Tazang Gr

The type section is located at Yatungou of Shengli Village and Jianantangzi of Tazang Village in Nanping Country, Sichuan. The reference section is located at Congya of Longkan Village. It was named by Gu Xueda and Huang Shengbi in 1987. Tazang Gr was equivalent to a set of volcanic rocks, carbonate rocks and mudstone mélange distributed in Minjiang-Heye fault zone. This group was called as the Heihe Gr and Boyuhe Fm by the area survey team of Gansu Geological Bureau (1970). The former belongs to the Lower Permian and the latter belongs to Middle Triassic based on the plant Neocalamites sp. In 1976, the second area survey team of Sichuan Geological Bureau identified the strata as Carboniferous-Permian. In 1987, the team identified them as the Bozigou Fm and the Zagashan Fm, belonging to the Early and Middle Triassic respectively. In 1985, in a report on the study of the Xikang Group, a set of colluvium limestone near Jiuzhaigou was named the Longkang Fm, which was dated to the Ladinian of Middle Triassic. In 1987, Gu Xueda and Huang Shengbi named the Tazang Gr as a representative of this set of strata because of its unique basic volcanic rocks and carbonate gravel mélange, which was different from the Bozigou Fm, Zhagarshan Fm and Paleozoic strata. This formation was firstly cited by Sichuan Bureau of Geology and Mineral Resources, and regarded as Ladinian of Middle Triassic

Synonym: Tazang Fm

This formation, 2800 m thick, is mainly composed of sandy slate, intermediate-basic volcanic rock and contaminated rocks with carbonate, which can be divided into two parts. The lower part is composed of light gray metamorphic sandstone intercalated with lenticular and breccia-bearing limestone, developed in Longkang area. There are spilling-sedimentary rhymes composed of a large number of amygdaloidal spilite, amphibolite, volcanic breccia, and radiolarian chert in the lower part. The upper part is composed of terrestrial clastic flysch-type sandy slate intercalated with marl. There are variegated sandy mudstone, Fe-Mn bearing limestone or Fe-Mn ore layer.

The lower part yields bivalves Daonella lommeli, conodonts Neogondolella excelsa, N. polygnathiformis and crinoid Taumatocrinus hsui.

It is interpreted as marine volcanic eruption-sedimentary rock series.