The tectonic boundary between thin-bedded yellow grey aleuritic clayish shale at a 220Ð45 bedding to the southwest of Than Sa formation (∈3ts) and thin-bedded dark grey limestone at a 330Ð55 bedding to the northwest of Na Quan formation (D1-D2nq).
The site shows a tectonic boundary – a NW-SE fault more than 100m wide – between shale of Than Sa formation (∈3ts) and limestone of Na Quan formation (D1-D2nq). In addition, there is a gradual upward transition to limestone of Na Dang formation (D2gv-D3frnd), followed by that of Lung Nam formation (C1ln). Again, the contrast between the young to old karst landforms and the denudation-erosion hilly landform on the terrigenous rocks is also of interest. In addition to the significance similar to that of the previous site, this site shows further upward stratigraphic succession.
Abrupt moderately-bedded dark grey limestone of Na Quan formation
Kink folds in dark grey thin-bedded limestone of Na Dang formation