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[Display omitted] • Decarbonation of skarn deposits was more efficient than other carbon sources. • Skarn deposits may have contributed to the rise of CO 2 concentration at 145 Ma. • Skarn deposits may have influenced the ecological system in East Asia. Magmatic-hydrothermal systems transport metal, sulfur, and carbon from deep to shallow crust, providing materials to the society and potentially affecting Earth's long-term environment. The fluxes of elements and, accordingly the environmental effects, are ultimately functions of the time-integrated amounts and durations of magmatic-hydrothermal system. In this study, we calculate the duration of prograde metamorphism induced by fluid infiltration and amount of carbon released by skarn ore deposits. This study finds that skarn ore deposits can decarbonize CO 2 at an efficiency up to 1014 g/(y.km3), which is much higher than volcanism on different tectonic settings. The CO 2 flux of skarn deposits increased from late Jurassic to early Cretaceous and reached a maximum value to 7.8 Mt/y at J/K boundary. Our finding provided an previously unquantified but important outgassing source in the subduction zone. This result consistent with global warming pattern based on global sedimentary records. The maximum outgassing at J/K boundary may have important impact on global warming and perhaps mass extinction. [ABSTRACT FROM AUTHOR]

A continuous succession of marine and marginal-marine sediments of Rhaetian (Late Triassic) and Hettangian (Early Jurassic) age is present in the Larne Basin in Northern Ireland. These strata cover a period in Earth's history that included the emplacement of the Central Atlantic Magmatic Province (CAMP), the End Triassic Mass extinction (ETE), the Triassic–Jurassic Boundary (TJB), and major perturbations in the global carbon cycle. The Waterloo Bay section in the Larne Basin offers a well exposed sedimentary succession that spans this interval, and it has previously been proposed as a candidate GSSP for the base of the Jurassic System. A high-resolution δ13C org and organic carbon record for this locality is presented here, with these new data tied to previous stratigraphic descriptions, ammonite biostratigraphy, atmospheric carbon dioxide concentration (p CO 2) estimates, and nearby borehole sections that do not suffer from the thermal alteration that has affected the Waterloo Bay section. Several new exposures, unaffected by thermal metamorphism, are described that could provide future palynological and micropalaentological studies across this important boundary interval. Correlation is established between the well-studied sections in north Somerset and the likely position of the TJB in the Larne Basin, and records of soft sediment deformation, synsedimentary fault movement, relative sea-level change and their likely causes are discussed. [ABSTRACT FROM AUTHOR]

The Triassic/Jurassic boundary (TJB, 201.3 Ma) is characterized by profound turnovers in both marine and terrestrial biota, known as end-Triassic mass Extinction event (ETE). During this severe event, distinct negative carbon isotope excursions (CIEs) have been globally observed, and they were linked to volcanogenic emissions or methane release by dissociation of clathrates. The triggering factor of the negative CIEs was attributed to the emplacement of the Central Atlantic Magmatic Province (CAMP) and the break-up of the Pangea. Specifically, three significant carbon-cycle disruptions named Precursor, Initial and Main CIE have been recorded in several stratigraphic successions deposited in terrestrial and pelagic environments. We investigated the organic carbon isotope curve from the subtidal facies of the Mount Sparagio section (Sicily, Italy), which is a continuous peritidal succession representing an Upper Triassic to Lower Jurassic carbonate platform edging the south-western side of the Tethys Ocean. For the first time, we achieved a complete profile of organic carbon stable isotopic composition (δ13C org) during the end-Triassic mass Extinction event (ETE) in a carbonate shallow water environment. The δ13C org profile highlights the 3 negative excursions that characterized the Triassic/Jurassic boundary time interval in pelagic and deep-water successions. The documented CIEs correspond to significant biotic turnovers recognized along the Mt. Sparagio section, suggesting that also the Upper Triassic-Lower Jurassic carbonate platforms were affected by the onset of the Central Atlantic Magmatic Province. Furthermore, although the Mt. Sparagio section has been studied in detail for microfacies associations and it is well biostratigraphically constrained with shallow marine macro- and microfossils, only the documented δ13C org negative shifts allowed to correlate peritidal environments to pelagic successions, making the organic carbon curve (δ13C org) a powerful tool for global correlations. • A complete and reliable δ13C org profile across the Triassic/Jurassic boundary from a Tethyan carbonate platform, recognizing the 3 negative excursions that characterized the Triassic/Jurassic boundary in pelagic successions, that are in stratigraphic order the Precursor, the Initial, and the Main CIE. • Correspondence between the negative CIEs and the biotic turnovers testifies the influence of the CAMP on shallow water communities across the Triassic/Jurassic boundary. • Extinction trends consisting of decreasing in thickness and dimension of macrobenthic communities characterized the ETE of peritidal environments. • The δ13C org correlation between peritidal environments with pelagic successions confirms the organic carbon isotopes as a powerful tool for global correlations. [ABSTRACT FROM AUTHOR]

• δ34S and concentrations of multiple S-phases measured in Permian-Triassic section. • First δ34S measurement of organic sulfur compounds in P-T section. • Opposing δ34S DBT and δ34S TRIS excursions reflect fluctuating ocean redox. • Dynamic diagenetic sulfurisation resolved by δ34S DBT , but not bulk kerogen. • Negative δ34S DBT-TRIS values identify organic sulfurisation with greater bias against 34S than pyritization. Sulfur cycle fluxes implicated in the Permian-Triassic mass extinction have traditionally been studied by the sulfur phase abundances in sedimentary rocks and the stable sulfur isotopic value (δ34S) of seawater sulfate inferred from mineral sulfate analyses. This information might be complemented by studies of the reduced inorganic sulfur and organic sulfur produced following bacterial sulfate reduction. To explore this potential the δ34S and concentration analyses of total reduced inorganic sulfur (TRIS) and organic sulfur – separately in the forms of kerogen (Ker) and individual organosulfur compounds, specifically dibenzothiophenes (DBTs) – has been conducted on sediments across the Late Permian to Early Triassic marine type section of Meishan-1 (South China). The relatively steady δ34S profiles (e.g., < 5 ‰ variation) of all sulfur phases measured through much of the late Permian were indicative of a primary seawater sulfate control, but other biogeochemical modulators caused prominent δ34S fluctuations of TRIS and DBT adjacent to the extinction event. The late Triassic δ34S TRIS profile of Meishan-1 displayed a notable 34S enrichment (+15 ‰ increase) in bed 22–24 sediments concomitant with lower δ34S DBT values (−7 ‰ decrease), whereas co-eval δ34S KerS values remained relatively constant. The contrasting δ34S DBT and δ34S KerS data suggests the dynamic behavior of specific diagenetic sulfurisation processes may be resolved by the δ34S of discrete organic sulfur compounds (i.e., dibenzothiophenes, DBTs), but dissipated by the sulfurisation collective represented by the bulk kerogen fraction. The inverse isotopic trend observed between DBT and TRIS resulted in negative Δδ34S DBT-TRIS values identifying an organic sulfurisation pathway(s) with an unusual preference over pyrite (FeS 2) for the lighter stable sulfur isotope. A redox control of the δ34S DBTs and δ34S TRIS deviations in the bed 22–24 extinction interval was confirmed by coincident variation in TRIS/(TRIS + KerS) and pyrite (Py) and highly reactive (HR) iron ratios (Fe Py /Fe HR). The iron (Fe) speciation data indicated a transition to ferruginous conditions, ruling out Fe2+ limitation as a factor in the bias against 34S evident in DBT formation. The 34S depletion of the DBTs promoted by the ferruginous setting may arise from the rapid and irreversible reaction of organic substrates with labile sulfur anions (e.g. HS-) or be supported by an especially localised sediment–water depositional microenvironment. Our study highlights the potential of incorporating stable sulfur isotope analytics of reduced and organic sulfur phases, particularly of specific organic compounds, into a holistic assessment of the dynamic sulfur biochemical periods of Earth's past. [ABSTRACT FROM AUTHOR]

A continuous succession of marine and marginal-marine sediments of Rhaetian (Late Triassic) and Hettangian (Early Jurassic) age is present in the Larne Basin in Northern Ireland. These strata cover a period in Earth's history that included the emplacement of the Central Atlantic Magmatic Province (CAMP), the End Triassic Mass extinction (ETE), the Triassic–Jurassic Boundary (TJB), and major perturbations in the global carbon cycle. The Waterloo Bay section in the Larne Basin offers a well exposed sedimentary succession that spans this interval, and it has previously been proposed as a candidate GSSP for the base of the Jurassic System. A high-resolution δ13C org and organic carbon record for this locality is presented here, with these new data tied to previous stratigraphic descriptions, ammonite biostratigraphy, atmospheric carbon dioxide concentration (p CO 2) estimates, and nearby borehole sections that do not suffer from the thermal alteration that has affected the Waterloo Bay section. Several new exposures, unaffected by thermal metamorphism, are described that could provide future palynological and micropalaentological studies across this important boundary interval. Correlation is established between the well-studied sections in north Somerset and the likely position of the TJB in the Larne Basin, and records of soft sediment deformation, synsedimentary fault movement, relative sea-level change and their likely causes are discussed. [ABSTRACT FROM AUTHOR]

Drift of oxygen concentrations in the atmosphere was one of the main drivers of the evolution of vertebrates. The drop in oxygen concentrations at the Permian–Triassic (PT) boundary may have been the biggest challenge to vertebrates. This hypoxic condition forced theropods to lose certain genes to maximize their efficiency of oxygen usage. Recent studies show that omentin and insulin-sensitive glucose transporter 4 (GLUT4) are missing in the bird genome. Since these gene products play essential roles in maintaining insulin sensitivity, this loss forced theropods to become insulin resistant. Insulin resistance may have been the key to allowing theropods to become hyperathletic under hypoxic conditions and to outcompete mammals during the Triassic period. A second challenge was the gradual increase in oxygen concentrations during the late Jurassic, Cretaceous, and Tertiary periods when reactive oxygen species (ROS) leakage from mitochondria became a problem. Since the simplest solution was the expansion of body size, some theropods became bigger to reduce ROS leakage per volume. Another solution was the development of a constitutively active countermeasure against ROS. A recent study shows that Neoaves have constitutively active nuclear factor erythroid 2-related factor 2 (NRF2) due to deletion of the C-terminal part of the KEAP1 protein, thus allowing Neoaves to express antioxidant enzymes to overcome ROS leakage. Birds are well known to have long lifespans despite their high oxygen consumption. In mammals, high oxygen consumption induces reactive oxygen species (ROS) leakage and shortens the lifespan. By contrast, birds have high oxygen consumption without this ROS leakage, a phenomenon termed the 'Bird Paradox'. This paradox has attracted many investigators to speculate about the protective mechanisms at work to overcome this ROS leakage. I propose that theropods developed insulin resistance to adapt themselves to the low-oxygen environment of the Triassic period. This insulin resistance may have allowed theropods to maximize the efficiency of oxygen usage, almost outcompeting mammals during the Triassic period. Another epoch-making event was constitutive nuclear factor erythroid 2-related factor 2 (NRF2) activation induced by deletion of the C-terminal part of Kelch-like ECH-associated protein (KEAP1), preventing ROS leakage, just in Neoaves but not in the Palaeognathae, thus suggesting that this deletion may have occurred during the early Tertiary period. [ABSTRACT FROM AUTHOR]

