Distinctive compositional characteristics and evolutionary trend of Precambrian glaucony: Example from Bhalukona Formation, Chhattisgarh basin, India

•Glaucony usually formed in a shallow marine environment in the Precambrian.•Precambrian glaucony exhibits high K2O, Al2O3 and MgO and low Fe2O3 contents.•Maturation of glaucony takes place by the addition of total Fe2O3 at a constant K2O.•‘Pseudomorphic replacement’ theory explains origin of glaucony.

Up to 20% of framework quartz and feldspar grains in wave-reworked sandstones in the Precambrian Bhalukona Formation, central India are replaced by glaucony, which is characterized by high K2O, Al2O3, MgO and low total Fe2O3 content. Textural evidence indicates that incipient glaucony within cleavages and fractures of detrital grains evolved to pellets. K2O content of glaucony remains high (av. >8%), despite its low total Fe2O3 content. Glaucony evolved with addition of total Fe2O3 at a constant K2O. During the course of maturation Al2O3 was released while total Fe2O3, MgO and SiO2 were added to the glaucony structure. Glaucony originated in a high aK+ and high aSi+ pore water environment by pseudomorphic replacement of grains. Continental weathering-related supply of Fe, Mg, K and Si facilitated glaucony formation in shallow marine sediments. The origin, evolution and geochemistry of shallow marine-originated Precambrian glaucony completely differ from those of their Phanerozoic counterpart.