Morphological Characteristics Of Quarternary Accretive Vermicular Red Earth And Its Environmental Implications

Global environmental change and regional response is a research topic of great concern to the scientific community today.As an important stage of past climate change research,the Quaternary has received more and more attention.Accretionary reticulated red clay is a good carrier for recording climate change information experienced during the Quaternary period in low latitudes.Up to now,many scholars have done a lot of research on reticulated laterite from sedimentology,geochemistry,environmental mineralogy,environmental magnetism and other aspects,which has made outstanding contributions to the chronology,genesis and provenance of reticulated laterite.However,the study of reticulate morphology is relatively weak.At present,some inferences about the morphological characteristics of reticulate patterns are mainly based on visual observation.The conclusions are speculative and lack the support and verification of quantitative analysis.In addition,previous studies used fewer morphological indicators of reticulation,resulting in a lack of comprehensive and profound understanding of the changing characteristics.However,as a product of climate in a specific environment,reticulation contains important climatic and environmental information,which needs to be excavated urgently.In view of this,this study quantitatively expresses the morphological characteristics of reticulation of Tangxi laterite section,Jinhua?TX section?,and compares and analyses with geochemical data to explore the environmental indicative role of reticulation morphology.The specific process is as follows:on the one hand,based on ENVI 5.1,Supervised Classification of TX reticulated laterite image is carried out to realize the interpretation of reticular pattern.At the same time,based on Fractal,Landscape Ecology,Geometric Morphology and other theories and methods,the evaluation index of reticulation morphological characteristics is established,which includes the number,size,shape and distribution of reticulation.Relying on Grasshopper software running in Rhino environment,operation sets are compiled and data are calculated.On the other hand,on the basis of calculating the major elements of reticulated laterite,the weathering indices including CIA,ba,SiO₂/Al₂O₃,SiO₂/R₂O₃ and Al₂O₃/Fe₂O₃ are further calculated.Then,the reticulated morphological characteristics are compared with geochemical data to find the relationship between them,so as to explore the indicative significance of reticulated morphological characteristics to the environment.Preliminary conclusions are as follows:?1?The 24 reticulation morphological indices selected in this study show fluctuating changes in the profile.Generally speaking,along the top-down layer of TX section,the number and area of the reticulated pattern show a fluctuating downward trend,while the shape of the reticulated pattern changes from relatively complex to simple and regular,and the distribution of the reticulated pattern tends to disperse;?2?In the reticulated layer of TX profile,from top to bottom,the content of Si decreases and the content of Fe and Al increases,and the SiO₂/Al₂O₃ and SiO₂/R₂O₃decrease as a whole,indicating that the weathering intensity increases as a whole.The characteristic of high CIA value and low Ba value shows that Tangxi red soil has experienced a strong weathering leaching process;?3?SiO₂/Al₂O₃?SiO₂/R₂O₃ are positively correlated with Elongation Index,Shape Complexity,Space Enveloping Area of Reticulation,Landscape Shape Index and Fractal Dimension,but negatively correlated with Shape Ratio,Near-Round Ratio,Circular Proximity and Compactness.The first principal component score and comprehensive score of the reticulation morphological index have similar change trend with the SiO₂/Al₂O₃ and SiO₂/R₂O₃.However,the relationship between the SiO₂/Al₂O₃?SiO₂/R₂O₃ and the indices of the reticulation size is relatively complex.By comparing and analyzing the parameters of reticulation morphology with geochemistry,it is found that there is a certain corresponding relationship between reticulation morphology and weathering intensity in the profile.The reticulation pattern is a response to environmental change,and has certain relevance to the process of soil formation,which has certain environmental indicative significance.