Abstract:

The reorganization of volcanic cooling unit is a key to analyze volcanic stratigraphy and litho-facies. The study of the sections of Yingcheng Formation in Songliao basin shows that there are four types of cooling unit including pyroclastic, lava, pyroclastic+lava and lava+pyroclastic in the outcrop of the southeast margin and Xujiaweizi fault depression. The type of pyroclastic is an end unit reflecting the processes of hydro explosion. The type of lava is another end unit reflecting the processes of magma effusion. The type of pyroclastic+lava is a basic unit reflecting the consequent processes of hydro-magma eruption. The type of lava+pyroclastic is a reformed or special unit. Cooling unit itself and its stacking contain meaning of litho-facies. The cooling unit is a genetic stratigraphic unit in volcanic stratigraphy, which is fundamental to learn architecture, forming and preservation of volcanic strata. The recognition of volcanic cooling units and analysis of superimposition give a stratigraphic architecture of the First Member, Yingcheng Formation in Xujiaweizi of Songliao basin.

Key words: volcanic stratigraphy, cooling unit, stratal aichitecture, Yingcheng Formation, Songliao basin, volcanic rocks