SOME FEATURES OF THE TECTONICS OF COAL DEPOSITS WITHIN THE WESTERN MONOCLINE

(TOM–USA DISTRICT OF KUZBASS)

V. Ya. Koudelny, Yu. N. Popov

(Presented at the scientific seminar of the Department of Geology and Exploration of Mineral Deposits)

In the tectonic zoning of Kuzbass, along its southeastern and northeastern margins, a single Pri-Alatau and Pri-Gornaya Shoria zone of monoclines is distinguished [2]. In earlier zoning schemes [1, 3, 5, 6], the structures of Kuzbass adjoining the Kuznetsk Alatau and Gornaya Shoria were either assigned to one zone or considered as independent geotectonic elements within it.

It seems legitimate to us to raise the question of distinguishing two independent zones: the Pri-Kuznetsk-Alatau zone of monoclines and dome-like uplifts, and the Pri-Gornaya Shoria zone of monoclines and gentle folds. The principal difference between these zones, despite a certain external similarity of structures, lies in their genetic features, determined by the different influence of tectonic movements of neighboring, more ancient edifices and of the basement. If in the first zone the structures formed substantially under the influence of movements from the side of the Kolyvan–Tomsk folded arc and under the influence of uneven subsidence of blocks of the Caledonian basement, as was well shown by A. Z. Yuzvitsky [8], then the question of the genesis of the structures of the second zone remains debatable to this day. The influence of movements of the ancient edifices of Gornaya Shoria on the formation of structures in the Tom–Usa and Mrass districts is not so obvious, and many researchers are inclined to assign them a passive role.

In substantiating the designation of the Pri-Gornaya Shoria subzone, A. A. Belitsky and E. M. Pakh [1] note that “the coal-bearing deposits of this part of the basin are arranged sublatitudinally, inheriting the strike of the rocks of Gornaya Shoria.” They further indicate that “...the orientation of folds and faults within the subzone undoubtedly testifies to tangential movements from the side of Salair.”

A similar point of view on the influence of Salair movements was expressed by E. M. Senderzon, I. I. Molchanov, A. I. Boev, and L. A. Moiseev. They noted that, despite the proximity of the Tom–Usa district to the Kuznetsk Alatau and Altai, the simplicity of its structure attracts attention, especially in the western and northwestern parts. In their opinion, this indicates the insignificant influence of the aforementioned mountain edifices on the tectonic life of the district, which, as in the rest of the basin area, was formed mainly—

...as a result of pressure from the west, from the Salair side. The influence of the Kuznetsk Alatau affected the tectonics of the district only in the form of a general uplift of the coal-bearing sequences of the southeastern margin of the basin, accompanied by faults and magmatic activity. The uplift of the Salair was reflected on the southeastern periphery of the basin in the form of movements that produced, for the most part, gently undulating folded structures. Among structures of this kind is the large Podobas depression, on the southeastern edge of which the Tom–Usa district is situated.

Other views have been expressed by V. A. Khakhlov and V. I. Yavorsky. Thus, V. A. Khakhlov [7] noted that in the southeastern part of Kuzbass he had identified a whole series of compressions from the Kuznetsk Alatau side, as a result of which the productive deposits were overlain by Lower Carboniferous limestones. V. I. Yavorsky [9] likewise acknowledges the influence of pressures from the Kuznetsk Alatau on the formation of structures in the southeast of the basin, while emphasizing that “...in comparison with the pressure that spread from the Salair side and the Tom–Kolyvan Upland, the pressure from the Kuznetsk Alatau was less effective and extended into the interior of the basin for only 20–30 kilometers.”

A. I. Boev and E. S. Dolzhenko, characterizing the tectonics of the Usa and Mrassu districts, allow that “the formation of a belt of intense and characteristic folding occurred as a consequence of the encounter of two oppositely directed pressures—on the part of the Salair uplift, which here proved, apparently, to be more weakened, and on the part of the Kuznetsk Alatau” [2].

Our observations in the mines and open-pit coal workings of the Tom–Usa district, as well as the study of tectonics in the riverbank outcrops of the Tom and Usa rivers, make it possible to relate the deformation of the sedimentary strata of the southeastern margin of Kuzbass primarily to tectonic movements of the Kuznetsk Alatau and Gornaya Shoria. Changes in the facies of the deposits of the Balakhon and Kolchugino series, in their thickness and coal content, and in the regularities of change in coal quality caused by the regional metamorphism of the latter, unequivocally indicate the location of areas of denudation within these regions. The tectonics of the Tom–Usa and Mrassu districts characterizes one of the junctions of Kuzbass with the older structures of platform type.

