Evolution of the Landscape of the Western Part of the Turan–Uyuk Basin (Tuva Highland) in the Late Pleistocene

A complex of works including geomorphological deciphering, field survey, drilling, electric prospecting, and dating of deposits using the radiocarbon method and optically stimulated luminescence are used for the interpretation of the Late Quaternary evolution of the western part of the Turan–Uyuk Basin. It is established that the total thickness of the deposits of the basin reaches 190 m. The Late Quaternary evolution of the basin includes the following main stages: (1) accumulation of alluvium and active lateral migrations of the Uyuk riverbed and simultaneous sedimentation of lacustrine sequences in the basin of the Belye lakes during most of the Late Pleistocene (at least, beginning from 77–87 ka) and the first part of the Holocene (prior to 6.1–6.2 ka); the formation of floodplain massifs of the 1st and 2nd generations; the internal delta of the Uyuk River, which dams the present-day Belye lakes, started to form no later than 25–16 ka; (2) the increase in freshet activity and activation of deep and lateral erosion between 6.1–6.2 and 2.4–2.6 ka; the formation of the 3rd generation floodplain; (3) the decrease in freshet activity and the size of the paleoriverbeds, the predominance of lateral migrations of the riverbed, and accumulation of alluvium in the last 2.4–2.6 ka; the formation of the 4th generation floodplain. The last stage is characterized by a shorter period of strong activation of cryogenesis. Permafrost began to form no earlier than 2.8 ka, and cryogenesis was mostly active at 1.35–1.10 ka. The Late Pleistocene stage of accumulation was preceded by a strong downcutting of the Uyuk valley, probably caused by the activation of tectonic movements. The chronological boundaries of this downcutting are determined only approximately: between 360–380 and 77–87 ka. The presence of a large dam lake, which occupied the central and western part of the basin and was suggested by some researchers, is not confirmed.