Abstract:

Prototype basins in the middle Yangtze and its adjacent region can be divided into nine mega- sequences. Sequence I-VI are composed of Mesozoic-Palaeozoic marine beds; Sequence VⅡ is made up of the early-middle Jurassic terrestrial deposits; Sequence VⅢ consists of Jurassic foredeep deposits; Sequence IX is characterized by the late Cretaceous and Tertiary rift basin deposits. During the Sinian Period, the central region was in the environment of platform facies while the south region was in the environment of shallow marine shelf and the north region was mainly in the environment of epicontinent sea. The Cambrian to the early Ordovician is characterized by typical continent marginal basins. Rift basins were well developed during the middle-late Ordovician-Silurian; Extensive transgression events occurred during the Devonian and Carboniferous which connected with several places of the South China Sea waters and the Pacific Ocean sea waters; From the Permian to the middle Triassic, the prototype basins were in the stage of transformation with Mianlue palaeo-oceanic basin(which separated Qinling micro-plates from the Yangtze plate)opening towards east and the former regional uplift in the northern margin of the Yangtze was transformed into the continent marginal basins of deepening northward. During the late Triassic, two episodic depositional cycles occurred in the region where Badong Formation is characterized by slow subsidence deposits and Jiuligang Formation by rapid subsidence deposits. The prototype basins experienced slow deposition in the early Jurassic and rapid deposition dominated by underwater sedimentation in the middle Jurassic. Two tectonic evolution stages can be classified in the late Jurassic, tectonic activities in the early stage was relatively quiet and in the late stage was quite strong. During the late Cretaceous-early Tertiary, the basins became smaller in size dominated by lacustrine and fluvial deposits. Therefore,the middle Yangtze and its adjacent region have experienced in geological history four types of prototype basins with the characteristics of episodic sedimentation.

Key words: prototype basin, mega-sequence, sedimentary framework, episodic evolution, middle Yangtze and adjacent region