Article

Revised perspectives on Devonian biozonation and environmental volatility in the wake of recent time-scale revisions

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Abstract

Revised time-scales for the Devonian Period have highlighted major discrepancies in the frequency of evolutionary, eustatic, carbon cycle, and biotic events. The number of conodont biozones per million years shows strong variation among stages. Using two alternative time scales, the lowest values are in the Emsian and highest in the Givetian, Frasnian, and Famennian stages. A similar result is obtained by dividing the Devonian time scale into 12 equal 5-million year bins and determining the number of conodont zonal subdivisions in each bin. The record of ammonoid biozones also shows interesting parallels. The acuity of biostratigraphic zonation and zonal subdivisions appears to be correlative with the frequency of environmental perturbations, including eustatic, positive carbon isotopic excursions, and hypoxic/anoxic related bioevents, and these are similarly unevenly distributed. All calculations of environmental volatility metrics show the late Eifelian through early Frasnian to be the most volatile interval of the Devonian, followed by the mid-late Famennian, while the Lochkovian through Emsian and mid-Frasnian through early Famennian are the least volatile. Furthermore, the majority of major bioevents occur in the Eifelian through early Frasnian, and late Famennian. The strong evidence for higher biotic and environmental volatility in the late Eifelian through early Frasnian and late Famennian rock record corresponds to the coolest paleoclimate conditions in the Devonian according to recent conodont apatite δ¹⁸O compilations, and the transition from an overall cooling to warming paleotemperature trend during the mid-Givetian. Regardless of mechanism, strong variations in volatility occurred during the Devonian Period. Intervals with greater biostratigraphic resolution also show much stronger environmental volatility including a series of relatively quasi-stable conditions punctuated by major turnovers with abrupt sea-level rise, widespread hypoxia, and changes in the carbon cycle. It was during these intervals that much net evolutionary and ecological change appears to have taken place.

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... Linked periodic restriction and ventilation in continentmarginal troughs is a key aspect in the formation and preservation of HEBS. Sea-level instability during the Middle Devonian is well documented, and this may have contributed to the prominent biotic crises during this period (Brett et al., 2018). The Re-Os and biostratigraphic age constraints for the HEBS overlap with the Kačák, P. pumilio, and Taghanic biotic events (Becker et al., 2012;McGhee et al., 2013;Narkiewicz et al., 2016;Brett et al., 2018). ...
... Sea-level instability during the Middle Devonian is well documented, and this may have contributed to the prominent biotic crises during this period (Brett et al., 2018). The Re-Os and biostratigraphic age constraints for the HEBS overlap with the Kačák, P. pumilio, and Taghanic biotic events (Becker et al., 2012;McGhee et al., 2013;Narkiewicz et al., 2016;Brett et al., 2018). These events had a global extent and may have initiated a prolonged period of decline in biodiversity (Fan et al., 2020). ...
... These events had a global extent and may have initiated a prolonged period of decline in biodiversity (Fan et al., 2020). Key aspects include abrupt faunal changes, eustatic sea-level rise, continental shelf flooding, and black shale deposition (House, 1996(House, , 2002Haq and Schutter, 2008;Becker et al., 2012;Brett et al., 2018). We hypothesize that metal enrichment may be a hallmark feature of Middle Devonian eustatic/ biotic events. ...
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... The Late Devonian is a crucial period in Earth history, characterized by several bio-events (e.g. House, 2002;Ma et al., 2016;Becker et al., 2016a;Brett et al., 2018;Qie et al., 2019a) and representing a critical stage for the early evolution of plants documented by the first occurrence of forests and earliest seed plants (Scott and Glasspool, 2006;Berry and Marshall, 2015). Stromatoporoid-coral reefs flourished during the Middle Devonian and Frasnian, but disappeared during the Late Devonian mass extinction (=Upper Kellwasser event) near the F-F (Frasnian-Famennian) boundary. ...
... The Lower and Upper Kellwasser horizons represent a mass extinction event in the late Frasnian (e.g. Becker et al., 2016a;Brett et al., 2018) which witnessed the disappearance of many organisms, including the loss of the stromatoporoid-coral reef ecosystem (Flügel and Kiessling, 2002). Based on recent modeling (e.g. ...
... The Nehden and the Enkeberg events of the early and middle Famennian are associated with transgressions and the deposition of black sediments in the prima and marginifera zones, respectively (e.g. Becker et al., 2016a;Brett et al., 2018). The Condroz event coincides with a sea-level fall in the rhomboidea Zone (Becker and House, 1997;Becker et al., 2016a). ...
... For example, radioisotopic ages D10-D12 have large stratigraphic and age uncertainties, and thus the model 95% highest density interval only slightly constricts at those events, since there is a large spread in positions that the algorithm can select to represent those events (Fig. 9). Better age precision may be achieved by redating some of these volcanic layers, but our ability to decrease relative stratigraphic uncertainty in our modeling may be limited by the actual lack of biotic variability during certain stages, particularly the Emsian (Brett et al., 2020). By contrast, the radioisotopic ages and conodont biozone assignments for D16-D18 are tightly constrained, so much so that the conodont zonal boundaries are within the resolution of the uncertainty on the radioisotopic ages, and the model 95% highest density interval in the Frasnian near D16-D18 is much more restricted than that in the Pragian and early Emsian near D10-D12 (Fig. 9). ...
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... A similar feedback may have also been important in the Devonian when biological turnover was also linked to environmental volatility and periods of shelf anoxia Frontiers in Earth Science | www.frontiersin.org August 2021 | Volume 9 | Article 669476 (Bond and Wignall, 2008;Brett et al., 2020). Application of this upwelling model to even younger ironstones and contemporaneous trace element enriched black shales may also provide important new constraints regarding the redox structure and oxygenation history of the Mesozoic oceans. ...
