Seismic
data show that a set of Eocene lacustrine source rocks
exists in the Qiongdongnan (QDN) Basin, northern South China Sea (SCS).
The high content of C30 4-methylsteranes detected in the
crude oil suggests the existence and the effectiveness of the lacustrine
source rocks, and these compounds were not found in the Oligocene
and Miocene source rocks. The above date indicates that the Eocene
source rocks are effective and oil-prone. Lacustrine source rocks
in faulted period have high organic matter abundance and better organic
matter types in the SCS and other typical passive continental margin
basins in the world. Lacustrine source rocks in the Eocene source
rocks (E2w) from the Baiyun Sag of the Pearl River Mouth
Basin have relatively high total organic content (TOC) values, which
can be explained by moderate to high paleoproductivity and anoxic
environment. Therefore, it can be speculated that the Eocene source
rocks have good hydrocarbon potential in the QDN Basin. The developmental
pattern of Eocene source rocks is revealed as follows: In mid-deep
lake environment, high-quality source rocks could be formed, because
of high productivity and better organic matter preservation conditions,
and the central depression belt is the most favored zone beneficial
to Eocene source rock formation, because of the relatively large-scale
mid-deep lake facies. In shore-shallow lake and delta environment,
high-quality source rocks could not be formed, because of the poor
organic matter preservation conditions.