Tectonic Evolution And Petroleum Accumulation In Mesozoic And Cenozoic Yanqi Basin

Yanqi basin is a Mesozoic and Cenozoic superposed basin in the southern Tianshan folded belt. It locates in the special structural spot among Tarim, Jugger and Shanshan Block and experiences so complexed structure changes and extremely later reformation that the strata in basin eroded strongly and it is rather difficult to realize the evolution. There exist much difference in the basin attribute and the development of bearing, developing, declining and disappearing. Since 1993's full-scale exploration in Yanqi basin, there has found Baolang oilfield and Benbutu oilfield. The exploration rate has slowed down year after year in the following years. Little reserve has been got around these two oilfields. Recently the basin has been in its grown exploration stage that it is in dire need of seek for new target. Therefore it is significant to further petroleum exploration, sysmaticly researching on the basin's development, especially Mesozoic and Cenozoic evolution history, discussing the Jurassic basin prototype, late reformation features and its influence on petroleum accumulation. The work will insolubly be good example to structural research and petroleum exploration of many likely basins in western china.The thesis is directed by the rule of united, dynamic and integration, uses the thought of reformed basins and projects the reformation courses. It contrasts the basin with surrounding likely basins such as Kuche depression, Kumishi basin and You'erdusi basin in order to discuss the basin attribute, structural evolution rules and their influence on petroleum accumulation.Yanqi basin in Jurassic is an extended and faulted basin in the weak extensional background through research on the tectonic environment, sedimentary features and its evolution, contrast with neighboring Jurassic, eroded thickness and paleo-despositional boundary, profile of equilibrium and recovered paleostructures. The area of Yanqi, Kuche and Kumi should be a connected and united basin and deposit in stable circumstance in this period. The dynamic mechanism could be the synthetical result of heat sink and extensive subsidence caused by the crustal cooling and stress relaxation after collisional orogenic epoch. It can also be thought as the combination of the two crustal movements in horizontal and vertical direction. Based on the above research, the evolution of Yanqi basin could be divided into five stages which are Triassic foreland basin stage in Yanqi-Kuche area, Jurassic extensive basin stage after the orogenic epoch, Cretaceous uplift and erosion stage by compression, Eogene regional subsidence stage cause by breakdown and extension, in-land broken foreland basin stage in Neocene and Quaternary. The present Yanqi basin is a typical Mesozoic residual basin which suffered strong reformation in late Yanshan movement and mid-late Himalayan movement on the Jurassic base. The extensive structure in Jurassic basin keeps little and perfumes compression features by so intensive remold that today's framework developed finally.The sedimentary research on mid-late Triassic and early-mid Jurassic basin shows that lakes are abundant with broad width at the stage, whose sedimental evolution has well correlated with that of the other basins in northwest region in the same period andhas much relation with adjacent areas. The sedimentation in Jurassic is rather broader with peneplane feature.Through analysizing the Jurassic original sedimentary range in Yanqi basin, it is considered that the paleo-boundary in Jurassic is broader than the present residual boundary. The ratio of conglomerate to clastic, mineral maturation index and heavy mineral stability factor in clastic rock all indicate that the north of the basin is nearer to the provenance than the south so that the hydrodynamism of the north is more active than the south and the water in the south is rather stable. From the above it concludes that the Jurassic boundary in the north is near the present and is in the far north than the residual boundary and that the paleodeposition boundary of...