The Upper Triassic coal-bearing basin in NW Th¸i Nguyªn City is filled up with Norian- Rhaetian sediments of the V¨n L·ng formation. The geochemical characteristics of sandstones from this formation express their redepositing origin from older sediments, distributed in adjacent areas. They allow us to reconstruct the tectonic setting of the basin, and show that the basin was formed and developed on the passive continental margin, that is a general structure of Mesozoic in North ViÖt Nam.