Mass Extinction Interval Research Articles

Lithium isotopes track changes in continental weathering regimes across the end-Permian mass extinction in Southwest China

It has been assumed there was a massive amount of volcanic CO2 injection into the Permian-Triassic atmosphere and ocean systems, leading to rapid climatic warming and expansion of marine anoxia. However, it remains intriguing how Earth recovered from such a CO2-driven hyperthermal condition. One potential mechanism involves the negative feedback between continental silicate weathering and atmospheric CO2, which could have helped maintain habitability across the end-Permian mass extinction (EPME) interval. This process can be examined using lithium isotopes (δ7Li), which reflect the balance of physical erosion and chemical weathering, and chemical weathering indices such as the Chemical Index of Alteration (CIA), which indicates the chemical alteration of parent materials during weathering. In this study, we analyze siliciclastic sedimentary rocks from the Lopingian to Lower Triassic depositional sequences in the HK-1 drill core at the Lengqinggou section, a terrestrial coastal depositional environment in Southwest China, to reconstruct changes in continental chemical weathering intensity across the EPME. We observed a significant ∼4 ‰ positive shift in δ7Li, accompanied by a marked decrease in Li content from 26 ppm to 6 ppm. Our corrected CIA data (CIAcorr) also exhibits a considerable decrease from 94 to 59 across the EPME. The new δ7Li and CIAcorr data from the terrestrial section indicate a decrease in overall chemical weathering intensity in Southwest China, alongside an increase in physical erosion rates, suggesting a shift from a transport-limited to a kinetically limited weathering regime across the EPME. These changes in the continental weathering regime appear to be linked to active volcanic activity near the South China Block, which led to massive deforestation and the collapse of soil systems. Dramatic reductions in chemical weathering intensity may result in inefficient atmospheric CO2 consumption through silicate weathering if other climatic and tectonic conditions remain constant, potentially contribute to maintaining high global surface temperatures and prolonged marine anoxia into the Early Triassic.

The postcranial anatomy of Moschorhinus kitchingi (Therapsida: Therocephalia) from the Karoo Basin of South Africa.

Therocephalia are an important clade of non-mammalian therapsids that evolved a diverse array of morphotypes and body sizes throughout their evolutionary history. The postcranial anatomy of therocephalians has largely been overlooked, but remains important towards understanding aspects of their palaeobiology and phylogenetic relationships. Here, we provide the first postcranial description of the large akidnognathid eutherocephalian Moschorhinus kitchingi by examining multiple specimens from fossil collections in South Africa. We also compare the postcranial anatomy with previously described therocephalian postcranial material and provide an updated literature review to ensure a reliable foundation of comparison for future descriptive work. Moschorhinus shares all the postcranial features of eutherocephalians that differentiate them from early-diverging therocephalians, but is differentiated from other eutherocephalian taxa by aspects concerning the scapula, interclavicle, sternum, manus, and femur. The novel anatomical data from this contribution shows that Moschorhinus possessed a stocky bauplan with a particularly robust scapula, humerus, and femur. These attributes, coupled with the short and robust skull bearing enlarged conical canines imply that Moschorhinus was well equipped to grapple with and subdue prey items. Additionally, the combination of these attributes differ from those of similarly sized coeval gorgonopsians, which would have occupied a similar niche in late Permian ecosystems. Moreover, Moschorhinus was the only large carnivore known to have survived the Permo-Triassic mass extinction. Thus, the subtle but important postcranial differences may suggest a type of niche partitioning in the predator guild during the Permo-Triassic mass extinction interval.

Shifts in magnetic mineral assemblages support ocean deoxygenation before the end-Permian mass extinction

Expansion of oceanic anoxia is a prevailing hypothesis for driving the marine end-Permian mass extinction and is mainly based on isotopic geochemical proxies. However, long-term oceanic redox conditions before the end-Permian mass extinction remain unresolved. Here we report a secular redox trend based on rock magnetic experiments and cerium anomalies through the Changhsingian and across the Permian-Triassic boundary at the Meishan section, China. Magnetic mineral assemblages changed dramatically at ca. 252.8 million years age (Ma), which indicates that oceanic deoxygenation started about 0.9 million years earlier than the end-Permian mass extinction. The magnetite-dominant post end-Permian mass extinction interval suggests a ferruginous dysoxic conditions with enhanced weathering in the earliest Triassic. Also, a gradual magnetite abundance decrease to pre-extinction levels is observed at ca. 251.5 Ma, coinciding temporally with the waning of Siberian Trap and arc volcanism. All of these observations demonstrate that environmental deterioration began much earlier than the end-Permian mass extinction and finally collapsed in the end-Permian.

