Search

The Carnian Pluvial Event (CPE) was an interval marked by global climatic and environmental change, along with biotic turnover, which occurred during the early Late Triassic. Although the causes and consequences of this event remain unclear, one possible scenario is enhanced volcanism injecting greenhouse gases into the atmosphere, perturbing the global carbon cycle, and negatively impacting the global environment. However, there is an underlying challenge in showing a true cause- and-effect relationship between volcanism and the CPE, as both the sedimentary and volcanic records are difficult to date accurately enough to demonstrate temporal correspondence. However, mercury (Hg) can be used to fingerprint catastrophic volcanism in the sedimentary record. We examined two sections that record the CPE at Laishike and Wayao in Guizhou Province, southwest China, which display high Hg contents along with spikes of Hg/total organic content (TOC), Hg/Al, Hg/total sulfur (TS), and Hg/(Mo/Al) during the CPE that indicate a shift to excess Hg loading. These Hg anomalies are correlative with the global negative excursion in δ13Ccarb values at the CPE, which suggests that increased volcanism injected both massive amounts of Hg and isotopically light carbon into the atmosphere, and these were ultimately recorded in marine sediments. This interpretation is supported by slightly negative or near-zero Δ199Hg values that are consistent with a volcanic Hg source. Our study supports the hypothesis that enhanced volcanism played a major role in the evolution of biota and the environment during the CPE.

The Rhynchonellida is a major group of brachiopods that survived the “big five” mass extinctions and flourished after the Permian/Triassic (P/Tr) crisis. However, phylogenetic and character evolution in the Rhynchonellida across the P/Tr transition is poorly understood. In view of the widespread homoplasy across this order, we employ a tip-dated Bayesian analysis to reconstruct phylogenetic relationships for late Permian–Triassic rhynchonellides. The same data were also analyzed using three other methods: undated Bayesian, equal-weighting, and implied-weighting parsimony. Compared with trees generated by other methods, those constructed by tip-dating best account for the homoplasy in this group and are closer to previous assumptions on the evolution of this order. Based on the analyses of multiple trees, the major increase in lineage richness occurred in the Early and early Middle Triassic. Also, richness in the Anisian almost reached the highest level seen in the Triassic. According to fossil records, a pronounced reduction in shell size and in the development of ornamentation occurred after the P/Tr extinction, which is largely due to the loss of large and highly sculptured genera and the diversification of small-sized and weakly ornamented genera. Ancestral-state estimation of shell size and development of ornamentation, coupled with comparisons of other characters, indicate that the Early–Middle Triassic mature “small-sized taxa” may have characters displayed by juveniles of their ancestors. This suggests that for these genera, paedomorphosis was possibly a strategy to survive and diversify in the harsh environment after the P/Tr extinction.

The Permian-Triassic mass extinction severely depleted biodiversity, primarily observed in the body fossil of well-skeletonized animals. Understanding how whole ecosystems were affected and rebuilt following the crisis requires evidence from both skeletonized and soft-bodied animals; the best comprehensive information on soft-bodied animals comes from ichnofossils. We analyzed abundant trace fossils from 26 sections across the Permian-Triassic boundary in China and report key metrics of ichnodiversity, ichnodisparity, ecospace utilization, and ecosystem engineering. We find that infaunal ecologic structure was well established in the early Smithian. Decoupling of diversity between deposit feeders and suspension feeders in carbonate ramp-platform settings implies that an effect of trophic group amensalism could have delayed the recovery of nonmotile, suspension-feeding epifauna in the Early Triassic. This differential reaction of infaunal ecosystems to variable environmental controls thus played a substantial but heretofore little appreciated evolutionary and ecologic role in the overall recovery in the hot Early Triassic ocean.

