The mid-Yanshan tectonic movement had rebuilt the tectonic framework in western China.At the end of Late Jurassic

the Yarlung-Tsangbo oceanic lithosphere of the Neo-Tethys subducted northward

Bangong CoNu Jiang ocean was closed

Lasha and Qiangtang blocks collided

and the Okhotsk sea in the north was also closed.The regional tectonic compression reactivated the ancient suture and large old faults and accelerated the uplifting of the Orogenic belt in western China.It also led to the formation of angular unconformities of various scopes and types between the Jurassic and Cretaceous in the western basins

the formation of new structures at the margins of the basin and along the faults

and further reconstruction of the existing structures.Accompanying with the movement

the basins in western China entered a new evolution stage since the Cretaceous (the timing might be a little bit different in different regions).The significances of Yanshan movement to hydrocarbon accumulation and reservoir readjustment include:(1)it exerted dual influences to the underlying source rocks through speeding up thermal evolution in the relatively continuous and rapid subsidence zones at piedmont and postponing the peak of hydrocarbon generation and expulsion in zones experienced multi-stage uplifting and slow subsidence

thus providing conditions for the highly effective hydrocarbon accumulation during the Himalayan period;(2)deformation

uplifting

weathering

erosion

and leaching greatly improved the poroperm characteristics of the reservoirs underlying the unconformities

and extensive glutenite reservoirs of high quality were deposited in the lower part of the Cretaceous above the unconformities;(3)the various types of traps in combination with the paleohighs and faulted zones laid down foundation for the formation of different types of hydrocarbon accumulations in various strata.