Authigenic carbonate formation at hydrocarbon seeps in continental margin sediments: A comparative study

Naehr, T. H.; Eichhubl, Peter; Orphan, Victoria J.; Hovland, Martin; Paull, C. K.; Ussler, William; Lorenson, Thomas D.; Greene, H. Gary

doi:10.1016/j.dsr2.2007.04.010

Cited by 244 publications

(186 citation statements)

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“…The occurrence and formation of carbonate minerals depleted in 13 C is common among marine methane seeps (Stakes et al 1999;Luff and Wallmann 2003;Gieskes et al 2005;Naehr et al 2007;Paull et al 2007), and is used as an indicator of seepage occurrence in the geologic record (Peckmann et al 1999;Schwartz et al 2003;Campbell 2006;Gontharet et al 2007). Carbonate minerals precipitate because of the high carbonate alkalinity associated with vigorous sulfate reduction common to methane seeps.…”

Section: Introductionmentioning

confidence: 99%

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

et al. 2010

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The Coal Oil Point seep field located offshore Santa Barbara, CA, consists of dozens of named seeps, including a peripheral ∼200 m 2 area known as Brian Seep, located in 10 m water depth. A single comprehensive survey of gas flux at Brian Seep yielded a methane release rate of ∼450 moles of CH 4 per day, originating from 68 persistent gas vents and 23 intermittent vents, with gas flux among persistent vents displaying a log normal frequency distribution. A subsequent series of 33 repeat surveys conducted over a period of 6 months tracked eight persistent vents, and revealed substantial temporal variability in gas venting, with flux from each individual vent varying by more than a factor of 4. During wintertime surveys sediment was largely absent from the site, and carbonate concretions were exposed at the seafloor. The presence of the carbonates was unexpected, as the thermogenic seep gas contains 6.7% CO 2 , which should act to dissolve carbonates. The average δ 13 C of the carbonates was −29.2±2.8‰ VPDB, compared to a range of −1.0 to +7.8‰ for CO 2 in the seep gas, indicating that CO 2 from the seep gas is quantitatively not as important as 13 Cdepleted bicarbonate derived from methane oxidation. Methane, with a δ 13 C of approximately −43‰, is oxidized and the resulting inorganic carbon precipitates as highmagnesium calcite and other carbonate minerals. This finding is supported by 13 C-depleted biomarkers typically associated with anaerobic methanotrophic archaea and their bacterial syntrophic partners in the carbonates (lipid biomarker δ 13 C ranged from −84 to −25‰). The inconsistency in δ 13 C between the carbonates and the seeping CO 2 was resolved by discovering pockets of gas trapped near the base of the sediment column with δ 13 C-CO 2 values ranging from −26.9 to −11.6‰. A mechanism of carbonate formation is proposed in which carbonates form near the sediment-bedrock interface during times of sufficient sediment coverage, in which anaerobic oxidation of methane is favored. Precipitation occurs at a sufficient distance from active venting for the molecular and isotopic composition of seep gas to be masked by the generation of carbonate alkalinity from anaerobic methane oxidation.

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Section: Introductionmentioning

confidence: 99%

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

et al. 2010

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“…2b). In ancient and modern oceans, the δ 13 C carb values of certain authigenic carbonates are relatively high due to methanogenesis in the sediments (e.g., Naehr et al 2007;Heindel et al 2015;Li et al 2015). Microbial methanogenesis enriches the residual pore water within the sediments in 13 C, representing another potential mechanism for the relatively high δ…”

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Authigenic carbonate precipitation at the end-Guadalupian (Middle Permian) in China: Implications for the carbon cycle in ancient anoxic oceans

Saitoh

Ueno

Isozaki

et al. 2015

Prog. in Earth and Planet. Sci.