The Guadalupian–Lopingian boundary (GLB), also Middle–Late Permian boundary, mass extinction severely destroyed metazoan reef ecosystems, although some studies argued that both biotic and environmental turnover across the GLB are not so obvious. When compared with prolifically developed reefs in the Capitanian, the Wuchiapingian reef examples appear depauperate and almost 89% of the carbonate production in these bioconstructions was lost. Here, we report a typical sponge reef from the Wuchiapingian stage in the Tieqiao section, central Guangxi Province, South China. The Tieqiao reef might represent the only example of a Wuchiapingian metazoan reef in the eastern Palaeo-Tethys region. It provides insight into ecosystem restoration following the GLB extinction. Major constructors of the Tieqiao reef are sponges ( Peronidella , Parauvanella , Sollasia , Tabulozoa, and Amblysiphonella ), algae ( Anthracoporella , Archaeolithporella , Permocalculus , Gymnocodium ) and Tubiphytes . This reef is well constrained as middle–late Wuchiapingian in age by the Clarkina orientalis conodont zone. Carbonate carbon isotope excursions experienced negative spikes near the GLB and multiple perturbations in the early–middle Wuchiapingian, and remained relatively stable during re-establishment of metazoan reefs in middle–late Wuchiapingian. Conodont oxygen isotopes showed that the sea surface temperature (SST) was extremely high, > 30 °C during late Capitanian time, punctuated by a short cooling event and global regression associated with the GLB extinction, and followed by high SST and rapid rise in sea level in the early Wuchiapingian. The reemergence of the Tieqiao reef coincided with the initial cooling in surface oceans and sea-level fall during the middle–late Wuchiapingian. Accordingly, reef ecosystems experienced a long-term depletion worldwide in early–middle Wuchiapingian time and then recovered ~ 2.5 Myr after the GLB extinction based on estimate in integration of both conodont biostratigraphy and radiometric ages.

Biotic activities are involved in almost all sedimentation processes throughout the evolutionary history of life on our planet. However, deep-time organism-induced sedimentation and biosedimentary records remain unclear in terms of lithologic types, strata stacking patterns and possible controlling factors. We document biosedimentary features of major transitions from microbe-dominated switching to metazoan-dominated biosedimentary systems based on the global distributions of both microbial and metazoan carbonates through Precambrian to Phanerozoic times, with emphasis on sedimentary records from China. The compilation of 150 and 180 well-documented metazoan and microbial reefs, respectively, from China, reveals that metazoan reefs proliferated during the Middle Ordovician, Middle Devonian and Middle Permian, whereas microbial reefs were well developed during the Cambrian, Late Devonian and Early–Middle Triassic, plus a moderate development during the early Silurian. These stratigraphic abundances of metazoan and microbial carbonates of China generally match the global patterns. The updated variation trends of microbial and metazoan carbonates throughout the late Precambrian and Phanerozoic reveal that there were five major microbe-metazoan transitions (MMTs): the late Ediacaran, the Cambrian, and the aftermaths of the mass extinctions of the end-Ordovician, Late Devonian, and end-Permian. The late Ediacaran MMT began with microbe-dominated oceans with occasional occurrences of metazoans. The presence of Cloudina-dominated reefs in the latest Ediacaran marks the completion of the switching of this microbe-dominated depositional system into a metazoan-dominated system. The Cambrian saw the expansion of skeletal microbes (i.e., Epiphyton, Renalcis) in the oceans; and the stratigraphic successions yield the most diverse biosedimentary deposits and/or structures of the entire Phanerozoic. The Cambrian MMT was the longest microbial-metazoan alternation period and is marked by two metazoan occurrence peaks marked by dominance of abundant archaeocyath buildups during its Epoch 2 and by maceriate and lithistid sponge reefs during the late Furongian Epoch. The early Silurian in China saw the deposition of a thick suite of organic-rich black shales followed by alternations of microbe-rich sediments (oil shales) and metazoan-bearing deposits, which are replaced by microbial and metazoan reefs during the late early Silurian. The Late Devonian MMT started during the late Frasnian and persisted into the early Mississippian, and thus extended slightly longer than the aftermath of the Frasnian–Famennian extinction interval. Alternating occurrences of microbial and metazoan reefs characterize this Late Devonian MMT. Almost all microbe-mediated sediments/structures observed in the Cambrian MMT reoccurred in the aftermath of the end-Permian mass extinction during the Early–Middle Triassic MMT, suggesting high similarities between those two MMTs. Cambrian and Early–Middle Triassic MMTs also share comparable carbon and sulfur isotopic perturbations, warming regimes, and generally oxygen-deficient seawaters. Some of these environmental and climatic extremes may also occur during other MMTs, but they usually did not occur synchronously. Most MMTs seem to have undergone four developmental stages. They initiated as microbe-dominated successions (Stage A), and then were characterized by alternations of microbe-dominated and of metazoan-bearing or bioturbated successions (Stage B). Both microbial and metazoan reefs co-occurred during Stage C; and a dominance of metazoan reefs marks the development of Stage D. Ediacaran and Cambrian MMTs seem to have undergone the first three development stages, whereas the three post-extinction MMTs experienced the full set of Stages A−D, corresponding to metazoan survival, initial recovery and full recovery. The majority of volatile-rich Large Igneous Provinces (LIPs), coupled with intensive acidification events, anoxia and global warming regimes, took place during the Mesozoic–Cenozoic. However, microbe-dominated sediments were only widely deposited during the Early Triassic, and greatly declined after that time. Therefore, it seems that microbial abundance in MMTs may not be directly related to these extreme LIP events. This is probably because a primary source of food for the metazoans might have shifted to phytoplankton (e.g., coccoliths, dinoflagellates, and radiolarians) in the marine waters since the Triassic. Certainly, the pre-Mesozoic oceans were not dominated by phytoplankton. Perturbations in the carbon isotope record characterize all MMTs, and thus may be reliable proxies indicating MMT biosedimentary systems.

