Zimenqiao Fm

The type section is lies on the east side of the Wantou Highway, Zimenqiao Town, Shuangfeng, Hunan. It was named by Tian Qijun in 1929.

Synonym:

Luocheng Fm (in Guangxi)

Limestone and Claystone. In central Hunan, it is composed of dark-gray and gray-black moderately thick-bedded limestone and clayey limestone, intercalated with marl and mudstone, containing siliceous lumps and bands. Also, clayey matter is decreasing while calcareous matter is increasing ascending, turning into almost completely thick-bedded limestone at the top, with more or less dolomite intercalated. Thickness mostly ~100 m.

From north to south, clayey component is decreasing while calcareous matter is increasing. In southern Hunan, it is dominated by gray thick- and extremely thick-bedded limestones, intercalated with dolomitic limestone and dolomite, and its lower part is intercalated with minor marl, often containing siliceous lumps and bands. In the sedimentation area near the old land in northern central Hunan, the formation is composed of shale and marl intercalated with limestone and chert, only ~30 m thick.

Coral Yuanophyllum and Thysanophyllum-Kueichouphyllum sinense zones, the Brachiopod Gigantoproductus Kansuella zone, the Conodont Gnathodus bilineatus zone, Adetognathus unicornis and Declinognathodus noduliferus zones as well as a large amount of foraminifers.

It is interpreted as platform neritic deposits