Unconformity boundary between upper Cambrian and lower-middle Devonian sedimentary rocks containing bivalve fossils in Luu Ngoc commune

Unconformity boundary between thin-bedded white grey and golden brown sandy siltstone interbedded with layers of dark grey siliceous calcareous clay at a 50Ð85 bedding to the northeast of Than Sa formation (Î₃ts), being pressed and sheared in the NW-SE direction, with thin-bedded dark grey limestone at a 240Ð75 bedding to the southwest of Na Quan formation (D₁-D₂nq).

Boundary between thin-bedded limestone, calcareous shale containing bivalve fossils