Evidence for glaciation predating MIS-6 in the eastern Nyainqêntanglha, southeastern Tibet

Southeastern Tibet is one of the most glaciated regions on the Tibetan Plateau both at present and during the Quaternary. Numerical dating of glacial deposits has allowed the establishment of a provisional chronology of Quaternary glacial fluctuations in this region, with the oldest glaciation (Guxiang Glaciation) occurring in marine oxygen isotope stage 6 (MIS-6). However, glaciations predating MIS-6 have been identified at many locations on the Tibetan Plateau and its surrounding mountains, posing the question: as a major glaciation center both at present and during the Quaternary, did a glaciation prior to MIS-6 ever occur in southeastern Tibet?

Zhou et al. (2021) provide evidence for a glacier advance in the Bodui Zangbo River valley in the eastern Nyainqêntanglha, southeastern Tibet that predates the Guxiang Glaciation. In the Bodui Zangbo main valley, there exists a level of discontinuous valley shoulders that are ~500-600 m above the Guxiang Glaciation moraine. On some of the valley shoulders there exists distinct glacial deposits, which are relatively well preserved on shoulders at Nitong, Baiyu, and Qingduo (Figures 1 and 2). Morphostratigraphically, these glacial deposits should be emplaced by a glacial expansion predating the Guxiang Glaciation in MIS-6. Considering the morainic morphology of the glacial deposits at Nitong is the most typical among the three sites, the newly identified glacial advance was named by the authors as Nitong Glaciation.

The glacial deposits at Nitong and Baiyu were dated using the Ti-Li-center ESR (electron spin resonance) signals. After excluding outliers, the deposition age of the glacial deposits was estimated to be 580.6±97.3--465.2±86.6 ka, yielding a peak age of 506.3±60.4 ka (1σ uncertainty) by using a normal kernel density function. Taking into account the age error and global climatic conditions, it is most likely that the Nitong Glaciation occurred during MIS-12, despite the possibility of happening during MIS-14 or even earlier. The glacial advance during MIS-12 has also been verified at many other locations on and surrounding the Tibetan Plateau. It is likely that the coupling of two critical drivers (surface uplift of the Tibetan Plateau and its surrounding mountains and decreased temperatures during MIS-12) caused the extensive glacier advance during MIS-12 in and surrounding the Tibetan Plateau. The finding is critical to better understand the whole history of Quaternary glacial fluctuations and tectonic uplift in southeastern Tibet.