Sedimentary characteristics

distribution patterns and forming conditions of beach-bar sandbodies in the upper fourth member of the Eocene Shahejie Formation on the south slope of the Huimin sag have been systematically analyzed in this paper based on detailed core description and analyses of grain sizes

well log

seismic and the regional geological background data.The result indicates that the beach-bar sandstones are dominated by siltstones and fine-grained silty sandstones of high mud content

thus have unfavorable physical properties.Vertically

the beach-bar sandbodies are common in the first sand group but sporadic in the second

the third and the fourth sand groups.Laterally

beach-bars in the studying area distribute along the Xiakou fault.Stable water depth and stronger waves were beneficial to the formation of beach-bar sandbodies.The slope break caused by the Xiakou fault was helpful for beach-bar sandbodies to be formed along the thrown side of the fault but also restricted the horizontal spreading of the beach-bar.Sediments from the basement and earlier deposited layers in flood-overflow lake provided better sediment source for the beach-bar to develop than that from the terminal fan during floo-ding period.