ON THE DISCOVERY OF TRILOBITES OF THE GENUS BULAIASPIS IN THE LOWER CAMBRIAN DEPOSITS OF THE BATENEVSKY RIDGE

V. D. Tomashpolskaya, R. B. Karpinsky

(Presented by the scientific seminar of the Department of General Geology)

In the summer of 1958 we first found remains of trilobites of the genus Bulaiaspis in carbonate deposits in the area of the village of Sukhaya Erba. In the same year we made extensive collections of archaeocyathan fauna in the same and overlying beds in the area between the village of Sukhaya Erba and the settlement of Bagrad.

The geological setting in which these trilobites were found is briefly as follows.

On various Precambrian sequences, characterized only by algae, including upon the effusives of the Loshchenkovskaya Formation, there rests unconformably a Lower Cambrian sequence, within which two formations are clearly distinguished: the Bagradskaya and the Chesnokovskaya.

Both of these formations in the area of the villages of V. Erba–Bagrad form a simple syncline, which we call the Bagradskaya syncline.

In terms of lithological characteristics and stratigraphic position, two subformations are distinguished from bottom to top within the Bagradskaya Formation.

The lower subformation is represented essentially by light-colored massive or schistose limestones, among which interbeds of light dolomites and dark bedded limestones sometimes appear. The color of the limestones is most often light gray, but it may also be light pink or light coffee-colored. The dolomites are massive in texture, light gray in color, and have a porosity characteristic of them and inclusions of quartz. The thickness of the dolomite interbeds is measured in tens of meters.

The dark limestones are usually clearly bedded; they are interbedded with dolomites and have a thickness of units and tens of meters. They are confined to the middle and upper parts of the subformation. The subformation contains interbeds of gravelites composed of fragments of siliceous rocks.

In the middle part of the subformation, in an interbed of thin-platy gray-black limestones, we collected remains of gastropods, represented by two genera: Scenella cf. clothо Walc. and Helcionella sp.¹

The thickness of the lower subformation is 1300 m. The upper subformation of the Bagradskaya Formation, about 600 m thick, is composed mainly of light-gray massive and coarse-platy limestones with interbeds of dark-gray limestones, and, rarely, of dolomites and siliceous rocks.

¹ Determinations by N. A. Aksarina, junior paleontologist of ZSGU.

In interbeds of dark limestones on the summit of the mountain with elevation 590.3 m, hyoliths were found.

Near the roof of the upper subformation of the Bagrad Formation, in a small lenticular interbed of dark-gray limestone occurring among massive light-colored limestones, in 1958 we for the first time found on the Batenevsky Ridge trilobites of the genus Bulaiaspis: Bulaiaspis taseevica Rep. and Bulaiaspis vologdini Lerm. (point 1710).

From these same beds the trilobite fauna was later collected by I. T. Zhuravleva, D. I. Musatov, and others [8]. L. N. Repina [10] also found olenellids here (p. Fallotas, pibella).

On the southern limb of the same syncline, the deposits of the Bagrad Formation are exposed, apparently by their upper part, and are represented by members of dark-gray limestones with rare interbeds of siliceous shales and light limestones. We did not find fauna in these deposits. The rocks of the formation are gathered into rather complex folds and are overlain by a bed of homogeneous light massive limestones of the Chesnokovka Formation with archaeocyaths, which are found already at the very base of the formation.

The contact of the Bagrad Formation with the underlying Yenisei Formation is disjunctive, and therefore the lower parts of the Bagrad Formation are absent in this limb. The northern contact of the formation, where it borders on the overlying Chesnokovka Formation, is undoubtedly transgressive.

I. T. Zhuravleva and others [5], within the distribution of the rocks of the Bagrad Formation (according to our scheme), found archaeocyaths and trilobites of the impoverished Bazhanikha complex.

In the area of the village of B. Erba, deposits of the Bagrad Formation are exposed only in a small area between Mount Peshchernaya (elev. 727.4) and Mount Chesnokovaya. Here the deposits of the formation are bounded along a disjunction by the underlying Yenisei Formation, are overlain by limestones of the Chesnokovka Formation, and are represented by members of alternating dark-gray bedded and light limestones, gathered into steep compressed folds complicated by small additional folds. In the dark limestones we found hyoliths, and in the light ones—isolated archaeocyaths.

Trilobites of Bulaiaspis were not found in these beds.

