Frasnian-Famennian Boundary Research Articles

CONODONT BIOSTRATIGRAPHY OF UPPER DEVONIAN TEPHRA BEARING DEPOSITS IN THE İSTANBUL-ZONGULDAK TERRANE, NW TURKEY: INSIGHTS ON THE KELLWASSER EVENTS

New evidence for a biostratigraphic assessment of the limestone succession comprising K‐bentonite levels exposed in the Yılanlı Formation of the Istanbul-Zonguldak Terrane are provided from conodonts at the Gavurpınarı quarry in Bartın area (NW Turkey). The succession depicts a shallow marine, nearshore facies setting that comprises rare and low diversity conodont associations mainly exemplified by the species of Ctenopolygnathus, Icriodus and Polygnathus. Conodont faunas from the lower part of the section are of late Frasnian age, including the taxa Icriodus subterminus Youngquist, 1947, Polygnathus aff. xylus Stauffer, 1940, Icriodus iowaensis iowaensis Youngquist & Peterson, 1947 and Ctenopolygnathus brevilaminus Branson & Mehl, 1934, and the upper part is assigned to early Famennian marked by the first appearance of Icriodus cornutus Sannemann, 1955. The local biostratigraphic framework of the Yılanlı Formation is correlated with the upper Frasnian Lower rhenana to the lower Famennian Middle triangularis standard conodont zonations. Considering the described species, the Frasnian-Famennian boundary corresponds to a slight change in conodont fauna and is assigned within the local Icriodus iowaensis iowaensis Zone. Accordingly, the novel K-bentonite age data potentially indicates the evidence for the Kellwasser events in northern Turkey, improving paleogeographic correlations of the Istanbul-Zonguldak Terrane with other terranes in Laurasia and Peri-Gondwana.

Late Devonian felsic magmatism in southern New Brunswick and its association with a large igneous province that may have contributed to the Frasnian-Famennian extinction

Felsic rocks of the Piskahegan Group and coeval plutons form a major part of a Late Paleozoic epicontinental caldera in southwestern New Brunswick, Canada. The caldera forms an elliptical structure with a length of ∼34 km and a width of ∼13 km. It hosts a significant polymetallic deposit of tin, molybdenum, indium and bismuth associated with mid-sequence granitic intrusions. The caldera formed in the aftermath of the late Early to Middle Devonian Acadian Orogeny during the opening of the late Paleozoic Maritimes Basin in the Northern Appalachian Belt. Its surrounding successions are largely composed of bimodal igneous rocks that were derived from two distinct sources: upper mantle-derived mafic magma and lower crust-derived felsic magma. The rocks that marked the beginning of volcanic activity in the caldera are no younger than 374.2 ± 2 Ma, whereas the uppermost dated volcanic unit in the complex yielded an age of 364.6 ± 0.7 Ma. The latter is conformably overlain by a succession of red beds and undated basalts that also overlie penecontemporaneous felsic volcanic rocks adjacent to the caldera. The post-orogenic felsic rocks are fractionated, peraluminous A-2 type rocks with silica contents ranging from ∼70 to ∼79 wt% along with high K2O contents and ɛNd(t) ranging from −0.10 to +1.05. They were generated by the melting of lower crustal basement rocks linked to a lithospheric plate that was metasomatized during the Neoproterozoic. Based on available geochemical, geophysical and structural data on Late Paleozoic rocks of southeastern Canada, the melting may have been triggered by the injection of profuse mafic magma that eventually formed a thick underplating at the base of the crust in association with heat derived from an underlying mantle plume and conveyed by transtensional structures. Basal rocks of the Piskahegan Group (the Intracaldera Sequence) and penecontemporaneous volcanic rocks in Nova Scotia are interpreted as small erosional remnants of a Large Igneous Province (LIP) based on the extensive exposure of large coeval plutons throughout southeastern Canada. The new geochronological data suggests that profuse late Frasnian magmatism in this LIP could have contributed to the environmental deterioration that led to a significant extinction at the Frasnian-Famennian boundary (the Kellwasser Event).

