Chemical Composition And Controlling Factors Of Deep Soils In The Pearl River Delta Economic Zone

An ecological geochemical survey has been initiated in the Pearl River Delta Economic Zone since 2005 as part of the National Multi-Purpose Regional Geochemical Survey.The deep soils?150²00cm?were collected at a density of 1sample site/4 km² in accordance to a standard field procedure,covering an area of almost 50,000 km².Samples from 16 km² were composited for chemical analysis.Each sample was air-dried at ambient temperature,disaggregated and sieved<20 mesh.The<20 mesh material was then crushed to<200 mesh prior to chemical analysis and was determined for 53 components?Ag,As,Au,B,Ba,Be,Bi,Br,Cd,Ce,Cl,Co,Cr,Cu,F,Ga,Ge,Hg,I,La,Li,Mn,Mo,N,Nb,Ni,P,Pb,Rb,S,Sb,Sc,Se,Sn,Sr,Th,Ti,Tl,U,V,W,Y,Zn,Zr,SiO₂,Al₂O₃,TFe₂O₃,MgO,CaO,Na₂O,K₂O,total carbon and organic carbon?by different method that yielded the total content.Additional parameter was pH in the<10 mesh fractions.The aim of this study is to reveal information about chemical composition and parent materials and identify geochemical controls on the elemental composition of deep soils.Geochemical data are compositional data which contain only relative information.Statistical distribution measures were compared between compositional and centered logratio?clr?transformed data.The clr transformation reduced skewness and kurtosis of almost all variables.It is better suited to identify data outliers and discover correlations of variables in clr transformed data.Ternary plots of different parameters were applied to display weathering trend of deep soils.Median values and range of the selected elements has been compared to model compositions of upper continental crust?UCC?.Some element?Al,Ce,La,Pb,Rb,Ti,Zr?are enriched relative to UCC whereas others?Ba,Ca,Mg,Mn,Na,K,P,Sr?are depleted.Enrichment factors?EFs?for Ca versus Sr and K versus Rb?normalized to Al?were plotted together with bedrocks EFs and the model UCC composition EF,in order to discriminate provenance sources.Additionally,ratios of Al₂O₃/TiO₂,Cr/Zr and Th/Sc were used to obtain some information about the parent materials.It suggests that parent materials can be divided into two classes.One is felsic rocks while the other contains of a few mafic rocks to some extent.A principal component analysis?PCA?was performed on clr-transformed data.The first four PCs account for 65%of the variance in the dataset.PC1 and PC2 revealed that deep soil composition was strongly influenced by parent materials and marine,while it is hard to understand what PC3 and PC4 mean without enough information.Overall,geogenic factors are much more important for geochemical composition in deep soils of the Pearl River Delta Economic Zone.