Genesis Of The Glauconites In The Miocene Zhujiang Formation,Baiyun Sag,Pearl River Mouth Basin

The authigenetic glauconite is widely used as a typical “facies mineral” in the study of the sequence stratigraphy and the identification of sedimentary environment.This paper focused on the glauconites which were well-developed in the Miocene Zhujiang Formation,Baiyun Sag,Pearl River Mouth Basin.Through the systematic studies of mineralogy and geochemistry,this paper had identified the genetic mechanism,features and geological significance of glauconites in the Miocene Zhujiang Formation.The following points were obtained:(1)The glauconites were mainly granular and filling in the biological coelom holes.The occurrence of the glauconites in Zhujiang Formation proved that they were authigenetic.(2)The content of the expansion layer in the crystal structure of the glauconite was low.As the increase of grade of maturity,the distance between the(001)diffraction peak and the(020)diffraction peak d [(001)-(020)] gradually decreased.(3)The glauconited were low mature to mature,and the appearance of high mature state's authigenetic glauconite indicated that the deposition rate was relatively slow in a long period of time.There was a negative correlation between the content of Al2O3 and TFeO because of alteration.(4)The forming material of glauconites were derived from the Mesozoic intermediate-felsic volcanic rocks,granites and sedimentary rocks.The sedimentary environment is marine weak oxidizing to weak reduction environment.(5)There was one formation origin for the glauconites in the aspect of the mineral reaction mechanism,which was the theory of the lamellar lattice.In the aspect of controlling factor of glauconitization,the poor Fe content is because the pyrites in the Zhujiang Formation which lead partial Fe3+ to becoming Fe2+.