The fate of the Xigaze forearc basin after Late Cretaceous filling (South Tibet)

The Xigaze forearc basin is a key region to understand the evolution of active continental margins related to Neo-Tethyan oceanic subduction. Most studies have focused on the sedimentary evolution during filling of the marine basin, but we here provide a detailed sedimentological and biostratigraphic analysis of the last, uppermost Cretaceous to Paleogene phases of forearc sedimentation documented by the shallow marine to deltaic to fluvial Qubeiya, Quxia, and Jialazi formations exposed in the Cuojiangding area. By comparing these sequences with regional tectonic and global climate events and sea-level curves, a reconstruction of the environmental evolution during this final filling stage is proposed, placing emphasis on the eustatic control of carbonate deposition in the Qubeiya and Jialazi formations. These transgressive intervals are separated by two regressive episodes unrelated to global sea-level trends that led to the demise of the carbonate platform. The first episode, documented by fan-delta deposits of the Quxia Formation, occurred at the time of initial India-Asia collision. The second episode, documented in the central part of the Jialazi Formation, occurred during the Paleocene-Eocene Thermal Maximum, likely driven by an intensified hydrological cycle. These results provide new insight into the palaeo-tectonic and palaeo-environmental evolution during the closure of the Neotethys seaway between India and Asia.