Chamashan Gr
Type Locality and Naming
The type section is Chamagong-Genbagong section at Chamagong, Yawa District, Batang County, western Sichuan Province (99°09’00”E, 30°03’00”N), which lies about 6.5 km northeast of Batang Town, the seat of Batang County and was measured by the No. 3 Brigade of Sichuan Regional Geological Servey Team in 1967. In the type section, the group is over 1341 m thick. The group was named by Compiling Group for Sichuan Regional Stratigraphic Scale (1978). The name is derived from Chamagong in Batang County, Ganzi Tibetan Autonomous Prefecture, western Sichuan Province. This formation spans Ediacarn-Cambrian boundary. The Group was originally named as Chamashan Formation. Subsequently Gu and Liu (1997) replace it with Chamagong Group because they realized Changshan should be misspelled for Chamagong as there is no such geographic name of Chamashan in Batang County, and elsewhere in China, but Chamagong. However, this change is apparently invalid for a well-established formal unit and this new name is not accepted by this book.
Synonym: （查马山群）; Chamashan Fm, Chamagong Gr
Lithology and Thickness
The Chamashan Group is a carbonate and metamorphic volcanic sequence with a few of clastic rocks, consisting mainly marble, crystalline limestone, siliceous dolomitic limestone, green schist, metamorphosed intermediate-basic volcanic rocks, and volcanic breccia. Thickness is 1341 m at Chamagong.
Relationships and Distribution
Lower contact
The basal boundary of the group is unknown as no lower part of the formation is exposed.
Upper contact
It is conformably overlain by the Xiaobachong Fm.
Regional extent
The Chamashan Group is distributed along a north-south direction in northwestern part of Batang County, with a tendency of deceasing carbonate rocks and increasing clastic rocks northward; also, with a tendency of deceasing thickness northward, ranging from 1,341 m at Chamagong, about 1,200 m in Jiake-Dangcun area, and to about 1,000 m at Meiwutang.
GeoJSON
Fossils
No fossils have been found from the group.
Age
Depositional setting
Additional Information