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

1. Introduction

Modern glauconite forms in the depth range of 50—500 m and is most abundant between 200 m and 300 m deep on the sea floor(Odin and Matter,1981).There is a tendency to apply the same bathymetric interpretation for ancient glauconites.However,authigenic glauconitemay form in a wide spectrum of shallow marine environments including wave-agitated estuaries and coastlines(Banerjee et al.,2015,2016a;Chafetz and Reid,2000).Very few studies,however,investigate the relationship between glauconite composition and palaeoenvironmental conditions(Banerjee et al.,2016b).K2O and TFe2O3content of glauconite varies with sedimentation rate,nature of substrate,and depositional environment(Amorosi,2013;Banerjee et al.,2015,2016a,2016b;Bansal,2017).Highlyevolved glauconites containing ＞7.5% K2O are commonly related to the mega-condensed section.Amorosi(2013)proposed three types of sequencestratigraphic condensed sections on the basis of glaucony abundance and maturity:(i)simple omission surfaces,containing ＜20%of“slightly-evolved” glaucony;(ii)condensedsections,including20%—50%of“evolved”glaucony;and(iii)mega-condensed sections,with＞50%of highly-evolved glaucony.However,glauconite forming within the K-feldspar substrate may also exhibit high K2O content(Banerjee et al.,2015;Bansal et al.,2017).The TFe2O3content of glauconite possibly depends on sufficient supply of Fe and redox condition of the depositional setting(Banerjee et al.,2016a;Meunier and El Albani,2007).Ce anomaly values of the glauconite provide valuable information regarding redox conditions of the depositional setting(Banerjee et al.,2015;Elder field and Pagett,1986;Wright et al.,1987).Composition of glauconite also depends on its origin and evolutionary paths,which are explained by theories including the “layer lattice” theory(Burst,1958a,1958b;Hower,1961), “verdissement” theory(Odin and Matter,1981),and“pseudomorphic replacement”theory(Banerjee et al.,2008,2015;Dasgupta et al.,1990).“Verdissement theory” involves an initial precipitation of K-and Fe-poor glauconitic smectite within porous substrate and its subsequent maturation by addition of K at constant Fe.An integrated study involving detailed petrography,mineralogy,mineral chemical analysis,and REE chemistry of glauconites is likely to provide a better perspective of factors affecting the composition of glauconite.

The present study explores the influence of depositional conditions on the composition of glauconite.This study investigates the geochemical characteristics of glauconites within the Maastrichtian Lameta Formation in central India.Resting conformably over the Bagh Group,the Lameta Formation comprises arenaceous,argillaceous,and calcareous green sandstones underlying the Deccan Traps.This study presents detailed petrography,X-Ray Diffraction(XRD),Mössbauer spectroscopy,mineral chemistry,and REE chemistry of glauconite.The major findings of the paper include evaluating the effect of depositional redox conditions and nature of substrate on glauconite composition.The composition of glauconite has been further related to the estuarine depositional environment.

2. Geological background

The Lameta Formation crops out at the western segment of the Narmada Basin in central India(Fig.1;Tandon,2000).Although most of the outcrops occur as disconnected patches along the basin,they are well developed around Phutlibaori area in western India(Fig.1;Tandon,2000).Ahmad and Akhtar(1990)and Kumar et al.(1997)considered that the Lameta Formation conformably overlies the Bagh Group(Table 1).It is a roughly 4—5-m-thick succession comprising arenaceous,argillaceous,and calcareous sandstone(Tripathi,2005).The Lameta Formation occurs beneath the basal Deccan Traps in the west through a 15-cmthick siliceous layer(Fig.2);while in the east(towards Jabalpur),it is contemporaneous with early Deccan volcanism(Salilet al.,1997;Tandon,2000).The Lameta Formation has gained attention for over a century because of its association with a thick pile of Deccan Traps and its diverse faunal assemblage.It has been assigned a Maastrichtian age on the basis of Igdabatis(Besse et al.,1986),palynomorph Aquilapollenites indicus(Dogra et al.,1988),and palaeobatid frogs(Buffetaut,1987;Jaeger et al.,1989;Sahni and Bajpai,1988).Recently,Prasad et al.(2016)reported isolated archosaur teeth of pre-Late to Late Maastrichtian age within the green sandstone beds of Phutlibaori area.The Late Maastrichtian(～66 Ma)age of the overlying Deccan Traps further corroborates the assigned age of the Lameta Formation(Courtillot et al.,1988;Tandon and Andrews,2001;Venkatesan et al.,1993).

