Genesis study of high abundant 17α(H)-diahopanes in Lower Cretaceous lacustrine source rocks of the Lishu Fault Depression, Songliao Basin, Northeast China

摘要

Relatively abundant 17α(H)-diahopanes have been detected in the lower cretaceous lacustrine source rocks from the Lishu Fault Depression in the Songliao Basin Northeast China. Rich long chain tricyclic terpanes(carbon number up to C35) and gammacerane have been observed in those source rocks with relatively abundant 17α(H)-diahopanes, which is rarely seen in previous reports. In this paper, the formation of 17α(H)-diahopanes has been discussed from three aspects including maturity, oxidation-reduction nature of depositional environment and parent material composition by the GC/MS analyses. 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 17α(H)-diahopanes argues strongly for a common origin, and the origin is related to the algaes in saline water environment. The algaes in saline water environment may be a kind of origin of 17α(H)-diahopanes.