STRATIGRAPHIC SECTION AND GENESIS OF QUATERNARY DEPOSITS ON THE RIGHT SLOPE OF THE TOM RIVER NEAR THE VILLAGE OF STARO-ABASHEVO (Kuzbass)

E. D. RYABCHIKOVA

(Presented by Prof. A. G. Sivov)

Among the Quaternary deposits of Kuzbass, loess rocks are widely distributed. Separate data on their composition, structure, thicknesses, and conditions of occurrence are available in the works of A. M. Kuzmin [5], E. V. Shumilova [14], F. P. Nifantov [10], B. F. Mikhalchenko [8], Yu. B. Fainer [13], and other researchers. However, none of them dealt specifically with the lithology, paleontology, and stratigraphy of loess rocks. In addition, all the Anthropogene sections described by the above-mentioned geologists are located north of the city of Novokuznetsk.

In studying the loess rocks of the southeastern part of Kuzbass, our attention was drawn to the stratigraphic section near the village of Staro-Abashevo, situated approximately 20 km south of the city of Novokuznetsk. The steep bluff of the right bank of the Tom River, reaching a height of 30–36 m and gradually decreasing toward the village, which is located on the terrace of the Abasheva River, is composed mainly of loess rocks. This section of Quaternary deposits is the only one on the right bank of the Tom River in the stretch from the city of Mezhdurechensk to Novokuznetsk. The outcrop extends along the river for 700–800 m, merging with the watershed southeast of the village.

The socle of the terrace, represented by Permian argillites and aleurolites, rises 6 m above the low-water level of the Tom River. Layer-by-layer facies-mineralogical analysis of the section (compiled from a deep excavation in the bank bluff) made it possible to determine the composition and structure of the terrace and of the overlying loess deposits.

The description is given from bottom to top.

1. At the base of the terrace sequence lies a bed (3.2–3.5 m thick) of pebble deposits with a gravelly-sandy-clayey filler. The pebbles are polymictic, covered with a rusty film of iron hydroxides, owing to which they acquire a reddish coloration. The pebble, gravel, and sand material includes well-rounded fragments of white and black flint, quartzites, sandstone, argillite, and igneous rocks. There is a considerable admixture of coal fragments. The sandy and aleuritic grains consist mainly of fragments of quartz, feldspars, mica, and clayey pellets. The sizes of the pebbles gradually decrease toward the top. Judging by the composition, conditions of occurrence, good roundness, and sorting of the pebble material, the described bed of pebbles is associated with the facies of channel alluvium.

2. Upward in the section, the loose pebbles are gradually replaced by ze...

Bulk chemical composition of Quaternary deposits of the Staro-Abashevo exposure

Table 1

grayish-brown sandy-clayey deposits, which at the base have oblique discontinuous bedding owing to lens-like accumulations of gravelly-sandy material with a large number of ferruginous-manganese concretions. The thickness of the member is 3.0–3.5 m. Toward the top of the member the material becomes increasingly fine, the content of coarse dust increases (Table 2), and the rock acquires a loess-like appearance (clearly visible in the dry state): looseness, macroporosity, and a considerable amount of the “loess” (0.05–0.01 mm) fraction—39.1–41.6%. Effervescence with hydrochloric acid is absent throughout the member. This is already, probably, alluvium of the floodplain facies, which emerged onto the subaerial surface from below the river level and here, under subaerial conditions, acquired a loess-like appearance. The loams are penetrated by a large number of cylindrical branched cavities formed in place of decayed roots of herbaceous plants.

1. The loessified alluvial loams are capped by a gray buried soil (1.5 m thick), which also confirms an interruption in sedimentation and emergence onto the subaerial surface. The transition boundary between them in the exposure is difficult to discern.

The dark grayish-brown humus subhorizon is unevenly colored because of numerous brownish-yellow spots of iron oxides; it is very dense, with a well-expressed fine-nutty structure, which downward becomes prismatic. The cavities between structural units are filled with amorphous silica, and the faces are coated with dark films of sesquioxides.

The analytical data summarized in Tables 1, 2, and 3 fully reflect the structure of the genetic profile of this soil: absence of carbonates, low humus content, comparatively high content of silica (62–67%), and low quartz content (45.5%).

In morphological features the buried soil resembles the modern light-gray podzolized forest gley soil. The conditions of occurrence, sandiness, ferruginization, insignificant humus content, and complete absence of carbonates allow it to be assigned to the class of hydromorphic soils. Until additional data are obtained, we shall provisionally call it a “gray” alluvial soil.

