6th International Conference on Gas Hydrates

PAST AND PRESENT RECORDS OF GAS HYDRATE GEOCHEMICAL SIGNATURES IN A TERRIGENOUS MATERIALS DOMINATED ACTIVE.. Lin, Saulwood; Lim, Yee Cheng; Wang, Chung-ho; Chen, Yue-Gau; Yang, Tsanyao Frank; Wang, Yuanshuen; Chung, San-Hsiung; Huang, Kuo-Ming 2008

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  PAST AND PRESNT RECORDS OF GAS HYDRATE GEOCHEMICAL IGU I A TIGNU MTEILS DOMINTED ACTIVE MA, SHW OF TW  Saulwood Lin*, Yee Cheng Lim Institute of OceanographyNational Taiwan University 1, Section 4, Roosevelt Road, Taipei, 10617 TAIWAN  Chung-Ho Wang Institute of Earth Sciences, Academia Sinica Taipei, TAIWAN  Yue-Gau Chen, Tsanyao Frank Yang Department of Geosciences, National Taiwan University Taipei, TAIWAN  Yuanshuen Wang, San-Hsiung Chung Central Geological Survey, MOEATaipei, TAIWAN  Kuo-Ming Huang Ching Yun UniversityJung-Li, TAIWAN  ABSTRACT Temporal vriations ingas hydrate related geochmical signatures under iffernt deposition cnditios e thprimpuosfthisstuy. Areted wglocateosh Suthwteraiwrcivshig terigen riv materials, 10 MT/yr, t prst tim. It ist clea h sep viront vaiedingthepst glacl.  25tes lon iston re was taken ofsreSouthwestern Taiwan or/v Mario DuFresne. Short pistocores andboxcores ere alsotaken n r/vOR-1. Smpleswernlyzd for  water disslved sulfide, sulfte, mth, chlorid, del 8, calciu, agnium, lklinity, pH, nsimnt AVS, pyriteinrganic rbondel O-1, C3.  hnes indositio evirnmet lay mjor le inth stud e. Te stag ofgoicl proc re idntified inth 25eters logce, terchabtwrucaxic desitioal virts, withrucing onditioin th top 10m, oxic inn 10-20 mteran rduing blo th 20ete.  Highctrationsofdisslvedsulfide, rapidslfte pletio, incesofmean, dcrasofalcium wer fu inr water inth to mofsedimts tothr with hig ontrtios fpyite, lativelyhigpotionofcarse-grainsdimnt. Cctrtios fpyriteervr lo insdimnts betw 15to 20te but crea rapidly fro 20to25 tes ithaxum cotratioat 4ul/g.  Chloid octrtiosalsincreasdtoamximu conetratio f630 mM  m.  The rap inrs fhloride dicte g hyrte frtio t thisdepth. AuthigeniccarbonteProcedings ofthe 6t Interationl Cfernc oGas Hydrates (ICGH 208), Vauvr,BiColumb, AND, July6-10,28.nodules wer found insedimnts below 20 m.  The carbonte contet also increasd rapidly beathispth. Stable isotopiccaroncpositionfthe ra vriedpidlybneth20m ith lo at -28 rmil.  Th xistee fxic/rduingltetiosinictes tht me sp my vr in the past in the study ar.   Keywords: gas hydrte, activ margin, gas sep, South China Se, Taiwn  INTRODUCTION Gas venting asresult of gas hydrate issociation throuh dimnts cldinucenumber fgcmicl pros.  Strog hical variations, e.g., abrmalprwater clorid, sulfte dletion, stale oxyen istopeviationthigic crotefrtioith soted stable arad xygen istopic ariatio, fregisteed theirrpstativeces in simnts[1, 2] whic able sy idntificationof various tagsofgs migratiod their pints. Migration to the surfcoulddiscntine hcduit froba is blok bytectoic tivity, saled ythigenicaroor yratefrmtionrxhusted esvir. Suseqnt sedimt epositio coldcnl th gchicl igatur leavinglittle tras ofasydrate rlate ctivitiesn the saflor. While numbeof tors ouldinduc venting withinth simnt, btatial vidindicateat levl chages cld proe lar scle of gas ydrtedisoiation adg/fluidflo[3]. Howe, pnin adsling o the nduit cld ls cur iregularly intectoicactive nvirmnt asvs slt of prsur iffr during the  lel low/higtand. Ithis stuy, wexin25meters ng giat toncor llected at th notharSouth China Sentintalrginr Tiw, wer activtetoic ativities hve b fud. Mthan migrtio upto the a floor becmsaprimyegysorcforchsynthtic couities nea th s flor.  I oxicsednts, rpiderbicmethanidatio (AO) ocd via sulfate rductio.  