Sassen-1999-Thermogenic gas hydrates and hydro(2)

gas

R.Sassenetal./OrganicGeochemistry30(1999)485±497489

Fig.4.Exposedandundercutvein-?llinggashydratelayersatstationGCHYD-1,GC234site.Notescalebar.ventsfromthebrinepooltothewatercolumn.Thehydrocarbongeochemistryofthebrinepoolisdissimi-lartothatoftheBushHillandGC234sitesinthatbacterialmethanedominates(MacDonaldetal.,1990b).Gashydratehasnotbeendocumentedatthissite.

3.Samplesandmethods

Duringthe1995and1997divesoftheJohnsonSea-Link(JSL)researchsubmersible,themainhydro-carbonpoolsrelatedtogasventingandabundantgashydrateswithinchemosyntheticcommunities(ventgases,gashydrates,sedimentgases)weresampled.ThesamplingstrategyatBushHillandGC234wasintendedtoencompasszonesofmaximumpotentialimpactfromabundantgashydrates.Therefore,thegas-hydraterichzonesofourstudymaynotberepre-sentativeoftheentireexpanseofthechemosyntheticcommunitieswestudied,norofotherlow-temperaturecommunitieselsewhere.Eachgashydratesiteincludesmultipleexposuresofgashydrate,andforthisreason,speci?clocalitiesarede?nedforfuturereference.AttheBushHillsite,samplesofventgases,gashydrates,andassociatedsedimentswerecollectedatstationsidenti?edasBHHYD-1(Figs.2and3)andBHHYD-2;theGC234sitesampleswerecollectedatasinglestationidenti?edasGCHYD-1(Fig.4).Samplesoftubewormsedimentswereacquiredinthevicinityofgashydratelocalitiesatstationsde?nedasBHST-2(seeFig.2)andGCAT-2.Forpurposesofcomparisonwithasettinglackinggashydrate,samplesofventinggaswerecollectedattheGC233brinepoolatastationidenti?edasBPRN-1(Fig.5).WesampledfreegasnaturallyventingintothewatercolumnatBushHillandGC234,withinH0.5mofunderlyingmassivegashydratesatmounds.Thisinti-mateassociationsuggeststhattheventgasisrepresen-tativeofthehydrocarbonpoolfromwhichthegashydratecrystallized.Themechanicalarmofthesub-mersiblewasusedtoholdgas-tightLexantubes(30cminlengthand7.5cminsidediameter)overgasbubbletrainsuntiltheambientseawaterinthetubewasdis-placed.GasventingfromtheGC233brinepool

was

490R.Sassenetal./OrganicGeochemistry30(1999)485±497

Fig.5.Methanotrophicmusselbedsatedgeofdarkmethane-saturatedbrinesatstationBPRN-1,brinepoolsiteatGC233.Notescalebar.

collectedthesameway.Intactventgassampleswererecoveredattheseasurface,transferredtovacutainers,andfrozenatà208C(SassenandMacDonald,1997).SamplesofsolidgashydratewereacquiredatmoundˉanksatBushHillandGC234wheretheyoutcrop,orwherebestsituatedbeneathathinveneerofunderconsolidatedhemipelagicsediment.Themech-anicalarmoftheresearchsubmersibleallowedustocollectsolidgashydrate(SassenandMacDonald,1997).Aninvertedsteelcupwithsharpenededgeswasusedtochipfragmentsfromlargerhydratemasses,whichˉoatedupintothecup.Thecupandgashydrateweretransferredtoapressurevesselcontain-ingambientseawater.Aftersealing,thepressurevesselwasusedtotransportthegashydratesamplestotheseasurfaceatapproximateinsitupressureandtemperature.Discretegashydratewasdecomposedwithinthepressurevesselonthesurface,andtheresul-tantgaswastransferredtovacutainersandfrozenatà208C.Samplesofsediments(generallyrepresenting15±25cmsections)werecollectedfromcrestsofgashydratemounds(Fig.2)usingLexanpushcores30cminlengthand7.5cminsidediameter.Depthofcorepenetrationwasgenerallycontrolledbydirectcontactwiththeharduppersurfaceofmassivegashydrate.Sedimentsamplesfromthemoundswerethusinti-matelyassociatedwithgashydrate.Othersedimentsampleswerecollectedneartubewormsadjacenttogashydratemounds(Fig.2).Uponrecovery,sedimentsampleswerecannedwithsodiumazidebactericideandfrozenatà208C.AnalysesofgassamplesfocusedonC1±C5gaschro-matography,measurementofd13CanddDofmethane,andmeasurementsofd13ConC2±C5hydro-carbonsandCO2.Somedegassingofsedimentcoresamplesoccurredduringtheascentoftheresearchsub-mersible;C1±C5gasconcentrationsreportedinTable2shouldberegardedasminimums.Thed13Cvaluesarereportedaspartsperthousand(-)relativeto

the

R.Sassenetal./OrganicGeochemistry30(1999)485±497

491

Fig.pictheBHHYD-1(top)6.Diagramspropertiessummarizingand-2ofsampleventgasmolecular(bottom)andisoto-stations,andgasBushhydrateHill.

samplesatPeedeevaluesbelemnite(PDB)standard(20.2-);thedDoceanwaterarereported(SMOW)as-relativetothestandardmeanHewlett±PackardC±Cstandardgaseswere(2àseparated5-).

