Frasnian-Famennian Boundary Research Articles

What caused the five mass extinctions?

Although a majority of biologists are convinced that a mass extinction is underway on earth today, the human history with direct observatory data is too short to predict its future trends. At least five mass extinctions occurred during the Phanerozoic Eon, causing the rapid extinction of at least 75% of existing marine species; they also seriously affected species diversity on land once the terrestrial ecosystem developed. The causes and consequences of these mass extinctions have become the most useful analogs for understanding whether the current global ecosystem is experiencing an extinction event. Previous multidisciplinary studies of the extinction patterns of fossil groups and concurrent environmental changes of the five mass extinctions during the past 500 million years (occurring in the end-Ordovician, Late Devonian Frasnian-Famennian, end-Permian, end-Triassic, and end-Cretaceous) suggested that no catastrophic event wiped out all organisms on earth. However, all five mass extinctions were associated with serious environmental deterioration and major paleoclimatic changes. The end-Ordovician mass extinction, occurring 445.2–443.8 million years ago, consists of two phases separated by an interval dominated by the cold Hirnantia fauna. The wax and wane of glaciation and associated widespread anoxia were the major causes of the two phases of the end-Ordovician mass extinctions. The Late Devonian mass extinction consists of a few different events from the Givetian to the Devonian-Carboniferous boundary, of which the most important is the Kellwasser event around the Frasnian-Famennian boundary. This extinction most seriously affected the coral and stromatoporoid reefs, and caused the extinction of two brachiopod orders (Pentamerida and Atrypida). As of yet, there is no consensus on the cause of this extinction event. Global cooling related to the widespread development of the terrestrial vegetation ecosystem and marine anoxia are the two most plausible scenarios. Although impact events were reported from a few horizons in the Late Devonian, they cannot account for the multiple phases of the Late Devonian mass extinctions. The end-Permian mass extinction about 252 million years ago has been universally documented as the most serious, which caused the disappearances of about 95% of all marine and 75% of all terrestrial species. Based on the latest high-precision geochronology data from South China, this extinction happened within an interval of less than 61 thousand years. This extinction was associated with a sharp negative excursion of δ 13Ccarb. A rapid temperature rise of 6–8 °C also occurred within the extinction interval. The Siberian Traps eruption and volcanism in South China, triggered by the dispersal of the supercontinent Pangea, is the most plausible explanation for the end-Permian mass extinction. The end-Triassic mass extinction at 201.564±0.015 Ma also seriously affected both marine and terrestrial ecosystems. Amphibians and reptiles both suffered a great loss during this extinction, and they were subsequently replaced by highly diverse dinosaurs. Marine conodonts and Ceratitida became extinct, and the sponge Demospongea and the brachiopod order Spiriferinida were also greatly affected. Recent studies suggest that the extinction stage may have extended over 10–20 million years, and the volcanism of the Central Atlantic Magmatic Province may be the cause. The end-Cretaceous mass extinction has been the best-known event among the general public because it caused the extinction of various dinosaurs that prevailed during the Mesozoic Era. The cause of this extinction has been documented as the extraterrestrial Chicxulub impact event. However, detailed paleontological studies suggested that the extinction is more likely to have been caused by another major volcanism event, the massive eruption of the Deccan Traps. In summary, global changes in atmospheric CO2 and paleotemperature (both icehouse and greenhouse), oceanic acidification, sea-level changes, and anoxia triggered by massive volcanic eruptions are the most plausible causes of the past extinctions. Massive volcanism not only ejected a huge amount of CO2 and volcanic sulfates, but also caused a massive release of thermogenic CO2 and methane stored in the deposits of inland basins and continental shelves. Extraterrestrial impact, supernova explosion, and solar flares could instantaneously wipe out all organisms on earth, but they are not the main causes of the five mass extinctions experienced in the history of the earth.