We examined microbialites deposited near the Permian–Triassic boundary (PTB) at the Xiejiacao section of South China, including the size and morphology of pyrite framboids, carbonate carbon isotopes (δ13C carb), carbonate associated sulfur isotope (δ34S CAS), major and trace elements, and total organic carbon (TOC) concentrations. The microbialite unit is much thicker than the PTB beds in deeper water sections, providing more detailed geochemical records from that time. A prominent negative δ13C carb excursion was recognized in association with the second phase of the Permian–Triassic mass extinction (PTME), comparable with that of several other shallow platform facies sections worldwide. δ34S CAS stratigraphic profiles also show a negative excursion, with minimum values occurring slightly later than those of δ13C carb. The minimum peak can be calibrated to the middle part of the conodont Isarcicella staeschei Zone, corresponding to the second phase of PTME. Over all, the carbon and sulfur isotopes demonstrate a coupled long-term relationship with large negative excursions during the Permian–Triassic transition followed by gradual recovery in the lowest Triassic, represented an extremely low concentration of sulfate in the ocean during this period. In contrast, the C S isotopes are strongly decoupled within the microbialite unit, which could be linked with the oxygen-poor conditions and microbial sulfate reduction (MSR: Sulfate reducing microorganisms facilitated the precipitation of sulfide and carbonate, such as SO 4 2− + 2CH 2 O → H 2 S + 2HCO 3 −). The second phase of PTME was calibrated to the top of the microbialite unit, which was marked by the second δ13C carb -δ34S CAS negative excursions. The distinct marine oxygen deficiency was indicated by the small pyrite framboids, relatively high values of U EF (>1) and Ce/Ce* (>0.8). Combined with the previous biostratigraphic work, we propose that continuous volcanic activity induced intensified marine anoxia, leading to biotic mortality in the second phase of the PTME. Overall, our isotopic and geochemical data, integrated with results of previous studies, provided a new explanation for the carbon and sulfur isotope variations and additional evidences into the concurrent environmental changes during the Permian–Triassic transition. • Despite showing a coupled long-term relationship during the P–Tr transition, C-S isotopes were decoupled within microbialite. • Decoupled C-S isotopes within microbialite could be linked with oxygen-poor condition and active microbial sulfate reduction. • The 2nd phase of PTME is marked by δ13C carb and δ34S CAS negative excursions and marine anoxia induced by volcanic activity. [ABSTRACT FROM AUTHOR]

Marine ecosystem recovery after the latest Permian mass extinction (LPME) was a protracted process during the Early Triassic (∼252–247 Ma) owing to repeated climatic and environmental perturbations. Chemical weathering can supply nutrients to the ocean and may have played an important role in the Early Triassic carbon cycle and biological recovery. However, only limited geochemical records of chemical weathering during the Early Triassic have been presented to date, and the relationship between changes in weathering intensity and the slow recovery of marine ecosystems is effectively unknown. Here, we report magnesium (Mg) isotopic compositions of the siliciclastic components from shallow-marine carbonates in two well-studied Upper Permian-Lower Triassic sections in Iran and South China to track changes in chemical weathering intensity after the LPME. Both sections display a wide range of δ26Mg values (−2.09‰ to +1.10‰ at Zal, −2.30‰ to +0.33‰ at Zuodeng). We identified two distinct stages (I and II) in each section based on δ26Mg values and major elemental ratios. Variations of δ26Mg values in Stage I (Changhsingian to mid-Dienerian) are mainly controlled by mineralogical composition that can obscure weathering signals. By contrast, δ26Mg variations in Stage II (upper Dienerian to upper Spathian) are independent of lithology and inferred to reflect control by chemical weathering intensity. The trends in chemical weathering intensity within Stage II correspond to first-order variations in climate and carbon cycling. Marine ecosystem recovery during the Early Triassic may have been linked to recurrent episodes of intense chemical weathering caused by CO 2 degassing and climate warming. This study demonstrates the potential utility of the Mg isotopic compositions of the silicate fraction in marine carbonates as a proxy for chemical weathering intensity, laying the groundwork for general applications of this method to deep-time Earth systems. [ABSTRACT FROM AUTHOR]

Deep lithospheric processes associated with the formation of major orogens, including the removal of lower crust and underlying mantle through delamination associated with orogen building are poorly constrained. With a view to evaluate the potential link between deep geodynamic processes and magmatic events, we performed in situ zircon Hf-O-Li isotopic analyses of granitoids from the Eastern and Western Junggar, Altai and Beishan orogens, within the Central Asian Orogenic Belt (CAOB). The ε Hf (t) and δ18O values of magmatic zircons crystallized during 443 Ma and 252 Ma indicate diverse and heterogeneous magma sources. The corresponding δ7Li peaks at ~440 Ma and ~250 Ma, suggesting two distinct high-temperature magmatic events. Based on a comparison with global data, we argue that large-scale delamination formed through Gondwana and Pangaea supercontinent assembly, may have occurred at Ordovician to Silurian boundary (OSB) and Permian to Triassic boundary (PTB), which we term as super-delamination. The subsequent widespread magmatism and volcanism might have made significant impact on the Earth surface ecosystems, ultimately leading to the OSB and PTB mass extinction events. We propose super-delamination as a potential mechanism to explain the link between Earth's internal and external processes, thus providing novel insights into the trigger for mass extinction events. Unlabelled Image First zircon Hf-O-Li isotopic data set spanning the OSB and PTB. High-temperature magmatic events occurred at the OSB and PTB. Super-delamination was responsible for the OSB and PTB mass extinction. [ABSTRACT FROM AUTHOR]

A global-scale mass extinction event occurred in the Late Devonian, and its triggering mechanisms have remained a subject of controversy. The key to resolving this controversy lies in elucidating paleoenvironmental characteristics and their coupling relationship with the mass extinction. Marine evaporites serve as sensitive indicators that can be used for reconstructing the geochemical history of ancient oceans. In this study, we present a dual sulfur and oxygen isotopic dataset of marine anhydrites in the Lunatian gypsum deposit (Yunnan, China), and investigate its paleoenvironmental significance within the framework of the Late Devonian mass extinction. These anhydrites originate in arid and hot continental margin seas near convergent plate boundaries, forming as a result of the dehydration of marine gypsums during burial processes. Anhydrites exhibit a conspicuous positive anomaly in δ34S values (23.6–25.1‰, averaging 24.3‰), primarily attributed to bacteria-mediated sulfate reduction. The δ18O values of the Lunatian anhydrites (12.2–15.2‰, averaging 14.0‰) indicate a slightly higher oxygen isotope composition for Late Devonian seawater (8.7–11.7‰, averaging 10.5‰) compared to those of contemporary seawater (9.5–10.1‰). Such an oxygen isotopic characteristic for the Lunatian anhydrites is intricately associated with the chemical processes that occur during the diffusion of sulfides into the upper seawater. The anhydrite-forming evaporating system has a noticeable brine layering where the surface seawater is less dense than the deeper brine, and bacterial processes gradually increase δ34S in the deep brine. When the deep brine and surface seawater rapidly mix, it leads to a significant positive shift in the sulfur isotope composition of the resulting evaporites. Our sulfur and oxygen isotope data from Lunatian anhydrites validate the existence of an exceedingly anoxic marine environment during the Late Devonian, potentially serving as a pivotal factor in the mass extinction event. Schematic diagrams showing (a) the sedimentary environment and diagenetic processes of the Lunatian anhydrites, (b) three strong positive anomaly events of sulfur isotopes of global seawater since the Phanerozoic, and (c) plots of the measured δ34S vs. δ18O data for the Lunatian anhydrites. [Display omitted] • Late Devonian seawater shows a significant positive anomaly of sulfur isotope. • Bacterial reduction activity led to the elevated sulfur isotope levels of seawater. • Anoxia in paleoenvironment is a key driver of the Late Devonian mass extinction. • Sulfur isotope analysis of evaporites can swiftly identify Late Devonian strata. [ABSTRACT FROM AUTHOR]

The last phase of the end-Ordovician extinction event involved substantial sea-level changes. The Oslo/Asker District in Norway is a rare place where the deeper-water early Hirnantian fauna is succeeded by the equivalent deeper-water Edgewood-Cathay Fauna. Both faunas are highly diverse, with the same small-shelled brachiopods, Onniella, Leangella, and Eoplectodonta, dominating. They also share a large number of long-ranging and eurytopic genera. Taxa from contemporary shallower-water environments are rare. Near a third of the brachiopod genera in the Norwegian deeper-water early Hirnantian Fauna went extinct, including seven genera that survived into the Ordovician/Silurian boundary strata. Deeper-water early Hirnatian and Edgewood-Cathay collections are not well-known worldwide. Global quantitative samples from low latitudes, including the Norwegian samples, were compared against each other using NMDS (Non-metric Multidimensional Scaling) with the Bray-Curtis index. Qualitative samples used NMDS with the Raup-Crick index and Network Analysis. The Raup-Crick index sharply differentiated the early Hirnantian and Edgewood-Cathay faunas, possibly due to sensitivity to extinction and origination data. In contrast, the paleogeographic affinity between collections of the two faunas is pronounced using the Bray-Curtis index. Network Analysis also demonstrates regionality; the Edgewood-Cathay Fauna is especially heterogeneous. This contrasts with the shallower-water Hirnantia Fauna, which is more cosmopolitan. Quiet waters below the storm-wave base possibly hindered the spread of larvae, and anoxic plumes of water may have caused further barriers to the lateral spreading of the Edgewood-Cathay Fauna. As in Norway, long-ranging, eurytopic taxa were shared between the two faunas with few typical shallow-water taxa. • The end Ordovician Extinction event was two-phased and coincided with a glaciation in Gondwana • The shallow-water Hirnantian brachiopod fauna occurred globally with limited regional differentiation during the glaciation • The offshore, deeper, and diverse Hirnantian fauna are more heterogenic than previously thought and differ considerably geographically • This is even more pronounced in the post-glacial, offshore Edgewood-Cathay Fauna • Regionality played a prominent role in contrast to the more cosmopolitan shallow-water faunas. [ABSTRACT FROM AUTHOR]

