SUPERPOSITION AND RECONSTRUCTION OF MARINE MESO-PALEOZOIC STRATA BY MESO-CENOZOIC BASINS IN SOUTHERN CHINA

This paper focuses on the main basin prototypes developed in four tectonic evolution periods and their superposition in southern China during the Meso-Cenozoic.According to the superposition and tectonic reconstruction of basin prototype, five types of late reconstruction could be recognized for marine Meso-Paleozoic in southern China, namely the persistent foredeep superposition, foredeep-slide-faultdepression superposition, foredeep-slide or fault superposition, nappe structure and shadow basin, and relict reconstruction.Moreover we discuss their main tectonic characteristics and difference in the condition for oil-gas preservation.The study indicates that the persistent foreland basin superposition, represented by the Sichuan Basin, is most favorable for preservation of marine Meso-Cenozoic natural gas.The second favorable type is the foredeep-slide-fault-depression superposition, with its examples in Jiangsu Basin and Wannan-Subei Basin in middle-lower Yangtze.Under the early foreland basin superposition (Late Triassic to Middle Jurassic)and the late fault depression-depression superposition (since Middle Cretaceous), it successively constituted a regional enclosed condition for marine Meso-Paleozoic, and offered a condition for preservation of the second oil-gas formation of marine Meso-Paleozoic although it had been deformed by the strong Yanshanian compression-strike-slip during Late Jurassic to Early Cretaceous.The foredeepslide or fault superposition, represented by the Chuxiong Basin and Shiwan Mountain Basin, set up a regional enclosed condition for marine Meso-Paleozoic in the early stage (Late Triassic to Middle Jurassic), but then imposed an effect upon preservation of marine oil-gas, because it led the basins as a whole to form block structures under the effect of strike-slip and thrust since the second structure stage. In addition, it is pointed out that much attention should be drawn to the "shadow basin" in nappe structure, especially to oil-gas preservation condition below the regional decollement layer as well as the relict reconstructed weak deformation belt such as Nanpanjiang depression.