Songdagou Fm

The type section of the Songdagou Formation is Jianding-Longyong section. The section is located near Songdagou in Zongza District, Batang County, Sichuan Province (99°22’30”E, 29°19’30”N). It lies about 6.1 km east of the seat of Zongza Township and was measured by the Sichuan Third Regional Survey Team in 1974. In the type section, the formation is over 2017.12 m thick, but there may have overlap of strata due to fault cutting. The Songdagou Formation was named by the No. 2 Brigade of Sichuan Third Regional Geological Survey Team (1977). The name is derived from Songdagou in Zongza District, Batang County, Ganzi Tibetan Autonomous Prefecture, western Sichuan Province.

Synonym: （颂达沟组）

The Songdagou Formation is mainly a metamorphic clastic sequence, composed of greyish green and greyish yellow phyllitic slate, interbedded with find-crystalline limestone and silty slate in the lower part (ca. 700 m thick); greyish green siltstone, interbedded with quartzose sericitc-phyllite, yellow sericitic slate interbedded with sandy slate, and grayish green phyllite, alternated with silty sericitic slate in the middle part (ca. 470 m); greyish yellow, greyish green slate, silty slate, thin-bedded to massive siltstone, grayish green and grayish yellow phyllite, intercalated with medium- to coarse- crystalline limestone or limestone lenses in the upper part (ca. 850 m).

The interval of 30 m thick in the top of the formation yields late Furongian trilobites Calvinella sp. and Haniwa sp. and brachiopod Finkelnburgia. In addition to Calvinella and Haniwa, the formation also yield trilobites Mictosaukia in other locality in Zongza area.