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The end-Permian mass extinction (EPME) was known as the most severe biocrisis of the past 600 Ma. In order to explore the redox state of deep water environments, and the causal relationship between anoxia/euxinia and the EPME, this study selected the Penglaitan section in Guangxi, China, and measured the iron speciation and concentrations of trace elements and major elements. Several redox proxy approaches, including both iron speciation proxies and the excess fractions and enrichment factors of redox sensitive elements (RSEs), indicate that anoxia in the Penglaitan depositional environment was sporadic, with the majority of the section deposited under oxic conditions. This includes the interval immediately prior to and during the EPME; euxinia did not occur at the Penglaitan section around the EPME. Thus, anoxia was not the primary driver for the EPME at the Penglaitan section, and the accumulation of free H2S in the oceanic water-column could not have been the only proximal kill mechanism for the EPME at the Penglaitan section.

The end-Permian mass extinction (EPME) has been recorded as the most severe biodiversity crisis in Earth's history, although the timing of the marine and terrestrial extinctions remains debatable. We present a new high-resolution magnetostratigraphic succession across the EPME and the Permian-Triassic boundary (PTB) from the Meishan sections in southeastern China, which contain the global boundary stratotype section and point (GSSP) for the base of the Triassic (also the Induan Stage) and the base of the Changhsingian Stage. We identified five normal and five reverse magnetozones, including MS1n to MS5n and MS1r to MS5r, from oldest to youngest, in the Changhsingian and Induan Stages. The Induan Stage was determined to consist of two polarity intervals, where the upper one is reverse (MS5r), and the lower one is normal (MS5n). The Changhsingian Stage is dominated by normal polarity, intercalated with four short-term reverse magnetozones (MS1r to MS4r). Consequently, the PTB and the Wuchiapingian-Changhsingian boundary are clearly located in MS5n and MS1n, respectively. These new magnetostratigraphic results provide a potential reference geomagnetic polarity pattern with which to refine the geomagnetic polarity time scale for the EPME and the Permian-Triassic transition.

The end-Permian mass extinction (EPME; ca. 251.94 Ma) is the most severe mass extinction in the geological record. Detailed paleobiological investigations show a very rapid EPME event, and recently published δ238U data show a large negative excursion and thus a massive shift to globally expanded anoxia at the main extinction phase in the latest Permian. The negative shift in δ238U is in correlation with a globally characterized negative δ13C excursion near the Permian-Triassic boundary (PTB). In some highly expanded PTB carbonate sections, however, there are two distinct negative δ13C excursions whereas uranium isotopes (δ238U) from such sections have not yet been examined, leaving a gap in the understanding of the global perturbations of marine redox conditions immediately following the EPME. Here, we present a new δ238U study of syn-depositional dolostones from a well-characterized and highly expanded drill core, which recorded two pronounced negative δ13C excursions across the PTB, from the Carnic Alps, Austria. This drill core extends 331-meters across the PTB and provides a unique opportunity to explore the detailed timing, duration, and extent of marine redox chemistry changes before, during, and immediately after the EPME. Our new δ238U record shows two negative shifts, which are correlated with the two negative δ13C excursions. The first negative δ238U excursion preceding the EPME confirms the recently published δ238U records from across the EPME and support that syndepositional marine dolostones can record δ238U trends of seawater similar to that of limestones. Modeling of uranium isotope cycling in the latest Permian and earliest Triassic oceans suggests two distinct stages of expanded marine anoxia separated by a brief interval (∼100 kyr) of reoxygenation across the PTB. The first anoxic episode lasted for ∼ 60 kyr while anoxic seafloor area expanded to cover >18% of the entire seafloor, coeval with the main EPME horizon, agreeing with marine anoxia as a proximate kill mechanism for the EPME. The second anoxic event was less intense compared to the first anoxic pulse but sustained for a longer duration. A global modeling of coupled C, P, and U cycles show that two pulses of volcanic carbon injection that drives global warming and increased phosphorus weathering rate can reasonably reproduce our data to match two phases of anoxia. The model also demonstrates that the loss of terrestrial vegetation in the EPME is crucial to generating an intervening interval of oxygenated ocean. Our new study adds to a growing body of evidence that the global marine redox conditions underwent rapid oscillations during the EPME event and continued afterward, which may have played a central role in delaying the marine ecosystem recovery in the Early Triassic.

