ON THE STRATIGRAPHIC SCOPE OF THE ERUNAKOV FORMATION IN THE ERUNAKOV AND TERSIN DISTRICTS OF KUZBASS

A. I. LEZHNIN

(Presented by Professor A. G. Sivov)

1. Along with the adoption in 1954 and 1956 of a new stratigraphic scheme for the coal-bearing deposits of Kuzbass, the stratigraphic conferences (5) advanced a number of urgent tasks for the further improvement of this scheme: a detailed, integrated characterization of the subdivisions of the Kolchugino Series, identification of the character of mutual transitions of productive facies over the area, patterns of coal accumulation, establishment of the scope of the Taylugan subformation, and others.

In 1962–63, the trust “Kuzbassuglegeologiya,” with the participation of the author, carried out a synthesis of the accumulated extensive factual material in order to refine the tectonic structure and clarify the oil-and-gas prospects of large anticlinal uplifts within the Erunakov, Tersin, Uskat, and northern part of the Baydaev districts. The results of this work and of field observations conducted by the author in 1964 in the Leninsk and Erunakov districts make it possible to address the question of the scope of the Erunakov Formation in its stratotype section along the bank of the Tom River (Figs. 1 and 2) and, at the same time, to note a number of regularities in the areal variation of this industrial coal-bearing sequence. As the lower and upper boundaries of the Erunakov Formation we accept the same boundaries that were designated for it by the stratigraphic conferences (5), although its lower boundary, in our view, still requires clarification.

1. The stratotype section of the Erunakov Formation was first described by V. I. Yavorsky (1931, 1933) and D. G. Samylkin (1935). The most complete and comparatively detailed study of its lithology, coal content, and stratigraphy was carried out by G. P. Radchenko by 1938 [11]. The general section of the formation compiled by the latter consisted of the disconnected Erunakov (X), Babekamensk (IV), and Barzas–Taylugan (VIII) sections, which were rather unequal in their degree of geological study, the detail of exposure, and lithologic-facies composition, and therefore did not have a reliable correlation with one another. The first of the sections is continuous and has been studied in considerable detail paleontologically and lithologically (5; 6; 7; 10–12; 16). The thickness of the Leninsk and Gramoteino subformations here is 1085 m, and that of the lower part of the Taylugan subformation is 194 m [11]. The second and third sections are exposed with some breaks, have been studied comparatively poorly [5; 6; 11–13; 16], and by a number of investigators [1; 7; 10] are not used to the proper extent in the correlation and subdivision of the reference sections of the Erunakov Formation of Kuzbass.

Fig. 1. Schematic map of the geological structure of the Pritomsk part of the Erunakov and Tersin districts.
1 — Jurassic; 2 — Triassic; 3 — Taylugan Subformation; 4 — Gramoteino Subformation; 5 — Lenino Subformation; 6 — Ilyinka Formation; 7 — stratigraphic boundaries; 8 — axes of synclines and anticlines; 9 — faults; 10 — stratigraphic and reference sections of the Erunakov Formation.

G. P. Radchenko [11] assigned to the Tailygan subformation (as the upper horizon of the formation) a 1100-m-thick upper part of the Babekamenka section, including seams I–XX and the underlying interval with predominantly gaps in the column. Seam XX was correlated by him with seam “C” of the Barzas–Tailygan section. This section (VIII), in its lower part, is confidently correlated with the Erunakov section and, as a whole, in effect fills the gaps of the Babekamenka section.

The total thickness of the Erunakov formation within its present boundaries was determined by G. P. Radchenko [11] as about 2145 m. The same volume of the formation (2135–2215 m) also appears in the report by G. P. Radchenko and S. G. Gorelova (1960) on the stratigraphy of the Kolchugino series in its reference sections. In practice and in the literature [6, 13], a formation volume of 2000–2580 m is still accepted. However, already by 1958 a complete continuous section of the formation had been obtained in the Zhernovskaya area, with a thickness of only 1540 m (II). In this connection the question arose of determining the true volume of the formation in its stratotype.

