Paleocryogenesis and erosional landform development in the Baikal region, Siberia, during the second half of the Late Pleistocene and the Holocene

Abstract

In the Cis- and Trans-Baikal regions of the southern part of Eastern Siberia, the detailed study and dating of geoarchaeological deposits and the erosion channel network (gullies, floodplains, and river terraces), along with the interpretation of high-resolution satellite images, have revealed areas of modern cryogenic processes as well as horizons with cryoturbations from the second half of the Late Pleistocene and the Holocene (MIS 3–1). Modern cryogenic landforms are found in swampy areas on gentle slopes, floodplains, and river terraces and are mainly represented by cryogenic cracks, hummocks, and thaw sinks; in river beds they are represented by icings. This paper establishes the formation ages of cryogenic horizons and distinguishes the permafrost phenomena of MIS 3–1.The stages of cryogenesis are associated with cold events, permafrost aggradation, the activation of cryogenic processes, and ice wedge polygon relief formation. During interglacials and interstadials, climate warming lead to permafrost degradation, ice thawing, active layer growth, erosion, cryokarst (thermokarst) development, suffusion, the acceleration of slope processes, the infilling of cryogenic relief forms, erosion network changes, the activation of erosion-accumulative processes, and sedimentation in river valleys.The second half of the Late Pleistocene contains five stages of active cryogenesis (49–42 k, 38–32.5 k, 29–23 k, 21–14.5 k, 12.9–11.7 k cal. BP),11Most dates are calibrated BP. Uncalibrated dates are presented as BP. each of which can be further divided into shorter phases. For example, in the Nadeino section (Western Trans-Baikal), three layers are distinguished with cryoturbations dated ~14.5–14.4 k, ~12.7–12.5 k, and 11.9–11.7 k cal. BP. In the Nizhniaia Bulanka section, one cryogenic horizon (formed at ~12.8–11.8 k cal. BP) was identified. Cryogenic horizons are categorized as syngenetic or epigenetic depending on the formation process.Polygonal-block reliefs (hummocks) are clearly visible in high-resolution space images of river basins on floodplains, terraces, watersheds, and gentle slopes within arable lands. These hummocks range from 4 to 50 m wide and 0.5–3 m high, and are divided by swales and hollows. The paleocryogenic relief on the watersheds and slopes formed in Early MIS 2 (29–23 k cal. BP) and, subsequently, experienced several stages of aggradation and degradation, resulting in a hummocky-hollow relief with sporadic permafrost distribution. Degradation of the permafrost during Late Glacial (15–11 k BP) and Early Holocene warming caused the formation of thermokarst (cryokarst), sheet and gully erosion, suffusion, sedimentation in river valleys, and changes in the microrelief of the upper links of the erosion network. Existing dells, rills, and gullies are the modern manifestations of paleocryogenic depressions and troughs.