Xiangmaoshan Fm
Type Locality and Naming
Type section of Xiangmaoshan Formation is the Erdaogou-Sandaogou section, measured between the Erdaogou and Sandaogou (second and third ditches) on the east bank of the Shule River, about 24 km southeast of Changmapuzi Town in Yuerhong Township, Yumen City (County), Jiuquan City, Gansu Province (96°58’E, 39°41’N). The Xiangmaoshan Mountain lies about 5 km southwest of the type section, and was measured by No. 2 Brigade of Gansu Regional Geological Survey Team in 1951. In the type section, the formation is over 1121 m thick as its top part is not exposed. Originally the formation was named Xiangmaoshan Group by Compiling Group for Gansu Regional Stratigraphic Scale (1980) to replace the Erdaogou Group, a name preoccupied by the Erdaogou Limestone (now Erdaogou Member) of Silurian System in Jilin Province. The name is derived from Xiangmaoshan Mountain in Shibaocheng Township, Subei Mongolian Autonomous County, Jiuquan City, Gansu Province. The unit was lowered in rank as Xiangmaoshan Formation by Yang (1997).
Synonym: （香毛山组）; The Germo Formation, named by Xiang (1981c) for the strata at Germogou, Jintieshan, Sunan, Zhangye City, Qinghai Province is regarded to be synonymous with the Xiangmaoshan Formation by Yang (1997) because of its similar lithology and similar early Miaolingian trilobite assemblage
Lithology and Thickness
The Xiangmaoshan Formation is mainly an epimetamorphic clastic sequence, consisting of grey to dark grey silty slate, phyllitic slate, and sandy slate, intercalated with sandstone, and with a layer of grey and grayish white lenticulated crystalline limestone near the top part.
Relationships and Distribution
Lower contact
In the type section, the contact relationship of the Xiangmaoshan Fm to both the underlying and overlying formations are unknown as the formation is cut by faults below and above. Regionally, the formation is usually contacted with underlying Heicigou Fm by fault, or occasionally in comfortable contact. In some area the formation rests unconformably on the metamorphic rocks of the Beidahe Gr of Paleoproterozoic Erathem.
Upper contact
In the type section, the contact relationship of the Xiangmaoshan Fm to both the underlying and overlying formations are unknown as the formation is cut by faults below and above, In some area the formation has the fault contact relationship with the overlying Yingou Fm of Lower Ordovician.
Regional extent
The Xiangmaoshan Formation is exposed in the Qilian Area of Qiadam-Qilian-Alxa Region, distributed interruptedly in Subei County (Yuerhong, Xiangmaoshan, Yingzuishan, Shibaocheng, and Dabinggou), Sunan County (Haoqing, Jingtieshan, Dayehekou, Germo), Yumen City (Changma and Shiyouhe) of Gansu Province; and in Qilian County (Chauncigou), Daliang of Menyuan County, and in Huzhu County (Huashixia) of Qinghai Province. The thickness of the formation ranges generally from 228 to 1127 m.
GeoJSON
Fossils
In the type section, the limestone near the top of the formation yields trilobites Maryvillia sp., Proceratopyge sp., and unidentified taxa belong to Dorypygidae, Lisanidae and Parabolinoididae; and diverse brachiopods Acrothele orbicularis, Briggeria sp., Eoorthis cf. shakuotsnensis，Lingulella sp. and Wimanella? sp. In other section the formation yields additional trilobite Hedinaspis sp.
Age
Depositional setting
Additional Information