The Study On Tectonic Evolution In North Songliao Basin

Songliao Basin is the most largest continental petroliferous basin found in Chinaand even the world. It has experienced multi-stage tectonic modification andsedimentary filling, and has formed multiple sets of reservoir-cap assemblages. So thegeologist paid much attention to the evolution of Songliao basin. However, the previoushave made lots of work on the detailed description of the static geological elements ofsingle-basin, but made superficially study on the dynamic process of the evolutionaryhistory because of the short of datum and the limitation of techniques.With the development of exploration, the discovery of new phenomena, and theabtaining of geological datum of peripheral areas, and based on the seismic structuralinterpretation, this study has analyzed the distribution characteristics of unconformi-ties, fractures and structural styles; restored the denudation which was caused by thelate regional tectonic of each structural layer by the erosion quantity technology;analyzed emphatically the characteristic of the profile and graphic evolution; discussedthe different stages of geodynamic mechanisms, which lay a geological foundation forthe holistic, dynamic, systematic analysis of hydrocarbon accumu-lation, seekingnew areas of exploration, and re-scrutinizing the oil and gas resources and theenrichment patterns. Through this study, the main task and understanding are asfollows:(1) Based on the seismic profile interpretation, and combined the drilling andgeological datum, this study anatomised the structural geometric features of thenorthern part of Songliao Basin. There are5regional unconformities recognized in thesedimentary cover, including the unconformities forming in late rifing, late depositionstage of Nenjiang group, late deposition stage of Mingshui group, late Paleogene andlate Cenozoic. And the unconformities forming in late deposition stage of Nenjianggroup is a extensional angular unconformity, but the unconformities forming in latedeposition stage of Mingshui group is a compressed angular unconformity. Summed up the plane and profile distribution characteristics of the fault located in deep basementand sedimentary cover. And after multi-phase tectonic movements, includingcompression and extention, there developed a variety of structural styles in SongliaoBasin, which can be divided into four major categories: extentional, compressional,reversal, and transform structural styles.(2)This study restored the denudation mainly used the seismic trendency method,and realized that the largest erosion scale happened in the late deposition of Nenjianggroup and Mingshui group. And there separately north-eastern in the late depostionstage of Nenjiang group and south-eastern in the late depostion stage of Mingshuigroup suffered the most serious erosion.(3) By producing two maps of profile evolution by the utilization of balancedcross-section technology, and weaving four ancient tectonical plane maps of the thirdsegment of Nenjiang group before and after the deformation of the late Nenjiang groupand the late of Mingshui group, the forming, the developing and the transformingprocess and charateristics of middle and shallow stratums in Songliao Basin have beenanalyzed and studied, and the tectonic reverse happened in the late deposition stage ofMingshui Group made the tectonic framework of the basin undergo enormous changes.(4) Through the analysis of structural geometry and kinematic, combined with theregional geological background of Songnen Block, the dynamic background of eachsingle-basin, the evolution discipline and the genetic mechanism have been analyzed.And it simply summarized as:1) During late Triassic and middle Jurassic, the NorthChina plate and Siberian plate collided, which caused intracontinental orogenesis. Sounder the remote delivery compressive stress of the plates collision, the lithospherewithin the continent, or at the continent margin and adjacent to the orogen, bended anddeveloped foreland basin;2) During late Jurassic and early Cretaceous, Kula platesubduction induced mantle plume to rise and fall, made asthenosphere circulate in onedirection and mantle magma diapir, which resulted in the lower crust plasticallystreching and thinning, and resulted in the upper crust brittlely extending anddeveloping rifted-basin there;3)From Early Cretaceous, the subduction angle of westpacific towards the Eurasian plate became larger, and the Subduction zone and therising hot spots of mantle material melting constantly eastward, The melt cooled down,and the thermosaging happened there, and developing depression basin.