Longzhang Fm

The type section is located near Dixu Dam-Longzhang in Guangnan County, Yunnan. It was named by the Dianqiangui Institute of Petroleum Geology in 1983. And it was first publicly cited by the Yunnan Bureau of Geology and Mineral Resources in 1990.

Synonym: In the past, it was generally called "Luolou Group” (Guangxi Bureau of Geology and Mineral Resources, 1985). In 1983, the denominator established the Bagan Fm and Longzhang Fm in view of the fact that the Early Triassic deposits in this area are quite different from that of the Luolou Gr in western Guangxi to represent the Early Triassic volcanic clastic rocks in the adjacent areas of Yunnan and Guangxi.

It is dominated by mudstone and siltstone, intercalated with micrite limestone and siliceous rock. It can be divided into Upper and Lower members. Lower Member is composed of dark gray mudstone, siliceous mudstone intercalated with siltstone, thin-medium-thick micrite, fine silt crystalline limestone, with well-developed horizontal laminae, and 168 m thick. Upper Member is dominated by the dark gray mudstone with dark gray muddy silt crystal ash in between thin layer of rock or lens, 33 m thick, with a stable thickness of 100-200 m.

In the Lower Member: Ammonoids: Meekoceras sp., Paranorites sp., Xenodiscoides sp., Xenoceltites sp., Pseudosageceras sp.; Bivalves: Bakevellia sp. In the Upper Member: Ammonoids: Columbites sp., Paranannites sp., Leiophyllites sp.; Bivalves: Posidonia sp., P. cf. pannonica.

This formation is dominated by mainly sedimentary marine volcano-sedimentary rock series.

see the Bagan Formation.