1. In Fig. 2 are shown the 10 most fundamentally important sections of the Erunakov formation in the Erunakov and Tersin districts. The correlation of sections was carried out by us by the method of geological mapping of strata and tracing of marker horizons from the reference Erunakov section to neighboring lines, areas, and deposits, with comprehensive use of the lithologic-facies properties of the rocks, the character of cyclicity and coal saturation of the sections, and their paleontological and electric-log characteristics. Along with this, tectonic breaks were established and traced, and their parameters were determined. The regularities, already revealed in the course of correlation, in changes in the lithologic-facies aspect of the rocks and in the thicknesses of seams, members, and subformations were also taken into account.

2. From the standpoint of the facies-cyclic method [3, 4, 7], which provides fairly reliable variants of correlation in the absence or limited number of distinct lithological and paleontological marker horizons, cycles of the I, II, III, IV, and V orders may be distinguished in the section of the coal-bearing strata of Kuzbass; in our opinion, these should correspond, respectively, to the following stratigraphic subdivisions of the regional scale: series, formation, subformation, supermember (stage, according to N. B. Vassoevich, 1951), and member. In this connection it is appropriate to cite the statement of A. G. Sivov, who developed the views of M. A. Usov: “...in all variants of systematics the natural rhythmicity (metamerism) of the geological process must be recognized as the leading principle in constructing the regional scale, whose various-scale stratigraphic units are identified on the basis of the stratigraphic-tectonic method” [14, p. 119]. According to A. M. Kuzmin [8], an even finer rhythmicity is distinguished in Kuzbass, corresponding in stratigraphic amplitude to a seam (bed). By members he means small intervals of the section made up of rhythmically interbedded rock layers. The boundaries of members often bear traces of erosion and breaks. At the base of members, “within a bed, relatively coarse sediments will play the predominant role, while upward within each member the deposited material becomes, from layer to layer, finer-grained” [8, p. 86]. By supermembers (stages), in our opinion, it is advisable to call a rhythmic group of 2–5 rock members, including 2–6 coal seams, which correspond to cycles of the IV order and, in turn, alternate rhythmically in the section of subformation-cycles of the III order. The lower part of a supermember (a cycle of the IV order), as a rule, is associated with the thickest beds of coarse-grained rocks and the thickest cycles of the V order. In the upper half of the supermembers, by contrast, a finer granulometric composition is noted.

rocks, up to marls and limestones, maximum coal content, abundance of pelecypod, ostracod, and estheriid faunas, and minimum average thicknesses of cycles of the fifth order. The same principle is applied successively in grouping cycles of the fourth order into cycles of the third order—A, B, V, G—which, in our opinion, are respectively equal in volume to the Uskat, Leninsk, Gramotein, and Tailugan subsuites. But this question still requires further study, and we shall not touch upon it here.

Cyclicity of the third and fourth orders within the Erunakov Formation is the most persistent in comparison with small-scale cyclicity and attests to the good correlatability of the sections (Fig. 2). To cycle B, for example, is confined a unit with the maximally thick coal seams (cycles XIV–XVII). Among the cycles of the fourth order, cycles VIII–XI, XVI, XIX, XXIII have marker significance; they are characterized by their thickness, by the number and specific position in the section of coal seams, and by other properties. At the base of cycle XVI in the Babekamensk, Bolsherechensk, and Kusheyakovsk (northern) sections there is an anomalously thick (40–60 m) unit of sandstones with the inclusion even of two interbeds of conglomerate. This unit appears as a result of the gradual replacement of siltstones by sandstones. In a number of areas this unit corresponds to an increased distance between seams 73 and 74. In cycles XVII of the Babekamensk (V. I. Yavorskii, 1931) and XVIII of the Ust-Tersin (V. I. Budnikov, 1957) sections, spatially persistent, up to 5 km, interbeds of clayey limestones are observed.