The overlying Chesnokovka Formation is represented by a bed of homogeneous massive or coarse-platy limestones of gray or grayish-white color, characterized by the presence of archaeocyathan fauna from the very base.

In the lower parts of the limestones of the Chesnokovka Formation (points 948, 958, 940, K-110, 303, 304), composing the southern limb of the Bagrad syncline and attaining a thickness of about 200 m, the following forms are found among the archaeocyaths: Ajacicyathus patulus (Born.), A. ijiskii (Toll.), A. grandis (Vologd.), Archaeolynthus tubexternus (Vologd.) Archaeocynthus sp., Archaeocyathus sp., Altaia mutabilis Posp., Archaeosicon (?) sp., Coscinocyathus aff. retetabule Vologd., Dictyocyathus javorskii Vologd., Dictyocyathus sp., Loculicyathus membranivestites Vologd., Loculicyathus sp., Nochoricyathus howelli Zhur., Nochoricyathus lenaicus Zhur., Nochoricyathus cf. mariinskii Zhur., Russocyathus sp., Tersia sp., Protophaetra sp.

In higher units of the Chesnokovka Formation, expressed near the closure of the syncline (points 951, 952, 954, 940, 966, 970, 975, 417, 416, 428) and having a thickness of 200 m, the composition of the archaeocyaths is represented already by the following forms: Ajacicyathus cf. grandis (Vologd.), Aj. aff. laevigatus (Vologd.), Aj. clarus (Vologd.), Aj. cf. immanis (Vologd.), Archaeolynthus sp., Archaeolynthus aff. tubexternus (Vologd.), Arch. cf. bimurus (Vologd.) Archaeosicon (?) sp., Archaeocyathus sp., Archaeofungia gerassimovensis Krasn., Altaia sp., Archaeolynthus bimurus (Vol.), Bicyathus

sp., Coscinocyathus rojkovii Vol., Carinocyathus sp., Cystocyathus sp., Clathriasterocyathus sp., Dictyocyathus cf. javorskiji Vologd., D. cf. tuvaensis Vologd., Ethmophyllum sp., Loculicyathus congruens Vologd., L. tolli Vologd., Lucyathus sp., Lenocyathus sp., Nochorocyathus mirabilis Zhur., Orbinochorois sp., Protopharetra sp., Retecyathus sp., Szecyathus sp., Tumulocyathus pustulatus Vologd., Thalamocyathus sp., Tumulocyathus admirabilis Vologd., Tersia sp.

Schematic geological map of the area near the village of Verkhnyaya Erba

1 — dolomites, quartzites, marbles (Yenisei Formation), 2 — interbedding of light and dark-gray limestones with rare interlayers of dolomites (Bagrad Formation), 3 — light-gray massive limestones (Chesnokov Formation), 4 — Devonian effusives, 5 — points with fauna, 6 — archaeocyaths, 7 — trilobites, 8 — gastropods, 9 — hyoliths, 10 — tectonic boundaries, 11 — stratigraphic boundaries, 12 — inferred boundaries.

Table of the species composition of the most widespread archaeocyaths

Continuation of table

Legend: ×× — very many; × — many; — — very few; + — isolated.

Almost at the very top of the Chesnokovskaya Formation, forming the hinge of the synclinal fold described and reaching a thickness of 150 m (points 53, 418, 105, 950, 957, 973, 972), the archaeocyaths are dominated by: Ajacicyathus anabarensis (Vologd.), A. khemtchikensis (Vologd.), A. subtilis (Vologd.), A. cf. immanis (Vologd.), A. suchiensis (Krasn.), A. cf. flexum (Vologd.), A. cf. clarus (Vologd.), Archaeolynthus sp., Archaeolynthus tubexterius (Vologd.), Aptocyathus sp., Annulocyathus sp., Bronchocyathus sp., Coscinocyathus cf. rojkovj Vologd., C. cf. loculatus Vologd., C. sp., Clathricoscinus infirmus (Vol.), Carinocyathus (Vologd.), Dictyocyathus javor­skij (Vologd.), Ethmophyllum sp., Loculicyathus sp., Lucyathus sp., Orbicyathus sp., Nochorojcyathus sp., Retecyathus sp., Szecyathus sp., Syringocyathus sp., Thalamocyathus sp., Taylorcyathus sp., Tegerocyathus sp. (Table 1).

