High-resolution Quantitative Paleogeographic Study Of The Permian In South China

The Permian sediments from the South China Block were significantly diverse,with multiple horizons of source rock developed,and the paleogeographic features were also complicated.Under the guidance of the latest Permian chronostratigraphic framework,the time-properties of rock stratigraphic units in each region were re-determined,and the reconstructed paleogeographic maps with the highest resolution(a totally seventeen Permian paleogeographic maps recovered from this study based on chronological property and crucial geological events)were completed under this condition based on 812 long integrated stratigraphic profiles.The Permian paleogeographic evolution of the South China Block can be divided into three stages:(1)Asselian-Artinskian,the South China Block was widely occupied by broad carbonate platforms and the bulky Kangdian Oldland.Several ancient lands were joint by the lowest point of the retreat during the mid-to-late Artinskian,and the southern and northern margins of South China were still marine environments at this time.(2)Late Artinskian-Roadian,the sea level gradually raised,and deep-water basins began to present in the northern margin of South China,Hunan-Guizhou-Guangxi,and the Lower Yangtze regions;the Kangdian Oldland was extremely shrinking during this period.Wardian-Capitanian,the sea level of South China gradually declined with the basin areas greatly dwindle.The Cathaysia Oldland in the east gradually expanded,and a shallow marine clastic deposition system was formed at its western margin.By the end of the Middle Permian,the South China Block presented the lowest sea level during the Late Paleozoic.During this period,except for a few areas such as central Guangxi and southern Hunan,the main body of the South China Block was above sea level,shown an extensively sedimentary hiatus.(3)Wuchiapingian-mid-Changhsingian,the sea level of the South China Block gradually increased.Adequate terrestrial supplies and frequently sea-level fluctuations provided suitable conditions for extensive coal accumulation in South China;during the late Changhsingian,the sea level of South China gradually decline,the extent of each basin had been significantly reduced;by the end of the Permian,the sea level of the South China Block fallen into the lowest point in late Permian.It was proposed that the Permian paleogeographic evolution of the South China Block was mainly controlled by regional sea level eustacy,but the Dongwu Uplift Movement and Emeishan Large Igneous Province strongly reshaped the late Permian paleogeographic pattern of the South China Block and greatly increased the supply of terrestrial clastics.Employing the GPlates software,it was the first time for the South China paleogeography to be restored accurately to its original position under the global plate tectonic framework.The dynamic characteristics of the South China Block during the Permian were quantitatively analyzed.With the benefit of big data,it was a feasible method to modify the global paleogeographic reconstruction based on the high-resolution regional paleogeographic maps.There were multiple sets of source rocks developed in South China during Permian,such as the Chihsia,Kuhfeng,Longtan,and Talung formations.The thickness of high-quality source rocks and the Color Alteration Index of conodonts were calculated and discussed,in conclusion,that the eastern-Sichuan and western-Hubei and Lower Yangtze regions were dessert areas for hydrocarbon-generation,while other regions experienced high-over maturity to generate oil or gas.The Permian source rock from the South China Block was considered to present four fundamental features:large thickness,wide distribution,high organic matter abundance,and a high degree of thermal evolution.