NEW DATA ON THE STRATIGRAPHY AND LITHOLOGY OF THE UPPER PRECAMBRIAN AND LOWER CAMBRIAN DEPOSITS OF THE BATENEV RIDGE

A. F. Senakolis, I. I. Koptev, V. A. Shipitsyn

(Presented by Prof. A. M. Kuzminykh)

In the course of detailed geological mapping and thematic investigations into the lithology of Cambrian deposits in the area of the settlement of Yuliya—Katyushkina village (Batenev Ridge), we obtained new materials on the stratigraphy, paleontology, and lithology of the ancient strata of this area. Below are given a description of the stratigraphy and lithology, and lists of organic remains, chiefly from the Upper Precambrian–Lower Cambrian sequence exposed 6 km east of Katyushkina village on the right side of the Podtemnyi ravine. The distinctive character of the organic remains first discovered in this area (trilobites, hyoliths, algae, archaeocyathids, and brachiopods) and the specific features of the lithology of this sequence make it possible to raise the question of distinguishing a new series¹, for which the provisional name Kureninskaya is proposed for the time being (after the Kuren River, in whose area outcrops of the rocks of the series are widespread).

On the geological maps of previous investigators (B. N. Krasilnikov, B. P. Zubkus), the deposits of the Kureninskaya Series are combined with Precambrian volcanogenic-sedimentary formations of the Loshchenkovskaya and marbled limestones of the Goldzhinskaya formations into a single stratigraphic subdivision, with an age of the upper parts of the Lower Cambrian (B. P. Zubkus) or the lower parts of the Middle Cambrian (B. N. Krasilnikov). These authors provide no paleontological substantiation for the age of the sequence.

V. D. Tomashpolskaya and R. B. Karpinsky (1958) separate this sequence from the Loshchenkovskaya and Goldzhinskaya formations, regarding it as predominantly Sinian in age. These authors likewise do not substantiate their point of view with paleontological data.

A preliminary study of the paleontological remains and a lithological study of the rocks make it possible, within the limits of the area of interest to us (Fig. 1), to confirm the separation earlier proposed by V. D. Tomashpolskaya and R. B. Karpinsky of the Precambrian Goldzhinskaya and Loshchenkovskaya formations, to agree with these investigators’ opinion on distinguishing the overlying sequence as an independent complex, for which we propose the name Kureninskaya Series, and to refine the age of the overlying volcanogenic sequence.

The rocks of the Goldzhinskaya Formation are exposed in the eastern part of the area described and are represented predominantly by black

Section along line AB

Legend:

Fig. 1. Schematic geological map of the area of the Kuren’ site: 1 — Quaternary deposits; 2 — volcanogenic unit; 3–9 — deposits of the Kuren’ Series: 3 — terrigenous-carbonate deposits of member 7; 4 — massive, outwardly homogeneous limestones of member 6; 5 — variegated member 5; 6 — black bedded limestones of member 4; 7 — dolomites of member 3; 8 — carbonate-terrigenous member 2; 9 — limestone-dolomite member 1; 10 — volcanogenic-sedimentary formations of the Lyoshchekovskaya Formation; 11 — thin-platy marbled limestones of the Goldzhinskaya Formation; 12 — disjunctive fault; 13 — localities with faunal remains: a) trilobites, b) archaeocyaths; 14 — localities with remains of algae and Problematica: a) algae, b) Katagraphia, c) Problematica.

thin-bedded and thin-platy marbled limestones. In the roof of the Goldzhin Formation problematic formations of the Saralinskia type (sample 3694) have been found; these are widespread in Upper Precambrian deposits of many districts of the Kuznetsk Alatau (the Bidzha Formation of V. A. Borisov, distributed within Bateny somewhat east of the area described [1]; the Poludennaya Formation of G. A. Ivankin et al. from the area of the middle course of the Bely Iyus River [2]; the Glavstan Formation of the Sarala district, etc.). Interbeds and packets of dirty-gray shales and clayey marbled limestones are of secondary importance within the formation. The beds of this formation have a northeastern strike and a steep (80–85°) dip to the west.