Chitinozoan response to the ‘Kellwasser events’: population dynamics and morphological deformities across the Frasnian–Famennian mass extinction

AbstractFossil (zoo)plankton dynamics during Devonian ocean‐anoxic and extinction events can shed light on the palaeoceanographic and geochemical processes that shaped the middle Palaeozoic biosphere. However, datasets on (Upper) Devonian marine palynology, illustrating such dynamics, remain underexplored. The type section of the Sweetland Creek Shale in Iowa (USA) offers a detailed conodont zonation for the upper Frasnian and across the Frasnian–Famennian boundary, records the Upper and Lower Kellwasser events and has pristine preservation of organic material, making this an ideal section to study the effects of this catastrophic event on chitinozoan zooplankton populations. A total of 3998 specimens were recovered, imaged and classified into 12 distinct species, 10 of which were previously unknown. This study demonstrates the unrealized potential of chitinozoans as a regional biostratigraphic tool in the Upper Devonian. The Lower Kellwasser Event is characterized by a drop in chitinozoan abundance and the run up to the Upper Kellwasser Event marks a period of rapid species turnover rates. Interestingly, every assemblage in this interval is nearly monospecific. Patterns of changing spine morphologies in Fungochitina pilosa, Ramochitina sp. A and Saharochitina sp. A are herein explored as potential ecophenotypic expressions. We identify Angochitina monstrosa as a new disaster species. The discovery of two teratological chitinozoans specimens, in combination with the presence of the disaster species Angochitina monstrosa and deformation in contemporaneous conodonts, supports our previous discovery that marine teratology is a feature of many Palaeozoic extinction events, possibly triggered by the injection of hydrothermal brines into the ocean.

A new Late Devonian plant assemblage in West Junggar, Xinjiang, China and its floral evolution during the Devonian

Mid to Late Devonian witnessed the emergence of the first forest and global flora prosperity on the Earth. West Junggar, a distinct sub-terrain of the Kazakhstan Paleoblock, in which Middle to Upper Devonian plant fossil-rich deposits are exposed, that significantly contribute to our understanding of Devonian plant diversity and flora evolution. In this study, we report a new plant assemblage from the Hongguleleng Formation in the Kekesayi and western Yangzhuang sections of West Junggar, Xinjiang, China. The dominant palynomorphs in this assemblage are retusoid and laevigate trilete spores with occasional scolecodonts. Macroplants of the assemblage consist of tree-like and herbaceous lycopsids. At least two floral turnovers were documented in West Junggar during the Devonian. The first one occurred at the end of the Givetian Age and saw the transformation of the Hujiersite Flora dominated of herbaceous lycopsids, turning into the flora with arborescent plants as typical of the Zhulumute Flora. The second turnover might occur near the Frasnian-Famennian boundary and saw the forest of the Zhulumute Flora shifting into the Hongguleleng Flora with more widely-distributed members.

Linking anoxia, biotic events, and basin evolution in the Late Devonian Illinois Basin, North America: A geochemical approach

Epeiric seas and their sedimentary deposits are vital for understanding the history of Earth's oceans, but the lack of modern analogues and the frequent dominance of uniform mudrocks in these environments hinder our ability to identify key markers and interpret sea-level changes and past climatic/biotic events in epeiric sea successions. This study focuses on the Late Devonian Illinois Basin, where fine-grained mudrocks, occasionally organic-rich, were deposited in one of many variably interconnected epeiric seas that flooded much of the North American craton. Through the correlation of gamma logs from 50 wells across the basin and the generation of high-resolution chemostratigraphic profiles for four cores, a basin evolution model for the Upper Devonian New Albany Shale (NAS) in the southeastern depocenter of the Illinois Basin (USA) is established. Results indicate that NAS deposition occurred in three phases, characterized as one aggradational-progradational, one progradational, and one retrogradational package. The basin experienced an initial flooding event at the base of the NAS, followed by a second transgression immediately after the Frasnian-Famennian boundary (FFB). The mid- to upper Famennian interval witnessed progressive sea-level rise (a third transgression) and full basin inundation, extending nearly to the top of the NAS. Based on redox proxy data, four discrete anoxic pulses were identified during NAS deposition. By incorporating published biostratigraphic and geochemical datasets, we then correlate these signals observed in the Illinois Basin across the Appalachian, Michigan, Permian, and Anadarko basins of the broader North American Seaway. Additionally, some of the anoxic pulses are linked to key biotic crises of the Late Devonian, such as the Rhinestreet, Upper Kellwasser, and Enkeberg events, which caused substantial turnover in the marine biosphere. This study contributes an integrated basin evolution framework for the Late Devonian North American Seaway and serves as an exemplar of utilizing geochemical signals to correlate sea-level changes, anoxic pulses, and key biotic events in ancient mud-dominated epeiric seas.

