Ranfangdi Fm

The type section is located in the northeast of the Tieyingzi Village in the West Hills of the Rafangdi Region, Keshiketeng Banner, Inner Mongolia. It was named by the 2^nd Regional Geological Survey Party of Liaoning Province in 1971.

Volcanics and Clastics. Composed of intermediate and acidic volcanic rocks, intercalated with sedimentary rocks. Lower part is composed of grey-green altered andesite, intercalated with acidic crystal-clastic tuff, with its base being massive instable tuffaceous conglomerate, with a thickness of 319 m. Middle part is composed of grey metamorphosed sandy conglomerate, fine-grained sandstone and siltstone, intercalated with secondary quartzite and acidic lava, locally with coal seams, with a thickness of 589 m. Upper part of the formation is composed of grey intermediate-acidic tuff, tuffaceous breccia and andesite, intercalated with slate and rhyolite, with a thickness of 1246 m. The large-scale lake-basin accumulations that were formed during the volcanic eruption had resulted in a local formation of a small amount of good-quality thin-bedded coal seams in such areas as in Arjitu and other places. Total thickness of the formation is 2134 m.

The middle part of the formation yields bivalve fossils represented by Aviculopecten and Allorisma. In the West Hills of the Taipingzhuang area it yields Bivalves such as Palaeanodonta, and Plant fossils (phytolites) such as Ullmannia, Gigantopteris, Walchia, Sphenopteris, etc., with the continental volcanic rocks and clastic rocks being dominant, intercalated with marine strata.

It is interpreted as continental volcanic rocks, and including large-scale lake basin deposits.

The isotope age of the andesite from the Xiaojingzi locality in the eastern part of the section where the formation has been established is 207 Ma [NOTE: This would imply it includes latest Triassic, not Permian, if verified].