LATE GLACIATION AND HOLOCENE DEVELOPMENT OF THE EROSION- ACCUMULATION PROCESSES IN THE SMALL BASINS OF THE WESTERN TRANSBAIKALIA

Abstract

Detailed investigations of soil-sediment sequences of three sections (Nizhnyaya Bulanka, Nadeino and Kuytun) in the Kuytunka river basin (Western Transbaikalia) was carried out. Three stages of activation of erosion- accumulation processes in small drainage basins of Western Transbaikalia are determined: Pre Holocene (13.0– 10.7), Early- (10.3–8.0) and Late Holocene (last 2.5 14C kyr). During these stages several phases of sedimentation and soil-forming process are distinguished. High intensity of aeolian processes together with washout and sedimentation during time spans of 10.7–10.0 and 9.5–9.0 kyr were determined on erosion landforms and alluvial fans. The main causes of deposition processes intensification have been revealed and quantitative data about their intensity were obtained. Intensification of soil-forming process in conditions of mountain-forest-steppe landscapes of Western Transbaikalia begins when sedimentation rates reach 0.06–0.37 mm/yr. Within the sedimentation rate interval 0.3–0.6 mm/yr humus interlayers alternate with layers of colluvial and aeolian deposits. At the rate above 0.6 mm/yr sedimentation of sandy loam and sands with inclusions of rubble are observed. Duration of soil development is 300–3500 years. Sediment accumulation phases have duration from 70 to 2000 years. Development of erosion-accumulation processes are characterized by polychronicity related to different response of small drainages basins to global, regional and local environmental changes. Rhythmical development of the washout, erosion, accumulation and soil-forming processes provides long-term activity of erosional landforms.