Carbonate lithium isotope systematics indicate cooling triggered mass extinction during the Frasnian-Famennian transition

We present comprehensive Li-C-Sr isotopic studies on two classic marine carbonate sections (Yangdi and Dongcun) transecting the Late Devonian Frasnian-Famennian (FF) boundary from South China to constrain the causes of the FF mass extinction. Both sections show positive Li and C isotopic excursions in carbonate and unchanged conodont 87Sr/86Sr ratios across the FF boundary. Low Li/Ca and Sr/Ca ratios, but heavy Li isotope composition (δ7Li) of the Dongcun section indicate possible diagenetic alteration on carbonate Li isotopic records. By contrast, the Yangdi section records more primary seawater δ7Li signal, showing a ∼ 2 ‰ positive excursion before the FF boundary, although reconstructed paleo-seawater δ7Li values (from 11.8 ± 1.4‰ to 13.8 ± 1.4‰) are lower than modern times. Combined box model with Monte Carlo simulation demonstrates that low seawater δ7Li requires low riverine δ7Li and small effective Li isotopic fractionation by marine sinks (Δ7Lisw-ms). The latter is likely due to high silicon concentration in the paleo-seawater and rapid formation of clay minerals. Positive δ7Li excursion but invariant 87Sr/86Sr ratios in the seawater are related to attenuated continental weathering (reduced riverine fluxes but increased riverine δ7Li), and enlarged effective Δ7Lisw-ms. Based on the present data we suggest that rapid climate cooling is responsible for the weathering transition and must have exerted significant influence on the marine environment. Global climate cooling weakens seawater stratification while intensifying oceanic circulation and upwelling, resulting in enhanced primary productivity, precipitation of the Kellwasser black shales and a remarkable positive C isotopic excursion in carbonate. Additionally, rapid climate cooling around the FF boundary has significantly threatened the ecological system and finally triggered mass extinction especially for the faunas adapted to warm temperatures.

Trilobites showed strong resilience capacity through the Late Devonian events despite an inexorable decline

The Kellwasser events constituted a major biocrisis at the Frasnian–Famennian boundary, that killed many organisms. The subsequent Hangenberg event also had important effects on marine fauna, although it is not traditionally considered a mass extinction. This study aims to understand the tempo and mode of the Late Devonian extinctions using trilobites as a case of study. To estimate the trilobite dynamics both taxonomic richness and morphological disparity were assessed. The diversity was calculated using conodont biozones, which provide a high-resolution timeline, allowing tracking changes in taxonomic richness and the environmental events implied. The morphological disparity was analysed using space occupancy measures and visualized in morphospaces. The Frasnian began with a diversification of trilobites at generic levels. The number of orders remained constant and relatively high with the presence of Corynexochida, Harpetida, Odontopleurida, Phacopida and Proetida. Environmental conditions were favourable for the proliferation of trilobites until the late Frasnian. However, the Kellwasser events disrupted trilobite evolution, leading to a double extinction event. A first random extinction affected low taxonomic levels, while the second extinction was selective, causing losses at both the generic and order levels, and a strong decrease in morphological disparity. Nonetheless, in response to the end-Frasnian environmental changes, blind and reduced-eye trilobites became more common. Following a dip in generic richness at the beginning of the Famennian, the two surviving orders, Phacopida and Proetida, recovered. Although no novelties characterized them, they partially refilled the morphospace. A slight decline occurred in the middle Famennian before a strong morphological and taxonomical diversification was identified in the expansa and preasulcata zones. The final Hangenberg event at the end of the Famennian affected trilobites at all taxonomic ranks as the Kellwasser events. Only Proetida survived.

