Longkouchong Fm

It is separated by the disappearance of thick-bedded limestone and the appearance of sandy shale from the underlying Qiziqiao Fm. It is a conformable contact.

It is separated by the disappearance of sandstone and the appearance of thick-bedded limestone from the overlying Qilijiang Fm. It is a conformable contact.

This formation is distributed in the central part and east of Hunan Province, where the lithology is marked by siltstone, sandstone and sandy shale, intercalated with variable amounts of limestone.

At Longkouchong of Xiangxian County, Shiwan of Hengshan County and Yujiawan of Xiangtan County, it is dominated by siltstone and quartz sandstone, intercalated with shale and minor limestone, and is 200-400 m in thickness. Southward, the sand becomes finer grained, the content of sand decreases, and calcareous content and mud increase.

In the areas north of Shetianqiao in Shaodong and south of Longkouchong, it is dominated by mica-rich siltstone, intercalated with sandy shale and limestone, of 300 m in thickness. In the area from Yangjiatan to Tangwan in Lianyuan County, it may reach more than 500 m in thickness, and is intercalated with thick-bedded limestone of tens to 200 m thick in its middle part, but it rapidly gets thinner, even thins out, along strike.

At Shetianqiao of Shaodong, it is about 300 m thick, dominated by sandy shale or sandy marl, intercalated with siltstone and minor limestone with reduced sand content.