Pochengshan Fm

The type section of the Pochengshan Formation is Pochengshan section, located on the north slope of the Pochengshan Hills (96°07’E, 40°55’N). In the type section the formation is 1389 m thick (Fan, 1989). The Pochengshan Formation was named by Fan (1989). The name is derived from Pochengshan Hills in Mingshui Township, Subei Mongolian Autonomous County, Jiuquan City, western Gansu Province.

Synonym: （破城山组）

The Pochengshan Formation is a clastic sequence. The formation is roughly divided into four parts, from bottom up: 1, brownish red, greyish green, thin-bedded argillaceous slate and siliceous slate (195 m thick); 2, dark grey, black siliceous rock, greenish grey and dark grey sandy limestone, intercalated with lenticular limestone or calcareous dolomite (206 m); 3, brownish grey, thin-bedded, fine-grained quartzose sandstone, argillaceous and calcareous siltstone, intercalated with thin-bedded siliceous rock and conglomerate (565 m); 4, greyish black siliceous rock, intercalated with calcareous siltstone and sandstone (423 m) .

The 2nd to 4th parts of the formation yield trilobite Eoredlichia and brachiopods Obolus and Acrothele.

The Eoredlichia from the formation was identified by a trilobite worker from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, but was considered to be a taxon belonging to Protolenidae by the trilobite worker from Xi’an Institute of Geology and Mineral Resources. The later taxon occurs slightly higher in position than Eoredlichia.