Geochemical characteristics of tertiary oil-generating strata in Jiyang Sag

The Jiyang Sag was a near-sea basin in Oligocene time of mild and wet climate. The flourishing living things in this basin and the continuous depressions created a favorable environment for oil generation. Occasional transgressions resulted in special water-medium conditions, giving rise to a unique biological group of abundan terrestrial and fresh-water biota and organisms characteristic of semi-saline environments as well as small amounts of marine biota. Discussions are also made of the evolution of organic matter on the basis of changes of geochemical indexes for oil-generating rocks at different depths in the Dongying Depression.