摘要
Based on the field geological investigation,a parallel unconformity surface between the Upper Triassic Ma’antang Formation and Xiaotangzi Formation is found in the Hanwang section of Mianzhu in Northwest Sichuan Province. The unconformity surface is related to the Late Triassic tectonic activities and the global and regional sea level changes.It indicates that the Longmen Mountains partly uplifted from the Late Carnian to Early Norian.From this sedimentary section,it is concluded that the paleoclimate changed from arid to humid,then to arid,from Late Carnian to Early Norian and that this process is related to global climate changes under the background of megamonsoon system.