ON THE AGE OF THE MASSIVE ARCHAEOCYATHID LIMESTONE STRATA IN THE AREA OF THE VILLAGE OF KATYUSHKINA

(Batenev Ridge)

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

(Presented by Professor A. G. Sivov)

Along the northwestern slopes of the Batenev Ridge, along the right side of the valley of the Son River, in the sector from the village of Katyushkina northeastward to the settlement of Son, there is exposed, as a belt up to 1.5 km wide, a rather uniform—by external appearance—sequence of massive light-gray and gray limestones, the lithological features of which were described by A. F. Senakolis [2]. B. N. Krasilnikov referred to this sequence as the Upper Petykhina sequence, with an age of the upper half of the Lower Cambrian to the lower half of the Middle Cambrian; V. M. Yaroshevich [5] called this same sequence the Bolshaya Erba Formation, while V. D. Tomashpolskaya [4] included it in the Chesnokov Formation of the middle Lower Cambrian. D. I. Musatov [1] names these deposits the Usin Formation.

The archaeocyathid fauna in the belt of distribution of the indicated sequence has long been known. According to determinations by P. S. Krasnopeeva [5], in an outcrop located 4 km northeast of the village of Katyushkina and confined to the middle part of the sequence, the following occur: Ajacicyathus amplus (Vol.), A. sp., Archaeofungia minimalis Krasn. (MS), Archaeolynthus polaris Vol., Leptocyathus katuschkensis Krasn. (MS), Ethmophyllum dispervallum Vol., E. cf. ulmensis Vol., E. jaroschevitschi Krasn. (MS), E. minussensis Krasn. (MS), Thalamocyathus aff. howelli (Vol.), Coscinocyathus dianthus Born.

Somewhat farther south, at approximately the same stratigraphic level, A. B. Gintsinger and others (materials of the Novosibirsk Conference, 1965) collected trilobites—Poliellina—and archaeocyathids in this same limestone belt: Ajacicyathus directus Vol., A. acutus Vol., A. solebrosus Vol., A. proskuriakovi Toll., A. aff. patulus Vol., Coscinocyathus aff. cornucopia Born., C. aff. bedfordi Vol., Loculocyathus membranivestites Vol., Uralocyathus aff. callosus (Vol.), Tumulocyathus rarispinaticulus Bojar., T. aff. pustulatus Vol., T. aff. admirabilis Vol., Dokidocyathus sp., Altaia mutabilis Krasn., Archaeolynthus aff. bimurus Vol., Ethmophyllum aff. pseudotichus Vol., Gordonocyathus sp., Heckericyathus sp., Siringocnema sp., Szecyathus sp. The listed archaeocyathid assemblage makes it possible to correlate it with the Sanaashtykgol assemblage, which is not contradicted by finds of trilobites of the genera Poliellina and Erbiopsidella.

The detailed geological mapping work carried out by us in this area made it possible to collect additional material, allowing us to refine the age of this carbonate sequence and to view somewhat differently the question of its correlation with already known formations.

of the Kuznetsk Alatau, and to assess differently the stratigraphic significance of certain archaeocyathid–trilobite assemblages (in particular, the Solontsy assemblage).

As was already noted above, the lithology and structure of this carbonate sequence were studied by A. F. Senakolis and V. A. Shipitsyn [2], according to whose data, in the section along the right side of the valley of Podtemnyi Log (a right tributary of the Son River), two parts are distinguished within the sequence: the lower—massive light-gray limestones with a total thickness of not less than 700 m, and the upper—black, bedded, platy limestones 120 m thick. The base of the sequence is concealed beneath a cover of Quaternary deposits filling the valley of the Son River. Upstream along the channel of Podtemnyi Log, within the lower part of the carbonate sequence, four members are distinguished stratigraphically from bottom to top; they differ in algal assemblages and were formed under somewhat different facies conditions, although in general they have an externally similar composition.

Additional collections of trilobites, archaeocyathids, and algae made in the summer of 1964 made it possible to expand the paleontological characterization of the distinguished members. In the lower member, which has an incomplete thickness of about 300 m, the algal flora is depauperate in character and is represented by the following quantitatively predominant forms: Epiphyton rectum Korde, E. paniculatum sp. nov., E. cf. furcatum Korde, Girvanella sibirica Masl.; less common are Chabakovia nodosa Korbe, Epiphyton aff. reniforme Korde, Renalcis granosus Vol., Proaulopora sp., Botominella sp.; the trilobite—Erbiopsidella sp. Rare cups of archaeocyathids also occur here, among which V. D. Alimova identified Aptocyathus gordoni Vol., Coscinocyathus sp., Szecyathus sp. Trilobite remains are noted only in thin sections. At the top of the lower member there lies a bed of milky-white limestone, almost entirely composed of tangled fibrous bundles of indeterminate Cyanophyta.

