两种硅酸盐碎屑组分^(234)U/^(238)U测试前处理方法的比较及启示

The Comparison of Two Pre-treatment Methods for the^(234)U/^(238)U Measurement of Silicate Detrital Fractions and Its Enlightment Significance

沉积物不同组分(化学相态)的精确提取是还原其所经历地质过程或环境要素的关键。本文比较了两种针对铀系同位素(^(234)U/^(238)U)测试开发的沉积物碎屑组分提取方法,结果表明Francke提出的方法对岩石样品淋洗效果更好。对长江、黄河和台湾浊水溪沉积物样品,Dosseto和Francke建议的方法各有优势。此外,本文还发现台湾浊水溪流域岩石露头样品的(^(234)U/^(238)U)并没有如预期处于久期平衡状态,可能是因为岩石样品混入了部分次生物质,也可能与该岩石露头样品多为砂岩、孔隙较发育而产生了明显的优先淋滤有关。本研究对于表生环境下沉积物硅酸盐碎屑组分(^(234)U/^(238)U)的精确测定具有一定的参考价值,同时对于岩石铀系不平衡研究也有一定启示意义。

Precise extraction of different sediment fractions(chemical phases)is critical to reveal the exactly experienced geological processes or environmental factors.Two sequential extraction methods developed for measuring uranium isotopes of sediment fractions have been compared in this study.The results show that the method proposed by Francke is better than the other one in terms of the leaching effect for the treatment of rock samples.For the treatment of sediment samples collected from the Yangtze River,Yellow River,and Zhuoshui River,the two methods proposed by Dosseto and Francke have their own respective advantages.In addition,the expected ^(234)U-^(238)U secular equilibrium in bedrocks was not found in the outcropped rock samples(mainly sandstones)from the Zhuoshui River watershed in the Taiwan Island.This could be resulted from the mixing of a part of secondary substances or the obvious preferential leaching of outcropped rocks due to the developed pores in sandstone which is the majority of samples collected from the outcrop.This study is of important reference value for the precise determination of ^(234)U/^(238)U ratios of sediment detrital fractions deposited in the supergene en-vironment of the earth,and also of a certain enlightment significance for studying the disequilibrium of the ^(234)U-^(238)U sys-tem for sedimentary rocks.