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The Upper Silurian Salina Group of eastern North America is well known for its thick evaporite successions and hydrocarbon resources. These strata have been assigned to numerous chronostratigraphic schemes within Ohio and Michigan and are currently identified by varying subsurface and outcrop nomenclatural schemes. These chronostratigraphic challenges have persisted for over 50 yr and dramatically inhibit the correlation of events recorded in the Silurian section of eastern North America with the global record of Silurian biogeochemical events. To help resolve the chronostratigraphic correlation of these units, we provide new high-resolution δ13Ccarb chemostratigraphic analyses of a core located in central Ohio for strata assigned to the Greenfield and Tymochtee Formations and integrate existing biostratigraphic, chemostratigraphic, and subsurface geophysical data in western, southern, and eastern Ohio. The new data presented here, integrated for the first time with basinwide subsurface geophysical data, demonstrate a mid-late Homerian Stage global sea-level lowstand, suggest a short interval of tectonic stability within the study area at the beginning of “Salina B–G” deposition, during which accommodation was occupied by the Greenfield Formation and laterally equivalent strata, and provide chronostratigraphic constraints for basin flexure and potential forebulge migration associated with renewed tectonic activity. The new chronostratigraphic correlation of these strata provides a broader picture of Silurian environmental change across the eastern half of the Laurentian paleocontinent.

Conodonts are an extinct group of primitive jawless vertebrates whose elements represent the earliest examples of a mineralized feeding apparatus in vertebrates. Their relative relationship within vertebrates remains unresolved. As teeth, conodont elements are not homologous with the dentition of vertebrates, but they exhibit similarities in mineralization, growth patterns, and function. They clearly represent an early evolutionary experiment in mineralized dentition and offer insight into analogous dentition in other groups. Unfortunately, analysis of functional performance has been limited to a handful of derived morphologies and material properties that may inform ecology and functional analysis are virtually unknown. Here we applied a nanoscale approach to evaluate material properties of conodont bioapatite by utilizing Atomic Force Microscopy (AFM) nanoindentation to determine Young’s modulus (E) along multiple elements representing different ontogenetic stages of development in the coniform-bearing apparatus of Dapsilodus obliquicostatus. We observed extreme and systematic variation in E along the length (oral to aboral) of each element that largely mirrors the spatial and ontogenetic variability in the crystalline structure of these specimens. Extreme spatial variability of E likely contributed to breakage of elements that were regularly repaired/regrown in conodonts but later vertebrate dentition strategies that lacked the ability to repair/regrow likely required the development of different material properties to avoid structural failure.

This is a map. It has an introduction, but no abstract.

The Ireviken Biogeochemical Event (IBE) consists of the Ireviken Extinction Event (IEE) and is superseded by the Ireviken positive d13Ccarb Excursion (ICIE). During the Ireviken Extinction Event 80% of the conodont species and 50% of the trilobite species went extinct and Acritarchs, chitinozoans, graptolites, corals, and brachiopods communities were severely affected as well. Currently there are no indications that the Ireviken Biogeochemical event can be linked to a LIP or a bolide impact which are the usual triggers for most known biogeochemical events. The IBE has been tentatively linked to SEDEX brine expulsion, however convincing high-resolution data supporting the SEDEX brine expulsion theory was lacking.The Altajme core from Gotland Sweden covers the entirety of the Ireviken Biogeochemical Event and using an ITRAX XRF core scanner we were able to create a new dataset with a 1cm(~150-400 yr.) resolution. This dataset enables us to shed new light on the origin of the IBE and serves as a template for a cyclostratigraphic age model (using the detrital proxies of Ti and Al) which puts the IBE within a precise temporal framework.The occurrence of peak values of Nb, Mn, Cu, Ba, Pb, Zn, As, Ag in the Altajme core follows the temporal sequence of element peaks which is characteristic for the cooling of a hydrothermal system. A Pb:Zn ratio of >1 and low Cu/(Zn+Pb) ratio categorises the hydrothermal system as being the sedimentary exhalative (SEDEX) brine expulsion type system. Through these results we can undoubtedly link the Ireviken Biogeochemical Event to a SEDEX brine expulsion. Numerous SEDEX style ore deposits of Proterozoic to Cenozoic age are known, but it has been difficult to connect them with similarly aged biogeochemical events. This study demonstrates that through extremely high resolution XRF/element data we can observe the far-field signature of a SEDEX brine expulsion and thus showing us the way to recognize more biogeochemical events triggered by SEDEX brine expulsions.

