The origin of 4-methyl steranes and pregnanes from Tertiary strata in the Qaidam Basin, China

A geochemical study of oils and source rocks in Tertiary saline lake facies, from the Qaidam Basin of China, demonstrates that pregnanes are mainly derived from the thermal degradation of organic matter in source rocks synchronous with hydrocarbon genesis, whereas 4-methyl steranes may principally be a product of microbial activity during diagenesis.