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Authigenic carbonate type U1. (A) Carbonate-cemented fine laminated sedimentary Unit 1; (B) thin section image perpendicular to lamination shows alternating micrite- and clay-rich layers with biofilm and ostracods; (C) thin section image perpendicular to lamination shows irregular alternating micrite- and clay-rich layers with biofilm; (D) thin section image parallel to lamination shows sections of degassing vesicles coated with biofilm (dark colour) and pyrite framboids (dark spots); (E) SEM image with vesicle coated with biofilm; (F) SEM image showing interface laminae with biofilm and coccolith coating. White arrows indicate clay-rich intervals, dark grey arrows indicate the micrite-rich intervals and black arrows point to the biofilm coating.
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During TTR11 Cruise (2001), three areas of active fluid venting and mud volcanism were investigated in the Black Sea below the oxic zone at depths varying between 800 and 2200 m. Authigenic carbonates often associated with microbial mats were recovered from the sea floor and the shallow subsurface. Structural and petrographic observations allowed t...
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... the interface between the sedimentary layers. ! Type U1-This type of slab consists of cemented Unit 1 and was commonly retrieved from the top and the lower part of the youngest sedimentary Unit 1. The slabs can be subdivided in two subtypes. Subtype U1a is composed of very friable and poorly cemented sedimentary Unit 1 and is light grey in colour (Fig. 4A). The porous slabs preserved the millimetric sedimentary laminae and their subparallel orientation. The laminations that compose the slabs consist of alternations of clayand carbonate-rich layers. The external uneven flatlike surfaces show microbial remains-filled microvesicles whose origin is ascribed to gas seepage. Thin section ...
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... laminations that compose the slabs consist of alternations of clayand carbonate-rich layers. The external uneven flatlike surfaces show microbial remains-filled microvesicles whose origin is ascribed to gas seepage. Thin section petrography shows layers of clayey sediment that are separated by mostly continuous biofilm and micrite-rich intervals (Fig. 4B). The better cemented subtype U1b displays a greater amount of micrite filling the pores (Fig. 4C). Pyrite framboid aggregates are locally visible along the microbial biofilm layers between the laminae. Thin sections taken parallel to the sedimentary layers reveal the presence of vesicles contoured with the same biofilm, micrite, and ...
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... external uneven flatlike surfaces show microbial remains-filled microvesicles whose origin is ascribed to gas seepage. Thin section petrography shows layers of clayey sediment that are separated by mostly continuous biofilm and micrite-rich intervals (Fig. 4B). The better cemented subtype U1b displays a greater amount of micrite filling the pores (Fig. 4C). Pyrite framboid aggregates are locally visible along the microbial biofilm layers between the laminae. Thin sections taken parallel to the sedimentary layers reveal the presence of vesicles contoured with the same biofilm, micrite, and pyrite framboids (Fig. 4D) similarly to that reported by Belenkaya and Stadnitskaya (1998) and ...
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... better cemented subtype U1b displays a greater amount of micrite filling the pores (Fig. 4C). Pyrite framboid aggregates are locally visible along the microbial biofilm layers between the laminae. Thin sections taken parallel to the sedimentary layers reveal the presence of vesicles contoured with the same biofilm, micrite, and pyrite framboids (Fig. 4D) similarly to that reported by Belenkaya and Stadnitskaya (1998) and Belenkaya (2003). Ostracod shells, well preserved or fragmented, were also identified in the cement and usually with a partial coating of biofilm. SEM images confirmed the presence of biofilm-coated degassing vesicles ( Fig. 4E) and coccolith-rich layers mixed with ...
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... the same biofilm, micrite, and pyrite framboids (Fig. 4D) similarly to that reported by Belenkaya and Stadnitskaya (1998) and Belenkaya (2003). Ostracod shells, well preserved or fragmented, were also identified in the cement and usually with a partial coating of biofilm. SEM images confirmed the presence of biofilm-coated degassing vesicles ( Fig. 4E) and coccolith-rich layers mixed with micritic carbonate cement (Fig. 4F). Tubular degassing features oriented perpendicularly to sedimentary lamination were observed and appeared micrite and microbial biofilm coated. In both subtypes U1a and U1b, the slabs can peel off along the clay-rich layers, indicating that they are weak surfaces ...
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... that reported by Belenkaya and Stadnitskaya (1998) and Belenkaya (2003). Ostracod shells, well preserved or fragmented, were also identified in the cement and usually with a partial coating of biofilm. SEM images confirmed the presence of biofilm-coated degassing vesicles ( Fig. 4E) and coccolith-rich layers mixed with micritic carbonate cement (Fig. 4F). Tubular degassing features oriented perpendicularly to sedimentary lamination were observed and appeared micrite and microbial biofilm coated. In both subtypes U1a and U1b, the slabs can peel off along the clay-rich layers, indicating that they are weak surfaces in contrast to the micrite-rich layers that cement the rock together. ! ...
