黄土的连续提取实验及Rb/Sr值意义

通过连续提取实验 ,将黄土和古土壤中元素的赋存状态分成六种形态 :水可溶态、可交换态、碳酸盐结合态、铁锰氧化物结合态、有机物结合态和残留态。结果表明 ,K和Rb等元素 ,主要赋存于残留态中 ,而Ca、Sr等元素主要赋存于碳酸盐结合态和残留态中。Sr在黄土和古土壤中的赋存状态明显与Ca的分布有关。在风化成壤作用中 ,碳酸盐的淋溶和含Ca硅酸盐矿物的分解 ,引起Sr的淋失 ,而Rb保持稳定。因此 ,Rb Sr值指示了黄土和古土壤遭受的淋溶程度 ,反映了黄土高原的降雨量 ,是夏季风强度变化的替代性指标

SEQUENTIAL EXTRACTION PROCEDURE OF LOESS AND PALEOSOL AND THE IMPLICATIONS OF Rb/Sr RATIOS

A six step sequential chemical extraction experiment has been conducted on samples of loess and paleosols from Luochuo section,each for one of following:(1) soluble;(2) exchangeable;(3) carbonate bounded;(4) Fe Mn oxide bounded;(5) the organic matter bounded;and (6) residual forms of elements. Results show that elements,such as K and Rb,are predominantly associated with the residual,whereas Ca and Sr are mainly in carbonate bounded and residual forms. As Sr is preferentially partitioned into Ca rich minerals such as carbonates and plagioclase,its distribution is associated with Ca in loess and paleosols. Sr is likely to be leached when carbonates are eluviated and Ca containing silicates are decomposed during weathering and pedogenesis,while Rb tends to stay ?in situ.? Therefore,Rb/Sr ratios can be used to indicate leaching degree that loess and paleosols have undergone,reflect precipitation variations in the Loess Plateau and serve as a proxy index of the summer monsoon intensity.