Structural changes i..

13 Pages·2016·2.87 MB·English

by  Martina Havelcová

JournalofEnvironmentalRadioactivity158-159(2016)89e101
ContentslistsavailableatScienceDirect
Journal of Environmental Radioactivity
journal homepage: www.elsevier.com/locate/jenvrad
Structural changes in amber due to uranium mineralization
Martina Havelcova(cid:1)a,*, Vladimír Machovi(cid:3)c a,b, Ji(cid:3)rí Mizera c,a, Ivana Sýkorova(cid:1)a,
Milo(cid:3)s Rene(cid:1) a, Lenka Borecka(cid:1) a, Ladislav Lap(cid:3)ca(cid:1)k b, Olga Bi(cid:3)ca(cid:1)kova(cid:1)a, Old(cid:3)rich Jane(cid:3)cek d,
Zdene(cid:3)k Dvo(cid:3)ra(cid:1)k d
aInstituteofRockStructureandMechanics,ASCR,VHole(cid:3)sovi(cid:3)cka(cid:1)ch41,18209Praha8,CzechRepublic
bInstituteofChemicalTechnologyPrague,Technicka(cid:1)5,16628Praha6,CzechRepublic
cNuclearPhysicsInstitute,ASCR,Hlavní130,25068R(cid:3)e(cid:3)z,CzechRepublic
dSevero(cid:3)cesk(cid:1)edoly,a.s.,DolyBílina(NorthBohemianMines,BílinaMines),5.kv(cid:3)etna213,41829Bílina,CzechRepublic
a r t i c l e i n f o a b s t r a c t
Articlehistory: The presence of uranium, with a bulk mass fraction of about 1.5 wt% and radiolytic alterations are a
Received18November2015 featureofCenomanianamberfromK(cid:3)ri(cid:3)zany,atthenortheasternedgeoftheNorthBohemianCretaceous
Receivedinrevisedform uraniumoredistrict.Poresandmicrocracksintheamberwerefilledwithamineraladmixture,mainlyin
30March2016
the form of Zr-Y-REE enriched uraninite. As a result of radiolytic alterations due to the presence of
Accepted4April2016 uranium,structuralchangeswereobservedintheK(cid:3)ri(cid:3)zanyamberincomparisonwithareferenceamber
fromNove(cid:1)Stra(cid:3)secíincentralBohemia;thiswasofsimilarageandbotanicaloriginbutdidnotcontain
elevated levels of uranium. Structural changes involved an increase in aromaticity due to dehydroar-
Keywords:
omatizationofaliphaticcyclichydrocarbons,lossofoxygenfunctionalgroups,anincreaseinthedegree
Fossilresin
Amber ofpolymerization,crosslinkingofCeCbonds,formationofathree-dimensionalhydrocarbonnetworkin
Uranium thebulkorganicmatrix,andcarbonizationoftheorganicmatrixaroundtheuraniniteinfill.
Radiolyticalteration ©2016ElsevierLtd.Allrightsreserved.
Micro-FTIR
Mapping
SEM/EDX
1. Introduction The radiolytic alteration of organic assemblages has been
studied by analysis of organic matter present in various forms
In organic geochemistry, the interaction of ionizing radiation (usuallyasbitumensandkerogens)andamountsinuraniumand
with natural organic matter is an interesting phenomenon that thoriumsedimentarydeposits(e.g.,Courtetal.,2006;K(cid:3)ríbeketal.,
should be studied for several reasons, and can be viewed from 1999; Landais,1996; McCreadyet al., 2003; Sange(cid:1)lyet al., 2007).
variousstandpoints.Theenergytransferredbyionizingradiationto Fixationofuraniumbycoal,andtheinfluenceofuraniumonthe
organicmattercaninduceacomplexseriesofreactionsgenerating structural transformation of coal organic matter, has also been
and altering organic matter in various environments. Vice versa, studied (e.g., Havelcova(cid:1) et al., 2014b; Meunier et al., 1990;
theorganicmatterplaysanimportantroleinthetransport,accu- Nakashima et al., 1984). The main alterations in organic matter,
mulation and hydrothermal mineralization of uranium and which take place in the presence of uranium, are oxidation,
thorium in sediments, and it is also a sensitive marker allowing biodegradation,radiolysis,andthermaldegradation.Complexation
characterization of the paleoenvironmental, geochemical, and andredox reactions are twomainprocesses involved in uranium
diagenetichistoryofsediments.Processingoforganicmatteralso oreformation,promotedbythepresenceoforganicmatter.During
takesplaceinextraterrestrialenvironmentssuchascometaryand thermaltreatment,solubleU(VI)species,includingorganicuranyl
interstellaricesandplanetaryatmospheres,andmusthaverepre- complexes, can be reduced to insoluble U(IV) species (Landais,
sentedanimportantprocessofprebioticorganicevolutiononthe 1996).
earlyEarth(Courtetal.,2006;Landais,1996). Court et al. (2006) summarized the effects of radiolytic alter-
ationoforganicmatter,asreportedpreviouslyintheliterature:i)
enrichmentin13C;ii)greateraromaticity;iii)decreaseddegreeof
alkylation of polyaromatic hydrocarbons; iv) decreased pyrolysis
* Correspondingauthor. andyieldsofsolventextracts;v)greaterstructuraldisorganisation;
E-mailaddress:[email protected](M.Havelcova(cid:1)).
http://dx.doi.org/10.1016/j.jenvrad.2016.04.004
0265-931X/©2016ElsevierLtd.Allrightsreserved.
