ON THE STRATIGRAPHY OF ANCIENT STRATA IN THE AREA OF THE UPPER REACHES OF THE SUKHAYA YERBA RIVER (BATENEVSKY RIDGE)

I. I. KOPTEV, V. E. NOMOKONOV, A. K. SEMASHKO, V. A. SHIPITSYN

(Presented by the scientific seminar of the departments of general geology, paleontology, and geology of oil and gas)

The carrying out of detailed geological mapping in the area of Son station—the Yuliya mine—in the summer of 1965 made it possible to obtain new geological and paleontological materials that allow the existing ideas about the stratigraphy of this area to be refined and supplemented.

It should be noted that, before our work, paleontological remains from this area were known only at one point (archaeocyaths), but they had not been collected or identified. In this connection, the stratigraphy of this area was represented in a very schematic way; the structural and age relationships of the strata had not been studied. Various authors showed different strata here, the characteristics of whose material composition and paleontological content were given on the basis of comparison with neighboring areas. Only V. D. Tomashpolskaya [5] distinguished in this area two independent new strata (the Son and Litvin formations of the Cambrian), whose age was established by her conditionally.

The study of the remains of trilobites, algae, and archaeocyaths that we collected for the first time at several points, and the establishment, during detailed mapping, of the relationships among the strata distinguished here, made it possible not only to refine the stratigraphy of this area, but also to identify certain features of the stratigraphy of ancient strata that are common to the Batenevsky Ridge.

In particular, the materials obtained make it possible to speak of the presence of a number of major breaks and unconformities in the section of the Upper Precambrian—Cambrian, of the need to distinguish certain strata at the rank of independent formations, and of the discrepancy between the working stratigraphic legend for the eastern slope of the Kuznetsk Alatau, adopted in December 1965 at the Krasnoyarsk Geological Administration, and the actually observed section.

According to our data, the stratigraphy of the area described is as follows (section along the left side of the valley of the Poperechny ravine).

1. The most ancient rocks are black and dark-gray massive and platy marbled limestones, which we have conditionally assigned to the middle part of the Martyukhino Formation. A characteristic feature of this stratum is the presence in its composition of packets and elongated lens-shaped bodies of black and dark-brown, often breccia-like silicilites, clearly emphasizing the internal structure of the stratum. Under the microscope the siliceous rocks in many cases contain spicules of sponges—

blocks and spherical formations resembling radiolarians, which indicates their primary sedimentary origin. In places the siliceous rocks are phosphatic. In addition, among the limestones that predominate in the sequence there occur isolated beds and packets, not persistent along strike, of yellowish porous and white saccharoidal dolomites. In the limestones, at several levels, oncolites of Osagia aff. tenuilamellata Reitl. have been found (according to V. A. Shipitsyn). The incomplete thickness of the sequence is 1200 m.

V. D. Tomashpolskaya [5] separated this sequence as an independent Litvin Formation of Lower Cambrian age, in contact with the surrounding rocks along disjunctive disturbances. We determine the age of the sequence as Late Precambrian, on the basis of the degree of metamorphism and the structural relationships with the surrounding rocks (Fig. 1).

1. Above, with a conglomerate at the base and with an azimuthal unconformity, lies a sequence varied in composition, which we have provisionally assigned to the upper part of the Martyukhin Formation. This sequence is exposed on both limbs of a syncline extending southwestward from Lake Zavodskoye, and is well revealed on the watershed ridges between the Lukovyi, Poperechnyi, and Malyi Kardonnyi ravines. The sequence consists of light dolomites, gray and light-gray limestones, conglomerates, siltstones, and sandstones. In the section along the left side of Poperechnyi ravine, the sequence begins with a packet of conglomerates 30 m thick. The same conglomerates, but with coarser fragments, are exposed on the watershed of the Poperechnyi and Lukov ravines, where their thickness is 70–100 m. In a northeastern direction along strike, the conglomerates pass into sandstones and siltstones. The pebbles are represented by well-rounded fragments of the underlying marbles and silicitites. In Fig. 1 it is clearly seen that the base of the conglomerates, which has a NE strike and a considerable azimuthal unconformity, overlaps the sublatitudinally striking beds of the underlying sequence.

