Section of the Upper Balakhon and Lower Balakhon Formations of the Tom-Usa and Mrassky Districts of Kuzbass

M. N. LUBYANOVSKII and A. I. BOEV

The Tom-Usa and Mrassky coal-bearing districts occupy an extensive area on the southeastern margin of Kuzbass. The coal-bearing deposits of the districts extend in a broad belt from the mouth of the Chek-Su River in the northeast to the Kondoma-Mrass watershed in the southwest. The districts are separated from one another by a conventional boundary drawn along the watershed between the Tom and Mrassu rivers. The area of the Tom-Usa district is about 720 km², and that of the Mrassky district 300 km².

The rocks composing the southeastern margin of Kuzbass are represented by deposits of the marine Lower Carboniferous, the Ostrog, Lower Balakhon, Upper Balakhon, and Kuznetsk formations. Among the sedimentary rocks occur sills and dikes of diabases. This entire rock complex is overlain at the surface by loose Quaternary deposits.

The marine Lower Carboniferous deposits, observed everywhere at the base of the coal-bearing complex, rest on Upper Devonian red-colored calcareous siltstones and argillites, which are replaced downward in the section by marly limestone with thin interbeds of argillites of the same color.

The boundary between the deposits of the Lower Carboniferous and the Upper Devonian is drawn to a certain extent conditionally, since the transition between them is gradual. Moreover, the upper horizons of the deposits assigned to the Upper Devonian lack fauna that would characterize their age more definitely. This boundary is drawn at the base of the reddish-brown shales and marly limestones that are replaced upward in the section by limestones which unquestionably already belong to the Lower Carboniferous.

In the lower part, the Lower Carboniferous deposits are represented by gray crystalline limestones with fauna, partly by marly and oolitic limestones. Above the limestones there can be traced greenish jasper-like shales, argillites, and greenish-gray sandstones. Some beds of these rocks are strongly silicified. Among the limestones occur beds of quartz sandstones, siltstones, and argillites.

The Ostrog Formation lies on the marine Lower Carboniferous deposits.

Table A

Balakhon Series \((C_3-P_1)\), 1851 m

Ostrog Formation \((C_3^1)\), 296 m — Lower Balakhon Formation \((C_2-C_3^{?})\), 643 m — Upper Balakhon Formation \((P_1^{?})\), 912 m

Mazurovo Subformation \((C_2-C_3^{?})\), 340 m — [[unclear: Alzhedievskaya/Alzhedievka]] Subformation \((C_3^{?})\), 303 m — Intermediate Subformation \((P_1^{?})\), 291 m — Ilyinskaya Subformation \((P_1^{?})\), 406 m — Kemerovo Subformation \((P_1^{?})\), 118 m — Usyatskaya Subformation \((P_1^{?})\), 94 m

Tom-Usa district
Olzherassk [[unclear: abbreviated]]
Verkhnetomsk [[unclear: abbreviated]]

Balakhon Series \((C_3-P_1)\), 1774 m

Ostrog Formation \((C_3^1)\), 256 m — Lower Balakhon Formation \((C_2-C_3^{?})\), 648 m — Upper Balakhon Formation \((P_1^{?})\), 870 m

Mazurovo Subformation \((C_2-C_3^{?})\), 366 m — [[unclear: Alzhedievskaya/Alzhedievka]] Subformation \((C_3^{?})\), 282 m — Intermediate Subformation \((P_1^{?})\), 274 m — Ilyinskaya Subformation \((P_1^{?})\), 319 m — Kemerovo Subformation \((P_1^{?})\), 112 m — Usyatskaya Subformation \((P_1^{?})\), 105 m

Balakhon Series \((C_3-P_1)\), 1840 m

Ostrog Formation \((C_3^1)\) — Lower Balakhon Formation \((C_2-C_3^{?})\), 676 m — Upper Balakhon Formation \((P_1^{?})\), 864 m

Mazurovo Subformation \((C_2-C_3^{?})\), 394 m — [[unclear: Alzhedievskaya/Alzhedievka]] Subformation \((C_3^{?})\), 282 m — Intermediate Subformation \((P_1^{?})\), 271 m — Ilyinskaya Subformation \((P_1^{?})\), 337 m — Kemerovo Subformation \((P_1^{?})\), 140 m — Usyatskaya Subformation \((P_1^{?})\), 104 m

Mrassky district
Sibiryaginsk [[unclear: abbreviated]]

Balakhon Series \((C_3-P_1)\)

Lower Balakhon Formation \((C_2-C_3^{?})\) — Upper Balakhon Formation \((P_1^{?})\), 865 m

Mazurovo Subformation \((C_2-C_3^{?})\) — [[unclear: Alzhedievskaya/Alzhedievka]] Subformation \((C_3^{?})\), 295 m — Intermediate Subformation \((P_1^{?})\), 263 m — Ilyinskaya Subformation \((P_1^{?})\), 339 m — Kemerovo Subformation \((P_1^{?})\), 149 m — Usyatskaya Subformation \((P_1^{?})\), 116 m

Legend: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11.

