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1988 Hydrothermal Fluids and Petroleum in Surface Sediments of Guaymas Basin, Gulf of California: A Case Study J. M. Gieskes
B. R. Simoneit
T. Brown
Timothy J. Shaw University of South Carolina - Columbia, [email protected]
Y. C. Wang
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Publication Info Published in The Canadian Mineralogist, Volume 26, Issue 3, 1988, pages 589-602. © The aC nadian Mineralogist 1988, Mineralogical Association of Canada Gieskes, J. M., Simoneit, B. R., Brown, T., Shaw, T., Wang, Y. C., & Magenheim, A. (1988). Hydrothermal fluids and petroleum in surface sediments of Guaymas Basin, Gulf of California: a case study. The Canadian Mineralogist, 26(3), 589-602.
This Article is brought to you by the Chemistry and Biochemistry, Department of at Scholar Commons. It has been accepted for inclusion in Faculty Publications by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Author(s) J. M. Gieskes, B. R. Simoneit, T. Brown, Timothy J. Shaw, Y. C. Wang, and A. Magenheim
This article is available at Scholar Commons: https://scholarcommons.sc.edu/chem_facpub/316 Canadian Mineralogist Vol. 26, pp. 589-602 (1988)
HYDROTHERMAL FLUIDS AND PETROLEUM IN SURFACE SEDIMENTS OF GUAYMAS BASIN. GULF OF CALIFORNIA: A CASE STUDY
JORIS M. GIESKES Scnpps Institution of Oceanography, Ocean Research Division, A-015, University of California, San Diego, LaJolla, California 92093, U.S.A.
BERND R.T. SIMONEIT Petroleum Research Group, College of Oceanography, Oregon State University, Corvallis, Oregon 97331, U.S.A. THOMAS BROWN, TIMOTHY SHAW, YONG-CHEN WANG, ANDREW MAGENHEIM Scnpps Institution ofOceanography, Ocean Research Division, A-015, University ofCalifornia, SanDiego, LaJolla, California 92093, U.S.A.
Abstract nusentrc 1981 et 1988. Nous avons porte une attention tome speciale aux courtes carottcs prelevecs dans la couche de Surface sediments in hydrothcrmally active zones of the surface au moyen du submersible DSV ALVIN; les prele- Guaymas Basin, Gulf of California, have been analyzed vements ont die faits dans des regions d'advection verti for the inorganic chemical composition of sediments and cal des fluides d'originc hydrothcrmale, aussi bien dans their interstitial waters, as well as for their organic che des zones a fort ccoulcmcnt advectif que prcs des ecoule- mistry. Analysis of the inorganic constituents ofvent fluids ments diffus a travers Icscpaisscs accumulations de la bac- establishes end-member concentrations of hydrothermal tcric Beggialoa. La composition des caux interstiticlles fluids and also indicates that little change in chemical com montrc que les fluides qui contiennent une composante position has occurred between 1981 and 1988. Special atten hydrothcrmale ainsi que I'cau de mer atteigncnt la surface, tion is given to short surface cores collected with DSV et sont gencralcment munis de sulfurc d'originc peu pro- ALVIN in areas characterized by upward advection of fluids fonde; ce milieu peut done fournir une source d'energie of hydrothermal origin, both in areas of strong advective pour assurer la croissance de bactcries qui catalyscnt l'oxy- flow as well as seepage through large bacterial mats of Beg- dation dc sulfure. Nos etudes sur la composition du petrole giatoa. Interstitial-water compositions suggest that fluids d'originc hydrothcrmale montrem qu'il s'agit d'un condense consisting of hydrothermal and scawater components rise (hydrocarburcs C|-C20 el hydrocarbures polynucleaires to the surface, often carrying a supply of sulfide of shal aromatiques); en grande partic, cettc fraction a migre'avec low origin; this in turn may serve as an energy source for les fluides transported par advection verticale a partir d'une the growth of sulfide-oxidizing bacteria. Studies of the com faible profondcur en dessous de I'interfacc cau-scdiment. position of hydrothermally generated petroleum show that Le petrole des sediments sc trouvc surtout dans les fissu it is a condensate (C|-C2o hydrocarbons and polynuclcar res des fragments a ciment siliceux, et est transforme par aromatic hydrocarbons), and much of this material has biodegradation. Pres de I'event, le petrole est un condense migrated with the upward-advccling fluids from short non allcre, cc qui indiquc que le taux dc migration active depths below the sediment-water interface. The petroleum dans cc milieu surpassc le taux de biodegradation. in the sediments is found mainly in fractures in silica- (Traduit par la Redaction) cemented clasts and it is biodegraded. In the vent/mound, the petroleum is an unaltered condensate, indicating active Mots-clis: accumulations dc Beggialoa, condense, ecoule migration that exceeds biodegradation. mcnt diffus, gaz, golfe dc la Californic, bassin de Guay mas, composition du fluidc hydrothermal, petrole Keywords: Beggialoa mats, condensate, diffuse flow, gas. hydrothermal, composition de l'eau intcrstiticlle, car- Gulf of California, Guaymas Basin, hydrothermal fluid bone organique, hydrocarburcs polynucleaires aroma composition, hydrothermal petroleum, interstitial-water tiques, formation de sulfurcs. composition, organic carbon, polynuclcar aromatic hydrocarbons, sulfide generation. Introduction The hydrothermal system in Guaymas Basin ofthe SOMMAIRE Gulf of California (Fig. 1) is of special interest in the study of hydrothermal ore deposition, especially Les sediments dc surface des zones a manifestations because here newly formed oceanic basement con hydrothcrmalcs dans le bassin dc Guaymas, dans le golfe sists either of sill intrusions in rapidly deposited, de Californic, ont etc analyses afin de determiner la com organic carbon-rich sediments, or of massive intru position chimiquc (fractions inorganique et organiquc) des sediments et dc I'cau intcrstiticlle. L'analysedc la fraction sions at greater depths (Moore 1973, Williams et al. inorganique dc 1'eau des events definil la concentration des 1979, Einsele et al. 1980, Gieskes et al. I982a,b, elements dans Ics fluides hydrothcrmaux avant leur dilu 1988). Hydrothermal interactions involve both the tion, et momrc que tres peu dc changements sonl survc- alteration of basaltic rocks and of sediments, the lat- 589 590 THE CANADIAN MINERALOGIST
