Xihu lake depression in the East China Sea has gone through three stages of development since the late Cretaceous

forming three sets of oil and gas systems of Pinghu Formation Huagang Formation

Huagang Formation and Eocene

the former two sets are-known systems

the latter system is a conjectured one. Hydrocarbon source rocks in these two systems are in the stage of maturation. The closure of oil and gas bearing roof rocks in Huagang Formation deteriorates from southward towards northward and the south part with real meaning for oil and gas exploration. Comprehensive analyses indicate that the key moment for oil and gas bearing system in Pinghu Foprmation and is about 7 Ma

oil and gas bearing system in Huagang Formation is about 1.64 Ma.