We report two shallow marine, ichnofauna-bivalve-microbial mat biofacies from the Lower Triassic Xiahuancang Formation of the southern Qilian area, Qinghai Province, northwestern China, which was located at moderate-high paleolatitudes on the northern margin of the Paleotethys Ocean. Paleoenvironmental analyses show that Members I and II of the Xiahuancang Formation represent a shoreface and a lower shoreface to offshore transition setting, respectively. Biofacies 1, recognized from Member I, is characterized by a diverse ichnofauna (including deep-tiers of Rosselia and Diplocraterion), Claraia-dominated bivalves, and microbially induced sedimentary structures (MISSs). Biofacies 2, in succeeding Member II, is dominated by a diverse ichnofauna, epifaunal and shallow infaunal bivalves, and wrinkle structures. Primary co-occurrences, preservational features, and palimpsest or crosscutting relationships of all components within the biofacies indicate that microbial mats, bivalves, and trace-makers actively interacted with one another during deposition. They largely represent contemporaneous biotic associations. Microbial mats are interpreted to have grown under well-oxygenated conditions after storm deposition due to the association of deep-tiering infauna and diverse epifauna as well as well-developed cross-stratification, and the top layer of microbial mats could serve as an oasis for metazoans. Microbial mats not only proliferated in harsh environments, but also coexist with epifauna and deep-tiering infauna in well-oxygenated settings following the end-Permian crisis. Their occurrences in the Early Triassic are unrelated to environmental stresses, which are coincident with their sedimentologic record from other geological time intervals. Apparently, the southern Qilian ichnofauna-bivalve-microbial mat biofacies with juxtaposed epifauna, infauna and MISS- or wrinkle-related microbial mats represents a matground-adapted benthic metazoan ecosystem in the earliest Triassic, which provided sufficient oxygen, food, and other hydrodynamic conditions hospitable for metazoans and ecosystems to recover and reached a fairly high level (recovery stage 3) in a tough time when most biotas suffered biotic depletion and environmental stress. The biotic components in unique biofacies may represent a phase shift community in siliciclastic settings during the Early Triassic.

The Earth has been beset by many crises during its history, and yet comparing the ecological impacts of these mass extinctions has been difficult. Key questions concern the kinds of species that go extinct and survive, how communities rebuild in the post-extinction recovery phase, and especially how the scaling of events affects these processes. Here, we explore ecological impacts of terrestrial and freshwater ecosystems in three mass extinctions through the mid-Phanerozoic, a span of 121 million years (295–174 Ma). This critical duration encompasses the largest mass extinction of all time, the Permian–Triassic (P–Tr) and is flanked by two smaller crises, the Guadalupian–Lopingian (G–L) and Triassic–Jurassic (T–J) mass extinctions. Palaeocommunity dynamics modelling of 14 terrestrial and freshwater communities through a long sedimentary succession from the lower Permian to the lower Jurassic in northern Xinjiang, northwest China, shows that the P–Tr mass extinction differed from the other two in two ways: (i) ecological recovery from this extinction was prolonged and the three post-extinction communities in the Early Triassic showed low stability and highly variable and unpredictable responses to perturbation primarily following the huge losses of species, guilds and trophic space; and (ii) the G–L and T–J extinctions were each preceded by low-stability communities, but post-extinction recovery was rapid. Our results confirm the uniqueness of the P–Tr mass extinction and shed light on the trophic structure and ecological dynamics of terrestrial and freshwater ecosystems across the three mid-Phanerozoic extinctions, and how complex communities respond to environmental stress and how communities recovered after the crisis. Comparisons with the coeval communities from the Karoo Basin, South Africa show that geographically and compositionally different communities of terrestrial ecosystems were affected in much the same way by the P–Tr extinction.