The deposits of the Upper Devonian and the Visean stage, according to V. I. Yavorsky [9], lie almost horizontally, forming gentle flexure-like folds; that is, in the interval between the ancient deposits of Gornaya Shoria and the younger deposits of Kuzbass there passes a zone of very weakly dislocated rocks. In the central and northeastern part of the Tom–Usa district, at the boundary with this zone, the deposits of the Lower Balakhon subseries are intensely folded and affected by disjunctives with displacement amplitudes of up to several hundreds of meters. The presence of schistose rocks observed in the railway cuttings above the settlement of Kameshok attests to the intensity of tectonics in this part. Apparently, this part of the district represents an “area of junction” of Kuzbass with the Kuznetsk anticlinorium. The “junction” itself occurs along a system of faults in the basement. The latter may also have served as pathways for the penetration of magmatic melt, which formed sills and dikes in the coal-bearing deposits. Faults in the coal-bearing deposits were transformed into a series of rupture disturbances. The folded character of a number of them indicates their relatively early inception and a long period of development.

Toward the basin, away from this “zone of convergence,” the tectonics become somewhat simpler. The deposits of the Promezhutochnaya and Ishanovskaya suites are gathered into relatively large asymmetric folds with limb dips of up to 70–80°; the overlying suites already occur monoclinally, with a gentle dip to the northwest.

Taking into account the varied character and complexity of the structures within the Tom–Usa district, G. P. Radchenko [4] distinguished five tectonic zones. Prospecting and exploration work in recent periods has significantly refined ideas about the tectonics of the district, and now four parallel tectonic zones are distinguished: the belt of the Western monocline, the Central zone of complex folds, the zone of gentle folds, and the Eastern monocline [2]. Considering that the coal seams of the Western monocline are of primary industrial interest in the district—where all mines and open pits are concentrated and where detailed geological exploration has been carried out—a characterization of the tectonics of the coal-bearing deposits will be given below chiefly within the limits of this structure.

The Western monocline may be regarded as a separate element of the southeastern margin of the Kuznetsk depression. The coal-bearing strata of the Kolchugino and Balakhonka series that compose the structure, at the present erosion level, occur in the form of a gentle arc whose concavity faces into the basin. The average dip azimuths of the Upper Balakhonka subseries here vary from 290° in the northeastern half of the arc to 325° in its southwestern part. The average dip angles within the monocline decrease from 30–35° in the northeast to 5–10° in the southwestern part of the structure. However, in individual areas, where flexures and additional folds are developed, they are subject to changes even over short distances.

In general, the simple large plicative structure of the Western monocline is quite substantially complicated by a number of additional folds and disjunctives of various morphology and orders. By the present time, almost the entire area of the element of the basin structure under consideration has been explored in detail; and if one takes into account that all mining enterprises of the district operate within the monocline, it is possible to judge the details of its tectonics from rather substantial volumes of mine and quarry geological documentation. Our group carried out generalizations of this documentation, as well as special observations of the character of the tectonics in mine workings and natural exposures. In doing so, particular attention was devoted to studying the arrangement of details in the structure of high-order dislocation forms, as well as tectonic jointing. The plicative structure of the Western monocline may also be regarded as the western limb of the large Kushtuboi anticline, which is part of the Chulzhan zone of folds. Without going into the details of the structure of the zone, let us note only the clearly expressed, predominantly northeastern plunge of the axes of the folds included in it. In connection with this, north of the Berezovsky areas there is a periclinal closure of the anticline in the seams of the Upper Balakhonka subseries. The orientation of the fold axes in plan repeats the direction of the basin boundary with the structures of Gornaya Shoriya.

A generalization of the geological and mine-surveying documentation of mine workings carried out at the mines and open pits of the district, as well as the results of special tectonic studies in underground workings and in open pits conducted by a group of scientific workers and engineers of Tomsk Polytechnic Institute, made it possible to characterize the folding, the jointing of the coal and enclosing rocks, the bedding-

... disturbances, major and minor ruptural disturbances, and elements of tectonics in the magmatic formations of the district. At the same time, the structural features of various parts of the district were established, as well as important typical interrelationships among different structural elements, which can be used to predict the degree of disturbance of mine fields.

For the areas of the Western Monocline, which account for the main volume of our investigations, these regularities are reduced to the following:

1. Additional folding within the monocline has become fairly widespread. It is expressed both in the form of weak undulation, observed almost everywhere, and in the form of distinct flexures and additional folds. The axes of the latter are oriented diagonally to the strike of the monocline and plunge gently along azimuth 0–30°.

