Abstract:

The Tarim Basin is an important target area for petroleum prospec-ting in Palaeozoic rocks in China.The platform marine carbonates and clastic rocks of Palaeozoic age are 4000—10000 meters thick and widely spread in Tarim Basin,and lie beneath the Meso-Cenozoic of 1000—10000 meters thick,occupying an area of appoximately 500000 squarekilometers.Frequent oil and gas in dications and commercial amount ofoil flows already found there are possibly derived from the Palaeozoicrocks.In Tarim,the basement is composedof Archaean-Proterozoic crystal-line complexes and metamorphic rocks.The emergence of this platformstarted from Jinning movement.It is suggested that the latitudinal upliftand subsidence formed by this event had controlled the marine regression and transgression and the sediment distribution.The NWW trending,the prototype,both of uplift and subsidence formed in Caledonian mo-vement,were further developed during the period of Hercynian movementand had simultaneously Controlled the distribution of Palaeozoic sedimen-tary zones.Now,eight tectonic units,either NEE and NWW strike,can be subdivided on the basis of the Hercynian tectonic framework.The Yanshanian and,especially,the Himalayan movements exerted an activeeffect on the remigration and accumulation of the Palaeozoic oil and gas.The Palaeozoic oil source rocks are in good abundance.The majoroil source rocks are Carboniferous,Lower Permian and Lower Cambrian,while the less impotant are Middle and Lower Ordovician,Lower Silurian and Upper Sinian.Preliminary study shows that both light oiland gas may occur in the Upper Palaeozoic,but only gas occurs in Lower Palaeozoic rocks.The Carboniferous-Lower Permian carbonates are the most importantoil reservoirs Nevertheless the Upper Sinian dolomites are also of great significance.It is suggested that fractures,planes of unconformity andorganic reefs are probably well developed in these rocks.The data available demonstrate that the marginal zone of the Bachu Uplift and the updip parts of the Maigaiti and northern Tarim PlatformSlopes are promising Palaeozoic belts for oil and gas prospecting.