The Capitanian (Guadalupian, Middle Permian) mass extinction in NW Pangea (Borup Fiord, Arctic Canada): A global crisis driven by volcanism and anoxia

Until recently, the biotic crisis that occurred within the Capitanian Stage (Middle Permian, ca. 262 Ma) was known only from equatorial (Tethyan) latitudes, and its global extent was poorly resolved. The discovery of a Boreal Capitanian crisis in Spitsbergen, with losses of similar magnitude to those in low latitudes, indicated that the event was geographically widespread, but further non-Tethyan records are needed to confirm this as a true mass extinction. The cause of this crisis is similarly controversial: While the temporal coincidence of the extinction and the onset of volcanism in the Emeishan large igneous province in China provides a clear link between those phenomena, the proximal kill mechanism is unclear. Here, we present an integrated fossil, pyrite framboid, and geochemical study of the Middle to Late Permian section of the Sverdrup Basin at Borup Fiord, Ellesmere Island, Arctic Canada. As in Spitsbergen, the Capitanian extinction is recorded by brachiopods in a chert/limestone succession 30–40 m below the Permian-Triassic boundary. The extinction level shows elevated concentrations of redox-sensitive trace metals (Mo, V, U, Mn), and contemporary pyrite framboid populations are dominated by small individuals, suggestive of a causal role for anoxia in the wider Boreal crisis. Mercury concentrations—a proxy for volcanism—are generally low throughout the succession but are elevated at the extinction level, and this spike withstands normalization to total organic carbon, total sulfur, and aluminum. We suggest this is the smoking gun of eruptions in the distant Emeishan large igneous province, which drove high-latitude anoxia via global warming. Although the global Capitanian extinction might have had different regional mechanisms, like the more famous extinction at the end of the Permian, each had its roots in large igneous province volcanism

Controls on the formation of microbially induced sedimentary structures and biotic recovery in the Lower Triassic of Arctic Canada

Microbially induced sedimentary structures (MISS) are reportedly widespread in the Early Triassic and their occurrence is attributed to either the extinction of marine grazers (allowing mat preservation) during the Permo-Triassic mass extinction or the suppression of grazing due to harsh, oxygen-poor conditions in its aftermath. Here we report on the abundant occurrence of MISS in the Lower Triassic Blind Fiord Formation of the Sverdrup Basin, Arctic Canada. Sedimentological analysis shows that mid-shelf settings were dominated by deposition from cohesive sand-mud flows that produced heterolithic, rippled sandstone facies that pass down dip into laminated siltstones and ultimately basinal mudrocks. The absence of storm beds and any other “event beds” points to an unusual climatic regime of humid, quiet conditions characterized by near continuous run off. Geochemical proxies for oxygenation (Mo/Al, Th/U, and pyrite framboid analysis) indicate that lower dysoxic conditions prevailed in the basin for much of the Early Triassic. The resultant lack of bioturbation allowed the development and preservation of MISS, including wrinkle structures and bubble textures. The microbial mats responsible for these structures are envisaged to have thrived, on sandy substrates, within the photic zone, in oxygen-poor conditions. The dysoxic history was punctuated by better-oxygenated phases, which coincide with the loss of MISS. Thus, Permo-Triassic boundary and Griesbachian mudrocks from the deepest-water settings have common benthos and a well-developed, tiered burrow profile dominated by Phycosiphon. The presence of the intense burrowing in the earliest Triassic contradicts the notion that bioturbation was severely suppressed at this time due to extinction losses at the end of the Permian. The notion that Early Triassic MISS preservation was caused by the extinction of mat grazers is not tenable

Biotic responses to volatile volcanism and environmental stresses over the Guadalupian-Lopingian (Permian) transition