90 M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101
vi) lower H/C and higher O/C ratios; vii) increased hardness and biologicalmatterthatisincorporatedintosediments.Inanaerobic
reflectance; viii) increased thermal maturity, as indicated by an environments,e.g.,duringformationofapeatswampandpartic-
elevated Rock-Eval peak pyrolysis temperature. Based on experi- ularlyduringcoalformation,theresinisconcentratedanditsmass
mental data obtained on a set of naturally occurring organic as- can increase. Despite chemical alteration during diagenesis, bio-
semblages, the authors further concluded that the radiolytic markers still have the characteristic basic skeletal structures of
modification of hydrocarbon complex mixtures proceeds via their precursors in natural resins, and can thus be used as che-
cleavage, aromatization and oxidation, and by transforming mosystematicmarkers(Langenheim,2003;Ottoetal.,2002).
aliphatichydrocarbonsintoaromatichydrocarbons.Inthepyrolysis Inthepresentwork,thestructureofasampleofuranium-rich
products of the complex hydrocarbon mixture, a decrease in the Cretaceous (Cenomanian) amber from K(cid:3)ri(cid:3)zany, at the north-
average size and degree of alkylation of polycyclic aromatic hy- easternedgeoftheNorthBohemianCretaceousuraniumoredis-
drocarbonscausedbyirradiation,aswellasenrichmentin13C,was trict, was studied using various techniques: elemental,
observed. Radiolysis of water produces hydroxyl radicals, whose micropetrographic,andthermalanalyses,opticalandelectronmi-
reactionsincreasethedegreeofoxidationduetotheformationof croscopy, infraredspectroscopyand microspectroscopy, gas chro-
phenols,aromaticketones,aldehydes,andcarboxylicacids(Court matography with mass spectroscopy detection (GC/MS), and
etal.,2006). analyticalpyrolysis(Py-GC/MS).AnambersampleofCenomanian
Radiolysis is a spatially localized process and thus the inter- agefromNove(cid:1)Stra(cid:3)secí,withalowuraniumcontent,wasanalysed
pretationofanalyticaldataobtainedinalargerorevenbulkrock asareferencesample.
sampleisdifficult.Theradiationdoseabsorbedbyorganicmatteris Thestudywasaimedatidentifyingandinterpretingchangesin
impartedonlytothemassofmaterialwithinreachoftheemitted the polymeric structure of fossil resins due to radiolytic and
particles, i.e., mainly alpha particles in the case of uranium and chemicalalterationsthatprobablyoccuredinthepresenceoflocal
thorium decay. Their effective range in organic matter, within uraniummineralization.
whichtheparticleshavesufficientenergytoalterthematerial,has
been estimated to be 50 mm (Sange(cid:1)lyet al., 2007). In coal, e.g., a 2. Experimental
localincreaseinthedegreeofcoalificationandiso-oranisotropic
haloesaroundmineralgrainsandalongcracksfilledwithminerals 2.1. Samplesandgeologicalsetting
istypicalforradiolyticalteration(Tayloretal.,1998).
Decayofuraniumandthoriumcaninduceradiolyticpolymeri- A sample of uranium-rich amber of Cretaceous (Cenomanian)
zationoflighthydrocarbonssuchasmethane,andtheformationof age(94e100Ma)fromtheK(cid:3)ri(cid:3)zanylocalityinthe Czech Republic
complexpolyaromatichydrocarbons(Courtetal.,2006).Through wasstudied.TheK(cid:3)ri(cid:3)zanyuraniumdepositislocatedatthenorth-
radiation-induced polymerization of liquid and/or gaseous pyrol- easternedgeoftheNorthBohemianCretaceousuraniumoredis-
ysates, thoriferous and uraniferous bitumen nodules in Phanero- trict(NBCUOD,Fig.1).Thedepositwasminedfrom1982to1990
zoicsandstoneswereformed.Inthese,alphaparticlescausedthe and was ranked among smaller uranium deposits in the North
rupture of bonds and formation of free radicals by removing Bohemianuraniumdistrict.Thetotalmineproductionoflow-grade
hydrogen,andsubsequentcrosslinkingasnewCeCbondsformeda uraniumore(0.07e0.1wt%U)was1108tofU;forcomparison,the
three-dimensionalnetworkofhydrocarbons.Themolecularweight totaluraniumproductioninNBCUODminedfrom1967to1996was
increased and the materials quickly became insoluble (McCready 28046t(Kafka,2003).
etal.,2003). Twoformations-lowerfreshwatercontinentalandupperma-
Thepresentworkis,toourknowledge,thefirstreportofura- rinesediments-formthefullydevelopedCenomaniansequence.
niummineralizationinafossilplant(tree)resin-amber.Theability The basement is formed by low metamorphosed metasediments
of some resins to fossilize and to be preserved in the geological (phyllites and quartzites) and small bodies of Upper Proterozoic
recordisafascinatingaspect.Themainprocessinfossilisationof and Upper Devonian granitic rocks. Freshwater sediments are
resins and formation of amber is polymerization of terpenoid developed in depressions of the paleorelief and consist of con-
compounds that form the general polymeric structure. Because glomerates,pebblytofine-grainedsandstones,andlacustrinesilt-
resin is a mixture of compounds, fossil resins are not completely stones.Alloftheserocksareoftenrichinorganicmatter(coalified
consistent heteropolymers. Moreover, some terpenoids are non- plant detritus). The sediments of marine Cenomanian cover the
polymerisable, and they stay protected in the fossilized polymer wholeareaofNBCUOD.ThebasalpartofthemarineCenomanian
structure.Polymerizabilitydependsonthemolecularstructureof sedimentsisformedbywashoutnon-graded,wave-cutandbeach
terpenoids. Mainly the conjugated diene in terpenoid acids (lab- sediments, and their upper part by shallow marine sandstones.
daneskeletaltype)enablespolymerizationand,hence,formation Uranium mineralization developed in the basal part of the Cen-
of amber. Other terpenes, for example, abietic and pimaric acids, omanianformation,andisdividedintofourorehorizonsaccording
themostabundantcomponentsinresinsofPinaceae,remaindueto to their stratigraphical positions: The A horizon occurs in the
theirskeletonbeingunpolymerized.Highpressure,heat,bacterial freshwaterstreamandlacustrinesandstones,themainBhorizon
processes,andthestrengthofmineralcrystallizationcauseoxygen occursatthebaseofmarineCenomanianinwash-out,fine-grained
deprivationanddisplacementofresinoussubstancesintocracksin sandstonesandsiltstones,andCandDhorizonsarefoundinfriable
the fossilized wood matter and beyond. Individual tree species sandstones and the uppermost Cenomanian fucoidal sandstones.
