Some Results of the Study of the Tectonics of Coal Deposits in the Kuzbass

V. Ya. Koudelny, Yu. N. Popov, V. V. Nikolaev, L. M. Petrovsky

(Presented by Professor A. M. Kuzmin)

The geology of the Kuzbass is highly complex and distinctive. This is reflected in the fact that there is perhaps not a single system for developing coal deposits that has not been applied, to one degree or another, in the Kuzbass. The Kuzbass is the birthplace of many new mining systems that take account of its specific mining-geological conditions. It was here that the shield system for developing steeply dipping thick seams was born and introduced into practice, as well as the combined system with flexible covering for extracting coal seams of inclined and gently dipping occurrence.

The mechanization of such labor-intensive operations as coal cutting, roof control, the automation of production processes in coal mining, and the solution of other problems already today require a more complete knowledge of the mining-geological conditions of exploitation of mine fields and open pits. Tectonics is becoming perhaps the leading factor here.

The tectonics of the Kuzbass is closely connected with the tectonics of the mountain structures surrounding it. A broad complex of geological investigations, both within the territory of the basin itself and in the Kuznetsk Alatau, Mountain Shoria, Salair, and the West Siberian Lowland, has made it possible to resolve many questions in this branch of geology. Researchers’ views on the structure of the basin more or less coincide, although the mechanism and time of formation of its structures remain disputed.

The different ages of the ancient mountain structures framing the Kuzbass and the very close connection of the basin’s tectonics with the phenomena that took place along its margins have been the reason why, up to the present time, there is no unified point of view on the geotectonic position of the Kuzbass [4, 5, 11, 21, 22]. In accordance with one or another explanation of the structure of the basin, views change regarding the causes and character of its tectonics.

The age relationships of the structural elements of the coal-bearing deposits of the Kuzbass are also debatable. All researchers indisputably recognize two phases of tectogenesis: the Early Cimmerian, which folded the Paleozoic and Triassic deposits, and the Late Cimmerian phase, which caused the folding of Jurassic deposits. Some...

other phases of tectogenesis are also distinguished by researchers [3, 7, 17, 19, 22]. The absence of clear signs of breaks or unconformities in the Upper Paleozoic coal-bearing sequence, which is considerable in thickness, the limited distribution and insufficient study of Mesozoic and younger formations, as well as the debatable age of some deposits of Kuzbass, do not yet make it possible to resolve unambiguously the question of the phases of tectogenesis. It is beyond doubt that the phases of tectogenesis in Kuzbass were manifested repeatedly, including after the New Cimmerian phase. The wide development of plicatogenic ruptures and the intense dislocation of Jurassic deposits, according to exploration data from the Leninsky, Tersinsky, and Tom-Usinsky districts, confirm this proposition.

The complex structures observed in immediate proximity to the Salair and the Kolyvan-Tomsk folded arc become simpler as one approaches the center of the basin, being replaced by calm brachyfolds and then by monoclinal zones near the southeastern and eastern margins of Kuzbass. At the same time, not only quantitative changes are observed. Here there are complex qualitative changes in the structures, since in these same directions the character of tectonic disturbance, coal content, rock composition, and their metamorphism change substantially.

A distinctive feature of the tectonics of the basin is also that the tectonic structures of its individual parts were formed as a result of movements of adjoining, more ancient mountain edifices that differ in mobility and degree of consolidation. The influence of the latter on the formation of the structures of Kuzbass varies sharply. It is maximal in the Near-Salair zone and somewhat less in the Near-Kolyvan-Tomsk zone. Exploration and mining operations show that the influence of the ancient edifices of the Kuznetsk Alatau and Mountain Shoria on the formation of structures in the eastern and southeastern margins of Kuzbass was clearly underestimated. The tectonics here proved to be more complex than had previously been supposed.

