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南海东沙东北部碳酸盐岩和泥质沉积物中的生物标志化合物组合及其碳同位素组成分析表明,研究区内甲烷缺氧氧化作用(anaerobic oxidation of methane-AOM)发育。研究区内碳酸盐岩中含丰富的AOM标志化合物,2,6,11,15-四甲基十六烷(Crocetane-Cr.)、2,6,10,15,19-五甲基番茄烷(Pentamethylicosane-PMI)和2,6,10,15,19,23-六甲基二十四烷(Squalane-Sq角鲨烷)的13C亏损强烈(δ13C值介于-74.2‰~-119.0‰PDB之间),表明碳酸盐岩形成于AOM,同时反映该研究区曾发生过强烈、持续的富CH4流体释放活动。柱状泥质沉积物中,AOM生物标志化合物在硫酸岩-甲烷过渡带(SMI—Sulfate-Methane Interface)边界附近相对丰度高,SMI之上样品中含量低,或未检出,表明现代环境在SMI附近有大量嗜甲烷微生物生长,使得深部上升的甲烷被大量消耗,很少有甲烷逸出海底。AOM生物标志化合物可用来指示SMI边界。不同站位、不同岩性AOM生物标志化合物组成(包括碳同位素组成)的差异反映了嗜甲烷古细菌组成的不同。
Biomarker assemblages and their carbon isotopic compositions in carbonate rocks and muddy sediments in the northeastern Dongsha, South China Sea show that anaerobic oxidation of methane-AOM develops in the study area. Carbonate rocks in the study area are rich in AOM marker compounds, 2,6,11,15-tetramethylhexadecane (Crocetane-Cr.), 2,6,10,15,19-Pentamethyl Tomato 13C of Pentamethylicosane-PMI and 2,6,10,15,19,23-Hexamethyldetradecane (Squalane-Sq Squalane) were strongly depleted (δ13C values ranged from -74.2 ‰ to -119.0 ‰ PDB), indicating that carbonate rocks formed on the AOM, reflecting the intense and sustained enrichment of CH4-rich fluids in the study area. Among the columnar argillaceous sediments, the AOM biomarker has high relative abundance near the boundary of the SMI-Sulfate-Methane Interface and low or no detectable content of the sample above the SMI, indicating that the modern environment is at A large number of methanogenic microorganisms grow near SMI, causing deep ascent of methane to be consumed in large quantities, leaving few methane to escape from the sea floor. AOM biomarkers can be used to indicate SMI boundaries. The differences in the composition of AOM biomarkers (including carbon isotope composition) at different stations and in different lithologies reflect the differences in the composition of the methotrexate archaebacteria.