Youfang Fm
Type Locality and Naming
The type section of the Youfang Formation is the Chenjiaba section, it is the upper portion of the same section shared by the underlying Qiujiahe Formation. The section is located about 2.5 km south of Chenjiaba in Chaotian Township, Chaotian District, or about 6 km northwest of Chaotian Town, the seat of Chaotian District, Guangyuan City, Sichuan Province (105°50’48” E, 32°41’00” N). The type section was measured by the Sichuan Second Regional Geological Survey Team in 1963, and in the section the formation is 201.3 m thick. The Youfang Formation was named by Sichuan Second Regional Geological Survey Team (1977). The name is derived from Youfang in the Chenjia (or Chenjiaba) Town, the seat of revoked Chenjia Township (now incorporated into Chaotian Township), Chaotian District, Guangyuan City, northeastern Sichuan Province. It was first appeared in a 1963 manuscript by Wu Shiliang et al.
Synonym: （油坊组）
Lithology and Thickness
The Youfang Formation is basically a clastic sequence. It consists of greyish black, medium-bedded, siliceous epi-metamorphic lithic sandstone with interbeds of black phyllite. The formation contains three layers of coarse-grained lithic sandstone with minor pebbles, with one layer at the base and two others in the middle part respectively.
Relationships and Distribution
Lower contact
The Youfang Fm rests conformably on the underlying Qiujiahe Fm. The lower boundary of the formation is marked by lithological change from the quartz-phyllite of Qiujiahe Fm to lithic sandstone of Youfang Fm.
Upper contact
It is in disconformable contact with the Chenjiaba Fm of Lower Ordovician System. The upper boundary is defined by the disconformable plane.
Regional extent
The Youfang Formation is exposed in Northern Qangtang-Simao Region, distributed in a narrow northeast- and southwest-trending area in northern and northeastern Sichuan Province (Chaotian, Beichuan, Maoxian, Pingwu, and Qingchuan counties or districts). The thickness of the formation varies from 130 to 613 m.
GeoJSON
Fossils
No fossil has been found in the formation yet.
Age
Depositional setting
Additional Information