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The origin and maturation of lagoonal glauconites: a case study from the Oligocene Maniyara Fort Formation, western Kutch, India

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Title The origin and maturation of lagoonal glauconites: a case study from the Oligocene Maniyara Fort Formation, western Kutch, India
 
Creator BANERJEE, S
CHATTORAJ, SL
SARASWATI, PK
DASGUPTA, S
SARKAR, U
BUMBY, A
 
Subject lagoonal glauconites
infillings
faecal pellet
foraminifers
glauconite maturity
cerium anomaly
Oligocene
India
RARE-EARTH-ELEMENTS
CONTINENTAL-SHELF
KOREAN PENINSULA
HAMPSHIRE BASIN
SOUTH-AFRICA
SEDIMENTS
GEOCHEMISTRY
MARGIN
BALTOSCANDIA
ENVIRONMENT
 
Description An integrated study of the sedimentology, micropalaeontology, mineralogy and geochemistry of glauconites in the Oligocene Maniyara Fort Formation (western Kutch, India), has been undertaken. Authigenic glauconites, mostly of evolved type, formed within a back-barrier lagoonal environment. Foraminifera help constrain the biostratigraphy and along with sedimentological evidence, provide information on the depositional conditions. Glauconite in the Maniyara Fort Formation occurs either as infillings within intra-particle pores of larger foraminifers, or as an altered form of faecal pellets. X-ray diffraction studies reveal the less mature nature of glauconite infillings compared to the glauconite pellets. Electron microprobe investigation confirms a relative enrichment of K2O and total Fe2O3 in the latter. Both varieties of glauconite formed by initial authigenic precipitation of K-poor glauconite and subsequently matured by addition of potassium in the interlayer sites and fixation of total iron in the octahedral sites; calcium, magnesium and aluminum were released from the glauconite structure concomitantly. Alkaline conditions during the entire process of glauconite formation did not allow dissolution of foraminiferal tests. Mineralogical and chemical characteristics of the Maniyara Fort Formation glauconites are more similar to deep marine glauconites than those reported from other shallow or marginal marine settings. A low negative cerium anomaly, as well as abundant pyrite, suggests formation of glauconite in sub-oxic micro-environments, created by decay of organic matter associated with foraminiferal chambers and faecal pellets. Sub-oxic condition apparently prevailed relatively longer within the Maniyara Fort Formation lagoons. Copyright (c) 2011 John Wiley & Sons, Ltd.
 
Publisher WILEY-BLACKWELL
 
Date 2014-10-17T05:08:55Z
2014-10-17T05:08:55Z
2012
 
Type Article
 
Identifier GEOLOGICAL JOURNAL, 47(4)357-371
0072-1050
1099-1034
http://dx.doi.org/10.1002/gj.1345
http://dspace.library.iitb.ac.in/jspui/handle/100/16029
 
Language en