PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
OF THE ORDER OF THE OCTOBER REVOLUTION
AND THE ORDER OF THE RED BANNER OF LABOR
NAMED AFTER S. M. KIROV

Vol. 236　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1976

MATERIALS ON THE DEVONIAN STRATIGRAPHY

OF THE SOUTHWESTERN PART OF THE SOUTH MINUSINSK BASIN

P. N. PARSHIN

(Presented by the scientific seminar of the Problem Geological Laboratory of TPI)

Sections of the lower part of the Devonian on the southwestern margin of the South Minusinsk Basin are often reference sections for stratigraphic correlations throughout the entire Altai-Sayan region. Therefore, new materials on these sections are of particular interest. In light of certain newly available data, a brief characterization of the above-mentioned section is given below.

At the base of the Tashtyp Devonian section of the South Minusinsk Basin lies the Mamat Formation, distinguished by S. I. Makarov [7]. Deposits of the Mamat Formation are regarded as the oldest Devonian formations of the South Minusinsk Basin. N. G. Chochia traces deposits characteristic of the Mamat Formation over the area from the mouth of the Chanysh River in the Gorno-Altai region and the mouth of the Kamenushka River (upper reaches of the Abakan River) to the area of the settlement of Verkhnii Matur.

The formation is represented by red and brownish-gray conglomerates and sandstones. The conglomerates contain well-rounded pebbles, composed almost entirely of siliceous, jasper-like rocks, up to pure quartz. The composition of the pebbles is very consistent throughout the entire area of development of this formation. The thickness of the formation ranges from 150 m near the settlement of Myuzigol to 1390 m on the Choochek Ridge.

The formation rests with a sharp angular unconformity on rocks of the Cambrian basement and is overlain by the overlying sedimentary-volcanogenic Kharadzhul Formation [7].

The Kharadzhul Formation was established as a formation by A. G. Sivov [5]. In places, the rocks of the formation overlie deposits of the Mamat Formation; in places, with angular unconformity, they rest directly on pre-Devonian formations, and are represented by effusives of varying basicity, their tuffs, tuff-conglomerates, with subordinate interbeds and lenses of varicolored sandstones and conglomerates. Characteristic of the Kharadzhul Formation are banded “ribbon” porphyrites. The thickness of the formation is up to 1500 meters.

Higher in the section occur sediments of the Chilan, Imek, and Tolochkov formations, which are often difficult to subdivide. These formations are traced most completely in the section along the left bank of the Tashtyp River, in which only the basal part of the Chilan Formation is not exposed.

In sections along the left and right banks of the Abakan River, near the Perevoznoye ulus and the village of Bolshoi Monok, subdivision of the Chilan, Imek, and Tolochkov formations is very difficult. Deposits of the Chilan Formation in the headwaters of the Butrakhty River and the Chilan River unconformably, with a basal conglomerate,

overlie the deposits of the underlying Kharadzhul Formation, as is indicated, in particular, by the presence in the basal conglomerates of the Chilan Formation of pebbles of “ribbon” porphyries of the Kharadzhul Formation. Somewhat south and west of the sources of the Butrakhta River, as A. G. Sivov [6] indicates, the deposits of the formation described rest already directly on the basement.

The Chilan Formation was first established by N. A. Belyakov and V. S. Meleshchenko [4]. Its stratotype is the section observed along the left bank of the Tashtyp River in the area of the Chilan ulus. In this section, sills of labradorite porphyries, which were regarded as effusive formations, were erroneously included in the Chilan Formation; the thickness of the formation was also erroneously overestimated to 1140 meters.

According to our 1962 description, the section along the left bank of the Tashtyp River is as follows (from bottom to top):

1. Porphyries, more than 80 m thick.
2. Turfed interval, 2.5 m.
3. Red-colored sandstones, up to 1 m.
4. Gray, yellowish-gray to greenish-gray sandstones (according to some researchers, tuffaceous sandstones) with interbeds of siltstone, 4 m. Plagioclase fragments in the sandstones (tuffaceous sandstones?) are represented by oligoclase-andesine.
5. Red-colored sandstones up to 35 m thick.
6. Sill of labradorite porphyries, in which the presence of copper mineralization has been noted, 50 m.
7. Red-colored sandstones, 50 m.
8. Sill of labradorite porphyries, 30 m.
9. Red-colored sandstones, 30 m.
10. Sill of labradorite porphyries, 40 m.
11. Red-colored sandstones, up to 140 m thick.

Thus, the total thickness of the Chilan Formation in the section is 250 meters. Its total thickness, taking into account the basal part developed somewhat south of the section described, is about 300 meters. In bed 4 of the section described above the author collected (for the first time from the Chilan Formation) flora in which A. R. Ananiev established the following species:

1. Protobarinophyton obrutschevii Ananiev,
2. Psilophyton goldschmidtii Halle,
3. Hostimella sp.,

on the basis of which he considers the age of the enclosing rocks to be Lower Devonian. Together with the impressions of flora, a remnant (tail) of Eurypterida was found.

