Reduced magnetization produced by increased methane flux at a gas hydrate vent |
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| Institution: | 1. School of Earth and Ocean Sciences, University of Victoria, PO Box 3055, Victoria, BC, Canada V8W 3P6;2. Geological Survey of Canada, Pacific-Sidney Subdivision, Pacific Geoscience Centre, 9860 West Saanich Road, Sidney, BC, Canada V8L 4B2;1. Department of Geology & Physics of the Earth, Department of Petroleum Engineering, Kazakh-British Technical University, Almaty 050000, Kazakhstan;2. IPEC, Edinburgh, EH14 4AS, United Kingdom;3. Department of Petroleum Engineering, M. Auezov South Kazakhstan State University, Shymkent 160012, Kazakhstan;1. CSIR- National Institute of Oceanography, Dona Paula, Goa, 403004, India;2. School of Earth Ocean and Atmospheric Sciences, Goa University, 403206, Goa, India;3. CSIR–National Geophysical Research Institute, Uppal Road, Hyderabad, 500007, India;1. Key Laboratory of Marine Geology and Metallogeny, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China;2. Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China;4. South China Sea Marine Survey and Technology Center, State Oceanic Administration, Guangzhou 510300, China |
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| Abstract: | Magnetic susceptibility measurements on near-surface sediment cores from the North Cascadia accretionary sedimentary prism show that seismic blanking or wipe-out zones in the upper few hundred metres of sediments are associated with a prominent low magnetic susceptibility signature. Seismic blanking and low magnetization are both attributed to high upward methane flux within a vent zone, as evidenced by the presence of massive gas hydrate within the cores. Sedimentological analysis of these cores also reveals the presence of authigenic pyrite within the areas of magnetic susceptibility lows. This phenomenon is suspected to be produced by the reducing environment associated with the high upward methane flux and increased bacterial activity within the topmost sediments, resulting in diagenesis of highly magnetic detrital minerals such as magnetite into nearly non-magnetic pyrite. These low magnetic susceptibility zones may produce magnetic anomalies with a magnitude of 10–35 nT near the seafloor. Such anomalies might be detected using high-resolution near-bottom magnetometers to provide a means of mapping zones of methane venting. |
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