Likewise, as in the north, at its base there is a conglomerate lying without any visible angular unconformity on various beds of the Vizean (its lower half) that are nevertheless close in age.

The deposits of the Ostrog Formation are represented by monotonous medium-grained sandstones of dirty-gray color with a greenish tint. In the middle and upper parts of the formation the sandstones alternate with members of siltstones and argillites with nonworkable coal interbeds (Table A).

The upper boundary of the Ostrog Formation is provisionally drawn along a thick horizon of conglomerates and sandstones underlying the siltstone complex of the Lower Balakhon Formation. The total thickness of the formation in the Tom-Usa and Mrassky districts is 256–296 m. The formation contains no workable coal seams.

According to exploration data from 1954–1956, the Upper Balakhon and Lower Balakhon formations have, in the Tom-Usa and Mrassky districts, a combined thickness of 1520–1600 m.

Until recently there was no complete, continuous, and reliable section of these two formations, since the presence of considerable plicative and disjunctive disturbance in the lower horizons did not permit such a section to be compiled at any single locality. The composite section of the Balakhon Formation in its former scope, initially compiled by G. P. Radchenko¹ in the Tom-Usa district from bank exposures of rivers and data from core drilling, made it possible to estimate approximately the thickness of the formation at 2240 m. Subsequently, during the detailed drilling of the Nazas exploration line (in the central part of the Tom-Usa district), the thickness of the formation was reduced to 1555 m (in the initial correlation, 1700 m). However, even this figure raised some doubt, because it was not possible to compile a continuous stratigraphic section owing to the strong dislocation of the Mazurovka and Alykaevo subformations.

In 1955 the Usa Expedition completed detailed drilling of a second exploration line—the Verkhnaya Tom line—along which it proved possible to compile, in our opinion, a reliable section of the Upper and Lower Balakhon formations. The combined thickness of the formations along this line is determined as 1518 m (not counting the thickness of the Syrkashevka and Maizas diabase sills).

In 1956 a third exploration line—the Sibirgino line—was drilled in the central part of the Mrassky district. Here the thickness of the deposits of both formations is about 1540 m.

Thanks to comparison of the geological sections obtained along the three exploration lines mentioned above, and also taking into account the fourth section along Prospecting-Exploration Line 12, drilled in 1952 in the southern part of the Mrassky district, it is possible to trace well the changes in lithologic composition of the rocks and the coal content of the individual subformations.

A description of the normal section of the Lower and Upper Balakhon formations, in accordance with the scheme of their subdivision adopted in 1954–1956, is given successively from the upper subformations to the lower ones.

Upper Balakhon Formation ($P_1^{b e}$)

The Usyat subformation ($P_1^{us}$), exposed by exploration work over the entire area of the Tom-Usa and Mrassky districts, has been studied most fully. It includes the uppermost horizons of the Upper Balakhon Formation, from the roof of seam 1 to the roof of seam VI. In areas where seam 1 is absent as a result of erosion, the boundary of the Usyat subformation is drawn along the base of the conglomerates that usually occur in the roof of this seam. Lithologically, the subformation is represented predominantly by thick—

with layers of coarse-grained sandstones, and contains, in the Mrassky District and over most of the Tom-Usa District, the thickest and most persistent coal seams: III and IV—V. Rocks of clayey composition are confined to the roof and floor of the coal seams.

Between seams IV—V and III there lies a very characteristic gravelite horizon, from 1.0 to 4.0—6.0 m thick, with scattered large pebbles in it. In certain areas, by the size of the pebbles, the gravelite bed may be called a conglomerate.

Seam I is very irregular in thickness, chiefly because of its erosion; in the northern part of the Tom-Usa District it has been completely eroded, while in the southern part its thickness becomes workable (0.80—1.08 m). In the Mrassky District the thickness of the seam varies on average from 0.74 to 1.19 m, in some areas decreasing to nonworkable.

