Materials on the Stratigraphy of Devonian Formations of the Kolyvan-Tomsk Folded Zone

P. N. Parshin

(Presented by Prof. A. M. Kuzmin)

The stratigraphy of the Devonian formations of the Kolyvan-Tomsk folded zone has been discussed in the works of B. F. Speransky [5], A. I. Gusev [2], A. V. Tyzhnov [6], V. V. Vdovin [1], A. L. Matveevsky [3], and others. However, the considerable tectonic disturbance and metamorphism of the Paleozoic formations, as well as their almost universal concealment beneath Cenozoic formations, greatly hinder stratigraphic subdivision and correlation in the region described.

For the area of the Yurga Tom region, the most complete scheme, and the one adopted in the practice of geological mapping within the region, was that of A. V. Tyzhnov (Table 1).

Table 1

During subsequent geological mapping, a sequence of effusive-sedimentary formations more than a kilometer thick, exposed near the village of Mitrofanovo along the left bank of the Tom River and having here, in general, a westward dip at angles of 70–90°, also came to be assigned to the Mitrofanovo member (suite). At the end of the traced section (1.7 km west of the village of Mitrofanovo), in a trench we established a sharply unconformable superposition upon this sequence of carbonaceous-argillaceous shales of the Upper (?) Devonian, which here dip southward at an angle of 15 to 20°.

It may also be assumed that the formations of the Mitrofanovo member (“the Mitrofanovo sequence proper” of A. V. Tyzhnov) likewise rest unconformably upon the above-described bank section of the effusive-sedimentary sequence, since, unlike the latter, the Mitrofanovo member is crumpled

into rather gentle folds with dip angles not exceeding 30–40°.

Since the age of the Mitrofanovo member is accepted as Late Nezhivetian, or more precisely (as we shall try to show somewhat below), apparently Zhivetian–Frasnian, the age of the steeply dipping effusive-sedimentary formations of the left-bank section along the Tom’ River is more ancient—at least pre-Late Nezhivetian. Provisionally we accept it as \(D_{1-2}\) (by analogy with the Tal’bes Formation (suite) of Kuzbass and the Omutnaya Formation (suite) of the Tom’–Ya interfluve, with which these formations have certain common features). An even older age for them is not excluded.

For the Pachino Formation, in the practice of geological mapping in the territory of the Kolyvan–Tomsk folded zone it is customary to assign the index \(D_3\). A. V. Tyzhnov [6], who first distinguished these deposits under the name “Pachino sequence,” also considered these sediments to be of the same age; while the Yashkino member of limestones developed within this formation (“Yashkino limestone,” according to A. V. Tyzhnov), in the cited work, occupies a somewhat indefinite age position, although it is described together with formations that are united into the Pachino Formation.

Within the Yashkino limestone two varieties are observed, caused by different manifestations of the processes of hydrothermal bleaching: light-gray marbled limestones and darker, somewhat less marbled limestones. In the latter, B. B. Chernyshev, from collections by L. N. Kraevskaya made in 1940, identified: Alveolites mailiexi Lecompte, A. suborbicularis Lam., Heliolites polymorpha Goldf. According to B. B. Chernyshev’s conclusion, the age is more probably \(D_2\) [3].

The limestones of the second variety to the south, near the village of Burlakovo, according to our data, pass facies-wise into clayey shales, from which Z. F. Pivovarova, from collections by V. F. Loskutov, identified the fauna Thamnopora nicholsoni Frech., Alveolitella polenovi Petz., Coenites fascicularis Radugin. According to Z. F. Pivovarova’s conclusion, the age is Zhivetian. Thus, the age of the entire Pachino Formation should be accepted as \(D_{2-3}\).

In the clayey shales of the Mitrofanovo member there is a fauna of very poor preservation, represented (according to identifications by L. N. Kraevskaya) by Anatyris phalaena Phill. (imprint of a valve), Atrypa sp., Spirifer sp. (verneuly ?), Ambocolida cf. Umbonata Hall., var. sibirica Krajew., Stropheodonta interstrialis Phill., Lexomena rugiferum Phill. On this basis A. V. Tyzhnov assigned the Mitrofanovo member (sequence) to the Frasnian stage. During subsequent survey work (1957–1960), V. F. Loskutov additionally collected here a brachiopod fauna (identified by M. A. Rzhonsnitskaya): Uncinulus ex gr. reticularis Linn., Eoreticularis sp. indet., Stropheodonta cf. interstrialis nalivkini Rzon., permitting judgment of the Zhivetian age of the enclosing rocks. Thus, from the entire faunal assemblage, the age of the Mitrofanovo member is most probably Zhivetian–Frasnian, approximately the same as the age of the Yashkino limestone member (which, in contrast to the Mitrofanovo member, has only isolated diabase interbeds up to 0.5 m thick).

At the northwestern margin of the village of Baranovo, along the banks of the Vlaskovo stream, over a distance of up to 300 m across the strike, outcrops are traced of effusive-sedimentary formations strongly altered by hydrothermal activity, broken into individual blocks by a series of sublatitudinal and submeridional faults. These rocks are usually correlated with the Mitrofanovo member.

In one of the blocks least affected by hydrothermal alteration, located in the central part of this section, among diabase porphyrites, a six-meter interbed of tuffaceous sandstones with abundant fauna and flora has been exposed. The flora is very poorly preserved. From the fauna in our collections L. N. Kraevskaya identified Schisophoria cf. praeimpressa N., Cyrtospirifer ex gr. archiaci Murch., C. sulcifer (?), most characteristic of the Sulcifer beds of the Famennian in Kazakhstan. Typical representatives of the Sulcifer fauna were first established by D. V. Nalivkin in the Meister beds of Kazakhstan, also of Famennian stage. Thus, the Baranovka member most probably has a Famennian age \(D_3^2\) and is not identical to the Mitrofanovka member of Givetian–Frasnian age. The Mitrofanovka Formation loses its independent stratigraphic significance and should be regarded as a member within the Pachino Formation.

LITERATURE

1. V. V. Vdovin. Geotectonic structures of the Kolyvan–Tomsk arc. Transactions of the Mining-Geological Institute, West Siberian Branch, Academy of Sciences of the USSR, issue 15, 1956.

2. A. I. Gusev. Geological structure and mineral resources of the area of the city of Novosibirsk. Publishing House of the West Siberian Geological Trust, Tomsk, 1934.

3. A. L. Matveevskaya, E. F. Ivanova. Geological structure of the southern part of the West Siberian Lowland in connection with questions of oil-and-gas potential. Publishing House of the Academy of Sciences of the USSR, Moscow, 1960.

4. K. V. Radugin. On the continuation to the north of the Kuznetsk coal basin. Bulletin of the West Siberian Geological Trust, issue 3, 1934.

5. B. F. Speransky. Materials on the geology of the Gorlovka coal deposit. Bulletin of the Siberian Department of the Geological Committee, vol. III, issue 6, 1924.

6. A. V. Tyzhnov. Materials on the stratigraphy and tectonics of the Devonian deposits of the Kuznetsk coal basin. Bulletin of the West Siberian Geological Administration, vol. XI, issue 1, 1931.