Marine Cretaceous sediments in the western India were related to the formation of an epicontinental seaway which advanced from the west(Tandon,2000).The Late Cretaceous carbonate deposition of the Bagh Group indicates a marine transgression.Tripathi(2006)suggested that marine transgression took place in half-grabens parallel to the Precambrian tectonic framework.Whereas the marine influences were confined only to the west of the Narmada Basin(Fig.1),continental deposition possibly continued around in the Jabalpur in the east and Nagpur in the southeast(D'Emic et al.,2009;Kumar and Tandon,1977,1978,1979;Pascoe,1950;Tandon,2000).The sea regressed owing to the surface uplift related to the active rifting and plume tectonics during the late Maastrichtian(Tandon,2000).

Tandon(2000)worked extensively on the sedimentology of the Lameta Formation in the Phutlibaori area and interpreted the Maastrichtian coastline(Fig.1).The Lameta Formation of the Phutlibaori area consists of friable,medium-to coarse-grained and well-sorted glauconitic sandstone(Figs.2 and 3a).The lower part of the section is a large-scale trough cross-stratified glauconitic sandstone.Individual co-sets of crossstratified beds measure up to 1 m in height.The crossstratified beds show bimodal palaeocurrent direction along ENE—WSW direction in places.The upper part of the section exhibits small-scale cross-stratification,wave ripples and planar lamination(Figs.2 and 3b).Sandstone of the Lameta Formation around Phutlibaori comprises quartz(～50%),feldspar(～25%)and bioclasts(～25%).The sandstones are classified as bioclasts-rich arkose(Bansal,2017).Glauconite content of thesediment,originating from K-feldspars is～20%.Quartz grains are rounded to sub-rounded,moderately well sorted and exhibit mostly point contact and occasionally straight contact.The sandstone exhibits extensive replacement of framework grains by calcite.Mediumto coarse-grained,clear calcite frequently replaces feldspar and glauconite grains,and also occupies the pore spaces(Fig.4c).The studied section contains abundant bivalves(oyster),gastropods,shark teeth,and fossilized wood logs.

Majorelement composition of glauconite is important to study the origin and evolution of glauconite.Electron probe micro-analysis(EPMA)data of glauconites are provided in Table 3.All elemental determinations were made on an anion equivalent basis to the structural formulae per O10(OH)2.All analyses have been normalized to 100 wt%on an anhydrous basis for different cross-plots.The K2O content varies from 5.51%to 8.29%in fully-evolved glauconite and from 7.04%to 7.90%for incipient variety in feldspar grains(Table 3).The K2O content of the glauconite suggests “evolved” to “highly-evolved” stage of maturation(Amorosi,1997;Odin and Matter,1981).The TFe2O3content of glauconite varies from 12.56%to 18.90%(Table 3).The MgO content of glauconite varies from 3.47%to 5.14%.The CaO content of all varieties of glauconites is negligible(av.0.50%).The SiO2content of glauconites varies from 48.98%to 55.73%,while the Al2O3content varies from 7.96%to 14.11%.

