The driving mechanism of the high-frequency lithofacies cycles in the Middle Jurassic Xiali Formation in the Yanshiping area, northern Xizang

The Walsh spectral analysis employs the discontinuous square waves or Walsh function instead of the continuous sine and cosine waves of the Fourier analysis. Because the Walsh function is discontinuous itself, the Walsh spectral analysis is widely used in detecting the periods in stratigraphic cycles. A succession of highfrequency lithofacies cycles composed of sandstone and mudstone occur in the Middle Jurassic Xiali Formation in the Yanshiping area, northern Xizang. According to the analysis of lithology and tinctures using the Walsh power spectra and filtering, the significant peak periods on both lithology and dinctorial spectra are in a very good correspondence with the Milankovtch cycles. The sea-level periodic changes are interpreted as the driving mechanism of the high-frequency lithofacies cycles in the Xiali Formation. The sedimentary duration of the whole Xiali Formation is about 3.689 Ma, with a sedimentary rate of about 0.111 m/ka.