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Based on δ13C data from two drillcores recovered from the Siljan district, we present a first continuous carbon isotope record of the upper Tremadocian-lower Katian limestone succession of central Sweden. New names for some isotopic carbon excursions from the Cambrian-Ordovician boundary through the basal Darriwilian are introduced. The Mora 001 core from the western part of the Siljan impact structure ranges through the Lower-Middle Ordovician, whereas the Solberga 1 core from its eastern part ranges through the Middle-lower Upper Ordovician. Upper Tremadocian and Floian units are extremely condensed and include extensive stratigraphic gaps. Multiple hardgrounds, sometimes with minor karstic overprint, imply recurrent periods of erosion and/or non-deposition. Like in other parts of Sweden, the Dapingian and Darriwilian succession is characterized by a relatively complete sedimentary record and low sedimentation rates. [ABSTRACT FROM AUTHOR]

Based on the Tingskullen drillcore, we present the first continuous carbon isotope stratigraphy from the Lower–Middle Ordovician “orthoceratite limestone” of Öland, Sweden. The extremely condensed Tremadocian and Floian stages include large gaps as well as the Ceratopyge Regressive Event and the widespread Evae transgression accompanied by prominent shifts in the δ 13C record. The Dapingian and Darriwilian stages are characterised by low sedimentation rates and a relatively complete sedimentary record. A total of 99 whole-rock samples were analysed for carbon isotope geochemistry from the Ordovician part of the succession (46 m thick). The most striking anomaly detected is the middle Darriwilian isotope carbon excursion (MDICE) that appears unusually well developed and complete for the region, and thus forms an important proxy for intercontinental correlation of the succession. [ABSTRACT FROM AUTHOR]

Based on the Shidi-1 drill core, this paper presents new and highly time resolved carbon isotope data (δ13C carb) for the Early Ordovician through Early Silurian of the Yangtze Platform, South China. Five carbon isotopic shifts (C1-C5) through the late Tremadocian to the Katian have been recognized in the Shidi-1 drill core recordings. Together with previously published isotope data, a composite carbon isotope curve for the Yangtze platform, permits the identification of a continuous Ordovician carbon isotope trend with five prominent carbon isotope shifts; including the TSICE, the Late Tremadocian positive Isotopic Carbon Excursion (LTICE, named herein), the Late Floian Rise, the MDICE and the Pagoda Isotopic Carbon Excursion (PICE, named herein). The identification and documentation of these anomalies further strengthen the regional and global correlation of the Ordovician succession on the Yangtze platform. The long-term trend in carbon isotopes indicates that organic carbon burial increased gradually throughout the Great Biodiversification Event (GOBE). A tipping point is also marked by the Dapingian-Darriwilian border, which is followed by a notable shift in the environment and creatures in the middle Darriwilian. • A continuous high-resolution δ13C carb curve for nearly the whole Ordovician of South China. • Six prominent and globally comparable carbon isotope shifts have been recognized. • Complied δ13C carb data suggest the important turnover of organisms and environment in the Darriwilian. • The δ13C carb values suggest the increased burial rates of organic matter throughout the Ordovician related to GOBE. [ABSTRACT FROM AUTHOR]

The Collisional Orogeny in the Scandinavian Caledonides (COSC) project focuses on processes related to the closure of the Iapetus Ocean, causing the Ordovician-Silurian continent-continent collision between Baltica and Laurentia. The rock succession in the second drill core (COSC-2) from the Jämtland County, central Sweden, provides the base for detailed sedi - mentological, stratigraphic, geophysical, geochemical, geothermal and structural studies. The basement, comprising 1.66-1.65 Ga Transscandinavian Igneous Belt porphyries intruded by 1.47 Ga and 1.27-1.26 Ga mafic dykes and sills, is heavily weathered towards the top. Here it grades into typical saprock and saprolite (including immature soil reflecting the sub-Cambrian peneplain). The overlying sedimentary sequence starts with basal conglomerates and heterogeneous sediments with shell fragments, indicating an early Cambrian rather than a Neoproterozoic age for the marine transgression in the area. The developing early Cambrian basin was rapidly filled, initially by mostly coarse-grained sediment gravity flows. These strata are covered by sandstone turbidites that show an upward transition into the Alum Shale Formation, representing a tectonically quieter period (mid-Cambrian/Maolingian to Early Ordovician/Tremadocian). The upper part of the Alum Shale Formation is overlain by a late Early Ordovician turbidite succession. Local sources of sediments below the Alum Shale Formation and the extended deposition period may indicate continuous sedimentation in a pull-apart basin pre - served in a window beneath the Caledonian thrust sheets. [ABSTRACT FROM AUTHOR]

