南盘江盆地早—中三叠世层序地层格架及相对海平面变化研究

南盘江盆地的早—中三叠世地层中 ,沉积相形成复杂而有序的空间变化和时间变化。二叠纪与三叠纪之交的大规模台地淹没事件之后 ,三叠纪碳酸盐台地从缓坡型演化为镶嵌陆架型 ;空间上 ,从连陆台地到浊积盆地相分异特别明显 ,而且在盆地中发育若干的孤立台地 ,特别是南宁和靖西一带 ,孤立台地上早三叠世的鲕粒滩以及连陆台地边缘的礁滩相灰岩更是引人注目。尽管不同相带的三级沉积层序相序组构千差万变 ,并且它们的形成时限也不尽相同 ,但是由其所表征的相对海平面变化则具有大致的同步性 ,因此在早—中三叠世地层中可以识别出 6个三级沉积层序。以地层记录中的两种相变面和两种穿时性为基本要素 ,可以建立南盘江盆地早—中三叠世的层序地层格架。

SEQUENCE STRATIGRAPHY AND RELATIVE SEA-LEVEL CHANGES FROM THE EARLY TO THE MIDDLE TRIASSIC IN THE NANPANJIANG BASIN

There are complex and regular changes in depositional facies from the early to the middle Triassic strata in the Nanpanjiang Basin. After the obvious drowning event of the carbonate platform in the transitional period at the turn between the Permian and the Triassic, the succession of the carbonate platform was evolved as the type of rimmed shelf from the ramp type. The differentiation of depositional facies became more clear in space, which are marked by the changes from the connective platform to the turbidite basin as well as several isolated platforms that are developed in the basin. The outstanding characters are the development of oolitic beach of the early Triassic epoch in Nanning and Jingxi isolated platforms as well as the reef and beach limestone in the margin of connective platform. Although there is difference in the time span and the architecture of facies succession of third order sedimentary sequences, the process of third order relative sea level changes is general synchronous. So, six third order sequences could be discerned in the early to middle epoch of Triassic in the Nanpanjiang Basin.In terms of the key elements that are two types of facies changing surfaces and two types of diachronism in the stratigraphic records,the framework of sequence stratigraphy from the early to the middle epoch of Triassic in the Nanpanjiang Basin could be constructed.