DISTRIBUTION AND SOURCE OF HEAVY MINERALS IN THE SURFACE SEDIMENT OF THE TIDAL SAND RIDGES AREA IN SOUTH YELLOW SEA
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摘要: 对2008年采自南黄海苏北近岸废黄河水下三角洲以南潮流沙脊区的301个表层沉积物中重矿物进行了研究。结果表明潮流沙脊区沉积物中重矿物具有以下3个显著的特点:重矿物含量高、矿物颗粒表面多有磨蚀且铁染较重、优势矿物含量分布在小区域内具有跳跃性,这些特点凸显了研究区沉积环境的独特性,即水动力强、砂含量高、氧化程度高及沙脊区的水深变化快。沉积物中优势重矿物组合为普通角闪石-绿帘石,特征矿物为云母、赤铁矿和褐铁矿、钛铁矿和磁铁矿。矿物组合特征表明沉积物来源依然是控制沉积区重矿物变化的主要因素,即古黄河和古长江物质是潮流沙脊区沉积物组成的物质基础,未见有明显的其他来源物质输入。古黄河物质在潮流沙脊区全区都有分布,从北到南影响逐渐减弱,古长江物质从南到北主要影响到潮流沙脊区的中部,向北扩展不明显,稳定矿物特别是锆石的分布大致界定了长江物质的影响范围。矿物含量及分区表明,潮流沙脊区外部沉积物氧化、侵蚀程度重于其他分区,沉积物矿物组成与向海相邻区域沉积物组成趋于一致,是沙脊逐渐萎缩的表现。通过片状矿物和沉积物风化系数的变化推测,在潮流沙脊区中部存在一条从废黄河水下三角洲到长江口东北部的近似南北向的沉积物扩散通道。Abstract: A total of 301 surface samples collected in 2008 from the tidal sand ridges area located to the south of the abandoned yellow river subaqueous delta in the south yellow Sea were analyzed for heavy minerals. Some distinct characteristics of heavy minerals are observed in the study area:(1) the high weight content of heavy minerals; (2) abraded mineral grains and iron-stained grain surface; and (3) sharp content variation in dominant minerals from area to area. These characteristics were dependent upon the depositional environment which was featured by strong hydrodynamics, high content of sand fraction, strong oxidation, and quick variation in water depth in the sand ridges area. Common hornblende and epidote dominate. Mica, hematite, limonite, ilmenite and magnetite are recognized as diagnostic minerals. The mineral assemblages suggest that the source would be the dominant factor controlling the distribution pattern of heavy minerals. The sediments of the tidal sand ridges area are mainly from the Yellow River and the Yangtze River. The contribution of other material sources is not obvious. The materials from the Yellow River are widely distributed in the whole tidal sand ridges area. However, its impact gradually becomes weak form north to south. By contrast, the materials of Yangtze River are mainly distributed in the middle and southern parts of the tidal sand ridges area. The distribution of stable minerals, especially zircon could be used to denote the distribution area of the materials from the Yangtze River. The content of heavy minerals and their spatial distribution demonstrate that high oxidation and severe erosion mainly occur in the outer part of tidal sand ridges area. There is no obvious differentiation of mineral composition between the sand ridges and the adjacent areas, showing that sand ridges are in the process of shrinking. The distribution of schistose minerals and weathering index indicate that there might be a path for sediment dispersion from the abandoned Yellow River subaqueous delta to the northeastern of Yangtze River mouth passing through the middle part of the tidal sand ridges area.
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Keywords:
- tidal sand ridges /
- sediment /
- heavy mineral /
- source /
- South Yellow Sea
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