USING CLIMATE VARIABILITY TO TRACK TOPOGRAPHIC GROWTH OF THE NORTHEASTERN MARGIN OF THE TIBETAN PLATEAU

Mountain building on the northeastern margin of the Tibetan Plateau ~15-8 Ma created topographic highs that may have separated once continuous sedimentary basins and altered local climate. Interbasin paleoclimate variability can be characterized using stable isotopes from calcareous basin fill. In this study, interbasin isotopic variations across the region are compared to identify the development of topographic highs that separate individual basins. Four sedimentary basins from northwest to southeast, Guide, Jian Zha, Xunhua, and Linxia, are oriented nearly parallel to the NE margin of the Tibetan plateau margin. The Jian Zha and Xunhua basins are surrounded by the Neogene Laji Shan to the north and east, the Cretaceous West Qingling Shan to the south and the (Cretaceous-Neogene ?) Zamazari Shan to the west. The easternmost Linxia basin is open on its eastern and northern margins, and the westernmost Guide basin is open to the west and northwest. Over the past 10 Ma, the oxygen isotope records of Jian Zha and Xunhua basins show discrete offsets up to 4.5 per mil, whereas the records from Guide and Linxia basins are remarkably uniform over time. We infer that the creation of relief in the Laji Shan (and potentially in the Zamazari Shan) that led to the isolation of the Jian Zha and Xunhua basins had a significant impact on local climate that resulted in the observed large oxygen isotope shifts. A similar effect is not seen in the Linxia and Guide basins possibly because their margins remain open. While interbasin climate variability complicates the regional climate picture, it sheds light on the space-time evolution of the Laji Shan mountain range and associated basin isolation.