Unravelling the Pleistocene glacial history of the Pamir mountains, Central Asia

Several hundred thousand year old moraines preserved in the semi-arid environment of High Mountain Asia attest to Middle Pleistocene glaciations, but the regional correlation of glacial stages and the spatial extent of the glacial advances remain poorly constrained. We examined glacial landforms and Quaternary sediments in the Bartang valley, northwestern Pamir, a region with no previous quantitative glacial chronology. Using cosmogenic Be-10 exposure ages, we dated glacially polished bedrock, moraines, and mass wasting deposits. Our data show that the northwestern Pamir was heavily glaciated in the Middle Pleistocene (>= 220 ky) with large valley glaciers occupying some of the major valleys in the western Pamir. During the penultimate glacial cycle (191-130 ky) these valleys may have been largely ice free. Catastrophic mega debris flows with volumes >= 0.05 km(3) occurred after the ice retreat and reflect paraglacial destabilization of glacial sediments. The age of the best-dated mega debris flow (81 +/- 4 ky) is similar to moraine ages similar to 70-80 ky documented throughout the Pamir, demonstrating that remobilized sediments may provide valuable age constraints on glacial histories. In order to facilitate regional comparison of glacial chronologies, we developed a Gaussian separation algorithm, which determines a moraine age from a distribution of boulder exposure ages based on the assumption that post-depositional processes prevail over inheritance, and that the oldest boulder ages best represent the timing of moraine formation. We compiled moraine boulder exposure ages from the Pamir and adjacent regions and provide a summary of Middle and early Late Pleistocene glacial cycles of western High-Mountain Asia. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study in Bartang valley of northwestern Pamir utilizes cosmogenic Be-10 exposure ages to establish the timing and locations of glacial activities during the Middle Pleistocene, and highlights the instability of glacial sediments through catastrophic mega debris flows occurring after glacial retreat, with remobilized sediments providing valuable age constraints on glacial histories. The developed Gaussian separation algorithm allows for regional comparison of glacial chronologies, providing a summary of Middle and early Late Pleistocene glacial cycles in western High-Mountain Asia.