Temporal correlation between dyke swarms and crustal extension in the middle Palaeozoic Vilyui rift basin, Siberian platform

This paper presents results from new 40Ar/39Ar isotope dating of nine mafic dykes from three large dyke swarms (Vilyui–Markha, Kontai–Dzherba, and Chara–Sinsk) of the Yakutsk–Vilyui large igneous province (LIP), in addition to a reconstruction of the subsidence history of the middle Palaeozoic Vilyui paleorift basin (eastern Siberian platform). All previously published 40Ar/39Ar and U–Pb dates are summarized. Statistical analysis of the dyke ages reveals repeated magmatic events in the study area. Two major pulses of mafic magmatism are identified: one at the Frasnian–Famennian boundary, with a main peak at ca. 374.1Ma, and another in the latest Devonian with a peak at ca. 363.4Ma. The time of maximum intensity of dyke intrusion coincides (within uncertainty) with rapid subsidence in the Vilyui basin. The minimum total volume of middle Palaeozoic magmatism produced in the Yakutsk–Vilyui LIP is 100–215Kkm3, which is much less than earlier estimates. Most of the mafic material within the Yakutsk–Vilyui LIP is related to the Vilyui basin and associated dyke swarms. Backstripping analysis of sedimentation in depressions of the Vilyui basin was carried out. Estimates were obtained for the spatial distribution of the stretching factor of the crust and mantle lithosphere, averaging 1.17 and 1.44, respectively. The amount of extension due to dyke intrusion is estimated to be ~6%. Backstripping analysis of sedimentation in the Vilyui basin was used to assess the effect of both intraplate far-field forces and upwelling magma flows initiated by a mantle plume. A numerical thermomechanical model was developed to investigate the relations between two possible mechanisms by which the Vilyui rift was initiated: intraplate extension (passive rifting) and the ascent of a mantle magmatic diapir (active rifting). A model considering both of these mechanisms shows the contribution of the far-field extension forces and the effect of convective flows around the mantle plume, assuming a temperature of 1500°C for a heat source operating for ≥10Myr. The best-fit model predicts the formation of the Vilyui basin under extensional conditions with a depth-integrated horizontal driving force of 2.0×1013N/m, which corresponds to a lithostatic pressure of 0.73.

A multiproxy analysis of the Frasnian-Famennian transition in western New York State, U.S.A

The Late Devonian Frasnian-Famennian transition is well exposed along Walnut Creek in the western New York State region of the Appalachian Basin. The studied stratigraphic interval encompasses approximately 29m of section from the organic-rich Pipe Creek Formation, the equivalent of the Lower Kellwasser carbonaceous horizon of Europe, to a thin black shale layer at the top of the overlying Hanover Formation that correlates with the Upper Kellwasser horizon. The Walnut Creek section comprises five depositional cycles that are likely eustatic in nature, perhaps modulated by tectonic dynamics of the basin. Clastic proxy trends (Ti/Al, Zr/Al) suggest that deposits spanning the Frasnian-Famennian boundary (FFB) accumulated in association with rising sea level, a trend documented from elsewhere in the basin. Increasing Si/Al across the FFB may reflect elevated post-extinction biosiliceous productivity documented from Lower Famennian deposits elsewhere. The Walnut Creek section includes two positive δ13Corg excursions of >3‰, the stratigraphically lower event associated with the Pipe Creek Formation and the highest excursion approximately coincident with the Upper Kellwasser equivalent black shale layer. These isotopic events are interpreted to record episodes of increased global productivity and organic carbon sequestration at the end of the Frasnian Stage. Redox proxy trends (Mo and U enrichment and pyrite framboid size-distributions) documented from black shale associated with the positive excursions suggest sediment accumulation under suboxic to intermittently anoxic or euxinic bottom-water conditions in an unrestricted open-marine setting. The paleoclimate history of the end of the Frasnian based on Th/K data is one of fluctuating atmospheric conditions, including a brief cooling trend at the FFB. Though the Walnut Creek section sheds no light on the triggering mechanism or mechanisms of the Late Devonian extinction, inferred climate fluctuations associated with the FFB reflected in the Th/K data may have contributed to the severity of the biological crisis.

