NATURE AND RATES OF LANDSCAPE EVOLUTION IN A HYPER-ARID INTERMONTANE BASIN, QAIDAM, NORTHERN TIBET

The Qiadam Basin in northern Tibet is a large intermontane depression dominated by a hyper-arid climate. Alluvial fans, pediment surfaces, shorelines and a thick succession of sediments within the basin coupled with moraines and associated landforms in the adjacent high mountains record a complex history of Late Quaternary paleoenvironmental change and landscape evolution. The Qaidam basin, one of the largest hyper-arid intermontane basins on Earth, is a natural laboratory to examine the nature of intermontane basin evolution within a continent-continent collision zone. Furthermore, it provides an opportunity to relate the timing of landscape evolution in a hyper-arid environment to climatic change and associated glacial and hydrological changes. Critical sites along the southern and northwestern margins of the Qaidam Basin provide evidence of a strong link between times of climatic amelioration, deglaciation, lake desiccation and alluvial fan sedimentation. From these observations we believe that the major landscape changes took place very rapidly over short intervals of time during periods of climatic instability. To test this hypothesis, we have undertaken remote sensing, field mapping, geomorphological and sedimentological analysis, and numerical dating of Late Quaternary landforms within the Qiadam basin. In particular, we have undertaken an extensive program of cosmogenic radionuclide (CRN) surface exposure dating to define the ages of Late Quaternary landforms. This is allowing us to test our hypothesis that the timing of formation of landforms is synchronous with times of climatic instability.