Without a visibly structurally expressed unconformity, and with a thin (units of meters) conglomerate at its base, the volcanogenic-sedimentary Loshchenkov Formation lies above. The underlying conglomerate consists of well-rounded siliceous pebbles in a cherry-brown quartz-sandstone cement. The formation contains greenstone porphyrites, not infrequently with a fluidal texture and fragments of the same porphyrites in a lava cement, tuff sandstones, tuff conglomerates, tuffites, clay shales, lydite, and black thin-bedded marbled limestones with oncolites. The thickness of the formation in the section described is 220 m, but in a southwesterly direction it rapidly increases to 1 km (Mt. Romanovskaya), and porphyrite conglomerates begin to play the predominant role in the structure of the formation there.

By stratigraphic position and material composition the Loshchenkov Formation can confidently be correlated with the Kulbyurstyug Formation of the Bely Iyus River district [2], the lower subformation of the Sosnovka Formation of V. A. Borisov [1], and their analogues.

In thin sections, the limestones of the Goldzhin and Loshchenkov formations are distinguished by complete recrystallization of the carbonate material. “Pelitomorphic,” microgranular calcite is absent in all varieties of carbonate rocks. Grain size ranges from 0.03 to 0.1 mm. Their characteristic feature is crystallization schistosity, expressed in an ordered orientation, along the bedding, of elongated grains of recrystallized carbonates. This texture testifies to a clearly expressed regional metamorphism of the rocks of the formations. The absence of organogenic and detrital varieties, characteristic of the overlying Kurenin Series, is conspicuous.

On the porphyrites of the Loshchenkov Formation there also lies, without a visibly structurally expressed unconformity, a terrigenous–dolomite–limestone sequence (the Kurenin Series), within which 7 packets can be distinguished. These packets, in turn, may be grouped into two subdivisions, the rank of which, for lack of sufficient material, is not yet established. These two subdivisions include the 3 lower packets on the one hand and the 4 upper packets on the other. In the lower three packets, remains of skeletal organisms have not yet been encountered, while the problematic forms found in them indicate their Precambrian (Riphean and Vendian) age. By contrast, in the upper three packets abundant fossils of many groups of animals and algae are encountered, characteristic of the Lower Cambrian (the poorly preserved algal remains occurring in the middle packet cannot be determined). The lower three packets are characterized by the wide development of dolomites, whereas higher up they occur only as fragments in sandy varieties of rocks or (very rarely) as thin (several centimeters) interbeds among the predominant limestones.

The lower limestone–dolomite member, 120 m thick, is composed of dark-gray platy limestones and light-gray massive “sparkling” dolomites. The limestones are distinguished by distinct bedding, a clastic structure, and a significant admixture of terrigenous material. The dolomites, as a rule, lack clear bedding and contain oncolites, among which Osagia tenuelamellata Reitl. is identified, a characteristic form of the middle Riphean of the Siberian Platform and occurring in the lower and middle parts of the Sosnovskaya Formation [1].

The following member, the second, is composed of interbedded conglomerates, sandstones, argillites, and limestones. The limestones are usually dark gray, medium- and fine-grained, oncolitic. In them there is often an admixture of tuffaceous material—fragments of porphyrites, volcanic glass, and water-clear crystals of plagioclase with serrated, ragged edges. The argillites have a dirty greenish coloration and are often cross-bedded and lumpy on the surface. The conglomerates consist of fragments of oncolitic dolomites with Osagia tenuelamellata Reitl., porphyrites, and argillites. The average size of the fragments is 5 cm. Among the limestones there occur lenses of black siliceous rocks, which at first glance resemble concretions. Microscopic study of the silicilites shows that they are organogenic formations consisting of accumulations of spherical bodies 0.2–0.8 mm in size. These bodies have a radial-fibrous internal structure, caused by the radial distribution of a black (bituminous?) substance in a homogeneous fine-grained siliceous aggregate. The spherical bodies themselves are enclosed in a fine-grained siliceous aggregate. Most of all, these siliceous rocks resemble radiolarites. The total thickness of the member is 260 m. In the northeastern part of the area, carbonate varieties noticeably predominate, whereas in the southwestern direction terrigenous character increases. The size of the fragments in the conglomerates increases, the sandstones become coarser-grained and pass into gravelites, and the content of terrigenous admixture in the limestones increases.