A new subspecies of the Late Devonian antiarchan fish Bothriolepis leptocheira from South Timan (Russia) and signs of biotic crisis near the Frasnian-Famennian boundary

A new subspecies of the Late Devonian antiarchan fish Bothriolepis leptocheira from South Timan (Russia) and signs of biotic crisis near the Frasnian-Famennian boundary

Stratigraphy and paleoenvironmental analysis of the Frasnian-Famennian (Upper Devonian) boundary interval in Tioga, north-central Pennsylvania

Two pulses of extinction in the late Frasnian (Late Devonian), the Lower and Upper Kellwasser (LKW and UKW) events, coincided with the deposition of organic-rich strata in many parts of the world, including the Appalachian Basin. Here, we describe two stratigraphic sections from Tioga, north-central Pennsylvania, that span the Frasnian-Famennian (F-F) boundary interval. The F-F boundary and UKW-equivalent strata are probably located in the covered interval between the two sections, but the LKW-equivalent Pipe Creek Formation is well exposed. We propose several stratigraphic revisions, including raising the Lock Haven Formation to group status and dividing it into formations, as well as redefining the base of the Canaseraga Formation and subdividing it into members. Paleoenvironments at Tioga range from offshore/outer shelf to middle shoreface. A regression follows the LKW transgression, as evidenced by the sharp superposition of middle shoreface sands on outer-shelf mudstones, similar to large facies changes associated with the LKW in other settings. The LKW is typically interpreted as representing deposition under dysoxic-anoxic conditions, and trace and body fossil content suggest that the Pipe Creek Formation represents dysoxic but not permanently anoxic conditions. These stratigraphic revisions and records of environmental change will provide the framework for more detailed studies of the LKW and UKW extinction events in the Appalachian Basin.

Pteraspidomorphs (Vertebrata), the Old Red Sandstone, and the special case of the Brecon Beacons National Park, Wales, U.K.

Pteraspidomorphi are Ordovician to Devonian, jawless vertebrates devoid of paired fins that have developed a variety of phenotypes of mostly demersal aquatic animals of the neritic province. Some, however, were active swimmers in the water column or near to the surface. They show many convergences in adaptive variations with the other ossified agnathan vertebrates or ostracoderms, that is the osteostracans, galeaspids and pituriaspids. They are traditionally known as Old Red Sandstone (ORS) fish, and have been interpreted as fresh-water inhabitants. However, recent palaeoecological and sedimentological analyses have shown that they were near-shore, shallow-marine fishes in the Ordovician, that they occupied marine environments on the Silurian Baltic platform and a wide variety of environments in the Devonian, including those of the ORS (lagoonal, estuarine, deltaic, and open platform). Their peak of diversity was reached in the Early Devonian, and they all disappeared before the Frasnian-Famennian boundary biotic crisis. Within Earth sciences, they are used in biostratigraphy, palaeoecology, and palaeobiogeography. They are good tools for dating siliciclastic sedimentary series of the Silurian and Devonian, including the ORS, and they are good markers of the margins of Ordovician to Devonian palaeocontinents (Laurentia, Baltica, Siberia, Gondwana).

Upper Devonian reefs and microbialite at Maoying, South China—implications for paleoenvironmental changes

