2013年我国首次在南海东北部东沙陆坡实施天然气水合物钻探,并获取块状等可视天然气水合物样品.为了解钻区地层、天然气水合物产出带（the zone of gas hydrate occurrence）或天然气水合物储层的地层时代和沉积速率特征,对其中5个站位...2013年我国首次在南海东北部东沙陆坡实施天然气水合物钻探,并获取块状等可视天然气水合物样品.为了解钻区地层、天然气水合物产出带（the zone of gas hydrate occurrence）或天然气水合物储层的地层时代和沉积速率特征,对其中5个站位（GMGS05、GMGS07、GMGS08、GMGS09和GMGS16）的岩心沉积物进行钙质超微化石、有孔虫生物地层学和沉积速率变化的研究.钻孔取心最大深度为213.55m.共识别出第四纪中更新世以来3个钙质超微化石事件和2个有孔虫事件,确定了钻探区所钻达最老地层为中更新统;天然气水合物产出带的地层时代为中更新世-全新世约0.44Ma以来.钻区0.12Ma以来的沉积速率介于36.9~73.3cm/ka之间,平均值高达54.2cm/ka,0.44Ma以来平均沉积速率为47.4cm/ka,表明东沙海域天然气水合物钻探区位于一高沉积速率堆积体上,高沉积速率更有利于天然气水合物的成藏,该结论与前人研究结果一致.展开更多
In 2013, the China Geological Survey and Guangzhou Marine Geological Survey conducted the second Chinese gas hydrate expedition in the northern South China Sea （SCS） and successfully obtained visible gas hydrate sam...In 2013, the China Geological Survey and Guangzhou Marine Geological Survey conducted the second Chinese gas hydrate expedition in the northern South China Sea （SCS） and successfully obtained visible gas hydrate samples. Five of the thirteen drilling sites were cored for further research. In this work, Site GMGS2-08 is selected for the stable isotopic analy- sis of foraminifera present in the boreholes in order to reveal the carbon isotopic characteristics of the foraminifera and their response to methane release in the gas hydrate geological system. Our results show that the methane content at Site GMGS2-08 is extremely high, with headspace methane concentrations up to 39300 μmol L^-1. The hydrocarbon δ^13C values, ranging from -69.4%o to -72.3‰ PDB, distinctly indicate biogenic generation. Based on the δD analytical results （-183‰ to -185‰ SMOW）, headspace methane is further discriminated to be microbial gas, derived from CO2 reduction. By isotopic measurement, five light δ^13C events are found in the boreholes from Site GMGS2-08, with foraminiferal δ^13C values being ap- parently lower than the normal variation range found in the glacial-interglacial cycles of the SCS. The δ^13C values of benthic Uvigerina peregrina are extremely depleted （as low as -15.85‰ PDB）, while those of planktonic Globigerinoides ruber reach -5.68‰ PDB. Scanning electron micrograph （SEM） studies show that foraminiferal tests have experienced post-depositional alteration, infilled with authigenic carbonate, and the diagenetic mineralization is unlikely to be related to the burial depths. The correlation calculation suggests that the anaerobic oxidation of organic matter has only weak influences on the δ^13C com- position of benthic foraminifera. This means that the anomalous δ^13C depletions are predominantly attributed to the overprint- ing of secondary carbonates derived from the anaerobic oxidation of methane （AOM）. Furthermore, the negative δ^13C anoma- lies, coupled with the positive δ^18O anomalies observed at Site GMGS2-08, are most likely the critical pieces of evidence for gas hydrate dissociation in the geological history of the study area.展开更多
文摘2013年我国首次在南海东北部东沙陆坡实施天然气水合物钻探,并获取块状等可视天然气水合物样品.为了解钻区地层、天然气水合物产出带（the zone of gas hydrate occurrence）或天然气水合物储层的地层时代和沉积速率特征,对其中5个站位（GMGS05、GMGS07、GMGS08、GMGS09和GMGS16）的岩心沉积物进行钙质超微化石、有孔虫生物地层学和沉积速率变化的研究.钻孔取心最大深度为213.55m.共识别出第四纪中更新世以来3个钙质超微化石事件和2个有孔虫事件,确定了钻探区所钻达最老地层为中更新统;天然气水合物产出带的地层时代为中更新世-全新世约0.44Ma以来.钻区0.12Ma以来的沉积速率介于36.9~73.3cm/ka之间,平均值高达54.2cm/ka,0.44Ma以来平均沉积速率为47.4cm/ka,表明东沙海域天然气水合物钻探区位于一高沉积速率堆积体上,高沉积速率更有利于天然气水合物的成藏,该结论与前人研究结果一致.
基金supported by the National Natural Science Foundation of China (Grant No. 41372012)the Key Scientific Project from China Geological Survey (Grant No. GZH201100305-06-02)the Key Laboratory of Marine Mineral Resources (Grant No. KLMMR-2013-A-32)
文摘In 2013, the China Geological Survey and Guangzhou Marine Geological Survey conducted the second Chinese gas hydrate expedition in the northern South China Sea （SCS） and successfully obtained visible gas hydrate samples. Five of the thirteen drilling sites were cored for further research. In this work, Site GMGS2-08 is selected for the stable isotopic analy- sis of foraminifera present in the boreholes in order to reveal the carbon isotopic characteristics of the foraminifera and their response to methane release in the gas hydrate geological system. Our results show that the methane content at Site GMGS2-08 is extremely high, with headspace methane concentrations up to 39300 μmol L^-1. The hydrocarbon δ^13C values, ranging from -69.4%o to -72.3‰ PDB, distinctly indicate biogenic generation. Based on the δD analytical results （-183‰ to -185‰ SMOW）, headspace methane is further discriminated to be microbial gas, derived from CO2 reduction. By isotopic measurement, five light δ^13C events are found in the boreholes from Site GMGS2-08, with foraminiferal δ^13C values being ap- parently lower than the normal variation range found in the glacial-interglacial cycles of the SCS. The δ^13C values of benthic Uvigerina peregrina are extremely depleted （as low as -15.85‰ PDB）, while those of planktonic Globigerinoides ruber reach -5.68‰ PDB. Scanning electron micrograph （SEM） studies show that foraminiferal tests have experienced post-depositional alteration, infilled with authigenic carbonate, and the diagenetic mineralization is unlikely to be related to the burial depths. The correlation calculation suggests that the anaerobic oxidation of organic matter has only weak influences on the δ^13C com- position of benthic foraminifera. This means that the anomalous δ^13C depletions are predominantly attributed to the overprint- ing of secondary carbonates derived from the anaerobic oxidation of methane （AOM）. Furthermore, the negative δ^13C anoma- lies, coupled with the positive δ^18O anomalies observed at Site GMGS2-08, are most likely the critical pieces of evidence for gas hydrate dissociation in the geological history of the study area.