The third member—dolomitic—is composed of “sparkling” light-gray and white dolomites of organogenic structure. These rocks were formed with the broad participation of various algae. Carbonate material was deposited at the site of algal growth, as indicated by the wide development of biohermal varieties and the absence of sorting in the detrital varieties. Among the predominant organogenic dolomites there occur two- and three-meter beds of dolomite breccias, the cement of which is calcareous material. The composition of the dolomite member is generally homogeneous and persistent along strike, although the appearance of thin interbeds of clayey dolomites is observed when moving to the southwest. The thickness of the member is 165 m. Among organic remains in this member there have been found: Vesicularites concretus Z. Zhur., V. magnus Milst., V. cf. flexuesus Reitl., Osagia cf. torta Milst., Vermiculites forma indet., Glebosites forma indeterm. The listed problematica usually occur in deposits distinguished as Riphean and Vendian.

The three members of the Kureninskaya Series described above, by their assemblage of problematica and lithologic composition (predominance of dolomites), may be correlated with the middle part of the Sosnovskaya Formation [1] and the Tarzhul Formation of the region of the B. Iyus River [2].

The overlying fourth member is composed mainly of microgranular oolitic and oncolitic limestones, clayey limestones, and carbonate sandstones. Rare thin interbeds of dark-gray clayey dolomites occur. At the base of the member

there are beds of carbonate breccias formed as a result of erosion of the underlying dolomites. The cement of the breccias is a cherry-red carbonate-clayey material. Toward the southwest, among the limestones, interbeds of sandstones appear at various levels; their fragments consist chiefly of light-colored dolomites and siliceous rocks, and the cement is a calcareous-clayey mass. In the same direction, an increase in the admixture of clayey material in the limestones is noticeable. A yellowish-brown color of these rocks upon weathering is characteristic. The lower beds of the member contain a larger amount of terrigenous admixture. Thickness 210 m. Algal formations in the limestones of this member cannot be determined because of poor preservation.

The next—the fifth—member has a very variegated composition and, from base to top, is saturated with organic remains of trilobites, hyoliths, archaeocyaths, brachiopods, pterocyathids, various algae, and problematica. The member begins with varicolored beds—cherry-red, pink, yellow, green, and gray organogenic-detrital limestones, clayey limestones, and argillites, about 60 m thick. In the roof of the varicolored beds trilobites were encountered (outcrop 2987): Calodiscus cf. chachlovi Fedjan, Serrodiscus cf. levis Repina, Serrodiscus cf. pokrovskajae Polet., Chondragraulina sp., Hebediscus? sp., Erbia sp., Proerbia sp., Neoredlichina sp., Neocobboldia sp., and others. Here also (and in outcrop 3642) hyoliths, archaeocyaths, brachiopods, and algae are abundant: Adiaksia eleganta gen. nov., Subtifloria delicata Masl., Girvanella sibirica Nasl., Epiphyton sp., Renalcis sp., Vologdinelleae sp., Bija sibirica Vologdin. Higher in the fifth member, black clayey and conglomerate-like limestones predominate. White epiphyton limestones occur in fragments of the latter. Oolitic and organogenic-detrital varieties are widespread. In this part of the member (outcrops III-38; 3086) trilobites were encountered: Onchocephalina cf. incrassa Rep., Redlichina sp., Onchocephalina sp., Proerbia cf. semota Lerm., Kootenia cf. ontoensis, N. Tchern., a form close to Namanoiclla Tomaschr. and others; brachiopods—Kutorgina sp., Obolella sp., and others; hyoliths, archaeocyaths, pterocyathids, and algae (outcrop 3506): Renalcis cf. granosus Vol., R. gelatinosus? Korde, Epiphyton benignum Korde, E. scapulum Korde, E. cf. bifidum Korde, Kordephyton sp., Subtifloria sp., Vologdinelleae sp.