Figure S1. Palaeogeography of Xinjiang and stratigraphy of the studied formations; Figure S2. Nonmetric multidimensional scaling ordinations of food-web; Figure S3. Rarefaction analysis of number of species against number of guilds; Figure S4. Diversity versus duration of time bin plot of the palaeocommunities in Xinjiang; Figure S5. Boxplots showing the variation range in PC1 and PC2 for species-level networks for each community. Community robustness decreases with elevating PC scores for both components; Figure S6-19. Plots showing secondary extinction versus primary perturbation for each of the 14 communities. Period of community is indicated by color, with red for Permian, purple for Triassic and blue for Jurassic; Figure S20-32. Plots showing secondary extinction versus primary perturbation for each of the 13 communities (randomly reduced species richness to 54). Period of community is indicated by color, with red for Permian, purple for Triassic and blue for Jurassic; Table S4. Mann-Whitney U tests results of the collapse thresholds between the original and the reduced species richness communities; Section S1. Sampling and uneven strata issues; Section S2. Principal components analysis (PCA); Section S3. Sources used to compile the database.

Summary The Late Permian mass extinction is the largest mass extinction of whole geological history, followed by a prolonged life recovery expending the early Triassic. To better understand the recovery pattern of primary productivity through Permo-Triassic intervals and its longer-term changes in early Triassic, we applied biomarkers to reveal the community evolutions of marine primary producers. Our results indicate a possible rapid recovery of eukaryotic primary producers after the extinction during Griesbachian-Dienerian.

The Guryul Ravine section in Kashmir, northern India is an important reference section for global Lower Triassic stratigraphy. Once a candidate Global Stratotype Section and Point (GSSP) for the Permian-Triassic Boundary (PTB), the section has attracted intense attention for the PTB beds, but few studies have concerned the entire Lower Triassic stratigraphy. As one of the most continuous marine Lower Triassic successions on the northern margins of Gondwana, the Guryul Ravine section provides an important conodont biostratigraphic yardstick for worldwide correlations. This study presents recent results of the Lower Triassic conodont zonation from the Guryul Ravine section. A total of 6500 elements including 1600 P1 elements were recovered. Ten conodont zones were recognized from the Griesbachian to Spathian: Hindeodus parvus, Isarcicella staeschei, Clarkina planata, Neoclarkina krystyni, Neospathodus dieneri, Ns. pakistanensis, Novispathodus waageni, Scythogondolella mosheri, Nv. pingdingshanensis, and Nv. abruptus – Nv. brevissimus zones. The PTB is placed within Bed 52 in Unit E2, 80 cm above the base of Unit E2, based on the first occurrence (FO) of H. parvus. The Induan–Olenekian boundary (IOB) is tentatively placed at the base of Member G according to the positive maximum δ13Ccarb values, but it could be slightly higher based on conodonts. The Smithian-Spathian boundary (SSB) is drawn at the top of Member H based on the FO of Nv. pingdingshanensis and the carbon mdpt(N3-P3). Several conodont taxa are newly recognized near the top of the study section where the conodont fauna is dominated by segminiplanate elements of the Neogondolellinae. Many of these age-diagnostic species have been identified in other sections around the world, and their occurrence in Guryul Ravine supports their potential for worldwide correlation. The conodont sequence erected from the study section corresponds well to those of South China (e.g. Meishan) and elsewhere worldwide. The newly established conodont zonation from Kashmir provides a high precision time-frame to consider biotic evolution and environmental change during the Early Triassic, a crucial period of Earth history.

