南盘江坳陷石炭系层序地层格架及古地理环境

THE FRAMEWORK OF SEQUENTIAL STRATIGRAPHY AND PALAEOGEOGRAPHIC ENVIRONMENT OF CARBONIFEROUS IN NANPANJIANG SAG

南盘江坳陷石炭系划分为12个三级层序。其中下石炭统、上石炭统分别包含5个和7个三级层序,每个三级层序平均延时6Ma。按界面性质可将三级层序划分为5个Ⅰ型层序和7个Ⅱ型层序。上述十二个三级层序构成二个超层序(二级层序)。超层序内部的三级层序发育齐全,其最顶部的一个三级层序(SQ12)处于石炭系 二叠系过渡层。SS1低水位时期,右江地区为台 盆相间古地理格局,钦防地区的海盆则有所缩小;海侵时期盆地内部成为统一的台地和盆地,而高水位体系域沉积期则台地扩大,台盆缩小。SS2海侵时期,南盘江坳陷再一次分化成台 盆相间地理环境,高水位体系域沉积期则表现为水体变浅,岸线向盆地方向迁移。

The Carboniferous in Nanpanjiang sag is divided into 12 third-order sequences, in which 5 and 7 sequences respectively belong to C_1 and C_2. The average duration of a third-order sequence is 6 Ma. These third-order can be classified into 5 Ⅰ-type and 7 Ⅱ-type sequences according to the boundary characteristics and form 2 supersequences(second-order sequence). The third-order sequence in supersequence is developed completely and the top third-order sequence(SQ_(12)) is a transitional bed between C and P. In the lowstand SS_1, platform alternated with basin in the Youjiang area and the sea basin shrank in the Qin-Fang area. The uniform platform and basin were formed in the transgression atage, whereas the platform extended and basin shrank in the sedimentation stage of highstand system domain. During the transgression SS_2, the Nanpanjiang sag became the palaeogeographic environment of platform alternating with basin again. And in the sedimentation stage of highstand system domain, the waters became shallow and the coast line moved toward the basin.