Analysis Of Subsidence History Of Southern Ordos Basin From Jurassic To Early Cretaceous

Research on basin subsidence history can provide important information for structural evolution of a basin,act as main parameters for dividing structural evolution stage of the basin quantitatively or semi-quantitatively and provide important references for formation mechanism of the basin.Time from Late Triassic to Early Cretaceous is the main time of basin development.Previous researches on subsidence of Late Triassic are detailed while those on time from Jurassic to Early Cretaceous are relatively lack.This research has important meaning for understanding subsidence mechanism,cause,tectonic stage and process.To analyze subsidence history of southern Ordos Basin,this paper,based on previous researches,collect drilling data of southern Ordos Basin.Firstly,use related methods of well geology to interpret sedimentary facies and lithology that are reflected by well logs.Next use ideas and technology of basin simulation to obtain subsidence value and speed infor Mation of the region in different times.Then collect previous data of other geologists to broaden research scale to the whole south of Ordos Basin.Analyze total subsidence rates and tectonic subsidence rates to divide stages of basement evolution of the basin,describe subsidence values and location of subsidence center and recover basement forms of the basin in different times.Finally subsidence evolution history and the law of distribution and delivery of subsidence center can be obtained.Jurassic subsidence of southern Ordos Basin is Mainly influenced by Yanshan movement,from 198 Ma to 157 Ma.After the short-term lift around the whole basin led by Yinzhi movement,the southern basin starts to subside.The subsidence evolution history can be divided into five stages:(1)In Fuxian stage,total subsidence and tectonic subsidence values of the research region are small while those of southwestern are large,and the southwestern basin is the subsidence center;(2)In Yanan stage,the subsidence rate of southwestern basin is low while fast subsidence happens to the research region,and the subsidence center moves from west to middle gradually;(3)In Zhiluo stage,the southwestern basin subside more slowly while the research region still go fast,and the subsidence center is in the middle totally;(4)InAnding stage,the two parts both subside slowly,and the subsidence center is still in the middle,and by the way,tectonic subsidence dominates total subsidence in the former four times.(5)In Early Cretaceous stage,fast subsidence occurs to the southwestern basin while the research region subsides relatively slowly.Tectonic subsidence value is not the Main part of total subsidence value,losing leadership.Sedimentary load and compaction start to dominate total subsidence.The subsidence center moves to the west again.