Abundant, exceptionally preserved coprolites are documented from the Luoping biota (Anisian, Middle Triassic) of Yunnan Province, southwest China. These coprolites can be categorized into four morphological types: A) bead to ribbon-shaped, B) short to long cylindrical-shaped, C) flattened, disk-like, and D) segmented faeces. Detailed multi-disciplinary studies reveal that coprolite type A was likely produced by invertebrate animals, while coprolite types B to D could be faeces generated by carnivorous fishes or marine reptiles, perhaps from different taxonomic groups. When compared with coprolites reported from the Lower Triassic, the Luoping forms indicate more complicated predation-prey food web networks. These evidences, combined with body fossil discoveries from Luoping, suggest the emergence of complex trophic ecosystems in the Anisian, marking the full biotic recovery following the Permian–Triassic Mass Extinction.

A detailed, 10 m.y. redox history of Changhsingian to Anisian (latest Permian to Middle Triassic) oceans in ramp settings is reconstructed based on framboidal pyrite analysis from South China. The result shows that the well-established phenomenon of intense ocean euxinia-anoxia is faithfully recorded in pyrite framboid data. Three major euxinia-anoxia episodes, namely, the end-Changhsingian to end-Smithian, middle to late Spathian, and early to middle Anisian, have been recognized from the ramp successions. The first reducing episode is subdivided into four subepisodes: Permian-Triassic boundary, Griesbachian-Dienerian boundary, earliest Smithian, and end-Smithian. Redox variations broadly track other oceanographic proxies. Euxinia-anoxia episodes coincide with positive excursions of conodont ΩCe anomalies, negative excursions of δ34Scas (carbonate-associated sulfate), increases in sea-surface temperature, and negative excursions of δ13C in most cases. However, euxinia-anoxia near the Dienerian-Smithian boundary coincided with positive excursions of δ13C and a general cooling period. This exception may be the result of locally developed water-column anoxia. The Permian-Triassic boundary subepisode witnessed two ephemeral euxinia-anoxia events separated by a dysoxic to oxic period. The former, together with a rapid increase in sea-surface temperature (up to 8 °C), may have been responsible for the biodiversity crisis, while the latter anoxic event destroyed ecosystem trophic structures. In addition to the Permian-Triassic boundary euxinia-anoxia event, which spread over habitats in all oceans, the Spathian and Anisian euxinia-anoxia episodes also prevailed in global oceans. Variation of the oxygen minimum zone are suggested as the driving mechanism that facilitated the movement of oxygen-poor water columns in various paleogeographic settings over this critical period.

As the higher trophic guilds in marine food chains, top predators such as larger fishes and reptiles are important indicators that a marine ecosystem has recovered following a crisis. Early Triassic marine fishes and reptiles therefore are key proxies in reconstructing the ecosystem recovery process after the end-Permian mass extinction. In South China, the Early Triassic Jurong fish fauna is the earliest marine vertebrate assemblage in the recovery period. It is constrained as mid-late Smithian in age based on both conodont biostratigraphy and carbon isotopic correlations. The Jurong fishes are all preserved in calcareous nodules embedded in black shale of the Lower Triassic Lower Qinglong Formation, and the fauna comprises at least three genera of Paraseminotidae and Perleididae. The phosphatic fish bodies often show exceptionally preserved interior structures, including network structures of possible organ walls and cartilages. Microanalysis reveals the well-preserved micro-structures (i.e. collagen layers) of teleost scales and fish fins. Abundant small pyrite framboids, 2–5 μm in diameter, are detected from the nodules and fish body surfaces, indicating a calm, euxinic burial environment. Coccoid-like microspheroids are also very abundant in the host rocks and near the fish fossil surfaces, implying that microbes may have participated in the burial process of the fishes. Taphonomic analysis uncovers the four-step formation process of the fish nodules. (1) Fishes lived in the oxic seawater in the upper ocean, and (2) their bodies sank to the anoxic seabed after death, with the body surface being wrapped by bacteria. (3) Microbial biofilms sealed body surfaces to prevent or delay the decay of the fleshy body. The decomposition of the body cavity and interior organs produced some CO2 and H2S gases. The former formed bicarbonate ions in seawater and attracted calcium ions to facilitate the precipitation of calcium carbonate, while the H2S combined with iron ions in seawater to form pyrite framboids. (4) The fish nodule gradually grew by precipitation of calcium carbonate in layers and embedding with pyrite framboids, and later the fish fossil nodule was compacted during diagenesis. Global faunal correlations indicate that the Jurong fishes are closely related to the Early Triassic fish faunas from Chaohu, Anhui Province and Madagascar.

