百色盆地古近系那读组和百岗组层序地层划分与沉积演化

Sequence stratigraphy and sedimentary evolution of Nadu formation and Baigang formation of the Paleogene in Baise Basin

野外剖面显示百色盆地古近系那读组内部、那读组与百岗组之间存在不整合面。综合分析地震、测井等资料,将盆地古近系那读组和百岗组划分为1个二级层序,3个三级层序。那读组那三段构成三级层序的层序Ⅰ,那读组那二和那一段构成三级层序的层序Ⅱ,百岗组构成三级层序的层序Ⅲ。层序Ⅰ和层序Ⅱ是盆地断陷期的沉积,具有相似的充填特征,层序Ⅲ是盆地坳陷期的沉积。层序Ⅱ既发育厚度大、分布范围广的深湖亚相泥岩,又发育河流相、三角洲相和扇三角洲相砂岩,是盆地内主要的生储盖组合发育层序。盆地北部层序Ⅱ,Ⅲ发育的扇三角洲是盆地有利储集岩。各层序低水位体系域发育长轴分布的河流相和三角洲相砂岩,这些砂岩是盆地隐蔽性圈闭勘探的有利储层。

The outcrops indicate that the unconformity boundaries exist in the interior of Nadu formation and between Nadu formation and Baigang formation of the Paleogene in Baise Basin. Based on the analysis of seismic data and well logs,the Nadu formation and Baigang formation of the Paleogene can be divided into one second-order sequence, and three third-order sequences. The member 3 of the Nadu formation forms sequence stratigraphy Ⅰ, the members 2 and 1 of the Nadu formation form sequence stratigraphy Ⅱ, and Baigang formation forms sequence stratigraphy Ⅲ. Sequence stratigraphy Ⅰ and Ⅱ are deposited during faulted period, and sequence stratigraphy Ⅲ is deposited during depreesion period. Sequence stratigraphy Ⅱ contains not only mudstonds of deep-lake subfacies with large thickness and wide distribution, but also rich sandstones of fluvial facies, fan delta facies, delta facies, and is the main sequence with source-reservoir-caprock assemblage combination. The sandstones of fan delta facies deposited in the north of the basin are available reservoirs. The long-axial widely distributed sandstones of fluvial facies and delta facies developed in the lowstand systems tract of each sequence are the potential reservoirs for hydrocarbon exploration of subtle traps.