A delta facies is a cone-shaped depositional system that forms in an area where a river flows into the ocean or a lake. It is a type of transitional facies, and it can cover hundreds of thousands of square kilometres. Deltas are important locations for the accumulation of terrestrial sediments, and the depositional environment is complex and varying with numerous lithologies. Delta facies mainly comprise sandy sediments and have bedding that dips towards the sea. They are transitional areas between terrestrial and marine facies where terrestrial, freshwater and marine organisms coexist. They are also favourable locations for the formation and accumulation of oil and gas. Generally, delta facies can be divided into plain facies, delta front facies and prodelta facies. They can also be categorised as the top accumulation layer, front accumulation layer and bottom accumulation layer.