Recognizing the manifestation in Kuzbass of various phases of tectogenesis, it should be noted that, other conditions being equal, tectonics becomes more complicated with increasing age of the rocks. This feature of the basin tectonics is expressed in the fact that at present two structural stages are clearly distinguished for the coal-bearing deposits, caused by the manifestation of the ancient and New Cimmerian phases of tectogenesis. The possibility of a significant influence on the formation of tectonic structures by other phases of tectogenesis is not excluded.

The features of the tectonics of Kuzbass and their consideration in prospecting, exploration, and mining operations have long attracted the attention of researchers and have served as the basis for tectonic zoning of the basin. Several zoning schemes and geotectonic maps have been proposed, compiled with allowance for the morphological and, to some extent, genetic features of the tectonic structures [3, 17, 22].

The study of the Kuzbass basement by geophysical methods and deep rotary drilling in many parts of the basin, in connection with the search for oil and gas deposits, has substantially refined ideas about its tectonics, especially in areas poorly developed by industry. At the same time, the coal content of various suites at deep horizons was studied, which increased the reliability of coal reserves when they were estimated for the basin as a whole.

In almost all zoning schemes, the Near-Salair, Kolyvan-Tomsk, Central, and Eastern tectonic zones are distinguished, with their subdivision into subzones. While the question of the number of zones is resolved practically unambiguously, the positions of their boundaries differ. The diversity...

…the basin’s structures is, to a certain extent, a reflection of various structural-stratigraphic stages on the modern erosional surface. It is still not possible to compile maps showing tectonic zones for individual series or suites. The comparatively poor study of the structures beneath the Central Field of the Jurassic and in other places, especially in the southeast and northwest, and the gradual transitions from one type of structure to another, substantially complicate the question of the position of the boundaries between zones and subzones. In many places these boundaries cut across structural and stratigraphic boundaries without sufficient grounds for doing so.

Despite the shortcomings noted, zoning schemes play a major role in the further development of ideas about the structure of the basin and in solving many questions of exploration methodology for mine and open-pit fields. In each zone the principal structural units (large folds, tectonic faults) have been established and studied, and certain general regularities of their manifestation have been identified [3, 9, 10, 15, 17]. This makes it possible to raise, on a justified basis, the question of predicting the structure of deep horizons of deposits and of areas not yet covered by exploration.

The degree of tectonic disturbance of rocks and coal within one and the same zone is not uniform. The above-mentioned features of the basin’s structure, as well as the facies conditions under which coal seams formed, created deposits that are very diverse in type. The question of creating a geological-industrial classification of coal deposits according to structural-tectonic criteria has come to the fore [8, 14, 16].

Solving this question is inconceivable without a detailed study of small structural forms and their features in different districts. Significant results have been obtained in this respect. The foundations of mine geology laid by M. A. Usov have been successfully developed by his students and followers. Detailed study of structures in mine workings, using precise mine-surveying documentation, has made it possible not only to understand the full diversity of tectonic faults and to create their classifications [1, 6, 18, 20], but also to obtain material that serves as a basis for forecasting tectonics during exploratory and production work.

The Kuznetsk Basin is characterized by a great diversity of fold forms and types of folding. Here one can distinguish all morphological types of folding established by V. V. Belousov [4], from complete to discontinuous, with various transitions and complications.

Each type of folding is characteristic only of certain parts of the basin. Thus, complete folding is clearly expressed in the western parts of the Salair and near-Kolyvan–Tomsk tectonic zones. Crest-like folding occurs in the eastern part of the Salair zone (Belovo, Leninsk, and other districts). Along the eastern margin of the basin, folding has become widespread that in some of its features resembles discontinuous folding. The Central zone is characterized by the broad development of folding of an intermediate type, with features inherent in crest-like or discontinuous folding.

This regularity in the spatial distribution of folding types is the result of the differing mobility of blocks of the various-age basement. It is no accident that in the zones of complete and crest-like folding there are steeply dipping reverse faults with displacement amplitudes on the order of hundreds of meters and the first kilometers. All of them are parallel to the axes of major folds and are confined predominantly to the closures of anticlines. The frequency of reverse faults decreases as plicative…

structures. If in the western subzone of the Salair zone the distance between them is 0.5–0.7 km, then eastward it increases to 5–7 km. The zones of intermediate and discontinuous folding are characterized by other features of tectonic ruptures.

