Bagan Fm

The Bagan Fm. was named by Institute of Petroleum Geology of Yunnan-Guizhou-Guangxi Region in 1983 and first publicly cited by Wang Zunzhou et al in 1992. Its type locality lies near Weiba to Longzhang in Guangnan County, Yunnan Province.

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.

Mainly composed of the rhythmic layers of tuffaceous siltstone, mudstone and tuffite. Lower part is dominated by volcanic clastic rocks, and the Upper part is dominated by sandy mud. Therefore, this Formation could be divided into 2 members: Lower member is an interbedded dark gray, blue gray thin layer of tuffaceous mudstone and the same color medium and thick layer of tuff, interbedded with siliceous layers and tuffaceous siltstone, fine horizon bedding and ripple bedding are developed, and commonly include pyrite crystals; with a thickness of 160 m. Upper member is dominated by yellow-gray, gray-green medium-thick tuffaceous mudstone, mixed with blue-gray tuff, tuff and siltstone, fine horizon beddings are developed, scattered pyrite can be seen locally; the thickness of this member is 74 m.

The bottom is characterized by gray tuffaceous mudstone with Pseudoclaraia wangi. The lower section includes bivalves: Pseudoclaraia wangi, Claraia hubeiensis, C. cf. griesbachi, C. guizhouensis, C. concentrica, C. yunnanensis, C. tumida; ammonoid: Ophiceras sp., Lytophiceras sp., Koninckites sp. etc. The upper section contains bivalves: Claraia stachei, C. aurita, C. radialis and ammonoid: Paranorites sp.

It is interpreted as deep-water volcano-sedimentary products.