This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists o...This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation stage.The TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.展开更多
基金Ministry of Mines, Government of India for financial support through grant F No. 14/77/2015Met. IV
文摘This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation stage.The TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.
