Timing and spatial patterns of basin segmentation and climate change in northeastern Tibet

Spatiotemporal patterns of Cenozoic deformation along the margins of the Tibetan Plateau can provide key evidence with which to investigate the mechanisms of continental deformation and plateau growth as well as their impact on regional climate. Along the northeastern margin of the Tibetan Plateau, Cenozoic deformation and regional aridification have been attributed to the upward and outward growth of the plateau. Analysis of stratigraphic and stable isotopic data shows that, in early to middle Miocene time, intracontinental mountain ranges subdivided a broad foreland basin, which developed on the northern margin of the Tibetan Plateau shortly after collision between India and Eurasia, into smaller intramontane basins. Stratigraphic and stable isotope data collected from a number of subbasins along the northeastern Tibetan Plateau, spanning as much as 30 m.y. in age and ranging to 3 km in thickness, reveal a pattern of deformation and basin isolation that began ca. 22 Ma with the initial unroofing of the eastern Laji Shan near the town of Minhe and partially separated the Xining basin from the Hualong, Linxia, and Xunhua basins to the south. Westward paleoflow indicators on the eastern margin of the Guide basin indicate that the Zamazari Shan had attained topographic relief by ca. 20 Ma and separated the Guide basin from the Jian Zha, Hualong, and Xunhua basins to the east. Deformation of the Laji Shan-Jishi Shan progressed to the south, deforming the Jishi Shan ca. 13 Ma and separating the Linxia Basin from the Hualong and Xunhua basins to the west. Final separation between the Jian Zha and Xining basins occurred at 10-8 Ma with the growth of the western Laji Shan and Riyue Shan. Unique stable isotope records reflect the different hydrologic and tectonic settings of each basin and highlight the importance of local climate conditions in each basin. However, ca. 14 Ma all basins underwent a synchronous change in climate toward more arid conditions, as indicated by a gradual to abrupt positive shift in δ¹⁸O values. This climate event corresponds with aridification events to the west near the Qaidam basin and may be related to the reorganization of vapor transport pathways around a growing eastern Tibetan Plateau.