The Dainan Formation in the Gaoyou Depression is a complete sedimentary cycle. It consists of lacustrine facies in an onlapping style at the lower partand fluvial facies at the upper part in a filling pattern

showing a evolution-ary process from lacustrine to fluvial facies. The various sedimentary systems as Majiazui-Lianmengzhuang long-axialdelta

Zhenwu - Caozhuang fan-delta and Zheduo delta are respectively inthe west

south steep slope and north gentle slope of the depression. Amongthem

the fan delta and long-axial delta systems are favourable for hydro-carbon accumulation.