1. According to determinations by O. A. Betekhtina (1957–1959) and Yu. S. Papina (1960–1963), a characteristic abiella–estheriid complex (zone: biocoenosis “v”) is confined to the interval of cycles XVII and XVIII of the section. Its composition includes numerous large and very large Abiella concinna (Iones), a mass of estheriids, and various small anthraconauts of flattened form. This complex is clearly traceable in the Severo-Taldin (2), Ust-Tersin, Shirotnoe I, and in a whole series of other sections of the Tersin district. Apparently, the same complex is represented by mass accumulations of estheriids and small anthraconauts, determined by O. A. Betekhtina (1957) from collections by Kh. Sh. Kurbangalieva in outcrop No. 302 of the Babekamensk section, between seams XVII–XVIᵃ, and outcrop No. 11, situated 2 km northwest of the village of Ust-Naryk. The section of the latter corresponds to the interval of seams 78–79 of the Bolsherechensk section.

In the Barzas section, from collections by P. P. Radchenko [11], O. A. Solntsev identified Abiella concinna (Iones) and various anthraconauts in the interval of seams 78–82. In the Tailugan outcrop, M. F. Neuburg (1931) found the presence of estheriids, and D. M. Fedotov (1937) notes the presence of Abiella concinna (Iones). This indicates the necessity of re-correlating the Tailugan and Barzas sections with each other, since the abiella–estheriid horizon of the Tailugan section most likely corresponds to the complex already described above in cycles XVII–XVIII. In this connection it is advisable to cite the following additional considerations. First, G. P. Radchenko and D. G. Samylkin noted that the coal-bearing strata exposed in the area between the mouth of the Bolshaya Kuksha River and the settlement of Tailugan, “in their external appearance, lithological composition, the presence of thin interbeds of hard coal and carbonaceous shale, and the abundance here of finds of pelecypod fauna, are very similar to the lower parts of the Erunakov Formation” [12, p. 530]; they allowed for the possibility of the presence near the Bolshaya Kuksha River of a thrust with a very considerable amplitude. By the present time, in the Erunakov and Tersin districts a conformable ԥ

18 km — 14 km — 11 km — 3 km — 15 km — 5 km — 1–4 km — 7 km — 0–10 km

Severo-Taldinskaya area — Sosnovsky section — Bolsherechensky section — Babby-Kamensky section — Ust-Tersinsky section — Kusheyakovsky section — Shirotny section — Barzassky section — Erunakovsky section — Erunakovsky section

I — II — III — IV — V — VI — VII — VIII — IX — X

Suite

Subsuite

Cycle

Horizon

Tailyugan — \(P_{3}^{2}\) \((546–814)\)

Gramoteinskaya — \(P_{2}^{6}\) \((?–500)\)

Leninskaya — \(P_{2}^{\ln}\) \((497–650\ \text{m})\)

Ilyinskaya — \(P_{2}^{il}\) \((?)\)

Malyinskaya — \(P_{2}^{ml}\), \(A > 2000\ \text{m}\)

B = 462–662–546 m; B = 506–835–545 m; \((502 + 570) - 500\ \text{m}\)

VIII — 154 m; X–115 m; IX–100 m; XI–100 m; XI+68; XII–158 m; XI–139 m; X+02; XI+96; X+60; XIII–60; XVIII–96; XIX–93; XX+00; XXIII+87

Fig. 2. Scheme of correlation of reference sections of the Erunakov Formation of the Erunakov and Tersin districts of Kuzbass.

1 — sandstones and conglomerates; 2 — siltstones and argillites; 3 — coals and carbonaceous argillites; 4 — limestones; 5 — gaps in sections; 6 — tectonic faults; 7 — fauna of the Abieliozoster zone; 8 — flora of the Annularia zone.

a fault of latitudinal strike with a stratigraphic amplitude of 250–410 m. In the coastal section it probably passes near the Kukshinsky profile, in the cores of some boreholes of which strong fracturing of the rocks is noted, and thereby accounts for the repetition, in the Tailugan outcrop, of part of the Barzas section. Secondly, the considerable similarity, emphasized above [12], of the deposits of the Tailugan section to deposits now assigned to the upper horizons of the Il’inskaya Formation recalls the analogous case of assigning the sections along the Bol’shaya Ters’ River to the Il’inskaya Formation on the basis of their lithologic–facies character, paleontological remains (V. I. Budnikov, 1957), and concretionary assemblage (N. G. Belenko, 1962). However, detailed drilling work, the results of our correlation, and new floristic data (S. G. Gorelova, 1963) proved the isochronous nature of the deposits exposed along the Bol’shaya Ters’ River in the interval of beds 83–91. It should be noted that even earlier D. M. Fedotov (1937) regarded the above-mentioned deposits above the mouth of the Bol’shaya Tustuyer River, with accumulations of large Abiella concinna (Iones), as the upper horizons of the Erunakov Formation. Taken together, all this gives us grounds to believe that the deposits along the Bol’shaya Ters’ River (VI, beds 83–91) and in the Tailugan outcrop are very similar in lithological properties and are isochronously coeval. Consequently, the section of the Tailugan outcrop (beds P and C), owing to fault tectonics (Figs. 1, 2), secondarily repeats the middle part of the Barzas section, rather than overlying the latter.