Fig. 2. Cartoon version of hydrothermal deposit - ALVIN dive 1630. A: diffuse flow, temperature km <206°C; B: yellow bacterial mat; C: yellow bacterial 27*00N ;*• patches or • HVDMTHERml mat, sampled for core 1630-ACI; D: orange bacterial SINTER & MOUNDS mat; E: hydrothermal spires(1-1.5 m tall); F: fault zone (<30cm). Fic. I. Map of study area - note cores 1617-AC 1, 1619- AC2, 1629-AC2, 1630-ACI, and 1984-AC1, all in the Studies of Deep Sea DrillingProject (DSDP) cores southern hydrothermal field. Shaded areas represent obtained from Sites 477, 478, and 481 involved extent of sill complexes (Lonsdale & Becker 1985). interstitial-water chemistry (Gieskes et al. 1982a), solid-phase geochemistry and mineralogy (Kastner 1982, Kelts 1982, Niemitz 1982), and physical proper ter also providing a medium for the thermal genera ties of the sediments (Einsele el al. 1980, Einsele tion of hydrocarbons (Einsele et al. 1980, Kastner 1982).The results led Kastner (1982) and Gieskes el 1982, Simoneil 1983, 1984a,b, 1985a,b, Simoneit & al. (1982b) to conclude that two major hydrother Lonsdale 1982, Kawka & Simoneit 1987, Simoneit mal systems could be distinguished in Guaymas et al. 1984). Basin:
10 20 30 40 SO 60 10 20 30 40 SO $0 0 10 20 30 40 SO 60 Mg(mM) Mg(mM) Mg(mM)
20 30 40 $0 60 10 20 30 40 SO 10 20 30 40 SO 60 Mfl(mM) Mg(mM) Mg(mM)
200 •
9110 • 3 • Fig. 3. Compositional changes versus magnesium concen C 100 trations in hydrothermal vents of southern hydrother S • •• • mal field, Guaymas Basin, 1988. $0 •*^*s,*<.
0 10 20 30 40 SO 60 Mg(mM) HYDROTHERMAL FLUIDS AND PETROLEUM, GUAYMAS BASIN 591
(1) Hydrothermal activity associated with relatively short push cores was obtained in zones of diffuse thin, shallow basaltic sill intrusions in highly porous flow or below Beggialoa bacterial mats. In the sediments. This activity is usually of short duration present study we concentrate on one ALVIN dive and is associated with temperatures <200°C in the area in particular, but discuss the results in a broader vicinity ofthe sills. Decreased porosities indicate that context. expulsion of pore waters accompanies the sill emplacement. Study Area (2) Hydrothermal activity associated with large mag- In August 1985 several dives were made in the matic intrusions at greaterdepths; this activity occurs southern vent field of the southern trough of in a deep-seated, recharging, circulation system. Guaymas Basin (Fig. 1). In particular, core 1630- Hydrothermally altered waters, after reaction with ACI was obtained in an area where hydrothermal underlying basalts, interact with overlying sediments deposits indicated only very recent growth along a and lead to greenschist formation at temperatures of >300°C (Kastner 1982, Kelts 1982). Mass-balance considerations of oxygen isotopes (Kastner 1982) TABLE 1. COMPARISON OF HYDROTHERMAL ENDMEMBER indicated that open-system conditions prevailed dur CONCENTRATIONS OF VENT FLUIDS IN SOUTHERN VENT FIELD ing greenschist formation. This woik Lonsdale & Becker (1985) suggested the presence Campbellera/. (1988) of an additional hydrothermal system in which slow 597-617 610 recharging convection occurs within the sediments Cr
Hydrothermal fluids have been observed to exit Ca2' (mM) 28 27 the sediment column in several ways (Lonsdale & Becker 1985). Fluids emanate from hydrothermal NH4*(mM) IS 13 mounds and chimneys at temperatures up to 3I5°C HjS(mM) 6 6 (Von Damm et al. 1985). They seem to have their K*(mM) 43 47 origin at greater depths, and must have flowed Mn(uM) 140 110 rapidly along fissures and faults in the sedimentary column. Hydrothermal deposits typically occur along fault zones in the sediments. Fluids also emanate diffusely through the sediments. Areas of diffuse TABLE 2. VISUAL OBSERVATIONS OF"ALVIN" CORE 1630-ACI SmearSlid* flow are typically characterized by shimmering water Interval Dononans just above the sediments, or by bacterial mats of Sanplt CentralDescription Material Color 0-1.5 Homogeneous marine mud Diatoms Green*brown giant Beggialoa on top of the sediments. ' >704 High-temperature vent fluids emanating from 2 1.5-3 Marine mud with disseouutcd Diatoms Green-brown hydrothermal mounds and chimneys have been panicles >70» studied by Von Damm et al. (1985) and Campbell 3 3-4.5 Homogeneous nurine mud Diitotm Green-brown et al. (1988). Their chemical composition is similar >703 4 4.5-6 Petroliferous nurine mud >70* Green-brown to that ofthe fluids in the deeper parts of DSDP Hole with disseminations ofsandy 477A (Gieskes et al. 1982a). Together with the often diatom rich clasts 5 6-7.5 Black, petroliferousmud with >70S Green-brown extensive size of the hydrothermal deposits, this sug one tube like and one platy gests that these fluids are associated chiefly with diatom rich clast impregnated with bitumen deeper-seated systems, which should operate on a 6 7.5-9 Very petroliferous green mud; >7M Green-brown longer basis than sill-induced systems. numerous clastsofglobularand platy nature, impregnated with In the present study we investigated the chemis bitumen try of sediments and interstitial waters associated 7 9-10.5 Very petroliferous mud with Dutomi Green-brown numerous globularclasts and with diffuse flow through the sediments. Of impor one platy clast with bitumen tance is the question with regard to the origin of 8 10.5-12 Petroliferous green mud with Diatoms Green-brown hydrothermal fluids in this type of system. Diffuse very porous clasts with little >60% bitumen flow has been observed both in the vicinity of large 9 1213.5 Petroliferous green mud. fewer Diatoms Green-brown hydrothermal deposits, and in zones removed from cUsa,one bemg large and xtn, such deposits. It is of interest to determine whether porous but without bitumen 10 13-5-15 Petroliferous"clayey" mud with Diatoms Green-brown fluids in this type of system are associated mainly smaller clasts with a sill-induced hydrothermal system, with a 15-16.5 Petroliferous"clayey" mud with Diatoms Grey deeper-seated system, or with both. M few small dans >50* During DSV ALVIN operations in Guaymas Basin 12 16.5-18 Petroliferous"clayey" mud with Diatoms Grey in 1982 and 1985 (Gieskes et al. 1988), a series of few small dasts 592 THE CANADIAN MINERALOGIST