With a record that spans approximately 300 million years (late Cambrian through the Triassic/Jurassic transition, i.e., the “Conodontozoic”), conodonts witnessed all principal events in the evolution of life on Earth, from the invasion of the land to the exploration of the air, from the explosion of biomineralization in the oceans to the rise of dinosaurs and mammals, including three of the major extinction events that occurred in the Phanerozoic. Mainly used for biostratigraphic or geochemical studies, the potential of conodonts to help unravel changes perceived to be of global extent rarely has been explored. While specialists have identified rapid changes in conodont element morphology throughout their history, the conodont animal has often been perceived to have been a static entity in a constantly evolving world, when biological equilibrium in the oceans was undergoing profound alteration and faunal recoveries took place in phases that seem to have had recurrent patterns. It is now essential that we begin to further investigate how conodonts, as biologic entities, responded to or were impacted by palaeogeographic changes, eustatic and climatic fluctuations, shifting redox conditions, and major faunal turnovers and reorganizations that took place during the “Conodontozoic”.

High-resolution paired analyses of δ13Ccarb and δ13Corg 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 δ13Ccarb and δ13Corg) and allows the calculation of changes in organic carbon burial (forg) throughout the late Wenlock. The paired data suggest a ~ 38% increase in forg during the peak of the positive δ13Ccarb 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 CO2, in support of previous interpretations of regression and global cooling coinciding with the Mulde Extinction Event.

This is a map. There is no abstract.

The first appearance of pinnacle reef tracts, composed of hundreds to thousands of localized biogenic structures protruding tens to hundreds of meters above the surrounding mid-Silurian seafloor, represents a step change in the evolution of the marine biosphere. This change in seafloor morphology opened a host of new ecological niches that served as “evolutionary cradles” for organism diversification. However, the exact timing and drivers of this event remain poorly understood. These uncertainties remain, in large part, due to a paucity of index fossils in the reef facies, the difficulty of correlating between the offshore pinnacle reefs and more temporally well-constrained shallow marine facies, and cryptic unconformities that separate amalgamated reefs. Here we use δ 13 Ccarb stratigraphy within a sequence stratigraphic framework to unravel these complex relationships and constrain the origination of Silurian pinnacle reef tracts in the North American midcontinent to near the Pt. celloni Superzone—Pt. am. amorphognathoides Zonal Group boundary of the mid-Telychian Stage. In addition, we identify a striking relationship between pulses of reef development and changes in global δ 13 Ccarb values and sea level. Viewed through this new perspective, we correlate prolific periods of reef development with short-lived carbon isotope ( δ 13 Ccarb) excursions and eustatic sea level change that, ultimately, reflect perturbations to the global carbon cycle. From changes in the dominance of microbial reefs of the Cambrian to metazoan colonization of reefs in the Middle Ordovician, through the subsequent collapse of metazoan diversity with the Late Ordovician mass extinction, and the first appearance of early Silurian (Llandovery) pinnacle reef tracts and their proliferation during the late Silurian (Wenlock-Pridoli) and Devonian, major reef formation intervals increasingly coincide with δ 13 Ccarb excursions. These patterns suggest that Paleozoic reef evolution was the product of environmental forcing by perturbations of the global carbon cycle.

Paired records of δ13Ccarb and δ13Corg 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 δ13Corg during the initiation of the Ireviken Extinction Event (IEE) and prior to the onset of the Ireviken positive δ13Ccarb Excursion (ICIE). The record of carbon isotopic changes through this interval illustrate that both Δ13C (the difference between δ13Ccarb and δ13Corg) as well as the relative flux of organic carbon burial (forg) 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 forg) 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.

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.

