The establishment of Upper Cretaceous Mamole Formation in Asuo Town of Nima County, northern Tibet, and its significance

In this study, a set of purple red braided river delta plain subfacies sediments were firstly discovered in Asuo Town of Nima County, northern Tibet. Rock association is mainly composed of medium conglomerate in sandstone, medium conglomerate in complex composition and fine conglomerate in sandstone, intercalated with gravel and lithic sandstones. We establish the Mamole Formation based on the section measurement and regional correlation. The authors collected zircon samples from lithic sandstones in Mamole Formation, and the analytical results show that the youngest detrital zircon age is 89Ma and there exist three peak ages for the samples, i.e., 125Ma, 550Ma and 980Ma. The ages 550Ma and 980Ma represent respectively the Pan-African and Green Weir-Jinning period magma thermal events. The principal peak of 125Ma represents the magmatic activity related to the evolution of Bangong Co-Nujiang Tethyan Ocean in Cretaceous. The deposition time of Mamole Formation was 99~90Ma, and the appearance of Mamole Formation indicates that in the Nima area the ocean-continent transition ended and evolved into intracontinental environment in the early Late Cretaceous.