producedifferenttypesofresins;however,notalltypesofresins The main shapes of the ore bodies are plates and lenses, mostly
canfossilize.Thefreshnaturalresinmustberesistanttodecay.The horizontal. The area of the ore bodies exceeded their thickness,
resin,sealedandpreservedinrocks,changesitsstructureovertime varying from decimetres to several metres, by many fold. The
with the formation of complex compounds of higher molecular mineral assemblage and geochemical composition in the
weight and conversion of volatile and reactive components into sandstone-hosted infiltration-type uranium mineralization occur-
(cid:3)
stablecompounds.Thisleadstocuringoftheresin.Thisprocessis ring in NBCUOD is diversiform and unique (Cadek et al., 1975;
slow and depends on complex geological conditions, including Scharmetal.,1980;Smetanaetal.,2002;Sulovský,2005).Urani-
composition of the original resin. Resin can fossilize as either a nite, complex U-containing gels, hydrozircon, baddeleyite, and
precipitatedproductoftreebark,orinanon-excludedforminside UeTheCaphosphates(ningyoite,brockite)arethemaincarriersof
the tree. “Amber” is a term that refers to materials derived from uranium.InthewholeNBCUOD,fourmainmineraltypeshavebeen
M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101 91
Fig.1. SchematicgeologicalmapoftheCzechRepublicshowinglocationsofuraniumdepositsincludingthelocationoftheK(cid:3)ri(cid:3)zanyamber(afterK(cid:3)ríbek,1989;modified).Thenon-
uraniferoussite,Nove(cid:1)Stra(cid:3)secí,whereareferencelow-uraniumamberwassampled,isalsoshown.
recognised: uraninite-hydrozircon, uraninite, hydrozircon, and butalsoduetoanidenticalorverysimilarbotanicaloriginofboth
uraninite-ningyoite. A general feature of all uranium ore types is fossilresins(Havelcova(cid:1)etal.,2014a).Thesamplewasfoundinan
thepresenceofrareearthelements(REE)andY,bothasadmixtures operating surface mine, where Carboniferous refractory clays
in authigenic minerals (hydrozircon, uraninite, ningyoite, and belongingtotheKladnoFormationaremined.Theamberoccured
brockite) and as proper REE or Y minerals (crandallite group, within alayerof darkclays with plentiful charred plant remains,
chernovite-(Y), rhabdophane group, and synchysite) (Scharmova(cid:1) whichwereformedintheareaoflittoralpeat-bogswithabundant
andScharm,1994;Sulovský,2005). halophytic(salt-tolerant)vegetation.Itwaspresentintheformof
Theambersamplewasfoundinnon-graded,fine-tomedium- tinyspheresandcylinders(sizeof2e3mm,rarelyupto1.5cm),
grained sandstones with a high content of irregular shaped pale yellow (almost colourless) to yellow, and, after ageing for
quartz grains, sized 1e3 cm. These sandstones are part of basal severalmonths,changedtoabrown,partlytransparentcolour.
marine Cenomanian sediments (uranium ore horizon B). Amber
occurredinthesesandstonesasbigloaf-shapedbulbs,10e20cmin
2.2. Instrumentation
size. Freshly excavated amber had a honey-like, yellow, orange,
light brown or red-brown colour, and was translucent-to-
Theelementalorganiccompositionoftheambersampleswas
transparent, which changed after several months to a dark
determinedusingaFlashFA1112(ThermoFinnigan)CHNS/Omi-
brown,opaquecolour.
cro-analyzer.
As a reference, amber formed in roughly the same epoch and
Severalmajorandtraceelementswereassayedbyinstrumental
undersimilarconditions,butintheabsenceofuraniumminerali-
zation, a sample of the Cenomanian age from Nove(cid:1) Stra(cid:3)secí (see neutron activation analyses (INAA). Irradiations for INAA were
carriedoutintheLVR-15experimentalnuclearreactoroftheR(cid:3)e(cid:3)z
Fig.1) was analysed. This sample was chosen not only due to a
similarageandlocation,relativelyclosetoK(cid:3)ri(cid:3)zany(about100km), Research Centre within the CANAM infrastructure (project No.
LM2011019 of the MinistryofEducation,YouthandSports of the
92 M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101
Czech Republic). Detailed descriptions and discussions of the SpectralLibraryorwithliteraturedata(Philp,1985).
(cid:3)
analyticalprocedurescanbefoundin,e.g.,MizeraandRanda(2010)
(cid:3)
andRandaetal.(2007).Unfortunately,ahighuraniumcontentin
the K(cid:3)ri(cid:3)zanyamber hindered assaying major elements such as Al, 3. Results
Mg,Ca,andTiusingtheshorttimeirradiationmodeofINAA,and
even in the long time irradiation mode, determination of some 3.1. Micropetrographicandelementalanalyses
elementswashinderedbyinterferencefromtheneutron-induced
fissionofuranium. Petrographical characteristics (maceral composition) and the
Microchemicalanalysisusingenvironmentalscanningelectron basicorganicelemental(CHNSeO)compositionofthefossilresins
microscopy (ESEM-EDX) employed a Philips XL30 ESEM FEI elec- are presented inTable 1. The contents of several majorand trace
tronmicroscopeequippedwithelectrondetectors,SED(GSED)for elements,mainlycharacterizingthemineralphaseoftheresins,are
micromorphology and BSED (GBSED) for phase contrast, both in presentedinTable2.
