The Physical And Geochemical Characteristics And Formative Environment Of Red Earth In Jinhua-Quzhou Basin

Quaternary red earth is widely distributed in Jinhua-Quzhou basin.Choosing the red earth in Jinhua-Quzhou basin as the subject,quaternary red earth was studied and divided into several types,based on some methods of sedimentology,soil science and environmental geochemistry.The results show that:(1) The distribution of red earth in Jinhua-Quzhou basin ranges from Longmen to Xianxia mountain.And red earth mainly distribute in Yongchang,Tangxi,Langya, Luodian,Xianqiao and Pujiang county.The shapes of red earth areas include both large and particle aresa.(2) In grain-size distributions of red earth in Jinhua-Quzhou basin,Silt(4-63μm) and clay(＜4μm) are dominant components,and sand(＞63μm) content is small.The average grain value of red earth is high,and the value of sorting coefficient is different in each profile.There are three kinds of grain-size frequency curves,namely single peak,two peaks and multiple peaks frequency curves of red earth.Meanwhile, the fractal dimensions of red earth are notable.We can divide red earth in Jinhua-Quzhou basin into three types according to the grain-size characteristics.(3) The major elements are consist of SiO₂,Fe₂O₃ and Al₂O₃ mainly,and K,Na, Ca.Mg and P are very low.The average contents of TiO₂,Fe₂O₃ and Al₂O₃are higher than those of UCC,but The average contents of K,Na,Ca,Mg are lower than those of UCC.There is a more significantly negative linear correlation between SiO₂ and (Fe₂O₃+Al₂O₃) than that of SiO₂ and Fe₂O₃.Contrast with UCC,contents of Zn,Rb and Sr are lower,but contents of Zr and Pb are higher.We also can divide red earth in Jinhua-Quzhou basin into three types according to the geochemical characteristics.(4) Based on the research of physical and geochemical characteristics,the red earth in Jinhua-Quzhou basin can be divided into two types,that is homogeneous red earth and heterogenous red earth.The latter can be divided farther into alluvial-flood red earth and weathering crust red earth.Silt(4-63μm) and clay(＜4μm) are dominant components of homogeneous red earth,but sand(＞63μm) content is small.The average grain value of red earth is high, the value of sorting coefficient is low and degrees of particle fractions are high; grain-size frequency curves mostly are positive offset with single-peak shape and small-tail.The contents of Al₂O₃,Fe₂O₃ and TiO₂ are high,but those of K₂O,Na₂O,CaO and MgO are low.The trace element contents of Sr,Y,Zn,Pb and Ba are high, the contents of Cu,Cr are low,and the value of Rb/Sr decreases from bottom to top. TX,SSSW and LD profiles are good examples.Heterogenous red earth developed from weathering crust and alluvial-flood sediments.Silt content of the former declines significantly,but sand content increases highly.The contents of Al₂O₃,Fe₂O₃ and TiO₂ are lower than those of homogeneous red earth,but the contents of K₂O,Na₂O,CaO and MgO are higher than those of homogeneous red earth.The trace element contents of Sr,Y,Zn,Pb and Ba are low, the contents of Cu,Cr are higher than those of homogeneous red earth.The values of CIA and Rb/Sr increase from bottom to top.YT,XQ,QJ and PL profiles axe good examples.To the latterer,silt content also declines significantly,but sand content increases highly.The variations of contents of Al₂O₃,Fe₂O₃ and TiO₂ are complex. The trace element contents of of Cu,Y,Pb are different from weathering crust red earth.The values of CIA and Rb/Sr increase from bottom to top.HHT profile is a good example.(5) The chemical composition of red earth in Jinhua-Quzhou basin indicate that the environment were warm and humid.The ferromanganese nodules characteristics are the results of environmental variations.The difference of CIA between plinthitic and typical red earth in homogeneous red earth.denotes that the weathering intensity of the plinthitic red earth are stronger than typical red earth,which indicates more warm and humid environment.