Marine snowstorm during the Permian–Triassic mass extinction

Abstract The Permian–Triassic mass extinction (PTME) interval is marked by major excursions in both inorganic and organic carbon (C) isotopes. Carbon cycle models predict that these trends were driven by large increases in productivity, yet organic C–rich rocks are not recorded in most PTME shelf sedimentary successions. Anomalous C-rich facies have been reported from rare abyssal plains records now exposed in Japan and New Zealand, where black shales at the PTME are extraordinarily organic-rich units. We examined organic matter at the Waiheke, New Zealand, section, and results show that these deposits are dominated by lamalginites composed of unicellar solitary or colonial phytoplankton produced during algal blooms that falls as “marine snow.” We modeled the impact of ash fall from eruptions in the Siberian Traps large igneous province and argue that they fertilized the Panthalassa Ocean with P and Fe, leading to a marine “snowstorm” and significant C drawdown marking this major biobloom during the PTME.

Lipid biomarkers recording marine microbial community structure changes through the Frasnian-Famennian mass extinction event.

Studying the response and recovery of marine microbial communities during mass extinction events provides an evolutionary window through which to understand the adaptation and resilience of the marine ecosystem in the face of significant environmental disturbances. The goal of this study is to reconstruct changes in the marine microbial community structure through the Late Devonian Frasnian-Famennian (F-F) transition. We performed a multiproxy investigation on a drill core of the Upper Devonian New Albany Shale from the Illinois Basin (western Kentucky, USA). Aryl isoprenoids show green sulfur bacteria expansion and associated photic zone euxinia (PZE) enhancement during the F-F interval. These changes can be attributed to augmented terrigenous influxes, as recorded collectively by the long-chain/short-chain normal alkane ratio, carbon preference index, C30 moretane/C30 hopane, and diahopane index. Hopane/sterane ratios reveal a more pronounced dominance of eukaryotic over prokaryotic production during the mass extinction interval. Sterane distributions indicate that the microalgal community was primarily composed of green algae clades, and their dominance became more pronounced during the F-F interval and continued to rise in the subsequent periods. The 2α-methylhopane index values do not show an evident shift during the mass extinction interval, whereas the 3β-methylhopane index values record a greater abundance of methanotrophic bacteria during the extinction interval, suggesting enhanced methane cycling due to intensified oxygen depletion. Overall, the Illinois Basin during the F-F extinction experienced heightened algal productivity due to intensified terrigenous influxes, exhibiting similarities to contemporary coastal oceans that are currently undergoing globalized cultural eutrophication. The observed microbial community shifts associated with the F-F environmental disturbances were largely restricted to the extinction interval, which suggests a relatively stable, resilient marine microbial ecosystem during the Late Devonian.

The Cretaceous/Tertiary boundary event in Tibet

The Cretaceous/Tertiary boundary in the Gamba and Tingri regions of Tibet occurs between the Zongshan and Jidula Formations. Arenaceous facies similar to those of the Jidula Formation are widespread in Tibet and Pakistan; collectively, these represent the diachronous deposits of the Latest Cretaceous-Early Tertiary regression. Major faunal changes took place in Tibet during the Late Cretaceous. Ali of the Cretaceous ammonoids, planktonic and benthonic foraminifera, rudistid and inoceramid bivalves became extinct over the Campanian Maastrichtian interval in a stepwise pattern, with abrupt Late Campanian and Late Maastrichtian extinction events (Tabs. 3, 4). A large number of new taxa appeared during the Danian (Tabs. 3, 4). These faunal changes in the shallow-water marine facies of Tibet demonstrate that this region was not isolated from major global faunal changes taking place in the Cretaceous/Tertiary boundary mass extinction interval.

