Establishment Of Chemical Stratigraphic Framework And Paleoclimate Analysis On The Lower Member Of Shahezi Formation In Songke 2 Well, Songliao Basin

With the development of the Continental Scientific Drilling Project in the Songliao Basin of Northeast China and the successful completion of songke-2 well,the complete Cretaceous continental sedimentary record of Songliao Basin in Northeast China has been obtained.It provides valuable materials for the study of geological events,biological evolution,paleoclimate,paleoecology and other scientific issues in the Cretaceous greenhouse climate period.The continuous lacustrine sediments in the basin record the information of deep-time paleoenvironment,paleoclimate and other geological evolution.Through careful study and fine description of the core of songke 2 well,it is helpful to understand the deep-time of the terrestrial sedimentary system under the greenhouse climate Response characteristics of climate and environment change.In this study,the core of lower Shahezi Formation(4550-5725 m in depth)of songke well 2 is used as the research material,and the geochemical data measured by hand-held XRF and X-ray fluorescence analysis are used for screening and processing.The geochemical facies are divided by principal component analysis with mathematical method,and the chemical stratigraphic belt,single element index and element ratio index are divided by orderly cluster analysis In plot processing,the chemical stratigraphic framework,paleoenvironmental and paleoclimate evolution stages and regulation on the lower member of Shahezi Formation are preliminarily determined by using the comprehensive ensemble empirical mode decision(ceemd)and evolution harmonic analysis(EHA)analysis methods.The lower member of Shahezi Formation is divided into three geochemical facies: terrigenous clastic facies,heavy mineral facies and carbonate facies;seven chemical stratigraphic belts are divided,with depth ranges of 5725-5610 m,5610-5515 m,5515-5320 m,5320-5180 m,5180-5010 m,5010-4760 m and4760-4550 m.At the same time,two chemical stratigraphic interfaces are recognized:the depth is about 5200-5150 m,the early Cretaceous Berriasian stage has a short-term climate mutation or strong tectonic activity,and the depth is about 4600 m,which may have a strong climate fluctuation.Based on the data of lake level(GR)and physical weathering index(K / RB),the natural mode function(IMFs)is decomposed and reconstructed by ceemd,Comparing the change curve driven by climate change,it is found that the climate change on the lower member of Shahezi Formation is mainly dry and wet cycles,which is consistent with the overall characteristics of greenhouse climate change in the Cretaceous period;the lower member of Shahezi Formation can be divided into four dry and wet cycles,each cycle is about 1.2mA,and its duration may be According to the cycle frequency composition,the climate change on the lower member of Shahezi Formation is mainly modulated by the long slope,and the long eccentricity may play a similar role in the dry and wet cycles on the lower member of Shahezi Formation.