On the Stratigraphy and Paleontology of the Lower Cambrian in the Upper Reaches of the Ulen River (Batenevsky Ridge)

G. M. Ekhanin, V. D. Kamelina, V. A. Shipitsyn

(Presented by Professor, Doctor K. V. Radugin)

On the southeastern margin of the Batenevsky Ridge, in the basin of the upper course of the Ulen River, a sequence of limestones is widely developed which the geologists of the Western Expedition of KTU call the Usin Formation. V. M. Yaroshevich assigned it to the Bol’sheerbinskaya Formation [3]. In view of the lithological uniformity and the absence of marker beds, the internal structure of the sequence has remained unclear up to the present time. Extensive lists of archaeocyaths, indicating a Lower Cambrian age for the limestones, were given only for the sequence as a whole, without subdividing it into smaller units.

In 1962–1964 G. M. Ekhanin compiled detailed sections of the Lower Cambrian sequence in the area of the upper course of the Ulen River, with bed-by-bed sampling of organic remains: trilobites, archaeocyaths, and algae, whose identification was carried out respectively by L. M. Mikhailova, V. D. Kamelina, and V. A. Shipitsyn.

As a result of the work carried out, it was established that individual parts of the “Usin Formation” are separated by erosional breaks, well recorded by the appearance of conglomerate-breccias, sandstones, and grits, the clastic material of which consists of products of the reworking of underlying rocks, by the disappearance from the section of certain members and beds, or by the reduction of their thicknesses as a result of erosion. These parts are distinguished by us as the Tazman, Vizim, and Alokolun formations, included in a series for which the name Usin is retained.

The Tazman Formation is distributed on the western slopes of Mount Tazman, on the right side of the valley of the Bolshoi Ulen River (one of the headwaters of the Ulen River) north of Mount Tazman, and on Mount Vizim. Its composition, from bottom to top, includes (Fig. 1):

1. Dark-gray limestones, lying on Precambrian rocks, with remains of Newlandia. The immediate contact between the Precambrian and

Fig. 1. Geological sections of the Usin Series: A—through Mt. Vizim; B—on the southwestern slope of Mt. Tazman. 1–4—Tazman Formation (1—first member; 2—second member; 3—algal limestones of the third member; 4—yellowish-gray algal limestones, calcareous breccias, and siliceous rocks of the fourth member); 5—Vizim Formation (archaeocyathid-algal limestones with interbeds of calcareous sandstones and siltstones); 6—Alokolup Formation (limestones with interbeds of sandstones and gritstones); 7—boundaries of breaks; 8—tectonic disturbances; 9–11—collection points of organic remains (9—trilobites; 10—archaeocyathids; 11—algae).

and the Tazman limestones is not exposed, and therefore the relationship between them remains unclear. Thickness 400 m.

1. Light-gray massive limestones containing indeterminate remains of algae. Thickness about 200 m.

2. Light-gray limestones, almost entirely composed of algal remains: Botominella aff. lineata Reitl. Only in the roof of this member are Epiphyton sp., Girvanella sp., and Vologdinelleae sp. noted in places. Thickness of the member 300 m.

3. Gray and yellowish-gray limestones interbedded with yellowish-gray silicified calcareous breccias and dark-gray and gray siliceous rocks. Below is given a detailed bed-by-bed description of this member from bedrock exposures on the southern slope of Mt. Vizim (from bottom to top):

a. Gray or yellowish-gray, mottled sedimentary calcareous breccias with lenses of calcareous sandstones and limestones. They contain small fragments of archaeocyathids: Archaeolynthus sp., Ajacicyathus sp., and algae: Epiphyton sp., Vologdinelleae sp., Girvanella sibirica Masl., Kordephyton crinitum (Korde), Subtifloria delicata Masl., Botominella aff. lineata Reitl. Immediately at the southern foot of Mt. Vizim, representatives of pterocyathids of the family Achorocyathidae Jank. were noted among the rocks of the bed described (identification by T. B. Yankauskas). Thickness 16 m.

b. Interbedding of thin beds of the same limestones and dirty-gray and dark-gray siliceous rocks containing sponge spicules. Thickness 7 m.