The dynamics of marine stepwise mass extinction

Mass extinction is characterized by the loss of 50 - 90 + percent of genetically and ecologically diverse species within 1 - 3.5 Myr intervals. Three conflicting theories exist: (1) Graded Mass Extinction; (2) Stepwise Mass Extinction; and (3) Catastrophic Mass Extinction. These can only be adequately tested with high resolution (cm-scale) stratigraphic data spanning the entire mass extinction interval and adjacent strata. Such data are presently available only for the Eocene-Oligocene (E-O), Cretaceous-Tertiary (K-T) and Cenomanian-Turonian (C-T) extinctions. In general, prevalent uniformitarian stratigraphic philosophy and use of the modern Earth/Life system as a model for the Phanerozoic has hindered the search for, and expectations of, high-resolution stratigraphic data critical) to mass extinction research. The modern Earth/Life "model" predicts highly variable, environmentally and biologically resilient systems and predominantly autocyclic stratigraphic response to large-scale forcing mechanisms.

Facies stacking and distribution in the Gabbs Formation (Late Triassic, west-Central Nevada, U.S.A.): An environmental baseline to the end-Triassic carbonate crisis

The primarily carbonate Gabbs Formation of west-central Nevada, U.S.A., remains an important, rare example of Panthalassan shallow-marine environments from the Late Triassic and through the Triassic–Jurassic boundary. Its relevance as a locality persists, particularly as the end-Triassic mass extinction interval is increasingly recognized as a carbonate crisis, evidenced by the global decline of carbonate facies and calcareous marine organisms. However, important transitions across key stratigraphic boundaries in this region have tended to be evaluated in isolation, producing an incomplete picture of sedimentation through the duration of the Late Triassic leading up to the geochemical crises and mass extinction at the close of the Triassic. In this work, multiple correlative measured sections are used to describe the facies in the mixed carbonate-siliciclastic ramp and characterize controls on carbonate facies. The outer ramp transition to inner ramp facies of the Gabbs represent a transgressive–regressive–transgressive cycle culminating in a transition to terrigenous inputs and a gradual decline of carbonate sediments stratigraphically below the mass extinction interval. This predictable loss of carbonate facies and the near continuous deposition of the Gabbs Formation allow for evidence of facies changes and acidifying conditions in the latest Triassic to be considered independently, in contrast to other global Late Triassic sections where depositional hiatuses or abrupt facies changes often compound these records. Establishing a baseline sedimentation for the Late Triassic demonstrates that the final loss of carbonate facies can be decoupled from the onset of acidifying conditions, resulting in a more precise timeline of latest Triassic environmental upheaval.

The Sedimentary Geochemistry and Paleoenvironments Project.

The Sedimentary Geochemistry and Paleoenvironments Project.

Dead clades walking are a pervasive macroevolutionary pattern

D. Jablonski [Proc. Natl. Acad. Sci. U.S.A. 99, 8139-8144 (2002)] coined the term "dead clades walking" (DCWs) to describe marine fossil orders that experience significant drops in genus richness during mass extinction events and never rediversify to previous levels. This phenomenon is generally interpreted as further evidence that the macroevolutionary consequences of mass extinctions can continue well past the formal boundary. It is unclear, however, exactly how long DCWs are expected to persist after extinction events and to what degree they impact broader trends in Phanerozoic biodiversity. Here we analyze the fossil occurrences of 134 skeletonized marine invertebrate orders in the Paleobiology Database (paleobiodb.org) using a Bayesian method to identify significant change points in genus richness. Our analysis identifies 70 orders that experience major diversity losses without recovery. Most of these taxa, however, do not fit the popular conception of DCWs as clades that narrowly survive a mass extinction event and linger for only a few stages before succumbing to extinction. The median postdrop duration of these DCW orders is long (>30 Myr), suggesting that previous studies may have underestimated the long-term taxonomic impact of mass extinction events. More importantly, many drops in diversity without recovery are not associated with mass extinction events and occur during background extinction stages. The prevalence of DCW orders throughout both mass and background extinction intervals and across phyla (>50% of all marine invertebrate orders) suggests that the DCW pattern is a major component of macroevolutionary turnover.