The structure of seam III is maintained throughout both districts. Its thickness varies from 8.5 to 11.0 m. Seam IV—V in the Mrassky District and in the southern half of the Tom-Usa District is represented by a single thick package—up to 12 m—divided by thin (0.15—0.20 m) interbeds of rock. In the north of the Olzherasskoye deposit it splits, as a result of which seams IV and V acquire independent significance, with thicknesses of 3.29 and 5.50 m respectively; still farther to the northeast the thickness of these seams decreases respectively to 1.20 and 2.0 m.

The thickness of the Usyat subformation varies on average from 104—118 m in the Mrassky District to 97—105 m in the Tom-Usa District. The total coal content of the subformation is respectively 17—18% (Table A).

The Kemerovo subformation \((P_1^{km})\) has by now been covered in detail by exploration over the entire area of the districts described. The rocks composing the subformation are rather varied, but on the whole it may conventionally be divided into two parts: an upper part, where sandstones predominate, and a lower part composed mainly of clayey rocks.

The lower horizons of the subformation, containing seams from XIII to XVII, are characterized by interbedding of dirty-gray, lenticularly bedded sandstones and siltstones. Within this complex, clayey rocks predominate. Coal seams XVI and XVII are among the most persistent, both in thickness and in structure, over the entire area of both districts. The remaining seams are relatively stable.

The rocks enclosing seams from XII to VIII—IX are represented mainly by dark-gray siltstones interbedded with thick packages of black argillites and thin-bedded sandstones. The greatest thicknesses of fine-grained sandstone packages occur at the base of seam VIa. The irregular structure and thickness of seam VIII—IX, which is enclosed between beds of coaly argillite and siltstone, are noteworthy. The thickness of seam VIII—IX in the Tom-Usa District varies from nonworkable to 10—14 m.

The interval between seams VIII—IX and VI is composed of beds of light-gray, massive, competent sandstones, in whose roof lies seam VI, the most persistent both in thickness and in structure. In the northern half of the Tom-Usa District, scattered pebbles of igneous and sedimentary rocks occur in this interval, sometimes forming accumulations in the form of conglomerate interbeds.

Among the seams of the Kemerovo subformation, in individual deposits of the Tom-Usa and Mrassky districts, seams XI and VIII—IX stand out by thickness. The latter has its greatest development in the northeast of the Tom-Usa District.

The thickness of the subformation is 112–116 m; up to 12 seams have been identified in it, of which 8 everywhere retain workable thickness. The total thickness of all coal seams is 17–18 m. The coal-bearing coefficient of the Kemerovo subformation in the Tom-Usa district is 15.2, and in the Mrassky district, 15.2.

The Ishanovo subformation \((P_1^i)\) has its upper boundary along the floor of seam XVII, while the lower boundary is drawn along the floor of seam XXXV.

In contrast to the overlying Kemerovo subformation, sandstones predominate here, composing a bed 25–85 m thick that is well traced in the sections of the Tom-Usa and Mrassky districts.

In the lower part of the Ishanovo subformation, an isolated horizon with coal seams from XXXII to XXXV can be distinguished. The strata enclosing the coal seams are represented by fine-grained gray sandstones. Clayey rocks, as a rule, occur in the roof and floor of the seams. The coal seams have a complex structure and usually consist of three, four, or more coal benches.

Seam XXXII is overlain by a thick bed of the so-called Verkhne-Rechensk sandstones, 50–55 m thick. Then the section is replaced by a new complex of rocks with a predominance of siltstones and clayey sandstones, with coal seams XXXI, XXX, and XXVII. Most of the sandstones are fine- and medium-grained, yellowish-gray and gray, massive. Only rarely are lens-shaped inclusions of clayey rocks and carbonized plant remains encountered; discontinuous-wavy and oblique bedding is observed. Toward the southwest along strike, the thickness of the sandstones decreases to 10–12 m. Characteristic of this sandstone bed is the absence of conglomerate interbeds.

Coal seams XXVII, XXX, and XXXI are separated by siltstone interbeds. The structure of the seams is complex. Thus, seam XXX for the most part has up to 6–7 rock interbeds. This horizon of the subformation is characterized by the greatest coal saturation.

