泥河湾盆地洞沟剖面的光谱光度时间序列

泥河湾盆地东部的洞沟剖面出露一套以湖相为主的地层,其顶部覆盖了末次间冰期古土壤与末次冰期黄土。测量了该剖面的光谱光度和磁化率,结果显示,亮度(L*)随深度的变化趋势基本与色度a*、色度b*相反,即低亮度值对应高色度值。砂层的亮度值相对低,而质量磁化率高。亮度记录可以与洛川黄土剖面的磁化率记录对比,即亮度低值段可与磁化率高值段对比,这可能源于两者都受东亚季风的控制。对比后获得了30个时间控制点,在此基础上,建立了洞沟剖面测量参数的时间序列。谱分析表明,各参数的时间序列显示了主要的米兰科维奇周期,这显示泥河湾古湖沉积物对古气候的周期性变化敏感。

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.