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... Percival et al., 2018). Despite these difficulties, it is apparent that the Late Devonian was a time of major climate change marked by the transition from greenhouse to icehouse conditions and overall eustatic change (Johnson et al., 1985;Streel et al., 2000;Joachimski and Buggisch, 2002;Balter et al., 2008;Bond and Wignall, 2008;Lakin et al., 2016;de Vleeschouwer et al., 2017;Brett et al., 2018;Wang et al., 2018;Song et al., 2020). Biocrises are commonly correlated with hypoxic highstands during repeated transgressive-regressive cycles (Johnson et al., 1985;Brett and Baird, 1996;Bond and Grasby, 2017). ...
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... A similar feedback may have also been important in the Devonian when biological turnover was also linked to environmental volatility and periods of shelf anoxia Frontiers in Earth Science | www.frontiersin.org August 2021 | Volume 9 | Article 669476 (Bond and Wignall, 2008;Brett et al., 2020). Application of this upwelling model to even younger ironstones and contemporaneous trace element enriched black shales may also provide important new constraints regarding the redox structure and oxygenation history of the Mesozoic oceans. ...
... The record of Devonian extinctions, in variable scales, results of many efforts of researches in the last decades, with a set of events recognized in different basins from the world (synthesis in House, 2002;Becker et al., 2016;Brett et al., 2018). The fossil record is useful to infer paleoenvironmental and evolutionary changes even considering the possibility of some preservational bias (e.g., Signor-Lipps Effect;Signor III and Lipps, 1982). ...
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The Devonian System of Euramerica contains at least 14 transgressive-regressive (T-R) cycles of eustatic origin. These are separated into three groups (or depophases) and from Carboniferous cycles by three prominent regressions. Twelve post-Lochkovian T-R cycles are recognized, and they commonly appear to result from abrupt deepening events followed by prolonged upward shallowing. Deepening events in the western United States (especailly Nevada), western Canada, New York, Belgium, and Germany have been dated in the standard conodont zonation and are demonstrably simultaneous in several or all five regions. This synchroneity indicates control by eustatic sea-level fluctuations rather than by local or regional epeirogeny. Facies shifts in shelf sedimentary successions are more reliable indicators of the timing of sea-level fluctuations than are strandline shifts in the cratonic interior, because the latter are more influenced by local epeirogeny. Strandline shifts are most useful in estimating the relative magnitude for sea-level fluctuations. Devonian facies progressions and the three prominent regressions are of a duration and an order of magnitude that could have been caused by episodes of growth and decay of Devonian oceanic ridge systems. The described T-R cycles could have formed in response to mid-plate thermal uplift and submarine volcanism. The latter process may have been a control on small-scale (1-5 m thick) upward-shallowing cycles within the major T-R cycles. Continental glaciation could have been a factor in sea-level fluctuations only in the Famennian and could not have been responsible for the Devonian facies progressions or the numerous T-R cycles. The Frasnian extinctions were apparently cumulative rather than due to a single calamity. Two rapid sea-level rises occurred just before, and one at, the Frasnian-Famennian boundary. It is probable that this series of deepening events reduced the size of shallow-shelf habitats, caused repeated anoxic conditions in basinal areas, and drowned the reef ecosystems that had sustained the immensely diverse Devonian benthos. -Authors
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The Early Paleozoic featured nine intervals of strong expansion of an upper slope, dysoxic/anoxic (d/a) water mass with eustatic rise or epeirogenic transgression. Strong expansion of this d/a water mass led to deposition of time-specific, macroscale alternations of dark grey-black mudstone within oxic, green to red mudstone on the middle–lower slope. This d/a facies even onlapped warm- (carbonate) and cool-water (siliciclastic) shelves. As in the Mesozoic, d/a muds were deposited in shallow water, perhaps tens of metres deep, with sea-level rise. These nine d/a macroscale alternations correspond to intervals of “global hyperwarming”—times of very intense greenhouse conditions that resulted from a feedback initiated by higher insolation and heat storage as shallow seas onlap tropical palaeocontinents. Warm epeiric seas heated the ocean, and thermal expansion accelerated eustatic rise. Ever more extensive epeiric seas heightened oceanic and global temperature as heat storage capacity increased. Deep ocean circulation intensity fell below that of a greenhouse interval and lead to d/a deposition low on the slope and on the platforms to provide the signature of global hyperwarming. Global hyperwarming differs from a hothouse interval as it does not require CO2 input from large igneous provinces to produce high temperatures and never shows deep-sea anoxia. Late Ordovician and Late Devonian black mudstones that cover much of Laurentia record epeirogenic transgressions that led to global hyperwarming, and suggest that cold water upwelling or plant terrestrialisation had nothing to do with epeiric sea anoxia. Global hyperwarming reduced oxygen solubility in these seas, and erosion of orogens produced muddy water that limited light penetration and promoted shallow-water anoxia. The global hyperwarming hypothesis means that relative eustatic and epeirogenic sea levels complement the effect of global pCO2 on climate, and sea level must also be regarded as a primary driver of Phanerozoic climate.
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The oxygen isotopic composition of conodont apatite from two Frasnian-Famennian boundary sections was measured in order to reconstruct variations in marine paleotemperatures during the late Frasnian mass-extinction event. The measured conodont apatite delta18O values reveal two positive excursions with maximum amplitudes of +10/00 to +1.50/00 that parallel positive excursions in the carbonate carbon isotopic composition. The +30/00 excursions in carbonate delta13C have been interpreted as consequences of enhanced organic carbon burial rate resulting in a decrease in atmospheric CO2 concentration. Climatic cooling as a potential consequence of lower atmospheric CO2 concentration is confirmed by the conodont apatite delta18O records, which translate into cooling of low-latitude surface waters by 5 7 °C. Repeated cooling of the low latitudes during the late Frasnian had a severe impact on the tropical shallow-water faunas that were probably adapted to warm surface-water temperatures and severely affected during the late Frasnian crisis. These prominent variations in ocean-water temperature were stressful to the tropical shallow-water fauna and potentially culminated in low origination rates of new species, one of the major factors of the decline in diversity during the latest Frasnian.
