Magnetic susceptibility in surface sediments in the southern South China Sea and its implication for sub-sea methane venting

Abstract

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 45.06×10⁻⁸ m³/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.

Keywords

magnetic susceptibility / magnetic particle / oil/gas & gas hydrate / surface sediment / southern South China Sea

References

Behain, D., Fertig, J., Meyer, H., et al., 2003. Properties of a Gas Hydrate Province on a Subduction-Collision Related Margin off Sabah, NW Borneo (Popscoms). Geophysical Research Abstracts, (5): 10008

Berner U., Faber E.. Jin X. L.. Hydrocarhon Gases in Surface Sediments of the South China Sea. Marine Geology and Geophysics of the South China Sea, 1990, Beijing: China Ocean Press 199-21l.

Calvert S. E., Pedersen T. F., Thunell R. C.. Geochemistry of the Surface Sediments of the Sulu and South China Seas. Marine Geology, 1993, 114(3–4): 207-231.

Canfield D. E., Berner R. A.. Dissolution and Pyritization of Magnetite in Anoxic Marine Sediments. Geochimica et Cosmochimica Acta, 1987, 51(3): 645-659.

Chen Z., Gu S., Yan W., . Carbonate Sediment Characteristics on Surface Sediments in the South Nansha Trough and Adjacent Sea Area. Acta Oceanologica Sinica, 2002, 24(5): 142-146.

Chen Z., Xia B., Yan W., . Distribution, Chemical Characteristics and Source Area of Volcanic Glass in South China Sea. Acta Oceanologica Sinica, 2005, 27(5): 73-81.

Chen Z., Yan W., Huang C. Y., . Geological Settings and Indicators of Potential Gas Hydrates in the Nansha Trough Area, South China Sea. Earth Science Frontiers, 2007, 14(6): 299-308.

Chen Z., Yan W., Chen M. H., . Formation of Authigenic Gypsum and Pyrite Assemblage and Its Significance to Gas Ventings in Nansha Trough, South China Sea. Marine Geology &Quaternary Geology, 2007, 27(2): 91-100.

Deng H., Yan P., Liu H. L.. Seismic Characteristics of Gas Hydrate in the Nansha Waters. Marine Geology & Quaternary Geology, 2004, 24(4): 89-94.

Drobner E., Huber H. J., Wächterhauser G., . Pyrite Formation Linked with Hydrogen Evolution under Anaerobic Conditions. Nature, 1990, 346(6286): 742-744.

Ellwood B. B., Balsam W. L., Roberts H. H.. Gulf of Mexico Sediment Sources and Sediment Transport Trends from Magnetic Susceptibility Measurements of Surface Samples. Marine Geology, 2006, 230(3–4): 237-248.

Ellwood B. B., Crick R. E., El Hassani A., . Magnetosusceptibility Event and Cyclostratigraphy Method Applied to Marine Rocks: Detrital Input versus Carbonate Productivity. Geology, 2000, 28: 1135-1138.

Elmore R. D., Leach M. C.. Remagnetization of the Rush Springs Formation, Cement, Oklahoma: Implications for Dating Hydrocarbon Migration and Aeromagnetic Exploration. Geology, 1990, 18: 124-127.

Horng C. S., Chen K. H.. Complicated Magnetic Mineral Assemblages in Marine Sediments Offshore Southwestern Taiwan: Possible Influence of Methane Flux on the Early Diagenetic Process. Terrestrial Atmospheric and Oceanic Sciences, 2006, 17(4): 1009-1026.

Hounslow M. W., Maher B. A.. Quantitative Extraction and Analysis of Carriers of Magnetization in Sediments. Geophysical Journal International, 1996, 124(1): 57-74.

Housen B. A., Musgrave R. J.. Rock-Magnetic Signature of Gas Hydrates in Accretionary Prism Sediments. Earth and Planetary Science Letters, 1996, 139(3–4): 509-519.

Huang X., Chen F., Liu J.. The Geochemical Characteristics of Surface Sediments at the South Western Nansha, South China Sea. Geological Research of South China Sea, 2003, 14: 45-55.

Hutchison C. S.. Marginal Basin Evolution: The Southern South China Sea. Marine and Petroleum Geology, 2004, 21(9): 1129-1148.

Ingram G. M., Chisholm T. J., Grant C. J., . Deepwater North West Borneo: Hydrocarbon Accumulation in an Active Fold and Thrust Belt. Marine and Petroleum Geology, 2004, 21(7): 879-887.

Kasten S., Freudenthal T., Gingele F. X., . Simultaneous Formation of Iron-Rich Layers at Different Redox Boundaries in Sediments of the Amazon Deep-Sea Fan. Geochimica et Cosmochimica Acta, 1998, 62: 2253-2264.

Larrasoaña J. C., Roberts A. P., Musgrave R. J., . Diagenetic Formation of Greigite and Pyrrhotite in Gas Hydrate Marine Sedimentary Systems. Earth and Planetary Science Letters, 2007, 261(3–4): 350-366.

Lee G. H., Watkins J. S.. Seismic Sequence Stratigraphy and Hydrocarbon Potential of the Phu Khanh Basin, Offshore Central Vietnam, South China Sea. AAPG Bulletin, 1998, 82(9): 1711-1735.

Liu H. L., Yan P., Sun Y., . Layer-Block Tectonics of the Nansha Microplate. Geology in China, 2002, 29(4): 378-381.

Liu Q. S., Liu Q. S., Chan L. S., . Magnetic Enhancement Caused by Hydrocarbon Migration in the Mawangmiao Oil Field, Jianghan Basin, China. Journal of Petroleum Science and Engineering, 2006, 53: 25-33.

