Heavy mineral distributions and their implications for sediment dynamics in the Yalu Estuary and its adjacent sea area

The chatacteristics of heavy mineral composition and distribution were analyzed in the surface sediment of the Yalu Estuary and its adjacent sea area,and its seabed sediment movement was also discussed.Results indicate that there exist two types of heavy mineral assemblages in the study area,one is biotite-hornllende-epidote,and another can be divided int of our sub-types,is composed of hornllende,epi-dote,and metal minerals(magnetite,ilmenite,hematite and limonite) .Variations of stable heavy mineral and unstable heavy mineral contents,seabed sediment transportrate and direction,and sectional distribution of grain size show that the estuarine seabed sediments in the north of 10 m isobath are transported landwards.This pheno menon is distinct from previous studies,is mainly caused by sel-fadjustment of the Yalu River catchments associating with human activities,especially large hydraulic project construction and sand dredging.Furt hermore,results of heavy mineral analysis also indicates that the estuarine seabed sediments in the south of 10 misobath are mainly directed seaw ards,and the sediments of the adjacent sea area of the Yalu Estuary are transported from the east,as well as the west to the medium.However,these conclusions still need to be furt hertestified using the method of geochemistry and sediment dynamics.Stable heavy mineral contents of garne and tourmalin in the west of the northern Huanghai Sea are larger than those in the east of the northern Huang hai Sea according to the comparison of heavy mineral distributions between these two areas.The mostevident difference among the east of the northern Huanghai Sea from the west of the northern Huanghai Sea,the south and the north of the southern Huanghai Sea,is that autogenetic pyrite does not occur in the sediments of the east of the nor thern Huanghai Sea.