1—!"-*T"* vents in the southern vent field(Fig. 1). End-member concentrations of hydrothermal fluids are obtained from extrapolation of correlation plots of concen trationsofvariousconstituents versusthose ofmag nesium (Von Damm et al. 1985,Campbell et al. 1988; Fig. 3). The common assumption is that the end- member fluids contain no Mg2+ or SO.,2-. Extrapo lated hydrothermal fluid concentrations are com paredwith those presented by Campbellel al. (1988) and, in agreement with the latter authors' observa tions, no significant change has occurred over the last seven years (Table 1). This attests to the longevity *i®§MW of the hydrothermal system associated with mound 5 mm formation in the southern hydrothermal field. !& Core 1630-ACI - solids. In Table 2 we present visualobservations ofcentrifuged materialsobtained during the extraction of the interstitial fluids from Fig. 4. Detail of "oil shale" piece. Core 1630-ACI, sec the sediments. The petroliferous nature of the sedi tion 7. ments is most apparent below a depth of -8 cm, coinciding with the depth at which most cementa fault zone, at least 30 m away from largerhydrother tion has occurred in this core (see below). Numer mal mounds. A cartoon of the area is presented in ous silica-cemented clastsoccur in the sediments, par Figure 2. One push core (1630-ACI) was obtained ticularly in section 6 (7.5-9 cm). Figure 4 presents in a yellow Beggialoa bacterial mat, and another a closeup of one clast demonstrating the "reservoir push core (1630-PC) sampled the top of one of the rock" nature ofthese clasts, i.e., it appears to sand hydrothermal spires. The material of this hydrother wich bitumen-like material. X-ray diffraction anal mal spire consists mainly of barite and precipitated ysis of this clast revealed the presence of mostly amorphous silica, saturated with petroleum conden amorphous silica with minor amounts of clay(Si02 sate. Upon rising through the thermocline, several -89.1%; AI2Oj - 1.83%; Ca -1.94%). Scanning chimney pieces jumped out of the collection basket electron microscope (SEM) observations have rev as a result of the release of pressurized gas and oil, ealed that the clasts consist mainly of cemented dia which rose ahead of the ALVIN, thus causing the toms, the cement appearing to be amorphous silica. submarine to surface in a large oil slick. Core 1630- The cement may have formed by the precipitation PC, ofabout 25 cm length, was half-filled with chim of silica from dissolved silica-rich hydrothermal ney material and the liquid phase above this was fluids. In part this silica enrichment of the fluids can about one half water and one half oil. Below we dis have been the result of diatom dissolution at depth. cuss the nature of this oil compared to that found The bulk chemical composition of the sediments trapped between cemented pieces of silica in core is presented in Figure 5. The concentration of Al is 1630-ACI. Interstitial water samples were obtained given in wt.% (salt-corrected), whereas the other ele from push core 1630-ACI, and these were analyzed ments are presented as mole ratios with respect to for major ionic constituents (hydrogen sulfide Al. Such mole ratios are often indicators of chemi onboard ship; major constituents in home labora cal change in the sediments. Ti/Al ratios, and espe tory). Solids analyses were carried out using wet- cially Fc/AI ratios, are quite variable in the upper chemical techniques (Donnelly 1980, Brown, M.S. 10cm of the core. Si/Al ratios are high in the upper thesis in prep.). 12cm of the core representing a substantial biogenic Also studied were core 1617-AC1, obtained from silicacomponent; lower ratios at greaterdepths may an area of strong diffusive flow, and cores 1619- signify dissolution of diatoms. The increase in K/AI AC2, 1629-AC2, and 1984-AC1 from areas of bac below 10 cm is significant and probably represents terial mats. Interstitial-water data obtained from uptake of K * in clay minerals. these cores arc compared with results from core 1630- Core 1630-ACI - interstitial water. The depth dis ACI and hydrothermal fluids obtained from tributions ofall components (Fig. 6) with the excep hydrothermal vents in the southern vent field in 1988. tion of sulfide show a change of slope at a depth of -8 cm, i.e., in the zone where the largest amounts ofclasts have been observed. Sulfide concentrations Results reach a maximum at -7 cm depth. We suggest that Inorganic chemistry the silica cement in this layer is laterally continuous Vent fluids. During February 1988 two of us and that it represents a barrier to upward flow of (BRTS and AM) obtained hydrothermal fluids from hydrothermal fluids which, judging from the chem- HYDROTHERMAL FLUIDS AND PETROLEUM, GUAYMAS BASIN 593
Fe/AI SI/AI
0035 0.1 02 03 1 6 8 1 0 » ' " <
s • > cm ) 10 t 1 IS y
P/AI Ca/AI Mg/AI K/AI
000 0.01 0. 0.0 0.1 0.2 0 0.175 0.200 0225 0250 ^ ' / J—- s i 5 r cm / cm % 10 ' \ 10 J 15 \ IS 5
Fig. 5. Chemical composition of bulk sediments, core 1630-ACI.