The Hangenberg Event was one of the most significant mass extinctions accompanied by large-scale climate changes at the end of the Devonian period. Lack of precise and accurate geochronological constraints in the eastern Paleotethys has hindered a high-resolution global correlation of the Hangenberg Event. Here, we report the U–Pb dates of zircons from the bentonite samples intercalated with strata recording the Hangenberg Event in the Muhua region, Guizhou, South China, using both sensitive high-resolution ion microprobe (SHRIMP) and chemical abrasion - isotope dilution - thermal ionization mass spectrometry (CA-ID-TIMS) methods. A bentonite within the Hangenberg Event strata in the Muhua area was dated at 360.47 ± 0.68 Ma by CA-ID-TIMS, which is more precise than the results obtained by SHRIMP methods (361.5 ± 2.9 Ma and 359.8 ± 1.5 Ma). Thus, we propose that the Hangenberg Event took place at 360.47 ± 0.68 Ma in South China, based on the first precise CA-ID-TIMS zircon age from the Daposhang section. The age obtained from South China for the Devonian–Carboniferous boundary overlaps with that in Geologic Time Scale 2020, within the total uncertainties. • New U-Pb CA-ID-TIMS and SHRIMP zircon dates are reported from two bentonites around the Hangenberg Event in South China. • The Hangenberg Event occurred at 360.47 ± 0.68 Ma in the Daposhang section. • New age for Devonian–Carboniferous boundary overlaps with that in GTS 2020. [ABSTRACT FROM AUTHOR]

Current understanding of biodiversity changes in the Permian is presented, especially the consensus and disagreement on the tempo, duration, and pattern of end-Guadalupian and end-Permian mass extinctions. The end-Guadalupian mass extinction (EGME; i.e., pre-Lopingian crisis) is not as severe as previously thought. Moreover, the turnovers of major fossil groups occurred at different temporal levels, therefore the total duration of the end-Guadalupian mass extinction is relatively extended. By comparison, fossil records constrained with high-precision geochronology indicate that the end-Permian mass extinction (EPME) was a single-pulse event and happened geologically instantaneous. Variation of geochemical proxies preserved in the sedimentary records is important evidence in examining potential links between volcanisms and biodiversity changes. Some conventional and non-traditional geochemical proxy records in the Permian show abrupt changes across the Permian-Triassic boundary, reflecting climate change, ocean acidification and anoxia, carbon cycle perturbation, gaseous metal loading, and enhanced continental weathering. These, together with the stratigraphic coincidence between volcanic ashes and the end-Permian mass extinction horizon, point to large-scale volcanism as a potential trigger mechanism. To further define the nature of volcanism which was responsible for global change in biodiversity, main characteristics of four Permian large igneous provinces (LIPs; i.e., Tarim, Panjal, Emeishan, and Siberian) are compared, in terms of timing and tempo, spatial distribution and volume, and magma-wall rock interactions. The comparison indicates that volcanic fluxes (i.e., eruption rates) and gas productions are the key features distinguishing the Siberian Traps from other LIPs, which also are the primary factors in determining the LIP's potential of affecting Earth's surface system. We find that the Siberian Traps volcanism, especially the switch from dominantly extrusive eruptions to widespread sill intrusions, has the strongest potential for destructive impacts, and most likely is the ultimate trigger for profound environmental and biological changes in the latest Permian-earliest Triassic. The role of Palaeotethys subduction-related arc magmatism cannot be fully ruled out, given its temporal coincidence with the end-Permian mass extinction. As for the Emeishan LIP, medium volcanic flux and gas emission probably limited its killing potential, as evident from weak changes in geochemical proxies and biodiversity. Because of its long-lasting but episodic nature, the Early Permian magmatism (e.g., Tarim, and Panjal) may have played a positive role in affecting the contemporaneous environment, as implicated by coeval progressive climate warming, termination of the Late Palaeozoic Ice Age (LPIA), and flourishing of ecosystems. Unlabelled Image • Current understanding of biodiversity changes in the Permian is summarized. • Conventional and non-traditional geochemical proxy records in the Permian are assessed. • Main characteristics of four Permian large igneous provinces are compared. • The potential links between the Siberian Traps and EPME, and the Emeishan LIP and EGME, are examined. • In addition to the Siberian Traps, continental arc magmatism could also played an important role in the EPME. [ABSTRACT FROM AUTHOR]

Following the Middle Permian (Capitanian) mass extinction there was a global 'reef eclipse', and this event had an important role in the Paleozoic-Mesozoic transition of reef ecosystems. Furthermore, the recovery pattern of reef ecosystems in the Wuchiapingian of South China, before the radiation of Changhsingian reefs, is poorly understood. Here, we present a detailed sedimentological account of the Tieqiao section, South China, which records the only known Wuchiapingian reef setting from South China. Six reef growing phases were identified within six transgressive-regressive cycles. The cycles represent changes of deposition in a shallow basin to a subtidal outer platform setting, and the reefal build-ups are recorded in the shallowest part of the cycles above wave base in the euphotic zone. Our results show that the initial reef recovery started from the shallowing up part of the 1st cycle, within the Clarkina leveni conodont zone, which is two conodont zones earlier than previously recognized. In addition, even though metazoans, such as sponges, do become important in the development of the reef bodies, they are not a major component until later in the Wuchiapingian in the 5th and 6th transgressive-regressive cycles. This suggests a delayed recovery of metazoan reef ecosystems following the Middle Permian extinction. Furthermore, even though sponges do become abundant within the reefs, it is the presence and growth of the encrusters Archaeolithoporella and Tubiphytes and abundance of microbial micrites that play an important role in stabilizing the reef structures that form topographic highs. • We record six-phases of reef growth on the Laibin-Heshan platform. • Reefs recovered faster than previously reported after the end-Capitanian extinction. • Decoupled recovery of metazoan and non-metazoan reefs • Encrusters had a significant role in reef-building. [ABSTRACT FROM AUTHOR]

• Humans are not psychologically equipped for colonizing other planets. • Our species' track record on earth suggests we are not ready to colonize other planets. • Humanity will only be prepared to colonize Mars when it can live on earth sustainably. The idea of colonizing Mars as an opportunity to sustain the human species is a popular one currently. However, it is based on false premises and ignores the abundant evidence demonstrating that our species is not capable of living on any planet sustainably. Human psychology, and the problems associated with our species' biases and cognitive limitations, will follow us to any planet and replicate the same issues we face on earth. [ABSTRACT FROM AUTHOR]

The end-Ordovician mass extinction (EOME) is widely interpreted as consisting of two pulses associated with the onset and demise of the Gondwana glaciation, respectively, with the second pulse eradicating the distinctive, glacially related Hirnantian benthic biota (HBB). A global review of occurrence data of latest Ordovician benthic marine organisms reveals that virtually all warm-water benthic assemblages previously assigned to the HBB comprise two distinct and clearly postglacial faunas, both younger (middle and late Hirnantian, respectively) than the cool-water Hirnantia fauna (latest Katian to early Hirnantian). The newly recognised three Transitional Benthic Faunas (i.e., TBFs 1–3) can be closely tied to graptolite, conodont, and chitinozoan biozonations, the Hirnantian Isotope Carbon Excursion (HICE), and the glaciation, thereby providing an integrated, much higher-resolution timescale for understanding the tempo and nature of the EOME. At this finer resolution, we postulate a more profound impact of the first pulse of the EOME than hitherto envisaged, as evidenced by opportunistic expansion of the Hirnantia fauna globally and the complete absence of metazoan reefs in its immediate aftermath. We also argue, based on high-quality data from well-documented benthic groups in South China (i.e., brachiopods, tabulate and rugose corals, trilobites, and sponges), that the magnitude of the second pulse of the EOME caused by the deglaciation has been overestimated because the two postglacial faunas (i.e., TBFs 2–3) were part of a subsequent recovery phase of marine ecosystems rather than contributing to biodiversity decline. Thus, it is more plausible to reinterpret the EOME as a single-pulse, rapid event that was followed by a prolonged initial recovery intermittently impeded by climatic shocks through the Hirnantian, prior to the onset of a progressive reestablishment of marine ecosystems during the early Silurian (Rhuddanian and Aeronian) associated with an overall amelioration of climatic conditions. [ABSTRACT FROM AUTHOR]

During the End-Permian mass extinction event (EPME) there is extensive evidence for depletion of oxygen in the marine realm. Atmospheric models based upon biogeochemical cycling predict a comparable decline leading up to this event and have been postulated as a possible driver for marine depletion. However, these models contrast with broadly contemporaneous empirical evidence from charcoal in coals. New charcoal data from the temporally well-constrained late Permian Xuanwei Formation coals of eastern Yunnan Province, China, deposited just prior to the onset of the Permian-Triassic Transitional Beds, supports the coarser analysis and further challenges these biogeochemical models. Inertinite group macerals, comprising fusinite, semifusinite, macrinite, inertodetrinite, secretinite, all funginite with elevated reflectance, and some micrinite, are proxies for wildfire activity, and indicate abundant evidence for this phenomenon in the latest Permian and preclude low levels of atmospheric oxygen concentration coevally. Henceforward, we will employ the term 'inertinite group macerals sensu amplo' to refer to just these precise macerals, though these encompass what are the overwhelming preponderance of inertinites in most coals. Both inertinite abundance and reflectance indicate an increase in fire activity and intensity towards the End-Permian faunal crisis. Quantitatively, these inertinite data indicate atmospheric oxygen concentration was high and at the close of the Paleozoic was probably elevated to levels well above those of the present-day. The elevated fire activity at this time may have functioned as a causal link to explain some localized oxygen depletion in the marine realm as a result of post-fire increased run-off and erosion. However, globally depressed atmospheric oxygen concentration at the End-Permian was not a driver of extensive marine anoxia at that time. • The inertinite content and reflectance in final coals of the Paleozoic are increasing upwards. • Wildfires were becoming more frequent and intense at the onset of the End Permian Mass Extinction event. • It is highly probable that atmospheric oxygen levels remained high. • Fires could provide a linking mechanism between events in the terrestrial and marine realm. [ABSTRACT FROM AUTHOR]