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The formation of upper Paleozoic (Viséan to Sakmarian-Artinskian) Eurameri-can cyclothems, which resulted from base-level fluctuations of up to 100 m, commonly are attributed to large-scale waxing and waning of Gondwanan glaciers. However, evaluation of the geographic and chronostratigraphic distribution of Gondwana deposits reveals that glaciation was not the primary cause of base-level changes of that magnitude. Gondwana strata contain three non-overlapping glacial successions. Glacial I (Frasnian to possibly Tournaisian) and Glacial II (Namurian to lowermost West-phalian) rocks were deposited by alpine glaciers. Water sequestered by these glaciers was insufficient to account for the base-level changes. In contrast, Upper Carboniferous (Stephanian) to Lower Permian (Sakmarian-Artinskian) Glacial III rocks were wide-spread and indicate deposition by ice sheets that may have covered a total area of between 17.9 and 22.6 × 10 6 km 2 . Complete ablation of a single ice sheet of this size would produce eustatic changes of ~100 m. However, multiple ice sheets were likely present, which would have resulted in considerably smaller fluctuations in sea level dur-ing Glacial III deposition. The argument that Glacial I and II deposits were originally comparable in extent to those of Glacial III, but were eroded during the advance of Glacial III ice-sheets, is untenable. Weathered granite profiles on the pre-Glacial III unconformity occur scat-tered over a 1200-km length of the central Transantarctic Mountains. The profiles indi-cate prolonged subaerial exposure and, thus, an absence of ice cover. These and non-glacial successions in Gondwana constrain the size of ice sheets before Glacial III deposition and imply that glaciation prior to Glacial Episode III was not the primary cause of base-level changes linked to upper Paleozoic Euramerican cyclothems.
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The main conodont zonation schemes for the Přídolí and the Lochkovian presents some problems that make difficult their use in several geographical areas. Data from several sections in Sardinia and the Carnic Alps not only allow to built a regional zonation scheme for these areas, but also suggest possible solutions of global validity. In the Carnic Alps and Sardinia, the Přídolí is subdivided into three zones: eosteinhornensis s.l., Lower and Upper detortus. The latter results after the subdivision of the former detortus Zone on the basis of the Last Appearance Datum of some coniform species (Dapsilodus obliquicostatus, Coryssognathus dubius and Panderodus recurvatus) that became extinct almost simulta-neously in the latest Přídolí. Daps. obliquicostatus is chosen as the marker, being the most common and easily identifi-able species. In the Lochkovian six zones are discriminated: hesperius, carlsi, transitans, eleanorae, trigonicus and pan-dora β. The hesperius Zone, which includes the postwoschmidti subzone in its upper part, is expanded to include most of the eurekaensis zone of the "global" scheme, because the marker Oz. eurekaensis is not present. The carlsi Zone corre-sponds to the upper part of the eurekaensis Zone and to the lower part of the former mid-Lochkovian delta Zone (= omoalpha Zone). The rest of the Middle Lochkovian is subdivided into the three zones (transitans, eleanorae and trigonicus) already proposed in Nevada and Spain, followed by the pandora β Zone. All the zones are discussed and checked for their applicability in other palaeogeographical regions. • Key words: biostratigraphy, conodont zonation, Přídolí, Lochkovian, Carnic Alps, Sardinia. CORRADINI, C. & CORRIGA, M.G. 2012. A Přídolí–Lochkovian conodont zonation in Sardinia and the Carnic Alps: im-plications for a global zonation scheme.
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Klug, C., Kröger, B., Kiessling, W., Mullins, G.L., Servais, T., Frýda, J., Korn, D. & Turner, S. 2009: The Devonian nekton revolution. Lethaia, 10.1111/j.1502-3931.2009.00206.x Traditional analyses of Early Phanerozoic marine diversity at the genus level show an explosive radiation of marine life until the Late Ordovician, followed by a phase of erratic decline continuing until the end of the Palaeozoic, whereas a more recent analysis extends the duration of this early radiation into the Devonian. This catch-all approach hides an evolutionary and ecological key event long after the Ordovician radiation: the rapid occupation of the free water column by animals during the Devonian. Here, we explore the timing of the occupation of the water column in the Palaeozoic and test the hypothesis that ecological escalation led to fundamental evolutionary changes in the mid-Palaeozoic marine water column. According to our analyses, demersal and nektonic modes of life were probably initially driven by competition in the diversity-saturated benthic habitats together with the availability of abundant planktonic food. Escalatory feedback then promoted the rapid rise of nekton in the Devonian as suggested by the sequence and tempo of water-column occupation. □Devonian, diversity, ecology, food webs, nekton, plankton, radiation.
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A Late Devonian polymictic diamictite extends for more than 400 km from northeastern Pennsylvania across western Maryland and into east-central West Virginia. The matrix-supported, unbedded, locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter. The mostly rounded clasts are both locally derived and exotic; some exhibit striations, faceting, and polish. The diamictite commonly is overlain by laminated siltstone/mudstone facies associations (laminites). The laminites contain isolated clasts ranging in size from sand and pebbles to boulders, some of which are striated. The diamictite/laminite sequence is capped by massive, coarse-grained, pebbly sandstone that is trough cross-bedded. A stratigraphic change from red, calcic paleo-Vertisols in strata below the diamictite to non-calcic paleo-Spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite. The diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the Late Devonian of the Appalachian basin. These deposits record a Late Devonian episode of climatic cooling so extreme that it produced glaciation in the Appalachian basin. Evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite, overlain by glaciolacustrine varves containing dropstones, and capped by sandstone interpreted as braided stream outwash.The Appalachian glacigenic deposits are contemporaneous with glacial deposits in South America, and suggest that Late Devonian climatic cooling was global. This period of dramatic global cooling may represent the end of the mid-Paleozoic warm interval that began in the Middle Silurian.
