yanchang 4 + 5 sector to yanchang 3 sector lithofacies palaeogeography pattern was stable, because the constitution background was steady, and the source direction had no change, and supply was abundant . in those sectors the basin development was in lake retreat, and in the period of extinction gradually, and formatted construction delta deposit, but in yanchang 33 period the sedimentary speed were greater than construction speed, showing that overriding river mouth bars were abundant 长4+5?长3期湖盆发展处于湖退、萎缩逐渐消亡时期,由于构造背景稳定,物源来源方向没有变化,物源供给充分,所以岩相古地理格局基本一致,形成建设性三角洲沉积,但长3~3期沉积速率大于构造沉降速率,表现为叠置河口砂坝极其发育。