Walasi Fm

Named in 1974 by the First Regional Geological Survey Team of Sichuan Geological Bureau. Named profile is located in the east 10 km of Tongpu District, Jiangda County, Tibet, Walasi, which is on the north side of Sichuan-Tibet highway. The original Walasi Fm represents the Middle Triassic Anisian flysch like deposits in the Jiangda area, Tibet.

Synonym: Fuwalasi Fm. The Chengdu Institute of Geology and Mineral Resources of the Chinese Academy of Geological Sciences and the regional survey team of the Sichuan Bureau of Geology and Mineral Resources (1992) combined the Walasi Fm with the overlying Congla Fm, collectively known as the Wakasi Fm.

This formation can be divided into two members: The bottom of the Lower member is andesitic porphyrite conglomerate, and the lower part is mainly grey black sandstone, siltstone and slate interbedded thick layer conglomerate, the upper part is dark gray banded siltstone, gray black slate with interlayer andesitic porphyrite, tuffaceous andesitic porphyrite and gray black thick layer siliceous limestone with thickness of 1546 m. Upper member is mainly composed of conglomerate, sandstone, slate and a small amount of flysch constituted with thin limestone, the top of which is thin limestone with a thickness of 769 m.

The fossils are mainly ammonoids and bivalves. Ammonoids in lower member is Paracrochordiceras sp.; Bivalves: Entolioides walashiensis, Plagistoma Beyrichi etc. In the upper member, the ammonoids are the Japonites- Hollandites assemblages. Also contains bivalves Posidonia pannonica etc.

This formation is mainly marine volcanic sedimentary rock series.