Tumugou Fm

The type section is located at Tumugou of Deda Village in Batang County, Sichuan. It is named by the third area survey team of Sichuan Geological Bureau in 1966. The original Tumugou Fm represents the strata of clastic rock and volcanic rock in the early Late Triassic in Yidun area, Sichuan, which lies between the Lanashan Fm of Upper Triassic and the Qugasi Fm of Upper Triassic.

Synonym:

This formation is mainly composed of metamorphosed rocks. Lower part is composed of two sets of conglomerates and two sets of gray thin-bedded limestone intercalated with slate, about 843 m. Upper part consists of a set of thermal contact metamorphic rocks with a thickness of more than 1255 m.

The lithology and thickness vary greatly regionally, and two facies’ zones can be roughly divided laterally. The eastern Ganzi and Muli facies zone is represented by the Tongba section in Muli with lower part of marlstone intercalated with sandy slate and upper part of silty slate with a total thickness of 1335.6 m. In western Yidun and Derong facies zone, the lower part is characterized by a transition from the conglomerate at the bottom to the sandstone, slate, and massive limestone interbedded with volcanic rocks, whereas, the upper part is mainly composed of quartz fine sandstone interbedded with siltstone and slate, with a total thickness of 1300 to 5700 m

The lower part of this formation in the western and eastern area mainly yields bivalves with other fossils like ammonoids and Brachiopoda, which belongs to Myophoria napengensis-Juvavites assemblage.

It is interpreted marine environment.