![]() ![]() Compositional evolution like this is exhibited by Precambrian glauconites involving abiotic substrates, but is unusual for the Phanerozoic. The minimal increase in K 2 O content of incipiently formed glauconite, best exhibited by those formed within quartz grains is possibly related to stratigraphic condensation. ![]() Incipiently formed glauconite records a marginal increase in K 2 O content accompanied by release of Al 2 O 3 and SiO 2 to form evolved glauconite pellets those forming within quartz grains involve an addition of Fe 2 O 3 (total) content during maturation. A consistently high value of K 2 O as well as Fe 2 O 3 contradicts the two popular theories, 'layer lattice' and 'verdissement', and support replacement origin of glauconite in a high a Siþ and high a Kþ pore water environment. Mossbauer spectroscopy reflects a minor substitution of Al 3þ-Fe 3þ (total) in tetrahedral sites and significant substitution of the same in octahedral sites. XRD, FEG-SEM and spectroscopy of glauconite pellets indicate an 'evolved' stage of maturation. Unlike most Phanerozoic examples, Ukra glauconite forms by the variable degree of replacement of quartz, feldspar and mica grains. The concentration of glau-conite steadily increases towards the maximum flooding surface, maximizing around 50%, and sharply falls at the onset of progradation. Glauconite occurs at the top part of transgressive systems tract deposits built on a marine shelf. An integrated study involving sedimentology, mineral chemistry and spectroscopy highlights a distinctive compositional evolution of Cretaceous glauconite within the Ukra Hill Member. ![]()
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