The late Silurian Lau/Kozlowskii bioevent marks a time interval with substantial loss in marine biodiversity linked to the largest positive carbon isotope excursion (Mid-Ludfordian CIE; MLCIE) recorded in the Phanerozoic (δ13C carb peaks at +8–10‰). The positive δ13C excursion and the extinctions have been linked to increased marine productivity (ocean eutrophication), leading to increased organic carbon burial, and expansion of marine anoxia in shallow continental seas. To explore this idea, we reconstruct the contemporaneous global extent of marine anoxia using uranium (U) isotopes from Ludfordian marine carbonates sampled from two widely spaced paleogeographic locations. Our δ238U results demonstrate that the overall MLCIE was not coupled to expanding marine anoxia and a presumed associated increased marine primary productivity. Instead, a time interval of widespread global anoxia occurred only before and during the onset of the MLCIE (up to end of P. siluricus conodont zone; ca. δ13C ∼ 2.6‰), which is when the extinctions took place. Strong climatic variability at this time suggests anoxia and climate change led to the extinctions of the Lau/Kozlowskii bioevent. The major part of the rise to the peak (δ13C ∼ 10‰) and falling limb of the MLCIE was not coupled with corresponding changes in δ238U values. Thus, increased marine primary productivity and marine anoxia may have caused the initial carbon cycle disturbance and the extinctions but was not a main driver for the continued growth and exceptional magnitude of the MLCIE. • We present δ238U data across the late Silurian Lau event from two paleocontinents. • δ238U records provide a consistent picture of the global extent of marine euxinia. • Marine euxinia was extensive during the extinction event. • The largest δ13C excursion of the Phanerozoic evolved after euxinia expanded. • Terrestrial organic carbon burial may have contributed to the δ13C excursion. [ABSTRACT FROM AUTHOR]

High-resolution paired analyses of δ13C carb and δ13C org from a new drill core from Gotland, Sweden, demonstrate asynchronous positive change in the carbon isotope records during the onset of one of the major Silurian biogeochemical events known as the Mulde Event or "Big Crisis". The detailed carbon isotope record presented here provides Δ13C (the difference between δ13C carb and δ13C org) and allows the calculation of changes in organic carbon burial (f org) throughout the late Wenlock. The paired data suggest a ~ 38% increase in f org during the peak of the positive δ13C carb excursion and the high-resolution record reveals several short-lived inflections in Δ13C that have not been previously identified. When combined with sedimentological and sequence stratigraphic data from multiple paleocontinents, the new data presented here provide strong evidence for a transient global decrease in CO 2 , in support of previous interpretations of regression and global cooling coinciding with the Mulde Extinction Event. [ABSTRACT FROM AUTHOR]

The orthoceratite limestone of the Ordovician epicontinental sea of Baltoscandia is one of the oldest Phanerozoic examples of pelagic marine red beds (MRBs). Being enriched in authigenic haematite, MRBs are considered to be sensitive palaeoceanographic redox indicators. In this paper, the origin of the reddening of the Ordovician MRBs and its timing and redox conditions were addressed at two sections, and in a drill core in the Kinnekulle area, Sweden, through the application of diffuse reflectance spectroscopy, sedimentary petrology (microfacies and electron microprobe), bulk-rock and in-situ element geochemistry (laser-ablation ICP-MS) and molybdenum stable isotope systematics. Enrichment in haematite (up to ~0.05 wt%) occurred during very early diagenesis under low sedimentation rates (~5 mm/kyr), which is comparable to several examples of Phanerozoic MRBs. The reddening was associated with the mm-scale, in-situ mobility of Fe, Mn, As, Mo and U, due to Fe–Mn redox cycling between primary and secondary minerals and pore water under oxic and suboxic to anoxic conditions; it was not related to significant changes in seawater chemistry. Stratigraphic red-to-grey transitions likely coincided with two mid-Darriwilian global regressions (the so-called Täljsten and at the base of the Gullhögen Formation), likely due to the effects of changing sedimentation rates and sub-bottom redox potentials. The Ordovician MRBs coincided with a positive δ13C excursion during the middle Darriwilian, which is different to MRB examples cited from the Devonian to the Cretaceous age, which frequently coincide with shifts to lower values of δ13C. Although MRBs are believed to show a time-specific occurrence in greenhouse or transitional greenhouse-to-icehouse climatic modes by several authors, our study suggests that causal links between MRBs and global carbon cycle remain unclear. [ABSTRACT FROM AUTHOR]

