Fengjia’ao Fm
Type Locality and Naming
The type section of the Fangjia’ao Formation is the West Hill Ridge section. It is located on the hill ridge west of Fengjia’ao Village, about 7 km north of the Xijiadian Town, Danjiangkou, Hubei Province (111°12’58”E, 32°50’52”N). It is the middle portion of the same section shared by the overlying Xijiadian Formation and underlying Yanwugou Formations. It was measured by Zhu and Tao (1988) from Hubei School of Geology (now Huibei University of Geological Staff). In the type section, the Fengjia’ao Formation is 25 m thick. The Fangjia’ao Formation was named by Zhu and Tao (1988). The name is derived from Fengjia’ao Village in Xijiadian Township, Danjiangkou City (county level), northwestern Hubei Province.
Synonym: (冯家凹组)
Lithology and Thickness
The Fengjia’ao Formation is a carbonate sequence. The type section embraces two lithological beds, from bottom up: (1) grey, thick-bedded limestone intercalated with a layer of thin-bedded, carbonaceous marlstone at the base (11 m thick); (2) grey, median-bedded limestone intercalated with a layer of yellowish grey bioclastic limestone at the top (14 m).
Relationships and Distribution
Lower contact
The Fengjia’ao Fm is in conformable contact with underlying Yanwugou Fm. The lower boundary of the formation is marked by lithological change from carbonaceous clay slate of the Yanwugou Formation to the thick-bedded limestone of the Fengjia’ao Fm.
Upper contact
The Fengjia’ao Fm is in conformable contact with overlying Xijiadian Fm. The upper boundary is marked by lithological change from the medium-bedded limestone of the Fengjia’ao Formation to thin-bedded marlstone of the Xijiadian Fm.
Regional extent
The Fengjia’ao Formation is exposed in the Jiangbei Slope Area of South China Region, distributed in northwestern and northern Hubei Province (Danjiangkou and Laohekou cities) and southwestern Henan Province (Xichuan and Dengzhou counties). The thickness of the formation varies from 19.0 to 35.5 m.
GeoJSON
Fossils
Bed 1 of the formation in the type section yields trilobites Dinesus granulosa, Kootenia (Kootenia) baishagonensis，K. (K.) grachilens, K. (K.) sp., K. (Tienzhuia) distensa, Xilingxia elongata, Kunmingaspis qiannanensis, K. sp., and Solenoparia sp.; and the Bed 2 yields Bailiella? sp., Corynexochus donggouensis, Mufushania？sp., Pagetia dayongensis, Peronopsis cf. rakuroensis, and Solenoparia minuta. In the Haoping section, near Xijiadian, the formation yields additional trilobites Changaspis transversus, Cheiruroides arcticus, Parachangaspis haopingensis and Pagetia sp.
Age
Depositional setting
Additional Information