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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.

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).