珠江三角洲第四纪沉积物Cd元素的分布特征及成因

Distribution and origin of cadmium in the Quaternary sediments of the Pearl River delta plain,Guangdong Province, southern China

根据珠江三角洲平原区44个钻孔揭示的第四系,对晚更新世以来沉积物的地球化学特征进行了系统分析,结合沉积物粒度,探讨了珠江三角洲平原区第四纪沉积物Cd的分布特征、高含量来源及迁移富集规律。研究结果表明:①珠江三角洲第四纪沉积物的Cd含量地区差异较大,西江、北江冲积区为主要富集区,而潭江和东江冲积区为背景区。②物质来源、沉积物粒度、沉积环境与有机质含量共同影响了珠江三角洲第四纪沉积物Cd的含量分布,西江、北江冲积区受控于富Cd的泥盆系、石炭系砂页岩,而东江、潭江冲积区主要由贫Cd的燕山期花岗岩等限定;沉积物平均粒径(φ值)与Cd含量存在显著正相关关系;另外,温暖湿润、海陆交互作用强烈的沉积环境与富含有机质的地区有利于Cd的聚积富集。③西江、北江流域相对富Cd岩石风化的产物,特别是具高强度Cd含量的铅锌多金属矿区,是西江、北江冲积区Cd高含量的主要来源。④珠江三角洲第四纪沉积物Cd的高含量区分成西江、北江西北部和东南濒海两大片区,究其原因,前者由区域发育的铅锌多金属矿控制,后者则受海陆交互作用沉积环境的影响。

Through a comprehensive analysis of the geochemical characteristics of the Quaternary sediments from 44 cores in the Pearl River delta plain in combination with grain sizes of the sediments, the authors studied the cadmium content of the Quaternary sedi- ments in this area, which included distribution characteristics, source of high values, migration and enrichment. The result shows that： cadmium values of the Quaternary sediments in different areas of the Pearl River delta plain are markedly different from each other, the main enrichment areas are Xijiang River and Beijiang River alluvial plains, and Tanjiang River and Dongjiang River alluvial plains constitute the background area; the main factors that control the cadmium content of sediments in this area seem to be the source material, sediment grain size, sedimentary environment and organic matter. Xijiang River and Beijiang River alluvial plains are con- trolled by the Devonian and Carboniferous cadmium-rich sandstone and shale, while the Tanjiang River and Dongjiang River alluvial plains are constrained by the cadmium-poor Yanshanian granites. A distinct positive correlation is found between average particle size and cadmium content. Beside, warm and moist environment, intense land-sea interaction and rich organic matter are beneficial to the accumulation of cadmium-rich sediments; weathering products of Cd-rich rocks, especially the well developed lead-zinc polymetallic ore deposits in the Xijiang River and Beijiang River basin, constitute the main source of cadmium high-value zone; and the cadmium high-value zone of the Quaternary sediments in the Pearl River delta plain can be divided into northwestern and southeastern districts, which are constrained by the lead-zinc polymetallic ore deposits and the sedimentary environment of land-sea interaction respectively.