Late Permian Eustatic Fluctuation In North Part Of Central Yangtze Platform And Its Influence On Biotic Crisis Events

The biotic extinction events in late Permian, which have been an important issue in the geologic community for the past decades, are the most severe and sweeping events in the history of biotic evolution. People have applied different methods to investigate their characteristics, extent, phases and mechanism from different perspective.The most successive and widespread Permian-Triassic strata in south China, facilities the research on late Permian biotic extinction events. Aiming at erecting the Global Stratotype Section and Point of Permian-Triassic boundary, people have carried on detailed research on these events in Yangtze platform. Actually, the lower Yangtze platform was the most thoroughly studied area, while the upper and middle Yangtze platform were not studied as well as it. The north part of central Yangtze platform yields widespread carbonate sediment, carbonate platform slope sediment and basin sediment of Lopingian. Studying late Permian biotic events in this area will further the understanding of those events.This paper was based on high precision biostratigraphy of late Permian, especially near the Guadalupian/Lopingian and Permian/Triassic boundary. Be the method of carbonate microfacies analysis and sequence stratigraphy, this paper tried to recognize third-order sequences and eustatic fluctuation in the studied area, and then took integrated analysis of the relationship between eustatic fluctuation and biotic extinction events.The central Yangtze platform is located south to Qingling orogenic belt, north to Jiangnan orogenic belt, east to Qiyu mountain, and west to Tannu fault. For studying the late Permian sea level change and its influence on the biotic extinction events in this area, the author selected Xiakou section of Yichang city, Jiantianba section of Lichuan city, Tianqiao, Maoershan and Kutaoxi section of Enshi city, and Ermen section of Huangshi city. Xiakou section and Jiantianba section was deposited in edge of carbonate platform. Tianqiao section was deposited in slope of carbonate platform. Kutaoxi and Ermen section were formed in basin environment.Xiakou section concentrated block carbonate sediments in Wuchiapingian, sponge bafflestone in early Changhsingian and calcareous argillite with thin limestone interbeds in middle and late Changhsingian. Jiantianba section yields block reef sediments of Changhsingian. Tianqiao section has bioclastic limestone of late Wuchiapingian, chert and argillaceous chert of middle and upper Wuchiapingian, and thick mudstone of Changhsingian. Maoershan section concentrated coal-bearing series, and thick mudstone and wackstone in lower Wuchiapingian, and thick chert and argillaceous chert in middle and upper Wuchiapingian. Kutaoxi section yields bioclastic limestone from bottom of Wuchiapingian, and chert and argillaceous chert from middle and upper Wuchiapingian. In Changhsingian, it concentrated thick mudstone. Huangshi section yields siliceous argillite with limestone interbeds in Wuchiapingian. Its Changhsingian lithology changes from wackstone with argillite beds to siliceous and calcareous argillite. In conclusion, the west part of the studied area was a northeast oriented basin during late Permian. The sea become deeper from west to north east in this area. The Lichuan area was an edge of carbonate platform. The Tianqiao area was a slope of carbonate platform. Kutaoxi and Jianshi area were deep sea basin. And Xiakou area was the edge of north carbonate platform. The middle and southeast part of the studied area maintained deep sea basin in late Permian.Sequence stratigraphy is an effective method to analyze the eustatic fluctuation. The determination of sequence order, age of sequence boundary and duration of each sequence are based on high precision biostratigraphy. And biostratigraphy is also vital for comparing different section in different area. The precision of sequence stratigraphy depends on the precision of biostratigraphy much. Only in the isochronous frame of biostratigraphy, could the sequence stratigraphy and eusta...