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Carbonate rocks of the Rhenohercynian and Saxothuringian zones of the Variscan Mountains, Prague Syncline, Carnic Alps, Montagne Noire, Pyrenees, and Cantabrian Mountains were investigated for δ13Ccarb. The values were measured on bulk carbonate, selected carbonate components and cements. Many of the studied carbonates are interpreted to exhibit primary marine δ13C values with only some showing evidence of diagenetic alteration. A δ13C curve is presented for the entire Devonian time interval. Positive δ13C excursions are documented in the woschmidti-postwoschmidti, sulcatus, kitabicus, Upper serotinus, kockelianus, Middle varcus, falsiovalis, Upper rhenana, linguiformis to Middle triangularis, and Middle to Upper praesulcata conodont Zones. Some excursions are recorded worldwide and interpreted to be of global significance as e.g. at the Silurian–Devonian and Frasnian–Famennian boundaries. Some of the others are described for the first time from Central and Southern Europe, and their global nature has to be verified by further investigations. Most δ13C excursions coincide with sea-level changes and the deposition of black shales. A coupling of changes in sea-level, weathering intensity, nutrient supply, organic carbon production, and climate is assumed as driving force of the carbon isotope excursions.
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The Late Devonian was an epoch of dramatic evolutionary and environmental changes linked primarily with the Frasnian-Famennian (F-F) mass extinction. Current data and ideas support a prolonged, multi-causal nature of the biodiversity crisis, which favor Earth-bound mechanisms rather than a global cosmic catastrophe. The better under-standing of the Late Devonian ocean-climate-biosphere system leads to several questions, and provides an agenda for future research. (1) Magnitude and rank of biotic changes: more detailed biodiversity studies are needed to place the end-Frasnian extinction in its Late Devonian context. In particular, the emerging severity of the end-Givetian and end-Famennian extinctions contrasts with the current overemphasis on the stepwise F-F crisis. (2) Timing of the key boundaries: a lack of radioisotopic dates hampers any estimation of true biodiversity dynamics, and the integrated comparison with reported ages of impact craters and magmatic events. (3) Marine vs. terrestrial events: insight into global ecosystem changes and correlation should be strengthened by chemostratigraphy, exemplified by the carbon isotope link between marine- and land-derived organic materials. (4) High-resolution (bio)geochemical patterns: isotope secular trends are poorly known at the intra-zonal and inter-basin scales, exemplified by prominent carbon isotope shifts across the Lower-Middle Frasnian passage. Further evidence is also awaited to verify cooling (vs. anoxia) pulses as the main stress factor in the F-F and end-Famennian marine settings, as well as climatic feedback with evolving weathering regimes on land and nutrient dynamic in marine realm. (5) Near-equatorial vs. high-latitude domains: refined data from extratropical successions, e.g. from the Kolyma Block, are still awaited. (6) Tectonic and volcanic-activity: an integrated analysis of tectonic and igneous events, possibly triggered by superplume activity. will serve to evaluate any possible link with the Late Devonian biospheric perturbations. (7) Cyclostratigraphical perspective: includes growing research on refined magnetosusceptibility (MS) and various sea-level signatures to test whether they result from variation in Milankovitch frequency orbital variability. In addition, eustatic sea-level trends and their assumed glacioeustatic forcing have only recently been subject to discussion.
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Is there precedence in Earth history for the rapid release of carbon dioxide (CO2) by fossil-fuel burning and its environmental consequences? Proxy evidence indicates that atmospheric CO2 concentrations were higher during long warm intervals in the geologic past, and that these conditions did not prevent the precipitation and accumulation of calcium carbonate (CaCO3) as limestone; accumulation of alkalinity brought to the ocean by rivers kept surface waters supersaturated. But these were steady states, not perturbations. More rapid additions of carbon dioxide during extreme events in Earth history, including the end-Permian mass extinction (251 million years ago) and the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) may have driven surface waters to undersaturation, although the evidence supporting this assertion is weak. Nevertheless, observations and modeling clearly show that during the PETM the deep ocean, at least, became highly corrosive to CaCO3. These same models applied to modern fossil fuel release project a substantial decline in surface water saturation state in the next century. So, the answer to the original question may be no, there may be no precedent in Earth history for the type of disruption we might expect from the phenomenally rapid rate of carbon addition associated with fossil fuel burning.