1. Upsection, the gray buried soil is overlain, with erosion, by a member of yellow-brown, noncarbonate, homogeneous loess-like loams with numerous cavities from plant roots, indicating the participation of the soil-forming factor in their formation.

The presence of small lenses of sand, gravel, fine fragments of argillite, gray patches of clearly aqueous loam, brown spots of iron oxides, and also the mechanical composition (Table 2) indicate an aqueous origin of the parent rocks, transformed under the subaerial conditions of a dry climate into loess-like loams. At the same time, the possibility of an influx of aeolian dust is not excluded (the “loess” fraction in the top amounts to 53.6–54.1%).

The total absorption capacity of the loess-like loams, characterizing their absorptive ability, was determined by the method of L. I. Kul’chitskii [6] on an FEK-M-56 photoelectrocolorimeter. Its value in this member is 18.4–23.9 mg-eq per 100 g of rock, which is in full agreement with the hydromica composition of the colloidal fraction (according to thermal-analysis data) and the mechanical composition. Organic matter was determined by the method of I. V. Tyurin using phenylanthranilic acid as an indicator [1]. The humus content in this member is low—0.17–0.34%.

The silt and fine-sand fractions (0.01–0.25 mm), which constitute the bulk, were subjected jointly to mineralogical analysis.

Table 2

Granulometric composition of Quaternary deposits* of the Staro-Abashevo section

* The analysis was carried out by the pipette method, with preparation of samples by microaggregate analysis. Performed by engineer of the lithological laboratory of the Tomsk Polytechnic Institute E. K. Chuguevskoi.

loess rocks. From them, heavy and light minerals were separated with Thoulet’s solution and identified by the immersion method*. The principal rock-forming minerals are quartz and feldspars (Table 3), which, together with the other minerals of the light fraction, constitute more than 98–99% of the insoluble mass of the rock. The yield of the heavy fraction is only 0.37–1.8%.

Despite its insignificant content, the heavy fraction is rich in mineral species; it includes as many as 15–20 minerals.

Ore minerals, represented as grains of magnetite and ilmenite, amount to 19–24%.

Minerals of the epidote group are represented mainly by epidote, which varies from 37 to 46.5%. It occurs as irregularly shaped, weakly greenish, subrounded and angular fragments.

Of the amphiboles, the loess-like loams of this section (including the described member) contain abundant green hornblende (25.5–28%) and isolated grains of tremolite and actinolite.

Minerals of the resistant group occur in small amounts: zircon, tourmaline, garnet, rutile, and leucoxene. Together they make up 6–7%.

In addition, sphene, limonite, apatite, and muscovite are constantly present in the heavy fraction.

From the mineralogical characterization given above it follows that, among the heavy minerals of the Quaternary deposits, minerals unstable under weathering predominate, namely hornblende and epidote. The weathering coefficient (the ratio of the sum of resistant minerals to unstable ones) is 0.39–0.53, which, together with the external appearance of the minerals, indicates weak weathering of the loess rocks [12].

To resolve the question of the origin of the loess-like loams of this member, attention should be paid to its sandiness, the presence of small lenses of gravel and sand at the base of the member, brown spots of iron oxides, individual spots of gray silty loam, the complete absence of carbonates, and a gradual increase in the content of the coarse-silty fraction toward the top of the member. The loess-like appearance was probably also acquired by the rock in the process of weathering under subaerial conditions, with greater or lesser participation of aeolian and deluvial factors.

1. The middle horizon of the buried soil, formed on the underlying loess-like loams, has the following morphological features: a whitish color with a brownish tint; a well-expressed fine-nutty structure, which downward becomes prismatic. Cavities between structural units are filled with amorphous silica, and the faces are covered with dark films of sesquioxides. Effervescence with hydrochloric acid is absent throughout the entire profile.

The humus content decreases downward through the soil profile from 0.88% to 0.17%. The maximum absorption capacity, 28 mg-eq per 100 g of rock, falls in the illuvial horizon, into which colloidal solutions carried down from above were washed; in the humus subhorizon its value is 19.9 mg-eq.

In morphological features and the available analytical data, this buried soil resembles a modern light-gray podzolized gley forest soil. But there are still insufficient data to clarify the genesis of the described buried soil.

1. Upward in the section, the buried soil is replaced, without a sharp transition—

* The analyses were performed in the mineralogical laboratory of the West Siberian Geological Administration.

Table 3. Mineralogical composition of the Quaternary deposits of the Staro-Abashevo exposure

the section by a new bed of light yellow-brown loess-like loams, macroporous, nonbedded, silty, and carbonate-bearing at the base of the bed. The thickness of the bed is 3 m.

