Search

The Lena River is one of the largest rivers in the world; it determines the geomorphology and controls the exogenous processes of Northeastern Siberia. The Lena River is a remarkable case of palaeogeographic inheritance, traceable throughout the Quaternary period. As a result, the history of the river is complicated and can be divided into several epochs. The stages of channel evolution, the influence of the Verkhoyansk Ridge glaciation on channel position and the number, and the age and origin of river terraces have all been a matter of debate for more than half a century. Large-scale geological investigations of bank exposures conducted during the Soviet period provided important stratigraphic data which have been used by various authors to reconstruct the geological history of the Lena River. However, these interpretations vary widely with no consensus on the number, age or genesis of the terraces. This complicates palaeogeographic reconstruction of the Lena valley, especially because of the debates around position and age of various Quaternary terraces. Many researchers have remarked that the absence of absolute dating is a major barrier to improved understanding. To address this problem, in 2019-2021 we investigated the Ust-Buotama outcrop in the middle reaches of Lena River (61.232091 °N., 128.602046 ° E.). This section is the best exposure of the Bestyakh terrace, the most distinctive of the accumulation terraces of the Lena River. The outcrop, located on the right bank of the river 130 km upstream the city of Yakutsk, has a maximum height of ~120 m, including an aeolian dune. The terrace contains 3 recognised main geological units: Bestyakh, Mavrinka and Dolkuma, the genesis and age of which are debated. We sampled 9 tubes from the Mavrinka and Dolkuma units. Using optically stimulated luminescence and post-infrared stimulated luminescence we obtained 8 finite ages, while the lowermost sample was in full saturation. Our chronology is based on sand-sized multi-grain quartz and feldspar aliquots. Luminescence measurements were carried out for quartz and feldspar to determine whether the signals were sufficiently bleached prior to sedimentation. The quartz OSL signals are fast-component dominated and dose recovery ratios are satisfactory (1.04±0.03; n=20). Quartz/feldspar age ratios (1.06±0.12) demonstrate that quartz OSL signals were very likely sufficiently bleached. Independent age control (radiocarbon dating results from the aeolian dune) supports our luminescence ages. Our results indicate that: (i) the base of the section (Mavrinka alluvial formation) was deposited before 300 ka; (ii) the middle part, represented by Dolkuma aeolian unit formed during MIS 2, and (iii) the final stages are marked by a palaeosol formed 15.1±2.6 ka ago. For the first time we identified a stage of strong aeolian activity in the middle reaches of the Lena River during MIS 2, forming a 55-60 m thick aeolian field. This aeolian reworking of the Lena alluvial sediments may be the source of the large sand deserts in the Lena valley, and the large area of dust sedimentation in the Beringia region (Yedoma formation). This study was supported by project ? 21-17-00054 «Quaternary aeolian relief and cover deposits of Lena river basin (Eastern Siberia): structure, age and palaeoenvironment significance» [ABSTRACT FROM AUTHOR]