Abstract: Mesozoic faults at the eastern margin of the Songliao Basin were well developed. Based on detailed field geological survey of the Yingcheng Formation at the eastern margin of the Songliao Basin，the nature, attitude and spatial and temporal distribution regularities of these faults were systematically described. The formation of these Mesozoic faults was divided into four epochs, namely, Later Variscan-Indosinian, Yingcheng, the last stage of Yingcheng epochs and the late stage of the Later Cretaceous. Based on the distribution regularity of the craters in the Yingcheng Formation, the concealed faults of the Yingcheng epoch were identified for the first time and were considered to have controlled the formation and distribution of the volcanic rocks of the Yingcheng Formation. The NS trending faults of the Yingcheng epoch discovered in the area could also sever as a comparison for the NS faults of the Yingcheng Formation in the Qingshen gas field in the Xujiaweizi area. It was suggested that and alternative tectonic stress field of EW trending extense depression and of EW trending compressive thrust existed in the Yingcheng epoch. A NE-SW trending tectonic stress field was introduced by two left-lateral strike-slip faults called the Jiamusi-Yitong and Siping-Harbin respectively at the final stage of the Yingcheng epoch, and the resulted stress field in turn controlled the intrusion of some NE trending basic dikes and development of several NE and NW trending strike-slip faults. It was believed that the faults in the study area could be compared with those in the Xujiaweizi area of both the Yingcheng epoch and of the final stage of the Yingcheng epoch, which set a basis for predicting the distribution regularities of volcanic rock reservoirs in the Qingshen gas field.

Key words: eastern margin of the Songliao Basin, Yingcheng Formation, fault, volcanic rock reservoir