南海北部甲烷渗漏系统环境变化的碳、氧同位素记录

冷泉碳酸盐岩记录了甲烷渗漏活动和流体组分随时间的变化过程，对示踪冷泉系统沉积环境变化具有非常重要的意义.对南海北部获取的冷泉碳酸盐岩进行了碳、氧同位素剖面研究，并对南海北部冷泉碳酸盐岩的碳、氧同位素变化范围进行了统计分析.研究结果及已发表的δ13C和δ18O剖面数据表明，南海北部冷泉碳酸盐岩剖面的δ13C和δ18O之间普遍存在相关性，相关系数R2最高可达0.933 1.经统计，南海北部冷泉碳酸盐岩样品δ13C和δ18O均具有较大的变化范围，其最大变化分别为34.50×10-3和5.89%(Vienna Pee Dee Belemnite，V-PDB).冷泉碳酸盐岩δ13C和δ18O的相关性特征可能指示了初始流体的变化、后期矿物形成/重结晶作用、渗漏系统较为复杂或者成岩作用等环境变化信息.对不同碳酸盐岩样品来说，δ13C的变化主要由海水的参与程度决定，而δ18O的变化可能与温度和Mg元素参与方解石沉淀的程度有关. 

Environmental Changes in Methane Seeps Recorded by Carbon and Oxygen Isotopes in the Northern South China Sea

Cold seep carbonates record the changes of fluids and environments in the methane seepages, which is important to reveal the sedimentary environment changes. The carbon and oxygen isotope profiles of the northern South China Sea and their vary intervals were studied. The results show that there are correlations between δ13C and δ18O along the profiles. Combined with the published δ13C and δ18O data, it is suggested that the correlations between them along the profiles are common, with the maximum correlation coefficient R2 of 0.933 1. Accroding to the statistics results, both the δ13C and δ18O vary greatly for the cold seep carbonates in the northern South China Sea, which maximal varing interval can be 34.50×10-3 and 5.89%(Vienna Pee Dee Belemnite, V-PDB), respectively. The correlations between δ13C and δ18O along the profiles perhaps indicate the changes of original fluids, the mineral formation or recrystallization, the complex methane seep systems and the diagenetic effects. For different cold seep carbonates, the vary intervals of δ13C were influenced by the participation degree of seawater, and the vary intervals of δ18O perhaps were related with the precipitation temperature and the Mg of calcite.