ON THE STRATIGRAPHY OF THE PHOSPHORITE FORMATION

IN THE KOLYVAN–TOMSK FOLDED ZONE

P. N. PARSHIN

(Presented by the scientific seminar of the Problem Geological Laboratory of TPI)

The Middle Paleozoic formations of the Kolyvan–Tomsk folded zone contain a large number of faunal remains. However, the sporadic character of the outcrops, the metamorphism of the sediments, and, as a rule, the considerable “scatter” of organic remains through the section have usually made it difficult both to determine accurately the age from the identified fauna and to tie the fauna precisely to the section. The latter was often determined as a whole from several collection points in individual sections assigned, on lithological grounds, to some particular suite. Naturally, faunal determinations could only to some extent confirm the correlation of the age position of these suites with the international stratigraphic scale. But in individual cases the paleontological material nevertheless permits more precise chronological correlations of separate sections and lithological units; and then it often becomes clear that the lithological method for stratigraphic correlation does not always yield positive results.

Thus, in the practice of geological mapping, the confinement of phosphoritization in limestones and argillaceous shales to the falenian horizon of the Famennian stage is often established. Materials on phosphate occurrences in the Devonian of the Kuzbass and the Kolyvan–Tomsk folded zone have been generalized in works of the West Siberian Geological Administration and published by G. S. Kharin and V. I. Lel’chuk [6]. In this connection, the authors cited arrive at the conclusion that “phosphate occurrences in the Kuzbass and the Kolyvan–Tomsk folded zone are confined to the Pozharishche beds, assigned to the faunal zone Anathyris phalaena of lower Frasnian age [6].”

On this basis G. S. Kharin proposes a threefold division of the Pachinskaya suite (Kolyvan–Tomsk folded zone), using, as a marker horizon of the middle Pachinskaya sub-suite, phosphate occurrences whose establishment is equivalent to establishing the falenian horizon. Unfortunately, this proposition is apparently not always correct. It may be considered proven for the group of phosphate occurrences in the northwestern part of the Kuzbass, located in a northeastern direction along the boundary, established by A. V. Tyzhnov ([4, 5] and subsequent works), between the Zarubinskaya (Kuzbass) and Kolyvan–Tomsk facies zones of the Upper Devonian. These are the Terekhinskoye, Sosnovskoye, Zarubinskoye, and Kolmogorovskoye phosphate occurrences. But to the northwest (down the Tom River) from this group of phosphate-occurrence sites, i.e., toward the area of development of sediments of the Kolyvan–Tomsk zone, the strict confinement of phosphate occur-

the occurrences to the Famenian horizon is not maintained. Along the Tom River, below the mouth of the Pacha River, and along the Pacha River, near the limestone quarries, phosphate occurrences are apparently confined to the lower members of the Pacha Formation, whose age is most probably Late Givetian. Along the Tom River, the fauna enclosed in limestone concretions, not strictly confined to any particular horizon, in the opinion of A. V. Tykhnov, occurs more often in the Middle Devonian than in the Upper Devonian. “The plant remains encountered in these deposits also indicate a Middle Devonian age” ([2], p. 54). A more rigorous stratigraphic assignment on the basis of fauna is provided by the Yashkino limestone member of the Pacha Formation and by the clayey shales underlying this member (in the latter, phosphorite concretions and nodules are also noted, first described by V. I. Lel’chuk and G. S. Kharin).

The limestones contain a fauna (first collected in 1940 by L. N. Kraevskaya and studied by B. B. Chernyshev): Alveolites mailieuxi Lec. (occurs in the Safonovo beds of the Givetian of Kuzbass), Alveolites suborbicularis Lam. (ranges from S to D), Heliolites vulgaris Tschern. (widespread in the Shanda beds of the Eifelian of Kuzbass), Pachyfavosites polymorphys Goldf. (Middle Devonian). The age is most probably \(D_2\). In the clayey shales underlying the limestones near the village of Burlakovo, according to the collections of V. F. Loskutov (1961) and identifications by Z. P. Pivovarova, there is a fauna of the Givetian Stage: Thamnopora nicholsoni Frech, Alveolitella polenowi Petz., Coenites faschicularis Radugin.