Organic geochemistry evidence for wildfire and elevated pO2 at the Frasnian–Famennian boundary

The Devonian experienced radiations of plants and animals, as well as a major mass extinction event during the Frasnian–Famennian (FF) interval. Proposed triggers have been linked to volcanism, extraterrestrial impact, sea-level fluctuations, and climate cooling, etc. However, the nature of the wildfires and its role in the biotic evolution have been rarely investigated for the FF interval. Here, we report organic geochemistry proxies (e.g., polycyclic aromatic hydrocarbons, PAHs) in three sections from New York (USA) to further investigate the wildfire activity and its potential link with the environmental and biotic perturbations around the FF interval. The studied intervals are dominated by three-ring PAHs which display an increasing abundance stratigraphically towards the FF boundary (FFB). An increase of 6-ring over 3-ring PAHs across the FFB is also observed for the studied sections, indicating elevated burning temperature. Additionally, slightly increased plant wax abundance and average chain length values and relatively constant Pr/Ph ratios are observed. Collectively, these results propose an increased burning frequency over the FF interval caused by elevated pO2 level, rather than a change in aridity. Terrestrial input only slightly increased across the FFB, and there is limited evidence for ocean anoxia. This correlates with the hypothesis that pCO2 drawdown and climate cooling could have been a driving mechanism of the FF biocrisis.

Mercury isotope evidence for regional volcanism during the Frasnian-Famennian transition

Mercury (Hg) concentrations and isotopes are widely used as proxies for volcanic inputs to paleodepositional systems. Enhanced volcanism during the Late Devonian was previously mainly inferred in the western Paleo-Tethys Ocean region from high Hg enrichments around the Upper Kellwasser horizon (UKW) and Frasnian-Famennian Boundary (FFB). In this study, we generated high-resolution Hg concentration data for four UKW-FFB sections (Walnut Creek and Dupont-GHS in the U.S.A., and Yangdi and Nandong in South China) and Hg isotope data for two of them (Walnut Creek and Nandong) in order to test the geographic distribution and stratigraphic range of volcanic inputs during the Frasnian-Famennian transition. Within the uppermost Frasnian Palmatolepis linguiformis Zone and the lowermost Famennian Lower Pa. triangularis Zone, Nandong (Paleo-Tethys Ocean) exhibits enrichment factors (HgEF > 2) and mass independent fractionations (MIF) of odd isotopes (Δ199Hg ∼0 ‰) that are consistent with significant volcanic inputs. Positive Δ199Hg values and an absence of Hg enrichments in the equivalent stratigraphic intervals at Walnut Creek and Dupont-GHS (peri-Panthalassic region) indicate that Late Devonian volcanism was a regional rather than a global phenomenon, and that it may have been associated with subduction zones and/or a large igneous province (LIP) of limited size in the Paleo-Tethyan region rather than with a major continental LIP of potentially global significance.

Upper Frasnian and Lower Famennian (Upper Devonian) conodonts of the Compte section (Spanish Central Pyrenees)

Through the study of conodonts, strata around the Frasnian–Famennian boundary in the Compte section were analyzed in detail. Twenty-four samples in a 12 m thick sequence yielded 13 species of conodonts belonging to Ancyrodella, Ancyrognathus, Icriodus, Palmatolepis, and Polygnathus. Besides conodonts, other groups such as foraminifers, radiolarians, brachiopods, ostracods and crinoids were also found in the sequence. The conodont record, shows the FZ13, from the uppermost Frasnian, and the minuta and crepida zones from the lower Famennian. The last Frasnian fossil was obtained from Bed 92b and the first Famennian fossil was from Bed 92d, which are separated by about 45 cm. Thus, between these two samples, the lowest three Famennian conodont zones have to be represented or missing. The absence of any stratigraphic hiatus between these levels suggests that extreme condensation took place in the early Famennian in the CP section.