Permian–Triassic boundary microbialites (PTBMs) are organosedimentary carbonates formed immediately after the end-Permian mass extinction. All those reported PTBMs constrained by convincing conodont biozones are present stratigraphycally not higher than the Hindeodus parvus zone and most of them are dominated by thrombolites. This paper provides the first record of a brief, but spectacular development of stromatolite-dominated PTBMs within the basal Isarcicella isarcica conodont zone of the earliest Triassic from the Xikou section of South Qinling Block that was at the margin of the North China Block during the Permian–Triassic transition and was geographically separated from the major occurrence of post-extinction microbialites in the South China Block. This stromatolite cap overlies a 3.7-m-thick oolitic limestone and is composed of a lower 0.2-m-thick bed and an upper 0.5-m-thick bed, separated by a 0.2-m-thick greyish green siliciclastic mudstone. These two stromatolite beds mainly consist of columnar stromatolites with subordinate domal stromatolites. The intercolumn and interstitial spaces within the stromatolites are filled with oolitic grainstones. At the microscopic scale, laminoid structures in stromatolites comprise wavy, millimetric-domical and tangled laminae. The increased grain and fossil contents and/or bioturbation in the domical and tangled laminae indicate that the formation of these laminae is likely related to an increase in the populations and the disruptions by benthic metazoans, as well as an influx of sediment grains. The δ13Ccarb values fluctuate between 2‰ and 3‰ in the uppermost Permian strata; a distinct negative shift of 1.9‰ occurs at the topmost oolitic grainstone, just below the lower stromatolite bed, and the lowest value of −0.1‰ is located at the base of the upper stromatolite bed. The stratigraphic succession from stromatolites to thrombolites of the PTBMs may represent a transgressive succession and/or a transient ecosystem recovery immediately after the end-Permian mass extinction. The thrombolites-dominated PTBMs mainly developed in near-equator shallow marine geographic locations, and stromatolite-dominated PTBMs mainly developed at higher latitude settings, which probably indicates that a relatively lower diversity and abundance of marine benthic metazoans existed at higher latitudes after the end-Permian mass extinction.

Although the micropaleontology of Ordovician deep-sea cherts is relatively well documented, microfossil assemblages in Ordovician shallow-marine cherts are less well-known. Nodular cherts in the Middle Ordovician carbonates of the Yijianfang Formation (Well YJ1X) in the Tarim Basin, northwestern China, contain a rich microfossil assemblage deposited in a shallow marine setting. These cherts contain 11 genera and 13 species of acritarchs and filamentous cyanobacteria. The acritarch assemblage includes eight genera and eight species, namely, Aremoricanium sp., Cheleutochroa oculata, Cymatiogalea sp., Cymatiosphaera sp., Dictyotidium microreticulatum, Leiosphaeridia sp., Polygonium gracile, and Pterospermella sp. Filamentous cyanobacteria include two genera and four species, namely, Siphonophycus typicum, Siphonophycus kestron, Siphonophycus solidum, and Oscillatoriopsis longa, and a colony of Eoentophysalis sp. coccoidal cells. The acritarch assemblage indicates a Middle–Late Ordovician age. The Yijianfang Formation fossil assemblage indicates a deep offshore depositional environment. Sedimentological evidence also suggests that the limestone that hosts the chert interval was deposited in a low- to moderate-energy, restricted, inner carbonate platform. Cherts formed by silicification during late diagenesis. By complementing previous studies of acritarchs in shales, this work improves the understanding of the Middle Ordovician paleogeography and microbial world.

An enriched bed of diverse plant cuticles is reported for the first time from the upper Guodikeng Formation of the Dalongkou section in Jimsar, Xinjiang Uygur Autonomous Region, Northwest China. The cuticles were attributed to a seed fern and several types of coniferalean plants based on the epidermal characters. The most predominant plant in the flora is a peltasperm seed fern, Germaropteris martinsii (Germar in Kurtze 1839) Kustatscher, Kerp et Van Konijnenburg-van Cittert, 2014. It is characterized by small, tongue-shaped pinnules with papillate polygonal epidermal cells and irregularly distributed stomatal apertures encircled by 5–7 subsidiary cells. Germaropteris martinsii has been mostly documented from the mid-latitudinal to equatorial Euramerica and Cathaysia floras and indicates relative drier habitats. The current material from the much higher paleolatitudinal Angara realm not only extends the paleogeographical range of G. martinsii but also sheds substantial light on the regional paleoclimatic and paleoenvironmental conditions. In addition to xerophilous seed plants, few impression fossils of hydrophilous plants (lycopsids and calamites) also occurred in the cuticle-bearing bed. Compared to the underlying floras, the plant assemblage described herein is distinguished by a high proportion of seed ferns and conifers, which probably indicates a shift in paleoclimatic conditions within the Guodikeng Formation.

The Lopingian is the uppermost series of the Paleozoic and it is bracketed by two major biological events, including the pre-Lopingian crisis and the end-Permian mass extinction (EPME). A high resolution temporal framework is essential to understand the patterns and causes of the extinction. Lopingian strata of South China have been intensively studied because three GSSPs have been defined in the region. Based on the review and updates to data from the Shangsi section as well as correlation with the Meishan section, the time framework for the Lopingian is revised, including biostratigraphy, chemostratigraphy, magnetostratigraphy, cyclostratigraphy and geochronology. The temporal framework is constrained by both precise geochronologic data and a high resolution conodont succession, and provides the possibility that the current high resolution marine international standard can also be applied to nonmarine strata by means of geochronology, magnetostratigraphy and cyclostratigraphy. The entire Lopingian high resolution conodont succession is for the first time, since the Lopingian Series was adopted as the international standard, recognized at a single section in South China and the succession correlates very well with the Lopingian GSSP sections at Penglaitan and Meishan. The Permian-Triassic boundary (PTB) of the Shangsi section is constrained to the basal 6 cm interval of Bed 28b in view of ammonoids, bivalves, conodonts, U-Pb ages and the EPME. The mass extinction interval is between Bed 27 and lower Bed 28a according to the EPME pattern at the Shangsi section, and the alternative interval between extinct Permian species and new Triassic species is from upper Bed 28a to lower Bed 28b. Unitary Association (UA) analysis of Lopingian conodonts reveals 15 unitary association zones (UAZs) based on seven important Lopingian sections of South China. Most of the UAZs correlate well with the standard biozonation, except for UAZ 3 to UAZ 5 and UAZ 12. The correspondence between UAZs and standard conodont biozones at the Shangsi section provides a practical example to understand controls on conodont UAZ determination. The Lopingian conodont succession is temporally calibrated by geochronologic ages, identified 405-kyr eccentricity cycles, and a Monte Carlo analysis at the Shangsi and Meishan sections. Updated ages for the base of the Lopingian and base of the Changhsingian are provided.

