Characteristics and resource potential of source rocks in the foreland basins in central and western China

The thrust belt-related foreland basins in central and western China are characterized by non-marine source rocks.The source rocks in peripheral and retro-arc foreland basins were formed in the period when the basins were developing,such as the Permian source rocks found in the northwestern and southern Junger basin,the southwestern Tarim basin,the Tuha basin and the Triassic source rocks found in the western Sichuan and western Ordos basins.The source rocks in reactivated foreland basins were formed in the Triassic-Jurassic,the Cretaceous,and the Paleogene,before the thrust-related foreland basins were formed.Based on their sedimentary environments,all of the source rocks in the foreland basins may be classified into five types: passive continental margin marine facies,relic marine-lacustrine facies,limnetic facies,intracontinental fresh-water lacustrine facies,and intracontinental semi-saline to saline lacustrine facies.The organic matter from the limnetic coal measure is of type III and gas bearing.The organic matter from the other four types of source rocks is of type I and II and oil-bearing.Oil and gas resources in the foreland basins in the central and western China are ca.89.17×10~8 t and ca.101 464×10~8 m~3 respectively,showing that gas is enriched in Chinese foreland basins compared with foreland basins elsewhere.