Hongtuwa Fm
Type Locality and Naming
The type section is located at Hongtuwa (a porcelain kiln), about 20 km northeast of Jingyuan, Gansu. It was named by Wu Xiuyuan et al. in 1987.
Lithology and Thickness
Claystone. Varicolored shale intercalated with limestone. Lower part is dominated by black to gray-black shale and calcareous shale, intercalated with thin-bedded limestone and coal streaks. Upper part consists of light-gray and brownish yellow silty shale, intercalated with black clayey limestone and shale.
Relationships and Distribution
Lower contact
Conformable contact with the underlying Qingyuan Fm at the type section.
Upper contact
Conformable contact with the overlying Yanghugou Fm at the type section.
Regional extent
Distributed at the east sector of the North Qilian Mts, i.e. Yongchang of Gansu, and Zhongning, Zhongwei, etc. of Ningxia.
GeoJSON
Fossils
The base contains the Conodont Declinognathodus noduliferous zone, the Middle and Upper parts yield Ammonoids Bilinguites superbilingue, B. metabilinguis, Cancelloceras asiamum, etc., which correspond to the R2−G1 zone of Goniatites, and Conodonts Idiognathodus sinuatus, I. corrugatus and I. sulcatus.
Liu Zicai et al. (1983) and Yang Fengqing et al. (1983) divided it into three subzones of two Ammonoid zones, i.e. the Reticuloceras zone and Gastrioceras, at Xiaoyuuchuan, Zhongwei of Ningxia, the original upper member of the Yiqingyuan Fm (corresponding to the Hongtuwa Fm). Gao Lianda (1987) established the Spore-pollen Reticulatisporites reticulatus-Densosporites triangularis zone in the upper member of the Qingyuan Fm.
Age
Depositional setting
It is interpreted as confined neritic deposits
Additional Information