The limestones of the Yashkino member southward pass facially into the volcanogenic-sedimentary Mitrofanovo member, of the same transitional Givetian–Frasnian age as the Yashkino member. In the upper part of the Mitrofanovo member, according to its position in the section and isolated finds of Famenian fauna, apparently corresponding to the Famenian horizon, phosphate–carbonate concretions are also noted. Still farther west, on the right bank of the Tom River, below Yurgа station, phosphate occurrences are confined to gray and dark-gray shales of the upper part of the Yurga Formation (Kulakovo beds according to A. L. Matveevskaya, 1960), whose Late Famenian age was first proved by M. V. Yanishevsky [7] and confirmed by L. N. Kraevskaya (1958).

A. V. Tykhnov (1940), on the basis of the lithological similarity of the Kulakovo member of the Yurga Formation to the dark-gray shales of the Pacha Formation near the village of Pacha, assigned the Kulakovo member to the upper part of the Pacha Formation and therefore considered the upper age boundary of the Pacha Formation to lie within the Famenian Stage.

As a result of study of the fauna from the detailed collections of A. M. Demidov and L. S. Skripko (1958), L. N. Kraevskaya and A. M. Yaroshinskaya established that the Upper Famenian formations in the area of the village of Kulakovo are the oldest, forming the cores of small anticlines; on their flanks they are overlain by clayey shales of the Etroeungt and Tournaisian, also rather fully characterized here faunistically.

Within the Late Famenian fauna, L. N. Kraevskaya identified brachiopod forms described by D. V. Nalivkin from the Sulcifer beds of Kazakhstan. The latter conformably overlie Frasnian deposits and are likewise conformably overlain by Lower Carboniferous deposits through transitional Etroeungt beds. Among endemic species, Cyrtospirifer tscheryschewi Khalf. and Cyrtospirifer jurgenensis Krajev. were encountered, characteristic of Famenian deposits on the margins of Kuzbass (Demidov, Skripko, 1958).

Thus, it may be regarded as established that phosphate occurrences from southeast to northwest, across the strike of the central part of the Kolyvan–Tomsk folded zone, occupy different stratigraphic levels: Givetian (possibly Upper Givetian)—

in the extreme eastern part (the mouth of the Pacha River (the Nizhnefranskii—near the village of Mitrofanovo, and the Verkhnefamenskii—in the extreme western part of the section of the zone accessible for study (the right bank of the Tom River near the village of Kulakovo). Since the most probable facies setting of phosphorite accumulation is the shelf part of a marine basin [1, 3], which is generally confirmed also by analysis of the facies setting of the above-mentioned phosphorite occurrences [6], one may also speak of the migration of the shelf zone of the Kolyvan-Tomsk Sea in the Middle and Upper Devonian in a northwestern direction, from the mouth of the Pacha River toward the Yurga station. Probably only those phosphorite occurrences developed along the shelf zones of some definite moment of geological time can be of the same age. Their confinement to the Falenian horizon of the Lower Frasnian substage is the most widespread, but nevertheless a particular case; therefore, the appearance of phosphorite-bearing horizons in a section alone (without additional faunistic and structural-facies analysis) cannot be used to judge the chronology of that section.

LITERATURE

1. A. V. Kazakov. Phosphate facies. The origin of phosphorites and geological factors in the formation of phosphorite deposits. Proceedings of the Scientific Research Institute of Fertilizers, Moscow, issue 15, 1939.

2. 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–Leningrad, 1960.

3. N. M. Strakhov. Fundamentals of the Theory of Lithogenesis, vol. II, Publishing House of the Academy of Sciences of the USSR, Moscow–Leningrad, 1962.

4. A. V. Tyzhnov. Materials on the stratigraphy and tectonics of the Devonian deposits of the Kuznetsk Basin. Bulletin of ZSGU, vol. XI, issue 1, Tomsk, 1931.

5. A. V. Tyzhnov. Geological structure of the northern part of Kuzbass and the problem of its oil and gas potential. Bulletin of ZSGU, No. 4, Novosibirsk, 1941.

6. G. S. Kharin, V. I. Lel’chuk. Phosphate-bearing character of the Upper Devonian of Kuzbass and the Kolyvan-Tomsk folded zone. Bulletin of ZS and NTGU, No. 2, Tomsk, 1962.

7. M. E. Yanishevsky. On the kulm beds of the environs of the city of Tomsk. Geological Bulletin, No. 3, St. Petersburg, 1915.