Abstract: The Triassic System in the Youjaing rejuvenated geosyncline,more than 9,000 m thick,is characterized by the good Bouna Sequence and pictographic casts,belonging to a typical flysch formation.The Youjiang Indosinian reju- venated geosyncline was formed on the basis of the post-Caledonian South China paraplatform.It had experienced an entire process of the development of a geosyncline:the extension of the continental crust produced a down-faulted trough—the widening and deepening of the trough gave rise to a deep water basin—the occurrence of turbidity currents generated flysch—the fold uplift ended the development of a geosyncline,So it is an excellent example for the transformation of a platform into a geosyncline.