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A review of the literature shows that the Famennian global Annulata Event(s) can be recognized as a transgressive, often hypoxic and eutrophic, interval that interrupts an overall regressive eustatic trend in more than 40 regions of North America, Europe, North Africa, Asia and Australia. According to differences in palaeogeography, sedimentology and biota, these occurrences are assigned to 10 event settings. The first detailed data on facies, ammonoid and conodont faunas are presented for the Rheris Basin of the eastern Anti-Atlas (southern Morocco) and compared with previously studied sections of the adjacent Tafilalt Platform, Tafilalt Basin and Maider Basin. The rather argillaceous succession at El Gara resembles the Tafilalt Basin (Hassi Nebech section) in its lack of black shales/limestones and similar ammonoid and conodont assemblages. However, the Sulcoclymenia sulcata Zone (Upper Devonian III-C2) below the Annulata Events contains ammonoid taxa that are unique for all of the Anti-Atlas and North Africa: Protornoceras ornatum Dybczynski, 1913, Genuclymenia aff. angelini (Wedekind, 1908), Protactoclymenia aff. implana (Czarnocki, 1989) and ?Pleuroclymenia sp. juv. The first regional record of the marker conodont Pseudopolygnathus granulosus Ziegler, 1962 also distinguishes the pre-event assemblage. As in many other regions, there is a major decline in ammonoids well before the Lower Annulata Event, which suggests an episode of extreme oligotrophy. Both Annulata Events at El Gara are whitish-weathered marly shales with only small specimens of Platyclymenia and Prionoceras (sensu lato), which are also typical for the annulata Zone (UD IV-A) of other Tafilalt sections, but benthonic organisms are nearly absent. This suggests local low-oxygen conditions, but only a moderate production of organic carbon, insufficient for black shale formation, unlike many German sections or in the Maider Basin (section Mrakib). The latter region represents a deeper shelf basin that had much higher productivity and a unique 'Gundolficeras-Erfoudites- Protactoclymenia-Stenoclymenia-Guerichia biofacies' of the Lower Annulata Shale. The upper part of the annulata Zone at El Gara is characterized by Platyclymenia (Platyclymenia) levata n. sp. Other new taxa of the same zone in the Anti-Atlas are Posttornoceras ascendens n. sp. and Stenoclymenia rectangula n. sp. Whilst the ammonoid faunal overturn between UD III-C and UD IV-A was severe, the strong reduction in conodont diversity with the two Annulata Events was mostly (apart from two taxa) a palaeoecologically triggered, only episodic, feature. The comparison of the various Anti-Atlas Annulata Event beds and assemblages enables the distinction of event biofacies types, which reflect local differences of bathymetry, trophic conditions and seafloor ventilation. © 2016 The Author(s). Published by The Geological Society of London. All rights reserved.
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The latest Devonian–Mississippian interval records the long-term transition from Devonian greenhouse conditions into the Late Palaeozoic Ice Age (LPIA). This transition was punctuated by three short glaciation events in the latest Famennian, mid-Tournaisian and Visean stages, respectively. Primary evidence for glaciation is based on diamictite deposits and striated pavements in South America, Appalachia and Africa. The aim of this review is to assess the primary biostratigraphic and sedimentological data constraining diamictite deposits through this transition. These data are then compared to the wider record of eustasy, mass extinction and isotope stratigraphy in the lower palaeolatitudes. Precise age determinations are vital to integrate highand low-palaeolatitude datasets, and to understand the glacial control on wider global changes. Palynological techniques currently provide the best biostratigraphic tool to date these glacial deposits and to correlate the effects of glaciation globally. This review highlights a high degree of uncertainty in the known history of early LPIA glaciation as much of the primary stratigraphic data are limited and/or unpublished. Future high-resolution stratigraphic studies are needed to constrain the history of glaciation both spatially and temporally through the latest Devonian and Mississippian.
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The Middlesex Shale, the basal black shale in the Sonyea Group, represents the first major Frasnian sea level rise and redevelopment of an extensive anoxic substrate in the Appalachian Basin. The last occurrence of Ancyrodella alata and Ad. rugosa just below the base of the Middlesex in the West River Shale, and the appearance of Ad. gigas. Ancyrognathus? aff. Ag. ancyrognathoideus, and Palmatolepis punctata in, or just above the Middlesex indicate an assignment very near or at the start of Montagne Noire Zone 5 (punctata Zone).
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During the Global Taghanic Biocrisis ( c. 385 Ma), Middle Devonian faunas worldwide underwent extinction. In the biocrisis type region, the northern Appalachian Basin, biodiversity changes occurred through three bioevents that ultimately resulted in the loss of numerous endemic taxa. Carbon isotope excursions during this biocrisis have been documented in various stratigraphic successions, but never in the type region. Herein, we reconstruct changes in δ ¹³ C carb from the biocrisis type region and compare these changes to local faunal transitions. An approximately 1.5‰ negative excursion corresponds to the first bioevent, a time of inferred global warming and replacement of most endemic taxa of the mid-palaeolatitude Appalachian Basin by invasive palaeoequatorial taxa. An approximately 2‰ positive excursion is associated with the second bioevent, recognized as a return of the endemic fauna and the loss of invasive taxa. This positive excursion occurs near the Polygnathus ansatus–Ozarkodina semialternans zonal boundary and is recognized elsewhere. Faunal cosmopolitanism associated with the third bioevent corresponds with an inflection in the carbon isotope record from negative to positive trending values, which agrees with a positive carbon record excursion seen elsewhere at the semialternans – Schmidtognathus hermanni zonal boundary. This new carbon isotope record provides an important reference for recognizing this biocrisis in other areas and facies. Supplementary material The δ ¹³ C and δ ¹⁸ O dataset collected for this study is available at http://www.geolsoc.org.uk/SUP18840 .
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Detailed correlation, based on conodont sequences, between middle and upper Lochkovian carbonate successions from two key peri-Gondwanan regions, the Spanish Central Pyrenees and the Prague Synform, is attained for the first time. This correlation facilitates the definition of tie points for further multidisciplinary studies that seek to establish high-resolution temporal subdivision and global correlation. Some intervals have a precision of less than 0.5 my, which is significantly greater than in previous studies. The estimated elapsed time considered herein is about 3.2 My and is subdivided into five major zones of global scope: transitans-trigonicus, trigonicus-kutscheri, kutscheri-pandora β, pandora β-gilberti and gilberti-steinachensis β. By providing tie points and globally applicable criteria, this research contributes to the international cooperative effort to subdivide the Devonian standard stages into globally recognised substages.This article is protected by copyright. All rights reserved.