|iM o wo «o eoo too raw
Ca Mfl
mM
Ml CI S04 H2S&NH4 Fig. 6. Interstitial waicr chemistry, core 1630-ACI. 594 THE CANADIAN MINERALOGIST
CI Ca K LI the upper 8 cm, presumably as a result of ammonifi- mM mM mM |iM - 50 • i—' ••• 850 40 -14000 cation processes associated with the sulfate reduc tion process. It does appear, however, that the high 800 ; a • -Ca '
O-CI . dissolved NH4 * and the low S042" at greater depths 40 ' "8**^ 30 • 3000 Si* »-K 750 arc primarily due to a hydrothermal component. A-U •^^^s. 700 - 30 . 20 - 2000 o Comparison to other ALVIN cores 650 o""^^^ Figure 8 illustrates interstitial water profiles for
20 ,o "^ 10- 1000 cores 1617-ACI, 1619-AC2, 1629-AC2, 1630-ACI 600 and I984-AC1. All these cores come from dives in • -^•^J the southern vent field (Fig. 1). Core 1617-ACI was 550 - 10 o J 0 10 20 30 40 50 60 obtained in a zone characterized by strong upwel- Mg (mM) ling of hydrothermal fluids (evident from flow through holes in the sediment); cores 1619-AC2, 1629-AC2 and 1984-AC1 were taken in bacterial mats. The concentration profiles of Ca2+ and Mg2* suggest that the interstitial waters, although show NH4 S04 mM mM ing typical upward curvature, usually associated with 20 upward migration of fluids (Maris & Bender 1982, Sayles & Jenkins 1982), do appear to be character 15 ized by mixtures of seawater and hydrothermal fluids in different proportions. Estimates ofthe hydrother mal contribution are based chiefly on the Mg2* 10 concentration, which should be vanishingly low in hydrothermal fluids (Table I). Cores 1617-ACI and 1630-ACI contain at least a 90% hydrothermal com 5 ponent in their deeper parts, whereas core 1619-AC2 shows the least hydrothermal component. 0 u 0 10 20 30 40 50 60 Of interest are the profiles of dissolved sulfate. Mg(mM) Though in core 1617-ACI changes in Mg2' and S042" are linearly correlated, this is not the case in Fig. 7. Correlation between imcrslilial water components cores 1629-AC2, 1630-ACI, 1984-AC1 and perhaps and magnesium in core 1630-ACI. in 1619-AC2. This strong sulfate depletion can be understood in terms of sulfate reduction processes taking place in the upper 10 cm of the sediments, ical changes below this depth, appear to dominate leading to the production of significant amounts of the interstitial fluids. Silica cements might allow sulfides (Fig. 5). Upward transport of this sulfide upward diffusion of dissolved constituents, but not would then provide the necessary sulfide to the bac actual fluid flow. terial mats for continued growth. Sulfate reduction Of particular interest is the dissolved H2S profile, processes arc probably enhanced as a result ofhigher which shows a distinct maximum at a depth of ~7 prevailing temperatures in these sediments. Thus, it cm. To investigate the problem of whether signifi is likely that the added transport of sulfide towards cant reactions have affected the concentration-depth the surface of the sediments as a result of upward profiles within the coring interval, we have assumed convection of highly diluted hydrothermal fluids cre Mg2+ to be conservative, i.e. the concentration ates the appropriate conditions for the growth of bac changes represent mixing between seawater and a terial mats on top of the sediments in many areas modified hydrothermal fluid. Figure 7 presents corre of the Guaymas Basin. lation plots ofseveral constituents versus magnesium Figure 9 is a correlation diagram for the various concentrations. It is evident that for K+, Li+, Ca2* "end-member" compositions of the ALVIN cores, and CI", conservative behavior can be inferred, but i.e., the compositions at which the concentrations not for S042~ or, to some extent, NH4+. The Mn2* of most of the constituents become constant with concentration variations indicate production of depth. The data are plotted versus changes in con Mn2* within the sampling interval. centration from that in seawater using Mg2* as a The sulfate trend implies removal of S042~, reference on the assumption that this constituent presumably as a result of sulfate reduction in the shows conservative behavior. For comparison the upper 8 cm. This would be consistent with rapid data of the lowermost part of DSDP Hole 477A increase in sulfide in this interval (Fig. 6). In addi (Gieskes et al. 1982a) and those ofthe average vent- tion, a slight production of ammonia is evident in fluid composition of the southern hydrothermal field HYDROTHERMAL FLUIDS AND PETROLEUM. GUAYMAS BASIN 595
mM mM
» 40 » 10 20 30 40 '.>•" 5 W 5 cm '( > n cm 10 10 vf \iI F\\ 15 1 \ 15 r i 20 20 • w 25 25
Ca Mg CI
Li S04 H,S W,
Fig. 8. Interstitial waler chemistry in cores 1617-ACI, 1619-AC2, 1629-AC2, 1630-ACI, and 1984-ACI.
(Von Damm et al. 1985, Campbell el al. 1988;Table in the data may occur as a result of the interstitial- 1) are also plotted. Changes in Li* are very similar water retrieval process. Core samples are extracted to those expected from a mixture of seawater and at room temperature (- 25°C), whereas in situ tem of the end-member hydrothermal fluid. Though K* peratures may have been as high as 100QC. For K* concentration changes appear to follow a well- this could lead to lower K* concentrations, i.e., defined mixing line, the change in K* calculated for artifacts would be opposite to those found in DSDP the hydrothermal end-member (AK* -23 mM) is sediments (Sayles & Manhcim 1974, Gieskes 1974). much smaller than that observed in the vent fluids On the other hand, K* concentration changes of (AK * - 37 mM). For changes of CI" concentration, DSDP Site 477 arc in close agreement with those of the observations suggest higher concentrations than vent fluids. The other process involves reactions in expected from vent fluids. For S042~, NH4*, and the sediments during relatively slow percolation of Ca2*, considerable scatter occurs, indicating that hydrothermal fluids through the sediments. Uptake reactions in the sediments may strongly affect the of K* at temperatures below ~200°C into auto data. This, especially for Ca2*, is also evident from genic feldspars was noted in Site 477 (Kastner 1982), Figure 8, in which Ca2* changes do not necessarily and solids data on core 1630-ACI (Fig. 5) also indi reflect changes in Mg2*. Smaller changes in Ca2* cate K*uptake. Changes in S042" and NH4* differ in some cores may be the result of CaS04 precipi ent from those expected from simple mixing of tation at greater depth (Stout & Campbell 1983, hydrothermal end-member fluid and seawater can Gieskes et al. 1988). be understood in terms of enhanced bacterial Two processes must be considered to explain activity. In addition, possible precipitation of differences between observed changes in composi CaS04 at depth (Stout & Campbell 1983, Gieskes et tion and those expected from simple end-member al. 1988), as well as possible dissolution of calcium mixing. The first possibility is that potential artifacts carbonate (Von Damm et al. 1985) will affect con- 596 THE CANADIAN MINERALOGIST
Ml 60
• ' / 477 1K»#
s j/mi 1BI7 E 40 E 40 • CD •/ s 2 •0 IKS yT < /•l»4 20 20 '/•
yr •Wit 0 0 200 400 600 800 1000 0 40 80 120 16 ALI (UH AC) mM
60
• IS»' 'mSjj^ 5^1817 S E 40 • ^r 40 o> S S W84 •a 20 s^ • 20 aitn
jS MIS /• iei» 0'—•—i——>—. i . i -10 -20 -30 10 20 30 40 50 AS04 mM ACa RIM Fig. 9. Correlation plots for hydrothermal end-member composition of ALVIN cores. Hole 477A(Gieskes et al. 1982a), and average vent fluids (o) in somhern field (Von Damm et al. 1985. Campbell et al. 1988; Table I). Data in terms of changes from seawater concentrations.
