On the Characterization of Quaternary Deposits of the Urop Coal Deposit in Kuzbass

A. A. Kurbatova, E. D. Ryabchikova, E. K. Chuguevskaya, V. M. Kabanova

(Presented by Prof. Dr. A. G. Silov)

In the Urop-Yuzhny area of the Urop coal deposit, boreholes 1066 and 1062 (Inskaya exploration line), drilled by the Urop Geological Prospecting Party, exposed a section of Quaternary formations 45–49 m thick. This is one of the most complete sections on the right bank of the Inya River.

Lithologically, this section is divided rather clearly into three parts: upper, middle, and lower. The upper part of the section (10–15 m thick) is composed of loess-like loams containing buried soil horizons. The main characteristics of this unit are as follows: in their grain-size composition there is a predominance of the silt fraction, 52.81–72.5% (according to microaggregate analysis), with “loess” dust predominating over fine dust. In terms of the content of the clay fraction (\(<0.005\) mm), the loess-like deposits are heavy silty clays.

Chemical analysis of the loess-like loams and clays shows their relatively higher carbonate content (2.6–6.2%), elevated pH value (8.0–8.3), reduced absorption capacity (16.9–25.3 mg-eq/100 g of rock), and insignificant humus content (0.21–0.38%, more rarely 0.45–0.52%). The laboratory analyses carried out make it possible to distinguish the buried soils from the enclosing rocks not only by their increased humus content (0.48–1.45%), but also by the increased content of the clay fraction, up to 31.3–40.5% (according to microaggregate composition), the absence of carbonate content, and elevated values of absorption capacity.

The middle part of the section (6–17 m thick) is represented by loams and clays of yellow-brown and grayish-brown color, and by ferruginized dark-brown clays in borehole 1062.

The lower part of the section of the Quaternary sequence in the Urop-Yuzhny area is composed of the so-called “blue” clays, more rarely loams, of lacustrine-marsh facies. The latter fill irregularities of the ancient relief and were exposed by all boreholes of the Inskaya exploration line. These are gray, greenish-gray to dirty-gray, sometimes darker and denser, sometimes lighter and weakly cemented silty clays, more rarely loams, containing a large amount of plant detritus, as a result of which anomalous values of humus content are observed (up to 5.02%). Their heavier grain-size composition (clay fraction \(<0.005\) mm amounts to 26.34–50.79%) is consistent with the increased absorption capacity (from 16.9 to 33.8 mg-eq/100 g of rock).

In borehole 1066, at the base of the “blue” clays, there lies a layer of sandy-gravel-pebble deposits with a clayey matrix (1.6 m thick). The sizes of the pebbles, composed of quartz, siliceous shale, quartzite, and sandstone, reach 3×4 cm. The good rounding of the latter indicates the accumulation of this layer under channel conditions. The cement contains frequent admixtures of coal and soot; all the foregoing points to erosion of the underlying coal-bearing strata.

The mineralogical composition of the section studied is as follows: among the minerals of the light fraction, quartz and feldspars predominate. The amount of quartz in the loess-like loams (35–45%) and in the buried soils (40–47%) remains more or less the same. The feldspar content decreases somewhat in the buried soils (16–22%) compared with the loess-like strata (25–27%). In the remaining lithological varieties of the section, the amount of quartz (50%) and feldspars (22–30%) remains constant, with the sole exception of the very base of the section, where the quartz content in dense greenish-gray, locally parallel-thin-bedded clays falls to 30%, and that of feldspars to 13%, owing to an increase in the amount of fragments of clayey rocks. Moreover, the grains of these minerals are unrounded, more rarely subrounded, and have an irregular shape.

In the heavy fraction, epidote-zoisite is markedly predominant (41–60%), its content increasing in the buried soils and at the base of the section (up to 60%). The content of hornblende, however, decreases from top to bottom (from 23% in the loess-like loams to 6.3% at the base of the section).

