Facies analysis and depositional systems of Cenozoic sediments in the Hoh Xil basin, northern Tibet

A sedimentary succession more than 5800 m thick, including the Lower Eocene to Lower Oligocene Fenghuoshan Group, the Lower Oligocene Yaxicuo Group, and the Lower Miocene Wudaoliang Group, is widely distributed in the Hoh Xil piggyback basin, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan plateau. The strata of the Fenghuoshan and Yaxicuo groups have undergone strong deformation, whereas only minor tilting has occurred in the Wudaoliang Group. We analyze their sedimentary facies and depositional systems to help characterize continental collision and early uplift of the Tibetan plateau. The results indicate fluvial, lacustrine, and fan-delta facies for the Fenghuoshan Group, fluvial and lacustrine facies for the Yaxicuo Group, and lacustrine facies for the Wudaoliang Group. Development of the Hoh Xil basin underwent three stages: (1) the Fenghuoshan Group was deposited mainly in the Fenghuoshan-Hantaishan sub-basin between 56.0 and 31.8 Ma ago; (2) the Yaxicuo Group was deposited mainly in the Wudaoliang and Zhuolai Lake sub-basins between 31.8 and 30.0 Ma ago; and (3) the Wudaoliang Group was deposited throughout the entire Hoh Xil basin during the Early Miocene. The Fenghuoshan and Yaxicuo groups were deposited in piggyback basins during the Early Eocene to Early Oligocene, whereas the Wudaoliang Group was deposited in a relatively stable large lake. The Hoh Xil basin underwent two periods of strong north–south shortening, which could have been produced by the collision between India and Asia and the early uplift of the Tibetan plateau. The study suggests the Hoh Xil region could reach a high elevation during the Late Oligocene and the diachronous uplift history for the Tibetan plateau from east to west.