DISCUSSION ON THE BOUNDARY BETWEEN JURASSIC AND CRETACEOUS IN SOUTH-CENTRAL DAXINGANLING REGION, INNER MONGOLIA

By discussion on the unconformity between Jurassic and Cretaceous in the south-central Daxinganling region, combining with regional stratigraphic correlation and isotope data, the boundary with identifiablity, objectivity and stability is determined. With study on the geotectonic setting for the forming of major strata, it is believed that the Tuchengzi Formation is a set of continental redbeds formed in the collision of post-orogenic extensional tectonic stage and is also the marker bed of the end of Jurassic, while Manketouebo Formation, Manitu Formation and Baiyingaolao Formation are volcanic strata formed in the post-collisional orogenic collapse tectonic stage. The Cretaceous crustal evolution begins with massive volcanic eruptions. The boundary of Jurassic and Cretaceous is between the Tuchengzi Formation and Manketouebo Formation, which is characterized by regional unconformity or disconformity. The unconformity surface is formed in the transition period from extension to collapse of post-collisional orogeny tectonic background.