Chehe Fm

The type section is located at Yechehe River of Nandan County, Guangxi Zhuang Autonomous Region. It was named by Zhang Zhaojin in 1941.

Historically, in both side of Nandan-Hechi Road there is a set of strata characterized by quartz sandstone in the lower, grayish shale in the middle and alternating shaly limestone and purple shale in the upper, to which Zhang Z.J. (1941) gave a special name as Chehe Bed without strict definition. During the field investigation in 1961, based on the biostratigraphical study the No. 5 Prospecting Team subdivided the Chehe Bed equivalent into Yilan Fm, Tangding Fm (including Tangxiang Mbr and Nabiao Mbr) and Givetian Luofu Fm. However, some geologists considered that these stratigraphic units were defined on the basis of different fossil contents and is difficult to be recognized by lithology, particularly for the field mapping. Study in detail shows that the lithology of Luofu Fm is relatively distinguished by occurrence of sandstone and limestone lenses, while the Tangding and Nabiao Fms are not easily separated. Thus, the names of Tangding and Luofu Formations are kept and others such as Chehe, Nabiao and Tangxiang Fms are abandoned.).

Claystone. This generalized "formation" group is composed of black carbonaceous mudstone, siltstone, and calcareous mudstone intercalated with a few chert, sandstone, and clayey limestone beds. The thickness is more than 800 m.

In Dachang area, it contains reef limestone; and in Chehe area, the formation is commonly metamorphosed in its lower part. In Dashan area, the upper part of Chehe Fm is intercalated with five beds of 0.15-0.35 cm thick intermediate acidic tuff. The abundance of chert increases and the thickness decreases to 283 m in the Shanglin area.

the generalized "formation" group is characterized by tentaculites, ammonoids, trilobites and thin-shell brachiopods, and includes tentaculite zones from Nowakia subtilis zone to N. otomari zone; ammonoids of Anatoceras-Erbenoceras, Latancestes noeggerati, Pinacites jugleri zones; and trilobites of Plagiolaria nandanensis fauna.

The generalized "formation" group is interpreted as a deep-water anoxic basin environment.