| Quaternary aggradation red earth is a good carrier on the study of Quaternary environmental varied in southern China where is the red earth distribution. Aeolian features of red earth at Jiujiang belonging to quaternary aggradation red earth are supported by many research results, but it has been rather intense weathering and leaching after deposition, and there is much research shortage on the distinction between previous depositional information and post weathering information. This paper based on previous work, had divided whole-rock into three groups using wet sieving and sedimentation methods in accordance with different grain sizes, and they are sand components (>63μm), silt components (4～63μm), and clay components(<4μm).And then this paper had measured and analysised several physical and chemical indicators of clay and silt components (Because of sand content was very low and had not done), and had compared with the whole rock, trying to distinguish previous depositional information and post weathering information. Main results of this paper are as follows:(1) The XRF test results of JL red earth section at Jiujiang showed that the main major chemical composition of whole-rock samples and clay components and silt components were SiO2, Al2O3, and TFe2O3. And the contents of major elements had the same order from more to less, but the contents of Si, Al, Fe, etc. elements in different grain-size components were quite different. The average contents of SiO2 in the whole rock, clay components, silt components were separately 68.75%,50.54% and 78.54%; the average contents of Al2O3 in theirs 14.52%,22.99% and 3.87%; the average contents of TFe2O3 in theirs were separately 6.88%,11.79%,2.48%.(2) Measured the contents of V, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, etc. nine kinds of trace elements in different components of red earth at Jiujiang. Compared with the UCC average contents, the whole-rock samples'elements of Cu, Zn, Rb, Nb were slightly lower; Ba was relatively poor; Sr was significant poor features. The clay components'elements of V and Ni enriched; and Y, Pb, Rb slightly enriched; Zn, Zr, Ba were relative scarcity, Sr was poor. The silt components'silt elements of Y, Zr, Pb relative enriched, V was slightly higher than the average of UCC, other elements were poor.(3) Compared with the whole rock samples, CIA values, ba values and ICV etc. chemical weathering parameters were different in value, but theirs vertical curve had the same trends with the depth, A-CN-K diagram also showed that the clay components and whole-rock chemical weathering trend were basically the same. CIA of clay components of the whole section is higher than the whole-rock samples', and the average values of CIA in brown sediments was 86.81%(more 4.77% than whole-rock samples), while that of reticulate red earth components was 88.84%(more 1.15% than whole rock samples), and clay components in the information may be revealed closer to the actual situation of weathering. CIA values, ba values etc. weathering parameters of whole-rock and clay components consistently shown the weathering intensity of the reticulate red clay was stronger than the brown sediments in the upper section.(4) Magnetic susceptibility of red earth at Jiujiang had different distribution features in different grain-size components, and magnetic susceptibility of clay components had more contribution to the whole-rock. Magnetic susceptibility of clay components in the whole section varied from 13.54×10-8 m3·kg-1 to 202.11×10-8 m3·kg-1, and the average was 49.20×10-8m3·kg-1, and it was significantly higher than the silt components (magnetic susceptibility varied from3.01×10-8m3·kg-1 to 35.12×10-8m3·kg-1, and the average was only 9.27×10-8m3·kg-1), also higher than the average of magnetic susceptibility in the whole section that was 36.34×10-8m3·kg-1, and that illustrated clay components contained more magnetic materials, and magnetic materials had the trend moving to the fine components with the stronger degree of the weathering. The fluctuations and trends of magnetic susceptibility in three samples are consistent with each others, but their values and volatility were different. study of ARM, SIRM, etc. other magnetic parameters showed that the magnetic minerals in the upper section were more dominated by ferrimagnetic minerals, hematite and other incomplete anti-ferromagnetic minerals was relatively large in the lower section.(5)Principal component analysis showed that 15μm～30μm components were the first dominant grain size in the size composition of whole-rock and silt components, its vertical curve reflect changes of the original sedimentary environment. Using the grain-size age model and the data of ESR's age, had set up time scale. Spectrum analysis of content of 15μm～30μm component in red earth at Jiujiang showed that climate transition cycles occurred during 734ka-784kaB.P., corresponding to the section location is about 7.5m, from the previous quasi- 41ka and quasi-30ka cycles rate of the earth's axis tilt changing into quasi-100ka of earth orbital eccentricity cycles, and that answered to MPT in the global.(6)Vertical variation of physical and chemical indicators in the red earth clay components and whole-rock samples had consistent trends, and that of clay components might more effective about details and levels of the weathering information. This paper divided whole section into three parts according to the features of CIA, magnetic susceptibility, ICV, Na/K, Al/Fe, Fe/Mn, etc. physical and chemical indicators of clay components.The average values of CIA in clay components at the bottom of section (1428cm-1846cm)were the highest and had larger fluctuations, and the magnetic susceptibility values was low but SIRM wad high, and the average values ofNa/K, ICV, Fe/Mn were rather high, Al/Fe ratio is very low, indicating that this segment had experienced more wet environment, the more obvious physical and chemical indicators of clay component change also reflected the environment change characteristics of alternating wet and dry.The average values of CIA in clay components in the middle of section(526cm-1426cm), was slightly lower than that of bottom section, and its magnetic susceptibility was slightly higher, and the values of Na/K, ICV, Fe/Mn decreased, Al/Fe ratio had been increased but still low, the vertical curve of ICV, Al/Fe in the layer had a more obvious fluctuations, showed enrichment conditions of Al, Fe in the reticulate red earth had different manifestations in different environmental conditions, indicating that the environmental fluctuations in the period of formation of the reticulate red earth.Compared with the bottom and the middle section, there was a significant change of the weathering indicators features in the upper section(0cm～524cm), CIA value of clay components was small on the whole section, magnetic susceptibility of clay components and SIRM of whole-rock was higher and severely, Na/K ratio decreased with depth increased, ICV decreased with the depth increased, Fe/Mn ratio decreased to the bottom and middle section, indicating the change of the formation environment between this layer and layer of reticulate red earth was significant, and the overall environment was dry and cold, CIA and magnetic susceptibility can reveal the fluctuations in this layer.Various physical and chemical indicators of JL section at Jiujiang of the, especially that characteristics of clay components had significant changed before and after the Pleistocene, reflecting the hot and humid environment changing into cold and dry climate, revealing the fluctuations of temperature and precipitation not only in the brown sediments but also in the reticulate red earth, answered to the global climate change process. |
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