GEOMORPHOLOGY AND GEOLOGY OF QUATERNARY DEPOSITS IN THE TOMSK URBAN AREA

B. V. Plotnikov

(Presented by Prof. Dr. K. V. Radugin)

The geological-geomorphological structure of the area of the city of Tomsk has been the subject of study by many geologists, geomorphologists, and soil scientists. Quaternary deposits were discussed by I. D. Chersky, A. M. Zaitsev, N. F. Kashchenko, V. A. Obruchev, M. E. Yanishevsky, S. S. Neustruev, K. V. Radugin, M. A. Usov, E. V. Shumilova, K. A. Kuznetsov, V. A. Khakhlov, L. A. Ragozin, B. V. Mizerov, M. P. Nagorsky, and others. Without dwelling on an analysis of all the known works, we shall consider only a few that remain of great importance at the present time.

In 1925, S. S. Neustruev, studying the post-Tertiary deposits of the Tom River, distinguished four terraces in the area of Tomsk: I—the floodplain terrace; II—the terrace above the floodplain, on which the food market and Gorky Street are located; III—the Middle terrace, on which the university and the main post office are located; and IV—the Upper terrace—the terrace of the Camp Garden.

In 1933, a group of the West Siberian Geological Exploration Trust headed by K. V. Radugin [8] carried out geomorphological studies along the Taiga–Tomsk line. On the basis of the results of these studies, K. V. Radugin distinguished seven independent terraces of the Tom River. Following A. M. Kuzmina [3], he subdivides the post-Pliocene deposits with reference to Alpine geochronology. K. V. Radugin established that between S. S. Neustruev’s III and IV terraces there is the Voskresenskaya terrace, and above IV (the Camp Garden terrace) two more may be distinguished: VI—the Rezhenka terrace and VII—the Voronovskaya terrace. In addition, above terrace VII, K. V. Radugin separately distinguished a leveled surface of the Tom–Chulym watershed, composed of a series of ancient post-Pliocene deposits (the Taiga clays).

One of the most recent published works devoted to the study of the relief of surface rocks and soils in the area of Tomsk is the work of K. A. Kuznetsov [1, 2]. K. A. Kuznetsov, studying the genesis and evolution of the soils of the terraces of the Tom River in the area of Tomsk, came to the conclusion that the soils of the low and high terraces differ in structure, genesis, and age. Using the scheme of the geomorphological structure of the Tomsk area proposed by K. V. Radugin, he agrees with Radugin’s identification of the IV Voskresenskaya terrace. K. A. Kuznetsov questions K. V. Radugin’s identification of the VI—Rezhenka and VII—Voronovskaya terraces as independent geomorphological elements, since analysis of the soils of the cover deposits of these terraces yields similar results. On this basis, K. A. Kuznetsov combines the Rezhenka and Voronovskaya terraces into one upper—sixth—terrace.

In studying the area of archaeological excavations on the Basandaika River, L. A. Ragozin [7] proposed his own scheme for subdividing the terrace complex of the Tom River, differing from the schemes proposed earlier. In his opinion, there are only three terraces within the territory of Tomsk. He regards the IV—Voskresenskaya—terrace of K. V. Radugin as the oldest terrace. The deposits of this terrace, along its northeastern margin, are inclined toward the side of more ancient deposits. In his view, the formation of the III terrace is connected with the Bystraya phase of Alpine tectogenesis. L. A. Ragozin considers the surface of the terrace to be primary. Its socle is located at an elevation close to the low-water level of the Tom River.

L. A. Ragozin regards as the second terrace above the floodplain the terrace on which the university and the post office are located, i.e., the third terrace according to K. V. Radugin. He considers the height of the terrace top to be primary, and not a lowered level, which ranges within 20–27 m. He agrees with K. V. Radugin’s opinion that the elevations of the terrace socle correspond to the low-water level of the Tom River.

According to L. A. Ragozin, the first terrace above the floodplain and the floodplain terrace correspond to K. V. Radugin’s second and first terraces.

All the high terraces (V, VI, VII) of K. V. Radugin are regarded by L. A. Ragozin as slopes of the watershed plateau.

B. V. Mizerov [4], studying the stratigraphy of Quaternary deposits in the eastern part of the West Siberian Lowland, when distinguishing river terraces, comes to the conclusion that the formation of deposits, expressed and not expressed in the relief of river terraces and river valleys corresponding to the modern river network, begins in the lower part of the Upper Quaternary.