Org.C% The end-member hydrothermal fluid composition used in the above comparison is derived from vent 12 3 4 5 fluids. Because of the constancy ofthis composition over a long period of time, we interpret the end- member to be a result of a deep-seated hydrother mal system (Kastner 1982, Gieskes et al. 1982b). Unfortunately, because ofthe possibility of modifi cations due to reactions during the slow ascent of the fluids through the sediment column, we are not able to judge whether the differences from the sim ple mixing line are due to a different hydrothermal end-member, i.e., associated with a sill-induced sys tem. However, there is little doubt that subsurface mixing of seawater and hydrothermal fluids does occur, and that local chemical reactions near the sur face (e.g., silica dissolution, gypsum precipitation, sulfate reduction) can act as important modifiers to the chemical composition of the interstitial waters. Below we show evidence also that important modifi cations of organic matter occur in the sediments when compared to organic materials obtained from Fig. 10. Total organic carbon in ALVIN cores 1617-ACI, hydrothermal vents. 16I9-AC2,1629-AC2and 1630-ACI. Solid circles: 1617- ACI; open circles: I6I9-AC2; triangles: I629-AC2; Organic Geochemistry crosses: 1630-ACI. Organic carbon Determinations of organic carbon contents were centration changes in Ca-*. Similarly, higher-than- carried out on dried, ground, bulk samples using a expected changes in CI" concentration may be the coulometric method. In all cores, organic carbon result oi hydration reactions in the sediments. contents decrease with depth from surface values of HYDROTHERMAL FLUIDS AND PETROLEUM, GUAYMAS BASIN 597 about 4% organic C to 1.5-2.5% at 10 cm sub- hydrothermal activity is indicated by this PAH dis bottom (Fig. 10). In core 1630-ACI, a distinct tribution coupled with the presence of peri- decrease occurs below the clast-rich layer. Organic condensed alicyclic PAH (e.g., methylenephenan- matter diagenesis may have been more extensive in threne. Fig. 14b; Simoneit 1983, I984a,b). Biomar- cores 1619-AC2and 1629-AC2, possibly because of kers used as petroleum maturity indicators, such as a longer period of exposure to enhanced tempera triterpancs, steranes and extended tricyclic terpanes, ture conditions and hence a more advanced stage of are not detectable in this sample. Their absence, cou organic carbon catagenesis. Temperature gradients pled with the resolved compound and UCM distri in such sediments have been measured during butions, support an origin from a biodegraded con ALVIN dives in 1988, and typical values in mat areas densate. However, various maturity indices can be are: 5 cm -5°C; 10 cm -25°C, 15 cm -50°C, 50 cm calculated for the dimethylnaphthalenes (DNR) and -90CC, I m -110°C (Sayles unpub. data, Somoneit methylphenanthrenes (MPI) (Fig. 14; Radke & Welte unpub. data). 1983, Radke elal. 1982, Alexander etal. 1984, 1985). These indices (Table 3) are within the range typical Petroleum of immature petroleums. The immaturity, coupled The occurrence of petroleum in the sediments of with the high thermal gradient and observed oil dis Guaymas Basin is one of the chief characteristics of charges, are consistent with the interpretation of a hydrothermal processes in this area (Simoneit 1983, short migration distance, for petroleum in this sam 1984a,b, 1985a,b, Simoneit & Lonsdale 1982, ple, from source sediment to the seabed (Kawka & Simoneit et al. 1984). The hydrothermal spire sam Simoneit 1987); the immaturity also indicates that ple (1630-PC) contained abundant oil, and bitumen sediment samples 6, 7 and 10, and clast sample 6, residues were found in clasts and mud of core 1630- can be interpreted analogously. Long distance (> 1 ACI (Fig. 2). Lighter normal hydrocarbons from the km) migration at low temperature would be expected latter had vanished mostly due to the effects of bio to deplete the high molecular weight PAH in the degradation, and to some extent due to recovery, petroleum. storage, and drying. However, the remaining bitu The GC-MS data for the total extract ofthe sedi men portion is of particular interest as it contains ment from section 2 (Fig. 1la) indicate it to be a mix the heavier non-biodegraded remnants. ture of thermogenic and natural products. The The total n-heptane extracts of mud (sediment) dominant peak is phenanthrene, and the clusters are and clasts from core 1630-ACI were analyzed by gas various series of alkyl PAH with mainly C2 and C3 chromatography (GC, operating conditions as in alkyl substitution. These compounds are of a ther Simoneit 1984a) and the representative traces are mogenic origin and probably represent the water- shown in Figures 11 and 12, respectively. Sediment soluble fraction of the condensates encountered samples 6, 7 and 10 (Figs. 1lb.c.d.) are identical in deeper in the core. The cluster of peaks at longer GC that their extracts consist primarily of aromatic retention time consists of various natural product hydrocarbons, and the same is the case for clasts 6 derivatives such as mainly hopenes with exocyclic and 7 (Figs. 12a,b,c,). Three samples from section double bonds, stanols and other unknown C28 and 7 (namely sediment, "shale" 7, and another clast 7) C30 triterpenoids. Normal