Biostratigraphic significance and geometric morphometrics of Euestheria gutta (Crustacea: Branchiopoda: Spinicaudata): An index fossil of continental Permian–Triassic transitional beds

The Permian–Triassic mass extinction was the largest biotic extinction event in the Phanerozoic and affected both marine and continental life. Marine Permian–Triassic transitional sequences can be correlated in many regions, but this has proved difficult for continental successions. A growing number of studies show that spinicaudatans are some of the most common fossils in continental strata and can be used as index fossils for continental stratigraphic division and correlation. Here we document the morphology and biostratigraphic significance of Euestheria gutta based on well‐preserved fossils from southwestern China. It shows strong intraspecific morphological variation, while the most important feature is the strongly convex larval valve and significant finely pitted to weakly reticulated ornamentation on the growth bands. Evidence from palaeobotany, charcoal, and organic carbon isotopes indicated that the continental mass extinction in southwestern China was marked by the catastrophic loss of tropical rainforest vegetation, enhanced wildfire and a negative carbon isotope excursion (CIE) during the P–Tr transition. Meanwhile, abundant E. gutta first appeared at the onset of the negative CIE and just above the horizon of the loss of macroflora. Based on the global geographic distribution of E. gutta and temporal correlation, we conclude that this species existed from the latest Permian to the earliest Triassic, and the occurrence of E. gutta could be used as an index fossil of the continental mass extinction interval or P–Tr transitional beds.

Mercury fluxes record regional volcanism in the South China craton prior to the end-Permian mass extinction

Abstract Enhanced regional subduction-related volcanism in the South China craton concurrent with Siberian Traps large igneous province magmatism was a likely contributor to major biotic and environmental stresses associated with the Permian-Triassic boundary (ca. 252 Ma) mass extinction. However, the timing, intensity, and duration of this regional volcanic activity remain uncertain. We analyzed mercury (Hg) concentrations in three widely separated marine sections in the South China craton (Shangsi, Ganxi, and Chaohu) as well as Hg isotopic compositions in one section (Shangsi) from the Upper Permian (Changhsingian) through the lowermost Triassic (Induan) in order to track volcanic inputs. Four mercury enrichment (ME) intervals, dating to the lowermost Changhsingian (ME1), mid–Clarkina changxingensis zone (ME2), upper C. changxingensis to lower C. yini zones (ME3), and latest Permian mass extinction (LPME) interval (ME4), were recognized on the basis of elevated Hg/total organic carbon ratios. These records provide evidence of strong volcanism in the Tethyan region starting ∼2 m.y. before the LPME, whereas only the ME4 event is recorded in extra-Tethyan sections. Mercury isotopes support the inference that pre-LPME Hg peaks were related to regional subduction-related volcanism, and that Hg emissions at the LPME were the result of Siberian Traps large igneous province intrusions into organic-rich sediments. This study demonstrates the feasibility of distinguishing flood-basalt from subduction-related volcanic inputs on the basis of marine sedimentary Hg records.

Paleozoic-Mesozoic Eustatic Changes and Mass Extinctions: New Insights from Event Interpretation.

Recent eustatic reconstructions allow for reconsidering the relationships between the fifteen Paleozoic–Mesozoic mass extinctions (mid-Cambrian, end-Ordovician, Llandovery/Wenlock, Late Devonian, Devonian/Carboniferous, mid-Carboniferous, end-Guadalupian, end-Permian, two mid-Triassic, end-Triassic, Early Jurassic, Jurassic/Cretaceous, Late Cretaceous, and end-Cretaceous extinctions) and global sea-level changes. The relationships between eustatic rises/falls and period-long eustatic trends are examined. Many eustatic events at the mass extinction intervals were not anomalous. Nonetheless, the majority of the considered mass extinctions coincided with either interruptions or changes in the ongoing eustatic trends. It cannot be excluded that such interruptions and changes could have facilitated or even triggered biodiversity losses in the marine realm.

Uncharted Permian to Jurassic continental deposits in the far north of Victoria Land, East Antarctica

