MORPHOLOGICAL FEATURES OF NURA RIVER AND ITS VALLEYS

Veselova L.K.,Zhangozhina G.M.

Al-Farabi Kazakh National University, Kazakhstan

MORPHOLOGICAL FEATURES OF NURA river and its valleys

River valley is one of the most important concepts of geological and geographical sciences having important scientific and practical significance. The reconstruction of modern landscapes, tectonic movements, the search of many mineral resources (gold, diamond, cassiterite, etc.), the construction of various hydraulic structures connect with river valleys. The relief of river valleys, differing from other types of relief, is developed in almost all physical and geographical zones and provinces in all geostructural subdivisions of land. Among the other exogenous factors in the formation of the relief the fluvial processes developing in time and space almost continuously, the most feasible movement of solid substance masses is in the earth's surface.

Despite the relatively little atmospheric precipitation (150-300 mm) and generally low hypsometric position the surface of the researched area is dotted with valleys, especially higher parts of the watershed areas are dense. All the valleys of the area are characterized by very small deviations: Tunduk river - 0,002, Aschysu river - 0.001, Nura river - 0.0008, Sherubaynur river - 0,002, etc. Small slopes and gentle slopes, as well as a small depth of the cut usually defined by units or the first tens of meters and large width are distinctive features of almost all valley shapes, not only main ones but also the tributaries. The width of the main valleys often reaches 8-10 km and in places of articulation with tributaries of the first order gets even 15-20 km. In G.Ts.Medoeva’s opinion [1], flat wide valleys are indispensable elements of any part of small hill relief. As a result of the regressive erosion of the tops of the valleys and their tributaries of any orders differ with more sharp contours, steep slopes and narrow couches. Therefore, separate surface water zones are expressed by horizontal relief. River captures (e.g., in the upper reaches of Sherubaiynura) are connected with the regressive nature of the bottom erosion expression. Into flat and wide valleys made by alluvium are incised by twisting as riverbed with the depth of 0.5-1.5 m and a width of 3-15 m. In some valleys (for example, rivers Sherubaiynura and Tunduk) of both slopes of the main watershed there are areas within which the riverbed paved its way into the bedrock of folded foundation, while the left or right of the bottom surface remained intact, which is composed by alluvial sediments. Such areas are epigenetic.

The morphology of the bottom of large valleys is complicated by the river terraces; they are hard mapped, as in most cases poorly preserved in the relief. This is due to the fact that they were either washed out to considerable extents of the lateral erosion, or filled with dealluvial and pluvial deposits. For example, in the valley of river Sherubaiynura four of them clearly marked, including the floodplain, accumulative enclosed terrace.

A very interesting feature of the broad and shallow valleys of the Central Kazakhstan is the fact that under the diurnal surface the ancient buried valleys were found [2, 3]. According to drilling works the existence of buried ancient erosive cuttings was proved under the modern valleys Nura, Sherubaiynura, Sarysu, Olenty, etc. In contrast to the modern valleys the buried ones are characterized by a sharp outlines and great depth, sometimes reaching 100 m or more. Profiles of the slopes of the ancient valleys are complicated by horizontal platforms, limited terraces. These areas are buried sculptural terraces. The ancient valleys are well studied here. They are filled with Mesozoic and Cainozoic sediments, often represented by variegated clay, sandy horizons. Comparison of different structures of the ancient valleys within the Kazakh hills reveals the uniqueness of the processes on the whole territory. Analysis of ancient valleys indicates a new phase of uplift, which Saryarka experienced in the upper Oligocene. In the most of valleys the sediment top of Chiliktinskaya suite is eroded, and sands and gravels overlie on clay. Ancient valley of great Nura is traced by drilling in areas of Solenosnoe, Sergiopol, Temirtau, Samarskoe, Chernigovka. The total length of the ancient valley is about 300 km [4].

Geometrically, the river basin network of Nura river are expressed by detrital type [5]. This type of river network is formed on the flat surface with a relatively homogeneous almost equally and easily pliable to erosion substrate of horizontal bedding. On the surface of accumulative plain Neogene the erosion begun in ancient Quaternary time, formed a type of dendritic river basins. With the development of regressive erosion and, in accordance with this, the density growth of the hydrographic network, i.e. the increase of number and length of the tributaries, surface variegates were considerably denuded. According to N.G.Kassin’s opinion [2], from the past solid cape of Neogene accumulation some fragments left. They meet by the individual spots on the lower watershed, and in some valleys the terrace 3-above the floodplain is composed by them and they are preserved in the ancient buried valleys.

Thus, the hydrographic network of Nura river basin and their valleys filled and formed on the flat surface of friable and homogeneous substrate of the Neogene in the dendritic type, as we see, has been keeping the same geometric plan till nowadays in areas where rocks of the initial substrate have survived.

References:
1. Medoyev G.Ts. The structure surface Sary-Arka. "Exploration and conservation of mineral resources", 1956, № 10. P. 531-533.

2. Kassin N.G. About the ancient valleys of Central Kazakhstan. "Problems of modern geology", 1936, v.6. №1. P. 77-81.

3. Medoyev G.Ts. Buried valleys of Sary-Arka. "Izv. VGO ", 1956, v.88. № 2. P. 174-178.

4. Zhangozhina G.M. To issues of the ancient valleys of Kazakhstan / / Materials of inter.scien.-practical conference. «IV Zhandaevskie readings." - Almaty, 2007. P. 84-86.

5. M.A.Usova’s main ideas in geology / / Under red.K.I.Satpaeva, Alma-Ata, 1960. P. 195-198.