Widespread stromatolites and other microbialite deposits characterize Lower Triassic marine successions worldwide. This study documents a stromatolite deposit, 1.1 m thick, from the upper Spathian (Lower Triassic) of the Susong area, South China. The stromatolite comprises distinct laminated domes in the basal part and columns at the upper part. Dark laminae are loosely spaced and interlayered with thicker light colored laminae. Diffusive dark colored laminae are composed of peloidal micrite that grade locally into microclotted structures, and yield copies of bacteria clump-like and coccoid-like spheroid aggregates. The former are characterized by cloudy, micrite nuclei rimmed by coarse-grained, euhedral sparry calcite crystals, while the latter are comprised of solid calcite crystal nuclei coated with rather thin micrite envelopes. The cloudy, micrite nuclei resemble bacteria clump-like structures observed in present-day travertine. Both the coccoid-like spheroids and bacteria clump-like structures are surrounded by coarse-grained euhedral calcite crystals, suggesting a similar accretion mechanism. Both spherical structures therefore could be crucial in the accretion of the Susong stromatolite. The laminated/microclotted structures are interpreted as the result of variation in timing of lithification relative to the timing of the decay of microbes. Micro-analysis also unravels the common occurrence of authigenic micro-quartz crystals in association with Fe-bearing illite clay minerals in the stromatolite columns. Their coalescing nature with each other, together with the associated pyrite grains, strongly support the formation of micro-quartz crystals from microbial reduction of an Fe-bearing smectite precursor by sulfate reducing bacteria. A comparison of the Susong stromatolite with its counterparts from the upper Lower Triassic strata in Dajiang, South China reveals many similarities in stromatolite microstructures, suggesting that a harsh, euxinic–anoxic environment resulting in the bloom of sulfate reducing bacteria most likely extended into the latest Spathian in South China.

Microbially induced sedimentary structures (MISSs) are commonly present in siliciclastic shallow marine settings following the end-Permian mass extinction, but have been rarely reported in the post-extinction terrestrial ecosystems. Here, we present six types of well-preserved MISSs from the upper Sunjiagou Formation and lower Liujiagou Formation of Induan (Early Triassic) age in the Yiyang area, Henan Province, North China. These MISSs include: polygonal sand cracks, worm-like structures, wrinkle structures, sponge pore fabrics, gas domes, and leveled ripple marks. Microanalysis shows that these MISSs are characterized by thin clayey laminae and filamentous mica grains arranged parallel to bedding plane as well as oriented matrix supported quartz grains, which are indicative of biogenic origin. Facies analysis suggests that the MISS-hosting sediments were deposited in a fluvial sedimentary system during the Early Triassic, including lake delta, riverbeds/point bars, and flood plain paleoenvironments. Abundant MISSs from Yiyang indicate that microbes also proliferated in terrestrial ecosystems in the aftermath of the Permian–Triassic (P–Tr) biocrisis, like they behaved in marine ecosystems. Microbial blooms, together with dramatic loss of metazoans, may reflect environmental stress and degradation of terrestrial ecosystems or arid climate immediately after the severe Permian–Triassic ecologic crisis.