2. The Western Monocline is characterized by comparatively complex ruptural tectonics. Gently dipping disjunctives of two systems are the most widespread. One of them has dip azimuths of 90–120° and dip angles up to 10–15°; the second, respectively, 35–30° and 10–15°. A close relationship has been noted between additional folds and ruptural disturbances; in this case, the orientation of the axial lines of folds and of the lines of seam truncation by displacers, as a rule, coincide.

A group of steeply dipping disjunctives, which are strike-slip faults, has been studied. The latter have a sublatitudinal strike and dip angles of 70–90°.

1. In the studied areas, two systems of joints cutting normally and six systems of obliquely cutting fractures were clearly manifested. Normally cutting fractures occur everywhere; obliquely cutting ones are localized mainly in places where additional folds and ruptural disturbances have developed.

2. Structural elements in magmatic formations can, with a certain degree of reliability, be used to clarify the age relationships between tectonic elements in the coal-bearing deposits.

3. The spatial-genetic relationships among folds, major and minor tectonic ruptures, and fracturing have been clarified. A similar interrelationship was also noted by us in other districts of Kuzbass.

The authors of the work came to the conclusion that the tectonics of the Tom-Usa district is determined chiefly by movements from the side of the Kuznetsk Alatau and Gornaya Shoria. A peculiar structure arose in the district, in which four tectonic zones are clearly distinguished. On the basis of a study of the structure of the southeastern zones using materials from exploratory work, an attempt was made to establish certain regularities of tectonics that would make it possible to assess the complexity of the structure of particular areas.

The regularities established from mine workings were extended to areas not yet developed by mining. This made it possible to preliminarily assess the tectonic complexity of the Raspadskoye deposit and of the coal deposits of the Mrassky district.

At the same time, certain questions of the methodology for prospecting coal deposits of the district were considered. The possibility was shown of using the established regularities for the purposes of forecasting the tectonic structure of areas being explored. An increase in the reliability of predictive constructions, in the authors’ opinion, can be achieved by generalizing the materials of the mine geological service and specialized ...

by the documentation of cores from exploratory boreholes. It has been shown that the peculiarities of the structural forms in the district significantly reduce the possibilities for identifying and studying them by geophysical methods. The study of borehole cores substantially increases the reliability of the structural correlation of tectonic ruptures, and great importance is attached to it. A number of examples have shown the methodology for identifying disjunctives in borehole sections.

The comparatively short period of exploitation of the coal deposits of the Tom–Usa district and, as a consequence, the small areas of seams covered by mine workings with reliable geological documentation, do not allow the tectonic features of the district to be considered fully studied. In the course of the development of exploitation works, new regularities may be established and those already established may be refined. This gives grounds to believe that further study of the elements of the district’s tectonics is an important task for coal prospectors.

REFERENCES

1. A. A. Belyatskii, E. M. Pakh. Regularities of the tectonic structure of the Kuznetsk Basin.—In: “The Principal Ideas of M. A. Usov in Geology.” Alma-Ata. Publishing House of the Academy of Sciences of the Kazakh SSR, 1960.

2. Geology of Coal and Oil-Shale Deposits of the USSR. Vol. 7. Moscow–Leningrad, “Nedra,” 1969.

3. V. S. Murovtsev and O. G. Zhero. Tectonics of Kuzbass.—In: “Geological Structure and Prospects for the Oil-and-Gas Potential of Kuzbass.” Proceedings of SNIIGGIMS. Issue 4, 1959.

4. G. P. Radchenko. The Tom–Usa coal-bearing district of the Kuznetsk Basin. Bulletin of the West Siberian Geological Administration, 1947, No. 4.

5. E. M. Senderzon, G. M. Kostamanov. Elements of tectonics and age relationships of disjunctive disturbances in the Kuznetsk Basin. Proceedings of the Coal Geology Laboratory, Academy of Sciences of the USSR. Issue VI, 1956.

6. A. V. Tykhnov. Prospects for the oil-and-gas potential of the Kuznetsk Basin.—In: Prospects for the Oil-and-Gas Potential of Western Siberia. Moscow, Gostoptekhizdat, 1948.

7. V. A. Khakhlov. The southeastern margin of Kuzbass.—In: “Mineral Resources of the West Siberian Territory.” Vol. III, Coal, Novosibirsk, 1935.

8. A. Z. Yuzvitskii. Conditions for the formation of structures in the northeastern part of the Kuznetsk Basin. Novosibirsk, “Nauka” Publishing House, 1970.

9. V. I. Yavorskii. Conditions for the formation of coal-bearing deposits of the Kuznetsk Basin and their tectonics. Moscow, Gostoptekhizdat, 1957.