Abstract: Through the signal decomposition of gamma ray curves and the spectrum analysis of detailed components using discrete wavelet transform technique, the dominant frequency and sedimentary cycle thickness for the detailed components are determined. According to the corresponding relations between ratio of sedimentary cycle thickness and ratio of astronomical period, the sedimentary cycles related to individual astronomical period are ascertained, and the time limitation of these cycles restricted by absolute geologic age. The case study from Yanchang formation indicates that the time limitation numbers of these cycles classified by detailed components are twice of astronomical periods, that is, taking the astronomical period as classifying basis of datum-cycle sequence classification, the each sedimentary cycle can be divided into two datum-cycle sequences. The research shows that the rational and effective classification and correlation of the datum-cycle sequence can be carried out based on astronomical period, discrete wavelet transformation and spectrum analysis, and the stratigraphic ages are ascertained by restriction of corresponding absolute geological ages.

Key words: astronomical period, basal-level cycle, discrete wavelet transform, spectrum analysis, Yanchang formation