Seth Young

• Florida State University

The Silurian was marked by repeated extinctions, carbon cycle volatility, and significant intervals of climatic change. The most notable of these events were the Ludfordian Lau/Kozlowskii extinction and associated Mid-Ludfordian Lau carbon isotope excursion, both of which have been linked to a period of global cooling and expanded reducing conditio...

Marine biodiversity increased markedly during the Ordovician Period (~487–443 million years ago). Some intervals within the Ordovician were associated with unusually rapid and prominent rises in taxonomic richness, the reasons for which remain debated. Links between increased oxygenation and biodiversification have been proposed, although supportin...

Geological and palaeoenvironmental background information, locality descriptions, supplementary figure and data tables.

The oxygen content of ancient seawater has been hypothesized to be a major controlling factor for biodiversity throughout Earth's history. The Great Ordovician Biodiversification Event (GOBE) represents one of the largest increases in biodiversity during the Phanerozoic, with peak rates of diversity occurring in the Middle–Late Ordovician. Multiple...

The end-Devonian Hangenberg Crisis was one of the biggest Phanerozoic mass extinctions. However, the mechanism(s) that triggered this event is still debated. In this study, multiple geochemical paleoredox proxies (redox-sensitive trace metals [e.g., Mo, U, Re, V] and isotope systems [Mo, U, S, C]) were applied to the Exshaw Formation black shales t...

The Silurian period was once believed to be a calm greenhouse with a high sea level and no major geological or biological events. However, recent research shows it was one of the most dynamic phases in Phanerozoic, with major sea level changes and several important extinction events, including the Mulde/lundgreni event at ~428 Ma (Munnecke et al.,...

New δ³⁴Spy (pyrite) and δ³⁴SCAS (carbonate‐associated sulfate) across the Llandovery‐Wenlock boundary (∼432 Ma) provide evidence for the expansion of reduced marine environments during the Ireviken Biogeochemical Event. This event consists of a major positive carbon isotope excursion, increased biotic turnover, and other major perturbations and cha...

The Lanna area in the province of Närke, south-central Sweden, hosts a succession of cool-water carbonate strata that are largely devoid of tectonic and diagenetic alteration, and span the Floian through lower Darriwilian Global stages (Ottenbyan–Kundan Regional stages). In this study we assess the integrated biostratigraphic and chemostratigraphic...

Fluctuations in marine oxygen concentrations have been invoked as a primary driver for changes in biodiversity throughout Earth history. Expansions in reducing marine conditions are commonly invoked as key causal mechanisms for mass extinctions, while increases in marine oxygenation are becoming an increasingly common causal mechanism invoked for b...

Tracking climatic changes throughout the Ordovician is crucial to a better understanding of the coevolution of life and environment on Earth. Ordovician climate fluctuations have been the subject of a vigorous and productive body of work over the past two decades. Here we present a synthesis of studies that have focused on reconstructing Ordovician...

The timing and connections between global cooling, marine redox conditions, and biotic turnover are underconstrained for the Late Ordovician. The second most severe mass extinction occurred at the end of the Ordovician period, resulting in ~85% loss of marine species between two extinction pulses. As the only “Big 5” extinction that occurred during...

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 iod...

The Silurian was a dynamic time characterized by significant climatic and sea level changes, biotic crises, and carbon cycle volatility. The largest magnitude perturbation to the Silurian global carbon cycle was the mid-Ludfordian carbon isotope excursion, termed the Lau CIE, which was coincident with the Lau/Kozlowskii extinction (LKE). Much of th...

The Silurian was a time of major climatic transition punctuated by multiple biotic crises and global carbon cycle perturbations. The most severe of these biotic events was the late Silurian (Ludfordian) Lau/Kozlowskii extinction event (LKE) and the associated Lau carbon isotope excursion (CIE). Although the extinction event and Lau CIE are globally...

