Proceedings of the Tomsk Order of the Red Banner of Labor Polytechnic Institute named after S. M. Kirov

Vol. 151　　　　　　　　　　　　　　　　　　　　　　　　　1966

On the Biostratigraphy of the Cambrian of the Krasnoyarsk Ridge

T. V. Yankaūskas

(Presented by the interdepartmental conference of the Geological Prospecting Faculty)

Cambrian deposits are widely distributed within the Krasnoyarsk Ridge (the northwestern part of the Eastern Sayan). They compose extensive areas in the middle course of the Mana River, in the headwaters of the Bazaikha River, and in the vicinity of the city of Krasnoyarsk. Being richly characterized by diverse organic remains and possessing considerable thicknesses, they have long attracted the attention of researchers. It is sufficient to note that any of the proposed (and previously proposed) schemes of biostratigraphic subdivision of the Cambrian deposits of the Sayan–Altai relies to a significant degree on the Mana and Bazaikha sections.

However, despite the major advances achieved in the study of the geology of the Cambrian of the Krasnoyarsk Ridge, many fundamentally important questions, both theoretical and practical, are still being sharply debated. This is due to the complex tectonic structure of the region and to the still insufficient study of some of its hard-to-reach areas. The most controversial questions concern the position of the lower boundary of the Cambrian and, in connection with this, the scope of the Cambrian system; the position of the boundary between its lower and middle divisions; and the sequence of deposition of several units distinguished here—the Anastas’ino, Koi, Kolbino, and Torgashino formations.

The author has attempted to fill, at least in part, a gap in our knowledge of the geology of this very interesting region. As a result of the investigations we carried out, some new materials were obtained that bring closer the resolution of a number of disputed questions. An analysis of data from other researchers and our own observations allows us to set forth below considerations concerning the extent and structure of the Cambrian system in this area. It should also be noted that in the present work the main attention is devoted to the analysis of controversial questions, and descriptions are almost not given of individual units previously distinguished here and already described.

The Cambrian formations of the Krasnoyarsk Ridge are represented by a thick complex of deposits of the miogeosynclinal type and constitute the foredeep (Mana) trough, confined to the northeastern limb of the East Sayan anticlinorium.

At the base of the Cambrian system of the Krasnoyarsk Ridge lies a thick (4000 m) series of deposits, subdivided into two conformably overlying formations of approximately equal thickness. The older—the Anastas’ino—is composed at the base of dirty-green quartzose

and polymictic sandstones, siltstones, and conglomerates; in the middle part and at the top—gray and black silty and clayey platy limestones and dolomites, often interbedded with green clay shales. The overlying Ungut Formation is composed of light-colored massive and thick-bedded dolomites and limestones. Dolomites predominate below, limestones above. Both formations were combined by I. I. Koptev [6] under the general name of the Anastas’ya Series, as it will hereafter be called by us.

The stratigraphic position of the Anastas’ya Series is determined by its occurrence above unquestionably Precambrian, deeply metamorphosed formations (the Kuvai Series) and below the conformably overlying Kolba Series, characterized in its middle and upper parts by trilobites of the Lena Stage of the Lower Cambrian. The age of the series has remained controversial up to the present, both because it has been poorly studied and because of the different theoretical views of the researchers who have investigated it. In the numerous stratigraphic schemes proposed for the region of the middle course of the Mana River, where deposits of the Anastas’ya Series are predominantly developed, and for the entire Krasnoyarsk Range, this sequence has been assigned now to the Precambrian, now to the Cambrian. Thus V. V. Khomentovskii, M. A. Semikhatov, and L. N. Repina, who in 1956 found pteropods (hyoliths) in the Anastas’ya Formation, on this basis assigned it to the Cambrian system [35]. The same views were held by I. A. Molchanov [10], who had earlier studied these deposits, and later by the geologists I. P. Zhuiko and V. V. Bezzubtsev, who carried out geological mapping at a scale of 1:200,000 in 1956–1957 in the middle course of the Mana River and in the upper reaches of the Bazaiha River, as well as by A. A. Predtechenskii [11, 12, 13], who took part in their work. At present the geologists of the Krasnoyarsk Geological Administration V. I. Popov, L. V. Yakonyuk, and others, who are conducting geological mapping at a scale of 1:50,000 in the same area, hold the same position.