3. Methods

Detailed bed-by-bed analysis of exposures of the Lameta Formation in Phutlibaori area was carried out to prepare a graphic log with precise sample positions(Fig.2).Petrographic investigations were carried out using Leica DM 4500P polarizing microscope attached to a Leica DFC420 camera.The rock samples were soaked in water,treated with anhydrous Na2CO3powder and H2O2solution,and kept on a hot plate for 15—20 min,followed by cooling,washing and drying of the mixture to separate the glauconite pellets for geochemical and mineralogical analyses. Glauconite grains were concentrated using Franz magnetic separator(LB-1)with 15°slope and 15°lateral tilt and 1.5—1.8 A current at Department of Earth Sciences,Indian Institute of Technology Bombay.Glauconite pellets were finally hand-picked using Zeiss Stemi 2000 stereo zoom microscope.The powdered samples were scanned from 4°to 30°with a step size of 0.026°2θ,with a scan speed of 96 s/step,using nickel filter copper radiation in an Empyrean X-Ray Diffractometer with Pixel 3D detector at Department of Earth Sciences,Indian Institute of Technology Bombay.The samples were scanned each time under the same instrumental settings after airdrying,ethylene glycol treatment(100°C for 1 h)to evaluate the number of expandable layers and finally after heating at 490°C for 2 h to investigate if the hydroxides are extraneous to the glauconite structures.Mössbauer spectra of two powdered glauconite samples were measured to calculate the Fe2+/Fe3+ratio for structural analysis at Solid State Physics Division,Bhabha Atomic Research Centre Mumbai.Aγ-raysource of57Co in Rh matrix at room temperature was used and α-Fe absorber was used at room temperature to calibrate the Doppler velocity V and also as the standard for the isomer shift(IS).The major element geochemistry of the green pellets and substrates were investigated in 5 thin sections on 38 points using a Cameca SX 5 Electron Probe Micro Analyzer at Department of Earth Sciences,Indian Institute of Technology Bombay,with accelerating voltage 15 kV,specimen current of 40 nA and beam diameter of 1 μm(peak:10—20 s and background counting:5—10 s).Minerals as well as synthetically developed phases were used as standards.Duplicate analysis of individual points records analytical error of less than 1%.Concentrations of REE were determined using Thermo Fisher Scientific,Germany(Element XR)at Thermo Fisher Lab in Mumbai.About 25 mg of cleaned glauconite pellets were precisely weighed and dissolved in a mixture of～2.5 ml of HF—HNO3(2:1)in teflon bombs for REE analysis.The solution was kept in an ultrasonic bath for 45 min,evaporated and dried down.The residue was treated with concentrated 8N HNO3and evaporated.The same step was repeated thrice before diluting the sample with 25 ml of 1N HNO3.Ruthenium(Ru)was added as internal standard to all samples and standards to monitor the instrumental drift induced during analysis.USGS geochemical reference standards(SCo-1,SCo-2,SBC-1)were used to assess the accuracy of the analyses.

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4. Results

4.1. Mode of occurrence of glauconite

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4.2. Mineralogy and textural analysis of glauconite pellets

XRD peaks distinguish glauconite from other clay minerals and provide useful insights regarding the stage of glauconite maturation corresponding to the expandable layers.The air-dried samples of the glauconite pellets exhibit the prominent basal reflection(001)at 10.0poorly developed(020)reflection at 4.5and(003)reflection at 3.3(Fig.6).Theand(112)reflections are absent in these samples. The peaks are unmoved after glycol treatment and heating at 400°C indicating minimal inter-stratification between expandable and non-expandable layers(Thompson and Hower,1975).Peaks appear sharp and intense with narrow base in all three modes of sample scanning.A minor peak of illite at 5.0 coexists in all modes of scanning(Fig.6).The prominent basal reflection at 10.0 and the presence of(020)and(003)reflection at 4.5 and 3.3 are characteristics of glauconite(Odin and Matter,1981).Poorly-developed peak at 4.5 indicates disordered nature of the lattice(Burst,1958b).Narrow and symmetric peaks further support the interpretation.The absence ofand(112)reflections indicate a “highly-evolved” to “evolved” nature of the glauconite containing approximately 10%expandable layers,corresponding to～7.5%K2O content(Odom,1984).Odin and Matter(1981)classified glauconite into four types:(i)2%—4%for the nascent,(ii)4%—6%for the slightly-evolved,(iii)6%—8%for the evolved,and(iv)＞8%for the highly-evolved.

