Genesis mechanism and potential controlling factors of different types of glauconite in Cambrian strata, northern China

Single-layer glauconites with thicknesses ranging from millimeters to centimeters have been widely developed in the Cambrian tidal flat-shoal environments in the Xuzhou area, northern China. The Cambrian glauconite-bearing sedimentary sequences in this area were combined to reconstruct the glauconite formation and its subsequent occurrence environments. Glauconites were generally formed in tidal flat-lagoon environments with low sedimentation rates and coexisted in oolitic shoals, intertidal flats, and subtidal flats, together with granular fractions formed under different types of strong hydrodynamic conditions. The glauconites occur in granular, micellar, and re-agglomerated granular forms with similar chemical compositions, consisting mainly of SiO₂, FeO, Al₂O₃, and K₂O. The Stage 4–Wuliuan is characterized by a hot climate, many types of glauconite, and large variations in maturity. The limestone, quartz sandstone, and silty mudstone all contain glauconite pellets. The glauconite with felsic material as the substrate has a pseudomorphic replacement genesis. The glauconite with mica as the substrate has a layer lattice theory genesis. The micellar glauconite may have been formed by loss of structural water during maturation of the glauconite pellets, i.e., biogenesis and authigenic precipitation genesis. The Guzhangian–Paibian is characterized by a warm climate, a single glauconite type, high maturity, and stability. The reagglomerated granular glauconite distributed in the dolomitic limestone and dolomite is mostly of grain verdissement origin. The ion contents released by the different substrates were different, and transportation also inhibited the glauconite development, making the degree of glauconization in the Cambrian unstable. The influence of substrate composition on glauconite maturity remains uncertain, but glauconites of stable size (∼100 μm), regular shape, and uniform color generally show higher and more stable levels of glauconitization. Glauconite has a robust temperature tolerance and can develop in environments characterized by weakly oxidizing to weakly reducing conditions, transgression-regression stage of sea level rise and flourishing biological conditions. The accumulation phase of glauconite may indicate a major transition in the Cambrian ecosystem.