Sulfteisusring methanoxidtionwith thprodction of dislv sulfid a bicrboate.CH4 + S42- -- HCO31- + HS1- + H2O       (1)  2FeOH+ 32S -- 2 Fe + So 4 H2            (2)  3eS + 2o-- Fe3S4                                                     (3)  Fe3S4+ 2 o-- 2 FeS2                                      (4)  Iron xides ar unstable inreducing sedimnts ad eact withdisolvedulfid toformta-sbleir sulfid minrals (FSanF3S4) with pyrite (FeS2)begthe pmint frfstaleironslfid inral [4].  With oxidation oetha, calciuconteayprecipitated frming uthigenic crb.  Ca2+ + CO32- -- CaCO3                                  (5) Aughigeniccarbonteandpyrite beco twominrals mly fu inthAOMrlated envirots.   STUDY AREA outhwesternTaiwn issituated t the boundary betw th Philippine EursiaPlateswithfast mvingrte ofbt 8cm p yar [5].  The acrtionay wdg ofshresouthsternTiw ischrterizey aie fnticlin ad fultsith trn sitcingrNW-SE, soth f2ºNtoE-SW, noth f2º [6].  Thisdeormatio zoe islocatedt efrontal eg fth crenarywge fth Luz Ac anChin psiv ontintal marginsubduction-ollisiotem[7].  Feqnt erthqakes cured inthe rgioasrsult of apid latemvnts. Thxistenc ofa riesofnrl flts interscte bythrust ltsinthe cetioary pisof uwete Tiwn myprvid godcnitsr gas ndfluidvting uwtothe surface. Mvolcaes wrerete nla[8] ll s the sfloo[9].  In aditioto thrtedwg, tudy ar lsorceivsahig flux ofrignous penseimt xportedrmthe ajcet Koing, Erjn ad Tseng ivrsith ambd avgrivarticleload of120MT/yr.  Highcoetrtios of s hyrte deriv ethan wr fundineimntsvlyingwter [10].  ShalloSMI (sulfate methan fc)s s as 1mr b sedimnt/waterinterfceoredontopofth ticlin ridges [11].  MATERILS ANDALYTICL METHOD  giant piston core was colleted on r/v MarionDufres at thYun-Ridgeinthective cotintal mrgin, fshre suthwster Tiw(Figr 1).     Figure1. Study area.  Sedimnt samples wr sctiond into 2-cm sctio d centrifugedfopre water. Porewater ulfatehlorid cntrtios msudby Diox 450i io hrmtogrphqipp with condutivity deteto and IonPac AS4anioehagecolu. Porewter dissolved sulfid trtions  lyzeby thmthylen blu methd[12]. Man coetratios inpor ater r colleted obrd thehadcthoandmeasurby gashrotogry. Pre wter irn amns ion we nalyzusingflatoic bsrptiopctromter (rk-Elmer 30). Poe ater stable O-18isotopic valuswer surdfolloingthe Epstein-Myd techniqu[13] n lyzd uina SIRA10rtio mas spectrmeter anrotedser ill elativtoth V-SMOW(Vien tandan Ocen ater) stadr. Grainsiz wr surdbyalasegin-ize pticle ealyze (Colter LS230). Pyritesulfrndcid volatileslfide(AV contratios in sdimnts wr determined b the Cr(I)+6NHl extractionchniquacold l mtho [14, 5]. Total ron d rganiccarbn wrlyzed using LECO/SAlyze (SC-4) equippwithahig tempertu rsistae furacn aIR detector. alciucabonteotet wsclcula fo diffre tw the total arbonargnic ctet asuming lcite ws the lycarbonte phase. Crbon doxygen isotopic anlyse of calcite wer prfmd FinigMAT-DELAisotopatio asectrmter quippd ger sytem withutotic tub ackes. hel C-13andO-18 vlues rxprsd r mill rlativ tothe V-PDB (iena Pe D Blenite) star. RESULT ANDISCUIONS  Abundant evidences showed that methane are migrating to the surface sediment in the active margin, southwest of Taiwan present time.  High concentrations of gas hydrate derived methane were found in the study area sediments [10].  Near surface rapid sulfate depletions were also in the same region as a result of high flux of methane [11].  In addition, chemosynthetic vent community and large sizes of authigenic carbonate were also found in the study region [16, 17]. The phenomena of gas venting to the surface occurred not only at the present time but also in the past with intermittent stage in the active margin sediments, southwest of Taiwan.  Three different depositional stages were found in the vertical sequences in the giant piston core collected at the Yuan-An Ridge, a lower section older vent, middle oxic sediment, and an upper, new vent type sediments.  The lower section is characterized by high concentrations of methane, high in pore water chloride, complete depletion of sulfate, and high in methane, authigenic carbonate and pyrite. The middle section is unique in high iron oxide, very low in pyrite, but also in methane and pore water chloride.  