c. Platy, breccia-like silicified limestones with remains of indeterminate archaeocyaths. Thickness 1 m.

d. Thin interbedding of gray and greenish-gray siltstones, calcareous-clayey and siliceous-clayey shales with gray limestones. In the limestones algae are recorded everywhere: Epiphyton cf. procerum Lud., Adiaksia eleganta Schip., Subtifloria delicata Masl., Botominella aff. lineata Reitl., Girvanella sibirica Masl., Proaulopora rarissima Vol., Amganella sp., Kordephyton sp., and rare sponge spicules. Thickness 14 m.

e. Dirty brownish-gray platy limestones, upward replaced by light varieties with remains of archaeocyaths: Archaeolyathus sp., Ajacicyathus immanus (Vol.), Loculicyathus membranivestites Vol., Szecyathus cylindricus Vol., and algae: Adiaksia eleganta Schip., Subtifloria delicata Masl., Botominella aff. lineata Reitl., Vologdinelleae sp. Thickness 1 m.

f. Yellowish-gray fine-grained limestones. Thickness 2 m.

The described bedded unit is also well exposed on the right bank of the Bol’shoi Ulen’ River, immediately northwest of Mt. Tazman, near the crossing. Here, upon light-gray massive limestones of the third unit, containing remains of Botominella sp. and Subtifloria sp., gray siliceous shales with remains of sponge spicules lie without visible traces of erosion. Higher up they are replaced by thin interbedding of the same siliceous shales, green and dirty-green siltstones, and gray limestones. In the limestones algae, Epiphyton sp., are abundant. The unit is capped by green siltstones containing the thinnest interbeds of siliceous and siliceous-calcareous rocks, in which sponge spicules Protospongia and Monactinellida (determinations by I. T. Zhuravleva) and hyoliths (determinations by N. P. Meshkova) are recorded. The total thickness of the unit here is also 41 m.

Thus, in the Tazman Formation two biostratigraphic assemblages are clearly distinguished. The lower assemblage (third unit) contains abundant algae: Botominella aff. lineata Reitl. and rare Epiphyton sp. and Vologdiellae sp. The stratigraphic analogues of the unit containing similar or closely related algal assemblages should be considered the Tunguzhul’ Formation of the basin of the middle course of the Belyi Iyus River [2] and, probably, the middle subformation of the Middle Kiy (Ust’-Kundat) Formation of the Kiya River basin [1], the latter being taken as the stratotype of the Ust’-Kundat horizon of the Lower Cambrian for the Sayano-Altai folded region. The composition of the archaeocyaths of the fourth unit very much resembles the analogous assemblage of the Adiak Formation of Gornaya Shoria and the Belokamenka beds of the Bograd horizon in the stratotype section. The basis used is the scheme of biostratigraphic subdivision of the Lower Cambrian of Western Siberia adopted in February 1965 in Novosibirsk. Such a correlation is also confirmed by the presence in the microflora of Adiaksia eleganta Schip. and Subtifloria delicata Masl., with insignificant development of the genus Epiphyton.

The Vizim Formation is exposed on the summit of Mt. Vizim and on the left side of the valley of the Alokolunga River, one of the tributaries of the Bol’shoi Ulen’ River. On the southern slope of Mt. Vizim it lies on the eroded surface of the fourth unit of the Tazman Formation (Fig. 1), having at its base a bed of basal calcareous sandstones and grits. The formation here includes, from bottom to top:

1. Gray and yellowish-gray platy calcareous sandstones and grits, interbedded with wavy-laminated and massive...

calcareous siltstones and siliceous-calcareous rocks. In the rocks, fragments of archaeocyaths and algae are quite often observed: Subtifloria delicata Masl., Botominella aff. lineata Reitl., Adiaksia eleganta Schip., Girvanella sibirica Masl., Epiphyton sp. Thickness 10 m.

1. Light-gray massive limestones with interbeds of banded varieties. In the lower part of the bed the following algae were noted: Epiphyton evolutum Korde, Girvanella sibirica Masl., G. conferta Chapm., Subtifloria sp., Vologdinelleae sp. Thickness 15 m.

