Extinction And Recovery Of Foraminifera And Calcareous Algae During The Permian-Triassic Transition

End-Permian mass extinction and subsequent biotic recovery was one of the great revolutions in the life's history, witnessing the change of marine ecosystem structure from Paleozoic type to Modern type. And the mass extinction and biotic recovery during the Permian-Triassic transition has become one of the hotspots in the paleontological research. This study focuses on two kinds of microfossils including foraminifera and calcareous algae to uncover the extinction pattern and recovery process.For studying the extinction pattern near the Permian-Triassic boundary, three geologic sections in different sedimentary facies were selected, including Meishan section in the slope facies, Dajiang section in the shallow water microbialites facies, and Liangfengya section in the shallow water non-microbialites facies. The results show that foraminifera exhibits two-episodes extinction pattern near the Permian-Triassic boundary at both Meishan and Liangfengya sections. All large and complicated foraminifers became extinction in the first episodic extinction (Bed25at the Meishan section), including fusulinids. Some of small foraminifers survived in the first episodic extinction, but most of survivors became extinction in the second crisis (Bed28at the Meishan section). At the Dajiang section, the first episodic extinction was clear and happed at the boundary between bioclastic limestone and microbialites. Only five species were found in the microbialites, and two species became extinction in the second crisis. The foraminiferal diversity in the microbialites was very low comparing with the same strata at the Meishan and Lengfengya sections, implying that the environment developing diverse cyanobacteria might not be suitable for the survival of foraminifers. Therefore, foraminifera exhibit two-stage extinction pattern in both shallow water and deep water.Diverse calcareous algae and Tubiphytes occurred at the top of Permian in all three sections, but both calcareous algae and Tubiphytes did not surviv the first episodic crisis, exhibiting a single extinction pattern. The single extinction is not conflict with the two-stage extinction of foraminifera because different biotic taxa have different tolerance on severe surroundings. Calcareous algae and Tubiphytes generally lived in the photic zone with clear seawater. However, foraminifers have a higher tolerance on the unstable surroundings. Furthermore, different foraminiferal types also have different tolerant, e.g. fusulinids with large and complicated test generally have a lower tolerance and became extinction in the first crisis. And such, the extinction progress of microfossils suggests a two-stage extinction pattern near the Permian-Triassic boundary:these taxa with lower tolerance and narrow habits became extinction in the first crisis including calcareous algae, Tubiphytes, fusulinids and other large and complicated foraminifers; some of small foraminifers survived this crisis, but most of them disappeared in the second crisis. This conclusion further implies that there were two episodic disaster events during the Permian-Triassic transistion rather than a single one.High-resolution sampling of>10,000microfossils from seven Upper Permian-Middle Triassic palaeo-equatorial sections in South China refutes claims for a reported5myr recovery delay after the end-Permian mass extinction. We show that level bottom seafloor diversity began to recover in the early Smithian, little more than1myr after mass extinction, whilst recovery of reef-building metazoans began4myr later in the Anisian. A further mass extinction in the late Smithian, identified in the pelagic fossil record, is only marked by a temporary pause in diversification amongst benthic communities. Curiously, in the Early Triassic offshore diversity increase began before that in shallower settings in South China. The recovery from the end-Permian mass extinction was therefore significantly more rapid and environmentally more complex than hitherto known.Quantitative analyses of P-Tr foraminifers from South China reveal that foraminiferal test sizes decreased sharply through the P-Tr interval. Of these, large foraminifers wiped out in the end-Permian crisis. In addition, both size decrease in the survivors and small newcomers played an important role in the Lilliput effect in the aftermath of the extinction event, lasting about the entire Early Triassic. The severe size reduction of foraminifers occurred immediately after the end-Permian mass extinction and lasted to the latest Induan. Although test sizes tended to increase through the Induan to Olenekian, they never recovered to the pre-extinction levels. Foraminiferal test size variations are one of the important proxies indicating environmental changes. Foraminiferal test size variations through the P-Tr interval may be triggered by several defaunation events such as anoxia, ocean acidification and global warming. These events may also be responsible for the end-Permian mass extinction, Lilliput effect, and the subsequent delayed biotic recovery.Carbonate carbon isotope (δ13Ccarb) has become one of significant hotspots in the Permian-Triassic interval for its rapid negative excursion during the end-Permian extinction event. The mechanism for δ13Ccarb negative excursion in the end-Permian crisis and subsequent large perturbations in the entire Early Triassic has long been debated. This paper focuses on the evolution of δ13Ccarb-depth gradient among different water-depths Permian-Triassic boundary sections, including Yangou, Meishan, and Shangsi sections. The results show that a large δ13Ccarb-depth gradient occurred near the end-Permian extinction horizon, reflecting a synchronous stratified Paleotethys Ocean with widespread anoxic/euxinic deep water. The evolution of δ13Ccab-depth gradient combined with paleontology and geochemistry data suggest that abundant cyanobacteria and vigorous biological pump appeared in the immediately aftermath of the end-Permian extinction is the deepest cause resulting in the large δ13Ccarb-depth gradient, and the enhanced continental weathering by volcanism provided a mass of nutriment for cyanobacteria. Photic zone euxinia resulted from onset of chemocline upward excursion is the immediate cause for the mass extinction while the instability of chemocline may be the reason for the delayed and involuted biotic recovery.A detailed,20myr redox history of Permian to Triassic oceans (Changxingian to Carnian stages) has been constructed using Ce-anomaly and Th/U ratios from conodont albid crown apatite material. The results show that the well-established phenomenon of intense ocean anoxia (coincident with the end-Permian mass extinction) is faithfully recorded in conodont ΩCe and Th/U data. Extending this conodont redox record shows that end-Permian anoxia persisted into the earliest Dienerian Stage and that two equally intense oceanic anoxic events also occurred later in the Early Triassic (middle Smithian-earliest Spathian, and middle Spathian), followed by a weaker manifestation of anoxia in the Anisian Stage, only seen in ΩCs data. Marine benthic radiation, following the end-Permian mass extinction, began after the middle Smithian-earliest Spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions. The failure of the middle Spathian anoxic event to retard the evolutionary rebound suggests shallow marine shelf seas remained well ventilated at this time even if the oceans did not. Other attributes of the Early Triassic record also closely coincide with redox fluctuations: phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope excursions that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light, remineralised carbon in shallow carbonate settings.