It is well documented that Upper Ordovician and Silurian successions record multiple marine turnover events – including the second-largest mass extinction in the Phanerozoic – widespread glaciation, and multiple global carbon cycle perturbations. Whereas causal mechanisms for the Late Ordovician major mass extinction event involving climate, paleoc...

Ediacaran sediments record an unusual global carbon cycle perturbation that has been linked to widespread oceanic oxygenation, the Shuram negative C isotope excursion (NCIE). However, proxy‐based estimates of global ocean redox conditions during this event have been limited largely due to proxy specificity (e.g., euxinic sediments for Mo and U isot...

The late Ludlow Lau Event was a severe biotic crisis in the Silurian, characterized by resurgent microbial facies and faunal turnover rates otherwise only documented during the "big five" mass extinctions. This asynchronous late Silurian marine extinction event preceded an associated positive carbon isotope excursion (CIE), the Lau CIE, although a...

A stepwise change in atmospheric oxygen (O2) levels during the Ordovician has been attributed to the emergence of land plants. This phenomenon is tied to a major baseline shift in the stable carbon isotope (δ13C) curve and inferred increase in nutrient delivery and enhanced primary productivity in nearshore settings, which led to high organic carbo...

Repeated biotic crises have become the hallmark for the Silurian with the three most significant marine turnover events being related to dramatic global environmental perturbations. Causal mechanisms linking these marine extinction events with positive carbon isotope (δ ¹³ C) excursions, paleoceanographic change, and climate remain poorly constrain...

The Homerian Stage (upper Wenlock) of the Silurian has become associated with a rapid succession of extinction events that affected both planktic and (nekto)benthic organisms (the ‘Big Crisis’, ‘lundgreni Event’, ‘Mulde Event’). This mid-Silurian extinction interval coincides globally with a distinct positive carbon isotope excursion (CIE) and shif...

The Evans Ferry section from the Appalachian Basin of eastern North America has been analyzed for chemostratigraphic trends to elucidate possible causal mechanisms facilitating the Great Ordovician Biodiversification Event (GOBE). Paired stable isotope (δ ¹³ C and δ ³⁴ S) analyses were used in this carbonate-dominated locality from the Appalachian...

The recently published Lethaia paper by Bergström et al. (https://doi.org/10.1111/let.12269) on the age of the Ordovician Winneshiek Shale (Iowa, USA), and the impact that formed the Decorah crater which hosts this rock unit, is an interesting scientific contribution, although there are a number of problems with the interpretations and data present...

As carbonate sediments are strongly influenced by syndepositional conditions, carbonate rocks form an invaluable source of paleoenvironmental information. Analyses of late Cambrian (Furongian) to Middle Ordovician cool-water carbonates from the Baltoscandian paleobasin typically reveal consistent overall stratigraphic patterns and trends in microfa...

A high‐resolution chemostratigraphical (coupled δ13Ccarb and δ18Ocarb) study of the topmost Floian through the middle Darriwilian (Ordovician) succession at the Hällekis quarry, Kinnekulle, southern Sweden, shows relatively steady isotopic values with overall minor changes, although some notable short‐ and long‐term shifts are discernible. A pronou...

Calibration of ancient marine sulfate levels has been done largely using experimental studies of the kinetic isotope effect associated with microbial sulfate reduction and work from modern ocean basins or high-sulfate lakes that are largely restricted and meromictic. The sulfur isotope record of sulfates and sulfides from sedimentary sequences have...

Iron redox cycling in metal-rich, hypersaline, anoxic brines plays a central role in the biogeochemical evolution of life on Earth, and similar brines with the potential to harbor life are thought to exist elsewhere in the solar system. To investigate iron biogeochemical cycling in a terrestrial analog we determined the iron redox chemistry and iso...

A pioneer δ13Corg study through the upper Sandbian and Katian (Upper Ordovician) succession in the Röstånga 1 drill core in the classical geological outcrop area at Röstånga in southernmost Sweden produced a wealth of new carbon isotope data which are useful for local and regional correlations. Among the Upper Ordovician positive δ13C excursions, t...

