珠江三角洲地区上更新统与全新统之间广泛发育1层杂色黏土,其成因多认为主要是由上更新统沉积物在末次冰盛期暴露于地表风化而成.对取自珠江三角洲3条钻孔(PRD09、PRD16和PRD17)的岩心样品分析表明,受风化作用的影响,其稀土元素含量和分异特征发生了较明显的变化.杂色黏土层的稀土总量大大低于下伏沉积物,而在邻近风化层的下伏沉积物中稀土元素却表现为明显富集,尤其是重稀土元素的富集.风化作用强度较大的PRD09孔和PRD17孔下伏沉积物中的稀土富集程度高于风化作用强度相对较小的PRD16孔.珠江三角洲在末次冰盛期时普遍发育的酸性介质条件,促进了风化层的稀土元素发生溶解和迁移.在风化过程中,由于轻、重稀土元素具有不同的溶解迁移能力和吸附能力,导致杂色黏土层的REE指标值(LREE/HREE、(La/Gd)N和(La/Yb)N)高于下伏沉积物.风化过程对Ce、Eu异常有一定的影响,但不十分明显,杂色黏土层的Ce、Eu异常值仅略低于下伏沉积物.%A layer of mottled clays, sandwiched between the Upper Pleistocene and the Holocene, is widely distributed in the Pearl River Delta area. It was the weathering product of the Upper Pleistocene sediments and mainly formed during the last glacial maximum. Geochemical analysis on three cores (PRD09, PRD16 and PRD17) suggests an apparent change in REE content and fractionation during the weathering. The total REE concentrations of the mottled clays are largely lower than those of underlying sediments. The proximate underlying sediments show a clear enrichment in REE, particularly in HREE. PRD09 and PRD17, subjected to a more intensive weathering, exhibit more enrichment in REE than PRD16 that shows a less weathering intensity. The acidic condition developed in the Pearl River Delta area during the last glacial, which enhanced the mobility of the REE elements. Higher LREE/HREE, (La/Gd)N and ( La/Yb) N values in mottled clays than in underlying sediments were resulted from different mobility and adsorption on clay minerals of LREE and HREE during weathering. It seems that the weathering had less influence on anomaly of Ce and Eu. The mottled clays show slightly more negative Ge and Eu anomaly than underlying sediments.
展开▼
