Phytoplankton dynamics from the Cambrian Explosion to the onset of the Great Ordovician Biodiversification Event: a review of Cambrian acritarch diversity

Most early Palaeozoic acritarchs are thought to represent a part of the marine phytoplankton and so constituted a significant element at the base of the marine trophic chain during the ‘Cambrian Explosion’ and the subsequent ‘Great Ordovician Biodiversification Event.’ Cambrian acritarch occurrences have been recorded in a great number of studies. In this paper, published data on Cambrian acritarchs are assembled in order to reconstruct taxonomic diversity trends that can be compared with the biodiversity of marine invertebrates. We compile a database and calculate various diversity indices at global and regional (i.e. Gondwana or Baltica) scales. The stratigraphic bins applied are at the level of the ten Cambrian stages, or of fourteen commonly used biozones in a somewhat higher resolved scheme. Our results show marked differences between palaeogeographical regions. They also indicate limitations of the data and a potential sampling bias, as the taxonomic diversity indices of species are significantly correlated with the number of studies per stratigraphic bin. The total and normalized diversities of genera are not affected in the same way. The normalized genus diversity curves show a slow but irregular rise over the course of the Cambrian. These also are the least biased. A radiation of species and to a lesser extent of genera in the ‘lower’ Cambrian Series 2 appears to mirror the ‘Cambrian Explosion’ of metazoans. This radiation, not evident on Gondwana, is followed by a prominent low in species diversity in the upper Series 3 and lower Furongian. Highest diversities are reached globally, and on both Baltica and Gondwana, in the uppermost Cambrian Stage 10, more precisely in the Peltura trilobite Zone, preceding a substantial phase of acritarch species extinction below and at the Cambrian/Ordovician boundary. Nearly all the genera present in Stage 10 survived into the Ordovician. The forms that emerged during the Cambrian therefore became the foundation for the more rapid radiation of acritarchs during the ‘Great Ordovician Biodiversification Event’

Complex response of dinoflagellate cyst distribution patterns to cooler early Oligocene oceans

Previous studies have made extensive use of dinoflagellate cysts to reconstruct past sea surface temperature (SST). Analysis of associations of dinoflagellate cysts using two new ocean datasets for the mid Eocene (Bartonian) and early Oligocene (Rupelian) reveals clear latitudinally constrained distributions for the Bartonian, but unexpected changes in their Rupelian distribution; a significant number of species with low and mid latitude northern hemisphere occurrences in the Bartonian extend their northward ranges in the Rupelian, including some forms characterised as ‘warm water’ by previous studies. This suggests either that dinoflagellates are faithfully tracking a complex oceanographic response to Rupelian cooling, or that dinoflagellate sensitivity/adaptability to a range of ecological variables means that at a global scale their distributions are not primarily controlled by sea surface temperature-variability. Previous use of dinoflagellate cysts for palaeoclimate work has relied on rather subjective and inconsistent identification of ‘warm’ and ‘cold’ water forms, rather than comprehensive analysis of community associations at the global-scale. It is clear from this study that a better understanding of the (palaeo-)ecology of dinoflagellates and their cysts is required. Rupelian dinoflagellate cyst distribution may reflect changes in a range of environmental variables linked to early Oligocene climate-cooling, for example changes in nutrient fluxes triggered by glacially-induced base-level fall; complex reorganisation of ocean current systems between the Bartonian and Rupelian, or muted changes to Rupelian summer SSTs in the northern hemisphere that have previously been reported. Many extant dinoflagellate species also exhibit relatively broad temperature tolerance. Moreover, they have potentially extensive cryptic diversity, and are able to produce dormant cysts during short-lived environmental deterioration, all of which may act to limit the value of undifferentiated dinoflagellate cyst assemblages for identifying climate signals

Chitinozoan biostratigraphy of the regional Arenig Series in Wales and correlation with the global Lower–Middle Ordovician series and stages