The Chilan Formation is overlain by deposits of the Imek Formation, first established as a formation by N. A. Belyakov and V. S. Meleshchenko in 1949 [4]. This formation has a very limited areal distribution in the near-mouth part of the Imek River; therefore it would perhaps have been more correct to distinguish it at the rank of a member in the upper part of the Chilan Formation, like other red-colored members occupying several different stratigraphic levels and, as a rule, containing plant remains. The Imek Formation is composed mainly of red-colored sandstones, siltstones, marls, and limestones. N. A. Belyakov and V. S. Meleshchenko found in the deposits of the formation impressions of plants identified by A. N. Krishtofovich, on the basis of which the deposits containing the indicated flora were assigned to the Lower Devonian [5]. The thickness of the formation is 152 m. Higher in the section lie the deposits of the Tolochkov Formation.

The Tolochkov Formation was first established by N. A. Belyakov and V. S. Meleshchenko in 1949 [5]. In the section along the left bank of the Tashtyp River, the deposits of this formation gradually upward in the section without any traces

are replaced without interruption by deposits of the Imek Formation, so that it is difficult to draw a strict boundary between these formations. In this section the boundary between the Tolochkov and Imek formations is drawn at the appearance of a predominately red coloration of the marls in their interbedding with gray-toned marls. In the section along the Abakan River it is not possible to trace the lower boundary of the Tolochkov Formation at all. In the near-margin areas of the southwestern part of the basin, the sediments of the Tolochkov Formation rest directly on basement rocks. The Tolochkov Formation is composed of variegated marls, siltstones, sandstones, and gravelites, sometimes alternating with gray-colored and green-colored varieties. Characteristic of this formation are interbeds (packs) of cupriferous sandstones, especially well developed in the lower course of the Tashtyp River between the Pechen and Ust-Tashtyp uluses. Finds of flora are sometimes associated with these interbeds. The thickness of the formation is up to 1500 m.

The sediments overlying the Tolochkov Formation are known as the Pechen Series (formation) [5]. The name was given after the Pechen ulus, situated on the left bank of the Tashtyp River. This series has been traced most completely along the left bank of the Tashtyp River and along the Abakan River in the area of the Perevoznoe and Ust-Tashtyp uluses and the village of Bolshoi Monok. In this area the Pechen Series transgressively overlaps the deposits of the Tolochkov Formation, and farther west, the basement rocks. In the section along the Tashtyp River the Pechen Series is divided rather distinctly into the carbonate Tashtyp Formation and the red-colored Sirin Formation (subformations in the terminology of V. I. Krasnov [3]). V. S. Meleshchenko [4], V. I. Krasnov [2, 3], and some other researchers assign the Tashtyp and Sirin formations to different series (derivatives of different adjacent sedimentation cycles). In the sections on the right and left banks of the Abakan River, as will be seen below from the description of these sections, the division of the Pechen Series into formations becomes difficult. Section of the Pechen Series on the right bank of the Abakan River near the village of Bolshoi Monok (from bottom to top):

1. Tashtyp Formation. Platy clayey limestones without any signs of organic remains. Visible thickness up to 30 m. The relationship with the underlying rocks is not precisely established.

2. Sirin Formation.
   a) Diabase porphyrites, thickness 340 m.
   b) Tuff conglomerate, thickness up to 1 m.
   c) Limestone, thickness 0.5 m.
   d) Diabase porphyrites, thickness up to 420 m.
   e) Conglomerates and tuff conglomerates with large pebbles of porphyrites, granite, limestone, and quartz. Visible thickness more than 100 m. The total thickness of the Sirin Formation is more than 860 m.

Section along the left bank of the Abakan River south of the Perevoznoe ulus (from bottom to top):

1. Green gravelite with scale-like pebbles of siltstones of the underlying Tolochkov Formation.

2. Gray platy limestones, 20 m thick.
   The limestone packet of bed 2 rapidly wedges out to the northeast (along strike) (within some 100–120 m).

3. Diabase porphyrites, thickness 80 m.

4. Red tuff conglomerates, thickness 8 m.

5. Gray, platy limestone, with a characteristic “Tashtyp” fauna. Thickness 40 m. To the northeast (along strike) the thickness of the bed rapidly decreases.

6. Diabase porphyrites with lenses of red tuff conglomerates. In the lower part of the bed there is a half-meter interbed of tuff-gravelite of bright bluish-green color. Thickness more than 100 m. The porphyrites have clear spheroidal jointing.

