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Distinguishing celadonite from glauconite for environmental interpretations:a review

Journal of Palaeogeography 2023年第2期12卷 179-194页

作者： Pragya Singh Santanu Banerjee Tathagata Roy Choudhury Satadru Bhattacharya kanchan pande Department of Earth Sciences Indian Institute of Technology BombayPowaiMumbai400076India Space Applications Centre Indian Space Research OrganisationAhmedabad380015India

Celadonite and glauconite are comparable in terms of physical,chemical and mineralogical *** of both these minerals requires slightly oxygen-depleted conditions in a semiconfined micro-environment,facilitating the uptake of Fe into the *** glauconite is ubiquitous in marine deposits,celadonite forms in both marine and non-marine environments,more commonly by altering intermediate to mafic rocks.A review of data across the geological column shows that both these minerals are more common in the Mesozoic and Cenozoic,which may be related to extensive *** composition of celadonite and glauconite is highly variable and is controlled by the availability of cations within the pore water *** major element composition of celadonite overlaps with that of evolved to highly evolved glauconite to a large *** data and representative samples of celadonite and glauconite reveal subtle differences in X-ray diffraction parameters and Fourier transform infrared(FTIR)*** shows sharper basal and hkl reflections than *** characteristically exhibits distinct 111-021,003-022,023 and 130-131,and 060 reflections at less than 1.51A,indicating a betterordered crystallographic structure than *** FTIR spectra of celadonite and glauconite show similar absorption bands although Si-O bending,Si-O stretching and OH-stretching bands are sharper and well resolved in celadonite than that of *** palaeoenvironmental interpretations,it is,therefore,necessary to examine the subtle differences in X-ray diffraction parameters and FTIR spectra to confirm the identification of these two *** composition of celadonite relates closely to the host rock and depositional *** celadonite associated with mafic rock shows relatively high Fe,Mg and low Al *** contrast,those associated with felsic to intermediate composition rocks show slightly higher contents of Al and

关键词： Celadonite Glauconite Authigenic green silicates Large igneous province Marine Fourier transform infrared spectroscopy X-ray diffraction

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Origin and geochemical characterization of the glauconites in the Upper Cretaceous Lameta Formation, Narmada Basin, central India

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Journal of Palaeogeography 2018年第2期7卷 99-116页

作者： Udita Bansal Santanu Banerjee Dhiren K.Ruidas kanchan pande Department of Earth Sciences Indian Institute of Technology Bombay

This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation *** TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.

关键词： Glauconite Estuary Mineral chemistry Cerium anomaly Redox condition Lameta Formation Narmada Basin

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^(40)Ar-^(39)Ar GEOCHRONOLGY OF THE OPHIOLITE OF INDUS SUTURE ZONE,LADAKH,INDIA:IMPLICATION FOR THE TIMING OF INITIATION OF THE COLLISION

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地学前缘 2000年第S1期7卷 97-98页

作者： kanchan pande,Rajneesh Bhutani (Physical Research Laboratory,Navrangpura,Ahmedabad\|380009,India)

The collision between and Indian and Asian plate has not only give rise to some of the highest mountains of the world but also is responsible for the various global phenomena associated with paleoclimate and paleo\|*** indirect approaches have been employed in order to constrain the age of initiation of this collision (Beck et al 1995,*** 1996,Dewey 1989).Still it is being quoted anywhere between ca.60 to 40Ma in the *** main reason for the poor constraints on the age of the initiation of the collision is unavailability of a direct method to date *** this paper we present the Ar\|Ar ages of the ophiolites from the Indus Suture,Ladakh and discuss the scope of this approach in constraining the age of the collision more narrowly.1\ Samples and methodology\;Several ophiolitic melange occurrences have been reported belonging to the Indus Suture in the Ladakh *** are characterized by the typical oceanic floor assemblages like chert,limestone etc mixed with the peridotites,serpentinites,dolerites,basalts,and pillow lavas (*** 1990).We present here the 40 Ar\| 39 Ar age spectra of two volcanics from the Sumdo Nala section of central Ladakh and one pillow lava from Chiktan,which is about 100km west of the Sumdo *** samples were analysed using Ar\|Ar step heating method following the procedures described by Venketesan et al.1993.

关键词： ophiolite Ar\|Ar geochronology suture zone Ladakh

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^(40)Ar-^(39)Ar GEOCHRONOLOGY OF THE SUTURE ZONE, LADAKH, INDIA

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地学前缘 2000年第S1期7卷 102-104页

作者： Rajneesh Bhutani, kanchan pande (Physical Research Laboratory, Navrangpura, Ahmedabd\|380 009, India)

Introduction\;A suture zone in an orogenic belt marks the paleo\|plate boundaries with its characteristic ocean floor assemblages. In Himalayas, the best and most spectacular example of the continent\|continent collision orogeny, the suture zone can be traced all along the 2500km long mountain chain and marks the boundary between the Indian and Asian plates. Ladakh region of North\|West Himalaya probably presents the best preserved history of pre\|, syn\|, and post\|collision signatures. It has rocks ranging from Precambrian passive margin sediments to the post collision molasses. The suture zone in Ladakh, referred to as the Indus Suture Zone (ISZ), is characterized by the several occurrences of ophiolitic melange. (M.P. Searle et al, 1987) .Apart from these, various linear belts of the volcanic rocks have been found in the Indus Suture Zone, though their inter relationship is not very clear (*** 1990).

关键词： Ar\|Ar geochronology Ladakh ophiolite suture zone

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