The remote lower reaches of the Rennick Glacier in the far north of Victoria Land hold some of the least-explored outcrop areas of the Transantarctic basin system. Following recent international field-work efforts in the Helliwell Hills, we here provide a comprehensive emendation to the regional stratigraphy. Results of geological and palaeontological reconnaissance and of petrographic, geochemical and palynostratigraphic analyses reveal a stack of three previously unknown sedimentary units in the study area: the Lower Triassic Van der Hoeven Formation (new unit, 115+ m thick) consists mainly of quartzose sandstone and non-carbonaceous mudstone rich in continental trace fossils. The Middle to Upper Triassic Helliwell Formation (new unit, 235 m thick) consists of coal-bearing overbank deposits and volcaniclastic sandstone and yielded typical plant fossils of the Gondwanan Dicroidium flora together with plant-bearing silicified peat. The succession is capped by c . 14 m of the sandstone-dominated Section Peak Formation (uppermost Triassic–Lower Jurassic). Our results enable more detailed correlation of the Palaeozoic–Mesozoic successions throughout East Antarctica and into Tasmania. Of particular interest is one section that spans the end-Permian mass extinction interval, which promises to allow detailed reconstructions of high-latitude vegetation dynamics across this critical interval in Earth history. Supplementary material: A Supplementary Data File containing supplementary information, figures S1–S7, and additional references is available at https://doi.org/10.6084/m9.figshare.c.5118431

Estimating dispersal and evolutionary dynamics in diploporan blastozoans (Echinodermata) across the great Ordovician biodiversification event

AbstractEchinoderms make up a substantial component of Ordovician marine invertebrates, yet their speciation and dispersal history as inferred within a rigorous phylogenetic and statistical framework is lacking. We use biogeographic stochastic mapping (BSM; implemented in the R package BioGeoBEARS) to infer ancestral area relationships and the number and type of dispersal events through the Ordovician for diploporan blastozoans and related species. The BSM analysis was divided into three time slices to analyze how dispersal paths changed before and during the great Ordovician biodiversification event (GOBE) and within the Late Ordovician mass extinction intervals. The best-fit biogeographic model incorporated jump dispersal, indicating this was an important speciation strategy. Reconstructed areas within the phylogeny indicate the first diploporan blastozoans likely originated within Baltica or Gondwana. Dispersal, jump dispersal, and sympatry dominated the BSM inference through the Ordovician, while dispersal paths varied in time. Long-distance dispersal events in the Early Ordovician indicate distance was not a significant predictor of dispersal, whereas increased dispersal events between Baltica and Laurentia are apparent during the GOBE, indicating these areas were important to blastozoan speciation. During the Late Ordovician, there is an increase in dispersal events among all paleocontinents. The drivers of dispersal are attributed to oceanic and epicontinental currents. Speciation events plotted against geochemical data indicate that blastozoans may not have responded to climate cooling events and other geochemical perturbations, but additional data will continue to shed light on the drivers of early Paleozoic blastozoan speciation and dispersal patterns.

Evidence for volcanism and weathering during the Permian-Triassic mass extinction from Meishan (South China) osmium isotope record

The Permian–Triassic mass extinction event is the most severe biotic crisis during the Phanerozoic. The trigger of this event has been widely linked with massive volcanic activity associated with the Siberian Traps Large Igneous Province. However, the direct link is still lacking to fully understand the event. In this study, we apply osmium isotope (187Os/188Os, or Osi) stratigraphy across the Permian–Triassic boundary interval in the Meishan section of South China. The Os isotope stratigraphy reveals multiple shifts to more unradiogenic 187Os/188Os composition that are interpreted to reflect pulses of volcanism across the mass extinction interval. Additionally, a shift to a more radiogenic 187Os/188Os composition is also found immediately above the mass extinction interval, which is taken to reflect the enhanced weathering of the continental crust in response to greenhouse gas release into the atmosphere and the associated hyperthermal.

Globally enhanced Hg deposition and Hg isotopes in sections straddling the Permian–Triassic boundary: Link to volcanism