Reefal carbonate deposits in South China preserve a record of community structure and environmental change across the Frasnian-Famennian boundary and through the Late Devonian, detailing a regional response to one of the largest mass extinction events in Earth history. The Upper Devonian (Frasnian to Famennian) limestone outcrops in the Maoying area of northern Ziyun County, South China, record a carbonate platform depositional setting with some patch reef development. The Upper Devonian carbonate deposits in Maoying area are distinctive from those in correlative sections in Dushan County with rare argillaceous limestone and dolomitic limestone as well as less dolostone. Exposures to the south in the Guilin area of northeastern Guangxi Province are similar to those seen in the study area. Upper Devonian carbonates in the Maoying area are divided into two lithologic groups, reef limestones or dolostone beds, composed of five lithologically distinctive intervals. The Upper Devonian strata have a cumulative thickness of 530m. The Upper Devonian reefs in the Maoying area were developed on a shell pavement of brachiopod- and bivalve-shell shoal packstones and evolved into patch reefs in the interior of the carbonate platform. Patch-reef development was limited to early Frasnian time. Reef-building organisms are dominated by massive and tabular stromatoporoids, Amphipora sp., Stachyodes sp., and coral Thamnopora sp., while brachiopods and algae accumulated between stromatoporoid skeletal frameworks. Three evolutionary stages of the Frasnian patch reefs, including an initial development stage, maturity stage and demise stage, can be recognized according to sedimentary structures and fossil assemblage characteristics. The Frasnian strata overlying the patch reefs represent a well-bedded back-reef depositional setting and are mainly composed of Amphipora floatstone and packstone containing a few bulbous stromatoporoids and small fasciculate corals. Famennian strata are characterized by laminated limestone and fenestrate limestone that are interbedded with infrequent mudstone and argillaceous limestone horizons. A prominent microbialite bed developed in the laminated limestone of the Famennian carbonate platform consists of stromatolite and thrombolite framestone. This bed can be correlated, in horizon and age, with microbial reefs and mounds in the Famennian offshore carbonate platform in the Huanan Epeiric Sea (such as Famennian microbial reefs and mounds in Guilin). This represents a biogenic carbonate formation characterized by microbial fabrics that accumulated in a nearshore carbonate platform setting after the global Frasnian/Famennian biotic extinction event, which promoted the growth of microbialites during the latest Devonian in South China.

Review of some Frasnian ahermatypic coral localities from Germany and description of a new genus Spinaxon (Anthozoa, Rugosa, Upper Devonian)

1. IntroductionThe Palaeozoic superorder Rugosa passed through several crises before the final extinction at the Permian–Triassic boundary. The most important one, the global Upper Kellwasser Event at the Frasnian–Famennian boundary, led to the disappearance of all coral reefs; they reappeared during top-Famennian times (Strunian). For a long period, the coral world of the Famennian (both photic and aphotic zones) was a terra incognita – but this changed surprisingly after the monograph of Polish ahermatypic Famennian Rugosa (Rozkowska, 1969), and with the discovery of similar faunas mainly in Germany and Morocco, and also in northern China (Liao & Cai, 1987; Cai, 1988; Wu & Liao, 1988; Guo 1990). Knowledge about Famennian shallow water Rugosa increased more slowly: especially through Sorauf (1992: unique first upper Famennian, though pre-Strunian Rugosa fauna from North America) and Berkowski (2002: first upper Famennian, also pre-Strunian survivors of Frasnian Phillipsastreidae in Poland). Unfortunately, up to now there still are no certain Rugosa occurrences from the basal Famennian (Lower, Middle, and Upper Palmatolepis triangularis Zones, perhaps also Lower Palmatolepis crepida Zone). The only one Rugosa, which I could collect from the Middle Palmatolepis triangularis Zone, together with Nephranops incisus (Roemer, 1866), was an undeterminable ampleximorph taxon from Rubeland in the German Harz Mts.At present, the Upper Givetian and the Frasnian ahermatypic Rugosa are th

