徐家围子断陷南部沙河子组层序地层格架及沉积特征

SEQUENCE STRATIGRAPHIC FRAMEWORK AND SEDIMENTARY CHARACTERISTICS FOR SHAHEZI FORMATION IN SOUTH XUJIAWEIZI FAULT DEPRESSION

针对徐家围子断陷南部沙河子组层序地层格架划分不清、沉积特征不明的现状,综合利用岩心、测井及地震等资料,应用Vail层序地层学理论,开展了徐家围子断陷南部沙河子组层序划分研究,并结合构造活动背景、物源供给情况分析了层序格架内的沉积相类型和演化特征。研究认为:南部沙河子组划分为1个二级层序,进一步划分为4个三级层序,每个三级层序均具有二分结构,发育湖侵、湖退2个体系域;研究区主要发育扇三角洲相、辫状河三角洲相和湖泊相等沉积相类型,以三角洲前缘亚相中的水下分流河道为主力储层砂体;南部沙河子组可归结为断控斜坡背景和缓坡背景的2种沉积模式,具有格架控砂、继承演化、分源沉积、连片发育的沉积演化特征。

In the light of the unclear current conditions of the sequence stratigraphic framework division and sedi- mentary characteristics for Shahezi Formation in South Xujiaweizi Fault Depression, by comprehensively using the core, well logging, seismic data and so on, the sequence division of the formation is conducted with the help of Vail sequence stratigraphy theory, and in the meantime integrating with the documents of the tectonic settings and provenance supply, the types of the sedimentary facies and evolutionary characteristics within the sequence frame- work are analyzed. The studies show that South Shahezi Formation can be divided into one second-class sequences and furthermore it can he classified into four third-class sequences, and moreover each third-class sequence posses- ses dichotomy structure and develops lacustrine transgressive and regressive system tracts; the sedimentary facies types such as fan delta, braided river delta and lacustrine facies and so on are well developed in the study area; South Shahezi Formation can be summarized into two sedimentary modes： fault-controlled steep and gentle slope settings, and furthermore possess the following sedimentary evolution characteristics： framework controlled sand, successive evolution, separated-source sedimentation and contiguous distribution.