Dating fluvial terraces on the southeastern Tibetan Plateau using the uranium comminution age method

Abstract

Fluvial incision plays a crucial role in shaping regional landscapes, reflecting the dynamic interplay between tectonic forces and climate fluctuations. Accurate dating of fluvial terraces, which record both aggradation and incision processes, is essential for understanding the evolution of drainage systems. However, conventional dating methods such as radiocarbon (¹⁴C), optically stimulated luminescence (OSL), and cosmogenic radionuclide (CRN) techniques face limitations, particularly for terraces outside their optimal ranges or those with complex burial histories. This study introduces a novel approach based on the recoil loss of ²³⁴U from particle surfaces following fragmentation from bedrock, enabling the dating of silt terrace sediments without the need for well-buried or sorted samples. We apply this approach to terrace sequences along the Lancang and Jinsha rivers on the southeastern fringe of the Tibetan Plateau, an area that has been extensively studied for its geomorphology and sedimentology to investigate fluvial responses to tectonic and climatic drivers. Our results reveal a consistent decrease in ²³⁴U/²³⁸U ratios with increasing terrace height, approaching equilibrium values. The deposition ages derived from this method closely align with K-feldspar post-infrared infrared stimulated luminescence (pIRIR) ages from the Lancang River and show a positive correlation with electron spin resonance (ESR) ages from the Jinsha River. Based on the terrace ages presented here, we estimate long-term incision rates of 0.46 mm/yr for the Lancang River and 0.31 mm/yr for the Jinsha River since the middle Pleistocene. These findings underscore the potential of the uranium comminution age method as an effective tool for dating fluvial terrace deposits, providing an additional dating method to conventional dating techniques.