Mercury Anomalies Link to Extensive Volcanism Across the Late Devonian Frasnian–Famennian Boundary in South China

The Late Devonian Frasnian–Famennian (F–F) mass extinction has been long-time debated by non-volcanic causes, extra-terrestrial impacts, and large igneous province (LIP) eruptions. To better understand the ultimate cause of the F–F mass extinction, here we investigate the chemostratigraphy of mercury (Hg) and total organic carbon (TOC) on two marine F–F strata in the Dushan area, South China. In both sections, high Hg and Hg/TOC anomalies were observed near the F–F boundary. These anomalies are in line with those recently observed in Morocco, Germany, Poland, and north Russia, suggesting a global Hg flux. The Late Devonian LIP eruptions, which are believed to have emitted massive amounts of Hg, could be responsible for the global Hg and Hg/TOC anomalies around the F–F boundary. The observed Hg and Hg/TOC anomalies coincide with the extinction of Frasnian fauna in the Dushan area, implying a causal link between the Viluy, Kola, and Pripyat-Dnieper-Donets LIP eruptions and the F–F mass extinction.

Mechanical and chemical preparation techniques applied to Frasnian Cephalopods from Lompret (Belgium)

When embarking on a preparation project it is essential to consider a variety of techniques. A combination of different mechanical and chemical treatments may be necessary, even within the same formation. This article explores this principle using a case study of large accumulations of Frasnian cephalopods collected between 2015 and 2021 from the active quarry of Lompret near Chimay (province of Hainaut, Belgium). The quarry comprises strata that can be linked to the Kellwasser event, an important mass-extinction event near the Frasnian-Famennian boundary. Several of the lithological entities from this quarry require specific approaches in terms of preparation. This article will explicitly focus on preparation techniques applied to cephalopods. This informative and diverse group of macro-organisms can contribute to a better understanding of marine environmental changes during an ecological crisis. A thorough preparation of all the collected specimens from this specific location is required, as this peculiar fauna is in desperate need of a taxonomic review. We will demonstrate to what extents the uses of potassium hydroxide (KOH) and Rewoquat W 3690 PG as solvents have proven to be particularly effective in dissolving clay-rich sediments during preparation.

Upper Devonian mercury record from North America and its implications for the Frasnian–Famennian mass extinction

The Frasnian–Famennian biotic crisis (~372 Ma) was one of the “big five” mass extinction events in the Phanerozoic. This event was associated with dramatic climatic and oceanographic perturbations, including oceanic anoxia, global cooling, sea-level fluctuations. Large-scale volcanic activity is one of several possible triggers that have been suggested as the ultimate cause of this crisis, based on Hg enrichment data from widespread sections. However, there are also sections that do not show a Hg enrichment across the Frasnian–Famennian boundary. To further investigate the hypothesis of a volcanic trigger for the Frasnian–Famennian mass extinction event, mercury (Hg) analyses were performed on six North American records (five from the Appalachian Basin and one in the Illinois Basin) that include the Frasnian–Famennian boundary. There is no uniformly observed Hg enrichment at or below the Frasnian–Famennian boundary across the six sites. A potentially volcanically driven Hg anomaly is found in the Illinois Basin; however, the Hg enrichment occurs stratigraphically above the Frasnian–Famennian boundary. Mercury records from the studied sites question the timing of the volcanism that may be responsible for the mass extinction event. Further studies are needed to fully understand the geographic distribution and eruption history of the large igneous provinces, as well as the link between Hg and volcanism during the Frasnian–Famennian interval.

Late Devonian benthic ostracods from South China and their response to the Frasnian–Famennian event

Late Devonian ostracods are described for the first time from the Frasnian–Famennian (F–F) transition of the Zengpiyan section, Guangxi, South China. Forty‐five ostracod species belonging to 25 genera are identified and figured and one is new:Jenningsina guilinensissp. nov. The Frasnian–Famennian boundary (F–FB) in the Zengpiyan section is coincident with the lithological boundary between the Guilin Formation and the Dongcun Formation, and could be marked by the disappearance ofRectobairdia proximischimensis(Lethiers & Casiers, 1998) andJenningsina guilinensissp. nov. The ostracods belong to the Eifelian Mega‐Assemblage, which implies a shallow‐water palaeoenvironment. The ostracod fauna and sedimentary features of the Guilin and Dongcun formations at the Zengpiyan section suggest a transition from subtidal to low‐energy tidal flat on the Guilin Platform during the Frasnian‐Famennian event. The extinction rate of benthic ostracod species is about 61% during the F–F event in the Zengpiyan section. Two stages of faunal changes have been recognized in the event and the second stage is more severe than the first one.