Abstract We have conducted non-equilibrium molecular-dynamics (NEMD) simulation to show that externally-applied magnetic fields, including their reversals in direction, have important effects on gas-release dynamics from methane hydrates. In particular, we apply fluctuation-dissipation analysis in the guise of Onsager's hypothesis to study hydrate kinetics at lower applied-field intensities, including temporary hydrate destabilisation in the wake of field-polarity switch; we scale down to the lowest practicable field intensities, of the order of 1 T. We conjecture, that these NEMD-based findings, particularly those involving polarity switch, may have ramifications for superchron-related Earth's magnetic-field polarity swaps affecting methane release into the geosphere, although a good deal of further work would be needed to provide a more definitive causal link. Graphical abstract Unlabelled Image Highlights • Gas hydrate destabilisation is theorised via Earth's magnetic field change. • Evidence for this hypothesis is presented from a NEMD simulation study. • Through the 'Belfast hypothesis', we introduce a tentative link to mass extinction events. [ABSTRACT FROM AUTHOR]

Abstract Global warming is inferred to have been one of the main causes of the Permian-Triassic (P-Tr) boundary mass extinction. Although a strong temperature rise in tropical sea-surface temperatures during the latest Permian has been documented, coeval climate changes in terrestrial sections are less well-known. Here, we analyzed multiple weathering indexes (including CIA, CIW, and PIA) for two terrestrial sections in North China (Shichuanhe and Yima), all of which show a major excursion toward higher values (greater weathering intensity) around the end-Permian plant extinction (EPPE). At Shichuanhe, the CIA (chemical index of alteration) increases from 70 to 75 over the interval of 11–36 m, which straddles the EPPE at 33 m, and then decreases from 75 to 71 in the overlying strata. At Yima, CIA increases from 63 to 79 over the interval of 57–68 m, extending up to the EPPE at 68 m, and then gradually decreases from 78 to 72 in the overlying strata. These results imply a strong warming event coupled with intense chemical weathering in soil environments leading up to the end-Permian plant extinction. The decline in CIA values following the EPPE may reflect loss of weathered soils through physical erosion rather than climatic cooling. Estimation of atmospheric temperatures from the CIA data indicate rapid rises at Shichuanhe (from ~11.6 °C to 16.5 °C) and Yima (from 9.3 °C to 18.4 °C) during the end-Permian crisis. The findings in this study are consistent with the hypothesis that a sharp temperature rise caused the extinction of terrestrial organisms during the end-Permian crisis. Highlights • Chemical weathering indices (CIA, CIW, PIA) were applied to two terrestrial P-Tr boundary sections of the North China Craton. • All indices show large increases during the end-Permian extinction (EPE), reflecting a shift to warmer climatic conditions. • CIA-based temperature estimates imply warmings of ~5 °C at Shichuanhe and ~9 °C at Yima during the P-Tr transition. • Post-EPE declines in CIA do not indicate reduced chemical weathering intensities but exposure of less weathered bedrock. • Our results show the utility of chemical weathering studies of fine-grained terrestrial sediments during major bioevents. [ABSTRACT FROM AUTHOR]

Abstract We report small microbialites from the calcareous mudstone slightly above the Permian–Triassic boundary (PTB) in the Tieshikou section, southern Jiangxi Province, South China. The newly found microbialite is a bowl-like structure, which contrasts with the surrounding calcareous mudstone. The small microbialite is composed of columnar forms and fan-shaped structures. Mini-columnar structures resemble mini stromatolites. In plane view, most branches are patchy or strip-shaped, with clotted structures, resembling that of a thrombolite. Fan-shaped cement precipitates are comprised of multiple crystal fans that have a radiating texture and that show distinct growth laminae. The radiating fabrics are represented by rod-shaped filaments under SEM, which are interpreted as calcified trichomes/filaments. Prominent micropores occur within the rods, and they may be the plane views of multiple sheaths of the false branching zone of trichomes. Thus, both the columnar forms and radiating fans are probably microbial in origin. Moreover, three types of nano-sized structures: intraparticle micropores, fibrous biofilms, and filamentous sheaths are also pronounced in both the columnar structures and cement fans of the Tieshikou microbialite, all suggestive of biogenicity. These well-preserved fibrous biofilms probably represent calcified extracellular polymeric substances (EPS), and linear sheaths are interpreted as the traces of bacterial activities during the precipitation of dolomite crystals. The Tieshikou microbialite therefore shares similar biogenetic mechanisms with other PTB microbialites. The combination of the absence of pyrite framboids, slightly negative carbon isotope values, and an association with abundant ammonoids, bivalves, and gastropods indicates oxic conditions during the growth of the Tieshikou microbialite. Moreover, the nodular preservational state resembles widely distributed nodular mudstones or muddy limestones of the Lower Triassic successions worldwide. This implies that nodular mudstone or argillaceous limestones may also have been deposited in microbe-rich environments, in which terrigenous supply was abundant. Highlights • Small microbialites from mudstone near Permian–Triassic boundary • Laminated columnar structures and fibrous cement fans • Rod-shaped objects with micropores represent false branching zone of trichomes. • Four types of nano-sized structures suggestive of biosignatures • Microbial proliferation in limestone nodules in the post-extinction siliciclastic setting [ABSTRACT FROM AUTHOR]

Abstract The Permian-Triassic boundary (PTB) at ~252 Ma coincided with the largest mass extinction of the Phanerozoic. Previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records, with little attention to date given to the phytoplankton that form the base of the marine trophic web. Although the fossil record of Permian-Triassic phytoplankton is relatively poor owing to preservational factors, sufficient material is now available to evaluate secular changes in acritarch communities through the mass extinction interval. In this contribution, we evaluate diversity and abundance changes among 8 genera and 25 species of acritarchs, including large-spherical, small-spherical, long-spined, and short-spined forms ranging from the Upper Permian Clarkina yini to the Lower Triassic Isarcicella isarcica zones in eight sections representing different sedimentary facies of the South China Craton. Acritarchs declined sharply from the latest Permian (C. meishanensis Zone) to the earliest Triassic (I. staeschei Zone), with extinctions and abundance changes concentrated at two horizons, the first in the latest Permian C. meishanensis Zone (Bed 25 at Meishan D) and the second in the earliest Triassic I. staeschei Zone (Bed 28 at Meishan D), mirroring the pattern of mortality among marine invertebrates. Differences in the nature and intensity of these two extinction episodes (the second having a relatively larger effect on acritarch community composition) suggest that these events may have resulted from different types of environmental perturbations. Highlights • Eight genera and twenty-five species (belong to four forms) of acritarchs were record from eight sections in South China. • Two extinction events for the acritarchs across the Permian-Triassic transition. • The second event were more severe than the first one. This may result from the different causes for the two events. [ABSTRACT FROM AUTHOR]

Abstract The widespread development of microbialites in shallow areas of the Tethys Ocean at the start of the Early Triassic reflects the deterioration of marine ecosystems in the aftermath of the extinction that marked the demise of the majority of Palaeozoic marine faunas. Here we present a study of the evolving microbialite forms and associated biotic assemblages of this pioneering microbialite interval from exposures at Chongyang, Hubei Province, China. This research provides a perspective on the effects of eustatic transgression on marine ecosystems as water depths increased at the beginning of Mesozoic, through the study of the changing forms, microfacies and distribution of microbialites. Microbialite forms evolved from stratiform stromatolites to a sequence of tabular thrombolites (with an intercalated layer of columnar stromatolites), followed by domical thrombolites that were overlain, in turn, by oolites. The stratiform stromatolites contain poorly preserved remains of calcified cyanobacteria, but microfossils with chambered structure can also be seen. Metazoan fossils increased from the base of the overlying tabular thrombolite, reflecting increasing biodiversity with deepening of seawater. The occurrence of columnar stromatolites within the tabular thrombolite may indicate a temporary sea-level shallowing. Foraminiferans and other metazoans are absent within the columnar stromatolites, but spherical cyanobacterial remains are extremely abundant. Well-preserved calcified cyanobacteria may reflect an absence of metazoan predation and/or carbonate supersaturation of seawater. As water deepened, domical thrombolites developed and the more complex seafloor relief created varied niches between and within the domes that harboured more ecologically diverse communities. During the process of transgression within the microbialite interval, carbon isotopes exhibit a negative relationship with biodiversity, implying that upwelling of anoxic deep-ocean water, if associated with the negative excursion of carbon isotope values, did not inhibit the diversification of benthic organisms at least on shallow carbonate platforms in the period immediately after the end-Permian mass extinction. Highlights • Stromatolites changed into thrombolites during Early Triassic transgression. • Moderate sea-level rise favors the diversification of marine animals. • Enhanced metazoan predation has a marked impact on the fabric of microbialites. • Carbon isotopic value exhibits negative correlation with the depth of sea water. [ABSTRACT FROM AUTHOR]

Abstract Mercury (Hg) enrichment in stratigraphic successions is now widely used as a proxy for volcanic inputs, often for the purpose of documenting a relationship between large igneous province (LIP) magmatism and ecosystem perturbations. Earlier studies of Hg in Ordovician/Silurian boundary (OSB) sections in South China and Laurentia identified transient spikes in Hg/TOC ratios, on the basis of which a link between volcanism and the Late Ordovician mass extinction (LOME) was claimed. However, Hg enrichments must be tested based on normalization to their main host phase, and Hg/TOC is a suitable proxy only if Hg is mainly complexed by organic matter in the sediment. Here, we demonstrate that Hg in three OSB sections in South China (Qiliao, Yanzhi, and Jiaoye) is overwhelmingly associated with pyrite, as shown by r (Hg–TS) > 0.9 (versus r (Hg–TOC) < 0.1) and by EDS elemental mapping. This association requires that Hg concentrations be normalized to pyrite content as proxied by total sulfur [TS], rather than to total organic carbon [TOC]. The resulting Hg/TS profiles show no significant enrichments at any level within the Upper Ordovician–lower Silurian of the study sections. Also, mercury isotope data show constant mass-independent fractionation (Δ 199 Hg) values (+0.11 ± 0.03‰) that are inconsistent with volcanic inputs. We therefore infer that previous reports of Hg enrichments in OSB sections were due to the presence of Hg-rich sulfides, and that Hg data from both the present and earlier studies provide no evidence of any volcanic influences on the LOME. The results of the present study highlight the need for caution in applying the Hg proxy for volcanic inputs and the importance of evaluating the main host phase of Hg in paleo-marine sediments. Highlights • First report of pyrite (instead of organic matter) as major host for Hg in Ordovician–Silurian boundary strata. • Absence of Hg/TS (mercury/total sulfur) spikes in three Ordovician–Silurian boundary sections in South China. • Mercury isotope data show constant MIF (Δ 199 Hg) values that are inconsistent with volcanic inputs. • Evidence against published claims of volcanic Hg inputs and volcanic influences on Late Ordovician Mass Extinction. • Demonstrates need to identify and normalize Hg to its main host phase in marine sediments when used as a volcanic proxy. [ABSTRACT FROM AUTHOR]

