Magnetic Susceptibility in Surface Sediments in the Southern South China Sea and Its Implication for Sub-sea Methane Venting

• Published in: Journal of earth science (Wuhan, China) Vol. 20; no. 1; pp. 193 - 204
• Main Author: 陈忠 颜文 汤贤赞 刘建国 陈木宏 杨华平
• Format: Journal Article
• Language: English
• Published: China University of Geosciences (Wuhan) China University of Geosciences (Wuhan) 01.02.2009; Springer Nature B.V
• Subjects: Biogeosciences; Chemical analysis; Continental shelves; Earth and Environmental Science; Earth science; Earth Sciences; Geochemistry; Geology; Geotechnical Engineering & Applied Earth Sciences; Magnetism; Manganese; Marine; Marine geology; Methane; Ocean floor; Oceans; Pyrite; Seawater; Sediment samplers; Sediments; Sulfides; Water analysis; 中南部; 南海南部; 甲烷排放; 硫化物矿物; 磁化率; 磁黄铁矿; 表层沉积物; South China Sea; ISEW, South China Sea; magnetic particle; surface sediment; magnetic susceptibility; southern South China Sea; oil/gas & gas hydrate
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-009-0019-y

In order to understand the characteristics of magnetic variability and their possible implication for sub,sea methane venting, magnetic susceptibility （MS） of 145 surface sediment samples from the southern South China Sea （SCS） was investigated. Magnetic particles extracted from 20 representative samples were also examined for their mineral, chemical compositions and micromorphology. Results indicate that MS values range between -7.73×10^-8 and 45.06×10^-8m^3/kg. The high MS zones occur at some hydrocarbon-bearing basins and along main tectonic zones, and low ones are distributed mainly within the river delta or along continental shelves. Iron concretions and manganese concretions are not main contributors for high MS values in sediments, while authigenic iron sulphide minerals are possibly responsible for the MS enhancement. This phenomenon is suspected to be produced by the reducing environment where the high upward venting methane beneath the seafloor reacts with seawater sulfate, resulting in seep precipitation of highly susceptible intermediate mineral pyrrhotite, greigite and paramagnetic pyrite. It suggests that MS variability is possibly one of the geochemical indicators for mapping sub-sea zones of methane venting in the southern SCS.