Two negative carbon isotope excursions (3.5–6.5‰) across the Wuchiapingian-Changhsingian boundary (WCB) are observed globally (sections in China, Canada, and Iran); however, the causative mechanism of these excursions is debated. Here, high-resolution osmium isotope (187Os/188Os or Osi) chemostratigraphy of four globally correlated WCB sections (3 in China - Meishan, Shangsi and Lianyuan and 1 in Canada - Buchanan Lake) show two separate Osi excursions to less radiogenic compositions that are coincident with the carbon isotope shifts for two of the South China sections (Lianyuan, Meishan). In contrast, only a single Osi excursion to less radiogenic compositions, coinciding with the earliest Changhsingian carbon isotope shift, is observed for the Shangsi and Buchanan Lake sections. The Osi shift is interpreted to reflect increased unradiogenic Os input from basaltic magmatism in South China, possibly related to the Emeishan large igneous province (LIP). However, 187Os/188Os data suggest that only the earliest Changhsingian volcanism had global impact on both the ocean and atmosphere. The lack of any evidence for a biotic event associated with the WCB therefore may have been due to the more regional rather than global impact of volcanism during the latest Wuchiapingian. In contrast, during the earliest Changhsingian, volcanism was sufficient to cause a more global signal in the ocean osmium record, but was inadequate, or too prolonged, to drive any significant environmental change. Volcanism, however, may have provided the isotopically light carbon that drove the negative carbon isotope excursions across the WCB.

A continuous strontium isotope profile with high-resolution sampling is desirable to calibrate multiple global events, realize temporal correlation among different continents, and understand tectonic history of the Permian Period. In this paper, we analyzed 90 micritic limestone samples from South China and 7 samples from Iran, with the aim to gain new 87Sr/86Sr data and obtain a curve of Sr isotopes for the Permian. The concentrations of Mg, Fe, Mn, and Sr are used to discriminate possible diagenesis of the samples. A comparison of those 87Sr/86Sr values between South China and southern Urals confirms that Sr-isotope proxy has the potential to be used for time calibration and correlation in regions where biostratigraphic or radiometric markers are not available. The 87Sr/86Sr curve obtained in this study shows a trend comparable with the LOcally WEighted Scatterplot Smoothing (LOWESS) regression curve from the previous studies. A continuous decline trend from the latest Carboniferous to late Guadalupian was shown, and the lowest 87Sr/86Sr values in the late Capitanian was constrained within the interval from the conodont Jinogondolella shannoni/J. altudaensis to J. xuanhanensis zones. It is followed by an increasing trend to more radiogenic values in the Lopingian with a minor fluctuation in the early Wuchiapingian. We consider that mid-ocean ridge spreading and increasing continental weathering during the transition from convergence to the breakup of Pangea as the dominant factors driving the changes of the seawater Sr isotope ratios.

The paleogeographic evolution of the North Qiangtang Block during the Middle and Late Permian has been a contentious issue in recent decades. In this study, the Permian foraminiferal faunas were studied from the Raggyorcaka and Wangka areas in northern and eastern Tibet. The foraminifera from the Xueyuanhe Formation in the Raggyorcaka area suggest a Changhsingian rather than a Guadalupian (Middle Permian) age, as previously determined. A review of Permian strata in the North Qiangtang Block confirms the widespread onset of the Lopingian (Late Permian) paralic sedimentary facies containing gigantopterid plant fossils and the fusuline Palaeofusulina fauna, which lies unconformably over the different pre-Lopingian strata. The similar Lopingian facies and pronounced unconformity across the North Qiangtang and Simao blocks are interpreted as the initial collision between the Simao/Indochina and the South China blocks.

Despite a continuous increase in fossil charcoal records from Late Palaeozoic deposits, which are used as direct evidence for palaeo-wildfires, detailed studies on the charcoal particles are still rare. To investigate the relationship between wildfire activities and the evolution of the terrestrial ecosystem at the end of the Permian, we report on the charcoal recovered from the classic non-marine Permian–Triassic Dalongkou section in Jimsar, Xinjiang Uygur Autonomous Region, Northwest China. Allochthonous and parautochthonous charcoals, identified by both macroscopic and microscopic morphological techniques, were collected from several stratigraphic horizons. These charcoals were classified into 11 categories (which do not represent the taxonomic group) according to their anatomical characteristics and gross morphology. The reflectance values of the charcoals indicate that surface fires were dominant throughout the sequence, with fire regime changing in a distinct interval. The distribution and abundance of all categories and the reflectance of the charcoals suggest that the intensity of wildfires increased in the upper part of the Guodikeng Formation. This trend coincides with the Hg/TOC peaks and a conspicuous excursion in the organic carbon isotope (δ13Corg) values, which may indicate volcanic activities and the disturbance of the carbon cycle that occurred during the Permian–Triassic transition. It is reasonable to infer that the end-Permian mass extinction (EPME) is located at the intensive wildfire interval. The reduction in spore pollen and the decrease in charcoal reflectance hint at a vegetational impoverishment that occurred after this interval. We proposed that increased wildfires, promoted by dry climate conditions and volcanism, aggravated the collapse of the forest ecosystem during the latest Permian.

