Study On The Clay Minerals And Weathering Characteristics Of Aggradated Red Earth

Based on amount of field work,this thesis selected three aggradated red earth profiles from mid-subtropics as research objects,which are YD?from Zhejiang?,WJL?from Jiangxi?and CJY?from Hunan?.Using methods such as Mineralogy and Geochemistry to discuss the clay minerals components of aggradated red earth and their weathering characteristics.Totally 149 samples have been collected from these three sections,and 80 of them were selected for sedimentation experiments;also the<2?m fraction were extractd from 80 samples for XRD diffraction analysis.Based on the result of the analysis pattern to determine its clay minerals type and components,calculate the crystalline of Illite.Meanwhile,we relates the results above with the outcome of the XRF element of total rocks samples to explore the weathering characteristics of accumulated laterite section,which is laying a foundation for further understanding the formation environment and vermiculated red soil mechanism.This thesis initially draws the following conclusions:?1?The turbid liquid of 80 YD,WJL and CJY three aggradated red earth profiles<2?m samples were made into MgCl₂,glycerol,ethylene glycol and KCl saturated orientation samples.And some KCl saturated samples were treated through high temperature of 400?and 550?Use the PANalytical X^'Pert Pro MPD X-ray diffractometer from the Dutch PANalytical Company to measure and analyze comprehensively,getting the result that the main categories of the mid-subtropical aggradated red earth clay mineral is kaolinite,illite,vermiculite,montmorillonite,illite-montmorillonite mixed layer and kaolinite-montmorillonite mixed minerals,which reflect the hot and humid weathering characteristics.?2?The three aggradated red earth clay YD,WJL,CJY are divided into three stratigraphic units from top to bottom,which are yellow brown soil layer,reticulated yellow brown soil layer and reticulated red clay layer,and the there are some aggradated clay mineral type The yellow brown soil layer was mainly main by vermiculite,montmorillonite,illite,illite montmorillonite mixed layer.The samples of the reticulated yellow-brown soil in the middle of the section are mainly made of kaolinite,illite and illite-montmorillonite mixed minerals.Some samples also contain vermiculite,montmorillonite and a small amount of kaolinite-montmorillonite mixed mineral.The vermiculite mainly appears in the upper sample of the layer,while the kaolinite-montmorillonite mixed mineral appears in the lower sample of the layer.The reticulated red clay samples in lower profile is mainly made up with kaolinite,montmorillonite,illite-montmorillonite mixed mineral,and the kaolinite-montmorillonite mixed mineral takes the primary part,while the vermiculite is in a small amount.The amount of montmorillonite in the reticulated layer increases with depth increase,and the amount of illite decreases relatively.In view of the presence of kaolinite-montmorillonite mixed minerals in the reticulated layer and the increase of kaolinite,the form environment of reticulated red earth was warm and humid with a certain dry and wet season change.The types and combination characteristics of the three-profiles clay minerals consistently show that the reticulated red earth formation environment was warmer and wetter than the yellow-brown soil and yellow-brown soil in the upper part of the profile;from the bottom to the top of the profile,and the aggradated red earth's form environment was turn from warmth and wetness to dry gradually.?3?Calculate the crystallinity of illite by using the half height and half width of the illite?001?diffraction peak.The IC value of illite crystallinity in the three profiles of YD,WJL and CJY are roughly between 0.39 and 0.80,and the YD profile changes between 0.42 and 0.68,while the WJL profile varies between 0.39 and 0.80,and the CJY profile updates between 0.42 and 0.66.The crystallites of the three profiles updates in a similar variance.According to Diekmann's classification of illite crystallinity,all of them are in medium to good crystallinity range.In contrast,the IC value of reticulated red earth?0.59⁰.72?is slightly higher than that of reticulated yellow-brown soil?0.51⁰.66?and yellow-brown soil?0.44⁰.54?,which indicated that the degree of Weathering was gradually weakening from Middle Pleistocene to Late Pleistocene,and also revealed the red earth profile changed from bottom to top and the climate changed from warm and wet to dry and cool.?4?Comprehensive analyze the profile mineral composition,illite crystallinity and chemical weathering parameters such as CIA,ba,SA,SAF and other changes along the profile.Aggradated red earth recorded the Quaternary environment in the mid-subtropical region.These three sections consistently show that the middle and lower environment of the reticulated red earth was relatively stable,and the values of IC,CIA,ba,SA,SAF,clay content?<2?m?and other parameters are not fluctuating,but the IC value has a certain trend which manifested as characteristics of the value increasing along with the depth increase?the degree of crystallization is deteriorated?.From the yellow-brown soil to the upper part of the reticulated red earth layer,the numerical fluctuations of parameters such as IC,CIA,ba,SA,SAF,and clay content?<2?m?increase,indicating that the environmental instability is enhanced,especially in the upper part of the reticulated red earth and yellow-brown layer which has the greatest variation,and the IC and CIA values showed a downward trend from bottom to top.The longitudinal variation of illite crystallinity and clay mineral combination characteristics can effectively indicate the trend of chemical weathering of aggradated red earth gradually weakening since the middle Pleistocene.