Methane-derived authigenic carbonates from the Ulleung basin sediments,East Sea of Korea |
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| Authors: | Dhongil Lim Jinyong Choi Zhaokai Xu Moonkoo Kim Donglim Choi Hoisoo Jung Panmook Lee |
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| Institution: | 1. South Sea Institute, Korea Ocean Research and Development Institute, 391 Jangmok-ri Jangmok-myun Geoje 656-830, Republic of Korea;2. Department of Oceanography, Kunsan National University, Kunsan 573-701, Republic of Korea;3. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;4. Marine Geoenvironment and Resources Research Division, Korea Ocean Research and Development Institute, Ansan, P.O. Box 29, Seoul 425-600, Republic of Korea;5. Marine and Ocean Engineering Research Institute, Korea Ocean Research and Development Institute, 171 Jang-dong Yuseong, Daejeon 305-343, Republic of Korea |
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| Abstract: | Authigenic carbonates were sampled in methane-enriched piston core sediments collected from gas venting sites on the western continental slope of the Ulleung Basin, East Sea of Korea. Multidisciplinary investigations on these carbonates, including the scanning electronic microscope (SEM) observations and mineralogical-geochemical compositions, were carried out to identify the carbon and oxygen sources and the forming mechanism of these carbonates. The authigenic carbonates from the study area correspond to semi-consolidated, compact concretions or nodules ranging from 2 to 9 cm in size. X-ray diffraction and electron microprobe analyses showed that most of the sampled carbonate concretions were composed of almost purely authigenic high-Mg calcite (10.7–14.3 mol% MgCO3). Characteristically, microbial structures such as filaments and rods, which were probably associated with the authigenic minerals, were abundantly observed within the carbonate matrix. The carbonates were strongly depleted in δ13C (−33.85‰ to −39.53‰ Peedee Belemnite (PDB)) and were enriched in δ18O (5.16–5.60‰ PDB), indicating that the primary source of carbon is mainly derived from the anaerobic oxidation of methane. Such methane probably originated from the destabilization of the underlying gas hydrates as strongly supporting from the enriched 18O levels. Furthermore, the strongly depleted δ13C values (−60.7‰ to −61.6‰ PDB) of the sediment void gases demonstrate that the majority of the gas venting at the Ulleung Basin is microbial methane by CO2 reduction. This study provides another example for the formation mechanism of methane-derived authigenic carbonates associated with gas-hydrate decomposition in gas-seeping pockmark environments. |
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| Keywords: | Authigenic carbonates Methane seep environments Gas hydrate East Sea (Japan Sea) |
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