In the upper, essentially terrigenous part of this member, brachiopods and trilobites occur (Bonnia sp., Onchocephalina sp., Pagetidae, not more precisely determinable) (outcrop 3099a). The total thickness of the member is 230 m. The entire member is characterized by a considerable content of terrigenous admixture and by the organogenic-detrital character of the limestones. In thin section, the clayey mass of the argillites is distinguished by an almost isotropic structure and a disordered orientation of flakes of sericite-like material. Occasionally, microsegregations of siliceous material, carbonate grains, and a tuffogenic admixture are found in it.

The next—the sixth—member is composed, in outward appearance, of rather uniform microgranular limestones of light-gray and gray color and massive texture. At the base of the member, on the siltstones of the preceding one, there lies, with a gradual transition, a five-meter bed of gray trilobite-brachiopod shell limestones, locally with archaeocyaths and algae. No changes in the composition of the member along strike are observed. Its thickness is 160 m. In several outcrops (3475, 3100, 3099b), organic remains were encountered in the limestones of the member, among which algae were identified—Epiphyton sp. and Renalcis sp.;

trilobites—Redlichina sp., Onchocephalina sp., Erbia sp. (E. granulosa?), brachiopods—Kutorgina and others, archaeocyaths.

The seventh member, which completes the section of the Kuren’ series, consists of thinly interbedded flysch-like clayey and clayey-calcareous rocks with a characteristic “ribbed” weathering surface (in a section transverse to the bedding). The thickness of individual interbeds does not exceed 1–1.5 cm. The clayey interbeds are, in textural features, analogous to the argillites of the fifth (variegated) member. The calcareous varieties of rocks are usually recrystallized, but in some samples their organogenic-clastic structure is noticeable. Thickness 75 m. In the middle part of the member (sample K-11) indeterminable remains of large trilobites occur.

For all the members of the Kuren’ series in the area described, the characteristic attitude is a dip to the northwest at an angle of 80–50°. Closer to the top of the series the dip angles become gentler (down to 40°).

The age of the lower three members, as already noted, is determined from the assemblage of algae and problematics as Middle Riphean—Vendian; the fourth member contains no determinable fossils, while the upper three members are undoubtedly Lower Cambrian. The composition of the trilobites and algae from the lower parts of the variegated (fifth) member indicates that its age is no younger than Sanashtykgol. The presence of common forms (Calodiscus, Neoredlichina, Hebediscus, Erbia, and a number of algae) with the fauna of the Adiak (Mrass) Formation of Gornaya Shoria, common forms (Serrodiscus) with the Shashkunar and Isha formations of Gorny Altai [5], and the identical composition of some algae, brachiopods, and hyoliths with the Ust’-Kundat Formation of the Kiya River make it possible to speak of a Bazaikha-Kameshki age for the base of the variegated member. The overlying members of the Kuren’ series contain an as yet poorly studied assemblage of organic remains, but the presence in the sixth member of the trilobites Redlichina and Onchocephalina indicates its Dobrutian age (Upper Sanashtykgol?). It should be noted that some forms considered Sanashtykgol (Chondragraulina, Calodiscus pokrovskajae, Proerbia) [7] also occur at the base of the fifth member together with more ancient ones.

It is most logical to draw the boundary between the Cambrian and the Precambrian within the series at the base of member 4, taking into account the break at its base (breccias made up of dolomite fragments) and, probably, the significant erosion of dolomites, which occur as fragments in sandstones at various stratigraphic levels within member 4. The probable erosion of the dolomites may also be indicated by the fact that in neighboring areas the Riphean dolomite sequence always has a considerable thickness (the dolomites of the Sosnovka Formation—more than 100 m [1], the Tarzhul Formation—several thousand meters [2]).

