Study on Sequence Stratigraphic Framework and Relative Sea-level Changes of the Permian in Guizhou and Guangxi Areas, South China

The Permian system in Guizhou and Guangxi provinces of south China is characterized by obviously different depositional facies, such as the coal measures in connective platform and the sponge reefs in its margin as well as in isolated platforms, which formed a specially sedimentary setting of platform-basin-hill-trough. The period with the most apparent differences in depositional facies is correspond to the developing period of sponge reefs. The Permian system in researching areas could be divided into three series, which are named as Chuanshanian series. Yangsingian series and Lepingian series respectively. Two obvious unconformities can be recognized in the Permian of these areas, one is related to the main episode of Qiangui epeirogeny in the transitional period between the Chuanshanian epoch and the Yangsingian epoch, another was formed during the main episode of the Dongwu revolution in the transitional period between Yangsingian epoch and Lepingian epoch. These unconformities delegate not only the typical sequence boundaries but also the changing surfaces of sedimentary-basin natures. Several third-order sequences, which are described as SQ19 to SQ25 in this paper could be discerned in Permian system. The Chuanshanian series and the top part of the Carboniferous constitute one third-order sequence(SQ19). In settings of isolated platform and inter-platform ditch is composed by a set of limestones belonging to the middle to upper part of the Maping Fm. . However, in the background of the connective platform, Maping limestones makes up its transgressive system tract and the coal-measures of the Liangshan Fm. forms its high-stand system tract. The strata of Yangsinian epoch could be divided into four third-order sequences(SQ20-SQ23), whose general charaters could be summarized as follow: transgressive system tract and the early high-stand system tract consist chiefly of limestones of open-platform facies; more dololimestones and limedolostones of restricted-platform facies are developed in late high-stand system tract; in the margin of the connective and the windward parts of isolated platform, SQ23 is marked by a set of sponge-reef limestones. Two third-order sequences (SQ24 and SQ25) could be discerned in the Lepingian series. The SQ24 is composed by a set of coal-measures called the Longtan Fm. in the setting of the connective platform and is also constituted by a special set of coal-measures thatshan Fm. in the isolated platform but is represented by grainstones of beach fades in the margin of the connective platform. The SQ25 consist of a set of sponge-reef limestones in the margin of the connective platform and the windward part of isolate platform, which is a set of limestones of open-platform facies called the Changxing Fm. in the connective platform. In the background of inter-platform ditch, both SQ24 and SQ25 are constituted by a set of deep-water sediments called the Linghao Fm. . The particular drowning event of carbonate platform occurred in transitional period between the Permian and Triassic, lead to the generation of a drowning nonconformities. In term of their geological meanings, sequence boundaries could be grouped into four types, which are tectonic nonconformity, sedimentary nonconformity, drowning nonconformity and their relative surfaces.