Study On The Cyclical Stratigraphy Of The Da'anzhai Section Of Gong 39 Well Area In Central Sichuan

Based on the theory of cyclostratigraphy, a study on cyclostratigraphy of the Daanzhai Section in Gong 39 well aera, central Sichuan basin was carried out by using the GR logging data as the palaeoclimatology index in this paper. And we identified the Milankovitch cycle through the comprehensive usage of spectrum analysis and wavelet analysis.The basic theory of cyclostratigraphy and the strostratigraphic research on the study aera were the two major parts of this thesis, In particular, the theory of cyclostratigraphy contains many contents. Such as the research status of cyclostratigraphy, the internal mechanism between the cycle of the astronomical orbital period and the stratigraphic record, and the discussion of various mathematical methods which are necessary to strostratigraphic analysis.The mathematical methods used in the analysis include denoising processing, frequency spectrum analysis and wavelet analysis. Denoising was a process to exclude the interference of other non astronomical orbital factors to the signal, which made the subsequent processing results easy to be analyzed and to explained. The spectrum analysis was mainly used to discuss the periodic components contained in frequency domain. While, the wavelet analysis was a method that explicate the signal in both time domain and frequency domain, which remedy the limitation of spectrum analysis.The module extremum and the wavelets curve were studied on the base of wavelet analysis, so that we can estimate whether the periodic component in the signal was driven by the astronomical orbit cycle. If so, the type of Milankovich cycle and the number of that could be determined.Through the study of seven wells of GR logging data, we identificated the Milankovich cycle reserved in the Daanzhai Section. The results showed that these cycles driven by precession, obliquity and eccentricity were still preserved in the formation. Furthmore, we calculated all levels of Milankovich cycles and the average sedimentary rate of the Daanzhai Section. Calculations indicated that the average thickness of precession cycles, obliquity cycles and eccentricity cycles was 3.27m,6.10m and 12.46m respectively, and the average sedimentary rate of the Daanzhai Section was 149.62m/Ma.