Pedogenically degenerated illite and chlorite lattices aid to palaeoclimatic reconstruction for chronologically constrained(8-130 ka) loess-palaeosols of Dilpur Formation,Kashmir,India  

作　　者：Meenakshi J.P.Shrivastava Rakesh Chandra 

机构地区：[1]Department of Geology,University of Delhi,Delhi,110007,India [2]Department of Earth Sciences,University of Kashmir,Jammu and Kashmir,190006,India

出　　处：《Geoscience Frontiers》2020年第4期1353-1367,共15页地学前缘（英文版）

基　　金：We acknowledge the Project Grant(IUAC-AUC No.60323)in the form of Fellowship(to Meenakshi)provided by the Inter University Accelerator Centre(IUAC),New Delhi.Mr.Vijay Rajpal,Department of Geology,University of Delhi is acknowledged for the XRD analysis.

摘　　要：Chronologically well-constrained loess-palaeosols(recorded glacial and inter-glacial climate) revealed pedogenesis induced ionic substitutions,caused end-member compositional deviations in illite and chlorite,linked to widespread climatic changes occurred during Late Pleistocene.Further,micro-level climatic resolution is yet to be resolved.Thus,layer-wise X-ray diffraction analyses of clay separates,followed by Rietveld refinement revealed varied cell parameters and interatomic distances.Obtained values for detrital and pedogenic illite and chlorite when plotted against stratigraphic succession show notable changes in the crystallographic axes.The illite lattices associated with inadequately pedogenized palaeosols have been altered into illite/smectite mixed layers,but,the chlorite lattices represent expansion of a-,b-and contraction of c-axes with much greater amount of distortions,suggestive of warm-humid and acidic environment.The detrital 48,44 and 83,74 bonded illite and chlorite with2 sub-types each,when pedogenized retained 48,44 and 34;and 83 and 74 bonds(in their neo-formed 3 and 2 sub-types),respectively.The Al-O bond shows expansion,but,unchanged Si-O and decreased Si-K and K-O bonds show loss of Al and retention of Si and K ions in the illite lattices.The illite with 32 atoms and 48 bonds represent contraction of K-O,Si-K,Al-O and Si-O bonds caused bond reinforcement;however,loss of Al3+reflects all-out illite alteration.Owing to Al-O and K-O bond expansion,major K+ and Al3+ ionic loss occurred during the LGM,however,further ionic loss depends upon the magnitude of the loess-palaeosol weathering that they have suffered.The clilate sensitive Fe,Mg and Al ionic losses for Fe-O,Mg-O and Al11-O9 bond length expansions were recognized in the chlorite lattices.Such ionic losses are common,but,complete distortion is attributed to Al,Si,Fe and Mg ionic losses,followed by weakening of Al-O,Si-O,Fe-O and Mg-O bonds.Though,Si-O4 and Fe1-O4 bonds,and Si and Fe1 st ions remain intact.Thus,three major glacial episo

关 键 词：Crystallographic defects Cell parameters Inter-atomic distances Glacial-interglacial periods Rietveld refinement LGM 

分 类 号：P642.131[天文地球—工程地质学] P532[天文地球—地质矿产勘探]