The Permian Period is punctuated by Earth system changes unlike any other in geological history. The start of the Permian witnessed the termination of the Late Paleozoic Ice Age, followed by the climatic transition from icehouse to greenhouse conditions. The Guadalupian-Lopingian (Middle-Late Permian) was characterized by two biocrises associated to volcanisms: (i) the end-Guadalupian crisis and (ii) the end-Permian mass extinction. Seawater Sr isotope (87Sr/86Sr) records can shed light on the evolution of the Permian Earth system. The Permian 87Sr/86Sr record suffers from a number of issues including low resolution and potential diagenetic alteration. In this paper, we summarize the existing Permian 87Sr/86Sr records and focus on the current challenges. We also present a new, high-resolution Permian 87Sr/86Sr curve derived from pristine brachiopod shells based on data resulting from careful diagenetic screening. Our new record shows that the 87Sr/86Sr of seawater decreased continuously from the earliest Permian to the middle Capitanian (late Guadalupian), with the lowest ratio of 0.706832 registered in the Colania douvillei-Kahlerina pachiytheca Zone. Subsequently, 87Sr/86Sr ratios increased from the late Capitanian to the latest Permian and reached a ratio of 0.707167 just 0.8 m below the first occurrence of the Hindeodus parvus. We employed a stochastic oceanic box model to explore the potential drivers of the Permian seawater Sr isotope record. Our results support that changes in the hydrothermal input, rather than changes in continental weathering intensity, are the most likely controlling factor for the observed variations in Permian seawater 87Sr/86Sr. Therefore, we suggest that the marine hydrothermal system (and hence ocean basin dynamics and deep-sea temperatures) may have been the driver of the pronounced decreasing 87Sr/86Sr trend across the Permian.

The Permian–Triassic transition witnessed the largest mass extinction event in Earth's history, multiple mechanisms have been proposed to explain the cause of this catastrophe, however, relatively less attention has been paid to the paleogeography and major element chemistry of seawater and its possible link to mass extinction during this interval. Syndepositional massive marine dolostones could record the Mg isotope signature of contemporaneous seawater that hold clues of ancient Mg cycling. In this study, we investigated Mg isotopes of dolomite from three widely spaced carbonate sections in the Paleotethys to trace oceanic Mg cycling during this critical period. The latest Permian dolostones from all studied sections have similar δ 26 Mg values around − 2.1 ± 0.1 ‰ . However, a remarkable and consistent increase in δ 26 Mgdolomite across the extinction interval occurred in both eastern and western margins of the Paleotethys. The results suggest that δ 26 Mg of seawater in Paleotethys fluctuated by 0.4‰ within ∼750 kyr across the Permian-Triassic transition. Modeling reveals that the high rate of change in δ 26 Mgseawater required an extremely short residence time for seawater Mg. This is attributed to dramatically intensified dolomitization in a restricted oceanic environment, with Mg isotope evidence revealing that the Paleotethys Ocean experienced transient restriction events, in association with radical changes in the major cation composition of seawater, around the end-Permian mass extinction event (EPME).

The end-Permian mass extinction has been widely documented to be accompanied with oceanic anoxia, which was considered as one of the most plausible killing mechanisms. However, it is still unclear when anoxia began to occur and how widely affected during the pre-extinction interval. In this study, Lopingian bottom-water oxygen level changes around the Wuchiapingian–Changhsingian boundary (WCB) at the northern Penglaitan section in Guangxi are analysed based on trace fossil assemblages and ichnofabric indices. Detailed bed-by-bed ichnological analyses confirm the presence of trace fossils Chondrites intricatus , C. isp., Palaeophycus isp., Planolites isp. A, P. isp. B, Thalassinoides isp. A, T. isp. B, Trichichnus linearis , Zoophycos isp., and other bioturbational structures. The ichnofabric indices around the WCB are mostly 1–2, but rapidly increase to 4–5 in some short intervals. The distinct fluctuations of ichnofabric indices suggest that the oxygen level of sediments was generally deficient, but the dysoxic or anoxic periods were punctuated by several short oxic intervals. Thus, it can be inferred that the benthic organisms were under secularly environmental stresses around the WCB at the northern Penglaitan section. The anoxic conditions unfavourable for aerobiosis in the deep basin may start in the late Wuchiapingian. However, more sections need to be studied to determine whether this is a local or regional phenomenon.

