Chemical Stratigraphic And Paleoclimate Analysis Of Nenjiang Formation In SK-1

The Continental Scientific Drilling Project of the Songliao basin has obtained a complete Cretaceous sedimentary record of continental facies,which bear the information of paleoclimate and paleoenvironment evolution in Northeast Asia.Large scale transgression occurred in the early Cretaceous Nenjiang formation in Songliao Basin,and fine-grained deposition dominated.With the discovery of abundant exploitable oil and gas resources in fine-grained sedimentary rocks,the study of fine sedimentary rocks is a hot topic.Fine sediment is an important reservoir of unconventional oil and gas resources,and also an important carrier of paleoclimate information.In this study,the core of the member 1 and 2 of the Nenjiang formation of SK1 well is taken as the research object,and geochemical data are obtained by X fluorescence analysis.By means of mathematical statistics,including principal component analysis and ordered cluster analysis,the member 1 or 2 of the Nenjiang formation are divided into seven substratigraphic units with Paleoenvironmental Significance respectively,and the chemical stratigraphic framework of the Nenjiang formation is established.Combined with spectral trend attribute analysis(INPEFA),the paleoclimate and paleoenvironment evolution stage of the one or two member of the Nenjiang formation is determined from the perspective of Climatic Stratigraphy.The paleoclimate change of the member 1 of the Nenjiang formation can be divided into three stages.At the depth is 1133.76-1103 m,the ancient lake berth is at the high water level,the bottom water is in the state of reduction,the climate is moist,the transgression events occur,and the salinity is elevated.At the depth of 1103-1066 m,the lake level is at a high level and the high salinity corresponds to the high salinity and high alkalinity.At the depth of 1066-1025 m,the climate is moist,the water level of the lake is rising,the salinity is reduced,and the low alkalinity is low,which shows that the possibility of transgression is small.The main factor of the increase of total organic carbon burial may be the abundant biological productivity.The paleoclimate change of the member 2 of the Nenjiang formation can be divided into three stages.At the depth of 1785.5-1724 m,the climate is moist and the high salinity corresponds to the high lake level.It is inferred that there are transgression events,the water body is in the reduction condition,the total organic carbon is buried,the depth is 1724-1613 m,the climate is moist,the supply of fresh water causes the dilution to reduce the salinity,and the water body gradually becomes oxygen rich,resulting in the total organic carbon.At the depth of 1613-1583 m,the climate is in a dry state,the level of the lake rises and the salinity is elevated,which may explain the occurrence of transgression events,and the existence of foraminifers also indicates the occurrence of transgression events.In addition,the comparison between the chemical stratigraphic frame and the different chemical facies belts and the evolution stages of the climate stratigraphy shows that many boundary lines correspond well,which indicates that the objective of the stratigraphic division and the paleoclimate and paleoenvironment changes in the sedimentary strata are related to the changes of the paleoclimate through mathematical statistics.