A number of other researchers adhere to a different point of view. Thus, as a result of many years of very detailed investigations, K. V. Radugin came to the conclusion that Upper Precambrian deposits are widely developed within the Krasnoyarsk Range. Having found, in the deposits here united under the name of the Anastas’ya Series, hyoliths, epiphytons (Anastas’ya Formation), and a diverse complex of filamentous algae (Ungut Formation), he subdivided these sequences into three paleontologically characterized systems—the Krasnoyarsk, Mana, and Chud systems [14, 16, 18, 20, 22], each of which is separated from the preceding one by major tectono-denudational breaks and, in turn, is subdivided into divisions and stages.

I. I. Koptev [4, 6, 9] wrote of the Precambrian (Sinian) age of the Anastas’ya Series. He found tower-shaped gastropods, hyoliths, and filamentous algae in the Ungut Formation; however, following K. V. Radugin, he allowed for the possibility that the indicated forms had already appeared in the Late Precambrian.

Recently V. V. Khomentovskii [29], having somewhat revised his views, came to the conclusion that the Anastas’ya Formation is of Precambrian (Vendian) age. The Ungut Formation (the upper subformation of the Zherzhul Formation, according to his scheme [35]) is correlated by him with the Bazaiha Horizon of the Lower Cambrian.

The opinion that the Anastas’ya Series may be of Precambrian age is also shared by the paleontologist S. S. Gudymovich (see his article in the present volume).

The materials presented above clearly demonstrate how, depending on the theoretical views of researchers, the question of the position of the lower boundary of the Cambrian is resolved in different ways. When these views change, its position in the same section changes accordingly. But, apparently, this question is not as fundamental as some researchers believe. More important is the faultless establishment of the sequence of the stratigraphic subdivisions distinguished and the accuracy of correlating them, on the basis of organic remains, with deposits of other regions. And where within these sequences to draw one or another (always conventional!) boundary, and according to what natural criteria, depends entirely on the general agreement of researchers, after which any geological boundary acquires the right to exist and is fixed by the law of priority. Therefore, a change in the position of any previously agreed boundary can be made only when the necessity of this is recognized by at least a majority of specialists.

In this connection, I would like to emphasize the illogicality of the opinion of a number of researchers who assign, wholly or in part, the deposits of the Anastas’ino Series to the Precambrian. For if one is to believe the information reported in the Soviet and foreign literature, nowhere and by no one below the reliably established lower boundary of the Cambrian have the organic remains listed above for the Anastas’ino Series (epiphytons, geolites, tower-shaped gastropods, filamentous algae, etc.) yet been encountered; on the contrary, they are very widely distributed in Early Cambrian deposits of other regions of Siberia, etc. At present we see no serious grounds for revising this position, and therefore the age of the Anastas’ino Series (in the light of modern views in paleontological science) must be assessed as Cambrian.

The considerations presented are supported by a number of new facts. In the summer of 1963, after three years of searching, the author finally succeeded in discovering in the Anastas’ino Series several specimens of archaeocyaths—Archaeolynthus sp. and Dictyociathus sp. nov. The find was made in black massive limestones of the upper Ungut Formation on the watershed of the Zherzhul and Kolba rivers, left tributaries of the Mana River, at the latitude passing between the settlements of Murtuk and Bultusuk (one specimen was left in the outcrop as material evidence). In the collection of algae gathered by the author from the upper and middle parts of the Ungut Formation, the following Cambrian forms have been identified: Epiphyton (many species), Renalcis gelatinosus Korde, R. jacuticus Korde, R. seriata Korde, R. pectunculus Korde, Renalcis sp. nov., Proaulopora glabra Krasn., P. rarisima Vologd., Rasumovskia sp., Botominella sp., Lenaella Korde, sp. nov., Girvanella sibirica Maslov., G. conferta (Nich. et Eth), and others, not yet described. At the base of this formation, in the Baranchik rock near the settlement of Bol. Ungut, S. S. Gudymovich also discovered, among massive epiphyton bioherms, algae of the above-mentioned genera. In the upper part of the Anastas’ino Formation in the same area, he also established, in addition to the “ubiquitous” epiphytons, the algae Renalcis sp., Girvanella sibirica Maslov., G. conferta (Nich) and Rasumovskia (?). In the lower part of the carbonate portion of the Anastas’ino Formation, in micro-lumpy black platy limestones, the author discovered remains of tubular algae very close to Botominella (middle course of the Zherzhul River, 25 km above the mouth, right side of the valley), as well as giolites and epiphytons in its middle part (right bank of the Kolba River, 500 m below the village of Anastas’ino).

