Xiaobachong Fm

The type section is the upper portion of the same section shared by the Chamashan Fm, the Chamagong-Genbagong section in Batang County, western Sichuan Province (99°09’50”E, 30°01’51”N). It lies about 6.5 km northeast of Batang Township and measured by the No. 3 Brigade of Sichuan Regional Geological Survey Team in 1967. The thickness of Xiaobachong Formation in the type section is over 2,740 m as neither the upper part nor top boundary of the formation are exposed in the type locality. The Xiaobachong Formation was named by Compiling Group for Sichuan Regional Stratigraphic Scale (1978). The name is derived from Xiaobachong at Xiaoba Village, which is close to Chamagong, Batang County, Ganzi Tibetan Autonomous Prefecture, western Sichuan Province.

Synonym: （小坝冲组）

The Xiaobachong Formation is a sequence of metamorphic volcanic rocks and clastic rocks. The exposed part of the formation is divided into five lithologic beds, from the bottom up: 1, greyish green, thin- to thick-bedded chloritic dolomite-quartz-schist (411.9 m thick); 2, dark grey to black, sericite-schist bearing graphites, sericite-quartz-schist with brown, thin-bedded metamorphic sandstone at the base (270.6 m); 3, light grey sericite-quartz-schist, sericite-schist, muscovite-quartz-schist, alternated with light green thin- to medium-bedded chloritic dolomite-quartz-schist (591.8 m); 4, black, thin- to medium-bedded carbonaceous phyllite in lower part; greenish grey, thin- to medium-bedded chloritic dolomite-quartz-schist with interbeds of dark grey sericite-quartz-schist in the middle part; and black, thin- to medium-bedded sericite-schist bearing graphites, alternated with sericitic phyllite and sericite-quartz-schist in the upper part (403.4 m); 5, greyish green and dark green, intermediate-basic volcanic rocks with interbeds of marble and with no upper part exposed (over 1062.0 m).

No fossils have been found from the formation.