PERIODICITIES IN LOESS-PALEOSOL SEQUENCE OF CHINA

Periodicity in Chinese loess-paleosol sequence has long-time been investigated. However, there are many drawbacks in the previous works so that the conclusions are still controversial and the interpretation is equivocal. In this study, two typical loess-paleosol sequences (148 m and 191 m in thickness, respectively) in the Loess Plateau are sampled and total 2872 samples are measured in order to reconstruct the palaeoclimatic changes during the past three million years. On the basis of the new and sensitive proxy indicator of paleoclimate and the newly developed independent (orbitally-untuned) time scale, time series of the dust storm variations, which is highly related to the paleoenvironmental system changes, is obtained. By wavelet transfer and power spectrum analyses, the results show that there are approximately 400, 200, 100, 66, 57, 41, 31, 27 and 22 kyr cycles in the loess record. The orbital cycles are weak and are not completely presented in the new time series; there are also non-orbital cycles. Because the eccentricity frequencies of the solar irradiance of the approximately 400-kyr and 100-kyr are preserved in these sequences, the missing of 41-kyr-obliquity and 22-kyr-precession cycles in part of the time series may be explained by lower time-resolution of the loess-paleosol deposit. The presentation of the non-orbital cycles may be explained by the unstable depositional process of the dust and pedogenic process in the paleosol units, which misrepresents or obliterates imprint of the solar irradiance frequency. This conclusion may imply that it should be cautious when investigate the specific paleoenvironmental changes recorded in the loess, especially in the paleosol units.