Sequence stratigraphic framework and palaeogeographic environments of the Permian strata in the Nanpanjiang depression, Guangxi

The Permian strata in the Nanpanjiang depression, Guangxi may be divided into twelve third-order sequences, each of which spans an average time duration of 3 Ma. These third-order sequences may be (subdivided) into four I-type ad eight II-type sequences according to sequence boundaries, and comparable in (general) in spite of sequence differences in different regions. They are also involved in two supersequences. (During) the deposition of the supersequence SS1, the Nanpanjiang depression displayed the platform-basin palaeogeographic framework, where the narrow platform margin-platform slope deposits are developed. The bathyal environments then occupied the Qinzhou-Fangcheng region. At the end of the deposition of the supersequence SS2, there was the transition from a platform-basin palaeogeographic framework to platform-in-basin framework in the Youjiang Basin. The main part of the Upper Yangtze ancient land was then an open platform-retricted platform, passing into the continental environments in the areas near the Sichuan-Yunnan ancient land.