Tong'an Fm

Southernmost Sichuan. The Tong’an Fm was named by the Tong'an Party of Geology, Sichuan Bureau of Geology in 1957. The type locality is Tong'an, Huili County, Sichuan Province. The reference section is in Lixi, Huili County, Sichuan Province.

Synonym: （通安组）

The Tong'an Fm is composed of carbonaceous sedimentary metamorphosed rock intercalated with minor metamorphosed volcanic rock, and has four parts. Lower part is composed of purple-grey and purple-red metamorphosed feldspar quartz sandstone, mica schist, sericite schist, phyllite and carbonaceous slate, locally accompanied with dolomitic marble and calcareous slate. The strata bear oblique bedding and microplants, such as Trematosphaeridium. Lower-Middle part, 20 m to 513 m, is dominated by greyish dolomitic marble and silicified dolomitic marble accompanied with minor phyllite, slate, ferruginous meta-sandstone or iron ore lenses, commonly bearing copper. Upper-Middle part, 2523 m to 2954 m, consists of carbonaceous sericite phyllite and slate intercalated with crystalline limestone, dolomitic limestone (or dolomitic marble, marble), hematite lenses and meta-sandstone. Upper part, 625 m to 2100, is mainly crystalline limestone (or marble) and dolomitic limestone, sandwiched with minor phyllite and slate. Copper mineralization occurs locally in marble. It has also stromatolites.

Stromatolites, such as：Conophyton f., Kussiella f., Colonnella f., Cryptozoon f. It is rich in microplants, the main taxa are Pseudozonosphaera, Stenomarginata, Micrhystridium, Trachysphaeridium, Asperatopsophosphaera, Polyporata, Quadratimorpha etc.