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Yin, Hongfu. & Feng, Qinglai. “The Protracted Permo-Triassic Crisis and Multi-Episode Extinction Around the Permian-Triassic Boundary.” Global and Planetary Change. 55.1-3 (2007): 1-20.Abstract:The Permo-Triassic crisis was a major turning point in geological history. Following the end-Guadalupian extinction phase, the Palaeozoic biota underwent a steady decline through the Lopingian (Late Permian), resulting in their decimation at the level that is adopted as the Permian-Triassic boundary (PTB). This trend coincided with the greatest Phanerozoic regression. The extinction at the end of the Guadalupian and that marking the end of the Permian are therefore related. The subsequent recovery of the biota occupied the whole of the Early Triassic. Several phases of perturbations in delta 13Ccarb occurred through a similar period, from the late Wuchiapingian to the end of the Early Triassic. Therefore, the Permian-Triassic crisis was protracted, and spanned Late Permian and Early Triassic time. The extinction associated with the PTB occurred in two episodes, the main act with a prelude and the epilogue. The prelude commenced prior to beds 25 and 26 at Meishan and coincided with the end-Permian regression. The main act itself happened in beds 25 and 26 at Meishan. The epilogue occurred in the late Griesbachian and coincided with the second volcanogenic layer (bed 28) at Meishan. The temporal distribution of these episodes constrains the interpretation of mechanisms responsible for the greatest Phanerozoic mass extinction, particularly the significance of a postulated bolide impact that to our view may have occurred about 50,000Myr after the prelude. The prolonged and multi-phase nature of the Permo-Triassic crisis favours the mechanisms of the Earth's intrinsic evolution rather than extraterrestrial catastrophe. The most significant regression in the Phanerozoic, the palaeomagnetic disturbance of the Permo-Triassic Mixed Superchron, widespread extensive volcanism, and other events, may all be related, through deep-seated processes that occurred during the integration of Pangea. These combined processes could be responsible for the profound changes in marine, terrestrial and atmospheric environments that resulted
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Xu, L. & Lin, Y. Platinum-Group Elements of the Meishan Permian-Triassic Boundary Section: Evidence for Flood Basaltic Volcanism. Chemical Geology. 246.1-2 (2007): 55-64.Abstract:Permian-Triassic boundary sections record the most severe mass extinction event in geological history. However, there is a long-standing controversy of whether bolide impact and/or basaltic flood volcanism triggered the mass extinction. Platinum-group elements (PGEs) are enriched in most extraterrestrial materials, but highly depleted in the terrestrial crust materials. We analyzed Ir, Ru, Rh, Pt and Pd in a set of samples from the global stratotype section and point (GSSP) of the Permian-Triassic boundary at Meishan, China, using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) and nickel sulfide fire assay (NiS-FA) combined with Te coprecipitation. The samples have no Ir anomaly (5-53 pg/g), and their PGE patterns normalized to chondrites are highly fractionated with Ir/Pd ratios of 0.02-0.03xCI, distinct from most extraterrestrial materials. In contrast, these patterns are closely parallel to those of the Siberian and probably Emeishan flood basalts, suggestive of possible sources of PGEs from the basalts. The abundances of PGEs increase in order of the pyrite lamina on the top of bed 24, bed 25 and bed 26, and then decrease to bed 28, probably indicative of a maximum eruption of the flood basalts during deposition of bed 26. The new data favor massive volcanism, rather than extraterrestrial impact, as a major cause of the Permian-Triassic boundary mass extinction.