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... the interface between the sedimentary layers. ! Type U1-This type of slab consists of cemented Unit 1 and was commonly retrieved from the top and the lower part of the youngest sedimentary Unit 1. The slabs can be subdivided in two subtypes. Subtype U1a is composed of very friable and poorly cemented sedimentary Unit 1 and is light grey in colour (Fig. 4A). The porous slabs preserved the millimetric sedimentary laminae and their subparallel orientation. The laminations that compose the slabs consist of alternations of clay- and carbonate-rich layers. The external uneven flat- like surfaces show microbial remains-filled micro- vesicles whose origin is ascribed to gas seepage. Thin section ...
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... that compose the slabs consist of alternations of clay- and carbonate-rich layers. The external uneven flat- like surfaces show microbial remains-filled micro- vesicles whose origin is ascribed to gas seepage. Thin section petrography shows layers of clayey sediment that are separated by mostly continuous biofilm and micrite-rich intervals (Fig. 4B). The better cemented subtype U1b displays a greater amount of micrite filling the pores (Fig. 4C). Pyrite framboid aggregates are locally visible along the microbial biofilm layers between the laminae. Thin sections taken parallel to the sedimentary layers reveal the presence of vesicles contoured with the same biofilm, micrite, and ...
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... uneven flat- like surfaces show microbial remains-filled micro- vesicles whose origin is ascribed to gas seepage. Thin section petrography shows layers of clayey sediment that are separated by mostly continuous biofilm and micrite-rich intervals (Fig. 4B). The better cemented subtype U1b displays a greater amount of micrite filling the pores (Fig. 4C). Pyrite framboid aggregates are locally visible along the microbial biofilm layers between the laminae. Thin sections taken parallel to the sedimentary layers reveal the presence of vesicles contoured with the same biofilm, micrite, and pyrite framboids (Fig. 4D) similarly to that reported by Belenkaya and Stadnitskaya (1998) and ...
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... better cemented subtype U1b displays a greater amount of micrite filling the pores (Fig. 4C). Pyrite framboid aggregates are locally visible along the microbial biofilm layers between the laminae. Thin sections taken parallel to the sedimentary layers reveal the presence of vesicles contoured with the same biofilm, micrite, and pyrite framboids (Fig. 4D) similarly to that reported by Belenkaya and Stadnitskaya (1998) and Belenkaya (2003). Ostracod shells, well preserved or fragmented, were also identified in the cement and usually with a partial coating of biofilm. SEM images confirmed the presence of biofilm-coated degassing vesicles ( Fig. 4E) and coccolith-rich layers mixed with ...
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... the same biofilm, micrite, and pyrite framboids (Fig. 4D) similarly to that reported by Belenkaya and Stadnitskaya (1998) and Belenkaya (2003). Ostracod shells, well preserved or fragmented, were also identified in the cement and usually with a partial coating of biofilm. SEM images confirmed the presence of biofilm-coated degassing vesicles ( Fig. 4E) and coccolith-rich layers mixed with micritic carbonate cement (Fig. 4F). Tubular degassing features oriented perpendicularly to sedimentary lamination were observed and appeared micrite and microbial biofilm coated. In both subtypes U1a and U1b, the slabs can peel off along the clay-rich layers, indicating that they are weak surfaces ...
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... that reported by Belenkaya and Stadnitskaya (1998) and Belenkaya (2003). Ostracod shells, well preserved or fragmented, were also identified in the cement and usually with a partial coating of biofilm. SEM images confirmed the presence of biofilm-coated degassing vesicles ( Fig. 4E) and coccolith-rich layers mixed with micritic carbonate cement (Fig. 4F). Tubular degassing features oriented perpendicularly to sedimentary lamination were observed and appeared micrite and microbial biofilm coated. In both subtypes U1a and U1b, the slabs can peel off along the clay-rich layers, indicating that they are weak surfaces in contrast to the micrite-rich layers that cement the rock together. ! ...
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... The limestone beds also lack internal sedimentary structures, suggestive of an early diagenetic origin (e.g., spherulitic limestones; Emmings et al., 2020c). Enrichment in redox-sensitive elements suggests early diagenetic precipitation via anaerobic oxidation of methane (Mazzini et al., 2004), similar to Pendleian spherulitic limestones observed in the Craven Basin (Emmings et al., 2020a). Siderite-cemented beds (chemofacies B) are most commonly interbedded with the claystone facies and exhibit relatively high concentrations of Mg, Fe and Mn, and moderate Ca (Fig. 8), consistent with dolomite and/or siderite cementation. ...