Field emission gun-scanning electron microscopy(FEG-SEM)study of glauconite exhibits well-developed,slightly-sinuous and sub-parallel lamellae(Fig.7).The lamellar structure of the glauconite further corroborates the “highly-evolved” nature of glauconite(Odin and Matter,1981;Wigley and Compton,2007).

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4.3. Structural analysis of glauconite using Mössbauer spectroscopy

Mössbauer spectra of glauconites in the Lameta Formation exhibit three doublets.Doublets A and C with isomer shift(δ)values of 0.37—0.42 mm/s corresponds to ferric ions,while doublet B(δ =1.06—1.13 mm/s)indicates ferrous ions(Table 2;Fig.8).

1)Authigenic glauconite of the Lameta Formation formed in an estuarine depositional environment.

4.4. Major element composition of glauconite

The presence of shark teeth, oyster and wood logs in the Lameta Formation around Phutlibaori indicates a marginal marine depositional setting.Tandon(2000)considered an E—W-oriented estuarine channel origin of the Lameta Formation in the study area.The dominantly aggrading,well-sorted sandstones with largescale cross-stratifications,exhibiting bi-directional palaeocurrent as well as fossil assemblage indicate an estuarine depositional environment.Presence of abundant thick-shelled bivalves including oysters attests to the estuarine origin(Fig.3c).

Glauconite is defined as Fe-rich dioctahedral mica with tetrahedral Al(or Fe3+)usually greater than 0.2 atoms per formula unit and octahedral R3+greater than 1.2 atoms(Bailey,1980).The tetrahedral charge of glauconite in the Lameta Formation varies from 0.17 to 0.32 atoms per formula unit whereas the octahedral R3+varies from 1.32 to 1.54 atoms per formula unit(Table 4).The tetrahedral charges of a few glauconites,do not fully comply with the glauconite composition prescribed by the Association Internationale Pour I'Etude des Argiles(AIPEA).We therefore provide the glauconite composition in a cross-plot of 4M+/Si(M+=interlayered cations)vs.(Fe octahedral)/(sum of octahedral charge)(cf.Meunier and ElAlbani,2007)(Fig.9).All data points plot within the field of glauconite.The average formula of the glauconites is as follows:

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Glauconites in the Lameta Formation contain high K,high Si,high Mg,high Al and moderate Fe.Most of the glauconite datum plots fall in the field of“glauconitic minerals”in a cross-plot of K2O and TFe2O3(Fig.10).A few data of glauconites,however,plot in the field of“compositional gap” of Odin and Matter(1981).An Al2O3versus TFe2O3cross-plot exhibits negative correlation(r2=0.9)(Fig.11a).The data indicate substitution of Al3+ions by Fe3+ions in the octahedral site during the course of glauconitization(Amorosi et al.,2007;Banerjee et al.,2008,2012a,2012b,2015,2016b;Bansal et al.,2017;Bornhold and Giresse,1985;Chang et al.,2008;Dasgupta et al.,1990;Eder et al.,2007;Odin and Matter,1981;Sánchez-Navas et al.,2008;Tang et al.,2017;Velde,1985).The relationship between K2O and Al2O3content of glauconite exhibits moderate negative correlation(r2=0.7)(Fig.11b).The plot suggests simultaneous addition of K in the interlayer with Al3+—Fe3+substitution in the glauconite structure.K2O exhibits moderate negative correlation with SiO2(r2=0.7),implying that the release of Si as K is added into glauconite structure(Fig.11c).K2O versus MgO cross-plot exhibits no correlation(Fig.11d).Thesecross-plots suggest that during the course of evolution,K and Fe are added while Al and Si are removed from the glauconite structure.The Mg content of glauconite is independent of stage of glauconite evolution.Fixation of K in the interlayer sites is synchronous with Al3+—Fe3+substitution in the octahedral site.

