松辽盆地嫩江组油页岩发育控制因素

Major Factors Controlling Formation of Oil Shale in Nenjiang Formation of Songliao Basin

松辽盆地嫩江组一段和二段发育的油页岩是极其优质烃源岩,生物标志化合物参数指示油页岩母质生源主要来自于水生生物其繁盛受温湿气候和湖泊富营养化控制.岩石学、元素地球化学、生物标志化合物等参数表明,高盐和缺氧条件下的稳定水体分层是嫩一段油页岩沉积时期有机质保存的主控因素,而嫩二段油页岩沉积时期水体盐度分层明显减弱,此时藻类个体增大和孤立藻数量增多条件下的高生物生产力有利于有机质富集.为揭示嫩江组不同沉积环境下油页岩发育的控制因素,建立了嫩一段油页岩沉积时期保存条件控制和嫩二段油页岩沉积时期生物生产力控制的两种有机质富集模式,这对含氧淡水大型陆相湖泊的有机质富集成因探讨具有重要借鉴意义.

Oil shales are present in the Nenjiang Formation of Songliao basin, representing excellent source rocks. Their biomarker compositions provide evidence for a major eontribution of aquatic organism. Phytoplankton blooms were promoted by warm-humid climate, and lake eutrophication. Based on the parameters from petrology, element geochemistry and biomarker, a stratified water column with high salinity and anoxic bottom water conditions contributes to OM （organic matter） preservation in the lower oil shale layer. In contrast, under decreased salinity stratified water, high bioproductivity in combination with OM preservation favoured by enhanced algae sizes and telalginite concentrations are suggested as the OM enrichment mecha- nisms in the upper oil shale layer. In this study, a model of predominant preservation within the lower oil shale layer and a model of dominant productivity within the upper oil shale layer are established. This result can be used as an important indicator for probing into the genesis of OM enrichment in the large continental lake with partial oxygenation and fresh water.