ON THE NATURE OF THE BOUNDARY BETWEEN PERMIAN AND TRIASSIC DEPOSITS IN THE KUZNETSK BASIN

M. D. PARFENOVA

(Presented by the interdepartmental seminar of the GRF)

It is generally known that in Kuzbass and in a number of other regions of Siberia, the Upper Permian deposits gradually, without breaks or unconformities, pass into the Lower Triassic. The boundary between these deposits is taken to be the replacement of the variegated coal-bearing rocks of the Yerunakovskaya Formation by the tuffaceous rocks of the Lower Maltsevo Formation. The former, as a rule, contain Upper Permian flora, as well as a fauna of bivalves and ostracods. The latter include remains of Lower Triassic flora and a fauna of estheriids. Both the Permian and Triassic deposits contain distinctive complexes of spores and pollen. The boundary deposits of the Permian and Triassic have been studied by various authors (G. P. Radchenko, S. G. Gorelova, O. A. Betekhtina, E. M. Andreeva, A. A. Kurbatova, and others). However, tracing the boundary between Permian and Triassic deposits is often difficult, since at the base of the Triassic deposits one often observes not tuffaceous rocks but variegated ones, similar to the Upper Permian; moreover, they quite often contain no visible organic remains. It is not surprising that under such circumstances there is much disagreement regarding the position of the boundary between the Permian and Triassic deposits.

At present, we have new materials on this question, which make it possible not only to refine the boundary between the Triassic and Permian deposits, but also to put forward new ideas about its nature.

The boundary deposits of the Permian and Triassic systems are exposed on the left bank (above the mouth of the Naryn River) and the right bank (above Babiy Kamen) of the Tom River. In recent years these boundary deposits have been penetrated by boreholes 4182 and 4161 in the Zhernovskoye deposit.

We studied plant remains from the indicated boreholes and a collection of new flora samples from the section on the right bank of the Tom River, the Osinova–Babiy Kamen area. The plant remains studied from the boreholes and the section are represented by impressions of articulate-stemmed plants, cordaites, ferns, conifers, and by spore-pollen complexes. The study of leaf flora and spore-pollen complexes showed the presence, between the Upper Permian and Lower Triassic deposits, of a transitional horizon characterized by a mixed floristic complex.

Thus, in the section of borehole 4182 of the Zhernovskoye deposit, in variegated rocks similar to the Yerunakovskaya rocks, within the depth interval 254.5–260.2 m, there are spore complexes of Early Triassic and Late Permian age. A. A. Kurbatova identified in this borehole, within the indicated depth interval, spores and pollen of Early Triassic composition: Calamo-

spora microrugosa (Ibr) Lub., Remysporites psilopterus (Lub.), Gnetaceaepollenites, Entylissa caperata Lub., Marsupipollenites retroflexus (Lub.) Lub., Tristachia (?) microtuberculata Rom., Cordaitina rotata (Lub.) Sam., Lucisporites Pot. et Klaus., Bifurcatisporites scabrellus Rom., Trachytriletes Naum., and others—a Late Permian assemblage with an abundance of cordaite pollen and spores of Late Permian ferns.

In the section on the right bank of the Tom River, Osinova River—Babii Kamen, a horizon with mixed flora is noted above bed P-46 (according to G. P. Radchenko, 1936), with a thickness on the order of 24 m. In this horizon we identified, from the Permian leaf flora, Noeggerathiopsis cf. aequalis (Goep.) Zal., Noeggerathiopsis candalepensis Zal., Noeggerathiopsis sp., Prynadaeopteris cf. antriscifolia (Goep.) Radcz., Callipteris sp.; from the Triassic leaf flora—a fern, Taeniopteris sp., conifers, and articulate-stemmed plants. In this same horizon A. A. Kurbatova determined much pollen of cordaites and spores of Late Permian ferns.

All of the foregoing allows us to conclude that between the Permian and Triassic deposits in the Kuznetsk Basin there is a transitional horizon, characterized by a mixed floral assemblage composed of representatives of Permian and Triassic forms.

The boundary between the Permian and Triassic deposits, according to the generally accepted rule of Frech, should be drawn at the base of the transitional horizon. In the present section this boundary passes along bed P-46, which is somewhat below the boundary accepted at the present time.

REFERENCES

1. Problems of the Geology of Kuzbass. Vol. 1, 1956.

2. A. A. Kurbatova. On the question of the position of the Permian–Triassic boundary in the Kuznetsk Basin according to spore-pollen analysis. In: Reports of the Paleobotanical Conference. Tomsk, State University, 1962.

3. Materials on the phytostratigraphy of the Upper Permian deposits of the Altai–Sayan mountainous region. Leningrad, 1962.