Structural Complexes of the Northeastern Part of the Kuznetsk Alatau

B. D. Vasil’ev

(Presented by Prof. A. M. Kuz’min)

The structural heterogeneity of the northern part of the Kuznetsk Alatau and adjacent areas in vertical section has long been noted and, with varying degrees of detail, has been reflected in the works of a number of researchers. At the same time, naturally isolated bodies (units) were distinguished, the volume and number of which, for different authors, did not remain constant even for one and the same territory. The absence of unified tectonic terminology led to the fact that, on the one hand, the same naturally isolated structural bodies were given the names of geological formations in the sense of M. A. Usov \[29, 18, 4, 1, et al.\], structural stages \[7, 12, 9, 8, 2, 22, 24, et al.\], structural tiers \[28, 11, 21, et al.\], or structural complexes \[17, 19\]. On the other hand, structural units of different rank were sometimes distinguished under one and the same term.

In the specialized literature on this question \[27, 16, 3, 23\] there is likewise no unity of views regarding the scope of the structural stage and other taxonomic units. Thus, the term “structural complex” is regarded by S. A. Salun as a term of free usage; according to M. V. Muratov, “structural (folded) complex” is a synonym of the term “structural stage”; A. A. Bogdanov proposes the term “folded complex” as a taxonomic unit larger than the “structural stage.”

Taking into account the diversity in tectonic terminology and the insufficiently precise definitions of a number of terms, their scope and criteria for distinguishing them, we are compelled to state in what sense these terms are used by us in describing the tectonics of the region and on the basis of which criteria they have been distinguished. It seems expedient to us, as applied to the conditions of the Kuznetsk Alatau and adjacent areas, to distinguish the following subordinate structural taxonomic units: structural complex, structural stage, structural substage, and structural tier.

A structural complex characterizes definite geotectonic conditions of development, is composed of an assemblage of formations of one class with its own inherent internal structure, and is separated from another by a long interruption, by a sharply expressed regional angular unconformity, indicating a fundamental reorganization of the structural plan. Such structural complexes will be the pre-geosynclinal, geosynclinal, transitional, and platform complexes \[17\] or,

respectively, the basement complex, the main geosynclinal complex, and the molasse complex, after M. V. Muratov [23]. Each structural complex in a given territory may be represented by one or several structural stages, which are composed of formations of a single class but are separated from one another by a regional angular unconformity with a restructuring of the structural plan.

An example of structural stages within the transitional complex ($D_1$—P) of the Minusinsk trough may be provided by two stages separated by the surface of a regional pre-Givetian unconformity. The lower of them ($D_1^2$—$D_2^1$) was initially distinguished as a substage [12], and later as a special transitional structural complex [19]. It extends far beyond the limits of the Minusinsk trough, whereas the upper structural stage of the transitional complex ($D_2^2$—P) owes its formation to the inception and development of the Minusinsk trough after the sharp structural reorganization that took place in the Middle Devonian and caused the trough to become individualized. Often, however, a structural complex has a single structural plan and consists of one stage.

Structural substages within a stage are distinguished by angular unconformities but have a common structural plan.

Structural tiers within a substage are separated by hidden unconformities, expressed in an abrupt change of lithology, a break in sedimentation, and erosion without manifestation of folding.

The definitions given above indicate that the distinction of particular structural units in tectonic analysis should be carried out not only by structural methods but chiefly by historical-geological methods. Each of the structural units distinguished is separated by an unconformity; however, these unconformities are not equivalent. Since in modern geological literature and in numerous textbooks on structural geology the term “unconformable occurrence” is assigned different meanings, and even the basic approach to the definition of “unconformity” often differs, we consider it necessary to note that we understand “unconformity” not only, and not so much, structurally as genetically (historical-geologically), and we regard only continuously accumulated beds, members, and formations as conformably deposited, even if they occur nonparallel.

This is exactly how M. A. Usov [30] understood the term, distinguishing three main types of stratigraphic structures: a) conformable bedding, b) hidden unconformity, corresponding to a more or less major continental hiatus in the deposition of sediments (and erosion), and c) obvious, or angular, unconformity, recording not only a break in deposition but also significant dislocations in the underlying mass of sediments, accompanied by denudation. Having defined a hiatus as an unconformity, M. A. Usov [29] indicated numerous criteria for identifying breaks. However, since a hidden unconformity, according to M. A. Usov, corresponds to a “more or less major continental hiatus,” in each specific case researchers face the problem of determining the duration of the hiatus in order to be able to speak of conformable or unconformable occurrence of particular sequences—a task made all the more difficult because the minimum duration of a hiatus necessary for identifying an unconformity has not been defined by anyone.