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4.5. REE chemistry of glauconite and its implications

REE concentrations and patterns are useful in interpreting their relative inputs from seawater and/or substrate.Further,the Ceanomaly(Ce/Ce＊)values can provide useful insight in understanding the redox conditions.REE concentrations of six glauconite pellets were carried out(Table 5).Glauconites in the Lameta Formation show a moderate variation of REE(i.e.,a minimum of 148 ppm,a maximum of 528 ppm,and an average of 319 ppm).LREE concentrations are much higher(av.289 ppm)than HREE(av.30 ppm).

Chondrite-normalized patterns reveal weak LREE/HREE fractionation(8.17—12.48)and exhibit rare negative(Eu/Eu＊=0.17—0.18)or no Eu anomaly(Fig.12).The strong HREE depletion in chondritenormalized patterns suggests that∑REE is related to the presence of tiny relics of K-feldspar substrate in the glauconite.Post Archaean Sedimentary Shale(PASS)-normalized patternsare “hat-shaped”,exhibiting strong HREE depletion and MREE enrichment(Fig.13).The REE patterns of glauconite indicate the authigenic origin of glauconites as reported for other marine authigenic minerals(Banerjee et al.,2012a,2012b;Jarrar et al.,2000).All glauconites bear upper crustal signatures in a cross-plot of Yvs.La(Li et al.,2017;Zhao et al.,2013)(Fig.14).

Glauconite mainly occurs as three different forms,i.e.,linear stringers within cleavages and fractures of feldspar,along peripheries of feldspars,and as pellets(Figs.4 and 5).The linear and interconnected stringers of glauconite extend upto 250 μm longand 50 μm wide.In places,glauconite completely replaces the K-feldspar grain,referred to as fully-evolved glauconite pellets.The incipiently-formed glauconite pellets often leave traces of K-feldspar.Fully-evolved glauconite pellets are mostlyovoid,elongated.The longaxis of the elongated pellets ranges from 250 μm to 300 μm.Occasionally,the pellets are perfectly rounded,varying in diameter from 100μmto150μm.The glauconite pellets are intact in nature and exhibit light green color under plane-polarized light.Under cross-polarized light,they exhibit high interference color ranging from third-order green to dark green color.The texture of glauconites appears pitted due to the random arrangement of micro-platelets with pinpoint extinction.Most glauconite pellets display deeply penetrating fractures originating at the periphery and taper toward the center.Feldspars as well as glauconite pellets are replaced extensively by calcite. Nearly-complete replacement of glauconite is often marked by relicts of glauconite completely surrounded by calcite cements(Fig.4c).Calcite cementation possibly formed in a shallow burial condition after the formation of glauconite.X-ray mapping clearly distinguishes glauconite forming within cleavages and peripheries of feldspar grains by high concentrations of K,Fe and Mg,and moderate concentrations of Al and Si(Fig.5).Textural evidences confirm that glauconite forms mainly by the replacement of K-feldspars.Incipient glauconite forms along cleavage and fractures of K-feldspars as small blebs and streaks within the feldspar grains(Fig.4a).Subsequently it grows as linear and interconnected stringers of glauconite till the K-feldspar is completely replaced.

