Magnetostratigraphy Of Cretaceous-cenozoic Strata In Southwestern Margin Of Sichuan Basin And Its Geological Significance

The southwestern margin of the Sichuan Basin is located in the Longmenshan Foreland Basin,lying in the west of the eastern margin of the Tibetan Plateau.It nicely and continuously preserved the Mesozoic-Cenozoic red terrestrial sediments,so that being a key position that recorded the process of uplift of the Tibetan Plateau and evolution of Sichuan Basin.However,continnous,accurate stratigraphic chronology data is still lacking.In this paper,we select the Cretaceous-Cenozoic section in Ya'an area as our research object,and conduct high-resolution magnetic stratigraphy geochronological research.We finally obtained the following conclusions:(1)A high-resolution chronological framework of the southwestern Sichuan basin from the Cretaceous period to the Tertiary period is established,the time limit of each stratum unit is determined precisely,which provides accurate chronological constraints for the research of sedimentology,paleoclimatology,thermochronology,and structural magnetism in the next step;(2)The age of bottom boundary of Cretaceous in our study area was limited to 124.16 Ma,providing crucial chronological evidence for the regional tectonic event in Early Cretaceous time;(3)The age of the top boundary of the profile,which is the end time of the deposition in the Sichuan Basin is limited to about 33~30 Ma preliminarily.This age is close to the time of tectonic thermal events in the Longmenshan area on the west side,which provides important materials and evidence for exploring the uplift model of the Tibetan Plateau;(4)Two high deposition rate periods,late Cretaceous to early Paleocene period(73.65~66.40 Ma)and middle Eocene period(47.35~45.72 Ma)are formed,which represent the sedimentary response of the interior of the basin to the uplift activities of orogenic belt surrounds the basin.