According to the studies of O. A. Betekhtina (2), the upper horizons of the Erunakov Formation in the North-Taldin area as a whole contain a characteristic fauna, differing from the usual Kolchugin fauna and similar to the fauna of the upper half of the Babekamenka section. The latter was studied by L. L. Khalfin (1950) from collections by V. I. Yavorsky and is characterized by a diversity of small anthraconautids.

According to the studies of S. G. Gorelova (1963), the interval of the section with beds 73–83 contains the annularian assemblage (zone), characterized by a great diversity of species and by the mass occurrence of whorls of Annularia lanceolata Radcz., Paracalamites Goeppertii Radcz., Prinadacopteris anthrishifolia (Goepp) Zal., Glottophyllum cuneatum (Schmal.) Zal., Tychtopteris cuneata Zal., Noeggerathiopsis candalepensis Zal., N. insignis Radcz., Lepeophyllum kostomanovi Gorel., Crassinervia sibirica Gorel., Nephropsis cordata Radcz., as well as by the presence of insects, ostracods, fish scales, and fragments of mineralized wood. This assemblage was traced by S. G. Gorelova in the reference Erunakov section and throughout the Tersin district, including the northern part of the Kusheyakov profile (V). In the North-Taldin section the indicated assemblage is confined to the interval of beds 76–92, where O. A. Betekhtina [2] notes mass occurrences of Annularia lanceolata Radcz., Noeggerathiopsis candalepensis Zal., N. insignis Radcz., Prinadacopteris anthrishifolia (Goepp) Zal., and numerous forms of Mesozoic aspect.

Thus, in all the sections studied where bed-by-bed paleontological collecting was carried out, despite substantial facies differences, the marker faunistic (abiellid–estheriellid) and floristic (annularian) horizons are confidently traced. According to L. L. Khalfin (16), such horizons may be regarded as reference paleontological horizons, as horizons of age isochroneity. Their enormous significance for the regional stratigraphy of the coal-bearing deposits of Kuzbass is difficult to overestimate.

1. According to a personal communication from the Moscow University graduate student Chandra Sandzhoy, who in 1962–64 carried out lithologic–petrographic ...

study of the sections of the Tersin district, the petrographic composition of the rocks of the Tailugan subformation of the Babbe-Kamen and Tersin districts shows great similarity and confirms the correlation of sections that we have carried out.

1. According to this correlation, the group of beds XVIII—XX of the Babbe-Kamen section corresponds to beds 74—78 of the Erunakov and Barzas coastal sections. In the stratotypic Erunakov section, taking into account our refinements from sections of adjacent lines of boreholes, the thickness of the Leninskaya subformation is 660 m, and that of the Gramoteinskaya is 415 m. The thickness of the Tailugan subformation in the Babbe-Kamen area is 548 m. Consequently, the full thickness of the Erunakov Formation in the stratotypic section is 1623 m.

2. In the eastern and northeastern directions, a regular, successive decrease—sometimes with local deviations—is established in the thickness of the formation, its subformations, and members. For example, if in the Erunakov section the thicknesses of the Leninskaya and Gramoteinskaya subformations are respectively 660 and 415 m, then on the Shirotny 1 profile they are 508 and 413 m, on the Sosnovka profile 562 and 375 m, and on the Kusheyakovka (northern) profile 510 and 386 m. A certain reduction in the thickness of the Tailugan subformation in the North Taldinsk area (I), as compared with that in the Zhernovka area (II), is apparently due to the relative excess, which took place, of the rate of subsidence of the Earth’s crust in the first of these sedimentation areas over the rate of supply of clastic material from the comparatively distant provenance area. This lag was to some extent compensated by more abundant accumulation of the original coal-forming material.