The early Silurian was a period of widespread environmental, oceanographic, and biotic change in the aftermath of one of the largest mass extinctions in the Phanerozoic. Lower Silurian (Llandovery) strata worldwide generally record a period of episodic biotic extinction/origination possibly linked to widespread anoxia, continued glaciation, and dyn...

The marine redox evolution in the Ordovician is highly dynamic which directly effects multiple biogeochemical event and cycles. The largest biodiversification event in the Paleozoic was the Great Ordovician Biodiversification Event (GOBE) and occurs prior to the first of the “Big 5” mass extinctions. The GOBE is a roughly threefold increase in fami...

Middle-Late Ordovician sequences from the Appalachian Basin and Arbuckle Mountain regions of North America were analyzed for carbonate-associated sulfate (δ34SCAS) and pyrite (δ34Spyr) paired with carbonate (δ13Ccarb) and organic matter (δ13Corg) chemostratigraphy. Two major negative drops in δ34SCAS (12‰ excursions) are recognized: the older decli...

The present study on bulk carbonate 87Sr/86Sr stratigraphy represents a companion work to earlier research that presented a conodont apatite-based Ordovician seawater 87Sr/86Sr curve for the Tremadocian-KatianStages (485-445 Ma). Here, we directly compare the curve based on conodont apatite (including some new data not published in earlier work) wi...

Application of the recently introduced Baltic delta C-13 isotope zonation to a composite North American Darriwilian through Hirnantian succession shows that in most intervals there is good trans-Atlantic agreement not only between the isotope zones but also with the available biostratigraphic data. This indicates that this isotope zonation is a use...

Variations in aquatic chemistry, methane dynamics and microbial communities are observed in small ice-covered lakes. Lakes on Mars would also exhibit variation.

The delta C-13(org) chemostratigraphy of the Hirnantian and lower Rhuddanian in the biostratigraphically well-controlled Rostanga-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 correspo...

Stable isotopic studies of Archean–Paleoproterozoic sedimentary rocks older than 2.4 Ga have documented large mass-anomalous fractionations of sulfur isotopes (Δ33S=>0±0.2‰), while younger rocks record little to no anomalous fractionation of sulfur isotopes. This change from large anomalous fractionations to sulfur isotope values that fall on the t...

The previously established graptolite and chitinozoan Hirnanian-Telychian biostratigraphy in the unique Osmundsberget North outcrop in the Siljan region, south-central Sweden, is integrated with new conodont biostratigraphy and δ13Corg, δ13Ccarb and δ34Spyr chemostratigraphy. At this locality, the middle Hirnantian (latest Ordovician) topmost part...

The permanent ice cover of Lake Vida (Antarctica) encapsulates an extreme cryogenic brine ecosystem (-13 °C; salinity, 200). This aphotic ecosystem is anoxic and consists of a slightly acidic (pH 6.2) sodium chloride-dominated brine. Expeditions in 2005 and 2010 were conducted to investigate the biogeochemistry of Lake Vida's brine system. A phylog...

A long-standing problem in the Ordovician stratigraphy of south-eastern Norway has been to the relations between the Mjøsa Formation in the Lake Mjøsa region and coeval strata in the Oslo region. The recent discovery of the globally distributed Guttenberg δ13C excursion (Guttenberg Isotopic Carbon Excursion) in the Mjøsa region provided the impetus...

A rise in atmospheric O(2) has been linked to the Cambrian explosion of life. For the plankton and animal radiation that began some 40 million yr later and continued through much of the Ordovician (Great Ordovician Biodiversification Event), the search for an environmental trigger(s) has remained elusive. Here we present a carbon and sulfur isotope...

Widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long-term inhibitor of evolutionary radiation on early Earth. In recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later Cambrian oceans, possibly influencing evolutionary...