Paired records of δ13C carb and δ13C org across the Llandovery-Wenlock boundary demonstrate asynchronous behavior during the onset of the Ireviken Biogeochemical Event (IBE). The extremely high-resolution data produced from the Altajme Core, drilled from Gotland, Sweden, capture a negative excursion in δ13C org during the initiation of the Ireviken Extinction Event (IEE) and prior to the onset of the Ireviken positive δ13C carb Excursion (ICIE). The record of carbon isotopic changes through this interval illustrate that both Δ13C (the difference between δ13C carb and δ13C org) as well as the relative flux of organic carbon burial (f org) vary in unique ways and at different times during the progression of the IBE. Both process-oriented variables within the global carbon cycle (Δ13C and f org) track a series of events that help to demonstrate potential causative mechanisms of both the extinction and carbon cycle perturbation. The sequence of events demonstrated here largely mirror the cascade of events that took place during the Cretaceous Oceanic Anoxic Event 2 (OAE2) and a detailed comparison between the two events is provided here for the first time. The unique insight into the IBE presented in this work results primarily from the novel, nearly Neogene-scale resolution of the paired isotope data, which demonstrates the critical importance of high-resolution chemostratigraphic research to evaluating ancient perturbations to the Earth-life system. Additional data sets of equal or greater resolution through this interval will be critical to evaluate the global synchroneity of these short-lived events during the IBE, and similar high-resolution studies of other Paleozoic biogeochemical events may shed light on potentially similar causative mechanisms. • Clear demonstration of the scale of high-resolution sampling required for future studies of this and other events • First paired demonstration of a negative δ13C org excursion during rising δ13C carb values at the onset of the Ireviken Event • First continuous high-resolution record and calculation of Δ13C and f org during a Silurian global carbon cycle perturbation • Likely the highest resolution paired record of δ13C carb and δ13C org ever produced from a Paleozoic biogeochemical event • Further demonstration of the Silurian Ireviken biogeochemical event as a potential Paleozoic Oceanic Anoxic Event [ABSTRACT FROM AUTHOR]

New conodont and stable isotope data are presented from the classical Baizitian section in the Yanbian County of Sichuan Province, South China. The Telychian to Sheinwoodian strata were sampled and studied for carbon isotope stratigraphy and conodont biostratigraphy. The paired δ13C carb and δ13C org data reveal a pronounced positive excursion, the Manitowoc carbon isotope excursion (Manitowoc CIE, 'Manitowoc Excursion') spanning the upper Pterospathodus eopennatus Zone and the lower Pterospathodus amorphognathoides amorphognathoides Superzone, with an increase of ca. 2‰ in δ13C carb and ca. 5‰ in δ13C org. Well-bracketed by conodont biostratigraphy, the Manitowoc CIE is an essential tie-point for correlation between the Baizitian succession and the Telychian strata of Baltica and Laurentia. Our new δ13C carb and δ13C org data imply that the carbon isotope excursion previously recognized as the 'Ireviken Excursion' (Early Sheinwoodian Carbon Isotope Excursion) at Baizitian should be revised as being the Manitowoc CIE. The Δ13C data presented in this study further suggest a slight concurrent drop of atmospheric CO 2 , and thus add evidence for a perturbation of the global carbon cycle during the middle Telychian. Based on the combined information from the conodont apatite oxygen isotope records from Estonia and the significant stratigraphic gaps recognized at the Baizitian section, we propose that the latter stratigraphic gaps should correlate with the Telychian Valgu and the early Sheinwoodian glaciation. • A first paired early Silurian δ13C carb and δ13C org record from South China. • Integrated conodont and chemostratigraphy shows stratigraphic gaps in South China related to Telychian and Sheinwoodian glacials. • The stratigraphic value of the Telychian Manitowoc Carbon Isotope Excursion for global correlations. • elationship between the δ18O record and early Silurian climate change and glacioeustasy. • Early Silurian as a time of drastic climate changes includes various cooling events and Gondwana glaciations such as the Valgu Glaciation, the Late Telychian Glaciation during the Manitowoc Icehouse, and the Sheinwoodian Glaciation. [ABSTRACT FROM AUTHOR]

The Great Ordovician Biodiversification Event (GOBE) represents the greatest increase in marine animal biodiversity ever recorded. What caused this transformation is heavily debated. One hypothesis states that rising atmospheric oxygen levels drove the biodiversification based on the premise that animals require oxygen for their metabolism. Here, we present uranium isotope data from a Middle Ordovician marine carbonate succession that shows the steepest rise in generic richness occurred with global marine redox stability. Ocean oxygenation ensued later and could not have driven the biodiversification. Stable marine anoxic zones prevailed during the maximum increase in biodiversity (Dapingian-early Darriwilian) when the life expectancy of evolving genera greatly increased. Subsequently, unstable ocean redox conditions occurred together with a marine carbon cycle disturbance and a decrease in relative diversification rates. Therefore, we propose that oceanic redox stability was a factor in facilitating the establishment of more resilient ecosystems allowing marine animal life to radiate., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2022.)