汉江上游庹家湾剖面化学风化特征及其意义

Chemical Weathering Characteristics of Tuojiawan Profile in the Upper Hanjiang River Valley and Its Environmental Significance

通过对庹家湾黄土剖面元素的分析,揭示汉江上游地区黄土中常量元素的地球化学行为及对气候变化的响应。用XRay荧光光谱仪、MS-2型磁化率仪分别测量了庹家湾剖面元素含量及磁化率值,实验结果显示:庹家湾剖面的风成黄土化学成分以SiO_2、Al_2O_3和Fe_2O_3为主,三者含量分别为355.83 g/kg、79.62 g/kg、62.64 g/kg;以Ti为参比,Na、Ca、Mg、Si、K表现为迁移淋失,Fe、Al元素相对富集,元素的活动性及其迁移序列为Na>Ca>Mg>Si>K>Al>Fe;Fe和Al元素含量曲线及CIA曲线在228~260 cm(L_1~S_1)和294~370 cm(L_1~S_2)深度处出现明显的峰值,并与磁化率曲线呈现出高度一致性,指示该层化学风化程度明显高于典型黄土,接近于古土壤(S_0),OSL年龄在27.5~21.5 ka B.P.之间。庹家湾剖面常量元素在剖面的变化,表明在汉江上游地区晚更新世末期的气候并非是持续干燥寒冷,而是存在一定的气候波动,在27.5~21.5 ka B.P.期间风化成壤作用较为明显,气候相对温暖湿润。

The chemical characteristics of major elements and magnetic susceptibility of Tuojiawan profile in the upper Hanjiang River are studied. The change of the indexes revealed that major elements geochemical behavior and the corresponding laws of climate change in the Upper Hanjiang River. With X-Ray fluorescence spectrometer, MS-2 magnetic susceptibility instrument measured element content and magnetic susceptibility values. Results show that： The major elements are SiO2, Al2O3 and Fe2O3. Na,Ca,Mg,Si,K are leached out while Ti,Fe,Al relatively enriched in the paleosol S0. The element mobility and migration ability of the major elements are ranked in the followed order： Na 〉 Ca 〉 Mg 〉 Si 〉 K 〉 Al 〉 Fe. Magnetic susceptibility values showed obvious peak value in 228~260 cm and 294~370 cm depth, the variation in content of Fe and Al elements and chemical alteration index curve and magnetic susceptibility curve showing a high consistency, at this depth are characterized by high value. It was shown that the chemical weathering intensity of this depth was obviously higher than that of Malan loess, close to the palaeosol（S0）, belonging to the weak palaeosol（L1~S1 and L1~S2）.The age range of L1~S1 and L1~S2 was 27.5~21.5 ka B.P.. The change of the indexes showed the climate and pedogenic environmental changed since Pleistocene. Including the cold and arid glacial and a short time the climate was warm and wet in the glacial period（27.5~21.5 ka B.P.）, the gradually intensified southeast monsoon during the early Holocene periods, the strongest monsoon in the mid-Holocene, and the monsoon recession and the climate drying during the late Holocene.