15hydrocarbonusingaactivatedturealumina5890gaschromatographusinganKnownprogrammedcolumnwerevolumesoffromauthentic100(18mtoF-180/100)tempera-hydrocarbon1608Cat32standards8C/min.Concentrationsusedtoidentifyppmofeachandhydrocarbonquantitatepeakisresponses.ofCtotalbyCsedimentvolume,andnormalizedexpressedaspercentin1±C5hydrocarbons.Analysesofd13CofC1HoustonhydrocarbongasesandCO±52wereperformedattheWoodlands,AreagraphTexas)ResearchusingaVarianCouncil3400(HARC;gaschromato-ThetographicwithcapillaryseparationaFinniganwasMATperformed252IRMS.Gaschroma-from508columnto2108C(25at50m),8C/min.temperatureonaAnalysisprogrammedPoraplotQof

methane

948076

9

3

C2

........457031253O1dCàà2222àààà+2à511000001100...........%C00000000000-n<<0C5.53C1-2dnà5%C22083302200-...........i0000000000011

287

5

C5

......66644631C-222222diàààààà4%C36272686800-...........n0001110010063180729

C4

........232232543C1-22222222dnàààààààà169663156004...........%C00021210100-i<92698894

C4........777776783C1-22222222diàààààààà%327163414915C...........1382716292211039557644

C.........356455556631C222222222dààààààààà%245664434611C...........24709262200111726072624C.........290899989931C232222222dàààààààààs

elp%194172177884mC...........50310253377a99878789799seta80307353350rD190697910060d12111112212ydChàààààààààààsa01925597435gC...........164223228845d3n1C44444444466adàààààààààààsagLev45277711160tnSi77933398876JeD8886668888822222222222vfa

a

a

a

oeeeeeettttttsna

a

aaaaaaossrrrrraadddddsrdss

ie

tlggyyyyyayaa.

ihhhhhghgg)8spttttt9omnnsssssspaeeaaaaanann9mSVVGGGGGee1VGeVV(.olcall

clllllllootilllllllpniiiiiiiooiHHHHHHH44ooe33PPnettoahhhhhhh22eesscsssssssnsiouuuuuuuCCniiardLBBBBBBBGGrBBSnmaor111111211ra---------fluDDDDDDDDD11acnYYYYYYY--taeoYYliHHHHHHHNNDotHHMatHHHHHHHCCRRa

SBBBBBBBGGPPBBTable1

492R.Sassenetal./OrganicGeochemistry30(1999)485±497

Fig.pictheGCHYD-1(top)7.Diagramspropertiessummarizingsamplingofventstation,gasmolecularGCand234gas(bottom)site.

hydratesamplesandisoto-atd(Austin,DwasperformedmassTexas)byCoastalScienceLaboratorieswasperformedspectrometer.usingusingGasanaPorpakchromatographicupgradedMicromass602Qcolumn(1.5separationm).4.Resultsanddiscussion4.1.Ventgases

COThebulkofthermogenichydrocarbongasesandshallow2fromcolumn.sediments,thesubsurfaceaHowever,aandfractionexithydrocarbonbyventingsystemtothebypasswaterunderrapid(ambientphasechangeoftheventgasundergoestemperature(Sassenand(HMacDonald,1997)importantH5400kPa),andcrystallizesassolid78C)gasandhydrate.pressureItisthecarbonprimarytocharacterizeventgasesbecausetheyarepoolsstartingarederived.

materialsfromwhichotherhydro-ventTheunalteredgasmolecularsamplesfromandBushisotopicHillcompositions(Fig.6)areoftwoofMethaneJollietField,hydrocarbonasreportedgasesbyinKennicuttsubsurfacesimilaretreservoirstosamplesCfromistheBushmajorHill(90.4%componentand95.9%);oftwoal.individualvent(1988).gasincreasing2+hydrocarbonsamountscarbonnumber,decreaseinandrelativenabundancewith(showsà44.1-(<0.1%)andà46.0(Table-PDB)1).variesThe-Cd513occursbyC1.9of-,methaneintraceanddDTheCisotopiclittlevariationproperties(àof198methane-andandà200associated-SMOW).C2±and4hydrocarbonsventMacDonald,indicate1997).athermogenicorigin(Sassenà5.4gassamplesshowsThelittled13variationCofCO(2fromthecompositionThermogenic-PDB;Tableà4.9-andvent1).

gasfromGC234Figs.methane6andtod13(93.7%7).theOneventgasfromBushHillissimilar(compareinofsampletheCofGC234ventgashas1±C5(TableCofà48.7-PDBandadDdistribution)ofwithaoffromthe1).Themoleculardistributionsàand203d-13CSMOWvalues+2.9suggest-BushC2±CPDBHill5hydrocarbons(Table(Table1).arealsosimilartoventgas1).TheCompositionald13CofventgassimilaritiesCO2issameventgasesatbothsitesarederivedisInMesozoicsubsurfacehydrocarbonsystem.

fromtheTwolargelycontrast,bacterialventmethanegasfrom(MacDonaldthebrinepooletinGC233methaneventare(97.8%gassamplesand97.4%);showthermogenichighpercentagesal.,1990b).Cofbonsminorcomponents,andtheC2andC34andC5hydrocar-ThePDB,dare13SMOW;andCabsentvaluesthedoforDmethanebelowdetectionvaluesareareàlimits(Table1).à64.3200-andà65.5-àthelattergascontainsCO-andà165-2withad13vent25.3ductionmethane-PDB(Tableareconsistent1).TheisotopicpropertiesofCtheofandKaplan,ofCOwithanoriginfromre-1986;2viaColemanbacterialetmethanogenesisal.,1996).(Jenden4.2.Gashydratecrystallization

bbs.99jianzhu.com内容：建筑图纸、PDF/word 流程，表格，案例，最新,施工方案、工程书籍、建筑论文、合同表格、标准规范、CAD图纸等内容。