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Payne, J. L. & Kump, L. R. “Evidence for Recurrent Early Triassic Massice Volcanism from Quantative Interpretation of Carbon Isotope Fluctuations.” Earth and Planetary Science Letters. 256.1-2 (2007): 264-277.Abstract:Carbon cycle disturbance associated with mass extinction at the end of the Permian Period continued through the Early Triassic, an interval of approximately 5 million years. Coincidence of carbon cycle stabilization with accelerated Middle Triassic biotic recovery suggests a link between carbon cycling and biodiversity, but the cause of Early Triassic carbon isotope excursions remains poorly understood. Previous modeling studies have focused exclusively on the initial negative excursion in delta super(1) super(3)C across the Permian-Triassic boundary and have not addressed the cycles of positive and negative excursions observed through the Early Triassic. This study uses a simple carbon cycle box model to investigate potential causes underlying the series of Early Triassic carbon isotope excursions and to assess possible relationships between isotope excursions and coeval patterns of carbonate deposition. According to the model, introduction of carbon with the isotope composition of volcanic CO sub(2) produces small negative carbon isotope excursions followed by larger and more protracted positive excursions. Positive excursions result because increased pCO sub(2) causes warming, enhancing marine anoxia and associated regeneration of phosphate and thus allowing greater productivity. In addition, carbonate weathering is more sensitive than organic carbon weathering to changes in atmospheric pCO sub(2) and climate, causing an increase in the overall delta super(1) super(3)C composition of weathered carbon. Therefore, the full Early Triassic record of negative and positive carbon isotope excursions can only be accounted for within the model by several pulses of carbon release characterized by varying mixtures of organic and mantle isotope compositions. Thermal metamorphism of coal and carbonate rocks in the crust of the Siberian craton during eruption of the Siberian Traps flood basalts provides the most plausible mechanism for such a carbon release scenario. If multiple episodes of CO sub(2) release account for Early Triassic carbon cycle instability (regardless of their precise trigger), then cessation of CO sub(2) release is likely to explain acceleration of biotic recovery early in the Middle Triassic.
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Kaiho, K. & Chen, X. Q. “Close-Up of the End-Permian Mass Extinction Horizon Recorded in the Meishan Section, South China: Sedimentary, Elemental, and Biotic Characterization and a Negative Shift of Sulfate Sulfur Isotope Ratio.” Palaeogeography, Palaeocilmatology, Palaeoecology. 239.3-4 (2006): 396-405.Abstract:The Permian/Triassic (P/Tr) boundary beds of the Meishan section, South China, have been re-studied in detail based on complete samples across the P/Tr transition. Under the microscope, the end-Permian mass extinction horizon is calibrated to a 12-mm stratal interval, the top being 19 mm below the top of Bed 24e of the Changhsing Formation. This abrupt disappearance of skeletal fragments of major benthos characterizes the end-Permian extinction event, suggesting a catastrophic event. An abrupt decrease in the super(3) super(4)S/ super(3) super(2)S ratios of seawater sulfate is confirmed to coincide with the end-Permian event horizon. The sulfur isotope event is thought to have been caused by an overturn of a stratified ocean dominated by H sub(2)S, implying coincidence of the oceanic mixing and the mass extinction. Coincident Siberian flood volcanism may have triggered a long-term (>10 super(3) years) cooling leading an ocean mixing. A presumed comet impact to the ocean could have directly caused ocean mixing and the mass extinction.
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Jianzin, Yu. & Yuangiao, Peng. “Terrestrial Events Across the Permian-Triassic Boundary Along the Yunnan-GUizhou Border, SW China.” Global and Planetary Change. 55.1-3 (2007): 193-208.Abstract:The border area between western Guizhou and eastern Yunnan Provinces in SW China is an ideal place to undertake research considering the terrestrial-ecological system evolution across the Permian-Triassic boundary (PTB). The study of plant and palynomorph fossils, clay minerals, inorganic geochemistry and sedimentary facies in this area enable us to interpret the events occurring at that time. The extinction pattern of the flora interpreted from megafloral and palynomorph data is demonstrated by a sudden decline of species numbers at the PTB after a long-term of gradual changes, followed by a delayed extinction in the basal Triassic. The two boundary claybeds (Beds 66 and 68 in the Chahe Section, beds 47 and 49 in the Zhejue Section) are considered to be volcanogenic. The inorganic geochemical anomalies occurred between Beds 63 and 69, Chahe Section and Beds 45 and 50, Zhejue Section. Sedimentary facies changed from channels of braided rivers, into flood plains of braided rivers, then to shallow lakes, reflecting a gradual transgression by lakes across the area. Our conclusions are that the mass extinction across the PTB in western Guizhou and eastern Yunnan was probably caused by the Siberian basaltic eruption episode and the siliceous volcanism in South China. These lithospheric events represented by volcanisms heralded a series of climatic and environmental events, giving rise to a catastrophe for the biosphere.
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