highvacuumandenvironmentalmodes.Themicroprobeanalyses The K(cid:3)ri(cid:3)zany amber mainly contained resinite (maceral of lip-
ofuraninitewereperformedusingaCamecaSX-100microprobein tinitegroup)withremnantsofcoalifiedwoodtissuethathasbeen
theWDXmode. classified as huminite and its macerals - ungelified textinite and
Micropetrographyofamberwasstudiedonparticulatepolished gelified ulminitewith a random reflectance Rr ¼ 0.24% (Table 1).
sectionsusinganOlympusBX51andaCarlZeissAxioImagerM2m Large differences wereobserved in the morphologies and optical
microscopes for reflected light, and procedures according to the propertiesofbothresiniteandulminite,probablycausedbyuneven
standards of the International Organization for Standardization radiolyticalterations.Innormallight,resiniteisabrownmaterial
(ISO 7404), Sýkorova(cid:1) et al. (2005), and Taylor et al. (1998). The withahomogeneous,slightlyporoustofine-grainedtexture,witha
composition of liptinite macerals was checked in fluorescence reflectance value of about 0.10%. Around cracks filled with
modeaccordingtoTayloretal.(1998)andISO7404. uranium-bearing minerals, and in dispersed sub-microscopic in-
Thermogravimetricanddifferentialthermogravimetricanalyses termixtureswithuranium,resinitechangedtogreycolouredmat-
(TGA and DTG, respectively) employed a Perkin Elmer TGA 6 terwithareflectanceof0.17%,uptowhitehaloeswithreflectance
analyzer. The analyses were carried out under a nitrogen atmo- reaching0.35%(Fig.2A,C).Inbluelight,resinitehadabrightyellow
sphereataheatingrateof10(cid:1)Cmin(cid:3)1.Kineticdatawereevaluated fluorescence colour that diminished with increasing radiolytic
usingPerkinElmerPyris™software,version5.0. alteration and changed to dull brown or black in the haloes
Fourier transform infrared (FTIR) spectra of the bulk samples (Fig.2B).Brightzonesalsoappearedalongcracksinthehuminite.
were collected on a Nicolet 6700 FTIR spectrometer (Thermo Thereflectanceofalteredulminiteincreasedfrom0.24%to0.37%in
Nicolet Instruments Co.) with a N2 purging system. Spectrawere brighthaloesandzonesalongcracksandfissures(Fig.2D).
acquiredusingasinglereflectionATR(AttenuatedTotalReflection) A sample of fossil resin from Nove(cid:1) Stra(cid:3)secí was also mainly
SmartOrbit accessory equipped with a single bounce diamond resinite, with a rare admixture of huminite particles, named cor-
crystal(angleofincidence45(cid:1)).Eachsamplespectrumaveraged64 pohuminite(Table1andFig.3C).Resinite,withareflectancevalue
scans and the resolution was 2 cm(cid:3)1. The spectra were ratioed of0.15%,hadabrightyellowfluorescencecolour.Numerousdarker
againstasingle-beamspectrumofthecleanATRcrystalandcon- cracks and hems caused by weathering occured at the edges of
vertedintoabsorbanceunitsbyATRcorrection.Datawerecollected resinitegrains(alteredresiniteinTable1),whichrarelycontained
overawavenumberrange4000-400cm(cid:3)1. fine-grained inorganic material (Fig. 3A,B). Rare formations of
Micro-ATR FTIR analysis (ATR mapping) employed a Nicolet corpohuminite(Rr¼0.25%)wereidentifiedasarestofcorktissue
6700 spectrometer combined with a Thermo Continuum IR mi- hemmingresiniteformations(Fig.3C,D).
croscope. Thesystemisequippedwitha XeYeZmotorisedstage TheelementalcompositionoftheK(cid:3)ri(cid:3)zanyamber(Table2),be-
withincrementalstepsof1mm.Apolishedsectionwasplacedon sidestheanomalousenrichmentin U,alsoshowedhighlevelsof
themicroscopestageandtheareaofinvestigation(700(cid:4)500mm) otherelements,especiallyFeandZn.Comparedtotheamberfrom
wasselectedthrougha15(cid:4)objective.Spectrawereacquiredovera Nove(cid:1) Stra(cid:3)secí, most elements were substantially higher in the
wavenumberrangeof4000e650cm(cid:3)1,from64scans,ataspectral K(cid:3)ri(cid:3)zanyamber,probablyreflectingahighermineralcomponent.
resolutionof4cm(cid:3)1.AnATRgermaniumcrystaldirectlyconnected
totheobjectivewasused,resultingininvestigatedareasofabout
40(cid:4)40mm.Astepsizeof30(cid:4)20mmwasused(640pointswere 3.2. CompositionofuraniniteintheK(cid:3)ri(cid:3)zanyamber
measured). Data collection and post-run processing were carried
outusingNicoletOmnicAtlmsimagingsoftware. Some cracks occurring in the amber from K(cid:3)ri(cid:3)zany were filled
For GC/MS analysis, amber samples were sonicated with with uraninite (Fig. 4). Microprobe analysis shows that uraninite
dichloromethane.TheextractswereanalysedusingaTraceUltra- displayed anomalous enrichment in Zr (up to 4.97 wt% ZrO2, see
DSQ II (Thermo Scientific) instrument equipped with a capillary Table3).TheanomalousenrichmentinZrintheexaminedurani-
columnTR-5MS. The GC ovenwas heated from 37 (cid:1)C (3 min) to niteisuniqueincomparisonwithworldwideuraniniteoccurrences
100(cid:1)Catarateof10(cid:1)C/minandthento300(cid:1)C(8min)atarateof and ore deposits. This enrichment was highly correlated with
10(cid:1)C/min.Asaninternalcalibrationstandard,5-a(H)-androstane unique UeZr-REE mineralization occurring in NBCUOD (C(cid:3)adek
inisooctanewasused.TMAH-Py-GC/MSanalyseswereperformed et al., 1975; Scharm et al., 1980; Sulovský, 2005). Similar, but
using a CDS Pyroprobe 5150 pyrolysis unit (CDS Analytical) con- distinctly lower Zr concentrations were found in uraninite from
nected to the above GC/MS instrument. Samples of powdered partiallysimilarrolltypeuraniumdepositsontheColoradoPlateau
amber,togetherwith10mLofa25wt%aqueoussolutionofTMAH (upto0.93wt%ZrO2;ZhaoandEwing,2000).Zirconiumenriched
(tetramethylammonium hydroxide) for methylation trials, were uraninite also occurred in Egypt, in a hydrothermal ore deposit
heated at 610 (cid:1)C for 30 s. The Py-GC interface was kept at the associatedwithhigh-Kcalc-alkalinegranites(upto2.49wt%ZrO2;
maximumallowedtemperatureof300(cid:1)C.TheTR-5MScolumnwas Shahin,2014).LowtotalsofallanalysesofuraniniteintheK(cid:3)ri(cid:3)zany
usedandthetemperatureprogramofthecolumnswassetfrom35 amber (see Table 3) could be due to hydration and oxidation of
to300 (cid:1)C at a rate of 5 (cid:1)C/min. Identification of compounds was uraninite,similartoaninterpretationbyZhaoandEwing(2000)for
based on comparison of spectra with the NIST/EPA/NIH Mass uraninitefromtheColoradoPlateau.
