Longitudinal profiles of the terraces in the middle Katun and Chuya valleys (Gorny Altai)

Saveleva P.J.

V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia

poli@igm.nsc.ru

Тhere are erosion- accumulative terraces in the valleys of Chuya and Katun mountain rivers, which are unique by in terms of their number and height of. Such interesting object could not be left without attention Altai researchers: the first hypotheses about morphology and structure of these terraces have been begun to appear in publications since the beginning of the 20th century. In spite of the so long period of studies many questions, concerning quantities, the age, relationship and the genesis of deposits these terraces, as well as their correlation with neotectonic changes and climate fluctuations, are still actively discussed.

On the basis of the geomorphologic structure terrace in the middle stream of the Katun and Chuya valleys were divided into high and low (middle) by L.N. Ivanovsky [1]. Such division of terraces is used till now by many authors. High terraces are characterized by smooth edges, uneven surfaces, covered by fans of slope deposits, with a slight slope to the river. In the Katun river valley high terraces terrace mainly occupy the big areas, but on the Chua they are more often represented by rare "scraps" in small extensions of the valley. The middle terraces, height up to 80-100 meters on shore line, differ by equal grounds, distinct edges and by end joint and prevalence. N.A. Efimtsev and B.M. Bogachkin in their works had proved that the terraces are not accumulative they and are cutting into in sedimentary thicknesses (the Middle Neopleistocene Inya thickness and the Late Neopleistocene-Holocene Saldgar thickness), what was the reason for the revision of the views not only on the origin of sediments, composing the terrace, but also on the formation of the edges [2, 3].

The aim of the work was to identify the features of Katun and Chuya river valleys development during the Nеopleistocene-Holocene on the basis of the analysis of the terraces morphology in the longitudinal profile. Although the study of the mountain rivers valleys on longitudinal profiles are recognized as necessary by majority of researchers [1, 3], the morphology of terraces profiles have not been studied yet enough. Terraces along the entire extension of the Chuya valley have not been traced and compared with Katun’s ones, their high-rise group, conformed to certain stages of erosion cutting, also has not been studied, as well the role of exogenous and tectonic factors in the formation of the valleys relief in the Nеopleistocene-Holocene has not been finally determined.

We have compiled longitudinal profiles of the Katun valleys (from the mouth of the Kaznahta to Kadrin rivers) and Chuya (from the mouth of the Chagan-Uzun river to the confluence with the Katun). All ledges of terraces expressed in the relief were determined during the field observations and by interpretation of aerial photograph and high-resolution satellite imagery. High-rise position of the terrace and the river were calculated by topographic maps of 1:25 000 scale. It was established that the terraces remain parallel to each other and their height on the edge of the river increases down the valley direction. The cutting-in terraces like a "fan" split into multiple erosion levels. Such morphology of valleys is created by the regressive erosion developing upwards on valleys from the mouths of the side tributaries or on the sites of the riverbeds slope change [1, 4]. We have divided the section of the Katun’s middle stream into 33 erosion-accumulative levels, characterized by a certain hypsometric position (Tab.). For example, the 10 meter high terrace of XIII level in the Ebelu river area rises to 21 m near the mouth of the Chuya, then 21 m - up to 50-52 m near Big Ilgumen and etc. These levels, extended on lengthy areas, conform to individual erosion-accumulative cycles (stages) of the basic valley. Singular terraces, as usual, are timed to the mouths of the side tributaries and local raises as the most dynamically unstable sections of the valleys. So the terrace of 85 m height (XXII level) near the mouth Chuya is simultaneously local for the Katun valley and the cycle for Chuya. The erosion cutting depth of middle terraces for each level in general uniforms - 5-12 m. For high terraces error in correlation of the longitudinal profile is more, because its surfaces have changed by denudational - accumulative processes, nevertheless, it can be assumed that the cutting depth of levels averages of 10-20 m.