Devonian climate, sea level and evolutionary events: an introduction

The face of Planet Earth has changed significantly through geological time. Dynamic processes active today, such as plate tectonics and climate change, have shaped the Earth’s surface and impacted biodiversity patterns from the beginning. Organisms, on the other hand, have the capacity to significantly alter Earth’s hydrological and geochemical cycles, its atmosphere and climate, sediments, and even hard rocks deep down under the surface. Abiotic– biotic interactions characterize Earth’s system history and, together with biotic competition and food webs, were the main trigger of evolutionary change, innovations and biodiversity fluctuations. Within the Palaeozoic, the Devonian was an especially interesting time interval as it was characterized by the ‘mid-Paleozoic predator revolution’ (Signor & Brett 1984; Brett 2003) and the related ‘nekton revolution’ (Klug et al. 2010), characterized by the blooms of free-swimming cephalopods, including the oldest ammonoids, and fish groups (e.g. toothed sharks and giant placoderms), the rise of more advanced vertebrates, including the oldest tetrapods (e.g. Blieck et al. 2007, 2010; Niedzwiedzki et al. 2010), the most extensive reef complexes of the Phanerozoic (e.g. Kiessling 2008), and the ‘greening of land’ by the diversification and spread of land plants, including the oldest forests (e.g. Stein et al. 2012; Giesen & Berry 2013), which resulted in new soil types and changing weathering. These major evolutionary trends did not unfold in a long interval of environmental stability, but in times of numerous and repeated, geologically brief, global events that punctuated prolonged periods, up to several million years in duration, of relative stability, termed ecological-evolutionary subunits (EE subunits: Boucot 1990; Brett & Baird 1995; Brett et al. 2009). The bounding events, even those of lesser intensity, produced major re-structuring in local to global ecosystems and are seen as critical drivers of long-term evolutionary patterns (Brett 2012). These linked abiotic and biotic events and extinctions of different magnitude have been summarized by House (1983, 1985, 2002), Walliser (1984, 1996) and, more recently, by Becker et al. (2012). The Devonian event succession is summarized in Figure 1. Two first-order mass extinctions at the Frasnian–Famennian boundary (Kellwasser Crisis) and at the end of the Devonian (Hangenberg Crisis), characterized by the loss of major fossil groups (classes and orders) and complete ecosystems (e.g. metazoan reefs, early forests), have to be viewed in the context of a complex global event sequence. There are important similarities between discrete pulses/phases of the major biotic crises and individual smaller-scale events. In our understanding, second-order global events are characterized by sudden extinctions in many groups and ecosystems, including the complete disappearance of several widespread and diverse organism groups (orders and families). Examples are the basal Emsian atopus Event, where the planktonic graptolites finally died out, the Taghanic Crisis, Frasnes events and Lower Kellwasser Event. Third-order global events show globally elevated extinction rates, often at lower taxonomic level (genera and species), but within many clades and in several ecosystems. Examples are the Silurian–Devonian boundary Klonk Event, and the Daleje, Chotěc, Kacak, Condroz and Annulata events. Fourth-order global extinctions refer to the sudden disappearance of relatively fewer but widespread groups, which implies a global, not regional, trigger. This category may include the Lochkovian–Pragian boundary

Sedimentary and faunal evidence for the Late Devonian Kellwasser and Annulata events in the Balkan Terrane (Bulgaria)

The global Upper Kellwasser (Frasnian–Famennian boundary interval) and Annulata Events (base of upper Famennian, Upper Devonian IV-A) are recorded for the first time in deep marine sedimentary successions of western Bulgaria. Within the upper Parchar Formation of the Lyubash-Golo Bardo Unit, a distinctive black shale unit yielded frequent, partly still articulated bivalves (Guerichia) and a Platyclymenia-fauna, including the name-giving Pl. annulata, although smooth platyclymeniids are more common. This interval reflects within a thick Eovariscan flysch succession an episode of starved sedimentation, increased organic productivity, oxygen deficiency, and bloom of opportunistic specialists. The event biofacies agrees with a basinal setting far away from land and its nutrient input. The Upper Kellwasser interval is recognized within the thick flysch sequence of the Katina Formation in the Svoge Unit. It is characterized by an interruption of carbonate deposition, as it is typical for other basinal settings, for example, of the Rhenish and Thuringian basins of Germany.

Evidence for global Famennian and Tournaisian geologic events in the section of an isolated carbonate platform in the eastern Urals

The composition of stable carbon and oxygen isotopes in the section of an isolated carbonate platform is analyzed. Traces of several global and subglobal transgressions and regressions have been found in the limestone strata. Some of these phenomena were associated with the Upper Kellwasser (at the Frasnian–Famennian boundary) and multiphase Hangenberg (at the Devonian–Carboniferous boundary) Events. Nevertheless, there were no considerable sea level fluctuations in the platform water area. There is no evidence for subaerial erosion. The bottom water during sedimentation was mostly in oxic conditions.

Palynological age constraint of Les Vilelles unit, Catalan Coastal Chain, Spain.