The Changhsingian stage preceding the end-Permian mass extinction (EPME) was not only a significant period of global climatic–environmental change, but also an important period of widespread formation of organic-rich deposits. However, no consensus has been reached regarding the direct cause of mortality of the EPME and the main forcing mechanisms responsible for organic matter (OM) enrichment. As such, we conducted a petrological and geochemical study of the organic-rich deposits in the Talung Formation (Changqiao section), Lower Yangtze region, South China. Results show that the Lower Yangtze region was dominated by climatic fluctuations between cool–arid and warm–humid conditions during most of the Changhsingian. A paleoenvironmental reconstruction suggests that the early–middle Changhsingian was characterized by long-term anoxic to intermittent euxinic conditions, seasonal coastal upwelling, and weak basinal restriction. By contrast, the late Changhsingian was characterized by intensified euxinic conditions, weakened upwelling, and enhanced basinal restriction. The entire Changhsingian was also marked by high productivity, low detrital input, weak hydrodynamic conditions, and limited hydrothermal and volcanic activity. Quantitative analysis shows that the upwelling-driven high productivity and intensified anoxia–euxinia caused the OM enrichment, while other factors such as climate-controlled detrital inputs were less important. Two stages of climatic–oceanic dynamics were identified that reflect the relative roles and contributions of these different controlling factors. The paleoenvironmental reconstruction also indicates that euxinic conditions formed slightly earlier in deep waters, which may have been due to the combined effects of the persistent high productivity, weaker oceanic circulation, and intensified basinal restriction. Shoaling of these euxinic waters, combined with enhanced volcanism, climate warming, and ocean acidification occurred during the Permian–Triassic transition interval, could have contributed to the main stage of the EPME. • The deep-water euxinic conditions occurred slightly earlier than the shallow waters. • Both high productivity and anoxia-euxinia contributes the most to the OM enrichment. • Upwelling, rather than other factors, plays a major role in the OM accumulation. • Shoaling of anoxic/euxinic waters could contribute to the main pulse of the EPME. [ABSTRACT FROM AUTHOR]

The end Permian to Middle Triassic interval (∼252–242 Ma) witnessed the largest marine mass extinction and the most delayed recovery in the Phanerozoic. The nature and mechanism of these biotic and environmental changes remain unclear. This special issue focuses on the Triassic marine sediments in South China, which provide unique documentation of the collapse and recovery of marine ecosystems. Six papers focus on biotic changes and their ecological significance in Early and Middle Triassic times, documenting evidence from bivalves, marine reptiles, stromatolites, hybodontid teeth, vertebrate coprolites, and other putative fossils. Two papers study conodont biostratigraphy across the Permian-Triassic boundary (PTB) and Induan-Olenekian boundary. Two papers reconstruct the palaeoenvironments of the Early Triassic Chaohu Fauna and Middle Triassic Luoping Biota. Two further papers present new marine δ13C records and biomarker data and link them to volcanic eruptions in Early Triassic times. These new findings are important for understanding the co-evolution between biotic and environmental changes in the aftermath of Permian-Triassic boundary mass extinction. [ABSTRACT FROM AUTHOR]

Abstract Late Permian mass extinction (LPME) research has focused primarily on Tethyan sections because it is believed that these successions are more complete than those from other localities, and provide a more comprehensive record of the largest, most devastating extinction event in Earth history. The Kisejin section, a previously undocumented mid-Tethyan, Upper Permian-Lower Triassic succession located in the Central-Iran Plate. The Kisejin section contains a continuous Permian-Triassic sequence with only small breaks in sedimentation and was examined in order to determine sedimentologic, biostratigraphic, and carbon isotopic trends across the Permian-Triassic transition. Abnormal (anachronistic) carbonates developed in the study area following the LPME, and include microbialites, edgewise conglomerates, sparitic microspheres, and microbially-coated grains; microbialites occur as thrombolites, stromatolites, and as agglutinated forms. Renalcis -type calcimicrobes are documented for the first time from Permian-Triassic boundary microbialites (PTBMs) of Iran. Coated grains fall into two groups, and include pre-PTBM ooids, which are dense and cloudy, and possibly microbial in origin, and post-PTBM cortoids with destructive and constructive micrite envelopes. Latest Permian conodonts (H. praeparvus, M. ultima), coupled with carbon isotopic values, place the Permian-Triassic boundary within the lowermost thrombolite unit, about 2.1 m above the boundary between the Nessen Formation and the Elika Formation, and indicate that microbialite growth began during the latest Permian. Our study of this previously unknown section shows that, unlike other well-known PTB sections from Iran, the microbialite pattern is complicated, and is more similar to PTBM successions from Turkey. In addition, we note a similarity between the unusual facies of the Kisejin section and those of eastern Tethyan sections from China (i.e. sparry microspheres and Renalcis -type calcimicrobes); these unusual facies have not been previously reported from other well-known Iranian sections, including Julfa and Abadeh, which are thick and have been extensively studied. Highlights • First sedimentologic, biostratigraphic, C-Isotope study of the P-T boundary at the Kisejin section • Anachronistic facies and C-Isotope excursions near the Permian-Triassic boundary in the mid-Tethys • First documented occurrence of sparitic microspheres and Renalcis -type calcimicrobes from PTB sediments of Iran [ABSTRACT FROM AUTHOR]

Abstract The geological persistence of biotic assemblages and their reorganization or destruction by mass extinctions are key features of long-term macroevolutionary and macroecological patterns in the fossil record. These events affected biotic history disproportionately and left permanent imprints on global biodiversity. Here we hypothesize that the geological persistence and incumbency of paleocommunities and taxa are maintained by patterns of biotic interactions that favour the ecological persistence and stable coexistence of interacting species. Equally complex communities produced by alternative macroevolutionary histories, and hence of different functional structure, may support less stable species coexistence, and are therefore less persistent. However, alternative communities with the same functional structure as a persistent paleocommunity, but variable clade richnesses, tend to be as or more stable than observed palecommunities, thus demonstrating that geological persistence is not the result of constrained patterns, or ecological locking. Numerically modeled food webs for seven tetrapod-dominated paleocommunities spanning the traditionally-recognized Permian-Triassic boundary in the Karoo Basin of South Africa, show that incumbency before the Permian-Triassic mass extinction was maintained by a dynamically stable, community-level system of biotic interactions, thereby supporting the hypothesis. The system's structure was lost through successive extinction pulses, and replaced initially by a rich but geologically ephemeral Early Triassic fauna, which itself was replaced by a novel Middle Triassic community with renewed incumbency. The loss of persistence and incumbency, therefore, did not result simply from the extinction of species; instead the largest declines were accompanied by the addition of new species to the system in the earliest aftermath of the event. We therefore further hypothesize that ecological reorganization and evolutionary innovation in the wake of mass extinctions play key roles in the destruction of highly stable, preexisting systems of biotic interaction. In the case of the Karoo Basin paleocommunities, we estimate that a return to stable interactions, and thus incumbency, was achieved in approximately 4–17 Ma. [ABSTRACT FROM AUTHOR]

Abstract The stratigraphic section at Bethulie, South Africa, is reported to contain the vertebrate-defined Permian–Triassic boundary succession in the terrestrial realm of the Karoo Basin. The model of vertebrate turnover, from the Daptocephalus to Lystrosaurus Assemblage Zones, tightly constrains the boundary sequence to a short stratigraphic interval where siltstone color begins to change from greenish gray to grayish red, the latter color interpreted to be a consequence of aridification. The biological response to this facies change has been termed "the Great Dying," and the sedimentary rocks that are preserved are ascribed to a playa lake depositional setting. This drying event is believed to be contemporaneous across the basin, although previous studies have shown that the facies appears at multiple horizons at all purported Permian–Triassic boundary sections in the basin. Here, we report results of a multidisciplinary effort to characterize the vertebrate assemblage-zone boundary interval exposed at Bethulie using the lithostratigraphic, petrographic, geochemical, and rock magnetic properties of these rocks. In this stratigraphic succession at its "type" location, the 3-m thick assemblage-zone boundary interval is distinguished by thick beds of greenish-gray, greenish-gray mottled to grayish-red, and grayish-red siltstone, all of which change facies characteristics laterally along strike. Specifically, about 220 m to the southeast of the type section, sediments lose all grayish-red coloration, whereas the interval becomes laminated to the northwest. Petrographically, most siltstone is homogenized, with few burrows and small-scale cross-bedded structures with mudchips. There are no gypsiferous or calcareous beds, nor is there evidence of disturbed structures, authigenic breccia, or pseudomorphs associated with dessication. Mean elemental composition of both greenish-gray and grayish-red beds are indistinguishable, geochemically, and both are dominated by illite and chlorite clay species. Mössbauer spectroscopic analyses reveal the presence of a small concentration of fine-grained hematite in the grayish-red siltstone, with its presence mainly found as coatings on clay minerals. Rock magnetic experiments (isothermal remanent magnetization, acquisition and backfield DC demagnetization; magnetic hysteresis; susceptibility vs. temperature) yield data that demonstrate no essential differences between the different colored siltstones. And, both lithologies host mangnetite/maghematite and hematite. Our results do not support the previous interpretation that this inferred Permian–Triassic boundary interval represents the onset of playa lake deposits under conditions of aridification. Rather, our evidence supports the existence of a "wet" landscape at what is considered the Daptocephalus / Lystrosaurus assemblage-zone boundary. [ABSTRACT FROM AUTHOR]

