The Early Paleozoic sequence of the lower reaches of the Song Ma, Vietnam, is almost identical with that of the Pingbian-Maguan area, southeastern Yunnan. The sinistral displacement of the Red River fault reaches at least 400 km. If the displacement is removed, the Triassic flysch deposits of the Youjiang area would be connected with the huge Songpan-garze clastic basin by the Song Da zone. They combine to form the passive margin of the Yangtze Block. The Song Da zone is a Triassic rift belt, rather than a plate suture zone.