The obtained results allow us to make the following conclusions on the history of the development of the Chuya and the Katun valleys. During the Neopleistocene and Holocene there was an intensive directed cutting of a river network of Southeast Altai, interchanging with filling stages of the valleys. In the Middle Neopleistocene, when the Chuya and the Katun river valleys filled with a large number of clastic materials, there was a partial alignment and flattening profile of the valley. The presence of numerous signs of covering solid bases of high terraces and great thickness of sediments (Inya thickness), filling the deepening of the valleys, says that the primary roughness of the basement bed of valleys was significant. The drilling data near the mouth of the Ina river have showed the depression of basement bed of the Katun’s river valley more than 80 meters relative to modern of the river edge in this area [2, 3]. This means that the formation of Inya thickness sediments has been occurred in more sharp bend of the valleys profile. In subsequent stages of development of the valleys the slope of the rivers changed insignificantly, which is expressed in the reiteration of the slope terraces and modern thalwegs of the rivers in the longitudinal profile. The fanlike type of terraces splitting terraces is caused by activity of exogenous processes in the conditions of the general basin elevation. It is known that the role of tectonics in this case is only the background which is superimposed by the exogenous rhythms of relief origin. During the Neopleistocene intensity of erosion-accumulative processes in Gorny Altai was generally depended on repeated climate changes [4].

The study was supported by RFBR Grant № 10-05-00673а and by interdisciplinary integration projects of SB RAS № 53, 147.

Sections of the Katun river valley		Kadrin - Ailagush	Ailagush – B. Ilgumen		B. Ilgumen - Saldjar		Saldjar – B. Jaloman		B. Jaloman - M. Jaloman		M. Jaloman - Inya		Inya - Chuya		Chuya -L.Inegen		L.Inegen - H.Inegen		H.Inegen - Sok-Jarik		Sok-Jarik - Ebelu		Ebelu - Argut		Argut - Kaznahta
Mark of the river edge (m)		633,9-640	640-656,4		656,4-675		675-680		680-690,4		690,4-701,4		701,4-722,3		722,3-733		733-741		741-744		744-750,1		750,1-765,8		765,8-773
№ of level		The height of the terraces on the edge of the river (м)
Low and middle terraces	I	1
	II	3-2		2				2-1
	III	5		5		4		3
	IV	28-25				20		15		15-10		5-3
	V	45				30, 25				20,12		6
	VI	50		50-35		30, 27, 30-27		25
	VII			45		40, 35				32-27		8
	VIII					42-40,35
	IX			60-55		50, 45, 42, 40, 37				35-32		15		1-2
	X					50, 47-43								5		2
	XI					50, 49-45		45, 42								7-5		2-1
	XII									46, 40-37		40-37								7				5		2
	XIII					52-50		48, 48		50-45		42-40		21		17		20-18		18-15		13		10
	XIV					58-55		55
	XV							60, 55				50-47		42-40,26		26		25-20				33-30
	XVI					70-60						55-52				32						35		35-33		35
	XVII					85-80						70-65,63-60, 60		60-47,44-41		47-45		47-45
	XVIII											70-68				56
	XIX											75		67-62		64-62		56						50-45		45-43, 43-40
	XX													72-70		70
	XXI													83-78				76				80, 75		70
	XXII															85
	XXIII													102-100		100-102		100		95-90				85
High terraces	XXIV					135		130		125-120				114		111-108		110
	XXV															135-130		125		125-120				115-110
	XXVI									145-140				140-138		140-135		132
	XXVII							160										145				146
	XXVIII					175, 170		170				160-158, 165-155		157, 154, 158-156
	XXIX									180-170						170-175
	XXX											190-186		183-180		185-170
	XXXI											195, 190						184-180
	XXXII					230-225								205		203, 200-195						200-187		192		215
	XXXIII													267-258, 260-258

Table. The heights position of erosion levels of the middle Katun valley of various sections.

References:

1. Ivanovsky L.N. (1998)The study of river terraces in the Central Altai, Geography and natural resources, 3,Geo, 133-140 pp. (In Russian)

2. Efimcev N.А. (1964) About the structure and origin of the anthropogenic sediments of the Chua and Katun rivers valleys in Altai, Bulletin of the commission for the study of the Quaternary period, 29,115-131 pp. (In Russian)

3. Bogachkin B.М. (1981) The history of tectonic development of the Gorny Altai in the Cenozoic, Moscow: Science, 132 p. (In Russian)

4. Sladkopevcev S.А. (1973) The development of river valleys and neotectonic, Moscow: Nedra, 184 pp. (In Russian)