郑州邙山桃花峪高分辨率晚更新世黄土地层

风成邙山黄土分布于河南郑州西北黄河南岸。黄土序列较完整,初步研究了桃花峪剖面S₂以上黄土地层,S₀、L₁、S₁、L₂和S₂分别厚0.6m、70.8m、9.9m、12.4m和1.0m。特别有意义的是晚更新世马兰黄土厚度巨大,分辨率高。以10cm间距对邙山桃花峪剖面进行了磁化率测量,并与海洋氧同位素时间序列进行对比,按Kukla等的磁化率年龄模式,获得相应的年代时间标尺。对末次冰期黄土以40cm间距进行了粒度分析,不同冰期或冰阶的平均沉积速率和分辨率有很大的差异。特别是末次冰期晚冰阶黄土粒度所反映的冬季风振荡的频率和幅度都超过了格陵兰冰芯记录。邙山晚更新世黄土地层是进行高分辨率黄土地层与短时间尺度过去全球变化研究的极好对象. 

THE HIGH-RESOLUTION LATE PLEISTOCENE LOESS STRATIGRAPHY IN TAOHUAYU,MANGSHAN,ZHENGZHOU

For its characteristic high-resolution the eolian Manshan loess is exposed along the south bank of Huanghe River,situated on the northwest suburbs of Zhengzhou City,Henan Province,which is wholly composed of loess strata,over 160 m thick,upward from loess L₁₅ or paleosol WS₁.The loess sequence in this area are perfect and the typical loess profiles are exposed in Taohuayu and Zhaoxiayu,in which the strata upward from paleosol S₂ at Taohuayu profile have been preliminary studied.According to the lithology,susceptibility,TL and ¹⁴C dating,the stratigraphical units have been subdivided into S₀,L₁,S₁,L₂ and S₂ with 0.6m,70.8m,9.9m,12.4m and 1.0m thick respectively.It is of great significance that there exist quite a thickness of Malan Loess (L₁) formed in the Late Pleistocene.
We have sampled at an interval of 10cm and measured the profile magnetic susceptibility in the field and mass magnetic susceptibility in the laboratory respectively.The values of magnetic susceptibility of the Mangshan Loess is smaller than that inside the Loess Plateau.We have correlated the magnetic susceptibility profile with the SPECMAP marine oxygen isotope time series and inferred that the rapid changes in susceptibility values at the L₁/S₀,S₁/L₁ stratigraphic boundaries correspond with the oxygen isotope stage 2/1 (12.05ka) and 5/4(73.91ka) transitions respectively.With the two marked points,by using the Kukla''s susceptibility age model to calculate the age of successive stratigraphic levels we then derived a chronology.Grain size of the loess during the last glaciation (L₁) was analyzed at an interval of 40cm,and depositional rate of each unit has also been calculated.
The susceptibility of Chinese loess mainly manifests the prosperity or decline of the southerly summer monsoon from the low latitude ocean,so the susceptibility values may be used as a proxy index for the change strength of summer monsoon climate.Average deposit rate and resolution in late Pleistocene loess at Mangshan reveal a great difference of dust deposit blown and entrained by the northerly winter monsoon from the high latitudes area between glaciation and interglaciation or stadial and interstadial.The maximum mean deposit rate is up to 2.47mm/a during the last glaciation,whereas the minimum is 0.18mm/a yet during the last interglaciation.The frequency and amplitude of winter monsoon variations revealed by the grain size record whose mean resolution come to 40.5 a/10cm dring the last stadial in the last glaciation at Mangshan are more detailed than that by the Greenland ice core.
The late Pleistocene loess strata in Mangshan are both related to and different from that inside the Loess Plateau.For its high-resolution the Mangshan loess during last glaciation can reflect the abrupt climate changes of East Asian monsoon,and is a excellent record for the Past Global Changes study on high-resolution and short timescale.