4.6. Palaeoredox of glauconite

True Ce anomalies of the samples were calculated using the method of Bau and Dulski(1996).The Pr/Pr＊ratio was used to evaluate the effect of La abundance in four samples(P-1,P-3,P-5 and P-6),as the other two samples(P-2 and P-8)show anomalously high Pr values misleading the true Ce anomaly values(Table 5).The former group of samples plot in and around IIIb field in the cross-plot of Ce anomaly vs.Pr/Pr＊(Fig.15).The relationship between Ce anomaly and Pr/Pr＊indicates true negative Ce anomaly(cf.Bau and Dulski,1996,Fig.15).All true Ce anomaly values plot close to the oxic—anoxic boundary in a cross-plot between Ce anomaly and Nd concentration(Wright et al.,1987)(Fig.16).The logarithmic value of the true negative Ce anomaly varies from-0.07 to 0.04,representing suboxic depositional conditions(Elder field and Pagett,1986;Wright et al.,1987)(Fig.16).Further,the average of all glauconites provides negative Mn redox potential(Mn＊)values(-0.85)indicating suboxic conditions(Bellanca et al.,1996;Machhour et al.,1994),since Mn has a tendency to incorporate under more oxygenated conditions above the redox boundary.Nd concentrations of the glauconites ranging from 27.67 ppm to 95.84 ppm indicate moderate sedimentation rates(cf.Wright et al.,1987,Fig.16).

5. Discussion

Authigenic glauconites have been reported from estuarine depositional conditions in a few studies(Banerjee et al.,2015;Chafetz and Reid,2000;Dasgupta et al.,1990).However,the influence of depositional conditions on glauconite composition has not been discussed before.The origin of glauconite is usually explained by three common theories,i.e.,verdissement,layer lattice and replacement.The“verdissement theory” (Odin and Matter,1981)involves precipitation of initial “glauconitic smectite”within the pores of bioclasts and faecal pellets,accompanied by continuous dissolution and recrystallization of the substrate.The incipient glauconitic smectite precipitates evolve to glauconitic mica as K2O content increases at a constant TFe2O3content(Fig.17).The “layer lattice theory” (Burst,1958a,1958b;Hower,1961)involves the transformation of degraded layer lattice silicates to glauconite with simultaneous increase of K2O and TFe2O3content(Fig.17).Textural evidences indicate pseudomorphic replacement of K-feldspars by glauconite in the Lameta Formation(see also Banerjee et al.,2015;Bansal et al.,2017;Dasgupta et al.,1990).The K2O content of the incipient variety is at least 7%.The compositional overlap between incipient and evolved varieties indicates that the K2O content is independent of the stage of glauconitization.The high K2O contents in both incipient and fully-evolved varieties reflect derivation of K+from the K-feldspar substrate.

The formation of glauconite within K-feldspar grains have been addressed before(Banerjee et al.,2008,2015;Bansal et al.,2017;Chattoraj et al.,2009;Dasgupta et al.,1990).The absence of broken pellets and the presence of deeply-penetrating fractures indicate the autochthonous origin of glauconite (cf.Bandopadhyay,2007;Banerjee et al.,2008,2016b;Deb and Fukuoka,1998).Autochthonous glauconite has been reported from estuarine/shallow marine depositional settings(Banerjeeet al.,2015;Chafetzand Reid,2000;Dasgupta et al.,1990).Although modern glauconites are reported abundantly from shelf region(200—300 m),Banerjeeet al.(2016a)recently reported that ancient glauconite formed in varying depositional environments ranging from deep marine(Baldermann et al.,2012)to shallow marine(Banerjee et al.,2012a;Bansal et al.,2017),lagoonal(Banerjee et al.,2012b),estuarine and tidal flats(Dasgupta et al.,1990;Huggett and Gale,1997)and inner to outer shelf(Banerjee et al.,2008,2016b;Chattoraj et al.,2009;Kelly and Webb,1999).The origin of glauconite in shallow marine depositional environments possibly involves different seawater composition and sediment accumulation rates than the present-day seas(Chafetz and Reid,2000).Shelf-originated glauconites form at sediment—water interface in a low energy environment where rate of sedimentation is considerably slow.However,Chafetz and Reid(2000)argued that glauconites within the Riley Formation and Wilberns Formation(upper Cambrian,southwestern United States)formed in very shallow-marine depositional conditions(from 1 m to 5 m)at normal sedimentation rates.Occurrence of glauconite within cross-stratified sandstone beds in the Lameta Formation indicates high-energy conditions;while Nd concentrations of the glauconites,ranging from 27.67 ppm to 95.84 ppm,indicate a moderate sedimentation rate(cf.Wright et al.,1987,Fig.16).