Biotic extinction during the Guadalupian-Lopingian (G-L) transition is actively debated, with its timing, validity, and causality all questioned. Here, we show, based on detailed sedimentary, paleoecologic, and geochemical analyses of the Penglaitan section in South China, that this intra-Permian biotic crisis began with the demise of a metazoan reef system and extinction of corals and alatoconchid bivalves in the late Guadalupian. A second crisis, among nektonic organisms, occurred around the G-L boundary. Mercury concentration/total organic carbon (Hg/TOC) ratios show two anomalies. The first Hg/TOC peak broadly coincides with the reef collapse and a positive shift in Δ199Hg values during a lowstand interval, which was followed by microbial proliferation. A larger Hg/TOC peak is found just above the G-L boundary and speculatively represents a main eruption episode of the Emeishan large igneous province (ELIP). This volatile volcanism coincided with nektonic extinction, a negative δ13Ccarb excursion, anoxia, and sea-level rise. The temporal coincidence of these phenomena supports a cause-andeffect relationship and indicates that the eruption of the ELIP likely triggered the G-L crisis

Progressive environmental deterioration in northwestern Pangea leading to the latest Permian extinction

Stratigraphic records from northwestern Pangea provide unique insight into global processes that occurred during the latest Permian extinction (LPE). We examined a detailed geochemical record of the Festningen section, Spitsbergen. A stepwise extinction is noted as: starting with (1) loss of carbonate shelly macrofauna, followed by (2) loss of siliceous sponges in conjunction with an abrupt change in ichnofabrics as well as dramatic change in the terrestrial environment, and (3) final loss of all trace fossils. We interpret loss of carbonate producers as related to shoaling of the lysocline in higher latitudes, in relationship to building atmospheric CO2. The loss of siliceous sponges is coincident with the global LPE event and is related to onset of high loading rates of toxic metals (Hg, As, Co) that we suggest are derived from Siberian Trap eruptions. The final extinction stage is coincident with redox-sen- sitive trace metal and other proxy data that suggest onset of anoxia after the other extinction events. These results show a remarkable record of progressive environmental deterioration in northwestern Pangea during the extinction crises

Ecological disturbance in tropical peatlands prior to marine Permian-Triassic mass extinction

The Permian-Triassic mass extinction is widely attributed to the global environmental changes caused by the eruption of the Siberian Traps. However, the precise temporal link between marine and terrestrial crises and volcanism is unclear. Here, we report anomalously high mercury (Hg) concentrations in terrestrial strata from southwestern China, synchronous with Hg anomalies in the marine Permian-Triassic type section. The terrestrial sediments also record increased abundance of fossil charcoal coincident with the onset of a negative carbon isotope excursion and the loss of tropical rainforest vegetation, both of which occurred immediately before the peak of Hg concentrations. The organic carbon isotope data show an ∼5‰–6‰ negative excursion in terrestrial organic matter (bulk organic, cuticles, and charcoal), reflecting change in atmospheric CO2 carbon-isotope composition coincident with enhanced wildfire indicated by increased charcoal. Hg spikes provide a correlative tool between terrestrial and marine records along with carbon isotope trends. These data demonstrate that ecological deterioration occurred in tropical peatlands prior to the main marine mass extinction

Mercury anomalies across the end Permian mass extinction in South China from shallow and deep water depositional environments

Life on Earth suffered its greatest bio-crisis since multicellular organisms rose 600 million years ago during the end-Permian mass extinction. Coincidence of the mass extinction with flood basalt eruptions in Siberia is well established, but the exact causal connection between the eruptions and extinction processes in South China is uncertain due to their wide spatial separation and the absence of direct geochemical evidence linking the two. The concentration and stable isotope analysis of mercury provides a way to test these links as its concentration is thought to be tied to igneous activity. Mercury/total organic carbon ratios from three Permian-Triassic boundary sections with a well-resolved extinction record in South China show elevated values (up to 900 ppb/wt. % relative to a background of <100 ppb/wt. %) that exactly coincides with the end-Permian mass extinction horizon. This enrichment does not show any correlation with redox and sedimentation rate variations during that time. Hg isotope mass-independent fractionation (Δ199Hg), with sustained positive values, indicate a predominant atmospheric-derived signature of volcanic Hg in deep-shelf settings of the Daxiakou and Shangsi sections. In contrast, the nearshore environment of the Meishan section displays a negative Δ199Hg signature, interpreted to be related to terrestrial Hg sources. Such temporal differences in Δ199Hg values shed new light on Hg geochemical behavior in marine settings, and also on kill mechanisms associated with volcanism that were responsible for biotic mortality at the end of the Permian

