COMPARATIVE PETROLEUM GEOLOGICAL STUDY BETWEEN MIDDLE YANGTZE AREA AND UPPER AND LOWER YANGTZE AREAS

The character of lower architexture of Middle Yangtze Area is similar to that of Upper Yangtze Area while the upper architexture is similar to that of Lower Yangtze Area.In fact,it is a polysuperposed basin consisting of an Upper Triassic-Upper Jurassic basin,a Lower and Middle Triassic-Upper Paleozoic basin,and a Sinian-Silurian basin.Generally speaking,the petroleum richness in such a poly-superposed basin would be much higher than that in a simple basin.The petroleum prospects of deep objectives may be concluded as.1.oil/gas accumulation in Indosinian unconformity,2.oil/gas accumulation in basement rocks and ancient buried hills,and 3.oil/gas accumulation controlled by overthrusts.However,the sedimentation and tectonic movement from Proterozoic to Paleozoic in Middle Yangtze area are more active than those in Upper Yangtze Area while Mesozoic sedimentation and tectonic movements are relatively less active than those in Lower Yangtze Area.Such characteristics provide an unique favourable condition for generation,migration and accumulation of oil/gas in Middle Yangtze Area.