铜川地区11.4～1.5 ka B.P.期间黄土地球化学风化特征及其古气候意义

通过对铜川剖面黄土-古土壤地层中常量元素和微量元素的地球化学特征进行分析,结合AMS-~(14)C年代学数据,利用Na/K值、CIA(化学风化指数)、A-CN-K三角图、Bc(退碱系数)、Ki(残积系数)、Rb/Sr值和Ba/Sr值等指标,探讨了该地区11.4～1.5 ka B.P.间黄土-古土壤地层的化学风化特征及其古气候意义。结果表明:(1)Na/K、CIA和A-CN-K三角图等分析指示铜川剖面11.4～1.5 ka B.P.间黄土-古土壤地层处于初等化学风化作用阶段。(2)Bc、Ki、CIA、Rb/Sr和Ba/Sr等指标的变化趋势同黄土-古土壤地层具有很好的对应性,较好的记录了铜川地区11.4～1.5 ka B.P.间的气候变化特征,可以将该地区的气候变化划分为4个阶段:11.4～10.2 ka B.P.气候寒冷干燥;10.2～9.1 ka B.P.温度逐渐上升,气候略温偏干;9.1～4.4 ka B.P.气候温暖湿润;4.4～1.5 ka B.P.气候逐渐转为冷干。(3)元素地球化学参数记录的铜川地区全新世最适宜期为9.1～6.0 ka B.P.,并且在6.0～5.0 ka B.P.期间存在次一级的气候恶化事件。

Characteristics of Geochemical Weathering of Loess in the Tongchuan Area during 11.4~1.5 ka B.P. and Its Paleoclimatic Implications

The major and trace elements contents in loess-paleosoil strata were analyzed to characterized geochemical weathering along a profile of Tongchuan during 11.4-1.5 ka B.P. and its paleoclimatic implications were discussed in terms of chronologic dating, Na₂O/K₂O ratio, chemical index of alteration (CIA), A-CN-K diagram, return coefficient (Bc), eluvial coefficients (Ki), Rb/Sr ratio and Ba/Sr ratio. The results showed that:(1) the chemical weathering in loess-paleosoil strata of Tongchuan profile during 11.4-1.5 ka B.P. was relatively weak; (2) variation trends of Bc, Ki, CIA, Rb/Sr and Ba/Sr ratios corresponded well with the loess-paleosoil strata, which recorded climate changes well during 11.4-1.5 ka B.P. in the Tongchuan region, the major climate changes could be divided into four stages:the climate was very dry and cold during11.4-10.2 ka B.P., the climate was slightly warm and dry with temperature rising gradually during 10.2~9.1 ka B.P., the climate was warm and humid during 9.1~4.4 ka B.P., the climate turned to cold and dry gradually during 4.4-1.5 ka B.P.; (3) the Holocene optimum in Tongchuan was in 9.1-6.0 ka B.P. and a climatic event of cold fluctuation during 6.0-5.0 ka B.P. was recorded according to records of elemental geochemical parameters.