and isoprenoidal alkanes are all identical (Fig. lie, Figs. 12b,c). "Shale" 7 are not detectable, and their absence compared to was analyzed by gas chromatography - mass spec other shallow sediments from the basin (e.g., trometry (GC-MS) and details are given below. The Simoneit et al. 1979) indicates that this sample has clasts from sections 8 and 9 are, however, different. been biodegraded. The presence ofthe labile hopenes Their extracts are comprised primarily of low indicates that the sediment has not been heated amounts of unidentified compounds. Also, the sedi > - 50°C, and thus the aromatic compounds prob ment from section 2 contains a different suite of ably have migrated as a cold aqueous phase. compounds as discussed below. Sample 1630-PC, from the vent spire (Fig. 2), was Sample 1630-ACI,7 from one of the "oil shale" subsampled and sealed immediately upon arrival clasts in section 7 (Fig. 4) was analyzed by GC-MS. onboard. The distribution of the volatile hydrocar The total hydrocarbons are comprised mainly of bons is shown in the GC trace (Fig. 15); they range unresolved branched and cyclic components (also from methane to n-decane, a typical condensate termed unresolved complex mixture, UCM); the petroleum. It should be noted that homologs major resolved chromatographic peaks are poly —300°C) reflecting These aromatic hydrocarbons are derived from high- in a) 11 12 oo
a)
IW«^*m-w*«U»-u. b) n
m o > cc & z a .^jAAiJi^^ > lll^iii^U> a > o z 01 5 4 s d) z ro 50 t-> O ^yiMSw S L^JjUduUt'-u L_a H d) e) 7
Ll_jJL1JJi»^ _JL ._ W uU. Tims- Time
Fig. 11. Gaschromaiogramsfor total extracts(n-hcptanc)of sediment(mud)samplesfromcore 1630-ACI:(a) Section2; (b) Section6; (c)Section7;(d) Section10.(1 = phenanthrene,2 = methylphcnanthrenes,3 = pyrcnc,4 = dibenzothiophcne,5 = alkylnaphlhalencs,6 = perylene.In(a)alkylcarba- zoles are mainly trimethyl.) Fig. 12. Gas chromatogramsfor total extracts(n-hcptane)of clasts (oil veins)from core 1630-ACI:(a)Section6; (b)Section7, "shale" piece;(c)Section 7, other clasts; (d) Section 8; (e) Section 9. Peak identification numbers arc same as in Figure II. a) 13 14 m/z 1630-AC 1,7 163848. 1630-AC 1,7 a) its I 4576. b) 138 J^. RIC 26192. C) 192.
x d) 286 <
11E64. O e) 229, H X tn jlA 12888. sc f) 234 2 > SCAN lu. r 1999 lies 1208 1309 1499 1589 SCAN
12964. b) 1630-PC > z c 1138. ra 1630-PC h) tsa -i Jy^<>%-jj*Wv^v-sA^^ «—*~-w 7S **A*atA-fc> O
i) 192, c RIC. 2 JJL 4896. O j) 2« . c A iiii. •* • •. > 4369. -<: 2 k) 223 > ,»iLii v. i) 234; iMiU 1—I— ~i—>- 1599 SCAN 1MB isae 1188 1288 1388 1488 sow
Fig.13.Totalioncurrenttracesfor lolalhydrocarbonfractions:(a)sample1630-AC1.7;(b)sample1630-PC(numbersrefertocarbonchainlengthof n-alkanes,iparcisoprenoidalkanes,Prpristane,Phphytane;in(a)thedominantresolvedpeaksarehomologousseriesof alkylbenzenes,alkylmdanes, alkylnaphthalcnes,alkylbenzothiophcncsandalkylphenanihrenes,allwithacarbonsubstitucntrangeof1-3,withIheparentPAHaspenanthrene,diben- zothiphcne, pyrenc and perylene). ,,,nn/-/ iw » Fig 14. Selectedmass fragmcntograms(m/z versusscannumber) for the phenanthreneseriesof sample 1630-ACI, 7 (a-f) andsample 1630-PC(g-1):ta,g) m/z 178(1 = phenanthrene,2 =anthracene);(b.h)m/z 190(3 = mcthylcnephenanihrene);(c,i)m/z 192(4 = meihylphenanthrenes);(d,j)m/z 206 (5=C2phenanthrenes);(c,k)m/z220(6=C,phenanthrcnes,7=unidentified);(f.l)m/z234(8=bcnzo(b)naphthothiophene,9=C4phenanthrenes). 600 THE CANADIAN MINERALOGIST
TABLE 3. MATURITY INDICES CALCULATED FOR THE ALKYL-PAH SERIES IN SAMPLES FROM ALVIN DIVE 1630 high-temperature component reflecting hydrother mal activity. However, the distribution of thesecom Index 1630-AC1-7 1630-PC Reference pounds in 1630-PC is not identical to that sample MP1I 0.30 0.79 Radke and Welte (1983) 1630-ACI,7 (cf. Fig. 14h-l versus Fig. 14b-f) andis MPI2 0.31 0.93 Radke and Welle (1983) due to unknown influences. The dimethylnaphthalene (DNR) and methyl- DNR-1 4.4 1.9 Radke ttal. (1982) phenanthrene (MP!) indices for the chimney sam DNR-2 55 38 Alexander «tt/. (1985) ple (Table 2) fall in the immature and oil or conden DNR-3 60 40 Alexander « a/. (1985) saterangewindow (Radke & Welte 1983). This is also DNR-4 70 50 Alexander el at. (1985) consistent with a short migration distance from source to seabed, and the alkane distribution sug DNR-5 90 61 Alexanderttal. (1985) gests no biodegradation occurred en route. MPt=methylphenanihrene index;DNR=dimethylnaphihalene ratio In summary, the petroleum in dive area 1630con sists of immature condensates containing hydrocar bons from methane to about n-C,0, with admixed temperature catagenetic processes (Whelan el al. PAH components from high-temperature 1988). The ratios of the iso- to the normal alkanes (> - SOO^C) hydrothermal alteration oforganic mat (C, and C5) are in the range of 3.3 to 1.0 and can ter. In the mound/chimney system (Fig. 2) this con be interpreted as immature to mature (Thompson densate is present as unaltered oil (i.e., non- 1979, Whelan et al. 1988). Solvent extracts of the biodegraded, Simoneit 1985a), even at the exterior bulk sample 1630-PC exhibit identical GC traces for surface of the chimney/mound matrix(sample 1630- interior (in contrast with vent fluid) and exterior sub- PC). This indicates that active petroleum migration samples.GC-MS fingerprinting (e.g.. Fig. 