Langyashan Fm
Type Locality and Naming
The type section of the Langyashan Formation is located at the Lanyashan Forest Station in Langya District, Chuzhou, Anhui Province (118°16’04”E, 32°15’42”N). The section lies about 7 km southwest of the seat of Langya District and was remeasured by the Anhui Regional Geological Survey Team in 1977. In the type section, the Lanyashan Formation is 409.05 m thick. The Langyashan Formation was named by Dong (1949). The name is derived from Lanyashan Mountain in Langya District, Chuzhou City, eastern Anhui Province. Originally the unit was called Langyashan Limestone by Dong (1949) and was renamed Langyashan Formation by Zhu et al. (1964). Based on fossil assemblages, Anhui Regional Geological Survey Team (1977, 1988), Lu and Zhu (1980) and Zhu et al. (1984) subdivided the formation into three formations, the Longpan Fm below, the restricted Langyashan Fm, and the Cheshuitong Fm above, which are forms of lithostratigraphic units with biostratigraphic meaning and are rejected by Li and Jiang (1997) and Compiling Committee for Chinese Stratigraphic Lexicon et al. (1999). The original concept of the formation by Dong (1949) is followed herewith.
Synonym: （琅琊山组）
Lithology and Thickness
The Langyashan Formation is a carbonate sequence, and can be divided into three parts. Lower part consists of grey, light grey and purplish red, thin- to thick-bedded limestone and striped limestone, intercalated with yellow marlstone in its lower part; Middle part consists of grey to greyish black, thin- to thick-bedded argillaceous striped limestone intercalated with dolomitic limestone, sandy limestone and crystalline limestone; Upper part consists of grey to dark grey, medium- to mega-thick-bedded striped limestone intercalated with sandy and dolomitic limestone.
Relationships and Distribution
Lower contact
The Langyashan Fm is in conformable contact with the underlying Yangliugang Fm. The lower boundary of the formation is defined by disappearance of the purplish bands in the striped dolomitic and argillaceous limestone of the Yangliugang Fm and appearance of grey, light grey limestone at the base of the Langyashan Fm
Upper contact
The Langyashan Fm is in conformable contact with the overlying Shang’ouchong Fm. The upper boundary is defined by disappearance of the limestone with bands or striped structure at the top of the Langyashan Fm and appearance of thick-bedded and massive limestone at the base of Shang’ouchong Fm.
Regional extent
The Langyashan Formation is exposed in the Jiangbei Slope Area of South China Region, restricted in eastern Anhui Province (Chuxian, and Quanjia). The thickness of the formation varies from 409 to 717 m.
GeoJSON
Fossils
In the type section, the lower part of the formation yields trilobites Homagnostus sp., Palaeadotes langyashanensis, Proceratopyge chuhsiensis, and Pseudagnostus sp.; the middle part yields trilobites Homagnostus sp., Langyashania distincta, Paramaladioidella subconica, Proceratopyge sp., Prochuangia Longispina, Pseudagnostus subquadratus, Pseudaphelaspis langyashanensis, Rhaptagnostus langyashanensis, and Yuepingia brevica; and the upper part yields trilobites Pagodia major and unidentified saukiids.
Age
Depositional setting
The formation represents sediments deposited on platform-frontal slope.
Additional Information