摘要
A环上带C-2或C-3位取代基的甲基藿烷常常用于反映细菌的新陈代谢过程(Summons et al., 1999)。通过GC-MS和GC-MS-MS分析,在济阳坳陷古近系湖相沉积岩中检测到了丰富而完整的C28-C362α-甲基藿烷系列。2-甲基藿烷来源于蓝细菌体内的2β-甲基细菌藿烷多醇(Summons et al.,1999),在成岩作用中这种多羟基化合物易于结合到干酪根中,并在随后的热降解生烃过程中释放出2-甲基藿烷。2-甲基藿烷具有与藿烷类似的异构化反应,但转化速率和热力学平衡点有所变化。2-甲基藿烷的发育与古沉积环境的关系最为密切,高丰度2-甲基藿烷仅出现在浅水、低能量的碳酸盐岩沉积环境中,随着成熟度增加,2-甲基藿烷指数增大,随着湖盆水体扩大和深度增加,2-甲基藿烷指数迅速减小;在整个生烃阶段泥质岩中2-甲基藿烷都不发育。2-甲基藿烷的组成和分布形式反映了水体氧化还原条件的变化。2-甲基藿烷对于古沉积环境的恢复和古生态的重建具有重要意义,应用于陆相盆地的油气勘探则有助于更加准确地厘定有效烃源岩体。
In this paper, abundant and complete C28-C36 2α-methylhopane series are identified in the Jiyang Eogene lacustrine deposition with the GC-MS and GC-MS-MS. 2-methylhopanes from 2-methylbacteriohopanepolyols (2-methyl-BHPs) may be regard as biomarkers for cyanobacteria (Summons, et al, 1999). 2-methyl-BHPs are bonded into kerogen during diagenesis and subsequently released due to thermal degradation of kerogen. Isomerization of 2-methylhopanes is trending in line with that of hopanes with the increase of maturity except some differences in velocity and equilibrium points. The abundance of 2-methylhopanes may be controlled by depositional environments; they are prominent only in carbonate deposition formed in a shallow environment with low energy; the 2-methyl hopanes index (C31MHI) increases with the maturity and decreases with expansion and deepening of the lake. C31 MHI is always low in mudstones and shales. It is also showed that the distributions of 2-methylhopaes are related with the redox condition of the water. Therefore, the study on 2- methylhopaes is useful to rebuilding a depositional environment as well as precise ascertainment of effective source rocks in oil exploration.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2006年第6期902-909,共8页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号400030002)资助成果。