13b) indi exceeds microbial degradation. Condensate migra cates that samples 1630-PC and 1630-ACI have tion seems to be from shallow depth (i.e., few meters different compositions, partly as a result of losses sub-bottom, consisting of the early petroleum- of the normal and isoprenoidal alkanes from the lat generation products moving over a short distance) ter. The dominant n-alkancs range from or I a8 nIO ^^«^fc_ —A- 40°C- Tlme- Fiti. 15. Gas chromalogram for headspace analysis of oil on water in sample 1630-PC (i.e., the volatile components; numbers refer lo alkanes, n = normal, i = iso). HYDROTHERMAL FLUIDS AND PETROLEUM. GUAYMAS BASIN 601 ings in silica clasts (Fig. 4). Because the wallrock is mal spires/mounds (1630-PC) and nearby sediments porous silica and not carbonate, it is concluded that (1630-ACI). In the sediments, the petroleum the oil filled fractures by bulk-phase migration and occupies mainly fractures in silica-cemented diato- was biodegraded during deposition in situ. Addi maccous mudstonc clasts. Gcochemical analyses of tional and variable degradation and loss of volatiles the petroleum at both sites have shown that it con occurred after recovery. Carbonate precipitation of sists of immature condensates with a hydrothermal the respiratory carbon dioxide from microbial PAH component. In core 1630-ACI the petroleum petroleum degradation was not obvious in the core. is biodegraded. 7. Petroleum has and is actively migrating in bulk Conclusions as a condensate (CH4 to ~n-C20, the early petroleum-generation products) over relatively short Studies of the composition of interstitial waters distances (less than a few meters). The steep ther and petroleums obtained from short ALVIN push mal gradient, reaching - 100°C at 1 m sub-bottom, cores in an area of upwelling fluids in Guaymas Basin provides the drive for this migration; most of the oil have revealed the following: emanates to the seawater rising as plumes. 1. Water samples taken in 1988 from hydrothermal vents indicate a hydrothermal fluid end-member chemistry very similar to those observed in 1982and Acknowledgements 1985, thus indicating a long-term stability of the We thank O.E. Kawka, M. Brault and G.M. hydrothermal system active in this area. Wang for data and assistance, and the captain, pilots 2. In regions characterized by shimmering waters and crew of the RV A TLANTISII and DSV ALVIN overlying the sediments, "diffuse" flow occurs for their support at sea for sample acquisition. This through the high-porosity sediments as well as paper has benefitted substantially form the reviews through small holes. Core 1617-ACI, taken in an of Drs. A. Campbell, J. Whelan and T. Barrett. area of diffuse flow, contains porewaters with a sub Financial support from the National Science Foun stantial hydrothermal component (low Mg2*, SO.,2 , dation, Division of Ocean Sciences (Grants OCE-85- high Ca2+, Li*, K+, CI"), which becomes constant 12832 and OCE-86-1316 to BRTS, Grant OCE-86- below a depth of 4 cm into the sediment. 13517 to JMG) and Chevron Oil Field Research 3. In areas characterized by the formation of Beg Company is gratefully acknowledged. gialoa bacterial mats, upward-moving porewaters have a much more diluted hydrothermal component References (e.g., cores 1619-AC2, I629-AC2). A strong deple tion of sulfate in the upper 10 cm of the sediment Alexander, R., Kagi, R. & Siieppard, P. (1984): 1,8- leads to a large flux of sulfide to the sediment-water Dimcthylnaphthalcnc as an indicator of petroleum interface. This sulfide is then in turn consumed by maturity. Nature 308, 442-443. the Beggialoa. We postulate that bacterial sulfate ,, Rowland, S.J., Sheppard, P.N. & Ciiikila, T.V. (1985): The effects of thermal matu reduction is enhanced both as a result of higher tem rity on distributions of dimethylnaphthalenes and peratures in these sediments, and increased nutrients trimcthylnaphthalencs in some ancient sediments and in the rising porewaters. petroleums. Geochim. Cosmochim. Acta 49, 4. In layers enriched in diatoms, cementation ofsedi 385-395. ments by silica precipitation can lead to the block Brown, T. (in prep.): Wet Chemical Analysis of age of upward-flowing hydrothermal fluids. This Marine Sediments - Application to Hydrothermal results in channelling of migrating hydrothermal Sediments of Guaymas Basin. M.S. thesis, San fluids to fractures associated with faults, and thereby Diego State University, San Diego, California. focuses the location of hydrothermal deposits on the Campbell, A.C., Bowers, T.S., Measures, C.I., Falkner, K.K., Kadem, M. & Edmond, J.M. seafloor. Core 1630-ACI is representative of such (1988): A time scries ofvent fluid compositions from cementation. 2I°N, EPR (1979, 1981, 1985) and the Guaymas 5. A comparison of interstitial-water compositional Basin, Gulf ofCalifornia (1982,1985). J. Geophys. changes in cores 1617-ACI, 16I9-AC2, 1629-AC2, Res. 93, 4537-4549. 