The compositional evolution of glauconite in the Lameta Formation is comparable to those reported in Precambrian varieties(Dasgupta et al.,1990;Ivanovskaya et al.,2006;Sarkar et al.,2014;see other examples in Fig.17).Precambrian glauconites form in shallow marine arkosic to sub-arkosic sandstones(Banerjee et al.,2016a).The Precambrian glauconites are distinguished by their chemical composition,containing high K2O,Al2O3,MgO,and low-to-moderate TFe2O3contents.Most Phanerozoic glauconites exhibit low-to-high K2O,moderate MgO,Al2O3,and high TFe2O3contents.The compositional evolution of these Phanerozoic glauconites relates their origin to either“verdissement” or“layer lattice” theories(Fig.17).Precambrian glauconites invariably consist of a high K2O content,related to the replacement of K-feldspar substrate(Banerjee et al.,2008,2016a).A high K2O content of glauconite,exceeding 7.5%,indicates mega-condensed section in the Phanerozoic(Amorosi,2013).However,the high K2O content of glauconite in the Lameta Formation corresponds to the K-feldspar substrate,and is unrelated to significant stratigraphic condensation.

在可持续发展政策不断推进的过程中，我国对环境保护的重视程度在不断深化。但是在实际工程中，部分能源企业的环保意识尚未形成，措施的落实力度有待提升。对于地方监督和管理部门来说，主要负责管理环境保护，进一步加剧了环境污染程度，也没有将监督管理部门对环境保护的责任充分发挥出来。

The mineral chemistry of glauconite is highly sensitive to local micro-environmental conditions(El Albani et al.,2005).The K2O content of the fullyevolved glauconite varies from 5.51%to 8.29%,while the same varies from 7.04%to 7.90%within the incipient variety(Table 3).This anomaly may be explained by the decrease in the K+ion activity by freshwater input in local micro-environments within glauconite.El Albani et al.(2005)recorded similar decrease in K2O contents of glauconite related to freshwater input in a lagoonal environment.

The MgO content of glauconite in the Lameta Formation is higher(av.4.18%)than those reported in other occurrences(see Banerjee et al.,2016b;Bansal et al.,2017).The high MgO content of the glauconites is possibly related to contemporaneous basaltic volcanism of Deccan Traps.The TFe2O3contents of these glauconites vary from 12.56%to 18.90%.The amount of TFe2O3content depends on the availability of Fe and redox conditions of the depositional environments(Banerjee et al.,2016a;El Albani et al.,2005).Seawater contains negligible Fe and therefore it is unlikely to contribute significant Fe to the glauconite.Fe and Mn significantly fractionates across the redox boundary.While Fe tends to be fixed under reducing conditions,Mn is incorporated more under oxidizing conditions(Bellanca et al.,1996).Mn redox potential(Mn＊)is calculated as log[(Mn sample/Mn shale)/(Fe sample/Fe shale)](cf.Bellanca et al.,1996;Machhour et al.,1994).The glauconites of the Lameta Formation exhibit negative Mn＊values(av.-0.85).The average negative Mn＊values support the formation of glauconite under suboxic conditions(Bellanca et al.,1996;Machhour et al.,1994).Cerium(Ce)is another potential indicator of palaeoredox condition.It fractionates under oxidizing conditions above the redox boundary.According to Wright et al.(1987),the negative values of Ce anomaly below-0.10 indicate oxic conditions.Ce anomaly values of glauconites in the Lameta Formation plot close to the oxic—anoxic boundary in a cross-plot between Ce anomaly and Nd concentration(Wright et al.,1987),indicating a suboxic depositional condition(Fig.16).The suboxic depositional condition restricted the mobility of Fe ions into glauconite structure and resulted in a moderate TFe2O3content(Banerjee et al.,2016a).