2. Light-gray, with a pinkish or yellowish tint, thin-bedded platy calcareous sandstones and sandy limestones with sponge spicules and algal remains: Subtifloria delicata Masl., Vologdinelleae sp. Thickness 4 m.

3. Brownish-gray fine-grained massive calcareous sandstones and siltstones. Thickness 5 m.

4. Massive light-gray limestones with interbeds and lenses, of the same color and structure, of archaeocyath-algal limestones. In the lower part of the member the archaeocyaths identified are: Archaeolynthus sp., Ajacicyathus sp., Tersia nodosa Vol., Ladaecyathus sp., Loculicyathus membranivestites (Vol.), Szecyathus sp.; and algae: Chabakovia nodosa Korde, Epiphyton simplex Korde, E. furcatum Korde, E. cf. rectum Korde, E. cf. procerum Gud., E. cf. racemosum Korde, Girvanella sibirica Masl., Globuloella sp., Renalcis sp., Vologdinelleae sp. In the upper part, among the archaeocyaths appear Ethmophyllum sp., Coscinocyathus dianthus Vol., Dictiocyathus cf. javorskii Vol.; and algae: Epiphyton procerum Gud., E. aff. evolutum Korde, E. furcatum Korde, Girvanella sibirica Masl., G. conferta Chapm., Kordephyton crinitum (Korde), Chabakovia nodosa Korde, Globuloella sp., Subifloria sp., Renalcis sp., Proaulopora sp. Thickness of the member 150 m.

5. Limestones of the same color, in places with a cream tint, massive, composing the upper third of Mt. Vizim. From this member V. M. Yarolevich collected archaeocyaths, an extensive list of which is given in his monograph [3]. Thickness 40–60 m.

On the left side of the valley of the near-mouth part of the Alyokolunga River (Fig. 1), only the lower part of the formation is exposed. Here the limestones are light gray in color and massive in texture. In the middle part of the section of the formation, archaeocyaths were collected: Archaeolynthus sp., Szecyathus cf. parvus Vol., Coscinocyathus sp., Kijacicyathus cf. lavrenovae (Krasn.), Loculicyathus sp., Tumulocyathus sp., Ethmophyllum sp., Coscinocyathus cf. parvus Vol., Tumuliolynthus musatovi (Zhur.), Annulofungia tailori Krasn., Carinocyathus sp.; and algae: Epiphyton procerum Gud., E. evolutum Korde, E. cf. rectum Korde, E. furcatum Korde, Chabakovia nodosa Korde, Ch. cf. monstrata Korde, Renalcis cf. granosus Vol., Globuloella sp., Girvanella sp.

In the upper part of the formation, approximately 100 m above the first locality, the following archaeocyaths were noted: Loculicyathus membranivestites Vol., Tumuliolynthus sp.; and algae: Epiphyton cf. rectum Korde, E. cf. fruticosum Vol., Vologdinelleae sp. The thickness of the Vizim Formation here, because of erosion before the formation of the younger Alyokolung Formation, decreases to 160–170 m. Along the section of Mt. Tazman the Vizim Formation is completely eroded. Here the rocks of the Alyokolung Formation lie directly on the rocks of the Tazman Formation.

The lower part of the Vizim Formation is characterized by the development of Bazaikha-Kameshki forms of archaeocyaths and algae, while in the upper parts young forms appear that are usual for the Sanashtykgol complex. It should be noted that the forms of the Bazaikha horizon occur in a single thickness together with the Sanashtykgol forms. According to the latest scheme for subdividing the Lower Cambrian deposits of the Sayan-Altai folded-

oblast (Novosibirsk, 1965), the rocks of the Vizim Formation will correspond to the Bograd horizon.

The Alokolung Formation is distributed in the basin of the near-mouth part of the Alokolung River, on the western slopes of Mt. Tazman, and in some other areas of the upper reaches of the Ulen River (Fig. 1). The formation rests with erosion on rocks of the Vizim Formation (left side of the valley of the near-mouth part of the Alokolung River) and the Tazman Formation (western slope of Mt. Tazman), having at its base a thin bed of calcareous sandstones.

