THE EVOLUTION OF LATE-MESOZOIC TECTONIC- PETROGRAPHIC FACIES IN COQN BASIN,TIBET

Mesozoic is the main period of formation and development of Coqn basin. Under the influence of the two Tethy structural belts(North and South), the EW tectonic-petrographic facies zoning is fairly obvious inside the basin. The zone of facies corresponds with specified depositional environment, namely the transition stage from marine facies to delta facies, to offshore beach facies, to plateau facies and to land facies. The strata records of Mesozoic Coqn basin show that the basin has gone through a tectonic cycle process of depression-stabilization-swelling, showing the depositional history of rift to ocean basin to residual sea sealing up and faulted basin development.There are a series of residual basin sediments in Chuanba-Selincuo area of this basin, which are favorable producing oil and rich in organism. Meanwhile, the region has undergone a cycle of ingression-regression in Cretaceous, providing a favourable depositional condition for the formation and allocation of the cap formation. All that can be said is that this region has hopeful prospects for oil and gas prospecting.