Liu Z. H.. Distribution of Sedimentary Basins and Petroleum Potential in Southern South China Sea. Geotectonica et Metallogenia, 2005, 29(3): 410-4l7.

Lu Z. Q., Wu B. H., Qiang Z. J., . Brightness Temperature Anomalies in Satellite-Based Thermal Infrared Remote Sensing along the Offshore China Seas. Geoscience, 2005, 19(1): 74-82.

Luo B. J., Song Z. G., Wang Y. X., . The Multidisciplinary Oceanographic Expedition Team of Academia Sinica to Nansha Islands Organic Geochemistry of Sediments in Nansha Islands and Adjacent Sea Area. Quaternary Sedimentary Geology of Nansha Islands and Adjacent Sea Area, 1993, Wuhan: Hubei Science and Technology Press 166-195.

Luther G. W.. Pyrite Synthesis via Polysulfide Compounds. Geochimica et Cosmochimica Acta, 1991, 55(10): 2839-2849.

Milkov A. V., Sassen R.. Economic Geology of Offshore Gas Hydrate Accumulations and Provinces. Marine and Petroleum Geology, 2002, 19(1): 1-11.

Musgrave R. J., Bangs N. K., Larrasoaña J. C., . Rise of the Base of the Gas Hydrate Zone since the Last Glacial Recorded by Rock Magnetism. Geology, 2006, 34: 117-120.

Neretin L. N., Boettcher M. E., Jorgensen B. B., . Pyritization Processes and Greigite Formation in the Advancing Sulfidization Front in the Upper Pleistocene Sediments of the Black Sea. Geochimica et Cosmochimica Acta, 2004, 68(9): 2081-2093.

Novosel I., Spence G. D., Hyndman R. D.. Reduced Magnetization Produced by Increased Methane Flux at a Gas Hydrate Vent. Marine Geology, 2005, 216(4): 265-274.

Rehder G., Suess E.. Methane and p _CO2 in the Kuroshio and the South China Sea during Maximum Summer Surface Temperatures. Marine Chemistry, 2001, 75(1–2): 89-108.

Riedel M., Novosel I., Spence G. D., . Geophysical and Geochemical Signatures Associated with Gas Hydrate Related Venting in the Northern Cascadia Margin. GSA Bull., 2006, 118: 23-38.

Schoenfeld J., Kudrass H. R.. Hemipelagic Sediment Accumulation Rates in the South China Sea Related to Late Quaternary Sea-Level Changes. Quaternary Research, 1993, 40(3): 368-379.

Schlueter H. U., Hinz K., Block M.. Tectonostratigraphic Terranes and Detachment Faulting of the South China Sea and Sulu Sea. Marine Geology, 1996, 130(1–2): 39-78.

Shen Y., Buick R.. The Antiquity of Microbial Sulfate Reduction. Earth-Science Reviews, 2004, 64(3–4): 243-272.

Staub J. R., Among H. L., Gastaldo R. A.. Seasonal Sediment Transport and Deposition in the Rajang River Delta, Sarawak, East Malaysia. Sedimentary Geology, 2000, 133(3–4): 249-264.

Su G. Q., Wang T. X.. Zhou D.. Basic Characteristics of Modern Sedimentation in South China Sea. Oceanology of China Seas, 1994, Dordrecht: Kluwer Academic Publishers 407-418.

Su G. Q., Wang Y. Q., Wang T. X.. The Multidisciplinary Oceanographic Expedition Team of Academia Sinica to Nansha Islands Detrital Minerals and Clay Minerals in Nansha Islands and Adjacent Sea Area. Quaternary Sedimentary Geology of Nansha Islands and Adjacent Sea Area, 1993, Wuhan: Hubei Science and Technology Press 59-88.

Su X., Chen F., Yu X., . A Pilot Study on Miocene through Holocene Sediments from the Continental Slope of the South China Sea in Correlation with Possible Distribution of Gas Hydrates. Geoscience, 2005, 19(1): 1-13.

Szarek R., Kuhnt W., Kawamura H., . Distribution of Recent Benthic Foraminifera on the Sunda Shelf (South China Sea). Marine Micropaleontology, 2006, 61: 171-195.

Wood A. K., Ahmad Z., Shazili N. A. M., . Geochemistry of Sediments in Johor Strait between Malaysia and Singapore. Continental Shelf Research, 1997, 17(10): 1207-1228.

Wu B. H., Zhang G. X., Zhu Y. H., . Progress of Gas Hydrate Investigation in China Offshore. Earth Science Frontiers, 2003, 10(1): 177-188.

Wu S., Zhang G., Huang Y., . Gas Hydrate Occurrence on the Continental Slope of the Northern South China Sea. Marine and Petroleum Geology, 2005, 22(3): 403-412.

Yao B. C.. The Forming Condition and Distribution Characteristics of the Gas Hydrate in the South China Sea. Offshore Oil, 2007, 27(1): 1-10.

Yao B. C., Liu Z. H.. Sedimentary Basins and Petroleum Resources in Nansha Offshore Area, South China Sea. China Offshore Oil and Gas, 2006, 18(3): 150-160.

Zhang, H. Q., Yang, S. X., Wu, N. Y., et al., 2007. Successful and Surprising Results for China’s First Gas Hydrate Drilling Expedition. Fire in the Ice Newsletter, Fall: 6–9

Zhu Y. H., Zhang G. X., Lu Z. Q., . Gas Hydrate in the South China Sea: Background and Indicators. Acta Petrolei Sinica, 2001, 22(5): 6-10.