In the same directions, the total and workable coal content of the formation decreases sharply: from 10.7 and 10.4% in the North Taldinsk area to 5.65 and 4.93% in the Erunakov area and 3.46 and 0.97% on the North Tustuyer profile, situated east of the Kusheyakovka profile. At the same time, there is a decrease in the number of beds of workable thickness, a reduction in the thicknesses of the coal beds, an increase in their splitting, and an increase in the grain size of the clastic material, the thickness of sandy members, and the coefficient of sandiness.

Analogous regularities of sediment accumulation are noted, according to our materials (1963), also in the deposits of the Ilyinskaya Formation of the Tersin, Erunakov, and Uskat districts. Consequently, in Ilyinskaya and Erunakov time the provenance area was located northeast of the indicated districts, while the maximum subsidence of the Earth’s crust occurred in the west of the Erunakov district and, judging from the deposits of the Ilyinskaya Formation, even west of the Uskat district (Karagailinsky area), where the accumulation of deposits of the Kolchugino Formation was subject to small rhythmic tectonic oscillations to a lesser degree than in areas tending toward the slowly, pulsationally rising provenance area. Subsequently, in pre-Jurassic time, the indicated part of the geosyncline, as the most weakened and thereby prepared for subsequent jump-like movements (M. A. Usov, [15]), underwent intense processes of tangential compression from the side of the Salair and, to a lesser degree, from the side of the Kuznetsk Alatau. As a result, the axial part of the Kuznetsk geosyncline was displaced 20—30 km to the east, up to its present position.

1. In the Triassic period, in general, a similar disposition of provenance and sediment-accumulation areas as in the Permian is preserved. According to G. P. Radchenko and V. T. Belousova (1940) and I. V. Lebedev (1956), the lithological composition of Triassic rocks in the eastern direction also becomes more coarse-grained, up to interbeds of conglomerate. These

rocks and the basalt sills included in them participate in major plicative and rupture folding together with the Permian rocks underlying them. The aforementioned certain similarity of the paleogeographic conditions of sedimentation of the Triassic, Erunakov, and Il’insk formations; the joint participation of these deposits in major piedmont folding; and the quite satisfactory correlation of sections of the Tailugan subformation over a distance of 30–50 km, overlain by the Triassic without visible changes in the bedding conditions of the rocks, indicate the absence of a structural or markedly expressed angular unconformity. At the same time, the change in thickness of the Permian sediments above the very upper coal seam from 0.0 on the Inskaya exploration line, situated 28 km northwest of the North-Talda area (1), to 12 m in the northern part of the Zhernov profile (Fig. 1); the formation of a boundary weathering crust 6 m thick in the North-Talda area (2); the appearance at the base of the Triassic of uneven-grained sandstones with limestone pebbles (III) and a bed of conglomerates (Inskaya and Zhernov areas), consisting of rounded pebbles of limestones, effusives, siliceous rocks, and sandstones of non–Upper Permian aspect, speak in favor of the presence of a stratigraphic unconformity between the Permian and Triassic, very analogous to the stratigraphic unconformity that occurs between the Balakhon and Kolchugin series. This analogy is also emphasized by a certain similarity in the material composition of the non-coal-bearing deposits of the lower Triassic and the Kuznetsk formation, represented essentially by argillites and aleurolites with the inclusion of variegated beds and interlayers of marls and limestones with gastropod impressions. Judging from the considerable thickness (up to 50 m) of the conglomerate at the base of the Triassic system in the Inskaya area and its direct superposition on a thick coal seam of the upper Tailugan subformation, the greatest pre-Triassic hiatus in comparison with all sections known here should be assigned to this area of Kuzbass; however, additional data are needed to determine its amplitude. The formation of the mentioned conglomerate is connected with the beginning of a new large (first-order) cycle of sedimentation after the interruption that had taken place (the formation of the weathering crust) and, probably, corresponds to the beginning uplift of the northern half of the Salair or the Tom–Kolyvan folded zone. This is also indicated by the manifestation of effusive activity in the deposits of the Tailugan subformation (the presence of tuffogenic rocks according to K. D. Zhdanova, 1960) at the Urop deposit, situated northwest of the Inskaya line.