In the next member, also 300 m thick, conditions for the existence of algae were favorable, and consequently their remains are more abundant and more diverse. Epiphyton paniculatum sp. nov., E. rectum Korde, E. aff. reniforme Korde, Tubophyllum victori Krasn. are massively developed; less common are Kordephyton crinitum (Korde), Renalcis granosus Vol., Proaulopora sp., Botominella sp.; single specimens of Epiphyton cf. furcatum Korde, Girvanella sibirica Masl., Vologdinella sp. are noted, and rare Epiphyton fruticosum Vol. appear at the top of the member. Among the archaeocyathids V. D. Alimova identified Tumilocyathus sp., Bicyathus sp., Ajacicyathus sp., Coscinocyathus sp.

The third member, 35 m thick, is represented by oolitic limestones that are well traceable as a marker horizon along the strike and have a SE dip at azimuth 90–130° at an angle of 30–50°. In the nuclei of the oolites, fragments of tubes of Proaulopora sp. and Botominella sp. are occasionally observed.

The section of the lower part of the carbonate sequence ends with a member of light massive limestones 100 m thick. This member is characterized by the mass development of Epiphyton fruticosum Vol. and Renalcis granosus Vol.; Girvanella sibirica Masl. and Epiphyton aff. reniforme Korde are less common. Throughout the section, remains of archaeocyathids occur fairly frequently. In the middle part of the member, together with trilobites, the following were identified: Erbocyathus heterovallum (Vol.), Tegerocyathus sp., Archaeocyathus sp., Ethmophyllum sp., Tegerocyathus abakanensis (Vol.), Syringocnema sp.; and at the top (1–2 m below the roof) the following were encountered: Tegerocyathus aff. edelsteini (Vol.), Vologdinocyathus sp., Archaeocyathus regularis Krasn. In the middle part of the member, at three points situated 120 and 10 m from one another along the strike, A. F. Senakolis and A. K. Semashko collected

trilobites, among which I. I. Koptev and A. K. Semashko identified: Chondragraulos minussensis Lerm., Ch. ujaricus Rep., Antagmopleura sp., Chondranomocare cf. planum Rom., Chondranomocare? sp. nov. (gen. nov.?), Erbia cf. sibirica (Schm.), Erbia granulosa Lerm., Edelsteinaspis sp., Granularia obrutchevi Lerm., Bonnia sp., Kootenia sp., Kooteniella slatkowskii (Schm.), Onchocephalina sp., Proerbia cf. torgaschinica Rep., Koptura sp., a form close to the genus Solenopleura, Nisusia sp. The listed fauna was encountered mainly at one locality; at two other localities only some of these forms are repeated, with the exception of Koptura sp.

Above lie black, thin-bedded platy limestones 120 m thick, whose contact with the underlying light-colored limestones can be observed directly in the outcrop. At the boundary of these members, with their parallel bedding, traces of erosion are noted: the top of the light-colored limestones is uneven, with pockets and depressions filled with material of the overlying member of black limestones. The beds of black limestones dip on average at azimuth 110 at an angle of 50°. In the middle part of the upper dark-colored member there is a 15-meter bed of light-colored massive limestone. Algae in the black limestones are few in number and are represented by girvanellas, forming lumpy nodules and aggregates (Girvanella sibirica Masl. and G. ducii Weth, the diameter of whose tubes is 0.02 mm). In the bed of light-colored limestone, isolated Renalcis granosus Vol. and Epiphyton cf. fruticosum Vol. were noted.

At 45 m above the base of the bedded black limestones, A. F. Senakolis collected trilobites, among which we identified: Onchocephalina cf. accuminata Rep., Laminurus sp., Jangudina quadrata Koptev (MS), Bonnia sp., Namanoia cf. inserta N. Tchern.

The paleontological characterization given above for the members of the carbonate sequence described allows one to assert that the lower two members, on the basis of their algal and archaeocyathid assemblage, can almost certainly be placed at the level of the Sanashtykgol Horizon; moreover, in the lower beds of the lower member there are relics of the Bagrad assemblage (Chabakovia nodosa), while in the roof of the second member elements of the Obruchev assemblage appear (Epiphyton fruticosum).

By the mass development of Renalcis granosus and Epiphyton fruticosum, and by most of the trilobites and archaeocyathids, the fourth member can be placed at the level of the Obruchev Horizon, although typical Middle Cambrian trilobites (Chondranomocare, Koptura) already appear here.

At first glance, the fauna of the member of black limestones has a more ancient (Solontsy) age in comparison with the underlying one, but its higher stratigraphic position in the given section is not in doubt on geological grounds. Incidentally, we note that a similar position of the Solontsy assemblage above the Obruchev assemblage has already been recorded at several localities (the area of Sukhie Solontsy according to data of V. D. Tomashpolskaya, the area of Mal. Syi according to data of I. I. Koptev and others). This once again emphasizes the correctness of the unified scheme adopted in Novosibirsk, in which the Solontsy fauna is not regarded as an independent assemblage. The presence in this member of Renalcis granosus and Epiphyton fruticosum indicates the closeness of its age to Obruchev time.