Taking into account the remarks made and the previously published data on stratigraphy [5, 6], we turn to an analysis of the tectonic structure of the northeastern part of the Kuznetsk Alatau. First of all, within the area two structural complexes are clearly separated: geosynclinal and transitional.

a. The geosynclinal structural complex is represented by dislocated and metamorphosed sequences of the Late Precambrian, Lower and Middle Cambrian, and by the bodies of a large granitoid intrusion of the Martaiga complex that cut through them. The sedimentary and volcanogenic sequences of the indicated age range in the Kuznetsk Alatau, as was shown earlier [20, 32], belong to formations of the geosynclinal class (after N. S. Shatsky and N. P. Kheraskov), and the presence among them of greenstone volcanogenic sequences and large intrusive bodies of the “formation of granitoid batholiths of variegated composition” [13] testifies to eugeosynclinal conditions in the development of the region in the Late Precambrian and Cambrian.

The lower boundary of the geosynclinal complex is not exposed in the region; the upper boundary is the surface of the Lower Devonian regional angular unconformity, separating the overlying transitional structural complex, composed of formations of another class and possessing a different structural plan.

All Cambrian and Precambrian sequences within the region, as will be shown below, are dislocated according to one plan: they are gathered into large folds of submeridional NNW strike, with limb dips of 50–70°, and are complicated by narrow “near-fault” folds of northeastern strike. The unified structural plan makes it possible to distinguish, within the geosynclinal complex in our region, only one structural stage for all sequences of the Late Precambrian–Middle Cambrian, which in the subsequent discussion, for brevity, is called pre-Devonian. However, this stage is not structurally homogeneous and is subdivided by us into substages and structural tiers on the basis of an analysis of the relationships of the suites and sequences composing it. Let us examine these relationships, taking into account the remarks made above concerning tectonic terminology.

The Kashkatak sequence in the territory studied has no base, as does the sequence of the Dachny spring; therefore, their relationships with the underlying formations have not been clarified. The Lower Kundat (Makarak) sequence overlies the sequence of the Dachny spring conformably; the boundary between them is drawn conventionally by the appearance in the section of the first horizon of volcanogenic rocks. The lithology of the sequences near this boundary changes gradually, as is indicated by the interbedding of carbonate and volcanogenic rocks in the lower part of the effusive-sedimentary sequence.

The dolomite sequence of the Glubokii spring overlies the underlying one with erosion and a concealed unconformity. This is indicated by the sharp change in lithology at the boundary of the sequences and by thin conglomerates at the base of the dolomite sequence on the Kundat River below the mouth of the B. Natal’evka, where the pebbles contain black marbles, quartzites, and volcanogenic rocks of the underlying sequence. A break is also indicated by the occurrence of oncolitic dolomites of this sequence below the mouth of the Elizavetinka River directly upon red-colored sandstones and diagenetized effusives; that is, here we have a sharp change of facies in the vertical section, from continental to marine. Despite this, structurally the dolomite sequence is not separated from the underlying rocks; it participates with them in common structures and everywhere rests only on the effusive-sedimentary Lower Kundat sequence. Therefore we regard the relationship between these sequences as a concealed unconformity.

The Middle Kiia (Ust’-Kundat) suite differs from the dolomite sequence of the Glubokii spring by a considerable instability of facies and the presence of local erosional breaks. It lies, at the mouth of the Sobolinka and below the mouth of the Glubokii spring, on the dolomite sequence of the Precambrian, and their relationships here have not been firmly established, since directly

no contact was observed. Structurally, however, they do not have sharp differences. But in the basin of Vaskin Spring, in the lower part of the Srednekiiskaya Suite, there occur red-colored conglomerates with pebbles of marble and quartzite, while below the mouth of the Kiika the deposits of the Srednekiiskaya Suite lie directly on black anthraconite marbles of the Kashkadak sequence, having at their base sandy limestones with lenses of microquartzite inequigranular sandstones. The very occurrence of the Srednekiiskaya Suite on Precambrian sequences that differ sharply in age and stratigraphic position testifies to an unconformity, and this unconformity should be regarded as angular. Indirect evidence of a major hiatus and erosion prior to deposition of the Srednekiiskaya Suite is also the fact that here the volcanogenic sequence drops out of the section; in other areas (Sarala, B. Iyus, Bateny, Gornaya Shoriya) it occurs stratigraphically above the Precambrian dolomites but below the carbonate-shale deposits with Cambrian fauna.