The principal minerals of the colloid-dispersed fraction are hydromica and kaolinite, more rarely beidellite.

The mineralogical composition presented indicates a significant role of eluvial-deluvial processes in the accumulation of the loess sequence.

Palynological analysis made it possible to establish a rhythmic change in the vegetation cover during Quaternary time: several spore-pollen assemblages were obtained in the section studied; their description is given from the more ancient to the younger.

At the base of the section (interval 41–42 m), hygrophilous forms predominate (46%). These are spores of bryales, more rarely sphagnum mosses, mosses, Botrychium, and Equisetum; there are many indeterminate aquatic forms. Of the arboreal plants, only fir pollen is present (10%); the herbaceous spectrum is represented by pollen of mixed herbs, with a slight predominance of chenopods and wormwoods. Pollen grains of willow and hemlock are present here in small amounts but invariably.

The presence of coarse-clastic material at the base of the section studied and redeposited Tertiary pollen indicate erosion of Early Quaternary and more ancient deposits. Therefore, the age of the deposits containing the above spore-pollen assemblage, on the basis of the predominance in it of younger floral elements, may be dated to the lower horizons of the Middle Pleistocene.

The next assemblage (interval 36–33.5 m) is characterized by a sharp change in the quantitative ratios of the forms encountered: the content of hygrophiles decreases (9%); among arboreal plants, fir pollen is replaced by birch and alder pollen (4.5%); among herbaceous plants there is much pollen of chenopods (40%) and wormwoods (15.5%). The simultaneous presence in the assemblage of both hygrophiles and xerophytes is characteristic.

The spore-pollen assemblage from the interval of the section 33.5–22 m is characterized by the absolute predominance of xerophytes (up to 80%)—chenopods, wormwood, ephedra; by an even greater enrichment in mineralized grains of wormwood (21–20%); and by a small amount of arboreal pollen (6–4.3%), represented by pollen of birch and conifers, moreover,

one should note a sharp reduction in spruce pollen (to 2.5%), or its disappearance. A similar steppe complex has been described by a number of authors for territories adjacent to Kuzbass (G. F. Bukreeva, 1966; O. V. Matveeva, 1953, 1958; L. I. Efimova, 1966; A. A. Kurbatova and L. V. Aleksandrova, 1964) and is dated to the Middle Pleistocene.

The last complex (interval 18.5–8 m) is enriched in conifer pollen (to 21.6%), with spruce pollen predominating (to 15.8%). Birch pollen occurs singly. Among herbaceous plants, a high content is noted of mineralized wormwood pollen (to 44.5%), Chenopodiaceae (31.6%), Compositae (9.9%), grasses (5.8%), and others.

The upper part of the section (from 8 m) contains no spores or pollen.

In summary, in the studied section we note repeated changes of vegetation: in the lower part, a typical forest-steppe complex with a weak degree of forestation. It is not uniform in its composition and probably characterizes a transitional moment in the change of vegetation from a moisture-loving type to a xerophytic one.

In the middle part of the section there is a xerophytic steppe complex, and in the upper part of the section a new change in vegetation cover—the phase of steppe spruce.

Thus, in the section studied, three strata of different ages and different facies are clearly distinguished: the first (from top to bottom) is loess, upper Pleistocene in age; the second is yellow-brown, transitional both lithologically and palynologically, provisionally dated for the time being to the Middle–Upper Pleistocene; the third (“blue” clays) is Middle Pleistocene in age.

REFERENCES

1. M. P. Grichuk. Principal features of changes in the vegetation cover of Siberia during the Quaternary period. In: Paleogeography of the Quaternary Period of the USSR. Moscow State University Press, 1961.

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

3. B. F. Mikhalchenko, A. A. Kurbatova, L. V. Aleksandrova. On the stratigraphy and lithology of Quaternary deposits in the southwestern part of Kuzbass. Abstracts of reports, All-Union Conference on the Study of the Quaternary Period, Novosibirsk, 1964.