ON THE BIOSTRATIGRAPHY OF CAMBRIAN DEPOSITS IN THE AREA OF MOUNT BALYKHTAG (BATENEVSKY RIDGE)

A. K. SEMASHKO, V. A. SHCHIPITSYN

(Presented by Professor A. G. Sivov)

In the summer of 1964, the authors of this article took part in the geological survey of the area of the Yuliya mine, located on the eastern slope of the Kuznetsk Alatau. As a result, new materials were obtained on the basis of which it appears possible to refine the paleontological content and age of the well-known Obruchev horizon. Particular attention was paid to establishing the stratigraphic sequence of the Cambrian carbonate deposits in the area of Mount Balykhtag (elevation 798.2 m), situated 4 kilometers NNE of the Yuliya mine.

Detailed geological observations were accompanied by the collection of paleontological remains—trilobites, archaeocyaths, and algae. The trilobites were studied by A. K. Semashko; the algae, by V. A. Shchipitsyn; the archaeocyaths, unfortunately, remained unstudied, with the exception of isolated forms.

Earlier, thematic investigations were carried out in the area by V. D. Tomashpolskaya and R. T. Bognibova, but since the results of these works have not yet been published, they are not considered in our article.

The geological structure of the area is deciphered thanks to the alternation of lithologically heterogeneous members. It has been established that the limestones compose the limb of a synclinal structure plunging in a SSW direction and complicated by additional folds and disjunctive disturbances of small amplitude. In the northern part, the Cambrian rocks are brought by a regional fault into contact with a carbonate-terrigenous sequence of Precambrian age—the Goldzhin Formation.

At the base of the section lie light-colored massive limestones of member A, containing an abundant fauna of trilobites and archaeocyaths. By origin, the limestones belong to deposits of reef facies [5], since the carbonate material is composed chiefly of remains of calcareous algae, often found in life position. The visible thickness of the member is not less than 200 m.

As can be seen from the accompanying scheme, point 2 lies west of the summit of the mountain and is situated within the field of development of the limestones of member A. Here a trilobite fauna was discovered, among which the following forms were identified: Erbia sibirica (Schm.) E. granulosa Lerm., Proerbia torgaschinica Rep., P. anomalica Rep., Edelsteinaspis gracilis Lerm.,

E. ornata Lerm., Kootenia anomalica Rep., Kooteniella acuta N. Tchern., Kooteniella sp., Bonnia globosa Tomashp., Bonnia sp., Paleooryctocephalus angulatus Rep., Eocorynexochus sp., Chondragraulos ujaricus Rep., Ch. minussensis Lerm., Pseudanomocarina sp.

Section along line I–I

Legend

Fig. 1. Sketch of the geological structure of the area of Mount Balykhtag: 1) Quaternary deposits; 2) unit “G”—dark-gray oncolitic limestones; 3) unit “V”—light-gray massive limestones; 4) unit “B”—black platy limestones; 5) unit “A”—light-gray massive limestones; 6) disjunctive faults; 7) fauna-collection points: a—trilobites, b—archaeocyaths; 8) microflora-collection points.

On the eastern spur of Mount Balykhtag (point 3057), at approximately the same stratigraphic level, algae were identified: Epiphyton jenisseicum Vologd., E. bublitschenkoi Vologd., E. fruticosum Vologd., E. fasciculatum Chapm., E. cf. reniforme Korde, Renalcis granosus Vologd., Botominella elanskensis (Reitl.), Kordephyton cf. crinitum (Korde), Paleonites (?) sp., Girvanella sibirica Masl., G. conferta Chapm. In the same unit, 40 m above the base of the platy limestones of unit “B” (point 1), trilobites were found: Bonnia globosa Tomashp., Bonnia sp., Kooteniella sp., Edelsteinaspis sp., Pseudanomocarina sp., and Elrathiella (?) sp. This list, with the exception of the last genus, corresponds to some extent to the list of trilobite fauna from point 2, but is poorer in species and in number-

faunal composition, which is explained by the incompleteness of the collections. We correlate this fauna with the fauna of locality 2.

Among the algae, the following have been identified here: Epiphyton fasciculatum Chapm., E. bublischenkoi Vologd., E. cf. reniforme Korde, Renalcis granosus Vologd., R. sp. nov., Botominella elanskensis (Reitl.), Tubophyllum longum (Korde), Paleonites (?) sp., Kordephyton cf. crinitum (Korde), Girvanella sibirica Masl., G. conferta Chapm.