Integration of sedimentologic, chemostratigraphic, biostratigraphic, and geochronologic data identifies the profound influence that sudden bursts of carbonate sedimentation, sea-level oscillation, and hypersalinity, associated with Ireviken and Mulde carbon cycle perturbations, had on the evolution of the Michigan Basin during the Silurian. Conodonts and carbon isotope (δ13Ccarb) stratigraphy of the Lockport and Engadine Dolomites constrain the rapid build-up and progradation of a thick biohermal wedge along the basin margins to the Sheinwoodian-age Ireviken Excursion, a recently identified period of global reef growth. This event significantly changed the hydrologic architecture of the basin, ultimately resulting in restricted seawater exchange that drove evaporite deposition. Zircon U Pb ages of ~428 Ma from bentonites near the base of the evaporite-bearing Salina Group, together with δ13Ccarb profiles transecting the basin, constrain the onset of hypersalinity to initiation of the late Homerian Mulde Excursion. Importantly, the double δ13Ccarb peak of this event parallels a complex pattern of dramatic sea-level oscillations, on the order of 100 m, recorded within the A-0 to A-2 evaporites and associated pinnacle reefs. Ascending δ13Ccarb values were accompanied by sea-level fall, karstification, and the formation of evaporites in the basin center. Intra-excursion sea-level rebounds triggered exceptionally rapid upward pinnacle reef growth. Subsequent sea-level fall again exposed the ramp and pinnacle reefs resulting in basin-wide restriction and massive salt deposition that, ultimately, encased the reefs in salt. The return to baseline δ13Ccarb values was accompanied by flooding and carbonate sedimentation. Our integrated approach, with high-resolution δ13Ccarb stratigraphy from closely spaced (intra-basinal) sections as a central component, enables finely tuned chronostratigraphic correlation, recognition of unconformity-bound facies packages (i.e., systems tracts), and constrains variations in sea level and sedimentation rates. These findings have immediate applications to predictive static reservoir models for the evaluation of the reefs as repositories for anthropogenic CO2 sequestration, gas storage reservoirs, and hydrocarbon exploration. Ultimately, our findings demonstrate that a cascade of rapid environmental changes, including pulses of carbonate sedimentation, high-amplitude sea-level oscillations, and evaporite deposition, were associated with the Ireviken and Mulde perturbations of the Silurian carbon cycle.

The eastern and southeastern margins of the Appalachian Basin contain extensive exposures of Telychian through Pridoli (upper Silurian) strata. Litho- and biostratigraphic analyses of these strata over the last century provided a general means for their chronostratigraphic correlation to global series and stage boundaries. However, a rarity of zonally diagnostic fauna limited precise correlation both within and beyond the Appalachian Basin. Recent conodont biostratigraphic studies substantially revised the chronostratigraphic position of these strata by more than a series in some cases. Much of the interval, however, remained biostratigraphically unzoned and the precise position of series and stage boundaries remained tentative. To improve the chronostratigraphic correlation of these strata to global series and stage boundaries we provide new integrated conodont and high-resolution δ13Ccarb chemostratigraphic analyses from two outcrops located in West Virginia and Virginia, spanning the upper Rose Hill through Tonoloway formations (upper Telychian through Pridoli). These new data show that the Silurian carbon isotope record for this portion of the Appalachian Basin is shifted to more negative δ13Ccarb values than typical global data. However, the overall isotopic records appear correlative at least within the Appalachian Basin thereby providing a means for future correlation within the basin for intervals in which biostratigraphy is traditionally lacking. These coupled data demonstrate that the Ireviken and Mulde excursions are contained within our sections. The high-amplitude Lau Excursion was, however, not observed and the present biostratigraphic data suggest that a majority of the Ludlow Series was either not recorded or was later removed by erosion. These coupled analyses therefore indicate that the Ludlow-Pridoli boundary resides within the Wills Creek Formation and we propose that the overlying isotopic record presented here records the Late Ludlow Carbon Isotope Excursion (LLCIE) and Silale Low, previously identified only within the Baltic Basin.