The paleontological characterization of the Anastas’ino Series would not be complete without mention of the discovery in its deposits by K. V. Ra-

by Dugin [19, 21] of a new group of the most ancient archaeocyathid-like animals, subsequently studied in detail [36] and monographically described (works in press) by him and by the author. The fossils occur together with archaeocyaths (see above) in a member of black and white massive, more rarely bedded, limestones in the upper part of the Ungut Formation (the Akhor Horizon of the Man’ system of the Late Precambrian—according to the scheme of K. V. Radugin [22]). This upper, limestone part of the Ungut Formation, owing to the distinctness of its paleontological and, to some extent, lithological characteristics, deserves to be distinguished as an independent formation, which, following K. V. Radugin, may be called the Akhor Formation. Because of an intense pre-Kolbin erosional break, it has unfortunately been preserved only in the cores of synclinal structures of the Anastas’ino Series; nevertheless it is known in considerably distant areas and, thanks to the distinctive character of the assemblage contained in it, with abundant representatives of the new group of archaeocyathid-like animals (pterocyathids), it is an excellent marker “horizon.” The thickness of this new formation is variable and ranges from 100 to 700 m. In the area of the headwaters of the Elovka River, where its stratotypic section is situated (right bank of the Elovka River, 6000 m above the mouth), its thickness is no more than 300 m; in the middle course of the Murtuk River—100–150 m; on the divide of the Kolba and Zherzhula rivers—not less than 300 m; in the section along the Bazaikha River and its left tributary, the Korbik River, where the rocks of the formation are represented by white algal limestones—700 m.

Thus, by the present time a sufficiently rich and varied paleontological characterization of the Anastas’ino Series has been established (hyoliths, gastropods, archaeocyaths, pterocyathids, filamentous and other algae). The fossil assemblages of both the Ungut and Anastas’ino formations of this series correspond in composition to Early Cambrian assemblages of other regions of Siberia and cannot even partly be correlated either with the Vendian (Yudoma) assemblage of the Late Precambrian, or, still less, with the Sinian system of China!

It is important to note that everywhere within Siberia the Cambrian system (in more or less complete sections) begins with beds that do not contain archaeocyaths or trilobites; however, in them there is a very specific fossil assemblage—hyoliths, sponge spicules, epiphytons, primitive brachiopods, turreted gastropods, remains of sabelliditid worms, and others, to which some pterocyathids should also be added. The establishment of the unquestionably Cambrian age of the Anastas’ino Series therefore allows us, in this connection, to agree with the opinion of a number of researchers (Vologdin [2], Sivov [30], Predtechenskii [12], and others) on the advisability of distinguishing, at the base of the Cambrian system, one more stage (below the Aldan), paleontologically characterized by Cambrian forms but not yet containing trilobites. In the Krasnoyarsk Ridge it is thus represented by the Anastas’ino and Ungut formations, without its upper (Akhor) part, and by the Kalat Formation (an analogue of the Anastas’ino Formation in the lower course of the Bazaikha River). In the north of the Kuznetsk Alatau it corresponds to the lower part of the Ust’-Kundat Formation, where V. V. Khomentovskii and others discovered hyoliths, epiphytons, and brachiopods. In the summer of 1964 B. D. Vasil’ev also found in it eight-rayed sponge spicules. The upper part of this formation, as is known, containing the oldest archaeocyath assemblage of Siberia [28] (pterocyathids have also been found here by the author), should in our opinion be correlated with the Akhor Formation of the Krasnoyarsk Ridge. The Anastas’ino Series is confidently correlated with the Ushakovka and Mota formations of the Cis-Sayan region, paleontologically characterized

with remains of the worms Sabellidites Jan., hyoliths, turreted gastropods, brachiopods, sponges Chancelloria, etc. [2]. In the Batenëvo Range it is matched by the Zykovskaya Formation (with epiphytons, gastropods, and hyoliths) of the area of the village of Bol. Erba and the Sladkie Korni River [32], and by the lower beds of the Kutenbuluk Formation in the area of the Kuten-Buluk hollow and the Sukhiye Solontsy locality [22].

In other regions of Siberia, the Anastas’ino Series apparently corresponds to the lower beds of the Tyusser Formation of the Kharaulakh Massif, the Kessyusa Formation of the Olenek Uplift, the Zherba Formation and the lower beds of the Yudeya Formation of the Patom Upland, etc.