At the top of this same unit, 1 m from the contact with black platy limestones, algae are sparse and are represented by the following forms: Epiphyton cf. reniforme Korde, Renalcis sp., Botominella elanskensis (Reitl.), Paleonites (?) sp., Girvanella sibirica Masl., Girvanella conferta Chapm.

Above lies unit Б, composed of dark-gray and black, brownish-tinged platy and bedded limestones, which is repeated twice in the section owing to an additional anticlinal fold. At many outcrops of unit “Б,” remains of trilobites and archaeocyaths are noted. Algae are very rare. The thickness of the unit is 100–110 m.

In this unit the following were found: Erbia sibirica (Schm.), Proerbia anomalica Rep., Kooteniella acuta N. Tchern., K. slatkowskii (Schm.), K. sp., Kootenia hirsuta Suv., K. sp., Bonnia sp., Olenoides sp., Amgaspis sp., Chondragraulos minussensis Lerm., Gaphuraspis aff. gaphuri Ivsh., Taxioura sp., Menneraspis delicata Jegor., archaeocyaths Tegerocyathus sp., Claruscyathus sp., Szecyathus sp. (preliminary identifications by V. D. Alimova), and algae Botominella elanskensis (Reitl.), Paleonites (?) sp., Epiphyton sp.

The next unit, В, is composed of white massive limestones of organogenic-algal origin, like unit А. The fauna is represented by trilobites; archaeocyaths were not discovered. The thickness of the limestones is not less than 150 m. The contact between the light massive limestones and the dark-gray oncolitic limestones is disjunctive; therefore the thicknesses given are incomplete. The trilobite fauna and algae in this unit were collected from two localities situated 300 m apart and lying at approximately the same stratigraphic level. At locality 2856 were found—Amgaspis medius N. Tchern., Kooteniella mutabilis N. Tchern., K. slatkowskii (Schm.), Olenoides laevigatus N. Tchern., Pseudanomocarina aojiformis N. Tchern., Chondragraulos minussensis Lerm. and algae: Epiphyton reniforme Korde, E. sp. nov., Renalcis granosus Vol., Kordephyton cf. crinitum (Korde), Girvanella sibirica Maslov, G. conferta Chapm.; and at locality 8—Kootenia aff. florens Suv., Kootenia sp., Kooteniella immanis Sivov, Olenoides calvus Laz., Chondragraulos minussensis Lerm., Pseudanomocarina sp., Chondranomocare sp., Erbia granulosa Lerm., Granularia sp., and the same algae as at locality 2856.

The youngest rocks in the area are the dark-gray massive oncolitic limestones of unit “Г,” whose thickness increases in a south-southeasterly direction and amounts to several hundreds of meters.

Here rare fragments of indeterminate trilobites have been noted, as well as tubular algae probably belonging to the tribe Vologdinelleae Korde and forms resembling solenopores. The oncolites are nodules composed mainly of interlacing tubes of girvanellas.

Table 1 shows the vertical distribution of trilobites by units.

Analyzing the species composition of trilobites in units А and Б, we may note that here, along with “surviving” forms, for example vi-

dams of the genera Proerbia Lerm., Bonnia Walcott and Eocorynexochus Korob., and forms characteristic only of the Obruchev horizon—Kootenia anomalica Rep., K. hirsuta Suv., Kooteniella acuta N. Tchern., Paleoorcytocephalus angulatus Rep., Chondragraulos ujaricus Rep., Menneraspis delicata Jegor., as well as trilobites of a broad vertical range (see Table 1), there is a considerable number of trilobites,

Table 1

which, first appearing in the Obruchev horizon, become widely distributed in the Amga Stage. These trilobites include representatives of the genera Olenoides Meek, Amgaspis N. Tchern., Gaphuraspis

Ivsh., Chondranomocare Polet. and species of the genus Pseudanomocarina N. Tchern. first found in the Obruchev horizon.

Thus, on the basis of the joint occurrence of the above-listed trilobite forms in the Obruchev horizon, it should be regarded as transitional. This point of view is held by P. S. Krasnopeeva [4], V. M. Yaroshevich [8], and N. P. Suvorova [7]. However, since the designation of transitional horizons is not accepted, the Obruchev horizon should be assigned to the very base of the Middle Cambrian.

A somewhat different picture emerges when the trilobite fauna in Bed V is analyzed.

