Abstract: Two large volcanic-sedimentary cycles developed in Early Cretaceous in deep Xujiaweizi Fault Depression in Songliao Basin, i.e. the first and third members of Yingcheng Formation. Each volcanic cycle features in multi-period and intermittent eruption, and the volcanic rocks of each period are overlaid spatially. According to the volcanic characteristics, volcanic phase sequence, and rock rhythm combination characteristics, combined with the correlation between sedimentary formations and volcanic rocks at the intermittent period, the first and third members of Yingcheng Formation are divided into three eruption periods, i.e. Yc1 1, Yc1 2, Yc1 3, Yc3 1, Yc3 2, and Yc3 3 from bottom to top. Volcanic rocks of different eruption periods vary a lot in structure, facies, lithological composition, reservoir types, and degree of oil and gas enrichment. The division is of great significance to the identification of the law of regional volcanic activity, the study on distribution of volcanic facies, and the oil and gas distribution and enrichment.

Key words: Xujiaweizi Fault Depression, Yingcheng Formation, volcanic rocks, volcanic eruption, period, division, significance