Geochemical data of Jiufutang Formation (upper Jurassic) source rocks in Ludong depression, Kailu basin reveals that the composition and distribution of biomakers are related to the water nature and oxidation-reduction of depositional environment. The saturated hydrocarbons of source rock samples from the western part of the depression show n-alkanes distribution with an odd carbon number predominance (C15 ￣C19), abundant isoprenoids (Pr/Ph<0.5 in most samples), absence of rearranged bicyclanes and diasteranes, and high amount of gammacerane and carotenoids. Their aromatic fractions contain relatively high amount of methylated MTTCs. These composition characteristics suggest brackish water and reducing depositional environment. In contrast, the source rocks in the eastern part of the depression have Pr/Ph values of more than 1.0, abundant rearranged bicyclanes, hopanes and diasteranes, and low amount of gammacerane and carotenoids, reflecting oxidic fresh lake depositional environment.
Journal of Jianghan Petroleum Institute