Organic Matter Characterization in Sediments from ...

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ScienceDirect Procedia Earth and Planetary Science 17 (2017) 550 – 553

15th Water-Rock Interaction International Symposium, WRI-15

Organic matter characterization in sediments from the WagnerConsag Basins, Gulf of California: evidence of hydrothermal activity Catalina Ángelesa, Rosa Ma. Prol-Ledesmab,1, Kinardo Flores Castroc a

Posgrado en Ciencias del Mar y Limnología, Universidad Nacional. Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México D.F., Mexico b Departamento de Recursos Naturales, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México D.F., Mexico c Centro de Investigaciones en Ciencias de la Tierra. Universidad Autónoma del Estado de Hidalgo, Pachuca, México

Abstract Recent findings of high heat flow and gas vents in the Wagner-Consag basins support the hypothesis of active hydrothermal activity in the area. Chemical studies of the sediments from the Wagner Basin show that they have been subject to alteration of the sediment organic matter due to hydrothermal activity, similar to what has been reported in the Central Gulf of California (Guaymas Basin), where high heat flow has been related to hydrocarbon generation and thermogenic methane abundance. Organic matter in the sediment provides evidence of maturation related to elevated temperatures in the ocean bottom nearby the gas-venting features. The presence of specific organic compounds like polycyclic aromatic hydrocarbons (PAH’s), mono- and dimethylated alkanes and naphthalene trimethylated isomers, in addition to the large sulfur content of the sediments, indicates hydrothermal alteration of the sediment organic matter (SOM). Identification of the isoprenoid (PM1) related to the phylum Crenarchaeota is evidence of high temperature (75 to 105° C) as this is the optimal temperature for those organisms. This coincides with identification of Archea by DNA sequencing from the sediments surrounding the gas vents. High variability was observed in the maturity of organic matter in the sediments of the basins in correlation with the presence of hydrothermal activity. © 2017 2017The TheAuthors. Authors. Published by Elsevier Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of WRI-15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 Keywords: Submarine hydrothermal vents, biomarkers, organic matter maturation, microbial activity.

* Corresponding author. Tel.: +525556224131; fax: +525555502486 E-mail address: [email protected]

1878-5220 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.139

Catalina Ángeles et al. / Procedia Earth and Planetary Science 17 (2017) 550 – 553

1. Introduction Hydrocarbon formation by maturation of organic matter in sediments has been documented in the Guaymas Basin, Escanaba Trough, Bransfield Strait and Atlantis II Deep, in relation with hydrothermal activity 1,2, similar phenomena have been observed in continental hydrothermal systems hosted in sedimentary rocks 3. The constitution of the initial sedimentary organic matter determines the types of petroleum products that form in basins: terrestrial detritus from mainly vascular plants yields an aromatic kerogen (e.g. coal), for the generation of natural gas, whereas marine/lacustrine organic matter from primarily microbial and planktonic residues yields an aliphatic kerogen (e.g. sapropel) which has a potential to produce paraffinic petroleum. Kerogens in sedimentary basins are commonly mixtures of these inferred endmembers. The Gulf of California contains 8 active extensional basins that form the Gulf of California rift system and one of the highest sedimentation rates. These characteristics have triggered the formation of different types of hydrocarbons in the active oceanic rifts as reported for the Guaymas Basin4. Here we present the results of chemical analyses of organic matter from sediment samples collected in areas of active venting in the Wagner and Consag Basins. 2. Study area The Wagner and Consag basins are the northernmost active basins, where the sedimentation rate has been calculated5 to be 3.77 cm yr-1; therefore, the basins present a thick sediment cover of at least 5 km and bathymetry data show a maximum depth of 200m (Fig. 1a). Sub-bottom profiling of the sediments revealed various structures related to gas venting, which include faults and massive gas-charged zones very close to the surface in the centres of domes with gas flares 31.2

31.1

A B

31

30.9

C 30.8

E

30.7

D 30.6

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-114.3

-114.2

-114.1

-114

-113.9

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Fig. 1. a) Location and bathymetry of the Wagner and Consag basins. Stars indicate gas flare location; b) Location of sampling sites (A, B, C, D, E), crosses denote gas vents and triangles denote mud volcanoes (modified after6)

High heat flow data measured in both basins (above 1 W m-2) is evidence of the active rifting process in this area7. Seismic tomography data discovered very low velocity anomalies in the mantle 8; this is evidence of active rifting. 2.1. Chemistry and mineralogy of the sediments Sediment samples (Fig. 1b) collected under the flares of the Wagner and Consag basins consist of silty sand or shell gravels of very fine to medium grain size. Around the major gas vents of the NE Wagner Basin, the sediments are grey muds that locally contain up to 2 % modal of disseminated pyrite grains and up to 35 % modal of barite spheroidal aggregates. In such sediments calcite occurs in minor amounts.