Les Vilelles unit is a detrital sequence exposed at the southwestern margin of the Catalan Coastal Chain (CCC), NE Spain, below the Carboniferous turbiditic series. Based on the palynological content, the age of this unit was initially assigned to the Middle-Late Devonian (Eifelian to Famennian). Additional radiolarian and conodont findings were considered to be Early–Middle Mississippian (Tournaisian to early Visean). To clarify this age discrepancy a new and more comprehensive palynostratigraphic analysis has been conducted in the upper part of the section representative of Les Vilelles unit. This has provided an assemblage of miospores, acritarchs, prasinophyta phycomata and chitinozoans that can be confidently assigned to a latest Frasnian interval, in contact with the Frasnian–Famennian boundary. Therefore, the present analysis refines the Middle–Late Devonian age formerly assigned, establishes a latest Frasnian age for the top of the unit, and provides new insights to the better understanding of the unconformity and hiatus separating the pre-Carboniferous and Carboniferous CCC series in the Priorat Massif. The study also includes a systematic section with the description of three newly established miospore species: Dibolisporites coniugatum , Dibolisporites prioratum and Rugospora spinosa .

Kellwasser horizons, sea-level changes and brachiopod–coral crises during the late Frasnian in the Namur–Dinant Basin (southern Belgium): a synopsis

Abstract In Belgium, the Lower Kellwasser Event (LKW) corresponds to the relative sea-level maximum of the first (‘Aisemont sequence’ (AS)) of the two late Frasnian third-order sequences that are recognized here, but the Upper Kellwasser Event (UKW) may have been triggered by a series of tsunamites. The end of the middle Frasnian carbonate platform and reefs is caused by the sea-level drop and emersion of the last middle Frasnian third-order sequence (‘Lion sequence’) in the Lower rhenana Zone. The end of the ‘Petit-Mont’ mudmound growth during the transgressive (TST) and highstand (HST) systems tracts of the AS was caused by sea-level fall and emersion at the top of this sequence. The coral and brachiopod extinction in the Upper rhenana Zone, during the second late Frasnian third-order sequence (‘Lambermont sequence’ (LS)), is progressive and due to the widespread development of the dysoxic and anoxic facies, before the UKW. Only the LS TST has been identified. No sea-level fall has been recognized in relation to the UKW or near the Frasnian–Famennian boundary. The late Frasnian extinctions are more likely to be related to the decrease in the atmospheric oxygen rate and its impact on marine environments and, to complete, the UKW.

Revised correlation of the Frasnian–Famennian boundary and Kellwasser Events (Upper Devonian) in shallow marine paleoenvironments of New York State

The Frasnian–Famennian boundary (Upper Devonian) is exposed in a 200 km-long outcrop belt in New York State, with deeper paleoenvironments to the west and shallower ones to the east. Geochronology in the eastern end of the outcrop belt has been based primarily on lithostratigraphic correlation with western sections, which were dated using conodonts. We collected conodonts and brachiopods from several measured sections and numerous other localities, and these collections suggest that these east–west lithostratigraphic correlations require revision. We correlate the Wiscoy Formation with the upper Angola Formation and the Canaseraga with the upper Hanover. Thus, the Canaseraga Formation contains the Frasnian–Famennian boundary and Upper Kellwasser Event, and the dark shale above the Wiscoy is equivalent to the Pipe Creek Formation and Lower Kellwasser Event. These new correlations imply that the Lower Kellwasser Event had greater impact on the shelly benthos of New York than the Upper Kellwasser, at least for the subset of taxa examined here. All strophomenid brachiopods and rugose corals were extirpated at the Lower Kellwasser, along with numerous other brachiopods. The final species of atrypid brachiopod persisted to the Upper Kellwasser. • Frasnian–Famennian (Upper Devonian) biostratigraphy of New York State is evaluated. • Conodonts and brachiopods were collected from shallow-water, siliciclastic facies. • New correlations are proposed for the F–F boundary and Kellwasser extinction events. • The revised correlations will facilitate study of these extinction events. • The Lower Kellwasser extinction was severe for corals and brachiopods in New York.