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Northern Appalachian Basin deposits and associated fossils have served as exemplars for ecological-evolutionary investigations, and as the reference interval for the concept of coordinated stasis. Here, we examine faunal and environmental changes within the uppermost Hamilton and lowermost Genesee Groups of the late Middle Devonian succession of New York State. Dramatic diversity loss, faunal migrations, and ecological restructuring recognized in these strata have been used previously to define the end of the Hamilton ecological-evolutionary subunit, and, furthermore, these strata and corresponding faunal changes represent the type region for the global Taghanic Biocrisis. We present and analyze a new, high-resolution data set of post-Taghanic Genesee fossil assemblages, in which we recognize 11 biofacies corresponding to an onshore-offshore (depth) gradient. The Genesee Fauna shows an unexpectedly high taxonomic similarity to nearshore biofacies of the pre-Taghanic Hamilton Fauna, related to the persistence of siliciclastic-dominated nearshore settings through the Taghanic Biocrisis, whereas the onset of anoxic/dysoxic conditions typified offshore portions of the environmental gradient. The “Nearshore Refugium Model” of Erwin offers a possible explanation for the persistence of taxa through the biocrisis in nearshore settings. This constriction was followed by subsequent expansion of these residual taxa to offshore environments in relatively similar associations, as increased Acadian orogenic activity and resultant delta progradation increased habitable space offshore by decreasing the extent of deeper-water, oxygen-poor settings. Although taxonomic similarity was high between the Hamilton and Genesee Faunas, biofacies structure differed primarily because of tectonically driven physical transformations to the basin and associated biotic turnover. Nevertheless, the combination of high taxonomic persistence of Hamilton nearshore taxa and the introduction of relatively few new taxa in the Genesee Fauna resulted in a taxonomic holdover that was much higher than observed in the original formulation of coordinated stasis.
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Middle Devonian spore successions from northwestern and southeastern Poland show a rapid reduction of taxonomic diversity that occurs close to the boundary between the Middle and Late Givetian. Similar diversity decline was recorded from European Russia and Belarus where it is well marked, and from northern France and Scotland where less taxa are thought to be involved. The assemblages from Poland are assigned to the local ‘Geminospora’ extensa (Ex) and Geminospora aurita (Aur) Biozones. The Ex 3 Sub-biozone, the highest of the three sub-units of the Ex Biozone, is the time equivalent of the Taghanic Crisis interval or most of it. Spore assemblages of the lower part of the Ex 3 Sub-biozone that are recorded from the lithostratigraphic members reflecting the initial transgressive pulse of the T–R cycle, show no diversity reduction. But the aneurophyte spores Rhabdosporites langii became less frequent in that unit while Aneurospora extensa, also belonging to the aneurophytes, flourished. The diversity reduction occurs in the higher part of the Ex 3 Sub-biozone where as many as nine well established species disappear. The impoverished assemblages of the Aur Biozone are dominated by archaeopterid spores and they lack aneurophyte spores. It is supposed that during the Taghanic Crisis, the initial sea level rise caused a serious loss of habitats for aneurophytes — the producers of R. langii. The following, repeated shoreline shifts were the important modifier of the ecosystem pattern and they speeded up the spread of highly competitive archaeopterids. Those shifts were especially extensive in cratonic, low-relief areas in the eastern part of Laurussia. The dryness of climate extinguished a high number of plants, and had a particularly adverse influence on aneurophytes.
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New data compilations for successive formation scale intervals, approximately third-order sequences, permit a statistical characterization of the ecological-evolutionary subunits (EESUs) or faunas of the Latest Silurian to mid-Late Devonian interval in the Appalachian Basin. Cluster analysis using the Jaccard coefficient of similarity show that certain formations cluster tightly together on the basis of faunal composition while in other cases units are sharply set off from superseding units. This result indicates both the coherence of faunal composition within EESUs and the discreteness of their boundaries. The results also require minor revision of EESUs previously delineated, including the addition of three new units. The Esopus Formation is designated as a distinct unit separate from the Schoharie on the basis of brachiopods from shallow water facies of the Skunnemunk outlier in New York; in addition, a short-lived Stony Hollow fauna is recognized in shallow shelf facies of the Union Springs Formation and coeval units (formerly referred to as the lower Marcellus Formation) and the lower transgressive beds of the overlying Oatka Creek Formation. This fauna, consisting of subtropical Old World Realm (OWR) emigrants, is distinctive from both the underlying Onondaga fauna and that of the overlying Hamilton Group. Moreover, the Tully Formation presents another case of a short-lived incursion of tropical OWR taxa followed by the extermination of this fauna and reappearance of a suite of typically Hamilton taxa. This case illustrates that EESUs may persist globally despite their local extermination or emigration from a large region, such as the Appalachian Basin. Review of the broader context of EESU turnover suggests that these crises are geologically rapid and synchronous. Moreover, most of the Devonian EESU boundaries coincide with recognized global bioevents, within the limits of combined biostratigraphic and sequence stratigraphic resolution. Hence, these crises, although perhaps locally accentuated in the Appalachian Basin, are allied to global causes. They appear mostly to be associated with rapid rises in sea level, periods of widespread climatic change and hypoxic events in basinal areas.
Article
The late Mid Devonian Eday Marl Formation from the Orcadian Basin, Scotland is a terrestrial equivalent of the marine Devonian Taghanic Crisis. The Eday Marl from Orkney contains a high-resolution archive of climatic change controlled by the relative strength of the seasonal insolation. This includes several distinct and discrete episodes of basin flooding as demonstrated by the deposition of lacustrine laminites, bedded evaporites, marginal sheet flood sands and marine influenced bioturbated sheet sands. These flooding events are intercalated with intense and sustained episodes of aridity indicating that insolation was relatively weak and the monsoon climate was ineffective at drawing in seasonal rainfall. Recognition of these basin flooding events has enabled the definition of three new units (the Wha Taing, Roeberry and Berstane members). The Eday Marl Formation can be correlated offshore and also recognised within marginal facies as an aeolian intercalation. An environmental, hydrological and climatic interpretation is given for the different events recognised in the Eday Marl. This sequence of events, when combined with the palynological age dates, enables a detailed correlation to be made with the marine Tully Formation of New York State. This suggests that regressions forced by climatic aridity are significant for understanding the deposition of the shallow water carbonates of the Tully Formation, in what is otherwise, a clastic depositional system. Comparison with the pelagic marine record shows that the latter, as yet, gives only limited resolution of the Taghanic Crisis. Recognising the Taghanic as a rapid alternation of cool arid and relatively hotter pluvial events provides a unifying explanation for the associated collapse in the terrestrial vegetation and the parallel faunal changes in the marine realm.