The end-Permian mass extinction (EPME) was the most severe extinction event of the Phanerozoic. To investigate oceanic redox conditions around the EPME, we conducted a series of geochemical analyses, including iron speciation, trace element geochemistry, total organic carbon (TOC), and nitrogen isotopes of kerogen (δ15Nkero), around the EPME at the Shangsi section, South China. Three intervals with different redox conditions can be distinguished based on iron speciation. During the first interval (early and middle Changhsingian), bottom waters were pervasively euxinic. In the second interval (late Changhsingian and the EPME), bottom water fluctuated between oxic and anoxic, but non-sulfidic conditions, with the oxic mode becoming increasingly predominant over time. During the third interval, following the EPME, bottom waters appeared to have been consistently anoxic, although again not pervasively euxinic. This redox history is supported by enrichments in the authigenic fraction of redox-sensitive elements. These relatively high δ15Nkero values (> 1.0‰) corresponding with Changhsingian euxinia suggest reducing bottom waters did not impinge on the photic zone. The shift to values near 0‰ within and above the EPME indicates an ecological expansion of diazotrophs. Stratigraphic trends of Nixs, Cdxs, Pxs, and TOC indicate that primary productivity was highest in the first interval, coinciding with euxinic bottom water, then decreased during the lower part of Interval 2 and remained at low level through the remainder of the studied section. The temporal relationship between redox condition and primary productivity suggests that euxinia was supported by high productivity and carbon export in the early Changhsingian. The expansion of N2 fixation coincides closely with the previously documented warming of the ocean surface at Shangsi and may be related to reduced oceanic circulation and suppressed vertical mixing. The temporal distribution of deepwater anoxia and euxinia suggests that they were not primary causes for the extinction of benthos at Shangsi.

The end-Permian mass extinction reflects the most severe life crisis during the Phanerozoic and was associated with major global environmental changes. However, the consistency of the time and pattern of the terrestrial and marine extinctions remains controversial. In this paper, we presented detailed analyses of the high-resolution biostratigraphical and geochemical data from terrestrial sections in South China. Our analyses show that the transitional Kayitou Formation actually recorded the process of terrestrial mass extinction as evidenced by the mass disappearance of the Gigantopteris megaflora in the lower part, the dramatic reduction in abundance of palynomorphs in the middle, and the last occurrences of plant remains and abundant charcoal fossils in the uppermost part. It is associated with a distinct negative shift of δ13Corg, beginning in the middle part of the formation, which is correlative with that in the top of Bed 26 at the marine Meishan section. In addition, the Kayitou Formation is characterized by a distinct shift of lithofacies of fresh lake-swamp or river flat environment from olive/grey/black mudstone, siltstone, fine to coarse sandstone in the lower part to gradually increasing maroon rocks, to purely maroon mudrocks with poorly-sorted breccia, calcic palaeosols and calcareous nodules in the lowest part of the Dongchuan Formation, which indicates a dramatic collapse of soil system associated with rapid deforestation and climatic warming and drying. In the coastal area, the Kayitou Formation contains marine beds with the typical Permian–Triassic mixed faunas and floras which are correlative with the latest Changhsingian marine mixed fauna 1 at Meishan. The Kayitou Formation also recorded a distinct transgression that began in the latest Changhsingian. All above phenomena suggest that the Kayitou Formation is actually the witness of the terrestrial end-Permian mass extinction; and it is mostly or entirely of latest Changhsingian (Permian), rather than Triassic age.

Understanding the interplay of climatic and biological events in deep time requires resolving the precise timing and pattern of paleotemperature changes and their temporal relationship with carbon cycle variations and biodiversity fluctuations. In situ oxygen isotope analyses of conodont apatite from South China enables us to reconstruct high-resolution seawater temperature records across the Permian–Triassic boundary (PTB) intervals in the upper slope (Meishan), lower slope (Shangsi), and carbonate platform (Daijiagou and Liangfengya) settings. Constrained by the latest high-precision geochronological dates and high-resolution conodont biozones, we can establish the temporal and spatial patterns of seawater temperature changes and assess their potential connections with the carbon cycle disruption and biodiversity decline. We find a rapid warming of ~ 10 °C during the latest Permian–earliest Triassic that postdated the onset of the negative shift in δ13Ccarb by ~ 81 kyr (thousand years), the abrupt decline in δ13Ccarb by ~ 32 kyr and the onset of mass extinction by ~ 23 kyr, which contradicts previous claims that the extreme temperature rise started immediately before or coincided with the onset of mass extinction. Our new evidence indicates that climate warming was most likely not a direct cause for the main pulse of the end-Permian mass extinction (EPME), but rather a later participant or a catalyst that increased the pace of the biodiversity decline. In addition, a prominent cooling is recorded in the earliest Changhsingian, with the main phase (a drop of ~ 8 °C in ~ 0.2 Ma) confined to the lower part of the Clarkina wangi zone and synchronous with the positive limb of the carbon isotope excursion (CIE) around the Wuchiapingian–Changhsingian boundary (WCB) in Meishan and Shangsi. Further long-term and high-resolution studies from other sections are needed to confirm the full contexts and underlying dynamics of the WCB “cooling event”.