A. M. Demidov and L. S. Skripko, in 1958 and 1959, studying the engineering-geological conditions of the reservoir of the Tomsk Hydroelectric Power Station on the Tom River (upstream from Tomsk), divide the entire complex of Quaternary deposits into floodplain and undifferentiated low terraces of the valley of the Tom River and its tributaries; the first terrace above the floodplain, with a sediment thickness of 10–18 m; the second terrace above the floodplain of the Tom River (Borovaya); the third terrace above the floodplain (Yarskaya); the fourth terrace above the floodplain of the Tom River (Lagernaya); and the fifth terrace above the floodplain (Voronovskaya).

In addition, they distinguish an erosional-accumulative plain represented by deposits of the proluvial-deluvial type, lying on Paleozoic rocks. These deposits evidently correspond to the taiga clays of K. V. Radugin [8].

The scheme for subdividing Quaternary deposits adopted by A. M. Demidov and L. S. Skripko is, in its essence, close to the schemes of S. S. Neustruev [5] and K. V. Radugin [8]. In it, the VI—Rezhenskaya terrace of K. V. Radugin is excluded, and the III—Yarskaya terrace is introduced; II—Borovaya, corresponding to III—Beloborodovskaya according to K. V. Radugin.

Most researchers, including S. S. Neustruev [5], L. A. Ragozin [7], and K. V. Radugin [8], based the subdivision of the Quaternary deposits composing the terraces mainly on the morphological features of the terraces (the height of the tops and socles). Some elevations were taken incorrectly. Thus, for example, the height of the top of the Universitetskaya terrace (the third according to K. V. Radugin) is 20 m lower than that of the Voskresenskaya. In accordance with this, the heights of the socles were also determined: for the Universitetskaya terrace—at the level of the Tom River or slightly above it, and for the Voskresenskaya terrace—9–10 m above the level of the Tom River. The age of the terraces was determined in the same way: the Universitetskaya, with lower surface elevations, remained younger than the Voskresenskaya. In fact, however, the socle of the Universitetskaya terrace is on average 10 m above the low-water level of the Tom River and 6–8 m above the socle of the Voskresenskaya terrace (Table 1).

The Rezhen and Voronovo terraces were quite incorrectly combined by K. A. Kuznetsov [2] into one, the sixth, mainly on the basis of the similarity of analyses of the soils of the cover strata. He failed to take into account the main point: that all the high terraces, beginning with the third and ending with the seventh, are covered by a single

Table 1

thickness of cover loams (silty, loess-like) and the soils formed on them, which are, in their composition, rather similar.

The area of the city of Tomsk is confined to the zone of junction of two large geological structures: on the one hand, the West Siberian Lowland; on the other, the Sayan–Altai folded zone. The development of these structures proceeded differently, and their oscillatory movements undoubtedly affected the junction zone, within which the area of the city of Tomsk is located.

Theoretical propositions developed by Academicians M. A. Usov [9, 10] and V. A. Obruchev state that oscillatory movements of the earth’s crust are reflected in every geological section. These oscillatory movements, developing in time and space, found their expression not only in the geological but also in the geomorphological structure of the area of the city of Tomsk.

Analyzing the large body of factual material collected on the terraces of the Tom, both on the right and on the left bank, the author concludes that all the terraces represent geological documents testifying that even in Quaternary time the area under study was not a region of absolute rest.

The history of formation of the Quaternary deposits of the area of the city of Tomsk is rather complex. It cannot be properly understood on the basis of morphological features or features of the soil cover, while remaining only within the boundaries of the Tomsk area.

When the geomorphological structure of the valley of the Tom in the Kuznetsk basin is compared with that in the area of the city of Tomsk, certain differences are observed.

According to E. V. Shumilova [15], in the Kuznetsk depression there are 8 terraces of the Tom; F. P. Nifantov, in the area of the city of Kemerovo, distinguishes—

there are 5 terraces; in the area of the city of Tomsk we have distinguished eight terraces. The number of river terraces in individual sections of a valley may vary. It depends on numerous factors: on the tectonics and the character of the rocks composing the given area, the type of valley, and the degree of preservation of the terraces and their deposits. Of great importance in subdividing the terrace complex is the degree to which the area has been studied.

It is characteristic that such differences occur even when comparing sections of the right and left banks of the Tom River near the city of Tomsk. The relative elevations of the surface of the left slope of the valley are lower than those of the right. According to our observations and according to the data of M. P. Nagorskii, on the left side of the valley superposed types of terraces, composed of Quaternary deposits, predominate, whereas on the right bank inset terraces predominate.