The upper section differs from the other two lower sections in the normal seawater chloride, rapid depletion of sulfate and appearing of high dissolved sulfide, almost no methane, and high in coarse-grained sediments.  In addition, concentrations of authigenic carbonate appeared at the boundary these three stages.  The appearances of high concentrations of iron oxide in the middle section indicate that the middle section is deposited in oxic environment while the upper and lower sections are deposited in anoxic condition with rapid methane oxidation. Conclusion While gas hydrate derivd methan veting may be a continus pocs thty trsport csidrable amnt ofth to th cn ad may pla sigificat rle in altering thetmospheric ge house ga compsitio, diffrnt stags of mthn migrtion wr found in th activarin  th Suth China Se nar Taiw.  Existence of high proptio of irnoxide in the middle stion indicte tht sdimnts wr dposite during oxic normal marin coition.  Ue a lower sctions wer chterized by aarbic mthan oid adgs hya frmtio.  REFERENCES [1] Sues E, Torres ME, Bohrmann G,Collier RW, Grinrt JLinke PRehdr, TehuAWallmann K, Wckler G, Zuleger E. as hydrate destabilizatio: nhacwatering, bnthic material turoverd large mthne plumes t eCsc cgt in.Erd Platary Siene Ltters 1999: 701-15. [2] Kulm LD, Suess . Relationship betwn carbotedeposits and fluid vting:Orgoetionary rism. Joural of Gopysical Research 1990:95:8899-8915. [3] Pull C, Buelow W, UslerW, Brwski W. Increasd contintal-argin lumping frequncy ding-levl losndsbove ashdrate-br simets. Geoy 1996:24143-146. [4] Benr RA. Early iagsis Atheorticl approach. Pincton: Pincton Uivrity, 1980. [5] Hu JC, Yu SB, elier J, Chu HT. ctivedeformation of Taiw fromGPS easurmnts and numerical simulations.Journal of Geophysical Research 2001:106:2265-2280. [6] LiuCS, Huang IL, Teng LS. Structural features off sothwester Taiwn. Marine Geology 197:13:305-319. [] Liu S, Defntaines B, Lu CY, Lallemnd S. Deformatio patter of ancretionry weginth trnsitiozfm subdtocollisio offshr outhwesterTiw. Marin andPetrleGlogy 2004:25:123-137.[8] Yang TF, YhGH, Fu CC, Wng CC, L TF, Lee HFCen CHalia V, SungQC. Compsitio adxlatiofluxof ase fromud volcaoes in Tiwn. EvironmentalGeology 2004:46:1003-1011. [9] hiu JK, TsengWH, Liu CS. Distribution of gasyedimnts ad muvolcanes ffshresouthwestern Taiwn. Ter. Atmos. Ocean. Sci. 2006:17703-722. [10] Chag PC, Yg TF, Lin S,  HF, Lan TF, Hong WL, LiuShenJCWangY. Extremly ig methn cotratio inbotto water ndcordsimets frm ffshre suths Taiw. Tr. Atms. Ocen. Sci.2006:17903-920. [11] Lin S, Hsieh WC, Lim YC, ag TF, Liu CS, WangY. Methanmigrationd itsinfluenco sulfate rductio in the GoWthr RidgeReio, SothhSctinetal main sdimnts. Ter. Atmos. Oan. Si. 2006:17:883-902. [12]Clin JD. Spctrhtometric deterination of hydrogensulfide innaturl was.Limologyan Ocaraphy196:14:454-458. [13] Epstein S, Myd T. Vriation f O-18 otet of waters fromnatul sources. Gechimic et Cchimic 1953:14:213-224.[14] CanfieldDE, Raiswell R, Westrich JT, Reaves , Brne A. T us of crmiu reductio inth lysis of rdinganicslfu sedimtsad hle. Cheical Geoloy 1986:54149-155. [15] Cornwell JC, Morse JW. The characterization of irn sulfide mineralsin marine sdiments. Marine Chistry1987:22193-206.[16] L S, im YC, Hsieh C, Yang TF, Wag Y.Gsydratend patial venting variationsinthe continetal mrgin offsrSouthweter Taiw. AU, Fll Metin, a Fcis. EOSrs. 87 (52), Abstract OS12C-05, 206. [1] Lin S, im YC, Yang T, Chen YG, Liu C, WangChung SH. Authigenic carbonte formtio and spatial venting phom  thective vtingr of thasiv tintal arginoffshe Suwster Tiwan. EGU, Gnl Asbly, Viena. Abtrct 207-A03314, 2007  

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