Thus, the Anastas’ino Series of the Krasnoyarsk Ridge, richly characterized by a diverse complex of organic remains, represents a single cycle of sedimentation, lies at the base of the Cambrian system, and may be regarded as the lower substage of its lower division, or else as an independent Early Cambrian stage, which, following A. A. Predtechensky [12], might be called, for example, the Manian.

The Anastas’ino Series is overlain by the Kolba Series with a parallel but clearly expressed unconformity. Within it, from bottom to top, the Koya (1500 m), Leiba (850 m), Krol (1000–1500 m), Vyezhego Log (variegated—240 m), Gogolev (300–1100 m), and Ermakovo (350 m) formations have been distinguished [4, 6, 24, 25], etc. (In the opinion of A. A. Predtechensky [12] and others, the Koya Formation lies below the Anastas’ino and is Precambrian.)

The Koya and Leiba formations are composed of red-colored, green, and gray polymictic and quartz sandstones, siltstones, shales, conglomerates, and dolomites. Paleontologically they are characterized rather poorly: in the Koya Formation only “Cambrian spores” have been found; in the Leiba Formation—brachiopods Lingula [6].

The Krol Formation is composed at the base of red-colored sandstones, dolomites, locally platy limestones, and green clayey shales; in the middle and upper parts, of dark bedded limestones. At the base of the formation, in lenses of gray massive limestones, the author found archaeocyaths Archaeolynthus sp., Tumuliolithus karakolensis Zhur., several species of pterocyathids, and algae Epiphyton, Rasumovskia, Renalcis. In the upper part of the formation, L. N. Repina [24–28] and I. I. Koptev [4, 6, 8] collected and monographically studied numerous trilobites of the Bulaiaspis group.

The stratigraphically higher formations of the Kolba Series are represented predominantly by dark bedded limestones (to a lesser extent by light-colored ones) and contain an abundant trilobite fauna, on the basis of which these deposits are unanimously correlated by the above-mentioned researchers with the Lena Stage of the Siberian Platform.

Special attention should be given to consideration of the highly controversial question of the stratigraphic position of the Torgashino Formation. The famous “Torgashino limestones” are excellently exposed in the lower reaches of the Bazaikha River, near the city of Krasnoyarsk, and have been well studied; however, to this day there is no unanimous opinion among researchers regarding their stratigraphic relationships with the Kolba Series (Formation). Without entering into the history of the question, we shall note that at present there are two points of view on this issue.

1. The Torgashino Formation contains deposits of the entire Lower and partly Middle Cambrian; the Kolba Series (Formation) is its analogue, but is represented in different facies.

1. The Torgashino Formation is a younger unit in relation to the Kolba Formation and rests upon it unconformably.

The first point of view is defended by a group of staff members of the Siberian Branch of the Academy of Sciences of the USSR—L. N. Repina, V. V. Khomentovskii, I. T. Zhuravleva, and others [29]—who refer to the generally accepted correlations of the Kolba Series with the Lena stage of the platform, and of the Torgashino with the Aldan (lower parts) and Lena (upper parts of the formation).

The second point of view is held by I. I. Koptev [6, 8], A. A. Predtechenskii [11—13], A. P. Shcheglov [12], and others. Analysis of the fauna of both units enabled I. I. Koptev to demonstrate the paleontological distinctness of each of them, and the establishment by him of its superposition upon the Kolba Series of a thick unit of light-colored massive limestones with trilobites of the Elan horizon (the Shakhmatovo Formation) in the upper reaches of the Bazaikha River led him to the conclusion that the Torgashino Formation is younger.

A weak link in I. I. Koptev’s constructions is the absence, in the Shakhmatovo Formation, of older trilobites and archaeocyaths so characteristic of the Torgashino Formation; this allows supporters of the first point of view to correlate the Shakhmatovo Formation with the upper parts of the Torgashino, and the underlying Kolba Formation with its middle part, and thus to continue correlating these sections as before.

In 1962, the author, working as a member of the geological detachment of the Department of General Geology of the Tomsk Polytechnic Institute, found numerous archaeocyaths in the area of the settlement of Murtyk, on the left bank of the middle course of the Mana River, in white massive limestones. The work of previous investigators had not covered this territory in any detail; as a result, a thick (not less than 500 m) unit of archaeocyath limestones was missed. On the map of V. V. Khomentovskii and others [35] it falls within an area covered by the conventional symbols of the Zherzhul Formation (upper subformation). Subsequent detailed mapping established the unconformable superposition of this unit upon the Ungut Formation (upper and middle course of the Murtyk River) and upon the Gogolevka (Novovasilyevka) Formation of the Kolba Series (!), in which the author found trilobites of the Jacutidae (identified by I. I. Koptev)—the upper reaches of the Bultusuk River.

