Cold seep status archived in authigenic carbonates: Mineralogical and isotopic evidence from Northern South China Sea

Lu, Yang; Sun, Xiaoming; Lin, Zhiyong; Xu, Li; Lu, Hongfeng

doi:10.1016/j.dsr2.2015.06.014

Cited by 31 publications

(9 citation statements)

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“…A variety of carbonate minerals have been found in cold seep carbonates including aragonite, calcite, low-Mg calcite (LMC), high-Mg calcite (HMC), protodolomite, dolomite, ankerite and siderite (e.g. Lu et al 2015, and references therein). Several factors have been found to influence the Mg-Cacarbonate mineralogy such as the degree of supersaturation, the concentration of Mg 2 + and Ca 2 + in pore water/seawater, sulphate and phosphate concentration, temperature, partial pressure of CO 2 , microbial activity, hydrocarbon flux and available nucleation sites/templates (Walter 1986;Aloisi et al 2000;Peckmann et al 2001;Lopez et al 2009;Roberts et al 2010;Krause et al 2012;Roberts et al 2013;Panieri et al 2017b).…”

Section: Mineralogymentioning

confidence: 99%

U-Th chronology and formation controls of methane-derived authigenic carbonates from the Hola trough seep area, northern Norway

et al. 2017

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We investigated methane-derived authigenic carbonate (MDAC) crusts and nodules from a cold seep site on the northern Norwegian continental shelf in ca. 220 m water depth to determine the timing and mode of their formation. Gas bubbling observed during remotely operated vehicle (ROV)-assisted sampling of MDAC crusts revealed ongoing seep activity. Authigenic carbonates were present as crusts on the seafloor and as centimetre-size carbonate-cemented nodules at several intervals within an adjacent sediment core. Aragonite-dominated mineralogy of the MDAC crusts suggests formation close to the seafloor at higher rates of sulphate-dependent anaerobic oxidation of methane (AOM). In contrast, dolomite-cemented nodules are consistent with the formation at the sulphate-methane-transition zone deeper within the sediment at lower rates of AOM. The δ 13 C-carbonate values of bulk rock and of micro-drilled aragonite samples vary between − 22.2‰ and − 34.6‰ (VPDB). We interpret the carbon in aragonite to be mainly derived from the anaerobic oxidation of thermogenic methane, with a minor contribution from seawater dissolved inorganic carbon (DIC). AOM activity is supported by high concentrations of AOM-related biomarkers of archaea (archaeol and 2-sn-hydroxyarchaeol) and sulphate-reducing bacteria (iso and anteiso-C 15:0 fatty acids) in the crusts. The dolomite nodules exhibit higher δ 13 C-carbonate values (− 12‰ VPDB) suggesting a smaller amount of methane-derived carbon, presumably due to the contribution of DIC migrating from depth, and lower AOM rates. The latter is supported by orders of magnitude lower concentrations of archaeol and sn-2-hydroxyarchaeol in the sediment interval containing the largest dolomite nodules. δ 18 O values of pure aragonite samples and dolomite nodules indicate the precipitation of carbonate close to isotopic equilibrium with seawater and no influence of gas hydrate-derived water. U-Th dating of two MDAC crusts shows that they formed between 1.61 ± 0.02 and 4.39 ± 1.63 ka BP and between 2.65 ± 0.02 and 4.32 ± 0.08 ka BP. We infer both a spatial and temporal change in methane flux and related MDAC formation at this seep site. These changes might be caused by regional seismic events that can affect pore pressure or re-activation of migration pathways thus facilitating fluid flow from deep sources towards the seabed.

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Section: Mineralogymentioning

confidence: 99%

U-Th chronology and formation controls of methane-derived authigenic carbonates from the Hola trough seep area, northern Norway

et al. 2017

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“…The areas for low‐Mg calcite (LMC), high‐Mg calcite (HMC) and dolomite are highlighted in grey according to Lu et al . (2015). 1 = LMC, 2 = HMC, 3 = dolomite (upper right).…”

Section: Resultsmentioning

confidence: 99%

“…It is known for its ubiquitous pockmarks, normal faults, mud diapirs and mud volcanoes, connecting deep sedimentary strata with the seafloor (Hou et al ., 2008; Sun et al ., 2012a,b; Li et al ., 2013), and facilitating the establishment of methane seeps and the formation of gas hydrates; the latter were sampled for the first time in 2007 (Zhang et al ., 2007; Liu et al ., 2012). Extensive and long‐lasting supply of methane in the Shenhu area favoured the formation of abundant and widespread seep carbonates (Ge et al ., 2015; Lu et al ., 2015), having formed between approximately 330 to 150 ka (Tong et al ., 2013).…”

Section: Geological Settingmentioning

confidence: 99%

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Reducing microenvironments promote incorporation of magnesium ions into authigenic carbonate forming at methane seeps: Constraints for dolomite formation

