Original Appearances And Its Evolution And Reformation In Mesozoic Yanqi Basin In Xinjiang

Yanqi Basin is a Meso-Cenozoic reformed residual basin in the southern Tianshan folded belt and locates among Tarim, Junggar and Turpan basins. The present appearance of Yanqi basin is entirely different with its ancient because of later strong reformation. Yanqi basin was underwent complex structure change and strata were eroded strongly which restrict the cognition of the basin, such as generation, development, decline and disappear, et al. Since full-scale exploration in Yanqi basin in 1993 by Henan oil field, there have found two oil fields(Biaoliang oil field and Bengbutu oil field) and four bearing-oil sections(Baobei, Baozhong, Bengbutu and Bengbutudong) and Jurassic is the mainly exploited stratum. But there have not any achievement in exploration since 1998. It was found that a suit of thicker Mesozoic strata lie underneath Huola mountain in the west of Yanqi basin which was approved by exploratory drill chen2, it shows that the original appearances of Yanqi basin entirely differ with the present. This thesis use the reformed basin as the guideline, insist the thought of integer, dynamic and comprehension, use the large numbers of analysis on apatite and zircon fission track as clew, combine with several subjects and techniques and give prominence to the evolvement and reformation process. On the basis of the large numbers of age analysis on apatite and zircon fission track, through the research on the present structural framework, mineral characteristics and depositional environment in remanet strata and comprehensive compare with its neighboring Mesozoic basins in strata, sedimentary facies and hydrocarbon source rock, this thesis systemically discussion on the uplift timing of these mountains around Yanqi basin, original appearances in Mesozoic and characteristics of evolution and later reformation and provide important theoretical basis for petroleum exploration. The paper is briefed as follows:1. Analysis on these apatite and zircon fission tracks from mountains and in the front of them shows that they have the characteristic of mult-stages uplift. These mountains were uplifted late in Mesozoic and began in the middle-late period in lower Cretaceous.2. Analysis on mineral characteristics (percent of shingly fragment, maturation index and heavy mineral coefficient of stability) and depositional environment in Mesozoic remanet strata show that provenance located in the north of Yanqi basin, clast were moved from north to south in Mesozoic, and the sedimentary environment in northern basin were braided stream facies while shallow lacustrine stream facies in southern basin. On these basis, the original appearances was discussed through comparing with its neighboring Mesozoic basins, Yourdusi, Kumux, Kongquehe slope and Kuqa basin, in strata, sedimentary facies and hydrocarbon source rock. The results revealed that Kuqa was coherent with Yanqi and Kumux and there were covered with thin Xiaoqungou group in mid-late Trias, but Yourdusi and Kongqhehe slope, respectively located in the north and south of Yanqi basin, had no sediment because of high topography, the five areas, Yourdusi basin, Kuqa basin, Yanqi basin and Kumux basin, were coherent and formed the north of the larger Tarim basin at the beginning of early Jurassic, the appearances were continued to early period in early Cretaceous, above those areas were divided into five separate basins and began respective evolution because that Tiansha and these mountains around Yanqi basin were uplifted from middle-late period in early Cretaceous to late Cretaceous.3. Through the age analysis on apatite and zircon fission track, there have five stages of tectonic movements, respectively occurred in late Trias, from mid-late period in early Cretaceous to late Cretaceous, Eocene, Oligocene and Miocene. Yanqi Basin experienced five evolution stages including Forland Basin(P₂-T), Extensional Basin(J- k₁¹), Compression and Erosion stage(K₁^2-3-K₂) and Regeneration Forland Basin(E-Q).4. Yanqi basin experienced two stages of reformations in late period of Yanshan and Himalaxiyan, there are three kinds of reformation types in basin, respectively uplift-erosion reformation, composite reformation and thrust-fold reformation and its reformation intension were divided into stronger, strong and medium grades.