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对珠江口盆地东部陆坡GMGS 08C孔的3层自生碳酸盐岩(结核状)和有孔虫(底栖和浮游)开展高分辨率氧碳同位素分析和AMS~(14) C测年,第1层自生碳酸盐岩δ~(13) C为-38.85‰,第2、3层的δ~(13) C介于-41.36‰~-56.74‰,平均值-51.64‰,均低于-40‰。δ~(18) O值介于2.94‰~4.18‰,平均值3.68‰,明显偏重。这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;自生碳酸盐岩层位的底栖有孔虫Uvigerina peregrina和浮游有孔虫Globigerinoides ruber的δ~(13) C值几乎同时出现极负偏,最低值分别达到-12.17‰和-9.06‰,有孔虫δ~(18) O总体上正偏,最大正偏幅度达1.50‰,说明其负偏与后期源于甲烷厌氧氧化作用(Anaerobic Oxidation of Methane,简称AOM)的成岩作用有关。自生碳酸盐岩及其与有孔虫异常碳(偏负)氧(偏正)、粥状沉积是GMGS 08C孔水合物分解甲烷渗漏的重要指标,据此推断该孔在末次冰期(MIS2—MIS3)发生过至少2次天然气水合物分解释放-冷泉甲烷渗漏活动,分别距今36ka和31~26ka,主要发生在低海平面期,说明冷泉活动明显受海平面变化影响。
High-resolution oxygen and carbon isotope analysis and AMS ~ (14) C dating of three-layer spontaneous carbonate rocks (tuberculate) and foraminifera (benthic and planktonic) in the GMGS 08C hole on the eastern slope of the Pearl River Mouth Basin were conducted. The δ 13 C of the first layer of authigenic carbonate rocks is -38.85 ‰, the δ 13 C of the second and third layers is -41.36 ‰ ~ -56.74 ‰, the average value is -51.64 ‰, 40 ‰. δ ~ (18) O values ranged from 2.94 ‰ to 4.18 ‰, with an average of 3.68 ‰, significantly overweight. This indicates that it is a product of gas hydrate decomposition formed by microbial hypoxia oxidation of methane, which is mainly caused by biogenic origin; Ubiquitous foraminifera Uvigerina peregrina and Globigerinoides ruber The δ ~ (13) C value of the foraminifera was almost negative at the same time with the lowest values of -12.17 ‰ and -9.06 ‰, respectively. The negative bias is related to the diagenesis of later Anaerobic Oxidation of Methane (AOM). Intrinsic carbonates and their association with foraminifera anomalous carbon (partial to neutral) and porphyritic sediments are important indicators of methane leakage from GMGS 08C hydrate decomposition. Based on this, -MIS3) occurred at least two times of gas hydrate decomposition and release-cold spring methane leakage activities, respectively, 36ka and 31 ~ 26ka, respectively, mainly occurred in the low sea level period, indicating that the cold spring activity was obviously affected by the sea level change.