Massive occurrences of microbialites near the Permian–Triassic boundary have been interpreted as being due to benthic microbial proliferation in unusual marine conditions after the end-Permian mass extinction. Here, we present large populations of Polybessurus-like microfossils in the microbialites of the South China Craton to reveal their morphological structures, growth patterns, and ecological implications. These distinctive microfossils are composed of layered stalks and spherical endpoints. The spheroids, 20–40 μm in diameter, comprising external thin micritic walls and internal sparry parts, are interpreted as coccoid cyanobacteria. The stalks consist of multiple “stacked-cup” micritic envelopes consisting of micron-sized magnesian calcite/dolomite grains and are catalogued as calcified remains of coccoid cyanobacterial extracellular polymeric substances (EPS). Early microbially mediated calcification of EPS increased the preservation potential of microfossils. The microfossils stand upright as coccoid unicells supported by the highly unidirectional secretion of EPS, revealing their benthic behaviours. The successively secreted EPS lift the cells away from the substrate, expanding their ecological niches to gain more sunlight for photosynthesis in the barren marine floor. The distinctive Polybessurus-like microfossils can be viewed both in laminae of stromatolites and in spotted/digitate clots of thrombolites, suggesting their critical roles in microbe-dominated reefs in the aftermath of the end-Permian mass extinction. The morphological features and growth patterns of the Polybessurus-like fossils resemble their Proterozoic counterpart—Polybessurus bipartitus Fairchild ex Green et al. (1987) . The widespread Polybessurus-like fossils in the Permian–Triassic boundary microbialites of the South China Craton suggest pervasive retrogressive ecosystems on carbonate platforms after the largest extinction event during the Earth's history.

Climatic warming has been widely cited as a driver for many mass extinction events in Earth history, including the middle-late Permian Guadalupian-Lopingian boundary (GLB) mass extinction and end-Permian mass extinction (EPME) investigated in this study. However, the role of warming in driving the EPME event is under debate because current paleotemperature studies indicate the rapid increase in sea-surface temperature postdate the onset of the EPME event, and a reliable paleotemperature record across the GLB event is lacking. Here, we present a high-resolution and successive δ 18 O record using low-Mg calcite shells of brachiopods (bLMCs) from a single stratigraphic section in central China to reconstruct paleotemperature changes from the middle to the latest Permian. After a rigorous screening for diagenesis, our data show a ∼1.0‰ decrease in δ 18 Ocalcite (and thus climatic warming) during the middle Capitanian, followed by a gradual ∼2.0‰ increase (climatic cooling) during the late Wuchiapingian. From the latest Wuchiapingian to the early Changhsingian, δ 18 O decreased gradually and reached the lowest values of -4.0‰ (and thus rapid climatic warming) immediately before the Permian-Triassic boundary. The two warming events are coeval with the onset of the Emeishan Large Igneous Province and the Siberian Traps Large Igneous Province, respectively, suggesting the two volcanic events are the plausible drivers of these climatic warming events. A close comparison of paleontological and geochemical records indicates that the warming events occurred predate the GLB and EPME events, this is in contrast with conodont δ 18 Oapatite data which document the rapid climatic warming lagged the onset of the extinction event. The comparison between δ 18 O of bLMCs and δ 18 O of conodonts from the same section shows that the long-term trends are similar, but, at higher temporal resolution, discrepancies are present, entailing further investigation in the near future. Our study confirms that δ 18 O of the brachiopod shells underwent important changes during the end of Paleozoic, highlighting that sea surface temperature is a key factor to understand the biosphere history, since it changes simultaneously with the biological crises, and that bLMCs are invaluable archive for tracking physical and chemical conditions of past oceans.

As an important tool in natural resource exploration, palaeogeography provides a portrayal of deep time Earth. The South China Block located in the eastern Palaeotethys includes multiple natural resources (e.g., coal, shale gas, bauxite, etc.) in the Permian, which are well known for their important economic significance. In this paper, data gathered from literature amount to 431 stratigraphic sections of Wuchiapingian age from South China. These data were quantitatively analyzed and dynamically reconstructed in the global context under the revised plate motion model by GPlates software for the first time. A schematic 3-D model was constructed based on the high-resolution reconstructions in this paper, showing two relatively large highlands developed in the South China Block during the Wuchiapingian, including the Kangdian Highland in the west and the Cathaysia Highland in the east and a small Yunkai Highland in the south. A broad platform-dominated depositional system with small uplifts and depressions was developed between these two highlands. These reconstructions show great potential to explore enriched coal seams and shale gas in the peripheral areas of the two ancient highlands in the west and east of the South China Block. Based on the dynamic evolution of this depositional system, South China experienced an overall sea-level rise with frequent secondary transgressions and regressions during the Wuchiapingian. This is in contrast to the widespread continental and evaporite deposits on much of Pangea and its surrounding margins after the end-Guadalupian global regression. Compilation of conodont biostratigraphic data suggest that the temporal and spatial constraints on the unconformity across the Guadalupian-Lopingian boundary (GLB) resulted from Dongwu Uplift movement. The regression began during the Jinogondolella shannoni Zone and ended in the Clarkina leveni Zone, but the response time varies in different localities of South China. These results provide detailed information about sea-level eustacy, tectonic uplift, sedimentary hiatus, resource accumulation and palaeoclimate change from the South China Block during the Wuchiapingian.

