ABSTRACT

This work reconstructs the depositional history and estimates the mass of sediments stored in the Hoh Xil basin, northern Tibet, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan Plateau. The mass estimate is derived from over 75 geologic sites and 21 measured stratigraphic sections, with a total thickness of 13,478 m. The results show that the Hoh Xil basin underwent six stages of development from the Early Eocene to the Early Miocene, with a hiatus in sedimentation in the Late Oligocene. The Fenghuoshan Group was deposited during the first four stages 56.0-52.0, 52.0-43.0, 43.0-38.2, and 38.2-31.5 Myr; the Yaxicuo Group comprises stage 5, 31.5-30.0 Myr; the Wudaoliang Group covered the entire basin during the last stage, 23.0 to 16.0 Myr. The strata of the Fenghuoshan and Yaxicuo groups were strongly deformed, mainly during the Late Oligocene, whereas only minor tilting has occurred since then in the Wudaoliang Group. The depositional history indicates that the Hoh Xil basin could have been formed as a piggyback basin and that the onset of northeastward growth of the central Tibet was from the Early Eocene (about 56 Myr) to the Late Oligocene.

The analyses of subsidence history and mass accumulation indicate that both accelerated subsidence and sudden increases of accumulation rate occurred at the four periods of about 52.0, 40.5, 34.5, and 31.5 Myr in three sub-basins and over the entire basin from the Early Eocene to the Early Oligocene. During the four periods, the deposits were either lacustrine turbidite sandstone or fan-delta conglomerate, which resulted from the tectonic movement. On the basis of the mechanism of northeastward growth of the piggyback basins and the consistency of accelerated subsidence, depositional systems, and mass accumulation, we suggest the continental collision and early uplift of the Tibetan Plateau controlled the formation and evolution of the Hoh Xil basin. The event that occurred at 52.0 Myr could represent the continental collision between India and Asia, whereas the other three events that happened during about 40-30 Myr could show the early uplift of the Tibetan Plateau. This study on sedimentary records in the Hoh Xil basin, along with widespread magmatic activity in eastern and western Tibet, suggests a diachronous uplift history for the Tibetan Plateau from east to west.