Abstract This study evaluates the utility of sedimentary mercury (Hg) contents as a proxy for fingerprinting ancient massive volcanism, which is often associated with biogeochemical perturbations. Herein we present new Hg geochemical data from anoxic marine basins across the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma) as a test of the complex Hg cycle. The T-OAE was likely initiated by the main eruptive phase of the Karoo–Ferrar large igneous province, which caused a subsequent cascade of environmental perturbations and resulting mass extinction. At present the leading interpretation of sedimentary Hg anomalies has been volcanogenic outgassing as the primary source. Our study and compilation results suggest, however, that Hg/TOC anomalies were restricted to shallow-water, and/or proximal environments, while deep-water, more distal depositional settings document no significant Hg-related anomalies. Furthermore, asynchronous stratigraphic deviations in Hg enrichments favor terrestrially sourced materials and local redox variability, rather than direct volcanogenic emissions, as a primary control mechanism. Additionally, Hg isotope signatures from our only study site documenting an Hg anomaly are also consistent with a terrestrial Hg origin during the T-OAE. Therefore, our results suggest that Hg anomalies in the geological record need to be re-evaluated as a "smoking gun" proxy that only infers volcanogenic inputs. Highlights • Mercury concentration and isotopes from anoxic basins across the Toarcian OAE. • Compilation shows mercury anomalies are observed near landmasses. • Compilation suggests that Hg is dominantly delivered via terrestrial sources. • Mercury isotopes from one section agree with terrestrial source delivering Hg. • Sedimentary Hg anomalies are not a direct proxy for past volcanism. [ABSTRACT FROM AUTHOR]

Abstract Although expanded ocean anoxia has long been believed to be a direct killing mechanism causing mortality of organisms during the Permian-Triassic mass extinction, little has been published on the extent and timing of this anoxia in Gondwana. The Guryul Ravine section in Kashmir, northern India, is a classic Permian–Triassic boundary (PTB) section containing high-quality marine sedimentary and fossil records, and thus provides a unique opportunity to study the redox conditions associated with the biotic crisis in the Gondwana region. Here, high-resolution biotic and redox data were generated from Kashmir to achieve an improved understanding of the nature of environmental stresses associated with the Earth's largest biocatastrophe. Our study, which evaluates pyrite framboid size and morphology, reveals two pronounced stages of oceanic oxygen deficiency, in the assigned latest Permian Hindeodus praeparvus – Clarkina meishanensis Zone and the earliest Triassic Isarcicella staeschei Zone. Updated marine invertebrate fossil records show three sharp species richness declines at Guryul Ravine. The first decline occurred within uppermost Permian storm beds and is interpreted to represent a facies control, in which a storm-agitated environment was inhospitable for benthos. The latter two biotic declines coincided with two marine anoxic events, as documented by pyrite framboid size distributions. The same two anoxic events are also recognized from PTB beds in the adjacent, relatively shallower Barus Spur section in Kashmir, in which newly obtained faunal data help to constrain placement of the PTB. The present study represents a new report of the two-stage pattern of oceanic anoxia during the Permian–Triassic transition. We propose that the two anoxic events at Guryul Ravine correlate precisely with anoxic events in the Meishan GSSP and some sections in South China, suggesting that this event sequence might have been characteristic of the Permian–Triassic transition in some specific geological settings. The close relationship between oxygen depletion and species richness decline suggests that the former were an important contributor to the latter. In addition, we find that many framboids exhibit surface oxidation, reducing their overall size. However, our statistical analysis suggests that the mean oxidation-related reduction in size is <2.2%, thus having little effect on redox interpretations based on pyrite framboid sizes. Our results demonstrate that, unlike many geochemical proxies, the pyrite framboid technique is still valid for redox interpretations of weathered samples. Graphical abstract Unlabelled Image Highlights • Five redox stages were recognized in Guryul Ravine section. • Two stages of oceanic oxygen deficiency during P-Tr transition were revealed in Guryul Ravine and Barus Spur section. • Three sharp biodiversity declines were found at Guryul Ravine, the latter two coincided with anoxic events. • Oxidation-induced size reduction has little effects on the redox interpretation of pyrite framboids. [ABSTRACT FROM AUTHOR]

Abstract The Late Ordovician mass extinction (LOME) was a severe biocrisis during the Phanerozoic and in this extinction, trilobites, brachiopods, mollusks, graptolites, conodonts and other types suffered severe mortality, and 85% of marine invertebrate species were eliminated. The potential cause of this mass extinction remains unclear, although glaciation and marine anoxia have received the greatest attention. Herein, we present findings on pyrite morphology, pyritic sulfur isotopic composition and total organic carbon content (TOC) to analyze the evolution of redox conditions across the Ordovician-Silurian boundary in the Yangtze area of South China. Our results show that long-term euxinic conditions interrupted by episodic dysoxic/oxic events occurred from the upper Katian stage to the lower Rhuddanian stage. The two extinction pulses of LOME were coincident with euxinic conditions, suggesting that marine euxinia may have been the main cause of this mass extinction event. Graphical abstract Image 1 Highlights • Pyrite morphology provides new evidence for redox conditions across O-S boundary. • Long-term euxinic conditions intercalated with dysoxic-oxic conditions across O-S boundary. • Euxinia was a kill mechanism for the Late Ordovician Mass Extinction. [ABSTRACT FROM AUTHOR]

Abstract Previous studies suggested that anoxia was a causal factor in the end-Permian mass extinction (EPME), marked by abrupt enrichment of pyrite framboids in the post-EPME microbialites of the earliest Triassic on shallow platforms, and that this dysoxic–anoxic phase followed a time of well‑oxygenated seafloors. Here, we report persistent dysoxia throughout the latest Permian and euxinia just before the EPME, based on a new redox history reconstruction study using framboidal pyrite size distribution as well as sulfur isotopic compositions of pyrites, from the Taiping section on the Pingguo Platform in the Nanpanjiang Basin in China. Further, we show that the EPME was followed here by rapid oxygenation, not an anoxic incursion. This revised redox history might be an unusual localized phenomenon when compared to other platforms, or it could be solid sedimentary evidence for redox oscillations outside the bioclast-enriched photic zone, which broadens our understanding of terrestrial–marine ecosystem interactions before and during the EPME. Highlights • Pyrite framboid size distributions and δ34S pyrite suggest low oxygen levels throughout the EPME in the Taiping section; • Shallow marine euxinia occurred prior to the EPME on the Pingguo Platform; • Large-sized framboidal pyrites in the basal Permian-Triassic microbialite indicate an earliest Triassic oxygenation event; • A potential terrestrial input controlled fractionation of δ34S pyrite was proposed to interpret the pre-EPME heavy δ34S pyrite ; • Shallow dysoxia of the Nanpangjiang Basin might have invaded from intra shelf basins rather than the Panthalassic Ocean. [ABSTRACT FROM AUTHOR]

Abstract We describe an outcrop of the Cretaceous–Paleogene (K–Pg) boundary exposed due to construction near New Albany, Union County, Mississippi. It consists of the Owl Creek Formation and overlying Clayton Formation. The Owl Creek Formation is rich in the ammonites Discoscaphites iris and Eubaculites carinatus , which, along with biostratigraphically important dinoflagellate cysts and calcareous nannofossils, indicate deposition occurred within the last 1 million years, most likely last 500 kyrs, of the Cretaceous. The base of the overlying Clayton Formation marks the K–Pg boundary, and consists of a 15–30 cm thick muddy, poorly sorted quartz sand containing abundant spherules representing ejecta derived from the Chicxulub impact event. Impact spherules range in size from 0.5 mm to 1 mm in diameter and are hollow and well preserved, with details such as smaller vesicular spherules enclosed within. The spherules are altered to clay minerals such as smectite and are typical of those found at K–Pg boundary sites in the Gulf of Mexico and beyond. Spherules are scattered throughout the bed, and surface counts suggest an average of 4 spherules per cm2. Macrofossils within the spherule bed represent a rich fauna of ammonites, benthic molluscs (bivalves and gastropods), echinoids, as well as crabs and sharks. Macrofossil preservation ranges from whole to fragmentary, with most fossils preserved as internal moulds. The infill of the fossils is lithologically identical to the matrix of the spherule bed, including impact ejecta preserved within phragmocones and body chambers of ammonites, and differs from the underlying Owl Creek Formation. This suggests that the animals were either alive or loosely scattered on the sea floor at the time of deposition. Grain size changes indicate multiple events were responsible for deposition, and together with taphonomic evidence are consistent with dynamic high energy post-impact processes. Later sea level change during the Paleocene is responsible for a sharp contact at the top of the spherule bed. Geochemical evidence from the Owl Creek and Clayton Formations at this locality indicate numerous local paleoenvironmental changes affected the Mississippi Embayment at the time of the K–Pg boundary and mass extinction event. Highlights • Describes new outcrops containing the Cretaceous–Paleogene (K–Pg) boundary from Union County, Mississippi. • The fossiliferous Owl Creek Formation contains ammonites and diverse benthic molluscan fauna. • Biostratigraphic correlation by macro and microfossils is consistent with deposition during the latest Maastrichtian. • A 15–30 cm-thick event bed with macrofossils and impact spherules occurs above the K–Pg boundary. • Spherule bed was emplaced rapidly by multiple processes following the Chicxulub impact event. [ABSTRACT FROM AUTHOR]

Abstract A new assemblage of calcareous algae and microproblematica is reported from the Changxing Formation at the Liangfengya section in Chongqing, South China. This assemblage comprises eighteen species of seven genera, including three genera of gymnocodiaceaens (Gymnocodium , Permocalculus , and Tauridium), three genera of dasycladaleans (Epimastopora , Macroporella , and Mizzia), and one genus of microproblematica (Pseudovermiporella). A new algal species, Tauridium elongatum nov. sp., is described. Quantitative analysis indicates that the last occurrences of 22% of the species (4 out of 18) fall into a 52 cm thick interval of the uppermost Changhsingian. No calcareous algae are found in the Permian-Triassic boundary (P-T boundary) beds and the overlying Feixianguan Formation. Four out of 10 species have a stratigraphic abundance greater than 10% and all vanished in the uppermost Changhsingian. An abrupt extinction for calcareous algae occurred in the Clarkina yini conodont Zone. [ABSTRACT FROM AUTHOR]