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3. Methodology 25 sediment samples were collected during the oceanographic cruise Wag-01 on the R/V “El Puma”. The stations were located in areas were the presence of flares was observed. Samples were collected from depths from 94 to 230 m with a Smith-McIntyre dredge. As soon as the sediments were recovered the temperature was measured (from 15.3 to 26.3ºC). Two corers were used to obtain sediment samples, which were divided in two subsamples: surface sample that was directly in contact with the ocean water and a deeper sample between 4 and 12 cm deep. A total of 37 samples were processed for analyses. They were kept frozen until they were dried and all bioclastic matter was separated (between 0.01 and 4.3 wt%). Determination of the organic matter content in the samples was performed following the procedure proposed by9 with modifications10. Organic matter was extracted from 100 g of each sample using high purity organic solvents (hexane, ethylene acetate and methanol). The extracted matter was analysed in a gas chromatograph (GC-MS 5973 Network, injector 7683 B, coupled to a selective mass detector HP argilent 6890 N). 4. Results The fine sediments have higher organic matter content; however, the samples collected in the Wagner-Consag basins do not present any correlation between the bitumen content and the average grain size, nor with temperature and depth. The percentage of total organic matter that was calculated from the bitumen content, varies between 1 and 5% wt. The extracted organic matter content is lower in the upper sediments as result of the biologic activity. Low OM content occurs at depths of few centimeters due to the rapid sedimentation rate. The composition of the organic matter is diverse (Table 1). The predominant compounds are: aliphatic alkanes (from n-C16 to n-C31); compounds derived from isoprenoids Pristane (Pr) y Phytane (Ph); and some mono- and dimethylated compounds (p.e. 2-metil nonadecane), Additionally, other cyclic and branched hydrocarbons (p.e. 11-decil-eneicosane, cyclooctacosane) as well as aromatic polycyclic hydrocarbons (p.e. trimethylnaphthalene) were identified. Table 1. Parameters calculated from isoprenoid concentration. Sample Pr/Ph Pr/nC17 Ph/nC18 W18 1.04 0.92 0.78 W18a 1.55 1.16 0.93 W18b 2.20 1.85 1.03 E1 0.77 2.16 1.10 E3a 0.42 1.01 1.07 E3b 0.59 1.16 1.13 E7 0.47 1.52 0.95 E8 0.41 1.39 2.31 E9 0.60 2.83 2.40 W30 1.56 1.01 0.87 W31 1.38 1.23 1.25 W31a 0.96 1.38 2.16 W31b 0.51 1.01 1.12 W31c 0.87 0.66 0.93 W31d 1.40 1.46 1.09 W31f 1.37 1.02 0.93

% nor-Pr 17.56 10.42 10.86 0.00 0.00 0.00 0.00 3.42 0.00 7.61 17.10 14.20 13.32 10.01 11.14 0.00

% Pr 17.61 32.74 40.00 19.28 7.70 8.79 11.36 17.52 22.35 31.51 30.90 38.74 40.27 28.38 32.26 14.53

% Ph 16.92 21.16 18.16 25.13 18.32 14.83 23.91 42.56 37.11 23.05 19.86 16.51 16.31 30.41 17.90 28.72

%PMI 47.91 35.67 30.97 55.59 73.98 76.38 64.73 36.50 40.54 37.83 32.15 30.55 30.10 31.20 38.70 56.75

%nor-Pr, %Pr, %Ph, %PMI calculated on the basis of total isoprenoids in the sample

The samples that contain isomers of trimethylnaphthalene were characterized by the predominance of the 2,3,6trimethylnaphthalene over the 1,4,6- trimethylnaphthalene, which is evidence of thermal maturity11. Sulfur crystal precipitation was observed in some samples while processing them, sulfur content is higher than 83%. 5. Discussion and conclusions The organic compounds contained in the studied sediment samples have a marine origin, as the terrigen material content is small. The observed compounds: aliphatic alkanes (from n-C16 to n-C31); Pristane (Pr) y Phytane (Ph);


