Jurassic Litho-Stratigraphic Framework And Sedimentary Basin Evolution In Lancangjiang Region Of East Tibet

The Lancangjiang area layer which located in the east of Tibet is mainly located in the Qiantang Sanjiang tectonic stratigraphic area.The traffic is very convenient.There is Sichuan Tibet highway south line,Sichuan Tibet highway north line,Yunnan Tibet highway and other main highways throughout the area.And the economy is common in the area,mainly for agriculture and animal husbandry.The area is rich in mineral resources.The predecessors have carried out relatively more exploration and research work in the area,and have accumulated quite abundant achievements.However,there are relatively few studies on the Jurassic strata in the region,and the Jurassic sedimentary minerals are narrower,especially in the study of oil shale and other minerals.The relationship between Jurassic sedimentary mineral and palaeogeography,sedimentary facies,lithostratigraphic framework and sedimentary basin evolution needs to be improved.It is hoped that through the study of the Jurassic lithostratigraphic framework and sedimentary basin evolution in the Lancangjiang region of the East Tibet,the basic understanding of the evolution law of the Jurassic sedimentary basin in the eastern Tibet is preliminarily obtained,and the drawing work of the related maps is completed,and through the study of the lithostratigraphic framework and the evolution law of the basin and ground in the study area to explore the Jurassic sedimentary minerals and judge the specific environmental constraints and judge the formation of oil and gas resources in the jurassic.This paper combines the previous regional geological survey,geochemical exploration,paleontological fossils,remote sensing,geophysical logging and other data,referring to plate tectonic theory,biostratigraphy,basin analysis principles and sedimentary environment and facies,sequence stratigraphy,Sanjiang Tethys sedimentary geology and metallogenic thought methods,and the theory of plate tectonics as the main trunk.On the basis of "tectonic basin control and basin control phase" as the basic research ideas,on the basis of multiple stratigraphic compartmentalization in the study area,the typical stratigraphic sections are analyzed and contrasted according to the sedimentary facies markers,combined with some single factor conditions,the characteristics of lithofacies palaeogeography and lithostratigraphic framework of the study area are synthetically analyzed.Finally,To discuss the relationship between the sedimentary minerals and the lithofacies palaeogeographic environment.Based on the three aspects of stratigraphy,lithostratigraphy and biostratigraphy,the Jurassic strata in the east of Tibet are divided and the stratigraphic framework is established,and the theory of sequence stratigraphy,based on the signs of sedimentary geochemistry,geophysics,paleontology and sedimentology,is used for reference.On the basis of the analysis of the sedimentary facies of the typical stratigraphic section,the sedimentary facies is compared with the principle of superiority method,and the lithostratigraphic framework map is plotted.On the basis of the sedimentary facies analysis and comparison,the Jurassic lithofacies palaeogeography in the east of Tibet is synthetically analyzed with the combination of the paleostructure,the stratum thickness and the lithostratigraphic framework.The early Middle Jurassic lithofacies palaeogeographic map and late Jurassic lithofacies palaeogeographic map of Lancangjiang region of the East Tibet are plotted and the paleogeographic map of late Jurassic in the Lancangjiang region of the East Tibet is plotted,and According to the analysis of sedimentary facies and research results of lithofacies palaeogeography in each single section,the sedimentary minerals in the region and the specific sedimentary environment and constraints formed by shale gas resources are discussed.The geodetic structure and its development and evolution directly determine the type and nature of the sedimentary basin.Different sedimentary basins produce different sedimentary environments and palaeogeography,thus developing different types of sedimentary facies.In the early Middle Jurassic period,the marine environment is mainly in eastern Tibet.There are some delta facies near the paleo continental area,and marine and terrestrial interlacing and river lacustrine deposits.With the uplift of the crust,to the late Jurassic,the eastern part of Sichuan is mainly ancient land,and develops lacustrine facies and fluvial facies.Especially in the Changdu Mangkang basin,the lacustrine deposits are dominant.Zuogong riwoqe West is still the marine environment.The sedimentary facies and the filling sequence of different sedimentary facies are different,indicating different sedimentary environments.Sedimentary minerals have specific metallogenic specialization,so they can be mineralized and become the mineralization in specific sedimentary environments.In the eastern Jurassic,gypsum deposits mainly exist in marl and siltstone,belonging to the river and lake facies zone.The salt deposits mainly occur in the coastal shallow sea environment.The oil and gas in the area are influenced by sedimentary structure and organic matter content in shale.Metal minerals are mainly developed in Jurassic structural fractures,with little influence on sedimentary environment.Through this research,we have basically revealed the characteristics of Jurassic lithostratigraphic framework in eastern Tibet and the evolution of Jurassic sedimentary basins in eastern Tibet.This study further enriches the achievements of the Jurassic sedimentary facies in the east of Tibet,as well as the research results of lithofacies palaeogeography,which can provide a hint for the study of other similar sedimentary basins.The main genetic mechanisms,occurrence rules and preservation of sedimentary minerals are all influenced and restricted by the palaeogeographic environment and lithofacies characteristics.This paper discusses sedimentary facies and lithofacies palaeogeography,and expects to provide help for future resource exploration.