Identification Of The Jiange Paleo-Uplift In North Sichuan Basin And A Study Of Its Formation Mechanism And Evolution History

Analysis of the formation mechanism and evolution of paleouplift could provide the basis for studying the inland tectonic movement. Besides, paleouplift is now an important hydrocarbon exploration target. By using seismic profiles, well data and outcrops of North Sichuan Basin, this thesis propose for the first time the exicstence of a Late Triassic paleouplift in the study area, which is named Jiange Paleouplift, since its center is around Jiange County. The formation of this paleouplift could explain well the lack of upper parts of Xujiahe Formation in the study area. Its identification will be of great signicance to help understand well the regional tectonic evolution, and also to help guide the hydrocarbon exploration efforts in the study area. Following the identification of its existence and basic characteristics, combined with Bischke Plot Analysis, the paper analyzed the formation and evolution history of the paleouplift by analyzing the time-strata relationship of seismic profiles and cross well lines. This thesis also studied its formation mechanism by interpretating the regional seismic profiles based on the Fault-related Fold Theory. Balanced crossed section and AFTA method are employed to help understand the later alteration history of Jiange Paleouplift, while detrial zircon dating and analysis of paleocurrent and detrital composition are used to help discuss the source rock of the paleouplift.Based on these studies, this dissertation has reached the following conclusions:(1) Jiange Paleouplift spreads around Jiangyou, JianGe, Guangyuan and Wangcang. It has undergone a complete uplift cycle. It began to form during the sedimentation of the third member of Xujiahe Foramtion, grew until the sedimentation of the sixth member and finally disappeared at the end of Early Jurassic, lasting about 21 Ma, causing the sedimentation gap of about 350m. The later alteration history of the paleouplift can be divided into three stages, namely Stage of Integral Burial during 189-160Ma, Stage of Differential Burial during 160-65Ma and Stage of Differential Uplifting and Alteration of Thrust Structures and Local Structures from 65Ma to present.(2) The formation of the Jiange Paleouplift was controlled by compressional stress from South Qinling aera. Its discovery proves the existence of the Late Triassic Foreland Basin system of northern margin of Yangtze Plate. Longmen Shan Thrust Fault later strongly alterated the paleouplift, leading to the almost complete disappearance of the northwest winge of the paleouplift.(3) The major source direction of the studied area is Qinling, mostly from South Qinling. Detrital zircon age distribution indicates that South Qinling area started to be active from Late Triassic, while northern segment of Longmen Shan was not uplifted too much during Late Triassic.(4) Jiange Paleouplift had a direct influence on the depositional system of source rock, reservoir propertyand also the accumulation of hydrocarbons, thus, it could help guide the hydrocarbon exploration efforts of North Sichuan Basin.