The archaeocyaths were identified by V. D. Kamelina, and also by participants in the First All-Union Colloquium on Archaeocyaths in Moscow (1964), according to whom the author’s collection contains Bazaikha, Sanashtykgol, and also Kameshki forms.

Thus, “Aldan” archaeocyaths have been found in the area of the settlement of Murtyk stratigraphically above the “Lena” trilobites, which once again eloquently confirms the correctness of the opinion previously expressed by A. G. Vologdin, A. G. Sivov, A. A. Predtechenskii, I. I. Koptev, and others concerning the high stratigraphic position of the Sanashtykgol complex of archaeocyaths in the section of the Cambrian system of Siberia, and concerning the need to refine the proposed [28] biostratigraphic scheme for subdividing the Cambrian deposits of the Sayan–Altai region.

The youngest Cambrian formations should be considered the deposits of the Tyulup Series, widely distributed in the middle course of the Mana River [6, 35] (thickness 6000 m). With younger formations they are bordered mainly by disjunctive contacts, and only in two places in the upper reaches of the Bazaikha River, where they are exposed from beneath Devonian deposits, do they rest sharply unconformably on the eroded surface of the Kolba Series and the Shakhmatovo (Torgashino) Formation [6]. The age of the Tyulup Series was assessed by V. V. Khomentovskii [35], and after him by I. I. Koptev [6], as

Upper Cambrian–Ordovician; D. A. Vasiliev assigned it to the Devonian [1]. It is hardly possible to agree with the latter opinion, since the intensely dislocated (with bedding dips of up to 90°) six-kilometer Tyulyup Series cannot be younger than the age indicated by V. V. Khometovsky.

Thus, the Cambrian system of the Krasnoyarsk Ridge is represented by a thick complex (15 km) of deposits of the miogeosynclinal type. It is characterized by a clearly expressed cyclic structure. In all, three cycles are recognized: the Anastas’insk, Kolbin, Shakhamatov, and Tyulyup cycles. Each of them is composed at the base of terrigenous rocks and, in the middle and upper parts, of carbonate rocks (with the exception of the entirely terrigenous Tyulyup cycle); each corresponds to a definite major stage in the development of the earth’s crust of this region and is characterized paleontologically by its own specific assemblage of fossils.

The Lower Cambrian deposits, making up the Anastas’insk, Kolbin, and partly Torgashin cycles (9 km), are most widespread. Middle Cambrian deposits occur over very limited areas and are represented by beds with “Elan” trilobites in the upper parts of the Torgashin Formation. The parallel occurrence of the Lower and Middle Cambrian sequences indicates the manifestation in this region of the first phase of Salair folding in the Middle or Upper Cambrian epoch. The deposits of the Tyulyup Series are dislocated in the same (northwestern) direction; however, the disjunctive character of its boundaries with the older deposits does not make it possible to determine its tectonic relations to them.

Undoubtedly, the Lower Cambrian section of the Krasnoyarsk Ridge is the most complete of all known in the Sayan–Altai folded region and may be recommended as one of the principal reference sections for compiling a unified scheme of the biostratigraphic subdivision of the Lower Cambrian.

LITERATURE

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4. I. I. Koptev. On the stratigraphy of the Lower Cambrian of the northwestern part of the Eastern Sayan. Izv. TPI, vol. 120, Tomsk, 1961.

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6. I. I. Koptev. Stratigraphy and Paleontology of the Lower Cambrian of the Northwestern Part of the Eastern Sayan. Author’s abstract of dissertation. Publishing House of Tomsk State University, Tomsk, 1962.

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8. I. I. Koptev. On the correlation of the Kolbin and Torgashin formations of the Cambrian of the Krasnoyarsk Ridge. Materials on Regional Geology. Trudy SNIIGGIMS, issue 24, Gosgeoltekhizdat, 1962.

9. I. I. Koptev. On the correlation of Lower Cambrian sections of the northwestern part of the Eastern Sayan and the Siberian Platform. Materials on Geology and Mineral Resources of Western Siberia. Reports of the Conference. Publishing House of Tomsk State University, Tomsk, 1964.

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