This study documents the sedimentology, structures, and foraminifer content of Triassic formations from the eastern part of the Truong Son Belt (Northern Vietnam). Sedimentary rocks in the eastern Song Da and Sam Nua basins occur on both sides of the Middle Triassic Song Ma suture zone that separates the Indochina Block from the South China Block. The main outcomes of our study include detailed stratigraphic successions that we have established for the two basins. New foraminifer determinations indicate a Middle to Late Triassic age for the carbonate deposition. The depositional settings of the carbonate deposits and their deformation patterns support a southward “subduction” beneath the Indochina Block, ending with the collision with the South China Block during the Middle Triassic. Moreover, our new biostratigraphic dating of the stratigraphic successions can be used to compare the Triassic carbonate platforms from Northern Vietnam with other platforms elsewhere, including those that have already been well documented in Indonesia.