A Devonian age for the Sarhlef Formation (Jebilet Massif, Morocco) – evidence from new biostratigraphic data based on metamorphosed conodonts

The Sarhlef Formation, which hosts the massive sulphide deposits of the Moroccan Meseta, has been considered as Carboniferous in age. Moreover, palynological analysis of the black shales hosting the Draa Sfar deposit (Central Jebilet) has allowed to restrict the age of the Sarhlef Formation to the late Visean (Asbian). However, this age is not compatible with geochronological data of various magmatic intrusions present in Central Jebilet. New biostratigraphic results based on metamorphosed conodonts from 34 samples (three cores, DS170, DF306 and DS125) of the Draa Sfar deposits provide a new biostratigraphic framework of the Sarhlef Formation. The collected fauna is affected by pyritization, silicification and tectonic deformation. Some non-pyritised or partially pyritized conodonts show a conodont color alteration (CAI) change varying from black to translucent (CAI 5 to CAI 8). The conodont fauna comprise representatives of the genera Icriodus, Polygnathus, Ancyrodella, Palmatolepis, Ancyrognathus, Ancyroides, and Palmatolepis showing that age spans from the Frasnian to Late Famennian. This age is more compatible with the radiometric data of the intrusive magmatic rocks. In core DS170, the Upper Kellwasser Horizon at the Frasnian-Famennian boundary has been identified by lithological characteristics and stratigraphy. The proposed Late Devonian age of the Sarhlef Formation provides new insights on the geological evolution and stratigraphy of the entire region.

Biostratigraphy of the Upper Devonian Khoshyeilagh Formation in NE Iran based on conodonts and other faunas

The Khoshyeilagh Formation located in the northeast of Iran yielded seven conodont species and sub-species and 19 macro- and microfossil taxa that allow recognition of two conodont biozones and one biozone based on calcareous microfossils. The latest Frasnian age (the Upper rhenana to linguiformis zones) is attributed to the topmost strata with Icriodus alternatus. Its replacement with I. cornutus indicates the Famennian (Lower triangularis to Lower crepida zones) corresponding to the Umbellina Zone. The fossil assemblages identified in the Khoshyeilagh Formation represent a shallow marine environment with a tropical climate at the time of deposition. The fossil species from the Khoshyeilagh Formation and the sedimentary basins in Algeria, Libya, Morocco, Poland, and Russia reveal a close connection between the Iranian plateau and the northern parts of Gondwana in the Late Devonian. The biofacies and lithofacies analyses show a sea-level decline at the end of Frasnian, followed by a considerable sea-level drop, as in other regions of the world. After a short time, in the Famennian, the deepening occurred in some parts of the area and the open marine facies (bioclast spicule wackestone-packstone) were deposited. This study is the first attempt to determine the Frasnian-Famennian boundary based on conodont assemblages and other fossil species such as umbellulids, tentaculites, and ostracods. The distribution of these species is interpreted in sedimentological, stratigraphic, sequence stratigraphy, and the global eustatic context. Keywords: biofacies, conodont, Frasnian-Famennian boundary, Late Devonian, NE Iran.

Famennian conodonts from the Hongguleleng Formation at the Bulongguoer stratotype section, western Junggar, Northwest China

The Hongguleleng Formation, the highest and most important Devonian marine carbonate horizon in western Junggar, contains an endemic shallow-water Icriodus–Polygnathus conodont fauna with rare palmatolepids and other genera. The conodont faunas from the Bulongguoer and the Wulankeshun sections are similar, with high abundance (about 40%) of endemic taxa (13 taxa), indicating isolation of the Junggar Basin during early Famennian. Non-endemic species in the faunas suggest that the Lower Member of the Hongguleleng Formation is assignable to the Pa. rhomboidea Zone to the Pa. marginifera marginifera Zone of early Famennian, not including the Frasnian–Famennian boundary. The Upper Member may be of late Famennian–early Tournaisian in age on the basis of our preliminary faunal analysis.

