四川盆地上三叠统须家河组高分辨率层序地层研究

摘要

In order to further understand the sequence stratigraphic framework and spatial and temporal distribution of Xujiahe Formation in Sichuan Basin,based on the high-resolution sequence stratigraphy and sedimentology theory,and in combination with the data of a large number of outcrops,drilling cores,well logging and seismic,this paper studied the high-resolution sequence stratigraphy and sedimentary facies of Xujiahe Formation in Sichuan Basin.Research found that despite the complexity of structure,the different direction of the material supply,the change of rock facies belts and different naming system in each partition,there are traceable unconformity and maximum flooding surface which enable the study went on.Through the sequence boundary tracking and analysis of sedimentary cycle,Xujiahe Formation can be divided into 3 super long-term cycles,6 long-term cycles and 21 middle-term cycles.According to the sequence stratigraphy contrast in the whole Sichuan Basin,the thickness of north-south strata is stable,however,east-west strata distribution is complex.The whole LSC6 and most of LSC5 are absent in the west,while most of LSC1 is absent in the east.Because the settlement-deposition center is located at the Longmenshan frontal depression,and the sedimentary rate is very high in the west of the basin,the overall distribution of the sedimentary body present like a wedge,which is thick in the west and thin in the east.On the basis of the study of sequence stratigraphy,chronostratigraphic framework was tentatively created.Through the comprehensive comparison of sequence stratigraphy,chrono-stratigraphy and biostratigraphy,the relative age of each cycle and the value of the unconformity sedimentary interval are concluded.This provides theoretical support for the next step of production and practices in Sichuan Basin.%为了进一步认识四川盆地须家河组的层序格架和时空分布,基于高分辨率层序地层学及沉积学相关理论,通过露头剖面、钻井岩心的观察及测井、地震等资料的分析,开展了四川盆地须家河组层序地层研究,结果发现盆地内虽然具有构造复杂、物源多样、岩相不均、组名不统一的特点,但依然具有全盆地范围内可追溯的不整合面和湖泛面.通过层序界面追踪及沉积旋回分析,将四川盆地须家河组划分为3个超长期基准面旋回、6个长期基准面旋回及21个中期基准面旋回,并建立了盆地内各级旋回的对比关系.通过全盆地对比结果表明,须家河组在南北方向上各级旋回个数变化不大,沉积厚度相对稳定;东西方向上旋回变化复杂,西部缺失LSC6旋回和大部分LSC5旋回,东部则缺失大部分LSC1旋回,由于沉降与沉积中心位于龙门山前缘坳陷,盆地近西部沉积速率极高,整体的沉积体展布呈现西厚东薄的楔形体形态特征.在层序对比研究的基础上,尝试性地建立了年代地层格架,通过层序地层学与年代地层学、古生物地层学的综合对比,推测了各旋回的相对年龄值以及不整合面的沉积间断时间,为四川盆地须家河组下一步油气资源探勘开发提供了理论支持.