Tuodian Fm

It was named by the Petroleum Prospecting Party under the Geological Department of Yunnan Province as the Tuodian Horizon in 1960, and was first published for its application by the Geological Bureau of Yunnan Province in 1974. The naming locality is situated in the Tuodian region of Shuangbo County, with the section extending from the Xiazhuang Village to the Pengpu area of Xiangyun County, Yunnan Province serving as its reference section.

Synonym: （妥甸组）

The formation represents a set of alternating layers of purple sandstones and mudstones, intercalated with yellow-green mudstones. It is divisible into three members: Lower member consisting of purple mudstone and silty mudstone, intercalated with grey-violet fine-grained sandstone and siltstone, locally with marl lenses, with a thickness of 675.9 m. Middle member consists of dark-purple massive mudstone, intercalated with brown-yellow argillaceous fine-grained sandstone, siltstone and marl lenses, with the sandstone being possessed of horizontal and micro-oblique beddings, with a thickness of 498 m. Lower part of the Upper member consists of dark-purple and purple massive mudstones and calcareous mudstones, intercalated with yellow, yellow-green and grey-green calcareous mudstones and marls. The upper part of the upper member consisting of dark grey-green, grey-green and yellow-green thin-bedded to thick-bedded mudstones and calcareous mudstones, intercalated with many layers of marls, with a thickness of 435.3 m. The total thickness of the formation is 1609.2 m.

The lower member yields Charophyte fossils as represented by Euaclistochara lufengensis and E. nuguishanensis. The lower part of the upper member yields “conchostracan” fossils as represented by Eosestheriopsis dianzhongensis, and the upper part of the upper member yields “conchostracans” as represented by Eosestheriopsis dianzhongensis and E. subquadrata, as well as Ostracod fossils as represented by Darwinula oblonga and D. incurva.

It is interpreted as a fluvial-lacustrine environment.