Xiashaximiao Fm
Type Locality and Naming
It was named by Yang Boquan, Sun Wanquan as the Shaximiao Horizon in 1946. The naming locality is situated in the vicinity of the Shaxi Temple in Hechuan County of Sichuan Province, with the section extending from the Shaxi Temple to the Baitaping area of Hechuan County serving as its reference section.
Synonym: Shaximiao Fm
Lithology and Thickness
This formation is composed mainly of purple mudstone and sandy mudstone, intercalated with fine-grained sandstone and siltstone. With a layer of medium-grained sandstone (known as the Guankou Sandstone) with large-scale oblique beddings. It is 246.5 m in total thickness.
Relationships and Distribution
Lower contact
The basal part of the formation in northwest Sichuan (e.g., Guangyuan region) is in a conformable contact with the underlying Qianfoya Fm (the newly-established Tiangou Fm), and with a layer of grey-green shale (or mudstone) rich in conchostracan fossils. In central Sichuan and Chongqing is it conformable onto the underlying Xintiangou Fm
Upper contact
The top part of the formation is in a conformable contact with the overlying Shangshaximiao Fm
Regional extent
The formation is distributed in the Sichuan Basin, as well as in the Zigui Basin of Hubei Province, being composed commonly of grey and violet-grey sandstones, purple mudstone and siltstone, with its basal part often containing conglomerate, and with its top part commonly representing yellow-green and grey shales rich in conchostracan fossils, intercalated with siltstone. In the Zigong and Rongchang regions the shales from the formation contain a 0.3-2 m thick black shale and oil shale. Its thickness varies from 200 m to 300 m, with its maximum thickness found in the Wanyuan area being of 600 m.
GeoJSON
Fossils
It yields Eosestheria fossils as represented by Euestheria ziliujingensis; bivalve fossils as represented by Psilunio chaoi, Lamprotula (Eolamprotula) cremeri; plant fossils as represented by Coniopteris tatungensis; and Reptilia fossils as represented by Shunosaurus tii and Omeisaurus tianfuensis. (Zhang Wentang and others, 1976; Dong Zhiming and others, 1983).
Age
Depositional setting
The strata of this formation were deposited under the shallow fresh water environment, judging from the fossil assemblage.
Additional Information