Late Oligocene formation of the Qaidam Basin revealed by calcite U-Pb dating: Insights into the northward growth of Tibetan Plateau

Abstract

The Qaidam Basin, nestled within the Tibetan Plateau, serves as a vital geological archive documenting the history of plateau growth. However, uncertainties regarding the Cenozoic chronostratigraphy have persisted due to challenges in dating techniques. Here, we presented in situ U-Pb dating on diagenetic calcite cements from lacustrine limestone interbeds in the Xichagou section, western Qaidam Basin. Our work reveals robust and consistent ages of ∼19.6 Ma and ∼13.5 Ma for the upper Xiaganchaigou and lower Xiayoushashan formations, respectively, representing the first radiometric ages for the Cenozoic sediments in the Qaidam Basin. Using these U-Pb ages as chronological anchors, we relocated the correlation of the recognized magnetic polarities with the reference geomagnetic polarity timescale, and further refined the Cenozoic chronostratigraphy together with borehole logging data and correlation with other adjacent sections. Our work revised the onset of deposition of the lowermost Lulehe Formation from the early Eocene to the late Oligocene (∼27.4 Ma) in the western Qaidam Basin. In conjunction with previously published data from the northeastern Qaidam Basin, our findings emphasize that Cenozoic sediment accumulation began almost simultaneously across the entire Qaidam Basin in the late Oligocene, likely caused by synchronous tectonic-driven basin subsidence and uplift of neighboring mountain in response to the India-Eurasian collision. Comparative analysis with the nearby Hoh Xil, Jiuquan and Yin'E basins highlights a progressive northward expansion of the Tibetan Plateau since the late Oligocene, characterized by concurrent basin formation and mountain building processes, rather than uniform plateau-wide elevation gain. The findings underscore the importance of integrating radiometric dating techniques with magnetostratigraphy and structural data to refine regional chronostratigraphic frameworks and understand the dynamic processes shaping the evolution of the Tibetan Plateau.