Stratigraphic Sequence Division and the Characteristics of Sedimentary System of Lower Cretaceous in Yinger Depression,Jiuquan Basin

Guided by the methods of sequence stratigraphy and based on the seismic data,drilling and well logging data,other people's research on the sequence stratigraphy in Jiuquan basin,this paper analyzes the characteristics of the third-order sequence well logging,and recognizes the criterion of the third-order sequence boundary in seismic section,such as local truncation,onlap,and so on.From all this study above,the sequence boundary can be identified,and we recognize 1 first-order sequence,3 second-order sequences,7 third-order sequences and 18 system tracts.According to the sequence stratigraphy study,we conclude that the Xiagou Formation of the Lower Cretaceous in Yinger depression has the characteristics of near more provenances,rapid subsidence,and rapid deposition.The mild slope of the depression develops large scale fan deltas,and the steep slope develops nearshore subaqueous fans.Among these,the nearshore subaqueous fan in the south steep slope should be a favorable exploration target.