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We challenge the prevailing view that the end‐Permian extinction impeded the Triassic evolution of sponges. Here, we report a deep‐water community dominated by abundant keratose sponges in the lowest Triassic strata from Southwest China. The sponge fossils occur as dark elliptical imprints in mudstone with distinct oscula on their tops. The structure of preserved fibers suggests closest affinity with the extant Dictyoceratida, an aspiculate demosponge. The exceptional preservation plays a crucial role in retaining their exquisite structures. Sedimentary, taphonomic, pyrite framboid, and trace elemental analyses indicate that the sponges proliferated in an oxygen‐poor habitat, demonstrating the high tolerance of sponges to severe conditions. Sponge proliferation is a signal of environmental upheaval but they also stabilized the ecosystem, driving the first phase of biotic recovery after the end‐Permian extinction. [ABSTRACT FROM AUTHOR]

The widespread development of Permian/Triassic boundary microbialites is a key biosedimentary response to the mass extinction event. The microbial communities that precipitated these structures remain, however, poorly resolved. Here, we report abundant columnar microfossils from five Permian‐Triassic successions in South China. Four phases of the microfossil life cycle are recorded: baeocytes, juvenile column, mature column, and baeocyte‐splitting, which are interpreted as Pleurocapsales (cyanobacterial clade that reproduces by multiple fission). The great thickness (up to 13 m) of these microbial deposits and Raman spectrum analysis indicate a strong calcification capacity of the Pleurocapsales. Pronounced peaks of Mg/(Mg + Ca) ratios from microbialite and distinct Mg‐enrichment in microfossils indicate that Pleurocapsales blooms may also have facilitated dolomitization of the microbialites. Common occurrence, strong biomineralization capacity, baffling framework, and the close association with carbonate minerals suggest that Pleurocapsales were key constructors of post‐extinction microbialites. Plain Language Summary: As a biosedimentary response to the end‐Permian mass extinction, the widespread occurrence of microbialites has attracted increasing levels of interests from geologists worldwide. However, the major constituents of microbial communities that constructed the microbialites have long been disputed. Our new study describes morphological features, growth direction and reproduction characteristic of columnar microfossils obtained from the microbialites, and all characteristics indicate that these microfossils are assignable to a type of photosynthesizing bacteria, known as Pleurocapsales cyanobacteria. Both biomineralization and dolomitization of these Pleurocapsales are evaluated based on in‐situ observations and geochemical analyses. The new results show that the cluster‐branching morphologies, together with common occurrence and strong calcification capacity indicate that Pleurocapsales were key constructors of the microbialites. High Mg/(Mg + Ca) ratios coinciding with the microbialites and Mg‐enrichment in the microfossils suggest that the Pleurocapsales may have catalyzed dolomitization of the microbialites after the end‐Permian mass extinction. Key Points: Four phases of a microbe life cycle are recognized from fossils within microbialites reflecting Pleurocapsales asexual reproductionCommon occurrence and baffling framework indicate that Pleurocapsales cyanobacteria are important in constructing microbialitesPleurocapsales cyanobacteria were an important component of microbialite calcification and magnesium enrichment [ABSTRACT FROM AUTHOR]

Redox variations across the Permian‐Triassic boundary (PTB) have long been debated, especially during the proliferation of PTB microbialites. Here, we report redox fluctuations across the PTB to evaluate links between the two based on pyrite framboid analysis from basin to platform settings in South China. During the end‐Permian extinction, abundant framboids indicate a widespread anoxia that was likely a direct cause of extinction. In the earliest Triassic (Hindeodus parvus conodont zone), pyrite framboids were absent in ramp to basin and shallow, nonmicrobialite platform sections. In contrast, the coeval microbialites yield abundant framboids indicative of dysoxia. The fact that framboids were only confined to PTB microbialites and absent in other habitats indicates that microbe bloom may have stimulated dysoxic watermass and triggered the framboid growth within microbe aggregates. Thus, microbialites were not built in reducing settings, but instead, microbial proliferation caused local, dysoxia within shallow oxygenated platforms after the extinction. Plain Language Summary: The widespread occurrence of microbialites immediately after the end‐Permian extinction has attracted interest about their formation conditions. Microbialites are generally believed to be formed during microbial bloom in reducing conditions linked to the mass extinction. However, the cause‐and‐effect relationship between microbe bloom and reducing states of seawater has long been disputed. Our new results based on analyses of 17,306 pyrite framboid diameters and morphologies derived from various Permian‐Triassic boundary sections in South China show that microbialite formation (microbial bloom) was not triggered by reducing waters upwelled from deeper water masses, instead, it caused local, dysoxic areas within oxygenated platforms after the end‐Permian crisis. Key Points: A total of 17,306 pyrite framboids are analyzed in size and morphology from the Permian‐Triassic boundary beds of 26 sections, South ChinaFramboids were absent in ramp to basin and shallow, nonmicrobialite platforms after the extinction, but occurred in coeval microbialitesMicrobe bloom/microbialite growth was not triggered by reducing condition, but stimulated dysoxic water mass and triggered framboid growth [ABSTRACT FROM AUTHOR]

