Early Diagenesis Records and Pore Water Composition of Methane-Seep Sediments from the Southeast Hainan Basin, South China Sea

“…The profiles of PO Figure 2f) [43]. Nevertheless, the NH 4 + maximum in core DH-CL 14 is still far lower than that in the Black Sea (<4.5 mM) [80] and the SCS (<3 mM) [81]. The quasi-linear relation of NH 4 + and logarithmic trend of PO 4 3− in pore water with depth display the consistent OMO rates, except that at a depth of 430 cm in unit B (Figure 2e,f).…”

Section: Aom Vs Omo Coupled With Fe/mn Reduction In Unit Bmentioning

confidence: 99%

Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea

Xiao

Zhou

et al. 2019

Minerals

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Fe and Mn oxides and (oxy)-hydroxides are the most abundant solid-phase electron acceptors in marine sediments, and dissimilatory Fe/Mn reduction usually links with the anaerobic oxidation of methane (AOM) and organic matter oxidation (OMO) in sediments. In this study, we report the results from subsurface marine sediments in the Dongsha hydrate-bearing area in the South China Sea. The petrological and geochemical signatures show that the Fe/Mn reduction mediated by AOM and OMO might occur in sediments above the sulfate-methane transition zone. X-ray diffraction and scanning electron microscopy analyses of sediments indicate that Fe(III)/Mn(IV)-oxides and authigenic carbonate minerals coexisted in the Fe/Mn reduction zone. The lower δ13C values of dissolved inorganic carbon, coupled with an evident increase in total inorganic carbon contents and a decrease in Ca2+ and Mg2+ concentrations indicate the onset of AOM in this zone, and the greater variation of PO43− and NH4+ concentrations in pore water suggests the higher OMO rates in subsurface sediments. Geochemical and mineralogical analyses suggest that the previously buried Fe(III)/Mn(IV) oxides might be activated and lead to the onset of Fe/Mn reduction induced by AOM and OMO. These findings may extend our understanding of the biogeochemical processes involved in Fe/Mn reduction in continental shelves with abundant methane, organic matter, and terrigenous metal oxides.

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“…A one-dimensional column model was built according to statistics and some relevant conceptual models [39]. The sulfate-methane interface (SMI) is usually located at a depth of 7-15 m below seafloor (mbsf) where methane leakage flux existed in the Qiongdongnan Basin [40]. At the same time, we calculated the SMI depth of T1 according to the sulfate profile, that is about 22 mbsf.…”

Section: Conceptual Model and Boundary Conditionsmentioning

confidence: 99%

Numerical Simulation on Authigenic Barite Formation in Marine Sediments

Shang

Tian

et al. 2019

Minerals

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Submarine cold seep and its associated authigenic minerals in sediment are meaningful to indicate the existence of underlying natural gas hydrate. The anaerobic oxidation of methane (AOM) is coupled with sulfate reduction (SR) and influences the dissolution and precipitation of barite. However, the forming mechanism of barite is not yet clearly understood. In order to investigate the forming process of authigenic barite and its relationship with methane leakage flux, based on the measured data of the Qiongdongnan Basin in the Northern slope of the South China Sea, we constructed a 1D model of a sedimentary column to reproduce the formation of barite using the numerical simulation method. The results show that the original equilibrium of barite was broken by the cold seep fluids and Ba2+ was carried upward to the sulfate-rich zone leading to the formation of barite front. When there is no flux of methane from the bottom of sediment, the barite front disappears. The relationship between methane leakage flux and authigenic minerals was also discussed. It can be concluded that high methane flux corresponds to a shallow barite front in the sediment, furthermore, the barite content first increases and then decreases as the methane flux increases. At the same time, an inverse relationship between the ratio of authigenic barite to calcite and methane flux was obtained.

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Early Diagenesis Records and Pore Water Composition of Methane-Seep Sediments from the Southeast Hainan Basin, South China Sea

Cited by 6 publications

References 40 publications

A preliminary study on the active cold seeps flow field in the Qiongdongnan Sea Area, the northern South China Sea

A preliminary study on the active cold seeps flow field in the Qiongdongnan Sea Area, the northern South China Sea

Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea

Numerical Simulation on Authigenic Barite Formation in Marine Sediments

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