Conference Paper
New subdivisions and refinement of the Euramerican Devonian eustatic sea level framework of Johnson and others (1985) and Johnson and Klapper (1992) are introduced, based on stratigraphic syntheses of Middle-Upper Devonian successions in three central and western North American cratonic basins. Accurate comparisons of the relative sea level histories, afforded by refined correlations, indicates that as many as six major sea level cycles (designed as Transgressive-Regressive (T-R) cycles) controlled the timing and patterns of marine deposition of mid-Eifelian-early Frasnian strata in all three areas. Deepening events that mark the beginnings of four of the six cratonic North American Devonian T-R cycles correspond directly to Euramerican eustatic T-R cycles Ie to IIb of Johnson and others (1985) and Johnson and Klapper (1992). A deepening event in the late Givetian (beginning in the interval of the Upper subterminus Fauna) is recognized and provides the basis for subdivision of Euramerican T-R cycle IIa into cycles IIa-1 and IIa-2. An early Frasnian deepening event (beginning during M.N. Zone 3 of Klapper, 1989) is recognized in the Iowa Basin and possibly in the southeastern Elk Point Basin, and provides the basis for provisional subdivision of Euramerican T-R cycle IIb into cycles IIb-1, and IIb-2.
Article
Eight ammonoid extinction events occurring within 30 million years seem to be correlated with sedimentary changes in global sea level and temperature. These evolutionary patterns may be regarded as a bioseismograph reflecting events causing environmental change.
Article
In the clastic Genesee Group of the Catskill delta, lateral changes of the fauna are believed to reflect onshore-offshore physicochemical gradients. A shoreward increase of infauna is interpreted as adaptation to increased environmental stress. Free immobile taxa were concentrated offshore, while vagile forms, presumably able to cope with shifting substrata, are dominant nearshore. A shorewards replacement of brachiopods by bivalves reflects the eurytopy and infaunal habits of the bivalves. In Gencsee time, progradation was first rapid, then slow. The sequence is reversed in the superjacent Sonyea Group and the accompanying reversal of faunal patterns is strong evidence of faunal control by the rate of progradation. This indicates the hazardous nature of attempts to trace ‘community evolutioneditor’ using only a few studies from each period.
Article
Million year-scale (3rd-order) depositional sequences (few 10s to ~ 100 m-thick) are common in the Devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin. Tectonically driven changes in mid-ocean ridge spreading rates/lengths are too slow to account for the calculated 3rd-order rise/fall rates and typical orbital frequencies (~ 20–400 ky) are too fast. We analyzed oxygen isotopes from conodont apatite to evaluate if Early–Middle Devonian 3rd-order sea-level changes were controlled by paleoclimatically driven ice volume (glacio-eustasy) and seawater temperature change (thermo-eustasy). Two successive depositional sequences in the western U.S. (Nevada) and Czech Republic (Prague Basin) were sampled. The δ18O values range from 17.8‰ to 20.2‰ (SMOW) and show similar trends across the Emsian–Eifelian boundary with increasing and peak values in the lower costatus, decreasing values in the mid costatus, and increasing values in the upper costatus to australis zones. The similarities between these widely separated localities indicate that the isotopic trends are global rather than controlled by local variations in seawater temperature, evaporation/freshwater influx, or diagenesis. In the Nevada section, where the sea-level history is the most complete and best understood, the isotopic values increase and peak in late highstand and lowstand system tracts and decrease to the lowest values in the transgressive and maximum flooding intervals suggesting the My-scale sea-level changes were paleoclimatically controlled. The magnitude of isotopic shift from lowstand to maximum flooding intervals ranges from 0.8‰ to 1.5‰ and occurred over time spans of < 1.7 My. The only known mechanism to explain such large and rapid isotopic shifts is glacio-eustasy. If a reasonable range of My-scale subtropical sea surface temperature changes are assumed (~ 1–3 °C), then this requires glacio-eustatic sea-level changes of > 35 m to explain the remaining isotopic shifts. These amplitudes imply that significant continental ice sheets grew and melted on the < 1.7 My time scales during the Early–Middle Devonian and, like recent reports for the mid-Cretaceous and early Eocene, challenge previous assumptions of ice-free greenhouse climates. A plausible climate driver for these My-scale paleoclimate changes is long-period eccentricity (~ 2.4 My) and obliquity (~ 1.2 My) variations.
Article
Much has been written over the last 20 yr on the Upper Kellwasser Event (Frasnian/Famennian or F/F boundary) as the major extinction event of the Middle Palaeozoic (Devonian) and as the fifth largest extinction event in the Phanerozoic; this opinion was based on analysis of family range data. These views are misleading. A current analysis of family extinction data, largely based on The Fossil Record 2, but updated in some respects, supersedes the data base of Raup and Sepkoski (1982) and shows that the Famennian has the highest total family extinction of marine taxa, with the Givetian in second and Frasnian in third place. If these new data are related to current (unreliable) estimated length of stages, then the severest extinction rates are: first, the Givetian at 14.2 family extinctions per Ma, secondly the Frasnian at 11.2 and thirdly the Eifelian at 6.8. Many short-term ‘events’ have been named for the Devonian based on short-term distinctive sedimentary and/or faunal perturbations. A review of these shows how they are often transgression/regression couplets, many with an association of anoxia and poor in benthos, or spreads of pelagic faunas, and some are phased and complex. Evidence is presented to suggest that the transgressive pulses correspond to warm temperatures which are terminated by cooling. Possible links with orbitally forced patterns are considered. A common explanation seems required, not just for the Kellwasser Event, but for all these events. The relation of the family stage extinctions, especially the Kačák, Taghanic, Kellwasser and Hangenberg Events, which are of much more limited duration, is discussed particularly in relation to new and more precise data of the extinction events known within these stages. In the absence of detailed studies for many groups, those that have been well documented may serve as a temporary proxy for others.