Thus, the upper boundary of the Erunakov formation represents a clearly expressed tectono-denudational break in the sense of M. A. Usov (1936), L. L. Khalfin (1960), and A. G. Sivov (1955), characterized by an obvious stratigraphic unconformity of the contacting Permian and Triassic deposits, the presence at the base of the latter of polymictic conglomerates, and in the roof of the former—remnants of an ancient weathering crust, an abrupt change of facies, of lithological and chemical-petrographic (9) composition, of the character and composition of organic remains, and, indirectly, by the manifestation of effusive activity in the upper part of the Erunakov formation.

LITERATURE

1. N. M. Belyanin. Subdivision and correlation of sections of the Erunakov formation of Kuzbass. Problems of the Geology of Kuzbass, vol. 1, Ugletekhizdat, 1956.

2. O. A. Betekhtina, Yu. K. Kazanskii. On the boundary between the Permian and Triassic in the western part of the Erunakov district of Kuzbass. Problems of the Geology of Kuzbass, issue 2, Publishing House of Tomsk University, 1959.

3. L. N. Botvinkina. Correlation of coal seams by the method of facies-cyclic analysis. In: Collection in Memory of Academician P. I. Stepanov, Publishing House of the Academy of Sciences of the USSR, Moscow, 1952.

1. V. I. Budnikov. The role of facies-cyclic analysis in the subdivision and correlation of coal-bearing deposits of Kuzbass. Materials of the 1st Meeting of the Siberian Thematic Commission on the History of Coal Accumulation, issue 1, Publishing House of the Siberian Branch of the Academy of Sciences, 1961.

2. Problems of the Geology of Kuzbass, vol. 1, Ugletekhizdat, Moscow, 1956.

3. S. G. Gorelova. New data for the paleobotanical substantiation of the subdivision of the Kolchugino Series of Kuzbass. Soviet Geology, no. 11, 1961.

4. Yu. A. Zhemchuzhnikov, V. S. Yablokov. On the correlation of sections of the Erunakov Subformation of the Kuznetsk Basin. In: In Memory of Academician P. I. Stepanov, Publishing House of the Academy of Sciences of the USSR, 1952.

5. A. M. Kuzmin. Bed and interbed. Transactions of the Mining-Geological Institute, West Siberian Branch of the Academy of Sciences of the USSR, issue 11, 1950.

6. N. A. Lobova, N. I. Shcherbakov. The tops of the Erunakov Formation and its boundary with the Triassic along the North-Talda exploration line in the Erunakov district of Kuzbass. Problems of the Geology of Kuzbass, vol. 2, 1959.

7. M. F. Neiburg. Stratigraphic subdivision of the Kolchugino Formation of Kuzbass. Proceedings of the Academy of Sciences of the USSR, nos. 4–5, 1943.

8. G. P. Radchenko. Description of coastal sections along the Tom River from the mouth of the Suriekova River to Babiy Kamen in the Kuznetsk Basin. Materials on the Geology of Western Siberia, issue 5 (47), 1938.

9. D. G. Samylkin, G. P. Radchenko. Erunakov district. Geology of the USSR, vol. XVI (Kuznetsk Basin), 1940.

10. E. M. Senderzon. Certain regularities of Upper Permian coal accumulation in the Kuznetsk Basin. Materials of the Siberian Thematic Commission on the History of Coal Accumulation, issue 2, Publishing House of the Siberian Branch of the Academy of Sciences of the USSR, 1962.

11. A. G. Sivov. On the principles of constructing a regional stratigraphic scale and its subdivisions. Materials of the Novosibirsk Conference on the Doctrine of Geological Formations, vol. 1, Novosibirsk, 1955.

12. M. A. Usov. Vertical zones of folding. Problems of the Geology of Siberia, Academy of Sciences of the USSR, 1945.

13. L. L. Khalfin. On reference paleontological horizons and boundaries, using the Kuznetsk Basin as an example. Problems of the Geology of Kuzbass, vol. 2, 1959.