Takna Fm
Type Locality and Naming
South Lhasa Block - Linzhou Basin. The Takna Formation was erected by Luo Zhongshu in 1973. The section for the designation is at the Takna Village south of the Pengbo farm of the Lhumzhub County (Chen Chuzhen & Wang Yujing, 1984). The reference section is at Langbagou (Kaiji) of Maqu of the Doilungdeqen County, Xizang (Wang Naiwen et al, 1983; Wang Sien et al, 1989).
Synonym: Takena Fm
Lithology and Thickness
Lower part of the Takna Formation is represented by gray green and yellow green siltstone with mudstone and limestone and gray green and yellow green paper-like mudstone. Upper part is gray green and blue green siltstone and clayey shale intercalated or interbedded with sandstone. The Takna Formation is 170-621.6 m thick.
Relationships and Distribution
Lower contact
The base of the formation marked by gray green and yellow green siltstone with mudstone and limestone lies conformably on the underlying Chumulong Fm that consists of gray black thick-bedded siltstone and mudstone. But in some areas, the contact is not observed.
Upper contact
Conformable below the Shexing Fm
Regional extent
The present formation mainly occurs in Langba (Kaiji) of North Maqu of Lhasa and Takna, Niumagou, Biaoxin, Shuolong, Queguo and Xiangga of Lhumzhub. It is persistent in lithology.
GeoJSON
Fossils
In Maqu and the Pengpo farm of Lhasa, it bears richly ammonites Acanthohoplites sp., Parahoplites cf. melchioris, Parancyloceras sp., Uhligella cf. chansayensis, etc.; Foraminifera Orbitolina sp., O. (Mesorbitolina) texana, Praeorbitolina cornugi, etc.; ostracods Neithea quinqaecostata, Cyprina zeribensis, Opis cf. replete, Eriphyla cf. lenticula, etc.
Age
Depositional setting
It belongs to typical biota thriving neritic deposition
Additional Information