Article
Coordinated stasis, as defined herein, represents an empirical pattern, common in the fossil record, wherein groups of coexisting species lineages display concurrent stability over extended intervals of geologic time separated by episodes of relatively abrupt change. In marine benthic fossil assemblages, where the pattern was first recognized, the majority of species lineages (60 to more than 80%) are present in their respective biofacies throughout timespans of 3–7 million years. Most lineages display morphological stasis or only very minor, typically non-directional, anagenetic change in a few characters throughout a prolonged time interval; evidence for successful speciation (cladogenesis) is rare, few lineages (<10%) become extinct, and very few new immigrant taxa become established within a region or province during such intervals. Moreover, species associations (biofacies) are nearly constant during an interval of stability, showing very similar taxonomic membership, species richnesses, dominance-diversity patterns and guild structure throughout. Conversely, during the intervening episodes of rapid change, many species (generally 70% or more) become extinct, at least locally, some lineages undergo rapid speciation and/or anagenetic change, and new immigrant taxa become successfully (semi-permanently) established. All (or most) biofacies arrayed across an environmental gradient display rapid and nearly synchronous changes in various aspects, including species composition, richness, dominance and guild structure. These intervals of abrupt evolutionary and ecological change typically represent only a small fraction (<10%) of the duration of the stable units. The resulting stable blocks of species separated by turnover events comprise “ecological-evolutionary sub-units” in the Appalachian Basin type example, and are considered to be components of the longer, more generalized ecological evolutionary units (EEUs) recognized by Boucot, Sheehan, and others.
Article
A new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged. More firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry, this consensus recognizes the interdependent roles of sedimentation, primary production, and microbial metabolism in favor of earlier end-member models (e.g., “production vs. preservation”). In this study, one of the classic stratigraphic sequences upon which the “preservation” end-member was based is re-interpreted in light of this new consensus. The study employs an extensive new sedimentological–biogeochemical database from cores drilled in western New York. The database spans over 500 m and 15 my of Devonian deposition in the Appalachian basin and provides a framework for comparative study of organic matter burial. The major conclusions are: (1) few organic-rich units were deposited under pervasive anoxic–sulfidic water columns; (2) establishment and breakdown of seasonal thermoclines, on annual or longer timescales, were the predominant mode of stratification; and (3) under such conditions, remineralization of bio-limiting nutrients may have played a key role in organic matter burial by creating a “eutrophication pump.” This pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments, and episodically in bottom waters. A final conclusion asserts that the master variable for organic matter accumulation was relative sea-level change, which exerted influence on clastic dilution, preservation, and production processes. Sea-level rise events led to sediment starvation and organic carbon concentration in distal basin sediments, as well as to decreased effectiveness of seasonal mixing and thus longer build-up intervals for remineralized nutrients. Episodic mixing of nutrient-enriched bottom waters led to enhanced production. Ultimately, increased clastic sediment delivery and water column mixing during relative sea-level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply, thus terminating deposition of strata enriched in organic carbon.
Article
Late Devonian glaciation is well-documented in three Brazilian basins, and newer work has shown a wider extent for this event, reaching Bolivia, Peru, Central African Republic, Niger, and the USA. Physical evidence for this event includes glacial pavements and polymict striated, and faceted clasts as dropstones and within marine resedimented deposits. Late Devonian (Frasnian? and Famennian) onset of Gondwanaland's glaciations resulted in fundamental changes in coeval and later (Mississippian) depositional systems worldwide. Palynomorphs date the more widespread event within the Retispora lepidophyta (miospore) palynozone, which often occurs with the marine acritarch Umbellasphaeridium saharicum. This initial glaciation continued into earliest Carboniferous (Tournaisian) time. There were several consequences from the short-term glacioeustasy. In North America, central Europe and southern China there is a coeval sea-level fall that exhumed and eroded carbonate platforms, deposited siliciclastics, and generated lacunae in the Famennian record. The lowstand resulted in extensive carbonate breccias, shallow-water deposits and evaporites in western U.S.A. Lowstand clastic wedges were deposited in a regression (eastern U.S.A.) with widespread black shales. In Moravia, Famennian siliciclastic influx increased as a result of subaerial weathering in newly-emergent highs that resulted from sea-level drop. Partial sea-level drops were also manifested by ferruginous oolites, which developed in nearshore environments and were subsequently dispersed down adjacent slopes by storm resedimentation. In southern China, aggradation, siliciclastic influx, reflux-dolomitization from evaporation, and shallow-water carbonate resulted from Famennian sea-level fall. The coupling of glacial and lowstand events explains the sudden appearance of shallow-marine, as well as subaerially-affected features after the Frasnian transgression that breached the North American craton.
Changing physical and biotic conditions on eastern Laurussia Evidence from Late Devonian basinal deltaic sediments on northeastern Kentucky
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Devonian eustatic events
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The Devonian on the stratigraphic table of Germany 2016
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The late Middle Devonian (Givetian) Global Taghanic Biocrisis in its type area (Northern Appalachian Basin): geologically rapid faunal transitions driven by global and local environmental changes
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The Devonian on the stratigraphic table of Germany 2016
  • Schindler