The Experimental Simulation Study Of “Glauconization” Mechanism Of Geological Process

The geological origin of glauconite,a diagnostic mineral of neritic environment,has been widely investigated but still controversial,which is ascertained to be precipitated and matured for 1Ma long under conditions of very low sedimentation rates,and its gradual maturation during glauconitization.The starting,or parent,materials that have been previously documented undergoing glauconitization include feldspar,biotite,muscovite,potassium-rich minerals,quartz,calcite,dolomite,phosphate minerals,potassium-poor minerals,volcanic glass,plutonic rock fragments,and even carbonate bioclasts This study uses three different kinds of initial materials:(1)Montmorillonite which has a low iron content,(2)Basalt,andesite and rhyolite,(3)Quartz.0.02-0.1 mol/LFe3+,0.05-0.2mol/LK+solutions were prepared,adjusting to different pH&Eh,respectively.The products were analyzed using X-ray powder diffractometry(XRD),Frourie Transform Infrared(FTIR)spectrometry,Electron Spin Resonance(ESR)spectrometry,Scanning Electron Microscopy(SEM)and Mossbauer spectroscopy.The products was observed as the flake like neo-forming morphology under the SEM.Qualitative analysis of XRD results suggested that the main phase was mica group mineral and the(060)reflection suggested the presence of glauconite(0.1520nm)and/or Fe-illite(0.1498nm).The assemblage of glauconite and Fe-illite formed in dilute acidic solution,while the Fe-illite and the mix-layer Fe-illite and montmorillonite were formed in the neutral and alkaline solutions.Furthermore,the Fe3+Fe3+OH,Al3+Fe2+OH and/or Mg2+Fe3+OH(3550-3562cm-1)stretching vibrations show in FTIR spectra of products formed in acidic solution,which is also confirmed by the ESR signals at 1.978,suggesting that ferric iron entered the octahedral position of TOT sheets.Bands of Al3+Fe2+OH?Mg2+Fe3+OH(3550-3562cm-1)and Al3+Fe3+OH(870cm-1)vibrations were detected in products formed in neutral and alkaline solutions.Further analysis by Mossbauer spectrum showed that Fe3+ substituted for Al3+and Mg2+which incorporated in the site of M2 octahedrons of montmorillonite.The simulating experiments suggested that the pH and redox conditions(Eh)of the environment were vitally significant and thus constrained the species of products.Therefore,glauconization and illitization occurred under different conditions,the former preferred to occur in acidic environment but the latter preferred to occur in near neutral to alkaline environment.XRD patterns of basalt,rhyolite and their reaction products show 1.02nm characteristic diffraction peak attributed to mica minerals and d060 value suggested the presence of glauconite(0.1520nm).In neutral and weakly alkaline condition,the Fe3+Fe3+OH(3526cm-1)and Fe3+Fe3+OH(819cm-1)stretching vibrations were present in FTIR spectra of basaltic product,the Fe3+Fe3+OH,Al3+Fe2+OH and/or Mg2+Fe3+OH(3550-3562cm-1)stretching vibrations in FTIR spectra of andesitic products were detected;In neutral and weakly acidic condition,the Fe3+Fe3+OH(3526cm-1)stretching vibrations were observed in FTIR spectra of the rhyolite products.The results of SEM analysis showed that the glauconitization of massive basalt and andesite is a two-stage process:(1)the early pyritization or the formation of iron compounds(goethite)on the surface or in the pore of basalt and andesite in iron rich environment;(2)the dissolution and reprecipitation of silicates such as feldspars and pyrite or iron compounds when the environment changes.The glauconitization of non-mica minerals shows as:the formation of iron compounds as the core first,and then the dissolution of silicates or other silicon containing compounds in the surrounding environment,which produce Si,A1 to iron compounds for absorption.The products of massive rhyolite contained pyrite either,but Muscovite is the major source of the glauconitization,associated with the dissolution and reprecipitation of muscovite.The results show that different parent phases decided different initial conditions and mechanisms of glauconitization.For quartz as initial materials,XRD pattern of products show peaks at around 1.0nm and glauconite(060)characteristic peak with a d-spacing of 0.1520nm.The Fe3+Fe3+OH(3526cm-1)stretching vibrations also appear in FTIR spectra.However,the glauconitization of quarts only occurs in strong alkaline environment,which is rare in nature.Characterization of three groups of the experimental result shows that with the origination of the what kind of parent material is not important,if the starting material containing silicon,the rich potassium and/or iron rich solution is the key to happen "glauconitization";If the starting material including silicon,silicon has become another key factor of "glauconitization".Ensure the material source is formed under the condition of glauconite,the pH and Eh of solution could be the main factors that restrict glauconitization.