Iron Features And Formation Environment Of Vermicular Red Earth

Vermicular red earth is one of the most important materials for Quaternary research in southern China. The formation of vermicular red earth has experienced a special environment. It has great research significance about the relationship between environment and vermicular red earth in this area. By field investigation, we founding that the vermicular red earth can appear in different parent materials in southern Anhui, northern Jiangxi, northern Zhejiang, and middle regions of Zhejiang. There are many types of vermicular red earth. One type is bedrock residual material, based on residual material of rock weathering with different thickness; the reticulation even appears in bedrock, or in rock fissures. Another type is sediment type, based on different kinds of sediments. Vermicular red earth developed in parent material of alluvial and slope facies deposition has texture heterogeneity, called non-homogeneous sedimentary type; that developed in eolian parent materials has a uniform texture, called homogeneous sedimentary type.50 vermicular red earth samples of different types had been collected in 10 locations, such as Anhui Xuancheng (XC), Jiujiang in North Jiangxi (JL), Anji in north of Zhejiang (AJ), North Lake Bridge in Hangzhou (BHQ), Tangxi in middle of Zhejiang (TX), Shangshan in Pujiang (SSW), Development Zone in Pujiang (PF), Luodian in Jinhua (LD), Seventh prison in Jinhua (QJ), Xia Yu village in Jinhua (XYC). The 50 samples are further separated into 50 red reticulations and 50 white reticulations in the laboratory.Based on this, this paper studies vermicular red earth's sedimentary characteristics, some physical and chemical properties of iron morphological characteristics and the formation of environmental mainly by means of sedimentology, soil science as well as environmental geochemistry. Initially getting the following main conclusions:The grain size distribution is different between non-homogeneous sedimentary type and homogeneous sedimentary type. Gravels>2mm can be founded in non-homogeneous type (samples of PF and LD), and sand (>63μm) content is higher.homogeneous sedimentary type(samples of XC,AJ,JL,TX,SSW)doesn't contain gravels, and lower sand(>63μm) content. If gravel>2mm component is not considered, silt (4-63μm) content is the most, followed by clay (<4μm), and sand (>63μm) is minimum in red and white reticulation of different types of vermicular red earth. The clay in white reticulation (27%-35%) is less than red white reticulation (30%-45%) (XYC excluded); sand content is more than red white reticulation (BHQ excluded).From the chart of silt-clay-sand, compared to the red reticulation, the white reticulation tends to be coarser. Size frequency distribution curves shows that fine tail of red reticulation is more projecting than white, but the coarse tail is the opposite.The grain size parameters shows that:the average particle size (Mφ/φ) of red and white reticulation is>7, grain size is finer, kurtosis (Kg) varied from 2 to 3, corresponding to medium and wide kurtosis, high mixed degree of particle fractions and poor sorting; sorting coefficient (σ) is between 1.7 and 2.5, the sorting coefficient of non-homogeneous sedimentary type is larger. Compared to the white reticulation, the average particle size and sorting coefficient of red reticulation is greater than white, but the skewness, kurtosis is less than the white reticulation.XRF test shows that the differences of iron content between red and white is great, the other chemical composition is similar in overall. K2O,Na2O,CaO,MgO leached greatly, the content of four chemical substances is separately in the range of 1%-3%,0.1%-0.2%, 0.1%-0.3%,0.3%-0.7%; the content of SiO2,Fe2O3,Al2O3 are higher, the total content of SiO2,Fe2O,Al2O3 is between 84% to 96.5%, red samples(84%-94%) is slightly lower white(91%-97%).For the red reticulation in different types of vermicular red earth, Fe2O3 content is mostly between 7% and 10%(except for XYC), and more than white (1.5%-4%), difference of SiO2 and Al2O3 between red and white is little, Ti is stable component, enriching with the leaching of other elements, the Ti2O shows a little difference between red and white. Difference of T Fe2O3 between red and white is the important results of the reticulation.Iron morphology and composition is different between red and white reticulation.The iron free-degree in red (70%-80%) is higher than white (40%-60%), the amorphous iron content in red (<10g/kg) is higher than white (<5g/kg), Fe2O3 activation grade of red reticulation (0.05-0.15) is less than white. The chelated iron in red and white is less than 1g/kg, with a little difference between red and white.The crystalline iron takes the largest percentage in total iron in red reticulation (above 60%), followed by silicate iron(15%-30%); silicate iron in white is between 50% and 80% in most sections, taking the largest percentage, crystalline iron also takes the largest percentage (50%-60%) in some sections. Compared to the white reticulation, crystalline iron takes a larger percentage in red, the D-value is between 16% and 50%, silicate iron takes a less percentage, and the D-value is between 15% and 50%. The non-Chelated amorphous iron takes the same percentage basically (<10%) in white and red. chelated iron in red (<2%) is less than white (<1.5%).There is a large content of goethite in red reticulation with the strongest diffraction intensity analyzed by means of XRD, and there are many goethites. The content of goethite and hematites are very little in white. The lepidocrocite is relatively little in the red and white reticulation; the ferrihydrite's content in white reticulation is higher than red.(4) Reticulation development was free from parent material constraints, but had a special climate. The D-value of Ti/Zr in red and white reticulation is basically less than 1.5, indicating that reticulate structure was not primary structure or caused by material difference, but was secondary structure in special circumstances. It shows that the difference of iron content is the main reason for the formation of textured. The ba values in red and white are relatively small(< 0.5), Showing that the red and white both has a high degree of weathering. SiO2/Al2O3 is generally between 5 and 10 in red and white. The SiO2/Al2O3 ratio of red (4.5-9.5) is less than white (5.5-11); the difference is between 0.5 and 2.6. The Al2O3/Fe2O3 ratio of red (2-4.5) is less than white (4-18), the difference is between 1.5 and 15, showing that different of iron content and iron forms are the most significant between the red and white. The Rb/Sr in red is less than in white; the difference is basically between 0.1 and 0.5, showing that the white reticulation experienced a strong leaching environment with high mobility of water in the formation. Also may explain that the loss of iron in white reticulation reasoned by more water environment.The content of various iron forms, structure of iron and iron mineral composition in red white reticulation shows that during the formation of vermicular red earth climate alternated between wetness and dryness. After the formation of vermicular red earth climate change to be dry, precipitation decreased. Difference of Local environment in soil is the key to the formation of reticulation.In the time of reticulation's formation part of the soil was the in the environment of more water, restoring and strong liquidity, causing iron loss, forming the white reticulation, after the formation of reticulation, this part of soil remained local water-rich environment, resulting in lower degree of crystalline; part of soil had been in a drier local environment, even in hot and humid weather conditions during the time of reticulation's formation, iron didn't loss, this part of soil might accept the iron from the soil solution, in the dry season a lot of goethite had been produced and accumulated, forming the red reticulation.