M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101 93
Table1
Basicpetrographicandelementalcharacterizationofambersamples.
Sample Maceralcomposition Ca Ha Na Sa Oa H/Cb O/Cb SOMc
K(cid:3)ri(cid:3)zany Liptinite:96.5vol%(82.7vol%resinite-liptodetrinite-bituminite,13.8vol%alteredliptinite) 85.5 10.8 2.1 0.7 1.0 1.51 0.01 1.2
Huminite:3.5vol%(0.5vol%textinite,1.5vol%ulminite,
1.5vol%alteredulminite)
Nove(cid:1)Stra(cid:3)secí Liptinite:98.2vol%(92.0vol%resinite,6.2vol%alteredresinite) 76.7 10.1 1.9 0.1 11.2 1.58 0.11 9.8
Huminite:1.8vol%(corpohuminite)
a wt.%,drymatter.
b Atomicratio.
c SOM-solubleorganicmatter,wt.%.
Table2 CombustionoftheamberfromK(cid:3)ri(cid:3)zanystartedbelow100(cid:1)Cand
ElementalcompositionofambersamplesobtainedbyINAA(inmgkg(cid:3)1;n.d.-not the first significant weight loss was observed at 101 (cid:1)C, corre-
determined). spondingtolossofwateradsorbedinthepores.Themainpeakwas
Sample Na Sc Cr Fe Co Zn As Br Sb locatedat430(cid:1)C.SimilarvalueswerefoundbyRagazzietal.(2003)
K(cid:3)ri(cid:3)zany 189 1.42 104 25498 26.8 4054 360 41.6 11.9 inamberspecimensfromtheDolomites,Italy,ofmucholderage
Nove(cid:1)Stra(cid:3)secí 68.6 0.423 3.52 191 0.208 n.d. 5.38 1.23 0.131 (Triassic, ~225 Ma). Complete combustion of the sample was not
achieved and only 47 wt% was degraded at 500 (cid:1)C. On the other
Sample Sm Eu Tb Yb Hf Ta W Th U
hand,thecombustionprofileoftheNove(cid:1)Stra(cid:3)secíamberbeganat
K(cid:3)ri(cid:3)zany 461 0.437 3.90 15.4 9.68 0.548 188 4.23 14725 about 250 (cid:1)C and total combustion of the sample was achieved
Nove(cid:1)Stra(cid:3)secí 8.58 0.092 n.d. n.d. n.d. n.d. 146 n.d. 1.40
Fig.2. MicrographsofpolishedsectionsontheamberfromK(cid:3)ri(cid:3)zany.(A)Fissuresinunevenlyalteredresinitewithincreasedreflectancefrom0.12%to0.33%.(B)Yellowfluorescence
ofunalteredresiniteandbrowntodarkfluorescenceofalteredresinite.(C)Alteredmatteralongthecrackinresinitefilledwithminerals.(D)Alteredulminitewithincreased
reflectancefrom0.26%to0.37%inwhitezonesalongfissures.(Forinterpretationofthereferencestocolourinthisfigurelegend,thereaderisreferredtothewebversionofthis
article.)
3.3. TGA/DTGmeasurements below500(cid:1)C.Themainpeakindicatingamaximumrateofweight
losswasat422(cid:1)C,whichisalmostidenticaltothevalueof421(cid:1)C
Thermogravimetricandderivativethermogravimetricanalyses foundbyRagazzietal.(2003)inamberfromtheRaritanFormation,
(TGAandDTG,respectively)haverecentlybeenappliedinstudies NewJersey,USA,ofsimilarage(Turonian,94-90Ma)andelemental
offossilresinstoobservethedegreeofresinpolymerizationduring composition(C78.41wt%,H10.06wt%,O11.24wt%).
amberization (Rodgers and Currie, 1999; Ragazzi et al., 2003;
Trevisanietal.,2005;Cebulaketal.,2003).
3.4. Infraredspectroscopy
ResultsofTGA/DTGmeasurementscarriedoutwiththeamber
samples from K(cid:3)ri(cid:3)zany and Nove(cid:1) Stra(cid:3)secí are illustrated in Fig. 5.
Althoughthechemicalstructureofamberisquitecomplexand
94 M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101
Fig.3. MicrographsofpolishedsectionsontheamberfromNove(cid:1)Stra(cid:3)secí.(A)Resinite(R¼0.15%)withcracks.(B)Brightyellowfluorescenceofresinitewithdarkercracksand
hemsontheedge.(C)Resiniteformationwithinternalcracksandcolouredreflexes,hemmedbyagreycorpohuminitenetwork.(D)Yellow-greenfluorescenceoftheresinite
formationwithadarkhemofcorpohuminite.(Forinterpretationofthereferencestocolourinthisfigurelegend,thereaderisreferredtothewebversionofthisarticle.)
