Abstract: The Dalong Formation section in Changjianggou,Guangyuan,Sichuan is characterized by limestones intercalated with mudstones,abundant biotic assemblages and deeper shallow-water environments indicated by reduction,low energy,low velocity and oxygen depletion. The bio-diversity and anoxic slope environments made the study area to be favourable for the formation of excellent source rocks,with the average organic carbon contents almost up to 5%,and thus may be potential marker horizons for future petroleum exploration in Sichuan.