Changing redox conditions at cold seeps as revealed by authigenic carbonates from Alaminos Canyon, northern Gulf of Mexico

Birgel, Daniel; Dong, Feng; Roberts, Harry H.; Peckmann, Jörn

doi:10.1016/j.chemgeo.2011.03.004

Cited by 140 publications

(91 citation statements)

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“…Ce anomalies are used to indicate redox conditions of seep carbonate precipitation environments [50,[54][55][56]. The negative Ce anomaly indicates oxidizing environments while no or positive Ce anomaly indicates reducing environments.…”

Section: Formation Conditions Of Xigaze Seep Carbonatesmentioning

confidence: 99%

First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet, China

Tong

Chen

2012

Chin. Sci. Bull.

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Hydrocarbon seeps, widely occurring in continental margins, have become increasingly focused owing to their close relationships with gas hydrates, strong greenhouse gas methane, and biological resources in extreme environments. Ancient hydrocarbon seeps have already been recognized from Devonian to Quaternary strata worldwide based on seep carbonates or seep-related fossil chemosynthetic assemblages. However, seep-related deposits are rarely found from ancient strata in the mainland China. Here, we report the first discovery of an ancient seep deposit, specifically late Cretaceous seep carbonates from Xigaze in Tibet, China. Xigaze seep carbonates, occurring as nodules, are enclosed in upper Cretaceous turbidite strata in Xigaze forearc basin. These carbonates are composed of authigenic carbonate (56.2% on average), clastic quartz and feldspar (27.3% on average), and clay minerals (chlorite, illite and smectite, 16.5% on average). Clotted micrites, peloids and framboid pyrites are frequently observed, all of which are common in modern seep carbonates. The carbonates have negative  13 C values varying from 27.7‰ to 4.0‰ (V-PDB), suggesting that thermogenic methane is the primary carbon source. Ce/Ce* values revised by eliminating La effects show no real Ce anomaly, indicating the carbonates were primarily precipitated in a weak reducing environment. Overall, these features provide unequivocal evidences that the seafloor of Xigaze forearc basin developed hydrocarbon seeps in late Cretaceous. seep carbonate, carbon isotope, sedimentary fabric, Xigaze, late Cretaceous Citation:Tong H P, Chen D F. First discovery and characterizations of late Cretaceous seep carbonates

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Section: Formation Conditions Of Xigaze Seep Carbonatesmentioning

confidence: 99%

First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet, China

Tong

Chen

2012

Chin. Sci. Bull.

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“…0.2e0.4) under oxygenated conditions and positive under anoxic conditions (e.g., Olivier and Boyet, 2006;Hu et al, 2014;Tostevin et al, 2016). Nevertheless, it has been observed that the presence/absence of a negative Ce anomaly in authigenic methaneimprinted carbonates can be due to mineral formation in high pore water alkalinity where organic matter occurs (Pourret et al, 2008;Kim et al, 2012) to the intermittent oxygenation of sediments (Birgel et al, 2011;Hu et al, 2014) and can be also affected by leaching procedure (Zhang et al, 2015). Discontinuous fluids discharge and downward flow of sea water during periods of reduced seepage can produce carbonates with a particular geochemical signature and disguise the original Ce anomaly (Solomon et al, 2008;Kim et al, 2012;Hu et al, 2014) resulting in a Ce/Ce* ratio close to 1.…”

Section: Redox Conditions During Sedimentationmentioning

confidence: 99%

“…Siderite, on the other hand, yields higher (Mo/U) EF values (average 32.2), which are evidence of precipitation under strong anoxic conditions. Varying (Mo/U) EF , Ce anomalies and carbonate phases are better explained by temporary oxic conditions and variations in sulfide concentration induced by seepage flux changes (Feng et al, 2009;Birgel et al, 2011;Hu et al, 2014). These changes have probably been triggered by allogenic rapid changes in palaeoenvironmental and palaeoceanographic conditions (Rovere, unpublished data).…”

Section: Redox Conditions During Sedimentationmentioning

confidence: 99%

“…This, in turns, increases the pore water alkalinity and favors the precipitation of authigenic carbonates. It has been proved that the discontinuous seepage of methane may influence the overall geochemical composition of the authigenic carbonates affecting both stable isotope composition of carbon and oxygen (Birgel et al, 2011;Hu et al, 2014) and REE distribution (Solomon et al, 2008;Kim et al, 2012;Hu et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Franchi

Rovere

Gamberi

et al. 2017

Marine and Petroleum Geology

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a b s t r a c tPaola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ).Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO 2 -rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area.In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water.Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the 13 C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13 C-rich dissolved inorganic carbon (DIC) and 18 O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO 2 .

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“…Therefore the possibility of contamination requires careful assessment before the observed REE + Y compositions of the Doushantuo cap carbonates can be reliably used to deduce chemical peculiarities of precipitating waters and depositional environments. In order to minimize contamination, several approaches were taken in this study: 1) materials that are associated with later-stage mineral cements filling in fractures, sheet cracks, and cavities were avoided; 2) samples without evidence of recrystallization and metamorphism by examining thin sections under crossed-polarized light were used; 3) mm-sized chips free of visible later-stage minerals after crushing were carefully handpicked using an optical microscope; and 4) gentle acid was employed to dissolve collected samples and acid-insoluble residues were discarded; we emphasize that the same dissolution experiments as ours were performed for dissolving marine carbonates, which yielded primary REE + Y distributions (Feng et al, 2010;Birgel et al, 2011).…”

Section: Contamination Evaluationmentioning

confidence: 99%

Geochemical constraints on the origin of Doushantuo cap carbonates in the Yangtze Gorges area, South China

Wang

Lin

Chen

2014

Sedimentary Geology

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Changing redox conditions at cold seeps as revealed by authigenic carbonates from Alaminos Canyon, northern Gulf of Mexico

Cited by 140 publications

References 85 publications

First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet, China

First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet, China

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Geochemical constraints on the origin of Doushantuo cap carbonates in the Yangtze Gorges area, South China

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