The Permian-Triassic mass extinction (PTME) strongly devastated marine ecosystems, and, consequently, sponges, especially the reef-building clades, suffered dramatic losses in biodiversity. The Early Triassic therefore was believed to be an evolutionary gap for sponges. Microbialites spread over shallow marine carbonate settings across the entire low-latitude Tethys region following the PTME and occupied the ecospace that the pre-extinction metazoan reefs left. Here, we report putative keratose sponge consortia from the microbialites near the Permian-Triassic boundary in the Xiushui, Laolongdong, and Dongwan sections, South China. The putative keratose sponges exhibit vermiform, filamentous textures forming maze-like networks. Within the keratose sponge-microbial fabrics, the calcified sponge skeleton might firm the overall framework of microbialite, promoting construction of the sponge-microbial build-ups. The coeval occurrence of putative keratose sponges in both eastern Palaeotethys and central Neotethys regions indicates that sponges may have widely spread and played important roles in constructing metazoan-microbial reefs in earliest Triassic. Besides, several characteristics are conducive to keratose sponge surviving the stressful environments after the PTME. Global dataset shows that keratose sponges mostly confined to tropic and temperate zones. Keratose sponges overall flourished in coincidence with occurrence abundance peaks of microbial reefs during the Phanerozoic history, and they seem to be particularly abundant and widespread in the Cambrian-Ordovician, Late Devonian and the aftermath of the end-Permian mass extinction. • Keratose sponge consortia from the microbialite deposits near the P-Tr boundary in South China. • Calcified sponge skeleton might have firmed the framework of sponge-microbial build-ups. • Deep-time keratose sponges favorite low-latitude regions and overall flourished in the aftermaths of major extinctions. [ABSTRACT FROM AUTHOR]

Unusual sedimentary deposits such as stromatolites, thrombolites, dendrolites, and giant ooids are widely distributed in the Permian–Triassic boundary (PTB) successions of shallow platform facies worldwide. These microbial fabrics, however, are rarely present in the same section. The genesis of these PTB microbialites and the oceanographic conditions linking to the end-Permian mass extinction still remain disputed despite intense study. Here, we report a stromatolite-dendrolite-thrombolite-giant ooid association from the PTB beds of the Yudongzi section on the northwestern margin of the Yangtze Platform, South China, which was situated in low latitudes during the Permian-Triassic (P-Tr) transition. The Yudongzi microbialites rest on an irregular contact with underlying Permian bioclastic limestone and are comprised of lower bedded stromatolite, digitate dendrolite, upper bedded stromatolite, and thrombolite units. The bedded stromatolite is characterized by undulating laminated structures and various amalgamated and layered clots. The digitate dendrolite is made up of digitate-like branches, formed by clots distributed in an arched arrangement, and characterized by abundant branching dendroids. The thrombolite displays distinct clotted textures that comprise a mixture of dark-colored microbial fabric and light-colored interstitial sediment. In microbialite, columnar structures identified as Gakhumella -like calcimicrobe are very abundant. Each individual of Gakhumella -like structure has densely arranged segments forming a columnar- to fan-shaped micro-structure. Single segments are arch-shaped and form a thin chamber between segments. Coccoid-like, bacterial clump-like, and other spheroidal aggregates are also commonly present and suggestive of a biogenetic origin for the Yudongzi microbialites. Moreover, distinct aragonite crystal fans are also for the first time found in the PTB microbialites in South China, suggesting that the fans may have resulted from high inorganic carbon concentrations, and thus high levels of carbonate dioxide in the seawater. The Yudongzi microbialites are capped by shelly grainstone and a massive giant oolite, implying that the demise of the Yudongzi microbialites may be due to destruction by strong wave currents in a high energy setting. Some ooids are coated unevenly by micritic laminae (or envelopes) indicating the possibility of a microbe-related origin. These microbial-coated giant ooids, together with the massive microbialites, may imply the long-term of microbial bloom in the oceans immediately after the end-Permian extinction. The co-existence of abundant Gakhumella-like microorganisms and oxygen-dependent invertebrates, together with some coccoid-like spheroids, aragonite cement crystal fans, and pyrite framboids indicative of oxygen-poor conditions, implies that oxygenation state of the PTB microbialites is much more complex than previously recognized, demonstrating need for continued multidisciplinary examination of facies changes associated biotic mass extinction. [Display omitted] • PTB microbialite complex comprises bedded stromatolite, digitate dendrolite, thrombolite and giant ooids. • Microbial fabrics include undulating laminated structures, digitate-like branches, and clotted textures. • Ooids are coated by micritic laminae indicating the possibility of a microbe-related origin. • Columnar structures identified as Gakhumella are very abundant and belong to the benthic Pleurocapsale cyanobacteria. • Aragonite crystal fans are distinct, and may have resulted from high bicarbonate in the seawater. [ABSTRACT FROM AUTHOR]

