Tianmashan Fm
Type Locality and Naming
Sichuan Basin - west. The No.519 Geological Team under the Southwest Bureau of Geology erected the Tianmashan bed in 1955. The section for the designation is at Tianmashan northeast of Zhengxing of the Shuangliu County of Sichuan. The reference section is at Feixianguan of Lushan county of Sichuan.
Lithology and Thickness
The Tianmashan Formation is built up by a set of rhythmic beds of brown red conglomerate, sandstone and mudstone, with conglomerate at the base, about 12.6 m thick, and above it there occur brown red thick-bedded and massive powder-fine sandstone, sandy conglomerate and mudstone with marl lenses. It is 370.2 m thick.
Relationships and Distribution
Lower contact
Its base is a disconformable contact marked by gray massive conglomerate that is distinguished from brown red massive mudstone with sandstone of the underlying Penglaizhen Fm (late Jurassic).
Upper contact
Its top an unconformable contact bounded by the appearance of gray massive conglomerate at the base of the Jiaguan Fm.
Regional extent
The formation is distributed in the northwestern part of the Sichuan basin, which varies considerably both in lithology and thickness, coarse and thick in the west and fine and thin in the east. It is absent in Emei, Leshan and Meishan areas of the southeast part of the Sichuan basin. In the Lushan and Guanxian of west Sichuan basin, it is relatively coarse with sandy conglomerate being developed, with conglomerate lenses of small thickness, ranging from 16 to 197 m in thickness. Further east to the northern sector of the Longquan mountain of Chengdu, the Tianmashan Formation is dominated by massive sandstone with thin-bedded mudstone, with a small amount of lenticular conglomerate, up to 260 m in thickness.
GeoJSON
Fossils
The formation yields ostracods Cypridea sp., Mongolianella sp., and Deyangia lushanensis. In Yaan, Shuangliu, Guanghan and Jintang, it yields ostracods Cypridea sp., Deyangia lushanensis, D. postacuta, Lycopterocypris sp., Mongolianella sp., Minheella sp., Jingguella obtusura, Ziziphocypris sp.
Age
Depositional setting
It belongs to fluvial deposition.
Additional Information