Late Pleistocene–Holocene environmental changes in ultra-continental subarid permafrost-affected landscapes of the Terekholʹ Basin, South Siberia

This study is an attempt to use closely related inter-complementary paleo-archives of a local landscape to access understanding of Late Pleistocene–Holocene environmental changes in the region. The study site is a small intermountain basin in the Sayan-Tuva Upland, 51°N., 97°E., 1300 m a.s.l. Paleo-archives covering about 13,000 yrs were studied: paleosol-sedimentary sequences on a delta-alluvial fan of a small river, lacustrine sediments in bottom cores and on palsa-islands and soils of palsa-islands. The following sequence of environmental changes was established. The fluvial activity in the basin reached its maximum at the end of the Late Pleistocene. The sharp decrease of the fluvial activity is terminated by two successive paleosols of Pleistocene–Holocene transition. The older paleosol indicates meadow-steppe (or tundra-steppe) conditions with a shallow permafrost table and impeded drainage. The younger paleosol testifies on sharp aridization, biological activity suppression, contrasting water regime, and warming. Dammed lake appeared in the midst of the trough about 11,000 cal yr BP. ntation on delta-alluvial fan was fairly inconsiderable in Holocene. The first part of Holocene (before 4000 cal yr BP) was most balanced in annual distribution of precipitation. Runoff, even being prominently enhanced in a fluvial and relatively warm sub-phase 8000–6250 cal yr BP, was canalized, without giving seasonal floods. Sub-phase 6250–3800 is characterized by increased continentality and relative aridization caused reduction of runoff, lowering of the lake level, and enhancement of cryogenic processes. The next phase 3800–2000 cal yr BP was more humid. It caused slight revival of fluvial processes and rise of lake level. The last 2000 years climate was more continental and the most arid within the studied period. The lake level and runoff values dropped again, and fluvial activity totally decreased. In contemporary soils aridization is reflected in widely spread Natric features and progressive salinization.