Novel 1H-Pyrrole-2,5-dione (maleimide) proxies for the assessment of photic zone euxinia

1H-Pyrrole-2,5-diones (maleimides) and 1-alkyl-2,3,6-trimethylbenzenes (aryl isoprenoids), degradation products of tetrapyrrole pigments and carotenoids respectively, were analysed and compared with pristane/phytane (Pr/Ph) ratios to reconstruct past redox conditions in three geologic sections. One section comes from the Middle–Late Devonian and was deposited before the Frasnian–Famennian boundary mass extinction. The two other sections span the Late Permian to the Early Triassic as well as the Late Triassic to the Early Jurassic, and recorded the Permian–Triassic (P/T) and Triassic–Jurassic (T/J) extinction events respectively. The 2-methyl-3-iso-butyl-maleimide (Me,i-Bu maleimide) to 2-methyl-3-ethyl-maleimide (Me,Et maleimide) and 2-methyl-3-n-propyl-maleimide (Me,n-Pr maleimide) to Me,Et maleimide ratios (Me,i-Bu/Me,Et and Me,n-Pr/Me,Et ratios) in the studied sections revealed a moderate to strong negative correlation to the aryl isoprenoid ratio (AIR), defined as (C13–C17 1-alkyl-2,3,6-trimethylbenzenes)/(C18–C22 1-alkyl-2,3,6-trimethylbenzenes), indicating that these maleimide ratios can be used as robust, specific indicators of photic zone euxinia (PZE). These results agreed with Pr/Ph ratios, which were used as diagnostic indicators to differentiate between oxic and anoxic conditions. In agreement with previous studies, the novel maleimide proxies suggest that all three mass extinctions were largely characterised by PZE depositional conditions.

UPPER FRASNIAN (UPPER DEVONIAN) BRYOZOANS IN PROXIMAL FACIES OF SOUTHERN BELGIUM

Seven bryozoan species are described from the shallow-water Aisemont and Lambermont formations (upper rhenana Conodont zone, upper Frasnian) in southern Belgium. The studied interval is situated between the lower and upper Kellwasser events. Among the recognized taxa two species are new: Triznotrypa potii n. sp. and Isostylus veserensis n. sp. In addition, the following species were identified in this assemblage: Fistulipora pavimenta Bigey, 1988, Canutrypa hemispheroidea (Yang, 1954), Eostenopora conspersa Volkova, 1974, Leptotrypella radiata Bigey, 1988, and Anastomopora inflata (Bigey, 1988). The studied bryozoan assemblage of the Frasnian age shows palaeogeographic connections to Iran, Russia (Altai) and Afghanistan. Most of them are documented for the first time in this area and it provides important knowledge of the distribution of bryozoans in the late Frasnian and near the Frasnian-Famennian boundary.

THE LAST GASP: TRACE FOSSILS TRACK DEOXYGENATION LEADING INTO THE FRASNIAN-FAMENNIAN EXTINCTION EVENT

ABSTRACT The Frasnian–Famennian boundary is correlated with one of several Late Devonian extinction pulses that resulted in a significant decrease in diversity as well as ecological restructuring. This event is recognized within the globally correlated Upper Kellwasser interval that is well exposed and biostratigraphically well constrained in shale units of western New York State. The ichnological and geochemical signals of the interval stratigraphically below the Upper Kellwasser event at these localities provides insight into the onset of this important extinction event. Detailed analysis of ichnogeneric composition, relative size of burrow populations, amount of bioturbation, and trace metal concentrations vary in concert. Deep-penetrating, pyritized Skolithos burrows terminate abruptly at a thin, laminated black shale interval with enriched Mo levels, up to 31 ppm, and are overlain by an interval of gray-green bioturbated shales dominated by Chondrites. These textural and chemical shifts reveal that b...

Geochemical evidence for euxinia during the Late Devonian extinction events in the Michigan Basin (U.S.A.)

