松辽盆地兴城地区泉四段浅水三角洲沉积特征

Sedimentary characteristics of shallow water delta of Quan-4 member in Xingcheng area, Songliao Basin

松辽盆地北部兴城地区泉四段主要发育泥岩、粉砂质泥岩、泥质粉砂岩和粉砂岩沉积.通过泥岩颜色、古生物化石、沉积构造和测井相特征等分析,确定研究区泉四段为一套退积型浅水三角洲沉积,包括三角洲平原和三角洲前缘2种亚相,分流河道和决口扇微相较发育.应用高分辨率层序地层学原理,对泉四段进行层序划分,结合砂泥岩分布规律,编制研究区沉积相平面展布图,并分析其垂向演化规律.研究认为,泉四段内部可划分出Q4-SSC1～Q4-SSC7等7个短期旋回,其中,Q4-SSC7时期水体达到最深,研究区内仅发育三角洲前缘亚相;Q4-SSC1时期河道砂体最为发育,为储集层发育的最佳时期.泉四段自上而下经历了由三角洲平原到三角洲前缘水体由浅变深的一个沉积演化过程,反映了研究区泉四段沉积时期为一次湖侵的沉积过程.

The fourth member of Quantou Formation in Xingcheng area in Songliao Basin is mainly consisted of mudstone, silty mudstone, pelitic siltstone and siltystone. Based on the analysis of mudstone color, palaeophyte fossil, sedimentary structure and logging facies, the fourth member of Quantou Formation was confirmed as retrograding shallow water deka depositional system which develops delta plain and delta front subfacies, and distributary channel and crevasse splay are the main microfacies. According to the principle of high sequence resolution stratigraphy, this paper divided the sequence of Quan-4 member, combining with the distribution regularity of sandstone and mudstone, prepared the distribution layout of sedimentary facies, and analyzed the regularity of vertical evolution. The result shows that： Quan-4 member can be divided into seven short-term sequences, from Q4-SSC 1 to Q4-SSCT. During the Q4-SSC7 period, water reached the deepest, and only developed delta front subfacies; during the period of Q4-SSC 1, channel sand body is mostly developed, which is the best period for development of reservoir. In the vertical, Quan-4 member experienced a sedimentary evolution process from shallow to deep water, which is an transformation process from delta plain to delta front, reflecting an lake invasion of the sedimentary process in the study area.