Times of metal-rich brine discharge into ancient ocean basins, associated with the formation of sedimentary-exhalative (sedex) Zn-Pb-Ba ore deposits, coincided with short-duration positive excursions ("spikes") in the global marine Sr isotope record. While these spikes are unexplained by conventional oceanic models, chronostratigraphic correlations, combined with mass balance evidence and oceanographic modeling, suggest that the flux of radiogenic Sr from sedex brines during ore formation is sufficient to explain these previously enigmatic Sr-87/Sr-86 spikes. We review existing Sr-87/Sr-86 data and present new data as verification of these global Sr-87/Sr-86 spikes and their correlations with the formation of giant sedex ore deposits. Major events include an 1 x 10(-4) (similar to 0.7078-similar to 0.7079) excursion contemporaneous with formation of the Rammelsberg deposit at -389 Ma; spikes on the order of 1 to 3 x 10(-4), coeval with formation of the Meggen deposit at similar to 381 Ma, several ore deposits in the Macmillan Pass district at similar to 379 to 375 Ma, and the Silvermines deposits at similar to 352 Ma; and two >6 x 10(-4) spikes coincident with formation of the giant Navan deposit at similar to 346 Ma and Red Dog deposits at similar to 337 Ma. Moreover, the timing of peak 8(87)Sr/Sr-86 spikes correlates with global delta C-13 and delta O-18 spikes,deposition of metal-rich black shales and ironstones, metal-induced malformation (teratology) of marine organisms, and mass extinctions. The relationships among these features were poorly understood, but our new model explains how the flux of key biolimiting nutrients and metals contained in sedex brines, demonstrably equivalent to or exceeding that of the total modern riverine flux to the ocean, spurred ocean eutrophication, which, ultimately, through a series of positive feedback mechanisms, may have triggered global chemical and biological events. If, as we hypothesize, sedex hydrothermal systems are recorded in the global marine isotopic, geologic, and biological records, our findings define a new approach to the study of and exploration for sedex deposits. We demonstrate that fluid inclusion solute chemistry and isotopic and stratigraphic studies of sedex deposits, coupled with chronostratigraphic correlation and high-resolution Sr-87/Sr-86 isotope chemostratigraphy, can be used to answer long-standing questions about geologic processes responsible for formation of these extraordinary deposits. This approach provides evidence for the age, duration, and fluxes of fluids and metals vented into the ocean by these giant hydrothermal systems. Accordingly, the marine Sr-87/Sr-86 curve constitutes a global exploration tool that could be applied to assess the mineral potential of sedimentary basins.To illustrate the potential of this tool to identify favorable stratigraphic ages and basins with potential for undiscovered giant sedex deposits, we highlight several spikes, on par with those characteristic of the Red Dog and Navan deposits, which have not been correlated with known metal deposits. Given these strong temporal correlations, mass balance estimates, and results of ocean chemistry modeling, our study suggests that further work is warranted to determine the extent to which periodic venting of hydrothermal basinal brines into the ocean has influenced the evolution of marine chemistry. Ultimately, these global signatures can be applied to the study of and exploration for sedex deposits.

The Moose River Basin in Ontario, Canada, contains nearly 1 km of Silurian marine strata, and although it has been studied for more than a century, its precise correlation globally has not been constrained. Herein, a core from the Victor Mine in the Moose River Basin was examined for conodont biostratigraphy and carbonate carbon (δ13Ccarb) isotope chemostratigraphy to provide a detailed chronostratigraphic framework for the Silurian strata (Severn River, Ekwan River, and Attawapiskat formations) in the Moose River Basin. The recovery of Aspelundia expansa, Aspelundia fluegeli fluegeli, Distomodus staurognathoides, Ozarkodina polinclinata estonica, Pterospathodus eopennatus, and Aulacognathus bullatus, as well as the lower Aeronian, upper Aeronian, lower Telychian (Valgu), and ascending limb of the Sheinwoodian (Ireviken) positive carbonate carbon (δ13Ccarb) isotope excursions provide significantly improved chronostratigraphic correlation of Llandovery strata in the Moose River Basin.

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 carbon burial. The timing and magnitude of this baseline shift, however, is still elusive in part because of the lack of high-resolution δ13C data that span this period. Much of the existing Ordovician δ13C literature is focused on isotopic excursions with less emphasis on identifying long-term shifts in baseline (pre- and post-excursion) values. This study presents new high resolution δ13C data from stratigraphic sections at Germany Valley (West Virginia) and Union Furnace (Pennsylvania) in the Central Appalachian Basin. These sections span the entire Sandbian Stage and continue into the lower Katian Stage. The δ13C data from both sections are characterized by relative stability carbon isotope values (mean = −0.61‰) in the lower Sandbian, followed by a + 1.2‰ shift in the upper Sandbian (mean = +0.62‰). Herein, we propose that the positive shift represents a long-term global shift in baseline δ13C values of dissolved inorganic carbon. The timing of this positive shift coinciding with the diversification of early land plants (i.e., bryophytes) supports earlier models that suggested enhanced organic carbon burial rates served as a mechanism for the stepwise oxygenation of the atmosphere during the Late Ordovician.