Above the conglomerates, on the left side of the valley of Poperechnyi ravine, lies a packet of dark-gray massive and thick-bedded dolomites 120–150 m thick. Along strike to the NE and SW the color of the dolomites becomes lighter. In the northern limb of the syncline the dolomites of this packet are light gray with a bluish tint. Indeterminate algal remains of poor preservation occur.

The overlying—third—packet, 700–1000 m thick, in the southern limb of the syncline is composed of interbedded calcareous gravelites, sandstones, siltstones, and dolomitic limestones, while in the northern limb it consists of light dolomitic limestones containing a small number of interbeds of sandy-argillaceous rocks. In the limestones of the northern limb there have been found (identified by S. S. Gudymovich) Epiphyton decurtatum Gud., E. manaeense Gud., E. complex Gud., known from the Ungut Formation of the Mana River area in the Eastern Sayan [1].

Still higher in the same section (southern limb) lies a 15 m packet of black argillaceous limestones, and the section ends with the overlying—fifth—packet of light massive limestones more than 80 m thick. In the latter, along Poperechnyi ravine, indeterminate algal remains of poor preservation have been encountered; and along strike to the NE, in both limbs of the syncline, abundant microflora remains have been found in them: Botominella aff. lineata Reitl., B. densata Schip., B. lineata Reitl., and a number of new species (identified by V. A. Shipitsyn).

The organic remains listed above make it possible to regard the age of the sequence described as transitional from Precambrian to Lower Cambrian, while its unconformable occurrence upon the underlying sequence

Fig. 1. Schematic geological map of the upper reaches of the Sukhaya Erba River:
1 — modern alluvial–proluvial deposits;
2 — Berikul (?) Formation of the Middle Cambrian — effusives and tuffs of intermediate and alkaline composition;
3 — Karasuk Formation of the Middle Cambrian: a — lower subformation — sandstones, siltstones, interbeds of gray limestones; b — middle subformation — siltstones, argillaceous limestones, interbeds of sandstones; c — upper subformation — gray bedded “pseudoolitic” limestones;
4 — Bogoyul Formation of the Lower–Middle Cambrian — light-gray massive limestones;
5–6 — Martiukha Formation of the Upper Precambrian; 5 — upper subformation — conglomerates, dolomites, limestones, sandstones, shales; 6 — middle subformation — dark-gray, marbled limestones with interbeds and lenses of siliceous rocks (silicolites, lydite);
7 — granitoids of the Uibat pluton;
8 — disjunctive faults;
9 — stratigraphic contacts: a — conformable, b — unconformable;
10 — boundaries of undetermined character and concealed beneath deposits;
11 — points where organic remains were collected — archaeocyaths, trilobites, algae;
12 — bedding attitudes.

allows it to be distinguished as an independent formation. The two members described by us have been assigned provisionally to the Martiukha Formation, since in the working legend of the KSU there is no place in this stratigraphic interval for other formations. However, the facts presented indicate that, in the interval from the top of the Kulbiorstiug Formation of the Upper Precambrian to the base of the Ust-Kundat Formation—the lower Cambrian—one cannot restrict oneself to distinguishing a single Martiukha Formation. Within this so-called formation there are major unconformities, on the basis of which it should be divided, at least, into two independent formations. This conclusion is probably valid not only for the area described, but also for the entire eastern slope of the Kuznetsk Alatau.

For the upper part of the Martiukha Formation, here distinguished as an independent formation, the name Tunguzhul Formation could be adopted. This term was proposed earlier [2] for a limestone-dolomite unit overlying, in the area of Mt. Koshkulak and the village of Efremkino, the thick dolomitic Tarzhul Formation with Upper Precambrian algae and underlying the effusive-sedimentary Kolodzhul Formation of the Lower Cambrian. The unit described here is in many respects analogous to the Tunguzhul in its stratotypic section (Mt. Koshkulak), both in lithologic composition and in paleontological content (an abundance of remains of Botominella).

