A unique Fe-rich carbonate chimney associated with cold seeps in the Northern Okinawa Trough, East 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

“…Sivan et al obtained the δ 56 Fe values of iron cations in pore water (−1.66% to −2.33% ) [21], which were similar to those of the other sediments with an active dissimilatory bacterial iron reduction [25]. Recently, Fe-rich carbonate chimneys/pipes (mainly composed of aragonite, magnesium-rich calcite, dolomite, ankerite, and siderite) in the northern Okinawa Trough were systematically investigated and might be attributed to the involvement of Fe-driven AOM [26][27][28]. Field observations revealed that metal-driven AOM generally occurred at sites where other electron acceptors, especially sulfates, were depleted just like those in brackish water estuaries [14] or in methanogenic zones below the SMTZ with abundant Fe/Mn-oxides and dissolved low-valence Fe/Mn cations [20,[29][30][31].…”

“…González et al reported that the formation of 13 C-depleted Fe-Mn carbonate nodules was fueled by the anaerobic oxidation of thermogenic hydrocarbons and organic matter within the channel floor sediments in the Gulf of Cadiz [59]. Sun et al, Peng et al, and Li et al sequentially found that the carbonate deposits linked to Fe-driven AOM in the northern Okinawa Trough were mainly composed of aragonite, Mg-calcite, dolomite, and siderite [26][27][28]. In core DH-CL14, the authigenic minerals in unit B mainly include calcite, aragonite, dolomite, siderite, and rhodochrosite ( Figures 3, 4 and S2).…”

“…In this case, the study area is located in the northeastern unstable continental slope of the SCS [84] (Figure 1), and the sediments with abundant Fe/Mn-oxides from the shelf of the SCS might be integrally transported into the Dongsha area due to the structural or gravity instability. The previously deposited Fe/Mn-oxides, in particular, goethite, ferrihydrite, and birnessite with large specific surface areas [28,60,61,85], would spontaneously trigger the onset of AOM in the sediments with high-flux methane seeps. Obviously, the Fe/Mn source, in this case, evidently differs from those previously reported in the northern Okinawa Trough (i.e., Fe 3+ derived from deep-source fluids at methane seeps) [26][27][28].…”

Using iron speciation in authigenic carbonates from hydrocarbon seeps to trace variable redox conditions

“…pyrite, siderite, ankerite) are among the diagenetic products of this process, and are frequently observed in association with the predominant calcium carbonate minerals at seeps (e.g. Chen et al, 2006;Dewangan et al, 2013;Gonz alez et al, 2012;Peckmann et al, 2001;Sun et al, 2015;Zhang et al, 2014). Numerous seafloor observations revealed significant variability of chemical and physical parameters and associated early diagenetic conditions within shallow subsurface sediments at seeps (e.g.…”

“…Lyons and Severmann, 2006;Owens et al, 2012;Raiswell and Canfield, 2012;Severmann et al, 2010;Scholz et al, 2014a,b), Fe is a potential redox proxy that allows constraining the formation conditions of marine sediments and sedimentary rocks. Studies on Fe in sediments at seeps and in authigenic seep deposits mainly focused on the geochemical cycling of Fe and the involved biogeochemical processes Beal et al, 2009;Gonz alez et al, 2012;Lemaitre et al, 2014;Pierre et al, 2014;Riedinger et al, 2014;Sivan et al, 2014;Sun et al, 2015;Zhang et al, 2014). In particular, Fe oxides can stimulate sulfate-driven AOM at seeps (Beal et al, 2009;Sivan et al, 2014).…”