Abstract: Recent geological survey on the outcrops of the Yingcheng Formation exposed in the Liutai area at the eastern margin of the Songliao Basin and related laboratory analysis reveal that a set of seemingly normal clastic sedimentary rocks in the second member of the Yingcheng Formation is in fact a set of transitional rocks between lava and normal sedimentary rocks. This succession of rocks contain clastic lava, tuff, tuffite, tuff clastic rock and normal clastic rock, which suggest they were formed in a transitional environment of volcanic slope to fluvial plain or lake. There are 4 end members of volcanic clasts, including catapult airfall, ejection airfall, base surge and volcanic clasts flow. If the volcanic clasts were deposited on volcanic slope and/or fluvial plain, they would occur in the 4 faceis mentioned above or in alluvial fan and braid stream. If the volcanic clasts were deposited in lake, they would occur in delta, fandelta, shallow-deep lake, and swamp. The architecture of facies could present the forming process of volcanic eruption-clastic accumulation. The characteristics of sedimentary cycles of the second member of the Yingcheng Formation show that there are 3 kinds of basin fillings: sedimentary-valcanic, sedimentary and volcanic. The entire succession should be from coarse clastic rocks to volcanic rocks and volcanic clastic rocks and to fine clastic rocks, corresponding to rifting, volcanic activities and sedimentation in rift basin respectively.

Key words: Songliao Basin, the second member of Yingcheng Formation, volcanic clasts, sedimentory facies, architecture