Quantitative Source Analysis Of Surface Sediments In Northern Jiangsu Coast Based On Geochemical Characteristics Of Mica

Source analysis of continental shelf in eastern China is one of the current research focus and difficulties.As its’ epitome,northern Jiangsu coast has attracted academic’s attentions.However,former scholars’ understanding on the boundary between the Changjiang River and the abandoned Yellow River in Northern Jiangsu Coast was not consistent.In addition,researches on quantitative source analysis of surface sediments in northern Jiangsu coast based on geochemical characteristics of mica were rarely reported at present.Considering those above,field investigation and samples collection were carried out in this study.Light and heavy minerals,together with biotites and muscovites were separated by specific gravity,centrifugation,magnetic separation,sieve method and handpicked purify.And then,mineral characteristics of light and heavy minerals,together with element contents in biotites and muscovites were identified and detected by stereomicroscope,polarization microscope and ICP-MS etc.Besides,difference indicators of mineral assemblages,major elements,trace elements and rare earth elements(REE)were preliminary selected between the Changjiang River and the abandoned Yellow River.Consequently,specific diagnostic indicators using for distinguishing the two rivers were carefully examined.And their source indications were also discussed.In addition,quantitative source analysis model of surface sediments in northern Jiangsu coast was built.And the material contributions of the Changjiang River and the abandoned Yellow River were calculated.Finally,their boundary line was determined.Results showed that:1.Although most characteristics of mineral assemblages and geochemical elements are similar,some obvious differences existed between the Changjiang River and the abandoned Yellow River.Heavy minerals assemblages were mainly hornblende-limonite-actinolite-epidote in the Changjiang Estuary sediments,and hornblende-actinolite-limonite-epidote in the abandoned Yellow River Estuary.Meanwhile,light minerals were mainly Quartz and feldspar in them both.In addition,their characteristic minerals were “Authigenic Carbonate and plagioclase” and “garnet,limonite and apatite”,respectively.Contents of some indicators such as major element(P2O5、Sr、Zr、Ba etc.),trace elements(Li,V,Cr,Cu,Zn,Pb,Be,Ge,Mo,Hf,Tl,Th and U),REE and normalized REE,and REE parameters(∑REE,∑REE/Al,∑LREE,∑HREE,∑L/HREE,(Gd/Yb)N,and(La/Yb)N)in muscovites of the Changjiang River were higher than those in the abandoned Yellow River,while other indicators were less difference or lower than the latter.As to biotites,some indicators values of major element(MnO,Na2 O,P2O5,TFe2O3,Zr and CaO),trace elements(Cr,Co,Ni,Cu,Zn,Pb,Cd,Hf and Th),REE and normalized REE,and REE parameters(∑REE,∑REE/Al,∑LREE,∑HREE,∑L/HREE and(Gd/Yb)N)in the Changjiang River were higher than those in the abandoned Yellow River,while others were little higher or lower than the latter.2.Only some exclusive indicators of mineral assemblages,together with major elements,trace elements and REE in biotites and muscovites could be used as specific diagnostic indicators for distinguishing the two rivers.They were contents of some special mineral(authigenic Garbonate,plagioclase,garnet,limonite and apatite),values of some other mineral indicators(ratios of quartz to feldspar,biotite contents,weathering rate of mica),contents of some major element indicators in biotites(Al2O3/K2 O,CaO/K2 O,MgO/TiO2,Mn O/Sr,Al2O3/TFe2O3,TFe2O3/Zr,K2O/Zr,MnO/Zr,K2O/TiO2,and Ba/Sr)and in muscovites(Zr,Sr,P2O5 and Ba),concentrations of some trace elements in biotites(Tl,Th、Hf,Cs,Rb,Nb,Ga,Ge,Cd,Cr,Co,Ni and Zn)and in muscovites(Tl,Ga,Sc,Nb,Hf,Ta,V,W,Pb,U and Cr),and values of some REE parameters in biotites(∑REE,∑REE/Al,∑LREE,∑HREE,(Gd/Yb)N,δCe,(La/Sm)N and δEu).3.Quantitative source analysis model(Yij=a1Y1ij+a2Y2ij+εij)of surface sediments in northern Jiangsu coast was accurate reliable,taking the Changjiang River and the abandoned Yellow River as the end-members.4.Simulation results showed that the boundary line of the Changjiang River and the abandoned Yellow River lay between Yankou town and Bencha town in Rudong County.This indicated that surface sediments north to the boundary line were mainly contributed by the Changjiang River,while those north to it mainly contributed by the abandoned Yellow River.Results above were not only useful explorations for quantitative source analysis of surface sediments in Northern Jiangsu and continental shelf in eastern China,but also could provide new ideas,new methods,new references and new basis for quantitative source analysis.There are two innovative points in this study: using geochemical characteristics of mica to distinguish sediments of the Changjiang River and the abandoned Yellow River,and building source analysis model to quantitatively analysis the sources of surface sediments in northern Jiangsu coast.