CHARACTERISTICS OF THE CARBONIFEROUS-PERMIAN VOLCANIC ROCKS AND HYDROCARBON ACCUMULATIONS IN TWO GREAT BASINS, XINJIANG AREA

The Carboniferous-Permian volcanic rocks were very well developed with wide distribution and big thickness in the Junggar and Tarim basins,Xinjiang area.The Carboniferous volcanic rocks are widely distributed in the West Uplift,Luliang Uplift,Central Uplift and East Uplift of the Junggar Basin,which can be divided into upper and lower Carboniferous(total 5 formations).The quantity of the Permian volcanic rocks is small.The tuffs and tuffaceous sandstones are shown in only certain layers.The Carboniferous volcanic rocks of the Tarim Basin are mainly distributed at the margin of basin but the Permian volcanic rocks are common in the whole basin with large thickness and variety of rock types.The main types are basic and ultrabasic rocks and then are intermediate-acid rocks.Their distribution is characterized by lateral zonation and vertical cyclicity.The volcanism accelerated immature source rocks to enter oil generation threshold in advance,at the same time it also caused mature source rocks became over matured.Intermediate-acid volcanic lava is the main reservoirs of the Carboniferous.Magmatism activities provide the pathway for hydrocarbon migration.The volcanic rocks can form big oilfields of 100 million tons so we should focus on study of reservoir-forming and distributions of the Carboniferous-Permian volcanic rocks in oil-gas exploration of Xinjiang area and regard these reservoirs as one of important targets in petroleum exploration.