On the basis of the lists of fossils from all members of the carbonate sequence, one may draw the conclusion of a successive, gradual replacement of organic remains from bottom to top; and on the basis of the study of the lithology, A. F. Senakolis [2] drew the conclusion of a close genetic connection

members among themselves, of their continuous formation under the conditions of one and the same sedimentation basin.

Southeast of the belt of outcrops of the rocks of the carbonate sequence described, there is an area of distribution of an effusive sequence, assigned, from organic remains, from bottom to top, and on the basis of study of the lithology by V. M. Yaroshevich, B. N. Krasilnikov, V. D. Tomashpolskaya, and others, to the Middle Cambrian, and by D. I. Musatov—to the Syi Formation of the upper Lower Cambrian. We have already noted [3] that in lenses of massive limestones among the effusives there occur Erbocyathus cf. chakassensis Jarosh., Ethmophyllum sp., Archaeocyathus sp., Menneraspis delicata Jegor., Pseudoeteraspis sp., Chondragraulos sp., Bonnia sp., Proerbia sp., Namanoia cf. incerta N. Tchern.

This effusive sequence is in contact with the carbonate one along a disjunctive disturbance, but it is generally recognized that it lies higher, in the keystone part of a synclinal fold. The higher stratigraphic position of the effusives is undoubtedly demonstrated on the other limb of the mentioned syncline, where the contact with the carbonate sequence (in a somewhat different facies) is stratigraphic [3].

On the basis of the above, it may be accepted that the formation of the rocks of the carbonate sequence described (its exposed part) began no later than the beginning of Sanashtykgol time and continued through Obruchev time inclusive. Taking into account the presence of Middle Cambrian forms of trilobites in the Obruchev complex (the 4th member of massive light-colored limestones), it would be more correct to draw the boundary between the Lower and Middle Cambrian at the base of the 4th member, i.e., to assign the deposits with the Obruchev complex to the Middle Cambrian.

Speaking of the correlation of the indicated carbonate sequence with deposits of the same age in other areas of the eastern slope of the Kuznetsk Alatau, and of its naming, it should first of all be noted that its greatest similarity is to the carbonate part of the section of the Sukhie Solontsy stream (the Solontsy Formation of V. D. Tomashpolskaya, the Bolshaya Erba Formation of V. M. Yaroshevich). B. N. Krasilnikov was evidently correct in distinguishing the sequence as an Upper Potekhino sequence with an age of Lower–Middle Cambrian. The least successful, it seems to us, is the naming of this sequence as the Usa Formation. This term has recently begun to be applied as the name for sequences differing in composition and age, formed in the time interval from the Kundat to the Sanashtykgol horizons inclusive. In essence, this term has lost its meaning and in no way corresponds to the concept of a formation. If all the sequences included in the Usa Formation are analyzed, it will become clear that the Usa Formation is not a concrete geological body, but a large biostratigraphic subdivision, corresponding in volume to almost the entire Lower Cambrian. The use of this term is also illegitimate because the Usa Formation has no paleontologically characterized stratotype section.

Using the example of the carbonate sequence described by us, it is clear that not all Lower Cambrian deposits of the eastern slope of the Kuznetsk Alatau can be fitted into a stratigraphic scheme consisting of two formations—the Usa and the Syi—each of which has neither a definite paleontological content nor even a stratotype section. Indeed, what name, as a formation, can be given to the characterized carbonate sequence, the age of which is determined within the limits of Sanashtykgol and Obruchev time? Usa or Syi? Obviously, neither term is suitable.

The history of the geological development of this area in the Cambrian is much more complex than one might imagine on the basis of a stratigraphic column of the Lower Cambrian comprising two formations.

Leaving the question of the name of the unit open, we emphasize once again that it is characterized by internal lithological and paleontological unity and encompasses the interval from the upper part of the Lower Cambrian to the lower part of the Middle Cambrian.

REFERENCES

1. D. I. Musatov. Stratigraphy of the Cambrian deposits of the eastern slope of the Kuznetsk Alatau. Geologiya i geofizika, No. 2, 1962.

2. A. F. Senakovlis, V. A. Shipitsyn. Structure of the reef-limestone unit and the distribution within it of algal flora (village of Katyushkina, Batenev Ridge). Geologiya i geofizika, No. 1, 1965.

3. A. F. Senakovlis, I. I. Koptev, V. A. Shipitsyn. New data on the stratigraphy and lithology of the Upper Lower Cambrian deposits of the Batenev Ridge. Izv. TPI, vol. 151, 1965.

4. V. D. Tomashpolskaya. Abstract of dissertation, 1964.

5. V. M. Yaroshevich. Stratigraphy of the Sinian and Cambrian deposits of the Batenev Ridge, the Azyr-Tal Range, and the basin of the Bely Iyus River (eastern slope of the Kuznetsk Alatau). Tr. IGT SO AN SSSR, issue 17, 1962.