The Belokamenskaya Suite differs from the Srednekiiskaya Suite in its strictly maintained facies character and, accordingly, in its homogeneity, despite its considerable thickness. It is noteworthy that the facies change at the base of the Belokamenskaya Suite is abrupt; moreover, the various facies of the Srednekiiskaya Suite are everywhere replaced by a single facies of Belokamenskaya reef limestones. This facies change is accompanied by erosion of the ancient red-colored weathering crust, as a result of which the limestones of the basal beds of the Belokamenskaya Suite have an irregular reddish coloration. On the Kiya River, below the mouth of the Kundat, the boundary of the suites is also recorded by sedimentary (illuvial) red-colored dikes in the limestones. All this indicates that the Belokamenskaya Suite rests on the Srednekiiskaya with erosion and an unconformity. However, the break in sedimentation was not long, since there is no sharp break in the fauna; on the contrary, continuity of the archaeocyath fauna is observed. Structurally, the suites do not have sharp differences. On the basis of the foregoing, we consider that the Belokamenskaya Suite rests on the Srednekiiskaya with a hidden unconformity.

The Berikulskaya Suite lies, in the basin of the B. Belokamenka, on rocks of the Belokamenskaya and Srednekiiskaya suites. This fact alone indicates an angular unconformity at the base of the Berikulskaya Suite.

The Myagkii Log Suite rests with erosion on the Berikulskaya and is formed mainly at the expense of erosion of the latter during continuing volcanic activity. We believe that it lies with a hidden unconformity, although a more thorough verification of this conclusion is necessary.

Thus, in the stratigraphic section of the Late Precambrian–Middle Cambrian structural stage of the geosynclinal complex, we distinguish three hidden and two angular unconformities. In accordance with the principles set forth above for distinguishing different taxonomic structural units, hidden unconformities are boundaries of structural tiers, and angular unconformities within a stage are boundaries of structural substages. On this basis we subdivide the Dodevonian geosynclinal structural stage into three substages: Late Precambrian, Lower Cambrian, and Middle Cambrian, separated by angular unconformities at the base of the Srednekiiskaya and Berikulskaya suites. Each substage is divided into two structural tiers, separated by hidden unconformities. The Kashkadak sequence is not taken into account in this subdivision, since its stratigraphic relations with the others have not been established, and the degree of metamorphism and the general structural pattern do not provide sufficient grounds for distinguishing an independent...

independent structural sublevel or tier. This question requires elaboration using materials from adjacent regions.

1. The transitional structural complex in the northeastern part of the Mariinsk taiga is represented by Lower–Middle Devonian (pre-Frasnian) strata [6] and by the Kiya gabbro–alkaline-syenite intrusive complex. The variegated terrigenous Koblenzian unit, lying with a sharp angular unconformity on eroded folds and intrusive massifs of the geosynclinal structural complex, and the Eifelian volcanogenic unit resting unconformably above it, are folded into NW-trending folds with dips averaging 30° and are complicated by numerous faults.

In terms of composition and structure, the variegated unit corresponds to the continental variegated clastic formation (after A. B. Ronov and V. E. Khain, [25]). Variegated clastic units of this stage of development in adjacent regions are regarded as molasse [33, 10, 23, 3, 20].

The overlying volcanogenic unit, with angular unconformity, corresponds to a subaerial volcanogenic formation (after A. B. Ronov and V. E. Khain). Its analogues within the Minusinsk trough are assigned by a number of researchers to the porphyry formation in the broad sense of this term [27], to the basalt formation [15, 10], or to the trachyandesite formation [13]. More often, however, these units in adjoining territories are not subdivided, but are combined into a single volcanogenic-sedimentary series (the Byskar, Kop’ev, etc.) and are then assigned to the “continental variegated effusive-clastic formation” [25], or are distinguished as a special formational type—the “basalt-tuff volcanogenic-variegated formation” [14].