Volcanism and carbon cycle perturbations in the High Arctic during the Late Jurassic – Early Cretaceous

This is the final version. Available on open access from Elsevier via the DOI in this recordLarge perturbations in the global carbon cycle recorded as carbon-isotope (δ13C) excursions (CIEs) in both organic carbon and carbonate records have been linked to volcanism during the emplacement of Large Igneous Provinces (LIPs). This link is based primarily on the purported temporal coincidence between CIEs and LIP emplacement. Mercury (Hg) concentration in sedimentary rocks has been used as a regional to global tracer of large-scale volcanic activity, yet few studies have been undertaken on Upper Jurassic – Lower Cretaceous sediments from Boreal localities compared to those for Tethyan (northern mid-latitude) successions. This has limited our understanding of the regional-to-global spatial impact of volcanic activity during this period. This study examines the Hg record as a proxy for volcanism, and the δ13C records from organic matter (δ13Corg) of CIEs from the uppermost Jurassic to Lower Cretaceous (Callovian – Aptian) successions from Axel Heiberg and Spitsbergen in the Canadian Arctic and Svalbard archipelagos, respectively. This interval includes three regional- to global CIEs. These sections show no significant variation in the ratio of Hg to total organic carbon (TOC) across the Boreal-wide Volgian negative CIE (Volgian Isotopic Carbon Excursion, “VOICE”), which has not been associated with LIP volcanism. The examined successions spanning this interval all show some influence from changing environmental or post-burial parameters, however, which could have (partially) overprinted a volcanic signal. Despite some problems in stratigraphically constraining the Weissert Event, increased Hg/TOC ratios are observed across this interval, which may be partially driven by volcanism associated with the emplacement of the Paraná-Etendeka Traps. A spike in Hg/TOC is observed immediately prior to the negative peak of the Aptian Oceanic Anoxic Event (OAE1a) CIE, supporting recent evidence of a pulse of High Arctic Large Igneous Province (HALIP) volcanic activity preceding this oceanic anoxic event

Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery

The end-Permian mass extinction, ~252 million years ago, is notable for a complex recovery period of ~5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota

Multiple S-isotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction

Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes (32S, 33S, 34S and 36S) for pyrites in sedimentary rocks from the Meishan section in South China. We observe a sulphur isotope signal (negative δ34S with negative Δ33S) that may have resulted from limitation of sulphate supply, which may be linked to a near shutdown of bioturbation during shoaling of anoxic water. These results indicate that episodic shoaling of anoxic water may have contributed to the profound biodiversity crisis before the final catastrophe. Our data suggest a prolonged deterioration of oceanic environments during the Late Permian mass extinction

Cellular Active N-Hydroxyurea FEN1 Inhibitors Block Substrate Entry to the Active Site

The structure-specific nuclease human flap endonuclease-1 (hFEN1) plays a key role in DNA replication and repair and may be of interest as an oncology target. We present the first crystal structure of inhibitor-bound hFEN1 and show a cyclic N-hydroxyurea bound in the active site coordinated to two magnesium ions. Three such compounds had similar IC50 values but differed subtly in mode of action. One had comparable affinity for protein and protein– substrate complex and prevented reaction by binding to active site catalytic metal ions, blocking the unpairing of substrate DNA necessary for reaction. Other compounds were more competitive with substrate. Cellular thermal shift data showed engagement of both inhibitor types with hFEN1 in cells with activation of the DNA damage response evident upon treatment. However, cellular EC50s were significantly higher than in vitro inhibition constants and the implications of this for exploitation of hFEN1 as a drug target are discussed