeographical implications

Fourteen samples of the Valga-10 drill core, south Estonia, from the lower Jelgava Formation (middle Pirgu Regional Stage, Upper Katian) to the lowermost Õhne Formation (lowermost Juuru Regional Stage, Lower Rhuddanian) were investigated for acritarchs. The section is biostratigraphically and chemostratigraphically well constrained; it comprises the rugata, taugourdeaui and scabra chitinozoan zones, the ordovicicus and giradeauensis conodont zones and the Hirnantian Isotopic Carbon Excursion (HICE). The good preservation allowed the identification of three prasinophyte phycomata and 52 acritarch species including the four new species Evittia porkuniensis, Helosphaeridium tongiorgii, Nexosarium leherissei and ? Veryhachium bulliferum. One new combination is proposed: Poikilofusa obliquipunctata (Uutela & Tynni 1991) comb. nov. Comparison with contemporaneaous palynofloras shows that eastern Laurentia and Baltica share a high number of species during the latest Katian–Hirnantian. Some of these species show a potential for future improvement of biostratigraphical correlation between the uppermost Katian–Hirnantian strata of low to mid-latitude carbonate platforms in eastern Laurentia and Baltica. Conversely, significant taxonomic differences exist between the assemblage studied and typical Gondwanan palynofloras. These results suggest that the Laurentian/Baltic and Gonwanan phytoplanktonic palaeoprovinces existed during latest Ordovician times. Published data reveal similar distribution pattern for chitinozoans and graptolites during the Hirnantian. A bathymetric ridge rise associated with the opening of the Rheic Ocean, coupled with the Hirnantian glacially-driven sea-level fall might have prevented water mass exchange and mixing/migration of phytoplankton between Gondwana and Laurentia/Baltica, thus being at the origin of the observed acritarch bioprovincialism. Additionally, distribution and diversity patterns of acritarchs are compared to those of other microfossils in the Valga-10 section. Near the base of the Hirnantian (Porkuni Regional Stage), benthic organisms (ostracods and scolecodonts) and phytoplankton (acritarchs) show increasing diversity with appearances of new taxa and new morphologies. Planktonic (chitinozoans) and nektonic (conodonts) organisms show a different pattern, with a decline in diversity during the earliest Hirnantian and a marked increase in the later part of the stage. Two alternative hyptotheses are proposed to explain these differences in diversification patterns: (1) the development of a shallower, proximal environment in the locality studied during the Hirnantian glaciation may have been more favourable to the diversification of benthonic organisms; (2) the planktonic and nektonic organisms suffered the effects of glaciation more than benthonic ones.

New Monticuliporidae (Bryozoa, Trepostomata) from the Cystoid Limestone Formation (Upper Ordovician) of the Iberian Chains (NE Spain)

Bryozoans are among the most abundant fossil groups in the cool water limestones that characterize the uppermost Katian (Upper Ordovician) of Southwestern Europe and North Africa. The Cystoid Limestone Formation, the representative unit of those widespread rocks in the Iberian Chains (NE Spain), yields one of the most diversified bryozoan faunas of the whole area. Herein the first systematic description of the trepostomate family Monticuliporidae is undertaken, this is one of the most diverse families within the associations collected. Four species of the genera Monticulipora and Prasopora are described, including the new species Monticulipora cystiphragmata n. sp. and Prasopora spjeldnaesi n. sp., and an indeterminate Monticuliporidae. Monticulipora and Prasopora have shown to be very similar genera, with several species that are difficult to distinguish between them. Their diagnoses include common features such as the wall microstructure, density of mesozoecia, and number of acanthostyles. Herein a new generic diagnosis of Monticulipora is proposed, putting special emphasis on the shape and distribution of cystiphragms. The species Monticulipora kolaluensis is identified for the first time out of Siberia. Although the record of these new taxa can indicate a certain isolation of the Iberian Chains region within the North Gondwana platform, the occurrence of Prasopora carnica shows a relation to the neighbouring Carnic Alps (Italy and Austria).

Biodiversity patterns of Ordovician marine microphytoplankton from Baltica: Comparison with other fossil groups and sea-level changes

Based on the extensive literature on Ordovician acritarchs, biodiversity curves of marine microphytoplankton of the palaeocontinent Baltica have been compiled. The dataset is derived from more than 100 publications and includes over 600 species whose ranges can be used in diversity analysis. Stratigraphically well-constrained data from the Rapla and Männamaa boreholes, northern Estonia, are analysed separately in order to provide additional information on the Middle to Late Ordovician microphytoplankton evolution on shallow shelf settings. The total species diversity and normalised diversity curves based on range-through data show a slight decrease from the Tremadocian to Floian, which may partly be attributed to limited data available. A continuous increase in diversity from the base of the Dapingian to late Darriwilian — early Katian can be observed, with highest total diversity approaching 250 species in the Keila Regional Stage. The highest appearance rates are recorded in the Dapingian and Darriwilian. Diversity progressively diminished after the early Katian with a more pronounced decrease in the upper Ordovician Porkuni Regional Stage, corresponding to the Hirnantian. A significant faunal turnover took place in the uppermost Ordovician Pirgu and Porkuni stages, with high extinction rates as well as the appearance of many acritarch taxa that are typical of the Silurian floras. The phytoplankton diversity curves match rather well with those of several other fossil groups in Baltica, notably brachiopods and ostracods. Comparison with other palynomorphs reveals both similarities and differences. The chitinozoans show the highest diversities in the upper Darriwilian, but their later decline predates that of acritarchs. A rapid diversification of scolecodonts (jawed polychaetes) can also be observed in the upper Darriwilian. However, unlike acritarchs or chitinozoans, their diversity continues to increase until the uppermost Katian. The acritarch diversity changes are analysed and discussed in the context of palaeogeographic (northwards drifting of Baltica) and palaeoclimatologic changes (rising sea levels up to the middle part of the Upper Ordovician). The increasing diversity of the phytoplankton not only roughly correlates with the Baltic and global sea-level changes, but also with the diversification of marine invertebrate groups.