Characteristics Of Sediment Granularity, Element Geochemistry And Their Significance For Identifying Sedimentary Dynamic Environment In The Jiulongjiang Estuary

Sedimentary environment in the estuary is a key problem of modern sedimentation research. This paper relies on the horizontal subject with Taiwan, which named FEASIBILITY STUDY OF COASTAL PROTECTION AND RESTORATION IN QUEMOY (JIN-MEN). The granularity and geochemical characteristics of the investigated sediment samples have been analyzed, which are derived from contiguous sea regions of Jiulongjiang estuary. Granularity parameters and distribution characteristics have been depicted and further studies have been made on the transportation action of the sediments, enrichment rules of elements, and elements distribution controlling factors. Then the modern depositional dynamic environment has been discussed in this paper on the basis of the granularity parameters and the elements combination characteristics.Clayey silt is the major sediment type in study area. Sand and silty sand display two-peak distribution in the frequency curves and is high in saltation load content. The major of sandy silt, clayey silt and sand-silt-clay is suspension component. Sandy silt displays single peak distribution while clayey silt and sand-silt-clay display two peaks in the frequency curves. SiO₂ and Al₂O₃ are high in element content of sediment and total component accounted for 66.07% to 86.58%. This shows that the major chemical composition of sediments is silicate and aluminum-silicate.Sediments from entrance of estuary are coarse and high in saltation load content. There are many types of shoal area sediments from nearshore, including sand-silt-clay, sandy silt and some silty sand and more suspension component. The above two parts are most likely terrigenous clastic and accumulate SiO₂,K₂O,Cu,Zr. The major type of sediments is clayey silt in the middle and offshore region of the bay and sediments concentrate Al₂O₃,Fe₂O₃,MgO,P,Mn,Ti,Pb,Zn,Cr,Co,Ni,V.The modern sedimentary environment in Jiulongjiang Estuary can be classified into three types based on the characteristics of sediments granularity. The first deposition zone located in the mouth of Jiulongjiang anabranch. Most of sediments are sand and silty sand. This represents one kind of reciprocation high-energy environment under intensity hydrodynamic condition. The second deposition zone located in middle of the bay, north channel of Jiyu Island, water channel of Song-gu and eastern offshore of Yuzaiwei. Most of sediments are sandy silt and sand-silt-clay. It shows a type of complex and comparatively stable hydrodynamic condition. The third deposition zone located in the mouth of Jiulongjiang south anabranch, western of Jiyu Island and wide sea area of Xiamen harbor. Most of sediments are clayey silt and sand-silt-clay. This represents one kind of comparatively high-energy tidal deposition environment.The study area can be divided into four geochemical districts. District A located in he mouth of Jiulongjiang anabranch, nearshore of Haicang and Xiangbi and eastern of Yuzaiwei, which are most likely terrigenous clastic and accumulate SiO₂,K₂O,Cu,Zr. District B concentrate Al₂O₃,Fe₂O₃,MgO,P,Mn,Ti,Pb,Zn,Cr,Co,Ni,V and have significant differences with district A. Each district has its own unique element distribution law, and geochemical districts are consistent with depositional dynamic environment zones.The result of element analysis by R-factor of study area shows that sediments of Jiulongjiang estuary most likely come from terrigenous clastic.The dominant factors which make the difference of the granularity and geochemical characteristics and its spatial distribution are transportation, sorting and transformation effect by hydrodynamic. In addition, man-made alteration is a certain extent of geochemical spatial distribution.