红土中细粒状铁锰结核的存在及其对粒度测试的影响

EFFECTS OF FINE FERROMAGNETIC NODULES ON GRAIN SIZE ANALYSIS OF QUATERNARY RED CLAY IN SOUTHERN CHINA

设计了针对红土的两种粒度分析方法,对比分析了铁锰结核对红土粒度分析结果的影响以及加入HCl对铁锰结核与红土粒度测试的影响。结果表明:(1)细粒铁锰结核对粒度测试结果有较大影响,特别是粗粒含量的增加。而盐酸可以有效地与细粒铁锰结核反应,使得粒度测试结果更接近真实值。因此,对于铁锰结核发育的红土层,若需通过粒度来分析其沉积动力特征,其粒度测试的前处理过程加入盐酸是非常有必要的。(2)盐酸的加入对红土中<4μm的黏土粒组有较大影响,这可能是盐酸与黏土矿物发生了化学反应,使得黏土粒组的相对含量减少。因此,对于铁锰结核发育的红土层,若需要通过粒度分析其风化过程,其前处理应当慎重选择是否加入盐酸。

In recent years,increasing interest has been focused on the Quaternary red clay（QRC）in the middle and lower reaches of the Yangtze River.The provenance of the QRC is a common concern.Grain size analysis,as a conventional technique,has been widely used to study the provenance and transport dynamics.But the pretreatment of samples are different for different researchers.In the QRC,there are many fine ferromagnetic nodules which can not be separated by hand.The existence of these tiny ferromagnetic nodules influences the analysis results seriously.This paper tries to find the influences of the nodules and the way to remove it.Our results showed that：（1）fine ferromagnetic nodules have a great influence on grain size analysis,especially they may increase the content of coarse components.And hydrochloric acid can effectively react with fine ferromagnetic nodules,making the grain size results closer to the true value.Therefore,for the red clay,which contains fine ferromagnetic nodules,the hydrochloric acid is necessary in the pretreatment of grain size analysis for the purpose of sedimentary dynamics analysis.（2）The hydrochloric acid has a great influence on the 〈4μm group.It is not recommended in the pretreatment of grain size analysis for the purpose of weathering features analysis.