The distinctive compositional evolution of glauconite in the Cretaceous Ukra Hill Member (Kutch basin,India) and its implications |
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| Institution: | 1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Xueyuan Lu 29, Beijing 100083, China;2. School of Geosciences, The University of Sydney, Sydney, NSW 2006, Australia;3. School of Geography, Planning and Environmental Management, The University of Queensland, Brisbane, QLD 4072, Australia;1. Wadia Institute of Himalayan Geology, 33 GMS Road, Dehradun, India;2. Centre for Earth Sciences, Indian Institute of Science, Bangalore 560012, India;3. HNB Garhwal University, Srinagar, Garhwal, India;4. Birbal Sahni Institute of Palaeosciences, Lucknow 226007, India;5. Physical Research Laboratory, Ahmedabad 308009, India;6. Institute of Water Policy, Lee Kuan Yew School of Public Policy, NUS, Singapore;7. Geography Department, National University of Singapore, Singapore;1. Department of Geology and Mineral Exploration, Institute of Natural Resources, Tomsk Polytechnic University, 634050 Tomsk, Russia;2. Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400076, Maharashtra, India;3. Department of Plant Physiology and Biotechnology, Biological Institute, Tomsk State University, 634050 Tomsk, Russia;4. Lab №12, Institute of High Technology Physics, Tomsk Polytechnic University, 634050 Tomsk, Russia;1. Institute of Applied Geosciences, Graz University of Technology (NAWI Graz Geocentre), Rechbauerstraße 12, 8010 Graz, Austria;2. Geosciences Environment Toulouse (GET), CNRS, UMR5563, 14 Avenue Edouard Belin, 31400 Toulouse, France;3. Institute of Technology and Testing of Building Materials, Graz University of Technology, Inffeldgasse 24, 8010 Graz, Austria;4. Department of Geography and Geology, University of Greifswald, F.-L.-Jahn-Straße 17A, 17487 Greifswald, Germany;5. Geoscience Centre (GZG), University of Göttingen, Goldschmidtstraße 3, 37077 Göttingen, Germany;1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhostraße 1-3, 24111 Kiel, Germany;2. Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany |
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| 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 Al3+-Fe3+ (total) in tetrahedral sites and significant substitution of the same in octahedral sites. A consistently high value of K2O as well as Fe2O3 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 K2O content accompanied by release of Al2O3 and SiO2 to form evolved glauconite pellets; those forming within quartz grains involve an addition of Fe2O3 (total) content during maturation. The minimal increase in K2O 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 K2O and Fe2O3 (total) content of glauconites is reduced around peripheries and fractures during diagenesis, adding to compositional variability. |
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| Keywords: | Glauconite Compositional evolution Replacement Mineral chemistry Spectroscopy Reverse glauconitization |
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