A new δ 13 C carb curve was obtained from an expanded peritidal succession in western Sicily and was used to investigate the relationships between isotopic signatures and biological events on carbonate platforms across the Triassic-Jurassic boundary (TJB). The resulting curve shows two main negative carbon isotopic excursions (CIEs) that fit well with the “Initial” and “Main” CIEs that are recognized worldwide and linked to the End-Triassic Extinction (ETE). In the studied section, the first negative CIE marks the disappearance of the large megalodontids, which were replaced by small and thin-shelled specimens, while the “Main” CIE corresponds to the last occurrence (LO) of the megalodontids and, approximately 50 m upsection, to the total demise of the Rhaetian benthic foraminifer community. Upward, the carbon curve shows a positive trend (ca. +1‰) and a gradual recovery of the benthic communities after an approximately 10 m-thick barren interval populated only by the problematic alga Thaumatoporella parvovesiculifera . A comparison between the Mt. Sparagio δ 13 C carb curve and other coeval C carb and C org curves from carbonate platform, ramp and deep basin successions indicates similar isotopic trends; however, the diverse magnitudes and responses of benthic communities confirm that the carbon cycle perturbations have been globally significant, and were influenced by external forces such as CAMP volcanism. The multiphase nature of the extinction pulses could have been caused by local environmental changes related to transgression/regression phenomena. Overall, this study adds new data and a new timing to the effect of the acidification process on carbon productivity and benthic communities in different environments across the TJB. [ABSTRACT FROM AUTHOR]

The Cretaceous–Paleogene (K–Pg) mass extinction event 66 million years ago led to large changes to the global carbon cycle, primarily via a decrease in primary or export productivity of the oceans. However, the effects of this event and longer-term environmental changes during the Late Cretaceous on the global sulfur cycle are not well understood. We report new carbonate associated sulfate (CAS) sulfur isotope data derived from marine macrofossil shell material from a highly expanded high latitude Maastrichtian to Danian (69–65.5 Ma) succession located on Seymour Island, Antarctica. These data represent the highest resolution seawater sulfate record ever generated for this time interval, and are broadly in agreement with previous low-resolution estimates for the latest Cretaceous and Paleocene. A vigorous assessment of CAS preservation using sulfate oxygen, carbonate carbon and oxygen isotopes and trace element data, suggests factors affecting preservation of primary seawater CAS isotopes in ancient biogenic samples are complex, and not necessarily linked to the preservation of original carbonate mineralogy or chemistry. Primary data indicate a generally stable sulfur cycle in the early-mid Maastrichtian (69 Ma), with some fluctuations that could be related to increased pyrite burial during the ‘mid-Maastrichtian Event’. This is followed by an enigmatic +4‰ increase in δ 34 S CAS during the late Maastrichtian (68–66 Ma), culminating in a peak in values in the immediate aftermath of the K–Pg extinction which may be related to temporary development of oceanic anoxia in the aftermath of the Chicxulub bolide impact. There is no evidence of the direct influence of Deccan volcanism on the seawater sulfate isotopic record during the late Maastrichtian, nor of a direct influence by the Chicxulub impact itself. During the early Paleocene (magnetochron C29R) a prominent negative excursion in seawater δ 34 S of 3–4‰ suggests that a global decline in organic carbon burial related to collapse in export productivity, also impacted the sulfur cycle via a significant drop in pyrite burial. Box modelling suggests that to achieve an excursion of this magnitude, pyrite burial must be reduced by >15%, with a possible role for a short term increase in global weathering rates. Recovery of the sulfur cycle to pre-extinction values occurs at the same time (∼320 kyrs) as initial carbon cycle recovery globally. These recoveries are also contemporaneous with an initial increase in local alpha diversity of marine macrofossil faunas, suggesting biosphere-geosphere links during recovery from the mass extinction. Modelling further indicates that concentrations of sulfate in the oceans must have been 2 mM, lower than previous estimates for the Late Cretaceous and Paleocene and an order of magnitude lower than today. [ABSTRACT FROM AUTHOR]

Oceanic de‑oxygenation is considered to have been an important kill mechanism contributing to the latest Permian mass extinction and subsequent protracted recovery of marine biotas, but its extent, magnitude, and related controlling factors remain controversial. Here, we undertake a synthesis and reevaluation of previously published Fe-S-P-N data to better understand spatial and temporal variation of marine de‑oxygenation along a proximal-to-distal gradient in the eastern Paleotethys Ocean during the Permian-Triassic transition. Our results indicate: i) transient oxygenation of outer-shelf to basinal settings and de‑oxygenation of middle-shelf settings at the extinction horizon; ii) in outer-shelf to basinal settings, a shift from episodically euxinic conditions in the latest Permian (C. changxingensis Zone) to mainly ferruginous conditions in the earliest Triassic (H. parvus-I. isarcica zones); and iii) in middle-shelf settings, a shift from oxic-dysoxic (C. changxingensis Zone) to euxinic (C. yini - C. meishanensis zones) and then back to oxic conditions (H. parvus - I. isarcica zones). Proximal-to-distal redox variations are closely linked to spatial gradients in the marine sulfur, nitrogen and phosphorous cycles. A global comparison demonstrates that the Paleotethys, Neotethys, Boreal, and Panthalassic oceans all experienced shallow-marine de‑oxygenation during the latest Permian mass extinction, which may have been a major factor in the marine biocrisis. Globally, the extent and magnitude of oceanic de‑oxygenation presented a link to the distance to the Siberian Traps Large Igneous Province and, thus, to the volume of volcanic-related sulfur release during the Permian-Triassic boundary crisis. [ABSTRACT FROM AUTHOR]

The Permian-Triassic mass extinction (PTME), the largest biocrisis in Earth's history, is regarded as having been triggered by volcanism, although the source and nature of this volcanic activity in the South China region remains in debate. In this regard, determining the geochemical composition of the volcanic and terrestrial source fluxes to marine depositional systems is crucial for differentiating material derived from the Siberian Traps Large Igneous Province versus regional volcanic arcs. Here, we report zirconium (Zr) isotopic compositions (δ94/90Zr) of Permian-Triassic boundary strata from a deep carbonate-ramp setting at Xiakou, South China, providing new insights regarding the provenance of volcanic ash layers and their host silicic mudstones. The δ94/90Zr composition of magmatically sourced materials is generally controlled by degree of melt crystallization and has the potential to discriminate between primitive and evolved igneous sources. At Xiakou, the pre-PTME Lower Unit contains volcanic ash layers with δ94/90Zr (+0.05 ± 0.03‰, 2SD) similar to that of upper continental crustal (UCC), recording dominantly detrital zircon sources. About 10 kyr before the mass extinction, a single ash layer (Bed 249) records a transient excursion to mantle-like values (∼0‰), followed by a protracted shift across the Permian-Triassic boundary (PTB) toward signatures characteristic of more evolved felsic sources (+0.19 ± 0.12‰) accompanied by a positive shift in Nd isotopes (ε Nd (t)). The high δ94/90Zr of volcanic ash layers from the Middle Unit (corresponding approximately to the interval between the PTME and PTB) indicates dominance of regional felsic volcanic sources. In this interval, volcanic ash δ94/90Zr values at Xiakou are distinctly higher than those at Meishan, suggesting that primary volcanic signatures are better preserved in deep-water facies (Xiakou) than in shallow-water facies (Meishan). In the Middle (excluding the Bed 249) and Upper (post-PTME) units, positive covariation of δ94/90Zr with Al 2 O 3 /TiO 2 , Zr/TiO 2 and Zr/Sc ratios was the product of mixing of detrital and volcanic materials, with the latter having a dominantly felsic source. This study provides new insight into the sources of zircons in PTB sections of South China, and it demonstrates the general utility of sedimentary Zr isotopic compositions in determining magmatic provenance. • Deep-water facies (e.g., Xiakou) preserve Zr-isotope signatures of volcanic ash well • Zr isotopes document intense felsic regional arc volcanism during PTB transition • Geochemical proxies record evolution of source magma chemistry in volcanic arc system • A positive shift of Nd isotopes indicates regional inputs from juvenile continental crust • Zr and Nd isotopes useful in documenting mixing of volcanic and detrital materials [ABSTRACT FROM AUTHOR]

The Late Devonian Kellwasser Events are two major biodiversity crises recorded at and just below the Frasnian-Famennian stage boundary for which the ultimate cause or causes of diversity depletion remain unclear. The discovery of anomalous mercury (Hg) enrichments in Upper Kellwasser Event (UKE) strata has led to increased interest in a potential volcanic trigger for one or both events. However, UKE Hg anomalies are found mainly on the continental shelves of the Palaeotethys Ocean, and Hg isotope values from at least one distal basin indicate a non-volcanic Hg source. These findings suggest volcanism during the UKE may have had regional rather than global impacts. In comparison to the UKE, few works have investigated the sedimentary Hg record of the Lower Kellwasser Event (LKE). Here, we contribute new Hg data from the LKE of the Appalachian Basin and compare this to a compilation of global Hg data from both events. The Appalachian Basin contains no sedimentary Hg enrichments consistent with massive volcanism during the LKE, and Hg concentrations are strongly correlated with total organic carbon. We argue that organic matter drawdown exerted a primary control upon Hg concentration in the Appalachian Basin. While basins more proximal to the Palaeotethys Ocean preserve potentially volcanogenic LKE Hg anomalies, the absence of such anomalies here reflects volcanism during the LKE that was at most only regionally significant, as hypothesized for the UKE. Volcanism is therefore an unlikely trigger of the global Kellwasser diversity depletions. Broader sampling of the Kellwasser record will assist in the development of an extinction model that accounts for variations in global Hg concentrations, as the depressed origination rates, prolonged background environmental stress, and variations in intra-basinal expression that characterize both events may indicate that the trigger of diversity loss in this interval is unique among the "Big Five" mass extinctions. • We present new mercury (Hg) data from the Late Devonian of the Appalachian Basin. • We find no volcanogenic Hg anomalies during the Kellwasser Events. • Organic matter drawdown primarily controls Hg concentration in this basin. • Volcanism during the Lower Kellwasser Event was at most a regional process. • Broader spatial sampling is necessary to uncover further inter-basinal variations. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) isotopic compositions in seawater are important parameters for tracing the biogeochemical cycling of Cd in modern oceans and may be used as a direct proxy for nutrient utilization by phytoplankton and an indirect proxy for primary productivity. In this study, we measured the stable Cd isotope ratios (δ 114 Cd) of marine sedimentary carbonates from the Meishan section in Changxing County of Zhejiang Province, South China, the Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary (PTB). The results suggest that the inferred marine primary productivity recorded in the marine carbonates from the Late Permian (i.e., before the mass extinction) was high and relatively stable (the δ 114/110 Cd values of carbonates range from +0.31‰ to +0.60‰; after correction for salinity-controlled fractionation into inorganic calcite, the δ 114/110 Cd values of palaeo-seawater range from +0.47‰ to +0.79‰). During the mass extinctions, the δ 114/110 Cd values of carbonates abruptly decreased at the beginning of each episode of mass extinction, suggesting that the primary productivity of the palaeo-ocean declined before each episode of extinction events at the PTB. We suggest that the mass extinction events at the PTB in the Meishan section could be a ripple effect due to the destruction of primary producers at the base of the food chain in the palaeo-ocean ecosystem. [ABSTRACT FROM AUTHOR]