6. Conclusions

The major conclusions of this study of glauconite are as follows:

有邻居听到阿里的号声，跑了过来。最先来的是细婆。细婆端了一碗热干面，大声说：“阿里，看，细婆给你送热干面来了。”

The ΔEQ has a lower value for doublet A(0.40—0.42 mm/s)than for doublet C(1.07—1.22 mm/s).Therefore,doublet A is assigned to ferric ions to cis M(2)position,and doublet C is assigned to ferric ions to trans M(1)position.Doublet B belongs to ferrous ions and has a higher ΔEQ value of 2.21—2.45 mm/s,corresponding to trans M(1)position in octahedral site(Hogg and Meads,1970;Kotlickiet al.,1981;McConchieet al.,1979;Rolf et al.,1977).The Fe2+/Fe3+ratio of glauconite was calculated by taking into consideration the χ2 value( fitting parameter)and the relative area(under curve)of the component belonging to the cationic composition of the octahedral sheets.The Fe2+/Fe3+ratio of 0.15,obtained by Mössbauer spectroscopic study of glauconite,was used for calculation of octahedral and tetrahedral charge as well as the structural formula of glauconites.Mössbauer study confirms the exact allocation of total Fe in tetrahedral and octahedral sites and provides the general formula of glauconite(provided in next section).

2)The glauconite in the Lameta Formation is characterized by high K2O,high Si2O,high MgO,high Al2O3 and moderate Fe2O3.

美国协作暑期图书馆项目（Collaborative Summer Library Program，简称为CSLP）始于1987年，是一个由各州共同组成的联盟，共同为儿童提供高质量的暑期阅读计划材料，以最低的成本为公共图书馆服务。目前CSLP拥有来自美国全部50个州的代表，包括哥伦比亚特区、美属萨摩亚、百慕大等地区的代表也加入其中。虽然是一个公益性组织，但CSLP具有严格的组织体系，有董事会和各种委员会。

3)The consistently-high K2O content and textural evidences indicate pseudomorphic replacement of K-feldspars by glauconite in the Lameta Formation.

4)The compositional evolution of glauconite in the Lameta Formation is comparable to those observed in many Precambrian varieties.

5)Ce anomaly values and Mn＊values indicate suboxic depositional conditions.The mobility of Fe ions is reduced during the glauconitization,resulting in moderate TFe2O3contents.

6)The “hat-shape” of the PASS-normalized-REE patterns of glauconite indicates the authigenic origin of glauconites.The REE content in glauconite derives from relicts of K-feldspar substrate.

Acknowledgements

Authors are indebted to their host institutes for infrastructure facilities.Santanu Banerjee is thankful to Ministry of Mines,Government of India for financial support through grant F No.14/77/2015-Met.IV.Authors thank S.C.Patel and Javed M.Shaikh for providing analytical support at the DSTIITB National facility for EPMA,Department of Earth Sciences,Indian Institute of Technology Bombay.Authors also thank S.S.Meena of Bhabha Atomic Research Centre for Mössbauer spectroscopic study of glauconite.

从目前的研究情况来看，不论国内还是国外，对于水在终端使用过程中的能耗特征都缺乏深入、全面的研究，而这一环节的能源强度实际上超过了其他所有环节的能源强度，在这一环节节约用水将有可能以最小的成本带来最大的节水节能效应，这也是需求侧管理思想的核心。因此，水系统水—能关系未来的研究重点应该放在水资源的终端消费领域，探讨家庭、行业节水与节能的相互关系，从而通过需水管理达到水资源和能源的可持续利用，促进城市节能减排与可持续发展。

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