In the Late Triassic

the western Sichuan Basin was the primary depocenter in the northern part of the upper Yangtze area.Meanwhile

a secondary depocenter took shape in the area between Daxian and Wanyuan in front of Dabashan Mountain

indicating the initial subsidence of the Dabashan foreland basin in the Late Triassic.During the Early Jurassic to the early of Middle Jurassic

the depocenter in the northern part of the upper Yangtze area moved eastward to the front of the Dabashan Mountain.At that time

there were two co-existing depocenters with their depositional thickness not too big.In the middle and late of Middle Jurassic

the two depocenters shifted northward to Dabashan Mountain with great thickness of sedimentary formation

indicating dramatic subsidence of the foreland basin.In the Late Jurassic

the two depocenters migrated eastward and westward respectively with considerable difference in sedimentation and relatively bigger thickness

revealing the continuous and stable subsidence of the foreland basin.