On the northern limb of the same syncline, the first finds of archaeocyath remains are also near the base of the Chesnokovskaya Formation¹ and are represented by forms occurring in the first and second members of the southern limb of the same syncline.

On the basis of the factual material presented above, two complexes are clearly distinguished within the Chesnokovskaya Formation.

The lower complex, stratigraphically confined to the lower part of the Chesnokovskaya Formation and characterized by numerous species of the genera Ajacicyathus, Archaeolynthus, Coscinocyathus, Nochorojcyathus, Dictyocyathus, and others, is very similar to the faunal complex of the Bazaikhskaya Formation, the Torgashinskaya Formation (lower parts), the Balakhtisonskaya Formation (lower parts), and to the fauna of the limestones of the Kiya River and others.

P. S. Krasnopeeva called such a complex the Chesnokovskaya complex [6].

The upper complex, stratigraphically confined to the upper parts of the Chesnokovskaya Formation and characterized by the appearance of such genera as Syringocyathus, Tercyathus, Tegerocyathus, Aptocyathus, Annulocyathus, is very similar to the faunal complex of the upper parts of the Balakhtisonskaya and Torgashinskaya Formations, to the fauna of the Verkhnemonokskaya Formation, and is called by many geologists the Sanashtykol complex. However, there is no complete analogy between these complexes and the Sanashtykol complex, since it contains only individual forms of archaeocyaths and trilobites known from the Sanashtykol limestones.

Following P. S. Krasnopeeva, we propose to call this complex the Upper Chesnokovskaya complex [6].

I. T. Zhuravleva, L. N. Repina, and others [5, 10], in several articles, give a description of the area of the village of Bolshaya Erba, where they distinguish the combined Bazaikhian, Bazaikhian, Kameshkovian, Sanashtykolian, and even Solontsovian horizons with the corresponding fauna of archaeocyaths and trilobites.

The beds with Bulaiaspis are assigned by them to the Kameshkovian horizon.

It follows from our materials that the beds with Bulaiaspis lie stratigraphically below the Chesnokovskaya Formation and that the Bagradskaya Formation may be an analogue of the Kolbinskaya Formation of the Eastern Sayan.

REFERENCES

1. Vologdin A. G. Atlas of guide fossils of the fauna and flora of the USSR, 1940.
2. Zhuravleva I. T. Archaeocyaths of the Cambrian of the eastern slope of the Kuznetsk Alatau. Transactions of the Paleontological Institute, vol. 56, 1955.
3. Zhuravleva I. T., Repina L. N. Generic complexes of trilobites and archaeocyaths of the Lower Cambrian of the Altai-Sayan region. Doklady of the Academy of Sciences of the USSR, vol. 129, No. 1, 1959.
4. Zhuravleva I. T. Archaeocyaths of the Bazaikhian horizon of the Kiya River. Doklady of the Academy of Sciences of the USSR, vol. 124, No. 2, 1959.

1. Zhuravleva I. T., Repina L. N., Khomentovskii V. V. Scheme for the subdivision of the Lower Cambrian deposits of the Sayano-Altai region, journal Geology and Geophysics, No. 1, 1962.

2. Krasnopeeva P. S. Archaeocyaths and archaeocyath–trilobite horizons of the Cambrian of the Altai-Sayan region. Materials on the Geology of Western Siberia, issue 61, ZSGU, 1958.

3. Musatov D. I., Nemirovskaya V. N., Shirokova E. V., Zhuravleva I. T. The Sretenskii section of the Cambrian in the Eastern Sayan. Materials on the Geology and Mineral Resources of Krasnoyarsk Krai, issue 2, 1961.

4. Musatov D. I. Stratigraphy of the Cambrian deposits of the eastern slope of the Kuznetsk Alatau. Academy of Sciences of the USSR, journal Geology and Geophysics, No. 2, 1961.

5. Koptev I. I. New data on the age of the Torgashino limestone, journal Geology and Exploration, Izvestiya vuzov, No. 4, 1961.

6. Repina L. N. On the discovery of olenellids in the Lena stage of the Batenevsky Ridge. DAN USSR, vol. 136, No. 4, 1960.

1. From the beds with Bulaiaspis of the Bagradskaya Formation, the limestones with archaeocyaths of the Chesnokovskaya Formation are 200–250 meters away. ↩