A high-resolution 87Sr/86Sr curve and paired δ13C carbonate-organic data set is generated for the Llandovery Series from the Ikla drill core in Estonia. A δ13C carbonate curve is also presented from the Pancake Range in Nevada. Observed 87Sr/86Sr values in the Ikla drill core are at a minimum in the early Llandovery Rhuddanian Stage (∼ 0.7079 to 0....

δ13C values of numerous limestone samples from Katian (Upper Ordovician) successions in Oklahoma and the Upper Mississippi Valley document the presence of at least three of the four positive excursions that have been recognized in the lower–middle Katian interval in the Cincinnati region in Ohio, Kentucky, and Indiana. A comparison with Estonia rev...

The Late Ordovician Hirnantian Stage (∼ 444 million years ago) was one of three time periods during the past half billion years in which large continental glaciers formed over Earth's polar regions. The effects of this glaciation were far-reaching and coincided with one of the largest marine mass extinction events in Earth history. The cause of thi...

Whereas no studies have previously been carried out on the δ13C chemostratigraphy of the Sandbian-Katian (Upper Ordovician) succession anywhere in Norway, such investigations in Sweden and the East Baltic region have made the δ13C chemostratigraphy of that interval well known. In an attempt to document for the first time the presence of the globall...

A large drop in seawater 87Sr/86Sr during the Middle Ordovician was among the most rapid in the entire Phanerozoic. New 87Sr/86Sr measurements from Nevada indicate that the rapid shift began in the Pygodus serra conodont zone of the upper Darriwilian Stage. We use a numerical model to explore the hypothesis that volcanic weathering provided the flu...

The only published δ13C data from the Ordovician of China are from the Lower and Upper Ordovician, and only the latter records include a significant excursion, namely the Hirnantian excursion (HICE). Our recent chemostratigraphic work on the Upper Ordovician (Sandbian–Katian) Pagoda and Yanwashan formations at several localities on the Yangtze Plat...

Late Sandbian–Early Katian marine carbonates from two sections in North America and one in south China were analyzed for paired δ13Ccarb and δ13Corg, and revealed similar δ13Ccarb but varying trends in δ13Corg stratigraphy while all sections recorded a well-known positive δ13Ccarb shift. These δ13Corg records are the first through the Guttenberg δ1...

The Late Cambrian SPICE event is an inorganic carbon isotope excursion that is documented in carbonate rocks around the world. At most localities, the excursion begins near 0 per mil and rises to between + 4 and +5 per mil. These localities include China, Siberia, Kazakhstan, Australia, and North America (Great Basin, US midcontinent, and Applachia...

The Paleozoic Era contains many large, commonly globally expressed positive carbon isotope excursions recorded in carbonate rocks. In younger Mesozoic rocks, similar excursions are often easily linked to organic-rich deposits formed from enhanced carbon burial under ocean-scale anoxia -i.e., oceanic anoxic events (OAEs). These events are important...

The Global Boundary Stratotype Section and Point (GSSP) for the Katian Stage of the Upper Ordovician Series is defined as the 4.0 m-level above the base of the Bigfork Chert in the Black Knob Ridge section, southeastern Oklahoma. This point in this section is coincident with the first appearance of the graptolite Diplacanthograptus caudatus, which...

The Guttenberg carbon isotope excursion (GICE) documented from eastern North America demonstrates the effects that regional, geochemically distinct water masses, upwelling, and ocean circulation have on the carbon isotope record from carbonate platforms. Late Turinian–Chatfieldian carbonates from Oklahoma, Kentucky, Virginia, and West Virginia reco...

The timing and causes of the transition to an icehouse climate in the Late Ordovician are controversial. Results of an integrated delta13C and sequence stratigraphic analysis in Nevada show that in the Late Ordovician Chatfieldian Stage (mid-Caradoc) a positive delta13C excursion in the upper part of the Copenhagen Formation was closely followed by...