Mercury (Hg/TOC) spikes from eight Permian–Triassic boundary (PTB) sections in this study display patterns similar to each other across the so-called extinction interval as well as strong variation in sedimentation rates from section to section. Mercury may have been originated from the synchronous magmatism of the Siberian Traps Large Igneous Province (STLIP).At the GSSP in Meishan, China, Hg/TOC peaks were observed in the latest Permian mass extinction interval (LPME) and Early Triassic mass extinctions (ETME). The successions at Hovea-3 (Australia), Ursula Creek (Canada), Idrijca (Slovenia), Rizvanuša (Croatia) exhibit Hg/TOC peaks at the LPME and PTB. The Rizvanuša section displays one peak at the ETME horizon, Zal and Abadeh (Iran) successions at the LPME and ETME horizons, while Misci/Seres (Tyrol/Italy) section shows an enrichment at the LPME. The largest Hg/TOC peaks at the LPME, PTB and ETME are, perhaps, linked to the beginning of stage 2 (extrusive hiatus) of the Siberian Traps LIP. The meaning of the Hg/TOC spike between the LPME event and the PTB in seven of these sections is fuzzy.In the δ202Hg (MDF) vs Δ201Hg (MIF) cross plot, the majority of samples from the extinction interval appear within the volcanic-emission box and a few samples plot in the sediment/soil/peat box. Hg-isotope signatures resulted from mixing processes of volcanic and normal marine sediment Hg, generating four horizontal trends whose Δ201Hg shows negligible to no variation. Less terrigenous-Hg influx was noticed in the sections closer to the STLIP (Rizvanuša, Idrijca and Seres/Misci, all in Europe) in which Δ201Hg (MIF) is close to zero. Marked influence occurs in sections far distant from the STLIP (Meishan, Ursula Creek and Hovea-3) that exhibit negative Δ201Hg (MIF). The two sections from Iran, at intermediate distance from the STLIP, exhibit the highest, positive Δ201Hg values (Abadeh section) and the lowest, negative Δ201Hg values (Zal section). A Δ199Hg (MIF) vs Hg (n·ng−1) cross plot suggests that volcanic Hg has been contaminated by normal marine source-Hg influx in these sections helping to shape two major curved trends.The negative C-isotope excursions and Hg/TOC enrichments in the studied sections are nearly coeval and this supports the hypothesis of synchronism between the Permian–Triassic transition biotic crises (LPME and ETME) and the start of the stage 2 of the Siberian Traps (sill-intrusion style of magmatism).

Facies and evolution of the carbonate factory during the Permian–Triassic crisis in South Tibet, China

AbstractThe nature of Phanerozoic carbonate factories is strongly controlled by the composition of carbonate‐producing faunas. During the Permian–Triassic mass extinction interval there was a major change in tropical shallow platform facies: Upper Permian bioclastic limestones are characterized by benthic communities with significant richness, for example, calcareous algae, fusulinids, brachiopods, corals, molluscs and sponges, while lowermost Triassic carbonates shift to dolomicrite‐dominated and bacteria‐dominated microbialites in the immediate aftermath of the Permian–Triassic mass extinction. However, the spatial–temporal pattern of carbonates distribution in high latitude regions in response to the Permian–Triassic mass extinction has received little attention. Facies and evolutionary patterns of a carbonate factory from the northern margin of peri‐Gondwana (palaeolatitude ca 40°S) are presented here based on four Permian–Triassic boundary sections that span proximal, inner to distal, and outer ramp settings from South Tibet. The results show that a cool‐water bryozoan‐dominated and echinoderm‐dominated carbonate ramp developed in the Late Permian in South Tibet. This was replaced abruptly, immediately after the Permian–Triassic mass extinction, by a benthic automicrite factory with minor amounts of calcifying metazoans developed in an inner/middle ramp setting, accompanied by transient subaerial exposure. Subsequently, an extensive homoclinal carbonate ramp developed in South Tibet in the Early Triassic, which mainly consists of homogenous dolomitic lime mudstone/wackestone that lacks evidence of metazoan frame‐builders. The sudden transition from a cool‐water, heterozoan dominated carbonate ramp to a warm‐water, metazoan‐free, homoclinal carbonate ramp following the Permian–Triassic mass extinction was the result of the combination of the loss of metazoan reef/mound builders, rapid sea‐level changes across Permian–Triassic mass extinction and profound global warming during the Early Triassic.

New U-Pb zircon age and carbon isotope records from the Lower Silurian Longmaxi Formation on the Yangtze Platform, South China: Implications for stratigraphic correlation and environmental change