Table3
Resultsofmicroprobeanalysesofuraninite(wt%)inlocations1,2,and3withina
crackintheamberfromK(cid:3)ri(cid:3)zany(seeFig.4),andcorrespondingcrystallochemical
formulae.
1 2wt.% 3 1 2apfua 3
UO2 77.43 85.22 76.40 U 1.63 1.64 1.62
ThO2 0.04 0.00 0.13 Si 0.02 0.01 0.02
SiO2 0.16 0.10 0.17 P 0.05 0.05 0.06
P2O5 0.62 0.72 0.77 Zr 0.23 0.21 0.20
ZrO2 4.89 4.97 4.25 Y 0.01 0.00 0.00
Y2O3 0.18 0.00 0.00 Ca 0.07 0.06 0.07
Ce2O3 0.01 0.03 0.00 Fe 0.03 0.05 0.04
La2O3 0.04 0.00 0.01 Mn 0.00 0.00 0.02
CaO 0.72 0.69 0.65 Ti 0.01 0.01 0.02
FeO 0.37 0.63 0.47
MnO 0.05 0.03 0.11
TiO2 0.08 0.22 0.34
PbO 0.02 0.17 0.10
Fig.4. BackscatteredelectronmicrographofacrackintheamberfromK(cid:3)ri(cid:3)zanyfilled Total 84.61 92.78 83.40
withuraninite.Thenumberedpointsindicatelocationswherethemicroprobeanalyses a Atomsperformulaunit(O¼4).
wasperformed(seetheresultsinTable3).
Both spectral methods were successfully applied in structural
diverse,therearespectralbandsintheirinfrared(IR)spectrathat
analysisofvalchovite,theCenomanianamberfromMoravia,Czech
are clearly distinguishable. These allow fast and non-destructive Republic(Streibletal.,1976;Va(cid:1)vra,1993;Jehli(cid:3)ckaetal.,2004).
characterizationofthedegreeofmaturationordegradationofan
TheIRspectraofbulkambersamplesareshowninFig.6.Both
ambersamplebasedondeterminationofoxygenfunctionalgroups
spectraweredominatedbybandsbelongingtotheanti-symmetric
and the relative abundance of aliphatic and aromatic structures andsymmetricstretchingvibrationsofthealiphaticCeHbondsof
(Becketal.,1964).RecentstudiesoftenreliedontheATRtechnique,
methyl,methylene,andmethinegroupsinthewavenumberregion
whichdoesnotrequirespecialsamplepreparationformeasuringIR 3000-2700cm(cid:3)1.Inthesecondderivativeofthespectra,sixbands
spectra. Also IR microspectroscopy is a suitable tool to assess
sotfrbuacntudrsalozfoanliapthioanticofanordgaarnoicmpahtiacssetsruucstinugretsh,eanredlactairvbeoanbyulngdroaunpces (wCeHr)e,~d2is8t6in5g(uCiHsh3a),b~le28a4t5a(bCoHu2t),~a2n9d58~2(8C2H53c),m~(cid:3)219(2C0H(2C).HT2h)e, ~b2a8n9d5s
(Sange(cid:1)lyetal.,2007).BesidesIRspectroscopy,Ramanspectroscopy oanfdbe1n3d7i5ngcmvi(cid:3)b1r.aTthioenpsroefseCnHc2eaonfdarCoHm3atgircosutpruscwtuerreesfwouansdinadtic1a4t5ed0
canbeutilizedforcharacterizationofnon-fluorescentfossilresins.
M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101 95
Fig.5. TGA(thickline)andDTG(thinline)curvesofambersamplesfromK(cid:3)ri(cid:3)zany(left)andNove(cid:1)Stra(cid:3)secí(right).
Fig.6. InfraredspectraoftheambersamplesfromK(cid:3)ri(cid:3)zany(upperspectrum)andNove(cid:1)Stra(cid:3)secí(lowerspectrum).
by quite insignificant bands of aromatic stretching vibrations at groups than the amber fromK(cid:3)ri(cid:3)zany. Bands at ~1740, ~1735, and
3060-3080 cm(cid:3)1, which overlapped with a stretching vibration 1709-1693 cm(cid:3)1 can be assigned to esters,ketones,and carboxyl
bandofanexomethylenegroup(vHeC¼C).Thestretchingvibrations groups, respectively. The stretching vibration bands of the CeO
of the aromatic ring C]C bond was observed at ~1600 cm(cid:3)1. It bondwerepositionedat1270e1200cm(cid:3)1inthecarboxylicacids.
followsfromcomparisonofspectraofbothambersamplesthatthe Thebandsat1180e1150cm(cid:3)1belongtoesters.Theabundanceof
K(cid:3)ri(cid:3)zanyambercontainedmorearomaticstructures.Thearomatic hydroxylgroupswasassessedfromtheintensitiesofthestretching
characterofthissamplewasalsoindicatedbyhigherintensitiesof vibrationbandsoftheOeHbondat3400-3300cm(cid:3)1,butsample
bandsassignedtoout-of-planevibrationsofaromaticCeHbondsat humidity contributed to absorption in this region of the spectra.
883, 813, 792, and 739 cm(cid:3)1. A low intensity band at 886 cm(cid:3)1, Humidityalsocontributedtoabsorptionat~1640cm(cid:3)1.
togetherwithashoulderat1644cm(cid:3)1intheNove(cid:1)Stra(cid:3)secíamber,
indicated a very low number of exocyclic double bonds in this
3.5. Infraredmicrospectroscopy
sample.