Ecological and Taxonomical Succession of Rhynchonellids (Brachiopoda) in the Devonian and Early Carboniferous of Transcaucasia

The Devonian and Early Carboniferous brachiopod assemblages of the order Rhynchonellida from Transcaucasia (Nakhchivan Autonomous Republic of Azerbaijan and Armenia) are described. The succession of dominating rhynchonellid superfamilies and ecological types has been identified. Rhynchonellids were numerous in the Devonian; in the Early and Middle Devonian, the representatives of the superfamily Uncinuloidea prevailed. Their relict species survived up to the beginning of Famennian. The free-lying and anchoring cavern-dwelling rhynchonellids dominated in the Early and Middle Devonian. This ecological subtype is recognized for the first time. The rhynchonellid taxonomic and ecological groups changed at the Frasnian–Famennian boundary but rhynchonellids remained a significant part of the brachiopod fauna. The variability of rhynchonellids decreased at the Famennian–Tournaisian boundary but the superfamily Rhynchotrematoidea and the rhynchonellid anchoring ecological type continued to dominate starting from the Frasnian. The role of Rhynchonellida in the Early Carboniferous brachiopod fauna is insignificant. The decrease of variability within some zones is probably connected with taphonomic conditions.

Astronomical time calibration of the Upper Devonian Lali section, South China

Abstract The Late Devonian Period was a critical geological interval, affected by numerous significant global bio- and environmental events, including the Kellwasser, annulata and Hangenberg events, and a major climate transition leading to the Carboniferous ice ages. The timing and pattern of these events are unclear due to lack of the precise time scale. In this study, an analysis of calcium concentration series was carried out on the Upper Devonian cyclostratigraphic slope-facies of the Lali section, South China. Objective testing of the section indicates the presence of astronomical forcing: long orbital eccentricity, short eccentricity, obliquity, and precession index. Two independent astrochronologies were developed for the Ca series and compared with spectral analysis. The age of the Devonian–Carboniferous boundary (358.9 ± 0.4 Ma) was selected as an “anchor”, and an Astronomical Time Scale (ATS) was constructed from the late Frasnian to early Tournaisian based on 405-kyr cycles. The ATS indicates a duration of the Famennian Stage of 14.4 ± 0.28 myr, and assigns 373.3 ± 0.49 Ma to the Frasnian–Famennian boundary. The durations of the Famennian conodont zones are also indicated. The timing of Famennian bio- and environmental events also can be established by the ATS. The Upper Kellwasser horizon starts at 373.4 Ma and is constrained to a duration of 100-kyr; a sharp positive carbon isotope excursion CIE, +3‰ recognized across the Frasnian–Famennian boundary lasts 300 kyr. The Lower and Upper annulata events each last 50-kyr with positive CIEs; and the ages of two CIE peaks are 361.7 Ma and 361.3 Ma, respectively. Five transgressive events, including the Nehden, Enkeberg, Dasberg, Strunian, and Hangenberg transgressions occur at 370.6 Ma, 368 Ma, 360.4 Ma, 360.1 Ma, and 358.9 Ma, respectively. Five regressive events i.e., the linguiformis, prima, Condroz, velifer, and Derwer regressions occur at 373.4 Ma, 371 Ma, 369 Ma, 362.3 Ma, and 359.2 Ma, respectively.

Size reduction of conodonts indicates high ecological stress during the late Frasnian under greenhouse climate conditions in South China

The Late Frasnian mass extinction (LFME) during extreme greenhouse conditions had a serious impact on biotic evolution. Herein, based on detailed size measurements of 1783 elements of the conodont genera Polygnathus and Palmatolepis at the Lali and Duan sections in South China, conodont animals underwent significant size reduction at the genus level during the late Frasnian. The “Bergmann's rule” controlled the evolution of Frasnian conodont animals, and their size reduction during the late Frasnian may have resulted from long-term global warming and indicated high ecological stress before the Frasnian-Famennian boundary (FFB). This phenomenon can explain why the decline of benthic faunas, such as corals, brachiopods or metazoan reefs, predated the extinction of pelagic faunas, such as conodonts in the Upper Kellwasser (UKW) event and at the FFB.