The Arenig Fawr area of North Wales constitutes the type area for the British Lower to Middle Ordovician Arenig Series and is complemented by sections in the Carmarthen and Whitland areas of South Wales. We describe chitinozoan assemblages from both areas in order to aid correlation of the Arenig Series in its type region with the global Ordovician series and stages. Chitinozoans recorded from Arenig Fawr provide permissive rather than conclusive evidence but suggest that the Henllan Ash Member correlates with the upper Floian Stage Slice Fl3 or lower Dapingian Stage Slice Dp1. Better results were obtained from South Wales where six chitinozoan assemblages are distinguished, ranging in age from late Tremadocian to middle Darriwilian (early Llanvirn). Most species are known from South China, Gondwana and/or Baltica where there are controls on ranges. They show that much of the lower Arenig (Moridunian) succession in South Wales correlates with the upper Floian Stage (Fl3). Correlatives of the lower and middle Floian Stage (Fl1, Fl2), if present, must be represented by the Ogof Hên Formation and lowest Carmarthen Formation. Chitinozoan assemblages from the upper Arenig Series (Fennian Stage) are more readily correlated with Gondwanan biozones and indicate correlation of the Fennian Stage with the Dapingian and lower Darriwilian (Dw1) stages. The middle Arenig Whitlandian Stage is constrained in South Wales to an interval from the uppermost Floian Stage to the basal Dapingian Stage, resulting in an inferred increased rate of sediment accumulation

Integrated stratigraphical study of the Rhuddanian-Aeronian (Llandovery, Silurian) boundary succession in the Rheidol Gorge, Wales:A proposed Global Stratotype Section and Point for the base of the Aeronian Stage

The Rheidol Gorge section, approximately 17 km east of Aberystwyth, mid Wales, exposes a ca. 20 m-thick succession of Llandovery (Silurian) strata from the upper Rhuddanian Pernerograptus revolutus Biozone through the lower Aeronian Demirastrites triangulatus Biozone and basal Neodiplograptus magnus Biozone. The section records deposition under a range of bottom-water oxygenation states. The Rhuddanian-Aeronian boundary is located 0.8 m above an abrupt lithological change from predominantly organic-poor, bioturbated `oxic' mudrocks to an interval of black, richly graptolitic `anoxic' shales. The graptolite fauna through the boundary interval, including the local lowest occurrence of D. triangulatus, allows precise correlation with other parts of the world. Graptolite assemblages indicative of separate divisions in the underlying revolutus Biozone and of the lower and upper parts of the triangulatus Biozone are also present. Chitinozoans are relatively well preserved in the section and indicate the Spinachitina maennili Biozone throughout the boundary interval, as is widely the case. The results of carbon isotope analyses from organic matter indistinctly show the weak interval of positive shift in d13C org values through the Rhuddanian-Aeronian boundary interval, as observed globally, though local or regional processes appear largely to overprint the global signal. Overall, the excellent biostratigraphical record, well-documented local and regional stratigraphical context, historical significance, as well as easy access and assured longterm preservation, mean that the Rheidol Gorge section can be proposed as a strong candidate for a new Global Stratotype Section and Point for the base of the Aeronian Stage.. Silurian, Llandovery, Rhuddanian, Aeronian, Global Stratotype Section and Point, Graptolites, Chitinozoa, Carbon Isotope

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

A revised sedimentary and biostratigraphical architecture for the Type Llandovery and Garth areas, Central Wales : a field guide

The guide presents some of the results of collaborative research undertaken by the British Geological Survey, National Museum of Wales, and Leicester and Ghent universities in the Type Llandovery and Garth areas of Central Wales (Figure 1a and b), focusing on the late Ashgill, Llandovery and early to mid Wenlock strata. It is based on an earlier version produced for the Ludlow Research Group (LRG) Annual Field Meeting to the Llandovery and Garth areas in September 2009, but contains new data and interpretations based on significant subsequent discoveries in the Type Llandovery area. It highlights the following: The significance of the intra-Ashgill Shelvian Event. A reinterpretation of the Hirnantian glacio-eustatic event. A revised and unified lithostratigraphy for the Llandovery and Garth areas, which addresses the problems of correlating between the northern and southern Llandovery areas. New graptolite, acritarch and chitinozoan dating, especially in the Aeronian, Telychian and Wenlock. The importance of re-sedimentation processes including slumping and synsedimentary sliding within the succession. The relationship between the Llandovery and the overlying Wenlock successions