All types of folding in the Kuzbass have been studied fairly thoroughly. This applies above all to large folds, comparable in size with mine fields and first-order disjunctives. As for small structural forms that do not extend beyond individual extraction areas, their genetic and morphological features have not yet been studied sufficiently.

Small supplementary folds are combined into three groups, each of which bears characteristic features associated with its genesis [3]. In different tectonic zones the supplementary folds have their own features.

Folds are most diverse in areas where complete folding is developed. In the Salair and Prikol’yvan’-Tom’ zones, folds of the first and second groups are especially frequent; by their origin they are due to the formation of the principal folds and tectonic ruptures. Along with the simplification of first-order structures, the role of supplementary folds of these groups decreases noticeably, but the role of folds of the third group increases, whose morphological features are distinguished by great complexity and variety.

In the Central zone, where bends of the axes of the principal folds are very frequent, supplementary folds of the third group are distinguished by instability of form and orientation of their axes. Here the axes of small folds are not infrequently arranged fanwise. With relatively small angles of dip of the limbs of these folds, the coal seams are characterized by very complex hypsometry.

For the Eastern tectonic zone, supplementary folding is less characteristic. In this zone folds of all three groups occur, but only in individual areas with a complex structural setting.

The formation of folds was accompanied by intensive intra-bed movements, which led to the squeezing out of coal with the formation of pinches and swellings. The latter, together with fracturing, are a rather important mining-geological factor affecting the development of coal deposits. Seams with disturbed coal are especially characteristic of zones where complete folding is developed. Pinches and swellings are usually confined to the hinge parts of folds, but not infrequently they also occur on their limbs, where they are usually associated with bedding-parallel tectonic ruptures.

Small tectonic ruptures, widely developed in the basin, are divided into three groups, chiefly according to the principle of their localization and partly according to genetic characteristics. The first group includes small disjunctives occurring in the flanks of large ruptures, where, having various forms and orientations, they create a dense network—a zone of influence of the large rupture up to 500 m thick.

Disjunctives of the second group arose at different stages in the formation of the principal and supplementary folds and are genetically associated with them. They often affect the hinges of folds, as well as sectors where their axes bend, where supplementary folding is localized.

The third group includes small disjunctives formed as a result of intra-seam bedding-parallel movements. They are concentrated in a definite part of the coal seam, transforming the coal into a structureless mass with all possible pinches and swellings.

Like supplementary folds, small ruptures in different parts of the basin have their own features. Thus, in the Prokop’evsk-Kiselevsk ...

in an area where small faults of all three groups have manifested themselves, they, unlike the large-amplitude ones—which usually produce duplication of seams—in four cases out of five form a gap. Among them, reverse faults and thrusts account for 50%, strike-slip faults for 30%, and upthrusts for 20%. The overwhelming majority of them belong to the diagonal type, fewer to the longitudinal type, and especially few to the transverse type.

Small faults of the eastern subzone of the Prisalaïr zone belong mainly to the first and second groups. In form, these are longitudinal and diagonal, conformable and nonconformable reverse faults with duplication of seams. Faults of the second group developed in the centriclines of folds, where they are represented by longitudinal and diagonal conformable reverse faults, reverse strike-slip faults, and upthrusts with small amplitudes.

The regularities established in the Prisalaïr tectonic zone in the character and localization of disjunctives of high orders were fully confirmed in the study of the Kolyvan’-Tomsk zone. The exception was the widespread development here of plicatogenic faults. These include some of the direct thrusts occurring on the western limbs of large synclines. On the opposite limbs, conformable reverse faults predominate. It should be emphasized that many direct thrusts were initiated at early stages of folding in a fairly simple tectonic setting, and later some of them underwent considerable complications and acquired a folded character. In their initiation, the principal role apparently was played by the bedding and jointing of the rocks. It has been established that the angles between the surfaces of the displacers and the bedding remain approximately the same, and their amplitude rarely exceeds 100 m.

