Characteristics Of Sediment Granularity, Element Geochemistry And Their Significance For Identifying Sedimentary Environment In The Contiguous Sea Areas Of Changjiang River Estuary

The contiguous sea areas of Changjiang River Estuary are essential regions for researching the material flux and land-sea interaction in East China Sea . This paper has analyzed the granularity and geochemical characteristics of the investigated sediment samples which are derived from Changjiang River Estuary's contiguous sea regions in 2004 and 2006. Granularity parameters and distribution characteristics have been depicted. And further studies have been made on the transportation action of the sediment, enrichment rules of elements, and elements distribution controlling factors.Then the modern depositional dynamic environment is discussed in this paper on the basis of the granularity parameters and the elements combination characteristics. The silty sand and sandy silt are sorted worst in study areas, and their frequency curves display two-humped distribution, which mainly results from the mixing of two different sorting granularity component. The two kinds of sediment mostly distribute in the tidal sand ridges of the continental shelf of East China Sea. The sediment types of near-shore sub-aqueous Changjiang delta and Zhejiang coastal clayey areas are mainly composed of silt and clayey silt, but the sorting is worse. Their frequency curves display single peak distribution. The material from Changjiang River is dominant source for this region.The study areas can be divided into five depositional environment units based on the characteristics of sediments granularity. Zone A is sub-aqueous Changjiang delta front, and the sediment types are diverse and complex. Zone B includes the pro delta and the clayey zone of Hangzhou bay, where the sediment is composed of silt and clayey silt. Zone C is Yangtze shoal tidal sand sheet, and the sediments are mainly composed of sand. Zone D is tidal sand ridge in the East China Sea, and the principal sediments component is silty sand. Zone E, the marsh land among the tidal sand ridges, which is covered mainly by sandy silt.The sand/mud ratios of sediment reflect different depositional dynamic environments and modes of sediment transport. The hydrodynamic force of Yangtze shoal is stronger, and the sediment there moves in the way of jump; and the force of tidal sand ridges is weaker, so sediment there moves in the way of both jump and suspension. The perturbation force is stronger in the delta front than in the pro delta and muddy zone of East Sea shelf. The way of sediment transport in these three zones is mainly suspension.In the study areas, element contents of sediments can be divided into two types. Some increase and others decrease following the sequence of sand-sandy silt-silt-clayey silt. Element enrichment rules are consistent with element granularity control law.The study area can be divided into four geochemical provinces. Provinceâ… , delta front, is characterized by high contents of SiO2, CaO, Zr, V, K2O, Pb and Ba. Provinceâ…¡, pro delta and Hangzhou bay muddy zone, enriches Al2O3, TFe2O3, Zn and Ni elements. Provinceâ…¢is a transition zone. Provinceâ…£, shelf in the East China Sea, enriches SiO2 and Sr. Each province has its own unique element distribution law, and geochemical provinces are consistent with depositional dynamic environment zones.