The Physical And Chemic Characters Of The Quaternary Red Soil In Xuancheng, Anhui Province And Its Paleoenvironmental Significance

The reticulate or vermiculated red clay(VRC) were wildly deposited in southern China, which is a kind of important and potential continental records of paleoenvironmental changes and has been extensively studyed by many reseachers. However, the formation and provenance of the VRC still stay controversial. Here we chose Langxi(LX) VRC section near the typical Xiangyang section in Xuancheng to collect samples. LX section 8.45m thick, is characterized by a stiff laryer of cementing ferro-manganese(CFM), a gray-white laryer strongly vermiculated (g-VRC) and a blood-red larger strongly vermiculated(r-VRC). Investigation of these three characteristic layers maybe would provide useful imformation to answer the questions raised above. Particle size anlysis, method of enviromental magntism and anlysis of elemental concentration were used, with carefully considering and evaluating research findings from others at the same time. Finally, the conclusions are as follows:(1) VCR in LX section has a higher content of grain-size <5 μ m fraction(43%) than course silt fraction (10-50μm) whose content is 37%. Resulting from strongly weathering, particle size in LX section is generally finer than that in Xiashu loess and loess-paleosol in Luochuan section. Near-source supply plalys a role for the formation of LX section.(2) Stable single-domain (SSD) particles of ferrimagnetic minerals are enriched in the part of LX section above CFM. Otherwise, SSD particles of antiferromagnetic minerals dominate the magnetic property of g-VRC layer. There is a trasition layer (4.2-5.2m deep) between g-VRC layer and r-VRC where, SSD particles and superparamagnetic(SP) paricles of ferrimagnetic minerals or antiferromagnetic minerals coexist. The content of multiple domain(MD) in the following part of LX section below 5.3m-depth increases slowly. As a whole, the source areas of LX section is stable, meaning that it is the weathering process rather than source changes that results in the grain size and the components of magnetic minerals varying with the depth.(3) multiple causes are resposible for the formation of VRC. Before g-VRC layer formed, the layer had been soaking in shoal water until all the water evaporated which created a semi oxidation and semi reduction environment instand of hot and humid environment-related oxidation. When water flows in the plant root-related hollow structure and soil crack, deferrization would happen in the sorrounding to form vermiculated clay in r-VRC layer.(4) K、Li、Na and Ga have escaped away from CFM layer, by the contrast, Ba、 Mn、Fe、Zn、Mg、Sr、Ca、Pb and Al have enriched in the same layer. A reasonable cause of CFM layer has been developed based on the elemental distribution:Ba、Mn and Fe enriched underwater flow out in the form of small overland flow, in which situation Mn、Ba、Fe、Zna nd Sr could easily precipitate in, however, K、Na and Li are bound to flow away soluted in the water.