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2015年全国沉积学大会

作者： Baozhu Deng Yongbiao Wang Adam Woods Sheng Li Guoshan Li Weihan Chen State Key Laboratory of Geological Processes and Mineral Resources School of Earth Sciences China University of Geosciences Department of Geological Sciences California State University

"Anachronistic facies" refers mainly to carbonate sediments that reflect peculiar marine environments, most of which are related to microbial activities. Anachronistic facies are common sediments in the early history of the earth, but mainly occur in the aftermath of mass extinctions during the Phanerozoic. The aftermath of end-permian mass extinction is one of the periods when anachronistic facies formed widely. In South China, different types of anachronistic facies come out regularly in time succession. Microbialites are often the first anachronistic sediments that formed immediately above the end-permian mass extinction boundary in shallow carbonate platforms,and are subsequently followed by oolite and oncolite, and sometimes intercalated by vermicular limestone. Because different types of anachronistic facies represent different depositional environments,this succession pattern of anachronistic facies preserved in the stratigraphy well recorded the evolution of marine environments following the end-permian mass extinction. Based on the sedimentological analysis on the Cili section in South China,this study suggests that the transition from microbialites to oolitic limestone is associated with the rise of sea level and intensification of hydrodynamics, while the shift from oolite to oncolite reflects rapid sea level increasing at the beginning of early Triassic. However,the occurrence of vermicular limestones that are intercalated within the oolitic limestones is considered the result of temporarily-formed restricted platform environment. Anachronistic facies reaches 25m-thick at the Cili section. Stratratigraphic correlation reveals that this anachronistic facies interval approximately corresponds to the 20 cm thicksequence from beds 27 to 29 at the Global Stratotype Section and Point(GSSP) section of Meishan in Zhejiang Province, indicating much higher carbonate sedimentation rates in shallow water platforms than in deeper environments in the aftermath of end-

关键词： end-permian mass extinction Anachronistic facies Sea level change South China

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Different accretion and diagenetic patterns within the fabrics of the permian–Triassic boundary microbialites on the Leye isolated carbonate platform, South China Block

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Journal of Palaeogeography 2021年第2期10卷 197-208页

作者： Xi-Yang Zhang Yue Li Guan Wang Hong-Qiang Yang Key Laboratory of Ocean and Marginal Sea Geology South China Sea Institute of OceanologyInnovation Academy of South China Sea Ecology and Environmental EngineeringChinese Academy of SciencesGuangzhou 510301Guangdong ProvinceChina State Key Laboratory of Palaeobiology and Stratigraphy Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and PaleoenvironmentChinese Academy of SciencesNanjing 210008Jiangsu ProvinceChina.

A comprehensive study on the accretion and diagenesis of the permian–Triassic boundary microbialites is conducive to a better understanding of the ecological community after the end-permian mass extinction. Here we studied the special microbialite sequences at the Tianba section of Leye isolated carbonate platform, South China Block. The microbialites are shown as small columnar stromatolites, stromatolitic thrombolites, spotted thrombolites,and domical digitate thrombolites in an ascending order. Thin section analyses, coupled with cathodoluminescence photos and oxygen isotopic data, reveal that all types of microbially-mediated laminae/clots are partly *** of the Polybessurus-like fossils commonly occur in the recrystallized fabrics of stromatolitic laminae. However,the Polybessurus-like fossils are rare in quantity and generally fragmentary and structureless in stromatolitic clots and spotted clots. Such taphonomic features are likely interpreted as the early decomposition by heterotrophic bacteria in an oxygen-depleted microenvironment caused by rapid accumulations of organic matter in the calm *** enrichments of ~(13)C in the laminae of stromatolite and in the clots of stromatolitic thrombolite and spotted thrombolite than in adjacent interstitial matrixes signify the photosynthesis-dominated isotopic fractionation during the growth of microbial communities. Rare calcimicrobial structures but many calcite crystal fans were found in the ~(13)C-depleted digitate clots. These phenomena indicate that seawater on the carbonate platform was ~(12)C-enriched and supersaturated, accelerating carbonate precipitations and decompositions of organic matter within the microbial community. Different preservations of the Polybessurus-like fossil revealed the complicated microbiallydominated sedimentation and post-depositional diagenesis in the abnormal seawater after the catastrophe.

关键词： Microbialite Calcimicrobe Carbon isotope Diagenesis end-permian mass extinction South China Block

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