The distinctive compositional evolution of glauconite in the Cretaceous Ukra Hill Member (Kutch basin, India) and its implications. (April 2017)

• Record Type: Journal Article
• Authors: Bansal, Udita; Banerjee, Santanu; Pande, Kanchan; Arora, Ashwin; Meena, S.S.
• Is Part Of: Marine and petroleum geology. Volume 82(2017)
• Page Start: 97
• Page End: 117
• Publication Date: 2017-04
• Subjects: Glauconite -- Compositional evolution -- Replacement -- Mineral chemistry -- Spectroscopy -- Reverse glauconitization; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2017.01.017
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: An integrated study involving sedimentology, mineral chemistry and spectroscopy highlights a distinctive compositional evolution of Cretaceous glauconite within the Ukra Hill Member. Glauconite occurs at the top part of transgressive systems tract deposits built on a marine shelf. The concentration of glauconite steadily increases towards the maximum flooding surface, maximizing around 50%, and sharply falls at the onset of progradation. Unlike most Phanerozoic examples, Ukra glauconite forms by the variable degree of replacement of quartz, feldspar and mica grains. XRD, FEG-SEM and spectroscopy of glauconite pellets indicate an 'evolved' stage of maturation. Mossbauer spectroscopy reflects a minor substitution of Al 3+- Fe 3+ (total) in tetrahedral sites and significant substitution of the same in octahedral sites. A consistently high value of K2 O as well as Fe2 O3 contradicts the two popular theories, 'layer lattice' and 'verdissement', and support replacement origin of glauconite in a high aSi+ and high aK+ pore water environment. Incipiently formed glauconite records a marginal increase in K2 O content accompanied by release of Al2 O3 and SiO2 to form evolved glauconite pellets; those forming within quartz grains involve an addition of Fe2 O3 (total) content during maturation. The minimal increase in K2 O content of incipiently formed glauconite, best exhibited by those formed within quartz grains is possibly related to stratigraphic condensation. Compositional evolution like this is exhibited by Precambrian glauconites involving abiotic substrates, but is unusual for the Phanerozoic. Original K2 O and Fe2 O3 (total) content of glauconites is reduced around peripheries and fractures during diagenesis, adding to compositional variability. Highlights: Evolved glauconite forms preferably near the maximum flooding zone. Glauconite forms by the replacement of with quartz, feldspar and mica. Origin and evolution of glauconite is similar to those formed in Precambrian. Slight increase in K2 O relates to time-dependent fixation during evolution of glauconite. On alteration glauconite got enriched in SiO2 and Al2 O3 content.