Tectonic And Sedimentary Evolution Of Permian Southern Qilian Basin

Southern Qilian basin is located in the southern part of Qilian fold belt, southwest adjacent to Qaidam basin, the northwest part is cutted off by sinistral strike-slip Altyn Tagh fault, the northern parts connect to the Middle Qilian block, the Southeast is linked together with the West Qinling.Many of the previous research mainly focused on Caledonian, Hercynian, indo-chinese period,but did a little research on the prototype basin and evolution process in Hercynian, indo-chinese period.Through the studies on the structural and sedimentary evolution of Permian Southern Qilian basin this article recovers the original Permian basin in different times so as to provide theoretical basis and base information for the gas and oil exploration of Permian Southern Qilian basin.This article takes "entirety,dynamic,system,integration"as the guidance, and is based on the existed geological research achievement, comprehensively uses region geological survey and geophysics method,also combine the outdoor survey with inside research. Based on Permian marine stratigraphic division of Southern Qilian basin, this article restores prototype basin in different period of Southern Qilian basin; Based on multiterm profiles through the basin, do research on the structural characteristics of basin; Make use of the balanced cross section technique to recover the structural characteristics of basin in different periods.Thereby, carry on the multiple perspectives, omni-directional research of the evolutionary process of Permian Southern Qilian basin.The research results indicate that South Qilian basin has experienced in the Permian transgression-Late Permian regression cycles.In Lemengou sedimentary period the basin was shore facies as a whole and belonged to depression basin;In the middle Permian Caodigou group sea level rose relatively and formed marginal depressions basin composing of a deep change from north to south Delta-siliciclastic and shore-shallow continental shelf-carbonate platform depositional system.In the late Permian Hajier sedimentary period the basin formed shore-carbonate platform sedimentary facies from west to east;To the late PermianZhongshigong group the basin shrinked constantly so that it became a restricted epicontinental sedimentary basin with river-delta facies from east to west. In the whole study area, the structural deformation of the sedimentary cover was very low and the intensity of the fault increased from east to west;The deformation intensity casued by folding process in southern Shinaihai-Caodabanshan profile was stronger than that in Hateer-Dayanglong profile; The Indosinian-Early Yanshanian regional tectonism dominated the eastern basin and the Late Yanshanian-Himalayan tectonism was dominant in the western basin.