陕西洛川黄土沉积物中稀土元素及其它微量元素的化学淋滤研究

BEHAVIOURS OF REE AND OTHER TRACE ELEMENTS DURING PEDOLOGICAL WEATHERING——EVIDENCE FROM CHEMICAL LEACHING OF LOESS AND PALEOSOL FROM THE LUOCHUAN SECTION IN CENTRAL CHINA

本文采用化学淋滤的方法对洛川黄土沉积物的酸溶和酸不溶相中稀土元素(REE)以及其它微量元素的分布分配特征进行了系统的分析。研究表明黄土和古土壤中的酸不溶相是古风尘中的稳定组分,保留了源区的特征;酸溶相是风化成壤过程中的易变组分,记录了风尘堆积后的成岩变化。酸不溶相中的REE和酸溶相中的Sr,Pb元素分别可以作为示踪源区特征和风化成壤过程的地球化学指标。

The Luochuan loess - paleosol sequence in the Loess Plateau of central China has served as the type section for measuring global climatic changes during the Quaternary. Eight samples, including four loess (LH012, LH017, LH022, LH031), three paleosol (LH025, LH027, LH028) and one calcareous concretion (LH030), have been taken from the uppermost part of the section and been subjected to chemical leaching and analyses in order to investigate the behaviours of major, trace and rare earth elements (REE) during pedological weathering under arid -semiarid climate conditions.The acid-soluble (AS) fraction of these loess-paleosol samples seems to be mainly composed of carbonates with minor amount of oxyhydroxide coatings while the acid-insoluble (AI) phase appears to be a resistant fraction of inherited aerosol. Elements associated with carbonates, such as Na, Ca, Mg and Sr, therefore, display the most mobile behaviour during pedological weathering and can serve as an indicator of climate changes, whereas elements mainly distributed in the AI phase, such as Al, K, Ba,.Rb and REE, express the immobile character and can be used to trace the provenance of loess and paleosol.