Migration of the sulphate–methane reaction zone in marine sediments of the Sea of Marmara—can this mechanism be tectonically induced?

Abnormally High CH4 Concentrations in Seawater at Mid-Depths on the Continental Slopes of the Northern South China Sea

“…Apart from this, CH 4 is generated in hydrothermal vents (e.g., Chen et al 2005) and is released from sediments mainly through fermentation in an anoxic environment (Martens and Klump 1980;Kipphut and Martens 1982;Ivanov et al 1991;Tsurushima et al 1996;Marty et al 2001;Amouroux et al 2002;Chang and Yang 2003;Halbach et al 2004;Kankaala and Bergström 2004). The South China Sea's (SCS) standing as the largest marginal sea in the world ( 3.5 × 10 6 km 2 ) notwithstanding, not until very recently has CH 4 been systematically studied there, and then only for bottom water and sediments Yang et al 2006).…”

Low-temperature zircon growth related to hydrothermal alteration of siderite concretions in Mississippian shales, Scotland

“…The diagenetic zone of methanogenesis spreads beneath that of sulfate reduction, which suggests that the concretions grew on the passage between those two shallow-diagenetic zones. The zone of sulfate reduction can occur immediately below the water/sediment interface down to several centimeters or tens of meters (Devol et al 1984;Halbach et al 2004), which supports precompactional, early-diagenetic formation of the concretions. 5.…”

Sediment echo types and acoustic characteristics of gas-related acoustic anomalies in Jinhae Bay, southern Korea

“…Continued formation of methane below the sulphate zone leads to the formation of free gas if methane solubility in pore water is exceeded. Depths of SMT range from less than a meter to over 10 m (Iversen and Jørgensen, 1985;Whiticar, 1999;Halbach, 2004). Excess gas can escape to the water column, resulting in pockmarks and domes on the seafloor (Field and Jennings, 1987;Judd and Hovland, 1992).…”

“…These acoustic anomalies are affected by gas concentration, water depth, and sedimentary environment (Judd and Hovland, 1992;Taylor, 1992;Garcia-Gill et al, 2002). Depths of these acoustic anomalies are further controlled by the sulphate-methane transition (SMT) zone (Whiticar, 2002;Halbach, 2004;Laier and Jensen, 2007), where upward diffusing methane and downward diffusing sulphate are consumed in the anaerobic oxidation of methane process. Continued formation of methane below the sulphate zone leads to the formation of free gas if methane solubility in pore water is exceeded.…”