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... The mound-shaped features are tentatively interpreted as representing mud volcanoes, although a different origin, such as authigenic carbonate mounds (e.g., [82,83]), cannot be completely ruled out. This hypothesis is based on the following literature and seismic data: (i) mud volcanoes and mud diapirs were identified about 7 km north of Capo San Marco [12] and in the Licata offshore, about 40 km eastward from the study area [81]. ...
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... As a result, carbonate alkalinity increase induces the precipitation of carbonate minerals close to the seafloor. These carbonates serve as an excellent archive of past seepage (Ritger et al., 1987;Bohrmann et al., 1998;Aloisi et al., 2000;Peckmann et al., 2001;Mazzini et al., 2004;Gontharet et al., 2007;Naehr et al., 2007;Haas et al., 2010;Sun et al., 2015;Himmler et al., 2019;Wang et al., 2022). ...
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... Macroscopic petrography of extant seep carbonates can be studied either directly on the seabed (e.g., Himmler et al. 2011: fig. 2a-d), on hand samples retrieved from the seabed by submersibles (e.g., Mazzini et al. 2004 fig. 3 b-d, e), observation of retrieved samples is a more unequivocal way to observe macroscopic petrography of extant seep deposits. This is with the proviso that the features targeted do not exceed the size of the sample extracted. ...
... Sediment baffling and trapping by chemosynthetic microbial mats can be one of the causes for laminated fabrics in seep carbonates (Himmler et al. 2016); microbial mats, in general, may become permineralized by Mg calcite and aragonite precipitates (Reitner et al. 2005b), and sediment baffling may even further contribute to the expression of particular laminae. Cementation of sedimentary laminations accentuated by gas hydrate can also result in layered carbonates (Mazzini et al. 2004). Fillings of tubular conduits (e.g., Greinert et al. 2002: fig. ...
Precipitation of cements forming methane-derived carbonates is inherent to marine hydrocarbon seep environments. Carbonate deposits enriched in methanogenic carbon are found in ancient rock formations as old as the Silurian. In contrast to their recent equivalents, they are mostly found on land in uplifted ancient sedimentary formations. Unlike their extant equivalents, ancient seeps are no longer active and have been frequently subjected to burial which has not yet affected recent seeps. Furthermore, aragonite forming bulk of extant seep carbonates is largely recrystallized into calcite in their ancient equivalents. Some exposures of fossil rock formations offer a three-dimensional view of plumbing system supplying ancient seeps, but this is largely hidden below the seabed where extant seeps are located.Despite distinct approaches required by occurrence and history of ancient and extant seep deposits, the petrographic features characterizing them are similar. Both are composed of microcrystalline carbonates with a variable amount of dispersed pyrite. Sparry cements, especially botryoidal aragonite and calcite, are the hallmark of seep deposits and are one of the first features noticed by any researcher. These features of seep carbonate remained virtually unchanged throughout 420 Ma of their known history and allow for easy recognition of such carbonates in the fossil record.KeywordsAragoniteAuthigenesisBotryoidalCalciteCementationHydrocarbonsMethaneMicriteMicrofaciesMineralogySeepageSpariteSulfate
... The carbonate minerals formed via Reaction 1.5 include microcrystalline high-Mg (>5% Mg) calcite, as well as dolomite, aragonite, and iron-rich carbonates (Stakes et al. 1999;Campbell et al. 2002;Greinert et al. 2002;Luff and Wallmann 2003;Mazzini et al. 2004;Reitner et al. 2005;Naehr et al. 2007;Pierre et al. 2014;Hryniewicz this volume-a). Transformations during burial and later in diagenesis can yield low-Mg calcite (Joseph et al. 2013). ...
