Devonian Sequence Stratigraphy and Relative Sea-level Changes in Guizhou and Guangxi Area, South China

There is a great change of paleogeography setting resulted from the Caledonian orogeny at the end of Silurian in Guizhou and Guangxi area in south China, the Dianqiangui oldland in early Paleozoic evolved as the Dianqiangui sea in late Plaeozoic. In the initial stage of Devonian Period, seawater is onlaped gradually from the south to the north caused by transgression, so the bottom part of Devonian system is constituted by a set of transgressive clastic sedimentary rock. The great scale transgressive event at the end of the early Epoch of Devonian forms evident differentiation of depositional facies in Guizhou and Guangxi province, a lot of isolated carbonate platforms are developed in Dianqiangui Basin, the special paleogeographic setting marked by platforms-basins-hills-trough is formed and lasted to the early stage of the late Epoch of Devonian. The strata of the upper Epoch of Devonian become regressive thin out from paleosea to oldland resulted from the Ziyun epeirogeny that took place in the transitional period from Devonian Period to Carboniferous Period. On the basis of the study on the evolutional natures of sediments in time and the distribution characters of sedimentary facies in space, 13 third-order sedimentary sequences are discerned in Devonian strata in Guizhou and Guangxi province, which could be grouped into one second-order tectonic sequence. In terms of the correlation on biostratigraphy, the sea-level changes delegated by third-order sequences with different architecture natures of facies-succession also could be correlative in research region, in the end, the framework of sequence stratigraphy could be constructed. Many characters such as two elementary natures of third-order sequences——“the regularity of facies-succession in space and the synchronism of the changes of sedimentary environment in time”, two kinds of diachronism that are relative to two types of facies-changing surfaces——“the diachronism of facies-changing caused by static facies-changing surface and the diachronism of punctuated formed by dynamic facies-changing surfaces in strtigraphic records, are clearly demonstrated in the framework of sequence stratigraphy.