TheIRspectraalsoallowedanassessmentofoxygenfunctional
IR microspectroscopy was used to obtain information on
gbraonudpssoifnthbeotCh]amObbeornsdamatp~l1e7s0.C0ocmmp(cid:3)a1riinngththeiersItRrestpcehcitnrgavitibisractlieoanr structuralchangesoftheorganicmatterintheK(cid:3)ri(cid:3)zanyamberasa
function of the distance from uranium-containing mineral in-
thattheamberfromNove(cid:1)Stra(cid:3)secíhadahighercontentofcarboxyl
clusions. A suitable rectangular area in a polished section of the
96 M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101
amber, with dimensions 700 (cid:4) 500 mm, was chosen for infrared Table4.
microspectroscopy mapping. This area is depicted on the micro- ThechromatogramoftheNove(cid:1)Stra(cid:3)secíamberextractshowed
graph in Fig. 7 together with 640 measuring points. Cracks filled terpenesthatarenotstructurallyattachedtothepolymermatrix.
withmineralmattercontainingmainlyuraninitearevisibleclearly Majorcomponentsarediterpenoidsoftheabietaneclass,typicalfor
inthemicrograph. conifers.ResinsoffossilandextanttaxaofCupressaceaeandTax-
TheIRmicrospectrawereusedforcalculatinga2Dmapbased odiaceaecontainditerpenoidsoftheabietaneclass,andfrequently
on the band intensities of aliphatic CeH bonds of methylene/ alsophenolicabietanesandsomecharacteristicsesquiterpenoidsof
methyl groups at 2920 cm(cid:3)1 (Fig. 8). In the 2D map, spots with cedrane and cuparane classes (von Rudloff et al.,1980; Otto and
variousuraniumconcentrationsmeasuredbySEM/EDXhavebeen Wilde, 2001; Otto et al., 2002). Since phenolic abietane (ferrugi-
marked. Infrared microspectra scanned from individual spots are nol) and sesquiterpenoids associated with Cuppressaceae and
presentedinFig.9.Thedarkareasinthe2Dmaprepresentcracks Taxodiaceaearepresent(cuparene)intheNove(cid:1)Stra(cid:3)secíamber,its
filledwithhighuranium-containingmineralmatter,whichcauses origin from this group of conifers is likely. Cadinene-type com-
radiolyticalterationsintheamber.Inspotswithaverylowuranium pounds (dihydro-ar-curcumene, calamenene) are the most abun-
content, the microspectra had very intense bands of aliphatic dant sesquiterpenes, and indicatea classification of this amber
structures,andthebandintensityofaliphaticCeHbondsdecreased within Class II, derived from polymers of these bicyclic sesqui-
withincreasinguraniumconcentration,whiletherelativecontent terpenoids (Anderson et al., 1992; Langenheim, 2003). These
of aromatic C]C bonds and oxygen functional groups (RCOOH, compoundsare,however,widelydistributedamonghigherplants
RCOR0, RCOOR0, ROH) increased. A ternary diagram, presented in andtheyarenotsource-specific.Themonoterpenoidscamphorand
Fig.10, illustrates therelative abundanceofaliphaticCeH bonds, borneolwerealsodetected.Thesecompoundsarefoundinhigher
carbonylgroups,andaromaticC]Cbondsduetoradiolyticalter- amounts in resins of angiosperms, but also in lower amounts in
ation of the K(cid:3)ri(cid:3)zany amber. In construction of the diagram, in- resinsofgymnosperms.Monoterpenoidspredominateinthevol-
tensitiesofthebandsat2920,~1700,and~1600cm(cid:3)1,respectively, atile fraction of the natural resins of many conifers and are not
wereused.Itisobviousthattheincreaseinuraniummassfraction chemotaxonomicsourceindicators.
from 0.02 to 0.66 wt% is accompanied by a drastic decrease in In the extractof the K(cid:3)ri(cid:3)zanysample, the series of diterpenoid
aliphatic CeH bonds and a slight increase in carbonyl groups. At compounds revealed signs of alteration. These compounds are
higheruraniummassfractionsof12.5and28.0wt%,thealiphatic derivatives of abietane and pimarane precursors without conju-
CeHbondsandoxygenfunctionalgroupscompletelydisappeared. gated dienes, and thus non-polymerizable. Degradation of amber
was also indicated by the presence of an unresolved complex
mixture (UCM) in chromatograms. The UCM hump occurs when
3.6. GC/MSanalysis compoundscannotberesolvedandidentifiedbyGC.The UCMis
thoughttobecomposedofamixtureofconstitutionalisomers,and
IntheGC/MS(gaschromatography/massspectrometry)analysis linear, branched and cyclic hydrocarbons (Gough and Rowland,
of total extracts of the amber samples, mainly terpenes were 1990).
identified (Fig.11). They are diagenetic products (biomarkers) of
terpenoids, which are common constituents of resins of higher 3.7. TMAH-PyeGC/MSanalysis
plants. Concentrationsof theidentified compounds are shownin
Characterizationofamberanditsclassificationcanalsobecar-
ried out using TMAH-PyeGC/MS (tetramethylammonium
hydroxide-pyrolysis-gaschromatography/massspectrometry).This
methodisusedinordertoimprovepyrolyticanalysisofmaterials
that release polar functional groups. Free carboxylic groups are
methylatedtotheircorrespondingmethylestersinthepresenceof
TMAH, and separated and detected using GC/MS. The total ion
pyrogramsfromTMAH-PyeGC/MSanalysisofambersamplesare
shown in Fig.12. The identified peaks are listed in Table 5. The
pyrolysates contained terpenes, together with cycloalkanes and
cycloalkenes formed by defunctionalization and crosslinking of
CeC bonds in the three-dimensional hydrocarbon network.
Cycloalkanes and cycloalkenes, which are non-specific markers,
were also identified in pyrograms of both amber samples. A sig-
nificantUCMhumpcanbenoticedinthepyrogramoftheuranif-
erousK(cid:3)ri(cid:3)zanyamber,similartoitsextractchromatogram.
