Główne rysy rzeźby zachodniego skłonu Chenteju i jego przedpola w dorzeczach Sugnugurin-goł i Bajan-goł

Abstract

The geomorphology research covered western slope of the Chentej in the Sugnugurin-gol and Bajan-gol basins as well as the forefield within the higher Chara-gol basin. A wide depression called Batsumber Valley is seen here. Geomorphological mapping for the areas under consideration, i.e. in the middle Batsumber Valley in foreststeppe zone and in the higher basin within Southern-Siberia taiga, was done on the 1:25,000 basis. For the entire area, a geomorphological survey map 1:100 000 was prepared (fig. 1). Within the western slope of the Chentej two planation levels are well seen, their altitude being from 500 to 550 m, from 300 to 350 m, from 120 to 150 and about 60 m over the valley bottoms. Lower zones (120—150 m and 60 m) are closely related to longitudinal profiles of the present valley bottoms. Higher zones (500—550 m and 300—350 m) are generally inclined westward. Their surface cuts both metamorphic and magma rale forms (granites, sienites, granodisrites and adamelites). However, they are disturbed by dislocations running from south-east to north-west and thus in general consistent with the dislocation involving the main Baga-Chentej ridge from south-east. The zones being disturbed by dislocations indicate that movements related to old dislocations which are often associated to granitoide intrusions are of yong age. The highest floor within the Baga-Chentej was rearranged by cryoplanation processes. Numerous well developed ledges, terraces and cryoplanation surfaces are seen in the longitudinal profile (fig. 2). The height of rapids which separate the surfaces from each other varies from 20 to 80 m. A high correlation of the western slope valleys in the Chentej with the geological structure, i.e. both with the litology and tectonics (dislocations, dips and rifts), exists. In the longitudinal profile of valleys numerous constructions are observed being structural ravines associated to granite or quartzite sandstone occurrence. Sometimes, enlargements are also present within the granites, but when this is the case there are many rifts within them which are concentrated along the upcast regions. The climatic asymmetry of the valleys is highly evident, both within the high-mountain tundra, South-Siberian taiga and within the forest-steppe valleys. This asymmetry is dictated by the permafrost and by present and Pleistocene processes associated with the active bed. The Baga-Chentej western slope is passing in well-shaped linear rapids-like windings into vast tectonic foremountain valleys separating the high-mountain relief of the Chentej from West-Chentej uplands. The valleys are linked by narrower ravine-like ones. On the east and north-east the Batsumber Valley is bordered by tectonic-rapids slopes. The western slope of the Batsumber Valley is also rapids-like but it is strongly winding and numerous isolated elevations are present over the forefield. The rapids are predetermined by a huge dislocation, but its further growth was related to dip of beds and of resistant sandstones and low-resistant shales which are in general depressing westward and north-westward. Thus, tectonic-based structural rapids were produced, including many peninsulas and deep bays as well as witness-like isolated elevations.