Sequence-stratigraphic and sedimentologic theories and methods were employed in the study of sequence stratigraphic features and sedimentary system distributions in the Baiyanghe Formaiton of the Laojunmiao structural belt in Yumen oilfield

Jiuxi Basin

northwestern China.Data gathered through core and outsrrop observation and analyses

drilling and logging

and sesimic events

were resorted to establish sequence stratigraphic framework

determine the types and distribution of sedimenatry facies

and understand evolution pattern and controlling factors in the Formation.The result shows that the Formation can be described as a complete three-order sequence

which can be divided into 7 quasi-sequence sets.Sedimentary facies including alluvial fans

braided rivers

braided river deltas and lake depostis

were recognized in the sequence.Depositional facies varied vertically from alluvial fans to braided river delta and then to lake flooding mudstone and finally to delta.Horizontally

the facies presents itself as a near southeast-northwest sedimenatry system-a sedimentary sequence of water transgression and regression.Paleogeomorphology controlled the distribution of the sediments of lowstand system tract of the three-order sequence and climate affected the types of sediments and controlled the superimposed style and evolution pattern of the sediment in the Formation.