THE PALEOCURRENT PATTERN OF EARLY TERTIARY REDBEDS IN THE HOH XIL BASIN,NORTHERN TIBET PLATEAU:IMPLICATIONS FOR AN EARLY UPLIFT AND UNROOFING |
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| Abstract: | We focus on early Cenozoic uplift, erosion and growth of northern Tibet plateau by reconstructing paleo\|drainage pattern in the Hoh Xil basin. Stratigraphical infilling sequences and lithic type orogenic basins are determined largely by contemporaneous tectonic activity. It is therefore reasonable to infer that paleoflow variability record give useful information about regional tectonic events. We now report paleocurrent data from outcrop measurement of 4 expedition profiles across the basin during 1997—1998.The west\|east trending Hoh Xil basin is the largest redbeds basin in northern Tibet plateau. It is 400km in axial length and has maximum width of 200km, which extends along Jin zone, separated the Qiangtang from the Bayankara block. It accommodates more than 5000m of terrestrial sediments during the Eocene to Oligocene dated by preliminary magnetostratigraphy and minor fossils.Detailed sedimentological observation and lithic facies associations analysis of the Eocene Fenghuoshan Group show to have evolved vertically from alluvial fan system in the lowest part, into stacked megasequences of coarsening\|upward fan\|delta system in the middle and upper part. The braided fluvial conglomeratic deposits occur at intervals along the basin margin and grade basin ward interbedded sandstone and mudstone. The Oligocene Yaxicuo Group is locally present and forms as laterally elongate sub\|basins, which is of a maximum thickness of 2000m, as seen in the Wudaoliang and the Hantaishan area. Alluvial fan associations in this sub\|basin in the proximal part adjacent to the southern faulted border and prograded northward to floodplain in distal part. |
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| Keywords: | paleocurrent pattern early Tertiary redbeds uplift e rosion Hoh Xil Northern Tibet |
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