Pingtoushan Fm
Type Locality and Naming
Beishan (Gansu-Inner Mongolia border region). The Pingtoushan Fm was named by the No. 2 party of Regional Geological Survey, Gansu Bureau of Geology in 1968. The type section is at Pingtou Mountain, 65 km west of the major peak of Mazong Mountain, Subei Mongolia Autonomous County, Gansu Province.
Synonym: （平头山组）
Lithology and Thickness
In the type section, the Pingtoushan Fm is composed of carbonate rock with clastic rock series. It is subdivided into three parts. Lower part consists of grey-to-grey black dolomite with chert concretions and bands. Middle part is grey-white calcareous quartz sandstone, wormkalk and oolitic limestone; the cross bedding and ripple marks are seen in sandstone. Upper part is grey thin-bedded fine-crystalline limestone intercalated with dolomite. The formation is about 3000 m thick.
Relationships and Distribution
Lower contact
It is in disconformable contact with underlying the Gudongjing Gr of the Changcheng System, but in conformable contact in most places of the distribution area, with an unconformable contact occasionally.
Upper contact
Disconformable overlain by the Yemajie Fm of early Qingbaikouan (lower formation of the Yuanzaoshan Gr)
Regional extent
Beishan (Gansu-Inner Mongolia border region). It is distributed at Luoyachu Mt., Pingtou Mt., Shuangying Mt., Xiaomazong and Dahuoluo Mts. It is stable in lithological character, but quite variable in thickness. For example, at southwest of Wangxu Mtu. in Ejin Qi, Inner Mongolia it is recorded 4164 m thick, where the clastic rock increases, but at Dahong Mt., in Jinta County, Gansu Province and Qiongtag Mt., Xinjiang, it is composed of stromatolite-bearing dolomite (only 1000 m thick).
GeoJSON
Fossils
The lower part is rich in stromatolites, such as Conophyton indigestum, C. nodosum, Jacutophyton f., Kussiella f., Baicalia cf. rara etc.; the middle part contais stromatolites, such as Baicalia f. and microplants such as Trachysphaeridium sp., Pterospermopsis sp., Brochopsophosphaera sp.; stromatolites in the upper part are Giganstraticonnus regularis, Anabaria f., Scopulimorpha f.
Age
Depositional setting
Additional Information