Study on Sedimentary Characteristics of Chang 9 Member of Triassic in Ordos Basin

The Triassic Yanchang Formation in the Ordos Basin is one of main exploration targets. Based on detailed outcrop at southern margin Basin, combined with previous results, a systematic analysis lithology, rock assemblage, sedimentary facies characteristics and temporal evolution carried out. results show that Changchang 9 oil-bearing group can be divided into lithofacies types, three types facies, meandering river, river delta, braided delta are developed. develops riverbed retention deposits, beaches, There four microfacies natural dikes rupture fans. five deltas: underwater distributary channels, dikes, divert bays, estuary dams, remote sand dams. Braided deltas develop two kinds between channels; Chang has coarse-fine-coarse compound rhythm vertical direction; bodies front places for oil gas migration accumulation.