Here, alongside a few long-ranging forms, there are typical representatives of the Middle Cambrian, characteristic of the Amgan stage. These are Kootenia aff. florens Suv., Kooteniella immanis Sivov., Kooteniella mutabilis N. Tchern., Olenoides calvus Laz., Olenoides laevigatus N. Tchern., Pseudanomocarina aojiformis N. Tchern., and Amgaspis medius N. Tchern. The absence of Gaphuraspis gaphuri Ivsh. and of some species of the genus Pseudanomocarina N. Tchern. is explained by the incompleteness of the collections.

The trilobite fauna of this bed is typically Middle Cambrian, and on this basis we assign the deposits of this bed to the Amgan stage of the Middle Cambrian.

Table 2

The most diverse species composition of algae is represented in Bed A (Table 2). Here, alongside forms that are recorded in deposits older than the Obruchev horizon and that pass into the Obruchev horizon—Renalcis granosus Vologd., Kordephyton cf. crinitum (Korde), Paleonites (?) sp., Botominella elanskensis (Reitl.), Epiphyton fasciculatum Shapm., E. fruticosum Vologd.—there are species known previously from the lower Middle Cambrian—Epiphyton cf. reniforme Korde,

E. jenisseicum Vologd., E. bublitschenkoi Vologd., Tubophyllum longum (Korde) [1, 2, 3].

The algae of member B are represented by a species of the Elan horizon of the Siberian Platform—Botominella elanskensis (Reitl.) and Paleonites (?) sp. [6].

In member B the algal assemblage is very close to the assemblage of member A, which should probably be explained by identical conditions of limestone formation. The differences consist in the mass development of the Middle Cambrian Epiphyton reniforme Korde and E. sp. nov., in the presence of a few Lower Cambrian relicts, and in the disappearance of certain species occurring in abundance in member A.

The age of member G remains unclear, since the trilobites are indeterminate, and the algae of the genus Girvanella Nich. et Eth., represented here, have no stratigraphic significance.

Conclusions

1. In the section of the Mount Balykhtag area, four members of carbonate rocks are clearly distinguished, each of which is characterized by a definite assemblage of trilobites and algae.

There is a close connection among the three lower assemblages of organic remains, expressed in the common occurrence of many forms.

The trilobites of members A and B are similar in composition, although differences are also observed. This is connected with the relatively different ages of the deposits, different facies conditions of sediment accumulation, and, evidently, the incompleteness of collections in member B.

The deposits of member V, which lie stratigraphically higher, belong to a younger horizon of the Middle Cambrian.

1. The fact that trilobites Olenoides sp. and Amgaspis sp. are found together with archaeocyaths in one outcrop deserves attention. Possibly this area will prove to be the most promising for clarifying the question of the persistence of archaeocyaths into the Middle Cambrian.

2. The similarity of the algal assemblages from members A and V testifies to similar conditions of sediment accumulation. The conditions for the existence of algae during deposition of member B were unfavorable, which was expressed in a sharp impoverishment of their composition.

Literature

1. A. G. Vologdin. The Most Ancient Algae of the USSR. Publishing House of the Academy of Sciences of the USSR, 1962.

2. G. A. Ivankin, I. I. Koptsev, V. E. Nomokonov. On the stratigraphy of the Upper Precambrian and Cambrian of the Kulburtsty district (eastern slope of the Kuznetsk Alatau). Geology and Geophysics, No. 4, 1964.

3. K. B. Korde. Cambrian algae of the southeast of the Siberian Platform. Transactions of the Paleontological Institute, Academy of Sciences of the USSR, vol. 89, 1961.

4. P. S. Krasnopeeva. New data on the stratigraphy of archaeocyaths of Western Siberia. Doklady of the Academy of Sciences of the USSR, vol. 99, No. 4, 1954.

5. G. F. Krasheninnikov. Facies, genetic type, and formation. Izvestiya of the Academy of Sciences of the USSR, Geological Series, No. 8, 1962.

6. E. A. Reitlinger. Atlas of microscopic organic remains and problematics of the ancient strata of Siberia. Transactions of the Geological Institute, Academy of Sciences of the USSR, issue 25, 1959.

7. N. P. Suvorova. Trilobites, Corynexochids, and their historical development. Transactions of the Paleontological Institute, vol. SIII, 1964.

8. V. M. Yaroshevich. On the structural-facies zones of the Cambrian of the eastern slope of the Kuznetsk Alatau. Doklady of the Academy of Sciences of the USSR, vol. 121, No. 2, 1958.