Sedimentary Environment And Envolution Of The Changcheng System,paleoproterozoic In The Jixian,Tianjin

The effectiveness of petroleum systems in the Proterozoic strata of the North China Craton has been proven.Tianjin Jixian is a standard section for precambrian stratigraphic studies in China,but the study of the sedimentary facies of the Changcheng system in the Paleoproterozoic is relatively rare and the understanding is not uniform.In this paper,taking the stratum of the Changcheng System,Paleoproterozoic in Xiaying Town,Jixian,Tianjin as an example,based on previous research,through field observation and measurement,combined with indoor wafer identification,XRD test and other technologies,we did a detailed analysis on the sedimentary of the Changzhougou Formation,Chuanlinggou Formation and Tuanshanzi Formation.The results show that the Changzhougou Formation can be divided into three members,the Chuanlinggou Formation is divided into three members,and the Tuanshanzi Formation is divided into four members according to lithologic changes and cycles.The Changzhougou Formation is dominated by quartz sandstone,which can be divided into 6 types according to the sedimentary characteristics of the rock.The type of frequency curve,the particle size corresponding to the peak value,and the particle size corresponding to the intercept point of the jumping suspension component on the probability accumulation curve can be used to distinguish the river-forming sands of the Changzhougou Formation and the coastal sand bodies.The Chuanlinggou Formation is dominated by gray-green and black shales,mainly illite and quartz.The Tuanshanzi Formation is dominated by crystalline dolomite and clastic rocks.According to the sedimentary characteristics of dolostone,it can be divided into 5 types.Generally,the climate from the Changzhougou Formation to the Tuanshanzi Formation changed from humid to arid,and the sedimentary water gradually changed from oxidized to relatively reduced,The salinity of the water body continues to increase and reaches its peak in the Tuanshanzi Formation,laying a foundation for the deposition of carbonate rocks in the Tuanshanzi Formation.The Changzhougou Formation is mainly dominated by braided fluvial fuchsia sandstone and coastal facies milky or gray-white sandstone.The Chuanlinggou Formation is mainly dominated by reduced-color mud deposits in the shallow sea shelf phase and semi-deep sea slope facies.The Tuanshanzi Formation is dominated by carbonate and clastic rock mixed tidal flats,open terraces,and gentle slope depositions at the platform edge.From the coarse-grained clastic rocks of the Changzhougou Formation to the fine-grained shale of the Chuanlinggou Formation and the mixed formation of carbonate rocks and clastic rocks of Tuanshanzi,a complete transgressive and regressive stratigraphic sequence is formed.The Paleoproterozoic Changcheng System in the North China has developed well in terms of source-reservoir-cap assemblages,and finding anticline traps and fault traps in the Changcheng System in North China has become an important direction for oil and gas exploration.