Yang

Lin

et al. 2021

Sedimentology

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In part composed of Mg calcite and dolomite with a nearly continuous spectrum of MgCO 3 contents, carbonates forming at marine methane seeps are ideal candidates to study the formation of early diagenetic dolomite at surface conditions. Laboratory experiments, modelling and the co-variation of mineralogical and geochemical attributes of seep carbonates suggest that sulphidelocally released from sulphate-driven anaerobic oxidation of methanedrives catalytic dolomite formation at seeps. Direct comparison of the concentration of dissolved sulphide with the MgCO 3 content of seep carbonate could test this hypothesis. Although the concentration of sulphide during precipitation of carbonate cannot be determined, sedimentary fabrics probably had an effect on local sulphide concentration. Carbonates from the seabed of the Shenhu seepage area of the South China Sea reveal longitudinal, winding and branched fabrics with a width of 400 to 700 μm, interpreted to represent burrows piercing semi-consolidated sediment. The abandoned burrows were infilled with fine-grained sediment, which was subsequently cemented by microcrystalline dolomite and Mg calcite. The degree of cation ordering of dolomite in burrow infills and host sediment is similar, indicating virtually coeval dolomite formation. The Mg/Ca mole ratios of carbonate minerals are lower in burrow infills than in the surrounding sedimentary matrix. Similarly, δ 13 C carbonate values tend to be higher for burrow infills (from −41 to −33‰) than for the matrix (from −43 to −38‰), suggesting stronger seawater influence on pore waters in the burrows. More reducing microenvironments of the sedimentary matrix supposedly came along with higher concentrations of dissolved sulphide, which allowed more Mg 2+ ions to enter the crystal lattice and led to more catalytic dolomite formation in the host sediment. The distribution of MgCO 3 contents and δ 13 C values in the authigenic Shenhu carbonates reinforces the hypothesis that sulphide release by sulphate-driven anaerobic oxidation of methane is a key factor in the formation of dolomite at seeps.

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“…Barium diffused upward and precipitated as authigenic barium sulfate above the SMTZ [46,47]. The level of authigenic barium sulfate precipitation depended on the upward diffusion of dissolved Ba 2+ flux and the length of time that the SMTZ remained at that horizon [16,40,41,42,43,44,45,46,47,48]. Results showed that there were two significant enrichments of Ba in core SH3 sediments above the modern SMTZ horizon and the paleo-SMTZ horizon (Figure 3), indicating that precipitation of barium sulfate may have occurred in sediments.…”

Section: Resultsmentioning

confidence: 99%

Geochemical Evidence of Metal-Driven Anaerobic Oxidation of Methane in the Shenhu Area, the South China Sea

Xie

Liu

et al. 2019

IJERPH

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Anaerobic oxidation of methane (AOM) is a common biochemical process in the ocean and it plays an important role in global climate change, elemental circulation, and atmospheric evolution over geological time. In this paper, we analyzed of δ34S, Fe, Mn, Ca/Ti, and Sr/Ti ratios, and the date of carbon and sulfur from the site SH3 of Shenhu area. Result showed that (1) 0–6 mbsf (meter blow the sea floor) was mainly affected by OSR (anaerobic oxidation of organic matters) and 7–15 mbsf was a paleo-SMTZ (sulfate–methane transition zone) position. The modern SMTZ was mainly distributed at 19–25 mbsf. The barium sulfate precipitation above the modern SMTZ indicating that the current methane leakage was stable and lasted longer during geological history. (2) By studying the change of magnetic and the different carbonate minerals, results showed that there were two AOM stages. During the early stage, Fe2+ were mainly produced by sulfide abiotic reductive dissolution. During the later stage, Fe2+ were mainly produced by the metal-AOM. (3) Study of the mineral characteristics of the paleo-SMTZ and the modern SMTZ showed that the modern SMTZ carbonate minerals were mainly low-Mg calcite and aragonite, while the paleo-SMTZ carbon minerals were mainly high Mg minerals. The reason for this difference is that the modern SMTZ layer was only experienced the first stage of anaerobic oxidation of methane. In the paleo-SMTZ layer, it has experienced two stage of anaerobic oxidation of methane. During the last stage of metal-AOM, the low Mg carbonate minerals were converted into high Mg carbonate minerals. This research confirms the presence of metal-driven methane anaerobic oxidation at the bottom of sulfate-driven methane anaerobic oxidation and during the metal-driven methane anaerobic oxidation, methane and metal oxides or hydroxides would couple to convert the in situ metal oxides or hydroxides into metal ions, meanwhile the phosphorus adsorbed on the surface of the metal oxides is released into adjacent pore water, and convert to new P-bearing minerals under suitable conditions.

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Cold seep status archived in authigenic carbonates: Mineralogical and isotopic evidence from Northern South China Sea

Cited by 31 publications

References 100 publications

U-Th chronology and formation controls of methane-derived authigenic carbonates from the Hola trough seep area, northern Norway

U-Th chronology and formation controls of methane-derived authigenic carbonates from the Hola trough seep area, northern Norway

Reducing microenvironments promote incorporation of magnesium ions into authigenic carbonate forming at methane seeps: Constraints for dolomite formation

Geochemical Evidence of Metal-Driven Anaerobic Oxidation of Methane in the Shenhu Area, the South China Sea

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