Dasuangou Fm

The type section is located in the Dasuan trench, Kaishantun area, Jilin Province.It was named by Sun Hengyuan in 1979, and was officially issued in 1988.

Volcaniclastics. Lower part is composed of grey tuffaceous conglomerate. Upper part is composed of black-grey and grey tuffaceous sandstone and siltstone, intercalated with calcareous sandstone and lenticular limestone. The clastic grains are increasing in size in ascending order, with the carbonate layers decreasing and the volcanic components increasing in amount. Thickness is 1016 m.

The siltstone and limestone lenses yield abundant fossils, including Fusulinida represented by Pseudodoliolina pseudolepida, Parafusulina gigantea, Metadoliolina lepida, Codonofusiella, Skinnerella typicalis and Chusenella, etc.; and Brachiopods represented by Waagenoconcha abichi, Striatifera prinadai, Muirwoodia, Neospirifer striatoparadoxus, Leptodus nobilis and Stenoscisma gigantea, etc

It is interpreted as a marine volcanic-arc clastics formation.

The Sidonggou Fm that Sun Hengyuan established in 1979 represents a suite of shallow-sea volcaniclastic formation, yielding big-sized Fusulinida fossils such as Parafusulina; bivalves such as Aviculopecten; bryozoan such as Polypora; and brachiopods such as Spirifer, etc., it is in a conformable contact with the underlying Kedao Fm. The upper part of the Dasuangou Fm or the Sidonggou Fm is similar to that of the Miaoling Fm in their lithological and paleontological characteristics, and they are hard to be differentiated from one another. So it awaits a further study and decision whether the name of the formation should be maintained or to make a further subdivision of it.