The end-Permian marine extinction (EPME) eliminated >80% of species globally, making it the most severe extinction of the Phanerozoic. Anoxia and euxinia are potential kill mechanisms that may have contributed to this biotic crisis. However, redox changes in the atmosphere-ocean system are likely to have been complex, with both the vertical location of the oxic-anoxic boundary (in the water column or sediments), and the total area or volume of anoxic and euxinic water in the global ocean changing over time. In this study, we generated iron speciation and major and trace element data from 141 samples of the Meishan-1 core, which was drilled at a site 550 m to the west of the Meishan D section. Iron speciation results, in combination with authigenic concentrations and enrichment factors of redox-sensitive metals (Mo, V, and U), and previously published macrofossil, trace fossil, and bioturbation evidence, suggest that: 1) Beds 21-24d were deposited beneath a predominantly oxic water column, 2) Beds 24e-28 were deposited under a persistently anoxic watermass with intermittently euxinic bottom water, and 3) Beds 29–34 were deposited under primarily ferruginous conditions. Excess fractions and enrichment factors of U, V and Mo in the anoxic and euxinic intervals of the Meishan-1 core suggest that authigenic precipitation of redox-sensitive trace metals mainly occurred before and during the EPME, with nearly no detectable authigenic U, V, or Mo accumulating after the EPME. Our results, along with published U, V and Mo concentrations from across the Neotethys, Paleotethys, and Panthalassic Ocean basins, indicate that oceanic trace metal reservoirs were depleted before and during the main extinction interval. This depletion of oceanic trace elements suggests a spatial expansion of both anoxic and euxinic watermasses prior to and during the EPME. The apparent coincidence in timing between the mass extinction and the areal expansion of anoxic and euxinic watermasses suggests that these factors played important roles in the loss of marine biota around the Permian-Triassic boundary (PTB), through oxygen deprivation and H2S toxicity.

This paper documents smaller foraminifers from the Maokou Formation (Guadalupian) at the Tieqiao section in Laibin area, South China. The assemblage of smaller foraminifers reported herein consists of 69 species of 42 genera. Although the Maokou Formation of this section was deposited in a relatively deep-water environment, smaller foraminifers are diverse and abundant, especially in debris flow deposits and thin turbidite beds. This fauna bears most similarity with coeval foraminiferal assemblages from the other Palaeotethyan regions. There is a sharp decrease in the diversity and abundance of smaller foraminifers at the lithological boundary between the Maokou and Heshan formations. An overwhelming majority of genera of smaller foraminifers that occur in the Maokou Formation at this section can be found in the Lopingian strata of South China. The study of smaller foraminiferal fauna of the Guadalupian at the Tieqiao section indicates a much less pronounced effect of the pre-Lopingian crisis on smaller foraminifers.

The Lopingian is one of the fastest rising periods of seawater strontium isotopic ratios (87Sr/86Sr) in earth history, and its mechanisms and increasing rates of the 87Sr/86Sr evolution were still disputed widely. These disputations among researchers were caused mainly by timeframe selection (sections’ thickness or data of radiometric ages), and different stratigraphic boundaries and un-upmost dated ages. This paper examined published 87Sr/86Sr data of the Lopingian, and projected them on timescales based on evolutionary and age constrained conodonts fossils. 87Sr/86Sr evolution vs fossil constraining timescales was re-established in this period. This research suggests: (1) 87Sr/86Sr excursion projects on fossil zones can truly support 87Sr/86Sr evolutionary pattern in the period; (2) 87Sr/86Sr evolution provides a new approach for stratigraphic research of marine carbonate sections in lieu of biostratigraphic data; (3) 87Sr/86Sr stratigraphy works on marine carbonate sections of different sedimentation rates even between different basins; (4) the 87Sr/86Sr data and its shift was dependent on samples materials and chemical treatment methods; (5) the increasing rate of marine water 87Sr/86Sr in the Late Permian is suggested as 5.4×10−5/Ma or slightly lower; (6) sedimentation age and its 87Sr/86Sr of the Lopingian marine carbonate suggested as: DPRO=259-(RS−0.70695)/5.4×10−5±1 Ma.

Previous studies suggested rapid evolution of conodonts across the Permian–Triassic boundary (PTB), and the end-Permian mass extinction pattern varies in different sections in South China. Here we document a high-resolution conodont succession from a carbonate facies of the Changhsingian Stage and across the PTB at the Daijiagou section, about 35 km north to Chongqing City, Southwest China. Two genera and twelve species are identified. Seven conodont zones are recognized from the uppermost part of the Lungtan Formation to the lowest Feixianguan Formation. They are the Clarkina liangshanensis , C. wangi , C. subcarinata , C. changxingensis , C. yini , C. meishanensis , and Hindeodus parvus zones in ascending order. Based on the high-resolution biostratigraphical framework at Daijiagou, the end-Permian mass extinction was rapid and it began in the base of the Clarkina meishanensis Zone. Associated with the extinction, a negative excursion of δ 13 C carb started in the middle part of Clarkina yini Zone with a progressive shift of 1.6‰ to the middle part of the Clarkina meishanensis , followed by a sharp shift of 3.51‰ from the Clarkina meishanensis Zone to the Hindeodus parvus Zone. Our study also suggests that the Triassic index species Hindeodus parvus co-occurred with Hindeodus changxingensis and Clarkina zhejiangensis and directly overlies the Clarkina meishanensis Zone at the Daijiagou section. All these data from the Daijiagou section and some previous studies of other sections in Sichuan, Guizhou provinces and Chongqing City suggest that the first occurrences of Hindeodus parvus are slightly earlier than the sharp negative excursion of δ 13 C carb and the FAD at the Meishan GSSP section. We consider that the slight difference of the end-Permian mass extinction, chemostratigraphy and conodont biostratigraphy at Daijiagou and its adjacent areas is most likely subject to different lithofacies, fossil preservation, and the constraint on the stratigraphic resolution rather than a different tempo of the end-Permian mass extinction in a global sense. The whole Changhsingian conodont succession at Daijiagou provides a high-resolution correlation with other equivalent sections in the Palaeotethys. The controversial results of biostratigraphy and chemostratigraphy between the sections investigated in this paper and the Meishan GSSP section also provide some important implications that accurate chronocorrelation requires the evaluation of multiple, varied stratigraphcal signals rather than relying solely on the FAD of the Triassic index species Hindeodus parvus for recognizing the Permian–Triassic boundary (PTB). Growth series of abundant specimens for each species are figured. The taxonomy of some Hindeodus species in the PTB interval is updated.