1. Above the limestone-dolomite unit, in the northern limb and the hinge part of the syncline of the section described, lie uniform light-colored massive reef limestones of the Bogoyul) Formation, with a fauna of archaeocyaths and trilobites of the Obruchevka complex (in its broad sense). In the southern limb of the syncline this contact is complicated by a disjunctive dislocation. Among the trilobites in these limestones A. K. Semashko identified: Bonnia globosa Tomaschp., Erbia sp., Ploerbia anomalica Rep., Antagmopleura sp., Granularia (?) sp., Paleoorictocephalus angulatus Rep., Chondranomocare sp.; archaeocyaths are represented by Tegerocyathus edelsteini (Vol.), Tegerocyathus sp., Ethmophyllum sp. (identified by O. G. Okuneva). In a number of outcrops of the unit a stable algal assemblage is established: Epiphyton reniforme Korde, E. cf. fruticosum Vol., Renalcis granosus Vol., R. cf. levis Vol., Kordephyton crinitum (Korde), Girvanella sibirica Masl., Vologdinelleae* sp. (identified by V. A. Shipitsyn).

At the contact of the limestones described with the underlying Tunguzhul limestones of the third bed, in the northern limb of the syncline along Poperechnyi Log, cherry-red calcareous-clayey rocks 1 m thick are observed. Two kilometers to the northeast, in this same limb of the fold, the archaeocyath limestone unit begins with conglomerates resting already on the fifth bed of the Tunguzhul Formation. The pebbles of these conglomerates consist of rounded fragments of black and white algal limestones, dolomites, and silicilites. Their incomplete exposed thickness is several meters; the thickness of the overlying limestones is about 400 m.

Archaeocyath-trilobite limestones of the Bogoyul Formation are also exposed on the northern slopes of Mt. Skalistaya, on both sides of the valley of Peshchernyi Log, as a narrow band several tens of meters wide. The nature of their contact with the underlying limestone-siliceous rocks of the Martiukha Formation has not been established (it is covered), but it may be noted that in nearby (about 10 m) outcrops of both units no signs of a disjunctive contact are observed. The contact itself has a strike coinciding with the strike of the belt of limestones of the Bogoyul Formation and the base of the sandy-shaly beds of the overlying Karasuk Formation. The beds of the underlying Martiukha—

*) This name has been adopted in the working legend of the KSU in place of the term “Syiskaya.” In our opinion, both these names are unsuccessful and should be replaced by the term “Efremkino” [2].

of the Khin Formation have a strike sharply different from the strike of the contact, which may indicate a significant unconformity at the base of the Bogogol Formation. On the northern slopes of Mt. Skalistaya, the following trilobites have been found in limestones of the Bogogol Formation: Erbia granulosa Lerm., Bonnia globosa Tomaschp., B. aff. dubia Pokr., Batenioides (?) sp., Pumilina sp. nov., Solontzella sp. nov.; archaeocyathids and algae: Epiphyton reniforme Korde, Renalcis granosus Vol., Kordephyton crinitum (Korde), Girvanella sibirica Masl., Vologdinelleae sp.

The hiatus established here, on geological and paleontological grounds, at the base of the Obruchev horizon is also confirmed in the neighboring area, in the section along Podtemnyi Log [3].

1. The exposed part of the section along the left side of Poperechnyi Log ends with limestones of the Bogogol Formation; however, along Peshchernyi Log these limestones are overlain by a sandy–carbonate–clayey unit—the Karasuk Formation of the Middle Cambrian. The latter is exposed in a broad belt along both sides of the valley of the Sukhaya Erba River and can be traced northeastward to the Yuliya mine. Exposure of the contact between the Bogogol and Karasuk formations by mine workings on the right side of the valley of Peshchernyi Log made it possible to establish that light, unbedded, reef archaeocyathid–trilobite limestones are abruptly replaced by clearly bedded sandstones, carbonate–siliceous shales, and black manganese-bearing limestones. To the southwest, on the right side of Ust-Peshchernyi Log, the basal horizons of the Karasuk Formation already overlie the black marbles of the Martyukha Formation. This latter circumstance makes it possible to regard the superposition of the Karasuk Formation upon the underlying deposits as unconformable.

