Genetic analysis of high frequency cycles of Qigequan formation of Sanhu region in the eastern Qaidam Basin

Key words:  Qaidam Basin  Qigequan formation  high frequency cycle  Milankovitch cycle  wavelet analysis  fast Fourier analysis

Abstract:

Qigequan formation of Sanhu region in the eastern Qaidam Basin is characterized by high frequency cycle The formation gamma ray curve was studied by methods of wavelet time-frequency analysis and fast Fourier spectrum analysis respectively. The identification results and strong and weak points of wavelet analysis and Fourier analysis for Milankovitch cycle were discussed. The results show that the ratio of cyclic formation thickness obtained by wavelet analysis and Fourier analysis for Milankovitch cycle is close to Milankovitch periodic ratio, and the high frequency cycles in Qigequan formation are controlled by Milankovitch climatic cycle. The average thickness of cyclic formation controlled by eccentricity period is 12. 93 m. The average thicknesses controlled by the dip of earths axis in long time cycle and short time cycle are 6,32 m and 5.00 m respectively. The average thicknesses of cyclic formation controlled by precession of the equinoxes in long time cycle and short time cycle are 2.78 m and 2.34 m respectively. The deposition rate of high frequency cycle is about 0.13 m/ka. Milankovitch cycle can be identified accurately by using these two analyzing methods.