The cycles filtered from natural gamma-ray logging curves of Lower-Middle Cambrian in the Tarim Basin and their significance in sedimentary sequence division

The sedimentary fill of a basin always reflects periodic geological and astronomical processes.The sequence of the Lower-Middle Cambrian in the Tarim Basin has been preserved well with no erosion and has some gamma-ray (GR) well logging curves.Thirteen GR curves in the Lower-Middle Cambrian around Manjiaer depression were applied to wave analysis in terms of the empirical mode decomposition, and the time cycles of 0.3 Ma, 1~2 Ma and 10~11 Ma were obtained.The 0.3 Ma period corresponds to the change cycle of the earth's orbital eccentricity, the 1~2 Ma period to that of the glacier-type eustasy, and the 10~11 Ma period to that of the earth's rotation angular velocity or that of the solar energy.These periods have supplemented and corrected previous geological and astronomical cyclic sequence and are of significance in understanding both paleoclimate change and high frequency sedimentary sequence.