High dependence of Ordovician ocean surface circulation on atmospheric CO 2 levels

International audienc

Chitinozoans from the upper Tremadocian (Lower Ordovician) Watch Hill Formation of the Lake District, northern England

The Global Stratotype Section and Point (GSSP) for the Lower Ordovician Floian Stage is defined by the first appearance datum (FAD) of the graptolite Tetragraptus approximatus at Diabasbrottet Quarry, Hunneberg, southern Sweden. Correlation of sections with the Floian GSSP when graptolites are absent, however, must rely on other criteria. Among other fossil groups with potential for biostratigraphical correlation at this level are chitinozoans. Here we describe a chitinozoan assemblage from the Watch Hill Formation in the Skiddaw Group of northern England. The Watch Hill Formation is dated on graptolite evidence as late Tremadocian, but the assemblage contains Euconochitina symmetrica, a species previously considered to indicate the eponymous lowermost Arenig (Floian) chitinozoan biozone in a long-established Gondwanan Ordovician biozonal scheme. The hitherto earliest Floian index species has also been reported recently from Tremadocian successions in South China and Morocco. We here confirm its extended range into the Tremadocian and its continued significance as an index species for the Tremadocian–Floian boundary interval

Cyclostratigraphic analysis of the Middle to lower Upper OrdovicianPostolonnec Formation in the Armorican Massif (France): integratingpXRF, gammay-ray and lithological data

International audienceThe Middle to lower Upper Ordovician sections of the Crozon Peninsula area (Postolonnec Formation, ArmoricanMassif, western France) show multi-order eustatic sea-level changes (Dabard et al., 2015). The sections arecharacterized by siliciclastic facies, which were deposited in tidal to storm-dominated shelf environments. Dabardet al. (2015) analysed the facies, their stacking patterns, and gamma-ray data and applied backstripping toidentify subsidence and several orders of sea-level change. The main stratigraphic constraints are coming from(chitinozoan) biostratigraphy. The 3th to 5th orders changes are hypothesized to correspond to various frequenciesrelated to astronomical forcing.This study investigates the potential added value of portable X-Ray Fluorescence (pXRF) and the applicationof spectral analyses. High-resolution (cm-scale) non-destructive pXRF and natural gamma-ray measurementswere carried out on 14 m of section that was equally logged on a cm resolution. The pXRF measurementson the surface of the outcrops are compared with earlier results of wavelength dispersive XRF spectrometryand ICP-MS. The potassium records of the pXRF and gamma-ray logs are comparable and essentially reflectlithological variations (i.e. between mudstone and coarse sandstones). Other reliably measured elements alsoreflected lithological aspects such as clay-sandstone alternations (e.g. K, Rb, Ti), placer locations (Zr, Ce, Ti) andpotentially clay mineralogy and condensation horizons (Ni, Zn, Co, Mn).Spectral analyses of the various proxies (lithology, natural gamma-ray and pXRF) are compared with eachother. Both the new high-resolution data (14 m of section) as well as the published low-resolution data (whichspan almost 400 m of Darriwilian-Sandbian) were analyzed. The study reveals strong indications for the imprintof obliquity, precession and eccentricity. Obtaining age constraints, in addition to the existing biostratigraphicalframework is a challenge in these sections, but would help to resolve temporal uncertainties and confirm ourinterpretations. The relative strength of the potential obliquity and precession-eccentricity signals also can providefurther insights in the global glaciation history of the Middle to Late Ordovician given that a larger obliquitycomponent can be expected if there was a more developed polar ice sheet on the Gondwanan palaeocontinent.Dabard M.P., Loi A., Paris, F., Ghienne J.F., Pistis M., and Vidal M. (2015): Sea-level curve for the Middleto early Late Ordovician in the Armorican Massif (western France): Icehouse third-order glacio-eustaticcycles. Palaeogeography, Palaeoclimatology, Palaeocology, 436, 96-111, doi:10.106/j.palaeo.2015.06.03