Part of the section, namely members 1 through 5, is usually assigned to the Tashtyp Formation, while member 6 is assigned to the Syrin Formation. As is evident from the description given, the sequence of alternation of beds in the sections near the Perevoznoe ulus and the village of Bolshoi Monok is the same; only in the latter section do the thicknesses of the effusive components increase, and the thickness of the last limestone bed decreases (and very sharply, from 40 to 0.5 m).

Thus, correlation of the Tashtyp and Syrin formations in the two sections described, the distance between which does not exceed 2 kilometers, encounters serious difficulties. If the boundary between the formations is taken along the top of the first limestone bed, as is done in the section near the village of Bolshoi Monok, then in the section near the Perevoznoe ulus only the first limestone bed, 20 m thick, should be assigned to the Tashtyp Formation, while the second bed, with a rich Tashtyp fauna (member 5), should be assigned to the Syrin Formation; conversely, if the boundary between the Tashtyp and Syrin formations is drawn along the top of the second limestone bed in the section near the Perevoznoe ulus (which in our view is more correct), then in the section near the village of Bolshoi Monok the boundary between the formations should be drawn along the top of the second limestone bed (member 6).

An even more difficult task is the drawing of the boundary between the formations described somewhat farther north, in the section between the Perevoznoe and Ust-Tashtyp uluses. Here, above the red beds of the Tolchekov Formation (the contact proves to be turf-covered), the following section is observed (from bottom to top):

1. Dark-gray to black limestones, flaggy, overturned; at the end of the member, with a vertical zone of brecciation. Visible thickness 50 m.

2. Brightly colored blue-green tuff breccias and tuff sandstones, passing into green porphyrites with small plagioclase laths. Thickness 25 m.

3. Bright-brown porphyrites, 1.5 m.

4. Interbedding of members of marly sandstones and, more rarely, limestones of green, red, and yellowish-gray color, 60 m.

5. Greenish-gray diabase porphyrites. Thickness up to 40 m.

6. Dark-gray, flaggy limestone. Thickness 1 m.

7. Diabase porphyrites, 30 m.

8. Medium-grained, gray, calcareous, flaggy sandstones, 1 m.

9. Then follow diabase porphyrites with frequent thin interbeds of red-colored sandstones, tuff conglomerates, and tuff breccias, cut by dikes of labradorite porphyrites. Thickness more than 200 m.

The boundary between the Tashtyp and Syrin formations in the section described is most often drawn along the top of bed 4; it seems to us, on the basis of comparison of this section with the two described above, that it would be more correct to draw this boundary somewhat higher, namely along the top of the calcareous sandstone of bed 8. But even in this case such a boundary will be conventional.

To the west of the area described (the right and left banks of the Abakan River), upstream along the Tashtyp River, the role of effusive formations in the structure of the Pechinov Series (Formation) [5] rapidly diminishes, and in the area of Mount Kurbezek (east of the village of Tashtyp) we already see, first, its fairly clear subdivision into the carbonate Tashtyp and the red-colored sandy-marly Syrin formations and, second, the complete absence of effusive sheets within the entire section.

The description given of the sections of the Pechinov Series shows how difficult it is sometimes to distinguish clear boundaries of formations within it, and in particu-

...of the Tashtyp Formation, regarded by many geologists as a marker horizon of the Devonian on the southwestern margin of the South Minusinsk Basin. The presence of limestone beds that rapidly pinch out laterally, described in the section near the ulus of Perevoznoye, may indicate discontinuous (to lenticular) deposition of the Tashtyp limestones, which occur, strictly speaking, at different stratigraphic levels and are capable of being replaced laterally by other sediments. This statement applies to an even greater degree to the deposits of the Imek Formation as understood by V. I. Krasnov [2, 3].

REFERENCES

1. A. I. Anatol’eva. Some questions of the stratigraphy of the Devonian deposits of the Minusinsk intermontane trough. Izv. Sib. otd. AN SSSR, No. 6, 1958.

2. V. I. Krasnov. On the Lower Devonian of the South Minusinsk Basin. DAN SSSR, vol. 128, No. 6, 1959.

3. V. I. Krasnov. On the stratigraphic subdivision of the South Minusinsk Devonian. Tr. SNIIGGiMS, issue 8, 1960.

4. V. S. Meleshchenko. On some questions of the stratigraphy of the Devonian deposits of the Minusinsk Basin. Tr. VSEGEI. Paleontology and Stratigraphy, 1953.

5. A. G. Sivov, A. L. Loborev. Character of mineralization along the Sayan overthrust in the Western Sayan. Vestn. Zap. Sib. geol. upr., No. 3, 1942.

6. A. G. Sivov. Elements of the stratigraphy and tectonics of the Devonian deposits of the South Minusinsk Basin. Tr. Tomsk State University, vol. 132, 1954.

7. A. G. Sivov. On the Chilan Formation of the Devonian of the South Minusinsk Basin. Materials on the Geology and Mineral Resources of Western Siberia. Tomsk State University Publishing House, Tomsk, 1964.