In one way or another, they belong to the class of orogenic formations (after N. P. Kheraskov) or to the group of transitional formations (after L. B. Rukhin) and characterize a definite stage of geotectonic development of the region, which has been called postgeosynclinal, terminal, srogenic, transitional, semiplatform, posthumous, etc. The presence within this structural complex in the region of subalkaline and alkaline intrusions also testifies to a special transitional, semiplatform geotectonic regime in the development of the region in the Lower–Middle Devonian.

In the present work we cannot discuss the question of formations in greater detail, since, in considering a relatively small area, we do not have sufficient material for this. Moreover, this question is not of primary importance for us: the concept of formations (in the sense of N. S. Shatsky) is used by us only to substantiate the distinction of structural complexes, whose complete characterization can be compiled only on the basis of study of the entire folded region.

It should be noted that the transitional structural complex in adjacent regions is represented more fully. Thus, within the Minusinsk trough it encompasses suites in the age interval from the Lower Devonian through the Permian inclusive, and is divided into two structural stages by the surface of the pre-Givetian regional angular unconformity, as we noted above. Within the northeastern part of the Mariinsk taiga we have only the lower, pre-Givetian structural stage of the transitional complex.

The relationships of the variegated (Krasnogorsk) and volcanogenic (Palatninsk) units composing this structural stage are as follows: the volcanogenic unit rests on the eroded folds of the variegated unit and on rocks of the pre-Devonian geosynclinal structural com-

complex undoubtedly indicates an angular unconformity, which makes it possible to distinguish, within the pre-Givetian stage, two structural substages, taking into account that the structural pattern of the dislocations of these strata is preserved. A more detailed subdivision is difficult.

Thus, within the northeastern part of the Martayga, two structural complexes are distinguished, corresponding to two types of geotectonic regime: geosynclinal and transitional. Each of them in our area is represented by only one structural stage: the Late Precambrian–Middle Cambrian (pre-Devonian) structural stage of the geosynclinal complex, with the intrusion of granitoids of the Martayga complex, and the pre-Givetian Devonian structural stage of the transitional complex, composed of Koblenzian and Eifelian deposits with an intrusive gabbro-syenite complex of the Kiya complex cutting through them.

REFERENCES

1. A. R. Anan’ev. On the question of the Cambrian and Precambrian in the Mariinsk taiga of the Kuznetsk Alatau. Transactions of the Mining-Geological Institute, WSF AS USSR, issue 2, 1948.

2. I. I. Belostotskii, L. P. Zonenshain, B. N. Krasil’nikov, G. A. Kudryavtsev, A. A. Mossakovskii, I. F. Pozhariskii, N. N. Kheraskov. Tectonic zoning and regularities in the formation of the Altai–Sayan folded region. Bulletin of MOIP, Geological Section, vol. 34, No. 6, 1959.

3. A. A. Bogdanov. On the term “structural stage.” Bulletin of MOIP, Geological Section, vol. 38, No. 1, 1963.

4. A. Ya. Bulynnikov. Ore potential of the eastern part of the Mariinsk taiga. Vestnik ZSGU, No. 3–4, 1943.

5. B. D. Vasil’ev. Stratigraphy of the pre-Devonian deposits of the northeastern part of the Mariinsk taiga (Kuznetsk Alatau). Izv. TPI, vol. 165, 1968.

6. B. D. Vasil’ev. On the stratigraphy of the Devonian of the central part of the Mariinsk taiga (Kuznetsk Alatau). Izv. TPI, vol. 165, 1968.

7. T. M. Dembo. Geological structure and gold mineralization of the northern part of the Kuznetsk Alatau. Transactions of NIGRIzoloto, issue 19, 1952.

8. A. L. Dodin. Geological structure and principal features of the metallogeny of iron in Gornaya Shoriya and the Kuznetsk Alatau. In: Iron-Ore Deposits of the Altai–Sayan Mountain Region, vol. 1, book 2. Publishing House of the Academy of Sciences of the USSR, Moscow, 1959.

9. Ya. G. Kats. Principal stages in the development of the central part of the Minusinsk intermontane trough in the Devonian. Izvestiya Vuzov. Geology and Exploration, No. 12, 1959.

