沉积环境的氧化还原性对重排甾烷形成的作用

The Effect of Oxidation Reduction Nature of Depositional Environments on the Formation of Diasteranes

陆东凹陷上侏罗统生油岩样品饱和烃色质分析表明，重排甾烷随井深出现含量下降的逆转现象，表明热演化不完全是这类化合物形成的主要控制因素。重排甾烷的分布与岩石中的粘土矿物组成关系也不密切，意味着各种粘土矿物的酸性催化作用无明显差别。经研究发现，重排甾烷的形成与沉积环境的氧化还原性有关。在Ｐｒ／Ｐｈ小于０．５的缺氧强还原地层中由于甾烯碳骨架的酸性重排作用受到抑制，因而所形成的重排甾烷很少；随Ｐｒ／Ｐｈ增加，沉积环境变为弱氧化—氧化时，重排甾烷含量显著增高。

The GC/MS analyses for alkanes from Late Jurassic source rocks of the Liudong depression,Kailu Basin,northeastern China showed that the concentration of diasteranes in some samples decreases anomalously with depth,suggesting that in this case the formation of these compounds may be not depended on maturity.On the other hand,there is not an obvious relationship between the content of diasteranes and the composition of clay minerals in rocks,indicating that the acid catalytic nature of different clay minerals is similar.It is found that the formation of diasterane is related to the oxidation reduction nature of depositional environment.The anoxic and high reducing deposits(Pr/Ph<0.5) may lead to suppress the acid catalyzed rearrangement process of sterene formed early during diagenesis.So,these sediments contain a low content of diasteranes.Conversely,when the depositional condition becomes less anoxic and oxic,with an increase in Pr/Ph,the concentration of diasteranens increases significantly.It seems that the oxicity of sediments during diagenesis may be responsible for the formation of diasteranes.