The Meishan section, South China is the Global Stratotype Section and Point (GSSP) for the Permian-Triassic boundary (PTB), and is also well known for the best record demonstrating the Permian-Triassic mass extinction (PTME) all over the world. This section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest Phanerozoic biocrisis of life on Earth; many important scenarios interpreting the great dying have been proposed on the basis of data from Meishan. Nevertheless, debates on biotic extinction patterns and possible killers still continue. This paper reviews all fossil and sedimentary records from the Permo-Triassic (P-Tr) transition, based on previously published data and our newly obtained data from Meishan, and assesses ecologically the PTME and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis. Eight updated conodont zones: Clarkina yini, Clarkina meishanensis, Hindeodus changxingensis, Clarkina taylorae, Hindeodus parvus, Isarcicella staeschei, Isarcicella isarcica, and Clarkina planata zones are proposed for the PTB beds at Meishan. Major turnover in fossil fragment contents and ichnodiversity occurs across the boundary between Bed 24e-5 and Bed 24e-6, suggesting an extinction horizon in a thin stratigraphic interval. The irregular surface in the middle of Bed 27 is re-interpreted as a firmground of Glossifungites ichnofacies rather than the previously proposed submarine dissolution surface or hardground surface. Both fossil fragment contents and ichnodiversity underwent dramatic declines in Beds 25-26a, coinciding with metazoan mass extinction. Fossil fragment content, ichnodiversity and all ichnofabric proxies (including burrow size, tiering level, bioturbation level) indicate that the P-Tr ecologic crisis comprises two discrete stages, coinciding with the first and second phases of the PTME in Meishan. Ecologic crisis lagged behind biodiversity decline during the PTME. Pyrite framboid size variations suggest that depositional redox condition was anoxic to euxinic in the latest Changhsingian, became euxinic in Beds 25-26a, turned dysoxic in Bed 27, then varied from euxinic to anoxic through most of the Griesbachian. The ~9°C increase in seawater surface temperature from Bed 24e to Bed 27 at Meishan seems to result in dramatic declines in biodiversity and fossil fragment contents in Beds 25-26a, but had little effect on all ecologic proxies. Both metazoans and infauna seem not to have been affected by the pre-extinction anoxic-euxinic condition. The anoxic event associated with the PTME may have occurred in a much shorter period than previously thought and is only recorded in Beds 25-26a at Meishan. Fossil fragment contents, ichnofaunas, ichnofabrics and pyrite framboid size all show that no signs of oceanic acidification and anoxia existed in Bed 27. The early Griesbachian anoxia may have resulted in rarity of ichnofauna and metazoans in the lower Yinkeng Formation, in which the ichnofauna is characterized by small, simple horizontal burrows of Planolites, and metazoan faunas are characterized by low diversity, high abundance, opportunist-dominated communities. The rapid increase of ~9°C in sea-surface temperature and a short anoxia or acidification coincided with the first-pulse biocrisis, while a prolonged and widespread anoxia probably due to a long period of high seawater temperate condition may be crucial in mortality of most organisms in the second-pulse PTME. Marine ecosystems started to recover, coupled with environmental amelioration, in the late Griesbachian.

Early Middle Triassic stromatolites are documented for the first time from the Guanling Formation of the Luoping area, eastern Yunnan Province, SW China. The Luoping stromatolites show six types of constructional microbial forms: ?1) typical stratified columnar structures with crinkled laminae. Dark colored laminae are composed of filamentous cyanobacteria, showing a vertical growth fabric. ?2) Laminoid fenestrae and ?3) clotted structures are also commonly present; these clotted fabrics also show an interweaved pattern of ?4) prostrate filaments, which are reflected by strong fluorescence in sharp contrast to dolomite cement in fluorescent images. ?5) Rod-like aggregates, filled with minute dolomite rhombs, are very common in laminae; they resemble present-day cyanobacterial trichome, and thus may represent fossilized cyanobacteria. ?6) Moreover, small pits, coccoid spheroids, calcified biofilms, and fibrous structures are also common in stromatolite laminae. The last two may represent calcified extra-cellular polymer secretions (EPS) that contribute to the development and lithification of stromatolites. Authigenic quartz grains are also common and may have involved biological processes in their formation. These six functional-groups driving accretion and lithification processes of stromatolite documented in literature, both the lithified cyanobacteria/oxygenic phototrophs and sulphate-reducing bacteria (SRB) which induced microbial formation of dolomite are evident in the Luoping stromatolites, suggestive of biogenic origin. The Luoping stromatolites differ from the Early Triassic counterparts in having a great amount of biomass in filamentous cyanobacteria and SRB, whereas both anoxygenic phototrophic bacteria and SRB characterize the Early Triassic stromatolites. Abundant filamentous cyanobacteria may indicate proliferation of oxygenic phototrophs in a normal, oxic habitat. However, abundant SRB indicate sulfate reduction in a stressed habitat. Accordingly, the Luoping stromatolites, coupled with coeval unusual biosedimentary structures, indicate that the post-extinction devastated oceanic conditions may not only have prevailed in the Early Triassic but also have extended to the early Anisian (Middle Triassic) in South China, just before the full recovery of marine ecosystems in middle-late Anisian. 111 Program of China (B08030 to SCX); National Natural 460 Science Foundation grant (No 41272023 to ZQC); grant-in-aid for the study on the 10 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 Permian−Triassic mass extinction and recovery from the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (to ZQC).