In order to resolve questions of subdividing the Kuren’ series into smaller stratigraphic units and of drawing within it the boundary between the Cambrian and the Precambrian, we carried out a bed-by-bed study, in thin sections, of the lithological features of the carbonate rocks of all its members. It was established that all the carbonate rocks of the series represent a single genetic type [4]; their accumulation and transformation generally proceeded under the same conditions throughout the entire period of formation of the sequence. In all horizons the carbonate rocks are represented by three principal components: a) microgranular calcite, b) carbonate clasts that entered the sediment in a solid state, and c) a noncarbonate admixture. In addition, secondary calcite, formed—

entered the stage of diagenesis and metagenesis [5]. These three constituent parts make it possible to judge the primary material of the sediments that subsequently gave rise to the limestones. The microgranular calcite, which often constitutes the main part of the rock, does not make it possible to judge its genesis and, in this connection, is of no importance in solving the problem we have posed.

Carbonate fragments that entered the sediment in a solid state are nuclei formed during the filling of cavities and hollows of shells and other bodies, chiefly of organogenic origin. At all stratigraphic levels within the series, carbonate rocks predominate whose sediment consisted mainly of nuclei. Terrigenous admixture and other particles are quantitatively subordinate and are distributed unevenly in the section, playing different roles in the composition of the carbonate rocks of the various members. Predominantly this is clayey material, more rarely coarser material, which subsequently produced beds of obliquely laminated clayey limestones, terrigenous rocks, and breccias of carbonate composition. The nuclei, which play the most important role in the composition of the carbonate rocks, have distinct rounded, pear-shaped, oval, and drop-like outlines. They may consist of monocrystals or of an aggregate of calcite grains. During diagenesis, a calcite monocrystal could grow further, enclosing clayey or bituminous matter and changing the color of the regenerated part in comparison with the coloration of the primary nucleus. Accumulation of nuclei led to the formation of varieties of rocks that, with a certain degree of conventionality, may be called shell or organogenic-clastic limestones. These rocks appear beginning with the first member and occur in one quantity or another throughout the entire section of the Kurenin Series. In all probability, their formation is connected with the life activity of various organisms and the mechanical redeposition of the products of this life activity. The mechanical nature of the carbonate sediments is indicated by the rhythmicity of sediment accumulation, oblique bedding in clayey varieties with an admixture of nuclei, and interbeds of terrigenous rocks.

Shell limestones are, as it were, the “background” of the entire sequence, in which the most varied rocks occur at different stratigraphic levels. This feature of the sequence also makes it possible to speak in general of uniform conditions throughout the entire time of its formation, although the presence of breaks in this large sedimentary cycle is not excluded. All carbonate rocks of the series also have the same degree of metamorphism, much less than that of the rocks of the underlying Goldzhin and Loshchenkov formations.

On the seventh member of the Kurenin Series there lies a volcanogenic sequence of intermediate-basic composition, which is especially widespread somewhat south of the area described, in the vicinity of elevation 808.5 m. Many researchers consider this sequence to be young, unconformably overlapping all the previously described deposits. Thus, B. N. Krasilnikov, V. D. Tomashpolskaya, and R. B. Karpinsky assigned it to the Middle Cambrian (the Yuli and Taidon formations), and M. K. Vinkman and A. B. Gintsinger (1962) tentatively to the Byskar Series of the Devonian.