Several mass extinction events occurred in the Late Devonian, but the trigger for these events remains elusive. In this study, geochemical evidence in the Late Devonian Antrim Shale, Michigan Basin, U.S.A., records episodic euxinia contemporaneous with these extinction events. Diagnostic changes in iron proxy data and elevated trace metal enrichments correspond to the Kellwasser Crisis. In this study, carbon, sulfur, iron and trace metal geochemistry preserved in the Antrim Formation validates the establishment and expansion of euxinic conditions associated with the Kellwasser Crisis and the Frasnian–Famennian boundary. The strength of the sequential extraction iron mineral data presented here, in concert with trace metal and sulfur isotope proxies, provides definitive signatures of euxinia when other data may be more ambiguous in regard to paleoredox conditions. During the time of the Frasnian–Famennian boundary extensive sulfide oxidation at the chemocline, the result of Fe-limiting conditions within the basin, provides an alternative explanation for the oceanic decline in δ34SSO4 during, and following, the Frasnian–Famennian event. Our geochemical evidence, indicating the presence of anoxia in the Michigan Basin, is consistent with data from other globally distributed locations. Euxinia should be considered a key driver for these global extinction events, and possibly others such as the Hangenberg Event in the Late Devonian.

The impact of astronomical forcing on the Late Devonian greenhouse climate

The geological record of the Paleozoic often exhibits cyclic features, in many cases the result of changes in paleoclimate. However, a thorough understanding of the processes that were driving Paleozoic climate change has not yet been reached. The main reason is relatively poor time-control on Paleozoic paleoclimate proxy records. This problem can be overcome by the identification of cyclic features resulting from astronomical climate forcing in the stratigraphic record. To correctly identify these cyclic features, it is necessary to quantify the effects of astronomical climate forcing under conditions different from today. In this work, we apply Late Devonian (375Ma) boundary conditions to the Hadley Centre general circulation model (HadSM3). We estimate the response of Late Devonian climate to astronomical forcing by keeping all other forcing factors (e.g. paleogeography, pCO2, vegetation distribution) fixed. Thirty-one different “snapshots” of Late Devonian climate are simulated, by running the model with different combinations of eccentricity (e), obliquity (ε) and precession (ω˜). From the comparison of these 31 simulations, it appears that feedback mechanisms play an important role in the conversion of astronomically driven insolation variations into climate change, such as the formation of sea-ice and the development of an extensive snow cover on Gondwana. We compare the “median orbit” simulation to lithic indicators of paleoclimate to evaluate whether or not HadSM3 validly simulates Late Devonian climates. This comparison suggests that the model correctly locates the major climate zones. This study also tests the proposed link between the formation of ocean anoxia and high eccentricity (De Vleeschouwer et al., 2013) by comparing the δ18Ocarb record of the Frasnian–Famennian boundary interval from the Kowala section (Poland) with a simulated time series of astronomically forced changes in mean annual temperature at the paleolocation of Poland. The amplitude of climate change suggested by the isotope record is greater than that of the simulated climate. Hence, astronomically forced climate change may have been further amplified by other feedback mechanisms not considered here (e.g. CO2 and vegetation). Finally, the geologic and simulated time series correlate best when the Frasnian–Famennian negative isotope excursion aligns with maximum mean annual temperature in Poland, which is obtained when eccentricity and obliquity are simultaneously high. This finding supports a connection between Devonian ocean anoxic events and astronomical climate forcing.

Reducing time-scale uncertainty for the Devonian by integrating astrochronology and Bayesian statistics

Dealing with uncertainties is inherent to the scientific process. In the process of building geologic time scales, the reported uncertainties are at least as important as the estimates of the numerical ages. Currently all time scales for the Devonian are based on conventional age-depth models, constructed by linear or cubic interpolation between different dated positions. Unfortunately, such models tend to produce overoptimistic confidence intervals. In this study we apply Bayesian statistics to the Devonian time scale to better incorporate stratigraphic and radioisotopic uncertainty. This approach yields a Devonian time scale characterized by increasing uncertainty with growing stratigraphic distance from a radioisotopically dated sample. This feature is absent from The Geologic Time Scale 2012 ; therefore, that time scale is overoptimistic. We further constrain the obtained time scale by incorporating astrochronological duration estimates for the Givetian and Frasnian stages. The combination of radioisotopic dating and astrochronology results in a reduction of the uncertainty on the numerical age of the stage boundaries concerned by several million years. For example, we estimate the age of the Frasnian- Famennian boundary at 373.9 ± 1.4 Ma.