The mechanical composition of the loess-like loams of this bed is exceptionally homogeneous (Table 2). The predominant fraction is the coarse-silty “loess” fraction according to N. I. Kriger [4] (58.0–58.5%). Among the distinctive features of the chemical composition one may note an increased content of ferric oxide (1.40%) and calcium oxide (2.77%).

The mineralogical characteristics (Table 3) of the loess-like loams of this bed differ from those given above only quantitatively. Characteristic is the highest content of mica (20%) and calcite (2.5%).

According to the results of thermal and electron-microscopic analyses, the colloid-dispersed fraction is represented by hydromica with a small admixture of calcite and thermally inert minerals.

The presence of all the features of loess rocks, the consistent granulometric and mineralogical composition, the absence of bedding, a slight admixture of fine gravel of local rocks, and numerous voids left by the roots of herbaceous plants make it possible to suggest their eolian-deluvial origin, accompanied by the superposition of soil-forming processes.

1. Before proceeding to describe the upper buried soil, it is necessary to note certain features of the conditions of its occurrence. All the beds of loess-like loams and buried soils described above are arranged parallel to the basal channel gravel. The upper buried soil and the cover loess-like loams lie mantle-like, following the relief of the older rocks. Evidently, the terrace deposits and the deposits of the upper bed of loess-like loams overlying them (bed 6) were denuded after deposition, and this relief is repeated by the upper buried soil and the cover loess-like loam. Their mantle-like occurrence is well traced along strike without cuttings, since the upper buried soil is marked by a strip of wormwood and other herbaceous plants growing above the bluff along the bank at the place where the soil crops out. The cover loess-like loam is not turfed over, holds vertical columns 3–4 m high well, and tracing its conditions of occurrence presents no difficulty.

The upper buried soil, with a total thickness of 1.7 m, has different morphological features than the two lower ones. It is a dark-brown silty-sandy loam, weakly porous, structureless, and noncarbonate. At the base of the buried soil and in the top of the underlying parent material, the so-called “krotoviny” are visible—sections of burrows of various burrowing animals, filled with crumbs consisting of a mixture of particles from different soil horizons [2].

Humus is distributed unevenly in the profile of the upper buried soil: at the top (7.4–8.1 m) it amounts to 0.71–0.81%, and in the illuvial horizon to 0.38–0.24%. The value of the absorption capacity increases toward the base of the soil from 21.8 to 27.4 mg-eq per 100 g of rock.

The morphological features, as well as the distribution of humus, the great thickness of the soil, and the presence of ancient krotoviny may indicate a similarity of the upper buried soil to chernozems.

1. The section is crowned by cover loess-like loams (thickness 5–6 m), on which the modern soil has developed. It has already been noted above that the loess-like loams, following the eroded, more ancient relief, form, as it were, a ridge, with its gentle side directed downward along the course of the Tom River and toward the Abasheva River, i.e., they lie mantle-like, descending from the watershed of the Tom River (this is indicated by mate-

materials of the geological survey). The loams possess all the characteristics of loess deposits: a light yellowish-brown color, loose, floury, macroporous, with numerous small cylindrical cavities (up to 1 mm in diameter) formed in the places of decayed roots of herbaceous plants (in some, decayed fragments of plants have been preserved).

In the loesslike loams a mass of small gastropod mollusks was collected; according to the determination of A. S. Steklov, they all belong to the “loess” complex and are terrestrial.

So far four species of mollusks have been collected, the latter being distributed irregularly. This, in our opinion, should indicate that they were not washed in from elsewhere, but were buried in place.

The results of laboratory analyses likewise reveal all the properties of loesslike deposits in the loams described.

The predominant fraction in the mechanical composition is the coarse-silty “loess” fraction [4]—48.7–63.6%. Carbonate content varies from 0% (under the modern soil) to 3.98%. The humus content is relatively high, 0.22–0.57%.

The value of the absorption capacity, 16.9–24.8 mg-eq per 100 g of rock, is in full agreement with the hydromicaceous type of the colloidal clay fraction and its relatively high content (the fraction <0.005 mm amounts to 16.9–28.0%).

The pH value of the suspension of the loesslike loams, determined on an LPU-01 potentiometer, reaches 8.27–8.39 in the described bed, which corresponds to alkaline conditions and is explained by the presence of calcium carbonates.

In the chemical composition of the cover loesslike loams, silica predominates (61%), followed by aluminum oxide (13.94%). The calcium oxide content (5%), in comparison with other beds of loesslike loams, has increased severalfold.

By the value of the silica coefficient (the ratio of silicon oxide to aluminum oxide), which reflects the zonality of weathering processes, the south of Kuzbass may be compared with eastern Stavropol [7].

