Age Redetermination Of The Kangtuo Formation In Eastern Yibucaka Lake, Northern Qiangtang

Large part of the Qiangtang basin is covered by terrestrial Red-bedding which mainly consists by intermontane fluvial or lacustrine sediments and minor molasse formation. Though the Red-bedding is one of the best records of Tibetan plateau uplifting and erosion, its detailed geological traits are still debated because of less research work on it until now. There are large suits of Red-bedding in Rongma area, north edge of south Qiangtang terrane, which was assigned to Oligocene-Miocene Kangtuo Formation previously. However, more and more evidences show part of this red unit may belong to Late Cretaceous terrestrial detritus strata, after comparing to neighbor region results.According to our research on field profiles and indoor works which focus on sedimentology, petrography and structures, we reanalysis red-bedding basin evolution. Our paleogeographic reconstruction was based on heavy mineral analysis, paleocurrents analysis, and provenancediscussion. Moreover, structural deformation has been used to constrain its age. Basic conclusions are as follow 1) Research on sedimentology illustrates that the sedimentary facies of red-bedding include alluvial fan, fan delta facies, lacustrine delta facies, lacustrine facies and braided fluvial; 2) Dickinson triangular diagrams of sandstone detrital modes show recycled orogeny provenance traits; 3) Paleocurrents data reveal elevation differences and changing of neighbor uplifted mountains which was various during their uplift; 4) The distinct distance of provenance and source rocks was revealed by heavy mineral analysis, 5) the detrital zircon U-Pb spectrum confirm the red-bedding could be as old as the Late Cretaceous; and 6) structural results separated the red-bedding into two large groups, one with strong deformation and the other without.Final and most important conclusion is that we separated Cretaceous Abushan Formation(~105Ma) from Tertiary Kangtuo Formation on east of Yibucaka flank. That helped a lot to us with reevaluation red-bedding in central Tibet as well as our mapping works.