Abstract: The organic matters in the sediment core sample HD196A obtained from the eastern South China Sea were measured with GC and GC-MS techniques.More than 90 types of hydrocarbon compounds including n-alkanes,isoprenoid,branched alkanes and polycyclic aromatic hydrocarbons (PAHs) were identified.The HD196A-30 in the middle core sample and HD196A-55 near the bottom of the core sample were analyzed.The distribution curve of n-alkanes,the range of carbon chain,the position of main peaks and the values of CPI and OEP show that the organic matters in the sediments are the mixtures of terrestrial plants,marine phytoplankton algae and bacteria.The organic matters from terrestrial plants are dominated.The organic matters in the sediments are matured in this area.Squalene was identified in the core sample,which showed that biological methane synthesizing and bacteria function occurred in this area.The ubiquity of phenanthrene series,chrysene series compounds,perylene and retene compounds in the sediment indicated that PAHs mainly came from the terrestrial plants.Abundance of perylene designated the fast accumulation of terrestrial organic matter and reductive condition.The geological background and the analysis result showed that HD196A site had the conditions of gas source,temperature and pressure to form gas hydrate.The sampling site fits quite well to the area with high anomalies fueled by hydrocarbon seep,which indicates that this area is favorable for exploration of oil,gas and gas hydrate.

Key words: eastern South China Sea, sediment, organic matter, gas hydrate, odd-even predominance value, polycyclic aromatic hydrocarbon, n-alkane, geochemical characteristics

摘要： 采用色谱和色谱-质谱技术测定了南海东部沉积物柱样HD196A中的有机物,共检测出正构烷烃、类异戊二烯烃、支链烷烃和多环芳烃等90多种烃类化合物.对样品柱中部的HD196A-30子样(3.40 m)和近底部的HD196A-55子样(6.20 m)进行了地球化学特征分析.由正构烷烃分布曲线的形状、碳数范围、主峰位置以及CPI值和OEP值等特征可见,沉积物中的有机质主要来源于陆地高等植物、海洋浮游生物藻类和细菌源共存物,并以源于陆源高等植物的有机质占优势.同时,多环芳烃中菲系列成熟度参数的分布反映了该区沉积物成熟度较高.在样品中检测到角鲨烯,表明这一地区存在生物甲烷合成和细菌作用,具有生成油气及天然气水合物可能性.从柱状样品的中部到底部,S₈相对浓度的急剧增加,表示底部子样接近了硫酸盐甲烷交接带.结合区域构造背景和分析结果表明,HD196A站位具有天然气水合物形成的气源条件和温压条件.该区已有的研究资料报道的高值异常区与本次研究站位相吻合,显示该海区具有烃渗漏来源,是海底油、气和天然气水合物勘探的有利地区.

关键词: 南海东部, 沉积物, 有机质, 天然气水合物, 奇偶优势指数, 多环芳烃, 正构烷烃, 地球化学特征