In the early Eocene

Jianghan Basin was a shallow saline lake fed by rivers.Three types of sands were formed within this lake: deltaic sands

nearshore beach sands and offshore beach sands.Among them

the more important are Hougang deltaic sands which are composite

overlapped ones

and which were developed during the desalinating period.The principle features of the saline lacustrine and deltaic sediments are the antithetic and complementary to each other.Because of slight subsiding

lower rate of sedimentation

shallow water body and higher salinity at earlier Eocene

the basin studied was not favorable for organism breeding.Therefore

the abundance of organic matters in the basin was poor

with sapropel predominantion

and conditions for oil generation was less favorable.Though sands exist in this lacustrine basin which are favorable for oil accumulation

oil and gas reservoirs could be rarely formed.It seems that the potential region for searching small oil and gas fields might be to the cast where offshore lacustrine beach sands exist

and to the west where front deltaic sands exist.