The Ordovician–Silurian (O–S) transition was a period of dramatic climatic, environmental, and biological change. Numerous studies have documented the Late Ordovician glacial or mass extinction interval, but the Early Silurian has received significantly less attention. This study presents a U-Pb zircon age data and organic carbon isotope (δ13Corg) records from the Upper Ordovician to Lower Silurian succession of South China to better constrain carbon isotope perturbations and to evaluate their possible causes and relationships to paleoenvironmental change during Early Silurian time. A volcanic ash bed located at the top of the organic-rich Lower Silurian Longmaxi Formation yields a 206Pb/238U zircon age of 440 ± 3 Ma (MSWD = 1.4), which is consistent with the Rhuddanian–Aeronian (R–A) boundary age. The newly acquired age is similar to that documented an ash bed in Scotland (439.57 ± 1.13 Ma) perhaps indicating synchronous volcanism. The δ13Corg values show a negative excursion in the organic-rich lower Longmaxi Formation that is interrupted by a positive excursion in the organic-lean upper part of the unit. The positive excursion begins immediately above the dated ash bed thus assigning it to the R–A boundary. The documented δ13Corg trend is comparable to those of other sections throughout the world, and is suggestive of a global perturbation of carbon cycle. The negative δ13Corg excursion of the Rhuddanian stage was coeval with deposition of organic-rich shale under anoxic/euxinic conditions, whereas the subsequent positive δ13Corg excursion coincided with a change to suboxic conditions that could have diminished organic matter preservation. We propose that the negative δ13Corg excursion could be considered as the defining isotopic characteristic of the Rhuddanian oceanic anoxic event (Rhuddanian OAE). Results of the present study in tandem with published age data from the Guanyinqiao Bed immediately below the base of the Longmaxi Formation suggest that the negative δ13Corg excursion and associated Rhuddanian OAE persisted for approximately 3 Myr. This relatively long-lived event reflects a sustained addition of isotopically light carbon into the atmosphere-ocean system, possibly related to the release of volcanic CO2. The enhanced burial of organic carbon in association with the Rhuddanian OAE could have removed the substantial 12C from the carbon reservoir and lowered atmospheric pCO2 thus resulting in a subsequent positive δ13C excursion and global cooling at the R-A boundary.

Palaeoenvironmental changes recorded in the palynology and palynofacies of a Late Permian Marker Mudstone (Galilee Basin, Australia)

Reconstructing the terrestrial palaeoenvironment during the end-Permian is made challenging by widespread erosion and ecosystem destruction. High-resolution sampling for palynofacies and palynology in sections that preserve the boundary interval allows for detailed examination of the drastic environmental changes that characterize the Permian–Triassic mass extinction. In the Bowen and Galilee basins in eastern Australia, this environmental perturbation is recorded within a Marker Mudstone that occurs above the uppermost Permian coal seams. The Marker Mudstone is used as a stratigraphic reference level at many localities, but has previously only been studied at a single locality in the Bowen Basin. In the present study, borehole Tambo 1-1A drilled in the Galilee Basin was selected to clarify whether this black, organic-rich mudstone marks a marine transgression, and to examine potential indicators of the end-Permian mass extinction. A total of 22 samples were taken from the mudstone unit, and from the over- and underlying strata and processed for palynology, palynofacies, and carbon isotope analysis.Biostratigraphic data indicate that the Marker Mudstone itself covers the uppermost part of unit APP5, with the first index taxa of unit APP6 floras occurring in samples less than 80cm above this interval. This can be correlated with several other localities in the Bowen and Sydney basins where this shift occurs just above the uppermost Permian coal seam. Palynofacies data agree with previous interpretations of a southwards prograding delta that subsides as base level rises to form an extensive waterbody in which the Marker Mudstone was deposited. A change from translucent phytoclast-dominated to opaque phytoclast-dominated palynofacies within the Marker Mudstone suggests a shift to more oxic conditions in the water column, while base level begins to fluctuate, or increased terrestrial input from fluvial systems as the hinterland rises. Algal bodies resembling Botryococcus are found in the strata above the Marker Mudstone, but differ in morphology from the algal bodies found in the deltaic facies below. The presence of acanthomorph acritarchs in the Marker Mudstone and in the overlying Rewan Formation may indicate marine influence. Forms resembling fungal spores are present, but they do not show a “spike” as seen in other P–T boundary localities.The relative position of unit APP6 to the P–T boundary itself remains unclear. APP6 assemblages are dominated by simple acavate trilete and cavate trilete spores, which suggests stressed environment dominated by ferns and lycopods. The presence of degraded phytoclasts towards the top of the Marker Mudstone may also be used to suggest a mass-extinction interval. They may also be indicative of shifting local palaeoenvironmental changes, an interpretation that is supported by the low magnitude negative excursion of the δ13C isotope values within the Marker Mudstone. More datasets from the Bowen and Galilee basins will be essential to decoupling these signals.