Genesis And Geological Significance Disscusion Of The Cambrian Glauconite In The Dabeiwang Profile,Xuzhou

The origin and geological significance of glauconite in the strata from Mantou to Xuzhuang formation are studied in the Dabeiwang district of Xuzhou,Jiangsu Province based on the theories and methods of sedimentary petrology,sequence stratigraphy,mineralogy and petrology,according to the data obtained by field profile measurement,rock slice identification,X-ray diffraction,and electron probe microanalysis.The sedimentary faces of Mantou to Xuzhuang formation in the study area are mainly composed of carbonate tidal flat and shoreside,including three subfaces and three microfacies.And limestone containing glauconite is usually developed in lagoon or outslope,while sandstone containing glauconite is formed in shoal or shoreface.The development position of strata containing glauconite in the third-order sequence is concentrated in the transgressive system tract,condensed zone and high-water system tract with relatively high sea level.Besides,nine kinds of typical depositional sequences containing glauconitic layers are identified and divided based on the theory of meterscale sequences,and the morphology of glauconite in those sequences is characterized by granular,micellar and detrital illusion.Moreover,four kinds of glauconite development pattern including lagoon type,outslope type,shoal type,and shoreface type are further established,based on the sedimentary environment,sedimentary sequence and petrological characteristics of strata containing glauconite.The genesis of glauconite with different morphologies is discussed from the aspects of genetic mechanism,material sources and metallogenic conditions.The type I granular glauconite is autochthonous origin.It is formed in outslope,taking powder as the substrate,and dissolving the continental weathered products as well as the alteration of quartz and feldspar as material source,and following the mechanism of the layer lattice theory and the pesudomorphic replacement theory;the type II granular glauconite is parautochthonous origin.It is originally formed in the shallow part of the lagoon,taking fecal pellets and carbonate particles as the substrate,and following the verdissement of grains theory.After being mature,it is transported to different places by waves,tides,storms and so on;the type III granular glauconite is also autochthonous origin and formed in the shallow part of the lagoon,taking fecal pellets and carbonate particles as the substrate,and dissolving the continental weathered products as material source,and following the verdissement of grains theory;micellar glauconite is autochthonous origin and formed in lagoon,and dissolving the continental weathered products as material source,and following the authigenic precipitation and cementation theory;detrital illusion glauconite is also autochthonous origin and formed in shoal,and taking mica or degraded mica as the substrate,and dissolving the continental weathered products as well as the alteration of quartz and feldspar as material source,and following the mechanism of the layer lattice theory and the pesudomorphic replacement theory.Finally,on the basis of genetic analysis,the indicative significance of different types of glauconite on the physical and chemical conditions of the sedimentary environment is discussed,and it is also considered that strata containing glauconite can be used as one of the identification marks of transgressive system tract and high-water system tract within the third-order sequence.