All this shows that a one-sided approach to assessing the geomorphological structure of a territory is unacceptable. The compilation of the most objective scheme for the geomorphological subdivision of an area is evidently possible only with the broadest study of all features of the area, using data on the morphology of the terraces, their lithology, stratigraphy, paleontology, and archaeology.

The materials obtained make it possible to answer a number of questions that for a long time had not been resolved and had been the subject of debate among researchers. In essence, the proposed scheme is a development of the scheme of K. V. Radugin.

According to the proposed geomorphological scheme (Table 1), at present only in the area of the city of Tomsk can eight terraces of the Tom River be clearly distinguished. All deposits of the Quaternary period in the territory studied, represented in the form of terraces expressed and not expressed in the relief, are subdivided by us into four age epochs: lower ($Q_1$), middle ($Q_2$), upper ($Q_3$), and modern ($Q_4$).

To the lower epoch are assigned the deposits of the Voronovskaya ($Q_1^1$) and Lagernaya ($Q_1^2$) terraces.

The middle epoch combines the deposits of the Vokzalnaya ($Q_2^1$) and Universitetskaya ($Q_2^2$) terraces. To the upper epoch are assigned the deposits of the Voskresenskaya ($Q_3^1$) and Superposed ($Q_3^2$) terraces, and to the modern epoch—the deposits of the Zaoistochnaya ($Q_4^1$) and Zaozernaya ($Q_4^2$) terraces.

Morphologically, all the terraces may be divided into high (VII, VI, V, IV), middle (III), and low (II and I) terraces. The elevations of the tops of the terrace socles are taken relative to the low-water level of the Tom River and are shown in Table 1.

In the northern part of the city all terraces, from the first through the eighth inclusive, occur.

In the southern part of the city of Tomsk there are the second, third, fourth, fifth, sixth, seventh, and eighth (superposed) terraces, with the primary forms of the third and fourth terraces lowered as a result of the erosional activity of the Ushaika River; naturally, their present surface elevations fluctuate within 30–40 m.

In distinguishing the terraces as independent geomorphological units, a major difficulty was the establishment of stratigraphic boundaries between the alluvial deposits composing the different terraces and the thickness of loess-like and silty loams covering all the high terraces.

Finds of mammoth remains at the base of the loess-like sequence of the Camp Garden and on the third terrace (on Voskresenskaya Hill), finds of pelecypods (by the engineer of Tomgiprotrans, S. M. Bolshakov) in the sequence of cover loams of the middle and high terraces, well traceable in sections of all the high and middle terraces, horizontally bedded—

...sands with rare pebbles and gravel, lying at the base of the mantle loess-like and silty loam sequence, make it possible to distinguish the mantle loess-like sequence, together with the underlying layer of horizontally bedded sands with rare pebbles, as an independent terrace of the superimposed type (Table 3). It turns out that the middle and all the high terraces, beginning with the third and ending with the seventh (inclusive), are buried terraces.

The socles of the first, sixth, and seventh terraces are loose Paleogene deposits represented by clays and sands. For the second, third, fourth, and fifth terraces, the socles are Paleozoic clay shales and sandstones, or their eluvium. A certain exception is represented by areas situated north of the city of Tomsk, i.e., in the valley of the Kirgizka River, where the socles of all terraces consist of loose Paleogene deposits. Brief descriptions are given below of the factual material confirming the scheme we propose.

The factual material collected by the author for the Tomsk area makes it possible to distinguish a complex of Quaternary sediments represented by the alluvium of the Tom River. This complex of deposits is expressed in the form of accumulative terraces of inset, superimposed, and buried types.

In the formation of accumulative terraces, a definite sequence in sediment accumulation is observed.

The formation of the middle and high terraces took place in 3 stages: the stage of downcutting erosion, the stage of lateral erosion, and the stage of valley aggradation. In the first stage, downcutting erosion takes place with a very slight accumulation of channel alluvium in the form of coarse clastic material: boulders, pebbles, gravel, and various-grained sands. In the second stage (the stage of lateral erosion), basal pebble beds and floodplain deposits are deposited simultaneously, i.e., channel and floodplain alluvium are deposited. Here, deposits of oxbow alluvium are also developed to a minor extent. In the third stage, i.e., in the stage of valley aggradation, it is filled with fine-clastic material that is less of oxbow origin. In cross section these deposits resemble lens-shaped bodies.

The low terraces pass through two stages of their formation—the stage of downcutting erosion and the stage of lateral erosion. As a result, the second and first (floodplain) terraces are composed of channel and floodplain alluvium, with a minor development of oxbow alluvium.