1630-ACI and 1984-ACI indicates that they Donnelly, T.W. (1980): Chemical composition of represent mixtures of seawater and hydrothermal deep sea sediments - Sites 9 through 425, Leg 2-54, fluids; in situ chemical reactions have caused over DSDP. Initial Reports Deep Sea Drilling Project 54, prints on these changes, so that the data cannot be 899-949. U.S. Gov. Printing Office, Washington, used to distinguish whether the hydrothermal end- D.C. Einsele, G. (1982): Mechanism of sill intrusion in soft member is typically associated with a deep-seated sediment and expulsion of pore waters. Initial hydrothermal system or with a sill-induced Reports Deep Sea Drilling Project 64 (2), 1169-1176. hydrothermal system. U.S. Gov. Printing Office, Washington, D.C. 6. In dive area 1630 large amounts of petroleum , Gieskes, J.M., et al. (1980): Intrusion of (both oil and gas) are associated both with hydrother basaltic sills into highly porous sediments and the 602 THE CANADIAN MINERALOGIST resulting hydrothermal activity. A/«rrwe283,44l-445. Pacific. Science 217, 245-248. Gieskes, J.M. (1974): Interstitial water studies, Leg 25. .& Manheim, F.T. (1974): Interstitial solutions Initial Reports Deep Sea Drilling Project 25, 361- and diagenesis in deeply buried marine sediments: 394. U.S. Gov. Printing Office, Washington, D.C. results from the DeepSea DrillingProject. Geochim. , Elderfield, H., Lawrence, J.R., Johnson, J., Cosmochim. Acta 39, 103-127. Meyers, B. & Campbell, A. (1982a): Geochemis Simoneit, B.R.T. (1983): Organic matter maturation try ofinterstitial waters and sediments, Leg 64, Gulf and petroleum genesis: geothermal versushydrother of California. Initial Reports Deep Sea Drilling mal. In The Role of Heat in the Development of Project 64(2), 675-694. U.S. Gov. Printing Office, Energy and Mineral Resources in the Northern Basin Washington, D.C. and Range Province. Geolherm. Res. Council, Spe _, Kastner, M., Einsele, G., Kelts, K. & Nie- cial Rep. 13, Davis, California, 215-241. mitz, J. (1982b): Hydrothermal activity in the (1984a): Effects of hydrothermal activity on Guaymas Basin, GulfofCalifornia: A synthesis. Ini sedimentary organic matter: Guaymas Basin, Gulf tial Reports Deep Sea Drilling Project 64(2), 1159- of California - Petroleum genesis and protokcro- 1168. U.S. Gov. Printing Office, Washington, D.C. gen degradation. In Hydrothermal Processes at Campbell, A.C, Shaw, T., Brown, T. & Seafloor Spreading Centers (P.A. Rona, K. Bos- Sturz, A. (1988): Interstitial water and hydrother trom, L. Laubier& K.L. Smith, Jr., cds.). Plenum mal water chemistry, Guaymas Basin, Gulf of Press, New York, 451-471. California. In The Gulf and Peninsular Province of . (1984b): Hydrothermal effects on organic mat the Californias. Amer. Assoc. Petrol. Geol. Mem. ter - high versus low temperature components. In (in press). Advances in Organic Geochemistry 1983. Organic Kastner, M. (1982): Evidence for two distinct Geochem. 6, 835-864. hydrothermal systems in the Guaymas Basin. Ini . (1985a): Hydrothermal petroleum: composition tial Reports Deep Sea Drilling Project 64(2), I MS- and utility as a biogenic carbon source. In MS?. U.S. Gov. Printing Office, Washington, D.C. Hydrothermal Vents of (he Eastern Pacific: An Kawka. O.E. & Simoneit, B.R.T. (1987): Survey of Overview. (M.L. Jones, cd.). Bull. Biol. Soc. Wash. hydrothcrmally-gcncratcd petroleums from the 6, 49-56. Guaymas Basin spreading center. Org. Geochem. 11, (1985b): Hydrothermal petroleum: genesis, 311-328. migration and deposition in Guaymas Basin, Gulf Kelts, K.R. (1982): Petrology of hydrothermally of California. Can. J. Earth. Sci. 11, 1919-1929. metamorphosed sediments at DSDP Site 477, & Lonsdale, P.F. (1982): Hydrothermal Southern Guaymas Rift, Gulf of California. Initial petroleum in mineralized mounds at the seabed of Reports Deep Sea Drilling Project 64(2), 1123-1146. Guaymas Basin. Nature 295, 198-202. U.S. Gov. Printing Office, Washington, D.C. _, Mazurek, M.A., Brenner, S., Crisp, P.T. & Lonsdale, P. & Becker, K. (1985): Hydrothermal Kaplan, I.R. (1979): Organic geochemistry of plumes, hot springs, and conductive heat flow in the recent sediments from Guaymas Basin, Gulf of southern trough of Guaymas Basin. Earth Planet. California. Deep-Sea Res. 26A, 879-891. Sci. Lett. 73,211-225. _, Philp, R.P., Jenden, P.D. & Galimov, E.M. Maris, C.R.P. & Bender, MX. (1982): Upwelling of (1984): Organic geochemistry of Deep Sea Drilling hydrothermal solutions through ridge flank sedi Project sediments from the Gulf of California - ments shown by pore water profiles. Science 216, Hydrothermal effects on unconsolidated diatom 623-626. ooze. Organic Geochem. 7, 173-205. Merewether, R., Olsson, M.S. & Lonsdale, P. Stout, P.M. & Campbell, A.C. (1983): Hydrothermal (1985): Acoustically detected hydrocarbon plumes alteration of near surface sediments, Guaymas rising from 2 kilometer depths in Guaymas Basin, Basin, Gulf of California. Cenozoic Marine GulfofCalifornia. J. Geophys. Res. 90,3075-3085. Sedimentation, Pacific SEPM, Los Angeles, Moore, D.G. (1973): Plate-edge deformation and 223-231. crustal growth, Gulf of California structural Thompson, K.F.M. (1979): Light hydrocarbons in sub province. Geol. Soc. Amer. Bull. 84, 1883-1906. surface sediment. Geochim. Cosmochim. Acta 43, Niemitz, J. (1982): Geochemistry of sediments. Leg 64, 657-672. 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Cosmochim. Acta centers of Guaymas Basin, Gulf of California. J. 46, 1-10. Geophys. Res. 84, 6757-6769. Sayles, F.L. & Jenkins, W.J. (1982): Advection of Received July 9,1987; revised manuscript accepted May pore fluids through sediments in the equatorial 21, 1988.