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Carbonate precipitation is a major process in the global carbon cycle. It was recently proposed that authigenic carbonate (carbonate precipitated in situ at the sediment-water interface and/or within the sediment) played a major role in the carbon cycle throughout Earth's history. The carbon isotopic composition of authigenic carbonates in ancient oceans have been assumed to be significantly lower than that of dissolved inorganic carbon (DIC) in seawater, as is observed in the modern oceans. However, the δ 13 C carb values of authigenic carbonates in the past has not been analyzed in detail. Here, we report authigenic carbonates in the uppermost Guadalupian (Middle Permian) rocks at Chaotian, Sichuan, South China. Monocrystalline calcite crystals <20 mm long are common in the black mudstone/chert sequence that was deposited on a relatively deep anoxic slope/basin along the continental margin. Textures of the crystals indicate in situ precipitation on the seafloor and/or within the sediments. The calcite precipitation corresponds stratigraphically with denitrification and sulfate reduction in the anoxic deep-water mass, as indicated by previously reported nitrogen and sulfur isotope records, respectively. Relatively high δ 13C carb values of the authigenic carbonates (largely −1 ‰) compared with those of organic matter in the rocks (ca. −26 ‰) suggest that the main carbon source of the carbonates was DIC in the water column. The calcite crystals precipitated in an open system with respect to carbonate, possibly near the sediment-water interface rather than deep within the sediments. The δ 13C carb values of the carbonates were close to the δ 13 C DIC value of seawater due to mixing of 13 C-depleted remineralized organic carbon (that was released into the water column by the water-mass anaerobic respiration) with the large DIC pool in the oceans. Our results imply that δ 13 C carb values of authigenic carbonates in the anoxic oceans might have been systematically different from the values in the oxic oceans in Earth's history, controlled by the depth of the redoxcline in the water column and sediments. If our model is correct, authigenic carbonates with relatively high δ 13C carb values in the ancient anoxic oceans may have had a less substantial influence on the bulk δ 13C carb values in geologic records than has been previously suggested.

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“…Although the discovery of the Black Sea AOM ecosystem has expanded our view of anaerobic methanotrophy and carbonate precipitation, the unique geochemical setting of this euxinic basin makes it difficult to extrapolate associated findings to the more globally relevant carbonate precipitation associated with AOM along continental margins. At such locations, carbonate slabs and pavements range from outcrops of vuggy, highly porous rock to lower-permeability massive structures 6,16 . Sr-isotope data and the presence of carbonate precipitation products favoured under high-bicarbonate, low-sulphate conditions suggest that carbonate is largely precipitated within the sediment, and is subsequently exposed through uplift and/or erosion 16 .…”

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confidence: 99%

“…At such locations, carbonate slabs and pavements range from outcrops of vuggy, highly porous rock to lower-permeability massive structures 6,16 . Sr-isotope data and the presence of carbonate precipitation products favoured under high-bicarbonate, low-sulphate conditions suggest that carbonate is largely precipitated within the sediment, and is subsequently exposed through uplift and/or erosion 16 . There is no large-scale visible surficial manifestation of ANME/SRB biomass, as observed in the Black Sea 18 , and the potential for carbonate-associated methanotrophic activity by extant endoliths (organisms living within the pore spaces of rocks) has not been examined.…”

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confidence: 99%

“…An estimated 14% of biologically oxidized methane at active seep settings precipitates in this manner 13 , leading to a range of carbonate minerals 14 . The resulting precipitation products may vary in size, ranging from microcrystals 15 to extensive structures of pavements, slabs and mounds produced by upward growth (known as chemoherms) or post-formation winnowing 14,16,17 . Carbonate volumes have been estimated for a few regions of active seepage and may exceed a million cubic metres at areas such as the Costa Rica margin 4 , Hydrate Ridge 6 and the Chilean subduction zone 5 , suggesting that these methane-derived structures have the potential to serve as a significant habitat within the seep ecosystem.…”

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confidence: 99%

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Carbonate-hosted methanotrophy represents an unrecognized methane sink in the deep sea

et al. 2014

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The atmospheric flux of methane from the oceans is largely mitigated through microbially mediated sulphate-coupled methane oxidation, resulting in the precipitation of authigenic carbonates. Deep-sea carbonates are common around active and palaeo-methane seepage, and have primarily been viewed as passive recorders of methane oxidation; their role as active and unique microbial habitats capable of continued methane consumption has not been examined. Here we show that seep-associated carbonates harbour active microbial communities, serving as dynamic methane sinks. Microbial aggregate abundance within the carbonate interior exceeds that of seep sediments, and molecular diversity surveys reveal methanotrophic communities within protolithic nodules and well-lithified carbonate pavements. Aggregations of microbial cells within the carbonate matrix actively oxidize methane as indicated by stable isotope FISH-nanoSIMS experiments and 14 CH 4 radiotracer rate measurements. Carbonate-hosted methanotrophy extends the known ecological niche of these important methane consumers and represents a previously unrecognized methane sink that warrants consideration in global methane budgets.

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Authigenic carbonate formation at hydrocarbon seeps in continental margin sediments: A comparative study

Cited by 244 publications

References 50 publications

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas

Authigenic carbonate precipitation at the end-Guadalupian (Middle Permian) in China: Implications for the carbon cycle in ancient anoxic oceans

Carbonate-hosted methanotrophy represents an unrecognized methane sink in the deep sea

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