10. Ya. G. Kats. Certain questions of the Paleozoic history of development of the Minusinsk intermontane trough. Vestnik MGU, Geology, No. 1, 1962.

11. Yu. A. Kosygin. Tectonics of the territory of the USSR. Priroda, No. 9, 1955.

12. Ya. G. Kats, B. N. Krasil’nikov, A. A. Mossakovskii, E. D. Sulidi-Kondrat’ev, N. N. Kheraskov. Stratigraphy of Paleozoic deposits of the Minusinsk basin and its mountain framing. Transactions of VAGT, issue 4, 1958.

13. Yu. A. Kuznetsov. Principal Types of Magmatic Formations. Moscow, “Nedra,” 1964.

14. I. V. Luchitskii. On the Devonian volcanogenic red-bed formation of the Minusinsk intermontane trough. Doklady of the Academy of Sciences of the USSR, vol. 116, No. 2, 1957.

15. I. V. Luchitskii. Volcanism and Tectonics of the Devonian Depressions of the Minusinsk Intermontane Trough. Publishing House of the Academy of Sciences of the USSR, Moscow, 1960.

16. Materials on Tectonic Terminology, part 1. Transactions of the Institute of Geology and Geophysics, Siberian Branch, Academy of Sciences of the USSR, issue 12, 1961.

17. V. S. Meletchenko, E. N. Yanov, I. N. Kazakov. Principal features of the tectonics of the Sayano-Altai folded region. Transactions of VSEGEI, issue 32, 1960.

18. V. K. Mondich. Geological outline of the Berikul’ gold-mining district. Transactions of the Zolotorazvedka Trust and NIGRIzoloto Institute, issue 7, 1937.

19. A. A. Mossakovskii. On the tectonics of the Kuznetsk Alatau. Izvestiya of the Academy of Sciences of the USSR, Geological Series, No. 12, 1961.

20. A. A. Mossakovskii. Tectonic Development of the Minusinsk Depressions and Their Mountain Framing in the Precambrian and Paleozoic. Gosgeoltekhizdat, 1963.

21. D. I. Musatov. Kuznetsk Alatau. Tectonics. In: Geology of the USSR, vol. XV, Krasnoyarsk Territory, part 1. Gosgeoltekhizdat, 1961.

22. D. I. Musatov, A. P. Tarkov. Tectonic structure of the central part of the Sayano-Altai folded region. Materials on the Geology of Krasnoyarsk Territory, issue 2, 1961. Publishing House of KGU.

23. M. V. Muratov. Structural complexes and stages in the development of geosynclinal folded regions. Izvestiya of the Academy of Sciences of the USSR, Geological Series, No. 6, 1963.

1. D. V. Nalivkin. Geology of the USSR. Publishing House of the Academy of Sciences of the USSR, Moscow, 1962.

2. A. B. Ronov and V. E. Khain. Devonian lithological formations of the world. Sov. Geol., collection 41, 1954.

3. L. B. Rukhin. Transitional formations. Materials of the Novosibirsk Conference on the Study of Geological Formations. Vol. 1, Novosibirsk, 1955.

4. S. A. Salun. On the terms “structural stage” and “tier.” Bull. MOIP, 5, 1957.

5. Tectonic map of the USSR and adjacent countries at a scale of 1 : 5,000,000. Explanatory note edited by N. S. Shatsky. Gosgeoltekhizdat, 1957.

6. M. A. Usov. Phases and cycles of tectogenesis of the West Siberian Territory. Tomsk. Publishing House of the WSGRT, 1936.

7. M. A. Usov. Structural Geology. Publishing House of the Academy of Sciences of the USSR, 1940.

8. N. P. Kheraskov. Problems in the methodology of distinguishing fold regions of different ages. In: “Abstracts of Reports of the Conference on Problems of Tectonics,” Publishing House of the Academy of Sciences of the USSR, Moscow, 1962.

9. V. V. Khomentovsky. Formations of structural-facies zones of southwestern Siberia and the associated mineral resources. In: “Regularities in the Distribution of Mineral Resources,” vol. III. Publishing House of the Academy of Sciences of the USSR, Moscow, 1960.

10. E. D. Shlygin. Caledonides of Siberia and Europe. In: “The Principal Ideas of M. A. Usov in Geology.” Publishing House of the Academy of Sciences of the Kazakh SSR, Alma-Ata, 1960.