Higher in the section, a new marker horizon of Kudren sandstones is distinguished (after the name of the Kudre-gol River, where they were first described by G. P. Radchenko). The thickness of the sandstone bed is 80–85 m. In the lower horizons of the sandstones, small beds and lenses of conglomerate have been established, more often disorderly accumulations of individual pebbles of igneous rocks and bedded accumulations of carbonized plant remains. The higher horizons of the sandstone unit are represented by homogeneous, monolithic, dark-gray sandstones. The thickness of the Kudren sandstones is variable; in the southwestward direction it decreases to 35–40 m, and at the same time the distance between seams XXVII and XXX increases to 45–47 m.

In the roof of the Kudren sandstones occur seams XXIV, XXV, and XXVI, which have very inconsistent thickness and structure. Seam XXIV usually consists of 6–7 coal benches where it has greater thickness.

The sandstones between seams XXV and XXIV are very uniform, monolithic, predominantly medium-grained, gray and dark-gray, and very hard.

Above, these sandstones are replaced by clayey sandstones and siltstones enclosing seams XXIII, XXIIa, and XXII. These horizons are everywhere characterized by the presence only of thin coal seams, not exceeding 0.60–1.10 m in thickness. In the Mrassky district and in the southern half of the Tomsk deposit these seams almost nowhere attain workable thickness, and in some areas they are completely eroded. The most persistent of them is seam XXIII. The so-called Paspakchin sandstones, occurring between seams XVII and XXI, are composed of

as a single thick bed; well maintained in thickness, fine-grained, homogeneous, massive. Seam XXI is the uppermost seam of the Ishanovskaya subformation.

In conclusion it should be noted that the Ishanovskaya subformation has now been studied not only from bank outcrops along the Tom’ and Usa rivers, but also from core-drilling boreholes. The thickness of the subformation within the limits indicated above ranges from 379 to 406 m in the Tom’-Usa district and from 339 to 379 m in the Mrassky district. Among the seams, the greatest thicknesses (from 4 to 7—9 m) are reached by XXIV, XXVII, XXX and XXXII—XXXIII. At the same time, these seams have a rather complex structure. The thickness of individual workable benches ranges from 0.70 to 1.5—2.0 m. The Ishanovskaya subformation contains from 14 to 20 seams, but not all of them, and not everywhere, retain workable thickness. A considerable part of the seams over a large area is non-workable. The total thickness of the seams is: in the Tom’-Usa district—33 m, in the Mrassky district 32 m. The coal-bearing coefficient is estimated at 8.4.

Intermediate subformation ($P_1^p$). The upper boundary is conventionally drawn along the floor of seam XXXV, and the lower boundary along the floor of seam XLI. The rocks of this subformation, like those of the overlying one, are characterized by a predominance of sandstones, traceable well along strike in the form of thick beds up to 35—50 m.

In the deposits of the subformation lies the so-called Syrkashevsky diabase sill. It does not have a strictly definite stratigraphic position in the section. In the northern and central part of the Tom’-Usa district the sill is confined to horizons distinguished under the local name of Koraic and Pristanskie sandstones and between the group of seams XXXVIII and XLI.

In the southern part of the Tomsk deposit the sill fills the interval between seams XXXVIII$^a$ and XXXIX$^a$; updip, at the outcrops of the seams beneath the overburden, it rises to the roof of seam XXXIV. In the section along the Sibirginskaya exploration line it has been established that the Syrkashevsky sill occupies an even higher stratigraphic position and intrudes between seams XXIV and XXV, but its thickness here decreases sharply to 55—60 m. Along the contacts of the sill, distinct phenomena of contact metamorphism are observed. Sandstones and argillaceous rocks near the sill resemble quartzites in appearance, acquire a light, up to white, coloration, and the coals of the seams near the sill are lean to anthracites. The structure of the sill is zonal; in its marginal parts there occur dark, almost black rocks, replaced by fine-crystalline diabases of greenish-gray, more often dark-gray color and a granular-porphyritic structure. In the central part the diabase is coarse-crystalline, with a considerable content of feldspars and quartz.

Above the diabase, in the section along the Nazasskaya line, there lies a complex of rocks represented by frequent interbedding of sandstones, siltstones and argillaceous sandstones, forming a bed from 35 to 50 m. The argillaceous rocks are predominantly thin-platy. The sandstones occurring in this unit are mainly gray and are characterized by lenticular cross-bedding.

Higher in the section there appears a packet of hard gray sandstones, overlain by a ten-meter bed of argillaceous rocks. Coal seams XXXVII and XXXVI are very poorly maintained in thickness and over the larger area are characterized by non-workable thickness.

