珠江三角洲南部晚第四纪环境变化的稀土元素记录

摘要

The rare earth element (BEE) distribution in Core PRD05 is closely related to sedimentary environmental changes during the Late Quaternary in the southern Pearl River Delta. Before approximately 31 000 cai a BP, a fluvial setting developed in the study area. The sediments have a lower ∑REE concentration and show HREE enrichment, which are effects of grain size and heavy mineral concentration. The sediments dated to 31 000 to 16 600 cai a BP were possibly deposited in a brackish-water environment, with a high ∑REE and a clear enrichment of LREE relative to HREE. The upper part of these sediments underwent subaerial weathering and erosion during the last glacial maximum. Their REE pattern is subparallel to that of the lower part of sediments, with a slightly higher enrichment of LREE. During the first phase of the postglacial sea-level rise (from around 16600 to 10300 cal a BP), a swamp environment developed in the study area. Organic-rich conditions resulted in high ∑REE concentrations.Since 10 300 cai a BP, an estuarine environment with short-term fluctuations developed and persisted until 5600 cai a BP. Correspondingly, the sediments generally exhibit an enrichment of ∑REE, particularly LREE. A fluvial environment developed at around 5600 cai a BP, and was succeeded by an alluvial plain setting with occasional tidal influence. REE concentrations strikingly decreased and frequently fluctuated.%珠江三角洲南部平原PRD05孔稀土元素(REE)的分布特征与晚第四纪沉积环境变化密切相关.随着不同时期沉积环境的波动,稀土元素分布也发生相应的变化.约31 000 cal a BP以前,研究区发育河流环境,受矿物组成和沉积物粒度的影响,∑REE含量偏低,且重稀土元素(HREE)相对富集.31 000-16600cal a BP期间,∑REE含量明显高于前一阶段,并显示轻稀土元素(LREE)富集;稀土元素分布模式表现为河口半咸水环境特征;其上部沉积物经历了末次冰盛期的风化作用,稀土元素分布模式与下部近平行,但LREE的富集程度略高.16 600-10 300 cal a BP为冰后期海平面上升初期,研究区发育沼泽环境,由于有机质含量高而导致稀土元素含量普遍较高.10300-5600 cal a BP为全新世海侵期,研究区持续发育河口湾-浅海环境,其∑REE含量总体较高,并显示LREE富集;随着水体深度和盐度条件发生多次波动,稀土元素分布特征也表现出小幅度变化.5600 cal a BP以来,河流作用逐渐增强,并受到潮汐作用间歇性影响,其∑REE含量显著下降,但波动频繁.