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末次间冰期古土壤的Zr/Rb值时空分布特征及其影响因素 被引量:7

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摘要 Zr/Rb比值被认为比粒度更为可靠的冬季风指标,该指标的使用基于两项假设:(1)Zr在粗颗粒中富集而Rb在细颗粒中富集,因此Zr/Rb可记录到粒度的分选信息;(2)Zr和Rb在风化过程中都稳定,因而沉积后的风化或成壤作用不会改变原先的Zr/Rb.研究沿黄土高原的西北-东南断面3个末次间冰期古土壤(S1)的Zr,Rb,Ti,Hf等元素和元素比值在空间上的分布特征,并对这两项假设进行检验.结果表明,从黄土高原西北部到东南部,在末次间冰期Zr和Rb元素丰度均表现出增加的趋势.但在末次冰期早期和倒数第2次冰期晚期,Zr元素丰度由西北向东南呈现递减的趋势,Rb元素丰度则仍表现为递增的趋势.同一剖面间冰期的Rb元素丰度总是高于冰期时段的水平.在黄土高原西北部风化作用较弱的定西剖面,间冰期的Zr元素丰度低于冰期时段的水平.在远离源区、风化作用较强的天水和蓝田剖面,间冰期的Zr元素丰度高于冰期时段的水平.Zr/Hf值在较窄的范围内波动,定西剖面的Zr/Hf值相对恒定,天水和蓝田剖面S1土体部分的Zr/Hf值略高于L1和L2部分.这些结果支持Rb在细颗粒富集的假设和实验观察,但不完全支持Zr在粗颗粒中富集的假设和实验观察.在假定Zr不淋失的基础上,Rb变化率的结果表明Rb的淋失随着风化作用的增强而逐渐增加.因而也不支持关于Rb的稳定性的假设.无疑,Zr/Rb值的最终展现是源区因素、搬运以及沉积后的风化作用之间平衡的结果.在化学风化作用较强的情况下(CIA>65),使用Zr/Rb来反映粒度变化或者冬季风强度的波动需要谨慎.此外我们发现,Zr/Rb始终被约束在1.7以上。
出处 《科学通报》 CAS CSCD 北大核心 2008年第2期238-246,共9页 Chinese Science Bulletin
基金 教育部重点项目基金(批准号:200065) 美国自然科学基金(批准号:NSFBCS-0078557)
关键词 ZR RB 搬运 风化 源区
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参考文献36

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