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| 长江口晚新生代沉积物的物源研究: REE和Nd同位素制约* | |
| 引用本文： | 杨守业,韦刚健,夏小平,孙敏,唐珉.长江口晚新生代沉积物的物源研究: REE和Nd同位素制约*[J].第四纪研究,2007,27(3):339-346. |
| 作者姓名： | 杨守业 韦刚健 夏小平 孙敏 唐珉 |
| 作者单位： | 1. 同济大学海洋地质国家重点实验室,上海,200092 2. 中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室,广州,510640 3. 香港大学地球科学系,香港 |
| 基金项目： | 国家自然科学基金 , 上海市青年科技启明星计划 , 中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室合作基金 |
| 摘 要： | 长江三角洲地区第四纪以来堆积了200多米厚的碎屑沉积物,主要由河湖相和滨浅海相组成,构成了多个沉积旋回。选择长江口地区一个320m深的PD钻孔,运用多通道等离子体质谱MC ICP-MS方法,开展沉积物中的REE和Nd同位素组成分析,研究了上新世以来三角洲地区沉积物物源的变化。沉积物中REE和Nd同位素组成具有明显的变化规律,Ce呈弱的负异常,介于0.83~0.99之间,而Eu呈现中等亏损,在0.53~0.73之间变化。岩芯中上新统沉积物中Ce异常变化大,而Eu亏损相对第四系沉积物更显著。143 Nd/144 Nd比值在钻孔中变化较小,介于0.511975~0.5122367之间,平均值为0.512062。相关分析揭示粒度和化学风化对Nd同位素组成影响小。REE和Nd同位素判别图解揭示河口地区上新统沉积物主要来自长江流域中、下游的近源物源区,而第四系沉积物的物源虽然存在一定的变化,但是总体上与上新统沉积物来源明显不同,主要来自更广泛的流域物源区,尤其是长江上游的风化物质被大量输运到河口三角洲地区。在第四纪构造和气候因素控制下,古长江水系具有不同的演化阶段,流域源岩经历的风化作用强度也不同,因此河流沉积物的源汇过程也相应地发生变化。 |
| 关 键 词： | 长江三角洲 沉积物 第四纪 稀土元素 同位素 物源 |
| 文章编号： | 1001-7410（2007）03-339-08 |
| 收稿时间： | 2006-07-15 |
| 修稿时间： | 2006-08-20 |
PROVENANCE STUDY OF THE LATE CENOZOIC SEDIMENTS IN THE CHANGJIANG DELTA: REE AND ND ISOTOPIC CONSTRAINTS |
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| Yang Shouye,Wei Gangjian,Xia Xiaoping,Sun Min,Tang Min.PROVENANCE STUDY OF THE LATE CENOZOIC SEDIMENTS IN THE CHANGJIANG DELTA: REE AND ND ISOTOPIC CONSTRAINTS[J].Quaternary Sciences,2007,27(3):339-346. | |
| Authors: | Yang Shouye Wei Gangjian Xia Xiaoping Sun Min Tang Min |
| Institution: | 1.State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092 ; 2.Guangzhou Institute of Geochemistry, Key Laboratory of Isotope Geochronology and Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 ; 3. Department of Earth Sciences, Hong Kong University, Hong Kong |
| Abstract: | The Changjiang Delta area has accumulated large amount of clastic sediments during the Quaternary. The deposition thickness is more than 200m, which is primarily composed of fluvial, lacustrine, littoral, and neritic facies and comprises several sedimentary cycles. A 320m deep core, the Core PD, was drilled from the Changjiang Delta for sedimentological and geochemical analyses. The compositions of rare earth element (REE) and Nd isotope from the core were measured by MC ICP-MS in order to study the variation of sediment source since the Pliocene. REE and Nd isotopes exhibit distinct variations. Cerium exhibits weak depletion, ranging from 0.83 to 0.99, whereas medium europium anomaly (0.53~0.73) can be observed in the core. The Pliocene sediments are characterized by larger variations of Ce anomaly and more significant Eu depletion than the Quaternary sediments. The 143 Nd/144 Nd ratios show small variations, ranging between 0.511975 and 0.5122367 and averaging at 0.512062. The correlation plots indicate that the REE and Nd isotopic compositions were less influenced by sediment grain size and chemical weathering and, therefore, were primarily controlled by provenance rocks. The discrimination plots of REE parameters vs Nd isotope suggest that the Pliocene sediments at the Changjiang Delta were primarily derived from the proximal provenances similar as todays middle-lower reaches, whereas the overlying Quaternary sediments were mostly sourced from the distal and wider provenances despite the variable sediment sources. In particular, the weathered sediments from the upper reaches were significantly transported to the estuarine and delta areas. The ancient Changjiang River might have undergone different evolution phases under the tectono-climatic coupling controls. The source rocks experienced variable weathering intensities since the Pliocene, which resulted in the variations of the source-to-sink process of the river sediments. |
| Keywords: | The Changjiang Delta sediment Quaternary rare earth element isotope provenance |
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