Volcanism and impact scenarios are two of the most plausible ways of interpreting the causes of the largest biological mass extinction at the end-Permian. Microspherules have previously been widely reported from tens of different Permian–Triassic boundary (PTB) sections in South China and some other regions. These microspherules have been interpreted as either the product of volcanic eruptions or an impact event. In order to test these scenarios, we collected 60 samples from 12 intensively-studied PTB sections in South China. In addition, four soil samples close to these PTB layers were also collected for comparison. Our investigation indicates that abundant microspherules with mosaic or dot shape crystals on rounded surface are present in the surface samples in the PTB layers at Meishan, Meili, and Shatian sections and most soil background samples in South China. Those microspherules consist of four different types based on their main chemical composition, surface features, and internal structure including iron, magnetite–silicate, glassy, pyrite microspherules and framboids. In contrast, microspherules have not been found in a few sections in remote areas such as the Selong Xishan section in Tibet and the Dalongkou section in Xinjiang, Northwest China, in the deeply-excavated samples at the Shangsi section and the hard tuff layers around the PTB at the Xiaochehe Section in Guiyang. Microspherules decrease in abundance with depth in PTB clay beds. All these microspherules except the pyrite microspherules and framboids are found in both the PTB layers and the nearby soil background samples. The iron microspherules are pure iron oxides such as magnetite, hematite or maghemite and contain low concentrations of nickel and chromium, and lack an Ni–Fe core and general extraterrestrial mineral wustite. All these external and chemical characteristics suggest that most of iron microspherules previously reported from PTB sections in South China are modern industrial fly ashes. A low ratio of Fe 3 + /Fe Total in crystals of magnetite–silicate microspherules and high ZnO contents can identify them as industrial contaminants. The pyrite microspherules and framboidal pyrite found from bed 24e and bed 26 at the Meishan sections are of depositional or/and diagenetic origins, and only the rounded quartz and the fragments containing extremely high SiO 2 and TiO 2 are possibly of volcanic origin.

Large carbon cycle perturbations are associated with the end-Permian mass extinction and subsequent recovery, but Late Permian (Lopingian) carbon cycle dynamics prior to the mass extinction event remain poorly documented. Here we present a high-resolution δ13Ccarb chemostratigraphic framework from latest Guadalupian to earliest Triassic time, calibrated with high-resolution conodont biostratigraphy and high-precision geochronology. We observe two large negative excursions in δ13Ccarb, the first in uppermost Guadalupian strata and the second at the end of the Changhsingian stage, and between these events distinctive excursions from the middle Wuchiapingian to the early Changhsingian. The end-Changhsingian excursion represents a major reorganization of the global carbon cycle associated with the end-Permian mass extinction. However, the extent to which the end-Guadalupian and Wuchiapingian/Changhsingian boundary excursions result from local versus global controls remains unresolved. Regardless of their underlying causes, these three excursions provide chemostratigraphic markers for global correlation of Lopingian strata.

The microfacies sequence in the key interval of Beds 24–29 of the Meishan section comprehensively recorded the geological events during the Permian-Triassic transition, including the anoxia, storm disturbance, hard-ground/firm-ground form, volcanic eruption, weathering input, and microbialite development. This investigation of event sequences on the microfacies provided synthetically some clues to clarifying the previously proposed mechanisms of the end-Permian extinction. The deposit succession in Bed 24 of the Changxing Formation was developed dominantly with organic-rich lamina, but interrupted intermittently by storm disturbances. It indicates characteristically a stagnated, stratified and anoxic ocean during the latest Permian. The latest Permian transgression occurred rapidly at the top of Bed 24d and was characterized by the hard-ground interface. Abundant clay mineral of illite indicates the occurrence of persistent weathering of continental volcanics and then buried in ocean throughout this key Permo-Triassic transitional interval. However, the “boundary ash clay” of Bed 25 yielding normal grading of hyaloclastite was the result of precipitation of volcanic dusts. The firm-ground substrate in Unit 27-2 was lithe and excavated intensively by trace fossil Glossifungites; it means also the occurrence of the earliest Triassic rapid transgression and coincides with the first appearance of conodont Hindeodus parvus. Dune-shaped microbialite in Unit 27-5 defines biostratigraphically that its development, especially in the carbonate platform of South China, should correspond to the earliest Triassic; and it also indicates the final episode of the end-Permian extinction event.