Abstract:

The volcanic lava, tuff and tuffaceous sandstones were recognised in member 2 of Yingcheng Formation, Cretaceous in the survey of outcropped geological section with a detailed measurement in the eastern margin of Songliao basin. The tuff rocks include ignimbrite, lithic crystal tuff, ash ball tuff and breccia tuff. It indicates that a certain scale of volcanic activities still existed during the forming of member 2 of Yingcheng formation, which was a stage without strong volcanic activities. This kind of deposition distinguished from the normal deposition, has a special characteristics controlled by both volcanism and sedimentation. The member 2 of Yingcheng formation is a suit of transition rocks between volcanic rocks and terrigenous clastic rocks, and the provenances derived not only from syngenetic volcanic eruption, but also from the member 1 and the lower member of Yingcheng Formation, as well as the weathering of older strata. These suits of rocks are special in types because of the existence of the two kinds of provenances including volcanic substance and terrigenous denudation substance, and the two kinds of mechanisms including volcanic accumulation and normal sedimentation. It is indicated that special volcanic-deposit types were existed, during the stage of member 2 of Yingcheng Formation which are pyroclastic flow channel deposits in alluvial plain, base surge deposits and air-fall volcanic ash deposits in flooding basin.

Key words: the eastern margin of Songliao basin, Yingcheng Formation, volcaniclasitic rock, volcanic-sedimentation, provenance analysis