Shazhenxi Fm
Type Locality and Naming
The type section is located at Shaxi town in Zigui country, Hubei. It was named by Chen Chuzhen in 1979. Shazhenxi Fm is equivalent to the lower coal measures of the original Xiangxi Group. In 1924, the Xiangxi System is named by Li Siguang, which is regarded as the Late Triassic. In 1925, Xie Jiarong and Zhao Yazeng divided the Xiangxi System into lower and upper coal-bearing measures, belonging to the Upper Triassic and Lower Jurassic respectively. Then Si Xingjian in 1937, 1940 regarded it as the early Jurassic. Shi Xingjian, Zhou Zhiyan (1962) and the former Beijing Institute of Geology (1960) all ascribed the coal-bearing measures to the Rhaetian of the Upper Triassic. Chen Chuzhen et al. (1979) divided the Xiangxi Gr in Zigui Basin in detail and established the Shazhenxi Fm.
Synonym:
Lithology and Thickness
The Formation is mainly composed of grayish-yellow and greyish-green thin to thick-bedded siltstone intercalated with quartz sandstone, carbonaceous shale, shale, coal seam and siderite nodules.
Relationships and Distribution
Lower contact
The Shazhenxi Fm is disconformable in contact to the underlying Badong Fm with a bed of yellowish-green siltstone.
Upper contact
It is disconformable in contact to the overlying Tonzhuyuan Fm of lower Jurassic with a bed of white massive pebbly quartz sandstone at the top.
Regional extent
The formation is restrictively distributed in Zigui and Lichuan basin of Hubei. Thickness varies greatly, the northern Zigui Basin is thinner, the southern Xiangxi Basin is 37 to 139 m, the western Badong Basin is 106 to 110 m, and the southern Lichuan Basin is thickened. Coeval with Wanglongan Fm (Rhaetian) and Jialigang Fm (Norian) in nearby region.
GeoJSON
Fossils
Bivalves: Modiolus cf. problematicus, Unionites emeiensis; Conchostracan: Euestheria yipinglangensis, E. contracta；Plants: Cycadocarpidium erdmanni, Pterophyllum sinense, Sinoctenis calophylla, Clathropteris mongugaica, Dictyophyllum nathorsti, Lepidopteris ottonis.
Age
Depositional setting
It is interpreted as a terrestrial setting.
Additional Information