Abstract We document a diverse ichnoassemblage from marine interbeds of the Lower Triassic terrestrial succession in the Houzhougongmiao (HZGM) section of Shaanxi Province, northwestern China. Integrated biostratigraphic data (bivalve, palynology and conchostracan) reveals that the ichnofossil-bearing marine beds are Griesbachian (Induan, Early Triassic) in age. The marine interbeds are interpreted to be the result of the earliest Triassic transgression of the Paleotethys Ocean northward onto the southern margin of the North China Craton. The HZGM ichnoassemblage includes 17 ichnospecies in 16 ichnogenera and is dominated by shallow-tier Asteriacites and Biformites produced by ophiuroids, the scratch marks or trackways Dimorphichnus , Diplichnites , and Monomorphichnus produced by arthropods, and a rare occurrence of the fish swimming trace Undichna. Of these, the hook-shaped imprints Biformites , representing the moving arm impressions of ophiuroids, are reported for the first time from the Lower Triassic. These trace-makers are interpreted to have lived in a low energy, semi-restricted, shallow embayment environment. Although possessing relatively high ichnodiversity, the HZGM ichnoassemblage differs clearly from other coeval diverse ichnocoenoses in the lack of complex burrow forms (i.e. Thalassinoides , Diplocraterion , or Rhizocorallium) and a mixed layer, and in having abundant shallow tiers. In addition, high ichnodiversity may occur at both high and low latitudes during the Griesbachian (or Induan). Accordingly, the resting trace or trackway-dominated ichnoassemblage from the HZGM section may represent the initial recovery of the trace-maker ecosystem after the Permian-Triassic mass extinction. Trace-makers such as arthropods and ophiuroids were perhaps opportunistic organisms that proliferated in marginal marine settings when other biota were still suffering post-extinction biotic depletion and environmental stresses. Graphical abstract Image 1 Highlights • We report a diverse marine ichnoassemblage from the late Griesbachian. • Dominated by Asteriacites and Biformites produced by ophiuroids, arthropods trackways. • The HZGM ichnoassemblage lack of complex burrow forms (i.e. Thalassinoides , Rhizocorallium). • High ichnodiversity may occur at both high and low latitudes during the Griesbachian. • Arthropods and ophiuroids perhaps were opportunistic organisms. [ABSTRACT FROM AUTHOR]

