THE DISCOVERY OF THE 400,000 YEARS CLIMATIC PERIOD IN CHINESE LOESS AND ITS BEARING ON PALEOCLIMATE

Magnetic susceptibility measurement was conducted at every10cm interval in the Baoji section,a 160 m thick loess-paleosoldeposit near the city of Baoji,Shaanxi Province.An independent timescale was constructed under control of geomagnetic polarity reversals byassuming that each paleosol and its underlying loess between twopaleomagnetic controls is a basic unit for linear interpolation based ontheir thickness,which indicate that the sediments represent the geologicalinterval 0 to 2.5 Ma BP.Fourier power spectra of the susceptibilitytime series monitor strong peak at quasi-period of 400 ka,which is dueto the eccentricity of the Earth's orbit,as well as 100 ka,40 ka and20 ka periods,in agreement with the astronomical theory of climaticforcing.A primary mode for the Matuyama climatic history is sum-marized as periodic 400 ka fluctuations superimposed by variation ofshorter periods,in the lower Matuyama,the dominant shorter period is100 ka cycle while 40 ka cycle in the upper Matuyama.

THE DISCOVERY OF THE 400,000 YEARS CLIMATIC PERIOD IN CHINESE LOESS AND ITS BEARING ON PALEOCLIMATE

Magnetic susceptibility measurement was conducted at every 10cm interval in the Baoji section,a 160 m thick loess-paleosol deposit near the city of Baoji,Shaanxi Province.An independent time scale was constructed under control of geomagnetic polarity reversals by assuming that each paleosol and its underlying loess between two paleomagnetic controls is a basic unit for linear interpolation based on their thickness,which indicate that the sediments represent the geological interval 0 to 2.5 Ma BP.Fourier power spectra of the susceptibility time series monitor strong peak at quasi-period of 400 ka,which is due to the eccentricity of the Earth's orbit,as well as 100 ka,40 ka and 20 ka periods,in agreement with the astronomical theory of climatic forcing.A primary mode for the Matuyama climatic history is sum- marized as periodic 400 ka fluctuations superimposed by variation of shorter periods,in the lower Matuyama,the dominant shorter period is 100 ka cycle while 40 ka cycle in the upper Matuyama.