Below is its bed-by-bed description for the section on the left side of the near-mouth part of the Alokolung River (from bottom to top):

1. Brown calcareous sandstones and grits, passing along strike into conglomerate-breccias. Thickness 4 m.

2. Light-gray massive limestones. Thickness 35 m.

3. Gray or brownish-gray limestones with a large number of small trilobites Jangudina quadrata Koptev, Glabrella sp., Olgaspis sp. Thickness 35 m.

4. Light-gray massive limestones with rare archaeocyaths of poor preservation. Thickness 25 m.

5. Pink thin-bedded calcareous sandstones. Thickness 0.5–1.0 m.

6. Light-gray and pinkish-gray fine-grained limestones. In the upper parts of the member there is an interbed of light-pink limestones with Vologdinelleae sp. Thickness 85 m.

7. Lumpy brownish-gray and gray fine-grained limestones with numerous remains of small trilobites and algae Girvanella sp. Thickness 4–5 m.

8. Covered interval, corresponding in thickness to 9 m.

9. Brownish-gray or gray fine-grained limestones with numerous remains of small trilobites Jangudina quadrata Koptev, Glabrella sp., Olgaspis (?) sp. Thickness 5 m.

10. Dark-gray and gray fine-grained limestones with numerous remains of small trilobites. Thickness 5 m.

11. Light-gray and gray lumpy fine-grained platy limestones with trilobite remains: Jangudina cf. quadrata Koptev, Glabrella sp., Olgaspis sp. Thickness 1 m.

12. Covered interval, corresponding in thickness to 20 m.

13. Gray fine-grained platy limestones with numerous remains of small trilobites: Jangudina Koptev, Olgaspis sp. Thickness 25 m.

The Alokolung Formation, containing a trilobite fauna that is characteristic of the Solontsy beds of the Obruchev horizon, corresponds in age to the upper half of the Lower Cambrian and is correlated with the Efremkino Formation of the basin of the middle course of the Bely Iyus River [2].

The total thickness of the Usin Series is 1450–1460 m.

From the material set forth above, the following principal conclusions follow:

1. The Usin Formation of the southeastern margin of the Batenevsky Ridge, in age, encompasses almost the entire Lower Cambrian (from the Ust-Kundat to the Obruchev horizon) and, in rank, corresponds to a series.

2. The Lower Cambrian section in the basin of the upper course of the Ulen River is not continuous. Separate parts of the Usin Series are separated by breaks, clearly recorded by the disappearance from the section of beds and by products of erosion of the underlying rocks.

3. Algae provide distinct biostratigraphic assemblages within the Usin Series and may be used for subdivision and correlation of the Lower Cambrian on a par with archaeocyaths and trilobites.

In conclusion it should be noted that the presented section of the Usin

series, although it is not continuous, contains almost all the known biostratigraphic complexes of the Lower Cambrian. This circumstance gives grounds for recommending it as a reference section for subdividing the Usinsk Series of the region.

REFERENCES

1. B. D. Vasil’ev, V. D. Kamelina. On the key reference section of the Lower Cambrian. Materials on the Mineralogy, Petrography, and Useful Minerals of Western Siberia and Krasnoyarsk Krai, Tomsk State University Press, Tomsk, 1965.

2. G. A. Ivankin, I. I. Koptev, V. E. Nomokonov, V. A. Shipitsyn. On the stratigraphy of the ancient strata of the eastern slope of the Kuznetsk Alatau. Materials on the Mineralogy, Petrography, and Useful Minerals of Western Siberia and Krasnoyarsk Krai, Tomsk State University Press, Tomsk, 1965.

3. V. M. Yaroshevich. Stratigraphy of the Sinian and Cambrian deposits of the Batenevsky Ridge, the Azyr-Tal Range, and the basin of the Bely Iyus River. Proceedings of the Institute of Geology and Geophysics, Siberian Branch, USSR Academy of Sciences, issue 17, Novosibirsk, 1962.