Abstract A new Permian–Triassic boundary microbialite (PTBM) is described from the Xiajiacao section of western Hubei Province, South China. The new microbialite, 3.16 m thick, comprises a thin layer of stromatolite and a thick thrombolite unit. An irregular contact separates the uppermost Permian skeletal packstone from the post-extinction stromatolite, but it is not yet possible to discriminate whether it was formed by submarine solution in the wake of ocean acidification or subaerial exposure due to regional regression, or a combination of both. The stromatolite shows "cabbage-like" morphology, and the thrombolite is characterized by centimetric clotted texture. Abundant columns of the microproblematica structure Gakhumella , coccoid-like spheroids, bacterial clump-like spheroids, and hollow spheroids are recognized in both stromatolites and thrombolites and may have played an important role in accretion of the microbialites. Pyrite framboid analysis indicates that microbialites may have been affected by lower dysoxic to upper dysoxic conditions in the immediate aftermath of the Permian–Triassic extinction. Stratigraphic abundance of both high-temperature grains (β-quartz and glassy balls) peaked ~ 20 cm below the biotic extinction horizon, implying that either intensive volcanic eruption occurred only just prior to biotic extinction, or volcanism was still intensive during biotic extinction, but volcanic grains were not deposited in the Xiajiacao locality, likely due to the shallow, agitated environment caused by the regional regression. Overall, microbial bloom, indicated by the widespread PTBMs, seems to have been little affected by the contemporaneous volcanism. Highlights • Gakhumella,and coccoid-like, bacterial clump-like and hollow spheroids are crucial in accretion of microbialite; • Pyrite framboid size and morphology show that the microbialite may have been deposited in lower to upper dysoxic conditions. • Microbial bloom, indicated by the widespread PTBMs seems not to be linked with the contemporaneous volcanism. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Unlabelled Image Highlights • The ichnofauna-bivalve-microbial mat biofacies is characterized by diverse ichnofauna, bivalves, and MISS; • Low ichnodiversity in the Induan cannot be taken as an indicator of environmental stresses in all cases; • Microbial mats proliferated in both harsh environments and well-oxygenated settings following the end-Permian crisis; • The southern Qilian biofacies represents a matground-adapted metazoan ecosystem during the earliest Triassic; • Such unique biofacies represent community phase shifts in siliciclastic settings during the Early Triassic. [ABSTRACT FROM AUTHOR]

Two Anisian (Middle Triassic) marine ichnocoenoses are reported from the Boyun and Junmachang (JMC) sections located along the eastern and western margins of the Kamdian Continent, Yunnan Province, Southwest China, respectively. The Boyun ichnoassemblage is middle Anisian in age and is dominated by robust Rhizocorallium , while the JMC ichnoassemblage is of an early Anisian age and is characterized by the presence of Zoophycos . The ichnoassemblage horizons of the Boyun section represent an inner ramp environment, while the JMC section was likely situated in a mid-ramp setting near storm wave base as indicated by the presence of tempestites. The ichnofossil-bearing successions are usually highly bioturbated in both the Boyun (BI 3–5, BPBI 5) and JMC (BI 3–4, BPBI 3–4) sections. Three large, morphologically complicated ichnogenera: 1) Rhizocorallium ; 2) Thalassinoides ; and, 3) Zoophycos characterize the Anisian ichnocoenoses. Of these, Rhizocorallium has mean and maximum tube diameters up to 20.4 mm and 28 mm, respectively, while Thalassinoides mean and maximum tube diameters are 14.2 mm and 22 mm, respectively. Zoophycos is present in the early Anisian strata of the JMC section, and represents the oldest known occurrence of this ichnogenus following the latest Permian mass extinction. Similar to coeval ichnoassemblages elsewhere in the world, the Yunnan ichnocoenoses embrace a relatively low ichnodiversity, but their burrows usually penetrate deeply into the sediment, and include large and complex Rhizocorallium and Thalassinoides . All of these ichnologic features are indicative of recovery stage 4 after the latest Permian crisis. Anisian ichnoassemblages occur globally in six different habitat settings, and all show similar ecologic characteristics except for slightly different degrees of ichnotaxonomic richness, indicating that depositional environment is not a crucial factor shaping the recovery of the trace-makers, but may have an impact on their ichnodiversity. When compared with some important Early Triassic (mainly Spathian) ichnoassemblages worldwide, the Anisian ichnocoenoses examined for this study are slightly less diversified, and possess more or less the same maximum burrow sizes, but the penetration depth of burrows and the distribution of burrow sizes are much larger than those from the Early Triassic. It is worthy of note that the lower ichnodiversity of the Anisian ichnocoenoses may have resulted from intense bioturbation by deeper tiers, representing a taphonomic product that is totally unrelated to environmental stress. In addition, Anisian Rhizocorallium and Thalassinoides have much larger burrow sizes than the same ichnotaxa from the Lower Triassic, implying that ichnocoenoses may have recovered in Spathian, but did not stabilize until the Anisian. [ABSTRACT FROM AUTHOR]

