Jianshan Fm
Type Locality and Naming
It was named by the Comprehensive Research Team under the Tibetan No. 4 Geological Party in 1976. The naming section is located on the northeastern margin of the Lunpola Basin in Anduo County, Tibet, about 45 km west of the Zigedan Co (90°15′, 32°05′), with its reference section being situated on the bank of the Zamunaqu River about 10 km east of Luoma, Anduo County, Tibet (E 92°50′, N 32°30′).
Synonym: （尖山组）
Lithology and Thickness
Lower part consists of grey, yellow-grey and grey-black argillaceous shales, intercalated with thin-bedded limestones and marls; its basal part, of dark-grey and grey-black medium-bedded limestone and oolitic and pisiform limestone. Middle part is grey and brown-grey thick-bedded and massive limestone and oolitic limestone. Upper part consists of grey silty mudstone, mudstone, microcrystal limestone and marl; with its top part serving as a rhythmic layering of brown-grey sandstone, mudstone and marl. It is over 2114-m thick.
Relationships and Distribution
Lower contact
No base of it has been found. Regionally, the next older unit is the Tumengela Gr of late Triassic (= uppermost Jiezha Gr coal-bearing clastics, also called Tumengela Fm).
Upper contact
Its top part together with its overlying Sewa Fm (Saiwa Fm) represents a continuous transitional of deposition.
Regional extent
The formation is distributed mainly in the area from the Jianshan Mt of the Lunpola Basin to Zamunaqu and Luoma of An’duo County, with a consistent lithology, yet a changeable thickness varying in a range from 300 m to over 2114 m.
GeoJSON
Fossils
It yields ammonites in the area of the Zamunaqu River as represented by Glevicera sp., Arnioceras sp.; bivalves as represented by Trigonia (Myophorella) sp., T. (Vaugonia) sp., Pleuromya sp., Astarte cf. extensa, Pholadomya aequalis; and in the area of Jianshan it yields such ammonites as Baucaulticeras cf. baucaultianum, Angulaticeras cf. lacunatum; to the west of Anduo County there are found such ammonites as Dumortieria multicostata and etc.
Age
Depositional setting
It represents a continuous transitional of deposition.
Additional Information