Distribution of Gases in Bottom Sediments of the Southwestern Sub-Basin South China Sea (Bien Dong)

For the first time, this paper presents the distribution of gases (CO 2 , hydrocarbon C1-C4, H 2 , He) in 39 gas samples in bottom sediments from 19 gravity cores located in the southwestern sub-basin of the South China Sea (known as Bien Dong). The surface sediments in the studied area are mostly clay and silty clay (mud). In general, the concentration of methane varies in a wide range of 0.5–440 ppm. Anomalous values of methane were detected at many locations along the slope area of the southwest sub-basin of the South China Sea. The value of 40 ppm could be considered as a background concentration of methane in the studied region. The presence of a large-scale degassing zone of methane in the studied area was proposed. Besides, heavy hydrocarbon gases (ethylene, ethane, propane, and butane) were also determined with the highest values up to 70 ppm, 124 ppm, and 50 ppm for ethylene, ethane and propane, respectively. In addition, data of carbon dioxide, hydro and helium expose some anomalous values of H 2 up to 56.7 ppm.