南海北部烟囱状冷泉碳酸盐岩的沉积环境分析  

Sedimentary environment of the cold-seep carbonate chimneys,north of the South China Sea

作　　者：杨克红[1,2] 初凤友[1,2] 赵建如[1,2] 韩喜球[1,2] 叶黎明[1,2] 章伟艳[1,2] 

机构地区：[1]国家海洋局海底科学重点实验室,浙江杭州310012 [2]国家海洋局第二海洋研究所,浙江杭州310012

出　　处：《海洋学报》2013年第2期82-89,共8页

基　　金：国家自然科学基金(41106047);国家海洋局第二海洋研究所基本科研业务费专项(JG1002);国家重点基础研究发展规划项目(2009CB219506);国家海洋局青年基金(2008313)

摘　　要：对南海北部陆坡具有圈层结构的烟囱状冷泉碳酸盐岩的岩石学、矿物学和地球化学特征进行了研究,结果表明:烟囱内外层具有明显不同的特征,内层碳酸盐含量比外层高,内层的碳酸盐矿物也更富含MgCO3,并且矿物颗粒较大,结晶程度较高;外层的铝、硅等陆源碎屑元素比内层含量高。内外层的碳、氧同位素也具有明显差别。对于研究的两个样品,内层的δ13 C分别为-40.80×10-3和-31.27×10-3,δ18 O分别为2.67×10-3和2.00×10-3,而外层的δ13 C分别为-31.26×10-3和-30.99×10-3,δ18 O分别为0.48×10-3和1.85×10-3。结合前人在该区域附近的研究结果认为,烟囱状碳酸盐岩具有内层比外层相对较负δ13C和较为富集δ18 O的特征。1mm间隔取样的δ13C和δ18 O剖面变化与烟囱状碳酸盐岩的圈层结构吻合较好,由外层至内层δ13C的变化范围为-27.50×10-3～-32.05×10-3,δ18 O的变化范围为0.78×10-3～2.34×10-3。外层6mm的δ13 C和δ18 O具有明显的负线性相关,相关系数r2为0.996 7。根据上述特征,讨论了渗漏甲烷流体的性质、扩散机制及对沉积环境的影响,推测具有圈层结构的烟囱状碳酸盐岩是由单一渗漏通道形成的,生长顺序有待进一步定年证实。烟囱外部6mm受海水影响较大。研究结果对于恢复南海北部陆坡甲烷渗漏系统、建立冷泉和热泉之间的联系具有一定意义。Some cold-seep carbonate chimneys collected from the north continental slope of the South China Sea were studied for petrology, mineralogy and geochemistry. The cross cut samples clearly showed distinctive layers. In the inner layer, the carbonate content was higher, and contained higher MgCO3 and bigger minerals, and the minerals crystallized better. While the outer layer contained higher detritus such as Al and Si. The isotopes compositions of δ^13C and δ^18O were different between the inner and outer layers. For the two studied samples, in the inner layer, δ^13C is -40. 80×10-3 and -31.27×10-3 ,and δ^18O is 2. 67×10-3 and 2. 00×10-3 , individually, and in the outer layer, δ^13C is -31.26×10-3 and -30. 99×10-3 , and δ^18O is 0. 48×10-3 and 1.85×10-3 , individually. Integrating the former researches near this area, the pattern that δ^13C was increasing and δ^18O was decreasing from the inner layer to the outer layer. The δ^13C and δ^18O curves using lmm interval samples range from -27. 50 ×10-3 to -32.05 ×10-3 and 0. 78 ×10-3 to 2.34 ×10-3 from the outer layer to the inner layer individually, which showed the layer structure well. In the outer 6 mm, the δ^13C and 8130 had a strongly negative correlation, which correlation coefficient r2 was 0. 996 7. According to the above results, the characteristic of CH4 fluid, its diffusing model and its influences on the sedimentary environment were discussed. The carbonate chimneys studied in this paper were supposed to form in a single channel, but which layer was older needs more dating researches. The outer 6 mm was influenced strongly by the seawater. The results can be used to recover the methane seep system of the northern continental slope of the South China Sea and can also give some relationships between cold seeps and hydrothermal seeps.

关 键 词：烟囱状碳酸盐岩 圈层结构 冷泉 南海北部 

分 类 号：P736.41[天文地球—海洋地质]