Changtai Fm
Type Locality and Naming
Named the Changtai Group by the Third Regional Survey of Sichuan Bureau of Geology in 1974; renamed the present name in 1982. The naming section is located at Yaqianke (N31°02′35'; E99°34′57″), Nata Township east of the Changtai District, Baiyu County, Sichuan Province.
Lithology and Thickness
Sequence of sandy, muddy and pebbly clastic rocks with marlstone and lenticular or layered basalt, containing coals. The thickness in type section is up to 1329 m. In Jiawa, Litang County, it is 369 m thick. Its thickness ranges 134-1330 m among the reference section.
Relationships and Distribution
Lower contact
It unconformably overlies the Upper Triassic Tumugou Fm in type section; but equivalent Pliocene-age fills of down-faulted basins overlie many other Miocene/Paleogene formations. See "regional extent" for some of these equivalents.
Upper contact
The upper part is undefined.
Regional extent
The formation is distributed as a NNW-SSE-trending band along a fault zone and represented by intermontane downfaulted basin deposits. This formation is distributed in Baiyu County, Litang County, Ganzi County, Songpan County. It is equivalent to the Jianchuan Fm, Xinpan Fm and Mangbang Fm in Yunnan Province, all of which contain volcanic rocks.
GeoJSON
Fossils
This formation in type section yields the gastropods Planorbis youngi and P. cf. chihliensis. In Jiawa, Litang County, this formation produces the plants Ailanthus sp., Salix sp. and Quercus sp.
Age
Depositional setting
Intermontane downfaulted basin deposits.
Additional Information