Yinkeng Fm

The formation was named in 1965 by the stratigraphic research team of Guichi, Anhui, and the named section is located in the north of Niujiaoling and the southeast slope of Longshan, west of Yinkeng, Guichi, Anhui. Lowermost formation in Qinglong Gr.

Synonym: After naming, Wang Yichang et al. (1966) and Min Qingkui et al. (1982) successively named the strata with the same meaning as the Yinkeng Fm in Tongling and Nanjing as Xiaolingting Fm and Qinglong Fm (narrow sense). In 1970, the Jiangsu district survey team assigned this part of strata to the lower part of the Xiaqinglong Fm. It is suggested that the Xiaolingting Fm, Qinglong Fm (narrow sense) and Xiaqinglong Fm should be abandoned, and the Yinkeng Fm should still be used.

It is mainly composed of thin gray to medium thick limestone interbedded with yellow-green calcareous shale. Generally, it can be divided into three lithologic members: First member is mainly composed of yellow-green and grey-green calcareous shale, with a small amount of argillaceous limestone and limestone lens on the top. The lower part of the Second member is interbedded with yellow-green calcareous shale and thin gray limestone. The upper part is interbedded with gray, dark gray thin to medium thick limestone and yellow-green calcareous shale, and partly interbedded with contemporaneous pebbly limestone. The bottom of the Third member is purplish gray calcareous shale, and the top is gray, dark gray thin to medium thick limestone interbedded with yellow-green calcareous shale. The thickness of the standard site is 82 m. In the west of Jiujiang, gray marl interbedded with gravity flow deposited gravel and arenaceous limestone with thickness of 240 ~to590 m is dominant. In the area of Anqing and Chaohu Lake, it is mainly composed of mud and shale with a small amount of marl and nodular limestone with a thickness of 80 to 140 m. In the area along the Yangtze River in Anhui and Jiangsu, shale and limestone with thickness of 95 to 250 m are the main rocks. In the area of Jingxian, Ningguo, Liyang and Changzhou, the content of mud and shale is less, and the limestone is increased with a thickness of 100 ~ 200 m. In the area of Yixing, Changxing and Guangde, it is characterized by thin layer stucco limestone splint and boulder limestone with thickness of 200 to 230 m. In Wuxi area, it is characterized by the development of thick layers of sparry oolitic algal ash nodular limestone, limestone and dolomite, with a thickness of 126 m. The Suzhou area is mainly composed of medium-thin stucco limestone with a thickness of 102 m. In Xiuning and Jingdezhen areas, there are stucco-limestone, sparry oolitic limestone and arenaceous limestone. In the area of Jiangshan, Zhejiang Province and Shangrao, Jiangxi Province, mud, shale and siltstone are dominant, with a thickness of up to 396 m.

Ammonoid zones: (1) Ophiceras-Lytophiceras zone, (2) Gyronites-Prionolobus zone, (3) Flemingites zone. Bivalve fossils zones: (1) Towapteria scythica zone, (2) Pseudoclaraia wangi zone, (3) Claraia stachei zone, (4) Claraia aurita zone. Conodonts: (1) Neogondolella carinata zone, (2) Neospathodus dieneri zone, (3) Neospathodus cristagalli zone