The volcanic rocks in Xujiaweizi fault-depression

Songliao basin

was mainly erupted in Late Jurassic to Early Cretaceous.Their occurences are characterized by a certain geometric pattern.On the basis of the structural position of volcanic eruption and the occurrences in the basin

three types of eruption have been identified

including eruption on the upthrown side of fault

along fracture belt and on downthrown side. Different occurrences are often corresponding to different basin structures. The volcanic rocks occurring along fault plane would transit gradually to sublacustrine fan—turbidite fan; the volcanic rocks occurring on the upthrown side of fault would distribute in the manner of alternating beds of volcanic rocks and sandstones; the volcanic rocks occurring on the downthrown side have mostly been covered by fine grain sediments.