Chisha Fm
Type Locality and Naming
It was named by the Regional Survey Party of Anhui Province in 1973. The naming section is located in the vicinity of Chisha Village till the Maren Hills, Fanchang County, Anhui Province.
Synonym: （赤沙组）
Lithology and Thickness
It represents essentially a set of volcanic rocks with intermediate volcanics being predominant. The basal part of the formation is composed of light-grey trachytic andesite, turning upwards largely into dacite, grey andesite, vesicular andesite and andesitic dacite, intercalated with a small amount of rhyolite and tuffaceous siltstone. No fossils have been found. It is of 594 m in thickness.
Relationships and Distribution
Lower contact
It is in an extrusive unconformable contact with the underlying Zhongfencun Fm (not found in Jurassic Lexicon yet). But radiometric dates for this Zhongfencun Fm are ca. 132 ±2 range => earlist Hauterivian (Guangfu Xing, Jianqing Li, Zheng Duan, Mingxuan Cao, Minggang Yu, Pingli Chu, Rong Chen. Mesozoic–Cenozoic Volcanic Cycle and Volcanic Reservoirs in East China. Journal of Earth Science, 2021, 32(4): 742-765. doi: 10.1007/s12583-021-1476-1).
Upper contact
Regionally, the schematic strat column indicates the next younger unit as Kedoushan Fm (not found in Jurassic Lexicon yet). But radiometric dates for this Kedoushan Fm are ca. 130.7 ±1.5 Ma range => mid Hauterivian (Guangfu Xing, Jianqing Li, Zheng Duan, Mingxuan Cao, Minggang Yu, Pingli Chu, Rong Chen. Mesozoic–Cenozoic Volcanic Cycle and Volcanic Reservoirs in East China. Journal of Earth Science, 2021, 32(4): 742-765. doi: 10.1007/s12583-021-1476-1).
Regional extent
The formation belongs to an accumulation of volcano-extrusive facies, and is distributed essentially in the areas of Fanchang and Nanling counties. Its lithology in various places is consistent, yet with great changes in thickness from place to place, resulting in a reduction of thickness to 167 m easterly to the area of Shengshan Mts. Its lower part is composed of dark-grey dacitic breccia-bearing crystal tuff; its upper part, of dacitic porphyrite and trachytic porphyry. In the Laowuji area, it is of 267 m in thickness, and to the vicinity of Jiyanxue it is only 39-m thick.
GeoJSON
Fossils
Age
Depositional setting
Additional Information