Changlongjie Fm
Type Locality and Naming
The type section is located at the road cut section from Xikuangshan Mine to Laojiangchong Village, Lengshuijiang, Hunan Province. It was named by Tian Qijun in 1938 without type section indicated.
Lithology and Thickness
Mudstone, limestone. The lithology of the Formation is dominated by thin-bedded limestone and mudstone and may be subdivided into three parts: Lower part, about 12 m thick, is composed of yellow thin-bedded mudstone with well-developed horizontal bedding. Middle part is characterized by thin-bedded (10-20 cm) limestone with normal graded bedding. Upper part, about 20 m thick, is characterized by mudstone and thin-bedded limestone or lenses. The Formation is about 55 m thick in total.
Relationships and Distribution
Lower contact
Disconformable contact to the underlying shell limestone of Shetianqiao Fm, which yields abundant corals, stromatoporoids, and oncolites in the top.
Upper contact
Overlain by thick-bedded limestone of the Tuzitang Fm (= Tuzitang Limestone lower member of the Xikuangshan Fm).
Regional extent
The Changlongjie Fm is widely distributed in central Hunan Province, but the thickness greatly varies with the maximum reaching 300 m. In southern Hunan, the limestone beds gradually increase and contain abundant brachiopods.
GeoJSON
Fossils
The formation is characterized by having small-sized brachiopods of Yunnanellina in the lower part, and of Yunnanella-Yunnanellina assemblage in the middle part. Along with the appearance of thin-bedded limestone, it yields conodonts Palmatolepis crepida.
In southern Hunan, the limestone beds gradually increase and contain abundant brachiopods including Cyrtiopsis davidsoni Gr., Cy. spiriferoides Gr., Platyspirifer sp., Dmitria sp.
Age
Depositional setting
It is interpreted as a shelf with distal storm events.
Additional Information