A fundamental geochemical process operating at methane seeps is the anaerobic oxidation of methane (AOM) by which methane is oxidized and sulfate is reduced. This process takes place in the sulfate-methane transition zone (SMTZ), generally located below the sediment-water interface. Methane has a low δ13C signature, and this is transferred to the dissolved inorganic carbon (DIC) reservoir during AOM. The increase in alkalinity from AOM can cause various carbonate minerals to precipitate with low δ13C. Indeed, very low δ13C values of ancient calcium carbonates are taken as prima facie evidence that the carbonates formed in a cold hydrocarbon seep environment. Isotope systems applied to ancient hydrocarbon seeps include those of carbon, oxygen, strontium, neodymium, and sulfur. These provide information on carbon source, carbonate formation temperature, the involvement of deep-sourced fluids, and fluid pathways in transferring methane to the SMTZ. Variations of rare earth elements (REEs) provide clues to the environmental conditions under which seep carbonates formed, with implications for the precipitation depth and flow regime. Other trace elements (Fe, Mn, Sr, Mg) in seep carbonates reflect mineralogical differences, and redox-sensitive trace elements (Mo, U, Cd, Sb, As) provide constraints on fluid flux and the dynamics of redox conditions.KeywordsAnaerobic oxidation of methane (AOM)Organoclastic sulfate reductionSulfate-methane transition zoneMethanotrophyAnaerobic methanotrophic archaea (ANME)Iron cyclingSulfur cyclingCarbon isotopesOxygen isotopesStrontium isotopesNeodymium isotopesTrace elementsSulfur isotopesCarbonate-clumped isotopesRare earth elements
... Stable carbon isotopes of authigenic carbonates are critical to deciphering the source of seepage fl uids (e.g., Campbell, 2006). Such fl uids likely originate from a mixture of sources with varying proportions, resulting in distinct carbon isotopic compositions (Mazzini et al., 2004). These sources comprise carbon primarily derived from: 1) methane via AOM (typically ranging between -90‰ and -30‰) (Claypool and Kaplan, 1974); 2) the oxidation of marine organic matter (usually -20‰); 3) inorganic carbon present in seawater (0.5‰< 13 C <2‰) (e.g., Irwin et al., 1977). ...
Carbonate samples were collected from the northern Okinawa Trough in the East China Sea in 2013. The petrology, mineralogy, carbon and oxygen isotopes, and rare earth elements (REEs) of these samples were analyzed. Aragonite, high-Mg calcite, and dolomite were the main carbonate minerals, the contents of which varied greatly among the carbonate samples. Petrological observations revealed the common occurrence of framboidal pyrites. The δ13C values of carbonates varied from −53.7‰ to −39.39‰ (average of −47.3‰ based on Vienna Pee Dee Belemnite (V-PDB), n=9), and the δ18O values ranged from 0.6‰ to 3.4‰ (average of 1.9‰; V-PDB, n=9). The carbon and oxygen isotope characteristics indicated that the carbonates precipitated during the anaerobic oxidation of methane. The carbon source was a mixture of thermogenic methane and biogenic methane, possibly with a greater contribution from the former. The oxygen isotope data showed that gas hydrate dissociation occurred during carbonate precipitation. The Ce anomalies suggested that the carbonates precipitated in an anoxic environment. A slight enrichment of middle REEs (MREEs) could be attributable to the early diagenesis. The structures, minerals, oxygen isotopes, and MREEs all indicated that the carbonates experienced some degree of early diagenesis. Therefore, the influence of early diagenesis should be considered when using geological and geochemical proxies to reconstruct original methane seepage environments.
... [2][3][4][5][6][7] The natural hydrates mainly comprise methane gas. 8 Natural hydrates are ascertained to be a future energy source if used with feasible technology and will have economic value. 9 The synthetic hydrates provide multifaceted applications such as storage media for greenhouse gases, 10-16 carbon dioxide capture from fuel gas, 17 methane recovery from coal mine gas, 18,19 desalination, [20][21][22] cold storage, [23][24][25][26][27] and gas transportation. ...
Natural gas (NG) is considered a modern source of energy. Gas hydrates are anticipated to be an alternative method for gas storage and transportation applications. The process must be handy, rapid, and proficient for scale-up. In the present study, methane (CH4) and carbon dioxide (CO2) hydrates are synthesized by varying the guest (gas) to host (water) volume. The experiments are performed in a non-stirred system. The results specify that the maximum storage capacity is achieved when the molar liquid water-gas ratio is about 4.08 and 8.25 for CH4 and CO2 hydrates. At the optimal water-gas ratios, the total CH4 and CO2 gas uptake capacity is about 14.3 ± 0.4 and 9.1 ± 0.4 liters at standard temperature and pressure (STP) conditions. The gas uptake gradually increases with the solution volume and abruptly falls after a threshold point. The hydrate grows across the reactor's metal surface; when the process fully covers the surface, the growth continues horizontally (increase in thickness). With varying the liquid water-gas ratio (low to high), the formation kinetics (t90) is delayed. The hydrate growth rate gradually decreases and does not significantly influence the hydrate formation temperatures. Optimizing the molar liquid water-gas ratio yields a high gas storage capacity and faster process kinetics. This journal is
