Zhanhua sag is a subOsag in the northeastern Jiyang depression. During the late ShaO4 ( Es4) — ShaO3 ( Es3) epoch (the Fourth O Third Member of Shahejie Formation , Palaeogene) ,Zhanhua sag was developed into a faultOsag basin steep in the north and gentle in the south. During the late Es4 epoch , the northeastern Zhanhua sag was consisted of two subOsags , one was located in the east and the other in the west . The deposits were mainly fanOdelta , gypsumOsalt lake and lacustrine facies ,which generally distributed in annuluses. In the Es3 epoch , the deposits were mainly semiOdeepOdeep lake facies , fanOdelta and sublacustrine fan facies. The semiOdeepOdeep lake facies was the most developed deposits and distributed a little more further to the north of the basin. The shoreOshallow lake facies were mainly distributed on the north edges of the bulges in the south.The fanOdelta facies were mainly distributed on the edges of the
bulges. There were two types of sublacustrine fan facies , i. e. ,normal type and trough type. The normal sublacustrine fan facies were developed on the north edge of Gudao bulge in the south part , and the trough ones were situated on the slope zones on the steep banks of Yihezhuang bulge and Chengzikou bulge.During the middle of Es3 epoch , sublacustrine fan facies was greatly developed , two sublacustrine fans which were developed
originally on the edges of Chengzikou bulge and Gudao bulge were intersected at the area around well Y115. The shape of resulting sublacustrine fan was protruded towards the west by the obstruction of Guxi fracture belt .