As a consequence of the end-Permian mass extinction, microbes proliferated in the post-extinction shallow marine ecosystems, in which they grew as various microbially induced sedimentary structures (MISSs) in siliciclastic settings. This paper reports, for the first time, the discovery of abundant MISSs from the lowest Triassic sandstones of shallow-water margin origin in the Zhihema sections of the southern Qilianshan region, West China. The sandstones are characterized by well-developed cross-beddings and ripple marks, and a Claraia -dominated bivalve assemblage of middle-late Griesbachian age. These sedimentary structures, together with the bivalves, suggest a high-energy peritidal zone of a shoreface setting in a clastic shallow sea environment. Seven types of MISSs are recognized and described here: pictograph-like sand cracks/crack-fills, polygonal sand crack-fills, erosional remnants, multidirectional linear grooves, sinuous crack-fills, fusiform sand cracks/crack-fills, and leveled ripple marks. Most of the newly found MISSs are morphologically comparable with their ancient and modern counterparts. Detailed optical microscope and scanning electron microscope (SEM) analyses reveal that thin clayey laminae and filamentous mica grains are aligned parallel to bedding plane, and that the matrix-supported quartz grains, overall, are oriented; both of which are interpreted to indicate biogenic origin. The biogenic origin of these MISSs is reinforced by the presence of copious putative nanoglobules and filamentous biofilm-like organic objects in the interspaces of clay minerals in laminated layers. These nanometer-scale objects are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization. The presence of MISSs on the northern margins of Paleo-Tethys indicates that the post-extinction microbial mats had expanded their distributions from low-latitude to moderate-high latitude regions. Moreover, unlike some previously reported microbial mats that contain very rare body and trace fossils, the southern Qilianshan MISSs were found in association with abundant vertical burrows and bivalves, suggesting that the MISS-forming microbial mats may have served as oases for trace-making organisms and opportunistic bivalves to flourish in shallow-marine habitats immediately after the end-Permian mass extinction. [ABSTRACT FROM AUTHOR]

The end-Permian mass extinction (EPME) severely impacted global biodiversity. Extinction selectivity of biotas behaved differently in various environmental settings, and biotic variations before, during, and after the EPME on the shallow platform remain unclear. This paper describes a new microbialite near the Permian-Triassic (P-Tr) boundary (PTB) from the Xiejiacao section, South China. The PTB microbialite comprises thrombolite and dendrolite fabrics and yields abundant columnar cyanobacteria and various microspheroids. Abundant metazoan fossils, including conodonts, foraminifers, ostracods, gastropods, ammonoids, brachiopods, and ophiuroids, are reported from the uppermost Permian bioclastic limestone, PTB microbialite (PTBM), and lowest Triassic strata in Xiejiacao. Stratigraphic occurrences of these taxa display a two-fold decline pattern of the end-Permian mass extinction, calibrating to the base and top of the PTB microbialite and corresponding to the first extinction phase (EP1) and second extinction phase (EP2) of the EPME, respectively. This two-fold extinction pattern is also reinforced by fossil fragment components of various clades through the P-Tr transition in Xiejiacao. Updated dataset of metazoan fossil records from 25 PTBM sections in South China is also compiled, and it shows the two-fold declines in biodiversity. The dominance role of foraminifers in the latest Permian faunas switched to ostracods in the PTB microbialite after EP1, and then to bivalves after EP2. Proportions of infaunal, stationary, and omnivore forms declined continuously across the EP1 and EP2, while pelagic, fast-moving, suspension-feeding, and predatory taxa underwent stepwise increases across these two extinctions. Proportions of epifaunal, slow-moving, and deposit-feeding taxa increased after EP1 but decreased after EP2. This might be associated with the extinction of brachiopods and, the immigration, and the proliferation of mollusks (bivalves, gastropods, and ammonoids). The metazoan fossil dataset of all PTBM sections across South China refutes the taphonomic window hypothesis and the refuge scenario, instead, supports that the post-extinction unique palaeoceanographic conditions in microbial ecosystems may have been beneficial to diversification of the PTBM faunas. The dataset of the stratigraphic distributions of all PTBM taxa in all palaeoenvironmental settings across South China shows that the drastic decline in biodiversity of the PTBM faunas during the cessation of microbialite was not due to facies control on fossil preservation, but closely related to the biotic extinction in EP2 of the EPME. • New PTB microbialite comprises thrombolite and dendrolite fabrics • Species ranges display a two-fold decline pattern, coinciding with two phases of the EPME • Proportions of infaunal, stationary, omnivore forms decline across the EP1 and EP2 • Proportions of pelagic, fast-moving, suspension-feeding and predatory taxa increase after the EPME [ABSTRACT FROM AUTHOR]