In the section of the right side of Podtemnyi Log, the direct contact of the volcanogenic sequence with the underlying rocks is obscured by numerous dikes of porphyrites intruding here. In the area of elevation 808.5 m, the impression is created that the volcanogenic rocks wedge into the upper members of the Kurenin Series. Still farther to the southwest, all seven members of the latter along the strike abut against the volcanogenic sequence. This fact allowed the majority of previous researchers

regard the occurrence of the volcanogenic unit upon the underlying deposits as unconformable. The materials obtained by us may indicate a very rapid facies transition of the rocks of at least the upper four members of the Kurenin Formation along strike in a southwesterly direction into the volcanogenic unit. In this case the lower parts of the volcanogenic unit will correspond to the upper four members of the Kurenin Formation, and the upper parts of the effusive-clastic unit will overlap the rocks of the Kurenin Formation. The following facts confirm this point of view: 1) the rocks of most members of the Kurenin unit, in a southwesterly direction along strike, become more terrigenous and often contain an admixture of tuffaceous material; 2) within the volcanogenic unit, near its top, almost along the strike of the upper member of the Kurenin Formation, north of the 808.5 m summit, there is a thick lens of limestones with archaeocyaths and trilobites: Proerbia sp., Menntraspeis delicata Jegor., Bonnia sp., and Namanoia cf. incerta N. Tchern. In age the limestones of this lens scarcely differ from the limestones of the upper members of the Kurenin Formation; 3) as already noted, the beds of the Kurenin unit pinch out along strike in the field of distribution of volcanogenic rocks, and almost at a right angle to the contact. If an unconformable overlap of the tuffaceous-effusive unit is assumed, we would have to speak of its discordant relation to the underlying rocks and of different structural levels, whereas by fauna the age of these “levels” is one and the same. Such breaks, with the manifestation of major folding within the upper parts of the Lower Cambrian, have not yet been noted by anyone and are hardly possible here.

Thus, in our opinion, the volcanogenic unit described is of uppermost Lower Cambrian age and, probably, in its lower parts corresponds at least to several upper members of the Kurenin Formation. In composition the volcanogenic unit is rather variegated. It includes porphyrites, tuff-conglomerates and lava-conglomerates; interbeds of clayey-calcareous and sandy rocks are encountered more rarely, as well as lenses of light-gray limestones with archaeocyaths and trilobites of the uppermost Lower Cambrian. It is characteristic that limestone lenses within the volcanogenic unit occur only in the northern part and disappear completely toward the southwest. Lavas and lava breccias with a distinct fluidality are abundant in the composition of the volcanogenic unit.

Thus, the results obtained by us make it possible to affirm that the Goldzhin and Loshchenkov formations in this area are undoubtedly Precambrian. The overlying Kurenin Formation can be subdivided into two parts: a lower—Precambrian (Middle Riphean—Vendian)—and an upper—Lower Cambrian. The presence of a major break between these parts within the Kurenin Formation is not excluded. The overlying effusive-tuffaceous unit, in its lower parts, apparently replaces along strike the upper members of the Kurenin Formation, and in its upper part contains limestone lenses with a typical Lower Cambrian fauna of archaeocyaths and trilobites.

REFERENCES

1. V. A. Borisov, A. Yu. Rozanov. New data on the biostratigraphy of the ancient units of the Batenev Ridge. Doklady AN SSSR, vol. 158, no. 2, 1964.

2. G. A. Ivankin et al. New data on the stratigraphy of the Cambrian and Precambrian of the eastern slope of the Kuznetsk Alatau. Materials on the Geology and Mineral Resources of Western Siberia, Tomsk, 1964.

1. B. N. Krasilnikov. Geological structure of the Batenev Ridge (explanatory note). Gosgeoltekhizdat, Moscow, 1958.

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

3. L. N. Repina et al. Biostratigraphy of the Lower Cambrian of the Sayan-Altai folded region. “Nauka” Publishing House, Moscow, 1964.

4. N. M. Strakhov. Fundamentals of the theory of lithogenesis. Vols. I and II, Publishing House of the Academy of Sciences of the USSR, Moscow, 1960.

5. Collective of authors. Ed. L. L. Khalfin. Biostratigraphy of the Paleozoic of the Sayan-Altai folded region. Vol. 1, Novosibirsk, 1960.

1. The term “series” is used here provisionally, since the interrelations of the individual parts within the series have not been fully clarified. ↩