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

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 sediments in this area, which included distribution characteristics, source of high values, migration and enrichment. The result shows that: ① 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; ② 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 controlled 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 (φ) 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; ③ 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 ④ 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.