and 2-metil nonadecane are typical of hydrothermal systems, as they are produced by cyanobacteria observed in those systems12. The highest values were observed in the areas where the largest hydrothermal manifestations were observed: high heat flow and intense gas venting. Ph enrichment and the presence of isoprenoid (PM1) can be related to the phylum Crenarchaeota, this is supported by recent findings by DNA sequencing 13 of the abundance of the phylum Archea in the sediments surrounding the gas vents. Other hydrocarbons as 11-decil-eneicosane, cyclooctacosane and trimethylnaphthalene can be produced by biodegradation or be a residue of high-temperature pyrolisis. The predominance of the 2,3,6-trimetil naphthalene over the 1,4,6- trimethylnaphthalene is considered as evidence of thermal maturity11. The presence of trimethylnaphthalene and its relation with the high sulfur content has been observed also in the Guaymas Basin organic matter, where it is associated with the occurrence of high temperature hydrothermal vents. The diversity in conditions of the biologically mediated water-sediment interaction are evident in the large variations in the maturity of organic matter in the sediment samples (CPI calculations) that can be attributed to local temperature anomalies related with active venting. The Pr/Ph ratio shows an enrichment in Ph, which can be related to methanogenic microorganisms. Identification of PAH’s, mono and dimethylated alkanes, trimethylnaphthalene isomers and their relative proportions in the sediment samples from the Wagner and Consag basins confirm the influence of hydrothermal activity in the organic matter maturation. The abundance of sulfur in the sediment is assumed to be derived from hydrothermal fluid discharge on the ocean bottom. Acknowledgements This research on the geothermal systems of Baja California and the Gulf of California is funded by the projects: SENER-CONACyT 152823, IMPULSA IV-UNAM, FONCICYT 94482. We are very grateful to the crew of the R/V El Puma and the Comisión Académica de Buques Oceanográficos. We thank R. Rodolfo-Metalpa, A. Estradas, K. Choumiline, M.A. Aguilar-Juárez, J.G. Gómez, F. Sandoval and M. López for their help. References 1. Simoneit, B. R. T. Hydrothermal effects on organic matter – High versus low temperature components. In: Advances on Organic Geochemistry 1983. Organic Geochemistry, 1984, 6, 857-864. 2. Simoneit, B.R.T. Petroleum generation, an easy and widespread process in hydrothermal systems: an overview. Applied Geochemistry.1990. 5, 3-15. 3. Weston, R.J., Woolhouse, A.D., Organic geochemistry of the sedimentary basins of New Zealand part IV. A biomarker study of the petroleum seepage and some well core bitumens from the geothermal region of Ngawha Springs. Applied Geochemistry, 1987. 2, 305-319. 4. Simoneit, B. R. T. Effects of hydrothermal activity on sedimentary organic matter: Guaymas Basin, Gulf of California –petroleum genesis and protokerogen degradation. In: Hydrothermal Processes at the Sea Floor Spreading Centers (eds. Rona, P. A., Böstrom, K., Laubier, L. y Smith, K. L. Jr.) NATO-ARI Series Plenum Press, 1984. 453-474. 5. Baba, J., Peterson, C.D. & Schrader, H.J. Fine-grained terrigenous sediment supply and dispersal in the Gulf of California during the last century. In: J.P. Dauphin, B.R. Simoneit, Eds. The Gulf and Peninsular Provinces of the Californias, (AAPG Mem, 1991), 1991. 47, 589-602. 6. Canet, C., Prol-Ledesma, R.M., Dando, P.R., Vázquez-Figueroa, V., Shumilin, E., Birosta, E., Sanchez, A., Robinson, C.J., Camprubí, A., Tauler-Tauler, E. Discovery of massive seafloor gas seepage along the Wagner fault, Northern Gulf of California. Sedimentary Geology. 2010. 228, 292−303 7. Prol-Ledesma, R.M., Torres-Vera, M.A., Rodolfo-Metalpa, R., Ángeles, C., Lechuga Deveze, C.H., Villanueva-Estrada, R.E., Shumilin, E. and Robinson, C., High heat flow and ocean acidification at a nascent rift in the northern Gulf of California. Nature Communications. 2013. doi:10.1038/ncomms2390. 8. Wang, Y., Forsyth, D. W., Savage, B. Convective upwelling in the mantle beneath the Gulf of California, Nature, 2009. 462(7272), 499–501. 9. Walkey, A., Black, I. A. An examination of the Degthareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Science. 1934. 27, p. 29-38. 10. Okuda, T. Some problems for the determination of organic carbon in marine sediments. Boletín del Instituto Oceanográfico de la Universidad de Oriente. 1964. 3, p. 106-117. 11. Alexander, R., Kaki, R.I., Rowland, S.J., Sheppard, P.N., Chirila, T.V. The effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphtahlenes in some Ancient sediments and petroleums. Geochimica et Cosmochimica Acta, 1985. 49, 385-395. 12. Dembitsky, V. M., Dor, I.; Shkrob, I., Aki, M. Branched alkanes and other apolar compounds produced by the cyanobacterium Microcoleus vaginatus from the Negev Desert. Russian Journal of Bioorganic Chemistry, 2001.27, 110-119. 13. Juárez, K., Villaltoro, F., Tobon, E., Dávila, S., Prol-Ledesma, R.M., Archaeal communities at gas-venting basins in the Gulf of California (Wagner and Consag Basins). 15th International Congress on Microbial Ecology (ISME). Seul, Corea. 24-28 Aug. 2014.

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