The Extraction, Verification And Application Of The Milankovitch Cycle In Pre-mesozoic

How to extract the corresponding Milankovitch cycles?eccentricity,obliquity and precession?from log curves has been a frequently discussed problem since the Milankovitch theory was proposed.Predecessors have obtained a series of research results.There are wells which are located in the sedimentary center of Ordos basin.The authors take their Permian formation from the 8^th Member of Xiashihezi Formation as an example to explore the concerned issue by Matlab software.Firstly,the natural gamma logging data of each well are processed by db5 wavelet in continuous wavelet transform to obtain the frequency of different scales,and then calculate the ratio among frequencies.Secondly,based on formers' research,theoretical Milankovitch period of the target formation can be calculated,and then theoretical frequencies and theoretical frequency ratio are figured out.Thirdly,the frequency ratio from logging data is compared with the theoretical frequency ratio,and then the Milankovitch cycle is selected.Finally,the wavelet curves related to each Milankovic cycle are confirmed as d9,d6,d5.The d9 corresponds to eccentricity,the d6 corresponds to obliquity,and the d5 corresponds to precession.The extracted astronomical period is verified and its rationality is verified,through the fast Fourier transform and the corresponding astronomical period of extraction.Based on the research results of this paper,the deposition rate of the research layer can be calculated,and the sedimentation rate in this region can be seen in three scales?eccentricity,obliquity and precession?;By calculating the deposition rate of the same layer,the direction of the source is analyzed according to the change of deposition rate.The research results are of great significance for more accurate division of strata,calibration of astronomical age and analysis of source.