4. Discussion
Theelementalanalysisofafossilresin(amber)fromauranium
depositinK(cid:3)ri(cid:3)zany,atthenortheasternedgeoftheNorthBohemian
Cretaceousuraniumoredistrict(NBCUOD),revealedananomalous
enrichmentinuraniumofabout1.5wt%(seeTable2).Amberisnot
resistanttostructuralalterationbygeothermalprocesses,andthe
radiolyticalterationofamberduetoradiationemittedbytheura-
niumdecaychainmayhaveplayedauniqueroleinchangesinthe
compositionandstructureoftheuraniferousK(cid:3)ri(cid:3)zanyamber.These
Fig.7. MicrographofanareainapolishedsectionfromtheK(cid:3)ri(cid:3)zanyamberchosenfor changeshavebeenobservedincomparisonwithareferenceamber
infraredmicrospectroscopymapping. sampleofsimilarageandbotanicalorigin,butwithalowuranium
M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101 97
Fig.8. A2DbandintensitymapusedforquantificationofaliphaticCeHbondsbyinfraredmicrospectroscopyonapolishedsectionfromtheK(cid:3)ri(cid:3)zanyamber(arectanglemarkedin
Fig.7),withuraniumconcentrations(wt.%)inselectedspotsmeasuredbySEM/EDX.
Fig.9. InfraredmicrospectraobtainedonapolishedsectionfromtheK(cid:3)ri(cid:3)zanyamberinspotswithvariousuraniumconcentrations(seeFig.8;scannedarea30(cid:4)20mmineach
spot).
content-theamberfromNove(cid:1)Stra(cid:3)secí. aromatic character and lower content of carbonyl and carboxyl
Uraniumenrichmentandtheassociatedradiationaffectedthe groups than the amber from Nove(cid:1) Stra(cid:3)secí, which may point to
composition of the uraniferous amber by reducing the relative dehydroaromatizationandlossoftheoxygenfunctionalgroupsin
proportionofhydrogen,asindicatedmainlybytheH/Cratio,andin theuraniferoussample.Quitealowlevelofexocyclicdoublebonds
parallel,bydecreasingtheoxygenproportion(O/Cratio)inthebulk intheNove(cid:1)Stra(cid:3)secíamberisasimilarfindingtothatreportedfor
sample(seeTable1).AsimilareffectfortheH/Cratio,butnotfor Cenomanianfossil resins fromother partof the Czech Republic -
the O/Cratio, wasobservedforcoal orkerogen (Havelcov(cid:1)aetal., valchovite,neudorfite,andmuckite.TheseresinsalsolackedtheIR
2014b; Landais, 1996).This finding corresponds with results ob- bandsindicativeofexocyclicmethylenegroups(Streibletal.,1976),
tained in the bulk amber samples by infrared spectroscopy. The contrary to the IR spectra of the well-known Baltic amber of the
ATR-FTIRspectra(seeFig.6)showthattheK(cid:3)ri(cid:3)zanyamberhasmore Eocene-Oligoceneage(Grimaltetal.,1988).
98 M.Havelcova(cid:1)etal./JournalofEnvironmentalRadioactivity158-159(2016)89e101
possible zonal graphitization of the K(cid:3)ri(cid:3)zany uraniferous amber.
Strongcross-linkingoftheamberstructurewasconfirmedbyvery
lowyieldsofextractionwithdichloromethane(seeSOMinTable1).
The uranium distribution within the K(cid:3)ri(cid:3)zany amber was
generallynon-uniformandtheanomalousenrichmentwasnoted
mainly in cracks. Microprobe analysis identified the ZreY-REE-
enriched uraninite as the main mineral carrier of uranium (see
Fig.4andTable3),inagreementwithprevailingmineraltypesin
the whole NBCUOD. Micropetrographic evidence for radiolytic
alterationintheuraniferousamber(seeFig.2)wasindicatedbythe
morphologies and optical properties of resinite and ulminite.
Aroundtheuraninite-filledcracks,resinitechangedtowhitehaloes
withreflectancereaching0.35%,anditsbrightyellowfluorescence
diminishedanddarkenedinthehaloes.Brightzonesalsoappeared
along cracks in huminite. Radiolytic alteration of ulminite was
observedbyitsincreasedreflectanceinthehaloesandzonesalong
the cracks. The size of the observed haloes corresponded to the
Fig.10. Ternarydiagramdemonstratingchangesintherelativeabundanceofaliphatic estimatedeffectiverangeofabout50mm,withinwhichthealpha
tCheeHK(cid:3)brio(cid:3)znandys,acmarbbeorn.ylgroups,andaromaticC]Cbondsduetoradiolyticalterationof particles have sufficient energy to alter organic matter (Sange(cid:1)ly
et al., 2007). The Nove(cid:1) Stra(cid:3)secí amber (see Fig. 3) also contained
numerouscracksandhemsattheedgesofresinitegrains,whose
Changesinmolecularstructureofamberduetothepresenceof darkcolourindicatedweathering,inagreementwiththehighO/C
highlevels ofuraniumwere alsoindicated bythermogravimetric ratioandhighercontentofoxygen-containinggroupsinthebulk
analysis.At500(cid:1)C,lessthanhalfofthemassoftheK(cid:3)ri(cid:3)zanyamber sample.
wascombusted,whereastotalcombustionofthereferenceamber StructuralchangesoforganicmatterintheuraniferousK(cid:3)ri(cid:3)zany
from Nove(cid:1) Stra(cid:3)secí was achieved below this temperature (see amberasafunctionofthelocalcontentofuraniumwereobserved
Fig. 5). These data indicate a high degree of polymerization, and indetail(witha30mmresolution)byATR-FTIRmicrospectroscopy
Fig.11. TotalionchromatogramsofextractsofambersamplesfromK(cid:3)ri(cid:3)zany(top)andNove(cid:1)Stra(cid:3)secí(bottom).TheidentifiedcompoundsarelistedinTable4.Thenumbers
correspondtonumbersinTable4.