Chronology for terraces of the Nalinggele River in the north Qinghai-Tibet Plateau and implications for salt lake resource formation in the Qaidam Basin

The Nalinggele River, located in the northern Qinghai-Tibetan Plateau, is the largest river originating from the northern slope of the eastern Kunlun Mountains and flowing into the enclosed Qaidam Basin. Controversy exists whether the formation of its terraces reflects the history of the plateau uplift, or climate changes, or both. The salt lakes in the enclosed Qaidam Basin fed by this river bear an unusual world-class enrichment of lithium and boron elements, which are critical resources for regional economy. The concentration of lithium is one of the highest found in brine resource in the world, and sourced from the upstream water of the river. The chronology of the river terraces is essential to understand the plateau uplift history, the regional climate change, the evolution of the terminal salt lakes, and the process of enrichment of the valuable elements. However, the age constraint for the terraces of the rivers in the east Kunlun Mountains is still limited and debated, and no dating work has been reported yet for terraces of the Nalinggele River. Five terraces were identified in this river. In this study, the terraces were dated using quartz optically stimulated luminescence (OSL) dating. The results indicate that the OSL ages (∼7.5 ka, ∼9.9 ka, ∼11.3 ka, and ∼13.1 ka) of the four terraces (T1, T2, T3, and T4) are consistent with geomorphic relationship, and that they formed since ∼13.1 ka and were probably triggered by climatic change rather than by the plateau uplift. The sediment of T5 is too coarse to collect OSL samples and not dated. Based on our dating we confirm the previous view that the lithium concentration in the terminal salt lakes should have initiated since 15-13 ka. We further propose that the formation of salt lakes and the enrichment of their resources in the Qaidam Basin should have occurred mainly in interglacial periods (e.g. the Holocene), a warm and humid period, not as previously thought to be in the glacial periods, a dry and cold period, and that during the glacial periods the basin was mainly under wind erosion.