Within the Karasuk Formation in this area, four parts can be distinguished (from below):

a) interbedded dirty-gray sandstones, siltstones, carbonate–siliceous shales, and black manganese-bearing limestones—the thickness of the member is from 30 to 100 m. In a limestone interbed on the right side of Ust-Peshchernyi Log, the following trilobites have been found: Oryctocephalina aff. reticulata Lerm., Peronopsis sp., Prochedinella sp., Pagetidae. At approximately the same stratigraphic level, 10 km to the northeast, beyond the limits of the area described, on the left side of the Sukhaya Erba River, near the fur farm, last year we collected trilobites: Oryctocephalops frischenfeldi Lerm., Prochedinella erbiensis Siv., Olenoides sp., Chondranomocare aff. irbinica Rep., Antagmopleura sp., Pagetia sp., Erbia sibirica (Schm.), Erbia granulosa Lerm., Gaphuraspis gaphuri Ivsch., Pachyaspis sp., Corynexochus sp., Bathynotus sp. nov., and a number of other new genera and species (determinations by A. K. Semashko);

b) the second member, about 400 m thick, is composed of interbedded gray sandstones and siltstones;

c) the third member consists of alternating beds of sandstones, siltstones, and gray clayey limestones. Its thickness is about 250–400 m. Gradual transitions are observed at the base and top of this member;

d) the fourth member is composed of platy gray detrital (“pseudo-oolitic”) limestones, with an incomplete thickness of about 200 m. In these limestones, on the left side of the Sukhaya Erba River above the mouth of Poperechnyi Log, we collected trilobites, among which Amgaspidella aff. elongata N. Tchern. and Olenoides (?) sp. can be identified.

The fauna listed above indicates the unquestionably Middle Cambrian age of the deposits containing it, which are predominantly terrigenous; moreover, the species composition of the fauna is very close to that from the limestones of Mt. Sladkie Koreni. Paleontologically, it would seem that these are coeval deposits, but lithologically the rocks of the Mt. Sladkie

Korenya and the area described differ sharply. D. I. Musatov [4] distinguishes two types of sections of the Karasuk Formation—terrigenous and carbonate; however, the facies variability of the Karasuk Formation has not been reliably proven by anyone. On the contrary, facts are now available indicating the presence of both terrigenous and carbonate sequences of the lower half of the Middle Cambrian in one and the same area. Thus, in the area of the villages of Efremkino—Malaya Syya [2], a sequence of white massive limestones with typical Middle Cambrian fauna is exposed (the Karasuk Formation according to V. M. Yaroshevich and D. I. Musatov). Here, too, a sequence of gray sandstones, siltstones, and argillaceous limestones is exposed (the unnamed formation), resting with a break upon massive light-colored archaeocyathid-trilobite limestones with fauna of the Obruchev complex. Both of these sequences are Middle Cambrian, but there is no reason to speak of their facies transitions in this area, since they are in contact with one another and have nothing in common in composition.

The terrigenous composition of the Karasuk Formation in the area described is maintained over considerable distances to the NE and SSW without noticeable changes, but in the area of Mount Sladkie Korenya (7 km away) we already encounter purely carbonate rocks. Here, too, it is hardly possible to speak of facies variability. The terrigenous sequence of the Middle Cambrian is also exposed near the ulus Tolcheya and at a number of other localities. In our opinion, in the lower half of the Middle Cambrian two independent formations should be distinguished—the Karasuk (carbonate) and the unnamed (terrigenous). The question of their mutual relations must be resolved by means of additional observations.

1. The youngest rocks in the area described are effusives and their tuffs of intermediate and alkaline composition, which we conditionally assign to the Berikul Formation of the upper half of the Middle Cambrian. This sequence rests with a sharp angular unconformity upon various complexly dislocated rocks of more ancient age.

Thus, the factual material presented makes it possible to raise the question of the presence in the section of the pre-Devonian sequences of the area of at least three stratigraphic breaks, and of the necessity of distinguishing two additional formations that did not find a place in the working stratigraphic legend for the eastern slope of the Kuznetsk Alatau adopted in Krasnoyarsk in December 1965.

REFERENCES

1. S. S. Gudymovich. On epiphytons of the Anastas’in and Ungut formations of the Late Precambrian (?)—Lower Cambrian of the northeastern part of the Eastern Sayan. Izv. TPI, vol. 151, 1966.

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 Geology and Mineral Resources of Western Siberia. Tomsk State University Publishing House, 1964.

3. M. I. Koptev et al. On the question of the age of the sequence of massive archaeocyathid limestones in the area of the village of Katyushkino. Izv. TPI, vol. 155, Tomsk State University Publishing House, 1966.

4. D. I. Musatov. The Cambrian of the Kuznetsk Alatau. In: Stratigraphy of the USSR, Cambrian Systems. “Nedra” Publishing House, 1965.

5. V. D. Tomashpol’skaya. Author’s abstract of dissertation, 1964.