Geochemical Study Of Datangpo Formation Of Nanhua System In Shennongjia Area And Petroleum Significance

Studies have shown that the Neoproterozoic paleoclimate is one of the periods with the most dramatic changes in geological history,with multiple global glacial periods.In recent years,research has found that the Neoproterozoic strata in the eastern part of the Hubei Xiadong area,which is a classic profile,Stratigraphic development is complete,while the Nanhua strata in the northern part of the Hubei Shennongjia area are more well developed and are ideal areas for the study of Nanhua strata in the northern margin of Yangtze.The Datangpo formation of the Nanhua system belongs to the interglacial deposits between the Sturtian and Marinoan glaciations.On the basis of detailed measurement of three representative sections of Nanhua system in Shennongjia area?the sections of Dajiu lake,Songluo and Wenshui river?,this paper has carried out systematic geochemical sampling analysis on the section samples.A systematic study of the sedimentary paleoenvironment of the Datangpo Formation in Shennongjia area has been carried out.Geochemical analysis and test data and stratigraphic profile data of other profiles such as Gucheng,Wangjiajie,Yuquan,Changsha Dam,Huangjiahejiao,Zhongshanling Roadway,Minle,Yanglizhang,Baishixi,Daotuo,Xixibao,Guizhou Congjiang and Xiangxinanzhao Cave have been collected.Regional comparative analysis has been carried out.Based on the study of paleoenvironment,the relationship between source rock development and paleoenvironment of Datangpo Formation in Shennongjia area is analyzed in detail.The main findings are as follows:?1?Using CIA?ICV?Al₂O₃/Mg O?Mg/Ca?Fe O/Mn O and other related indicators,the study shows that the sedimentary period of the Datangpo Formation in Shennongjia is generally warm and humid,and the abrupt changes in the indicators of the strata samples in the Nanhua Glacial and Interglacial periods in Shennongjia are obvious,indicating the drastic changes in climate.?2?Studies on K/Na?Ca O/?Ca O+Fe??Rb/K and other indexes of Datangpo Formation samples in Shennongjia warm water section show that the salinity of the water body in Datangpo Formation in Shennongjia area is relatively stable during the sedimentation period,and it is seawater with medium and low salinity.However,the ratio of ice age samples indicates that the Nantuo Ice Age and Gucheng Ice Age in Shennongjia area may be high salinity water deposits.?3?the study of Ni/Co?V/?V+Ni??Ce_anom?Fe/Mn and other indicators of samples from various sections in Shennongjia area shows that the sedimentary water of Datangpo formation in the study area is generally a weak oxidation-weak reduction water environment.?4?The regional comparative study in Yangtze region shows that the stratigraphic lithology of Datangpo Formation starts to show dichotomy in profile from Gucheng of Hubei to disappearance of upper and lower dichotomy in Sanjiang profile of northern Guangxi.In addition,the thickness of the first member of Datangpo Formation experienced a process from thin to thick and then to thin from the ancient city of Hubei to Sanjiang in northern Guangxi.The paleoclimate of the Datangpo Formation in the Yangtze region did not change obviously in the region during the sedimentary period,and it was all warm and humid.The salinity of the sedimentary water varies obviously in the region.The northern margin of Yangtze?Songluo section,Dajiuhu section,Wenshui river road section?is low salinity water sediment,while the southern margin of Yangtze?Zhao cave in western Hunan?is relatively higher salinity water,and the middle of Yangtze plate is higher salinity water.The redox levers of sedimentary water changes frequently,and the main belongs to weak oxidation-weak reduction water enviroment.?5?The organic geochemistry study of the source rocks of the Datangpo Formation in Shennongjia area shows that during the interglacial period of the Datangpo Formation,bacteria and algae,especially benthic macroalgae,were extremely developed in Shennongjia area,with a high level of paleoproductivity of organic matter and good preservation conditions of organic matter in the formation water.Good climate and sedimentary water environment make the source rocks of Datangpo Formation have high abundance of organic matter,reaching good source rock standard and having good material basis for oil generation.The source rocks of Datangpo Formation in Shennongjia are favorable source rocks for deep strata in this area.