Inverse Modeling For Subsidence History In Southern Ordos Basin From Jurassic To Early Cretaceous

Ordos Basin is a polycyclic superposition basin that is formed in an earlier geological history and has experienced a longer evolution.It was a part of North China Basin before the Late Jurassic and became an independent basin between the Late Jurassic and the Early Cretaceous,which was finalized in the Himalayan movement period.The sedimentary characteristics of Ordos Basin in its main developmental stages that from Late Triassic to Early Cretaceous have been studied in detail by predecessors.However,most of the studies on the southern part of the basin are focused on the sedimentary system of hydrocarbon-bearing strata,while little attention has been paid to the analysis of basin subsidence history and the restoration of basin basement structure,and no systematic discussion has been made on the formation and evolution history of the basin in the Mesozoic and Late Mesozoic.In this study,we collected a large number of drilling data in southern Ordos Basin,selected three drilling profiles for inversion simulation,interpreted the lithology and the sedimentary environment with Logging data.Back-stripping technique was used to solve the problem of sedimentation history of Ordos Basin,analyze the basin subsidence characteristics and subsidence mechanism.The results show that the Fuxian formation was mainly dominated by alluvial fan and fluvial facies.During the Yan'an period,the sedimentary area and Lake were gradually spread with the development of fluvial and delta facies,which were reduced during the Zhiluo period.Zhiluo formation was dominated by braided stream in the beginning and meandering stream later.However,the lake basin expanded to the west and north during the Anding period.In the early Cretaceous,the center of the lake basin shifted to the west,and the eastern river system advanced to the lake through the lake delta system.Meanwhile,the subsidence center of the basin has shifted obviously.There is no centralized subsidence center in the Fuxian period.A significant shift occurred in the sedimentation center of the basin.There is no centralized subsidence center in the Fuxian period.The maximum sedimentary subsidence in the Yan'an period is mainly distributed in the central part of the study area(Qingyang-Huachi-Xifeng),and the eastern part(Ansai-Zhitan),which shifted to the west part of Huanxin-Qingyang-Xifeng in the Zhiluo period and to the south in Anding period.The subsidence center of the lower Cretaceous Zhidan Group is similar to that of the Zhiluo Group.Most of the subsidence curves in the study area show two-stage upward convexity,which is a typical episodic subsidence feature of foreland basins.The asymmetric subsidence model indicates that the thrust loads along the western margin of Liupanshan thrust belt played a major role in controlling the subsidence of the Ordos basin,and the loads along the southern margin of Qinling Orogenic belt also played a certain role in the Anding period.