The interval between seams XXXVI and XXXV is composed of a thick bed of the so-called Pristanskie sandstones, which lie on conglomerate and are overlain by siltstones. The sandstones, about 70—75 m thick, are fairly persistent along strike. In the direction to the southwest—

their thickness noticeably decreases. In the lower horizons they are medium- and coarse-grained, while in the upper beds they are medium-grained, with coarse oblique bedding. Interbeds of gravelite occur.

The total thickness of the intermediate subformation is 271–291 m. The thickness contains up to 11 coal seams, of which 3–5 have workable thickness. The aggregate thickness of the coal seams is 3–6 m; the coal-bearing coefficient is 2.7–1.1.

Lower Balakhon Formation ($C_2—C_3$)

Alykaevskaya subformation ($C_{2—3}^{al}$). The Alykaevskaya subformation is especially characterized by frequent interbedding of various rocks, forming packets with thicknesses from several centimeters to 10–13 meters. Most often the rocks of the subformation are represented by clayey sandstones and siltstones. Sandstones occur as thin interbeds. The subformation contains 9–13 coal seams and coal streaks; however, the overwhelming majority of them are nonworkable, are not persistent in thickness, and are of no practical interest. The aggregate thickness of the seams along the Nazas line is 7.6 m; along the Verkhnaya Tom and Sibirginskaya lines it is 5.7–3 m. The coal-bearing coefficient of the subformation is, respectively, 2.0 m in the Tom-Usa district and 1.04 in the Mrassky district.

The upper boundary of the Alykaevskaya subformation is provisionally drawn at the floor of seam XLI. The thickness of the subformation is 348–280 m.

Mazurovskaya subformation ($C_{2—3}^{mz}$). The thickness of the Mazurovskaya subformation is about 370 m. In general, the productive deposits of this subformation consist chiefly of clayey and fine-grained sandstones, with a minor participation of siltstones and argillites. The upper horizons of the subformation begin with packets of fine-grained sandstones and end with the so-called Maizas diabase sill.

The lower and middle horizons of the subformation are represented, for the most part, by sandstones and clayey sandstones enclosing up to 5–12 thin coal interbeds with an aggregate thickness of up to 5–6 m. The coal seams are very discontinuous and attain workable thickness only in limited areas. The sandstones are characterized by a dirty-gray color. In most cases they are fine- and medium-grained, often contain disseminated pebbles, and are distinguished by sharply expressed lenticular bedding. Siltstones have limited distribution and occur as separate small beds. Usually they are dark, to black, without visible bedding.

The Maizas diabase sill occupies, in the stratigraphic section, a position between seams LII and LIII. The thickness of the sill is variable. Along the Verkhnaya Tom and Sibirginskaya prospecting lines the sill reaches 120–130 m. Along the Nazas line the sill is represented by two unequal packets, 13 and 5 m thick.

The Mazurovskaya subformation contains from 5 to 9 coal seams, of which 2 are workable seams. The coal-bearing coefficient is 1.07–1.7.

In conclusion it should be said that geological exploration work carried out during the last 4–5 years has made it possible to construct, for the first time for the southeastern part of Kuzbass, a continuous stratigraphic section of the Upper Balakhon and Lower Balakhon formations, and to obtain a complete and clear conception of the composition, structure, and stratigraphic sequence of all horizons participating in the structure of the Tom-Usa and Mrassky districts.

As is evident from the factual material presented above, the Upper Balakhon and Lower Balakhon formations contain, in the Tom-Usa district, a total of 68 coal seams with an aggregate thickness of 88 m, of which 34 seams attain workable thickness. In the Mrassky district the number of seams

decreases to 46, with a total thickness of 77 m. Only 27 workable seams have been established. Of the total number of seams within the entire Tom-Usa and Mrassky districts, 23–26 seams enclosed in the four upper subformations of the Upper Balakhon Formation—the Usyat, Kemerovo, Ishanovo, and Promezhutochnaya—are of industrial value.

In the northeastern part of the Tom-Usa district, in the area of the interfluve of the Tom and Nazas-Su, the seams of the Alykaevo subformation will undoubtedly prove valuable. However, even there the industrial value of individual coal seams is not the same. Most of the seams are discontinuous and in some areas lose workable thickness. In the remaining part of the Tom-Usa district, as well as in the Mrassky district, the lower members are unlikely to be of practical interest to the coal industry.

Trust “Kuzbassuglegeologiya”

1. Vestnik Zap.-Sib. geologicheskogo upravleniya, 1947, No. 4. ↩