中文摘要：

源于深部天然气藏渗漏或天然气水合物分解释放的甲烷，可导致海洋沉积物中生成δ^13C明显负偏的碳酸盐矿物。对NH-1孔沉积物样品的碳酸盐含量、全岩碳酸盐及生物碳酸盐δ^13C、有机碳含量等参数进行了分析。结果表明：沉积物中碳酸盐含量较高（平均6．90％）；全岩碳酸盐δ^13C（-6．09‰～-0．48‰）与正常海相碳酸盐相比明显负偏；浮游有孔虫（Grube）壳体碳酸盐δ^13C（-0．834‰～0．004‰）明显低于正常值。结合海域的地质特点，认为这很可能是沉积物中较高甲烷通量背景条件下自生碳酸盐的形成所导致的。有机碳、氮数据与全岩碳酸盐δ^13C的相关性分析指示了有机质也可能是全岩碳酸盐δ^13C偏低的根源之一。因此，NH-1孔碳酸盐碳同位素特征是较高甲烷通量背景下甲烷缺氧氧化-硫酸盐还原及有机质缺氧氧化-硫酸盐还原等地球化学过程的综合反映。全岩碳酸盐δ^13C含量可用于指示沉积物中自生碳酸盐矿物及较高甲烷通量的存在。

英文摘要：

Methane derived from the decomposition of gas hydrate or seepage of gas reservoir at depth can result in carbonate minerals with much lower than normal δ^13C content in the overlying marine sediments. Sediment samples of Core NH-1 were analyzed for total carbonate content, δ^13C of total carbonates and biogenie carbonates, and organic carbon content. The resuits show that δ^13C of total carbonates were between -6.09‰ and -0.48‰, while δ^13 of planktonic foraminifera shells （ Globigerinoides tube） were between -0. 834‰ and 0. 004‰. Sediment total carbonate contents were higher with an average of 6.90%. It was deducted that δ^13C of authigenic carbonates in the sediments would be much more negative than normal, which may suggest high methane flux in sediments at this site. High methane flux was suggestive of the possible existence of gas hydrate formation or gas reservoir at depth at this site. δ^13C of total carbonates correlated well with organic carbon contents as well as nitrogen contents, which indicated that organic matter contributed partially to the negative δ^13C values of authigenic carbonates. The δ^13C carbon isotope characters of carbonate in the sediments of Core NH-1 reflect a combined geochemistry process of methane anoxic oxidation and sulfate reduction with the organic carbon anoxic oxidation and sulfate reduction in the background of high methane flux. It was shown that δ^13C of total carbonates could be used to estimate δ^13C of authigenic carbonates and could be used as a substitutional indicator for the existence of high methane flux in sediments.