Various kinds of gravity flow sediments including terrigenous elastic gravity flow deposits and carbonate gravity flow deposits developed in the west margin of Ordos Basin from late Early to Middle Ordovician.The terrigenous elastic gravity flow deposits are more significant due to its great thickness and broad distribution extent.The gravity flow sediments could be classified into(1)low-density turbidity current deposit;(2)high-density turbidity current deposit;(3)matrix-rich debris flow deposit;(4)matrix-poor debris flow deposit.The first two types are well developed. Based on the study of sedimentary sequence

paleocurrent direction

distribution of turbidite in time and space

and major provenance

three submarine fans named Tongxin

Helanshan and Zhuozishan submarine fans have been identified with the total area of more than 43000km

2

and the thickness approximately 3000m.Among these submarine fans

Helanshan submarine fan is a high energy one

the other two are low energy ones. The submarine fan systems mentioned above possess good hydrocarbon prospects.