Xizhashan Fm
Type Locality and Naming
The Xizhashan Formation was erected by the Comprehensive Geological Prospecting Brigade under the Xizang Bureau of Geology and Mineral Resources in 1979. The section for the designation is in Pengqurianongba-Takaxiageiqu of Lajiangshan of Deqing township of the Baingoin County (90°10′E; 30°30′N) and in Xizashan east of the Baingoin County, Xizang.
Lithology and Thickness
Lower part of the Xizhashan Formation is built up by gray calcareous siltstone, sandstone and Orbitolina limestone and black shale. Middle part is purple red conglomerate with grit lenses, gray green conglomerate, gravel-bearing sandstone, medium and fine-grained sandstone and siltstone, forming rhythms. Upper part is variegated gravel-bearing tuffaceous grit, sandstone, calcareous sandstone with sandy conglomerate, marl and Orbitolina limestone, with the top unknown. It exceeds 1800 m in thickness.
Relationships and Distribution
Lower contact
The base of the formation marked by gray white sandstone with limestone lies conformably on the underlying Lajiangshan Fm marked by purple red sandstone and conglomerate,
Upper contact
Top unknown. China Lexicon chart implies a major regional disconformity, then Zongbai Gr of Paleogene.
Regional extent
The present formation occurs extensively as a stripe in the Deqing, Lajiangshan, Xiongqian and Shencuo areas on the western and northern sides of the Nam lake. It is persistent in lithology and ranges from 1500 to 2000 m in thickness.
GeoJSON
Fossils
In the Lajiangshan area, it bears foraminifera Orbitolina spp., etc.; bivalves Hippuritidae spp.; ammonite Pseudohaploceras spp., P. cf. douvilei, P. cf. leptoviense, etc.
Age
Depositional setting
Additional Information