梨树断陷下白垩统湖相烃源岩异常高丰度17α(H)-重排藿烷的成因探讨

Genesis Study of High Abundant 17α(H)-diahopanes in Lower Cretaceous Lacustrine Source Rocks of Lishu Fault Depression in Songliao Basin

在梨树断陷下白垩统营城组和沙河子组(K1sh)湖相烃源岩中存在异常丰富的17α(H)-重排藿烷系列化合物,饶有兴趣的是,在这些样品中还同时检测出极其丰富的长链三环萜烷(碳数可达C35)和伽马蜡烷,这一现象在以前的文献上鲜见报道。对烃源岩样品的饱和烃进行色质分析,从成熟度、沉积环境的氧化还原性和生源构成3个方面探讨研究区17α(H)-重排藿烷的成因。结果表明:成熟度和沉积环境的氧化还原性对梨树断陷湖相烃源岩17α(H)-重排藿烷的形成影响不大。在生源构成方面,17α(H)-重排藿烷与长链三环萜烷之间呈现出很好的正相关关系,表明两者可能有着相同的生源,与咸化环境下藻类贡献有关。咸化环境下藻类可能是17α(H)-重排藿烷的一种生源。

Relatively abundant 17a ( H ) -diahopanes were detected in the lower Cretaceous lacustrine source rocks from the Lishu Fault Depression in Songliao Basin.The rich long-chain tricyclic terpanes ( carbon number up to C35 ) and gammacerane were detected in those source rocks with relatively abundant 17a ( H ) -diahopanes , which was rarely seen in previous literature reports.In this paper , the formation of 17a ( H ) -diahopanes was discussed from three aspects of maturity , oxidation-reduction nature of depositional environment and parent material composition by the GC/MS analyses for the studied samples.The results reveal that maturity and oxidation-reduction nature of depositional environment have little effect on the formation of 17α ( H ) -diahopanes in the investigated area.However , the positive correlation between long-chain tricyclic terpanes and 17a ( H ) -diahopanes are argued strongly for a common origin , it is related to the contribution of algaes in saline water environment.The algaes in saline water environment may be a kind of origin of 17a ( H ) -diahopanes.