Sedimentary Geochemical Response to Gas Hydrate Episodic Release on the Northeastern Slope of the South China Sea
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摘要: 南海地区天然气水合物资源丰富，针对其分解方式的研究有助于资源的开采.对南海东北部天然气水合物钻探区GMGS08站位岩心沉积物开展沉积学、地球化学分析研究.结果表明：该站位自上而下分布11层含自生碳酸盐岩和双壳碎屑层(其中6层呈粥状沉积)以及2层自生碳酸盐岩灰岩层；各层自生碳酸盐岩除一个样品δ13C值稍高(-38.85×10-3)外，其他的δ13C值介于-41.36×10-3~-56.74×10-3，均低于-40.00×10-3，δ18O值介于2.94×10-3~5.37×10-3，明显偏重，表明其为天然气水合物分解的产物，形成于微生物对甲烷的缺氧氧化作用，甲烷主要源自生物成因；各层自生碳酸盐岩层中的有机质碳同位素负偏明显，最低达-82.44×10-3，可能与微生物活动有关；根据自生碳酸盐岩的分布推断该站位至少发生过6次天然气水合物分解释放，每期次自生碳酸盐岩的差异说明其甲烷通量强弱不同.
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关键词:
- 粥状沉积 /
- 自生碳酸盐岩 /
- 碳同位素 /
- 天然气水合物多期次分解 /
- 海洋地质
Abstract: The resource of gas hydrate in South China Sea is plentiful. It redound to resource development by investigating how the gas hydrate decompose. A sedimentology and geochemistry study has been done in gas-hydrate-bearing borehole sediment collected at site GMGS08 within the gas hydrate drilling area in the northeastern South China Sea. Results show that 11 layers of authigenic carbonate and bivalve bioclast, and 2 layers of carbonate limestone are distributed from top to bottom in hole GMGS08. Authigenic carbonate and bivalve bioclast primarily occurred in soupy structure sediments with high water content. The δ13C values of authigenic carbonate ranged from -41.36×10-3 to -56.74×10-3 except one sample with a higher δ13C value of -38.85×10-3, and the δ18O values were apparently heavy ranging from 2.94×10-3 to 5.37×10-3, suggesting they were attributed to gas hydrate dissociation via microbial anaerobic oxidation of methane, which was predominantly biogenic gas. The δ13C values of organic carbon varied from -21.33×10-3 to -82.44×10-3, in which the δ13C negative excursion intervals corresponded to authigenic carbonate layers. According to the distribution of authigenic carbonate, it is concluded that at least 6 episodes of gas hydrate release existed in geologic record, and the varying sizes of authigenic carbonate among the layers indicated the intensity of methane flux in each episode was different.-
Key words:
- soupy structure /
- authigenic carbonate /
- carbon isotope /
- gas hydrate episodic release /
- marine geology
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图 1 南海东北部天然气水合物钻探区地理位置和研究站位位置
据张光学等(2014)修改
Fig. 1. The geography location and sites location on the gas hydrate-drilling area of the northeastern slope of the South China Sea
图 2 GMGS08站位沉积特征及自生碳酸盐岩层的分布
Fig. 2. Sedimentary characteristics and the distribution of autigenic carbonate layers in site GMGS08
图 3 GMGS08站位部分自生碳酸盐岩层和粥状沉积
岩心照片上的数字表示海底以下深度(mbfs)
Fig. 3. Core photos of typical authigenic carbonate layers and soupy structure sediments in site GMGS08
图 5 GMGS08站位自生碳酸盐岩层部分层位粗组分(大于0.063 mm)的组成
数字1、2等代表自生碳酸盐岩层数；1.00~1.15 m等代表取样深度
Fig. 5. Compositions of the coarse fraction(≥0.063 mm) from authigenic carbonate layers in site GMGS08
表 1 GMGS08站位各层位自生碳酸盐岩的碳氧同位素值
Table 1. The δ13C and δ18O values of autigenic carbonates in site GMGS08
岩心管号 深度(cm) δ13C δ18O 自生碳酸盐岩层 08B-1H-1a 65~70 -49.27 3.69 第1层 08B-1H-1a 75~80 -43.28 3.17 08B-1H-1a 115~120 -45.14 3.58 08B-1H-2a 170~175 -41.36 2.96 08B-1H-2a 205~210 -48.77 3.79 08B-1H-3a 325~330 -49.31 3.76 08B-1H-3a 340~345 -50.32 3.96 08B-1H-3a 355~360 -51.90 3.94 08B-1H-3a 370~375 -50.41 3.48 08B-1H-CC 535~540 -56.09 4.02 08C-1H-1a 215~220 -43.23 3.03 08C-1H-1a 310~315 -52.01 3.85 08C-1H-2a 375~380 -56.74 4.04 08C-1H-3a 540~545 -55.47 4.07 08C-1H-3a 565~570 -56.35 3.94 08C-1H-3a 620~625 -52.22 4.06 08C-2A-1 1 000~1 006 -43.84 2.94 第2层 08C-2A-1 1 030~1 035 -53.75 3.77 08C-2A-1 1 080~1 085 -55.18 3.70 08C-2A-2a 1 100~1 105 -54.73 3.97 08C-2A-2a 1 140~1 145 -49.05 3.37 08C-2A-3 1 245~1 250 -55.27 4.18 08C-2A-3 1 300~1 305 -44.92 3.11 08C-3M-1a 1 370~1 375 -51.09 3.76 08C-3M-1b 1 440~1 445 -49.92 3.54 第2层 08C-3M-1b 1 485~1 490 -50.50 3.70 第2层 08C-5C-CC 2 153~2 163 -38.85 3.73 第3层 08F-1M-1a 5 800~5 815 -48.32 4.05 第4层 08E-1C-CC 5 881~5 897 -45.59 4.31 第4层 08F-2M-1 6 100~6 115 -50.02 3.71 第6层 08E-3C-1a 6 110~6 115 -49.66 5.66 第6层 08F-2M-1 6 147~6 152 -43.05 2.97 第6层 08F-2M-1 6 147~6 152 -51.35 4.68 第6层 08F-2M-1 6 147~6 152 -43.67 3.76 第6层 08E-3C-CC 6 161~6 177 -50.50 5.37 第7层 08F-2M-CC 6 255~6 270 -47.71 4.19 第8层 08E-5M-1 6 580~6 590 -49.83 4.87 第9层 08E-5M-1 6 640~6 654 -48.10 5.13 第9层 08E-5M-1 6 715~6 730 -56.19 3.71 第9层 08E-5M-2a 6 780~6 790 -51.79 4.97 第9层 08F-8M-1a 8 120~8 130 -46.36 3.14 第10层 08F-8M-1a 8 175~8 183 -49.77 3.69 第10层 08F-8M-1a 8 200~8 205 -45.27 3.62 第10层 08F-8M-1a 8 400~8 415 -48.67 3.84 第11层 08F-9M-1a 8 455~8 463 -48.91 3.66 第11层 08F-9M-1b 8 500~8 510 -48.77 3.64 第11层 08F-11H-1a 9 330~9 340 -49.92 3.87 第12层 
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