DISTRIBUTION AND SOURCE OF HEAVY MINERALS IN THE SURFACE SEDIMENT OF THE TIDAL SAND RIDGES AREA IN SOUTH YELLOW SEA

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.