Cenozoic depositional sequences in the piedmont of the west Kunlun and their paleogeographic and tectonic implications

Abstract

The West Kunlun forms the northwestern margin of the Qinghai-Tibet Plateau. Well developed Cenozoic depositional sequences in the piedmont along the margins of the Tarim basin record changes in sedimentary environment and the uplift of the West Kunlun during the Cenozoic. During latest Cretaceous to Oligocene deposition in the west Kunlun occurred in a marine environment (the Tarim Bay). During the Paleogene gypsum beds, bivalve shell limestones and variegated clastics were deposited. Rapid sedimentation during the Late Miocene resulted in the deposition of molasse sediments 2000–3000 m thick, indicating a relatively high depositional rate. The Upper Miocene sequences show a coarsening-up tendency, indicating a rapid and accelerated uplift of the West Kunlun from Late Miocene to Early Pleistocene times. Molasse deposition was interrupted in the Early Pleistocene by a tectonic pulse, which resulted in tilting of the molasse and underlying sediments at high-angle towards the Tarim Basin. Undeformed Middle to Late Pleistocene coarse fluvial and pluvial deposits overlie the steeply dipping molasse and older rocks unconformably, and represent the resumption of rapid deposition. A continual high rate of uplift during the Holocene is presumed on the basis of an incised drainage system that flows from West Kunlun into the Tarim Basin and cuts Middle to Late Pleistocene gravels and older sediments to a depth from 50 m to more than 100 m, although climatic changes may also have played a part.