Recognition Of Milankovitch Cycles Formation

This paper, guided by cycle stratigraphy theory, discusses the identification method for detecting the Milankovitch cycles from geophysical logging data, and carries out the study of the Late Paleozoic Milankovitch cycles in the north china region.This paper introduces the theory and geological significance of the Milankovitch cycles. It is discussed that geological significance of the geophysical logging data is the basis and advantage of cycle analysis and how to identify the Milankovitch cycles with logging data.It is discussed that the obvious effect of the cycle identification method of current is spectral analysis and wavelet analysis of the basic principles and steps. The short-come of Fourier transform method is analyzed through studying and applying the principle of the spectrum analysis, for which it is discussed that the wavelet analysis have advantages to identify cycles. By comparative analyzing, the wavelet analysis of logging data is confirmed for studying the deposition cycles. This paper focuses on one-dimensional Morlet wavelet transform of the principles and methods and introduces the method of studying Milankovitch cycle pretreatment.Through the Application of wavelet multi-scale decomposition, different levels of cyclic cycle is obtained. A method to recognize the Milankovitch cycle is present after corresponding the Milankovitch cycle and the Application of wavelet cycles, determining the Milankovitch cycle division of the steps. The Milankovitch cycle is identified by wavelet energy spectrum analysis of logging data. The wavelet scales are chosen by calculating the transformation scale model of the maximum value. the corresponding relationship between Milankovitch cycle and wavelet scale are also determined. In this way, different levels of Milankovitch cycle are devided by different scales of wavelet coefficient curve. The average thickness of the Milankovitch cycle at all levels is calculated.Based on the above wavelet analysis method, the paper mainly studies the Milankovitch cycles of the late paleozoic in north china by logging data of different wells. The result shows the Milankovitch cycles are recorded in all the wells. Using the Milankovitch cycles result, the paper calculates the average cycle thickness, deposition rate and the duration of layers; extracts the average cycle thickness and deposition rate of the specific period for comparative study with the theory of Milankovitch cycle and geological background.