All terraces of the right bank of the Tom River near the city of Tomsk have clearly expressed socles, which become lower from the ancient to the younger terraces. The socles of the high and middle terraces (VIII, VII, VI, V, IV, and III) lie above the low-water level from 60.0 to 3.0 m.

At the base of the terraces, as a rule, lies clastic material consisting of pebbles, gravel, and more rarely boulders with various-grained sand, representing deposits of the channel type. The thickness of these basal terrace layers reaches 10 m on the right bank and up to 25 m on the left bank of the river.

The basal pebble beds of all terraces (from the first to the seventh) are overlain by silty clays with very thin interlayers of plant remains, mainly at the top of the layer. By genesis these clays are of the floodplain type. Their color varies from gray with a bluish tint to dark blue. In deposits not exposed at the ground surface, opened by artificial excavations—for example, in the Kashtak quarry—the clays are blue in color. This indicates the reducing environment in which the clays accumulated and in which they have lain up to the present time.

Pebble beds of the third, fourth, and fifth terraces are overlain by clays of this color, where the groundwater level lies above the top of the layer of silty clays.

Schematic geomorphological structure of the valley of the Tom River in the area of the city of Tomsk

Visible elevation scales: 320, 310, 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200 m; left scale also shows 190, 180 m.

Visible labels in the diagram:

• Tom River
• \(I\text{-}Q_3\)
• \(II\text{-}Q_3\)
• \(III\text{-}Q_3\)
• \(IV\text{-}Q_2\)
• \(V\text{-}Q_2\)
• \(VI\text{-}Q_2\)
• \(VII\text{-}Q_2\)
• \(P_3\)
• \(P_2\)
• \(C_1\)
• \(P\text{-}T\) [[unclear: accompanying inscription within the lower unit]]

Legend:

• \(IV\text{-}Q_2\) — number and age of the terrace
• □ — disjunctive fault

The basal pebble beds of the sixth and seventh terraces are overlain by clays of brown and yellowish-brown colors, especially where they occur in the oxidation zone, which also accounts for their color.

The clays overlying the basal pebble beds of the first and second terraces are gray and dark gray, with a bluish tint at the base of the layer. This can be explained by the large amount of humus, whose content at the top of the layer reaches 30%. Here the groundwater level lies somewhat above the base of the clay layer. The thickness of the clayey layer reaches as much as 8.0 m.

On all the high and middle terraces (the seventh, sixth, fifth, fourth, and third), above the clays there lies a stratum of the aggradational-alluvium type, represented by cross-bedded, predominantly fine- and medium-grained quartz–feldspar sands, sandy loams, loams, and, less commonly, clays and lenses of gravel. The thickness of this type of deposit reaches 40 m. On the low (first and second) superimposed terraces such deposits are absent.

In the aggradational alluvium a regularity is observed in the sediment accumulation of the individual interbeds and of the entire stratum. At the base of the layer there is coarser-grained material than at the top of the layer, i.e., there is a change in the granulometric composition of the section from bottom to top. A rhythmicity is observed in the accumulation of Anthropogene sediments.

The mineralogical composition of both the heavy and the light fractions of the terrace sediments differs little from one another. Among the minerals of the light fraction, quartz, feldspar, and clay minerals are most widespread.

Among the minerals of the heavy fraction, the most frequently encountered are epidote–zoisite, leucoxene, hornblende, and pyroxene; zircon, rutile, and sphene are rarer. Ore minerals are widely distributed.

The uniform and rather persistent mineralogical composition of the terrace sediments, both in the horizontal and in the vertical direction, allows us to conclude that there was a constant source area for the clastic material accumulated in the Quaternary period in the Tomsk region.

Since the mineralogical composition of modern channel and floodplain deposits, including the deposits of islands and spits, differs hardly at all from the mineralogical composition of terrace deposits, and since the source area of the modern deposits is the Sayan–Altai mountain region, the question of the constancy of the hydrographic network in the latest period of the Cenozoic raises no doubt for us.

The climatic conditions of sediment accumulation of the terrace deposits may be compared with the modern climate by the content of a certain fraction of feldspar and quartz (for the section as a whole).

Under warm climatic conditions, the content of feldspar is less than that of quartz of the same fraction. Therefore, it may be said that the climatic conditions of accumulation of the clastic material of the first and second terraces were close to modern conditions.

The accumulation of sediments of the fourth, sixth (with the exception of the basal pebble beds and varved clays), seventh, and eighth terraces took place under warmer conditions than those of the first and second terraces, while the sediments of the third and fifth terraces accumulated under intermediate climatic conditions, i.e., under conditions colder than those of the fourth, sixth, seventh, and eighth terraces.