The mineralogical composition of the cover bed differs little from that of the above-described underlying rocks.

The sheetlike occurrence of the cover loesslike loams, their sustained thickness throughout the section, their homogeneous silty composition, and the presence of terrestrial mollusks occurring through the entire thickness make it possible to assume an aeolian genesis for these deposits. The presence of a small quantity of fragments (2–10 mm in size) of local rocks indicates the participation of deluvial processes in the formation of the products of this unit. The processes of weathering and soil formation transformed the deposited material in the syngenetic and epigenetic stages.

Spore-and-pollen studies carried out for all the samples collected did not yield positive results. All the samples proved to be barren.

The age of the Anthropogene deposits of the Staro-Abashevo section can for the present be judged only from indirect data. Judging by the height of the scarp, the complex structure of the section, in which three buried soils are distinguished, and the elevation of the section surface, this is probably the third floodplain terrace. According to the scheme of Yu. B. Fainer [13], the alluvium of the third floodplain terrace formed in Middle Pleistocene time. As was shown above, after deposition of the terrace alluvium and its transformation by weathering processes into loesslike loams under subaerial conditions, the terrace surface was denuded; to this

probably required a considerable amount of time. Consequently, the cover member of loess-like loams, which overlaps, in addition to the third, also the second above-floodplain Upper Quaternary terrace (as indicated by drilling materials obtained during geological mapping work by the parties of the West Siberian Geological Mapping Expedition), is probably no older than the second half of the Upper Pleistocene.

The characteristics of the geological section near the village of Staro-Abashevo serve as evidence that the basis for developing a detailed stratigraphic scheme of the Anthropogene in loess areas should be reference sections studied by a complex of methods. Ancient fossil soils have important paleogeographic significance, making it possible, when their genetic type is correctly determined, to reconstruct a broad complex of the physical-geographical conditions of the past (climate, vegetation, etc.) [3].

LITERATURE

1. E. V. Arinushkina. Guide to the Chemical Analysis of Soils. Moscow State University Press, 1962.

2. S. G. Boch, V. I. Gromov, K. V. Nikiforova, V. V. Popov, E. V. Shantser, and others. Brief Field Manual for Comprehensive Geological Surveying of Quaternary Deposits. Moscow, 1957.

3. I. P. Gerasimov. Buried soils and their paleogeographic significance. In: Materials of the All-Union Conference on the Study of the Quaternary Period, vol. I, Academy of Sciences of the USSR Press, 1961.

4. N. I. Kriger. Loess, Its Properties and Relation to the Geographical Environment. Nauka, Moscow, 1965.

5. A. M. Kuzmin. Materials toward the subdivision of the glacial period in the Kuznetsk-Altai region. Proceedings of the West Siberian Department of the Geological Committee, vol. VIII, issue 2, Tomsk, 1929.

6. L. I. Kulchitsky. Determination of the absorption capacity of clays by the method of adsorption of the organic dye methylene blue. Weathering Crust, issue 3, 1960.

7. A. I. Larionov, V. A. Priklonsky, V. P. Ananyev. Loess Rocks of the USSR and Their Construction Properties. Gosgeoltekhizdat, Moscow, 1959.

8. B. F. Mikhalchenko. On the stratigraphy and lithology of Quaternary deposits of the western part of the Kuznetsk Basin. Proceedings of TPI, vol. 151, Tomsk, 1966.

9. S. S. Morozov. An attempt to study the material composition and physical properties of buried soils of different genetic types in Quaternary deposits of Ukraine and the Central Chernozem belt for paleogeographic purposes. In: Materials of the All-Union Conference on the Study of the Quaternary Period, vol. I, Academy of Sciences of the USSR Press, 1961.

10. B. P. Nifantov. Engineering-geological characterization of loess-like rocks of the Belovo district of Kuzbass. Collection of Scientific Papers, vol. VII, TISI, Tomsk, 1960.

11. M. F. Veklich, A. T. Artyushenko, N. A. Sirenko, and others. Reference Geological Sections of the Anthropogene of Ukraine, part 1. Naukova Dumka, Kiev, 1967.

12. A. S. Ryabchenkov. On the question of the origin of the loess of Ukraine in the light of mineralogical data. Bulletin of the Commission for the Study of the Quaternary Period, no. 20, 1955.

13. Yu. B. Fainer. History of the Development of the Kuznetsk Basin in the Mesozoic and Cenozoic Eras. Dissertation. Novosibirsk, 1967.

14. E. V. Shumilova. Terraces of the Tom River in Its Middle Course. Publication of the WSG, G.G.G., Tomsk, 1934.