四川盆地元坝中部断褶带须四段高分辨率层序地层

High resolution sequence stratigraphy of the fourth member of Xujiahe Formation in central fault-fold belt of Yuanba area, Sichuan Basin

依据地层发育特征,对元坝中部断褶带须四段进行高分辨率层序地层划分。首先,根据现代辫状河与辫状河三角洲沉积特征,厘清辫状河与辫状河三角洲沉积体系发育部位,依据钻井和测井资料,确定须四段发育辫状河和辫状河三角洲相;然后,根据高分辨率层序地层学原理,识别出具有层序地层意义的2种河道类型,即低可容纳空间侧向叠置河道和高可容纳空间垂向叠置河道,进而判断基准面旋回转换位置,明确须四段可划分出2个四级旋回及3个亚段:上砂段、腰带段及下砂段;最后,井-震结合进行须四段层序地层综合解释,建立区域等时层序地层格架,为进一步分析等时层序格架内沉积相展布特征奠定了基础。

On the basis of formation development characteristics, this paper studied the high resolution sequence stratigraphy division of the fourth member of Xujiahe Formation in central fault-fold belt of Yuanba area. Firstly, based on the sedimentary characteristics of modern braided river and braided river delta, we clarified the braided river sedimentary system and braided river delta sedimentary system. Through the drilling and logging data, we defined that the study area developed braided river facies and braided river delta facies. And then, according to the principle of high resolution sequence stratigraphy, we identified two types of braided channel which have sequence stratigraphy significance, including high accommodation vertical superimposed braided channel and low accommodation lateral superposed braided channel, which can be used to judge the transformation position of base level cycle for single well high resolution sequence division. It was considered that the fourth member of Xujiahe Formation can be divided into two fourth-order cycles and three sub-members. Finally, combined with the seismic sequence interpretation of the fourth member of Xujiahe Formation, we established regional sequence stratigraphic framework, which provides foundation for the further study on sedimentary facies distribution in sequence stratigraphic framework.