The age of the terrace formations, and consequently of the terraces of our scheme, was determined mainly from paleontological remains, from the elevations of the plinths, and from the stratigraphic position of the individual layers of the entire terrace, and fits well into the stratigraphic scheme of the fourfold division of the Anthropogene proposed by S. B. Shatsky,

S. G. Boch, I. I. Krasnovym, and others for the West Siberian Lowland.

If, in subdividing Anthropogene deposits, one does not take into account the regularities in the formation of alluvial sequences and does not trace each of the layers of the sequence over the area of its distribution, then the basal pebble beds or the floodplain deposits resting upon them, having similar elevations of the base, soil horizons, and tops of the beds, a similar character of the constituent rocks, and similar granulometric and mineralogical composition, may be combined into coeval beds. This will completely distort the concept of the terrace complex of Anthropogene deposits. If each complex of deposits reflects one tectonic cycle, then, by combining beds, we shall obtain a reduced number of tectonic cycles, and this means also the number of terraces.

Each tectonic impulse corresponds to a definite sedimentary complex, expressed in our region by terraces. The workers of the Tomsk Complex Expedition, without taking the above circumstances into account, combined channel and floodplain deposits of low terraces that are different in age but close in their elevations into one first terrace of the Tom River. The same was done with the third (Voskresenskaya), fourth (Universitetskaya), and fifth (Vokzalnaya) terraces that we identified. They were combined into one third terrace of the Tom River. Such a “pulling up” of the geological structure of the Tomsk region to a unified scheme leads to a distorted idea of the geological structure of the region. This method is condemned by major geologists of our country (N. I. Nikolaev, L. A. Ragozin, and others), and it must be abandoned.

Local stratigraphic schemes must reflect the true geology of the region, and, with the proper approach to the study of the geological structure of the region, they must fit into a general—unified—scheme, if the latter has been compiled on the basis of particular schemes.

REFERENCES

1. Kuznetsov K. A. Soils of the environs of the city of Tomsk. Proceedings of TSU, vol. 92, series G, 1937.

2. Kuznetsov K. A. Soils of the southeastern part of the West Siberian Plain. Proceedings of TSU, vol. 106, soil-science series, 1949.

3. Kuzmin A. M. Materials toward the subdivision of the glacial period in the Kuznetsk-Altai region. Izvestia of the West Siberian Branch of the Geological Committee, vol. VIII, 1929.

4. Mizerov B. V. Some principal moments in the Cenozoic history of the Tomsk Cis-Ob region. Proceedings of TSU, vol. 124, Tomsk, 1953.

5. Neustruyev S. S. On the question of the study of post-Tertiary deposits of Siberia. Soil Science, No. 3, 1925.

6. Nikolaev N. I. Recent Tectonics of the USSR. Publishing House of the Academy of Sciences of the USSR, vol. 8, 1949.

7. Ragozin L. A. Geological sketch of archaeological excavations on the bank of the Tom River at the mouth of the Basandaika River. Proceedings of TSU, vol. 98, Basandaika, 1947.

8. Radugin K. V. Materials on the geology of loose deposits of the Tomsk–Taiga region. Publication of ZSGGGT, issue 9, 1934.

9. Usov M. A. Elements of the geomorphology and geology of loose deposits. ZSGU Publishing House, Tomsk, 1934.

10. Usov M. A. Phases and cycles of tectogenesis of the West Siberian Territory. Tomsk, 1936.

11. Khakhlov V. A., Ragozin L. A. Stratigraphy of Quaternary deposits of the southeastern part of Tomsk Oblast. Notes of TSU, No. 9, 1948.

12. Shantser E. V. Alluvium of rivers of the temperate belt and its significance for understanding the regularities of the structure and formation of alluvial suites. Academy of Sciences of the USSR, Proceedings of the Institute of Geological Sciences, issue 135, geological series (No. 55), 1951.

13. Shumilova E. V. Lithology of the loose sequence of the section beneath the Camp Garden near the city of Tomsk. Bulletin of the West Siberian Trust, issue No. 4, 1936.

14. Shumilova E. V. Terraces of the Tom River in its middle course. Materials on the Geology of the West Siberian Territory, issue 8, Tomsk, 1934.

1. Yanishevsky M. E. On the Miocene flora of the environs of Tomsk. Proceedings of the Geological Committee. New series, issue 131, 1915.

2. Ragozin L. A. Features of the neotectonics of the valley of the Yenisei River from Krasnoyarsk to the mouth of the Bolshaya Pit River. Materials on the Geology of Krasnoyarsk Krai, Gosgeoltekhizdat, 1960.