Small faults in the Central zone are represented mainly by conformable, gently dipping, and sometimes plicatogenic reverse faults. The overwhelming majority of them belong to the second group.

In the Eastern zone, small disjunctive forms of dislocations have also manifested themselves quite distinctly. As exploration and production work has shown, in the Tom’-Usa region the Main monocline is complicated by gently dipping diagonal conformable and nonconformable reverse faults and by a series of subparallel, also diagonal, steeply dipping strike-slip faults. The amplitudes of these disjunctives usually amount to 3–7 m and rarely exceed 25 m.

In all zones there are areas where all possible combinations of small faults of different groups can be observed. Such areas, as a rule, have a multivariant correlation of coal seams, and the conduct of production work in them, because of complex mining-engineering conditions, often proves practically impossible.

The regularities revealed in the character of manifestation and localization of fault forms of dislocations have been taken as the basis for forecasting the tectonics of unopened portions of mine fields [2, 9, 10]. Unfortunately, at present it is possible to give chiefly a qualitative assessment of the relative complexity of particular structural elements. The next task of research is to develop methods for obtaining a quantitative assessment of the degree of disturbance of rocks and coals.

Of no small importance is the fact that in Kuzbass a close genetic connection has been demonstrated between small faults and folds and the tectonic jointing of rocks. The study of the latter has proved very important, since it has made it possible to characterize more fully the mining-geological conditions of fields being explored and to solve questions of the genesis of various structures. Recently it has been, if not the leading, then at least a leading link in developing questions of forecasting condi-

of the development of coal deposits, especially from the cores of exploratory boreholes.

Tectonic fracturing in the basin belongs to two genetic groups—normal-cutting and oblique-cutting (after A. D. Belitskii). Normal-cutting fracturing is distributed throughout the entire basin. Being normal to the bed, fractures of this group are arranged longitudinally, transversely, and diagonally to the strike of the axes of the principal folds. Its systems are clearly recorded in the coal-bearing deposits of all tectonic zones.

Oblique-cutting fractures predominate over normal-cutting ones in coal seams situated in zones of full folding, and have subordinate significance in other zones. Other conditions being equal, the network of tectonic fracturing becomes more complicated as one approaches areas of plicative and disjunctive complications of the principal structures, and this provides grounds for considering it as an indicator of the degree of structural complexity. Forecasts of the degree of complexity of areas based on fracturing are more accurate and specific than forecasts by analogy using the general regularities of the tectonics of deposits and of the basin.

From the orientation of normal-cutting fractures it is possible to determine the visible dip angles of beds when clear signs of bedding are absent in cores, while a change in the orientation of fractures may be regarded as a reliable signal of a change in the attitude elements of the rocks. On the basis of comparing diagrams of fracture orientation, it is possible to determine the position of fold closures, to substantiate the presence or absence of disjunctives, and their form, orientation, and amplitude. Data on the orientation of normal-cutting fractures may also be used to determine the direction of dip of a limb, the plunge angle of the fold axis, and areas of sharp bends of the fold in the vertical plane. The solution of these problems is based on the use of a rigid geometric relationship between normal-cutting fractures and fold axes, especially in areas of development of full folding. Methods have also been developed for studying the fracturing of rocks and other elements of tectonics from core, for diagnosing disjunctive and plicative disturbances in borehole sections, and for determining the attitude elements of rocks from unoriented cores [12, 13].

The geological-industrial evaluation of coal deposits at the exploration stage is carried out mainly on the basis of materials from the geological documentation of boreholes. The completeness and reliability of these materials determine the degree of accuracy of concepts regarding the tectonics of the areas being explored. In connection with the increased requirements for the reliability of exploration and the great diversity of the geological-structural features of different regions of the basin, ways are constantly being sought to improve methodological procedures and technical means of exploration.

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