We investigated the Cretaceous-Paleogene (K/Pg) transition at the Galanderud section, northern Alborz (Iran) to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little-studied area of the eastern Tethys. We applied a high-resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages, clay mineralogy, rock magnetic properties, stable isotopes, and geochemistry. In this section, the K/Pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer, a marked decrease in magnetic susceptibility, a negative 2.2‰ δ 13 C excursion, and a peak in iridium. In the uppermost Maastrichtian, foraminifera are well preserved and diversified suggesting a stable, mesotrophic environment. By contrast, the K/Pg boundary and basal Danian is marked by high values of epifaunal benthic morphogroups, low planktic diversity, and high percentages of opportunistic species ( Guembelitria cretacea and Cervisiella operculata ) suggesting highly stressed and variable conditions, partly due to the dramatic collapse of calcareous primary producers. Benthic foraminiferal assemblages indicate outer neritic-uppermost bathyal depths with slight bathymetric variations. The most peculiar and unique aspect of the Galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the K/Pg boundary, each marked by positive shifts in δ 13 C and δ 18 O values, and consisting of >80% carbonate. We propose that the chalk/clay deposits in the basal Danian reflect changes in seawater chemistry and dynamic changes in circulation (upwelling) alternating with episodes of enhanced weathering and runoff. This section on the northern margin of eastern Tethys provides new clues about the pattern of the K/Pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase. [ABSTRACT FROM AUTHOR]

Igneous intrusion into organic-rich sedimentary rocks and coals has been suggested as a factor in the large-scale release of 13 C–depleted thermogenic CH 4 , which may have led to global warming and mass extinction events in the geologic past. If a significant release of 13 C–depleted thermogenic CH 4 results from the intrusion of coal or organic-rich rocks, then it should produce 13 C–enriched residual coal and dispersed organics in rocks adjacent to the intrusion due to the release of isotopically lighter CH 4 gas. A review of the literature suggests only minor changes in the δ 13 C org of coals adjacent to intrusions; however, a few studies have shown that changes in δ 13 C org in intruded shales may be slightly more pronounced. The current study further evaluates the geochemical, isotopic, and petrographic changes that result from contact metamorphism and specifically compares the intrusion of coal to that of an organic-rich shale collected from the same general vicinity. Data for two different transects of intruded Pennsylvanian coal (Danville (No. 7) Coal) and an intruded organic-rich shale in the southern part of the Illinois Basin are presented. Both transects show similar increases in mean vitrinite reflectance (R r ); reflectance increases from background levels of 0.66% to 4.40% in the Danville (No. 7) Coal and 0.71% to 4.78% in the organic-rich shale. In addition, both transects show the formation of isotropic coke, and even development of fine circular mosaic anisotropic coke structure at and near the contact with the intrusion, along with the visual loss of liptinites at higher reflectances. In the Danville Coal transect, volatile matter, N, H, S, and O decrease whereas fixed carbon, C, and ash increase approaching the intrusion. The coal shows a marked decrease in remaining hydrocarbon potential (S 2 ) and hydrogen index (HI) and an increase in T max (°C). Trends in most of the Rock-Eval parameters for the organic-rich shale are less clear due to variations in the amount of organic matter present, but a significant increase in thermal maturity (T max , 0 C) is observed. No systematic changes in δ 13 C occur in the No. 7 Coal transect as the intrusion is approached, with δ 13 C varying between − 25.4‰ and − 24.8‰. The organic-rich shale transect shows a minor 1.2‰ enrichment in δ 13 C (from − 25.2‰ to − 24.0‰) within 2 m of the intrusion. These isotopic shifts are not of a magnitude that would be expected if associated with a large-scale release of thermogenic CH 4 . In addition, no evidence exists in either transect for 13 C–depleted condensed gas or pyrolytic carbon at the intrusion contact that could have moderated the isotopic signature. These data agree with those reported previously that indicate no clear isotopic evidence for large-scale CH 4 generation due to rapid heating by igneous intrusion into coals or sedimentary rocks. [ABSTRACT FROM AUTHOR]

Recent research has demonstrated that the Lilliput effect (reduction of body size in biota associated with the aftermath of mass extinctions) affected all trophic levels in the marine realm following the Cretaceous-Paleogene (K-Pg) event. However, it is unclear if this size change was strictly a marine signal, or a global phenomenon that also affected continental ecosystems. Herein we present the results of an ichnological proxy for body size of soil-dwelling insects across the K-Pg boundary in Big Bend National Park, Texas, U.S.A. Quantitative efforts focused on Naktodemasis bowni , which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci. These traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments. As an approximation for the body size of the subterranean insects, this dataset indicates that a smaller N. bowni diameter (D N ) is statistically correlated (α < 0.05) with several edaphic factors including poor soil drainage and weak soil development (Entisols). Additionally, the D N in strata immediately superjacent to the highest Cretaceous-specific taxa is smaller by 23% (5.6 ± 1.8 mm) in comparison to D N within the subjacent Cretaceous interval (7.3 ± 2.7 mm). This abrupt shift occurs in a well-drained Inceptisol, and cannot be attributed to facies changes, drainage, or paleosol maturity. Furthermore, a reduced D N (6.6 ± 2.3 mm) persists above this anomalous shift for at least 20 stratigraphic meters within chron 29r. The cause for this negative response in body size within soil-dwelling biota may be attributed to plant-community shifts in taxonomic composition and ecological strategies, which would have caused fundamental alterations to the diet of the herbivorous, subterranean insects. This study provides empirical evidence that the Lilliput effect was not restricted to marine environments during the aftermath of the K-Pg event. [ABSTRACT FROM AUTHOR]

The end-Permian mass extinction was the most severe biotic crisis in Earth's history. In its direct aftermath microbial communities colonized some of the space left vacant after the severe decline of skeletal metazoans. The Permian-Triassic boundary microbialites were peculiarly abundant on low-latitude shallow-marine carbonate shelves of central Tethyan continents. Armenia features particularly well preserved and diverse basal Triassic sponge-microbial build-ups (BTSMBs), which were not studied in detail to date. Here, the Chanakhchi section in southern Armenia is described petrographically and by means of stable isotope analyses. The Armenian BTSMBs formed in a distally open marine setting on a pelagic carbonate ramp in the course of two phases of microbial growth during the Induan (Lower Triassic). The BTSMBs are represented by predominantly thrombolitic but also dendrolitic and digitate stromatolite biostromes and mounds that vary in height between 5 cm to 12 m. The digitate stromatolites are associated with calcium carbonate crystal fans (CCFs). Microfacies analyses revealed that the BTSMBs exhibit a number of different growth forms and internal fabrics. The formation of CCFs was apparently not devoid of biological influence and took place above the sediment surface. The abundance of sponges in the BTSMBs reveals that ecologically complex metazoan-microbial reefs have been present already early after the end-Permian mass extinction. However, the formation of biostromes and mounds did not depend on sponges or other metazoans. BTSMBs that formed during the second microbial growth phase revealed similar δ 13 C-values like the surrounding sediment. In contrast, the δ 13 C microbialite and δ 13 C sediment values from the BTSMBs and CCFs of the first growth phase show a difference of up to + 2.3‰, suggesting a significant influence of photoautotrophy during microbially induced carbonate precipitation. [ABSTRACT FROM AUTHOR]

We propose a model of multispecies populations surviving on distributed resources. System dynamics are investigated under changes in abiotic factors such as the climate, as parameterized through environmental temperature. In particular, we introduce a feedback between species abundances and resources via abiotic factors. This model is apparently the first of its kind to include a feedback mechanism coupling climate and population dynamics. Moreover, we take into account self-limitation effects. The model explains the coexistence of many species, yet also displays the possibility of catastrophic bifurcations, where all species become extinct under the influence of abiotic factors. We show that as these factors change there are different regimes of ecosystem behavior, including a possibly chaotic regime when abiotic influences are sufficiently strong. [ABSTRACT FROM AUTHOR]

Although oceanic anoxia is regarded as a leading cause of the Permian-Triassic boundary (PTB) mass extinction, its timing, extent, and underlying causes remain unclear. Here, we conducted a high-resolution Fe-S-C-Mo geochemical study of the entire Changhsingian and lowermost Induan succession in a carbonate-ramp setting at Ganxi, western Hubei Province, South China. Six stratigraphic units representing discrete redox intervals were identified based on integrated Fe-S-C-Mo data. Units I–III are of latest Wuchiapingian to early Changhsingian age, with Units I and III characterized by euxinia and Unit II by uncertain redox conditions. Unit IV, of mid-Changhsingian age, records a gradual transition from euxinic to ferruginous conditions. Units V and VI, spanning the latest Permian mass extinction (LPME) to earliest Triassic interval, were deposited under dominantly ferruginous conditions punctuated by both euxinic and oxic episodes. Redox variations at Ganxi were controlled by contemporaneous oceanographic changes in the upper oceanic thermocline region: (i) euxinia in Units I and III may record elevated marine productivity (as suggested by mean organic carbon accumulation rates, or OCAR, of 6.5 and 5.1 mg/cm 2 /kyr, respectively) that was possibly related to upwelling; (ii) the euxinic-to-ferruginous transition from Unit IV to Units V–VI can be attributed to a combination of reduced sulfate availability and rising terrigenous iron inputs (mean Fe of 1.7% and 3.9%, respectively, for Units V–IV and VI compared to 1.0% for Units I–III); and (iii) transient intervals of euxinia in Units V and VI were facilitated by enhanced sulfate fluxes related to episodic volcanism during this interval. An integration of the redox data from Ganxi with previously published data from the Shangsi and Xiakou sections suggests that enhanced weathering fluxes were most likely the key factor controlling the marine redox transition from euxinic to ferruginous conditions during the latest Permian across the South China region. [ABSTRACT FROM AUTHOR]