SPECTROPHOTOMETRIC TIME SERIES OF DONGGOU SECTION IN NIHEWAN BASIN

Donggou section located in the east of Nihewan basin contains a suite of strata mainly consisting of lacustrine sediments. The last interglacial paleosol and last glacial loess units overlie the top of this section. Previous paleogeomagnetic study revealed that this section records Brunhes chron, Jaramillo subchron and Olduvai subchron. We measured both spectrophotometric parameters and magnetic susceptibility of successive samples collected from this section. Results show that the lightness (L^*) value varies in an almost reverse tendency if it is compared with chroma a^* and chroma b^*, i.e. the low lightness value corresponding to the high chroma value. The lightness values of the intercalated sand layers are relatively low, while the magnetic susceptibility is relatively high. We find that the lightness record of Donggou section can be correlated to the magnetic record of the loess section in Luochuan if the low value of the former is compared with the high value of the latter. This correlation is thought to be valid because both parameters are controlled by the change of the same aeolian flux in the past. The correlation permits us to extract 30 time control ties. Based on these ties, a time series of Donggou section is constructed by interpolating. Spectrum analysis indicates that the time series of each parameter exhibits main Milankovitch periods. Among them, periods of 23 and 19ka are close to the theoretic value of the precession. This means the sedimentation in the extinct Nihewan lake is very sensitive to periodical paleoclimatic change. The age of the paleomagnetic boundary assigned by this time series is close to the widely accepted data. This fact indirectly indicates that the suggested correlation is credible. This time series implies that the age of the Xiaochangliang paleolithic site is about 1 467~1 539 ka.